Solid-solid contacts due to surface roughness and their effects on suspension behaviour

Solid-solid contacts due to microscopic surface roughness in viscous fluids were examined by observing the translational and rotational behaviours of a suspended sphere falling past a lighter sphere or down an inclined surface. In both cases, a roll-slip behaviour was observed, with the gravitational forces balanced by not only hydrodynamic forces but also normal and tangential solid-solid contact forces. Moreover, the nominal separation between the surfaces due to microscopic surface roughness elements is not constant but instead varies due to multiple roughness scales. By inverting the system, so that the heavy sphere fell away from the lighter sphere or the plane, it was found that the average nominal separation increases with increasing angle of inclination of the plane or the surface of the lighter sphere from horizontal; the larger asperities lift the sphere up from the opposing surface and then gravity at large angles of inclination is too weak to pull the sphere back down to the opposing surface before another large asperity is encountered. The existence of microscopic surface roughness and solid-solid contacts is shown to modify the rheological properties of suspensions. For example, the presence of compressive, but not tensile, contact forces removes the reversibility of sphere-sphere interactions and breaks the symmetry of the particle trajectories. As a result, suspensions of rough spheres exhibit normal stress differences that are absent for smooth spheres. For the conditions studied, surface roughness reduces the effective viscosity of a suspension by limiting the lubrication resistance during near-contact motion, and it also modifies the suspension microstructure and hydrodynamic diffusivity.     

Transfer of highly hydrophilic ions from water to nitrobenzene, studied by three-phase and thin-film modified electrodes

The study by voltammetry of hydrophilic ion transfers across the interface between an aqueous solution and an immiscible organic solvent is limited by the presence of supporting electrolytes in both phases. Such a study is impossible for ions having a higher affinity for water than ions of the electrolytes. Indirectly, methods based on modified solid electrodes can be used; these are obtained by the deposition of an organic phase containing a molecule having redox properties, the modified electrode being in contact with an aqueous solution of the appropriate electrolyte. The three-phase electrode is very convenient for that purpose. However, this experimental tool also has its own limitation, due mainly to the redox species produced in the organic phase. The oxidized, or reduced, form of the redox molecule must have a very low affinity for water, as otherwise its transfer masks that of the ion under study. Ferrocene is almost useless because of the affinity of the ferrocenium cation for water, decamethylferrocene being a better choice. The present work illustrates how the use of lutetium bisphthalocyanines widely expands the possibilities, as these molecular sandwich complexes can be reduced as well as oxidized, the products of the reactions having a very low affinity for water. This made the determination of the Gibbs energy possible for the transfers of highly hydrophilic ions from water to nitrobenzene: Cl(-) (40 kJ mol(-1)), F(-) (57 kJ mol(-1)), H2PO4(-) (64 kJ mol(-1)). Nothing being really known about the transfer of F(-) or H2PO4(-) from water to organic solvents, these are the first values ever published. H(+), OH(-), and HSO4(-) have also been studied, showing that these species, which have a poor affinity for nitrobenzene, are prone to association reactions with the reduced or oxidized forms of the lutetium bisphthalocyanine.     

Prevalence and correlates of handgun access among adolescents seeking care in an urban emergency department

Objective

To determine prevalence and correlates of handgun access among adolescents seeking care in an urban Emergency Department (ED) in order to inform future injury prevention strategies.

Methods

In this observational cross-sectional study performed in the ED of a large urban hospital, 14- to 18-year-old adolescents completed a computerized survey of risk behaviors. Adolescents seeking ED care (for injury or medical complaint) were approached seven days a week over a 22-month period. Validated measures included measures of demographics, sexual activity, substance use, injury, violent behavior, and handgun access. A logistic regression model predicting handgun access was performed.

Results

A total of 3050 adolescents completed the survey (44% male, 58.9% African-American), with 417 (12%) refusing to participate. One-third of the sample (n = 1003) reported access to a handgun, and of those 54% were males (n = 542). Logistic regression results indicated that older age (AOR: 1.58; 95% CI: 1.30-1.94), African-American race (AOR: 1.34; 95% CI: 1.11-1.61), male gender (AOR: 1.99; 95% CI: 1.66-2.37), and being employed (AOR: 1.35; 95% CI: 1.11-1.65), as well as seeking ED care for a medical complaint as compared to intentional injury (AOR: 1.69; 95% CI 1.62-2.50) predicted handgun access. Binge drinking (AOR: 1.75; 95% CI: 1.37-2.27), marijuana use (AOR: 1.93; 95% CI: 1.58-2.36), sexual activity (AOR: 1.64; 95% CI: 1.32-2.02), prior injury by a gun (AOR: 1.80; 95% CI: 1.32-2.46), serious physical violence (AOR: 1.37; 95% CI: 1.13-1.66) and group fighting (AOR: 2.07; 95% CI: 1.68-2.56) also predicted access.

Conclusions

High rates of handgun access were evident among adolescents presenting in an inner city ED, including those seeking care for non-injury related reasons. Adolescents with access to handguns were more likely to report risk behaviors and past injury, providing clinicians with an opportunity for injury prevention initiatives.     

Road accidents and rainfall in a large Australian city

We investigate the impact of rainfall on daily road accidents in the metropolitan area of Melbourne, Australia, over 1987-2002. Our analysis from several viewpoints of the accident count, which has been normalised for variation in traffic volume, indicated that the effect of rainfall is multifaceted. Owing to a large non-linear trend a subdivision into three epochs (1987-1991, 1992-1996 and 1997-2002) was made. Nominal daytime and nighttime as well as 3h raw counts were available for the first two epochs only. Generally, the effect of rainfall across the epochs shows a tendency for larger values in autumn with smaller values in spring. For the daily, daytime and nighttime cases there is an approximate 40% decrease in both the volume-normalised dry and wet means from the first to second epoch. Since the second epoch is wetter than the first, and both dry and wet cases are affected in a similar way, then it appears that a non-weather influence is at work. It is suggested that law enforcement measures may be largely responsible. We obtained a conservative estimate of relative risk of an accident in wet conditions based on a matched-pair analysis of 3h dry and wet periods over the first two epochs (1987-1996). As with other studies we find that the risk is greater than unity in almost all cases suggesting that the presence of rainfall consistently represents a driving hazard. Rainfall occurring after a dry spell has an enhanced effect on the volume-normalised accident count as the spell duration increases. The effect of dry spells is more clearly described when broken down by rain class. Generally, there is an increase in the impact of a dry spell when it first rains as the spell duration and rainfall amount increase.     

Polarized temporal impulse response for scattering media from third-order frequency correlations of speckle intensity patterns

Second- and third-order frequency correlations of speckle intensity patterns are used to characterize scattering media for multiple polarization states. The polarized temporal responses thus obtained are sensitive to the degree of scatter, with results being predictable by a diffusion model with sufficiently strong scatter. Experimental data are used to reconstruct various transfer functions.     

Syntheses of Ag, PbSe, and PbTe nanocrystals and their binary self-assembly exploration at low size-ratio

Nanocrystals of Ag, PbSe, and PbTe were prepared via a high-temperature organic solution approach, respectively. Using a size-selection technique, the size-distribution of each set of nanocrystals could be fine-tuned and finally monodisperse products were achieved. Superlattice structure of binary self-assemblies in low size-ratio were also explored and characterized by transmission electron microscopy. It is realized that a success of achieving binary self-assembly pattern is greatly dependent on several key factors including particle size-distributions, relative concentrations of both components, as well as the size-ratios between Ag and PbSe (or PbTe) nanocrystals.     

Microwave-assisted rapid discharge sintering of a bioactive glass�Cceramic

Bioactive glass-ceramics have been developed as successful bone graft materials. Although conventional sintering in an electrically-heated furnace is most commonly used, an alternative microwave plasma batch processing technique, known as rapid discharge sintering (RDS), is examined to crystallise the metastable base glass to form one or more ceramic phases. Apatite-mullite glass-ceramics (AMGC) were examined to elucidate the effects of RDS on the crystallization of a bioactive glass-ceramic. By increasing the fluorine content of the glass, the fluorapatite (FAp) and mullite crystallization onset temperatures can be reduced. Samples were sintered in a hydrogen and hydrogen/nitrogen discharge at temperatures of ≈800 and 1000 °C respectively with the higher sintering temperature required to form mullite. Results show that the material can be densified and crystallised using RDS in a considerably shorter time than conventional sintering due to heating and cooling rates of ≈400 °C/min.     

Model of remote-sensing reflectance including bidirectional effects for case 1 and case 2 waters

A remote-sensing reflectance model based on a lookup table is proposed for use in analyzing satellite ocean color data in both case 1 and case 2 waters. The model coefficients are tabulated for grid values of three angles--solar zenith, sensor zenith, and relative azimuth--to take account of directional variation. This model also requires, as input, a phase function parameter defined by the contribution of suspended particles to the backscattering coefficient. The model is generated from radiative transfer simulations for a wide range of inherent optical properties that cover both case 1 and 2 waters. The model uncertainty that is due to phase function variability is significantly reduced from that in conventional models. Bidirectional variation of reflectance is described and explained for a variety of cases. The effects of wind speed and cloud cover on bidirectional variation are also considered, including those for the fully overcast case in which angular variation can still be considerable (approximately 10%). The implications for seaborne validation of satellite-derived water-leaving reflectance are discussed.     

Application of a nonuniform spectral resampling transform in Fourier-transform spectrometry

We describe a nonuniform spectral resampling transform (NUSRT) that resamples a frequency-scaled spectrum that has been measured by a Fourier-transform spectrometer (FTS). Frequency scaling of a spectrum can arise from measurements made with off-axis detectors and Doppler shift induced by motion of a spaceborne FTS relative to an input radiation source. In addition, a spectrum may need to be rescaled in frequency to match spectral lines for applications such as the retrieval of atmospheric state parameters. The NUSRT is cast as a linear algebraic expression that relates a nonuniformly sampled interferogram to an input spectrum. A polynomial approximation is applied to this expression that reduces the inverse of the NUSRT to a series of Fourier transforms that can be implemented as fast Fourier transforms (FFTs). We show that this NUSRT algorithm requires on the order of 6N log N flops, which reduces the computational cost of rescaling by more than 1 order of magnitude compared with conventional FFT-based Shannon interpolation techniques while comparable accuracy is maintained.     

Encoding microcarriers by spatial selective photobleaching

Bead-based assays on very large numbers of molecules in gene expression studies, drug screening and clinical diagnostics, require the encoding of each of the microspheres according to the particular ligand bound to its surface. This allows mixing the uniquely encoded microspheres and subjecting them to an assay simultaneously. When a particular microsphere gives a positive reaction, the substance on its surface can be identified by reading the code. Previously reported techniques for colour encoding polymer microspheres only allow for a limited number of unique codes. Graphical encoding methods use metallic particles, which are rather uncommon in screening applications. Here, we demonstrate a new approach to encode polymer microspheres that are commonly used in screening applications, such as polystyrene microspheres, with a method that provides a virtually unlimited number of unique codes. Patterns can be written in fluorescently dyed microspheres by 'spatial selective photobleaching' and can be identified by confocal microscopy. Such encoded microparticles can find broad application in the collection and analysis of genetic information, high-throughput screening, medical diagnostics and combinatorial chemistry, and can also be used for labelling of consumer goods or as security labels to prevent counterfeiting.