Integrated orbital servicing study for low-cost payload programs. Volume 2: Technical and cost analysis

Orbital maintenance concepts were examined in an effort to determine a cost effective orbital maintenance system compatible with the space transportation system. An on-orbit servicer maintenance system is recommended as the most cost effective system. A pivoting arm on-orbit servicer was selected and a preliminary design was prepared. It is indicated that orbital maintenance does not have any significant impact on the space transportation system

Long-period waves over California\u27s continental borderland Part II. Tsunamis

During the Chilean tsunami of 22 May 1960, precise readings of sea level were digitally recorded every 15 seconds by the La Jolla low-frequency wave instrument. The tsunami remained above background for a week. The record gave a good opportunity to measure the decay of tsunami energy as a function of frequency. Energy is reduced by 1/e about once each half day. The decay is somewhat more rapid at high frequen cies and at high energy densities. The total energy of the tsunami is estimated to be of the order of 3 x 1023 ergs

Long-period waves over California\u27s continental borderland Part I. Background spectra

Long ocean waves, with frequencies between 0.2 and xo cycles per hour (cph), have been recorded simultaneously at La Jolla on the California coast and at San Clemente Island, about rno km seaward. The spectral power is greatest at the lowest frequencies but remains fairly uniform (about 5 x 10-2 cm2/cph) between 0.7 and 10 cph. Comparison of the Island and shore records shows that at the lowest frequencies (below 0.7 cph) the two records are consistently in phase and are highly coherent, as might be expected; above 0.7 cph they are out of phase, and the coherence is low...

Long-period waves over California\u27s continental borderland. Part III The decay of tsunamis and the dissipation of tidal energy

The characteristic damping (energy e-folding) time derived from the decay of the tsunami pulse can be compared to the dissipation time of the lunar semidiurnal tides as inferred from the discrepancies in the orbital motions of the Moon, Sun, and Mercury. The times are comparable, of the order of ½ day, and this suggests that the same processes are responsible for the dissipation of the tide waves and tidal waves

Hematopoietic development of embryonic stem cells in vitro: cytokine and receptor gene expression

A novel system to study early hematopoietic development is described. This report documents the in vitro capacity of murine embryonic stem (ES) cells to differentiate into hematopoietic precursors of most, if not all, of the colony-forming cells found in normal bone marrow. This system is used to correlate the genetic expression of cytokines, their receptors, the β-globins, and the hematopoietic cell surface markers throughout the time course of ES cell differentiation with the hematopoietic development that occurs in these cultures.A novel system to study early hematopoietic development is described. This report documents the in vitro capacity of murine embryonic stem (ES) cells to differentiate into hematopoietic precursors of most, if not all, of the colony-forming cells found in normal bone marrow. This system is used to correlate the genetic expression of cytokines, their receptors, the β-globins, and the hematopoietic cell surface markers throughout the time course of ES cell differentiation with the hematopoietic development that occurs in these cultures

Dynamical variations of the differential rotation in the solar convection zone

Recent analyses of helioseismological observations seem to suggest the presence of two new phenomena connected with the dynamics of the solar convective zone. Firstly, there are present torsional oscillations with periods of about 11 years, which penetrate significantly into the solar convection zone and secondly, oscillatory regimes exist near the base of the convection which are markedly different from those observed near the top, having either significantly reduced periods or being non-periodic. Recently spatiotemporal fragmentation/bifurcation has been proposed as a possible dynamical mechanism to account for such observed multi-mode behaviours in different parts of the solar convection zone. Evidence for this scenario was produced in the context of an axisymmetric mean field dynamo model operating in a spherical shell, with a semi-open outer boundary condition and a zero order angular velocity obtained by the inversion of the MDI data, in which the only nonlinearity was the action of the Lorentz force of the dynamo generated magnetic field on the solar angular velocity. Here we make a detailed study of the robustness of this model with respect to plausible changes to its main ingredients, including changes to the alpha and eta profiles as well as the inclusion of a nonlinear alpha quenching. We find that spatiotemporal fragmentation is present in this model for different choices of the rotation data and as the details of the model are varied. Taken together, these results give strong support to the idea that spatiotemporal fragmentation is likely to occur in general dynamo settings.Comment: 14 pages, 30 figures, submitted to Astronomy and Astrophysics, also available at http://www.eurico.web.co

Evolving information systems: meeting the ever-changing environment

To meet the demands of organizations and their ever-changing environment, information systems are required which are able to evolve to the same extent as organizations do. Such a system has to support changes in all time-and application-dependent aspects. In this paper, requirements and a conceptual framework for evolving information systems are presented. This framework includes an architecture for such systems and a revision of the traditional notion of update. Based on this evolutionary notion of update (recording, correction and forgetting) a state transition-oriented model on three levels of abstraction (event level, recording level, correction level) is introduced. Examples are provided to illustrate the conceptual framework for evolving information systems

The effect of absent blood flow on the zebrafish cerebral and trunk vasculature

The role of blood flow in vascular development is complex and context-dependent. In this study, we quantify the effect of the lack of blood flow on embryonic vascular development on two vascular beds, namely the cerebral and trunk vasculature in zebrafish. We perform this by analysing vascular topology, endothelial cell (EC) number, EC distribution, apoptosis, and inflammatory response in animals with normal blood flow or absent blood flow. We find that absent blood flow reduced vascular area and EC number significantly in both examined vascular beds, but the effect is more severe in the cerebral vasculature, and severity increases over time. Absent blood flow leads to an increase in non-EC-specific apoptosis without increasing tissue inflammation, as quantified by cerebral immune cell numbers and nitric oxide. Similarly, while stereotypic vascular patterning in the trunk is maintained, intra-cerebral vessels show altered patterning, which is likely to be due to vessels failing to initiate effective fusion and anastomosis rather than sprouting or path-seeking. In conclusion, blood flow is essential for cellular survival in both the trunk and cerebral vasculature, but particularly intra-cerebral vessels are affected by the lack of blood flow, suggesting that responses to blood flow differ between these two vascular beds

Generalized h-index for Disclosing Latent Facts in Citation Networks

What is the value of a scientist and its impact upon the scientific thinking? How can we measure the prestige of a journal or of a conference? The evaluation of the scientific work of a scientist and the estimation of the quality of a journal or conference has long attracted significant interest, due to the benefits from obtaining an unbiased and fair criterion. Although it appears to be simple, defining a quality metric is not an easy task. To overcome the disadvantages of the present metrics used for ranking scientists and journals, J.E. Hirsch proposed a pioneering metric, the now famous h-index. In this article, we demonstrate several inefficiencies of this index and develop a pair of generalizations and effective variants of it to deal with scientist ranking and with publication forum ranking. The new citation indices are able to disclose trendsetters in scientific research, as well as researchers that constantly shape their field with their influential work, no matter how old they are. We exhibit the effectiveness and the benefits of the new indices to unfold the full potential of the h-index, with extensive experimental results obtained from DBLP, a widely known on-line digital library.Comment: 19 pages, 17 tables, 27 figure