42,862 research outputs found
Cached Sufficient Statistics for Efficient Machine Learning with Large Datasets
This paper introduces new algorithms and data structures for quick counting
for machine learning datasets. We focus on the counting task of constructing
contingency tables, but our approach is also applicable to counting the number
of records in a dataset that match conjunctive queries. Subject to certain
assumptions, the costs of these operations can be shown to be independent of
the number of records in the dataset and loglinear in the number of non-zero
entries in the contingency table. We provide a very sparse data structure, the
ADtree, to minimize memory use. We provide analytical worst-case bounds for
this structure for several models of data distribution. We empirically
demonstrate that tractably-sized data structures can be produced for large
real-world datasets by (a) using a sparse tree structure that never allocates
memory for counts of zero, (b) never allocating memory for counts that can be
deduced from other counts, and (c) not bothering to expand the tree fully near
its leaves. We show how the ADtree can be used to accelerate Bayes net
structure finding algorithms, rule learning algorithms, and feature selection
algorithms, and we provide a number of empirical results comparing ADtree
methods against traditional direct counting approaches. We also discuss the
possible uses of ADtrees in other machine learning methods, and discuss the
merits of ADtrees in comparison with alternative representations such as
kd-trees, R-trees and Frequent Sets.Comment: See http://www.jair.org/ for any accompanying file
ACTIVITIES OF NURSE PRACTITIONERS AS IDENTIFIED BY MEDICAL DIRECTORS OF UNIVERSITY STUDENT HEALTH SERVICES
University health services play a very important role in the general health, performance, and well-being of the students, the university itself, and the community. As stated by the American College Health Association, the goal of a university health service is to promote and maintain those conditions which will permit and encourage each individual to realize optimum physical, emotional, intellectual, and social well-being.
University students have special health care needs such as drug and alcohol abuses, emotional problems, and gynecological, sexual, and contraceptive problems. It is the goal of the health professionals involved with students to meet those needs. Because of these special health care needs, the increasing number of university students, and the present problems associated with medical care and medical distribution, nurse practitioners have become involved in some university percent of these nurse practitioners are in college health services.3 It was believed by the investigators of this study that nurse practitioners could play a special role in this area of health care.
As student health medical directors are key persons in defining nurse practitioner activities, the purpose of this study was to determine the activities the directors identified as appropriate for nurse practitioners to perform in a university health care setting. The type of activities identified by them may be crucial in the decision to utilize nurse practitioners in the university student health setting
Conservation laws in the quantum Hall Liouvillian theory and its generalizations
It is known that the localization length scaling of noninteracting electrons
near the quantum Hall plateau transition can be described in a theory of the
bosonic density operators, with no reference to the underlying fermions. The
resulting ``Liouvillian'' theory has a global supersymmetry as well as
a hierarchy of geometric conservation laws related to the noncommutative
geometry of the lowest Landau level (LLL). Approximations to the Liouvillian
theory contain quite different physics from standard approximations to the
underlying fermionic theory. Mean-field and large-N generalizations of the
Liouvillian are shown to describe problems of noninteracting bosons that
enlarge the supersymmetry to or .
These noninteracting bosonic problems are studied numerically for by Monte Carlo simulation and compared to the original N=1 Liouvillian
theory. The generalizations preserve the first two of the hierarchy of
geometric conservation laws, leading to logarithmic corrections at order 1/N to
the diffusive large-N limit, but do not preserve the remaining conservation
laws. The emergence of nontrivial scaling at the plateau transition, in the
Liouvillian approach, is shown to depend sensitively on the unusual geometry of
Landau levels.Comment: 13 page
Notes on High Energy Limit of Bosonic Closed String Scattering Amplitudes
We study bosonic closed string scattering amplitudes in the high-energy
limit. We find that the methods of decoupling of high-energy zero-norm states
and the high-energy Virasoro constraints, which were adopted in the previous
works to calculate the ratios among high-energy open string scattering
amplitudes of different string states, persist for the case of closed string.
However, we clarify the previous saddle-point calculation for high-energy open
string scattering amplitudes and claim that only (t,u) channel of the
amplitudes is suitable for saddle-point calculation. We then discuss three
evidences to show that saddle-point calculation for high-energy closed string
scattering amplitudes is not reliable. By using the relation of tree-level
closed and open string scattering amplitudes of Kawai, Lewellen and Tye (KLT),
we calculate the high-energy closed string scattering amplitudes for arbitrary
mass levels. For the case of high-energy closed string four-tachyon amplitude,
our result differs from the previous one of Gross and Mende, which is NOT
consistent with KLT formula, by an oscillating factor.Comment: 14 pages, no figure. Equations and Conclusion adde
High-energy String Scatterings of Compactified Open String
We calculate high-energy massive string scattering amplitudes of compactified
open string. We derive infinite linear relations, or stringy symmetries, among
soft high-energy string scattering amplitudes of different string states in the
Gross kinematic regime (GR). In addition, we systematically analyze all hard
power-law and soft exponential fall-off regimes of high-energy compactified
open string scatterings by comparing the scatterings with their 26D
noncompactified counterparts. In particular, we discover the existence of a
power-law regime at fixed angle and an exponential fall-off regime at small
angle for high-energy compactified open string scatterings. The linear
relations break down as expected in all power-law regimes. The analysis can be
extended to the high-energy scatterings of the compactified closed string,
which corrects and extends the previous results in [28] .Comment: 16 pages, 1 table. v2:typos corrected,references added. v3,v4:Eq.(26)
typos. Eq.(27) correcte
Stringy Symmetries and Their High-energy Limits
We derive stringy symmetries with conserved charges of arbitrarily high spins
from the decoupling of two types of zero-norm states in the old covariant first
quantized (OCFQ) spectrum of open bosonic string. These symmetries are valid to
all energy and all loop orders in string perturbation theory. The high-energy
limit of these stringy symmetries can then be used to fix the proportionality
constants between scattering amplitudes of different string states
algebraically without referring to Gross and Mende's saddle point calculation
of high-energy string-loop amplitudes. These proportionality constants are, as
conjectured by Gross, independent of the scattering angle and the order of
string perturbation theory. However, we also discover some new nonzero
components of high-energy amplitudes not found previously by Gross and Manes.
These components are essential to preserve massive gauge invariances or
decouple massive zero-norm states of string theory. A set of massive scattering
amplitudes and their high energy limit are calculated explicitly to justify our
results.Comment: 10 pages. A corrected version of hep-th/0303012. Final version to
appear in Phys. Lett.
Zero-norm states and High-energy Symmetries of String Theory
We derive stringy Ward identities from the decoupling of two types of
zero-norm states in the old covariant first quantized (OCFQ) spectrum of open
bosonic string. These Ward identities are valid to all energy and all loop
orders in string perturbation theory. The high-energy limit of these stringy
Ward identities can then be used to fix the proportionality constants between
scattering amplitudes of different string states algebraically without
referring to Gross and Mende's saddle point calculation of high-energy
string-loop amplitudes. As examples, all Ward identities for the mass level 4
and 6 are derived, their high-energy limits are calculated and the
proportionality constants between scattering amplitudes of different string
states are determined. In addition to those identified before, we discover some
new nonzero components of high-energy amplitudes not found previously by Gross
and Manes. These components are essential to preserve massive gauge invariances
or decouple massive zero-norm states of string theory. A set of massive
scattering amplitudes and their high energy limits are calculated explicitly
for each mass level to justify our results
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