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Practical Limitations (practical + limitation)
Selected AbstractsScreening for gestational diabetes; past, present and futureDIABETIC MEDICINE, Issue 5 2002F. W. F. Hanna Abstract Gestational diabetes is carbohydrate intolerance, with onset or first recognition of hyperglycaemia during pregnancy. Several studies have suggested that gestational hyperglycaemia is associated with adverse maternal and fetal outcomes, promoting the case for screening. Conversely, others argue that screening for gestational diabetes may colour the clinical judgement, influencing further management, e.g. more ,unjustified' caesarean sections. Additionally, the lack of definitive data either on a clear-cut glycaemic threshold for the development of adverse outcomes or on the impact of intervention is emphasized by opponents of screening. This review attempts to evaluate the available data on screening for gestational diabetes. Oral glucose tolerance test is promoted on the basis that the diabetogenic stress of pregnancy is encountered during late gestation and is best recognized in the fed state. There are different tests, including the 1 h/50-g, 2 h/75-g and 3 h/100-g tests, with practical limitations, including the time and cost involved and the unpleasant supra-physiological glucose load that is unrelated to body weight, and issues of reproducibility and sensitivity/specificity profiles. Despite its convenience, the poor sensitivity of random glucose has precluded its routine use for screening. Fasting glucose appears to be promising but further testing is required to ensure satisfactory sensitivity/specificity in different populations. Despite its limitations, the oral glucose tolerance test has become established as the ,most acceptable' diagnostic test for gestational diabetes. More convenient methods, e.g. fasting or random or post-load glucose, have to be validated therefore against the oral glucose tolerance test to gain acceptance for routine screening. Diabet. Med 19, 351,358 (2002) [source] Adapted liquid crystal display backlighting unit for densitometry of stained polyacrylamide electrophoresis gelsELECTROPHORESIS, Issue 6 2009Han Yen Tan Abstract Appropriate monochromatic illumination that is spatially uniform will ensure densitometry of stained polyacrylamide electrophoresis gels with high sensitivity and repeatability. The approach of using an array of LEDs as an illuminator has practical limitations. Here we describe an alternative method based on adapted liquid crystal display backlighting. By changing the fluorescent light source and using a region where light intensity is uniform, we demonstrate the ability to achieve highly sensitive and repeatable densitometry measurements of polyacrylamide electrophoresis gels with Coomassie-stained proteins. [source] Beyond six scents: defining a seventh Thymus vulgaris chemotype new to southern France by ethanol extractionFLAVOUR AND FRAGRANCE JOURNAL, Issue 3 2009Ken Keefover-Ring Abstract The concept of plant chemotype has long been useful to describe secondary chemical phenotypes; however, the idea has practical limitations, especially when applied to ecological questions. This work reports the discovery of a new 1,8-cineole chemotype of Thymus vulgaris from a well-studied area in southern France. Multivariate statistical analysis of ethanol-extracted plant terpenes was used to describe this new chemotype and three others found at the site, and the results are used to discuss the chemotype concept. While the total amount of essential oils among these chemotypes showed no difference, the concentration of the main terpene differed significantly, with the 1,8-cineole and cis -sabinene hydrate chemotypes having the lowest amounts of their respective main components, and the linalool chemotype having the highest. The , -terpinyl acetate chemotype had intermediate levels of its main terpene. A factor analysis revealed four factors which explained almost 89% of the total variation in plant essential oils. Each factor represented a separate chemotype, including a cis -sabinene hydrate, linalool, ,- terpinyl acetate and the new 1,8-cineole chemotype. Although the concept of plant chemotype is still valid, better definitions are important when evaluating the influences of a plant's secondary chemistry on other community members. Copyright © 2009 John Wiley & Sons, Ltd. [source] Numerical solutions of fully non-linear and highly dispersive Boussinesq equations in two horizontal dimensionsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2004David R. Fuhrman Abstract This paper investigates preconditioned iterative techniques for finite difference solutions of a high-order Boussinesq method for modelling water waves in two horizontal dimensions. The Boussinesq method solves simultaneously for all three components of velocity at an arbitrary z -level, removing any practical limitations based on the relative water depth. High-order finite difference approximations are shown to be more efficient than low-order approximations (for a given accuracy), despite the additional overhead. The resultant system of equations requires that a sparse, unsymmetric, and often ill-conditioned matrix be solved at each stage evaluation within a simulation. Various preconditioning strategies are investigated, including full factorizations of the linearized matrix, ILU factorizations, a matrix-free (Fourier space) method, and an approximate Schur complement approach. A detailed comparison of the methods is given for both rotational and irrotational formulations, and the strengths and limitations of each are discussed. Mesh-independent convergence is demonstrated with many of the preconditioners for solutions of the irrotational formulation, and solutions using the Fourier space and approximate Schur complement preconditioners are shown to require an overall computational effort that scales linearly with problem size (for large problems). Calculations on a variable depth problem are also compared to experimental data, highlighting the accuracy of the model. Through combined physical and mathematical insight effective preconditioned iterative solutions are achieved for the full physical application range of the model. Copyright © 2004 John Wiley & Sons, Ltd. [source] MHC studies in nonmodel vertebrates: what have we learned about natural selection in 15 years?JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2003L. Bernatchez Abstract Elucidating how natural selection promotes local adaptation in interaction with migration, genetic drift and mutation is a central aim of evolutionary biology. While several conceptual and practical limitations are still restraining our ability to study these processes at the DNA level, genes of the major histocompatibility complex (MHC) offer several assets that make them unique candidates for this purpose. Yet, it is unclear what general conclusions can be drawn after 15 years of empirical research that documented MHC diversity in the wild. The general objective of this review is to complement earlier literature syntheses on this topic by focusing on MHC studies other than humans and mice. This review first revealed a strong taxonomic bias, whereby many more studies of MHC diversity in natural populations have dealt with mammals than all other vertebrate classes combined. Secondly, it confirmed that positive selection has a determinant role in shaping patterns of nucleotide diversity in MHC genes in all vertebrates studied. Yet, future tests of positive selection would greatly benefit from making better use of the increasing number of models potentially offering more statistical rigour and higher resolution in detecting the effect and form of selection. Thirdly, studies that compared patterns of MHC diversity within and among natural populations with neutral expectations have reported higher population differentiation at MHC than expected either under neutrality or simple models of balancing selection. Fourthly, several studies showed that MHC-dependent mate preference and kin recognition may provide selective factors maintaining polymorphism in wild outbred populations. However, they also showed that such reproductive mechanisms are complex and context-based. Fifthly, several studies provided evidence that MHC may significantly influence fitness, either by affecting reproductive success or progeny survival to pathogens infections. Overall, the evidence is compelling that the MHC currently represents the best system available in vertebrates to investigate how natural selection can promote local adaptation at the gene level despite the counteracting actions of migration and genetic drift. We conclude this review by proposing several directions where future research is needed. [source] Temporal Changes in Brain Volume and Cognition in a Randomized Treatment Trial of Vascular DementiaJOURNAL OF NEUROIMAGING, Issue 1 2001Joseph P. Broderick MD ABSTRACT Objective. To measure changes in brain and ischemic volume over time by magnetic resonance imaging (MRI) as part of a randomized treatment trial of vascular dementia. Methods. Participants who met criteria for vascular dementia underwent comprehensive neurological and neuropsychological testing on entrance, during, and at completion of the 1-year study. For those centers who had easily available MRI, MRI of the brain was to be performed on entry and completion of the study. Image analysis was performed on all balanced and T2-weighted MR films to determine ventricular, sulcal, ischemic, and hemispheric brain volumes. Results. Of the 105 patients who met the criteria for vascular dementia, 40 had a baseline MRI study that met protocol requirements and was of excellent image quality. The baseline ventricular volume in these 40 patients with high-quality MR correlated with most measures of cognitive and behavioral function, including the total Alzheimer's Disease Assessment Score (ADAS) (r= 0.51, P= .0024), as well as activities of daily living (r= 0.61, P= .0002). The baseline ischemic brain volume correlated well only with the gait and postural stability scale (r= 0.74, P= .009). Of the 40 participants, 25 had MRI studies at baseline and at completion of the study that were comparable and of excellent image quality. For these 25 patients, the mean ventricular volumes increased by 9% over the study year (P= .001) and the mean ischemic brain volume increased by 18% (P= .01). Temporal changes in the sulcal and nonischemic brain volume did not reach significance. None of the 14 clinical score measures changed significantly between baseline and completion of the study in these 25 patients. Conclusion. In summary, ventricular volume correlated well with cognitive measures in patients with vascular dementia and was a more sensitive marker for change during the study year than the clinical scales used in this study. This study also points out the practical limitations of brain imaging as a surrogate measure of clinical outcome in multicenter randomized treatment trials of brain disease. [source] Induced pluripotent stem cells (iPSCs): the emergence of a new champion in stem cell technology-driven biomedical applicationsJOURNAL OF TISSUE ENGINEERING AND REGENERATIVE MEDICINE, Issue 6 2010Anjan Kumar Das Abstract Pluripotent stem cells possess the unique property of differentiating into all other cell types of the human body. Further, the discovery of induced pluripotent stem cells (iPSCs) in 2006 has opened up new avenues in clinical medicine. In simple language, iPSCs are nothing but somatic cells reprogrammed genetically to exhibit pluripotent characteristics. This process utilizes retroviruses/lentiviruses/adenovirus/plasmids to incorporate candidate genes into somatic cells isolated from any part of the human body. It is also possible to develop disease-specific iPSCs which are most likely to revolutionize research in respect to the pathophysiology of most debilitating diseases, as these can be mimicked ex vivo in the laboratory. These models can also be used to study the safety and efficacy of known drugs or potential drug candidates for a particular diseased condition, limiting the need for animal studies and considerably reducing the time and money required to develop new drugs. Recently, functional neurons, cardiomyocytes, pancreatic islet cells, hepatocytes and retinal cells have been derived from human iPSCs, thus re-confirming the pluripotency and differentiation capacity of these cells. These findings further open up the possibility of using iPSCs in cell replacement therapy for various degenerative disorders. In this review we highlight the development of iPSCs by different methods, their biological characteristics and their prospective applications in regenerative medicine and drug screening. We further discuss some practical limitations pertaining to this technology and how they can be averted for the betterment of human life. Copyright © 2010 John Wiley & Sons, Ltd. [source] Terrestrial carnivores and human food production: impact and managementMAMMAL REVIEW, Issue 2-3 2008PHILIP J. BAKER ABSTRACT 1The production of food for human consumption has led to an historical and global conflict with terrestrial carnivores, which in turn has resulted in the extinction or extirpation of many species, although some have benefited. At present, carnivores affect food production by: (i) killing human producers; killing and/or eating (ii) fish/shellfish; (iii) game/wildfowl; (iv) livestock; (v) damaging crops; (vi) transmitting diseases; and (vii) through trophic interactions with other species in agricultural landscapes. Conversely, carnivores can themselves be a source of dietary protein (bushmeat). 2Globally, the major areas of conflict are predation on livestock and the transmission of rabies. At a broad scale, livestock predation is a customary problem where predators are present and has been quantified for a broad range of carnivore species, although the veracity of these estimates is equivocal. Typically, but not always, losses are small relative to the numbers held, but can be a significant proportion of total livestock mortality. Losses experienced by producers are often highly variable, indicating that factors such as husbandry practices and predator behaviour may significantly affect the relative vulnerability of properties in the wider landscape. Within livestock herds, juvenile animals are particularly vulnerable. 3Proactive and reactive culling are widely practised as a means to limit predation on livestock and game. Historic changes in species' distributions and abundance illustrate that culling programmes can be very effective at reducing predator density, although such substantive impacts are generally considered undesirable for native predators. However, despite their prevalence, the effectiveness, efficiency and the benefit:cost ratio of culling programmes have been poorly studied. 4A wide range of non-lethal methods to limit predation has been studied. However, many of these have their practical limitations and are unlikely to be widely applicable. 5Lethal approaches are likely to dominate the management of terrestrial carnivores for the foreseeable future, but animal welfare considerations are increasingly likely to influence management strategies. The adoption of non-lethal approaches will depend upon proof of their effectiveness and the willingness of stakeholders to implement them, and, in some cases, appropriate licensing and legislation. 6Overall, it is apparent that we still understand relatively little about the importance of factors affecting predation on livestock and how to manage this conflict effectively. We consider the following avenues of research to be essential: (i) quantified assessments of the loss of viable livestock; (ii) landscape-level studies of contiguous properties to quantify losses associated with variables such as different husbandry practices; (iii) replicated experimental manipulations to identify the relative benefit of particular management practices, incorporating (iv) techniques to identify individual predators killing stock; and (v) economic analyses of different management approaches to quantify optimal production strategies. [source] Establishment of a pharmacoepidemiological database in Germany: methodological potential, scientific value and practical limitationsPHARMACOEPIDEMIOLOGY AND DRUG SAFETY, Issue 3 2008Dipl., Iris Pigeot Dr rer.nat. Abstract Purpose We present a new population-based pharmacoepidemiological (PE) database obtained from statutory health insurances (SHIs) that is able to generate signals, to monitor prescribed drugs and to describe drug utilisation. We discuss methodological features of the database and we assess to which degree this database reflects basic demographic characteristics and hospitalisation rates of the general population. Methods Files of three SHIs were linked with drug dispensation data from a pharmacies' electronic data processing centre on an individual basis using the unique subject identification number (ID) at a trusted third party centre. Plausibility checks and descriptive analyses were carried out. Results The database covers 3.6 million SHI-members, provides drug utilisation data and data on hospitalisations. SHI membership is fairly stable over time. Our data indicate marked differences in socio-demographic characteristics between SHIs. Hospital admission rates standardised for age vary between 0.164 and 0.229 per person year, which is in good agreement with official statistics (0.20). The age distribution shows good agreement for men and some underrepresentation for women above the age of 60 as compared to the general population. Conclusions Confounder information on medical conditions, concomitant medications and socio-demographic variables can be obtained from the database, while the assessment of confounders related to lifestyle requires supplementary data collection. The database allows for a population-based approach and reflects daily practice including off-label use of drugs. Independent recording of exposure and outcome data prevents reporting bias on medication or outcome. Legal conditions that allow continuous updating of the database need to be settled. Copyright © 2008 John Wiley & Sons, Ltd. [source] Analysis of split-plot designs: an overview and comparison of methodsQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 7 2007T. Næs Abstract Split-plot designs are frequently needed in practice because of practical limitations and issues related to cost. This imposes extra challenges on the experimenter, both when designing the experiment and when analysing the data, in particular for non-replicated cases. This paper is an overview and discussion of some of the most important methods for analysing split-plot data. The focus is on estimation, testing and model validation. Two examples from an industrial context are given to illustrate the most important techniques. Copyright © 2006 John Wiley & Sons, Ltd. [source] Limitations in predicting dyebath exhaustion using optical spectroscopyCOLORATION TECHNOLOGY, Issue 3 2010Melih Günay There are practical limitations in predicting dyebath concentrations and dyebath exhaustion using absorbance measurements from optical spectroscopy. The purpose of this paper is to examine the common assumptions of prediction models that cause prediction errors, and especially when multiple dye combinations are used. If a linear model is used to map absorbance to concentration, then five assumptions must hold: measurement repeatability, linear scaling, spectral additivity, linear independence of the constituent spectra and the absence of spectral morphing. Violation of one or more of these assumptions will lead to errors in predicting the concentrations of dyes in a dyebath and subsequent exhaustion calculations. [source] | |||||||||||||||||||