982 research outputs found

    Double-Electromagnetically Induced Transparency in a Y-type atomic system

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    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

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    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

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    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

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    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

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    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

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    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 BB splines and BB 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

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    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

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    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 θ\theta=90^\circ 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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