1,650 research outputs found
Demonstration of an optical polarization magnifier with low birefringence
In any polarimetric measurement technique, enhancing the laser polarization
change of a laser beam before it reaches the analyzer can help in improving the
sensitivity. This can be performed using an optical component having a large
linear dichroism, the enhancement factor being equal to the square root of the
ratio of the two transmission factors. A pile of parallel plates at Brewster
incidence looks appropriate for realizing such a polarization magnifier. In
this paper, we address the problem raised by the interference in the plates and
between the plates, which affects the measurement by giving rise to
birefringence. We demonstrate that wedged plates provide a convenient and
efficient way to avoid this interference. We have implemented and characterized
devices with 4 and 6 wedged plates at Brewster incidence which have led to a
decisive improvement of the signal to noise ratio in our ongoing Parity
Violation measurement.Comment: 08 october 200
Constructing Fresnel reflection coefficients by ruler and compass
A simple and intuitive geometical method to analyze Fresnel formulas is
presented. It applies to transparent media and is valid for perpendicular and
parallel polarizations. The approach gives a graphical characterization
particularly simple of the critical and Brewster angles. It also provides an
interpretation of the relation between the reflection coefficients for both
basic polarizations as a symmetry in the plane
Fresnel coefficients as hyperbolic rotations
We describe the action of a plane interface between two semi-infinite media
in terms of a transfer matrix. We find a remarkably simple factorization of
this matrix, which enables us to express the Fresnel coefficients as a
hyperbolic rotation.Comment: 6 pages, 3 figure
Optical Properties of Pentacene and Perfluoropentacene Thin Films
The optical properties of pentacene (PEN) and perfluoropentacene(PFP) thin
films on various SiO2 substrates were studied using variable angle
spectroscopic ellipsometry. Structural characterization was performed using
X-ray reflectivity and atomic force microscopy. A uniaxial model with the optic
axis normal to the sample surface was used to analyze the ellipsometry data. A
Strong optical anisotropy was observed and enabled the direction of the
transition dipole of the absorption bands to be determined. Furthermore,
comparison of the optical constants of PEN and PFP thin films with the
absorption spectra of the monomers in solution shows significant changes due to
the crystalline environment. Relative to the monomer spectrum the HOMO-LUMO
transition observed in PEN (PFP) thin film is reduced by 210 meV (280 meV).
Surprisingly, a second absorption band in the PFP thin film shows a slight
blueshift (40 meV) compared to the spectrum of the monomer with its transition
dipole perpendicular to that of the first absorption band.Comment: 6 pages, 6 figures, submitted to J. Chem. Phy
The Impact of Online Reviews on Brand Equity
The goal of this research is to see how online consumer reviews affect brand equity. Customers of Jordanian online clothing stores make up the study population. Due to the difficulty of reaching all members of the population, an appropriate sampling approach was used, which is often used in research conditions. Appropriate sampling is a non-random sampling method that uses people who are easily accessible. A structured online survey was used to gather primary data. This survey was conducted among Jordanian customers of online clothes retailers. Customers were thus encouraged to take part in the survey by text messages, official websites, and social media channels. The research hypotheses were tested using structural equation modeling. The study results showed that the majority of online review dimensions had an impact on brand equity except for reviews time. However, social impact had the highest impact on brand equity. According to the study’s conclusions, marketers must connect with internet marketing methods, particularly social media, and include them into their marketing strategy
Spectroscopic distinction between the normal state pseudogap and the superconducting gap of cuprate high T_{c} superconductors
We report on broad-band infrared ellipsometry measurements of the c-axis
conductivity of underdoped RBa_{2}Cu_{3}O_{7-d} (R=Y, Nd, and La) single
crystals. Our data provide a detailed account of the spectral weight (SW)
redistributions due to the normal state pseudogap (PG) and the superconducting
(SC) gap. They show that these phenomena involve different energy scales,
exhibit distinct doping dependencies and thus are likely of different origin.
In particular, the SW redistribution in the PG state closely resembles the one
of a conventional charge- or spin density wave (CDW or SDW) system.Comment: 4 pages, 4 figure
Line tension and structure of smectic liquid crystal multilayers at the air-water interface
At the air/water interface, 4,-8-alkyl[1,1,-biphenyl]-4-carbonitrile (8CB)
domains with different thicknesses coexist in the same Langmuir film, as
multiple bilayers on a monolayer. The edge dislocation at the domain boundary
leads to line tension, which determines the domain shape and dynamics. By
observing the domain relaxation process starting from small distortions, we
find that the line tension is linearly dependent on the thickness difference
between the coexisting phases in the film. Comparisons with theoretical
treatments in the literature suggest that the edge dislocation at the boundary
locates near the center of the film, which means that the 8CB multilayers are
almost symmetric with respect to the air/water interface.Comment: 21 pages, 6 figure
A Case of Chronic Cough and Pneumonia Secondary to a Foreign Body
Foreign body aspiration occurs when a solid or semisolid object becomes lodged in the larynx or trachea. It can be a life-threatening emergency, especially if it is large enough to occlude the airway. However, small aspirated objects may go unnoticed until symptoms occur. Therefore, it is frequently misdiagnosed. A high level of clinical suspicion, patient\u27s risk factors, and thorough history and physical examination are essential in making the diagnosis. It should be considered in cases where there is unresolved chronic cough with or without associated recurrent pneumonia especially in patients with risks for aspiration
Use of a Simulation Model to Evaluate the Influence of Reproductive Performance and Management Decisions on Net Income in Beef Production
A stochastic dynamic model of reproduction and a deterministic cow-herd economic simulation model were used to evaluate how management decisions and reproductive performance interact to influence net income in a cow-calf operation (1,000 cows) for 1 yr of production. The stochastic model was used to determine herd performance when length of breeding season (45, 70, or 120 d) interacted with three postpartum intervals of an estrus (48, 65, or 90 d) and three conception rates at first service (60, 70, or 80%). Short, moderate, and long postpartum intervals were used to reflect differences in reproductive performance. In addition, replacement heifers were bred beginning either 3 wk ahead of the cow herd or at the same time as the cow herd. Fifty-four simulations were generated. Inputs into the economic model were herd performance, livestock and feed prices, nonfeed costs, and feed requirements for 1 yr of production. Feed requirements were calculated separately for each postpartum interval to reflect three different body condition scores, thin, moderate, and good, to correspond with long, moderate, and short postpartum intervals. Net income was greatest with 704 breeding seasons when the postpartum interval was short or moderate. When the postpartum interval was long, net income was greatest with 1204 breeding seasons because pregnancy rates, as a result of the long breeding season, were highest and feed costs were lowest for thin cows. Overall, net income was greatest when cows were managed to have postpartum intervals of moderate length. Breeding heifers 3 wk before the cows provided the most economic benefit with long postpartum intervals
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