2,058 research outputs found
An experimental study on (2) modular symmetry in the quantum Hall system with a small spin-splitting
Magnetic-field-induced phase transitions were studied with a two-dimensional
electron AlGaAs/GaAs system. The temperature-driven flow diagram shows the
features of the (2) modular symmetry, which includes distorted
flowlines and shiftted critical point. The deviation of the critical
conductivities is attributed to a small but resolved spin splitting, which
reduces the symmetry in Landau quantization. [B. P. Dolan, Phys. Rev. B 62,
10278.] Universal scaling is found under the reduction of the modular symmetry.
It is also shown that the Hall conductivity could still be governed by the
scaling law when the semicircle law and the scaling on the longitudinal
conductivity are invalid. *corresponding author:[email protected]: The revised manuscript has been published in J. Phys.: Condens.
Matte
Effects of Zeeman spin splitting on the modular symmetry in the quantum Hall effect
Magnetic-field-induced phase transitions in the integer quantum Hall effect
are studied under the formation of paired Landau bands arising from Zeeman spin
splitting. By investigating features of modular symmetry, we showed that
modifications to the particle-hole transformation should be considered under
the coupling between the paired Landau bands. Our study indicates that such a
transformation should be modified either when the Zeeman gap is much smaller
than the cyclotron gap, or when these two gaps are comparable.Comment: 8 pages, 4 figure
Spin-dependent thermoelectric transport through double quantum dots
We study thermoelectric transport through double quantum dots system with
spin-dependent interdot coupling and ferromagnetic electrodes by means of the
non-equilibrium Green function in the linear response regime. It is found that
the thermoelectric coefficients are strongly dependent on the splitting of
interdot coupling, the relative magnetic configurations and the spin
polarization of leads. In particular, the thermoelectric efficiency can achieve
considerable value in parallel configuration when the effective interdot
coupling and tunnel coupling between QDs and the leads for spin-down electrons
are small. Moreover, the thermoelectric efficiency increases with the intradot
Coulomb interactions increasing and can reach very high value at an appropriate
temperature. In the presence of the magnetic field, the spin accumulation in
leads strongly suppresses the thermoelectric efficiency and a pure spin
thermopower can be obtained.Comment: 5 figure
Experimental Studies of Low-field Landau Quantization in Two-dimensional Electron Systems in GaAs/AlGaAs Heterostructures
By applying a magnetic field perpendicular to GaAs/AlGaAs two-dimensional
electron systems, we study the low-field Landau quantization when the thermal
damping is reduced with decreasing the temperature. Magneto-oscillations
following Shubnikov-de Haas (SdH) formula are observed even when their
amplitudes are so large that the deviation to such a formula is expected. Our
experimental results show the importance of the positive magneto-resistance to
the extension of SdH formula under the damping induced by the disorder.Comment: 9 pages, 3 figure
Cold Nuclear Matter In Holographic QCD
We study the Sakai-Sugimoto model of holographic QCD at zero temperature and
finite chemical potential. We find that as the baryon chemical potential is
increased above a critical value, there is a phase transition to a nuclear
matter phase characterized by a condensate of instantons on the probe D-branes
in the string theory dual. As a result of electrostatic interactions between
the instantons, this condensate expands towards the UV when the chemical
potential is increased, giving a holographic version of the expansion of the
Fermi surface. We argue based on properties of instantons that the nuclear
matter phase is necessarily inhomogeneous to arbitrarily high density. This
suggests an explanation of the "chiral density wave" instability of the quark
Fermi surface in large N_c QCD at asymptotically large chemical potential. We
study properties of the nuclear matter phase as a function of chemical
potential beyond the transition and argue in particular that the model can be
used to make a semi-quantitative prediction of the binding energy per nucleon
for nuclear matter in ordinary QCD.Comment: 31 pages, LaTeX, 1 figure, v2: some formulae corrected, qualitative
results unchange
Deformations of the hemisphere that increase scalar curvature
Consider a compact Riemannian manifold M of dimension n whose boundary
\partial M is totally geodesic and is isometric to the standard sphere S^{n-1}.
A natural conjecture of Min-Oo asserts that if the scalar curvature of M is at
least n(n-1), then M is isometric to the hemisphere S_+^n equipped with its
standard metric. This conjecture is inspired by the positive mass theorem in
general relativity, and has been verified in many special cases. In this paper,
we construct counterexamples to Min-Oo's conjecture in dimension n \geq 3.Comment: Revised version, to appear in Invent. Mat
Electronic and phononic states of the Holstein-Hubbard dimer of variable length
We consider a model Hamiltonian for a dimer including all the electronic one-
and two-body terms consistent with a single orbital per site, a free Einstein
phonon term, and an electron-phonon coupling of the Holstein type. The bare
electronic interaction parameters were evaluated in terms of Wannier functions
built from Gaussian atomic orbitals. An effective polaronic Hamiltonian was
obtained by an unrestricted displaced-oscillator transformation, followed by
evaluation of the phononic terms over a squeezed-phonon variational wave
function. For the cases of quarter-filled and half-filled orbital, and over a
range of dimer length values, the ground state was identified by simultaneously
and independently optimizing the orbital shape, the phonon displacement and the
squeezing effect strength. As the dimer length varies, we generally find
discontinuous changes of both electronic and phononic states, accompanied by an
appreciable renormalization of the effective electronic interactions across the
transitions, due to the equilibrium shape of the wave functions strongly
depending on the phononic regime and on the type of ground state.Comment: 11 pages, RevTeX, 10 PostScript figures; to appear in Phys. Rev.
Classification of Widely and Rarely Expressed Genes with Recurrent Neural Network
A tissue-specific gene expression shapes the formation of tissues, while gene expression changes reflect the immune response of the human body to environmental stimulations or pressure, particularly in disease conditions, such as cancers. A few genes are commonly expressed across tissues or various cancers, while others are not. To investigate the functional differences between widely and rarely expressed genes, we defined the genes that were expressed in 32 normal tissues/cancers (i.e., called widely expressed genes; FPKM >1 in all samples) and those that were not detected (i.e., called rarely expressed genes; FPKM <1 in all samples) based on the large gene expression data set provided by Uhlen et al. Each gene was encoded using the gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment scores. Minimum redundancy maximum relevance (mRMR) was used to measure and rank these features on the mRMR feature list. Thereafter, we applied the incremental feature selection method with a supervised classifier recurrent neural network (RNN) to select the discriminate features for classifying widely expressed genes from rarely expressed genes and construct an optimum RNN classifier. The Youden's indexes generated by the optimum RNN classifier and evaluated using a 10-fold cross validation were 0.739 for normal tissues and 0.639 for cancers. Furthermore, the underlying mechanisms of the key discriminate GO and KEGG features were analyzed. Results can facilitate the identification of the expression landscape of genes and elucidation of how gene expression shapes tissues and the microenvironment of cancers
Continuous immobilized yeast reactor system for complete beer fermentation using spent grains and corncobs as carrier materials
Despite extensive research carried out in
the last few decades, continuous beer fermentation has not yet managed to outperform the traditional batch technology. An industrial breakthrough in favour of
continuous brewing using immobilized yeast could be expected only on achievement of the following process characteristics: simple design, low investment costs, flexible operation, effective process control and good
product quality. The application of cheap carrier materials of by-product origin could significantly lower the investment costs of continuous fermentation systems.
This work deals with a complete continuous beer fermentation system consisting of a main fermentation reactor (gas-lift) and a maturation reactor (packedbed) containing yeast immobilized on spent grains and
corncobs, respectively. The suitability of cheap carrier materials for long-term continuous brewing was proved. It was found that by fine tuning of process
parameters (residence time, aeration) it was possible to adjust the flavour profile of the final product. Consumers considered the continuously fermented beer to be of a regular quality. Analytical and sensorial profiles of both continuously and batch fermented beers were compared.(Fundação de Amparo a Pesquisa do Estado de São Paulo, Brazil (FAPESPFundação para a Ciência e a Tecnologia (FC
Dark Matters in Axino Gravitino Cosmology
It is suggested that the axino mass in the 1 MeV region and gravitino mass in
the eV region can provide an axino lifetime of order of the time of photon
decoupling. In this case, some undecayed axinos act like cold dark matters and
some axino decay products (gravitinos and hot axions) act like hot dark matters
at the time of galaxy formation.Comment: 9 pages, Late
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