1,177 research outputs found
Capacitated Vehicle Routing with Non-Uniform Speeds
The capacitated vehicle routing problem (CVRP) involves distributing
(identical) items from a depot to a set of demand locations, using a single
capacitated vehicle. We study a generalization of this problem to the setting
of multiple vehicles having non-uniform speeds (that we call Heterogenous
CVRP), and present a constant-factor approximation algorithm.
The technical heart of our result lies in achieving a constant approximation
to the following TSP variant (called Heterogenous TSP). Given a metric denoting
distances between vertices, a depot r containing k vehicles with possibly
different speeds, the goal is to find a tour for each vehicle (starting and
ending at r), so that every vertex is covered in some tour and the maximum
completion time is minimized. This problem is precisely Heterogenous CVRP when
vehicles are uncapacitated.
The presence of non-uniform speeds introduces difficulties for employing
standard tour-splitting techniques. In order to get a better understanding of
this technique in our context, we appeal to ideas from the 2-approximation for
scheduling in parallel machine of Lenstra et al.. This motivates the
introduction of a new approximate MST construction called Level-Prim, which is
related to Light Approximate Shortest-path Trees. The last component of our
algorithm involves partitioning the Level-Prim tree and matching the resulting
parts to vehicles. This decomposition is more subtle than usual since now we
need to enforce correlation between the size of the parts and their distances
to the depot
Continuous-wave and passively Q -switched cladding-pumped planar waveguide lasers
Greater than 12W of average output power has been generated from a diode-pumped YbYAG cladding-pumped planar waveguide laser. The laser radiation developed is linearly polarized and diffraction limited in the guiding dimension. A slope efficiency of 0.5WW with a peak optical optical conversion efficiency of 0.31WW is achieved. In a related structure, greater than 8W of Q -switched average output power has been generated from a NdYAG cladding-pumped planar waveguide laser by incorporation of a Cr 4+ YAG passive Q switch monolithically into the waveguide structure. Pulse widths of 3ns and pulse-repetition frequencies as high as 80kHz have been demonstrated. A slope efficiency of 0.28WW with a peak optical optical conversion efficiency of 0.21WW is achieved
Continuing professional development:introducing the ERS International Certificate in Respiratory Sleep Medicine
Certification of specialists in respiratory sleep medicine for the purposes of continuing professional developmen
CW and passively Q-switched double-clad planar waveguide lasers
Greater than 12 W of average output power have been generated from a diode pumped Yb:YAG cladding-pumped planar waveguide laser. The developed laser radiation is linearly polarized and diffraction limited in the guiding dimension. A slope efficiency of 0.5 W/W with a peak optical-optical conversion efficiency of 0.31 W/W is achieved. In a related structure, greater than 8 W of Q-switched average output power has been generated from a Nd:YAG cladding-pumped planar waveguide incorporating Cr:YAG passive Q-switch monolithically into the waveguide structure. Pulse widths of 3 nsec and PRFs as high as 80 kHz have been demonstrated. A slope efficiency of 0.28 W/W with a peak optical-optical conversion efficiency of 0.21 W/W is achieved
Facility for studying the effects of elevated carbon dioxide concentration and increased temperature on crops
The requirements for the experimental study of the effects of global climate change conditions on plants are outlined. A semi-controlled plant growth facility is described which allows the study of elevated CO2 and temperature, and their interaction on the growth of plants under radiation and temperature conditions similar to the field. During an experiment on winter wheat (cv. Mercia), which ran from December 1990 through to August 1991, the facility maintained mean daytime CO2 concentrations of 363 and 692 cm3 m-3 for targets of 350 and 700 cm3 m-3 respectively. Temperatures were set to follow outside ambient or outside ambient +4-degrees-C, and hourly means were within 0.5-degrees-C of the target for 92% of the time for target temperatures greater than 6-degrees-C. Total photosynthetically active radiation incident on the crop (solar radiation supplemented by artifical light with natural photoperiod) was 2% greater than the total measured outside over the same period
Overcoming controllability problems in distributed testing from an input output transition system
This is the Pre-print version of the Article. The official published version can be accessed from the link below - Copyright @ 2012 Springer VerlagThis paper concerns the testing of a system with physically distributed interfaces, called ports, at which it interacts with its environment. We place a tester at each port and the tester at port p observes events at p only. This can lead to controllability problems, where the observations made by the tester at a port p are not sufficient for it to be able to know when to send an input. It is known that there are test objectives, such as executing a particular transition, that cannot be achieved if we restrict attention to test cases that have no controllability problems. This has led to interest in schemes where the testers at the individual ports send coordination messages to one another through an external communications network in order to overcome controllability problems. However, such approaches have largely been studied in the context of testing from a deterministic finite state machine. This paper investigates the use of coordination messages to overcome controllability problems when testing from an input output transition system and gives an algorithm for introducing sufficient messages. It also proves that the problem of minimising the number of coordination messages used is NP-hard
Tracking a northern fulmar from a Scottish nesting site to the Charlie-Gibbs Fracture Zone : Evidence of linkage between coastal breeding seabirds and Mid-Atlantic Ridge feeding sites
Peer reviewedPublisher PD
Behavioral and physiological changes around estrus events identified using multiple automated monitoring technologies
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