179 research outputs found
Industrialization, electromagnetic fields, and breast cancer risk.
The disparity between the rates of breast cancer in industrialized and less-industrialized regions has led to many hypotheses, including the theory that exposure to light-at-night and/or electromagnetic fields (EMF) may suppress melatonin and that reduced melatonin may increase the risk of breast cancer. In this comprehensive review we consider strengths and weaknesses of more than 35 residential and occupational epidemiologic studies that investigated the association between EMF and breast cancer. Although most of the epidemiologic data do not provide strong support for an association between EMF and breast cancer, because of the limited statistical power as well as the possibility of misclassification and bias present in much of the existing data, it is not possible to rule out a relationship between EMF and breast cancer. We make several specific recommendations for future studies carefully designed to test the melatonin-breast cancer and EMF-breast cancer hypotheses. Future study designs should have sufficient statistical power to detect small to moderate associations; include comprehensive exposure assessments that estimate residential and occupational exposures, including shift work; focus on a relevant time period; control for known breast cancer risks; and pay careful attention to menopausal and estrogen receptor status
Lippmann-Schwinger description of multiphoton ionization
We outline a formalism and develop a computational procedure to treat the
process of multiphoton ionization (MPI) of atomic targets in strong laser
fields. We treat the MPI process nonperturbatively as a decay phenomenon by
solving a coupled set of the integral Lippmann-Schwinger equations. As basic
building blocks of the theory we use a complete set of field-free atomic
states, discrete and continuous. This approach should enable us to provide both
the total and differential cross-sections of MPI of atoms with one or two
electrons. As an illustration, we apply the proposed procedure to a simple
model of MPI from a square well potential and to the hydrogen atom.Comment: 25 pages, 3 figure
A procedure to extract the complex amplitudes of He photodouble ionization from experimental data
A procedure to extract the two complex amplitudes that govern the He photodouble ionization process from the experimental data is proposed. The results are compared with the predictions of the convergent close coupling and hyperspherical R-matrix with semiclassical outgoing wave theories
Two electron interference in angular resolved double photoionization of Mg
The signature of the target wavefunction has been observed in the symmetrized amplitude of the resonant double photoionization of Mg. This observation is based on our experimental study of angle-resolved double photoionization of Mg at the photon energy of 55.49 eV (2p → 3d resonance) under equal energy sharing conditions
Interpreting Attoclock Measurements of Tunnelling Times
Resolving in time the dynamics of light absorption by atoms and molecules,
and the electronic rearrangement this induces, is among the most challenging
goals of attosecond spectroscopy. The attoclock is an elegant approach to this
problem, which encodes ionization times in the strong-field regime. However,
the accurate reconstruction of these times from experimental data presents a
formidable theoretical challenge. Here, we solve this problem by combining
analytical theory with ab-initio numerical simulations. We apply our theory to
numerical attoclock experiments on the hydrogen atom to extract ionization time
delays and analyse their nature. Strong field ionization is often viewed as
optical tunnelling through the barrier created by the field and the core
potential. We show that, in the hydrogen atom, optical tunnelling is
instantaneous. By calibrating the attoclock using the hydrogen atom, our method
opens the way to identify possible delays associated with multielectron
dynamics during strong-field ionization.Comment: 33 pages, 10 figures, 3 appendixe
Correlation effects during liquid infiltration into hydrophobic nanoporous mediums
Correlation effects arising during liquid infiltration into hydrophobic
porous medium are considered. On the basis of these effects a mechanism of
energy absorption at filling porous medium by nonwetting liquid is suggested.
In accordance with this mechanism, the absorption of mechanical energy is a
result expenditure of energy for the formation of menisci in the pores on the
shell of the infinite cluster and expenditure of energy for the formation of
liquid-porous medium interface in the pores belonging to the infinite cluster
of filled pores. It was found that in dependences on the porosity and,
consequently, in dependences on the number of filled pores neighbors, the
thermal effect of filling can be either positive or negative and the cycle of
infiltration-defiltration can be closed with full outflow of liquid. It can
occur under certain relation between percolation properties of porous medium
and the energy characteristics of the liquid-porous medium interface and the
liquid-gas interface. It is shown that a consecutive account of these
correlation effects and percolation properties of the pores space during
infiltration allow to describe all experimental data under discussion
Ejection of quasi-free electron pairs from the helium atom ground state by single photon absorption
We investigate single photon double ionization (PDI) of helium at photon
energies of 440 and 800 eV. We observe doubly charged ions with close to zero
momentum corresponding to electrons emitted back-to-back with equal energy.
These slow ions are the unique fingerprint of an elusive quasi-free PDI
mechanism predicted by Amusia et al. nearly four decades years ago [J. Phys. B
8, 1248, (1975)] . It results from the non-dipole part of the electromagnetic
interaction. Our experimental data are in excellent agreement with calculations
performed using the convergent close coupling and time dependent close coupling
methods
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