376 research outputs found
Covariant Field Equations, Gauge Fields and Conservation Laws from Yang-Mills Matrix Models
The effective geometry and the gravitational coupling of nonabelian gauge and
scalar fields on generic NC branes in Yang-Mills matrix models is determined.
Covariant field equations are derived from the basic matrix equations of
motions, known as Yang-Mills algebra. Remarkably, the equations of motion for
the Poisson structure and for the nonabelian gauge fields follow from a matrix
Noether theorem, and are therefore protected from quantum corrections. This
provides a transparent derivation and generalization of the effective action
governing the SU(n) gauge fields obtained in [1], including the would-be
topological term. In particular, the IKKT matrix model is capable of describing
4-dimensional NC space-times with a general effective metric. Metric
deformations of flat Moyal-Weyl space are briefly discussed.Comment: 31 pages. V2: minor corrections, references adde
Mass Parameterizations and Predictions of Isotopic Observables
We discuss the accuracy of mass models for extrapolating to very asymmetric
nuclei and the impact of such extrapolations on the predictions of isotopic
observables in multifragmentation. We obtain improved mass predictions by
incorporating measured masses and extrapolating to unmeasured masses with a
mass formula that includes surface symmetry and Coulomb terms. We find that
using accurate masses has a significant impact on the predicted isotopic
observables.Comment: 12 pages, 4 figure
Comparisons of Statistical Multifragmentation and Evaporation Models for Heavy Ion Collisions
The results from ten statistical multifragmentation models have been compared
with each other using selected experimental observables. Even though details in
any single observable may differ, the general trends among models are similar.
Thus these models and similar ones are very good in providing important physics
insights especially for general properties of the primary fragments and the
multifragmentation process. Mean values and ratios of observables are also less
sensitive to individual differences in the models. In addition to
multifragmentation models, we have compared results from five commonly used
evaporation codes. The fluctuations in isotope yield ratios are found to be a
good indicator to evaluate the sequential decay implementation in the code. The
systems and the observables studied here can be used as benchmarks for the
development of statistical multifragmentation models and evaporation codes.Comment: To appear on Euorpean Physics Journal A as part of the Topical Volume
"Dynamics and Thermodynamics with Nuclear Degrees of Freedo
A Novel Culture-Dependent Gesture Selection System for a Humanoid Robot Performing Greeting Interaction
In human-robot interaction, it is important for the robots to adapt to
our ways of communication. As humans, rules of non-verbal communication,
including greetings, change depending on our culture. Social robots should
adapt to these specific differences in order to communicate effectively, as a correct
way of approaching often results into better acceptance of the robot. In this
study, a novel greeting gesture selection system is presented and an experiment
is run using the robot ARMAR-IIIb. The robot performs greeting gestures appropriate
to Japanese culture; after interacting with German participants, the selection
should become appropriate to German culture. Results show that the
mapping of gesture selection evolves successfully
Proton Decay in a Minimal SUSY SO(10) Model for Neutrino Mixings
A minimal renormalizable SUSY SO(10) model with B-L symmetry broken by {\bf
126} Higgs field has recently been shown to predict all neutrino mixings and
the ratio in agreement with observations.
Unlike models where B-L is broken by {\bf 16} Higgs, this model guarantees
automatic R-parity conservation and hence a stable dark matter as well as the
absence of dim=4 baryon violating operator without any additional symmetry
assumptions. In this paper, we discuss the predictions of the model for proton
decay induced at the GUT scale. We scan over the parameter space of the model
allowed by neutrino data and find upper bounds on the partial lifetime for the
modes yrs and yrs for the
average squark mass of a TeV and wino mass of 200 GeV, when the parameters
satisfy the present lower limits on mode. These
results can be used to test the model.Comment: 17 pages, 6 figures; Minor corrections with improved predictions;
references update
Stability of Black Holes and Black Branes
We establish a new criterion for the dynamical stability of black holes in spacetime dimensions in general relativity with respect to axisymmetric
perturbations: Dynamical stability is equivalent to the positivity of the
canonical energy, \E, on a subspace, , of linearized solutions
that have vanishing linearized ADM mass, momentum, and angular momentum at
infinity and satisfy certain gauge conditions at the horizon. This is shown by
proving that---apart from pure gauge perturbations and perturbations towards
other stationary black holes---\E is nondegenerate on and that,
for axisymmetric perturbations, \E has positive flux properties at both
infinity and the horizon. We further show that \E is related to the second
order variations of mass, angular momentum, and horizon area by \E = \delta^2
M - \sum_A \Omega_A \delta^2 J_A - \frac{\kappa}{8\pi} \delta^2 A, thereby
establishing a close connection between dynamical stability and thermodynamic
stability. Thermodynamic instability of a family of black holes need not imply
dynamical instability because the perturbations towards other members of the
family will not, in general, have vanishing linearized ADM mass and/or angular
momentum. However, we prove that for any black brane corresponding to a
thermodynamically unstable black hole, sufficiently long wavelength
perturbations can be found with \E < 0 and vanishing linearized ADM
quantities. Thus, all black branes corresponding to thermodynmically unstable
black holes are dynamically unstable, as conjectured by Gubser and Mitra. We
also prove that positivity of \E on is equivalent to the
satisfaction of a "local Penrose inequality," thus showing that satisfaction of
this local Penrose inequality is necessary and sufficient for dynamical
stability.Comment: 54 pages, Latex, 2 figures, v2: Anzatz for momentum in proof of
Gubser-Mitra conjecture corrected; factor of 2 in symplectic form corrected;
several typos in formulas corrected; v3: revised argument concerning horizon
gauge condition on p. 10; typos corrected and several minor changes;
reference added; v4: formula (86) for \E corrected, footnote adde
Understanding drivers of domestic public expenditure on reproductive, maternal, neonatal and child health in Peru at district level:an ecological study
Background Peru has increased substantially its domestic public expenditure in maternal and child health. Peruvian departments are heterogeneous in contextual and geographic factors, underlining the importance of disaggregated expenditure analysis up to the district level. We aimed to assess possible district level factors influencing public expenditure on reproductive, maternal, neonatal and child health (RMNCH) in Peru. Methods We performed an ecological study in 24 departments, with specific RMNCH expenditure indicators as outcomes, and covariates of different hierarchical dimensions as predictors. To account for the influence of variables included in the different dimensions over time and across departments, we chose a stepwise multilevel mixed-effects regression model, with department-year as the unit of analysis. Results Public expenditure increased in all departments, particularly for maternal-neonatal and child health activities, with a different pace across departments. The multilevel analysis did not reveal consistently influential factors, except for previous year expenditure on reproductive and maternal-neonatal health. Our findings may be explained by a combination of inertial expenditure, a results-based budgeting approach to increase expenditure efficiency and effectiveness, and by a mixed-effects decentralization process. Sample size, interactions and collinearity cannot be ruled out completely. Conclusions Public district-level RMNCH expenditure has increased remarkably in Peru. Evidence on underlying factors influencing such trends warrants further research, most likely through a combination of quantitative and qualitative approaches
Numerical evolutions of nonlinear r-modes in neutron stars
Nonlinear evolution of the gravitational radiation (GR) driven instability in
the r-modes of neutron stars is studied by full numerical 3D hydrodynamical
simulations. The growth of the r-mode instability is found to be limited by the
formation of shocks and breaking waves when the dimensionless amplitude of the
mode grows to about three in value. This maximum mode amplitude is shown by
numerical tests to be rather insensitive to the strength of the GR driving
force. Upper limits on the strengths of possible nonlinear mode--mode coupling
are inferred. Previously unpublished details of the numerical techniques used
are presented, and the results of numerous calibration runs are discussed.Comment: RevTeX 4, 17 pages, 26 figures. Slightly revised. To be published in
PRD (April 2002
MOVICAB-IDS: Visual Analysis of Network Traffic Data Streams for Intrusion Detection
MOVICAB-IDS enables the more interesting projections of a massive traffic data set to be analysed, thereby providing an overview of any possible anomalous situations taking place on a computer network. This IDS responds to the challenges presented by traffic volume and diversity. It is a connectionist agent-based model extended by means of a functional and mobile visualization interface. The IDS is designed to be more flexible, accessible and portable by running on a great variety of applications, including small mobile ones such as PDA’s, mobile phones or embedded devices. Furthermore, its effectiveness has been demonstrated in different tests
IDS Based on Bio-inspired Models
Unsupervised projection approaches can support Intrusion Detection Systems for computer network security. The involved technologies assist a network manager in detecting anomalies and potential threats by an intuitive display of the progression of network traffic. Projection methods operate as smart compression tools and map raw, high-dimensional traffic data into 2-D or 3-D spaces for subsequent graphical display. The paper compares three projection methods, namely, Cooperative Maximum Likelihood Hebbian Learning, Auto-Associative Back-Propagation networks and Principal Component Analysis. Empirical tests on anomalous situations related to the Simple Network Management Protocol (SNMP) confirm the validity of the projection-based approach. One of these anomalous situations (the SNMP community search) is faced by these projection models for the first time. This work also highlights the importance of the time-information dependence in the identification of anomalous situations in the case of the applied methods
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