Intermediate Growth Stages Research Articles

Changes in chemical composition and nutritive value of urea treated whole crop wheat during exposure to air

Utilisation of winter wheat for silage production is popular in northern Europe as the crop can be grown in a wide range of climates and soil conditions. However, unacceptable losses of dry matter (DM) and a decline in nutritive value of the ensiled crop can occur during conservation and feed-out. Changes in chemical composition and nutritive value of fermented whole crop wheat during exposure to air was investigated using a range of maturities of wheat (growth stages (GS) 49 (boot), 71 (seed coat water ripe) and 87 (hard dough)) and levels of urea (0, 20 and 40 kg/t DM) in small scale silos. The experiment was a factorial design with initial DM of forage, level of application of urea and period of exposure of silage to air being the factors. The effect of increasing concentration of urea reduced the maximum temperature of the silage on exposure to air ( P<0.001) and increased the time taken to achieve the maximum temperature ( P<0.001). Increasing the initial DM content of forage ensiled depressed the maximum temperature recorded in the silo as well as increased the period of time to reach maximum temperature ( P<0.001 for both effects). Losses in DM from the conserved forages were greatest in crops ensiled at an immature stage of growth not treated with urea. Addition of urea at ensiling reduced the losses in DM ( P<0.001). However, at intermediate stages of growth (GS 71) and low levels of application of urea (20 kg/t DM), the rate of loss of soluble carbohydrates were increased ( P<0.05) compared to untreated forages. Ammonia released as a result of urea treatment at ensiling reduced the rate of loss of DM and of loss of nutritive value (neutral detergent cellulase digestion (NDCD); P<0.001). However, no changes in the concentration of starch during exposure to air were observed for any treatment. Treatment of whole crop wheat with urea is an effective method of preserving forage nutritive value during ensiling and on exposure to air at feed-out.

Direct Dynamics Studies of CO-Assisted Carbon Nanotube Growth

Semiempirical direct dynamics simulations are used to study the potential role of CO in the gas-phase catalytic growth of carbon nanotubes. Calculations employing a fully self-consistent AM1 semiempirical electronic Hamiltonian predict that CO molecules can chemically adsorb to the open edge of partially grown zigzag and armchair nanotubes. The adsorbed CO molecules can form either pentagonal or hexagonal carbon rings by an electrocyclic reaction with neighboring adsorbed CO groups. Formation of hexagonal carbon rings in zigzag nanotubes is kinetically and thermodynamically favored by a CO insertion reaction with CO-saturated ends. These results provide some computational evidence that gas-phase CO can adsorb and contribute to the intermediate and latter stages of carbon nanotube growth. This study assumes that growth proceeds by the addition of carbon to the nanotube edge held open by metal catalyst particles, as opposed to a root growth or capped end growth mechanism.

Microstructural evolution of precursor-derived gallium nitride thin films

Gallium nitride thin films on sapphire substrates were produced from a gallium dimethylamide-based liquid precursor by chemical solution deposition. After pyrolysis in ammonia atmosphere, films obtained from precursors with low polymer content consisted of an irregular and facetted epitaxial GaN interface layer covered by a thin layer of polycrystalline grains, whereas precursors of higher polymer concentration lead to entirely polycrystalline GaN films. At an intermediate growth stage, the formation of a gallium oxide nitride phase was observed. Epitaxial GaN growth is discussed with respect to possible material transport paths, including vapor phase transport.

Factors influencing fire behaviour in shrublands of different stand ages and the implications for using prescribed burning to reduce wildfire risk

Fire behaviour under experimental conditions is described in nine Mediterranean gorse shrublands ranging from 3–12 years of age with different fuel loads. Significant differences in the fire-line intensity, fuel load and rate of fire spread have been found to be related to the stage of development of the communities. Fire spread is correlated with fuel moisture using multiple regression techniques. Differences in fuel moisture between mature and young communities under moderate weather conditions have been found. The lower moisture content identified in the mature shrubland is due both to the decreasing moisture content of senescent shrubland in some species, mainly in live fractions of Ulex parviflorus Pourr. fuel, and to a substantial increase in dead fuel fractions with low percentages of moisture content. The result is that the older the shrubland is, the greater will be the decrease in the total moisture content of the vegetation. In these moderate weather conditions, the fire intensity of the mature community was as high as the maximum intensity recommended for prescribed fires. This fact seems to indicate that, even under moderate conditions, prescribed burning as an alternative management tool in the mature shrubland must always take into account fuel control; on the other hand, this technique could be applied more easily when the shrubland is at an intermediate growth stage (4–5 years of age). Therefore, more frequent low-intensity prescribed fires are indicated to abate the risk of catastrophic fire.

Progressive changes in strain patterns and fold styles in a deforming ductile orogenic wedge: an experimental study

Experiments with scaled, viscous pitch models demonstrate successive stages of growth (Stages I, II and III) of a ductile orogenic wedge with progressive deformation, which are kinematically as well as dynamically distinct from each other. In Stage I, vertical growth of the wedge is significant indicating dominant role of horizontal tectonic forces relative to the gravity forces. With progressive deformation, the wedge attains a stable height when Stage II begins. Migration of the wedge front in the transport direction maintaining constant height during Stage II implies a balance between gravity and horizontal contraction. In the last stage (Stage III), as the action of horizontal tectonic forces tend to weaken gradually, the wedge undergoes collapse under the influence of gravity. The three stages of wedge growth show characteristic strain distributions. In each stage, shape of the strain ellipses (indicator of finite strain at that stage) and their orientation (inclination of the ellipse major axes with respect to the direction of horizontal force) vary from hinterland toward foreland as well as from depth to shallower level. Strain ellipses at a given domain also exhibit changes in shape (aspect ratio) and orientation with advancing stages of deformation (Stages I to III). There is thus a spatial as well as temporal variation in strain observed in the deforming wedge. The experimental analysis is essentially two-dimensional as the flow of pitch in the third direction (parallel to the wedge front) is constrained. Experiments were also performed with layered, anisotropic viscous models to study the spatial and temporal variations of fold styles in a deforming wedge. In Stage I, shallow level folds are upright and symmetrical whereas those at depth are inclined to nearly recumbent and strongly asymmetrical, showing vergence toward foreland. The intermediate stage of wedge growth (Stage II) is characterised by development of ‘back folds’ and refolded folds, the development of which are consistent with the temporal variations of finite strain within a deforming wedge. New steeply inclined, foreland-vergent asymmetric folds develop in the extreme frontal part of the wedge during the gravity-induced collapse (Stage III).

Limiters in Third-Generation Wind Wave Models

Third-generation ocean wave models include a so-called limiter in the integration of the source terms to guarantee numerical stability at economical numerical time steps. The original limiter has previously been associated with the sensitivity of model results to the numerical time step. More recent limiters appear to remove this sensitivity by eliminating the numerical convergence from the resulting integration scheme. This is contrary to rudimentary numerical principles as well as the underlying philosophy of third-generation wave models. The present study investigates the effects of limiters and large model time steps using time-limited wave growth test. It is shown that the conventional limiter results in stable model results even if the numerical time step violates the time scales of wave growth. Contrary to common belief, its impact is not necessarily limited to the equilibrium range of the spectrum, and the limiter systematically enhances growth rates in the intermediate stages of wave growth. Particularly initial growth errors increase significantly with increasing maximum discrete spectral frequency f max . Relaxation of the limiter is shown to reduce initial growth errors, but does so at the expense of notable errors in the spectral shape. In the present paper the limiter was relaxed by introducing a new asymmetric limiter that retains full convergence. Initial results obtained with this limiter are similar to those of the advocated nonconvergent limiters. Although this limiter still needs rigorous testing and further development, its initial results suggest that there is no justification for using nonconvergent limiters.

Flow-induced Wall Shear Stress in Abdominal Aortic Aneurysms: Part I - Steady Flow Hemodynamics

Numerical predictions of blood flow patterns and hemodynamic stresses in Abdominal Aortic Aneurysms (AAAs) are performed in a two-aneurysm, axisymmetric, rigid wall model using the spectral element method. Homogeneous, Newtonian blood flow is simulated under steady conditions for the range of Reynolds numbers 10 h Re h 2265. Flow hemodynamics are quantified by calculating the distributions of wall pressure (p w ), wall shear stress ( w ), Wall Shear Stress Gradient (WSSG). A correlation between maximum values of hemodynamic stresses and Reynolds number is established, and the spatial distribution of WSSG is considered as a hemodynamic force that may cause damage to the arterial wall at an intermediate stage of AAA growth. The temporal distribution of hemodynamic stresses in pulsatile flow and their physical implications in AAA rupture are discussed in Part II of this paper.

Effects of a Microbial Inoculant and Organic Fertilizers on the Growth, Photosynthesis and Yield of Sweet Corn

Summary A microbial inoculant known as Effective Microorganisms or EM is a mixed culture of naturally-occurring, beneficial microorganisms (predominantly lactic acid bacteria, yeast, actinomycetes, photosynthetic bacteria and certain fungi) that has been used with considerable success to improve soil quality and the growth and yield of crops, particularly in nature farming and organic farming systems. Despite this success, the exact mechanisms of how this EM elicits such beneficial effects is largely unknown. Consequently, a study was conducted to determine the effects of EM and organic fertilizer on the growth, photosynthesis, and yield of sweet corn (Zea mays L.) under glasshouse conditions, compared with chemical fertilizer. An organic fertilizer consisting of a mixture of oilseed mill sludge, rice husk and bran, and fish processing waste, was inoculated and fermented with EM as the microbial inoculant. The organic fertilizer and chemical fertilizer were then applied to respective pots to compare the growth, yield and physiological response of sweet corn plants. EM applied with the organic fertilizer was shown to promote root growth and activity, and to enhance photosynthetic efficiency and capacity, which resulted in increased grain yield. This was attributed largely to a higher level of nutrient availability facilitated by EM application over time. Interestingly, during the early stage of the experiment, the growth and dry matter yield of plants that received organic fertilizer were actually lower than those treated with chemical fertilizer that provided higher initial levels of macronutrients. However, during the intermediate and late growth stages, EM increased the nutrient availability of the organic fertilizer to a higher level, than the chemical fertilizer. Consequently, even though there was an early lower growth rate for plants that received EM-fermented organic fertilizer compared with chemical fertilizer, the final biomass and grain yield from organic fertilizer was equal to or higher than from chemical fertilizer.

The Structure and Texture Development of Ni Alloy Electrodeposits. 1. Nickel-Iron Electrodeposits

SUMMARYElectrodeposited nickel-iron alloys have been studied using ‘direct’ methods e.g. X-ray diffraction and transmission electron microscopy on coatings having different thicknesses, deposited on copper substrates at different current densities. The work has confirmed and extended the ideas of Finch et al1.21.22 and Pangarov16.23.24 to alloy deposition. It has been shown that a better understanding, particularly of the initial deposition stages, can be obtained by considering crystallographic, energy and electrochemical effects in combination rather than individually. Initially alloy is deposited on a ‘foreign’ substrate i.e. copper but subsequently the alloy deposit serves as the ‘substrate’. Similarly ‘old’ crystallites have to compete for growth with ‘newly’ nucleated ones as the deposit develops. The three stages of growth observed in nickel-iron are discussedWhereas during initial nucleation the original substrate surface is the dominating influence, in the later stages the electrolytic parameters determine the structure of the deposit. If the crystallographic structure of the outer deposit differs markedly from that of the initial stages, then a transitional growth stage is involved. For example, in bcc nickel-iron deposits the film formed at the substrate/coating interface develops with a {110} texture, at intermediate thickness (0·5 μm to 1·0 μm) the {211} texture predominates whereas in ‘bulk deposits’ above 1·5 μm the {111} texture predominates. Furthermore, the structures of deposits studied in the present work tended to be fine grained in the initial stages but developed a coarser columnar structure due to selected grain growth with favoured grains becoming broader during the intermediate and final stage of growth.

Estimation of Channel Sinuosity from Paleocurrent Data: A Method Using Fractal Geometry

ABSTRACT In ancient fluvial deposits, exposure limitations seldom allow direct measurement of channel and valley lengths--the requisite parameters for determination of channel sinuosity. However, sinuosity can be indirectly estimated from dispersion of paleocurrent data, because it is observed in modern rivers that the migration paths of ripples and dunes usually follow the local orientation of the thalweg. A natural channel can be described to be broadly sinuous in plan. A magnified view of any small part of it is also sinuous in shape. This scale independence of shape can be observed at smaller and yet smaller scales. Fractal patterns, which also have this property, are used here to model channel plan form at the scale of bedform migration paths. It is assumed that the sinuosity of a fractal pattern represents the channel sinuosity over a single meander wavelength, and the orientations of the smallest segments of the patterns are considered to represent the bedform migration directions. An attempt has been made in this study to establish a functional relationship between the sinuosity of the patterns and the dispersion (consistency ratio) of its segment orientations. From a number of fractal patterns of different sinuosity values, the following relationship is noted: ln Sinuosity = 2.49 - 0.0475 Consistency + 0.000234 Consistency2 This relationship can be used to estimate, from paleocurrent data, the sinuosity of short stretches of ancient channels whose sinuosity was steady over time, e.g., bank-stabilized (non-migrating) channels. Published data from a number of modern rivers are used to test the equation, and the goodness-of-fit hypothesis cannot be rejected at 5% level of significance. The lateral growth of a meander generally involves a gradual increase in the sinuosity of the thalweg. A growing natural meander is modeled by grouping together a number of fractal patterns of different sinuosity values. In a group, the pattern having the maximum sinuosity value represents the thalweg at the last stage of growth, while the rest of the patterns represent the thalwegs at intermediate stages of growth. Partial removal of earlier deposits by erosion associated with the growth of meander is taken into account by excluding the parts of the fractal patterns that represent the intermediate growth stages and lie outside final meander loop. The segment orientations from all the patterns in each group are pooled and compared with the maximum sinuosity value. From a number of such groups (of different maximum values of sinuosity) the relation between the consistency ratio and the maximum sinuosity is found to be ln Sinuosity = 4.2416 - 0.0801 Consistency + 0.0004 Consistency2 An empirical test of this equation using data from a single ancient meandering river deposit yields satisfactory results.

Cell growth analysis during steady and non‐steady growth in leaves of perennial ryegrass (Lolium perenne L.) subject to defoliation

ABSTRACTThe effect of defoliation on leaf elongation rate (LER) and on the spatial distribution of epidermal cell lengths in the leaf growth zone was studied in vegetative main tillers of perennial ryegrass (Lolium perenne L. cv Modus) grown in a controlled environment. A new material approach was used to analyse the responses of epidermal cell expansion and production during the initial, non‐steady growth phase following defoliation. The analysis involved assigning an identity to individual expanding cells, assessing the displacement and estimating the expansion of cells with assigned identity during day 1 and day 2 after defoliation. LER decreased by 34% during the first 2 d after defoliation and did not recover to the pre‐defoliation rate within the 14 day regrowth period. Decreased LER on day 1 and day 2 after defoliation was associated with (i) a decrease in the length of the leaf growth zone; (ii) a decrease in the length at which epidermal cells stopped expanding; (iii) a reduced expansion of cells at intermediate growth stages; and (iv) a reduction in cell production (i.e. division) and an associated decrease in the number of expanding cells in the growth zone. However, defoliation had no effect on the expansion of cells located in the proximal part of the growth zone. Reduced LER at 14 d after defoliation was associated with a reduced cell production rate (27% lower than the pre‐defoliation rate) and decreased final cell size (− 28%).

Effects of Drainage after Submerged Direct-Seeding on the Effectiveness of Fertilized Nitrogen and the Growth an Yield of Rice Plants.

近年, 水稲の湛水土中直播栽培において出芽安定化のために播種後の落水管理が一般に行われてきている.そこで, 播種後の水管理と施肥窒素の動態や水稲の窒素吸収との関係について検討し, 落水管理が水稲の生育・収量へ及ぼす影響を明らかにするための試験を行った.水管理と出芽との関係については本試験においても播種後落水を行うことによる出芽率の向上および初期生育の促進が確認された.苗立ち後の生育は肥効調節型の被覆尿素肥料(LP100)を基肥に施用した場合には播種後の水管理による生育・収量の差は小さかったが, 速効性肥料である硫安を基肥に施用して播種後の落水管理を行った区では硫安施肥を行って湛水管理を行った区に比較して幼穂分化期までの窒素吸収量が低下し籾数不足による減収を生じた.基肥に硫安を施用し播種後落水管理を行った場合には, 初期生育および初期分げつが顕著となるために生育初期の窒素吸収量が顕著に増大すること, また, 落水にともなう施肥窒素の硝酸化成によると推定される土壌中アンモニウム態窒素含有量の低下が生じることが示されたため, これらの要因により幼穂分化期までの窒素吸収量に差を生じたものと推察された.このことから, 播種後落水管理を行う場合には初期の肥効を抑制するとともに, 生育中期の窒素不足を回避するような施肥法を行うことが, 直播栽培における出芽・苗立ちの安定化と生育・収量の安定化の両立に重要となると考えられる.

The role of Ca2+ ions in modulating changes induced in bean plants by an excess of Cu2+ ions. Chlorophyll fluorescence measurements

Ca2+‐dependent influence of excess Cu2+ on the photosynthetic akpparatus monitored through chlorophyll fluorescence measurements was investigated in runner bean plants (Phaseolus coccineus L. cv. Pie kny Jaś) at three different growth stages. It was observed that the toxic effect of excess Cu2+ on plants depends both on their growth stages and the Ca2+ content in the medium. Increased Ca2+ content limits Cu2+ action on plants at their initial growth stage (I) through: stabilization of the PSII complex (increase of the ratio of variable to minimal fluorescence [Fv/F0]), improved electron flow and reoxidative processes of the quinone primary electron acceptor of PSII (QA) (increase of quantum yield of PSII electron transport [φe] and photochemical quenching of fluorescence [qP] values) and elimination of nonphotochemical energy dissipation (decrease of nonphotochemical fluorescence quenching from the Stern‐Volmer equation [NPQ] and fraction of the absorbed light energy not used for photochemistry [LNU] values). At this growth stage excess Cu2+ decreases the rates of QA reduction as a result of decreased PSII activity at its donor side only at lower Ca2+ level. At the intermediate growth stage (II) the plants were less sensitive to Cu2+ treatment and also to changed Ca2+ content. A weakening of some photochemical processes by excess Cu2+ could be observed only at a higher Ca2+ dose. At the final growth stage of plants (III) Ca2+ ions exerted a decisively different effect on the mechanism of excess Cu2+ action on bean plants, visualized by decreased PSII stabilization and utilization of absorbed light energy at increased Ca2+ content in the medium.

Seasonal mycorrhizal colonization of winter wheat and its effect on wheat growth under dryland field conditions

A field experiment was conducted to determine the seasonal patterns of arbuscular mycorrhiza (AM) in a dryland winter wheat (Triticum aestivum L.) system and to determine wheat growth and P uptake responses to inoculation with mycorrhizal fungus. Broadcast-incorporated treatments included (1) no inoculation with mycorrhizal fungus, with and without P fertilizer, and (2) mycorrhizal fungal inoculation at a rate of 5000 spores of Glomus intraradices (Schenck and Smith), per 30 cm in each row, with and without fertilizer P. Winter wheat was seeded within a day after treatments were imposed, and roots were sampled at five growth stages to quantify AM. Shoot samples were also taken for determination of dry matter, grain yield and yield components, and N and P uptake. No AM infection was evident during the fall months following seeding, which was characterized by low soil temperature, while during the spring, the AM increased gradually. Increases in wheat grain yields by enhanced AM were of similar magnitude to the response obtained from P fertilization. However, responses differed at intermediate growth stages. At the tillering stage, P uptake was mainly increased by P fertilization but not by fungal inoculation. At harvest, enhanced AM increased P uptake regardless of whether or not fertilizer P was added. The AM symbiosis increased with rising soil temperatures in the spring, in time to enhance late-season P accumulation and grain production.

Characterization of defect structures in magnetic liquid encapsulated Kyropoulos grown InP single crystals

Synchrotron White Beam X-ray Topography (SWBXT) has been used as a nondestructive diagnostic technique for the characterization of defect structures in large wafers cut from S and Fe-doped InP single-crystal boules. Wafers cut both longitudinally and laterally with respect to the growth axis were studied in order to reveal the overall defect distribution in the boules. Studies carried out on longitudinally cut S-doped crystals enabled information to be obtained on interface shape, from the observation of growth striations, as well as defect distribution. The conditions for optimal visibility of the growth striations were determined and it was found that the morphology of the growth interface was a sensitive function of local growth conditions. The formation of extensive slip bands from peripheral regions was also observed. This indicates that large thermal stresses were generated during crystal growth leading to such significant plastic deformation processes. Studies carried out on a series of laterally sliced, Fe-doped wafers cut from the same boule revealed dislocations in well-defined fourfold symmetric distributions. A finite element thermal-elastic stress analysis was performed for an intermediate growth stage to investigate the nature of the stress which causes this fourfold distribution. The calculated excess shear stress from this analysis agrees qualitatively with the observed dislocation distribution and slip system activity. The influence of an applied magnetic field on precipitate distributions in InP boules was preliminarily studied by examining a longitudinal cut, heavily Fe-doped InP wafer, which was grown in the presence of an intermittent applied field. Topographs recorded from this wafer revealed that no formation of large precipitates was discernible in either the initial or intermediate growth stages when the magnetic field was applied. On the other hand, the formation of large precipitates was observed in regions near the final stage of crystal growth when the magnetic field was turned off. Further such investigations are underway.

REFLECTION ELECTRON MICROSCOPY METHODOLOGY FOR QUANTIFICATION OF CLUSTER GROWTH: INDIUM CLUSTERS ON THE InP(110) SURFACE

Dynamical reflection electron microscopy (REM) can provide a wealth of time-resolved data pertinent to the initial and intermediate stages of cluster growth. REM allows one to follow and quantify the size and shape evolution of individual clusters. Average cluster size and cluster density data can be obtained as a function of time due to the large field of view produced by REM image foreshortening. We describe here a methodology for extracting these data from dynamical REM experiments, based on a geometrical model for the interpretation of REM images from two- and three-dimensional clusters. This methodology has been applied to studies of In cluster growth on InP (110) surfaces at 650°C. The average In cluster height and length initially increased as a fourth root of time, with a constant contact angle with the surface, consistent with surface-diffusion-limited growth of 3D clusters. The same behavior was found in the later stage of cluster growth, but the intermediate stage showed anomalous power laws for the cluster height and base length, accompanied by a decrease in the contact angle between the In clusters and the InP (110) surface. This anomalous regime can be explained by growth of In clusters into the InP substrate, when the true contact angle is no longer defined with respect to the InP(110) surface.

Variations in growth of Cape petrel Daption capense chicks

This study reports on the growth of Cape petrel chicks at Nelson Island, South Shetland Islands, Antarctica, during the breeding seasons 1990/91 and 1991/92. Parameters of logistic growth model fitted to mass, wing, culmen and tarsus measurements were compared between available composite data sets. Differential growth rate of morphometric characters and their proportional development at hatching and fledging conform to the pattern observed in other fulmarine petrels, overall growth rate being among the fastest found in Procellariiformes. Composite growth curves varied significantly between populations, but few annual, seasonal, and intercolony differences were found within the Nelson Island population. As the differences between chicks from equally disturbed colonies were less marked than in comparison with the control colony, regular handling most probably reduced the growth in this study. Larger eggs produced heavier rather than structurally larger hatchlings, which attained higher peak and fledging mass and size. Strength of the relationship between egg‐size and chick measurements initially declined with chick age but, in contrast with results of earlier studies, increased again after around the middle of the chick‐rearing period. This suggests that pre‐hatching maternal factors probably influenced initial and fledging (peak) size and mass of chicks via egg‐size, while intermediate stages of growth were less affected. A difference in mass between chicks from small and large eggs was maintained until fledging and increased gradually until peak mass was reached.

Characterization of structural defects in MLEK grown InP single crystals using synchrotron white beam X-ray topography

Structural defects in MLEK grown InP single crystals have been studied using synchrotron white beam X-ray topography. Results here are presented for both a S-doped boule which was wafered longitudinally (i.e., parallel to the growth axis) and an Fe-doped boule which was wafered laterally (i.e., perpendicular to the growth axis). For longitudinal wafers from the S-doped boule, slip bands were observed to have nucleated from high-stress concentration located at the peripheral regions of the boule and to have propagated into the interior of the samples. In the same crystals, the growth interface morphology at different stages of crystal growth was determined. The interface is revealed as contours of equal lattice parameter, visible via strain contrast, as the concentration of the dopant changed periodically during growth. The interface shape was observed to be slightly convex to the melt, once the growth conditions were stabilized. For the laterally sliced wafers from the Fe-doped boule, systematic studies revealed that the density of dislocations changed during growth. A high density of uniformly distributed dislocations were observed in wafers taken from the early and later stages of growth. On the other hand, dislocations in well-defined four-fold symmetric distributions were observed in wafers sliced from the intermediate growth stages. The origins of this four-fold distribution were investigated using a thermal stress model which consisted of imposing a compressive radial stress, uniformly distributed around the boule circumference. The calculated stress distributions also showed four-fold symmetry in agreement with the observed dislocation distributions.

Unstable Polymer Bilayers. 2. The Effect of Film Thickness

The dewetting of a polycarbonate (PC) film from a poly(styrene-co-acrylonitrile) (SAN) film on a silicon substrate is studied at 180 °C, a temperature above the glass transition temperatures of PC and SAN. The viscosity ratio of PC to SAN is ∼10. Using optical microscopy and video image analysis, the hole diameter D is measured at SAN layer thicknesses L from 125 to 1850 nm. For a PC thickness H of 200 nm, D varies linearly with time, which signifies a constant hole velocity. Initially, the hole velocity increases linearly with L and then becomes nearly constant for L > 1000 nm, which is the dissipation depth. Atomic force microscopy (AFM) studies show that the SAN thickness inside the hole is less than the original L. Analysis of the hydrostatic and dynamic pressures acting on the SAN inside and outside the hole is used to explain this result. For a very thin SAN film (i.e., L ∼ 50 nm), D initially increases quickly with time, slows down, and then increases again. Using AFM, the retarded intermediate growth stage is shown to coincide with hole impingement on the silicon substrate. With an increase of H to 310 nm, D is found to accelerate with time. As L decreases from 1850 to 125 nm, the power law exponent ranges from x = 1.1 to 1.6, where D ∼ tx. A cross-sectional transmission electron image of the three-phase boundary shows that SAN is pulled into the rim in contrast to simple dewetting assumptions. Using the measured shape of the rim, the flow field within the rim is calculated as an initial improvement over the simple dewetting model.

An intermediate (1.0–1.5 monolayers) stage of heteroepitaxial growth of InAs on GaAs(100) during submonolayer molecular beam epitaxy

Intermediate (1–1.5 monolayer) stage of InAs deposition on the GaAs(100) singular and vicinal (3° towards [011] direction) surfaces results in the formation of different InAs surface arrangements. The formation of few monolayer-height quantum wires along [001] direction occurs immediately after 1 monolayer InAs deposition on the singular surface. The characteristic period equals ∼ 30 nm. Increase in mean thickness of InAs to 1.5 monolayer results in a less pronounced surface corrugation (“parquet” like structures) and the characteristic period increases to 50–60 nm. The wire-like structures on vicinal surfaces occurs independently of the mean thickness of InAs (within the region 1–1.5 monolayers).