Search Results - (Author, Cooperation:J. Connolly)

2018-03-12

Nature Publishing Group (NPG)

0969-7128

1476-5462

Biology

Medicine

2015-10-16

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

*Biodiversity ; *Climate ; Climate Change/statistics & numerical data ; Conservation of Natural Resources ; Disasters/statistics & numerical data ; Droughts ; *Ecosystem ; Grassland ; Human Activities ; *Plant Physiological Phenomena

2018-10-16

Nature Publishing Group (NPG)

0969-7128

1476-5462

Biology

Medicine

2014-11-02

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 ; Drosophila melanogaster/genetics/immunology ; Evolution, Molecular ; Gene Knockdown Techniques ; Host-Pathogen Interactions/genetics/immunology ; Humans ; Macrophages/immunology ; Nerve Growth Factor/genetics/*immunology ; Phagocytosis/genetics/immunology ; Receptor, trkA/genetics/*immunology ; Staphylococcal Infections/genetics/*immunology ; Staphylococcus aureus/*immunology ; Zebrafish/genetics/immunology

2012-07-17

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 ; *Archaeology ; *Caves ; DNA/analysis ; Emigration and Immigration/history ; Feces ; *Fossils ; History, Ancient ; Humans ; Molecular Sequence Data ; North America ; Oregon ; Population Dynamics ; Radiometric Dating ; Rodentia ; Technology/history ; Time

2011-08-13

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

*Biodiversity ; Ecology/methods ; *Ecosystem ; Extinction, Biological ; Models, Biological ; Plant Development ; *Plant Physiological Phenomena ; *Plants/classification ; Poaceae ; Species Specificity

0022-3999

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Medicine

Psychology

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The quantum well solar cell is an alternative to more conventional multiband gap approaches to higher cell efficiency. Preliminary studies have shown that the insertion of a series of quantum wells into the depletion region of a GaAs/AlxGa1−xAs p-i-n solar cell can significantly enhance the cell's short-circuit current. We present here a model for the spectral response of GaAs and AlxGa1−xAs p-n and p-i-n solar cells, with and without quantum wells, based on a standard solution of the minority-carrier equations. Particular emphasis is placed on modeling the absorption coefficient of the AlxGa1−xAs and of the quantum wells. We find that our model can accurately predict the spectral response of a wide variety of cells: both conventional p-n junctions in GaAs and AlxGa1−xAs, and various geometries of quantum well solar cell in AlxGa1−xAs/GaAs (x∼0.3). We discuss the strengths and weaknesses of the model and its underlying assumptions, and conclude by using the model to design p-i-n quantum well solar cells with higher short-circuit current outputs.

Electronic Resource

1525-1314

Blackwell Publishing Journal Backfiles 1879-2005

Geosciences

Abstract C-O-H fluid produced by the equilibration of H2O and excess graphite must maintain the atomic H/O ratio of water, 2:1. This constraint implies that all thermodynamic properties of the fluid are uniquely determined at isobaric-isothermal conditions. The O2, H2O and CO2 fugacities (fo2, fH2O and fCO2) of such fluids have been estimated from equations of state and fit as a function of pressure and temperature. These fugacities can be taken as characteristic for graphitic metamorphic systems in which the dominant fluid source is dehydration, e.g. pelitic lithologies. Because there are no compositional degrees of freedom for graphite-saturated fluids produced entirely by dehydration, the variance of the dehydration process is not increased in comparison with that in non-graphitic systems. Thus, compositional ‘buffering’of C-O-H fluids by dehydration equilibria, a common petrological model, requires that redox reactions, decarbonation reactions or external, H/O ± 2, fluid sources perturb the evolution of the metamorphic system. Such perturbations are not likely to be significant in metapelitic environments, but their tendency will be to increase the fO2 of the fluid phase. At high metamorphic grades, pyrite desulphidation reactions may cause a substantial reduction of fH2O and slight increases in fO2 and fCO2 relative to sulphur-free fluid. At low metamorphic grade, sulphur solubility in H/O ± 2 fluids is so low that pyrite decomposition must occur by sulphur-conserving reactions that cause iron depletion in silicates, a common feature of sulphidic pelites. With increasing temperature and sulphur solubility, pyrite desulphidation may be driven by dehydration reactions or infiltration of H2O-rich fluids. The absence of magnetite and the assemblages carbonate + aluminosilicate or pyrite + pyrrhotite + ilmenite from most graphitic metapelites is consistent with an H/O = 2 model for GCOH(S) fluid. For graphitic rocks in which such a model is inapplicable, a phase diagram variable that defines the H/O ratio of GCOH(S) fluid is more useful than the conventional fO2 variable.

Electronic Resource

1525-1314

Blackwell Publishing Journal Backfiles 1879-2005

Geosciences

In the contact aureole of the Oligocene granodiorite of Cima di Vila, granitic pegmatites of Variscan age were strongly deformed during eo-Alpine regional metamorphism, with local development of ultramylonites. In the ultramylonite matrix, consisting of quartz, plagioclase, muscovite and biotite, microstructures show grain growth of quartz within quartz ribbons, and development of decussate arrangements of mica. These features indicate that dynamic recrystallization related to mylonite development was followed by extensive static growth during contact metamorphism. K-feldspar porphyroclasts up to 1.5 cm are mantled by myrmekite that forms a continuous corona with thickness of about 1 mm. In both XZ and YZ sections, myrmekite tubules are undeformed, and symmetrically distributed in the corona, and oligoclase-andesine hosts have random crystallographic orientation. Myrmekite development has been modelled from the P–T–t evolution of the ultramylonites, assuming that the development of the ultramylonites occurred during eo-Alpine metamorphism at c. 450 °C, 7.5 kbar, followed by contact metamorphism at c. 530 °C, 2.75 kbar. Phase diagram pseudosections calculated from the measured bulk composition of granitic pegmatite protolith indicate that the equilibrium assemblage changes from Qtz–Phe–Ab ± Zo ± Cpx ± Kfs during the ultramylonite stage to Qtz–Pl(An30–40)–Ms–Kfs–Bt(Ann55) during the contact metamorphic stage. The thermodynamic prediction of increasing plagioclase mode and anorthite content, change of white mica composition and growth of biotite, occurring during the end of the heating path, are in agreement with the observed microstructures and analysed phase compositions of ultramylonites. Along with microstructural evidence, this supports the model that K-feldspar replacement by myrmekite took place under static conditions, and was coeval with the static growth accompanying contact metamorphism. Myrmekite associated with muscovite can develop under prograde (up-temperature) conditions in granites involved in polymetamorphism.

Electronic Resource

1525-1314

Blackwell Publishing Journal Backfiles 1879-2005

Geosciences

We formulate an algorithm for the calculation of stable phase relations of a system with constrained bulk composition as a function of its environmental variables. The basis of this algorithm is the approximate representation of the free energy composition surfaces of solution phases by inscribed polyhedra. This representation leads to discretization of high variance phase fields into a continuous mesh of smaller polygonal fields within which the composition and physical properties of the phases are uniquely determined. The resulting phase diagram sections are useful for understanding the phase relations of complex metamorphic systems and for applications in which it is necessary to establish the variations in rock properties such as density, seismic velocities and volatile-content through a metamorphic cycle. The algorithm has been implemented within a computer program that is general with respect to both the choice of variables and the number of components and phases possible in a system, and is independent of the structure of the equations of state used to describe the phases of the system.

Electronic Resource

1469-8986

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Psychology

Visual evoked potentials (VEPs) were recorded from five sites (T3, T4, Cz, O1, O2) to six intensities of light flashes. Peak-to-trough amplitudes were measured for the P100-N120 and N120-P200 waveforms as well as baseline (prestimulus)-to-peak amplitudes for each component (i.e. P100, N120, and P200). Different methods of defining augmenting/reducing were compared. These included subtracting the VEP epoch mean level from mean levels within a timeband corresponding to P100 and calculating slopes both for these values and for the P100-N120 amplitudes across intensities. The technique of using slopes to describe amplitude-intensity functions was found to be unjustified and misleading. The Augmenting/Reducing groups defined by the slopes of peak-to-trough amplitudes or slopes of the timeband “amplitudes” proved to be almost mutually exclusive. Results also showed that the frequency with which actual VEP peaks occur within the appropriate timeband is very low and differs topographically. Augmenting/Reducing was then defined by monotonic increases in the P100-N120 peak-to-trough amplitudes. Augmenters and Reducers differed from each other not only for amplitude-intensity patterns but on a number of latency measures. Hemisphere differences were also found between groups. An inverse relationship was found between occipital and vertex amplitude-intensity patterns such that vertex augmenting was accompanied by occipital reducing and vice versa. Temporal and vertex amplitude-intensity patterns were similar.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

A double-heterojunction angled stripe AlGaAs device consisting of an index-guided ridge waveguide with gain-guided facet regions has produced cw output powers of 20 mW with less than 1% spectral modulation from a 300-μm-long diode. These properties enable these devices to have important use in high-sensitivity fiber optic gyroscopes and as broadband traveling-wave optical amplifiers.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

A wavelength-locked, AlGaAs channeled-substrate-planar distributed feedback laser has been made that operates to 40 mW pulsed. The Bragg grating is situated at the shoulders of the layers of AlGaAs and GaAs. Overall power efficiencies of 15% have been measured at 40 mW of output power.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Thin active region single stripe aluminum gallium arsenide traveling-wave amplifiers have been used to generate and amplify 15 ps optical pulses to nearly 50 mW average powers and to peak powers in excess of 3 W. No appreciable temporal pulse distortion is observed after amplification. These peak power levels should prove to be sufficient to induce nonlinear optical effects in fibers.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

High-power GaAs/AlGaAs double-heterostructure lasers have been fabricated on Si substrates using a single-step metalorganic chemical vapor deposition process. An output power of 130 mW (per facet) and a slope efficiency of 38% have been obtained under pulsed operation. The peak emission wavelength of the laser was 8823 A(ring) and the beam full width at half power for the parallel and perpendicular far-field radiation patterns were 6° and 41°, respectively.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We describe room-temperature 2.78 μm AlGaAsSb/InGaAsSb multiquantum well lasers. Pulsed laser operation was observed at 15 °C with a threshold current of 1.1 A (10 kA/cm2), and a maximum power output of 30 mW, and a maximum differential quantum efficiency of 9%. Lasers operated pulsed up to 60 °C with a characteristic temperature of 58 K over the range of 0–40 °C. To date, 2.78 μm is the longest emission wavelength for a room-temperature III–V laser. © 1995 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We report the use of laser diode amplifiers, whose facets have unequal mirror reflectivities, as asymmetric Fabry–Perot modulators. Due to the presence of optical gain in these devices we observe modulation of reflected light with both large absolute modulation depth and high contrast ratio.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We have demonstrated continuous wave operation of 2.7-μm InGaAsSb/AlGaAsSb multiquantum-well diode lasers up to a temperature of 234 K (−39 °C). These devices were grown by molecular-beam-epitaxy. They have a tendency to operate in a dominant single mode over well-defined temperature and current intervals. A comparison of spontaneous emission spectra shows that above threshold, the quasi-Fermi level is pinned and that most of the carriers are injected into nonlasing states. This effect leads to a rapid decrease of differential efficiency with increasing temperature. © 1995 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Emission of a 100 mW cw beam into a nearly diffraction limited near-circular spot by a grating surface emitting (GSE) semiconductor laser, with radiance of 5.3×106 W/sr cm2, is described. The distributed out-coupled master oscillator power amplifier (DOC-MOPA) devices comprise active grating outcoupled power amplifiers and monolithic distributed feedback laser oscillators. With single wavelength (930 nm) operation demonstrated to 260 mW, they produce narrow linewidth (10 MHz) beams and near-ideal far-field patterns. The DOC-MOPA promises to become an efficient, compact source of high-quality ≥1 W cw light. Such fully collimated high power cw beams demonstrate the potential of GSE lasers to serve in systems requiring higher power than available from conventional edge-emitting technology.

Electronic Resource