Variability In Experimental Results Research Articles

Time-dependent concentration of chlorides at the concrete surface revisited

ABSTRACT Service-life modeling of concrete structures exposed to chlorides has received increasing attention in recent years. Despite developments in understanding the transport phenomenon, most models still have limitations, and their results should be interpreted cautiously. This paper presents a state-of-the-art review of recent advances in time-variant models of surface chloride concentration (Cs ) used as a boundary condition in service-life models, examining the role that boundary conditions can play in service-life estimates. Moreover, an overview of the root causes of variability in experimental results and a critical review of the strengths and limitations of time-variant Cs is provided. The results of numerical studies show that the time-variant boundary conditions considered in this work performed reasonably well with short-term empirical data and matched well with field observations. However, this review highlights the need for long-term field data to validate the performance and reliability of results obtained from service-life models using time-variant boundary conditions.

Variability of mitochondrial respiration in relation to sepsis-induced multiple organ dysfunction.

Ample experimental evidence suggests that sepsis could interfere with any mitochondrial function; however, the true role of mitochondrial dysfunction in the pathogenesis of sepsis-induced multiple organ dysfunction is still a matter of controversy. This review is primarily focused on mitochondrial oxygen consumption in various animal models of sepsis in relation to human disease and potential sources of variability in experimental results documenting decrease, increase or no change in mitochondrial respiration in various organs and species. To date, at least three possible explanations of sepsis-associated dysfunction of the mitochondrial respiratory system and consequently impaired energy production have been suggested: 1. Mitochondrial dysfunction is secondary to tissue hypoxia. 2. Mitochondria are challenged by various toxins or mediators of inflammation that impair oxygen utilization (cytopathic hypoxia). 3. Compromised mitochondrial respiration could be an active measure of survival strategy resembling stunning or hibernation. To reveal the true role of mitochondria in sepsis, sources of variability of experimental results based on animal species, models of sepsis, organs studied, or analytical approaches should be identified and minimized by the use of appropriate experimental models resembling human sepsis, wider use of larger animal species in preclinical studies, more detailed mapping of interspecies differences and organ-specific features of oxygen utilization in addition to use of complex and standardized protocols evaluating mitochondrial respiration.

Probabilistic Modeling of Reprogramming to Induced Pluripotent Stem Cells

Reprogramming of somatic cells to induced pluripotent stem cells (iPSCs) is typically an inefficient and asynchronous process. A variety of technological efforts have been made to accelerate and/or synchronize this process. To define a unified framework to study and compare the dynamics of reprogramming under different conditions, we developed an insilico analysis platform based on mathematical modeling. Our approach takes into account the variability in experimental results stemming from probabilistic growth and death of cells and potentially heterogeneous reprogramming rates. We suggest that reprogramming driven by the Yamanaka factors alone is a more heterogeneous process, possibly due to cell-specific reprogramming rates, which could be homogenized by the addition of additional factors. We validated our approach using publicly available reprogramming datasets, including data on early reprogramming dynamics as well as cell count data, and thus we demonstrated the general utility and predictive power of our methodology for investigating reprogramming and other cell fate change systems.

Olfaction variation in mouse husbandry and its implications for refinement and standardization: UK survey of animal scents.

Olfaction plays a crucial role in mouse communication, providing information about genetic identity, physiological status of conspecifics and alerting mice to potential predators. Scents of animal origin can trigger physiological and behavioural responses that could affect experimental responses and impact positively or negatively on mouse welfare. Additionally, differing olfactory profiles could help explain variation in results between laboratories. A survey was sent to animal research units in the UK to investigate potential transfer of scents of animal origin during routine husbandry procedures, and responses were obtained from animal care workers and researchers using mice in 51 institutions. The results reveal great diversity between animal units regarding the relevant husbandry routines covered. Most [71%] reported housing non-breeding male and female mice in the same room, with 76% reporting that hands were not washed and gloves not changed between handling male and female mice. The most commonly reported species housed in the same facility as mice was the rat (91%), and 41% of respondents were aware that scents from rats could affect mice. Changing of gloves between handling mice and other species was reported by 79% of respondents. Depending on the aspect considered, between 18 and 33% of respondents believed human and non-human animal odours would strongly affect mouse physiology, behaviour or standardization, while approximately 32-54% believed these effects would be weak. This indicates uncertainty regarding the significance of these factors. Understanding and controlling these practices could reduce unwanted variability in experimental results and maximize welfare.

Human Life History Dimensions in Reproductive Strategies Are Intuitive Across Cultures

Psychological research has been criticized for its extensive use of American university students to make broad claims about human psychology and behavior. Critics recommend a broader base of participants because there is substantial variability in experimental results across populations, and North American and Western European psychology pool participants may be outliers in comparison with the rest of the species. This challenge is especially pertinent for claims of species-universal evolved psychological architecture. One such claim has been made regarding recognition of human life history strategies. For example, previous research demonstrates that North American women and men can identify male and female characters with fast (high mating effort, low parental investment) and slow (low mating effort, high parental investment) life history strategies, make accurate predictions about their behavioral tendencies, and respond to them in ways that would facilitate participants’ own reproductive success. The current project validates the understanding of fundamental life history dimensions across a wide range of cultures, therefore supporting the idea that there is a universality in human’s ability to use, and perceive others’ use of, life history strategies. Results for each language sample replicated patterns from North American participants. Ratings for characters clustered into two dimensions, mating effort and parental investment. Items most central to the theoretical constructs had the highest factor loadings.

Murine pressure overload models: a 30-MHz look brings a whole new "sound" into data interpretation.

Transverse aortic constriction (TAC) and angiotensin II (ANG II) subcutaneous osmotic pump infusion are frequently used murine models of pressure overload hypertrophy. The aim of this paper is to investigate time- and stressor-dependent functional and structural changes using echocardiographic B-mode, M-mode, and Doppler characterization. Ten-week-old male C57BL6/J wild-type mice received 4-wk ANG II (1.5 mg·kg(-1)·day(-1), n = 19) or saline (n = 10) infusion followed by echocardiography (Vevo2100, Visual Sonics), or underwent TAC (n = 63) or a sham operation (n = 30). In the TAC protocol, echocardiography was performed after 2 wk (n = 22 TAC, n = 10 sham), after 4 wk (n = 20 TAC, n = 10 sham), and after 10 wk (n = 21 TAC, n = 10 sham). ANG II infusion was associated with a mixed pressure and volume overload, with a variable contribution of volume overload caused by aortic valve insufficiency (grade 0.5-3.5/4). The degree of aortic valve insufficiency correlated with the degree of left ventricular dilation (r(2) = 0.671, P < 0.001). After TAC, all hypertrophic remodeling patterns known in human disease were observed: 1) low-flow, low-gradient with preserved ejection fraction (EF); 2) concentric hypertrophy with normal EF and flow; 3) concentric hypertrophy with moderately decreased EF and/or flow; 4) eccentric hypertrophy with normal EF and flow; 5) eccentric hypertrophy with moderately decreased EF and/or flow; and 6) eccentric hypertrophy with severely depressed EF. Eccentric remodeling was time dependent, with 5% of mice developing this phenotype at 2 wk, 39% at 4 wk, and 59% at 10 wk. Comprehensive echocardiographic analysis allows identification of homogeneous subgroups of mice subjected to hypertrophic stress, reducing variability in experimental results and facilitating clinical translation.

Temperature effects on brain tissue in compression

Extensive research has been carried out for at least 50 years to understand the mechanical properties of brain tissue in order to understand the mechanisms of traumatic brain injury (TBI). The observed large variability in experimental results may be due to the inhomogeneous nature of brain tissue and to the broad range of test conditions. However, test temperature is also considered as one of the factors influencing the properties of brain tissue. In this research, the mechanical properties of porcine brain have been investigated at 22°C (room temperature), and at 37°C (body temperature) while maintaining a constant preservation temperature of approximately 4–5°C. Unconfined compression tests were performed at dynamic strain rates of 30 and 50s−1 using a custom made test apparatus. There was no significant difference (p=0.8559–0.9290) between the average engineering stresses of the brain tissue at the two different temperature conditions. The results of this study should help to understand the behavior of brain tissue at different temperature conditions, particularly in unconfined compression tests.

Stable propagation of human embryonic and induced pluripotent stem cells on decellularized human substrates

Human pluripotent stem cells (hPSCs) that include human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs) have gained enormous interest as potential sources for regenerative biomedical therapies and model systems for studying early development. Traditionally, mouse embryonic fibroblasts have been used as a supportive feeder layer for the sustained propagation of hPSCs. However, the use of nonhuman-derived feeders presents concerns about the possibility of xenogenic contamination, labor intensiveness, and variability in experimental results in hPSC cultures. Toward addressing some of these concerns, we report the propagation of three different hPSCs on feeder-free extracellular matrix (ECM)-based substrates derived from human fibroblasts. hPSCs propagated in this setting were indistinguishable by multiple criteria, including colony morphology, expression of pluripotency protein markers, trilineage in vitro differentiation, and gene expression patterns, from hPSCs cultured directly on a fibroblast feeder layer. Further, hPSCs maintained a normal karyotype when analyzed after 15 passages in this setting. Development of this ECM-based culture system is a significant advance in hPSC propagation methods as it could serve as a critical component in the development of humanized propagation systems for the production of stable hPSCs and its derivatives for research and therapeutic applications.

The weirdest people in the world?

Behavioral scientists routinely publish broad claims about human psychology and behavior in the world's top journals based on samples drawn entirely from Western, Educated, Industrialized, Rich, and Democratic (WEIRD) societies. Researchers - often implicitly - assume that either there is little variation across human populations, or that these "standard subjects" are as representative of the species as any other population. Are these assumptions justified? Here, our review of the comparative database from across the behavioral sciences suggests both that there is substantial variability in experimental results across populations and that WEIRD subjects are particularly unusual compared with the rest of the species - frequent outliers. The domains reviewed include visual perception, fairness, cooperation, spatial reasoning, categorization and inferential induction, moral reasoning, reasoning styles, self-concepts and related motivations, and the heritability of IQ. The findings suggest that members of WEIRD societies, including young children, are among the least representative populations one could find for generalizing about humans. Many of these findings involve domains that are associated with fundamental aspects of psychology, motivation, and behavior - hence, there are no obvious a priori grounds for claiming that a particular behavioral phenomenon is universal based on sampling from a single subpopulation. Overall, these empirical patterns suggests that we need to be less cavalier in addressing questions of human nature on the basis of data drawn from this particularly thin, and rather unusual, slice of humanity. We close by proposing ways to structurally re-organize the behavioral sciences to best tackle these challenges.

Matrigel: A complex protein mixture required for optimal growth of cell culture

Numerous cell types require a surface for attachment to grow and proliferate. Certain cells, particularly primary and stem cells, necessitate the use of specialized growth matrices along with specific culture media conditions to maintain the cells in an undifferentiated state. A gelatinous protein mixture derived from mouse tumor cells and commercialized as Matrigel is commonly used as a basement membrane matrix for stem cells because it retains the stem cells in an undifferentiated state. However, Matrigel is not a well-defined matrix, and therefore can produce a source of variability in experimental results. In this study, we present an in-depth proteomic analysis of Matrigel using a dynamic iterative exclusion method coupled with fractionation protocols that involve ammonium sulfate precipitation, size exclusion chromatography, and one-dimensional SDS-PAGE. The ability to identify the low mass and abundance components of Matrigel illustrates the utility of this method for the analysis of the extracellular matrix, as well as the complexity of the matrix itself.

The Weirdest People in the World?

Behavioral scientists routinely publish broad claims about human psychology and behavior in the world’s top journals based on samples drawn entirely from Western, Educated, Industrialized, Rich and Democratic (WEIRD) societies. Researchers - often implicitly - assume that either there is little variation across human populations, or that these “standard subjects” are as representative of the species as any other population. Are these assumptions justified? Here, our review of the comparative database from across the behavioral sciences suggests both that there is substantial variability in experimental results across populations and that WEIRD subjects are particularly unusual compared with the rest of the species - frequent outliers. The domains reviewed include visual perception, fairness, cooperation, spatial reasoning, categorization and inferential induction, moral reasoning, reasoning styles, self-concepts and related motivations, and the heritability of IQ. The findings suggest that members of WEIRD societies, including young children, are among the least representative populations one could find for generalizing about humans. Many of these findings involve domains that are associated with fundamental aspects of psychology, motivation, and behavior - hence, there are no obvious a priori grounds for claiming that a particular behavioral phenomenon is universal based on sampling from a single subpopulation. Overall, these empirical patterns suggests that we need to be less cavalier in addressing questions of human nature on the basis of data drawn from this particularly thin, and rather unusual, slice of humanity. We close by proposing ways to structurally re‐organize the behavioral sciences to best tackle these challenges.

Friction-induced vibration: Should low-order models be believed?

Much of the literature of friction-induced vibration focusses on highly simplified models that may include three or fewer modes to describe the independent subsystems. The degree to which these models approximate the behaviour of fuller models remains largely untested. This paper presents a systematic analysis of an example system to explore its convergence behaviour. First, the sensitivity to variations in contact parameters is considered, shedding light on the variability of experimental results. Second, the number of modes required for a ‘minimal’ model is explored. While three modes can often provide a reasonable local approximation to a more general model, the choice of which three is sometimes counter-intuitive. A method for automatic model reduction is proposed and found to be highly effective. The results challenge the general applicability of the oft-quoted two-degree-of-freedom model of ‘mode-coupling’, and also indicate some reasons for the difficulty encountered in validating models of friction-induced vibration.

Optimal Circular Block Designs for Neighbouring Competition Effects

Competition or interference occurs when the responses to treatments in experimental units are affected by the treatments in neighbouring units. This may contribute to variability in experimental results and lead to substantial losses in efficiency. The study of a competing situation needs designs in which the competing units appear in a predetermined pattern. This paper deals with optimality aspects of circular block designs for studying the competition among treatments applied to neighbouring experimental units. The model considered is a four-way classified model consisting of direct effect of the treatment applied to a particular plot, the effect of those treatments applied to the immediate left and right neighbouring units and the block effect. Conditions have been obtained for the block design to be universally optimal for estimating direct and neighbour effects. Some classes of balanced and strongly balanced complete block designs have been identified to be universally optimal for the estimation of direct, left and right neighbour effects and a list of universally optimal designs for v<20 and r<100 has been prepared.

Verification of uncertainty budgets

The quality of analytical results is expressed by their uncertainty, as it is estimated on the basis of an uncertainty budget; little effort is, however, often spent on ascertaining the quality of the uncertainty budget. The uncertainty budget is based on circumstantial or historical data, and therefore it is essential that the applicability of the overall uncertainty budget to actual measurement results be verified on the basis of current experimental data. This should be carried out by replicate analysis of samples taken in accordance with the definition of the measurand, but representing the full range of matrices and concentrations for which the budget is assumed to be valid. In this way the assumptions made in the uncertainty budget can be experimentally verified, both as regards sources of variability that are assumed negligible, and dominant uncertainty components. Agreement between observed and expected variability is tested by means of the T-test, which follows a chi-square distribution with a number of degrees of freedom determined by the number of replicates. Significant deviations between predicted and observed variability may be caused by a variety of effects, and examples will be presented; both underestimation and overestimation may occur, each leading to correcting the influence of uncertainty components according to their influence on the variability of experimental results. Some uncertainty components can be verified only with a very small number of degrees of freedom, because their influence requires samples taken at long intervals, e.g., the acquisition of a new calibrant. It is therefore recommended to include verification of the uncertainty budget in the continuous QA/QC monitoring; this will eventually lead to a test also for such rarely occurring effects.

Flow and transport in hierarchically fractured rock

We construct multiple realizations of hierarchical fracture networks with fractal dimensions between one and two, then simulate single-well pumping tests and natural-gradient tracer tests on them. We calculate averages and standard deviations of test results over the multiple realizations, and show individual results for selected cases to highlight key features of flow and transport through hierarchically fractured rock. These studies are intended to illustrate the range of possible behavior that can be obtained during fracture-dominated hydraulic and tracer tests, and provide insights into how to interpret field responses. The fractal dimension of the fracture network itself is generally larger than the fractal dimension of the flow field arising during a well test. The performance measures of the natural-gradient tracer tests, including the total flow through the fracture network, tracer travel time, front width, and maximum breakthrough concentration, can all be correlated to fractal dimension. Although some of the features observed in the flow and transport behavior within the hierarchically fractured rock have been observed by other authors using non-fractal fracture network concepts (e.g. channelized flow with early breakthrough times, crossing breakthrough curves), others arise directly from the fractal nature of the fracture network, in which variability occurs on all scales (e.g. front width and maximum breakthrough concentration that are constant over a wide range of fractal dimensions). Generally, transport simulations show large variability within a given realization and among realizations with the same fractal dimension, even in networks whose dimension is close to two. This finding is consistent with the large variability in experimental results observed at fractured rock field sites.

Different Role of the Histamine H 3 -Receptor in Vagal-, Betanechol-, Pentagastrin-induced Gastric Acid Secretion in Anaesthetized Rats

Background : To date, involvement of the histamine H 3 -receptor in the control of gastric acid secretion in rats is not conclusively defined because of the variability of experimental results. This study was therefore aimed at investigating the role of H 3 -receptors in acid secretion produced by nervous or pharmacological stimulation in anaesthetized rats. Methods : Gastric acid output was measured by flushing the rat stomach lumen with 5 ml saline and titrating the flushed perfusate. Hypersecretory responses were evoked through direct vagal stimulation (0.5 msec, 10 Hz, 50 V for 30 min every 30 min) or by stimulation with pentagastrin (20, 40, 100, 250 μg/kg/h i.v.) or betanechol (100, 250, 500 μg/kg/h i.v.). The selective H 3 ligands (R)- α -methylhistamine and thioperamide (100 μg/kg i.v.) were tested alone or in combination on both basal and electrically/pharmacologically induced secretion. Results : Vagally-induced response was significantly reduced by the agonist R- α -methylhistamine and this effect was antagonized by the antagonist thioperamide at a dose unable by itself to modify vagal response. Thioperamide significantly increased acid response only on pentagastrin low dose (20 μg/kg/h) and this effect was counteracted by R- α methylhistamine, which was ineffective when administered alone. Betanechol-induced hypersecretion was substantially unaffected by the H 3 ligands, which were also inactive on basal acid output. Conclusions : Although this functional study confirms the presence of histamine H 3 -receptors in the rat stomach, they appear to have minor weight in regulation of the acid secretion in this species.

Validation of a protocol for kinetic study of VFA removal under simulated conditions of landfill leachate treatment on anaerobic filter

An original experimental procedure was developed to investigate the kinetics of VFA biodegradation under simulated conditions of landfill leachate treatment on a laboratory-scale anaerobic filter. The procedure was designed to maintain stable biological conditions in the reactor throughout the study in order to avoid interference due to microbial growth or decay. Six series of experiments were performed over a period of several months, and the rates of biodegradation of acetate, propionate and butyrate were determined. The purpose of this paper is to validate the procedure by statistical calculations of experimental data. Computation of the data showed that the variability of experimental results was only related to experimental and analytical errors and that no significant changes in biological conditions occurred over at least 92 days. In addition, calculations of first-order kinetics showed that the determinations of the kinetic constants were very reproducible compared to analytical errors in VFA determinations. Finally, determinations of biomass concentrations by organic solids measurements confirmed that the experimental procedure allowed quasi steady and homogeneous biological conditions to be maintained in the experimental reactor over a period of 144 days.

Postoperative course after portacaval anastomosis in rats is determined by the portacaval pressure gradient

Variability in experimental results have led to criticism regarding the validity of the rat after portacaval anastomosis (PCA) as a model of changes induced by portal-systemic shunting (PSS). A nonsuture technique using cyanoacrylate glue has been reported to yield a better experimental preparation. To investigate if variations in splanchnic hemodynamics could explain different outcomes after the procedure, male rats received either an end-to-side PCA or sham operations (16 rats each). The PCA was constructed using the "suture" or "glue" technique (8 rats each). Beginning on postoperative day 24 under methoxyflurane and ketamine anesthesia, pressures were recorded from the portal vein, inferior vena cava, and femoral artery. Blood flow to the splanchnic organs and the percent PSS were assessed using the microsphere technique. The rate of delivery of NH3 from the portal vein to the systemic circulation and the concentration of glutamine in the cerebrospinal fluid were determined. In PCA rats, weight gain was significantly impaired, and all animals had evidence of liver atrophy (in both suture and glue groups) when compared with sham animals; a trend toward greater weight gain was seen in glue rats. Portal vein inflow, PSS, NH3 delivery, and CSF glutamine were significantly increased in both PCA-suture and PCA-glue animals compared with sham rats, although no significant differences were seen between the two PCA techniques. When PCA rats from either technique were grouped according to the pressure gradient between portal vein and inferior vena cava, striking differences between animals were now evident.(ABSTRACT TRUNCATED AT 250 WORDS)

Effectiveness of animal rotation in achieving uniform dust exposures and lung dust deposition in horizontal flow chambers.

An important source of variability of experimental results in inhalation toxicology originates from the nonuniformity of chamber concentrations. Two horizontal flow inhalation chambers were used in evaluating the effect of cage rotation within each chamber on the amount of alpha-quartz deposited in the lungs of male Fischer 344 rats. The alpha-quartz lung burden was determined by quantitative X-ray diffraction. A carefully designed animal rotation schedule significantly reduced the variability in the amount of alpha-quartz deposited in the animals, thereby minimizing effects of chamber nonuniformity due either to design or dust generator characteristics.

Human lymphocyte transformation induced by mitogens and antigens in a serum-free tissue culture system

The use of serum to supplement lymphocyte tissue culture media introduces uncontrolled variables; different serum sources, lots and concentrations can produce variability in experimental results, serum can stimulate or inhibit lymphocytes, and components of serum can react with substances whose effects on lymphocytes are being studied. To avoid these problems, we studied the ability of human peripheral mononuclear cells to survive and to respond to stimulation in an entirely synthetic medium, RPMI-1640 supplemented with L-glutamine, gentamicin, HEPES buffer and magnesium. Optical cell concentration in this serum-free RPMI-1640 was 2.5 × 10 6 cells/ml, whereas optimal cell concentration in serum containing RPMI-1640 was 1 × 10 6 cells/ml. In this serum-free RPMI-1640, 50% of the cellular input was recovered as viable cells after 7 days of culture, which was similar to results in serum containing RPMI-1640. Mononuclear cell transformation was induced by phytohemagglutinin, concanavalin A, pokeweed mitogen, streptolysin O and candida. Optimal doses of stimulants and the kinetics of the responses were similar in serum-free and serum containing RPMI-1640. This system can be used to avoid the problems inherent in systems which supplement tissue culture media with serum.