The Q2Q^2 dependence of the hard diffractive photoproduction of vector meson or photon and the range of pQCD validity

We consider two coupled problems. We study the dependence on photon virtuality $Q^2$ for the semihard quasi--elastic photoproduction of neutral vector mesons on a quark, gluon or real photon (at $s\gg p_{\bot}^2,\;Q^2; \; p_{\bot}^2\gg \mu^2 \approx (0.3$ GeV)$^2$). To this end we calculate the corresponding amplitudes (in an analytical form) in the lowest nontrivial approximation of perturbative QCD. It is shown that the amplitude for the production of light meson varies very rapidly with the photon virtuality near $Q^2=0$. We estimate the bound of the pQCD validity region for such processes. For the real incident photon the obtained bound for the $\rho$ meson production is very high. This bound decreases fast with the increase of $Q^2$, and we expect that the virtual photoproduction at HERA gives opportunity to test the pQCD results. The signature of this region is discussed. For the hard Compton effect the pQCD should work good at not too high $p_{\bot}$, and this effect seems measurable at HERA.Comment: ReVTeX, 36 pages, 5 Postscript figures, uses epsf.st

Effects of Tillage and Manure on Emergence and Establishment of Russian Wildrye in a Saltgrass Meadow

Saltgrass [Distichlis stricta (Torr.) Rydb.] meadows are found in lowland areas throughout the western United States. Saltgrass meadows are frequently more moist than upland sites and have good production potential if relatively unpalatable saltgrass is replaced by a more palatable species. The electrical conductivity and sodium absorption ratio of saltgrass meadow soils often increase with soil profile depth, while total N and sodium-bicarbonate extractable P decrease. Cultural practices that do not mix the deeper, more saline horizons with the surface should increase seedling germination and establishment. Field studies evaluated the effects of chisel plowing followed by vertical-axis tilling, conventional tilling (moldboard-plowing and discing), and manure (0, 11, 22, 45, and 90 Mg/ha) on soil physical and chemical characteristics as they relate to germination and establishment of Russian wildrye [Elymus junceus Fisch.]. Chisel plowing followed by vertical-axis tilling increased seedling emergence by 23% over conventional tillage. Manure increased seedling growth and emergence, but had no effect on stand ratings. The poor physical conditions created on the conventionally tilled plots when the B and C horizons were brought to the surface and organic matter was buried by the plow are believed to have caused the difference in seedling counts between the two tillage treatments.This material was digitized as part of a cooperative project between the Society for Range Management and the University of Arizona Libraries.The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202

From plasma to nanoparticles: optical and particle emission of a spark discharge generator

The increased demand for high purity nanoparticles (NPs) of defined geometry necessitates the continuous development of generation routes. One of the most promising physical techniques for producing metal, semiconductor or alloy NPs in the gas phase is spark discharge NP generation. The technique has a great potential for up-scaling without altering the particles. Despite the simplicity of the setup, the formation of NPs in a spark discharge takes place via complex multi-scale processes, which greatly hinders the investigation via conventional NP measurement techniques. In the present work, time-resolved optical emission spectroscopy (OES) was used to provide information on the species present in the spark from as early as approximately 100 ns after the initiation of the discharge. We demonstrate that operando emission spectroscopy can deliver valuable insights into NP formation. The emission spectra of the spark are used to identify, among others, the main stages of material erosion and to calculate the quenching rate of the generated metal vapour. We demonstrate that the alteration of key control parameters, that are typically used to optimize NP generation, clearly affect the emission spectra. We report for Cu and Au NPs that the intensity of spectral lines emitted by metal atoms levels off when spark energy is increased above an energy threshold, suggesting that the maximum concentration of metal vapour produced in the generator is limited. This explains the size variation of the generated NPs. We report a strong correlation between the optical and particle emission of the spark discharge generator, which demonstrate the suitability of OES as a valuable characterization tool that will allow for the more deliberate optimization of spark-based NP generation

Review of Spark Discharge Generators for Production of Nanoparticle Aerosols

In the growing field of nanotechnology there is an increasing need to develop production methods for nanoparticles, especially methods that provide control and reproducibility. The spark discharge generator (SDG) is a versatile device for the production of nanoparticle aerosols. It can produce aerosol nanoparticles in the entire nanometer range (1-100 nm), and beyond. Depending on requirements, and the system used, these nanoparticles can be completely contamination free and composed of one or more materials. This provides a unique opportunity to create new materials on the nanoscale. Already in use in semiconductor, materials, health and environmental research, the SDG shows promise for yet more applications. If needed, particle production by the SDG could be scaled up using parallel generators facilitating continuous high-volume production of aerosol nanoparticles. Still, there is a surprisingly low knowledge of fundamental processes in the SDG. In this article we present a thorough review of the most common and relevant SDGs and the theory of their operation. Some possible improvements are also discussed

Characteristics of airborne gold aggregates generated by spark discharge and high temperature evaporation furnace: Mass-mobility relationship and surface area

The properties of gas-borne aggregates are important in nano-technology and for potential health effects. Gold aggregates from three generators (one commercial and one custom built spark discharge generator and one high-temperature furnace) have been characterized. The aggregate surface areas were determined using five approaches - based on aggregation theory and/or measured aggregate properties. The characterization included mass-mobility relationships, effective densities (assessed by an Aerosol Particles Mass analyzer), primary particle analysis (based on Transmission Electron Microscopy), as well as total mass and number concentration outputs. The relationships between mass and mobility are well described by power-law functions with exponents of 2.18-2.35. For all generators, the primary particles of the aggregates were fused together by a bridge with a diameter typically similar to 60-70% of the primary particle diameter (5-10 nm). The total mass outputs were 6.1-48.1 mg/m3 and the predicted surface area outputs in the range 0.9 x 10(-3)-17 x 10(-3) cm(2)/cm(3). The aggregate effective densities differed considerably between generators. The difference could partly be explained by the differences in primary particle diameter, but not fully. This in turn may be explained either by a varying primary particle size with aggregate size, or by that there are slight differences in the morphology of the aggregates from the generators. (C) 2015 The Authors. Published by Elsevier Ltd

Observation of a new superfluid phase for ³He embedded in nematically ordered aerogel

Here we deposit the data which is shown in the figures of the Nature Communications article titled: Observation of a new superfluid phase for ³He embedded in nematically ordered aerogelIn bulk superfluid 3He at zero magnetic field, two phases emerge with the B phase stable everywhere except at high pressures and temperatures where the A phase is favored. Aerogels with nanostructure smaller than the superfluid coherence length are the only means to introduce disorder into the superfluid. Here we use a torsion pendulum to study 3He confined in an extremely anisotropic, nematically ordered aerogel consisting of roughly 10 nm thick alumina strands, spaced by about 100 nm, and aligned parallel to the pendulum axis. Kinks in the development of the superfluid fraction (at various pressures) as the temperature is varied correspond to phase transitions. Two such transitions are seen in the superfluid state, and we identify the superfluid phase closest to Tc at low pressure as the Polar state, a phase that is not seen in bulk 3He.National Science Foundation, via DMR 1202991 and PHY 150830