On the computational complexity of dynamic slicing problems for program schemas

This is the preprint version of the Article - Copyright @ 2011 Cambridge University PressGiven a program, a quotient can be obtained from it by deleting zero or more statements. The field of program slicing is concerned with computing a quotient of a program that preserves part of the behaviour of the original program. All program slicing algorithms take account of the structural properties of a program, such as control dependence and data dependence, rather than the semantics of its functions and predicates, and thus work, in effect, with program schemas. The dynamic slicing criterion of Korel and Laski requires only that program behaviour is preserved in cases where the original program follows a particular path, and that the slice/quotient follows this path. In this paper we formalise Korel and Laski's definition of a dynamic slice as applied to linear schemas, and also formulate a less restrictive definition in which the path through the original program need not be preserved by the slice. The less restrictive definition has the benefit of leading to smaller slices. For both definitions, we compute complexity bounds for the problems of establishing whether a given slice of a linear schema is a dynamic slice and whether a linear schema has a non-trivial dynamic slice, and prove that the latter problem is NP-hard in both cases. We also give an example to prove that minimal dynamic slices (whether or not they preserve the original path) need not be unique.This work was partly supported by the Engineering and Physical Sciences Research Council, UK, under grant EP/E002919/1

Effectiveness of a Perceived Solid Barrier as an Exclusion Fence to Prevent White-Tailed Deer Damage

We hypothesized that a visually solid barrier of cloth would provide an effective exclusion fence for free ranging white-tailed deer (Odocoileus virginianus). Three plots consisting of 2, 10 m x 10 m squares were established in pastures. Data were collected daily for consumption of com provided (2.27 kg) and events recorded by infrared game monitors. Following construction of the burlap fence at 1.7 m height, corn consumption decreased (0.07 ± 0.01 kg/day, P \u3c .001). The number of Infrared monitor events recorded also decreased within the enclosures (2.13 ± 0.04 events/day, P \u3c .001) compared to controls (46.0 ± 2.2 events/day). During the second stage of the experiment, two of the three plots were reestablished 45 days later. Fence heights began at 65 cm and were raised 15 cm each 5 days, until reaching 1.7 m. At 1.7 m, corn consumption decreased by 30% (1.56 ± 0.23 kg/day, P \u3c .01). The number of infrared monitor-recorded events was also lower at fence heights \u3e65 cm (P \u3c .03). Results indicate that a visually solid barrier has potential to be an effective exclusion fence

Effectiveness of a White-Tailed Deer Exclusion Fence Based on Traction Limitations of the Hoof: The Slipper Fence

We hypothesized that an exclusion fence could be devised to capitalize on traction limitations of the hooves of white-tailed deer (Odocoileus virginianus). Hexagonal plots (9.8 m wide) enclosed by a 2.4 m field fence with two openings (4.9 m) were established. Data were collected daily on consumption of corn provided (2.27 kg) and events recorded by infrared monitors (IR) for treatment and control sites. Five-day treatment periods consisted of test panels (4.9 m x 2.4 m) placed in plot openings at 0°, 5° and 10° slopes, and lubricant applied at the 10° slope. Deer consumed all corn provided at control sites. At the 10 ° slope, daily corn consumption decreased (1.50 kg ± 0 .26, p \u3c .0 l ), and IR events were lower (p \u3c .01) at treatment sites (23.6 ± 3.2) compared to controls (50.3 ± 9.6). With the addition of a lubricant, corn consumption decreased further (p \u3c .001) to 0. 17 kg ± 0.03, and IR recorded events were lower (p \u3c .001) at treatment sites (6.58 ± 0 .89) compared to controls (44.8 ± 3.1). Results of this study indicate that traction limitation of the hoof can be exploited

The Evolution of Quasar CIV and SiIV Broad Absorption Lines Over Multi-Year Time Scales

We investigate the variability of CIV 1549A broad absorption line (BAL) troughs over rest-frame time scales of up to ~7 yr in 14 quasars at redshifts z>2.1. For 9 sources at sufficiently high redshift, we also compare CIV and SiIV 1400A absorption variation. We compare shorter- and longer-term variability using spectra from up to four different epochs per source and find complex patterns of variation in the sample overall. The scatter in the change of absorption equivalent width (EW), Delta EW, increases with the time between observations. BALs do not, in general, strengthen or weaken monotonically, and variation observed over shorter (<months) time scales is not predictive of multi-year variation. We find no evidence for asymmetry in the distribution of Delta EW that would indicate that BALs form and decay on different time scales, and we constrain the typical BAL lifetime to be >~30 yr. The BAL absorption for one source, LBQS 0022+0150, has weakened and may now be classified as a mini-BAL. Another source, 1235+1453, shows evidence of variable, blue continuum emission that is relatively unabsorbed by the BAL outflow. CIV and SiIV BAL shape changes are related in at least some sources. Given their high velocities, BAL outflows apparently traverse large spatial regions and may interact with parsec-scale structures such as an obscuring torus. Assuming BAL outflows are launched from a rotating accretion disk, notable azimuthal symmetry is required in the outflow to explain the relatively small changes observed in velocity structure over times up to 7 yr

Clustering of solutions in the random satisfiability problem

Using elementary rigorous methods we prove the existence of a clustered phase in the random $K$-SAT problem, for $K\geq 8$. In this phase the solutions are grouped into clusters which are far away from each other. The results are in agreement with previous predictions of the cavity method and give a rigorous confirmation to one of its main building blocks. It can be generalized to other systems of both physical and computational interest.Comment: 4 pages, 1 figur

Transport Property Requirements for Flow Battery Separators

Flow batteries are a promising technology for storing and discharging megawatt hours of electrical energy on the time scale of hours. The separator between the positive and negative electrodes strongly affects technical and economic performance. However, requirements for separators have not been reported in a general manner that enables quantitative evaluation of new systems such as nonaqueous flow batteries. This gap is addressed by deriving specifications for transport properties that are chemistry agnostic and align with aggressive capital cost targets. Three key transport characteristics are identified: area-specific resistance RΩ, crossover current density ix, and the coupling between crossover and capacity loss Ψ. Suggested maximum area-specific resistances are 0.29 and 2.3 Ω·cm[superscript 2] for aqueous and nonaqueous batteries, respectively. Allowable crossover rates are derived by considering the possible fates of active molecules that cross the separator and the coupling between Coulombic efficiency (CE) and capacity decline. The CE must exceed 99.992% when active species are unstable at the opposing electrode, while a CE of 97% can be tolerated when active molecules can be recovered from the opposing electrode. The contributions of diffusion, migration, and convection are discussed, quantified, and related to the physical properties of the separator and the active materials.United States. Department of Energy. Office of Basic Energy Sciences (Joint Center for Energy Storage Research

Optical and ultraviolet observations of nova Vul 1987

The outburst for a nova discovered in Nov. 1987 and followed since then is summarized. Although it was possible to observe it with the IUE at maximum, its ultraviolet energy faded rapidly, and after the first 2 weeks it was impossible to observe it at IUE wavelengths. It is observed to form a thick dust shell and is in the nebular stage

Conditioning and Habituation of White-Tailed Deer to Two Common Deterrents

It was hypothesized white-tailed deer (Odocoileus virginianus) could be readily conditioned to 2 commonly used deterrents, Deer-Away® Big Game Repellent (BGR) and blood meal (BM). Plots were randomly assigned BGR, BM and control. Free-ranging deer were initially conditioned to forage for corn at each 49m 2 bare earth plots delivered at 0500 hr and 1600 hr by programmable siing-type feeders. Hoof prints were counted within a 3.7m 2 sample area of each plot to quantify activity. Following preconditioning, data were collected during 5, 5-day periods. Application of BGR and BM to their respective bare earth plots occurred during periods 2, 4 and 5. Initial exposure decreased the number of hoof-prints for BGR (P = 0.011) and BM (P = 0.033) compared to the control. Subsequent exposure to BGR during periods 4 and 5 did not differ from the control (P \u3e 0.227). Prints counted following exposure to BM were similar to the control in period 4 (P = 0.267), but lower (P = 0.045) in period 5. Within each treatment group , prints counted were lower during period 2 compared to periods 1, 3, 4 and 5 for both BGR (P =0.001) and BM (P = 0.018). No differences (P \u3e 0.05) were found among periods 1,3,4 and 5 within each treatment. Results support the hypothesis that white-tailed deer can readily be conditioned to these two commonly used deterrents

The Potential of Texture as a Deer Deterrent: The Slime Effect

We examined the potential of altering the surface texture of plant material as a potential deterrent to consumption by white-tailed deer. Two u-shaped garden plots were divided into 16, uniform plots (2.2mx4.3m) each containing approximately 50 chrysanthemums (C. morifolium). The plots were randomly assigned to one of the treatments or as a control. Immediately after planting, ten plants were randomly selected and marked within each plot. Plants were misted and treatments applied by hand broadcast. Treatments consisted of methyl cellulose (38.2g) and two-levels of a proprietary polymer (9. lg and 45.5g). Upon contact with water, methyl cellulose became a viscous slime while the proprietary polymer was similar to gelatin. Each substance was visible on the plants throughout the study. Bite marks were counted on the ten marked plants within each plot, on 4 occasions at 3-day intervals. None of the treatments were effective in deterring deer from consuming plant material. Differences were noted among plot locations, suggesting deer entered the garden predominantly from a single general direction and consumed forages most readily available