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Introduction: With limited funds available, meeting global health targets requires countries to both mobilize and prioritize their health spending. Within this context, countries have recognized the importance of allocating funds for HIV as efficiently as possible to maximize impact. Over the past six years, the governments of 23 countries in Africa, Asia, Eastern Europe and Latin America have used the Optima HIV tool to estimate the optimal allocation of HIV resources. Methods: Each study commenced with a request by the national government for technical assistance in conducting an HIV allocative efficiency study using Optima HIV. Each study team validated the required data, calibrated the Optima HIV epidemic model to produce HIV epidemic projections, agreed on cost functions for interventions, and used the model to calculate the optimal allocation of available funds to best address national strategic plan targets. From a review and analysis of these 23 country studies, we extract common themes around the optimal allocation of HIV funding in different epidemiological contexts. Results and discussion: The optimal distribution of HIV resources depends on the amount of funding available and the characteristics of each country's epidemic, response and targets. Universally, the modelling results indicated that scaling up treatment coverage is an efficient use of resources. There is scope for efficiency gains by targeting the HIV response towards the populations and geographical regions where HIV incidence is highest. Across a range of countries, the model results indicate that a more efficient allocation of HIV resources could reduce cumulative new HIV infections by an average of 18% over the years to 2020 and 25% over the years to 2030, along with an approximately 25% reduction in deaths for both timelines. However, in most countries this would still not be sufficient to meet the targets of the national strategic plan, with modelling results indicating that budget increases of up to 185% would be required. Conclusions: Greater epidemiological impact would be possible through better targeting of existing resources, but additional resources would still be required to meet targets. Allocative efficiency models have proven valuable in improving the HIV planning and budgeting process. Keywords: HIV modeling; allocative efficiency; cost-effectiveness; optimal HIV investment; resource allocation; resource needs, 1 | INTRODUCTION If decisions on the allocation of health resources were guided by the principals of health economics alone, funds would be allocated in ways intended to lead to [...]

The shear viscosity and self-diffusion transport coefficient of xylene isomers using the OPLS set of parameters for substituted benzenes are calculated. Comparison with experimental results for density and viscosity shows that these properties can be well reproduced using this potential, and therefore it is assumed that the diffusion coefficients should be also accurate to the same degree.

It is well established that the Green–Kubo type of expression of the friction coefficient for a massive colloidal particle, i.e., the force autocorrelation integral, vanishes at long times if the liquid volume is finite. Here I show that the nonzero friction coefficient, defined as the ratio of force on the particle and the average liquid velocity, can be found in the framework of the linear response theory as the ratio of the force autocorrelation integral and the correlation integral of liquid velocity and force on the particle. The finite inverse friction coefficient can be alternatively expressed as the autocorrelation integral of the liquid velocity. [ABSTRACT FROM AUTHOR]

We calculate viscosity and thermal conductivity in systems of Lennard–Jones particles consisting of coexisting solid and liquid with different interface wetting properties using the recently developed equilibrium boundary fluctuation theory. We compare the slip length and equivalent liquid length obtained from these calculations with those obtained from nonequilibrium molecular dynamics. The equilibrium and nonequilibrium calculations of the slip length and the sum of the thermal equivalent lengths are in good agreement. We conclude that for both interfacial properties, the nonequilibrium simulations were probing the linear response. The significant dependence of the intrinsic equivalence length on the interfacial temperature difference used to generate the thermal gradient is explained as a consequence of the different thermodynamic states of the two interfaces. [ABSTRACT FROM AUTHOR]

Shear flow in fluids confined between planar solid walls is conventionally simulated by moving the walls past each other at constant relative velocity. In infinite fluids (in periodic boundary conditions), it is simulated using one of the “synthetic” nonequilibrium algorithms (the so-called Sllod and Dolls algorithms). Here I formulate the boundary conditions for the motion of confining walls that make these three algorithms equivalent in the weak-field limit. [ABSTRACT FROM AUTHOR]

We demonstrate that the linear response theory of interface friction presented by Bocquet and Barrat [Phys. Rev. E 49, 3079 (1994)] results in a friction coefficient that is not an intrinsic property of the interface and thus does not correspond to the actual interfacial friction coefficient. We point out that this previous derivation includes an unsubstantiated identification of the velocity field in the nonuniform system with the perturbation applied to the equations of the motion. We present an alternative equilibrium theory of the friction associated with the confined fluid and show how this friction is related to the intrinsic interfacial friction. [ABSTRACT FROM AUTHOR]

We propose a phenomenological model for shear-induced melting aimed at assisting the design of experimental studies of this phenomenon. For increasing strain rates, the model predicts the changes in liquid fraction and shear stress as a function of interfacial supercooling. We discuss the experimental conditions under which shear-induced melting could be observed in a range of materials. [ABSTRACT FROM AUTHOR]

We present a method for the direct calculation at equilibrium of the shear viscosity and thermal conductivity over distances as short as one molecular diameter. The method is directly applicable to the calculation of viscosity and thermal conductivity in inhomogeneities such as the interface between coexisting phases. The method makes use of a novel extension of our recently developed boundary fluctuation theory. [ABSTRACT FROM AUTHOR]

In this paper we present, for the first time, a linear-response theory of transport coefficients—shear viscosity and thermal conductivity—involving thermal, as opposed to mechanical, fields. The theory involves the explicit treatment of the boundaries and the constraints that are applied to them. Expressions for the shear viscosity and thermal conductivity are obtained in terms of the fluctuations at the boundaries of the variable conjugate to that which is constrained. We explain how the choice of ensemble, as defined by the boundary constraints, determines the form in which the transport coefficients are evaluated. [ABSTRACT FROM AUTHOR]

We present a factorization of the Ewald sum permitting efficient computation of the reciprocal space part of the molecular representation for the heat flux vector. We use the derived expression to evaluate thermal conductivity of a model of ethanol at several near-ambient state points. [ABSTRACT FROM AUTHOR]

We use nonequilibrium molecular-dynamics (NEMD) simulations to characterize the response of a fluid subjected to an electric field. We focus on the response for very weak fields. Fields accessible by conventional NEMD methods are typically of the order of 109 V m-1, i.e., several orders of magnitude larger than those typically used in experiments. Using the transient time-correlation function, we show how NEMD simulations can be extended to study systems subjected to a realistic dc electric field. We then apply this approach to study the response of molten sodium chloride for a wide range of dc electric fields. [ABSTRACT FROM AUTHOR]

We study the dependence of viscosity of ethanol on shear rate using constant volume and constant pressure nonequilibrium molecular dynamics simulations, with the emphasis of the interrelationship between breaking, stability, and alignment of hydrogen bonds and shear thinning at high shear rates. We find that although the majority of hydrogen bond breakings occur at low shear rates, we do not observe shear thinning until there is some shear-induced alignment of the hydrogen bonds with the direction of shear. [ABSTRACT FROM AUTHOR]

We systematically investigate the cooperative effects in shear stress relaxation using equilibrium molecular-dynamics simulations in periodic boundary conditions containing a variable degree of strain. We show that, even in simple liquids, shear stress relaxation is a cooperative effect associated with a correlation length that increases with isobaric decrease in temperature. If the system size is less than the correlation length, shear stress in the system is determined by the boundary strain. Transport, however, does not depend on the boundary conditions. We relate these two effects to the number and properties of the configurations accessible to the system. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We show that at high densities, as the system size decreases, liquid becomes able to permanently sustain increasing internal shear stress after a constant deformation, although the other characteristic liquid properties, such as the pair distribution function and diffusion coefficient do not change under strain. The system size necessary for observation of this effect increases with the decrease in temperature, and it is stronger in pair potentials with steeper repulsive part. We relate this result to the size of the “cooperatively rearranging regions” of the Adam–Gibbs theory of glass transition. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We study the shear stress relaxation and temperature dependence of the diffusion coefficient, viscosity, and thermal conductivity along a high-density Lennard-Jones isochore of the reduced density of 1.0, as it crosses the freezing and melting lines, in equilibrium and under constant strain. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We study the properties of molten sodium chloride in alternating electric fields of two amplitudes and for a large range of frequencies using nonequilibrium molecular dynamics simulations, and compare the responses with two different methods of temperature control to the predictions of linear response theory. We find that the considerable nonlinearity in the resulting current density observed at low frequencies can be explained by the characteristics of the nonlinear response to constant fields. We also comment on the differences in the dissipation mechanisms and the entropy change with two thermostats. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We investigate the influence of thermostatting methods on the electrical conductivity and structure of molten and supercritical sodium chloride obtained in nonequilibrium molecular dynamics simulations in strong constant (dc) electric fields. The strong dependence of the results on the type of thermostat employed in simulations becomes apparent only at extremely high fields (>0.5 × 10[sup 9] V/m). For this range of fields, quantitative differences of unexpected size can be seen in the melt. In the supercritical fluid, different thermostats predict qualitatively very different behavior and structure. While the kinetic-type thermostats predict increased association of ions in the field, configurational thermostat predicts enhanced dissociation. [ABSTRACT FROM AUTHOR]

The shear viscosity of molten sodium chloride is determined under a wide range of strain rates using nonequilibrium molecular dynamics (NEMD) simulations in the canonical (N,V,T) ensemble. Questions have been recently raised on the use of kinetic temperature thermostats, based on the equipartition principle, in simulations of nonequilibrium fluids and using a configurational temperature thermostat has been suggested to be more realistic. To further ascertain the results obtained in this work, we study molten NaCl with both kinetic and configurational temperature thermostats. Since configurational thermostats have been so far restricted to simple fluids or alkanes, we first apply configurational expressions for the temperature to molten NaCl, test the values so obtained in equilibrium molecular dynamics simulation for various system sizes and state points and finally use them to thermostat molten NaCl under shear. NEMD results obtained for both thermostats show that except for the so-called normal stress coefficients, molten salt under shear exhibits mostly the same features as a simple fluid under shear, i.e., features in agreement with the mode-coupling theory. The choice of the thermostatting method is found to have little influence on the results for the range of shear rates investigated. [ABSTRACT FROM AUTHOR]