Cortical thickness mapping to identify focal osteoporosis in patients with hip fracture.

BACKGROUND: Individuals with osteoporosis are predisposed to hip fracture during trips, stumbles or falls, but half of all hip fractures occur in those without generalised osteoporosis. By analysing ordinary clinical CT scans using a novel cortical thickness mapping technique, we discovered patches of markedly thinner bone at fracture-prone regions in the femurs of women with acute hip fracture compared with controls. METHODS: We analysed CT scans from 75 female volunteers with acute fracture and 75 age- and sex-matched controls. We classified the fracture location as femoral neck or trochanteric before creating bone thickness maps of the outer 'cortical' shell of the intact contra-lateral hip. After registration of each bone to an average femur shape and statistical parametric mapping, we were able to visualise and quantify statistically significant foci of thinner cortical bone associated with each fracture type, assuming good symmetry of bone structure between the intact and fractured hip. The technique allowed us to pinpoint systematic differences and display the results on a 3D average femur shape model. FINDINGS: The cortex was generally thinner in femoral neck fracture cases than controls. More striking were several discrete patches of statistically significant thinner bone of up to 30%, which coincided with common sites of fracture initiation (femoral neck or trochanteric). INTERPRETATION: Femoral neck fracture patients had a thumbnail-sized patch of focal osteoporosis at the upper head-neck junction. This region coincided with a weak part of the femur, prone to both spontaneous 'tensile' fractures of the femoral neck, and as a site of crack initiation when falling sideways. Current hip fracture prevention strategies are based on case finding: they involve clinical risk factor estimation to determine the need for single-plane bone density measurement within a standard region of interest (ROI) of the femoral neck. The precise sites of focal osteoporosis that we have identified are overlooked by current 2D bone densitometry methods.

An Arbitrary Lagrangian Eulerian Method for Three-Phase Flows with Triple Junction Points

We present a moving mesh method suitable for solving two-dimensional and axisymmetric three-liquid flows with triple junction points. This method employs a body-fitted unstructured mesh where the interfaces between liquids are lines of the mesh system, and the triple junction points (if exist) are mesh nodes. To enhance the accuracy and the efficiency of the method, the mesh is constantly adapted to the evolution of the interfaces by refining and coarsening the mesh locally; dynamic boundary conditions on interfaces, in particular the triple points, are therefore incorporated naturally and accurately in a Finite- Element formulation. In order to allow pressure discontinuity across interfaces, double-values of pressure are necessary for interface nodes and triple-values of pressure on triple junction points. The resulting non-linear system of mass and momentum conservation is then solved by an Uzawa method, with the zero resultant condition on triple points reinforced at each time step. The method is used to investigate the rising of a liquid drop with an attached bubble in a lighter liquid.

A discretized proportional base driver for Silicon Carbide Bipolar Junction Transistors

Silicon Carbide Bipolar Junction Transistors require a continuous base current in the on-state. This base current is usually made constant and is corresponding to the maximum collector current and maximum junction temperature that is foreseen in a certain application. In this paper, a discretized proportional base driver is proposed which will reduce, for the right application, the steady-state power consumption of the base driver. The operation of the proposed base driver has been verified experimentally, driving a 1200V/40A SiC BJT in a DC-DC boost converter. In order to determine the potential reduction of the power consumption of the base driver, a case with a dc-dc converter in an ideal electric vehicle driving the new European drive cycle has been investigated. It is found that the steady-state power consumption of the base driver can be reduced by approximately 63 %. The total reduction of the driver consumption is 2816 J during the drive cycle, which is slightly more than the total on-state losses for the SiC BJTs used in the converter. © 2013 IEEE.

A discretized proportional base driver for silicon carbide bipolar junction transistors

Silicon carbide (SiC) bipolar junction transistors (BJTs) require a continuous base current in the on-state. This base current is usually made constant and is corresponding to the maximum collector current and maximum junction temperature that is foreseen in a certain application. In this paper, a discretized proportional base driver is proposed which will reduce, for the right application, the steady-state power consumption of the base driver. The operation of the proposed base driver has been verified experimentally, driving a 1200-V/40-A SiC BJT in a dc-dc boost converter. In order to determine the potential reduction of the power consumption of the base driver, a case with a dc-dc converter in an ideal electric vehicle driving the new European drive cycle has been investigated. It is found that the steady-state power consumption of the base driver can be reduced by approximately 60%. The total reduction of the driver consumption is 3459 J during the drive cycle, which is slightly more than the total on-state losses for the SiC BJTs used in the converter. © 2013 IEEE.

Small-Signal Equivalent-Circuit Model and Characterization of 1.55-mu m Buried Tunnel Junction Vertical-Cavity Surface-Emitting Lasers

The work was supported in part by the National Natural Science Foundation of China under Grant 60536010, Grant 60606019, Grant 60777029, and Grant 60820106004, and in part by the National Basic Research Program of China under Grant 2006CB604902, Grant 2006CB302806, and Grant 2006dfa11880.

一种减小Mg记忆效应的GaN基pn结的生长方法

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Theoretical design and performance of InxGa1-xN two-junction solar cells

The efficiencies of InxGa1-xN two-junction solar cells are calculated with various bandgap combinations of subcells under AM1.5 global, AM1.5 direct and AM0 spectra. The influence of top-cell thickness on efficiency has been studied and the performance of InxGa1-xN cells for the maximum light concentration of various spectra has been evaluated. Under one-sun irradiance, the optimum efficiency is 35.1% for the AM1.5 global spectrum, with a bandgap combination of top/bottom cells as 1.74 eV/1.15 eV. And the limiting efficiency is 40.9% for the highest light concentration of the AM1.5 global spectrum, with the top/bottom cell bandgap as 1.72 eV/1.12 eV.

Electroluminescence from nano-crystalline Si/SiO2 structures embedded in pn junctions

Phosphorous-doped and boron-doped amorphous Si thin films as well as amorphous SiO2/Si/SiO2 sandwiched structures were prepared in a plasma enhanced chemical vapor deposition system. Then, the p-i-n structures containing nano-crystalline Si/SiO2 sandwiched structures as the intrinsic layer were prepared in situ followed by thermal annealing. Electroluminescence spectra were measured at room temperature under forward bias, and it is found that the electroluminescence intensity is strongly influenced by the types of substrate. The turn-on voltages can be reduced to 3 V for samples prepared on heavily doped p-type Si (p(+)-Si) substrates and the corresponding electroluminescence intensity is more than two orders of magnitude stronger than that on lightly doped p-type Si (p-Si) and ITO glass substrates. The improvements of light emission can be ascribed to enhanced hole injection and the consequent recombination of electron-hole pairs in the luminescent nanocrystalline Si/SiO2 system. (C) 2008 Elsevier Ltd. All rights reserved.

Simulation of In0.65Ga0.35N single-junction solar cell

The performances of In0.65Ga0.35N single-junction solar cells with different structures, including various doping densities and thicknesses of each layer, have been simulated. It is found that the optimum efficiency of a In0.65Ga0.35N solar cell is 20.284% with 5 x 10(17) cm(-3) carrier concentration of the front and basic regions, a 130 nm thick p-layer and a 270 nm thick n-layer.

Quantum efficiency and temperature coefficients of GaInP/GaAs dual-junction solar cell

GaInP/GaAs dual-junction solar cell with a conversion efficiency of 25.2% has been fabricated using metalorganic chemical vapor deposition (MOCVD) technique. Quantum efficiencies of the solar cell were measured within a temperature range from 25 to 160A degrees C. The results indicate that the quantum efficiencies of the subcells increase slightly with the increasing temperature. And red-shift phenomena of absorption limit for all subcells are observed by increasing the cell's work temperature, which are consistent with the viewpoint of energy gap narrowing effect. The short-circuit current density temperature coefficients dJ (sc)/dT of GaInP subcell and GaAs subcell are determined to be 8.9 and 7.4 mu A/cm(2)/A degrees C from the quantum efficiency data, respectively. And the open-circuit cell voltage temperature coefficients dV (oc)/dT calculated based on a theoretical equation are -2.4 mV/A degrees C and -2.1 mV/A degrees C for GaInP subcell and GaAs subcell.

The junction temperature and forward voltage relationship of GaN-based laser diode

In GaAs-based light-emitting diode (LED) or laser diode (LD), the forward voltage (V) will decrease linearly with the increasing junction temperature (T). This can be used as a convenient method to measure the junction temperature. In GaN-based LED, the relationship is linear too. But in GaN-based LD, the acceptor M (g) in p-GaN material can not ionize completely at-room temperature, and the carrier density will change with temperature. But we find finally that, this change won't lead to a nonlinear relationship of V-T. Our experiments show that it is Linear too.

Frequency dependence of junction capacitance of GaN p-i-n UV detectors

In this paper frequency dependence of small-signal capacitance of p-i-n UV detectors, which were fabricated on GaN grown on sapphire substrate by metalorganic chemical vapor deposition, has been studied. The Schibli-Milnes model was used to analyze the capacitance-frequency characteristics. According to high frequency C-V measurements, the deep level mean concentration is about 2.98 x 10(20) cm(-3). The deep level is caused by the un-ionised Mg dopant. The calculated Mg activation energy is 260 meV and the hole thermal capture cross section of the deep level is about 2.73 x 10(-22) cm(2). The applicability of the Schibli-Milnes model is also discussed when the concentration of deep levels exceeds that of the heavily doped n-side. It is concluded that the analytic expression of the Schibli-Milnes model can still be used to describe the capacitance-frequency characteristics of GaN p-i-n UV detectors in good agreement with experiment. (c) 2005 Elsevier Ltd. All rights reserved.

Electrical properties and electroluminescence of 4H-SiC p-n junction diodes

Homoepitaxial growth of 4H-SiC on off-oriented Si-face(0001) substrates was performed by using the step-controlled epitaxy technique in a newly developed low-pressure hot-wall CVD (LP-HWCVD) system with a horizontal air-cooled quartz tube at around 1500 degreesC and 1.33 x 10(4) Pa by employing SiH4 + C2H4 + H-2. In-situ doping during growth was carried out by adding NH3 gas into the precursor gases. It was shown that the maximum Hall mobility of the undoped 4H-SiC epilayers at room temperature is about 430 cm(2) (.) V-1 (.) s(-1) with a carrier concentration of similar to 10(16) cm(-3) and the highest carrier concentration of the N-doped 4H-SiC epilayer obtained at NH3 flow rate of 3 sccm is about 2.7 x 10(21) cm(-3) with a mobility of 0.75 cm(2) (.) V-1 (.) s(-1). SiC p-n junctions were obtained by epitaxially growing N-doped 4H-SiC epilayers on Al-doped 4H-SiC substrates. The C - V characteristics of the diodes were linear in the 1/C-3 - V coordinates indicating that the obtained p-n junctions were graded with a built-in voltage of 2.7 eV. The room temperature electroluminescence spectra of 4H-SiC p-n junctions are studied as a function of forward current. The D-A pair recombination due to nitrogen donors and the unintentional, deep boron center is dominant at low forward bias, while the D-A pair recombination due to nitrogen donors and aluminum acceptors are dominant at higher forward biases. The p-n junctions could operate at temperature of up to 400 degreesC, which provides a potential for high-temperature applications.

Synthesis and photoluminescence properties of vertically aligned ZnO nanorod-nanowall junction arrays on a ZnO-coated silicon substrate

Arrays of vertically well-aligned ZnO nanorod-nanowall junctions have been synthesized on an undoped ZnO-coated silicon substrate by a carbothermal reduction and vapour phase transport method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) show that the nanostructures are well-oriented with the c-axis perpendicular to the substrate. The room temperature photoluminescence (PL) spectrum of the as-prepared ZnO nanostructure reveals a dominant near-band-edge (NBE) emission peak and a weak deep level (DL) emission, which demonstrates its good optical properties. Temperature-dependent PL spectra show that both the intensity of NBE and DL emissions increased with decreasing temperature. The NBE emission at 3.27 eV is identified to originate from the radiative free exciton recombination. The possible growth mechanism of ZnO nanorod-nanowall junctions is also proposed.