47,661 research outputs found
Contracted Representation of Yang's Space-Time Algebra and Buniy-Hsu-Zee's Discrete Space-Time
Motivated by the recent proposition by Buniy, Hsu and Zee with respect to
discrete space-time and finite spatial degrees of freedom of our physical world
with a short- and a long-distance scales, and we reconsider the
Lorentz-covariant Yang's quantized space-time algebra (YSTA), which is
intrinsically equipped with such two kinds of scale parameters, and
. In accordance with their proposition, we find the so-called contracted
representation of YSTA with finite spatial degrees of freedom associated with
the ratio , which gives a possibility of the divergence-free
noncommutative field theory on YSTA. The canonical commutation relations
familiar in the ordinary quantum mechanics appear as the cooperative
Inonu-Wigner's contraction limit of YSTA, and $R \to \infty.
A Viscoelastic model of phase separation
We show here a general model of phase separation in isotropic condensed
matter, namely, a viscoelastic model. We propose that the bulk mechanical
relaxation modulus that has so far been ignored in previous theories plays an
important role in viscoelastic phase separation in addition to the shear
relaxation modulus. In polymer solutions, for example, attractive interactions
between polymers under a poor-solvent condition likely cause the transient
gellike behavior, which makes both bulk and shear modes active. Although such
attractive interactions between molecules of the same component exist
universally in the two-phase region of a mixture, the stress arising from
attractive interactions is asymmetrically divided between the components only
in dynamically asymmetric mixtures such as polymer solutions and colloidal
suspensions. Thus, the interaction network between the slower components, which
can store the elastic energy against its deformation through bulk and shear
moduli, is formed. It is the bulk relaxation modulus associated with this
interaction network that is primarily responsible for the appearance of the
sponge structure peculiar to viscoelastic phase separation and the phase
inversion. We demonstrate that a viscoelastic model of phase separation
including this new effect is a general model that can describe all types of
isotropic phase separation including solid and fluid models as its special
cases without any exception, if there is no coupling with additional order
parameter. The physical origin of volume shrinking behavior during viscoelastic
phase separation and the universality of the resulting spongelike structure are
also discussed.Comment: 14 pages, RevTex, To appear in Phys. Rev
Theory of magnetotunneling spectroscopy in spin triplet p-wave superconductors
We study the influence of a magnetic field on the zero-bias conductance
peak (ZBCP) due to zero-energy Andreev bound state (ZES) in normal metal /
unconventional superconductor. For p-wave junctions, ZBCP does not split into
two by even for sufficiently low transparent junctions, where ZBCP clearly
splits for d-wave. This unique property originates from the fact that for
p-wave superconductors, perpendicularly injected quasiparticle form ZES, which
contribute most dominantly on the tunneling conductance. In addition, we show
that for +i-wave superconductor junctions, the height of ZBCP is
sensitive to due to the formation of broken time reversal symmetry state.
We propose that tunneling spectroscopy in the presence of magnetic field,
, , is an promising method to determine the pairing
symmetry of unconventional superconductors.Comment: 4 pages, 6 figures, using jpsj2.cl
Reflectance measurement of two-dimensional photonic crystal nanocavities with embedded quantum dots
The spectra of two-dimensional photonic crystal slab nanocavities with
embedded InAs quantum dots are measured by photoluminescence and reflectance.
In comparing the spectra taken by these two different methods, consistency with
the nanocavities' resonant wavelengths is found. Furthermore, it is shown that
the reflectance method can measure both active and passive cavities. Q-factors
of nanocavities, whose resonant wavelengths range from 1280 to 1620 nm, are
measured by the reflectance method in cross polarization. Experimentally,
Q-factors decrease for longer wavelengths and the intensity, reflected by the
nanocavities on resonance, becomes minimal around 1370 nm. The trend of the
Q-factors is explained by the change of the slab thickness relative to the
resonant wavelength, showing a good agreement between theory and experiment.
The trend of reflected intensity by the nanocavities on resonance can be
understood as effects that originate from the PC slab and the underlying air
cladding thickness. In addition to three dimensional finite-difference
time-domain calculations, an analytical model is introduced that is able to
reproduce the wavelength dependence of the reflected intensity observed in the
experiment.Comment: 24 pages, 7 figures, corrected+full versio
A nucleosome-free dG-dC-rich sequence element promotes constitutive transcription of the essential yeast RIO1 gene
RIO1 is an essential gene that encodes a protein serine kinase and is transcribed constitutively at a very low level. Transcriptional activation of RIO1 dispenses with a canonical TATA box as well as with classical transactivators or specific DNAbinding factors. Instead, a dGdCrich sequence element, that is located 40 to 48 bp upstream the single site of mRNA initiation, is essential and presumably constitutes the basal promoter. In addition, we demonstrate here that this promoter element comprises a nucleosomefree gap which is centered at the dGdC tract and flanked by two positioned nucleosomes. This element is both, necessary and sufficient, for basal transcription initiation at the RIO1 promoter and, thus, constitutes a novel type of core promoter element
Cosmic censorship in overcharging a Reissner-Nordstr\"{o}m black hole via charged particle absorption
There is a claim that a static charged black hole (Reissner-Nordstr\"{o}m
black hole) can be overcharged by absorbing a charged test particle. If it is
true, it might give a counter example to the weak cosmic censorship conjecture,
which states that spacetime singularities are never observed by a distant
observer. However, so far the proposed process has only been analyzed within a
test particle approximation. Here we claim that the back reaction effects of a
charged particle cannot be neglected when judging whether the suggested process
is really a counter example to the cosmic censorship conjecture or not.
Furthermore, we argue that all the back reaction effects can be properly taken
into account when we consider the trajectory of a particle on the border
between the plunge and bounce orbits. In such marginal cases we find that the
Reissner-Nordstr\"{o}m black hole can never be overcharged via the absorption
of a charged particle. Since all the plunge orbits are expected to have a
higher energy than the marginal orbit, we conclude that there is no supporting
evidence that indicates the violation of the cosmic censorship in the proposed
overcharging process.Comment: 18 pages, revtex4, minor revision and reference added, version to
appear in PR
Theory of Spin polarized Tunneling in Superconducting Sr2RuO4
A theory of tunneling conductance in ferromagnetic metal/insulator/triplet -
supercondcutor junctions is presented for unitary and non-unitary spin triplet
pairing states which are promising candidates for the superconducting paring
symmetry of Sr2RuO4. As the magnitude of the exchange interaction in the
ferromagnetic metal is increased, the conductance for the unitary pairing state
below the energy gap is reduced in contrast to the case for the non-unitary
pairing state
On broad iron K-alpha lines in Seyfert 1 galaxies
The X-ray spectrum obtained by Tanaka et al from a long observation of the
active galaxy MCG shows a broad iron K line skewed to low
energies. The simplest interpretation of the shape of the line is that it is
due to doppler and gravitational redshifts from the inner parts of a disk about
a massive black hole. Similarly broad lines are evident in shorter observations
of several other active galaxies. In this paper we investigate other line
broadening and skewing mechanisms such as Comptonization in cold gas and
doppler shifts from outflows. We have also fitted complex spectral models to
the data of MCG to see whether the broad skewed line can be mimicked
well by other absorption or emission features. No satisfactory mechanism or
spectral model is found, thus strengthening the relativistic disk line model.Comment: uuencoded compressed postscript. The preprint is also available at
http://www.ast.cam.ac.uk/preprint/PrePrint.htm
Temperature-dependence of spin-polarized transport in ferromagnet / unconventional superconductor junctions
Tunneling conductance in ferromagnet / unconventional superconductor
junctions is studied theoretically as a function of temperatures and
spin-polarization in feromagnets. In d-wave superconductor junctions, the
existence of a zero-energy Andreev bound state drastically affects the
temperature-dependence of the zero-bias conductance (ZBC). In p-wave triplet
superconductor junctions, numerical results show a wide variety in
temperature-dependence of the ZBC depending on the direction of the magnetic
moment in ferromagnets and the pairing symmetry in superconductors such as
, and -wave pair potential. The last one is a
promising symmetry of SrRuO. From these characteristic features in the
conductance, we may obtain the information about the degree of
spin-polarization in ferromagnets and the direction of the -vector in
triplet superconductors
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