Stepwise refinement of heap-manipulating code in Chalice

Stepwise refinement is a well-studied technique for developing a program from an abstract description to a concrete implementation. This paper describes a system with automated tool support for refinement, powered by a state-of-the-art verification engine that uses an SMT solver. Unlike previous refinement systems, users of the presented system interact only via declarations in the programming language. Another aspect of the system is that it accounts for dynamically allocated objects in the heap, so that data representations in an abstract program can be refined into ones that use more objects. Finally, the system uses a language with familiar imperative features, including sequential composition, loops, and recursive calls, offers a syntax with skeletons for describing program changes between refinements, and provides a mechanism for supplying witnesses when refining non-deterministic programs

Simulation and design of the HT-KZ Ultra-high energy cosmic rays detector system for cosmic rays with energies above 1017 eV

In the field of High Energy Physics today there are several open topics left. The Higgs boson has been recently discovered, neutrino oscillations are being studied, and some hints of the dark matter have been detected as well. Another remaining mystery is the origin and the nature of the Ultra-High Energy Cosmic Rays. There is an active project at Nazarbayev University to construct the HorizonT-Kazakhstan detector system in collaboration with the Tien Shan high-altitude Science Station (TSHSS), a part of Lebedev Physical Institute of the Russian Academy of Sciences. The full R&D is underway. A significant part of this process is the simulation, testing and construction of individual particle detectors due to the requirements of robustness and high linear range of such detectors combined with low cost and long-term operations with minimal maintenance. In this paper, the latest results of the simulation activities and experiment testing of different detection components as applicable to the HorizonT-Kazakhstan requirements are presented

Simulation and design of the HT-KZ Ultra-high energy cosmic rays detector system for cosmic rays with energies above 1017 eV

In the field of High Energy Physics today there are several open topics left. The Higgs boson has been recently discovered, neutrino oscillations are being studied, and some hints of the dark matter have been detected as well. Another remaining mystery is the origin and the nature of the Ultra-High Energy Cosmic Rays. There is an active project at Nazarbayev University to construct the HorizonT-Kazakhstan detector system in collaboration with the Tien Shan high-altitude Science Station (TSHSS), a part of Lebedev Physical Institute of the Russian Academy of Sciences. The full R&D is underway. A significant part of this process is the simulation, testing and construction of individual particle detectors due to the requirements of robustness and high linear range of such detectors combined with low cost and long-term operations with minimal maintenance. In this paper, the latest results of the simulation activities and experiment testing of different detection components as applicable to the HorizonT-Kazakhstan requirements are presented

Horizon-T Experiment Calibrations – MIP Signal from Scintillator and Glass Detectors

Horizon-T, a modern Extensive Air Showers (EAS) detector system, is constructed at Tien Shan high-altitude Science Station of Lebedev Physical Institute of the Russian Academy of Sciences at approximately 3340 meters above the sea level in order to study in the energy range above 1016 eV coming from a wide range of zenith angles (0o - 85o). The detector includes eight charged particle detection points and a Vavilov-Cherenkov radiation detector. Each charged particle detector response is calibrated using single MIP (minimally ionizing particle) signal. The details of this calibration are provided in this article. This note is valid for data before March 2017 and will not be updated following any detector calibration and configuration changes as a large upgrade has been implemente

Horizon-T extensive air showers detector system operations and performance

“Horizon-T” is an innovative detector system located at Tien Shan high-altitude Science Station (TSHASS) at approximately 3340 meters above the sea level. It consists of eight detection points separated by the distance up to one kilometer that can measure time characteristics of the Extensive Air Showers (EAS) and record signal shapes with time resolution of ~10 ns. It was constructed to register EAS in the energy range above 1016 eV coming from a wide range of zenith angles (0o - 85o). The system includes both the plastic scintillator particle detectors as well as the Vavilov - Cerenkov radiation detectors subsystem to observe the Cerenkov light from the EAS in the atmosphere directly. The time resolution and signal shape analysis capabilities of the detection points are used to study EAS development in the atmosphere. The development of the EAS is a process that can be studied both spatially and temporally. For the spatial part, a distributed network of detection points is required. For the time part, a signal shape must be recorded and analysed at each point with time resolution on the order of ~10 ns. In this paper, the current system description and performance level are described. Additionally, the latest data examples showing the unusual EAS examples above 1017 eV are included

Horizon-T extensive air showers detector system operations and performance

“Horizon-T” is an innovative detector system located at Tien Shan high-altitude Science Station (TSHASS) at approximately 3340 meters above the sea level. It consists of eight detection points separated by the distance up to one kilometer that can measure time characteristics of the Extensive Air Showers (EAS) and record signal shapes with time resolution of ~10 ns. It was constructed to register EAS in the energy range above 1016 eV coming from a wide range of zenith angles (0o - 85o). The system includes both the plastic scintillator particle detectors as well as the Vavilov - Cerenkov radiation detectors subsystem to observe the Cerenkov light from the EAS in the atmosphere directly. The time resolution and signal shape analysis capabilities of the detection points are used to study EAS development in the atmosphere. The development of the EAS is a process that can be studied both spatially and temporally. For the spatial part, a distributed network of detection points is required. For the time part, a signal shape must be recorded and analysed at each point with time resolution on the order of ~10 ns. In this paper, the current system description and performance level are described. Additionally, the latest data examples showing the unusual EAS examples above 1017 eV are included

What is the maximum differential group delay achievable by a space-time wave packet in free space?

The group velocity of 'space-time' wave packets $-$ propagation-invariant pulsed beams endowed with tight spatio-temporal spectral correlations $-$ can take on arbitrary values in free space. Here we investigate theoretically and experimentally the maximum achievable group delay that realistic finite-energy space-time wave packets can achieve with respect to a reference pulse traveling at the speed of light. We find that this delay is determined solely by the spectral uncertainty in the association between the spatial frequencies and wavelengths underlying the wave packet spatio-temporal spectrum $-$ and not by the beam size, bandwidth, or pulse width. We show experimentally that the propagation of space-time wave packets is delimited by a spectral-uncertainty-induced `pilot envelope' that travels at a group velocity equal to the speed of light in vacuum. Temporal walk-off between the space-time wave packet and the pilot envelope limits the maximum achievable differential group delay to the width of the pilot envelope. Within this pilot envelope, the space-time wave packet can locally travel at an arbitrary group velocity and yet not violate relativistic causality because the leading or trailing edge of superluminal and subluminal space-time wave packets, respectively, are suppressed once they reach the envelope edge. Using pulses of width $\sim$4ps and a spectral uncertainty of $\sim$ 20 pm, we measure maximum differential group delays of approximately $\pm$ 150 ps, which exceed previously reported measurements by at least three orders of magnitude

Synthesizing Iterators from Abstraction Functions

A technique for synthesizing iterators from declarative abstraction functions written in a relational logic specification language is described. The logic includes a transitive closure operator that makes it convenient for expressing reachability queries on linked data structures. Some optimizations, including tuple elimination, iterator flattening, and traversal state reduction, are used to improve performance of the generated iterators. A case study demonstrates that most of the iterators in the widely used JDK Collections classes can be replaced with code synthesized from declarative abstraction functions. These synthesized iterators perform competitively with the hand-written originals. In a user study the synthesized iterators always passed more test cases than the hand-written ones, were almost always as efficient, usually took less programmer effort, and were the qualitative preference of all participants who provided free-form comments

On Sets with Cardinality Constraints in Satisfiability Modulo Theories

Boolean Algebra with Presburger Arithmetic (BAPA) is a decidable logic that can express constraints on sets of elements and their cardinalities. Problems from verification of complex properties of software often contain fragments that belong to quantifier-free BAPA (QFBAPA). Deciding the satisfiability of QFBAPA formulas has been shown to be NP-complete using an eager reduction to quantifier-free Presburger arithmetic that exploits a sparse-solution property. In contrast to many other NP-complete problems (such as quantifier-free first-order logic or linear arithmetic), the applications of QFBAPA to a broader set of problems has so far been hindered by the lack of an efficient implementation that can be used alongside other efficient decision procedures. We overcome these limitations by extending the efficient SMT solver Z3 with the ability to reason about cardinality constraints. Our implementation uses the DPLL(T) mechanism of Z3 to reason about the top-level propositional structure of a QFBAPA formula, improving the efficiency compared to previous implementations. Moreover, we present a new algorithm for automated decomposition of QFBAPA formulas. Our algorithm alleviates the exponential explosion of considering all Venn regions, significantly improving the tractability of formulas with many set variables. Because it is implemented as a theory plugin, our implementation enables Z3 to prove formulas that use QFBAPA constructs alongside constructs from other theories that Z3 supports (e.g. linear arithmetic, uninterpreted function symbols, algebraic data types), as well as in formulas with quantifiers. We have applied our implementation to verification of functional programs; we show it can automatically prove formulas that no automated approach was reported to be able to prove before

Counting constraints in flat array fragments

We identify a fragment of Presburger arithmetic enriched with free function symbols and cardinality constraints for interpreted sets, which is amenable to automated analysis. We establish decidability and complexity results for such a fragment and we implement our algorithms. The experiments run in discharging proof obligations coming from invariant checking and bounded model-checking benchmarks show the practical feasibility of our decision procedure