Order Modes Research Articles

Accurately Measuring Molecular Rotational Spectra in Excited Vibrational Modes.

Although gas phase rotational spectroscopy is a mature field for which millions of rotational spectral lines have been measured in hundreds of molecules with sub-MHz accuracy, it remains a challenge to measure these rotational spectra in excited vibrational modes with the same accuracy. Recently, it was demonstrated that virtually any rotational transition in excited vibrational modes of most molecules may be made to lase when pumped by a continuously tunable quantum cascade laser (QCL). Here, we demonstrate how an infrared QCL may be used to enhance absorption strength or induce lasing of terahertz rotational transitions in highly excited vibrational modes in order to measure their frequencies more accurately. To illustrate the concepts, we used a tunable QCL to excite v3 R-branch transitions in N2O and either enhanced absorption or induced lasing on 20 v3 rotational transitions, whose frequencies between 299 and 772 GHz were then measured using either heterodyne or modulation spectroscopy. The spectra were fitted to obtain the rotational constants B3 and D3, which reproduce the measured spectra to within the experimental uncertainty of ± 5 kHz. We then show how this technique may be generalized by estimating the threshold power to make any rotational transition lase in any N2O vibrational mode.

ELMA: Energy-Based Learning for Multi-Agent Activity Forecasting

This paper describes an energy-based learning method that predicts the activities of multiple agents simultaneously. It aims to forecast both upcoming actions and paths of all agents in a scene based on their past activities, which can be jointly formulated by a probabilistic model over time. Learning this model is challenging because: 1) it has a large number of time-dependent variables that must scale with the forecast horizon and the number of agents; 2) distribution functions have to contain multiple modes in order to capture the spatio-temporal complexities of each agent's activities. To address these challenges, we put forth a novel Energy-based Learning approach for Multi-Agent activity forecasting (ELMA) to estimate this complex model via maximum log-likelihood estimation. Specifically, by sampling from a sequence of factorized marginalized multi-model distributions, ELMA generates most possible future actions efficiently. Moreover, by graph-based representations, ELMA also explicitly resolves the spatio-temporal dependencies of all agents' activities in a single pass. Our experiments on two large-scale datasets prove that ELMA outperforms recent leading studies by an obvious margin.

Intramode Brillouin Scattering Properties of Single-Crystal Lithium Niobate Optical Fiber

Ordinary step-type fiber usually has only one obvious Brillouin scattering gain peak with a low gain coefficient, resulting in a poor sensing performance. As a promising material for nonlinear photonics, lithium niobate can significantly improve the Brillouin gain due to its higher refractive index when replaced with the core material. Furthermore, the higher-order acoustic modes make the Brillouin gain spectrum exhibit multiple scattering peaks, which could improve the performance of sensors. In this study, we simulated the Brillouin scattering properties of different modes of intramode in step-index lithium niobate core fibers. We analyzed the intramode-stimulated Brillouin scattering properties of different pump–Stokes pairs for nine LP modes (LP01, LP11, LP21, LP02, LP31, LP12, LP41, LP22, and LP03) guided in fiber. The results show that both the effective refractive index and Brillouin scattering frequency shift are decreased with the increase in the nine mode orders, and the values of which are 2.2413 to 2.1963, and 21.17 to 20.73 GHz, respectively. The typical back-stimulated Brillouin scattering gain is obtained at 1.7525 m−1·W−1. These simulation results prove that the Brillouin gain of the LiNbO3 optical fiber structure can be significantly improved, which will pave the way for better distributed Brillouin sensing and for improving the transmission capacity of communication systems.

Experiences of Nurses on Tutor-marker Feedback in their Postgraduate Open and Distance Learning Course at the University of Namibia

The development of education in Namibia is guided by four broad goals: access equity, quality and democracy. Open and distance learning (ODL) remains one of the most convenient modes of study, promoting access to higher education in Namibia. However, studies have pointed out that feedback plays a significant role in the improvement of distance education and students’ performance. Institutions of higher education need to constantly assess the experiences of students who choose to study through this mode in order to devise strategies that can be used to address the challenges. The experiences of postgraduate nursing students regarding tutor-marker feedback in Namibia have not been extensively researched. The purpose of this study was to explore and describe the experiences of nurses regarding tutor-marker feedback in their postgraduate ODL course at the University of Namibia. A qualitative, explorative and contextual study was conducted. The sample comprised postgraduate nursing diploma students specialising in nursing education and health service management in the 2020 academic year, studying through ODL. Purposive sampling was utilised. Data were collected from 17 participants using semi-structured interviews. The data were analysed using qualitative thematic analysis and strategies to ensure trustworthiness. Ethical considerations related to the study were implemented. The analysed data revealed three themes, namely: students’ experience of tutor-marker feedback, challenges of marking feedback, and recommendations for improvement. Therefore, the findings of this study call for actions and plans from ODL management teams to address the challenges identified in this study. For effective learning to take place in ODL, timely and helpful feedback from tutors should be provided.

Arbitrary higher-order optical spatial state generation by using spontaneously broken degeneracy modes in helically twisted ring-core hole assisted fibers.

A helically twisted ring-core hole assisted fiber (HAF) is proposed for an arbitrary higher-order spatial state generation. In usual circular core fibers, HE and EH modes are degenerate and have vector field distributions. We will show the degeneracy of these modes having specific azimuthal mode order is lifted by periodically placing air-holes around the core with specific symmetry while preserving their vector field distributions. It is called spontaneously broken degeneracy (SBD) in this paper. Azimuthal order of the SBD modes can be changed with the arrangement of surrounding air-holes. By using this SBD modes, it is shown that arbitrary higher-order spatial state generation, including orbital angular momentum (OAM) state, is possible based on a geometric phase existing in twisted fibers. Furthermore, by using periodically inverted twisting, efficient OAM state generation is possible by accumulating the geometric phase. The topological charge can be changed by changing the arrangement of surrounding air-holes. Since the mechanism does not depend on a phase matching, such as a long-period grating, but on a topological effect, the wavelength dependence is very small, leading to novel and efficient mechanism for the manipulation of the spatial state of the light.

Exploring the ellipticity dependency on vector helical Ince-Gaussian beams and their focusing properties.

We present a numerical study of the intensity and polarization structure of vector helical Ince-Gaussian (VHIG) modes, which present a distinct subclass of vector Ince-Gaussian modes with defined parameter settings. The intensity profile of VHIG beams has an elliptic hollow structure, while the polarization distribution shows multiple single-charge polarization vortices arranged along a line. By selecting the mode order, phase factor and ellipticity of the VHIG beams, we can control the number of elliptic rings, the number of polarization vortices, and the topology of the vector singularity. Furthermore, we simulate the focusing properties of VHIG beams based on vector diffraction theory. Our results indicate that the ellipticity parameter of VHIG beams could be a valuable degree of freedom to generate attractive transverse profiles and longitudinal distributions under focusing, which may have implications for lithography, material processing, optical communication, and even optical trapping and manipulation.

Development of a Spacerless Flow-Cell Cavity for Vibrational Polaritons.

We developed a spacerless flow-cell cavity for the observation of vibrational strong coupling and demonstrate its availability in two samples with a C≡N bond: a metal complex (aq) and an ionic liquid. It is shown that the cavity length can be tuned over a wide range to investigate coupling with different order Fabry-Pérot cavity modes without reassembling the cavity. In the ionic liquid, analyses based on the coupled harmonic oscillator model with multiple vibrational modes show that the Rabi splitting parameters and the square root of the integrated absorption intensity are proportional among the three neighboring vibrational modes. Our spacerless cell structure simplifies the comparison of the different vibrational strong coupling measurements, such as the mode order dependence and the coupling to different molecular vibrations.

Simulation on a non-axisymmetric ring resonator with a nano-antenna for heat-assisted magnetic recording

Heat-assisted magnetic recording is a technology to improve recording density of hard disk drives. The authors’ group previously proposed a device, in which a Au nano-antenna as a near-field transducer was attached to a GaAs ring resonator as a light source. The ring resonator should stably oscillate with a single mode to generate near-field light at the tip of the nano-antenna with sufficient energy density. A non-axisymmetric ring resonator structure was proposed this time to improve the energy density and laser oscillation stability. When the decenter between the inner and outer circles of the ring resonator increased, the resonance frequency increased and eigenmodes with higher radial mode order disappeared, which leads to stable laser oscillation. Moreover, when the decenter was 200 or 250 nm, the normalized energy density at the tip of nano-antenna increased 1.2–2.4 times compared with an axisymmetric ring resonator structure while keeping the quality factor to more than 5000.

Development of a model of an electrical complex for gas air cooling devices of gas field №1 gazprom dobycha Yamburg LLC with a centralized power supply system in the MATLAB/SIMULINK program

THE PURPOSE. To develop a model in MATLAB/SIMULINK environment for the system of mechatronic movement modules (MMD) of the electrical complex, which includes gas air coolers with centralized system of power supply of the gas field 1 of "Gazprom dobycha Yamburg" LLC. To analyze the energy efficiency of MMD ETC ACHE. To perform the experimental research of the EMD EMD ETC ACHE model in the dynamic modes in order to determine the regularity of the influence of single (group) starts on the power supply source overload. To develop a switching algorithm for MMD ETK AHE at direct starts of asynchronous motors (AD), providing restoration of the technological mode within the optimum time after the voltage disappearance for the centralized power supply system.METHODS. The results presented in work are received with use of methods of the theory of electric and magnetic circuits, the theory of electric drive and electric machines, methods of optimization of power supply systems, analytical and numerical methods of applied mathematics, methods of mathematical and computer modeling.RESULTS. In article urgency of a theme is described, features of construction and modelling of ETK GP in the environment MATLAB/SIMULINK with the centralized system of power supply are considered. The comparative analysis of existing methods and calculation of parameters of the substitution schemes of the MMD ETK GP was carried out. Approximate calculation of mechanical and inertial characteristics for creating a model of load (resistance moment) for the motor. The model of EMD of electric motor drive compressor unit was created, as close as possible to the real existing system on the basis of catalog (passport) data of individual elements of electric motor drive unit. There were analyzed and developed proposals to enhance power efficiency of EMD ETC AHE and algorithms, which provide optimal direct start-up of the AHE fan group within the set time after the power failure without overloading of the power supply source, were proposed.CONCLUSIONS. On the basis of results of computer modeling, the peculiarities of operation of EMD ETH ACHE, which require further study and development of corrective measures to improve energy efficiency and reliability of power supply system of GP. Combination of direct starts of single (group) fans of ACHE, obtained at this stage of research of EMD EMD ETC ACHE model, will create the basis (algorithm) for automated control system of this complex, which will ensure restoration of technological mode within optimum time after power outage without overloading of centralized power supply source. Calculation of parameters of individual elements of MMD model of ETC AVO will allow to use data to create other models of ETC GP, which will allow to conduct in-depth research and improve the energy efficiency of the entire system of power supply of GP.

Characteristics of Oscillation in Cavity of Helmholtz Nozzle Generating Self-excited Pulsed Waterjet

Cavity flow oscillations in the axisymmetric cavity are critical to the operating efficiency of self-excited pulsed waterjets, which are widely employed in many practical applications. In this study, the behaviors of a turbulent flow in axisymmetric cavities causing cavity flow oscillations are investigated based on wall pressure characteristics. Experiments are performed using four Helmholtz nozzles with varying length-to-radius ratios at flow velocities of 20–80 m/s. Three orders of hydrodynamic modes in axisymmetric cavity are obtained through the spectral analysis of wall pressure. Based on the experimental results, the empirical coefficient of Rossiter’s formula is modified, and the values of the parameter phase lag and the ratio of convection velocity to free stream velocity are obtained as 0.061 and 0.511, respectively. In addition, the spectral peak with a relatively constant frequency shows that the flow-acoustic resonance is excited significantly. A modified model is introduced based on the fluidic networks to predict the lock-on frequency. The results obtained can provide a basis for the structural optimization of the nozzle to improve the performance of self-excited pulsed waterjets.

Dual-Polarized Inverted Quad-Ridged Flared Horn Antenna With One-Decade Bandwidth for OTA Testing

This letter presents a dual-polarization inverted quad-ridged flared horn antenna with an extremely wideband of more than one decade in the range of 2–20 GHz. The modes of the inverted quad-ridged waveguide are analyzed first. A cross-shaped inverted ridge, with low TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode cutoff frequency and a tip significantly higher than the horn aperture, is proposed. The inner surface of the horn wall is based on a composite curve flare rate. It is optimized to cooperate with the inverted ridge. Furthermore, the polytetrafluoroethylene back cavity replaces metal back cavity to suppress the high- order mode in the back cavity. The measured isolation between the two orthogonal linearly-polarized ports is nearly 45 dB and the reflection coefficient is less than –15 dB over the entire working frequency band.

Metamaterial-enabled arbitrary on-chip spatial mode manipulation

On-chip spatial mode operation, represented as mode-division multiplexing (MDM), can support high-capacity data communications and promise superior performance in various systems and numerous applications from optical sensing to nonlinear and quantum optics. However, the scalability of state-of-the-art mode manipulation techniques is significantly hindered not only by the particular mode-order-oriented design strategy but also by the inherent limitations of possibly achievable mode orders. Recently, metamaterials capable of providing subwavelength-scale control of optical wavefronts have emerged as an attractive alternative to manipulate guided modes with compact footprints and broadband functionalities. Herein, we propose a universal yet efficient design framework based on the topological metamaterial building block (BB), enabling the excitation of arbitrary high-order spatial modes in silicon waveguides. By simply programming the layout of multiple fully etched dielectric metamaterial perturbations with predefined mathematical formulas, arbitrary high-order mode conversion and mode exchange can be simultaneously realized with uniform and competitive performance. The extraordinary scalability of the metamaterial BB frame is experimentally benchmarked by a record high-order mode operator up to the twentieth. As a proof of conceptual application, an 8-mode MDM data transmission of 28-GBaud 16-QAM optical signals is also verified with an aggregate data rate of 813 Gb/s (7% FEC). This user-friendly metamaterial BB concept marks a quintessential breakthrough for comprehensive manipulation of spatial light on-chip by breaking the long-standing shackles on the scalability, which may open up fascinating opportunities for complex photonic functionalities previously inaccessible.

Intelligent Campus and English Visual Education System Design Based on Internet of Things

With the continuous development of the Internet of Things technology, learning and acquiring knowledge through Internet will become an important way for human beings to learn, work, and conduct research. In the field of English language teaching, the cutting-edge research on the Internet of Things-based interactive teaching models is important. The intelligent campus is a new type of campus built aided by advanced techniques such as machine learning and the Internet of Things. In the smart campus, the classroom usually consists of a tangible physical space and an invisible digital space, which can be used to support teaching content through various types of intelligent equipment, promote classroom interaction, and achieve more convenient visualization of educational functions. Based on the initial results of the Internet of Things research, this research establishes a visual education system based on the Internet of Things. At the same time, the Internet of Things is used to study the interactive English teaching mode in order to improve the level of English teaching and thus enhance the technology level of the intelligent campus.

Divergence-degenerate spatial multiplexing towards future ultrahigh capacity, low error-rate optical communications

Spatial mode (de)multiplexing of orbital angular momentum (OAM) beams is a promising solution to address future bandwidth issues, but the rapidly increasing divergence with the mode order severely limits the practically addressable number of OAM modes. Here we present a set of multi-vortex geometric beams (MVGBs) as high-dimensional information carriers for free-space optical communication, by virtue of three independent degrees of freedom (DoFs) including central OAM, sub-beam OAM, and coherent-state phase. The novel modal basis set has high divergence degeneracy, and highly consistent propagation behaviors among all spatial modes, capable of increasing the addressable spatial channels by two orders of magnitude than OAM basis as predicted. We experimentally realize the tri-DoF MVGB mode (de)multiplexing and data transmission by the conjugated modulation method, demonstrating lower error rates caused by center offset and coherent background noise, compared with OAM basis. Our work provides a potentially useful basis for the next generation of large-scale dense data communication.

Research on oil exploration seismic Rayleigh wave imaging based on multi-channel analysis of surface waves and genetic-damped least squares joint inversion

Rayleigh waves in oil exploration seismic records usually have strong energy and are considered as noise, but Rayleigh waves also carry information about subsurface. In this paper, we process Rayleigh waves from a set of oil seismic data to detect underground structures of shear-wave velocity (vs) using multi-channel analysis of surface waves (MASW). Fundamental mode and higher order mode dispersion curves of the Rayleigh wave were automatically extracted by a modified phase shift method. We then use the genetic and damped least squares (DLS) joint inversion algorithm to inverse the dispersion curves and obtain a one-dimensional (1D) vs structure under each shot gather. Finally, all 1D vs structures were combined to create a 3.2 km long two-dimensional (2D) section, revealing a stratum structure down to 80 m depth. The results show that MASW technology successfully improves the use of oil seismic data, the automatic dispersion extraction method based on modified phase shift improves the efficiency of data processing, and the joint inversion algorithm reduces the dependence of the Rayleigh wave dispersion inversion on initial model.

The Significance of Adopting E-Learning in Institutions of Higher Learning during the COVID-19 Pandemic and Beyond

The confirmation of the first case of the Covid-19 pandemic in Kenya on 13thMarch 2020 led to suspension of face-to-face learning and closure of all schools and institutions of higher learning. In order to avoid massive loss in the development of human capital with significant long-term economic and social implications, institutions of higher learning were asked to adopt alternative ways and means to face-to-face instructional methods to enable learning to continue. This study points out that E-Learning had been widely adopted by Institutions of higher learning worldwide prior to COVID-19 pandemic. To date Institutions of higher learning have continued to use E-Learning in a blended mode in order to reduce the potential of COVID-19 transmission. The development of Information Technology, acceptance of E-Learning system by learners and instructors, prior experience in the use of E-learning platforms and need for self directed learning are some of the factors that have accelerated the adoption of E-Learning by institutions of higher learning worldwide. The findings of this paper show that the adoption of E-Learning by institutions of higher learning has numerous benefits and advantages. This study recommends that institutions of higher learning should involve all stakeholders in the development and implementation of E-Learning systems, develop E-Learning policies, carry out capacity building and change management, avail continuous technical support to learners and educators so that e-Learning is widely accepted and adopted

Cytotoxic performance of green synthesized Ag and Mg dual doped ZnO NPs using Salvadora persica extract against MDA-MB-231 and MCF-10 cells

In this study, dual doped Zinc oxide nanoparticles consisted of silver and magnesium were prepared by Salvadora persica extract. Powder X-ray diffraction (PXRD) analysis displayed the formation of wurtzite ZnO phase nanostructures and dual doped nanoparticles. The morphological observations of scanning electron microscopy (SEM) confirmed the hexagonal morphology of prepared nanoparticles. The Raman scattering of this product exhibited the first and second orders of polar and non-polar modes that are the characteristic bonds of a wurtzite structure. The toxicity effects of synthesized un-doped, as well as Ag and Mg dual doped ZnO NPs on breast cancer cell (MDA-MB-231) and breast normal cell (MCF-10A) lines, were investigated by the means of MTT test. Accordingly, in comparison to the case of silver and magnesium doped zinc oxide nanoparticles, the un-doped ZnO NPs caused a more toxic impact on MDA-MB-231cells. There was a lack of any significant toxicity effects from un-doped and Ag and Mg dual doped ZnO nanoparticles on the experimented normal cell line (MCF-10A). The gathered results were indicative of a lower toxicity effect in doped nanoparticles when compared to un-doped nanoparticles and therefore, it can be stated that the doping of silver and magnesium metals produces more reliable zinc oxide nanoparticles.

Passively harmonic mode-locked erbium-doped fiber laser based on 2H-MoTe2 saturable absorber

We demonstrated a harmonic mode-locked Erbium-doped fiber laser based on a saturable absorber (SA) of 2H-MoTe2, which is a member of the transition metal dichalcogenides. The SA mode-locker was made by integrating the 2H-MoTe2 into a D-shaped fiber, and then was inserted into an erbium-doped fiber laser for mode-locking. The nonlinear modulation depth and saturation power of 2H-MoTe2-based SA were 10.9% and 19 MW cm−2, respectively. The fundamentally mode-locked pulse train had a pulse width of 577 fs and a repetition rate of 14.32 MHz. The highest order of harmonic mode locking was 55th, which had the repetition rate of 787.6 MHz, pulse width of 820 fs and average output power of 11.8 mW. To the best of our knowledge, this is the highest operating repetition frequency that has ever been demonstrated in a 2H-MoTe2-based fiber laser. The experimental results validate the feasibility of 2H-MoTe2 as a promising SA for generating ultrashort pulses with high repetition rates.

Optimization of work and rest modes of flight crew members in order to improve flight safety in civil aviation

Introduction. The researchers carried out the analysis of work and rest modes (WRM) according to the survey data of 667 pilots and the results of investigations of 83 aviation accidents (AA) that occurred in the Russian Federation with heavy aircraft (HA) weighing more than 5,700 kg for the period 2010-2021. We also considered the data of official statistics for the period from 2005 to September 2021. The obtained results indicate the facts of non-compliance with the work and rest modes (WRM), which may be one of the causes of aviation accidents (AA). In this regard, it is relevant to optimize the work and rest modes in order to improve flight safety in civil aviation and organize their stricter control. The study aims to assess the impact of the actual compliance with the WRM of the crew members of the Civil Aviation Aircraft (CAA) on the occurrence of aviation accidents and to develop proposals for their optimization and control. Materials and methods. The authors studied a compliance of work and rest modes based on the results of 667 online questionnaires developed on the basis of recommendations of the International Civil Aviation Organization (ICAO) on the introduction of a risk management system in airlines related to pilot fatigue, and data from 83 aviation accidents (AA) for the period from 2010 to 2020, presented in the reports of the Interstate Aviation Committee (IAC) on the results of the investigation the causes of their occurrence. When assessing the relevance of the topic, we considered the data of official statistics. Results. The data of the study indicate that in 18% of cases, one of the main causes of AA was non-compliance with WRM. Among the causes of aviation accidents, the following are important: exceeding the norms of flight time for a month (detected in 10% of cases) and for a year (up to 30%); insufficient preflight rest (46.5% of aircraft commanders and 7.4% of co-pilots); lack of full-fledged vacation for a year (32% of cases). In many cases the Researchers revealed several facts of different violations of work and res modes simultaneously. Data of online questionnaire survey confirm the high prevalence of severe fatigue among pilots: 44% rarely have time to rest between flights, 86% go on a night flight shift without having a full day's sleep. We determined the interrelations between the frequency of fatigue of pilots associated with various types of violations of WRM and the risk of air crashes: the prevalence of fatigue and the frequency of disasters increased with a decrease in the duration of pre-flight rest, an increase in vacation arrears and other factors from 1.2 to 2.1 times. Conclusion. The results of the study confirm the high significance of WRM disorders in the occurrence of aviation accidents (AA). The researchers compiled a comprehensive program to reduce accidents in air transport associated with violations of WRM and the development of fatigue among crew members. We have provided proposals to amend the current Regulations on WRM. Ethics. Authors carried out the study in accordance with the International Code of Medical Ethics (1949) and the provisions of the Helsinki Declaration adopted by the World Medical Association (1964). When conducting an online questionnaire survey, before the start of the study, we have introduced all participants with the methodology of its conduct, associated risks and signed an informed voluntary consent.

Evaluating the Normalized Coprime Factor-based Stability Metric for Rigid Systems

Abstract The introduction of flexibility into rigid-body manipulator systems generally complicates the use of simple end-point feedback control. These flexibilities induce an unmodeled oscillation that cannot be necessarily compensated through end-point feedback control. The normalized coprime factor (NCF) based robustness metric ($\varepsilon_{max}$) has been well established in the realm of optimal control and can be applied to a rigid system with flexible modes in order to determine postures that will be robust to the flexibilities. This work illustrates that for rigid (double integrator) systems there is a fixed normalized coprime-factor robustness and, that for the special case of SISO systems, deviation from rigidity yields a similar change in NCF robustness.