Microscopic calculation of the spin-dependent neutron scattering lengths on 3He

We report on the spin.dependent neutron scattering length on 3He from a microscopic calculation of p-3H, n-3He, and d-2H scattering employing the Argonne v18 nucleon-nucleon potential with and without additional three-nucleon force. The results and that of a comprehensive R-matrix analysis are compared to a recent measurement. The overall agreement for the scattering lengths is quite good. The imaginary parts of the scattering lengths are very sensitive to the inclusion of three-nucleon forces, whereas the real parts are almost insensitive.Comment: 9 pages, 1 figur

Elastic p-3He and n-3H scattering with two- and three-body forces

We report on a microscopic calculation of n-3H and p-3He scattering employing the Argonne v_{18} and v_8' nucleon-nucleon potentials with and without additional three-nucleon force. An R-matrix analysis of the p-3He and n-3H scattering data is presented. Comparisons are made for the phase shifts and a selection of measurements in both scattering systems. Differences between our calculation and the R-matrix results or the experimental data can be attributed to only two partial waves (3P0 and 3P2). We find the effect of the Urbana IX and the Texas-Los Alamos three-nucleon forces on the phase shifts to be negligible.Comment: submitted to Phys. Rev.

Variational Calculation on A=3 and 4 Nuclei with Non-Local Potentials

The application of the hyperspherical harmonic approach to the case of non-local two-body potentials is described. Given the properties of the hyperspherical harmonic functions, there are no difficulties in considering the approach in both coordinate and momentum space. The binding energies and other ground state properties of A=3 and 4 nuclei are calculated using the CD Bonn 2000 and N3LO two-body potentials. The results are shown to be in excellent agreement with corresponding ones obtained by other accurate techniques.Comment: 12 pages, 6 tables, RevTex

A survey of green plant tRNA 3'-end processing enzyme tRNase Zs, homologs of the candidate prostate cancer susceptibility protein ELAC2

<p>Abstract</p> <p>Background</p> <p>tRNase Z removes the 3'-trailer sequences from precursor tRNAs, which is an essential step preceding the addition of the CCA sequence. tRNase Z exists in the short (tRNase Z^S) and long (tRNase Z^L) forms. Based on the sequence characteristics, they can be divided into two major types: bacterial-type tRNase Z^Sand eukaryotic-type tRNase Z^L, and one minor type, <it>Thermotoga maritima </it>(TM)-type tRNase Z^S. The number of tRNase Zs is highly variable, with the largest number being identified experimentally in the flowering plant <it>Arabidopsis thaliana</it>. It is unknown whether multiple tRNase Zs found in <it>A. thaliana </it>is common to the plant kingdom. Also unknown is the extent of sequence and structural conservation among tRNase Zs from the plant kingdom.</p> <p>Results</p> <p>We report the identification and analysis of candidate tRNase Zs in 27 fully sequenced genomes of green plants, the great majority of which are flowering plants. It appears that green plants contain multiple distinct tRNase Zs predicted to reside in different subcellular compartments. Furthermore, while the bacterial-type tRNase Z^Ss are present only in basal land plants and green algae, the TM-type tRNase Z^Ss are widespread in green plants. The protein sequences of the TM-type tRNase Z^Ss identified in green plants are similar to those of the bacterial-type tRNase Z^Ss but have distinct features, including the TM-type flexible arm, the variant catalytic HEAT and HST motifs, and a lack of the PxKxRN motif involved in CCA anti-determination (inhibition of tRNase Z activity by CCA), which prevents tRNase Z cleavage of mature tRNAs. Examination of flowering plant chloroplast tRNA genes reveals that many of these genes encode partial CCA sequences. Based on our results and previous studies, we predict that the plant TM-type tRNase Z^Ss may not recognize the CCA sequence as an anti-determinant.</p> <p>Conclusions</p> <p>Our findings substantially expand the current repertoire of the TM-type tRNase Z^Ss and hint at the possibility that these proteins may have been selected for their ability to process chloroplast pre-tRNAs with whole or partial CCA sequences. Our results also support the coevolution of tRNase Zs and tRNA 3'-trailer sequences in plants.</p

The evolution of the plastid chromosome in land plants: gene content, gene order, gene function

This review bridges functional and evolutionary aspects of plastid chromosome architecture in land plants and their putative ancestors. We provide an overview on the structure and composition of the plastid genome of land plants as well as the functions of its genes in an explicit phylogenetic and evolutionary context. We will discuss the architecture of land plant plastid chromosomes, including gene content and synteny across land plants. Moreover, we will explore the functions and roles of plastid encoded genes in metabolism and their evolutionary importance regarding gene retention and conservation. We suggest that the slow mode at which the plastome typically evolves is likely to be influenced by a combination of different molecular mechanisms. These include the organization of plastid genes in operons, the usually uniparental mode of plastid inheritance, the activity of highly effective repair mechanisms as well as the rarity of plastid fusion. Nevertheless, structurally rearranged plastomes can be found in several unrelated lineages (e.g. ferns, Pinaceae, multiple angiosperm families). Rearrangements and gene losses seem to correlate with an unusual mode of plastid transmission, abundance of repeats, or a heterotrophic lifestyle (parasites or myco-heterotrophs). While only a few functional gene gains and more frequent gene losses have been inferred for land plants, the plastid Ndh complex is one example of multiple independent gene losses and will be discussed in detail. Patterns of ndh-gene loss and functional analyses indicate that these losses are usually found in plant groups with a certain degree of heterotrophy, might rendering plastid encoded Ndh1 subunits dispensable

Meridianstroemungsrechnung mit dem Ziel der Pumpgrenzvorhersage: Weiterentwicklung des Berechnungsverfahrens Abschlussbericht

Improved material technologies permits one, in modern gas turbine construction, to raise the turbine inlet temperature continually to improve the thermal efficiency. The optimisation of the overall process requires a simultaneous raising of the compressor pressure ratio, where increasing demands must be made of the numerical design and calculation checking process. Only 2 dimensional processes can at present be considered for the calculation of the flow field and characteristic for such multi-stage axial compressors. The further development of such a program for the calculation checking of the 2D meridian flow with axial symmetry of multi-stage axial compressors was the object of the completed research project. At the beginning of the period of work, a functioning process of calculation was available, which was worked out in an earlier project at AG Turbo. Based on the finite element method and with the aid of the flow function, the movement equations in the meridian plane are solved. Flow deflection and loss production of the sets of blades are modelled by empirical correlations and are imposed on the flow field with the aid of field forces. A main point of the work of the project was formed by the picturing of radial mixing effects. The equation of Gallimore and Cumpsty was used for this subject, according to which the radial mixing effects are modelled on the basis of turbulent diffusion. A second main point of the work is the working out and testing of a new concept for calculating the loss and deflection of the blade profiles for 2 dimensional calculation processes. Altogether, at the end of the project, a further improved tool for quicker and more precise calculation of the flow fuild of multi-stage axial compressors is available. (orig./AKF)Verbesserte Werkstofftechnologien erlauben im modernen Gasturbinenbau eine kontinuierliche Anhebung der Turbineneintrittstemperaturen zur Steigerung des thermischen Wirkungsgrades. Dabei erfordert die Optimierung des Gesamtprozesses eine gleichzeitige Erhoehung des Verdichterdruckverhaeltnisses, wodurch auch an die numerischen Auslegungs- und Nachrechenverfahren wachsende Ansprueche gestellt werden muessen. Zur Stroemungsfeld- und Kennfeldberechnung kommen fuer solche vielstufigen Axialverdichter bis heute nur 2-dimensionale Verfahren in Frage. Die Weiterentwicklung eines solchen Programmes zur Nachrechnung des 2D-rotationssymmetrischen Meridianstroemung vielstufiger Axialverdichter war auch Gegenstand des abgeschlossenen Forschungsvorhabens. Zu Beginn der Laufzeit stand ein funktionsfaehiges Rechenverfahren zur Verfuegung, das in einem frueheren Vorhaben innerhalb der AG Turbo erarbeitet worden ist. Auf der Basis der Finite-Elemente-Methode und unter Zuhilfenahme der Stromfunktion werden die Bewegungsgleichungen in der Meridianebene geloest. Stroemungsumlenkung und Verlustproduktion der Schaufelgitter werden mit empirischen Korrelationen modelliert und dem Stroemungsfeld mit Hilfe von Feldkraeften aufgepraegt. Einen Schwerpunkt der Arbeiten des Vorhabens hat die Abbildung radialer Mischungseffekte gebildet. Zu diesem Themenbereich ist der Ansatz nach Gallimore und Cumpsty verwendet worden, nach dem radiale Mischeffekte auf der Basis turbulenter Diffusion modelliert werden. Im zweiten Arbeitsschwerpunkt ist ein neues Konzept zur Berechnung von Verlust und Umlenkung der Schaufelprofile fuer 2-dimensionale Rechenverfahren erarbeitet und erprobt worden. Insgesamt steht am Ende des Vorhabens ein weiter verbessertes Werkzeug zur schnellen und praezisen Berechnung des Stroemungsfeldes vielstufiger Axialverdichter zur Verfuegung. (orig./AKF)SIGLEAvailable from TIB Hannover: F97B96+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany); Siemens A.G., Muenchen (Germany)DEGerman

Turbotech. Teilprojekt 1.1.2.4: Rotationssymmetrische Berechnung der Meridianstroemung in vielstufigen Axialverdichtern unter Einbeziehung der Gittercharakteristiken und Seitenwandgrenzschicht Abschlussbericht

The objective of this study is to develop a method for calculating the meridian flow field in multistage, highly loaded axial-flow compressors with variable geometry. For the present state of research, the complexity of the flow field present in a multistage turbomachine requires considerable concessions with regard to the general applicability of the numerical methods used. Although first promising applications of three-dimensional field methods have been existing for the calculation of multistage turbomachinery, the use of these methods for the calculation of multistage machinery is not to be expected in the foreseeable future. Therefore, the meridian flow methods based on the assumption of rotationally symmetrical flow have become generally accepted for technical problems. Within the framework of the present study, therefore, a method for the calculation of the meridian flow field in multistage axial-flow compressors was developed on the basis of the finite element method. A newly developed iteration method helps mastering the problems occurring during the recalculation of compressors with high compression ratio as a result of the nonlinearity of the equation of motion. The calculation of side wall boundary layer development using a two-dimensional integral method permits modeling the boundary layer stabilization which was experimentally verified for multistage axial-flow compressors. In addition to this, such a method, besides determining the annular chamber blocking, can be used to make statements on the boundary loss. (orig.)SIGLEAvailable from TIB Hannover: F95B1957+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany); Siemens AG, Erlangen (Germany)DEGerman