Soft Sphere Packings at Finite Pressure but Unstable to Shear

When are athermal soft sphere packings jammed ? Any experimentally relevant definition must at the very least require a jammed packing to resist shear. We demonstrate that widely used (numerical) protocols in which particles are compressed together, can and do produce packings which are unstable to shear - and that the probability of generating such packings reaches one near jamming. We introduce a new protocol that, by allowing the system to explore different box shapes as it equilibrates, generates truly jammed packings with strictly positive shear moduli G. For these packings, the scaling of the average of G is consistent with earlier results, while the probability distribution P(G) exhibits novel and rich scalingComment: 5 pages, 6 figures. Resubmitted to Physical Review Letters after a few change

Structural Synthesis for GXW Specifications

We define the GXW fragment of linear temporal logic (LTL) as the basis for synthesizing embedded control software for safety-critical applications. Since GXW includes the use of a weak-until operator we are able to specify a number of diverse programmable logic control (PLC) problems, which we have compiled from industrial training sets. For GXW controller specifications, we develop a novel approach for synthesizing a set of synchronously communicating actor-based controllers. This synthesis algorithm proceeds by means of recursing over the structure of GXW specifications, and generates a set of dedicated and synchronously communicating sub-controllers according to the formula structure. In a subsequent step, 2QBF constraint solving identifies and tries to resolve potential conflicts between individual GXW specifications. This structural approach to GXW synthesis supports traceability between requirements and the generated control code as mandated by certification regimes for safety-critical software. Synthesis for GXW specifications is in PSPACE compared to 2EXPTIME-completeness of full-fledged LTL synthesis. Indeed our experimental results suggest that GXW synthesis scales well to industrial-sized control synthesis problems with 20 input and output ports and beyond.Comment: The long (including appendix) version being reviewed by CAV'16 program committee. Compared to the submitted version, one author (out of her wish) is moved to the Acknowledgement. (v2) Corrected typos. (v3) Add an additional remark over environment assumption and easy corner case

Specification: The Biggest Bottleneck in Formal Methods and Autonomy

Advancement of AI-enhanced control in autonomous systems stands on the shoulders of formal methods, which make possible the rigorous safety analysis autonomous systems require. An aircraft cannot operate autonomously unless it has design-time reasoning to ensure correct operation of the autopilot and runtime reasoning to ensure system health management, or the ability to detect and respond to off-nominal situations. Formal methods are highly dependent on the specifications over which they reason; there is no escaping the “garbage in, garbage out” reality. Specification is difficult, unglamorous, and arguably the biggest bottleneck facing verification and validation of aerospace, and other, autonomous systems. This VSTTE invited talk and paper examines the outlook for the practice of formal specification, and highlights the on-going challenges of specification, from design-time to runtime system health management. We exemplify these challenges for specifications in Linear Temporal Logic (LTL) though the focus is not limited to that specification language. We pose challenge questions for specification that will shape both the future of formal methods, and our ability to more automatically verify and validate autonomous systems of greater variety and scale. We call for further research into LTL Genesis

Czynniki wpływające na wytrzymałość cegieł z gliny ogniotrwałej

In this investigation some factors affected the performance of the fire clay refractory bricks such as size of grog, percentage of water added to the raw material, percentage of grog and temperature of firing were studied. The results showed that if the percentage of grog increased the shrinkage of bricks decreased, as well as density of bricks was increasing the porosity and water absorption also increased. Furthermore, with increasing of the added water to the raw material the porosity of the bricks increased and if water absorption increased, density decreased. The characteristics of raw material by such methods as x-ray and chemical analysis were also examined.W pracy zbadano niektóre czynniki wpływające na wytrzymałość cegieł z gliny ogniotrwałej, tj. rozmiar kruszywa szamotowego, procent dodanej wody, zawartość procentowa kruszywa szamotowego, czy temperatura wypalania. Wyniki wskazały, że gdy zawartość procentowa kruszywa szamotowego zwiększyła się to kurczliwość cegieł malała. Analogicznie, gdy gęstość cegieł rosła, porowatość i absorpcja wody również rosła. Zwiększając ilość wody dodawanej do surowca, wywoływało się zwiększenie porowatości cegieł, zaś gdy absorpcja wody zwiększała się - gęstość materiału malała. Charakterystyka materiału za pomocą promieni X oraz analizy chemicznej została również przedstawiona