3,590 research outputs found
Assessment of ultraviolet radiation exposures in photobiological experiments
The interfering effect of ultraviolet (UV) radiation on the natural function of biological processes is wavelength specific and the UV spectrum must be weighted with the action spectrum for the process. The UV spectral irradiance may be measured with calibrated spectroradiometers. Alternatively, the biologically effective UV may be measured with broadband devices. This paper reviews the techniques for assessing biologically effective exposures in photobiological experiments.
UV meters, such as the Robertson-Berger (RB) meter, or passive dosimeters, such as polysulphone, that possess a spectral response approximating the human erythemal response can be used to estimate erythemally effective exposure or actinic exposure due to solar UV. The sensitivity of the RB meter is about 0.56 uW cm-2 and polysulphone can record an exposure of about 2mJ cm-2. For photobiological processes other than erythema these devices are not suitable to determine the exposure. In terms of these applications, a spectrum evaluator consisting of four different types of dosimeter material can be employed to evaluate the UV spectrum of the source. This method can be useful both for solar UV studies and research with UV lamps that possess radiation wavelengths shorter than 295nm. The device can be used to measure exposures where the actinic and erythemal action spectra differ significantly. It can also be used to assess exposure due to low levels of UV (about 0.01uW cm-2) caused by radiation filtered through glasses or plastic
Universality in the off-equilibrium critical dynamics of the diluted Ising model
We study the off-equilibrium critical dynamics of the three dimensional
diluted Ising model. We compute the dynamical critical exponent and we show
that it is independent of the dilution only when we take into account the
scaling-corrections to the dynamics. Finally we will compare our results with
the experimental data.Comment: Final Version, 5 Latex pages (RevTeX) plus 3 eps figure
Effect of cloud on UVA and exposure to humans
The daily autumn and winter UVA exposures and 6-minute UVA irradiance data for a Southern Hemisphere, subtropical site (Toowoomba, Australia, 27.6 S, 151.9 E) are presented. This data is used to quantify the effect of cloud on UVA using an integrated sky-camera and radiation system. Additionally, an estimate of the effect of enhanced UVA exposure on humans is made. The measurement system consisted of broadband visible-infrared and UVA sensors together with a sun tracking, wide-angle video camera. The mean daily June exposure was found to be 409 kJm-2. Under the constraints of the uncertainty of both the UVA measurement system and clear-sky model, one case of enhanced UVA irradiance was found. Three cases of cloud enhancement of daily UVA exposure, approaching clear-sky levels, were also determined using a calculated clear-sky envelope. It was also determined that for a fulltime outdoor worker, the additional UVA exposure could approach approximately that of one third of a full winter's day. For indoor workers with an outside lunch break of noon to 1 pm, the additional UVA exposure was on average 6.9 kJm-2 over three cloud enhanced days. To the authors' knowledge this is the first paper to present some evidence of cloud enhanced UVA human exposure
On the Four-Dimensional Diluted Ising Model
In this letter we show strong numerical evidence that the four dimensional
Diluted Ising Model for a large dilution is not described by the Mean Field
exponents. These results suggest the existence of a new fixed point with
non-gaussian exponents.Comment: 9 pages. compressed ps-file (uufiles
Correlation between magnetic and transport properties of phase separated LaCaMnO
The effect of low magnetic fields on the magnetic and electrical transport
properties of polycrystalline samples of the phase separated compound
LaCaMnO is studied. The results are interpreted in the
framework of the field induced ferromagnetic fraction enlargement mechanism. A
fraction expansion coefficient af, which relates the ferromagnetic fraction f
with the applied field H, was obtained. A phenomenological model to understand
the enlargement mechanism is worked out.Comment: 3 pages, 3 figures, presented at the Fifth LAW-MMM, to appear in
Physica B, Minor change
Slow Dynamics in Glasses
We will review some of the theoretical progresses that have been recently
done in the study of slow dynamics of glassy systems: the general techniques
used for studying the dynamics in the mean field approximation and the
emergence of a pure dynamical transition in some of these systems. We show how
the results obtained for a random Hamiltonian may be also applied to a given
Hamiltonian. These two results open the way to a better understanding of the
glassy transition in real systems
Replica Symmetry Breaking in the Random Replicant Model
We study the statistical mechanics of a model describing the coevolution of
species interacting in a random way. We find that at high competition replica
symmetry is broken. We solve the model in the approximation of one step replica
symmetry breaking and we compare our findings with accurate numerical
simulations.Comment: 12 pages, TeX, 5 postscript figures are avalaible upon request,
submitted to Journal of Physics A: Mathematical and Genera
A Generalization of the Brodsky-Lepage Formalism
We present an approach that generalizes in a natural way the perturbative QCD
formalism developed by Brodsky and Lepage for the study of exclusive hadronic
processes to the case of mesons. As an application of our approach we
consider here the production of meson pairs, involving tensor and pseudotensor
mesons, in photon-photon collisions.Comment: LaTeX, 5 pages, 1 embedded ps figure, uses macros sprocl.sty,
epsfig.sty. Talk delivered by F. Murgia at the PHOTON'97 Conference, Egmond
aan Zee, The Netherlands, May 10-15, 1997. To be published in the proceedings
by World Scientifi
Off-Equilibrium Dynamics at Very Low Temperatures in 3d Spin Glasses
We present a high statistic systematic study of the overlap correlation
function well below the critical temperature in the three dimensional Gaussian
spin glass. The off-equilibrium correlation function has been studied
confirming the power law behavior for the dynamical correlation length. In
particular we have computed the dynamical critical exponent in a wide range
of temperatures, , obtaining a dependence in a
very good agreement with recent experiments. Moreover, we report a study of the
violation of the fluctuation-dissipation theorem for very low temperatures
and . All our numerical results avoid a droplet model
interpretation even when is as low as .Comment: LaTeX, 14 pages and 5 figures. A minor arithmetic error corrected and
references update
Ising spin glass transition in magnetic field out of mean-field
The spin-glass transition in external magnetic field is studied both in and
out of the limit of validity of mean-field theory on a diluted one dimensional
chain of Ising spins where exchange bonds occur with a probability decaying as
the inverse power of the distance. Varying the power in this long-range model
corresponds, in a one-to-one relationship, to change the dimension in
spin-glass short-range models. Evidence for a spin-glass transition in magnetic
field is found also for systems whose equivalent dimension is below the upper
critical dimension at zero magnetic field.Comment: 5 pages, 1 table, 6 figures, data analysis mistake corrected, new
figures, new scaling approach to critical properties introduce
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