Brittle fracture down to femto-Joules - and below

We analyze large sets of energy-release data created by stress-induced brittle fracture in a pure sapphire crystal at close to zero temperature where stochastic fluctuations are minimal. The waiting-time distribution follows that observed for fracture in rock and for earthquakes. Despite strong time correlations of the events and the presence of large-event precursors, simple prediction algorithms only succeed in a very weak probabilistic sense. We also discuss prospects for further cryogenic experiments reaching close to single-bond sensitivity and able to investigate the existence of a transition-stress regime.Comment: REVTeX, new figure added, minor modifications to tex

New twist field couplings from the partition function for multiply wrapped D-branes

We consider toroidal compactifications of bosonic string theory with particular regard to the phases (cocycles) necessary for a consistent definition of the vertex operators, the boundary states and the T-duality rules. We use these ingredients to compute the planar multi-loop partition function describing the interaction among magnetized or intersecting D-branes, also in presence of open string moduli. It turns out that unitarity in the open string channel crucially depends on the presence of the cocycles. We then focus on the 2-loop case and study the degeneration limit where this partition function is directly related to the tree-level 3-point correlators between twist fields. These correlators represent the main ingredient in the computation of Yukawa couplings and other terms in the effective action for D-brane phenomenological models. By factorizing the 2-loop partition function we are able to compute the 3-point couplings for abelian twist fields on generic non-factorized tori, thus generalizing previous expressions valid for the 2-torus.Comment: 36 pages, 1 figure; v2: typos corrected, proof in the Appendix improve

A Systematic Approach for Evaluating Satellite Communications Systems

The aerospace environment imposes straight opera- tive conditions so every electronic system usually needs to be validated for these. The same way, communica- tion systems need to be evaluated before their intro- duction in aerospace applications. In the paper we present a new methodology for the evaluation of com- munication systems in space applications. The meth- odology aims, by abstraction, at identifying all the critical aspects for the evaluation and at defining a standard and reusable framework in order to be appli- cable to any Communication Systems. The methodol- ogy has been applied for the evaluation of three Data Bus for satellite communications: 1553, 1-Wire and Profibus DP RS 485 based systems have been analyzed and evaluate

Chandra observations of the recurrent nova CI Aql after its April 2000 outburst

We report the results of two Chandra observations of the recurrent nova CI Aql at 14 and 16 months after its outburst in April 2000, respectively. The X-ray emission is faint in both cases, without any noticeable change in spectrum or intensity. Although the emission is very soft, it is not luminous enough to be due to late-time H-burning. This implies that the luminous supersoft phase ended even before the time predicted by the most recent calculations. The details of the X-ray spectrum, together with the fact that the observed X-ray intensity is brighter than pre-outburst (1992/1993), suggest that the observed X-ray emission is either due to ionization of the circumstellar material or due to the shocks within the wind and/or with the surrounding medium.Comment: 10 pages ApJ style with 5 figures; accepted for publication in Ap

Single-Event Upset Analysis and Protection in High Speed Circuits

The effect of single-event transients (SETs) (at a combinational node of a design) on the system reliability is becoming a big concern for ICs manufactured using advanced technologies. An SET at a node of combinational part may cause a transient pulse at the input of a flip-flop and consequently is latched in the flip-flop and generates a soft-error. When an SET conjoined with a transition at a node along a critical path of the combinational part of a design, a transient delay fault may occur at the input of a flip-flop. On the other hand, increasing pipeline depth and using low power techniques such as multi-level power supply, and multi-threshold transistor convert almost all paths in a circuit to critical ones. Thus, studying the behavior of the SET in these kinds of circuits needs special attention. This paper studies the dynamic behavior of a circuit with massive critical paths in the presence of an SET. We also propose a novel flip-flop architecture to mitigate the effects of such SETs in combinational circuits. Furthermore, the proposed architecture can tolerant a single event upset (SEU) caused by particle strike on the internal nodes of a flip-flo