A Standard Reference Material (SRM
™
) for the Seebeck coefficient is critical for inter-laboratory data comparison and for instrument calibration. To develop this SRM
™
, we have conducted an ...international round-robin measurement survey of two candidate materials—undoped Bi
2
Te
3
and constantan (55% Cu and 45% Ni alloy). Measurements were performed in two rounds by twelve laboratories involved in active thermoelectric research using a number of commercial and custom-built measurement systems and techniques. We report the results of these measurements and the statistical analysis performed. Based on this extensive study, we have selected Bi
2
Te
3
as the prototype standard material.
The Chandra X-ray Observatory (CXO) observed Jupiter during the period 24-26 February 2003 for approx. 40 hours (4 Jupiter rotations), using both the spectroscopy array of the Advanced CCD Imaging ...Spectrometer (ACIS-S) and the imaging array of the High-Resolution Camera (HRC-I). Two ACIS-S exposures, each -8.5 hours long, were separated by an HRC-I exposure of approx. 20 hours. The low- to middle-latitude nonauroral disk X-ray emission is much more spatially uniform than the auroral emission. However, the low- to middle-latitude X-ray count rate shows a small but statistically significant hour angle dependence and depends on surface magnetic field strength. In addition, the X-ray spectra from regions corresponding to 3-5 gauss and 5-7 gauss surface fields show significant differences in the energy band 1.26-1.38 keV, perhaps partly due to line emission occurring in the 3-5 gauss region but not the 5-7 gauss region. A similar correlation of surface magnetic field strength with count rate is found for the 18 December 2000 HRC-I data, at a time when solar activity was high. The low- to middle-latitude disk X-ray count rate observed by the HRC-I in the February 2003 observation is about 50% of that observed in December 2000, roughly consistent with a decrease in the solar activity index (F10.7 cm flux) by a similar amount over the same time period. The low- to middle-latitude X-ray emission does not show any oscillations similar to the approx. 45 min oscillations sometimes seen from the northern auroral zone. The temporal variation in Jupiter's nonauroral X-ray emission exhibits similarities to variations in solar X-ray flux observed by GOES and TIMED/SEE. The two ACIS-S 0.3-2.0 keV low- to middle-latitude X-ray spectra are harder than the auroral spectrum and are different from each other at energies above 0.7 keV, showing variability in Jupiter's nonauroral X-ray emission on a timescale of a day. The 0.3-2.0 keV X-ray power emitted at low to middle latitudes is 0.21 GW and 0.39 GW for the first and second ACIS-S exposures, respectively. We suggest that X-ray emission from Jupiter's disk may be largely generated by the scattering and fluorescence of solar X rays in its upper atmosphere, especially at times of high incident solar X-ray flux. However, the dependence of count rate on surface magnetic-field strength may indicate the presence of some secondary component, possibly ion precipitation from radiation belts close to the planet.
Northern auroral regions of Earth were imaged with energetic photons in the 0.1–10
keV range using the High-Resolution Camera (HRC-I) aboard the Chandra X-ray Observatory at 10 epochs (each
∼
20
min
...duration) between mid-December 2003 and mid-April 2004. These observations aimed at searching for Earth's soft (
<
2
keV
) X-ray aurora in a comparative study with Jupiter's X-ray aurora, where a pulsating X-ray “hot-spot” has been previously observed by Chandra. The first Chandra soft X-ray observations of Earth's aurora show that it is highly variable (intense arcs, multiple arcs, diffuse patches, at times absent). In at least one of the observations an isolated blob of emission is observed near the expected cusp location. A fortuitous overflight of DMSP satellite F13 provided SSJ/4 energetic particle measurements above a bright arc seen by Chandra on 24 January 2004, 20:01–20:22
UT. A model of the emissions expected strongly suggests that the observed soft X-ray signal is bremsstrahlung and characteristic K-shell line emissions of nitrogen and oxygen in the atmosphere produced by electrons.
Using the Advanced CCD Imaging Spectrometer (ACIS), the Chandra X-Ray Observatory observed the Saturnian system for one rotation of the planet ( similar to 37 ks) on 2004 January 20 and again on ...January 26-27. In this Letter we report the detection of X-ray emission from the rings of Saturn. The X-ray spectrum from the rings is dominated by emission in a narrow ( similar to 130 eV-wide) energy band centered on the atomic oxygen K alpha fluorescence line at 0.53 keV. The X-ray power emitted from the rings in the 0.49-0.62 keV band is 84 MW, which is about one-third of that emitted from Saturn's disk in the photon energy range 0.24-2.0 keV. Our analysis also finds a clear detection of X-ray emission from the rings in the 0.49-0.62 keV band in an earlier (2003 April 14-15) Chandra ACIS observation of Saturn. Fluorescent scattering of solar X-rays from oxygen atoms in the H sub(2)O icy ring material is the likely source mechanism for ring X-rays, consistent with the scenario of the solar photoproduction of a tenuous oxygen atmosphere and ionosphere over the rings recently discovered by Cassini.
In an effort to develop a Standard Reference Material (SRM™) for Seebeck coefficient, we have conducted a round-robin measurement survey of two candidate materials-undoped Bi2Te3 and Constantan (55 % ...Cu and 45 % Ni alloy). Measurements were performed in two rounds by twelve laboratories involved in active thermoelectric research using a number of different commercial and custom-built measurement systems and techniques. In this paper we report the detailed statistical analyses on the interlaboratory measurement results and the statistical methodology for analysis of irregularly sampled measurement curves in the interlaboratory study setting. Based on these results, we have selected Bi2Te3 as the prototype standard material. Once available, this SRM will be useful for future interlaboratory data comparison and instrument calibrations.
X-rays from solar system objects Bhardwaj, Anil; Elsner, Ronald F.; Randall Gladstone, G. ...
Planetary and space science,
06/2007, Letnik:
55, Številka:
9
Journal Article
Recenzirano
Odprti dostop
During the last few years our knowledge about the X-ray emission from bodies within the solar system has significantly improved. Several new solar system objects are now known to shine in X-rays at ...energies below 2
keV. Apart from the Sun, the known X-ray emitters now include planets (Venus, Earth, Mars, Jupiter, and Saturn), planetary satellites (Moon, Io, Europa, and Ganymede), all active comets, the Io plasma torus (IPT), the rings of Saturn, the coronae (exospheres) of Earth and Mars, and the heliosphere. The advent of higher-resolution X-ray spectroscopy with the Chandra and XMM-Newton X-ray observatories has been of great benefit in advancing the field of planetary X-ray astronomy. Progress in modeling X-ray emission, laboratory studies of X-ray production, and theoretical calculations of cross-sections, have all contributed to our understanding of processes that produce X-rays from the solar system bodies.
At Jupiter and Earth, both auroral and non-auroral disk X-ray emissions have been observed. X-rays have been detected from Saturn's disk, but no convincing evidence of an X-ray aurora has been observed. The first soft (0.1–2
keV) X-ray observation of Earth's aurora by Chandra shows that it is highly variable. The non-auroral X-ray emissions from Jupiter, Saturn, and Earth, those from the disk of Mars, Venus, and Moon, and from the rings of Saturn, are mainly produced by scattering of solar X-rays. The spectral characteristics of X-ray emission from comets, the heliosphere, the geocorona, and the Martian halo are quite similar, but they appear to be quite different from those of Jovian auroral X-rays. X-rays from the Galilean satellites and the IPT are mostly driven by impact of Jovian magnetospheric particles.
This paper reviews studies of the soft X-ray emission from the solar system bodies, excluding the Sun. Processes of production of solar system X-rays are discussed and an overview is provided of the main source mechanisms of X-ray production at each object. A brief account on recent development in the area of laboratory studies of X-ray production is also provided.
Recent XMM-Newton and Chandra observations have revealed that Jupiter's X-ray emission comprises both, thermal and non-thermal spectral components. While the emission from the low-latitude planetary ...disk has the properties of scattered solar X-rays, with a thermal spectrum and typical coronal emission lines, the auroral soft (≪ 2 keV) X-rays are thought to be produced by ion charge exchange; very recently, a higher energy auroral component has been revealed by XMM-Newton: this is attributed to energetic electron bremsstrahlung, is dominant above 2 keV, and is variable, displaying both thermal and non-thermal characteristics. The disk and soft X-ray auroral components are separated spectroscopically in the high resolution data provided by the XMM-Newton Reflection Grating Spectrometer. Our results on the morphology, dynamics and energetics of the aurorae support current models developed to explain Jupiter's complex magnetosphere.
Spectral characteristics ({lambda}{sub max}, {Delta}{nu}{sub 1/2}, {epsilon}) and association constants (K) of charge-transfer (CT) complexes of tetracyanoethylene (TCNE) with 89 hydrocarbon donors ...(D) including cycloalkanes, alkenes, alkynes, benzene, benzene-d{sub 6}, alkylbenzenes, styrenes, biphenyls, polyphenylalkenes and phenylalkynes in CH{sub 2}Cl{sub 2} are presented. New data and reevaluation of older published data indicate that many donor/TCNE systems contain significant concentrations of the D{sub 2}(TCNE) in addition to the predominant D(TCNE) species. The donor orbitals from which CT transitions originate are determined by the correlation of {lambda}{sub max} and {Delta}{nu}{sub 1/2} values of CT bands of the complexes with the ionization bands in the photoelectron spectra of the donor molecules. Positive relationships between both CT energies and thermodynamic stabilities of complexes with respect to the number and geometry of substituent alkyls are established for alkene-, alkyne-, and alkylbenzene-TCNE complexes. The K values of functionally similar complexes are related to the bulk and location of substituent alkyl groups which sterically affect the interaction of the donor molecule and TCNE. Stabilities and CT energies of complexes are correlated with intramolecular conjugative and inductive effects between functional groups, as well as geometric and structural factors that control the angular orientation of the groups to each other.
Low-to middle-latitude X-ray emission from Jupiter Bhardwaj, Anil; Elsner, Ronald F; Gladstone, GRandall ...
Journal of Geophysical Research. A. Space Physics,
11/2006, Letnik:
111, Številka:
A11
Journal Article
Recenzirano
The Chandra X-ray Observatory (CXO) observed Jupiter during the period 24-26 February 2003 for 640 hours (4 Jupiter rotations), using both the spectroscopy array of the Advanced CCD Imaging ...Spectrometer (ACIS-S) and the imaging array of the High-Resolution Camera (HRC-I). Two ACIS-S exposures, each 68.5 hours long, were separated by an HRC-I exposure of 620 hours. The low-to middle-latitude nonauroral disk X-ray emission is much more spatially uniform than the auroral emission. However, the low- to middle-latitude X-ray count rate shows a small but statistically significant hour angle dependence and depends on surface magnetic field strength. In addition, the X-ray spectra from regions corresponding to 3-5 gauss and 5-7 gauss surface fields show significant differences in the energy band 1.26-1.38 keV, perhaps partly due to line emission occurring in the 3-5 gauss region but not the 5-7 gauss region. A similar correlation of surface magnetic field strength with count rate is found for the 18 December 2000 HRC-I data, at a time when solar activity was high. The low-to middle-latitude disk X-ray count rate observed by the HRC-I in the February 2003 observation is about 50% of that observed in December 2000, roughly consistent with a decrease in the solar activity index (F10.7 cm flux) by a similar amount over the same time period. The low-to middle-latitude X-ray emission does not show any oscillations similar to the 645 min oscillations sometimes seen from the northern auroral zone. The temporal variation in Jupiter's nonauroral X-ray emission exhibits similarities to variations in solar X-ray flux observed by GOES and TIMED/SEE. The two ACIS-S 0.3-2.0 keV low-to middle-latitude X-ray spectra are harder than the auroral spectrum and are different from each other at energies above 0.7 keV, showing variability in Jupiter's nonauroral X-ray emission on a timescale of a day. The 0.3-2.0 keV X-ray power emitted at low to middle latitudes is 0.21 GW and 0.39 GW for the first and second ACIS-S exposures, respectively. We suggest that X-ray emission from Jupiter's disk may be largely generated by the scattering and fluorescence of solar X rays in its upper atmosphere, especially at times of high incident solar X-ray flux. However, the dependence of count rate on surface magnetic-field strength may indicate the presence of some secondary component, possibly ion precipitation from radiation belts close to the planet.
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