EPR and ENDOR of the PO 4 2− radical in anhydrite,celestite and barite

Electron paramagnetic resonance (EPR) and eletron nuclear double resonance (ENDOR) low temperature measurements of natural anhydrite CaSO₄, celestite SrSO₄ and barite BaSO₄ have revealed the presence of PO ₄ ^2– radical. The principal values of the g tensor and the A tensor [MHz] of hyperfine interaction (HFI) are found to be g _xx =2.0124, g _yy =2.0159, g _zz =2.0098, A _xx =82.1, A _yy =81.4, A _zz =77.2 in CaSO4, g _xx =2.0250, g _yy =2.0070, g _zz =2.0131, A _xx =84.8, A _yy =82.7, A _zz = 90.5 in SrSO₄, g _xx =2.0302, g _yy =2.0079, g _zz =2.0135, A _xx =85.2, A _yy =82.3, A _zz =90.0 in BaSO₄. The principal axes A _xx , A _yy and A _zz are parallel to the crystallographic axes a, b, c in all three matrices. In anhydrite the principal g axes coincide with the A axes. In celestite and barite such coincidence is found to be only along the b axis (a low symmetry effect). The coherence effect of splitting of ENDOR lines by a strong microwave field has been detected. From the analysis of the relative intensities of the ENDOR lines of the PO ₄ ^2– radical in CaSO₄ the relation of probabilities of cross-relaxation processes W _x/W _xx =3.5 are evaluated.     

超高压变质作用不同阶段的流体变化：碧溪岭榴辉岩的氢、硼同位素分析

大别山碧溪岭榴辉岩中有三种含水矿物:多硅白云母、角闪石和黑云母,它们分别是超高压(UHP)阶段(即柯石英榴辉岩相阶段)或者石英榴辉岩相阶段、退变质后成合晶阶段和角闪岩相退变质阶段的产物,本文利用离子探针技术对它们进行了氢同位素和硼同位素的分析。三种矿物内部的同位素组成都是均一的,多硅白云母的δD为-105‰±9‰,δ~(11)B为-25.9‰±2.0‰;角闪石的δD为-100‰±9‰,δ~(11)B为-24.4‰±0.9‰;黑云母的δD为-65‰±4‰,δ~(11)B为-19.3‰±1.3‰。多硅白云母和角闪石的氢-硼同位素组成在误差范围内是相同的,而和黑云母则有明显的差别,这表明,从UHP阶段或者石英榴辉岩相阶段到随后的后成合晶阶段,变质流体是内部缓冲的,而在角闪岩相变质阶段,则有了外来流体的加入,这个流体是相对富集D和~(11)B的。碧溪岭榴辉岩矿物相对于其地壳原岩表现出低δ~(11)B的特征,说明俯冲过程中板块经历了强烈的脱硼。     

The interpretation of non-linear radio spectra of discrete radio sources by a general mechanism

The analysis of discrete radio sources spectra in the range 10–5000 MHz reveals that deviations from a power law in the low-frequency region may be due to distortion of differential energy spectra of relativistic electrons at low energies. An empirical expression for an energy-spectrum law was found to be in a good agreement with most of the radio spectra measured. The main physical parameters of 92 sources are evaluated. It is concluded that a low-energy electron excess exists with respect to the lawE ^– in most of the discrete sources which radiate non-linear low-frequency spectra.The forms of radio and energy spectra are further considered in a logarithmic scale.     

The spectra of some discrete radio sources in 10–5000 MHz frequency range

On the basis of the absolute measurements in the 12.6–25 MHz frequency range and the relative measurements at frequencies 750, 1400, 2695 and 5000 MHz (NRAO) and 408, 1410 and 2650 MHz (Parkes), 57 standard spectra were obtained which are linear (on a log-log scale) in the range 12.6–5000 MHz. The comparison of the flux densities presented in the surveys at 10.03, 22.25, 26.3, 38, 86 and 178 MHz and the standard spectra was carried out and thus the correction coefficient was calculated. It was shown that the scale of absolute fluxes CKL on the frequencies 38 and 178 MHz is lowered on 28% and 8% respectively. The possible sources of divergences of the results of measurements in decametric wavelength is discussed. Making use of the corrected data at 38 MHz and 178 MHz, of the results at higher frequencies mentioned above and of the original results of measurements in the 12.6–25 MHz range, the spectra of 55 discrete sources were constructed. The spectra of 149 sources are also obtained on the basis of the surveys at 10.03, 22.25, 26.3, 38 and 178 MHz corrected according to standard spectra.     

Properties of the Variability of the Solar Constant as an Index of Solar Activity

Geomagnetism and Aeronomy - The properties of the solar constant variability are considered according to the results of satellite observations ( http://lasp.colorado.edu/home/sorce/data/tsi-data/...     

EPR study of chromium-doped forsterite crystals: Cr<Superscript>3+</Superscript>(<Emphasis Type="Italic">M</Emphasis>1) with and without associated nearest-neighbor Mg<Superscript>2+</Superscript>(<Emphasis Type="Italic">M</Emphasis>2) vacancy

Electron paramagnetic resonance (EPR) study of single crystals of chromium-doped forsterite grown by the Czochralski method in two different research laboratories has revealed, apart from the known paramagnetic centers Cr³⁺(M1), Cr³⁺(M2) and Cr⁴⁺, a new center \textCr ³⁺ (M 1)-V_{\textMg ²⁺} (M 2) {\text{Cr}}^{ 3+ } (M 1){-}V_{{{\text{Mg}}^{ 2+ } }} (M 2) formed by a Cr³⁺ ion substituting for Mg²⁺ at the M1 structural position with a nearest-neighbor Mg²⁺ vacancy at the M2 position. For this center, the conventional zero-field splitting parameters D and E and the principal g values and A values of the ⁵³Cr hyperfine splitting have been determined as follows: D = 33.95(3) GHz, E = 8.64(1) GHz, g = [1.9811(2), 1.9787(2), 1.9742(2)], A = [51(3), 52(2), 44(3)] MHz. The center has been identified by comparing EPR spectra with those of the charge-uncompensated ion Cr³⁺(M1) and the ion pair Cr³⁺(M1)–Li⁺(M2) observed in forsterite crystals codoped with chromium and lithium. It has been found that the concentration of the new center decreases to zero, whereas that of the Cr³⁺(M1) and Cr³⁺(M1)–Li⁺(M2) centers increases with an increase of the Li content from 0 up to ~0.03 wt% (at the same Cr content ~0.07 wt%) in the melt. The known low-temperature luminescence data pertinent to the centers under consideration are also discussed.     

Magnetically-Driven Planetary Radio Emissions and Application to Extrasolar Planets

At least six intense nonthermal planetary radio emissions are known in our solar system: the auroral radio emissions from the Earth, Jupiter, Saturn, Uranus and Neptune, and the radio bursts from the Io-Jupiter flux tube. The former are thought to be driven by the solar wind flow pressure or energy flux on the magnetospheric cross-section, while the latter is a consequence of the Io-Jupiter electrodynamic interaction. Although in the solar wind, the flow ram pressure largely dominates the magnetic one, we suggest that the incident magnetic energy flux is the driving factor for all these six radio emissions, and that it can be estimated in the same way in all cases. Consequences for the possible radio emission from extrasolar planets are examined. ‘Hot Jupiters’, if they are magnetized, might possess a radio emission several orders of magnitude stronger than the Jovian one, detectable with large ground-based low-frequency arrays. On the other hand, `giants' analogous to the Io-Jupiter interaction in the form of a pair star/hot-Jupiter are unlikely to produce intense radio emissions, unless the star is very strongly magnetized. This revised version was published online in July 2006 with corrections to the Cover Date.     

Electric potential jumps in the Io-Jupiter flux tube

The Io flux tube (IFT), along which Io interacts with the Jovian magnetosphere, is the place of plasma acceleration processes resulting in auroral like emissions, in UV, IR and Radio emissions in the decameter range. At Earth, the study of the acceleration processes is mainly made by in situ measurements. Acceleration processes at Jupiter were first deduced from the observation of a particular kind of decameter radio emissions from the IFT: the short (S-)bursts. These radio bursts present a negative drift in the time-frequency domain, which is related to the motion of the energetic electrons which produce them. The measure of their drift thus permits the kinetic energy of the electrons to be obtained, as well as its variations along the IFT which have been interpreted as electric potential jumps. Using an enhanced S-burst detection and drift measurement method, more than 1 h of quasi-continuous decametric emissions recorded at the Kharkov UTR-2 radiotelescope have been analyzed. We observe the evolution of the electron kinetic energy with the longitude of Io with a resolution of , and detect the presence of acceleration structures with characteristics being consistent with electric potential jumps of few hundred volts, and moving along the IFT in the upward direction (toward Io) at the local sound velocity.     

The three-dimensional structure of the corona above active region NOAA 9591 from microwave observations

We study the active region NOAA 9591 using observations at 1.92–10.17 cm obtained on two large Russian radio instruments: the RATAN-600 radio telescope and the Siberian Solar Radio Telescope. The active region was associated with an isolated spot at the photospheric level, whose magnetic field had a well-defined Delta configuration. The radio observations show that the structure of the coronal source located above the spot cannot be described in a simple (unipolar) cyclotron model. A comparison with X-ray observations indicates that the three-dimensional structure of the corona above the spot can be represented as a strongly elongated loop whose apex resembles a cusp brightening (a qualitative model for the structure is presented). Unexpectedly, radiation with a high degree of polarization (～25%) was detected far (～100 000 km) from the photosphere. The need for a quantitative model for coronal sources above the strong Delta-configuration magnetic fields, which are known to play an important role in active solar processes (flares, phenomena such as coronal-mass ejections) is outlined. Thanks to its simple morphology, which enabled the identification of a pure Delta configuration, the active region NOAA 9591 provides high-quality observational material for the creation of such a model.