1,571 research outputs found
Consistent SDNs through Network State Fuzzing
The conventional wisdom is that a software-defined network (SDN) operates under the premise that the logically centralized control plane has an accurate representation of the actual data plane state. Nevertheless, bugs, misconfigurations, faults or attacks can introduce inconsistencies that undermine correct operation. Previous work in this area, however, lacks a holistic methodology to tackle this problem and thus, addresses only certain parts of the problem. Yet, the consistency of the overall system is only as good as its least consistent part. Motivated by an analogy of network consistency checking with program testing, we propose to add active probe-based network state fuzzing to our consistency check repertoire. Hereby, our system, PAZZ, combines production traffic with active probes to continuously test if the actual forwarding path and decision elements (on the data plane) correspond to the expected ones (on the control plane). Our insight is that active traffic covers the inconsistency cases beyond the ones identified by passive traffic. PAZZ prototype was built and evaluated on topologies of varying scale and complexity. Our results show that PAZZ requires minimal network resources to detect persistent data plane faults through fuzzing and localize them quickly
Bond breaking with auxiliary-field quantum Monte Carlo
Bond stretching mimics different levels of electron correlation and provides
a challenging testbed for approximate many-body computational methods. Using
the recently developed phaseless auxiliary-field quantum Monte Carlo (AF QMC)
method, we examine bond stretching in the well-studied molecules BH and N,
and in the H chain. To control the sign/phase problem, the phaseless AF
QMC method constrains the paths in the auxiliary-field path integrals with an
approximate phase condition that depends on a trial wave function. With single
Slater determinants from unrestricted Hartree-Fock (UHF) as trial wave
function, the phaseless AF QMC method generally gives better overall accuracy
and a more uniform behavior than the coupled cluster CCSD(T) method in mapping
the potential-energy curve. In both BH and N, we also study the use of
multiple-determinant trial wave functions from multi-configuration
self-consistent-field (MCSCF) calculations. The increase in computational cost
versus the gain in statistical and systematic accuracy are examined. With such
trial wave functions, excellent results are obtained across the entire region
between equilibrium and the dissociation limit.Comment: 8 pages, 3 figures and 3 tables. Submitted to JC
On Black Attractors in 8D and Heterotic/Type IIA Duality
Motivated by the study of black attractors in 8D supergravity with 16
supersymmetries, we use the field theory approach and 8D supersymmetry with non
trivial central charges to shed light on the exact duality between heterotic
string on T^2 and type IIA on real connected and compact surfaces {\Sigma}2. We
investigate the two constraints that should be obeyed by {\Sigma}2 and give
their solutions in terms of intersecting 2-cycles as well their classification
using Dynkin diagrams of affine Kac-Moody algebras. It is shown as well that
the moduli space of these dual theories is given by
SO(1,1)x((SO(2,r+2))/(SO(2)xSO(r+2))) where r stands for the rank of the gauge
symmetry G_{r} of the 10D heterotic string on T^2. The remarkable cases
r=-2,-1,0 as well as other features are also investigated.Comment: LaTex, 18 pages, 2 figures, To appear in JHE
Conservative management of a high output enterocutaneous fistula in abdominal tuberculosis
A 25-year-old lady with a high-output, tuberculous, entero-cutaneous fi stula was managed successfully by conservative means in a teaching hospital in Nairobi, Kenya
Classification of N=2 supersymmetric CFT_{4}s: Indefinite Series
Using geometric engineering method of 4D quiver gauge
theories and results on the classification of Kac-Moody (KM) algebras, we show
on explicit examples that there exist three sectors of infrared
CFTs. Since the geometric engineering of these CFTs involve type II
strings on K3 fibered CY3 singularities, we conjecture the existence of three
kinds of singular complex surfaces containing, in addition to the two standard
classes, a third indefinite set. To illustrate this hypothesis, we give
explicit examples of K3 surfaces with H and E hyperbolic
singularities. We also derive a hierarchy of indefinite complex algebraic
geometries based on affine and T algebras going beyond the
hyperbolic subset. Such hierarchical surfaces have a remarkable signature that
is manifested by the presence of poles.Comment: 12 pages, 2 figure
Fractional Statistics in terms of the r-Generalized Fibonacci Sequences
We develop the basis of the two dimensional generalized quantum statistical
systems by using results on -generalized Fibonacci sequences. According to
the spin value of the 2d-quasiparticles, we distinguish four classes of
quantum statistical systems indexed by , ,
and . For quantum gases of quasiparticles
with , , we show that the statistical weights densities
are given by the integer hierarchies of Fibonacci sequences. This is a
remarkable result which envelopes naturally the Fermi and Bose statistics and
may be thought of as an alternative way to the Haldane interpolating
statistical method.Comment: Late
Comparing Strategies to Prevent Stroke and Ischemic Heart Disease in the Tunisian Population: Markov Modeling Approach Using a Comprehensive Sensitivity Analysis Algorithm.
Background. Mathematical models offer the potential to analyze and compare the effectiveness of very different interventions to prevent future cardiovascular disease. We developed a comprehensive Markov model to assess the impact of three interventions to reduce ischemic heart diseases (IHD) and stroke deaths: (i) improved medical treatments in acute phase, (ii) secondary prevention by increasing the uptake of statins, (iii) primary prevention using health promotion to reduce dietary salt consumption. Methods. We developed and validated a Markov model for the Tunisian population aged 35–94 years old over a 20-year time horizon. We compared the impact of specific treatments for stroke, lifestyle, and primary prevention on both IHD and stroke deaths. We then undertook extensive sensitivity analyses using both a probabilistic multivariate approach and simple linear regression (metamodeling). Results. The model forecast a dramatic mortality rise, with 111,134 IHD and stroke deaths (95% CI 106567 to 115048) predicted in 2025 in Tunisia. The salt reduction offered the potentially most powerful preventive intervention that might reduce IHD and stroke deaths by 27% (−30240 [−30580 to −29900]) compared with 1% for medical strategies and 3% for secondary prevention. The metamodeling highlighted that the initial development of a minor stroke substantially increased the subsequent probability of a fatal stroke or IHD death. Conclusions. The primary prevention of cardiovascular disease via a reduction in dietary salt consumption appeared much more effective than secondary or tertiary prevention approaches. Our simple but comprehensive model offers a potentially attractive methodological approach that might now be extended and replicated in other contexts and populations
Extremal Black Attractors in 8D Maximal Supergravity
Motivated by the new higher D-supergravity solutions on intersecting
attractors obtained by Ferrara et al. in [Phys.Rev.D79:065031-2009], we focus
in this paper on 8D maximal supergravity with moduli space
[SL(3,R)/SO(3)]x[SL(2,R)/SO(2)] and study explicitly the attractor mechanism
for various configurations of extremal black p- branes (anti-branes) with the
typical near horizon geometries AdS_{p+2}xS^{m}xT^{6-p-m} and p=0,1,2,3,4;
2<=m<=6. Interpretations in terms of wrapped M2 and M5 branes of the 11D
M-theory on 3-torus are also given.
Keywords: 8D supergravity, black p-branes, attractor mechanism, M-theory.Comment: 37 page
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