Thermo electronic laser energy conversion

The thermo electronic laser energy converter (TELEC) is described and compared to the Waymouth converter and the conventional thermionic converter. The electrical output characteristics and efficiency of TELEC operation are calculated for a variety of design variables. Calculations and results are briefly outlined. It is shown that the TELEC concept can potentially convert 25 to 50 percent of incident laser radiation into electric power at high power densities and high waste heat rejection temperatures

Experimental Comparisons of Derivative Free Optimization Algorithms

In this paper, the performances of the quasi-Newton BFGS algorithm, the NEWUOA derivative free optimizer, the Covariance Matrix Adaptation Evolution Strategy (CMA-ES), the Differential Evolution (DE) algorithm and Particle Swarm Optimizers (PSO) are compared experimentally on benchmark functions reflecting important challenges encountered in real-world optimization problems. Dependence of the performances in the conditioning of the problem and rotational invariance of the algorithms are in particular investigated.Comment: 8th International Symposium on Experimental Algorithms, Dortmund : Germany (2009

The plasmatron: Advanced mode thermionic energy conversion

A theory of the plasmatron was developed. Also, a wide range of measurements were obtained with two versatile, research devices. To gain insight into plasmatron performance, the experimental results are compared with calculations based on the theoretical model of plasmatron operation. Results are presented which show that the plasma arc drop of the conventional arc (ignited) mode converter can be suppressed by use of an auxiliary ion source. The improved performance, however, is presently limited to low current densities because of voltage losses due to plasma resistance. This resistance loss could be suppressed by an increase in the plasma electron temperature or a decrease in spacing. Plasmatron performance characteristics for both argon and cesium are reported. The argon plasmatron has superior performance. Results are also presented for magnetic cutoff effects and for current distributing effects. These are shown to be important factors for the design of practical devices

Modal cut-off and the V-parameter in photonic crystal fibers

We address the long-standing unresolved problem concerning the V-parameter in a photonic crystal fiber (PCF). Formulate the parameter appropriate for a core-defect in a periodic structure we argue that the multi-mode cut-off occurs at a wavelength lambda* which satisfies V_PCF(lambda*)=pi. Comparing to numerics and recent cut-off calculations we confirm this result.Comment: 3 pages including 2 figures. Accepted for Optics Letter

Partly Occupied Wannier Functions

We introduce a scheme for constructing partly occupied, maximally localized Wannier functions (WFs) for both molecular and periodic systems. Compared to the traditional occupied WFs the partly occupied WFs posses improved symmetry and localization properties achieved through a bonding-antibonding closing procedure. We demonstrate the equivalence between bonding-antibonding closure and the minimization of the average spread of the WFs in the case of a benzene molecule and a linear chain of Pt atoms. The general applicability of the method is demonstrated through the calculation of WFs for a metallic system with an impurity: a Pt wire with a hydrogen molecular bridge.Comment: 5 pages, 4 figure

On the frequency and remnants of Hypernovae

Under the hypothesis that some fraction of massive stellar core collapses give rise to unusually energetic events, termed hypernovae, I examine the required rates assuming some fraction of such events yield gamma ray bursts. I then discuss evidence from studies of pulsars and r-process nucleosynthesis that independently suggests the existence of a class of unusually energetic events. Finally I describe a scenario which links these different lines of evidence as supporting the hypernova hypothesis.Comment: TeX, To appear in ApJ Letter

Does academic self-concept predict further and higher education participation?

Despite the major increase in university student numbers in recent years there remains a strong negative socio-economic gradient in participation. The main reason for these differences has been shown to be educational factors, including prior attainment, family background and perceptions about costs and returns to education. In this paper, we examine the role of young people’s belief in their own academic ability (academic self-concept) as a way to explain differences in university participation rates. Using Next Steps data, we examine whether young people with higher academic self-concept are more likely to study A Levels, participate in further education and attend university. For those who do attend university, we examine whether young people with higher self-belief attend high status universities or study high status subjects. Results show that on average, controlling for prior attainment and other background characteristics, having high academic self-concept increases the odds in participating in A Level study, decreases the odds in taking part in further education, increases the odds in taking part in higher education (but the significance level disappears after taking A Levels is taken into account) and increases the odds of studying at a high-status university. While academic self-concept is an important predictor of later educational transitions, it does not entirely account for the social gradient in participation of university, further education or higher education. These findings have important policy implications for higher education participation and widening participation in particular