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1.
An improved ozone Differential Absorption Lidar (DIAL) system has been designed for tropospheric and lower stratospheric ozone monitoring in Northern Greece. The system is based on a frequency quadrupled pulsed Nd:YAG laser and the Raman shifting technique in D2 and H2 gases. The lidar system emits simultaneously 4 wavelengths (266 mn, 289 nm, 299 nm and 316 nm) at 10 Hz repetition rate using a single low pressure Raman cell. The optical receiving system is based on a 50 cm concave telescope which is directly coupled to a specially conceived grating spectrometer. This lidar system uses analog (12 bits-40 MHz) and photon counting (250 MHz) detection systems, able to measure lidar signals up 16 km height. Ozone vertical profiles are to be measured from 0.8 km up to 15 km height, with a 30–500 m spatial and a 1-minute temporal resolution. In this paper the major technical characteristics of the improved lidar system are presented. The system is foreseen to provide the first daytime/nighttime ozone vertical profiles during early winter 1999.  相似文献   

2.
介绍了2010年上海天文台卫星激光测距的常规观测和白天千赫兹激光测距情况。在国际上首次对同步轨道卫星开展了千赫兹激光测距,作用距离达38800多千米,测距系统性能达到国际先进水平。利用2套独立的激光测距系统,开展了激光收发分离测距实验,为行星际异步应答式激光测距模拟试验提供了实测数据。最后概述了空间碎片目标激光测距进展情况。  相似文献   

3.
A laboratory plasma experiment has been built to study the eruption of arched magnetic flux ropes (AMFRs) in the presence of a large magnetized plasma. This experiment simulates the eruption of solar AMFRs in two essential steps: i) it produces an AMFR (n=6.0×1012 cm?3, $T_{\rm e} = 14~\mathrm{eV}$ , B≈1 kilo-gauss, L=0.51 m) with a persistent appearance that lasts several Alfvén transit times using a lanthanum hexaboride (LaB6) plasma source, and ii) it generates controlled plasma flows from the footpoints of the AMFR using laser beams. An additional LaB6 plasma source generates a large magnetized plasma in the background. The laser-generated flows trigger the eruption by injecting dense plasma and magnetic flux into the AMFR. The experiment is highly reproducible and runs continuously with a 0.5 Hz repetition rate; hence, several thousand identical loop eruptions are routinely generated and their spatio-temporal evolution is recorded in three-dimensions using computer-controlled movable probes. Measurements demonstrate striking similarities between the erupting laboratory and solar arched magnetic flux ropes.  相似文献   

4.
We analyse the spectral shape and possible spurious distortions of the Sunyaev-Zel'dovich effect, arising from the interaction of the cosmic background radiation with hot gases of rich clusters, in the millimetric region. We show that one can measure this effect with high accuracy with present-day infrared detectors, obtaining a larger amount of information than by using radio systems. In particular, one can accurately measure the temperature of the cosmic background radiation without the usual absolute calibration of the detector.  相似文献   

5.
We analyse in detail the spectral shape of the Sunyaev-Zel'dovich effect in the cosmic background radiation, taking into account the relativistic corrections for a hot electron gas. We calculate the displacement of the zero-signal frequency, which is especially informative in a new method for measuring the millimetric temperature of the background radiation; we also present a simple analytical expression, to be used to fit the experimental data in spectral measurements of the effect in very hot cluster gases.  相似文献   

6.
高重频激光测距数据处理方法   总被引：1，自引：0，他引：1  
该文探讨了高重频激光测距工作中的数据处理问题。该数据处理采用了屏幕显示以及数学分析方法,以剔除卫星激光测距数据中的观测异常值,提取有效的数据点,并最终生成标准点数据。通过对奥地利GRAZ激光测距站高重频数据资料的处理表明,该数据处理方法是有效的。  相似文献   

7.
This review deals with the historical development of a chemical kinetics and photochemical data base for use in atmospheric modeling. Initiated by the suggestion that the release of nitric oxide into the stratosphere from the exhaust gases of supersonic aircraft could seriously deplete stratospheric ozone, the quest for such a data base began in 1971. The present article traces the development of the detailed chemistry of the homogeneous gas-phase reactions which control the levels of ozone in the stratosphere. It also includes coverage of the more recent heterogeneous chemistry which is believed to be involved in the Antarctic “ozone hole,” as well as the background to the on-going establishment of a reaction rate data base for application to tropospheric chemistry and modeling.  相似文献   

8.
The interaction of supersonic plasma jets with dense gases and plasmas has been studied experimentally and theoretically. Collimated plasma jets were generated from the laser pulse interaction with solid targets. The jet propagates with the velocity exceeding 400 km/s and transports the energy of a few kJ/cm2. The interaction of such a jet with an Ar and He gases at various pressures has been studied by using optical and X-ray diagnostics. Qualitative estimates and numerical simulations with a radiative hydrodynamic code explain a sequence of physical processes during the interaction. Experimental and numerical results show that, by changing ambient material, the working surface structure changes from an adiabatic outflow to a radiative cooling jet. The applications of this phenomenon to astrophysical conditions and the inertial confinement fusion are discussed.  相似文献   

9.
Ultra-high-resolution spectroscopic measurements (R ≈ 107) of water vapor and silicon monoxide in sunspots are presented. Observations were performed using the Cologne Tunable Heterodyne Infrared Spectrometer (THIS) at the McMath–Pierce Solar Observatory. Mid-infrared molecular absorption lines around 10 μm were recorded and resolved in full detail. The linewidth and shape can thus be determined with high precision and were used to calculate kinetic temperatures which are much higher than the physical temperatures of the sunspot. Only 15% of the wavelengths between 9 and 12μ can be covered using CO2 and all its isotopologues as laser gases (Kostiuk and Mumma, 1983).  相似文献   

10.
We investigate the stochastic gravitational wave background that results from neutron star birth throughout the Universe. The neutron star birth rate, as a function of redshift, is calculated using an observation-based model for the evolving star formation rate, together with an estimate of the rate of core-collapse supernovae in the nearby Universe and an estimate of the neutron star/black hole branching ratio. Using three sample waveforms, based on numerical models of stellar core collapse by Zwerger & Müller, the spectral flux density, spectral strain, spectral energy density and duty cycle of the background have been computed. Our results show, contrary to recent claims, that the spectrum of the stochastic background clearly reflects the different physics in the core-collapse models. For a star formation model that is corrected for dust extinction, the neutron star formation rate throughout the Universe is high enough to result in a nearly continuous background of gravitational waves, with spectral features that can be related to emission mechanisms.  相似文献   

11.
Effects of O+ ions on magnetic reconnection in the magnetotail are examined in a Harris equilibrium using a combination of linear Vlasov theory and large-scale driven and non-driven two-dimensional fully kinetic particle simulations. Linear theory of multiple species plasma indicates that the growth rate is rather insensitive to the composition of the background (lobe) or its temperature but more sensitive to the properties of the current carriers. Thus O+ can affect significant changes to the linear growth rate of tearing mode only as a current carrier. However, it is demonstrated that in the nonlinear stage reconnection can effectively move trace material from the lobes into the current sheet proper. If the supply of lobe markers (like O+) is sufficiently permanent in the lobe, an initially proton-dominated current sheet can be virtually replaced by the marker ions through this “flushing effect”. The dominance of marker ions introduces finite Larmor radius signatures with marker gyroradii scales rather than that of the protons. In this way, the presence of heavier marker species in the lobe can lead to (i) reduced efficiency of energy conversion, (ii) reduction in the number and repetition frequency of secondary islands, (iii) broadening of the quadrupole magnetic structure, (iv) slowing down of the coalescence process and (v) modification of the composition of the ion current carriers. Using Cluster observations, we show the evidence for the “flushing effect” in the data. Detailed comparison with observations is planned for future work.  相似文献   

12.
Abstract— Micrometeorites (MMs) currently represent the largest steady‐state mass flux of extraterrestrial matter to Earth and may have delivered a significant fraction of volatile elements and organics to the Earth's surface. Nitrogen and noble gases contents and isotopic ratios have been measured in a suite of 17 micrometeorites recovered in Antarctica (sampled in blue ice at Cap Prudhomme) and Greenland (separated from cryoconite) that have experienced variable thermal metamorphism during atmospheric entry. MMs were pyrolized using a CO2 laser and the released gases were analyzed for nitrogen and noble gas abundances and isotopic ratios by static mass spectrometry after specific purification. Noble gases are a mixture of cosmogenic, solar, atmospheric, and possibly chondritic components, with atmospheric being predominant in severely heated MMs. δ15N values vary between ?240 ± 62‰ and +206 ± 12‰, with most values being within the range of terrestrial and chondritic signatures, given the uncertainties. Crystalline MMs present very high noble gas contents up to two orders of magnitude higher than carbonaceous chondrite concentrations. In contrast, nitrogen contents between 4 ppm and 165 ppm are much lower than those of carbonaceous chondrites, evidencing either initially low N content in MMs and/or degradation of phases hosting nitrogen during atmospheric entry heating and terrestrial weathering. Assuming that the original N content of MMs was comparable to that of carbonaceous chondrites, the contribution of nitrogen delivery by these objects to the terrestrial environment would have been probably marginal from 3.8 Gyr ago to present but could have been significant (?10%) in the Hadean, and even predominant during the latest stages of terrestrial accretion.  相似文献   

13.
Ten splash‐form tektites from the Australasian strewn field, with masses ranging from 21.20 to 175.00 g and exhibiting a variety of shapes (teardrop, ellipsoid, dumbbell, disk), have been imaged using a high‐resolution laser digitizer. Despite challenges due to the samples’ rounded shapes and pitted surfaces, the images were combined to create 3‐D tektite models, which captured surface features with a high fidelity (≈30 voxel mm?2) and from which volume could be measured noninvasively. The laser‐derived density for the tektites averaged 2.41 ± 0.11 g cm?3. Corresponding densities obtained via the Archimedean bead method averaged 2.36 ± 0.05 g cm?3. In addition to their curational value, the 3‐D models can be used to calculate the tektites’ moments of inertia and rotation periods while in flight, as a probe of their formation environment. Typical tektite rotation periods are estimated to be on the order of 1 s. Numerical simulations of air flow around the models at Reynolds numbers ranging from 1 to 106 suggest that the relative velocity of the tektites with respect to the air must have been <10 m s?1 during viscous deformation. This low relative velocity is consistent with tektite material being carried along by expanding gases in the early time following the impact.  相似文献   

14.
The boloSource() algorithm is a tool to separate the signal of compact sources from that of the diffuse background in the timeline of far-infrared measurements performed by the PACS camera of the Herschel Space Observatory. An important characteristic and quality indicator of this method is that how well it can reproduce the flux of faint standard stars which have reliable flux estimates. For this propose we selected a few calibrator targets and constructed light curves by extracting point source flux for each repetition of the measurements independently using standard aperture photometry methods. These were compared with the light curves obtained using the boloSource() method on the same dataset. The results indicate that boloSource() provides a similar level of photometric accuracy and reproducibility as the usual flux extraction and photometry methods. This new technique will be developed further and also tested against other methods in more complex fields with the goal to make it usable for large-scale studies in the future.  相似文献   

15.
Cosmic ray streaming instabilities at supernova shocks are discussed in the quasi-linear diffusion formalism which takes into account the feedback effect of wave growth on the cosmic ray streaming motion. In particular, the non-resonant instability that leads to magnetic field amplification in the short wavelength regime is considered. The linear growth rate is calculated using kinetic theory for a streaming distribution. We show that the non-resonant instability is actually driven by a compensating current in the background plasma. The non-resonant instability can develop into a non-linear regime generating turbulence. The saturation of the amplified magnetic fields due to particle diffusion in the turbulence is derived analytically. It is shown that the evolution of parallel and perpendicular cosmic ray pressures is predominantly determined by non-resonant diffusion. However, the saturation is determined by resonant diffusion which tends to reduce the streaming motion through pitch angle scattering. The saturated level can exceed the mean background magnetic field.  相似文献   

16.
The problem of instability arising in a composite system consisting of an infinitely conducting hydromagnetic fluid interacting through gravitational forces with one or more than one neutral gas, is investigated, allowing for a possible relative streaming between the component fluids. Instability criteria are derived for special cases of a two-component (static or relatively streaming) system and for a three-component system consisting of two gases contra-streaming in the presence of a stationary background gas. It is found that for a static system only one unstable mode exists for wave numbers less than a critical value given by the square root of the sum of the squares of the Jeans's wave numbers for individual gases. However, for a configuration, where components are endured with characteristic streaming speeds, there are present simultaneously more than one unstable modes.  相似文献   

17.
W.B. Streett 《Icarus》1976,29(2):173-186
The phase behavior of multicomponent gas mixtures is far more complex than that of pure gases. It follows that the physical structure and hydrodynamic behavior of planets composed of mixtures of gases can be far more complex than has been suggested by models developed around the framework of a body of pure hydrogen. At high pressures, mixtures of gases often exhibit limited mutual solubility, not only between solid and fluid phases, but also between coexisting fluid phases as well. In binary mixtures in which the more volatile component has the higher molecular weight, a reversal in the relative densities of coexisting fluid and solid phases can occur at high pressures because of differences in the effects of pressure on solubilities in the two phases. The results of recent laboratory experiments on phase behavior in mixtures of gases at high pressures are reviewed, and attention is drawn to their implications for the deep atmosphere and interior structures of the other planets.  相似文献   

18.
We estimate the flux of the gamma-ray burst (GRB) neutrino background and compute the event rate at SK and TITAND in the collapsar model, assuming that GRB formation rate is proportional to the star formation rate. We find that the predicted background neutrino flux is highly sensitive to unknown model parameters, mainly to the mass–accretion rate, to the fraction of disk energy emitted in thermal neutrinos (as opposed to emission through electromagnetic processes), and to the fraction of collapsar events leading to GRBs. The predicted neutrino flux varies over many orders of magnitude as the values of unknown model parameters are varied. We investigate the detection possibility of thermal neutrinos from collapsars which lead to GRBs by TITAND. We find that the GRB neutrino background might be detected by TITAND within 10 yrs only for the optimistic cases in which the average mass–accretion rate is high ( a few M s−1), and the probability that one collapsar generates a GRB is high (f=0.5–1.0).  相似文献   

19.
One of the widely accepted models for solar radio pulsations invokes radial oscillations of a magnetic flux tube. Due to acoustic, radiative damping, this theory does not easily explain the long length of the pulse trains, the large modulation depths or the great stability of the pulse repetition rate often observed. Torsional waves efficiently modulate synchrotron emission, and since they do not undergo radiative damping, can produce stable pulse repetition rates and long pulse trains.  相似文献   

20.
A series of experiments is underway using the Omega laser to examine radiative shocks of astrophysical relevance. In these experiments, the laser accelerates a thin layer of low-Z material, which drives a strong shock into xenon gas. One-dimensional numerical simulations using the HYADES radiation hydrodynamics code predict that radiation cooling will cause the shocked xenon to collapse spatially, producing a thin layer of high density (i.e., a collapsed shock). Preliminary experimental results show a less opaque layer of shocked xenon than would be expected assuming that all the xenon accumulates in the layer and that the X-ray source is a pure Kα source. However, neither of these assumptions is strictly correct. Here we explore whether radial mass and/or energy transport may be significant to the dynamics of the system. We report the results of two-dimensional numerical simulations using the ZEUS-2D astrophysical fluid dynamics code. Particular attention is given to the simulation method.  相似文献   

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