Public Investment, Government Indebtedness and Transitional Dynamics

This paper considers an endogenous growth model with public capital and government debt. In setting the level of public investment each period, the government is assumed to follow two commonly used in the growth literature fiscal rules: public investment is either equal to a constant fraction of output or equal to a constant share of tax revenues. In our model, we allow revenues to be raised by the government through progressive income taxation and bonds issue. For both fiscal rules, we show that the potential occurrence of either indeterminacy or instability crucially depends on whether the government is a debtor or a creditor. In particular, government indebtedness causes the economy to be prone to either belief-driven aggregate fluctuations or unstable dynamics. This is a novel result in the related literature which has largely overlooked the role of public debt as a possible contributing factor to the presence of indeterminacy and instability in growth models

Oriented polaritons in strongly-coupled asymmetric double quantum well microcavities

Replacing independent single quantum wells inside a strongly-coupled semiconductor microcavity with double quantum wells produces a special type of polariton. Using asymmetric double quantum wells in devices processed into mesas allows the alignment of the electron levels to be voltage-tuned. At the resonant electronic tunnelling condition, we demonstrate that `oriented polaritons' are formed, which possess greatly enhanced dipole moments. Since the polariton-polariton scattering rate depends on this dipole moment, such devices could reach polariton lasing, condensation and optical nonlinearities at much lower threshold powers.Comment: 3 figure

On Central Bank Transparency, Independence and Public Debt Policy

In this paper we examine the case of partial central bank transparency and the interaction between public debt management and the design of monetary institutions. In particular, we establish a relationship between central bank transparency and nominal debt and find that it depends on whether the public has (ex-ante) under or overestimated the preferences of the central banker. Furthermore, we analytically examine the relationship between central bank transparency and central bank conservativeness and find it positive

On Central Bank Transparency, Independence and Public Debt Policy

In this paper we examine the case of partial central bank transparency and the interaction between public debt management and the design of monetary institutions. In particular, we establish a relationship between central bank transparency and nominal debt and find that it depends on whether the public has (ex-ante) under or overestimated the preferences of the central banker. Furthermore, we analytically examine the relationship between central bank transparency and central bank conservativeness and find it positive

Polariton Condensate Transistor Switch

A polariton condensate transistor switch is realized through optical excitation of a microcavity ridge with two beams. The ballistically ejected polaritons from a condensate formed at the source are gated using the 20 times weaker second beam to switch on and off the flux of polaritons. In the absence of the gate beam the small built-in detuning creates potential landscape in which ejected polaritons are channelled toward the end of the ridge where they condense. The low loss photon-like propagation combined with strong nonlinearities associated with their excitonic component makes polariton based transistors particularly attractive for the implementation of all-optical integrated circuits

Lasing threshold doubling at the crossover from strong to weak coupling regime in GaAs microcavity

In a polariton, laser coherent monochromatic light is produced by a low-energy state of the system at the bottom of a polariton ‘trap’, where a condensate of polaritons is formed, requiring no conventional population inversion. Following the recent realization of polariton light-emitting diodes (LEDs) based on GaAs microcavities (MCs) operating up to room temperature, efforts have been directed towards the demonstration of an electrically injected polariton laser. However, until now, low-threshold polariton lasing in GaAs MCs under optical pumping has been reported only at low temperatures. Here, we investigate the temperature dependence of lasing threshold across the border of the strong-to-weak coupling regime transition in high-finesse GaAs MCs under non-resonant optical pumping. Remarkably, we find that although lasing in the strong coupling regime is lost when the temperature is raised from 25 to 70 K, the threshold only doubles, in stark contrast with the expected difference of two orders of magnitude. Our results can be explained by considering temperatureinduced thermalization of carriers to high wavevector states, increasing the reservoir’s overall carrier lifetime, resulting in an order of magnitude higher steady-state carrier density at 70 K under similar pumping conditions

Hybrid organic-inorganic polariton laser

Organic materials exhibit exceptional room temperature light emitting characteristics and enormous exciton oscillator strength, however, their low charge carrier mobility prevent their use in high-performance applications such as electrically pumped lasers. In this context, ultralow threshold polariton lasers, whose operation relies on Bose-Einstein condensation of polaritons - part-light part-matter quasiparticles, are highly advantageous since the requirement for high carrier injection no longer holds. Polariton lasers have been successfully implemented using inorganic materials owing to their excellent electrical properties, however, in most cases their relatively small exciton binding energies limit their operation temperature. It has been suggested that combining organic and inorganic semiconductors in a hybrid microcavity, exploiting resonant interactions between these materials would permit to dramatically enhance optical nonlinearities and operation temperature. Here, we obtain cavity mediated hybridization of GaAs and J-aggregate excitons in the strong coupling regime under electrical injection of carriers as well as polariton lasing up to 200 K under non-resonant optical pumping. Our demonstration paves the way towards realization of hybrid organic-inorganic microcavities which utilise the organic component for sustaining high temperature polariton condensation and efficient electrical injection through inorganic structure

Spontaneous spin bifurcations and ferromagnetic phase transitions in a spinor exciton-polariton condensate

We observe a spontaneous parity breaking bifurcation to a ferromagnetic state in a spatially trapped exciton-polariton condensate. At a critical bifurcation density under nonresonant excitation, the whole condensate spontaneously magnetizes and randomly adopts one of two elliptically polarized (up to 95% circularly-polarized) states with opposite handedness of polarization. The magnetized condensate remains stable for many seconds at 5 K, but at higher temperatures it can flip from one magnetic orientation to another. We optically address these states and demonstrate the inversion of the magnetic state by resonantly injecting 100-fold weaker pulses of opposite spin. Theoretically, these phenomena can be well described as spontaneous symmetry breaking of the spin degree of freedom induced by different loss rates of the linear polarizations.This work was supported by Grants EPSRC No. EP/G060649/1, EU No. CLERMONT4 235114, EU No. INDEX 289968, Spanish MEC (MAT2008-01555), Greek GSRT ARISTEIA Apollo program and Fundación La Caixa, and Mexican CONACYT No. 251808. FP acknowledges financial support through an EPSRC doctoral prize fellowship at the University of Cambridge and a Schrödinger fellowship at the University of Oxford.This is the final version of the article. It first appeared from the American Physical Society via http://dx.doi.org/10.1103/PhysRevX.5.03100

Impact of a Novel Adaptive Optimization Algorithm on 30-Day Readmissions Evidence From the Adaptive CRT Trial

AbstractObjectivesThis study investigated the impact of the Medtronic AdaptivCRT (aCRT) (Medtronic, Mounds View, Minnesota) algorithm on 30-day readmissions after heart failure (HF) and all-cause index hospitalizations.BackgroundThe U.S. Hospital Readmission Reduction Program, which includes a focus on HF, reduces Medicare inpatient payments when readmissions within 30 days of discharge exceed a moving threshold based on national averages and hospital-specific risk adjustments. Internationally, readmissions within 30 days of any discharge may attract reduced or no payment. Recently, cardiac resynchronization therapy (CRT) devices equipped with the aCRT algorithm allowing automated ambulatory device programming were introduced. The Adaptive CRT trial demonstrated the algorithm’s safety and comparable outcome against a rigorous echocardiography-based optimization protocol.MethodsWe analyzed data from the Adaptive CRT trial, which randomized patients undergoing CRT defibrillation on a 2:1 basis to aCRT (n = 318) or to CRT with echocardiographic optimization (Echo, n = 160) and followed up these patients for a mean of 20.2 months (range: 0.2 to 31.3 months). Logistic regression with generalized estimating equation methodology was used to compare the proportion of patients hospitalized for HF and for all causes who had a readmission within 30 days.ResultsFor HF hospitalizations, the 30-day readmission rate was 19.1% (17 of 89) in the aCRT group and 35.7% (15 of 42) in the Echo group (odds ratio: 0.41; 95% confidence interval [CI]: 0.19 to 0.86; p = 0.02). For all-cause hospitalization, the 30-day readmission rate was 14.8% (35 of 237) in the aCRT group compared with 24.8% (39 of 157) in the Echo group (odds ratio: 0.54; 95% CI: 0.31 to 0.94; p = 0.03). The risk of readmission after HF or all-cause index hospitalization with aCRT was also significantly reduced beyond 30 days.ConclusionsUse of the aCRT algorithm is associated with a significant reduction in the probability of a 30-day readmission after both HF and all-cause hospitalizations. (Adaptive Cardiac Resynchronization Therapy Study [aCRT]; NCT00980057