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[en] This paper is devoted to a microscopic study of the elementary excitations of a hard-sphere Fermi gas which are produced by a weakly interacting probe. The authors apply linear-response theory in a correlated basis and calculate the density-density response function II(q,ω) and corresponding dynamic structure factor S(q,ω), as functions of the transferred momentum hq and energy hω. Systems with single-particle level degeneracy v = 4 and v = 2 are considered, in correspondence with symmetrical nuclear matter and pure neutron matter. The results are referred to a hard-core radius of c = 0.4 fm/sup /minus/1/, again with nuclear systems in mind
[en] We examine the possibility that a significant component of the energy density of the Universe has an equation of state different from that of matter, radiation, or cosmological constant (Λ ). An example is a cosmic scalar field evolving in a potential, but our treatment is more general. Including this component alters cosmic evolution in a way that fits current observations well. Unlike Λ , it evolves dynamically and develops fluctuations, leaving a distinctive imprint on the microwave background anisotropy and mass power spectrum. copyright 1998 The American Physical Society
[en] Some form of missing energy may account for the difference between the observed cosmic matter density and the critical density. Two leading candidates are a cosmological constant and quintessence (a time-varying, inhomogeneous component with negative pressure). We show that an ideal, full-sky cosmic background anisotropy experiment may not be able to distinguish the two, even when non-linear effects due to gravitational lensing are included. Because of this ambiguity, microwave background experiments alone may not determine the matter density or Hubble constant very precisely. We further show that degeneracy may remain even after considering classical cosmological tests and measurements of large scale structure. copyright 1999 The American Physical Society
[en] Calculation for electron impact total ionization cross sections on halogen compounds (BF, SiF, BCI, SiCl) are performed employing Spherical Complex Optical Potential and Complex Optical Potential - ionization contribution (CSP-ic) formalisms. In this article we are presenting data for energies ranging from above threshold to 2000 eV. Our results are compared with available experimental and theoretical data wherever available. It is found that the present result gives a better account of the ionization cross sections. (author)
[en] The crystal structure of a high-pressure phase of the BiSn alloy has been solved from synchrotron powder diffraction data. The alloy with a two-phase mixture Bi+Sn was found to transform into a new intermediate phase after annealing at 150 deg. C under a pressure of 3 GPa. The structure is of the Si VI type: orthorhombic with 16 atoms in the unit cell, space group Cmca. Two symmetrically distinct atomic sites allow a (partial) ordering in the structure. The Cmca structure transforms to a disordered body-centered cubic structure at 12 GPa
[en] Full text: Acceleration grid power supplies (AGPS) provides 8 MW power at -96 kV to the beam source of DNB (diagnostic neutral beam) and SPIDER (source for production of ion of deuterium extracted from RF plasma) for acceleration of negative ions with specific modulation. High voltage power supplies (HVPS) based on PSM (pulse step modulation) topology has already demonstrated its ability for broadcast transmitters, accelerators of RF source, neutral beam injectors. PSM based 96 kV/75 A AGPSs have been developed to feed the acceleration grid of beam sources. Design redundancy ∼ 15% allows for tolerating SPS modules failure without leaving the ongoing campaign. The AGPS is designed to turn off in a time much lower than 100 μs to minimize the energy (20 J) delivered to the arc in case of short circuit or breakdown. AGPS is mainly composed of multisecondary transformers (3 nos., 2.8 MVA each), switched power supply (SPS) modules (150 nos., 60 kW each), FPGA/real-time based controller and other auxiliaries including passive protection devices; factory tested in witness of IO. Novel, state-of-the-art technologies for HV insulation such as multiple bushings integrated on large resin insulators and building feedthroughs have been developed. To ensure described functionalities a single AGPS is controlled by 9 powerful synchronous FPGAs managed by real-time controller which support high performance requirement of PSM based HVPS like low ripple, high resolution, programmable rise time, fast dynamics, full depth modulation, fast switching off and fast (a few milliseconds) re-application in case of breakdowns. Deliveries of AGPSs are sequenced to allow early operational drills at ITER-India lab while other unit is being installed at NBTF site. Present article describes operational drills including protection functions, insulation test and specified behaviour of AGPS on dummy load at ITER-India lab. This allows for offering DNB-AGPS for extended factory acceptance testing. (author)
[en] A Neutral Beam (NB) Injection system is used for heating or diagnostics of the plasma in a Tokamak. The Diagnostics Neutral Beam (DNB) system for ITER (International Thermonuclear Experimental Reactor) based on acceleration of negative ions; injects a neutral (H0) beam at 100 KeV with specified modulation into the plasma for charge exchange recombination spectroscopy. DNB Power Supply (DNBPS) system consists of various high voltage power supplies, high current power supplies and RF Generators. The system operates in a given operating sequence; very high electromagnetic transients are intrinsically generated during frequent short circuit at the accelerator grid (breakdowns) and sudden loss of load (Beam off). Instrumentation is to be provided to operate the DNBPS system remotely with required control and protection in synchronisation with ITER operation as directed by CODAC (COntrol Data Access and Communication); the central control system for ITER. Instrumentation functionality includes 1. Operation and control of DNBPS subsystems and associated auxiliaries 2. Protection of DNB components and power supplies using interlock system, 3. To ensure safe operation of high voltage hazardous systems 4. Acquisition of injector performance parameters and 5. To facilitate test and maintenance of individual subsystem. This paper discusses about proposed DNBPS instrumentation architecture. The design generally follows the protocols from the ITER- Plant Control Design Handbook (PCDH). (author)
[en] The Working Group III contribution to the IPCC Fourth Assessment Report (AR4) focuses on new literature on the scientific, technological, environmental, economic and social aspects of mitigation of climate change, published since the IPCC Third Assessment Report (TAR) and the Special Reports on CO2 Capture and Storage (SRCCS) and on Safeguarding the Ozone Layer and the Global Climate System (SROC).The main aim of this summary report is to assess options for mitigating climate change. Several aspects link climate change with development issues. This report explores these links in detail, and illustrates where climate change and sustainable development are mutually reinforcing. Economic development needs, resource endowments and mitigative and adaptive capacities differ across regions. There is no one-size-fits-all approach to the climate change problem, and solutions need to be regionally differentiated to reflect different socio-economic conditions and, to a lesser extent, geographical differences. Although this report has a global focus, an attempt is made to differentiate the assessment of scientific and technical findings for the various regions. Given that mitigation options vary significantly between economic sectors, it was decided to use the economic sectors to organize the material on short- to medium-term mitigation options. Contrary to what was done in the Third Assessment Report, all relevant aspects of sectoral mitigation options, such as technology, cost, policies etc., are discussed together, to provide the user with a comprehensive discussion of the sectoral mitigation options. The report is organised into six sections after the introduction: - Greenhouse gas (GHG) emission trends; - Mitigation in the short and medium term, across different economic sectors (until 2030); - Mitigation in the long-term (beyond 2030); - Policies, measures and instruments to mitigate climate change; - Sustainable development and climate change mitigation; - Gaps in knowledge
[en] To determine if trinitrotoluene (TNT) forms nonextractable residues in earthworms and to measure the relative degree of accumulation as compared to TNT and its deaminated metabolites, Eisenia fetida was exposed to 14C-TNT using dermal contact to filter paper or exposure to soil. Nonextractable residues made up 32-68% of total body burden depending on exposure media and depuration time. Parent TNT accounted for less than 3% of radioactivity, while ADNTs accounted for 7-38%. Elimination half-lives were 61-120 h for TNT, ADNTs, and DANTs, which was significantly lower than the half-lives found for nonextractable residues, 201-240 h. However, over 80% of the nonextractable residue was solubilized using weak acid (pH 2). Based on our findings that TNT accumulation occurs primarily as nonextractable residues, which have a longer half-life, and that nonextractable residues can be solubilized, we propose that nonextractable residues could be used as a selective biomarker for assessing TNT contamination. - Highlights: → Trinitrotoluene accumulation in earthworms primarily occurs as nonextractable residues. → Nonextractable residues have a significantly longer half life in the worm as compared to TNT and its solvent-extractable deaminated metabolites. → Nonextractable residue may be useful as a biomarker for exposure to TNT. - The majority of trinitrotoluene accumulation in earthworms occurs as nonextractable residues that have a significantly longer half life in the worm as compared to TNT and its solvent-extractable deaminated metabolites.
[en] The nature of galaxy structures on large scales is a key observational prediction for current models of galaxy formation. The Sloan Digital Sky Survey (SDSS) and the 2dF galaxy survey have revealed a number of structures on 40-150 h-1 Mpc scales at low redshifts, and some even larger ones. To constrain galaxy number densities, luminosities, and stellar populations in large structures at higher redshift, we have investigated two sheet-like structures of galaxies at z = 0.8 and 1.3 spanning 150 h-1 comoving Mpc embedded in large quasar groups (LQGs) extending over at least 200 h-1 Mpc. We present first results of an analysis of these sheet-like structures using two contiguous 1 deg Galaxy Evolution Explorer (GALEX) fields (FUV and NUV) cross-correlated with optical data from the SDSS. We derive a sample of 462 Lyman break galaxy (LBG) candidates coincident with the sheets. Using the GALEX and SDSS data, we show that the overall average spectral energy distribution of a LBG galaxy at z ∼ 1 is flat (in fλ) in the rest-frame wavelength range from 1500 A to 4000 A, implying evolved populations of stars in the LBGs. From the luminosity functions we get indications for overdensities in the two LQGs compared to their foreground regions. Similar conclusions come from the calculation of the 2-point correlation function, showing a 2σ overdensity for the LBGs in the z ∼ 0.8 LQG on scales of 1.6 to 4.8 Mpc, indicating similar correlation scales for our LBG sample as their z ∼ 3 counterparts.