Showing papers by "Chalmers University of Technology published in 1991"
TL;DR: In the last decade, a new pattern of Hg pollution has been discerned, mostly in Scandinavia and North America, mostly due to more widespread air pollution and long-range transport of pollutants.
Abstract: During the last decade a new pattern of Hg pollution has been discerned, mostly in Scandinavia and North America. Fish from low productive lakes, even in remote areas, have been found to have a high Hg content. This pollution problem cannot be connected to single Hg discharges but is due to more widespread air pollution and long-range transport of pollutants. A large number of waters are affected and the problem is of a regional character. The national limits for Hg in fish are exceeded in a large number of lakes. In Sweden alone, it has been estimated that the total number of lakes exceeding the blacklisting limit of 1 mg Hg kg-1 in 1-kg pike is about 10 000.
894 citations
TL;DR: In this article, the physicochemical properties of polypropylene-maleic anhydride copolymer copolymers were characterized by contact angle measurements, and the chemical structure was identified with ESCA and FTIR.
Abstract: Cellulose fibers were surface modified with polypropylene–maleic anhydride copolymer. The physical properties of such fibers were characterized by contact angle measurements, and the chemical structure was identified with ESCA and FTIR. ESCA showed that the modifying agent was localized at the surface of the fibers. The modified fibers were compounded with polypropylene, and composites with various amount of fibers were manufactured by injection molding. All mechanical properties were improved when treated fibers were used. SEM showed improved dispersion, wetting of fibers, and adhesion. The nature of adhesion was studied using FTIR. It was found that the surface modifying agent is covalently bonded to the fibers through esterification. The degree of esterification is enhanced by activating the modifying agent before fiber treatment. This study has shown the effects of treatment conditions on activation of reactive species and chemical reaction between fiber and modifying agent. Moreover, a better understanding has been achieved of the nature of adhesion for the system.
762 citations
TL;DR: A computerized analysing system is described for the measurement of wall thickness and plaque area on the carotid and femoral arteries and it is suggested that if measurements on the near wall are performed, measurements from the far wall should be presented separately, and if lumen diameter is measured, that this measurement is carried out according to the leading edge principle.
Abstract: SUMMARY
A B-mode [two-dimensional (2D)] image from the carotid artery may be described as containing seven echo zones. The aim of the present work is to discuss how lumen diameter and wall thickness can be measured from these zones, and to review some of the basic principles of ultrasound physics and imaging. Simple experiments were performed to identify the echoes defining intima-lumen interfaces. The results showed that:
1
The intima-media thickness of the near wall cannot be measured in a valid way.
2
The lumen diameter of a blood vessel is defined by the distance from the leading edge of the intima-lumen interface of the near wall (echo zone 3) to the leading edge of the lumen-intima interface of the fall wall (echo zone 5).
3
Previously published studies have validated the intima-media complex of the far wall as the distance from the leading edge of the lumen-intima interface of the far wall to the leading edge of the media-adventitia interface of the far wall (echo zone 7). We suggest that if measurements on the near wall are performed, measurements from the far wall should also be presented separately, and if lumen diameter is measured, that this measurement is carried out according to the leading edge principle.
We describe a computerized analysing system for the measurement of wall thickness and plaque area on the carotid and femoral arteries. The system is based on a low-cost PC and a frame grabber board and calculates minimum, maximum and mean values of lumen diameter and wall thickness from a section of the artery.
535 citations
TL;DR: Addition of calcium chloride to wheat rolls significantly reduced iron absorption, suggesting that the effect of calcium is related to the mucosal transfer of iron.
459 citations
TL;DR: Light emission characteristics from the tunnel gap of a scanning tunneling microscope are used to elucidate the interaction of tunneling electrons with tip-induced plasmon modes on Ag, Au, and Cu surfaces.
Abstract: Light emission characteristics from the tunnel gap of a scanning tunneling microscope are used to elucidate the interaction of tunneling electrons with tip-induced plasmon modes on Ag, Au, and Cu surfaces. Enhanced redshifted spectra are observed in the tunneling regime. Model calculations of optical spectra in this range agree well with the experimental data. Isochromat spectra are used to demonstrate that the principal excitation process occurs via inelastic tunneling.
396 citations
TL;DR: A review of the design and fabrication of resonant sensors that are based on resonating silicon structures is presented in this article, where the most important aspects are: resonator materials, fabrication technology, type of resonator, mode of vibration, quality of vibration and temperature stability.
Abstract: This paper is a review of the design and fabrication of resonant sensors that are based on resonating silicon structures. Some of the design aspects that control the performance of the resonator sensor are analysed. The most important aspects are: resonator materials, fabrication technology, type of resonator, mode of vibration, quality of vibration and temperature stability. Q-factor-reducing damping factors are discussed and the different techniques that are available for excitation and detection of the vibration of the resonator are described. Descriptions of published resonant silicon sensors are presented.
313 citations
08 Jul 1991
TL;DR: This paper shows how to put time into Milner's CCS to model real time systems and develops an expansion theorem for real time concurrency, which is an extension of the expansion theorem of CCS.
Abstract: This paper shows how to put time into Milner's CCS to model real time systems. In particular, we will develop an expansion theorem for real time concurrency, which is an extension of the expansion theorem of CCS. The essential step made in this work is that a more general form of action prefix, μ@t.P is introduced, where t is a time variable. Intuitively, μ@t.P is an agent which may perform μ and become P[d/t] in doing so, where t is replaced by d, the time delay before μ is actually performed. The original form μ.P of action prefix of CCS is just a simple case of μ@t.P when t does not occur free in P — P does not depend on the time at which μ is performed.
272 citations
TL;DR: In this article, it was shown that CH3HgCl is the dominant McHg species at the lowest concentration of sulphide/thiols (0.1 nM).
Abstract: Sulphur is an essential element for aquatic biosystems, the life processes of which lead to the formation of low molecular weight S compounds in the water. The results of our calculations indicate a pronounced tendency for Hg(II) to form HgS (or HgOHSH) and Hg(SR)2 complexes in the presence of H2S and thiols. Likewise, McHg will form CH3HgSH and CH3HgSR complexes, but in this case the chloride complex will dominate at low concentrations of H2S and thiols. In acidic low salinity water, CH3HgCl is the dominant McHg species at the lowest concentration of sulphide/thiols (0.1 nM), whereas a hundredfold increase of the sulphide/thiol concentration, or an increase of the pH to neutral or slightly alkaline conditions, will result in a total dominance for CH3HgSH and CH3HgSR.
267 citations
TL;DR: In this article, a 17 kW propane fired flue gas generator was used, while the kinetics of specific Hg reactions were investigated in a continuous flow reactor, and it was shown that Hg is readily oxidized by Cl2 and HCl both at room and at elevated temperatures (up to 900 °C) but not by NH3, N2O, SO2 or H2S.
Abstract: Atmospheric Hg is present in different physical and chemical forms, which determine its atmospheric transformation and transport capacities The chemistry of Hg in flue gases is thus of importance for the deposition pattern around point source emissions In order to apply Hg cleaning methods in flue gases its speciation is also of importance To investigate this under realistic conditions, a 17 kW propane fired flue gas generator was used, while the kinetics of specific Hg reactions were investigated in a continuous flow reactor Elemental Hg is readily oxidized by Cl2 and HCl both at room and at elevated temperatures (up to 900 °C) but not by NH3, N2O, SO2 or H2S It reacts with O2 if a catalyst, such as activated carbon, is present A slow reaction between Hg and NO2 has also been noted
251 citations
TL;DR: A flux chamber technique applied to volatile mercury species has been developed and evaluated in this article, which can be used to measure the direction and magnitude of mercury transfer between the atmosphere and lake or soil surfaces.
Abstract: A flux chamber technique applied to volatile mercury species has been developed and evaluated. This technique can be used to measure the direction and magnitude of mercury transfer between the atmosphere and lake or soil surfaces. Measurements have been performed over four oligotrophic forest lakes in southwestern Sweden during 1988 and 1989. Net emission fluxes of mercury were measured from the lakes. The measured daytime fluxes during the warmer season (water temperatures 13–23 °C) were within the range 3–20 ng h -1 m -2 (average 7.9 ng h -1 m -2 ). The average night-time fluxes measured during the same season were 2 to 3 times smaller. Two sets of measurements, performed during the winter when water temperatures were ≤ 2 °C, gave flux values close to zero. Flux measurements were also performed over soil in a coniferous forest. Compared to the situation for the forest lakes, the fluxes of mercury over forest soil are much lower in magnitude, with values ranging from approximately − 2 to + 2 ng h -1 m -2 during different seasons. Emission was observed with an average of 0.3 ng h -1 m -2 when soil temperature was about 10 °C, while dry deposition was measured with an average of 0.9 ng h -1 m -2 , when soil temperature was < 3 °C. DOI: 10.1034/j.1600-0889.1990.t01-1-00009.x-i1
245 citations
TL;DR: Two different regimes of viscous behavior are found in the time window accessible in MD simulation studies, one of which is of the hopping type, and the other is found to be strongly cooperative in nature.
Abstract: Molecular-dynamics (MD) simulations have been carried out on a two-component Lennard-Jones system, quenched into supercooled and amorphous states. Two different regimes of viscous behavior are found in the time window accessible in MD simulation studies (of the order of nanoseconds if units appropriate for argon are used). The results for the time dependence of the self-intermediate scattering function ${\mathit{F}}^{\mathit{s}}$(q,t) show two different slow relaxation processes, where the slowest (\ensuremath{\alpha} relaxation) can be represented by a stretched exponential, exp[-(t/${\mathrm{\ensuremath{\tau}}}_{\mathrm{rel}}$${)}^{\mathrm{\ensuremath{\beta}}}$]. In the frequency domain this gives rise to a quasielastic peak, and it is found that its area, the nonergodicity parameter ${\mathit{f}}^{\mathit{s}}$(q)==a, shows an anomalous decrease when increasing the temperature towards a critical value ${\mathit{T}}_{\mathit{c}}$. This happens in the supercooled-liquid regime, and it is one of the basic predictions of the recent mode-coupling theory for the liquid-glass transition problem. In the strongly supercooled-liquid regime the diffusion is of the hopping type, and it is found to be strongly cooperative in nature.
TL;DR: In this paper, different contributions to the dielectric permittivity in ferroelectric liquid crystals are discussed, with emphasis on the soft mode and the Goldstone mode and their location in the spectrum.
Abstract: Different contributions to the dielectric permittivity in ferroelectric liquid crystals are discussed, with emphasis on the soft mode and the Goldstone mode and their location in the dielectric spectrum. Experimentally, the complex dielectric permittivity has been studied as a function of temperature and frequency in the range 5 Hz - 13 MHz for three different ferroelectric liquid crystal materials. The main problems encountered in dielectric measurements at low and high frequency are discussed in some detail. The soft mode dielectric behaviour has been studied as a function of temperature, frequency and bias electric field. The applicability of the Curie-Weiss law for the soft mode dielectric contribution in the A* phase was analyzed. In the C* phase the temperature dependence of the dielectric contribution of the Goldstone mode has been measured. By applying a bias electric field, we have been able to study the soft mode dielectric behaviour also deep into the C* phase. In the A* and C* phases ...
TL;DR: Seven men with well-controlled, noninsulin-dependent (type 2) diabetes ingested on two different mornings, in random order, meals with or without a 5.0-g sodium alginate supplement (algae-isolate, 75% soluble fiber), which induced significantly lower postprandial rises in blood glucose, serum insulin and plasma C-peptide.
Abstract: Seven men with well-controlled, noninsulin-dependent (type 2) diabetes ingested on two different mornings, in random order, meals with or without a 5.0-g sodium alginate supplement (algae-isolate, 75% soluble fiber). The meals contained similar amounts of digestible carbohydrates, fat and protein. The gastric emptying rate of the meal containing sodium alginate, measured by detection of 51Cr mixed into the meals, was significantly slower than that of the fiber-free meal. Sodium alginate also induced significantly lower postprandial rises in blood glucose, serum insulin and plasma C-peptide. The diminished glucose response after the addition of sodium alginate could be correlated to the delayed gastric emptying rate induced by the fiber (rs = 0.92, P less than 0.01).
TL;DR: In this article, an alternative variational approach is suggested that remedies these deficiencies and gives results in good agreement with numerical results, however, it is found that the predictions for some of the important pulse parameters are qualitatively wrong and could lead to incorrect conclusions.
Abstract: Optical pulses, which propagate under the combined effects of nonlinearity, dispersion, and diffraction, may collapse in space and time. The standard method for analyzing these collapses is the aberrationless paraxial ray approximation. This method is known to give a quantitatively correct, although not particularly accurate, picture of most properties of the pulse dynamics. However, it is found that the predictions for some of the important pulse parameters are qualitatively wrong and could lead to incorrect conclusions. An alternative variational approach is suggested that remedies these deficiencies and gives results in good agreement with numerical results.
TL;DR: In this article, the effect of phytate hydrolysis by endogenous and exogenous phytases was studied for their effect on increasing iron availability in cereals, including wheat bran and whole meal flours.
Abstract: Phytate (inositol hexaphosphate) hydrolysis by endogenous and exogenous phytases was studied for their effect on increasing iron availability in cereals. Wheat bran and whole meal flours of rye and oats were soaked at optimal conditions for phytase activity (55°C, pH 5) for different time intervals. Phytate and its degradation products were determined by HPLC and related to iron solubility under simulated physiological conditions. Small amounts of phytate (< lμmol/g) had a strong negative effect on iron solubility. When inositol hexa- and pentaphosphates of wheat bran and rye flour were completely hydrolyzed by activating endogenous phytase, iron solubility under simulated physiological conditions increased from 3 to 53% (wheat) and 5 to 21% (rye). Addition of wheat phytase to uncooked oatmeal increased iron solubility from 4 to 11 and in precooked to 18%, while endogenous phytase of uncooked oatmeal had less effect on phytate digestion and iron solubility.
TL;DR: In this paper, a method to investigate the rhythm of the human shoulder, i.e. the interplay between the motion of constituent parts of the shoulder, has been devised and tested.
TL;DR: In this paper, conditions for discontinuous bifurcations of the incremental fields in elastic-platic materials subjected to the condition of either plane stress or plane strain are derived and explicit expressions for the critical hardening modulus and the corresponding Bifurcation directions are obtained for a quite general class of plasticity models.
TL;DR: In this article, the influence of operating conditions, particle properties and bed diameters on radial voidage profiles in circulating fluidized beds operating in the fast regime has been investigated in gas-solid systems.
TL;DR: In this article, an instable intermediate, HgSO3, which decomposes to produce Hg+ which in turn is rapidly reduced to Hg0. This reaction may influence the concentration of Hg in cloud and rain-water by reducing water soluble Hg2+ to volatile Hg 0.
Abstract: Divalent Hg is reduced by sulfite in aqueous solutions. The proposed mechanism involves the formation of an instable intermediate, HgSO3, which decomposes to produce Hg+ which in turn is rapidly reduced to Hg0. The overall rate of the reaction is inversely dependent on the concentration of sulfite. This reaction may influence the concentration of Hg in cloud- and rain-water by reducing water soluble Hg2+ to volatile Hg0. At low concentrations of SO2(g) (5 μg m−3, 25 °C), the rate of the conversion of Hg(SO3)2
2− to Hg0 becomes significant (> 1 % h−1) at pH < 5.5. At higher S02 concentrations (500 pg m−3), the same rate is expected at pH < 4.5.
TL;DR: The findings may possibly explain the physiological stress on the rotator cuff muscles as compared with the deltoid and trapezius muscles in work with elevated arms.
TL;DR: In this paper, an enthalpy diagram for the H 2 + O 2 reaction on Pt at high temperatures, ∼ 1000 K, and pressures in the range 1-1000 m Torr was constructed, based on dissociative sticking of H 2 and O 2 and hydrogen addition to oxygen.
TL;DR: A systematic theoretical study of the CD of [poly(dA‐dT)]2 and its complexes with achiral small molecules is presented and the induced CD of a groove bound molecule is one order of magnitude stronger than that of an intercalated molecule.
Abstract: A systematic theoretical study of the CD of [poly (dA-dT)]2 and its complexes with achiral small molecules is presented. The CD spectra of [poly (dA-dT)]2 and of poly (dA):poly(dT) are calculated for various DNA structures using the matrix method. The calculated and experimental spectra agree reasonably well for [poly(dA-dT)]2 but less well for poly(dA):poly(dT). The calculated CD spectrum of [poly(dA-dT)]2 fails to reproduce the wavelength region of 205-245 nm of the experimental spectrum. This discrepancy can be explained by a magnetic dipole allowed transition contributing significantly to the CD spectrum in this region. The induced CD of a transition moment of a molecule bound to [poly(dA-dT)]2 is also calculated. As was the case for [poly(dG-dC)]2, the induced CD of a groove bound molecule is one order of magnitude stronger than that of an intercalated molecule. The calculations also show considerable differences between pyrimidine-purine sites and purine-pyrimidine sites. Both signs and magnitudes of the CD induced into ligands bound in the minor groove agree with experimental observations.
TL;DR: In this article, a bed expansion model is derived from a modified two-phase flow model, and the results from the model are compared with measurements in both a cold two-dimensional bed and a 16 MW th fluidized bed boiler, as well as with data found in the literature.
TL;DR: In this article, the performance of silicone and EPDM rubber composite insulators was investigated in a long-term outdoor test with high direct and alternating voltages, and the results showed that the difference in performance were related to the differences in the surface structural changes and in the dynamic ability of the surface to compensate the aging.
Abstract: In a long-term outdoor test with high direct and alternating voltages, silicone and ethylene propylene diene monomer (EPDM) rubber composite insulators have, at the beginning, shown a performance superior to that of glass and porcelain insulators. In the long-term test, however, the silicone rubber composite insulator has, in spite of the aging of both insulator types, kept its good performance, while the performance of the EPDM rubber composite insulator was drastically deteriorated. In order to get a better insight into the results obtained, the wettability and the surface structural changes of the insulators were studied by the drop deposition method using a goniometer and by advanced techniques such as scanning electron microscopy, electron spectroscopy for chemical analysis, Fourier-transform infrared spectroscopy, and secondary ion mass spectrometry. The results show that the differences in performance are related to the differences in the surface structural changes and in the dynamic ability of the surface to compensate the aging. Silicone rubber insulators have higher repellency than the EPDM insulators, especially when aged. The reason seems to be low silicone polymer diffusion from the bulk which covers the insulator surface, embeds the pollutants, and keeps the surface hydrophobic. Porcelain insulators with silicone elastomer coatings show lower water repellency than insulators with massive silicone rubber sheds. When aged, EPDM insulators do not, however, seen to possess the same dynamic recovery of their surface, thus becoming hydrophilic. >
TL;DR: In this paper, the microstructural development of fly ash replacement pastes with progressive hydration was investigated using scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDXA).
TL;DR: In this paper, a no-ghost theorem is proved for a string theory based on an SU(1,1) Wess-Zumino-Novikov-Witten model and an arbitrary unitary conformal field theory.
TL;DR: In this paper, an experimental investigation of surface pressure distributions (mean and r.m.s.) on two tubes (circular cylinders) mounted in an in-line or tandem arrangement was carried out in a low-speed, closed-circuit wind tunnel.
TL;DR: In this article, the authors studied the low-temperature behavior of lead-alloy Josephson tunnel junctions with area S\ensuremath{m}${\mathrm{m}}^{2}, isolated from their electromagnetic environment by high-resistance metallic resistors inserted into the current and voltage leads.
Abstract: We have studied the low-temperature behavior of lead-alloy Josephson tunnel junctions with area S\ensuremath{\approxeq}0.01 \ensuremath{\mu}${\mathrm{m}}^{2}$, isolated from their electromagnetic environment by high-resistance metallic resistors inserted into the current and voltage leads. Under irradiation with microwaves frequencies, f=3.5--10 GHz, the dc differential resistance dV/dI, as a function of the dc current I, showed peaks at I=\ifmmode\pm\else\textpm\fi{}2ef. This effect, and other observations, arises due to the periodic electrical recharging of the junction by discrete Cooper pairs, and can be explained by the ``orthodox'' theory of Bloch oscillations.
TL;DR: In this paper, three different finite difference schemes for solving the heat equation in one space dimension with boundary conditions containing integrals over the interior of the interval are considered, based on the forward Euler, the backward Euler and the Crank-Nicolson methods.
Abstract: Three different finite difference schemes for solving the heat equation in one space dimension with boundary conditions containing integrals over the interior of the interval are considered. The schemes are based on the forward Euler, the backward Euler and the Crank-Nicolson methods. Error estimates are derived in maximum norm. Results from a numerical experiment are presented.
TL;DR: In this article, the authors introduce materials for energy efficiency and solar energy utilization and discuss some current trends for basic research and development, which involve thin surface coatings, such as solar absorber surfaces, transparent infrared reflectors and transparent conductors, large area chromogenics for transmittance control in smart windows, and transparent convection-suppressing materials, whereas solar cell materials are not included.
Abstract: This paper introduces materials for energy efficiency and solar energy utilization and discusses some current trends for basic research and development. Most of the materials involve thin surface coatings. Overviews are given for solar absorber surfaces, transparent infrared reflectors and transparent conductors, large-area chromogenics for transmittance control in “smart windows”, and transparent convection-suppressing materials, whereas solar cell materials are not included. The paper also treats a few examples of specific coatings that are presently being investigated; data are given for angular-selective transmittance through porous Cr films with oblique columnar microstructure, transparent and conducting non-stoichiometric SnO2 films, and chromogenic effects in Li-intercalated VO2 films.