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At least 541 records · Page 30Linked to original sources
PubMed2007

A microscale device for measuring emissions from materials for indoor use.

Emission test chambers or cells are used to determine organic vapour emissions from construction products under controlled conditions. Polymeric car trim component emissions are typically evaluated using direct thermal desorption/extraction. The Microchamber/Thermal Extractor (mu-CTE, Markes International) was developed to provide both a complementary tool for rapid screening of volatile organic compound (VOC) emissions--suitable for industrial quality control--and a means for thermal extraction of larger, more representative samples of car trim components. To determine the degree of correlation between conventional emission test methods and the microchamber, experiments were carried out under different conditions of temperature, air change rate and sample conditioning time. Good quantitative and qualitative correlation was obtained for measurements at ambient temperature. Moreover, it was shown that ambient-temperature emissions data collected using the mu-CTE as rapidly as possible--i.e. with minimal or no sample conditioning time--nevertheless provided a reliable guide as to how well that material would perform in subsequent 3-day chamber tests of VOC emissions. The parameters found to have the greatest influence on data correlation for experiments carried out at elevated temperatures were the sample mass (for bulk emissions testing) and the conditioning time. The results also showed that, within the constraints of inherent sample homogeneity, the mu-CTE gave reproducible emissions data, despite its small sample size/capacity relative to that of conventional chambers. Preliminary results of modelling the air flow within a microchamber using computational fluid dynamics showed a high degree of turbulent flow and two potential areas of still air which could cause sink effects. However, the experimental data reported here and in previous studies showed enhanced recovery of semivolatile components from the mu-CTE relative to a recovery from a 1 m(3) conventional chamber. This indicates that if these areas of relatively still air are present within the microchamber, they do not appear to be significant in practice.

Journal Article↗
PubMed2005

Time course of postnatal motor development in ferrets: ontogenetic and comparative perspectives.

We assess relative time courses of motor development in ferrets and rats and evaluate ferrets as experimental animals for studies of motor development. Motor behaviour of ferret pups was characterized in daily sessions from postnatal day (P) 2 to P63. Observations concerning rotational locomotion ('pivoting'), crawling, walking, upright standing ('rearing') and walking on a narrow path; righting on a surface, in mid-air and on an inclined plane ('geotaxis') were quantified in detail and compared with published data on rat motor development. Besides providing a comprehensive characterization of ferret motor development, our results demonstrate that relative time courses of emergence of motor skills in ferrets and rats are highly similar despite substantially different duration of postnatal periods. The relationship between species was determined by linear regression analysis of an x-y-plot of postnatal ages (y: ferret days; x: rat days) corresponding to given levels of performance of specific skills. The model equation y = 2.46x-4.18 represents the conversion between time courses of rat and ferret motor development. Remarkably, the model explained 81% of data variance (r2 = 0.81) and should hence be useful for translation of motor developmental data between ferret and rat and for comparisons between motor and other functions in ferrets. The highly conserved relative time course also has more general implications for the understanding of comparative aspects of development. In addition, the high reproducibility of data within the present study underscores the suitability of the ferret as an experimental animal for studies of motor development.

Aging↗
PubMed2003

Low-level arsenite induced gene expression in HEK293 cells.

Chronic, low-level exposure to arsenic frequently results in skin, lung, bladder, and kidney cancer. Since arsenic is primarily excreted via the kidney, this study focused on this target tissue. Gene array was used as a sensitive low-level monitor of the impact of arsenic on this target tissue. Arsenite [As(III)] was chosen as the chemical species of arsenic since As(III) species are touted as the cellular toxic form of arsenic. Human embryonic kidney cell line HEK293 cells were incubated with 1, 10, and 25 microM arsenite [As(III)] for 6 or 24 h. Total RNA from treated and control cells was isolated, reverse transcribed, and labeled with Cy3 or Cy5, and hybridized to a human cDNA microarray. Hybridizations were performed four times using independent total RNA preparations to ensure reproducibility. Raw data from 10 and 25 microM treated cells exposed for 6 h was normalized within, and between, hybridizations followed by identification of genes affected by arsenite exposure based on practical significance (2-fold change up or down) and reproducibility (affected in four of six measurements). In these studies, 20 genes (HMOX1, MT1E, or FOSL1, etc.) were up-regulated, and 19 genes (MYC, JAK1, or CENPE, etc.) were down-regulated. Genes identified at 10 and 25 microM arsenic exposure were then examined after 1 microM treatment for 6 or 24 h. Expression of affected genes showed a dose-dependent (1-25 microM) trend that was apparently not time-dependent (6 vs. 24 h). The affected genes indicate that even this realistic, low-level arsenite exposure was recognized by the HEK293 cells (e.g. metallothionein genes) and produced an oxidative stress (e.g. heme oxygenase gene). These affected genes were characterized as stress response genes, proto-oncogene, signaling molecules, transcription factors, chemokine receptors, proteolytic enzymes, ESTs, and unknown genes. These findings imply that arsenite induces complex cellular injury and the cellular adaptation to As(III) is associated with alterations in the expression of many genes.

Arsenites↗
PubMed2006

Live or computerized simulation of clinical encounters: do clinicians work up patient cases differently?

Computer simulation of clinical encounters is increasingly used in clinical settings to train patient work-up. The aim of this prospective, controlled study was to compare the characteristics of data collection and diagnostic exploration of physicians working up cases with a standardized patient and in a computerized simulation. Six clinicians of different clinical experience in internal medicine worked up three cases with a standardized patient and through a computer simulation allowing free inquiry. After each encounter, we asked the subjects to justify the information collected and to comment on their working diagnoses. The characteristics of data collected and working diagnoses generated were assessed and compared, according to the simulation method used. In the computer simulation, physicians limited their data collection and focused earlier and more specifically on information and working diagnoses with high levels of relevance. They reached a similar diagnostic accuracy and made decisions of a similar relevance. Computer simulation with a free-inquiry approach reproduces the data collection and the diagnostic exploration observed in a standardized-patient simulation and promotes an early collection of relevant data. Its contribution to extend the competence of learners in clinical settings should be further evaluated.

Clinical Competence↗
PubMed1996

Assumptions and validations of statistical tests for functional neuroimaging.

We contrast two statistical methods: three-dimensional cluster analysis and statistical parametric mapping. We show that three-dimensional cluster analysis is based on a neurobiological theory of the regulation of blood flow and, unlike statistical parametric mapping, carries a minimum of assumptions that are tested. Statistical parametric mapping is a formal approach, which is based on a multitude of assumptions of which the majority have not been validated. We also demonstrate that in practice three-dimensional cluster analysis has a reasonable balance between sensitivity and the probability of false positives, giving high reproducibility with data on e.g. colour discrimination.

Brain↗
PubMed2002

Two immunotoxicity ring studies according to OECD TG 407-comparison of data on cyclosporin A and hexachlorobenzene.

Two international ring studies were performed to develop appropriate parameters within standard toxicology study for screening of immunotoxicological potential of unknown substances. These studies followed OECD TG 407 and included a number of additional examinations. CSA was selected as model for its immunosuppressive and HCB as model for its immunostimulating effects. Reproducibility of data was defined by significant findings in at least 50% of participating laboratories. In-life clinical observations, values for WBC parameters, and changes of lymphoid organ weights suggested immune effects. Elevated IgM titers indicated increased antibody formation in HCB-exposed rats. Cellularity of T-cell compartments in thymus (medulla), spleen (PALS), and lymph nodes (paracortical zone of mesenteric and popliteal LN) were dose dependently decreased in CSA-treated rats. The numbers of follicular germinal centers were reduced in LN. HCB induced cellular proliferation in spleen marginal zones and endothelial activation in HEV of mesenteric and popliteal LN and GALT and in small pulmonary venules. Data obtained by specific immune parameters indicated immune effects; however, statistical inference was limited to low numbers of participating laboratories. In spleen, both substances decreased lymphoblast proliferation after ConA mitogen stimulation. Reduced numbers of antibody-forming cells in PFC assay indicated impaired T-cell-dependent humoral immunity by CSA, which was not seen for HCB. Altered fractions for B- and T-cell subpopulations were identified in spleen for both substances. In order to predict immunomodulatory effects of CSA or HCB, histomorphologic examination of lymphoid tissues resulted in the most reliable and sensitive data to distinguish immunosuppression and -stimulation.

Administration, Oral↗
PubMed1994

Role of active changes in venous capacity by the carotid baroreflex: analysis with a mathematical model.

To elucidate the role of venous capacity active changes in short-term cardiovascular homeostasis, a mathematical model of the carotid-sinus baroreflex system has been developed. In the model the cardiovascular system is represented as the series arrangement of six lumped compartments, which synthesize the fundamental hemodynamic properties of the systemic arterial, systemic venous, pulmonary arterial, and pulmonary venous circulations as well as of the left and right cardiac volumes. Cardiac outputs from the left and right ventricles are computed as a function of both downstream arterial pressure (afterload) and upstream atrial pressure (preload). Four distinct feedback regulatory mechanisms, working on systemic arterial resistance, heart rate, systemic venous unstressed volume, and systemic venous compliance, are assumed to operate on the cardiovascular system in response to carotid sinus pressure changes. All model parameters, both in the cardiovascular system and in feedback regulatory mechanisms, have been assigned on the basis of physiological data now available. The model is used here to simulate the pattern of the main hemodynamic quantities in the short time period (1-2 min) after acute carotid sinus activation in vagotomized subjects. Simulation results indicate that the model can reproduce experimental data quite well, with reference both to open-loop experiments and to an acute blood hemorrhage performed in closed-loop conditions. Moreover, computer simulations indicate that active changes in venous unstressed volume are of primary importance in regulating cardiac output and systemic arterial pressure during activation of the carotid sinus baroreflex.

Animals↗
PubMed1988

Theoretical studies of the structure and molecular dynamics of a peptide crystal.

Energy minimizations and molecular dynamics simulations have been performed on the cyclic peptide cyclo-(Ala-Pro-D-Phe)2 in both the isolated and crystal states. The results of these calculations have been analyzed, both to investigate our ability to reproduce experimental data (structure and vibrational and NMR spectra) and to investigate the effects of environment on the energy, structure, and dynamics of peptides. Comparison of the minimized and time-averaged crystal systems with the experimental peptide structure shows that the calculations have closely reproduced the experimental structure. Molecular dynamics of the isolated molecule has led to a new conformation, which is approximately equal to 8.5 kcal/mol more stable than the conformation that exists in the crystal, the latter conformation being stabilized by intermolecular (packing) forces. This illustrates the considerable effect that environment can have on the conformation of peptides. The crystal environment has also been shown to significantly reduce the dynamic conformational fluctuations seen for the isolated molecule. The behavior of the peptide during the isolated simulation also supports the experimental NMR observation of a symmetric structure that differs from the asymmetric, instantaneous structures which characterize the molecule during the dynamics. Calculations of vibrational frequencies of the peptide in the crystal and isolated states show the expected shifts in bond-stretching frequencies due to intermolecular interactions. Finally, we have calculated NMR coupling constants from the dynamics simulation of the isolated peptide and have compared these with the experimental values. This has led to a possible reinterpretation of the experimental data.

Crystallization↗
PubMed1983

Clinical validation of fully automated computation of ejection fraction from gated equilibrium blood-pool scintigrams.

A fully automated procedure for the computation of left-ventricular ejection fraction (EF) from cardiac-gated Tc-99m blood-pool (GBP) scintigrams with fixed, dual, and variable ROI methods is described. By comparison with EF data from contrast ventriculography in 68 patients, the dual-ROI method (separate end-diastolic and end-systolic contours) was found to be the method of choice; processing time was 2 min. Success score of dual-ROI procedure was 92% as assessed from 100 GBP studies. Overall reproducibility of data acquisition and analysis was determined in 12 patients. Mean value and standard deviation of differences between repeat studies (average time interval 27 min) were 0.8% and 4.3% EF units, respectively, (r = 0.98). We conclude that left-ventricular EF can be computed automatically from GBP scintigrams with minimal operator-interaction and good reproducibility; EFs are similar to those from contrast ventriculography.

Adult↗
PubMed2003

Development of new pseudopotential methods: improved model core potentials for the first-row transition metals.

We have recently developed new nonrelativistic and scalar-relativistic pseudopotentials for the first-row transition metal and several main-group elements. These improved Model Core Potentials were tested on a variety of transition metal complexes to determine their accuracy in reproducing electronic structures, bond lengths, and harmonic vibrational frequencies with respect to both all-electron reference data as well as experimental data. The new potentials are also compared with the previous model core potentials available for the first-row transition metals. The new potentials do a superior job at reproducing atomic data, reproduce molecular data as well as the previous version, and in conjunction with new main-group pseudopotentials that have L-shell structure of the valence basis set, they are slightly faster.

Journal Article↗
PubMed2006

An efficient computational method for predicting rotational diffusion tensors of globular proteins using an ellipsoid representation.

We propose a new computational method for predicting rotational diffusion properties of proteins in solution. The method is based on the idea of representing protein surface as an ellipsoid shell. In contrast to other existing approaches this method uses principal component analysis of protein surface coordinates, which results in a substantial increase in the computational efficiency of the method. Direct comparison with the experimental data as well as with the recent computational approach (Garcia de la Torre; et al. J. Magn. Reson. 2000, B147, 138-146), based on representation of protein surface as a set of small spherical friction elements, shows that the method proposed here reproduces experimental data with at least the same level of accuracy and precision as the other approach, while being approximately 500 times faster. Using the new method we investigated the effect of hydration layer and protein surface topography on the rotational diffusion properties of a protein. We found that a hydration layer constructed of approximately one monolayer of water molecules smoothens the protein surface and effectively doubles the overall tumbling time. We also calculated the rotational diffusion tensors for a set of 841 protein structures representing the known protein folds. Our analysis suggests that an anisotropic rotational diffusion model is generally required for NMR relaxation data analysis in single-domain proteins, and that the axially symmetric model could be sufficient for these purposes in approximately half of the proteins.

Anisotropy↗
PubMed2003

Evaluation of annotation strategies using an entire genome sequence.

MOTIVATION: Genome-wide functional annotation either by manual or automatic means has raised considerable concerns regarding the accuracy of assignments and the reproducibility of methodologies. In addition, a performance evaluation of automated systems that attempt to tackle sequence analyses rapidly and reproducibly is generally missing. In order to quantify the accuracy and reproducibility of function assignments on a genome-wide scale, we have re-annotated the entire genome sequence of Chlamydia trachomatis (serovar D), in a collaborative manner. RESULTS: We have encoded all annotations in a structured format to allow further comparison and data exchange and have used a scale that records the different levels of potential annotation errors according to their propensity to propagate in the database due to transitive function assignments. We conclude that genome annotation may entail a considerable amount of errors, ranging from simple typographical errors to complex sequence analysis problems. The most surprising result of this comparative study is that automatic systems might perform as well as the teams of experts annotating genome sequences.

Amino Acid Sequence↗
PubMed2006

Estimates of the uncertainties associated with models of the nucleon structure functions in the Delta production region.

Theoretical studies of the inclusive electron-nucleus cross section at beam energies up to a few GeV show that, while the region of the quasielastic peak is understood at the quantitative level, the data in the Delta production region are sizably underestimated. We analyze the uncertainty associated with the description of the nucleon structure functions W1 and W2 and its impact on the nuclear cross section. The results of our study suggest that the failure to reproduce the data is to be mostly ascribed to the poor knowledge of the neutron structure functions at low Q2.

Journal Article↗
PubMed1989

Reproducibility of microscopic and cultural data in repeated subgingival plaque samples.

In association studies, micro-organisms can only be recognized as suspects for playing a major rôle in the development of a pathological environment, if their destructive action goes along with a marked proportional increase of their numbers or if their first detection can be related to the clinical onset of the disease. Limitations in the reproducibility of repeated samples have to be taken into account, when changes of the microbial composition of subgingival environments are to be studied, and when local clinical changes are to be related to shifts in the composition of the pertaining microbiological compartment. To study reproducibility, a total of 109 sites was sampled repeatedly with sterile paperpoints at an interval of 7 to 10 days in 24 patients suffering from periodontal disease and 12 edentulous patients wearing successful and failing osseointegrated titanium implants. Using continuous anaerobic techniques, the samples were cultured on nonselective and selective media and were studied by darkfield microscopy. Both the intertest-agreements of frequencies of detection (kappa-statistics) as well as the discrepancies of proportions of bacterial groups and selected bacterial species were determined. The standard deviation of proportional differences between first and second samples ranged between 6.4% (fusiform organisms) and 17.2% (coccoid cells) for darkfield parameters, between 4.3% (B. melaninogenicus on ETSA/Kana.) and 14.0% (B. gingivalis on ETSA/Kana.) for selected bacterial species and between 6.9% (gram-negative anaerobic cocci) and 24.0% (gram-positive facultative cocci) for bacterial groups classified according to gram stain characteristics and atmospheric growth conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacteria↗
PubMed1994

A reliable approach for sequencing clone-specific CDRIII regions in B-cell lymphoma.

We report a reliable approach for sequencing lymphoma-specific CDRIII regions. CDRIII regions present in DNA prepared from routinely fixed and paraffin-embedded diagnostic lymph node material were amplified by the use of consensus VH and JH primers via PCR. PCR products were subcloned directly, without purification or modification of PCR fragments. Only small amounts of miniprep plasmid DNA of recombinant clones were required for cycle sequencing, resulting in autoradiograms of high quality. The easy and reproducible method which we describe has enabled us to determine the lymphoma-specific CDRIII region in 7/11 high-grade non-Hodgkin's lymphomas as well as in 3/3 cases of ALL and 1/1 case of a centroblastic/centrocytic lymphoma. The obtained sequence data can serve to generate lymphoma-specific oligonucleotides, which then can be used as PCR primers or hybridization probes for the detection of minimal residual disease in individual patients.

Base Sequence↗
PubMed1994

Tension transduction device for functional evaluation of the rat peroneal nerve.

Current techniques for evaluating animal model nerve regeneration lack accurate, sensitive and reproducible methods to determine neuromuscular function. We have developed a tension transduction apparatus which measures the magnitude of ankle dorsiflexion produced by normal rats during bipolar stimulation of the surgically exposed peroneal nerve. Three groups of animals were used to evaluate the consistency and overall reliability of this apparatus. Within the first group of 4 animals, we determined variability in a single testing period of 8 successive stimulations. The mean normalized standard deviation of dorsiflexion tension produced was 2.9% of the mean. In the second group, comparison of right and left dorsiflexion tension in 8 animals showed a difference of less than 2% (right: 134.2 g; left: 131.6 g), demonstrating that one lower limb can be used as a control for the contralateral limb. In the third group, 12 animals were tested on two separate occasions, 2 months apart, tension production increased 10% (from 122 to 134 g) and corresponded with an average weight increase, per animal, of 100 g (30%) during the 2-month rest period. Despite the increase in weight and strength, the initial procedure had a negative effect upon the maximum tension produced compared to a previously unoperated leg (prior operation: 134 g; no prior operation: 144 g). The reproducibility of data obtainable with this new device allows for its incorporation in future studies, as well as the correlation of such functional data with other current methods of studying nerve regeneration.

Animals↗
PubMed2002

The anharmonic potential energy surface of methyl fluoride.

A large experimental spectroscopic data set sensitive to the cubic anharmonic potential energy surface (PES) of methyl fluoride has been compiled from the literature for six symmetric and asymmetric top isotopomers of methyl fluoride: 12CH3F, 13CH3FF, 12CD3F, 13CD3F, 12CHD2F and 12CH2DF. This empirical data set has been used to critically assess the best available literature ab initio cubic force field and various 'improved' theoretical force fields. A perturbation-resonance approach to the calculation of the observables from the force constants has been utilized and existing PESs were found to reproduce the data poorly. The careful treatment required for the correct theoretical reproduction of empirical spectroscopic constants arising from highly correlated least-squares fits to the original data is discussed. A new fit to the data has been performed (optimising 19 of the 38 cubic force constants) resulting in a much improved PES. The latter has been used to predict currently unknown spectroscopic constants for the least well-characterised isotopomer 12CH2DF. The prospects for a future empirical determination of the complete cubic force field of methyl fluoride are discussed and new data most likely to yield new information on the PES identified.

Chemical Phenomena↗
PubMed2001

Growing dynamics of Internet providers.

In this paper we present a model for the growth and evolution of Internet providers. The model reproduces the data observed for the Internet connection as probed by tracing routes from different computers. This problem represents a paramount case of study for growth processes in general, but can also help in the understanding the properties of the Internet. Our main result is that this network can be reproduced by a self-organized interaction between users and providers that can rearrange in time. This model can then be considered as a prototype model for the class of phenomena of aggregation processes in social networks.

Journal Article↗