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Local variations in filler particle concentration and/or shape and orientation in static filler/polymer composites are modelled as distributions of percolation thresholds. The concentration variations can be due to insufficient mixing, formation of semicrystalline voids during cooling from the melt, shrinkage during polymer curing, flow during physical compression or the like. Irregular filler shapes, especially elongated shapes, reduce the percolation threshold; thus, natural variations in the shapes and orientations of filler particle aggregates lead to locally varying percolation thresholds. A distribution of percolation thresholds leads to an apparent average percolation threshold based on the conductivity below the mean percolation threshold. For filler concentrations above the apparent percolation threshold, the dielectric constant continues to increase before reaching a lowered peak value at the mean percolation threshold and then decreasing. This can explain some 'anomalous' published experimental results concerning the dielectric constant just above the percolation threshold. In the frequency plane, the percolation threshold distribution can lead to a slight reduction of the apparent critical exponents x and y of the frequency dependencies of the conductivity and relative dielectric constant, respectively. Our experimental results on ethylene butylacrylate copolymer/carbon black composites support the theory.

Processing issues and the electrical and mechanical properties of a novel combination of a natural carbonaceous filler, Karelian shungite, and a water soluble thermosetting polymer, melamine-formaldehyde, were investigated. Two types of shungite with different carbon contents were investigated and compared to a commercial carbon black. The larger particle size and chemically more active surface of the shungites compared to carbon black leads to easy handling with little dusting and allows water to be used as dispersant. Laminates of melamine-formaldehyde reinforced with random cellulose fibers and filler were prepared by film stacking. The layered structure results in anisotropic resistivities for the shungites with fairly low in-plane percolation thresholds and a dissipative resistivity above the percolation transition. In comparison, carbon black had a lower percolation threshold and a low isotropic resistivity above the percolation transition. The mechanical properties of the composites were slightly deteriorated by all three fillers, indicating poor interfacial adhesion. The results of Fourier transform infrared (FTIR) measurements are interpreted as indicating hydrogen bonding and thus relatively weak adhesion between filler and polymer. Aqueous mixtures of melamine-formaldehyde and shungite filler had lower viscosities than corresponding melamine-formaldehyde and carbon black filler mixtures. POLYM. COMPOS., 26:552–562, 2005. © 2005 Society of Plastics Engineers

Thin composite laminates based on melamine-formaldehyde (MF) and cellulose are made electrostatically dissipative or conductive by addition of carbon black (CB). CB in an ethanol dispersion was applied to MF sheets containing α-cellulose. Areas around cellulose fibers are favored sites for CB and during subsequent hot-pressing further redistribution took place, enriching the CB content adjacent to fibers. Thus, the mobility of CB during processing provides a spontaneously formed network with the cellulose fibers as the backbone. Longitudinal and transverse DC resistivity measurements had nearly the same percolation threshold and only slightly different resistivities indicating that an important conduction mechanism takes place through connection points between laminas. The elastic modulus is greatly increased already at very small loadings of CB. POLYM. COMPOS., 26:144–151, 2005. © 2005 Society of Plastics Engineers

The ac electrical properties of acetylene black composites mixed into ethylene butylacrylate copolymer (EBA) and into poly (methyl methacrylate) (PMMA) have been measured in thermal cycling and isothermal annealing experiments. The results show that changes in electrical properties are due to rearrangement of gaps between the carbon black aggregates. This has been concluded using an exponent z that relates the critical frequency ωc denoting the crossover of the conductivity from the dc-plateau to its frequency-dependent part to the dc conductivity, σdc, according to ωc ∝σdcz. Below the melting range of EBA and the glass transition of PMMA z is about one corresponding to strong variation of the conductivity and weak dependence of the permittivity on the gaps. Above the melting range of EBA z is about 1.5, indicating strong dependence of both the conductivity and the permittivity on the gaps, as predicted by percolation theory. This was not found in the PMMA composites above the glass transition. We conclude that the polymer matrix affects the nature of the gaps between carbon black aggregates, either allowing their size to vary continuously (z about 1) or letting them open and close (z about 1.5).

SEM micrographs of carbon black polymer composites have been analysed in terms of their fractal geometry. Acetylene black/ethylene butylacrylate copolymer samples have a fractal dimension of about 1.8 at low filler concentrations that increases to 2.1 at high concentrations. The numerical values indicate a cross-over from diffusion limited cluster aggregation (DLCA) to reaction limited cluster aggregation (RLCA). Furnace black/EPDM composites have a fractal dimension of 1.9 at low concentrations and of 2.4 at higher filler fraction. We believe that in this case the increase in fractal dimension is only apparent and due to interpenetration. Possible connections between fractal geometry (fractal dimension and correlation length) and electrical conductivity are discussed. No clear connection could be determined.

The dielectric behaviour of various carbon black polymer composites has been characterized by the critical frequency ωc denoting the crossover from the dc plateau of the conductivity to its frequency dependent ac behaviour. The critical frequency can be related to the dc conductivity using a power law, ωc∝σdcz, with the exponent z. Presently accepted models predict z to be greater than one when varying the filler content. However, in accordance with published experimental results this work shows that z is rather close to one indicating a nearly constant static permittivity. Furthermore, the above power law makes it possible to describe all investigated compounds using a single master curve ranging over ten decades of dc conductivity. These findings are explained by a qualitative percolation model based on electron tunnelling. Increasing the dc conductivity along the percolation curve does not require the establishment of more physical links between carbon black aggregates. Rather, new conduction paths of nearly the same lengths but with higher tunnelling probability due to smaller gaps satisfy the percolation theory. This scenario allows the number of capacitive gaps to be nearly constant making z near one.

A model describing some of the factors that influence company patenting is presented. It can be used to help define and implement company patent strategy as well as to address specific issues such as considerations when initiating patent activities, evaluation of patent work and measures to be taken to alleviate shortcomings in patenting efforts. The model is primarily based on previously known factors. Sub-components of the model can be used to describe the need and ability of a company to patent. Data on patents as a competitive means are presented. The model is illustrated by applying it to a small selection of computer software producing companies employing between five and thirty persons. The empirical base consists of interviews and patent searches. A key result explaining the low patenting intensity in this sample of small computer software producing companies is that even though they seem to have relatively good formal patent knowledge, strategic patent knowledge is limited. A surprising finding was that the high costs normally associated with patenting were not considered a major problem among these companies.

Relations between major product diversity (diversification) and the economic performance of 20 large Swedish industrial corporations during the time period 1971–1991 have been studied. Publicly available data concerning major product groups and corporate economic performance have been used. The quite limited diversification/concentration of the corporations’ product portfolios has mainly taken place through purchase/sale of product groups. Many movements have taken place during the period but the corporations have all stayed with their established basic products. Very little diversification was based on internal development. Not surprisingly, sales and employment growth (both extensive variables) and diversity are positively related. Employment growth has taken place mainly outside Sweden through market expansion rather than new product development. None of the intrinsic parameters studied (for example profit margin) distinguishes between highly diversified or diversifying corporations and other corporations. Neither do R&D expenditures or numbers of patent applications. There is a clear tendency for the ratio of value added to sales to decrease during the period studied. This may mean that the corporations have specialised their operations to selected parts of the value added chain, thus concentrating core competencies.

Demand for engineers trained in software development and applications has outstripped supply in Sweden (and many other industrial countries) in recent years. This is partly due to the phenomenal growth of embedded software in the industrial sector. Because ‘software’ is so often associated with computers and telecommunications only, and not with embedded software in industrial products, the economic growth of the latter is traced from 1981 to 1995 to show its importance. Sectors studied include computers, machinery, electronics, transportation equipment and telecommunications. While the computer industry accounted for about 75% of all Swedish software in 1981, in 1995 it only accounted for not quite 30%. The Swedish machinery, electronics and transportation equipment sectors combined accounted for more software production than the Swedish computer sector. The drivers of this development (ever larger and faster microprocessors) continue to form the future of high technology, which by definition co...

Conductivity and dielectric constant of a three-component 0-3 composite of epoxy resin-barium titanate-carbon black (0-3 composites are systems in which the filler is in the form of 0-dimensional (point-like, disperse) particles in a three-dimensional polymeric matrix 1 ) have been investigated both at DC and the frequency range of 20-10 6 c/s. The effect of barium titanate concentration on percolation threshold, critical indices and the mechanism of conduction has been examined. An attempt was made to describe the electrical properties of composites with models originally developed for two-component systems' dielectric-conductor. With increasing barium titanate concentration the agreement of experimentally found frequency dependencies of conductivity and dielectric constant with models based on Debye's equation was found to degrade. An adequate description of electrical properties of composites' dielectricferroelectric-conductor should be based on the Havriliak-Negami equation.

The ordering of electrically conducting polyaniline particles dispersed in a non-conducting liquid, 1,2,4-trichlorobenzene, in a weak electric field (of the order V mm −1 ) has been studied. The time needed for the formation of conducting chains, depending on the applied voltage, the polyaniline concentration and the viscosity of the suspension medium, was used to calculate the effective relative electric permittivity for polyaniline, ɛ p = 4.8, responsible for the dipole-dipole interaction leading to the structure formation. Nonlinear limit current-voltage characteristics typical of electrorheological suspensions were observed. The formation of the conducting chains could be followed in an optical microscope.

The relation between the electrical noise generated during flow of aqueous poly(ethylene oxide) PEO solutions in three capillaries of different lengths and entry shape but the same diameter and the flow behaviour was investigated. Flow into the square cut off capillary entry was characterised by a low pressure loss regime followed at higher shear rates by a high pressure loss regime while flow into the trumpet shaped capillary end exhibited only the low pressure loss regime. The high pressure loss flow was associated with strong electrical noise generation. The results suggest that the noise generation mechanism includes a current source supplied by the flow through the capillary volume with an associated streaming potential and a modulation of the current by mixing and turbulence at the capillary entrance. The noise measuring technique can potentionally be used to study disturbances in the entry flow to capillaries.

Polymers containing electrically conductive fillers show interesting electrical properties like semiconductors and metals without losing the processability of polymers. Typical applications are as antistatic (electrostatic dissipation) materials, electro-magnetic interference shielding materials, heaters and sensors. The selection of filler and polymer governs the properties obtained in such composites.

Photoacoustic spectroscopy, especially in the near infrared, for principal food component analysis (protein, fat, carbohydrate and moisture contents) is discussed. The thermal diffusion length is discussed as is the problem of signal saturation. An illustrative comparison of photoacoustic spectroscopy and Fourier transform mid-infrared-attenuated total reflectance spectroscopy (FTIR-ATR) as applied to cheese analysis is given.

Current noise and conductivity in composites of conductive spherical polyaniline particles covered with non-conductive poly(vinyl alcohol) layers dispersed in the same polymer medium were investigated. As the polyaniline particles are fully separated by insulating material, conductive percolation is not possible and electrical conductivity occurs only by thermally assisted charge hopping or possibly tunnelling. An interpretation in terms of quiet conductive paths through the polyaniline particles and noisy conductance through the poly(vinyl alcohol) matrix is given.

Electrical current noise and electrical resistivity as well as viscosity were measured in aqueous solutions of gelatin containing KCl during the sol—gel transition. While the viscosity rises toward infinity at the transition, the current noise power and the resistivity are continuous functions of the time and are therefore potentially useful probes for characterizing polymers undergoing gelation.

This study concerns gestation times (time between patent application and market introduction) and post-market introduction growth rates of 90 highly successful Swedish technical innovations. Innovations in small firms (1–49 employees) are characterized by short gestation times and high growth rates. Those in medium-sized firms (50–499 employees) show intermediate gestation times and relatively low growth rates. Innovations in large firms belonging to the Wallenberg sphere of influence show long gestation times and high growth rates (an unexpected result), in contrast to those in other large Swedish firms, which are characterized by intermediate gestation times and relatively low growth rates. The assumption that the distribution of innovation growth rates in all the firms can be interpreted as being log normal with a Pareto inverse power tail for the very high growth rates is compatible with the data. Innovations in the small firms and in the Wallenberg firms are overrepresented in the Pareto inverse power tail portion of the distribution. These results are both unexpected and significant.

Statistical data concerning student and employee numbers, numbers of degrees awarded, success rates; floor space, operating and research budgets, industrial support of research and some other indicators have been assembled for nine technically oriented universities. Analysis shows that the operating budgets per student vary by a factor of 6 while the teaching budgets per taught student vary by a factor of almost 4. Teaching floor space per taught student varies by a factor of 3. The numbers of doctorates awarded per first degree awarded vary by almost a factor of 6. The universities with the best international reputations are characterized by high research intensities, large budgets per student and relatively great autonomy.

SUMMARY The paths of university students from first matriculation to achievement of the doctorate are compared for nine technically-oriented universities in six countries. Although the ages at which doctorates are awarded vary by 6 or 7 years, the amount of effort invested in research in preparation of dissertations appears to vary little, from just under 3 years to just over 3½ years. The differences in ages at doctorate are mainly due to differences in the breadths of secondary education, in language studies and abilities, in military service and in teaching and administration required of doctoral students. The latter can be reduced by requiring an increased number of qualified researchers to take active roles in university level teaching.

Electrical noise measurements have been used to study electrical conduction in carbon black-filled linear low density polyethylene. Measurements of the resistivity, real part of the relative permittivity, thermal noise, and current noise have been carried out for carbon black contents and temperatures below, near, and above the percolation threshold for electrical conduction. The current noise shows a 1 /fα frequency dependence, with α near unity close to the percolation threshold, but increasing to 1.5 at higher resistivities or temperatures.

An inventory of the most successful technical innovations in Sweden during the period 1945–1980 has been made. A hundred of them have been selected. Each of them has reached an economic turnover in excess of 20 million Swedish crowns per year ($3.5 million). Analyses of the innovations, the innovators and the companies have been made. The innovation frequency, that is, the number of innovations per year, shows a continuous increase of about 5 percent per year during the period. The gestation period, that is, the time between making the invention and introducing it on the market, varies greatly but has an average value of about seven years. No long-term change in the gestation time could be determined. The increase in economic turnover per year for the innovations can be described by a double logarithmic distribution. For a fourth of the innovations the economic turnover per year is at least doubled each year. Also, there is a clear correlation between the number of patents and the number of successful innovations in a company. On the average there are 1.5 innovators per innovation, the number increasing during the period 1945–1980 from 1.3 to 1.8. The proportion of foreigners among the innovators is about 6 percent, somewhat less than the proportion of foreign workers in the manufacturing industry. Only one woman is found among the 137 innovators. The ages of the innovators at the time of the invention is relatively high, on the average 40 years, but shows considerable variation. The education of the innovators is relatively high with two-third of them holding an academic degree and one-third of them holding a higher academic degree. Only 5 percent have only elementary school or similar background. The 100 innovations alone account for 5 percent of the economic value added in Swedish industry. Eighty percent of the innovations have been conceived in and developed by existing large companies. The distribution between various branches of industry correlates well with R&D expenditures in the respective branches. Twenty percent of the innovations have been the basis for new company formation. The role of universities in the innovations is a dominating one in medical innovations, but less important in other branches of industry.

Two infrared spectroscopic methods, optothermal near infrared (NIR) spectroscopy and Fourier transform mid-infrared-attenuated total reflection (FTIR-ATR) spectroscopy, were applied to 24 cheese samples in order to obtain protein, fat and moisture contents. Reference values of the protein, fat and moisture contents in weight percent were obtained using standard wet chemistry analysis. Prediction correlation coefficients between 0.93 and 0.96 and standard errors of prediction between 2% and 5% were obtained using optothermal spectroscopy while the corresponding values for FTIR-ATR were 0.81-0.92 and 4-9%. Inhomogeneities in the cheeses, primarily due to the fat droplets, are probably the main reason for the differences in the error sizes. The superior results for optothermal spectroscopy are the more attractive because the instrument is easier to use than the FTIR-ATR instrument, it provides results more quickly with simpler statistical analysis and it is more compact and robust.

A model is presented which can be used to understand the observed 1/f electrical noise in nerve cell membranes. It is based on recent theories of normal mode vibrations in liquid crystals.

A quantitative analysis of innovation activity and its relation to traditional academic activity at Chalmers University of Technology is presented. A list of 14 yardsticks of faculty performance is given and compared with the innovation activities. A description of the steadily increasing patent application and spin-off company activity at Chalmers is presented. The undergraduate grades of spin-off company founders are compared with those of non-founders. The average grades in the two groups are very similar, but the spreads in grades of the individual students in the two groups are significantly different. Spin-off company founders tend to have a wider spread in grades than non-founders. A study of science citations vs patent applications for 44 researchers/inventors at Chalmers reveals a strong positive rank correlation between these two activities.

We present an electrostatic model of mechano-electric transduction in the inner ear in which a membrane charge located near an ionic channel regulates its permeability. Dose-response curves similar to empirically obtained curves characterize the model, as well as a natural rectification of the nerve signals. The model predicts a sharpening of the frequency response due to the exponential non-linearity inherent in the model. The proposed model is also applicable to other mechanoreceptors.

The application of photoacoustic spectroscopy to the spectroscopy of layered samples with thicknesses of tens of microns is demonstrated both theoretically and experimentally. Theoretical expressions for the signal damping and phase delay are developed in terms of the thermal diffusion length, which is determined by the chopper frequency and the thermal properties of the sample. The theory is supported by measurements of both amplitude and phase on a color photographic film containing three light absorbing layers. The application of the method is further illustrated by a simple study of fading leaves.

Inelastic light scattering from the free surface of the liquid crystal ethyl p-[(p-methoxybenzylidene)amino] cinnamate (EAC) has been used to determine its surface tension and viscosities in both the nematic and smectic-A mesophases. In the nematic mesophase (117-138 ?C) the molecules are parallel to the surface and are aligned by the 2 kG magnetic field. At 133 ?C the surface tension (dyn cm?1) and viscosities (P) (?; ?1, ?2, ?3) are (47?5?2?5; 0?09?0?02, 0?14?0?02, 0?30?0?10), and at 120 ?C they are (50?0?2?5; 0?17?0?04, 0?18?0?02, 0?30?0?15). For the smectic-A mesophase (107-117 ?C) the molecules are perpendicular to the free surface and to the smectic-A layers. The scattering spectrum is independent of ?2 in this case. Thus at 109 ?C the three parameters (?; ?1, ?3) were obtained: (52?5?2?5; 0?19?0?04, 0?70?0?30).

A survey of companies which have been spun-off from Chalmers University of Technology, Goteborg, Sweden, has been made and compared to an inventory of patent activity at Chalmers. The results are compared to similar studies of spin-off companies in Boston and California. We find spin-off rates between those reported for California and those which can be calculated for MIT. The situation with regard to spin-off founders offers many similarities to the situation at MIT and Stanford. However, on the average the companies from Chalmers are smaller and newer.

The DC electrical resistances of certain chloroprene rubbers with carbon black filling exhibit positive temperature coefficients (PTC effect) for certain concentrations of the conductive filler. The electrical noise exhibited by these rubbers has been studied. The thermal noise is shown to obey Nyquist's theorem to a good approximation. The current noise shows a 1/f frequency dependence, and the noise power is proportional to the square of the applied bias voltage. This applies to samples exhibiting a wide range of resistivities, from over 107 Omega cm (20% carbon black) to under 100 Omega cm (35% carbon black by weight).

The interface zone between titanium implants and bone is considered at the macroscopic, microscopic, and molecular levels. A high rate of successful dental implants of pure titanium is associated with a very close apposition of the bone to the titanium surface, called osseointegration. At the macroscopic level, osseointegration allows efficient stress transfer from the implant to the bone without abrasion or progressive movement that can take place if a fibrous layer intervenes. At the microscopic level, surface roughness and porosity provide interlocking of the implant and bone tissue which grows into direct contact with titanium. Sections studied in the electron microscope show that calcified tissue can be identified within 50 A of the implant surface. The interface zone includes a tightly adherent titanium oxide layer on the surface of the implant which may be similar to a ceramic material in relation to tissue response. The five year success rate of 90% in 2895 implants in clinical trials since 1965 is associated with the favorable behavior of bone tissue at the interface zone with pure titanium.

The charge content in lipid multilayers is obtained from measurements of the capacitance of metal-lipid-semiconductor structures as a function of applied d.c.-voltage across the structure. It is also shown that by applying a voltage across the structure charges can be injected from the semiconductor and stored in the lipid. The measurements reported here were all performed on a stearic acid multilayer about 1000 A thick.

Laser light scattering and optical mixing spectroscopic techniques have been used to study the dispersion relation of kHz frequency thermally excited capillary waves on the free surfaces of p-azoxyanisole and p-azoxyphenetole. The experimentally determined dispersion relation agrees well with the predictions of hydrodynamic theory, both with respect to the frequency and to the damping of the waves.

The spectrum of light scattered inelastically from the nematic liquid crystal p-azoxyphenetole has been studied by optical-mixing spectroscopy. The experimental results support recent hydrodynamic theories of fluctuations in nematic liquid crystals. The unknown Frank elastic constants K2 and K3 (in CGS units) have been determined to be 6?1 ? 10?7 ?15% and 17?2 ? 10?7 ?25%, respectively.

Studies of the crystallization of the free surface of p-azoxyphenetole (PAP) show that for a surface supercooling greater than about 3-6°C anomalously fast crystallization takes place. Typical propagation speeds are 10-15 cm s−1, compared with only a few mm s−1 for less supercooling. p-azoxyanisole (PAA) does not appear to show the fast crystallization even when supercooled as much as 12°C.

Possible spatial effects in an extended world dynamics model including diffusion are discussed. The rate equations are similar to those describing autocatalytic chemical reactions, which exhibit spatial inhomogeneities under certain conditions. The extended world dynamics model should exhibit similar spatial structure due to strong positive feedback loops (autocatalytic steps).

Rastogi and Yadava1 have reported a study on the generation of propagating spatial waves by the Zhabotinskii reaction in a Corning glass tube 0.5 cm in diameter and 40 cm long. They found that waves of wavelength about 7 cm propagated upwards in the tube at about 0.5 cm min−1 with a period of about 10 min. They attempted to describe their experimental results by using a diffusion equation with source based on the chemical reaction A + C → 2C, after the manner of Busse2. Gray3 has criticized this treatment, pointing out that the above chemical reaction alone describes an explosive situation, and that solutions of the rate equations such as those given by Busse and by Rastogi and Yadava contain negative concentrations of the reactant C. Gray's arguments are certainly correct, but they do not indicate how to interpret the experimental results reported by Rastogi and Yadava.

The power spectral density of light scattered inelastically from the free surface of viscoelastic polymer solutions is derived. The theoretical results for stiff rod polymers are compared with previously reported light scattering data on cellulose solutions, and the agreement between theory and experiment is good.

Inelastic light scattering measurements of capillary wave frequency and damping in the kHz range for several solutions of sodium carboxymethylcellulose in redistilled water are reported. The capillary waves were thermally excited and had extremely low amplitudes. Light beating spectroscopy was used. For these solutions the capillary wave damping was very much lower than expected from hydrodynamic theory. A surface zone theory is proposed to interpret the experimental results.

Light scattering techniques are used to study the dispersion relation of low amplitude capillary waves, or ripplons, on water covered by various monomolecular films. Preliminary experiments on pure water ripplons (without film) confirm previous work, and show that the damping of the ripplons is anomalously high. We have invoked the concept of a highly structured water surface region in order to interpret our data.Further experiments on 0.01 N HCl covered by various monomolecular films indicate that the existing theories apparently are not completely appropriate for interpreting our measurements. However, we have been able to ascertain that films with small polar head groups interact very little with the water surface, while films with large polar head groups interact so strongly that they are even able to alter the effective water surface viscosity. This is evidence for the existence of a highly structured water surface region since the films cannot affect the bulk of the 0.01 N HCl as a whole.