Probing the inter-layer exciton physics in a MoS2_2/MoSe2_2/MoS2_2 van der Waals heterostructure

Stacking atomic monolayers of semiconducting transition metal dichalcogenides (TMDs) has emerged as an effective way to engineer their properties. In principle, the staggered band alignment of TMD heterostructures should result in the formation of inter-layer excitons with long lifetimes and robust valley polarization. However, these features have been observed simultaneously only in MoSe$_2$/WSe$_2$ heterostructures. Here we report on the observation of long lived inter-layer exciton emission in a MoS$_2$/MoSe$_2$/MoS$_2$ trilayer van der Waals heterostructure. The inter-layer nature of the observed transition is confirmed by photoluminescence spectroscopy, as well as by analyzing the temporal, excitation power and temperature dependence of the inter-layer emission peak. The observed complex photoluminescence dynamics suggests the presence of quasi-degenerate momentum-direct and momentum-indirect bandgaps. We show that circularly polarized optical pumping results in long lived valley polarization of inter-layer exciton. Intriguingly, the inter-layer exciton photoluminescence has helicity opposite to the excitation. Our results show that through a careful choice of the TMDs forming the van der Waals heterostructure it is possible to control the circular polarization of the inter-layer exciton emission.Comment: 19 pages, 3 figures. Just accepted for publication in Nano Letters (http://pubs.acs.org/doi/10.1021/acs.nanolett.7b03184

The CAPM strikes back? An equilibrium model with disasters

Embedding disasters into a general equilibrium model with heterogeneous firms induces strong nonlinearity in the pricing kernel, helping explain the empirical failure of the (consumption) CAPM. Our single-factor model reproduces the failure of the CAPM in explaining the value premium in finite samples without disasters and its relative success in samples with disasters. Due to beta measurement errors, the estimated beta-return relation is flat, consistent with the beta “anomaly,” even though the true beta-return relation is strongly positive. Finally, the consumption CAPM fails in simulations, even though a nonlinear model with the true pricing kernel holds exactly by construction

Longitudinal cohort study of horse owners

This report summarises the findings of a three-year mixed methods research study designed to capture factors that influence horse owner Hendra virus (HeV) risk mitigation practices. The research project focuses on horse owners; their knowledge, attitudes, and risk mitigation practices, i.e. uptake of vaccination, property management, and biosecurity practices. A flexible research methodology enabled the tracking of core subject areas over time whilst also responding to new or evolving shifts in the HeV landscape, e.g. new HeV cases, event management, and issues arising in the vaccine roll-out. By tracking relationships within the data and engaging with stakeholders and the horse owner population, it is hoped that findings from the study will help to identify important linkages and effective strategies for communication/information and policy implementation

Longitudinal cohort study of horse owners

This report summarises the findings of a three-year mixed methods research study designed to capture factors that influence horse owner Hendra virus (HeV) risk mitigation practices. The research project focuses on horse owners; their knowledge, attitudes, and risk mitigation practices, i.e. uptake of vaccination, property management, and biosecurity practices. A flexible research methodology enabled the tracking of core subject areas over time whilst also responding to new or evolving shifts in the HeV landscape, e.g. new HeV cases, event management, and issues arising in the vaccine roll-out. By tracking relationships within the data and engaging with stakeholders and the horse owner population, it is hoped that findings from the study will help to identify important linkages and effective strategies for communication/information and policy implementation

Thermodynamics and magnetic field profiles in low-kappa type-II superconductors

Two-dimensional low-kappa type-II superconductors are studied numerically within the Eilenberger equations of superconductivity. Depending on the Ginzburg-Landau parameter \kappa=\lambda/\xi vortex-vortex interaction can be attractive or purely repulsive. The sign of interaction is manifested as a first (second) order phase transition from Meissner to the mixed state. Temperature and field dependence of the magnetic field distribution in low-kappa type-II superconductors with attractive intervortex interaction is calculated. Theoretical results are compared to the experiment.Comment: 4 pages, 3 figure

On the Initial Conditions for Brane Inflation

String theory gives rise to various mechanisms to generate primordial inflation, of which ``brane inflation'' is one of the most widely considered. In this scenario, inflation takes place while two branes are approaching each other, and the modulus field representing the separation between the branes plays the role of the inflaton field. We study the phase space of initial conditions which can lead to a sufficiently long period of cosmological inflation, and find that taking into account the possibility of nonvanishing initial momentum can significantly change the degree of fine tuning of the required initial conditions.Comment: 11 pages, 2 figure

Dependence of the flux creep activation energy on current density and magnetic field for MgB2 superconductor

Systematic ac susceptibility measurements have been performed on a MgB$_2$ bulk sample. We demonstrate that the flux creep activation energy is a nonlinear function of the current density $U(j)\propto j^{-0.2}$, indicating a nonlogarithmic relaxation of the current density in this material. The dependence of the activation energy on the magnetic field is determined to be a power law $U(B)\propto B^{-1.33}$, showing a steep decline in the activation energy with the magnetic field, which accounts for the steep drop in the critical current density with magnetic field that is observed in MgB$_2$. The irreversibility field is also found to be rather low, therefore, the pinning properties of this new material will need to be enhanced for practical applications.Comment: 11 pages, 6 figures, Revtex forma

Analysis of woodfuel supply and demand balance in Kiambu, Thika and Maragwa districts in central Kenya

This study was undertaken in Kiambu, Thika and Maragwa districts of Central Kenya and it aimed at developing micro-level wood energy plan that would act as a case study for future decentralized wood energy plans in Kenya. Primary data was collected from households, service/production institutions comprising of factories/industries, schools, restaurants, hospitals and prisons using structured questionnaires. The study established a deficit between supply and demand balance of -41.7, -45.6 and -50.1% of woodfuel in 2006 for Kiambu, Thika and Maragwa districts respectively. The strategies suggested in micro-level wood energy plans to curb these deficits include allocation of gazetted plantation forest to fuel wood production, increase of improved stove technology, increase of on-farm tree land area and use of alternative energy sources. The combination of all these strategies gave a surplus of 22,903, 46,947 and 32,409 tons of woodfuel in Kiambu, Thika and Maragwa districts, respectively by 2018. The study recommended implementation of the identified strategies aimed at reducing the huge deficit between supply and demand, enhancing inter-institutional collaboration in all sectors related to wood energy development, developing clear policies to guide charcoal and firewood production and marketing and having regular wood energy surveys

Inflationary Initial Conditions Consistent with Causality

The initial condition problem of inflation is examined from the perspective of both spacetime embedding and scalar field dynamics. The spacetime embedding problem is solved for arbitrary initial spatial curvature Omega, which generalizes previous works that primarily treat the flat case Omega=1. Scalar field dynamics that is consistent with the embedding constraints are examined, with the additional treatment of damping effects. The effects of inhomogeneities on the embedding problem also are considered. A category of initial conditions are identified that are not acausal and can develop into an inflationary regime.Comment: 9 pages, 3 figures. Minor changes, matches version to appear in Physical Review