A DSMC investigation of gas flows in micro-channels with bends

Pressure-driven, implicit boundary conditions are implemented in an open source direct simulation Monte Carlo (DSMC) solver, and benchmarked against simple micro-channel flow cases found in the literature. DSMC simulations are then carried out of gas flows for varying degrees of rarefaction along micro-channels with both one and two ninety-degree bends. The results are compared to those from the equivalent straight micro-channel geometry. Away from the immediate bend regions, the pressure and Mach number profiles do not differ greatly from those in straight channels, indicating that there are no significant losses introduced when a bend is added to a micro-channel geometry. It is found that the inclusion of a bend in a micro-channel can increase the amount of mass that a channel can carry, and that adding a second bend produces a greater mass flux enhancement. This increase happens within a small range of Knudsen number (0.02 Knin 0.08). Velocity slip and shear stress profiles at the channel walls are presented for the Knudsen showing the largest mass flux enhancement

Book Reviews

Book reviews by Julius Cohen, Edward F. Barrett, Roger P. Peters, Thomas M. Scanlon, and Clarence Manion

Book Reviews

Book reviews by Felix Morley, Aaron I. Abell, Thomas M. Scanlon, Anton-Hermann Chroust, and Richard O\u27Sullivan

Characteristics of HIV-infected adolescents enrolled in a disclosure intervention trial in western Kenya

Knowledge of one's own HIV status is essential for long-term disease management, but there are few data on how disclosure of HIV status to infected children and adolescents in sub-Saharan Africa is associated with clinical and psychosocial health outcomes. We conducted a detailed baseline assessment of the disclosure status, medication adherence, HIV stigma, depression, emotional and behavioral difficulties, and quality of life among a cohort of Kenyan children enrolled in an intervention study to promote disclosure of HIV status. Among 285 caregiver-child dyads enrolled in the study, children's mean age was 12.3 years. Caregivers were more likely to report that the child knew his/her diagnosis (41%) compared to self-reported disclosure by children (31%). Caregivers of disclosed children reported significantly more positive views about disclosure compared to caregivers of non-disclosed children, who expressed fears of disclosure related to the child being too young to understand (75%), potential psychological trauma for the child (64%), and stigma and discrimination if the child told others (56%). Overall, the vast majority of children scored within normal ranges on screenings for behavioral and emotional difficulties, depression, and quality of life, and did not differ by whether or not the child knew his/her HIV status. A number of factors were associated with a child's knowledge of his/her HIV diagnosis in multivariate regression, including older age (OR 1.8, 95% CI 1.5-2.1), better WHO disease stage (OR 2.5, 95% CI 1.4-4.4), and fewer reported caregiver-level adherence barriers (OR 1.9, 95% CI 1.1-3.4). While a minority of children in this cohort knew their HIV status and caregivers reported significant barriers to disclosure including fears about negative emotional impacts, we found that disclosure was not associated with worse psychosocial outcomes

Affective Experience, Desire, and Reasons for Action

What is the role of affective experience in explaining how our desires provide us with reasons for action? When we desire that p, we are thereby disposed to feel attracted to the prospect that p, or to feel averse to the prospect that not-p. In this paper, we argue that affective experiences – including feelings of attraction and aversion – provide us with reasons for action in virtue of their phenomenal character. Moreover, we argue that desires provide us with reasons for action only insofar as they are dispositions to have affective experiences. On this account, affective experience has a central role to play in explaining how desires provide reasons for action

Comprehensive evaluation of caregiver-reported antiretroviral therapy adherence for HIV-infected children

For HIV-infected children, adherence to antiretroviral therapy (ART) is often assessed by caregiver report but there are few data on their validity. We conducted prospective evaluations with 191 children ages 0-14 years and their caregivers over 6 months in western Kenya to identify questionnaire items that best predicted adherence to ART. Medication Event Monitoring Systems(®) (MEMS, MWV/AARDEX Ltd., Switzerland) electronic dose monitors were used as external criterion for adherence. We employed a novel variable selection tool using the LASSO technique with logistic regression to identify items best correlated with dichotomized MEMS adherence (≥90 or <90 % doses taken). Nine of 48 adherence items were identified as the best predictors of adherence, including missed or late doses in the past 7 days, problems giving the child medicines, and caregiver-level factors like not being present at medication taking. These items could be included in adherence assessment tools for pediatric patients

A kinetic model of the Boltzmann equation for non-vibrating polyatomic gases

A kinetic model of the Boltzmann equation for non-vibrating polyatomic gases is proposed, based on the Rykov model for diatomic gases. We adopt two velocity distribution functions (VDFs) to describe the system state; inelastic collisions are the same as in the Rykov model, but elastic collisions are modelled by the Boltzmann collision operator (BCO) for monatomic gases, so that the overall kinetic model equation reduces to the Boltzmann equation for monatomic gases in the limit of no translational–rotational energy exchange. The free parameters in the model are determined by comparing the transport coefficients, obtained by a Chapman–Enskog expansion, to values from experiment and kinetic theory. The kinetic model equations are solved numerically using the fast spectral method for elastic collision operators and the discrete velocity method for inelastic ones. The numerical results for normal shock waves and planar Fourier/Couette flows are in good agreement with both conventional direct simulation Monte Carlo (DSMC) results and experimental data. Poiseuille and thermal creep flows of polyatomic gases between two parallel plates are also investigated. Finally, we find that the spectra of both spontaneous and coherent Rayleigh–Brillouin scattering (RBS) compare well with DSMC results, and the computational speed of our model is approximately 300 times faster. Compared to the Rykov model, our model greatly improves prediction accuracy, and reveals the significant influence of molecular models. For coherent RBS, we find that the Rykov model could overpredict the bulk viscosity by a factor of two

Open source Direct Simulation Monte Carlo (DSMC) chemistry modelling for hypersonic flows

An open source implementation of chemistry modelling for the direct simulation Monte Carlo (DSMC) method is presented. Following the recent work of Bird [1] an approach known as the quantum kinetic (Q-K) method has been adopted to describe chemical reactions in a 5-species air model using DSMC procedures based on microscopic gas information. The Q-K technique has been implemented within the framework of the dsmcFoam code, a derivative of the open source CFD code OpenFOAM. Results for vibrational relaxation, dissociation and exchange reaction rates for an adiabatic bath demonstrate the success of the Q-K model when compared with analytical solutions for both inert and reacting conditions. A comparison is also made between the Q-K and total collision energy (TCE) chemistry approaches for a hypersonic flow benchmark case