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1

Digitale Medien

High-purity ion beam production at high current densities with a liquid-helium-cooled series-field-coil extraction ion diode (1991)

Hanson, D. L. ; Porter, J. L. ; Williams, R. R.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 70 (1991), S. 2926-2938

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Experiments are described in which a high-purity, high-power (0.15 TW, 1 MeV) proton beam is generated from an ion source consisting of H2 gas frozen onto a liquid-helium-cooled copper anode at 4.2 K in a series-field-coil extraction diode on the 0.7 TW HydraMITE-II accelerator. Peak anode proton current densities of 2 kA/cm2 were measured. This current density is a factor of 100 higher than those obtained in previous liquid-helium-cooled cryogenic diode experiments on small accelerators and is in the range required for high-power ion beam applications. Thomson parabola, Faraday cup, and carbon activation measurements indicate an ion beam proton fraction close to 100% for the cryogenic source, compared to 50–70% for the standard hydrocarbon anode tested. The cryogenic proton source is believed to consist of no more than a few monolayers of molecular hydrogen. The hydrogen-coated cryogenic anode shows a faster initial anode turn-on than other materials. However, source-limited emission from the thin hydrogen layer results in a somewhat longer current risetime, reduced ion diode efficiency, lower proton current enhancement over the Child–Langmuir limit, and a proton spectrum of lower average energy than for the hydrocarbon anode. Techniques to overcome these limitations are discussed. Cryogenic ion sources consisting of frozen N2, CH4, and Ne have also been studied. In each case, high intensity beams consisting predominantly of components of the refrigerated gas were produced.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.349317

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2

Digitale Medien

Twistor representation of Yang–Mills fields on Minkowski space (1991)

Fioravanti, Mario A. ; Porter, John R.

College Park, Md. : American Institute of Physics (AIP)

Journal of Mathematical Physics 32 (1991), S. 259-265

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ISSN: 1089-7658

Quelle: AIP Digital Archive

Thema: Mathematik , Physik

Notizen: A correspondence between (not necessarily self-dual nor anti-self-dual) Yang–Mills fields on Minkowski space, and pairs of cohomology classes γ, φ, on null twistor space PN(large-closed-square) is established; γ∈H1CR (PN(large-closed-square),@sg) defines a deformed Cauchy–Riemman (C–R)(γ) structure on a principal bundle over PN, and φ∈H1CR(γ) (PN(large-closed-square),O(−4)⊗@sg). The correspondence depends on the choice of a spacelike hyperplane in Minkowski space. Here, γ and φ provide initial values in the spin bundle over this hyperplane for a system of evolution equations, along the null geodesic spray congruence in the spin bundle over Minkowski space.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.529129

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3

Digitale Medien

An experimental study of the molecular mixing process in an axisymmetric laminar vortex ring (1991)

Southerland, Kenneth B. ; Porter, John R. ; Dahm, Werner J. A. ; [weitere]

New York, NY : American Institute of Physics (AIP)

Physics of Fluids 3 (1991), S. 1385-1392

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ISSN: 1089-7666

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Results are presented from an experimental study of the molecular mixing of a dynamically passive conserved scalar quantity in an axisymmetric laminar vortex ring. The experiments are based on highly resolved laser-induced fluorescence imaging measurements of the scalar field ζ(x,t) in the diametral plane of the ring, from which the evolution of the molecular mixing rate field ∇ζ⋅∇ζ(x,t) can be directly examined. In particular, the structure and dynamics of the mixing process are addressed during the three characteristic stages in the ring evolution, namely, (i) the ring generation stage, (ii) the ring pinch-off stage, and (iii) the asymptotic stage of the ring. Results show a layering of the mixing process in which the diffusional cancellation term ∇(∇ζ):∇(∇ζ) plays a major role in setting the overall mixing rate achieved. The scalar field measurements are also used to extract detailed information about the underlying velocity field in the ring.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.858069

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4

Digitale Medien

Investigation of products arising from enzymatic digestion of advanced glycated albumin by high-performance liquid chromatography/mass spectrometry (1991)

Lapolla, A. ; Gerhardinger, C. ; Baldo, L. ; [weitere]

New York, NY : Wiley-Blackwell

Rapid Communications in Mass Spectrometry 5 (1991), S. 624-628

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ISSN: 0951-4198

Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Physik

Notizen: The structural investigation of the products arising from 28 days incubation of albumin with high glucose concentration and further enzymatic hydrolysis has been carried out by means of high-performance liquid chromatography/mass spectrometry (HPLC/MS) under plasmaspray conditions. By this approach many different compounds have been detected, and for most of them, possible structures have been proposed on the basis of literature data and molecular weight assignments.

Zusätzliches Material: 5 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/rcm.1290051212

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5

Digitale Medien

Combined processing of polypropylene film by coextrusion and zone-annealing (1991)

Kunugi, Toshio ; Yoneyama, Yuko ; Suzuki, Akihiro ; [weitere]

New York, NY [u.a.] : Wiley-Blackwell

Journal of Applied Polymer Science 43 (1991), S. 429-435

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ISSN: 0021-8995

Schlagwort(e): Chemistry ; Polymer and Materials Science

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie , Maschinenbau , Physik

Notizen: In order to improve the mechanical properties of polypropylene film, a new processing combining extrusion and zone-annealing has been applied. It was found that there are suitable conditions for each step in the combined processing. When the coextrusion draw ratio was low, the total draw ratio and modulus could be increased by the zone-annealing subsequently done. The highest modulus was obtained when the film was coextruded at extrusion draw ratio 4 and then zone-annealed at 120°C under 7 kg/mm2. The value was 12 GPa in Young's modulus or 17 GPa in dynamic modulus. The peak temperature of αc dynamic dispersion for the combinedly processed film was 109°C, which is higher by 10°C than that for the as-coextruded film. Four drawing methods were compared in dynamic viscoelasticity. These methods are the coextrusion, zone-drawing/zone-annealing, two-step coextrusion, and the combined processing by coextrusion and zone-annealing. The highest dynamic modulus for each method was arranged in the above order. The combined processing indicated the most effective improvement in mechanical properties, because it is believed that lamellae in the original film were broken by cooperating interaction of shear stress, compression, and tension on coextrusion and then the superstructure with a high crystallinity and a high molecular orientation was formed on zone-annealing.

Zusätzliches Material: 7 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/app.1991.070430303

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6

Digitale Medien

Rolling and roll-drawing of ultrahigh molecular weight polyethylene reactor powders (1991)

Wang, Li-Hui ; Porter, Roger S.

New York, NY [u.a.] : Wiley-Blackwell

Journal of Applied Polymer Science 43 (1991), S. 1559-1564

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ISSN: 0021-8995

Schlagwort(e): Chemistry ; Polymer and Materials Science

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie , Maschinenbau , Physik

Notizen: Ultrahigh molecular weight polyethylene (UHMWPE) reactor powders have been found to be processable in the solid state by the techniques of rolling and roll-drawing. Plates of compacted UHMWPE reactor powder were prepared below their melting points. These plates were then rolled at 124°C. The maximum uniaxial draw ratio (DR) obtained by multiple rolling was about 10. In additional experiments, rolled plates of a DR of 6 were further drawn by tensile stretching at a temperature of 135°C. The specimens prepared by rolling and by the two-stage draw were characterized by tensile measurements, differential scanning calorimetry (DSC), and X-ray diffraction. Results show that, on rolling alone, the tensile modulus and tensile strength achieved were 3 GPa and 42 MPa, respectively, at a DR of 9.6. The rolled plates were effectively drawn further to a total DR of 86. Such highly drawn films exhibited tensile moduli and tensile strength up to 81 and 1.3 GPa, respectively. A high crystallinity and high crystal orientation were also obtained by the two-stage draw.

Zusätzliches Material: 6 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/app.1991.070430819

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7

Digitale Medien

Ion exchange and affinity chromatography in the scaleup of the purification of α-galactosidase from soybean seeds (1991)

Porter, Jill E. ; Ladisch, Michael R. ; Herrmann, Klaus M.

New York, NY [u.a.] : Wiley-Blackwell

Biotechnology and Bioengineering 37 (1991), S. 356-363

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ISSN: 0006-3592

Schlagwort(e): α-galactosidase ; soybeans ; lectin ; scaleup ; chromatography ; Chemistry ; Biochemistry and Biotechnology

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung

Notizen: Soybeans (Glycine max) contain an α-galactosidase that makes up a small fraction of the total protein of the seed. The properties of this enzyme are of interest because of its potential to convert the galactooligosaccharides, stachyose and raffinose, in soybean meal to sugars digestible in the human gastro intestinal tract and thereby increase potential uses of this vegetable protein source in human and animal foods. Study of this enzyme required the isolation of milligram quantities of electrophoretically pure protein from ground soybeans and therefore, scaleup of laboratory procedures by a factor of 300 times. Large scale acid precipitation, ammonium sulfate precipitation, and centrifugal recovery of the precipitated protein allowed α-galactosidase to be isolated from 45.5 kg soybean meal containing 17.1 kg protein, to obtain an enzyme extract with a specific activity of 90 to 100. A novel combination of strong anion exchange and cation exchange chromatography followed by Concanavalin-A affinity chromatography with a methyl α-D mannoside gradient gave α-galactosidase with an average specific activity of 56,000. Ion exchange chromatography preceding Concanavalin-A affinity chromatography allowed elimination of a relatively costly melibiose affinity chromatography step (which followed the Concanavalin-A column In the laboratory procedure) thereby making scaleup practical.

Zusätzliches Material: 9 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/bit.260370409

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8

Digitale Medien

Spray-to-bubbly transition for distillation systems containing two liquid phases (1991)

Davies, Bruce ; Ali, Zafar ; Porter, Kenneth E.

Hoboken, NJ : Wiley-Blackwell

AIChE Journal 37 (1991), S. 597-606

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ISSN: 0001-1541

Schlagwort(e): Chemistry ; Chemical Engineering

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung

Notizen: The tray hydrodynamics were determined for a system containing water and kerosene as immiscible liquids. Plates with hole diameters ranging from 3.18 to 12.70 mm were used in a 44.5-cm2 perspex air-water-kerosene simulator. Experiments were also carried out in a 50-mm-ID column using different depths of oil and water mixtures to study the drop and bubble mechanisms. A spray-to-bubble transition occurred for the two liquid-phase system experiments. The liquid holdup at the transition increased directly with gas velocity and hole diameter, and decreased with increasing free area. At the same hole velocity, the presence of two liquid phases caused the transition to occur at different liquid holdups than for the single pure liquid. Two different modes of coalescence were observed in the small column work. New correlations have been proposed for the liquid holdup at the transition which allow for the presence of two liquid phases.

Zusätzliches Material: 21 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/aic.690370413

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9

Digitale Medien

A raman LAM study of lamellar thickness of virgin polyethylene powder (1991)

Wang, Li Hui ; Ottani, Stefano ; Porter, Roger S.

Bognor Regis [u.a.] : Wiley-Blackwell

Journal of Polymer Science Part B: Polymer Physics 29 (1991), S. 1189-1192

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ISSN: 0887-6266

Schlagwort(e): Chemistry ; Polymer and Materials Science

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie , Physik

Notizen: The lamellar thickness of polyethylene virgin reactor powder has been successfully measured using the Raman longitudinal acoustic mode (LAM). Relatively high lamellar thicknesses have been found. These values change with polymerization temperature in an unusual way, with lamellar thickness being larger for lower polymerization temperature, i.e., at higher undercooling for crystallization. Agreement within an experimental error of 10% has been obtained between values from LAM and those calculated by the Thompson - Gibbs equation from the melting point measured by differential scanning calorimetry.

Zusätzliches Material: 3 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/polb.1991.090291003

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10

Digitale Medien

A calorimetric investigation on high molecular weight polyethylene reactor powders (1991)

Ottani, Stefano ; Porter, Roger S.

Bognor Regis [u.a.] : Wiley-Blackwell

Journal of Polymer Science Part B: Polymer Physics 29 (1991), S. 1179-1188

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ISSN: 0887-6266

Schlagwort(e): Chemistry ; Polymer and Materials Science

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie , Physik

Notizen: Reactor powders of high- and ultrahigh-molecular weight polyethylene have been investigated. Two different Ziegler-Natta synthesis processes were used: polymerization in a slurry and in the gas phase. Synthesis temperature range was 30-85°C. Monoclinic crystals were identified in samples synthesized at 30°C. Investigations of thermal parameters were carried out by differential scanning calorimetry. A range of heating rates (0.4-10.0°C/min) was used to obtain information on sample reorganization on heating. The corresponding melt-crystallized samples were scanned and their thermal parameters were compared with those obtained from the original nascent powders. Percent crystallinity and average lamellar thickness, computed by the Thompson-Gibbs equation, were found to be controlled by conditions of synthesis. For reactor powders, the fraction of crystallinity is found to be insensitive to synthesis temperature. Crystallinity is controlled mainly by the synthesis process type: slurry or gas phase. Lamellar thickness was found to decrease as synthesis temperature was increased. This trend is the opposite of what is obtained on melt crystallization and can be interpreted on the basis of Lauritzen and Hoffman's theory of crystal growth. Nascent reactor powders give experimental support for the dependence of lamellar thickness on crystallization temperature that follows the pattern described in the theory at high undercooling. The influence of molecular weight on crystallinity and lamellar thickness of both nascent powders and melt-crystallized samples was also studied. Catalyst and synthesis conditions were found to control crystallinity and crystallite dimensions of the reactor powders. Thus, polyethylenes suitable for a specific purpose can be obtained directly on synthesis.

Zusätzliches Material: 5 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/polb.1991.090291002

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