Performance analysis of waveguide-mode resonant optical filters with stochastic design parameters.

The performance of optical filters with resonant waveguide gratings is investigated numerically in a stochastic context, assuming random fluctuations of various design variables. Specifically, we derive stochastic models based on polynomial chaos expansions, whose involved coefficients are obtained by computing spectral projections via sparse-grid quadrature. The latter exploits purely deterministic results from a rigorous coupled-wave analysis solver and requires less simulation data than standard Monte Carlo (MC) techniques. The statistical moments of the filter's spectral response are calculated reliably, as the comparison against reference results from MC analysis verifies, and the extraction of the Sobol indices reveals the structure's sensitivity with respect to specific design parameters. Moreover, the present analysis clearly points out that neglecting even small geometric variations in the filter design may produce misleading conclusions regarding the corresponding performance, with undesirable consequences in real-life applications.

Temporal characteristics of resonant surface polaritons in superlensing planar double-negative slabs: development of analytical schemes and numerical models.

The temporal behavior of electric fields in arbitrary double-negative planar slabs is systematically investigated in this paper, from both analytical and numerical perspectives. Concerning infinite slabs, a set of exact expressions for an exponential current excitation is derived through an efficient complex analysis, and an integrated study of surface polariton frequencies is performed. Subsequently, the significant case of a source with a random spatial profile is explored in order to obtain rigorous relations for the field and transient phenomena damping time with respect to problem parameters. On the other hand, a robust finite-difference time-domain methodology is introduced for the comprehensive examination of finite slabs, whose numerical simulations dictate the adoption of a resonatorlike discipline. This inevitable, yet very instructive, convention is physically justified by the almost perfect surface mode reflections at the edges of the slab. In this manner, the proposed formulation reveals a prominent increase in the excited polariton amplitude, relative to the corresponding infinite arrangements, which leads to larger transient times.

Bone morphogenetic protein expression in newborn rat kidneys after prenatal exposure to radiofrequency radiation.

Effects of nonthermal radiofrequency radiation (RFR) of the global system of mobile communication (GSM) cellular phones have been as yet mostly studied at the molecular level in the context of cellular stress and proliferation, as well as neurotransmitter production and localization. In this study, a simulation model was designed for the exposure of pregnant rats to pulsed GSM-like RFR (9.4 GHz), based on the different resonant frequencies of man and rat. The power density applied was 5 microW/cm2, in order to avoid thermal electromagnetic effects as much as possible. Pregnant rats were exposed to RFR during days 1-3 postcoitum (p.c.) (embryogenesis, pre-implantation) and days 4-7 p.c. (early organogenesis, peri-implantation). Relative expression and localization of bone morphogenetic proteins (BMP) and their receptors (BMPR), members of a molecular family currently considered as major endocrine and autocrine morphogens and known to be involved in renal development, were investigated in newborn kidneys from RFR exposed and sham irradiated (control) rats. Semi-quantitative duplex RT-PCR for BMP-4, -7, BMPR-IA, -IB, and -II showed increased BMP-4 and BMPR-IA, and decreased BMPR-II relative expression in newborn kidneys. These changes were statistically significant for BMP-4, BMPR-IA, and -II after exposure on days 1-3 p.c. (P <.001 each), and for BMP-4 and BMPR-IA after exposure on days 4-7 p.c. (P <.001 and P =.005, respectively). Immunohistochemistry and in situ hybridization (ISH) showed aberrant expression and localization of these molecules at the histological level. Our findings suggest that GSM-like RFR interferes with gene expression during early gestation and results in aberrations of BMP expression in the newborn. These molecular changes do not appear to affect renal organogenesis and may reflect a delay in the development of this organ. The differences of relative BMP expression after different time periods of exposure indicate the importance of timing for GSM-like RFR effects on embryonic development.