Distribution by Scientific Domains

Kinds of Limitations

  • activity limitation
  • adl limitation
  • airflow limitation
  • behavioural limitation
  • carbon limitation
  • certain limitation
  • chronic airflow limitation
  • co2 limitation
  • cognitive limitation
  • common limitation
  • current limitation
  • data limitation
  • design limitation
  • diffusion limitation
  • diffusional limitation
  • dispersal limitation
  • egg limitation
  • energy limitation
  • environmental limitation
  • exercise limitation
  • food limitation
  • functional limitation
  • fundamental limitation
  • general limitation
  • greatest limitation
  • growth limitation
  • hydraulic limitation
  • important limitation
  • inherent limitation
  • iron limitation
  • key limitation
  • kinetic limitation
  • light limitation
  • main limitation
  • major limitation
  • many limitation
  • mass transfer limitation
  • mass transport limitation
  • material limitation
  • methodologic limitation
  • methodological limitation
  • mobility limitation
  • n limitation
  • nitrogen limitation
  • nutrient limitation
  • one limitation
  • other limitation
  • own limitation
  • oxygen limitation
  • p limitation
  • performance limitation
  • phosphate limitation
  • phosphorus limitation
  • physical limitation
  • physiological limitation
  • pollen limitation
  • pollinator limitation
  • possible limitation
  • potential limitation
  • practical limitation
  • present limitation
  • rate limitation
  • recruitment limitation
  • resource limitation
  • role limitation
  • seed limitation
  • serious limitation
  • several limitation
  • severe limitation
  • significant limitation
  • social limitation
  • space limitation
  • study limitation
  • substantial limitation
  • technical limitation
  • time limitation
  • transfer limitation
  • transport limitation
  • water limitation
  • well-known limitation
  • work limitation

  • Terms modified by Limitations

  • limitation inherent
  • limitation policy

  • Selected Abstracts


    EVOLUTION, Issue 6 2010
    Genetic diversity at the S-locus controlling self-incompatibility (SI) is often high because of negative frequency-dependent selection. In species with highly patchy spatial distributions, genetic drift can overwhelm balancing selection and cause stochastic loss of S-alleles. Natural selection may favor the breakdown of SI in populations with few S-alleles because low S-allele diversity constrains the seed production of self-incompatible plants. We estimated S-allele diversity, effective population sizes, and migration rates in Leavenworthia alabamica, a self-incompatible mustard species restricted to discrete habitat patches in rocky glades. Patterns of polymorphism were investigated at the S-locus and 15 neutral microsatellites in three large and three small populations with 100-fold variation in glade size. Populations on larger glades maintained more S-alleles, but all populations were estimated to harbor at least 20 S-alleles, and mate availabilities typically exceeded 0.80, which is consistent with little mate limitation in nature. Estimates of the effective size (Ne) in each population ranged from 600 to 1600, and estimated rates of migration (m) ranged from 3 × 10,4 to nearly 1 × 10,3. According to theoretical models, there is limited opportunity for genetic drift to reduce S-allele diversity in populations with these attributes. Although pollinators or resources limit seed production in small glades, limited S-allele diversity does not appear to be a factor promoting the incipient breakdown of SI in populations of this species that were studied. [source]


    JOURNAL OF PHYCOLOGY, Issue 5 2010
    Cécile Jauzein
    Alexandrium catenella (Whedon et Kof.) Balech has exhibited seasonal recurrent blooms in the Thau lagoon (South of France) since first reported in 1995. Its appearance followed a strong decrease (90%) in phosphate (PO43,) concentrations in this environment over the 1970,1995 period. To determine if this dinoflagellate species has a competitive advantage in PO43, -limited conditions in terms of nutrient acquisition, semicontinuous cultures were carried out to characterize phosphorus (P) uptake by A. catenella cells along a P-limitation gradient using different dilution rates (DRs). Use of both inorganic and organic P was investigated from measurements of 33PO43, uptake and alkaline phosphatase activity (APA), respectively. P status was estimated from cellular P and carbon contents (QP and QC). Shifts in trends of QP/QC and QP per cell (QP·cell,1) along the DR gradient allowed the definition of successive P-stress thresholds for A. catenella cells. The maximal uptake rate of 33PO43, increased strongly with the decrease in DR and the decrease in QP/QC, displaying physiological acclimations to PO43, limitation. Concerning maximal APA per cell, the observation of an all-or-nothing pattern along the dilution gradient suggests that synthesis of AP was induced and maximized at the cellular scale as soon as PO43, limitation set in. APA variations revealed that the synthesis of AP was repressed over a PO43, threshold between 0.4 and 1 ,M. As lower PO43, concentrations are regularly observed during A. catenella blooms in Thau lagoon, a significant portion of P uptake by A. catenella cells in the field may come from organic compounds. [source]


    JOURNAL OF PHYCOLOGY, Issue 6 2001
    Margaret Davey
    Iron starvation induced marked increases in flavodoxin abundance and decreases in light-saturated and light-limited photosynthesis rates in the diatom Chaetoceros muelleri. Consistent with the substitution of flavodoxin for ferredoxin as an early response to iron starvation, increases of flavodoxin abundance were observed before declines of cell division rate or chl a specific photosynthesis rates. Changes in the abundance of flavodoxin after the addition of iron to iron-starved cells indicated that flavodoxin was not actively degraded under iron-replete conditions. Greater declines in light-saturated oxygen evolution rates than dark oxygen consumption rates indicated that the mitochondrial electron transfer chain was not affected as greatly by iron starvation as the photosynthetic electron transfer chain. The carbon:nitrogen ratio was unaffected by iron starvation, suggesting that photosynthetic electron transfer was a primary target of iron starvation and that reductions in nitrate assimilation were due to energy limitation (the C:N ratio would be expected to rise under nitrogen-limited but energy-replete conditions). Parallel changes were observed in the maximum light-saturated photosynthesis rate and the light-limited initial slope of the photosynthesis-light curve during iron starvation and recovery. The lowest photosynthesis rates were observed in iron-starved cells and the highest values in iron-replete cells. The light saturation parameter, Ik, was not affected by iron starvation, nor was the chl-to-C ratio markedly reduced. These observations were consistent with iron starvation having a similar or greater effect on photochemical charge separation in PSII than on downstream electron transfer steps. Declines of the ratio of variable to maximum fluorescence in iron-starved cells were consistent with PSII being a primary target of iron starvation. The functional cross-section of PSII was affected only marginally (<20%) by iron starvation, with the largest values observed in iron-starved cells. The rate constant for electron transfer calculated from fast repetition rate fluorescence was found to covary with the light-saturated photosynthesis rate; it was lowest in the most severely starved cells. [source]


    FAMILY COURT REVIEW, Issue 2 2007
    Steven K. Erickson
    Psychologists are frequently consulted by the courts to provide forensic evaluations in a variety of family court proceedings. As part of their evaluations, psychologists often use psychological tests to assess parents, guardians, and children. These tests can have profound effects on how psychologists arrive at their opinions and are often cited in their reports to the court. However, psychological tests vary substantially in their suitability for these purposes. Most projective tests in particular appear to possess little scientific merit for evaluations within family court proceedings. Despite these serious limitations, expert testimony derived from evaluations using both projective and objective tests is often admitted uncontested. This article reviews the psychometric properties of psychological tests that are widely used in family court proceedings, cautions against their unfettered use, and calls upon attorneys to inform themselves of the limitations of evaluations that incorporate these tests. [source]

    Factors associated with discussion of care plans and code status at the time of hospital admission: Results from the Multicenter Hospitalist Study,

    Andrew D. Auerbach MD
    Abstract BACKGROUND: Hospital admission is a time when patients are sickest and also often encountering an entirely new set of caregivers. As a result, understanding and documenting a patient's care preferences at hospital admission is critically important. OBJECTIVE: To understand factors associated with documentation of care planning discussions in patients admitted to general medical services at 6 academic medical centers. DESIGN: Observational cohort study using data collected during the Multicenter Hospitalist Study, conducted between July 1, 2002 and June 30, 2004. SETTING: Prospective trial enrolling patients admitted to general medicine services at 6 university-based teaching hospitals. PATIENTS: Patients were eligible for this study if they were 18 years of age or older, admitted to a hospitalist or nonhospitalist physician, and able to give informed consent. MEASUREMENTS: Presence of chart documentation that the admitting team had discussed care plans with the patient within the first 24 hours of hospitalization. Notations such as "full code" were not counted as a discussion, whereas notations such as "discussed care wishes and plan with patient" were counted. RESULTS: A total of 17,097 patients over the age of 18 gave informed consent and completed an interview and chart abstraction; of these, 1776 (10.3%) had a code status discussion (CD) documented in the first 24 hours of their admission. Patients with a CD were older (69 years vs. 56 years, P < 0.0001), more often white (52.8% vs. 43.3%, P < 0.0001), and more likely to have cancer (19.8% vs. 11.4%, P < 0.0001), or depression (35.1% vs. 30.9%, P < 0.0001). There was marked variability in CD documentation across sites of enrollment (2.8%-24.9%, P < 0.0001). Despite strong associations seen in unadjusted comparisons, in multivariable models many socioeconomic factors, functional status, comorbid illness, and documentation of a surrogate decision maker were only moderately associated with a CD (adjusted odds ratios all less than 2.0). However, patients' site of enrollment (odds ratios 1.74-5.14) and informal notations describing prehospital care wishes (eg, orders for "do not resuscitate"/"do not intubate;" odds ratios 3.22-11.32 compared with no preexisting documentation) were powerfully associated with CD documentation. Site remained a powerful influence even in patients with no documented prehospital wishes. LIMITATIONS: Our results are derived from a relatively small number of academic sites, and we cannot connect documentation differences to differences in patient outcomes. CONCLUSIONS: Documentation of a CD at admission was more strongly associated with informal documentation of prehospital care wishes and where the patient was hospitalized than legal care planning documents (such as durable power of attorney), or comorbid illnesses. Efforts to improve communication between hospitalists and their patients might target local documentation practices and culture. Journal of Hospital Medicine 2008;3(6):437,445. © 2008 Society of Hospital Medicine. [source]


    Gordon D. Hastie
    Abstract Accurate estimates of diving metabolic rate are central to assessing the energy needs of marine mammals. To circumvent some of the limitations inherent with conducting energy studies in both the wild and captivity, we measured diving oxygen consumption of two trained Steller sea lions (Eumetopias jubatus) in the open ocean. The animals dived to predetermined depths (5,30 m) for controlled periods of time (50,200 s). Rates of oxygen consumption were measured using open-circuit respirometry before and after each dive. Mean resting rates of oxygen consumption prior to the dives were 1.34 (±0.18) and 1.95 (±0.19) liter/min for individual sea lions. Mean rates of oxygen consumption during the dives were 0.71 (±0.24) and 1.10 (±0.39) liter/min, respectively. Overall, rates of oxygen consumption during dives were significantly lower (45% and 41%) than the corresponding rates measured before dives. These results provide the first estimates of diving oxygen consumption rate for Steller sea lions and show that this species can exhibit a marked decrease in oxygen consumption relative to surface rates while submerged. This has important consequences in the evaluation of physiological limitations associated with diving such as dive duration and subsequent interpretations of diving behavior in the wild. [source]

    Pulmonary Function and Ventilatory Limitation to Exercise in Congenital Heart Disease

    Paolo T. Pianosi MD
    ABSTRACT Pulmonary function in older children and adolescents following surgical repair of congenital heart disease is often abnormal for various reasons. Many of these patients report symptoms of exercise intolerance although the reason(s) for this symptom can be complicated and sometimes interrelated. Is it simply deconditioning due to inactive lifestyle, chronotropic or inotropic insufficiency? or could there indeed be ventilatory limitation to exercise? These are the questions facing the clinician with the increasing frequency of patients undergoing repair early in life and growing into adulthood. Understanding pulmonary functional outcomes and means of determining ventilatory limitation to exercise is essential to thoroughly address the problem. This article reviews pulmonary function in patients with congenital heart disease and then describes a newer technique that should be applied to determine ventilatory limitation to exercise. [source]

    In Vivo Perfusion of Human Skin Substitutes With Microvessels Formed by Adult Circulating Endothelial Progenitor Cells

    BACKGROUND At present, tissue-engineered human skin substitutes (HSSs) mainly function as temporary bioactive dressings due to inadequate perfusion. Failure to form functional vascular networks within the initial posttransplantation period compromises cell survival of the graft and its long-term viability in the wound bed. OBJECTIVES Our goal was to demonstrate that adult circulating endothelial progenitor cells (EPCs) seeded onto HSS can form functional microvessels capable of graft neovascularization and perfusion. MATERIALS AND METHODS Adult peripheral blood mononuclear cells (PBMCs) underwent CD34 selection and endothelial cell (EC) culture conditions. After in vitro expansion, flow cytometry verified EC phenotype before their incorporation into HSS. After 2 weeks in vivo, immunohistochemical analysis, immunofluorescent microscopy, and microfil polymer perfusion were performed. RESULTS CD34+ PBMCs differentiated into EPC demonstrating characteristic EC morphology and expression of CD31, Tie-2, and E-selectin after TNF,-induction. Numerous human CD31 and Ulex europaeus agglutinin-1 (UEA-1) microvessels within the engineered grafts (HSS/EPCs) inosculated with recipient murine circulation. Limitation of murine CD31 immunoreactivity to HSS margins showed angiogenesis was attributable to human EPC at 2 weeks posttransplantation. Delivery of intravenous rhodamine-conjugated UEA-1 and microfil polymer to HSS/EPCs demonstrated enhanced perfusion by functional microvessels compared to HSS control without EPCs. CONCLUSION We successfully engineered functional microvessels in HSS by incorporating adult circulating EPCs. This autologous EC source can form vascular conduits enabling perfusion and survival of human bioengineered tissues. [source]

    Usefulness and Limitation of Dobutamine Stress Echocardiography to Predict Acute Response to Cardiac Resynchronization Therapy

    ECHOCARDIOGRAPHY, Issue 1 2010
    F.R.C.P.C., Mario Sénéchal M.D.
    Background: It has been hypothesized that a long-term response to cardiac resynchronization therapy (CRT) could correlate with myocardial viability in patients with left ventricular (LV) dysfunction. Contractile reserve and viability in the region of the pacing lead have not been investigated in regard to acute response after CRT. Methods: Fifty-one consecutive patients with advanced heart failure, LV ejection fraction , 35%, QRS duration > 120 ms, and intraventricular asynchronism , 50 ms were prospectively included. The week before CRT implantation, the presence of viability was evaluated using dobutamine stress echocardiography. Acute responders were defined as a ,15% increase in LV stroke volume. Results: The average of viable segments was 5.8 ± 1.9 in responders and 3.9 ± 3 in nonresponders (P = 0.03). Viability in the region of the pacing lead had an excellent sensitivity (96%), but a low specificity (56%) to predict acute response to CRT. Mitral regurgitation (MR) was reduced in 21 patients (84%) with acute response. The presence of MR was a poor predictor of response (sensibility 93% and specificity 17%). However, combining the presence of MR and viability in the region of the pacing lead yields a sensibility (89%) and a specificity (70%) to predict acute response to CRT. Conclusion: Myocardial viability is an important factor influencing acute hemodynamic response to CRT. In acute responders, significant MR reduction is frequent. The combined presence of MR and viability in the region of the pacing lead predicts acute response to CRT with the best accuracy. (Echocardiography 2010;27:50-57) [source]

    Limitation of nesting resources for ants in Colombian forests and coffee plantations

    Abstract 1.,This study examines limitation of nesting resources for leaf-litter and twig-nesting ants as a mechanism of diversity loss across an intensification gradient of coffee production in Colombia. Twelve farms were selected and classified into four management types: forest, polygeneric shade coffee, monogeneric shade coffee, and sun coffee (unshaded coffee monocultures). 2.,At each of the farms, four treatment subplots were established at the corners of each of 10 25 m2 plots: (i) twig augmentation (adding 10 empty bamboo twigs); (ii) litter augmentation (tripling existing litter profile); (iii) twig and litter augmentation; and (iv) no manipulation control, for a total of 480 subplots. A twig addition experiment was also performed on coffee bushes. 3.,The results showed significantly more ant colonies in the forest and monogeneric shade coffee litter augmentation plots after 4 months. Litter-nesting ant species richness was higher in all three shade systems than in the sun coffee. The identities of ants nesting on coffee bushes were different from those in the soil level litter. Fewer species nested in bamboo twigs placed in litter in the most intensive systems. 4.,More ants nested in the resource addition treatments, and more ant species were found in forested habitats; however, a single mechanism cannot explain the observed patterns. It was concluded that a combination of bottom-up and top-down effects might lead to the loss of associated fauna with the intensification of these agroecosystems. [source]

    Maternal Effort is State Dependent: Energetic Limitation or Regulation?

    ETHOLOGY, Issue 4 2008
    Anke Rehling
    Many small altricial rodents have a postpartum oestrus and are often simultaneously pregnant and lactating. Negative influences of concurrent pregnancy and lactation on both lactational performance and the litter in utero are commonly observed and have been interpreted as resulting from high simultaneous energetic demands of gestation and lactation. We studied these effects in the precocial guinea-pig (Cavia aperea f. porcellus) that, like many altricial rodents, has a postpartum oestrus, but in which the peaks of energy expenditure on lactation and gestation are widely separated. This life history allowed to investigate whether physiological regulation other than by energetic limitations may be responsible for allocation conflicts arising when lactation and gestation overlap. By comparing simultaneously pregnant and lactating females with lactating non-pregnant females, we show that females in the former group nurse less and wean earlier than females of the latter group. In a comparison of litter size, litter mass, and pup mortality of females that had not been lactating during pregnancy with females that had been simultaneously pregnant and lactating, we show that the latter do not reduce investment in the following litter. In our study, energetic constraints on ad libitum fed females are unlikely and we therefore suggest that the results must be explained by regulatory constraints on lactational effort. We point out that this explanation has not been excluded for the effects observed in altricial small mammals. [source]

    Kant on the Laws of Nature: Laws, Necessitation, and the Limitation of Our Knowledge

    James Kreines
    First page of article [source]

    The Free Movement of Goods as a Possible ,Community' Limitation on Industrial Conflict

    EUROPEAN LAW JOURNAL, Issue 4 2000
    Giovanni Orlandini
    The aim of this essay is to underline the fact that the process of achieving single market integration is very likely to influence the regulation of industrial conflict. In this perspective, the Commission v France judgment is analysed, in which the ECJ,through a combined interpretation of Article 30 (now 28) and Article 5 (now 10) of the Treaty,states that a Member State is obliged to adopt all ,appropriate measures' to remove any ,obstacles' impeding the free circulation of goods caused by private persons. A new Regulation (n. 2679/98) has followed the ECJ decision, instituting a system of notification of such obstacles arising, or the threat of them, and the right of the Commission to demand a formal reply from a State on whether it has taken, or will be taking the necessary and proportionate measures. The analysis of the principles adopted by the ECJ and of the Regulation shows that, at Community level, pressure is exerted on States to prevent the exercise of collective action as effectively as possible, if this damages inter-State trade. A transnational limit on industrial conflict thus emerges in the Community order, which may well affect the equilibria of national industrial relations in various ways. [source]

    Limitation of oxygenic photosynthesis and oxygen consumption by phosphate and organic nitrogen in a hypersaline microbial mat: a microsensor study

    Rebecca Ludwig
    Abstract Microbial mats are characterized by high primary production but low growth rates, pointing to a limitation of growth by the lack of nutrients or substrates. We identified compounds that instantaneously stimulated photosynthesis rates and oxygen consumption rates in a hypersaline microbial mat by following the short-term response (c. 6 h) of these processes to addition of nutrients, organic and inorganic carbon compounds, using microsensors. Net photosynthesis rates were not stimulated by compound additions. However, both gross photosynthesis and oxygen consumption were substantially stimulated (by a minimum of 25%) by alanine (1 mM) and glutamate (3.5 mM) as well as by phosphate (0.1 mM). A low concentration of ammonium (0.1 mM) did not affect photosynthesis and oxygen consumption, whereas a higher concentration (3.5 mM) decreased both process rates. High concentrations of glycolate (5 mM) and phosphate (1 mM) inhibited gross photosynthesis but not oxygen consumption, leading to a decrease of net photosynthesis. Photosynthesis was not stimulated by addition of inorganic carbon, nor was oxygen consumption stimulated by organic compounds like glycolate (5 mM) or glucose (5 mM), indicating that carbon was efficiently cycled within the mat. Photosynthesis and oxygen consumption were apparently tightly coupled, because stimulations always affected both processes to the same extent, which resulted in unchanged net photosynthesis rates. These findings illustrate that microsensor techniques, due to their ability to quantify all three processes, can clarify community responses to nutrient enrichment studies much better than techniques that solely monitor net fluxes. [source]

    Young Infants' Performance in the Object-Variation Version of the Above-Below Categorization Task: A Result of Perceptual Distraction or Conceptual Limitation?

    INFANCY, Issue 3 2002
    Paul C. Quinn
    Five experiments were conducted to examine the performance of young infants on above versus below categorization tasks. Experiments 1 and 2 showed that infants did not form abstract categorical representations for above and below when familiarized with different objects depicted in a constant spatial relation relative to a horizontal bar and tested on a novel object depicted in the familiar and novel spatial relation. Experiments 3 through 5 examined perceptual-attentional distraction versus conceptually based generalization explanations for young infant performance in the object-variation version of the above-below categorization task. Experiments 3 and 4 demonstrated that infants still did not form abstract categorical representations for above and below when object variation was removed from the familiarization trials or when object novelty was reduced during the preference test trials. However, Experiment 5 showed that 3- and 4-month-olds succeeded on the above versus below categorization task when familiarized with object variation and preference tested with a familiar versus novel object-bar relation. These results indicate that young infants can form categorical representations for above and below in the object-variation version of the above-below categorization task, but that such representations are specific to the particular objects presented. Young infant performance in the object-variation version of the above-below categorization task thus reflects a conceptually based generalization limit rather than a problem of perceptual-attentional distraction. [source]

    Xeroderma pigmentosum with limited involvement of the UV-exposed areas: a case report

    Mostafa Mirshams-Shahshahani MD
    A 21-year-old woman with skin type IV, who had developed photophobia and brown, spotty, hyperpigmented lesions on her face from early childhood, presented to our center for treatment of her facial lesions. Examination on admission revealed numerous, freckle-like, hyperpigmented macules and actinic keratoses over the central part of the face, with sparing of the forehead, chin, and peripheral area (Fig. 1). The area involved was approximated to be around 2% of the total body surface. The dorsal parts of the hands showed no lesions (Fig. 2), but guttate hypomelanotic lesions were apparent on both forearms. Figure 1. Limitation of xeroderma pigmentosum lesions to the center of the face Figure 2. Hands are devoid of any lesions Histologic examination of biopsies from four different facial lesions revealed them to be keratoacanthoma (1.5 × 2.5 cm ulcerative nodule on the right cheek), sclerosing basal cell epithelioma (nasal lesion), lentigo simplex, and hypertrophic actinic keratosis. Corneal clouding, conjunctival injection, loss of lashes, and atrophy of the lids were apparent on ophthalmologic examination. Other parts of the physical examination, including examination of the oral cavity, were nonsignificant. In addition, except for the presence of mild eczema in a sibling, the patient's family history regarding the presence of any similar problem and also any other important dermatologic or general disorder was negative. [source]

    Proximate mechanisms of variation in the carotenoid-based plumage coloration of nestling great tits (Parus major L.)

    B. Tschirren
    Abstract Many vertebrates use carotenoid-based signals in social or sexual interactions. Honest signalling via carotenoids implies some limitation of carotenoid-based colour expression among phenotypes in the wild, and at least five limiting proximate mechanisms have been hypothesized. Limitation may arise by carotenoid-availability, genetic constraints, body condition, parasites, or detrimental effects of carotenoids. An understanding of the relative importance of the five mechanisms is relevant in the context of natural and sexual selection acting on signal evolution. In an experimental field study with carotenoid supplementation, simultaneous cross-fostering, manipulation of brood size and ectoparasite load, we investigated the relative importance of these mechanisms for the variation in carotenoid-based coloration of nestling great tits (Parus major). Carotenoid-based plumage coloration was significantly related to genetic origin of nestlings, and was enhanced both in carotenoid-supplemented nestlings, and nestlings raised in reduced broods. We found a tendency for ectoparasite-induced limitation of colour expression and no evidence for detrimental effects of carotenoids on growth pattern, mortality and recruitment of nestlings to the local breeding population. Thus, three of the five proposed mechanisms can generate individual variation in the expression of carotenoid-based plumage coloration in the wild and thus could maintain honesty in a trait potentially used for signalling of individual quality. [source]

    Limitation in obtainable surface roughness of hardened cement paste: ,virtual' topographic experiment based on focussed ion beam nanotomography datasets

    P. TRTIK
    Summary Surface roughness affects the results of nanomechanical tests. The surface roughness values to be measured on a surface of a porous material are dependent on the properties of the naturally occurring pore space. In order to assess the surface roughness of hardened cement paste (HCP) without the actual influence of the usual sample preparation for nanomechanical testing (i.e. grinding and polishing), focussed ion beam nanotomography datasets were utilized for reconstruction of 3D (nanoscale resolution) surface profiles of hardened cement pastes. ,Virtual topographic experiments' were performed and root mean square surface roughness was then calculated for a large number of such 3D surface profiles. The resulting root mean square (between 115 and 494 nm) is considerably higher than some roughness values (as low as 10 nm) reported in the literature. We suggest that thus-analysed root mean square values provide an estimate of a ,hard' lower limit that can be achieved by ,artefact-free' sample preparation of realistic samples of hardened cement paste. To the best of our knowledge, this ,hard' lower limit was quantified for a porous material based on hydraulic cement for the first time. We suggest that the values of RMS below such a limit may indicate sample preparation artefacts. Consequently, for reliable nanomechanical testing of disordered porous materials, such as hardened cement paste, the preparation methods may require further improvement. [source]

    Limitation and stress , always or never?

    Ch. Körner
    No abstract is available for this article. [source]

    Mechanisms of iron regulation in mycobacteria: role in physiology and virulence

    G. Marcela Rodriguez
    Summary The role of iron in mycobacteria as in other bacteria goes beyond the need for this essential cofactor. Limitation of this metal triggers an extensive response aimed at increasing iron acquisition while coping with iron deficiency. In contrast, iron-rich environments prompt these prokaryotes to induce synthesis of iron storage molecules and to increase mechanisms of protection against iron-mediated oxidative damage. The response to changes in iron availability is strictly regulated in order to maintain sufficient but not excessive and potentially toxic levels of iron in the cell. This response is also linked to other important processes such as protection against oxidative stress and virulence. In bacteria, iron metabolism is regulated by controlling transcription of genes involved in iron uptake, transport and storage. In mycobacteria, this role is fulfilled by the iron- dependent regulator IdeR. IdeR is an essential protein in Mycobacterium tuberculosis, the causative agent of human tuberculosis. It functions as a repressor of iron acquisition genes, but is also an activator of iron storage genes and a positive regulator of oxidative stress responses. [source]

    Limitation of population recovery: a stochastic approach to the case of the emperor penguin

    OIKOS, Issue 9 2009
    Stéphanie Jenouvrier
    Major population crashes due to natural or human-induced environmental changes may be followed by recoveries. There is a growing interest in the factors governing recovery, in hopes that they might guide population conservation and management, as well as population recovery following a re-introduction program. The emperor penguin Aptenodytes forsteri population in Terre Adélie, Antarctica, declined by 50% during a regime shift in the mid-1970s, when abrupt changes in climate and ocean environment regimes affected the entire Southern Ocean ecosystem. Since then the population has remained stable and has not recovered. To determine the factors limiting recovery, we examined the consequences of changes in survival and breeding success after the regime shift. Adult survival recovered to its pre-regime shift level, but the mean breeding success declined and the variance in breeding success increased after the regime shift. Using stochastic matrix population models, we found that if the distribution of breeding success observed prior to the regime shift had been retained, the emperor penguin population would have recovered, with a median time to recovery of 36 years. The observed distribution of breeding success after the regime shift makes recovery very unlikely. This indicates that the pattern of breeding success is sufficient to have prevented emperor penguin population recovery. The population trajectory predicted on the basis of breeding success agrees with the observed trajectory. This suggests that the net effect of any facors other than breeding success must be small. We found that the probability of recovery and the time to recovery depend on both the mean and variance of breeding success. Increased variance in breeding success increases the probability of recovery when mean success is low, but has the opposite effect when the mean is high. This study shows the important role of breeding success in determining population recovery for a long-lived species and demonstrates that demographic mechanisms causing population crash can be different from those preventing population recovery. [source]

    Nutrient Limitation and Stoichiometry of Carnivorous Plants

    PLANT BIOLOGY, Issue 6 2006
    A. M. Ellison
    Abstract: The cost-benefit model for the evolution of carnivorous plants posits a trade-off between photosynthetic costs associated with carnivorous structures and photosynthetic benefits accrued through additional nutrient acquisition. The model predicts that carnivory is expected to evolve if its marginal benefits exceed its marginal costs. Further, the model predicts that when nutrients are scarce but neither light nor water is limiting, carnivorous plants should have an energetic advantage in competition with non-carnivorous plants. Since the publication of the cost-benefit model over 20 years ago, marginal photosynthetic costs of carnivory have been demonstrated but marginal photosynthetic benefits have not. A review of published data and results of ongoing research show that nitrogen, phosphorus, and potassium often (co-)limit growth of carnivorous plants and that photosynthetic nutrient use efficiency is 20 - 50 % of that of non-carnivorous plants. Assessments of stoichiometric relationships among limiting nutrients, scaling of leaf mass with photosynthesis and nutrient content, and photosynthetic nutrient use efficiency all suggest that carnivorous plants are at an energetic disadvantage relative to non-carnivorous plants in similar habitats. Overall, current data support some of the predictions of the cost-benefit model, fail to support others, and still others remain untested and merit future research. Rather than being an optimal solution to an adaptive problem, botanical carnivory may represent a set of limited responses constrained by both phylogenetic history and environmental stress. [source]

    Slow development of leaf photosynthesis in an evergreen broad-leaved tree, Castanopsis sieboldii: relationships between leaf anatomical characteristics and photosynthetic rate

    PLANT CELL & ENVIRONMENT, Issue 3 2001
    S.-I. Miyazawa
    ABSTRACT Changes in net photosynthetic rate on a leaf area basis and anatomical properties during leaf development were studied in an evergreen broad-leaved tree, Castanopsis sieboldii and an annual herb, Phaseolus vulgaris. In C. sieboldii, surface area of mesophyll cells facing the intercellular air spaces on a leaf area basis (Smes) was already considerable at the time of full leaf area expansion (FLE). However, surface area of chloroplasts facing the intercellular air spaces on a leaf area basis (Sc), and chlorophyll and Rubisco contents on a leaf area basis increased to attain their maximal values 15,40 d after FLE. In contrast, in P. vulgaris, chloroplast number on a leaf area basis, Sc and Smes at 10 d before FLE were two to three times greater than the steady-state levels attained at around FLE. In C. sieboldii, the internal CO2 transfer conductance (gi) slightly increased for 10 d after FLE but then decreased toward the later stages. Limitation of photosynthesis by gi was only about 10% at FLE, but then increased to about 30% at around 40 d after FLE. The large limitation after FLE by gi was probably due to the decrease in CO2 concentration in the chloroplast caused by the increases in thickness of mesophyll cell walls and in Rubisco content per chloroplast surface area. These results clearly showed that: (1) in C. sieboldii, chloroplast development proceeded more slowly than mesophyll cell expansion and continued well after FLE, whereas in P. vulgaris these processes proceeded synchronously and were completed by FLE; (2) after FLE, photosynthesis in leaves of C. sieboldii was markedly limited by gi. From these results, it is suggested that, in the evergreen broad-leaved trees, mechanical protection of mesophyll cells has priority over the efficient CO2 transfer and quick construction of the chloroplasts. [source]

    Differentials in Adult Mortality and Activity Limitation by Years of Education in the United States at the End of the 1990s

    Michael T. Molla
    This study examines mortality differentials and health disparities between educational groups within the 1998 adult population (ages 25 and older) in the United States. Mortality differentials are measured using average life expectancy and health disparities by expected years without activity limitation. The results indicate that for both sexes, higher education is associated with higher life expectancy. Those with higher levels of education also have higher life expectancy without activity limitation. Adults with higher education can also expect to enjoy a greater percentage of their expected lives free of any form of activity limitation. At each level of education, adult females have a higher level of activity limitation compared to adult males. At the same level of education, adult females expect to enjoy smaller percentages of their remaining lives free of activity limitation compared to adult males of the same age. [source]

    Constitutional Tax and Expenditure Limitation in Colorado: The Impact on Municipal Governments

    Tom Rown
    Tax and expenditure limitations (TELs) have become a pervasive influence on local government fiscal affairs. Explanations for the spread of TELs suggest that voters thought local government was growing more than needed. Thus, TELs were intended to constrain growth and reduce the size of local governments. This article's purpose was to determine the impact of two separate kinds of TELs, one a property tax measure, and the other a comprehensive revenue and expenditure limit, upon the growth of municipal governments in Colorado. Using a panel data set on municipal budgets (1975,1996), the article demonstrates three major points: 1) the effectiveness of a TEL in achieving reductions in local government revenue and spending growth depends upon the nature of the TEL; 2) the comprehensive TEL did effectively constrain growth and reduce local government reliance on the property tax, despite the local options for exemption; and 3) TELs do not have uniform impacts among governments of different population. [source]

    Limitation of nocturnal import of ATP into Arabidopsis chloroplasts leads to photooxidative damage,

    THE PLANT JOURNAL, Issue 2 2007
    Thomas Reinhold
    Summary When grown in short day conditions and at low light, leaves of Arabidopsis plants with mutations in the genes encoding two plastidial ATP/ADP transporters (so-called null mutants) spontaneously develop necrotic lesions. Under these conditions, the mutants also display light-induced accumulation of H2O2 and constitutive expression of genes for copper/zinc superoxide dismutase 2 and ascorbate peroxidase 1. In the light phase, null mutants accumulate high levels of phototoxic protoporphyrin IX but have only slightly reduced levels of Mg protoporphyrin IX. The physiological changes are associated with reduced magnesium,chelatase activity. Since the expression of genes encoding any of the three subunits of magnesium,chelatase is similar in wild type and null mutants, decreased enzyme activity is probably due to post-translational modification which might be due to limited availability of ATP in plastids during the night. Surprisingly, the formation of necrotic lesions was absent when null mutants were grown either in long days and low light intensity or in short days and high light intensity. We ascribe the lack of lesion phenotype to increased nocturnal ATP supply due to glycolytic degradation of starch which may lead to additional substrate-level phosphorylation in the stroma. Thus, nocturnal import of ATP into chloroplasts represents a crucial, previously unknown process that is required for controlled chlorophyll biosynthesis and for preventing photooxidative damage. [source]

    High-Resolution Single-Turnover Mapping Reveals Intraparticle Diffusion Limitation in Ti-MCM-41-Catalyzed Epoxidation,

    ANGEWANDTE CHEMIE, Issue 5 2010
    Cremer, Gert De
    Katalyse in neuem Licht: Mithilfe hochauflösender Fluoreszenzmikroskopie gelang es erstmals, Transportphänomene und deren Rolle in der Katalyse auf Einzelpartikelebene zu kartieren. Der Thiele-Modul konnte partikelweise in nur einem einzigen Experiment gemessen werden, und er beweist das Vorliegen von Diffusionsbeschränkungen bei der Ti-MCM-41-katalysierten Epoxidierung eines fluoreszierenden Reportermoleküls (siehe Bild; TBHP=tert -Butylhydroperoxid). [source]

    Der Eurocode 2 für Deutschland , Erläuterungen und Hintergründe

    Rissbreiten und Verformungen, Teil 3: Begrenzung der Spannungen
    Berechnung- und Bemessungsverfahren; Normen, Vorschriften, Richtlinien Abstract Der neue Eurocode 2: "Bemessung und Konstruktion von Stahlbeton- und Spannbetontragwerken , Teil 1-1: Allgemeine Bemessungsregeln und Regeln für den Hochbau" (EC2-1-1) mit seinem Nationalen Anhang ist nach einer ausführlichen Erprobungsphase bereit zur bauaufsichtlichen Einführung in Deutschland. In mehreren Beiträgen sollen Erläuterungen und Hintergründe zu einigen Regelungen im Eurocode 2 und zu den Entscheidungen für Regeln im Nationalen Anhang vorgestellt werden, die entweder zu Änderungen gegenüber DIN 1045-1 oder zu Abweichungen vom Eurocode 2 führten. Der Teil 3 enthält Erläuterungen zur Begrenzung der Spannungen, Rissbreiten und Verformungen. The Eurocode 2 for Germany , Explanations and Backgrounds Part 3: Limitation of Stresses, Cracks and Deformations The new Eurocode 2 "Design of concrete structures , Part 1-1: General rules and rules for buildings" (EC2-1-1) and its National Annex has undergone a phase of detailed testing and is now ready for the implementation in Germany. In some articles should be given explanations and backgrounds of some rules in Eurocode 2 and of decisions for rules in the National Annex, which have been taken either to changes compared with DIN 1045-1 or to differences to Eurocode 2. Article 3 contains explanations for the limitation of stresses, cracks and deformations. [source]

    Content of polyunsaturated fatty acids (PUFAs) in serum and liver of rats fed restricted diets supplemented with vitamins B2, B6 and folic acid

    BIOFACTORS, Issue 1-4 2004
    Jerzy Bertrandt
    Abstract The aim of study was to investigate an influence of nutritional deficiency and dietary addition of vit. B2, B6 and folic acid on PUFAs content in rats' serum and liver. Limitation of consumption full value diet to 50% of its previously determined daily consumption, enriched with m/a vitamins, significant decreased of linoleic (LA) and ,-linolenic (ALA) acids as well as distinctly increased arachidonic (AA) and docosahexaenoic (DHA) acids content in serum in 30th day. In 60th day lower content of AA and DHA fatty acids was found. Nutrition with such diet, lasting 90 days caused decrease of LA content and increase of AA. Diet limitation to its 30% of daily consumption decreased of eicosapentaenoic acid (EPA) and DHA in the 30th day, while AA and DHA content was increased in the 60th day. Distinct decrease of AA content and increase of EPA content were found in the 90th day of experiment. Use of diets, with limited consumption to 50% caused increase of LA and ALA acids content while AA and DHA acids content were significantly decreased in the liver, in 90th day. Limited consumption supplemented diet to 30% caused in liver significant decrease of LA and increase of EPA acids content. [source]

    Limitation of immunoaffinity column for the removal of abundant proteins from plasma in quantitative plasma proteomics

    Tomoko Ichibangase
    Abstract In plasma proteomics, before a proteome analysis, it is essential to prepare protein samples without high-abundance proteins, including albumin, via specific preparation techniques, such as immunoaffinity capture. However, our preliminary experiments suggested that functional changes with use alter the ability of the immunoaffinity column. Thus, in this study, to evaluate the changes of the removal ability of abundant proteins from plasma by the immunoaffinity column, plasma proteome analysis was performed for the long-term test for the reproducibility of the affinity column using the fluorogenic derivatization,liquid chromatography,tandem mass spectrometry method combined with an IgY column. The specific adsorption for albumin decreased with an increase in the number of the column usage before its expiration date. Moreover, it was demonstrated that hydrophobic high molecular weight compounds in plasma adsorbed onto the column materials surface contributed to the functional changes from specific immunoaffinity adsorption into hydrophobic interaction. These results suggested that, in quantitative plasma proteomics studies, it is important to keep in mind the risk of not only the nonselective loss but also the changes in the adsorption ability of the immunoafinity column. Copyright © 2008 John Wiley & Sons, Ltd. [source]