Flow tracing fidelity of scattering aerosol in laser Doppler velocimetry

An experimental method for determinating the flow tracing fidelity of a scattering aerosol used in laser Doppler velocimeters was developed with particular reference to the subsonic turbulence measurements. The method employs the measurement of the dynamic response of a flow seeding aerosol excited by acoustic waves. The amplitude and frequency of excitation were controlled to simulate the corresponding values of fluid turbulence components. Experimental results are presented on the dynamic response of aerosols over the size range from 0.1 to 2.0 microns in diameter and over the frequency range 100 Hz to 100 kHz. It was observed that unit density spherical scatterers with diameters of 0.2 microns followed subsonic air turbulence frequency components up to 100 kHz with 98 percent fidelity

Cytogenetic studies of PCB77 on brown trout (<i>Salmo trutta fario</i>) using the micronucleus test and the alkaline comet assay

Polychlorinated biphenyls (PCBs) are stable pollutants, which can be found in almost every compartment of terrestrial and aquatic ecosystems. They are very lipophilic and therefore have the potency of accumulating in the fat stores of animals. The mechanisms by which PCBs exert their adverse effects are still unclear. It is known that PCBs induce some important biotransformation enzymes, but their mutagenic properties are still controversial. The DNA breakage and clastogenic potency of a planar PCB77 (3,3',4,4'-tetrachlorobiphenyl) was determined in vivo in fish, using the single cell gel electrophoresis or comet assay and the micronucleus test, on erythrocytes of the brown trout exposed for 3, 9 and 14 days to initial PCB concentrations of 780 and 918 pg/ml, dissolved in the water, Blood was taken by a caudal puncture and the erythrocytes were either deposited in an agarose gel (0.6%) for the comet assay or smeared directly on slides for the micronucleus test. Five fish were studied per treatment and 50 and 2000 erythrocytes per concentration and per animal were analysed for the comet assay and the micronucleus test respectively. ethyl methanesulphonate (EMS) at a concentration of 25 mg/l water was used as a positive control. Although EMS induced a statistically significant increase of single strand breaks in the comet assay, in neither of the two tests used, were mutagenic effects due to PCB exposure observed

Fluid dynamic studies on scattering aerosol and its generation for application as tracer particles in supersonic flow measurements utilizing laser Doppler velocimeter

An experimental study on the particle-fluid interactions of scattering aerosols was performed using monodisperse aerosols of different particle sizes for the application of laser Doppler velocimeters in subsonic turbulence measurements. Particle response was measured by subjecting the particles to an acoustically excited oscillatory fluid velocity field and by comparing the ratio of particle velocity amplitude to the fluid velocity amplitude as a function of particle size and the frequency of oscillation. Particle velocity was measured by using a differential laser Doppler velocimeter. The test aerosols were fairly monodisperse with a mean diameter that could be controlled over the size range from 0.1 to 1.0 micron. Experimental results on the generation of a fairly monodisperse aerosol of solid particles and liquid droplets and on the aerosol response in the frequency range 100 Hz to 100 kHz are presented. It is indicated that a unit density spherical scatterer of 0.3 micron-diameter would be an optimum choice as tracer particles for subsonic air turbulence measurements

Lifshitz Tails in Constant Magnetic Fields

We consider the 2D Landau Hamiltonian $H$ perturbed by a random alloy-type potential, and investigate the Lifshitz tails, i.e. the asymptotic behavior of the corresponding integrated density of states (IDS) near the edges in the spectrum of $H$. If a given edge coincides with a Landau level, we obtain different asymptotic formulae for power-like, exponential sub-Gaussian, and super-Gaussian decay of the one-site potential. If the edge is away from the Landau levels, we impose a rational-flux assumption on the magnetic field, consider compactly supported one-site potentials, and formulate a theorem which is analogous to a result obtained in the case of a vanishing magnetic field

Physics Analysis Expert PAX: First Applications

PAX (Physics Analysis Expert) is a novel, C++ based toolkit designed to assist teams in particle physics data analysis issues. The core of PAX are event interpretation containers, holding relevant information about and possible interpretations of a physics event. Providing this new level of abstraction beyond the results of the detector reconstruction programs, PAX facilitates the buildup and use of modern analysis factories. Class structure and user command syntax of PAX are set up to support expert teams as well as newcomers in preparing for the challenges expected to arise in the data analysis at future hadron colliders.Comment: Talk from the 2003 Computing in High Energy and Nuclear Physics (CHEP03), La Jolla, Ca, USA, March 2003, 7 pages, LaTeX, 10 eps figures. PSN THLT00

Rabl's model of the interphase chromosome arrangement tested in Chinise hamster cells by premature chromosome condensation and laser-UV-microbeam experiments

In 1885 Carl Rabl published his theory on the internal structure of the interphase nucleus. We have tested two predictions of this theory in fibroblasts grown in vitro from a female Chinese hamster, namely (1) the Rabl-orientation of interphase chromosomes and (2) the stability of the chromosome arrangement established in telophase throughout the subsequent interphase. Tests were carried out by premature chromosome condensation (PCC) and laser-UV-microirradiation of the interphase nucleus. Rabl-orientation of chromosomes was observed in G1 PCCs and G2 PCCs. The cell nucleus was microirradiated in G1 at one or two sites and pulse-labelled with 3H-thymidine for 2h. Cells were processed for autoradiography either immediately thereafter or after an additional growth period of 10 to 60h. Autoradiographs show unscheduled DNA synthesis (UDS) in the microirradiated nuclear part(s). The distribution of labelled chromatin was evaluated in autoradiographs from 1035 cells after microirradiation of a single nuclear site and from 253 cells after microirradiation of two sites. After 30 to 60h postincubation the labelled regions still appeared coherent although the average size of the labelled nuclear area fr increased from 14.2% (0h) to 26.5% (60h). The relative distance dr, i.e. the distance between two microirradiated sites divided by the diameter of the whole nucleus, showed a slight decrease with increasing incubation time. Nine metaphase figures were evaluated for UDS-label after microirradiation of the nuclear edge in G1. An average of 4.3 chromosomes per cell were labelled. Several chromosomes showed joint labelling of both distal chromosome arms including the telomeres, while the centromeric region was free from label. This label pattern is interpreted as the result of a V-shaped orientation of these particular chromosomes in the interphase nucleus with their telomeric regions close to each other at the nuclear edge. Our data support the tested predictions of the Rabl-model. Small time-dependent changes of the nuclear space occupied by single chromosomes and of their relative positions in the interphase nucleus seem possible, while the territorial organization of interphase chromosomes and their arrangement in general is maintained during interphase. The present limitations of the methods used for this study are discussed

The XMM-Newton view of the Crab

Aims. We discuss the current X-ray view of the Crab Nebula and Pulsar, summarising our analysis of observations of the source with the EPIC-pn camera on board the XMM-Newton observatory. Different modes of EPIC-pn were combined in order to yield a complete scenario of the spectral properties of the Crab resolved in space and time (pulse phase). In addition we give a description of the special EPIC-pn Burst mode and guidance for data reduction in that mode. Methods. We analysed spectra for the nebula and pulsar separately in the 0.6−12.0 keV energy band. All data were processed with the SAS 6.0.0 XMM-Newton Scientific Analysis System package; models were fitted to the data with XSPEC 11. The high time resolution of EPIC-pn in its Burst mode (7 μs) was used for a phase resolved analysis of the pulsar spectrum, after determination of the period with epoch folding techniques. Data from the SmallWindow mode were processed and corrected for pile-up allowing for spectroscopy simultaneously resolved in space and time. Results. The spatial variation of the spectrum over the entire region of the Crab shows a gradual spectral softening from the inner pulsar region to the outer nebula region with a variation in photon index, Γ, from 2.0 to 2.4. Pulse phase resolved spectroscopy of the Crab Pulsar reveals a phase dependent modulation of the photon index in form of a significant hardening of the spectrum in the inter-peak phase from Γ = 1.7 during the pulse peak to Γ = 1.5

Studies of orbital parameters and pulse profile of the accreting millisecond pulsar XTE J1807-294

The accreting millisecond pulsar XTE J1807-294 was observed by XMM-Newton on March 22, 2003 after its discovery on February 21, 2003 by RXTE. The source was detected in its bright phase with an observed average count rate of 33.3 cts/s in the EPIC-pn camera in the 0.5-10 keV energy band (3.7 mCrab). Using the earlier established best-fit orbital period of 40.0741+/-0.0005 minutes from RXTE observations and considering a circular binary orbit as first approximation, we derived a value of 4.8+/-0.1 lt-ms for the projected orbital radius of the binary system and an epoch of the orbital phase of MJD 52720.67415(16). The barycentric mean spin period of the pulsar was derived as 5.2459427+/-0.0000004 ms. The pulsar's spin-pulse profile showed a prominent (1.5 ms FWHM) pulse, with energy and orbital phase dependence in the amplitude and shape. The measured pulsed fraction in four energy bands was found to be 3.1+/-0.2 % (0.5-3.0 keV), 5.4+/-0.4 % (3.0-6.0 keV), 5.1+/-0.7 % (6.0-10.0 keV) and 3.7+/-0.2 % (0.5-10.0 keV), respectively. Studies of spin-profiles with orbital phase and energy showed significant increase in its pulsed fraction during the second observed orbit of the neutron star, gradually declining in the subsequent two orbits, which was associated with sudden but marginal increase in mass accretion. From our investigations of orbital parameters and estimation of other properties of this compact binary system, we conclude that XTE J1807-294 is very likely a candidate for a millisecond radio pulsar.Comment: 4 pages, 4 figures, Accepted for publication in Astronomy and Astrophysics letter

Development and validation of the <i>in vivo</i> alkaline comet assay for detecting genomic damage in marine flatfish

Biomonitoring is an important subject within environmental sciences. Biomonitoring tests are required to be quick, relatively inexpensive, accurate, and reproducible. No genetic test currently fulfils all of these requirements. The chromosome aberration and sister chromatid exchange tests are very time consuming, the DNA adduct technique is rather expensive, and the micronucleus test has not inconclusively proven its use as a reliable monitoring tool. This work is focused on the validation of the comet assay as a candidate for monitoring marine ecosystems. For the comet assay, this work deals with the effectiveness of tissue dissociation, storage of cells in lysing buffer and in liquid nitrogen, different electrophoretic conditions, neutralisation and fixation of slides, interindividual variation between samples, and responsiveness of four tissue types to ethyl methanesulphonate (EMS). The main conclusions are: (i) dissociation of solid tissues in a phosphate buffer supplemented with 200 mM N-t-butyl-alpha-phenylnitrone provides cells with an acceptable background DNA damage; (ii) freezing of cells or tissues in liquid nitrogen generally leads to an increase in DNA breakage, especially for liver, gill and kidney tissue; (iii) storage of slides in the lysing solution for up to one week gives minor changes in comet tails; (iv) differences in protocols for neutralisation and fixation may influence the results; (v) high intra- and interindividual variations in comets (length and DNA content) may obscure the interpretation of comet results; (vi) blood, gill, liver and kidney all showed a statistically significant increase of DNA damage after exposure to 50 mg EMS/l; (vii) electrophoresis at low voltage for longer periods is to be preferred to high voltage and short electrophoresis times. The simplicity and sensitivity of the comet assay make it an adequate test system for biomonitoring of chronic low level exposure. However, protocols and experimental conditions have to be chosen carefully