ABSTRACT
In this work we offer a simple analytical method which allows us to determine and study the effects of the selective switching of photonic stop-bands in multi-component photonic crystals (Mc-PhCs) of any dimensionality. The calculations for Mc-PhCs with low dielectric contrast have been performed in the framework of the model based on the scattering form factor analysis. It has been shown that the effects of selective switching of photonic stop-bands predicted theoretically and found experimentally before in three-dimensional (3D) Mc-PhC have a general character and may be observed also in one-dimensional (1D) and two-dimensional (2D) Mc-PhCs. It is found that 1D, 2D and 3D Mc-PhCs demonstrate unexpectedly similar quasi-periodic behaviour of photonic stop-bands as a function of the reciprocal lattice vector. A proper choice of the structural and dielectric parameters can create a resonance photonic stop-band determining the Bragg wavelengths, to which a photonic crystal can never be transparent.
ABSTRACT
We report the observation of a Fano resonance between continuum Mie scattering and a narrow Bragg band in synthetic opal photonic crystals. The resonance leads to a transmission spectrum exhibiting a Bragg dip with an asymmetric profile, which can be tunably reversed to a Bragg rise. The Fano asymmetry parameter is linked with the dielectric contrast between the permittivity of the filler and the specific value determined by the opal matrix. The existence of the Fano resonance is directly related to disorder due to nonuniformity of a-SiO2 opal spheres. The theoretical "quasi-3D" model produces results in excellent agreement with the experimental data.
ABSTRACT
Pathogenesis of placental insufficiency during pregnancy with gestosis was investigated by high-tech methods including ultrasonography, dopplerometry, echocardiography, and measurement of placental and endothelial growth factors. Their utility for the evaluation of the severity of placental insufficiency was demonstrated. Diagnostic criteria for compensated and uncompensated placental insufficiency were proposed along with an algorithm for the examination of pregnant women with gestosis and obstetric strategies at different severity of this disorder. Also, criteria for prolongation of pregnancy with uncompensated placental insufficiency, indications for planned and emergency delivery by cesarean section were developed. The importance of differential approach to the choice of obstetric strategy to reduce perinatal and maternal morbidity and mortality in case of gestosis and placental insufficiency is emphasized.
Subject(s)
Delivery, Obstetric/methods , Placental Insufficiency/etiology , Practice Guidelines as Topic , Pre-Eclampsia/diagnosis , Ultrasonography, Doppler/methods , Adult , Diagnosis, Differential , Echocardiography/methods , Female , Follow-Up Studies , Humans , Morbidity/trends , Placental Insufficiency/diagnosis , Placental Insufficiency/prevention & control , Pre-Eclampsia/epidemiology , Pre-Eclampsia/therapy , Pregnancy , Pregnancy Outcome , Retrospective Studies , Risk Factors , Russia/epidemiology , Young AdultABSTRACT
A longitudinal retrospective study of 803 women and a prospective study of 739 women were carried out. A complex system of the examination of women with a high placental insufficiency risk, starting from the first trimester, was developed; the appropriateness of the application of new technologies of placental system and fetal examination were substantiated. The authors offer optimal regimens of pharmacocorrection of fetal condition disturbances and the activation of compensatory and adaptive reactions of the fetoplacental complex in placental insufficiency of various origins. The optimal obstetric tactics, the possibilities of therapy and pregnancy prolongation, and indications to operative delivery were defined on the basis of the features of placental dysfunction pathogenesis and a thorough analysis of the features of placental insufficiency in women with a high risk of perinatal complications.
