2,338 research outputs found
Plastic Flow in Two-Dimensional Solids
A time-dependent Ginzburg-Landau model of plastic deformation in
two-dimensional solids is presented. The fundamental dynamic variables are the
displacement field \bi u and the lattice velocity {\bi v}=\p {\bi u}/\p t.
Damping is assumed to arise from the shear viscosity in the momentum equation.
The elastic energy density is a periodic function of the shear and tetragonal
strains, which enables formation of slips at large strains. In this work we
neglect defects such as vacancies, interstitials, or grain boundaries. The
simplest slip consists of two edge dislocations with opposite Burgers vectors.
The formation energy of a slip is minimized if its orientation is parallel or
perpendicular to the flow in simple shear deformation and if it makes angles of
with respect to the stretched direction in uniaxial stretching.
High-density dislocations produced in plastic flow do not disappear even if
the flow is stopped. Thus large applied strains give rise to metastable,
structurally disordered states. We divide the elastic energy into an elastic
part due to affine deformation and a defect part. The latter represents degree
of disorder and is nearly constant in plastic flow under cyclic straining.Comment: 16pages, Figures can be obtained at
http://stat.scphys.kyoto-u.ac.jp/index-e.htm
Principles of Discrete Time Mechanics: I. Particle Systems
We discuss the principles to be used in the construction of discrete time
classical and quantum mechanics as applied to point particle systems. In the
classical theory this includes the concept of virtual path and the construction
of system functions from classical Lagrangians, Cadzow's variational principle
applied to the action sum, Maeda-Noether and Logan invariants of the motion,
elliptic and hyperbolic harmonic oscillator behaviour, gauge invariant
electrodynamics and charge conservation, and the Grassmannian oscillator. First
quantised discrete time mechanics is discussed via the concept of system
amplitude, which permits the construction of all quantities of interest such as
commutators and scattering amplitudes. We discuss stroboscopic quantum
mechanics, or the construction of discrete time quantum theory from continuous
time quantum theory and show how this works in detail for the free Newtonian
particle. We conclude with an application of the Schwinger action principle to
the important case of the quantised discrete time inhomogeneous oscillator.Comment: 35 pages, LateX, To be published in J.Phys.A: Math.Gen. Basic
principles stated: applications to field theory in subsequent papers of
series contact email address: [email protected]
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Involvement of Bruton's tyrosine kinase in FcepsilonRI-dependent mast cell degranulation and cytokine production.
We investigated the role of Bruton's tyrosine kinase (Btk) in FcepsilonRI-dependent activation of mouse mast cells, using xid and btk null mutant mice. Unlike B cell development, mast cell development is apparently normal in these btk mutant mice. However, mast cells derived from these mice exhibited significant abnormalities in FcepsilonRI-dependent function. xid mice primed with anti-dinitrophenyl monoclonal IgE antibody exhibited mildly diminished early-phase and severely blunted late-phase anaphylactic reactions in response to antigen challenge in vivo. Consistent with this finding, cultured mast cells derived from the bone marrow cells of xid or btk null mice exhibited mild impairments in degranulation, and more profound defects in the production of several cytokines, upon FcepsilonRI cross-linking. Moreover, the transcriptional activities of these cytokine genes were severely reduced in FcepsilonRI-stimulated btk mutant mast cells. The specificity of these effects of btk mutations was confirmed by the improvement in the ability of btk mutant mast cells to degranulate and to secrete cytokines after the retroviral transfer of wild-type btk cDNA, but not of vector or kinase-dead btk cDNA. Retroviral transfer of Emt (= Itk/Tsk), Btk's closest relative, also partially improved the ability of btk mutant mast cells to secrete mediators. Taken together, these results demonstrate an important role for Btk in the full expression of FcepsilonRI signal transduction in mast cells
The axial anomaly and the phases of dense QCD
The QCD axial anomaly, by coupling the chiral condensate and BCS pairing
fields of quarks in dense matter, leads to a new critical point in the QCD
phase diagram \cite{HTYB,chiral2}, which at sufficiently low temperature should
terminate the line of phase transitions between chirally broken hadronic matter
and color superconducting quark matter. The critical point indicates that
matter at low temperature should cross over smoothly from the hadronic to the
quark phase, as suggested earlier on the basis of symmetry. We review here the
arguments, based on a general Ginzburg-Landau effective Lagrangian, for the
existence of the new critical point, as well as discuss possible connections
between the QCD phase structure and the BEC-BCS crossover in ultracold trapped
atomic fermion systems at unitarity. and implications for the presence of quark
matter in neutron stars.Comment: 8 pages, Proceedings of Quark Matter 2008, Jaipu
Design and performance of the muon monitor for the T2K neutrino oscillation experiment
This article describes the design and performance of the muon monitor for the
T2K (Tokaito-Kamioka) long baseline neutrino oscillation experiment. The muon
monitor consists of two types of detector arrays: ionization chambers and
silicon PIN photodiodes. It measures the intensity and profile of muons
produced, along with neutrinos, in the decay of pions. The measurement is
sensitive to the intensity and direction of the neutrino beam. The linearity
and stability of the detectors were measured in beam tests to be within 2.4%
and 1.5%, respectively. Based on the test results, the precision of the beam
direction measured by the muon monitor is expected to be 0.25 mrad.Comment: 22 page
Use of B-natriuretic peptide as a diagnostic marker in the differential diagnosis of transfusion-associated circulatory overload
Transfusion-associated circulatory overload (TACO) occurs when the transfusion rate or volume exceeds the capacity of a compromised cardiovascular system. Characteristic symptoms and signs associated with TACO are neither sensitive nor specific. B-natriuretic peptide (BNP) is a 32-amino-acid polypeptide secreted from the cardiac ventricles in response to ventricular volume expansion and pressure overload. This study was performed to explore the usage of BNP in the differential diagnosis of TACO. STUDY DESIGN AND METHODS: Pre- and posttransfusion BNP levels were determined in 21 patients with suspected TACO and 19 control patients. The BNP was considered significant if the posttransfusion-to-pretransfusion ratio was at least 1.5 and the posttransfusion BNP level was at least 100 pg per mL. RESULTS: The BNP test has a sensitivity and specificity of 81 and 89 percent, respectively, in diagnosis of TACO. It has a positive predictive value of 89 percent, a negative predictive value of 81 percent, and an accuracy of 87 percent. In logistic regression analysis, BNP was found to have significant predictive power independent of other clinical variables in models predicting which patients had TACO. CONCLUSIONS: Our study suggests that in patients who present symptoms suggestive of TACO, BNP can be a useful adjunct marker in confirming volume overload as the cause of acute dyspnea and symptoms related to cardiovascular compromise.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75697/1/j.1537-2995.2005.04326.x.pd
Dynamics of Highly Supercooled Liquids:Heterogeneity, Rheology, and Diffusion
Highly supercooled liquids with soft-core potentials are studied via
molecular dynamics simulations in two and three dimensions in quiescent and
sheared conditions.We may define bonds between neighboring particle pairs
unambiguously owing to the sharpness of the first peak of the pair correlation
functions. Upon structural rearrangements, they break collectively in the form
of clusters whose sizes grow with lowering the temperature . The bond life
time , which depends on and the shear rate \gdot, is on the order
of the usual structural or relaxation time in weak
shear \gdot \tau_{\alpha} \ll 1, while it decreases as 1/\gdot in strong
shear \gdot\tau_{\alpha} \gg 1 due to shear-induced cage breakage.
Accumulated broken bonds in a time interval () closely
resemble the critical fluctuations of Ising spin systems. For example, their
structure factor is well fitted to the Ornstein-Zernike form, which yields the
correlation length representing the maximum size of the clusters composed
of broken bonds. We also find a dynamical scaling relation, , valid for any and \gdot with in two dimensions and
in three dimensions. The viscosity is of order for any and
\gdot, so marked shear-thinning behavior emerges. The shear stress is close
to a limiting stress in a wide shear region. We also examine motion of tagged
particles in shear in three dimensions. The diffusion constant is found to be
of order with for any and \gdot, so
it is much enhanced in strong shear compared with its value at zero shear. This
indicates breakdown of the Einstein-Stokes relation in accord with experiments.
Some possible experiments are also proposed.Comment: 20pages (including figures
Epitaxial Growth of a Full-Heusler Alloy CoFeSi on Silicon by Low-Temperature Molecular Beam Epitaxy
For electrical spin injection and detection of spin-polarized electrons in
silicon, we explore highly epitaxial growth of ferromagnetic full-Heusler-alloy
Co2FeSi thin films on silicon substrates using low-temperature molecular beam
epitaxy (LTMBE). Although in-situ reflection high energy electron diffraction
images clearly show two-dimensional epitaxial growth for growth temperatures
T_G of 60, 130, and 200 C, cross-sectional transmission electron microscopy
experiments reveal that there are single-crystal phases other than Heusler
alloys near the interface between Co_2FeSi and Si for T_G = 130 and 200 C. On
the other hand, almost perfect heterointerfaces are achieved for T_G = 60 C.
These results and magnetic measurements indicate that highly epitaxial growth
of Co_2FeSi thin films on Si is demonstrated only for T_G = 60 C.Comment: 3 pages, 3 figure
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