Search Results - (Author, Cooperation:J. W. Allen)

2014-12-06

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

2014-06-14

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

2011-06-04

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Adhesins, Escherichia coli/*chemistry/metabolism ; Crystallization ; Escherichia coli Proteins/*chemistry/metabolism ; Fimbriae Proteins/*chemistry/metabolism ; *Models, Molecular ; Protein Binding ; Protein Structure, Quaternary

1089-7550

AIP Digital Archive

Physics

The Kondo properties of the impurity Anderson model provide a theoretical framework for relating thermodynamic and angle integrated electron spectroscopy data in many heavy fermion materials. We describe the success and the challenges of this approach, summarize a detailed analysis of CeSi2, and give a perspective on the relation to the lattice Anderson model. © 2000 American Institute of Physics.

Electronic Resource

1471-0528

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

In high risk pregnancies with severe fetal distress, a reduction of fetal movements may take place before fetal death occurs. This decrease is accompanied by a weakening of the fetal movements. One hundred and twenty pregnant women (310 recordings) between 20 and 41 weeks gestation recorded fetal movements and classified them into weak, strong, and rolling. The movements noted by the woman were correlated to those recorded by a fetal movements recorder. The rate of weak movements gradually decreased until the 36 to 37th week, while the strong and rolling movements increased. From the 36 to 37th week till term weak movements increased again with a decline in strong and rolling movements. Before fetal death, or in severe fetal distress with decreased total movements, the relative rate of weak movements increased. Reduction in daily total movements without a change in the distribution of the type of movement may not indicate fetal distress.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

A series of chlorine-doped epitaxial layers of ZnSe have been grown by molecular-beam epitaxy. Measurements have been made of the relative intensity of the blue photoluminescence at room temperature, of the decay time of this emission, and of the concentrations of deep levels determined by photocapacitance techniques. A GaAs buffer layer improves the light emission and decreases the deep-level concentrations. Over the uncompensated donor concentration range 2×1016 to 3×1018 cm−3 the photoluminescence intensity, decay rate, and deep-level concentrations only vary by one order of magnitude. The results are consistent with the room-temperature blue emission resulting in recombination of a free hole with electrons on relatively isolated donors, this radiative recombination competing with a strong nonradiative Hall–Shockley–Read recombination via deep levels in the lower half of the energy gap. The significance of these results for the making of light-emitting diodes and lasers is discussed. © 1995 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The film thickness, chemical state, and polarization screening for a-SiN1.4 :H films deposited by glow discharge over hydrogenated amorphous silicon (a-Si:H) were determined by x-ray photoelectron spectroscopy (XPS) and Auger spectroscopy. The nitride films were observed to be single phase and the escape depth for 1400-eV electrons in the a-SiN1.4 :H film was determined to be 30 A(ring). The band offsets for the a-Si:H/a-SiN1.4 :H interface were determined by XPS and Bremsstrahlung isochromat spectroscopy (BIS) to be 1.2 eV for the valence band and 2.2 eV for the conduction band, while the band gap for a-SiN1.4 :H was found to be 5.3 eV in accordance with the optical gap. By combining optical absorption measurements with the valence-band density of states and conduction-band density of states determined by electron spectroscopy, a semiquantitative estimate of the band tailing within the nitride gap was obtained. Correlation of the defect absorption with the electron spin resonance measurements suggest that the dangling bond defect level in a-SiN1.4 :H lies approximately 2.5 eV from the nitride valence band and is, therefore, somewhat below the a-Si:H conduction band. This study has demonstrated that BIS is an effective technique for determining the conduction-band offsets in heterostructures without relying on valence-band offset or band-gap measurements.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The decay time of the blue luminescence at room temperature in n-type ZnSe grown by metalorganic chemical vapor deposition has been measured, using a mode-locked laser as excitation source and a streak camera for detection. Over an uncompensated donor concentration range 1017–1018 cm−3 the decay time is of the order of 100 ps. The short time is a result of strong nonradiative recombination: it is argued that the concentration of Hall–Shockley–Read recombination centers is high.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

It is shown that the blue luminescence band appearing at room temperature in ZnSe is seen in metalorganic chemical vapor deposition (MOCVD) epilayers with carrier concentration 1×1018 cm−3. The photon energy at the emission peak is the same in this material as in material with much lower carrier concentration. Properties of the blue band are surveyed to discriminate between different possible assignments. It is concluded that Shirakawa and Kukimoto [J. Appl. Phys. 51, 2014 (1980)] were correct in assigning it to a transition between a free hole and an electron bound to a donor. However, not all donors contribute. There is a cutoff energy within the spread of donor levels above which there is negligible contribution to the emission. It is suggested that the cutoff corresponds to a localization edge of the same nature as the mobility edge.

Electronic Resource

1365-2494

Blackwell Publishing Journal Backfiles 1879-2005

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

During 1984 and 1985, trials at sixteen sites throughout Wales measured the yield response in upland swards from applying 40 and 80 kg N ha−1 at three dates, 20 August, 4 September and 18 September. All sites were between 230 m and 345 m above sea level. Grass yields were measured by cutting plots during October and November.Nitrogen increased the herbage dry-matter (DM) yield at all sites in both years. The yield response per kg N applied varied between sites. Mean yield response for the two years declined from 16·2 kg DM kg N−1 with 40 kg N ha−1 applied on 20 August to 8·9 kg DM kg N−1 with 80 kg N ha−1 applied on 18 September. In general there was a decline in response to N with increased rate and delay in time of application. The results indicate that responses above an optimum of 9 kg DM kg N−1 can be obtained well into September. A general rule that 1 kg N can be economically applied per 4 summed day degrees air temperature 〉6 °C remaining in the autumn up to 30 November is suggested.Delay in application and increasing N rate increased crude protein in the herbage but had only small effects on modified acid detergent (MAD) fibre and sugar. Generally, grass quality was good. Sward density assessed during the spring after nitrogen had been applied appeared to have been unaffected by the treatments.

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] Wafers of semi-insulating gallium arsenide were prepared from bulk ingots by cutting grinding and etching. Typical dimensions were 3 x 3 x 0-15 mm. Tin contacts of 0-5 mm. diameter were alloyed at the centres of the two large faces. This configuration makes any surface leakage paths between ...

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] Fig. 1. Energy-levels of the model to be considered Fig. 2. Fermi-level as a function of acceptor concentration for fixed donor concentration (schematic) As normally prepared in this laboratory undoped gallium arsenide is n-type with about 1016 electrons/ cm.3, which come from a residual impurity ...

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] The conditions under which one might observe this effect are as follows. We define a critical concentration N Q of zinc atoms above which most of them will not be ionized, and below which most of them will be. Then we require the surface concentration to be greater than N0 and the intrinsic number ...

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] We wish to point out that the interaction of an exciton with an electric field may be more easily observed. Suppose the exciton is describable in te?ms of a hydrogen-like s-function. Then it can be shown that in an electric field F its energy is decreased to a first approximation by : A E == - y. ...

Electronic Resource

1432-0886

Springer Online Journal Archives 1860-2000

Biology

Medicine

Abstract Mouse spermatogenic cells are known to express HSP70-2, a member of the HSP70 family of heatshock proteins. The purpose of the present study was to characterize further the expression and localization of HSP70-2 in meiotic cells of mice and hamsters. After separating mouse spermatogenic cells into cytoplasmic and nuclear fractions, proteins were separated by two-dimensional gel electrophoresis and detected with HSP-specific antibodies. Of several HSP70 proteins identified in the cytoplasm, only HSC70 and HSP70-2 were also detected in the nucleus. Immunocytological analyses of spermatocyte prophase cells revealed that HSP70-2 was associated with the synaptonemal complex. Surfacespread synaptonemal complexes at pachytene and diplotene stages labeled distinctly with the antiserum to HSP70-2. Synaptonemal complexes from fetal mouse oocytes failed to show any evidence of HSP70-2. Reverse-transcriptase-polymerase chain reaction (RT-PCR) analyses of gene expression confirmed this sex specificity; Hsp70-2 mRNA was detected in mouse testes, but not ovaries. These findings are suggestive of a previously unsuspected sexual dimorphism in structure and/or function of the synaptonemal complex.

Electronic Resource

1432-0886

Springer Online Journal Archives 1860-2000

Biology

Medicine

Abstract. Mouse spermatogenic cells are known to express HSP70-2, a member of the HSP70 family of heat-shock proteins. The purpose of the present study was to characterize further the expression and localization of HSP70-2 in meiotic cells of mice and hamsters. After separating mouse spermatogenic cells into cytoplasmic and nuclear fractions, proteins were separated by two-dimensional gel electrophoresis and detected with HSP-specific antibodies. Of several HSP70 proteins identified in the cytoplasm, only HSC70 and HSP70-2 were also detected in the nucleus. Immunocytological analyses of spermatocyte prophase cells revealed that HSP70-2 was associated with the synaptonemal complex. Surface-spread synaptonemal complexes at pachytene and diplotene stages labeled distinctly with the antiserum to HSP70-2. Synaptonemal complexes from fetal mouse oocytes failed to show any evidence of HSP70-2. Reverse-transcriptase-polymerase chain reaction (RT-PCR) analyses of gene expression confirmed this sex specificity; Hsp70-2 mRNA was detected in mouse testes, but not ovaries. These findings are suggestive of a previously unsuspected sexual dimorphism in structure and/or function of the synaptonemal complex.

Electronic Resource

1057-9257

Zinc selenide ; Luminescence ; Deep levels ; Chemistry ; Polymer and Materials Science

Wiley InterScience Backfile Collection 1832-2000

Electrical Engineering, Measurement and Control Technology

Physics

Although zinc selenide and related materials are promising for blue light-emitting diodes and lasers, present performance is unsatisfactory. The blue radiative efficiency at room temperature is low and the decay time of luminescence is correspondingly short. It is argued that the problem is non-radiative recombination by the Hall-Shockley-Read mechanism at deep levels and that the concentration of these levels must be high. Experimental evidence for the existence of such levels is presented. Characterisation and control of deep levels will be essential for progress in this area.

2 Ill.

Electronic Resource

1057-9257

Chemistry ; Polymer and Materials Science

Wiley InterScience Backfile Collection 1832-2000

Electrical Engineering, Measurement and Control Technology

Physics

Electronic Resource

1057-9257

Excitons ; Zinc selenide ; Chemistry ; Polymer and Materials Science

Wiley InterScience Backfile Collection 1832-2000

Electrical Engineering, Measurement and Control Technology

Physics

We have measured the absorption spectrum of the n = 1 free exciton in ZnSe from 4.2 to 190 K. By fitting to a Lorentzian, we have found the exciton peak energy, width and oscillator strength. The values are compared with published ones, which were mainly obtained by less direct methods. The importance of the electron-hole interaction in radiative processes in ZnSe is emphasised.

2 Ill.

Electronic Resource