A survey of the gomphonemaceae and cymbellaceae (Bacillariophyta) from the Jolmolungma Mountain (Everest) region of China

Gomphonemaceae and Cymbellaceae from Jolmolungma Mountain region of China, comprised 79 taxa belonging to five genera. The dominant species were Gomphonema angustatum var. productum, G. gracile var. gracile, G. parvulum var. parvulum, G. hedini, Cymbella aequalis var. pisciculus, C. delicatula, C. cistula, C. cistula var. hebetata, C. cesatii, C. cymbiformis, C microcephala, C. minuta var. minuta., C. minuta var. silesiaca, C. pusilla, C. affinis. Some arctic and alpine forms also occurred, and the following taxa were unique to this region: Cymbella delicatula, C. naviculiformis, C. gracilis, C. minuta var. minuta, C. affinis, C. cistula, C. cymbiformis, C. cistula var. hebetata, C. arctica, Didymosphenia geminata, Gomphonema hedinii, G. olivaceum. Numbers of taxa in each samples varied greatly, It appears that species diversity of diatoms is related not only to macro-environments (e.g., geographic zonation) but also to microenvironments (e.g., microhabitats and microclimates). Cymbella spp. are not only comparatively widespread in the region but also outnumber Gomphonema spp. A large number of species found in the Jolmolungma Mountain region are also found in Tibet and the headwaters of Yangtze River.

The reproductive strategies of an endemic Tibetan fish, Gymnocypris selincuoensis

The reproductive traits of Gymnocypris selincuoensis from Selincuo Lake and its tributaries were investigated in 1997 and 1998. The youngest mature male was age 7 with a standard length (SL) of 172.0 mm, and the youngest mature female was age 8 with a SL of 194.0 mm. The L(50)s Of SL and age at first maturity were respectively 250.32 mm and age 9 for males and 224.71 mm and age 8 for females. The gonadosomatic index (GSI) significantly changed with seasons for mature individuals but not for immature individuals. GSIs of mature females at stages IV and V of ovary development increased with SL and reached a maximum value at the SL range from 370 mm to 390 mm; the GSIs of mature males were negatively correlated with SL. The breeding season lasted from early April to early August. Egg size did not significantly change with SL but increased with the delay of spawning. The individual absolute fecundity varied from 1,341 to 28,002 eggs (mean 12,607+/-7,349), and the individual relative fecundity varied from 6.4 to 42.0 eggs.g(-1) (mean 25.5+/-9.7). The individual fecundity increased with total body weight; it also increased with SL for those of SL less than 370 mm. There was a rest of spawning for mature individuals.

Effect of cycles of feed deprivation on growth and food consumption of immature three-spined sticklebacks and European minnows

Individual juvenile three-spined sticklebacks Gasterosteus aculeatus and European minnow Phoxinus phoxinus, from sympatric populations, were subjected to four cycles of I week of food deprivation and 2 weeks of ad libitum feeding. Mean specific growth rate during the weeks of deprivation was negative and did not differ between species. The three-spined stickleback showed sufficient growth compensation to recover to the growth trajectory shown by control fish daily fed ad libitum. The compensation was generated by hyperphagia during the re-feeding periods, and in the last two periods of re-feeding, the gross growth efficiencies of deprived three-spined sticklebacks were greater than in control fish. The expression of the compensatory changes in growth and food consumption became clearer over the successive periods of re-feeding. The European minnow developed only a weak compensatory growth response and the mass trajectory of the deprived fish deviated more and more from the control trajectory During re-feeding periods, there were no significant differences in food consumption or gross growth efficiency between control and deprived European minnows. The differences between the two species are discussed in terms of the possible costs of compensatory growth, the control of growth and differences in feeding biology (C) 2003 The Fisheries Society of the British Isles.

Photosynthetic characteristics of the terrestrial blue-green alga, Nostoc flagelliforme

Photosynthetic responses of rewetted Nostoc flagelliforme to CO2, desiccation, light and temperature were investigated under emersed conditions in order to characterize its ecophysiological behaviour in nature. Net photosynthesis increased to a maximum rate at about 30 % water loss, then decreased, while dark respiration always decreased with the progress of desiccation. Light-saturated photosynthesis and dark respiration were significantly reduced at 8 degreesC, but remained little affected by changes of temperature within the range of 15-35 degreesC. Photosynthetic efficiency (alpha) was maximal at the beginning of desiccation and then reduced with increased water loss. Saturating irradiance for photosynthesis was about 194-439 mu mol quanta m(-2) s(-1), being maximal at about 30 % water loss. No photoinhibition was observed at irradiances up to 1140 mu mol m(-2) s(-1). Light compensation points were about 41-93 mu mol m(-2) s(-1). Photosynthesis of N. flagelliforme was CO2-limited at the present atmospheric CO2 level. The CO2-saturated photosynthesis increased with increase of irradiance (190-1140 mu mol m(-2) s(-1)) and temperature (8-25 degreesC) and decreased significantly with water loss (0-75 %). Photosynthetic affinity for CO2 was sensitive to temperature and irradiance. The CO2 compensation point (Gamma) increased significantly with increased temperature and was insensitive to irradiance. Desiccation did not affect Gamma values before water loss exceeded 70 %. Photorespiratory CO2 release did not occur in N. flagelliforme at the current atmospheric CO2 level.

Fabrication of nanoscale metallic air-bridges by introducing a SiO2 sacrificial layer

A new method to fabricate nanoscale metallic air-bridges has been investigated. The pillar patterns of the air-bridge were defined on a SiO2, sacrificial layer by electron-beam lithography combined with inductively coupled plasma etching. Thereafter, the span (suspended part between the pillars) patterns were defined with a second electron-beam exposure on a PMMA/PMMA-MAA resist system. The fabrication process was completed by subsequent metal electron-beam evaporation, lift-off in acetone, and removal of the sacrificial layer in a buffered hydrofluoric (HF) solution. Air-bridges with two different geometries (line-shaped and cross-shaped) were studied in detail. The narrowest width of the air-bridges was around 200 nm, and the typical length of the air-bridges was 2-5 mu m. The advantages of our method are the simplicity of carrying out electron-beam exposure with good reproducibility and the capability of more accurate control of the pillar sizes and shapes of the air-bridge. (C) 2007 Elsevier Ltd. All rights reserved.

Bulge testing and fracture properties of plasma-enhanced chemical vapor deposited silicon nitride thin films

The mechanical properties and fracture behavior of silicon nitride (SiNx) thin film fabricated by plasma-enhanced chemical vapor deposition is reported. Plane-strain moduli, prestresses, and fracture strengths of silicon nitride thin film; deposited both oil a bare Si substrate and oil a thermally oxidized Si substrate were extracted using bulge testing combined with a refined load-deflection model of long rectangular membranes. The plane-strain modu i and prestresses of SiNx thin films have little dependence on the substrates, that is, for the bare Si substrate, they are 133 +/- 19 GPa and 178 +/- 22 MPa, respectively, while for the thermally oxidized substrate, they are 140 +/- 26 Gila and 194 +/- 34 MPa, respectively. However, the fracture strength values of SiNx films grown on the two substrates are quite different, i.e., 1.53 +/- 0.33 Gila and 3.08 +/- 0.79 GPa for the bare Si substrate a A the oxidized Si substrate, respectively. The reference stresses were computed by integrating the local stress of the membrane at the fracture over the edge, Surface, and volume of the specimens and fitted with the Weibull distribution function. For SiNx thin film produced oil the bare Si Substrate, the Volume integration gave a significantly better agreement between data and model, implying that the volume flaws re the dominant fracture origin. For SiNx thin film grown on the oxidized Si substrate, the fit quality of surface and edge integration was significantly better than the Volume integration, and the dominant surface and edge flaws could be caused by buffered HF attacking the SiNx layer during SiO2 removal. Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.

Nature of interfacial defects and their roles in strain relaxation at highly lattice mismatched 3C-SiC/Si (001) interface

Misfit defects in a 3C-SiC/Si (001) interface were investigated using a 200 kV high-resolution electron microscope with a point resolution of 0.194 nm. The [110] high-resolution electron microscopic images that do not directly reflect the crystal structure were transformed into the structure map through image deconvolution. Based on this analysis, four types of misfit dislocations at the 3C-SiC/Si (001) interface were determined. In turn, the strain relaxation mechanism was clarified through the generation of grow-in perfect misfit dislocations (including 90 degrees Lomer dislocations and 60 degrees shuffle dislocations) and 90 partial dislocations associated with stacking faults. (C) 2009 American Institute of Physics. [doi:10.1063/1.3234380]

MBE InAs quantum dots grown on metamorphic InGaAs for long wavelength emitting

GaAs-based InAs quantum dots using InGaAs composition-graded metamorphic layers have been investigated by molecular beam epitaxy. Emission with the wavelength similar to 1.5 mu m from the dots was obtained at room temperature with the relatively large full width at half maximum. The emission wavelength is relatively stable when subjected to fast annealing. The number density of dots reached similar to 6 x 10(10) cm(-2). Undulated morphology was observed on the surface of the sample, which has some influence on the dot size and distribution. In epilayers, misfit dislocations were confined within the step-graded InGaAs metamorphic buffer layer. (c) 2006 Elsevier B.V. All rights reserved.

A new method to fabricate InGaN quantum dots by metalorganic chemical vapor deposition

A new method to form nanoscale InGaN quantum dots using MOCVD is reported, This method is much different from a method. which uses surfactant or the Stranski-Krastannow growth mode. The dots were formed by increasing the energy barrier for adatoms, which are hopping by surface passivation, and by decreasing the growth temperature. Thus, the new method can be called as a passivation-low-temperature method. Regular high-temperature GaN films were grown first and were passivated. A low-temperature thin layer of GaN dot was then deposited on the surface that acted as the adjusting layer. At last the high-density InGaN dots could be fabricated on the adjusting layer. Atomic force microscopy measurement revealed that InGaN dots were small enough to expect zero-dimensional quantum effects: The islands were typically 80 nm wide and 5 nm high. Their density was about 6 x 10(10) cm(-2). Strong photoluminescence emission from the dots is observed at room temperature, which is much stronger than that of the homogeneous InGaN film with the same growth time. Furthermore, the PL emission of the GaN adjusting layer shows 21 meV blueshift compared with the band edge emission of the GaN due to quantum confine effect. (C) 2002 Elsevier Science B.V. All rights reserved.

Determination of the interdiffusion coefficients of liquid Zn and Sn using Ta/Zn-Sn/Si trilayers

In this paper we present a new method for measuring diffusion coefficients in liquid metals under convection-less conditions with solid/liquid-liquid/solid trilayer. The advantage of this kind of trilayer is that effects from gravity-induced convection and Marangoni-convection can be omitted, so that the diffusion coefficient is determined more accurately. The Ta/Zn-Sn/Si trilayer were prepared with a multi-target ion-beam sputtering deposition technique and annealed in an electric furnace under an argon atmosphere. The interdiffusion of liquid zinc and tin at 500 degrees degree C was investigated. The diffusion concentration profiles were determined by energy dispersive spectroscopy. The interdiffusion coefficients range from 1.0x10(-6)cm(2)/s to 2.8x10(-6)cm(2)/s, which is less than previous values measured by capillary reservoir technique under 1g-environment where various convection exist. The precise interdiffusion coefficients of liquid zinc and tin result from the removing of disturbances of various kinds of convection.

Comparative Raman scattering studies of GaAs/AlxGa1-xAs and AlxGa1-xAs/AlAs superlattices

The room-temperature Raman scattering studies of longitudinal optic phonons in AlAs/AlxGa1-xAs and GaAs/AlxGa1-xAs short-period superlattices with different layer thicknesses were reported. The AlAs LO modes confined in AlAs layers and GaAs-like LO modes confined in AlxGa1-xAs layers were observed in AlAs/AlxGa1-xAs superlattices under off-resonance conditions. And the GaAs LO modes confined in GaAs layers and AlAs-like LO modes confined in AlxGa1-xAs layers were observed in GaAs/AlxGa1-xAs superlattices. In addition, the AlAs interface mode in AlAs/AlxGa1-xAs was also observed under near-resonance conditions. Based on the linear chain mode, the frequencies of confined LO modes measured by Raman scattering were unfolded according to q=m/(n+1)(2 pi/a(0)) by which the dispersion curves of AlAs-like and GaAs-like LO phonons in AlxGa1-xAs mixed crystal were obtained.

Structural characterization of SiGe/Si single wells grown by disilane and solid-Ge molecular beam epitaxy with varied disilane cracking temperature

Structural properties of SiGe/Si single wells are studied by double-crystal X-ray diffraction. Four SiGe/Si single wells have been grown on Si (0 0 1) at 750 degrees C by disilane and solid-Ge molecular beam epitaxy with varied disilane cracking temperature. Using dynamic theory, together with kinematic theory and the specific growth procedure adopted, structural parameters in the multilayer structure are determined precisely. The results are compared with those obtained from PL and XTEM as well as AES measurements. It is found that disilane adsorption is dependent on cracking temperature as well as Ge incorporation. Disilane adsorption is increased by cracking disilane while it decreased with Ge incorporation (C) 1998 Elsevier Science B.V. All rights reserved.

Threshold reduction in strained-layer InGaAs/GaAs quantum well lasers by liquid phase epitaxy regrowth

When liquid phase epitaxy regrowth at 780 degrees C for 2 h is applied to the samples after molecular beam epitaxy, a decrease of the threshold current density in strained InGaAs/GaAs quantum well lasers by a factor of 3 to 4 is obtained. We suggest that this improvement is attributed to the reduction of nonradiative centers associated with deep levels at the three regions of the active region, the graded layer and the cladding layer. Indeed, a significant reduction of deep center densities has been observed by using minority and majority carrier injection deep level transient spectroscopy measurements. (C) 1998 Elsevier Science B.V. All rights reserved.

Homoepitaxial growth and characterization of 4H-SiC epilayers by low-pressure hot-wall chemical vapor deposition

Horizontal air-cooled low-pressure hot-wall CVD (LP-HWCVD) system is developed to get high quality 4H-SiC epilayers. Homoepitaxial growth of 4H-SiC on off-oriented Si-face (0001) 4H-SiC substrates purchased from Cree is performed at a typical temperature of 1500 degrees C with a pressure of 40 Torr by using SiH4+C2H4+H-2 gas system. The surface morphologies and structural and optical properties of 4H-SiC epilayers are characterized with Nomarski optical microscope, atomic force microscopy (AFM), x-ray diffraction, Raman scattering, and low temperature photoluminescence (LTPL). The background doping of 32 pm-thick sample has been reduced to 2-5 x 10(15) cm(-3). The FWHM of the rocking curve is 9-16 arcsec. Intentional N-doped and B-doped 4H-SiC epilayers are obtained by in-situ doping of NH3 and B2H6, respectively. Schottky barrier diodes with reverse blocking voltage of over 1000 V are achieved preliminarily.

Evaluating the effect of dislocation on the photovoltaic performance of metamorphic tandem solar cells

The photovoltaic conversion efficiency for monolithic GaInP/GaInAs/Ge triple-junction cell with various bandgap combination (300 suns, AM1.5d) was theoretically calculated. An impressive improvement on conversion efficiency was observed for a bandgap combination of 1.708, 1.194, and 0.67 eV. A theoretical investigation was carried out on the effect of dislocation on the metamorphic structure's efficiency by regarding dislocation as minority-carrier recombination center. The results showed that only when dislocation density was less than 1.6x10(6) cm(-2), can this metamorphic combination exhibit its efficiency advantage over the fully-matched combination. In addition, we also briefly evaluated the lattice misfit dependence of the dislocation density for a group of metamorphic triple-junction system, and used it as guidance for the choice of the proper cell structure.