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Resource Demands (resource + demand)
Selected AbstractsThe Plant's Capacity in Regulating Resource DemandPLANT BIOLOGY, Issue 6 2005R. Matyssek Abstract: Regulation of resource allocation in plants is the key to integrate understanding of metabolism and resource flux across the whole plant. The challenge is to understand trade-offs as plants balance allocation between different and conflicting demands, e.g., for staying competitive with neighbours and ensuring defence against parasites. Related hypothesis evaluation can, however, produce equivocal results. Overcoming deficits in understanding underlying mechanisms is achieved through integrated experimentation and modelling the various spatio-temporal scaling levels, from genetic control and cell metabolism towards resource flux at the stand level. An integrated, interdisciplinary research concept on herbaceous and woody plants and its outcome to date are used, while drawing attention to currently available knowledge. This assessment is based on resource allocation as driven through plant-pathogen and plant-mycorrhizosphere interaction, as well as competition with neighbouring plants in stands, conceiving such biotic interactions as a "unity" in the control of allocation. Biotic interaction may diminish or foster effects of abiotic stress on allocation, as changes in allocation do not necessarily result from metabolic re-adjustment but may obey allometric rules during ontogeny. Focus is required on host-pathogen interaction under variable resource supply and disturbance, including effects of competition and mycorrhization. Cost/benefit relationships in balancing resource investments versus gains turned out to be fundamental in quantifying competitiveness when related to the space, which is subject to competitive resource exploitation. A space-related view of defence as a form of prevention of decline in competitiveness may promote conversion of resource turnover across the different kinds of biotic interaction, given their capacity in jointly controlling whole plant resource allocation. [source] Environmental Predictors of Geographic Variation in Human Mating PreferencesETHOLOGY, Issue 4 2002Kevin J. McGraw Sexual selection theory classically posits consistent and directional mate-preferences for male traits that provide benefits to females. However, flexible mate-choice tactics may persist within a species when males display multiple desirable features that confer different benefits to females under variable environmental conditions. Ecological factors such as population density, resource demand, and sex ratio can influence the value that female animals place on certain male characteristics across mating environments. In this study, I used human mate-preference data from `lonely hearts' advertisements in the newspapers of 23 cities in the USA to assess geographic differences in female preferences for male traits (e.g. physical attributes, resource-holding potential, emotional characteristics, personal interests) in relation to these ecological parameters. I found that females placed more emphasis on the resource-accruing ability of prospective mates in densely populated cities and cities having greater resource demands (higher cost of living). In contrast, women from densely populated or resource-demanding cities placed less emphasis on the emotional aspects or personal interests of males. Preferences for physical features were not environmentally linked, but instead were a function of the degree to which females advertised their own physical attractiveness. Collectively, these results suggest that certain mate-choice criteria employed by women are sensitive to variation in local environmental conditions and that variable levels of resource or mate availability may favor different mating tactics across human populations. [source] Improving node behaviour in a QoS control environment by means of load-dependent resource redistributions in LANs,INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 4 2005Bernd E. Wolfinger Abstract An important means to guarantee an acceptable quality of service in networks with real-time communication requirements is the reservation of resources at connection setup time. However, such reserved resources, e.g. transmission bandwidth, may be unused as a consequence of the variations in the actual resource demands. Therefore, a more efficient resource utilization is possible if communicating stations or end-users dynamically hand over some of the free resources temporarily to the other communication partners, e.g. of a ,broadcast network'. This paper concentrates on two fundamental problems of such a demand-based sharing of resources: on the one hand, estimation of the current resource requirement on the basis of load measurements is investigated and, on the other hand, we elaborate efficient algorithms for resource sharing respecting real-time requirements. The algorithms proposed for load estimation and for resource sharing are evaluated analytically with respect to their efficiency for worst-case, average-case and realistic load scenarios. Our approach suggested for resource and traffic management allows one to achieve significantly better utilization of network resources. Copyright © 2005 John Wiley & Sons, Ltd. [source] Assessing suturing techniques using a virtual reality surgical simulatorMICROSURGERY, Issue 6 2010Hamed Kazemi M.Eng. Advantages of virtual-reality simulators surgical skill assessment and training include more training time, no risk to patient, repeatable difficulty level, reliable feedback, without the resource demands, and ethical issues of animal-based training. We tested this for a key subtask and showed a strong link between skill in the simulator and in reality. Suturing performance was assessed for four groups of participants, including experienced surgeons and naive subjects, on a custom-made virtual-reality simulator. Each subject tried the experiment 30 times using five different types of needles to perform a standardized suture placement task. Traditional metrics of performance as well as new metrics enabled by our system were proposed, and the data indicate difference between trained and untrained performance. In all traditional parameters such as time, number of attempts, and motion quantity, the medical surgeons outperformed the other three groups, though differences were not significant. However, motion smoothness, penetration and exit angles, tear size areas, and orientation change were statistically significant in the trained group when compared with untrained group. This suggests that these parameters can be used in virtual microsurgery training. © 2010 Wiley-Liss, Inc. Microsurgery 30:479,486, 2010. [source] Sex-specific physiological, allocation and growth responses to water availability in the subdioecious plant Honckenya peploidesPLANT BIOLOGY, Issue 2 2009J. Sánchez-Vilas Abstract The gender of dimorphic plant species is often affected by ecophysiological variables. Differences have been interpreted as a response of the sexes to meet specific resource demands associated with reproduction. This study investigated whether sex-specific variations in ecophysiological traits in response to water availability determine the performance of each sex in different habitats, and therefore promote extreme spatial segregation of the sexes in the subdioecious plant, Honckenya peploides. Twenty-seven plants of each sex were individually potted in dune sand and assigned randomly to one of three water treatments. Well-watered plants were watered daily to field capacity, whereas plants in the moderate and high-water stress treatments received 40% and 20%, respectively, of the water given to well-watered plants. Photochemical efficiency, leaf spectral properties and components of relative growth rate (leaf area ratio and net assimilation rate) were measured. Photochemical efficiencies integrated over time were higher in male than in female plants. Water deficit decreased maximum quantum yield in female plants more rapidly than in male plants, but female plants (unlike male plants) had recovered to initial values by the end of the experiment. Maximum quantum yield in male plants was more affected by water stress than in female plants, indicating that male plants were more susceptible to photoinhibition. The two sexes did not differ in growth rate, but male plants invested a higher proportion of their biomass in leaves, had a higher leaf area per unit biomass and lower net assimilation rate relative to female plants. Female plants had a higher water content and succulence than male plants. Differences in stomatal density between the sexes depended on water availability. The results suggest that the two sexes of H. peploides have different strategies for coping with water stress. The study also provides evidence of sex differences in allocation traits. We conclude that between-sex differences in ecophysiological and allocation traits may contribute to explain habitat-related between-sex differences in performance and, therefore, the spatial segregation of the sexes. [source] Dairy cows trapped between performance demands and adaptability,JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 7 2009Wilhelm Knaus Abstract The tremendous increase in the lactation performance of dairy cows during the last 60 years has had dramatic consequences on fertility and vitality (fitness) of the animals. Unprecedented average lactation performance levels have resulted in an equally unprecedented reduction in longevity. Economic pressure to further reduce the age at first calving is still high, although the negative correlation between precocious maturity and longevity is well documented in the relevant literature. Ever more aggressive selection and feeding measures are being taken to shorten the rearing time of heifers in order to reduce the cost of replacement heifers. An additional decrease in the stayability of cows has to be expected when the age at first calving is lowered even further. For reasons of profitability, dairy cows should complete an average of at least four lactations. Cows from the most important dairy breeds in the United States and Bavaria, Germany, already dropped below that crucial threshold many years ago. The same phenomenon has been observed in dairy cows in Austria over the past few years. Holstein cows that were culled in Austria in 2007 had an average of only 3.3 parities. To improve this situation, dairy cattle breeding programs should put a much higher emphasis on selection for traits of longevity and lifetime performance and, in return, markedly reduce the emphasis on selection for lactation performance in general and early-lactation performance test results in particular. Over millions of years of evolutionary adaptation, cattle have acquired the ability to utilize fibrous low-quality plant substrate. Only a strongly forage-based feeding regimen is, in the long run, in accordance with their digestive and metabolic configuration. The massive use of concentrates (mostly grain) in cattle rations increases the risk of digestive and metabolic disorders in cattle and consequently leads to impaired animal welfare. Finally, the careful management of scarce resources demands that a closer look be taken at the food balance in dairy rations, i.e., an awareness of how much food that is edible for humans is being fed to livestock. Copyright © 2009 Society of Chemical Industry [source] | ||||||||||