The inverse electromagnetic scattering problem in a piecewise homogeneous medium

This paper is concerned with the problem of scattering of time-harmonic electromagnetic waves from an impenetrable obstacle in a piecewise homogeneous medium. The well-posedness of the direct problem is established, employing the integral equation method. Inspired by a novel idea developed by Hahner [11], we prove that the penetrable interface between layers can be uniquely determined from a knowledge of the electric far field pattern for incident plane waves. Then, using the idea developed by Liu and Zhang [21], a new mixed reciprocity relation is obtained and used to show that the impenetrable obstacle with its physical property can also be recovered. Note that the wave numbers in the corresponding medium may be different and therefore this work can be considered as a generalization of the uniqueness result of [20].Comment: 19 pages, 2 figures, submitted for publicatio

Efficient Spatial Redistribution of Quantum Dot Spontaneous Emission from 2D Photonic Crystals

We investigate the modification of the spontaneous emission dynamics and external quantum efficiency for self-assembled InGaAs quantum dots coupled to extended and localised photonic states in GaAs 2D-photonic crystals. The 2D-photonic bandgap is shown to give rise to a 5-10 times enhancement of the external quantum efficiency whilst the spontaneous emission rate is simultaneously reduced by a comparable factor. Our findings are quantitatively explained by a modal redistribution of spontaneous emission due to the modified local density of photonic states. The results suggest that quantum dots embedded within 2D-photonic crystals are suitable for practical single photon sources with high external efficiency

Hydration and mobility of HO-(aq)

The hydroxide anion plays an essential role in many chemical and biochemical reactions. But a molecular-scale description of its hydration state, and hence also its transport, in water is currently controversial. The statistical mechanical quasi-chemical theory of solutions suggests that HO[H2O]3- is the predominant species in the aqueous phase under standard conditions. This result is in close agreement with recent spectroscopic studies on hydroxide water clusters, and with the available thermodynamic hydration free energies. In contrast, a recent ab initio molecular dynamics simulation has suggested that HO[H_2O]4- is the only dominant aqueous solution species. We apply adiabatic ab initio molecular dynamics simulations, and find good agreement with both the quasi-chemical theoretical predictions and experimental results. The present results suggest a picture that is simpler, more traditional, but with additional subtlety. These coordination structures are labile but the tri-coordinate species is the prominent case. This conclusion is unaltered with changes in the electronic density functional. No evidence is found for rate-determining activated inter-conversion of a HO[H2O]4- trap structure to HO[H2O]3-, mediating hydroxide transport. The view of HO- diffusion as the hopping of a proton hole has substantial validity, the rate depending largely on the dynamic disorder of the water hydrogen-bond network.Comment: 7 pages, 5 figures, additional results include

Fatigue Damage in Notched Composite Laminates Under Tension-Tension Cyclic Loads

The results are given of an investigation to determine the damage states which develop in graphite epoxy laminates with center holes due to tension-tension cyclic loads, to determine the influence of stacking sequence on the initiation and interaction of damage modes and the process of damage development, and to establish the relationships between the damage states and the strength, stiffness, and life of the laminates. Two quasi-isotropic laminates were selected to give different distributions of interlaminar stresses around the hole. The laminates were tested under cyclic loads (R=0.1, 10 Hz) at maximum stresses ranging between 60 and 95 percent of the notched tensile strength

A Consistent Orbital Stability Analysis for the GJ 581 System

We apply a combination of N-body modeling techniques and automated data fitting with Monte Carlo Markov Chain uncertainty analysis of Keplerian orbital models to radial velocity data to determine long term stability of the planetary system GJ 581. We find that while there are stability concerns with the 4-planet model as published by Forveille et al. (2011), when uncertainties in the system are accounted for, particularly stellar jitter, the hypothesis that the 4-planet model is gravitationally unstable is not statistically significant. Additionally, the system including proposed planet g by Vogt et al. (2012) also shows some stability concerns when eccentricities are allowed to float in the orbital fit, yet when uncertainties are included in the analysis the system including planet g also can not be proven to be unstable. We present revised reduced chi-squared values for Keplerian astrocentric orbital fits assuming 4-planet and 5-planet models for GJ~581 under the condition that best fits must be stable, and find no distinguishable difference by including planet g in the model. Additionally we present revised orbital element estimates for each assuming uncertainties due to stellar jitter under the constraint of the system being gravitationally stable.Comment: 26 pages, 8 figures, 6 tables, accepted for publication in the Astrophysical Journa

On the exterior boundary-value problem for the time-harmonic Maxwell equations

AbstractFor the exterior boundary-value problem of electromagnetic reflection at perfect conductors a new integral equation approach is developed. It extends the method introduced by Brakhage and Werner and by Leis for exterior boundary-value problems for the scalar Helmholtz equation to the underlying case of Maxwell's equations. In a unified approach for all frequencies the existence of a solution is established by using the first part of Fredholm's alternative only

Reducing Stigma toward the Transgender Community: An Evaluation of a Humanizing and Perspective-Taking Intervention

Transgender (TG) individuals, or those whose gender identities, expressions and/or behaviors differ from their biological sex (Kirk & Kulkarni, 2006) feel there is a pervasive pattern of discrimination and prejudice directed toward them (Lombardi et al., 2001). In comparison to their heterosexual peers, LGBT youth and emerging adults are at increased risk for a host of adverse outcomes including: suicide, depression, harassment, and victimization (IOM, 2011). Stigma has been characterized as encompassing several components: labeling, making an association between the label and a negative stereotype, separating those who are different as an “out-group” and discriminating. In a recent analysis of the transgender experience, Hill (2002) described three key constructs that can be used to understand negative emotions and behaviors toward transgender individuals: transphobia – an emotional disgust toward gender non-conforming individuals; genderism – a belief that gender non-conforming individuals are pathological or disordered; gender bashing – assault or harassment of gender non-conforming individuals. Recent work on minority stress posits a distal-proximal model of stress in which a person identifies with and makes proximal, distal social attitudes that can have negative effects on their psychological well-being (Meyer, 2003). Thus, stigmatized attitudes and behaviors not only have the potential to contribute to violence or discriminatory behavior but also have a direct impact on the psychological health of the target individual. Thus, the question of how to change negative attitudes and behaviors toward TG individuals is paramount. Researchers have sought to develop interventions aimed at reducing stigma with three basic strategies identified: protest, education and contact (Corrigan & Penn, 1999). However, to date only two such strategies have garnered empirical support: contact and education. In relation to mental illness, education strategies have received limited support (Holmes et al., 1999; see Luty et al., 2007 for an exception). In contrast, contact-based interventions yield the most dramatic changes in attitudes and behaviors; contact involving media depictions have also been demonstrated to yield positive attitude change. Comparing traditional diagnosis-centered teaching about mental illness to a humanizing approach that required students to write a first-person narrative about suffering from a mental illness, Mann and Himelein (2008) found that attitudes changed only when students were required to adopt the perspective of a mentally ill individual. In their recent meta-analysis, Pettigrew and Tropp (2006) demonstrated that contact reduces prejudice and is particularly effective when it occurs under favorable conditions (e.g., conditions of equality, cooperation, and institutional support). While a wealth of research has supported the contact hypothesis related to changing negative attitudes toward ethnic minorities, the mentally ill, the homeless, gays/lesbians and other stigmatized groups, there have been a limited number of studies evaluating associations between contact and attitudes toward the TG community (Harvey, 2002; Hill & Willoughby, 2005) and no controlled studies to evaluate the efficacy of such methods. The current study extends work evaluating anti-stigma interventions to the TG community and seeks to evaluate whether attitude change will differ between participants receiving basic education about the transgender community and those who are educated about TG through media depictions of TG families and are asked to engage in a perspective-taking task. We hypothesize that participants in the humanizing condition who view a documentary and write a first-person narrative of transgender experiences will show a more significant change in transphobia, genderist attitudes and desire for social distance across time relative to participants in the education-only condition signaling less stigmatized and prejudicial attitudes at post-test. Hodson (2011) recently examined the existing contact literature and found that, consistent with Pettigrew’s (1998) focus on individual differences, intergroup contact was effective (and perhaps even more effective) among individuals who were intolerant and cognitively rigid. Religious fundamentalism has been associated with anti-homosexual sentiment (Fulton et al., 1999). Whether religiosity is similarly associated with negative attitudes toward TG individuals will be explored. Whether religiosity and prior contact with the LGBTQ community will moderate intervention outcomes will also be explored