Finite Size and Current Effects on IV Characteristics of Josephson Junction Arrays

The effects of finite size and of finite current on the current-voltage characteristics of Josephson junction arrays is studied both theoretically and by numerical simulations. The cross-over from non-linear to linear behavior at low temperature is shown to be a finite size effect and the non-linear behavior at higher temperature, $T>T_{KT}$, is shown to be a finite current effect. These are argued to result from competition between the three length scales characterizing the system. The importance of boundary effects is discussed and it is shown that these may dominate the behavior in small arrays.Comment: 5 pages, figures included, to appear in PR

GRACE and TIMI risk scores but not stress imaging predict long-term cardiovascular follow-up in patients with chest pain after a rule-out protocol

Objective To determine the long-term prognostic value of stress imaging and clinical risk scoring for cardiovascular mortality in chest pain patients after ruling out acute coronary syndrome (ACS). Methods A standard rule-out protocol was performed in emergency room patients with a normal or non-diagnostic admission electrocardiogram (ECG) within 6 h of chest 4 pain onset. ACS patients were identified by troponin T, recurrent angina and serial ECG. Dobutamine stress echocardiography (DSE) was performed after ACS was ruled out. Myocardial perfusion scintigraphy (MPS) was performed within 6 months in an outpatient setting according to the physician's discretion. Results 524 patients were included. GRACE and TIMI risk scores were 75 (57-96) and 1 (0-2) in the rule-out ACS group, and 89 (74-107) and 2 (1-3) in the ACS group, respectively (median, interquartile range). Follow-up (median 9.4 (8.9-10.0) years) was complete in 96%. 350 of 379 rule-out ACS patients had an interpretable DSE and 52 patients underwent an MPS. 21 of the rule-out ACS patients (6%) died of a cardiovascular cause compared with 24 (17%) ACS patients (p <0.001). For rule-out ACS patients, C-statistics were 0.829 and 0.803 for the GRACE and TIMI scores. In these patients, DSE and MPS outcome did not predict long-term cardiovascular mortality. In multivariate analysis, known chronic heart failure, ACE inhibitor use, and GRACE score were independent predictors of cardiovascular mortality. Conclusions TIMI and GRACE score but not DSE and MPS are accurate predictors of long-term cardiovascular mortality, even in chest pain patients with a normal or non-diagnostic electrocardiogram undergoing a rule-out protoco

Domain Walls Motion and Resistivity in a Fully-Frustrated Josephson Array

It is identified numerically that the resistivity of a fully-frustrated Josephson-junction array is due to motion of domain walls in vortex lattice rather than to motion of single vortices

Row-switched states in two-dimensional underdamped Josephson junction arrays

When magnetic flux moves across layered or granular superconductor structures, the passage of vortices can take place along channels which develop finite voltage, while the rest of the material remains in the zero-voltage state. We present analytical studies of an example of such mixed dynamics: the row-switched (RS) states in underdamped two-dimensional Josephson arrays, driven by a uniform DC current under external magnetic field but neglecting self-fields. The governing equations are cast into a compact differential-algebraic system which describes the dynamics of an assembly of Josephson oscillators coupled through the mesh current. We carry out a formal perturbation expansion, and obtain the DC and AC spatial distributions of the junction phases and induced circulating currents. We also estimate the interval of the driving current in which a given RS state is stable. All these analytical predictions compare well with our numerics. We then combine these results to deduce the parameter region (in the damping coefficient versus magnetic field plane) where RS states can exist.Comment: latex, 48 pages, 15 figs using psfi

Resistance of Josephson Junction Arrays at Low Temperatures

We study motion of vortices in arrays of Josephson junctions at zero temperature where it is controlled by quantum tunneling from one plaquette to another. The tunneling process is characterized by a finite time and can be slow compared to the superconducting gap (so that $\tau \Delta >> 1$). The dissipation which accompanies this process arises from rare processes when a vortex excites a quasiparticle above the gap while tunneling through a single junction. We find that the dissipation is significant even in the case $\tau \Delta >> 1$, in particular it is not exponentially small in this parameter. We use the calculated energy dissipation for the single vortex jump to estimate the physical resistance of the whole array.Comment: 24 pages, LaTeX references added, to appear in PR

Quantum superconductor-metal transition in a proximity array

A theory of the zero-temperature superconductor-metal transition is developed for an array of superconductive islands (of size d) coupled via a disordered two-dimensional conductor with the dimensionless conductance g>>1. At T=0 macroscopically superconductive state of the array with the lattice spacing b>>d is destroyed at g < g_c \approx 0.1 ln^2(b/d). At high temperatures the normal-state resistance between neighboring islands at b=b_c is much smaller than h/4e^2.Comment: RevTeX, 7 pages, 2 eps figure

Edge effects in a frustrated Josephson junction array with modulated couplings

A square array of Josephson junctions with modulated strength in a magnetic field with half a flux quantum per plaquette is studied by analytic arguments and dynamical simulations. The modulation is such that alternate columns of junctions are of different strength to the rest. Previous work has shown that this system undergoes an XY followed by an Ising-like vortex lattice disordering transition at a lower temperature. We argue that resistance measurements are a possible probe of the vortex lattice disordering transition as the linear resistance $R_{L}(T)\sim A(T)/L$ with $A(T) \propto (T-T_{cI})$ at intermediate temperatures $T_{cXY}>T>T_{cI}$ due to dissipation at the array edges for a particular geometry and vanishes for other geometries. Extensive dynamical simulations are performed which support the qualitative physical arguments.Comment: 8 pages with figs, RevTeX, to appear in Phys. Rev.

Bispecific antibody CD73xEpCAM selectively inhibits the adenosine-mediated immunosuppressive activity of carcinoma-derived extracellular vesicles

Tumor-derived extracellular vesicles (EVs) carry potent immunosuppressive factors that affect the antitumor activities of immune cells. A significant part of the immunoinhibitory activity of EVs is attributable to CD73, a GPI-anchored ecto-5'-nucleotidase involved in the conversion of tumor-derived proinflammatory extracellular ATP (eATP) to immunosuppressive adenosine (ADO). The CD73-antagonist antibody oleclumab inhibits cell surface-exposed CD73 and is currently undergoing clinical testing for cancer immunotherapy. However, a strategy to selectively inhibit CD73 exposed on EVs is not available. Here, we present a novel bispecific antibody (bsAb) CD73xEpCAM designed to bind with high affinity the common EV surface marker EpCAM and concurrently inhibit CD73. Unlike oleclumab, bsAb CD73xEpCAM potently inhibited the immunosuppressive activity of EVs from CD73pos/EpCAMpos carcinoma cell lines and patient-derived colorectal cancer cells. Taken together, selective blockade of EV-exposed CD73 by bsAb CD73xEpCAM may be useful as an alternate or complementary targeted approach in cancer immunotherapy

Finite temperature transport at the superconductor-insulator transition in disordered systems

I argue that the incoherent, zero-frequency limit of the universal crossover function in the temperature-dependent conductivity at the superconductor-insulator transition in disordered systems may be understood as an analytic function of dimensionality of system d, with a simple pole at d=1. Combining the exact result for the crossover function in d=1 with the recursion relations in d=1+\epsilon, the leading term in the Laurent series in the small parameter \epsilon for this quantity is computed for the systems of disordered bosons with short-range and Coulomb interactions. The universal, low-temperature, dc critical conductivity for the dirty boson system with Coulomb interaction in d=2 is estimated to be 0.69 (2e)^2 /h, in relatively good agreement with many experiments on thin films. The next order correction is likely to somewhat increase the result, possibly bringing it closer to the self-dual value.Comment: 9 pages, LaTex, no figure