In the last 30 days

• Open/close Molecular beam epitaxial growth and characterization of defects induced by cavitation impacts on polysilicon thin films

  D O Macodiyo et al 2007 J. Phys.: Conf. Ser. 61 750 Tag this article

  Article References Full text PDF (674 KB)

  Polycrystalline silicon were grown at high temperature in a gas-source molecular beam epitaxy (MBE) and then exposed to cavitation impacts from the backside at different scanning times to introduce compressive stress. The micro-Raman spectroscopy showed that regions of greater structural change due to cavitation impacts experience higher full width at half maximum (FWHM) and that stress was a function of number of scans. AFM was used to analyze the surface morphology of the specimen in the as-grown condition and after exposed to cavitation impacts. The structural features were characterized by X-ray diffraction (XRD) and high resolution transmission electron microscope (HRTEM). HRTEM observations showed that nanoparticles size of grains at the growth/death zone of interface. The dislocations types, twinnings and defects caused by cavitation impacts are discussed.

• Open/close Polymer chemistry and hydrogel systems

  E H Schacht 2004 J. Phys.: Conf. Ser. 3 22 Tag this article

  Article References Full text PDF (188 KB)

  Hydrogels are an interesting class of materials that can be prepared by a variety of methods. The properties of these materials depend on their building blocks and the preparation procedures and can be largely varied.

  Among the various classes of hydrogels, are the gels based of physically structuring biopolymers, like gelatine. By chemically modifying these biopolymers, hydrogels with a dual crosslinkage (physical and chemical) can be prepared.

  Hydrogels serve a broad range of applications, including biomaterials, matrices for drug delivery and scaffolds for tissue engineering.

• Open/close Experimental study of the synthesis and characterisation of silica nanoparticles via the sol-gel method

  S Tabatabaei et al 2006 J. Phys.: Conf. Ser. 26 371 Tag this article

  Article References Full text PDF (636 KB)

  Silica nano-particles were synthesised by chemical methods from tetraethylorthosilicate (TEOS), ethanol (C ₂H ₅OH) and deionized water in the presence of ammonia as catalyst at room temperature. The morphology and structure of colloidal silica particles formed depend on the molar ratio of reagents. The formation of silica particles has been investigated using different solvents: ethanol and ethanol-glycerol. The nature and morphology of particles was investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD).

• Open/close CMS conditions data access using FroNTier

  B Blumenfeld et al 2008 J. Phys.: Conf. Ser. 119 072007 Tag this article

  Article References Full text PDF (478 KB)

  The CMS experiment at the LHC has established an infrastructure using the FroNTier framework to deliver conditions (i.e. calibration, alignment, etc.) data to processing clients worldwide. FroNTier is a simple web service approach providing client HTTP access to a central database service. The system for CMS has been developed to work with POOL which provides object relational mapping between the C++ clients and various database technologies. Because of the read only nature of the data, Squid proxy caching servers are maintained near clients and these caches provide high performance data access. Several features have been developed to make the system meet the needs of CMS including careful attention to cache coherency with the central database, and low latency loading required for the operation of the online High Level Trigger. The ease of deployment, stability of operation, and high performance make the FroNTier approach well suited to the GRID environment being used for CMS offline, as well as for the online environment used by the CMS High Level Trigger. The use of standard software, such as Squid and various monitoring tools, makes the system reliable, highly configurable and easily maintained. We describe the architecture, software, deployment, performance, monitoring and overall operational experience for the system.

• Open/close Optical properties of graphene

  L A Falkovsky 2008 J. Phys.: Conf. Ser. 129 012004 Tag this article

  Article References Full text PDF (550 KB)

  Reflectance and transmittance of graphene in the optical region are analyzed as a function of frequency, temperature, and carrier density. We show that the optical graphene properties are determined by the direct interband electron transitions. The real part of the dynamic conductivity in doped graphene at low temperatures takes the universal constant value, whereas the imaginary part is logarithmically divergent at the threshold of interband transitions. The graphene transmittance in the visible range is independent of frequency and takes the universal value given by the fine structure constant.

• Open/close Metallic hydrogen: The most powerful rocket fuel yet to exist

  Isaac F Silvera and John W Cole 2010 J. Phys.: Conf. Ser. 215 012194 Tag this article

  Article References Full text PDF (1.90 MB)

  Wigner and Huntington first predicted that pressures of order 25 GPa were required for the transition of solid molecular hydrogen to the atomic metallic phase. Later it was predicted that metallic hydrogen might be a metastable material so that it remains metallic when pressure is released. Experimental pressures achieved on hydrogen have been more than an order of magnitude higher than the predicted transition pressure and yet it remains an insulator. We discuss the applications of metastable metallic hydrogen to rocketry. Metastable metallic hydrogen would be a very light-weight, low volume, powerful rocket propellant. One of the characteristics of a propellant is its specific impulse, I _sp. Liquid (molecular) hydrogen-oxygen used in modern rockets has an Isp of ~460s; metallic hydrogen has a theoretical I _sp of 1700s! Detailed analysis shows that such a fuel would allow single-stage rockets to enter into orbit or carry economical payloads to the moon. If pure metallic hydrogen is used as a propellant, the reaction chamber temperature is calculated to be greater than 6000 K, too high for currently known rocket engine materials. By diluting metallic hydrogen with liquid hydrogen or water, the reaction temperature can be reduced, yet there is still a significant performance improvement for the diluted mixture.

• Open/close The investigation of preparation by magnetron sputtering and application in amorphous silicon solar cells of pyramid-like textured ZnO:Al thin film

  Y H Hu et al 2011 J. Phys.: Conf. Ser. 276 012167 Tag this article

  Article References Full text PDF (464 KB)

  In this paper, the pyramid-like texture aluminum doped zinc oxide (ZnO:Al) thin films was prepared by adding negative bias voltage and controlling the sputtering parameters properly, and the lowest resistivity of 7.8×10 ⁻⁴ ·cm, light transmittance above 83% was achieved, respectively. Instead of the traditional tin oxide doped with fluorine (SnO ₂:F), using the ZnO:Al film as a front electrode transparent conducting oxide (TCO) layer for hydrogenated amorphous silicon (a-Si:H) solar cells, the higher contact potential barrier of ZnO:Al /p-a-SiC:H have to be overcome. In this paper, we attempt to resolve the contact potential barrier by inserting a buffer layer of microcrystalline silicon (μc-Si:H) between ZnO:Al layer and p-SiC: H windows layer, and its efficiency increases from 7.6% for the SnO ₂:F TCO to 8.3% for the ZnO:Al /μc-Si:H TCO.

• Open/close A quantitative comparison between xen and kvm

  Andrea Chierici and Riccardo Veraldi 2010 J. Phys.: Conf. Ser. 219 042005 Tag this article

  Article References Full text PDF (503 KB)

  Virtualization is a proven software technology that is rapidly transforming the IT landscape and fundamentally changing the way that people compute. Recently all major software producers (e.g. Microsoft and RedHat) developed or acquired virtualization technologies. Our institute is a Tier1 for LHC experiments and is experiencing lots of benefits from virtualization technologies, like improving fault tolerance, providing efficient hardware resource usage and increasing security. Currently the virtualization solution adopted is xen, which is well supported by the Scientific Linux distribution, widely adopted by the HEP community. Since the HEP linux distribution is based on RedHat ES, we feel the need to investigate performance and usability differences with the new kvm technology recently acquired by RedHat. The case study of this work will be the LHCb experiment Tier2 site hosted at our institute, where all major grid elements run on xen virtual machines smoothly. We will investigate the impact on performance and stability that a migration to kvm would entail on the Tier2 site, as well as the effort required by a system administrator to deploy the migration. Several quantitative test results will be shown and explained in detail.

• Open/close The Load Level of Modern Wind Turbines according to IEC 61400-1

  K Freudenreich and K Argyriadis 2007 J. Phys.: Conf. Ser. 75 012075 Tag this article

  Article References Full text PDF (132 KB)

  The paper describes some effects on the load level of state-of-the art multi megawatt wind turbines introduced by the new edition of the standard IEC 61400–1:2005 "Wind Turbines – Part 1: Design requirements". Compared to the previous edition, especially the extreme load determination has been modified by applying stochastic and statistical analyses. Within this paper the effect on the overall load level of wind turbines is demonstrated and occurring problems are discussed. Load simulations have been carried out for four state-of-the-art multi-megawatt wind turbines of different design concepts and from different manufacturers. The blade root bending moments and tip deflection have been determined by applying different extrapolation methods. Advantages and disadvantages of these methods and tail fittings for different load components and wind turbine technologies are discussed and interpreted. Further on, the application of the extreme turbulence model is demonstrated. The dependence of the load level on the turbulence intensity and control system, as well as the interaction with extrapolated loads is discussed and limitations outlined. The obtained load level is compared to the overall load level of the turbines according to the previous edition of the standard, IEC 61400-1:1999.

• Open/close LAPACKrc: Fast linear algebra kernels/solvers for FPGA accelerators

  Juan Gonzalez and Rafael C Núñez 2009 J. Phys.: Conf. Ser. 180 012042 Tag this article

  Article References Full text PDF (630 KB)

  We present LAPACKrc, a family of FPGA-based linear algebra solvers able to achieve more than 100x speedup per commodity processor on certain problems. LAPACKrc subsumes some of the LAPACK and ScaLAPACK functionalities, and it also incorporates sparse direct and iterative matrix solvers. Current LAPACKrc prototypes demonstrate between 40x-150x speedup compared against top-of-the-line hardware/software systems. A technology roadmap is in place to validate current performance of LAPACKrc in HPC applications, and to increase the computational throughput by factors of hundreds within the next few years.