Constitutive Model for Time-Dependent Flows of Shear-Thickening Suspensions.

We develop a tensorial constitutive model for dense, shear-thickening particle suspensions subjected to time-dependent flow. Our model combines a recently proposed evolution equation for the suspension microstructure in rate-independent materials with ideas developed previously to explain the steady flow of shear-thickening ones, whereby friction proliferates among compressive contacts at large particle stresses. We apply our model to shear reversal, and find good qualitative agreement with particle-level, discrete-element simulations whose results we also present.

Point-prevalence survey of carbapenemase-producing Enterobacteriaceae and vancomycin-resistant enterococci in adult inpatients in a university teaching hospital in the UK.

Infections with carbapenemase-producing Enterobacteriaceae (CPE) and vancomycin-resistant enterococci (VRE) are associated with increased morbidity and mortality, but the carriage rates of CRE and VRE among hospital inpatients are unknown. A point-prevalence survey was conducted to determine CPE and VRE carriage rates in hospitalized adults. Eight hundred and eighteen of 960 (85.2%) adult inpatients were invited to participate in the study. Of these, 595 patients (72.7%) consented and provided specimens. Of 540 samples tested, none were positive for CPE. One hundred and thirty of 540 (24.1%) samples were VRE positive, and 34 of 40 (85%) of wards had cases. Universal screening for CPE may not be cost-effective in low-prevalence settings, but targeted screening of high-risk patients should continue. The optimal screening strategy for VRE remains to be determined, as universal screening and isolation is not feasible in the study setting.

Molecular physics of a polymer engineering instability: experiments and computation.

Entangled polymer melts exhibit a variety of flow instabilities that limit production rates in industrial applications. We present both experimental and computational findings, using flow of monodisperse linear polystyrenes in a contraction-expansion geometry, which illustrate the formation and development of one such flow instability. This viscoelastic disturbance is observed at the slit outlet and subsequently produces large-scale fluid motions upstream. A numerical linear stability study using the molecular structure based Rolie-Poly model confirms the instability and identifies important parameters within the model, which gives physical insight into the underlying mechanism. Chain stretch was found to play a critical role in the instability mechanism, which partially explains the effectiveness of introducing a low-molecular weight tail into a polymer blend to increase its processability.

Syndrome of inappropriate ADH secretion in a woman with preeclampsia.

While preeclampsia is common in pregnancy, associated hyponatraemia is rare with very few cases reported in the literature. We report the case of a previously healthy nulliparous woman who presented at 34 weeks' gestation with hypertension and proteinuria. On admission her serum sodium was 122mmol/L and by day 6, in the absence of fluid restriction, it had fallen to 116mmol/L. Urine and plasma osmolalities suggested a syndrome of inappropriate antidiuretic hormone secretion. She was delivered on the sixth day by caesarean section because of fetal distress and worsening preeclampsia. Postoperatively fluid intake was restricted and her sodium normalised within 48h. Preeclampsia results in a low effective circulating volume which can cause a non-osmotic release of antidiuretic hormone and a resultant increase in the urine/plasma osmolality ratio to greater than 1. In patients with preeclampsia, hyponatraemia may further increase the risk of seizures and should therefore be closely monitored and treated without delay.

The myth of objectivity: is medicine moving towards a social constructivist medical paradigm?

Biomedicine is improperly imbued with a nomothetic methodology, which views 'disease' in a similar way to other 'natural' phenomena. This arises from a 300-year history of a positivist domination of science, meaning that objectivist research (e.g. randomized controlled trials or biochemical research) attracts more funding and is more readily published than 'softer' qualitative research. A brief review of objectivism and subjectivism is followed by a definition of an emerging medical paradigm. Current 'inappropriate' medical practices become understandable in this broader context, and examples are given. A constructivist paradigm can continue to incorporate 'objective' clinical findings and interventions, as well as the recent evidence for the doctor-patient relationship as a major contributor to patient outcomes.

Fecal incontinence in scleroderma: assessment of the anal sphincter with thin-section endoanal MR imaging.

PURPOSE: To compare the magnetic resonance (MR) imaging appearance of the anal sphincter in patients with fecal incontinence and scleroderma with that in patients with fecal incontinence alone, scleroderma alone, or neither. MATERIALS AND METHODS: The study population comprised 14 patients with fecal incontinence and scleroderma, four with scleroderma alone, 13 with incontinence alone, and six with neither. T1- and T2-weighted spin-echo, magnetization transfer contrast-weighted, and dynamic gadolinium-enhanced images were obtained and analyzed for the integrity, thickness, and length of sphincter components. Magnetization transfer contrast ratios and T2 were calculated to assess fibrosis of the internal sphincter. The percentage enhancement above baseline was calculated at 30-second intervals for the internal and the external sphincter. RESULTS: Eleven patients with incontinence and scleroderma showed descent of rectal air and feces into the anterior anal canal, with forward deviation of the significantly (P < .05) atrophied internal sphincter, which showed a slower gadolinium-enhancement pattern compared with that in other groups. Patients with incontinence alone showed no evidence of internal sphincter deviation or altered vascularity but had a significant reduction (P < .05) in deep external sphincter bulk. CONCLUSION: In patients with fecal incontinence and scleroderma, endoanal MR imaging helps delineate the anterior sphincter deformity and shows the slower gadolinium-enhancement pattern on dynamic studies of the internal sphincter.

The strength of a heat-pressed all-ceramic restorative material.

A heat-pressed technique (IPS Empress, Ivoclar) has been described to construct single unit crowns, inlay/onlays and veneers using precerammed and precoloured glass-ceramic ingots. The aim of the study was to evaluate the strength of materials obtained using this technique. Strengths were determined by means of shell (disc rupture) tests. Seven groups of 10 specimens each were prepared with different combinations of core, incisal and glaze firing. Shell strength values of these seven groups varied between 167 +/- 18 and 81 +/- 9 MPa. After analysis, results showed that there was no statistical difference between groups when the core porcelain was in tension. However, there was a significant difference between those groups in which the lower surface was either core or incisal porcelain. The component thicknesses of the core and incisal materials did not change the strength of the complete specimen.

Influence of layer and stain firing on the fracture strength of heat-pressed ceramics.

Fracture strength (T = torque to initiate fracture; K(IC) = fracture toughness) and the fractography of heat-pressed leucite reinforced ceramic (IPS Empress, Ivoclar AG-Schaan, Liechtenstein) were analysed by the notched disc test technique and scanning electron microscopy methodologies. To determine the effects of additional firing schedules on the heat-pressed core ceramic, three groups of specimens were prepared. These groups were heat-pressed core, heat-pressed core and simulated stain firing, and heat-pressed core and simulated layer firing. Statistical analysis of both T and K(IC) values showed that there was no statistically significant difference between these three groups (P > 0.05). Scanning electron microscopy analysis of the fractured surfaces revealed that crack propagation occurred around some of the leucite particles and also partly and directly through other leucite particles.

Light-activated restorative materials: a method of determining effective radiation times.

The aim of this investigation was to develop a test method that allows an operator to determine the appropriate radiation time for any light-activated material, irrespective of the characteristics of the light-activation unit or material to be cured. A computer-based radiometer was used to monitor the radiation energy transmitted through a number of light-activated materials during irradiation, and a method was devised to determine the predicted radiation time for any given material/shade/light unit combination based upon the change in transmission against time that occurred as the material polymerized. Additional test samples were cured for the predicted radiation times and upper and lower surface microhardness measurements were taken to verify the validity of the test method. Predicted times varied from 16 to 44 s for 2 mm thick samples of the materials/shade/light-activation units used. This method may allow operators to determine appropriate radiation times for any new light-activated restorative they decide to use with their own light-activation unit.

Microleakage of direct and indirect inlay/onlay systems.

The purpose of this in vitro study was to evaluate the microleakage of direct and indirect inlay/onlay systems. Two of the groups investigated have indirect applications only and consist of microfine composites. The other two groups of inlay/onlay systems have both direct and indirect applications and are hybrid composites. Standardized MOD preparations were cut in 60 extracted human premolars. One gingival margin was placed in enamel above the cementoenamel junction (CEJ) and the other was placed in dentine below the CEJ. The inlays were made and luted according to each manufacturer's recommendation. The restored teeth were thermocycled and immersed in a basic fuchsin solution for 24 h. Following the mesiodistal sectioning of the specimens, extent of dye penetration at the restoration-glass ionomer cement and tooth-glass ionomer cement interfaces were scored using a stereomicroscope. Both direct and indirect inlays showed substantial leakage at gingival-dentine margins. However, there was only superficial leakage at enamel margins. Comparing the overall indirect inlay systems, EOS inlay leaked the most (P < 0.05). Indirect Brilliant Dentin inlays showed a significantly smaller amount of leakage than the other inlay systems. SR-Isosit and Estilux Posterior C VS inlays provided a favourable marginal seal. In the case of Brilliant Dentin and Estilux Posterior C VS, indirect inlays leaked more than direct inlays. Generally, no significant difference was observed between the interfaces evaluated in microleakage performance.

Composite inlay/luting resin bond strength--surface treatment effects.

PURPOSE: To investigate the effect of surface treatments on the bond strength between two resin' composite inlay materials and their luting materials. MATERIALS AND METHODS: A notched disc specimen design was used to evaluate the torque to fracture: test specimens consisting of two half notched disc specimens bonded together, controls consisting of complete resin composite material specimens. RESULTS: Both surface treatment and bond resin application had a significant influence on interfacial bond strength--the torque required to initiate failure being expressed as a percentage of the value required to fracture the control specimens. CONCLUSION: The results allow conclusions to be drawn regarding the attainment of optimal bonding between the resin composite inlays and luting materials investigated.

The fracture resistance of dental materials.

A novel test procedure was developed that provides the basis for a standard plain strain fracture toughness test to evaluate fracture resistance of resin-based materials. This procedure utilizes a notched disc specimen. Using this technique, a new concept of Torque to initiate fracture (T)' was suggested. Also, fracture resistance can be assessed by means of critical stress intensity factor (K[IC]). Using this method, the fracture resistance of direct restorative materials, resin-based inlay/onlays and luting cements can be evaluated.

Light curing unit effectiveness assessed by dental radiometers.

OBJECTIVES: The purpose of this investigation was to assess the effectiveness of five commercially available hand-held dental radiometers and a computer-based experimental radiometer. METHODS: Light intensity of five visible light activation units was determined using the dental radiometers. The influence of curing light intensity on depth of cure of a hybrid composite material was determined using a digital penetrometer. RESULTS: The radiometers evaluated varied with respect to sensor aperture diameter, scale readings (analogue or digital) and the units of measurement (arbitrary or mW cm2). The experimental computer-based radiometer allowed continuous recording of intensity against time; thus the light output could be monitored over the entire irradiation period. CONCLUSIONS: When light intensity readings were normalized with regard to a standardized light sensing device aperture of 4 mm diameter, a linear relationship was found between depth of cure and the logarithm of the intensity of the light. The results of this investigation support the use of dental radiometers for periodically monitoring visible light activation units.

Depth of cure of radiation-activated composite restoratives--influence of shade and opacity.

Inadequate depth of cure may reduce the longevity of visible light-activated composite restorations. Radiation-activated composites, originally marketed for the restoration of anterior teeth, have been developed and refined for restoring occlusal and proximal cavities in posterior teeth. Clinical factors such as the accessibility of the light source, the direction of the light, intervening tooth tissue and cavity depth may limit depth of cure. Unfortunately, a hard top surface is no indication of adequate polymerization at the base of the cavity. The current investigation used a penetrometer to evaluate the depth of cure of a range of recently introduced 'universal' composite materials and assess the influence of shade and opacity on depth of cure. Depth of cure of the enamel opacity is always greater than that of the same shade of dentine for each manufacturer's product range.

Determination of radiation energy emitted by light activation units.

Since the introduction in the 1970s of single paste composite materials, there has been a rapid increase in the range of both materials and activation light units. This investigation is being undertaken as part of a larger study where the characteristics of both composite materials, light activation units and composite material/light activation unit combinations, are being evaluated. This section of the study was undertaken to determine the characteristics of four light activation units. The equipment was developed to measure radiation energy over a wide range of illumination. This range can be from the relatively low intensity of radiation transmitted through restorative materials to the intensities of direct radiation from light activation units. The four light units tested had various radiation outputs between 225,000 lx and 75,000 lx. All the units, apart from one, showed a decrease in light output with successive applications. The units emitted radiation outside the optimum range of 440-500 nm, which may produce damaging radiation and glare. Although the extreme intensities varied threefold the effect on depth of cure of one-material varied by only 16%.

The attenuation of radiation by porcelain and its effect on polymerization of resin cements.

The influence of porcelain thickness and opacity on the polymerization of two dual activated (microfine and hybrid) and one light irradiated (hybrid) resin cements was assessed by hardness measurements. The surface microhardness values of the upper and lower surface of 1 mm thick resin cement specimens were determined. Specimens were polymerized using 40s irradiation beneath different thicknesses and opacities of porcelain discs. The results showed that increasing the thicknesses and opacity of the porcelain produced a statistically significant decrease in microhardness of the resin-based cements. The effect of attenuation is less for the microfine cement than for the hybrids. In the case of hybrid cements, the light activated material performed better than the dual activated cement.

Depth of cure of radiation-activated materials--effect of mould material and cavity size.

A method for determining depth of cure of radiation-activated restorative materials has been developed. The effect of mould material and cavity size on depth of cure was determined using a digital penetrometer method. Values were obtained for three selected shades of three dentine products and, in addition, the same three shades of an enamel variant were assessed. All these values were obtained using a 4 mm diameter x 6 mm deep stainless steel mould.