5,220 research outputs found

    Stabilization of collapse and revival dynamics by a non-Markovian phonon bath

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    Semiconductor quantum dots (QDs) have been demonstrated to be versatile candidates to study the fundamentals of light-matter interaction [1-3]. In contrast with atom optics, dissipative processes are induced by the inherent coupling to the environment and are typically perceived as a major obstacle towards stable performances in experiments and applications [4]. In this paper we show that this is not necessarily the case. In fact, the memory of the environment can enhance coherent quantum optical effects. In particular, we demonstrate that the non-Markovian coupling to an incoherent phonon bath has a stabilizing effect on the coherent QD cavity-quantum electrodynamics (cQED) by inhibiting irregular oscillations and boosting regular collapse and revival patterns. For low photon numbers we predict QD dynamics that deviate dramatically from the well-known atomic Jaynes-Cummings model. Our proposal opens the way to a systematic and deliberate design of photon quantum effects via specifically engineered solid-state environments.Comment: 5 pages, 4 figure

    Covariant transverse-traceless projection for secondary gravitational waves

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    Second-order tensor modes induced by nonlinear gravity are a key component of the cosmological background of gravitational waves. A detection of this background would allow us to probe the primordial power spectrum at otherwise inaccessible scales. Usually, the energy density of these gravitational waves is studied within perturbation theory in a particular gauge -- a connection between our physical spacetime and a fictitious background. It is a widely recognized issue that the second-order, scalar-induced gravitational waves are gauge dependent. This issue arises because they are not well-defined as tensors in the physical spacetime at second-order and are thus unphysical. In this paper, we propose the covariant transverse-traceless projection of the extrinsic curvature to study cosmological gravitational waves on a spatial hypersurface. We define a new energy density which is based purely on spacetime tensors, independent of perturbation theory, and thus is gauge invariant by definition. We show that, in the context of second-order perturbation theory, this new energy density contains only propagating modes in the constant-time hypersurface in the Newtonian gauge. We further show that we can recover the same gravitational waves after a transformation to the synchronous gauge, so long as we correctly identify the Newtonian hypersurface.Comment: 14 pages, 2 figure, major revisio

    Morphological Diversity between Culture Strains of a Chlorarachniophyte, Lotharella globosa

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    Chlorarachniophytes are marine unicellular algae that possess secondary plastids of green algal origin. Although chlorarachniophytes are a small group (the phylum of Chlorarachniophyta contains 14 species in 8 genera), they have variable and complex life cycles that include amoeboid, coccoid, and/or flagellate cells. The majority of chlorarachniophytes possess two or more cell types in their life cycles, and which cell types are found is one of the principle morphological criteria used for species descriptions. Here we describe an unidentified chlorarachniophyte that was isolated from an artificial coral reef that calls this criterion into question. The life cycle of the new strain includes all three major cell types, but DNA barcoding based on the established nucleomorph ITS sequences showed it to share 100% sequence identity with Lotharella globosa. The type strain of L. globosa was also isolated from a coral reef, but is defined as completely lacking an amoeboid stage throughout its life cycle. We conclude that L. globosa possesses morphological diversity between culture strains, and that the new strain is a variety of L. globosa, which we describe as Lotharella globosa var. fortis var. nov. to include the amoeboid stage in the formal description of L. globosa. This intraspecies variation suggest that gross morphological stages maybe lost rather rapidly, and specifically that the type strain of L. globosa has lost the ability to form the amoeboid stage, perhaps recently. This in turn suggests that even major morphological characters used for taxonomy of this group may be variable in natural populations, and therefore misleading

    The published research paper: is it an important indicator of successful operational research at programme level?

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    Is a published research paper an important indicator of successful operational research at programme level in low-income countries? In academia, publishing in peer-reviewed scientific journals is highly encouraged and strongly pursued for academic recognition and career progression. In contrast, for those who engage in operational research at programme level, there is often no necessity or reward for publishing the results of research studies; it may even be criticized as being an unnecessary detraction from programme-related work. We present arguments to support publishing operational research from low-income countries; we highlight some of the main reasons for failure of publication at programme level and suggest ways forward

    Implementing general measurements on linear optical and solid-state qubits

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    We show a systematic construction for implementing general measurements on a single qubit, including both strong (or projection) and weak measurements. We mainly focus on linear optical qubits. The present approach is composed of simple and feasible elements, i.e., beam splitters, wave plates, and polarizing beam splitters. We show how the parameters characterizing the measurement operators are controlled by the linear optical elements. We also propose a method for the implementation of general measurements in solid-state qubits.Comment: 8 pages, 3 figure

    Pregnancy and childbirth outcomes among adolescent mothers: A World Health Organization multicountry study

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    Tuvo como objetivo investigar el riesgo de resultados adversos del embarazo entre adolescentes en 29 países. El diseño utilizado fue un análisis secundario utilizando datos transversales basados en instalaciones de la Encuesta multipaís sobre salud materna y neonatal de la Organización Mundial de la Salud. Se tomó el análisis de veintinueve países de África, América Latina, Asia y Oriente Medio. La población estimada fue de mujeres ingresadas para el parto de 359 centros de salud durante 2 a 4 meses entre 2010 y 2011. Se utilizaron modelos de regresión logística multinivel para estimar la asociación entre la edad materna joven y los resultados adversos del embarazo. Se analizaron un total de 124 446 madres de ≤24 años y sus bebés. En comparación con las madres de 20 a 24 años, las madres adolescentes de 10 a 19 años tenían mayores riesgos de eclampsia, endometritis puerperal, infecciones sistémicas, bajo peso al nacer, parto prematuro y afecciones neonatales graves. El mayor riesgo de muerte neonatal temprana intrahospitalaria entre los bebés nacidos de madres adolescentes se redujo y fue estadísticamente insignificante después del ajuste por edad gestacional y peso al nacer, además de las características maternas, el modo de parto y la malformación congénita. La cobertura de los uterotónicos profilácticos, los antibióticos profilácticos para la cesárea y los corticosteroides prenatales para el parto prematuro a las 26 - 34 semanas fue significativamente menor entre las madres adolescentes. El embarazo adolescente se asoció con mayores riesgos de resultados adversos del embarazo. Las estrategias de prevención del embarazo y la mejora de las intervenciones de atención médica son cruciales para reducir los resultados adversos del embarazo entre las mujeres adolescentes en países de bajos y medianos ingresos

    Computer simulations of electrorheological fluids in the dipole-induced dipole model

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    We have employed the multiple image method to compute the interparticle force for a polydisperse electrorheological (ER) fluid in which the suspended particles can have various sizes and different permittivites. The point-dipole (PD) approximation being routinely adopted in computer simulation of ER fluids is shown to err considerably when the particles approach and finally touch due to multipolar interactions. The PD approximation becomes even worse when the dielectric contrast between the particles and the host medium is large. From the results, we show that the dipole-induced-dipole (DID) model yields very good agreements with the multiple image results for a wide range of dielectric contrasts and polydispersity. As an illustration, we have employed the DID model to simulate the athermal aggregation of particles in ER fluids both in uniaxial and rotating fields. We find that the aggregation time is significantly reduced. The DID model accounts for multipolar interaction partially and is simple to use in computer simulation of ER fluids.Comment: 22 pages, 7 figures, submitted to Phys. Rev.

    Reasoning of Motion through Task Order for Teaching by Non-Professional User

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