883 research outputs found
Consistent particle-based algorithm with a non-ideal equation of state
A thermodynamically consistent particle-based model for fluid dynamics with
continuous velocities and a non-ideal equation of state is presented. Excluded
volume interactions are modeled by means of biased stochastic multiparticle
collisions which depend on the local velocities and densities. Momentum and
energy are exactly conserved locally. The equation of state is derived and
compared to independent measurements of the pressure. Results for the kinematic
shear viscosity and self-diffusion constants are presented. A caging and
order/disorder transition is observed at high densities and large collision
frequency.Comment: 7 pages including 4 figure
Systematic coarse-graining of the dynamics of entangled polymer melts: the road from chemistry to rheology
For optimal processing and design of entangled polymeric materials it is
important to establish a rigorous link between the detailed molecular
composition of the polymer and the viscoelastic properties of the macroscopic
melt. We review current and past computer simulation techniques and critically
assess their ability to provide such a link between chemistry and rheology. We
distinguish between two classes of coarse-graining levels, which we term
coarse-grained molecular dynamics (CGMD) and coarse-grained stochastic dynamics
(CGSD). In CGMD the coarse-grained beads are still relatively hard, thus
automatically preventing bond crossing. This also implies an upper limit on the
number of atoms that can be lumped together and therefore on the longest chain
lengths that can be studied. To reach a higher degree of coarse-graining, in
CGSD many more atoms are lumped together, leading to relatively soft beads. In
that case friction and stochastic forces dominate the interactions, and actions
must be undertaken to prevent bond crossing. We also review alternative methods
that make use of the tube model of polymer dynamics, by obtaining the
entanglement characteristics through a primitive path analysis and by
simulation of a primitive chain network. We finally review super-coarse-grained
methods in which an entire polymer is represented by a single particle, and
comment on ways to include memory effects and transient forces.Comment: Topical review, 31 pages, 10 figure
Capillary Rise in Nanopores: Molecular Dynamics Evidence for the Lucas-Washburn Equation
When a capillary is inserted into a liquid, the liquid will rapidly flow into
it. This phenomenon, well studied and understood on the macroscale, is
investigated by Molecular Dynamics simulations for coarse-grained models of
nanotubes. Both a simple Lennard-Jones fluid and a model for a polymer melt are
considered. In both cases after a transient period (of a few nanoseconds) the
meniscus rises according to a -law. For the polymer melt,
however, we find that the capillary flow exhibits a slip length ,
comparable in size with the nanotube radius . We show that a consistent
description of the imbibition process in nanotubes is only possible upon
modification of the Lucas-Washburn law which takes explicitly into account the
slip length .Comment: 4 pages 4 figure
Dissipative Particle Dynamics with Energy Conservation
The stochastic differential equations for a model of dissipative particle
dynamics with both total energy and total momentum conservation in the
particle-particle interactions are presented. The corresponding Fokker-Planck
equation for the evolution of the probability distribution for the system is
deduced together with the corresponding fluctuation-dissipation theorems
ensuring that the ab initio chosen equilibrium probability distribution for the
relevant variables is a stationary solution. When energy conservation is
included, the system can sustain temperature gradients and heat flow can be
modeled.Comment: 7 pages, submitted to Europhys. Let
Particle-Based Mesoscale Hydrodynamic Techniques
Dissipative particle dynamics (DPD) and multi-particle collision (MPC)
dynamics are powerful tools to study mesoscale hydrodynamic phenomena
accompanied by thermal fluctuations. To understand the advantages of these
types of mesoscale simulation techniques in more detail, we propose new two
methods, which are intermediate between DPD and MPC -- DPD with a multibody
thermostat (DPD-MT), and MPC-Langevin dynamics (MPC-LD). The key features are
applying a Langevin thermostat to the relative velocities of pairs of particles
or multi-particle collisions, and whether or not to employ collision cells. The
viscosity of MPC-LD is derived analytically, in very good agreement with the
results of numerical simulations.Comment: 7 pages, 2 figures, 1 tabl
Dissipative Particle Dynamics with energy conservation
Dissipative particle dynamics (DPD) does not conserve energy and this
precludes its use in the study of thermal processes in complex fluids. We
present here a generalization of DPD that incorporates an internal energy and a
temperature variable for each particle. The dissipation induced by the
dissipative forces between particles is invested in raising the internal energy
of the particles. Thermal conduction occurs by means of (inverse) temperature
differences. The model can be viewed as a simplified solver of the fluctuating
hydrodynamic equations and opens up the possibility of studying thermal
processes in complex fluids with a mesoscopic simulation technique.Comment: 5 page
Cost‐effectiveness of Anti‐CD19 chimeric antigen receptor T‐Cell therapy in pediatric relapsed/refractory B‐cell acute lymphoblastic leukemia. A societal view
Introduction: In several studies, the chimeric antigen receptor T-cell therapy tisagenlecleucel demonstrated encouraging rates of remission and lasting survival benefits in
pediatric patients with relapsed/refractory (r/r) acute lymphoblastic leukemia (ALL).
We assessed the cost-effectiveness of tisagenlecleucel (list price: 320 000 EUR)
among these patients when compared to clofarabine monotherapy (Clo-M), clofarabine combination therapy (Clo-C), and blinatumomab (Blina) from both a healthcare
and a societal perspective. We also assessed future medical and future non-medical
consumption costs.
Methods: A three-state partitioned survival model was used to simulate a cohort of
pediatric patients (12 years of age) through different disease states until the end of
life (lifetime horizon). Relevant outcomes were life years, quality-adjusted life years
(QALYs), healthcare costs, societal costs, and the incremental cost-effectiveness ratio
(ICER). Uncertainty was explored through deterministic and probabilistic sensitivity
analyses as well as through several scenario analyzes.
Results: Total discounted costs for tisagenlecleucel were 552 679 EUR from a societal perspective, which was much higher than the total discounted costs from a
healthcare perspective (ie, 409 563 EUR). Total discounted societal costs for the
comparator regimens ranged between 160 803 EUR for Clo-M and 267 259 EUR for
Blina. Highest QALYs were estimated for tisagenlecleucel (11.26), followed by Blina
(2.25), Clo-C (1.70) and Clo-M (0.74). Discounted societal ICERs of tisagenlecleucel
ranged between 31 682 EUR/QALY for Blina and 37 531 EUR/QALY for Clo-C and
were considered cost-effective with a willingness-to-pay (WTP) threshold of 80 000
EUR/QALY. None of the scenarios exceeded this threshold, and more than 98% of
the iterations in the probabilistic sensitivity analysis were cost-effective.
Discussion: At the current price and WTP threshold, tisagenlecleucel is cost-effective from both a healthcare and a societal perspective. Nevertheless, long-term effectiveness data are needed to validate the several assumptions that were necessary for this model
Forced Imbibition - a Tool for Determining Laplace Pressure, Drag Force and Slip Length in Capillary Filling Experiments
When a very thin capillary is inserted into a liquid, the liquid is sucked
into it: this imbibition process is controlled by a balance of capillary and
drag forces, which are hard to quantify experimentally, in particularly
considering flow on the nanoscale. By computer experiments using a generic
coarse-grained model, it is shown that an analysis of imbibition forced by a
controllable external pressure quantifies relevant physical parameter such as
the Laplace pressure, Darcy's permeability, effective pore radius, effective
viscosity, dynamic contact angle and slip length of the fluid flowing into the
pore. In determining all these parameters independently, the consistency of our
analysis of such forced imbibition processes is demonstrated.Comment: 4 pages, 5 figure
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