Showing papers by "Chalmers University of Technology published in 1993"

PNA hybridizes to complementary oligonucleotides obeying the Watson–Crick hydrogen-bonding rules

Abstract: DNA analogues are currently being intensely investigated owing to their potential as gene-targeted drugs. Furthermore, their properties and interaction with DNA and RNA could provide a better understanding of the structural features of natural DNA that determine its unique chemical, biological and genetic properties. We recently designed a DNA analogue, PNA, in which the backbone is structurally homomorphous with the deoxyribose backbone and consists of N-(2-aminoethyl)glycine units to which the nucleobases are attached. We showed that PNA oligomers containing solely thymine and cytosine can hybridize to complementary oligonucleotides, presumably by forming Watson-Crick-Hoogsteen (PNA)2-DNA triplexes, which are much more stable than the corresponding DNA-DNA duplexes, and bind to double-stranded DNA by strand displacement. We report here that PNA containing all four natural nucleobases hybridizes to complementary oligonucleotides obeying the Watson-Crick base-pairing rules, and thus is a true DNA mimic in terms of base-pair recognition.

A valveless diffuser/nozzle-based fluid pump

Abstract: A new valveless fluid pump has been designed and tested. The pump consists of two fluid diffuser/nozzle elements on each side of a chamber volume with an oscillating diaphragm. The vibrating diaphragm produces an oscillating chamber volume, which together with the two fluid-flow-rectifying diffuser/nozzle elements, creates a one-way fluid flow. A micropump prototype with a chamber diameter of 19 mm with conical diffuser/nozzle elements has been built and tested. The maximum liquid flow rate is 16 ml/min and the maximum pump pressure is 2 m H 2 O. The pump frequency is of the order of 100 Hz.

Wave-breaking-free pulses in nonlinear-optical fibers

Abstract: A qualitative as well as quantitative investigation is made of the conditions for avoiding wave breaking during pulse propagation in optical fibers. In particular, it is shown that pulses having a parabolic intensity variation are approximate wave-breaking-free solutions of the nonlinear Schrodinger equation in the high-intensity limit. A simple expression for the compression factor of a fiber-grating compressor based on parabolic pulses is also derived.

Transparent conductive electrodes for electrochromic devices: A review

Abstract: This paper reviews the optical and electrical performance of thin films that are useful as transparent electrodes in electrochromic devices. The properties of certain heavily doped wide-bandgap semiconductor oxides (especially In2O3:Sn) and of certain coinage metal films are discussed.

Control by variable rotor speed of a fixed-pitch wind turbine operating in a wide speed range

Abstract: Variable rotor speed control of a fixed-pitch wind turbine is investigated on a system consisting of a wind turbine which can operate in a wide speed range, from 0 to 38 RPM. It produces any desired output from the rated (20 kW) to no-load, providing there is enough wind. A special technique is used to determine the operating point of the wind turbine by using the measured rotor speed and power. A difficult problem with this type of wind turbine control is to make the upper speed limit reasonably high to capture as much energy as possible but still low enough to avoid power peaks. >

Novel Schiffman phase shifters

Abstract: In a standard Schiffman phase shifter a coupled section and a uniform transmission line are used to give a differential phase shift. In order to achieve larger bandwidth it is necessary to use tight coupled sections which are difficult to realize. It is shown how different configurations of coupled lines or parallel connected coupled lines can be used together with a uniform transmission line, other coupled lines, or parallel connected coupled lines in order to obtain a differential phase shifter with loose coupled lines and the same performance as for the standard case. The measurements confirm the calculated results, leading to a more realizable structure. >

Numerical solution of an evolution equation with a positive-type memory term

Abstract: We study the numerical solution of an initial-boundary value problem for a Volterra type integro-differential equation, in which the integral operator is a convolution product of a positive-definite kernel and an elliptic partial-differential operator. The equation is discretised in space by the Galerkin finite-element method and in time by finite differences in combination with various quadrature rules which preserve the positive character of the memory term. Special attention is paid to the case of a weakly singular kernel. Error estimates are derived and numerical experiments reported.

Patch recovery based on superconvergent derivatives and equilibrium

Abstract: In this paper a postprocessing technique is developed for determining first-order derivatives (fluxes, stresses) at nodal points based on derivatives in superconvergent points. It is an extension of the superconvergent patch recovery technique presented by Zienkiewicz and Zhu. In contrast to that technique all flux or stress components are interpolated at the same time, coupled by equilibrium equations at the superconvergent points. The equilibrium equations and use of one order higher degree of interpolation polynomials of stress give a dramatic decrease in error of recovered derivatives even at boundaries.

Reduction potentials and their pH dependence in site‐directed‐mutant forms of azurin from Pseudomonas aeruginosa

Abstract: A spectroelectrochemical method has been used to determine the reduction potential of the copper site in wild-type and 22 mutant forms of azurin from Pseudomonas aeruginosa at 25 °C and in the range pH 4–8; the effect of buffers and ionic strength on the potentials has also been studied. Amino-acid residues changed include Met121, which provides an S atom at a distance of about 0.3 nm from the metal, some amino acids in the hydrophobic patch, other residues believed to be important in electron transfer with physiological partners and some internal amino acids. The observed potentials span a range of about 300 mV. In all cases the potentials increase with decreasing pH, but the pKa values describing the pH dependence are essentially unchanged except in three mutants, where they change by pH 0.6–1.1 (up in one and down in two). The largest potential changes were found in some Met121 mutants, at which position large hydrophobic residues raise the potential, whereas negatively charged residues lower it; a decreased potential is also found in the Met121 End mutant, which probably has H2O coordinated to the metal. Gly45 has its carbonyl group coordinated to copper, but the potential of Gly45 Ala is close to that of the wild type. Some substitutions in the hydrophobic patch cause an increase in the potential, whereas substitutions involving His35 and Glu91 do not result in significant changes. No single mechanism for tuning the potential of the copper site can be discerned, but in many cases there are probably indirect effects of the protein conformation causing changes in metal-ligand interactions.

Lactic Fermentation of Non‐Tannin and High‐Tannin Cereals: Effects on In Vitro Estimation of Iron Availability and Phytate Hydrolysis

Abstract: The effect on iron availability estimated in vitro and phytate hydrolysis was investigated in non-tannin and high-tannin cereals, lactic fermented as flour/water slurries or gruels. A natural starter culture initiated fermentation and addition of germinated flour and phytase in the fermentation process was tested. Lactic fermentation of nontannin cereals with added flour germinated sorghum seeds or wheat phytase increased iron solubility from about 4% up to 9 and 50%, respectively. Soaking flour in water before adding starter culture had a similar effect. The increase in soluble iron was strongly related to enzymatic degradation of phytate (p 90% after soaking the flour prior to fermentation and almost complete with 50 mg phytase added. High-tannin cereals showed a minor increase in soluble iron after fermentation, ascribed to the inhibitory effect of tannins (both on iron solubility and on enzymatic hydrolysis of phytate). Lactic-fermented cereal foods have a potential in developing countries to improve iron nutrition.

High Dietary Calcium Level Decreases Colonic Phytate Degradation in Pigs Fed a Rapeseed Diet

Abstract: The degradation of phytate (inositol hexaphosphate) in rapeseed meal diet not containing phytase activity was studied in 15 growing ileum-fistulated pigs. Stomach and small intestinal degradation and total gastrointestinal degradation were compared. The effect of addition of calcium carbonate to the rapeseed meal diet at two levels (9.2 and 18.5 g/kg diet) was investigated. A commercial barley-wheat-soybean diet with intrinsic phytase activity was used as reference. Phytate and its hydrolysis products in diets, ileal digesta and feces were determined by HPLC ion-pair chromatography. Hydrolysis of phytate in the stomach and small intestine was 35-45% in pigs fed the rapeseed meal diet independent of calcium addition, and 65% in pigs fed the reference diet. Total gastrointestinal degradation of phytate in pigs fed the rapeseed diet was 97, 77 and 42% (P < 0.001) when calcium intakes were 4.5, 9.9 and 15 g/d, respectively; total gastrointestinal degradation was 72% in pigs fed the reference diet. The intestinal phytate degradation pattern, when rapeseed diet was fed, indicated the activity of an unspecific phosphatase, whereas that of the reference diet indicated intrinsic dietary phytase activity. We conclude that dietary supplementation of calcium carbonate decreases the phytate degradation in the colon of pigs, but not in the stomach and small intestine.

Controlled interactions in cellulose‐polymer composites. 1: Effect on mechanical properties

Abstract: The surface properties of cellulose fibers have been modified by heat treatment, by silane coupling agents, and by maleated polypropylene grafts. The effectiveness of these methods has been evaluated by electron spectroscopy (ESCA), by contact angle measurements, and by inverse gas chromatography. The latter analyses yielded information on the fibers' acid/base interaction potential. Cellulose was found to be amphoteric, with prevalent acidic properties. Heat and chloro-silane treatments accentuated acidity, while amino-silane treatment produced net basicity in the fiber surface. Modification with maleated polypropylene reduced specific interactions and converted the fiber to a predominantly dispersion-force solid. The modified fibers were used in composites with polypropylene (neutral), polystyrene (base), and chlorinated polyethylene (acid) as matrix. Stress/strain and dynamic mechanical parameters were found to vary with acid/base interactions between polymer and fiber, significant improvements being noted in elastic and storage moduli, in tensile strength and elongation. In polypropylene, properties were unaffected by acid/base considerations. Acid/base forces, not necessarily dominant, merit consideration in the design of surface modification strategies intended to optimize composite mechanical properties.

Binding of 4',6-diamidino-2-phenylindole (DAPI) to AT regions of DNA: evidence for an allosteric conformational change.

Abstract: The interaction of 4',6-diamidino-2-phenylindole (DAPI) with several double-helical poly- and oligonucleotides has been studied in solution using optical spectroscopic techniques: flow linear dichroism (LD), induced circular dichroism (CD), and fluorescence spectroscopy. In AT-rich sequences, where DAPI is preferentially bound, LD indicates that the molecule is edgewise inserted into the minor groove at an angle of approximately 45-degrees to the helix axis. This binding geometry is found for very low as well as quite high binding ratios. The concluded geometry is in agreement with that of the DAPI complex in a crystal with the Drew-Dickerson dodecamer, and the DAPI complex with this dodecamer in solution is verified to have an ICD spectrum similar to that of the complex with [poly(dA-dT)]2 at low binding ratios. The observation of two types of CD spectra characteristic for the binding of DAPI to DNA, and also for the interaction with [poly(dA-dT)]2, demonstrates that the first binding mode, despite its low apparent abundance (a few percent), is not due to a specific DNA site. The effect may be explained in terms of an allosteric binding such that when DAPI molecules bind contiguously to the AT sequence the conformation of the latter is changed. The new conformation, which according to LD appears to be stiffer than normal B-form DNA, is responsible for the second type of induced CD spectrum in the DAPI chromophore. Although the spectroscopic results indicate a change of DNA conformation, consistent with an allosteric binding model, they do not explicitly require any cooperativity, but accidental neighbors could also explain the data.

Linked interpolation for Reissner-Mindlin plate elements: Part I—A simple quadrilateral

Abstract: In most plate elements using the Reissner-Mindlin assumptions, the interpolations used for the lateral displacements (w) and the rotation (θ) involve the independent representation of each variable by its nodal values, usually with identical interpolations. To ensure a higher order of expansion for displacement w its representation is linked in the present paper with both sets of nodal variables. Conditions necessary for the use of such expansions are established here and the paper shows the development of a linear quadrilateral element (Q4BL) whose performance and robustness are good (although it possesses one singularity if only three degrees of freedom are prescribed). In Part II we apply the identical formulation to develop a triangular element (T3BL) which performs equally well and is fully robust.

Discontinuous Displacement Approximation for Capturing Plastic Localization

Abstract: It is proposed to capture localized plastic deformation via the inclusion of regularized displacement discontinuities at element boundaries (interfaces) of the finite element subdivision. The regularization is based on a kinematic assumption for an interface that resembles that which is pertinent to the classical shear band concept. As a by-product of the regularization, an intrinsic band width is introduced as a ‘constitutive’ property rather than a geometric feature of the finite element mesh. In this way the spurious mesh sensitivity, which is obtained when the displacement approximation is continuous, can be avoided. Another consequence is that the interfacial relation between the elements is derived directly from the conventional constitutive properties of the continuously deforming material. An interesting feature is that the acoustic tensor will not only play a role for diagnosing discontinuous bifurcation but will also serve as the tangent stiffness tensor of the interface (up to within a scalar factor). An analytical investigation of the behaviour of the interface is carried out and it is shown that dilatation may indeed accompany slip within a ‘shear’ band for a general plasticity model. The significance of proper mesh alignment is demonstrated for a simple problem in plane strain and plane stress. It is shown that a unique structural post-peak response (in accordance with non-linear fracture mechanics) can be achieved when the plastic softening modulus is properly related to the bandwidth. The paper concludes with a numerical simulation of the gradual development of a shear band in a soil slope.

Gaseous emissions from circulating fluidized bed combustion of wood

Abstract: The emissions of NO, N2O, CO and SO2 were investigated during combustion of wood in a circulating fluidized bed boiler as a function of various parameters, including bed temperature, air supply and load. Emissions from mixtures of wood and coal were also investigated. The results show that the nitrogen oxide emission is directly related to the nitrogen content of the wood. The small amount of char in the bed during combustion of wood results in a much smaller reduction in the NO formed in the case of wood compared to that during combustion of coal and reduces the impact of bed temperature and air supply on the NO emissions during combustion of wood as compared to coal. Emission of N2O during combustion of wood was negligible.

Ultrashort solitons at the minimum-dispersion wavelength: effects of fourth-order dispersion.

Abstract: The effects of fourth-order dispersion on optical-fiber-guided ultrashort solitons are examined. It is shown that the solitons decay as a result of dispersive radiation, the nature of which is analyzed. An exact pulse solution is presented, and its properties are evaluated. Finally, the combined effects of fourth-order dispersion and intrapulse Raman scattering are discussed.

Phase memory effects in mesoscopic rings with superconducting "mirrors"

Abstract: We find a drastic difference between the magnetoresistance of normal-metal (Ag) mesoscopic rings with superconducting boundaries (mirrors) and that of plain rings. The amplitude of h/2e Aharanov-Bohm oscillations is enhanced more than 100 times in rings with mirrors in the measuring leads. Rings with mirrors in stubs perpendicular to the current flow show h/4e and h/2e oscillations and evidence of a superconducting transition. The resutls are interpreted as due to a phase coupling between the superconductors via normal electrons, and to a confinement of quasiparticles to the ring by Andreev reflections.

Electrochromic materials: Microstructure, electronic bands, and optical properties

Abstract: Crystals of all the well known electrochromic metal (Me) oxides are composed of MeO6 octahedra in various corner-sharing and edge-sharing arrangements. Cluster-type and columnar microstructures, based on the MeO6 units, exist in electrochromic films. The coordination of the ions leads to schematic electronic band structures that, at least for the (defect) perovskite and rutile lattices, are able to explain the presence or absence of cathodic and anodic electrochromism. Small polaron absorption prevails in disordered oxides, while crystalline tungsten oxide can show free-electron effects.

Formation of entanglements at brushlike interfaces in cellulose–polymer composites

Abstract: Cellulose fibers were grafted with compatibilizing agents, such as maleated polypropylenes of different molecular weights. Steric effects and surface free-energy effects were found to stimulate the stretching of grafted chains away from the cellulose fiber surface, giving rise to a brushlike configuration in a polypropylene (PP) melt. Inverse gas chromatography measurements on modified fibers using a model compound for PP as adsorbate showed that interactions of PP and grafted fibers, which were mainly diffusion-dependent, increased with increasing molecular weight of the compatibilizer. Dynamic mechanical measurements and tensile testing of composites showed that the presence of compatibilizing agents enhanced stress transfer and increased interphase thickness considerably, the most significant effect being obtained for the high molecular weight compatibilizers. Apparently, the longer the grafted chains, the larger the fraction of matrix molecules involved in the interactions and, thus, the thicker the interphase. The improvement of adhesion between treated fibers and PP, as detected by peel testing, was proven to be caused mainly by entanglements formed between compatibilizing agents and PP. © 1993 John Wiley & Sons, Inc.

Coulomb blockade of two-electron tunneling.

Abstract: We study the Coulomb blockade in a superconducting grain, connected to two normal electrodes by tunnel junctions. At small bias, the conductance of this system is due to electrons passing in pairs through the grain. The linear conductance is periodic in the gate voltage. The period and the conductance activation energy are determined by the charge 2e, rather than e. At resonance the current first grows linearly with the applied bias and then drops as the quasiparticle transport channel opens up.

Pressure Forces on a Circular Cylinder in Cross Flow

Abstract: Mean pressure forces have been measured at Reynolds numbers from about 100 to 3 × 105 (fluctuating pressure forces from about 650). In the range Re = 103 − 104 there was a change in the sectional r.m.s. lift coefficient by about one order of magnitude while the corresponding change in the mean pressure drag coefficient was 20%.

The stability of rational approximations of analytic semigroups

Abstract: This paper contains two new characterizations of generators of analytic semigroups of linear operators in a Banach space. These characterizations do not require use of complex numbers. One is used to give a new proof that strongly elliptic second order partial differential operators generate analytic semigroups inL p , 1

The effect of chemical composition of interphase on dispersion of cellulose fibers in polymers. I. PVC-coated cellulose in polystyrene

Abstract: Cellulose fibers surface-coated with butyl benzyl phthalate (BBP)-plasticized PVC were evaluated as a reinforcement in thermoplastic matrices. Coated fibers were agglomerated during compounding with polypropylene (PP) and polyethylene (PE). However, an excellent dispersion and improved processability were achieved in polystyrene (PS). Melt rheology was also seen to be affected by fiber coating, and viscosity was lower for coated fibers. Fiber coatings seem to lubricate the blending process as well as to protect fiber from damage during processing. Fiber length was unaffected during treatment when coated fibers were used, as shown by microscopic investigation of extracted fibers, whereas the length of untreated fibers was reduced during processing. Introducing surface-coated fibers into PS resulted in an increased elongation at break and improved impact strength of composites. The pullout of the fibers is suggested to be responsible for both improvements. The interphase achieved in PS with PVC/BBP-coated fibers was simulated with PS/PVC/BBP blends. From DSC and DMTA, it was shown that BBP is a cosolvent for PS and PVC and that a single-phase material was achieved at the relevant concentrations, which also was confirmed by optical clarity. © 1993 John Wiley & Sons, Inc.