Long-term XMM-Newton investigation of two particle-accelerating colliding-wind binaries in NGC6604: HD168112 and HD167971

The long-term (over more than one decade) X-ray emission from two massive stellar systems known to be particle accelerators is investigated using XMM-Newton. Their X-ray properties are interpreted taking into account recent information about their multiplicity and orbital parameters. The two targets, HD168112 and HD167971 appear to be overluminous in X-rays, lending additional support to the idea that a significant contribution of the X-ray emission comes from colliding-wind regions. The variability of the X-ray flux from HD168112 is interpreted in terms of varying separation expected to follow the 1/D rule for adiabatic shocked winds. For HD167971, marginal decrease of the X-ray flux in September 2002 could tentatively be explained by a partial wind eclipse in the close pair. No long-term variability could be demonstrated despite the significant difference of separation between 2002 and 2014. This suggests the colliding-wind region in the wide orbit does not contribute a lot to the total X-ray emission, with a main contribution coming from the radiative shocked winds in the eclipsing pair. The later result provides evidence that shocks in a colliding-wind region may be efficient particle accelerators even in the absence of bright X-ray emission, suggesting particle acceleration may operate in a wide range of conditions. Finally, in hierarchical triple O-type systems, thermal X-rays do not necessarily constitute an efficient tracer to detect the wind-wind interaction in the long period orbit.Comment: 12 pages, 4 postscript figures, 6 table

Long baseline interferometry: a promising tool for multiplicity investigations of massive stars

Massive binaries are crucial laboratories that allow us to investigate processes occurring in quite extreme conditions, such as particle acceleration, high-energy emission, or even dust formation. All these processes are intimately dependent on binarity. Our understanding of the underlying physics strongly requires preliminary multiplicity studies likely to uncover still undetected binaries, and determine their orbital parameters. However, classical spectroscopic approaches sometimes fail to provide a solution to this issue. Long baseline interferometry turns out to be a promising complementary technique to address the question of the multiplicity of massive stars. A campaign has been initiated with the VLTI to take benefit of this technique.Comment: 1 page, to appear in the proceedings of the ESO conference "The Interferometric View on Hot Stars", held in Vina del Mar, Chile (2-6 March 2009), RevMexA

Higher Order Graviton Scattering in M(atrix) Theory

In matrix theory the effective action for graviton-graviton scattering is a double expansion in the relative velocity and inverse separation. We discuss the systematics of this expansion and subject matrix theory to a new test. Low energy supergravity predicts the coefficient of the $v^6/r^{14}$ term, a two-loop effect, in agreement with explicit matrix model calculation.Comment: 15 pages, 1 epsf figure, LaTeX. Minor change

Nonperturbative Solution of the Super-Virasoro Constraints

We present the solution of the discrete super-Virasoro constraints to all orders of the genus expansion. Integrating over the fermionic variables we get a representation of the partition function in terms of the one-matrix model. We also obtain the nonperturbative solution of the super-Virasoro constraints in the double scaling limit but do not find agreement between our flows and the known supersymmetric extensions of KdV.Comment: 12 pages, CERN-TH.6761/9

An efficient temporal logic for robotic task planning

Computations required for temporal reasoning can be prohibitively expensive if fully general representations are used. Overly simple representations, such as totally ordered sequence of time points, are inadequate for use in a nonlinear task planning system. A middle ground is identified which is general enough to support a capable nonlinear task planner, but specialized enough that the system can support online task planning in real time. A Temporal Logic System (TLS) was developed during the Intelligent Task Automation (ITA) project to support robotic task planning. TLS is also used within the ITA system to support plan execution, monitoring, and exception handling

A quasi-Newton proximal splitting method

A new result in convex analysis on the calculation of proximity operators in certain scaled norms is derived. We describe efficient implementations of the proximity calculation for a useful class of functions; the implementations exploit the piece-wise linear nature of the dual problem. The second part of the paper applies the previous result to acceleration of convex minimization problems, and leads to an elegant quasi-Newton method. The optimization method compares favorably against state-of-the-art alternatives. The algorithm has extensive applications including signal processing, sparse recovery and machine learning and classification

Evaluative priming in the pronunciation task a preregistered replication and extension

We replicated and extended a study by Spruyt and Hermans (2008) in which picture primes engendered an evaluative-priming effect on the pronunciation of target words. As preliminary steps, we assessed data reproducibility of the original study, conducted Pilot Study I to identify highly semantically related prime-target pairs, reanalyzed the original data excluding such pairs, conducted Pilot Study II to demonstrate that we can replicate traditional associative priming effects in the pronunciation task, and conducted Pilot Study III to generate relatively unrelated sets of prime pictures and target words. The main study comprised three between-participants conditions: (1) a close replication of the original study, (2) the same condition excluding highly related prime-target pairs, and (3) a condition based on the relatively unrelated sets of prime pictures and target words developed in Pilot Study III. There was little evidence for an evaluative priming effect independent of semantic relatedness

Scanning tunneling spectroscopy of a dilute two-dimensional electron system exhibiting Rashba spin splitting

Using scanning tunneling spectroscopy (STS) at 5 K in B-fields up to 7 T, we investigate the local density of states of a two-dimensional electron system (2DES) created by Cs adsorption on p-type InSb(110). The 2DES, which in contrast to previous STS studies exhibits a 2D Fermi level, shows standing waves at B = 0 T with corrugations decreasing with energy and with wave numbers in accordance with theory. In magnetic field percolating drift states are observed within the disorder broadened Landau levels. Due to the large electric field perpendicular to the surface, a beating pattern of the Landau levels is found and explained quantitatively by Rashba spin splitting within the lowest 2DES subband. The Rashba splitting does not contribute significantly to the standing wave patterns in accordance with theory.Comment: 9 pages, 9 figures, submitted to Phys. Rev.

Charge correlations and optical conductivity in weakly doped antiferromagnets

We investigate the dynamical charge-charge correlation function and the optical conductivity in weakly doped antiferromagnets using Mori-Zwanzig projection technique. The system is described by the two-dimensional t-J model. The arising matrix elements are evaluated within a cumulant formalism which was recently applied to investigate magnetic properties of weakly doped antiferromagnets. Within the present approach the ground state consists of non-interacting hole quasiparticles. Our spectra agree well with numerical results calculated via exact diagonalization techniques. The method we employ enables us to explain the features present in the correlation functions. We conclude that the charge dynamics at weak doping is governed by transitions between excited states of spin-bag quasiparticles.Comment: 5 pages, 2 figures, to appear in Europhys. Letter