Investigation of 6S 1/2–8S 1/2 two-photon transition of cesium atoms by a single 822 nm laser

We experimentally investigate the 6S 1/2–8S 1/2 two-photon transition in cesium vapor by a single laser. A blue (455.5 and 459.3 nm) fluorescence signal is observed as a result of 822.5 nm laser beams illuminating the Cs vapor with a counter-propagating configuration. The dependences of the fluorescence intensity on the polarization combinations of the laser beams, laser power and vapor temperature are studied to obtain optimal experimental parameters. The frequency difference between the two hyperfine components of 4158 (7) MHz is measured with a Fabry–Perot interferometer as a frequency reference. Such a large spectral isolation and the insensitivity to the Earth’s magnetic field enable the 6S 1/2–8S 1/2 transition to be a stable frequency standard candidate for a frequency-doubled 1644 nm laser in the U-band window for quantum telecommunication.

Ultra-high Accuracy Microwave Positioning System based on Free Space Frequency Synchronization

The ultra-high accuracy indoor and outdoor positioning is fundamental for a variety of applications such as industrial automation, Internet of Things and structure monitoring. Approaches based on optical methods, ultrasound and computer vision areoften suffer from limited coverage areas, obstruction by objects and high computing load. While the GNSS and conventionalradar-like radio frequency (RF) methods can suffer from insufficient accuracy and are not feasible for many scenarios. Now weachieve an inverse GPS microwave positioning system based on ultra-stable frequency synchronization in free space andcarrier phase difference principle to surpass the limitation of current methods. The stability of frequency synchronization link isbetter than 10−13/s . The distance resolution retrieved from phase information is 25 micrometres and the Mean Squred Error(MSE) of three-dimensional positioning is 16 micrometres. An ultra-high accuracy positioning system with large coverage area,compatibility and versatility can potentially be achieved gearing to extensive needs.

INFLUENCE OF THE MESH SHAPE OF THE FINE LITTER CLEANER FOR RAW COTTON ON THE CLEANING EFFECT

Increasing the efficiency of cleaning raw cotton from weeds will ultimately improve the quality of products in the textile industry. It has been established that when using cylindrical mesh on purifiers with peg drums, the exciting force acting on the strips from the side of the net has a stable frequency, determined mainly by the frequency of rotation of the peg drum. This mode of operation of the cleaner does not effectively remove trash impurities. To improve the efficiency of the cleaner, it is proposed to use a grid in the form of a multifaceted prism. It was found that, by design conditions, the minimum number of mesh faces is four. The dependence of the cleaning effect on the number of faces of the perforated mesh of the cleaner has been experimentally obtained. It was found that with an increase in the number of mesh edges, the cleaning effect and fiber damage decrease. With the number of faces equal to six, it is possible to achieve an increase in the cleaning effect by an average of 16 % with a slight increase in fibre damage.

Selfish chromosomal drive shapes recent centromeric histone evolution in monkeyflowers

Centromeres are essential mediators of chromosomal segregation, but both centromeric DNA sequences and associated kinetochore proteins are paradoxically diverse across species. The selfish centromere model explains rapid evolution by both components via an arms-race scenario: centromeric DNA variants drive by distorting chromosomal transmission in female meiosis and attendant fitness costs select on interacting proteins to restore Mendelian inheritance. Although it is clear than centromeres can drive and that drive often carries costs, female meiotic drive has not been directly linked to selection on kinetochore proteins in any natural system. Here, we test the selfish model of centromere evolution in a yellow monkeyflower (Mimulus guttatus) population polymorphic for a costly driving centromere (D). We show that theDhaplotype is structurally and genetically distinct and swept to a high stable frequency within the past 1500 years. We use quantitative genetic mapping to demonstrate that context-dependence in the strength of drive (from near-100%Dtransmission in interspecific hybrids to near-Mendelian in within-population crosses) primarily reflects variable vulnerability of the non-driving competitor chromosomes, but also map an unlinked modifier of drive coincident with kinetochore protein Centromere-specific Histone 3 A (CenH3A). Finally, CenH3A exhibits a recent (<1000 years) selective sweep in our focal population, implicating local interactions withDin ongoing adaptive evolution of this kinetochore protein. Together, our results demonstrate an active co-evolutionary arms race between DNA and protein components of the meiotic machinery inMimulus, with important consequences for individual fitness and molecular divergence.

Toward Wideband Frequency Rejection: An Efficient Frequency Selective Scheme

This paper outlines a Frequency Selective Surface configuration designed for wideband filtering characteristics. The proposed design topology includes two-layer conductive elements printed on an FR4 substrate with a thickness of 1.6 mm. On the front side, a square loop and four branches are placed, and on the other side of the substrate, there is another square loop supported by two modified vertical arms. The use of square loops as one of the trendy elements in frequency selective designs provides the opportunity to tune the resonances and obtain the desired Performance; The proposed 10 mm × 10 mm frequency selective surface unit cell structure rejects the frequency band of 2-14 GHz covering WiMAX, WLAN, and X band in-service frequency ranges. It has three resonant frequencies and works well in various incident angles. There is a good match between the simulated results and the tested results. Stable frequency response, simple structure, and easy production are useful features of the developed scheme.

Checking the adequacy of the method for generating a random process of disturbance of oscillations of rail carriages according to the impulse response of the forming filter

Usually, to study the vibrations of rail carriages, the equivalent geometric unevenness of the track obtained as a result of processing the records of the track measuring car is taken as a disturbance. Such a record contains a certain set of irregularity wavelengths, for example, 50, 25 and 12.5 m. However, when it is used to simulate disturbances at different operation speeds, these wavelengths will correspond to frequencies depending on the given speed of motion, which is not permissible, since a stable frequency range from 0.2 to 10 Hz is required to excite the vibrations of all the bodies included in the carriage. To eliminate this drawback, in the previously performed works it was proposed to generate a random process of geometric irregularities for a given operation speed by changing the set of wavelengths included in the irregularities. In this paper, based on the study of random oscillations of a simplified model of a rail carriage, as a system with one degree of freedom, the adequacy of the method for generating a random disturbance process is verified in two ways. In the first method, it was found that the characteristics of random oscillations of such a model, obtained in the time domain on the basis of numerical integration of the equation of motion when specifying the generated disturbance, have satisfactory convergence with similar characteristics found by the frequency method using Shannon's formula. In the second verification method, the cross-correlation function and the mutual spectral density between the disturbance and the bouncing oscillations were determined from the generated disturbance realization and obtained by numerical integration of the vibration process realization. Then, using the method of identifying the dynamic system, experimental amplitude and phase frequency characteristics were found, which showed satisfactory convergence with the corresponding calculated characteristics obtained by numerically solving the equation of oscillations of the model under study. On the basis of the results obtained, it was concluded that the considered method of generating a random process of disturbance is sufficiently adequate and that it can be applied to solve problems of the dynamics of rail carriages.

A Single-Phase Globally Stable Frequency-Locked Loop Based on the Second-Order Harmonic Oscillator Model

This paper presents a novel frequency-locked-loop (FLL) scheme that provides estimates of the in-phase and square-phase fundamental components of a distorted single-phase reference signal and an estimate of its fundamental angular frequency. The main feature of the proposed scheme is that its design is fully based on the dynamical model of a single-phase signal generator, namely, the second-order harmonic oscillator (SOHO), which adds originality to the scheme. In fact, the proposed scheme owns a particular structure involving a set of orthogonal signals, which can be seen as the fixed-frame representation of three-phase balanced signals. Additionally, a plug-in block is included as a mechanism to mitigate the effect of the harmonic distortion. A proof of global stability for the proposed scheme based on nonlinear argumentation is also included, which contributes to the novelty of the work and ensures convergence disregarding the initial conditions of the to-be-estimated signal components. In addition, explicit conditions are presented for the tuning of control parameters. Experimental results corroborate the performance of the proposed scheme under angular frequency variations, phase jumps, voltage sags and harmonic distortion on the reference signal. For comparison purposes, also the state-of-the-art second-order-generalized-integrator-based FLL and the single-phase synchronous-reference frame phase-locked loop are tested.

Energy and Communication Efficient FSS for Equivalent Model of Hard-Coated Energy Saving Glass

An energy and communication efficient FSS is presented for equivalent model of ESG with hard coating. An FSS with second order band-pass response has been realized by full wave 3D simulations and results have been imitated using an equivalent circuit model to calculate the value of lumped elements. The design is composed of three cascaded FSSs with two glass layers of 6 mm each in between. Due to this topology the transmission of useful RF/microwave signals has been improved for a wider bandwidth, increased thermal insulation, stable frequency and polarization at oblique incidence and security for WLAN at 2.45 GHz.