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Experimental Tests (experimental + test)
Selected AbstractsAN EXPERIMENTAL TEST ON RETIREMENT DECISIONSECONOMIC INQUIRY, Issue 3 2007ENRIQUE FATAS As part of the current debate on the reform of pension systems, this paper presents an original experimental test where subjects face three different payoff sequences with identical expected value. Two central questions are analyzed. First, whether the distribution of retirement benefits across time influences the retirement decision. And second, whether actuarially fair pension systems distort the retirement decision. The results indicate both that a lump-sum payment rather than annuity benefits is far more effective in delaying the retirement decision and that recent reforms that encourage the link between lifetime contributions and pension benefits to delay the retirement decision should take into account timing considerations. (JEL C91, H55, J26) [source] PHENOTYPIC PLASTICITY OF HERMAPHRODITE SEX ALLOCATION PROMOTES THE EVOLUTION OF SEPARATE SEXES: AN EXPERIMENTAL TEST OF THE SEX-DIFFERENTIAL PLASTICITY HYPOTHESIS USING SAGITTARIA LATIFOLIA (ALISMATACEAE)EVOLUTION, Issue 4 2008Marcel E. Dorken Separate sexes can evolve under nuclear inheritance when unisexuals have more than twice the reproductive fitness of hermaphrodites through one sex function (e.g., when females have more than twice the seed fertility of hermaphrodites). Because separate sexes are thought to evolve most commonly via a gynodioecious intermediate (i.e., populations in which females and hermaphrodites cooccur), the conditions under which females can become established in populations of hermaphrodites are of considerable interest. It has been proposed that resource-poor conditions could promote the establishment of females if hermaphrodites are plastic in their sex allocation and allocate fewer resources to seed production under these conditions. If this occurs, the seed fertility of females could exceed the doubling required for the evolution of unisexuality under low-, but not high-resource conditions (the sex-differential plasticity hypothesis). We tested this hypothesis using replicate experimental arrays of the aquatic herb Sagittaria latifolia grown under two fertilizer treatments. The results supported the sex-differential plasticity hypothesis, with females having more than twice the seed fertility of hermaphrodites under low-, but not high-fertilizer conditions. Our findings are consistent with the idea that separate sexes are more likely to evolve under unfavorable conditions. [source] EVOLUTION OF BIRD SONG AFFECTS SIGNAL EFFICACY: AN EXPERIMENTAL TEST USING HISTORICAL AND CURRENT SIGNALSEVOLUTION, Issue 8 2007Elizabeth P. Derryberry Mating signals act as behavioral barriers to gene flow in many animal taxa, yet little is known about how signal evolution within populations contributes to the formation of these barriers. Although variation in mating signals among populations is known to affect mating behavior, there is no direct evidence that the evolution of mating signals changes signal effectiveness within a natural population. Making use of historical recordings of bird song, I found that both male and female white-crowned sparrows (Zonotrichia leucophrys) respond more strongly to current than to historical songs, indicating that historical songs are less effective as signals in the current contexts of both mate choice and male,male competition. Finding that historical signals are less effective suggests that signal evolution within populations may ultimately contribute to the formation of behavioral barriers to gene flow between populations. [source] THE ADAPTIVE SIGNIFICANCE OF TEMPERATURE-DEPENDENT SEX DETERMINATION: EXPERIMENTAL TESTS WITH A SHORT-LIVED LIZARDEVOLUTION, Issue 10 2005Daniel A. Warner Abstract Why is the sex of many reptiles determined by the temperatures that these animals experience during embryogenesis, rather than by their genes? The Charnov-Bull model suggests that temperature-dependent sex determination (TSD) can enhance maternal fitness relative to genotypic sex determination (GSD) if offspring traits affect fitness differently for sons versus daughters and nest temperatures either determine or predict those offspring traits. Although potential pathways for such effects have attracted much speculation, empirical tests largely have been precluded by logistical constraints (i.e., long life spans and late maturation of most TSD reptiles). We experimentally tested four differential fitness models within the Charnov-Bull framework, using a short-lived, early-maturing Australian lizard (Amphibolurus muricatus) with TSD. Eggs from wild-caught females were incubated at a range of thermal regimes, and the resultant hatchlings raised in large outdoor enclosures. We applied an aromatase inhibitor to half the eggs to override thermal effects on sex determination, thus decoupling sex and incubation temperature. Based on relationships between incubation temperatures, hatching dates, morphology, growth, and survival of hatchlings in their first season, we were able to reject three of the four differential fitness models. First, matching offspring sex to egg size was not plausible because the relationship between egg (offspring) size and fitness was similar in the two sexes. Second, sex differences in optimal incubation temperatures were not evident, because (1) although incubation temperature influenced offspring phenotypes and growth, it did so in similar ways in sons versus daughters, and (2) the relationship between phenotypic traits and fitness was similar in the two sexes, at least during preadult life. We were unable to reject a fourth model, in which TSD enhances offspring fitness by generating seasonal shifts in offspring sex ratio: that is, TSD allows overproduction of daughters (the sex likely to benefit most from early hatching) early in the nesting season. In keeping with this model, hatching early in the season massively enhanced body size at the beginning of the first winter, albeit with a significant decline in probability of survival. Thus, the timing of hatching is likely to influence reproductive success in this short-lived, early maturing species; and this effect may well differ between the sexes. [source] An Experimental Test of the Theory of Planned BehaviorAPPLIED PSYCHOLOGY: HEALTH AND WELL-BEING, Issue 2 2009Falko Sniehotta The Theory of Planned Behavior (TPB) is one of the leading theories of health behavior, yet supporting evidence is exclusively based on correlational research. This study aims to test the TPB experimentally. N = 579 participants were randomised to receive persuasive messages addressing salient beliefs elicited in a pilot study, following a 2*2*2 factorial design. Participants were randomised to a behavioral-belief-intervention (BBI) or not, a normative-belief-intervention (NBI) or not, and a control-belief-intervention (CBI) or not. The primary outcome was objectively recorded attendance at university sports facilities over 2 months; and the secondary outcomes were post-intervention TPB measures. Main effects of the BBI on attitudes and of the NBI on subjective norm, PBC, attitudes, and intentions were found. The CBI did not alter post-intervention cognitions, but was the only intervention to change behavior not mediated by cognitions. While the findings support the TPB's assumptions on intention formation, behavior change results are not in line with the theory and therefore further question the TPB's leading role in behavioral science. [source] Experimental Tests of Normative Group Influence and Representation Effects in Computer-Mediated CommunicationHUMAN COMMUNICATION RESEARCH, Issue 3 2002When Interacting Via Computers Differs From Interacting With Computers Two experiments addressed the questions of if and how normative social influence operates in anonymous computer-mediated communication (CMC) and human-computer interaction (HCI). In Experiment 1, a 2 (public response vs. private response) × 2 (one interactant vs. four interactants) × 3 (textbox vs. stick figure vs. animated character) mixed-design experiment (N = 72), we investigated how conformity pressure operates in a simulated CMC setting. Each participant was asked to make a decision in hypothetical social dilemmas after being presented with a unanimous opinion by other (ostensible) participants. The experiment examined how the visual representation of interaction partners on the screen moderates this social influence process. Group conformity effects were shown to be more salient when the participant's responses were allegedly seen by others, compared to when the responses were given in private. In addition, participants attributed greater competence, social attractiveness, and trustworthiness to partners represented by anthropomorphic characters than those represented by textboxes or stick figures. Experiment 2 replicated Experiment 1, replacing interaction with a computer(s) rather than (ostensible) people, to create an interaction setting in which no normative pressure was expected to occur. The perception of interaction partner (human vs. computer) moderated the group conformity effect such that people expressed greater public agreement with human partners than with computers. No such difference was found for the private expression of opinion. As expected, the number of computer agents did not affect participants' opinions whether the responses were given in private or in public, while visual representation had a significant impact on both conformity measures and source perception variables. [source] Mixed p-z approach for analytical analysis of an induction motor fed from space-vector PWM voltage source inverterEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 6 2002J. Klima This paper proposes an analytical method for calculating both the steady-state and transient performance of an induction motor fed from the three-phase voltage source inverter. As a modulation technique of the inverter we consider space vector modulation. The proposed method makes use of the Laplace and modified Z-transformation of the space vectors (mixed p-z approach) to predict current response of induction motor. From the Laplace transform of the stator voltage vector we can also derive Fourier analysis to predict the voltage harmonic spectrum. Experimental tests have been carried out confirming the validity of the analytical results. [source] Application of interface finite elements to three-dimensional progressive failure analysis of adhesive jointsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 5 2003J. P. M. GONÇALVES ABSTRACT The paper presents a new model for three-dimensional progressive failure analysis of adhesive joints. The method uses interface elements and includes a damage model to simulate progressive debonding. The interface finite elements are placed between the adherents and the adhesive. The damage model is based on the indirect use of fracture mechanics and allows the simulation of the initiation and growth of damage at the interfaces without considering the presence of initial flaws. The application of the model to single lap joints is presented. Experimental tests were performed in aluminium/epoxy adhesive joints. Linear elastic and elastoplastic analyses were performed and the predicted failure load for the elastoplastic case agrees with experimental results. [source] Do male hoots betray parasite loads in Tawny Owls?JOURNAL OF AVIAN BIOLOGY, Issue 4 2000Stephen M. Redpath Bird song structure may honestly reveal the health and vigour of individual males to potential mates and competitors. If this is the case then song may reflect the level of parasitic infections in males. We initially examined the relationship between blood parasite infections and the time taken to respond by 22 male Tawny Owls to a broadcast hoot. We then examined the call structure (total length and frequency) in relation to parasite infection, an index of owl condition and an index of food abundance. Owls with higher parasite loads responded more slowly to an intruder, although this relationship was not significant once condition and vole abundance were controlled for. We found no relationship between call length and any of the measured variables. However, the high frequency and the range of frequencies used in calls decreased with increasing parasite load. Thus, there was the potential for individuals to assess male parasite load from the speed of response and the structure of the call. Experimental tests of these relationships are now required. [source] Measuring Permeability of Rigid Materials by a Beam-Bending Method: I, TheoryJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2000George W. Scherer When a saturated porous material is deformed, pressure gradients are created in the liquid, and the liquid flows within the pores to equilibrate the pressure. This phenomenon can be exploited to measure permeability: A rod of saturated porous material is instantaneously bent by a fixed amount, and the force required to sustain the deflection is measured as a function of time. The force decreases as the liquid flows through the pore network, and the rate of decrease depends on the permeability. This technique has been applied successfully to determine the permeability of gels, as well as their viscoelastic properties; in this paper the method is extended to ceramic materials, such as porous glass and cement paste. The theory has been modified to take account of the compressibility of the solid and liquid phases (whereas, those factors are negligible for gels). Analyses are presented for constant deflection, constant rate of deflection, and sinusoidal oscillation, where the solid phase is either purely elastic or viscoelastic, and the beam is either cylindrical or square. Experimental tests on Vycor® glass and cement paste will be presented in companion papers. [source] Investigation of the Thermal Behaviour of Non-metallic Curved-Face-Width Spur GearsLUBRICATION SCIENCE, Issue 4 2004L. Andrei Abstract This paper describes a curved-face-width spur gear, specially designed for manufacture from non-metallic materials. The benefits of this gear are the higher contact ratio, bending and Hertzian contact resistance, and greater tooth stiffness compared to standard spur gears. A modified geometry is proposed for the gear tooth, the height of which varies along the gear face width. Due to the reduction in tooth height, in sections away from the gear centre, lower sliding friction is expected, with consequences for the gear's thermal behaviour. The complex gear geometry makes the design of a die difficult; therefore the gears were cut on a milling machine, using a special kinematic generation process and related equipment. The tooth flank profile, an involute or near involute in sections away from the gear half-width plane, as well as the flank surface quality determined by the single-cutter tool used for gear manufacture, influence the meshing condition, and can be detrimental to the thermal behaviour of the gear. Experimental tests were carried out to examine the influence of load and speed on the temperature of the curved-face-width spur gears with modified geometry. The measured temperature of the non-standard gear is further compared with the predicted temperature of plastic standard spur gears of the same specification. [source] Edge assembly-based memetic algorithm for the capacitated vehicle routing problemNETWORKS: AN INTERNATIONAL JOURNAL, Issue 4 2009Yuichi Nagata Abstract Vehicle routing problems are at the heart of most decision support systems for real-life distribution problems. In vehicle routing problem a set of routes must be determined at lowest total cost for a number of resources (i.e., fleet of vehicles) located at one or several points (e.g., depots, warehouses) to efficiently service a number of demand or supply points. In this article a new memetic algorithm is suggested for the standard capacitated vehicle routing problem. The proposed algorithm combines the edge assembly (EAX) crossover with well-known local searches and allows for infeasible solutions with respect to capacity and route duration constraints after invoking the crossover. To address the constraint violation, an efficient modification algorithm is also suggested. Experimental tests on 47 standard benchmarks demonstrate that the suggested method is robust and competitive, finding new best-known solution to 20 well-studied instances and repeating the existing best-known solution for 24 problems in a reasonable computing time. © 2009 Wiley Periodicals, Inc. NETWORKS, 2009 [source] Depth profiling of polymer films with grazing-incidence small-angle X-ray scatteringACTA CRYSTALLOGRAPHICA SECTION A, Issue 3 2009Marsha A. Singh A model-free method of reconstructing depth-specific lateral scattering from incident-angle-resolved grazing-incidence small-angle X-ray scattering (GISAXS) data is proposed. The information on the material which is available through variation of the X-ray penetration depth with incident angle is accessed through reference to the reflected branch of the GISAXS process. Reconstruction of the scattering from lateral density fluctuations is achieved by solving the resulting Fredholm integral equation with minimal a priori information about the experimental system. Results from simulated data generated for hypothetical multilayer polymer systems with constant absorption coefficient are used to verify that the method can be applied to cases with large X-ray penetration depths, as typically seen with polymer materials. Experimental tests on a spin-coated thick film of a blend of diblock copolymers demonstrate that the approach is capable of reconstruction of the scattering from a multilayer structure with the identification of lateral scattering profiles as a function of sample depth. [source] Fundamentplatten aus Stahlbeton und Stahlfaserbeton.BETON- UND STAHLBETONBAU, Issue 9 2006Experimentelle Untersuchungen zur Gebrauchstauglichkeit und Tragfähigkeit Ein- und Mehrfamilienhäuser werden zunehmend statt auf Streifenfundamenten auf Fundamentplatten gegründet. Vorteile ergeben sich neben der wirtschaftlicheren Ausführung der Aushubarbeiten durch die einfachere Herstellung der Platte. Bei der Ausführung als Stahlfaserbetonplatte ergeben sich besonders wirtschaftliche Lösungen dann, wenn an die Gebrauchstauglichkeit keine besonderen Anforderungen wie Wasserdichtheit oder Rißbreitenbeschränkung gestellt werden. An der Fachhochschule Aachen wurden vergleichende experimentelle Untersuchungen an Bodenplatten aus Beton, Stahlbeton und Stahlfaserbeton unter Lastbeanspruchung durchgeführt. Es konnte nachgewiesen werden, daß Stahlfaserbeton für Fundamentplatten ein geeigneter Werkstoff ist, wenn Mindestanforderungen an die Steifigkeit des Bodens eingehalten werden. Bei erhöhten Anforderungen an die Gebrauchstauglichkeit werden Stahlbeton oder Kombinationen aus Stahlfaserbeton und Stahlbeton als sinnvoll erachtet, wenn diese auf Basis einer elastischen Schnittgrößenermittlung bemessen werden. Reinforced Concrete and Steel Fibre Reinforced Concrete Rafts Experimental tests on serviceability and ultimate loading performance Houses and residential buildings are increasingly built on rafts instead of strip foundations. The main advantages of rafts are more efficient excavation works and easy concreting of the rafts itself. The use of steel fibre reinforced concrete slabs offers economic advantages if there are no special requirements on service ability such as water tightness or crack limitations. At Aachen University of Applied Sciences a comparative experimental study on the load carrying behaviour of rafts made of concrete, reinforced concrete and steel fibre reinforced concrete was carried out. The tests have proven steel fibre concrete as suitable material for rafts in case of sufficient stiffness of the subbase. In case of special requirements on service ability, reinforced concrete or combined fibre and bar reinforced concrete should be used. In that case stresses should be calculated based on the elastic theory. [source] Experimental tests of the function of mirror-image flowersBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 2 2005LINLEY K. JESSON Enantiostyly, the reciprocal deflection of the style to the left or right side of the floral axis has evolved independently in at least a dozen angiosperm families. Unlike other plant sexual polymorphisms, the adaptive significance of these mirror-image flowers remains unclear. Most authors have interpreted enantiostyly as a floral mechanism that promotes cross-pollination. However, any functional interpretation is complicated by the fact that enantiostyly occurs in two forms. In monomorphic enantiostyly there are left- and right-styled flowers on the same plant, while in dimorphic enantiostyly they are on separate individuals. In this paper we develop a model of pollen transfer which indicates that monomorphic enantiostyly should reduce geitonogamous pollination compared to a non-enantiostylous condition, and that the lowest levels of geitonogamous pollination should occur in dimorphic enantiostyly. We tested these predictions using floral manipulations of bee-pollinated Solanum rostratum in garden arrays. We compared mating patterns and fertility in five array types: non-enantiostylous and straight-styled, monomorphic enantiostylous, dimorphic enantiostylous, and arrays uniform for either left or right stylar deflection. Outcrossing rates in non-enantiostylous arrays (t = 0.33 ± 0.04) were significantly lower than all other arrays, while monomorphic enantiostylous arrays (t = 0.74 ± 0.06) had significantly lower outcrossing rates than dimorphic enantiostylous arrays (t = 0.88 ± 0.04) and those uniform for stylar deflection (t = 0.84 ± 0.04). In dimorphic enantiostylous arrays, intermorph pollen transfer accounted for 75% of all outcrossing events. In pollen-limited situations, both types of enantiostylous arrays had significantly higher female fertility than arrays fixed for one direction, demonstrating that enantiostyly promotes pollen transfer between flowers of opposite stylar orientation. Our results provide support for the hypothesis that enantiostyly functions to increase the precision of cross-pollination in bee-pollinated plants by reducing geitonogamy. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 85, 167,179. [source] Second-Law Based Thermodynamic Analysis of a Novel Heat ExchangerCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 1 2009Y.-L. He Abstract In the present investigation, second-law based thermodynamics analysis was applied to a new heat exchanger with helical baffles. The helical baffles are designed as quadrant ellipses and each baffle occupies one quadrant of the cross-section of the shell side. Experimental tests were carried out with cold water in the tube side with a constant flow rate, and hot oil on the shell side with flow rate range from 4,24,m3/h. The temperatures and pressures for the inlet and outlet of both sides were measured. The heat transfer, pressure drop, entropy generation, and exergy loss of the new heat exchanger were investigated and compared with the results for a conventional shell-and-tube heat exchanger with segmental baffles. The computed results indicated that both the entropy generation number and exergy losses of the new heat exchanger design are lower than those of the heat exchanger with segmental baffles, which means that the novel heat exchanger has a higher efficiency than the heat exchanger with segmental baffles, from the second-law based thermodynamics viewpoint. [source] How do plants know when other plants are flowering?ECOLOGY LETTERS, Issue 11 2009Resource depletion, mast-seeding in a perennial wildflower, pollen limitation Abstract Mast-seeding is the synchronous and periodic reproduction by plant populations. This phenomenon has been widely studied from a community-level perspective, but we know extremely little about how plants are able to synchronize reproduction. Here, we present the first experimental test of proximate mechanisms of mast-seeding, by preventing reproduction in an iteroparous, mast-seeding wildflower. Through a series of experiments, we show that mobile carbohydrate stores (NSC) control alternate-year flowering by individual plants; seed set depletes NSC which prevents flowering the following year. Plants are synchronized by density-dependent pollen limitation; when plants flower asynchronously, they set fewer seeds, which prevents NSC depletion. Therefore, these individual plants flower in subsequent years and become synchronized. Because mast-seeding is a consequence of physiological controls of reproduction, differences in plant resource acquisition and allocation could dramatically change patterns of seed production, and changes in plant consumers and pollinators could change selection on physiological and developmental pathways. [source] AN EXPERIMENTAL TEST ON RETIREMENT DECISIONSECONOMIC INQUIRY, Issue 3 2007ENRIQUE FATAS As part of the current debate on the reform of pension systems, this paper presents an original experimental test where subjects face three different payoff sequences with identical expected value. Two central questions are analyzed. First, whether the distribution of retirement benefits across time influences the retirement decision. And second, whether actuarially fair pension systems distort the retirement decision. The results indicate both that a lump-sum payment rather than annuity benefits is far more effective in delaying the retirement decision and that recent reforms that encourage the link between lifetime contributions and pension benefits to delay the retirement decision should take into account timing considerations. (JEL C91, H55, J26) [source] Reactivity to alcohol assessment measures: an experimental testADDICTION, Issue 8 2009Scott T. Walters ABSTRACT Aims Previous research has suggested that alcohol screening and assessment may affect drinking. Design This study was a randomized test of reactivity to alcohol assessment questionnaires among a group of heavy drinking college students. Setting and participants A total of 147 university students completed a screening questionnaire and were randomized to either immediate assessment or delayed assessment. The immediate assessment group completed a set of drinking questionnaires at baseline, 3, 6 and 12 months, while the delayed assessment group completed questionnaires only at 12 months. Measurements Primary outcomes included overall volume of drinking, risky drinking and use of risk reduction behaviors. Findings We found a significant effect of assessment on measures of risky drinking and risk reduction behaviors, but not on overall volume of drinking. Specifically, at 12 months, participants who had previously completed drinking assessments had a lower peak blood alcohol concentration (BAC) (d = ,0.373), were more likely to report a low score on the Alcohol Use Disorders Identification Test (AUDIT; odds ratio = 2.55) and tended to use more strategies to moderate their alcohol consumption (d = 0.352). Risk reduction behaviors that were affected tended to be those that limited alcohol consumption, rather than those that minimized consequences. Conclusions These results may have implications for the development of brief interventions. [source] An experimental test of the symbiosis specificity between the ciliate Paramecium bursaria and strains of the unicellular green alga ChlorellaENVIRONMENTAL MICROBIOLOGY, Issue 8 2007Monika Summerer Summary The ciliate Paramecium bursaria living in mutualistic relationship with the unicellular green alga Chlorella is known to be easily infected by various potential symbionts/parasites such as bacteria, yeasts and other algae. Permanent symbiosis, however, seems to be restricted to Chlorella taxa. To test the specificity of this association, we designed infection experiments with two aposymbiotic P. bursaria strains and Chlorella symbionts isolated from four Paramecium strains, seven other ciliate hosts and two Hydra strains, as well as three free-living Chlorella species. Paramecium bursaria established stable symbioses with all tested Chlorella symbionts of ciliates, but never with symbiotic Chlorella of Hydra viridissima or with free-living Chlorella. Furthermore, we tested the infection specificity of P. bursaria with a 1:1:1 mixture of three compatible Chlorella strains, including the native symbiont, and then identified the strain of the newly established symbiosis by sequencing the internal transcribed spacer region 1 of the 18S rRNA gene. The results indicated that P. bursaria established symbiosis with its native symbiont. We conclude that despite clear preferences for their native Chlorella, the host,symbiont relationship in P. bursaria is flexible. [source] The Effects of Experimentally Induced Polyandry on Female Reproduction in a Monandrous Mating SystemETHOLOGY, Issue 8 2006Göran Arnqvist Females of most insect species maximize their fitness by mating more than once. Yet, some taxa are monandrous and there are two distinct scenarios for the maintenance of monandry. While males should always benefit from inducing permanent non-receptivity to further mating in their mate, this is not necessarily true for females. Since females benefit from remating in many species, cases of monandry may reflect successful male manipulation of female remating (i.e. sexual conflict). Alternatively, monandry may favor both mates, if females maximize their fitness by mating only once in their life. These two hypotheses for the maintenance of monandry make contrasting predictions with regards to the effects of remating on female fitness. Here, we present an experimental test of the above hypotheses, using the monandrous housefly (Musca domestica) as a model system. Our results showed that accessory seminal fluid substances that males transfer to females during copulation have a dual effect: they trigger female non-receptivity but also seem to have a nutritional effect that could potentially enhance female fitness. These results suggest that monandry is maintained in house flies despite potential benefits that females would gain by mating multiply. [source] Electromagnetic torque of a synchronous machine during a single out-of-phase reclosingEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 4 2000A. C. Ammari The adoption of single-pole switching for a radial transmission line which connects large synchronous machines to the power system would submit these machines to repetitive mechanical stress. To evaluate the total mechanical stress, it is first necessary to determine the electromagnetic torque and to evaluate its transient maximum values at reclosing. In this paper, maximum values of the electromagnetic transient torque at single-pole reclosing are first computed using a simplified analytical approach. The analytical results are then validated by numerical simulations and by an experimental test on a laboratory synchronous machine. It will be shown that single-pole reclosing would be, in the worst case, as restricting as three out-of-phase synchronisation. [source] EXPERIMENTAL EVIDENCE FOR FREQUENCY DEPENDENT SELF-FERTILIZATION IN THE GYNODIOECIOUS PLANT, SILENE VULGARISEVOLUTION, Issue 6 2009Keiko Miyake After over a half century of empirical and theoretical research regarding the evolution and maintenance of gynodioecy in plants, unexplored factors influencing the relative fitnesses of females and hermaphrodites remain. Theoretical studies suggest that hermaphrodite self-fertilization (selfing) rate influences the maintenance of gynodioecy and we hypothesized that population sex ratio may influence hermaphrodite selfing rate. An experimental test for frequency-dependent self-fertilization was conducted using replicated populations constructed with different sex ratios of the gynodioecious plant Silene vulgaris. We found that hermaphrodite selfing increased with decreased hermaphrodite frequency, whereas evidence for increased inbreeding depression was equivocal. We argue that incorporation of context dependent inbreeding into future models of the evolution of gynodioecy is likely to yield novel insights into sex ratio evolution. [source] Consequences of maternal yolk testosterone for offspring development and survival: experimental test in a lizardFUNCTIONAL ECOLOGY, Issue 3 2007T. ULLER Summary 1Hormone-mediated maternal effects and developmental plasticity are important sources of phenotypic variation, with potential consequences for trait evolution. Yet our understanding of the importance of maternal hormones for offspring fitness in natural populations is very limited, particularly in non-avian species. 2We experimentally elevated yolk testosterone by injection of a physiological dose into eggs of the lizard Ctenophorus fordi Storr, to investigate its roles in offspring development, growth and survival. 3Yolk testosterone did not influence incubation period, basic hatchling morphology or survival under natural conditions. However, there was evidence for increased growth in hatchlings from testosterone-treated eggs, suggesting that maternal hormones have potential fitness consequences in natural populations. 4The positive effect of prenatal testosterone exposure on postnatal growth could represent a taxonomically widespread developmental mechanism that has evolved into an adaptive maternal effect in some taxa, but remains deleterious or selectively neutral in others. 5A broader taxonomic perspective should increase our understanding of the role of physiological constraints in the evolution of endocrine maternal effects. [source] The effect of dominance rank on fat deposition and food hoarding in the Willow Tit Parus montanus, an experimental testIBIS, Issue 1 2003Ken Lundborg We studied the effects of dominance rank on fat deposition and hoarding behaviour in Willow Tits Parus montanus. Dominant individuals can displace subordinates which gives them priority to new food sources; they can also pilfer stored food from subordinates. This gives subordinates less certain access than dominants both to their own caches and to new food sources. Theory predicts that subordinates should invest more than dominants both in body fat reserves and stored food. Empirical evidence is equivocal; some studies have shown that subordinates built up larger reserves than dominants, whereas others show the opposite. In an earlier indoor experiment, Pravosudov and Lucas found no effect of rank on either hoarding rate or fat reserves, but the experimental design was such that the results were ambiguous. This paper reports on a similar, but improved, experiment in outdoor aviaries. However, our results agree with the earlier experiment, since we found no effect of rank on either food storing or fat deposition. The reasons for this are explored. [source] High-nickel insects and nickel hyperaccumulator plants: A reviewINSECT SCIENCE, Issue 1 2009Robert S. Boyd Abstract Insects can vary greatly in whole-body elemental concentrations. Recent investigations of insects associated with Ni hyperaccumulator plants have identified insects with relatively elevated whole-body Ni levels. Evaluation of the limited data available indicates that a whole-body Ni concentration of 500 ,g Ni/g is exceptional: I propose that an insect species with a mean value of 500 ,g Ni/g or greater, in either larval/nymphal or adult stages, be considered a "high-Ni insect". Using the 500 ,g Ni/g criterion, 15 species of high-Ni insects have been identified to date from studies in Mpumalanga (South Africa), New Caledonia and California (USA). The highest mean Ni concentration reported is 3 500 ,g Ni/g for nymphs of a South African Stenoscepa species (Orthoptera: Pyrgomorphidae). The majority of high-Ni insects (66%) are heteropteran herbivores. Studies of high-Ni insect host preference indicate they are monophagous (or nearly so) on a particular Ni hyperaccumulator plant species. Much of the Ni in bodies of these insects is in their guts (up to 66%,75%), but elevated levels have also been found in Malpighian tubules, suggesting efficient elimination as one strategy for dealing with a high-Ni diet. Tissue levels of Ni are generally much lower than gut concentrations, but up to 1200 ,g Ni/g has been reported from exuviae, suggesting that molting may be another pathway of Ni elimination. One ecological function of the high Ni concentration of these insects may be to defend them against natural enemies, but to date only one experimental test has supported this "elemental defense" hypothesis. Community-level studies indicate that high-Ni insects mobilize Ni into food webs but that bioaccumulation of Ni does not occur at either plant-herbivore or herbivore-predator steps. Unsurprisingly, Ni bioaccumulation indices are greater for high-Ni insects compared to other insect species that feed on Ni hyperaccumulator plants. There is some evidence of Ni mobilization into food webs by insect visitors to flowers of Ni hyperaccumulator plants, but no high-Ni insect floral visitors have been reported. [source] Universal resistorless current-mode filters employing CCCIIsINTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS, Issue 5-6 2008Erkan Yuce Abstract In this paper, four different-type second-order current-mode filters, employing second-generation current-controlled conveyors (CCCIIs) and two capacitors, are proposed. The first two of the presented filters can simultaneously realize high-output impedance low-pass, band-pass and high-pass responses. Also, the two filters can provide notch and all-pass filter responses with interconnection of the relevant output currents. The first developed one needs no critical active and passive element matching conditions and/or cancellation constraints. The second and third introduced ones employ only grounded capacitors. The fourth proposed filter derived from the third one uses only plus-type single output CCCIIs (CCCII+s). The fifth filter can be constructed using commercially available active devices such as AD844s along with additional resistors instead of CCCII+s of the fourth proposed filter to perform experimental test easily. All of the proposed filters have low active and passive element sensitivities. Time and frequency domain analyses are performed for the first, second and third realized filters using SPICE simulation program. Also, experimental test is achieved for the fifth filter. In this study, stability problems attributed to non-ideal gains of the CCCIIs and signal limitations of the first, second and third introduced filters due to restricted power supply voltages are investigated. Copyright © 2007 John Wiley & Sons, Ltd. [source] A study on latent heat storage exchangers with the high-temperature phase-change materialINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 4 2001Qiao He Abstract This paper presents a theoretical analysis and an experimental test on a shell-and-tube latent heat storage exchanger. The heat exchanger is used to recover high-temperature waste heat from industrial furnaces and off-peak electricity. It can also be integrated into a renewable energy system as an energy storage component. A mathematical model describing the unsteady freezing problem coupled with forced convection is solved numerically to predict the performance of the heat exchanger. It provides the basis for an optimum design of the heat exchanger. The experimental study on the heat exchanger is carried out under various operating conditions. Effects of various parameters, such as the inlet temperature, the mass flow rate, the thickness of the phase-change material and the length of the pipes, on the heat transfer performance of the unit are discussed combined with theoretical prediction. The criterion for analyzing and evaluating the performance of heat exchanger is also proposed. Copyright © 2001 John Wiley & Sons, Ltd. [source] An experimental test of the link between foraging, habitat selection and thermoregulation in black rat snakes Elaphe obsoleta obsoletaJOURNAL OF ANIMAL ECOLOGY, Issue 6 2001Gabriel Blouin-Demers Summary 1Most physiological processes are temperature-dependent. Thus, for ectotherms, behavioural control of body temperatures directly affects their physiology. Ectotherms thermoregulate by adjusting habitat use and therefore thermoregulation is probably the single most important proximate factor influencing habitat use of terrestrial reptiles, at least in temperate climates. 2Snakes have been shown to raise their body temperature following feeding in a laboratory thermal gradient, presumably to enhance digestion. This experiment was exported to the field to explore the link between feeding, habitat selection and thermoregulation in free-ranging snakes. 3Experimental feeding was conducted in the laboratory and in the field on black rat snakes (Elaphe obsoleta obsoleta) that had temperature-sensitive radio-transmitters surgically implanted. 4Snakes had higher mean body temperatures following feeding than prior to feeding in a laboratory thermal gradient. 5Some, but not all evidence, indicated that black rat snakes increased their mean body temperature following feeding in the field. Indices of thermoregulation indicated that the snakes thermoregulated more carefully and more effectively after they had eaten. 6Forest edges provided the best opportunities for thermoregulation in the study area. Black rat snakes were less likely to move following feeding when fed in edges than when fed in the forest and were more likely to be found in edges following feeding, whether they had been fed in the forest or in an edge. 7Results of this study and one previous study suggest that thermoregulatory behaviour of snakes following feeding in the laboratory is a reliable predictor of their behaviour in the field. A review of 13 studies of the thermoregulatory behaviour of snakes following feeding in the laboratory revealed that not all species behave similarly. However, the quality and number of studies currently available is not adequate for testing hypotheses about which species should change thermoregulatory behaviour in response to eating and which should not. [source] An experimental test for effects of the maternal environment on delayed germinationJOURNAL OF ECOLOGY, Issue 5 2010Katja Tielbörger Summary 1.,Recent models on bet-hedging germination in annual plants assume a negative relationship between the proportion of offspring that germinate and the quality of the maternal environment. An increase in the proportion of seeds remaining dormant in the next year, when produced in seasons with high reproduction may result from selection that avoids overcrowding in the following year. 2.,We present the first empirical test of this prediction by utilizing a field experiment in Israel which manipulated the entire maternal environment. We subjected semi-arid and Mediterranean annual plant communities to different rainfall treatments: control, reduced and increased rainfall. We then related maternal environment quality to offspring germination fractions for three focal species in two consecutive seasons. 3.,There was a negative relationship between the quality of the maternal environment and offspring germination fraction in four out of twelve cases. The negative relationship was stronger for the least competitive species and in the environment with high competition intensity, supporting the role of competition for the observed pattern. 4.,Our results suggest that competition with all neighbours is more likely to explain the pattern than sib competition. 5.,Synthesis. Our findings provide the first experimental evidence of a highly reliable cue (productivity of maternal environment) that allows for plants to respond to their future biotic environment. There is an urgent need for testing predictions of theoretical models in natural populations and for incorporating the role of density dependence in studies of bet-hedging germination. 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