Silicon nanoparticles and interstellar extinction

To examine a recently proposed hypothesis that silicon nanoparticles are the source of extended red emission (ERE) in the interstellar medium, we performed a detailed modeling of the mean Galactic extinction in the presence of silicon nanoparticles. For this goal we used the appropriate optical constants of nanosized Si, essentially different from those of bulk Si due to quantum confinement. It was found that a dust mixture of silicon nanoparticles, bare graphite grains, silicate core-organic refractory mantle grains and three-layer silicate-water ice-organic refractory grains works well in explaining the extinction and, in addition, results in the acceptable fractions of UV/visible photons absorbed by silicon nanoparticles: 0.071-0.081. Since these fractions barely agree with the fraction of UV/visible photons needed to excite the observed ERE, we conclude that the intrinsic photon conversion efficiency of the photoluminescence by silicon nanoparticles must be near 100%, if they are the source of the ERE.Comment: Latex2e, uses emulateapj.sty (included), multicol.sty, epsf.sty, 6 pages, 3 figures (8 Postscript files), accepted for publication in ApJ Letters, complete Postscript file is also available at http://physics.technion.ac.il/~zubko/eb.html#SNP

New Interstellar Dust Models Consistent with Extinction, Emission, and Abundance Constraints

We present new interstellar dust models which have been derived by simultaneously fitting the far-ultraviolet to near-infrared extinction, the diffuse infrared (IR) emission and, unlike previous models, the elemental abundance constraints on the dust for different interstellar medium abundances, including solar, F and G star, and B star abundances. The fitting problem is a typical ill-posed inversion problem, in which the grain size distribution is the unknown, which we solve by using the method of regularization. The dust model contains various components: PAHs, bare silicate, graphite, and amorphous carbon particles, as well as composite particles containing silicate, organic refractory material, water ice, and voids. The optical properties of these components were calculated using physical optical constants. As a special case, we reproduce the Li & Draine (2001) results, however their model requires an excessive amount of silicon, magnesium, and iron to be locked up in dust: about 50 ppm (atoms per million of H atoms), significantly more than the upper limit imposed by solar abundances of these elements, about 34, 35, and 28 ppm, respectively. A major conclusion of this paper is that there is no unique interstellar dust model that simultaneously fits the observed extinction, diffuse IR emission, and abundances constraints.Comment: 70 pages, 23 figures, accepted for publication in the Astrophysical Journal Supplemen

Spatial Aspects of Multi-Sensor Data Fusion: Aerosol Optical Thickness

The Goddard Earth Sciences Data and Information Services Center (GES DISC) investigated the applicability and limitations of combining multi-sensor data through data fusion, to increase the usefulness of the multitude of NASA remote sensing data sets, and as part of a larger effort to integrate this capability in the GES-DISC Interactive Online Visualization and Analysis Infrastructure (Giovanni). This initial study focused on merging daily mean Aerosol Optical Thickness (AOT), as measured by the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Terra and Aqua satellites, to increase spatial coverage and produce complete fields to facilitate comparison with models and station data. The fusion algorithm used the maximum likelihood technique to merge the pixel values where available. The algorithm was applied to two regional AOT subsets (with mostly regular and irregular gaps, respectively) and a set of AOT fields that differed only in the size and location of artificially created gaps. The Cumulative Semivariogram (CSV) was found to be sensitive to the spatial distribution of gap areas and, thus, useful for assessing the sensitivity of the fused data to spatial gaps

Remote Sensing Data Visualization, Fusion and Analysis via Giovanni

We describe Giovanni, the NASA Goddard developed online visualization and analysis tool that allows users explore various phenomena without learning remote sensing data formats and downloading voluminous data. Using MODIS aerosol data as an example, we formulate an approach to the data fusion for Giovanni to further enrich online multi-sensor remote sensing data comparison and analysis

Analysis and forecast of performance characteristics of combine harvesters

ArticleThis article presents results of an experimental research of qualitative indicators of the modern combine harvesters (Case IH Axil Flow 8230, MasseyFergusonMFT7, JohnDeereS680i, ClaasLexion760, NewHolland CR9.80) used for winter wheat harvesting. Based on the results obtained, determination was made regarding the productivity of combine harvesters on the field, fuel consumption, and field conditions influence the grain loss and grain damage caused by a harvester. When conducting the experimental research of a combine's performance on the field a study of the effectiveness of the combine JohnDeereS680i was made on different modes. A program 'Machine Unit', designed by the authors, was used for the determination of productivity, fuel consumption and quality indicator for harvesting

Effects of Grain Size on the Spectral Energy Distribution of Dusty Circumstellar Envelopes

We study the effects of dust grain size on the spectral energy distribution (SED) of spherical circumstellar envelopes. Based on the self-similarity relations of dusty SEDs derived by Ivezic & Elitzur (1997), we expect an approximate invariance of the IR SED for models with different grain sizes. Approximate invariance follows from the fact that differently sized grains have similar optical properties at long wavelengths where the dust reprocesses the starlight. In this paper, we discuss what are the physical requirements on the model parameters to maintain the approximate invariance of the IR SED. Single grain size models are studied for a wide range of grain sizes in three optical depth regimes. In this study, we find limits for the cases where the IR SED is and is not capable of conveying information about grain sizes, and to what extent it does so. We find that approximate invariance occurs for a much larger range of grain sizes than previously believed, and, when approximate invariance holds, the SED is controlled mainly by one parameter, the reprocessing optical depth, a quantity that measures the fraction of starlight that is absorbed by the dust grains. Models with a grain size distribution are studied as well. For these models, we find that, in many instances, the concept of approximate invariance may be extended from the IR SED to all wavelengths. This means that, for a wide range of optical depths, models with different grain size distributions will produce very similar SEDs and, hence, the reprocessing optical depth is the only quantity that can be unambiguously obtained from the SED. The observational consequences of this result are discussed in detail

Stress-strain state of the mine massif around the chambers of the second stage of mining

A stress-strain state of the rock mass around the chambers of the second stage of mining was analyzed with the help of thermodynamic method. This study is the question of the day as the ore reserves in the chambers of the second stage of mining are, as a rule, extracted being surrounded by the filling mass, and due to this the highest rates of the ore losses and contamination with the filling mass are observed. In connection with this, the study of the stress-strained state of the filling mass and establishment of a method for improving the massif stability presents a great interest today. A calculation scheme for modeling thermodynamic processes in the rock mass around the chambers was developed with the purpose to study the stress field and determine principles of radial stress changing in the filling mass of the surrounding chamber. A chamber in the layer at the depth of 740-840 m was simulated with the following average geotechnical conditions: depth of the extraction chamber, angle of the deposit depression, horizontal thickness of deposit, rock strength in the hanging layer against uniaxial compression, rock strength in the bottom layer against uniaxial compression, and stowing strength against uniaxial compression. The study determined areas with tensile stress in the rocks of the bottom layer, ore mass and filling mass, and their parameters (size, maximum tension) and formulated empirical equations for the dependences between radial tensions and distance to the chambers L of the second stage of mining. The areas of destructive deformation and their dimensions in the stowing mass around the chambers of the second stage of mining at the level 740-840 m were established. Maximum values are defined for the stresses acting in the stowing mass which, exceeding the ultimate strength, cause the mass failure into the space of the chamber of the second stage. In order to prevent the stowing mass failure it is recommended to make a consolidating layer of the solid stowing at the 2/3 height of the chamber in order to resist the high tensile stresses and to ensure the mass stability

Energy Extraction Resistors for the Main Dipole and Quadrupole Circuits of the LHC

When the LHC will be operating at its maximum beam energy, its superconducting dipole chains store a total magnetic energy of more than 11 GJ. At the same time, the QF and QD quadrupole circuits store a total energy of 400 MJ. Even with the sectorisation of each of the three principal power circuits into eight individually powered segments, the stored energy of a single circuit is considerable. During normal operation the energy in the dipole circuits is safely returned to the mains grid, using the thyristor-based, 'booster' unit of the power converters, operating in inversion. For the quadrupole chains, where the converter is of a mono-polar topology, the stored energy is dissipated into the resistive part of the warm d.c. power lines (busbars and cables) in a slow, controlled run-down. When a magnet quenches, however, such a slow energy transfer, taking 20 minutes from the rated LHC current, will not be possible. The 'cold' diode, taking over the magnet current in case of a quench, will not survive this slow current decay. For this reason, energy extraction facilities will be inserted into the power circuits. These systems are being designed to absorb the total circuit energy and de-excite the chains with a current decay time constant of 104 s for the dipoles and 40 s for the quadrupoles. The resulting maximum decay rates (-125 A/s and -325 A/s respectively) are comfortably below the levels where quench-back will occur. The energy extraction systems are based on an array of special, mechanical d.c. circuit breakers and absorber resistors, which are switched into the circuit by opening of the breakers. The design and construction of these large power resistors of a unique concept are the topics of this paper. The project is being realised as collaboration between, IHEP-Protvino, CERN and European Industry