Comparative study of macroscopic quantum tunneling in Bi_2Sr_2CaCu_2O_y intrinsic Josephson junctions with different device structures

We investigated macroscopic quantum tunneling (MQT) of Bi$_2$Sr$_2$CaCu$_2$O$_y$ intrinsic Josephson junctions (IJJs) with two device structures. One is a nanometer-thick small mesa structure with only two or three IJJs and the other is a stack of a few hundreds of IJJs on a narrow bridge structure. Experimental results of switching current distribution for the first switching events from zero-voltage state showed a good agreement with the conventional theory for a single Josephson junction, indicating that a crossover temperature from thermal activation to MQT regime for the former device structure was as high as that for the latter device structure. Together with the observation of multiphoton transitions between quantized energy levels in MQT regime, these results strongly suggest that the observed MQT behavior is intrinsic to a single IJJ in high-$T_c$ cuprates, independent of device structures. The switching current distribution for the second switching events from the first resistive state, which were carefully distinguished from the first switchings, was also compared between two device structures. In spite of the difference in the heat transfer environment, the second switching events for both devices were found to show a similar temperature-independent behavior up to a much higher temperature than the crossover temperature for the first switching. We argue that it cannot be explained in terms of the self-heating owing to dissipative currents after the first switching. As possible candidates, the MQT process for the second switching and the effective increase of electronic temperature due to quasiparticle injection are discussed.Comment: 10pages, 7figures, submitted to Phys. Rev.

Muon-spin-relaxation and magnetic-susceptibility studies of effects of the magnetic impurity Ni on the Cu-spin dynamics and superconductivity in La_2-x_Sr_x_Cu_1-y_Ni_y_O_4_ with x = 0.13

Effects of the magnetic impurity Ni on the Cu-spin dynamics and superconductivity have been studied in La_2-x_Sr_x_Cu_1-y_Ni_y_O_4_ with x = 0.13 changing y finely up to 0.10. Compared with the case of the nonmagnetic impurity Zn, it has been found from the muon-spin-relaxation measurements that a large amount of Ni is required to stabilize a magnetic order of Cu spins. However, the evolution toward the stabilization of the magnetic order with increasing impurity concentration is qualitatively similar to each other. The area of the non-superconducting and slowly fluctuating or static region of Cu spins around Ni has been found to be smaller than that around Zn, suggesting that the pinning of rather long-ranged dynamical spin correlation such as the so-called dynamical stripe by Ni is weaker than that by Zn. This may be the reason why Zn destroys the superconductivity in the hole-doped high-T_c_ cuprates more markedly than Ni.Comment: 4 pages, 4 figures, accepted for publication in Phys. Rev.

The p38α MAPK Regulates Microglial Responsiveness to Diffuse Traumatic Brain Injury

Neuropathology after traumatic brain injury (TBI) is the result of both the immediate impact injury and secondary injury mechanisms. Unresolved post-traumatic glial activation is a secondary injury mechanism that contributes to a chronic state of neuroinflammation in both animal models of TBI and human head injury patients. We recently demonstrated, using in vitro models, that p38α MAPK signaling in microglia is a key event in promoting cytokine production in response to diverse disease-relevant stressors and subsequent inflammatory neuronal dysfunction. From these findings, we hypothesized that the p38α signaling pathway in microglia could be contributing to the secondary neuropathologic sequelae after a diffuse TBI. Mice where microglia were p38α-deficient (p38α KO) were protected against TBI-induced motor deficits and synaptic protein loss. In wild-type (WT) mice, diffuse TBI produced microglia morphological activation that lasted for at least 7 d; however, p38α KO mice failed to activate this response. Unexpectedly, we found that the peak of the early, acute phase cytokine and chemokine levels was increased in injured p38α KO mice compared with injured WT mice. The increased cytokine levels in the p38α KO mice could not be accounted for by more infiltration of macrophages or neutrophils, or increased astrogliosis. By 7 d after injury, the cytokine and chemokine levels remained elevated in injured WT mice but not in p38α KO mice. Together, these data suggest that p38α balances the inflammatory response by acutely attenuating the early proinflammatory cytokine surge while perpetuating the chronic microglia activation after TBI

Quantum Disordered Regime and Spin Gap in the Cuprate Superconductors

We discuss the crossover from the quantum critical, $z\!=\!1$, to the quantum disordered regime in high-T$_c$ materials in relation to the experimental data on the nuclear relaxation, bulk susceptibility, and inelastic neutron scattering. In our scenario, the spin excitations develop a gap $\Delta\!\sim\!1/\xi$ well above T$_c$, which is supplemented by the quasiparticle gap below T$_c$. The above experiments yield consistent estimates for the value of the spin gap, which increases as the correlation length decreases.Comment: 14 pages, REVTeX v3.0, PostScript file for 3 figures is attached, UIUC-P-93-07-06

Intracranial aneurismal pulsatility as a new individual criterion for rupture risk evaluation: Biomechanical and numerical approach (IRRAs project).

International audienceThis study was designed to highlight by means of numerical simulations, the correlation between aneurism sac pulsatility and the risk of rupture through the mechanical properties of the wall. In accordance to previous work suggesting a correlation between the risk of rupture and the material properties of cerebral aneurysms, twelve fluid-structure interaction (FSI) computations were performed on 12 "patient-specific" cases, corresponding to typical shapes and locations of cerebral aneurysms. The variations of the aneurismal volume during the cardiac cycle (3V) are compared using wall material characteristics of either degraded and non-degraded tissues. Aneurysms were located on 7 different arteries: Middle Cerebral Artery (4), Anterior Cerebral Artery (3), Internal Carotid Artery (1), Vertebral Artery (1), Ophthalmic Artery (1) and Basilar Artery (1). Aneurysms presented different shapes (uniform or multi-lobulated) and diastolic volumes (from 18 to 392 mm3). The pulsatility (3V/V) was significantly larger for a soft aneurismal material (average of 26 %) than for a stiff material (average of 4 %). The difference between 3V, for each condition, was statistically significant: p = 0.005. The difference in aneurismal pulsatility as highlighted in this work might be a relevant patientspecific predictor of aneurysm risk of rupture

Cu Nuclear Quadrupole Resonance Study of the Spin-Peierls Compound Cu1-xMgxGeO3: A Possibility of Precursory Dimerization

We report on a zero-field 63Cu nuclear quadrupole resonance (NQR) study of nonmagnetic Mg impurity substituted Cu1-xMgxGeO3 (single crystals; the spin-Peierls transition temperature Tsp~14, 13.5, and 11 K for x=0, 0.0043, and 0.020) in a temperature range from 4.2 K to 250 K. We found that below T*~77 K, Cu NQR spectra are broadened and nonexponential Cu nuclear spin-lattice relaxation increases for undoped and more remarkably for Mg-doped samples. The results indicate that random lattice distortion and impurity-induced spins appear below T*, which we associate with a precursor of the spin-Peierls transition. Conventional magnetic critical slowing down does not appear down to 4.2 K below Tsp.Comment: 4 pages, 4 figure

Ni-substituted sites and the effect on Cu electron spin dynamics of YBa2Cu{3-x}NixO{7-\delta}

We report Cu nuclear quadrupole resonance experiment on magnetic impurity Ni-substituted YBa$_2$Cu$_{3-x}$Ni$_x$O$_{7-\delta}$. The distribution of Ni-substituted sites and its effect on the Cu electron spin dynamics are investigated. Two samples with the same Ni concentration $x$=0.10 and nearly the same oxygen content but different $T_c$'s were prepared: One is an as-synthesized sample (7-$\delta$=6.93) in air ($T_c$$\approx 80 K$), and the other is a quenched one (7-$\delta$=6.92) in a reduced oxygen atmosphere ($T_c$$\approx 70 K$). The plane-site $^{63}$Cu(2) nuclear spin-lattice relaxation for the quenched sample was faster than that for the as-synthesized sample, in contrast to the $^{63}$Cu(1) relaxation that was faster for the as-synthesized sample. This indicates that the density of plane-site Ni(2) is higher in the quenched sample, contrary to the chain-site Ni(1) density which is lower in the quenched sample. From the analysis in terms of the Ni-induced nuclear spin-lattice relaxation, we suggest that the primary origin of suppression of $T_c$ is associated with nonmagnetic depairing effect of the plane-site Ni(2).Comment: 7 pages, 5 figure

Intraoperative assessment of biliary anatomy for prevention of bile duct injury: a review of current and future patient safety interventions

Background Bile duct injury (BDI) is a dreaded complication of cholecystectomy, often caused by misinterpretation of biliary anatomy. To prevent BDI, techniques have been developed for intraoperative assessment of bile duct anatomy. This article reviews the evidence for the different techniques and discusses their strengths and weaknesses in terms of efficacy, ease, and cost-effectiveness. Method PubMed was searched from January 1980 through December 2009 for articles concerning bile duct visualization techniques for prevention of BDI during laparoscopic cholecystectomy. Results Nine techniques were identified. The critical-view-of-safety approach, indirectly establishing biliary anatomy, is accepted by most guidelines and commentaries as the surgical technique of choice to minimize BDI risk. Intraoperative cholangiography is associated with lower BDI risk (OR 0.67, CI 0.61-0.75). However, it incurs extra costs, prolongs the operative procedure, and may be experienced as cumbersome. An established reliable alternative is laparoscopic ultrasound, but its longer learning curve limits widespread implementation. Easier to perform are cholecystocholangiography and dye cholangiography, but these yield poor-quality images. Light cholangiography, requiring retrograde insertion of an optical fiber into the common bile duct, is too unwieldy for routine use. Experimental techniques are passive infrared cholangiography, hyperspectral cholangiography, and near-infrared fluorescence cholangiography. The latter two are performed noninvasively and provide real-time images. Quantitative data in patients are necessary to further evaluate these techniques. Conclusions The critical-view-of-safety approach should be used during laparoscopic cholecystectomy. Intraoperative cholangiography or laparoscopic ultrasound is recommended to be performed routinely. Hyperspectral cholangiography and near-infrared fluorescence cholangiography are promising novel techniques to prevent BDI and thus increase patient safety

PATRIC, the bacterial bioinformatics database and analysis resource

The Pathosystems Resource Integration Center (PATRIC) is the all-bacterial Bioinformatics Resource Center (BRC) (http://www.patricbrc.org). A joint effort by two of the original National Institute of Allergy and Infectious Diseases-funded BRCs, PATRIC provides researchers with an online resource that stores and integrates a variety of data types [e.g. genomics, transcriptomics, protein-protein interactions (PPIs), three-dimensional protein structures and sequence typing data] and associated metadata. Datatypes are summarized for individual genomes and across taxonomic levels. All genomes in PATRIC, currently more than 10 000, are consistently annotated using RAST, the Rapid Annotations using Subsystems Technology. Summaries of different data types are also provided for individual genes, where comparisons of different annotations are available, and also include available transcriptomic data. PATRIC provides a variety of ways for researchers to find data of interest and a private workspace where they can store both genomic and gene associations, and their own private data. Both private and public data can be analyzed together using a suite of tools to perform comparative genomic or transcriptomic analysis. PATRIC also includes integrated information related to disease and PPIs. All the data and integrated analysis and visualization tools are freely available. This manuscript describes updates to the PATRIC since its initial report in the 2007 NAR Database Issu