110,919 research outputs found
Technique for measuring time-base errors of magnetic instrumentation recorders/reproducers
Time-base error analysis of magnetically recorded and played back digital data using tape flutter spectral density and amplitude probability distribution measurements and rms time plot
Thrust chamber performance using Navier-Stokes solution
The viscous, axisymmetric flow in the thrust chamber of the space shuttle main engine (SSME) was computed on the CRAY 205 computer using the general interpolants method (GIM) code. Results show that the Navier-Stokes codes can be used for these flows to study trends and viscous effects as well as determine flow patterns; but further research and development is needed before they can be used as production tools for nozzle performance calculations. The GIM formulation, numerical scheme, and computer code are described. The actual SSME nozzle computation showing grid points, flow contours, and flow parameter plots is discussed. The computer system and run times/costs are detailed
Axiomatic Holonomy Maps and Generalized Yang-Mills Moduli Space
This article is a follow-up of ``Holonomy and Path Structures in General
Relativity and Yang-Mills Theory" by Barrett, J. W. (Int.J.Theor.Phys., vol.30,
No.9, 1991). Its main goal is to provide an alternative proof of this part of
the reconstruction theorem which concerns the existence of a connection. A
construction of connection 1-form is presented. The formula expressing the
local coefficients of connection in terms of the holonomy map is obtained as an
immediate consequence of that construction. Thus the derived formula coincides
with that used in "On Loop Space Formulation of Gauge Theories" by Chan, H.-M.,
Scharbach, P. and Tsou S.T. (Ann.Phys., vol.167, 454-472, 1986). The
reconstruction and representation theorems form a generalization of the fact
that the pointed configuration space of the classical Yang-Mills theory is
equivalent to the set of all holonomy maps. The point of this generalization is
that there is a one-to-one correspondence not only between the holonomy maps
and the orbits in the space of connections, but also between all maps from the
loop space on to group fulfilling some axioms and all possible
equivalence classes of bundles with connection, where the equivalence
relation is defined by bundle isomorphism in a natural way.Comment: amslatex, 7 pages, no figure
The minimal structure containing the band 3 anion transport site. A 35Cl NMR study
35Cl NMR, which enables observation of chloride binding to the anion transport site on band 3, is used in the present study to determine the minimal structure containing the intact transport site. Removal of cytoskeletal and other nonintegral membrane proteins, or removal of the 40-kDa cytoskeletal domain of band 3, each leave the transport site intact. Similarly, cleavage of the 52-kDa transport domain into 17- and 35-kDa fragments by chymotrypsin leaves the transport site intact. Extensive proteolysis by papain reduces the integral red cell membrane proteins to their transmembrane segments. Papain treatment removes approximately 60% of the extramembrane portion of the transport domain and produces small fragments primarily in the range 3-7 kDa, with 5 kDa being most predominant. Papain treatment damages, but does not destroy, chloride binding to the transport site; thus, the minimal structure containing the transport site is composed solely of transmembrane segments. In short, the results are completely consistent with a picture in which the transport site is buried in the membrane where it is protected from proteolysis; the transmembrane segments that surround the transport site are held together by strong attractive forces within the bilayer; and the transport site is accessed by solution chloride via an anion channel leading from the transport site to the solution
Chloride binding to the anion transport binding sites of band 3. A 35Cl NMR study
Band 3 is an integral membrane protein that exchanges anions across the red cell membrane. Due to the abundance and the high turnover rate of the band 3 transport unit, the band 3 system is the most heavily used ion-transport system in a typical vertebrate organism. Here we show that 35Cl NMR enables direct and specific observation of substrate Cl- binding to band 3 transport sites, which are identified by a variety of criteria: (a) the sites are inhibited by 4,4'- dinitrostilbene -2,2'- disulfonate, which is known to inhibit competitively Cl- binding to band 3 transport sites; (b) the sites have affinities for 4,4'- dinitrostilbene -2,2'-disulfonate and Cl- that are quantitatively similar to the known affinities of band 3 transport sites for these anions; and (c) the sites have relative affinities for Cl-, HCO-3, F-, and I- that are quantitatively similar to the known relative affinities of band 3 transport sites for these anions. The 35Cl NMR assay also reveals a class of low affinity Cl- binding sites (KD much greater than 0.5 M) that are not affected by 4,4'- dinitrostilbene -2,2'- disulfonate. These low affinity sites may be responsible for the inhibition of band 3 catalyzed anion exchange that has been previously observed at high [Cl-]. In the following paper the 35Cl NMR assay is used to resolve the band 3 transport sites on opposite sides of the membrane, thereby enabling direct observation of the transmembrane recruitment of transport sites
Modeling of secondary organic aerosol yields from laboratory chamber data
Laboratory chamber data serve as the basis for constraining models of secondary organic aerosol (SOA) formation. Current models fall into three categories: empirical two-product (Odum), product-specific, and volatility basis set. The product-specific and volatility basis set models are applied here to represent laboratory data on the ozonolysis of α-pinene under dry, dark, and low-NOx conditions in the presence of ammonium sulfate seed aerosol. Using five major identified products, the model is fit to the chamber data. From the optimal fitting, SOA oxygen-to-carbon (O/C) and hydrogen-to-carbon (H/C) ratios are modeled. The discrepancy between measured H/C ratios and those based on the oxidation products used in the model fitting suggests the potential importance of particle-phase reactions. Data fitting is also carried out using the volatility basis set, wherein oxidation products are parsed into volatility bins. The product-specific model is most likely hindered by lack of explicit inclusion of particle-phase accretion compounds. While prospects for identification of the majority of SOA products for major volatile organic compounds (VOCs) classes remain promising, for the near future empirical product or volatility basis set models remain the approaches of choice
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