4,183 research outputs found
Logistic Knowledge Tracing: A Constrained Framework for Learner Modeling
Adaptive learning technology solutions often use a learner model to trace
learning and make pedagogical decisions. The present research introduces a
formalized methodology for specifying learner models, Logistic Knowledge
Tracing (LKT), that consolidates many extant learner modeling methods. The
strength of LKT is the specification of a symbolic notation system for
alternative logistic regression models that is powerful enough to specify many
extant models in the literature and many new models. To demonstrate the
generality of LKT, we fit 12 models, some variants of well-known models and
some newly devised, to 6 learning technology datasets. The results indicated
that no single learner model was best in all cases, further justifying a broad
approach that considers multiple learner model features and the learning
context. The models presented here avoid student-level fixed parameters to
increase generalizability. We also introduce features to stand in for these
intercepts. We argue that to be maximally applicable, a learner model needs to
adapt to student differences, rather than needing to be pre-parameterized with
the level of each student's ability
Nuclear star cluster formation in energy-space
In a virialized stellar system, the mean-square velocity is a direct tracer
of the energy per unit mass of the system. Here, we exploit this to estimate
and compare root-mean-square velocities for a large sample of nuclear star
clusters and their host (late- or early-type) galaxies. Traditional
observables, such as the radial surface brightness and second-order velocity
moment profiles, are subject to short-term variations due to individual
episodes of matter infall and/or star formation. The total mass, energy and
angular momentum, on the other hand, are approximately conserved. Thus, the
total energy and angular momentum more directly probe the formation of galaxies
and their nuclear star clusters, by offering access to more fundamental
properties of the nuclear cluster-galaxy system than traditional observables.
We find that there is a strong correlation, in fact a near equality, between
the root-mean-square velocity of a nuclear star cluster and that of its host.
Thus, the energy per unit mass of a nuclear star cluster is always comparable
to that of its host galaxy. We interpret this as evidence that nuclear star
clusters do not form independently of their host galaxies, but rather that
their formation and subsequent evolution are coupled. We discuss how our
results can potentially be used to offer a clear and observationally testable
prediction to distinguish between the different nuclear star cluster formation
scenarios, and/or quantify their relative contributions.Comment: 12 pages, 3 figures, 4 tables; accepted for publication in MNRA
Solving Pure Yang Mills in 2+1 Dimensions
We analytically compute the spectrum of the spin zero glueballs in the planar
limit of pure Yang-Mills theory in 2+1 dimensions. The new ingredient is
provided by our computation of a new non-trivial form of the ground state
wave-functional. The mass spectrum of the theory is determined by the zeroes of
Bessel functions, and the agreement with large N lattice data is excellent.Comment: 4 page letter; version to appear in Physical Review Letter
Exact Superpotentials in Four Dimensions
Supersymmetric gauge theories in four dimensions can display interesting
non-perturbative phenomena. Although the superpotential dynamically generated
by these phenomena can be highly nontrivial, it can often be exactly
determined. We discuss some general techniques for analyzing the Wilsonian
superpotential and demonstrate them with simple but non-trivial examples.Comment: 32 pages, RU-94-2
Aging and Holography
Aging phenomena are examples of `non-equilibrium criticality' and can be
exemplified by systems with Galilean and scaling symmetries but no time
translation invariance. We realize aging holographically using a deformation of
a non-relativistic version of gauge/gravity duality. Correlation functions of
scalar operators are computed using holographic real-time techniques, and agree
with field theory expectations. At least in this setup, general aging phenomena
are reproduced holographically by complexifying the bulk space-time geometry,
even in Lorentzian signature.Comment: 1 pdf figur
The Standard Model on a D-brane
We present a consistent string theory model which reproduces the Standard
Model, consisting of a D3-brane at a simple orbifold singularity. We study some
simple features of the phenomenology of the model. We find that the scale of
stringy physics must be in the multi-TeV range. There are natural hierarchies
in the fermion spectrum and there are several possible experimental signatures
of the model.Comment: 8 pages Latex, 1 fig. v2: discussion improved, added new reference
Development of superconducting YBa2Cu3O(x) wires with low resistance electrical contacts
Materials exhibiting superconductivity above liquid nitrogen temperatures (77 K) will enable new applications of this phenomena. One of the first commercial applications of this technology will be superconducting magnets for medical imaging. However, a large number of aerospace applications of the high temperature superconducting materials have also been identified. These include magnetic suspension and balance of models in wind tunnels and resistanceless leads to anemometers. The development of superconducting wires fabricated from the ceramic materials is critical for these applications. The progress in application of a patented fiber process developed by Clemson University for the fabrication of superconducting wires is reviewed. The effect of particle size and heat treatment on the quality of materials is discussed. Recent advances made at Christopher Newport College in the development of micro-ohm resistance electrical contacts which are capable of carrying the highest reported direct current to this material is presented
Schwarzschild Black Holes from Matrix Theory
We consider Matrix theory compactified on T^3 and show that it correctly
describes the properties of Schwarzschild black holes in 7+1 dimensions,
including the energy-entropy relation, the Hawking temperature and the physical
size, up to numerical factors of order unity. The most economical description
involves setting the cut-off N in the discretized light-cone quantization to be
of order the black hole entropy. A crucial ingredient necessary for our work is
the recently proposed equation of state for 3+1 dimensional SYM theory with 16
supercharges. We give detailed arguments for the range of validity of this
equation following the methods of Horowitz and Polchinski.Comment: 9 pages, latex; minor typos correcte
Creation of Fundamental Strings by Crossing D-branes
We study the force balance between orthogonally positioned -brane and
-brane. The force due to graviton and dilaton exchange is repulsive in
this case. We identify the attractive force that balances this repulsion as due
to one-half of a fundamental string stretched between the branes. As the
-brane passes through the -brane, the connecting string changes
direction, which may be interpreted as creation of one fundamental string. We
show this directly from the structure of the Chern-Simons terms in the D-brane
effective actions. We also discuss the effect of string creation on the 0-brane
quantum mechanics in the type I' theory. The creation of a fundamental string
is related by U-duality to the creation of a 3-brane discussed by Hanany and
Witten. Both processes have a common origin in M-theory: as two M5-branes with
one common direction cross, a M2-brane stretched between them is created.Comment: 6 pages, Late
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