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  • 122901.
    Yang, Ting
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.
    Malkoch, Michael
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.
    Hult, Anders
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.
    The influence of diffusion time on the properties of sequential interpenetrating PEG hydrogels2013In: Journal of Polymer Science Part A: Polymer Chemistry, ISSN 0887-624X, E-ISSN 1099-0518, Vol. 51, no 6, p. 1378-1386Article in journal (Refereed)
    Abstract [en]

    Four sets comprising a total of 16 sequential interpenetrating network (SeqIPN) hydrogels were efficiently fabricated via UV initiated thiol-ene coupling chemistry and from 2 kDa or 8 kDa primary poly(ethylene glycol) (PEG) networks (S2 and S8). Each primary system delivered four different SeqIPNs constructed after 2, 4, 20, and 44 h diffusion of secondary network PEG precursors, 2 kDa and 8 kDa. This allowed the assessment of both mechanical and swelling properties for a wide range of novel hydrogels ranging from loosely crosslinked SeqIPN 8-8 to densely crosslinked SeqIPN 2-2 systems. All gel fractions of secondary networks were above 83% and 44 h of diffusion was found sufficient to fully saturate the primary networks. Disperse red functionalized PEGs (2 kDa and 8 kDa) were further used as probes to investigate the diffusion mechanisms. The impact of diffusion time on loosely crosslinked S8 network with a swelling degree of 970% and tensile modulus of 175 kPa displayed a significant change in the final properties. For instance, a 2 h diffusion of 2 kDa PEG precursors generated a SeqIPN 8-2:2 comprising a secondary network solid content of 34% with a water swelling degree 580% and a tensile modulus of 365 kPa. On saturation, that is, 44 h of diffusion, SeqIPN 2-8:44 exhibited 64% of secondary network solid content, a swelling capacity of 380% and over fourfold of tensile modulus (758 kPa) when compared with the primary network S8. SeqIPN hydrogel with the highest tensile modulus and lowest degree of water swelling was obtained after 44 h diffusion of 2 kDa PEG precursors within the densely crosslinked S2 primary network. In this case, SeqIPN 2-2:44 noted a water swelling capability of 280% and a tensile modulus over 1 MPa. The latter was twofold when compared with S2 with a tensile modulus of 555 kPa. Consequently, the diffusion time of secondary network is a promising parameter to control and that enables the fabrication of PEG hydrogels with a wider window of mechanical and swelling properties.

  • 122902. Yang, W.
    et al.
    Yang, H.
    Chuwongin, S.
    Seo, J. -H
    Ma, Z.
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Hammar, Mattias
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Zhou, W.
    Frame-assisted membrane transfer for large area optoelectronic devices on flexible substrates2011In: 2011 IEEE Winter Topicals, WTM 2011, 2011, p. 113-114Conference paper (Refereed)
    Abstract [en]

    Frame assisted membrane transfer process was developed to transfer large area crystalline semiconductor nanomembranes on flexible plastic substrates. InP nanomembranes as large as 2cm×2cm was transferred successfully. Large area flexible photodetectors, solar cells and LED arrays all have been demonstrated experimentally, based on transferred InP nanomembranes.

  • 122903. Yang, W.
    et al.
    Yang, H.
    Qin, G.
    Pang, H.
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Hammar, Mattias
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Soref, R.
    Zhenqiang, M.
    Zhou, W.
    Crystalline silicon nanomembrane stacking for large-area flexible photodetectors2009In: IEEE International Conference on Group IV Photonics GFP, 2009, p. 110-112Conference paper (Refereed)
    Abstract [en]

    Flexible photodetectors were demonstrated experimentally on large-area crystalline silicon nanomembranes (3 mm×3 mm), based on wet transfer and metal-frame supported transfer processes. Very low dark current (a few nA) and linear photoresponses were demonstrated for both Si MSM and InP PIN photodiodes on flexible PET substrates.

  • 122904. Yang, W.
    et al.
    Zhou, W.
    Zhenqiang, M.
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Hammar, Mattias
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Flexible solar cells based on stacked crystalline semiconductor nanomembranes on plastic substrates2010In: Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference: 2010 Laser Science to Photonic Applications, CLEO/QELS 2010, 2010, p. 5501105-Conference paper (Refereed)
    Abstract [en]

    We report here experimental demonstration of flexible solar cells based on crystalline semiconductor nanomembranes (NMs) transferred onto flexible PET (polyethylene terephthalate) substrates. For 1 micrometer thick p-i-n InP NMs, we obtained an open circuit voltage of 0.68 V and power efficiency of 1.5% from the photovoltaic solar cells. The results agree very well with the anticipated thin film InP solar cell performance considering the low absorption in very thin InP NMs. The efficiency remains unchanged for bending radii greater than 42 mm. It drops to 50% of its original value at a bending radius of 32 mm. The results demonstrate a promising future for such, a new type of cost effective flexible thin film solar cells, based on crystalline semiconductor membranes.

  • 122905.
    Yang, Weihong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Blasiak, W.
    Flame entrainments induced by a turbulent reacting jet using high-temperature and oxygen-deficient oxidizers2005In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 19, no 4, p. 1473-1483Article in journal (Refereed)
    Abstract [en]

    The entrainments of a turbulent jet in co-flow under high-temperature and oxygen-deficient oxidizers have been numerically and theoretical studied. By describing the chemical flame reaction, the entrainment induced by a turbulent reacting jet flame is calculated along the entire chemical flame length by mean of a flame entrainment ratio. The results in the near field of a reacting jet are verified by comparison with the results of published measurements. The effects of preheat temperature, the oxygen concentration of the oxidizer, the heat release, and buoyancy on the entrainment rate are investigated. The following results were obtained: (1) The uniformity of the heat release in reacting jets has a strong effect on the flame entrainment: the more uniform the heat release, the greater the entrainment. The effect of heat release reduces the entrainment in the near field of the reacting jets with the same factor of the characteristic ratio, which is r = (T-f/T-o)(0.5). (2) The entrainment increases as the oxygen concentration is decreased. Furthermore, the entrainment is independent of the fuel flow rate and the preheat temperature of the oxidizer for the investigated temperature range (1073-1573 K). (3) The effect of the oxygen concentration and preheat temperature of the oxidizer on buoyancy was examined. A correction Richardson coordinate, which includes the effect of the oxygen concentration (stoichiometric ratio), was derived to describe the local influence of buoyancy force along the chemical flame length under the high-temperature and oxygen-deficient oxidizer conditions. It can be concluded that the buoyancy force increases with the reduction of the oxygen concentration in the oxidizer. (4) The global behavior of the entrainment was revealed. The entrainment of jet flames can be identified as two regimes: (i) the near field, where the entrainment coefficient is positive, and (ii) the far field, where the entrainment coefficient is negative. Corrections for the entrainment rates were derived in terms of a Froude number (Fr) for the momentum-buoyancy transition jet flame under the high-temperature and low-oxygen-concentration oxidizer conditions. Furthermore, the maximum entrainments along the flame length are estimated.

  • 122906.
    Yang, Weihong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Blasiak, W.
    Mathematical modelling of NO emissions from high-temperature air combustion with nitrous oxide mechanism2005In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 86, no 9, p. 943-957Article in journal (Refereed)
    Abstract [en]

    A study of the mathematical modelling of NO formation and emissions in a gas-fired regenerative furnace with high-preheated air was performed. The model of NO formation via N2O-intermediate mechanism was proposed because of the lower flame temperature in this case. The reaction rates of this new model were calculated basing on the eddy-dissipation-concept. This model accompanied with thermal-NO, prompt-NO and NO reburning models were used to predict NO emissions and formations. The sensitivity of the furnace temperature and the oxygen availability on NO generation rate has been investigated. The predicted results were compared with experimental values. The results show that NO emission formed by N2O-intermediate mechanism is of outstanding importance during the high-temperature air combustion (HiTAC) condition. Furthermore, it shows that NO models with N2O-route model can give more reasonable profile of NO formation. Additionally, increasing excess air ratio leads to increasing of NO emission in the regenerative furnace.

  • 122907.
    Yang, Weihong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Blasiak, W.
    Numerical simulation of properties of a LPG flame with high-temperature air2005In: International journal of thermal sciences, ISSN 1290-0729, E-ISSN 1778-4166, Vol. 44, no 10, p. 973-985Article in journal (Refereed)
    Abstract [en]

    This work is connected with properties of a flame obtained by combustion of liquified propane gas (LPG) with highly preheated air using a regenerative burner. The attention is focused on both the size and shape of the flame and the results were obtained in a semi-industrial furnace equipped with a regenerative burner system. Results of the CFD-based mathematical modeling have been compared with measurements of a number of parameters including the furnace-wall temperature and the concentrations of gaseous species in the furnace. The results indicate that the flame spread can be well predicted using the numerical model. A flame entrainment ratio has been proposed here for describing and classifying the physical changes of the flame shape. This ratio can be used to optimize the diameter and length of a combustion chamber for specific applications. It is also found that equipping a furnace with a regenerative burner can provide a high saving energy, a larger flame volume and a lower emission of NO. It has been obtained that a lower excess air ratio leads to a low peak temperature and a larger flame volume, thus a lower NO emission.

  • 122908.
    Yang, Weihong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Blasiak, Wlodzimierz
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    CFD as applied to high temperature air combustion in industries furnaces2006In: IRFR Combustion Journal, ISSN 1562-479X, no November 2006Article in journal (Refereed)
  • 122909.
    Yang, Weihong
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Blasiak, Wlodzimierz
    KTH, Superseded Departments, Materials Science and Engineering.
    Chemical flame length and volume in liquified propane gas combustion using high-temperature and low-oxygen-concentration oxidizer2004In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 18, no 5, p. 1329-1335Article in journal (Refereed)
    Abstract [en]

    In this paper, the effect of a high-temperature oxidizer at different oxygen concentrations on chemical flame length and volume has been numerically studied. Liquified propane gas (LPG) was used as the fuel. Hot exhaust flue gas was used as the dilution gas. The studied parameters include oxygen concentration and temperature of the oxidizer, fuel temperature, fuel firing rate, and diameter of the fuel nozzle. The following results were obtained: (1) Chemical flame length increased as either the oxygen content decreased, the oxidizer temperature increased, or the fuel temperature decreased; furthermore, the chemical flame length was independent of the fuel flow rate and the diameter of the fuel nozzle for the studied cases. (2) Chemical flame volume increased either as the oxygen content decreased and the oxidizer temperature increased, the fuel temperature was reduced, or the fuel firing rate was increased; chemical flame volume was dependent very much on the oxygen concentration in the oxidizer. (3) Influences of high temperature and low oxygen concentration in the oxidizer on the flame Froude number (Fr-f) were examined; regimes of momentum control or buoyancy control were determined on the assumption that the oxidizer temperature and oxygen concentration are changeable. (4) A simple correlation of the chemical flame length and volume, relative to the flow parameters, has been derived in terms of a Frf number for momentum-buoyancy transition jet flame under the high-temperature air combustion (HiTAC) condition. The criteria constants of the dimensionless chemical flame volume (V-*) and the dimensionless chemical flame length (L-*), to assess the momentum- or buoyancy-controlled flame, are given.

  • 122910.
    Yang, Weihong
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Blasiak, Wlodzimierz
    KTH, Superseded Departments, Materials Science and Engineering.
    Combustion performance and numerical simulation of a high-temperature air-LPG flame on a regenerative burner2004In: Scandinavian journal of metallurgy, ISSN 0371-0459, E-ISSN 1600-0692, Vol. 33, no 2, p. 113-120Article in journal (Refereed)
    Abstract [en]

    High-temperature air combustion is attracting great interest in the metallurgical industry lately as its claimed benefits include large energy saving, low air emissions, increased product quality and increased productivity. This paper presents a numerical study of combustion performance in a semi-industrial test furnace equipped with a regenerative burner and with a conventional turbulent jet burner. The numerical calculation is also validated by experiment. In this regard, flow field was calculated with k-epsilon turbulence model, the model of combustion employed the eddy dissipation concept with a two-step mechanism to describe chemical reactions; radiation was handled using the discrete transfer method. The results indicate that equipping a furnace with high-cycle regenerative burner systems can provide more uniform gas temperature profiles, a higher energy utilizing efficiency, a low NOx emission, a larger flame, the low maximum local heat release and the possibility of low combustion noise.

  • 122911.
    Yang, Weihong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Blasiak, Wlodzimierz
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    High temperature air combustion for steam reformers2005In: Hydrocarbon Processing, ISSN 0018-8190, Vol. 84, no 9, p. 115-122Article in journal (Refereed)
  • 122912.
    Yang, Weihong
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Blasiak, Wlodzimierz
    KTH, Superseded Departments, Materials Science and Engineering.
    Length and volume in LPG flame using high-temperature and low oxygen oxidizer2004In: International Symposium on Combustion, Abstracts of Works-in-Progress Posters, 2004Conference paper (Refereed)
    Abstract [en]

    The effect of a high temperature combustion oxidizer at different oxygen concentration on flame length and volume was numerically studied. LPG was used as the fuel. Flame length increased with either the decrease of oxygen content, or increase of oxidizer temperature, or decrease of fuel temperature. The flame length was independent of the fuel flow rate and the diameter of the fuel nozzle for studies cases. Flame volume increased either with the decrease of oxygen content and increase of oxidizer temperature, or with the reduction of fuel temperature, or with the increasing in fuel firing rate. Flame volume depended very much on the oxygen concentration in the oxidizer. This is an abstract of a paper presented at the 30th International Symposium on combustion (Chicago, IL 7/25-30/2004).

  • 122913.
    Yang, Weihong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Blasiak, Wlodzimierz
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Numerical study of fuel temperature influence on single gas jet combustion in highly preheated and oxygen deficient air2005In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 30, no 04-feb, p. 385-398Article in journal (Refereed)
    Abstract [en]

    Combustion of a single jet of propane in a cross-flowing stream of preheated and oxygen deficient air is numerically analyzed with emphasis on influences of fuel temperature. Both Eddy-Break-Up and PDF/mixture fraction combustion models coupled with RNG k-epsilon turbulent model were applied and the predicted results were compared. Thermal and prompt NO models were employed to calculate NO emissions. Results show that the Eddy-Break-Up model is more suitable for predicting temperature field and flame shape. It was showed that flame during high temperature air combustion condition is spread over a much larger volume. Flame volume increases with a reduction of oxygen concentration. and this trend is clearer if oxygen concentration in the preheated air is below 10%. Additionally, it is almost constant at fixed oxygen concentration and fuel inlet temperature for the temperature of the preheated and oxygen deficient air equal to 1041-1273 K. Increase of the fuel inlet temperature results in smaller flame, shorter mean residence time, smaller temperature peaks, and lower emission of NO.

  • 122914.
    Yang, Weihong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Mörtberg, Magnus
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Blasiak, Wlodzimierz
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Influences of flame configurations on flame properties and NO emissions in combustion with high-temperature air2005In: Scandinavian journal of metallurgy, ISSN 0371-0459, E-ISSN 1600-0692, Vol. 34, no 1, p. 7-15Article in journal (Refereed)
    Abstract [en]

    High-temperature air combustion using the high-cycle generator is attracting great interest in mettalurgical industries. Flame configurations play a very important role when a modern regenerative burner system is adopted in an industrial furnace because multi-burners are required. Numerical studies of combustion in a semi-industrial scale test furnace equipped with two sets of two-flame high-cycle regenerative system have been performed and results were compared with experimental values. Influences of flame configurations on combustion properties and NO emissions of LPG with high-temperature air were numerical studies as well as excess air ratio. The flame volume and size were figured out by a parameter named as oxidation mixture ratio. It is found that the flame configurations have strong influences on the combustion and flame properties as well as NO emission. Increasing the excess air ratio leads to increasing of NO emission. Lesser the ratio of fuel/air injection momentum larger is the NO production.

  • 122915.
    Yang, Weihong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Ponzio, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Lucas, Carlos
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Blaslak, Wlodzmierz
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
    Performance analysis of a fixed-bed biomass gasifier using high-temperature air2006In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 87, no 3, p. 235-245Article in journal (Refereed)
    Abstract [en]

    Gasification of biomass using high-temperature agents (air/steam) has been proven to have many features superior to those of conventional gasification using low-temperature agents. In this work, an experimental fixed-bed gasifier is utilized to investigate the gasification of biomass using high-temperature air up to 1473 K. A mathematical model has been formulated for the prediction of the main chemical and physical processes and is used to study the influence of temperature, oxygen concentration and flow rate of the feed gas. Predicted gas species concentration profiles and their maximum values are in reasonable agreements with the measurements. The results show that: (a) When the temperature of feed gas is increased, a higher gasification rate, a higher ignition front rate, and higher molar fractions of fuel gases (CO, H-2 and CmHn), thus a higher LHV are obtained. (b) Increased oxygen concentration leads to higher peak values of the fuel gas concentrations, a higher gasification rate, and a larger ignition front rate.

  • 122916. Yang, Weiquan
    et al.
    Yang, Hongjun
    Qin, Guoxuan
    Ma, Zhenqiang
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Hammar, Mattias
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Soref, Richard
    Zhou, Weidong
    Large-area InP-based crystalline nanomembrane flexible photodetectors2010In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 96, no 12, p. 121107-Article in journal (Refereed)
    Abstract [en]

    Large-area (3x3 mm(2)) flexible photodetectors were realized, based on crystalline InP semiconductor nanomembranes transferred to flexible polyethylene terephthalate substrates. Very low dark current (a few microamperes) and high responsivity (0.12 A/W) were demonstrated for flexible InP p-i-n photodetectors. Bending characteristics were also investigated for this type of flexible crystalline semiconductor photodetector, and it was found that, whereas the dark current was independent of bending radii, the photocurrent degraded, depending on the bending radii.

  • 122917.
    Yang, Weishan
    KTH, School of Industrial Engineering and Management (ITM), Industrial Ecology.
    Critical Review of EIA Implementation Framework and Operational Procedures in China: A Case Study of Panyu District Public Conflict2010Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The shifting tendency of environmental conflict of some specific projects from post-conflict to pre-conflict is taking place in China. The main reason is that the public raises awareness of environmental consequences and makes more transparence information exchanged among stakeholders. Therefore the authorities have to face the new challenges and figure out new solutions to handle the changing circumstances.

    One of the recent conflicts regarding Panyu’s incineration project is selected as a typical example analyzed in this report. This case indicates three main argued focal points at environmental perspective of project implementation which are currently unsatisfied in China’s society: 1. Failure of EIA making & approving system; 2. Inadequate public participation on the decision-making process; 3. Imbalance in stakeholders’ pattern of the project implementation process.

    This thesis have explored China’s EIA reports’ making, examining and approving system through investigation on its administrative, legislative and operational framework. The work was carried out during my internship in Safety Center of Henan Science Academy of Environmental Protection. The investigation also includes several interviews with different stakeholders of Panyu’s case.

    Based on the theoretical and empirical research, the thesis pointed out the root of defects of the existing EIA system in China is: 1. Public’s opinions can’t be truly reflected on the EIA report in the EIA making process; 2. Other stakeholders’ interests seriously affected the justice of EIA examination and approval process.

    The recommended approaches for improving the system include: 1. Strength public participation process to allow as much affected neighbors to realize the project and reflect their perception to decision-makers as possible; 2. Improve current EIA examination and approval procedures in order to weak the linkage between government and business sector. 3. Enhance the cooperation between environmental authority and other administrative board.

  • 122918. Yang, Wenchao
    et al.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Casting of Metals.
    Ji, Shouxun
    Halo formation of Zn-Al alloys under conventional solidification and intensive convection solidification2017In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 696, p. 460-469Article in journal (Refereed)
    Abstract [en]

    A halo occurred usually as an envelope of one phase around a primary phase in many alloys after solidification. Its formation mechanism was investigated for hypoeutectic, eutectic and hypereutectic compositions of Zn-Al alloys under conventional solidification and under intensive convection solidification. It was found that the Zn-rich halos occurred in the surroundings of the Al-rich primary phase for the hypereutectic Zn-Al alloys at Al> 5 wt% and no halos occurred for the hypoeutectic and eutectic Zn-Al alloys at Al <= 5 wt% under conventional solidification. However, the Zn-rich halos were completely absent from the Al-rich phase because of the uniform temperature distribution and enhanced mass transport under intensive convection solidification. Once the intensive convection was interrupted during solidification for the solid-liquid co-existing melt, a halo was formed on the surface of the existing Al-rich phase created either during the primary solidification or the eutectic solidification. Therefore, it was concluded that the halo formation should be a growth-dominant phenomenon not a nucleationdominant phenomenon. And, the interaction among the solid phases and the liquid phase was responsible for the halo formation, in which the difference in the elasticity modulus and the density of the different phases resulted in the variation of strain energy in the individual phase.

  • 122919.
    Yang, Wentao
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Transport planning.
    Simulation-based evaluation of a new floating vehicle speeding detection method2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Driving too fast is one of the major causes that lead to road crashes. A new speed enforcement management method based on autonomous vehicle technologies has the potential to enhance the speed limit compliance and improve traffic safety. This paper investigates the performance of this method in the detection stage under different scenarios. 27 scenarios are generated using microscopic simulation in VISSIM to collect performance data of this method. Analysis of variance (ANOVA) is used to examine the performance difference between scenarios, including the detectable distance, the number of lanes, the speed of the measuring vehicle, the flow of the traffic, the desired average speed of the traffic, and the desired speed variance of the traffic. As a result, the influences of the factors on the performance of the method are distinguished. The detectable distance, the speed of the measuring vehicle and the flow of traffic have non-linear effects on the number of detected speeding vehicles. The measuring vehicle can interact with more speeding vehicles when the average speed of the traffic is high and the speed variance is small.

  • 122920.
    Yang, Wenxing
    et al.
    Uppsala Univ, Angstrom Lab, Dept Chem, Box 523, SE-75120 Uppsala, Sweden.;Imperial Coll London, Dept Chem, London SW7 2AZ, England..
    Hao, Yan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Kloo, Lars
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Boschloo, Gerrit
    Uppsala Univ, Angstrom Lab, Dept Chem, Box 523, SE-75120 Uppsala, Sweden..
    Carrier Dynamics of Dye Sensitized-TiO2 in Contact with Different Cobalt Complexes in the Presence of Tri(p-anisyl)amine Intermediates2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 26, p. 14345-14354Article in journal (Refereed)
    Abstract [en]

    Heterogeneous charge transfer processes at sensitized wide bandgap semiconductor surfaces are imperative for both fundamental knowledge and technical applications. Herein, we focus on the investigation of carrier dynamics of a triphenylamine-based dye, LEG4, sensitized TiO2 (LEG4/TiO2) in contact with two types of electrolyte systems: pure cobalt-based electrolytes and in combination with an organic donor, tri(p-anisyl)amine (TPAA). Four different cobalt redox systems with potentials spanning a 0.3 V range were studied, and the carrier recombination and regeneration kinetics were monitored both at low and at high TiO2 (e(-)) densities (1.3 X 10(18) and 1.3 X 10(19) cm(-3), respectively). The results reveal that the introduction of the TPAA intermediate more effectively suppress the recombination loss of TiO2 (e(-)) under high charge conditions, close to open-circuit, as compared to low charge conditions. As a result, the charge transfer from the cobalt complexes to the oxidized dyes is significantly improved by the addition of TPAA. Dye-sensitized solar cells fabricated with the TPAA-containing electrolytes demonstrate remarkable improvement in both V-OC and J(SC) and lead to more than 25% increase of the light-to-electricity conversion efficiency. Furthermore, an unprecedented detrimental impact of TPAA on the device performance was identified when the redox potential of the TPAA donor and the cobalt complexes are close. This is ascribed to the formation of TPAA(center dot+) which can act as an active recombination centers and thus lower the solar cell performance. These insights point at a strategy to enhance the lifetimes of electrons generated in sensitized semiconductor electrodes by overcoming the charge recombination between TiO2 and the oxidized dye under high carrier densities in the semiconductor substrate and offer practical guidance to the design of future efficient electrolyte systems for dye-sensitized solar cells.

  • 122921. Yang, X. C.
    et al.
    Kritikos, M.
    Akermark, B.
    Sun, Licheng C.
    Axial ligand exchange reaction on ruthenium phthalocyanines2005In: Journal of Porphyrins and Phthalocyanines, ISSN 1088-4246, E-ISSN 1099-1409, Vol. 9, no 4, p. 248-255Article in journal (Refereed)
    Abstract [en]

    Bis(4-methylpyridine)phthalocyaninato ruthenium(II) has been synthesized. It was proved by single-crystal X-ray diffraction that the central Ru(II) atom is bonded to six N atoms in an elongated octahedral configuration, and the axial ligands have a significantly longer Ru-N bond distance, 2.101(4) angstrom, than the independent pyrrol Ru-N bond, 1.99 angstrom. Therefore, the axial ligands can be exchanged by other ligands. The ligand exchange reactions with diethyl pyridyl-4-phosphonate and diethyl pyridylmethyl-4-phosphonate were studied in high boiling-point solvents at elevated temperatures, ca 160 degrees C. Mono-ligand as well as double-ligand replaced complexes were obtained. The complexes have been isolated by column chromatography. These complexes have potential applications, such as in dye sensitized solar cells.

  • 122922. Yang, X. C.
    et al.
    Wu, Z. W.
    Sun, Licheng C.
    Ni, C. J.
    The bromination mechanism of 1-aminoanthraquinone-2,4-disulfonic acid in sulfuric acid2006In: Dyes and pigments, ISSN 0143-7208, E-ISSN 1873-3743, Vol. 71, no 3, p. 231-235Article in journal (Refereed)
    Abstract [en]

    I-Amino-4-bromoanthraquinotie-2-sulfoiiic acid (bromoamine acid) is an important intermediate for dyes. 1-Aminoanthraquinone2,4-disulfonic acid is the major impurity when 1-aminoanthraquinone is sulfonated in oleum to synthesize bromoamine acid. The mechanism of bromination of 1-aminoanthraquinone-2,4-disulfonic acid in sulfuric acid has been studied. It is proved that I-aminoanthraquinone-2,4-disulfonic acid undergoes de-sulfonation first to form 1-aminoanthraquinoine-2-sulfonic acid, and then bromination to form bromoamine acid. Based on this mechanism, a new optimal process for the synthesis of bromoamine acid is developed. In this way, bromoamine acid is afforded in high yield and good quality.

  • 122923. Yang, X.
    et al.
    Li, H.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala University, Sweden.
    Kang, T.
    Luo, W.
    Formation and electronic properties of palladium hydrides and palladium-rhodium dihydride alloys under pressure2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, no 1, article id 3520Article in journal (Refereed)
    Abstract [en]

    We present the formation possibility for Pd-hydrides and Pd-Rh hydrides system by density functional theory (DFT) in high pressure upto 50 GPa. Calculation confirmed that PdH2 in face-centered cubic (fcc) structure is not stable under compression that will decomposition to fcc-PdH and H2. But it can be formed under high pressure while the palladium is involved in the reaction. We also indicate a probably reason why PdH2 can not be synthesised in experiment due to PdH is most favourite to be formed in Pd and H2 environment from ambient to higher pressure. With Rh doped, the Pd-Rh dihydrides are stabilized in fcc structure for 25% and 75% doping and in tetragonal structure for 50% doping, and can be formed from Pd, Rh and H2 at high pressure. The electronic structural study on fcc type Pd x Rh1-xH2 indicates the electronic and structural transition from metallic to semi-metallic as Pd increased from x = 0 to 1.

  • 122924. Yang, X.
    et al.
    Zheng, N.
    Zhao, L.
    Deng, S.
    Li, Hailong
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Energy Processes.
    Yu, Z.
    Analysis of a novel combined power and ejector-refrigeration cycle2016In: Energy Conversion and Management, ISSN 0196-8904, E-ISSN 1879-2227, Vol. 108, p. 266-274Article in journal (Refereed)
    Abstract [en]

    A novel combined power and ejector-refrigeration cycle using zeotropic mixture is proposed. In the combined cycle, the turbine exhaust from the organic Rankine cycle entrains the vapor from the ejector-refrigeration cycle. And the zeotropic mixture is divided into the power cycle and the ejector-refrigeration cycle through a vapor-liquid separator. And these two flows have different composition. The cycle performance with different fluid composition is evaluated and it is compared with a conventional combined cycle. It is found that the cycle exergy achieves a maximum value of 10.29% with mixture isobutane/pentane (40%/60%), and the thermal efficiency gets a maximum value of 10.77% with mixture isobutane/pentane (70%/30%). The temperature glide in the evaporator achieves a maximum value of 15.09 K with mixture isobutane/pentane (80%/20%). The parametric analysis shows that the cycle performs better in lower condenser temperature. Though the refrigeration cycle achieves lower evaporating temperature in higher generating temperature, the power output is reduced.

  • 122925. Yang, X.-F.
    et al.
    Chen, X.-S.
    Lu, W
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Effects of Shape and Strain Distribution of Quantum Dots on Optical Transition in the Quantum Dot Infrared Photodetectors2008In: Nanoscale Research Letters, ISSN 1931-7573, Vol. 3, no 12, p. 534-539Article in journal (Refereed)
    Abstract [en]

    We present a systemic theoretical study of the electronic properties of the quantum dots inserted in quantum dot infrared photodetectors (QDIPs). The strain distribution of three different shaped quantum dots (QDs) with a same ratio of the base to the vertical aspect is calculated by using the short-range valence-force-field (VFF) approach. The calculated results show that the hydrostatic strain epsilon(H) varies little with change of the shape, while the biaxial strain epsilon(B) changes a lot for different shapes of QDs. The recursion method is used to calculate the energy levels of the bound states in QDs. Compared with the strain, the shape plays a key role in the difference of electronic bound energy levels. The numerical results show that the deference of bound energy levels of lenslike InAs QD matches well with the experimental results. Moreover, the pyramid-shaped QD has the greatest difference from the measured experimental data.

  • 122926.
    Yang, Xi
    KTH, School of Chemical Science and Engineering (CHE).
    Polylactide and polycaprolactone grafted starch – synthesis, characterization and degradation2011Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Pollution is one of the most important issues in the world today. Renewable and degradable plastics attract more attention to the research. Starch can not only be used as food but also it has many other applications. In papermaking industry, textile, food processing, adhesive industry and some other areas, starch has its place.

    However starch-based materials show very poor mechanical properties due to their strong water absorption and poor interfacial adhesion with other components. This study aims to improve properties of starch-based materials. Starch granules surface were modified by lactic acid. Then polylactide and polycaprolactone were grafted on those surface modified starch granules. With the help of SEM, it was easy to notice that after grafting reactions, the smooth surface of starch granules became rough. However because of the purification process it was hard to calculate the grafting degree. Some films of starch, polylactide, polycaprolactone and grafted starch with different ratios were prepared and their properties and degradation behaviors were studied with DSC, Instron, SEM and FTIR. With PLA or PCL and surface grafting PLA or PCL in the matrix, water resistance of starch improved a lot. However maybe during the grafting process starch became more water soluble (gelatinized or amorphous) so water resistances of those films with grafted starch were less than those with raw starch granules. Films with grafted starch showed higher weight loss after degradation. The poor mechanical properties due to the severe phase separation between starch and PLA were, however, improved by grafting. It was also interest to find that films with 25% starch and 75% PCL showed good mechanical properties. The largest elongation at break and the largest tensile stress at tensile strength were shown by films with 25% st-g-PCL2 and 75%PCL.

  • 122927.
    Yang, Xi
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Strategies for Utilizing Biobased and Recycled Resources for Polylactide Plasticization2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    There are many aspects that should be considered to achieve truly "environmental friendly" and "sustainable" materials. These include the raw material resource, the energy consumption, the chemicals generated and used, the emissions during production, processing, transportation, disposal and so on. The work presented in this thesis focused on development of strategies for valorization of biopolymers and further utilization of the derived chemicals for plasticization of polylactide (PLA). This would retain the material value of the biopolymers, the degradability and biobased nature of PLA, while simultaneously broadening the application areas and properties of PLA.

    Two green, and efficient methodologies for chemical recycling of poly(3-hydroxybutyrate) (PHB), a natural biodegradable biopolymer produced in microorganisms as an energy storage material, were demonstrated. Full degradation to monomeric degradation products: crotonic acid (CA), 3-hydroxybutanoic acid (3HB) and 3-methoxybutanoic acid (3MB) was obtained in only 20 minutes through microwave assisted degradation in green solvents. Degradation parameters, such as solvent and basicity, were carefully evaluated for achieving high yield and fast degradation and the constituent ratio of degradation products could be tuned by adjusting the degradation time under the optimized condition. Meanwhile PHB oligomers with crotonic end groups (dPHB) were formed by thermal degradation of PHB during extrusion, which is an industrially viable process. The effects of degradation temperature and degradation time on the formation of degradation products were carefully adjusted, and the degradation kinetics at different temperatures were evaluated. Glucose, a depolymerization product of cellulose and starch, was modified by hexanoic acid to star shaped glucose esters (GHx) with different varying degrees of substitution by adjusting the reaction time.

    Two methodologies to plasticize PLA by utilizing the products from PHB recycling or the synthesized glucose esters were evaluated aiming at plasticizers with enhanced migration resistance compared to the physical blends or commercial analogues: 1) anchoring linear oligomeric plasticizers onto PLA and 2) blending low molar mass star shaped molecules into the PLA matrix. Specifically, PLA-CA-PBSA was prepared by coupling poly(butylene succinate-co-adipate) (PBSA) to CA functionalized PLA, PLA-g-dPHB was obtained by coupling dPHB onto the PLA main chain via reactive extrusion. PLA blends with star shaped GHx were also prepared. Decrease of Tg was observed for all the plasticized PLA samples. Blending GHx reduced the Tg of PLA by about 30 ºC and a decrease in Tg for approximately 25 ºC and 20 ºC was realized by coupling PLA with dPHB or PBSA, respectively. All plasticized PLA materials showed increased elongation at break. For PLA-g-dPHB a 66-fold increased elongation at break was achieved. The crystallization capacity of both PBSA and dPHB coupled PLA was improved at the same times as the PLA was plasticized. This is explained by the grafting points acting as nucleating sites and is further facilitated by the improved chain mobility of the PLA chains.

    The proposed approaches for PHB recycling, modification of glucose and the coupling or blending strategies demonstrated great promise for the concept of utilizing recycled biopolymers/biomass for plasticization of PLA.

  • 122928.
    Yang, Xi
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    The Use of One-Time Password and RADIUS Authentication in a GSS-API Architecture2006Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The Generic Security Service Application Program Interface (GSS-API) is an architecture that facilitates applications using distributed security services in a mechanism-independent fashion. GSS-API is supported by various underlying mechanisms and technologies such as Kerberos version 5 and public-key technologies. However, no one-time password based GSS-API mechanism existed.

    This thesis focuses on an investigation using one-time passwords together with RADIUS authentication as a protection facility for a GSS-API mechanism. This thesis presents a security architecture using one-time passwords to establish a GSS-API security context between two communicating peers.

    The proposed one-time password based GSS-API mechanism could be used to enhance the security of user authentication. Moreover, the mechanism can greatly facilitate static-password based system’s transition to stronger authentication.

  • 122929.
    Yang, Xi
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Clénet, Jocelyn
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Xu, Huan
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Odelius, Karin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Two step extrusion process: From thermal recycling of PHB to plasticized PLA by reactive extrusion grafting of PHB degradation products onto PLA chains2015In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 48, no 8, p. 2509-2518Article in journal (Refereed)
    Abstract [en]

    A green and industrially viable two-step process was demonstrated for toughening polylactide (PLA) without compromising the biobased and biodegradable nature. First, poly(3-hydroxybutyrate) (PHB) biopolymer was thermally degraded in an extruder to create PHB oligomers (dPHB) with functional end-groups suitable for further reactions. Second, a reactive extrusion process was developed to covalently anchor dPHB onto the main chain of PLA. PLA with 20% (w/w) grafted dPHB demonstrated an impressive elongation at break of 538%, 66 times higher than that of pure PLA and significantly higher than the elongation at break of the corresponding physical blend. At the same time WAXD measurements illustrated that grafting significantly increased the crystallization ability of PLA. We present a viable recycling route for PHB and a highly promising approach for fully biobased toughened PLA with covalently anchored PHB plasticizers.

  • 122930.
    Yang, Xi
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Finne-Wistrand, Anna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Improved dispersion of grafted starch granules leads to lower water resistance for starch-g-PLA/PLA composites2013In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 86, p. 149-156Article in journal (Refereed)
    Abstract [en]

    Polylactide (PLA) was grafted on the surface of starch (St) granules to improve the interfacial adhesion between starch granules and PLA matrix in starch/PLA blends. The grafting significantly improved strain at failure values of St-g-PLA/PLA 25:75 blends as compared to starch/PLA 25:75 blends. However, unexpectedly the water resistance of the films significantly deteriorated after the surface grafting. SEM and FTIR analysis showed that St-g-PLA was evenly distributed at the film surface and in the bulk, while unmodified starch was encapsulated inside the PLA matrix. This resulted in rapid leaching of St-g-PLA from the films during aging in water, while the unmodified starch granules were protected by PLA matrix.

  • 122931.
    Yang, Xi
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Migration resistant glucose esters as bioplasticizers for polylactide2015In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 132, no 18, article id 41928Article in journal (Refereed)
    Abstract [en]

    Environmental and sustainability issues have catalyzed efforts to replace traditional polymer additives with biobased alternatives. Glucose pentaacetate (GPA) and sucrose octaacetate (SOA) as model commercial saccharide esters and three synthesized glucose hexanoate esters (GHs) were evaluated as bioplasticizers for polylactide (PLA). For the GHs different reaction times were utilized to reach plasticizers with different number of hexanoate groups to establish how the degree of substitution influences miscibility and migration resistance of the plasticizers. The synthesized GHs, GPA, and SOA all showed good miscibility with PLA. Largest improvements in strain at break were observed for the PLA films containing GH plasticizers. These films also exhibited simultaneous increase in stress at break as compared to plain PLA. The GH plasticizers had low tendency to migrate during aging in water and this migration resistance increased with increasing degree of substitution. The GHs are, thus, promising plasticizer alternatives for bioplastics as they also retain the biodegradable nature of these biobased materials.

  • 122932.
    Yang, Xi
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Odelius, Karin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Microwave-Assisted Reaction in Green Solvents Recycles PHB to Functional Chemicals2014In: ACS Sustainable Chemistry and Engineering, ISSN 2168-0485, Vol. 2, no 9, p. 2198-2203Article in journal (Refereed)
    Abstract [en]

    An efficient microwave-assisted process for chemical recycling of poly(3-hydroxybutyrate) (PHB) in green solvents was demonstrated. Previously, PHB has been thermally recycled to crotonic acid and unsaturated oligomers. Our aim was to utilize green solvents (water, methanol, and ethanol) under alkaline conditions to achieve fast hydrolysis and monomeric or oligomeric degradation products with carboxyl and hydroxyl or methoxy or ethoxy end groups. Preliminary screening confirmed that the most efficient degradation process was obtained in alkaline methanol. In addition, sample amount, sodium hydroxide concentration, and degradation time all influenced the degradation process and final degree of degradation. Comparison with pure thermal degradation clearly demonstrated the effectiveness of the microwave-assisted process as the time and temperature needed for complete degradation was significantly reduced. Several characterization techniques were utilized for mapping the degradation processes and resulting degradation products. After optimization of the process, complete degradation of PHB to monomeric degradation products (3-hydroxybutanoic acid, 3-methoxybutanoic acid, and crotonic acid) was reached after only 20 min of microwave heating at 110 degrees C. Functional chemicals for synthesis or modification of biopolymers are thus obtainable from microwave-assisted degradation of PHB in green solvents. This offers new possibilities for retaining the material value of PHB via chemical recycling.

  • 122933.
    Yang, Xi
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Xu, Huan
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Odelius, Karin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Poly(lactide)-g-poly(butylene succinate-co-adipate) with High Crystallization Capacity and Migration Resistance2016In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 9, no 5, article id 313Article in journal (Refereed)
    Abstract [en]

    Plasticized polylactide (PLA) with increased crystallization ability and prolonged life-span in practical applications due to the minimal plasticizer migration was prepared. Branched plasticized PLA was successfully obtained by coupling poly(butylene succinate-co-adipate) (PBSA) to crotonic acid (CA) functionalized PLA. The plasticization behavior of PBSA coupled PLA (PLA-CA-PBSA) and its counterpart PBSA blended PLA (PLA/PBSA) were fully elucidated. For both PLA-CA-PBSA and PLA/PBSA, a decrease of Tg to around room temperature and an increase in the elongation at break of PLA from 14% to 165% and 460%, respectively, were determined. The crystallinity was increased from 2.1% to 8.4% for PLA/PBSA and even more, to 10.6%, for PLA-CA-PBSA. Due to the inherent poor miscibility between the PBSA and PLA, phase separation occurred in the blend, while PLA-CA-PBSA showed no phase separation which, together with the higher crystallinity, led to better oxygen barrier properties compared to neat PLA and PLA/PBSA. A higher resistance to migration during hydrolytic degradation for the PLA-CA-PBSA compared to the PLA/PBSA indicated that the plasticization effect of PBSA in the coupled material would be retained for a longer time period.

  • 122934.
    Yang, Xiaobin
    KTH, School of Industrial Engineering and Management (ITM), Applied Mechanical Engineering (KTH Södertälje).
    Market estimates in China for Swedish health food using stochastic approach2011Independent thesis Advanced level (degree of Master (Two Years)), 10 credits / 15 HE creditsStudent thesis
  • 122935.
    Yang, Xiaofan
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Enterprise’ E-invoicing Adoption in China2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This master thesis is an empirical investigation project that has been carried out in cooperation with Trustweaver AB. The purpose is to identify the key factors that influence the adoption of electronic invoicing in Chinese enterprises. A background study on global e-invoicing adoption and current e-invoicing development in China is conducted. A research model integrated by the diffusion of innovation theory, the technology, organization, and environment framework and Iacovou et al. (1995) model is postulated.The research model consists of three constructs which are technological context, organizational context and environmental and external context. Key factors that are analyzed in the research are perceived benefits and barriers, leader’s attitude, technology and financial readiness, top management support, partner and competitive pressure, government pressure, and regulatory concern. Based on the research model and the theoretical basis for each of the explanatory variables, nine hypotheses stating the relationships between the key factors and enterprises’ e-invoicing adoption intention are proposed.An online survey has been conducted and 72 responses have been collected from management of Chinese enterprises. Descriptive statistics and paired-samples T test are used to describe the values distribution and test the difference between the variables. Factor analysis and reliability test are performed to evaluate the validity of variables and assess the stability of constructs. Linear regression analysis is employed in order to examine six proposed hypotheses, i.e. the relationships between technological and organizational characteristics and enterprises’ adoption of e-invoicing.The results generally offer support for the research model and eight of the hypotheses hold while one rejects. Analysis has shown that perceived barriers, management attitude and support, technology and financial readiness are the determinant factors of e-invoicing adoption. Results also indicate that environmental and external factors strongly influence enterprises’ adoption decision, whereby government pressure and policy support have the most significant effect. The findings could be taken account to improve e-invoicing diffusion in China. Some strategies are developed in the study to promote enterprises’ adoption of e-invoicing.

  • 122936.
    Yang, Xiaohu
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Energy Processes. Institute of the Building Environment & Sustainability Technology, School of Human Settlements and Civil Engineering, Xi’an Jiaotong University, Xi’an 710049, PR China; School of Sustainable Development of Society and Technology, Mälardalen University, 721 23 Västerås, Sweden.
    Bai, Q.
    Guo, Z.
    Niu, Z.
    Yang, C.
    Jin, L.
    Lu, T. J.
    Yan, J.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Energy Processes. School of Sustainable Development of Society and Technology, Mälardalen University, 721 23 Västerås, Sweden.
    Comparison of direct numerical simulation with volume-averaged method on composite phase change materials for thermal energy storage2018In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 229, p. 700-714Article in journal (Refereed)
    Abstract [en]

    Melting heat transfer in open-cell metal foams embedded in phase-change materials (PCMS) predicted by the volume-averaged method (VAM) was systematically compared with that calculated using direct numerical simulation (DNS), with particular attention placed upon the contribution of natural convection in the melt region to overall phase change heat transfer. The two-temperature model based on the assumption of local thermal non-equilibrium was employed to account for the large difference of thermal conductivity between metallic ligaments and PCM (paraffin). The Forchheimer extended Darcy model was employed to describe the additional flow resistance induced by metal foam. For the DNS, a geometric model of metal foam based on tetrakaidehedron cells was reconstructed. The DNS results demonstrated significant temperature difference between ligament surface and PCM, thus confirming the feasibility of local thermal non-equilibrium employed in VAM simulations. Relative to the DNS results, the VAM combined with the two-temperature model could satisfactorily predict transient solid-liquid interface evolution and local temperature distribution, although pore-scale features of phase change were lost. The presence of natural convection affected significantly the melting front shape, temperature distribution and full melting. The contribution of natural convection to overall phase change heat transfer should be qualitatively and quantitatively given sufficient consideration from both macroscopic (VAM) and microscopic (DNS) point of views. Besides, practical significance and economic prospective using metal foam in TES unit for WHR system to provide residential heating or hot water is discussed and analyzed.

  • 122937.
    Yang, Xiaohu
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Energy Processes. Xi'an Jiaotong University, Xi'an, China.
    Bai, Q.
    Zhang, Q.
    Hu, W.
    Jin, L.
    Yan, Jinyue
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Energy Processes. Mälardalen University (MDH), Västerås, Sweden.
    Thermal and economic analysis of charging and discharging characteristics of composite phase change materials for cold storage2018In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 225, p. 585-599Article in journal (Refereed)
    Abstract [en]

    This study conducted both experimental and numerical investigations on the solidification behavior in a metal foam composite phase change material (PCM) for cold storage. Volume-average-method was adopted with the help of Forchheimer-Darcy equation to model the fluid flow through porous media. Experimental measurements were performed to validate the analytical model and the numerical method, with good agreement achieved. Local thermal equilibrium and non-equilibrium states were justified numerically and experimentally. Effect of pore morphological parameters (porosity and pore density) upon the solidification features of composite PCM were investigated. For the appliance of composite PCM to cold storage, techno-economic characteristics was also assessed. Results demonstrated that the full solidification time for metal foams with a porosity of 0.93 and 0.97 can be saved 87.5% and 76.7% respectively compared with pure water. It indicated that porosity of metal foam played a dominant role in heat transfer enhancement; while pore density seemed to have little influence on phase change behavior according to the results. Local natural convection in the unsolidified phase caused a remarkable promotion of the interface evolution, and the full solidification time with natural convection considered can be saved by 14.3% compared with pure conduction for the case with the same porosity of 0.97. The economic analyses indicated that using composite PCM was profitable with a short payback period less than 2 years.

  • 122938.
    Yang, Xiaohu
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Energy Processes. Xi'an Jiaotong University, China; Mälardalen University, Sweden.
    Lu, Z.
    Bai, Q.
    Zhang, Q.
    Jin, L.
    Yan, Jinyue
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Energy Processes. Mälardalen University, Sweden.
    Thermal performance of a shell-and-tube latent heat thermal energy storage unit: Role of annular fins2017In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 202, p. 558-570Article in journal (Refereed)
    Abstract [en]

    This study conducts numerical investigations on melting process in a shell-and-tube latent heat thermal energy storage (LHTES) unit with annular fins. Commercial grade paraffin is employed as the phase change material (PCM) and water serves as the heat transfer fluid (HTF). Finite-volume-method (FVM) based numerical simulations are performed to investigate the effects of fin number, height and thickness on the phase change process. Particular attention is made to justify the contribution of local natural convection to the overall phase change process. Results demonstrate that the full melting time could be maximally reduced by 65% by inserting annular fins into PCM. For maximizing thermal performance, an optimal group fin parameter (fin number N = 31, thickness t/l = 0.0248 and interval l/L = 0.0313) is recommended for the present study.

  • 122939.
    Yang, Xiaotian
    KTH, Superseded Departments, Chemistry.
    Interfacing spectrophotometry to process liquors applications to kraft pulping2002Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This thesis summarizes the outcome of work performed withthe objective to contribute to the knowledge and development ofthe kraft cooking process using spectrophotometricinterfaces.

    In kraft cooking, it is desirable to maximize the removal oflignin in the cook without loss of pulp strength. Theselectivity can be improved by exchanging some of the hydrogensulfide ion in the white liquor for polysulfides. Paper Ipresents a spectrophotometric method for in-line monitoring ofthe electrochemical production of polysulfide using anATR-probe for the UV-Vis range. A linear relation existsbetween the ATR-probe response and the concentration ofabsorbing species. Thus the process can be followed by simplemonitoring of a few wavelengths.

    A spectrophotometric monitoring system using a durableNafion ionomer membrane interface for continuous on-linemeasurement of sulfide and dissolved lignin during kraftcooking has previously been developed by our group. In paperII, the permeation of low molecular weight anions from liquorshaving high ionic strengths through a membrane in Na+ form hasbeen studied. A general relation between penetration and ionsize approximated by molecular weight has been established. Thepenetration of different anions can be explained as a diffusionthrough the winding membrane channels. Further the differentanions transport independently without being interfered by thesample matrix.

    In light of this validation, we applied the membraneinterface to the determination of anthraquinone-2-sulfonate(AQ-S) in alkaline pulping liquor. In paper III, a simple andrapid spectrophotometric method was developed and implementedon real samples. Interferences from other compounds penetratingthe membrane were minimized by reduction of the penetrated AQ-Sand measurement at 520 nm. This method is quick and can be usedon-line. Further, we extended the method to determination ofanthraquinone (AQ) in pulping liquor (paper IV). Although AQ isregarded as insoluble, it was found that the apparentsolubility of AQ in alkaline solutions increases considerablyin the presence of lignin, reaching 0.14 g/L at 90 oC. Thismakes the calibration of AQ possible. Time-resolvedmeasurements of dissolved AQ in 3 kraft-AQ pulping processeswere performed.

    The results show that the membrane has great potential aspart of a selective interface in applications where theconcentrations of small anions are to be monitored in mediawith high ionic strength.

    Keywords: Kraft cooking, On-line, Sulfide, Lignin,Polysulfide excess sulfur, Anthraquinone-2-Sulfonate (AQ-S),Anthraquinone (AQ), Nafion Membrane, UV-Vis, ATR-probe,Spectrophotometric.

  • 122940. Yang, Xiaoxia
    et al.
    Dong, Hairong
    Wang, Qianling
    Chen, Yao
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Guided crowd dynamics via modified social force model2014In: Physica A: Statistical Mechanics and its Applications, ISSN 0378-4371, E-ISSN 1873-2119, Vol. 411, p. 63-73Article in journal (Refereed)
    Abstract [en]

    Pedestrian dynamics is of great theoretical significance for strategy design of emergency evacuation. Modification of pedestrian dynamics based on the social force model is presented to better reflect pedestrians' behavioral characteristics in emergency. Specifically, the modified model can be used for guided crowd dynamics in large-scale public places such as subway stations and stadiums. This guided crowd model is validated by explicitly comparing its density-speed and density-flow diagrams with fundamental diagrams. Some social phenomena such as gathering, balance and conflicts are clearly observed in simulation, which further illustrate the effectiveness of the proposed modeling method. Also, time delay for pedestrians with time-dependent desired velocities is observed and explained using the established model in this paper. Furthermore, this guided crowd model is applied to the simulation system of Beijing South Railway Station for predictive evacuation experiments.

  • 122941.
    Yang, Xiaoyong
    et al.
    Southwest Univ Sci & Technol, Stale Key Lab Environm Friendly Energy Mat, Natl Collaborat Innovat Ctr Nucl Waste & Environ, Mianyang 621010, Sichuan, Peoples R China.;Uppsala Univ, Condensed Matter Theory Grp, Mat Theory Div, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Banerjee, Amitava
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Uppsala Univ, Condensed Matter Theory Grp, Mat Theory Div, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Probing the active sites of newly predicted stable Janus scandium dichalcogenides for photocatalytic water-splitting2019In: Catalysis Science & Technology, ISSN 2044-4753, E-ISSN 2044-4761, Vol. 9, no 18, p. 4981-4989Article in journal (Refereed)
    Abstract [en]

    The Janus structures of transition metal dichalcogenides with intrinsic dipoles have recently drawn attention as efficient candidates in the class of non-precious metal photocatalysts for water splitting. Here, we have proposed Janus ScXY (X/Y = S, Se, or Te, X not equal Y) monolayers as promising catalysts for the hydrogen evolution reaction (HER). We have thoroughly investigated the structural stabilities of the ScXY monolayers, as a primary step to understand the splitting mechanism more accurately. It has been observed that Janus ScSSe and ScSeTe monolayers are dynamically, thermally and mechanically stable, whereas the ScSTe monolayer is dynamically unstable. Moreover, based on hybrid functional (HSE06) calculations, these stable ScSSe and ScSeTe monolayers are semiconductors with direct band gaps of 1.810 and 0.921 eV, respectively. Considering spin-orbit coupling on top of the HSE06 calculations results in an insignificant change in the band gaps. The steady optical responses of Janus ScSSe and ScSeTe, respectively, in the visible and near IR spectra demonstrate their photocatalytic activities in the respective regions. Interestingly, we have observed excellent performance shown by the ScSeTe monolayer, where both surfaces are catalytically active, and maintain close to thermoneutral conditions with near-zero adsorption free energy at different H* coverages. Comparatively, the ScSSe monolayer shows poor performance for the HER due to strong bonds with the adsorbed hydrogen. Also, it has been confirmed that even the application of +/- 2% strain on the ScSSe monolayer does not enhance its HER activity. Our theoretical predictions demonstrate that out of all the Janus ScXY monolayers studied here, ScSeTe is the most active catalyst for the HER to efficiently split water, which certainly could make it worth performing further experimental investigations.

  • 122942.
    Yang, Xiaoyong
    et al.
    Southwest Univ Sci & Technol, Natl Collaborat Innovat Ctr Nucl Waste & Environm, Mianyang 621010, Sichuan, Peoples R China.;Uppsala Univ, Dept Phys & Astron, Condensed Matter Theory Grp, Mat Them Div, Box 516, S-75120 Uppsala, Sweden..
    Singh, Deobrat
    Uppsala Univ, Dept Phys & Astron, Condensed Matter Theory Grp, Mat Them Div, Box 516, S-75120 Uppsala, Sweden..
    Xu, Zhitong
    Southwest Univ Sci & Technol, Natl Collaborat Innovat Ctr Nucl Waste & Environm, Mianyang 621010, Sichuan, Peoples R China..
    Wang, Ziwei
    Southwest Univ Sci & Technol, Natl Collaborat Innovat Ctr Nucl Waste & Environm, Mianyang 621010, Sichuan, Peoples R China..
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Uppsala Univ, Dept Phys & Astron, Condensed Matter Theory Grp, Mat Them Div, Box 516, S-75120 Uppsala, Sweden..
    An emerging Janus MoSeTe material for potential applications in optoelectronic devices2019In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 7, no 39, p. 12312-12320Article in journal (Refereed)
    Abstract [en]

    Motivated by the extraordinary physical and chemical properties of Janus transition-metal dichalcogenides (TMDs) due to the change of the crystal field originating from their asymmetry structures, the electronic and optical properties of the MoSeTe monolayer in 2H and 1T phases are systematically studied by first-principles calculations, and a detailed comparison with the parental MoSe2 and MoTe2 monolayer is made. It is found that 2H-MoSeTe exhibits a direct bandgap of 1.859 eV and an indirect band gap of 0.391 eV in the 1T phase, resulting in a different way to interact with sunlight. Besides, the obtained results show that the SOC has little effects on the band gaps. The calculated optical properties show a significant red shift from the MoSe2 to MoSeTe to MoTe2 monolayer. However, a blue shift is observed from the in-plane to out-of-plane direction. Moreover, both electron-electron and electron-hole correlation effects are considered for obtaining the optical spectra of systems by G(0)W(0) and G(0)W(0) + BSE approaches. Besides, the absorption coefficient value reaches up to 1 x 10(6) cm(-1) in both phases, implying the high efficiency in the utilization of solar energy for the MoSeTe monolayer. Additionally, the 1T-MoSeTe monolayer is a good hot mirror material in that its maximum reflectivity could reach up to 51% in the infrared region. Additionally, the average optical absorbance of the Janus MoSeTe monolayer in the visible light region is calculated to be about 2% and the corresponding average transmittance is around 80%. More importantly, the difference in the optical response for the two side surfaces is considered in our work due to the intrinsic asymmetric structure of Janus MoSeTe. These results not only predict the great potential application of Janus MoSeTe in optoelectronics-electronic devices, but may enable the discovery of new optical science and the realization of various light emissions, detection, modulation and manipulation functions of specific frequencies.

  • 122943. Yang, Xiaoyu
    et al.
    Wang, Lihui
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering. University of Skövde.
    VR-Assisted Assembly Planning2009In: Proceedings of the 3rd International Swedish Production Symposium, 2009, p. 423-428Conference paper (Refereed)
    Abstract [en]

    In this paper, we present an intelligent assembly planning and training system combining virtual reality (VR) and motion tracking technologies. The development conceptual prototype for assembly planning and training enables individuals to interact with virtual environment in real time. It extends the new technologies of motion tracking and integrates them with virtual environment technologies to create real-time virtual work cell simulations in which workers may be immersed with hands-on experiences. The experimental results to date are presented to demonstrate the contributions of human skills in achieving intelligent assembly planning.

  • 122944. Yang, Xichuan
    et al.
    Jiang, Xiao
    Zhao, Changzhi
    Chen, Ruikui
    Qin, Peng
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Donor-acceptor molecules containing thiophene chromophore: synthesis, spectroscopic study and electrogenerated chemiluminescence2006In: Tetrahedron Letters, ISSN 0040-4039, E-ISSN 1359-8562, Vol. 47, no 28, p. 4961-4964Article in journal (Refereed)
    Abstract [en]

    Donor-acceptor molecules containing thiophene chromophore with remarkably large Stokes shift (> 210 nm) have been found to exhibit strong and stable ECL emission via the singlet excited state without the addition of any co-reactant or a second compound.

  • 122945. Yang, Xichuan
    et al.
    Wang, Lei
    Li, Shifeng
    Cheng, Ming
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    A new type of organic sensitizers with pyridine-N-oxide as the anchoring group for dye-sensitized solar cells2013In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 3, no 33, p. 13677-13680Article in journal (Refereed)
    Abstract [en]

    A series of organic dyes with alkaline pyridine-N-oxide as the electron acceptor and anchoring group have been synthesized and applied in dye-sensitized solar cells. Photoelectrical data show a good coordination between pyridine-N-oxide and TiO2 films, which effectively guarantee the injection and adsorption of the dye molecules. With the simple WL102 dye, the best photon-to-electron conversion efficiency of 3.72% and an excellent IPCE value about 95% have been achieved under optimized conditions.

  • 122946.
    Yang, Xichuan
    et al.
    Dalian Univ Technol, State Key Lab Fine Chem, Linggong Rd 2, Dalian 116024, Liaoning, Peoples R China..
    Wang, Weihan
    Dalian Univ Technol, State Key Lab Fine Chem, Linggong Rd 2, Dalian 116024, Liaoning, Peoples R China..
    Zhang, Yanyun
    Dalian Univ Technol, State Key Lab Fine Chem, Linggong Rd 2, Dalian 116024, Liaoning, Peoples R China..
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry.
    Improving the power conversion efficiency of solid state dye sensitized solar cells with a N-oxoammonium salt: 2,2,6,6-Tetramethyl-1-oxopiperidinebromide2018In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 170, p. 1001-1008Article in journal (Refereed)
    Abstract [en]

    P-type doping is a rational strategy for the enhancement of hole transporting properties of the organic semiconductors as well as the device performance of organic photo-electric devices. We originally introduce a stable and solution processed p-type dopant based on N-oxoammonium salts termed 2,2,6,6-tetramethyl-1-oxopiperidinebromide salt (TEMPO-Br) for 2,2',7,7'-tetrakis(N, N-di-p-methoxyphenyl-amine)9,9'-spirobifluorene (Spiro-OMeTAD) based solid state dye sensitized solar cells (ssDSC). By introducing TEMPO-Br doped Spiro-OMeTAD and a commercialized D-pi-A sensitizer into ssDSCs, a promising device performance of 6.83% is achieved under simulated AM 1.5G solar irradiation (100 mW cm(-2)), which is significantly better than the control devices ( similar to 1.7 times). The doping effect of TEMPO-Br on the photophysical and electrochemical properties of Spiro-OMeTAD, solid state device performance, cationic dye regeneration kinetics and preliminary long-term stability have been systematically investigated. This work indicates a potential application of N-oxoammonium salts as chemical P-type dopants for triphenylamine based hole transporting materials in solid state photo-electric devices.

  • 122947. Yang, Xichuan
    et al.
    Zhao, Jianghua
    Wang, Lei
    Tian, Jie
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Phenothiazine derivatives-based D-pi-A and D-A-pi-A organic dyes for dye-sensitized solar cells2014In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 4, no 46, p. 24377-24383Article in journal (Refereed)
    Abstract [en]

    D-pi-A and D-A-pi-A-structured organic dyes represent different developmental directions of photosensitizers in dye-sensitized solar cells (DSSCs). In this work, two phenothiazine derivatives-based D-pi-A and D-A-pi-A-structured organic dyes have been synthesized and applied in DSSCs. The physical and electrochemical properties of both dyes have been investigated systematically. The results show that the D-A-pi-A-structured dye exhibits a broader spectrum response but lower molar coefficient of extinction when compared to the D-pi-A-structured dye. Regarding photovoltaic performance, the D-pi-A-structured dye yields a higher efficiency (h) of 7.5% with a higher short-circuit current density (J(sc)) of 16.36 mA cm(-2) and open-circuit voltage (V-oc) of 706 mV than that of the D-A-pi-A-structured dye. Incident photon-to-electron conversion efficiency (IPCE) studies and impedance analysis also support these results. These results demonstrate that the phenothiazine derivatives-based D-pi-A-structured organic dyes can compete with, and even exceed, D-A-pi-A-structured organic dyes under the same test conditions.

  • 122948.
    Yang, Xifeng
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Fu, Kai
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Fu, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
    Strain effect in determining the geometric shape of self-assembled quantum dot2009In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 42, no 125414Article in journal (Refereed)
    Abstract [en]

    The geometric shape of a self-assembled quantum dot (QD) formed by the strain-induced Stranski-Krastanov mode has been studied as a function of strain energy by the short-range valence-force-field approach. It has been shown by dynamic bond relaxation through strain energy minimization that for the most commonly used InAs QD in GaAs and InP matrices and Ge QD in Si matrix, a pyramidal shape is energy favoured over an hemispherical shape when the QD is not capped due to the lattice relaxation at the QD surface. When the QD becomes totally embedded in the background material, the elastic strain energy of a hemispherical InAs QD is minimal. The results agree with experimental observations. We further studied the coupling of strain fields of QDs in adjacent QD layers which shows that QDs in multiply stacked QD layers can be aligned along the layer growth direction in order to minimize the strain energy.

  • 122949.
    Yang, Xifeng
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Liu, Y. S.
    Fu, Ying
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Optical absorptions in AlxGa1-xAs/GaAs quantum well for solar energy application2012In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 112, no 5, p. 054314-Article in journal (Refereed)
    Abstract [en]

    We study the optical transitions among localized and extended states in quantum solar cells based on AlxGa1-xAs/GaAs quantum well (QW). The absorption coefficients of localized-to-localized, ground localized-to-extended, and extended-to-localized transitions are enhanced obviously as the size of the QW decreases. When the wave functions of incident electrons and holes spread along different sides of the structure, the absorption coefficient of extended-to-extended states becomes non-zero value when the QW is inserted. This process has a main contribution to the photocurrents. In addition, our studies also show these optical transitions have different sensitivities to the Fermi levels. Therefore, optical absorptions in AlxGa1-xAs/GaAs solar cells can be optimized by the sizes of QW and Fermi levels.

  • 122950.
    YANG, XINYI
    KTH, School of Industrial Engineering and Management (ITM).
    Chip Breaking Optimization During Turning Shoulder2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
2456245724582459246024612462 122901 - 122950 of 128023
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