1,878 research outputs found
Theoretical evidence for a dense fluid precursor to crystallization
We present classical density functional theory calculations of the free
energy landscape for fluids below their triple point as a function of density
and crystallinity. We find that for both a model globular protein and for a
simple atomic fluid modeled with a Lennard-Jones interaction, it is
free-energetically easier to crystallize by passing through a metastable dense
fluid in accord with the Ostwald rule of stages but in contrast to the
alternative of ordering and densifying at once as assumed in the classical
picture of crystallization.Comment: 4 pages, 3 figure
Mechanism for the stabilization of protein clusters above the solubility curve
Pan, Vekilov and Lubchenko[\textit{J. Phys. Chem. B}, 2010, \textbf{114},
7620] have proposed that dense stable protein clusters appearing in weak
protein solutions above the solubility curve are composed of protein oligomers.
The hypothesis is that a weak solution of oligomer species is unstable with
respect to condensation causing the formation of dense, oligomer-rich droplets
which are stabilized against growth by the monomer-oligomer reaction. Here, we
show that such a combination of processes can be understood using a simple
capillary model yielding analytic expressions for the cluster properties which
can be used to interpret experimental data. We also construct a microscopic
Dynamic Density Functional Theory model and show that it is consistent with the
predictions of the capillary model. The viability of the mechanism is thus
confirmed and it is shown how the radius of the stable clusters is related to
physically interesting quantities such as the monomer-oligomer rate constants
The effect of the range of interaction on the phase diagram of a globular protein
Thermodynamic perturbation theory is applied to the model of globular
proteins studied by ten Wolde and Frenkel (Science 277, pg. 1976) using
computer simulation. It is found that the reported phase diagrams are
accurately reproduced. The calculations show how the phase diagram can be tuned
as a function of the lengthscale of the potential.Comment: 20 pages, 5 figure
Experimental scaling law for the sub-critical transition to turbulence in plane Poiseuille flow
We present an experimental study of transition to turbulence in a plane
Poiseuille flow. Using a well-controlled perturbation, we analyse the flow
using extensive Particule Image Velocimetry and flow visualisation (using Laser
Induced Fluorescence) measurements and use the deformation of the mean velocity
profile as a criterion to characterize the state of the flow. From a large
parametric study, four different states are defined depending on the values of
the Reynolds number and the amplitude of the perturbation. We discuss the role
of coherent structures, like hairpin vortices, in the transition. We find that
the minimal amplitude of the perturbation triggering transition scales like
Re^-1
Dilaton constraints and LHC prospects
The Standard Model Higgs searches using the first 1-2 fb-1 of LHC data can be
used to put interesting constraints on new scalar particles other than the
Higgs. We investigate one such scenario in which electroweak symmetry is broken
via strongly coupled conformal dynamics. This scenario contains a neutral
scalar dilaton---the Goldstone boson associated with spontaneously broken scale
invariance---with a mass below the conformal symmetry breaking scale and
couplings to Standard Model particles similar (but not identical) to those of
the Standard Model Higgs boson. We translate the LEP and LHC Higgs limits to
constrain the dilaton mass and conformal breaking scale. The conformal breaking
scale f is constrained to be above 1 TeV for dilaton masses between 145 and 600
GeV, though it can be as low as 400 GeV for dilaton masses below 110 GeV. We
also show that (i) a dilaton chi with mass below 110 GeV and consistent with
the LEP constraints can appear in gg --> chi --> gamma gamma with a rate up to
~10 times the corresponding Standard Model Higgs rate, and (ii) a dilaton with
mass of several hundred GeV is much narrower than the corresponding Standard
Model Higgs, leading to improved search sensitivity in chi --> ZZ --> 4l.Comment: 15 pages, 12 figures, References added, Figure 10 modified, Figure 11
adde
Triplectic Quantization of W2 gravity
The role of one loop order corrections in the triplectic quantization is
discussed in the case of W2 theory. This model illustrates the presence of
anomalies and Wess Zumino terms in this quantization scheme where extended BRST
invariance is represented in a completely anticanonical form.Comment: 10 pages, no figure
Triplectic Gauge Fixing for N=1 Super Yang-Mills Theory
The Sp(2)-gauge fixing of N = 1 super-Yang-Mills theory is considered here.
We thereby apply the triplectic scheme, where two classes of gauge-fixing
bosons are introduced. The first one depends only on the gauge field, whereas
the second boson depends on this gauge field and also on a pair of Majorana
fermions. In this sense, we build up the BRST extended (BRST plus antiBRST)
algebras for the model, for which the nilpotency relations,
s^2_1=s^2_2=s_1s_2+s_2s_1=0, hold.Comment: 10 pages, no figures, latex forma
Local spin spirals in the Neel phase of La_{2-x}Sr_xCuO_4
Experimental observations of lightly doped La_{2-x}Sr_xCuO_4, x < 0.02,
revealed remarkable magnetic properties such as the incommensurate noncollinear
ordering (additional to the Neel ordering) and a tremendous doping dependence
of the uniform longitudinal susceptibility. We show that the spiral solution of
the t-t'-t''-J model obtained by taking into account the Coulomb trapping of
holes by Sr ions describes these puzzling data perfectly well. Our solution
firstly explains why the incommensurate structure is directed along the
orthorhombic b-axis, and secondly allows a numerical calculation of the
positions and shapes of the incommensurate neutron scattering peaks. Thirdly,
we calculate the doping dependence of the spin-wave gap, and lastly, we study
the longitudinal magnetic susceptibility and show that its doping dependence is
due to the noncollinearity of the spin spiral.Comment: 13 pages, 8 figure
Unconventional continuous phase transition in a three dimensional dimer model
Phase transitions occupy a central role in physics, due both to their
experimental ubiquity and their fundamental conceptual importance. The
explanation of universality at phase transitions was the great success of the
theory formulated by Ginzburg and Landau, and extended through the
renormalization group by Wilson. However, recent theoretical suggestions have
challenged this point of view in certain situations. In this Letter we report
the first large-scale simulations of a three-dimensional model proposed to be a
candidate for requiring a description beyond the Landau-Ginzburg-Wilson
framework: we study the phase transition from the dimer crystal to the Coulomb
phase in the cubic dimer model. Our numerical results strongly indicate that
the transition is continuous and are compatible with a tricritical universality
class, at variance with previous proposals.Comment: 4 pages, 3 figures; v2: minor changes, published versio
Towards Interpretable Deep Learning Models for Knowledge Tracing
As an important technique for modeling the knowledge states of learners, the
traditional knowledge tracing (KT) models have been widely used to support
intelligent tutoring systems and MOOC platforms. Driven by the fast
advancements of deep learning techniques, deep neural network has been recently
adopted to design new KT models for achieving better prediction performance.
However, the lack of interpretability of these models has painfully impeded
their practical applications, as their outputs and working mechanisms suffer
from the intransparent decision process and complex inner structures. We thus
propose to adopt the post-hoc method to tackle the interpretability issue for
deep learning based knowledge tracing (DLKT) models. Specifically, we focus on
applying the layer-wise relevance propagation (LRP) method to interpret
RNN-based DLKT model by backpropagating the relevance from the model's output
layer to its input layer. The experiment results show the feasibility using the
LRP method for interpreting the DLKT model's predictions, and partially
validate the computed relevance scores from both question level and concept
level. We believe it can be a solid step towards fully interpreting the DLKT
models and promote their practical applications in the education domain
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