Determination of autodyne oscillator parameters by the beating method

The research results of oscillator internal parameters influence the features of dynamic autodyne characteristics formation in the case of external oscillator signal influence are presented. The equivalent circuit with a single-circuit oscillating system is considered as a model of the autodyne oscillator. Abbreviated equations are obtained by an averaging method and then they are linearized for small disturbances in a vicinity of the steady-state mode. The obtained characteristics for the beating mode are compared with characteristics of autodynes for short-range radar technology. The essential differences in behavior of the oscillator with acting the external oscillator and the oscillator with acting the own reflected signal have been found. The physical sense of the frequency dispersion phenomenon for the autodyne frequency deviation in the vicinity of hypothetical “zero” beating is discovered. The research results of dynamic autodyne characteristics in the frequency conversion mode of signals modulated on amplitude or frequency are given. It is shown that to suppress the spurious harmonics of the beating frequency, it is advisable to take additional measures for generated frequency stabilization in autodyne frequency converters, for instance, using the external feedback in the oscillator or using the external high-Q resonator. The adequacy of theoretical conclusions is confirmed by results of experimental investigations of the hybrid-integrated module of 8 mm-range made on the basis of the planar two-meza Gunn diode. Oscillator characteristics obtained by the beating method are compared with results of investigation fulfilled with the help of modulation characteristics. It is shown that errors in experimental determination of dynamic characteristics of autodyne oscillators caused by frequency limitations of a pin-diode typical for the modulation characteristic method can be eliminated. Problems of practical application of obtained results in real radar systems using autodyne oscillators are discussed

Modulation characteristics of microwave autodyne oscillators

General relations for the analysis of autodyne and modulation characteristics are obtained in the form of differential equations with the retarded argument. Solutions for characteristics of frequency response of autodyne variations of the oscillation amplitude and phase as well as the auto-detecting signal of UHF oscillator under influence of the proper reflected radiation are derived. The solution of the same equation system is given for frequency responses of the modulation deepness of oscillation amplitude and frequency as well as the auto-detecting signal in the case of the reflection factor modulation by the high-frequency signal. Calculations of autodyne and modulation characteristics are fulfilled at different values of inherent parameters of UHF oscillators. Non-isochronous and non-isodromous properties of autodyne oscillators are investigated. Phenomena of frequency auto-detecting are considered. A method for dynamic properties determination is substantiated according to its modulation characteristics at the oscillation amplitude registration. The results of theoretical analysis are confirmed by experimental data obtained on the example of hybrid-integrated oscillator of 8mm-range on the Gunn diode

Analysis of signals of stabilized autodynes

Results of the autodyne signal analysis of the self-oscillating systems stabilized in frequency by the external high-quality cavity are given. The coupling between the main and stabilizing cavities is realized on the basis of a pass-reflective filter with a resistive link. Mathematical equations are obtained describing an autodyne response onto impact of the own radiated signal reflected from a target. The analysis of phase, amplitude, frequency and amplitude-frequency characteristics of the autodyne system is fulfilled. The calculation of an autodyne signal spectrum is discussed. A new type of nonlinear distortions of an autodyne signal is examined, which is caused by a frequency dispersion of an oscillating system of the stabilized autodyne. Advantages of the stabilized autodyne compared to the usual single-tuned autodyne oscillator are shown

Theory of stabilized autodyne oscillators at the large reflected signal

Research results on autodyne oscillator stabilized by an external high-Q cavity are presented for the case of the large reflected signal, when amplitude of the reflected wave is commensurable with amplitude of natural oscillations. Expressions describing an autodyne response of the oscillator on the influence of the proper radiation reflected from a target are obtained. Calculations of amplitude, frequency and spectral characteristics of the autodyne system are performed. Conditions of exact tuning of the stabilized cavity are determined. Investigations of stabilized autodyne parameters at small distance to the reflected object are provided. It is shown that to expand the dynamic range of the autodyne system it is expedient to use the large coupling between cavities. Recommendations concerning practical application of the obtained results in the short-range radar are given

Визуализация потока воздуха в вихревой трубе с использованием различных моделей турбулентности

Visualization of air flow in Ranque-Hilsch vortex tube performed by numerical simulations with standard k-ε and SAS-SST turbulence models is presented in the paper. SAS-SST turbulence model predicted the existence of secondary largescale vortex structures within the computational domain instead k-ε model showed axisymmetrical flow. Existence of large-scale secondary vortex structures is in agreement with experimental data.В статье представлены результаты визуализации потока воздуха в вихревой трубе Ранка-Хилша, выполненной с помощью численного моделирования. Были использованы k-ε и SAS-SST модели турбулентности. SAS-SST модель турбулентности показала наличие вторичных крупномасштабных вихревых структур в расчетном домене, в отличие от k-ε модели. Факт наличия крупномасштабных вторичных вихревых структур хорошо согласуется с экспериментальными данными

Model of ionic currents through microtubule nanopores and the lumen

It has been suggested that microtubules and other cytoskeletal filaments may act as electrical transmission lines. An electrical circuit model of the microtubule is constructed incorporating features of its cylindrical structure with nanopores in its walls. This model is used to study how ionic conductance along the lumen is affected by flux through the nanopores when an external potential is applied across its two ends. Based on the results of Brownian dynamics simulations, the nanopores were found to have asymmetric inner and outer conductances, manifested as nonlinear IV curves. Our simulations indicate that a combination of this asymmetry and an internal voltage source arising from the motion of the C-terminal tails causes a net current to be pumped across the microtubule wall and propagate down the microtubule through the lumen. This effect is demonstrated to enhance and add directly to the longitudinal current through the lumen resulting from an external voltage source, and could be significant in amplifying low-intensity endogenous currents within the cellular environment or as a nano-bioelectronic device.Comment: 43 pages, 6 figures, revised versio

The problem of osteoarthritis of the knee joint and running through the prism of magnetic resonance tomography

The number of women and the elderly has now increased among marathon runners. This cohort has a high risk of osteoarthritis development. The hypothesis, based on little scientific evidence, is that the additional stress on knee joints that occurs during long running can potentially lead to damage to joint structures and osteoarthritis development. The review presents modern generalized data on magnetic resonance imaging (MRI) of knee joints in long-distance runners. Special attention is paid to the syndrome of fluid increase in subchondral bone, which is determined by increasing the signal intensity in T2-weighted images (decrease in T1-weighted images), called bone marrow oedema (BMO). Classification and pathogenetic variants of BMO development (theory of intrusion and contusion) are presented. Particular cases of BMO development in marathon runners are considered. The dynamics of BMO in different time intervals after the races in beginners and professional marathon runners is described. Changes in MRI images of knee cartilage after running on the treadmill in healthy women and in women suffering from osteoarthritis are shown. A comparison of the frequency of osteoarthritis of knee joints in runners compared to footballers and weightlifters was made. The conclusion was made on the preventive effect of long walking and running (at least 12.5 km/week), including marathon distances, on the development and progression of osteoarthritis of knee joints

Hydrobionts of a freshwater oil-polluted northern lake: bioaccumulation of heavy metals in fish and the rate of ecosystem recovery

The response of phytoplankton, zooplankton, benthic and fish community structure to one of the biggest oil spill in history of Komi Republic (north-west part of Russia) was investigated using data from a long-term survey off the polluted lake. The characteristics of aquatic freshwater communities observed in the study area 10, 11 and 22 years after the spill (1994) were compared to find out the rate of natural recovery of the ecosystem after oil decontamination of bottom sediments. The concentrations of fifteen trace metals (Al, Cr, Fe, Co, Ni, Cu, Zn, As, Mo, Cd, Sb, Pb, U, Bi, Th) were analyzed in the tissues (muscle) of three fish species. The concentrations of Al (3-309 mg/kg), Cr (0,1-3,71 mg/kg), Fe (8,6-317 mg/kg), and Cu (0,09-99 mg/kg) in fishes from polluted lake resulted in most cases higher than reference thresholds. Quantitative and qualitative indicators of aquatic invertebrates from polluted lake reach those one of unpolluted lake but do not fully recover 22 years after the spill, despite that oil concentration in water column and in bottom sediments was lower than reference tresholds. We conclude that natural recovery rate of aquatic freshwater ecosystems in northern regions after oil pollution is extremely low. The purification of water and bottom sediments of oil-polluted northern water bodies is necessary for stimulation of ecosystem restoration