495 research outputs found
Na content dependence of superconductivity and the spin correlations in Na_{x}CoO_{2}\cdot 1.3H_{2}O
We report systematic measurements using the ^{59}Co nuclear quadrupole
resonance(NQR) technique on the cobalt oxide superconductors Na_{x}CoO_{2}\cdot
1.3H_{2}O over a wide Na content range x=0.25\sim 0.34. We find that T_c
increases with decreasing x but reaches to a plateau for x \leq0.28. In the
sample with x \sim 0.26, the spin-lattice relaxation rate 1/T_1 shows a T^3
variation below T_c and down to T\sim T_c/6, which unambiguously indicates the
presence of line nodes in the superconducting (SC) gap function. However, for
larger or smaller x, 1/T_1 deviates from the T^3 variation below T\sim 2 K even
though the T_c (\sim 4.7 K) is similar, which suggests an unusual evolution of
the SC state. In the normal state, the spin correlations at a finite wave
vector become stronger upon decreasing x, and the density of states at the
Fermi level increases with decreasing x, which can be understood in terms of a
single-orbital picture suggested on the basis of LDA calculation.Comment: version published in J. Phys. Condens. Matter (references updated and
more added
Prognostic role of amenorrhea induced by adjuvant chemotherapy in premenopausal patients with early breast cancer.
The prognostic role of drug-induced amenorrhea (DIA) was restrospectively evaluated in 221 out of 254 consecutive premenopausal patients treated with adjuvant CMF or a CMF-containing regimen; 33 patients were eliminated because of lack of menstrual data. All patients had metastatic axillary nodes; drug regimens were: CMF x 9 courses +/- Tamoxifen (TM) and CMF x 6 courses; median age was 43 (range 26-54). Premenopausal status was defined as last normal menses within the 6 weeks preceding initiation of chemotherapy: DIA as cessation of menses for at least 3 months not later than 3 months from the end of chemotherapy. DIA occurred in 166,221 (75.1%) patients and was strictly related to the age of the patients; also, the older the patients the shorter the time required to develop DIA. At median follow up of 69 months, Mantel-Byar analysis showed a longer disease free survival (DFS) for patients who developed DIA as compared with non amenorrheic women (P less than 0.001). DIA prognostic value was independent of age, number of involved nodes, tumour size and number of CMF cycles, as assessed by the Cox model (RH 0.43, 95% C.I. 0.24-0.77), in which DIA was entered as a time dependent covariate
Diffusive Spreading of Chainlike Molecules on Surfaces
We study the diffusion and submonolayer spreading of chainlike molecules on
surfaces. Using the fluctuating bond model we extract the collective and tracer
diffusion coefficients D_c and D_t with a variety of methods. We show that
D_c(theta) has unusual behavior as a function of the coverage theta. It first
increases but after a maximum goes to zero as theta go to one. We show that the
increase is due to entropic repulsion that leads to steep density profiles for
spreading droplets seen in experiments. We also develop an analytic model for
D_c(theta) which agrees well with the simulations.Comment: 3 pages, RevTeX, 4 postscript figures, to appear in Phys. Rev.
Letters (1996
High energy hadrons in EAS at mountain altitude
An extensive simulation has been carried out to estimate the physical
interpretation of dynamical factors such as , in terms of high
energy interaction features, concentrated in the present analysis on the
average transverse momentum. It appears that the large enhancement observed for
versus primary energy, suggesting in earliest analysis a significant
rise of with energy, is only the result of the limited resolution of the
detectors and remains in agreement with a wide range of models used in
simulations.Comment: 13 pages, 6 PostScript figures, LaTeX Subm. to JPhys
Coherence effect in a two-band superconductor: Application to iron pnictides
From a theoretical point of view, we propose an experimental method to
determine the pairing symmetry of iron pnictides. We focus on two kinds of
pairing symmetries, and , which are strong candidates for the
pairing symmetry of iron pnictides. For each of these two symmetries, we
calculate both the density and spin response functions by using the two-band
BCS model within the one-loop approximation. As a result, a clear difference is
found between the - and -wave states in the temperature
dependence of the response functions at nesting vector , which connects
the hole and electron Fermi surfaces. We point out that this difference comes
from the coherence effect in the two-band superconductor. We suggest that the
pairing symmetry could be clarified by observing the temperature dependence of
both the density and spin structure factors at the nesting vector in
neutron scattering measurements.Comment: 15 pages, 7 figures, 1 tabl
A striking correspondence between the dynamics generated by the vector fields and by the scalar parabolic equations
The purpose of this paper is to enhance a correspondence between the dynamics
of the differential equations on and those
of the parabolic equations on a bounded
domain . We give details on the similarities of these dynamics in the
cases , and and in the corresponding cases ,
and dim() respectively. In addition to
the beauty of such a correspondence, this could serve as a guideline for future
research on the dynamics of parabolic equations
Momentum-resolved superconducting gap in the bulk of BaKFeAs from combined ARPES and SR measurements
Here we present a calculation of the temperature-dependent London penetration
depth, , in BaKFeAs (BKFA) on the basis of
the electronic band structure [1,2] and momentum-dependent superconducting gap
[3] extracted from angle-resolved photoemission spectroscopy (ARPES) data. The
results are compared to the direct measurements of by muon spin
rotation (SR) [4]. The value of , calculated with \emph{no}
adjustable parameters, equals 270 nm, while the directly measured one is 320
nm; the temperature dependence is also easily reproduced. Such
agreement between the two completely different approaches allows us to conclude
that ARPES studies of BKFA are bulk-representative. Our review of the available
experimental studies of the superconducting gap in the new iron-based
superconductors in general allows us to state that all hole-doped of them bear
two nearly isotropic gaps with coupling constants and
Point-contact spectroscopic studies on normal and superconducting AFe_2As_2-type iron-pnictide single crystals
Point-contact Andreev reflection spectroscopy (PCARS) is applied to
investigate the gap structure in iron pnictide single crystal superconductors
of the AFe_2As_2 (A=Ba, Sr) family ("Fe-122"). The observed point-contact
junction conductance curves, G(V), can be divided into two categories: one
where Andreev reflection is present for both (Ba_{0.6}K_{0.4})Fe_2As_2 and
Ba(Fe_{0.9}Co_{0.1})_2As_2, and the other with a V^{2/3} background conductance
universally observed extending even up to 100 meV for Sr_{0.6}Na_{0.4}Fe_2As_2
and Sr(Fe_{0.9}Co_{0.1})_2As_2. The latter is also observed in point-contact
junctions on the nonsuperconducting parent compound BaFe_2As_2. Mesoscopic
phase-separated coexistence of magnetic and superconducting orders is
considered to explain distinct behaviors in the superconducting samples. For
Ba_{0.6}K_{0.4}Fe_2As_2, double peaks due to Andreev reflection with
strongly-sloping background are frequently observed for point-contacts on
freshly-cleaved c-axis surfaces. If normalized by a background baseline and
analyzed by the Blonder-Tinkham-Klapwijk model, the data show a gap size
~3.0-4.0 meV with 2\Delta_0/k_BT_c ~ 2.0-2.6, consistent with the smaller gap
size reported in the LnFeAsO family ("Fe-1111"). For the
Ba(Fe_{0.9}Co_{0.1})_2As_2, G(V) curves typically display a zero-bias
conductance peak.Comment: 12 pages, 6 figure
Sensitivity of the superconducting state and magnetic susceptibility to key aspects of electronic structure in ferropnictides
Experiments on the iron-pnictide superconductors appear to show some
materials where the ground state is fully gapped, and others where low-energy
excitations dominate, possibly indicative of gap nodes. Within the framework of
a 5-orbital spin fluctuation theory for these systems, we discuss how changes
in the doping, the electronic structure or interaction parameters can tune the
system from a fully gapped to nodal sign-changing gap with s-wave ()
symmetry (). In particular we focus on the role of the hole pocket at
the point of the unfolded Brillouin zone identified as crucial to
the pairing by Kuroki {\it et al.}, and show that its presence leads to
additional nesting of hole and electron pockets which stabilizes the isotropic
state. The pocket's contribution to the pairing can be tuned by doping,
surface effects, and by changes in interaction parameters, which we examine.
Analytic expressions for orbital pairing vertices calculated within the RPA
fluctuation exchange approximation allow us to draw connections between aspects
of electronic structure, interaction parameters, and the form of the
superconducting gap
Gemcitabine combined with continuous infusion 5-fluorouracil in advanced and symptomatic pancreatic cancer: a clinical benefit-oriented phase II study
Gemcitabine and 5-fluorouracil are the only two compounds with reproducible activity against advanced pancreatic cancer (APC). We have evaluated a novel combination of gemcitabine and 5-fluorouracil on the clinical benefit response (CBR) end point. Eleven consecutive patients with symptomatic APC were entered in a two-stage phase II trial. Gemcitabine was administered by intravenous (i.v.) bolus injection at the dose of 1000 mg m−2on days 1, 8, 15 and 5-fluorouracil 500 mg m−2was given by continuous i.v. infusion on days 1–5. Treatment was repeated every 28 days. A CBR was achieved in 7/11 patients. The mean time to loss of CBR was 26.5 weeks (range 14–18, median 22). Toxicity was mild and no APC patient experienced WHO grade 3 toxicity. The gemcitabine/5-fluorouracil combination is well tolerated and produces a symptomatic relief in the majority of APC patients. © 2000 Cancer Research Campaig
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