Sampling Techniques (sampling + techniques)

Distribution by Scientific Domains


Selected Abstracts


Online end-to-end quality of service monitoring for service level agreement management

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 4 2008
Xiaoyuan Ta
Abstract A major challenge in network and service level agreement (SLA) management is to provide Quality of Service (QoS) demanded by heterogeneous network applications. Online QoS monitoring plays an important role in the process by providing objective measurements that can be used for improving network design, troubleshooting and management. Online QoS monitoring becomes increasingly difficult and complex due to the rapid expansion of the Internet and the dramatic increase in the speed of network. Sampling techniques have been explored as a means to reduce the difficulty and complexity of measurement. In this paper, we investigate several major sampling techniques, i.e. systematic sampling, simple random sampling and stratified sampling. Performance analysis is conducted on these techniques. It is shown that stratified sampling with optimum allocation has the best performance. However, stratified sampling with optimum allocation requires additional statistics usually not available for real-time applications. An adaptive stratified sampling algorithm is proposed to solve the problem. Both theoretical analysis and simulation show that the proposed adaptive stratified sampling algorithm outperforms other sampling techniques and achieves a performance comparable to stratified sampling with optimum allocation. A QoS monitoring software using the aforementioned sampling techniques is designed and tested in various real networks. Copyright © 2007 John Wiley & Sons, Ltd. [source]


Deterministic Importance Sampling with Error Diffusion

COMPUTER GRAPHICS FORUM, Issue 4 2009
László Szirmay-Kalos
This paper proposes a deterministic importance sampling algorithm that is based on the recognition that delta-sigma modulation is equivalent to importance sampling. We propose a generalization for delta-sigma modulation in arbitrary dimensions, taking care of the curse of dimensionality as well. Unlike previous sampling techniques that transform low-discrepancy and highly stratified samples in the unit cube to the integration domain, our error diffusion sampler ensures the proper distribution and stratification directly in the integration domain. We also present applications, including environment mapping and global illumination rendering with virtual point sources. [source]


Structural Model Updating and Health Monitoring with Incomplete Modal Data Using Gibbs Sampler

COMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 4 2006
Jianye Ching
It is based on the Gibbs sampler, a stochastic simulation method that decomposes the uncertain model parameters into three groups, so that the direct sampling from any one group is possible when conditional on the other groups and the incomplete modal data. This means that even if the number of uncertain parameters is large, the effective dimension for the Gibbs sampler is always three and so high-dimensional parameter spaces that are fatal to most sampling techniques are handled by the method, making it more practical for health monitoring of real structures. The approach also inherits the advantages of Bayesian techniques: it not only updates the optimal estimate of the structural parameters but also updates the associated uncertainties. The approach is illustrated by applying it to two examples of structural health monitoring problems, in which the goal is to detect and quantify any damage using incomplete modal data obtained from small-amplitude vibrations measured before and after a severe loading event, such as an earthquake or explosion. [source]


A logical starting point for developing priorities for lizard and snake ecotoxicology: A review of available data

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 5 2002
Kym Rouse Campbell
Abstract Reptiles, specifically lizards and snakes, usually are excluded from environmental contamination studies and ecological risk assessments. This brief summary of available lizard and snake environmental contaminant data is presented to assist in the development of priorities for lizard and snake ecotoxicology. Most contaminant studies were not conducted recently, list animals found dead or dying after pesticide application, report residue concentrations after pesticide exposure, compare contaminant concentrations in animals from different areas, compare residue concentrations found in different tissues and organs, or compare changes in concentrations over time. The biological significance of the contaminant concentrations is rarely studied. A few recent studies, especially those conducted on modern pesticides, link the contaminant effects with exposure concentrations. Nondestructive sampling techniques for determining organic and inorganic contaminant concentrations in lizards and snakes recently have been developed. Studies that relate exposure, concentration, and effects of all types of environmental contaminants on lizards and snakes are needed. Because most lizards eat insects, studies on the exposure, effects, and accumulation of insecticides in lizards, and their predators, should be a top priority. Because all snakes are upper-trophic-level carnivores, studies on the accumulation and effects of contaminants that are known to bioaccumulate or biomagnify up the food chain should be the top priority. [source]


The use of peepers to sample pore water in acid sulphate soils

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2008
P. VanOploo
Summary Serious environmental impacts of acidic drainage from acid sulphate soils in coastal areas are the result of the interactions between the hydrologic cycle, land use and drainage management, and pore water chemistry. In this study, in situ, diffusion-controlled dialysis profile samplers, or peepers, were used to examine pore water chemistry of acid sulphate soils in a coastal, sugarcane-producing area in Eastern Australia. The peepers sampled pore water at 20-mm intervals over a 1.0-m length, permitting excellent resolution of the sharp transitions in pore water chemistry that occur around a soil profile's iron sulphide oxidation front. Comparison of peeper profiles with soil water profiles extracted from soil samples by centrifuging, illustrated the advantages of peepers over conventional soil water sampling techniques in unconsolidated, sulphidic soils. For conventional sampling, the low permeability, gel-like, unoxidized soil samples had to be frozen then thawed before water could be extracted by centrifuging. Peeper profiles of species not involved in redox reactions agreed well with those from centrifuged soil extracts. Redox sensitive species, however, were in poorer agreement because of the lengthy soil sample preparation and extraction procedures required for extraction by centrifuging. The approximately 6-day equilibration time required for peeper sampling allows them to follow monthly or seasonal changes in pore water chemistry in acid sulphate soils due to variations in climate, and land use and management. [source]


Being ,fat' in today's world: a qualitative study of the lived experiences of people with obesity in Australia

HEALTH EXPECTATIONS, Issue 4 2008
Samantha L. Thomas PhD
Abstract Objective, To develop an in-depth picture of both lived experience of obesity and the impact of socio-cultural factors on people living with obesity. Design, Qualitative methodology, utilizing in-depth semi-structured interviews with a community sample of obese adults (body mass index ,30). Community sampling methods were supplemented with purposive sampling techniques to ensure a diverse range of individuals were included. Results, Seventy-six individuals (aged 16,72) were interviewed. Most had struggled with their weight for most of their lives (n = 45). Almost all had experienced stigma and discrimination in childhood (n = 36), as adolescents (n = 41) or as adults (n = 72). About half stated that they had been humiliated by health professionals because of their weight. Participants felt an individual responsibility to lose weight, and many tried extreme forms of dieting to do so. Participants described an increasing culture of ,blame' against people living with obesity perpetuated by media and public health messages. Eighty percent said that they hated or disliked the word obesity and would rather be called fat or overweight. Discussion and Conclusion, There are four key conclusions: (i) the experiences of obesity are diverse, but there are common themes, (ii) people living with obesity have heard the messages but find it difficult to act upon them, (iii) interventions should be tailored to address both individual and community needs and (iv) we need to rethink how to approach obesity interventions to ensure that avoid recapitulating damaging social stereotypes and exacerbating social inequalities. [source]


Determining the relationship between drivers' level of education, training, working conditions, and job performance in Kenya

HUMAN RESOURCE DEVELOPMENT QUARTERLY, Issue 3 2003
Fredrick Muyia Nafukho
One major issue in human resource development (HRD) is to determine factors that predict the performance of employees. The primary purpose of this study was to determine how level of education, training, and the working conditions of matatu (public service vehicle) drivers determined their job performance in terms of reduced road traffic accidents. Proportionate and simple random sampling techniques were employed to select 143 drivers who completed and returned the questionnaires. Multiple regression analysis was used to test the hypotheses stated. The findings indicate that the variables of driver experience and hours worked had a significant relationship with the dependent variable rates of traffic accidents per driver as hypothesized. The variables of education level, training, salary earned, and average speed traveled did not have a significant relationship with the dependent variable. [source]


Online end-to-end quality of service monitoring for service level agreement management

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 4 2008
Xiaoyuan Ta
Abstract A major challenge in network and service level agreement (SLA) management is to provide Quality of Service (QoS) demanded by heterogeneous network applications. Online QoS monitoring plays an important role in the process by providing objective measurements that can be used for improving network design, troubleshooting and management. Online QoS monitoring becomes increasingly difficult and complex due to the rapid expansion of the Internet and the dramatic increase in the speed of network. Sampling techniques have been explored as a means to reduce the difficulty and complexity of measurement. In this paper, we investigate several major sampling techniques, i.e. systematic sampling, simple random sampling and stratified sampling. Performance analysis is conducted on these techniques. It is shown that stratified sampling with optimum allocation has the best performance. However, stratified sampling with optimum allocation requires additional statistics usually not available for real-time applications. An adaptive stratified sampling algorithm is proposed to solve the problem. Both theoretical analysis and simulation show that the proposed adaptive stratified sampling algorithm outperforms other sampling techniques and achieves a performance comparable to stratified sampling with optimum allocation. A QoS monitoring software using the aforementioned sampling techniques is designed and tested in various real networks. Copyright © 2007 John Wiley & Sons, Ltd. [source]


The well-being of gays, lesbians and bisexuals in Botswana

JOURNAL OF ADVANCED NURSING, Issue 6 2001
V.J. Ehlers BA BSSc MA DLitt RGN RM
The well-being of gays, lesbians and bisexuals in Botswana Aims.,To investigate the level of well-being of gays, lesbians and bisexuals (GLBs) in Botswana, how this level of well-being could be promoted and whether their health care needs were met by health care professionals. Rationale.,It is illegal to engage in same-sex activities in Botswana, punishable by imprisonment. Although Botswana's citizens have one of Africa's best health care systems, little is known about the health status, health care needs and general well-being of Botswana's GLBs. This survey attempted to uncover some of these potential health care needs, impacting on the GLBs' well-being. Design/methods.,The research framework adopted was the health and human rights approach, placing dignity before rights. A survey design, with structured questionnaires, was used. Snow-ball sampling techniques were used. Results.,Results indicated that varying degrees of distress were experienced by 64% of the GLBs in this study. The GLBs identified a need for human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) education and had concerns about their general health, discrimination against them and vulnerability to violence including sexual assaults. Conclusions.,The well-being of the GLBs in Botswana was influenced by both positive internal acceptance of their sexual orientation and negative external acceptance by society. Health care professionals played insignificant roles in the promotion of GLBs' well-being, and could make greater inputs into health education efforts, and more significant contributions towards enhancing the GLBs' levels of well-being. Enhanced collaboration between health professionals and human rights activists are recommended to reduce violations of Botswana's GLBs' dignity and to improve their quality of life, including enhanced access to and utilization of health care services. [source]


A Bayesian analysis of response to selection for uterine capacity in rabbits

JOURNAL OF ANIMAL BREEDING AND GENETICS, Issue 2 2001
Blasco
A divergent, eight generation selection experiment on uterine capacity in rabbits was performed. Rabbit does were ovariectomized unilaterally before puberty, and selected for increased and decreased litter size by ,best linear unbiased prediction' using data from up to four parities. Two different analyses were performed to estimate the response to selection. The first was based on least squares analysis; the second was based on Bayesian methods using Gibbs sampling techniques. Three different priors were used for variance components, but these had little influence on the results. Posterior means of heritabilities for uterine capacity, varied from 0.09 to 0.12, and repeatabilities from 0.18 to 0.22. The response to eight generations of selection was symmetrical and led to a divergence of 0.16 young rabbits per generation, which amounts to about 2% of the average litter size of the base population per generation. The pattern of response however, was not linear: a high initial response was followed by a period where little further response was observed, and a final burst of response was obtained during the last two cycles of selection. Análisis Bayesiona de la Respuesta a la selección por capacidad uterina en conejos Se llevó a cabo un experimento de selección divergente por capacidad uterina en conejos. Las conejas fueron ovariectomizadas unilateralmente antes de la pubertad, y fueron seguidamente seleccionadas para aumentar y disminuir el tamaño de camada mediante un BLUP que incluía datos de hasta el cuarto parto. Se realizaron dos tipos de análisis para estimar la respuesta, el primero basado en mínimos cuadrados y el segundo en técnicas bayesianas con la ayuda de muestreo de Gibbs. Aunque tres a prioris diferentes fueron usados para las componentes de varianza, esto apenas influyó en los resultados, pues las medias posteriores para las heredabilidades variarton de 0.09 a 0.12 y las medias de las repetibilidades variaron de 0.18 a 0.22. La respuesta a ocho generaciones de selección fue simétrica y condujo a una diverjencia de 0.16 conejos por generación, lo que representa un 2% de la media de la población base por generación. La respuesta no fue, sin embargo, lineal: una fuerte respuesta inicial fue seguida de un periodo de estancamiento y una nueva respuesta en los dos últimos ciclos de selección. Eine Bayes Analyse zu Auswirkungen der Selektion auf uterine Kapazität beim Kaninchen Ein Selektionsexperiment mit divergierender Selektion wurde über acht Generationen durchgeführt. Die Zibben wurden vor der Geschlechtreife einseitig ovarektomiert und auf höhere und niedrigere Wurfgröße über Best Linear Unbiased Prediction (BLUP) selektiert. Daten von bis zu vier Trächtigkeiten wurden verwendet. Zwei verschiedene Analysen wurden verwendet um den Selektionserfolg zu bestimmen. Die erste basierte auf der Least Square Analyse, die zweite auf der Bayes Methode des Gibbs Sampling. Drei verschiedene Priors wurden in der Varianzkomponentenschätzung verwendet, aber sie hatten wenig Einfluss auf die Endergebnisse. Die a posteriori Ergebnisse für die Heritabilitäten der uterinen Kapazität variierten von 0,09 bis 0,12, die Wiederholbarkeiten von 0, 18 bis 0,22. Die Selektionserfolg über acht Generationen war symmetrisch und führte zu einem Unterschied von 0,16 Jungtieren pro Generation, was ca. 2% der durchschnittlichen Wurfgröße, bezogen auf die Basispopulation je Generation, entspricht. Das Bild des Zuchtfortschritts war nicht linear: nach einem hohen Anfangserfolg wurde eine Periode geringen Erfolges beobachtet und ein Ende des Zuchtfortschrittes wurde in den letzten zwei Generationen erreicht. [source]


Medicinal plants of Erute county, Lira district, Uganda with particular reference to their conservation

AFRICAN JOURNAL OF ECOLOGY, Issue 2 2010
Christine Oryema
Abstract A medicinal plant study was carried out in eighteen parishes and 54 villages of Erute county, Lira district, Uganda. Parishes and villages were selected using stratified random sampling techniques. Questionnaires, interviews and discussions with the local people were used to obtain information on the names of the plants, their medicinal uses and conservation methods. The number of the medicinal plants species used was 180 belonging to 144 genera and 57 families of flowering plants. The major families recorded for medicinal purpose included Fabaceae (37 species), Asteraceae (26 species), Euphorbiaceae (eleven species), Vitaceae (eight species), Verbenaceae (seven species), Poaceae (six species), Solanaceae (five species), and Rubiaceae (four species). There is a need for putting in place measures to conserve these plants. Unfortunately, most of the healers or users were not interested in cultivation of the plants. The situation could worsen with the social changes and demand for land for agriculture in the district. Résumé Nous avons réalisé une étude des plantes médicinales dans 18 paroisses et 54 villages du Comté d'Erute, dans le district de Lira, en Ouganda. Paroisses et villages furent sélectionnés au moyen de techniques d'échantillonnage au hasard stratifié. On a eu recours à des questionnaires, des interviews et des discussions avec les populations locales pour obtenir des informations sur le nom des plantes, leur utilisation médicinale et les méthodes de conservation. Il y avait 180 plantes médicinales appartenant à 144 genres et à 57 familles de plantes à fleurs. Les principales familles rapportées dans le domaine médicinal comprenaient les Fabaceae (37 espèces), les Asteraceae (26 espèces), les Euphorbiaceae (11 espèces), les Vitaceae (8 espèces), les Verbenaceae (7 espèces), les Poaceae (6 espèces), les Solanaceae (5 espèces), et les Rubiaceae (4 espèces). Il faut instaurer des mesures pour conserver ces plantes. Malheureusement, la plupart des guérisseurs ou des utilisateurs n'étaient pas intéressés par la culture de ces plantes. La situation pourrait empirer en raison des changements sociaux et de la demande de terres pour l'agriculture dans ce district. [source]


Bill harnesses on nestling Tufted Puffins influence adult provisioning behavior

JOURNAL OF FIELD ORNITHOLOGY, Issue 3 2006
Carina Gjerdrum
ABSTRACT For burrow-nesting seabirds, investigators have examined nestling diet by attaching harnesses to the bills of nestlings to intercept food delivered by the parent. To determine whether this method provides an unbiased estimate of nestling diet, we evaluated its effect on the provisioning behavior of Tufted Puffins (Fratercula cirrhata) nesting on Triangle Island, British Columbia. Adults delivering food to nestlings with bill harnesses always hesitated before entering a burrow with food, increasing their susceptibility to kleptoparasitism by gulls, and did not always leave the food intended for the nestling. These responses by adult puffins could lead to underestimates of energy intake rates of nestlings and unreliable comparisons with other species if prey left by adults in nest burrows were the only source of data. We also compared estimates of the species, number, and size of prey delivered by adult puffins as determined by direct observation from blinds to samples of prey collected directly from nest burrows and found that the two sampling techniques produced similar results. However, identifying rare prey species and gathering precise information about prey length, mass, and condition require collection of prey, and we recommend using a combination of techniques to obtain the most reliable estimates of nestling diet. SINOPSIS Los investigadores de aves marinas que anidan en cavidades o guaridas, han examinado la dieta de los pichones colocando artefactos en el pico de los polluelos que intercepta la comida que traen los adultos. Para determinar si el método provee de un estimado sin sesgo de la dieta de pichones, evaluamos su efecto en la conducta de Fratercula cirrhata, de aves que anidaron en Triangle Island, Columbia Británica. Los adultos que trajeron comida a pichones que tenían artefactos en el pico, tuvieron reservas para entrar en la cavidad, exponiéndose a kleptoparasitismo por parte de gaviotas. Además no siempre le dejaron comida a los pichones. La respuesta de los adultos, puede llevar a subestimar las necesidades energéticas de los pichones y hacer comparaciones poco confiables con otras especies si se utiliza únicamente como datos, las presas dejadas en las guaridas por los adultos. También comparamos las especies utilizadas para alimentar a los polluelos, número de presas y su tamaño comparando observaciones directas de lo que se llevaba a los nidos, con lo que se dejaba en las guaridas y encontramos que ambos métodos arrojan resultados similares. Sin embargo, la identificación de presas raras, obtener información precisa sobre la longitud de la presa, peso y condición de esta, requieren el examinar las misma. Recomendamos utilizar una combinación de ambos métodos para obtener estimados confiables de la dieta de polluelos. [source]


Fully automated liquid extraction-based surface sampling and ionization using a chip-based robotic nanoelectrospray platform,

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 3 2010
Vilmos Kertesz
Abstract A fully automated liquid extraction-based surface sampling device utilizing an Advion NanoMate chip-based infusion nanoelectrospray ionization system is reported. Analyses were enabled for discrete spot sampling by using the Advanced User Interface of the current commercial control software. This software interface provided the parameter control necessary for the NanoMate robotic pipettor to both form and withdraw a liquid microjunction for sampling from a surface. The system was tested with three types of analytically important sample surface types, viz., spotted sample arrays on a MALDI plate, dried blood spots on paper, and whole-body thin tissue sections from drug dosed mice. The qualitative and quantitative data were consistent with previous studies employing other liquid extraction-based surface sampling techniques. Published in 2009 by John Wiley & Sons, Ltd. [source]


Optimising the determination of maize endosperm vitreousness by a rapid non-destructive image analysis technique,

JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 9 2004
Corinda Erasmus
Abstract A rapid non-destructive image analysis technique was developed and optimised for the determination of maize endosperm vitreousness without the need for sample preparation. Maize kernel translucency measurements were optimised for a light system consisting of positioning whole kernels on top of round illuminated areas smaller than the projected areas of the kernels, allowing light to shine through the kernels. A correction factor to allow for constant illumination of kernels was developed to adjust for kernel size variation in relation to constant light area. The intensity of translucency in maize is linearly correlated to the percentage of kernel illumination (r = 0.99, p < 0.001). Significant correlations were found between corrected translucency values and endosperm yields determined by hand dissection. These were: translucency as a percentage of the whole kernel and vitreous endosperm (mass%), r = 0.77; translucency as a percentage of the whole kernel and opaque endosperm (mass%), (r = ,0.72); translucency as a percentage of endosperm and vitreous endosperm (mass%), r = 0.81; and translucency as a percentage of endosperm and opaque endosperm (mass%), r = ,0.77; with n = 245 in all instances. Translucency varied by 29.5% between the lowest and highest values, and vitreous endosperm (mass%) varied by 16.8% between the lowest and highest values. Correlations increased significantly after corrections for kernel thickness. A thickness increase of 1 mm in the maize will cause a decrease of 21.86% in translucency and vice versa. The method allows for large samples (at least 49 kernels min,1) to be analysed for individual vitreous and opaque endosperm contents with no interferences with kernel structure. With further development of suitable automated sampling techniques, it could become a suitable potential method for in-line quantification of maize endosperm contents. Copyright © 2004 Society of Chemical Industry [source]


Dispersal and recruitment dynamics in the fleshy-fruited Persoonia lanceolata (Proteaceae)

JOURNAL OF VEGETATION SCIENCE, Issue 6 2007
Tony D. Auld
Abstract Question: What is the role of dispersal, persistent soil seed banks and seedling recruitment in population persistence of fleshy-fruited obligate seeding plant species in fire-prone habitats? Location: Southeastern Australia. Methods: We used a long-term study of a shrubby, fleshy-fruited Persoonia species (Proteaceae) to examine (1) seed removal from beneath the canopy of adult plants; (2) seedling recruitment after fire; (3) the magnitude and location of the residual soil seed bank; and (4) the implications for fire management of obligate seeding species. We used demographic sampling techniques combined with Generalised Linear Modelling and regression to quantify population changes over time. Results: Most of the mature fruits (90%) on the ground below the canopy of plants were removed by Wallabia bicolor (Swamp wallaby) with 88% of seeds extracted from W. bicolor scats viable and dormant. Wallabies play an important role in moving seeds away from parent plants. Their role in occasional long distance dispersal events remains unknown. We detected almost no seed predation in situ under canopies (< 1%). Seedling recruitment was cued to fire, with post-fire seedling densities 6-7 times pre-fire adult densities. After fire, a residual soil seed bank was present, as many seeds (77-100%) remained dormant and viable at a soil depth where successful future seedling emergence is possible (0-5 cm). Seedling survival was high (> 80%) with most mortality within 2 years of emergence. Plant growth averaged 17 cm per year. The primary juvenile period of plants was 7,8 years, within the period of likely return fire intervals in the study area. We predicted that the study population increased some five-fold after the wildfire at the site. Conclusions: Residual soil seed banks are important, especially in species with long primary juvenile periods, to buffer the populations against the impact of a second fire occurring before the seed bank is replenished. [source]


A grid-based method for sampling and analysing spatially ambiguous plants

JOURNAL OF VEGETATION SCIENCE, Issue 4 2001
Jeffrey S. Fehmi
Hickman (1993). Abstract. Spatial data can provide much information about the interrelations of plants and the relationship between individuals and the environment. Spatially ambiguous plants, i.e. plants without readily identifiable loci, and plants that are profusely abundant, present non-trivial impediments to the collection and analysis of vegetation data derived from standard spatial sampling techniques. Sampling with grids of presence/absence quadrats can ameliorate much of this difficulty. Our analysis of 10 fully-mapped grassland plots demonstrates the applicability of the grid-based approach which revealed spatial dependence at a much lower sampling effort than mapping each plant. Ripley's K -function, a test commonly used for point patterns, was effective for pattern analysis on the grids and the gridded quadrat technique was an effective tool for quantifying spatial patterns. The addition of spatial pattern measures should allow for better comparisons of vegetation structure between sites, instead of sole reliance on species composition data. [source]


Modeling of Bovine Type-I Collagen Fibrils: Interaction with Pickling and Retanning Agents

MACROMOLECULAR BIOSCIENCE, Issue 2 2007
Rosa E. Bulo
Abstract Bovine Type I collagen was investigated, building on a large scale computer model of a collagen fibril in water, and focusing on two stages of the leather manufacturing process. The effects of different salts (NaCl, CaCl2, and Na2SO4) on the swelling behavior of collagen at low pH (the pickling process) were studied. The salts suppress the swelling of the fibrils at low pH and we find specific stabilizing influences for CaCl2 and Na2SO4, due to weak Ca2+/Cl, and strong SO/lysine/arginine interactions, respectively. Using state-of-the-art sampling techniques, such as the metadynamics algorithm, to allow an efficient exploration of configuration space, we were able to investigate the effect of polyacrylate and poly(methyl acrylate) , two polymeric retanning agents , on the fibril. Both polymers interact with the ammonium groups on the surface, but polyacrylate shows significantly stronger interactions. We suggest that it is this stronger interaction that contributes to the reduced suitability of PAA as a tanning agent. [source]


DIET-TISSUE FRACTIONATION OF STABLE CARBON AND NITROGEN ISOTOPES IN PHOCID SEALS

MARINE MAMMAL SCIENCE, Issue 1 2002
VÉRONIQUE Lesage
Diet-tissue isotopic fractionation of carbon (C) and nitrogen (N) isotopes in short- and longer-term diet integrators of diet (i. e., blood serum and red cells), that involve non-invasive sampling techniques was examined using three species of phocid seals (harbor seals, gray seals, and harp seals) fed a known diet. Variability in diet-tissue fractionation values within and between species was also scrutinized to determine the legitimacy of using values obtained from one species to explore trophic positions and diets of other related species. All captive seals raised on a constant diet had tissues enriched in 13C and 15N relative to their diet. Diet-tissue isotopic fractionation values were generally consistent among conspecifics and among phocid species for a given tissue. Trophic isotopic enrichment in 13C was significantly higher in red blood cells (+1.5%±) than in blood serum (+0.8%±), whereas the reverse was observed for nitrogen isotopes (+1.7%± in red cells vs. +3.1%± in serum). However, 13C-depleted lipids were not extracted from blood tissues in this study. This results in a downward bias in the diet-tissue fractionation factors for carbon for both red cells and blood serum, particularly the latter because of their significantly higher lipid contents (x,± SD = 14.6 ± 2.3%; n= 20; red blood cells 3.8 ± 0.9%±; n= 50, muscle 7.7 ± 2.0; n= 21) in marine mammals. [source]


Investigating the use of sampling for maximising the efficiency of student-generated faculty teaching evaluations

MEDICAL EDUCATION, Issue 2 2005
Clarence D Kreiter
Purpose, Surveys of medical students are widely used to evaluate course content and faculty teaching within the medical school. Gathering information that accurately reflects student perceptions requires that students buy into the evaluation process and be willing to provide thoughtful responses to the teaching evaluation. To maintain student commitment, it is important that medical students are not overburdened with poorly planned evaluations. Sampling might decrease the number of evaluations required of students and might also reduce the proportion of non-responses and other forms of inattentive response biases. Methods, A sampling technique employed within a large medical lecture is described and evaluated. A generalisability study of the teacher evaluations is conducted. Results, A high response rate and high levels of reliability were obtained by sampling a small proportion of the total class. The largest source of error was related to rater and utilising sufficient numbers of student-raters is critical to achieving reliable results. Conclusion, Sampling can reduce evaluation demands placed on students, and preserve reliability and increase the validity of mean evaluation scores. With computer presentation, efficient sampling techniques become practical and should be part of software packages used to present teacher evaluations. [source]


Tissue-specific mechanical microdissection of higher plants

PHYSIOLOGIA PLANTARUM, Issue 3 2006
Marco Thome
Higher plants are multicellular organisms, which exhibit a high degree of differentiation with respect to their anatomy, metabolism and gene expression. Analysing entire plants or organs results in an average of information of all tissues and cells included in the sample. In this way neither physiological processes nor gene expression can be attributed to particular tissues. For revealing the contributions of specific tissues to the overall metabolism and the gene expression, highly spatially resoluted cell sampling is a prerequisite. Here, mechanical microdissection (MMD), a low cost and easy to handle alternative to existing sampling techniques (e.g. laser-assisted microdissection or glass capillary,based sampling) was tested on several plant species (Arabidopsis thaliana L., Cucurbita maxima Duch., Hordeum vulgare L. and Pelargonium hybrid cultivar ,Graveolens'). The applicability and potential of MMD for separating tissues from different organs of these plants was demonstrated. Furthermore, A. thaliana samples were, as examples, tested for their RNA quality by reverse transcription,PCR and for tissue specificity by amplifying messenger RNA of tissue marker genes. [source]


Sampling systems for isotope-ratio mass spectrometry of atmospheric ammonia

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 2 2006
Richard Skinner
Passive and active ammonia (NH3) sampling devices have been tested for their nitrogen (N) capture potential and ,15N fractionation effects. Several sampling techniques produced significantly different ,15NH3 signals when sampling the same NH3 source released from field site fumigation campaigns. Conventional passive NH3 -monitoring systems have shown to provide insufficient N for isotope-ratio mass spectrometry and various modified devices have been developed, based on existing diffusion tube designs, to overcome this problem. The final sampler design was then tested in a wind tunnel to verify that sampling NH3 in different environmental conditions did not significantly fractionate the ,15N signal. Copyright © 2005 John Wiley & Sons, Ltd. [source]


Sampling Techniques Influence Understory Plant Trajectories After Restoration: An Example from Ponderosa Pine Restoration

RESTORATION ECOLOGY, Issue 4 2003
Julie E. Korb
Abstract Although there is no one correct technique for sampling vegetation, the sampling design chosen may greatly influence the conclusions researchers can draw from restoration treatments. Considerations when designing vegetation sampling protocol include determining what sampling attributes to measure, the size and shape of the sampling plot, the number of replicates and their location within the study area, and the frequency of sampling. We installed 20 point-intercept transects (50-m long), 8 belt transects (10 × 50 m), 10 adapted Daubenmire transects (four 0.5 × 2-m plots), and 4 modified-Whittaker plots (20 × 50 m with smaller nested plots) in treatment and control units to measure understory herbaceous response in a forest restoration experiment that tested different treatments. Point-intercept transects on average recorded at least twice as much plant cover as did adapted Daubenmire transects and modified-Whittaker plots taken at the same location for all control and treatment units. Point-intercept transects and adapted Daubenmire plots on average captured fewer rare and exotic species in the control and treatment units in comparison with the belt transects and modified-Whittaker plots. Modified-Whittaker plots captured the highest species richness in all units. Early successional understory response to restoration treatments was likely masked by the response of the herbaceous community to yearly climatic variation (dry vs. wet years). Species richness and abundance were higher in wet years than dry years for all control and treatment units. Our results illustrate that sampling techniques can greatly influence perceptions of understory plant trajectories and therefore the interpretation of whether restoration goals have been achieved. In addition, our results suggest that restoration monitoring needs to be conducted for a sufficient length of time so that restoration treatment responses can be detected. [source]


Mechanisms of Submicron and Residual Ash Particle Formation during Pulverised Coal Combustion: A Comprehensive Review

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3-4 2005
D. Yu
Coal fly ash has been a traditional concern of utilities since coal was used to generate electricity because it may bring about a number of technical and economic problems such as slagging, fouling, corrosion, erosion, waste disposal and overall boiler efficiency reduction. Moreover, fine particulates that escape the combustion system are recognized to have a negative impact on health and the environment due to the enrichment of the toxic trace elements and being readily inhaled. This work gives a brief review of the studies carried out in the past decades and tries to elucidate those processes that contribute to ash formation. They include the mechanisms that control submicron ash formation and those that are related to residual ash formation. The mechanism of vaporization and condensation is believed to be the major source of submicron ash particles and is discussed in detail in this review. Residual ash formation is the consequence of the competition between ash coalescence and char fragmentation. Moreover, fragmentation of excluded minerals and rotationally induced shedding may also contribute to the residual ash formation. Our literature review has provided a number of experimental and theoretical results describing how the submicron ash and residual ash are formed, Finally we present some recommendations for possible future research topics, including sampling techniques, measurement techniques, experimental studies and modelling efforts. [source]


Risk behaviours of young Indo-Chinese injecting drug users in Sydney and Melbourne

AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH, Issue 1 2001
Lisa Maher
Objective: To investigate patterns of drug use and injection-related risk behaviours among young Indo-Chinese injecting drug users (IDUs). Method: Cross-sectional survey. A structured questionnaire was administered to 184 Indo-Chinese IDUs aged 15 to 24 in Sydney and Melbourne. Participants were recruited using snowball sampling techniques; measures included patterns of heroin and other drug use, injection-related risk behaviours, perceived susceptibility to HIV and HCV infection and access to services. Results: Despite perceived high availability of sterile injecting equipment, 36% had ever shared a needle and syringe and 22% had done so in the preceding month. Lifetime sharing was significantly associated with duration of injecting, history of incarceration and residence in Sydney. Sharing of injecting paraphernalia other than needles and syringes was also common, with young women and Sydney residents significantly more likely to report sharing equipment in the preceding month. Conclusions: Young Indo-Chinese IDUs are at high risk of infection with hepatitis C and other blood-borne viruses. Results indicate an urgent need for culturally appropriate and sustainable risk reduction programs which specifically target this population. Implications: Health services must respond swiftly to implement effective blood-borne virus prevention programs for young Indo-Chinese IDUs. Failure to do so may sustain the current epidemic of hepatitis C among IDUs. [source]


Diversity of Cicadellidae in agricultural production areas in the Ovens Valley, north-east Victoria, Australia

AUSTRALIAN JOURNAL OF ENTOMOLOGY, Issue 3 2010
Piotr Tr, bicki
Abstract There is a paucity of data on the distribution of Cicadellidae (leafhoppers) in Australia. This study quantifies the relative abundance, seasonal activity and diversity of leafhoppers in the Ovens Valley region of north-east Victoria, Australia. Species diversity and abundance was assessed at four field sites in and around the field borders of commercially grown tobacco crops using three sampling techniques (pan trap, sticky trap and sweep net). Over 51 000 leafhopper samples were collected, with 57 species from 11 subfamilies and 19 tribes identified. Greater numbers and diversity of leafhoppers were collected in yellow pan traps. The predominant leafhopper collected was Orosius orientalis (Matsumura). Twenty-three leafhopper species were recorded for the first time in Victoria and eight economically important pest species were recorded. Seasonal activity of selected leafhopper species, covering two sampling seasons, is presented. [source]


Bayesian Modeling of Age-Specific Survival in Bird Nesting Studies under Irregular Visits

BIOMETRICS, Issue 4 2003
Chong Z. He
Summary. In this article, a Bayesian model for age-specific nest survival rates is presented to handle the irregular visit case. Both informative priors and noninformative priors are investigated. The reference prior under this model is derived, and, therefore, the hyperparameter specification problem is solved to some extent. The Bayesian method provides a more accurate estimate of the total survival rate than the standard Mayfield method, if the age-specific hazard rates are not constant. The Bayesian method also lets the biologist look for high- and low-survival rates during the whole nesting period. In practice, it is common for data of several types to be collected in a single study. That is, some nests may be aged, others are not. Some nests are visited regularly; others are visited irregularly. The Bayesian method accommodates any mix of these sampling techniques by assuming that the aging and visiting activities have no effect on the survival rate. The methods are illustrated by an analysis of the Missouri northern bobwhite data set. [source]


Response rate and nonresponse bias in a questionnaire survey of dentists

COMMUNITY DENTISTRY AND ORAL EPIDEMIOLOGY, Issue 1 2005
Peter Parashos
Abstract , Objectives:, (a) To report on response rate and nonresponse bias of a questionnaire survey of dentists. (b) To make recommendations for future questionnaire survey research in dentistry. Methods:, A questionnaire was mailed to a stratified systematic sample of 908 Australian dentists. The strategy included three mailings, a final telephonic contact, university stationery, paid reply envelopes and personalized correspondence. Nonresponse bias was assessed by comparing responses to a simple ,yes/no' question from each contact (late responders), and by comparing demographic information (nonresponders). Results:, The response rate achieved was 87% and there was no evidence of nonresponse bias based on practice location or year of graduation. The cumulative proportions of ,yes/no' responses essentially remained constant after each contact, but significantly more late responders answered in the negative to the test question than did early responders. The telephonic contact aided in the identification of nonparticipants and ineligible units. Conclusions:, The current survey indicates that differences in data between early and nonresponders can occur despite there being no demographic differences. Therefore, assessment of nonresponse bias based on demographic data alone would seem to be insufficient. Questionnaire survey research must first be based on sound sampling techniques, and then on achieving as high a response rate as possible using the many incentives available. [source]