Change search
Refine search result
2442244324442445244624472448 122201 - 122250 of 126553
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 122201. Yu, J.
    et al.
    Yang, Y.
    Yang, Xiaohu
    Kong, Q.
    Liu, Y.
    Yan, Jinyue
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Energy Processes.
    Effect of porous media on the heat transfer enhancement for a thermal energy storage unit2018In: Energy Procedia, Elsevier Ltd , 2018, p. 984-989Conference paper (Refereed)
    Abstract [en]

    Thermal energy storage (TES) can effectively recover thermal energy from low-temperature waste heat and it has now been received increasing attentions in practical engineering applications. Nevertheless, the relatively low thermal conductivity of engineering available phase change materials (PCMs) greatly limits the energy efficiency of TES applications. To enhance the phase change process, open-cell metal foam with a porosity of 0.94 and pore density of 15 PPI (pore per inch) was employed to be inserted either in heat transfer fluid (HTF) or in phase change material (PCM). A two-dimensional axis-symmetric problem was numerically solved and was validated through comparing temperature history at selected points. Results demonstrated that the involvement of open-cell metal foam can effectively enhance the phase change heat transfer, greatly reducing the full melting time. By comparing the four cases (without metal foam, inserting metal foam into HTF, PCM and both domains), the case that both HTF and PCM domains were embedded with porous media can provide the best heat transfer enhancement, from which practical applications with thermal engineering may benefit.

  • 122202.
    Yu, Jia
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Maintenance Optimization Schedulingof Electric Power SystemsConsidering Renewable EnergySources2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Maintenance is crucial in any industry to keep components in a reasonable functionalcondition, especially in electric power system, where maintenance is done so that thefrequency and the duration of a fault can be shortened, thus increasing the availability of acertain component. And the reliability of the whole electric power system can also beimproved. In the many deregulated electricity markets, reliability and economic drivingforces are the two aspects that system operators mainly consider. It is expected for thesystem operator to provide consumers with the electricity of highest reliability and lowestcost. Therefore, in order to achieve this goal, providing the most economic maintenanceschedule is vital in today’s power systems. One technique is Reliability CentredMaintenance (RCM), which is an effective method to maintain a certain level ofreliability while carrying out maintenance schedules in an economic way.

    This thesis proposes an optimization problem for implementing the RCM method for apower system with renewable energy generators such as hydro power, wind power andsolar panel generators. This aim is achieved through the following steps:

    1- Literature review on power system reliability.

    2- Literature review on maintenance scheduling methods by focus on RCM method.

    3- Compare the difference of conventional generators and renewable generators andmodel renewable generators in the power system.

    4- Formulating the RCM method as an optimization problem.

    5- The formulated model in 4 should be simulated for a test system using MATLAB.

    6- The developed model in 5 is solved for different sets of available maintenanceIIstrategies.

    7- Summing all possible costs when different maintenance strategies are carried outand compare the costs. Choose the maintenance strategy with the lower cost tocarry out the maintenance.

  • 122203.
    Yu, Jiayao
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Gaze-typing for Everyday Use: Keyboard Usability Observations and a “Tolerant” Keyboard Prototype2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Gaze-typing opens up a new input channel, but its keyboard designs are not ready for everyday use. To investigate the gaze-typing keyboards for such use that are easy to learn, fast to type, and robust to use differences, I analyzed the usability of three widely used gaze-typing keyboards by a user study with typing performance measurements, synthesized the design space of everyday used gaze-typing keyboards under the topics of typing schemes and keyboard letter layouts, feedback, ease of text editing, and system design. In particular, I found gaze-typing keyboards need “tolerant” designs that allow implicit gaze control and balance between input ambiguity and typing efficiency. Therefore, I prototyped a gaze-typing keyboard using a shape-writing scheme meant for everyday typing by gaze gestures, with the adaption on segmenting the gaze locus when writing a word from continuous gaze data stream. The system affords real-time shape-writing in the speed of 11.70 WPM and the error rate of 0.14 evaluated with an experienced user and supports to type 20000+ words from the lexicon.

  • 122204. Yu, Jung-Hoon
    et al.
    Lee, Jin-Su
    Nam, Sang-Hun
    Hwang, Ki-Hwan
    Boo, Jin-Hyo
    Yun, Sang H.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. Sungkyunkwan University, South Korea .
    Structuring Poly(3,4-ethylenedioxythiophene): Poly(styrenesulfonate) Towards Enhancing Hole Collection Efficiency2014In: Journal of Nanoscience and Nanotechnology, ISSN 1533-4880, E-ISSN 1533-4899, Vol. 14, no 12, p. 9489-9492Article in journal (Refereed)
    Abstract [en]

    To date, organic photovoltaic devices (OPVs) have obtained relatively low power conversion efficiency, mostly because of the low charge carrier mobility of the polymers to be used. This limits the optimal film thickness for efficient absorption of the solar spectrum. The capability of efficient charge carrier collections is a main factor for utilizing thick OPVs, consequently enhancing the power conversion efficiency. In this report, we demonstrate a facile approach for enhancing the hole carrier collection by possibly shortening the hole collection path via structuring poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), which is widely used as a hole collecting intermediate layer in OPVs. For structuring the PEDOT:PSS, the nanosphere lithographic method was used. Furthermore, the effects of the structuring of PEDOT:PSS on optical properties were also investigated.

  • 122205.
    Yu, Kai
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Modeling of Multiple-Input Multiple-Output Radio Propagation Channels2002Report (Other academic)
  • 122206.
    Yu, Kai
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Modeling of Multiple-Input Multiple-Output Radio Propagation Channels2002Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    In recent years, multiple-input multiple-output (MIMO)systems appear to be very promising since they can provide highdata rates in environments with sucient scattering byexploiting the spatial domain. To design a real MIMO wirelesssystem and predict its performance under certain circumstances,it is necessary to have accurate MIMO wireless channel modelsfor dierent scenarios. This thesis presents dierent models forindoor MIMO radio propagation channels based on 5.2 GHz indoorMIMO channel measurements.The recent research on MIMO radio channel modeling isbriey reviewed in this thesis. The models are categorized intonon-physical and physical models. The non-physical modelsprimarily rely on the statistical characteristics of MIMOchannels obtained from the measured data while the physicalmodels describe the MIMO channel (or its distribution) via somephysical parameters. The relationships between dierent modelsare also discussed.For the narrowband case, a non line-of-sight (NLOS)indoor MIMO channel model is presented. The model is based on aKronecker structure of the channel covariance matrix and thefact that the channel is complex Gaussian. It is extended tothe line-of-sight (LOS) scenario by estimating and modeling thedominant component separately.As for the wideband case, two NLOS MIMO channel modelsare proposed. The rst model uses the power delay prole and theKronecker structure of the second order moments of each channeltap to model the wideband MIMO channel while the second modelcombines a simple single-input single-output (SISO) model withthe same Kronecker structure of the second order moments.Monte-Carlo simulations are used to generate indoor MIMOchannel realizations according to the above models. The resultsare compared with the measured data and good agreement has beenobserved.

  • 122207.
    Yu, Kai
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Multiple-Input Multiple-Output Radio Propagation Channels: Characteristics and Models2005Doctoral thesis, monograph (Other scientific)
    Abstract [en]

    In recent years, deploying multiple antennas at both transmitter and receiver has appeared as a very promising technology. By exploiting the spatial domain, multiple-input multiple-output (MIMO) systems can support extremely high data rates as long as the environments can provide sufficiently rich scattering. To design high performance MIMO wireless systems and predict system performance under various circumstances, it is of great interest to have accurate MIMO wireless channel models for different scenarios. In this thesis, we characterize and model MIMO radio propagation channels based on indoor MIMO channel measurements.

    The recent development on MIMO radio channel modeling is briefly reviewed in this thesis. The models are categorized into non-physical and physical models, and discussed respectively. The non-physical models primarily rely on the statistical characteristics of MIMO channels obtained from the measured data, while the physical models describe the MIMO channel (or its distribution) via some physical parameters. We also briefly mention the MIMO channel modeling work within the IEEE 802.11n and 3GPP/3GPP2 standardization work.

    For the narrowband case, a non line-of-sight (NLOS) indoor MIMO channel model is presented. The model is based on a Kronecker structure of the channel covariance matrix and the fact that the channel is complex Gaussian. It is extended to line-of-sight (LOS) scenario by estimating and modeling the dominant component separately. For the wideband case, two NLOS MIMO channel models are proposed. The first model uses the average power delay profile and the Kronecker structure of the second order moments of each channel tap to model the wideband MIMO channel, while the second model combines a simple single-input single-output (SISO) model with the same Kronecker structure of the second order moments. Monte-Carlo simulations are used to generate indoor MIMO channel realizations according to the above models. The results are compared with the measured data and good agreement has been observed.

    Under the assumption of spatial wide sense stationary, a lower bound of the maximum Kronecker model errors is obtained by employing a combination of grid search and semidefinite programming to explore the feasible region. Numerical examples show that the bound is tight for moderate number of grid points. By comparing the worst case model errors with the model errors obtained from the measured channels, we find that the channel correlation matrix in these measurements can, indeed, be well approximated by the Kronecker product of the correlation matrix at the transmitter and the receiver.

    To model wideband MIMO channels, it is important to investigate the angular statistics on both the tap and cluster levels. Based on 5~GHz indoor wireless channel measurements, a frequency domain space alternating generalized expectation maximization (FD-SAGE) algorithm is employed to estimate the multipath components from the measured data. We then manually identify the clusters of the multipaths and calculate the tap and cluster angular spreads (ASs) for each identified cluster. It is found that for the 100 MHz channels, the average tap AS is just a few degrees less than the cluster AS and the difference diminishes for small channel bandwidth.

  • 122208.
    Yu, Kai
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing.
    MIMO channel models2005In: Smart Antennas: State of the Art / [ed] Thomas Kaiser, André Bourdoux, Holger Boche, Javier Rodríguez Fonollosa, Jørgen Bach Andersen, and Wolfgang Utschick, Hindawi Publishing Corporation , 2005, p. 271-292Chapter in book (Other academic)
  • 122209.
    Yu, Kai
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Bengtsson, Mats
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    On The Error of Kronecker Structure Based MIMO Channel Model2004In: Proceedings of Nordic Radio Symposium, NRS 2004, 2004Conference paper (Other academic)
    Abstract [en]

    Herein, we investigate the mismatch of the Kronecker structure based MIMO channel model. Finding the minimum mismatch is trivial and the result is always 0. The maximization problem, on the other hand, is not convex in general. Therefore we combine semidefinite programming with a grid search, to find a lower bound of the maximum mismatch. Numerical examples show that the bound is tight even for moderate number of points in the grid. The resulting worst case model error, is much larger than the model error previously observed in measurement campaigns, which confirms that the channel correlation matrix can, indeed, be well approximated by the Kronecker product of the correlation matrices at the transmitter and receiver for the measured NLOS indoor scenarios.

  • 122210.
    Yu, Kai
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Bengtsson, Mats
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Beach, Mark
    Centre for Communication Research, University of Bristol, United Kingdom.
    Narrowband MIMO Channel Modeling for LOS Indoor Scenarios2002In: Proceedings XXVIIth Triennial General Assembly of the International Union of Radio Science (URSI), 2002Conference paper (Other academic)
    Abstract [en]

    Herein, a line-of-sight (LOS) multiple input multiple output (MIMO) channel model is presented based on 5.2 GHzindoor MIMO channel measurements. The signal from the dominant direction is estimated and removed from the channel data. The residual part is shown to be Rayleigh distributed and its covariance matrix can be well approximated by theKronecker product of the covariance matrices seen from the transmitter and receiver respectively. Therefore we model the whole narrowband LOS indoor MIMO channel as a static rank one matrix plus a statistical model based on Rayleigh distribution with a multiplicative covariance structure.

  • 122211.
    Yu, Kai
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Bengtsson, Mats
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Karlsson, Peter
    Telia Research AB, Malmö, Sweden.
    McNamara, Darren
    Centre for Communication Research University of Bristol, United Kingdom.
    Beach, Mark
    Centre for Communication Research University of Bristol, United Kingdom.
    Measurement Analysis of NLOS Indoor MIMO Channels2001In: Proceedings IST Mobile Communications Summit, 2001, p. 277-282Conference paper (Other academic)
    Abstract [en]

    In this paper, we present results from measurements conducted by the University of Bristol.We study the channel characteristics of Multiple-Input-Multiple-Output (MIMO) indoor channel at 5.2GHz. Our investigation shows that the envelope of the channel for non-line-of-sight (NLOS) indoorsituations is approximately Rayleigh distributed and consequently we focus on a statistical descriptionof the first and second order moments of the narrowband MIMO channel. Furthermore, it is shown thatfor NLOS indoor scenarios, the MIMO channel covariance matrix can be well modeled by a Kroneckerproduct of the covariance matrices describing the correlation at the transmitter and the receiver siderespectively. A statistical narrowband model for the NLOS indoor MIMO channel based on thiscovariance structure is presented along with some simulation results.

  • 122212.
    Yu, Kai
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Bengtsson, Mats
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    McNamara, Darren
    Centre for Communication Research University of Bristol, United Kingdom.
    Karlsson, Peter
    Telia Research AB, Malmö, Sweden.
    Beach, Marc
    Centre for Communication Research University of Bristol, United Kingdom.
    Modeling of wide-band MIMO radio channels based on NLoS indoor measurements2004In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 53, no 3, p. 655-665Article in journal (Refereed)
    Abstract [en]

    In this paper, we first verify a previously proposed Kronecker-structure-based narrow-band model for nonline-of-sight (NLoS) indoor multiple-input-multiple-output (MIMO) radio channels based on 5.2-GHz indoor MIMO channel measurements. It is observed that, for the narrow-band case, the measured channel coefficients are complex Gaussian distributed and, consequently, we focus on a statistical description using the first- and second-order moments of MIMO radio channels. It is shown that the MIMO channel covariance matrix can be well approximated by the Kronecker product of the covariance matrices, seen from the transmitter and receiver, respectively. A narrow-band model for NLoS indoor MIMO channels is thus verified by these results. As for the wide-band case, it is observed that the average power-delay profile of each element of the channel impulse response matrix fits the exponential decay curve and that the Kronecker structure of the second-order moments can be extended to each channel tap. A wide-band MIMO channel model is then proposed, combining a simple COST 259 single-input-single-output channel model and the Kronecker structure. Monte Carlo simulations are used to generate indoor MIMO channel realizations according to the models discussed. The results are compared with the measured data using the channel capacity and good agreement is found.

  • 122213.
    Yu, Kai
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Bengtsson, Mats
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    McNamara, Darren
    Centre for Communication Research, University of Bristol, United Kingdom.
    Karlsson, Peter
    Telia Research AB, Malmö, Sweden.
    Beach, Mark
    Centre for Communication Research, University of Bristol, United Kingdom.
    A 20 MHz HIPERLAN/2 MIMO Channel Model in NLOS Indoor Scenarios2002In: Nordic Conference on Radio Science and Communications (RVK), 2002, p. 311-315Conference paper (Other academic)
    Abstract [en]

    In this paper, we present results of 5.2 GHz wideband indoor multiple input multiple output (MIMO) channel measurementsunder the EU IST SATURN project. First we show the average power delay profile for the single input single output (SISO) channel. Furthermore, our investigation shows that for non-line-of-sight (NLOS) indoor scenarios, the MIMO channel covariance matrix of each normalized tap of channel impulse response can be be well approximated by the Kronecker product of the covariance matrices seen from the transmitter and receiver respectively.Based on the above results, a wideband statistical model for HiperLAN/2 MIMO channel is presented. Monte-Carlo simulations show reasonably good agreement between the measured data and our model. Finally, weuse this model to show the capacity characteristics of theHiperLAN/2 channel in NLOS indoor scenarios.

  • 122214.
    Yu, Kai
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Bengtsson, Mats
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    McNamara, Darren P.
    Centre for Communication Research University of Bristol, United Kingdom.
    Karlsson, Peter
    Telia Research AB, Malmö, Sweden.
    Beach, M.
    Centre for Communication Research University of Bristol, United Kingdom.
    Second order statistics of NLOS indoor MIMO channels based on 5.2 GHz measurements2001In: Global Telecommunications Conference, 2001. GLOBECOM '01. IEEE, 2001, p. 156-160Conference paper (Refereed)
    Abstract [en]

    Herein, results from measurements conducted by the University of Bristol are presented. The channel characteristics of Multiple Input Multiple Output (MIMO) indoor systems at 5.2 GHz are studied. Our investigation shows that the envelope of the channel for non-line-of-sight (NLOS) indoor situations are approximately Rayleigh distributed and consequently we focus on a statistical description of the first and second order moments of the narrowband MIMO channel. Furthermore, it is shown that for NLOS indoor scenarios, the MIMO channel covariance matrix can be well approximated by a Kronecker product of the covariance matrices describing the correlation at the transmitter and receiver side respectively. A statistical narrowband model for the NLOS indoor MIMO channel based on this covariance structure is presented.

  • 122215.
    Yu, Kai
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Bengtsson, Mats
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    McNamara, Darren P.
    Centre for Communication Research University of Bristol, United Kingdom.
    Karlsson, Peter
    Telia Research AB, Malmö, Sweden.
    Beach, Mark A.
    Centre for Communication Research University of Bristol, United Kingdom.
    A wideband statistical model for NLOS indoor MIMO channels2002In: IEEE 55TH VEHICULAR TECHNOLOGY CONFERENCE, VTC SPRING 2002, VOLS 1-4, PROCEEDINGS, 2002, p. 370-374Conference paper (Refereed)
    Abstract [en]

    Herein, results of 5.2 GHz wideband indoor multiple input multiple output (MIMO) channel measurements under the EU IST SATURN project are reported. Our investigation shows that for non-line-of-sight (NLOS) cases, the average power delay profiles fit the exponentially decaying curve quite well, therefore a simple wideband model for single-input single-output (SISO) proposed in COST259 has been used in our model. Furthermore, the investigations show that the MIMO channel covariance matrix of each normalized tap of the impulse response could be well approximated by the Kronecker product of the covariance matrices seen from the transmitter and receiver respectively. Based on the above results, a wideband statistical model is presented. Monte-Carlo simulations show reasonably good agreement between the measured data and our model. Finally, we use this model to show some capacity characteristics of Hiper-LAN/2 channels in NLOS indoor scenarios.

  • 122216.
    Yu, Kai
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Li, Q. H.
    Cheung, D.
    Prettie, C.
    On the tap and cluster angular spreads of indoor WLAN channels2004In: VTC2004-SPRING: 2004 IEEE 59TH VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5, PROCEEDINGS, NEW YORK: IEEE , 2004, p. 218-222Conference paper (Refereed)
    Abstract [en]

    Herein we present results on the cluster angular spread (AS), the tap AS and its variation with different channel bandwidths for a measured large office environment. The measurements were conducted in the 5 GHz band using a virtual cross antenna array at the receiver. A frequency domain space alternating generalized expectation maximization (FD-SAGE) algorithm is employed to estimate the multipath components. The clusters of the multipaths are then manually identified. For each measured location, 4-5 clusters are identified and the processed results show that the cluster AS ranges 5.6degrees-36.5degrees. Furthermore, we investigate the tap AS for each cluster. It is found that for the channels with 100 MHz bandwidth, the instantaneous tap AS ranges 0degrees-43degrees and the average tap AS of each cluster is just few degrees less than the AS of that cluster. The difference between the average tap AS and the cluster AS becomes smaller for less channel bandwidth.

  • 122217.
    Yu, Kai
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Li, Q. H.
    Ho, M.
    Measurement investigation of tap and cluster angular spreads at 5.2 GHz2005In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 53, no 7, p. 2156-2160Article in journal (Refereed)
    Abstract [en]

    In this paper, we present indoor measurement results on the cluster angular spread (AS), the tap AS and its variation with different channel bandwidths. A frequency domain space alternating generalized expectation maximization (FD-SAGE) algorithm is employed to estimate the multipath components from the measured data. We then manually identify the clusters of the multipaths and calculate the tap and cluster ASs for each identified cluster. It is found that for the 100 MHz channels, the average tap AS is just few degrees less than the cluster AS and the difference diminishes for less channel bandwidth.

  • 122218.
    Yu, Kai
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Li, Qinghua
    Cheung, David
    Lung, Jeng
    Measurement Investigation of Tap and Cluster Angular Spreads in 5 GHz Bands2003In: Proceedings Personal Computing & Communication Workshop, 2003Conference paper (Refereed)
  • 122219.
    Yu, Kai
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Models for MIMO propagation channels: a review2002In: Wireless Communications & Mobile Computing, ISSN 1530-8669, E-ISSN 1530-8677, Vol. 2, no 7, p. 653-666Article in journal (Refereed)
    Abstract [en]

    This paper reviews recently published results on multiple input multiple output (MIMO) channel modeling. Both narrowband and wideband models are considered. We distinguish between two main approaches to MIMO channel modeling, that is,. physically based and nonphysically based modeling. The nonphysical models primarily rely on the statistical characteristics of the MIMO channels obtained from the measured data, while the physical models describe the MIMO channel (or its distribution) via some physical parameters. We briefly review different MIMO channel models and discuss their relationships. Some interesting aspects will be described in more detail and we note areas in which few results are available.

  • 122220. Yu, L.
    et al.
    Shi, Y.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Dai, D.
    Tunable silicon micro-disk resonator with flexible graphenebased ultra-thin heaters2015In: Asia Communications and Photonics Conference, ACPC 2015, 2015Conference paper (Refereed)
    Abstract [en]

    A thermally-tuning silicon-on-insulator micro-disk resonator with a flexible graphenebased ultra-thin heater is demonstrated. The experimental results show graphene heaters have excellent performances on the heating efficiency and the temporal response. © 2015 OSA.

  • 122221. Yu, L.
    et al.
    Yakubov, G. E.
    Zeng, W.
    Xing, Xiaohui
    KTH, School of Biotechnology (BIO), Glycoscience.
    Stenson, J.
    Bulone, Vincent
    KTH, School of Biotechnology (BIO), Glycoscience.
    Stokes, J. R.
    Multi-layer mucilage of Plantago ovata seeds: Rheological differences arise from variations in arabinoxylan side chains2017In: Carbohydrate Polymers, ISSN 0144-8617, E-ISSN 1879-1344, Vol. 165, p. 132-141Article in journal (Refereed)
    Abstract [en]

    Mucilages are hydrocolloid solutions produced by plants for a variety of functions, including the creation of a water-holding barrier around seeds. Here we report our discovery of the formation of three distinct mucilage layers around Plantago ovata seeds upon their hydration. Each layer is dominated by different arabinoxylans (AXs). These AXs are unusual because they are highly branched and contain β-1,3-linked xylose in their side chains. We show that these AXs have similar monosaccharide and linkage composition, but vary in their polymer conformation. They also exhibit distinct rheological properties in aqueous solution, despite analytical techniques including NMR showing little difference between them. Using enzymatic hydrolysis and chaotropic solvents, we reveal that hydrogen bonding and side chain distribution are key factors underpinning the distinct rheological properties of these complex AXs.

  • 122222.
    Yu, Liang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Dong, Y-C
    Ye, G. Z.
    Sichen, Du
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Concentrating of vanadium oxide in vanadium rich phase(s) by addition of SiO2 in converter slag2007In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 34, no 2, p. 131-137Article in journal (Refereed)
    Abstract [en]

    The focus of the present work was to examine whether vanadium rich phase(s) could be obtained in converter slags having high V2O5 contents. Slags from SSAB Oxelosund, Sweden and Ma Steel, China were studied. Despite of the composition difference, slags from both industries were found to contain essentially the same phases after heat treatment. No vanadium rich phase could be obtained by only heat treatment of the slag. The addition of 12 mass%SiO2 changed substantially the phase relationships in the slags. Two vanadium rich phases were detected in the slag samples with SiO2 addition. One of the phases was expected to be a solid solution of 3CaO.V2O5 and 3CaO.P2O5 with < 3 mass%SiO2 dissolved. The other vanadium rich phase had high SiO2 content. About 67-68 mass% vanadium was captured by the vanadium rich phase(s) after the treatment. The present finding would open up new opportunities for recovery of vanadium from converter slags.

  • 122223.
    Yu, Liang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Dong, Yuan-Chi
    Li, Liaosha
    Sichen, Du
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Existence of a solid solution between 3CaO center dot V(2)O(5)and 3CaO center dot P2O52006In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 37, no 6, p. 1097-1099Article in journal (Refereed)
    Abstract [en]

    In the present work, a solid solution of 3CaO - V2O5 and 3CaO (.) P2O5 was found below 1573 K. The solution could be described as 3CaO + xV(2)O(5) + (I - X) P205. The solid solutions at three compositions, namely, X = (1)/(3), X = (1)/(2), and X = (2)/(3), were synthesized. X-ray diffraction (XRD) patterns revealed that the crystals exhibited a rhombohedra structure. X-ray indexes at these compositions were reported.

  • 122224.
    Yu, Liangcheng
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Towards Learning for System Behavior2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Traditional network management typically relies on clever heuristics to capture thecharacteristics of environments, workloads in order to derive an accurate model.While such methodology has served us well in early days, it is challenged by thegrowing intricacies of modern network design from various dimensions: the rocketingtraffic volumn, proliferation of software applications and varied hardware, higheruser-specific Quality of Experience (QoE) requirements with respect to bandwidthand latencies, overwhelming number of knobs and configurations and so forth. Allthese surging complexity and dynamics pose greater difficulty on us to understandand derive management rules to reach global optimum with heuristics that fits thedynamic context. Driven by the pulls of the challenges and encouraged by the successin machine learning techniques, this work elaborates on augmenting adaptive systemsbehaviors with learning approaches. This thesis specifically investigates the use caseof the packet scheduling. The work explores the opportunity to augment systemsto learn existing behaviors and explore custom behaviors with Deep ReinforcementLearning (DRL). We show the possibility to approximate the existing canonicalbehaviors with a generic representation, meanwhile, the agent is able to explorecustomized policy that are comparable to the state-of-art approaches. The resultsdemonstrate the potentials of learning based approaches as an alternative to canonicalscheduling approaches.

  • 122225.
    Yu, Lin
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Geochemistry and Ecotechnology.
    Modeling the Longevity of Infiltration System for Phosphorus Removal.2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A new modeling method for estimation of the longevity of infiltration system was suggested in this study. The model was one-dimensional, based on results from long-term infiltration sites in Sweden, taking some physical and chemical parameters as controlling factors. It defines the longevity of infiltration systems as the time during which the P solution in effulent is under national criteria (1 mg/L in this study), and it aims at providing the longevity for any given point of the infiltration system. The soil in the model was assumed to be totally homogenous and isotropic and water flow was assumed to be unsaturated flow and constant continuous inflow. The flow rate was calculated from the Swedish criteria for infiltration systems. The dominant process in the model would be the solute transport process; however, retardation controlled by sorption would play a more important role than advection and dispersion in determining the longevity in the model.

    By using the definition of longevity in this study, the longevity of the three soil columns at 1 m depth (Knivingaryd, Ringamåla and Luvehult) were 1703 days, 1674 days and 2575 days. The exhaustion time of the three soil columns under inflow of 5 mg/L were 2531 days, 2709 days and 3673 days. The calculated sorbed phosphorus quantity for soil from sites Kn, Lu and Ri when they reach estimated longevity were 0.177, 0.288 and 0.168 mg/g, while the maximum sorption of Kn, Lu and Ri were 0.182, 0.293 and 0.176 mg/g separately.

    From the result of sensitivity study of the model, the sorption capacity and flow velocity were most important to the longevity of the infiltration system. Lower flow velocity and higher P sorption capacity extend the longevity of an infiltration bed. Due to the sorption isotherm selected in this study and the assumption of instant equilibrium, the sorption rate of the soil column was quite linear, although the estimated longevity was much shorter than the real exhaustion time of the soil column. In fact the soil has almost reached its sorption maximum when the system reaches its longevity.

  • 122226. Yu, Longhai
    et al.
    Dai, Daoxin
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. Zhejiang University, China.
    Graphene-based transparent flexible heat conductor for thermally tuning nanophotonic integrated devices2014In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, no 25, p. 251104-Article in journal (Refereed)
    Abstract [en]

    Graphene, a well-known two-dimensional sheet, has attracted strong interest for both fundamental studies and applications. Due to its high intrinsic thermal conductivity, graphene has many potential applications in thermal management, such as in heat spreaders and flexible heaters. In this paper, a graphene-based transparent flexible heat conductor for nanophotonic integrated devices is demonstrated. The graphene heat conductor is designed to deliver heat from a non-local traditional metal heater to nanophotonic integrated devices for realizing efficient thermal tuning. With the present graphene heat conductor, a thermally tuning silicon Mach-Zehnder interferometer and micro-disk have been realized with good performance in terms of heating efficiency and temporal response. This indicates that the present graphene-based transparent flexible heat conductor provides an efficient and beneficial heating method for thermally tuning nanophotonic integrated devices.

  • 122227. Yu, Longhai
    et al.
    Yin, Yanlong
    Shi, Yaocheng
    Dai, Daoxin
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. Zhejiang University, China.
    Thermally tunable silicon photonic microdisk resonator with transparent graphene nanoheaters2016In: Operator Theory: Advances and Applications, ISSN 1004-4469, E-ISSN 2334-2536, Vol. 3, no 2, p. 159-166Article in journal (Refereed)
    Abstract [en]

    Efficient tunable photonic integrated devices are important for the realization of reconfigurable photonic systems. Thermal tuning is a convenient and effective approach, and silicon's large heat conductivity, thermo-optical coefficient, and CMOS fabrication compatibility make it a good candidate material for tunable optical microcavities, which are versatile elements in low-cost, large-scale photonic integrated circuits. Metal heaters are traditionally used for tuning, and a thick SiO2 upper-cladding layer is usually needed to prevent light absorption by the metal since that could reduce response speed and heating efficiency. In this paper, we propose and experimentally demonstrate thermally tunable silicon photonic microdisk resonators by introducing transparent graphene nanoheaters, which contact the silicon core directly without any isolator layer. The theoretical and experimental results show that the transparent graphene nanoheaters improve the heating efficiency, the temporal response, and the achievable temperature in comparison with a traditional metal heater. Furthermore, the graphene nanoheater is convenient for use in ultrasmall nanophotonic integrated devices due to its single-atom thickness and excellent flexibility. Both experiments and simulations show that the transparent graphene nanoheater is a promising option for other thermally tunable photonic integrated devices such as optical filters and switches.

  • 122228.
    Yu, Longhai
    et al.
    Zhejiang Univ. (China).
    Zheng, Jiajiu
    Zhejiang Univ. (China).
    Dai, Daoxin
    Zhejiang Univ. (China).
    He, Sailing
    Zhejiang Univ. (China).
    Observation of optically induced transparency effect in silicon nanophotonic wires with graphene2014In: Proceedings of SPIE - The International Society for Optical Engineering, 2014Conference paper (Refereed)
    Abstract [en]

    Graphene, a well-known two-dimensional sheet of carbon atoms in a honeycomb structure, has many unique and fascinating properties in optoelectronics and photonics. Integration of graphene on silicon nanophotonic wires is a promising approach to enhance light-graphene interactions. In this paper, we demonstrate on-chip silicon nanophotonic wires covered by graphene with CMOS-compatible fabrication processes. Under the illumination of pump light on the graphene sheet, a loss reduction of silicon nanophotonic wires, which is called optically induced transparency (OIT) effect, is observed over a broad wavelength range for the first time. The pump power required to generate the OIT effect is as low as ~0.1mW and the corresponding power density is about 2×10 3mW/cm2, which is significantly different from the saturated absorption effect of graphene reported previously. The extremely low power density implies a new mechanism for the present OIT effect, which will be beneficial to realize silicon on-chip all-optical controlling in the future. It also suggests a new and efficient approach to tune the carrier concentration (doping level) in graphene optically.

  • 122229. Yu, Longhai
    et al.
    Zheng, Jiajiu
    Xu, Yang
    Dai, Daoxin
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. Zhejiang University, China .
    Local and Non local Optically Induced Transparency Effects in Graphene-Silicon Hybrid Nanophotonic Integrated Circuits2014In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 8, no 11, p. 11386-11393Article in journal (Refereed)
    Abstract [en]

    Graphene is well-known as a two-dimensional sheet of carbon atoms arrayed in a honeycomb structure. It has some unique and fascinating properties, which are useful for realizing many optoelectronic devices and applications, including transistors, photodetectors, solar cells, and modulators. To enhance lightgraphene interactions and take advantage of its properties, a promising approach is to combine a graphene sheet with optical waveguides, such as silicon nanophotonic wires considered in this paper. Here we report local and nonlocal optically induced transparency (OIT) effects in graphenesilicon hybrid nanophotonic integrated circuits. A low-power, continuous-wave laser is used as the pump light, and the power required for producing the OIT effect is as low as similar to 0.1 mW. The corresponding power density is several orders lower than that needed for the previously reported saturated absorption effect in graphene, which implies a mechanism involving light absorption by the silicon and photocarrier transport through the silicongraphene junction. The present OIT effect enables low power, all-optical, broadband control and sensing, modulation and switching locally and nonlocally.

  • 122230. Yu, Meijuan
    et al.
    Yang, Feifei
    Chu, Wangsheng
    Wang, Yu
    Zhao, Haifeng
    Gao, Bin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Zhao, Wei
    Sun, Jianping
    Wu, Fangming
    Zhang, Xiaowei
    Shi, Yunyu
    Wu, Ziyu
    3D local structure around Zn in Kti11p as a representative Zn-(Cys)4 motif as obtained by MXAN2008In: Biochemical and Biophysical Research Communications - BBRC, ISSN 0006-291X, E-ISSN 1090-2104, Vol. 374, no 1, p. 28-32Article in journal (Refereed)
    Abstract [en]

    Zinc is an important component of many proteins that play key roles in transcription, translation, and catalysis. Kti11p, DESR1, both belonging to a protein family characterized by a CSL zinc finger domain, and the co-catalytic zinc-protein PML containing a Zn2+ binding domain called RING or C3HC4 finger are all structurally determined by NMR although the zinc sites are silent to this spectroscopical method. The comparison of X-ray absorption near-edge spectroscopy (XANES) data for the three proteins demonstrates that fingerprints effect is a reliable method for a primary characterization of ligand species. Ab initio full MS Calculations performed by MAN are applied to obtain chemical and stereo structural information around the Zn ion in Kti11p. For the first time this high-spatial resolution technique confirms the formation of a stable Zn tetrahedral configuration with four sulfur ligands, and returns extremely accurate bond angle information between ligands.

  • 122231. Yu, Nancy Yiu-Lin
    et al.
    Hallström, Björn M.
    KTH, School of Biotechnology (BIO), Proteomics and Nanobiotechnology. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Fagerberg, Linn
    KTH, School of Biotechnology (BIO), Proteomics and Nanobiotechnology. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Ponten, Fredrik
    Kawaji, Hideya
    Carninci, Piero
    Forrest, Alistair R. R.
    Hayashizaki, Yoshihide
    Uhlén, Mathias
    KTH, School of Biotechnology (BIO), Proteomics and Nanobiotechnology. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Daub, Carsten O.
    Complementing tissue characterization by integrating transcriptome profiling from the Human Protein Atlas and from the FANTOM5 consortium2015In: Nucleic Acids Research, ISSN 0305-1048, E-ISSN 1362-4962, Vol. 43, no 14, p. 6787-6798Article in journal (Refereed)
    Abstract [en]

    Understanding the normal state of human tissue transcriptome profiles is essential for recognizing tissue disease states and identifying disease markers. Recently, the Human Protein Atlas and the FANTOM5 consortium have each published extensive transcriptome data for human samples using Illumina-sequenced RNA-Seq and Heliscope-sequenced CAGE. Here, we report on the first large-scale complex tissue transcriptome comparison between full-length versus 5'-capped mRNA sequencing data. Overall gene expression correlation was high between the 22 corresponding tissues analyzed (R > 0.8). For genes ubiquitously expressed across all tissues, the two data sets showed high genome-wide correlation (91% agreement), with differences observed for a small number of individual genes indicating the need to update their gene models. Among the identified single-tissue enriched genes, up to 75% showed consensus of 7-fold enrichment in the same tissue in both methods, while another 17% exhibited multiple tissue enrichment and/or high expression variety in the other data set, likely dependent on the cell type proportions included in each tissue sample. Our results show that RNA-Seq and CAGE tissue transcriptome data sets are highly complementary for improving gene model annotations and highlight biological complexities within tissue transcriptomes. Furthermore, integration with image-based protein expression data is highly advantageous for understanding expression specificities for many genes.

  • 122232.
    Yu, Peng
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety. KTH.
    Komlev, Andrei A.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Villanueva, Walter
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety. KTH, School of Engineering Sciences (SCI), Mechanics.
    Li, Yichuan
    Ma, Weimin
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Bechta, Sevostian
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Pre-Test Simulations of SIMECO-2 Experiments on Stratified Melt Pool Heat Transfer2016Conference paper (Refereed)
    Abstract [en]

    Severe accident progression in light water reactors can lead to the formation of a melt pool in the lower head that can impose thermo-mechanical loads on the pressure vessel, and subsequently can lead to vessel failure. For quantification of the thermal load which is important to in-vessel corium coolability and retention, various experiments have been carried out to investigate the heat transfer characteristics of melt pools, including the SIMECO experiment accomplished at KTH (Sehgal et al., 1998), which used low melting-point materials as the simulant of corium. In order to reduce the gaps in temperature and scale between experimental and prototypical conditions, a new test facility named SIMECO-2 is being designed at KTH (supported by the EU project IVMR), which features higher temperature (up to 900 ℃℃) and larger scale (1 meter in diameter), aiming to investigate the natural convection heat transfer of a stratified melt pool and the effects of different parameters/factors such as temperature of melt, thickness of boundary crust, thickness of top layer, top layer cooling. The present study is to provide pre-test calculations using the PECM method (Tran and Dinh, 2009), with the objectives to provide insights and analytical support to the design of the SIMECO-2 facility, including determination of required input power, as well as estimate of the temperature and heat flux distributions in the layers and time to reach steady state mode. A calculation was first performed for a reference base case with one-layer pool for which a CFD simulation was also conducted as benchmark. The calculations were then carried on to investigate the influences of different boundary conditions and internal heat sources on heat transfer. Finally the thermal behavior of a two-layer melt pool configuration was addressed in detail, and suggestions for the experimental conditions were provided.

  • 122233.
    Yu, Peng
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Ma, Weimin
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety. Royal Inst Technol KTH, Div Nucl Power Safety, Roslagstullsbacken 21, S-10691 Stockholm, Sweden..
    Villanueva, Walter
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Karbojian, Aram
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Bechta, Sevostian
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Validation of a thermo-fluid-structure coupling approach for RPV creep failure analysis against FOREVER-EC2 experiment2019In: Annals of Nuclear Energy, ISSN 0306-4549, E-ISSN 1873-2100, Vol. 133, p. 637-648Article in journal (Refereed)
    Abstract [en]

    The failure of reactor pressure vessel (RPV) during a severe accident of light water reactors is a thermal fluid-structure interaction (FSI) problem which involves melt pool heat transfer and creep deformation of the RPV. The present study is intended to explore a reliable coupling approach of thermo-fluid-structure analyses which will not only be able to reflect the transient thermal FSI feature, but also apply the advanced models and computational platforms to melt pool convection and structural mechanics, so as to improve simulation fidelity. For this purpose, the multi-physics platform of ANSYS encompassing Fluent and Structural capabilities was employed to simulate the fluid dynamics and structural mechanics in a coupled manner. In particular, the FOREVER-EC2 experiment was chosen to validate the coupling approach. The natural convection in melt pool was modeled with the SST turbulence model with a well-resolved boundary layer, while the creep deformation for the vessel made of 16MND5 steel was analyzed with a new three-stage creep model (modified theta projection model). A utility tool was introduced to transfer the transient thermal loads from Fluent to Structural which minimizes the user effort in performing the coupled analysis. The validation work demonstrated the well-posed capability of the coupling approach for prediction of the key parameters of interest, including temperature profile, total displacement of vessel bottom point and the evolution of wall thickness profile in the experiment. Ltd. All rights reserved.

  • 122234.
    Yu, Peng
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Villanueva, Walter
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Galushin, Sergey
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Ma, Weimin
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Bechta, Sevostian
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.
    Coupled Thermo-Mechanical Creep Analysis For A Nordic BWR Lower Head Using Non-Homogeneous Debris Bed Configuration From MELCOR2018Conference paper (Refereed)
    Abstract [en]

    We present a coupled thermo-mechanical creep analysis for a Nordic BWR lower head with a non-homogeneous debris bed configuration generated with MELCOR code. A one-way coupling approach was adopted which uses the Phase-Change Effective Convectivity Model implemented in Fluent to simulate the convective heat transfer in the melt pool and the ANSYS Mechanical to simulate the vessel wall deformation induced by the thermal and mechanical load from the debris. An initial non-homogeneity of debris bed was estimated using MELCOR core relocation simulation results specifying the mass of each component (UO2/Zr/ZrO2/SS/SSOX) and temperature in each MELCOR cell of the lower head. A mapping scheme was designed to transfer this non-homogeneities debris bed to Fluent through User Defined Functions. All components were locally treated in Fluent as one ideal phase by averaging the weights of element-specific mass fractions inside each cell. Material properties (density, heat capacity, etc.) and volumetric heat in the debris were both spatial- and temperature-dependent. Meanwhile, additional simulations using homogeneous debris bed configuration but with the same amount of mass compositions were run for comparison. Results including temperature escalation, vessel failure timing and location were analyzed and compared.

  • 122235.
    Yu, Pian
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Resource- and Time-Constrained Control Synthesis for Multi-Agent Systems2018Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Multi-agent systems are employed for a group of agents to achieve coordinated tasks, in which distributed sensing, computing, communication and control are usually integrated with shared resources. Efficient usage of these resources is therefore an important issue. In addition, in applications such as robotics, a group of agents may encounter the request of a sequence of tasks and deadline constraint on the completion of each task is a common requirement. Thus, the integration of multi-agent task scheduling and control synthesis is of great practical interest. In this thesis, we study control of multi-agent systems under a networked control system framework. The first purpose is to design resource-efficient communication and control strategies to solve consensus problem for multi-agent systems.The second purpose is to jointly schedule task sequence and design controllers for multiagent systems that are subject to a sequence of deadline-constrained tasks. In the first part, a distributed asynchronous event-triggered communication and control strategy is proposed to tackle multi-agent consensus. It is shown that the proposed event-triggered communication and control strategy fulfils the reduction of both the rates of sensor-controller communication and controller-actuator communication as well as excluding Zeno behavior. To further relax the requirement of continuous sensing and computing, a periodic event-triggered communication and control strategy is proposed in the second part. In addition, an observer-based encoder-decoder with finite-level quantizeris designed to deal with the constraint of limited data rate. An explicit formula for the maximum allowable sampling period is derived first. Then, it is proven that exponential consensus can be achieved in the presence of data rate constraint. Finally, in the third part, the problem of deadline-constrained multi-agent task scheduling and control synthesis is addressed. A dynamic scheduling strategy is proposed and a distributed hybrid control law is designed for each agent that guarantees the completion and deadline satisfaction of each task. The effectiveness of the theoretical results in the thesis is verified by several simulation examples.

  • 122236.
    Yu, Pian
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre.
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, ACCESS Linnaeus Centre.
    Explicit computation of sampling period in periodic event-triggered multi-agent control2018In: Proceedings of the American Control Conference, Institute of Electrical and Electronics Engineers Inc. , 2018, p. 3038-3043Conference paper (Refereed)
    Abstract [en]

    This paper investigates the synchronization of nonlinear sampled-data multi-agent systems. The purpose is to obtain an explicit formula for the maximum allowable sampling period (MASP) that guarantees exponential synchronization. Two implementation scenarios are considered. We first propose an approach on finding the MASP for periodic time-triggered sampled-data control. Then, a periodic event-triggered communication and control strategy is formulated, where a communication function and a control function are designed for each agent to determine whether or not the sampled data or the control input should be transmitted at each sampling instant. It is shown that there is a tradeoff between the sampling frequency and the convergence performance. The theoretical results are illustrated in simulations.

  • 122237.
    Yu, Pian
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Explicit computation of sampling period in periodic event-triggered multi-agent control under limited data rate2018In: IEEE Transactions on Control of Network Systems, E-ISSN 2325-5870Article in journal (Refereed)
    Abstract [en]

    This paper investigates the coordination of nonlinear sampled-data multi-agent systems subject to data rate constraint. The purpose is to design resource-efficient communication and control strategies that guarantee exponential synchronization. Two implementation scenarios are considered, the period time-triggered control and the period event-triggered control. One of the main difficulties of the problem is to obtain an explicit formula for the maximum allowable sampling period (MASP). To this end, an approach on finding the MASP for periodic time-triggered control is proposed first. Then, an asynchronous period event-triggered control strategy is formulated, a communication function and a control function are designed for each agent to determine respectively whether or not the sampled data and the control input should be transmitted at each sampling instant. Finally, the constraint of limited data rate is considered. An observer-based encoder-decoder and a finite-level quantizer are designed respectively for the Sensor-Controller communication and the Controller-Actuator communication such that certain constraint on the data rate is satisfied. It is shown that exponential synchronization can still be achieved in the presence of data rate constraint. A simulation example is given to illustrate the effectiveness of the theoretical results

  • 122238.
    Yu, Pian
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Time-constrained multi-agent task scheduling based on prescribed performance control2018In: 2018 IEEE CONFERENCE ON DECISION AND CONTROL (CDC), IEEE , 2018, p. 2593-2598Conference paper (Refereed)
    Abstract [en]

    The problem of time-constrained multi-agent task scheduling and control synthesis is addressed. We assume the existence of a high level plan which consists of a sequence of cooperative tasks, each of which is associated with a deadline and several Quality-of-Service levels. By taking into account the reward and cost of satisfying each task, a novel scheduling problem is formulated and a path synthesis algorithm is proposed. Based on the obtained plan, a distributed hybrid control law is further designed for each agent. Under the condition that only a subset of the agents are aware of the high level plan, it is shown that the proposed controller guarantees the satisfaction of time constraints for each task. A simulation example is given to verify the theoretical results.

  • 122239.
    Yu, Pian
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Fischione, Carlo
    KTH, School of Electrical Engineering and Computer Science (EECS), Network and Systems Engineering.
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Distributed Event-Triggered Communication and Control of Linear Multiagent Systems Under Tactile Communication2018In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 63, no 11, p. 3979-3985Article in journal (Refereed)
    Abstract [en]

    This note is concerned with the consensus of linear multiagent systems under tactile communication. Motivated by the emerging tactile communication technology where extremely low latency has to be supported, a distributed event-triggered communication and control scheme is proposed for the data reduction of each agent. First, an event-triggered data reduction scheme is designed for the communication between neighbors. Under such a communication scheme, a distributed event-triggered output feedback controller is further implemented for each agent, which is updated asynchronously with the communication action. It is proven that the consensus of the underlying multiagent systems is achieved asymptotically. Furthermore, it is shown that the proposed communication and control strategy fulfils the reduction of both the frequency of communication and controller updates as well as excluding Zeno behavior. A numerical example is given to illustrate the effectiveness of the proposed control strategy.

  • 122240.
    Yu, Pian
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Dimarogonas, Dimos V.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Event-Triggered Output Feedback Control for Linear Systems under Tactile Communication2017In: 2017 IEEE 56th Annual Conference on Decision and Control, CDC 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 5451-5456Conference paper (Refereed)
    Abstract [en]

    This paper investigates an event-triggered output feedback control strategy of linear systems under tactile communication, for which two different frameworks are considered. Motivated by the emerging tactile communications technology where latencies are very small but at the price of limited message sizes, a perception-based deadband principle is proposed for the data reduction of communication. In each framework, under an assumption that the deadband factor is upper bounded with respect to the system model, it is proven that global asymptotic stability of the closed loop system is achieved. Then, an event-triggered output feedback controller under tactile communication is further introduced. It is shown that the designed controller is capable of reducing the frequency of controller updates as well as excluding Zeno behavior. Numerical examples are given to illustrate the effectiveness of the proposed control algorithm.

  • 122241.
    Yu, Q. Z.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Brage, Claes O.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Chen, G. X.
    Sjöström, Krister
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
    The fate of fuel-nitrogen during gasification of biomass in a pressurised fluidised bed gasifier2007In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 86, no 4, p. 611-618Article in journal (Refereed)
    Abstract [en]

    The distribution of fuel-nitrogen in gases, tar and char from gasification of biomass in a pressurised fluidised bed gasifier was investigated. Four species of biomass: birch, Salix, Miscanthus and Reed canary grass were gasified at 0.4 MPa and 900 degrees C. Oxygen-enriched nitrogen was used as fluidising agent. As a reference, gasification of Daw Mill coal was also carried out under the same experimental conditions. The experimental results illustrate that both the nature of the original fuels and the chemical structure of the nitrogen in the fuel have influence on the distribution of fuel-nitrogen in gases (NH3, HCN, NO), tar and char under the employed experimental conditions. The present work also shows that the types of nitrogen heterocyclic compounds (NHCs) in the tar from different kinds of biomass are the same and the major compound is pyridine. However, the distribution of the various NHCs in the tar from the four species of biomass varies: the higher the content of fuel-nitrogen, the higher the concentration of two-ring NHCs in the tar. An effective method for extracting NHCs from the acidic absorption of the product gas was introduced in the present work. The method makes use of solid phase extraction (SPE) by a silica-based C-18 tube to extract the NHCs which subsequently were analysed by gas chromatography (GC) with flame ionisation detection (FID). The recovery and reproducibility of the SPE technique for NHCs is discussed.

  • 122242.
    Yu, Q. Z.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Brage, Claes O.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Nordgreen, Thomas
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Sjöström, Krister
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Effects of Chinese dolomites on tar cracking in gasification of birch2009In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 88, no 10, p. 1922-1926Article in journal (Refereed)
    Abstract [en]

    To minimize tar in the producer gas from birch gasification at 700, 750 and 800 degrees C, four Chinese dolomites (Zhenjiang, Nanjing, Shanxi, Anhui) and a Swedish dolomite (Sala) used as reference were studied in a laboratory-scale atmospheric fluidized bed gasifier. The gasifier was equipped with a downstream fixed catalyst bed. The results imply that all dolomites but Anhui dolomite effectively decompose tar into gases. Anhui dolomite showed a low catalytic capacity to crack tar produced at 700 and 800 degrees C. The influence of various ratios of steam to biomass on tar content in the producer gas after passing over dolomite was studied. The tar cracking efficiency of the dolomites did not improve significantly with the ratio of steam to biomass in the region 0.11-0.52.

  • 122243. Yu, Qing C.
    et al.
    Hirst, Claire E.
    Costa, Magdaline
    Ng, Elizabeth S.
    Schiesser, Jacqueline V.
    Gertow, Karin
    KTH, School of Biotechnology (BIO).
    Stanley, Edouard G.
    Elefanty, Andrew G.
    APELIN promotes hematopoiesis from human embryonic stem cells2012In: Blood, ISSN 0006-4971, E-ISSN 1528-0020, Vol. 119, no 26, p. 6243-6254Article in journal (Refereed)
    Abstract [en]

    Transcriptional profiling of differentiating human embryonic stem cells (hESCs) revealed that MIXL1-positive mesodermal precursors were enriched for transcripts encoding the G-protein-coupled APELIN receptor (APLNR). APLNR-positive cells, identified by binding of the fluoresceinated peptide ligand, APELIN (APLN), or an anti-APLNR mAb, were found in both posterior mesoderm and anterior mesendoderm populations and were enriched in hemangioblast colony-forming cells (Bl-CFC). The addition of APLN peptide to the media enhanced the growth of embryoid bodies (EBs), increased the expression of hematoendothelial genes in differentiating hESCs, and increased the frequency of Bl-CFCs by up to 10-fold. Furthermore, APLN peptide also synergized with VEGF to promote the growth of hESC-derived endothelial cells. These studies identified APLN as a novel growth factor for hESC-derived hematopoietic and endothelial cells.

  • 122244. Yu, R. X.
    et al.
    Bai, Xue-Song
    Vressner, Andreas
    Hultqvist, Anders
    Lunds Tekniska Högskola, Sweden.
    Johansson, Bengt
    Olofsson, Jimmy
    Seyfried, Hans
    Sjöholm, J.
    Richter, Mattias
    Aldén, Marcus
    Effect of Turbulence on HCCI Combustion2007In: Session: Homogeneous Charge Compression Ignition (HCCI) (Part 4 of 8) Combustion Modeling / Optical Diagnostics, 2007Conference paper (Refereed)
    Abstract [en]

    This paper presents large eddy simulation (LES) and experimental studies of the combustion process of ethanol/air mixture in an experimental optical HCCI engine. The fuel is injected to the intake port manifolds to generate uniform fuel/air mixture in the cylinder. Two different piston shapes, one with a flat disc and one with a square bowl, were employed to generate different in-cylinder turbulence and temperature field prior to auto-ignition. The aim of this study was to scrutinize the effect of in-cylinder turbulence on the temperature field and on the combustion process. The fuel tracer, acetone, is measured using laser induced fluorescence (LIF) to characterize the reaction fronts, and chemiluminescence images were recorded using a high speed camera, with a 0.25 crank angle degree resolution, to further illustrate the combustion process. Pressure in the cylinder is recorded in the experiments. Spatial and temporal resolved LES was used to gain information on the turbulence mixing, heat transfer and combustion process. It was shown that gas temperature in the piston bowl is generally higher than that in the squish, leading to an earlier ignition in the bowl. Compared to the disc engine, the square bowl engine has a higher temperature inhomogeneity owing to the turbulence wall heat transfer. The experimentally observed higher combustion duration and slower pressure rise rate in the square bowl engine as compared to the disc engine can be explained by the higher temperature inhomogeneity in the square bowl engine.

  • 122245.
    Yu, Shengze
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Protein Science, Protein Engineering.
    Exploitation of interactions with the neonatal Fc receptor to manipulate biological half-lives for therapeutic applications2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Protein engineering provides powerful tools to create useful proteins with desired properties. In this thesis, rational design principles have been used for development of fusion proteins that can interact with the neonatal Fc receptor (FcRn) for potential medical applications. 

    FcRn is widely expressed in the human body. The natural ligands of FcRn are immunoglobulin G (IgG) and serum albumin (SA). FcRn can bind to both proteins in a pH dependent manner and endow them with an unusually long half-life in vivo. Protein building blocks interacting directly or indirectly with FcRn may potentially be used to either piggy-back on the FcRn-system for extension of the in vivo half-life or to saturate the system to decrease the in vivo half-life of the natural ligands. In this thesis, I have explored an FcRn binding affibody molecule (ZFcRn) and/or an albumin binding domain (ABD) for these purposes. 

    In study I and II, the prolactin receptor was found to often be expressed in glioblastoma multiforme tumors from patients as well as in glioblastoma multiforme cells lines. We investigated a novel antagonist of the prolactin receptor in vitro and found that it could block signaling through the receptor as well as cellular invasiveness. An antagonist of prolactin receptor could thus potentially become a drug for treatment of glioblastoma multiforme. However, the antagonist will likely have a short plasma half-life due to its small molecular size, which limits its usability. Therefore, it was expressed as a fusion to ABD, which interacts indirectly with FcRn. The produced fusion protein was found to be able to block signaling through the prolactin receptor in vitro and also had a prolonged plasma half-life in vivo

    The goal of study III was to investigate the properties of human growth hormone (hGH) when it was expressed as a protein fusion with ZFcRn, interacting directly with FcRn, and/or ABD. The fusion proteins, ZFcRn-hGH, ABD-hGH, and ZFcRn-ABD-hGH could be recombinantly expressed and successfully purified to homogeneity. They had the expected binding abilities to FcRn, SA and hGH receptor. They were all found to be able to induce signaling over the plasma membrane in a model cell line. 

    Patients suffering from many autoimmune diseases produce particular IgG molecules, which are responsible for the disease symptoms. A potential treatment could be to increase the catabolism of these IgGs to relieve disease symptoms. In study IV, an FcRn interacting affibody molecule was investigated for IgG depletion by blocking the IgG/FcRn interaction. In vitro, we first found that the affibody molecule shares a common binding site with IgG on FcRn, which indicates that the affibody should be able to block IgG from binding to FcRn. In vivo, we injected large amounts of the affibody molecules in different formats in mice and found up to 39% reduction of total endogenous IgG. In a clinical setting, reduction of total IgG level would also reduce the disease causing IgGs, and potentially ameliorate the symptoms of IgG-driven autoimmune diseases. 

    Taken together, I have in this thesis explored application of FcRn interacting molecules for extension of biological half-lives of therapeutically relevant proteins and reduction of total IgG level by FcRn blocking. 

  • 122246.
    Yu, Shengze
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Protein Science.
    Alkharusi, Amira
    Sultan Qaboos Univ, Coll Med & Hlth Sci, Muscat, Oman..
    Norstedt, Gunnar
    Sultan Qaboos Univ, Coll Med & Hlth Sci, Muscat, Oman.;Karolinska Inst, Ctr Mol Med, Stockholm, Sweden..
    Gräslund, Torbjörn
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Protein Science.
    An in vivo half-life extended prolactin receptor antagonist can prevent STAT5 phosphorylation2019In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 14, no 5, article id e0215831Article in journal (Refereed)
    Abstract [en]

    Increasing evidence suggests that signaling through the prolactin/prolactin receptor axis is important for stimulation the growth of many cancers including glioblastoma multiforme, breast and ovarian carcinoma. Efficient inhibitors of signaling have previously been developed but their applicability as cancer drugs is limited by the short in vivo half-life. In this study, we show that a fusion protein, consisting of the prolactin receptor antagonist PrlRA and an albumin binding domain for half-life extension can be expressed as inclusion bodies in Escherichia coli and efficiently refolded and purified to homogeneity. The fusion protein was found to have strong affinity for the two intended targets: the prolactin receptor (K-D = 2.3 +/- 0.2 nM) and mouse serum albumin (K-D = 0.38 +/- 0.01 nM). Further investigation showed that it could efficiently prevent prolactin mediated phosphorylation of STAT5 at 100 nM concentration and above, similar to the PrlRA itself, suggesting a potential as drug for cancer therapy in the future. Complexion with HSA weakened the affinity for the receptor to 21 +/- 3 nM, however the ability to prevent phosphorylation of STAT5 was still prominent. Injection into rats showed a 100-fold higher concentration in blood after 24 h compared to PrlRA itself.

  • 122247.
    Yu, Shengze
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Protein Science, Protein Engineering.
    Gräslund, Torbjörn
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Protein Science, Protein Engineering.
    Human growth hormone can transduce signals to phosphorylate STAT5 as a fusion with an affibody molecule binding the neonatal Fc receptor and an albumin binding domainManuscript (preprint) (Other academic)
    Abstract [en]

    Growth hormone replacement therapy has been used to treat children and adults with

    growth hormone deficiency for more than three decades. Growth hormone has a short

    biological half-life, requiring daily subcutaneous injections, and long acting versions are

    therefore desirable. In this study we have analyzed three fusion proteins, ZFcRn-hGH,

    ABD-hGH and ZFcRn-ABD-hGH, consisting of the human growth hormone (hGH) and an

    affibody molecule binding the neonatal Fc receptor (ZFcRn) and/or an albumin binding

    domain (ABD). Both ZFcRn and the ABD may have the ability to endow hGH with an

    extended plasma half-life. The fusion proteins could be recombinantly expressed in the

    periplasmic space of Escherichia coli and easily purified to homogeneity. All three fusion

    proteins appeared to have a strong interaction with the growth hormone receptor. ABDhGH

    and ZFcRn-ABD-hGH had a strong affinity for HSA (KD 0.006 and 0.02 nM,

    respectively). ZFcRn-hGH and ZFcRn-ABD-hGH had moderately strong affinity for mouse

    neonatal Fc receptor at pH 6.0 (KD 200 and 100 nM, respectively). The fusion proteins

    thus retained the expected binding abilities of the individual domains. Further

    characterization showed that the fusion proteins could induce phosphorylation of signal

    transducer and activator of transcription 5 (STAT5) in the model cell line U251-MG,

    further showing that the hGH-part of the fusion proteins was functional.

  • 122248. Yu, Shujun
    et al.
    Wang, Xiangxue
    Ai, Yuejie
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. North China Electric Power University, China.
    Liang, Yu
    Ji, Yongfei
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Li, Jiaxing
    Hayat, Tasawar
    Alsaedi, Ahmed
    Wang, Xiangke
    Spectroscopic and theoretical studies on the counterion effect of Cu(II) ion and graphene oxide interaction with titanium dioxide2016In: ENVIRONMENTAL SCIENCE-NANO, ISSN 2051-8153, Vol. 3, no 6, p. 1361-1368Article in journal (Refereed)
    Abstract [en]

    With the widespread use of graphene oxide (GO), it is inevitable that part of GO is released into the environment and co-exist with heavy metal ions as contaminants and is likely to be co-adsorbed on minerals and oxides. This study, for the first time, demonstrates the individual and mutual removal mechanism of GO and Cu(II) on titanium dioxide (TiO2) by batch experiments, spectroscopic analysis and density functional theory (DFT) computations. Electrostatic interaction and hydrogen bonding are the dominant modes of GO sorption onto TiO2, and the interaction of Cu(II) with TiO2 is mainly dominated by inner-sphere surface complexation. The presence of Cu(II) enhances GO coagulation on TiO2 and vice versa. The experimental results are further verified by DFT sorption energy (Es) calculations in the order (TiO2-GO)-Cu > TiO2-GO for GO interaction and (TiO2-GO)-Cu > TiO2-Cu for Cu(II) interaction. The mutual interaction is favorable for the simultaneous removal of GO and heavy metal ions by surface complexation between Cu(II) and oxygen-containing functional groups. These findings might facilitate better understanding of the co-removal behavior of carbon nanomaterials and heavy metal ions on oxides, which is crucial to decreasing the environmental toxicity of pollutants in the natural environment.

  • 122249. Yu, Shujun
    et al.
    Wang, Xiangxue
    Yao, Wen
    Wang, Jian
    Ji, Yongfei
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ai, Yuejie
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Alsaedi, Ahmed
    Hayat, Tasawar
    Wang, Xiangke
    Macroscopic, Spectroscopic, and Theoretical Investigation for the Interaction of Phenol and Naphthol on Reduced Graphene Oxide2017In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 51, no 6, p. 3278-3286Article in journal (Refereed)
    Abstract [en]

    Interaction of phenol and naphthol with reduced graphene oxide (rGO), and their competitive behavior on rGO were examined by batch experiments, spectroscopic analysis and theoretical calculations. The batch sorption showed that the removal percentage of phenol or naphthol on rGO in bisolute systems was significantly lower than those of phenol or naphthol in single-solute systems. However, the overall sorption capacity of rGO in bisolute system was higher than single-solute system, indicating that the rGO was a very suitable material for the simultaneous elimination of organic pollutants from aqueous solutions. The interaction mechanism was mainly pi-pi interactions and hydrogen bonds, which was evidenced by FTIR, Raman and theoretical calculation. FTIR and Raman showed that a blue shift of C=C and -OH stretching modes and the enhanced intensity ratios of I-D/I-G after phenols sorption. The theoretical calculation indicated that the total hydrogen bond numbers, diffusion constant and solvent accessible surface area of naphthol were higher than those of phenol, indicating higher sorption affinity of rGO for naphthol as compared to phenol. These findings were valuable for elucidating the interaction mechanisms between phenols and graphene-based materials, and provided an essential start in simultaneous removal of organics from wastewater.

  • 122250.
    Yu, Shun
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Molecular Interaction of Thin Film Photosensitive Organic Dyes on TiO2 Surfaces2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The photosensitive molecule adsorption on titanium dioxide (TiO2) forms the so-called “dye sensitized TiO2” system, a typical organic/oxide heterojunction, which is of great interest in catalysis and energy applications, e.g. dye-sensitized solar cell (DSSC). Traditionally, the transition metal complex dyes are the focus of the study. However, as the fast development of the organic semiconductors and invention of new pure organic dyes, it is necessary to expand the research horizon to cover these molecules and concrete the fundamental understanding of their basic properties, especially during sensitization.In this work, we focus on two different photosensitive molecules: phthalocyanines and triphenylamine-based dyes. Phthalocyanines are organic semiconductors with symmetric macro aromatic molecular structures. They possess good photoelectrical properties and good thermal and chemical stability, which make them widely used in the organic electronic industries. Triphenylamine-based dyes are new types of pure organic dyes which deliver high efficiency and reduce the cost of DSSC. They can be nominated as one of the strong candidates to substitute the ruthenium complex dyes in DSSC. The researches were carried out using classic surface science techniques on single crystal substrates and under ultrahigh vacuum condition. The photosensitive molecules were deposited by organic molecular beam deposition. The substrate reconstruction and ordering were checked by low energy electron diffraction. The molecular electronic, geometric structures and charge transfer properties were characterized by photoelectron spectroscopy, near edge X-ray absorption fine structure spectroscopy and resonant photoelectron spectroscopy (RPES). Scanning tunneling microscopy is used to directly image the molecular adsorption.For phthalocyanines, we select MgPc, ZnPc, FePc and TiOPc, which showed a general charge transfer from molecule to the substrate when adsorbed on rutile TiO2(110) surface with 1×1 and 1×2 reconstructions. This charge transfer can be prevented by modifying the TiO2 surface with pyridine derivatives (4-tert-butyl pyridine (4TBP), 2,2’-bipyridine and 4,4’-bipyridine), and furthermore the energy level alignment at the interface is modified by the surface dipole established by the pyridine molecules. Annealing also plays an important role to control the molecular structure and change the electronic structure together with the charge transfer properties, shown by TiOPc film. Special discussions were done for 4TBP for its ability to shift the substrate band bending by healing the oxygen vacancies, which makes it an important additive in the DSSC electrolyte. For the triphenylamine-based dye (TPAC), the systematic deposition enables the characterization of the coverage dependent changes of molecular electronic and geometric structures. The light polarization dependent charge transfer was revealed by RPES. Furthermore, the iodine doped TPAC on TiO2 were investigated to mimic the electrolyte/dye/TiO2 interface in the real DSSC.The whole work of this thesis aims to provide fundamental understanding of the interaction between photosensitive molecules on TiO2 surfaces at molecular level in the monolayer region, e.g. the formation of interfacial states and the coverage dependent atomic and electronic structures, etc. We explored the potential of the application of new dyes and modified of the existing system by identifying their advantage and disadvantage. The results may benefit the fields of dye syntheses, catalysis researches and designs of organic photovoltaic devices.

2442244324442445244624472448 122201 - 122250 of 126553
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf