Search Results - (Author, Cooperation:R. A. Hart)

2015-02-25

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

1077-3118

AIP Digital Archive

Physics

A modified hollow-bore ridge waveguide, utilizing a staggered ridge geometry, has been used successfully to obtain single-frequency operation from an array of CO2 waveguide lasers. The gain volume of the array is equivalent to six waveguide lasers of 37 cm length and 2.25×2.25 mm2 cross section. The output power from the sealed-off device reached 68 W cw. Stable single-frequency operation in the antisymmetric supermode was observed.

Electronic Resource

1467-9787

Blackwell Publishing Journal Backfiles 1879-2005

Geography

Economics

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We report the generation of pulsed optically pumped far-infrared (FIR) radiation with a repetition rate of 200 kHz. These pulses were obtained in a straightforward method by pumping a FIR resonator with a high repetition rate, rf-excited, waveguide CO2 laser. Pulses approximately 50 ns wide were generated both at 432.6 μm in HCOOH, and 117.7 μm in CH2F2. The pulse width of the FIR radiation was studied as a function of the CO2 pulse width, and the relative delay between the two was measured. Based on this data we conclude that the FIR radiation was gain switched and of a duration which was a function of either the gain bandwidth of the FIR transition, or more likely the FIR cavity parameters.

Electronic Resource

1745-4565

Blackwell Publishing Journal Backfiles 1879-2005

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Process Engineering, Biotechnology, Nutrition Technology

Aerobic Plate Count (APC) and spiral plate (Spiral) methods using both manual counting (MC) and laser counting (LC) procedures were compared for pure bacterial, yeast, and mold cultures and raw milk samples. All four combinations of methods (APC-MC, APC-LC, Spiral-MC, and Spiral-LC) gave similar log10 counts of studied pure microbial cultures, producing results that were not different for the purposes of practical microbiology. With bacterial and yeast cultures, counts differed by less than half a logarithmic cycle (the range of difference = -0.26 to +0.42), the range of difference being -0.03 to +0.62 for Aspergillus flavus and Penicillium camemberti molds. An exception was noticed with Rhizopus oligosporus mold when plates were read by laser due to large (10–15 mm) colony size. The difference between the readings made manually and by laser colony scanner was about one logarithmic cycle with both APC and Spiral methods. Statistical analyses of the manually read results of bacterial and Saccharomyces cerevisiae spiral plates showed no differences at the 0.05 level of significance between the readings made by four or five persons. For raw milk samples, Spiral-MC and Spiral-LC methods gave higher microbial numbers than APC-MC (63% of samples) and APC-LC (54% of samples) at 0.05 level of significance (p〈0.001). Of the LC results, 75% were within a ± 0.5 logarithmic cycle range when compared to MC results, of which 98% were within the same range. All results were still within a ± 1.0 logarithmic range. When APC and Spiral for raw milk samples were analyzed, LC gave higher microbial numbers compared to MC: 71% of the APC-LC results were higher than APC-MC results, and 85% of Spiral-LC results were higher than Spiral-MC results at 0.05 level of significance (p〈0.001). 77% of the results by either plating technique were within a ± 0.5 logarithmic range.

Electronic Resource

1745-4565

Blackwell Publishing Journal Backfiles 1879-2005

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Process Engineering, Biotechnology, Nutrition Technology

Enumeration of yeast and molds from 39 food samples, including 6 dairy products, 2 meat products, 5 cereal products, 9 fruits, 4 vegetables, 6 beverages, 4 spices, and 3 condiments on Trypan blue (at 1: 10,000 dilution) in potato dextrose agar (Trypan blue agar) was compared with Congo red (at 25:1,000,000 dilution) in potato dextrose agar (Congo red agar) using the hydrophobic grid-membrane filter (HGMF) technique of the ISO-GRID system. Yeast and mold grew well on both Trypan blue agar and Congo red agar, producing blue and red colonies, respectively, in the ISO-GRID system, when examined in incan-descent light. However, not all yeast and mold colonies grown on Congo red agar fluoresced under ultraviolet (UV) light (a recommended observation procedure). Thus, results indicated that Trypan blue agar observed in incandescent light is more convenient to use for enumerating yeast and mold in food samples.

Electronic Resource

1467-6435

Blackwell Publishing Journal Backfiles 1879-2005

Sociology

Economics

Electronic Resource

1467-8586

Blackwell Publishing Journal Backfiles 1879-2005

Economics

Electronic Resource

1467-9787

Blackwell Publishing Journal Backfiles 1879-2005

Geography

Economics

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] The evidence for the reactions is both geochemical and geophysical. The chemistry of basalts sampled on the ocean floor varies progressively with distance from principal sea-floor spreading ridges. Further, the seismic velocities of the uppermost rock layer of oceanic crust decrease progressively ...

Electronic Resource

0025-116X

Chemistry ; Polymer and Materials Science

Wiley InterScience Backfile Collection 1832-2000

Chemistry and Pharmacology

Physics

Polyimide wurden aus einer Vielfalt von Diaminen und Dianhydriden hergestellt. Ihre Stabilität bei 400°C in Luft wurde durch thermogravimetrische Analyse bestimmt. Wenn möglich, wurden hochmolekulare Filme verwendet, die durch thermische Kondensation der Poly-Amidsäure-Zwischenprodukte erhalten wurden. Wenn dies nicht möglich war, wurden Filme aus Polymeren, die mit Acetanhydrid cyclisiert waren, oder wärmebehandelte Pulver untersucht.Für die aus Pyromellithsäure-dianhydrid und einer Vielfalt von Diaminen hergestellten Polyimide wurde eine gut definierte Abstufung der Stabilität beobachtet. Die einfachsten und symmetrischsten Strukturen besaßen die höchste Wärmestabilität; die schlechtesten Resultate wurden mit elektronegativen Kopplungsgruppen erzielt.

Polyimides were synthesised from a number of diamines and dianhydrides and their stability determined by thermogravimetric analysis at 400°C in air. Wherever possible high molecular weight films obtained by thermal condensation of the polyamic acid intermediates were studied. If this was not possible, films obtained from acetic acid anhydride ciclised polymers or thermally cured powders were used.A well defiend order of stability was observed for the polyimides prepared from pyromellitic dianhydride and a variety of diamines. The simplest and most symmetrical structures had the greatest thermal stability. Lowest stabilities were observed when linking groups were electronegative in nature.

15 Ill.

Electronic Resource

0021-8995

Chemistry ; Polymer and Materials Science

Wiley InterScience Backfile Collection 1832-2000

Chemistry and Pharmacology

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

Aromatic polyimides were prepared from pyromellitic dianhydride and a number of aromatic diamines. The effect of certain variables on the polymerization to, and the degradation of, the intermediate polypyromellitamic acids was studied, and a previously unrecorded reaction intermediate was isolated and identified. From these studies the conditions necessary to obtain high molecular weights were defined. Techniques were developed for the fabrication of satisfactory films and moldings.

5 Ill.

Electronic Resource

0030-493X

Chemistry ; Analytical Chemistry and Spectroscopy

Wiley InterScience Backfile Collection 1832-2000

Chemistry and Pharmacology

The mass spectra of twenty three pyromellitimides are reported and discussed. Proposed ion structures are, in most cases, substantiated by precise mass measurement. All compounds examined exhibit molecular-ions. Ions formed by the loss of carbon dioxide from the molecular-ions, although intense in some cases, are not common to all the spectra.

12 Tab.

Electronic Resource

0030-493X

Chemistry ; Analytical Chemistry and Spectroscopy

Wiley InterScience Backfile Collection 1832-2000

Chemistry and Pharmacology

The electron-impact induced loss of CO2 from phthalanil and 4-phthalimidobiphenyl is paralleled by the formation of large amounts of CO2 on pyrolysis. CO is also a major pyrolysis product, but the loss of CO from these compounds under electron-impact is not an important fragmentation process.The mass spectra of meta and para-chlorophthalanils show prominent [M — CO2] peaks but the corresponding peak for the ortho isomer is of relatively low intensity. CO and CO2 are the principal gaseous products of the thermal decomposition of o-chlorophthalanil.

1 Tab.

Electronic Resource

0025-116X

Chemistry ; Polymer and Materials Science

Wiley InterScience Backfile Collection 1832-2000

Chemistry and Pharmacology

Physics

Schmelzpunkt, Löslichkeit und Infrarot-Spektren mehrerer aromatischer Imide, hauptsächlich zweifach substituierter N.N′-Diphenylpyromellitimide, wurden gemessen. Die Verschiedenartigkeit der beobachteten Eigenschaften in Abhängigkeit von der Struktur konnte durch gewisse Annahmen über Planarität, Polarisierung und intermolekulare Wechselwirkungen befriedigend erklärt werden.

The melting point, solubility and infrared spectra of a number of aromatic imides, mainly disubstituted N.N′-diphenylpyromellitimides, have been determined. The variation in properties observed could be explained satisfactorily by making certain assumptions about the planarity, polarisation and intermolecular interactions of the compounds.

1 Ill.

Electronic Resource

0449-2986

Chemistry ; Polymer and Materials Science

Wiley InterScience Backfile Collection 1832-2000

Chemistry and Pharmacology

1 Ill.

Electronic Resource

0449-296X

Physics ; Polymer and Materials Science

Wiley InterScience Backfile Collection 1832-2000

Chemistry and Pharmacology

The reaction of hydrazine hydrate with aromatic anhydrides may give either N-amino imides or cyclohydrazides. The conditions that favor the formation of N-aminoimides, in which the imide contains respectively a 5- and 6-membered ring, are discussed. These compounds may be reacted with aromatic anhydrides to give N-N-linked imides. The properties of a number of model compounds and polymers are described, and it is shown that those compounds which have alternating 5- and 6-membered imide rings give the maximum oxidative stability in air at 400°C.

3 Tab.

Electronic Resource