301 research outputs found
Response of the Higgs amplitude mode of superfluid Bose gases in a three dimensional optical lattice
We study the Higgs mode of superfluid Bose gases in a three dimensional
optical lattice, which emerges near the quantum phase transition to the Mott
insulator at commensurate fillings. Specifically, we consider responses of the
Higgs mode to temporal modulations of the onsite interaction and the hopping
energy. In order to calculate the response functions including the effects of
quantum and thermal fluctuations, we map the Bose-Hubbard model onto an
effective pseudospin-one model and use a perturbative expansion based on the
imaginary-time Green's function theory. We also include the effects of an
inhomogeneous trapping potential by means of a local density approximation. We
find that the response function for the hopping modulation is equal to that for
the interaction modulation within our approximation. At the unit filling rate
and in the absence of a trapping potential, we show that the Higgs mode can
exist as a sharp resonance peak in the dynamical susceptibilities at typical
temperatures. However, the resonance peak is significantly broadened due to the
trapping potential when the modulations are applied globally to the entire
system. We suggest that the Higgs mode can be detected as a sharp resonance
peak by partial modulations around the trap center.Comment: 22 pages, 9 figure
SU(3) truncated Wigner approximation for strongly interacting Bose gases
We develop and utilize the SU(3) truncated Wigner approximation (TWA) in
order to analyze far-from-equilibrium quantum dynamics of strongly interacting
Bose gases in an optical lattice. Specifically, we explicitly represent the
corresponding Bose--Hubbard model at an arbitrary filling factor with
restricted local Hilbert spaces in terms of SU(3) matrices. Moreover, we
introduce a discrete Wigner sampling technique for the SU(3) TWA and examine
its performance as well as that of the SU(3) TWA with the Gaussian
approximation for the continuous Wigner function. We directly compare outputs
of these two approaches with exact computations regarding dynamics of the
Bose--Hubbard model at unit filling with a small size and that of a
fully-connected spin-1 model with a large size. We show that both approaches
can quantitatively capture quantum dynamics on a timescale of ,
where and denote the hopping energy and the coordination number. We
apply the two kinds of SU(3) TWA to dynamical spreading of a two-point
correlation function of the Bose--Hubbard model on a square lattice with a
large system size, which has been measured in recent experiments. Noticeable
deviations between the theories and experiments indicate that proper inclusion
of effects of the spatial inhomogeneity, which is not straightforward in our
formulation of the SU(3) TWA, may be necessary.Comment: 21 pages, 8 figure
2-Carboxypyridinium hydrogen chloranilate. Corrigendum
Corrigendum to Acta Cryst. (2005), E61, o4215–o4217
Aerosol Insulin Induces Regulatory CD8 γδ T Cells That Prevent Murine Insulin-dependent Diabetes
Cellular immune hyporesponsiveness can be induced by the presentation of soluble protein antigens to mucosal surfaces. Most studies of mucosa-mediated tolerance have used the oral route of antigen delivery and few have examined autoantigens in natural models of autoimmune disease. Insulin is an autoantigen in humans and nonobese diabetic (NOD) mice with insulindependent diabetes mellitus (IDDM). When we administered insulin aerosol to NOD mice after the onset of subclinical disease, pancreatic islet pathology and diabetes incidence were both significantly reduced. Insulin-treated mice had increased circulating antibodies to insulin, absent splenocyte proliferation to the major epitope, insulin B chain amino acids 9–23, which was associated with increased IL-4 and particularly IL-10 secretion, and reduced proliferation to glutamic acid decarboxylase, another islet autoantigen. The ability of splenocytes from insulin-treated mice to suppress the adoptive transfer of diabetes to nondiabetic mice by T cells of diabetic mice was shown to be caused by small numbers of CD8 γδ T cells. These findings reveal a novel mechanism for suppressing cell-mediated autoimmune disease. Induction of regulatory CD8 γδ T cells by aerosol insulin is a therapeutic strategy with implications for the prevention of human IDDM
Influence of nut shell powder content on the tribological properties of recycled polyolefin composites
The purpose of this study is to investigate the influence of nut shell powder (NSP) content on the tribological properties of recycled polyolefin (R-PO) composites. NSP was previously grinded the dried nut shell by crusher machine cryogenically in liquid nitrogen. NSP/R-PO composites with NSP content of 5, 10 and 20 vol.% were prepared in this study. These composites were extruded by a twin screw extruder and injection-molded. Their tribological properties were measured by a reciprocating type sliding wear tester at constant normal load and sliding speed under dry condition. It was found that NSP is effective for reducing the wear resistance of R-PO, and the influence of NSP content on the tribological properties of NSP/R-PO composites does not remarkably appear, but they are improved with the addition of low content such as 5 vol.%. This may be attributed to the change of wear mechanism according to the filling of NSP. © 2016 Author(s).MEXT, Ministry of Education, Culture, Sports, Science, and Technolog
Impurity conduction in phosphorus-doped buried-channel silicon-on-insulator field-effect transistors
We investigate transport in phosphorus-doped buried-channel
metal-oxide-semiconductor field-effect transistors at temperatures between 10
and 295 K. In a range of doping concentration between around 2.1 and 8.7 x 1017
cm-3, we find that a clear peak emerges in the conductance versus gate-voltage
curves at low temperature. In addition, temperature dependence measurements
reveal that the conductance obeys a variable-range-hopping law up to an
unexpectedly high temperature of over 100 K. The symmetric dual-gate
configuration of the silicon-on-insulator we use allows us to fully
characterize the vertical-bias dependence of the conductance. Comparison to
computer simulation of the phosphorus impurity band depth-profile reveals how
the spatial variation of the impurity-band energy determines the hopping
conduction in transistor structures. We conclude that the emergence of the
conductance peak and the high-temperature variable-range hopping originate from
the band bending and its change by the gate bias. Moreover, the peak structure
is found to be strongly related to the density of states (DOS) of the
phosphorus impurity band, suggesting the possibility of performing a novel
spectroscopy for the DOS of phosphorus, the dopant of paramount importance in
Si technology, through transport experiments.Comment: 9 figure
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