Relaxing the nearest centre assumption in central place theory

Although a variety of modifications of classical central place theory has been proposed, one area that remains unexplored is the effect of relaxing the nearest centre assumption for the purchase of a specified basket of goods within a given hierarchical level. This article examines the effect of such a relaxation on central place market areas by using higher-order Voronoi diagrams. When used to model market areas, higher-order Voronoi diagrams can be interpreted as overlapping and probabilistic regions. These diagrams construct market areas based on the assumption that consumers choose from a set of nearest centres of the same hierarchical level. If consumers are assumed to be indifferent between the k centres, the appropriate market areas are given by the order-k Voronoi diagram. In this case, it is shown that sales potentials are consistent with those that result when the nearest centre assumption is in effect. If consumers are assumed to have a preference for nearer centres, market areas are defined by the ordered, order-k Voronoi diagram. This situation generates sales potentials which can vary between centres. Received: 2 February 1998 / Accepted: 21 January 1999     

Design and Analysis of Factorial Experiments Via Interactive Computing in APL

This paper discusses the use of interactive computing in APL for the design and analysis of an ad hoc experiment. As an example, a project involving a 16 × 4 × 2 experiment in 8 blocks of size 8 is reviewed. The desirability of utilizing single-degreeof-freedom pseudo-factors in both the design and analysis phases of such experiments is exhibited, and the detection of and compensation for heterogeneity of variance and outliers are discussed.     

MnS doped mesoporous silica catalysts for the generation of novel carbon nanocages

Novel MnS impregnated mesoporous silica systems have been originated for the generation of carbon nanocages. The procedure involves a simple catalytic vapour deposition (CVD) method. This is the first time that a transition metal sulfide has been used for the synthesis of carbon nanostructures.     

Factorial validity of Stephen's Social Behavior Assessment.

Conducted exploratory factor and item analyses of the Social Behavior Assessment (SBA), using teacher ratings of 301 elementary school pupils from regular classes (mean age 9.4 yrs), 39 learning disabled students (mean age 9.1 yrs), and 62 emotionally disturbed children (mean age 10.1 yrs). It was found that a 5-factor oblique solution was the most reasonable. Factors obtained from item analysis explained more of the variance than factors based on subcategory scores. A shorter revised instrument is proposed that consists of 71 items based on 4 underlying factors—Social Participation/Conversation, Academic Responsibility, Self-Control, and Consideration for Others. This revised SBA discriminated between Ss in regular classes and those enrolled in special education programs. Emotionally disturbed Ss had the most deviant scores on each of the 4 factors. (7 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sixteen-channel coherent broadcast network at 155 Mbit/s

An experimental 155.52 Mb/s coherent broadcast network with 16 channels using a conventional distributed feedback (DFB) laser operating at 1540 nm is described. It includes absolute laser frequency stabilization, a fiber span of 74.4 km, and a balanced polarization-diversity single-filter frequency-shift keying (FSK) heterodyne receiver. At a channel spacing of 8.5 GHz a power penalty of 0.3 dB is incurred due to adjacent channel crosstalk     

A two-platform task reveals a deficit in the ability of rats to return to the start location in the water maze.

The ability of rats to return to the start location was examined with a 4-arm radial water maze. The task required rats to find 2 hidden platforms in sequence. Rats were released from 1 of 3 arms and there was a platform located in the fourth arm. Once a rat found this platform, a 2nd platform was raised in another location, which was either the start location, for 1 group, or another fixed location, for a control group. Across 3 experiments, all rats learned the location of the 1st fixed platform in 80 to 120 trials. However, rats had difficulty finding a 2nd platform if it was at the start location. Control groups revealed that rats could learn 2 platform locations and that the difficulty in learning to return to the start location did not seem to be attributable to its aversive nature. In separate groups, exposure to the start location was increased by starting the rats from an initially stable platform. Rats still did not readily learn to return to the start location. The authors suggest that start location, when varied, cannot readily be used to define the location of a hidden platform. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evaluation of the mechanical behaviour of nanometre-thick coatings deposited using an atmospheric pressure plasma system

This study evaluated the use of pin-on-disc wear testing as a technique to examine the mechanical behaviour of nanometre thick plasma deposited coatings. The coatings were deposited onto polyethylene terephthalate and silicon wafer substrates by directly injecting an aerosol of siloxane liquid precursors into a helium/oxygen atmospheric pressure plasma. The siloxane precursors examined were hexamethyldisiloxane, polydimethylsiloxane and tetramethyldisiloxane. The mechanical performance of 21 (± 3) nm thick coatings was compared using a pin-on-disc wear test technique and fragmentation tests. An increase in the level of precursor plasma exposure was found to be associated with an increase in coating surface energy and a reduction in coating roughness and resulted in enhanced wear resistance. Fragmentation tests revealed a transition from ductile failure to brittle failure as the level of plasma exposure increased. This correlated with the reduction in coating wear rates. Wear track depth and proximity to the coating/substrate interface were both found to influence the rate or wear. A simple correlation between wear rate and applied force is presented as a method for comparing coating performance using pin-on-disc wear testing.     

The metal injection molding process comes of age

Metal injection molding is a new commercial process for producing complex component parts from steels and other ferrous alloys. The process combines the shape-making capability of plastic injection molding with high-temperature sintering technology to produce complex, high density metal parts with outstanding properties. The savings in production costs can be substantial over investment casting or expensive machining operations.