Search Results - (Author, Cooperation:D. C. Hamilton)

2018-08-24

American Society of Hematology (ASH)

0006-4971

1528-0020

Biology

Medicine

Hematopoiesis and Stem Cells, Myeloid Neoplasia

2013-07-03

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

2018-10-05

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Geosciences

Computer Science

Medicine

Natural Sciences in General

Physics

Geochemistry, Geophysics, Online Only, Planetary Science

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

The dissociative phase transition of fluid nitrogen at pressures in the range 30–110 GPa (0.3–1.1 Mbar), temperatures in the range 4000–14 000 K, densities up to 3.5 g/cm3, and internal energies up to 1 MJ/mol was investigated by shock compression. Equation-of-state, shock-temperature, and electrical-conductivity experimental data are presented and analyzed in detail.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

The electrical conductivity of shock-compressed liquid oxygen has been measured in the dynamic pressure range 18–43 GPa(180–430 Kbar). A double-shock equation-of-state point was also measured. The data and Hugoniot calculation, based on a chemical equilibrium model, indicate that liquid oxygen partially dissociates and forms a two-component conductive fluid. Details of the experimental design are given and the data are discussed in terms of electronic transport in disordered systems.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

By combining a toroidal electrostatic analyzer with a novel cylindrically symmetric isochronous time-of-flight mass spectrometer, we have developed an instrument that simultaneously determines the three-dimensional distribution function of ions and differentiates species. The ion mass is determined to high resolution (M/ΔM(approximately-greater-than)50) from the time of flight within a harmonic field configuration defined by hyperboloid equipotential surfaces. A second conventional time-of-flight channel makes use of particles leaving the thin entrance foil as neutrals. An additional solid state detector in which the neutrals are stopped allows the total energy and thereby the ionic charge of the incident ions to be determined as well. Information from the neutral and the ion channels can be combined to determine the total mass of an incident molecular ion and the mass of one atomic fragment. This also removes the ambiguity between molecular ions and isotopic species of the same mass. A laboratory prototype has been used to demonstrate the feasibility of the principle of operation.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

By combining a toroidal electrostatic analyzer with a novel cylindrically symmetric isochronous time-of-flight mass spectrometer, we have developed an instrument that simultaneously determines the three-dimensional distribution function of ions and differentiates species. The ion mass is determined to high resolution (M/ΔM(approximately-greater-than)50) from the time of flight within a harmonic field configuration defined by hyperboloid equipotential surfaces. A second conventional time-of-flight channel makes use of particles leaving the thin entrance foil as neutrals. An additional solid state detector in which the neutrals are stopped allows the total energy and thereby the ionic charge of the incident ions to be determined as well. Information from the neutral and the ion channels can be combined to determine the total mass of an incident molecular ion and the mass of one atomic fragment. This also removes the ambiguity between molecular ions and isotopic species of the same mass. A laboratory prototype has been used to demonstrate the feasibility of the principle of operation.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

We have developed a high-resolution mass analyzer that utilizes a measurement of an ion's time of flight (TOF) in an electrostatic field that is configured to produce a harmonic potential. The TOF corresponds to one-half period of a harmonic oscillator and is independent of ion energy, in analogy to the amplitude independence of a harmonic oscillator's period, and is proportional to the square root of the ion's mass per charge ratio. The TOF is determined from a start pulse from secondary electrons produced when the ion passes through a thin carbon foil (1–3 μg/cm2) at the entrance of the TOF region and a stop pulse from the ion striking a microchannel plate (MCP) upon exiting the region. The energy independence of the TOF implies there is no degradation of resolution from energy straggling in the foil. We have achieved a mass resolution M/ΔM (FWHM) of greater than 100 with a laboratory prototype. Three versions of this analyzer for solar wind measurements are included on upcoming space missions and will be flown on the GGS/WIND spacecraft, the SOHO spacecraft, and the ACE spacecraft.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

Hugoniot equation-of-state data for liquid 1-butene were measured in the shock pressure range 12–54 GPa (120–540 kbar) using a two-stage light-gas gun. The data are compared with previous data for polybutene, a stoichiometrically equivalent liquid with a smaller initial specific volume. The data for both butenes are in agreement with chemical equilibrium calculations which assume that shock-compressed hydrocarbons dissociate and form a two-phase mixture consisting of molecular hydrogen and carbon in a stiff, diamond-like phase.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

Equation-of-state, temperature, and electrical-conductivity data were measured for a solution of water, ammonia, and isopropanol at shock pressures up to 200 GPa. The chemical composition is similar to that of the fluid mixture thought to be the major constituent of the giant planets Uranus and Neptune. © 1997 American Institute of Physics.

Electronic Resource

1089-7690

AIP Digital Archive

Physics

Chemistry and Pharmacology

Electrical conductivities were measured for methane, benzene, and polybutene shock compressed to pressures in the range 20 to 60 GPa (600 kbar) and temperatures in the range 2000 to 4000 K achieved with a two-stage light-gas gun. The data for methane and benzene are interpreted simply in terms of chemical decomposition into diamondlike, defected C nanoparticles and fluid H2 and their relative abundances (C:H2), 1:2 for methane and 2:1 for benzene. The measured conductivities suggest that conduction flows predominately through the majority species, H2 for methane and C for benzene. These data also suggest that methane is in a range of shock pressures in which dissociation increases continuously from a system which is mostly methane to one which has a substantial concentration of H2. Thermal activation of benzene conductivities at 20–40 GPa is probably caused by thermal activation of nucleation, growth, and connectivity of diamondlike, defected C nanoparticles. At 40 GPa the concentration of these C nanoparticles reaches a critical density, such that further increase in density does not have a significant affect on the cross-sectional area of conduction and, thus, conductivity saturates. The electrical conductivity of polybutene (1:1) is very low. While the mechanism is unknown, one possibility is that the electronic bandgap of whatever species are present is large compared to the temperature. Electrical conductivity measurements are proposed as a way to determine the melting curve of diamondlike C nanoparticles at 100 GPa pressures. © 2001 American Institute of Physics.

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] The concept of an electrical current encircling the Earth at high altitudes was first proposed in 1917 to explain the depression of the horizontal component of the Earth’s magnetic field during geomagnetic storms. In situ measurements of the extent and composition of this current were ...

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] The outer limit of the Solar System is often considered to be at the distance from the Sun where the solar wind changes from supersonic to subsonic flow. Theory predicts that a termination shock marks this boundary, with locations ranging from a few to over 100 au ...

Electronic Resource

1572-9672

Springer Online Journal Archives 1860-2000

Physics

Abstract The Solar Wind and Suprathermal Ion Composition Experiment (SMS) on WIND is designed to determine uniquely the elemental, isotopic, and ionic-charge composition of the solar wind, the temperatures and mean speeds of all major solar-wind ions, from H through Fe, at solar wind speeds ranging from 175 kms−1 (protons) to 1280 kms−1 (Fe+8), and the composition, charge states as well as the 3-dimensional distribution functions of suprathermal ions, including interstellar pick-up He+, of energies up to 230 keV/e. The experiment consists of three instruments with a common Data Processing Unit. Each of the three instruments uses electrostatic analysis followed by a time-of-flight and, as required, an energy measurement. The observations made by SMS will make valuable contributions to the ISTP objectives by providing information regarding the composition and energy distribution of matter entering the magnetosphere. In addition SMS results will have an impact on many areas of solar and heliospheric physics, in particular providing important and unique information on: (i) conditions and processes in the region of the corona where the solar wind is accelerated; (ii) the location of the source regions of the solar wind in the corona; (iii) coronal heating processes; (iv) the extent and causes of variations in the composition of the solar atmosphere; (v) plasma processes in the solar wind; (vi) the acceleration of particles in the solar wind; and (vii) the physics of the pick-up process of interstellar He as well as lunar particles in the solar wind, and the isotopic composition of interstellar helium.

Electronic Resource

1572-9672

Springer Online Journal Archives 1860-2000

Physics

Abstract The Energetic Particles: Acceleration, Composition, and Transport (EPACT) investigation is designed to make comprehensive observations of solar, interplanetary, and galactic particles over wide ranges of charge, mass, energy, and intensity using a combination of 8 different particle telescopes. This paper summarizes the scientific goals of EPACT and provides a detailed description of the instrument design and capabilities. Electrons are measured from 0.2 to 10 MeV, primarily providing time markers for injections of solar particles. Hydrogen is measured from 1.4 to 120 MeV, and Helium is measured from 0.04 to 500 MeV nucl−1. The collection powers and energy ranges for heavier nuclei up to iron are ideal for observations of quiet-time populations such as particles accelerated by interplanetary shocks and the anomalous cosmic rays (thought to be accelerated at the boundary of the heliosphere). The large collection power available is also ideal for observations of3He,4He, and heavier nuclei in impulsive3He-rich solar events. There is even the possibility of observing ultra heavy nuclei (Z〉30) in large solar events for the first time. Finally, there is a telescope designed to measure isotopes from He (3.4–55 MeV nucl−1) to Fe (12–230 MeV nucl−1), which is intended for solar particles, the anomalous cosmic rays and galactic cosmic rays. The overall capabilities of EPACT provide scientifically interesting measurements over all phases of the solar cycle. There will also be important opportunities for combined studies with other spacecraft, such as SAMPEX, Ulysses, and Voyagers 1 and 2.

Electronic Resource

1572-9672

Springer Online Journal Archives 1860-2000

Physics

Abstract The Low Energy Charged Particle (LECP) instruments on Voyagers 1 (V1) and 2 (V2) measure the differential in energy fluxes and anisotropies of low energy ions≥30 keV and electrons≥20 keV differential in energy ion composition≥200 keV/nuc, and the integral rates of cosmic ray protons〉70 MeV (Krimigiset al., 1977). We discuss shock-accelerated ions and latitude-associated differences between V1 and V2 during 1991 to April 1994.

Electronic Resource