Generating energetic electron generation through staged-acceleration in the two-plasmon-decay instability in inertial confinement fusion

A new hot-electron generation mechanism in two-plasmon-decay instabilities is described based on a series of 2D, long-term ( 10 ps) particle-in-cell and fluid simulations under parameters relevant to inertial confinement fusion. The simulations show that significant laser absorption and hot-electron generation occur in the nonlinear stage. The hot electrons are stage accelerated from the low-density region to the high-density region. New modes with small phase velocities develop in the low-density region in the nonlinear stage and form the first stage for electron acceleration. Electron-ion collisions are shown to significantly reduce the efficiency of this acceleration mechanis

Net ecosystem exchange of carbon dioxide and water of far eastern Siberian Larch (Larix cajanderii) on permafrost.

Observations of the net ecosystem exchange of water and CO₂ were made during two seasons in 2000 and 2001 above a Larch forest in Far East Siberia (Yakutsk). The measurements were obtained by eddy correlation. There is a very sharply pronounced growing season of 100 days when the forest is leaved. Maximum half hourly uptake rates are 18 &micro;mol m^-2 s^-1; maximum respiration rates are 5 &micro;mol m^-2 s^-1. Net annual sequestration of carbon was estimated at 160 gCm^-2 in 2001. Applying no correction for low friction velocities added 60 g C m^-2. The net carbon exchange of the forest was extremely sensitive to small changes in weather that may switch the forest easily from a sink to a source, even in summer. June was the month with highest uptake in 2001. <P style='line-height: 20px;'> The average evaporation rate of the forest approached 1.46 mm day^-1 during the growing season, with peak values of 3 mm day^-1 with an estimated annual evaporation of 213 mm, closely approaching the average annual rainfall amount. 2001 was a drier year than 2000 and this is reflected in lower evaporation rates in 2001 than in 2000. <P style='line-height: 20px;'> The surface conductance of the forest shows a marked response to increasing atmospheric humidity deficits. This affects the CO₂ uptake and evaporation in a different manner, with the CO₂ uptake being more affected. There appears to be no change in the relation between surface conductance and net ecosystem uptake normalized by the atmospheric humidity deficit at the monthly time scale. The response to atmospheric humidity deficit is an efficient mechanism to prevent severe water loss during the short intense growing season. The associated cost to the sequestration of carbon may be another explanation for the slow growth of these forests in this environment

Longer growing seasons do not increase net carbon uptake in Northeastern Siberian tundra

With global warming, snowmelt is occurring earlier and growing seasons are becoming longer around the Arctic. It has been suggested that this would lead to more uptake of carbon due to a lengthening of the period in which plants photosynthesize. To investigate this suggestion, 8 consecutive years of eddy covariance measurements at a northeastern Siberian graminoid tundra site were investigated for patterns in net ecosystem exchange, gross primary production (GPP) and ecosystem respiration (Reco). While GPP showed no clear increase with longer growing seasons, it was significantly increased in warmer summers. Due to these warmer temperatures however, the increase in uptake was mostly offset by an increase in Reco. Therefore, overall variability in net carbon uptake was low, and no relationship with growing season length was found. Furthermore, the highest net uptake of carbon occurred with the shortest and the coldest growing season. Low uptake of carbon mostly occurred with longer or warmer growing seasons. We thus conclude that the net carbon uptake of this ecosystem is more likely to decrease rather than to increase under a warmer climate. These results contradict previous research that has showed more net carbon uptake with longer growing seasons. We hypothesize that this difference is due to site-specific differences, such as climate type and soil, and that changes in the carbon cycle with longer growing seasons will not be uniform around the Arcti

The growing season greenhouse gas balance of a continental tundra site in the Indigirka lowlands, NE Siberia.

Carbon dioxide and methane fluxes were measured at a tundra site near Chokurdakh, in the lowlands of the Indigirka river in north-east Siberia. This site is one of the few stations on Russian tundra and it is different from most other tundra flux stations in its continentality. A suite of methods was applied to determine the fluxes of NEE, GPP, &lt;i&gt;R&lt;/i&gt;&lt;sub&gt;eco&lt;/sub&gt; and methane, including eddy covariance, chambers and leaf cuvettes. Net carbon dioxide fluxes were high compared with other tundra sites, with NEE=&amp;minus;92 g C m&lt;sup&gt;&amp;minus;2&lt;/sup&gt; yr&lt;sup&gt;&amp;minus;1&lt;/sup&gt;, which is composed of an &lt;i&gt;R&lt;/i&gt;&lt;sub&gt;eco&lt;/sub&gt;=+141 g C m&lt;sup&gt;&amp;minus;2&lt;/sup&gt; yr&lt;sup&gt;&amp;minus;1&lt;/sup&gt; and GPP=&amp;minus;232 g C m&lt;sup&gt;&amp;minus;2&lt;/sup&gt; yr&lt;sup&gt;&amp;minus;1&lt;/sup&gt;. This large carbon dioxide sink may be explained by the continental climate, that is reflected in low winter soil temperatures (&amp;minus;14&amp;deg;C), reducing the respiration rates, and short, relatively warm summers, stimulating high photosynthesis rates. Interannual variability in GPP was dominated by the frequency of light limitation (&lt;i&gt;R&lt;sub&gt;g&lt;/sub&gt;&lt;/i&gt;&amp;lt;200 W m&lt;sup&gt;&amp;minus;2&lt;/sup&gt;), whereas &lt;i&gt;R&lt;/i&gt;&lt;sub&gt;eco&lt;/sub&gt; depends most directly on soil temperature and time in the growing season, which serves as a proxy of the combined effects of active layer depth, leaf area index, soil moisture and substrate availability. The methane flux, in units of global warming potential, was +28 g C-CO&lt;sub&gt;2&lt;/sub&gt;e m&lt;sup&gt;&amp;minus;2&lt;/sup&gt; yr&lt;sup&gt;&amp;minus;1&lt;/sup&gt;, so that the greenhouse gas balance was &amp;minus;64 g C-CO&lt;sub&gt;2&lt;/sub&gt;e m&lt;sup&gt;&amp;minus;2&lt;/sup&gt; yr&lt;sup&gt;&amp;minus;1&lt;/sup&gt;. Methane fluxes depended only slightly on soil temperature and were highly sensitive to hydrological conditions and vegetation composition

Gluon polarization in the nucleon from quasi-real photoproduction of high-pT hadron pairs

We present a determination of the gluon polarization Delta G/G in the nucleon, based on the helicity asymmetry of quasi-real photoproduction events, Q^2<1(GeV/c)^2, with a pair of large transverse-momentum hadrons in the final state. The data were obtained by the COMPASS experiment at CERN using a 160 GeV polarized muon beam scattered on a polarized 6-LiD target. The helicity asymmetry for the selected events is = 0.002 +- 0.019(stat.) +- 0.003(syst.). From this value, we obtain in a leading-order QCD analysis Delta G/G=0.024 +- 0.089(stat.) +- 0.057(syst.) at x_g = 0.095 and mu^2 =~ 3 (GeV}/c)^2.Comment: 10 pages, 3 figure

Measurement of the Spin Structure of the Deuteron in the DIS Region

We present a new measurement of the longitudinal spin asymmetry A_1^d and the spin-dependent structure function g_1^d of the deuteron in the range 1 GeV^2 < Q^2 < 100 GeV^2 and 0.004< x <0.7. The data were obtained by the COMPASS experiment at CERN using a 160 GeV polarised muon beam and a large polarised 6-LiD target. The results are in agreement with those from previous experiments and improve considerably the statistical accuracy in the region 0.004 < x < 0.03.Comment: 10 pages, 6 figures, subm. to PLB, revised: author list, Fig. 4, details adde

Electron accelerator for energy up to 5.0 MeV and beam power up to 50 kW with Х-ray converter

The paper describes the industrial electron accelerator ILU-10 for electron energy up to 5 MeV and beam power up to 50 kW specially designed for use in industrial applications. The ILU-10 accelerator generates the vertical electron beam. The beam line turns the beam through an angle of 90° and transports the beam to the vertically posed Xray converter to generate the horizontal beam of X-rays.Приводиться опис прискорювача електронів ІЛУ-10 на енергію 5 МеВ потужністю 50 кВт, спеціально розробленого для таких комплексів. Для спрощення конструкції конвеєрної системи подачі оброблюваної продукції в зону опромінення використовується випускний пристрій з поворотом пучка на 90 градусів інаступною конвертацією електронного пучка в гамма-випромінювання на вертикально розташованій мішені.Приводится описание ускорителя электронов ИЛУ-10 на энергию 5 МэВ мощностью 50 кВт, специально разработанного для таких комплексов. Для упрощения конструкции конвейерной системы подачи обрабатываемой продукции в зону облучения используется выпускное устройство с поворотом пучка на 90 градусов и последующей конвертацией электронного пучка в гамма-излучение на вертикально расположенной мишени

The COMPASS Experiment at CERN

The COMPASS experiment makes use of the CERN SPS high-intensitymuon and hadron beams for the investigation of the nucleon spin structure and the spectroscopy of hadrons. One or more outgoing particles are detected in coincidence with the incoming muon or hadron. A large polarized target inside a superconducting solenoid is used for the measurements with the muon beam. Outgoing particles are detected by a two-stage, large angle and large momentum range spectrometer. The setup is built using several types of tracking detectors, according to the expected incident rate, required space resolution and the solid angle to be covered. Particle identification is achieved using a RICH counter and both hadron and electromagnetic calorimeters. The setup has been successfully operated from 2002 onwards using a muon beam. Data with a hadron beam were also collected in 2004. This article describes the main features and performances of the spectrometer in 2004; a short summary of the 2006 upgrade is also given.Comment: 84 papes, 74 figure

Unbound states in quantum heterostructures

We report in this review on the electronic continuum states of semiconductor Quantum Wells and Quantum Dots and highlight the decisive part played by the virtual bound states in the optical properties of these structures. The two particles continuum states of Quantum Dots control the decoherence of the excited electron – hole states. The part played by Auger scattering in Quantum Dots is also discussed