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At least 19 recordsLinked to original sources
PubMed1990

[Hard metal-induced lung changes. Hard metal asthma--interstitial hard metal pneumopathy].

Hard metal pneumopathy and hard metal asthma are two separate forms of hard metal lung disease. Cobalt is the probable causal agent involved. Bronchial provocation with hard metal powder induces obstruction within 2 hours of the challenge. Suspected hard metal pneumopathy, however, should be confirmed or excluded by a period of non-exposure followed by re-exposure, since the long-term exposure in patients suffering from hard-metal pneumopathy leads to pulmonary fibrosis.

Adult↗
PubMed2006

Hardness measured with traditional Vickers and Martens hardness methods.

OBJECTIVE: To determine the differences, if any, between hardness measured with traditional Vickers and Martens hardness test methods on denture teeth under 2, 10 and 50 N loads. METHOD: Hardness of acrylic resin (VIV), composite resin (ORT) and porcelain (POR) denture tooth materials was measured using a traditional Vickers hardness (HV) method and Martens hardness (HM) method at 2, 10 and 50N test loads. Vickers hardness was also calculated from the force-indentation depth curves (HVfid) that were recorded during Martens hardness. Indentation creep of the three test materials was also determined during Martens hardness testing. RESULTS: HM values were the same irrespective of the test force used. However, HV values were different for the three test forces. ANOVA using Tukey's test of the HM data showed that the hardness of POR was significantly higher than VIV or ORT (P<0.001). Moreover, ORT had a significantly higher hardness than VIV (P<0.001). The statistical analysis of HVfid data showed similar results. ANOVA of the HV data showed the hardness of VIV to be significantly higher than ORT (P<0.001) under 2, 10 and 50 N test load. The HV values for POR under 2 and 10 N test load could not be calculated because of inability to measure the indentation diagonals. Under the 50 N load, the hardness of POR was significantly higher than VIV and ORT. POR had a significantly lower creep value than any other material tested while VIV showed a statistically significantly higher creep than ORT. SIGNIFICANCE: This study confirms that the visco-elastic recovery of the materials has a very significant effect on the outcome of the hardness tests of denture teeth and the Martens hardness test method has obvious advantages when testing dental materials.

Acrylic Resins↗
PubMed2005

Extension of scaled particle theory to inhomogeneous hard particle fluids. I. Cavity growth at a hard wall.

The methods of traditional scaled particle theory (SPT) are used to develop an extended scaled particle theory that is now applicable to hard particle fluids confined by hard walls. The new theory, labeled inhomogeneous SPT (I-SPT), introduces the function G that describes the average value of the anisotropic density of hard particle centers contacting a cavity placed at or behind a hard wall. We present an exact relation describing G for certain cavity sizes and, similar to the original SPT, an accurate interpolation scheme for larger cavity radii. Given G , the reversible work of inserting a cavity centered at or behind the hard wall can be estimated. The work predictions at low to moderate packing fractions are extremely accurate, though small deviations from simulation results become apparent at packing fractions close to the bulk hard sphere freezing transition. I-SPT also reveals the importance of the line tension in determining the free energy of cavity formation for cavities intersecting a hard wall, a term which has been previously neglected. Furthermore, this paper provides the initial groundwork needed to develop a more complete SPT-based theory that can accurately predict the depletion force between a hard particle and a hard structureless wall.

Journal Article↗
PubMed2003

Measurement of muscle hardness using a hardness meter: application to the masseter and temporal muscles and reproducibility of measurement.

This study was designed to evaluate the intra-examiner and inter-examiner reliability of measurements of masticatory muscle hardness and to confirm that the muscle hardness increases with contraction using a commercially available muscle meter. Twenty healthy asymptomatic female subjects participated in this study. Hardness was expressed as numerical relative values (0-100). First, muscle hardness was measured at a standardized point located in the masseter muscle and temporal muscle in a randomized order by two examiners, and again by one of the same examiners after ten minutes for the reproducibility study. Then the muscle hardness was measured at each point for 0 kgf, 3 kgf, 6 kgf, and 9 kgf levels of bite force. As a result, intraclass correlation coefficient (ICC) analysis revealed good intra-examiner reliability in the masseter muscle (ICC = 0.711), good intra-examiner reliability in the temporal muscle (ICC = 0.643), good inter-examiner reliability in the masseter muscle (ICC = 0.631), and unacceptable inter-examiner reliability in the temporal muscle (ICC = 0.008). Also, our results showed that muscle hardness increased with contraction, and relationships with a slope of 1.229, a y-intercept of 62.513, and a correlation coefficient of 0.448 were observed in the masseter muscle. However, no correlation was found between muscle hardness and bite force in the temporal muscle. The findings indicate that measurement of hardness provides reliable physiological information about the masseter muscle in this setting.

Adolescent↗
PubMed2006

Non-effect of water hardness on the accumulation and toxicity of copper in a freshwater macrophyte (Ceratophyllum demersum): how useful are hardness-modified copper guidelines for protecting freshwater biota?

Several nations have adopted hardness-modified copper (Cu) guidelines for protecting freshwater biota. However, there is a lack of good quality data and mechanistic understanding on the effects of true water hardness (calcium (Ca) and magnesium (Mg)) on the bioavailability and toxicity of Cu to freshwater biota, particularly macrophytes. This study determined the effect of true water hardness (35, 90 and 335 mg CaCO(3)/l, added as Ca and Mg chloride in a 1:1 mole ratio) on the cell surface binding affinity (log K), accumulation and toxicity (96 h growth (biomass and stem length) and photosynthetic pigment inhibition) of Cu in the free-floating submerged macrophyte, Ceratophyllum demersum, in a synthetic freshwater with constant alkalinity (16 mg CaCO(3)/l) and pH (7.0). There were no significant (P>0.05) differences in the cell surface binding affinity, accumulation or toxicity of Cu in C. demersum with a 10-fold increase in water hardness from 35 to 335 mg CaCO(3)/l. The mean 96 h EC(50) values (and 95% confidence intervals) for biomass, the most sensitive endpoint, were 8.4 (7.6-9.2), 8.9 (8.0-9.8) and 9.9 (9.1-10.7) microg/l Cu for 35, 90 and 335 mg CaCO(3)/l, respectively. Speciation calculations indicated only very small (1-6%) differences in the percentage distribution (i.e. bioavailability) of Cu over the hardness range. These collective results indicate no apparent competition between Cu and Ca/Mg for binding sites on the cell surface. Given that the mechanism of Cu uptake (via Cu-specific and Na-linked transporters) is fundamentally different to that of Cd, Ni, Pb and Zn (via Ca transporters), for which other hardness-dependent algorithms have been developed, it is doubtful whether a hardness-modified Cu guideline value will be sufficiently protective of sensitive freshwater biota, such as C. demersum, particularly in medium-hard fresh surface waters with low levels of dissolved organic carbon. The biotic ligand model offers a more flexible and mechanistic approach for deriving site-specific Cu (metal) guidelines for protecting freshwater biota.

Cell Membrane↗
PubMed2005

Voronoi neighbor statistics of hard-disks and hard-spheres.

The neighbor distribution in hard-sphere and hard-disk fluids is analyzed using Voronoi tessellation. The statistical measures analyzed are the nth neighbor coordination number (Cn), the nth neighbor distance distribution [fn(r)], and the distribution of the number of Voronoi faces (Pn). These statistics are sensitive indicators of microstructure, and they distinguish thermodynamic and annealed structures. A sharp rise in the hexagon population marks the onset of hard-disk freezing transition, and Cn decreases sharply to the hexagonal lattice values. In hard-disk random structures the pentagon and heptagon populations remain significant even at high volume fraction. In dense hard-sphere (three-dimensional) structures at the freezing transition, C1 is close to 14, instead of the value of 12 expected for a face-centered-cubic lattice. This is found to be because of a topological instability, where a slight perturbation of the positions in the centers of a pair of particles transforms a vertex in the Voronoi polyhedron into a Voronoi surface. We demonstrate that the pair distribution function and the equation-of-state obtained from Voronoi tessellation are equal to those obtained from thermodynamic calculations. In hard-sphere random structures, the dodecahedron population decreases with increasing density. To demonstrate the utility of the neighbor analysis, we estimate the effective hard-sphere diameter of the Lennard-Jones fluid by identifying the diameter of the spheres in the hard-sphere fluid which has C1 equal to that for the Lennard-Jones fluid. The estimates are within 2% deviation from the theoretical results of Barker-Henderson and Weeks-Chandler-Andersen.

Journal Article↗
PubMed2006

Bond-orientational analysis of hard-disk and hard-sphere structures.

We report the bond-orientational analysis results for the thermodynamic, random, and homogeneously sheared inelastic structures of hard-disks and hard-spheres. The thermodynamic structures show a sharp rise in the order across the freezing transition. The random structures show the absence of crystallization. The homogeneously sheared structures get ordered at a packing fraction higher than the thermodynamic freezing packing fraction, due to the suppression of crystal nucleation. On shear ordering, strings of close-packed hard-disks in two dimensions and close-packed layers of hard-spheres in three dimensions, oriented along the velocity direction, slide past each other. Such a flow creates a considerable amount of fourfold order in two dimensions and body-centered-tetragonal (bct) structure in three dimensions. These transitions are the flow analogs of the martensitic transformations occurring in metals due to the stresses induced by a rapid quench. In hard-disk structures, using the bond-orientational analysis we show the presence of fourfold order. In sheared inelastic hard-sphere structures, even though the global bond-orientational analysis shows that the system is highly ordered, a third-order rotational invariant analysis shows that only about 40% of the spheres have face-centered-cubic (fcc) order, even in the dense and near-elastic limits, clearly indicating the coexistence of multiple crystalline orders. When layers of close-packed spheres slide past each other, in addition to the bct structure, the hexagonal-close-packed (hcp) structure is formed due to the random stacking faults. Using the Honeycutt-Andersen pair analysis and an analysis based on the 14-faceted polyhedra having six quadrilateral and eight hexagonal faces, we show the presence of bct and hcp signatures in shear ordered inelastic hard-spheres. Thus, our analysis shows that the dense sheared inelastic hard-spheres have a mixture of fcc, bct, and hcp structures.

Journal Article↗
PubMed2005

Extension of scaled particle theory to inhomogeneous hard particle fluids. II. Theory and simulation of fluid structure surrounding a cavity that intersects a hard wall.

Integral equations describing the structure of a hard sphere fluid surrounding a cavity that intersects a hard wall are derived from scaled particle theory (SPT). The new expressions are solved exactly for specific cavity radii and the predictions are compared to simulation-generated results, showing excellent agreement. Additional simulation studies are conducted for cavity radii that fall outside the range of exact solution. For all cavity sizes, an enhancement of the local density of hard spheres over that of the hard wall contact value is seen for positions near the point of intersection of the cavity and the hard wall. The local density in front of the cavity and away from the hard wall is depleted at small cavity sizes, but eventually approaches the density profile created by a cavity placed within a bulk hard sphere fluid at larger cavity radii. The exact solutions and simulation results are also used to understand why a minimum appears in the inhomogeneous SPT function G (lambda,h) [D. W. Siderius and D. S. Corti, preceding paper, Phys. Rev. E 71, 036141 (2005)].

Journal Article↗
PubMed2001

In vitro comparison of the two hard-hard articulations for total hip replacements.

Polyethylene particle disease is one of the major causes of late aseptic loosening of total hip replacement. Two hard-hard articulations (alumina-on-alumina and metal-on-metal) have been developed in Europe as an alternative to the ultra-high molecular weight polyethylene (UHMWPE) articulations. Even though these hard-hard articulations are on the market and numerous reports have been published about them, only a very limited number of studies allowing a direct in vitro comparison of the two articulations have been published so far. This paper compares in vitro these two types of articulation (alumina-on-alumina and metal-on-metal), which have been tested with a hip simulator for their tribological behaviour using exactly the same experimental methodology. This comparison shows that these two types of hard-hard articulation have very similar abrasive wear behaviour with four main features: 1. A running-in wear period (1 x 10(6) cycles) gives a cumulative wear of about 20 microns with head diameters of 28 mm. 2. After the running-in wear, there is a stabilization of the linear wear behaviour with a low linear wear rate/10(6) cycles for both types of articulation. 3. The volumetric wear rate of both articulations (< 2.0 mm3/year for head diameters of 28 mm) is significantly lower than that observed for metal-on-polyethylene or ceramic-on-polyethylene articulations having the same head diameter. 4. Abrasive wear is readily apparent (indicating a mixed lubrication regime) with both types of articulation. The extremely low wear performance of these articulations is confirmed and they constitute a low-wear alternative to the UHMWPE articulations currently used.

Arthroplasty, Replacement, Hip↗
PubMed2001

Importance of pin geometry on pin-on-plate wear testing of hard-on-hard bearing materials for artificial hip joints.

The contact mechanics between the pin and the plate used in simple wear screening tests were investigated in this study. Both soft-on-hard, such as ultra-high molecular weight polyethylene (UHMWPE)-on-metal or UHMWPE-on-ceramic, and hard-on-hard, such as metal-on-metal, bearing couples were considered. The effect of the pin geometry and the misalignment between the pin and the plate were investigated on the predicted contact pressure distribution at the bearing surfaces using the finite element method. It was demonstrated that in the case of soft-on-hard bearing couples, neither the geometrical discontinuity of the pin surface nor the misalignment could cause a significant increase in the contact stress. However, for hard-on-hard combinations, even with a very small misalignment of 0.5 degrees between the pin and the plate, the geometrical discontinuity could lead to a more than tenfold increase in the predicted contact stress. This elevated contact stress may lead to a large scatter in the wear data and, even more importantly, structural damage of the bearing surfaces.

Biomechanical Phenomena↗
PubMed2007

On the quality of the hardness kernel and the Fukui function to evaluate the global hardness.

An approximated hardness kernel, which includes the second derivative with respect to the density of the kinetic energy, the electron-electron coulomb repulsion, and the exchange density functionals, has been tested for the calculation of the global hardness. The results obtained for a series of 40 cations and neutral systems and 16 anions represent in most cases an improvement of the results obtained using the HOMO-LUMO gap approach and indicate the viability of this approach to evaluate global hardness. In addition, the relevance of the Fukui function approximation and the role of the three components of the hardness kernel in the evaluation of the global hardness have been analyzed.

Anions↗
PubMed1994

Cobalt bioavailability from hard metal particles. Further evidence that cobalt alone is not responsible for the toxicity of hard metal particles.

Hard metal is an alloy of tungsten carbide (WC) in a matrix of cobalt metal (Co). The inhalation of hard metal dust can cause an alveolitis which may progress to interstitial fibrosis. This study was undertaken to compare, both in vivo and in vitro, the bioavailability of cobalt metal when mixed or not with WC and to assess whether this factor had any influence on the cellular toxicity of hard metal particles. In vivo, non-toxic doses of cobalt metal were administered intratracheally in the rat, alone (Co, 0.03 mg/100 g) or mixed with tungsten carbide (WC-Co, 0.5 mg/100 g containing 6.3% of cobalt metal particles). Sequential measurements of cobalt in the lung and in urine demonstrated that the retention time of the metal in the lung was longer in Co- than in WC-Co-treated animals. In vitro, the cellular cobalt uptake was higher when the metal was presented to the macrophages as WC-Co. However, there was no relationship between the cellular uptake of cobalt and the occurrence of toxicity, since the intracellular concentration of cobalt associated with the occurrence of a cytotoxic effect of WC-Co particles was insufficient to exert the same effect when resulting from exposure to Co alone. This clearly indicates that increased bioavailability of cobalt is not the mechanism by which hard metal particles exhibit their cellular toxicity. These observations confirm and extend our previous findings supporting the view that cobalt is not the only component responsible for the toxicity of hard metal particles which should be considered as a specific toxic entity.

Administration, Inhalation↗
PubMed2001

Effect of visual display terminal height on the trapezius muscle hardness: quantitative evaluation by a newly developed muscle hardness meter.

The aim of this study was to determine trapezius muscle hardness in 9 healthy volunteers before and after word processing tasks with a video display terminal (VDT) at three different heights. When using a desktop personal computer (PC), no change was observed in muscle hardness even after a 30-min task if a subject was in the reference posture with a declination angle formed by the Reid's line directed toward the upper edge of the PC screen and the horizontal plane within 5-10 degrees. However, an increase in muscle hardness was observed after a 15-min task in a posture of looking up at the screen (angle of elevation: 15-20 degrees) and after a 30-min task in a posture of looking down at the screen (angle of declination: 15-20 degrees). When the same tasks were performed with a notebook PC, muscle hardness increased after 15 min. Fifteen minutes of relaxation exercise reduced the muscle hardness caused by VDT work.

Adult↗