Learning from Constraints for Formal Property Checking

Constraints are commonly used in both simulation and formal verification in order to specify expected input conditions and state transitions. Constraint solving is a process to determine input vectors which satisfy the set of constraints during constrained random simulation. Even though constraints are used in formal property checking to restrict the search space, constraint solving has never had direct application to formal property checking. There are often many simple, yet powerful, invariants that can be learned from constraint solving during constrained random simulation. These invariants are shown in this paper to significantly simplify the formal verification problem. We use approximate constraint solving to compute an approximate set of valid input vectors. The approximate set of valid input vectors are a strict superset of the set of all legal input vectors. We use BDD techniques to compute these input vectors during constrained random simulation, then process the resulting BDDs for learning invariants which can be used during formal property checking. This paper presents efficient BDD algorithms to learn invariants from the BDDs generated from approximate constraint solving. We also present how these learned invariants can be applied to the formal property checking. Experimental results show that invariants learned during constraint solving can significantly improve the performance of formal property checking with many industrial designs.     

云计算概念、模型和关键技术

云计算指IP技术架构下的网络计算,其本质是ICT业务的一种新的应用方式。绝大数企业和运营商的数据中心的改造将是云计算未来发展的主要任务：使云计算技术更为普遍和更为广泛地为绝大部分企业、机构、团体和运营商服务。云计算技术将不仅提供传统意义的IT资源和应用服务,而且将支持包括IT、通信、电视、移动和物联等一切互联网技术融合后的资源使用和业务应用。云计算发展的关键技术主要有统一交换构架、统一虚拟化和统一计算系统,云计算发展的战略推手将是组建开放产业联盟和推动开放技术标准。     

High field transport in GaAs,InP and InAs

Calculations of the steady state and transient electron drift velocities and impact ionization rate are presented for GaAs, InP and InAs based on a Monte Carlo simulation using a realistic band structure derived from an empirical pseudopotential. The impact ionization results are obtained using collision broadening of the initial state and are found to fit the experimental data well through a wide range of applied fields. In InP the impact ionization rate is much lower than in GaAs and no appreciable anisotropy has been observed. This is due in part to the larger density of states in InP and the corresponding higher electron-phonon scattering rate. The transient drift velocities are calculated under the condition of high energy injection. The results for InP show that higher velocities can be obtained over 1000–1500 Å device lengths for a much larger range of launching energies and applied electric fields than in GaAs. For the case of InAs, due to the large impact ionization rate, high drift velocities can be obtained since the ionization acts to limit the transfer of electrons to the satellite minima. In the absence of impact ionization, the electrons show the usual runaway effect and transfer readily occurs, thus lowering the drift velocity substantially.     

Factoring Algorithms for Computing K-Terminal Network Reliability

Let GK denote a graph G whose edges can fail and with a set K ? V specified. Edge failures are independent and have known probabilities. The K-terminal reliability of GK, R(GK), is the probability that all vertices in K are connected by working edges. A factoring algorithm for computing network reliability recursively applies the formula R(GK) = piR(GK * ei) + qiR(GK - ei) where GK * ei is GK, with edge ei contracted, GK - ei is GK with ei deleted and pi ? 1 - qi is the reliability of edge ei. Various reliability-preserving reductions can be performed after each factoring operation in order to reduce computation. A unified framework is provided for complexity analysis and for determining optimal factoring strategies. Recent results are reviewed and extended within this framework.     

Visual Appearance of Chiral Nematic Cellulose‐Based Photonic Films: Angular and Polarization Independent Color Response with a Twist

Hydroxypropyl cellulose (HPC) is a biocompatible cellulose derivative capable of self‐assembling into a lyotropic chiral nematic phase in aqueous solution. This liquid crystalline phase reflects right‐handed circular polarized light of a specific color as a function of the HPC weight fraction. Here, it is demonstrated that, by introducing a crosslinking agent, it is possible to drastically alter the visual appearance of the HPC mesophase in terms of the reflected color, the scattering distribution, and the polarization response, resulting in an exceptional matte appearance in solid‐state films. By exploiting the interplay between order and disorder, a robust and simple methodology toward the preparation of polarization and angular independent color is developed, which constitutes an important step toward the development of real‐world photonic colorants.     

Chemical and Physical Sensing by Organic Field‐Effect Transistors and Related Devices

Organic semiconductor films are susceptible to noncovalent interactions, trapping and doping, photoexcitation, and dimensional deformation. While these effects can be detrimental to the performance of conventional circuits, they can be harnessed, especially in field‐effect architectures, to detect chemical and physical stimuli. This Review summarizes recent advances in the use of organic electronic materials for the detection of environmental chemicals, pressure, and light. The material features that are responsible for the transduction of the input signals to electronic information are discussed in detail.     

The effect of increased interrogation zone,reader antenna polarization and application factors in the performance of UHF RFID tag detection on modified atmosphere packaged meat

The effect of conveyor speed, test sample size, antenna to sample distance, antenna polarization and ideal tag location in relation to the coupling capabilities of ultra‐high frequency radio frequency identification on optimal reader antenna placement were studied. The influence of each individual factor and its interaction was determined using the general linear model analysis of variance. In decreasing order of significance of the variables tested were sample type (F = 4174.40, p < 0.0005), smaller samples preferred for coupling; distance (F = 863.83, p < 0.0005), where distance between sample and antenna should be kept to a minimum; inlay design (F = 167.82, p < 0.0005), where AD‐612 preformed best due to its large antenna area; and reader antenna polarization (F = 149.64, p < 0.0005), where circular polarization preformed better yet comparative advantage decreased with distance. A reader antenna offset of 95 mm, while not significant, (F = 1.73, p = 0.188) tended to decrease coupling capabilities of the system despite increasing the zone of influence. Ideal tag location on sample was found to be on the right, back and front face with y‐orientation proving superior than either x or z. A 190‐mm centre–to‐centre reader antenna offset resulted in a decrease in the average tag detection rate from 62 to 49% highlighting the importance of optimal reader antenna placement which needs to be confirmed if a similar result is to be obtained when a large number of tags are interrogated simultaneously. Copyright © 2010 John Wiley & Sons, Ltd.     

Influence of cyclic freeze-thaw on the mobilization of LNAPL and soluble oil in a porous media

Subsurface behavior of spilled fuel in freezing and frozen porous media including fractured bedrock is not well understood. To simulate a bedrock fracture, a freezing cell consisting of two parallel glass plates filled with glass beads was constructed to study the impact of cyclic freeze-thaw on LNAPL movement. The test procedure involved introduction of LNAPL atop the cell that contained water mixed with fluorescein dye. Freezing progressed from the top down, with observation and measurement of the LNAPL migration using a high-resolution digital camera and time-lapse photography. Both diesel and soluble oil were used for the experiments. Tests with soluble oil involved thorough mixing at 12.5% volume ratio with the fluorescein-water mixture in the freezing cell. The results showed upward mobility of the LNAPL under cyclic freezing and downward progressive expulsion of the soluble oil ahead of the advancing freezing front. The results corroborated literature findings on organic solute expulsion ahead of freezing front, and provided insight into the behavior of trapped LNAPL below the water table when subjected to freeze-thaw conditions. Additionally, micro fissures were observed in the formed ice inside the freezing cell under prolonged freezing. Such micro fissures may provide potential migration pathways for fresh spilled fuel in permafrost environments.