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PubMed2002

Superfluid bose liquid with a suppressed BEC and an intensive pair coherent condensate as a model of 4He.

One introduces a model of the superfluid state of a Bose liquid with repulsion between bosons, in which at T=0, along with a weak single-particle Bose-Einstein condensate, there exists an intensive pair coherent condensate, analogous to the Cooper condensate in a Fermi liquid with attraction between fermions. A closed system of nonlinear integral equations for the normal and anomalous self-energy parts is solved numerically, and a quasiparticle spectrum is obtained, which is in good agreement with the experimental spectrum of elementary excitations in superfluid 4He. It is shown that the roton minimum in the spectrum is associated with the negative minimum of the Fourier component of the pair interaction potential.

Journal Article↗
PubMedDate not supplied

[Theory of charge transfer enzymatic reactions].

The influence on the elementary act energy of the change in the energies of reactants solvation and their coulombic interaction due to the transfer of reaction from the aqueous to nonaqueous medium of low dielectric permittivity, particularly the enzyme globule, has been considered. A quantitative calculation of the energies has been carried out for the isotropic dielectric model taking into account the distance of reacting particles from the aqueous/nonaqueous interface. It has been shown that the transfer of the reaction into protein globule leads to a large energy gain and hence accelerates the reaction considerably. This is true in the case when the absolute charge of reactants decreases in the course of the reaction for both particles or for one of them situated further from the interface.

Electron Transport↗
PubMed1998

Acute effects of ambient inhalable particles in asthmatic and nonasthmatic children.

Although increases in inhalable particle (PM10) concentrations have been associated with acute reductions in the level of lung function and increased symptom reporting in children, including children with asthma, it is not clear whether these effects occur largely in asthmatic children, or even whether asthmatic children are more likely to experience these effects than children without asthma. To address these points, the following subgroups of children were selected from a survey population of all 2,200 elementary school children (6 to 13 yr of age) in a pulp mill community on the west coast of Vancouver Island: (1) all children with physician-diagnosed asthma (n = 75 participated), (2) all children with an exercise-induced fall in FEV1 without diagnosed asthma (n = 57), (3) all children with airway obstruction (FEV1/FVC < 0.76) without either of the above (n = 18), and (4) control children without any of the above (n = 56). The children were followed for as long as 18 mo with twice daily measurements of peak expiratory flow (PEF) and daily symptom diary recording. Maximum daily PM10 concentration was 159 microm/m3 (median, 22.1), but only 8 d (1.2%) had concentrations above 100 microg/m3. In an analysis that accounted for time-varying covariates, and serially correlated and missing data, for the entire sample of children, increases in PM10 were associated with reductions in PEF and increased reporting of cough, phlegm production, and sore throat. For the subgroup of children with diagnosed asthma, PEF in the time period with the highest PM10 concentrations fell by an estimated 0.55 L/min (95% CI, 0.06 to 1.05) for a 10 microg/m3 PM10 increase above the mean daily PM10 concentration of 27.3 microg/m3 and the odds of reported cough increased by 8% (95% CI, 0 to 16%); no consistent effects were observed in the other groups of children. It is concluded that children experience reductions in PEF and increased symptoms after increases in relatively low ambient PM10 concentrations, and that children with diagnosed asthma are more susceptible to these effects than are other children.

Adolescent↗
PubMedDate not supplied

Nanoscopic aspects of radiobiological damage: Fragmentation induced by secondary low-energy electrons.

Low-energy electrons (LEEs) are produced in large quantities in any type of material irradiated by high-energy particles. In biological media, these electrons can fragment molecules and lead to the formation of highly reactive radicals and ions. The results of recent experiments performed on biomolecular films bombarded with LEEs under ultra-high vacuum conditions are reviewed in the present article. The major type of experiments, which measure fragments produced in such films as a function of incident electron energy (0.1-45 eV), are briefly described. Examples of the results obtained from DNA films are summarized along with those obtained from the fragmentation of elementary components of the DNA molecule (i.e., thin solid films of H(2)O, DNA bases, sugar analogs, and oligonucleotides) and proteins. By comparing the results of these different experiments, it is possible to determine fundamental mechanisms that are involved in the dissociation of biomolecules and the production of single- and double-strand breaks in DNA, and to show that base damage is dependent on the nature of the bases and on their sequence context. Below 15 eV, electron resonances (i.e., the formation of transient anions) play a dominant role in the fragmentation of all biomolecules investigated. These transient anions fragment molecules by decaying into dissociative electronically excited states or by dissociating into a stable anion and a neutral radical. These fragments usually initiate other reactions with nearby molecules, causing further chemical damage. The damage caused by transient anions is dependent on the molecular environment.

DNA↗
PubMed1991

Higher prevalence of goiter in endemic area of blackfoot disease of Taiwan.

Blackfoot disease is an endemic peripheral vascular disorder which is confined to a limited land area on the southwest coast of Taiwan. It has long been related to the consumption of high levels of arsenic found in the artesian well water. Humic substances have also been extracted from the well water and have been reported as a possible source of environmental goitrogen. The purpose of this study was to examine whether the prevalence of goiter is increased in the blackfoot disease-endemic area. This study covered all the children in the elementary schools of Putai and Peimen. They were divided into two groups according to the location of schools in the endemic area or non-endemic area of blackfoot disease. Thyroid enlargement was examined by palpation as recommended by the World Health Organization. Thyroid antibodies and hormones were determined in school children with a goiter and age-sex-matched normal control children using particle agglutination methods and radioimmunoassays, respectively. Aspiration cytology was done in cases with a nodular goiter. In total 4,567 school children were examined, including 2,306 males and 2,261 females. One hundred and twenty school children (2.63%) had a goiter of grade I or above. The prevalence of goiters in school children from the endemic area was higher than that from the non-endemic area (3.44 vs 2.08%, p less than 0.01). The prevalence of goiters in females from the endemic area was higher than that from the non-endemic area (4.65 vs 2.69%, p less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Biomarkers↗
PubMed2005

Melting line of charged colloids from primitive model simulations.

We develop an efficient simulation method to study suspensions of charged spherical colloids using the primitive model. In this model, the colloids and the co- and counterions are represented by charged hard spheres, whereas the solvent is treated as a dielectric continuum. In order to speed up the simulations, we restrict the positions of the particles to a cubic lattice, which allows precalculation of the Coulombic interactions at the beginning of the simulation. Moreover, we use multiparticle cluster moves that make the Monte Carlo sampling more efficient. The simulations are performed in the semigrand canonical ensemble, where the chemical potential of the salt is fixed. Employing our method, we study a system consisting of colloids carrying a charge of 80 elementary charges and monovalent co- and counterions. At the colloid densities of our interest, we show that lattice effects are negligible for sufficiently fine lattices. We determine the fluid-solid melting line in a packing fraction eta-inverse screening length kappa plane and compare it with the melting line of charged colloids predicted by the Yukawa potential of the Derjaguin-Landau-Verwey-Overbeek theory. We find qualitative agreement with the Yukawa results, and we do not find any effects of many-body interactions. We discuss the difficulties involved in the mapping between the primitive model and the Yukawa model at high colloid packing fractions (eta>0.2).

Journal Article↗
PubMed1992

Prevalence of goiters in school children residing in villages where underground water is used.

A representative of Fuder village in Taichung County complained that many residents had a goiter problem, which he felt might be related to pollution from the nearby Youshi industrial area. The purpose of this study was to determine whether school children in the Fuder area have a high prevalence of goiters. We chose children of the Schichi elementary school in the Fuder area as the study population, and children of the Goumei elementary school, far from the Youshi industrial area, as controls. Both groups were from a similar geographic location (near the sea), had similar socioeconomic status, and both drank underground water. Thyroid enlargement was examined by palpation as recommended by the World Health Organization. Thyroid antibodies and hormones were determined in school children with a goiter and age-sex-matched normal control children using the particle agglutination method and radioimmunoassay, respectively. In total, 1,692 school children were examined, including 875 males and 817 females. Of these, 126 school children (7.4%) had a goiter of Grade I or above. The prevalence of goiters in Shichi and Goumei were 8.8% (59/671) and 6.6% (67/1,021), respectively. There was no significant difference between these two areas. We compared the prevalence of goiters in these two schools where underground water is drunk with another previous study in Peimen and Putai where tap water is used. There was a statistically significant difference (7.4% vs 2.6%, p < 0.0001). This suggests that the higher prevalence rate of goiters in Shichi and Goumei is related to the drinking of underground water. We recommend that the use of tap water and continued salt iodization is the way to prevent endemic goiter in these areas. A further comprehensive study is needed to determine the nature of the goitrogen in the underground drinking water of the Fuder area.

Child↗
PubMed1986

The study of a swept electron beam in order to apply Boag's theory for calculation of the collection efficiency: I. Beam and swept area characteristics.

The characteristics of swept electron beams produced by Sagittaire or Saturne type accelerators were investigated by film dosimetry. Beam sections perpendicular to the beam limiting system (BLS) axis are fully described by Gaussian curves close to the centre of the field defined by the BLS, but they become more and more distorted as the elementary beam approaches the BLS. The swept area was also evaluated and was related to the magnitude of the current applied to the two orthogonal magnets of the sweeping system.

Evaluation Studies as Topic↗
PubMed2002

Method of moments for the dilute granular flow of inelastic spheres.

Some peculiar features of granular materials (smooth, identical spheres) in rapid flow are the normal pressure differences and the related anisotropy of the velocity distribution function f((1)). Kinetic theories have been proposed that account for the anisotropy, mostly based on a generalization of the Chapman-Enskog expansion [N. Sela and I. Goldhirsch, J. Fluid Mech. 361, 41 (1998)]. In the present paper, we approach the problem differently by means of the method of moments; previously, similar theories have been constructed for the nearly elastic behavior of granular matter but were not able to predict the normal pressures differences. To overcome these restrictions, we use as an approximation of the f((1)) a truncated series expansion in Hermite polynomials around the Maxwellian distribution function. We used the approximated f((1)) to evaluate the collisional source term and calculated all the resulting integrals; also, the difference in the mean velocity of the two colliding particles has been taken into account. To simulate the granular flows, all the second-order moment balances are considered together with the mass and momentum balances. In balance equations of the Nth-order moments, the (N+1)th-order moments (and their derivatives) appear: we therefore introduced closure equations to express them as functions of lower-order moments by a generalization of the "elementary kinetic theory," instead of the classical procedure of neglecting the (N+1)th-order moments and their derivatives. We applied the model to the translational flow on an inclined chute obtaining the profiles of the solid volumetric fraction, the mean velocity, and all the second-order moments. The theoretical results have been compared with experimental data [E. Azanza, F. Chevoir, and P. Moucheront, J. Fluid Mech. 400, 199 (1999); T. G. Drake, J. Fluid Mech. 225, 121 (1991)] and all the features of the flow are reflected by the model: the decreasing exponential profile of the solid volumetric fraction, the parabolic shape of the mean velocity, the constancy of the granular temperature and of its components. Besides, the model predicts the normal pressures differences, typical of the granular materials.

Journal Article↗
PubMed1988

[Modelling of digestion in the rumen].

The ruminal ecosystem illustrates the main concepts of system analysis. Due to its structure and functional complexity and to its determinant role in ruminant nutrition and feeding, the reticulo-rumen has been the target of modelling works. The proposed models have been static or dynamic. The later have known a recent development but the former have until now largely contributed to the knowledge progress. The complexity of dynamic models is proportional to the number of biological mechanisms taken into account. The simplest models describe, for instance, a degradation or a transit elementary process. The aggregated models take simultaneously into account 2 to 4 processes while the general models aim at describing the digestive behaviour of the ruminal ecosystem by integrating its main functions. These mechanistic models have been studied for about 20 years. They are on the whole satisfactory but they are not sufficiently able to describe some diet differences and some variations in the dynamic properties of feed particles.

Animals↗
PubMed1985

Detection of Chlamydia trachomatis in clinical specimens by nucleic acid spot hybridization.

A nucleic acid spot hybridization assay was used to detect Chlamydia trachomatis DNA. The hybridization probes included DNA isolated from elementary bodies of lymphogranuloma venereum (LGV) strains and cloned fragments of both chromosomal and plasmid DNA. The sensitivity of the test was in the range 10 to 100 pg homologous DNA and 10 in vitro infected cells. Cross-reactivity with bacterial DNA was avoided when purified chlamydia-specific DNA fragments were used as probes. C. trachomatis was detectable in most of the clinical specimens with large amounts of infectious particles. Also some isolation-negative specimens gave a positive signal in the test.

Chlamydia trachomatis↗
PubMed2002

The [Lys(-2)-Arg(-1)-des(17-21)]-endothelin-1 peptide retains the specific Arg(-1)-Asp8 salt bridge but reveals discrepancies between NMR data and molecular dynamics simulations.

The [des(17-21)]-endothelin-1 (CSH-ET) and [Lys(-)(2)-Arg(-)(1)-des(17-21)]-endothelin-1 (KR-CSH-ET) peptides, designed by removing the five-residue hydrophobic tail from the endothelin-1 (ET-1) and [Lys(-)(2)-Arg(-)(1)]-endothelin-1 (KR-ET-1) peptides, respectively, were synthesized. Previous studies on KR-ET-1 showed that, in contrast to ET-1, this engineered compound displays a pH-dependent conformational change related to the formation of a stabilizing salt bridge between the Arg(-)(1) and Asp(8) side chains. CD and NMR spectra indicate that CSH-ET and KR-CSH-ET display conformational behavior similar to those of ET-1 and KR-ET-1, respectively. The short salt bridge-stabilized KR-CSH-ET peptide therefore appears to be an attractive elementary scaffold for drug design. The solution structure of the salt-bridged form of KR-CSH-ET was determined by NMR at pH 4.5 and is very similar to the corresponding form of the parent KR-ET-1 peptide. Molecular dynamics simulations of the salt-bridged form of KR-CSH-ET were performed using both the GB/SA implicit solvation scheme or an explicit solvation and the particle-mesh Ewald method for long-range electrostatic calculation. Unexpectedly, the Arg(-)(1)-Asp(8) salt bridge does not display in the simulation the stability that could be expected from the experimental data. The cooperative involvement of a cation-pi interaction in formation of the salt bridge has been hypothesized. Difficulties in accurately simulating cation-pi interactions might be responsible for the lack of stability in the simulation. At this time, however, no definitive explanation for the observed discrepancy between experiments and simulations is available, and further experimental studies appear to be necessary to fully understand in atomic detail the pH-dependent conformational change observed in the KR-ET-1 series.

Amino Acid Motifs↗
PubMed1995

BEAM: a Monte Carlo code to simulate radiotherapy treatment units.

This paper describes BEAM, a general purpose Monte Carlo code to simulate the radiation beams from radiotherapy units including high-energy electron and photon beams, 60Co beams and orthovoltage units. The code handles a variety of elementary geometric entities which the user puts together as needed (jaws, applicators, stacked cones, mirrors, etc.), thus allowing simulation of a wide variety of accelerators. The code is not restricted to cylindrical symmetry. It incorporates a variety of powerful variance reduction techniques such as range rejection, bremsstrahlung splitting and forcing photon interactions. The code allows direct calculation of charge in the monitor ion chamber. It has the capability of keeping track of each particle's history and using this information to score separate dose components (e.g., to determine the dose from electrons scattering off the applicator). The paper presents a variety of calculated results to demonstrate the code's capabilities. The calculated dose distributions in a water phantom irradiated by electron beams from the NRC 35 MeV research accelerator, a Varian Clinac 2100C, a Philips SL75-20, an AECL Therac 20 and a Scanditronix MM50 are all shown to be in good agreement with measurements at the 2 to 3% level. Eighteen electron spectra from four different commercial accelerators are presented and various aspects of the electron beams from a Clinac 2100C are discussed. Timing requirements and selection of parameters for the Monte Carlo calculations are discussed.

Electrons↗
PubMed2006

Low levels of air pollution induce changes of lung function in a panel of schoolchildren.

In search of sensitive screening parameters for assessing acute effects of ambient air pollutants in young schoolchildren, the impact of 8-h average air pollution before lung function testing was investigated by oscillatory measurements of resistance and spirometry with flow-volume loops. At a central elementary school in Linz, the capital of Upper Austria, 163 children aged 7-10 yrs underwent repeated examinations at the same time of day during 1 school year, yielding a total of 11-12 lung function tests per child. Associations to mass concentrations of particulate matter and nitrogen dioxide (NO(2)) measured continuously at a nearby monitoring station were tested, applying the Generalised Estimating Equations model. Reductions per 10 microg.m(-3) (both for particles and for NO(2)) were in the magnitude of 1% for most lung function parameters. The most sensitive indicator for acute effects of combustion-related pollutants was a change in maximal expiratory flow in small airways. NO(2) at concentrations below current standards reduced (in the multipollutant model) the forced expiratory volume in one second by 1.01%, maximal instantaneous forced flow when 50% of the forced vital capacity remains to be exhaled (MEF(50%)) by 1.99% and MEF(25%) by 1.96%. Peripheral resistance increased by 1.03% per 10 microg.m(-3) of particulate matter with a 50% cut-off aerodynamic diameter of 2.5 mum (PM(2.5)). Resistance is less influenced by the child's cooperation and should be utilised more often in environmental epidemiology when screening for early signs of small airway dysfunction from urban air pollution, but cannot replace the measurement of MEF(50%) and MEF(25%). In the basic model, the reduction of these parameters per 10 microg.m(-3) was highest for NO(2), followed by PM(1), PM(2.5) and PM(10), while exposure to coarse dust (PM(10)-PM(2.5)) did not change end-expiratory flow significantly. All acute effects of urban air pollution found on the lung function of healthy pupils were evident at levels below current European limit values for nitrogen dioxide. Thus, planned reduction of nitrogen dioxide emission (Euro 5; vehicles that comply with the emission limits as defined in Directive 99/96/EC) of 20% in 2010 would seem to be insufficient.

Air Pollution↗
PubMed1995

Beam characteristics of a new generation 50 MeV racetrack microtron.

The first of a new generation of microtron accelerators has been installed and tested. It is currently in use for multisegment conformal radiotherapy at our institution. The unit produces x rays and electrons from 10 to 50 MeV in 5 MeV increments. It incorporates a 64 leaf, doubly focused multileaf collimator (MLC), which can be used to shape x-ray and electron beams. Both x-ray and electron beams are produced by magnetically scanning the electron beams from the accelerator. The new generation unit incorporates a purging magnet to sweep away any primary or secondary electrons that pass through the target(s). In this paper, the beam characteristics of the accelerator that were studied during acceptance testing are described. Representative examples of depth doses, beam profiles, output factors, and elementary beam distributions are presented and discussed, in comparison with the earlier generation of microtron accelerators and with other radiotherapy machines.

Humans↗
PubMed2006

Study of the molecular structure, ionization spectrum, and electronic wave function of 1,3-butadiene using electron momentum spectroscopy and benchmark Dyson orbital theories.

The scope of the present work is to reconcile electron momentum spectroscopy with elementary thermodynamics, and refute conclusions drawn by Saha et al. in J. Chem. Phys. 123, 124315 (2005) regarding fingerprints of the gauche conformational isomer of 1,3-butadiene in electron momentum distributions that were experimentally inferred from gas phase (e,2e) measurements on this compound [M. J. Brunger et al., J. Chem. Phys. 108, 1859 (1998)]. Our analysis is based on thorough calculations of one-electron and shake-up ionization spectra employing one-particle Green's function theory along with the benchmark third-order algebraic diagrammatic construction [ADC(3)] scheme. Accurate spherically averaged electron momentum distributions are correspondingly computed from the related Dyson orbitals. The ionization spectra and Dyson orbital momentum distributions that were computed for the trans-conformer of 1,3-butadiene alone are amply sufficient to quantitatively unravel the shape of all available experimental (e,2e) electron momentum distributions. A comparison of theoretical ADC(3) spectra for the s-trans and gauche energy minima with inner- and outer-valence high-resolution photoelectron measurements employing a synchrotron radiation beam [D. M. P. Holland et al., J. Phys. B 29, 3091 (1996)] demonstrates that the gauche structure is incompatible with ionization experiments in high-vacuum conditions and at standard temperatures. On the other hand, outer-valence Green's function calculations on the s-trans energy minimum form and approaching basis set completeness provide highly quantitative insights, within approximately 0.2 eV accuracy, into the available experimental one-electron ionization energies. At last, analysis of the angular dependence of relative (e,2e) ionization intensities nicely confirms the presence of one rather intense pi(-2) pi(*+1) satellite at approximately 13.1 eV in the ionization spectrum of the s-trans conformer.

Journal Article↗
PubMed2002

Open problems in active chaotic flows: Competition between chaos and order in granular materials.

There are many systems where interaction among the elementary building blocks-no matter how well understood-does not even give a glimpse of the behavior of the global system itself. Characteristic for these systems is the ability to display structure without any external organizing principle being applied. They self-organize as a consequence of synthesis and collective phenomena and the behavior cannot be understood in terms of the systems' constitutive elements alone. A simple example is flowing granular materials, i.e., systems composed of particles or grains. How the grains interact with each other is reasonably well understood; as to how particles move, the governing law is Newton's second law. There are no surprises at this level. However, when the particles are many and the material is vibrated or tumbled, surprising behavior emerges. Systems self-organize in complex patterns that cannot be deduced from the behavior of the particles alone. Self-organization is often the result of competing effects; flowing granular matter displays both mixing and segregation. Small differences in either size or density lead to flow-induced segregation and order; similar to fluids, noncohesive granular materials can display chaotic mixing and disorder. Competition gives rise to a wealth of experimental outcomes. Equilibrium structures, obtained experimentally in quasi-two-dimensional systems, display organization in the presence of disorder, and are captured by a continuum flow model incorporating collisional diffusion and density-driven segregation. Several open issues remain to be addressed. These include analysis of segregating chaotic systems from a dynamical systems viewpoint, and understanding three-dimensional systems and wet granular systems (slurries). General aspects of the competition between chaos-enhanced mixing and properties-induced de-mixing go beyond granular materials and may offer a paradigm for other kinds of physical systems. (c) 2002 American Institute of Physics.

Journal Article↗
PubMed1997

Stochastic Token Theory

This paper presents a theory encompassing a collection of stochastic models developed earlier and concerning the evolution of subjective preferences under the influence of a stream of elementary events. The theory relies on two basic concepts. (1) The states: Each individual in the population of reference is regarded as evolving in real time through a sequence of internal states. These states can be probed by interviewing the subjects at some arbitrarily chosen times t1, em leader, tn. Each of these interviews yields a response which is a reflection of the current state. (2) The tokens: The individual is subjected to a stochastic stream of unobservable or unrecorded "particles" of information, called tokens. Each token has the potential of modifying the current state, and is accordingly formalized by a transformation on the set of states. The core of the theory and the major concern of this paper is the particular semigroup generated by all such transformations. Combinatorial and stochastic axioms are formulated which lead to testable conditions. The theorems of this paper generalize earlier results by the author and others.

Journal Article↗