3,820 research outputs found
Ionospheric electron heating, optical emissions, and striations induced by powerful HF radio waves at high latitudes: Aspect angle dependence
No full textIn recent years, large electron temperature increases of 300% (3000 K above background) caused by powerful HF-radio wave injection have been observed during nighttime using the EISCAT incoherent scatter radar near Tromsø in northern Norway. In a case study we examine the spatial structure of the modified region. The electron heating is accompanied by ion heating of about 100 degrees and magnetic field-aligned measurements show ion outflows increasing with height up to 300 m s−1 at 582 km. The electron density decreases by up to 20%. When the radar antenna was scanned between three elevations from near field-aligned to vertical, the strongest heating effects were always obtained in the field-aligned position. When the HF-pump beam was scanned between the same three positions, the heating was still almost always strongest in the field-aligned direction. Simultaneous images of the 630 nm O(1D) line in the radio-induced aurora showed that the enhancement caused by the HF radio waves also remained localized near the field-aligned position. Coherent HF radar backscatter also appeared strongest when the pump beam was pointed field-aligned. These results are similar to some Langmuir turbulence phenomena which also show a strong preference for excitation by HF rays launched in the field-aligned direction. The correlation of the position of largest temperature enhancement with the position of the radio-induced aurora suggests that a common mechanism, upper-hybrid wave turbulence, is responsible for both effects. Why the strongest heating effects occur for HF rays directed along the magnetic field is still unclear, but self-focusing on field-aligned striations is a candidate mechanism, and possibly ionospheric tilts may be important
Financial analysis, asset allocation, and portfolio construction: Theory & practice
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On financial statements modelling and fundamental analysis
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reproduced or transmitted in any forms or by any means now known or later devised, or sorted
in a data base or retrieval system, without the prior written permission of HF Consulting. This material has been shared with permission from the author and HF Consulting
The mathematics of statistical modelling: Abstract to specific
No full textThis material is copyrighted and the author retains all rights. No part of this material may be
reproduced or transmitted in any forms or by any means now known or later devised, or sorted
in a data base or retrieval system, without the prior written permission of HF Consulting. This material has been shared with permission from the author and HF Consulting
DISSOCIATION-ENERGY AND PHOTOCHEMISTRY OF NO3
No full textThe photodissociation of NO3 was studied using the method of molecular beam photofragmentation translational spectroscopy. The existence of two photodissociation channels was confirmed under collision-free conditions. At excitation energies below D0(O-NO2) for internally cold NO3, we observe a large quantum yield (0.70 +/- 0.10 at 588 nm) for a concerted three-center rearrangement resulting in NO(2PI) + O2 (3SIGMA(g)-,1DELTA). The quantum yield for the NO + O2 channel decreased sharply at wavelengths shorter than 587 nm, falling to <0.01 at 583 nm, while the NO2 + O(3p) quantum yield increased to >0.99. On the basis of this wavelength dependence and the product translational energy distributions, we conclude that the wavelength threshold for NO3(0,0,0,0) --> NO2(0,0,0) + O(P-3(2)) is 587 +/- 3 nm, i.e. D0(O-NO2) = 48.69 +/- 0.25 kcal/mol. From the enthalpies of formation of O(P-3(2)) and NO2 (2A1), we calculate DELTAH(f)-degrees (NO3) = 18.87 +/- 0.33 kcal/mol at 0 K and DELTAH(f)-degrees (NO3) = 17.62 +/- 0.33 kcal/mol at 298 K. This is 2.23 kcal/mol higher than the most recent thermochemical value but is consistent with a value calculated indirectly using the most recent values for the electron affinity (EA) of NO3 and DELTAH(f)-degrees-(NO3-). From the wavelength dependence and translational energy distributions for NO3 --> NO + O2, the potential energy barrier for NO3(2A'2) --> NO(2PI) + O2 (2SIGMA(g)-) was found to be 47.3 +/- 0.8 kcal/mol
Coordinated optical and radar observations of ionospheric pumping for a frequency pass through the second electron gyroharmonic at HAARP
No full textOn 4 February 2005, the High-frequency Active Auroral Research Program (HAARP) facility was operated in O and X mode while pointing into the magnetic zenith to produce artificial optical emissions in the ionospheric F layer. The pump frequency was set to 2.85 MHz to ensure passing through the second electron gyroharmonic of the decaying ionosphere. Optical recordings at 557.7 and 630 nm were performed simultaneously with the side-viewing high frequency (HF) and colocated ultra high frequency (UHF) ionospheric radars. No X-mode effects were found. For O-mode pumping, when passing from below to above the second gyroharmonic frequency, the optical intensity shows a distinct increase when the plasma frequency passes through the second electron gyroharmonic, while the UHF backscatter changes from persistent to overshoot in character. The optical intensity decreases when pump wave reflection ceases, dropping to zero when upper-hybrid resonance ceases. The HF radar backscatter increases when the upper-hybrid resonance frequency passes from below to above the second gyroharmonic frequency. These observations are consistent with the coexistence of the parametric decay and thermal parametric instabilities above the second gyroharmonic. The combined optical and radar data provide evidence that up to three electron-acceleration mechanisms are acting, sometimes simultaneously, depending on the pump frequency relative to the second gyroharmonic. In addition, we provide the first evidence of lower-hybrid waves in HF radar centerline data and show that the parametric decay instability producing Langmuir waves can be stimulated in the magnetic zenith at high latitudes despite the pump wave not reaching the nominal frequency-matching height
The electron energy distribution during HF pumping, a picture painted with all colors
No full textInternational audienceThe shape of the electron energy distribution has long been a central question in the field of high-frequency radio-induced optical emission experiments. This report presents estimates of the electron energy distribution function, fe(E), from 0 to 60 eV, based on optical multi-wavelength (6300, 5577, 8446, 4278Å) data and 930-MHz incoherent scatter radar measurements of ion temperature, electron temperature and electron concentration. According to our estimate, the electron energy distribution has a depression at around 2 eV, probably caused by electron excitation of vibrational states in N2, and a high energy tail that is clearly supra-thermal. The temporal evolution of the emissions indicates that the electron temperature still plays an important role in providing electrons with energies close to 2 eV. At the higher energies the electron energy distribution has a non-thermal tail. Keywords. Active experiments; Ionosphere atmosphere interaction; Ionospheric physic
Terminal suturing of Gondwana along the southern margin of South China Craton : evidence from detrital zircon U-Pb ages and Hf isotopes in Cambrian and Ordovician strata, Hainan Island
No full textThis work was supported by the National Natural Science Foundation of China (grants 41472086 and 41272120), “111” Project (B08030), the fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan) (CUG2012019240 and CUG2013019137). The first author also acknowledges China Scholarship Council (grant 201208420001) for supporting his research in the University of St. Andrews. Date of Acceptance: 20/11/2014Hainan Island, located near the southern end of mainland South China, consists of the Qiongzhong Block to the north and the Sanya Block to the south. In the Cambrian, these blocks were separated by an intervening ocean. U-Pb ages and Hf isotope compositions of detrital zircons from the Cambrian succession in the Sanya Block suggest that the unit contains detritus derived from late Paleoproterozoic and Mesoproterozoic units along the western margin of the West Australia Craton (e.g., Northampton Complex) or the Albany-Fraser-Wilkes orogen, which separates the West Australia and Mawson cratons. Thus, in the Cambrian the Sanya Block was not part of the South China Craton but rather part of the West Australian Craton and its environs. In contrast, overlying Late Ordovician strata display evidence for input of detritus from the Qiongzhong Block, which constituted part of the southeastern convergent plate margin of the South China Craton in the early Paleozoic. The evolving provenance record of the Cambrian and Ordovician strata suggests that the juxtaposition of South China and West Australian cratons occurred during the early to mid-Ordovician. The event was linked with the northern continuation of Kuungan Orogeny, with South China providing a record of final assembly of Gondwana.Peer reviewe
Temporal evolution of pump beam self-focusing at the High-Frequency Active Auroral Research Program
No full textOn 4 February 2005 the High-Frequency Active Auroral Research Program (HAARP) facility was operated at 2.85 MHz to produce artificial optical emissions in the ionosphere while passing through the second electron gyroharmonic. All-sky optical recordings were performed with 15 s integration, alternating between 557.7 and 630 nm. We report the first optical observations showing the temporal evolution of large-scale pump wave self-focusing in the magnetic zenith, observed in the 557.7 nm images. These clearly show that the maximum intensity was not reached after 15 s of pumping, which is unexpected since the emission delay time is <1 s, and that the optical signature had intensified in a much smaller region within the beam after 45 s of pumping. In addition, adjacent regions within the beam lost intensity. Radar measurements indicate a plasma depletion of ∼1% near the HF reflection altitude. Ray tracing of the pump wave through the plasma depletion region, which forms a concave reflecting radio wave mirror, reproduces the optical spatial morphology. A radio wave flux density gain of up to ∼30 dB may occur. In addition, the ray trace is consistent with the observed artificial optical emissions for critical plasma frequencies down to ∼0.5 MHz below the pump frequency
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