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Experimental Situations (experimental + situation)
Selected AbstractsEnvironmental and developmental controls on specific leaf area are little modified by leaf allometryFUNCTIONAL ECOLOGY, Issue 4 2008R. Milla Summary 1Recent work shows that large leaves tend to require higher biomass investments per unit leaf area than small leaves. As a consequence, specific leaf area (SLA), which is a focus trait for a bulk of physiological and ecological research programs, is dependent on leaf size variation. Here, we address whether size dependency alters the outcome of research dealing with SLA responses to environmental or developmental change. 2We compiled lamina mass (M) and surface area (A) data for 2158 leaves of 26 species, coming from studies investigating the reaction of SLA to variation in rainfall, growth,season length, light intensity, atmospheric CO2, fire frequency, type of branch and leaf and plant age. We fitted the function M = a Ab to the data of each experimental situation separately, and implemented a method to split SLA response as measured in the original study (SLADm) into response due to leaf size dependency (SLADa), and response due to treatment effects, after controlling for leaf size dependency (SLADt). 3The sign of the reaction did not differ between SLADm and SLADt. However, the magnitude of that response changed for most contrasts, though in variable ways. 4Conclusions of past experiments hold, for the most part, after re-analysis including size dependency. However, given the large heterogeneity found here, we advise that future work investigating SLA be prepared to account for leaf size dependency when the factors under focus are suspected to alter leaf size. [source] A keratinocytes,melanocytes coculture system for the evaluation of active ingredients' effects on UV-induced melanogenesisINTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 1-2 2003J.-F. Nicolaÿ Synopsis A new experimental design, more reliable for in vitro testing of active ingredients' effect on ultraviolet (UV)-induced melanogenesis has been carried out. It uses a bicompartmental coculture system where cell communication between keratinocytes and melanocytes can take place. Thus, this experimental situation enables to monitor the effect of biological agents released by both cell types on melanogenesis and the interference of tested compounds with this ,paracrine linkage'. Experiments with UVB-irradiated cocultures show the importance of cell communication in the melanogenic response. In this model, the endogenous mediator, nitric oxide (NO), increased melanin production. Different compounds were tested in the coculture system, and comparison with data obtained from irradiated monocultures of melanocytes enables to distinguish a specific effect on cell communication. In addition, this more close-to-reality experimental model proved to provide a valuable first approach for the assessment of the ,bioavailability' of the tested substances. Finally, the effect of an innovative photoprotective agent capable of ,boosting' UV-induced melanogenic cell communication is presented. Résumé Un nouveau concept expérimental, plus fiable pour l,évaluation in vitro de l,effet de principes actifs sur la mélanogénèse induite par les UV, a été mis en ,uvre. Il utilise un système de co-culture à double compartiment dans lequel une communication cellulaire entre les kératinocytes et les mélanocytes peut s,établir. Ainsi, ce système expérimental permet de suivre l,effet des agents biologiques libérés par les deux types de cellules sur la mélanogénèse, et les interférences des composés testés avec ce ,lien paracrine'. Les essais avec des co-cultures irradiées aux UV montrent l,importance de la communication cellulaire dans la réponse mélanogénique. Avec ce modèle, le médiateur oxyde nitrique endogène (NO) augmente la production de mélanine. Différents composés ont été testés avec ce système de co-culture, et une comparaison avec les données obtenues à partir de monocultutres de mélanocytes irradiées permet de distinguer un effet spécifique sur la communication cellulaire. En outre, ce modèle expérimental plus proche de la réalité s,est avéré apporter une première approche valable de l,évaluation de la ,biodisponibilité' des substances testées. Enfin, l,effet d,un agent protecteur innovant capable de stimuler la communication cellulaire mélanogénique induite par les UV est décrit. [source] Transfer from "edible" categorization training to feeding behavior in pigeons (Columba livia)1JAPANESE PSYCHOLOGICAL RESEARCH, Issue 1 2006SHUNJI AWAZU Abstract:, We investigated a transfer from an operant experimental situation to a feeding situation in pigeons using real objects as stimuli. Four pigeons were trained in an operant box to categorize familiar edible items as positives and inedible items as negatives with a go/no-go procedure. Next, two pairs of unfamiliar edible items were added as stimuli. One of the paired stimuli was arbitrarily assigned as positive and the other as negative. We tested the subjects in their home cages to see whether they would feed on the items they were trained to categorize as positives. In three of the six cases in which categorization training was successful, they continued to peck the positive items. This result suggests that the pigeons transfer what they learned in the operant training situation to the feeding situation. [source] Reactive Flow Model Parameter Estimation Using Genetic AlgorithmsPROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 3 2010Jose Baranda, Ribeiro Abstract An original real-coded genetic algorithm methodology that has been developed for the estimation of the parameters of the Tarver reactive flow model of shock initiation and detonation of heterogeneous solid explosives is described in detail. This methodology allows, in a single optimisation procedure and without the need for a starting solution, to search for the 15 parameters of the reaction rate law of the reactive flow model that fit the numerical results to the experimental ones. The developed methodology was applied and tested with an experimental situation, described in detail in the literature, involving the acceleration of a tantalum metal plate by an LX-17 explosive charge. The obtained parameters allow a very good description of the experimental results and are close to the ones originally used by Tarver and co-authors in their simulation of the phenomenon. [source] Extracting charge density distributions from diffraction data: a model study on ureaACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2000R. Y. De Vries The quality of the extraction of electron density distributions by means of a multipole refinement method is investigated. Structure factors of the urea crystal have been obtained from an electron density distribution (EDD) resulting from a density function calculation with the CRYSTAL95 package. To account for the thermal motion of the atoms, the stockholder-partioned densities of the atoms have been convoluted with thermal smearing functions, which were obtained from a neutron diffraction experiment. A POP multipole refinement yielded a good fit, R = 0.6%. This disagreement factor is based on magnitudes only. Comparison with the original structure factors gave a disagreement of 0.8% owing to differences in magnitude and phase. The fitted EDD still showed all the characteristics of the interaction density. After random errors corresponding to the experimental situation were added to the structure factors, the refinement was repeated. The fit was R = 1.1%. This time the resulting interaction density was heavily deformed. Repetition with another set of random errors from the same distribution yielded a widely different interaction density distribution. The conclusion is that interaction densities cannot be obtained from X-ray diffraction data on non-centrosymmetric crystals. [source] Effects of a Mechanical Barrier on the Integration of Cortical Onlay Bone Grafts Placed Simultaneously with Endosseous ImplantCLINICAL IMPLANT DENTISTRY AND RELATED RESEARCH, Issue 2 2002Luiz Z. Salata DDS ABSTRACT Background: Previous experimental studies on onlay bone graft integration have shown either advantages or disadvantages to the use of mechanical barriers. This indicates that the role played by the biologic properties of transplanted bone and membrane in graft revascularization and bone remodeling has not yet been established. The outcomes regarding osseointegration of titanium dental implants applied in such a condition are still contradictory. Purpose: The rabbit's radius model that is grafted onto the mandibular lower border and covered by membrane can reproduce a challenging experimental situation to preliminarily study the factors involved in osseointegration under deprived blood vessels source. Materials and Methods: Fourteen New Zealand White rabbits had a 2.5-cm segment of the right radius osteoectomized and fixed onto the right mandibular lower border using titanium screws. Two screw-shaped titanium implants (2.5 mm wide 2.5 mm long) were installed 7 mm apart in the mid length of the grafted bone. In experimental sites, the graft with the implants and graft-host bone junction were covered by expanded polytetrafluoroethylene (e-PTFE) membrane; control sites were left uncovered. Eight animals from the experimental group and six animals from the control group were sacrificed at 6 and 24 weeks after surgery. Ground sections obtained from en bloc tissues containing graft, implants, and recipient bone were subjected to histologic evaluation and histomorphometric analysis (area occupied by the graft and bone-to-implant contact). Results: The graft showed significantly more resorption after 24 weeks than at 6 weeks (p .05) irrespective of the treatment (with or without membrane), although the amount of new bone was greater at 24 weeks in sites where a membrane was covering the graft. Compared with 6 weeks postoperatively, the bone-to-implant contact was considerably improved at 24 weeks (p .05), and the membrane seemed beneficial for implant osseointegration when compared with unprotected sites (p .05). As a result of graft resorption, the amount of soft tissue was considerably expanded in sites beneath membrane, accompanied by a sustained process of trabecular bone deposition close to the barrier. Conclusions: Cortical onlay grafts covered by membrane demonstrated delayed remodeling, probably as a consequence of a hindered process of graft revascularization. Grafts covered by membrane might rely on previous host bone resorption both to become revascularized and to remodel. The findings that the membrane-protected grafts were most resorbed at 24 weeks might be attributable to better implant osseointegration, because the fixtures were exposed to greater mechanical stimulation in these sites. [source] COEVOLUTION OF COLOR PATTERN AND THERMOREGULATORY BEHAVIOR IN POLYMORPHIC PYGMY GRASSHOPPERS TETRIX UNDULATAEVOLUTION, Issue 2 2002Anders Forsman Abstract Ectothermic organisms, such as insects and reptiles, rely on external heat sources to control body temperature and possess physiological and behavioral traits that are temperature dependent. It has therefore been hypothesised that differences in body temperature resulting from phenotypic properties, such as color pattern, may translate into selection against thermally inferior phenotypes. We tested for costs and benefits of pale versus dark coloration by comparing the behaviors (i.e., basking duration and bouts) of pygmy grasshopper (Tetrix undulata) individuals exposed to experimental situations imposing a trade-off between temperature regulation and feeding. We used pairs consisting of two full-siblings of the same sex that represented different (genetically coded) color morphs but had shared identical conditions from the time of fertilization. Our results revealed significant differences in behavioral thermoregulation between dark and pale individuals in females, but not in males. Pale females spent more time feeding than dark females, regardless of whether feeding was associated with a risk of either hypothermia or overheating. In contrast, only minor differences in behavior (if any) were evident between individuals that belonged to the same color morph but had been painted black or gray to increase and decrease their heating rates. This suggests that the behavioral differences between individuals belonging to different color morphs are genetically determined, rather than simply reflecting a response to different heating rates. To test for effects of acclimation on behaviors, we used pairs of individuals that had been reared from hatchlings to adults under controlled conditions in either low or high temperature. The thermal regime experienced during rearing had little effect on behaviors during the experiments reported above, but significantly influenced the body temperatures selected in a laboratory thermal gradient. In females (but not in males) preferred body temperature also varied among individuals born to mothers belonging to different color morphs, suggesting that a genetic correlation exists between color pattern and temperature preferences. Collectively, these findings, at least in females, are consistent with the hypothesis of multiple-trait coevolution and suggest that the different color morphs represent alternative evolutionary strategies. [source] A comparison of Granger causality and coherency in fMRI-based analysis of the motor systemHUMAN BRAIN MAPPING, Issue 11 2009Andrew S. Kayser Abstract The ability of functional MRI to acquire data from multiple brain areas has spurred developments not only in voxel-by-voxel analyses, but also in multivariate techniques critical to quantifying the interactions between brain areas. As the number of multivariate techniques multiplies, however, few studies in any modality have directly compared different connectivity measures, and fewer still have done so in the context of well-characterized neural systems. To focus specifically on the temporal dimension of interactions between brain regions, we compared Granger causality and coherency (Sun et al., 2004, 2005: Neuroimage 21:647,658, Neuroimage 28:227,237) in a well-studied motor system (1) to gain further insight into the convergent and divergent results expected from each technique, and (2) to investigate the leading and lagging influences between motor areas as subjects performed a motor task in which they produced different learned series of eight button presses. We found that these analyses gave convergent but not identical results: both techniques, for example, suggested an anterior-to-posterior temporal gradient of activity from supplemental motor area through premotor and motor cortices to the posterior parietal cortex, but the techniques were differentially sensitive to the coupling strength between areas. We also found practical reasons that might argue for the use of one technique over another in different experimental situations. Ultimately, the ideal approach to fMRI data analysis is likely to involve a complementary combination of methods, possibly including both Granger causality and coherency. Hum Brain Mapp, 2009. © 2009 Wiley-Liss, Inc. [source] What Is Ecological Validity?INFANCY, Issue 4 2001A Dimensional Analysis Ecological validity has typically been taken to refer to whether or not one can generalize from observed behavior in the laboratory to natural behavior in the world. Although common in current discussions of research, the idea of ecological validity has a long history in psychological thought. A brief historical examination of this idea reveals that concerns with ecological validity are evident in multiple dimensions of experimental work, including the nature of the experimental setting, the stimuli under investigation, and the observer's response employed as the measure. One problem with this multidimensionality, however, is that no explicit criteria have been offered for applying this concept to an evaluation of research. One consequence of this problem is that concerns with ecological validity can be raised in most experimental situations. This article includes a discussion of some demands of ecological validity and the nature of these different dimensions, as well as a critical evaluation of research on the development of mobility with respect to these constraints. [source] Applications of gold cluster compounds in immunocytochemistry and correlative microscopy: comparison with colloidal goldJOURNAL OF MICROSCOPY, Issue 3 2000J. M. Robinson In this review, we discuss the immunocytochemical literature with respect to a comparison between conventional colloidal gold and gold cluster compounds as immunoprobes. The relative advantages and disadvantages of each of these types of particle for immunocytochemical applications are discussed. We present results from our own laboratories and those of others on the comparison of these immunoprobes in selected experimental situations. These results show the use of gold cluster compounds at both light and electron microscope levels. At the ultrastructural level, gold cluster compounds have been used in pre-embedding labelling of cultured cells, and for labelling of ultrathin cryosections and freeze-fracture preparations. Recently, fluorescently tagged gold cluster compounds have become available. Using ultrathin cryosections of human neutrophils as a model system, we demonstrate that a single immunoprobe (i.e. a fluorescently tagged gold cluster compound) is a robust probe for correlative fluorescence and electron microscopy. [source] Structural identifiability analysis of the dynamic gas,liquid film modelAICHE JOURNAL, Issue 8 2006J. Navarro-Laboulais Abstract A structural identification analysis of the dynamic gas,liquid film model is applied to identify its theoretically accessible parameters. The analysis was performed considering the different experimental situations found in nonstationary bubble-column reactors. The system has been modeled considering both the liquid and the gas phases in a well-mixed flow regime with a global second-order irreversible chemical reaction. To describe the mass-transfer phenomenon at the gas,liquid interface level, chemical reactions and diffusive mass transport were considered simultaneously in the liquid film. The identifiability analysis shows that the simultaneous measurement of concentrations in the liquid and the gas phases is required to determine the parameters. Furthermore, model parameters such as the diffusion coefficients, the specific interfacial area, or the film thickness cannot be uncoupled from other parameters, although the kinetic rate constants could be identified in the fast or slow chemical regimes. It is demonstrated that the specific interfacial area cannot be measured from chemical data coming from a nonstationary bubble-column reactor. This result is discussed with respect to the classical Danckwerts' method for determination of the interfacial area in gas,liquid equipment. © American Institute of Chemical Engineers AIChE J, 2006 [source] Caffeine increases spinal excitability in humansMUSCLE AND NERVE, Issue 3 2003C. Walton MSc Abstract The Hoffman reflex (H reflex) has long been established as a measure of spinal excitability. Caffeine is one of the most widely consumed drugs in the world. Because it is known to increase excitatory neurotransmission, we hypothesized that caffeine would increase spinal excitability and thus alter the H reflex by increasing its amplitude. Seven subjects each attended the laboratory on 2 days. Caffeine (6 mg/kg) was administered on one day and a placebo was administered on the other. The tibial nerve was stimulated at incremental intensities to create an H-reflex recruitment curve prior to capsule administration (pretest) and 1 h later (posttest) on each day. The slope of H-reflex recruitment curve normalized to that of the M wave (Hslp/Mslp) was compared (pretest to posttest). Caffeine increased spinal excitability 43 ± 17% (P < 0.05). Thus, caffeine may be used to safely increase spinal excitability in electrophysiological studies of the human neuromuscular system. Our results also suggest that caffeine intake should be controlled when the H reflex is used in diagnostic and experimental situations. Muscle Nerve 28: 359,364, 2003 [source] Hartree,Fock interactions in the integer quantum Hall effectPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2008Rudolf A. Römer Abstract We report on numerical studies into the interplay of disorder and electron,electron interactions within the integer quantum Hall regime, where the presence of a strong magnetic field and two-dimensional confinement of the electronic system profoundly affects thermodynamic and transport properties. We emphasise the behaviour of the electronic compressibility, the local density of states, and the Kubo conductivity. Our treatment of the electron,electron interactions relies on the Hartree-Fock approximation so as to achieve system sizes comparable to experimental situations. Our results clearly exhibit manifestations of various interaction-mediated features, such as non-linear screening, local charging, and g -factor enhancement, implying the inadequacy of independent-particle models for comparison with experimental results. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Clustering in the Presence of ScatterBIOMETRICS, Issue 2 2009Ranjan Maitra Summary:, A new methodology is proposed for clustering datasets in the presence of scattered observations. Scattered observations are defined as unlike any other, so traditional approaches that force them into groups can lead to erroneous conclusions. Our suggested approach is a scheme which, under assumption of homogeneous spherical clusters, iteratively builds cores around their centers and groups points within each core while identifying points outside as scatter. In the absence of scatter, the algorithm reduces to k -means. We also provide methodology to initialize the algorithm and to estimate the number of clusters in the dataset. Results in experimental situations show excellent performance, especially when clusters are elliptically symmetric. The methodology is applied to the analysis of the United States Environmental Protection Agency's Toxic Release Inventory reports on industrial releases of mercury for the year 2000. [source] Cell kinetic studies in the murine ventral tongue epithelium: thymidine metabolism studies and circadian rhythm determinationCELL PROLIFERATION, Issue 2002C. S. Potten Abstract. ,The oral mucosa is a rapidly replacing body tissue that has received relatively little attention in terms of defining its cell kinetics and cellular organization. The tissue is sensitive to the effects of cytotoxic agents, the consequence of which can be stem cell death with the subsequent development of ulcers and the symptoms of oral mucositis. There is considerable interest in designing strategies to protect oral stem cells and, hence, reduce the mucositis side-effects in cancer therapy patients. Here we present details of a new histometric approach designed to investigate the changing patterns in cellularity in the ventral tongue mucosa. This initial paper in a series of four papers presents observations on the changing patterns in the labelling index following tritiated thymidine administration, which suggest a delayed uptake of tritiated thymidine from a long-term intracellular thymidine pool, a phenomenon that will complicate cell kinetic interpretations in a variety of experimental situations. We also provide data on the changing pattern of mitotic activity through a 24-h period (circadian rhythms). Using vincristine-induced stathmokinesis, the data indicate that 54% of the basal cells divide each day and that there is a high degree of synchrony in mitotic activity with a mitotic peak occurring around 13.00 h. The mitotic circadian peak occurs 9-12 h after the circadian peak in DNA synthesis. The data presented here and in the subsequent papers could be interpreted to indicate that basal cells of BDF1 mice have an average turnover time of about 26-44 h with some cells cycling once a day and others with a 2- or 3-day cell cycle time. [source] | ||||||||||||||||