Physics Research International http://www.hindawi.com The latest articles from Hindawi Publishing Corporation © 2014 , Hindawi Publishing Corporation . All rights reserved. Structural and Optical Investigations of Heterostructures Based on :Si Solid Solutions Obtained by MOCVD Wed, 23 Jul 2014 06:40:34 +0000 http://www.hindawi.com/journals/physri/2014/782357/ We investigated MOCVD epitaxial heterostructures based on AlxGa1−xAs ternary solid solutions, obtained in the range of compositions and doped with high concentrations of phosphorus and silicon atoms. Using the methods of high-resolution X-ray diffraction, scanning electron microscopy, X-ray microanalysis, Raman spectroscopy, and photoluminescence spectroscopy we have shown that grown epitaxial films represent five-component (AlxGa1−xAs1−yPy)1−zSiz solid solutions. The implementation of silicon in solid solution with a concentration of ~ 0.01 at.% leads to the formation of the structure with deep levels, DX centers, the occurrence of which fundamentally affects the energy characteristics of received materials. P. V. Seredin Copyright © 2014 P. V. Seredin. All rights reserved. Synthesis, Structural and Optical Investigations of (Pb, Bi)TiO3 Borosilicate Glasses Sun, 13 Jul 2014 09:55:22 +0000 http://www.hindawi.com/journals/physri/2014/606709/ A new series of lead bismuth titanate borosilicate glasses with addition of one percent lanthanum oxide have been synthesized using melt-quench technique. X-ray diffraction patterns have been recorded to confirm the amorphous nature of the prepared glass samples. The synthesized glasses have been characterized by using various spectroscopic techniques such as UV-visible, infrared, and Raman spectroscopy. UV-visible measurements were recorded in the wavelength range from 200 to 1100 nm whereas IR and Raman spectroscopic measurements were recorded over a continuous wavenumber range from 400 to 5000 cm−1 and 1000 to 2000 cm−1 respectively. The different absorption peaks/bands were formed in IR spectral patterns. The spectral bands appear towards the lower wavenumber sides due to the Bi and Pb, content while the bands appear towards the higher wavenumber sides due to the formation of diborate and triborate network units. Chandkiram Gautam Copyright © 2014 Chandkiram Gautam. All rights reserved. Renormalization of QED Near Decoupling Temperature Tue, 24 Jun 2014 09:01:06 +0000 http://www.hindawi.com/journals/physri/2014/489163/ We study the effective parameters of QED near decoupling temperatures and show that the QED perturbative series is convergent, at temperatures below the decoupling temperature. The renormalization constant of QED acquires different values if a system cools down from a hotter system to the electron mass temperature or heats up from a cooler system to the same temperature. At , the first order contribution to the electron self-mass, is 0.0076 for a heating system and 0.0115 for a cooling system and the difference between two values is equal to 1/3 of the low temperature value and 1/2 of the high temperature value around . This difference is a measure of hot fermion background at high temperatures. With the increase in release of more fermions at hotter temperatures, the fermion background contribution dominates and weak interactions have to be incorporated to understand the background effects. Samina S. Masood Copyright © 2014 Samina S. Masood. All rights reserved. Vector Potential Quantization and the Quantum Vacuum Thu, 19 Jun 2014 10:46:32 +0000 http://www.hindawi.com/journals/physri/2014/187432/ We investigate the quantization of the vector potential amplitude of the electromagnetic field to a single photon state starting from the fundamental link equations between the classical electromagnetic theory and the quantum mechanical expressions. The resulting wave-particle formalism ensures a coherent transition between the classical electromagnetic wave theory and the quantum representation. A quantization constant of the photon vector potential is defined. A new quantum vacuum description results directly in having very low energy density. The calculated spontaneous emission rate and Lambs shift for the states of the hydrogen atom are in agreement with quantum electrodynamics. This low energy quantum vacuum state might be compatible with recent astrophysical observations. Constantin Meis Copyright © 2014 Constantin Meis. All rights reserved. Coherent and Incoherent Scattering Cross Sections of Some Lead and Sodium Compounds at Angles below 10° for 241Am Gamma Rays Mon, 02 Jun 2014 06:50:07 +0000 http://www.hindawi.com/journals/physri/2014/594767/ We report the total (coherent + incoherent) scattering cross sections of some lead and sodium compounds measured at angles less than 10° for 241Am (59.54 keV) gamma rays. The experimental cross sections so obtained are compared with the data interpolated from theoretical compilations based on nonrelativistic Hartree-Fock (NRHF) model for the samples of interest. In the low momentum transfer region studied, it is observed that the nonrelativistic theoretical total scattering cross sections computed using HF form factor and scattering function tabulated by NRHF are quite adequate in explaining the measured total scattering cross sections. L. Vinaykumar and T. K. Umesh Copyright © 2014 L. Vinaykumar and T. K. Umesh. All rights reserved. Free Convective Fluctuating MHD Flow through Porous Media Past a Vertical Porous Plate with Variable Temperature and Heat Source Tue, 06 May 2014 07:54:23 +0000 http://www.hindawi.com/journals/physri/2014/587367/ Free convective magnetohydrodynamics (MHD) flow of a viscous incompressible and electrically conducting fluid past a hot vertical porous plate embedded in a porous medium in the presence of heat source has been studied in this paper. The temperature of the plate varies both in space and time. The main objective of this paper is to study the effect of porosity of the medium coupled with the variation of plate temperature with regard to space and in time. The effect of pertinent parameters characterizing the flow has been presented through the graphs. It is important to record that the presence of porous media has no significant contribution to the flow characteristics and viscous dissipation compensates for the heating and cooling of the plate due to convective current. A. K. Acharya, G. C. Dash, and S. R. Mishra Copyright © 2014 A. K. Acharya et al. All rights reserved. Investigation of Gamma and Neutron Shielding Parameters for Borate Glasses Containing NiO and PbO Wed, 23 Apr 2014 07:19:01 +0000 http://www.hindawi.com/journals/physri/2014/954958/ The mass attenuation coefficients, , half-value layer, HVL, tenth-value layer, TVL, effective atomic numbers, , and effective electron densities, , of borate glass sample systems of (100--) Na2B4O7 : PbO : NiO (where and , and 10 weight percentage) containing PbO and NiO, with potential gamma ray and neutron shielding applications, have been investigated. The gamma ray interaction parameters, , HVL, TVL, , and , were computed for photon energy range 1 keV–100 GeV. The macroscopic fast neutron removal cross-sections () have also been calculated. Appreciable variations were noted for all the interaction parameters by varying the photon energy and the chemical composition of the glass samples. The better shielding properties of borate glass samples containing PbO were found. These results indicated that borate glass samples are a good radiation shielding material. Vishwanath P. Singh and N. M. Badiger Copyright © 2014 Vishwanath P. Singh and N. M. Badiger. All rights reserved. Linear Sigma Model at Finite Temperature and Baryonic Chemical Potential Using the -Midpoint Technique Thu, 06 Mar 2014 00:00:00 +0000 http://www.hindawi.com/journals/physri/2014/435023/ A baryonic chemical potential () is included in the linear sigma model at finite temperature. The effective mesonic potential is numerically calculated using the -midpoint rule. The meson masses are investigated as functions of the temperature () at fi…xed value of baryonic chemical potential. The pressure and energy density are investigated as functions of temperature at fixed value of . The obtained results are in good agreement in comparison with other techniques. We conclude that the calculated effective potential successfully predicts the meson properties and thermodynamic properties at finite baryonic chemical potential. M. Abu-Shady Copyright © 2014 M. Abu-Shady. All rights reserved. Estimating the Cation Distributions in Ferrites Using X-Ray, FT-IR, and Magnetization Measurements Tue, 04 Mar 2014 13:04:56 +0000 http://www.hindawi.com/journals/physri/2014/579745/ The fundamental requirements for the shift of critical frequency to microwave frequencies are smaller grains with single domain, high resistivity, high saturation magnetization, moderate permeability, moderate magnetic anisotropy, and low spin relaxation time. With these guidelines an attempt to produce high performance ferrite for high frequency applications the present work aimed to synthesize cobalt substituted Ni-Zn ferrites using sol-gel method. Investigation of effects of cobalt on crystallite size, saturation magnetization, initial permeability, magnetic anisotropy, and spin relaxation time reveals the suitability of these materials for high frequency applications. Further in this paper cat ion distribution was proposed from the basis of variations in these properties. The results of this paper are thus useful to tailor the properties apt for high frequency applications. M. Chaitanya Varma, GSVRK Choudary, A. Mahesh Kumar, and K. H. Rao Copyright © 2014 M. Chaitanya Varma et al. All rights reserved. Structural and Optical Properties of Germanium Thin Films Prepared by the Vacuum Evaporation Technique Mon, 17 Feb 2014 08:55:44 +0000 http://www.hindawi.com/journals/physri/2014/594968/ Germanium (Ge) thin films have been deposited onto the glass substrates by the vacuum evaporation technique. The effect of annealing temperature on the structural and optical properties of the germanium thin films was investigated. The structural and optical properties of thin films were characterized by XRD, SEM, and UV-Vis techniques. XRD results showed that the structure of the deposited thin films changed from amorphous phase for the films, which deposited at room temperature, to crystalline phase for the films, which deposited at high temperature. Optimum temperature to obtain a good crystalline structure was 525°C. The SEM image also showed that the crystallization of the thin films is increased with increasing of annealing temperature. Transmittance and reflectance spectral were used to calculate the absorption coefficient. Two absorption edges in two spectral regions were distinguished according to direct and indirect electron transitions. Energy band gap was calculated by using the Tauc relationship for both direct and indirect electron transitions. The average value of was equal to 0.79 eV and 0.61 eV for direct and indirect transitions, respectively. Z. Al-Sharafi, S. Mohyeddine, Samir Osman Mohammed, and R. M. Kershi Copyright © 2014 Z. Al-Sharafi et al. All rights reserved. Magnetohydrodynamic Boundary Layer Flow of Nanofluid over an Exponentially Stretching Permeable Sheet Wed, 08 Jan 2014 07:51:52 +0000 http://www.hindawi.com/journals/physri/2014/592536/ A mathematical model of the steady boundary layer flow of nanofluid due to an exponentially permeable stretching sheet with external magnetic field is presented. In the model, the effects of Brownian motion and thermophoresis on heat transfer and nanoparticle volume friction are considered. Using shooting technique with fourth-order Runge-Kutta method the transformed equations are solved. The study reveals that the governing parameters, namely, the magnetic parameter, the wall mass transfer parameter, the Prandtl number, the Lewis number, Brownian motion parameter, and thermophoresis parameter, have major effects on the flow field, the heat transfer, and the nanoparticle volume fraction. The magnetic field makes enhancement in temperature and nanoparticle volume fraction, whereas the wall mass transfer through the porous sheet causes reduction of both. For the Brownian motion, the temperature increases and the nanoparticle volume fraction decreases. Heat transfer rate becomes low with increase of Lewis number. For thermophoresis effect, the thermal boundary layer thickness becomes larger. Krishnendu Bhattacharyya and G. C. Layek Copyright © 2014 Krishnendu Bhattacharyya and G. C. Layek. All rights reserved. Preparation, Characterization, and Luminescence Properties of Orthorhombic Sodium Sulphate Tue, 24 Dec 2013 11:15:39 +0000 http://www.hindawi.com/journals/physri/2013/641631/ A highly efficient thermoluminescence Na2SO4 phosphor with thenardite polymorphic structure was prepared by simple slow evaporation technique followed by subsequent calcination at 200°C, 400°C, and 600°C for 4 h and the resultant crystals were characterized by various analytical techniques. All the samples exhibited thermodynamically stable thenardite phase and the grain growth was increased for the calcined samples. SEM analysis indicated the fine distribution of twinned orthogonal prism and pyramidal structure without any agglomeration. The electron spin resonance spectroscopy showed the existence of radicals as trap centre. The thermoluminescence behavior suggested the charge carrier recombination dynamics in the thenardite sample followed second-order kinetics. The trapping parameters such as activation energy (), order of kinetics (), and frequency factor () have been determined using Chen’s peak shape method. Further fading of the TL intensity of Na2SO4 showed that thenardite is quite suitable for radiation dosimetry even up to 15 days. The photoluminescence band of Na2SO4 reduced in its intensity after γ-irradiation, suggesting that defects are unstable and decay rapidly. Y. S. Vidya and B. N. Lakshminarasappa Copyright © 2013 Y. S. Vidya and B. N. Lakshminarasappa. All rights reserved. Molecular Tomography of the Quantum State by Time-Resolved Electron Diffraction Mon, 23 Dec 2013 09:40:53 +0000 http://www.hindawi.com/journals/physri/2013/236743/ A procedure is described that can be used to reconstruct the quantum state of a molecular ensemble from time-dependent internuclear probability density functions determined by time-resolved electron diffraction. The procedure makes use of established techniques for evaluating the density matrix and the phase-space joint probability density, that is, the Wigner function. A novel expression for describing electron diffraction intensities in terms of the Wigner function is presented. An approximate variant of the method, neglecting the off-diagonal elements of the density matrix, was tested by analyzing gas electron diffraction data for N2 in a Boltzmann distribution and TRED data obtained from the 193 nm photodissociation of CS2 to carbon monosulfide, CS, at 20, 40, and 120 ns after irradiation. The coherent changes in the nuclear subsystem by time-resolved electron diffraction method determine the fundamental transition from the standard kinetics to the dynamics of the phase trajectory of the molecule and the tomography of molecular quantum state. A. A. Ischenko Copyright © 2013 A. A. Ischenko. All rights reserved. Reconciliating the Vertical and Horizontal Gradients of the Sunspot Magnetic Field Mon, 23 Dec 2013 08:26:43 +0000 http://www.hindawi.com/journals/physri/2013/195403/ In the literature, we found 15 references showing that the sunspot photospheric magnetic field vertical gradient is on the order of 3-4 G/km, with field strength decreasing with height, whereas the horizontal gradient is nine times weaker on the order of 0.4-0.5 G/km. This is confirmed by our recent THEMIS observations. As a consequence, the vanishing of is not realized. In other words, a loss of magnetic flux is observed with increasing height, which is not compensated for by an increase of the horizontal flux. We show that the lack of spatial resolution, vertical as well as horizontal, cannot be held responsible for the nonvanishing observed . The present paper is devoted to the investigation of this problem. We investigate how the magnetic field is influenced by the plasma anisotropy due to the stratification, which is responsible for an “aspect ratio” between horizontal and vertical typical lengths. On the example of our THEMIS observations, made of two spectral lines formed at two different depths, which enables the retrieval of the three components entering , it is shown that once this aspect ratio is applied, the rescaled vanishes, which suggests a new methodology for MHD modeling in the photosphere. Véronique Bommier Copyright © 2013 Véronique Bommier. All rights reserved. Analytical Approach to Model and Diagnostic Distribution of Dopant in an Implanted-Heterojunction Rectifier Accounting for Mechanical Stress Thu, 05 Sep 2013 08:10:04 +0000 http://www.hindawi.com/journals/physri/2013/645620/ We calculate spatiotemporal distributions of dopant in an implanted-heterojunction rectifier. We analyzed the influence of inhomogeneity of heterostructure on dopant distribution. The influence of radiation processing of materials of the heterostructure, which has been done during ion implantation, on properties of the heterostructure has been also analyzed. It has been shown that radiation processing of materials of heterostructure leads to a decrease in mechanical stress in heterostructure. Our calculations have been done by using analytical approach, which gives us the possibility to obtain all results without joining solutions on all interfaces of heterostructure. E. L. Pankratov and E. A. Bulaeva Copyright © 2013 E. L. Pankratov and E. A. Bulaeva. All rights reserved. A Sturm-Liouville Problem with a Discontinuous Coefficient and Containing an Eigenparameter in the Boundary Condition Sun, 01 Sep 2013 11:12:20 +0000 http://www.hindawi.com/journals/physri/2013/159243/ We study a Sturm-Liouville operator with eigenparameter-dependent boundary conditions and transmission conditions at two interior points. We give an operator-theoretic formulation, construct fundamental solutions, investigate some properties of the eigenvalues and corresponding eigenfunctions of the discontinuous Sturm-Liouville problem and then obtain asymptotic formulas for the eigenvalues and eigenfunctions and find Green function of the discontinuous Sturm-Liouville problem. Erdoğan Şen Copyright © 2013 Erdoğan Şen. All rights reserved. Luminescence Studies of Eu3+ Doped Calcium Bromofluoride Phosphor Tue, 20 Aug 2013 08:12:12 +0000 http://www.hindawi.com/journals/physri/2013/494807/ The present paper reports photoluminescence (PL) and thermoluminescence (TL) properties of rare earth-doped calcium bromo-fluoride phosphor. The europium (Eu3+) was used as rare earth dopant. The phosphor was prepared by Solid state reaction method (conventional method). The PL emission spectrum of the prepared phosphor shows intense peaks in the red region at 611 nm for 5D0→7F2 transitions, and the PL excitation spectra show a broad band located around 220–400 nm for the emission wavelength fixed at 470 nm. The TL studies were carried out after irradiating the phosphor by UV rays with different exposure time. The glow peak shows second-order kinetics. The present phosphor can act as host for red light emission in display devices. Jagjeet Kaur, Yogita Parganiha, and Vikas Dubey Copyright © 2013 Jagjeet Kaur et al. All rights reserved. Self-Consistent Green Function Method in Nuclear Matter Tue, 16 Jul 2013 15:27:08 +0000 http://www.hindawi.com/journals/physri/2013/415605/ Symmetric nuclear matter is studied within the Brueckner-Hartree-Fock (BHF) approach and is extending to the self-consistent Green’s function (SCGF) approach. Both approximations are based on realistic nucleon-nucleon interaction; that is, CD-Bonn potential is chosen. The single-particle energy and the equation of state (EOS) are studied. The Fermi energy at the saturation point fulfills the Hugenholtz-Van Hove theorem. In comparison to the BHF approach, the binding energy is reduced and the EOS is stiffer. Both the SCGF and BHF approaches do not reproduce the correct saturation point. A simple contact interaction should be added to SCGF and BHF approaches to reproduce the empirical saturation point. Khaled S. A. Hassaneen Copyright © 2013 Khaled S. A. Hassaneen. All rights reserved. Effect of Electrohydraulic Discharge on Viscosity of Human Blood Sun, 07 Jul 2013 08:43:21 +0000 http://www.hindawi.com/journals/physri/2013/203708/ Electrohydraulic plasma discharge is a novel technology with high efficiency and high speed and can generate chemically active species like free radicals, ions, atoms, and metastables, accompanied by ultraviolet light emission and shock pressure waves. The aim of this work is to examine the effect of electrohydraulic discharge (EHD) system on viscosity of the human blood after different exposure time. The voltage pulsation introduces electric field and temperature jump and at the same time leads to haemolysis of the blood cells. The ratio of blood viscosity under the influence of magnetic field to the viscosity in the absence of magnetic field is directly proportional to the applied magnetic field . G. M. El-Aragi Copyright © 2013 G. M. El-Aragi. All rights reserved. Applicability of Different Isothermal EOS at Nanomaterials Mon, 17 Jun 2013 15:46:04 +0000 http://www.hindawi.com/journals/physri/2013/927324/ The present study explains the behaviour of nanomaterials such as AlN, CdSe, Ge, WC, and Ni- and Fe-filled-MWCNTs under high pressure. Among the number of isothermal EOSs available, we prefer only two parameter-based isothermal equations (i.e., Murnaghan equation, usual Tait's equation, Suzuki equation and Shanker equation). The present work shows the theoretical study of thermo-elastic properties especially relative compression (), isothermal bulk modulus (), and compressibility () of nanomaterials. After comparing all formulations with available experimental data, we conclude that pressure dependence of relative compression () for the nanomaterials, are in good agreement for all the equations at lower pressure range. At higher pressure range, Suzuki and Shanker formulations show some deviation from experimental values. Deepika P. Joshi and Anjali Senger Copyright © 2013 Deepika P. Joshi and Anjali Senger. All rights reserved. Renormalisation Group Analysis of Turbulent Hydrodynamics Wed, 12 Jun 2013 13:50:54 +0000 http://www.hindawi.com/journals/physri/2013/872796/ Turbulent hydrodynamics is characterised by universal scaling properties of its structure functions. The basic framework for investigations of these functions has been set by Kolmogorov in 1941. His predictions for the scaling exponents, however, deviate from the numbers found in experiments and numerical simulations. It is a challenge for theoretical physics to derive these deviations on the basis of the Navier-Stokes equations. The renormalization group is believed to be a very promising tool for the analysis of turbulent systems, but a derivation of the scaling properties of the structure functions has so far not been achieved. In this work, we recall the problems involved, present an approach in the framework of the exact renormalisation group to overcome them, and present first numerical results. Dirk Barbi and Gernot Münster Copyright © 2013 Dirk Barbi and Gernot Münster. All rights reserved. Scale-Free Networks with the Same Degree Distribution: Different Structural Properties Wed, 29 May 2013 08:34:17 +0000 http://www.hindawi.com/journals/physri/2013/234180/ We have analysed some structural properties of scale-free networks with the same degree distribution. Departing from a degree distribution obtained from the Barabási-Albert (BA) algorithm, networks were generated using four additional different algorithms (Molloy-Reed, Kalisky, and two new models named A and B) besides the BA algorithm itself. For each network, we have calculated the following structural measures: average degree of the nearest neighbours, central point dominance, clustering coefficient, the Pearson correlation coefficient, and global efficiency. We found that different networks with the same degree distribution may have distinct structural properties. In particular, model B generates decentralized networks with a larger number of components, a smaller giant component size, and a low global efficiency when compared to the other algorithms, especially compared to the centralized BA networks that have all vertices in a single component, with a medium to high global efficiency. The other three models generate networks with intermediate characteristics between B and BA models. A consequence of this finding is that the dynamics of different phenomena on these networks may differ considerably. José H. H. Grisi-Filho, Raul Ossada, Fernando Ferreira, and Marcos Amaku Copyright © 2013 José H. H. Grisi-Filho et al. All rights reserved. Semiclassical Modeling of Isotropic Non-Heisenberg Magnets for Spin and Linear Quadrupole Excitation Dynamics Wed, 27 Mar 2013 17:13:23 +0000 http://www.hindawi.com/journals/physri/2013/634073/ Equations describing one-dimensional non-Heisenberg model are studied by use of generalized coherent states in real parameterization, and then dissipative spin wave equation for dipole and quadrupole branches is obtained if there is a small linear excitation from the ground state. Finally, it is shown that for such exchange-isotropy Hamiltonians, optical branch of spin wave is nondissipative. Yousef Yousefi and Khikmat Kh. Muminov Copyright © 2013 Yousef Yousefi and Khikmat Kh. Muminov. All rights reserved. Advances in Novel Optical Materials and Devices Thu, 14 Mar 2013 11:54:00 +0000 http://www.hindawi.com/journals/physri/2013/430947/ Michael R. Gleeson, Yasuo Tomita, Sergi Gallego, and Robert McLeod Copyright © 2013 Michael R. Gleeson et al. All rights reserved. On the Divergenceless Property of the Magnetic Induction Field Mon, 25 Feb 2013 07:46:44 +0000 http://www.hindawi.com/journals/physri/2013/292834/ Maxwell's equations beautifully describe the electromagnetic fields properties. In what follows we will be interested in giving a new perspective to divergence-free Maxwell’s equations regarding the magnetic induction field: . To this end we will consider some physical aspects of a system consisting of massive nonrelativistic charged particles, as sources of an electromagnetic field (e.m.) propagating in free space. In particular the link between conservation of total momentum and divergence-free condition for the magnetic induction field will be deeply investigated. This study presents a new context in which the necessary condition for the divergence-free property of the magnetic induction field in the whole space, known as solenoidality condition, directly comes from the conservation of total momentum for the system, that is, sources and field. This work, in general, leads to results that leave some open questions on the existence, or at least the observability, of magnetic monopoles, theoretically plausible only under suitable symmetry assumptions as we will show. Sergio Severini and Alessandro Settimi Copyright © 2013 Sergio Severini and Alessandro Settimi. All rights reserved. A Minireview of the Natures of Radiation-Induced Point Defects in Pure and Doped Silica Glasses and Their Visible/Near-IR Absorption Bands, with Emphasis on Self-Trapped Holes and How They Can Be Controlled Wed, 13 Feb 2013 10:15:50 +0000 http://www.hindawi.com/journals/physri/2013/379041/ The natures of most radiation-induced point defects in amorphous silicon dioxide (a-SiO2) are well known on the basis of 56 years of electron spin resonance (ESR) and optical studies of pure and doped silica glass in bulk, thin-film, and fiber-optic forms. Many of the radiation-induced defects intrinsic to pure and B-, Al-, Ge-, and P-doped silicas are at least briefly described here and references are provided to allow the reader to learn still more about these, as well as some of those defects not mentioned. The metastable self-trapped holes (STHs), intrinsic to both doped and undoped silicas, are argued here to be responsible for most transient red/near-IR optical absorption bands induced in low-OH silica-based optical fibers by ionizing radiations at ambient temperatures. However, accelerated testing of a-SiO2-based optical devices slated for space applications must take into account the highly supralinear dependence on ionizing-dose-rate of the initial STH creation rate, which if not recognized would lead to false negatives. Fortunately, however, it is possible to permanently reduce the numbers of environmentally or operationally created STHs by long-term preirradiation at relatively low dose rates. Finally, emphasis is placed on the importance and utility of rigorously derived fractal-kinetic formalisms that facilitate reliable extrapolation of radiation-induced optical attenuations in silica-based photonics recorded as functions of dose rate backward into time domains unreachable in practical laboratory times and forward into dose-rate regimes for which there are no present-day laboratory sources. David L. Griscom Copyright © 2013 David L. Griscom. All rights reserved. A New Technology for Fast Two-Dimensional Detection of Proton Therapy Beams Sun, 30 Dec 2012 12:45:40 +0000 http://www.hindawi.com/journals/physri/2012/714782/ The Micromesh Gaseous Structure, or Micromegas, is a technology developed for high count-rate applications in high-energy physics experiments. Tests using a Micromegas chamber and specially designed amplifiers and readout electronics adapted to the requirements of the proton therapy environment and providing both excellent time and high spatial resolution are presented here. The device was irradiated at the Roberts Proton Therapy Center at the University of Pennsylvania. The system was operated with ionization gains between 10 and 200 and in low and intermediate dose-rate beams, and the digitized signal is found to be reproducible to 0.8%. Spatial resolution is determined to be 1.1 mm (1σ) with a 1 ms time resolution. We resolve the range modulator wheel rotational frequency and the thicknesses of its segments and show that this information can be quickly measured owing to the high time resolution of the system. Systems of this type will be extremely useful in future treatment methods involving beams that change rapidly in time and spatial position. The Micromegas design resolves the high dose rate within a proton Bragg peak, and measurements agree with Geant4 simulations to within 5%. Robert Hollebeek, Mitch Newcomer, Godwin Mayers, Brian Delgado, Gaurav Shukla, Richard Maughan, and Derek Dolney Copyright © 2012 Robert Hollebeek et al. All rights reserved. Nonlinear Optics of Nanostructures Sun, 09 Dec 2012 14:27:16 +0000 http://www.hindawi.com/journals/physri/2012/648758/ Vladimir I. Gavrilenko, Tatiana V. Murzina, and Goro Mizutani Copyright © 2012 Vladimir I. Gavrilenko et al. All rights reserved. Modeling of Optical Nanoantennas Thu, 08 Nov 2012 09:40:16 +0000 http://www.hindawi.com/journals/physri/2012/321075/ The optical properties of plasmonic nanoantennas are investigated in detail using the finite integration technique (FIT). The validity of this technique is verified by comparison to the exact solution generalized Mie method (GMM). The influence of the geometrical parameters (antenna length, gap dimension, and shapes) on the antenna field enhancement and spectral response is discussed. Localized surface plasmon resonances of Au (gold) dimers nanospheres, bowtie, and aperture bowtie nanoantennas are modeled. The enhanced field is equivalent to a strong light spot which can lead to the resolution improvement of the microscopy and optical lithography, thus increasing the optical data storage capacity. Furthermore, the sensitivity of the antennas to index changes of the environment and substrate is investigated in detail for biosensing applications. We confirm that our approach yields an exact correspondence with GMM theory for Au dimers nanospheres at gap dimensions 5 nm and 10 nm but gives an approximation error of less than 1.37% for gap dimensions 1 nm and 2 nm with diameters approaching 80 nm. In addition, the far-field characteristics of the aperture bowtie nanoantenna such as directivity and gain are studied. The promising results of this study may have useful potential applications in near-field sample detection, optical microscopy, and so forth. Bedir B. Yousif and Ahmed S. Samra Copyright © 2012 Bedir B. Yousif and Ahmed S. Samra. All rights reserved. Quantitative Comparison of Five Different Photosensitizers for Use in a Photopolymer Wed, 12 Sep 2012 11:18:07 +0000 http://www.hindawi.com/journals/physri/2012/975948/ Several studies of the time varying photon absorption effects, which occur during the photoinitiation process involving in photopolymer materials, have been presented. Three primary mechanisms have been identified: (i) the dye absorption, (ii) recovery, and (iii) bleaching. Based on an analysis of these mechanisms, the production of primary radicals can be physically described and modelled. In free radical photopolymerization systems, the excited dye molecules induce the production of the primary radicals, 𝑅•, which are key in determining how many monomers are polymerized. This, in turn, is closely related to the refractive index modulation formed during holographic recording. In this paper, to avoid the complexities involved in estimating the rate constant of intersystem crossing, 𝑘𝑠𝑡, in going from the excited singlet state dye to the excited triplet state dye, we introduce two rates, 𝑘𝑎𝑆 and 𝑘𝑎𝑇 these are the proposed rate constants of photon absorption in going from the ground state to the singlet and triplet states, respectively. Using the resulting model, four kinds of Xanthene dyes: Erythrosin B; Eosin Y; Phloxine B, Rose Bengal, and one Thiazine dye: Methylene Blue, are experimentally characterised for use in an AA/PVA photopolymer. Yue Qi, Michael R. Gleeson, Jinxin Guo, Sergi Gallego, and John T. Sheridan Copyright © 2012 Yue Qi et al. All rights reserved.