Emergency braking for free piston energy converters

Free piston energy converters are a potential technology for future hybrid vehicles, as well as stationary power generation applications. A candidate 2-stroke system comprises of two opposing combustion chambers with a common piston rod, and integrated with a tubular permanent magnet electrical machine for the conversion of mechanical to electrical energy. A key issue for the ultimate adoption of such systems, however, is their robustness in the event of a fault to enable a safe shutdown, with minimal mechanical or electrical damage. The paper considers system braking issues and the importance of early fault detection. Results are presented to demonstrate the effectiveness of passive and active braking techniques for a range of dc-link supply voltage and operating output power

Subglacial drainage processes at a High Arctic polythermal valley glacier

Peer reviewedPublisher PD

Instabilities in neutrino-plasma density waves

One examines the interaction and possible resonances between supernova neutrinos and electron plasma waves. The neutrino phase space distribution and its boundary regions are analyzed in detail. It is shown that the boundary regions are too wide to produce non-linear resonant effects. The growth or damping rates induced by neutrinos are always proportional to the neutrino flux and $G_{{\rm F}}^{2}$.Comment: 9 pages, a few words modified to match PRD publicatio

The origin of the red luminescence in Mg-doped GaN

Optically-detected magnetic resonance (ODMR) and positron annihilation spectroscopy (PAS) experiments have been employed to study magnesium-doped GaN layers grown by metal-organic vapor phase epitaxy. As the Mg doping level is changed, the combined experiments reveal a strong correlation between the vacancy concentrations and the intensity of the red photoluminescence band at 1.8 eV. The analysis provides strong evidence that the emission is due to recombination in which electrons both from effective mass donors and from deeper donors recombine with deep centers, the deep centers being vacancy-related defects.Comment: 4 pages, 3 figure

Convergence of the all-time supremum of a L\'evy process in the heavy-traffic regime

In this paper we derive a technique of obtaining limit theorems for suprema of L\'evy processes from their random walk counterparts. For each $a>0$, let $\{Y^{(a)}_n:n\ge 1\}$ be a sequence of independent and identically distributed random variables and $\{X^{(a)}_t:t\ge 0\}$ be a L\'evy processes such that $X_1^{(a)}\stackrel{d}{=} Y_1^{(a)}$, $\mathbb E X_1^{(a)}<0$ and $\mathbb E X_1^{(a)}\uparrow0$ as $a\downarrow0$. Let $S^{(a)}_n=\sum_{k=1}^n Y^{(a)}_k$. Then, under some mild assumptions, $\Delta(a)\max_{n\ge 0} S_n^{(a)}\stackrel{d}{\to} R\iff\Delta(a)\sup_{t\ge 0} X^{(a)}_t\stackrel{d}{\to} R$, for some random variable $R$ and some function $\Delta(\cdot)$. We utilize this result to present a number of limit theorems for suprema of L\'evy processes in the heavy-traffic regime

The magnetic properties of 177^{\rm 177}Hf and 180^{\rm 180}Hf in the strong coupling deformed model

This paper reports NMR measurements of the magnetic dipole moments of two high-K isomers, the 37/2$^-$, 51.4 m, 2740 keV state in $^{\rm 177}$Hf and the 8$^-$, 5.5 h, 1142 keV state in $^{\rm 180}$Hf by the method of on-line nuclear orientation. Also included are results on the angular distributions of gamma transitions in the decay of the $^{\rm 177}$Hf isotope. These yield high precision E2/M1 multipole mixing ratios for transitions in bands built on the 23/2$^+$, 1.1 s, isomer at 1315 keV and on the 9/2$^+$, 0.663 ns, isomer at 321 keV. The new results are discussed in the light of the recently reported finding of systematic dependence of the behavior of the g$_{\rm R}$ parameter upon the quasi-proton and quasi-neutron make up of high-K isomeric states in this region.Comment: 9 pages, 9 figures, accepted for publication in Physical Review

Physical Activity, Sedentary Time, and Fatness in a Biethnic Sample of Young Children.

PURPOSE: To investigate associations of objectively-measured physical activity (PA) and sedentary time (ST) with adiposity in a predominantly bi-ethnic (South Asian and White British) sample of young children. METHODS: The sample included 333 children aged 11 months to 5 years who provided 526 cross-sectional observations for PA and body composition. Total PA volume (vector magnitude counts per minute (cpm)), daily time at multiple intensity levels (the cumulative time in activity >500 cpm, >1000 cpm, >1500 cpm and so on up to >6000 cpm), and time spent sedentary (6000 cpm: -1.57 (-3.01 to -0.12) mm per 20 min/d). Substitution of 20 min/d of ST with MVPA was associated with a lower sum of skinfolds (-0.77 (-1.46 to -0.084) mm). CONCLUSIONS: High light-intensity PA appears to be beneficial for body composition in young South Asian and White British children, but higher-intensity PA is more advantageous.This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal