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Divin, A., Deca, J., Eriksson, A., Henri, P., Lapenta, G., Olshevsky, V. & Markidis, S. (2020). A Fully Kinetic Perspective of Electron Acceleration around a Weakly Outgassing Comet. Astrophysical Journal Letters, 889(2), Article ID L33.
Öppna denna publikation i ny flik eller fönster >>A Fully Kinetic Perspective of Electron Acceleration around a Weakly Outgassing Comet
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2020 (Engelska)Ingår i: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 889, nr 2, artikel-id L33Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The cometary mission Rosetta has shown the presence of higher-than-expected suprathermal electron fluxes. In this study, using 3D fully kinetic electromagnetic simulations of the interaction of the solar wind with a comet, we constrain the kinetic mechanism that is responsible for the bulk electron energization that creates the suprathermal distribution from the warm background of solar wind electrons. We identify and characterize the magnetic field-aligned ambipolar electric field that ensures quasi-neutrality and traps warm electrons. Solar wind electrons are accelerated to energies as high as 50-70 eV close to the comet nucleus without the need for wave-particle or turbulent heating mechanisms. We find that the accelerating potential controls the parallel electron temperature, total density, and (to a lesser degree) the perpendicular electron temperature and the magnetic field magnitude. Our self-consistent approach enables us to better understand the underlying plasma processes that govern the near-comet plasma environment.

Ort, förlag, år, upplaga, sidor
IOP PUBLISHING LTD, 2020
Nyckelord
Cometary atmospheres, Space plasmas, Astronomical simulations
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:kth:diva-271948 (URN)10.3847/2041-8213/ab6662 (DOI)000520966400001 ()2-s2.0-85080034664 (Scopus ID)
Anmärkning

QC 20200415

Tillgänglig från: 2020-04-15 Skapad: 2020-04-15 Senast uppdaterad: 2020-04-15Bibliografiskt granskad
O'Donncha, F., Iakymchuk, R., Akhriev, A., Gschwandtner, P., Thoman, P., Heller, T., . . . Fahringer, T. (2019). AllScale toolchain pilot applications: PDE based solvers using a parallel development environment. Computer Physics Communications, Article ID 107089.
Öppna denna publikation i ny flik eller fönster >>AllScale toolchain pilot applications: PDE based solvers using a parallel development environment
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2019 (Engelska)Ingår i: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, artikel-id 107089Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

AllScale is a programming environment targeting simplified development of highly scalable parallel applications by dividing development responsibilities into silos. The front-end AllScale API provides a simple C++ development environment through a suite of parallel constructs expressions denoting tasks operating concurrently. This interfaces with the other components of the toolchain (core-level API, compiler and runtime) which manages tasks related to the machine and system level, hidden to the user. The paper describes the development of two large-scale parallel applications within the AllScale API, namely, an advection– diffusion model with data assimilation and a Lagrangian space-weather simulation model based on a particle-in-cell method. We present mathematical formulations and implementations and evaluate parallel constructs developed using the AllScale API. The performance of the applications from the perspective of both parallel scalability, and more importantly productivity are assessed. We demonstrate how the AllScale API can greatly improve developer productivity while maintaining parallel performance in two applications with distinct numerical characteristics. Code complexity metrics demonstrate reduction in application specific implementations of up to 30% while performance tests on three different compute systems demonstrate comparable parallel scalability to an MPI version of the code.

Ort, förlag, år, upplaga, sidor
Elsevier B.V., 2019
Nyckelord
Advection–diffusion, Data assimilation, HPC, Numerical solvers, Partial differential equation, Particle-in-cell, Advection, Application programming interfaces (API), Codes (symbols), Machine components, Partial differential equations, Productivity, Scalability, Development environment, Mathematical formulation, Numerical characteristics, Particle in cell, Programming environment, Space weather simulation, C++ (programming language)
Nationell ämneskategori
Elektroteknik och elektronik
Identifikatorer
urn:nbn:se:kth:diva-268441 (URN)10.1016/j.cpc.2019.107089 (DOI)000528002400010 ()2-s2.0-85076580760 (Scopus ID)
Anmärkning

QC 20200423

Tillgänglig från: 2020-04-23 Skapad: 2020-04-23 Senast uppdaterad: 2020-05-07Bibliografiskt granskad
Peng, I. B., Vetter, J. S., Moore, S., Joydeep, R. & Markidis, S. (2019). Analyzing the Suitability of Contemporary 3D-Stacked PIM Architectures for HPC Scientific Applications. In: CF '19 - PROCEEDINGS OF THE 16TH ACM INTERNATIONAL CONFERENCE ON COMPUTING FRONTIERS: . Paper presented at 16th ACM International Conference on Computing Frontiers, CF 2019; Alghero, Sardinia; Italy; 30 April 2019 through 2 May 2019 (pp. 256-262). ASSOC COMPUTING MACHINERY
Öppna denna publikation i ny flik eller fönster >>Analyzing the Suitability of Contemporary 3D-Stacked PIM Architectures for HPC Scientific Applications
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2019 (Engelska)Ingår i: CF '19 - PROCEEDINGS OF THE 16TH ACM INTERNATIONAL CONFERENCE ON COMPUTING FRONTIERS, ASSOC COMPUTING MACHINERY , 2019, s. 256-262Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

Scaling off-chip bandwidth is challenging due to fundamental limitations, such as a fixed pin count and plateauing signaling rates. Recently, vendors have turned to 2.5D and 3D stacking to closely integrate system components. Interestingly, these technologies can integrate a logic layer under multiple memory dies, enabling computing capability inside a memory stack. This trend in stacking is making PIM architectures commercially viable. In this work, we investigate the suitability of offloading kernels in scientific applications onto 3D stacked PIM architectures. We evaluate several hardware constraints resulted from the stacked structure. We perform extensive simulation experiments and indepth analysis to quantify the impact of application locality in TI,Bs, data caches, and memory stacks. Our results also identify design optimization areas in software and hardware for HPC scientific applications.

Ort, förlag, år, upplaga, sidor
ASSOC COMPUTING MACHINERY, 2019
Nyckelord
processing-in-memory, 3D stacked mernory, PIM, NNARD RH, 1974, IEEE JOURNAL OF SOLID-STATE CIRCUITS, VSC 9, P256
Nationell ämneskategori
Elektroteknik och elektronik
Identifikatorer
urn:nbn:se:kth:diva-255514 (URN)10.1145/3310273.3322831 (DOI)000474686400036 ()2-s2.0-85066055698& (Scopus ID)
Konferens
16th ACM International Conference on Computing Frontiers, CF 2019; Alghero, Sardinia; Italy; 30 April 2019 through 2 May 2019
Anmärkning

QC 20191016

Tillgänglig från: 2019-10-16 Skapad: 2019-10-16 Senast uppdaterad: 2019-10-16Bibliografiskt granskad
Rivas Gomez, S., Markidis, S., Laure, E., Brabazon, K., Perks, O. & Narasimhamurthy, S. (2019). Decoupled Strategy for Imbalanced Workloads in MapReduce Frameworks. In: Proceedings - 20th International Conference on High Performance Computing and Communications, 16th International Conference on Smart City and 4th International Conference on Data Science and Systems, HPCC/SmartCity/DSS 2018: . Paper presented at 20th International Conference on High Performance Computing and Communications, 16th IEEE International Conference on Smart City and 4th IEEE International Conference on Data Science and Systems, HPCC/SmartCity/DSS 2018, 28 June 2018 through 30 June 2018 (pp. 921-927). Institute of Electrical and Electronics Engineers (IEEE)
Öppna denna publikation i ny flik eller fönster >>Decoupled Strategy for Imbalanced Workloads in MapReduce Frameworks
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2019 (Engelska)Ingår i: Proceedings - 20th International Conference on High Performance Computing and Communications, 16th International Conference on Smart City and 4th International Conference on Data Science and Systems, HPCC/SmartCity/DSS 2018, Institute of Electrical and Electronics Engineers (IEEE), 2019, s. 921-927Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

In this work, we consider the integration of MPI one-sided communication and non-blocking I/O in HPC-centric MapReduce frameworks. Using a decoupled strategy, we aim to overlap the Map and Reduce phases of the algorithm by allowing processes to communicate and synchronize using solely one-sided operations. Hence, we effectively increase the performance in situations where the workload per process becomes unexpectedly unbalanced. Using a Word-Count implementation and a large dataset from the Purdue MapReduce Benchmarks Suite (PUMA), we demonstrate that our approach can provide up to 23% performance improvement on average compared to a reference MapReduce implementation that uses state-of-the-art MPI collective communication and I/O.

Ort, förlag, år, upplaga, sidor
Institute of Electrical and Electronics Engineers (IEEE), 2019
Nyckelord
High Performance Computing, MapReduce, MPI One Sided Communication
Nationell ämneskategori
Datorteknik
Identifikatorer
urn:nbn:se:kth:diva-246358 (URN)10.1109/HPCC/SmartCity/DSS.2018.00153 (DOI)000468511200121 ()2-s2.0-85062487109 (Scopus ID)9781538666142 (ISBN)
Konferens
20th International Conference on High Performance Computing and Communications, 16th IEEE International Conference on Smart City and 4th IEEE International Conference on Data Science and Systems, HPCC/SmartCity/DSS 2018, 28 June 2018 through 30 June 2018
Anmärkning

QC 20190319

Tillgänglig från: 2019-03-19 Skapad: 2019-03-19 Senast uppdaterad: 2019-11-01Bibliografiskt granskad
Sishtla, C. P., Divin, A., Deca, J., Olshevsky, V. & Markidis, S. (2019). Electron trapping in the coma of a weakly outgassing comet. Physics of Plasmas, 26(10), Article ID 102904.
Öppna denna publikation i ny flik eller fönster >>Electron trapping in the coma of a weakly outgassing comet
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2019 (Engelska)Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 26, nr 10, artikel-id 102904Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Measurements from the Rosetta mission have shown a multitude of nonthermal electron distributions in the cometary environment, challenging the previously assumed plasma interaction mechanisms near a cometary nucleus. In this paper, we discuss electron trapping near a weakly outgassing comet from a fully kinetic (particle-in-cell) perspective. Using the electromagnetic fields derived from the simulation, we characterize the trajectories of trapped electrons in the potential well surrounding the cometary nucleus and identify the distinguishing features in their respective velocity and pitch angle distributions. Our analysis allows us to define a clear boundary in velocity phase space between the distributions of trapped and passing electrons. Published under license by AIP Publishing.

Ort, förlag, år, upplaga, sidor
AMER INST PHYSICS, 2019
Nationell ämneskategori
Beräkningsmatematik
Identifikatorer
urn:nbn:se:kth:diva-266916 (URN)10.1063/1.5115456 (DOI)000505980600044 ()2-s2.0-85074294951 (Scopus ID)
Anmärkning

QC 20200322

Tillgänglig från: 2020-03-22 Skapad: 2020-03-22 Senast uppdaterad: 2020-03-22Bibliografiskt granskad
Zhou, H., Toth, G., Jia, X., Chen, Y. & Markidis, S. (2019). Embedded Kinetic Simulation of Ganymede's Magnetosphere: Improvements and Inferences. Journal of Geophysical Research - Space Physics, 124(7), 5441-5460
Öppna denna publikation i ny flik eller fönster >>Embedded Kinetic Simulation of Ganymede's Magnetosphere: Improvements and Inferences
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2019 (Engelska)Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, nr 7, s. 5441-5460Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The largest moon in the solar system, Ganymede, is also the only moon known to possess a strong intrinsic magnetic field and a corresponding magnetosphere. Using the new version of Hall magnetohydrodynamic with embedded particle-in-cell model with a self-consistently coupled resistive body representing the electrical properties of the moon's interior, improved inner boundary conditions, and the flexibility of coupling different grid geometries, we achieve better match of magnetic field with measurements for all six Galileo flybys. The G2 flyby comparisons of plasma bulk flow velocities with the Galileo Plasma Subsystem data support the oxygen ion assumption inside Ganymede's magnetosphere. Crescent shape, nongyrotropic, and nonisotropic ion distributions are identified from the coupled model. Furthermore, we have derived the energy fluxes associated with the upstream magnetopause reconnection of similar to 10(-7) W/cm(2) based on our model results and found a maximum of 40% contribution to the total peak auroral emissions.

Ort, förlag, år, upplaga, sidor
AMER GEOPHYSICAL UNION, 2019
Nyckelord
Ganymede, simulation, magnetosphere, reconnection, COSTER RJ, 1979, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, V84, P5099 syliunas VM, 2000, GEOPHYSICAL RESEARCH LETTERS, V27, P1347 a Xianzhe, 2008, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, V113
Nationell ämneskategori
Geofysik
Identifikatorer
urn:nbn:se:kth:diva-259461 (URN)10.1029/2019JA026643 (DOI)000482985600033 ()2-s2.0-85069678381 (Scopus ID)
Anmärkning

QC 20190920

Tillgänglig från: 2019-09-20 Skapad: 2019-09-20 Senast uppdaterad: 2019-09-20Bibliografiskt granskad
Divin, A., Semenov, V., Zaitsev, I., Korovinskiy, D., Deca, J., Lapenta, G., . . . Markidis, S. (2019). Inner and outer electron diffusion region of antiparallel collisionless reconnection: Density dependence. Physics of Plasmas, 26(10), Article ID 102305.
Öppna denna publikation i ny flik eller fönster >>Inner and outer electron diffusion region of antiparallel collisionless reconnection: Density dependence
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2019 (Engelska)Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 26, nr 10, artikel-id 102305Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We study inflow density dependence of substructures within electron diffusion region (EDR) of collisionless symmetric magnetic reconnection. We perform a set of 2.5D particle-in-cell simulations which start from a Harris current layer with a uniform background density n(b). A scan of n(b) ranging from 0:02 n(0) to 2 n(0) of the peak current layer density (n(0)) is studied keeping other plasma parameters the same. Various quantities measuring reconnection rate, EDR spatial scales, and characteristic velocities are introduced. We analyze EDR properties during quasisteady stage when the EDR length measures saturate. Consistent with past kinetic simulations, electrons are heated parallel to the B field in the inflow region. The presence of the strong parallel anisotropy acts twofold: (1) electron pressure anisotropy drift gets important at the EDR upstream edge in addition to the E x B drift speed and (2) the pressure anisotropy term -del.P-(e)/(ne) modifies the force balance there. We find that the width of the EDR demagnetization region and EDR current are proportional to the electron inertial length similar to d(e) and similar to d(e)n(b)(0.22), respectively. Magnetic reconnection is fast with a rate of similar to 0.1 but depends weakly on density as similar to n(b)(-1/8). Such reconnection rate proxies as EDR geometrical aspect or the inflow-to-outflow electron velocity ratio are shown to have different density trends, making electric field the only reliable measure of the reconnection rate. Published under license by AIP Publishing.

Ort, förlag, år, upplaga, sidor
AMER INST PHYSICS, 2019
Nationell ämneskategori
Fusion, plasma och rymdfysik
Identifikatorer
urn:nbn:se:kth:diva-266922 (URN)10.1063/1.5109368 (DOI)000505980600024 ()2-s2.0-85073601321 (Scopus ID)
Anmärkning

QC 20200214

Tillgänglig från: 2020-02-14 Skapad: 2020-02-14 Senast uppdaterad: 2020-03-10Bibliografiskt granskad
Simmendinger, C., Iakymchuk, R., Cebamanos, L., Akhmetova, D., Bartsch, V., Rotaru, T., . . . Markidis, S. (2019). Interoperability strategies for GASPI and MPI in large-scale scientific applications. The international journal of high performance computing applications, 33(3), 554-568
Öppna denna publikation i ny flik eller fönster >>Interoperability strategies for GASPI and MPI in large-scale scientific applications
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2019 (Engelska)Ingår i: The international journal of high performance computing applications, ISSN 1094-3420, E-ISSN 1741-2846, Vol. 33, nr 3, s. 554-568Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

One of the main hurdles of partitioned global address space (PGAS) approaches is the dominance of message passing interface (MPI), which as a de facto standard appears in the code basis of many applications. To take advantage of the PGAS APIs like global address space programming interface (GASPI) without a major change in the code basis, interoperability between MPI and PGAS approaches needs to be ensured. In this article, we consider an interoperable GASPI/MPI implementation for the communication/performance crucial parts of the Ludwig and iPIC3D applications. To address the discovered performance limitations, we develop a novel strategy for significantly improved performance and interoperability between both APIs by leveraging GASPI shared windows and shared notifications. First results with a corresponding implementation in the MiniGhost proxy application and the Allreduce collective operation demonstrate the viability of this approach.

Ort, förlag, år, upplaga, sidor
SAGE PUBLICATIONS LTD, 2019
Nyckelord
Interoperability, GASPI, MPI, iPIC3D, Ludwig, MiniGhost, halo exchange, Allreduce
Nationell ämneskategori
Datorteknik
Identifikatorer
urn:nbn:se:kth:diva-254034 (URN)10.1177/1094342018808359 (DOI)000468919900011 ()2-s2.0-85059353725 (Scopus ID)
Anmärkning

QC 20190814

Tillgänglig från: 2019-08-14 Skapad: 2019-08-14 Senast uppdaterad: 2019-08-14Bibliografiskt granskad
Wallden, M., Markidis, S., Okita, M. & Ino, F. (2019). Memory Efficient Load Balancing for Distributed Large-Scale Volume Rendering Using a Two-Layered Group Structure. IEICE transactions on information and systems, E102D(12), 2306-2316
Öppna denna publikation i ny flik eller fönster >>Memory Efficient Load Balancing for Distributed Large-Scale Volume Rendering Using a Two-Layered Group Structure
2019 (Engelska)Ingår i: IEICE transactions on information and systems, ISSN 0916-8532, E-ISSN 1745-1361, Vol. E102D, nr 12, s. 2306-2316Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We propose a novel compositing pipeline and a dynamic load balancing technique for volume rendering which utilizes a two-layered group structure to achieve effective and scalable load balancing. The technique enables each process to render data from non-contiguous regions of the volume with minimal impact on the total render time. We demonstrate the effectiveness of the proposed technique by performing a set of experiments on a modern GPU cluster. The experiments show that using the technique results in up to a 35.7% lower worst-case memory usage as compared to a dynamic k-d tree load balancing technique, whilst simultaneously achieving similar or higher render performance. The proposed technique was also able to lower the amount of transferred data during the load balancing stage by up to 72.2%. The technique has the potential to be used in many scenarios where other dynamic load balancing techniques have proved to be inadequate, such as during large-scale visualization.

Nyckelord
large-scale visualization, distributed computing, load balancing, GPU
Nationell ämneskategori
Data- och informationsvetenskap Elektroteknik och elektronik
Identifikatorer
urn:nbn:se:kth:diva-265514 (URN)10.1587/transinf.2019PAP0003 (DOI)000499697000004 ()2-s2.0-85076443726 (Scopus ID)
Anmärkning

QC 20191213

Tillgänglig från: 2019-12-13 Skapad: 2019-12-13 Senast uppdaterad: 2020-01-08Bibliografiskt granskad
Sishtla, C. P., Olshevsky, V., Chien, W. D., Markidis, S. & Laure, E. (2019). Particle-in-Cell Simulations of Plasma Dynamics in Cometary Environment. In: Journal of Physics: Conference Series. Paper presented at 13th International Conference on Numerical Modeling of Space Plasma Flows, ASTRONUM 2018; Panama City Beach; United States; 25 June 2018 through 29 June 2018. Institute of Physics Publishing (IOPP), 1225(1), Article ID 012009.
Öppna denna publikation i ny flik eller fönster >>Particle-in-Cell Simulations of Plasma Dynamics in Cometary Environment
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2019 (Engelska)Ingår i: Journal of Physics: Conference Series, Institute of Physics Publishing (IOPP), 2019, Vol. 1225, nr 1, artikel-id 012009Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

We perform and analyze global Particle-in-Cell (PIC) simulations of the interaction between solar wind and an outgassing comet with the goal of studying the plasma kinetic dynamics of a cometary environment. To achieve this, we design and implement a new numerical method in the iPIC3D code to model outgassing from the comet: new plasma particles are ejected from the comet "surface" at each computational cycle. Our simulations show that a bow shock is formed as a result of the interaction between solar wind and outgassed particles. The analysis of distribution functions for the PIC simulations shows that at the bow shock part of the incoming solar wind, ions are reflected while electrons are heated. This work attempts to reveal kinetic effects in the atmosphere of an outgassing comet using a fully kinetic Particle-in-Cell model.

Ort, förlag, år, upplaga, sidor
Institute of Physics Publishing (IOPP), 2019
Serie
Journal of Physics: Conference Series, ISSN 1742-6588 ; 1225
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:kth:diva-262635 (URN)10.1088/1742-6596/1225/1/012009 (DOI)000478669600009 ()2-s2.0-85068062214 (Scopus ID)
Konferens
13th International Conference on Numerical Modeling of Space Plasma Flows, ASTRONUM 2018; Panama City Beach; United States; 25 June 2018 through 29 June 2018
Anmärkning

QC 20191018

Tillgänglig från: 2019-10-18 Skapad: 2019-10-18 Senast uppdaterad: 2020-04-21Bibliografiskt granskad
Organisationer
Identifikatorer
ORCID-id: ORCID iD iconorcid.org/0000-0003-0639-0639

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