3,781 research outputs found
Extraordinary transverse magneto-optical Kerr effect in a superlens
It has been shown that a slab of a negative index material can behave as a
superlens enhancing the imaging resolution beyond the wavelength limit. We show
here that if such a slab possesses in addition some magneto-optical activity,
it could act as an ideal optical filter and exhibit an extraordinary transverse
magneto-optical Kerr effect. Moreover, we show that losses, which spoil the
imaging resolution of these lenses, are a necessary ingredient to observe this
effect.Comment: 5 pages, 6 figure
Efectos espaciales en la formación de precios de oferta en mercados spot de generación eléctrica
El mecanismo de fijación del precio de oferta en el mercado eléctrico colombiano exhibe comportamientos estratégicos inherente a la estructura oligopólica de este mercado, no solo por su alto porcentaje hidrológico, aproximadamente 80%, sino también debido a la localización geográfica de las plantas de generación eléctrica cercanas a la Región Andina. En esta investigación se diseña una matriz de pesos espaciales, que recoge características de la localización geográfica de las plantas de generación eléctrica, la cual se incorpora en un panel espacial de tipo Durbin para identificar dichos comportamientos de la geografía económica, además de las variables fundamentales que explican la formación del precio en este mercado.The price bid mechanism in the Colombian electricity market exhibits a strategic behavior, inherent in their oligopolistic market structure, not only for its high hydrological percentage, about 80%, but also because the power plants geographical location, near to the Andean Region. This research designs a spatial weights matrix reflecting characteristics the power plants geographical location, who is incorporated into a spatial Durbin panel to identify the economic geography behaviors, in addition to the fundamentals that explain the prices formation in this market
Precios y desempeño regulatorio en el pool eléctrico español
Este trabajo examina la relación entre el Gap del precio marginal del sistema y
otras variables típicas del mercado, organización industrial y cambios regulatorios
en el pool eléctrico español. Se estima un modelo de panel de datos largo, en el
cual la dimensión temporal es mayor al número de empresas consideradas. Los
resultados indican que tanto la alta concentración del mercado como la posibilidad
de ser pivote generaron efectos nocivos sobre la determinación del precio.
Además, los cambios regulatorios implementados por las autoridades no indujeron
los efectos esperados, creando distorsión e incentivos incorrectos en este
mercado.This study examines the relation between the gap of the system marginal price and
other common variables in the market such as industrial organization and
regulatory changes in the Spanish electricity pool. We estimate a long panel model
where the time is larger than the number of firms. Our findings show that high
market concentration and the possibility of being a pivot agent generate adverse
effects on price determination. In addition, regulatory changes did not generate the
expected effects, creating distortion and incorrect incentives in the market
Asociación entre variables antropométricas y síntomas de disfunción eréctil en ciclistas
Magnetic-field control of near-field radiative heat transfer and the realization of highly tunable hyperbolic thermal emitters
We present a comprehensive theoretical study of the magnetic field dependence
of the near-field radiative heat transfer (NFRHT) between two parallel plates.
We show that when the plates are made of doped semiconductors, the near-field
thermal radiation can be severely affected by the application of a static
magnetic field. We find that irrespective of its direction, the presence of a
magnetic field reduces the radiative heat conductance, and dramatic reductions
up to 700% can be found with fields of about 6 T at room temperature. We show
that this striking behavior is due to the fact that the magnetic field
radically changes the nature of the NFRHT. The field not only affects the
electromagnetic surface waves (both plasmons and phonon polaritons) that
normally dominate the near-field radiation in doped semiconductors, but it also
induces hyperbolic modes that progressively dominate the heat transfer as the
field increases. In particular, we show that when the field is perpendicular to
the plates, the semiconductors become ideal hyperbolic near-field emitters.
More importantly, by changing the magnetic field, the system can be
continuously tuned from a situation where the surface waves dominate the heat
transfer to a situation where hyperbolic modes completely govern the near-field
thermal radiation. We show that this high tunability can be achieved with
accessible magnetic fields and very common materials like n-doped InSb or Si.
Our study paves the way for an active control of NFRHT and it opens the
possibility to study unique hyperbolic thermal emitters without the need to
resort to complicated metamaterials.Comment: 21 pages, 10 figure
Acute Effect of Resistance Training on Cognitive Function of Costa Rican Older Adults
Different types of exercise interventions have shown to improve cognitive performance; however, there is scarce evidence on the acute effect of resistance training (RT) on cognitions in older adults. The purpose of this study is to determine the acute effect of RT on cognitive performance in healthy older adults. 45 adults (Mean age = 65.3 ± 3.7 yr.) were randomly allocated to one of three groups: high-intensity RT (G1), low-intensity RT (G2), or inactive control (G3). Participants completed cognitive tests assessing processing speed, visuospatial processing, executive function, and cognitive control, working memory and immediate memory. The RT protocol for G1 and G2 consisted of six exercises. A 3x2 ANCOVA was performed with education as a covariate. Significant improvements were found on visuospatial processing in G1 (Pre = 61.6 ± 2.1 vs. Post = 69.7 ± 2.4; 95%CI = 4.8, 11.4; p ≤ 0.001) and G2 (Pre = 62.4 ± 2.2 vs. Post = 67.0 ± 2.5; 95%CI = 1.2, 8.1; p = 0.009). Other tested cognitive abilities were unchanged by acute exercise or rest. Acute RT enhanced or maintained cognitive performance in older adults. It was possible to successfully perform 1RM tests with older adults. Additional evidence is needed to determine effective protocols to improve cognition in older adulthood
The Association Between Abdominal Fat, Cardiorespiratory Fitness, and Clinical Markers of Metabolic Syndrome
Our purpose was to determine the association between abdominal fat and cardiorespiratory fitness (CRF) on markers of metabolic syndrome (MetS) total cholesterol (TC), high-density lipoprotein (HDL-C), low-density lipoprotein (LDL-C), triglycerides (TG), glucose, and blood pressure. We conducted a retrospective study on 165 adults (108 men) in which correlations between waist girth (WG), CRF and blood variables were determined. The cohort was partitioned by gender into quartiles and again by WG and differences in markers of MetS were compared across quartiles by ANOVA and by ANCOVA to determine the influence of CRF. Males in the lowest WG quartile exhibited greater HDL-C and lower diastolic blood pressure vs. the highest quartile (p < 0.05). TG were lower in the lowest vs. the third and highest quartile (p < 0.05), and glucose was greater in the highest vs. the first and second quartiles (p < 0.05). Females in the second WG quartile exhibited higher HDL-C vs. the highest quartile, and TG, glucose, systolic and diastolic blood pressure were lower in the lowest vs. the highest quartile (p < 0.05). After adjusting for CRF, diastolic blood pressure across WG in males were no longer significant, and HLD-C and TG quartile differences were no longer significant in females. We confirm WG as an important correlate of clinical markers of MetS in adults. CRF mitigates relationships between WG and clinical markers of cardio-metabolic risk in men and women
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