559 research outputs found
Suppression of 2D superconductivity by the magnetic field: quantum corrections vs superconductor-insulator transition
Magnetotransport of superconducting Nd_{2-x}Ce_xCuO_{4+y} (NdCeCuO) films is
studied in the temperature interval 0.3-30 K. The microscopic theory of the
quantum corrections to conductivity, both in the Cooper and in the diffusion
channels, qualitatively describes the main features of the experiment including
the negative magnetoresistance in the high field limit. Comparison with the
model of the field-induced superconductor-insulator transition (SIT) is
included and a crossover between these two theoretical approaches is discussed.Comment: 5 pages, 4 figures. Submitted to JETP Letter
Observation of the parallel-magnetic-field-induced superconductor-insulator transition in thin amorphous InO films
We study the response of a thin superconducting amorphous InO film with
variable oxygen content to a parallel magnetic field. A field-induced
superconductor-insulator transition (SIT) is observed that is very similar to
the one in normal magnetic fields. As the boson-vortex duality, which is the
key-stone of the theory of the field-induced SIT, is obviously absent in the
parallel configuration, we have to draw conclusion about the theory
insufficiency.Comment: 3 pages, 4 figure
Nucleation of Stable Superconductivity in YBCO-Films
By means of the linear dynamic conductivity, inductively measured on
epitaxial films between 30mHz and 30 MHz, the transition line to
generic superconductivity is studied in fields between B=0 and 19T. It follows
closely the melting line described recently in terms of a blowout of
thermal vortex loops in clean materials. The critical exponents of the
correlation length and time near , however, seem to be dominated by
some intrinsic disorder. Columnar defects produced by heavy-ion irradiation up
to field-equivalent-doses of lead to a disappointing reduction
of while for the generic line of the pristine film
is recovered. These novel results are also discussed in terms of a loop-driven
destruction of generic superconductivity.Comment: 11 pages including 7 EPS figures, accepted for publication in the
Proceedings of the Spring Meeting of the German Physical Society, Muenster
1999,Festkoerperprobleme/Advances in Solid State Physics 199
Teratogenic risk and contraceptive counselling in psychiatric practice: analysis of anticonvulsant therapy
<p>Background:
Anticonvulsants have been used to manage psychiatric conditions for over 50 years. It is recognised that some, particularly valproate, carbamazepine and lamotrigine, are human teratogens, while others including topiramate require further investigation. We aimed to appraise the documentation of this risk by psychiatrists and review discussion around contraceptive issues.</p>
<p>Methods:
A retrospective review of prescribing patterns of four anticonvulsants (valproate, carbamazepine, lamotrigine and topiramate) in women of child bearing age was undertaken. Documented evidence of discussion surrounding teratogenicity and contraceptive issues was sought.</p>
<p>Results:
Valproate was most commonly prescribed (n=67). Evidence of teratogenic risk counselling at medication initiation was sub-optimal – 40% of individuals prescribed carbamazepine and 22% of valproate. Documentation surrounding contraceptive issues was also low- 17% of individuals prescribed carbamazepine and 13% of valproate.</p>
<p>Conclusion:
We found both low rates of teratogenic risk counselling and low rates of contraception advice in our cohort. Given the high rates of unplanned pregnancies combined with the relatively high risk of major congenital malformations, it is essential that a detailed appraisal of the risks and benefits associated with anticonvulsant medication occurs and is documented within patients’ psychiatric notes.</p>
Microscopic Study of Quantum Vortex-Glass Transition Field in Two-Dimensional Superconductors
The position of a field-tuned superconductor-insulator quantum transition
occuring in disordered thin films is examined within the mean field
approximation. Our calculation shows that the microscopic disorder-induced
reduction of the quantum transition point found experimentally cannot be
explained if the interplay between the disorder and an electron-electron
repulsive interaction is ignored. This work is presented as a microscopic basis
of an explanation (cond-mat/0105122) of resistive phenomena near the transition
field.Comment: 16 pages, 5 figures. To appear in J.Phys.Soc.Jp
Scaling analysis of the magnetic-field-tuned quantum transition in superconducting amorphous In-O films
We have studied the magnetic-field-tuned superconductor-insulator quantum
transition (SIT) in amorphous In-O films with different oxygen content and,
hence, different electron density. While for states of the film near the
zero-field SIT the two-dimensional scaling behaviour is confirmed, for deeper
states in the superconducting phase the SIT scenario changes: in addition to
the scaling function that describes the conductivity of fluctuation-induced
Cooper pairs, there emerges a temperature-dependent contribution to the film
resistance. This contribution can originate from the conductivity of normal
electrons.Comment: 4 pages, 5 figures; accepted for publication in JETP Lett. 71 (4),
200
Disorder and Quantum Fluctuations in Superconducting Films in Strong Magnetic Fields
We find that the upper critical field in a two-dimensional disordered
superconductor can increase essentially at low temperatures. This happens due
to the formation of local superconducting islands weakly coupled via the
Josephson effect. The distribution of the superconducting islands is derived.
It is shown that the value of the critical field is determined by the interplay
of the proximity effect and quantum phase fluctuations. We find that the shift
of the upper critical field is connected with the pinning properties of a
superconductor.Comment: 4 page
Ultrametric spaces of branches on arborescent singularities
Let be a normal complex analytic surface singularity. We say that is
arborescent if the dual graph of any resolution of it is a tree. Whenever
are distinct branches on , we denote by their intersection
number in the sense of Mumford. If is a fixed branch, we define when and
otherwise. We generalize a theorem of P{\l}oski concerning smooth germs of
surfaces, by proving that whenever is arborescent, then is an
ultrametric on the set of branches of different from . We compute the
maximum of , which gives an analog of a theorem of Teissier. We show that
encodes topological information about the structure of the embedded
resolutions of any finite set of branches. This generalizes a theorem of Favre
and Jonsson concerning the case when both and are smooth. We generalize
also from smooth germs to arbitrary arborescent ones their valuative
interpretation of the dual trees of the resolutions of . Our proofs are
based in an essential way on a determinantal identity of Eisenbud and Neumann.Comment: 37 pages, 16 figures. Compared to the first version on Arxiv, il has
a new section 4.3, accompanied by 2 new figures. Several passages were
clarified and the typos discovered in the meantime were correcte
Stigma-directed services (Stig2Health) to improve 'linkage to care' for people living with HIV in rural Tanzania: study protocol for a nested pre-post implementation study within the Kilombero and Ulanga Antiretroviral Cohort
Background: HIV-related stigma is a major barrier to the timely linkage and retention of patients in HIV care in sub-Saharan Africa, where most people living with HIV/AIDS reside. In this implementation study we aim to evaluate the effect of stigma-directed services on linkage to care and other health outcomes in newly diagnosed HIV-positive patients. Methods: In a nested project of the Kilombero and Ulanga Antiretroviral Cohort in rural Tanzania, we conduct a prospective observational pre-post study to assess the impact of a bundle of stigma-directed services for newly diagnosed HIV positive patients. Stigma-directed services, delivered by a lay person living with HIV, are i) post-test counseling, ii) post-test video-assisted teaching, iii) group support therapy and group health education, and iv) mobile health. Patients receiving stigma services (enrolled from 1 (st) February 2020 to 31 (st) August 2021) are compared to a historical control receiving the standard of care (enrolled from 1 (st) July 2017 to 1 (st) February 2019). The primary outcome is 'linkage to care'. Secondary endpoints are retention in care, viral suppression, death and clinical failure at 6-12 months (up to 31 (st) August 2022). Self-reported stigma and depression are assessed using the Berger Stigma scale and the PHQ-9 questionnaire, respectively. The sample size calculation was based on cohort data from 2018. Assuming a pre-intervention cohort of 511 newly diagnosed adults of whom 346 (68%) were in care and on antiretroviral treatment (ART) at 2 months, a 10% increase in linkage (from 70 to 80%), a two-sided type I error rate of 5%, and 90% power, 321 adults are required for the post-implementation group. Discussion: We expect that integration of stigma-directed services leads to an increase of proportions of patients in care and on ART. The findings will provide guidance on how to integrate stigma-directed services into routine care in rural sub-Saharan Africa
Prevalence, incidence and predictors of renal impairment in persons with HIV receiving protease-inhibitors in rural Tanzania
OBJECTIVE: Ritonavir-boosted protease inhibitors (bPI) in people living with HIV (PLWH) have been associated with renal impairment. Limited data are available from rural sub-Saharan Africa. METHODS: Using data from the Kilombero and Ulanga Antiretroviral Cohort Study (KIULARCO) in rural Tanzania from 2005-01/2020, we assessed the prevalence of renal impairment (estimated glomerular filtration rate <60 mL/min/1.73m2) at the time of switch from first-line antiretroviral treatment (ART) to bPI-regimen and the incidence of renal impairment on bPI. We assessed risk factors for renal impairment using logistic and Cox regression models. RESULTS: Renal impairment was present in 52/687 PLWH (7.6%) at the switch to bPI. Among 556 participants with normal kidney function at switch, 41 (7.4%) developed renal impairment after a median time of 3.5 (IQR 1.6-5.1) years (incidence 22/1,000 person-years (95%CI 16.1-29.8)). Factors associated with renal impairment at switch were older age (adjusted odds ratio (aOR) 1.55 per 10 years; 95%CI 1.15-2.11), body mass index (BMI) /=18kg/m2; 95%CI 1.28-6.14) and arterial hypertension (aOR 2.33; 95%CI 1.03-5.28). The risk of renal impairment was lower with increased duration of ART use (aOR 0.78 per one-year increase; 95%CI 0.67-0.91). The renal impairment incidence under bPI was associated with older age (adjusted hazard ratio 2.01 per 10 years; 95%CI 1.46-2.78). CONCLUSIONS: In PLWH in rural sub-Saharan Africa, prevalence and incidence of renal impairment among those who were switched from first-line to bPI-regimens were high. We found associations between renal impairment and older age, arterial hypertension, low BMI and time on ART
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