Showing papers by "Chalmers University of Technology published in 1985"

Atmospheric mercury—a review*

Abstract: An attempt is made to assess present knowledge about atmospheric mercury: its occurrence in air and precipitation, chemical transformations taking place in the atmosphere, and mercury fluxes to and from the Earth’s surface. Tentative budgets are estimated for mercury in the global atmosphere and in the atmosphere over Europe and Sweden. Major features revealed by this include the following: For the global atmosphere, current anthropogenic emissions are comparable to emissions by natural processes (preindustrial). The present background fluxes are probably significantly augmented by anthropogenic emissions during the industrial era. A dominant fraction (≥80%) of the total mercury in the atmosphere consists of a volatile gaseous mercury form, presumably elemental mercury, Hg O . This mercury has an atmospheric residence time of at least a few months, maybe even one or two years, and is uniformly distributed throughout the troposphere (1-2 ng m -3 . The volatile mercury vapour (Hg O ) is oxidized in the atmosphere to unknown forms that are soluble and can be scavenged by precipitation or dry deposited at the surface. The oxidation process is not known but photochemical oxidants (including ozone) are likely to be important. The atmospheric residence time of the water soluble (non-volatile) mercury is in the range of a few days to a few weeks, corresponding to a characteristic transport distance of up to a few thousand kilometers. Even if a dominant fraction of the mercury emitted from an individual source, such as a chlor-alkali plant, is dispersed regionally or globally. a small fraction (< 10%) is deposited locally. Increases by a factor of 10 to 100. above background deposition rates, have been measured within the nearest km of such plants. At a distance of 10-50 km, the deposition normally approaches the background value. Around a large Swedish smelter, mercury levels in lake sediments are significantly augmented even beyond 50 km from the plant. The contribution to current mercury deposition in Sweden from anthropogenic mercury emissions in other European countries is most likely larger than the contributions from current Swedish emissions. Measurements of mercury in lake sediments and peat bogs show that in southern Scandinavia. the rate of mercury deposition has increased by a factor of about 5 during the last hundred years. The increase in northern Scandinavia is significantly less, at most a factor of two. These increases are caused, most likely, by anthropogenic emissions into the atmosphere mainly within the European region. DOI: 10.1111/j.1600-0889.1985.tb00062.x

Lambda lifting: transforming programs to recursive equations

Abstract: Lambda lifting is a technique for transforming a functional program with local function definitions, possibly with free variables in the function definitions, into a program consisting only of global function (combinator) definitions which will be used as rewrite rules. Different ways of doing lambda lifting are presented, as well as reasons for rejecting or selecting the method used in our Lazy ML compiler. A functional program implementing the chosen algorithm is given.

Brownian motion and vibrational phase relaxation at surfaces: CO on Ni(111).

Abstract: The temperature dependence of the internal stretch vibrational mode of CO chemisorbed on Ni(111) has been studied with the use of infrared spectroscopy. The width of the absorption peak of the bridge-bonded molecules exhibits a strong temperature dependence. A theory is developed which accounts well for the experimental results. It shows that the peak broadening is caused by anharmonic coupling to one particular low-frequency mode, namely a hindered rotation.

Compiling pattern matching

Abstract: Introduction Pattern matching is a very powerful and useful device in programming. In functional languages it emerged in SASL [Turn76] and Hope [BursS0], and has also found its way into SML [Miln84]. The pattern mathing described here is that of LML which is a lazy ([Frie76] and [Henri76]) variant of ML. The pattern matching in LML evolved independently of that in SML so they are not (yet) the same, although very similar. The compilation of pattern matching in SML has been addressed in [Card84]. The LML compiler project began as an attempt to produce efficient code for a typed functional language with lazy evaluation. Since we regard pattern matching as an important language feature it should also yield efficient code. Only pattern matching in case expressions is described here, since we regard this as the basic pattern matching facility in the language. All other types of pattern mathing used in LML can be easily translated into case expressions, see [Augu84] for details. The compilation (of pattern matching) proceeds in several steps: • transform all pattern matching to case expressions. • transform complex case expressions into expressions that are easy to generate code for. • generate G-code for the case expressions, and from that machine code for the target machine.

The bone-anchored hearing aid. Principal design and a psychoacoustical evaluation.

Abstract: Hearing aids can be divided into two groups, distinguished by the principle of how sound is transmitted to the cochlea. The greatest and most important group is that consisting of air conduction (AC) hearing aids, whereas the other group consisting of bone conduction (BC) hearing aids is relatively small but nevertheless important for patients with particular types of hearing disorder. Conventional bone conduction hearing aids are not in common use, mainly because of several drawbacks. The implantation of a titanium screw into the mastoid portion of the temporal bone has made it possible to obtain a permanent and reaction-free rigid penetration of the skin. A newly developed bone conduction hearing aid was connected to such a screw. This new hearing aid is named ‘the bone-anchored hearing aid’ (BAHA) and it is characterized by a single housing construction. The transducer piston of the BAHA is directly connected to the titanium screw by a low-profile coupling arrangement. Ten patients were equipped with t...

Geometric bounds on the Ornstein-Uhlenbeck velocity process

Abstract: Let X: Ω→C(ℝ+;ℝn) be the Ornstein-Uhlenbeck velocity process in equilibrium and denote by τA=τA(X) the first hitting time of \(A \subseteq \mathbb{R}^n \). If A, B∈ℛn and ℙ(X(O)∈A=ℙ(Xn(O)≦a), ℙ(Xn(O)∈B=ℙ(Xn(O)≧b)we prove that \(\mathbb{P}(\tau _A \underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{ \leqslant } t)\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{ \geqslant } \mathbb{P}(\tau _{\{ \chi _n \underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{ \leqslant } a\} } \underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{ \leqslant } t)\) and \(\mathbb{E}\left( {\int\limits_0^{t \wedge \tau A} {1_{\text{B}} (X({\text{s}})d{\text{s}}} } \right)\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{ \leqslant } \mathbb{E}\left( {\int\limits_0^{t \wedge \tau _{\left\{ {x_n \underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{ \leqslant } a} \right\}} } {1_{\left\{ {x_n \underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{ \geqslant } b} \right\}} (X({\text{s))}}d{\text{s}}} } \right)\). Here Xndenotes the n-th component of X.

Electron localization in alkali-halide clusters.

Abstract: The quantum path-integral molecular-dynamics method was applied to explore the structure, energetics, and dynamics of an excess electron interacting with an alkali-halide cluster. Four distinct modes of electron localization were established, which depend on the cluster composition, size, and structure; they involve an internal F-defect, an external surface state, dissociative detachment of an alkali atom, and structural isometrization induced by electron attachment.

A Note on the Noninvasive Estimation of Muscle Fiber Conduction Velocity

Abstract: Average muscle action potential conduction velocity values were obtained during isometric constant-force contractions by a cross-correlation technique. To minimize the bias introduced by nondelayed activity appearing on the two myoelectric derivations, the signals were doubly differentiated. This arrangement effectively reduced the nondelayed activity and increased the accuracy of the estimate.

Vibrational phase relaxation at surfaces: CO on Ni(111).

Abstract: The temperature dependence of the internal stretch vibrational mode of CO adsorbed on Ni(111) has been studied by infrared spectroscopy. The results are successfully analyzed by a model for vibrational phase relaxation. It is found that anharmonic coupling between the C-O stretch mode and a low-frequency frustrated rotation gives the dominant contribution.

Precision Geodesy Using the Mark-III Very-Long-Baseline Interferometer System

Abstract: Very-long-baseline interferometry (VLBI) has been used to make precise measurements of the vector separation between widely separated antennas. The system for acquiring and processing VLBI data known as Mark-III is described. Tests of the system show it to have millimeter-level accuracy on short baselines; measurements of baselines longer than a few hundred kilometers suggest that accuracy is limited by the uncertainty in the calibration of tropospheric path delay to the level of a few centimeters. VLBI experiments conducted between 1976 and 1983 have demonstrated the stability of the North American plate by showing that there is no change in the distance between easternl-California and Massachusetts at the level of a few millimeters per year or greater. Experiments made from 1980 to 1984 indicate that the distance from Massachusetts to Sweden is increasing by 1.7 ± 1 cm/year where the quoted standard deviation includes the estimated effects of systematic atic errors

The microstructure of a ZnO varistor material

Abstract: The microstructure of a ZnO varistor material has been investigated by a combination of X-ray diffractometry and analytical electron microscopy (SEM, TEM, STEM, EDX). The material was found to consist of: ZnO grains (doped with manganese, cobalt and nickel); smaller spinel grains which hinder the growth of ZnO grains during sintering; intergranular Bi-rich phases (namely α-Bi2O3, pyrochlore and an amorphous phase); and a small proportion of ZnO-ZnO interfaces which did not have any intergranular film but to which bismuth had segregated. The intergranular microstructure is largely a result of processes which occur during liquid phase sintering and subsequent cooling to room temperature.

Beam element matrices derived from Vlasov's theory of open thin‐walled elastic beams

Abstract: A uniform beam element of open thin-walled cross-section is studied under stationary harmonic end excitation. An exact dynamic (transcendentally frequency-dependent) 14 × 14 element stiffness matrix is derived from Vlasov's coupled differential equations. Special attention is paid to the computational problems arising when coefficients vanish in these equations because of symmetric cross-section, zero warping stiffness, etc. The dynamic element stiffness matrix is established via a generalized linear eigenvalue problem and a system of linear algebraic equations with complex matrices. A static stiffness matrix is also derived and the associated consistent mass and geometric stiffness matrices are given. Modal masses are evaluated. A FORTRAN program and a numerical example are included.

Critical Aspects of Measurement of Circular and Linear Dichroism: A Device for Absolute Calibration:

Abstract: The polarization effect of one or several tilted, parallel air-spaced fused silica plates is calculated. It is generally necessary to include higher order reflections. A device consisting of 1-4 plates tilted 10-45° from normal incidence is proposed for the calibration of differential linear dichroism (LD) in the measurement ranges 10−3 to 10−1 decadic absorbance units and the wavelength region 200-700 nm. The experimental LD measured in these ranges on commercial circular dichrometers, converted to LD mode according to Norden and Davidsson, was in excellent agreement with the calculated, nonempirical results. Since the response function of the instrument in this conversion mode is the same for LD and CD, the method also provides a means for absolute calibration of CD. The results can also be applied to polarized scattering and fluorescence. (For previous papers on this theme, see Refs. 6, 9 and 12.)

Chemical Composition and Morphology of Titanium Surface Oxides

Abstract: Titanium has emerged as one of the most tissue-compatible metallic materials. The high degree of biocompatibility is intimately connected with the oxide that forms on the metal surface. In the present work a broad characterization has been made of titanium samples pretreated both by presently used clinical procedures (mechanical machining, ultrasonic cleaning and autoclaving) and by alternative preparation procedures such as electropolishing and anodic oxidation. The former samples are found to have a surface oxide of TiO2 which is 30–50 A thick, with some trace element contamination and a relatively large carbon content (30–50% of a monoatomic layer). The anodically oxidized samples also consist of TiO2 with an oxide thickness range of 50–2000 A, but the morphology and crystallinity of the anodic oxides are found to depend on thickness and preparation conditions. The main methods of investigation used in the present study were ESCA, SIMS and transmission electron microscopy.

State-dependent volume isotope shifts of low-lying states of group-IIa and -IIb elements.

Abstract: Results of relativistic multiconfiguration Dirac-Fock calculations with an extended nucleus are used to analyze the volume isotope shifts of the resonance transitions in the group-11a and -11 b ele­ ments as well as in Vb. This is done together with a review of the isotope shift theory, including a critical evaluation and comparison of the semiempirical calculation of volume isotope shifts com­ monly used today. Electronic factors F;, proportional to differences of electronic densities over the nuclear volume, are discussed within various approximations and compared with experimental re­ sults.

Theory of Dielectric Properties of Heterogeneous Substances Applied to Water in a Paint Film

Abstract: The water content of 12 paints on steel substrate, exposed to 0.1M sodium chloride at 25 C for 24 h, was calculated from impedance measurements and compared with gravimetric determinations...

Surface modification of cellulose fibers. II. The effect of cellulose fiber treatment on the performance of cellulose–polyester composites

Abstract: Cellulose fibers treated with different coupling agents based on trichloro-s-triazine have been evaluated in terms of their reinforcement effect on unsaturated polyesters. The treatment with coupling agents containing double bonds resulted in what we believe to be the formation of covalent bonds between fiber and matrix. This has been compared with a treatment, which can only lead to formation of close interfacial molecular contact by wetting. The tensile properties of composites prepared from treated and untreated fibers were studied before and after exposure to water. It was found that all types of fiber treatment decreased water absorption and the reduction of mechanical properties in wet conditions, but that the degradation at the fiber/matrix interface which occurs from immersion in water and drying could only be avoided through the development of covalent bonds between fiber and matrix. Scanning electron microscopy was used to study the adhesion between fiber and matrix. An explanation of the reduction of mechanical properties of cellulose-fiber reinforced polymers in wet conditions is proposed.

Scaling Laws for Mode Lockings in Circle Maps

Abstract: The self-similar structure of mode lockings for circle maps is studied by means of the associated Farey trees. We investigate numerically several classes of scaling relations implicit in the Farey organization of mode lockings and discuss the extent to which they lead to universal scaling laws.