Absorption losses in periodic arrays of thin metallic wires

We analyze the transmission and reflection of the electromagnetic wave calculated from transfer matrix simulations of periodic arrangements of thin metallic wires. The effective permittivity and the absorption is determined. Their dependence on the wire thickness and the conductance of the metallic wires is studied. The cutoff frequency or effective plasma frequency is obtained and is compared with analytical predictions. It is shown that the periodic arrangement of wires exhibits a frequency region in which the real part of the permittivity is negative while its imaginary part is very small. This behavior is seen for wires with thickness as small as 17 $\mu$m with a lattice constant of 3.33 mm

Methods for determining Carbon dioxide production in soils

Many investigators have studied the organic matter in soils, in the attempt to determine its nature and composition, the rate and character of the decomposition which it undergoes, the products of decomposition, and especially the value of various kinds of organic materials which may be applied to soils, as indicated by decomposition studies

The effects of artificial farm manures on soils and crops

In the preliminary studies carried out in the laboratory and greenhouse, very similar effects were exerted on the bacterial activities in the soil and on the yield of oats from the use of the variously prepared artificial manures and from the application of farm manure. Well-rotted farm manure had a much greater effect on carbon dioxide production in sand cultures than did the artificial manures, but some of the artificial manures produced as large an influence as did the fresh farm manure. The sweet clover manure had a distinct beneficial effect, and the straw manure also increased the carbon dioxide production. The greater influence of the well-rotted farm manure was undoubtedly due to the greater decomposition occurring in that material than in the artificial manures. The nitrification studies in sand cultures in the greenhouse indicated that nitrate accumulation was depressed by the additions of farm manure and artificial manures, there being just as great a depression from the farm manure in 71/2 and 15 ton applications as from the artificial manures. The nitrifying power of the sand cultures was increased by the treatments, the artificial manures, in some cases, having a greater effect than the farm manure. The straw-clover manure and the sweet clover manure showed a greater effect than the farm manure. Apparently the greater nitrification brought about by the treatments was followed by a greater assimilation and, hence, there was a lower content of nitrates at 11 dates of sampling. In this test the artificial manures and the farm manure seemed to have similar effects on nitrification, but the artificial manures, in some cases, had a greater stimulative influence on the oats grown than did the farm manure. In the nitrate assimilation experiment in the laboratory, the application of farm manure appreciably stimulated the development of the nitrate assimilating organisms in the Carrington loam. The oats straw and the straw manure brought about a greater stimulation, but the artificial manures in general showed a smaller stimulation on this group of organisms. It is apparent that the artificial manures had no greater influence in increasing nitrate assimilation than did farm manure. These results were confirmed by later tests in the greenhouse and in the field on the Carrington loam, but it was noted that those artificial manures, which were not so well decomposed when applied to the soil, stimulated these nitrate assimilating organisms more and the effects persisted in the soil for a longer period. In the greenhouse experiments on Carrington loam, the artificial manures and farm manure had very similar effects on nitrate production, and while the influence on nitrification was not quite so great at first, the later effects were greater than those produced by farm manure. The influence of the various manures was similar on the crop of oats grown in this test. Field experiments on the Webster loam in 1926 and 1927 and on the Carrington loam in 1928 and 1929 with variously prepared artificial manures in comparison with farm manure indicate that nitrate assimilation, nitrification, nitrate accumulation and the numbers of bacteria, molds and actinomycetes were very similarly affected by the additions of the various manures. The yields of corn were also influenced in a very similar way by the artificial manures and farm manure, altho in some instances there were differences in yields which were out of line with the general trend of the results. From the results as a whole it is apparent that the proper composting of straw and cellulose residues may permit the production of artificial manures which will give similar effects on bacteriological conditions in the soil and on crop yields to those occasioned by farm manure. There is a similar stimulation in the nitrification process and in the numbers of organisms, and while nitrate assimilation is also stimulated by the artificial manures, the influence on this process is no greater than that produced by farm manure. While, therefore, there may be a reduced content of nitrates in the soils following the addition of these artificial manures, there is no greater reduction than that brought about by farm manure. As farm manure has a well-known beneficial effect on crop growth, it is apparent that there need be no deleterious effect from well-decomposed artificial manures either on crop yields or on soil conditions in general. In fact it would seem that quite as large beneficial effects should be exerted, and any increase in nitrate assimilation and decrease in nitrate content is more than offset, from a crop production standpoint, by the increased nitrification which is occasioned

Oxygen Absorption and Carbon Dioxide Production in Soils

Carbon dioxide production in the soil has long been regarded as a measure of biological activity. It has been suggested that oxygen absorption might give a more reliable measure of the total action of microorganisms than carbon dioxide production. Since the amount of oxygen consumed by aerobic organisms under constant environmental conditions bears a definite relation to the amount of carbon dioxide produced, it would seem that the ratio of carbon dioxide produced to oxygen consumed would show something concerning the nature of the organic matter of the soil, its composition and rate of decomposition and, therefore, be a better index of microbiological action than either alone

Vectorcardiographic changes during extended space flight

To assess the effects of space flight on cardiac electrical properties, vectorcardiograms were taken on the 9 Skylab astronauts during the flights of 28, 59, and 84 days. The Frank lead system was used and observations were made at rest; during 25%, 50% and 75% of maximum exercise; during a short pulse of exercise (150 watts, 2 minutes); and after exercise. Data from 131 in-flight tests were analyzed by computer and compared to preflight and postflight values. Statistically significant increase in QRS vector magnitude (six of nine crewmen); T vector magnitude (five of nine crewmen); and resting PR interval duration (six of nine crewmen) occurred. During exercise the PR interval did not differ from preflight. Exercise heart rates inflight were the same as preflight, but increased in the immediate postflight period. With the exception of the arrhythmias, no deleterious vectorcardiographic changes were observed during the Skylab missions

Interferometric observations of eta Carinae with VINCI/VLTI

Context: The bright star eta Carinae is the most massive and luminous star in our region of the Milky Way. Though it has been extensively studied using many different techniques, its physical nature and the mechanism that led to the creation of the Homunculus nebula are still debated. Aims: We aimed at resolving the central engine of the eta Carinae complex in the near-infrared on angular scales of a few milliarcseconds. Methods: We used the VINCI instrument of the VLTI to recombine coherently the light from two telescopes in the K band. Results: We report a total of 142 visibility measurements of eta Car, part of which were analyzed by Van Boekel et al. (2003). These observations were carried out on projected baselines ranging from 8 to 112 meters in length, using either two 0.35 m siderostats or two 8-meter Unit Telescopes. These observations cover the November 2001 - January 2004 period. Conclusions: The reported visibility data are in satisfactory agreement with the recent results obtained with AMBER/VLTI by Weigelt et al. (2006), asuming that the flux of eta Car encircled within 70 mas reaches 56% of the total flux within 1400 mas, in the K band. We also confirm that the squared visibility curve of eta Car as a function of spatial frequency follows closely an exponential model.Comment: Accepted for publication in A&A as a Research not

Nitrate assimilation in soils

Preliminary work with solution cultures inoculated with soil showed that 20.83 mgm. of nitrate nitrogen disappeared in eight days, while the total nitrogen increased. The results obtained with soil cultures were very similar to those obtained with the solution cultures. Treating the soil with straw in the greenhouse brought about a complete utilization of the nitrates, while there was a small accumulation of nitrate in the soil treated with farm manure. The nitrate-assimilating power of the soil was influenced by a number of factors, and, altho much information was secured by the methods employed, more work on the various factors affecting nitrate assimilation in soils is desirable. It was found that dextrose increased the nitrate-assimilating power of the soil. This material furnished a source of energy for those organisms which utilized both nitrate and ammonia, thus preventing an accumulation of nitrate. Since the nitrate content of the soil at any given time is the resultant of many different forces, some treatment which would eliminate all but nitrate assimilation would facilitate the accurate measurement of this process. The addition of a readily available energy source, especially one poor in nitrogen, tends to bring about this condition. Straw, partially decomposed straw and farm manure brought about an assimilation of nitrate immediately upon being added to the soil. The straw brought about a larger assimilation of nitrate than the straw manure or the farm manure. Manure, lime and rock phosphate applied over a period of years on Marshall silt loam and Grundy silt loam tended, in general, to lower: the nitrate-assimilating power of the soil. The nitrate-assimilating power of Carrington loam treated in the field with different manures varied thruout the season, showing only slight differences between the different treatments. Very similar results were secured with manure, lime and crop residues on both continuous corn and corn in the three-year rotation. Five cultures of nitrate-assimilating and nine cultures of denitrifying bacteria were isolated and studied in pure culture. No names have been suggested for these organisms and their systematic relationships have not been determined. A number of nitrate-assimilating and denitrifying tests were carried out with some of the organisms in pure culture. Nitrate assimilation is common to a large number of soil microorganisms. It has been suggested, however, that the molds are largely responsible for nitrate assimilation when the energy supply of the soil is increased. The results obtained in these experiments indicate that certain molds may be less efficient nitrate assimilators than some bacteria

Problems and Progress in Flare Fast Particle Diagnostics

Recent progress in the diagnosis of flare fast particles is critically discussed with the main emphasis on high resolution Hard X-Ray (HXR) data from RHESSI and coordinated data from other instruments. Spectacular new photon data findings are highlighted as are advances in theoretical aspects of their use as fast particle diagnostics, and some important comparisons made with interplanetary particle data. More specifically the following topics are addressed (a) RHESSI data on HXR (electron) versus gamma-ray line (ion) source locations. (b) RHESSI hard X-ray source spatial structure in relation to theoretical models and loop density structure. (c) Energy budget of flare electrons and the Neupert effect. (d) Spectral deconvolution methods including blind target testing and results for RHESSI HXR spectra, including the reality and implications of dips inferred in electron spectra (e) The relation between flare in-situ and interplanetary particle data.Comment: 15 pages, 13 figures, submitted to Advances in Space Researc

The spectral evolution of impulsive solar X-ray flares

The time evolution of the spectral index and the non-thermal flux in 24 impulsive solar hard X-ray flares of GOES class M was studied in RHESSI observations. The high spectral resolution allows for a clean separation of thermal and non-thermal components in the 10-30 keV range, where most of the non-thermal photons are emitted. Spectral index and flux can thus be determined with much better accuracy than before. The spectral soft-hard-soft behavior in rise-peak-decay phases is discovered not only in the general flare development, but even more pronounced in subpeaks. An empirically found power-law dependence between the spectral index and the normalization of the non-thermal flux holds during the rise and decay phases of the emission peaks. It is still present in the combined set of all flares. We find an asymmetry in this dependence between rise and decay phases of the non-thermal emission. There is no delay between flux peak and spectral index minimum. The soft-hard-soft behavior appears to be an intrinsic signature of the elementary electron acceleration process.Comment: 10 pages, 7 figures. Accepted for publication by A&