243 research outputs found
Phenomenology of a-axis and b-axis charge dynamics from microwave spectroscopy of highly ordered YBa2Cu3O6.50 and YBa2Cu3O6.993
Extensive measurements of the microwave conductivity of highly pure and
oxygen-ordered \YBCO single crystals have been performed as a means of
exploring the intrinsic charge dynamics of a d-wave superconductor. Broadband
and fixed-frequency microwave apparatus together provide a very clear picture
of the electrodynamics of the superconducting condensate and its thermally
excited nodal quasiparticles. The measurements reveal the existence of very
long-lived excitations deep in the superconducting state, as evidenced by sharp
cusp-like conductivity spectra with widths that fall well within our
experimental bandwidth. We present a phenomenological model of the microwave
conductivity that captures the physics of energy-dependent quasiparticle
dynamics in a d-wave superconductor which, in turn, allows us to examine the
scattering rate and oscillator strength of the thermally excited quasiparticles
as functions of temperature. Our results are in close agreement with the
Ferrell-Glover-Tinkham sum rule, giving confidence in both our experiments and
the phenomenological model. Separate experiments for currents along the and directions of detwinned crystals allow us to isolate the role
of the CuO chain layers in \YBCO, and a model is presented that incorporates
both one-dimensional conduction from the chain electrons and two-dimensional
transport associated with the \cuplane plane layers.Comment: 17 pages, 13 figure
Superconducting Magnetization above the Irreversibility Line in Tl2Ba2CuO6
Piezolever torque magnetometry has been used to measure the magnetization of
superconducting Tl2Ba2CuO6. Three crystals with different levels of oxygen
overdoping were investigated in magnetic fields up to 10 Tesla. In all cases,
the magnetization above the irreversibility line was found to depart from the
behaviour M ~ ln(Hc2/H) of a simple London-like vortex liquid. In particular,
for a strongly overdoped (Tc = 15K) crystal, the remnant superconducting order
above the irreversibility line is characterized by a linear diamagnetic
response (M ~ H) that persists well above Tc and also up to the highest field
employed.Comment: RevTeX, 11 pages, 7 encapsulated PostScript figures, submitted to
Physical Review
Systematic behaviour of the in-plane penetration depth in d-wave cuprates
We report the temperature T and oxygen concentration dependences of the
penetration depth of grain-aligned YBa_2Cu_3O_{7-\delta} with \delta= 0.0, 0.3
and 0.43. The values of the in-plane \lambda_{ab}(0) and out-of-plane
\lambda_{c}(0) penetration depths, the low temperature linear term in
\lambda_{ab}(T), and the ratio \lambda_{c}(0) /\lambda_{ab}(T) were found to
increase with increasing . The systematic changes of the linear term in
\lambda_{ab}(T) with T_c found here and in recent work on HgBa_2Ca_{n-1}
Cu_nO_{2n+2+\delta} (n = 1 and 3) are discussed.Comment: 4 pages, 4 figure
Should I Take Aspirin? (SITA): RCT of a decision aid for cancer chemoprevention.
Background Australian guidelines recommend that all people aged 50-70 years old consider taking low-dose aspirin to reduce the risk of colorectal cancer (CRC). Aim To determine the effect of a consultation with a researcher in general practice using a decision aid about taking low-dose aspirin to prevent CRC on informed decision-making and low-dose aspirin uptake compared to a general CRC prevention brochure. Design and Setting Individually randomised controlled trial in six general practices in Victoria, Australia, from October 2020 to March 2021. Method Patients aged 50-70 years attending a general practitioner (GP) were recruited consecutively. The intervention was a consultation using a decision aid to discuss taking aspirin to reduce CRC risk; control consultations discussed reducing CRC risk generally. The self-reported co-primary outcomes were informed choices about taking aspirin at one month and low-dose aspirin uptake at six months. Results 261 participants (86% of eligible patients) were randomised into trial arms (129 intervention, 132 control). 17.7% (20/113) of intervention and 7.6% (9/118) control participants reported making an informed choice at one month, an estimated 9.1% (95% CI 0.29% to 18.5) between-arm difference in proportions [odds ratio (OR) 2.47 (97.5% CI:0.94 to 6.52) p=0.074]. The proportions of individuals who reported using aspirin at six months were: 10.2% (12/118) intervention vs 13.8% (16/116) control (estimated between-arm difference: -4.0% (95% CI: -13.5 to 5.5); [OR= 0.68 (97.5% CI:0.27 to 1.70), p= 0.692]. Conclusion The decision aid improved informed decision-making; but has little effect on long-term regular use of aspirin to reduce CRC risk
Implications evinced by the phase diagram, anisotropy, magnetic penetration depths, isotope effects and conductivities of cuprate superconductors
Anisotropy, thermal and quantum fluctuations and their dependence on dopant
concentration appear to be present in all cuprate superconductors, interwoven
with the microscopic mechanisms responsible for superconductivity. Here we
review anisotropy, in-plane and c-axis penetration depths, isotope effect and
conductivity measurements to reassess the universal behavior of cuprates as
revealed by the doping dependence of these phenomena and of the transition
temperature.Comment: 14 pages, 13 figure
Muon spin rotation studies of electronic excitations and magnetism in the vortex cores of superconductors
The focus of this paper is on recent progress in muon spin rotation (muSR)
studies of the vortex cores in type-II superconductors. By comparison of muSR
measurements of the vortex core size in a variety of materials with results
from techniques that directly probe electronic states, the effect of
delocalized quasiparticles on the spatial variation of field in a lattice of
interacting vortices has been determined for both single-band and multi-band
superconductors. These studies demonstrate the remarkable accuracy of what some
still consider an exotic technique. In recent years muSR has also been used to
search for magnetism in and around the vortex cores of high-temperature
superconductors. As a local probe muSR is specially suited for detecting static
or quasistatic magnetism having short-range or random spatial correlations. As
discussed in this review, muSR experiments support a generic phase diagram of
competing superconducting and magnetic order parameters, characterized by a
quantum phase transition to a state where the competing order is spatially
nonuniform.Comment: 28 pages, 22 figure
Optical Sum Rule in Finite Bands
In a single finite electronic band the total optical spectral weight or
optical sum carries information on the interactions involved between the charge
carriers as well as on their band structure. It varies with temperature as well
as with impurity scattering. The single band optical sum also bears some
relationship to the charge carrier kinetic energy and, thus, can potentially
provide useful information, particularly on its change as the charge carriers
go from normal to superconducting state. Here we review the considerable
advances that have recently been made in the context of high oxides, both
theoretical and experimental.Comment: Review article accepted for publication in J. Low Temp. Phys. 29
pages, 33 figure
Stage III and oestrogen receptor negativity are associated with poor prognosis after adjuvant high-dose therapy in high-risk breast cancer
We report on the efficacy and toxicity of a sequential high-dose therapy with peripheral blood stem cell (PBSC) support in 85 patients with high-risk stage II/III breast cancer. There were 71 patients with more than nine tumour-positive axillary lymph nodes. An induction therapy of two cycles of ifosfamide (total dose, 7.5 g m−2) and epirubicin (120 mg m−2) was given, and PBSC were harvested during G-CSF-supported leucocyte recovery following the second cycle. The PBSC-supported high-dose chemotherapy consisted of two cycles of ifosfamide (total dose, 12 000 mg m−2), carboplatin (900 mg m−2) and epirubicin (180 mg m−2). Patients were autografted with a median number of 3.7 × 106 CD34+ cells kg−1 (range, 1.9–26.5 × 106) resulting in haematological reconstitution within approximately 2 weeks following high-dose therapy. The toxicity was moderate in general, and there was no treatment-related toxic death. Twenty-one patients relapsed between 3 and 30 months following the last cycle of high-dose therapy (median, 11 months). The probability of disease-free and overall survival at 4 years were 60% and 83%, respectively. According to a multivariate analysis, patients with stage II disease had a significantly better probability of disease-free survival (74%) in comparison to patients with stage III disease (36%). The probability of disease-free survival was also significantly better for patients with oestrogen receptor-positive tumours (70%) compared to patients with receptor-negative ones (40%). Bone marrow samples collected from 52 patients after high-dose therapy were examined to evaluate the prognostic relevance of isolated tumour cells. The proportion of patients presenting with tumour cell-positive samples did not change in comparison to that observed before high-dose therapy (65% vs 71%), but a decrease in the incidence and concentration of tumour cells was observed over time after high-dose therapy. This finding was true for patients with relapse and for those in remission, which argues against a prognostic significance of isolated tumour cells in bone marrow. In conclusion, sequential high-dose chemotherapy with PBSC support can be safely administered to patients with high-risk stage II/III breast cancer. Further intensification of the therapy, including the addition of non-cross resistant drugs or immunological approaches such as the use of antibodies against HER-2/NEU, may be envisaged for patients with stage III disease and hormone receptor-negative tumours. © 1999 Cancer Research Campaig
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