5,478 research outputs found
Solar-grade silicon prepared by carbothermic reduction of silica
An advanced carbothermic reduction (ACR) process was developed to produce solar grade (SC) silicon from high purity silica and carbon. Preparation of starting materials and operation of the arc furnace to product high purity silicon is described. Solar cells prepared from single crystal SG-Si had efficiencies of up to 12.3% practically identical to cells made from electronic grade silicon. The ACR process is not in the pilot stage for further evaluation
Altitude Performance and Operational Characteristics of an XT38-A-2 Turboprop Engine
The overall engine performance and the starting and windmilling characteristics of an XT38-A-2 turboprop engine have been investigated in the NACA Lewis altitude wind tunnel. The simulated flight conditions ranged from altitudes of 5000 to 45,000 feet at a flight Mach number of 0.30 and from Mach numbers of 0.301 to 0.557 at an altitude of 35,000 feet. The engine, equipped with a standard-area exhaust nozzle, was operated with independent control of fuel flow and propeller pitch; operation was thereby allowed over a wide range of engine conditions. Windmilling characteristics were obtained at altitudes of 15,000 feet and 35,000 feet. Analysis of the performance maps obtained at each flight condition revealed that both altitude and flight Mach number had a major effect on corrected engine variables. The large reductions in corrected shaft horsepower occurring when the altitude was increased were the result of decreases in compressor and turbine efficiencies. Windmilling engine starts were made at altitudes as high as 35,000 feet at an engine speed of 2000 rpm
Molecular screening of microorganisms associated with discolored wood in dead European beech trees suffered from extreme drought event using next generation sequencing
Drought events weaken trees and make them vulnerable to attacks by diverse plant pathogens. Here, we propose a molecular method for fast screening of microorganisms associated with European beech decline after an extreme drought period (2018) in a forest of Thuringia, Germany. We used Illumina sequencing with a recent bioinformatics approach based on DADA2 to identify archaeal, bacterial, and fungal ASVs (amplicon sequence variants) based on bacterial and archaeal 16S and fungal ITS genes. We show that symptomatic beech trees are associated with both bacterial and fungal plant pathogens. Although the plant pathogen sequences were detected in both discolored and non-discolored wood areas, they were highly enriched in the discolored wood areas. We show that almost each individual tree was associated with a different combination of pathogens. Cytospora spp. and Neonectria coccinea were among the most frequently detected fungal pathogens, whereas Erwinia spp. and Pseudomonas spp. were the dominant bacterial plant pathogens. We demonstrate that bacterial plant pathogens may be of major importance in beech decline
Critical behavior in a cross-situational lexicon learning scenario
The associationist account for early word-learning is based on the
co-occurrence between objects and words. Here we examine the performance of a
simple associative learning algorithm for acquiring the referents of words in a
cross-situational scenario affected by noise produced by out-of-context words.
We find a critical value of the noise parameter above which learning
is impossible. We use finite-size scaling to show that the sharpness of the
transition persists across a region of order about ,
where is the number of learning trials, as well as to obtain the
learning error (scaling function) in the critical region. In addition, we show
that the distribution of durations of periods when the learning error is zero
is a power law with exponent -3/2 at the critical point
Some Recent Studies Concerning Organometallic Compounds
In connection with studies concerned with the mechanism of reactions and the proof of structure, insofar as such work involves organometallic compounds, it is necessary to determine specifically the mode of attachment of the metal to such polyvalent elements as carbon, nitrogen, oxygen and sulfur. For this reason, experiments are in progress on organobarium and organostrontium halides, as well as organomagnesium halides where the metal is attached particularly to sulfur and to oxygen. Because the polar nature of organometallic compounds makes them of such promise in the electronic interpretation of reactions, a quantitative study is being made of the reaction with substituted ethylenic compounds. Preliminary results of this work indicate that no addition takes place. A study is also in progress of the reaction of organometallic compounds with positive and negative halogens. In studies on the mechanism of reduction by Grignard reagents, preliminary experiments show that magnesium halogen hybrides are not formed by catalytic reduction of organomagnesium halides
Azobenzene at Coinage Metal Surfaces: The Role of Dispersive van der Waals Interactions
We use different semi-empirical dispersion correction schemes to assess the
role of long-range van der Waals interactions in the adsorption of the
prototypical molecular switch azobenzene (C6H5-N2-C6H5) at the coinage metal
surfaces Cu(111), Ag(111) and Au(111). Compared to preceding density-functional
theory results employing a semi-local exchange and correlation functional we
obtain partly sizable changes of the computed adsorption geometry and
energetics. The discomforting scatter in the results provided by the different
schemes is largely attributed to the unknown form of the damping function in
the semi-empirical correction expression. Using the congeneric problem of the
adsorption of benzene as a vehicle to connection with experiment, we cautiously
conclude that the account of dispersive interactions at the metal surfaces
provided by the various schemes is in the right ballpark, with the more recent,
general schemes likely to overbind.Comment: 11 pages including 4 figures; related publications can be found at
http://www.fhi-berlin.mpg.de/th/th.htm
A Hybrid Monte Carlo Method for Surface Growth Simulations
We introduce an algorithm for treating growth on surfaces which combines
important features of continuum methods (such as the level-set method) and
Kinetic Monte Carlo (KMC) simulations. We treat the motion of adatoms in
continuum theory, but attach them to islands one atom at a time. The technique
is borrowed from the Dielectric Breakdown Model. Our method allows us to give a
realistic account of fluctuations in island shape, which is lacking in
deterministic continuum treatments and which is an important physical effect.
Our method should be most important for problems close to equilibrium where KMC
becomes impractically slow.Comment: 4 pages, 5 figure
Comparison of Relativistic Nucleon-Nucleon Interactions
We investigate the difference between those relativistic models based on
interpreting a realistic nucleon-nucleon interaction as a perturbation of the
square of a relativistic mass operator and those models that use the method of
Kamada and Gl\"ockle to construct an equivalent interaction to add to the
relativistic mass operator. Although both models reproduce the phase shifts and
binding energy of the corresponding non-relativistic model, they are not
scattering equivalent. The example of elastic electron-deuteron scattering in
the one-photon-exchange approximation is used to study the sensitivity of
three-body observables to these choices. Our conclusion is that the differences
in the predictions of the two models can be understood in terms of the
different ways in which the relativistic and non-relativistic -matrices are
related. We argue that the mass squared method is consistent with conventional
procedures used to fit the Lorentz-invariant cross section as a function of the
laboratory energy.Comment: Revtex 13 pages, 5 figures, corrected some typo
- …