Search Results - (Author, Cooperation:J. A. Elliott)

2015-03-25

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Amino Acid Sequence ; Animals ; Bone and Bones/chemistry ; Cattle ; Collagen Type I/*chemistry/genetics ; Female ; *Fossils ; Mammals/*classification ; Perissodactyla/classification ; *Phylogeny ; Placenta ; Pregnancy ; Proteomics ; South America

2012-02-11

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

A method is presented for modeling the geometrical packing of polydisperse mixtures of both spherical and nonspherical particles, which are models for filler particles used in the manufacture of polymer composites. The technique is based on the calculation of the dissipative dynamics of an ensemble of fused soft spheres at constant temperature and pressure. After validation of the method at low pressures by comparison with analytical equations of state for monodisperse and binary mixtures of hard spheres, the random packing of fused soft sphere cubes was studied. The effect of packing cubes together with spheres of varying size was then examined, with the aim of developing an understanding of how to minimize the amount of void space in composites containing angular particles. In one case, entropically driven demixing was observed in a cube-sphere mixture. © 2000 American Institute of Physics.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

Absolute rate theory and the sticking probability approach have been previously examined as possible means of predicting the rate of adsorption. However, when applied to examine adsorption kinetics, they have been found not to contain the coverage and pressure dependence required for several important systems including CO–Ni(111). Statistical rate theory (SRT) is being developed with the objective of predicting the rate of molecular (or atomic) transport across the interface between macroscopic phases in terms of experimentally controllable variables and material properties of the two phases. Previous applications of SRT to adsorption have been limited to systems for which both the gas phase pressure and the temperature could be assumed to be constant. Herein, the SRT approach is extended to systems in which the number of molecules in the system (and hence the gas phase pressure) is not constant. To examine this extension, SRT is used to formulate the equations governing the rate of adsorption in isothermal, beam-dosing experiments. These equations are then combined with the values of certain material properties that have previously been established and a hypothesis that the value of the equilibrium adsorption cross section is given by the area of an adsorption site. The kinetic data for CO adsorbing on Ni(111) data reported by three different laboratories are then examined. For each set of experimental data, constants had to be inferred that were related to the experimental apparatus used and as such they were not expected to have any coverage or pressure dependence. The good agreement found between the predicted and measured adsorption kinetics indicates that all of the necessary coverage and pressure dependence was explicitly predicted from the SRT approach. © 1997 American Institute of Physics.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

The equation traditionally used to interpret temperature programmed desorption (TPD) spectra, the Polanyi–Wigner equation, does not contain explicitly the coverage and temperature dependence necessary to predict TPD spectra in several important systems including CO–Ni(111). Herein, the statistical rate theory (SRT) approach is used to formulate equations for temperature programmed desorption which are then used to examine TPD spectra reported in the literature for CO–Ni(111). The molecular and material properties for the CO–Ni(111) system have been previously established. One experimental spectrum has been chosen to determine the apparatus constants. The material properties and the apparatus constants are then used in the SRT equations to predict the eight additional TPD spectra for different initial coverages. A critical comparison can then be made between the theory and these eight experimental spectra, since no fitting constants were used in these eight cases. The results show that there is clearly qualitative agreement. The SRT equations are then used along with the heat of adsorption to derive an equation for the pre-exponential factor appearing in the Polanyi–Wigner equation. A prediction is made for the pre-exponential factor that is in agreement with that found empirically. The agreement found between the SRT predictions and the measured spectra indicates that all of the coverage and temperature dependence necessary to predict TPD spectra is given explicitly by the SRT approach. Hence, the experimental support for the SRT approach is enhanced. The SRT equations are then used to predict CO–Ni(111) spectra that would occur if the heating rate were varied. © 1997 American Institute of Physics.

Electronic Resource

1365-2427

Blackwell Publishing Journal Backfiles 1879-2005

Biology

1. Connell’s (1978) intermediate disturbance hypothesis (IDH) has been proposed as one explanation of why diversity is often highest at intermediate levels of disturbance. We used a model phytoplankton responses to environmental change (PROTECH) to investigate the validity of this hypothesis.2. In a simulated phytoplankton assemblage of eight species, we found that the relationship between the increased intensity of a single forcing event and diversity was described by a positively skewed curve.3. A progressive increase in forcing frequency introduced a sharp decrease in diversity at a threshold frequency. However, the highest diversity values were found at an intermediate frequency of disturbance.4. We described the shape of this breakpoint response as like a ‘cliff’ and reconcile it with multiple stable-point theory. It is argued that the IDH should possibly be represented by this ‘cliff’ relationship, which may be applied to (or encourage the re-examination of) many previous studies.

Electronic Resource

1365-2427

Blackwell Publishing Journal Backfiles 1879-2005

Biology

1. A phytoplankton community model [Phytoplankton RespOnses To Environmental CHange (PROTECH)] was used to examine the effect of a wide range of varied light intensities and mixed depths upon simulated phytoplankton populations. Two different column lengths of the simulated water body were examined (the upper 5 m and the whole 14.5 m water column) for each scenario.2. The hypotheses tested were that: (i) under low light intensity and/or deep mixing the simulated community will be dominated by a phytoplankter with a low critical light intensity; (ii) at high light intensity and shallow mixing the simulated community will be dominated by small, fast-growing phytoplankters; (iii) under all conditions, except deep mixing, the largest proportion of phytoplankton biomass will be found near the surface.3. It was found under most conditions that, although there was a bloom in the upper column (dominated by algae such as Chlorella, Ceratium or Rhodomonas), the largest phytoplankton biomass in the water column was located 9 m below the surface and consisted of solely Asterionella. This bloom was missed by the 5-m samples. Thus, using the whole column sample lengths, hypothesis (i) was not rejected but hypotheses (ii) and (iii) were refuted.4. The inclusion of specific movement characteristics of phytoplankton in the model allowed the possibility of the dominance of multiple spaces within the water column and should be included in any model-based investigation of this topic. Further, the results from the model suggest that a reduced depth of mixing creates greater environmental heterogeneity, allowing more species to persist.

Electronic Resource

1365-2222

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Ground whole rye and airborne rye dust of comparable size distribution were tested for their ability to activate the complement cascade via the alternative pathway. Precipitin-negative pooled normal human serum was incubated with increasing amounts of the two rye dusts. Electrophoresis of the resultant supernatant fluids demonstrated the conversion of the proactivator of the third component of complement to the gamma-migrating activator of the third component. This activation was completely prevented by pre-treating the serum with the chelator EDTA, while pre-treatment with EGTA allowed suboptimal arc conversion, strongly implying that complement was activated via the alternative pathway. Quantification of the supernatant fluids showed dose-dependent complement consumption as defined by both CH100 immunoditfusion and CH50 tube haemolytic techniques.Airborne rye dust showed a greater quantitative potential than ground whole rye for activating the alternative pathway. These results indicate the possibility of the direct action of airborne organic dusts on the induction of inflammatory sequelae in the lungs of both sensitized and unsensitized individuals.

Electronic Resource

1600-0633

Blackwell Publishing Journal Backfiles 1879-2005

Biology

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

From July 1989 to December 1994, an echo sounder provided monthly estimates, usually for both day and night, of pelagic salmonid densities in the North and South Basins of Windermere, the largest natural lake in England. Sampling was along contiguous transects, three in the North Basin and five in the South Basin. Records for Arctic charr (Salvelinus alpinus) could not be separated from those for brown trout (Salmo trutta), but previous sampling by gill-nets and anglers showed that charr formed over 90% of this mixed population in the North Basin and about 60–75% in the South Basin. Associated with the increasing eutrophication of the lake, there has been a decline in anglers' catches of charr and, since 1984, an increase in brown trout taken in the pelagic zone of the South Basin. The echo-sounder data showed that pelagic salmonid density in the North Basin was about two to five times that in the more eutrophic South Basin in 1989, 1990 and 1991. Since the start, in April 1992, of the reduction of phosphorus discharged from sewage works, this ratio has decreased, especially at night when the highest densities were recorded. This improvement was chiefly due to a significant (P〈0.001) increase in the density of small fish (length 〈20 cm), in both the upper (depth 〈20 m) and deeper (depth 〉20 m) water layers. Although a similar improvement has still to be shown in the upper water layer by larger fish above the size limit for removal by angling (20 cm), there has been a significant increase (P〈0.01) in the density of these fish in the deeper water layer of the South Basin. The increased density of small fish suggests that the stock available to charr anglers (fish 〉20 cm at water depths 〈20 m) should increase in the next few years, especially in the South Basin. It is therefore important to continue the monitoring program and thus ensure that there is advance warning of any marked changes in charr stocks.

Electronic Resource

1095-8649

Blackwell Publishing Journal Backfiles 1879-2005

Biology

The critical thermal maximum for salmon and trout parr was not affected significantly by age or acclimation temperature, and increased asymptotically with the rate of temperature increase. Mean thermal maxima were estimated with poor precision at high and low rates of temperature increase, and high precision at rates of 1 and 2°Ch−1.

Electronic Resource

1432-1351

Pineal ; Melatonin ; Circadian Rhythm ; Activity ; Photoperiod

Springer Online Journal Archives 1860-2000

Biology

Medicine

Abstract Circadian regulation of pineal melatonin content was studied in Syrian hamsters (Mesocricetus auratus), especially melatonin peak width and the temporal correlation to wheel-running activity. Melatonin was measured by radioimmunoassay in glands removed at different circadian times with respect to activity onset (= CT 12). Pineal melatonin peak width (h; for mean ≥125 pg/gland) and activity duration (α) were both 4–5 h longer after 12 or 27 weeks than after 5 or 6 days in continuous darkness (DD). Increased peak width was associated with a delay in the morning decline (M) of melatonin to baseline, correlated with a similar delay in wheel-running offset. In contrast, the evening rise (E) in melatonin occurred at approximately the same circadian phase regardless of the length of DD. Fifteen min light pulses produced similar phase-shifts in melatonin and activity. In a phase advance shift, M advanced at once, while E advanced only after several days of adjustment. Independent timing of shifts in the E and M components of the melatonin rhythm suggest that these events are controlled separately by at least two circadian oscillators whose mutual phase relationship determines melatonin peak width. This two-oscillator control of melatonin peak width is integral to the circadian mechanism of hamster photoperiodic time measurement.

Electronic Resource

1573-1472

Springer Online Journal Archives 1860-2000

Geosciences

Physics

Abstract Although temperature fluctuations dominate the variance of optical refractive index fluctuations it has been shown recently that humidity fluctuations can also be important (e.g., Friche et al., 1975). This paper reports on simultaneous measurements of temperature, humidity and pressure so that the relative importance of all three can be investigated. For the dry site where the measurements were made, the humidity contribution was less than other investigators had found. The major contribution of the pressure fluctuations was through their covariance with temperature, but this term was found to be between 0.03 and 0.4% of the total variance. The results thus confirmed that pressure fluctuations can be neglected in most circumstances. Both the temperature and humidity spectra displayed -5/3 power laws at small scales while the temperature-humidity cospectrum decreased more rapidly than a -5/3 power law. The temperature-pressure cospectrum decreased even more rapidly than the temperature-humidity cospectrum. The temperature-pressure correlation coefficient was found to be about -0.1. The humidity-pressure correlation was typically between ±0.05 and the cospectrum poorly defined.

Electronic Resource

1573-7284

Nosocomial infection ; Acinetobacter baumannii ; Epidemiologic typing

Springer Online Journal Archives 1860-2000

Medicine

Abstract Nosocomial infections due toAcinetobacter baumannii dramatically increased in a Lebanese medical center following an outbreak of hostilities in Lebanon in 1984. The incidence of infection caused by this organism has remained high in this institution, thus requiring the implementation of a strain typing system to aid in infection control. Three methods were investigated for their utility in differentiating among a representative group of 36 nosocomialAcinetobacter baumannii isolates obtained over a 10 month period from specimens of hospitalized patients. Isolates were typed by antibiogram analyses, plasmid fingerprinting, and total cell protein profiles. Only three distinct total cell protein profiles were detected, with one pattern accounting for 26 (72.2%) of the isolates. However, eight different plasmid profiles were observed, with 20 (55.5%) isolates having the same profile. Eleven distinct antibiograms were seen with the most prevalent pattern occuring in 21 isolates. Twenty of the 21 (95%) isolates with the common antibiogram also had the same plasmid profile and total protein profile (44.4% of total isolates). The combination of these three typing methods was useful in tracing the spread of these organisms in the medical center. The data obtained suggest the distribution of a common strain among at least six wards of this hospital.

Electronic Resource

1573-1472

Springer Online Journal Archives 1860-2000

Geosciences

Physics

Abstract An instrument is described which is capable of making Eulerian measurements of microscale fluctuations in the static pressure when it is placed within the turbulent flow of the lower atmospheric boundary layer. The sampling ports are located on an accurately shaped streamlined circular disc; dynamic pressure changes at these ports, due to the flow fluctuations, are small when compared to the static pressure changes. Wind tunnel tests and anin situ test show that the instrument can sample the amplitudes and phases of fluctuations in the static pressure to better than ± 20% and to about ± 5 °, respectively.

Electronic Resource

1573-5117

phytoplankton; modelling; sensitivity analysis

Springer Online Journal Archives 1860-2000

Biology

Abstract The lake phytoplankton community model, PROTECH includes nested regression equations for the effect of surface:volume ratio, temperature and irradiance on growth rate. A sensitivity analysis was carried out of the effect of changing the regression slope coefficients on three aspects of the simulated output for Blelham Tarn, English Lake District, with fixed environmental variables. The assessed variables were K, the maximum biomass; K, time taken in days to reach K and the exponential growth rate, r'. It was found that the light adjustment equation was the most sensitive to changes in the slope parameters. Changes in the base growth rate and temperature adjustment functions had less effect. Because PROTECH uses the light adjustment equation the least, it was argued that any error caused by it was tolerable.

Electronic Resource

1573-5117

phytoplankton ; modelling ; environment

Springer Online Journal Archives 1860-2000

Biology

Abstract The phytoplankton community model, PROTECH, simulates algal growth and is sensitive to numerous environmental variables (temperature, depth, light, daylength, nutrient supply). This investigation examines the effects of altering, in turn, each of these variables upon the simulated algal growth. We compare these results with those predicted by a phytoplankton variation on Grime's C-S-R paradigm. Finally, it is concluded that PROTECH is a suitable tool for the exploration of community assembly in relation to the ecological theories of competition, succession and biodiversity.

Electronic Resource

1573-2959

Springer Online Journal Archives 1860-2000

Energy, Environment Protection, Nuclear Power Engineering

Abstract Plant species composition and community structure were compared among four sites in an upland black spruce community in northwestern Ontario. One site had remained undisturbed since the 1930s and three had been disturbed by either logging, fire, or both logging and fire. Canonical correspondence ordination analyses indicated that herbaceous species composition and abundance differed among the disturbance types while differences in the shrub and tree strata were less pronounced. In the herb stratum Pleurozium schreberi, Ptilium crista-castrensis and Dicranum polysetum were in greatest abundance on the undisturbed forest site, while the wildfire and burned cutover sites were dominated by Epilobium angustifolium and Polytrichum juniperinum. The unburned harvested site was dominated by Epilobium angustifolium, Cornus canadensis and Pleurozium schreberi. Species richness was lower on the undisturbed site than on any of the disturbed sites while species diversity (H′) and evenness (Hill's E5) were higher on the unburned harvested site than on the other sites. Results suggest that herb re-establishment is different among harvested and burned sites in upland black spruce communities and we hypothesize that differences in the characteristics of the disturbance were responsible, in particular, the impact of burning on nutrient availability. These differences need to be taken into account in determining the effects of these disturbances on biodiversity and long-term ecosystem management.

Electronic Resource

1573-4803

Springer Online Journal Archives 1860-2000

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Abstract Nafion® is a commercially available perfluorosulphonate cation exchange membrane commonly used as a perm-selective separator in chlor-alkali electrolysers and as the electrolyte in solid polymer fuel cells. This usage arises because of its high mechanical, thermal and chemical stability coupled with its high conductivity and ionic selectivity, which depend strongly on the water content. The membrane was therefore studied in different states of hydration with two complementary techniques: atomic force microscopy (AFM) and small angle X-ray scattering (SAXS) combined with a maximum entropy (MaxEnt) reconstruction. Tapping mode phase imaging was successfully used to identify the hydrophobic and hydrophilic regions of Nafion. The images support the MaxEnt interpretation of a cluster model of ionic aggregation, with spacings between individual clusters ranging from 3 to 5 nm, aggregating to form cluster agglomerates with sizes from 5 to 30 nm. Both techniques indicate that the number density of ionic clusters changes as a function of water content, and this explains why the bulk volumetric swelling in water is observed to be significantly less than the swelling inferred from scattering measurements.

Electronic Resource