45,956 research outputs found
Simulation of the small punch creep test with consideration of variation of material properties
A new finite element model of the small punch creep test is described. The material constitutive relationship for creep considered is a simple Norton power law: in this study the exponent in the power law is varied for each element to simulate the random behaviour of creep. The influence of this random variation, and the effect of the friction factor between the punch and specimen, on the deformation and stress field has been investigated
Density Variations over Subparsec Scales in Diffuse Molecular Gas
We present high-resolution observations of interstellar CN, CH, CH^{+},
\ion{Ca}{1}, and \ion{Ca}{2} absorption lines toward the multiple star systems
HD206267 and HD217035. Substantial variations in CN absorption are observed
among three sight lines of HD206267, which are separated by distances of order
10,000 AU; smaller differences are seen for CH, CH^{+}, and \ion{Ca}{1}. Gas
densities for individual velocity components are inferred from a chemical
model, independent of assumptions about cloud shape. While the component
densities can differ by factors of 5.0 between adjacent sightlines, the
densities are always less than 5000 cm^{-3}. Calculations show that the derived
density contrasts are not sensitive to the temperature or reaction rates used
in the chemical model. A large difference in the CH^{+} profiles (a factor of 2
in column density) is seen in the lower density gas toward HD217035.Comment: 9 pages, 2 figures. Accepted for publication in ApJ
Exact isovector pairing in a shell-model framework: Role of proton-neutron correlations in isobaric analog states
We utilize a nuclear shell model Hamiltonian with only two adjustable
parameters to generate, for the first time, exact solutions for pairing
correlations for light to medium-mass nuclei, including the challenging
proton-neutron pairs, while also identifying the primary physics involved. In
addition to single-particle energy and Coulomb potential terms, the shell model
Hamiltonian consists of an isovector pairing interaction and an average
proton-neutron isoscalar interaction, where the term describes the
average interaction between non-paired protons and neutrons. This Hamiltonian
is exactly solvable, where, utilizing 3 to 7 single-particle energy levels, we
reproduce experimental data for 0 state energies for isotopes with mass
through exceptionally well including isotopes from He to Ge.
Additionally, we isolate effects due to like-particle and proton-neutron
pairing, provide estimates for the total and proton-neutron pairing gaps, and
reproduce (neutron) = (proton) irregularity. These results provide a
further understanding for the key role of proton-neutron pairing correlations
in nuclei, which is especially important for waiting-point nuclei on the
rp-path of nucleosynthesis.Comment: 10 pages, 4 figure
The effect of electromechanical coupling on the strain in AlGaN/GaN heterojunction field effect transistors
The strain in AlGaN/GaN heterojunction field-effect transistors (HFETs) is
examined theoretically in the context of the fully-coupled equation of state
for piezoelectric materials. Using a simple analytical model, it is shown that,
in the absence of a two-dimensional electron gas (2DEG), the out-of-plane
strain obtained without electromechanical coupling is in error by about 30% for
an Al fraction of 0.3. This result has consequences for the calculation of
quantities that depend directly on the strain tensor. These quantities include
the eigenstates and electrostatic potential in AlGaN/GaN heterostructures. It
is shown that for an HFET, the electromechanical coupling is screened by the
2DEG. Results for the electromechanical model, including the 2DEG, indicate
that the standard (decoupled) strain model is a reasonable approximation for
HFET calculataions. The analytical results are supported by a self-consistent
Schr\"odinger-Poisson calculation that includes the fully-coupled equation of
state together with the charge-balance equation.Comment: 6 figures, revte
Direct visualization of iron sheath shielding effect in MgB_2 superconducting wires
Local magneto-optical imaging and global magnetization measurement techniques
were used in order to visualize shielding effects in the superconducting core
of MgB_2 wires sheathed by ferromagnetic iron (Fe). The magnetic shielding can
provide a Meissner-like state in the superconducting core in applied magnetic
fields up to ~1T. The maximum shielding fields are shown to correlate with the
saturation fields of magnetization in Fe-sheaths. The shielding has been found
to facilitate the appearance of an overcritical state, which is capable of
achieving a critical current density (J_c) in the core which is larger than J_c
in the same wire without the sheath by a factor of ~2. Other effects caused by
the magnetic interaction between the sheath and the superconducting core are
discussed.Comment: 4 pages, 3 figure
Experimental Demonstration of Five-photon Entanglement and Open-destination Teleportation
Universal quantum error-correction requires the ability of manipulating
entanglement of five or more particles. Although entanglement of three or four
particles has been experimentally demonstrated and used to obtain the extreme
contradiction between quantum mechanics and local realism, the realization of
five-particle entanglement remains an experimental challenge. Meanwhile, a
crucial experimental challenge in multi-party quantum communication and
computation is the so-called open-destination teleportation. During
open-destination teleportation, an unknown quantum state of a single particle
is first teleported onto a N-particle coherent superposition to perform
distributed quantum information processing. At a later stage this teleported
state can be readout at any of the N particles for further applications by
performing a projection measurement on the remaining N-1 particles. Here, we
report a proof-of-principle demonstration of five-photon entanglement and
open-destination teleportation. In the experiment, we use two entangled photon
pairs to generate a four-photon entangled state, which is then combined with a
single photon state to achieve the experimental goals. The methods developed in
our experiment would have various applications e.g. in quantum secret sharing
and measurement-based quantum computation.Comment: 19 pages, 4 figures, submitted for publication on 15 October, 200
- …