55 research outputs found
Anomalous optical absorption in a random system with scale-free disorder
We report on an anomalous behavior of the absorption spectrum in a
one-dimensional lattice with long-range-correlated diagonal disorder with a
power-like spectrum in the form S(k) ~ 1/k^A. These type of correlations give
rise to a phase of extended states at the band center, provided A is larger
than a critical value A_c. We show that for A < A_c the absorption spectrum is
single-peaked, while an additional peak arises when A > A_c, signalling the
occurrence of the Anderson transition. The peak is located slightly below the
low-energy mobility edge, providing a unique spectroscopic tool to monitor the
latter. We present qualitative arguments explaining this anomaly.Comment: 4 pages, 4 postscript figures, uses revtex
Linear optical properties of one-dimensional Frenkel exciton systems with intersite energy correlations
We analyze the effects of intersite energy correlations on the linear optical
properties of one-dimensional disordered Frenkel exciton systems. The
absorption line width and the factor of radiative rate enhancement are studied
as a function of the correlation length of the disorder. The absorption line
width monotonously approaches the seeding degree of disorder on increasing the
correlation length. On the contrary, the factor of radiative rate enhancement
shows a non-monotonous trend, indicating a complicated scenario of the exciton
localization in correlated systems. The concept of coherently bound molecules
is exploited to explain the numerical results, showing good agreement with
theory. Some recent experiments are discussed in the light of the present
theory.Comment: 18 pages, 3 figues, REVTeX, to appear in Physical Review
Photon Shielding Features of Quarry Tuff
Abstract. Cantera is a quarry tuff widely used in the building industry; in this work the shielding features of cantera were determined. The shielding characteristics were calculated using XCOM and MCNP5 codes for 0.03, 0.07, 0.1, 0.3, 0.662, 1, 2, and 3 MeV photons. With XCOM the mass interaction coefficients, and the total mass attenuation coefficients, were calculated. With the MCNP5 code a transmission experiment was modelled using a point-like source located 42 cm apart from a point-like detector. Between the source and the detector, cantera pieces with different thickness, ranging from 0 to 40 cm were included. The collided and uncollided photon fluence, the Kerma in air and the Ambient dose equivalent were estimated. With the uncollided fluence the linear attenuation coefficients were determined and compared with those calculated with XCOM. The linear attenuation coefficient for 0.662 MeV photons was compared with the coefficient measured with a NaI(Tl)-based �-ray spectrometer and a 137Cs source
Functional upgrading in China’s export processing sector
Functional upgrading occurs when a firm acquires more sophisticated functions within an existing value chain. In this paper, we analyze if there is evidence of this type of upgrading in China’s export processing regime by investigating dynamics in the relative prevalence of Import & Assembly (IA) versus Pure Assembly (PA) processing trade over the period 2000-2013. Firms in both regimes provide similar manufacturing services to foreign companies, but IA firms also conduct the sophisticated tasks of quality control, searching, financing and storing imported materials. Consistent with a trend of functional upgrading, we show that the share of IA trade in total processing trade has increased rapidly during the period 2000-2006, both overall and within product categories. Furthermore, we find that this trend has gone hand in hand with improvements in a sector’s labor productivity and unit values. Against expectations, we find that this process has slowed down notably during the period 2006-2013.status: publishe
A Spitzer IRS Survey of NGC 1333: Insights into disk evolution from a very young cluster
We report on the {\lambda} = 5-36{\mu}m Spitzer Infrared Spectrograph spectra
of 79 young stellar objects in the very young nearby cluster NGC 1333. NGC
1333's youth enables the study of early protoplanetary disk properties, such as
the degree of settling as well as the formation of gaps and clearings. We
construct spectral energy distributions (SEDs) using our IRS data as well as
published photometry and classify our sample into SED classes. Using
"extinction-free" spectral indices, we determine whether the disk, envelope, or
photosphere dominates the spectrum. We analyze the dereddened spectra of
objects which show disk dominated emission using spectral indices and
properties of silicate features in order to study the vertical and radial
structure of protoplanetary disks in NGC 1333. At least nine objects in our
sample of NGC 1333 show signs of large (several AU) radial gaps or clearings in
their inner disk. Disks with radial gaps in NGC 1333 show more-nearly pristine
silicate dust than their radially continuous counterparts. We compare
properties of disks in NGC 1333 to those in three other well studied regions,
Taurus-Auriga, Ophiuchus and Chamaeleon I, and find no difference in their
degree of sedimentation and dust processing.Comment: 67 pages, 20 figures, accepted to The Astrophysical Journal
Supplement Serie
Estrategias de estudio y trabajo en estudiantes universitarios de la UIB
El estudio se centra en el conocimiento de los procesos de aprendizaje que se desarrollan en la enseñanza superior, siendo su objetivo principal la evaluación de las estrategias de aprendizaje utilizadas por estudiantes universitarios a lo largo de su formación inicial. Responde a un diseño descriptivo-exploratorio, dirigido a las estrategias de estudio y trabajo de la población universitaria de la Universidad de las Islas Baleares (UIB). Para ello, se procedió a la elaboración de un cuestionario como instrumento de recogida de datos1 sobre estrategias de estudio y trabajo, categorizado en cuatro grupos de estrategias (disposicionales y de apoyo; de búsqueda, recogida y selección de información; de procesamiento y uso de información; metacognitivas, de regulación y control) y sus correspondientes subcategorÃas. Se trabajó con una muestra de 949 estudiantes de la UIB, clasificados por ámbitos disciplinares y estudios, agrupados en grandes dimensiones (sexo; estudios de ciclo corto y de ciclo largo; rama de estudios; dedicación al estudio y actividad laboral), aportando, para cada una de ellas los datos estadÃsticos en los que se constata una diferencia significativa.L’estudi està centrat en el coneixement dels processos d’aprenentatge que es desenvolupen a l’ensenyament superior, i el l’objectiu principal és l’avaluació de les estratègies d’aprenentatge utilitzades per estudiants universitaris al llarg de la seva formació inicial. Respon a un disseny descriptiu-exploratori, dirigit a les estratègies d’estudi i treball de la població università ria de la Universitat de les Illes Balears (UIB). En aquest sentit, es va confeccionar un qüestionari com a instrument de recollida de dades sobre estratègies d’estudi i treball, categoritzat en quatre grups d’estratègies (disposicionals i de suport; de cerca, recollida i selecció d’informació; de processament i ús d’informació; metacognitives, de regulació i control) i les subcategories corresponents. Es va treballar amb una mostra de 949 estudiants de la UIB, classificats per à mbits disciplinaris i estudis, agrupats en grans dimensions (sexe; estudis de cicle curt i de cicle llarg; branca d’estudis; dedicació a l’estudi i activitat laboral), que varen aportar, per a cadascuna, dades estadÃstiques en els quals es constata una diferència significativa.The study is focused on the knowledge of learning processes developed in Higher Education and the main objective is to assess the learning strategies of university students along their initial training. This is a response to a descriptive-exploratory design addressed to the learning and working strategies among the students of the University of the Balearic Islands (UIB). Regarding to this, a question paper was designed as a tool for the collection of data on the studying and working strategies sorted by four strategy groups (dispositional and backup groups; research, collection and selection of information; processing and use of information; metacognitive, regulation and control groups) with their respective subcategories. We took a sample of 949 students from the UIB, sorted by study and disciplinary areas, and we gathered them in larger-dimension groups (gender, shorter and longer degrees, field of study and commitment to studies and work). These groups provided, for each of the samples, statistical information in which an important difference is stated
Consenso mexicano sobre dolor torácico no cardiaco
Introducción: Dolor torácico no cardÃaco (DTNC) se define como un sÃndrome clÃnico caracte-rizado por dolor retroesternal semejante a la angina de pecho, pero de origen no cardiaco ygenerado por enfermedades esofágicas, osteomusculares, pulmonares o psiquiátricas.Objetivo: Presentar una revisión consensuada basada en evidencias sobre definición, epidemio-logÃa, fisiopatologÃa, diagnóstico y opciones terapéuticas para pacientes con DTNC.Métodos: Tres coordinadores generales realizaron una revisión bibliográfica de todas las publi-caciones en inglés y espaËœnol sobre el tema y elaboraron 38 enunciados iniciales divididosen tres categorÃas principales: 1) definiciones, epidemiologÃa y fisiopatologÃa; 2) diagnóstico,y 3) tratamiento. Los enunciados fueron votados (3 rondas) utilizando el sistema Delphi, y losque alcanzaron un acuerdo > 75% fueron considerados y calificados de acuerdo con el sistemaGRADE.
Resultados y conclusiones: El consenso final incluyó 29 enunciados Todo paciente que debutacon dolor torácico debe ser inicialmente evaluado por un cardiólogo. La causa más común deDTNC es la enfermedad por reflujo gastroesofágico (ERGE). Como abordaje inicial, si no existensÃntomas de alarma, se puede dar una prueba terapéutica con inhibidor de bomba de pro-tones (IBP) por 2-4 semanas. Si hay disfagia o sÃntomas de alarma, se recomienda hacer unaendoscopia. La manometrÃa de alta resolución es el mejor método para descartar trastornosmotores espásticos y acalasia. La pHmetrÃa ayuda a demostrar exposición esofágica anormal alácido. El tratamiento debe ser dirigido al mecanismo fisiopatológico, y puede incluir IBP, neu-romoduladores y/o relajantes de músculo liso, intervención psicológica y/o terapia cognitiva,y ocasionalmente cirugÃa o terapia endoscópica.
ABSTRACT
Introduction: Non-cardiac chest pain is defined as a clinical syndrome characterized by retros-ternal pain similar to that of angina pectoris, but of non-cardiac origin and produced byesophageal, musculoskeletal, pulmonary, or psychiatric diseases.Aim: To present a consensus review based on evidence regarding the definition, epidemiology,pathophysiology, and diagnosis of non-cardiac chest pain, as well as the therapeutic options forthose patients.
Methods: Three general coordinators carried out a literature review of all articles published inEnglish and Spanish on the theme and formulated 38 initial statements, dividing them into 3 maincategories: (i) definitions, epidemiology, and pathophysiology; (ii) diagnosis, and (iii) treatment.The statements underwent 3 rounds of voting, utilizing the Delphi system. The final statementswere those that reached > 75% agreement, and they were rated utilizing the GRADE system.Results and conclusions: The final consensus included 29 statements. All patients presentingwith chest pain should initially be evaluated by a cardiologist. The most common cause ofnon-cardiac chest pain is gastroesophageal reflux disease. If there are no alarm symptoms, the initial approach should be a therapeutic trial with a proton pump inhibitor for 2-4 weeks. Ifdysphagia or alarm symptoms are present, endoscopy is recommended. High-resolution mano-metry is the best method for ruling out spastic motor disorders and achalasia and pH monitoringaids in demonstrating abnormal esophageal acid exposure. Treatment should be directed at thepathophysiologic mechanism. It can include proton pump inhibitors, neuromodulators and/orsmooth muscle relaxants, psychologic intervention and/or cognitive therapy, and occasionallysurgery or endoscopic therapy
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