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At least 271 records · Page 15Linked to original sources

PubMed1998

Binaural masking level difference in human binaural interaction components.

OBJECTIVE: The purpose of this study was to compare the effects of monaural and binaural broadband masking noise on binaural interaction components (BICs) of the human auditory brain stem evoked potentials (ABEPs). DESIGN: The BICs of the human ABEPs were studied by subtracting the potentials to binaural clicks from the algebraic sum of monaurally evoked potentials to clicks alone or to clicks with ipsilateral monaural or binaural broadband masking noise. Alternating polarity, 11/sec clicks were presented at 65 dB nHL, and noise was presented at 45 dB nHL. Analysis included peak-to-prestimulus baseline amplitudes and latencies of BICs' peaks and troughs from the vertex-mastoid (A) and vertex-neck (Z) channels. In addition, 3-channel Lissajous' trajectory (3-CLT) analysis, estimating the single, centrally located dipole equivalent of surface activity, was performed on data recorded from three orthogonally positioned electrode pairs. 3-CLT measures included apex latency, amplitude, and orientation, as well as planar segment duration, size, shape, and orientation. RESULTS: All BICs 3-CLTs included five main components (labeled BdI, BdII, BdIII, BeI, and BeII). In general, apex latencies were longer with masking noise. However, BdII and BeI apex latencies were shorter with binaural than with ipsilateral monaural masking noise. Apex amplitude and planar segment size of component BeI, as well as P1 peak amplitude in BICs of the Z-channel records, were larger with binaural than with monaural noise. No significant difference between the monaural and binaural noise conditions was found in durations, shapes, and orientations of planar segments of BICs 3-CLT, nor in peak latency of BICs in the A- and Z-channel records. CONCLUSIONS: We suggest that these effects on the latency and amplitude of BICs reflect binaural processing in the human brain stem. In particular, the larger amplitudes and shorter latencies of P1 and BeI with binaural than with ipsilateral monaural masking may be associated with the psychophysical effect of binaural masking level difference.

Adolescent↗

PubMed2002

Male and female offending trajectories.

This paper uses a latent class modeling approach to examine gender related variations in offending trajectories from adolescence to young adulthood. This approach is applied to data gathered over the course of a longitudinal study of 896 New Zealand children studied from birth to age 21 years. The analysis identified five trajectory groups: a group of low-risk offenders, three groups of adolescent-limited offenders who varied in the timing of the onset of offending (early, intermediate, and late onset), and a group of chronic offenders. Identical offending trajectories applied for males and females. However, probabilities of trajectory group membership varied with gender, with females being more likely to exhibit low-risk or early onset adolescent-limited offending and males later onset and chronic offending. Examination of social, family, and individual factors associated with these trajectories suggested the presence of a series of common etiological factors relating to family functioning and early adjustment that discriminated between trajectory groups. These risk factors appeared to operate in a similar fashion for both males and females. Implications of these findings for trajectory theories of offending are discussed.

Adolescent↗

PubMed2003

The last 2 years of life: functional trajectories of frail older people.

OBJECTIVES: To characterize the functional trajectories during the last 2 years of life of patients with progressive frailty, with and without cognitive impairment, and to assess whether it was possible to identify discrete functional indicators that signal the end of life. DESIGN: A retrospective analysis of functional trajectories during the last 24 months of life. SETTING: Twelve demonstration sites of the Program of All-inclusive Care for the Elderly (PACE). PACE cares for frail older people who meet criteria for nursing home placement, with the goal of keeping the patient at home. PARTICIPANTS: Nine hundred seventeen patients who died while enrolled in PACE. MEASURES: At PACE entry and every 3 months thereafter, data were collected about the degree of dependence (none, partial, or full) in bathing, eating, and walking and the degree of incontinence (none, bladder, or bowel). Cognitive impairment was defined as six or more errors on the Short Portable Mental Status Questionnaire. To describe the end-of-life trajectories of patients, data were analyzed from observational windows of time, beginning with the patients' dates of death and extending backward in time to 24 months before death. Each analytical window was 3 months in duration. For each of the functional measures, the probability of functional deterioration in the last 2 years of life in patients with (64%) and without (36%) cognitive impairment was also compared. RESULTS: The mean age at death was 84; 69% of patients were women. For patients with and without cognitive impairment, a prolonged, steady increase in the rates of functional dependence that were evident at least 1 year before death, rather than sudden increases in functional dependence shortly before death, characterized the functional trajectories. It was not possible for any of the four measures to detect a time point before death at which there was an abrupt decline in function likely to signal impending death. For each measure, patients with cognitive impairment declined earlier, were more likely than patients without cognitive impairment to have the maximal level of dependence in the 0- to 3-month window before death (e.g., 56% vs 30% for mobility, P <.001), and were more likely to decline in the 2 years before death (e.g., 56% vs 36% for mobility, P <.001). CONCLUSION: Patients with advanced frailty, with or without cognitive impairment, have an end-of-life functional course marked by slowly progressive functional deterioration, with only a slight acceleration in the trajectory of functional loss as death approaches. Patients with cognitive impairment have particularly high rates of functional impairment at the time of death. These results suggest that end-of-life care systems that are targeted toward patients with functional trajectories clearly suggesting impending death (such as the Medicare hospice benefit) are poorly suited to older people dying with progressive frailty.

Activities of Daily Living↗

PubMed2006

Quasiclassical trajectory study of the Cl+CH4 reaction dynamics on a quadratic configuration interaction with single and double excitation interpolated potential energy surface.

An ab initio interpolated potential energy surface (PES) for the Cl+CH(4) reactive system has been constructed using the interpolation method of Collins and co-workers [J. Chem. Phys. 102, 5647 (1995); 108, 8302 (1998); 111, 816 (1999); Theor. Chem. Acc. 108, 313 (2002)]. The ab initio calculations have been performed using quadratic configuration interaction with single and double excitation theory to build the PES. A simple scaling all correlation technique has been used to obtain a PES which yields a barrier height and reaction energy in good agreement with high level ab initio calculations and experimental measurements. Using these interpolated PESs, a detailed quasiclassical trajectory study of integral and differential cross sections, product rovibrational populations, and internal energy distributions has been carried out for the Cl+CH(4) and Cl+CD(4) reactions, and the theoretical results have been compared with the available experimental data. It has been shown that the calculated total reaction cross sections versus collision energy for the Cl+CH(4) and Cl+CD(4) reactions is very sensitive to the barrier height. Besides, due to the zero-point energy (ZPE) leakage of the CH(4) molecule to the reaction coordinate in the quasiclassical trajectory (QCT) calculations, the reaction threshold falls below the barrier height of the PES. The ZPE leakage leads to CH(3) and HCl coproducts with internal energy below its corresponding ZPEs. We have shown that a Gaussian binning (GB) analysis of the trajectories yields excitation functions in somehow better agreement with the experimental determinations. The HCl(v'=0) and DCl(v'=0) rotational distributions are as well very sensitive to the ZPE problem. The GB correction narrows and shifts the rotational distributions to lower values of the rotational quantum numbers. However, the present QCT rotational distributions are still hotter than the experimental distributions. In both reactions the angular distributions shift from backward peaked to sideways peaked as collision energy increases, as seen in the experiments and other theoretical calculations.

Journal Article↗

PubMedDate not supplied

Contribution of click frequency bands to the human binaural interaction components.

The purpose of this study was to determine the contribution of click frequency bands (broad-band, >2000 Hz, <2000 Hz and <1000 Hz) to binaural interaction components (BICs) of the human auditory brainstem evoked potentials (ABEPs). The human BICs were studied by subtracting the potentials to binaural clicks from the algebraic sum of monaurally evoked potentials to either ear. Effective frequency bands were derived using clicks alone or clicks with ipsilateral or binaural masking noise, high- or low-pass filtered at different cut-off frequencies. Analysis included single-channel vertex-cervical spinous process VII derivation of BIC and ABEP, as well as estimating the single, centrally located dipole equivalent of the surface activity from three orthogonally positioned electrode pairs, using the three-channel Lissajous' trajectory (3-CLT) analysis. All BIC 3-CLTs included three major components (labeled BdII, BeI, and BeII) approximately corresponding in latency to IIIn, V and VI ABEP peaks. All apex latencies of BIC 3-CLT, except BeI, were longer in response to <2000 Hz and <1000 Hz (low-frequency) effective clicks. Apex amplitude of components BeI and BeII of BIC 3-CLT were smaller with low-frequency effective clicks than with broad-band or high-frequency (>2000 Hz) clicks. We suggest that binaural interaction component BeI is mainly tuned to high frequencies, showing no frequency effect on latency, and decreasing in amplitude with decreasing click high frequency content. In contrast, BdII and BeII of the human BICs are evoked more synchronously by high-frequency binaural inputs, but are also sensitive to low frequencies, increasing in latency according to the cochleotopic activation pattern. These differences between BIC components may reflect their roles in sound localization.

Acoustic Stimulation↗

PubMed2004

Comparison of cranial ontogenetic trajectories among great apes and humans.

Molecular data suggest that humans are more closely related to chimpanzees than either is to the gorillas, yet one finds the closest similarity in craniofacial morphology to be among the great apes to the exclusion of humans. To clarify how and when these differences arise in ontogeny, we studied ontogenetic trajectories for Homo sapiens, Pan paniscus, Pan troglodytes, Gorilla gorilla and Pongo pygmaeus. A total of 96 traditional three-dimensional landmarks and semilandmarks on the face and cranial base were collected on 268 adult and sub-adult crania for a geometric morphometric analysis. The ontogenetic trajectories are compared by various techniques, including a new method, relative warps in size-shape space. We find that adult Homo sapiens specimens are clearly separated from the great apes in shape space and size-shape space. Around birth, Homo sapiens infants are already markedly different from the great apes, which overlap at this age but diverge among themselves postnatally. The results suggest that the small genetic differences between Homo and Pan affect early human ontogeny to induce the distinct adult human craniofacial morphology. Pure heterochrony does not sufficiently explain the human craniofacial morphology nor the differences among the African apes.

Adult↗

PubMed1997

Molecular dynamics simulation of a dye molecule in the interior of a bilayer: 1,6-diphenyl-1,3,5-hexatriene in dipalmitoylphosphatidylcholine.

A molecular dynamics simulation was carried out for a dipalmitoylphosphatidylcholine (DPPC) membrane in its liquid crystalline state containing different concentrations of the dye molecule 1,6-diphenyl-1,3,5-hexatriene (DPH). From a numerical analysis of the trajectories, we obtained information concerning structural changes of the membrane due to the presence of the probe and some hydrodynamic information concerning the probe itself. The hydrodynamic properties regarding dye molecules that have been reported in this article are: rotational and translational diffusion coefficient and relaxation times. From this analysis, we estimated a range of values of 0.6-0.9 cP for the micro-viscosity in the mid-membrane. These simulations also afforded us some information regarding structural changes in the membrane as a consequence of the presence of the fluorescent dyes at different concentrations. Thus, the disorder inside the membrane, the surface area per lipid and thickness of the membrane were also investigated.

Journal Article↗

PubMed1999

Marijuana use among American Indian adolescents: a growth curve analysis from ages 14 through 20 years.

OBJECTIVE: To describe the developmental course of marijuana use among a group of American Indian adolescents, aged 14 through 20 years. METHOD: A group of 1,766 American Indian adolescents from 3 culture groups provided repeated measures of 30-day marijuana use twice a year across a 3-year period. Linking 5 age cohorts, hierarchical linear modeling was used to model a curvilinear trajectory of marijuana use. Gender and community differences were examined as well. RESULTS: Support was found for a "maturational" model of marijuana use across time: Use increased in middle adolescence, peaked in later adolescence, and began to decrease in early adulthood. Both gender and community differences in trajectories were significant as well. CONCLUSIONS: Marijuana use among American Indian adolescents follows a clear developmental trajectory. Growth curve analysis can provide an additional tool for studying the effects of interventions that may not be apparent in a traditional evaluation design.

Adolescent↗

PubMed1995

Protein conformational landscapes: energy minimization and clustering of a long molecular dynamics trajectory.

Using energy minimization and cluster analysis, we have analyzed a 1020 ps molecular dynamics trajectory of solvated bovine pancreatic trypsin inhibitor. Elucidation of conformational substates in this way both illustrates the degree of conformational convergence in the simulation and reduces the structural data to a tractable subset. The relative movement of structures upon energy minimization was used to estimate the sizes of features on the protein potential energy surface. The structures were analyzed using their pairwise root-mean-square C alpha deviations, which gave a global measure of conformational changes that would not be apparent by monitoring single degrees of freedom. At time scales of 0.1 ps, energy minimization detected sharp transitions between energy minima separated by 0.1 A rms deviation. Larger conformational clusters containing these smaller minima and separated by 0.25 A were seen at 1 ps time scales. Both of these small features of the conformational landscape were characterized by movements in loop regions associated with small, correlated backbone dihedral angle shifts. On a nanosecond time scale, the main features of the protein energy landscape were clusters separated by over 0.7 A rms deviation, with only seven of these substates visited over the 1 ns trajectory. These substrates, discernible both before and after energy minimization, differ mainly in a monotonic pivot of the loop residues 11-18 over the course of the simulation. This loop contains lysine 17, which specifically binds to trypsin in the active site. The trajectory did not return to previously visited clusters, indicating that this trajectory has not been shown to have completely sampled the conformational substates available to it. Because the apparent convergence to a single region of conformation space depends on both the time scale of observation and the size of the conformational features examined, convergence must be operationally defined within the context of the simulation.

Animals↗

PubMed2000

Modulation of glycophorin A transmembrane helix interactions by lipid bilayers: molecular dynamics calculations.

Starting from the glycophorin A dimer structure determined by NMR, we performed simulations of both dimer and monomer forms in explicit lipid bilayers with constant normal pressure, lateral area, and temperature using the CHARMM potential. Analysis of the trajectories in four different lipids reveals how lipid chain length and saturation modulate the structural and energetic properties of transmembrane helices. Helix tilt, helix-helix crossing angle, and helix accessible volume depend on lipid type in a manner consistent with hydrophobic matching concepts: the most relevant lipid property appears to be the bilayer thickness. Although the net helix-helix interaction enthalpy is strongly attractive, analysis of residue-residue interactions reveals significant unfavorable electrostatic repulsion between interfacial glycine residues previously shown to be critical for dimerization. Peptide volume is nearly conserved upon dimerization in all lipid types, indicating that the monomeric helices pack equally well with lipid as dimer helices do with one another. Enthalpy calculations indicate that the helix-environment interaction energy is lower in the dimer than in the monomer form, when solvated by unsaturated lipids. In all lipid environments there is a marked preference for lipids to interact with peptide predominantly through one rather than both acyl chains. Although our trajectories are not long enough to allow a full thermodynamic treatment, these results demonstrate that molecular dynamics simulations are a powerful method for investigating the protein-protein, protein-lipid, and lipid-lipid interactions that determine the structure, stability and dynamics of transmembrane alpha-helices in membranes.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2000

Computational studies of essential dynamics of Pseudomonas cepacia lipase.

In order to investigate the interfacial activation of a lipase from Pseudomonas cepacia (PcL), molecular dynamics (MD) simulations and essential dynamics (ED) analysis were performed in different solvent environments: vacuum and explicit water solvents. Starting from the active (open) structure of PcL, the essential dynamics analysis of the simulations revealed large correlated motions, which may be responsible for the activation of the enzyme. Fluctuations in the U1 (active-site lid) and U2 domains are found to be important in the activation of PcL. In contrast, the catalytic triad exhibits very little displacement. These results are consistent with the previous X-ray structural determination. A combined analysis of the trajectories showed some differences for the simulations in different solvent environments. It was found that the region around the helix alpha5 showed larger displacements in the water simulations. It can be concluded that the open structure of PcL becomes unstable in water solvents, leading to the closing of the so-called 'lid' region. The simulations and ED analysis on the closed structure of PgL provided additional information concerning the structural changes involved in the activation of the lipases. It was found that structural changes for PcL and PgL, which are responsible for the essential motions of the protein, showed contrasting behavior in the different solvent environments.

Binding Sites↗

PubMed2004

A simplified model for the assessment of the impact probability of fragments.

A model was developed for the assessment of fragment impact probability on a target vessel, following the collapse and fragmentation of a primary vessel due to internal pressure. The model provides the probability of impact of a fragment with defined shape, mass and initial velocity on a target of a known shape and at a given position with respect to the source point. The model is based on the ballistic analysis of the fragment trajectory and on the determination of impact probabilities by the analysis of initial direction of fragment flight. The model was validated using available literature data.

Accidents, Occupational↗

PubMed2005

Proton transfer in nanoconfined polar solvents. II. Adiabatic proton transfer dynamics.

The reaction dynamics for a model phenol-amine proton transfer system in a confined methyl chloride solvent have been simulated by mixed quantum-classical molecular dynamics. In this approach, the proton vibration is treated quantum mechanically (and adiabatically), while the rest of the system is described classically. Nonequilibrium trajectories are used to determine the proton transfer reaction rate constant. The reaction complex and methyl chloride solvent are confined in a smooth, hydrophobic spherical cavity, and radii of 10, 12, and 15 A have been considered. The effects of the cavity radius and the heavy atom (hydrogen bond) distance on the reaction dynamics are considered, and the mechanism of the proton transfer is examined in detail by analysis of the trajectories.

Kinetics↗

PubMed1989

Variation of movement characteristics with washing and capacitation of spermatozoa. I. Univariate statistical analysis and detection of sperm hyperactivation.

Movement alterations as spermatozoa are washed and capacitated in preparation for the zona-free sperm penetration assay were investigated using a videomicrographic computer-assisted system for tracking and analysis of sperm trajectories. Thirty-three semen samples from infertile men and 17 fertile controls were studied. Despite significant differences on the sperm penetration assay, univariate comparisons of movement characteristics between infertile and control samples failed to detect differences. For all samples combined, significant alterations in movement characteristics were detected after washing. After an 18-hour sperm capacitation, mean velocity, head yawing amplitude, and head yawing frequency still were significantly increased over seminal plasma values. Videomicrographic motion analysis thus allows detection of changes that are consistent with hyperactivated motility, as has been described for capacitating spermatozoa.

Diagnosis, Computer-Assisted↗

PubMed2003

DNA tri- and tetra-loops and RNA tetra-loops hairpins fold as elastic biopolymer chains in agreement with PDB coordinates.

The biopolymer chain elasticity (BCE) approach and the new molecular modelling methodology presented previously are used to predict the tri- dimensional backbones of DNA and RNA hairpin loops. The structures of eight remarkably stable DNA or RNA hairpin molecules closed by a mispair, recently determined in solution by NMR and deposited in the PDB, are shown to verify the predicted trajectories by an analysis automated for large numbers of PDB conformations. They encompass: one DNA tetraloop, -GTTA-; three DNA triloops, -AAA- or -GCA-; and four RNA tetraloops, -UUCG-. Folding generates no distortions and bond lengths and bond angles of main atoms of the sugar-phosphate backbone are well restored upon energy refinement. Three different methods (superpositions, distance of main chain atoms to the elastic line and RMSd) are used to show a very good agreement between the trajectories of sugar-phosphate backbones and between entire molecules of theoretical models and of PDB conformations. The geometry of end conditions imposed by the stem is sufficient to dictate the different characteristic DNA or RNA folding shapes. The reduced angular space, consisting of the new parameter, angle Omega, together with the chi angle offers a simple, coherent and quantitative description of hairpin loops.

Base Pair Mismatch↗

PubMed2006

Reliability of the intrinsic and extrinsic patterns of level walking in older women.

The aim of the study was to assess short- and long-term reliability of the harmonic analysis of the trajectories of head, upper trunk, and pelvis during walking in healthy older women, which reveals mechanisms to coordinate upper body segments and control head stability in the search for a safer gait. A stereophotogrammetric system was used to measure the displacement of markers located at head, shoulder, and pelvis level in 11 healthy older women (77+/-2 years) walking on an oval shaped 20-m walkway circuit, in three experimental sessions separated by 6 weeks. The harmonic analysis of the time-curves was highly reliable both within and between sessions (standard error of measurement ranging between 0.15 mm and 1.50mm for the amplitudes and 0.03 rad and 0.41 rad for the phases) and revealed different oscillatory patterns for the pelvis, head, and upper trunk. An intrinsic pattern, representing the natural overall movement symmetry of the whole population of older women of this study, was described by the first medio-lateral harmonic and second antero-posterior and vertical harmonics. An extrinsic pattern, characteristic of each individual in the population, was described by the first antero-posterior and vertical harmonics. The intrinsic pattern was both intra- and inter-subject repeatable (coefficient of multiple correlation, CMC, ranging between 0.82 and 0.99), while the extrinsic pattern was only intra-subject repeatable (CMC ranging between 0.70 and 0.90). Harmonic analysis reliably describes upper body kinematics in older women for detecting the intrinsic and extrinsic patterns of gait, which reveal fundamental mechanisms governing their walking.

Aged↗

PubMed2005

Field ion microscopy and 3-D atom probe analysis of Al3Zr particles in 7050 Al alloy.

Field ion microscope images have been used to measure the local evaporation field of a Al3Zr particle in 7050 Al alloy. Using the matrix Al evaporation field (19 V/nm) as a reference, the evaporation field of Al3Zr has been estimated to be 36 V/nm, similar to the theoretical value for the field evaporation of Al2+ or Zr3+ ions. A strong local magnification effect from the large difference in evaporation fields between the particle and matrix has been found to cause a severe distortion of the apparent particle morphology in a three-dimensional atom probe reconstruction when using parameters based on the Al matrix. Use of the measured evaporation field for Al3Zr has allowed accurate reconstruction of the morphology of the particle. A simple worst-case analysis predicts that trajectory overlaps increase with increasing cross-section of particle, and the calculated overlaps agree well with experimental estimates of approximately 1.4-2.0 nm for variations in the particle cross-section from 7 to 12 nm. The chemical composition of Al3Zr in a 7050 Al alloy has been measured to be 64.8-67.7 at% Al, 23.6-24.8 at% Zr, 6.9-9.1 at% Zn, 0.4-0.7 at% Cu, 0.5-1.2 at% Mg, with a (Al+Zn)/Zr ratio close to 3. Specimen analysis temperatures of either 25 or 80 K show little effect on the measured chemical compositions of the particle.

Alloys↗

PubMed1988

The development of Canadian nursing: professionalization and proletarianization.

In this article, the development of nursing in Canada is described in terms of three major time periods: the emergence of lay nursing, including organization and registration, 1870-1930; the move to the hospital, 1930-1950; and unionization and the routinization of health care, 1950 to the present. This development is viewed in the light of the orienting concepts of professionalization, proletarianization, and medical dominance (and gender analysis). This historical trajectory of nursing shows an increasing occupational autonomy but continuing struggles over control of the labor process. Nursing is now using theory, organizational changes in health care, and credentialism to help make nursing "separate from but equal to" medicine and to gain control over the day-to-day work of the nurse. Nursing can thus be viewed as undergoing processes of both professionalization and proletarianization. As nursing seeks to control the labor process, its occupational conflicts are joined to the class struggle of white-collar workers in general. Analysis of nursing indicates the problems involved in sorting out the meaning of concepts that are relevant to occupational or class analysis but which focus on the same empirical phenomenon.

Canada↗