Hierarchical visibility for guaranteed search in large-scale outdoor terrain

Searching for moving targets in large environments is a challenging task that is relevant in several problem domains, such as capturing an invader in a camp, guarding security facilities, and searching for victims in large-scale search and rescue scenarios. The guaranteed search problem is to coordinate the search of a team of agents to guarantee the discovery of all targets. In this paper we present a self-contained solution to this problem in 2.5D real-world domains represented by digital elevation models (DEMs). We introduce hierarchical sampling on DEMs for selecting heuristically the close to minimal set of locations from which the entire surface of the DEM can be guarded. Locations are utilized to form a search graph on which search strategies for mobile agents are computed. For these strategies schedules are derived which include agent paths that are directly executable in the terrain. Presented experimental results demonstrate the performance of the method. The practical feasibility of our approach has been validated during a field experiment at the Gascola robot training site where teams of humans equipped with iPads successfully searched for adversarial and omniscient evaders. The field demonstration is the largest-scale implementation of a guaranteed search algorithm to date.     

Understanding the Friction Mechanisms Between the Human Finger and Flat Contacting Surfaces in Moist Conditions

Human hands sweat in different circumstances and the presence of sweat can alter the friction between the hand and contacting surface. It is, therefore, important to understand how hand moisture varies between people, during different activities and the effect of this on friction. In this study, a survey of fingertip moisture was done. Friction tests were then carried out to investigate the effect of moisture. Moisture was added to the surface of the finger, the finger was soaked in water, and water was added to the counter-surface; the friction of the contact was then measured. It was found that the friction increased, up until a certain level of moisture and then decreased. The increase in friction has previously been explained by viscous shearing, water absorption and capillary adhesion. The results from the experiments enabled the mechanisms to be investigated analytically. This study found that water absorption is the principle mechanism responsible for the increase in friction, followed by capillary adhesion, although it was not conclusively proved that this contributes significantly. Both these mechanisms increase friction by increasing the area of contact and therefore adhesion. Viscous shearing in the liquid bridges has negligible effect. There are, however, many limitations in the modelling that need further exploration.     

Layer 2 and 3 virtual private networks: taxonomy, technology, and standardization efforts

Virtual private network services are often classified by the OSI layer at which the VPN service provider's systems interchange VPN reachability information with customer sites. Layer 2 and 3 VPN services are currently being designed and deployed, even as the related standards are being developed. This article describes the wide range of emerging L2 and L3 VPN architectures and technical solutions or approaches, and discusses the status of standards work. Some specific L2VPN and L3VPN technologies described here include virtual private LAN service, transparent LAN service, BGP/MPLS-based VPNs (RFC 2547bis), virtual router, and IPSec VPN approaches. We discuss recent and continuing standards efforts in the IETF 12vpn and 13vpn working groups, and related work in the pseudo-wire emulation edge-to-edge working group, as well as in some other standards fora, and describe some mechanisms that provide membership, reachability, topology, security, and management functions.     

On the analysis of two-dimensional discrete singular systems

In contrast to 1-D systems, the 2-D systems have no natural notion of causality. An artificial restriction traditionally imposed to allow recursive solution of these systems is that of recursibility. In this paper we study 2-Dsingular systems, taking advantage of the nonoriented or noncausal nature of these systems to provide a solution even if the requirement of recursibility does not hold. It is shown thatnonrecursible masks may be described using singular 2-D systems. The analysis approach relies on thefundamental matrix.Research supported by the US Fulbright Foundation in Greece and NSF Grant ECS-8805932.     

Electrical polarization control of vertical-cavity surface-emittinglasers using polarized feedback and a liquid crystal

We report electrical control of the polarization state of a vertical-cavity surface-emitting laser (VCSEL), The VCSEL is subject to strong external optical feedback (up to 6% of emission), with polarization controlled by a liquid-crystal (LC) element, It is found that the contrast ratio of the complete system can be enhanced compared to the contrast ratio of the LC element alone     

Preliminary investigations on some potential sources of protected methionine derivatives for ruminant rations

A series of N-substituted methionine derivatives were investigated for their potential to resist rumen degradation but still to release methionine in the duodenum. The method adopted was (a) to measure rumen methyl mercaptan concentrations in sheep following intraruminal doses of the materials and (b) to measure the ability of the materials to promote the growth of chicks receiving a methionine deficient diet.     

740 nm InP/GaInP quantum-dot laser with 190 A cm/sup -2/ room temperature threshold current density

InP quantum-dot lasers grown on GaAs substrates and emitting in the 730-740 nm band with threshold current density as low as 190 A cm/sup -2/ for a 2000 /spl mu/m-long device with uncoated facets are reported.     

The volatile flavour components of commercial port wines

Gas chromatographic-mass spectrometric examination of aroma extracts from both Ruby and Tawny port has led to the identification of 141 components, notably 2-methoxyphenol, dihydro-2-(3H)-furanone, β-methyl-γ-octalactone, cis-4-hydroxy-methyl-2-methyl-l,3-dioxolane, ethyl pyroglutamate and vitispirane. Odour evaluation of the components separated by gas chromatography indicates five regions as being of potential importance in port. 2-Methoxyphenol and dihydro-2-(3H)-furanone were found in two of these regions, three others being associated with esters of succinic acid. None of these components can, however, wholly explain the port-like odour.     

Effect of exercise and pre-slaughter stress on pork muscle characteristics

The effects of exercise, stress and chill temperature on pork muscle characteristics were studied in a 3 × 2 × 2 factorial experiment in which treatments were assigned to blocks made up of six pigs of the same sex from the same litter. Pigs were fed a corn-soybean meal diet with the two littermate pigs on each treatment fed together. Treatments were (1) a control group receiving no exercise and fed in an 8 m(2) pen; (2) a treatment group fed in an 8 m(2) pen and driven 1·6 km/day for 100 days prior to slaughter; and (3) a treatment group fed in pens with 40 m(2) floor space with feeders placed 5 m from their waterers. When the animals averaged approximately 105 kg in weight, one animal from each pair treated alike was subjected to standardized stress. After slaughter, one side was chilled at 2-3°C and the other at 13-15°C for 24 h. Both sides were then chilled at 2-3°C for an additional 24 h. Exercise did not affect average daily gain (ADG), feed efficiency, yield of total wholesale cuts, muscle pH, protein solubility, fiber diameter and sarcomere length of the Longissimus dorsi (LD) and Quadriceps femoris (QF) muscles or the tenderness of the QF muscle. Exercise decreased backfat thickness and the subjective tenderness of the LD muscle. The effects of stress on the characteristics evaluated were consistent with those that have been previously reported. Chilling temperature and interactions involving chilling temperature did not affect any of the characteristics studied. No exercise × stress interactions were observed. Protein solubility values indicated that pale, soft exudative (PSE) muscle was not a factor in any of the treatments. It was concluded that exercise will produce leaner carcasses but less tender muscle and that exercise will not counteract the effects of pre-slaughter stress.