Disturbances of electron density in the high latitude upper (F-region) ionosphere induced by X-mode HF pump waves from EISCAT UHF radar observations

The paper presents experimental results concerning disturbances of electron density in the high latitude ionosphere F-region, induced by powerfulHF radio waves (pump waves) with extraordinary (X-mode) polarization. The experiments were carried out at the EISCAT/Heating facility at Tromsø, Norway. The EISCAT UHF incoherent scatter radar (ISR), running at 930 MHz, co-located with a heating facility, was used to detect the disturbances of electron density. In the course of the experiments, the X-mode HF pump waves radiated into the F-region towards the magnetic zenith at different pump frequencies and ratios of the pump frequency to the critical frequency of the F2 layer.The effective radiated power was ERP = 360–820 MW. An increase in electron densities was found in a wide altitude range, giving rise to field-aligned ducts with enhanced electron density. The features and behavior of the ducts were investigated. It was revealed that the ducts are formed under quiet background geophysical conditions in a wide altitude range up to the upper altitude limit of EISCAT ISR measurements, when the pump frequencies were both below and above the critical frequency of the F2 layer (fH ≤ foF2 or fH > foF2). A plausible formation mechanism of the ducts is discussed.Представлены результаты экспериментальных исследований возмущений электронной концентрацииNe в высокоширотной F-области ионосферы, вызванные воздействием мощных КВ-радиоволн необыкновенной (Х-мода) поляризации. Эксперименты выполнялись на КВ нагревном стенде EISCAT/ Heating в г. Тромсё, Норвегия при эффективной мощности излучения 360–820 МВт. В качестве средства диагностики возмущений Ne использовался EISCAT радар некогерентного рассеяния радиоволн (НР) на частоте 930 МГц, пространственно совмещенный с КВ нагревным стендом. Обнаружено возрастание Ne в широком диапазоне высот, которое формирует каналы повышенной электронной плотности, вытянутые вдоль магнитного поля Земли. Исследованы характеристики и условия создания каналов. Обсуждается возможный механизм формирования каналов Ne при Х-нагреве высокоширотной F-области ионосферы

Optical and Ionospheric Phenomena at EISCAT under continuous X-mode HF pumping

We present experimental results from multiinstrument observations in the high-latitude ionospheric F2 layer at the EISCAT (European Incoherent Scatter Scientific Association) heating facility. The results come from a set of experiments, when an X-polarized HF pump wave at high heater frequencies (fH > 6.0 MHz) was injected into the F region of the ionosphere toward the magnetic zenith. Experiments were carried out under quiet magnetic conditions with an effective radiated power of 458–548 MW. HF pumping was produced at different heater frequencies, away from electron gyroharmonic frequencies, and different durations of heater pulses. We show the first experimental evidence of the excitation of artificial optical emissions at red (630 nm) and green (557.7 nm) lines in the high-latitude ionospheric F2 layer induced by an X-polarized HF pump wave. Intensities at red and green lines varied in the range 110–950 R and 50–350 R, respectively, with a ratio of green to red line of 0.35–0.5. The results of optical observations are compared with behaviors of the HF-enhanced ion and plasma lines from EISCAT UHF incoherent scatter radar data and small-scale field-aligned artificial irregularities from Cooperative UK Twin Located Auroral Sounding System observations. It was found that the X-mode radio-induced optical emissions coexisted with HF-enhanced ion and plasma lines and strong artificial field-aligned irregularities throughout the whole heater pulse. It is indicative that parametric decay or oscillating two-stream instabilities were not quenched by fully established small-scale field-aligned artificial irregularities excited by an X-mode HF pump wave

Phenomena induced by powerful HF pumping towards magnetic zenith with a frequency near the F-region critical frequency and the third electron gyro harmonic frequency

Multi-instrument observational data from an experiment on 13 October 2006 at the EISCAT/HEATING facility at Tromsø, Norway are analysed. The experiment was carried out in the evening hours when the electron density in the F-region dropped, and the HF pump frequency <I>f<sub>H</sub></I> was near and then above the critical frequency of the F2 layer. The distinctive feature of this experiment is that the pump frequency was just below the third electron gyro harmonic frequency, while both the HF pump beam and UHF radar beam were directed towards the magnetic zenith (MZ). The HF pump-induced phenomena were diagnosed with several instruments: the bi-static HF radio scatter on the London-Tromsø-St. Petersburg path, the CUTLASS radar in Hankasalmi (Finland), the European Incoherent Scatter (EISCAT) UHF radar at Tromsø and the Tromsø ionosonde (dynasonde). The results show thermal electron excitation of the HF-induced striations seen simultaneously from HF bi-static scatter and CUTLASS radar observations, accompanied by increases of electron temperature when the heater frequency was near and then above the critical frequency of the F2 layer by up to 0.4 MHz. An increase of the electron density up to 25% accompanied by strong HF-induced electron heating was observed, only when the heater frequency was near the critical frequency and just below the third electron gyro harmonic frequency. It is concluded that the combined effect of upper hybrid resonance and gyro resonance at the same altitude gives rise to strong electron heating, the excitation of striations, HF ray trapping and extension of HF waves to altitudes where they can excite Langmuir turbulence and fluxes of electrons accelerated to energies that produce ionization

Прогнозирование условий распространения декаметровых радиоволн в арктическом регионе

In this paper we present the results of studies the distinctive features of the decameter radio wave propagation based on the results of experimental measurements of radio wave propagation characteristics by the ionospheric oblique sounding (IOS) method and numerical simulation. An algorithm for numerical modeling the trajectory and energetic characteristics of the decameter radio wave propagation in the framework of geometric optics is described. The agreement between the simulated and experimental radio propagation parameters (for example, the values of the maximum observed frequencies) is demonstrated. It is proposed to use the developed diagnostic model of the HF radio channel for the purposes of forecasting in areas not provided with IOS stations.Представлены результаты исследований закономерностей ионосферного распространения декаметровых радиоволн, основанных на результатах экспериментальных измерений характеристик распространения радиоволн методом наклонного зондирования ионосферы (НЗИ) и данных численного моделирования. Описан алгоритм численного моделирования траекторных и энергетических характеристик процессов распространения декаметровых радиоволн в рамках метода геометрической оптики. Продемонстрировано соответствие рассчитанных по модели разработанного КВ-радиоканала и измеренных экспериментально параметров распространения радиосигнала (например, значений максимально наблюдаемых частот). Предлагается использовать разработанную диагностическую модель КВ-радиоканала для целей прогнозирования в высокоширотных районах, не обеспеченных станциями НЗИ

SIV Nef Proteins Recruit the AP-2 Complex to Antagonize Tetherin and Facilitate Virion Release

Lentiviral Nef proteins have multiple functions and are important for viral pathogenesis. Recently, Nef proteins from many simian immunodefiency viruses were shown to antagonize a cellular antiviral protein, named Tetherin, that blocks release of viral particles from the cell surface. However, the mechanism by which Nef antagonizes Tetherin is unknown. Here, using related Nef proteins that differ in their ability to antagonize Tetherin, we identify three amino-acids in the C-terminal domain of Nef that are critical specifically for its ability to antagonize Tetherin. Additionally, divergent Nef proteins bind to the AP-2 clathrin adaptor complex, and we show that residues important for this interaction are required for Tetherin antagonism, downregulation of Tetherin from the cell surface and removal of Tetherin from sites of particle assembly. Accordingly, depletion of AP-2 using RNA interference impairs the ability of Nef to antagonize Tetherin, demonstrating that AP-2 recruitment is required for Nef proteins to counteract this antiviral protein

Сравнение характеристик явлений в F-области высокоширотной ионосферы при излучении мощных КВ радиоволн антеннами с узкой и широкой диаграммой направленности

Physical experiments in natural free plasma (ionosphere) using controlled injection of powerful HF radio waves (HF pump waves) into the high latitude upper (F-region) ionosphere allow the investigation of various nonlinear phenomena. HF pump waves with ordinary (O-mode) polarization are commonly used for the modification of the upper ionosphere (F-region). This is due to the fact that extraordinary (X-mode) polarized HF pump waves are reflected from altitudes significantly below the reflection altitude of the O-polarized HF pump wave and the altitude of electrostatic plasma waves. Because of that they are not able to generate such waves or, as a consequence, cause artificial plasma turbulence and accompanying phenomena. However, the results of experiments carried out by AARI researchers at the EISCAT/Heating facility (Tromsø, Norway) have clearly demonstrated for the first time that X-polarized HF pump waves are able to produce artificial ionosphere disturbances which may be much stronger compared with O-mode disturbances. This opens up new possibilities for the investigation of nonlinear phenomena and ionospheric disturbances in the upper ionosphere, leading to the development of technologies allowing one to observe the processes in the Arctic zone ionosphere. In contrast to the traditional investigations of artificial ionospheric disturbances induced by O-mode HF pump waves, X-mode disturbances in the upper ionosphere are poorly investigated, the mechanisms of their generation are not understood. Therefore, such investigations require serious experimental and theoretical development. We present investigation results of the influence of the HF Phased Array beam width at the EISCAT/Heating facility (Tromsø, Norway) on the features of artificial disturbances in the high latitude upper (F-region) ionosphere induced by powerful HF radio waves. The paper analyzes the features, behavior, and spatial structure of electron density and temperature (Ne and Te), Langmuir and ion-acoustic plasma waves, artificial field-aligned irregularities (AFAIs), and narrowband (±1кHz relative to heating frequency) stimulated electromagnetic emission (NSEE) induced by X-mode HF pumping by phased Arrays with a narrow beam width of 5–6° (A1) and a wide beam width of 10–12° (at — 3 dB level) (A3). It is shown that the spatial size in the north-south direction of the Neducts and HF-enhanced plasma and ion lines (HFPL and HFIL) depends on the width of the HF Heating facility antenna beam. It corresponds to the angle width of 7° for the A3 antenna and 4° for A1, which is approximately two times less than the width of th pattern of A3 and A1. The relationship between the Ne duct transverse size and the size of the region occupied by the X-mode artificial irregularities is found. It has been established that the intensities of all the discrete components in the NSEE spectra are 10–20 dB higher when a powerful X-wave is emitted to the antenna A1, providing ERP = 820 MW, compared to radiation to the antenna A3, providing ERP = 230 MW. A comparison is made of the influence of the radiation pattern width of the antennas A1 and A3 on the characteristics of disturbances during O- and X-mode HF pumping. It is shown that Ne ducts and narrow band stimulated electromagnetic emission during O-mode heating, at frequencies below the critical frequency of the F2 layer, are not excited at all when the pump wave is emitted by both antennas A1 and A3. However, perturbations in the electron temperature, AFAI intensity, and the size of the region occupied by AFAIs are greater during O-mode heating than during X-mode heating.Выполнено сравнение характеристик искусственных ионосферных возмущений в F-области высокоширотной ионосферы при излучении мощных коротких радиоволн нагревного стенда EISCAT/ Heating (г. Тромсё, Норвегия) фазированными антенными решетками (ФАР) с узкой (5–6°) и широкой (10–12°) диаграммами направленности (антенны А1 и А3 соответственно). Рассмотрены характеристики, поведение и пространственная структура электронной концентрации и температуры, продольных плазменных волн (ленгмюровских и ионно-акустических), мелкомасштабных искусственных магнито-ориентированных неоднородностей и искусственного узкополосного (в полосе ±1 кГц относительно частоты нагрева) радиоизлучения ионосферы, вызванных воздействием мощных КВ радиоволн необыкновенной (Х-мода) и обыкновенной (О-мода) поляризаций при их излучении антеннами А1 и А3 в направлении магнитного зенита

HIV-1 Nef Employs Two Distinct Mechanisms to Modulate Lck Subcellular Localization and TCR Induced Actin Remodeling

The Nef protein acts as critical factor during HIV pathogenesis by increasing HIV replication in vivo via the modulation of host cell vesicle transport and signal transduction processes. Recent studies suggested that Nef alters formation and function of immunological synapses (IS), thereby modulating exogenous T-cell receptor (TCR) stimulation to balance between partial T cell activation required for HIV-1 spread and prevention of activation induced cell death. Alterations of IS function by Nef include interference with cell spreading and actin polymerization upon TCR engagement, a pronounced intracellular accumulation of the Src kinase Lck and its reduced IS recruitment. Here we use a combination of Nef mutagenesis and pharmacological inhibition to analyze the relative contribution of these effects to Nef mediated alterations of IS organization and function on TCR stimulatory surfaces. Inhibition of actin polymerization and IS recruitment of Lck were governed by identical Nef determinants and correlated well with Nef's association with Pak2 kinase activity. In contrast, Nef mediated Lck endosomal accumulation was separable from these effects, occurred independently of Pak2, required integrity of the microtubule rather than the actin filament system and thus represents a distinct Nef activity. Finally, reduction of TCR signal transmission by Nef was linked to altered actin remodeling and Lck IS recruitment but did not require endosomal Lck rerouting. Thus, Nef affects IS function via multiple independent mechanisms to optimize virus replication in the infected host

HIV-1 Nef Induces Proinflammatory State in Macrophages through Its Acidic Cluster Domain: Involvement of TNF Alpha Receptor Associated Factor 2

Background: HIV-1 Nef is a virulence factor that plays multiple roles during HIV replication. Recently, it has been described that Nef intersects the CD40 signalling in macrophages, leading to modification in the pattern of secreted factors that appear able to recruit, activate and render T lymphocytes susceptible to HIV infection. The engagement of CD40 by CD40L induces the activation of different signalling cascades that require the recruitment of specific tumor necrosis factor receptor-associated factors (i.e. TRAFs). We hypothesized that TRAFs might be involved in the rapid activation of NF-kappa B, MAPKs and IRF-3 that were previously described in Nef-treated macrophages to induce the synthesis and secretion of proinflammatory cytokines, chemokines and IFN beta to activate STAT1, -2 and -3. Methodology/Principal Findings: Searching for possible TRAF binding sites on Nef, we found a TRAF2 consensus binding site in the AQEEEE sequence encompassing the conserved four-glutamate acidic cluster. Here we show that all the signalling effects we observed in Nef treated macrophages depend on the integrity of the acidic cluster. In addition, Nef was able to interact in vitro with TRAF2, but not TRAF6, and this interaction involved the acidic cluster. Finally silencing experiments in THP-1 monocytic cells indicate that both TRAF2 and, surprisingly, TRAF6 are required for the Nef-induced tyrosine phosphorylation of STAT1 and STAT2. Conclusions: Results reported here revealed TRAF2 as a new possible cellular interactor of Nef and highlighted that in monocytes/macrophages this viral protein is able to manipulate both the TRAF/NF-kappa B and TRAF/IRF-3 signalling axes, thereby inducing the synthesis of proinflammatory cytokines and chemokines as well as IFN beta