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Selected AbstractsBrochosome influence on parasitisation efficiency of Homalodisca coagulata (Say) (Hemiptera: Cicadellidae) egg masses by Gonatocerus ashmeadi Girault (Hymenoptera: Mymaridae)ECOLOGICAL ENTOMOLOGY, Issue 5 2005Hans-Paul Velema Abstract., 1.,Many cicadellid females in the tribe Proconiini (Hemiptera: Cicadellidae) cover their egg masses with specialised, usually rod-shaped, brochosomes as the eggs are being laid. The brochosomes are produced in Golgi complexes in the Malpighian tubules of Cicadellidae. In contrast to the gravid females, adult males, pre-reproductive adult females, and nymphal males and females produce specialised, usually spherically shaped brochosomes. Brochosomes are also used to cover the external surfaces of nymphs and newly moulted adult males and females. 2.,The function of the brochosome covering the egg masses is unknown but various hypotheses have been suggested, including protecting the eggs against pathogens, predators, and parasitoids. Based on preliminary observations of Gonatocerus ashmeadi Girault (Hymenoptera: Mymaridae) parasitising the eggs of the cicadellid, Homalodisca coagulata (Say), it is speculated here that brochosomes covering an egg mass hinder parasitisation of eggs by G. ashmeadi. This hypothesis was tested by observing G. ashmeadi females foraging on leaves with H. coagulata egg masses heavily covered with rod-shaped brochosomes vs. those lacking brochosomes. 3.,Cox's proportional hazards model was used to evaluate the probability, per unit time, that a female G. ashmeadi displayed the sequence of behaviours that ended in successful oviposition as influenced by five variables: (a) presence or absence of brochosomes on an egg mass, (b) the leaf surface, upper or lower, being searched by the parasitoid (the egg masses are laid in the parenchyma on the lower leaf surface), (c) the parasitoid's previous ovipositional experience, (d) egg mass size, and (e) the parasitoid's age. 4.,Brochosomes significantly decreased oviposition efficacy of G. ashmeadi females. Scanning electron microscopy showed that females exposed to brochosome-covered egg masses had brochosomes adhering to their tarsi, legs, antennae, and eyes, all of which prompted extensive bouts of grooming. [source] Prey size selection in piscivorous pikeperch (Stizostedion lucioperca) includes active prey choiceECOLOGY OF FRESHWATER FISH, Issue 4 2002H. Turesson Abstract,,,Knowledge of the mechanisms behind prey selection in piscivorous fish is important for our understanding of the dynamics of freshwater systems. Prey selection can involve active predator choice or be a passive process. We experimentally studied size-selectivity in pikeperch, feeding on roach and rudd. When given a choice of different prey sizes, pikeperch selected small prey. Passive selection mechanisms (encounter rate, capture success and satiation) could not fully explain the pattern of diet choice. Instead, behavioural analysis revealed that the pikeperch actively selected small-sized prey. Optimal foraging theory, predicting that predators will choose prey sizes giving highest energy return per time spent foraging, is assumed to explain active choice. We measured handling times for a range of prey sizes and found that the most profitable sizes were also the chosen ones, both in experiments and in the field. This suggests that pikeperch choose their prey to maximise energy intake per unit time. [source] Factors affecting density-independent survival of an island population of tsetse flies in ZimbabweENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 2 2001J.W. Hargrove Abstract Analysis is presented of the factors affecting survival probability in populations of tsetse flies Glossina morsitans morsitans Westwood and G. pallidipes Austen (Diptera: Glossinidae) on Antelope Island, Lake Kariba, Zimbabwe. For mature male and female adult G. m. morsitans mean temperature (Tbar) accounted for 70 and 50%, respectively, of the variance in mark-recapture estimates of survival when the flies were not subjected to trapping. Saturation deficit (SD) only accounted for 36 and 33%, respectively. Maximum temperature (Tmax) and SD accounted for 36,42% of the variance in male and female G. pallidipes. For the corresponding Moran curve estimates of the survival over all developmental stages, SD lagged by three weeks accounted for 61 and 41% of the variance for male and female G. m. morsitans, respectively, and 64 and 56% for G. pallidipes. The corresponding figures for plots against Tmax were 44, 23, 23, and 21%, respectively. The same patterns were seen in the whole data set once allowance was made for the effect of trapping on survival and for an effect of season, correlated with an index of photosynthetic activity. For male G. m. morsitans there was a significant effect of saturation deficit, but not temperature, on immature survival. Decreased adult survival at high temperatures results from the need to feed more frequently and hence to take more risks per unit time. High saturation deficits result directly in reduced emergence of healthy flies from pupae. [source] Foraging effort in relation to the constraints of reproduction in free-ranging albatrossesFUNCTIONAL ECOLOGY, Issue 1 2003S. A. Shaffer Summary 1Theoretical models predict that animals will vary their effort to maximize different currencies such as time and energy when the constraints of reproduction change during breeding, but this has been poorly studied in free-ranging animals. 2Foraging effort (energy per unit time) was examined by comparing mass changes, foraging costs and activity-specific behaviours of Wandering Albatrosses (Diomedea exulans Linnaeus) during the incubation and chick-brooding stages. In 1998, 38 albatrosses (20 during incubation and 18 during brooding) were injected with doubly labelled water and equipped with satellite transmitters and activity data loggers. 3During incubation, albatrosses travelled 3·7 times farther and were at sea 3·2 times longer, yet foraging costs were significantly lower than trips made during brooding (incubation 4·52 ± 0·50 SD W kg,1vs brooding 4·98 ± 0·55 SD W kg,1). 4The rate of daily mass gain decreased significantly with time at sea during incubation whereas the rate of daily mass gain increased significantly with time at sea during brooding. 5Foraging effort was higher during brooding, suggesting that birds were minimizing time at sea to maximize the rate of food delivery to chicks. In contrast, foraging effort was lower during incubation, suggesting that birds were maximizing time at sea and minimizing the energy costs of foraging. 6Foraging costs were also different between sexes. However, this was related to body size differences and not to differences in foraging effort as suggested in previous studies. [source] Antisymmetry in male fiddler crabs and the decision to feed or breedFUNCTIONAL ECOLOGY, Issue 1 2002A. E. Pratt Summary 1,In male Sand Fiddler Crabs, Uca pugilator, a major cheliped (with claw), used in intersexual displays and intrasexual contests, develops opposite a minor cheliped used for feeding. Cheliped size demonstrates antisymmetry because greater development is equally likely on the right or left side. 2,The side with the major cheliped (major side) also has longer walking legs which may facilitate use of the claw. In contrast, eye stalk asymmetry is equally due to antisymmetry and fluctuating asymmetry. Fluctuating asymmetry is a subtle, non-adaptive departure from the population-level trajectory relating growth on major and minor sides. 3,In a South Carolina (USA) marsh, cheliped and leg antisymmetries are greater and eye stalk asymmetry is less among males able to defer feeding in favour of breeding. However, the composition of up-slope breeding and down-slope feeding subpopulations changes across the lunar cycle. 4,The number of mates sequestered in breeding burrows is positively correlated with cheliped and leg antisymmetry and negatively correlated with eye stalk asymmetry. Male fitness is a function of the product of time spent breeding and the number of mates per unit time while breeding. Both fitness components are predicted by relative cheliped antisymmetry and eye stalk fluctuating asymmetry, which are themselves significantly negatively correlated. [source] On accuracy of the finite-difference and finite-element schemes with respect to P -wave to S -wave speed ratioGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2010Peter Moczo SUMMARY Numerical modelling of seismic motion in sedimentary basins often has to account for P -wave to S -wave speed ratios as large as five and even larger, mainly in sediments below groundwater level. Therefore, we analyse seven schemes for their behaviour with a varying P -wave to S -wave speed ratio. Four finite-difference (FD) schemes include (1) displacement conventional-grid, (2) displacement-stress partly-staggered-grid, (3) displacement-stress staggered-grid and (4) velocity,stress staggered-grid schemes. Three displacement finite-element schemes differ in integration: (1) Lobatto four-point, (2) Gauss four-point and (3) Gauss one-point. To compare schemes at the most fundamental level, and identify basic aspects responsible for their behaviours with the varying speed ratio, we analyse 2-D second-order schemes assuming an elastic homogeneous isotropic medium and a uniform grid. We compare structures of the schemes and applied FD approximations. We define (full) local errors in amplitude and polarization in one time step, and normalize them for a unit time. We present results of extensive numerical calculations for wide ranges of values of the speed ratio and a spatial sampling ratio, and the entire range of directions of propagation with respect to the spatial grid. The application of some schemes to real sedimentary basins in general requires considerably finer spatial sampling than usually applied. Consistency in approximating first spatial derivatives appears to be the key factor for the behaviour of a scheme with respect to the P -wave to S -wave speed ratio. [source] Efficient allocation of resources to prevent HIV infection among injection drug users: the Prevention Point Philadelphia (PPP) needle exchange programHEALTH ECONOMICS, Issue 2 2006Zoë K. Harris Abstract The objective of this study is to determine the allocation of resources within a multi-site needle exchange program (NEP) that achieves the largest possible reduction in new HIV infections at minimum cost. We present a model that relates the number of injection drug user (IDU) clients and the number of syringes exchanged per client to both the costs of the NEP and the expected reduction in HIV infections per unit time. We show that cost-effective allocation within a multi-site NEP requires that sites be located where the density of IDUs is highest, and that the number of syringes exchanged per client be equal across sites. We apply these optimal allocation rules to a specific multi-site needle exchange program, Prevention Point Philadelphia (PPP). This NEP, we find, needs to add 2 or 3 new sites in neighborhoods with the highest density of IDU AIDS cases, and to increase its total IDU client base by about 28%, from approximately 6400 to 8200 IDU clients. The case-study NEP also needs to increase its hours of operation at two existing sites, where the number of needles distributed per client is currently sub-optimal, by 50%. At the optimal allocation, the estimated cost per case of HIV averted would be $2800 (range $2300,$4200). Such a favorable cost-effectiveness ratio derives primarily from PPP's low marginal costs per distributed needle. Copyright © 2005 John Wiley & Sons, Ltd. [source] Hospital Economics of the HospitalistHEALTH SERVICES RESEARCH, Issue 3 2003Douglas Gregory Objective To determine the economic impact on the hospital of a hospitalist program and to develop insights into the relative economic importance of variables such as reductions in mean length of stay and cost, improvements in throughput (patients discharged per unit time), payer methods of reimbursement, and the cost of the hospitalist program. Data Sources The primary data source was Tufts-New England Medical Center in Boston. Patient demographics, utilization, cost, and revenue data were obtained from the hospital's cost accounting system and medical records. Study Design The hospitalist admitted and managed all patients during a six-week period on the general medical unit of Tufts-New England Medical Center. Reimbursement, cost, length of stay, and throughput outcomes during this period were contrasted with patients admitted to the unit in the same period in the prior year, in the preceding period, and in the following period. Principal Findings The hospitalist group compared with the control group demonstrated: length of stay reduced to 2.19 days from 3.45 days (p<.001); total hospital costs per admission reduced to $1,775 from $2,332 (p<.001); costs per day increased to $811 from $679 (p<.001); no differences for readmission within 30 days of discharge to extended care facilities. The hospital's expected incremental profitability with the hospitalist was,$1.44 per admission excluding incremental throughput effects, and it was most sensitive to changes in the ratio of per diem to case rate reimbursement. Incremental throughput with the hospitalist was estimated at 266 patients annually with an associated incremental profitability of $1.3 million. Conclusion Hospital interventions designed to reduce length of stay, such as the hospitalist, should be evaluated in terms of cost, throughput, and reimbursement effects. Excluding throughput effects, the hospitalist program was not economically viable due to the influence of per diem reimbursement. Throughput improvements occasioned by the hospitalist program with high baseline occupancy levels are substantial and tend to favor a hospitalist program. [source] Challenges and Progress in High-Throughput Screening of Polymer Mechanical Properties by IndentationADVANCED MATERIALS, Issue 35 2009Johannes M. Kranenburg Abstract Depth-sensing or instrumented indentation is an experimental characterization approach well-suited for high-throughput investigation of mechanical properties of polymeric materials. This is due to both the precision of force and displacement, and to the small material volumes required for quantitative analysis. Recently, considerable progress in the throughput (number of distinct material samples analyzed per unit time) of indentation experiments has been achieved, particularly for studies of elastic properties. Future challenges include improving the agreement between various macroscopic properties (elastic modulus, creep compliance, loss tangent, onset of nonlinear elasticity, energy dissipation, etc.) and their counterpart properties obtained by indentation. Sample preparation constitutes a major factor for both the accuracy of the results and the speed and efficiency of experimental throughput. It is important to appreciate how this processing step may influence the mechanical properties, in particular the onset of nonlinear elastic or plastic deformation, and how the processing may affect the agreement between the indentation results and their macroscopic analogues. [source] On the general dynamic model of oceanic island biogeographyJOURNAL OF BIOGEOGRAPHY, Issue 6 2009Simone Fattorini Abstract Aim, To investigate the biological meaning of equations used to apply the general dynamic model (GDM) of oceanic island biogeography proposed by R. J. Whittaker, K. A. Triantis and R. J. Ladle. Location, Analyses are presented for 17 animal groups living on the Aeolian Islands, a volcanic archipelago in the central Mediterranean, near Sicily. Methods, In addition to the mathematical implementation of the GDM proposed by Whittaker, Triantis and Ladle, and termed here logATT2 (, where S is species number or any other diversity metric, t is island age, A is island area, and a, b, c and d are fitted parameters), a new implementation based on the Arrhenius equation of the species,area relationship (SAR) is investigated. The new model (termed powerATT2) is: . For logATT2 and powerATT2 models, equations were developed to calculate (1) the expected number of species at equilibrium (i.e. when the island has reached maturity) per unit area (Seq), and (2) the time required to obtain this value (teq). Whereas the intercept in the Gleason model (S = C + z log A) or the coefficient of the Arrhenius power model (S = CAz) of the SAR can be considered measures of the expected number of species per unit area, this is not the case for the parameter a of the ATT2 models. However, values of Seq can be used for this purpose. The index of ,colonization ability' (CAB), calculated as the ratio , may provide a measure of the mean number of species added per unit area per unit time. Results, Both ATT2 models fitted most of the data well, but the powerATT2 model was in most cases superior. Equilibrial values of species richness (Seq) varied from c. 3 species km,2 (reptiles) to 100 species km,2 (mites). The fitted curves for the powerATT2 model showed large variations in d, from 0.03 to 3. However, most groups had values of d around 0.2,0.4, as commonly observed for the z -values of SARs modelled by a power function. Equilibration times ranged from about 170,000 years to 400,000 years. Mites and springtails had very high values of CAB, thus adding many more species per unit area per unit time than others. Reptiles and phytophagous scarabs showed very low values, being the groups that added fewest species per unit area per unit time. Main conclusions, Values of equilibrial species richness per unit area are influenced by species biology (e.g. body size and ecological specialization). Theoretical and empirical evidence suggests that higher immigration rates should increase the z -values of the Arrhenius model. Thus, in the same archipelago, groups with larger z -values should be characterized by higher dispersal ability. Results obtained here for the parameter d conform to this prediction. [source] Ethanol production from raw starch by a recombinant yeast having saccharification and fermentation activitiesJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 10 2002Yoshitoshi Nakamura Abstract In order to develop a method for converting raw starch into ethanol efficiently, direct fermentation of ozonized raw starch using a recombinant yeast was investigated. Ozonolysis was carried out as a pretreatment to convert raw starch into ethanol rapidly and efficiently, and then the effect of the ozone degradation conditions on the degree of polymerization and the amount of amylose in a raw starch was determined. Since the degree of polymerization was low and the amount of amylose was high, raw starch treated with an ozone concentration of 40,gm,3 and an ozonation time of 30,min was the material chosen for alcohol fermentation. Though the recombinant yeast could not convert the untreated raw starch, it converted the soluble starch and the ozonized raw starch at a comparatively high yield into ethanol. About 56% of the ozonized raw starch decomposed, and the ethanol concentration obtained from the ozonized raw starch was markedly greater than that obtained from untreated raw starch. The dynamic behavior of cell growth, substrate degradation, and ethanol production was examined in a continuous culture under various dilution rates, and the optimal dilution rate, ie 0.15,h,1, was determined for maximizing the ethanol productivity (amount of ethanol produced per unit time). © 2002 Society of Chemical Industry [source] The influence of environmental factors, the pollen : ovule ratio and seed bank persistence on molecular evolutionary rates in plantsJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 1 2006C.-A. WHITTLE Abstract One of the main goals of molecular evolutionary biology is to determine the factors that influence the evolutionary rate of selectively neutral DNA, but much remains unknown, especially for plants. Key factors that could alter the mutation rate include environmental tolerances (because they reflect a plants vulnerability to changes in habitat), the pollen : ovule ratio (as it is associated with the number of mitotic divisions) and seed longevity (because this influences the number of generations per unit time in plants). This is the first study to demonstrate that seed bank persistence and drought tolerance are positively associated with molecular evolutionary rates in plants and that pollen : ovule ratio, shade tolerance and salinity tolerance have no detectable relationship. The implications of the findings to our understanding of the impact of environmental agents, the number of cell divisions and cell aging on neutral DNA sequence evolution are discussed. [source] Food choice in Siganus fuscescens: influence of macrophyte nutrient content and availabilityJOURNAL OF FISH BIOLOGY, Issue 2 2004R. D. Pillans Using multiple-choice feeding experiments, the selection of six species of macrophytes by the herbivorous rabbitfish Siganus fuscescens was examined. The rabbitfish showed distinct food choice in the laboratory; however, selection of macrophytes by S. fuscescens was not related to their absolute nutrient content (nitrogen, carbon, energy and ash free dry mass). Nutrient assimilation estimates showed that the macrophytes which were most preferred were those that S. fuscescens assimilated best. In S. fuscescens, the macrophytes that were preferred passed through the gut significantly faster than the less preferred species. Gut transit time had a significant effect on the absolute value of a food item in terms of net nutrient gain per unit time. This study showed that food value could be inferred from the absolute nutrient content of the macrophytes. Thus both the ability to assimilate nutrients as well as the absolute nutrient content of macrophytes must be quantified when assessing food value. [source] Separation of benzene and deuterated benzenes by reversed-phase and recycle liquid chromatography using monolithic capillary columnsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 15-16 2004Lee Wah Lim Abstract An alternate pumping-recycle system utilizing a commercially available low dead-volume switching valve was developed for microcolumn LC. The recycle system had two separation columns, and the dead volume of the recycling lines was kept to a minimum by avoiding passage of the sample through the pump chamber, sample injector, and the normal path length of a conventional UV detector. The drawback of the high total back pressure caused by the second column that is placed after the detector was overcome by on-column detection, and this eliminated the need for a high pressure flow cell. The system was used for the separation of an authentic mixture of benzene, benzene-1,3,5-d3, and benzene-d6. Baseline separation was accomplished after six cycles and the calculated theoretical plate number for benzene was 230,000. It was observed that the theoretical plate number (N) increased linearly with increasing number of cycles, and the N per unit time increased with increasing inlet pressure. The separation conditions were optimized and the separation of benzene and benzene-d6 was accomplished within 75 min at 2.5 MPa inlet pressure. [source] A simple low-SAR technique for chemical-shift selection with high-field spin-echo imagingMAGNETIC RESONANCE IN MEDICINE, Issue 2 2010Dimo Ivanov Abstract We have discovered a simple and highly robust method for removal of chemical shift artifact in spin-echo MR images, which simultaneously decreases the radiofrequency power deposition (specific absorption rate). The method is demonstrated in spin-echo echo-planar imaging brain images acquired at 7 T, with complete suppression of scalp fat signal. When excitation and refocusing pulses are sufficiently different in duration, and thus also different in the amplitude of their slice-select gradients, a spatial mismatch is produced between the fat slices excited and refocused, with no overlap. Because no additional radiofrequency pulse is used to suppress fat, the specific absorption rate is significantly reduced compared with conventional approaches. This enables greater volume coverage per unit time, well suited for functional and diffusion studies using spin-echo echo-planar imaging. Moreover, the method can be generally applied to any sequence involving slice-selective excitation and at least one slice-selective refocusing pulse at high magnetic field strengths. The method is more efficient than gradient reversal methods and more robust against inhomogeneities of the static (polarizing) field (B0). Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc. [source] Metabolite proton T2 mapping in the healthy rhesus macaque brain at 3 TMAGNETIC RESONANCE IN MEDICINE, Issue 5 2009Songtao Liu Abstract The structure and metabolism of the rhesus macaque brain, an advanced model for neurologic diseases and their treatment response, is often studied noninvasively with MRI and 1H-MR spectroscopy. Due to the shorter transverse relaxation time (T2) at the higher magnetic fields these studies favor, the echo times used in 1H-MR spectroscopy subject the metabolites to unknown T2 weighting, decreasing the accuracy of quantification which is key for inter- and intra-animal comparisons. To establish the "baseline" (healthy animal) T2 values, we mapped them for the three main metabolites' T2s at 3 T in four healthy rhesus macaques and tested the hypotheses that their mean values are similar (i) among animals; and (ii) to analogs regions in the human brain. This was done with three-dimensional multivoxel 1H-MR spectroscopy at (0.6 × 0.6 × 0.5 cm)3 = 180 ,L spatial resolution over a 4.2 × 3.0 × 2.0 = 25 cm3 (,30%) of the macaque brain in a two-point protocol that optimizes T2 precision per unit time. The estimated T2s in several gray and white matter regions are all within 10% of those reported in the human brain (mean ± standard error of the mean): N -acetylaspartate = 316 ± 7, creatine = 177 ± 3, and choline = 264 ± 9 ms, with no statistically significant gray versus white matter differences. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc. [source] A bivariate optimal replacement policy for a cold standby repairable system with repair priorityNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 2 2010Kit Nam Francis Leung Abstract In this article, an optimal replacement policy for a cold standby repairable system consisting of two dissimilar components with repair priority is studied. Assume that both Components 1 and 2, after repair, are not as good as new, and the main component (Component 1) has repair priority. Both the sequence of working times and that of the components'repair times are generated by geometric processes. We consider a bivariate replacement policy (T,N) in which the system is replaced when either cumulative working time of Component 1 reaches T, or the number of failures of Component 1 reaches N, whichever occurs first. The problem is to determine the optimal replacement policy (T,N)* such that the long run average loss per unit time (or simply the average loss rate) of the system is minimized. An explicit expression of this rate is derived, and then optimal policy (T,N)* can be numerically determined through a two-dimensional-search procedure. A numerical example is given to illustrate the model's applicability and procedure, and to illustrate some properties of the optimal solution. We also show that if replacements are made solely on the basis of the number of failures N, or solely on the basis of the cumulative working time T, the former class of policies performs better than the latter, albeit only under some mild conditions. © 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010 [source] Block replacement policies for a two-component system with failure dependenceNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 1 2003Philip A. Scarf Abstract Block replacement and modified block replacement policies for two-component systems with failure dependence and economic dependence are considered in this paper. Opportunistic maintenance policies are also considered. Where tractable, long-run costs per unit time are calculated using renewal theory based arguments; otherwise simulation studies are carried out. The management implications for the adoption of the various policies are discussed. The usefulness of the results in the paper is illustrated through application to a particular two-component system. © 2002 Wiley Periodicals, Inc. Naval Research Logistics, 2003 [source] On the (S , 1, S) lost sales inventory model with priority demand classesNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 6 2002R. Dekker Abstract In this paper an inventory model with several demand classes, prioritised according to importance, is analysed. We consider a lot-for-lot or (S , 1, S) inventory model with lost sales. For each demand class there is a critical stock level at and below which demand from that class is not satisfied from stock on hand. In this way stock is retained to meet demand from higher priority demand classes. A set of such critical levels determines the stocking policy. For Poisson demand and a generally distributed lead time, we derive expressions for the service levels for each demand class and the average total cost per unit time. Efficient solution methods for obtaining optimal policies, with and without service level constraints, are presented. Numerical experiments in which the solution methods are tested demonstrate that significant cost reductions can be achieved by distinguishing between demand classes. © 2002 Wiley Periodicals, Inc. Naval Research Logistics 49: 593,610, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/nav.10032 [source] Conundrums of competitive ability in plants: what to measure?OIKOS, Issue 3 2002LonnieW. A survey of recent literature indicates that competitive ability in plants has been measured, in most studies, only in terms of the relative intensity of size suppression experienced by competitors within one growing season. Far fewer studies have recorded relative success in terms of survival and even fewer studies have recorded fecundity under competition. Differences in size suppression are usually assumed to reflect differences in relative abilities to deny resources to competitors. However, most previous studies have failed to control or account for other sources of variation in the size suppression that plants experience under competition, i.e. variation between mixtures in the resource supply/demand ratio (approach to carrying capacity), or variation in the degree of niche overlap between competitors, or variation in the intensity of concurrent facilitative interactions between competitors. For future studies, much greater caution is required in recognizing these inherent limitations of traditional measures of competitive ability and, hence, guarding against unfounded conclusions or predictions about potential for competitive success that are based on these measures. There is also a significant challenge for future studies to adopt empirical approaches for minimizing these limitations. Some initial recommendations are considered here based on an emerging view of competitive ability measured in terms of traits associated with all three conventional components of Darwinian fitness, i.e. not just growth (plant size) but also survival and fecundity allocation (offspring production per unit plant size per unit time). According to this model, differences in competitive ability imply differences in the ability, despite intense competition (i.e. low resource supply/demand ratio), to recruit offspring into the next generation and thereby limit offspring recruitment by other plants. The important traits of competitive ability, therefore, are not only those that allow a plant to deny resources to competitors, suppress their sizes and hence, maximize the plant's own size, but also those traits that allow the plant to withstand suppression from competition enough to persist, both as an individual (through survival) and across generations (through descendants). [source] Using scanning electron, confocal and optical microscopes to measure microscopic holes in traysPACKAGING TECHNOLOGY AND SCIENCE, Issue 6 2005Laura Bix Abstract Package integrity is of paramount importance to the medical device industry. As healthcare costs soar and integrity testers become more and more sensitive, concern with the question ,what hole size allows microbial penetration into device packages?' is re-ignited. However, producing a consistent and measurable defect in the microcosm presents challenges. Varying techniques are currently employed to produce these defects. Use of an excimer laser is one of the most precise and accurate techniques, and holes ,certified' to be a given size can be purchased at a significant cost. To verify the accuracy and precision of holes drilled with an excimer laser, researchers measured laser-drilled ,exit' and ,entry' holes in glycol-modified polyetheylene terephthalate (PETG) trays using scanning electron microscopy (SEM) and confocal microscopy. This data and the certification data provided by the laser driller were analysed using a mixed-model analysis of variance (ANOVA). Both the effect of measuring technique and hole side (entry vs. exit) were found to be significant. These significant differences have the potential to impact the question that the industry faces with regard to penetration threshold. This suggests that a shift in thinking is needed. Perhaps it would be better if the industry stops thinking about hole size and begins to think in terms of what researchers have referred to as the ,effective hole', which is defined as the volume of gas that will flow through a hole of defined size per unit time. Copyright © 2005 John Wiley & Sons, Ltd. [source] GUIDELINES FOR IMPLEMENTING PREDICTIVE MAINTENANCE*PRODUCTION AND OPERATIONS MANAGEMENT, Issue 2 2002KATHLEEN E. MCKONE Recent advances in predictive maintenance technologies have led many manufacturers to abandon traditional periodic maintenance policies and replace them with predictive maintenance policies. The models in this paper explicitly evaluate the decision to utilize both predictive and periodic maintenance when the objective is to minimize expected maintenance costs per unit time. Renewal theory is used to obtain optimal policies as unique solutions of integral equations that depend on the failure distribution and prediction capabilities. Based on this research, we recommend that practitioners do not abandon the traditional maintenance methods but follow our guidelines for utilizing periodic maintenance in conjunction with the new technologies. [source] Optimal Design of VSI ,X Control Charts for Monitoring Correlated SamplesQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 8 2005Yan-Kwang Chen Abstract This paper develops an economic design of variable sampling interval (VSI),X control charts in which the next sample is taken sooner than usual if there is an indication that the process is off-target. When designing VSI,X control charts, the underlying assumption is that the measurements within a sample are independent. However, there are many practical situations that violate this hypothesis. Accordingly, a cost model combining the multivariate normal distribution model given by Yang and Hancock with Bai and Lee's cost model is proposed to develop the design of VSI charts for correlated data. An evolutionary search method to find the optimal design parameters for this model is presented. Also, we compare VSI and traditional ,X charts with respect to expected cost per unit time, utilizing hypothetical cost and process parameters as well as various correlation coefficients. The results indicate that VSI control charts outperform the traditional control charts for larger mean shift when correlation is present. In addition, there is a difference between the design parameters of VSI charts when correlation is present or absent. Copyright © 2005 John Wiley & Sons, Ltd. [source] Optimal replacement policy for obsolete components with general failure ratesAPPLIED STOCHASTIC MODELS IN BUSINESS AND INDUSTRY, Issue 3 2008Sophie MercierArticle first published online: 8 JAN 200 Abstract Identical components are considered, which become obsolete once new-type ones are available, more reliable and less energy consuming. We envision different possible replacement strategies for the old-type components by the new-type ones: either purely preventive, where all old-type components are replaced as soon as the new-type ones are available; either purely corrective, where the old-type ones are replaced by new-type ones only at failure; or a mixture of both strategies, where the old-type ones are first replaced at failure by new-type ones and next simultaneously preventively replaced after a fixed number of failed old-type components. To evaluate the respective value of each possible strategy, a cost function is considered, which represents the mean total cost on some finite time interval [0, t]. This function takes into account replacement costs, with economical dependence between simultaneous replacements, and also some energy consumption (and/or production) cost, with a constant rate per unit time. A full analytical expression is provided for the cost function induced by each possible replacement strategy. The optimal strategy is derived in long-time run. Numerical experiments conclude the paper. Copyright © 2008 John Wiley & Sons, Ltd. [source] Measurement error bias in pharmaceutical cost-effectiveness analysisAPPLIED STOCHASTIC MODELS IN BUSINESS AND INDUSTRY, Issue 5-6 2006*Article first published online: 20 DEC 200, Ian C. Marschner Abstract Drug development in the pharmaceutical industry is increasingly influenced by measures of cost-effectiveness, such as cost per life-year gained, and some governments make decisions about whether to pay for drugs based on cost-effectiveness considerations. While cost per life-year gained is a key measure of cost-effectiveness, costs associated with the intermediate outcome of improving a biomarker, such as cholesterol level or blood pressure, provide important supplementary information, particularly where mortality data may be limited. In this case, cost-effectiveness can be interpreted as the additional cost per unit time of achieving an additional beneficial biomarker response to treatment. A problem in this context is that biomarker assessment is typically subject to measurement error which leads to bias in assessing the benefit of a drug, and hence in the assessment of its cost-effectiveness. We discuss the adjustment of cost-effectiveness analyses for measurement error and consider the potential magnitude of bias that can arise. Using example calculations in the context of cholesterol-lowering therapy, it is demonstrated that such biases can be significant, leading to costs being overestimated by in excess of 25%. Ignoring measurement error in cost-effectiveness analyses can, therefore, have a substantial effect on the interpretation of such analyses. Copyright © 2006 John Wiley & Sons, Ltd. [source] 293 cell cycle synchronisation adenovirus vector productionBIOTECHNOLOGY PROGRESS, Issue 1 2009Tiago B. Ferreira Abstract As the market requirements for adenovirus vectors (AdV) increase, the maximisation of the virus titer per culture volume per unit time is a key requirement. However, despite the fact that 293 cells can grow up to 8 × 106 cell/mL in simple batch mode operations, for optimal AdV infection a maximum cell density of 1 × 106 cell/mL at infection time has usually been utilized due to the so called "cell density effect". In addition, AdV titer appears to be dependent upon cell cycle phase at the time of infection. To evaluate the dependence of AdV production upon cell cycle phase, 293 cells were chemically synchronised at each phase of the cell cycle; a 2.6-fold increase on AdV cell specific titer was obtained when the percentage of cells at the S phase of the cell cycle was increased from 36 to 47%; a mathematical equation was used to relate AdV cell specific productivities with cell synchronisation at the S phase using this data. To avoid the use of chemical inhibitors, a temperature shift strategy was also used for synchronisation at the S phase. S phase synchronisation was obtained by decreasing the culture temperature to 31°C during 67 h and restoring it to 37°C during 72 h. By using this strategy we were able to synchronise 57% of the population in the S phase of the cell cycle obtaining an increase of 7.3-fold on AdV cell specific titer after infection. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] | ||||||||||||||||||||||||||||||||||||||||