Dissociated screw dislocation which can relieve strain energy in the epitaxial layer of GeSi on Si(001)

A dissociated screw dislocation parallel to the interface was found in the epitaxial layer of the Ge0.17Si0.83 Si(001) system. It is shown that this dissociated screw dislocation which consists of two 30 degrees partials can relieve misfit strain energy, and the relieved misfit energy is proportional to the width of the stacking fault between the two partials.

Dislocation movement in nitrogen-doped Czochralski silicon

Dislocation movement in N-doped Czochralski silicon (Cz-Si) was surveyed by four point bend method. Dislocation movement velocities in Cz-Si doped with nitrogen, with both nitrogen and antimony, and with only antimony were investigated. The order of measured dislocation movement velocities, at 700 degrees C less than or equal to T less than or equal to 800 degrees C and under resolved stress sigma=4.1 kg/mm(2), was V-Sb.O > V-n.Sb.O>V-N.O. The experiments showed that nigtrogen doping could retard the movement of dislocations.

ELECTRON-STATES OF A VACANCY IN THE CORE OF THE 90-DEGREES PARTIAL DISLOCATION IN SILICON

An LCAO scheme (linear combination of atomic orbitals) taking into account ten atomic orbitals (s-, p-, and d-type) is used to calculate the electronic structure of a vacancy present in the core of the reconstructed 90 degrees partial dislocation in silicon. The levels in the band gap are extracted using Lanczos' algorithm and a continued fraction representation of the local density of states. The three-fold degenerate stale of the ideal vacancy is split into three levels with energies 0.26, 1.1, and 1.9 eV measured from the valence band edge.

Dislocation Reduction in GaN on Sapphire by Epitaxial Lateral Overgrowth

High quality GaN is grown on GaN substrate with stripe pattern by metalorganic chemical vapor deposition by means of epitaxial lateral overgrowth. AFM,wet chemical etching, and TEM experiments show that with a two-step ELOG procedure, the propagation of defects under the mask is blocked, and the coherently grown GaN above the window also experiences a drastic reduction in defect density. In addition, a grain boundary is formed at the coalescence boundary of neighboring growth fronts. The extremely low density of threading dislocations within wing regions makes ELOG GaN a potential template for the fabrication of nitride-based lasers with improved performance.

Strain relaxation of GeSi alloy with low dislocation density grown on low-temperature Si buffers

We have developed a low-temperature (LT) growth technique. Even with Ge fraction x upto 90%, the total thickness of fully relaxed GexSi1-x buffers can he reduced to 1.7 mu m with dislocation density lower than 5 x 10(6) cm(-2). The surface roughness is no more than 6 nm. The strain relaxation is quite inhomogeneous From the beginning. Stacking faults generate and form the mismatch dislocations in the interface of GeSi/LT-Si. (C) 1999 Elsevier Science B.V. All rights reserved.

Dislocation nucleation governed softening and maximum strength in nano-twinned metals

In conventional metals, there is plenty of space for dislocations-line defects whose motion results in permanent material deformation-to multiply, so that the metal strengths are controlled by dislocation interactions with grain boundaries(1,2) and other obstacles(3,4). For nano-structured materials, in contrast, dislocation multiplication is severely confined by the nanometre-scale geometries so that continued plasticity can be expected to be source-controlled. Nano-grained polycrystalline materials were found to be strong but brittle(5-9), because both nucleation and motion of dislocations are effectively suppressed by the nanoscale crystallites. Here we report a dislocation-nucleation-controlled mechanism in nano-twinned metals(10,11) in which there are plenty of dislocation nucleation sites but dislocation motion is not confined. We show that dislocation nucleation governs the strength of such materials, resulting in their softening below a critical twin thickness. Large-scale molecular dynamics simulations and a kinetic theory of dislocation nucleation in nano-twinned metals show that there exists a transition in deformation mechanism, occurring at a critical twin-boundary spacing for which strength is maximized. At this point, the classical Hall-Petch type of strengthening due to dislocation pile-up and cutting through twin planes switches to a dislocation-nucleation-controlled softening mechanism with twin-boundary migration resulting from nucleation and motion of partial dislocations parallel to the twin planes. Most previous studies(12,13) did not consider a sufficient range of twin thickness and therefore missed this strength-softening regime. The simulations indicate that the critical twin-boundary spacing for the onset of softening in nano-twinned copper and the maximum strength depend on the grain size: the smaller the grain size, the smaller the critical twin-boundary spacing, and the higher the maximum strength of the material.

Knotted wave dislocation with the hopf invariant

We study the wave dislocations with an induced gauge potential. The topological current characterized the wave dislocations is constructed with the dual of Abelian gauge field. And the topological charges and locations of the wave dislocations are determined by the phi-mapping topological current theory. Furthermore, it is shown that the knotted wave dislocations can be described with a Hopf invariant in the wave field. At last we discussed the evolution of the knotted wave dislocations.

Ontogenetic development of digestive enzymes and effect of starvation in miiuy croaker Miichthys miiuy larvae

The ontogenetic development of the digestive enzymes amylase, lipase, trypsin, and alkaline phosphatase and the effect of starvation in miiuy croaker Miichthys miiuy larvae were studied. The activities of these enzymes were detected prior to exogenous feeding, but their developmental patterns differed remarkably. Trypsin activity continuously increased from 2 days after hatching (dah), peaked on 20 dah, and decreased to 25 dah at weaning. Alkaline phosphatase activity oscillated at low levels within a small range after the first feeding on 3 dah. In contrast, amylase and lipase activities followed the general developmental pattern that has been characterized in fish larvae, with a succession of increases or decreases. Amylase, lipase, and trypsin activities generally started to increase or decrease at transitions from endogenous to exogenous feeding or diet changes, suggesting that these enzymatic activities can be modulated by feeding modes. The activities of all the enzymes remained stable from 25 dah onwards, coinciding with the formation of gastric glands and pyloric caecum. These results imply that specific activities of these enzymes underwent changes due to morphological and physiological modifications or diet shift during larval development but that they became stable after the development of the digestive organs and associated glands was fully completed and the organs/glands functioned. Trypsin and alkaline phosphatase were more sensitive to starvation than amylase and lipase because delayed feeding up to 2 days after mouth opening was able to adversely affect their activities. Enzyme activities did not significantly differ among feeding groups during endogenous feeding; however, all activities were remarkably reduced when delayed feeding was within 3 days after mouth opening. Initiation of larvae feeding should occur within 2 days after mouth opening so that good growth and survival can be obtained in the culture.

Effects of various algal diets and starvation on larval growth and survival of Meretrix meretrix

Effects of food availability on larval growth and survival of Meretrix meretrix were studied in two experiments by feeding the larvae with different algae diets and by starving the larvae for different periods of time. Newly hatched larvae of M meretrix were fed with five different marine microalgae species, singly and in various mixtures. Best growth was with Isochrysis galbana as a single species diet. Nutritional value of the other single species diets was in the order of Dunaliella sp.> Phaeodactylum tricornutum > Platymonas subcordiformis > Pavlova viridis. Of the mixtures tested, 50% I. galbana/50% Dunaliella sp., 50% I. galbana/50% P tricornutum, and 50% 1 galbana/50% P subcordiformis, supported growth and metamorphosis equivalent to those of the I. galbana control. At 25 degrees C, larvae of M meretrix were deprived of food for various days to study the growth compensation from the outset of development. The results showed that M meretrix larvae could survive long feeding delays, and even reach metamorphosis without food added, although starvation had significant effects on growth. These results suggested that M meretrix larvae had the capacity to survive 'starvation' using alternative sources of energy. It also showed that growth, survival and metamorphosis of M meretrix were affected by many factors besides food quality and quantity. (c) 2005 Elsevier B.V. All rights reserved.

Feeding, morphological changes and allometric growth during starvation in miiuy croaker larvae

We investigated the effects of the timing of first feeding (larvae in F0, F1, F2, F3 and S were first fed on day 3, 4, 5, 6 days after hatching (DAH) and unfed, respectively) on feeding, morphological changes, survival and growth in miiuy croaker larvae at 24A degrees C. The fed larvae initiated feeding on 3 DAH and reached point of no return (PNR) on 6 DAH. Larvae in F0 and F1 groups survived apparently better than F2 group at the end of the experiment on 36 DAH. High larval mortality occurred from 3 to 7 DAH in all feeding groups, accounting for 40% (F0, F1 and F2 groups) to 90% (F3 and S groups) of the total mortality. Larvae in F0 and F1 groups grew better than F2 group throughout the experiment. Eye diameter, body height, head height and mouth gape of the first feeding larvae were more sensitive to starvation than other morphometrics and could be used as indicators for evaluating their nutritional status. Results indicated that delayed first feeding over 1 day after yolk exhaustion could lead to poor larval survival and growth. To avoid starvation and obtain good growth in culturing, larvae feeding should be initiated within 1 day after yolk exhaustion at 24A degrees C.

Feeding resumption, morphological changes and mortality during starvation in Japanese flounder larvae

Japanese flounder Paralichthys olivaceus larvae established first feeding 3 days after hatching (DAH) at c. 17degreesC. Non-fed fish reached irreversible starvation at age 5 DAH. Non-fed fish showed similar feeding rate and feeding intensity as the fed fish when they were provided with prey before 5 DAH, after which the starved larvae did not feed even when prey became available. None of the six morphological measurements examined (total length, body height, eye height, head height, gut height and myotome height) showed significant differences between the non-fed and fed larvae until 5 DAH. Normal development continued only in the fed group, and the non-fed larvae showed reverse growth or body collapse after 5 DAH. Owing to the shrinkage and collapse at the top of head due to starvation, head height could be a sensitive indicator of starvation in Japanese flounder larvae. In the fed treatments, high mortality occurred from first feeding (3 DAH) to irreversible starvation (5 DAH), accounting for about two-thirds to three-quarters of the overall mortality (46-52%) throughout the experiments. This mortality was not prey density or larval density dependent. Mortality during the same period in the non-fed larvae accounted for about a third of the overall mortality (100%). (C) 2002 The Fisheries Society of the British Isles. Published by Elsevier Science Ltd. All rights reserved.

Nitrogen isotopic fractionation during a simulated diatom spring bloom: importance of N-starvation in controlling fractionation

N isotope fractionation (epsilon) was first determined during ambient NO3- depletion in a simulated diatom spring bloom. After 48 h of N-starvation, NH4+ was resupplied to the diatoms in small pulses to simulate grazer-produced N and then epsilon was determined. Large variations in epsilon values were observed: from 2.0-3.6 to 14-0 parts per thousand during NO3- and NH4+ uptake, respectively. This is the first study reporting an epsilon value as low as 0 to 2 parts per thousand for NH4+ uptake and we suggest that greater N demand after N-starvation may have drastically reduced NH3 efflux out of the cells. Thus the N status of the phytoplankton and not the ambient NH4+ concentration may be the important factor controlling epsilon, because, when N-starvation increased, epsilon values for NH4+ uptake decreased within 30 h. This study may thus have important implications for interpreting the delta(15)N of particulate N in nutrient-depleted regimes in temperate coastal oceans.

STARVATION-INDUCED CHANGES OF HEMOCYTE PARAMETERS IN THE ZHIKONG SCALLOP CHLAMYS FARRERI

Substantial nutritional and energetic demands m-e associated with immune activation and the maintenance of an efficient immune system. One-year-old Chlamys farreri (Jones and Preston) scallops were maintained ill lantern nets ill different nutritional conditions (satiation and starvation) for 40 days. After the 40-day treatments, the condition index and the total hemocyte count (THC) decreased significantly in the starved group compared with the satiated and initial control groups. The percentage of phagocytic hemocytes also was significantly reduced with starvation. In contrast. no significant effect of starvation was observed oil reactive oxygen species (ROS) production. The acid phosphatase (ACP) activities in cell-free hemolymph increased significantly in scallops in starved and satiated treatments compared with the initial control. whereas ACP activity in hemocyte lysate was significantly lower ill the starved group. These results indicate that starvation stress compromises immunological activities of scallops.