Product Vacua and Boundary State Models in d Dimensions

We introduce and analyze a class of quantum spin models defined on d-dimensional lattices Lambda subset of Z^d, which we call `Product Vacua with Boundary States' (PVBS). We characterize their ground state spaces on arbitrary finite volumes and study the thermodynamic limit. Using the martingale method, we prove that the models have a gapped excitation spectrum on Z^d except for critical values of the parameters. For special values of the parameters we show that the excitation spectrum is gapless. We demonstrate the sensitivity of the spectrum to the existence and orientation of boundaries. This sensitivity can be explained by the presence or absence of edge excitations. In particular, we study a PVBS models on a slanted half-plane and show that it has gapless edge states but a gapped excitation spectrum in the bulk

Stochastic Formation of Polariton Condensates in Two Degenerate Orbital States

We explore the exciton-polariton condensation in the two degenerate orbital states. In the honeycomb lattice potential, at the third band we have two degenerate vortex-antivortex lattice states at the inequivalent K and K'-points. We have observed energetically degenerate condensates within the linewidth ~ 0.3 meV, and directly measured the vortex-antivortex lattice phase order of the order parameter. We have also observed the intensity anticorrelation between polariton condensates at the K- and K'-points. We relate this intensity anticorrelation to the dynamical feature of polariton condensates induced by the stochastic relaxation from the common particle reservoir.Comment: 5 pages, 4 figure

The impact of long term institutional collaboration in surgical training on trauma care in Malawi

This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.Background Attempts to address the huge, and unmet, need for surgical services in Africa by training surgical specialists in well established training programmes in high-income countries have resulted in brain drain, as most trainees do not return home on completion of training for various reasons. Local postgraduate training is key to retaining specialists in their home countries. International institutional collaborations have enabled Kamuzu Central Hospital (KCH) in Lilongwe, Malawi, to start training their own surgical specialists from 2009. Results and discussion The direct impact of this has been an increase in Malawian staff from none at all to 12 medical doctors in 2014 in addition to increased foreign faculty. We have also seen improved quality of care as illustrated by a clear reduction in the amputation rate after trauma at KCH, from nearly every fourth orthopaedic operation being an amputation in 2008 to only 4 % in 2014. Over the years the training program at KCH has, with the help from its international partners, merged with the College of Medicine in Blantyre, Malawi, into a national training programme for surgery. Conclusions Our experiences from this on-going international institutional collaboration to increase the capacity for training surgeons in Malawi show that long-term institutional collaboration in the training of surgeons in low-income countries can be done as a sustainable and up-scalable model with great potential to reduce mortality and prevent disability in young people. Despite the obvious and necessary focus on the rural poor in low-income countries, stakeholders must start to see the value of strengthening teaching hospitals to sustainably meet the growing burden of trauma and surgical disease. Methods Annual operating data from Kamuzu Central Hospital’s Main Operating Theatre log book for the years 2008–2014 was collected. Observed annual numbers were presented as graphs for easy visualization. Linear regression curve estimations were calculated and plotted as trend lines on the graphs

Algebraic order and the Berezinskii-Kosterlitz-Thouless transition in an exciton-polariton gas

We observe quasi-long range coherence in a two-dimensional condensate of exciton-polaritons. Our measurements are the first to confirm that the spatial correlation algebraically decays with a slow power-law, whose exponent quantitatively behaves as predicted by the Berezinskii-Kosterlitz-Thouless theory. The exciton-polaritons are created by non-resonant optical pumping of a micro-cavity sample with embedded GaAs quantum-wells at liquid helium temperature. Michelson interference is used to measure the coherence of the photons emitted by decaying exciton-polaritons

Application of Time Projection Chambers with GEMs and Pixels to WIMP Searches and Fast Neutron Detection

We present work on the detection of neutral particles via nuclear recoils in gas-filled Time Projection Chambers (TPCs). We employ Gas Electron Multipliers (GEMs) to amplify the signal and silicon pixel electronics to detect the avalanche charge. These technologies allow ionization in the target gas to be detected with low noise, improved position and time resolution, and high efficiency. We review experimental results obtained in previous years, and report on ongoing simulation studies and construction of the first prototype at the University of Hawaii. We also present prospects of using such detectors to perform direction-sensitive searches for WIMP dark matter and fast neutron from fissionable material.Comment: Proceedings of 2nd International Conference on Technology and Instrumentation in Particle Physics (TIPP 2011), to be published in Physics Procedia, 8 pages, 9 figure

Spontaneous emission enhancement in strain-induced WSe2 monolayer based quantum light sources on metallic surfaces

Atomic monolayers of transition metal dichalcogenides represent an emerging material platform for the implementation of ultra compact quantum light emitters via strain engineering. In this framework, we discuss experimental results on creation of strain induced single photon sources using a WSe2 monolayer on a silver substrate, coated with a very thin dielectric layer. We identify quantum emitters which are formed at various locations in the sample. The emission is highly linearly polarized, stable in linewidth and decay times down to 300 ps are observed. We provide numerical calculations of our monolayer-metal device platform to assess the strength of the radiative decay rate enhancement by the presence of the plasmonic structure. We believe, that our results represent a crucial step towards the ultra-compact integration of high performance single photon sources in nanoplasmonic devices and circuits

Evidence of two lineages of metriorhynchid crocodylomorphs in the Lower Cretaceous of the Czech Republic

Metriorhynchid crocodylomorphs were an important component in shallow marine ecosystems during the Middle Jurassic to Early Cretaceous in the European archipelago. While metriorhynchids are well known from western European countries, their central and eastern European record is poor and usually limited to isolated or fragmentary specimens which often hinders a precise taxonomic assignment. However, isolated elements such as tooth crowns, have been found to provide informative taxonomic identifications. Here we describe two isolated metriorhynchid tooth crowns from the upper Valanginian (Lower Cretaceous) of the Stramberk area, Czech Republic. Our assessment of the specimens, including multivariate analysis of dental measurements and surface enamel structures, indicates that the crowns belong to two distinct geosaurin taxa (Plesiosuchina? indet. and Torvoneustes? sp.) with different feeding adaptations. The specimens represent the first evidence of Metriorhynchidae from the Czech Republic and some of the youngest metriorhynchid specimens worldwide.Web of Science66236735

Parent and Patient Satisfaction after Treatment for Supracondylar Humerus Fractures in 139 Children: No Difference between Skeletal Traction and Crossed Pin Fixation at Long-Term Followup

Aim. The aim of this study was to see whether the benefits of crossed wire fixation over skeletal traction in the treatment of pediatric supracondylar humerus fractures (SCHF) were mirrored in the children's or their caregivers' rating of the experience. Methods. As part of a study of the clinical outcome of SCHF, all the patients and the parents were asked to rate their experience of the treatment on a visual analogue scale (VAS). Results. There was no difference in the patients' or the parents' experience between the treatment groups. However there was a difference between the parents with children who experienced a neurovascular complication (mean VAS 6.1) and those that did not (mean VAS 4.3, P = 0.03). The boys rated the experience as less negative (mean VAS 3.6) than the girls (mean VAS 4.7, P = 0.02). Conclusion. In the long term, avoiding complications was more important to the parents than the choice of treatment for SCHF in the children