26 research outputs found
Mean parameter model for the Pekar-Fr\"{o}hlich polaron in a multilayered heterostructure
The polaron energy and the effective mass are calculated for an electron
confined in a finite quantum well constructed of
layers. To simplify the study we suggest a model in which parameters of a
medium are averaged over the ground-state wave function. The rectangular and
the Rosen-Morse potential are used as examples.
To describe the confined electron properties explicitly to the second order
of perturbations in powers of the electron-phonon coupling constant we use the
exact energy-dependent Green function for the Rosen-Morse confining potential.
In the case of the rectangular potential, the sum over all intermediate virtual
states is calculated. The comparison is made with the often used leading term
approximation when only the ground-state is taken into account as a virtual
state. It is shown that the results are quite different, so the incorporation
of all virtual states and especially those of the continuous spectrum is
essential.
Our model reproduces the correct three-dimensional asymptotics at both small
and large widths. We obtained a rather monotonous behavior of the polaron
energy as a function of the confining potential width and found a peak of the
effective mass. The comparison is made with theoretical results by other
authors. We found that our model gives practically the same (or very close)
results as the explicit calculations for potential widths .Comment: 12 pages, LaTeX, including 5 PS-figures, subm. to Phys. Rev. B, new
data are discusse
Sun Protection Intervention for Highway Workers: Long-Term Efficacy of UV Photography and Skin Cancer Information on Menâs Protective Cognitions and Behavior
The risk for skin cancer is increased among older males and outdoor workers who have high levels of ultraviolet (UV) exposure.
This study was designed to examine the long-term efficacy of UV photography interventions on male outdoor workers, the potential mediators of its impact, and the efficacy of UV photography and skin cancer vs. aging information with this population.
One hundred forty-eight male outdoor workers were randomly assigned to one of four intervention conditions or a control condition in a two by two plus one factorial design. The men in the intervention conditions received or did not receive a UV photo of their face and watched either a photoaging or skin cancer educational video. Participants completed pre-intervention, immediate post-intervention, and 2-month and 1-year follow-up assessments.
Analysis of covariance and structural equation modeling revealed that participants in the UV photography and cancer information interventions reported higher levels of sun protection cognitions, which were significant partial mediators of increases in sun protection behaviors and decreases in skin color.
This study provides evidence for effective sun protection interventions on male outdoor workers that may help reduce skin cancer risk