Tunneling of a Quantized Vortex: Roles of Pinning and Dissipation

We have performed a theoretical study of the effects of pinning potential and dissipation on vortex tunneling in superconductors. Analytical results are obtained in various limits relevant to experiment. In general we have found that pinning and dissipation tend to suppress the effect of the vortex velocity dependent part of the Magnus force on vortex tunneling.Comment: Latex, 12 page

Hypercholesterolaemia in pregnancy as a predictor of adverse pregnancy outcome

Background: Prevention of viable spontaneous preterm birth and low birth weight through screening is one of the key aims of antenatal care as these have implications for the child, mother and society. If women can be identified to be at high risk of these adverse birth outcomes in early pregnancy, they can be targeted for more intensive antenatal surveillance and prophylactic interventions.Objectives: This study is therefore aimed to determine the association between elevated maternal serum cholesterol level in pregnancy and adverse pregnancy outcome.Methods: It was a prospective observational cohort study in which eligible participants were enrolled at gestational age of 14 to 20 weeks. Blood samples were obtained to measure total serum cholesterol concentrations and the sera were then analyzed enzymatically by the cholesterol oxidase: p-aminophenazone (CHOD PAP) method. Pregnancy outcomes were obtained by extraction from medical records and the labour ward register.Results: The incidences of the two adverse pregnancy outcomes examined in the study (preterm births and low birth weight (LBW) in term neonates) were 8.0% and 14.4% respectively. Preterm birth was 6.89-times more common in mothers with high cholesterol than in control mothers with normal total cholesterol level (38.5% versus 5.4%, P=0.029) while LBW was 7.99-times more common in mothers with high total maternal cholesterol than in mothers with normal cholesterol (87.5% versus 10.5%, P=0.019).Conclusion: We can infer that the high maternal serum cholesterol hypercholesterolaemia) is associated with preterm delivery/ low birth weight (LBW) in term infants. However, further validation of these findings with more robust prospective and longitudinal characterization of maternal serum cholesterol profiles is required in subsequent investigations.Keywords: Adverse birth outcome, cholesterol, hypercholesterolaemia, LBW, preterm birth

The Analyticity of a Generalized Ruelle's Operator

In this work we propose a generalization of the concept of Ruelle operator for one dimensional lattices used in thermodynamic formalism and ergodic optimization, which we call generalized Ruelle operator, that generalizes both the Ruelle operator proposed in [BCLMS] and the Perron Frobenius operator defined in [Bowen]. We suppose the alphabet is given by a compact metric space, and consider a general a-priori measure to define the operator. We also consider the case where the set of symbols that can follow a given symbol of the alphabet depends on such symbol, which is an extension of the original concept of transition matrices from the theory of subshifts of finite type. We prove the analyticity of the Ruelle operator and present some examples

Vortex Quantum Nucleation and Tunneling in Superconducting Thin Films: Role of Dissipation and Periodic Pinning

We investigate the phenomenon of decay of a supercurrent in a superconducting thin film in the absence of an applied magnetic field. The resulting zero-temperature resistance derives from two equally possible mechanisms: 1) quantum tunneling of vortices from the edges of the sample; and 2) homogeneous quantum nucleation of vortex-antivortex pairs in the bulk of the sample, arising from the instability of the Magnus field's ``vacuum''. We study both situations in the case where quantum dissipation dominates over the inertia of the vortices. We find that the vortex tunneling and nucleation rates have a very rapid dependence on the current density driven through the sample. Accordingly, whilst normally the superconductor is essentially resistance-free, for the high current densities that can be reached in high-$T_c$ films a measurable resistance might develop. We show that edge-tunneling appears favoured, but the presence of pinning centres and of thermal fluctuations leads to an enhancement of the nucleation rates. In the case where a periodic pinning potential is artificially introduced in the sample, we show that current-oscillations will develop indicating an effect specific to the nucleation mechanism where the vortex pair-production rate, thus the resistance, becomes sensitive to the corrugation of the pinning substrate. In all situations, we give estimates for the observability of the studied phenomena.Comment: 8 pages (LaTeX), 2 postscript figures. Invited talk to the SATT8 (8th Italian Meeting on High-T_c Superconductivity), Como (Italy), Villa Olmo, 1-4 October 1996, to be published in La Rivista del Nuovo Cimento

Microscopic theory of vortex dynamics in homogeneous superconductors

Vortex dynamics in fermionic superfluids is carefully considered from the microscopic point of view. Finite temperatures, as well as impurities, are explicitly incorporated. To enable readers understand the physical implications, macroscopic demonstrations based on thermodynamics and fluctuations- dissipation theorems are constructed. For the first time a clear summary and a critical review of previous results are given.Comment: Presentations are made more straightforward. A detailed presentation that why the vortex friction is finite when the geometric phase exists, as required by referees, though I think it is obviou

Profile of clinically-diagnosed dementias in a neuropsychiatric practice in Abeokuta, South-Western Nigeria

Objective: Many subjects with dementia present primarily to neuropsychiatric practices because of behavioural and psychological symptoms (BPSD). This study reviewed the profile of clinically-diagnosed dementias and BPSD seen in a pioneer neuropsychiatric practice in Abeokuta, southwestern Nigeria over a ten year period (January1998 – December 2007). Methods: A review of hospital records of all patients with diagnoses of dementia or dementing illness using the ICD-10 criteria as well as specific diagnostic criteria for different dementia phenotypes. Associated BPSD, co-morbidities and treatments were also reviewed. Results: Out of a total of 240,294 patients seen over the study period, 108 subjects met clinical diagnostic criteria for probable dementia giving a hospital frequency of 45 per 100,000. Alzheimer’s disease (AD) and Vascular dementia (VaD) were the predominant phenotypes seen in 62 (57.4%) and 18 (16.7%) subjects respectively. Others include mixed dementia (4 cases), frontotemporal dementia (4 cases), Lewy body dementia (3 cases), alcohol-related dementia (3 cases), PD dementia (1 case) and unclassifiable (13 cases). Apathy, night time behaviour, aberrant motor behaviour, agitation and irritability were the most common BPSD features, while hypertension was the most common co-morbidity. Neuroleptics, anticholinergics and anti-hypertensives were most commonly prescribed. Anticholinesterase inhibitors were sparingly used. Conclusion: Probable AD was the most prevalent dementia phenotype seen in this practice. Increased awareness of dementia and better utilization of specific treatments are needed among psychiatrists and primary care practitioners in Nigeria.Keywords: Dementia phenotypes; BPSD; Neuropsychiatric practice; Nigeria; Afric

Geometric Laws of Vortex Quantum Tunneling

In the semiclassical domain the exponent of vortex quantum tunneling is dominated by a volume which is associated with the path the vortex line traces out during its escape from the metastable well. We explicitly show the influence of geometrical quantities on this volume by describing point vortex motion in the presence of an ellipse. It is argued that for the semiclassical description to hold the introduction of an additional geometric constraint, the distance of closest approach, is required. This constraint implies that the semiclassical description of vortex nucleation by tunneling at a boundary is in general not possible. Geometry dependence of the tunneling volume provides a means to verify experimental observation of vortex quantum tunneling in the superfluid Helium II.Comment: 4 pages, 2 figures, revised version to appear in Phys. Rev.

Berry's Phase in the Presence of a Stochastically Evolving Environment: A Geometric Mechanism for Energy-Level Broadening

The generic Berry phase scenario in which a two-level system is coupled to a second system whose dynamical coordinate is slowly-varying is generalized to allow for stochastic evolution of the slow system. The stochastic behavior is produced by coupling the slow system to a heat resevoir which is modeled by a bath of harmonic oscillators initially in equilibrium at temperature T, and whose spectral density has a bandwidth which is small compared to the energy-level spacing of the fast system. The well-known energy-level shifts produced by Berry's phase in the fast system, in conjunction with the stochastic motion of the slow system, leads to a broadening of the fast system energy-levels. In the limit of strong damping and sufficiently low temperature, we determine the degree of level-broadening analytically, and show that the slow system dynamics satisfies a Langevin equation in which Lorentz-like and electric-like forces appear as a consequence of geometrical effects. We also determine the average energy-level shift produced in the fast system by this mechanism.Comment: 29 pages, RevTex, submitted to Phys. Rev.

Magnetization Relaxation via Quantum and Classical Vortex Motion in a Bose Glass Superconductor

I show that in Bose Glass superconductor with high $j_c$ and at low $T$ the magnetization relaxation (S), dominated by quantum tunneling, is $\propto{\sqrt j_c}$, which crosses over to the conventional classical rate $\propto T/j_c$ at higher $T$ and lower $j_c$, with the crossover $T^*\sim j_c^{3/2}$. I argue that due to interactions between flux lines there exist three relaxation regimes, depending on whether $BB_\phi$, corresponding to Strongly-pinned Bose Glass (SBG) with large $j_{c2}$, Mott Insulator (MI) with vanishing S, and Weakly-pinned Bose Glass (WBG) characterized by small $j_{c1}$. I discuss the effects of interactions on $j_c$ and focus attention on the recent experiment which is consistently described by the theory.Comment: 4 pages, self-unpacking uuencoded compressed postscript file with figures already inside text; to appear in Phys. Rev. Lett.(1995