8,592 research outputs found
新収作品 : ジョルジュ・ド・ラ・トゥール《聖トマス》
We present a tomographic technique making use of a gigaelectronvolt electron beam for the determination of the material budget distribution of centimeter-sized objects by means of simulations and measurements. In both cases, the trajectory of electrons traversing a sample under test is reconstructed using a pixel beam-telescope. The width of the deflection angle distribution of electrons undergoing multiple Coulomb scattering at the sample is estimated. Basing the sinogram on position-resolved estimators enables the reconstruction of the original sample using an inverse radon transform. We exemplify the feasibility of this tomographic technique via simulations of two structured cubes—made of aluminium and lead—and via an in-beam measured coaxial adapter. The simulations yield images with FWHM edge resolutions of (177 ± 13) μm and a contrast-to-noise ratio of 5.6 ± 0.2 (7.8 ± 0.3) for aluminium (lead) compared to air. The tomographic reconstruction of a coaxial adapter serves as experimental evidence of the technique and yields a contrast-to-noise ratio of 15.3 ± 1.0 and a FWHM edge resolution of (117 ± 4) μm
Numerical stability of the AA evolution system compared to the ADM and BSSN systems
We explore the numerical stability properties of an evolution system
suggested by Alekseenko and Arnold. We examine its behavior on a set of
standardized testbeds, and we evolve a single black hole with different gauges.
Based on a comparison with two other evolution systems with well-known
properties, we discuss some of the strengths and limitations of such simple
tests in predicting numerical stability in general.Comment: 16 pages, 12 figure
Two-Dimensional Spectroscopy of Extended Molecular Systems: Applications to Energy Transport and Relaxation in an α-Helix
A simulation study of the coupled dynamics of amide I and amide II vibrations in an α-helix dissolved in water shows that two-dimensional (2D) infrared spectroscopy may be used to disentangle the energy transport along the helix through each of these modes from the energy relaxation between them. Time scales for both types of processes are obtained. Using polarization-dependent 2D spectroscopy is an important ingredient in the method we propose. The method may also be applied to other two-band systems, both in the infrared (collective vibrations) and the visible (excitons) parts of the spectrum.
Partially Turboelectric Aircraft Drive Key Performance Parameters
The purpose of this paper is to propose electric drive specific power, electric drive efficiency, and electrical propulsion fraction as the key performance parameters for a partially turboelectric aircraft power system and to investigate their impact on the overall aircraft performance. Breguet range equations for a base conventional turbofan aircraft and a partially turboelectric aircraft are found. The benefits and costs that may result from the partially turboelectric system are enumerated. A break even analysis is conducted to find the minimum allowable electric drive specific power and efficiency, for a given electrical propulsion fraction, that can preserve the range, fuel weight, operating empty weight, and payload weight of the conventional aircraft. Current and future power system performance is compared to the required performance to determine the potential benefit
High Specific Power Motors in LN2 and LH2
A switched reluctance motor has been operated in liquid nitrogen (LN2) with a power density as high as that reported for any motor or generator. The high performance stems from the low resistivity of Cu at LN2 temperature and from the geometry of the windings, the combination of which permits steady-state rms current density up to 7000 A/cm2, about 10 times that possible in coils cooled by natural convection at room temperature. The Joule heating in the coils is conducted to the end turns for rejection to the LN2 bath. Minimal heat rejection occurs in the motor slots, preserving that region for conductor. In the end turns, the conductor layers are spaced to form a heat-exchanger-like structure that permits nucleate boiling over a large surface area. Although tests were performed in LN2 for convenience, this motor was designed as a prototype for use with liquid hydrogen (LH2) as the coolant. End-cooled coils would perform even better in LH2 because of further increases in copper electrical and thermal conductivities. Thermal analyses comparing LN2 and LH2 cooling are presented verifying that end-cooled coils in LH2 could be either much longer or could operate at higher current density without thermal runaway than in LN2
Exact Resummations in the Theory of Hydrodynamic Turbulence: I The Ball of Locality and Normal Scaling
This paper is the first in a series of three papers that aim at understanding
the scaling behaviour of hydrodynamic turbulence. We present in this paper a
perturbative theory for the structure functions and the response functions of
the hydrodynamic velocity field in real space and time. Starting from the
Navier-Stokes equations (at high Reynolds number Re) we show that the standard
perturbative expansions that suffer from infra-red divergences can be exactly
resummed using the Belinicher-L'vov transformation. After this exact (partial)
resummation it is proven that the resulting perturbation theory is free of
divergences, both in large and in small spatial separations. The hydrodynamic
response and the correlations have contributions that arise from mediated
interactions which take place at some space- time coordinates. It is shown that
the main contribution arises when these coordinates lie within a shell of a
"ball of locality" that is defined and discussed. We argue that the real
space-time formalism developed here offers a clear and intuitive understanding
of every diagram in the theory, and of every element in the diagrams. One major
consequence of this theory is that none of the familiar perturbative mechanisms
may ruin the classical Kolmogorov (K41) scaling solution for the structure
functions. Accordingly, corrections to the K41 solutions should be sought in
nonperturbative effects. These effects are the subjects of papers II and III in
this series, that will propose a mechanism for anomalous scaling in turbulence,
which in particular allows multiscaling of the structure functions.Comment: PRE in press, 18 pages + 6 figures, REVTeX. The Eps files of figures
will be FTPed by request to [email protected]
Black Silicon with high density and high aspect ratio nanowhiskers
Physical properties of black Silicon (b-Si) formed on Si wafers by reactive
ion etching in chlorine plasma are reported in an attempt to clarify the
formation mechanism and the origin of the observed optical and electrical
phenomena which are promising for a variety of applications. The b-Si
consisting of high density and high aspect ratio sub-micron length whiskers or
pillars with tip diameters of well under 3 nm exhibits strong photoluminescence
(PL) both in visible and infrared, which are interpreted in conjunction with
defects, confinement effects and near band-edge emission. Structural analysis
indicate that the whiskers are all crystalline and encapsulated by a thin Si
oxide layer. Infrared vibrational spectrum of Si-O-Si bondings in terms of
transverse-optic (TO) and longitudinal-optic (LO) phonons indicates that
disorder induced LO-TO optical mode coupling can be an effective tool in
assessing structural quality of the b-Si. The same phonons are likely coupled
to electrons in visible region PL transitions. Field emission properties of
these nanoscopic features are demonstrated indicating the influence of the tip
shape on the emission. Overall properties are discussed in terms of surface
morphology of the nano whiskers
Subjective and objective assessment of neuromuscular fatigue in female painters
The aim of this study was to evaluate subjectively and objectively neuromuscular fatigue in female painters before and after a workingday. The subjects (n=11) were female painters aged 22–60 years. The subjects completed a questionnaire and gave a subjective evaluation on muscle fatigue sensation in hands, trunk, back and lower limbs according to Borg's Category Ratio (CR-10) scale. Thereafter they performed 3-minute test of painting a wall, in the course of which the electromyographical (EMG) power spectral median frequency (MF) slope for biceps brachii, trapezius, deltoid and infraspinatus muscles was measured. The results indicated a significant change in the subjective muscle fatigue sensation in hands by 40%, lower limbs by 54% and trunk by 57% after the working day, compared to the beginning of the working day. EMG power spectral MF slope of the measured muscles did not differ significantly during the 3-minute wall coloring test before and after working day. It was concluded that subjective muscle fatigue sensation in hands, lower limbs and trunk was higher after the working day whereas it was less pronounced in the back. Muscle fatigue evaluated objectively by MF slope of EMG power spectrum from biceps brachii, trepezius, deltoid and infraspinatus muscles was not evident during the wall coloring test before and after the working day
Effects of Dust on Gravitational Lensing by Spiral Galaxies
Gravitational lensing of an optical QSO by a spiral galaxy is often
counteracted by dust obscuration, since the line-of-sight to the QSO passes
close to the center of the galactic disk. The dust in the lens is likely to be
correlated with neutral hydrogen, which in turn should leave a Lyman-alpha
absorption signature on the QSO spectrum. We use the estimated dust-to-gas
ratio of the Milky-Way galaxy as a mean and allow a spread in its values to
calculate the effects of dust on lensing by low redshift spiral galaxies. Using
a no-evolution model for spirals at z<1 we find (in Lambda=0 cosmologies) that
the magnification bias due to lensing is stronger than dust obscuration for QSO
samples with a magnitude limit B<16. The density parameter of neutral hydrogen,
Omega_HI, is overestimated in such samples and is underestimated for fainter
QSOs.Comment: 18 pages, 4 figures, ApJ, in pres
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