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991.
We predict the presence of strong dichroic effects induced by x-ray beams carrying orbital angular momentum (OAM). Taking the difference between spectra obtained with positive and negative OAM states allows the separation of quadrupolar from dipolar transitions at, e.g., the transition-metal K edges, enabling the study of the unoccupied states in the absence of strong core-hole effects. We study the dependence of OAM-induced x-ray dichroism on different polarization vectors and derive sum rules relating the integrated intensity to ground-state hole densities. Calculations of spectral line shapes for cuprates, manganites, and ruthenates confirm the strong OAM-induced dichroism and indicate the potential of this new spectroscopy in the fields of orbital physics and magnetism. 相似文献
992.
A high-power linearly polarized Yb-doped silica fiber master oscillator power amplifier at 1150 nm is reported. It produced 3.35 W cw and 2.33 W of average power in 1 micros pulses at a 100 kHz repetition rate, both with 8 pm linewidth. This is the first report, to the best of our knowledge, of a high-power Yb-doped fiber amplifier at a wavelength longer than 1135 nm. The pulsed output was frequency doubled in a bulk periodically poled near-stoichiometric LiTaO(3) chip to generate 976 mW of average power at 575 nm with an overall system optical-to-optical efficiency of 9.8% with respect to launched pump power. 相似文献
993.
When graphite is doped with electrons, carbon-carbon bonds lengthen and Raman-active phonons soften as antibonding states fill. However, in semiconducting carbon nanotubes, one Raman-active G-band mode increases in frequency at low doping levels. We show how phase constraints on the conduction-band wave function expose a latent bonding character in the conduction band of certain nanotubes. In these tubes, filling the lowest conduction band shortens the axial bonds even as it lengthens the circumferential bonds. The A{1}{LO} phonon, which preferentially stretches the axial bonds, then hardens even as the other phonons soften. Quantum confinement eliminates the angular averaging taken for granted in higher-dimensional systems and develops a new class of states, neither bonding nor antibonding, whose character depends on the angular orientation of the bonds in question. 相似文献
994.
Passive phase locking of an array of four fiber amplifiers by an all-optical feedback loop 总被引:2,自引:0,他引:2
We report the passive phase locking of an array of four fiber amplifiers in a unidirectional ring cavity. The feedback loop consists of a single-mode fiber that filters intracavity the far-field pattern of the four emitted beams. The pointing of the laser output can be managed by the intracavity filtering. 相似文献
995.
We present a highly efficient integratable waveguide transformer that is capable of converting Gaussian-like waveguide modes to much more complicated non-Gaussian-like slot-waveguide modes, and vice versa. The structure consists of several pairs of complementary tapers capable of making this mode conversion virtually lossless. The capability of extremely low-loss mode transformation between these two classes of waveguides has been demonstrated by means of single- and double-slot transformers. Our simulation has shown that the total transformation losses are less than 0.01 and 0.02 dB per transformer, respectively, and can be easily achieved, with a total device length of less than 100 microm. 相似文献
996.
Pierre Lubin Stéphane Vincent Jean-Paul Caltagirone Stéphane Abadie 《Comptes Rendus Mecanique》2003,331(7):495-501
The scope of this paper is to show the results obtained for simulating three-dimensional breaking waves by solving the Navier–Stokes equations in air and water. The interface tracking is achieved by a Lax–Wendroff TVD scheme (Total Variation Diminishing), which is able to handle interface reconnections. We first present the equations and the numerical methods used in this work. We then proceed to the study of a three-dimensional plunging breaking wave, using initial conditions corresponding to unstable periodic sinusoidal waves of large amplitudes. We compare the results obtained for two simulations, a longshore depth perturbation has been introduced in the solution of the flow equations in order to see the transition from a two-dimensional velocity field to a fully three-dimensional one after plunging. Breaking processes including overturning, splash-up and breaking induced vortex-like motion beneath the surface are presented and discussed. To cite this article: P. Lubin et al., C. R. Mecanique 331 (2003). 相似文献
997.
The aim of the present paper is to study the effects of non-linear devices on the reliability-based optimal design of structural systems subject to stochastic excitation. One-dimensional hysteretic devices are used for modelling the non-linear system behavior while non-stationary filtered white noise processes are utilized to represent the stochastic excitation. The reliability-based optimization problem is formulated as the minimization of the expected cost of the structure for a specified failure probability. Failure is assumed to occur when any one of the output states of interest exceeds in magnitude some specified threshold level within a given time duration. Failure probabilities are approximated locally in terms of the design variables during the optimization process in a parallel computing environment. The approximations are based on a local interpolation scheme and on an efficient simulation technique. Specifically, a subset simulation scheme is adopted and integrated into the proposed optimization process. The local approximations are then used to define a series of explicit approximate optimization problems. A sensitivity analysis is performed at the final design in order to evaluate its robustness with respect to design and system parameters. Numerical examples are presented in order to illustrate the effects of hysteretic devices on the design of two structural systems subject to earthquake excitation. The obtained results indicate that the non-linear devices have a significant effect on the reliability and global performance of the structural systems. 相似文献
998.
Mikhail Panfilov Constantin Oltean Irina Panfilova Michel Buès 《Comptes Rendus Mecanique》2003,331(1):41-48
The quadratic law of laminar flow through porous media at high Reynolds numbers, which is well confirmed by the multiple experimental data, is shown to give rise to three fundamental paradoxes. All them can be resolved by assuming the singular structure of flow. The singularity is produced by the formation of jet brunches which invade the stagnant zones and sharply loss their kinetic energy. The numerical simulation confirms this effect. To cite this article: M. Panfilov et al., C. R. Mecanique 331 (2003). 相似文献
999.
Henri Bertin Michel Quintard Ph. Vincent Corpel Stephen Whitaker 《Transport in Porous Media》1990,5(6):543-590
Two-phase flow in stratified porous media is a problem of central importance in the study of oil recovery processes. In general, these flows are parallel to the stratifications, and it is this type of flow that we have investigated experimentally and theoretically in this study. The experiments were performed with a two-layer model of a stratified porous medium. The individual strata were composed of Aerolith-10, an artificial: sintered porous medium, and Berea sandstone, a natural porous medium reputed to be relatively homogeneous. Waterflooding experiments were performed in which the saturation field was measured by gamma-ray absorption. Data were obtained at 150 points distributed evenly over a flow domain of 0.1 × 0.6 m. The slabs of Aerolith-10 and Berea sandstone were of equal thickness, i.e. 5 centimeters thick. An intensive experimental study was carried out in order to accurately characterize the individual strata; however, this effort was hampered by both local heterogeneities and large-scale heterogeneities.The theoretical analysis of the waterflooding experiments was based on the method of large-scale averaging and the large-scale closure problem. The latter provides a precise method of discussing the crossflow phenomena, and it illustrates exactly how the crossflow influences the theoretical prediction of the large-scale permeability tensor. The theoretical analysis was restricted to the quasi-static theory of Quintard and Whitaker (1988), however, the dynamic effects described in Part I (Quintard and Whitaker 1990a) are discussed in terms of their influence on the crossflow.Roman Letters
A
interfacial area between the -region and the -region contained within V, m2
-
a
vector that maps
onto
, m
-
b
vector that maps
onto
, m
-
b
vector that maps
onto
, m
-
B
second order tensor that maps
onto
, m2
-
C
second order tensor that maps
onto
, m2
-
E
energy of the gamma emitter, keV
-
f
fractional flow of the -phase
- g
gravitational vector, m/s2
-
h
characteristic length of the large-scale averaging volume, m
-
H
height of the stratified porous medium
, m
-
i
unit base vector in the x-direction
-
K
local volume-averaged single-phase permeability, m2
-
K - {K}, large-scale spatial deviation permeability
-
{
K}
large-scale volume-averaged single-phase permeability, m2
-
K
*
large-scale single-phase permeability, m2
-
K
**
equivalent large-scale single-phase permeability, m2
-
K
local volume-averaged -phase permeability in the -region, m2
-
K
local volume-averaged -phase permeability in the -region, m2
-
K
- {K
}
, large-scale spatial deviation for the -phase permeability, m2
-
K
*
large-scale permeability for the -phase, m2
-
l
thickness of the porous medium, m
-
l
characteristic length for the -region, m
-
l
characteristic length for the -region, m
-
L
length of the experimental porous medium, m
-
characteristic length for large-scale averaged quantities, m
-
n
outward unit normal vector for the -region
-
n
outward unit normal vector for the -region
-
n
unit normal vector pointing from the -region toward the -region (n
= - n
)
-
N
number of photons
-
p
pressure in the -phase, N/m2
-
p
0
reference pressure in the -phase, N/m2
-
local volume-averaged intrinsic phase average pressure in the -phase, N/m2
-
large-scale volume-averaged pressure of the -phase, N/m2
-
large-scale intrinsic phase average pressure in the capillary region of the -phase, N/m2
-
-
, large-scale spatial deviation for the -phase pressure, N/m2
- pc
, capillary pressure, N/m2
-
p
c
capillary pressure in the -region, N/m2
-
p
capillary pressure in the -region, N/m2
- {p
c
}
c
large-scale capillary pressure, N/m2
-
q
-phase velocity at the entrance of the porous medium, m/s
-
q
-phase velocity at the entrance of the porous medium, m/s
- Swi
irreducible water saturation
-
S
/, local volume-averaged saturation for the -phase
-
S
i
initial saturation for the -phase
-
S
r
residual saturation for the -phase
-
S
*
{
}*/}*, large-scale average saturation for the -phase
-
S
saturation for the -phase in the -region
-
S
saturation for the -phase in the -region
-
t
time, s
-
v
-phase velocity vector, m/s
- v
local volume-averaged phase average velocity for the -phase, m/s
- {v
}
large-scale averaged velocity for the -phase, m/s
- v
local volume-averaged phase average velocity for the -phase in the -region, m/s
- v
local volume-averaged phase average velocity for the -phase in the -region, m/s
-
v
-{v
}
, large-scale spatial deviation for the -phase velocity, m/s
-
v
-{v
}
, large-scale spatial deviation for the -phase velocity in the -region, m/s
-
v
-{v
}
, large-scale spatial deviation for the -phase velocity in the -region, m/s
-
V
large-scale averaging volume, m3
-
y
position vector relative to the centroid of the large-scale averaging volume, m
- {y}c
large-scale average of y over the capillary region, m
Greek Letters
local porosity
-
local porosity in the -region
-
local porosity in the -region
-
local volume fraction for the -phase
-
local volume fraction for the -phase in the -region
-
local volume fraction for the -phase in the -region
- {}*
{
}*+{
}*, large-scale spatial average volume fraction
- {
}*
large-scale spatial average volume fraction for the -phase
-
mass density of the -phase, kg/m3
-
mass density of the -phase, kg/m3
-
viscosity of the -phase, N s/m2
-
viscosity of the -phase, Ns/m2
-
V
/V
, volume fraction of the -region (
+
=1)
-
V
/V
, volume fraction of the -region (
+
=1)
-
attenuation coefficient to gamma-rays, m-1
-
-
相似文献
1000.
Synthesis of Carbon/Sulfur Nanolaminates by Electrochemical Extraction of Titanium from Ti2SC 下载免费PDF全文
Dr. Meng‐Qiang Zhao Morgane Sedran Zheng Ling Maria R. Lukatskaya Olha Mashtalir Michael Ghidiu Boris Dyatkin Darin J. Tallman Prof. Thierry Djenizian Prof. Michel W. Barsoum Prof. Yury Gogotsi 《Angewandte Chemie (International ed. in English)》2015,54(16):4810-4814
Herein we electrochemically and selectively extract Ti from the MAX phase Ti2SC to form carbon/sulfur (C/S) nanolaminates at room temperature. The products are composed of multi‐layers of C/S flakes, with predominantly amorphous and some graphene‐like structures. Covalent bonding between C and S is observed in the nanolaminates, which render the latter promising candidates as electrode materials for Li‐S batteries. We also show that it is possible to extract Ti from other MAX phases, such as Ti3AlC2 , Ti3SnC2 , and Ti2GeC, suggesting that electrochemical etching can be a powerful method to selectively extract the “M” elements from the MAX phases, to produce “AX” layered structures, that cannot be made otherwise. The latter hold promise for a variety of applications, such as energy storage, catalysis, etc. 相似文献