Search Results - (Author, Cooperation:P. Coleman)

2011-01-22

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

2011-06-17

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

2013-02-01

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

2013-01-11

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

2018-07-10

The American Association of Immunologists (AAI)

0022-1767

1550-6606

Medicine

2015-08-01

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

2012-08-04

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

ARNTL Transcription Factors/genetics ; Animals ; *Circadian Rhythm ; Fluorometry ; Glutathione/metabolism ; Membrane Potentials ; Mice ; Mice, Mutant Strains ; NADP/metabolism ; Neurons/metabolism/*physiology ; Oxidation-Reduction ; Potassium Channels/metabolism ; Rats ; Suprachiasmatic Nucleus/cytology/metabolism/*physiology

1089-7550

AIP Digital Archive

Physics

Spin nematics are magnets with long-range tensor order in the absence of a sublattice magnetization; the formation of this novel spin state has been studied within the new quantum fluids perspective of magnetism. Here this recent work on spin nematics is reviewed, and experimental signatures and a candidate system are discussed.

Electronic Resource

1089-7674

AIP Digital Archive

Physics

Solid-fill nozzles for long-implosion Z-pinch experiments to produce argon K-shell x rays (photon energy 〉3.1 keV) have been developed. With a 7 cm diam nozzle, which is appropriate for a 200 ns driver, stable implosions at 180 ns and 4 MA have produced peak argon K-shell yields exceeding 15 kJ. As previously seen with short (∼100 ns) implosion times, the K-shell yield scales as the fourth power of peak current, I4. Limited testing with a 10 cm nozzle, which is appropriate for a 〉250 ns driver, has also achieved a stable implosion. © 2001 American Institute of Physics.

Electronic Resource

1089-7674

AIP Digital Archive

Physics

Recent observations are given for an argon double-shell gas puff imploded with up to 4 MA in 200 ns on the Double Eagle generator [G. B. Frazier et al., Digest of Technical Papers, Fourth IEEE Pulsed Power Conference (IEEE, Piscataway, NJ, 1983), p. 583]. Good K-shell x-ray output with good pinch quality was observed. A novel experimental procedure was used to selectively seed the inner or outer gas plenums with a chlorine tracer. The tracer data provide the first direct experimental evidence that the mass initially closest to the axis is the dominant contributor to the hot core of the radiating pinch. © 2000 American Institute of Physics.

Electronic Resource

1089-7674

AIP Digital Archive

Physics

The first observations of gaseous load implosions with over 15 MA in 〉110 ns on the Z generator [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] are reported. Starting from a diameter of over 8 cm, an argon double-shell Z pinch imploded to under 0.5 cm K-shell emission diameter. With a load mass of 0.8 mg/cm, K-shell x-ray output reached 274±24 kJ in a 15 TW peak power, 12 ns pulse. This record-high yield is consistent with the current-squared scaling predicted for the "efficient" emission regime. © 2001 American Institute of Physics.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

Timely estimates of z-pinch plasma conditions can aid in the optimization of plasma radiation source K-shell emission. For example, a shell-on-shell argon gas puff has many parameters, such as the axial gas density profile, inner to outer shell mass ratio, total mass, and pinch load length, which can be varied on a shot by shot basis. At the Double-EAGLE facility at Maxwell Physics International, digital cameras have been implemented to routinely record pinhole images, x-ray spectra, and axially resolved streak images. A computer algorithm has been implemented to take as input the data (pinch diameter, Ar Lyα to Heα line ratio, and K-shell power) and output the plasma parameters (density, electron temperature, and K-shell-emitting mass) as a function of z-pinch axial location. We describe the algorithm and present results for three different z-pinch loads. © 2001 American Institute of Physics.

Electronic Resource

1089-7623

AIP Digital Archive

Physics

Electrical Engineering, Measurement and Control Technology

We have developed a dual-plenum gas valve coupled to a double shell nozzle for the generation of "shell-on-shell" gas loads in z-pinch plasma radiation source experiments. The gas density profiles of the nozzles have been characterized with laser interferometry. This valve/nozzle combination has been successfully fielded on the Double-EAGLE and Saturn pulsed-power generators. The design and characterization of the shell-on-shell valve/nozzle are presented in this article. © 2000 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We describe experiments for a neon tandem-puff Z pinch modified with a small-diameter, high-Z wire target (i.e., pinch-on-wire). The radiative yield for photon energies in the range of 1–100 keV is measured. With a copper-wire target the integral yield (J) between 0.9 and 1.5 keV increases by a factor of 1.5 compared to the pinch without a target; the yield is unchanged or slightly increased for higher-Z wires. The high-energy integral yield, above 6 keV, increases by a factor of 2 or more with a copper target and as much as a factor of 5 with a tungsten target. This behavior cannot be accounted for by simple hydrodynamic compression of a hot plasma and suggests yield enhancement by a nonthermal mechanism. © 1997 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The development of a sensitive, depth-tuneable probe, with mapping capability, for low-energy ion implantation dosimetry, is described. The technique is based on the dependence of the extent of Doppler broadening of the positron annihilation linewidth upon the concentration of open-volume defects produced by the implanted ions. By varying the incident positron energy one can ensure that most of the annihilation events occur near the damage peak. A series of diagnostic measurements have been performed which demonstrate that the positron response lies on an almost universal curve, independent of ion mass and energy. The probe is highly sensitive, with a dose threshold in the 10−9 cm−2 range for many implants, and has the potential to measure dose/dose uniformity to better than 1×1011 cm−2 in the 1011−1012 cm−2 range in run times of a few seconds. Considerations underlying the development of a practical instrument based on these findings are discussed. © 1999 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The electron beam in a linear induction accelerator is generally susceptible to growth of the transverse beam breakup instability. In this paper we analyze a new technique for reducing the transverse coupling between the beam and the accelerating cavities, thereby reducing beam breakup growth. The basic idea is that the most worrisome cavity modes can be cutoff by a short section of coaxial transmission line inserted between the cavity structure and the accelerating gap region. We have used the three-dimensional simulation code SOS to analyze this problem. In brief, we find that the technique works, provided that the lowest TE mode cutoff frequency in the coaxial line is greater than the frequency of the most worrisome TM mode of the accelerating cavity.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Three series of experiments have been performed using two 40-Ω coaxial autoacceleration cavities to accelerate an intense relativistic electron beam. First, conventional magnetic transport was used to propagate a 1.8-MeV, 11-kA beam through two 1-m-long cavities. An increase of 700±130 keV in kinetic energy was achieved which represents 80% of the maximum theoretical acceleration for an 11-kA beam passing through two 40-Ω cavities. Multiple accelerated pulses were generated and no adverse interaction between the cavities was observed. In the second experiment, ion focused transport (IFT) was used to successfully propagate a 9-kA beam through the accelerator again achieving multipulse operation with both cavities. An energy increase of 560±30 keV was attained which is 78% of the theoretical maximum. Finally, IFT was used to propagate a (approximately-equal-to)25-kA beam through a 1-m-long cavity, then a 0.5-m-long cavity, demonstrating two stages of temporal energy compression. Gap leakage and current transport losses limited the acceleration to 1.25±0.16 MeV which corresponded to an 84% increase in kinetic energy.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

This paper presents a study of the microwave impedance of GaAs-AlxGa1−xAs resonant tunneling heterostructures. An equivalent-circuit model is proposed that accounts for the frequency variation of the measured impedance and whose elements correspond to physical phenomena believed to be present in the device. Empirical formulas are obtained which can be used to calculate the values of the equivalent-circuit elements from the structural parameters and the dc current-voltage characteristics of the device.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We report on new observations of positron stopping in a series of Al foils mounted on glass backplates for incident energies E in the range 10–50 keV. The measured median penetration depths for E(approximately-greater-than)30 keV are found to differ significantly from values derived from the empirical power law model of A. P. Mills, Jr. and R. J. Wilson [Phys. Rev. A 26, 490 (1982)]. The associated disparity between the measured implantation profiles and their analytic representations, and the consequent implications for defect profiling analysis, are discussed.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

New experiments and Monte Carlo simulations of positron implantation in gold are presented which, when compared with earlier work on aluminum, clearly demonstrate that the material dependence of positron implantation profiles is not adequately described by the simple mass density scaling factor in the widely used expression for median implantation depths. There is excellent agreement between the experimental results and the simulations which use the Penn dielectric formalism to describe inelastic scattering.

Electronic Resource