Showing papers by "DSM published in 1991"

Single electron pump fabricated with ultrasmall normal tunnel junctions

Abstract: We have designed and operated a device through which single electrons can be “pumped” reversibly. It consists of a linear array of three tunnel junctions voltage biased below the Coulomb gap. Phase shifted ac voltages applied to two gates pump one electron per cycle.

Lipase kinetics: hydrolysis of triacetin by lipase from Candida cylindracea in a hollow-fiber membrane reactor.

Abstract: The aptitude of a hollow-fiber membrane reactor to determine lipase kinetics was investigated using the hydrolysis of triacetin catalyzed by lipase from Canadida cylindracea as a model system. The binding of the lipase to the membrane appears not to be very specific (surface adsorption), and probably its conformation is hardly altered by immobilization, resulting in an activity comparable to that of the enzyme in its native form. The reaction kinetics defined on the membrane surface area were found to obey Michaelis-Menten kinetics. The specific activity of the lipase in the membrane reactor was found to be significantly higher than in an emulsion reactor. The activity and stability of the enzyme immobilized on a hydrophilic membrane surface seem not to be influenced significantly by the choice of the membrane material. The hollow-fiber membrane reactor is a suitable tool to assess lipase kinetics in a fast and convenient way.

A photoelectron-ion multiple coincidence technique applied to core ionization of molecules

Abstract: We describe a multiple coincidence technique designed for the measurement of the fragmentation of molecules after inner-shell excitation. The apparatus has been carefully calibrated and optimized for high mass resolution and high detection efficiencies, while maintaining low discrimination against energetic particles. The enhanced counting rates which result allow the determination of detailed information concerning the fragmentation processes.

Purification and properties of an aryl-alcohol dehydrogenase from the white-rot fungus Phanerochaete chrysosporium

Abstract: An intracellular aryl-alcohol dehydrogenase (previously referred to as aryl-aldehyde reductase) was purified from the white-rot fungus Phanerochaete chrysosporium. The enzyme reduced veratraldehyde to veratryl alcohol using NADPH as a cofactor. Other aromatic benzaldehydes were also reduced, but not aromatic ketones. Methoxy-substituted rings were better substrates than hydroxylated ones. The enzyme was also able to reduce a dimeric aldehyde (4-benzyloxy-3-methoxybenzaldehyde). The highest reduction rate was measured when 3,5-dimethoxybenzaldehyde was used as a substrate. On SDS/PAGE the purified enzyme showed one major band with a molecular mass of 47 kDa, whereas gel filtration suggested a molecular mass of 280 kDa. Polyclonal antibodies raised against the gel purified 47-kDa protein were able to immunoprecipitate the aryl-alcohol dehydrogenase indicating that its activity possibly resides entirely in this protein fragment. The pI of the enzyme was 5.2 and it was most active at pH 6.1. The aryl-alcohol dehydrogenase was partially inhibited by typical oxidoreductase inhibitors.

Molecular deformation of high‐modulus polyethylene fibers studied by micro‐raman spectroscopy

Abstract: Raman spectra of the CC stretching region of strained gel-spun ultradrawn ultrahighmolecular weight polyethylene fibers were recorded. On the low-wavenumber side of both the asymmetric and symmetric band, an additional broad band appeared during straining of the fiber, indicating the presence of CC bonds exhibiting high strain. The fraction of such CC bonds was estimated to be 40%. At 4% strain, the shifts of the CC stretching bands were found to increase linearly with the initial Young's modulus. From Raman spectra, information about strain distribution can be obtained. Considering the observed differences in strain distribution between fibers produced in a different way, it can be understood why one sample can be drawn to a higher extent without rupture of CC bonds. The results were discussed in conjunction with results of X-ray measurements reported by Prasad and Grubb. It is suggested that the fibers can be described by two crystalline fractions mixed on the molecular level and an additional small amount of a third fraction with a low Young's modulus.

Emission of microorganisms from biofilters

Abstract: Experiments are reported on the discharge of microbial germs by biofilter systems used for the treatment of waste gases containing volatile organic compounds. The systems investigated concern six full-scale filter installations located in the Netherlands in several branches of industry, as well as a laboratory-scale installation used for modelling the discharge process. It is concluded that the number of microbial germs (mainly bacteria and to a much smaller extent moulds) in the outlet gas of the different full scale biofilters varies between 103 and 104 m−3, a number which is only slightly higher than the number encountered in open air and of the same order of magnitude encountered in indoor air. It is furthermore concluded that the concentration of microorganisms of a highly contaminated inlet gas is considerably reduced by the filtration process. On the basis of the experiments performed in the laboratory-scale filter bed, it is shown that the effect of the gas velocity on the discharge process results from two distinctive mechanisms: capture and emission. A theoretical model is presented describing the rate processes of both mechanisms. The model presented and the experimentally determined data agree rather well.

Interim report of the DSM-IV Subcommittee on Gender Identity Disorders.

Abstract: This article summarizes the discussions and recommendations of the DSM-IV Subcommittee on Gender Identity Disorders, a subcommittee of the Child Psychiatry Work Group, regarding diagnostic issues. The issues reviewed include placement in the nomenclature, the concept of a spectrum of gender dysphoria rather than discrete levels of symptomatology, criticisms of current diagnostic criteria, subtyping by sexual orientation, and proposed changes in diagnostic criteria for the current DSM-III-R diagnoses of Gender Identity Disorder of Childhood, Transsexualism, and Gender Identity Disorder of Adolescence or Adulthood, Nontranssexual Type.

The drawing behavior of polyvinylalcohol fibers

Abstract: SYNOPSIS The solid-state drawing behavior and properties of solution-spun polyvinylalcohol fibers were investigated. A comparison was made with solution-spun, ultra-drawn polyethylene fibers. The maximum attainable draw ratio of polyvinylalcohol fibers is low ( - 20) , even at optimized conditions with respect to polymer concentration in solution. In contrast to polyethylene, the maximum attainable draw ratio hardly increases with increasing molecular weight. However, high modulus (- 70 GPa) and strength (- 2.3 GPa) polyvinylalcohol fibers can be produced, despite the low maximum attainable draw ratio. It is suggested that the observed phenomena, with respect to both the drawing behavior and properties of polyvinylalcohol fibers, originate from intermolecular hydrogen bonds in the polymer.

The chemistry of the carbothermal synthesis of β-SiC : reaction mechanism, reaction rate and grain growth

Abstract: Evidence is given that in the present case the reaction mechanism of β-SiC formation from silica and carbon is a direct solid-state reaction in which silica migrates over the silicon carbide surface to the carbon. A high value (440 kJ/mol) of activation energy is obtained for this reaction. This high value indicates that the reaction rate is determined by the diffusion of C atoms in carbon. As soon as the silica layers surrounding the silicon carbide particles have disappeared grain growth of β-SiC occurs. The mechanism for grain growth of β-SiC seems to be surface diffusion of Si and C atoms in SiC. The measured value of the activation energy for grain growth of β-SiC is 450 kJ/mol. Grain growth of α-SiC results in platelets.

Some problems in the non-linear viscoelasticity of amorphous glassy polymers

Abstract: The non-linear viscoelastic behaviour of glassy amorphous polymers is briefly reviewed. Conventional explanations such as frictional heating, strain dilatation, stress-activated flow, etc. are shown to be inadequate. The same holds for the rejuvenation hypothesis which says that large deformation processes create free volume. This hypothesis leads to a reasonable qualitative description but a quantitative one seems to be impossible, mainly because free volume is an ill-defined quantity. It is finally considered whether non-linear viscoelasticity and yielding might be explained from the non-linear force fields between the molecules. It turns out that the small-strain moduli and the yield stress can be predicted quantitatively while a qualitative explanation is obtained for some hitherto unexplained experimental facts. The implication is that the behaviour close to yield basically differs from that at small strains; so, flow at the yield point is not simply an acceleration of small-strain creep.

Curable liquid resin composition

Abstract: A curable liquid resin composition comprising a urethane (meth)acrylate polymer obtained by reacting: (A) a polyol compound containing as structural units groups which are represented by formulae: -CH2CH2O- or -CH2CH(CH2CH3)O-; (B) a polyisocyanate coumpound; and (C) at least one (meth)acrylate compound containing a hydroxyl group and coated articles produced therefrom. The curable liquid resin composition adheres well to various types of substrates and is therefore useful as a coating material for plastics, wood, porcelain, glass, paper, and the like, and as optical molding material three-dimensional molding material, printing plate material, and the like.

Roughening transition and deconstruction transition on Au(110)-(2×1)

Abstract: We present results obtained by Thermal Energy Atom Scattering (TEAS) on (2 × 1) reconstructed Au(110). We found a deconstruction transition at Tc = 650 K and observed step proliferation at a temperature TR = 690 K approximately. Furthermore we have investigated on the nature and correlation between steps. Below Tc we found a density of residual steps, an appreciable amount of which are of multiple height. Above Tc, the diffraction peak profile changes from Lorentzian to power law, indicating a mean square height difference which is logarithmic with site distance, characterizing the final state of the well-known Kosterlitz-Thouless-type roughening transition.

Production of 1-kestose with intact mycelium of Aspergillus phoenicis containing sucrose-1F-fructosyltransferase

Abstract: Favourable reaction conditions for the enzymatic production of 1-kestose by sucrose-1F-fructosyltransferase, SFT (EC 2.4.1.99) from Aspergillus phoenicis CBS 294.80 mycelium were established. The intracellular enzyme SFT works best at 60°C, exhibits a relatively high thermostability and possesses an alkaline pH optimum. An invertase also present in the mycelium of A. phoenicis possesses an acidic pH optimum. Consequently, around pH 8.0 sucrose is converted mainly to 1-kestose and nystose while fructose is only formed in relatively small amounts. Under optimal conditions (55° C, pH 8.0 and an initial sucrose concentration of 750 g 1-1) a yield of about 300 g 1-kestose per 1.01 reaction mixture could be achieved after 8 h.

Nanometric Si/C/N composite powders: Laser synthesis and IR characterization

Abstract: Synthesis of nanometric Si/C/N composite powders from pyrolysis of binary and ternary SiH 4 CH 3 NH 2 NH 3 gaseous mixtures, with a continuous-wave CO 2 laser, is reported. The composition of powders obtained under particular conditions is very similar to those which lead to densified materials presenting superplasticity phenomenon. The bulk characterization of the ceramic by infrared spectroscopy suggests that it is not a simple juxtaposition of SiC and Si 3 N 4 . The infrared surface spectrum reveals the presence of interatomic bonds between Si, C and N on the surface.

Method for the manufacture of polymer products from cyclic esters

Abstract: A method for the manufacture of polymer products from cyclic esters, according to which a catalyst and cyclic monomers are mixed in a mixing chamber and are optionally brought to a higher temperature, after which the mixture is injected, under pressure, into a cavity of a mold consisting of at least two parts and the mold is heated for some time at a temperature above the melting temperature of the monomers, after which the mold is opened and the product is removed from the mold. Polymer products manufactured by this method can be used in medical fields and particularly in reconstructive orthopedics.

Purification and characteriation of 3-hydroxyphenylacetate 6-hydroxylase: a novel FAD-dependent monooxygenase from a Flavobacterium species

Abstract: 3-Hydroxyphenylacetate 6-hydroxylase was purified 70-fold from a Flavohacterium sp. grown upon phenylacetic acid as its sole carbon and energy source. The presence of FAD and dithiothreitol during purification is essential for high recovery of active enzyme. SDSjPAGE of purified enzyme reveals a single band with a minimum molecular mass of 63 kDa. Analytical gel-filtration, sedimentation-equilibrium and sedimentation-velocity experiments indicate that the purified enzyme exists in solution mainly as a dimer, containing 1 molecule non-covalently bound FAD/subunit. 3-Hydroxyphenylacetate 6-hydroxylase utilizes NADH and NADPH as external electron donors with similar efficiency. The enzyme shows a narrow substrate specificity. Only the primary substrate 3-hydroxyphenylacetate is hydroxylated efficiently, yielding 2,5-dihydroxyphenylacetate as a product. During turnover, the substrate analogues 3,4-dihydroxyphenylacetate and 4-hydroxyphenylacetate are partially hydroxylated, exclusively at the 6' (2') position. The physiological product 2,5-dihydroxyphenylacetate acts as an effector, strongly stimulating NAD(P)H oxidation. The activity of 3-hydroxyphenylacetate 6-hydroxylase is severely inhibited by chloride ions, competitive to the aromatic substrate. In the native state of enzyme, two sulfhydryl groups are accessible to 5,5'-dithiobis(2-nitrobenzoate). Titration with stoichiometric amounts of either 5,5'-dithiobis(2-nitrobenzoate) or mercurial reagents completely blocks enzyme activity. Inactivation by cysteine reagents is inhibited by the substrate 3-hydroxyphenylacetate. The original activity is fully restored by treatment of the modified enzyme with dithiothreitol. The N-terminal amino acid sequence of the enzyme lacks the consensus sequence GXGXXG, found at the Ntermini of all flavin-dependent external monooxygenases sequenced so far. The amino acid composition of 3hydroxyphenylacetate 6-hydroxylase is also presented.

Multilayer antiballistic structure

Abstract: A multilayer antiballistic structure having good antiballistic properties comprises a first layer which comprises ceramic tiles and a second layer of composite material which comprises polyalkene filaments having a tensile modulus of at least 40 GPa and a tensile strength of at least 1 GPa and a matrix which at least partially surrounds the polyalkene filaments, while the antiballistic structure comprises, between the first and the second layer an intermediate layer of a material having a flexural modulus which is higher than the flexural modulus of the composite material of the second layer and is lower than the flexural modulus of the ceramic material. Good results are obtained if the intermediate layer comprises a composite material.

Coherent harmonic generation in VUV with the optical klystron on the storage ring Super-ACO

Abstract: The goal of this experiment is to explore the possibility of producing coherent light in the VUV spectral range using the nonlinear properties of the free electron laser gain that result when an electron beam is bunched by an external pulsed laser. The positive results, that have been obtained in 1987 on the old storage ring ACO, have lead us to install an experiment on Super-ACO, but with some modifications. This article presents the most recent results obtained on Super-ACO, where coherent photons have been produced at the 3rd (177 nm) and 5th (106 nm) harmonics of the incident laser. It presents also a brief summary of the practical interest and difficulties of this techniques.

Theories for network formation in multistage processes

Abstract: Two different theoretical approaches have been developed to describe network formation in a six-component, three-stage process with the stochastic theory of branching processes. Both approaches make use of probability-generating functions and cascade substitutions. In the POLYM approach, the products of the previous stage, namely, complete (branched) molecules, are used as building units in the subsequent stage. The molar masses and unreacted functionalities are identified by means of dummy variables. In the resulting formulas the sequence of the three stages is clearly visible. In the MONOM approach, the system is treated as a quasi-one-stage process; the original monomers are the building units in all three stages, the sequence of which is only apparent from the input parameters. In the MONOM approach the original monomers are used as building units, irrespective of the stage in which they react. A separate dummy variable is chosen for each possible reaction in each stage in the MONOM approach, so that the two approaches give analytically identical results, but along completely different derivations. This avoids correlation errors in the MONOM approach. Both approaches have incorporated kinetic effects by way of substitution effects in two of the monomers. The two approaches are prefaced by the treatment of several paradigms of increasing complexity to show the unity and strength of the theory and to warn against typical pitfalls.

Process for preparation of beta-lactams

Abstract: .beta.-Lactam derivatives are synthesized by an enzymatic reaction of the parent amino .beta.-lactam with the corresponding acylating agent, the concentration of the acylating agent plus the concentration of .beta.-lactam derivative in the reaction mixture being above about 400 mM.