81 research outputs found
Signatures of Inelastic Scattering in Coulomb-Blockade Quantum Dots
We calculate the finite-temperature conductance peak-height distributions in
Coublomb-blockade quantum dots in the limit where the inelastic scattering rate
in the dot is large compared with the mean elastic tunneling rate. The relative
reduction of the standard deviation of the peak-height distribution by a
time-reversal symmetry-breaking magnetic field, which is essentially
temperature-independent in the elastic limit, is enhanced by the inclusion of
inelastic scattering at finite temperature. We suggest this quantity as an
independent experimental probe for inelastic scattering in closed dots.Comment: 4 pages, 3 eps figures, revtex
Linear conductance in Coulomb-blockade quantum dots in the presence of interactions and spin
We discuss the calculation of the linear conductance through a
Coulomb-blockade quantum dot in the presence of interactions beyond the
charging energy. In the limit where the temperature is large compared with a
typical tunneling width, we use a rate-equations approach to describe the
transitions between the corresponding many-body states. We discuss both the
elastic and rapid-thermalization limits, where the rate of inelastic scattering
in the dot is either small or large compared with the elastic transition rate,
respectively. In the elastic limit, we find several cases where a closed
solution for the conductance is possible, including the case of a constant
exchange interaction. In the rapid-thermalization limit, a closed solution is
possible in the general case. We show that the corresponding expressions for
the linear conductance simplify for a Hamiltonian that is invariant under spin
rotations.Comment: 11 pages, no figures, revtex
Non-Centrosymmetric Heavy-Fermion Superconductors
In this chapter we discuss the physical properties of a particular family of
non-centrosymmetric superconductors belonging to the class heavy-fermion
compounds. This group includes the ferromagnet UIr and the antiferromagnets
CeRhSi3, CeIrSi3, CeCoGe3, CeIrGe3 and CePt3Si, of which all but CePt3Si become
superconducting only under pressure. Each of these superconductors has
intriguing and interesting properties. We first analyze CePt3Si, then review
CeRhSi3, CeIrSi3, CeCoGe3 and CeIrGe3, which are very similar to each other in
their magnetic and electrical properties, and finally discuss UIr. For each
material we discuss the crystal structure, magnetic order, occurrence of
superconductivity, phase diagram, characteristic parameters, superconducting
properties and pairing states. We present an overview of the similarities and
differences between all these six compounds at the end.Comment: To appear in "Non-Centrosymmetric Superconductors: Introduction and
Overview", Lecture Notes in Physics 847, edited by E. Bauer and M. Sigrist
(Springer-Verlag, Berlin Heidelberg, 2012) Chap. 2, pp. 35-7
A Solvable Regime of Disorder and Interactions in Ballistic Nanostructures, Part I: Consequences for Coulomb Blockade
We provide a framework for analyzing the problem of interacting electrons in
a ballistic quantum dot with chaotic boundary conditions within an energy
(the Thouless energy) of the Fermi energy. Within this window we show that the
interactions can be characterized by Landau Fermi liquid parameters. When ,
the dimensionless conductance of the dot, is large, we find that the disordered
interacting problem can be solved in a saddle-point approximation which becomes
exact as (as in a large-N theory). The infinite theory shows a
transition to a strong-coupling phase characterized by the same order parameter
as in the Pomeranchuk transition in clean systems (a spontaneous
interaction-induced Fermi surface distortion), but smeared and pinned by
disorder. At finite , the two phases and critical point evolve into three
regimes in the plane -- weak- and strong-coupling regimes separated
by crossover lines from a quantum-critical regime controlled by the quantum
critical point. In the strong-coupling and quantum-critical regions, the
quasiparticle acquires a width of the same order as the level spacing
within a few 's of the Fermi energy due to coupling to collective
excitations. In the strong coupling regime if is odd, the dot will (if
isolated) cross over from the orthogonal to unitary ensemble for an
exponentially small external flux, or will (if strongly coupled to leads) break
time-reversal symmetry spontaneously.Comment: 33 pages, 14 figures. Very minor changes. We have clarified that we
are treating charge-channel instabilities in spinful systems, leaving
spin-channel instabilities for future work. No substantive results are
change
Exchange and the Coulomb blockade: Peak height statistics in quantum dots
We study the effect of the exchange interaction on the Coulomb blockade peak
height statistics in chaotic quantum dots. Because exchange reduces the level
repulsion in the many body spectrum, it strongly affects the fluctuations of
the peak conductance at finite temperature. We find that including exchange
substantially improves the description of the experimental data. Moreover, it
provides further evidence of the presence of high spin states (S>1) in such
systems.Comment: 5 pages, 4 figures. Published version, title change
SPL7013 Gel (VivaGel®) Retains Potent HIV-1 and HSV-2 Inhibitory Activity following Vaginal Administration in Humans
SPL7013 Gel (VivaGel®) is a microbicide in development for prevention of HIV and HSV. This clinical study assessed retention and duration of antiviral activity following vaginal administration of 3% SPL7013 Gel in healthy women. Participants received 5 single doses of product with ≥5 days between doses. A cervicovaginal fluid (CVF) sample was collected using a SoftCup™ pre-dose, and immediately, or 1, 3, 12 or 24 h post-dose. HIV-1 and HSV-2 antiviral activities of CVF samples were determined in cell culture assays. Antiviral activity in the presence of seminal plasma was also tested. Mass and concentration of SPL7013 in CVF samples was determined. Safety was assessed by reporting of adverse events. Statistical analysis was performed using the Wilcoxon signed-rank test with Bonferroni adjustment; p≤0.003 was significant. Eleven participants completed the study. Inhibition of HIV-1 and HSV-2 by pre-dose CVF samples was negligible. CVF samples obtained immediately after dosing almost completely inhibited (median, interquartile range) HIV-1 [96% (95,97)] and HSV-2 [86% (85,94)], and activity was maintained in all women at 3 h (HIV-1 [96% (95,98), p = 0.9]; HSV-2 [94% (91,97), p = 0.005]). At 24 h, >90% of initial HIV-1 and HSV-2 inhibition was maintained in 6/11 women. SPL7013 was recovered in CVF samples obtained at baseline (46% of 105 mg dose). At 3 and 24 h, 22 mg and 4 mg SPL7013, respectively, were recovered. More than 70% inhibition of HIV-1 and HSV-2 was observed if there was >0.5 mg SPL7013 in CVF samples. High levels of antiviral activity were retained in the presence of seminal plasma. VivaGel was well tolerated with no signs or symptoms of vaginal, vulvar or cervical irritation reported. Potent antiviral activity was observed against HIV-1 and HSV-2 immediately following vaginal administration of VivaGel, with activity maintained for at least 3 h post-dose. The data provide evidence of antiviral activity in a clinical setting, and suggest VivaGel could be administered up to 3 h before coitus
Burden and risk factors for Pseudomonas aeruginosa community-acquired pneumonia:a Multinational Point Prevalence Study of Hospitalised Patients
Pseudornonas aeruginosa is a challenging bacterium to treat due to its intrinsic resistance to the antibiotics used most frequently in patients with community-acquired pneumonia (CAP). Data about the global burden and risk factors associated with P. aeruginosa-CAP are limited. We assessed the multinational burden and specific risk factors associated with P. aeruginosa-CAP.
We enrolled 3193 patients in 54 countries with confirmed diagnosis of CAP who underwent microbiological testing at admission. Prevalence was calculated according to the identification of P. aeruginosa. Logistic regression analysis was used to identify risk factors for antibiotic-susceptible and antibiotic-resistant P. aeruginosa-CAP.
The prevalence of P. aeruginosa and antibiotic-resistant P. aeruginosa-CAP was 4.2% and 2.0%, respectively. The rate of P. aeruginosa CAP in patients with prior infection/colonisation due to P. aeruginosa and at least one of the three independently associated chronic lung diseases (i.e. tracheostomy, bronchiectasis and/or very severe chronic obstructive pulmonary disease) was 67%. In contrast, the rate of P. aeruginosa-CAP was 2% in patients without prior P. aeruginosa infection/colonisation and none of the selected chronic lung diseases. The multinational prevalence of P. aeruginosa-CAP is low.
The risk factors identified in this study may guide healthcare professionals in deciding empirical antibiotic coverage for CAP patients
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