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Results for “Model interpretability”

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At least 937 records · Page 52Linked to original sources

PubMed1984

Searching-waiting strategy: a candidate for an evolutionary model of depression?

The model proposed here assumes that depressive disorders could reflect an extreme state of a current behavioral strategy. According to this model, a subject facing a problem of survival without apparent solution may choose between two behavioral patterns: searching for a solution or waiting for that solution to occur. This choice can be made after one or several estimations of the cost and benefit attached to each of these alternatives. Two of the main behavioral models of depression are interpreted according to this model: namely, infant response to maternal separation in monkeys and "behavioral despair" in rodents. Practical and theoretical consequences of this model are discussed.

Adaptation, Biological↗

PubMed1998

Component wave analysis of flash visual evoked potentials in preterm infants.

Waveform analyses of flash visual evoked potentials (VEPs) in neurologically normal preterm infants (postconceptional age 31-42 weeks) were performed using an autoregressive moving average (ARMA) model to interpret the evoked potentials as dynamic high-order responses to natural and experimental stimulation. Averaged VEP waveforms obtained were decomposed into 7-11 component impulse response waveforms by an ARMA component wave analysis. Based on the histogram of damping frequencies of different component impulse response waveforms, the waveforms were divided into 6 groups. All characteristic values in Group IV (6.5-12.0 Hz), such as the energy, the percent energy and the damping time of component impulse responses, changed significantly with increasing postconceptional age. Among the component impulse responses, neuronal networks generating impulse responses classified into Group IV appeared to be important to the developmental change of VEPs in preterm infants. The identification of an impulse response component with a dominant frequency which undergoes a well-identified change with age might prove to be a useful tool for discriminating between normal and abnormal changes in the VEP with age in preterm infants and could aid in the early diagnosis of abnormalities.

Child Development↗

PubMed2003

Hepatic artery malformations associated with a primary defect in intrahepatic bile duct development.

BACKGROUND/AIMS: The portal tracts contain bile ducts associated with branches of the portal vein and of the hepatic artery. Hepatic artery malformations are found in diseases in which fetal biliary structures persist after birth (ductal plate malformations). Here we investigated how hepatic artery malformations relate to abnormal bile duct development. METHODS: Hepatic artery and biliary development was analyzed in fetuses with Jeune syndrome or Meckel syndrome, which show ductal plate malformations. We also analyzed hepatic artery development in transgenic mice which exhibit biliary anomalies following inactivation of the genes for hepatocyte nuclear factor (HNF)-6 or HNF-1beta, two transcription factors expressed in biliary cells, but not in arteries. RESULTS: We show that arterial anomalies occurred in fetuses with Jeune syndrome or Meckel syndrome. We provide the first description of hepatic artery branch development in the mouse and show that inactivation of the Hnf6 or Hnf1beta gene results in anomalies of the hepatic artery branches. In the transgenic mice and in the human syndromes, the biliary anomalies preceded the arterial anomalies. CONCLUSIONS: A primary defect in biliary epithelial cells is associated with hepatic artery malformations in mice. Our data provide a model to interpret and study hepatic artery anomalies in humans.

Abnormalities, Multiple↗

PubMed2003

Sorption of selenium anionic species on apatites and iron oxides from aqueous solutions.

The sorption of selenite and selenate ions from aqueous solutions was investigated on hydroxyapatite, fluorapatite, goethite and hematite, in order to simulate the behavior of radioactive selenium in natural or artificial sorbing media. Correlation studies with acido-basic properties and solubility of the solids were also performed. The sorption is pH dependant, but these solids are very efficient for retaining selenite at pH values generally encountered in natural waters, with however higher K(d) values for oxides than apatites. Selenate ions are much less sorbed than selenite. Several methods such as electron microscopy and spectroscopic techniques were used to identify the sorption mechanisms. In the case of hydroxyapatite, sorption proceeds by substitution of phosphate groups in the lattice of the apatite crystal in the superficial layers of the solid. In the case of goethite and hematite, sorption can be interpreted and modeled by a surface complexation process, but there is a discrepancy between sorption site densities for selenite and for protons.

Adsorption↗

PubMed2001

Forecasting habitat suitability for ticks and prevention of tick-borne diseases.

Climate and vegetation are the major factors affecting the distribution of ticks. Consequently, spatial distributions can be analysed by statistical methods that look for correlations between abiotic factors and known data about tick presence/absence. Remote sensing features can be obtained from a wide database of sensors with different characteristics, then applied to the problem of mapping prediction of tick distribution. Some studies had demonstrated that the use of these abiotic variables from satellite imagery has biological significance, therefore statistical accuracy of these distribution models can be interpreted under an ecological framework. Furthermore, models can be linked to these predictive maps, enabling the forecast of spatial and temporal dynamics of ticks, looking for seasonal patterns of activity and accurate use of acaricide treatments.

Animals↗

PubMed1997

Applying radiobiological principles to combined modality treatment of head and neck cancer--the time factor.

PURPOSE: Combined modality treatment is indicated for most advanced stage head and neck cancers. It is postulated that the efficacy of combined modality regimens could be enhanced by applying principles derived from radiotherapy fractionation studies to optimize the time factor in treatment scheduling. METHODS AND MATERIALS: The premise that tumor clonogens surviving a therapeutic intervention undergo accelerated repopulation in a time-dependent fashion as their numbers are depleted is used as a model to interpret the results of various chemoradiotherapy and postsurgical radiotherapy protocols and to suggest ways in which future combined modality regimens can be more rationally designed. RESULTS: Meta-analyses of chemoradiotherapy trials show the general superiority of concomitant vs. neoadjuvant sequential protocols. There is also emerging evidence that both the duration of postoperative radiotherapy and the delay in its instigation affect treatment outcome. These results are compatible with the hypothesis that the overall duration of the "package deal" of combined modality treatment is an important determinant of outcome. However, a large decrease in duration of the "package deal" does not necessarily translate into a therapeutic gain because the total dose has to be lowered to prevent intolerable acute reactions. In these circumstances tumor control will improve only if the reduced treatment time circumvents more tumor cell regeneration than the cytoreduction that could be achieved by the extra dose tolerable in a longer time period. More modest reductions in treatment time can be accomplished without dose reduction and so avoid this risk. The design of new protocols should take account of the fact that regeneration of tumor clonogens can be predicted to be nonuniform with time. Thus, the greatest therapeutic gain should be achieved by targeting periods of maximal regenerative capacity for shortening or, alternatively, for intensification of treatment. These periods are the latter part of a course of radiotherapy or chemotherapy and the early postoperative phase after surgery. CONCLUSIONS: The rational design of combined modality protocols should include principles concerning the time factor derived from radiotherapy fractionation studies. Periods of maximal tumor cell regeneration should be targeted for shortening or for treatment intensification. Any dose sacrifice necessitated by reducing treatment duration must be less than the dose equivalent of regeneration during the same time period.

Cell Division↗

PubMed2000

Long-distance transport, storage and recall of morphogenetic information in plants. The existence of a sort of primitive plant 'memory'.

An asymmetrical treatment of Bidens seedlings (pricking one of the seedling cotyledons) causes the cotyledonary buds to grow asymmetrically after release of apical dominance by decapitation of the seedlings. The symmetry-breaking signal propagates within the seedlings at a rate of at least a fraction of a millimetre per second. This information may be 'stored' (STO function) within the seedlings, without taking effect, for at least 2 weeks; then the information may be 'recalled' (RCL function), thus permitting transduction of the signal into the final response (differential growth of the buds), as a consequence of subjecting the seedlings to various symmetrical or asymmetrical treatments. A similar behaviour was observed with stimuli other than pricking (including non-traumatic stimuli), with plants other than Bidens (flax, tomato), and with responses other than cotyledonary-bud growth (hypocotyl elongation, induction of meristems, thigmomorphogenesis). There are indications that storage may involve the activation of elements implicated in cell cycle control, and that the last steps of the final response involve genes such as tch1 and hsp70. The adaptive advantage for plants in possessing STO/RCL functions is discussed. Manipulating the STO/RCL functions may have interesting practical applications, e.g. in the resistance of plants to natural stresses. The existence of the STO/RCL functions in plants constitutes an elementary form of 'memory' which may provide an experimental system simpler than the animal brain to test the validity of the theoretical models of interpretation of important features such as memory storage and evocation.

Environment↗

PubMed2000

Electron microscopy of life-tested semiconductor laser diodes

Electron Microscopy on life-tested 980 nm SL SQW InGaAs/AlGaAs laser diodes is able to find and analyze lattice defects responsible for the detected failures. Anyway, the origin and evolution of those defects remains questionable. Only the comparative analysis of life-test measurements, EBIC-FIB/TEM images, and charge-transport physics is able to point out a coherent framework for complete decoding of the failure kinetics. Minority-carrier diffusion and their enhanced recombination at defective lattice points are indicated, as the energy supply required for defect reaction and growth. The rules of charge diffusion drive both the reaction model, the interpretation of EBIC images and the expected electrical and optical effects. Strain release at the ultimate propagation of defects into the strained InGaAs quantum layer is then easily related to the final state of the failed devices.

Journal Article↗

PubMed1998

The politics of methodology in 'post-medical geography': mental health research and the interview.

This paper argues that emerging 'post-medical geographies' require attention to the methodological in order to fully appreciate how different geographical knowledges are produced and contextualized within the politics of research relationships. 'Geographies of mental health and illness' are focused upon in order to argue that the 'peopling' of health research should also be accompanied by debate about what sorts of methodologies we employ in accessing these minds/bodies and voices. The research interview is a primary focus here. A critique of psychoanalytic approaches to geographical research argues that such 'models' of interpretation and management can mean that participants or research 'subjects' can be framed in almost diagnostic categories of behaviour. Empirical examples of mental health research in Nottingham are used to argue that more flexible approaches which pay attention to perceived dualisms (such as 'sanity' and 'insanity'), negotiation, embodiment, socio-spatial contexts and content within the interview situation may aid in understanding the politics which encompass geographical health research.

Bias↗

PubMed1999

Ionizing radiation-induced mutagenesis: radiation studies in Neurospora predictive for results in mammalian cells.

Ionizing radiation was the first mutagen discovered and was used to develop the first mutagenicity assay. In the ensuing 70+ years, ionizing radiation became a fundamental tool in understanding mutagenesis and is still a subject of intensive research. Frederick de Serres et al. developed and used the Neurospora crassa ad-3 system initially to explore the mutagenic effects of ionizing radiation. Using this system, de Serres et al. demonstrated the dependence of the frequency and spectra of mutations induced by ionizing radiation on the dose, dose rate, radiation quality, repair capabilities of the cells, and the target gene employed. This work in Neurospora predicted the subsequent observations of the mutagenic effects of ionizing radiation in mammalian cells. Modeled originally on the mouse specific-locus system developed by William L. Russell, the N. crassa ad-3 system developed by de Serres has itself served as a model for interpreting the results in subsequent systems in mammalian cells. This review describes the primary findings on the nature of ionizing radiation-induced mutagenesis in the N. crassa ad-3 system and the parallel observations made years later in mammalian cells.

Animals↗

PubMed2000

Lasting auditory attention impairment after persistent middle ear infections: a dichotic listening study.

Dichotic listening performance was studied in children who at an early age had undergone a myringotomy with insertion of ventilating tubes for persistent middle ear infections (otitis media with effusion; OME) and compared with age-equivalent children who had no history of otitis media or hearing problems. The OME group consisted of 19 children with a median age of 9 years; 15 of whom were right-handed, and 14 were boys. The comparison sample comprised 18 children with a median age was 9 years 4 months. Hand preference and sex were matched with the OME group. Both groups were tested with dichotic listening to consonant-vowel syllables and additional forced-attention tasks. The comparison sample showed a weak right-ear advantage, and age-adequate attentional modulations. The children in the OME group showed a strong right-ear advantage, but were not able to modulate the ear advantage during directed-attention tasks. Models for interpreting the result are discussed.

Attention↗

PubMed2006

Interpreting serological surveys using mixture models: the seroepidemiology of measles, mumps and rubella in England and Wales at the beginning of the 21st century.

A mixture modelling technique is applied to age-specific frequency distributions of quantitative results from serological surveys for measles, mumps and rubella using samples collected across the age range in England and Wales in 2000. In accordance with previous studies the analysis suggests that the antibody response to natural infection is stronger than that produced by vaccination, that vaccine-induced antibody levels wane with time and that levels of vaccine-induced antibody response vary for each virus infection being strongest for rubella and weakest for mumps. The current mumps epidemic in the United Kingdom is focused in cohorts born during 1982-1987 who were too old to have received routine MMR vaccination. In the cohort born in 1981-1985 the model estimates that 7.5% have no evidence of mumps specific IgG and 24.9% have the lowest level of detectable antibody. The similar proportions of mumps antibody in these categories among cohorts with opportunity for 1 or 2 doses of vaccine is a concern, as the degree to which these individuals are protected is unclear. Investigations into the efficacy of two doses of a mumps containing vaccine should be a priority during the current epidemic.

Antibodies, Viral↗

PubMed2004

Simultaneous surface plasmon resonance and quartz crystal microbalance with dissipation monitoring measurements of biomolecular adsorption events involving structural transformations and variations in coupled water.

Simultaneous quartz crystal microbalance with dissipation monitoring (QCM-D) and surface plasmon resonance (SPR) measurements are used to analyze the surface kinetics of two biomacromolecular systems, one lipid and one protein based, undergoing surface-induced conformational changes. First we establish a theoretical platform, which allows quantitative analysis of the combined SPR and QCM-D data. With this theoretical base, new information can be extracted, not obtainable with either technique alone. As an example we demonstrate how time-resolved measurements with these two techniques in combination--yielding three independent measured quantities--add new information about (i) kinetics, i.e. number of adsorbed molecules per unit area versus time, and (ii) temporal variation in the mass fraction of coupled water versus coverage. In particular, it is demonstrated for the first time, how the kinetics of the process during which adsorbed vesicles are spontaneously transformed into a supported phospholipid bilayer (SPB) on SiO(2) can be quantitatively separated into its two dominating states: adsorbed vesicles and supported planar bilayer patches. In addition, the relevance of dynamically coupled water for interpretation and modeling of the QCM-D response during bilayer formation is discussed and further illustrated with a second model system: streptavidin adsorption on a biotin-modified SPB. A very strong coverage dependence in the number of water molecules per protein sensed by the QCM is demonstrated, with strong implications for the use of QCM as a tool for quantitative determination of protein mass uptake kinetics.

Adsorption↗

PubMed1997

Laser temperature jump study of the helix<==>coil kinetics of an alanine peptide interpreted with a 'kinetic zipper' model.

The kinetics of the helix<==>coil transition of an alanine-based peptide following a laser-induced temperature jump were monitored by the fluorescence of an N-terminal probe, 4-(methylamino)benzoic acid (MABA). This probe forms a peptide hydrogen bond to the helix backbone, which changes its fluorescence quantum yield. The MABA fluorescence intensity decreases in a single exponential relaxation, with relaxation times that are weakly temperature dependent, exhibiting a maximum value of approximately 20 ns near the midpoint of the melting transition. We have developed a new model, the kinetic version of the equilibrium 'zipper' model for helix<==>coil transitions to explain these results. In this 'kinetic zipper' model, an enormous reduction in the number of possible species results from the assumption that each molecule contains either no helical residues or a single contiguous region of helix (the single-sequence approximation). The decay of the fraction of N-terminal residues that are helical, calculated from numerical solutions of the kinetic equations which describe the model, can be approximately described by two exponential relaxations having comparable amplitudes. The shorter relaxation time results from rapid unzipping (and zipping) of the helix ends in response to the temperature jump, while the longer relaxation time results from equilibration of helix-containing and non-helix-containing structures by passage over the nucleation free energy barrier. The decay of the average helix content is dominated by the slower process. The model therefore explains the experimental observation that relaxation for the N-terminal fluorescent probe is approximately 8-fold faster than that for the infrared probe of Williams et al. [(1996) Biochemistry 35, 691-697], which measures the average helix content, but does not account for the absence of observable amplitude for the slow relaxation in the fluorescence experiments (<10% slow phase). If we assume that the activation barrier for the coil-->helix rate is purely entropic, the model can also explain the maximum in the temperature dependence of the relaxation time for the fluorescent probe. Parameters that best reproduce the melting curves and the ratio of relaxation times predict a value of the cooperativity parameter sigma which is approximately 3-fold larger than previously reported values obtained from fitting equilibrium data only. The helix growth rate of approximately 10(8) s-1 that reproduces the experimental relaxation times is approximately 100-fold slower than those observed in molecular dynamics simulations. These parameters can be used to simulate the kinetically cooperative formation of a helix from the all-coil state.

Alanine↗

PubMed2007

Formation of polysaccharide gel layers in the presence of Ca2+ and K+ ions: measurements and mechanisms.

Understanding the adsorption properties of polysaccharides in terms of substrate affinity, kinetics, and layer structure is of paramount importance in numerous industrial and natural systems. The structural growth of the layers of two model polysaccharides--sodium alginate and polygalacturonic acid (PGA)--was characterized by quartz crystal microbalance with dissipation and atomic force microscopy. Monitoring the variations in frequency and dissipation energy provides insights into both the average adsorbed mass and the viscoelastic properties of the adsorbed layer of polyelectrolytes along with the associated ions and water molecules. Both polysaccharides had similar adsorption patterns with increasing ionic strengths and showed significant complexation of calcium ions. In the presence of calcium, the alginate gel layer exhibited significant swelling with an increasing concentration of monovalent salt that the PGA gel layer did not manifest. Basing our discussion on the "egg-box model", we interpreted these different swelling behaviors as resulting from differences in the complexation modes of the two polysaccharides. The dimerization of the polymers by cross-linking and the weaker dimer-dimer associations play major roles in the sensitivity of the polysaccharide gel matrix to high salt concentration environments.

Adsorption↗

PubMed2003

Influence of organic complexation on the adsorption kinetics of nickel in river waters.

The kinetics of Ni adsorption in rivers of widely different chemical characteristics have been studied by monitoring the uptake of 63Ni by suspended sediment particles. The rate and extent of adsorption was critically dependent on the presence and concentration of dissolved organic matter (DOM), defined analytically as the concentration of dissolved organic carbon (DOC). Thus, adsorption was greatest in experiments in which the DOM was decomposed by UV-oxidation and least in experiments in which Ni was preequilibrated with filtered river water before addition of particles. The extent of adsorption arising from the latter approach displayed a clear, inverse dependency on the concentration of DOC in the sample. These observations were interpreted and modeled in terms of the competing effects of DOM and particle sorption sites for dissolved Ni. Adsorption onto suspended particles in the absence of dissolved complexing ligands was adequately described by a reversible, two-stage reaction and a single set of adsorption rate constants. Forward and reverse rate constants defining Ni complexation with DOM of about 8 x 10(4) h(-1) M(-1) and 10 h(-1), respectively, were derived from data-fitting. The experimental and model results indicate that the toxicity, availability, and transport of Ni in freshwater environments are largely dictated by the concentration of DOM and the speciation of Ni entering the watercourse.

Adsorption↗

PubMed2005

Characterization of the PCB substrate range of microbial dechlorination process LP.

We have characterized the substrate range of Process LP, a PCB dechlorination activity mediated by anaerobic bacteria, in Housatonic River sediment (Lenox, MA). Process LP has the rare ability to remove unflanked para chlorines from polychlorinated biphenyls (PCBs). We used 2,6-difluoro-4-chlorobiphenyl (DFCB) to activate Process LP in anoxic sediment microcosms and tested its ability to dechlorinate 34 potential PCB substrates, all of which are significant components of PCB mixtures found in contaminated sediments. We used gas chromatography-mass spectrometry to monitor the dechlorination of DFCB and PCBs and the appearance of products. The preferred substrates for Process LP were PCB congeners in which the target para chlorines were flanked by meta chlorines, such as those having 3,4- and 2,4,5-chlorophenyl rings. The unflanked para chlorines on PCBs with 2,4-, 2,4,6-, and sometimes 4-chlorophenyl rings, were also substrates. Furthermore, the data revealed that Process LP can also meta-dechlorinate 2,3-, 2,3,4-, and 2,3,5-chlorophenyl groups on some congeners. A single ortho chlorine on the unattacked ring generally enhanced dechlorination activity, but the presence of 3 or 4 ortho chlorines or a 4-chlorophenyl group decreased the dechlorination efficiency. PCBs with 2,4-, 2,4,6-, 2,3-, and 2,3,5-chlorophenyl rings are often terminal dechlorination products of other microbial dechlorination activities. Since these PCBs are substrates for Process LP, this dechlorination activity works especially well in tandem with other dechlorination activities and further reduces the toxicity and persistence of PCBs. The data presented here will facilitate the construction of accurate models to interpret in situ PCB dechlorination and predict PCB fate.

Anaerobiosis↗

PubMed2001

Olefin epoxidation by molybdenum and rhenium peroxo and hydroperoxo compounds: a density functional study of energetics and mechanisms.

A density functional study on olefin epoxidation by rhenium and molybdenum peroxo complexes has been carried out. Various intermediates and transition structures of the systems CH3ReO3/H2O2, H3NMoO3/H2O2, and H3NOMoO3/H2O2 were characterized, including ligated and unligated mono- and bisperoxo intermediates as well as hydroperoxo derivatives. For the rhenium system the bisperoxo complex CH3ReO(O2)2*H2O was found to be most stable and the one with the lowest transition state for epoxidation of ethylene (activation barrier of 16.2 kcal/mol), in line with experimental findings. However, participation of monoperoxo and hydroperoxo complexes in olefin epoxidation cannot be excluded. For both molybdenum systems, hydroperoxo species with an additional ammonia model ligand in axial position were calculated to be most stable. Inspection of calculated activation barriers of ethylene epoxidation reveals that, in both molybdenum systems, hydroperoxo mechanisms are competitive if not superior to peroxo mechanisms. The reaction barriers of the various oxygen transfer processes can be rationalized by structural, orbital, and charge characteristics, exploiting a model that interprets the electrophilic nature of the reactive oxygen center.

Journal Article↗