579,857 research outputs found
Performance Evaluation with Stochastic Discount Factors
We study the use of stochastic discount factor (SDF) models in evaluating the investment performance of portfolio managers. By constructing artificial mutual funds with known levels of investment ability, we evaluate a large set of SDF models. We find that the measures of performance are not highly sensitive to the SDF model, and that most of the models have a mild negative bias when performance is neutral. We use the models to evaluate a sample of U.S. equity mutual funds. Adjusting for the observed bias, we find that the average mutual fund has enough ability to cover its transactions costs. Extreme funds are more likely to have good rather than poor risk adjusted performance. Our analysis also reveals a number of implementation issues relevant to other applications of SDF models.
Geometric phase and quantum phase transition in an inhomogeneous periodic XY spin-1/2 model
The notion of geometric phase has been recently introduced to analyze the
quantum phase transitions of many-body systems from the geometrical
perspective. In this work, we study the geometric phase of the ground state for
an inhomogeneous period-two anisotropic XY model in a transverse field. This
model encompasses a group of familiar spin models as its special cases and
shows a richer critical behavior. The exact solution is obtained by mapping on
a fermionic system through the Jordan-Wigner transformation and constructing
the relevant canonical transformation to realize the diagonalization of the
Hamiltonian coupled in the -space. The results show that there may exist
more than one quantum phase transition point at some parameter regions and
these transition points correspond to the divergence or extremum properties of
the Berry curvature.Comment: 6 pages, 3 figures. As a backup of a previous work and some typos in
the published version are fixe
Post-Newtonian SPH calculations of binary neutron star coalescence. I. Method and first results
We present the first results from our Post-Newtonian (PN) Smoothed Particle
Hydrodynamics (SPH) code, which has been used to study the coalescence of
binary neutron star (NS) systems. The Lagrangian particle-based code
incorporates consistently all lowest-order (1PN) relativistic effects, as well
as gravitational radiation reaction, the lowest-order dissipative term in
general relativity. We test our code on sequences of single NS models of
varying compactness, and we discuss ways to make PN simulations more relevant
to realistic NS models. We also present a PN SPH relaxation procedure for
constructing equilibrium models of synchronized binaries, and we use these
equilibrium models as initial conditions for our dynamical calculations of
binary coalescence. Though unphysical, since tidal synchronization is not
expected in NS binaries, these initial conditions allow us to compare our PN
work with previous Newtonian results.
We compare calculations with and without 1PN effects, for NS with stiff
equations of state, modeled as polytropes with . We find that 1PN
effects can play a major role in the coalescence, accelerating the final
inspiral and causing a significant misalignment in the binary just prior to
final merging. In addition, the character of the gravitational wave signal is
altered dramatically, showing strong modulation of the exponentially decaying
waveform near the end of the merger. We also discuss briefly the implications
of our results for models of gamma-ray bursts at cosmological distances.Comment: RevTeX, 37 pages, 17 figures, to appear in Phys. Rev. D, minor
corrections onl
Multi-layer local optima networks for the analysis of advanced local search-based algorithms
A Local Optima Network (LON) is a graph model that compresses the fitness
landscape of a particular combinatorial optimization problem based on a
specific neighborhood operator and a local search algorithm. Determining which
and how landscape features affect the effectiveness of search algorithms is
relevant for both predicting their performance and improving the design
process. This paper proposes the concept of multi-layer LONs as well as a
methodology to explore these models aiming at extracting metrics for fitness
landscape analysis. Constructing such models, extracting and analyzing their
metrics are the preliminary steps into the direction of extending the study on
single neighborhood operator heuristics to more sophisticated ones that use
multiple operators. Therefore, in the present paper we investigate a twolayer
LON obtained from instances of a combinatorial problem using bitflip and swap
operators. First, we enumerate instances of NK-landscape model and use the hill
climbing heuristic to build the corresponding LONs. Then, using LON metrics, we
analyze how efficiently the search might be when combining both strategies. The
experiments show promising results and demonstrate the ability of multi-layer
LONs to provide useful information that could be used for in metaheuristics
based on multiple operators such as Variable Neighborhood Search.Comment: Accepted in GECCO202
Leading Two-loop corrections to the mass of Higgs boson in the High scale Dirac gaugino supersymmetry
Precision measurements of the Higgs mass have become a powerful constraint on
models of physics beyond the standard model. We revisit supersymmetric models
with Dirac gauginos and study the contributions to the Higgs mass. We calculate
the leading two-loop corrections to the SM-like Higgs mass by constructing a
series of EFTs and iteratively integrating out heavy particles. We then apply
these calculations to a variety of scenarios, including a simple Dirac gluino,
and split Dirac models of supersymmetry. We present the detailed formulae for
threshold corrections and compare with previous results, where available. In
general, the contributions are small, but the additional precision allows us to
make more concrete statements about the relevant scales in Dirac SUSY models.Comment: 27 pages, 9 figure
Continuous and Discrete (Classical) Heisenberg Spin Chain Revised
Most of the work done in the past on the integrability structure of the
Classical Heisenberg Spin Chain (CHSC) has been devoted to studying the
case, both at the continuous and at the discrete level. In this paper we
address the problem of constructing integrable generalized ''Spin Chains''
models, where the relevant field variable is represented by a
matrix whose eigenvalues are the roots of unity. To the best of our
knowledge, such an extension has never been systematically pursued. In this
paper, at first we obtain the continuous generalization of the CHSC
through the reduction technique for Poisson-Nijenhuis manifolds, and exhibit
some explicit, and hopefully interesting, examples for and matrices; then, we discuss the much more difficult discrete case, where a
few partial new results are derived and a conjecture is made for the general
case.Comment: This is a contribution to the Proc. of workshop on Geometric Aspects
of Integrable Systems (July 17-19, 2006; Coimbra, Portugal), published in
SIGMA (Symmetry, Integrability and Geometry: Methods and Applications) at
http://www.emis.de/journals/SIGMA
A Questioning Agent for Literary Discussion
Developing a compelling and cohesive thesis for analytical writing can be a daunting task, even for those who have produced many written works, and finding others to engage with in literary discussion can be equally challenging. In this paper, we describe our solution: Questioner, a discussion tool that engages users in conversation about an academic topic of their choosing for the purpose of collecting thoughts on a subject and constructing an argument. This system will ask informed questions that prompt further discussion about the topic and provide a discussion report after the conversation has ended. We found that our system is effective in providing users with unique questions and excerpts that are relevant, significant, and engaging. Such a discussion tool can be used by writers building theses, students looking for study tools, and instructors who want to create individualized in-class discussions. Once more data is gathered, efficient and accurate machine learning models can be used to further improve the quality of question and excerpt recommendations. Co-creative discussion tools like Questioner are useful in assisting users in developing critical analyses of written works, helping to maximize human creativity
Application of Multilabel Learning Using the Relevant Feature for Each Label in Chronic Gastritis Syndrome Diagnosis
Background. In Traditional Chinese Medicine (TCM), most of the algorithms are used to solve problems of syndrome diagnosis that only focus on one syndrome, that is, single label learning. However, in clinical practice, patients may simultaneously have more than one syndrome, which has its own symptoms (signs). Methods. We employed a multilabel learning using the relevant feature for each label (REAL) algorithm to construct a syndrome diagnostic model for chronic gastritis (CG) in TCM. REAL combines feature selection methods to select the significant symptoms (signs) of CG. The method was tested on 919 patients using the standard scale. Results. The highest prediction accuracy was achieved when 20 features were selected. The features selected with the information gain were more consistent with the TCM theory. The lowest average accuracy was 54% using multi-label neural networks (BP-MLL), whereas the highest was 82% using REAL for constructing the diagnostic model. For coverage, hamming loss, and ranking loss, the values obtained using the REAL algorithm were the lowest at 0.160, 0.142, and 0.177, respectively. Conclusion. REAL extracts the relevant symptoms (signs) for each syndrome and improves its recognition accuracy. Moreover, the studies will provide a reference for constructing syndrome diagnostic models and guide clinical practice
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