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At least 1,171 records · Page 65Linked to original sources
PubMed1998

The effects of particle charge on the performance of a filtering facepiece.

This study quantitatively determined the effect of electrostatic charge on the performance of an electret filtering facepiece. Monodisperse challenge corn oil aerosols with uniform charges were generated using a modified vibrating orifice monodisperse aerosol generator. The aerosol size distributions and concentrations upstream and downstream of an electret filter were measured using an aerodynamic particle sizer, an Aerosizer, and a scanning mobility particle sizer. The aerosol charge was measured by using an aerosol electrometer. The tested electret filter had a packing density of about 0.08, fiber size of 3 microns, and thickness of 0.75 mm. As expected, the primary filtration mechanisms for the micrometer-sized particles are interception and impaction, especially at high face velocities, while electrostatic attraction and diffusion are the filtration mechanisms for submicrometer-sized aerosol particles. The fiber charge density was estimated to be 1.35 x 10(-5) coulomb per square meter. After treatment with isopropanol, most of fiber charges were removed, causing the 0.3-micron aerosol penetration to increase from 36 to 68%. The air resistance of the filter increased slightly after immersion in the isopropanol, probably due to the coating of impurities in isopropanol. The aerosol penetration decreased with increasing aerosol charge. The most penetrating aerosol size became larger as the aerosol charge increased, e.g., from 0.32 to 1.3 microns when the aerosol charge increased from 0 to 500 elementary charges.

Aerosols↗
PubMed1992

Translocation of a specific premessenger ribonucleoprotein particle through the nuclear pore studied with electron microscope tomography.

A specific premessenger ribonucleoprotein (RNP) particle in the salivary glands of the dipteran Chironomus tentans was studied with electron microscope tomography during translocation from the cell nucleus to the cytoplasm. The RNP particle consists of a thin RNP fiber tightly folded into a ribbon, which is bent into a ring-like structure. Upon translocation through the pore, the particle is first orientated in a specific manner at the pore entrance, and subsequently the bent ribbon is gradually straightened and transported through the pore with the 5' end of the RNA in the lead. Concomitantly, the elementary RNP fiber constituting the ribbon is gradually unpacked and will appear more or less extended on the cytoplasmic side of the pore complex. The ordered nature of the process suggests a specific recognition of the RNP particle at the nuclear pore.

Animals↗
PubMed2000

Revised fine splitting of excitons in diamond

We study low-strain synthetic high pressure, high temperature diamonds by cathodoluminescence and observe novel fine structure in the free exciton and the boron-bound exciton emission. The basic spectral structure is a doublet with DeltaE approximately 11 meV common to both exciton spectra. This resolves the previously found inequivalence of free exciton ( approximately 7 meV) and bound exciton ( approximately 12 meV) fine splitting. It is argued that for a spin-orbit interaction Delta(0) much smaller than the excitonic binding ( E(X) approximately 80 meV) and the excitonic localization ( E(loc) approximately 51 meV) at the boron acceptor, the orbital momentum and the spin of the particles constituting the electron-hole pair are recoupled to form spin singlet and triplet exciton states as the elementary excitations.

Journal Article↗
PubMed1989

[Aluminum deposition and Ca-hydroxyapatite formation in frontal cortex tissue of amyotrophic lateral sclerosis].

To investigate a possible participatory role of an environmental metals in a pathogenetic process of amyotrophic lateral sclerosis (ALS), elementary and structural analyses of calcified substance in frontal cortex (percental gyrus) tissues of ALS patients were conducted using particle-induced X-ray emission (PIXE) and X-ray diffraction methods, as compared with control subjects. In the results of PIXE analysis, aluminum (Al) and calcium (Ca) contents in the frontal cortex tissues of the ALS patients were significantly increased with a high calcium (Ca)/phosphorus (P) Ca-hydroxyapatite (Ca-HAp). Although the content of peak ratio, as compared with those of control subjects. Only the Al content in the ALS patients showed significantly negative correlations with age at onset and/or at death. X-ray diffraction patterns from the sample (ashed at low temperature) of the frontal cortex tissues of the ALS patients were very similar to those from a standard sample of Ca-hydroxyapatite (Ca-HAp). Although the content of Ca-HAp in the mixed sample of frontal cortex tissues from the ten control subjects were not detectable (less than 3ppm), those of the ALS patients were markedly high, i.e., 111ppm in the mixed sample of five young patients with age under 60 and 168ppm in that of five old patients with age over 60. These results strongly indicated that Al may induce a calcifying degeneration in the CNS tissue of ALS patients, consequently leading to Ca-HAp formation as the final chemical compound.

Adult↗
PubMed2000

Energy behaviour of neutrons generated by Witch-type distributed axi-symmetrical deuteron beams accelerated onto plane tritium targets

This paper is an analytical study of the spatial dependency of the d-T neutron energy in the vicinity of a homogeneous tritium-occluded plane target. Close to the target, and along the path of incidence of axially symmetric deuteron beams, the transverse density of accelerated deuterons is assumed to be governed by a law approximated by the 'Witch' function. In particular circumstances, the elementary neutron emission process in non-dispersive media can be considered to be omni-directional (due consideration being paid to collision kinetics, depending upon mass and kinetic energy of particles involved in the nuclear collision, nuclear reaction energy, etc.). Consequently, analytical expressions can be considerably simplified. By applying the classical kinetic energy and momentum conservation laws to nuclear processes, a theoretical description is obtained, taking into account the exoergic character of d-T fusion reaction. A number of expressions for energetic prediction of the fast neutron field are proposed. The associated relations, involving elementary functions, can be investigated using a desk-top computer. Computationally tractable tools are of importance in the study of diverse situations such as induced reactions and activation analysis using 14 MeV neutron generators, investigations in health-physics, radiation dose measurements, nuclear medicine, damage effects, and simulation studies.

Journal Article↗
PubMed2001

Freezing transition of hard hyperspheres.

We investigate the system of D-dimensional hard spheres in D-dimensional space, where D>3. For the fluid phase of these hyperspheres, we generalize scaled-particle theory to arbitrary D and furthermore use the virial expansion and the Percus-Yevick integral equation. For the crystalline phase, we adopt cell theory based on elementary geometrical assumptions about close-packed lattices. Regardless of the approximation applied, and for dimensions as high as D=50, we find a first-order freezing transition, which preempts the Kirkwood second-order instability of the fluid. The relative density jump increases with D, and a generalized Lindemann rule of melting holds. We have also used ideas from fundamental-measure theory to obtain a free energy density functional for hard hyperspheres. Finally, we have calculated the surface tension of a hypersphere fluid near a hard smooth (hyper-)wall within scaled-particle theory.

Journal Article↗
PubMedDate not supplied

[Activation energy of enzymatic hydrolysis of different substrates of alpha-chymotrypsin].

Analysis of the experimental data for the series of alpha-chymotrypsin-catalyzed reactions of ester hydrolysis was carried out on the basis of modern elementary act theory of chemical processes. It was concluded that activation energy of considered reactions is attributed by repulsion potential for nucleophilic particle and carbonyl centre. It was supposed that the reason for abrupt changes of activation energy accompanying small enzyme-substrate complex structure shifts lies in the corresponding changes of carbonyl centre polarizability governed by its electrophilic environment.

Chymotrypsin↗
PubMed2004

The peculiarities of homogeneous nucleation of reactive Cu0 colloidal particles in the presence of functional oligoperoxides.

A method is proposed that combines the stage of formation of colloidal metal and metal-oxide particles with the stage of their surface modification by functional surface-active oligoperoxides (FSAP), which are sorbed irreversibly. Investigation of copper particle homogeneous nucleation kinetics witnesses the significant influence of supermolecular micelle-like structures formed by FSAP in solution on the reduction rate of Cu2+ cations caused by a phenomenon analogous to micellar catalysis. The rate constants of copper reduction in different local zones of the process have been determined. Particle homogeneous nucleation kinetics in the presence of surface-active oligoperoxides has been found to correspond to the main regularities of the Michaelis-Menten equation describing micellar catalysis. The carrying out of copper particle formation in distinct zones correlates well with the particle size distribution. The presence of reactive ditertiary peroxidic fragments on the particle surface as a result of FSAP sorption confers reliable protection from oxidation, hydrophobicity, and ability to form free radicals and participate in elementary stages of radical processes.

Journal Article↗
PubMed1981

Norwalk-related viral gastroenteritis due to contaminated drinking water.

An explosive outbreak of gastrointestinal illness clinically compatible with infection by an agent serologically related to Norwalk virus agent occurred in an elementary school in May 1978. Seroconversion by radioimmunoassay to the Norwalk antigen was noted in two of three ill persons, but no viral particles were identified in stool. Illness developed in 72% of students and teachers at the school, and 32% of household contacts of these ill persons. Of household contacts of persons exposed at school but not clinically ill, 11% developed illness. This value, however, was not statistically different from the level of illness observed concurrently in household contacts of students at an unaffected school nearby. Epidemiologic investigation implicated water as the mode of transmission. Average consumption of one or more glasses per day was strongly associated with illness (p less than 0.00000001). Among soccer team members with limited school contact, water consumption at the school was associated with a 14-fold greater risk of illness (p less than 0.000001). Drinking water was most likely contaminated by back-siphonage through a cross-connection between the school's well and septic tank. This contamination occurred approximately 24 to 36 hours before the outbreak developed.

Adolescent↗
PubMed1985

Inhibition of growth of Chlamydia trachomatis by human gamma interferon.

Treatment of HEp-2 cell cultures with highly purified human gamma interferon before infection resulted in the reduction of Chlamydia trachomatis (L2/434/Bu) infectious particle yield. Electron microscope studies showed that interferon did not affect chlamydial conversion to reticulate bodies but influenced the extent of maturation to elementary bodies. High interferon concentrations (greater than 350 IU/ml) inhibited inclusion body formation and resulted in the appearance of aberrant reticulate bodies.

Cell Line↗
PubMed2001

Experimental Study of Fibrin/Fibrin-Specific Molecular Interactions Using a Sphere/Plane Adhesion Model.

Fibrin, the biopolymer produced in the final step of the coagulation cascade, is involved in the resistance of arterial thrombi to fragmentation under shear flow. However, the nature and strength of specific interactions between fibrin monomers are unknown. Thus, the shear-induced detachment of spherical monodispersed fibrin-coated latex particles in adhesive contact with a plane fibrin-coated glass surface has been experimentally studied, using an especially designed shear stress flow chamber. A complete series of experiments for measuring the shear stress necessary to release individual particles under various conditions (various number of fibrin layers involved in the adhesive contact, absence or presence of plasmin, the main physiological fibrinolytic enzyme) has been performed. The nonspecific DLVO interactions have been shown to be negligible compared to the interactions between fibrin monomers. A simple adhesion model based on the balance of forces and torque on particles, assuming an elastic behavior of the fibrin polymer bonds, to analyze the experimental data in terms of elastic force at rupture of an elementary intermonomeric fibrin bond has been used. The results suggested that this force (of order 400 pN) is an intrinsic quantity, independent of the number of fibrin layers involved in the adhesive contact. Copyright 2001 Academic Press.

Journal Article↗
PubMed1990

Pyrethroid modifications of the activation and inactivation kinetics of the sodium channels in squid giant axons.

The kinetics of sodium channel activation and inactivation were analyzed in the squid giant axons internally treated with various pyrethroids. Pyrethroids increased the steady-state sodium current in squid giant axons by removing the inactivation. The steady-state sodium conductances in control and pyrethroid-treated axons showed the same voltage dependence, indicating that the removal of inactivation by pyrethroids did not lead to an alteration of gating charge transfer. The pyrethroid-modified sodium channels were activated with a biphasic time course involving the movement of at least two gating particles, and both components were voltage-dependent. The slower component was abolished by treatment with either pronase or N-bromoacetamide. The net elementary charges transported in the electric membrane field were reduced in the course of slow activation of the pyrethroid-induced sodium current. It appears that the 'immobilization' of gating charge is related to the slow activation rather than the inactivation of the sodium channel.

Animals↗
PubMed2001

High-temperature ultrafast polariton parametric amplification in semiconductor microcavities.

Cavity polaritons, the elementary optical excitations of semiconductor microcavities, may be understood as a superposition of excitons and cavity photons. Owing to their composite nature, these bosonic particles have a distinct optical response, at the same time very fast and highly nonlinear. Very efficient light amplification due to polariton-polariton parametric scattering has recently been reported in semiconductor microcavities at liquid-helium temperatures. Here we demonstrate polariton parametric amplification up to 120 K in GaAlAs-based microcavities and up to 220 K in CdTe-based microcavities. We show that the cut-off temperature for the amplification is ultimately determined by the binding energy of the exciton. A 5-micrometer-thick planar microcavity can amplify a weak light pulse more than 5,000 times. The effective gain coefficient of an equivalent homogeneous medium would be 107 cm-1. The subpicosecond duration and high efficiency of the amplification could be exploited for high-repetition all-optical microscopic switches and amplifiers. 105 polaritons occupy the same quantum state during the amplification, realizing a dynamical condensate of strongly interacting bosons which can be studied at high temperature.

Journal Article↗
PubMed1997

Differences in the association of Chlamydia trachomatis serovar E and serovar L2 with epithelial cells in vitro may reflect biological differences in vivo.

Chlamydia trachomatis serovar E is one of the most common bacterial sexually transmitted pathogens. Since it is an obligate intracellular bacterium, efficient colonization of genital mucosal epithelial cells is crucial to the infectious process. Serovar E elementary bodies (EB) metabolically radiolabeled with 35S-Cys-Met and harvested from microcarrier bead cultures, which significantly improves the infectious EB-to-particle ratio, provided a more accurate picture of the parameters of attachment of EB to human endometrial epithelial cells (HEC-1B) than did less infectious 14C-EB harvested from flask cultures. Binding of serovar E EB was (i) equivalent at 35 and 4 degrees C, (ii) decreased by preexposure of EB to heat or the topical microbicide C31G, (iii) comparable among common eukaryotic cell lines (HeLa, McCoy), and (iv) significantly increased to the apical surfaces of polarized cells versus nonpolarized cells. In parallel experiments with C. trachomatis serovar L2, serovar E attachment was not affected by heparin or heparan sulfate whereas these glucosaminoglycans dramatically reduced serovar L2 attachment. These data were confirmed by competitive inhibition of serovar E binding and infectivity by excess unlabeled live and UV-inactivated serovar E EB but not by excess serovar L2 EB. The noninvasive serovar E strains in the lumen of the genital tract enter and exit the apical domains of target columnar epithelial cells to spread canalicularly in an ascending fashion from the lower to the upper genital tract. In contrast, the invasive serovar L2 strains are primarily submucosal pathogens and likely use the glucosaminoglycans concentrated in the extracellular matrix to colonize the basolateral domains of mucosal epithelia to perpetuate the infectious process.

Bacterial Adhesion↗
PubMed2004

Plasmon hybridization in spherical nanoparticles.

We show that the plasmon resonances in single metallic nanoshells and multiple concentric metallic shell particles can be understood in terms of interaction between the bare plasmon modes of the individual surfaces of the metallic shells. The interaction of these elementary plasmons results in hybridized plasmons whose energy can be tuned over a wide range of optical and infrared wavelengths. The approach can easily be generalized to more complex systems, such as dimers and small nanoparticle aggregates.

Journal Article↗
PubMed2001

Off-diagonal long-range order in Bose liquids: irrotational flow and quantization of circulation.

On the basis of gauge invariance, it is proven in an elementary and straightforward manner, but without invoking any ad hoc assumption, that the existence of off-diagonal long-range order in one-particle reduced density matrix in Bose liquids implies both the irrotational flow in a simply connected region and the quantization of circulation in a multiply connected region, the two fundamental properties of a Bose superfluid. The origin for both is the phase coherence of condensate wave functions. Some relevant issues are also addressed.

Journal Article↗
PubMed1967

Purification and chemical composition of reticulate bodies of the meningopneumonitis organisms.

Reticulate bodies of the meningopneumonitis (MP) microorganism were purified from L cells 18 hr after infection by the combination of differential centrifugation in 30% sucrose solution and potassium tartrate density gradient centrifugation. It was ascertained by electron microscopy that purified preparations of reticulate bodies obtained were almost entirely free of host-cell components and of infectious elementary bodies of MP microorganisms. Purified reticulate bodies were easily disrupted by mechanical agitation, and it was observed in shadowed preparation that ribosome-like particles 15 mmu in diameter were scattered from broken reticulate bodies. In shadowed preparations, reticulate bodies were found to range in size from 1.0 to 1.6 mu in diameter, but in cross-section the range was 0.5 to 1.0 mu. In these preparations, the purified reticulate bodies were irregular in shape, round or oval, and were composed of rather homogenous, amorphous, or reticulate material with moderate density. Some particles exhibited a less-dense internal structure, in which a coarse fibrous reticulum was seen. Chemical fractionation of (32)P-labeled purified reticulate bodies showed that they contained three times more ribonucleic acid (RNA) than deoxyribonucleic acid, with the RNA being composed primarily of 21S, 16S, and 4S RNA. No infectivity of purified reticulate bodies could be demonstrated.

Centrifugation, Density Gradient↗
PubMed2003

Slow dynamics of embedded fluid in mesoscopic confining systems as probed by NMR relaxometry.

Mesoscopic media such as porous materials or colloidal dispersions strongly influence the dynamics of the embedded fluid. In the strong-adsorption regime, it was recently proposed that the effective surface diffusion on flat surface is anomalous and exhibits long-time pathology, enlarging the time domain of the embedded-fluid dynamics towards the low-frequency regime. An interesting way to probe such a slow interfacial process is to use the field-cycling NMR relaxometry. This technique is used here to probe the fluid dynamics in two types of interfacial systems: i) a colloidal glass made of thin and flat particles; ii) a fully saturated porous media, the Vycor glass. Experimental results are critically compared to either a simple theoretical model of NMR dispersion involving elementary steps of the fluid dynamics near an interface (loops, trains, tails) or Brownian-dynamics simulations performed inside 3D reconstructions of these confined systems.

Journal Article↗