Search Results - (Author, Cooperation:R. S. Smith)

2011-03-26

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Animals ; Cataract/congenital/*genetics/pathology ; Cell Line ; Chick Embryo ; Crystallins/genetics/metabolism ; Cytoplasmic Granules/metabolism ; Embryonic Development ; Female ; *Gene Expression Regulation, Developmental ; Gene Knockdown Techniques ; Glaucoma/*genetics ; Humans ; Hypospadias/genetics ; Lens, Crystalline/embryology/*metabolism ; Male ; Mice ; Mutation ; Organogenesis ; Protein Biosynthesis ; RNA, Messenger/*genetics/*metabolism ; RNA-Binding Proteins/genetics/metabolism ; Ribonucleoproteins/genetics/*metabolism ; Spermatogenesis/genetics

2012-03-03

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Cell Wall/physiology/ultrastructure ; Elasticity ; Hydrostatic Pressure ; Lycopersicon esculentum/cytology/*growth & development ; Meristem/cytology/*growth & development ; Models, Biological ; *Morphogenesis ; Osmolar Concentration ; Osmotic Pressure ; Plant Shoots/cytology/*growth & development

2014-02-18

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Amino Acid Sequence ; Arabidopsis/anatomy & histology/genetics ; Brassicaceae/*anatomy & histology/*genetics ; Chromosome Mapping ; *Evolution, Molecular ; Gene Duplication ; *Gene Expression Regulation, Plant ; *Genes, Homeobox ; Genetic Complementation Test ; Molecular Sequence Data ; Plant Leaves/*anatomy & histology/*genetics

2018-03-16

The American Association for Cancer Research (AACR)

1078-0432

1557-3265

Medicine

1089-7550

AIP Digital Archive

Physics

Velocity modulation using AlxGa1−xAs layers is, in principle, an attractive way of improving the efficiency of conventional GaAs impact avalanche transit-time (IMPATT) devices. Critical to the concept, however, is a detailed understanding of the nature of high-field electron transport in AlxGa1−xAs. We explore this via Monte Carlo simulations, with particular reference to the behavior found under nonuniform field conditions. Preliminary experimental results are presented for a simple, single-drift IMPATT diode in which the drift region is made entirely from Al0.3Ga0.7As.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Silicon delta-doped samples of various densities were grown by molecular-beam epitaxy and analyzed using high-resolution secondary ion mass spectrometry. A marked difference was observed between profiles produced from samples doped below a surface density of 1.3×1013 cm−2, where all the silicon was incorporated on gallium sites, and highly doped samples, where autocompensation had occurred. All samples were grown at nominally 580 °C and all the doped planes showed some degree of broadening. A computer model of a two-step diffusion process was developed which produced a set of diffusion coefficients for the lower-doped samples. The diffusion coefficient associated with the post deposition growth for these low-doped samples was approximately 4.2×10−17 cm2 s−1. The more highly doped samples, because of their complicated profiles, were modeled using a graphical technique. This technique revealed the presence of a much larger diffusion coefficient, which is tentatively assigned to silicon diffusing as nearest-neighbor pairs.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Extremely narrow photoluminescence linewidths have been observed from 6-A(ring) quantum wells of GaAs/In0.11Ga0.89As/GaAs. The quality of these spectra is such that structure involving higher-order donor-exciton transitions are observed.

Electronic Resource

1365-2478

Blackwell Publishing Journal Backfiles 1879-2005

Geosciences

Physics

It is now believed that the negative transients observed in coincident-loop transient electromagnetic (TEM) measurements are caused by polarizable bodies (bodies whose conductivity increases as a function of frequency). Ordinarily the TEM response of polarizable bodies is obtained by calculating the frequency-domain response at many frequencies and transforming it to the time domain via Fourier, Laplace or Hankel transforms. This is normally a computationally laborious task. However, for some simple non-polarizable bodies the time-domain response is analytical and can be computed easily. When these simple bodies are weakly polarizable an approximate response can be obtained by convolving the easily-calculated, non-polarizable response with the impulse response of the polarization. The approximate response is found to be very similar to the exact response for the polarizabilities normally seen in geological materials.

Electronic Resource

1365-2494

Blackwell Publishing Journal Backfiles 1879-2005

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

The results are reported from an experiment on the effects of cutting date (14 June, 21 July and I September), fertilizer application (none or 80 kg ha−1 N plus 40 kg ha−1 P and K) and grazing treatments (none, autumn or autumn plus spring) on the vegetation of an upland mesotrophic grassland in Upper Teesdale. northern England, UK.Effects on plant species number and cover are reported for 4 years (1989–93) of treatment. Effects on ‘species -attributes’ are given for the fourth year.The cessation of grazing combined with the use of fertilizer progressively reduced species number by about 25%. Under traditional management (no fertilizer, cutting date on 21 July, autumn and spring grazing) the species number and cover remained relatively static over the 4 years.Comparison between treatments in the fourth year showed a reduction in species number under the fertilizer application, cutting date on 1 September and no-grazing treatments. Fertilizer use together with cutting date on 1 September particularly lowered species number and cover.Analysis of variance was used to assess the effect of treatment on species that occurred frequently in the sward. A cutting date of 1 September favoured Agrostis capillaris. Alopecurus pratensis, Poa trivialis, Phleum pratense and Trisetum flavescens, The absence of grazing favoured Dactylis glomerata and Holcus lanatus. The use of fertilizer particularly favoured A. pratensis and H. lanatus. Ordination methods were used to assess the effect of treatment on the less frequent species. These were primarily associated with the treatment combination that matched ‘traditional’ management. Deviations from this ‘traditional’ regime acted separately, rather than in combination, and favoured different grass species. Traditional management was associated with ruderal, stress-tolerant ruderal and competitive ruderal strategists and with longer seed germination times, heavier seeds, some of which needed scarifying or chilling to break dormancy, and transient seed banks that germinated in the autumn.The original sward was an Anthoxanthum odora-turn-Geranium sylvatirum grassland, Briza media subcommunity (MG3b). After 4 years, Festuca ovina-Agrostis capillaris-Galium saxatile grassland, Holcus lanatus-Trifolium repens subcom-munity (U4b) and Lolium perenne-Alopecurus pratensis-Festuca pratensis grassland (MG7c) were found in many of the fertilized and late-cutting treatments.

Electronic Resource

1365-2494

Blackwell Publishing Journal Backfiles 1879-2005

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

The plant species number and composition, iind yield of herbage biomass of an agriculturally improved hay meadow were assessed after 4 years under various combinations of grazing, fertilizer applicution. cutting date and seed addition treatments in a replicated split-plot design.Grazing treatments consisted of either autumn grazing with cattle and sheep, spring grazing with sheep or both regimes. Fertilizer application treatments consisted of either 25 kg ha−1 N plus 12–5 kg ha−1 P and K or no fertilizer. Cutting date treatments consisted of cuts on either 14 June, 2i July or 1 September. Seed addition treatments consisted of either no addition or sowing with a range of meadow species in the autumn. Data analysis was by correspondence analysis and analysis of variance.Species number decreased with fenilizer use and when the cutting date was 1 September. A range of species was affected by the main treatments and there were some first-order interactions, mainly between cutting date and fertilizer application. Rhinanthus minor was particularly favoured by the seed addition treatment. Species attnbutes in the regenerative and established phase were related to treatments and their effect on species composition.The National Vegetation Classification communities were associated with particular treatment regimes. The 21 July cutting date favoured ‘improved’ over ‘unimproved-traditional’ swards, with spring grazing favouring ‘unimproved-traditional’ swards.Lowest yields of herbage biomass were associated with autumn and spring grazing, the 14 June cutting date and no fenilizer treatments. The fenil-izer, 1 September cutting date and auiumn grazing treatments gave the highest yields.The implications of these results are discussed in terms of the conservation management required to return agriculturally improved mesotrophic grassland to a species composition similarto that of traditionally managed grassland.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

In this letter, photoluminescence results obtained from two different undoped multilayered pseudomorphic structures grown by molecular beam epitaxy are compared. Intense and spectrally narrow emission was observed from both GaAs/InxGa1−xAs/GaAs and AlxGa1−xAs/InxGa1−xAs/GaAs structures. Excitonic emission from the quantum wells was confirmed by measurements of photoluminescence excitation spectra. The intensity and temperature dependences of the photoluminescence also revealed emission arising from bound excitons and impurities in the quantum wells. Intrinsic and extrinsic emission from confined levels was confirmed by the recorded photoluminescence excitation spectra along with intensity and temperature dependences. In the asymmetric AlxGa1−xAs/InxGa1−xAs/GaAs structure large changes were observed in the photoluminescence intensity under continuous optical excitation which are caused by the optical excitation of defects in the ternary AlxGa1−xAs on top of the pseudomorphically grown InxGa1−xAs.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

X-ray photoelectron spectroscopy has been used to investigate thin single-crystal films of ytterbium arsenide grown epitaxially on GaAs by molecular beam epitaxy. Sputter profiles indicate the absence of oxide impurities and the presence of only trivalent ytterbium, which means that the epitaxial film is composed entirely of YbAs. X-ray diffraction analysis revealed a moderate imperfection of the crystalline quality of the YbAs and a lattice misfit of about 8×10−3 with respect to GaAs.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Using a tunable color center laser, photoluminescence excitation measurements were performed on GaAs:Er grown by molecular-beam epitaxy. These measurements show that only one type of Er3+ center is responsible for the sharply structured emission band at 1.54 μm. The multiplicity of the zero-phonon lines indicates that this Er3+ center has lower than cubic symmetry and that the luminescence arises from the intracenter transition 4I13/2→4I15/2 of Er3+ (4f 11).

Electronic Resource

1460-9568

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

We have examined the hypothesis, for the case of mouse axons, that isolating an axon from its cell body will lead to a rapid failure of fast axonal transport as anterogradely moving organelles vacate the axon in a proximo-distal direction, and retrogradely moving organelles vacate it in the opposite direction. We used CD1 and BALB/c mice and the Wallerian degeneration-resistant mutant C57BL/Ola. Sciatic nerves were cut high in the thigh; at various times up to 8 days later nerves were removed from the animal and individual myelinated axons from the segment distal to the cut were examined by video light microscopy to detect rapid organelle transport. Bidirectional fast organelle transport did decrease in amount with time but not nearly as rapidly as predicted, and anterograde and retrograde organelle velocities remained normal through time. In the C57BL/Ola mouse some structurally preserved axons contained organelles that transported at normal velocities in the anterograde and retrograde directions for as long as 8 days after axotomy. To test one of the possible origins of transported organelles in long-surviving axons we examined organelle transport very close to narrow lesions in axons bathed in a medium compatible with intracellular function. No organelles crossed the lesion but bidirectional organelle transport took place proximal and distal to the lesion; the amounts were compatible with the interpretation that ∼30% of organelles reversed transport direction on either side of the lesion. We propose that at least some of the organelles that undergo persistent transport in axons isolated from their cell bodies shuttle back and forth between the ends of the isolated segment.

Electronic Resource

1365-2478

Blackwell Publishing Journal Backfiles 1879-2005

Geosciences

Physics

The VLF filtering technique of Karous and Hjelt has been applied to fixed-loop step-response transient electromagnetic data. This allows the data measured in each channel to be converted to an equivalent current-density pseudosection.For a conductive half-space, the maximum value of the equivalent current density starts near the transmitter loop and migrates outwards as a function of delay time. The rate of migration tends to increase as a function of delay time, with the increase being faster for a surficial conductive layer than it is for a half-space.Theoretical and field examples show that the currents tend to be more persistent in the relatively conductive areas, so that a pseudosection which is the average of the current densities at all delay times will highlight the more conductive zones.In resistive ground, it is not so critical to average the pseudosections as a particular delay time may give a better idea of the conductivity structure. For example, the latest possible delay time will reveal the most conductive features.

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] SIR,-Professor Doty has many interesting things to say in his Granada lecture "The Academic Condition in the United States", printed in your issue of December 13, but he could hardly have been more mistaken in his choice of Aunt Sallies when calling for "the informed involvement of students who are ...

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] Slow muscle fibres isolated from Xenopus laevis have been found to be histochemically1, functionally1,2 and structurally (unpublished results of R. S. Smith and S. Page) distinct from the two types of fast fibres. In our previous study1 of the group of slow fibres, we were unable to find evidence ...

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] A similar type of fragmentation and distortion of the red cells is sometimes seen in hsemothorax fluids, and this led us to examine the red cells by supravital staining with methyl violet. By this means Heinz bodies were demonstrated in the majority of serous and cystic fluids, and sometimes in ...

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] THAT angiosperm species of drier habitats (excluding the succulents which have a different metabolic regime) have drier tissues than similar species of moister places, when each is observed in its modal habitat, has become established1-2. It is sometimes forgotten that the whole or greater part of ...

Electronic Resource

1749-6632

Blackwell Publishing Journal Backfiles 1879-2005

Natural Sciences in General

Electronic Resource