Ignition of composite propellant at subatmospheric pressures by means of carbon dioxide laser

Ignition behavior of solid propellant composed of 25 wt% polybutadiene and 75% ammonium perchlorate under subatmospheric conditions has been studied using a carbon dioxide laser whose radiant flux is uniformalized. Data of ignition time in Ar, N₂ and He atmospheres, and critical radiant flux and pressures over which ignition might be achieved, were obtained. Moreover, the data were compared with theoretical values, taking account of variable heat conductivity for the ambient gases with a surface ignition hypothesis. It is concluded that these ambient gases participate in the pre- and post-ignition reactions and the ignition preventive behavior of He atmosphere is not predictable merely based on its high transport properties. The detailed observation of the ignition transient near the critical pressure revealed that the ignition in Ar atmosphere occurs in gas phase under less than 100 torr whereas in He atmosphere it occurs always at the condensed phase surface.     

DS-CDMA system with variable-rate traffic

This letter analyzes the signal-to-noise ratio (SNR) performance of a single chip-rate DS-CDMA system that supports multi-rate traffic. A user model that allows users to dynamically switch traffic rates for different connection applications is assumed. SNR results with random chip sequences are also given     

A systematic approach to design and analysis of antennas on complexplatforms

The expansion in terrestrial and space communications often requires antennas to be installed in very confined areas on a tower or spacecraft. Since installation and structure variables increasingly dominate the overall communications system performance, an analysis of such structures can be very important. The structures of interest are often in the near field of the antenna, but most antenna design and analysis tools produce far-field results. A common satellite communications scenario involves scatterers such as solar panels or support structures that degrade antenna performance, especially if either the scatterers or the antenna can move in relation to each other. A systematic design and analysis approach that uses several well-known techniques in a cooperative design environment is presented, and illustrated using a scenario     

Optical and optoelectronic devices for optical fiber transmissionsystems

The present status and research trends in light sources, detectors, and various optical components are described, focusing mainly on those for single-mode fiber systems. Laser-diode and light-emitting-diode sources are described, and their problems and advantages are examined. The features of optical detectors, namely, avalanche and p-i-n photodiodes are discussed. A method of comparing the performance of optical receivers with different detectors, by examining the minimum detectable power at a specified error probability for the received pulses, is presented. Optical components such as optical filters, couplers, dividers, isolators, connectors, and switches are considered briefly. The potential of optoelectronic integrated circuits is discussed     

Kirkwoodsche Korrelationsfaktoren von binären Systemen mit Alkoholen und Diäthyläther

Kirkwood Correlation Factors of Binary Systems with Alcohols and Diethylether The KIRKWOOD theory allows the calculation of a correlation factor for describing the association of polar substances. For the systems n-hexane + diethylether cyclohexane + 1-propanol cyclohexane + 1-butanol benzene + methanol benzene + ethanol benzene + 1-propanol benzene + 1-butanol benzene + 1-hexanol benzene + 1-octanol the experimental values of dielectric constant and the calculated correlation factors are presented. From the concentration dependence of the correlation factors, calculated by use of the KIRKWOOD -FRÖHLICH -equation for mixtures, the existence of widely ramified associations of methanol and the formation of clusters of ethanol, propanol-(1), butanol-(1), hexanol-(1) and octanol-(1) is deduced. In the systems benzene + alcohol in most of the cases some specific interactions between the two components are supposed to exist.     

Synthesis of Heptakis (2-O-methyl)-β-cyclodextrin

The title compound was prepared by a reaction sequence comprising methylation of heptakis (6-bromo-6-deoxy)-β-cyclodextrin by the Kuhn procedure, regeneration of the primary hydroxyl groups from the resulting heptakis(2-O-methyl-6-bromo-6-deoxy)-β-dextrin via the 6-O-benzoate ester by benzoate exchange and subsequent deesterification. It was proved that the methyl groups in the tetradeca-O-methyl ether of β-dextrin are located 0–2 and 0–6 of the D-glucose residues.     

Chemical Modification of Maltotriose

Hot acetylation of maltotriose with acetic anhydride and sodium acetate led to the formation of an anomerically unsubstituted maltotriose decaacetate (2.8% yield) in amorphous form in addition to the principal product, β-maltotriose hendecaacetate (80% yield). The structure of the decaacetate was elucidated by chemical reactions and n.m.r. spectroscopy. α-Maltotriose hendecaacetate and deca-O-acetyl-α-maltotriosyl chloride were prepared to facilitate the structural assignment. From measurement of the optical rotation, it was assumed that the decaacetate is a mixture of both anomers in a constant proportion. The decaacetate was also obtained either by treatment of the β-hendecaacetate with hydrogen bromide in acetic acid followed by warm aqueous sodium acetate or by the reaction of the β-hendecaacetate with piperidine in tetrahydrofuran.