935 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
Earthquake detection capacity of Dense Oceanfloor Network system for Earthquakes and Tsunamis (DONET)
We adopted the Probability-based Magnitude of Completeness (PMC) method and
performed a case analysis of the Nankai Trough, a target region monitored for
future megathrust earthquakes. JAMSTEC (Japan Agency for Marine-Earth Science
and Technology) has created a seismicity catalog that includes events in this
region observed by DONET. Using seismicity data for 2015-2019, we found
spatiotemporal variability of completeness magnitude Mp. Mp was lower than 1 in
one of the areas where stations are densely deployed, whereas Mp was larger
than 2 at the periphery and outside of the DONET area. We then evaluated the
temporal evolution of Mp, highlighting how the failure of sets of observing
stations influenced Mp if not repaired. Stations are aggregated around the 12
science nodes (hubs that connect the stations) and connected through the two
oceanfloor backbone cables to JAMSTEC. We explored the possible use of PMC as a
tool with simulation computation of node malfunction. A simulation showed that
completeness estimates in the area near failure nodes were about 1 magnitude
larger. If such failure occurred for nodes near the region which straddles the
rupture zones of the previous Tonankai and Nankai earthquakes in 1940's, it
would most pronouncedly affect earthquake monitoring among nodes' failures. It
is desirable to repair these nodes or replace with new ones when their
malfunction occurs. We then demonstrated an example of how to use Mp
information as prior knowledge to seismicity-related studies. We used the b
value of the Gutenberg-Richter distribution, and computed it taking Mp into
consideration. We found that the spatial and temporal changes in b were
strongly correlated to the magnitude-6 class slow slip that grew over two years
on the Nankai Trough plate boundary, indicating the b value as a proxy that can
help to image stress heterogeneity when there is a slow slip event.Comment: 6 figure
The Josephson current in Fe-based superconducting junctions: theory and experiment
We present theory of dc Josephson effect in contacts between Fe-based and
spin-singlet -wave superconductors. The method is based on the calculation
of temperature Green's function in the junction within the tight-binding model.
We calculate the phase dependencies of the Josephson current for different
orientations of the junction relative to the crystallographic axes of Fe-based
superconductor. Further, we consider the dependence of the Josephson current on
the thickness of an insulating layer and on temperature. Experimental data for
PbIn/BaK(FeAs) point-contact Josephson junctions are
consistent with theoretical predictions for symmetry of an order
parameter in this material. The proposed method can be further applied to
calculations of the dc Josephson current in contacts with other new
unconventional multiorbital superconductors, such as and
superconducting topological insulator .Comment: 16 pages, 14 figure
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.
Electron-Phonon mechanism for Superconductivity in NaCoO: Valence-Band Suhl-Kondo effect Driven by Shear Phonons
To study the possible mechanism of superconductivity in NaCoO,
we examine the interaction between all the relevant optical phonons (breathing
and shear phonons) and -electrons of Co-ions, and study
the transition temperature for a s-wave superconductivity. The obtained is very low when the -valence-bands are far below the Fermi level.
However, is strongly enhanced when the top of the
-valence-bands is close to the Fermi level (say -50meV), thanks to
interband hopping of Cooper pairs caused by shear phonons. This ``valence-band
Suhl-Kondo mechanism'' due to shear phonons is significant to understand the
superconductivity in NaCoO. By the same mechanism, the kink
structure of the band-dispersion observed by ARPES, which indicates the strong
mass-enhancement () due to optical phonons, is also explained.Comment: 5 pages, 4 figures; v2:Added references, published in J. Phys. Soc.
Jp
Deformation of Electronic Structures Due to CoO6 Distortion and Phase Diagrams of NaxCoO2.yH2O
Motivated by recently reported experimental phase diagrams, we study the
effects of CoO6 distortion on the electronic structure in NaxCoO2.yH2O. We
construct the multiband tight-binding model by employing the LDA result.
Analyzing this model, we show the deformation of band dispersions and
Fermi-surface topology as functions of CoO2-layer thickness. Considering these
results together with previous theoretical ones, we propose a possible
schematic phase diagram with three successive phases: the extended s-wave
superconductivity (SC), the magnetic order, and the spin-triplet SC phases when
the Co valence number s is +3.4. A phase diagram with only one phase of
spin-triplet SC is also proposed for the s=+3.5 case.Comment: 4 pages, 5 figure
Systematic review of the incidence, presentation and management of gastroduodenal artery pseudoaneurysm after pancreatic resection.
Background: Gastroduodenal artery (GDA) pseudoaneurysm is a serious complication following pancreatic resection, associated with high morbidity and mortality rates. This review aimed to report the incidence of GDA pseudoaneurysm after pancreatic surgery, and describe clinical presentation and management. Methods: MEDLINE and Embase were searched systematically for clinical studies evaluating postoperative GDA pseudoaneurysm. Incidence was calculated by dividing total number of GDA pseudoaneurysms by the total number of pancreatic operations. Additional qualitative data related to GDA pseudoaneurysm presentation and management following pancreatic resection were extracted and reviewed from individual reports. Results: Nine studies were selected for systematic review involving 4227 pancreatic operations with 55 GDA pseudoaneurysms, with a reported incidence of 1·3 (range 0·2-8·3) per cent. Additional data were extracted from 39 individual examples of GDA pseudoaneurysm from 14 studies. The median time for haemorrhage after surgery was at 15 (range 4-210) days. A preceding complication in the postoperative period was documented in four of 21 patients (67 per cent), and sentinel bleeding was observed in 14 of 20 patients (70 per cent). Postoperative complications after pseudoaneurysm management occurred in two-thirds of the patients (14 of 21). The overall survival rate was 85 per cent (33 of 39). Conclusion: GDA pseudoaneurysm is a rare yet serious cause of haemorrhage after pancreatic surgery, with high mortality. The majority of the patients had a preceding complication. Sentinel bleeding was an important clinical indicator
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
Central Glucagon-like Peptide-1 Receptor Signaling via Brainstem Catecholamine Neurons Counteracts Hypertension in Spontaneously Hypertensive Rats
Glucagon-like peptide-1 receptor (GLP-1R) agonists, widely used to treat type 2 diabetes, reduce blood pressure (BP) in hypertensive patients. Whether this action involves central mechanisms is unknown. We here report that repeated lateral ventricular (LV) injection of GLP-1R agonist, liraglutide, once daily for 15 days counteracted the development of hypertension in spontaneously hypertensive rats (SHR). In parallel, it suppressed urinary norepinephrine excretion, and induced c-Fos expressions in the area postrema (AP) and nucleus tractus solitarius (NTS) of brainstem including the NTS neurons immunoreactive to dopamine beta-hydroxylase (DBH). Acute administration of liraglutide into fourth ventricle, the area with easy access to the AP and NTS, transiently decreased BP in SHR and this effect was attenuated after lesion of NTS DBH neurons with anti-DBH conjugated to saporin (anti-DBH-SAP). In anti-DBH-SAP injected SHR, the antihypertensive effect of repeated LV injection of liraglutide for 14 days was also attenuated. These findings demonstrate that the central GLP-1R signaling via NTS DBH neurons counteracts the development of hypertension in SHR, accompanied by attenuated sympathetic nerve activity
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