Rubidium spacecraft atomic timing system Final report

Rubidium 87 atomic time and frequency reference system for manned space fligh

Computer-assisted ex vivo, normothermic small bowel perfusion

Background: In the present study, a technique for computer-assisted, normothermic, oxygenated, ex vivo, recirculating small bowel perfusion was established as a tool to investigate organ pretreatment protocols and ischemia/reperfusion phenomena. A prerequisite for the desired setup was an organ chamber for ex vivo perfusion and the use of syngeneic whole blood as perfusate. Methods: The entire small bowel was harvested from Lewis rats and perfused in an organ chamber ex vivo for at least 2 h. The temperature was kept at 37 degrees C in a water bath. Three experimental groups were explored, characterized by different perfusion solutions. The basic perfusate consisted of syngeneic whole blood diluted with either NaCl, Krebs' solution or Krebs' solution and norepinephrine to a hematocrit of 30%. In addition, in each group l-glutamine was administered intraluminally. The desired perfusion pressure was 100 mm Hg which was kept constant with a computer-assisted data acquisition software, which measured an-line pressure, oxygenation, flow, temperature and pH and adjusted the pressure by changing the flow via a peristaltic pump. The viability of the preparation was tested by measuring oxygen consumption and maltose absorption, which requires intact enzymes of the mucosal brush border to break down maltose into glucose. Results: Organ perfusion in group 1 (dilution with NaCl) revealed problems such as hypersecretion into the bowel lumen, low vascular resistance and no maltose uptake. In contrast a viable organ could be demonstrated using Krebs' solution as dilution solution. The addition of norepinephrine led to an improved perfusion over the entire perfusion period. Maltose absorption was comparable to tests conducted with native small bower. Oxygen consumption was stable during the 2-hour perfusion period. Conclusions: The ex vivo perfusion system established enables small bowel perfusion for at least 2 h. The viability of the graft could be demonstrated. The perfusion time achieved is sufficient to study leukocyte/lymphocyte interaction with the endothelium of the graft vessels. In addition, a viable small bowel, after 2 h of ex vivo perfusion, facilitates testing of pretreatment protocols for the reduction of the immunogenicity of small bowel allografts. Copyright (C) 2000 S. Karger AG, Basel

CROP RESIDUE EFFECTS ON SOIL ENVIRONMENT AND DRYLAND MAIZE AND SOYA BEAN PRODUCTION

The research reported here provides data on the effects of crop residues on the surface of no-till soil upon the soil environment and resulting biological activity, including crop growth. For maize (Zea mays L.) and soya bean [Glycine max (L.) Merr.] production in eastern Nebraska, U.S.A. (4 years of data), increasing crop residue rate decreased maximum soil temperatures at the soil surface by at least 5°C, and generally increased soil water storage by at least 50 mm. Availability and uptake of nitrogen from the soil organic matter and applied fertilizers (and for soya bean from decomposition of crop residues) were increased by increasing the crop residue rate from 0 to 150% of the quantity left after grain harvest of the previous crop. Hardly any of the nitrogen in maize residues was used by the next crop. These changes in the soil environment resulted in less stress on crops produced on residue-covered soil than for those on bare soil. Consequently, each Mg ha-1 of crop residues on the soil surface increased grain and stover production by approximately 120 and 270 kg ha-1 for maize, and 90 and 300 kg ha-1 for soya bean, respectively. Results show that there are major direct crop growth benefits from leaving crop residues on the soil surface, in addition to cumulative benefits that may result from reduced erosion losses and enhanced soil organic-matter contents

Kondo Effect in Multiple-Dot Systems

We study the Kondo effect in multiple-dot systems for which the inter- as well as intra-dot Coulomb repulsions are strong, and the inter-dot tunneling is small. The application of the Ward-Takahashi identity to the inter-dot dynamical susceptibility enables us to analytically calculate the conductance for a double-dot system by using the Bethe-ansatz exact solution of the SU(4) impurity Anderson model. It is clarified how the inter-dot Kondo effect enhances or suppresses the conductance under the control of the gate voltage and the magnetic field. We then extend our analysis to multiple-dot systems including more than two dots, and discuss their characteristic transport properties by taking a triple-dot system as an example.Comment: 8 pages, 9 figure

Stereoscopic Polar Plume Reconstructions from Stereo/Secchi Images

We present stereoscopic reconstructions of the location and inclination of polar plumes of two data sets based on the two simultaneously recorded images taken by the EUVI telescopes in the SECCHI instrument package onboard the \emph{STEREO (Solar TErrestrial RElations Observatory)} spacecraft. The ten plumes investigated show a superradial expansion in the coronal hole in 3D which is consistent with the 2D results. Their deviations from the local meridian planes are rather small with an average of $6.47^{\circ}$. By comparing the reconstructed plumes with a dipole field with its axis along the solar rotation axis, it is found that plumes are inclined more horizontally than the dipole field. The lower the latitude is, the larger is the deviation from the dipole field. The relationship between plumes and bright points has been investigated and they are not always associated. For the first data set, based on the 3D height of plumes and the electron density derived from SUMER/\emph{SOHO} Si {\sc viii} line pair, we found that electron densities along the plumes decrease with height above the solar surface. The temperature obtained from the density scale height is 1.6 to 1.8 times larger than the temperature obtained from Mg {\sc ix} line ratios. We attribute this discrepancy to a deviation of the electron and the ion temperatures. Finally, we have found that the outflow speeds studied in the O {\sc vi} line in the plumes corrected by the angle between the line of sight and the plume orientation are quite small with a maximum of 10 $\mathrm{km s^{-1}}$. It is unlikely that plumes are a dominant contributor to the fast solar wind.Comment: 25 pages, 13 figure

Corn Stalk Nitrate Concentration Profile

The end-of-season nitrate test provides a method of assessing the N available to the corn (Zea mays L.) crop during the latter part of the season. This study was conducted to determine how stalk nitrate test results and interpretations are affected by sample composition. Stalks were collected from three filed sites and separated into phytomers (node plus internode above), which were subdivided into three or five segments after length was measured. Nitrate-N concentration of phytomers decreased linearly from the soil to the ear. Within a phytomer, segments also decreased acropetally (from base to apex). Node tissue NO3-N concentration did not differ from that of the internode segment immediately above the node. Weighted means were used to compute NO3-N concentration of stalk samples collected 5 cm higher (from 20 to 40 cm above the soil) or lower (from 10 to 30 cm above the soil). Although the three samples (10-30, 15-35, and 20-40 cm) differed in NO3-N concentration, the difference was only about 15% compared with the 25% difference in sampling position (± 5 cm of 20-cm sample length). The phytomer nearest the soil had 35 to 40% greater NO3-N concentrations than the section of stalk 15 to 35 cm above the soil. Critical values delineating yield-limiting adequate, and excessive N availability should be modified if stalk sections other than the standard 15 to 35 cm section are used. However, the qualitative nature of the stalk nitrate test and the range of NO3-N concentrations observed with reasonable corn cultural practices (1000x) make this test quite robust and precise definition of sample composition and critical values less necessary

Proton recoil polarization in exclusive (e,e'pp) reactions

The general formalism of nucleon recoil polarization in the (${\vec e},e'{\vec N}N$) reaction is given. Numerical predictions are presented for the components of the outgoing proton polarization and of the polarization transfer coefficient in the specific case of the exclusive $^{16}$O(${\vec e},e'{\vec p}p$)$^{14}$C knockout reaction leading to discrete states in the residual nucleus. Reaction calculations are performed in a direct knockout framework where final-state interactions and one-body and two-body currents are included. The two-nucleon overlap integrals are obtained from a calculation of the two-proton spectral function of $^{16}$O where long-range and short-range correlations are consistently included. The comparison of results obtained in different kinematics confirms that resolution of different final states in the $^{16}$O(${\vec e},e'{\vec p}p$)$^{14}$C reaction may act as a filter to disentangle and separately investigate the reaction processes due to short-range correlations and two-body currents and indicates that measurements of the components of the outgoing proton polarization may offer good opportunities to study short-range correlations.Comment: 12 pages, 6 figure

Leistungs- und Kostenrechnung in der Datenverarbeitung:Am Beispiel der Hochschulrechenzentren in NRW

Für Hochschulrechenzentren wird eine Leistungs- und Kostenrechnung vorgeschlagen, die Dienstleistungen und ihre Qualitätsmerkmale neben eine Prozeßkostenrechnung stellt. Mit der Prozeßkostenrechnung entstehen Steuerungs- und Vergleichsmöglichkeiten in und zwischen Hochschulrechenzentren. Über "Kostentreiber" werden die Leistungen weitgehend mengenabhängig. Eine Zuordnung der Kosten zu ihren Verursachern wird möglich. Die Prozesse werden für ein Hochschulrechenzentrum definiert, die einzelnen Kostenfaktoren erläutert und zusammengestellt. Es wird ein Berechnungsschema vorgeschlagen, Ausführungshinweise werden gegeben und die Ergebnisse diskutiert. Als Fallstudien werden die Prozeßkosten eines kleinen und eines großen Rechenzentrums angesprochen