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In this study, we investigated thermotolerance, several physiological responses and damage to reproductive cells in chlorpyrifos-resistant (Rc) and -susceptible (Sm) strains of the diamondback moth, Plutella xylostella subjected to heat stress. The chlorpyrifos resistance of these strains was mediated by a modified acetylcholinesterase encoded by an allele, ace1R, of the ace1 gene. Adults of the Rc strain were less heat resistant than those of the Sm strain; they also had lower levels of enzymatic activity against oxidative damage, higher reactive oxygen species contents, weaker upregulation of two heat shock protein (hsp) genes (hsp69s and hsp20), and stronger upregulation of two apoptotic genes (caspase-7 and -9). The damage to sperm and ovary cells was greater in Rc adults than in Sm adults and was temperature sensitive. The lower fitness of the resistant strain, compared with the susceptible strain, is probably due to higher levels of oxidative stress and apoptosis, which also have deleterious effects on several life history traits. The greater injury observed in conditions of heat stress may be due to both the stronger upregulation of caspase genes and weaker upregulation of hsp genes in resistant than in susceptible individuals.
This is the first report of microsatellite markers (simple sequence repeats, SSR) for fall webworm, Hyphantria cunea (Drury) (Lepidoptera: Arctiidae), an important quarantine pest in some European and Asian countries. Here, we developed 48 microsatellite markers for H. cunea from SSR enrichment libraries. Sequences isolated from libraries were sorted into four categories and analyzed. Our results suggest that sequences classified as Grouped should not be used for microsatellite primer design. The genetic diversity of microsatellite loci was assessed in 72 individuals from three populations. The number of alleles per locus ranged from 2 to 5 with an average of 3. The observed and expected heterozygosities of loci ranged from 0 to 0.958 and 0 to 0.773, respectively. A total of 18 out of 153 locus/population combinations deviated significantly from Hardy–Weinberg equilibrium. Moreover, significant linkage disequilibrium was detected in one pair of loci (1275 pairs in total). In the neutral test, two loci were grouped into the candidate category for positive selection and the remainder into the neutral category. In addition, a complex mutation pattern was observed for these loci, and FST performed better than did RST for the estimation of population differentiation in different mutation patterns. The results of the present study can be used for population genetic studies of H. cunea.
The thermodynamic La–Sr–Mn–Cr–O oxide database is obtained as an extension of thermodynamic descriptions of oxide subsystems using the calculation of phase diagrams approach. Concepts of the thermodynamic modeling of solid oxide phases are discussed. Gibbs energy functions of SrCrO4, Sr2.67Cr2O8, Sr2CrO4, and SrCr2O4 are presented, and thermodynamic model parameters of La–Sr–Mn–Chromite perovskite are given. Experimental solid solubilities and nonstoichiometries in La1−xSrxCrO3−δ and LaMn1−xCrxO3−δ are reproduced by the model. The presented oxide database can be used for applied computational thermodynamics of traditional lanthanum manganite cathode with Cr-impurities. It represents the fundament for extensions to higher orders, aiming on thermodynamic calculations in noble symmetric solid oxide fuel cells.
The high Al content AlGaN epilayers have been obtained by metalorganic chemical vapor deposition (MOCVD), and the optical property has been investigated by photoluminescence (PL) spectroscopy. Longitudinal-optic (LO) phonon mode has been studied by Raman scattering. Further analysis shows that the edge dislocation is an important factor influencing optical quality of AlGaN epilayers, and it also shows that the correlation between the A1 (LO) polar modes and the edge dislocation is intensive, which may be expected to become a characterization method of the related crystal defects.
The influence of pressure on the MOCVD grown InAlN/AlN/GaN heterostructure has been investigated by high-resolution X-ray diffraction, Hall measurement and atomic force microscopy. High pressure is beneficial to increase indium incorporation efficiency. The electrical properties of InAlN/AlN/GaN heterostructure become better with the pressure decreasing from 100 Torr to 50 Torr. Indium droplets tend to form on the InAlN surface at high pressure. The edge of the indium droplet is the Al-rich region while the interior is the In-rich region, demonstrated by the phase-contrast mode. Phase contrast across the V-defect is strong on the surface of InAlN grown at low pressure (50 Torr) whereas it is not evident at high pressure (100 Torr), indicating that large stress in the InAlN film will enhance the compositional variation.
The efficiency of acousto-optic interaction in single-mode strip silica waveguide is analyzed theoretically by determining the overlap integral between the optical and acoustic field distributions. The results show that there is a good overlap of the optical and SAW fields in the low SAW frequency range. At high acoustic frequencies, the overlap integral decreases with increasing acoustic frequency. At 216 MHz, the maximum of 0.8544 for the overlap integral is obtained, provided the H/Λ equals 0.02. At last, the diffraction efficiencies for acoustic frequency of 216 MHz are calculated as a function of the square root of acoustic power for different acoustic apertures.
Light-emitting diodes (LEDs) based on p-GaN/ZnO heterojunction were fabricated. GaN was deposited on sapphire using metal-organic chemical vapor deposition (MOCVD), and two kinds of ZnO i.e. ZnO thin film deposited by sputtering and ZnO nanorods (NRs) grown by hydrothermal method were used as n-type layer respectively. MgO film with the thickness around 10 nm was deposited by electron-beam deposition to act as an interlayer between GaN and ZnO. Photoluminescence, electroluminescence and I-V curves were measured to compare the properties of GaN based heterojunction LEDs with different architectures. The existence of MgO interlayer as well as the morphology of ZnO obviously influenced the electrical and optical properties of GaN based LEDs. The effect of MgO interlayer on ZnO growth, properties and I-V curves and emission spectra of LEDs is discussed in detail.
The I-V characteristics of AlGaN/GaN high electron mobility transistors in the temperature range between 100 K and 300 K are studied. It is found that both the maximum drain-source current and transconductance decrease with the increase of temperature. Decrease of the electron mobility with increasing temperature is considered to be the main cause for that condition. The threshold voltage shows a forward shift, which can be explained by the increase of Schottky barrier with increasing temperature. It is found that at VGS = 0 V the drain-source current reduces with the ascending temperature, which should be due to the variation of the electron mobility with the temperature. While at VGS = −5 V the drain-source current is found to increase with the ascending temperature, it is suggested to be caused by the positive temperature coefficient of the electron transport in the depleted region.
The temperature dependence of the I-V characteristics on Au/Ni-HEMT Schottky contacts was measured and analyzed. Large deviations from the thermionic emission and thermionic-field emission model were observed in the I-V-T characteristics. The thin surface barrier model only fits the measured curves in the high bias region, but deviates drastically in the low bias region. Using a revised thin surface barrier model, the calculated curves match well with the measured curves. It is also found that tunneling emission model is the dominant current transport mechanism at low temperature, yet thermionic-field emission model is the dominant current transport mechanism at high temperature.
Efficient generation regime with a high power output has been experimentally realized in a klystron-like relativistic backward wave oscillator, in which a modulation cavity is inserted between the slow wave structure to decrease the energy spread of modulated beam electrons, and an extraction cavity is employed at the end of the slow wave structure to further recover energy from the electron beam. At a guiding magnetic field of 2.2 T, a microwave pulse with power of 6.5 GW, frequency of 4.26 GHz, pulse duration of 38 ns, and efficiency of 36% was generated when the diode voltage was 1.1 MV, and diode current was 16.4 kA. When the diode voltage was 820 kV, efficiency up to 47% with microwave power 4.4 GW was also realized experimentally.
An important component of the U.S. effort to achieve thermonuclear
ignition in 2010 on the National Ignition Facility is the development of
high quality 2 mm diameter spherical capsules to function as the ablator
and contain the cryogenic DT fuel. Three ignition capsule designs have
been developed, and detailed fabrication specifications for each design
have been established and placed under change control. A research program
with activities coordinated mainly between Lawrence Livermore, General
Atomics and Los Alamos is underway to demonstrate fabrication of capsules
meeting specifications. The point design for ignition campaigns beginning
in 2010 is a Cu-doped Be capsule that has a radial gradient in Cu dopant
level in the capsule wall. This capsule is being produced by sputter
deposition of Be and Cu onto either a hollow glow discharge polymer (GDP)
spherical mandrel or a solid spherical mandrel, followed by removal of the
mandrel and polishing of the capsule. A key goal in the U.S. is to
demonstrate fabrication of this capsule by the end of 2006. Two other
ignition capsule designs are also being developed as contingencies to the
point design. One contingency design is a GDP capsule that has a radial Ge
dopant level in its wall. This capsule is produced by co-deposition of Ge
and GDP onto a PAMS mandrel followed by thermal removal of the mandrel.
The second contingency design is a uniform Cu-doped Be capsule that is
fabricated from high purity fine grain Be0.3at.%Cu alloy using a precision
machining route followed by polishing. Ignition targets to be fielded in
2010 will be filled with DT fuel through a small fill hole. Laser drilling
capability has been developed and used to drill approximately 5 μm
diameter holes through capsule walls for DT filling. Characterization
methods necessary for characterizing capsules are being developed.
Quantum dot infrared photodetectors (QDIPs) have been studied widely for normal-incidence infrared detection. The 3D confinement provided by quantum dots allows for the elimination of gratings that are typically required for normal-incidence detection in quantum well infrared photodetectors (QWIPs). Furthermore, the growth of Ge dots on Si substrates offers the potential for integration with existing CMOS platforms. To date, however, Ge QDIPs have typically been grown epitaxially by Stranski-Krastonov growth – producing pancake-like dots with base dimensions of 50-100 nm, heights of 7-10 nm, and an aerial dot density of 109–1010 cm−2. Such dots have poor lateral confinement, causing them to have non-ideal normal-incidence absorption characteristics, similar to quantum wells. In this work, we demonstrate infrared absorption in Ge dots with base dimensions of approximately 15 nm. These dots are epitaxially grown on pre-patterned Si substrates, with an aerial dot density of approximately 1011 cm−2. The substrates are prepared by using diblock copolymers to create a nano-pattern on the substrate surface which is transferred to the substrate by dry etching. The size of this pattern determines the base dimensions of the Ge dots. After growth, these dots are then tested for their infrared absorption properties using Fourier Transform Infrared (FTIR) Spectroscopy. The normal-incidence absorption of the dots can be studied with FTIR by varying the polarization angle of the infrared light. We present FTIR absorption spectra for samples grown with various conditions (e.g., different dot doping levels, numbers of layers, and dot base dimensions) and investigate the effects of different growth conditions on infrared absorption properties. We also report on the normal-incidence absorption characteristics of these dots by presenting absorption spectra for various polarization angles of infrared light.
Zinc oxide (ZnO) quantum dots (QDs) embedded films were fabricated on silicon substrates by metal organic chemical vapor deposition at 350°C. The QDs can be obtained in a matrix of amorphous ZnO films by introducing a large amount of precursors. The size of the QDs ranged from 3 to 12 nm, which was estimated by high-resolution transmission electron microscopy. The photoluminescence measured at 80 K showed that the emission of QDs embedded film ranged from 3.0 to 3.6 eV. The broad near-band-edge emission is due to the quantum confinement effect of the QDs. The quantum confinement effect of the QDs disappears after the post-growth annealing due to the ripening of QDs.
GaAs1−xNx layers and quantum dot-like structures were grown on (100) GaAs substrates by molecular beam epitaxy. The dependence of photoluminescence emission spectra on annealing temperature is consistent with literature at lower temperatures but after annealing at 750 °C a net red-shift is consistently observed. X-ray photoelectron spectroscopy measurements indicate that for different annealing times and temperatures, the nitrogen and arsenic surface concentrations changed compared to that of as-grown samples, specifically arsenic is lost from the material. Raman measurements are consistent with the trends in photoluminescence and also suggest the loss of arsenic occurs at higher annealing temperatures in both samples capped with GaAs and uncapped samples.
SiC homo-epitaxial layers have been grown using a halide chemical vapor deposition (HCVD) process. The thermodynamic process of SiC CVD in SiCl4-C3H8-H2 gas system was studied using equilibrium model. The predicted growth rate decreases gradually with the increase in growth temperature, and this trend is consistent with our experimental results. Good quality epitaxial layers with low density of basal plane dislocations could be grown. Some elementary screw dislocations present in the substrate do not seem to be propagating into the epitaxial layer.
The global scientific community recognizes the critical need for industries to develop and practice manufacturing techniques that minimize harm to our environment. In the National Science Board's report Environmental Science and Engineering for the 21st Century, the National Science Foundation was urged to promote “Environmental research, education, and scientific assessment [as] one of NSF's higher priorities.” Although there are a number of independent efforts to fold environmental issues in existing undergraduate curricula, no dominant method has emerged as a means of including these concepts. One of the difficulties in adjusting our materials science and engineering (MSE) curricula is the problem of how and what to include in an already full curriculum. In this paper, we propose a path for integrating environmental and sustainability concepts within the framework of existing curricula. We will suggest learning outcomes for each year of the MSE curriculum and offer examples.
A summer Research Experience for Undergraduate (REU) site program has been operating at Washington State University for the past five summers. Over this time we have experimented with several modes of organized summer research methods, including students working in individual projects as well as students working in teams. We have balanced the academic standing of the students (freshmen to seniors), as well providing a diverse demographic background. The results of these past five summers will be presented, as well as recommendations for which methods have been the most successful in terms of generating publications and presentations from the students as well as the likelihood of students entering graduate school.
The National Science Foundation's National Science Digital Library (NSDL) Program is a premier collective portal of authoritative scientific resources supporting education and research. With funding from NSF, the Materials Digital Library (MatDL) is a collaborative project being developed by the National Institute of Standards and Technology's Materials Science and Engineering Laboratory (NIST/MSEL), the Department of Materials Science and Engineering at the Massachusetts Institute of Technology (MIT), the Department of Chemical Engineering and the Department of Materials Science and Engineering at the University of Michigan (U-M), with Kent State University and University of Colorado at Boulder providing the materials science informatics and workflow technology backbone. As part of the NSDL program, MatDL aims to supports the interface of materials science information and its cognate disciplines, with an emphasis on soft matter. Initial content of MatDL begins with resources selected from NIST/MSEL. Students and faculty in three types of materials science and engineering (MSE) courses at MIT and U-M are taking part in a pilot to use and contribute to MatDL utilizing domain-specific authoring tools. Given the central and interdisciplinary role of materials science in science and engineering, two goals of MatDL are to: 1.) expand its founding partnership with additional participants from the MSE community; and 2.) facilitate the flow of digital materials related knowledge from laboratories where the most recent research discoveries are taking place to the classrooms where new scientists are being trained.