6,133 research outputs found
Intrinsic Josephson Effect and Violation of the Josephson Relation in Layered Superconductors
Equations describing the resistive state of a layered superconductor with
anisotropic pairing are derived. The similarity with a stack of Josephson
junctions is found at small voltages only, when current density in the
direction perpendicular to the layers can be interpreted as a sum of the
Josephson superconducting, the Ohmic dissipative and the interference currents.
In the spatially uniform state differential conductivity at higher voltages
becomes negative. Nonuniformity of the current distribution generates the
branch imbalance and violates the Josephson relation between frequency and
voltage.Comment: 11 pages, no figures, revtex, to be published in Phys. Rev. Let
Linear response and collective oscillations in superconductors with d-wave pairing
Simple and physically transparent equations for the linear response of
layered superconductors with d-wave symmetry of the order parameter are derived
by means of the quasiclassic kinetic theory of superconductivity. Responses to
solenoidal and potential electric fields have different frequency dependencies.
The conductivity describing the response to the solenoidal field is limited by
the momentum relaxation, like in a normal metal. The response to the potential
electric field depends, in addition, on the branch imbalance relaxation rate.
The damping of plasma oscillations of superconducting electrons is determined
by dielectric relaxation and is small. Relaxation of branch imbalance
determined by elastic scattering is large enough to make the Carlson-Goldman
mode in d-wave superconductors overdamped.Comment: 11 pages, latex, no figures, submitted to Physical Review
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Evolution of the charge carrier plasmon in the one-dimensional metal TTF-TCNQ as a function of temperature and momentum
We have investigated the charge carrier plasmon in the quasi one-dimensional metal TTF-TCNQ using electron energy-loss spectroscopy. Our data reveal a negative plasmon dispersion with a slope that is independent of temperature, which is in agreement to predictions from model calculations and previous room temperature data. A plasmon energy shift upon temperature is observed, and we discuss possible contributions to this shift. The spectral width of the plasmon is rather temperature independent, but increases clearly above a momentum value of about 0.3 Å-1
Josephson effect in point contacts between ''f-wave'' superconductors
A stationary Josephson effect in point contacts between triplet
superconductors is analyzed theoretically for most probable models of the order
parameter in UPt_{3} and Sr_{2}RuO_{4}. The consequence of misorientation of
crystals in superconducting banks on this effect is considered. We show that
different models for the order parameter lead to quite different current-phase
dependences. For certain angles of misorientation a boundary between
superconductors can generate the parallel to surface spontaneous current. In a
number of cases the state with a zero Josephson current and minimum of the free
energy corresponds to a spontaneous phase difference. This phase difference
depends on the misorientation angle and may possess any value. We conclude that
experimental investigations of the current-phase dependences of small junctions
can be used for determination of the order parameter symmetry in the mentioned
above superconductors.Comment: 11 pages, 8 figure
Thermally Assisted Penetration and Exclusion of Single Vortex in Mesoscopic Superconductors
A single vortex overcoming the surface barrier in a mesoscopic superconductor
with lateral dimensions of several coherence lengths and thickness of several
nanometers provides an ideal platform to study thermal activation of a single
vortex. In the presence of thermal fluctuations, there is non-zero probability
for vortex penetration into or exclusion from the superconductor even when the
surface barrier does not vanish. We consider the thermal activation of a single
vortex in a mesoscopic superconducting disk of circular shape. To obtain
statistics for the penetration and exclusion magnetic fields, slow and periodic
magnetic fields are applied to the superconductor. We calculate the
distribution of the penetration and exclusion fields from the thermal
activation rate. This distribution can also be measured experimentally, which
allows for a quantitative comparison.Comment: 7 pages, 4 figure
Decorrelation estimates for the eigenlevels of the discrete Anderson model in the localized regime
The purpose of the present work is to establish decorrelation estimates for
the locally renormalized eigenvalues of the discrete Anderson model near two
distinct energies inside the localization region. In dimension one, we prove
these estimates at all energies. In higher dimensions, the energies are
required to be sufficiently far apart from each other
Augmented Cocaine Seeking in Response to Stress or CRF Delivered into the Ventral Tegmental Area Following Long-Access Self-Administration Is Mediated by CRF Receptor Type 1 But Not CRF Receptor Type 2
Stressful events are determinants of relapse in recovering cocaine addicts. Excessive cocaine use may increase susceptibility to stressor-induced relapse through alterations in brain corticotropin-releasing factor (CRF) regulation of neurocircuitry involved in drug seeking. We previously reported that the reinstatement of cocaine seeking by a stressor (footshock) is CRF dependent and is augmented in rats that self-administered cocaine under long-access (LgA; 6 h daily) conditions for 14 d when compared with rats provided shorter daily cocaine access [short access (ShA) rats; 2 h daily]. Further, we have demonstrated that reinstatement in response to intracerebroventricular CRF administration is heightened in LgA rats. This study examined the role of altered ventral tegmental area (VTA) responsiveness to CRF in intake-dependent increases in CRF- and stress-induced cocaine seeking. Bilateral intra-VTA administration of CRF (250 or 500 ng/side) produced reinstatement in LgA but not ShA rats. In LgA rats, intra-VTA CRF-induced reinstatement was blocked by administration of the CRF-receptor type 1 (CRF-R1) antagonist antalarmin (500 ng/side) or CP-376395 (500 ng/side), but not the CRF-R2 antagonist astressin-2B (500 ng or 1 μg/side) or antisauvagine-30(ASV-30; 500 ng/side) into the VTA. Likewise, intra-VTA antalarmin, but not astressin-2B, blocked footshock-induced reinstatement in LgA rats. By contrast, neither intra-VTA antalarmin nor CP-376395 altered food-reinforced lever pressing. Intra-VTA injection of the CRF-R1-selective agonist cortagine (100 ng/side) but not the CRF-R2-selective agonist rat urocortin II (rUCN II; 250 ng/side) produced reinstatement. These findings reveal that excessive cocaine use increases susceptibility to stressor-induced relapse in part by augmenting CRF-R1-dependent regulation of addiction-related neurocircuitry in the VTA
Antibiotics in early life and childhood pre-B-ALL. Reasons to analyze a possible new piece in the puzzle
Acute lymphoblastic leukemia (ALL) is the most common pediatric cancer with precursor B-cell ALL (pB-ALL) accounting for~85% of the cases. Childhood pB-ALL development is infuenced by genetic susceptibility and host immune
responses. The role of the intestinal microbiome in leukemogenesis is gaining increasing attention since Vicente-Dueñas’
seminal work demonstrated that the gut microbiome is distinct in mice genetically predisposed to ALL and that the alteration of this microbiome by antibiotics is able to trigger pB-ALL in Pax5 heterozygous mice in the absence of infectious
stimuli. In this review we provide an overview on novel insights on the role of the microbiome in normal and preleukemic hematopoiesis, infammation, the efect of dysbiosis on hematopoietic stem cells and the emerging importance of
the innate immune responses in the conversion from preleukemic to leukemic state in childhood ALL. Since antibiotics,
which represent one of the most widely used medical interventions, alter the gut microbial composition and can cause a
state of dysbiosis, this raises exciting epidemiological questions regarding the implications for antibiotic use in early life,
especially in infants with a a preleukemic “frst hit”. Sheading light through a rigorous study on this piece of the puzzle
may have broad implications for clinical practice
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