Quantum bistability and spin current shot noise of a single quantum dot coupled to an optical microcavity

Here we explore spin dependent quantum transport through a single quantum dot coupled to an optical microcavity. The spin current is generated by electron tunneling between a single doped reservoir and the dot combined with intradot spin flip transitions induced by a quantized cavity mode. In the limit of strong Coulomb blockade, this model is analogous to the Jaynes-Cummings model in quantum optics and generates a pure spin current in the absence of any charge current. Earlier research has shown that in the classical limit where a large number of such dots interact with the cavity field, the spin current exhibits bistability as a function of the laser amplitude that drives the cavity. We show that in the limit of a single quantum dot this bistability continues to be present in the intracavity photon statistics. Signatures of the bistable photon statistics manifest themselves in the frequency dependent shot noise of the spin current despite the fact that the quantum mechanical average spin current no longer exhibits bistability. Besides having significance for future quantum dot based optoelectronic devices, our results shed light on the relation between bistability, which is traditionally viewed as a classical effect, and quantum mechanics

Sagnac Rotational Phase Shifts in a Mesoscopic Electron Interferometer with Spin-Orbit Interactions

The Sagnac effect is an important phase coherent effect in optical and atom interferometers where rotations of the interferometer with respect to an inertial reference frame result in a shift in the interference pattern proportional to the rotation rate. Here we analyze for the first time the Sagnac effect in a mesoscopic semiconductor electron interferometer. We include in our analysis Rashba spin-orbit interactions in the ring. Our results indicate that spin-orbit interactions increase the rotation induced phase shift. We discuss the potential experimental observability of the Sagnac phase shift in such mesoscopic systems

Theory of High-Force DNA Stretching and Overstretching

Single molecule experiments on single- and double stranded DNA have sparked a renewed interest in the force-extension of polymers. The extensible Freely Jointed Chain (FJC) model is frequently invoked to explain the observed behavior of single-stranded DNA. We demonstrate that this model does not satisfactorily describe recent high-force stretching data. We instead propose a model (the Discrete Persistent Chain, or ``DPC'') that borrows features from both the FJC and the Wormlike Chain, and show that it resembles the data more closely. We find that most of the high-force behavior previously attributed to stretch elasticity is really a feature of the corrected entropic elasticity; the true stretch compliance of single-stranded DNA is several times smaller than that found by previous authors. Next we elaborate our model to allow coexistence of two conformational states of DNA, each with its own stretch and bend elastic constants. Our model is computationally simple, and gives an excellent fit through the entire overstretching transition of nicked, double-stranded DNA. The fit gives the first values for the elastic constants of the stretched state. In particular we find the effective bend stiffness for DNA in this state to be about 10 nm*kbt, a value quite different from either B-form or single-stranded DNAComment: 33 pages, 11 figures. High-quality figures available upon reques

Left ventricular assist device (LVAD) enables survival during 7 h of sustained ventricular fibrillation

We describe the case of a patient implanted with a DeBakey left ventricular assist device (LVAD) as bridge to transplant who survived 7 h of ventricular fibrillation. He was successfully converted into a stable sinus rhyth

Antimicrobial Transformation Products in the Aquatic Environment: Global Occurrence, Ecotoxicological Risks, and Potential of Antibiotic Resistance

The global spread of antimicrobial resistance (AMR) isconcerningfor the health of humans, animals, and the environment in a One Healthperspective. Assessments of AMR and associated environmental hazardsmostly focus on antimicrobial parent compounds, while largely overlookingtheir transformation products (TPs). This review lists antimicrobialTPs identified in surface water environments and examines their potentialfor AMR promotion, ecological risk, as well as human health and environmentalhazards using in silico models. Our review also summarizesthe key transformation compartments of TPs, related pathways for TPsreaching surface waters and methodologies for studying the fate ofTPs. The 56 antimicrobial TPs covered by the review were prioritizedvia scoring and ranking of various risk and hazard parameters. Mostdata on occurrences to date have been reported in Europe, while littleis known about antibiotic TPs in Africa, Central and South America,Asia, and Oceania. Occurrence data on antiviral TPs and other antibacterialTPs are even scarcer. We propose evaluation of structural similaritybetween parent compounds and TPs for TP risk assessment. We predicteda risk of AMR for 13 TPs, especially TPs of tetracyclines and macrolides.We estimated the ecotoxicological effect concentrations of TPs fromthe experimental effect data of the parent chemical for bacteria,algae and water fleas, scaled by potency differences predicted byquantitative structure-activity relationships (QSARs) for baselinetoxicity and a scaling factor for structural similarity. Inclusionof TPs in mixtures with their parent increased the ecological riskquotient over the threshold of one for 7 of the 24 antimicrobialsincluded in this analysis, while only one parent had a risk quotientabove one. Thirteen TPs, from which 6 were macrolide TPs, posed arisk to at least one of the three tested species. There were 12/21TPs identified that are likely to exhibit a similar or higher levelof mutagenicity/carcinogenicity, respectively, than their parent compound,with tetracycline TPs often showing increased mutagenicity. Most TPswith increased carcinogenicity belonged to sulfonamides. Most of theTPs were predicted to be mobile but not bioaccumulative, and 14 werepredicted to be persistent. The six highest-priority TPs originatedfrom the tetracycline antibiotic family and antivirals. This review,and in particular our ranking of antimicrobial TPs of concern, cansupport authorities in planning related intervention strategies andsource mitigation of antimicrobials toward a sustainable future

Normalization of high pulmonary vascular resistance with LVAD support in heart transplantation candidates

Objective: Pulmonary hypertension (PH) and elevated pulmonary vascular resistance (PVR) lead to poor outcome after heart transplantation due to postoperative failure of the non-conditioned right ventricle. The role of continuous flow left ventricular assist device (LVAD) support in the reduction of elevated PVR was evaluated in a series of clinical implants. Methods: Among 17 patients with terminal heart failure receiving a MicroMed DeBakey LVAD as bridge to transplant, there were six patients with pulmonary hypertension (mean systolic PAP 47mmHg) and high PVR (398dynes/cm5), previously not considered suitable for heart transplantation, who underwent serial right heart catheters during their LVAD support period. Results: In these patients mean systolic pulmonary pressure dropped to 29mmHg and PVR decreased to a mean 167dynes/cm5 under LVAD support. Clinical improvement was significant in all patients. Four patients were successfully transplanted without major postoperative difficulties (mean duration 130 days support) and all are doing well to date. Post-transplant-PVR remained in the normal range in all transplanted patients. Conclusions: Elevated PVR and severe PH were both previously considered as contraindication for heart transplantation. A period of LVAD pumping leads to a progressive decrease of PVR and normalization of pulmonary pressures, making these patients amenable for heart transplantation. LVAD as bridge to heart transplantation is safe and highly beneficial for terminal heart failure patients with severe P

Semiclassical form factor for spectral and matrix element fluctuations of multi-dimensional chaotic systems

We present a semiclassical calculation of the generalized form factor which characterizes the fluctuations of matrix elements of the quantum operators in the eigenbasis of the Hamiltonian of a chaotic system. Our approach is based on some recently developed techniques for the spectral form factor of systems with hyperbolic and ergodic underlying classical dynamics and f=2 degrees of freedom, that allow us to go beyond the diagonal approximation. First we extend these techniques to systems with f>2. Then we use these results to calculate the generalized form factor. We show that the dependence on the rescaled time in units of the Heisenberg time is universal for both the spectral and the generalized form factor. Furthermore, we derive a relation between the generalized form factor and the classical time-correlation function of the Weyl symbols of the quantum operators.Comment: some typos corrected and few minor changes made; final version in PR

Incidence and pathophysiology of atrioventricular block following mitral valve replacement and ring annuloplasty

Background: In this retrospective study we evaluate the causative mechanisms underlying postoperative atrioventricular block (AVB) following mitral valve replacement and mitral valve annuloplasty. Methods: Between January 1990 and December 2003, 391 patients underwent mitral valve replacement or ring annuloplasty and quadrangular resection. Exclusion criteria were preoperative AV block, two or three valvular procedures, reoperations and procedures combined with coronary artery bypass grafting. The presence of the postoperative AVB was compared with preoperative and intraoperative variables. On 55 post-mortem specimens the relationship between the AV node, AV node artery and mitral valve annulus was investigated. Results: The mean age was 59±14 years and 44% of patients were female. Postoperatively AVB occurred in 92 (23.5%) patients. AVB III was found in 17 (4%) patents, in whom a pacemaker was implanted within median interval of 4 days. Second degree AVB occurred and first degree AVB in five (1.3%) and in 70 (18%) patients respectively. In dry dissected human hearts in 23% of investigated cases the AV node artery was discovered to run close to the annulus of the mitral valve. Conclusions: Data collected in this study showed that, sotalol and amiodarone as well as a prolonged cross-clamp time may slightly influence the 23% incidence of postoperative AVB. The morphological investigation showed that the AV node artery runs in close proximity to the annulus in 23% of cases. We speculate that damage of the AV node artery may play a role in development of AV