Limited Supply (limited + supply)

Distribution by Scientific Domains

Selected Abstracts

Analysis of metabolic variation and galanthamine content in Narcissus bulbs by 1H NMR,

Andrea Lubbe
Abstract Introduction , Galanthamine is a benzazepine alkaloid used as a drug to relieve symptoms of Alzheimer's disease. For pharmaceutical use this natural product has been extracted from the plant Leucojum aestivum (Amaryllidaceae) or produced synthetically. Limited supply of the natural source and high cost of synthetic production has led to a search for alternative sources of galanthamine. The bulbs of Narcissus pseudonarcissus (Amaryllidaceae) have been identified as a potential source of raw material for galanthamine extraction. Since inconsistent chemical composition can be an issue with medicinal plant material, it is of interest to know whether large variations occur between Narcissus bulbs grown in different geographical locations. Objective , To evaluate whether large differences exist in the overall metabolic profiles of Narcissus bulbs grown in the two most important cultivation regions. Methodology , 1H NMR and principal component analysis were used for an unbiased comparison of the bulb samples. Results , Overall metabolite profiles were quite similar, but galanthamine levels could slightly discriminate samples by geographical region. 1H NMR was used for quantitation of galanthamine, and was found to be comparable to quantitation by HPLC. Compared with conventional chromatographic methods, sample preparation for 1H NMR analysis is simple and rapid, and only a small amount of plant material is required. Conclusions , Since useful qualitative and quantitative information about the metabolic state of Narcissus bulbs can be obtained by 1H NMR, this method is useful for agricultural applications, and for quality control of raw material used in the pharmaceutical industry. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Antioxidants, showy males and sperm quality

Jonathan D. Blount
The fertility of males sometimes correlates with their ornamental display, but we do not have a mechanistic explanation to universally link these traits. We suggest that both sperm quality (fertility; integrity of DNA), and the substrates responsible for male ornamentation, may be vulnerable to free radical attack, which can be mitigated by antioxidants. Support for these ideas is at present weak, and requires validation in ecological contexts. We hypothesize that a link between ornamentation and sperm quality could arise if antioxidants are in limited supply, and the showiest males may be preferred because they are most likely to be fertile, or to provide sperm with undamaged genotypes that could give rise to fit offspring. [source]

Semaphorin 3A-Neuropilin-1 signaling regulates peripheral axon fasciculation and pathfinding but not developmental cell death patterns

Corinna Haupt
Abstract In early development, an excess of neurons is generated, of which later about half will be lost by cell death due to a limited supply of trophic support by their respective target areas. However, some of the neurons die when their axons have not yet reached their target, thus suggesting that additional causes of developmental cell death exist. Semaphorin 3A (Sema3A), in addition to its function as a guidance cue and mediator of timing and fasciculation of motor and sensory axon outgrowth, can also induce death of sensory neurons in vitro. However, it is unknown whether Neuropilin-1 (Npn-1), its binding receptor in axon guidance, also mediates the death-inducing activity. We show here that abolished Sema3A-Npn-1 signaling does not influence the cell death patterns of motor or sensory neurons in mouse during the developmental wave of programmed cell death. The number of motor and sensory neurons was unchanged at embryonic day 15.5 when this wave is concluded. Interestingly, the defasciculation of early motor and sensory projections that is observed in the absence of Sema3A or Npn-1 persists to postnatal stages. Thus, Sema3A-Npn-1 signaling plays an important role in the guidance and fasciculation of motor and sensory axons but does not contribute to the developmental elimination of these neurons. [source]

Modality options for renal replacement therapy: The integrated care concept revisited

Abstract As the End-stage renal disease population continues to grow, innovative strategies that optimize patient outcomes while capitalizing on the relative strengths of the existing modalities must be sought. Renal transplantation remains the preferred form of renal replacement therapy, but given the limited supply of donor organs, dialytic therapies will continue to constitute a large part of the modality mix. Matching patients to the most suitable modalities requires that a number of factors be considered. These include the patient's autonomy, medical and social factors, system-related issues, patient outcomes, and finances. While peritoneal dialysis and hemodialysis (HD) have traditionally been viewed as competing modalities, we propose that they, along with home and frequent HD regimens, may be used in a complementary manner, which is based on current evidence, and may provide optimal outcomes while containing treatment costs. In this review, we attempt to synthesize the current literature describing the various issues that affect modality selection, and offer an approach to achieving a balance between these many competing factors. [source]

Statistical Assessment of Numerical Models,

Montserrat Fuentes
Summary Evaluation of physically based computer models for air quality applications is crucial to assist in control strategy selection. The high risk of getting the wrong control strategy has costly economic and social consequences. The objective comparison of modeled concentrations with observed field data is one approach to assessment of model performance. For dry deposition fluxes and concentrations of air pollutants there is a very limited supply of evaluation data sets. We develop a formal method for evaluation of the performance of numerical models, which can be implemented even when the field measurements are very sparse. This approach is applied to a current U.S. Environmental Protection Agency air quality model. In other cases, exemplified by an ozone study from the California Central Valley, the observed field is relatively data rich, and more or less standard geostatistical tools can be used to compare model to data. Yet another situation is when the cost of model runs is prohibitive, and a statistical approach to approximating the model output is needed. We describe two ways of obtaining such approximations. A common technical issue in the assessment of environmental numerical models is the need for tools to estimate nonstationary spatial covariance structures. We describe in detail two such approaches. Résumé L'évaluation de modèles informatiques à bases physiques pour des applications à la qualité de l'air est cruciale pour aider à la sélection d'une stratégie de contrôle. Le choix d'une mauvaise stratégie de contrôle peut avoir des conséquences economiques et sociales coúteuses. Une approche pour évaluer la performance du modèle est la comparaison objective de concentrations modélisées avec des données de terrain observées. Pour les flux de dépôts secs et les concentrations de polluants de l'air, l'offre de données d'évaluation est très limitée. Nous développons une méthode formelle pour évaluer la performance de modèles numériques, qui peut être mise en oeuvre même lorsque les mesures de terrain sont trés clairsemées. Cette approche est appliquée à un modèle de qualité de l'air de l'Agence de la Protection de l'Environnement Américaine. Dans d'autres cas, comme une étude de l'ozone de la vallée Californienne centrale, le champ observé est relativement riche en données, et l'on peut utiliser peu ou prou des outils géostatistiques standards pour comparer le modèle aux données. Une autre situation se présente quand le coút du modèle est prohibitif et qu'une approche statistique pour effectuer des approximations des sorties du modèle est nécessaire. Nous décrivons deux manières d'obtenir de telles approximations. Un problème technique commun à l'évaluation des modèles environnementaux numériques est le besoin d'outils pour estimer les structures de la covariance spatiale non stationnaire. Nous decrivons en detail deux de ces approches. [source]

Effects of food limitation and emigration on self-thinning in experimental minnow cohorts

J. B. Dunham
Summary 1.,The theory of food-regulated self-thinning (FST) for mobile animals predicts population density (N) to be an inverse function of mean body mass (W) scaled to an exponent (b), such that N = k W,b, where k is a constant. FST also predicts energy requirements (or energy flow) to remain constant over time (termed energetic equivalence) as losses to cohorts (e.g. emigration and mortality) are balanced by increased growth of surviving individuals. 2.,To test these predictions, we analysed the dynamics of six experimental minnow cohorts. Replicate populations of fish were held under identical conditions with a constant and limited supply of food over a 126-day period. Half of the cohorts were open to emigration, and half were closed so that fish could only be lost through starvation mortality. 3.,Patterns of self-thinning indicated non-linear changes in population density and energy flow in relation to changes in mean body mass and time, respectively. Non-linear patterns of self-thinning were probably due to a delayed growth response to changes in population density effected through mortality and/or emigration. Contrary to results of similar experiments on other fish, emigration did not have a significant influence on the pattern of self-thinning. 4.,These results may be attributed to trophic interactions within cohorts and the importance of social behaviour to cohort dynamics. Both population density and energy flow in our experimental populations appeared to cycle, with episodes of starvation and mortality alternating with food recovery and weight gain, as predicted by recent models of stepwise die-off and stunted growth in animal cohorts. 5.,Most of the support for FST in mobile animals comes from observational data on mean body mass and population density. Potentially important mechanisms, including the manner in which individuals are lost or retained in populations, are usually not investigated directly. Such tests of FST can only provide equivocal support. Detailed observational study and controlled experiments are needed to understand casual mechanisms. [source]

Star polystyrenes by anionic star,star coupling reactions with divinylbenzene

Hyung-Jae Lee
Abstract The incremental addition of divinylbenzene was used to generate star polystyrenes in a nearly full conversion of a living polystyrenyl anion. The dramatic increase in the molecular weight of the star polystyrenes with a limited supply of the living polystyrene supported the formation of gradient-star polystyrenes through star,star coupling. The stoichiometric analysis of the star polymers revealed that their connection polymer had a shorter length than their branch polymer. The measured solution viscosity of the gradient-star polymers greatly deviated from a linear correlation with the molecular weight and was in parallel to a theoretical simulation based on a highly branched structure of the gradient-star polymer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2579,2586, 2006 [source]