The features of the use of radio waves with linear and circular polarization at incoherent scatter (IS) radars of the very high frequency (VHF) band are considered. We give examples of calculating the altitude distribution of the ionospheric electron density from the results of measurements calibrated with the ionosonde data when using the circularly polarized sounding signal, as well as from the IS signal power minima and maxima associated with the Faraday rotation when using a linearly polarized signal. The disadvantages of these methods are noted. In the first case, the ionosonde data are bound to the obtained by IS technique normalized altitude profile of the electron density only at one altitude point; at certain events in the ionosphere, the ionosonde data may be unreliable or even absent (for example, in the presence of the sporadic $\mathbf{E}_{s}$ layer). In the second case (the mode of analyzing the wavelike altitude profile of the IS signal power), there are errors in determining the centers of the nodal points, especially when signal-to-noise ratio is low. We proposed a version of calculating the absolute values of the electron density using an altitude profile that is the result of multiplying the voltages of two circularly polarized components of the linearly polarized IS signal with opposite directions of the electric field vector rotation, when the linearly polarized sounding signal is used. In this case, a wave-like alternating function associated with the Faraday Effect is obtained with the help of special calculations. This function is used to determine the intervals between its adjacent zero values, and the resulting height intervals are uniquely related to the average electron density for each of them. Due to the high accuracy of determining the points of intersection of the function with the abscissa axis, the accuracy of electron density measurements using the Faraday Effect increases significantly, especially in the presence of noise. We proposed a structure of upgraded hardware for implementation of such mode of additional processing of the IS signal orthogonal components. Using computer simulation, an example of the separate reception of circularly polarized components of the IS signal with their multiplication is given, including a situation when noise-like components are present.
This paper extends the work of the authors on highly sensitive broadband silicon germanium heterojunction bipolar transistor (SiGe HBT) low-noise amplifiers with regard to their optimization based on the genetic algorithm and proposes a design methodology. The methodology aims at achieving a sub-1 dB noise figure at room temperature. The amplifier uses inductively degenerated common-emitter transistors in a cascode configuration, and a noise figure close to the minimum achievable one is obtained by biasing the SiGe HBTs at an emitter current density corresponding to minimum noise. Noise matching is achieved by connecting several identical transistors in parallel, while impedance matching relies on limiting the number of passive components for the matching network to the absolute minimum. This is done by the base-collector capacitance used as a network element and by means of an additional noiseless on-chip component. A sub-1 dB noise figure of 0.6 dB is shown by simulation without optimization by the genetic algorithm, with a return loss better than 10 dB, using a 130 nm SiGe HBT process. The bandwidth of the low-noise amplifier spans from 300 MHz to 1.4 GHz. The methodology validates that SiGe HBTs are suitable for broadband ultra-low noise amplifiers for radio astronomy and that the performance of the proposed amplifier can be further optimized.
Despite the advances in cancer nanotheranostics, there are limitations associated with targeted delivery to the tumor and objective image interpretation. This paper investigates the role of a magnetic nanocomplex (MNC) synthesized from gadopentetic acid and antitumor agent doxorubicin (DOX) as a theranostic system to improve antitumor activity under constant magnetic (CMFs) and electromagnetic fields (EMFs) as well as provide additional prognostic information on magnetic resonance imaging (MRI) scans in animals with Lewis lung carcinoma. Heterogeneity values in the tumor core were twice higher than those in the tumor periphery or the peritumoral tissue on both T1-weighted and short tau inversion recovery (STIR) images. Heterogeneity parameters extracted from the tumor core and periphery as well as the fractal dimension of the peritumoral tissue were significantly different between conventional DOX and MNC + CMF + EMF treatment $\boldsymbol{(\mathrm{p}\leq 0.05)}$ on STIR images. Tumor growth kinetics correlated negatively $\boldsymbol{(\mathrm{r}_{\mathrm{s}}=-0.89)}$ with the fractal dimension of the peritumoral tissue on MRI scans after DOX, while a strong positive correlation $\boldsymbol{(\mathrm{r}_{\mathrm{s}}=0.83)}$ was noted in animals receiving MNC + CMF + EMF $\boldsymbol{(\mathrm{p}\leq 0.05)}$ . Treatment response evaluation based on multifunctional MNCs can deepen our understanding of physicochemical interactions between the tumor and its microenvironment and drive personalized approaches for cancer nanotheranostics.
The problem of finding the algorithm for estimating the spectral power density (SPD) of the input signal of the receiver when observing the signal from the output of the quadratic detector of the receiver is solved. Formulas for calculating the boundary errors in estimating the SPD parameter and the fluctuating sensitivity of a radiometric receiver operating according to the obtained algorithm are obtained. The possibility of using the likelihood functional for stationary Gaussian processes in solving the problem of signal processing after a quadratic detector is substantiated by simulation modelling.
New modification of the integral equation technique is used for mathematical modelling of the plane E- polarized electromagnetic wave scattering by a single flat electrically conductive strip and flat grating consisting of finite number of electrically conductive strips. The scattering problems are formulated in the form of two-dimensional external mixed boundary-value problems for the homogeneous Helmholtz equation on corresponding segment or system of segments. The target of the examination is to find correct, simple and effective mathematical model of the plane E- polarized electromagnetic wave scattering by electrically conductive strip gratings.
