211 research outputs found
Surface density of states of s+-wave Cooper pairs in a two-band model
We calculate surface density of state (SDOS) of s+-wave Cooper pair in
two-band superconductor model, where gap functions have different signs between
two bands. We find that Andreev bound state appears at surface due to the sign
change in the gap function in the interband quasiparticle scattering. However,
we do not obtain the zero-energy peak of SDOS in contrast to the d-wave case.
The tunneling spectroscopy of s+-wave is much more complex as compared to the
d-wave case realized in high-Tc cuprates.Comment: 7 pages, 10 figure
A unified origin for the 3D magnetism and superconductivity in NaCoO
We analyze the origin of the three dimensional (3D) magnetism observed in
nonhydrated Na-rich NaCoO within an itinerant spin picture using a 3D
Hubbard model. The origin is identified as the 3D nesting between the inner and
outer portions of the Fermi surface, which arise due to the local minimum
structure of the band at the -A line. The calculated spin wave
dispersion strikingly resembles the neutron scattering result. We argue that
this 3D magnetism and the spin fluctuations responsible for superconductivity
in the hydrated systems share essentially the same origin.Comment: 5pages, 6figure
Origin of Orthorhombic Transition, Magnetic Transition, and Shear Modulus Softening in Iron Pnictide Superconductors: Analysis based on the Orbital Fluctuation Theory
The main features in iron-pnictide superconductors are summarized as (i) the
orthorhombic transition accompanied by remarkable softening of shear modulus,
(ii) high-Tc superconductivity close to the orthorhombic phase, and (iii)
stripe-type magnetic order induced by orthorhombicity. To present a unified
explanation for them, we analyze the multiorbital Hubbard-Holstein model with
Fe-ion optical phonons based on the orbital fluctuation theory. In the
random-phase-approximation (RPA), a small electron-phonon coupling constant
() is enough to produce large orbital (=charge quadrupole)
fluctuations. The most divergent susceptibility is the
-antiferro-quadrupole (AFQ) susceptibility, which causes the s-wave
superconductivity without sign reversal (s_{++}-wave state). At the same time,
divergent development of -ferro-quadrupole (FQ) susceptibility is
brought by the "two-orbiton process" with respect to the AFQ fluctuations,
which is absent in the RPA. The derived FQ fluctuations cause the softening of
shear modulus, and its long-range-order not only triggers the
orthorhombic structure transition, but also induces the instability of
stripe-type antiferro-magnetic state. In other words, the condensation of
composite bosons made of two orbitons gives rise to the FQ order and structure
transition. The theoretically predicted multi-orbital-criticality presents a
unified explanation for abovementioned features of iron pnictide
superconductors.Comment: 19 pages, 15 figure
Critical Scale-invariance in Healthy Human Heart Rate
We demonstrate the robust scale-invariance in the probability density
function (PDF) of detrended healthy human heart rate increments, which is
preserved not only in a quiescent condition, but also in a dynamic state where
the mean level of heart rate is dramatically changing. This scale-independent
and fractal structure is markedly different from the scale-dependent PDF
evolution observed in a turbulent-like, cascade heart rate model. These results
strongly support the view that healthy human heart rate is controlled to
converge continually to a critical state.Comment: 9 pages, 3 figures. Phys. Rev. Lett., to appear (2004
Dynamics of Quasi-ordered Structure in a Regio-regulated pi-Conjugated Polymer:Poly(4-methylthiazole-2,5-diyl)
Dynamics of regio-regulated Poly(4-methylthiazole-2,5-diyl) [HH-P4MeTz] was
inves tigated by solid-state 1H, 2D, 13C NMR spectroscopies, and differential
scanning calorimetry(DSC) measurements. DSC, 2D quadrupolar echo NMR, 13C
cross-polarization and magic-angle spinning(CPMAS) NMR, and 2D spin-echo(2DSE)
CPMAS NMR spectroscopy suggest existence of a quasi-ordered phase in which
backbone twists take place with weakened pi-stackings. Two-dimensional exchange
2D NMR(2DEX) detected slow dynamics with a rate of an order of 10^2Hz for the
CD_3 group in d_3-HH-P4MeTz at 288K. The frequency dependence of proton
longitudinal relaxation rate at 288K shows a omega^-1/2 dependence, which is
due to the one-dimensional diffusion-like motion of backbone conformational
modulation waves. The diffusion rate was estimated as 3+/-2 GHz, which was
approximately 10^7 times larger than that estimated by 2DEX NMR measurements.
These results suggest that there exists anomalous dispersion of modulation
waves in HH-P4MeTz. The one-dimensional group velocity of the wave packet is
responsible for the behavior of proton longitudinal relaxation time. On the
other hand, the 2DEX NMR is sensitive to phase velocity of the nutation of
methyl groups that is associated with backbone twists. From proton T_1 and T_2
measurements, the activation energy was estimated as 2.9 and 3.4 kcal/mol,
respectively. These were in agreement with 3.0 kcal/mol determined by
Moller-Plesset(MP2) molecular orbital(MO) calculation. We also performed
chemical shielding calculation of the methyl-carbon in order to understand
chemical shift tensor behavior, leading to the fact that a quasi-ordered phase
coexist with the crystalline phase.Comment: 14 pages, 11 figures, to appear in Phys.Rev.
Superconductivity induced by inter-band nesting in the three-dimensional honeycomb lattice
In order to study whether the inter-band nesting can favor superconductivity
arising from electron-electron repulsion in a three-dimensional system, we have
looked at the repulsive Hubbard model on a stack of honeycomb (i.e.,
non-Bravais) lattices with the FLEX method, partly motivated by the
superconductivity observed in MgB2. By systematically changing the shape of
Fermi surface with varied band filling n and the third-direction hopping, we
have found that the pair scattering across the two-bands is indeed found to
give rise to gap functions that change sign across the bands and behave as an
s- or d-wave within each band. This implies (a) the electron repulsion can
assist gapful pairing when a phonon-mechanism pairing exists, and (b) the
electron repulsion alone, when strong enough, can give rise to a d-wave-like
pairing, which should be, for a group-theoretic reason, a time-reversal broken
d+id with point nodes in the gap
Recurrent advanced colonic cancer occurring 11 years after initial endoscopic piecemeal resection: a case report
<p>Abstract</p> <p>Background</p> <p>The high frequency of local recurrence occurring after endoscopic piecemeal resection (EPMR) for large colorectal tumors is a serious problem. However, almost all of these cases of local recurrence can be detected within 1 year and cured by additional endoscopic resection. We report a rare case of recurrent advanced colonic cancer diagnosed 11 years after initial EPMR treatment.</p> <p>Case presentation</p> <p>A 65-year-old male was diagnosed with a sigmoid colon lesion following a routine health check-up. Total colonoscopy revealed a 12 mm type 0-Is lesion in the sigmoid colon, which was diagnosed as an adenoma or intramucosal cancer and treated by EPMR in 1996. The post-resection defect was closed completely using metallic endoclips to avoid delayed bleeding. In 2007, at the third follow up, colonoscopy revealed a 20 mm submucosal tumor (SMT) like recurrence at the site of the previous EPMR. The recurrent lesion was treated by laparoscopic assisted sigmoidectomy with lymph node dissection.</p> <p>Conclusion</p> <p>When it is difficult to evaluate the depth and margins of resected tumors following EPMR, it is important that the defect is not closed in order to avoid tumor implantation, missing residual lesions and to enable earlier detection of recurrence. It is crucial that the optimal follow-up protocol for EPMR cases is clarified, particularly how often and for how long they should be followed.</p
Inverse Correlation between Serum Levels of Selenoprotein P and Adiponectin in Patients with Type 2 Diabetes
Background: We recently identified selenoprotein P (SeP) as a liver-derived secretory protein that causes insulin resistance in the liver and skeletal muscle; however, it is unknown whether and, if so, how SeP acts on adipose tissue. The present study tested the hypothesis that SeP is related to hypoadiponectinemia in patients with type 2 diabetes. Methodology/Principal Findings: We compared serum levels of SeP with those of adiponectin and other clinical parameters in 36 patients with type 2 diabetes. We also measured levels of blood adiponectin in SeP knockout mice. Circulating SeP levels were positively correlated with fasting plasma glucose (r = 0.35, P = 0.037) and negatively associated with both total and high-molecular adiponectin in patients with type 2 diabetes (r = 20.355, P = 0.034; r = 20.367, P = 0.028). SeP was a predictor of both total and high-molecular adiponectin, independently of age, body weight, and quantitative insulin sensitivity index (b = 20.343, P = 0.022; b = 20.357, P = 0.017). SeP knockout mice exhibited an increase in blood adiponectin levels when fed regular chow or a high sucrose, high fat diet. Conclusions/Significance: These results suggest that overproduction of liver-derived secretory protein SeP is connected with hypoadiponectinemia in patients with type 2 diabetes
Determining the Orientation of Protegrin-1 in DLPC Bilayers Using an Implicit Solvent-Membrane Model
Continuum models that describe the effects of solvent and biological membrane molecules on the structure and behavior of antimicrobial peptides, holds a promise to improve our understanding of the mechanisms of antimicrobial action of these peptides. In such methods, a lipid bilayer model membrane is implicitly represented by multiple layers of relatively low dielectric constant embedded in a high dielectric aqueous solvent, while an antimicrobial peptide is accounted for by a dielectric cavity with fixed partial charge at the center of each one of its atoms. In the present work, we investigate the ability of continuum approaches to predict the most probable orientation of the Ξ²-hairpin antimicrobial peptide Protegrin-1 (PG-1) in DLPC lipid bilayers by calculating the difference in the transfer free energy from an aqueous environment to a membrane-water environment for multiple orientations. The transfer free energy is computed as a sum of two terms; polar/electrostatic and non-polar. They both include energetic and entropic contributions to the free energy. We numerically solve the Poisson-Boltzmann equation to calculate the electrostatic contribution to the transfer free energy, while the non-polar contribution to the free energy is approximated using a linear solvent accessible surface area relationships. The most probable orientation of PG-1 is that with the lowest relative transfer free energy. Our simulation results indicate that PG-1 assumes an oblique orientation in DLPC lipid bilayers. The predicted most favorable orientation was with a tilt angle of 19Β°, which is in qualitative agreement with the experimentally observed orientations derived from solid-state NMR data
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