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PubMed1999

Competitive inhibition by inducer as a confounding factor in the use of the ethoxyresorufin-O-deethylase (EROD) assay to estimate exposure to dioxin-like compounds.

The ethoxyresorufin-O-deethylase (EROD) assay has been extensively used in whole animals and in cell culture as a biomarker of exposure to environmental contaminants such as dioxin-like compounds (DLCs). This paper addresses two controversial phenomena that arise when DLCs are examined by the EROD assay. Firstly, the maximum level of induced EROD activity varies with the identity of the inducing compound; secondly, the induced EROD activity reaches a concentration-dependent maximum level that is followed by an apparent reduction in activity when the concentration of inducer is further increased. These phenomena are completely explained by competitive inhibition of the EROD enzyme-substrate reaction by the dioxin-like compound. A kinetic model explains the biphasic appearance of EROD induction curves as a function of a compound's binding affinity with the Ah receptor (Kd) and its binding affinity to CYP 1A1 (Ki) which results in inhibition of the EROD enzyme-substrate reaction. These results limit the reliability of the information obtained from calibration curves of EROD activity versus concentration of a standard DLC such as 2,3,7,8-tetrachlorodibenzo-p-dioxin.

Animals↗

PubMed2003

A capillary electrophoresis method to study postmortem proteolysis in relation to pork tenderness.

Identification of factors that determine meat tenderness is of high priority. The aim of this work was to develop a method that can detect indicators of proteolysis in meat early postmortem. The method was validated on pork samples. A procedure to detect differences of extractable lower molecular weight compounds after a prerigor freeze/thaw cycle of meat was developed using capillary electrophoresis. The procedure was able to separate 39 peaks in the electropherograms. Eight of the peaks were correlated (P < 0.1) to Warner-Bratzler shear forces 1 day postmortem (WB1). A multiple linear regression model explained 69% of the variation in WB1 using the areas of four peaks. Several of the peaks used in modeling WB1 were related to the at-slaughter activity of the calpain system. The results presented show that the developed method is able to detect indicators of proteolysis and tenderness at an early time point after slaughter. The method is a new tool intended for studies regarding the mechanisms of postmortem proteolysis and tenderization.

Animals↗

PubMed2005

Infrared absorption spectrum of matrix-isolated noble-gas hydride molecules: fingerprints of specific interactions and hindered rotation.

Noble-gas hydride molecules with the general formula HNgY (Ng denotes noble-gas atom and Y denotes electronegative fragment) are usually prepared in solid noble gases. In many cases, the matrix-isolated HNgY molecules show a characteristic structure of the H-Ng stretching absorption: A close doublet as the main spectral feature and a weaker satellite at higher energy. This characteristic band structure is studied here for matrix-isolated HXeBr and HKrCl molecules. Based on the experimental and theoretical results, we suggest a model explaining the common features of the band structure of the HNgY molecules in noble-gas matrices. In this model, the main doublet bands are attributed to matrix sites where the splitting is caused by specific interactions of the embedded molecule with noble-gas matrix atoms in certain local morphology. The weaker blueshifted band is probably a fingerprint of hindered rotation (libration) of the embedded molecule in the lattice. This librational band has a mirror counterpart at lower energies appearing at higher matrix temperatures. Our present ab initio calculations for the one-to-one Xe...HXeBr complexes and the simulation of hindered rotation in a matrix support this image.

Journal Article↗

PubMed2000

Relationship between quality of life, social support and disease-related factors in HIV-infected persons in Venezuela.

This study examines the relationships among health-related quality of life (HRQL), social support, sociodemographic factors and disease-related factors in persons infected with the human immunodeficiency virus (HIV) living in Venezuela. A sample of 118 HIV-infected persons living in Caracas, Venezuela, was surveyed using a written questionnaire that included a Spanish translation of the Interpersonal Support Evaluation List (ISEL) developed for this study, the Medical Outcomes Study Short Form-36 (SF-36) and a symptom inventory. All three instruments showed good internal consistency reliability. Multiple regression analyses were used to model SF-36 sub-scale scores as a function of symptoms, social support, HIV-status and use of antiretroviral drugs. The models explained between 16 and 39% of the variance in the different HRQL domains. Controlling for other variables in the model, level of symptomatology was significantly associated with all HRQL domains except social functioning and role-emotional scores. Social support was significantly associated with all HRQL domains except physical functioning and bodily pain. The use of antiretroviral drugs was significantly associated with social functioning. The study indicates the importance of social support to the quality of life of HIV-infected individuals in this culture.

Adult↗

PubMed2006

An NMR relaxometry and gravimetric study of gelatin-free aqueous polyacrylamide dosimeters.

In conformal radiation therapy, a high dose of radiation is given to a target volume to increase the probability of cure, and care is taken to minimize the dose to surrounding healthy tissue. The techniques used to achieve this are very complicated and the precise verification of the resulting three-dimensional (3D) dose distribution is required. Polyacrylamide gelatin (PAG) dosimeters with magnetic resonance imaging and optical computed tomography scanning provide the required 3D dosimetry with high spatial resolution. Many basic studies have characterized these chemical dosimeters that polymerize under irradiation. However, the investigation of the fundamental properties of the radiation-induced polymerization in PAG dosimeters is complicated by the presence of the background gelatin matrix. In this work, a gelatin-free model system for the study of the basic radiation-induced polymerization in PAG dosimeters has been developed. Experiments were performed on gelatin-free dosimeters, named aqueous polyacrylamide (APA) dosimeters, containing equal amounts of acrylamide and N,N'-methylene-bisacrylamide. The APA dosimeters were prepared with four different total monomer concentrations (2, 4, 6 and 8% by weight). Nuclear magnetic resonance (NMR) spin-spin and spin-lattice proton relaxation measurements at 20 MHz, and gravimetric analyses performed on all four dosimeters, show a continuous degree of polymerization over the dose range of 0-25 Gy. The developed NMR model explains the relationship observed between the relaxation data and the amount of crosslinked polymer formed at each dose. This model can be extended with gelatin relaxation data to provide a fundamental understanding of radiation-induced polymerization in the conventional PAG dosimeters.

Acrylamides↗

PubMed1995

Testing the covarion hypothesis of molecular evolution.

The covarion hypothesis of molecular evolution states that the fixation of mutations may alter the probability that any given position will fix the next change. Tests of this hypothesis using the divergence of real sequences are compromised because models of rate variation among sites (e.g., the gamma version of the one-parameter equation) predict sequence divergence values similar to those for the covarion process. This study therefore focuses on the extent to which the varied and unvaried codons of two well-diverged taxa are the same, because fewer are expected by the covarion hypothesis than by the gamma model. The data for these tests are the protein sequences of Cu, Zn superoxide dismutase (SOD) for mammals and plants. Simulation analyses show that the covarion hypothesis makes better predictions about the frequencies of varied and unhit positions in common between these two taxa than does the gamma version of the one-parameter model. Furthermore, the analysis of SOD tertiary structure demonstrates that mammal and plant variabilities are distributed differently on the protein. These results support the conclusions that the variable and invariable codons of mammal and plant SODs are different and that the covarion model explains the evolution of this protein better than the gamma version of the one-parameter process. Unlike other models, the covarion hypothesis accounts for rate fluctuations among positions over time, which is an important parameter of molecular evolution.

Animals↗

PubMed2004

Component carbon fluxes and their contribution to ecosystem carbon exchange in a pine forest: an assessment based on eddy covariance measurements and an integrated model.

We used a combination of eddy flux, canopy, soil and environmental measurements with an integrated biophysical model to analyze the seasonality of component carbon (C) fluxes and their contribution to ecosystem C exchange in a 50-year-old Scots pine forest (Pinus sylvestris L.) in eastern Finland (62 degrees 47' N, 30 degrees 58' E) over three climatically contrasting years (2000-2002). Eddy flux measurements showed that the growing Scots pine forest was a sink for CO2, with annual net C uptakes of 131, 210 and 258 g C m-2> year-1 in 2000, 2001 and 2002, respectively. The integrated process model reproduced the annual course of daily C flux above the forest canopy as measured by the eddy covariance method once the site-specific component parameters were estimated. The model explained 72, 66 and 68% of the variation in daily net C flux in 2000, 2001 and 2002, respectively. Modeled annual C loss by respiration was 565, 629 and 640 g C m-2 year-1, accounting for 77, 77 and 65% of annual gross C uptake, respectively. Carbon fluxes from the forest floor were the dominant contributors to forest ecosystem respiration, with the fractions of annual respiration from the forest floor, foliage and wood being 46-62, 27-44 and 9-10%, respectively. The wide range in daily net C uptake during the growing season was largely attributable to day-to-day fluctuations in incident quantum irradiance. During just a few days in early spring and late autumn, ecosystem net C exchange varied between source and sink as a result of large daily changes in temperature. The forest showed a greater reduction in gross C uptake by photosynthesis than in C loss by respiration during the dry summer of 2000, indicating that interannual variability in ecosystem net C uptake at this site was modified mostly by summer rainfall and vapor pressure deficit.

Carbon↗

PubMed1999

[Therapeutic intervention in infantile autism and generalized developmental disorders: self-injury and self-stimulation].

INTRODUCTION: In this article we present a review of the aetiology and treatment of self-injury and self-stimulation in infantile autism and in generalized development disorders. We summarize 20 years of study and investigation in the treatment of these serious behaviour disorders, in a pioneer institution in Spain: the centre for rehabilitation 'El Cau' in Castellon. DEVELOPMENT: We describe the most frequent behaviour disorders, with particular reference to self-injury and self-stimulatory behaviour. Models explaining the aetiology and treatment are described in a brief general review of the subject, and we consider explicative models which integrate different treatments (in family and institutional contexts) by means of family therapy, psychoeducational models and social support networks.

Autistic Disorder↗

PubMed1994

Explaining attitudes toward medication compliance among a seriously mentally ill population.

Data from a clinical trial of consumer-delivered case management services were used to construct an explanatory model for attitudes toward medication compliance, focusing on psychosocial factors. A regression model explaining attitudes toward medication compliance shows that more positive attitudes toward compliance are related to older age, fewer symptoms, and a broader array of daily activities involving social relations. Participation in social activities is a practical goal of psychosocial rehabilitation services that support compliance with medication regimens and psychiatric treatment.

Activities of Daily Living↗

PubMed1999

[ANS fluorescence. II. Use of the method of fluorescent probe decay for studying the structural transformations in globular proteins].

Changes in ANS fluorescence decay parameters induced by the interaction of the probe with proteins have been investigated. The existence of at least two different modes of interactions between the ANS and protein was established. The interactions of the first type are connected with binding of an ANS molecule with the surface of a protein molecule. In this case ANS molecules are well acceptable for a solvent. The interactions of the second type are characteristic of the protein-embedded ANS molecules. The decay time values of the second type complexes change considerably (> 1.5-fold) during the protein molecule transformation into the molten globule-like conformation. The molecular model explaining such a behaviour is suggested.

Anilino Naphthalenesulfonates↗

PubMed1996

A model for the effect of cigarette smoking on lung cancer incidence in Connecticut.

Population based data on smoking history derived from NCHS surveys were used to develop a model for lung cancer incidence in Connecticut. Trends in smoking prevalence suggest that, while the prevalence in men increased earlier than women, more male smokers have quit than their female counterparts. These trends in smoking prevalence suggest striking gender differences in a period effect for the smoking prevalence. Estimates of the proportion of current smokers, ex-smokers, and the mean duration of smoking were used in a model for the lung cancer incidence rates. The form for the relationship between smoking history and the incidence rate for these subgroups was based on information from cohort studies. The models represented a mixture of the smoking subgroups where the effect of smoking was considered to be either a multiplicative effect on the underlying age distribution, or a separate effect in which the level of exposure was the sole contribution to risk among smokers. The multiplicative model explained more than 80 per cent of the deviance for the period and cohort effects, while the non-multiplicative model could only account for trends in females. Hence, these results suggest that a sizeable portion of the period and cohort contributions to the lung cancer incidence trends in Connecticut can be attributed to the multiplicative model that utilizes this smoking information, although the lack of more detailed information is a limiting factor in developing the model.

Adult↗

PubMed2005

Belief-desire reasoning as a process of selection.

Human learning may depend upon domain specialized mechanisms. A plausible example is rapid, early learning about the thoughts and feelings of other people. A major achievement in this domain, at about age four in the typically developing child, is the ability to solve problems in which the child attributes false beliefs to other people and predicts their actions. The main focus of theorizing has been why 3-year-olds fail, and only recently have there been any models of how success is achieved in false-belief tasks. Leslie and Polizzi (Inhibitory processing in the false-belief task: Two conjectures. Developmental Science, 1, 247-254, 1998) proposed two competing models of success, which are the focus of the current paper. The models assume that belief-desire reasoning is a process which selects a content for an agent's belief and an action for the agent's desire. In false belief tasks, the theory of mind mechanism (ToMM) provides plausible candidate belief contents, among which will be a 'true-belief.' A second process reviews these candidates and by default will select the true-belief content for attribution. To succeed in a false-belief task, the default content must be inhibited so that attention shifts to another candidate belief. In traditional false-belief tasks, the protagonist's desire is to approach an object. Here we make use of tasks in which the protagonist has a desire to avoid an object, about which she has a false-belief. Children find such tasks much more difficult than traditional tasks. Our models explain the additional difficulty by assuming that predicting action from an avoidance desire also requires an inhibition. The two processing models differ in the way that belief and desire inhibitory processes combine to achieve successful action prediction. In six experiments we obtain evidence favoring one model, in which parallel inhibitory processes cancel out, over the other model, in which serial inhibitions force attention to a previously inhibited location. These results are discussed in terms of a set of simple proposals for the modus operandi of a domain specific learning mechanism. The learning mechanism is in part modular--the ToMM--and in part penetrable--the Selection Processor (SP). We show how ToMM-SP can account both for competence and for successful and unsuccessful performance on a wide range of belief-desire tasks across the preschool period. Together, ToMM and SP attend to and learn about mental states.

Choice Behavior↗

PubMed2005

Dispersion of alumina-coated TiO2 slurries in the presence of poly(acrylic) acid influence of monovalent counterions.

The rheological behavior of concentrated alumina-coated TiO2 slurries has been investigated in connection with the type of surface counterions (monovalent cations: X = Li+, Na+, TMA+) in the absence and in the presence of polyacrylic acid (PAA). The study has been conducted in a pH range of 4-10 and with ionic strengths lower than 0.01 M. The pH and ionic strength were adjusted with XOH and XCl, respectively. The surface properties have been investigated by titration of surface counterions and the apparent yield stress has been measured using a dynamic stress rheometer. It appears from the results that the pH at the maximum yield stress and the magnitude of the yield stress depend on the nature of the counterion. The yield stress measurements were also conducted in the presence of PAA (0.5 segment/nm2) adsorbed on the particle surface. In that case, the mineral surface and adsorbed polymer were neutralized with XOH. The results show that the dispersion efficiency depends on the polymer counterion. In general, it is found that the maximum yield stress and the corresponding counterion surface density both follow the sequence TMA+ < Na+ < Li+. The adsorption of PAA apparently amplifies the effects observed with the corresponding cation. An electrostriction effect of the hydration layer at the interface is suggested in order to explain the increasing yield stress as the surface density of Li+ increases. The so-called structure-making/structure-breaking model explains the yield stress reduction with the TMA+ surface density.

Journal Article↗

PubMed2004

Estimating influenza-related hospital admissions in older people from GP consultation data.

UNLABELLED: This study seeks to determine the association between general practice (GP) consultations for influenza-like illness (ILI) and hospital admissions, and to estimate the number of excess hospitalisation due to ILI epidemics, for two age-groups: 51-65 years and >65 years. METHODS: Structural time series models (STSM) with stochastic trend and seasonal components were developed. Weekly data from Switzerland for 1987 to 1996/1997 were used. Hospital admission rates for pneumonia and influenza (P&I) and other respiratory conditions (ORC) were regressed against GP consultation rates. Excess hospitalisations were calculated as the difference between predicted hospital admissions during influenza epidemics and predicted hospital admissions using a baseline GP consultation rate. RESULTS: Excess admission rates were substantially higher in the oldest age-group (51-65 years: P&I 4.42, ORC 2.14; >65 years: P&I 6.30, ORC 4.74 per 10,000 population per year). The models explained between 43 and 76% of the variation in hospital admissions. The seasonal patterns were stable over the 10 years modelled and the variances of the trends were small.

Age Factors↗

PubMed1995

Planning reaches by evaluating stored postures.

This article describes a theory of the computations underlying the selection of coordinated motion patterns, especially in reaching tasks. The central idea is that when a spatial target is selected as an object to be reached, stored postures are evaluated for the contributions they can make to the task. Weights are assigned to the stored postures, and a single target posture is found by taking a weighted sum of the stored postures. Movement is achieved by reducing the distance between the starting angle and target angle of each joint. The model explains compensation for reduced joint mobility, tool use, practice effects, performance errors, and aspects of movement kinematics. Extensions of the model can account for anticipation and coarticulation effects, movement through via points, and hierarchical control of series of movements.

Biomechanical Phenomena↗

PubMed2006

Rank clocks.

Many objects and events, such as cities, firms and internet hubs, scale with size in the upper tails of their distributions. Despite intense interest in using power laws to characterize such distributions, most analyses have been concerned with observations at a single instant of time, with little analysis of objects or events that change in size through time (notwithstanding some significant exceptions). It is now clear that the evident macro-stability in such distributions at different times can mask a volatile and often turbulent micro-dynamics, in which objects can change their position or rank-order rapidly while their aggregate distribution appears quite stable. Here I introduce a graphical representation termed the 'rank clock' to examine such dynamics for three distributions: the size of cities in the US from ad 1790, the UK from ad 1901 and the world from 430 bc. Our results destroy any notion that rank-size scaling is universal: at the micro-level, these clocks show cities and civilizations rising and falling in size at many times and on many scales. The conventional model explaining such scaling on the basis of growth by proportionate effect cannot replicate these micro-dynamics, suggesting that such models and explanations are considerably less general than has hitherto been assumed.

Journal Article↗

PubMed1987

A model for the separation of large DNA molecules by crossed field gel electrophoresis.

The idea that large DNA molecules adopt a stretched conformation as they pass through gels suggests a simple mechanism for the separation of DNA by crossed field electrophoresis: at each change in field direction a DNA molecule takes off in the new direction of the field by a movement which is led by what was formerly its back end. The effect of this ratcheting motion is to subtract from the DNA molecule's forward movement, at each step, an amount which is proportional to its length. We find that this model explains most of the features of the separation, and we describe experiments, using a novel electrophoresis apparatus, which support the model. The apparatus turns the gel between two preset orientations in a uniform electric field at preset time intervals. This separation method has the practical advantage over some others that the DNA molecules follow straight tracks. A further advantage is that the parameters which determine the separation are readily predicted from the simple theory describing their motion.

DNA↗

PubMedDate not supplied

The effect of fear of movement on muscle activation in posttraumatic neck pain disability.

Studies using surface electromyography have demonstrated a reorganization of muscle activation patterns of the neck and shoulder muscles in patients with posttraumatic neck pain disability. The neurophysiologically oriented "pain adaptation" model explains this reorganization as a useful adaptation to prevent further pain and injury. The cognitive-behavioral-oriented "fear avoidance" model suggests that fear of movement, in addition to the effects of pain, modulates the muscle activation level. We analyzed the extent to which pain and fear of movement influenced the activation patterns of the upper trapezius muscle during the transition from acute to chronic posttraumatic neck pain. Ninety-two people with an acute traumatic neck injury after a motor vehicle accident were followed up for 24 weeks. Visual analog scale ratings of pain intensity, response on the Tampa Scale of Kinesophobia--fear of movement, and surface electromyography of the upper trapezius muscles during a submaximal isometric physical task were obtained at 1, 4, 8, 12, and 24 weeks after the motor vehicle accident. Multilevel analysis revealed that an increased level of both fear of movement (t value=-2.19, P=0.030) and pain intensity (t value=-2.94, P=0.004) were independently associated with a decreased level of muscle activation. Moreover, the results suggest that the association between fear of movement and lower muscle activity level is stronger in patients reporting high pain intensity (t value=2.15, P=0.033). The contribution of pain intensity to the muscle activation level appeared to decrease over time after the trauma (t value=2.58, P=0.011). The results support both the "pain adaptation" and the "fear avoidance" models. It is likely that the decrease in muscle activation level is aimed at "avoiding" the use of painful muscles.

Accidents, Traffic↗