Bragg Reflectors consist of periodic dielectric layers having an optical path length of quarter wavelength for each layer giving them important properties and makes them suitable for optoelectronics applications. The reflectivity can be increased by increasing the number of layers of the mirror to get the required value. For example for an 8 layers Bragg mirror (two layers for each dielectric pair), the contrast of the refractive index has to be equal to 0.275 for reaching reflectivity > 99%. Doubling the number of layers results in a reflectivity of 99.99%. The high reflectivity is purely caused by multiple-interference effects. It can be analyzed by using different matrix methods such as the transfer matrix method (TMM) which is the simplest method to study the characteristic of devices with different alternating layers.
This paper deal with the estimation of the shape parameter (a) of Generalized Exponential (GE) distribution when the scale parameter (l) is known via preliminary test single stage shrinkage estimator (SSSE) when a prior knowledge (a0) a vailable about the shape parameter as initial value due past experiences as well as suitable region (R) for testing this prior knowledge.
The Expression for the Bias, Mean squared error [MSE] and Relative Efficiency [R.Eff(×)] for the proposed estimator are derived. Numerical results about beha
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The present study was undertaken to determine the species of tumbling flower beetles (Coleoptera, Mordellidae) found in Iraq. Specimens have been collected from different localities of Iraq since 1970. Results show that the tumbling flower beetles (Mordellidae) are represented with a total of 13 species belonging to four genera of three tribes, two of these species were described by Dr. Horak (1985,1990) as new species for Iraq Mediimorda maceki HoraK and Mordellistena bolognaHorak; two were previously reported Stenalia escherichi Schilsk and Mordellistena pumila (Gyllenhal) and ten are new records for Iraq. Stenalia araxicola Khnzorian, Stenalia brunneipennis Mulsant, Variimorda
... Show MoreCurrently regions in the world are much affected with dust storms, rising and suspended dust, as Iraq is suffering of this state as well within an eye-catching manner, whereas the storms leave negative traces on environment and public health and many of the other vital utilities. This research aims to diagnosis of the reasons that resulted in increment of dust storms in Iraq basing on some recorded data and to be analyzed in conformity with the prevalent theories and concepts at the atmospheric science and environmental physics. Generally the study, has illustrated that the climate changes and increase of temperatures averages because of green house effect, that followed by clear changes at thermal wind and jet stream, that caused to ins
... Show MoreThe purpose of this paper is to present an approach to compute accurately the distributions of the frictional heat generated, contact pressure and thermal stresses at any instant during the sliding period (heating phase) of the single-disc friction clutch system works in the dry condition and the complex interaction among them.
Numerical work was achieved using the developed elastic and thermal finite element models (axisymmetric models) to simulate the engagement of the single-disc friction clutch system.
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Absorption and lifetime measurements were made for C6H6. and C6D6 molecules in pure solid phase and in solid matrices of Ar, N2, CO, and CO2. All measurement are made at low temperatures ranging between 12-50 K. A modified least square fitting deconvolution was utilized to measure the fluorescence lifetime with an error less than 1%. The results show that the use of matrix isolation technique offer a unique environment that minimize the perturbation of the molecular or atomic system and hence facilitate spectral analysis.
Films of PMMA and copper sulphate doped PMMA have been prepared by casting method. Absorbance and transmittance spectra were recorded in the wavelength range (300-900) nm in order to calculate, single oscillator energy, dispersion energy, average oscillator strength, the refractive index at infinite wavelength, M-1 and M -3 moments of the optical spectra, it was found that all these parameters were effected by doping.
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In this work, we have examined the spectral response of (p-CuAlSe2/n-Si) detector, (CAS) thin films deposited by thermal evaporation at RT with a thickness (450) nm, and annealing temperature at (473K) for 2 h. Optical transmission measurements displayed reasonably slight transmission besides higher absorbance trendy the visible region, energy gaps were observed by annealing, were found to be direct, and decreased with the effect of annealing. The extreme responsivity value arises at wavelength 459 nm, with improvement value of specific detectivity and quantum efficiency the annealing films be situated originate as greatest suitable aimed at numerous device application.
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