Spatial competition and market interdependence

This paper investigates the optimality properties of interdependent spatial markets in a situation of price-location competition. A framework is developed where interdependences on the demand side of the economy are fully accounted for. It is assumed that goods supplied in the economy are not independent in terms of consumption. In addition, consumers can capture economies of scope in travel by shopping for several goods on one trip. Two goods are available in addition to a composite product. The problem involves two non-cooperative firms that exhibit a Nash behavior in selling their single product to a population uniformly distributed around a circumference. The level of interdependence between markets is expressed by the transportation rate, and by two other parameters indicating the relations of complementarity/substitutability among goods. A numerical analysis of comparative statics is conducted to examine the role of these parameters on firms' optimal location and price configurations.An earlier version of this paper was presented at the 37th North American Meetings, Boston, November 1990.     

Structural and sequence elements required for the self-cleaving activity of the hepatitis delta virus ribozyme

The hepatitis delta virus (HDV) is a subviral RNA that contains a self-cleaving activity that is similar to the ribozyme activity found in certain plant pathogens. However, the sequences surrounding the cleavage site are unrelated to the hammerhead or hairpin ribozyme motifs, and it is considered to be a distinct ribozyme type. We made site-specific changes within two regions of the smallest contiguous HDV sequence that has optimal activity and kinetically analyzed the data at different temperatures to determine the potential roles of the residues. We distinguish between those changes that affect the rate of catalysis and those that promote the formation of inactive structures. We find that nucleotides +45 to +72 downstream from the cleavage site, which can form a hairpin structure, are dispensable for catalytic activity but that they enhance the cleavage efficiency. Nucleotides +17 to +19 and +28 to +30 form Watson and Crick base pairs that are important for activity, but the actual sequence is not critical. In contrast, the nucleotides between +21 and +26 are important for activity, and they may be involved in significant tertiary interactions.     

Spatial duopolistic competition with multipurpose and multistop shopping

This paper explores the impact of multipurpose and multistop shopping behavior on spatial competition among retail firms. The problem deals with a duopoly situation on a line segment. It is shown analytically that a unique location-price Nash equilibrium exists. In equilibrium, the locational configuration is dependent upon consumers' propensity for multipurpose shopping.     

Analysis of traffic hazard intensity: A spatial epidemiology case study of urban pedestrians

Traffic safety studies have underscored the hazardous conditions of pedestrians in the United States. This situation calls for increased public awareness of the pedestrian safety issue and better knowledge of the main factors contributing to traffic hazard for urban pedestrians. The purpose of this spatial epidemiology research is to gain greater insights into the geographic dimension exhibited by the intensity of traffic collisions involving urban pedestrians. Pedestrian crashes are studied in Buffalo, NY for years 2003 and 2004. Factors of hazard intensity are determined and compared for three age cohorts as well as for collisions occurring at intersections versus mid-block locations. Physical road characteristics and density of development, as well as socio-economic and demographic variables and potential trip attractors are examined. Spatial regression models are used to account for spatial dependencies. Econometric analysis underscores that all classes of environmental factors tested are significant drivers of pedestrian traffic hazard intensity. Results of the geographic analysis indicate that young and adult pedestrian traffic hazard intensities follow rather distinct logics. In addition, intersection and mid-block crashes differ by their socio-economic correlates, as well as their spatial distribution in the urban fabric.     

Impact of patient consciousness on the intensity of the do-not-resuscitate therapeutic plan

The pluri- or totipotency of gonial cells, isolated from rabbit fetuses at 18-20 days of pregnancy, has been investigated by transferring their nuclei into enucleated oocytes and following the development of the resulting reconstituted embryos both in vitro (in a total of 726 embryos) and in vivo (in 135 embryos). The gonial cells exhibited pseudopodial activity like that of primordial germ cells and ultrastructural studies confirmed that neither male nor female cells had entered meiosis. When the gonial cells were used immediately after isolation, about 37% of the reconstituted embryos of both sexes cleaved, with no significant difference according to sex. However, after a further 4-day culture of the cleaved embryos, the blastocyst formation rate was four times higher in those made with male (16%) than with female (4%) gonial cells. No implantation sites were detected following transfer of reconstituted embryos into recipient females. These results show that the nuclei of male and female rabbit diploid germ cells differ in their capability to be "reprogrammed" and bring about development to the blastocyst stage following nuclear transfer. The origin of this difference, which is evidenced long before the onset of meiosis is discussed.     

Spatial competition and contestability based on choice histories of consumers

The paper proposes an empirical framework for measuring competitive interactions between pairs of firms in a certain industry characterized by spatially differentiated firms and heterogeneity in consumer tastes. Recognizing that the degree of competition between firms depends on the extent to which a representative consumer switches among firms, the framework is built on the Latent Class Logit model and on consumer choice histories. It emphasizes the spatial dimension of competition, provides a disaggregated measure of demand contestability, and proposes a network‐based model of supplier competition using a new Global Pairwise Competition Index.     

Investigation of trapezoidal corrugated aramid/epoxy laminates under large tensile displacements transverse to the corrugation direction

Corrugated structures are noted for their exhibition of extreme anisotropic stiffness properties which may be useful in aircraft morphing wing skin applications. As part of a wider study to compare the stiffness properties of corrugated laminates made from different materials and geometries, anomalous experimental results were obtained with trapezoidal corrugated aramid/epoxy laminates subjected to large tensile deformations transverse to the corrugation direction. This study investigates the local failure mechanisms of these specimens that explain the obtained experimental results. Static and cyclic experimental testing identified three stages of behaviour in the structure’s stress vs. global strain response. The majority of the displacement comes from the second stage. This was attributed to the aramid fibre compressive properties and delaminations in the corrugated unit cell corner region. This local phenomenon is comparable to a pseudo-plastic hinge that allows large deformations over relatively constant stress levels. This behaviour is thought not to occur in glass and carbon fibre corrugated laminates because it was related specifically to the aramid fibre response. Analytical and numerical analysis showed that the equivalent transverse tensile elastic modulus of the corrugated laminate can be predicted; while the complete three-stage behaviour can also be modelled using non-linear finite element analysis with local elastic–plastic material definitions.     

User-defined challenges and desiderata for robotics and autonomous systems in health and social care settings

ABSTRACT

We report the needs and challenges identified by health and social care professionals and service users for robotics and autonomous systems that are of importance to researchers and policymakers. To this end, we held eight workshops in different locations across Cornwall (UK) in which we raised awareness of the applications and opportunities of assistive robots. The 223 participants could interact physically with four robots, watched a multimedia presentation including video and use-case scenarios and then took part in 33 focus groups. Content analysis was carried out based on summaries written by facilitators during the focus groups. The focus groups produced 163 challenges that may have digital solutions including 78 suitable for robotic assistive technology, in three main areas: maintaining independence at home, social isolation, and rurality. Although further research is needed with technology and its implementation, this study shows that health and social care professionals, patients, carers, and students are willing to consider using robotics and autonomous systems in health and social care settings.     

Network competition and branch differentiation with consumer heterogeneity

The paper provides a general framework for the analysis of noncooperative competition between multi-branch networks when consumers have heterogeneous preferences. This framework allows for ill-studied conditions, such as branch loyalty and economies of scope, to be explored in terms of their role in shaping address solutions and firm profits. Geographic and quality differentiation as well as firm profits are shown to be dependent upon the magnitude of the loyalty factor and upon the extend of economies of scope. Real world situations in the retail industry are interpreted in the light of the results of the analysis. Received: October 1998 / Accepted: June 1999