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  • 1.
    Dion, Claude
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Sjölund, Peder
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Petra, Stefan
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Jonsell, Svante
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Nylén, Mats
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Sanchez-Palencia, Laurent
    Kastberg, Anders
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Controllable 3D atomic Brownian motor in optical lattices2008Inngår i: The European Physical Journal - Special Topics, ISSN 1951-6355, Vol. 159, nr 1, s. 11-17Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study a Brownian motor, based on cold atoms in optical lattices, where atomic motion can be induced in a controlled manner in an arbitrary direction, by rectification of isotropic random fluctuations. In contrast with ratchet mechanisms, our Brownian motor operates in a potential that is spatially and temporally symmetric, in apparent contradiction to the Curie principle. Simulations, based on the Fokker-Planck equation, allow us to gain knowledge on the qualitative behaviour of our Brownian motor. Studies of Brownian motors, and in particular ones with unique control properties, are of fundamental interest because of the role they play in protein motors and their potential applications in nanotechnology. In particular, our system opens the way to the study of quantum Brownian motors.

    Fulltekst (pdf)
    FULLTEXT01
  • 2.
    Edmundsson, Niklas
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Högpresterande beräkningscentrum norr (HPC2N).
    Elmroth, Erik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Högpresterande beräkningscentrum norr (HPC2N).
    Kågström, Bo
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Högpresterande beräkningscentrum norr (HPC2N).
    Mårtensson, Markus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Högpresterande beräkningscentrum norr (HPC2N).
    Nylén, Mats
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Högpresterande beräkningscentrum norr (HPC2N).
    Sandgren, Åke
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Högpresterande beräkningscentrum norr (HPC2N).
    Wadenstein, Mattias
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Högpresterande beräkningscentrum norr (HPC2N).
    Design and Evaluation of a TOP100 Linux Super Cluster System2004Inngår i: Concurrency and Computation: Practice & Experiences, ISSN 1532-0634, Vol. 16, nr 8, s. 735-750Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The High Performance Computing Center North (HPC2N) Super Cluster is a truly self-made high-performance Linux cluster with 240 AMD processors in 120 dual nodes, interconnected with a high-bandwidth, low-latency SCI network. This contribution describes the hardware selected for the system, the work needed to build it, important software issues and an extensive performance analysis. The performance is evaluated using a number of state-of-the-art benchmarks and software, including STREAM, Pallas MPI, the Atlas DGEMM, High-Performance Linpack and NAS Parallel benchmarks. Using these benchmarks we first determine the raw memory bandwidth and network characteristics; the practical peak performance of a single CPU, a single dual-node and the complete 240-processor system; and investigate the parallel performance for non-optimized dusty-deck Fortran applications. In summary, this $500 000 system is extremely cost-effective and shows the performance one would expect of a large-scale supercomputing system with distributed memory architecture. According to the TOP500 list of June 2002, this cluster was the 94th fastest computer in the world. It is now fully operational and stable as the main computing facility at HPC2N. The system’s utilization figures exceed 90%, i.e. all 240 processors are on average utilized over 90% of the time, 24 hours a day, seven days a week.

  • 3.
    Elmroth, Erik
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap.
    Nylén, Mats
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Högpresterande beräkningscentrum norr (HPC2N).
    Oscarsson, Roger
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Högpresterande beräkningscentrum norr (HPC2N).
    A User-Centric Cluster and Grid Computing Portal2009Inngår i: International Journal of Computational Science and Engineering (IJCSE), ISSN 1742-7185, E-ISSN 1742-7193, Vol. 4, nr 2, s. 127-134Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The HPC2N Grid portal is a user-centric environment that provides a homogeneous interface to a set of heterogeneous High-Performance Computing (HPC) resources from standard web-browsers. The interface includes support for most everyday activities, such as to submit, manipulate and delete jobs, monitor queues and job status, obtain user-, project-, and resource information, view job output, etc. This contribution reviews the portal functionalities and presents the design and implementation of the underlying system architecture. Some major design considerations, features and limitations are discussed. The portal currently gives access to all major resources at HPC2N, in total comprising over 700 CPUs.

  • 4.
    Hagman, Henning
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sjölund, Peder
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Petra, Stefan J. H.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nylén, Mats
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Kastberg, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Ellmann, Harald
    Department of Physics, Stockholm University, AlbaNova University Center, SE-106 91 Stockholm, Sweden.
    Jersblad, Johan
    Department of Physics, Stockholm University, AlbaNova University Center, SE-106 91 Stockholm, Sweden.
    Assessment of a time-of-flight detection technique for measuring small velocities of cold atoms2009Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 105, nr 8, s. 083109-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A low noise time-of-flight detection system for laser cooled atoms has been constructed and incrementally optimized. Here, a thorough description of the construction is presented along with an analysis of the capabilities of the system. The quality of the detection (the resolution, the reproducibility, the sensitivity, etc.) is crucial for, e.g., the ability to see details in the velocity distribution profile, which is of interest for fundamental studies of statistical physics and of the laser cooling processes, and for detection of small initial velocities of an atomic cloud, important, e.g., when studying small drifts induced by Brownian motors and ratchets. We estimate the signal-to-noise ratio of our signal to be better than 1000:1 for a typical single shot, and we discuss the effect of the initial atomic cloud size, the probe size, and the effects of the wave packet spread during the fall time on the measured quantities. We show that the shape of the velocity distribution is well conserved during the mapping done in the detection, i.e., in the convolution with the probe beam, and that velocities as small as a few percent of the single photon recoil velocity can be resolved.

  • 5.
    Jonsell, Svante
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Dion, Claude
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nylén, Mats
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Petra, Stefan J.H.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sjölund, Peder
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Kastberg, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    A nonadiabatic semi-classical method for dynamics of atoms in optical lattices2006Inngår i: European Physical Journal D: Atomic, Molecular and Optical Physics, ISSN 1434-6060, E-ISSN 1434-6079, Vol. 39, nr 1, s. 67-74Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We develop a semi-classical method to simulate the motion of atoms in a dissipative optical lattice. Our method treats the internal states of the atom quantum mechanically, including all nonadiabatic couplings, while position and momentum are treated as classical variables. We test our method in the one-dimensional case. Excellent agreement with fully quantum mechanical simulations is found. Our results are much more accurate than those of earlier semi-classical methods based on the adiabatic approximation.

  • 6.
    Jonsell, Svante
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Sjölund, Peder
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Petra, Stefan
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Dion, Claude
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Nylén, Mats
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Sanchez-Palencia, Laurent
    Kastberg, Anders
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Raglande atomer nyktrar till2006Inngår i: Fysikaktuellt, ISSN 0283-9148, nr 2, s. 10-Artikkel i tidsskrift (Annet (populærvitenskap, debatt, mm))
  • 7.
    Sjölund, Peder
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Petra, Stefan J.H.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Dion, Claude
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Jonsell, Svante
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nylén, Mats
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Sanchez-Palencia, L.
    Laboratoire Charles Fabry de l’Institut d’Optique, CNRS and Université Paris-Sud XI, France.
    Kastberg, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Demonstration of a controllable three-dimensional Brownian motor in symmetric potentials2006Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 96, nr 19, s. 190602-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We demonstrate a Brownian motor, based on cold atoms in optical lattices, where isotropic random fluctuations are rectified in order to induce controlled atomic motion in arbitrary directions. In contrast to earlier demonstrations of ratchet effects, our Brownian motor operates in potentials that are spatially and temporally symmetric, but where spatiotemporal symmetry is broken by a phase shift between the potentials and asymmetric transfer rates between them. The Brownian motor is demonstrated in three dimensions and the noise-induced drift is controllable in our system.

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