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PubMed1978

A model for anomalous rectification: electrochemical-potential-dependent gating of membrane channels.

A model is presented for "anomalous rectification" based upon electrical measurements on the egg cell membrane of the starfish. The objective is to postulate a plausible molecular mechanism which yields an expression for the conductance similar to that deduced empirically by Hagiwara and Takahashi (1974), i.e.,: formula: (see text), where B, deltaVh and v are constant, cK is the external K+ concentration, and deltaV (= V - V0) is the displacement of the membrane potential from its resting value. It is shown that a similar dependence of the conductance on deltaV is expected for a particular class of models in which the K+ ions are also implicated in "gating". To give a specific example, we consider the case in which the formation of ion-permeable pores requires a voltage-induced orientation of membrane-bound, electrically-charged groups and subsequent complexation of these groups with the external cations. Furthermore, the proportionality between GK and CK1/2, when the internal K+ concentration is constant, is accounted for by conventional descriptions of the ionic fluxes using Eyring's rate reaction theory. In terms of the present model, B and deltaVh are explicit functions of the internal K+ concentrations and are thus constant only as long as this is unvaried. The particular value of v required to fit the data (v congruent to 8.4 mV) is rationalized by the assumption that each of the orientable groups carries three negative elementary charges. In addition, the predictions of the present model are compared with those deduced from an alternative viewpoint, which is related to Armstrong's "blocking particle hypothesis", in that the probability for opening and closing of the pore is assumed to depend on whether the pore is occupied or empty. Differences and similarities between the two models, as well as ways to discriminate between them, are discussed.

Animals↗

PubMed1998

Two-dimensional magnetic particles

Single two-dimensional (2D) atomically thick magnetic particles of cobalt and iron with variable size and shape were fabricated by combining a mask technique with standard molecular beam epitaxy. Reduction of the lateral size of in-plane magnetized 2D cobalt films down to about 100 nanometers did not essentially modify their magnetic properties; although the separation of boundaries decreased greatly, neither domain penetrated the particle, nor was any sizable shape anisotropy observed. The mutual interaction of 2D cobalt particles was negligible, and the magnetic state of a single particle could be switched without modifying the state of the neighbors. Perpendicularly magnetized iron particles did not exhibit such responses. These results suggest that only a few atoms forming a 2D in-plane magnetized dot may provide a stable elementary bit for nanorecording.

Journal Article↗

PubMed2000

Phage infection of the obligate intracellular bacterium, Chlamydia psittaci strain guinea pig inclusion conjunctivitis.

The infectious cycle of phiCPG1, a bacteriophage that infects the obligate intracellular pathogen, Chlamydia psittaci strain Guinea Pig Inclusion Conjunctivitis, was observed using transmission electron microscopy of phage-hyperinfected, Chlamydia-infected HeLa cells. Phage attachment to extracellular, metabolically dormant, infectious elementary bodies and cointernalisation are demonstrated. Following entry, phage infection takes place as soon as elementary bodies differentiate into metabolically active reticulate bodies. Phage-infected bacteria follow an altered developmental path whereby cell division is inhibited, producing abnormally large reticulate bodies, termed maxi-reticulate bodies, which do not mature to elementary bodies. These forms eventually lyse late in the chlamydial developmental cycle, releasing abundant phage progeny in the inclusion and, upon lysis of the inclusion membrane, into the cytosol of the host cell. Structural integrity of the hyperinfected HeLa cell is markedly compromised at late stages. Released phage particles attach avidly to the outer leaflet of the outer membranes of lysed and unlysed Chlamydiae at different stages of development, suggesting the presence of specific phage receptors in the outer membrane uniformly during the chlamydial developmental cycle. A mechanism for phage infection is proposed, whereby phage gains access to replicating chlamydiae by attaching to the infectious elementary body, subsequently subverting the chlamydial developmental cycle to its own replicative needs. The implications of phage infection in the context of chlamydial infection and disease are discussed.

Animals↗

PubMed2003

Actin-based motility as a self-organized system: mechanism and reconstitution in vitro.

Site-directed actin polymerisation in response to signalling is responsible for the formation of cell protrusions. These elementary 'actin-based motility processes' are involved in cell locomotion, cell metastasis, organ morphogenesis and microbial pathogenesis. We have reconstituted actin-based propulsive movement of particles of various sizes and geometries (rods, microspheres) in a minimum motility medium containing five pure proteins. The ATP-supported treadmilling of actin filaments, regulated by Actin Depolymerizing Factor (ADF/cofilin), profilin and capping proteins provides the thermodynamic basis for sustained actin-based movement. Local activation of Arp2/3 complex at the surface of the particle promotes autocatalytic barbed end branching of filaments, generating a polarized arborescent array. Barbed end growth of branched filaments against the surface generates a propulsive force and is eventually arrested by capping proteins. Understanding the mechanism of actin-based movement requires elucidation of the biochemical properties and mode of action of Arp2/3 complex in filament branching, in particular the role of ATP binding and hydrolysis in Arp2/3, and a physical analysis of the movement of functionalised particles. Because the functionalisation of the particle by an activator of Arp2/3 complex (N-WASP or the Listeria protein ActA) and the concentrations of effectors in the medium are controlled, the reconstituted motility assay allows an analysis of the mechanism of force production at the mesoscopic and molecular levels.

Actin Cytoskeleton↗

PubMed1991

Kinetic studies on the appearance of antigens of Chlamydia psittaci during its developmental cycle.

The kinetics of the antigen production of Chlamydia psittaci strains Izawa-1 and Pigeon-1041 (P-1041) was examined every 6 hr after infection up to 48 hr, by the indirect immunofluorescent antibody technique using monoclonal antibodies (MAbs). All three genus-specific antigenic determinants on lipopolysaccharide (LPS) appeared during the whole growth cycle. Antigenic determinants on proteins were, on the other hand, detected at various time periods from the early to the late stages of infection. However, a cross-reactive antigenic determinant on protein recognized by a MAb 3E9 was also detected during the whole growth cycle, similar to that on LPS. The time of appearance of common antigenic determinants on proteins of Izawa-1 and P-1041 was examined using cross-reactive MAbs, and it varied depending on heterologous and homologous MAbs. From the relationship between the detection of antigenic determinants and the morphological changes of chlamydial particles revealed by electron microscopy during the growth cycle, the antigenic determinants on proteins of Chlamydia psittaci were divided into two groups; one was specific to the elementary body and the other was coexisting in both the elementary body and the reticulate body.

Animals↗

PubMed1993

Poincare surface of section and quantum scattering.

A very simple model for the quantum-mechanical scattering of a particle is studied with a dual goal: The chaotic nature of the corresponding classical problem should be quite obvious, and the method of solution should use an approach that is closely related to the surface of section in classical mechanics. Moreover, the mathematical operations should be elementary so that the errors in a semiclassical approximation or in any computational work have a chance of being controllable. Finally, the mode of presentation is such as to be understandable for a newcomer to the field of chaos. The model is a variation of the Sinai billiard where the circular hard wall inside a box (parallelogram) is replaced by a trombone-shaped surface for the particle to enter and exit the box. The rim (circular boundary between trombone and box) is the surface of section, with the total current at fixed energy in either direction providing the measure for the wave functions. The Poincare map then becomes the product of two unitary transformations, where the first is diagonal in angular momentum, while the second is diagonal in angle.

Journal Article↗

PubMed2005

Alternative view of self-diffusion and shear viscosity.

By performing an elementary transformation, the conventional velocity autocorrelation function expression for the temperature and density dependent self-diffusion constant D(T,rho) has been reformulated to emphasize how initial particle momentum biases final mean displacement. Using collective flow variables, an analogous expression has been derived for 1/eta(T,rho), the inverse of shear viscosity. The Stokes-Einstein relation for liquids declares that D and T/eta should have a fixed ratio as T and rho vary, but experiment reveals substantial violations for deeply supercooled liquids. Upon analyzing the self-diffusion and viscous flow processes in terms of configuration space inherent structures and kinetic transitions between their basins, one possible mechanism for this violation emerges. This stems from the fact that interbasin transitions become increasingly Markovian as T declines, and though self-diffusion is possible in a purely Markovian regime, shear viscosity in the present formulation intrinsically relies on successive correlated transitions.

Journal Article↗

PubMed1998

A method and apparatus for monitoring the level of tritiated water vapor in air using a solid scintillator.

Tritium is presently used in large quantities in laboratories for technological studies, as fuel for the process of nuclear fusion, and in the manufacture of radio-luminescent items. It is also produced in fission nuclear plants (with a yield of 10(-4) if the fuel is 235U and twice as much if the fuel is 239Pu), particularly in those which use D2O as moderator. The weak energy of beta particles (Emean=5.7 keV) produced by tritium implies that it is only harmful if internalized. In nature tritium in air is mainly present under two different chemical forms: elementary (HT, DT, T2) and oxidized (HTO, DTO, T2O). The latter is extremely more dangerous than the former as far as radioprotection is concerned; for this reason the derived air concentration limit (8 x 10(5) Bq m(-3)) for the gaseous form is 25,000 times higher than the value for the oxidized one. The purpose of the work presented here is to realize an area monitor that is able to discriminate in real time between the two chemical forms. Using the properties of zeolite as an absorber and scintillator, it was possible to construct such a detector. In 1 h the instrument can reveal HTO concentrations 40 times below the derived air concentration. A concentration equal to the derived air concentration can be revealed within the first minute of counting and the performance may be further improved. Moreover, the prototype realized is able to work automatically and continuously for 5 h. The capability of discriminating the oxidized chemical form, the sensitivity, and the possibility of obtaining real time information make this instrument a good monitor in those cases where there is a real risk of tritium air contamination.

Air Pollutants, Radioactive↗

PubMed2004

Using air pollution based community clusters to explore air pollution health effects in children.

To study respiratory health effects of long-term exposure to ambient air pollutant mixture, we observed 7058 school children 5-16 years of age living in the four Chinese cities of Lanzhou, Chongqing, Wuhan, and Guangzhou. These children were enrolled from elementary schools located in eight districts, one urban district and one suburban district in each of the above cities. Ambient levels of PM(2.5), PM(10-2.5), total suspended particles (TSP), SO(2), and NO(x) were measured in these districts from 1993 to 1996. Based on a cluster analysis of arithmetic mean concentrations of PM(2.5), PM(10-2.5), (TSP-PM(10)), SO(2), and NO(x), we classified these children into four ordinal categories of exposure to ambient air pollutant mixtures. We tested for exposure-response relationships using logistic regression models, controlling for relevant covariates. We observed monotonic, positive relationships of exposure to the pollutant mixture with prevalence rates of cough with phlegm and wheeze. Other outcomes were not associated with the exposure in a monotonic exposure-response pattern. Even so, odds ratios for cough, phlegm, bronchitis, and asthma in the higher exposure district clusters were all higher than in the lowest exposure district cluster. We found evidence that exposure to the pollutant mixtures had adverse effects on children living in the four Chinese cities.

Adolescent↗

PubMed2005

Acetylene coupling on Cu(111): formation of butadiene, benzene, and cyclooctatetraene.

Acetylene trimerizes to benzene on the (111) face of copper, as it does on the (100) and (110) planes. However, Cu(111) also yields butadiene and cyclooctatetraene, the latter never previously found with Cu or any other material. No coverage threshold is observed for the onset of these coupling reactions, implying high adsorbate mobility: gaseous benzene is formed by a surface reaction rate-limited process, whereas butadiene and cyclooctatetraene are formed by desorption rate-limited processes. H/D isotope tracing shows that benzene formation proceeds via a statistically random associative mechanism, whereas butadiene formation is associated with strong kinetic isotope effects, probably associated with C-H cleavage. A pericyclic mechanism involving dimerization of C4H4 metallocycles is proposed to account for the formation of cyclooctatetraene. We also found that approximately 45 nm alpha-alumina supported copper particles operated under catalytic conditions at atmospheric pressure yield the same principal reaction products as those found with Cu(111) under vacuum conditions. It therefore seems likely that the elementary reaction steps that describe the surface chemistry of the model system are also important under practical conditions. Comparison of the structure, bonding, and reactivity of acetylene on Cu(111) and Pd(111) indicates that the effectiveness of copper in promoting C-H cleavage in adsorbed acetylene is associated with greater rehybridization of the C-C bond with concomitant weakening of the C-H bond.

Journal Article↗

PubMed2002

Modeling of ultrasonic fields radiated by contact transducer in a component of irregular surface.

The wedge of a contact transducer is imperfectly coupled to a component of irregular surface. A volume between the wedge and the component (filled by water or oil used as a coupling) is created that fundamentally modifies transducer radiation behavior. As a result, phenomena like beam spreading, skewing and splitting, generation of unwanted contributions that possibly lead to false alarms may occur. At first, the paper describes a model to account for the main effects observable in such a situation. The model is based on a matrix method which describes the behavior of transient elementary contributions as the variation of a pencil propagating into homogeneous regions (namely, the wedge, the coupling and the component) and through interfaces between them (refraction and reflection). The elementary contributions accounting for the finite size of the transducer are summed to predict transducer diffraction effects. In a second part, predicted fields are compared to measured results. The comparison concerns particle velocity fields measurements at the surface opposite to that (irregular) on which the transducer acts. The very good agreement obtained proves the validity of our approach.

Journal Article↗

PubMed2006

A fourier analysis on the maximum acceptable grid size for discrete proton beam dose calculation.

We developed an analytical method for determining the maximum acceptable grid size for discrete dose calculation in proton therapy treatment plan optimization, so that the accuracy of the optimized dose distribution is guaranteed in the phase of dose sampling and the superfluous computational work is avoided. The accuracy of dose sampling was judged by the criterion that the continuous dose distribution could be reconstructed from the discrete dose within a 2% error limit. To keep the error caused by the discrete dose sampling under a 2% limit, the dose grid size cannot exceed a maximum acceptable value. The method was based on Fourier analysis and the Shannon-Nyquist sampling theorem as an extension of our previous analysis for photon beam intensity modulated radiation therapy [J. F. Dempsey, H. E. Romeijn, J. G. Li, D. A. Low, and J. R. Palta, Med. Phys. 32, 380-388 (2005)]. The proton beam model used for the analysis was a near monoenergetic (of width about 1% the incident energy) and monodirectional infinitesimal (nonintegrated) pencil beam in water medium. By monodirection, we mean that the proton particles are in the same direction before entering the water medium and the various scattering prior to entrance to water is not taken into account. In intensity modulated proton therapy, the elementary intensity modulation entity for proton therapy is either an infinitesimal or finite sized beamlet. Since a finite sized beamlet is the superposition of infinitesimal pencil beams, the result of the maximum acceptable grid size obtained with infinitesimal pencil beam also applies to finite sized beamlet. The analytic Bragg curve function proposed by Bortfeld [T. Bortfeld, Med. Phys. 24, 2024-2033 (1997)] was employed. The lateral profile was approximated by a depth dependent Gaussian distribution. The model included the spreads of the Bragg peak and the lateral profiles due to multiple Coulomb scattering. The dependence of the maximum acceptable dose grid size on the orientation of the beam with respect to the dose grid was also investigated. The maximum acceptable dose grid size depends on the gradient of dose profile and in turn the range of proton beam. In the case that only the phantom scattering was considered and that the beam was aligned with the dose grid, grid sizes from 0.4 to 6.8 mm were required for proton beams with ranges from 2 to 30 cm for 2% error limit at the Bragg peak point. A near linear relation between the maximum acceptable grid size and beam range was observed. For this analysis model, the resolution requirement was not significantly related to the orientation of the beam with respect to the grid.

Algorithms↗

PubMed2001

Characterization of intracytoplasmic prokaryote infections in Dreissena sp. (Bivalvia: Dreissenidae).

This study characterizes intracytoplasmic infections with prokaryote microorganisms in Dreissena sp. (near Dreissena polymorpha) from northeastern Greece and represents the first report of such infections in freshwater bivalves. Light microscope observations of stained tissues revealed basophilic, cytoplasmic inclusion bodies in 87.5% (28/32) of the mussels sectioned. Inclusions in epithelial cells and connective tissues were noted, respectively, in 34.4 and 71.9% of the sample, with 5 mussels (15.6%) having both tissue types infected. Epithelial cell infections were observed in histological sections only in digestive gland tubules and ducts; within tubules, inclusions were present more often in secretory than digestive cells. Connective tissue infections, however, were systemic; among the 32 mussels sectioned, inclusions were found in the gills (65.6%), foot (12.5%), mantle (9.4%), labial palps (6.3%), digestive gland (6.3%), stomach (6.3%), and gonads (3.1%). Cytoplasmic inclusions (maximum dimension, 138 microm) were prominent enough in the gills to be visible in 17.0% of the 247 mussels dissected. Ultrastructurally, prokaryote cells in gill connective tissues were clearly characteristic of Chlamydiales-like organisms, with each intracytoplasmic inclusion containing a loosely packed mixture of elementary, reticulate, intermediate bodies, and blebs. Prokaryote colonies in digestive gland epithelial cells exclusively contained 1 of 4 morphological cell types and were considered Rickettsiales-like. Hexagonal, virus-like particles were present in the cytoplasm of the largest of these Rickettsiales-like prokaryotes. Although host stress was evident from localized cell necrosis and dense hemocyte infiltration, overall infection was fairly benign, with no major, adverse impact on body condition evident among sectioned or dissected mussels. A possible negative effect was partial constriction of gill water tubes, but at the infection intensity observed (typical range 1 to 7 inclusion bodies per section), significant interference with respiration and other metabolic functions of the gills was highly unlikely.

Animals↗

PubMed2002

A mechanism for mercury oxidation in coat-derived exhausts.

This paper evaluates an elementary reaction mechanism for Hg0 oxidation in coal-derived exhausts consisting of a previously formulated homogeneous mechanism with 102 steps and a new three-step heterogeneous mechanism for unburned carbon (UBC) particles. Model predictions were evaluated with the extents of Hg oxidation monitored in the exhausts from a pilot-scale coal flame fired with five different coals. Exhaust conditions in the tests were very similar to those in full-scale systems. The predictions were quantitatively consistent with the reported coal-quality impacts over the full range of residence times. The role of Cl atoms in the homogeneous mechanism is hereby supplanted with carbon sites that have been chlorinated by HCl. The large storage capacity of carbon for Cl provided a source of Cl for Hg oxidation over a broad temperature range, so initiation was not problematic. Super-equilibrium levels of Cl atoms were not required, so Hg was predicted to oxidize in systems with realistic quench rates. Whereas many fundamental aspects of the heterogeneous chemistry remain uncertain, the information needed to characterize Hg oxidation in coal-derived exhausts is now evident: complete gas compositions (CO, hydrocarbons, H2O, O2 NOx, SOx), UBC properties (size, total surface area), and the ash partitioning throughout the exhaust system are required.

Air Pollutants↗

PubMed1964

ELECTRON MICROSCOPY OF LATENT PSITTACOSIS VIRUS IN MCCOY CELLS.

Kajima, Masahiro (University of Notre Dame, Notre Dame, Ind.), Nehama Sharon, and Morris Pollard. Electron microscopy of latent psittacosis virus in McCoy cells. J. Bacteriol. 88:709-715. 1964.-Replication of psittacosis virus in McCoy cells was observed periodically by electron microscopy, and was correlated with the appearance of inclusion bodies in infected cells stained by acridine orange fluorochrome. Three well-defined morphological stages characterized the replication cycle: (i) noninfectious initial body, (ii) noninfectious intermediate body, and (iii) infectious mature or elementary body. When replication of virus was interrupted by aminopterin, the virus failed to develop beyond the noninfective initial body stage; however, after treatment of such cultures with folinic acid, intermediate and mature virus particles appeared in the cells. Latent psittacosis virus, as described here, represented a virus in which the replication process was interrupted at a noninfective (eclipse) stage of the developmental cycle.

Acridines↗

PubMed1976

Alterations in the ultrastructure of Chlamydia psittaci 6BC harvested from the allantoic fluid of chick embryos.

The allantoic fluid of chick embryos infected with Chlamydia psittaci is routinely used as a source of material for the study of the chemical and biological properties of the chlamydiae. We have examined pellets recovered from this allantoic fluid by low- and high-speed centrifugation, as well as high-speed pellets which had been stored at -70 degrees C, and we find that all of the pleomorphic forms of the chlamydiae are present in these materials. The reticulate bodies and large intermediate bodies are always seen to be morphologically damaged in that their cell envelopes are modified and in that they are distended and occasionally 'leaky.' No morphological evidence of damage was seen in small intermediate bodies or in elementary bodies in any of the materials which were examined. Thus the chlamydial population recovered from the allantoic fluid of infected chick embryos has been modified by selective damage to the least-condensed particles. We propose that the release of lysosomal enzymes from the host cell may coincide with the release of the chlamydia and that these enzymes may be responsible for this selective damage.

Allantois↗

PubMedDate not supplied

Slow dynamics in colloidal glasses and porous media as probed by NMR relaxometry: assessment of solvent levy statistics in the strong adsorption regime.

Mesoscopic media such as porous materials or colloidal pastes develop large specific surface area which strongly influence the dynamics of the embedded fluid. This fluid confinement can be used either to probe the interfacial geometry (frozen porous media) or the particle dynamics (paste and colloidal glass). In the strong adsorption regime, it was recently proposed that the effective surface diffusion on flat surface is anomalous and exhibits long time pathology (Lévy walks). This phenomena is directly related to the time and space properties of loop trajectories appearing in the bulk between a desorption and a readsorption step. The Lévy statistics extends the time domain of the embedded fluid dynamics toward the low frequency regime. An interesting way to probe such a slow interfacial process is to use field cycling NMR relaxometry. In the first part of this paper, we propose a simple theoretical model of NMR dispersion which only involves elementary time steps of the solvent dynamics near an interface (loops, trains, tails in relation with the confining geometry). In the second part, field cycling NMR relaxometry is used to probe the slow solvent dynamics in two type of interfacial systems: (i) a colloidal glass made of thin and flat particles (ii) two fully saturated porous media, the Vycor glass and MCM48 respectively. Experimental results are critically compared to closed-form analytical expressions and numerical simulations.

Adsorption↗

PubMed1994

Acute effects of summer air pollution on respiratory symptom reporting in children.

A daily diary of respiratory symptoms was collected from the parents of 1,844 school children in six U.S. cities to study the association between ambient air pollution exposures and respiratory illness. A cohort of approximately 300 elementary school children in each of six communities were asked to keep a daily log of the study child's respiratory symptoms for one year. Daily measurements of ambient sulfur dioxide, nitrogen dioxide, ozone, inhalable particles (PM10), respirable particles (PM2.5), light scattering, and sulfate particles were made, along with integrated 24-h measures of aerosol strong acidity. The analyses were limited to the five warm season months between April and August. Significant associations were found between incidence of coughing symptoms and incidence of lower respiratory symptoms and PM10, and a marginally significant association between upper respiratory symptoms and PM10. There was no evidence that other measures of particulate pollution including aerosol acidity were preferable to PM10 in predicting incidence of respiratory symptoms. Significant associations in single pollutant models were also found between sulfur dioxide or ozone and incidence of cough, and between sulfur dioxide and incidence of lower respiratory symptoms.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗