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A textbook model of a contagious disease, the dynamics of which are represented by the SIS epidemic model with saturating treatment, is considered. I show that this model, as originally formulated,...

OBJECTIVE: The Hopkins Verbal Learning Test-Revised (HVLT-R) provides a measure of verbal learning and memory. The aim of this study was to provide normative performance data on the HVLT-R for community-dwelling older individuals according to ethno-racial group, age, gender, and years of completed education, in Australia and the U.S. METHOD: The ASPirin in Reducing Events in the Elderly (ASPREE) study recruited 19 114 generally healthy community dwelling individuals aged 70 years and over (65 years and over for U.S minorities), who were without a diagnosis of dementia and scored above 77 on the modified Mini-Mental State (3MS) examination. Included in the analysis presented here were 16 251 white Australians, and in the U.S. 1 082 white, 894 African American and 314 Hispanic/Latino individuals at baseline. RESULTS: Performance on each of the components of the HVLT-R (trials 1–3, total, learning, delayed recall, delayed recognition, percentage retention and recognition discrimination index [RDI]) differed by demographic variables. In country and ethno-racial stratified analyses, female gender, younger age and higher education were significantly associated with better total recall, delayed recall and RDI. Among white Australians these characteristics were also associated with better retention. Age, education and gender-specific reference values across ethno-racial categories were determined. CONCLUSIONS: Ethno-racial, age, gender and education-stratified normative data from this large cohort of community-dwelling older individuals will serve as important reference standards in Australia and the U.S. to assess cognition in older individuals.

Various applied mathematics undergraduate skills are demonstrated via an adaptation of Crank's axisymmetric spherical diffusion model. By the introduction of a one-parameter Heaviside initial condition, the pharmaceutically problematic initial mass flux is attenuated. Quantities germane to the pharmaceutical industry are examined and the model is tested with data derived from industry journals. A binomial algorithm for the acceleration of alternating sequences is demonstrated. The model is accompanied by a MAPLE worksheet for further student exploration.

Ongoing inflammation in controlled HIV infection contributes to non-AIDS comorbidities. High bilirubin appears to exhibit an anti-inflammatory effect in vivo. We therefore examined whether increased bilirubin in persons with HIV was associated with differences in markers of inflammation and cardiovascular, bone, renal disease, and neurocognitive (NC) impairment.This cross-sectional study examined inflammatory markers in individuals with stable HIV infection treated with two nucleoside reverse transcriptase inhibitors and a boosted protease inhibitor. Individuals recruited were those with a normal bilirubin (NBR; 0-17 μmol/L) or high bilirubin (2.5 × upper limit of normal). Demographic and anthropological data were recorded. Blood and urine samples were taken for analyses. Pulse wave velocity (PWV) measurement, carotid intimal thickness (CIT), and calcaneal stiffness (CSI) were measured. Males were asked to answer a questionnaire about sexual function; NC testing was performed using CogState.101 patients were screened, 78 enrolled (43 NBR and 35 HBR). Atazanavir use was significantly higher in HBR. Whilst a trend for lower CIT was seen in those with HBR, no significant differences were seen in PWV, bone markers, calculated cardiovascular risk (Framingham), or erectile dysfunction score. VCAM-1 levels were significantly lower in the HBR group. HBR was associated with lower LDL and triglyceride levels. NBR was associated with a calculated FRAX significantly lower than HBR although no associations were found after adjusting for tenofovir use. No difference in renal markers was observed. Component tests of NC testing revealed differences favouring HBR but overall composite scores were similar.High bilirubin in the context of boosted PI therapy was found not to be associated with differences in with the markers examined in this study. Some trends were noted and, on the basis of these, a larger, clinical end point study is warranted.

We analyze the steady-state operation of a generalized reactor model that encompasses a continuous flow bioreactor and an idealized continuous flow membrane reactor as limiting cases. The biochemical reaction kinetics is governed by a Contois growth model subject to noncompetitive substrate inhibition with a variable substrate yield coefficient. The steady-state performance of the reactor is predicted and stability of the steady-state solutions as a function of dimensionless residence time reported. Our results identified two cases of practical interest. The first feature corresponds to the case where solutions to both no-washout and washout conditions are bistable. The second feature identifies the parameter region in which periodic solutions can occur when the yield coefficient is not constant. Both these features are often undesirable in practical applications and must be avoided. Scaling of the model equations reveals that both the second-bifurcation parameters are functions of the influent concentrat...

The activated sludge process is widely used to treat domestic and industrial wastewater. A significant drawback of this process is the production of “sludge”, the disposal of which can comprise a significant proportion of the total operating costs of a wastewater treatment plant. We analyze the steady-state operation of a membrane bioreactor system (MBR) incorporating a sludge disintegration unit (SDU) to reduce sludge production. We provide a qualitative understanding of the model by finding analytically the steady-state solutions of the model and determining its stability as a function of the residence time. In practice a target value of the mixed liquor suspended solids (MLSS) content within the membrane reactor is specified. Applying the mathematical technique of singularity theory we show that if the sludge disintegration factor is sufficiently high then the MLSS content is guaranteed to be below the target value. This model prediction, of key interest from a practical perspective, was not identified...

Spray drying is the primary process for the formation of dairy powders. In multistage drying operations, the post-spray-drying stage—for example, a fluidized bed drying stage—may not alter much of the surface composition formed earlier due to the extremely high surface viscosity. Spray drying of high-sugar-content product without a retardant on the surface to prevent sticky powder deposition in drying chamber may produce very low yields due to drying chamber wall deposition or cyclone deposition. The powder products are not flow able. A functional spray-dried product begins with its efficient incorporation into water; hence, surface composition plays a key role. This study is an attempt to explore the solid formation around the outermost layer of a single droplet of protein–sugar solution during the drying process using a continuum approach (diffusion–convection equations). The main feature of this model is that the multicomponent effect is lumped into the viscosity of the fluid at the surface, which inve...

Week 96 efficacy and safety of the non-nucleoside reverse transcriptase inhibitor (NNRTI) rilpivirine (RPV) was compared to efavirenz (EFV) in subset of 1,096 subjects who received emtricitabine/tenofovir disoproxil fumarate (FTC/TDF) in pooled data from 2 phase 3 studies.ECHO and THRIVE are double-blind, double-dummy, randomized, active-controlled, non-inferiority phase 3 studies of RPV versus EFV plus 2 NRTIs in antiretroviral-naïve adult subjects. The primary and secondary endpoints were the proportion of subjects with HIV-1 RNA50 copies/ mL using an intent-to-treat, time to loss of virologic response (ITT-TLOVR) analysis at weeks 48 and 96, respectively. Safety, tolerability, immunologic response, adherence level, and other measures were also evaluated.At week 48, noninferior efficacy of RPV+FTC/TDF over EFV+FTC/TDF was established, and at week 96 RPV+FTC/TDF remained noninferior (77% overall response rate in both groups). Through week 96, rates of virologic failure were higher in the RPV+FTC/ TDF group, with low and similar rates of virologic failure and resistance mutations occurring during the second year of follow-up. Treatment with RPV+FTC/TDF was associated with a lower rate of discontinuation due to adverse events and grade 2-4 adverse events including dizziness, abnormal dreams/nightmares, rash, and lipid abnormalities.The pooled ECHO and THRIVE studies demonstrated noninferiority of RPV+FTC/TDF in achieving virologic response with safety and tolerability advantages over EFV+FTC/TDF through 96 weeks. Higher rates of virologic failure in the RPV+FTC/TDF group were balanced with higher rates of discontinuations due to adverse events in the EFV+FTC/TDF group.

In this research we analyze the steady-state operation of a continuous flow bioreactor, with or without recycle, and an idealized or nonidealized continuous flow membrane reactor. The model extends to include a fixed bed reactor where a fraction of the biomass is detached by the flow. The reaction is assumed to be governed by Tessier growth kinetics. We show that a flow reactor with idealized recycle has the same performance as an idealized membrane reactor and that the performance of a nonidealized membrane reactor is identical to that of an appropriately defined continuous flow bioreactor with nonidealized recycle. The performance of all three reactor types can therefore be obtained by analyzing a flow reactor with recycle. The steady states of the recycle model are found and their stability determined as a function of the residence time. The performance of the reactor at large residence times is obtained.

Since the advent of combined antiretroviral therapy there have been reductions in mortality and morbidity from HIV, transforming the disease into a chronic medical condition where newly diagnosed individuals can expect to live a near-normal life expectancy. When choosing therapy, probably the most important consideration is the risk of developing drug-related toxicity both in the short and long term, and new strategies to permit individualization of therapy will play a vital role in reducing this risk. The management of comorbidities including cardiovascular, renal, hepatic, bone and CNS disease, coinfections and malignancy are important considerations when choosing combined antiretroviral therapy, as is the cost of therapy. In individuals failing therapy, treatment switches will be guided by the presence of present and previously detected resistance mutations. This article will focus on the evidence for current therapies and strategies in ART-naive individuals and the potential for use of novel agents in the future.

The impact on tree and amphibian diversity of line-planting of tropical hardwoods—mahogany (Swietenia macrophylla × S. mahagoni) and mahoe (Hibiscus elatus)—was studied in a secondary subtropical wet forest of Puerto Rico. Common coqui (Eleutherodactylus coqui) and melodious coqui (E. wightmanae) are the most frequent frog species; forest coqui (E. portoricensis) is less abundant. Although relative abundance means were slightly greater in the undisturbed forest and during the wet season, differences were not statistically significant suggesting that line-planting did not significantly affect amphibian diversity. The line-planted areas had a slightly higher, but not statistically significant diversity, richness, and evenness of tree species than the unplanted forest. Multi-response permutation procedure (MRPP) showed statistically significant community composition differences between line-planting and control plot trees (T = −5.89, A = .86; p < .001). But mean similarity among plots in both the line-plante...

This paper explores alternative infra(structure)-free (IF) scenarios at a community level to promote machi-zukuri (community/neighborhood planning), a bottom-up decentralization approach improving citizen′ and municipality involvement in city planning in Japan. Demographic analysis in Japan shows that the population is becoming more urbanized, with an increasingly centralized infrastructure, but that per capita waste generation is increasing because the number of people in each household is decreasing; therefore, integration of the energy, water and waste (EWW) cycles becomes more important. For residents who are unconnected to centralized sewage treatment in Japan, mainly concentrated in municipalities whose population is less than 100,000, there is a lack of alternatives for wastewater treatment, except the current technically-demanding ′joukasou′ on-site treatment system. The authors evaluated the 30-year life-cycle cost performance of three current systems with alternative (integrated-technology) IF scenarios focusing on wastewater treatment for a small community (20 households). These systems are; wastewater gardens with biogas production, an anaerobic digester gas system integrated with fuel cell technology and a heat and power unit (CHP) combined with a biogas-producing reed bed system, all of which treat wastewater and result in useful end products-, closing the life cycle with low maintenance, a lower environmental load-, and two to four times smaller development cost than centralized options in both rural and urban communities.

The combustion of thermoplastics is modelled using a critical mass flux hypothesis as the ignition and extinction criteria. Polymer degradation is modelled as a single-step first-order Arrhenius reaction term. A simple model for mass transport of polymer through the sample during pyrolysis is included. The degradation products are assumed to move out of the polymer instantaneously. The model consists of a nonlinear integral-differential advection-diffusion equation for the temperature in the thermoplastic, coupled to an ordinary differential equation, for the regression rate. Results are presented which quantify the effect that the thickness of the test sample has on the mass-loss rate, or equivalently heat-release rate, curve. From these we conclude that thermally thick samples are characterized by a region of steady burning which is independent of the initial sample thickness. The test method that we have in mind is the cone calorimeter.

The burning behaviour of thermally thin materials with high characteristic temperature is investigated using a previously developed dynamical systems model. Regimes of particular interest from the viewpoint of fire-retardancy are identified and exhibited in steady-state diagrams. We explain how regimes of practical interest can be identified from the limit-point unfolding diagram and use this to determine the region of existence of these regimes as a function of the pyrolysis kinetics. This methodology provides a framework for the systematic investigation into the effectiveness of fire-retard-ants.

Oxygen index methods are widely used to measure the flammability of polymers and to investigate the effectiveness of fire retardants. Using a dynamical systems model an oxygen index is identified with an extinction limit point. The action of the fire retardant is investigated by unfolding this bifurcation point with a suitable continuation parameter which reflects the mode of action of the additive. The fire retardant mechanisms that we consider are non-competitive char formation and dilution by addition of an inert filler. We investigate which types of material are best retarded by each mechanism.

The influence of a hypolimnetic reservoir discharge on breakdown of aspen (Populus tremuloides) leaves was investigated during the late summer and autumn at sites above and below a high mountain reservoir. During the two-year study, leaf packs (5-g envelopes) were secured to stream substrate in riffle/run areas. Leaves protected from invertebrates with fine mesh did not demonstrate differences in leaf loss between sites suggesting that microbial processing was equivalent. There were. however, significant differences in leaf loss in coarse mesh envelopes between sites, with losses higher at the site above the reservoir. Aquatic invertebrate communities colonizing the leaf packs also differed from above and below the reservoir suggesting that invertebrates played a role in the differing leaf loss. We hypothesize that during late summer and fall, leaf breakdown is slower below the reservoir because of the altered invertebrate community.

In this paper a model for the heterogeneously catalysed reaction of a gaseous species undergoing a single-step exothermic reaction in a well mixed diabatic continuously stirred tank reactor is developed and analysed. Low-temperature reaction conditions are assumed, so that the degradation of the inflow species in the gas phase is negligible. The adsorption and desorption of the active species onto a solid catalyst layer is explicitly modelled.Under the conditions used, the classic combustion S-shape steady-state curve is not exhibited. Instead the steady-state diagram consists of two disjoint solution curves: a solution curve containing a steady-state branch corresponding to full coverage of the catalyst with no conversion; and, an isola containing a steady-state branch that corresponds to low coverage of the catalyst with a high conversion of the inflow species. The steady-state curve contains one extinction point and no ignition points. Consequently the initial conditions determine onto which steady sta...

We describe a mathematical model to evaluate flammability parameters of thermally thin thermoplastics in radiative ignition experiments. The concept of a critical mass flux from the solid phase into the flame is used as the criticality condition. Kinetic parameter values are chosen by relating the Arrhenius parameters to the ‘characteristic temperature’ that is measured in Thermogravimetric experiments (TG). The specific application of our model we have in mind is piloted ignition in the Cone Calorimeter.

Complementary lines of evidence were used to understand distribution and effects of metal contaminants above and below Ridgway Reservoir on the Uncompahgre River in Colorado. Water chemistry identified sites that were contaminated by Zn, while analysis of bryophyte tissue identified sites which had statistically significant differences in metal uptakes, including metals which were not detected in water samples (i.e., Hg and Se). Macroinvertebrate metric values also detected environmental degradation at some sites and generally supported results of water and tissue analyses. In general, water quality improved longitudinally from upstream to downstream. The two stations above Ridgway Reservoir had relatively inferior water quality and higher metal concentrations compared to the station below the reservoir. The exception was in Se concentrations which were enriched in bryophyte tissue at the downstream station.

We establish a mathematical model for the ignition of a thermally thin polymeric material in the Cone Calorimeter (autoignition mode). The model contains equations for solid phase and gas phase variables, and the two phases are coupled nonlinearly. Of particular importance are the couplings through convective and radiative heat transfer. We use the model to evaluate the critical heat flux required for ignition and identify features of the model which require further experimental validation.

There are many recommended pharmacological and non-pharmacological therapies for the prevention of stroke, and an ongoing challenge is to improve their uptake. Personalized medicine is seen as a possible solution to this challenge. Although the use of genetic information to guide health care could be considered as the apex of personalized medicine, genetics is not yet routinely used to guide prevention of stroke. Currently personalized aspects of prevention of stroke include tailoring interventions based on global risk, the utilization of individualized management plans within a model of organized care, and patient education. In this review we discuss the progress made in these aspects of prevention of stroke and present a case study to illustrate the issues faced by health care providers and patients with stroke that could be overcome with a personalized approach to the prevention of stroke.

Hyporheic pot samples and Surber samples were used to biologically assess an area recovering from the effects of mine drainage. Data indicate that hyporheic samplers are an important component in assessing macroinvertebrate communities impacted by heavy metals.

Macroinvertebrates from the upper Arkansas River were studied to identify taxa sensitive to heavy metal (zinc) impacts. Field collections and introduced substrates indicated that Rithrogena hageni was intolerant of conditions caused by mine drainage into the Arkansas River. Numbers of R. hageni at the impacted site increased significantly after treatment of mine drainage water was initiated. Data collected from this study suggest that the use of colonized substrates may be useful in studying metal impacts on macroinvertebrate communities.

Tolerance of Hesperophylax sp. to a low pH mine tailings seep which contained high concentrations of heavy metals was documented in Lake County, Colorado.

The Asiatic clam (Corbicula fluminea Muller) was found in Arapahoe County, Colorado. This is the first record of this exotic clam from the state of Colorado.