4,941 research outputs found

    Are Time-Domain Self-Force Calculations Contaminated by Jost Solutions?

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    The calculation of the self force in the modeling of the gravitational-wave emission from extreme-mass-ratio binaries is a challenging task. Here we address the question of the possible emergence of a persistent spurious solution in time-domain schemes, referred to as a {\em Jost junk solution} in the literature, that may contaminate self force calculations. Previous studies suggested that Jost solutions are due to the use of zero initial data, which is inconsistent with the singular sources associated with the small object, described as a point mass. However, in this work we show that the specific origin is an inconsistency in the translation of the singular sources into jump conditions. More importantly, we identify the correct implementation of the sources at late times as the sufficient condition guaranteeing the absence of Jost junk solutions.Comment: RevTeX. 5 pages, 2 figures. Version updated to match the contents of the published articl

    Creating a Vision for XYZ Research Corporation: A Case Study

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    A strategic analysis was developed for XYZ Research Corporation (the true company's name is disguised). The strategic analysis involved a series of visits to the company to conduct focus groups with its employees and management. Five focus groups were carried out at XYZ Research Corporation. This method proved to be effective and valuable when aiming to gather detailed information on the specifics of a firm's operation. Information and insights on the company and its business that would not become evident through any kind of meticulous financial or economic analysis of the company's and industry's numbers - which in fact were unavailable or scarce - was efficiently obtained by personal communication from the employees in the interviews. The focus group and interview method is recommended as a valid alternative to gathering detailed data and information when facing limited availability of reliable quantitative economic data on sales, size, and other information on the industry. The amount and quality of person-to-person information gathered in the interviews made the questionnaire a more powerful tool versus the alternative of simply mailing it. In the process of developing a strategic plan for XYZ, data and information used to write an undergraduate level teaching case study was gathered. The focus group method allowed for digging out intricate functional relationships within the company and between the company and the industry, which allowed for writing a more complete and educationally interesting case study.Focus Groups, Strategic Analysis, Food Safety, Outsourcing, Research Methods/ Statistical Methods, A22, C99, L21, M10,

    Magnetism, structure, and charge correlation at a pressure-induced Mott-Hubbard insulator-metal transition

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    We use synchrotron x-ray diffraction and electrical transport under pressure to probe both the magnetism and the structure of single crystal NiS2 across its Mott-Hubbard transition. In the insulator, the low-temperature antiferromagnetic order results from superexchange among correlated electrons and couples to a (1/2, 1/2, 1/2) superlattice distortion. Applying pressure suppresses the insulating state, but enhances the magnetism as the superexchange increases with decreasing lattice constant. By comparing our results under pressure to previous studies of doped crystals we show that this dependence of the magnetism on the lattice constant is consistent for both band broadening and band filling. In the high pressure metallic phase the lattice symmetry is reduced from cubic to monoclinic, pointing to the primary influence of charge correlations at the transition. There exists a wide regime of phase separation that may be a general characteristic of correlated quantum matter.Comment: 5 pages, 3 figure

    Shallot virus X: a hardly known pathogen of the genus Allium

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    Crops belonging to the genus Allium, family Amaryllidaceae, are economically important and are widely cultivated around the globe. Some of the most problematic diseases of these crops are caused by members of three virus genera, Potyvirus, Carlavirus and Allexivirus. Shallot virus X (ShVX) is an Allexivirus that was first discovered in Russia in the nineties and it has since been described worldwide. The virus, transmitted mechanically or by the dry bulb mite (Aceria tulipae), affects virtually all members of the genus Allium and it causes yield reductions on these crops. ShVX is a positive-sense single-stranded monopartite RNA virus that contains six open reading frames (ORFs). The virus is mainly detected by RT-PCR but there are other serological and molecular techniques available for diagnosis. There are no methods described for managing crops infected by ShVX in the field, but tissue culture of meristems can render virus-free plants. Research on the ShVX-Allium pathosystem is needed for a comprehensive understanding of the physiological and molecular mechanisms used by the virus to infect its hosts and for developing methods for the effective control of viral infections.Los cultivos del g茅nero Allium, familia Amaryllidaceae, son econ贸micamente importantes y ampliamente sembrados alrededor del mundo. Algunas de las enfermedades m谩s problem谩ticas de estos cultivos son ocasionadas por virus de tres g茅neros, Potyvirus, Carlavirus y Allexivirus. Shallot virus X (ShVX) es un Allexivirus que fue descrito por primera vez en Rusia en la d茅cada de los noventa y desde entonces se ha descrito su presencia a nivel mundial. El virus, transmitido mec谩nicamente o por el eri贸fido de los bulbos (Aceria tulipae), afecta pr谩cticamente a todos los miembros del g茅nero Allium ocasionando la disminuci贸n en la producci贸n de estos cultivos. ShVX tiene un genoma monopartito representado por una cadena simple de ARN de polaridad positiva con seis marcos abiertos de lectura (ORFs). El virus se detecta principalmente por RT-PCR, pero existen otros m茅todos serol贸gicos y moleculares disponibles para su diagn贸stico. No existen m茅todos descritos para el manejo de plantas infectadas con ShVX en el campo, sin embargo se ha determinado que el cultivo de tejidos meristem谩ticos puede producir plantas libres de virus. Es necesario desarrollar investigaciones en el patosistema ShVX-Allium para lograr un entendimiento general sobre los mecanismos fisiol贸gicos y moleculares que utiliza el virus para infectar a su hospedero y para desarrollar m茅todos para el control efectivo de las infecciones virales.Gerencia de Comunicaci贸n e Imagen InstitucionalFil: Granda Jaramillo, Roberto. Universidad UTE. Facultad de Ciencias de la Ingenier铆a e Industrias; EcuadorFil: Flores, F. Universidad UTE. Facultad de Ciencias de la Ingenier铆a e Industrias. Centro de Investigaci贸n de Alimentos; Ecuador. Universidad de las Fuerzas Armadas. Departamento de Ciencias de la Vida y la Agricultura; Ecuado

    Time-domain modelling of Extreme-Mass-Ratio Inspirals for the Laser Interferometer Space Antenna

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    When a stellar-mass compact object is captured by a supermassive black hole located in a galactic centre, the system losses energy and angular momentum by the emission of gravitational waves. Subsequently, the stellar compact object evolves inspiraling until plunging onto the massive black hole. These EMRI systems are expected to be one of the main sources of gravitational waves for the future space-based Laser Interferometer Space Antenna (LISA). However, the detection of EMRI signals will require of very accurate theoretical templates taking into account the gravitational self-force, which is the responsible of the stellar-compact object inspiral. Due to its potential applicability on EMRIs, the obtention of an efficient method to compute the scalar self-force acting on a point-like particle orbiting around a massive black hole is being object of increasing interest. We present here a review of our time-domain numerical technique to compute the self-force acting on a point-like particle and we show its suitability to deal with both circular and eccentric orbits.Comment: 4 pages, 2 figures, JPCS latex style. Submitted to JPCS (special issue for the proceedings of the Spanish Relativity Meeting (ERE2010)

    Numerical implementation of isolated horizon boundary conditions

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    We study the numerical implementation of a set of boundary conditions derived from the isolated horizon formalism, and which characterize a black hole whose horizon is in quasiequilibrium. More precisely, we enforce these geometrical prescriptions as inner boundary conditions on an excised sphere, in the numerical resolution of the conformal thin sandwich equations. As main results, we first establish the consistency of including in the set of boundary conditions a constant surface gravity prescription, interpretable as a lapse boundary condition, and second we assess how the prescriptions presented recently by Dain et al. for guaranteeing the well-posedness of the conformal transverse traceless equations with quasiequilibrium horizon conditions extend to the conformal thin sandwich elliptic system. As a consequence of the latter analysis, we discuss the freedom of prescribing the expansion associated with the ingoing null normal at the horizon
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