Tailoring structure and magnetic properties of NixCo1−x(N(CN)2)2 molecular magnets
Not Available
Lee, Dooyong↗
Engineering topics
Williams, D. J.
Publications and source records attributed to Williams, D. J..
Magnetotransport of single crystalline NbAs
We report transport measurement in zero and applied magnetic field on a single crystal of NbAs. Transverse and longitudinal magnetoresistance in the plane of this tetragonal structure does not saturate up to 9 T. In the transverse configuration (H ∥ c, I ⊥ c) it is 230,000% at 2 K. The Hall coefficient changes sign from hole-like at room temperature to electron-like below ~150 K. The electron carrier density and mobility calculated at 2 K based on a single band approximation are 1.8 × 10 19 cm -3 and 3.5 × 10 5 cm 2 /Vs, respectively. These values are similar to reported values for TaAs and NbP, and further emphasize that this class of noncentrosymmetric, transition-metal monopnictides is a promising family to explore the properties of Weyl semimetals and the consequences of their novel electronic structure.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Investigation of the physical properties of the tetragonal CeMAl 4 Si 2 (M = Rh, Ir, Pt) compounds
The synthesis, crystal structure and physical properties studied by means of x-ray diffraction, magnetic, thermal and transport measurements of CeMAl 4 Si 2 (M = Rh, Ir, Pt) are reported, along with the electronic structure calculations for LaMAl 4 Si 2 (M = Rh, Ir, Pt). These materials adopt a tetragonal crystal structure (space group P4/mmm) comprised of BaAl 4 blocks, separated by MAl 2 units, stacked along the c-axis. Both CeRhAl 4 Si 2 and CeIrAl 4 Si 2 order antiferromagnetically below T N1 = 14 and 16 K, respectively, and undergo a second antiferromagnetic transitition at lower temperature (T N2 = 9 and 14 K, respectively). CePtAl 4 Si 2 orders ferromagnetically below T C = 3 K with an ordered moment of μ sat = 0.8 μ B for a magnetic field applied perpendicular to the c-axis. Electronic structure calculations reveal quasi-2D character of the Fermi surface.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Transport and thermodynamic properties of (Ca1-xLax)10(Pt3As8)(Fe2As2)5 superconductors
Single crystals of (Ca1-xLax)(10)(Pt3As8)(Fe2As2)(5) (x = 0-0.182) superconductors have been grown and characterized by x-ray, microprobe, transport, and thermodynamic measurements. Features in the magnetic susceptibility, specific heat, and two kinks in the derivative of the electrical resistivity around 100 K in the x = 0 compound support the existence of decoupled structural and magnetic phase transitions. With La doping, the structural/magnetic phase transitions are suppressed and a half dome of superconductivity with a maximal T-c around 26 K is observed in the temperature-concentration phase diagram.
36 MATERIALS SCIENCE↗
Fatigue Life Prediction for Steels in Pulsating Irradiated Systems
Continuous energy pulses at a repetition rate of 10 Hz and the use of ferritic-martensitic (FM) steel for construction are assumed for a hypothetical high-temperature neutron source under study. Initial analyses based upon published literature data and established fracture mechanics models indicate that the service life of such a system would be limited by fatigue, and that viability would require designers to limit the magnitude of the alternating stress, keeping it well below 10 MPa in order to achieve a service life of 1 year with an assumed availability of 85 percent. These standard analyses use analytical expressions from published sources such as Roark’s Handbook.
36 MATERIALS SCIENCE↗
Excitation of whistler-mode waves and resonant electron scattering in the Jovian magnetosphere
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in-situ Galileo whistler-mode plasma waves Jupiter↗
Enhanced Whistler-Mode Emissions: Signatures of Interchange Motion in the Io Tourus
During the Galileo inbound pass through the Io torus the plasma wave insturment detected intervals of enhanced whistler-mode emissions.
Io torus Whiltler-mode↗
Average energetic ion flux variations associated with geomagnetic activity from EPIC/STICS on Geotail
The magnetotail ion flux measurements from the Geotail spacecraft are analyzed both with and without the application of selection criteria that identify the plasma regime in which an observation is obtained. The different results are compared with each other. The initial results on the changes of energetic ion flux and composition correlated to average substorm activity in different magnetotail plasma regimes are discussed. The energetic ions are measured using the energetic particles and ion composition (EPIC) experiment and the suprathermal ion composition spectrometer (STICS). The plasma, wave and field instruments of the Geotail satellite were used to identify the principle magnetotail plasma regimes of plasma sheet, lobe, and magnetospheric boundary layer, as well as the magnetosheath and solar wind. Energetic O and H ions were observed in all the plasma regimes.
Christon, S. P.↗
Impact of differences in the solar irradiance spectrum on surface reflectance retrieval with different radiative transfer codes
Surface reflectance retrieval from imaging spectrometer data as acquired with the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) has become important for quantitative analysis. In order to calculate surface reflectance from remotely measured radiance, radiative transfer codes such as 5S and MODTRAN2 play an increasing role for removal of scattering and absorption effects of the atmosphere. Accurate knowledge of the exo-atmospheric solar irradiance (E(sub 0)) spectrum at the spectral resolution of the sensor is important for this purpose. The present study investigates the impact of differences in the solar irradiance function, as implemented in a modified version of 5S (M5S), 6S, and MODTRAN2, and as proposed by Green and Gao, on the surface reflectance retrieved from AVIRIS data. Reflectance measured in situ is used as a basis of comparison.
Staenz, K.↗
A flux rope followed by recurring encounters with traveling compression regions: GEOTAIL observations
This paper reports a peculiar series of events observed with Geotail on October 24, 1992 at X approximately equals -80 R(sub E). On this day a combination of a bipolar perturbation in B(sub y) and a double-peaked perturbation in B(sub z), signature of a flux rope, was observed. Following this flux rope, bipolar B(sub z) events, identifiable as Traveling Compression Regions (TCRs), were recurrently observed. The axis of the flux rope was deduced to be field-aligned. Energetic ions (electrons) streamed earthward (tailward) in the flux rope. During the TCRs, the E x B flow showed a bipolar north-then-south perturbation, consistent with expected lobe plasma motion. The TCRs corresponded to weak ground magnetic disturbances and Pi2 waves. The observations can be explained by a model in which quasi-stagnant plasmoids are recurrently generated.
Kawano, H.↗
Magnetopause encounters in the magnetotail at distances of approximately 80 R(sub e)
The GEOTAIL satellite experienced several encounters with the magnetopause during the interval 0300 to 0600 hours on 27 October 1992 at a gsm location of (X,Y,Z) approximately (-81, -8, 7.5) R(sub e). Energetic ions of both solar wind and ionospheric origin (H(+), He(++), and O(+)) were observed streaming in the anti-solar direction on both the lobe and magnetosheath side of the plasma mantle-magnetosheath boundary, with maximum fluxes occuring at the boundary. Even though the mantle plasma had penetrated well into the lobe through convective drift, the energetic ions were observed only at the magnetopause and provided a clear signature of the boundary region. Using a measured convective drift velocity and observed ergetic particle anisotropies, we estimated that the maximum distance from GEOTAIL that the energetic ions could have been accelerated or made contact with the boundary field lines was less than 8 - 39 R(sub e), implying that both solar wind and ionospheric ions are accelerated and contact the magnetopause many tens of earth radii behind the earth. We further found that the unusual magnetopause positions encountered at this time could be explained in part by solar wind aberration effects. However additional processes (e. g., magnetospheric breathing modes, convoluted tail topologies) are required to fully explain these observations.
Williams, D. J.↗
A filament of energetic particles near the high-latitude dawn magnetopause
The Geotail satelite detected a filament of tailward-streaming energetic particles spatially separated from the boundary layer of energetic particles at the high-latitude dawn magnetopause at a downstream distance of approximately 80 R(sub E) on October 27, 1992. During this event, the composition and charge states of energetic ions at energies above approximately 10 keV show significant intermix of ions from solar wind and ionospheric sources. Detailed analysis leads to the deduction that the filament was moving southward towards the neutral sheet at an average speed of approximately 80 km/s, implying an average duskward electric field of approximately 1 mV/m. Its north-south dimension was approximately 1 R(sub E) and it was associated with an earthward directed field-aligned current of approximately 5 mA/m. The filament was separated from the energetic particle boundary layer straddling the magnetopause by approximately 0.8 R(sub E) and was inferred to be detached from the boundary layer at downstream distance beyond approximately 70 R(sub E) in the distant tail.
Lui, A. T. Y.↗
Energetic atomic and molecular ions of ionospheric origin observed in distant magnetotail flow-reversal events
Energetic atomic (O(+1) and N(+1)) and molecular (O2(+1), NO(+1), and N2(+1)) ions of ionospheric origin were observed in Earth's magnetotail at X approximately -146 R(sub E) during two plasma sheet sunward/tailward flow-reversal events measured by instruments on the GEOTAIL spacecraft. These events were associated with concurrent ground-measured geomagnetic disturbance intensification at auroral-and mid-latitudes (Kp = 7(-)). Energetic ions in the sunward-component and tailward flows were from both the solar wind and ionosphere. Plasma and energetic ions participated in the flows. During tailward flow, ionospheric origin ion abundance ratios at approximately 200-900 km/s in the rest frame were N(+1)/O(+1) = approximately 25-30% and ((O2(+1), NO(+1), and N2(+1))/O(+1) = approximately 1-2%. We argue that tailward flow most likely initiated approximately 80-100 R(sub E) tailward of Earth and molecular ions were in the plasma sheet prior to geomagnetic intensification onset.
Christon, S. P.↗
Structured plasma sheet thinning observed by Galileo and 1984-129
On December 8, 1990, the Galileo spacecraft used the Earth for a gravity assist on its way to Jupiter. Its trajectory was such that it crossed geosynchronous orbit at approximately local midnight between 1900 and 2000 UT. At the same time, spacecraft 1984-129 was also located at geosynchronous orbit near local midnight. Several flux dropout events were observed when the two spacecraft were in the near-Earth plasma sheet in the same local time sector. Flux dropout events are associated with plasma sheet thinning in the near-profile of the near-Earth plasma sheet while 1984-129 provided an azimuthal profile. With measurements from these two spacecraft we can distinguish between spatial structures and temporal change. Our observations confirm that the geosynchronous flux dropout events are consistent with plasma sheet thinning which changes the spacecraft's magnetic connection from the trapping region to the more distant plasma sheet. However, for this period, thinning occurred on two spatial and temporal scales. The geosynchronous dropouts were highly localized phenomena of 30 min duration superimposed on a more global reconfiguration of the tail lasting approximately 4 hours.
Reeves, G. D.↗
Estimation of crown closure from AVIRIS data using regression analysis
Crown closure is one of the input parameters used for forest growth and yield modelling. Preliminary work by Staenz et al. indicates that imaging spectrometer data acquired with sensors such as the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) have some potential for estimating crown closure on a stand level. The objectives of this paper are: (1) to establish a relationship between AVIRIS data and the crown closure derived from aerial photography of a forested test site within the Interior Douglas Fir biogeoclimatic zone in British Columbia, Canada; (2) to investigate the impact of atmospheric effects and the forest background on the correlation between AVIRIS data and crown closure estimates; and (3) to improve this relationship using multiple regression analysis.
Staenz, K.↗
Fine structure of Langmuir waves produced by a solar electron event
Observations of highly structured bursts of Langmuir waves produced by energetic electrons ejected from a solar flare using wideband plasma wave measurements on the Galileo spacecraft are reported. Attention is given to the solar flare that occurred on December 10, 1990, while the spacecraft was at a radial distance of 0.98 AU from the sun. This flare emitted a stream of energetic electrons and an associated type III radio event, both of which were detected by Galileo. A large number of intense Langmuir wave bursts were detected near the local electron plasma frequency, which was about 25 kHz. The bursts, which lasted about 1.5 hr, coincided with the arrival of the solar electrons. The bursts are highly structured and consist mainly of isolated wave packets with durations as short as 1 ms and beat-type waveforms with beat frequencies ranging from 200 to 500 Hz. The highly structured envelopes of these waves are strongly suggestive of nonlinear parametric decay processes such as those predicted by various theories dealing with the saturation of beam-driven electrostatic instabilities.
Gurnett, D. A.↗
Global magnetospheric imaging
The demonstrated and developing methods for global magnetospheric imaging are presented and the scientific expectations of having global observations in conjunction with local measurements are discussed. The global observations of the previously invisible magnetosphere will provide the first look at the overall magnetosphere, its dynamics, and the interactions between its component parts. The capability of imaging magnetospheric plasmas marks the first occasion where an astrophysical plasma system which has been well characterized by in situ measurements, i.e., the earth's magnetosphere, can also be characterized globally by remote sensing.
Williams, D. J.↗