11,417 research outputs found
Massive Hyper-Kahler Sigma Models and BPS Domain Walls
With the non-Abelian Hyper-Kahler quotient by U(M) and SU(M) gauge groups, we
give the massive Hyper-Kahler sigma models that are not toric in the N=1
superfield formalism. The U(M) quotient gives N!/[M! (N-M)!] (N is a number of
flavors) discrete vacua that may allow various types of domain walls, whereas
the SU(M) quotient gives no discrete vacua. We derive BPS domain wall solution
in the case of N=2 and M=1 in the U(M) quotient model.Comment: 16 pages, 1 figure, contribution to the Proceedings of the
International Conference on "Symmetry Methods in Physics (SYM-PHYS10)" held
at Yerevan, Armenia, 13-19 Aug. 200
Bottom-up fabrication of Si nanodot transistors using the nc-Si dots solution
A new approach to fabricate nanometer-scale silicon devices is recently attracting much attention, which combines the conventional top-down silicon processing techniques and the bottom-up assembly of silicon nanodots, whose structures are controlled on the atomic scale. This technique enables to investigate the electronic states and transport properties of strongly-coupled multiple nanodots which will be crucial particularly for quantum information device applications. Various unique properties have been studied in such systems. For example, electrostatic interactions have been investigated for double Si dots [1] and for the two-dimensional Si multidots [2]. Coherent wavefunction coupling and associated quasi-molecular states have also been observed for a tunnel-coupled double Si nanodots [3]. In addition, metal-insulator transition has been investigated for an artificial lattice of self-organized nano-paraticles [4]. In this paper we propose and examine a novel technique of fabricating nanoscale transistors with a Si nanodot cluster as a channel based on the self-assembly of the nanocrystalline Si dots from the solution on the patterned SOI substrates
The role of infrared divergence for decoherence
Continuous and discrete superselection rules induced by the interaction with
the environment are investigated for a class of exactly soluble Hamiltonian
models. The environment is given by a Boson field. Stable superselection
sectors emerge if and only if the low frequences dominate and the ground state
of the Boson field disappears due to infrared divergence. The models allow
uniform estimates of all transition matrix elements between different
superselection sectors.Comment: 11 pages, extended and simplified proo
Fermi Surface and Anisotropic Spin-Orbit Coupling of Sb(111) studied by Angle-Resolved Photoemission Spectroscopy
High-resolution angle-resolved photoemission spectroscopy has been performed
on Sb(111) to elucidate the origin of anomalous electronic properties in
group-V semimetal surfaces. The surface was found to be metallic despite the
semimetallic character of bulk. We clearly observed two surface-derived Fermi
surfaces which are likely spin split, demonstrating that the spin-orbit
interaction plays a dominant role in characterising the surface electronic
states of group-V semimetals. Universality/disimilarity of the electronic
structure in Bi and Sb is discussed in relation to the granular
superconductivity, electron-phonon coupling, and surface charge/spin density
wave.Comment: 4 pages, 3 figures. to be published in Phys. Rev. Let
Lithium production on a low-mass secondary in a black hole soft X-ray transient
We examine production of Li on the surface of a low-mass secondary in a black
hole soft X-ray transient (BHSXT) through the spallation of CNO nuclei by
neutrons which are ejected from a hot (> 10 MeV) advection-dominated accretion
flow (ADAF) around the black hole. Using updated binary parameters, cross
sections of neutron-induced spallation reactions, and mass accretion rates in
ADAF derived from the spectrum fitting of multi-wavelength observations of
quiescent BHSXTs, we obtain the equilibrium abundances of Li by equating the
production rate of Li and the mass transfer rate through accretion to the black
hole. The resulting abundances are found to be in good agreement with the
observed values in seven BHSXTs. We note that the abundances vary in a
timescale longer than a few months in our model. Moreover, the isotopic ratio
Li6/Li7 is calculated to be about 0.7--0.8 on the secondaries, which is much
higher than the ratio measured in meteorites. Detection of such a high value is
favorable to the production of Li via spallation and the existence of a hot
accretion flow, rather than an accretion disk corona system in quiescent BHSXT.Comment: 4 pages, 3 figures, and 2 tables, submitted to Astrophyscal Jounal
Letter
Carbon fibre tips for scanning probe microscopy based on quartz tuning fork force sensors
We report the fabrication and the characterization of carbon fibre tips for
their use in combined scanning tunnelling and force microscopy based on
piezoelectric quartz tuning fork force sensors. We find that the use of carbon
fibre tips results in a minimum impact on the dynamics of quartz tuning fork
force sensors yielding a high quality factor and consequently a high force
gradient sensitivity. This high force sensitivity in combination with high
electrical conductivity and oxidation resistance of carbon fibre tips make them
very convenient for combined and simultaneous scanning tunnelling microscopy
and atomic force microscopy measurements. Interestingly, these tips are quite
robust against occasionally occurring tip crashes. An electrochemical
fabrication procedure to etch the tips is presented that produces a sub-100 nm
apex radius in a reproducible way which can yield high resolution images.Comment: 14 pages, 10 figure
Metallic mean-field stripes, incommensurability and chemical potential in cuprates
We perform a systematic slave-boson mean-field analysis of the three-band
model for cuprates with first-principle parameters. Contrary to widespread
believe based on earlier mean-field computations low doping stripes have a
linear density close to 1/2 added hole per lattice constant. We find a
dimensional crossover from 1D to 2D at doping followed by a breaking
of particle-hole symmetry around doping 1/8 as doping increases. Our results
explain in a simple way the behavior of the chemical potential, the magnetic
incommensurability, and transport experiments as a function of doping. Bond
centered and site-centered stripes become degenerate for small overdoping.Comment: submitted to PR
Probing top charged-Higgs production using top polarization at the Large Hadron Collider
We study single top production in association with a charged Higgs in the
type II two Higgs doublet model at the Large Hadron Collider. The polarization
of the top, reflected in the angular distributions of its decay products, can
be a sensitive probe of new physics in its production. We present theoretically
expected polarizations of the top for top charged-Higgs production, which is
significantly different from that in the closely related process of t-W
production in the Standard Model. We then show that an azimuthal symmetry,
constructed from the decay lepton angular distribution in the laboratory frame,
is a sensitive probe of top polarization and can be used to constrain
parameters involved in top charged-Higgs production.Comment: 22 pages, 18 Figures, Discussions about backgrounds and NLO
corrections added, figures modified, references added, Version published in
JHE
Comparative alterations in p53 expression and apoptosis in the irradiated rat small and large intestine.
Temporal and spatial relationships between radiation-induced apoptosis and expression of p53 mRNA and protein were compared in rat small and large intestine. Apoptosis was quantified using morphological criteria, and p53 expression determined by immunohistochemistry or whole-tissue Northern analysis. In the small intestine, peak levels of apoptosis appeared earlier (4 h) than in the large intestine (6 h). p53 mRNA transcript levels in small and large intestine were not significantly altered from control levels at any time after treatment. However, in treated small and large intestine, cells showed increased positivity for p53 protein, increasing 10-fold over control levels 4-5 h after irradiation. A strong spatial relationship was found between high incidence apoptosis and p53 protein positivity. We compared published data of stem cell population positions for small and large intestine with our results. Target cells for apoptosis and p53 expression occurred at approximately fifth position from the crypt base of the small intestine, a zone coincident with stem cell population. Target cell position for apoptosis and p53 expression in the large intestine was again at fifth or sixth position from the base, but this zone is not the reported stem cell position (first or second position) for large intestine. Results from our model of radiation-induced intestinal apoptosis indicate that p53 protein is closely associated both temporally and spatially with the induction of apoptosis, and support the work of others in suggesting that p53 expression is modulated post-transcriptionally. Furthermore, our results support a hypothesis that apoptotic targeting of damaged stem cell populations, early response for apoptotic removal of DNA-damaged cells and/or early repair of these damage cells are all important parameters that determine differences in levels of tumorigenesis in the small and large intestine
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