A virtually nondestructive EPR technique accounting for diagnostic X-rays

We have implemented the method proposed by Aldrich and Pass (Aldrich, J.E., Pass, B., 1988. Determining radiation exposure from nuclear accidents and atomic tests using dental enamel. Health Phys. 54, 469–471.) to measure both the interior and exterior portions of a tooth in order to determine the diagnostic X-ray component of the total dose in the teeth. This was done using a modified nondestructive approach of Haskell et al. (Haskell, E.H., Hayes, R.B., Romanyukha, A.A., Kenner, G.H., 2000. Preliminary report on the development of a virtually non-destructive additive dose technique for EPR dosimetry Appl. Radiat Isot. 52, 1065–1070.) given in Hayes et al. ( Hayes, R.B., Haskell, E.H., Barrus, J.K., Kenner, G.H., Romanyukha, A.A., 2000. Accurate EPR radiosensitivity calibration using small sample masses. Nucl. Instr. Meth. A. 441, 535–550). Here only 5% of the total tooth enamel sample from an enamel crown was used for individual sample sensitivity calibration. A cavity response correction for the low mass samples was also used ( Hayes et al., 2000). The teeth were American wisdom teeth having unknown doses applied by the IAEA in the range of 0 to 1 Gy as part of the second international intercomparison ( Wieser, A., Mehta, K., Amira, S., Aragno, S., Bercea, S., Brik, A., Bugai, A., Callens, F., Chumak, V., Ciesielski, B., Debuyst, R., Dubovsky, S., Duliu, O., Fattibene, P., Haskell, E., Hayes, R., Ignatiev, E., Ivannikov, A., Kirillov, V., Kleschenko, E., Nakamura, N., Nathe, M., Nowak, J., Onori, S., Pass, B., Pivovarov, S., Romanyukha, A., Scherbina, O., Shames, A., Sholom, S., Skvortsov, V., Stepanenko, V., Tikounov, D., Toyoda, S., 2000. The 2nd international intercomparison on EPR tooth dosimetry. Radiat. Meas. in press). Final dose reconstruction estimates of the IAEA applied values showed a very high correlation (R=0.996). The approximate excess dose measured on the outside of the teeth relative to the inside was 49±35 mGy which is attributed to the diagnostic X-ray exposure given to the America wisdom teeth prior to extraction. The method used showed only a small dependence on the accelerating voltage of the X-ray source.     

Comparison between blue lasers and light‐emitting diodes for future solid‐state lighting

Solid‐state lighting (SSL) is now the most efficient source of high color quality white light ever created. Nevertheless, the blue InGaN light‐emitting diodes (LEDs) that are the light engine of SSL still have significant performance limitations. Foremost among these is the decrease in efficiency at high input current densities widely known as “efficiency droop.” Efficiency droop limits input power densities, contrary to the desire to produce more photons per unit LED chip area and to make SSL more affordable. Pending a solution to efficiency droop, an alternative device could be a blue laser diode (LD). LDs, operated in stimulated emission, can have high efficiencies at much higher input power densities than LEDs can. In this article, LEDs and LDs for future SSL are explored by comparing: their current state‐of‐the‐art input‐power‐density‐dependent power‐conversion efficiencies; potential improvements both in their peak power‐conversion efficiencies and in the input power densities at which those efficiencies peak; and their economics for practical SSL.     

Inverse analysis and regularisation in conditional source-term estimation modelling

Conditional Source-term Estimation (CSE) obtains the conditional species mass fractions by inverting a Fredholm integral equation of the first kind. In the present work, a Bayesian framework is used to compare two different regularisation methods: zeroth-order temporal Tikhonov regulatisation and first-order spatial Tikhonov regularisation. The objectives of the current study are: (i) to elucidate the ill-posedness of the inverse problem; (ii) to understand the origin of the perturbations in the data and quantify their magnitude; (iii) to quantify the uncertainty in the solution using different priors; and (iv) to determine the regularisation method best suited to this problem. A singular value decomposition shows that the current inverse problem is ill-posed. Perturbations to the data may be caused by the use of a discrete mixture fraction grid for calculating the mixture fraction PDF. The magnitude of the perturbations is estimated using a box filter and the uncertainty in the solution is determined based on the width of the credible intervals. The width of the credible intervals is significantly reduced with the inclusion of a smoothing prior and the recovered solution is in better agreement with the exact solution. The credible intervals for temporal and spatial smoothing are shown to be similar. Credible intervals for temporal smoothing depend on the solution from the previous time step and a smooth solution is not guaranteed. For spatial smoothing, the credible intervals are not dependent upon a previous solution and better predict characteristics for higher mixture fraction values. These characteristics make spatial smoothing a promising alternative method for recovering a solution from the CSE inversion process.     

A novel technique for laser diode to single mode fiber coupling

An optical fiber coupler based on the semi-linear passive phase conjugate mirror is analyzed. The threshold coupling strength is determined from theoretical considerations. An estimate of 50% for the overall coupling efficiency is made, assuming there is good mode matching between the light incident on the fiber and the propagating mode. The coupler exhibits a high degree of alignment insensitivity allowing for simple manufacture.     

Lifted generalized permutahedra and composition polynomials

Generalized permutahedra are the polytopes obtained from the permutahedron by changing the edge lengths while preserving the edge directions, possibly identifying vertices along the way. We introduce a “lifting” construction for these polytopes, which turns an n  -dimensional generalized permutahedron into an (n+1)$(n+1)$-dimensional one. We prove that this construction gives rise to Stasheff ?s multiplihedron from homotopy theory, and to the more general “nestomultiplihedra”, answering two questions of Devadoss and Forcey.     

Design and Characterization of Fabry–Pérot MEMS-Based Short-Wave Infrared Microspectrometers

Microspectrometers based on the monolithic integration of a microelectromechanical system (MEMS) Fabry–Pérot filter and a Hg _x Cd_1–x Te-based infrared detector are discussed and measured results presented. The microspectrometers are designed to operate in the 1.5 μm to 2.6 μm wavelength range. Design equations are presented which account for the mechanical and optical characteristics of the device. Measurements indicate linewidths as narrow as 55 nm, switching times of 40 μs, and a tuning range of 380 nm, which is limited by snap-down. Optical characterization of the distributed Bragg mirrors and the Fabry–Pérot filter are presented, and these are shown to be in good agreement with simple first-order analytical models. Bowing of the movable Fabry–Pérot mirror due to stress gradients is identified as the dominant source of linewidth broadening.     

Regularized field map estimation in MRI

In fast magnetic resonance (MR) imaging with long readout times, such as echo-planar imaging (EPI) and spiral scans, it is important to correct for the effects of field inhomogeneity to reduce image distortion and blurring. Such corrections require an accurate field map, a map of the off-resonance frequency at each voxel. Standard field map estimation methods yield noisy field maps, particularly in image regions with low spin density. This paper describes regularized methods for field map estimation from two or more MR scans having different echo times. These methods exploit the fact that field maps are generally smooth functions. The methods use algorithms that decrease monotonically a regularized least-squares cost function, even though the problem is highly nonlinear. Results show that the proposed regularized methods significantly improve the quality of field map estimates relative to conventional unregularized methods.      

EMS供应商侵入ODM控制的移动PC领域

外包移动PC制造业务长期以来一直由台湾地区的ODM厂商所控制,最近几年由ODM厂商生产的移动PC所占比例已上升到80%以上,而且仍在继续上升。