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11.
David Alexander 《Astrophysics and Space Science》2007,307(1-3):197-202
The solar atmosphere displays a wide variety of dynamic phenomena driven by the interaction of magnetic fields and plasma.
In particular, plasma jets in the solar chromosphere and corona, coronal heating, solar flares and coronal mass ejections
all point to the presence of magnetic phenomena such as reconnection, flux cancellation, the formation of magnetic islands,
and plasmoids. While we can observe the signatures and gross features of such phenomena we cannot probe the essential physics
driving them, given the spatial resolution of current instrumentation. Flexible and well-controlled laboratory experiments,
scaled to solar parameters, open unique opportunities to reproduce the relevant unsteady phenomena under various simulated
solar conditions. The ability to carefully control these parameters in the laboratory allows one to diagnose the dynamical
processes which occur and to apply the knowledge gained to the understanding of similar processes on the Sun, in addition
directing future solar observations and models. This talk introduces the solar phenomena and reviews the contributions made
by laboratory experimentation. 相似文献
12.
Edison Liang 《Astrophysics and Space Science》2007,307(1-3):309-313
We review recent PIC simulation results which show that double-sided irradiation of a thin over-dense plasma slab with ultra-intense
laser pulses from both sides can lead to sustained comoving Poynting flux acceleration of electrons to energies much higher
than the conventional ponderomotive limit. The result is a robust power-law electron momentum spectrum similar to astrophysical
sources. We discuss future ultra-intense laser experiments that may be used to simulate astrophysical particle acceleration. 相似文献
13.
M. J. Liszewski J. J. Rosentreter K. E. Miller R. C. Bartholomay 《Environmental Geology》2000,39(3-4):411-426
The U.S. Geological Survey and Idaho State University, in cooperation with the U.S. Department of Energy, conducted a study
to determine strontium distribution coefficients (Kds) of surficial sediments at the Idaho National Engineering and Environmental Laboratory (INEEL). Batch experiments using
synthesized aqueous solutions were used to determine Kds, which describe the distribution of a solute between the solution and solid phase, of 20 surficial-sediment samples from
the INEEL. The Kds for the 20 surficial-sediment samples ranged from 36 to 275 ml/g. Many properties of both the synthesized aqueous solutions
and sediments used in the experiments also were determined. Solution properties determined were initial and equilibrium concentrations
of calcium, magnesium, and strontium, pH and specific conductance, and initial concentrations of potassium and sodium. Sediment
properties determined were grain-size distribution, bulk mineralogy, whole-rock major-oxide and strontium and barium concentrations,
and Brunauer-Emmett-Teller (BET) surface area. Solution and sediment properties were correlated with strontium Kds of the 20 surficial sediments using Pearson correlation coefficients. Solution properties with the strongest correlations
with strontium Kds were equilibrium pH and equilibrium calcium concentration correlation coefficients, 0.6598 and –0.6518, respectively. Sediment
properties with the strongest correlations with strontium Kds were manganese oxide (MnO), BET surface area, and the >4.75-mm-grain-size fraction correlation coefficients, 0.7054, 0.7022,
and –0.6660, respectively. Effects of solution properties on strontium Kds were interpreted as being due to competition among similarly charged and sized cations in solution for strontium-sorption
sites; effects of sediment properties on strontium Kds were interpreted as being surface-area related. Multivariate analyses of these solution and sediment properties resulted
in r2 values of 0.8071 when all five properties were used and 0.8043 when three properties, equilibrium pH, MnO, and BET surface
area, were used.
Received: 30 November 1998 · Accepted: 16 February 1999 相似文献
14.
Experimental and numerical investigation of groundwater head losses on and nearby short intersections between disc-shaped fractures
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Discrete fracture models are used for investigating precise processes of groundwater flow in fractured rocks,while a disc-shaped parallel-plates model for a single fracture is more reasonable and efficient for computational treatments.The flow velocity has a large spatial differentiation which is more likely to produce non-linear flow and additional head losses on and nearby intersections in such shaped fractures,therefore it is necessary to understand and quantify them.In this study,both laboratory experiments and numerical simulations were performed to investigate the total head loss on and nearby the intersections as well as the local head loss exactly on the intersections,which were not usually paid sufficient attention or even ignored.The investigation results show that these two losses account for 29.17%-84.97%and 0-73.57%of the entire total head loss in a fracture,respectively.As a result,they should be necessarily considered for groundwater modeling in fractured rocks.Furthermore,both head losses become larger when aperture and flow rate increase and intersection length decreases.Particularly,the ratios of these two head losses to the entire total head loss in a fracture could be well statistically explained by power regression equations with variables of aperture,intersection length,and flow rates,both of which achieved high coefficients of determination.It could be feasible through this type of study to provide a way on how to adjust the groundwater head from those obtained by numerical simulations based on the traditional linear flow model.Finally,it is practicable and effective to implement the investigation approach combining laboratory experiments with numerical simulations for quantifying the head losses on and nearby the intersections between disc-shaped fractures. 相似文献
15.
A recent article (Said-Ahmad, W., Amrani, A., Aizenshtat, Z., 2013. The action of elemental sulfur plus water on 1-octene at low temperatures. Organic Geochemistry 59, 82–86) is commented on in this discussion. Radical mechanisms proposed by Said-Ahmad et al. (2013) for the formation of sulfurized and oxidized organic compounds in experiments involving elemental sulfur and 1-octene under aqueous conditions, aimed at investigating the interaction of organic matter and sulfur compounds under geological conditions, are not compatible with their experimental results and other studies. In addition, results from the experiments aimed at demonstrating the role of HO radicals in the formation of oxidized organic compounds were incorrectly interpreted by the authors. In this discussion, alternative mechanisms for the formation of the sulfurized and oxygenated products reported by Said-Ahmad et al. (2013) are proposed. 相似文献
16.
D. D. Ryutov J. O. Kane A. Mizuta M. W. Pound B. A. Remington 《Astrophysics and Space Science》2007,307(1-3):173-177
The dynamics of photoevaporated molecular clouds is determined by the ablative pressure acting on the ionization front. An
important step in the understanding of the ensuing motion is to develop the linear stability theory for an initially flat
front. Despite the simplifications introduced by linearization, the problem remains quite complex and still draws a lot of
attention. The complexity is related to the large number of effects that have to be included in the analysis: acceleration
of the front, possible temporal variation of the intensity of the ionizing radiation, the tilt of the radiation flux with
respect to the normal to the surface, and partial absorption of the incident radiation in the ablated material. In this paper,
we describe a model where all these effects can be taken into account simultaneously, and a relatively simple and universal
dispersion relation can be obtained. The proposed phenomenological model may prove to be a helpful tool in assessing the feasibility
of the laboratory experiments directed towards scaled modeling of astrophysical phenomena.
PACS Numbers: 98.38.Dq, 98.38.Hv, 52.38.Mf, 5257.FG, 52.72.+v 相似文献
17.
Strong magnetic fields were generated using a fast pulsed power generator, to investigate the interaction of plasma flows
with magnetic fields and magnetized background plasmas. The inductive loads used in these experiments were designed using
a filament and a finite element modeling approaches. Magnetic fields up to 2 MG (200 T) were measured by using the Faraday
rotation technique. 相似文献
18.
More and more small bodies are found to be porous. Laboratory impact experiments of various porous materials have been performed, which increased our understanding of the impact process of porous bodies. In this review, we classify porous targets according to the internal structure, describe the physical properties that characterize these materials, and summarize some results of impact strength and the general tendency upon impact condition and material properties. The material property presented here includes a relation between applied load and distension although measured in static condition. Further investigation is required to clarify the role of crack growth and compaction in the time evolution of physical properties of porous materials upon impact. Laboratory experiments with detailed material properties will be useful as a database that can serve as a reference for numerical modeling and theoretical scaling considerations. 相似文献
19.
Comparison of laboratory testing protocols to field observations of the weathering of sulfide-bearing mine tailings 总被引:1,自引:0,他引:1
Carla Ardau David W. Blowes Carol J. Ptacek 《Journal of Geochemical Exploration》2009,100(2-3):182-191
A laboratory weathering study using a humidity cell procedure was conducted on two sulfide-bearing tailing samples from a metallurgical site in Ontario (Canada). The test was accompanied by microbiological studies to enumerate the major groups of sulfur-oxidizing bacteria and determine their potential role at different stages during the oxidation process. To evaluate the utility of this method, results were compared with those of previous laboratory and field studies on the same materials. The mineralogy of the laboratory samples differs only by the addition of a small amount of hydronium-bearing natrojarosite [(Na,H3O)Fe3(SO4)2(OH)6] to one sample. The progress of sulfide oxidation and the rates of solute release were determined to evaluate the extent of mineral dissolution. These processes were influenced strongly by the capacity of the material to generate acidity, which was enhanced by the presence of hydronium-bearing natrojarosite. Acid-neutralization processes occurring during the laboratory tests were affected by reaction kinetics, consistent with field observations. In particular, the extent of carbonate-mineral dissolution appears to be different in the laboratory than in the field, where more prolonged rock–water interaction allowed more complete chemical equilibration. As a consequence, the capacity of this test procedure to predict weathering reactions in mine tailings is limited by its inability to reproduce the weathering sequence observed in the field. The results of the microbiological study showed that distinct groups of sulfur-oxidizing bacteria operate at different stages of the oxidative process, as was observed in field studies where tailings oxidation occurred under natural conditions, suggesting that microbiological tests performed for laboratory studies are reflective of field conditions. 相似文献
20.
At present, there are few laboratory spectra of analogs of astrophysical interest in the far-infrared range (FIR). Laboratory infrared (IR) spectra of simple ices and its mixtures obtained at low temperature and pressure are found mainly up to 25 μm, and few up to 200 μm. On the other hand, there are some spectra for carbonaceous material and silicates up to 2000 μm. Our laboratory is equipped with an IR spectrometer that integrates a Michelson interferometer with a resolution better than 0.25 cm−1 and that operates under vacuum conditions of 10−1 mbar. There is also a silicon bolometer, a very high-sensitivity detector in comparison with the standard deuterated triglycine sulfate (DTGS) detectors. The use of the bolometer and the possibility of working under vacuum conditions inside the optics and the sample compartment of the spectrometer allow obtaining high-sensitivity spectra free from H2O vapor and CO2 gas bands. Those conditions are necessary to obtain high-quality spectra in the FIR where absorption bands are much less intense than those in the mid-IR region. In our laboratory there is also a high-vacuum chamber that allows different studies on ices deposited onto a cold finger. We have already carried out experiments on the study of ice density as a function of temperature, UV irradiation of ices, temperature-programmed desorption (TPD) and UV-vis reflectance. In this work, we present the design of the experimental setup we are building to carry out different experiments simultaneously on the same ice sample, including spectra measurements in the mid-IR range (MIR) and the FIR. This design integrates jointly the IR spectrometer, the high-vacuum chamber and the silicon bolometer. Lastly, we show a spectrum we have obtained of a solid of astrophysical interest such as crystalline forsterite grains by using the polyethylene pellet technique. 相似文献