966 research outputs found
Fulde-Ferrell-Larkin-Ovchinnikov State in the absence of a Magnetic Field
We propose that in a system with pocket Fermi surfaces, a pairing state with
a finite total momentum q_tot like the Fulde-Ferrell-Larkin-Ovchinnikov state
can be stabilized even without a magnetic field. When a pair is composed of
electrons on a pocket Fermi surface whose center is not located at Gamma point,
the pair inevitably has finite q_tot. To investigate this possibility, we
consider a two-orbital model on a square lattice that can realize pocket Fermi
surfaces and we apply fluctuation exchange approximation. Then, by changing the
electron number n per site, we indeed find that such superconducting states
with finite q_tot are stabilized when the system has pocket Fermi surfaces.Comment: 4 pages, 5 figure
MetaGeneAnnotator: Detecting Species-Specific Patterns of Ribosomal Binding Site for Precise Gene Prediction in Anonymous Prokaryotic and Phage Genomes
Recent advances in DNA sequencers are accelerating genome sequencing, especially in microbes, and complete and draft genomes from various species have been sequenced in rapid succession. Here, we present a comprehensive gene prediction tool, the MetaGeneAnnotator (MGA), which precisely predicts all kinds of prokaryotic genes from a single or a set of anonymous genomic sequences having a variety of lengths. The MGA integrates statistical models of prophage genes, in addition to those of bacterial and archaeal genes, and also uses a self-training model from input sequences for predictions. As a result, the MGA sensitively detects not only typical genes but also atypical genes, such as horizontally transferred and prophage genes in a prokaryotic genome. In this paper, we also propose a novel approach for analyzing the ribosomal binding site (RBS), which enables us to detect species-specific patterns of the RBSs. The MGA has the ingenious RBS model based on this approach, and precisely predicts translation starts of genes. The MGA also succeeds in improving prediction accuracies for short sequences by using the adapted RBS models (96% sensitivity and 93% specificity for 700 bp fragments). These features of the MGA expedite wide ranges of microbial genome studies, such as genome annotations and metagenome analyses
Origin of the Weak Pseudo-gap Behaviors in Na_{0.35}CoO_2: Absence of Small Hole Pockets
We analyze the ``normal electronic states'' of Na_{0.35}CoO_2 based on the
effective d-p model with full d-orbital freedom using the fluctuation-exchange
(FLEX) approximation. They sensitively depend on the topology of the Fermi
surfaces, which changes as the crystalline electric splitting (CES) due to the
trigonal deformation. We succeed in reproducing the weak pseudo-gap behaviors
in the density of states (DOS) and in the uniform magnetic susceptibility below
300K, assuming that six small hole-pockets predicted by LDA band calculations
are absent. When they exist, on the contrary, then ``anti-pseudo-gap
behaviors'' should inevitably appear. Thus, the present study strongly supports
the absence of the small hole-pockets in Na_{0.35}CoO_2, as reported by recent
ARPES measurements. A large Fermi surface around the \Gamma-point would account
for the superconductivity in water-intercalated samples.Comment: 5pages, to appear in J. Phys. Soc. Jpn. Vol.74 (2005) No.
The characteristics of Hayabusa returned samples and their distributions for NASA and international announcement of opportunity (AO).
第3回極域科学シンポジウム/第35回南極隕石シンポジウム 11月30日(金) 国立国語研究所 2階講
Probing ultrafast spin-relaxation and precession dynamics in a cuprate Mott insulator with 7-fs optical pulses
A charge excitation in a two-dimensional Mott insulator is strongly coupled
with the surrounding spins, which is observed as magnetic-polaron formations of
doped carriers and a magnon sideband in the Mott-gap transition spectrum.
However, the dynamics related to the spin sector are difficult to measure.
Here, we show that pump-probe reflection spectroscopy with 7-fs laser pulses
can detect the optically induced spin dynamics in NdCuO, a cuprate Mott
insulator. The bleaching signal at the Mott-gap transition is enhanced at
18 fs, which corresponds to the spin-relaxation time in magnetic-polaron
formations and is characterized by the exchange interaction. More importantly,
ultrafast coherent oscillations appear in the time evolutions of the
reflectivity changes, and their frequencies (1400-2700 cm) are equal to
the probe energy measured from the Mott-gap transition peak. These oscillations
originate from interferences between charge excitations with two magnons and
provide direct evidence for charge-spin coupling.Comment: 20 pages including 4 figures (Supplementary materials: 11 pages
including 4 figures
Weak-Coupling Theory for Multiband Superconductivity Induced by Jahn-Teller Phonons
Emergence of superconductivity in a two-band system coupled with breathing
and Jahn-Teller phonons is discussed in a weak-coupling limit. With the use of
a standard quantum mechanical procedure, the phonon-mediated attraction is
derived. From the analysis of the model including such attraction, a BCS-like
formula for a superconducting transition temperature is obtained.
When only the breathing phonon is considered, is the same as that
of the one-band model. On the other hand, when Jahn-Teller phonons are active,
is significantly enhanced by the interband attraction even within
the weak-coupling limit. Relevance of the present result to actual materials
such as iron pnictides is briefly commented.Comment: 4 pages, 3 figures
Orbital-Controlled Superconductivity in f-Electron Systems
We propose a concept of superconductivity controlled by orbital degree of
freedom taking CeMIn5 (M= Co, Rh, and Ir) as typical examples. A microscopic
multiorbital model for CeMIn5 is analyzed by fluctuation exchange
approximation. Even though the Fermi-surface structure is unchanged, the ground
state is found to change significantly among paramagnetic, antiferromagnetic,
and d-wave superconducting phases, depending on the dominant orbital component
in the band near the Fermi energy. We show that our picture naturally explains
the different low-temperature properties of CeMIn5 by carefully analyzing the
crystalline electric field states.Comment: 5 pages, 4 figure
SEM and TEM Observation of the Surfaces of the Fine-Grained Particles Retrieved from the Muses-C Regio on the Asteroid 25413 Itokawa
Surface materials on airless solar system bodies exposed to interplanetary space are gradually changed their visible to near-infrared reflectance spectra by the process called "space weathering", which makes the spectra darker and redder. Hapke et al. proposed a model of space weathering: vapor deposition of nanophase reduced iron (npFe(sup 0)) on the surfaces of the grains within the very surface of lunar regolith. This model has been proved by detailed observation of the surfaces of the lunar soil grains by transmission electron microscope (TEM). They demonstrated that npFe(sup 0) was formed by a combination of vapor deposition and irradiation effects. In other words, both micrometeorite impacts and irradiation by solar wind and galactic cosmic ray play roles on the space weathering on the Moon. Because there is a continuum of reflectance spectra from those of Q-type asteroids (almost the same as those of ordinary chondrites) to those of S-type asteroids, it is strongly suggested that reflectance spectra of asteroids composed of ordinary chondrite-like materials were modified over time to those of S-type asteroids due to space weathering. It is predicted that a small amount of npFe(sup 0) on the surface of grains in the asteroidal regolith composed of ordinary chondrite-like materials is the main agent of asteroidal space weathering
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