1,284 research outputs found
Superconductivity in an Einstein Solid AxV2Al20 (A = Al and Ga)
A cage compound AxV2Al20 (Al10V), that was called an Einstein solid by Caplin
and coworkers 40 years ago, is revisited to investigate the low-energy, local
vibrations of the A atoms and their influence on the electronic and
superconducting properties of the compound. Polycrystalline samples with A =
Al, Ga, Y, and La are studied through resistivity and heat capacity
measurements. Weak-coupling BCS superconductivity is observed below Tc = 1.49,
1.66, and 0.69 K for Ax = Al0.3, Ga0.2, and Y, respectively, but not above 0.4
K for Ax = La. Low-energy modes are detected only for A = Al and Ga, which are
approximately described by the Einstein model with Einstein temperatures of 24
and 8 K, respectively. A weak but significant coupling between the low-energy
modes, which are almost identical to those called rattling in recent study, and
conduction electrons manifests itself as anomalous enhancement in resistivity
at around low temperatures corresponding to the Einstein temperatures.Comment: 12 pages, 5 figures, to be published in J. Phys. Soc. Jp
Dynamic interactions between pancake vortex stacks and Josephson vortices in Bi2Sr2CaCu2O8 single crystals: relaxation and ratchets
We present a detailed study of the dynamic interactions between Josephson
vortices and stacks of pancake vortices in a Bi2Sr2CaCu2O8 single crystal,
obtained by measuring the effect of applied inplane magnetic field pulses on
the c-axis magnetisation. The predominant interaction is to relax the system
towards equilibrium. However, using a highly sensitive AC technique we are able
to measure also the forces acting to drive the system away from equilibrium,
consistent with the existence of dragging interactions between the Josephson
and pancake systems. Such forces were discussed recently as the basis of
possible flux ratchet devices.Comment: 4 pages, 4 figure
Mapping the dynamic interactions between vortex species in highly anisotropic superconductors
Here we use highly sensitive magnetisation measurements performed using a
Hall probe sensor on single crystals of highly anisotropic high temperature
superconductors to study the dynamic interactions
between the two species of vortices that exist in such superconductors. We
observe a remarkable and clearly delineated high temperature regime that
mirrors the underlying vortex phase diagram. Our results map out the parameter
space over which these dynamic interaction processes can be used to create
vortex ratchets, pumps and other fluxonic devices.Comment: 7 pages, 3 figures, to be published in Supercond. Sci. Techno
Chronic kidney disease and cause-specific hospitalisation: a matched cohort study using primary and secondary care patient data.
BACKGROUND: Although chronic kidney disease (CKD) is associated with various outcomes, the burden of each condition for hospital admission is unknown. AIM: To quantify the association between CKD and cause-specific hospitalisation. DESIGN AND SETTING: A matched cohort study in primary care using Clinical Practice Research Datalink linked to Hospital Episode Statistics in England. METHOD: Patients with CKD (estimated glomerular filtration rate <60 mL/min/1.73 m2 for ≥3 months) and a comparison group of patients without known CKD (matched for age, sex, GP, and calendar time) were identified, 2004-2014. Outcomes were hospitalisations with 10 common conditions as the primary admission diagnosis: heart failure; urinary tract infection; pneumonia; acute kidney injury (AKI); myocardial infarction; cerebral infarction; gastrointestinal bleeding; hip fracture; venous thromboembolism; and intracranial bleeding. A difference in the incidence rate of first hospitalisation for each condition was estimated between matched patients with and without CKD. Multivariable Cox regression was used to estimate a relative risk for each outcome. RESULTS: In a cohort of 242 349 pairs of patients, with and without CKD, the rate difference was largest for heart failure at 6.6/1000 person-years (9.7/1000 versus 3.1/1000 person-years in patients with and without CKD, respectively), followed by urinary tract infection at 5.2, pneumonia at 4.4, and AKI at 4.1/1000 person-years. The relative risk was highest for AKI with a fully adjusted hazard ratio of 4.90, 95% confidence interval (CI) = 4.47 to 5.38, followed by heart failure with 1.66, 95% CI = 1.59 to 1.75. CONCLUSION: Hospitalisations for heart failure, infection, and AKI showed strong associations with CKD in absolute and(or) relative terms, suggesting targets for improved preventive care
Anisotropies of the lower and upper critical fields in MgB single crystals
The temperature dependence of the London penetration depth () and
coherence length () has been deduced from Hall probe magnetization
measurements in high quality MgB single crystals in the two main
crystallographic directions. We show that, in contrast to conventional
superconductors, MgB is characterized by two different anisotropy
parameters ( and ) which strongly differ at low temperature and merge at .
These results are in very good agreement with recent calculations in weakly
coupled two bands suprerconductors (Phys. Rev. B, 66, 020509(R) (2002).Comment: 4 pages, 4 figure
Critical Fields and Critical Currents in MgB2
We review recent measurements of upper (Hc2) and lower (Hc1) critical fields
in clean single crystals of MgB2, and their anisotropies between the two
principal crystallographic directions. Such crystals are far into the "clean
limit" of Type II superconductivity, and indeed for fields applied in the
c-direction, the Ginzburg-Landau parameter k is only about 3, just large enough
for Type II behaviour. Because m0Hc2 is so low, about 3 T for fields in the
c-direction, MgB2 has to be modified for it to become useful for high-current
applications. It should be possible to increase Hc2 by the introduction of
strong electron scattering (but because of the electronic structure and the
double gap that results, the scatterers will have to be chosen carefully). In
addition, pinning defects on a scale of a few nm will have to be engineered in
order to enhance the critical current density at high fields.Comment: BOROMAG Conference Invited paper. To appear in Supercond. Sci. Tec
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An agency relationship under general conditions of uncertainty: A game theory application to the doctor-patient interaction
The supply of information, particularly of bad news, in an agency relationship is a sensitive issue. We employ a game theory approach to investigate conflicts in the particular case of the doctor–patient relationship when information affects the emotions of patients. The doctor does not know the type of agent and the patient does not know how much information he is given. Hence, the paper obtains results when there is conflict, rather than common interest in the objectives of the two parties. The perfect Bayesian equilibrium describes beliefs and strategies which guarantee adherence to the doctor’s recommendation. We show also that the patient may non-adhere to the recommendation not only when the doctor fails to identify the patient’s needs but also if he falsely believes that the doctor has not done so
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