6,366 research outputs found
First-principles investigation of magnetism and electronic structures of substitutional transition-metal impurities in bcc Fe
The magnetic and electronic structures of impurity atoms from Sc to Zn
in ferromagnetic body-centered cubic iron are investigated using the
all-electron full-potential linearized augmented plane-wave method based on the
generalized gradient approximation (GGA). We found that in general, the GGA
results are closer to the experimental values than those of the local spin
density approximation. The calculated formation enthalpy data indicate the
importance of a systematic study on the ternary Fe-C- systems rather than
the binary Fe- systems, in steel design. The lattice parameters are
optimized and the conditions for spin polarization at the impurity sites are
discussed in terms of the local Stoner model. Our calculations, which are
consistent with previous work, imply that the local spin-polarizations at Sc,
Ti, V, Cu, and Zn are induced by the host Fe atoms. The early transition-metal
atoms couple antiferromagnetically, while the late transition-metal atoms
couple ferromagnetically, to the host Fe atoms. The calculated total
magnetization () of bcc Fe is reduced by impurity elements from Sc to Cr as
a result of the antiferromagnetic interaction, with the opposite effect for
solutes which couple ferromagnetically. The changes in are attributed to
nearest neighbor interactions, mostly between the impurity and host atoms. The
atom averaged magnetic moment is shown to follow generally the well-known
Slater-Pauling curve, but our results do not follow the linearity of the
Slater-Pauling curve. We attribute this discrepancy to the weak ferromagnetic
nature of bcc Fe. The calculated Fermi contact hyperfine fields follow the
trend of the local magnetic moments. The effect of spin-orbit coupling is found
not to be significant although it comes into prominence at locations far from
the impurity sites.Comment: 26 pages, 11 figure
Trigeminal nerve morphology in the American alligator : implications for infering sensory potential in extinct species [abstract]
Among the many adaptations of modern crocodilians, one of the most intriguing is their derived sense of face touch, in which numerous trigeminal nerve-innervated dome pressure receptors speckle the face and mandible and sense vibrations and other mechanical stimuli, directing the animal towards, or away from stimuli. However, the morphological features of this system are not well known, and it remains unclear how aspects of the trigeminal system change during ontogeny and how they scale with other cranial and nervous structures
Stability of central finite difference schemes for the Heston PDE
This paper deals with stability in the numerical solution of the prominent
Heston partial differential equation from mathematical finance. We study the
well-known central second-order finite difference discretization, which leads
to large semi-discrete systems with non-normal matrices A. By employing the
logarithmic spectral norm we prove practical, rigorous stability bounds. Our
theoretical stability results are illustrated by ample numerical experiments
Resource Allocation for Wireless-Powered Full-Duplex Relaying Systems with Nonlinear Energy Harvesting Efficiency
In wireless power transfer (WPT)-assisted relaying systems, spectral efficiency (SE) of source-relay link plays a dominant role in system SE performance due to the limited transmission power at the WPT-aided relay. In this paper, we propose a novel protocol for a downlink orthogonal frequency division multiple access (OFDMA) system with a WPT-aided relay operating in full-duplex (FD) decode-and-forward (DF) mode, where the time slot durations of the source-relay and relay-users hops are designed to be dynamic, to enhance the utilization of degrees of freedom and hence the system SE. In particular, a multiple-input and signal-output (MISO) source-relay channel is considered to satisfy the stringent sensitivity of the energy harvesting (EH) circuit at the relay, while a single-input and single-output (SISO) relay-user channel is considered to alleviate the power consumption at the relay node. Taking into account the non-linearity of EH efficiency, a near-optimal iteration-based dynamic WPT-aided FD relaying (A-FR) algorithm is developed by jointly optimizing the time slot durations, subcarriers, and transmission power at the source and the relay. Furthermore, self-interference generated at the relay is utilized as a vital energy source rather than being canceled, which increases substantially the total energy harvested at the FD relay. We also reveal some implicit characteristics of the considered WPT-aided FD relaying system through intensive discussions. Simulation results confirm that the proposed A-FR achieves a significant enhancement in terms of SE with different relay's locations and the number of users, compared to the conventional symmetric WPT-aided FD relaying (S-FR) and the time-switching-based WPT-aided FD relaying (TS-FR) benchmarks
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Representation of Tropical Subseasonal Variability of Precipitation in Global Reanalyses
Tropical subseasonal variability of precipitation from five global reanalyses (RAs) is evaluated against Global Precipitation Climatology Project (GPCP) and Tropical Rainfall Measuring Mission (TRMM) observations. The RAs include the three generations of global RAs from the National Center for Environmental Prediction (NCEP), and two other RAs from the European Centre for Medium‑Range Weather Forecasts (ECMWF) and the National Aeronautics and Space Administration/Goddard Space Flight Center (NASA/GSFC). The analysis includes comparisons of the seasonal means and subseasonal variances of precipitation, and probability densities of rain intensity in selected areas. In addition, the space‑time power spectrum was computed to examine the tropical Madden‑Julian Oscillation (MJO) and convectively coupled equatorial waves (CCEWs)
The Chemical Compositions of Very Metal-Poor Stars HD 122563 and HD 140283; A View From the Infrared
From high resolution (R = 45,000), high signal-to-noise (S/N > 400) spectra
gathered with the Immersion Grating Infrared Spectrograph (IGRINS) in the H and
K photometric bands, we have derived elemental abundances of two bright,
well-known metal-poor halo stars: the red giant HD 122563 and the subgiant HD
140283. Since these stars have metallicities approaching [Fe/H] = -3, their
absorption features are generally very weak. Neutral-species lines of Mg, Si, S
and Ca are detectable, as well as those of the light odd-Z elements Na and Al.
The derived IR-based abundances agree with those obtained from
optical-wavelength spectra. For Mg and Si the abundances from the infrared
transitions are improvements to those derived from shorter wavelength data.
Many useful OH and CO lines can be detected in the IGRINS HD 122563 spectrum,
from which derived O and C abundances are consistent to those obtained from the
traditional [O I] and CH features. IGRINS high resolutions H- and K-band
spectroscopy offers promising ways to determine more reliable abundances for
additional metal-poor stars whose optical features are either not detectable,
or too weak, or are based on lines with analytical difficulties.Comment: Accepted for publication in ApJ (28 pages, 4 tables, 6 figures
Exact solutions of a restricted ballistic deposition model on a one-dimensional staircase
Surface structure of a restricted ballistic deposition(RBD) model is examined
on a one-dimensional staircase with free boundary conditions. In this model,
particles can be deposited only at the steps of the staircase. We set up
recurrence relations for the surface fluctuation width using generating
function method. Steady-state solutions are obtained exactly given system size
. In the infinite-size limit, diverges as with the scaling
exponent . The dynamic exponent
is also found to be by solving the recurrence relations
numerically. This model can be viewed as a simple variant of the model which
belongs to the Kardar-Parisi-Zhang (KPZ) universality class . Comparing its deposition time scale
with that of the single-step model, we argue that must be the same as
, which is consistent with our finding.Comment: 19 pages, REVTEX, 5 figures upon request, INHA-PHYS-94-00
Expression of CPI-17 in smooth muscle during embryonic development and in neointimal lesion formation.
Ca(2+) sensitivity of smooth muscle (SM) contraction is determined by CPI-17, an inhibitor protein for myosin light chain phosphatase (MLCP). CPI-17 is highly expressed in mature SM cells, but the expression level varies under pathological conditions. Here, we determined the expression of CPI-17 in embryonic SM tissues and arterial neointimal lesions using immunohistochemistry. As seen in adult animals, the predominant expression of CPI-17 was detected at SM tissues on mouse embryonic sections, whereas MLCP was ubiquitously expressed. Compared with SM alpha-actin, CPI-17 expression doubled in arterial SM from embryonic day E10 to E14. Like SM alpha-actin and other SM marker proteins, CPI-17 was expressed in embryonic heart, and the expression was down-regulated at E17. In adult rat, CPI-17 expression level was reduced to 30% in the neointima of injured rat aorta, compared with the SM layers, whereas the expression of MLCP was unchanged in both regions. Unlike other SM proteins, CPI-17 was detected at non-SM organs in the mouse embryo, such as embryonic neurons and epithelium. Thus, CPI-17 expression is reversibly controlled in response to the phenotype transition of SM cells that restricts the signal to differentiated SM cells and particular cell types
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