Behavior Of Modes Research Articles

Impact of COVID-19 Pandemic on Marketing of Education

The COVID-19 pandemic forced many schools to partially or totally switch to remote communication methods for delivering education in the years 2020-2021. It is believed that forced compliance with unfamiliar and even unpreferred modes of behavior can have a profound and lasting impact on people’s attitudes and opinions toward the behavior itself because of first-hand exposure and experience. It is, therefore, possible that this experience with remote teaching and learning could have materially changed both instructors’ as well as students’ attitudes toward remote delivery of education. Such changed attitudes may predict their future choices and behavior. This paper will present the important facets of education delivery systems identified, and the survey instrument developed to explore three areas: instructors’ and students’ prior attitudes and behaviors toward alternative education delivery modes, their experiences during the pandemic, and the effect of the experience on their attitudes. The paper will also present the results of a pilot study conducted using a sample of student respondents.

Fatigue performance of prefabricated composite T‐beams under cyclic overloading: An experimental study

AbstractExisting studies have proved that interfaces between the prefabricated layer and the cast‐in‐place layer significantly affect the static performance of prefabricated concrete structures using the wet connection method, but little has been known about the fatigue performance, especially at high load levels. This study investigated the fatigue behavior of prefabricated composite concrete beams under negative bending moment induced by the high‐stress level cyclic load. Fifteen composite T‐beams with three different designed sections were tested. The failure mode, cracking and deflection behavior, steel strain development, and the new‐old concrete interfacial deformation were recorded and analyzed. It was found that the stress redistribution occurred with the debonding cracks generated at the new‐old concrete interface, causing the degradation of the static and fatigue performance. Setting interfacial shear keys could prevent such debonding failure at static and low cyclic loading levels. Meanwhile, the corresponding mechanisms were verified through cross‐sectional analysis.

Observed wake branches from the 2-DOF forced motion of a circular cylinder in a free stream

The combined in-line (IL) and cross flow (CF) vibration of flexibly mounted cylinders in a free stream due to vortex-induced vibration (VIV) demonstrates significantly more complex dynamics than purely CF vibrations. In this study, the forces on a circular cylinder undergoing combined IL and CF motion in a free stream are investigated through an expansive series of forced motion experiments with force measurement and quantitative flow visualization. The motion of the cylinder is parameterized using sinusoidal motions with variation of the non-dimensional IL amplitude, non-dimensional CF amplitude, CF reduced velocity, and phase between IL and CF motion, while the Reynolds number is held constant at 7620. The resulting database of experimental measurements consists of 9555 variations of the governing motion parameters. The decomposed force coefficients are reported and mapped over the range of parameters. We observe a number of interesting wake-dependent parameter space features, such as regions of multiple branch responses, where the wake may exhibit multiple mode behaviors for the same cylinder motion parameters. Multiple branch regions are observed throughout the experimental data space.

Performance Characteristics of a Rotating Detonation Combustor Exiting Into a Pressurized Plenum to Simulate Gas Turbine Inlet

Abstract The present study aims to experimentally characterize the performance of a rotating detonation combustion (RDC) system integrated with a pressurized downstream plenum to simulate the high-pressure inlet conditions of power-generating gas turbines. A thorough understanding of the operational behavior including wave mode behavior, static pressure profile along the combustor length, and dynamic features of pressure fluctuations is crucial for successful integration of RDC with the turbine. In this study, two RDC configurations are investigated, RDC with a constant area annulus and RDC with a converging nozzle. In both cases, the RDC flow exited into a plenum chamber kept at pressures varying from 155 kPa to 330 kPa. RDC was operated on methane and oxygen-enriched air to represent reactants used in land-based power generation. Experiments were conducted for the two RDCs configurations operated at three reactant mass flow rates (0.23, 0.32, and 0.46 kg/s). The RDC performance is characterized by time-averaged static pressure measurements, and wave velocity determined by ionization probes. In addition, dynamic pressure measurements were recorded both inside and near the exit of RDC channel to investigate wave interactions between RDC and downstream plenum. Results show that the RDC with the converging nozzle achieved superior performance while minimizing detrimental interactions with the reflected shock and/or acoustic waves from the downstream plenum.

The Influence of Short Videos on College Students Purchasing Behavior

Short video has gradually developed into one of the practical expression ways of information content communication in the mobile Internetvarious social media and e-commerce use opportunities from this trend. College students are the most active and mainstream group in Short video. The fragmented communication mode, exciting content, and business behavior of short videos have been integrated into the group of college students, influencing them all the time, including but not limited to purchasing behavior. In this paper, college students are selected to build a mechanism model of the influence of word-of-mouth characteristics of social e-commerce networks on college students purchase intention, and the model is tested through empirical research. The results showed that when brand marketing is enhanced, brand interaction, experience perception, interest, and perception are enhanced. The more frequently consumers interact with the brand, the more frequently they connect and communicate with it, and their purchasing behavior will be enhanced.

MODAL BEHAVIOUR OF LONGITUDINALLY PERFORATED NANOBEAMS

Nano-electro-mechanical systems (NEMS) require perforated beams for structural integrity. Hole sizes, hole numbers, and scale effects need to be modelled appropriately in their design. This paper presents a new finite element model to investigate the modal behaviour of longitudinally perforated nanobeams (LPNBs) using the classical Euler–Bernoulli beam theory. A symmetric array of holes arranged parallel to the length direction of the beam with equal spacing was assumed for the perforation. The non-local Eringen’s differential form was used to incorporate the nanoscale sizes. The accuracy of the proposed model was verified by comparing the obtained results with the available analytical solutions for fully filled nanobeams. The effects of aspect ratios, non-local parameters, boundary conditions, and perforation characteristics on the modal behaviour of LPNBs were investigated. The non-local parameter reduced the natural frequency owing to a decrease in the stiffness of the structures. However, the perforation filling ratio led to higher values of the fundamental frequency. Furthermore, compared with other boundary conditions, clamped–clamped boundary conditions demonstrated the best performance in terms of the maximum frequency.

A low-profile wideband circularly polarized metasurface antenna based on characteristic mode analysis

Abstract A low-profile wideband circularly polarized (CP) metasurface antenna is demonstrated for C-band applications. The metasurface consists of 4 × 4 square patches with Z-shaped slots. Characteristic mode analysis is used to investigate the modal behavior of the metasurface, and a pair of degenerate modes is chosen as the operating modes. The CP radiation is realized by exciting a pair of degenerate modes of the metasurface through a slot antenna, which is used as a feed structure with a 90° phase difference. The CP bandwidth is further widened by combining the resonance modes of the metasurface and slot antenna. The measured results show that the −10 dB impedance bandwidth of the antenna is 3.47–4.76 GHz, and the 3 dB axial ratio bandwidth is 3.5–4.9 GHz with a peak gain of 6.9 dBic. Moreover, the antenna exhibits well left-hand CP radiation performances with a low profile of 0.046λ0.

Comprehensive Analysis of Aircraft Dynamics Stability with SCSim: Integration and Assessment

This research presents a comprehensive analysis of the dynamic stability of aircraft using modules of the software named SCSim (Stability and Control Simulation Tool), which is dedicated to the analysis of aircraft stability and control. The stability of an aircraft can be examined in two directions: longitudinal and lateral. The ability to determine an aircraft's limits and handling qualities depends on its stability. This study report demonstrates a complete dynamic stability analysis using SCSim with aerodynamic input data from the commercial software Advanced Aircraft Analysis (AAA). SCSim is implemented within a common framework in MATLAB, adapted from a MATHCAD script, providing an easier way to enter user-defined input data, and introducing a set of new features. The study is divided into three main parts, each based on an analysis of stability. First, static stability is examined to understand how the system behaves when it is in equilibrium. Then, dynamic stability is assessed to understand how the system reacts to perturbations and disturbances. Finally, handling qualities systematically assess the dynamic modes of the aircraft's behavior and establish the levels of handling qualities. In this paper, a generic model of a propeller-driven aircraft is used for the study due to the availability of flight parameters, geometric, and aerodynamic data. The obtained results demonstrate the capabilities of the Stability and Control Simulation Tool (SCSim) in designing and analysing an aircraft's stability under various flight conditions and configurations, with validation using AAA.

Assessment of modal density and free path distribution in central-planned halls.

Central-planned halls are highly widespread in the historical architectures of the Western world, such as rotundae, Christian baptisteries, and Roman tombs. In such halls, whispering galleries, flutter echoes, and sound focusing are the acoustic phenomena mainly investigated by scholars. Instead, modal behaviour and free path distribution are generally less treated in literature. The present study explores the modal density at low frequencies and the relationship with the most recurrent free path lengths in three historical nearly circular spaces, here assessed as case studies. Acoustic measurements allowed the collection of objective experimental data, i.e., room impulse responses and the resulting room acoustics criteria. Wave-based numerical models allowed for the investigation of the eigenfrequencies distribution, while the free paths trend has been experienced through ray-based models. The main outcomes of both analyses show the prominence of the circular modes, rather than the diametral and the elevation ones. Moreover, the mean free path calculated using ray-tracing proves to be higher than the theoretical value commonly assumed for any kind of shape. The consequent longer reverberations compared to halls with other shapes and the same volume justify the significant support historically provided to sound signals by circular halls.

Tracking the multifield dynamics with cosmological data: a Monte Carlo approach

We introduce a numerical method specifically designed for investigating generic multifield models of inflation where a number of scalar fields ϕ K are minimally coupled to gravity and live in a field space with a non-trivial metric 𝒢> IJ (ϕ K ). Our algorithm consists of three main parts. Firstly, we solve the field equations through the entire inflationary period, deriving predictions for observable quantities such as the spectrum of scalar perturbations, primordial gravitational waves, and isocurvature modes. We also incorporate the transfer matrix formalism to track the behavior of adiabatic and isocurvature modes on super-horizon scales and the transfer of entropy to scalar modes after the horizon crossing. Secondly, we interface our algorithm with Boltzmann integrator codes to compute the subsequent full cosmology, including the cosmic microwave background anisotropies and polarization angular power spectra. Finally, we develop a novel sampling algorithm able to efficiently explore a large volume of the parameter space and identify a sub-region where theoretical predictions agree with observations. In this way, sampling over the initial conditions of the fields and the free parameters of the models, we enable Monte Carlo analysis of multifield scenarios. We test all the features of our approach by analyzing a specific model and deriving constraints on its free parameters. Our methodology provides a robust framework for studying multifield inflation, opening new avenues for future research in the field.

Structure failure analysis on metro axle-box hanger due to modal resonance with rail corrugation

During the long-term service of a metro vehicle, different kinds of fracture failure occur on the bogie, with the axle-box hanger being a representative one. To investigate the cause of the hanger structure failure, a study was conducted that combined field investigation with finite element analysis, focusing on the modal resonance behavior between the hanger and the rail corrugation. Based on the findings, a structural optimization of the hanger was proposed and an experimental verification was conducted. The results show that the main reason for the hanger fracture failure is that the resonance phenomenon that occurred in the hanger structural modal frequency when exposed to the rail corrugation, leading to the poor lateral vibration environment of the hanger and the fracture failure in the long-term service operation. The first-order structural modal frequency of the hanger is 432 Hz, which is very close to the wheel/rail excitation frequency of 435 Hz caused by the rail corrugation. The modal frequency of three newly designed hangers can prevent the frequency caused by the rail corrugation. Experimental verification of the new hangers showed a 55.49% lower maximum average acceleration of hanger lateral vibration compared to the original structure, confirming the effectiveness of the redesigned hangers.

On the exploration of structured light transmission through a multimode fiber in a reference-less system

Recent advancements in optical wavefront shaping have brought multimode fibers (MMFs) into the spotlight as potential contenders for long-haul communication, positioning them as promising substitutes to single-mode fibers. MMFs offer greater data rates, countering the impending congestion of fiber-based networks. Additionally, their suitability for single fiber endoscope procedures presents them as compelling alternatives for minimally invasive endoscopy, providing information comparable to, if not surpassing, current cutting-edge technology. However, the complex modal behavior of light in MMFs hinders the implementation of these promising applications. Hence, precise modal excitation and control are crucial for improving the transmission of structured light in MMFs. This study introduces a groundbreaking approach that achieves the retrieval of the transmission matrix in a single step, thereby facilitating coherent light propagation through highly dispersive MMFs. By combining iterative phase retrieval algorithms with the measurement of phase shifts between experimentally established focal points, potential arbitrary interference control is enabled, leading to effective phase correction. The efficacy of our method is validated through the successful transmission of diverse structured light beams, including Laguerre–Gauss and Hermite–Gaussian types, as well as handwritten characters via MMF. The examination of structured light is simplified using an off-axis holographic technique that accurately captures both intensity and phase information. These results hold significant potential, paving the way for major advancements in long-distance communication and minimally invasive medical procedures, thereby transforming the telecommunications and healthcare sectors.

Modeling of a flexible perforated membrane backed by granular materials

It has recently been shown that adding activated carbon particles to the interior of a Helmholtz resonator can improve the resonator's absorption at low frequencies. A similar improvement has been found when a layer of activated carbon partially fills the space behind a finite, tensioned impermeable membrane. In that case, absorption peaks due to the modal response of the tensioned membrane were found to be significantly enhanced in the low frequency range. In the present work, the modeling aspects of the latter work are extended in a number of ways. First, the circular membrane is considered to be both tensioned and flexurally stiff, and further, it is micro-perforated: i.e., it has a finite flow resistance. Secondly, the particle layer behind the membrane is modeled by using a finite difference procedure that accounts for interaction of the particle layer and walls that contain it: i.e., the particle stack itself is allowed to exhibit modal behavior in the radial direction. Finally, the interaction of the membrane nearfield and the particle stack is fully accounted for. It is shown that previously observed behavior can be reproduced, and further that the modal behavior of the particle stack may also enhance the system's absorption.

Hydrodynamics of transient processes in a well with an electric submersible pump

The relevance. Associated with the problem of increase in efficiency of algorithms for monitoring and controlling the dynamic operation modes of wells equipped with an electric submersible pump with adjustable supply. The result summarizes and develops the previously published solution on the design of a dynamic well model, through the transition from linearized correlations to quadratic relationships between states at key points of a lift. These points properly reflect the observed forms of behavior in transient and equilibrium operating modes at full start-stop control ranges. The main aim. Updated description of a comprehensive quadratic barometric model of the «reservoir–lift–electric pump–well head» type well, focused on the tasks of automatic control and regulation in real time. Objects. Well with frequency-regulated submersible pump. Methods. Material balance, percolation, hydrostatics, quadratic kinetics of friction losses, numerical modeling of differential equations, finite-dimensional description of the complex hydrodynamics of the well, taking into account the potential and kinetic head losses in the lift. Results: (1) Updated mathematical description of the hydrodynamics of the well with an electric submersible pump creates the basis for: more reliable solution of inverse problems of parametric model support according to the data of field control, refined assessment of the adjustment potential, predicting the dynamics of a possible system output beyond the boundaries of functional stability, technologies of numerical and analytical design of optimal solutions when selecting the parameters of arrangement and laws of operational regulation, synthesis of dynamic observers of an extended state vector synchronously operating with the dynamics of controlling well-head and deep pressure. (2) The results of the computational analysis demonstrate a complex behavior that does not match the graph of the inflow and pump supply, when changing the frequency and wellhead pressure. This explains the observed effect of the multi-tempoity of transient processes during starts and stops and possible instability of the supply with a sharp decrease in frequency. (3) Estimates of discrepancy between the solutions for a quadratic model and a linearized prototype indicate an increase in errors of linearized analysis with strong deviations of operating modes from the equilibrium-calculated states. The refinements in dynamically disturbed operating modes delivered by the updated model are important for improving the reliability of operational control systems and parametric estimation for data control mode states.

A Traffic Equilibrium Model for Multi-Modal Networks with Uncertain Demands

In this study, an effective travel cost (ETC) traffic equilibrium model is proposed for multi-modal networks with uncertain demands. The multi-modal networks are transformed into supernetworks and travel demands are assumed to be closed intervals. Passenger flows and travel costs are also formulated as closed intervals to capture the effects of uncertain demands. The ETC concept is introduced and regarded as a choice criterion to develop an equilibrium model which captures travellers’ travel mode and route choice behavior under interval travel costs. The model is formulated as a variational inequality problem, and the method of successive average algorithm is adapted to interval mathematics to obtain the results in the form of interval variables. Illustrative examples are also presented to demonstrate the model’s characteristics and its differences from the traditional equilibrium model, in which the expected travel cost is regarded as the choice criterion.

Novel methodology for isolating rotational phenomena in tire testing

Due to electrification, tire/road noise is one of the key contributors to the vehicle noise performance. With the advent of component-based NVH representation, capturing the realistic dynamic behavior of the substructures is of primary interest for the industry. Tire dynamics are highly-subjected to changes due to operational conditions, such as preload, inflation, and rotating speed. Due to rotation, the standing wave pattern of a non-rotating tire mode shape can evolve into two opposite travelling waves with different natural frequencies, having the same mode shape. Separating the contributions of mode splitting due to rotation from mode splitting due to geometrical asymmetry caused by preload deformation is essential for a correct model validation. This paper presents a novel methodology for characterizing the modal behavior of rotating tires without contact patch deformation, observing rotational-only dependencies. By means of an original impact testing technique, a rubber sphere excites a free-spinning tire with constant energy at different velocities. By doing so, the changes due to pure rotational phenomena can be captured by contactless measurement devices, such as laser doppler vibrometer or high-speed cameras.

Schumpeter Lecture 2023: Rationality and Zero Risk

Abstract We adopt a definition of “rationality” as robustness to analysis: A mode of behavior is rational for a decision maker if she feels comfortable with it once it has been analyzed and explained to her. With this definition in mind, is it irrational to violate continuity axioms in one’s stated preferences? Specifically, does it make sense to avoid any positive probability of a negative outcome, no matter how small? Or, if a decision maker states such a “zero risk” policy, does she mean what she says? We propose to study this question axiomatically, asking which modes of behavior correspond to such statements. The baseline model evaluates a lottery by its expected utility and an extra additive term that measures the cost of deviating from a “zero risk” choice. A generalized version allows for multiple sets of principles, where the cost of risking a set of principles is added to the expected utility of a lottery. Stronger assumptions imply that the cost of violating a set of principles is additive in the individual costs. We develop a comparative behavioral analysis that allows making interpersonal comparisons about the relative importance of principles.

VIBRATION-BASED DAMAGE DETECTION FOR ONE-STORY STEEL FRAME STRUCTURE USING MODE SHAPE CURVATURE

Structural health monitoring techniques, particularly vibration-based damage detection, have gained significance in assessing civil structure condition. This paper focuses on utilising mode shape curvature for damage detection in a one-story steel frame structure. The study aims to overcome traditional inspection limitations by exploring vibration-based approaches. Experimental investigation is conducted to analyse intact and damaged structural modal behaviour. Modal analysis technique extracts modal frequencies and mode shapes, enabling analysis of mode shape curvature for damage detection and localisation. Preliminary findings show that damaged structures display deviations in mode shapes and reduced natural frequencies, providing evidence of structural damage. However, a significant issue arises near the support, where unexpected patterns emerge in the Total Damage Index (TDI) with increasing damage severity. This finding challenges the expected correlation between severity levels and TDI values, highlighting the need to consider factors like fixed supports. Misleading signs of damage in some segments underscore the importance of cautious result interpretation and accounting for noise. Future studies should focus on noise resistance, false indication mitigation, and understanding segments with fixed supports to enhance mode shape curvature analysis’s reliability for damage detection in civil structures.

Experimental and numerical evaluation of hydro-thermal ageing's effects on adhesive connections in offshore structures

In offshore structures, the need to replace or strengthen existing metal components arises over time. One possible solution is the use of bonded connections. Nevertheless, the durability of the adhesive connections is highly compromised by the prolonged contact with water.In this paper, an experimental and numerical evaluation of hydro-thermal ageing's effects on polyurethane adhesive connections has been analysed. An efficient semi-analytical procedure is developed for the design or verification of existing structures reinforced by bonded steel elements. The model can evaluate the interfacial shear stress at all loading stages up to the failure of bonded joints exposed to the marine environment. The model is based on Bernoulli beam theory and satisfies the requirements of equilibrium and strain compatibility, allowing for interfacial deformations.Furthermore, the mechanical behaviour of bonded connections subject to accelerated ageing has been experimentally investigated. More in detail, an experimental program including double lap shear and end-notch flexure tests was performed to evaluate the cohesive behaviour in Mode II of a polyurethane structural adhesive under the combined effects of water and temperature during 150 days of exposure. The experimental and numerical investigation shows how the performance of the adhesive joints is influenced by the ageing conditions.

Competing fracture modes in Al-steel resistance spot welded structures: Experimental evaluation and numerical prediction

Multi-material design has been increasingly used in the automotive industry for structural lightweighting. A novel resistance spot welding technique has been developed to join aluminium to steel with acceptable joint strength. However, aluminium to steel resistance spot welds can fail in either interfacial (IF) or pull-out (PO) fracture modes. In the present study, coupon-level tensile shear and coach peel samples are tested under quasi-static condition, and component-level T-joint structures are tested under impact load. Experimental results show that in the IF fracture mode, weld failure occurs due to the facture of the intermetallic layer, while in the PO fracture mode, weld failure occurs due to a combination of different mechanisms including through-thickness tearing of the weld nugget and possibly partial fracture of the intermetallic layer. In the finite element analysis, two force-based fracture criteria are implemented via mesh-independent connector element considering a general loading condition, and whichever fracture potential reaches unity first determines the fracture mode. The proposed method is validated by experiments and has the following features: firstly, it can capture the behaviour of fracture mode transitioning from IF to PO as weld diameter increases; secondly, it can simulate the maximum load and deformation at fracture; thirdly, it can indicate the global response and absorbed energy in impact analysis with reasonable accuracy. Furthermore, a distinct advantage of the model is that it is free of non-physical calibration. The parameters in the model are obtained from geometric and material properties of the weld directly. The developed method shows desirable performance and is potentially suitable for applications in large-scale automotive structural analysis and design.