Electromagnetic wave propagation through a dielectric-chiral interface and through a chiral slab

The reflection from and transmission through a semi-infinite chiral medium are analyzed by obtaining the Fresnel equations in terms of parallel- and perpendicular-polarized modes, and a comparison is made with results reported previously. The chiral medium is described electromagnetically by the constitutive relations D = εE + iγB and H = iγE + (1/μ)B. The constants ε, μ, and γ are real and have values that are fixed by the size, the shape, and the spatial distribution of the elements that collectively compose the medium. The conditions are obtained for the total internal reflection of the incident wave from the interface and for the existence of the Brewster angle. The effects of the chirality on the polarization and the intensity of the reflected wave from the chiral half-space are discussed and illustrated by using the Stokes parameters. The propagation of electromagnetic waves through an infinite slab of chiral medium is formulated for oblique incidence and solved analytically for the case of normal incidence

Modeling the global positioning system signal propagation through the ionosphere

Based on realistic modeling of the electron density of the ionosphere and using a dipole moment approximation for the Earth's magnetic field, one is able to estimate the effect of the ionosphere on the Global Positioning System (GPS) signal for a ground user. The lowest order effect, which is on the order of 0.1-100 m of group delay, is subtracted out by forming a linear combination of the dual frequencies of the GPS signal. One is left with second- and third-order effects that are estimated typically to be approximately 0-2 cm and approximately 0-2 mm at zenith, respectively, depending on the geographical location, the time of day, the time of year, the solar cycle, and the relative geometry of the magnetic field and the line of sight. Given the total electron content along a line of sight, the authors derive an approximation to the second-order term which is accurate to approximately 90 percent within the magnetic dipole moment model; this approximation can be used to reduce the second-order term to the millimeter level, thus potentially improving precise positioning in space and on the ground. The induced group delay, or phase advance, due to second- and third-order effects is examined for two ground receivers located at equatorial and mid-latitude regions tracking several GPS satellites

Etymology of Questions

pages 14-1

Assessing the outcome of inner limiting membrane peeling in treating idiopathic epiretinal membrane

Idiopathic Epiretinal membrane is a proliferation of contractile cells on the surface of the retina that typically occurs after posterior vitreous detachment. Though many questions have been raised on the causes of this condition, a greater debate has been on the treatment of this pathology. The literature suggest the potential benefit in peeling ILM, due to its inherent proliferative characteristics, along with the ERM, during the surgery, however sufficient data has yet to been found. Due to the lack of consensus in treatment of iERM, this study set forth to provide some insight on the surgical outcomes of patients that undergo combined peeling as well attempting to contribute to a potential surgical protocol in treating iERM. This was a retrospective case series study looking at 140 eyes from 126 iERM patients that underwent ERM surgical treatment at Beth Israel Deaconess Medical Center between 1998 and 2015. Pre- and post- operative visual acuities, lens status (phakic, aphakic, pseudophakic), type (kenalog with or without ICG) and duration (0.5min, 1 min, 1.5 min) of the stains used in the procedure, and any prior or successive surgeries were recorded and analyzed. Overall, ERM surgeries demonstrated a significant (p<0.0001) improvement in visual acuity. Furthermore, the combined peel patients demonstrated a significantly (p<0.0467) greater mean change in logMAR score when compared to ERM-only peel procedures. In addition, the combined peel group showed a smaller rate of recurrence. Lastly, simultaneous cataract surgery and the use of ILM stains did not have an impact on the outcome of ERM surgery. The study found that combined (ERM and ILM) peeling along with simultaneous cataract surgery, if a cataract was present, along with the utilization of ILM stains is cost-effective, safe, and effective approach in treating iERM and decreasing its recurrence

The atomic structure and properties of mirror coatings for use in gravitational wave detectors

Gravitational waves are a prediction of Einstein's General Theory of Relativity. They can be regarded as perturbations, or ripples, in the curvature of space-time that travel at the speed of light. Detectable gravitational waves are the result of the asymmetric acceleration of mass that occurs during massive astronomical events, such as coalescing compact binary systems and supernovae. The nature and detection of gravitational waves is the focus of Chapter 1. A direct detection of gravitational waves is still to be made, however, there is strong indirect evidence of their existence through the work Hulse and Taylor. They observed a binary pulsar system over a number of years and found it to have a decaying orbit that followed a decay rate consistent with a model in which energy is lost due to the production of gravitational waves. The most promising method for gravitational wave detection is through the use of long-baseline interferometric gravitational wave detectors, such as LIGO located in the US, GEO600 in Germany and Virgo in Italy. There are planned upgrades to current long-baseline interferometric gravitational wave detectors. These second generation of detectors will aim to improve sensitivity by a factor of around ten, allowing a much greater chance of detecting gravitational waves, particularly from sources such as coalescing compact binary systems. However, the sensitivity of these detectors will still be limited by noise sources, such as photon-shot, seismic and thermal noise, which could be further reduced by the development of new technologies. Chapter 2 discusses the current understanding of thermal noise arising from the mirror coatings in the detector test-masses. This will identify thermal noise as a particularly important noise source, limiting the sensitivity of detectors between the frequency range from a few tens Hertz to several hundred Hertz. There is an international network of scientists working on developing new technologies for future generations of interferometric gravitational wave detectors, which have the aim of increasing detector sensitivity and further reducing the effect of detector noise sources. The research presented in this thesis focuses on investigating the mechanical loss, which is directly related to the thermal noise, of the mirror coatings. In particular the first attempts at correlating changes in atomic structure of the coatings to the mechanical loss where various properties, such as heat-treatment and doping, of the coatings have been systematically changed will be presented. Chapter 3 will focus on the effect of heat-treatment of pure Ta2O5 coatings. The process of heat treating Ta2O5 coatings has observable effects on mechanical loss measured at low temperature, where loss peaks arise in the region of 10s of K and develop as the heat-treatment temperature rises. Heat-treatment also produces subtle changes to the averaged local atomic structure of the coatings where it can be seen that as the heat-treatment temperature is increased, the coatings became more ordered, moving towards crystallisation between heat-treatment at 300-600C coatings before fully crystallising at 800C. Atomic models show Ta2O2 ring fragments which are present in the crystalline phases of similar materials. In general it is observed that as heat-treatment temperature is increased there is an increase in the presence of the Ta2O2 ring fragments and a decrease in the presence of Ta-Ta bonds in the atomic structures. Changing the manufacturing deposition process for the Ta2O5 coatings also creates significant changes in the mechanical loss at low temperatures, where a `low water content' manufacturing processes gives rise to changes in the positions and shapes of the low temperature loss peaks. Preliminary investigations into the local atomic structure at different areas of a heat-treated coating shows that increasing heat-treatment temperature causes more ordered coating material nearer the substrate, compared with areas nearer the surface of the coating. Chapter 4 presents studies on the effect of doping Ta2O5 coatings with TiO2 with doping concentrations of 0, 8.3, 20.4, 25.7, 28.3, 53.8% (cation) TiO2. Mechanical loss measurements of multi-layer SiO2 and Ta2O5 doped with TiO2 coatings show that changing the TiO2 doping concentration reduces the mechanical loss of the coating by up to 40%. It is also shown that changing the TiO2 doping concentration can significantly change the local atomic structure of these coatings. Atomic models created for 20.4% and 53.8% Ti coatings indicate similar inter-atomic bond distances between the 20.4% and 53.8% Ti coatings. The models show that the distributions of Ta-Ti and Ti-O bonds in the atomic structure of the coatings as TiO2 doping is increased. There are also considerable contributions from Ta2O2 ring fragments that are seen in the pure Ta2O5 coatings, with the addition of TaTiO2 ring fragments. Further analysis of the atomic structures of these coatings revealed some preliminary correlations between the atomic structure and mechanical loss, were it is observed that 28.3% Ti coating is the most ordered atomic state out of all the Ti doped coatings and had the lowest measured mechanical loss. This suggests that there may be a link between slightly increased ordering in the atomic structures and a lower measurable mechanical loss. The amount of oxygen in a coating may play a key role important in the level of mechanical loss, as it is observed that the coating with the least oxygen deficiency coating is the coating with the lowest measured mechanical loss. Finally, Chapter 5 explores the material properties and atomic structures of HfO2 coatings, SiO2 coatings and substrates and HfO2 doped with SiO2 coatings. Pure HfO2 are studied as possible alternatives to Ta2O5 coatings. It appears that coatings subject to heat during the manufacturing process of just 100C or above appear part crystallised. Preliminary studies of a HfO2 coating doped with 30% (cation) SiO2 and heat-treated to 600C show that it is a promising coating for future study as it remains amorphous, with a room temperature mechanical loss value comparable to pure HfO2 coatings and therefore Ta2O5 coatings. SiO2 coatings deposited on SiO2 substrates are also studied and they show only subtle changes between them, which appear to lessen as the sample are heat-treated. Changes in the atomic structure of these coatings indicate an increase in order of the structure as heat-treatment temperature is increased, similar to the observed changes in the heat-treated Ta2O5 coatings

Intonation Patterns and Their Place in Teaching Pronunciation for Azeri-Speaking English language Learners

Although there has always been controversies around the importance of two levels of phonology (segmental and suprasegmental) in language teaching history, today there is a general consensus that both levels of phonology (segmental and suprasegmental) should be taken into consideration to reach the goals of pronunciation instruction. However time shortage is a factor that forces us as teachers to set priorities and be selective of materials that have more crucial role in understanding and being understood than others both in segmental and suprasegmental level. Our touchstone in this way is the degree to which these features affect the comprehensibility of materials. The current study examined the degree to which intonation patterns affect comprehensibility. The results of the study supported the initial prediction that Intonation patterns play no crucial role in pronunciation teaching to impede comprehension

Cerenkov radiation in chiral media

In this paper, the Cerenkov radiation in an unbounded homogeneous isotropic chiral medium is studied and analyzed classically. Starting from the Maxwell equations and the proposed constitutive relations for isotropic chiral media, we formulate the problem for the electric and magnetic fields emitted from a charged particle moving with a constant speed in a chiral medium, and find a formal solution for the electromagnetic field components and energy spectral density of radiation. Notable features, such as double cone of propagation, and important characteristics of the Cerenkov radiation in such media in terms of the relative velocity of the particle with respect to the two characteristic phase velocities in the medium are discussed

One- and Two-Dimensional Dyadic Green\u27s Functions in Chiral Media

The one- and two-dimensional dyadic Green\u27s functions are calculated for the one- and two-dimensional electric sources in an unbounded, lossless chiral medium that is electromagnetically describe

Reciprocity constraints on the matrix of reflection from optically anisotropic surfaces

We derive certain constraints on the reflection matrix for reflection from a plane, nonmagnetic, optically anisotropic surface using a reciprocity theorem stated long ago by van de Hulst in the context of scattering of polarized light. The constraints are valid for absorbing and chiral media and can be used as tools to check the consistency of derived expressions for such matrices in terms of the intrinsic parameters of the reflecting medium as illustrated by several examples.Comment: 14 pages, 2 figures, submitted to Jour. Opt. Soc. Am.

Investigating the medium range order in amorphous Ta₂O₅ coatings

Ion-beam sputtered amorphous heavy metal oxides, such as Ta2O5, are widely used as the high refractive index layer of highly reflective dielectric coatings. Such coatings are used in the ground based Laser Interferometer Gravitational-wave Observatory (LIGO), in which mechanical loss, directly related to Brownian thermal noise, from the coatings forms an important limit to the sensitivity of the LIGO detector. It has previously been shown that heat-treatment and TiO2 doping of amorphous Ta2O5 coatings causes significant changes to the levels of mechanical loss measured and is thought to result from changes in the atomic structure. This work aims to find ways to reduce the levels of mechanical loss in the coatings by understanding the atomic structure properties that are responsible for it, and thus helping to increase the LIGO detector sensitivity. Using a combination of Reduced Density Functions (RDFs) from electron diffraction and Fluctuation Electron Microscopy (FEM), we probe the medium range order (in the 2-3 nm range) of these amorphous coatings