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PubMed2004

When parents are deaf versus hard of hearing: patterns of sign use and school placement of deaf and hard-of-hearing children.

This paper investigates the importance of knowing whether or not deaf and hard-of-hearing students have one or more deaf or hard-of-hearing parents. As noted by Mitchell and Karchmer (2004), deaf and hard-of-hearing school-age children and youth in the United States with at least one parent identified as "hearing impaired" are nearly evenly split between having at least one deaf parent and having at least one hard-of-hearing parent. However, there is no literature on the importance, if any, of this distinction. Findings from the investigation reported herein suggest that the distinction between having a deaf versus a hard-of-hearing parent is quite substantial, particularly as it pertains to the use of signing in the home. Further, signing in the home, which is reliably predicted by parental hearing status, is a significant predictor of the school setting in which the student is currently placed and the instructional use of signing in the classroom. Limitations related to the available measure of parental hearing status are discussed.

Adolescent↗
PubMed2002

Wetting and capillary nematization of binary hard-platelet and hard-rod fluids.

Density-functional theory is used to investigate the phase behavior of colloidal binary hard-platelet and hard-rod fluids near a single hard wall or confined in a slit pore. The Zwanzig model, in which the orientations of the particles of rectangular shape are restricted to three orthogonal orientations, is analyzed by numerical minimization of the grand potential functional. The density and orientational profiles as well as the surface contributions to the grand potential are determined. The calculations exhibit a wall-induced continuous surface transition from uniaxial to biaxial symmetry for the hard-rod fluid. Complete wetting of the wall-isotropic liquid interface by a biaxial nematic film for rods and a uniaxial nematic film for platelets is found. For the fluids confined by two parallel hard walls, we determine a first-order capillary nematization transition for large slit widths, which terminates in a capillary critical point upon decreasing the slit width.

Journal Article↗
PubMed2002

How hard is a colloidal "hard-sphere" interaction?

Poly-12-hydroxystearic acid (PHSA) is widely used as a coating on colloidal spheres to provide a "hard-sphere-type" interaction. These hard spheres have been widely used in fundamental studies of nucleation, crystallization, and glass formation. Most authors describe the interaction as "nearly" hard sphere. In this paper we directly measure this interaction, using layers of PHSA adsorbed onto mica sheets in a surfaces force apparatus. We find that the layers, in appropriate solvents, have no long-range interaction. When the solvent is decahydronaphthalene (decalin), the repulsion rises from zero to the maximum measurable over a distance range of 15-20 nm. The data is converted to equivalent forces between spheres of different diameters, and modeled using a hard core potential. Using zeroth-order perturbation theory and computer simulation, we demonstrate that the equation of state does not deviate from that of a perfect hard-sphere system under any relevant experimental conditions.

Journal Article↗
PubMed2006

Voronoi neighbor statistics of homogeneously sheared inelastic hard disks and hard spheres.

In this work we extend our earlier Voronoi neighbor analysis [J. Chem. Phys. 123, 074502 (2005)] to homogeneously sheared inelastic hard-particle structures, the simplest model for rapid granular matter. The pair distribution function is partitioned into the nth neighbor coordination number (Cn), and the nth neighbor position distribution [fn(r)]. The distribution of the number of Voronoi faces (Pn) is also considered since C1 is its mean. We report the Cn and Pn for the homogeneously sheared inelastic hard-disk and hard-sphere structures. These statistics are sensitive to shear ordering transition, the nonequilibrium analogue of the freezing transition. In the near-elastic limit, the sheared fluid statistics approach that of the thermodynamic fluid. On shear ordering, due to the onset of order, the Cn for sheared structures approach that of the thermodynamic solid phase. The suppression of nucleation by the homogeneous shear is evident in these statistics. As inelasticity increases, the shear ordering packing fraction increases. Due to the topological instability of the isotropically perturbed face-centered cubic lattice, polyhedra with faces 12 to 18, with a mean at 14, coexist even in the regular close packed limit for the thermodynamic hard-sphere solid. In shear ordered inelastic hard-sphere structures there is a high incidence of 14-faceted polyhedra and a consequent depletion of polyhedra with faces 12, 13, 15-18, due to the formation of body-centered-tetragonal (bct) structures. These bct structures leave a body-centered-cubic-like signature in the Cn and Pn data. On shear ordering, close-packed layers slide past each other. However, with a velocity-dependent coefficient of restitution, at a critical shear rate these layers get disordered or amorphized. We find that the critical shear rate for amorphization is inversely proportional to the particle diameter, as compared to the inverse square scaling observed in dense colloidal suspensions.

Journal Article↗
PubMed2006

Wave packet autocorrelation functions for quantum hard-disk and hard-sphere billiards in the high-energy, diffraction regime.

We consider the time evolution of a wave packet representing a quantum particle moving in a geometrically open billiard that consists of a number of fixed hard-disk or hard-sphere scatterers. Using the technique of multiple collision expansions we provide a first-principle analytical calculation of the time-dependent autocorrelation function for the wave packet in the high-energy diffraction regime, in which the particle's de Broglie wavelength, while being small compared to the size of the scatterers, is large enough to prevent the formation of geometric shadow over distances of the order of the particle's free flight path. The hard-disk or hard-sphere scattering system must be sufficiently dilute in order for this high-energy diffraction regime to be achievable. Apart from the overall exponential decay, the autocorrelation function exhibits a generally complicated sequence of relatively strong peaks corresponding to partial revivals of the wave packet. Both the exponential decay (or escape) rate and the revival peak structure are predominantly determined by the underlying classical dynamics. A relation between the escape rate, and the Lyapunov exponents and Kolmogorov-Sinai entropy of the counterpart classical system, previously known for hard-disk billiards, is strengthened by generalization to three spatial dimensions. The results of the quantum mechanical calculation of the time-dependent autocorrelation function agree with predictions of the semiclassical periodic orbit theory.

Journal Article↗
PubMed1993

Mechanism of adsorption of hard and soft metal ions to Saccharomyces cerevisiae and influence of hard and soft anions.

The applicability of the hard-and-soft principle of acids and bases in predicting metal adsorption characteristics in a biological context was investigated for metabolism-independent uptake of the metal ions Sr2+, Mn2+, Zn2+, Cu2+, Cd2+, and Tl+ by Saccharomyces cerevisiae. Metal adsorption increased with external metal concentration (5 to 50 microM), although some saturation of uptake of the harder ions examined, Sr2+, Mn2+, and Zn2+, was evident at the higher metal concentrations. Cation displacement experiments indicated that, with the exception of Tl+, relative covalent bonding (H+ displacement) of the metals was greater at low metal concentrations, while weaker electrostatic interactions (Mg2+ plus Ca2+ displacement) became increasingly important at higher concentrations. These results were correlated with curved Scatchard and reciprocal Langmuir plots of metal uptake data. Saturation of covalent binding sites was most marked for the hard metals, and consequently, although no relationship between metal hardness and ionic/covalent bonding ratios was evident at 10 microM metal, at 50 microM the ratio was generally higher for harder metals. Increasing inhibition of metal uptake at increasing external anion concentrations was partially attributed to the formation of metal-anion complexes. Inhibitory effects of the hard anion SO42(-) were most marked for uptake of the hard metals Sr2+ and Mn2+, whereas greater relative effects on adsorption of the softer cations Cu2+ and Cd2+ were correlated with complexation by the soft anion S2O32(-). Inhibition of uptake of the borderline metal Zn2+ by SO42(-) and that by S2O32(-) were approximately equal.(ABSTRACT TRUNCATED AT 250 WORDS)

Adsorption↗
PubMed2004

Capillary freezing or complete wetting of hard spheres in a planar hard slit?

Extensive simulations of a hard sphere fluid confined between two planar hard walls show the onset of crystalline layers at the walls at about 98.3% of bulk crystallization density rho(f) independent of the wall separations L(z), and is, hence, a single wall phenomenon. As the bulk density far from the wall rho(b) increases, the thickness of the crystalline film appears to increase logarithmically, with (rho(f)-rho(b)) indicating complete wetting by the hard sphere crystal of the wall-fluid interface. Increasing rho(b) further, we observe a jump in the adsorption which depends on L(z) and corresponds to capillary freezing. The formation of crystalline layers below bulk crystallization, the logarithmic growth of the crystalline film, its independence of L(z), and its clear distinction from capillary freezing lend strong evidence for complete wetting by the hard sphere crystal at the wall-fluid interface.

Adsorption↗
PubMed2006

Depletion effects in smectic phases of hard-rod-hard-sphere mixtures.

It is known that when hard spheres are added to a pure system of hard rods the stability of the smectic phase may be greatly enhanced, and that this effect can be rationalised in terms of depletion forces. In the present paper we first study the effect of orientational order on depletion forces in this particular binary system, comparing our results with those obtained adopting the usual approximation of considering the rods parallel and their orientations frozen. We consider mixtures with rods of different aspect ratios and spheres of different diameters, and we treat them within Onsager theory. Our results indicate that depletion effects, and consequently smectic stability, decrease significantly as a result of orientational disorder in the smectic phase when compared with corresponding data based on the frozen-orientation approximation. These results are discussed in terms of the tau parameter, which has been proposed as a convenient measure of depletion strength. We present closed expressions for tau, and show that it is intimately connected with the depletion potential. We then analyse the effect of particle geometry by comparing results pertaining to systems of parallel rods of different shapes (spherocylinders, cylinders and parallelepipeds). We finally provide results based on the Zwanzig approximation of a fundamental-measure density-functional theory applied to mixtures of parallelepipeds and cubes of different sizes. In this case, we show that the tau parameter exhibits a linear asymptotic behaviour in the limit of large values of the hard-rod aspect ratio, in conformity with Onsager theory, as well as in the limit of large values of the ratio of rod breadth to cube side length, d, in contrast to Onsager approximation, which predicts tau approximately d (3). Based on both this result and the Percus-Yevick approximation for the direct correlation function for a hard-sphere binary mixture in the same limit of infinite asymmetry, we speculate that, for spherocylinders and spheres, the tau parameter should be of order unity as d tends to infinity.

Algorithms↗
PubMed2003

A comparison of three hard chairside denture reline materials. Part II. Changes in colour and hardness following immersion in three commonly used denture cleansers.

This study investigated the effects of daily use of three denture cleansers on three hard chairside reline materials over a 6-month period. Two controls were used; one dry and one involving storage in water. Colour and hardness were measured at 0 (baseline) and 6-months. There was no significant colour change with Tokuso Rebase Fast Set. Coe Kooliner and Total Hard changed colour more with the short acting peroxide cleanser (Steradent 3 Minutes) than with the overnight peroxide cleanser (Steradent Fresh) and the hypochlorite cleanser (Dentural). The hardness of all materials remained unchanged over the whole test period.

Acrylic Resins↗
PubMed2004

An interpretation of amphoteric gel hardness variation through potential and hardness measurement.

The hardness variation of amphoteric gel according to the surrounding solution conditions is quite unique. It hardens and softens reversibly regardless of its molecular network density. But this has been understood merely qualitatively. For the purpose of elucidation of the details of its behavior, we performed quantitative potential and hardness measurements on it. We observed the constant potential of amphoteric gels, approximately -60 mV, regardless of their swelling ratio and hardness. Such observations can be interpreted as the maintenance of the constant charge density of *COO- for any amphoteric gel, and they are further interpreted as intermolecular salt-linkage formation/disruption dominating the hardness of amphoteric gels.

Journal Article↗
PubMed1997

Distraction osteogenesis for lengthening of the hard palate: Part II. Histological study of the hard and soft palate after distraction.

To correct velopharyngeal incompetence, a new treatment concept was proposed in Distraction Osteogenesis for Lengthening of the Hard Palate: Part I (using lengthening of the hard and soft palate by distraction osteogenesis). Cephalometry and computed tomography showed successful elongation of the posterior hard palate with gradual calcification. Here the sequential use of fluorochrome markers (oxytetracycline, xylenol orange, DCAF [2,4-bis-N-N'-dicarboxymethyl aminomethyl fluorescein], and alizarin complexone) during the distraction and retention period is reported together with the histologic investigations using light and laser scan microscopy without prior demineralization. The experimental gap showed de novo osteogenesis in all dogs. The new bone was always in continuity with the original anterior and posterior palatal bone margins. It either bridged the experimental gap fully or left a small central zone of fibrous tissue, in which eventual ossification occurred. Several distinct zones could be distinguished: A small central zone was found with parallel strains of collagen fibers, oriented longitudinally in the direction of the distraction. Next to this zone a layer of undifferentiated mesenchymal precursor cells was seen in direct contact to newly formed bone. The next zone was coarse woven bone, showing a transition to mature lamellar bone through remodeling. No evidence of endochondral bone formation was found, i.e., all dogs showed exclusively intramembranous bone formation. The soft tissues showed no signs of alteration: in particular, there was no necrosis or scar formation. The soft tissues were not thinned but appeared to have followed the longitudinal displacement. In conclusion, gradual distraction osteogenesis of the hard palate could be a possible method for lengthening the palate to treat velopharyngeal incompetence.

Animals↗
PubMed2002

Evaluation of optical changes of three types of lenses: hard PMMA, hydrogel, and heparin surface modified hard lenses effected by silicone oil, used clinically as a substitute of the vitreous body.

The objective of these investigations was an in vitro evaluation whether silicone oil OXANE of viscosity 5700 cSt clinically used in eye surgery as a substitute of the vitreous body, being in contact with an artificial polymer lens used as an implant of human lens, causes the changes in its optical properties. The paper presents the results of spectral analysis of transmission of visible (VIS) radiation of three types of artificial lenses: hard PMMA, hydrogel, heparin surface modified (HSM) hard PMMA, and the same lenses damaged by YAG laser radiation with an energy increasing from 1.7 mJ to 3.7 mJ, exposed to clinically applied silicone oil. The studies were carried out, in two-week intervals, over a period of 20 weeks. Hard PMMA and HSM lenses were found not to have changed their optical properties after 20 weeks of exposure to silicone oil. The measured transmittance values were within the range of instrumental error (+/- 1%). Optical properties of hydrogel lenses exposed to silicone oils deteriorated with exposure and after 20-week exposure to silicone oil the average transmittance value decreased by about 18%, reaching its final value of 67.08 +/- 2.37% (RSD = 5.56%). A minimal decrease of the initial transmittance values was observed only for the lenses exposed to laser radiation of highest energy (3.7 mJ). After completed exposure to silicone oil, two kinds of lenses were found to have a slightly improved transmittance: hard PMMA lenses by about 4% and HSM lenses by about 2%. On the other hand, in case of hydrogel lenses the deterioration of optical properties to the extent comparable to that of hydrogel lenses not damaged by laser radiation was observed.

Heparin↗
PubMed1998

Hardness controlled enzymes and electronegativity controlled enzymes: role of an absolute hardness-electronegativity (eta-chi) activity diagram as a coordinate for biological activities.

We found that absolute hardness-absolute electronegativity (eta-chi) activity diagrams play an important role as a new coordinate of bioactivity in structure-activity relationships. In this paper, the eta-chi activity diagram, focusing on the molecular mechanism of bioactive compounds is used to discuss two major problems. First, the potency of bioactivities for xenobiotics such as polychlorinated dibenzo-p-dioxins (PCDDs) 3 and polychlorinated biphenyls (PCBs) 4, were found to be strongly related to their absolute hardness (eta). Second, the antibacterial activity of new quinolones such as norfloxacin 1 and enoxacin 2, was found to be strongly related to their absolute electronegativity (chi). These findings predict at least two chemical properties for a hardness-controlled or electronegativity-controlled enzyme.

4-Quinolones↗
PubMed2002

Peroxide interactions with hard tissues: effects on surface hardness and surface/subsurface ultrastructural properties.

Laboratory studies were performed to assess the impact of peroxide bleaching on enamel surface and subsurface physical and ultrastructural properties. Human enamel blocks were prepared, polished, and measured for native color. Cyclic bleaching treatments were carried out with soaks in whole stimulated saliva interspersed with bleaching treatments using bulk bleaching gels from commercial bleaching systems including Opalescence (20% and 10% carbamide peroxide systems) and Crest Whitestrips, a hydrogen peroxide gel formula, at doses of 5.3% and 6.5% hydrogen peroxide. Treatments ranged from conditions of normal use (14 hours as recommended for Crest Whitestrips) to excessive bleaching (70 hours). Controls included nontreated as well as treatments with placebo (not containing peroxide) gels. Surface hardness and confocal laser scanning microscopy (CLSM) techniques were used to characterize the effects of bleaching on the physical properties and ultrastructure of the teeth. Tooth color measurements revealed dose-response bleaching in vitro with the increases in L* and decreases in b* normally expected with effective bleaching. Placebo control treatments did not bleach. Surface hardness measurements showed no decreases associated with tooth bleaching. CLSM measurements also showed no effects from tooth bleaches on the surface or subsurface prism architecture of enamel. This was opposed to significant changes seen with even moderate levels of demineralization associated with the caries process. These studies support: (1) the safety of Crest Whitestrips formulas for enamel surfaces and tooth subsurfaces; and (2) the generic safety of peroxide bleaching of hard tissues associated with conditions of both recommended use and overuse.

Acrylic Resins↗
PubMed2005

Transient cavities and the excess chemical potentials of hard-spheroid solutes in dipolar hard-sphere solvents.

Monte Carlo computer simulations are used to study transient cavities and the solvation of hard-spheroid solutes in dipolar hard-sphere solvents. The probability distribution of spheroidal cavities in the solvent is shown to be well described by a Gaussian function, and the variations of fit parameters with cavity elongation and solvent properties are analyzed. The excess chemical potentials of hard-spheroid solutes with aspect ratios x in the range of 15< or =x< or =5, and with volumes between 1 and 20 times that of a solvent molecule, are presented. It is shown that for a given molecular volume and solvent dipole moment (or temperature) a spherical solute has the lowest excess chemical potential and hence the highest solubility, while a prolate solute with aspect ratio x should be more soluble than an oblate solute with aspect ratio 1x. For a given solute molecule, the excess chemical potential increases with increasing temperature; this same trend can be observed in hydrophobic solvation. A scaled-particle theory based on the solvent equation of state and a fitted solute-solvent interfacial tension shows excellent agreement with the simulation results over the whole range of solute elongations and volumes considered. An information-theoretic model based on the solvent density and radial distribution function is less successful, being accurate only for small solute volumes and low solvent densities.

Journal Article↗
PubMed2005

Uniform shear flow in dissipative gases: computer simulations of inelastic hard spheres and frictional elastic hard spheres.

In the preceding paper, we have conjectured that the main transport properties of a dilute gas of inelastic hard spheres (IHSs) can be satisfactorily captured by an equivalent gas of elastic hard spheres (EHSs), provided that the latter are under the action of an effective drag force and their collision rate is reduced by a factor (1+alpha)/2 (where alpha is the constant coefficient of normal restitution). In this paper we test the above expectation in a paradigmatic nonequilibrium state, namely, the simple or uniform shear flow, by performing Monte Carlo computer simulations of the Boltzmann equation for both classes of dissipative gases with a dissipation range 0.5 < or = alpha < or = 0.95 and two values of the imposed shear rate a. It is observed that the evolution toward the steady state proceeds in two stages: a short kinetic stage (strongly dependent on the initial preparation of the system) followed by a slower hydrodynamic regime that becomes increasingly less dependent on the initial state. Once conveniently scaled, the intrinsic quantities in the hydrodynamic regime depend on time, at a given value of alpha, only through the reduced shear rate a*(t) is proportional to a/square root(T(t)), until a steady state, independent of the imposed shear rate and of the initial preparation, is reached. The distortion of the steady-state velocity distribution from the local equilibrium state is measured by the shear stress, the normal stress differences, the cooling rate, the fourth and sixth cumulants, and the shape of the distribution itself. In particular, the simulation results seem to be consistent with an exponential overpopulation of the high-velocity tail. These properties are common to both the IHS and EHS systems. In addition, the EHS results are in general hardly distinguishable from the IHS ones if alpha approximately > 0.7, so that the distinct signature of the IHS gas (higher anisotropy and overpopulation) only manifests itself at relatively high dissipations.

Journal Article↗
PubMed1997

Accuracy of bedside chest hard-copy screen-film versus hard- and soft-copy computed radiographs in a medical intensive care unit: receiver operating characteristic analysis.

PURPOSE: To compare the clinical diagnostic accuracy of hard-copy readings of screen-film bedside chest radiographs and both hard- and soft-copy readings of bedside chest computed radiographs obtained in a medical intensive care unit. MATERIALS AND METHODS: Two samples of 95 cases were assembled from chest images obtained in 541 patients with either screen-film radiography or computed radiography. The cases were stratified according to the clinical problem for which the examination was ordered; the corresponding diagnosis was verified by a panel of two or three radiologists. Four radiologists blindly read the hard-copy images obtained with screen-film or computed radiography. Six months later, the radiologists read the computed radiographs by using an 8-bit, 1,684 x 2,048-pixel display. The data were analyzed by using multireader-multicase receiver operating characteristic (ROC) analysis of variance. RESULTS: No statistically significant differences in the area under the ROC curve were found between any of the methods. CONCLUSION: The results provide some justification for using bedside chest computed radiography and for reading soft-copy images from a high-quality display.

Female↗