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The carrier distribution and recombination dynamics of InGaN/GaN multiple quantum well (MQW) light-emitting diode structure are investigated. Two emission peaks were observed in the low temperature photoluminescence spectra of an InGaN/GaN MQW structure, but only one peak was observed in the electroluminescence (EL) spectra. Combined with the spatially resolved cathodoluminescence (CL) measurements, it is found that the electrically injected carrier distribution is governed by hole transport and diffusion in InGaN/GaN MQW structure due to the much lower mobility of hole. And the electron and hole recombination of EL occurs predominantly in the QWs that are located closer to the p-GaN layer. [ABSTRACT FROM AUTHOR]

This paper focuses on pricing American put options under the double Heston model proposed by Christoffersen et al. By introducing an explicit exercise rule, we obtain the asymptotic expansion of the solution to the partial differential equation for pricing American put options. We calculate American option price by the sum of the European option price and the early exercise premium. The early exercise premium is calculated by the difference between the American and European option prices based on asymptotic expansions. The European option price is obtained by the efficient COS method. Based on the obtained American option price, the double Heston model is calibrated by minimizing the distance between model and market prices, which yields an optimization problem that is solved by a differential evolution algorithm combined with the Matlab function fmincon.m. Numerical results show that the pricing approach is fast and accurate. Empirical results show that the double Heston model has better performance in pricing short-maturity American put options and capturing the volatility term structure of American put options than the Heston model. [ABSTRACT FROM AUTHOR]

Caffeoyl coenzyme A-O-methyltransferase (CCoAOMT) has a critical function in the lignin biosynthesis pathway. However, its role in pomegranate is not clear. In this research, we identified 11 members of the CCoAOMT gene family based on pomegranate genome-wide data. The 11 CCoAOMT genes were distributed non-uniformly on chromosomes 2, 3 and 4 of pomegranate. Phylogenetic analysis showed that pomegranate CCoAOMT9 and Camellia sinensis CCoAOMT genes clustered into one branch. Promoter cis-acting progenitor analysis revealed a role for the pomegranate CCoAOMT gene in the ABA/MeJA response. The expression of CCoAOMT8, CCoAOMT9 and CCoAOMT10 was higher in hard-seeded cultivars ('Hongyushizi' and 'Baiyushizi') than in soft-seeded cultivar (Tunisia) as detected and analyzed by q-PCR. The results suggested that CCoAOMT8, CCoAOMT9, and CCoAOMT10 might be related to lignin biosynthesis. The findings of this work provided a basis for further investigation of the role of the pomegranate CCoAOMT gene in lignin biosynthesis. [ABSTRACT FROM AUTHOR]

Context: Cardiomyocyte apoptosis plays a critical role in the progress of heart diseases. Fucoidan, a complex-sulfated polysaccharide, has been reported to possess potential cardioprotective efficacy in vivo. Objective: The present study determines whether fucoidan could provide cardioprotection on hypoxia-induced cardiomyocyte apoptosis. Materials and methods: H9c2 cardiomyoblast cells were incubated with various concentrations (15, 30, and 60 μg/ml) of fucoidan in a humidified incubator at 37 °C with 95% O2 and 5% CO2. After 6 h, hypoxia was processed and the cardioprotective effects of fucoidan were evaluated by applying MTT, ELISA, Hoechst 33258 nucleus staining, and western blot. Results: Following a 6 h exposure of H9c2 to hypoxic condition, significant reduction was found in cell survival (0.57-fold) and superoxide dismutase (SOD) activity (0.56-fold), which were associated with the increase of malondialdehyde (MDA) level (2.58-fold), creatine phosphokinase (CK, 3.57-fold), and lactate dehydrogenase (LDH) activities (2.39-fold). Moreover, hypoxia-induced apoptosis was confirmed by Hoechst 33258 nuclear staining, and these changes were accompanied by the increase of Bcl-2 (1.27-fold) and Bax expression (2.6-fold). However, preincubation of the cells with fucoidan prior to hypoxia exposure elevated the cell viability (30 μg/ml, 1.18-fold; 60 μg/ml, 1.32-fold) and SOD activity (30 μg/ml, 1.12-fold; 60 μg/ml, 1.25-fold), but decreased the MDA level (30 μg/ml, 0.70-fold; 60 μg/ml, 0.80-fold), CK (30 μg/ml, 0.69-fold; 60 μg/ml, 0.76-fold), and LDH (30 μg/ml, 0.67-fold; 60 μg/ml, 0.86-fold) leakages. Hoechst 33258 nuclear staining observations demonstrated the same protective effect of fucoidan on hypoxia-induced myocardial injury. Also, cardioprotective effects of fucoidan were reflected by increasing Bcl-2 (60 μg/ml, 1.84-fold), as well as decreasing Bax (60 μg/ml, 0.6-fold). Conclusion: Fucoidan had protective effect against hypoxia-induced cardiomyocytes apoptosis, and the mechanism might involve protections of the cell from oxidative injury. [ABSTRACT FROM AUTHOR]

The decadal spatio-temporal distribution of the fishing effort and catch per unit effort (CPUE) for Chilean jack mackerel, Trachurus murphyi, stock are poorly understood. Data from the Chinese jack mackerel fleet was used to describe the location of the fishing effort and the relationship between standardized CPUE and sea surface temperatures (SST) during the period 2001-2010. A significant change in the spatio-temporal distribution of fishing effort and standardized CPUE was observed for jack mackerel during the study period. From January to March, the average CPUE was generally <15 tonnes (t) per net, except for 2007-2009. CPUE increased significantly during the autumn-winter (April to August), then gradually decreased in the spring and early summer (September to December). Average standardized CPUE in 2001-2005 was 23.3 t per net, but decreased to 19.7 t per net in 2006-2010. The change in the gravity center location of CPUE between months was similar during the primary fishing period (autumn to winter) in 2001-2006. After 2006, the pattern began to differ in July-October, which resulted in fishers spending more time to search for aggregations. A seasonal change was observed in the range of SSTs associated with high CPUE. Generally, the optimal SST range was from 13.0-15.0°C in autumn, 12.0-14.0°C in winter, 13-16°C in spring, and 15-19°C before 2006. However, a 1-2°C decrease in the optimal range in recent years was associated with a shift in the fishing grounds location to the southern area. In 2009, the optimal SST range was lower than in all other years. Taken together, the results suggest that a more thorough understanding of the seasonal or decadal relationship between SST and location of the fishing grounds is critical to improving the efficiency of the fishery and its management. [ABSTRACT FROM AUTHOR]

Herein, investigation on synergistic effect during network formation for conductive network constructed with carbon nanofillers in different dimensions is conducted. Multi-walled carbon nanotubes (MWNTs) and carbon black (CB) are employed as conductive fillers in this system. Morphological control of the conductive network is realized by adjusting the ratio between different fillers. Classical percolation threshold theory and adjusted excluded volume theory are used to analyze the electrical percolating behavior of these systems. It is observed that the percolation threshold of hybrid fillers filled conductive polymer composites (CPCs) is much lower than that of MWNTs or CB filled CPCs, and it can be reduced from 2.4 to 0.21 wt% by replacing half of the MWNTs with CB. Possible mechanism of this phenomenon is discussed together with morphological observation. A model is proposed to understand the mechanism of the percolation behavior in the composites containing various proportions of nanofillers. Our work is important for the design and preparation of low cost conductive polymer composites with novel electrical property. [ABSTRACT FROM AUTHOR]

Abstract: We report on the formation of the planar waveguide by 550keV O ion followed by 250keV O ion implantation in lithium niobate (LiNbO3), at fluences of 6×1014 ions/cm2 and 3×1014 ions/cm2, respectively. The Rutherford backscattering/channeling spectra have shown the atomic displacements in the damage region before and after annealing. A broad and nearly homogeneous damage layer has been formed by double-energy ion implantation after annealing. Both the dark mode spectra and the data of refractive index profile verified that the extraordinary refractive index was enhanced in the ion implanted region of LiNbO3. A homogeneous near-field intensity profile was obtained by double-low-energy ion implantation. There is a reasonable agreement between the simulated modal intensity profile and the experimental data. The estimated propagation loss is about 0.5dB/cm. [Copyright &y& Elsevier]

n all-fiber, wavelength-tunable, passively mode-locked erbium-doped ring laser is presented. Erbium-doped fibers (EDF) are used as the gain media because of their large gain bandwidth. Nonlinear polarization rotation (NPR) plays the dual role of realizing mode-locking and effectively adjusting the intensity-dependent loss of the cavity. An unbalanced Mach-Zehnder interferometer (UMZI) is used as a tunable optical beam filter. By using the UMZI and adjusting the polarization controllers (PCs), a sub-picosecond mode-locking laser is realized that is self-starting with central lasing wavelengths that can be accurately tuned over a range of about $\sim $30 nm and also has controllable spacings between different tunable wavelengths. [ABSTRACT FROM AUTHOR]

A new processing technology, direct chill rheocasting (DCRC), has recently been developed by BCAST at Brunel University, for production of high quality Mg alloy billets and slabs. In the present paper the authors present the DCRC process and experimental results on microstructure and mechanical properties of DCRC billets. Basically, the DCRC process consists of a high quality semisolid slurry supply system, continuously feeding a conventional direct chill caster, to produce billets or slabs. Experimental results show that the DCRC billets have a fine and uniform microstructure throughout the cross section, the average grain size being ∼50 μm. Direct extrusion of the DCRC billets was conducted to assess the deformability and mechanical properties after extrusion. The average grain size is <3 μm in the as extruded state. The increased deformability of the DCRC billets has been attributed to the fine and uniform microstructure, while the improved mechanical properties of the extruded product is attributed to the fine grain size. [ABSTRACT FROM AUTHOR]

HBx, a transcriptional transactivating protein of hepatitis B virus (HBV), is required for viral infection and has been implicated in virus-mediated liver oncogenesis. However, the molecular mechanism for its influence on cell remains largely unknown. It was proved that HBx need the help of host cell proteins to exert its function by binding to them. During purifying of GSTX (fusion protein of GST and HBx) expressed in E. coli, we found that it can bind specifically with GrpE (HSP60) and DnaK (HSP70) of E. coli while GST cannot. Using GST pull-down, two-dimensional gel electrophoresis and mass spectrum, we found that GSTX can also bind to human mitochondrial HSP60 and HSP70, which are homologues of GrpE and DnaK. These interactions between HBx and mitochondrial HSP60 and HSP70 are supported by the result of co-immunoprecipitation experiment. It means that HBx can form complex with E. coli and human HSP60 and HSP70. The implication of HBx, HSP60 and HSP70 complex in molecular mechanism of virus infection is discussed. [ABSTRACT FROM AUTHOR]

The YWK-II component of human sperm membrane is related to the βA4-amyloid precursor protein (APP) of Alzheimer's disease. A yeast 2-hybrid system was used to screen a mouse testis cDNA expression library for potential ligands capable of interacting with the extracellular domain of the YWK-II component. One of the bound proteins was identified as hDIA1, which has 96% identity with p140mDia. These proteins are members of the formin homology family and participate in cytokinesis and organization of the actin cytoskeleton. By interacting with these diaphanous proteins, the YWK-II component may be involved in germ cell differentiation and in the structural formation of the acrosome. [ABSTRACT FROM AUTHOR]

The Women's Health Study trial previously reported no overall effect of low-dose aspirin (100 mg every other day) on invasive breast cancer over an average of 10 years of treatment. The present subgroup analyses further show no effects by tumour characteristics at diagnosis, suggesting that low-dose aspirin has no preventive effect on breast cancer. [ABSTRACT FROM AUTHOR]

An expression of the relation between junction temperature and forward voltage common for both GaN-based laser diodes (LDs) and light emitting diodes is derived. By the expression, the junction temperature of GaN-based LDs emitting at 405 nm was measured at different injection current and compared with the result of micro-Raman spectroscopy, showing that the expression is reasonable. In addition, the activation energy of Mg in AlGaN/GaN superlattice layers is obtained based on the temperature dependence of forward voltage. [ABSTRACT FROM AUTHOR]

The pressure-time relation in the shock flow field of a near-earth air blast is complex. The triple point (TP) path is the physical boundary between the free and non-free shock flow fields. Accurately predicting the TP path is the basis for studying the evolution law of the reflection flow field and the guarantee of effectively assessing the damage power of the warhead. Based on the assumption that the Mach stem center is on the projection point of the blast center on the ground, the TP path calculation method was constructed by the geometric relationship. The unknown coefficients were solved using the existing TP data and the least square method. The TP prediction model proposed was compared with the existing ones on the calibration, new numerical simulation TP, and the measured real blast datasets. The error of the new numerical simulation TP data is within ±15% of the real value. The results show that the TP path prediction model proposed performs better. Most of its prediction results are within ±20% of three datasets compared to other models for the working conditions with the scaled height of burst from 0.397 to 2.777 m/kg1/3 and the horizontal scaled distance within 10 m/kg1/3 in the conventional cylindrical TNT explosion with the length-diameter of 1 in the air. The reliability of the prediction model is verified. [ABSTRACT FROM AUTHOR]

The measurement of peak overpressure from the near-earth air blast is usually ineffective in the near field of special environments. It is of great significance to explore a method to obtain the distribution of the near-field peak overpressure by measuring the far-field shock data. The relationship between the near-field shock peak overpressure and the far-field shock peak overpressure in near-earth air blast is studied to predict the near-field peak overpressure. AUTODYN-2D is used to establish the numerical simulation near-earth air blast model of TNT with the cylindrical charge of different equivalent mass and length–diameter ratios (LDRs), the various scaled heights of burst (SHOBs), and the wide range scaled distance (SD). The numerical results are validated with the calculation of empirical equations and the real explosion data. The far-field peak overpressure is calculated by the polynomial fitting equation of near-field data. The relationship between the far-field numerical peak overpressure and the above calculation results is studied first. Then, the spatial distribution of near-field peak overpressure is analyzed. At last, the near-field prediction model based on the far-field data is established. The results show that the far-field-to-near-field conversion equations based on the converted far-field peak overpressure predict the near-field data well. The spatial equivalent conversion equations give a clear numerical relationship to the peak overpressure in the near field. The peak overpressure at different spatial locations in the near field is obtained by using the above two sets of equations and at least four sets of far-field peak overpressure data. The predicted peak overpressure is reliable when the LDR is from 0.5 to 7, the SHOB is from 0.496 to 2.977, the SD is from 4 to 15, and the angle is below 45 ∘ . The prediction of other positions is available for reference. Using the prediction model based on the far-field data provides a novel method for obtaining the near-field shock peak overpressure under special working conditions. [ABSTRACT FROM AUTHOR]

The significant effect of the thickness of Ni film on the performance of the Ohmic contact of Ni/Au to p-GaN is studied. The Ni/Au metal films with thickness of 15/50 nm on p-GaN led to better electrical characteristics, showing a lower specific contact resistivity after annealing in the presence of oxygen. Both the formation of a NiO layer and the evolution of metal structure on the sample surface and at the interface with p-GaN were checked by transmission electron microscopy and energy-dispersive x-ray spectroscopy. The experimental results indicate that a too thin Ni film cannot form enough NiO to decrease the barrier height and get Ohmic contact to p-GaN, while a too thick Ni film will transform into too thick NiO cover on the sample surface and thus will also deteriorate the electrical conductivity of sample. [ABSTRACT FROM AUTHOR]

The influence of unintentionally doped carbon impurities on electrical resistivity and yellow luminescence (YL) of low-temperature (LT) grown Mg doped GaN films is investigated. It is found that the resistivity of Mg doped GaN films are closely related to the residual carbon impurity concentration, which may be attributed to the compensation effect of carbon impurities. The carbon impurity may preferentially form deep donor complex CN-ON resulting from its relatively low formation energy. This complex is an effective compensate center for MgGa acceptors as well as inducing YL in photoluminescence spectra. Thus, the low resistivity LT grown p-type GaN films can be obtained only when the residual carbon impurity concentration is sufficiently low, which can explain why LT P-GaN films with lower resistivity were obtained more easily when relatively higher pressure, temperature, or NH3/TMGa flow rate ratio were used in the LT grown Mg doped GaN films reported in earlier reports. [ABSTRACT FROM AUTHOR]

The effect of quantum barrier (QB) thickness on performances of InGaN/GaN multiple-quantum-well light-emitting diodes (MQW LEDs) with relatively large barrier layer thicknesses has been investigated. It is found that the density and averaged size of V-defects increases with QB thickness, resulting in larger reverse- and forward-bias current in LEDs. Electroluminescence measurement shows that LED with thinner QB has higher internal quantum efficiency but lower efficiency droop-onset current density, which should be ascribed to the faster saturation of carrier leakage into V-defects. Correspondingly, above the droop-onset current density, severer Auger recombination and carrier overflow are induced by higher carrier density due to the less V-defect related carrier leakage, leading to the more serious droop phenomenon in LEDs with thinner QB. [ABSTRACT FROM AUTHOR]

In the structure of conventional InGaN-based laser diodes, considerable optical absorption loss exists in the p-doped region, especially in the p-doped upper waveguide layer. A structure of InGaN-based laser diodes with an undoped InGaN upper waveguide layer instead of p-doped GaN was designed and optimized. Instead of being located between AlGaN EBL and AlGaN cladding layer, the undoped InGaN layer was positioned between the AlGaN electron blocking layer and the active region of multi-quantum well. The optical and electrical characteristics of this type of laser diodes were simulated by the commercial software lastip, and it was found that the optical absorption loss was obviously lowered. Further theoretical analysis showed that the undoped InGaN upper waveguide layer eliminated the influence of electron leakage current, leading to a reduction of threshold current density and an increase of output light power of the InGaN-based laser diodes. [ABSTRACT FROM AUTHOR]

We have investigated the effect of light Si-doping on the optical properties of high quality GaN films with the method of low temperature photoluminescence. It is found that the peak (Ix) at 3.473 eV always appears in the photoluminescence spectra of lightly Si-doped GaN. The relative intensity of peak Ix to heavy-hole free exciton peak increases linearly with the increasing concentration of Si doping, providing a strong support to the assignment that Ix originates from inelastic scattering of free excitons by Si donors. In addition, a rarely reported peak (Px) at 3.365 eV can only be clearly observed in the PL spectrum of unintentionally doped GaN sample. Its intensity is found to reduce dramatically with the decrease of residual carbon concentration based on the secondary ion mass spectrometry analysis. Px is attributed to the excitons bound to carbon-related complex defects. [ABSTRACT FROM AUTHOR]

Saturation of the junction voltage in GaN-based laser diodes (LDs) is studied. It is found that there is a bump above the lasing transition in the I(dV/dI)-I curve, instead of a dip as that for GaAs-based LDs. The bump in I(dV/dI)-I curve moves to higher currents along with the lasing threshold. A model considering ambipolar conduction and electron overflow into p-AlGaN cladding layer due to poor carrier confinement in active region is used to explain the anomaly. The characteristic temperature of GaN-based LD is obtained by fitting threshold currents determined from I(dV/dI)-I curves. Moreover, it is found that GaN-based LDs show characteristics with a nonlinear series resistance, which may be due to the electron overflow into p-AlGaN cladding layer and the enhanced activation of Mg acceptors. [ABSTRACT FROM AUTHOR]

This paper describes the experimental work on the tests of nine concrete-filled square and rectangular hollow structural section (HSS) columns subjected to axial load, uniaxial bending or biaxial bending. The experimental results suggest that the overall buckling appears accompanying with local buckling near the mid-height of column. Good agreement was found between the semi-sine wave shape and the experimental deflection shape. It is found that the cross-section remains plane before the specimen reached its load-carrying capacity. Also, the experimental results are compared with the values calculated from the AISC-LRFD, EC4 and CECS design codes, which shows that all codes provide safe bearing capacities. Compared with columns subjected to an axial load or uniaxial bending, the calculated capacities of column subjected to biaxial bending are more conservative. Among these three design codes, the capacities based on the EC4 design code yield results which are the closest to the experimental ones. The results calculated from the AISC-LRFD design code are the most conservative. [ABSTRACT FROM AUTHOR]

The spectral responses of back-illuminated p-i-n AlGaN ultraviolet photodetector under different bias voltage are investigated. The device structure is composed of p-GaN/p-Al0.3Ga0.7N/i-Al0.3Ga0.7N/n-Al0.6Ga0.4N and Ohmic contacts, where the p-GaN layer is very thin. There are two peaks in the spectral response of photocurrent located at 350 and 290 nm, respectively. It is found that in some devices the relative intensity and phase of these two peaks may change strongly with applied forward bias. A detailed analysis suggests that the possible Schottky-type-like behavior of metal and p-GaN contact and an unsatisfactory doping of p-GaN and p-AlGaN are responsible for the abnormal phenomenon. [ABSTRACT FROM AUTHOR]

Confinement factor and absorption loss of AlInGaN based multiquantum well laser diodes (LDs) were investigated by numerical simulation based on a two-dimensional waveguide model. The simulation results indicate that an increased ridge height of the waveguide structure can enhance the lateral optical confinement and reduce the threshold current. For 405 nm violet LDs, the effects of p-AlGaN cladding layer composition and thickness on confinement factor and absorption loss were analyzed. The experimental results are in good agreement with the simulation analysis. Compared to violet LD, the confinement factors of 450 nm blue LD and 530 nm green LD were much lower. Using InGaN as waveguide layers that has higher refractive index than GaN will effectively enhance the optical confinement for blue and green LDs. The LDs based on nonpolar substrate allow for thick well layers and will increase the confinement factor several times. Furthermore, the confinement factor is less sensitive to alloys composition of waveguide and cladding layers, being an advantage especially important for ultraviolet and green LDs. [ABSTRACT FROM AUTHOR]

It is studied whether there is any regular relationship between the yellow luminescence band and electron mobility of n-type GaN. For a series of GaN samples grown with the same Si doping, it is found that the electron mobility decreases with an increase of relative intensity of yellow luminescence, accompanied by an increase of edge dislocation density. Further research indicates that it is acceptors introduced by edge dislocations which lead to the concomitant changes of yellow luminescence and electron mobility. Similar changes are induced by Si doping in the n-type GaN samples with relatively low edge dislocation density. However, the relationship between the yellow luminescence and electron mobility of n-type GaN is not a simple one. A light Si doping may simultaneously increase yellow luminescence and electron mobility when Si doping plays a dominant role in reducing the carrier scattering. This means that even the intensity of yellow luminescence is often used as an indicator of material quality for GaN, it does not have any monotonous correlation with the electron mobility of GaN. [ABSTRACT FROM AUTHOR]

The deep level luminescence of crack-free Al0.25Ga0.75N layers grown on a GaN template with a high-temperature grown AlN interlayer has been studied using spatially resolved cathodoluminescence (CL) spectroscopy. The CL spectra of Al0.25Ga0.75N grown on a thin AlN interlayer present a deep level aquamarine luminescence (DLAL) band at about 2.6 eV and a deep level violet luminescence (DLVL) band at about 3.17 eV. Cross-section line scan CL measurements on a cleaved sample edge clearly reveal different distributions of DLAL-related and DLVL-related defects in AlGaN along the growth direction. The DLAL band of AlGaN is attributed to evolve from the yellow luminescence band of GaN, and therefore has an analogous origin of a radiative transition between a shallow donor and a deep acceptor. The DLVL band is correlated with defects distributed near the GaN/AlN/AlGaN interfaces. Additionally, the lateral distribution of the intensity of the DLAL band shows a domainlike feature which is accompanied by a lateral phase separation of Al composition. Such a distribution of deep level defects is probably caused by the strain field within the domains. [ABSTRACT FROM AUTHOR]

The article cites a study analyzing the role of blood test in predicting risk factors for colorectal cancer in patients. Risk factors include physical inactivity, a low-fiber diet, and having a family member with this type of cancer. Some data suggest that low-grade inflammation may also increase the risk for colorectal cancer. C-reactive protein (CRP) is a protein in the blood that increases when inflammation is present in the body. If inflammation increases a person's risk for developing colorectal cancer, higher CRP levels might be a sign of that higher risk. The participants were female health professionals. Higher CRP levels probably do not predict higher risk for colorectal cancer in healthy women.

Time-resolved light-current curves, spectra, and far-field distributions of ridge structure InGaN multiple quantum well laser diodes grown on sapphire substrate are measured with a temporal resolution of 0.1 ns under a pulsed current condition. Results show that the thermal lensing effect clearly improves the confinement of the higher order modes. The thermal lens leads to a lower threshold current for the higher order modes, a higher slope efficiency, and a change in the lasing mode of the device. The threshold current for the higher modes decreases by about 5 mA in every 10 ns in a pulse, and the slope efficiency increases by 7.5 times on the average when higher modes lase. [ABSTRACT FROM AUTHOR]

Composites of fibronectin/mineral and osteogenic growth peptide/mineral were synthesized on calcium phosphate coated substrates immersed in Dulbecco's phosphate-buffered saline solution containing biomolecules. The kinetics of coprecipitation for two biomolecules was similar, and the biomolecules participated in the formation of the crystal latticework and influenced the mineral structure and composition. [ABSTRACT FROM AUTHOR]

Reports that strains in cubic GaN films grown on GaAs were measured by a triple-axis x-ray diffraction method. Residual strains in the as-grown epitaxial films; Dependence of the relief of strains in the GaN films on the growth conditions.

In order to enhance the optical confinement and to reduce the vertical electron leakage current of InGaN-based multiple quantum well (MQW) laser diodes, a 2 nm GaN/5 nm In0.05Ga0.95N composite layer is designed as the last barrier layer between the MQW and AlGaN blocking layer in the p-region. The device simulation shows that the laser diode then has a lower threshold current and a higher output light power under same injection current than the conventional laser diodes without such a composite barrier layer. It is found that the thickness of InGaN has little influence on the P- I characteristic, while the In composition significantly changes the threshold current and output light power properties of laser diodes, which is attributed to the enhanced optical confinement and reduced vertical electron leakage current escaping from active region to p-doped region. The influences of the two parameters to modal gain are analyzed, too. [ABSTRACT FROM AUTHOR]

GaN films were grown by metal-organic chemical vapor deposition (MOCVD) under various growth conditions. The influences of MOCVD growth parameters, i.e., growth pressure, ammonia (NH3) flux, growth temperature, trimethyl-gallium flux and H2 flux, on residual carbon concentration ([C]) were systematically investigated. Secondary ion mass spectroscopy measurements show that [C] can be effectively modulated by growth conditions. Especially, it can increase by reducing growth pressure up to two orders of magnitude. High-resistance (HR) GaN epilayer with a resistivity over 1.0 x 109Ω'cm is achieved by reducing growth pressure. The mechanism of the formation of HR GaN epilayer is discussed. An AlxGa1-xN/GaN high electron mobility transistor structure with a HR GaN buffer layer and an additional low-carbon GaN channel layer is presented, exhibiting a high two dimensional electron gas mobility of 1815cm²/Vs. [ABSTRACT FROM AUTHOR]

Neuroprotection following ischaemic stroke is driven by the interplay between regulatory transcription factors and endogenous protective factors. IRF4, a member of the interferon regulatory factor (IRF) family, is implicated in the survival of tumour cells. However, its role in the survival of normal cells including neurons remains elusive. Using genetic approaches, we established a central role for IRF4 in protection against ischaemia/reperfusion (I/R)-induced neuronal death. IRF4 was expressed in neurons, and induced by ischaemic stroke. Neuron-specific IRF4 transgenic (IRF4-TG) mice exhibited reduced infarct lesions, and this effect was reversed in IRF4-knockout mice. Notably, we revealed that IRF4 rescues neurons from I/R-induced death both in vivo and in vitro. Integrative transcriptional and cell survival analyses showed that IRF4 functions mechanistically as a transcription activator of serum response factor (SRF) crucial to salvage neurons during stroke. Indeed, the expression of SRF and SRF-dependent molecules was significantly upregulated upon IRF4 overexpression and conversely inhibited upon IRF4 ablation. Similar results were observed in oxygen glucose deprivation (OGD)-treated primary cortical neurons. Furthermore, we identified the IRF4-binding site in the promoter region of the SRF gene essential for its transcription. To verify the IRF4-SRF axis in vivo, we generated neuron-specific SRF knockout mice, in which SRF exerted profound cerebroprotective effects similar to those of IRF4. More importantly, the phenotype observed in IRF4-TG mice was completely reversed by SRF ablation. Thus, we have shown that the IRF4-SRF axis is a novel signalling pathway critical for neuronal survival in the setting of ischaemic stroke. [ABSTRACT FROM AUTHOR]

The growth condition of thin heavily Mg-doped GaN capping layer and its effect on ohmic contact formation of p-type GaN were investigated. It is confirmed that the excessive Mg doping can effectively enhance the Ni/Au contact to p-GaN after annealing at 550 °C. When the flow rate ratio between Mg and Ga gas sources is 6.4% and the layer width is 25 nm, the capping layer grown at 850 °C exhibits the best ohmic contact properties with respect to the specific contact resistivity (ρc). This temperature is much lower than the conventional growth temperature of Mg-doped GaN, suggesting that the deep-level-defect induced band may play an important role in the conduction of capping layer. [ABSTRACT FROM AUTHOR]

The effect of quantum well (QW) number on performances of InGaN/GaN multiple-quantum-well light-emitting diodes has been investigated. It is observed that V-defects, originated from various InGaN well layers intercepted by threading dislocations (TDs), increase in density and averaged size with more periods of QWs, resulting in larger reverse-bias leakage current and lower emission efficiency of light-emitting diodes. Conductive atomic force microscopy measurements demonstrate that V-defects may preferentially capture carriers, subsequently enhance local current and nonradiative recombinations at associated TD lines, which suggest that TD lines with V-defects at vertex have larger influence on emission efficiency than those without V-defects. [ABSTRACT FROM AUTHOR]

The Suaeda salsa glutathione S-transferase gene (GST) was introduced into arabidopsis under the control of the cauliflower mosaic virus 35S promoter. Transformants were selected for their ability to grow on medium containing kanamycin. Southern and northern blot analyses confirmed that GST was transferred into the arabidopsis genome, and the GST and GPX activities in transgenic plants (GT) were much higher than in wild-type plants (WT). There were no obvious morphological or developmental differences between transgenic and wild-type plants. One transgenic homozygous line (GT6–8) and WT plants were evaluated for salt tolerance and gene expression. Seed germination and seedling salt tolerance were improved after overexpression of GST in arabidopsis; the photosynthesis rate and the fresh weight of the GT6–8 line were distinctly higher than those of WT plants after NaCl treatment. Glutathione content increased substantially in salt-stressed arabidopsis plants of both genotypes, and the glutathione pool in GT6–8 plants was more oxidized than in WT plants under both control and stressful conditions. The MDA content, an indicator of lipid peroxidation, increased in WT plants but was not affected distinctly in GT6–8 seedlings after NaCl treatment. Results from different tests indicated that the expression of the GST gene promoted a higher level of salt tolerance in vivo in transgenic arabidopsis plants. [ABSTRACT FROM AUTHOR]

Alcohol has been hypothesized to promote ovarian carcinogenesis by its potential to increase circulating levels of estrogen and other hormones; through its oxidation byproduct, acetaldehyde, which may act as a cocarcinogen; and by depletion of folate and other nutrients. Case-control and cohort studies have reported conflicting results relating alcohol intake to ovarian cancer risk. We conducted a pooled analysis of the primary data from ten prospective cohort studies. The analysis included 529 638 women among whom 2001 incident epithelial ovarian cases were documented. After study-specific relative risks (RR) and 95% confidence intervals (CI) were calculated by Cox proportional hazards models, and then were pooled using a random effects model; no associations were observed for intakes of total alcohol (pooled multivariate RR=1.12, 95% CI 0.86-1.44 comparing > or =30 to 0 g day(-1) of alcohol) or alcohol from wine, beer or spirits and ovarian cancer risk. The association with alcohol consumption was not modified by oral contraceptive use, hormone replacement therapy, parity, menopausal status, folate intake, body mass index, or smoking. Associations for endometrioid, mucinous, and serous ovarian cancer were similar to the overall findings. This pooled analysis does not support an association between moderate alcohol intake and ovarian cancer risk. [ABSTRACT FROM AUTHOR]

Purpose: To investigate the effects of pre-exposure of mouse testis with low-doses of 16O 8 ions or 60Co gamma -rays on sperm shape abnormalities, lipid peroxidation and superoxide dismutase (SOD) activity induced by subsequent high-dose irradiation. Materials and methods: Testes of the B6C3F hybrid strain mice 1 were pre-irradiated with 0.05 Gy of 16O 8 ions or 60Co gamma -rays and then after 4 h given a test irradiation with 2 Gy of the same radiation type. SOD activity and thiobarbituric acid reactive substances (TBARS) in the testes were determined by spectrophotometric and TBA methods respectively at 4 h after irradiation. Testis weight, sperm count and sperm morphology were analysed at day 35 after irradiation. Results: Compared with controls, there was a significant increase in SOD activity and a significant decrease in TBARS level of pretreated testes. Testis weight loss, sperm count reduction and sperm abnormalities were significantly lower in the pretreated testes. The bioeffects of a 2 Gy dose of 16O 8 ions relative to 60Co gamma -rays were 1.84 0.28 for testis weight, 1.22 0.25 for sperm count and 1.29 0.10 for sperm abnormalities. Conclusions: These data suggest that pre-exposure of testes with a low dose of heavy ions or gamma -rays renders the organ more resistant to subsequent high-dose irradiation. The increase of SOD activity and the decrease of lipid peroxidation levels induced by lowdose ionizing irradiation may be involved in this resistance. The effects with heavy ion irradiation were greater than with gamma -rays. [ABSTRACT FROM AUTHOR]

Self-organized InGaN quantum dots (QDs) with emission wavelength from green to red range have been grown on GaN templated c-plane sapphire substrates by metal-organic chemical vapor deposition (MOCVD). The effects of matrix layer composition on the structural and optical properties of InGaN QDs have been investigated. A continued growth of QDs is observed during the growth of In0.1Ga0.9N matrix layer, which results in an increase of the QDs' size. By using In0.1Ga0.9N matrix layer instead of GaN one, the annealing induced blue-shift in emission energy of the InGaN QDs can be suppressed. After the growth of top GaN cap layer, a larger red-shift caused by the quantum confined Stark effect is observed in the sample with In0.1Ga0.9N matrix layer. Employing this method, InGaN QD sample emitting at 615 nm with an internal quantum efficiency of 24.3% has been grown. The significance of this method is that it allows a higher growth temperature of InGaN QDs with emission wavelength in the green range to improve the crystalline quality, which is beneficial to enhance the efficiency of green InGaN QD light-emitting-diodes and laser diodes. [ABSTRACT FROM AUTHOR]

An interesting phonon mode at around 685-705 cm-1 was clearly observed in the Raman spectra of InGaN/GaN multiple-quantum-wells nanopillars with different diameters at room temperature. The Raman peak position of this mode is found to show a distinct dependence on the nanopillar size, which is in well agreement with theoretical calculation of the surface optical (SO) phonon modes of nanopillars. Moreover, this kind of SO phonon was evidenced to be located on the pillar surface by using scanning confocal micro-Raman microscopy. [ABSTRACT FROM AUTHOR]

A close relationship is found between the blue and yellow luminescence bands in n-type GaN films, which are grown without intentional acceptor doping. The intensity ratio of blue luminescence to yellow luminescence (IBL/IYL) decreases with the increase in edge dislocation densities as demonstrated by the (102) full width at half maximum of x-ray diffraction. In addition, the IBL/IYL ratio decreases with the increase in Si doping. It is suggested that the edge dislocation and Si impurity play important roles in linking the blue and yellow luminescence. [ABSTRACT FROM AUTHOR]

The influence of defects on the responsivity of GaN Schottky barrier ultraviolet photodetectors with n--GaN/n+-GaN layer structures is investigated. It is found that employing undoped GaN instead of Si-doped GaN as the n--GaN layer brings about a higher responsivity due to a lower Ga vacancy concentration. On the other hand, the dislocations may increase the recombination of electron-hole pairs and enhance the surface recombination in the photodetectors. Employing undoped GaN and reducing the dislocation density in the n--GaN layer are necessary to improve the responsivity of Schottky barrier photodetectors. [ABSTRACT FROM AUTHOR]

The effects of dislocations and Si doping on the electrical properties of n-type GaN grown by metal organic chemical vapor deposition (MOCVD) are investigated. It is found that both electron mobility and carrier concentration are strongly influenced by edge dislocations. A moderate Si doping during the GaN growth improves the electron mobility, but the best doping effect depends on the dislocation density of the sample. High quality about 4-μm-thick MOCVD-grown GaN film with a room temperature electron mobility as high as 1005 cm²/V s is obtained by optimizing growth conditions. [ABSTRACT FROM AUTHOR]

The structural property of InN films grown on Ga-face GaN layers by metal-organic chemical vapor deposition has been studied by high-resolution x-ray diffraction. The mosaic tilt and twist are found to be strongly dependent on the surface lateral grain size. The twist decreases with increasing grain size and finally approaches to a constant level. On the other hand, the mosaic tilt increases substantially when the grain size becomes large enough and exceeds the width of step terraces on the GaN surface, showing an important mechanism for the defect generation in the InN/GaN system with large out-of-plane lattice mismatch. [ABSTRACT FROM AUTHOR]

We investigate the effects of lightly Si doping on the minority carrier diffusion length in n-type GaN films by analyzing photovoltaic spectra and positron annihilation measurements. We find that the minority carrier diffusion length in undoped n-type GaN is much larger than in lightly Si-doped GaN. Positron annihilation analysis demonstrates that the concentration of Ga vacancies is much higher in lightly Si-doped GaN and suggests that the Ga vacancies instead of dislocations are responsible for the smaller minority carrier diffusion length in the investigated Si-doped GaN samples due to the effects of deep level defects. [ABSTRACT FROM AUTHOR]

We investigate the origin of yellow luminescence in n-type GaN. It is found that the relative intensity of yellow luminescence increases as the full width at half maximum of the x-ray diffraction rocking curve at the (102) plane increases. This indicates that the yellow luminescence is related to the edge dislocation density. In addition, the relative intensity of yellow luminescence is confirmed to increase with increasing Si doping for the high quality GaN we have obtained. We propose that the yellow luminescence is effectively enhanced by the transition from donor impurities such as Si to acceptors around the edge dislocations in n-type GaN. [ABSTRACT FROM AUTHOR]

High-efficient GaN-based laser diodes (LDs) with tunnel junction are designed by replacing conventional p-type AlGaN cladding layers and p-type GaN contact with lower-resistant n-type AlGaN cladding layers and n-type GaN contact. In addition, the characteristics of the LDs with tunnel junction are numerically investigated by using the commercial software lastip. It is found that the performance of these LDs is greatly improved. As a comparison, the absorption loss and non-radiative recombination are greatly reduced. The threshold current and series resistance are decreased by 12% and 59%, respectively, and the slope efficiency is raised up by 22.3%. At an injection current of 120 mA, the output power and wall-plug-efficiency are increased by 34% and 79%, respectively. [ABSTRACT FROM AUTHOR]

The influences of a high-temperature (HT) AlN interlayer (IL) on the phase separation in crack-free AlGaN grown on GaN have been studied. The depth-dependent cathodoluminescence (CL) spectra indicate a relatively uniform Al distribution in the growth direction, but the monochromatic CL images and the CL spectra obtained by line scan measurements reveal a lateral phase separation in AlGaN grown on relatively thick HT-AlN ILs. Moreover, when increasing the thickness of HT-AlN IL, the domain-like distribution of the AlN mole fraction in AlGaN layers is significantly enhanced through a great reduction of the domain size. The morphology of mesa-like small islands separated by V trenches in the HT-AlN IL, and the grain template formed by the coalescence of these islands during the subsequent AlGaN lateral overgrowth, are attributed to be responsible for the formation of domain-like structures in the AlGaN layer. [ABSTRACT FROM AUTHOR]

The in situ optical reflectivity measurements are employed to monitor the GaN epilayer growth process above low-temperature AlN buffer layer on c-plane sapphire substrate by metalorganic chemical vapor deposition. It is found that the lateral growth of GaN islands and their coalescence is promoted in the initial growth stage if the AlN buffer layer is treated with a long annealing time and has an optimal thickness: As confirmed by atomic force microscopy observations, the quality of GaN epilayers is closely dependent on the surface morphology of AlN buffer layer, especially the grain size and nuclei density after the annealing treatment. [ABSTRACT FROM AUTHOR]