10,284 research outputs found
The academic value of internships: benefits across disciplines and student backgrounds
While student benefits from internship experience have been frequently documented in research, the emphasis has been on internship effects on employment and career indicators. This work is concerned with effects on academic outcomes and focuses on the robustness of such effects across academic disciplines as well as for different achievement levels of students, student gender, and ethnicity. We present findings from a longitudinal sample (n > 15,000) that covers an extensive range of subjects and disciplines for large Undergraduate cohorts. Main effects and interactions for student background characteristics were investigated showing stable academic benefits for advantaged and disadvantaged students. Further, using ordinal logistic multi-level modelling, we explored the impact on the probability of attaining a higher degree classification for different student scenarios, thus illustrating the practical significance of these internship effects. Effects are less likely to stem from maturation or self-selection. Findings are therefore discussed against a background of motivational approaches suitable to integrate both direct and indirect paths from internship experience to academic outcomes to career indicators
Monte Carlo Simulation of Long Chain Polymer Melts: Crossover from Rouse to Reptation Dynamics
We present data of Monte Carlo simulations for monodisperse linear polymer
chains in dense melts with degrees of polymerization between N=16 and N=512.
The aim of this study is to investigate the crossover from Rouse-like dynamics
for short chains to reptation-like dynamics for long chains. To address this
problem we calculate a variety of different quantities: standard mean-square
displacements of inner monomers and of the chain's center of mass, the recently
proposed cubic invariant, persistence of bond-vector orientation with time, and
the auto-correlation functions of the bond vector, the end-to-end vector and
the Rouse modes. This analysis reveals that the crossover from non- to
entangled dynamics is very protracted. Only the largest chain length N=512,
which is about 13 times larger than the entanglement length, shows evidence for
reptation.Comment: 38 pages of REVTeX, 14 PostScript figure
A Multicanonical Algorithm and the Surface Free Energy in SU(3) Pure Gauge Theory
We present a multicanonical algorithm for the SU(3) pure gauge theory at the
deconfinement phase transition. We measure the tunneling times for lattices of
size L^3x2 for L=8,10, and 12. In contrast to the canonical algorithm the
tunneling time increases only moderately with L. Finally, we determine the
interfacial free energy applying the multicanonical algorithm.Comment: 6 pages, HLRZ-92-3
Depletion induced isotropic-isotropic phase separation in suspensions of rod-like colloids
When non-adsorbing polymers are added to an isotropic suspension of rod-like
colloids, the colloids effectively attract each other via depletion forces. We
performed Monte Carlo simulations to study the phase diagram of such
rod-polymer mixture. The colloidal rods were modelled as hard spherocylinders;
the polymers were described as spheres of the same diameter as the rods. The
polymers may overlap with no energy cost, while overlap of polymers and rods is
forbidden.
Large amounts of depletant cause phase separation of the mixture. We
estimated the phase boundaries of isotropic-isotropic coexistence both, in the
bulk and in confinement. To determine the phase boundaries we applied the grand
canonical ensemble using successive umbrella sampling [J. Chem. Phys. 120,
10925 (2004)], and we performed a finite-size scaling analysis to estimate the
location of the critical point. The results are compared with predictions of
the free volume theory developed by Lekkerkerker and Stroobants [Nuovo Cimento
D 16, 949 (1994)]. We also give estimates for the interfacial tension between
the coexisting isotropic phases and analyse its power-law behaviour on approach
of the critical point
Symmetric Diblock Copolymers in Thin Films (I): Phase stability in Self-Consistent Field Calculations and Monte Carlo Simulations
We investigate the phase behavior of symmetric AB diblock copolymers confined
into a thin film. The film boundaries are parallel, impenetrable and attract
the A component of the diblock copolymer. Using a self-consistent field
technique [M.W. Matsen, J.Chem.Phys. {\bf 106}, 7781 (1997)], we study the
ordered phases as a function of incompatibility and film thickness in
the framework of the Gaussian chain model. For large film thickness and small
incompatibility, we find first order transitions between phases with different
number of lamellae which are parallel oriented to the film boundaries. At high
incompatibility or small film thickness, transitions between parallel oriented
and perpendicular oriented lamellae occur. We compare the self-consistent field
calculations to Monte Carlo simulations of the bond fluctuation model for chain
length N=32. In the simulations we quench several systems from to
and monitor the morphology into which the diblock copolymers
assemble. Three film thicknesses are investigated, corresponding to parallel
oriented lamellae with 2 and 4 interfaces and a perpendicular oriented
morphology. Good agreement between self-consistent field calculations and Monte
Carlo simulations is found.Comment: to appear in J.Chem.Phy
Kinetics of Phase Separation in Thin Films: Simulations for the Diffusive Case
We study the diffusion-driven kinetics of phase separation of a symmetric
binary mixture (AB), confined in a thin-film geometry between two parallel
walls. We consider cases where (a) both walls preferentially attract the same
component (A), and (b) one wall attracts A and the other wall attracts B (with
the same strength). We focus on the interplay of phase separation and wetting
at the walls, which is referred to as {\it surface-directed spinodal
decomposition} (SDSD). The formation of SDSD waves at the two surfaces, with
wave-vectors oriented perpendicular to them, often results in a metastable
layered state (also referred to as ``stratified morphology''). This state is
reminiscent of the situation where the thin film is still in the one-phase
region but the surfaces are completely wet, and hence coated with thick wetting
layers. This metastable state decays by spinodal fluctuations and crosses over
to an asymptotic growth regime characterized by the lateral coarsening of
pancake-like domains. These pancakes may or may not be coated by precursors of
wetting layers. We use Langevin simulations to study this crossover and the
growth kinetics in the asymptotic coarsening regime.Comment: 39 pages, 19 figures, submitted to Phys.Rev.
The topological glass in ring polymers
We study the dynamics of concentrated, long, semi-flexible, unknotted and unlinked ring polymers embedded in a gel by Monte Carlo simulation of a coarse-grained model. This involves the ansatz that the rings compactify into a duplex structure where they can be modelled as linear polymers. The classical polymer glass transition involves a rapid loss of microscopic freedom within the polymer molecule as the temperature is reduced toward Tg. Here we are interested in temperatures well above Tg where the polymers retain high microscopic mobility. We analyse the slowing of stress relaxation originating from inter-ring penetrations (threadings). For long polymers an extended network of quasi-topological penetrations forms. The longest relaxation time appears to depend exponentially on the ring polymer contour length, reminiscent of the usual exponential slowing (e.g., with temperature) in classical glasses. Finally, we discuss how this represents a universality class for glassy dynamics
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