249 research outputs found
Interfaces and Grain Boundaries of Lamellar Phases
Interfaces between lamellar and disordered phases, and grain boundaries
within lamellar phases, are investigated employing a simple Landau free energy
functional. The former are examined using analytic, approximate methods in the
weak segregation limit, leading to density profiles which can extend over many
wavelengths of the lamellar phase. The latter are studied numerically and
exactly. We find a change from smooth chevron configurations typical of small
tilt angles to distorted omega configurations at large tilt angles in agreement
with experiment.Comment: 9 pages, 6 figures 9 pages, 6 figure
Flowsheet simulation of solids processes: Current status and future trends
Complex manufacturing processes are nowadays applied for production of various solid products. It is very common that for production of particles with desired properties several transformation steps like drying, milling, classification, granulation, etc. should be involved. This leads to the process structures consisting of different apparatuses or transformation substeps connected with material and energy balances. Consequently, development of new processes or optimization of already existing, as well as an optimal control, is a very challenging task, which can be partially solved using numerical modelling.
For the simulation of modern production processes, the flowsheet calculations can be effectively used. Starting from the 80 s a lot of work focused on the flowsheet simulation of liquid-vapor systems has been done and as result various well-established systems exist today. With respect to the solid processes the intensive research has been started much later. In this contribution we present our view about a current role of flowsheet simulation for modeling of particulate materials and specify the open fields which can be covered in future research
A New Curriculum to Train Chemical Engineers to Solve 21st Century Grand Challenges
The Department of Chemical and Biological Engineering at the University of Sheffield
is embarked on a curriculum change project with roll out starting with level 1 in
September 2017. The drivers behind the change included the need to modernise the
curriculum both in terms of content, structure and delivery. The main objective was
to develop a modern Sheffield Chemical Engineer. The study is primarily about
investigating the efficacy of the change efforts that have been introduced, to track
progress and to determine whether we are meeting our stated objectives. The
objectives are in relation to student success, student experience, curriculum coherence
and student and staff well-being. Specifically, the new curriculum will be coherent,
embedded in design and practice with an emphasis on critical thinking, problem
solving, professionalism, ethics and sustainability. It will offer flexible learning
environments and pathways to facilitate deep engagement. It will promote and
facilitate industry involvement by focusing on both process and product engineering
to develop industry ready practical graduates with hands on experience. It will produce
graduates who are integrators, change agents and self-directed learners to lead
multidisciplinary teams, and be at the forefront of innovation. It will provide exposure
to niche research areas built on a strong core in engineering fundamentals. Lastly, it
will produce graduates capable of Engineering from molecules by applying systems
level thinking at many length scales. We have identified a third year module process
design as a significant check point to determine whether some of our curriculum
objectives are being met (Patwardhan et al, 2017)
Measurement of the active width in Sr-doped lanthanum manganate Sofc Cathodes using Nano-ct, impedance spectroscopy and Bayesian calibration
Bayesian model-based analysis (BMA) is a method for producing quantitative models of complex physical systems through the comparison between models and experimental data. A model of a porous LSM cathode (symmetrical cell) was applied to impedance data and its parameters estimated via Bayesian calibration. X-ray computed tomography provided microstructural information for the model. The combination of model calibration and microstructural characterization enabled an estimate of the active thickness for a porous LSM electrode. The active width extended only a few nanometers from the surface, strongly suggesting that future models should explicitly resolve the space-charge region
First order isotropic - smectic-A transition in liquid crystal-aerosil gels
The short-range order which remains when the isotropic to smectic-A
transition is perturbed by a gel of silica nanoparticles (aerosils) has been
studied using high-resolution synchrotron x-ray diffraction. The gels have been
created \textit{in situ} in decylcyanobiphenyl (10CB), which has a strongly
first-order isotropic to smectic-A transition. The effects are determined by
detailed analysis of the temperature and gel density dependence of the smectic
structure factor. In previous studies of the continuous nematic to smectic-A
transition in a variety of thermotropic liquid crystals the aerosil gel
appeared to pin, at random, the phase of the smectic density modulation. For
the isotropic to smectic-A transition the same gel perturbation yields
different results. The smectic correlation length decreases more slowly with
increasing random field variance in good quantitative agreement with the effect
of a random pinning field at a transition from a uniform phase directly to a
phase with one-dimensional translational order. We thus compare the influence
of random fields on a \textit{freezing} transition with and without an
intervening orientationally ordered phase.Comment: 8 pages, 8 figure
The Role of Gender on the Associations Among Children’s Attitudes, Mathematics Knowledge, Digital Game Use, Perceptions of Affordances, and Achievement
This study explored associations among children’s prior attitudes, prior mathematics knowledge, and frequency of digital game use, with children’s perceptions of game affordances, and transfer to out-of-game performance when interacting with digital math games, with respect to gender. Participants were 187 children (ages 8–12). An SEM mediation path analysis using MPLUS software showed significant direct effects for all pathways for all children, and significant indirect effects on all pathways for male children and five of six pathways for female children. More favorable attitudes, prior math knowledge, and perception of the helping affordances were associated with increased posttest performance, while increased frequency of digital game use and stronger perception of the hindering affordances was associated with decreased posttest performance. The model showed stronger connections for male children between frequency of digital game use, prior mathematics knowledge, and hindering affordances to the posttest, while female children showed stronger connections between attitude and perception of helping affordances to the posttest
Dynamics of Weak First Order Phase Transitions
The dynamics of weak vs. strong first order phase transitions is investigated
numerically for 2+1 dimensional scalar field models. It is argued that the
change from a weak to a strong transition is itself a (second order) phase
transition, with the order parameter being the equilibrium fractional
population difference between the two phases at the critical temperature, and
the control parameter being the coefficient of the cubic coupling in the
free-energy density. The critical point is identified, and a power law
controlling the relaxation dynamics at this point is obtained. Possible
applications are briefly discussed.Comment: 11 pages, 4 figures in uuencoded compressed file (see instructions in
main text), RevTeX, DART-HEP-94/0
A lattice model for the kinetics of rupture of fluid bilayer membranes
We have constructed a model for the kinetics of rupture of membranes under
tension, applying physical principles relevant to lipid bilayers held together
by hydrophobic interactions. The membrane is characterized by the bulk
compressibility (for expansion), the thickness of the hydrophobic part of the
bilayer, the hydrophobicity and a parameter characterizing the tail rigidity of
the lipids. The model is a lattice model which incorporates strain relaxation,
and considers the nucleation of pores at constant area, constant temperature,
and constant particle number. The particle number is conserved by allowing
multiple occupancy of the sites. An equilibrium ``phase diagram'' is
constructed as a function of temperature and strain with the total pore surface
and distribution as the order parameters. A first order rupture line is found
with increasing tension, and a continuous increase in proto-pore concentration
with rising temperature till instability. The model explains current results on
saturated and unsaturated PC lipid bilayers and thicker artificial bilayers
made of diblock copolymers. Pore size distributions are presented for various
values of area expansion and temperature, and the fractal dimension of the pore
edge is evaluated.Comment: 15 pages, 8 figure
Compositional effect of complex biorelevant media on the crystallization kinetics of an active pharmaceutical ingredient
Bile salts are endogenous surfactants present in the human gastrointestinal tract in the form of mixed micelles that also contain phospholipids. Due to the inevitable encounter of oral drug formulations with bile salts, it is important to understand the impact of bile salts on the crystallization tendency of poorly soluble compounds that form supersaturated solutions in vivo in order to maximize oral drug absorption. Although there has been an increasing number of studies focusing on the role of individual bile salts on drug crystallization, the effects of mixed micelles and biorelevant media composition on crystallization kinetics have only been studied to a limited extent. In this study, we evaluated the ability of binary and ternary bile salt combinations to maintain supersaturated aqueous solutions of telaprevir. Crystallization kinetics were also compared in more complex media that also contained the phospholipid, lecithin. These included fasted state simulated intestinal fluid (FaSSIF) (a widely used medium for formulation testing which contains a single bile salt, sodium taurocholate), and media that contained several endogenous bile salts. Finally, the combined effects of a polymer, hydroxypropyl methyl cellulose acetate succinate, and the testing media on crystallization kinetics were evaluated to provide insights into supersaturation formulation design. Solution bile salt composition was found to significantly influence crystallization kinetics. However, the presence of the polymer increased induction times sufficiently that differences between media were minimized. This study suggests that when evaluating the crystallization kinetics of systems with a propensity to undergo supersaturation in vivo, attention should be paid to selecting biorelevant media
Shear induced instabilities in layered liquids
Motivated by the experimentally observed shear-induced destabilization and
reorientation of smectic A like systems, we consider an extended formulation of
smectic A hydrodynamics. We include both, the smectic layering (via the layer
displacement u and the layer normal p) and the director n of the underlying
nematic order in our macroscopic hydrodynamic description and allow both
directions to differ in non equilibrium situations. In an homeotropically
aligned sample the nematic director does couple to an applied simple shear,
whereas the smectic layering stays unchanged. This difference leads to a finite
(but usually small) angle between n and p, which we find to be equivalent to an
effective dilatation of the layers. This effective dilatation leads, above a
certain threshold, to an undulation instability of the layers. We generalize
our earlier approach [Rheol. Acta, vol.39(3), 15] and include the cross
couplings with the velocity field and the order parameters for orientational
and positional order and show how the order parameters interact with the
undulation instability. We explore the influence of various material parameters
on the instability. Comparing our results to recent experiments and molecular
dynamic simulations, we find a good qualitative agreement.Comment: 15 pages, 12 figures, accepted for publication in PR
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