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  • 1
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 7 (1961), S. 211-216 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The reaction of gaseous components at a solid catalytic surface has long been a subject of prime engineering interest. Generally speaking one expects the reaction velocity constant to follow the Arrhenius exponential temperature dependence. However as the reaction temperature increases, the intrinsic reactivity of the surface will increase and mass transfer begins to limit the rate of the reaction. In the case of a porous solid catalyst, where most of the active surface is on the catalyst pellet interior, the rate-limiting process will frequently be internal diffusion, and in such a case the milder effect that temperature has on the diffusion process is the one observed in the gross kinetics, rather than the exponential Arrhenius dependence.The study reported here has examined the kinetics of the dehydrogenation of cyclohexane to benzene over a platinum-on-alumina pelleted catalyst. This is a notorious problem system, and in seeking to describe the observed rate data the authors provided a stern test for an analytical model treating the coordinate diffusion and reaction mechanisms. In particular the parameter of particle size was studied over a temperature range of from 640° to 910°F. For these runs reactor pressure was held constant at essentially 200 lb./sq. in. gauge (14.7 atm.), und the feed was maintained at 20 mole % cyclohexane, 80 mole % hydrogen.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 23 (1981), S. 953-964 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The homogeneity of a purified ribonuclease from brewers' yeast was determined by velocity sedimentation and polyacrylamide gel electrophoresis techniques. The velocity sedimentation pattern gave a single peak with a Sapp 3.46 and polyacrylamide gel electrophoresis showed one major band. The absorption spectrum of the enzyme showed maximum absorption at 277-278 nm and minimum at 252 nm. The enzyme was relatively stable to extreme pH values and high temperature. Both NaCl and KCl increased the enzyme activity whereas enzyme was inhibited by divalent metal ions. The inhibition of the enzyme was increased in the order of Ca2+ 〉 Mg2+ 〉 Fe2+Cu2+. Chemical modification studies of the enzyme showed that tryptophan residues and disulfide bonds were required for enzyme activity.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The sandwich paper electrophoresis technique, such as that of Foster (1952b), was modified to permit routine examination of as many as 15 samples of materials such as bacterial cultures, simultaneously, and with greater rapidity than with paper chromatography techniques. By the use of borate buffer at pH 9.6 with aniline hydrogen oxalate for development, materials such as glucose, fructose, 2-ketogluconic acid, and 5-ketogluconic acid could be separated in three hours.
    Additional Material: 3 Ill.
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  • 4
    Publication Date: 2011-08-17
    Description: A model for the formation and confinement of dense (at least about 1 billion per cu cm) clouds in QSOs and active galactic nuclei is presented wherein thermal instabilities behind radiative shocks cause the collapse of regions where the preshock density is enhanced over that of the surrounding medium. Such shocks (of total energy around 10 to the 51st ergs) are likely to occur if the frequent optical outbursts observed in many of these objects are accompanied by mass ejections of comparable energy. It is found that clouds quite similar to those thought to exist in QSOs etc. can be created in this manner at radii of the order of 10 to the 17th cm. The clouds can be subsequently accelerated to observed bulk velocities by either radiation pressure or a collision with a much stronger (total energy around 10 to the 53 ergs) shock. Alternatively, their high observed velocities could be caused by gravitational infall or rotation. The mass production required at inner radii by the outflow models can be supplied through a mechanism previously discussed by Shields (1977).
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 227
    Format: text
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  • 5
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    In:  Other Sources
    Publication Date: 2011-08-17
    Description: Explanations of the line feature in the hard X-ray (58 keV) spectrum of the compact X-ray source Hercules X-1 are presented. The most important characteristic of the emission (interpreted as a cyclotron emission from a strong magnetic field, i.e., B greater than one trillion Gauss) is that the FWHM is less than 12 keV, with a total observed luminosity in the line of approximately 1% of the total X-ray luminosity. If the source region is only at the magnetic poles of a neutron star, the electrons are confined to a path nearly parallel to the B-field lines, and the angle of emission will be narrow. Photon emission under such circumstances is also discussed; and it is suggested that photons can leave either through holes in the shell formed by the hard X-rays, or can escape through the shell itself. Attention is given to the accretion flow structure near the magnetopause, as a critical parameter of narrow line emission.
    Keywords: ASTROPHYSICS
    Type: Nature; vol2 274
    Format: text
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  • 6
    Publication Date: 2019-06-27
    Description: The paper presents an approximate solution to the iron K alpha line transfer problem in a stellar atmosphere illuminated by an external X-ray source as in a binary X-ray system. The emergent Comptonized line profile can independently yield information on the abundance of heavy elements in the primary atmosphere and on the solid angle subtended by the primary at the X-ray source.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 215
    Format: text
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  • 7
    Publication Date: 2019-06-27
    Description: Preheating of infalling gas by emergent X-rays can suppress accretion on to a compact X-ray source. For spherically symmetric accretion, the effect results in a new luminosity limit, orders of magnitude less than the Eddington limit, above which steady flow is impossible. The model may apply to the globular-cluster X-ray sources.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; 208; Sept. 1
    Format: text
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  • 8
    Publication Date: 2019-06-27
    Description: The detailed structure of the interaction of a strong stellar wind with the interstellar medium is presented. First, an adiabatic similarity solution is given which is applicable at early times. Second, a similarity solution is derived which includes the effects of thermal conduction between the hot (about 1 million K) interior and the cold shell of swept-up interstellar matter. This solution is then modified to include the effects of radiative energy losses. The evolution of an interstellar bubble is calculated, including the radiative losses. The quantitative results for the outer-shell radius and velocity and the column density of highly ionized species such as O VI are within a factor 2 of the approximate results of Castor, McCray, and Weaver (1975). The effect of stellar motion on the structure of a bubble, the hydrodynamic stability of the outer shell, and the observable properties of the hot region and the outer shell are discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 218
    Format: text
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  • 9
    Publication Date: 2019-06-27
    Description: The formation of X-ray spectral features due to iron in a relatively cool cloud of gas with a Thomson depth greater than 1 surrounding a compact source of continuum X-rays is described. Coupled equations are solved for the ionization structure of the cloud and for the radiative transfer of the X-rays. Photoionization suppresses the strength of emission lines and absorption edges. Comptonization of the radiation broadens emission lines, fills in absorption edges, and produces a high-energy cutoff. In order to describe multiple scattering, a Fokker-Planck equation is derived which includes an important modification of the Kompaneets equation. Narrow resonance lines are treated with an escape probability formalism.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 219
    Format: text
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