2,342 research outputs found
Virginia at War, 1865
Bringing the War (and a Series) to a Close
On January 1, 1865, in Richmond, Virginia, Judith Brockenbrough McGuire wrote in her diary, “Our children came over from Union Hill yesterday, to take their dinner from the contents of the captured box, and were detained by snow and rain. Whi...
Architecture of coatomer: Molecular characterization of delta-COP and protein interactions within the complex
Copyright © 2011 by The Rockefeller University Press.Coatomer is a cytosolic protein complex that forms the coat of COP I-coated transport vesicles. In our attempt to analyze the physical and functional interactions between its seven subunits (coat proteins, [COPs] alpha-zeta), we engaged in a program to clone and characterize the individual coatomer subunits. We have now cloned, sequenced, and overexpressed bovine alpha-COP, the 135-kD subunit of coatomer as well as delta-COP, the 57-kD subunit and have identified a yeast homolog of delta-COP by cDNA sequence comparison and by NH2-terminal peptide sequencing. delta-COP shows homologies to subunits of the clathrin adaptor complexes AP1 and AP2. We show that in Golgi-enriched membrane fractions, the protein is predominantly found in COP I-coated transport vesicles and in the budding regions of the Golgi membranes. A knock-out of the delta-COP gene in yeast is lethal. Immunoprecipitation, as well as analysis exploiting the two-hybrid system in a complete COP screen, showed physical interactions between alpha- and epsilon-COPs and between beta- and delta-COPs. Moreover, the two-hybrid system indicates interactions between gamma- and zeta-COPs as well as between alpha- and beta' COPs. We propose that these interactions reflect in vivo associations of those subunits and thus play a functional role in the assembly of coatomer and/or serve to maintain the molecular architecture of the complex.This work was supported by The Deutsche Forschungsgemeinschaft (SFB 352), the Human Frontier Science Program, and the Swiss National Science Foundation No. 31-43366.95
LIQUID METAL-HEATED SPACE RADIATOR-MOUNTED THERMIONIC GENERATOR. Quarterly Report No. 1, July 1-September 30, 1963
The design of the thermionic converter to be evaluated was completed. The converter incorporates a tantalum-10% tungsten alloy liquid metal containment tube insulated by BeO from a tungsten-25% rhenium emitter. A nickel collector with an interelectrode space of 8 mils was selected. The predicted performance of this converter indicates a power output of 4.7 w/cm/sup 2/ with an efficiency of 12% when the emitter temperature is 1500 deg C. A bifilar tungsten filament was selected for use as a heater in this program based on a study contained in this report. (auth
Nuclear Tetrahedral Symmetry: Possibly Present Throughout the Periodic Table
More than half a century after the fundamental, spherical shell structure in
nuclei has been established, theoretical predictions indicate that the
shell-gaps comparable or even stronger than those at spherical shapes may
exist. Group-theoretical analysis supported by realistic mean-field
calculations indicate that the corresponding nuclei are characterized by the
('double-tetrahedral') group of symmetry, exact or approximate. The
corresponding strong shell-gap structure is markedly enhanced by the existence
of the 4-dimensional irreducible representations of the group in question and
consequently it can be seen as a geometrical effect that does not depend on a
particular realization of the mean-field. Possibilities of discovering the
corresponding symmetry in experiment are discussed.Comment: 4 pages in LaTeX and 4 figures in eps forma
Kalman Filtering in the Air Quality Monitoring
Data assimilation is a process where an improved prediction is obtained from a weighted combination between experimental measurements and mathematical model data. In the present work this procedure is applied to pollutant atmospheric dispersion by using a Kalman filter (KF). This is interesting approach, because the KF gives an output in which the balance between the data from the diffusion model and the experimental data is done automaticaly, through the Kalman gain. In addition, the Kalman filter computes the propagation of the error
Tetrahedral Symmetry in Ground- and Low-Lying States of Exotic A ~ 110 Nuclei
Recent theoretical calculations predict a possible existence of nuclei with
tetrahedral symmetry: more precisely, the mean-field hamiltonians of such
nuclei are symmetric with respect to double point-group Td. In this paper, we
focus on the neutron-rich Zirconium isotopes as an example and present
realistic mean-field calculations which predict tetrahedral ground-state
configurations in 108,110Zr and low-lying excited states of tetrahedral
symmetry in a number of N > 66 isotopes. The motivations for focusing on these
nuclei, as well as a discussion of the possible experimental signatures of
tetrahedral symmetry are also presented.Comment: Accepted in Phys. Rev. C - Rapid Communication
Equilibrium and traveling-wave solutions of plane Couette flow
We present ten new equilibrium solutions to plane Couette flow in small
periodic cells at low Reynolds number (Re) and two new traveling-wave
solutions. The solutions are continued under changes of Re and spanwise period.
We provide a partial classification of the isotropy groups of plane Couette
flow and show which kinds of solutions are allowed by each isotropy group. We
find two complementary visualizations particularly revealing. Suitably chosen
sections of their 3D-physical space velocity fields are helpful in developing
physical intuition about coherent structures observed in low Re turbulence.
Projections of these solutions and their unstable manifolds from their
infinite-dimensional state space onto suitably chosen 2- or 3-dimensional
subspaces reveal their interrelations and the role they play in organizing
turbulence in wall-bounded shear flows.Comment: 23 pages, 12 figures, Accepted for publication in J. Fluid Mechanic
Probabilistic models of information retrieval based on measuring the divergence from randomness
We introduce and create a framework for deriving probabilistic models of Information Retrieval. The models are nonparametric models of IR obtained in the language model approach. We derive term-weighting models by measuring the divergence of the actual term distribution from that obtained under a random process. Among the random processes we study the binomial distribution and Bose--Einstein statistics. We define two types of term frequency normalization for tuning term weights in the document--query matching process. The first normalization assumes that documents have the same length and measures the information gain with the observed term once it has been accepted as a good descriptor of the observed document. The second normalization is related to the document length and to other statistics. These two normalization methods are applied to the basic models in succession to obtain weighting formulae. Results show that our framework produces different nonparametric models forming baseline alternatives to the standard tf-idf model
Who I Am: The Meaning of Early Adolescents’ Most Valued Activities and Relationships, and Implications for Self-Concept Research
Self-concept research in early adolescence typically measures young people’s self-perceptions of competence in specific, adult-defined domains. However, studies have rarely explored young people’s own views of valued self-concept factors and their meanings. For two major self domains, the active and the social self, this mixed-methods study identified factors valued most by 526 young people from socioeconomically diverse backgrounds in Ireland (10-12 years), and explored the meanings associated with these in a stratified subsample (n = 99). Findings indicate that self-concept scales for early adolescence omit active and social self factors and meanings valued by young people, raising questions about content validity of scales in these domains. Findings also suggest scales may under-represent girls’ active and social selves; focus too much on some school-based competencies; and, in omitting intrinsically salient self domains and meanings, may focus more on contingent (extrinsic) rather than true (intrinsic) self-esteem
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