44,044 research outputs found
Understanding the deformation mechanism of individual phases of a ZrTi-based bulk metallic glass matrix composite using in situ diffraction and imaging methods
The plasticity of a ZrTi-based bulk metallic glass composite consisting of glassy matrix and crystalline dendritic phase was studied in-situ under identical tensile loading conditions using scanning electron microscopy and synchrotron X-ray diffraction. A generic procedure was developed to separate the diffraction information of the crystalline phases away from that of the matrix and to precisely calculate the microscopic strains of the two phases at different macroscopic load steps. In this way, the time-evolved quantitative links between shear bands nucleation/propagation and the corresponding microscopic stress fields around them are established, providing more quantitative understanding on (1) how the shear bands are driven by the local stress field, and (2) the critical stresses required for the shear bands to nucleate in the crystalline phase, propagate through the crystalline/matrix interface, and finally into the matrix
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Recovery from acidosis is a robust trigger for loss of force in murine hypokalemic periodic paralysis.
Periodic paralysis is an ion channelopathy of skeletal muscle in which recurrent episodes of weakness or paralysis are caused by sustained depolarization of the resting potential and thus reduction of fiber excitability. Episodes are often triggered by environmental stresses, such as changes in extracellular K+, cooling, or exercise. Rest after vigorous exercise is the most common trigger for weakness in periodic paralysis, but the mechanism is unknown. Here, we use knock-in mutant mouse models of hypokalemic periodic paralysis (HypoKPP; NaV1.4-R669H or CaV1.1-R528H) and hyperkalemic periodic paralysis (HyperKPP; NaV1.4-M1592V) to investigate whether the coupling between pH and susceptibility to loss of muscle force is a possible contributor to exercise-induced weakness. In both mouse models, acidosis (pH 6.7 in 25% CO2) is mildly protective, but a return to pH 7.4 (5% CO2) unexpectedly elicits a robust loss of force in HypoKPP but not HyperKPP muscle. Prolonged exposure to low pH (tens of minutes) is required to cause susceptibility to post-acidosis loss of force, and the force decrement can be prevented by maneuvers that impede Cl- entry. Based on these data, we propose a mechanism for post-acidosis loss of force wherein the reduced Cl- conductance in acidosis leads to a slow accumulation of myoplasmic Cl- A rapid recovery of both pH and Cl- conductance, in the context of increased [Cl]in/[Cl]out, favors the anomalously depolarized state of the bistable resting potential in HypoKPP muscle, which reduces fiber excitability. This mechanism is consistent with the delayed onset of exercise-induced weakness that occurs with rest after vigorous activity
X-shaped and Y-shaped Andreev resonance profiles in a superconducting quantum dot
The quasi-bound states of a superconducting quantum dot that is weakly
coupled to a normal metal appear as resonances in the Andreev reflection
probability, measured via the differential conductance. We study the evolution
of these Andreev resonances when an external parameter (such as magnetic field
or gate voltage) is varied, using a random-matrix model for the
scattering matrix. We contrast the two ensembles with broken time-reversal
symmetry, in the presence or absence of spin-rotation symmetry (class C or D).
The poles of the scattering matrix in the complex plane, encoding the center
and width of the resonance, are repelled from the imaginary axis in class C. In
class D, in contrast, a number of the poles has zero real
part. The corresponding Andreev resonances are pinned to the middle of the gap
and produce a zero-bias conductance peak that does not split over a range of
parameter values (Y-shaped profile), unlike the usual conductance peaks that
merge and then immediately split (X-shaped profile).Comment: Contribution for the JETP special issue in honor of A.F. Andreev's
75th birthday. 9 pages, 8 figure
Simultaneous quantization of bulk conduction and valence states through adsorption of nonmagnetic impurities on Bi2Se3
Exposing the (111) surface of the topological insulator Bi2Se3 to carbon
monoxide results in strong shifts of the features observed in angle-resolved
photoemission. The behavior is very similar to an often reported `aging' effect
of the surface and it is concluded that this aging is most likely due to the
adsorption of rest gas molecules. The spectral changes are also similar to
those recently reported in connection with the adsorption of the magnetic
adatom Fe. All spectral changes can be explained by a simultaneous confinement
of the conduction band and valence band states. This is only possible because
of the unusual bulk electronic structure of Bi2Se3. The valence band
quantization leads to spectral features which resemble those of a band gap
opening at the Dirac point.Comment: 5 pages, 4 figure
Controlling Condensate Collapse and Expansion with an Optical Feshbach Resonance
We demonstrate control of the collapse and expansion of an 88Sr Bose-Einstein
condensate using an optical Feshbach resonance (OFR) near the 1S0-3P1
intercombination transition at 689 nm. Significant changes in dynamics are
caused by modifications of scattering length by up to +- ?10a_bg, where the
background scattering length of 88Sr is a_bg = -2a0 (1a0 = 0.053 nm). Changes
in scattering length are monitored through changes in the size of the
condensate after a time-of-flight measurement. Because the background
scattering length is close to zero, blue detuning of the OFR laser with respect
to a photoassociative resonance leads to increased interaction energy and a
faster condensate expansion, whereas red detuning triggers a collapse of the
condensate. The results are modeled with the time-dependent nonlinear
Gross-Pitaevskii equation.Comment: 5 pages, 3 figure
Phase reconstruction of strong-field excited systems by transient-absorption spectroscopy
We study the evolution of a V-type three-level system, whose two resonances
are coherently excited and coupled by two ultrashort laser pump and probe
pulses, separated by a varying time delay. We relate the quantum dynamics of
the excited multi-level system to the absorption spectrum of the transmitted
probe pulse. In particular, by analyzing the quantum evolution of the system,
we interpret how atomic phases are differently encoded in the
time-delay-dependent spectral absorption profiles when the pump pulse either
precedes or follows the probe pulse. We experimentally apply this scheme to
atomic Rb, whose fine-structure-split 5s\,^2S_{1/2}\rightarrow 5p\,^2P_{1/2}
and 5s\,^2S_{1/2}\rightarrow 5p\,^2P_{3/2} transitions are driven by the
combined action of a pump pulse of variable intensity and a delayed probe
pulse. The provided understanding of the relationship between quantum phases
and absorption spectra represents an important step towards full time-dependent
phase reconstruction (quantum holography) of bound-state wave-packets in
strong-field light-matter interactions with atoms, molecules and solids.Comment: 5 pages, 4 figure
A systematic study on the binding energy of hypernuclei
In this paper, we calculated the binding energy per baryon of the
hypernuclei systemically, using the relativistic mean field theory (RMF) in a
statistic frame. Some resemble properties are found among most of the
hypernuclei found in experiments. The data show that a hypernucleus
will be more stable, if it is composed of a hyperon adding to a
stable normal nuclear core, or a hyperon replacing a neutron in a
stable normal nuclear core. According to our calculations, existences of some
new hypernuclei are predicted under the frame of RMF.Comment: 8 pages, 6 figures, 3 table
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