8,015 research outputs found
Refractive index evaluation of porous silicon using Bragg reflectors
There are two main physical properties needed to fabricate 1D photonic
structures and form perfect photonic bandgaps: the quality of the thickness
periodicity and the refractive index of their components. Porous silicon (PS)
is a nano-structured material widely used to prepare 1D photonic crystals due
to the ease of tuning its porosity and its refractive index by changing the
fabrication conditions. Since the morphology of PS changes with porosity, the
determination of PS's refractive index is no easy task. To find the optical
properties of PS we can use different effective medium approximations (EMA). In
this work we propose a method to evaluate the performance of the refractive
index of PS layers to build photonic Bragg reflectors. Through a quality factor
we measure the agreement between theory and experiment and therein propose a
simple procedure to determine the usability of the refractive indices. We test
the obtained refractive indices in more complicated structures, such as a
broadband Vis-NIR mirror, and by means of a Merit function we find a good
agreement between theory and experiment. With this study we have proposed
quantitative parameters to evaluate the refractive index for PS Bragg
reflectors. This procedure could have an impact on the design and fabrication
of 1D photonic structures for different applications
Transient situations in traffic flow: Modelling the Mexico City Cuernavaca Highway
In this paper a recent variable anticipation cellular automata model for
single-lane traffic flow is extended to analyze the situation of free and
congested flow in the Highway from Mexico City to Cuernavaca. This highway
presents free flow in standard days; but in the returning day of long weekends
or holidays it exhibits congested flow and in rush hours jamming appears. We
illustrate how our CA model for traffic flow can deal appropriately with
transient situations and can be used to search new alternatives that allow to
improve the traffic flow in Mexican highways.Comment: Paper accepted to be published in the Proceedings of Second Mexican
Meeting on Mathematical and Experimental Physics (September 2004), El Colegio
Nacional, Mexico City, Mexic
Physical and Sexual Violence, Mental Health indicators, and treatment seeking among street-based population groups in Tegucigalpa, Honduras
To establish the prevalence of exposure to physical and sexual violence, mental health symptoms, and medical treatment-seeking behavior among three street-based subpopulation groups in Tegucigalpa, Honduras, and to assess the association between sociodemographic group, mental health indicators, and exposure to violence
The PSI-U1 snRNP interaction regulates male mating behavior in Drosophila
Alternative pre-mRNA splicing (AS) is a critical regulatory mechanism that operates extensively in the nervous system to produce diverse protein isoforms. Fruitless AS isoforms have been shown to influence male courtship behavior, but the underlying mechanisms are unknown. Using genome-wide approaches and quantitative behavioral assays, we show that the P-element somatic inhibitor (PSI) and its interaction with the U1 small nuclear ribonucleoprotein complex (snRNP) control male courtship behavior. PSI mutants lacking the U1 snRNP-interacting domain (PSIΔAB mutant) exhibit extended but futile mating attempts. The PSIΔAB mutant results in significant changes in the AS patterns of ∼1,200 genes in the Drosophila brain, many of which have been implicated in the regulation of male courtship behavior. PSI directly regulates the AS of at least one-third of these transcripts, suggesting that PSI-U1 snRNP interactions coordinate the behavioral network underlying courtship behavior. Importantly, one of these direct targets is fruitless, the master regulator of courtship. Thus, PSI imposes a specific mode of regulatory control within the neuronal circuit controlling courtship, even though it is broadly expressed in the fly nervous system. This study reinforces the importance of AS in the control of gene activity in neurons and integrated neuronal circuits, and provides a surprising link between a pleiotropic pre-mRNA splicing pathway and the precise control of successful male mating behavior
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