Universal point contact resistance between thin-film superconductors

A system comprising two superconducting thin films connected by a point contact is considered. The contact resistance is calculated as a function of temperature and film geometry, and is found to vanish rapidly with temperature, according to a universal, nearly activated form, becoming strictly zero only at zero temperature. At the lowest temperatures, the activation barrier is set primarily by the superfluid stiffness in the films, and displays only a weak (i.e., logarithmic) temperature dependence. The Josephson effect is thus destroyed, albeit only weakly, as a consequence of the power-law-correlated superconducting fluctuations present in the films below the Berezinskii-Kosterlitz-Thouless transition temperature. The behavior of the resistance is discussed, both in various limiting regimes and as it crosses over between these regimes. Details are presented of a minimal model of the films and the contact, and of the calculation of the resistance. A formulation in terms of quantum phase-slip events is employed, which is natural and effective in the limit of a good contact. However, it is also shown to be effective even when the contact is poor and is, indeed, indispensable, as the system always behaves as if it were in the good-contact limit at low enough temperature. A simple mechanical analogy is introduced to provide some heuristic understanding of the nearly-activated temperature dependence of the resistance. Prospects for experimental tests of the predicted behavior are discussed, and numerical estimates relevant to anticipated experimental settings are provided.Comment: 29 pages (single column format), 7 figure

Oscillatory decay of a two-component Bose-Einstein condensate

We study the decay of a two-component Bose-Einstein condensate with negative effective interaction energy. With a decreasing atom number due to losses, the atom-atom interaction becomes less important and the system undergoes a transition from a bistable Josephson regime to the monostable Rabi regime, displaying oscillations in phase and number. We study the equations of motion and derive an analytical expression for the oscillation amplitude. A quantum trajectory simulation reveals that the classical description fails for low emission rates, as expected from analytical considerations. Observation of the proposed effect will provide evidence for negative effective interaction.Comment: 4 pages, 3 figue

Collective Excitations of Bose-Einstein Condensates in a Double-Well Potential

We investigate collective excitations of Bose-Einstein condensates at absolute zero in a double-well trap. We solve the Bogoliubov equations with a double-well trap, and show that the crossover from the dipole mode to the Josephson plasma mode occurs in the lowest energy excitation. It is found that the anomalous tunneling property of low energy excitations is crucial to the crossover.Comment: 14 pages, 6 figure

Daily Sleep Quality is Associated with Daily Cognition in Late-Life

Background: Older adults often face sleep disturbance or cognitive decline that goes beyond the scope of normal aging. The present study examined the relationship between self-reported sleep quality and self-reported daytime attention in a community-dwelling sample of older men at the between-persons and within-persons levels of association. Methods: Thirty-eight participants (M age =75.36 years, SD age =7.51 years, range=66-90 years) completed a twice-daily sleep diary for one week. Sleep quality and attention were assessed using a single-item 0-10 rating scales from the morning diary (“How was the quality of your sleep last night?”) and from the evening diary (“How was your attention today?”). A two-level multilevel model was parameterized with days nested within individuals to examine whether nightly sleep quality predicts an individual’s daily attention rating. Results: A multilevel model predicting self-reported attention revealed (1) older individuals who reported better sleep quality reported having better daily attention [Beta=0.64, t(248.15)=10.12, p\u3c0.001] and (2) following a day of above-average sleep quality, older individuals experienced above-average attention [Beta=0.16, t(259.79)=2.75, p=.006]. Conclusion: Not only was overall sleep quality associated with self-reported attention, but a good night\u27s sleep was associated with better self-reported next-day attention. Results point to the potential importance of fluctuations in sleep quality for daytime functioning. Interventions aimed at improving nightly sleep consistency may be worth exploring as methods to improve daytime cognitive functioning in older adults. Support: This work was supported by the Sleep Research Society Foundation/Jazz Pharmaceuticals (001JP13, PI: Dzierzewski) and by the National Institute on Aging of the National Institutes of Health under Award Number K23AG049955 (PI: Dzierzewski), and National Heart Lung and Blood Institute at the National Institutes of Health under award number K24HL143055 (PI: Martin). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health or the Department of Veterans Affairs.https://scholarscompass.vcu.edu/gradposters/1089/thumbnail.jp

Contributions of VLDLR and LRP8 in the establishment of retinogeniculate projections

Background Retinal ganglion cells (RGCs), the output neurons of the retina, project to over 20 distinct brain nuclei, including the lateral geniculate nucleus (LGN), a thalamic region comprised of three functionally distinct subnuclei: the ventral LGN (vLGN), the dorsal LGN (dLGN) and the intergeniculate leaflet (IGL). We previously identified reelin, an extracellular glycoprotein, as a critical factor that directs class-specific targeting of these subnuclei. Reelin is known to bind to two receptors: very-low-density lipoprotein receptor (VLDLR) and low-density lipoprotein receptor-related protein 8 (LRP8), also known as apolipoprotein E receptor 2 (ApoER2). Here we examined the roles of these canonical reelin receptors in retinogeniculate targeting. Results To assess the roles of VLDLR and LRP8 in retinogeniculate targeting, we used intraocular injections of fluorescently conjugated cholera toxin B subunit (CTB) to label all RGC axons in vivo. Retinogeniculate projections in mutant mice lacking either VLDLR or LRP8 appeared similar to controls; however, deletion of both receptors resulted in dramatic defects in the pattern of retinal innervation in LGN. Surprisingly, defects in vldlr−/−;lrp8−/− double mutant mice were remarkably different than those observed in mice lacking reelin. First, we failed to observe retinal axons exiting the medial border of the vLGN and IGL to invade distant regions of non-retino-recipient thalamus. Second, an ectopic region of binocular innervation emerged in the dorsomedial pole of vldlr−/−;lrp8−/− mutant dLGN. Analysis of retinal projection development, retinal terminal sizes and LGN cytoarchitecture in vldlr−/−;lrp8−/− mutants, all suggest that a subset of retinal axons destined for the IGL are misrouted to the dorsomedial pole of dLGN in the absence of VLDLR and LRP8. Such mistargeting is likely the result of abnormal migration of IGL neurons into the dorsomedial pole of dLGN in vldlr−/−;lrp8−/− mutants. Conclusions In contrast to our expectations, the development of both the LGN and retinogeniculate projections appeared dramatically different in mutants lacking either reelin or both canonical reelin receptors. These results suggest that there are reelin-independent functions of VLDLR and LRP8 in LGN development, and VLDLR- and LRP8-independent functions of reelin in class-specific axonal targeting

Cardiac Rehabilitation Intervention and Quality of Life Indicators: A Validation Estimate of Ware's Model

Author Institution: Dept. of Counseling & Mental Health Services, University of Toledo, OHAuthor Institution: Dept. of Educational Foundations & Leadership, University of Akron, OHAuthor Institution: Dept. of Counseling, Summa Health System, University of Akron, OHAuthor Institution: Cardiac Rehabilitation Institute, Summa Health System, University of Akron, OHThe present study tests Ware’s (1987, 1990) prediction that patient evaluations of quality of life (QOL) are related to physical ability. QOL data from 302 patients were collected prior to initiation and upon completion of a 12-week cardiac rehabilitation program. Physical ability was measured in metabolic equivalents (METS). Pearson product moment correlation coefficients were calculated for the variables under study. Multiple regression analyses were conducted to test these relationships covarying patient diagnosis, and pre-treatment QOL score and patient demographics. Significant improvements from pre- to post-CR were found for METs and all QOL variables. Improvements in physical ability were significantly correlated with improvements in physical health related QOL indices, but not with mental health QOL indices. These relationships were present even when moderating variables were co-varied. Improvements in physical ability were predictive of decreased expectations that physical health would interfere with work or other daily activities. As the physical capabilities of our patients increased, they reported feeling less physical pain and were less limited by any pain they did experience. And, increased physical ability was associated with a brighter outlook on current and expected future health status. These findings provide support for Ware’s theory of QOL

Probing Pseudogap by Josephson Tunneling

We propose here an experiment aimed to determine whether there are superconducting pairing fluctuations in the pseudogap regime of the high-$T_c$ materials. In the experimental setup, two samples above $T_c$ are brought into contact at a single point and the differential AC conductivity in the presence of a constant applied bias voltage between the samples, $V$, should be measured. We argue the the pairing fluctuations will produce randomly fluctuating Josephson current with zero mean, however the current-current correlator will have a characteristic frequency given by Josephson frequency $\omega_J = 2 e V /\hbar$. We predict that the differential AC conductivity should have a peak at the Josephson frequency with the width determined by the phase fluctuations time.Comment: 4 pages, 2 eps figure

Administration of a Glycoprotein IIb/IIIa Receptor Blocker with a Thienopyridine Derivative Does Not Increase the Risk of Thrombocytopenia

Author Institution: Akron Cardiology Consulltants, OHAuthor Institution: Dept. of Educational Foundations & Leadership, University of Akron, OHAuthor Institution: Summa Health System, University of Akron, OHAuthor Institution: Dept. of Medicine, Northeast Ohio Universities College of Medicine, Rootstown, OHAuthor Institution: Cardiac Rehabilitation Institute, Summa Health Syste, University of Akron, OHThe combination of aspirin, a thienopyridine derivative, and a glycoprotein IIb/IIIa receptor inhibitor has become standard therapy for patients undergoing percutaneous coronary intervention (PCI). Recent studies have shown an increased incidence of thrombocytopenia in those patients receiving a high loading dose of clopidogrel (thienopyridine) with abciximab (IIb/IIIa receptor inhibitor) prior to coronary intervention. We reviewed the records of 504 patients who underwent PCI at a large tertiary care hospital and noted an incidence of thrombocytopenia of 4.8%, comparable to published historical controls who received abciximab without clopidogrel. In patients undergoing PCI, there was no difference in thrombocytopenia or bleeding complications between patients receiving a high or a low dose of a thienopyridine. We conclude that a high loading dose of a thienopyridine derivative prior to PCI may be administered safely and efficaciously in the setting of concomitant administration of abciximab without an undue risk of thrombocytopenia

Microscopic model of critical current noise in Josephson-junction qubits: Subgap resonances and Andreev bound states

We propose a microscopic model of critical current noise in Josephson-junctions based on individual trapping-centers in the tunnel barrier hybridized with electrons in the superconducting leads. We calculate the noise exactly in the limit of no on-site Coulomb repulsion. Our result reveals a noise spectrum that is dramatically different from the usual Lorentzian assumed in simple models. We show that the noise is dominated by sharp subgap resonances associated to the formation of pairs of Andreev bound states, thus providing a possible explanation for the spurious two-level systems (microresonators) observed in Josephson junction qubits [R.W. Simmonds et al., Phys. Rev. Lett. 93, 077003 (2004)]. Another implication of our model is that each trapping-center will contribute a sharp dielectric resonance only in the superconducting phase, providing an effective way to validate our results experimentally. We derive an effective Hamiltonian for a qubit interacting with Andreev bound states, establishing a direct connection between phenomenological models and the microscopic parameters of a Fermionic bath.Comment: 11 pages, 8 figure