41 research outputs found
A cluster theory for a Janus fluid
Recent Monte Carlo simulations on the Kern and Frenkel model of a Janus fluid
have revealed that in the vapour phase there is the formation of preferred
clusters made up of a well-defined number of particles: the micelles and the
vesicles. A cluster theory is developed to approximate the exact clustering
properties stemming from the simulations. It is shown that the theory is able
to reproduce the micellisation phenomenon.Comment: 27 pages, 8 figures, 6 table
Model of a fluid at small and large length scales and the hydrophobic effect
We present a statistical field theory to describe large length scale effects
induced by solutes in a cold and otherwise placid liquid. The theory divides
space into a cubic grid of cells. The side length of each cell is of the order
of the bulk correlation length of the bulk liquid. Large length scale states of
the cells are specified with an Ising variable. Finer length scale effects are
described with a Gaussian field, with mean and variance affected by both the
large length scale field and by the constraints imposed by solutes. In the
absence of solutes and corresponding constraints, integration over the Gaussian
field yields an effective lattice gas Hamiltonian for the large length scale
field. In the presence of solutes, the integration adds additional terms to
this Hamiltonian. We identify these terms analytically. They can provoke large
length scale effects, such as the formation of interfaces and depletion layers.
We apply our theory to compute the reversible work to form a bubble in liquid
water, as a function of the bubble radius. Comparison with molecular simulation
results for the same function indicates that the theory is reasonably accurate.
Importantly, simulating the large length scale field involves binary arithmetic
only. It thus provides a computationally convenient scheme to incorporate
explicit solvent dynamics and structure in simulation studies of large
molecular assemblies
Self Consistent Molecular Field Theory for Packing in Classical Liquids
Building on a quasi-chemical formulation of solution theory, this paper
proposes a self consistent molecular field theory for packing problems in
classical liquids, and tests the theoretical predictions for the excess
chemical potential of the hard sphere fluid. Results are given for the self
consistent molecular fields obtained, and for the probabilities of occupancy of
a molecular observation volume. For this system, the excess chemical potential
predicted is as accurate as the most accurate prior theories, particularly the
scaled particle (Percus-Yevick compressibility) theory. It is argued that the
present approach is particularly simple, and should provide a basis for a
molecular-scale description of more complex solutions.Comment: 6 pages and 5 figure
Density functional theory and demixing of binary hard rod-polymer mixtures
A density functional theory for a mixture of hard rods and polymers modeled
as chains built of hard tangent spheres is proposed by combining the functional
due to Yu and Wu for the polymer mixtures [J. Chem. Phys. {\bf 117}, 2368
(2002)] with the Schmidt's functional [Phys. Rev. E {\bf 63}, 50201 (2001)] for
rod-sphere mixtures. As a simple application of the functional, the demixing
transition into polymer-rich and rod-rich phases is examined. When the chain
length increases, the phase boundary broadens and the critical packing fraction
decreases. The shift of the critical point of a demixing transition is most
noticeable for short chains.Comment: 4 pages,2 figures, in press, PR
Ongoing Phase 1/2 Study Of Incb050465, A Selective Pi3kÎŽ Inhibitor, For The Treatment Of Patients (Pts) With Relapsed/Refractory (R/R) BâCell Malignancies (Citadelâ101)
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137307/1/hon2438_139.pd
A molecular dynamics study on the equilibrium magnetization properties and structure of ferrofluids
We investigate in detail the initial susceptibility, magnetization curves,
and microstructure of ferrofluids in various concentration and particle dipole
moment ranges by means of molecular dynamics simulations. We use the Ewald
summation for the long-range dipolar interactions, take explicitly into account
the translational and rotational degrees of freedom, coupled to a Langevin
thermostat. When the dipolar interaction energy is comparable with the thermal
energy, the simulation results on the magnetization properties agree with the
theoretical predictions very well. For stronger dipolar couplings, however, we
find systematic deviations from the theoretical curves. We analyze in detail
the observed microstructure of the fluids under different conditions. The
formation of clusters is found to enhance the magnetization at weak fields and
thus leads to a larger initial susceptibility. The influence of the particle
aggregation is isolated by studying ferro-solids, which consist of magnetic
dipoles frozen in at random locations but which are free to rotate. Due to the
artificial suppression of clusters in ferro-solids the observed susceptibility
is considerably lowered when compared to ferrofluids.Comment: 33 pages including 12 figures, requires RevTex
Many-body aspects of positron annihilation in the electron gas
We investigate positron annihilation in electron liquid as a case study for
many-body theory, in particular the optimized Fermi Hypernetted Chain (FHNC-EL)
method. We examine several approximation schemes and show that one has to go up
to the most sophisticated implementation of the theory available at the moment
in order to get annihilation rates that agree reasonably well with experimental
data. Even though there is basically just one number to look at, the
electron-positron pair distribution function at zero distance, it is exactly
this number that dictates how the full pair distribution behaves: In most
cases, it falls off monotonously towards unity as the distance increases. Cases
where the electron-positron pair distribution exhibits a dip are precursors to
the formation of bound electron--positron pairs. The formation of
electron-positron pairs is indicated by a divergence of the FHNC-EL equations,
from this we can estimate the density regime where positrons must be localized.
This occurs in our calculations in the range 9.4 <= r_s <=10, where r_s is the
dimensionless density parameter of the electron liquid.Comment: To appear in Phys. Rev. B (2003
Ti alloy with enhanced machinability in UAT turning
Metastable ÎČ-titanium alloys such as Ti 15V 3Al 3Cr 3Sn are of great technological interest thanks to their high fatigue strength-to-density ratio. However, their high hardness and poor machinability increase machining costs. Additionally, formation of undesirable long chips increases the machining time. To address those issues, a metastable ÎČ-titanium alloy (Ti 15V 3Al 3Cr 2Zr 0.9La) with enhanced machinability was developed to produce short chips even at low cutting speeds. A hybrid ultrasonically assisted machining technique, known to reduce cutting forces, was employed in this study. Cutting force components and surface quality of the finished work-pieces were analyzed for a range of cutting speeds in comparison with those for more traditional Ti 15V 3Al 3Cr 3Sn. The novel alloy demonstrated slightly improved machining characteristics at higher cutting speeds and is now ready for industrial applications