5,875 research outputs found
System balance analysis for vector computers
The availability of vector processors capable of sustaining computing rates of 10 to the 8th power arithmetic results pers second raised the question of whether peripheral storage devices representing current technology can keep such processors supplied with data. By examining the solution of a large banded linear system on these computers, it was found that even under ideal conditions, the processors will frequently be waiting for problem data
The electron-phonon coupling strength at metal surfaces directly determined from the Helium atom scattering Debye-Waller factor
A new quantum-theoretical derivation of the elastic and inelastic scattering
probability of He atoms from a metal surface, where the energy and momentum
exchange with the phonon gas can only occur through the mediation of the
surface free-electron density, shows that the Debye-Waller exponent is directly
proportional to the electron-phonon mass coupling constant . The
comparison between the values of extracted from existing data on the
Debye-Waller factor for various metal surfaces and the values known
from literature indicates a substantial agreement, which opens the possibility
of directly extracting the electron-phonon coupling strength in quasi-2D
conducting systems from the temperature or incident energy dependence of the
elastic Helium atom scattering intensities.Comment: 14 pages, 2 figures, 1 tabl
Superconducting properties of the In-substituted topological crystalline insulator, SnTe
We report detailed investigations of the properties of a superconductor obtained by substituting In at the Sn site in the topological crystalline insulator (TCI), SnTe. Transport, magnetization and heat capacity measurements have been performed on crystals of SnInTe, which is shown to be a bulk superconductor with at ~K and at ~K. The upper and lower critical fields are estimated to be ~T and ~mT respectively, while indicates this material is a strongly type II superconductor
Reducing Polarization Mode Dispersion With Controlled Polarization Rotations
One of the fundamental limitations to high bit rate, long distance,
telecommunication in optical fibers is Polarization Mode Dispersion (PMD). Here
we introduce a conceptually new method to reduce PMD in optical fibers by
carrying out controlled rotations of polarization at predetermined locations
along the fiber. The distance between these controlled polarization rotations
must be less than both the beat length and the mode coupling length of the
fiber. This method can also be combined with the method in which the fiber is
spun while it drawn. The incidence of imperfections on the efficiency of the
method is analysed.Comment: 4 page
Simulations of a lattice model of two-headed linear amphiphiles: influence of amphiphile asymmetry
Using a 2D lattice model, we conduct Monte Carlo simulations of micellar
aggregation of linear-chain amphiphiles having two solvophilic head groups. In
the context of this simple model, we quantify how the amphiphile architecture
influences the critical micelle concentration (CMC), with a particular focus on
the role of the asymmetry of the amphiphile structure. Accordingly, we study
all possible arrangements of the head groups along amphiphile chains of fixed
length and 16 molecular units. This set of idealized amphiphile
architectures approximates many cases of symmetric and asymmetric gemini
surfactants, double-headed surfactants and boloform surfactants. Consistent
with earlier results, we find that the number of spacer units separating
the heads has a significant influence on the CMC, with the CMC increasing with
for . In comparison, the influence of the asymmetry of the chain
architecture on the CMC is much weaker, as is also found experimentally.Comment: 30 pages, 17 fgure
The prognostic importance of chronic end-stage diseases in geriatric patients admitted to 163 Italian ICUs
BACKGROUND: The number of elderly patients undergoing major surgical interventions and then needing admission to intensive care unit (ICU) grows steadily. We investigated this issue in a cohort of 232,278 patients admitted in five years (2011-2015) to 163 Italian general ICUs. METHODS: Surgical patients older than 75 registered in the GiViTI MargheritaPROSAFE project were analyzed. The impact on hospital mortality of important chronic conditions (severe COPD, NYHA class IV, dementia, end-stage renal disease, cirrhosis with portal hypertension) was investigated with two prognostic models developed yearly on patients staying in the ICU less or more than 24 hours. RESULTS: 44,551 elderly patients (19.2%) underwent emergency (47.3%) or elective surgery (52.7%). At least one severe comorbidity was present in 14.6% of them, yielding a higher hospital mortality (32.4%, vs. 21.1% without severe comorbidity). In the models for patients staying in the ICU 24 hours or more, cirrhosis, NYHA class IV, and severe COPD were constant independent predictors of death (adjusted odds ratios [ORs] range 1.67-1.97, 1.54-1.91, and 1.34-1.50, respectively), while dementia was statistically significant in four out of five models (adjusted ORs 1.23-1.28). End-stage renal disease, instead, never resulted to be an independent prognostic factor. For patients staying in the ICU less than 24 hours, chronic comorbidities were only occasionally independent predictors of death. CONCLUSIONS: Our study confirms that elderly surgical patients represent a relevant part of all ICUs admissions. About one of seven bear at least one severe chronic comorbidity, that, excluding end-stage renal disease, are all strong independent predictors of hospital death
Quasiparticle scattering time in superconducting films: from dirty to clean limit
We study the quasiparticle energy relaxation processes in superconducting Nb
films of different thicknesses corresponding to different electron mean free
paths in a state far from equilibrium, that is the highly dissipative flux-flow
state driven up to the instability point. From the measured current-voltage
curves we derive the vortex critical velocity for several temperatures.
From the values, the quasiparticle energy relaxation time
is evaluated within the Larkin-Ovchinnikov model and
numerical calculations of the quasiparticle energy relaxation rates are carried
out to support the experimental findings. Besides the expected constant
behavior of for the dirty samples, we observe a strong
temperature dependence of the quasiparticle energy relaxation time in the clean
samples. This feature is associated with the increasing contribution from the
electron-phonon scattering process as the dirty limit is approached from the
clean regime
CSM Testbed Development and Large-Scale Structural Applications
A research activity called Computational Structural Mechanics (CSM) conducted at the NASA Langley Research Center is described. This activity is developing advanced structural analysis and computational methods that exploit high-performance computers. Methods are developed in the framework of the CSM Testbed software system and applied to representative complex structural analysis problems from the aerospace industry. An overview of the CSM Testbed methods development environment is presented and some new numerical methods developed on a CRAY-2 are described. Selected application studies performed on the NAS CRAY-2 are also summarized
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