1,091 research outputs found
Light deflection by photonic crystals
When propagating through periodically structured media, i. e. photonic
crystals, optical waves will be modulated with the periodicity. As a result,
the dispersion of waves will no longer behave as in a free space, and so called
frequency band structures appear. Under certain conditions, waves may be
prohibited from propagation in certain or all directions, corresponding to
partial and complete bandgaps respectively. Here we report a new fascinating
phenomenon associated with the partial gaps, that is, deflection of optical
waves. This phenomenon will render novel applications in manipulating light
flows.Comment: 3 pages, 4 figure
Ordered optimal solutions and parametric minimum cut problems
AbstractIn this paper, we present an algebraic sufficient condition for the existence of a selection of optimal solutions in a parametric optimization problem that are totally ordered, but not necessarily monotone. Based on this result, we present necessary and sufficient conditions that ensure the existence of totally ordered selections of minimum cuts for some classes of parametric maximum flow problems. These classes subsume the class studied by Arai et al. [Discrete Appl. Math. 41 (1993) 69–74] as a special case
Deconfounded Causal Collaborative Filtering
Recommender systems may be confounded by various types of confounding factors
(also called confounders) that may lead to inaccurate recommendations and
sacrificed recommendation performance. Current approaches to solving the
problem usually design each specific model for each specific confounder.
However, real-world systems may include a huge number of confounders and thus
designing each specific model for each specific confounder is unrealistic. More
importantly, except for those "explicit confounders" that researchers can
manually identify and process such as item's position in the ranking list,
there are also many "latent confounders" that are beyond the imagination of
researchers. For example, users' rating on a song may depend on their current
mood or the current weather, and users' preference on ice creams may depend on
the air temperature. Such latent confounders may be unobservable in the
recorded training data. To solve the problem, we propose a deconfounded causal
collaborative filtering model. We first frame user behaviors with unobserved
confounders into a causal graph, and then we design a front-door adjustment
model carefully fused with machine learning to deconfound the influence of
unobserved confounders. The proposed model is able to handle both global
confounders and personalized confounders. Experiments on real-world e-commerce
datasets show that our method is able to deconfound unobserved confounders to
achieve better recommendation performance.Comment: 9 pages, 5 figures; comments and suggestions are highly appreciate
The forgotten kids: Experiences of potential student-athletes at a postsecondary football preparatory school
The first preparatory institution was founded in 1635 to prepare elite men for public service, a role in the church, or admission to Harvard (Boyer, 1983). Nearly 400 years later, the objective of such institutions is no longer Harvard, but often an avenue for potential student-athletes (PSAs) to participate in collegiate sport (Thamel, 2007). The NCAA does not define nor regulate postgraduate preparatory institutions; however, Curran (2014) describes a preparatory institution (commonly referred to as prep schools) as a postgraduate institute that provides PSAs another year at a secondary institution prior to making the transition to college. Framed by Mincer’s (1958) model of Basic Human Capital, the purpose of this study is to examine the experiences of those attending or associated with one specific preparatory institution (X Academy). The first research question which explores prospective student-athletes choices to attend a preparatory institution revealed three final themes: (1) eligibility concerns, (2) athletic exposure and development, and (3) academic improvement. The second research question explores the experiences of those attending a preparatory institution also revealed three final themes: (1) focus and preparation, (2) melting pot, and (3) survival.  
Enhanced diffraction by a rectangular grating made of a negative phase--velocity (or negative index) material
The diffraction of electromagnetic plane waves by a rectangular grating
formed by discrete steps in the interface of a homogeneous, isotropic, linear,
negative phase--velocity (negative index) material with free space is studied
using the semi--analytic C method. When a nonspecular diffracted order is of
the propagating type, coupling to that order is significantly larger for a
negative index material than for conventional material. The computed coupling
strengths reported here are in agreement with recent experiments, and
illustrate the role of evanescent fields localized at the grating interface in
producing this enhanced coupling.Comment: 12 pages, 4 figure
Realization of Dirac Point with Double Cones in Optics
The Dirac point with a double-cone structure for optical fields, an optical
analogy Dirac fermions in graphene, can be realized in optically homogenous
metamaterials. The condition for the realization of Dirac point in optical
systems is the varying of refractive index from negative to zero and then to
positive. Our analytical and numerical analysis have verified that, similar to
electrons in graphene, the light field near the Dirac point possesses of the
pseudodiffusive property, obeying the 1/L scaling law, where L is the
propagating distance of light inside the media.Comment: 10 pages, 6 figure
Electric and Magnetic Excitation of Coherent Magnetic Plasmon Waves in a One-dimensional Meta-chain
A one-dimensional diatomic meta-chain with equal-size holes and
different-length slits is designed. Broadband coherent magnetic plasmon waves
(MPW) are formed in such a system, excited by both the electric resonance in
the slits and the magnetic resonance in the holes in a wide range of incidence
angles (00-400) and broad frequency bands (200-230 THz). The dispersion
properties of the MPW measured in our experiments agree with the theoretical
calculation based on the Lagrange model. The coherent MPWs reported in this
paper may have applications in subwavelength integrated nanocircuits
Polyethylene glycol combined with lactulose has better efficacy than polyethylene glycol alone in bowel preparation before colonoscopy: A meta-analysis
Background: The accuracy of diagnosis and the safety of treatment in colonoscopy depends largely on the quality of bowel cleansing. This study aimed to compare the efficacy and adverse reactions of Polyethylene Glycol (PEG) combined with lactulose with that of PEG alone in bowel preparation before colonoscopy.
Methods: The authors searched a number of databases including EMBASE, MEDLINE, Cochrane Library, and China Academic Journals Full-text Database. The authors screened according to literature inclusion and exclusion criteria, assessed the quality of the included literature, and extracted the data. The meta-analysis of included literature used RevMan 5.3 and Stata 14.0 software.
Results: A total of 18 studies, including 2274 patients, were enrolled. The meta-analysis showed that PEG combined with lactulose had a better efficacy (OR = 3.87, 95% CI 3.07‒4.87, p = 0.000, and I2 = 36.2% in the efficiency group; WMD = 0.86, 95% CI 0.69‒1.03, p = 0.032 and I2 = 0% in the BBPS score group) in bowel preparation for patients with or without constipation. Moreover, PEG combined with lactulose had fewer adverse reactions, including abdominal pain (OR = 1.42, 95% CI 0.94‒2.14, p = 0.094), nausea (OR = 1.60, 95% CI 1.13‒2.28, p = 0.009) and vomiting (OR = 1.77, 95% CI 1.14‒2.74, p = 0.011), than PEG alone. No significant reduction in the incidence of abdominal distention was observed.
Conclusion: PEG combined with lactulose may be a better choice for bowel preparation before colonoscopy compared with PEG alone
Resonant and anti-resonant frequency dependence of the effective parameters of metamaterials
We present a numerical study of the electromagnetic response of the
metamaterial elements that are usedto construct materials with negative
refractive index. For an array of split ring resonators (SRR) we find that the
resonant behavior of the effective magnetic permeability is accompanied by an
anti-resonant behavior of the effective permittivity. In addition, the
imaginary parts of the effective permittivity and permeability are opposite in
sign. We also observe an identical resonant versus anti-resonant frequency
dependence of the effective materials parameters for a periodic array of thin
metallic wires with cuts placed periodically along the length of the wire, with
roles of the permittivity and permeability reversed from the SRR case. We show
in a simple manner that the finite unit cell size is responsible for the
anti-resonant behavior
Vesicular glutamatergic transmission in noise-induced loss and repair of cochlear ribbon synapses
Noise-induced excitotoxicity is thought to depend on glutamate. However, the excitotoxic mechanisms are unknown, and the necessity of glutamate for synapse loss or regeneration is unclear. Despite absence of glutamatergic transmission from cochlear inner hair cells in mice lacking the vesicular glutamate transporter-3
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