Calculation Of Pressure Profiles Research Articles

Molecular dynamics study of the mechanical properties of drug loaded model systems: A comparison of a polymersome with a bilayer.

In this work we implement a new methodology to study structural and mechanical properties of systems having spherical and planar symmetries throughout Molecular Dynamics simulations. This methodology is applied here to a drug delivery system based in polymersomes, as an example. The chosen model drug was the local anesthetic prilocaine due to previous parameterization within the used coarse grain scheme. In our approach, mass density profiles (MDPs) are used to obtain key structural parameters of the systems, and pressure profiles are used to estimate the curvature elastic parameters. The calculation of pressure profiles and radial MPDs required the development of specific methods, which were implemented in an in-house built version of the GROMACS 2018 code. The methodology presented in this work is applied to characterize poly(ethylene oxide)-poly(butadiene) polymersomes and bilayers loaded with the model drug prilocaine. Our results show that structural properties of the polymersome membrane could be obtained from bilayer simulations, with significantly lower computational cost compared to whole polymersome simulations, but the bilayer simulations are insufficient to get insights on their mechanical aspects, since the elastic parameters are canceled out for the complete bilayer (as consequence of the symmetry). The simulations of entire polymersomes, although more complex, offer a complementary approach to get insights on the mechanical behavior of the systems.

Development of computational tool for the calculation of pressure profiles in the flow of oil and gas mixtures in horizontal pipelines

Development of computational tool for the calculation of pressure profiles in the flow of oil and gas mixtures in horizontal pipelines

Pressure profiles of High Energy Beam Transport vacuum system for the FAIR project

The pressure profile calculations of some beam lines from the High Energy Beam Transport (HEBT) vacuum system for the FAIR (Facility for Antiproton and Ion Research) accelerator facility are presented in this report. The calculations used both a simple analytical model and a Monte-Carlo method for a steady-state condition. The calculation results show that the pressure profiles for these beam lines are conductance limited. A simple experimental setup representing a small part of the HEBT section was also conducted.

Effect of spherically converging stress waves on the phase composition, structure, and physicochemical transformations of the mixture of aluminum and quartz powders

The phase composition and structure of a mixture of aluminum and quartz powders taken in a ratio of 1:1 have been studied after loading by spherical converging shock waves. A number of concentric layers (zones) have been observed in a meridian section of the sample after shock-wave loading. The pressures in the converging shock wave and in the diverging shock wave reflected from the center of the sample have been estimated as a function of the radial position of Lagrangian particles on the basis of the calculation of pressure profiles P(R, t). The data on the phase composition of different zones are considered in respect to the pressures induced by the converging and diverging shock waves at their boundaries. It has been established that pressures below ∼45 GPa cause only additional compacting of the material and deformation of aluminum and quartz. In this case, the quartz grain size substantially decreases up to the transition into the X-ray amorphous state. The attainment of a pressure of ∼45 GPa initiates the solid-state reaction of SiO2 decomposition, which leads to the precipitation of pure silicon and the evolution of oxygen. The beginning of the silicon precipitation and the chemical reaction of Al2O3 formation are separated over the pressure scale. The critical pressure, which is necessary for the solid-state chemical reaction of the Al2O3 formation is about 50 GPa.

A Lagrangian Approach for Oil Recovery in Two-Phase Porous Media Flow

Abstract This paper deals with a fully implicit finite difference scheme for the numerical solution of the Lagrangian form of the porous media fractional flow equation. It covers the theoretical background, description of mathematical formulations, basic assumptions in the models, normalization and transformation between Lagrangian and Eulerian formulations, specification of boundary conditions, discretization and solution method. Some numerical examples are described and the results compared favourably with co-current immiscible displacement data. The solution presented is more efficient than the finite element solution method in terms of requiring less matrix computation effort and it is much more stable than the explicit finite difference solution methods that have been presented in the literature. Due to the ease of formulation and use, the simulation algorithm presented can be used to formulate laboratory numerical simulators that can be used routinely for co-current flow numerical studies. Introduction An equation of the form: Equation (1) (Available In Full Paper) is one of the various Lagrangian forms of the fractional flow equation for two-phase, immiscible displacement in porous media. It is Lagrangian because this configuration allows the equation to be solved as a function of saturation and time. The Eulerian configuration enables the equation to be solved as a function of space and time. Bentsen(1) first derived Equation (1), also called the Bentsen equation(2,3). It was subsequently re-derived by Shen and Ruth(2,3) using a different derivation approach. The equation was derived by combining Darcy's equation for two-phase flow with the continuity equation and by transforming the resulting fractional flow Eulerian form to Lagrangian form. A summary of this derivation is presented later in the paper. This equation, together with normalized forms of the displacement (frontal advance) equation, can be solved to produce a numerical description of a two-phase, incompressible, immiscible displacement process in porous media. The main aim of using the Lagrangian approaches is to enable a more computationally efficient scheme and eliminate the need for space discretization as distance is eliminated from the resulting equation. The form presented in Equation (1) is particularly useful because it is very compact. Theoretical Background Douglas et al.(4) presented an Eulerian technique for solving linear waterflooding problems which involved using a transformed saturation variable and the use of a small mobile water saturation ahead of the flood front to enable the base of the flood front to move forward. Fayers and Sheldon(5) obtained solutions to the one-dimensional displacement equation using both the Lagrangian and the Eulerian approaches. McEwen(6) used the method of characteristics for a numerical solution of the linear displacement equation with capillary pressure. Hovanessian and Fayers(7) also solved numerically the equations describing waterflooding experiments that include both gravity and capillary effects. Their method is similar to that of Douglas et al.(4) because it involves the use of the Eulerian form of the fractional flow equation and the transformation of the resulting second-order non-linear partial differential equations. Hovanessian and Fayers(7) solution differs from those of Douglas et al.(4) because it includes the effect of gravity, allows for the calculation of pressure profiles and makes use of a tabular format for the input of relative permeability and capillary pressure values instead of the u

Computational investigation of pressure profiles in lipid bilayers with embedded proteins

The distribution of surface tension within a lipid bilayer, also referred to as the lateral pressure profile, has been the subject of theoretical scrutiny recently due to its potential to radically alter the function of biomedically important membrane proteins. Experimental measurements of the pressure profile are still hard to come by, leaving first-principles all-atom calculations of the profile as an important investigative tool. We describe and validate an efficient implementation of pressure profile calculations in the molecular dynamics package NAMD, capable of distinguishing between internal, bonded and nonbonded contributions as well as those of selected atom groups. The new implementation can also be used in conjunction with Ewald summation for long-range electrostatics, improving the accuracy and reproducibility of the calculated profiles. We then describe results of the calculation of a pressure profile for a simple protein–lipid system consisting of melittin embedded in a DMPC bilayer. While the lateral pressure in the protein–lipid system is nearly the same as that of the bilayer alone, partitioning of the lateral pressure by atom type revealed substantial perturbation of the pressure profile and surface tension in an asymmetric manner.

Methodological problems in pressure profile calculations for lipid bilayers

From molecular dynamics simulations of a dipalmitoyl-phosphatidyl-choline (DPPC) lipid bilayer in the liquid crystalline phase, pressure profiles through the bilayer are calculated by different methods. These profiles allow us to address two central and unresolved problems in pressure profile calculations: The first problem is that the pressure profile is not uniquely defined since the expression for the local pressure involves an arbitrary choice of an integration contour. We have investigated two different choices leading to the Irving-Kirkwood (IK) and Harasima (H) expressions for the local pressure tensor. For these choices we find that the pressure profile is almost independent of the contour used, which indicates that the local pressure is well defined for a DPPC bilayer in the liquid crystalline phase. This may not be the case for other systems and we therefore suggest that both the IK and H profiles are calculated in order to test the uniqueness of the profile. The second problem is how to include electrostatic interactions in pressure profile calculations when the simulations are conducted without truncating the electrostatic potential, i.e., using the Ewald summation technique. Based on the H expression for the local pressure, we present a method for calculating the contribution to the lateral components of the local pressure tensor from electrostatic interactions evaluated by the Ewald summation technique. Pressure profiles calculated with an electrostatic potential truncation (cutoff) from simulations conducted with Ewald summation are shown to depend on the cutoff in a subtle manner which is attributed to the existence of long-ranged charge ordering in the system. However, the pressure profiles calculated with relatively long cutoffs are qualitatively similar to the Ewald profile for the DPPC bilayer studied here.

Calculation of pressure profiles in accelerators using a matrix method

The pressure profile in a one-dimensional vacuum system can be calculated using a matrix calculus method. This method is very similar to that used to evaluate the transverse electron motion in accelerators. A computer program based on this method is presented and compared to the analytical calculation of some examples.

Melting mechanism in single screw extrusion

AbstractFlow visualization experiments of polycarbonate and polystyrene resin extrusion were performed to observe the melting mechanism and the flow kinematics around the solid‐bed in the melting zone of a single screw extruder. The axial solids content and pressure profile calculations of the Tadmor melting model were modified as a result of variable solid‐bed velocity and solid‐bed temperature observations.

Computer Design of Dense-Phase Pipelines

This paper demonstrates the importance of performing simultaneous temperature and pressure profile calculations when designing pipelines for single dense-phase fluids. The sensitivity of the pressure and temperature profiles to design parameters is examined and discussed in detail. profiles to design parameters is examined and discussed in detail. Introduction The pressure and temperature changes for single-phase flow along a pipeline are described by the following differential equations: dp p dv g dZ 2fv2p--- + -- v ---- +p --- ----- + ------- = 0,.......(1)dL gc dL gc dL gcd dh 1 dv g dZ 1 dQ---- +--- v --- + --- ---- + --- --- = 0,......(2)dL gc dL gc dL w dL where the following functional relationships must be specified. p =f(p, T)......................................(3)h =f(p, T)......................................(4)=f(p, T)......................................(5)f =f(N Re, k/d).................................(6) wheredvpN Re = ----.......................................(7) The expressions for p, h, and may be either analytical or graphical, and their complexity depends on the type of fluid being considered. Many different expressions for the friction factor, f, are also available; some are general and some are for specific pipeline and fluid systems. For hand calculations, Eqs. 1 and 2 must be integrated over the length of the pipeline to obtain analytical expressions for pressure and temperature as functions of length, flow rate, fluid properties, and pipe-to-sod interactions. This poses problems for the general case becausethe equations are nonlinear and coupled,the fluid properties depend on pressure and temperature in a complex manner, andthe friction factor is a nonlinear function of viscosity, density, and velocity. Thus, to obtain the analytical expressions, various simplifying assumptions must be made. This procedure has resulted in many design equations that apply to particular systems and are useful when the inherent assumptions are valid. However, in some cases, particularly when dealing with a fluid near the critical region particularly when dealing with a fluid near the critical region (i.e., dense fluid state), variations in the physical and thermodynamic properties are rather complex and no available integrated form of the equations can be used safely. If adequate information is available about the relationships expressed by Eqs. 3 through 6, Eqs. 1 and 2 can be integrated numerically to any desired accuracy without making any simplifying assumptions. Clearly, this approach is only practical when a digital computer is available, but it is completely general and may be followed for any single-phase flow in a pipe (gas, liquid, or dense phase). This procedure is the basis of the computer program used to perform all calculations discussed later. Extension of the approach to multiphase gas-liquid flow in pipes and structure of the program are discussed elsewhere. P. 40