Mode Spacing Research Articles

Risk Assessment of Household Gas Heaters in Tehran During an Earthquake Crisis by Using the Fuzzy FMEA Model

Background: A variety of gas heaters are used in residential, administrative, and commercial buildings in Iran. Home packages (HP) and central heating boiler rooms (CHBRs) are among the most common types of heating systems that can be damaged during earthquakes and, thus, harm the building and the residents. Methods: By doing a survey and an interview in 50 residential buildings in District 16 of Tehran, the risks of these facilities were assessed during earthquakes from the viewpoint of the residents. To do the risk assessment, the failure mode and effects analysis (FMEA) model in the fuzzy space were applied. To analyze the risk priority number (RPN), defuzzification and the center of gravity method were used. Based on the results, 11 indicators were identified and evaluated for each system. Results: The mean RPNs obtained for both systems were almost equal (the difference was about 2%). Thus, no definitive superiority can be presumed for HP or CHBR when earthquakes happen. The major difference in the risk of each system can be separately evaluated based on the conditions of each building, confidence about the quality of installation, connections, pipe materials, electric wire corrosion, etc. Conclusion: It is suggested that the risks of CHBR and HP during earthquakes are the same, and some issues such as design, economy, and technical issues play a greater role in contractors’ selection of the system.

Orbital angular momentum comb generation from azimuthal binary phases

Since Allen et al. demonstrated 30 years ago that beams with helical wavefronts carry orbital angular momentum (OAM), the OAM of beams has attracted extensive attention and stimulated lots of applications in both classical and quantum physics. Akin to an optical frequency comb, a beam can carry multiple various OAM components simultaneously. A series of discrete, equally spaced, and equally weighted OAM modes comprise an OAM comb. Inspired by the spatially extended laser lattice, we demonstrate both theoretically and experimentally an approach to producing OAM combs through azimuthal binary phases. Our study shows that transition points in the azimuth determine the OAM distributions of diffracted beams. Multiple azimuthal transition points lead to a wide OAM spectrum. Moreover, an OAM comb with any mode spacing is achievable through reasonably setting the position and number of azimuthal transition points. The experimental results fit well with theory. This work presents a simple approach that opens new prospects for OAM spectrum manipulation and paves the way for many applications including OAM-based high-security encryption and optical data transmission, and other advanced applications.

“DALSTON! WHO ASKED U?”: A Knowledge-Centred Perspective on the Mapping of Socio-Spatial Relations in East London

Since the turn of the millennium, Dalston in the London Borough of Hackney has experienced fundamental change through public and private investment in new infrastructure and processes of urban restructuring. This was paralleled by the reform of the national planning system, which aimed to devolve decision-making to the local level and increase the possibilities for residents and stakeholders to participate in planning processes. However, the difficulty of translating local needs and aspirations into policy goals and broadly accepted area action plans resulted in a crisis, which, in 2018, led to the introduction of the Dalston Conversation and subsequently the revision of planning goals. It is in this context that the Relational States of Dalston mapping project generated and assembled local knowledge about the web of socio-spatial relations between different local actors and in this way highlighted the significance and fragility of the communities’ networks and their spatial dimensions. The collection, ordering, integration, and production of knowledge can be seen as part of the core work in urban planning processes and policymaking. Which forms of knowledge are routinely used in planning contexts and define the relationship between planning action and urban transformation? To what extent could the mapping of local community relations add to this knowledge and help to improve decision-making processes in contested spaces of knowledge? In what ways could a relational understanding of space and architectural modes of research and representation contribute to the analysis, conceptualisation, and communication of local community relations? This article engages with these questions, using the mapping project in Dalston as a case study.

Single Hydrophone Passive Source Range Estimation Using Phase-Matched Filter

Algorithms working in mode space instead of directly matching the received complex sound pressure were developed to improve computational efficiency and robustness, but these algorithms may be inconvenient to apply in practice because manual operations are often inevitable when performing modal filtering. Based on a phase-matched filter, an imperfect matching scheme named the modal phase based matched impulse response (MP-MIR) is proposed to estimate the source range rapidly and conveniently with a single hydrophone. The field to be matched is still the received complex sound pressure. The replica field is a sum of several “phase” modes, which can be efficiently and conveniently synthesized merely with the horizontal wavenumbers of normal modes and the source–receiver range. The effectiveness of the proposed MP-MIR was demonstrated in localizing 84 emissions along a weakly range-dependent track at ranges of 2.54–20 km in the South China Sea. Although it was found, from cross-correlation coefficients, that the received signals showed strong variation even between adjacent emissions, MP-MIR outperformed the classical matched impulse response (MIR) with a lower standard deviation in most cases, demonstrating good robustness and potential for practical applications.

Group velocity dispersion in high-performance BH InAs/InP QD and InGaAsP/InP QW two-section passively mode-locked lasers.

High-performance buried heterostructure (BH) C-band InAs/InP quantum dot (QD) and L-band InGaAsP/InP quantum well (QW) two-section passively mode-locked lasers (MLLs) are investigated. From the irregularity of the longitudinal mode spacing in the comb spectra, we confirm that under stable passive mode locking, both devices have strong group velocity dispersion (GVD) and corresponding GVD-induced pulse width broadening. After compensation with anomalous dispersion fibers (SMF-28), short pulse trains with sub-ps pulse widths are achieved for both devices. This observation demonstrates our ability to generate high peak power sub-ps pulses using QD MLLs and QW MLLs for many photonic applications of optical communications.

Observation of flat-band and band transition in the synthetic space

Constructions of synthetic lattices in photonics attract growingly attentions for exploring interesting physics beyond the geometric dimensionality, among which modulated ring resonator system has been proved as a powerful platform to create different kinds of connectivities between resonant modes along the synthetic frequency dimension with many theoretical proposals. Various experimental realizations are investigated in a single ring resonator, while building beyond simple synthetic lattices in multiple rings with different types remains lacking, which desires to be accomplished as an important step further. Here, we implement the experimental demonstration of generating the one-dimensional Lieb lattice along the frequency axis of light, realized in two coupled ring resonators while the larger ring undergoing dynamic modulation. Such synthetic photonic structure naturally exhibits the physics of flat band. We show that the time-resolved band structure read out from the drop-port output of the excited ring is the intensity projection of the band structure onto specific resonant mode in the synthetic momentum space, where gapless flat band, mode localization effect, and flat to non-flat band transition are observed in experiments and verified by simulations. Our work gives a direct evidence for the constructing synthetic Lieb lattice with two rings, which hence makes a solid step towards experimentally constructing more complicated lattices in multiple rings associated with synthetic frequency dimension.

Identification Strategy Design with the Solution of Wavelet Singular Spectral Entropy Algorithm for the Aerodynamic System Instability

In order to effectively identify the signs of instability in the aerodynamic system of an axial compressor, a wavelet singular spectral entropy algorithm incorporated within the wavelet transform, singular value decomposition and information entropy is proposed to describe the distribution complexity of the spatial modalities in the flow field. This kind of identification design can accurately distinguish the boundary between the stable and unstable states of the internal flow field from the view of a dynamic system. On the basis of the information entropy algorithm, the wavelet singular spectral entropy algorithm is designed to integrate with the advantages of wavelet transform analysis on the time-frequency localization and singular value decomposition for signal processing and data mining together. So that the quantitative analysis of the definition of rebuilding a system image can be achieved by the solution of wavelet singular spectral entropy. This method can automatically extract the transient information of the space mode in the time-frequency domain. It effectively avoids the shortcoming that the feature extraction on spatial information cannot be accomplished from multiple angles with the single information entropy algorithm. In the data processing of instability signals under different speeds, the wavelet singular spectral entropy algorithm shows a greater advantage in the early warning for compressor stall. The result shows that the value of the wavelet singular spectral shows an obvious mutation when the aerodynamic system approaches the instability boundary. According to the threshold set, the identification hybrid algorithm can detect the stall precursor about 23~96 r in advance. Compared to the single information entropy algorithm, the hybrid wavelet singular spectral entropy algorithm is able to shift to an earlier precursor identification by about 11~82 r. This established hybrid identification algorithm accounts for the nonlinearity of the aerodynamic system, providing a new perspective for the nonlinear system instability identification.

Mode selection and amplification from optical frequency combs by optical injection locking: a numerical study of noise.

Noise, except for residual side modes, in mode selection and amplification from optical frequency combs by optical injection locking has not been studied in detail, to our knowledge. We report a numerical study of noise behaviors, including both residual side modes and the noise between them. It reveals that comb laser injection can introduce excessive noise, compared to optical injection with a single mode master laser through the interference between residual side modes and resonances within Arnol'd tongues created by periodic forcing in the optical phase, which can be a severe problem for the case of sub-GHz comb mode spacing. The dependences of residual side mode rejection and phase noise variance on comb mode spacing, seeding power, and detuning are discussed to help in low-noise system design and operation.

Cross coupling effects of modal space decoupling control for six degree of freedom 6-DOF parallel mechanism (6 DOF PM)

This study presented the performance of an alternative and effective control strategy through a decoupled controller by an input and an output transformation matrix, such that each Degrees of Freedom can be tuned independently with their bandwidth raised near to the eigenfrequencies. The simulation results of the Modal Space Decoupled Controller were analyzed in Matlab/Simulink environment and comparison made between the conventional PID controllers based on cross coupling effects. The results indicate that the conventional joint space conforms to the theoretical analysis when the compensation for the coupling effects was not considered. The results further showed that the Modal Space Decoupled Controller modified the dynamics characteristics, which can be attributed to reduction in the coupling effects between degrees of freedom motions.

Formation of a new sociogender order in the context of globalization: let’s look at the world in a new way

Globalization, continuing its development, brings new forms of its manifestation, changing many things in the political, economic, social and spiritual universe, increasingly introducing absurd (as it may seem) phenomena and deformations into everyday life. The article examines the little-studied issue of the development in the world of a complex and contradictory social process associated with the formation of a new gender order. The author builds a coherent conceptual basis for the analysis of a new social phenom- enon from the standpoint of a sociological approach developed under the guidance of professor G.Sillaste by the scientific school “Gender and Economic Sociology” on the conceptual interaction of paradigms of modes of social time, social change and social space. The essence, content, specifics, subject and objects of the new gender order emerging in the world are revealed; the features of its integration into various spheres of life of Russian society and the social risks that arise at the same time. The factors that determine the development of the global gender order and the forms of its country consolidation in the context of globalization, including its implementation in Russian society, are analyzed. The article opens a scientific discussion on understanding a new global social phenomenon, its spread in the country space, risks and threats to national interests, socio-cultural and spiritual values of the institution of the family. In the trajectory of the future, it is necessary to critically assess social risks and threats to the socio-political and cultural- ideological potential of gender norms, incl. gender neutrality imposed by the EU countries, addressed to the institutions of the family, marriage, parenthood, motherhood and fatherhood. Key words: gender (sociogender) order, country space, social changes, gender equality, gender inequality index, gender gap.

A Novel Grating Coupling Coefficient Extraction Method for DFB Laser Diodes Based on Side Mode Spacing

A novel method to extract the grating coupling coefficient of distributed feedback (DFB) lasers by comparing the theoretical and experimental values of the side mode spacing is demonstrated. Compared with the traditional method, the proposed method in this paper transforms the solution process of the lasing model with multiple unknown parameters into that with only the side mode spacing and coupling coefficient, which significantly reduces the computational workload. Furthermore, the bias current of the measured spectrum can be much higher than the threshold current, which makes the method less affected by noise. This paper theoretically analyzes the changing relationship between multiple parameters by calculating the lasing mode distribution, and the results show that the side mode spacing is only sensitive to the coupling coefficient. In addition, the grating coupling coefficients (57–61 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> ) of the fabricated DFB laser diodes are experimentally extracted at 40-80 mA currents. The variation of the coupling coefficient with current is less than 2‰/mA, and the method exhibits pretty good stability. Meanwhile, the grating coupling coefficient extraction method for the complex grating types is also considered in this paper.

Applications of Operational Modal Analysis in Gearbox and Induction Motor, Based on Random Decrement Technique and Enhanced Ibrahim Time Method

There have been steadily growing requirements from the academia and industry, demanding non-invasive methods and reliable measurement systems of research devoted to operational mode analysis (OMA). Due to the simplicity of performing only structures surface vibration measurements, OMA is frequently applied in machine fault diagnosis (MFD) and structure health monitoring (SHM). OMA can handle big structures, such as bridges, buildings, machines, etc. However, there is still an open question: how to properly handle the harmonic effects of rotating components and the difficulty of closely estimating space modes are still a nightmare to deal with. Therefore, the main objective of this paper is to identify the structure of natural frequencies by the regeneration of frequency response functions (FRFs) for complex structures based on OMA. The novelty of our approach is to use the random decrement technique (RDT), correlation function estimation (CFE), and enhanced Ibrahim time method (EITM) to overcome OMA’s difficulties and limitations. To reduce further rotational harmonics effects, gear mesh and side band frequencies, digital signal processing techniques based on notching filters, and liftering analysis techniques were also used. All the experiments were performed at the laboratory test rig and conducted by using three accelerometers, one impedance hammer, one force sensor, and one data acquisition board. To reduce data’s variabilities, each test was measured three times for 5 min. The data sampling frequency for all the experiments was 25.6 kHz. To validate the proposed methodology, extensive OMA tests were performed for the generation of FRFs. The measured objects were a steel bar, induction motor, and gearbox. Five structural natural frequencies for the induction motor and eight structural natural frequencies for the gearbox were generated, respectively.

Spatialising antagonism: A post-foundational analysis of the spatial dynamics of violence in nineteenth century Derry

This article offers a post-foundational analysis of the spatial dynamics of inter-communal violence in nineteenth-century Derry city. In doing so, the theoretical category of ‘antagonism’ is mobilised to develop a post-foundational view of the spatial, one that is well-placed to shed an innovative theoretical light on conflict in divided societies and contested spaces. It has recently been recognised that antagonism not only offers a route towards a truly post-foundational approach to the political, but also a consciously post-foundational spatial analysis. Spatialising antagonism at both a theoretical and empirical level helps to bring into further relief the imbrications of space, the political and various modes of violence. Specifically, thinking antagonism spatially in the context of contested spaces such as Derry, underlines the ways through which ontological or foundational violence can be concretised through spatial practices, thereby structuring and driving the spatial dynamics of violence.

Mode spacing multiplication of optical frequency combs without power loss.

We demonstrate the mode spacing multiplication of optical frequency combs (OFCs) using interleaving technique. The pulse train of an OFC after interleaving is phase modulated, and phase demodulation is necessary for mode spacing multiplication. This scheme enables mode spacing multiplication without power loss in principle, which is in contrast to the conventional mode filtering technique. During demonstration, the mode spacing of the OFC of a mode-locked Er-doped fiber laser (repetition rate of 97 MHz) is quadrupled by the interleaving process and successive phase demodulation.

Role of Junctionless Mode in Improving the Photosensitivity of Sub-10 nm Carbon Nanotube/Nanoribbon Field-Effect Phototransistors: Quantum Simulation, Performance Assessment, and Comparison.

In this article, ultrascaled junctionless (JL) field-effect phototransistors based on carbon nanotube/nanoribbons with sub-10 nm photogate lengths were computationally assessed using a rigorous quantum simulation. This latter self-consistently solves the Poisson equation with the mode space (MS) non-equilibrium Green’s function (NEGF) formalism in the ballistic limit. The adopted photosensing principle is based on the light-induced photovoltage, which alters the electrostatics of the carbon-based junctionless nano-phototransistors. The investigations included the photovoltage behavior, the I-V characteristics, the potential profile, the energy-position-resolved electron density, and the photosensitivity. In addition, the subthreshold swing–photosensitivity dependence as a function of change in carbon nanotube (graphene nanoribbon) diameter (width) was thoroughly analyzed while considering the electronic proprieties and the quantum physics in carbon nanotube/nanoribbon-based channels. As a result, the junctionless paradigm substantially boosted the photosensitivity and improved the scaling capability of both carbon phototransistors. Moreover, from the point of view of comparison, it was found that the junctionless graphene nanoribbon field-effect phototransistors exhibited higher photosensitivity and better scaling capability than the junctionless carbon nanotube field-effect phototransistors. The obtained results are promising for modern nano-optoelectronic devices, which are in dire need of high-performance ultra-miniature phototransistors.

Angular Displacement Control for Timoshenko Beam by Optimized Traveling Wave Method

The vibration of flexible structures in spacecraft, such as large space deployable reflectors, solar panels and large antenna structure, has a great impact on the normal operation of spacecraft. Accurate vibration control is necessary, and the control of angular displacement is a difficulty of accurate control. In the traditional control method, the mode space control has a good effect on suppressing low-order modes, but there is control overflow. The effect of traveling wave control on low-order modes is worse than the former, but it has the characteristics of broadband control. It can better control high-order modes and reduce control overflow. In view of the advantages and disadvantages of the two control methods, based on Timoshenko beam theory, this paper uses vector mode function to analyze the modal of spacecraft cantilever beam structure, establishes the system dynamic equation, and puts forward an optimized traveling wave control method. As a numerical example, three strategies of independent mode space control, traditional traveling wave control and optimized traveling wave control are used to control the active vibration of beam angle. By comparing the numerical results of the three methods, it can be seen that the optimal control method proposed in this paper not only effectively suppresses the vibration, but also improves the robustness of the system, reflecting good control performance. An innovation of this paper is that the Timoshenko beam model is adopted, which considers the influence of transverse shear deformation and moment of inertia on displacement and improves the accuracy of calculation, which is important for spacecraft accessory structures with high requirements for angle control. Another innovation is that the optimized traveling wave control method is exquisite in mathematical processing and has good results in global and local vibration control, which is not available in other methods.

Proper orthogonal decomposition, dynamic mode decomposition, wavelet and cross wavelet analysis of a sloshing flow

Internal hydrodynamics and its coupling with structural dynamics are non-negligible processes in the design phase of aerospace systems. An improved understanding of the nature of this coupling would allow for greater flexibility in modeling and design of such systems, and could lead eventually to the development of suitable active and/or passive control strategies for enhanced performances. In this manuscript we apply a number of data analysis techniques: proper orthogonal decomposition, dynamic mode decomposition and wavelet transform and their combination to time-resolved images of a liquid sloshing within an enclosure. We use these techniques to identify fluid-dynamic modes in space and time and to verify their coupling with the structural dynamics of vibrating structures.In particular we consider the transient case of a water tank mounted on a free oscillating cantilever. As the acceleration amplitude decays, we observe and quantify the transition from incoherent flow to standing waves. Our results show that the content of the images is very informative and can be used for quantitative analysis. As the main outcome, the hydrodynamic modes are identified using POD and DMD, and related to known features of sloshing flow, such as the frequency of the first symmetric free surface mode. Additionally we perform a comparison of wavelet transforms of POD time coefficients and measured acceleration signals at the tank base. Viewing the latter as the input and the former as the output of the fluid-dynamic system, we are able to correlate the enhanced damping of the cantilever oscillation to the different regimes of the hydrodynamic field.

A priorisparsification of Galerkin models

A methodology to generate sparse Galerkin models of chaotic/unsteady fluid flows containing a minimal number of active triadic interactions is proposed. The key idea is to find an appropriate set of basis functions for the projection representing elementary flow structures that interact minimally one with the other, resulting in a triadic interaction coefficient tensor with sparse structure. Interpretable and computationally efficient Galerkin models are obtained, since a reduced number of triadic interactions are computed to evaluate the right-hand side of the model. To find the basis functions, a subspace rotation technique is used, whereby a set of proper orthogonal decomposition (POD) modes is rotated into a POD subspace of larger dimension using coordinates associated with low-energy dissipative scales to alter energy paths and the structure of the triadic interaction coefficient tensor. This rotation is obtained as the solution of a non-convex optimisation problem that maximises the energy captured by the new basis, promotes sparsity and ensures long-term temporal stability of the sparse Galerkin system. We demonstrate the approach on two-dimensional lid-driven cavity flow at$Re = 2 \times 10^4$where the motion is chaotic and energy interactions are scattered in modal space. We show that the procedure generates Galerkin models with a reduced set of active triadic interactions, distributed in modal space according to established knowledge of scale interactions in two-dimensional flows. This property, however, is observed only if long-term temporal stability is included explicitly in the formulation, indicating that a dynamical constraint is necessary to obtain a physically consistent sparsification.

Physics informed DMD for periodic Dynamic Induction Control of Wind Farms

Dynamic Induction Control (DIC) is a novel, exciting branch of Wind Farm Control. It makes use of time-varying control inputs to increase wake mixing, and consequently improve the velocity recovery rate of the flow and the power production of downstream turbines. The Pulse and the Helix are two promising DIC strategies that rely on sinusoidal excitations of the collective pitch and individual pitch of the blades, respectively. While their beneficial effects are evident in simulations and wind tunnel tests, we do not yet fully understand the physics behind them. We perform a systematic analysis of the dynamics of pulsed and helicoidal wakes by applying a data-driven approach to the analysis of data coming from Large Eddy Simulations (LES). Specifically, Dynamic Mode Decomposition (DMD) is used to extract coherent patterns from high-dimensional flow data. The periodicity of the excitation is exploited by adding a novel physics informed step to the algorithm. We then analyze the power spectral density of the resulting DMD modes as a function of the Strouhal number for different pitch excitation frequencies and amplitudes. Finally, we show the evolution in time and space of the dominant modes and comment on the recognizable patterns. By focusing on the modes that contribute the most to the flow dynamics, we gather insight on what causes the increased wake recovery rate in DIC techniques. This knowledge can then be used for the optimization of the signal parameters in complex layouts and conditions.

Active vibration optimal control of piezoelectric cantilever beam with uncertainties

Considering the stiffness characteristics of piezoelectric layer, the bending stiffness of piezoelectric cantilever beam is obtained by applying the first-order shear deformation theory. The finite element model of piezoelectric cantilever beam is established by Hamilton variation principle, and the modal superposition method is employed to reduce the order of the finite element model. At the maximum strain point, the sensors/actuators are equipped in pairs. Based on the uncertain dynamic model of piezoelectric cantilever beam, the independent modal space control method based on LQR (linear quadratic regulator) control is employed for the active control of the smart beam structure, and the weighted matrices Q and R are selected according to the energy criterion. The numerical simulations and experiments verify the effectiveness of the proposed finite element model and the active vibration optimal control.