Showing papers by "Chalmers University of Technology published in 1987"

Templates for the Solution of Algebraic Eigenvalue Problems: A Practical Guide

Abstract: List of symbols and acronyms List of iterative algorithm templates List of direct algorithms List of figures List of tables 1: Introduction 2: A brief tour of Eigenproblems 3: An introduction to iterative projection methods 4: Hermitian Eigenvalue problems 5: Generalized Hermitian Eigenvalue problems 6: Singular Value Decomposition 7: Non-Hermitian Eigenvalue problems 8: Generalized Non-Hermitian Eigenvalue problems 9: Nonlinear Eigenvalue problems 10: Common issues 11: Preconditioning techniques Appendix: of things not treated Bibliography Index .

The Neutron Halo of Extremely Neutron-Rich Nuclei

Abstract: Empirical evidence suggests that neutron pairing plays an important role for the stability of nuclei near the neutron drip line. It is shown that the low binding of these nuclei will lead to a neutronization of the nuclear surface and possibly to large cross-sections for Coulomb dissociation, which then offers a new way to study clusters and their binding energies.

CMOS Circuit Speed and Buffer Optimization

Abstract: An improved timing model for CMOS combinational logic is presented. The model is based on an analytical solution for the CMOS inverter output response to an input ramp. This model yields a better understanding of the switching behavior of the CMOS inverter than the step-response model by considering the slope of the input waveform. Essentially, the propagation delay is shown to be the sum of the step-response delay and an input dependent delay that may account for as much as 50-100 percent of the total delay. The matching between the ramp input and the characteristic input waveforms is shown to be easily performed for excellent agreement in output response and propagation delay. Even though the short-circuit current is neglected, its influence is shown to be small and may be corrected. As an example, the timing model is used to optimize CMOS output buffers for minimum delay. If the intrinsic output load capacitance is included in the model, the optimum tapering factor is shown to be not e but a value in the range 3-5 depending on process parameters and design style. Also, due to the input dependence of the propagation delay, the last inverter stage in the buffer should have a larger tapering factor than the other stages for minimum delay.

Views: a way for pattern matching to cohabit with data abstraction

Abstract: Pattern matching and data abstraction are important concepts in designing programs, but they do not fit well together. Pattern matching depends on making public a free data type representation, while data abstraction depends on hiding the representation. This paper proposes the views mechanism as a means of reconciling this conflict. A view allows any type to be viewed as a free data type, thus combining the clarity of pattern matching with the efficiency of data abstraction.

Characterization of interaction between DNA and 4',6-diamidino-2-phenylindole by optical spectroscopy

Abstract: We have examined the interaction between 4',6-diamidino-2-phenylindole (DAPI) and DNA using flow linear dichroism (LD), circular dichroism (CD), and fluorescence techniques. We show the presence of two spectroscopically distinct binding sites at low binding ratios with saturation values of 0.025 and 0.17, respectively. In both sites DAPI is bound with its long axis approximately parallel to the grooves of the DNA helix. Resolution of CD spectra shows that an exciton component is present at higher binding ratios, which we attribute to the interaction of two accidentally close-lying DAPI molecules. We also find evidence that DAPI, at least in the high-affinity site, binds preferentially to AT-rich regions. From the spectroscopic results, supported by structural considerations, we can completely exclude that DAPI is bound to DNA by intercalation. Binding geometries and site densities are consistent with a location of DAPI in the grooves of DNA, with the high-affinity site most probably in the minor groove.

Attribute grammars as a functional programming paradigm

Abstract: The purpose of this paper is twofold. Firstly we show how attributes in an attribute grammar can be simply and efficiently evaluated using a lazy functional language. The class of attribute grammars we can deal with are the most general ones possible: attributes may depend on each other in an arbitrary way, as long as there are no truly circular data dependencies.

Prehydrolyzed Cellulose as Reinforcing Filler for Thermoplastics

Abstract: This paper presents the results of an experimental study of the mechanical properties of composites consisting of prehydrolyzed cellulose and thermoplastic matrices. The main feature of prehydrolyzed cellulose fibres is a high degree of brittleness, permitting the fibres to be finely comminuted in the shear field of normal compounding and processing machinery. Such an effect can be anticipated to improve the homogeneity and the mechanical parameters of the moulded samples. In the present work, this has been demonstrated with PP, HDPE and PS containing varying amounts of prehydrolyzed cellulose of different origin (bleached pulps). The tests were done on injection moulded samples. The compounding method (Buss-Kneader vs. twin-screw extruder) had only minor influence on the results. Theoretical assessment of the modulus values using the Tsai–Halpin equation gave somewhat lower values than those recorded on experimental samples. This was interpreted in terms of the disintegration of the cellulose co...

Degradation products of bran phytate formed during digestion in the human small intestine: effect of extrusion cooking on digestibility.

Abstract: To investigate the digestion of phytate in the stomach and small intestine in humans, studies were performed in subjects with established ileostomy. A recently developed high performance liquid chromatography method made it possible to analyze phytate and its degradation products in food and digesta. The digestibility of phytate in raw bran and extruded bran was investigated in seven ileostomy patients. Each subject was studied for two 4-d periods while consuming a constant low fiber diet with the addition of either 54 g/d of a bran-gluten-starch mixture or the corresponding extruded product. During passage through the subject's stomach and small intestine 58%, on average, of the phytate in unprocessed bran was hydrolyzed to inositol penta-, tetra- and triphosphates. When bran was subjected to extrusion cooking, 25% of the inositol hexaphosphate was hydrolyzed to penta- and tetraphosphate and the phytase activity ceased. Essentially no phytate digestion occurred when the ileostomy subjects consumed the extruded product. The reduced digestibility might be due to the lost phytase activity or to formation of indigestible phytate complexes during extrusion cooking.

Induced CD of DNA intercalators: electric dipole allowed transitions.

Abstract: The induced CD of an electric dipole allowed transition of a DNA intercalator has been calculated using the “matrix method” and a set of DNA ππ* transitions recently adopted for calculating the CD of DNA by Rizzo and Schellman [(1984) Biopolymers23, 435–470]. The induced CD is strongly dependent on the angular orientation of the intercalator and only moderately dependent on its location within the intercalation pocket. The dependence of the CD on the orientation and location of the intercalator was studied for some representative conformations of di- and tetranucleotide duplexes of (dGdC) and (dAdT). The effect of alternative DNA transition moment directions was also tested. The orientation dependence compares well with the previously predicted 1-2 cos2 γ dependence [B. Norden and F. Tjerneld (1982) Biopolymers21, 1713–1734]. Measured induced CD spectra of methylene blue (MB) intercalated in double-stranded poly(dAdT), poly(dGdC), and calf-thymus DNA are discussed on the basis of the results of the calculations. Major differences between the induced CD spectra are likely to reflect different modes of intercalation for the different nucleotide sequences. In particular, the concluded geometry in solution for MB intercalated in poly(dAdT) differs significantly from the corresponding geometry found in dinucleotide–intercalator crystals.

Gamma radiation from the N=Z nucleus 4080Zr

Abstract: The very neutron-deficient isotope /sup 80/Zr was produced in the reaction /sup 24/Mg(/sup 58/Ni, 2n)/sup 80/Zr at 190 MeV with a cross section of sigma = 10 +- 5 ..mu..b and was identified with the Daresbury Recoil Separator. The observation reflects a fiftyfold increase in sensitivity for in-beam spectroscopy of exotic nuclei. Coincidence measurements between the isolated isotope and prompt gamma radiation allowed the identification of decays from low-lying states at E = 290 and 828 keV which indicate that /sup 80/Zr has an extremely large quadrupole deformation of ..beta../sub 2/approx. =0.4.

The response of the seated human to sinusoidal vibration and impact.

Abstract: Low back pain has been shown to occur more frequently among vehicle drivers than in representative control groups. Thus the response of the human to vibration and impact is of interest. This study investigated the response of the spine to both impact and sinusoidal excitation in either a relaxed or erect seated posture. The sinusoidal testing apparatus used was a resonating system consisting of two parallel wooden beams, simply supported, and the impact testing apparatus a bearing-guided, spring-suspended platform, struck from below. Ten subjects (5 males, 5 females) were evaluated using both methods. Transfer functions were compared at 2-4 Hz, 4-8 Hz and 8-16 Hz intervals using a sign test. Although in 24 comparisons of either test method (vibration or impact) or posture (erect or relaxed) where eleven showed differences significant at the p less than .05 level, only 2 out of 24 comparisons were the differences distinct enough to be significant (at the p less than .01 level). Both of these latter differences were due to test method while the subjects were sitting erect. In those instances where there were no significant differences due to test method, the impact method may be a viable replacement for the vibration test method. Where the levels of significance are higher (p less than .01 or p less than .05), further study of the magnitude of the differences is indicated and may reveal further insight into the seated individual as a system.

Generalized Landau model of ferroelectric liquid crystals.

Abstract: Using a generalized Landau type of free-energy density, we develop a theoretical model which, in a unified way, describes the general features of the tilt, polarization, pitch, dielectric susceptibility, and heat capacity of ferroelectric liquid crystals. Rewriting the equations into dimensionless form, we show that six parameters are needed in order to account properly for the temperature dependence of the quantities in question. It is also shown that the introduction of a biquadratic coupling between the tilt and the polarization in the free-energy density, which is an essential part of the model, implies a crossover behavior of the polarization when plotted as a function of temperature.

Cellulose fiber‐polyester composites with reduced water sensitivity (1)—chemical treatment and mechanical properties

Abstract: Formaldehyde and di-methylomelamine were used to modify the surfaces of cellulose fibers. Composites were prepared with unsaturated polyester and treated cellulose as the reinforcing material. The tensile strength and the elongation of the cellulose fibers were determined in dry and wet conditions as well as the tensile strength and the tensile modulus of the cellulose-polyester composites. The water uptake of the composites was reduced by 46 to 52 percent. The wet strength of the composites was improved by more than 50 percent.

Error estimates and automatic time step control for nonlinear parabolic problems, I

Abstract: In this note we extend results by one of the authors on time discretization error estimates and related automatic time step control for stiff ordinary differential equations to the case of a nonlinear parabolic problem. The method for time discretization is the so-called Discontinuous Galerkin method based on using piecewise polynomials of degree $q \geqq 0$. We consider in this note the case $q = 0$ corresponding to a variant of the backward Euler method. We prove a new almost optimal error estimate and present a related new algorithm for automatic time step control. This algorithm is very simple but yet is efficient and gives control of the global error.

Discrete valence-electron states in thin metal overlayers on a metal

Abstract: We have measured photoelectron energy spectra from thin Na and Ba overlayers on Cu(111). The spectra show extremely narrow adsorbate-induced peaks, much narrower than observed for any other adsorbate system. These features arise from electrons trapped in the potential well between the vacuum barrier and the Cu(111) surface which has a high electron reflectivity for energies within the band gap producing the necks of the Cu Fermi surface.

The Boltzmann equation for weakly inhomogeneous data

Abstract: We solve the initial value problem associated to the nonlinear Boltzmann equation in the case in which the initial distribution has sufficiently small spatial gradients.