1,991 research outputs found
Quantification of optical pulsed-plane-wave-shaping by chiral sculptured thin films
The durations and average speeds of ultrashort optical pulses transmitted
through chiral sculptured thin films (STFs) were calculated using a
finite-difference time-domain algorithm. Chiral STFs are a class of
nanoengineered materials whose microstructure comprises parallel helicoidal
nanowires grown normal to a substrate. The nanowires are 10-300 nm in
diameter and m in length. Durations of transmitted pulses tend to
increase with decreasing (free-space) wavelength of the carrier plane wave,
while average speeds tend to increase with increasing wavelength. An increase
in nonlinearity, as manifested by an intensity-dependent refractive index in
the frequency domain, tends to increase durations of transmitted pulses and
decrease average speeds. The circular Bragg phenomenon exhibited by a chiral
STFs manifests itself in the frequency domain as high reflectivity for normally
incident carrier plane waves whose circular polarization state is matched to
the structural handedness of the film and whose wavelength falls in a range
known as the Bragg regime; films of the opposite structural handedness reflect
such plane waves little. This effect tends to distort the shapes of transmitted
pulses with respect to the incident pulses, and such shaping can cause sharp
changes in some measures of average speed with respect to carrier wavelength. A
local maximum in the variation of one measure of the pulse duration with
respect to wavelength is noted and attributed to the circular Bragg phenomenon.
Several of these effects are explained via frequency-domain arguments. The
presented results serve as a foundation for future theoretical and experimental
studies of optical pulse propagation through causal, nonlinear, nonhomogeneous,
and anisotropic materials.Comment: To appear in Journal of Modern Optic
Fiber Acoustic Waveguide : A Sensor Candidate
Sensor development plays a key role in the field of nondestructive evaluation and process control. The annual fiber optic sensor market alone is a multimillion dollar business (1). Acoustic waves are about five orders of magnitude slower than optical waves and can also be guided in cladded glass fibers, similar to optical fibers, with low loss and low dispersion (2â7). Fiber acoustic waveguides are believed to be a very attractive and basic component for further sensor development (8). In this paper a brief theoretical description of a weakly guiding acoustic fiber (7) is given. The material selection criteria for the core and the cladding of the fiber guide, the properties of single-mode operation, and some sensing mechanisms for temperature and pressure variations are discussed. The acoustic waveguide with a liquid core is also considered
Replacing Recipe Realism
Many realist writings exemplify the spirit of ârecipe realismâ. Here I characterise recipe realism, challenge it, and propose replacing it with âexemplar realismâ. This alternative understanding of realism is more piecemeal, robust, and better in tune with scientistsâ own attitude towards their best theories, and thus to be preferred
The Threat of Capital Drain: A Rationale for Public Banks?
This paper yields a rationale for why subsidized public banks may be desirable from a regional perspective in a financially integrated economy. We present a model with credit rationing and heterogeneous regions in which public banks prevent a capital drain from poorer to richer regions by subsidizing local depositors, for example, through a public guarantee. Under some conditions, cooperative banks can perform the same function without any subsidization; however, they may be crowded out by public banks. We also discuss the impact of the political structure on the emergence of public banks in a political-economy setting and the role of interregional mobility
Developing clinical practice guidelines: reviewing, reporting, and publishing guidelines; updating guidelines; and the emerging issues of enhancing guideline implementability and accounting for comorbid conditions in guideline development
Brief report:effects of sensory sensitivity and intolerance of uncertainty on anxiety in mothers of children with autism spectrum disorder
This study examined the relations between anxiety and individual characteristics of sensory sensitivity (SS) and intolerance of uncertainty (IU) in mothers of children with ASD. The mothers of 50 children completed the Hospital Anxiety and Depression Scale, the Highly Sensitive Person Scale and the IU Scale. Anxiety was associated with both SS and IU and IU was also associated with SS. Mediation analyses showed direct effects between anxiety and both IU and SS but a significant indirect effect was found only in the model in which IU mediated between SS. This is the first study to characterize the nature of the IU and SS interrelation in predicting levels of anxiety
- âŚ