Discovery of an Energetic Pulsar Associated with SNR G76.9+1.0

We report the discovery of PSR J2022+3842, a 24 ms radio and X-ray pulsar in the supernova remnant G76.9+1.0, in observations with the Chandra X-ray telescope, the Robert C. Byrd Green Bank Radio Telescope, and the Rossi X-ray Timing Explorer (RXTE). The pulsar's spin-down rate implies a rotation-powered luminosity Edot = 1.2 x 10^{38} erg/s, a surface dipole magnetic field strength B_s = 1.0 x 10^{12} G, and a characteristic age of 8.9 kyr. PSR J2022+3842 is thus the second-most energetic Galactic pulsar known, after the Crab, as well as the most rapidly-rotating young, radio-bright pulsar known. The radio pulsations are highly dispersed and broadened by interstellar scattering, and we find that a large (delta-f / f ~= 1.9 x 10^{-6}) spin glitch must have occurred between our discovery and confirmation observations. The X-ray pulses are narrow (0.06 cycles FWHM) and visible up to 20 keV, consistent with magnetospheric emission from a rotation-powered pulsar. The Chandra X-ray image identifies the pulsar with a hard, unresolved source at the midpoint of the double-lobed radio morphology of SNR G76.9+1.0 and embedded within faint, compact X-ray nebulosity. The spatial relationship of the X-ray and radio emissions is remarkably similar to extended structure seen around the Vela pulsar. The combined Chandra and RXTE pulsar spectrum is well-fitted by an absorbed power-law model with column density N_H = (1.7\pm0.3) x 10^{22} cm^{-2} and photon index Gamma = 1.0\pm0.2; it implies that the Chandra point-source flux is virtually 100% pulsed. For a distance of 10 kpc, the X-ray luminosity of PSR J2022+3842 is L_X(2-10 keV) = 7.0 x 10^{33} erg s^{-1}. Despite being extraordinarily energetic, PSR J2022+3842 lacks a bright X-ray wind nebula and has an unusually low conversion efficiency of spin-down power to X-ray luminosity, L_X/Edot = 5.9 x 10^{-5}.Comment: 8 pages in emulateapj format. Minor changes (including a shortened abstract) to reflect the version accepted for publicatio

Pulsar State Switching from Markov Transitions and Stochastic Resonance

Markov processes are shown to be consistent with metastable states seen in pulsar phenomena, including intensity nulling, pulse-shape mode changes, subpulse drift rates, spindown rates, and X-ray emission, based on the typically broad and monotonic distributions of state lifetimes. Markovianity implies a nonlinear magnetospheric system in which state changes occur stochastically, corresponding to transitions between local minima in an effective potential. State durations (though not transition times) are thus largely decoupled from the characteristic time scales of various magnetospheric processes. Dyadic states are common but some objects show at least four states with some transitions forbidden. Another case is the long-term intermittent pulsar B1931+24 that has binary radio-emission and torque states with wide, but non-monotonic duration distributions. It also shows a quasi-period of $38\pm5$ days in a 13-yr time sequence, suggesting stochastic resonance in a Markov system with a forcing function that could be strictly periodic or quasi-periodic. Nonlinear phenomena are associated with time-dependent activity in the acceleration region near each magnetic polar cap. The polar-cap diode is altered by feedback from the outer magnetosphere and by return currents from an equatorial disk that may also cause the neutron star to episodically charge and discharge. Orbital perturbations in the disk provide a natural periodicity for the forcing function in the stochastic resonance interpretation of B1931+24. Disk dynamics may introduce additional time scales in observed phenomena. Future work can test the Markov interpretation, identify which pulsar types have a propensity for state changes, and clarify the role of selection effects.Comment: 25 pages, 6 figures, submitted to the Astrophysical Journa

Preconditioned Data Sparsification for Big Data with Applications to PCA and K-means

We analyze a compression scheme for large data sets that randomly keeps a small percentage of the components of each data sample. The benefit is that the output is a sparse matrix and therefore subsequent processing, such as PCA or K-means, is significantly faster, especially in a distributed-data setting. Furthermore, the sampling is single-pass and applicable to streaming data. The sampling mechanism is a variant of previous methods proposed in the literature combined with a randomized preconditioning to smooth the data. We provide guarantees for PCA in terms of the covariance matrix, and guarantees for K-means in terms of the error in the center estimators at a given step. We present numerical evidence to show both that our bounds are nearly tight and that our algorithms provide a real benefit when applied to standard test data sets, as well as providing certain benefits over related sampling approaches.Comment: 28 pages, 10 figure

Comparative evaluation of approaches in T.4.1-4.3 and working definition of adaptive module

The goal of this deliverable is two-fold: (1) to present and compare different approaches towards learning and encoding movements us- ing dynamical systems that have been developed by the AMARSi partners (in the past during the first 6 months of the project), and (2) to analyze their suitability to be used as adaptive modules, i.e. as building blocks for the complete architecture that will be devel- oped in the project. The document presents a total of eight approaches, in two groups: modules for discrete movements (i.e. with a clear goal where the movement stops) and for rhythmic movements (i.e. which exhibit periodicity). The basic formulation of each approach is presented together with some illustrative simulation results. Key character- istics such as the type of dynamical behavior, learning algorithm, generalization properties, stability analysis are then discussed for each approach. We then make a comparative analysis of the different approaches by comparing these characteristics and discussing their suitability for the AMARSi project

Medial Prefrontal Cortical Activity Reflects Dynamic Re-Evaluation During Voluntary Persistence

Deciding how long to keep waiting for future rewards is a nontrivial problem, especially when the timing of rewards is uncertain. We carried out an experiment in which human decision makers waited for rewards in two environments in which reward-timing statistics favored either a greater or lesser degree of behavioral persistence. We found that decision makers adaptively calibrated their level of persistence for each environment. Functional neuroimaging revealed signals that evolved differently during physically identical delays in the two environments, consistent with a dynamic and context-sensitive reappraisal of subjective value. This effect was observed in a region of ventromedial prefrontal cortex that is sensitive to subjective value in other contexts, demonstrating continuity between valuation mechanisms involved in discrete choice and in temporally extended decisions analogous to foraging. Our findings support a model in which voluntary persistence emerges from dynamic cost/benefit evaluation rather than from a control process that overrides valuation mechanisms

Timing Sensitive Dependency Analysis and its Application to Software Security

Ich präsentiere neue Verfahren zur statischen Analyse von Ausführungszeit-sensitiver Informationsflusskontrolle in Softwaresystemen. Ich wende diese Verfahren an zur Analyse nebenläufiger Java Programme, sowie zur Analyse von Ausführungszeit-Seitenkanälen in Implementierungen kryptographischer Primitive. Methoden der Informationsflusskontrolle zielen darauf ab, Fluss von Informationen (z.B.: zwischen verschiedenen externen Schnittstellen einer Software-Komponente) anhand expliziter Richtlinien einzuschränken. Solche Methoden können daher zur Einhaltung sowohl von Vertraulichkeit als auch Integrität eingesetzt werden. Der Ziel korrekter statischer Programmanalysen in diesem Umfeld ist der Nachweis, dass in allen Ausführungen eines gegebenen Programms die zugehörigen Richtlinien eingehalten werden. Ein solcher Nachweis erfordert ein Sicherheitskriterium, welches formalisiert, unter welchen Bedingungen dies der Fall ist. Jedem formalen Sicherheitskriterium entspricht implizit ein Programm- und Angreifermodell. Einfachste Nichtinterferenz-Kriterien beschreiben beispielsweise nur nicht-interaktive Programme. Dies sind Programme die nur bei Beginn und Ende der Ausführung Ein- und Ausgaben erlauben. Im zugehörigen Angreifer-Modell kennt der Angreifer das Programm, aber beobachtet nur bestimmte (öffentliche) Aus- und Eingaben oder stellt diese bereit. Ein Programm ist nichtinterferent, wenn der Angreifer aus seinen Beobachtungen keinerlei Rückschlüsse auf geheime Aus- und Eingaben terminierender Ausführungen machen kann. Aus nicht-terminierenden Ausführungen hingegen sind dem Angreifer in diesem Modell Schlussfolgerungen auf geheime Eingaben erlaubt. Seitenkanäle entstehen, wenn einem Angreifer aus Beobachtungen realer Systeme Rückschlüsse auf vertrauliche Informationen ziehen kann, welche im formalen Modell unmöglich sind. Typische Seitenkanäle (also: in vielen formalen Sicherheitskriterien unmodelliert) sind neben Nichttermination beispielsweise auch Energieverbrauch und die Ausführungszeit von Programmen. Hängt diese von geheimen Eingaben ab, so kann ein Angreifer aus der beobachteten Ausführungszeit auf die Eingabe (z.B.: auf den Wert einzelner geheimer Parameter) schließen. In meiner Dissertation präsentiere ich neue Abhängigkeitsanalysen, die auch Nichtterminations- und Ausführungszeitkanäle berücksichtigen. In Hinblick auf Nichtterminationskanäle stelle ich neue Verfahren zur Berechnung von Programm-Abhängigkeiten vor. Hierzu entwickle ich ein vereinheitlichendes Rahmenwerk, in welchem sowohl Nichttermination-sensitive als auch Nichttermination-insensitive Abhängigkeiten aus zueinander dualen Postdominanz-Begriffen resultieren. Für Ausführungszeitkanäle entwickle ich neue Abhängigkeitsbegriffe und dazugehörige Verfahren zu deren Berechnung. In zwei Anwendungen untermauere ich die These: Ausführungszeit-sensitive Abhängigkeiten ermöglichen korrekte statische Informationsfluss-Analyse unter Berücksichtigung von Ausführungszeitkanälen. Basierend auf Ausführungszeit-sensitiven Abhängigkeiten entwerfe ich hierfür neue Analysen für nebenläufige Programme. Ausführungszeit-sensitive Abhängigkeiten sind dort selbst für Ausführungszeit-insensitive Angreifermodelle relevant, da dort interne Ausführungszeitkanäle zwischen unterschiedlichen Ausführungsfäden extern beobachtbar sein können. Meine Implementierung für nebenläufige Java Programme basiert auf auf dem Programmanalyse- System JOANA. Außerdem präsentiere ich neue Analysen für Ausführungszeitkanäle aufgrund mikro-architektureller Abhängigkeiten. Exemplarisch untersuche ich Implementierungen von AES256 Blockverschlüsselung. Bei einigen Implementierungen führen Daten-Caches dazu, dass die Ausführungszeit abhängt von Schlüssel und Geheimtext, wodurch diese aus der Ausführungszeit inferierbar sind. Für andere Implementierungen weist meine automatische statische Analyse (unter Annahme einer einfachen konkreten Cache-Mikroarchitektur) die Abwesenheit solcher Kanäle nach

Discovery of 59ms Pulsations from 1RXS J141256.0+792204 (Calvera)

We report on a multi-wavelength study of the compact object candidate 1RXS J141256.0+792204 (Calvera). Calvera was observed in the X-rays with XMM/EPIC twice for a total exposure time of ~50 ks. The source spectrum is thermal and well reproduced by a two component model composed of either two hydrogen atmosphere models, or two blackbodies (kT_1~ 55/150 eV, kT_2~ 80/250 eV, respectively, as measured at infinity). Evidence was found for an absorption feature at ~0.65 keV; no power-law high-energy tail is statistically required. Using pn and MOS data we discovered pulsations in the X-ray emission at a period P=59.2 ms. The detection is highly significant (> 11 sigma), and unambiguously confirms the neutron star nature of Calvera. The pulse profile is nearly sinusoidal, with a pulsed fraction of ~18%. We looked for the timing signature of Calvera in the Fermi Large Area Telescope (LAT) database and found a significant (~5 sigma) pulsed signal at a period coincident with the X-ray value. The gamma-ray timing analysis yielded a tight upper limit on the period derivative, dP/dt < 5E-18 s/s (dE_rot/dt <1E33 erg/s, B<5E10 G for magneto- dipolar spin-down). Radio searches at 1.36 GHz with the 100-m Effelsberg radio telescope yielded negative results, with a deep upper limit on the pulsed flux of 0.05 mJy. Diffuse, soft (< 1 keV) X-ray emission about 13' west of the Calvera position is present both in our pointed observations and in archive ROSAT all-sky survey images, but is unlikely associated with the X-ray pulsar. Its spectrum is compatible with an old supernova remnant (SNR); no evidence for diffuse emission in the radio and optical bands was found. The most likely interpretations are that Calvera is either a central compact object escaped from a SNR or a mildly recycled pulsar; in both cases the source would be the first ever member of the class detected at gamma-ray energies.Comment: 20 pages, 15 figures and 4 tables. Accepted for publication in MNRA

Statistical Static Timing Analysis for Performance of Logic Gates

In the recent nanotechnology, the variation in the gate propagation delay is the big concern. This paper proposes the new model for gate delay propagation using the Statistical Static Timing Analysis and the results of it are compared with another modelling called as Monte-Carlo analysis. The proposed model uses Statistical analysis to find accurate propagation delay of the logic gates with reduced simulation time for 16nm technology. DOI: 10.17762/ijritcc2321-8169.15057