On acrylonitrile polymerization in the presence of zinc salts

Acrylonitrile polymerization photoinitiated at 365 nm by pyrene and/or azobisisobutyronitrile in the presence of zinc salts in N,N-dimethylformamide solution has been studied by the rotating sector method. It was found that the ratio of the rate constants for propagation and termination (k_p/k_t) increases on addition of zinc salts (chloride, nitrate, acetate). This increase was more pronounced for the azobisisobutyronitrile photoinitiated polymerization of acrylonitrile then for its pyrene photoinitiated polymerization. The results confirm the previously expressed view concerning the dual role of zinc chloride in initiation as well as in propagation steps of acrylonitrile polymerization photoinitiated by aromatic hydrocarbons.

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, 365 / N,N- . , (k_p/k_t) ( , , ). , . , , , .

     

Degradation in gain for a free electron laser amplifier due to electron momentum spread

A finite spread in axial momentum for the electron beam in a free electron laser amplifier is shown to decrease the small-signal gain. For millimeter and sub-millimeter wave amplifiers, where exponential growth dominates the gain, it is shown that the gain is approximately 3 db below that for a cold beam if the relative momentum spread (u/u)_1/2 = (G_o/248)^1/2 (_o/L), where G_o1 is the gain in db for the cold-beam case, _o is the magnetic wiggler period, and L is the amplifier length. Exact numerical examples are given for representative FEL amplifiers at 35 and 550 GHz.This research was sponsored by the U.S. Office of Naval Research, and by the U.S.-Israel Binational Science Foundation.     

Quarter wave plates for submillimeter wavelengths

A review is given of different types of quarter wave plates as presently used in the optical and microwave spectral range, with a view to their application in the sub-mm wave-length range. Two types of quarter wave plates have been constructed and results of measurements at 640m are given.     

Polarization of coherent synchrotron radiation from an electron beam rotating in a plasma

After eliminating reflections from the walls of the plasma container, we observed polarization of the coherent synchrotron radiation from a relativistic electron beam rotating in a plasma. Several features of the polarization agree well with calculations based on the single particle synchrotron radiation theory. A particular polarization ratio (Fig. 3) does not, however. We deduce from this direct diffraction of the radiation by the beam electrons. This is strong evidence for beam-particle bunches of size cm. Also, there must be some absorption of the extraordinary wave to account for the observations. We suggest a way to apply these results to measure the pitch angle of the beam.Work supported by Army Research Office.     

Pathways of spontaneous and photoinduced hydrogen tunnelling in organic crystals

Optical excitation at liquid helium temperature of pentacene molecules embedded in benzoic acid crystals gives rise to defects in the environment of pentacene. By deuteration of the acid proton of the matrix and/or selective deuteration of the pentacene molecules, it has been proven that these defects are due to the displacement of acid protons of the matrix and are produced by reversible proton transfer between the benzoic acid host and the pentacene guest. The defect sites are unstable and decay with lifetimes ranging from subseconds to hours. Different defect sites also interconvert spontaneously in the dark or after absorption of a second photon.     

Determination of gold in ore samples by EDXRF after thiourea leaching and adsorption on activated charcoal

Summary A procedure was developed for the recovery of gold from ores of low gold content. Gold was leached from roasted samples with thiourea and removed from the leaching solution onto activated charcoal before measurement by an energy dispersive X-ray fluorescence spectrometer (EDXRF). The effect of grain size of gold particles on the leaching of gold and the effect of different minerals on the consumption of thiourea were examined. The effects of the amount of carbon and the gold concentration on the adsorption of gold and on the intensity of the L radiation of gold were also investigated. The detection limits, calculated in relation to the original solid sample, were 0.045 g/g (L) and 0.038 g/g (L). The procedure was tested with the Canmet MA-1b gold ore.     

Phytoecdysones ofSilene praemixta. I. Silenosterone

In addition to known ecdysteroids (2-deoxy--ecdysone and 2-deoxyecdysterone) fromSilene praemixta (Caryophyllaceae) we have isolated new ones — premixisterone and selenosterone (I), C₂₇H₄₂O₇, mp 115–117°C (from MeOH), [] _D ²⁸ +86.9 ± 2° (c 0.92, MeOH), yield 0.003%. The acetylation of (I) with (CH₃CO)₂O in Py gave 22-acetyl-selenosterone (II), C₂₉H₄₄O₆, mp 210–212°C (MeOH-C₆H₁₄), [] _D ²⁷ +45.5 ± 3° (c 0.16; MeOH). On the basis of physiocochemical and spectral characteristics it has been established that (I) has the structure of 14,22R,25-trihydroxy-5-cholest-7-ene-3,6-dione. The IR, PMR, and mass spectra of (I) and (II) are presented.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 793–797, November–December, 1979.     

Fluorometric assay of histamine in tissues and body fluids: Choice of the purification procedure and identification in the nanogram range

Summary Several procedures for the isolation of histamine from tissues and body fluids were examined. For the fluorometric assay of histamine concentrations higher than 1 g/g tissue or ml blood the extraction into n-butanol as well as the cation-exchange chromatography on Dowex 50W-X8 proved suitable. The determination of histamine in whole blood of dogs gave valid results only after chromatography on Dowex 50, in human plasma and gastric juice only after the combined application of both purification methods. Histamine was identified by thin-layer chromatography on cellulose, by inactivation in the presence of purified diamine oxidase from pig kidney and purified histamine methyltransferase from guinea-pig brain, by the biological activities and by the fluorescence spectra of the condensation product between histamine and o-phthaldialdehyde. Histamine concentrations in tissues and body fluids of man and some laboratory animals are reported.

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Fluorimetrische Bestimmung von Histamin in Geweben und Körperflüssigkeiten: Wahl eines geeigneten Reinigungsverfahrens und Identifizierung im ng-Bereich

Zusammenfassung Verschiedene Isolierungsverfahren für Histamin zur fluorimetrischen Bestimmung wurden geprüft. Für Histamingehalte von mehr als 1 g/g Gewebe oder Milliliter Vollblut eignet sich sowohl die Butanolextraktion als auch die Ionenaustausch-Chromatographie an Dowex 50W-X8, für Vollblut des Hundes nur das letztere Verfahren, für Plasma und Magensaft des Menschen nur die Kombination der beiden Isolierungsmethoden. Histamin wurde identifiziert durch Dünnschicht-Chromatographie auf Cellulose, Umsatz durch angereicherte Diaminoxydase und Histaminmethyltransferase, durch die Fluorescenzspektren nach Kondensation mit o-Phthaldialdehyd und durch seine biologische Aktivität. Die Histamingehalte in Geweben und Körperflüssigkeiten des Menschen und einiger Versuchstiere werden mitgeteilt.

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Members of SFB 37 (Restitution und Substitution innerer Organe of Deutsche Forschungsgemeinschaft).     

Colorimetric determination of molybdenum using sodium diethyldithiocarbamidate as reagent

Summary A method for the photometric estimation of molybdenum(V) by extraction of the complex formed with NaDDTC in 5 N HCl solution is discussed. The reduction of Mo(VI) to Mo(V) is achieved with hydrazine sulphate. The colour intensity of the chloroform extract of the complex is measured at 450 nm. Beer's law is obeyed up to 500 g/25 ml of molybdenum.

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Zusammenfassung Zur photometrischen Molybdänbestimmung wird der Komplex mit Diäthyldithiocarbamidat verwendet, der in 5 N salzsaurer Lösung gebildet und mit Chloroform extrahiert wird. Mo(VI) wird mit Hydrazinsulfat zur fünfwertigen Stufe reduziert. Die Messung erfolgt bei 450 nm; das Beersche Gesetz ist bis zu 500 g Mo/25 ml erfüllt.

     

Decreasing the detection limits to ppq levels for high purity silicon analysis by instrumental neutron activation analysis with kilogram sampling weight

The amount of silicon sample used in instrumental neutron activation analysis (INAA) is generally less than twenty grams and the detection limits are in the range of ppb to ppt. The detection limits can be decreased further in several ways. Increasing neutron flux density, extending irradiation period and/or using more effective detector can improve the detection limits to some extent. Increasing sample weight, however, is a more feasible way to decrease the detection limits by a factor of hundreds with no new investment in existing irradiation/counting systems. In this work, two 8-inch high-purity silicon samples were analyzed by INAA to evaluate the validity and limitations of this concept in respect to neutron flux inhomogeneity, neutron shielding and -ray counting efficiency.