Design of circular ARC finline tapers

The aim of this paper is the development of a technological simple procedure for the fabrication of tapers in finline technique with a high transmission and low reflection characteristics. This method employs tapers between rectangular waveguides and finline sections or between two electrically different waveguides in form of circular arcs which are matched to the required lapse of the slot width as a function of the characteristic impedance. The appicability of this method assumes that the transmission properties of the considered finline are known. Several examples show the feasibility of the method.     

Borasilazane Polymeric Precursors for Borosilicon Nitride

The reaction of H₃B·S(CH₃)₂ with the (CH₃SiHNH)_n cyclic oligomers obtained by ammonolysis of methyldichlorosilane (CH₃SiHCI₂) results in evolution of hydrogen and formation of cross-linked products that contain borazine rings as well as boron atoms that are linked to three nitrogen atoms. Pyrolysis of the products in a stream of argon gives a high yield of a black "borosilicon carbonitride," whereas pyrolysis in a stream of ammonia gives white "borosilicon nitride" in high yield.     

Voraussetzungen,Möglichkeiten und Grenzen der Korngrößenermittlung durch Ultraschallschwächungsmessungen

Ultraschallschwächungsmessungen im Rayleigh-Bereich zur Korngröβenermittlung. Weitere Einfluβgröβen für die Schwächungsmessung. Vergleich der mit Ultraschall und metallographisch ermittelten Korngröβe. Anwendungen.     

Media scaling in a multimedia communication system

HeiTS, the Heidelberg Transport System, is a multimedia communication system for real-time delivery of digital audio and video. HeiTS operates on top of guaranteedperformance networks that apply resource reservation techniques. To make HeiTS also work with networks for which no reservation scheme can be realized (for example, Ethernet or existing internetworks), we implement an extension to HeiTS which performs media scaling at the transport level: The media encoding is modified according to the bandwidth available in the underlying networks. Both transparent and nontransparent scaling methods are examined. HeiTS lends itself to implement transparent temporal and spatial scaling of media streams. At the HeiTS interface, functions are provided which report information on the available resource bandwidth to the application so that nontransparent scaling methods may be used, too. Both a continuous and discrete scaling solution for HeiTS are presented. The continuous solution uses feedback messages to adjust the data flow. The discrete solution also exploits the multipoint network connection mechanism of HeiTS. Whereas the first method is more flexible, the second technique is better suited for multicast scenarios. The combination of resource reservation and media scaling seems to be particularly well suited to meet the varying demands of distributed multimedia applications.     

Mass transfer behaviour of gas-liquid jet loop reactors

A special type of jet loop reactor (JLR), designed for continuous operation and short residence times was investigated with regard to its mass transfer behaviour, described by the volumetric mass transfer coefficient k_La. The jet stream and superficial gas velocities are varied in two JLRs of different sizes, equipped with different nozzles. Fully desalinated water, 0.08 molar NaCI solution and solutions of different concentration of carboxymethyl cellulose (CMC) are used as the liquid phase. A steady-state physical method is employed to determine k_La: air oxygen is purged from the liquid phase by gaseous nitrogen. The measurements show that the reactor is characterized by high power density and high mass transfer performance. No limit of mass transfer capacity was observed in the chosen ranges of volumetric gas and liquid flow rates, i.e. at a given jet stream velocity, the relationship between k_La and the superficial gas velocity is nearly linear. The investigations show that the mass transfer contributed by the jet stream largely depends on liquid phase composition.     

Simultaneous determination of primary and secondary amino groups in polyamide with 1-fluoro-2,4-dinitrobenzene

In order to determine chemically the amino end groups present in a polyamide, the polymer was treated with a solution of 1-fluoro-2,4-dinitrobenzene (FDNB) in 2,2,2-trifluoroethanol (TFE). The resulting N^ω-[2,4-dinitrophenyl-(1)]-(DNP-) polyamide was precipitated in water at pH 3, washed free of excess reagent, redissolved in TFE, and the optical density of the solution measured at λ_max = 350 nm (ε₃₅₀: 17300 [1000 cm²/mole]). Both the primary and secondary amino groups could be simultaneously determined by this method, since the absorption maximum of dinitrophenylated secondary amino groups is shifted to 390 nm (ε₃₉₀: 18000 [1000 cm²/mole]). Using this spectroscopic phenomenon a two-component analytical procedure was developed. With known concentrations of dinitrophenylated primary amines, secondary amines, and nylon-6 and nylon-6,6 oligomers, the following analytical equations were derived: (c₁: concentration of primary amino groups in mole/l; c₂: concentration of secondary amino groups in mole/l; D₃₅₀, D₃₉₀: optical density at 350 nm and 390 nm resp.). The coefficients of variation for four different commercially available nylon-6 fibres (unmodified and modified for dyeability) were in the range of 2.7 to 6.0%. The limiting concentration detectable was 6 × 10^?7 mole DNP-amino groups/l TFE. A kinetic analysis was performed for the reaction of FDNB with nylon-6 and with a model compound, ε-aminocaproic acid. Using the “absolute rate theory of Eyring”, it was found that the polymer and monomer both fulfilled the “principle of equal reactivity”. The activation parameters for the reaction were: ΔH^≠ : 15.9 ± 0.9 kcal/mole, ΔG^≠: 22.9 ±0.3 kcal/mole, and ΔS^≠: ?22.1 ± 1.9 e.u./mole.     

Sequencing and analysis of 51·6 kilobases on the left arm of chromosome XI from Saccharomyces cerevisiae reveals 23 open reading frames including the FAS1 gene

We have sequenced two segments containing a total of 51·6 kb of the left arm from chromosome XI of Saccharomyces cerevisiae. The first segment of 38·5 kb contains 18 open reading frames (ORFs) of more than 100 amino acid residues. Five ORFs encode known yeast genes, including the fatty acid synthase gene (FAS1). Three new yeast genes were discovered with homologies to non-yeast genes and ten new genes without homologies to any known sequences. The second segment of 13 kb contains five ORFs with two known yeast genes and three unknown genes. The sequences from cosmid pUKG041 were obtained entirely with the walking primer strategy resulting in a very low overall sequence redundancy of 2·8 and an average reading length of 443 bases.