8,681 research outputs found
Sciduction: Combining Induction, Deduction, and Structure for Verification and Synthesis
Even with impressive advances in automated formal methods, certain problems
in system verification and synthesis remain challenging. Examples include the
verification of quantitative properties of software involving constraints on
timing and energy consumption, and the automatic synthesis of systems from
specifications. The major challenges include environment modeling,
incompleteness in specifications, and the complexity of underlying decision
problems.
This position paper proposes sciduction, an approach to tackle these
challenges by integrating inductive inference, deductive reasoning, and
structure hypotheses. Deductive reasoning, which leads from general rules or
concepts to conclusions about specific problem instances, includes techniques
such as logical inference and constraint solving. Inductive inference, which
generalizes from specific instances to yield a concept, includes algorithmic
learning from examples. Structure hypotheses are used to define the class of
artifacts, such as invariants or program fragments, generated during
verification or synthesis. Sciduction constrains inductive and deductive
reasoning using structure hypotheses, and actively combines inductive and
deductive reasoning: for instance, deductive techniques generate examples for
learning, and inductive reasoning is used to guide the deductive engines.
We illustrate this approach with three applications: (i) timing analysis of
software; (ii) synthesis of loop-free programs, and (iii) controller synthesis
for hybrid systems. Some future applications are also discussed
Optimal feedback strategies for pursuit-evasion and interception in a plane
Variable-speed pursuit-evasion and interception for two aircraft moving in a horizontal plane are analyzed in terms of a coordinate frame fixed in the plane at termination. Each participant's optimal motion can be represented by extremal trajectory maps. These maps are used to discuss sub-optimal approximations that are independent of the other participant. A method of constructing sections of the barrier, dispersal, and control-level surfaces and thus determining feedback strategies is described. Some examples are shown for pursuit-evasion and the minimum-time interception of a straight-flying target
Exploration of the High Entropy Alloy Space as a Constraint Satisfaction Problem
High Entropy Alloys (HEAs), Multi-principal Component Alloys (MCA), or
Compositionally Complex Alloys (CCAs) are alloys that contain multiple
principal alloying elements. While many HEAs have been shown to have unique
properties, their discovery has been largely done through costly and
time-consuming trial-and-error approaches, with only an infinitesimally small
fraction of the entire possible composition space having been explored. In this
work, the exploration of the HEA composition space is framed as a Continuous
Constraint Satisfaction Problem (CCSP) and solved using a novel Constraint
Satisfaction Algorithm (CSA) for the rapid and robust exploration of alloy
thermodynamic spaces. The algorithm is used to discover regions in the HEA
Composition-Temperature space that satisfy desired phase constitution
requirements. The algorithm is demonstrated against a new (TCHEA1) CALPHAD HEA
thermodynamic database. The database is first validated by comparing phase
stability predictions against experiments and then the CSA is deployed and
tested against design tasks consisting of identifying not only single phase
solid solution regions in ternary, quaternary and quinary composition spaces
but also the identification of regions that are likely to yield
precipitation-strengthened HEAs.Comment: 14 pages, 13 figure
Nonlinear Evolution of Instabilities Between Dust and Sound Waves
We study the non-linear evolution of the acoustic 'Resonant Drag Instability'
(RDI) using numerical simulations. The acoustic RDI is excited in a dust-gas
mixture when dust grains stream through gas, interacting with sound waves to
cause a linear instability. We study this process in a periodic box by
accelerating neutral dust with an external driving force. The instability grows
as predicted by linear theory, eventually breaking into turbulence and
saturating. As in linear theory, the non-linear behavior is characterized by
three regimes - high, intermediate, and low wavenumbers - the boundary between
which is determined by the dust-gas coupling strength and the dust-to-gas mass
ratio. The high and intermediate wavenumber regimes behave similarly to one
another, with large dust-to-gas ratio fluctuations while the gas remains
largely incompressible. The saturated state is highly anisotropic: dust is
concentrated in filaments, jets, or plumes along the direction of acceleration,
with turbulent vortex-like structures rapidly forming and dissipating in the
perpendicular directions. The low-wavenumber regime exhibits large fluctuations
in gas and dust density, but the dust and gas remain more strongly coupled in
coherent 'fronts' perpendicular to the acceleration. These behaviors are
qualitatively different from those of dust 'passively' driven by external
hydrodynamic turbulence, with no back-reaction force from dust onto gas. The
virulent nature of these instabilities has interesting implications for
dust-driven winds in a variety of astrophysical systems, including around
cool-stars, in dusty torii around active-galactic-nuclei, and in and around
giant molecular clouds.Comment: 11 pages, 9 figure
Early College, Early Success: Early College High School Initiative Impact Study
In 2002, the Bill & Melinda Gates Foundation launched the ECHSI with the primary goal of increasing the opportunity for underserved students to earn a postsecondary credential. To achieve this goal, Early Colleges provide underserved students with exposure to, and support in, college while they are in high school. Early Colleges partner with colleges and universities to offer all students an opportunity to earn an associate's degree or up to two years of college credits toward a bachelor's degree during high school at no or low cost to the students. The underlying assumption is that engaging underrepresented students in a rigorous high school curriculum tied to the incentive of earning college credit will motivate them and increase their access to additional postsecondary education and credentials after high school. Since 2002, more than 240 Early Colleges have opened nationwideThis study focused on the impact of Early Colleges. It addressed two questions:1. Do Early College students have better outcomes than they would have had at other high schools?2. Does the impact of Early Colleges vary by student background characteristics (e.g., gender and family income)? To answer these questions, we conducted a lottery-based randomized experiment, taking advantage of the fact that some Early Colleges used lotteries in their admissions processes. By comparing the outcomes for students who participated in admissions lotteries and were offered enrollment with the outcomes for students who participated in the lotteries but were not offered enrollment, we can draw causal conclusions about the impact of Early Colleges.The primary student outcomes for this study were high school graduation, college enrollment, and college degree attainment. We also examined students' high school and college experiences. Data on student background characteristics and high school outcomes came from administrative records from schools, districts, and states; data on collegeoutcomes came from the National Student Clearinghouse (NSC); and data on high school and college experiences and intermediate outcomes such as college credit accrual camefrom a student surveyWe assessed the impact of Early Colleges on these outcomes for a sample of 10 Early Colleges that did the following:-Enrolled students in grades 9 -- 12 and had high school graduates in the study years (2005 -- 2011)-Used lotteries as part of the admission processes in at least one of the study cohorts (students who entered ninth grade in 2005 -- 06, 2006 -- 07, or 2007 -- 08)-Retained the lottery recordsEight of the 10 Early Colleges in the study were included in the student survey. The overall study sample included 2,458 students and the survey sample included 1,294 students. The study extended through three years past high school
Non-classical computing: feasible versus infeasible
Physics sets certain limits on what is and is not computable. These limits are very far from having been reached by current technologies. Whilst proposals for hypercomputation are almost certainly infeasible, there are a number of non classical approaches that do hold considerable promise. There are a range of possible architectures that could be implemented on silicon that are distinctly different from the von Neumann model. Beyond this, quantum simulators, which are the quantum equivalent of analogue computers, may be constructable in the near future
New Differential Cryptanalysis Results for the Lightweight Block Cipher BORON
BORON is a 64-bit lightweight block cipher based on the substitution-permutation network that supports an 80-bit (BORON-80) and 128-bit (BORON-128) secret key. In this paper, we revisit the use of differential cryptanalysis on BORON in the single-key model. Using an SAT/SMT approach, we look for differentials that consist of multiple differential characteristics with the same input and output differences. Each characteristic that conforms to a given differential improves its overall probability. We also implemented the same search using Matsui\u27s algorithm for verification and performance comparison purposes. We identified high-probability differentials which were then used in key recovery attacks against BORON-80/128. We first show that the previous differential cryptanalysis attack against 9-round of BORON was at most an 8.5 round attack due to the omission of the final block XOR layer. Then, we used 8-round differentials with a probability of and in key recovery attacks against 9 and 10 rounds of BORON-80 and BORON-128 with time/data/memory complexities of { and } respectively. Our key recovery framework provides a more accurate estimate of the attack complexity as compared to previous work. The attacks proposed in this paper are the best differential attacks against BORON-80/128 in the single-key model to date
The SAT-Based Automatic Searching and Experimental Verification for Differential Characteristics with Application to Midori64
In this paper, we show that it is inaccurate to apply the hypothesis of independent round keys to search for differential characteristics of a block cipher with a simple key schedule. Therefore, the derived differential characteristics may be invalid. We develop a SAT-based algorithm to verify the validity of differential characteristics. Furthermore, we take the key schedule into account and thus put forward an algorithm to directly find the valid differential characteristics. All experiments are performed on Midori64 and we find some interesting results
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