Search Results - (Author, Cooperation:S. Hooper)

2014-10-25

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Actomyosin/metabolism ; Animals ; Cell Membrane/metabolism ; Cytoskeleton/metabolism ; Dendritic Cells/immunology/*physiology ; Female ; Fibroblasts/*cytology/physiology ; Inflammation/immunology ; Lectins, C-Type/metabolism ; Lymph Nodes/*cytology/immunology/metabolism ; Male ; Membrane Glycoproteins/metabolism ; Mice ; Stromal Cells/*cytology/physiology ; ras Proteins/metabolism ; rho GTP-Binding Proteins/metabolism

1089-7550

AIP Digital Archive

Physics

There has been controversy concerning the energy gap of the cubic (zinc-blende) form of the wide-gap semiconductor GaN. Measurements are reported of the band gaps of both hexagonal (wurtzite) and cubic thin films deposited by a modified molecular-beam-epitaxy process on (001) GaAs and GaP substrates. The important difference from conventional MBE lies in the method of supplying nitrogen to the growing film. Here a rf nitrogen plasma source operating at 13 MHz is used. The structure of the films was monitored by x-ray diffraction and controlled by the addition of an As beam which results in growth of the cubic form—otherwise films grow with the hexagonal structure. The band gaps were measured at room temperature by optical reflectivity, as evidenced by the sharp reduction in interference oscillations as the photon energy approached the band edge, and confirmed by the observation of band-edge photoluminescence. The results can be summarized as Eg=3.42±0.02 eV for the hexagonal and 3.22±0.02 eV for the cubic form. The observation of films containing mixed hexagonal and cubic phases, which may have led to earlier errors in band-gap measurements, is also reported. © 1995 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We report on the growth of GaN with a zinc-blende, wurtzite, or a mixed phase structure on (001)GaP and (001)GaAs substrates by a low-temperature modified molecular beam epitaxy technique. By systematically varying the incident arsenic overpressure, films grown at a moderate substrate temperature of ≈620 °C show predominately wurtzite α-GaN, zinc-blende β-GaN, or a mixed phase of the two. Films containing only the metastable phase β-GaN were achieved by using a relatively high growth temperature of ≈700 °C and with an arsenic overpressure of ≈2.4×10−5 Torr. X-ray diffraction measurements indicate an improved crystalline quality for the layers grown at ≈700 °C compared to those grown at ≈620 °C as evident by a narrower full width at half-maximum of 35 min for β-GaN, which is among the narrowest reported to date. © 1995 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

GaN thin films were grown by molecular beam epitaxy on sapphire substrates. Scanning electron (SE) and atomic force microscopies reveal that on a typical film an assembly of oriented hexagonal microcrystallites rises above a background of polycrystalline or amorphous material. Cathodoluminescence (CL) spectra of the films feature bright UV exciton peaks and a broad green emission band. We identify the exciton peaks as those of the wurtzite form of GaN. A comparison of SE and CL micrographs of the same sample area shows that the luminescence emanates almost entirely from the hexagonal crystallites. © 1996 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Using gas-source molecular-beam epitaxy, and ammonia as a source of nitrogen, we have investigated the effect of buffer layer preparation on the electrical and optical properties of GaN epilayers. It is found that the buffer layer thickness and buffer anneal time have a dramatic effect on the Hall mobility and the background carrier density in the layers. With an optimized buffer layer, we have achieved mobility of ∼190 cm2/V s and have correlated this with a defect density as low as 2.1×109 cm−2 in the best layers. The variation of the intensity of defect related lines in photoluminescence spectra has been used to confirm the decrease of the defect density with increasing mobility in these layers. © 2001 American Institute of Physics.

Electronic Resource

1440-1681

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

1. During fetal life the lung develops as a liquid-filled organ. This liquid is produced by the fetal lung and leaves via the trachea from where it is either swallowed or enters the amniotic sac. Fetal lung liquid plays a crucial role in the growth and development of the lungs by maintaining them in a distended state. It is now recognized that the retention of liquid within the future airways is required to maintain the lungs at an appropriate level of expansion in order to stimulate their growth. Indeed, it is likely that most, if not all, of the conditions and malformations that lead to inadequate growth of the fetal lung do so by reducing the volume of lung liquid and hence the degree of lung expansion.2. The volume of fetal lung liquid is principally regulated by the resistance to lung liquid efflux through the fetal upper airway and by the presence of diaphragmatic activity associated with fetal breathing movements (FBM). During non-breathing periods, the relatively high resistance offered by the upper airway to the efflux of lung liquid opposes the loss of liquid from the lung, thereby maintaining fetal lung expansion. During episodes of FBM, when the larynx is actively dilated and the resistance to lung liquid efflux is reduced, lung liquid leaves the lungs at an increased rate. However, selective inhibition of diaphragmatic muscle activity in the foetus leads to a reduction in lung liquid volume, rather than an increase. This finding indicates that during periods of FBM, rhythmical contractions of the diaphragm retard the loss of lung liquid and help to maintain lung expansion when the upper airway resistance is reduced. It is now apparent that the maintenance of lung expansion by FBM is the basis for their role in promoting fetal lung growth.3. Successful transition from intra-uterine to extra-uterine life is dependent upon the clearance of liquid from the fetal lungs at the time of birth so that the lungs may effectively function as an organ of gas exchange. It is generally considered that, at the time of birth, increased circulating levels of the stress-related hormones, adrenaline and arginine vasopressin (AVP), play an important role in suppressing fetal lung liquid secretion and stimulating its reabsorption. The ability of adrenaline and AVP to perform this role, however, is dependent upon the exposure of the lung to increasing levels of gluco-corticoids late in gestation. Thus, the maturation of the fetal lung, induced by the preparturient increase in circulating cortisol levels, not only includes changes in lung compliance and surfactant synthesis, but also includes an increased ability of the lung to reabsorb liquid.4. Although it is well recognized that fetal lung growth is critically determined by the degree to which the lungs are expanded with lung liquid, the mechanisms underlying this relationship are poorly understood and are likely to be complex. The increase in fetal lung growth induced by experimentally increasing the degree of fetal lung expansion is very rapid and most probably results from an acceleration of the processes involved in normal fetal lung growth. The accelerated growth response is most likely mediated by a multitude of growth factors which act on different processes within individual cells and on different cell types within the lung to produce a coordinated growth response. Because increased fetal lung expansion rapidly increases the growth of hypoplastic fetal lungs, treatments leading to increased lung expansion in utem have the potential to be used to treat lung hypoplasia in human foetuses before the lungs are required to function as the sole organ of gas exchange. Further experimentation is required to determine whether such lungs have the ability to function effectively after birth.

Electronic Resource

1365-2842

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

summary  A number of indices have been developed for the measurement of tooth surface loss but they have not achieved universal acceptance. The aim of this study was to develop a new index suitable for the monitoring of incisal/occlusal tooth wear on serial study models. The new index recorded incisal/cuspal wear for individual teeth. Each tooth was scored on a six-point scale ranging from 0–5. Six assessors evaluated the index and it was applied to baseline and sequential models taken after 20 years. The study demonstrated the value of maintaining long-term dental records in the form of study models for monitoring progressive tooth wear.

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] High resolution gas chromatography of the methyl esters of individual isoprenoid fatty acids isolated from a geological source of the Eocene period has shown a diastereoisomer composition compatible with a chlorophyll derivation for the acids. The L-menthyl esters give enhanced separation ...

Electronic Resource

0747-5632

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Computer Science

Medicine

Psychology

Electronic Resource

0361-476X

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Education

Psychology

Electronic Resource

1600-051X

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Background: Studies in vitro suggest that abrasion and erosion may act synergistically to produce wear of enamel and dentine. Methods in situ are recently available to study separately erosion and abrasion of dental tissues. The aim of this study was to combine two in situ protocols to study the interplay between erosion and abrasion of enamel and dentine.Method: The study was a single-blind, randomised, five-treatment cross-over design involving 15 healthy volunteers. During each 10-day study period, subjects wore from 0900 to 1700 h an upper removable acrylic appliance holding one polished enamel and one polished dentine specimen. The specimen treatment regimens were:〈list xml:id="l1" style="custom"〉1Drinking water and brushing with toothpaste A.2Drinking water and brushing with toothpaste B.3Drinking orange juice.4Drinking orange juice and brushing with toothpaste A.5Drinking orange juice and brushing with toothpaste B.Drinking and brushing times were around 0900, 1100, 1300 and 1500 h. Drinks were consumed as 250 ml over 10 min and brushing ex vivo for 1 min to each specimen. Measurement of tissue loss was made on days 5 and 10 of each period using a profilometer.Results: All treatments produced increasing tissue loss over time, which was considerably greater for dentine than enamel. For enamel, the data at days 5 and 10 showed a significant effect for erosion (i.e. orange juice was significantly more erosive than water), but no significant effect for abrasion (i.e. no significant difference between the two toothpaste treatments). The combined orange juice and toothpaste effects were directional for synergy but did not reach significance. For dentine at day 10, many specimens exceeded the 50 μm set limit of the profilometer and only day 5 data were considered. There were significant effects for erosion (orange juice produced significantly more erosion than water) and for abrasion (paste A was significantly more abrasive to dentine than paste B). The synergy effect could not be examined for dentine due to the truncation effect as the set limit of the profilometer was exceeded.Conclusions: Erosion increases the susceptibility of enamel to toothpaste abrasion. Dentine is considerably more susceptible than enamel to erosion and abrasion alone or combined. Dentine loss appears to correlate with toothpaste abrasivity (RDA value).

Electronic Resource

1476-5535

Keywords: azo dyes; Caulobacter subvibriodes; oxygen-insensitive azoreductase

Springer Online Journal Archives 1860-2000

Biology

Process Engineering, Biotechnology, Nutrition Technology

An azo dye-degrading bacterium, Caulobacter subvibrioides strain C7-D, semi-constitutively produces an azoreductase that reduced the azo bond of the dyes Acid Orange (AO) 6, AO7, AO8, AO12, Acid Red (AR) 88, AR151, and Methyl Red (MR). This activity was oxygen insensitive. Of the dyes tested, AO7 was the best inducer and the most rapidly reduced substrate suggesting that dye AO7 most closely mimics the natural physiological substrate for this enzyme. The K m for AO7 was 1 μM. Purification of the azoreductase from C. subvibrioides strain C7-D was achieved through dye-ligand affinity chromatography using the dye Orange-A covalently coupled to an agarose support. The azoreductase is approximately 30 kDa and enzyme studies indicate a single azoreductase. The optimal activity, pH, cofactor usage, substrate specificity, molecular weight and K m characteristics of the enzyme set it apart from other known oxygen-insensitive azoreductases.

Electronic Resource

1434-6036

Springer Online Journal Archives 1860-2000

Physics

Abstract. The optimal-velocity model, as proposed by Bando et al. [1], shows unrealistic values of the acceleration for various optimal-velocity functions [2,3]. We discuss different approaches of how to correct this problem. Multiple look-ahead (many-neighbour interaction) models are the most promising candidates in reducing accelerations and decelerations to realistic values. We focus on two such models and, in particular, their linear stability and how these affect the vehicle dynamics and wave solutions. As found earlier [4], multiple look-ahead models reproduce many real flow features, and our results further support the necessity of this ansatz. However, the problem of non-locality arises when they are transformed into the corresponding continuum model. We discuss three methods of how to interpret many-neighbour interaction in macroscopic models.

Electronic Resource

1420-9071

Aplysia ; co-transmission ; modulation ; motorneuron ; muscle ; peptide

Springer Online Journal Archives 1860-2000

Biology

Medicine

Abstract Despite their ubiquitous presence in the central and peripheral nervous systems, the behavioral functions of peptide co-transmitters remain to be elucidated. The marine molluscAplysia, whose simple nervous system facilitates the study of the neural basis of behavior, was used to investigate the role of peptidergic co-transmission in feeding behavior. Several novel modulatory neuropeptides were purified, and localized to identified cholinergic motorneurons. Physiological and biochemical studies demonstrated that these peptides are released when the motorneourons fire at frequencies that occur during normal behavior, and that the peptides modify the relationship between muscle contraction amplitude and relaxation rate so as to maintain optimal motor output when the intensity and frequency of feeding behavior change.

Electronic Resource

1476-5535

Keywords: bioremediation; biodegradation; groundwater; intrinsic bioremediation; aromatic hydrocarbons; in situ; aerobic; anaerobic; modeling

Springer Online Journal Archives 1860-2000

Biology

Process Engineering, Biotechnology, Nutrition Technology

An industrial site contaminated with a mixture of volatile organic compounds in its subsurface differed from previously reported locations in that the contamination consisted of a mixture of chlorinated, brominated, and non-halogenated aromatic and aliphatic solvents in an alluvial aquifer. The source area was adjacent to a river. Of the contaminants present in the aquifer, benzene, toluene, and chlorobenzene (BTC) were of primary concern. Studies of the physical, chemical, and microbiological characteristics of site groundwater were conducted. The studies concentrated on BTC, but also addressed the fate of the other aquifer VOCs. Gas chromatographic analyses performed on laboratory microcosms demonstrated that subsurface microorganisms were capable of BTC degradation. Mineralization of BTC was demonstrated by the release of 14CO2 from radiolabelled BTC. In the field, distribution patterns of nutrients and electron acceptors were consistent with expression of in situ microbial metabolic activity: methane, conductivity, salinity and o-phosphate concentrations were all positively correlated with contaminant concentration; while oxidation-reduction potential, nitrate, dissolved oxygen and sulfate concentrations were negatively correlated. Total aerobes, aerotolerant anaerobes, BTC-specific degraders, and acridine orange direct microscopic microorganism counts were strongly and positively correlated with field contaminant concentrations. The relative concentrations of benzene and toluene were lower away from the core of the plume compared to the less readily metabolized compound, chlorobenzene. Hydrodynamic modeling of electron-acceptor depletion conservatively estimated that 450 kg of contaminant have been removed from the subsurface yearly. Models lacking a biodegradation term predicted that 360 kg of contaminant would reach the river annually, which would result in measurable contaminant concentrations. River surveillance, however, has only rarely detected these compounds in the sediment and then only at trace concentrations. Thus, the combination of field modeling, laboratory studies, and site surveillance data confirm that significant in situ biodegradation of the contaminants has occurred. These studies establish the presence of intrinsic bioremediation of groundwater contaminants in this unusual industrial site subsurface habitat.

Electronic Resource