982 research outputs found
Double-Electromagnetically Induced Transparency in a Y-type atomic system
We study the absorption and dispersion properties of a weak tunable probe
field in a four-level Y-type atomic system driven by two strong laser
(coupling) fields within the framework of density matrix formalism. It is found
that the probe absorption profile displays double-electromagnetically induced
transparency (double-EIT) and it is shown how to control it by changing the
Rabi frequencies as well as the atom field detuning of the coupling fields.Comment: 8 page
Quantized form factor shift in the presence of free electron laser radiation
In electron scattering, the target form factors contribute significantly to
the diffraction pattern and carry information on the target electromagnetic
charge distribution. Here we show that the presence of electromagnetic
radiation, as intense as currently available in Free Electron Lasers, shifts
the dependence of the target form factors by a quantity that depends on the
number of photons absorbed or emitted by the electron as well as on the
parameters of the electromagnetic radiation. As example, we show the impact of
intense ultraviolet and soft X-ray radiation on elastic electron scattering by
Ne-like Argon ion and by Xenon atom. We find that the shift brought by the
radiation to the form factor is in the order of some percent. Our results may
open up a new avenue to explore matter with the assistance of laser
A Fabry-Perot interferometer with quantum mirrors: nonlinear light transport and rectification
Optical transport represents a natural route towards fast communications, and
it is currently used in large scale data transfer. The progressive
miniaturization of devices for information processing calls for the microscopic
tailoring of light transport and confinement at length scales appropriate for
the upcoming technologies. With this goal in mind, we present a theoretical
analysis of a one-dimensional Fabry-Perot interferometer built with two highly
saturable nonlinear mirrors: a pair of two-level systems. Our approach captures
non-linear and non-reciprocal effects of light transport that were not reported
previously. Remarkably, we show that such an elementary device can operate as a
microscopic integrated optical rectifier
Van-der-Waals potentials of paramagnetic atoms
We study single- and two-atom van der Waals interactions of ground-state
atoms which are both polarizable and paramagnetizable in the presence of
magneto-electric bodies within the framework of macroscopic quantum
electrodynamics. Starting from an interaction Hamiltonian that includes
particle spins, we use leading-order perturbation theory for the van der Waals
potentials expressed in terms of the polarizability and magnetizability of the
atom(s). To allow for atoms embedded in media, we also include local-field
corrections via the real-cavity model. The general theory is applied to the
potential of a single atom near a half space and that of two atoms embedded in
a bulk medium or placed near a sphere, respectively.Comment: 18 pages, 3 figures, 1 tabl
Prediction of preeclampsia based on blood lead levels in early pregnancy
زمینه و هدف: پره اکلامپسی شایع ترین عارضه بالینی دوران بارداری است. با توجه به اهمیت پره اکلامپسی در بارداری و عدم وجود عوامل قطعی موثر بر آن، این پژوهش با هدف پیشگویی وقوع پره اکلامپسی بر اساس سطح سرب خون مادران باردار در نیمه اول بارداری انجام شد. روش بررسی: این مطالعه توصیفی - تحلیلی بر روی 1033 مادر باردار در درمانگاه های پره ناتال شهر تهران انجام شد. در بدو ورود به مطالعه نمونه خون جهت سنجش سرب اخذ و پرسشنامه دموگرافیک تکمیل گردید. مادران باردار از زمان ورود به مطالعه تا زمان زایمان تحت مراقبت و پیگیری قرار گرفتند. در صورت وجود فشار خون مساوی یا بیش از 140 بر 90 میلیمتر جیوه و پروتئیناوری پس از هفته 20 بارداری تشخیص پره اکلامپسی برای مادر داده می شد. برای تجزیه و تحلیل داده ها از آزمون های آماری من ویتنی و رگرسیون لجستیک در نرم افزارSPSS استفاده شد. یافته ها: از 1033 مادر باردار 20 نفر (9/1) مبتلا به پره اکلامپسی بودند. میانگین سطح سرب خون مادران µg/dl9/4 ± 7/4 بود. ارتباط میان سرب خون مادر و پره اکلامپسی مستقیم و معنادار بود (001/0>(P. سطح موثر سرب خون (نقطه ی برش) در پره اکلامپسی دارای حساسیت 85، ویژگی 5/70، ارزش اخباری منفی 6/99 و ارزش اخباری مثبت 4/5، µg/dl 5 بدست آمد. نتیجه گیری: نتایج این مطالعه نشان داد که سطح سرب µg/dl 5 و بالاتر در نیمه اول بارداری می تواند با حساسیت نسبتاً بالا با وقوع پره اکلامپسی همراه باشد؛ لذا انجام این آزمایش به عنوان روشی در اوایل بارداری، برای پیشگویی وقوع پره اکلامپسی در مادران باردار فاقد عوامل خطرزای مهم پره اکلامپسی، پیشنهاد می گردد
Relativistic polarization analysis of Rayleigh scattering by atomic hydrogen
A relativistic analysis of the polarization properties of light elastically
scattered by atomic hydrogen is performed, based on the Dirac equation and
second order perturbation theory. The relativistic atomic states used for the
calculations are obtained by making use of the finite basis set method and
expressed in terms of splines and polynomials. We introduce two
experimental scenarios in which the light is circularly and linearly polarized,
respectively. For each of these scenarios, the polarization-dependent angular
distribution and the degrees of circular and linear polarization of the
scattered light are investigated as a function of scattering angle and photon
energy. Analytical expressions are derived for the polarization-dependent
angular distribution which can be used for scattering by both hydrogenic as
well as many-electron systems. Detailed computations are performed for Rayleigh
scattering by atomic hydrogen within the incident photon energy range 0.5 to 10
keV. Particular attention is paid to the effects that arise from higher
(nondipole) terms in the expansion of the electron-photon interaction.Comment: 8 pages, 5 figure
Analytical evaluation of atomic form factors: application to Rayleigh scattering
Atomic form factors are widely used for the characterization of targets and
specimens, from crystallography to biology. By using recent mathematical
results, here we derive an analytical expression for the atomic form factor
within the independent particle model constructed from nonrelativistic screened
hydrogenic wavefunctions. The range of validity of this analytical expression
is checked by comparing the analytically obtained form factors with the ones
obtained within the Hartee-Fock method. As an example, we apply our analytical
expression for the atomic form factor to evaluate the differential cross
section for Rayleigh scattering off neutral atoms.Comment: 7 pages, 1 figur
Relativistic total cross section and angular distribution for Rayleigh scattering by atomic hydrogen
We study the total cross section and angular distribution in Rayleigh
scattering by hydrogen atom in the ground state, within the framework of Dirac
relativistic equation and second-order perturbation theory. The relativistic
states used for the calculations are obtained by making use of the finite basis
set method and expressed in terms of B-splines and B-polynomials. We pay
particular attention to the effects that arise from higher (non-dipole) terms
in the expansion of the electron-photon interaction. It is shown that the
angular distribution of scattered photons, while it is symmetric with respect
to the scattering angle =90 within the electric dipole
approximation, becomes asymmetric when higher multipoles are taken into
account. The analytical expression of the angular distribution is parametrized
in terms of Legendre polynomials. Detailed calculations are performed for
photons in the energy range 0.5 to 10 keV. When possible, results are compared
with previous calculations.Comment: 8 pages, 5 figure
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