8 research outputs found
Dipole Moment Variation Clears Up Electronic Excitations in the Stacked Complexes of Fluorescent Protein Chromophores
No full textMechanism of Guanosine Triphosphate Hydrolysis by the Visual Proteins Arl3-RP2: Free Energy Reaction Profiles Computed with Ab Initio Type QM/MM Potentials
No full textWe report the results of calculations of the Gibbs energy profiles of the guanosine triphosphate (GTP) hydrolysis by the Arl3-RP2 protein complex using molecular dynamics (MD) simulations with ab initio type QM/MM potentials. The chemical reaction of GTP hydrolysis to guanosine diphosphate (GDP) and inorganic phosphate (Pi) is catalyzed by GTPases, the enzymes, which are responsible for signal transduction in live cells. A small GTPase Arl3, catalyzing the GTP → GDP reaction in complex with the activating protein RP2, constitute an essential part of the human vision cycle. To simulate the reaction mechanism, a model system is constructed by motifs of the crystal structure of the Arl3-RP2 complexed with a substrate analog. After selection of reaction coordinates, energy profiles for elementary steps along the reaction pathway GTP + H2O → GDP + Pi are computed using the umbrella sampling and umbrella integration procedures. QM/MM MD calculations are carried out, interfacing the molecular dynamics program NAMD and the quantum chemistry program TeraChem. Ab initio type QM(DFT)/MM potentials are computed with atom-centered basis sets 6-31G** and two hybrid functionals (PBE0-D3 and ωB97x-D3) of the density functional theory, describing a large QM subsystem. Results of these simulations of the reaction mechanism are compared to those obtained with QM/MM calculations on the potential energy surface using a similar description of the QM part. We find that both approaches, QM/MM and QM/MM MD, support the mechanism of GTP hydrolysis by GTPases, according to which the catalytic glutamine side chain (Gln71, in this system) actively participates in the reaction. Both approaches distinguish two parts of the reaction: the cleavage of the phosphorus-oxygen bond in GTP coupled with the formation of Pi, and the enzyme regeneration. Newly performed QM/MM MD simulations confirmed the profile predicted in the QM/MM minimum energy calculations, called here the pathway-I, and corrected its relief at the first elementary step from the enzyme–substrate complex. The QM/MM MD simulations also revealed another mechanism at the part of enzyme regeneration leading to pathway-II. Pathway-II is more consistent with the experimental kinetic data of the wild-type complex Arl3-RP2, whereas pathway-I explains the role of the mutation Glu138Gly in RP2 slowing down the hydrolysis rate
Simulation of microstrip radio altimeter antenna for aircraft
No full textThe purpose of the article is to carry out mathematical modeling of the main characteristics and parameters of a microstrip antenna, the dielectric substrate of which is created from a domestic ceramic sample and to substantiate the use of a microstrip antenna as a transmitting and receiving antenna in a radio altimeter. It is shown that a microstrip antenna on a ceramic material substrate with a relative permittivity ε = 9.6 and a thickness of 0.2 mm has good electrical parameters in the frequency range of 31.5–33.5 GHz. Including the width of the antenna radiation pattern at the level of –3 dB is 12.5 degrees in the horizontal plane and 26.7 degrees in the vertical plane. In this case, the antenna gain is 17 dB and the level of the first side lobe is –20 dB relative to the main antenna lobe. Also the practical application of microstrip array antennas inphase as a transmitting and receiving antenna for a radio altimeter installed on aircraft is described in the article. The range of the altimeter reaches 300 m
Ultra-wideband Radio Receiver of the Measuring System of the Microwave Range
No full textThe purpose of the article is to substantiate the method and circuit design option for constructing an ultra-wideband radio receiver of the measuring system, mathematical modeling of the main parameters of the receiving path. It is shown the block diagram and general characteristics of the receiver. Including the dynamic range of received signals 111 dB, operating frequency range from 1 to 18 GHz. The article discusses the components of the receiver, such as: an automatic power control unit with a dynamic range of 50 dB and a tuning step of 1 dB, a preselector with six bandwidths 1–2,5; 2,5–4; 4–6; 6–11; 11–15; 15–18 GHz and a frequency conversion unit with three conversion steps. The structure is substantiated and the parameters of each of the blocks are given. A frequency conversion scheme with a final intermediate frequency of 0.75 GHz and a bandwidth of 500 MHz is considered in detail. Modeling of the noise figure, the distribution of the signal level along the receiver path from the input signal level and the results of modeling the output signal of the IF receiver
Element for Matching a Waveguide Transmission Line with a Diode
No full textThe article deals with the issues of matching a waveguide transmission line with millimeter wave diodes. The implementation of the transition of a rectangular waveguide to a microstrip switching line in the form of a line of the fin-line type is described. The computer simulation results of the transmission coefficient module of the developed element and the standing wave coefficient by voltage separately for the transition from a rectangular waveguide to a microstrip transmission line and as part of an amplitude detector are shown. A joint application of the developed element with a microstrip detector based on a Schottky diode in the frequency range from 118.1 to 178.4 GHz is proposed. The results of measuring its parameters and the results of determining the sensitivity are given, as well as the evaluation of the results obtained is performed. The obtained results proved the possibility of using the matching element of a waveguide transmission line with a diode in the millimeter wavelength range
Моделирование микрополосковой антенны радиовысотомера для летательного аппарата
No full textThe purpose of the article is to carry out mathematical modeling of the main characteristics and parameters of a microstrip antenna, the dielectric substrate of which is created from a domestic ceramic sample and to substantiate the use of a microstrip antenna as a transmitting and receiving antenna in a radio altimeter. It is shown that a microstrip antenna on a ceramic material substrate with a relative permittivity ε = 9.6 and a thickness of 0.2 mm has good electrical parameters in the frequency range of 31.5–33.5 GHz. Including the width of the antenna radiation pattern at the level of –3 dB is 12.5 degrees in the horizontal plane and 26.7 degrees in the vertical plane. In this case, the antenna gain is 17 dB and the level of the first side lobe is –20 dB relative to the main antenna lobe. Also the practical application of microstrip array antennas inphase as a transmitting and receiving antenna for a radio altimeter installed on aircraft is described in the article. The range of the altimeter reaches 300 m.Целью статьи является проведение математического моделирования основных характеристик и параметров микрополосковой антенны, диэлектрическая подложка которой создана из отечественного образца керамики, и обоснование применения микрополосковой антенны в качестве приемо-передающей антенны в радиовысотомере. Показано, что микрополосковая антенна имеет хорошие электрические параметры в частотном диапазоне 31,5–33,5 ГГц в случае размещения ее на подложке из керамического материала с относительной диэлектрической проницаемостью ε = 9,6 и толщиной 0,2 мм. В том числе ширина диаграммы направленности антенны по уровню –3 дБ составляет 12,5 град в горизонтальной плоскости и 26,7 град в вертикальной плоскости. При этом коэффициент усиления антенны равен 17 дБ, а уровень первого бокового лепестка составляет –20 дБ относительно главного лепестка антенны. Также в статье предложено практическое применение антенной решетки синфазных микрополосковых антенн в качестве приемо-передающей антенны радиовысотомера, устанавливаемого на летательные аппараты. Дальность действия высотомера достигает 300 м
Сверхширокополосный радиоприемник измерительной системы СВЧ диапазона
No full textThe purpose of the article is to substantiate the method and circuit design option for constructing an ultra-wideband radio receiver of the measuring system, mathematical modeling of the main parameters of the receiving path. It is shown the block diagram and general characteristics of the receiver. Including the dynamic range of received signals 111 dB, operating frequency range from 1 to 18 GHz. The article discusses the components of the receiver, such as: an automatic power control unit with a dynamic range of 50 dB and a tuning step of 1 dB, a preselector with six bandwidths 1–2,5; 2,5–4; 4–6; 6–11; 11–15; 15–18 GHz and a frequency conversion unit with three conversion steps. The structure is substantiated and the parameters of each of the blocks are given. A frequency conversion scheme with a final intermediate frequency of 0.75 GHz and a bandwidth of 500 MHz is considered in detail. Modeling of the noise figure, the distribution of the signal level along the receiver path from the input signal level and the results of modeling the output signal of the IF receiver.Целью статьи является обоснование способа и схемотехнического варианта построения сверхширокополосного радиоприемника измерительной системы, проведение математического моделирования основных параметров приемного тракта. Показаны структурная схема и общие характеристики приемника, в том числе динамический диапазон принимаемых сигналов, составляющий 111 дБ, рабочий диапазон частот от 1 до 18 ГГц. В статье рассмотрены составные блоки приемника, такие как блок автоматического регулирования мощности с динамическим диапазоном 50 дБ и шагом перестройки 1 дБ, преселектор с шестью полосами пропускания 1–2,5; 2,5–4; 4–6; 6–11; 11–15; 15–18 ГГц и блок преобразования частот с тремя ступенями преобразования. Обоснована структура и приведены параметры каждого из блоков. Подробно рассмотрена схема преобразования частот с конечной промежуточной частотой 0,75 ГГц и полосой пропускания 500 МГц. Представлены результаты моделирования коэффициента шума, распределения уровня сигнала по тракту приемника в зависимости от уровня входного сигнала и выходного сигнала ПЧ-приемника
Элемент согласования волноводной линии передачи с диодом
No full textThe article deals with the issues of matching a waveguide transmission line with millimeter wave diodes. The implementation of the transition of a rectangular waveguide to a microstrip switching line in the form of a line of the fin-line type is described. The computer simulation results of the transmission coefficient module of the developed element and the standing wave coefficient by voltage separately for the transition from a rectangular waveguide to a microstrip transmission line and as part of an amplitude detector are shown. A joint application of the developed element with a microstrip detector based on a Schottky diode in the frequency range from 118.1 to 178.4 GHz is proposed. The results of measuring its parameters and the results of determining the sensitivity are given, as well as the evaluation of the results obtained is performed. The obtained results proved the possibility of using the matching element of a waveguide transmission line with a diode in the millimeter wavelength range. Рассмотрены вопросы согласования волноводной линии передачи с диодами миллиметрового диапазона длин волн. Описана реализация перехода с прямоугольного волновода на микрополосковую линию передачи в виде линии типа фин-лайн. Показаны результаты компьютерного моделирования модуля коэффициента передачи разработанного элемента и коэффициента стоячей волны по напряжению отдельно перехода с прямоугольного волновода на микрополосковую линию передачи и в составе амплитудного детектора. Представлена реализация совместного применения разработанного элемента с микрополосковым детектором на базе диода Шоттки в диапазоне частот от 118,1 до 178,4 ГГц. Приведены результаты измерения его параметров и определения чувствительности. При оценке полученных данных подтверждена возможность применения разработанного элемента согласования волноводной линии передачи с диодом в миллиметровом диапазоне длин волн
