Little is known about the Endangered Grevy's zebra Equus grevyi in far northern Kenya, where the species exists in small, isolated populations at the periphery of its range. Understanding the threats facing this species is a prerequisite for effective conservation planning but its rarity makes obtaining accurate information challenging. We set out to establish the current status of, and attitudes towards, Grevy's zebra in northern Kenya using local knowledge as the primary source of information. Pastoralists perceived Grevy's zebra to be in decline as a result of drought, lack of pasture and water, and hunting for consumptive use. There was also evidence of competition with livestock. Attitudes towards Grevy's zebra were predominantly positive, influenced by a range of perceived benefits of living alongside the species, and an absence of severe costs. Coupled with evidence of local conservation efforts in several locations, this is a positive starting point for community-based conservation.

Methods that accurately estimate animal abundance or density are crucial for wildlife management. Although numerous techniques are available, there have been few comparisons of the precision and cost-effectiveness of different approaches. We assess the precision and cost of three methods for estimating densities of the Endangered Grevy's zebra Equus grevyi. We compare distance sampling and photographic capture–recapture, and a new technique, the random encounter model (REM) that uses camera-trap encounter rates to estimate density. All three methods provide comparable density estimates for Grevy's zebra and are preferable to the common practice of raw counts. Photographic capture–recapture is the most precise and line-transect distance sampling the least precise. Line transects and photographic capture–recapture surveys are cost-effective in the first year and REM is most cost-effective in the long-term. The methods used here for Grevy's zebra may be applied to other rangeland ungulates. We suggest that for single species monitoring programmes in which individuals can be identified, photographic capture–recapture surveys may be the preferred method for estimating wildlife abundances. When encounter rates are low, distance sampling lacks the precision of the other methods but its cost advantage may make it appropriate for long-term or multi-species monitoring programmes. The REM is an efficient and precise method of estimating densities but has high initial equipment costs. We believe REM has the potential to work well for many species but it requires independent estimates of animal movements and group size.

As is well known, most gas-fluidized beds of solid particles bubble; that is, they are traversed by rising regions containing few particles. Most liquid-fluidized beds, on the other hand, do not. The aim of the present paper is to investigate whether this distinction can be accounted for by certain equations of motion which have commonly been used to describe both types of bed. For the particular case of a bed of 200 μm diameter glass beads fluidized by air at ambient conditions it is demonstrated, by direct numerical integration, that small perturbations of the uniform bed grow into structures resembling the bubbles observed in practice. When analogous computations are performed for a water-fluidized bed of 1 mm diameter glass beads, using the same equations, with parameters modified only to account for the greater density and viscosity of water and to secure the same bed expansion at minimum fluidization, it is found that bubble-like structures cannot be grown. The reasons for this difference in behaviour are discussed.

This paper presents a linear stability analysis of a rapidly sheared layer of granular material confined between two parallel solid plates. The form of the steady base-state solution depends on the nature of the interaction between the material and the bounding plates and three cases are considered, in which the boundaries act as sources or sinks of pseudo-thermal energy, or merely confine the material while leaving the velocity profile linear, as in unbounded shear. The stability analysis is conventional, though complicated, and the results are similar in all cases. For given physical properties of the particles and the bounding plates it is found that the condition of marginal stability depends only on the separation between the plates and the mean bulk density of the particulate material contained between them. The system is stable when the thickness of the layer is sufficiently small, but if the thickness is increased it becomes unstable, and initially the fastest growing mode is analogous to modes of the corresponding unbounded problem. However, with a further increase in thickness a new mode becomes dominant and this is of an unusual type, with no analogue in the case of unbounded shear. The growth rate of this mode passes through a maximum at a certain value of the thickness of the sheared layer, at which point it grows much faster than any mode that could be shared with the unbounded problem. The growth rate of the dominant mode also depends on the bulk density of the material, and is greatest when this is neither very large nor very small.

The tendency of granular materials in rapid shear ow to form non-uniform structures is well documented in the literature. Through a linear stability analysis of the solution of continuum equations for rapid shear flow of a uniform granular material, performed by Savage (1992) and others subsequently, it has been shown that an infinite plane shearing motion may be unstable in the Lyapunov sense, provided the mean volume fraction of particles is above a critical value. This instability leads to the formation of alternating layers of high and low particle concentrations oriented parallel to the plane of shear. Computer simulations, on the other hand, reveal that non-uniform structures are possible even when the mean volume fraction of particles is small. In the present study, we have examined the structure of fully developed layered solutions, by making use of numerical continuation techniques and bifurcation theory. It is shown that the continuum equations do predict the existence of layered solutions of high amplitude even when the uniform state is linearly stable. An analysis of the effect of bounding walls on the bifurcation structure reveals that the nature of the wall boundary conditions plays a pivotal role in selecting that branch of non-uniform solutions which emerges as the primary branch. This demonstrates unequivocally that the results on the stability of bounded shear flow of granular materials presented previously by Wang et al. (1996) are, in general, based on erroneous base states.

Extensive monitoring of device characteristics in the manufacturing of ULSI with advanced LOCOS isolation revealed the strong dependence of device leakage currents on the process of patterning of silicon nitride films applied as a hard mask for local oxidation of silicon wafers. At the same time, the level of the leakage currents strongly correlated to stress-induced dislocation density in the device structures. Formation of microtrenches on the wafer surface at the nitride film edges was identified to have a major impact on the leakage currents. Surprisingly, structures having nitride film edge profiles with feet were consistently dislocation-free after the local oxidation. This showed that nitride etching process created surface damage that provided effective sites for crystal defect nucleation in silicon at the film edges. Computer simulations demonstrated that the feet at nitride edges substantially suppress stress growth during local oxidation.

Crystalline quality of locally oxidized silicon wafers has been studied. Wafers from different supply sources were found to be differently susceptible to stress-induced dislocation generation, although they had been produced to the same specification. On the basis of the analysis of a depth distribution of the dislocations, critical resolved shear stress of dislocation movement in the bulk areas of the wafers was determined. It varied from about 1.65 to 5.12 MPa and correlated positively to the surface defect density. The results show that uncontrollable variations of bulk silicon properties may significantly influence the stress-induced defect nucleation on the surface of wafers during processing.

The equations of motion for ‘rapid’ flow of a granular material have fully developed solutions representing flow driven by a body force, such as gravity, along a channel bounded by plane parallel walls. The stability of these solutions to small perturbations is investigated. For given properties of the particles and the channel walls it is found that the condition of critical stability is a relation between the mean concentration of the particles and the width of the channel. When the base state is unstable the fastest growing modes are travelling waves propagating in the axial direction and these induce characteristic patterns of variations in particle concentration, as well as velocity. These instabilities are contrasted with those found for Couette shearing in an earlier publication.

The purpose of the present study was to determine the effects of feeding nutritionally adequate and increased levels of vitamin A (retinyl acetate at 1·4, 34·4, and 206·4 mg/kg diet) in combination with adequate or increased Zn (12 and 240 mg/kg) and Cu (5 and 50mg/kg) on serum and tissue concentrations of retinol and retinyl palmitate and on indices of Cu and Zn status in female Sprague–Dawley rats, and to measure interactive effects of such nutrient imbalances. Rats fed on diets containing 34·4 and 206·4 mg vitamin A/kg had higher feed intakes and relative Liver weights than those fed on diets containing 1.4mg vitamin A/kg. An interaction between dietary Cu and Zn and an independent effect of vitamin A affected serum ceruloplasmin oxidase (EC 1.16.3.1) activity. Rats fed on high Zn, adequate-Cu diets (240 and 5 mg Zn and Cu/kg respectively) had lower serum ceruloplasmin oxidase levels than rats fed on adequate-Zn, adequate-Cu diets (12 and 5 mg Zn and Cu/kg respectively). This effect was not observed in rats fed on high-Zn, high-Cu diets (240 and 50mg Zn and Cu/kg respectively). Alterations in dietary levels of Cu and vitamin A independently affected haemoglobin levels. Serum cholesterol concentration was affected by interactions between Zn and vitamin A and Cu and vitamin A. Levels of retinol and retinyl palmitate in liver and kidney were significantly higher in rats fed on diets with increased dietary vitamin A than in those fed on diets with adequate vitamin A. Three-way interactions among Cu, Zn, and vitamin A affected levels of retinol in serum and liver. Two-way interactions between Cu and vitamin A affected liver retinyl palmitate and the sum of liver retinol + retinyl palmitate. An independent effect of dietary Zn on these variables was also observed. Interactions between Cu and vitamin A affected levels of Cu in liver and kidney, while Fe and Zn in kidney were affected by interactions between Cu and Zn. This study demonstrates that differing interactions among variables of vitamin A metabolism and mineral status occur with higher dietary levels of vitamin A, Zn and Cu in the rat

Tantallum silicide films were sputter deposited from targets with different Si/Ta stoichiometries. The films were then subjected to thermal treatments. Silicon precipitation was observed on films deposited from silicon rich targets. The effects of silicon precipitates on device characteristics was studied. A method to suppress silicon precipitation is reported.

Carrier transport in the channel region of polysilicon thin film MOSFETs is affected by the presence of grain boundary potential barriers and is further complicated by the modulation of the grain boundary barrier height with gate voltage. Passivation of the trap sites with atomic hydrogen reduces the barrier height and thereby improves the performance of polysilicon transistors. In this paper, we demonstrate the effectiveness of Rapid Thermal Annealing (RTA) using Si3N4 as a solid source of H as a passivation technique for both inversion and accumulation mode polysilicon MOSFETs. ON/OFF ratios of 107 can be obtained by RTA passivation for inversion mode polysilicon MOSFETs compared to 106 after furnace passivation permitting the potential application of these MOSFETs both as load transistors in SRAMs as well as pass transistors in DRAMs. In contrast, the ON&OFF ratio of accumulation mode polysilicon MOSFETs does not show any improvement even though ID and VT improve with passivation. This is because of excessive back channel leakage in accumulation mode MOSFETs which increases with passivation.

Solid Phase Epitaxy (SPE) of amorphous silicon thin films can be employed to build novel device structures for VLSI applications. One way of achieving SPE is to use a room temperature silicon implant to amorphize a polysilicon layer followed by a thermal treatment to promote epitaxial growth. Both vertical SPE, in which the epitaxial film is grown directly on silicon substrate, and lateral SPE, in which the epitaxial growth is extended over a thin layer of oxide using the vertical SPE region as a seed, have been realized using this approach. This paper presents results obtained by cross-sectional TEM analysis of the epitaxial films, with particular emphasis on the effects of implant schedule and annealing conditions on the epitaxial regrowth.

Polysilicon transistors offer the first entry into 3-dimensional ICs. This paper reviews some process and device considerations in using these devices in VLSI environments. The process issues include the choice of polysilicon grain size, layer thickness, doping, and methods of grain boundary passivation. The device considerations are closely related to the effects of grain boundaries in modifying the device characteristics. Three specific application examples are reviewed. It is concluded that polysilicon transistors offer new possibilities to enhance the performance of bulk technologies without resorting to any recrystallization techniques.

Solid-phase epitaxial regrowth of polysilicon films. amorphized by a room-temperature silicon implant. has been achieved using a (low temperature) furnace anneal or a (high temperature) rapid thermal anneal. Lateral extension of the growth onto an oxide layer, 4 μm wide, has also been observed. The electrical properties of the films were examined by building MO2S devices in them. Average electron mobilities of 520 cm2/v-sec and 200 cm2/v-sec have been measured for films regrown on top of silicon and oxide respectively.