760 research outputs found
Properties and stabilization of an extracellular α-glucosidase from the extremely thermophilic archaebacteria Thermococcus strain AN 1: enzyme activity at 130°C
An extracellular α-glucosidase from the thermophilic archaebacterium Thermococcus strain AN1 was purified 875-fold in five steps (Hiload Q-Sepharose, phenyl Sepharose, HPHT-hydroxyapatite, gel filtration and Mono Q chromatography) with a yield of 4%. It is a monomer with a molecular mass of about 60 kDa and a pI around 5. At 98°C, the purified enzyme in buffer has a half-life around 35 min, which is increased to around 215 min in presence of l% (w/v) dithiothreitol and 1% (w/v) BSA. Dithiothreitol (1%, w/v) and BSA (0.4%, w/v) also substantially increase the enzyme activity. The Km at 75°C is 0.41 mM with pNP-α- -glucopyranoside as substrate. The substrate preference of the enzyme is: pNP-α-D-glucoside > nigerose > panose > palatinose > isomaltose > maltose and turanose. No activity was found against starch, pullulan, amylose, maltotriose, maltotetraose, isomaltotriose, cellobiose and β-gentiobiose. A variety of techniques including immobilization (e.g., on epoxy and glass beads), chemical modification (cross- and cocross-linking) and the use of additives (including polyhydroxylic molecules, BSA, salts, etc.) were applied to enhance stability at temperatures above 100°C. The half-life could be increased from about 4 min at 110°C to 30–60 min at 130°C in presence of 90% (w/v) sorbitol, 1% (w/v) dithiothreitol and l% (w/v) BSA, and by cocross-linking with BSA in the presence of 90% (w/v) sorbitol. The stabilized enzyme showed good activity at 130°C
Gluon- vs. Sea quark-Shadowing
We calculate the shadowing of sea quarks and gluons and show that the
shadowing of gluons is {\it not} simply given by the sea quark shadowing,
especially at small . The calculations are done in the lab frame approach by
using the generalized vector meson dominance model. Here the virtual photon
turns into a hadronic fluctuation long before the nucleus. The subsequent
coherent interaction with more than one nucleon in the nucleus leads to the
depletion known as shadowing. A
comparison of the shadowing of quarks to E665 data for and
shows good agreement.Comment: 9 pages, 3 eps figure
Instability tests for air-jet textured yarns
The air-jet texturing process is briefly introduced and its advantages over other texturing processes are summarized. Characteristics of air-jet textured yarns are stated with special reference to the stability of the yarns. Test methods used in industry and research to determine the "stability" or "instability" of air-jet textured yarns are critically reviewed. These methods involve different basic principles and therefore inevitably give different results. There is no consensus on a standard method. Effects of various test parameters, such as specimen length, test duration, and the alternatives of using a single yarn, a hank, or a skein as a test specimen are investigated. An improved test method is suggested as a standard instability test, and various existing methods are compared with it. Results of all the methods show similar trends for varying values of air pressure. Other yarn characteristics such as linear density, breaking elongation, and tenacity are also determined, and their indications of yarn quality are compared with the indications of instability tests. Stability test results alone provide misleading information regarding air-jet textured yarn quality
Checklist of the Inland Fishes of Louisiana
Since the publication of Freshwater Fishes of Louisiana (Douglas, 1974) and a revised checklist (Douglas and Jordan, 2002), much has changed regarding knowledge of inland fishes in the state. An updated reference on Louisiana’s inland and coastal fishes is long overdue. Inland waters of Louisiana are home to at least 224 species (165 primarily freshwater, 28 primarily marine, and 31 euryhaline or diadromous) in 45 families. This checklist is based on a compilation of fish collections records in Louisiana from 19 data providers in the Fishnet2 network (www.fishnet2.net). The checklist has grown because of descriptions of three new species, new distribution records of both native and non-native species, and the addition numerous of marine species that are known to enter freshwaters in Louisiana
Charmonium Composition and Nuclear Suppression
We study charmonium production in hadron-nucleus collisions through the
intermediate next-to-leading Fock space component , formed by
a colour octet pair and a gluon. We estimate the size of this state
and show that its interaction with nucleons accounts for the observed
charmonium suppression in nuclear interactions.Comment: Plain TeX, 8 pages, 5 figures available upon reques
Structure Functions are not Parton Probabilities
The common view that structure functions measured in deep inelastic lepton
scattering are determined by the probability of finding quarks and gluons in
the target is not correct in gauge theory. We show that gluon exchange between
the fast, outgoing partons and target spectators, which is usually assumed to
be an irrelevant gauge artifact, affects the leading twist structure functions
in a profound way. This observation removes the apparent contradiction between
the projectile (eikonal) and target (parton model) views of diffractive and
small x_{Bjorken} phenomena. The diffractive scattering of the fast outgoing
quarks on spectators in the target causes shadowing in the DIS cross section.
Thus the depletion of the nuclear structure functions is not intrinsic to the
wave function of the nucleus, but is a coherent effect arising from the
destructive interference of diffractive channels induced by final state
interactions. This is consistent with the Glauber-Gribov interpretation of
shadowing as a rescattering effect.Comment: 35 pages, 8 figures. Discussion of physical consequences of final
state interactions amplified. Material on light-cone gauge choices adde
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The Vortical Structures in the Rear Separation and Wake Produced by a Supersonic Micro-Ramp
The vortical structures in the rear separation and wake region produced by a micro-ramp that immersed in a supersonic turbulent boundary layer are investigated. The small scale separation close to the trailing edge was reveled and this confirms the previous experimental observation. Between the reverse region and surrounding fast moving flow, a three-dimensional shear layer was formed, and vortices are generated. By using vortex line method, the spiral points were understood as the cross-sections of the Ω-shaped vortices that follow the shape of the separation. The vortical structure was analogous to that in the wake region, where similar Ω-shaped vortex can be observed which follows the deficit region caused by the micro-ramp. Finally, the revealed flow topology was conceived beneficial to studying the wall bounded turbulence which involves similar vortical structures but in a smaller scale, while the vortical pattern in the current micro-ramp wake is larger
Calculation of the T-matrix: general considerations and application of the point-matching method
The T-matrix method is widely used for the calculation of scattering by
particles of sizes on the order of the illuminating wavelength. Although the
extended boundary condition method (EBCM) is the most commonly used technique
for calculating the T-matrix, a variety of methods can be used.
We consider some general principles of calculating T-matrices, and apply the
point-matching method to calculate the T-matrix for particles devoid of
symmetry. This method avoids the time-consuming surface integrals required by
the EBCM.Comment: 10 pages. 2 figures, 1 tabl
Reasoning with comparative moral judgements: an argument for Moral Bayesianism
The paper discusses the notion of reasoning with comparative moral judgements
(i.e judgements of the form “act a is morally superior to act b”) from the point of view of several meta-ethical positions. Using a simple formal result, it is argued that only a version of moral cognitivism that is committed to the claim that moral beliefs come in degrees can give a normatively plausible account of such reasoning. Some implications of accepting such a version of moral cognitivism are discussed
Energy Losses (Gains) of Massive Coloured Particles in Stochastic Colour Medium
The propagation of massive coloured particles in stochastic background
chromoelectric field is studied using the semiclassical equations of motion.
Depending on the nature of the stochastic background we obtain the formulae for
the energy losses of heavy coloured projectile in nonperturbative hadronic
medium and for the energy gains in the stochastic field present, e.g., in the
turbulent plasma. The result appears to be significantly dependent on the form
of the correlation function of stochastic external fieldComment: 9 pages, BI-TP 94/15, plain LaTe
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