Understanding Cataract Risk in Aerospace Flight Crew And Review of Mechanisms of Cataract Formation

Induction of cataracts by occupational exposure in flight crew has been an important topic of interest in aerospace medicine in the past five years, in association with numerous reports of flight-associated disease incidences. Due to numerous confounding variables, it has been difficult to determine if there is increased cataract risk directly caused by interaction with the flight environment, specifically associated with added radiation exposure during flight. Military aviator records from the United States Air Force (USAF) and Navy (USN) and US astronauts at the National Aeronautics and Space Administration (NASA)/Lyndon B. Johnson Space Center (JSC) were evaluated for the presence, location and age of diagnosis of cataracts. Military aviators were found to have a statistically significant younger average age of onset of their cataracts compared with astronauts, however the incidence density of cataracts was found to be statistically higher in astronauts than in military aviators. USAF and USN aviator s cataracts were most commonly located in the posterior subcapsular region of the lens while astronauts cataracts were most likely to originate generally in the cortical zone. A prospective clinical trial which controls for confounding variables in examination technique, cataract classification, diet, exposure, and pharmacological intervention is needed to determine what percentage of the risk for cataracts are due to radiation, and how to best develop countermeasures to protect flight crews from radiation bioeffects in the future

Thermal Rounding of the Charge Density Wave Depinning Transition

The rounding of the charge density wave depinning transition by thermal noise is examined. Hops by localized modes over small barriers trigger ``avalanches'', resulting in a creep velocity much larger than that expected from comparing thermal energies with typical barriers. For a field equal to the $T=0$ depinning field, the creep velocity is predicted to have a {\em power-law} dependence on the temperature $T$; numerical computations confirm this result. The predicted order of magnitude of the thermal rounding of the depinning transition is consistent with rounding seen in experiment.Comment: 12 pages + 3 Postscript figure

Contributions of spontaneous phase slippage to linear and non-linear conduction near the Peierls transition in thin samples of o-TaS_3

In the Peierls state very thin samples of TaS_3 (cross-section area \sim 10^{-3} mkm^2) are found to demonstrate smearing of the I-V curves near the threshold field. With approaching the Peierls transition temperature, T_P, the smearing evolves into smooth growth of conductance from zero voltage interpreted by us as the contribution of fluctuations to the non--linear conductance. We identify independently the fluctuation contribution to the linear conductance near T_P. Both linear and non-linear contributions depend on temperature with close activation energies \sim (2 - 4) x 10^3 K and apparently reveal the same process. We reject creep of the {\it continuous} charge-density waves (CDWs) as the origin of this effect and show that it is spontaneous phase slippage that results in creep of the CDW. A model is proposed accounting for both the linear and non-linear parts of the fluctuation conduction up to T_P.Comment: 6 pages, 5 Postscript figure, RevTeX, accepted for publication in PR

Temporally ordered collective creep and dynamic transition in the charge-density-wave conductor NbSe3

We have observed an unusual form of creep at low temperatures in the charge-density-wave (CDW) conductor NbSe$_3$. This creep develops when CDW motion becomes limited by thermally-activated phase advance past individual impurities, demonstrating the importance of local pinning and related short-length-scale dynamics. Unlike in vortex lattices, elastic collective dynamics on longer length scales results in temporally ordered motion and a finite threshold field. A first-order dynamic phase transition from creep to high-velocity sliding produces "switching" in the velocity-field characteristic.Comment: 4 pages, 4 eps figures; minor clarifications To be published in Phys. Rev. Let

Tunable Charge Density Wave Transport in a Current-Effect Transistor

The collective charge density wave (CDW) conduction is modulated by a transverse single-particle current in a transistor-like device. Nonequilibrium conditions in this geometry lead to an exponential reduction of the depinning threshold, allowing the CDWs to slide for much lower bias fields. The results are in excellent agreement with a recently proposed dynamical model in which ''wrinkles'' in the CDW wavefronts are ''ironed'' by the transverse current. The experiment might have important implications for other driven periodic media, such as moving vortex lattices or ''striped phases'' in high-Tc superconductors.Comment: 4 pages, 4 figure

Taxing the Informal Economy: The Current State of Knowledge and Agendas for Future Research

This paper reviews the literature on taxation of the informal economy, taking stock of key debates and drawing attention to recent innovations. Conventionally, the debate on whether to tax has frequently focused on the limited revenue potential, high cost of collection, and potentially adverse impact on small firms. Recent arguments have increasingly emphasised the more indirect benefits of informal taxation in relation to economic growth, broader tax compliance, and governance. More research is needed, we argue, into the relevant costs and benefits for all, including quasi-voluntary compliance, political and administrative incentives for reform, and citizen-state bargaining over taxation

Federal Transfers and Fiscal Discipline in India: An Empirical Evaluation

This article examines the relationship between federal transfers and fiscal deficits in India. The current system of transfers has been criticized on the grounds that it distorts the incentives for states to promote fiscal discipline. We analyze the relationship between transfers, state domestic product, and fiscal deficit for a panel of states during the period 1990 to 2010. The article finds a positive long-run relationship and bidirectional causality between primary/gross fiscal deficits and non-plan transfers. Further, there is a negative long-run relationship and one-way causality from state domestic product to transfers. These results are confirmed by multivariate cointegration analysis, which finds a long-run relationship between fiscal transfers, state product per capita, and state primary deficit. The evidence in the article is consistent with the system of fiscal transfers being ‘‘gap filling.’

Attitudes of Irish dental, dental hygiene and dental nursing students and newly qualified practitioners to tobacco use cessation: a national survey.

Background: Ireland has some of the strictest smoking regulations in the world. Little is known of the attitudes of student Irish dental healthcare workers towards tobacco control and tobacco use cessation. This study aimed at determining the knowledge and attitudes of these students towards the deleterious effects of tobacco in the mouth and towards tobacco use cessation in dental practice. Method: A questionnaire survey was distributed to 654 students (including newly qualified) on dentistry, dental hygiene and dental nursing programmes in Irish dental schools. Information sought included college, course, year of study, sex, age, nationality, smoking status, knowledge of effects of tobacco in the mouth and attitudes towards tobacco use cessation in dental practice and towards the Irish smoking bans. Main Findings: There was a 90% response rate. In all, 12% of dental students, 25% of dental hygiene students and 31% of dental nursing students were current smokers. Newly qualified dental hygienists were as knowledgeable about tobacco effects in the mouth as newly qualified dentists. Overall, the majority in each student category believed that all three groups could be effective tobacco counsellors and should provide tobacco use cessation counselling to patients, although less than half of evening course dental nursing students felt that dental nurses could be effective counsellors or should provide counselling. There was overwhelming support for the Irish smoking ban. Only a minority of dental students and dental nursing students had received instruction in tobacco use cessation counselling. Conclusions: There are strong positive attitudes to tobacco use cessation counselling in dental practice among these young dental healthcare students. This is true even amongst those who have not received specific instruction in tobacco use cessation counselling