Contribution Of Modes Research Articles

Cell Death, by Any Other Name….

Studies trying to understand cell death, this ultimate biological process, can be traced back to a century ago. Yet, unlike many other fashionable research interests, research on cell death is more alive than ever. New modes of cell death are discovered in specific contexts, as are new molecular pathways. But what is "cell death", really? This question has not found a definitive answer yet. Nevertheless, part of the answer is irreversibility, whereby cells can no longer recover from stress or injury. Here, we identify the most distinctive features of different modes of cell death, focusing on the executive final stages. In addition to the final stages, these modes can differ in their triggering stimulus, thus referring to the initial stages. Within this framework, we use a few illustrative examples to examine how intercellular communication factors in the demise of cells. First, we discuss the interplay between cell-cell communication and cell death during a few steps in the early development of multicellular organisms. Next, we will discuss this interplay in a fully developed and functional tissue, the gut, which is among the most rapidly renewing tissues in the body and, therefore, makes extensive use of cell death. Furthermore, we will discuss how the balance between cell death and communication is modified during a pathological condition, i.e., colon tumorigenesis, and how it could shed light on resistance to cancer therapy. Finally, we briefly review data on the role of cell-cell communication modes in the propagation of cell death signals and how this has been considered as a potential therapeutic approach. Far from vainly trying to provide a comprehensive review, we launch an invitation to ponder over the significance of cell death diversity and how it provides multiple opportunities for the contribution of various modes of intercellular communication.

A strategy for sensing the petal mode in the presence of AO residual turbulence with the pyramid wavefront sensor

Context. With the Extremely Large Telescope (ELT) generation of telescopes come new challenges. The complexity of these telescopes’ pupils creates new problems for adaptive optics (AO) that prevent the telescopes from reaching the theoretical resolutions that their size allows. In particular, the large spiders necessary to support the massive optics of these telescopes create discontinuities in the wavefront measurement. These discontinuities appear as a new phase error dubbed the “petal mode.” This error is described as a differential piston between the fragment of the pupil separated by the spiders and is responsible for a strong degradation in the imaging quality, reducing the European ELT’s resolution to that of a 15m telescope. Aims. The aim of this paper is to study the measurement of the petal mode by AO sensors. In particular, we want to understand why the pyramid wavefront sensor (PyWFS), the first-light wavefront sensor of any ELT-generation telescope, cannot measure this petal mode under normal conditions, and how to enable this measurement by adapting the AO control scheme and the PyWFS. Methods. To facilitate our study, we considered a simplified version of the petal mode, featuring a simpler pupil than the ELT. This allowed us to quickly simulate the properties of the petal mode and its measurement by the PyWFS. We studied specifically how a system that separates the atmospheric turbulence from the petal measurement would behave. Studying the petal mode’s power spectral density, we proposed using a spatial filter to reduce the contribution of AO residuals to the benefit of petal mode contribution, eventually enabling it to be measured. Finally, we demonstrated our proposed system with end-to-end simulations. Results. A solution proposed to measure the petal mode is to use an unmodulated PyWFS (uPyWFS), but the uPyWFS does not make accurate measurements in the presence of atmospheric residuals. A spatial filtering step, consisting of a pinhole around the pyramid tip, reduces the first path residuals seen by the uPyWFS and restores its accuracy. This system was able to measure and control the petal mode during the end-to-end simulation. Conclusions. To address the petal problem, a two-path AO with a sensor dedicated to the measurement of the petal mode seems necessary. The question remains as to what could be used as the second path petalometer. Through this paper, we demonstrate that an uPyWFS can confuse the petal mode with the residuals from the first path. However, adding a spatial filter on top of said uPyWFS makes it a good petalometer candidate. This spatial filtering step makes the uPyWFS less sensitive to the first path residuals while retaining its ability to measure the petal mode.

Deep learning‐based response spectrum analysis method for building structures

AbstractThe response spectrum method has gained widespread acceptance in practical applications owing to its favorable compromise between accuracy and practical efficiency. The method predicts the peak responses of multi‐degree‐of‐freedom (MDOF) systems by combining modal responses. The Square Root of the Sum of Squares (SRSS) and Complete Quadratic Combination (CQC) rules are commonly used for modal combinations. However, it has been widely known that these rules have limitations in accurately predicting responses influenced by higher modes and cross‐modal correlations. To improve the accuracy of the response spectrum analysis method for building structures, this paper proposes a Deep learning‐based modal Combination (DC) rule by introducing modal contribution coefficients predicted by a deep neural network (DNN) model. The DC rule enhances prediction accuracy by considering the characteristics of ground motion and the dynamic properties of a structural system. The DC rule provides more accurate predictions than the conventional rules, particularly for irregular response spectra and responses affected by higher modes. The efficiency and applicability of the DC rule are demonstrated by numerical investigations of multistory shear buildings and steel frame structures with regular and irregular shapes. The source codes, data, and trained models are available for download at https://github.com/tyongkim/ERD2.

Low-order planar pressure reconstruction of stalled airfoils using particle image velocimetry data

We present planar time-resolved particle image velocimetry (PIV) measurements of flow in the streamwise surface-normal plane of a NACA 0012 airfoil at chord-based Reynolds number Rec=7×104. The angles of attack α=13∘ and 15∘ correspond to transient stall and deep stall flow regimes, respectively. A Poisson solver is utilized to reconstruct the instantaneous planar pressure fields from the PIV with satisfactory comparison in the mean pressure compared with dynamically matched Reynolds-averaged Navier-Stokes (RANS) simulations. Using the proper orthogonal decomposition (POD), a systematic reduced-order reconstruction of the velocity fields and subsequent pressure fields is used to quantify the required number of velocity modes to achieve a desired accuracy in the instantaneous pressure. Further, a Galerkin projection of the Poisson equation onto the POD subspace is used as a framework to identify the relative contribution of each velocity mode on the resulting pressure field via quadratic stochastic estimation (QSE). In both cases, the zeroth mode (corresponding to the mean) is of leading-order importance. In addition, a tendency of the zeroth mode to interact with vortex-shedding modes is identified. Published by the American Physical Society 2024

Unsteady Investigation of Intermediate Turbine Ducts Under the Influence of Purge Flows

Abstract The aerodynamic flow field at the outlet of a high-pressure turbine (HPT) stage in a modern turbofan engine is highly unsteady and strongly influenced by periodic fluctuations from the HPT rotor, also interacting with the HPT stationary vanes. Downstream of the last HPT stage, the flow enters the intermediate turbine duct (ITD), where new unsteady components are generated, due to the interaction between the incoming flow and the struts supporting the ITD. This paper illustrates the differences between the unsteady flow behavior in two state-of-the-art ITD configurations for turbofan engines: the turbine center frame and the turbine vane frame. The experimental results discussed in this work are obtained in the Transonic Test Turbine Facility, situated at Graz University of Technology, Austria. To achieve engine-representative operating conditions at the ITD inlet and outlet sections, the tested setups include not only the duct, but also the last HPT stage and the first low-pressure turbine stage row. Additionally, the test rig features a secondary air supply system, capable of feeding purge air to every stator–rotor cavity in the test vehicle. Unsteady measurement data at the inlet and outlet of the two duct configurations are acquired with fast-response aerodynamic pressure probes, for two purge flow conditions. Azimuthal mode decomposition is applied to phase-averaged data at selected radial positions, to isolate and quantify the contribution of different interaction modes to the overall unsteady flow field.

Syntheses, crystal structures, and energetic properties of four cyclo-pentazolate salts [NHn(CH3)4-n]+N5− (n = 0∼3)

The formation of non-metallic pentazolate salts from the combination of simple nitrogen-rich cations with cyclo-N5− is expected to be applied in propellants and explosives. In this work, a series of structurally similar cations ([NH3CH3]+, [NH2(CH3)2]+, [NH(CH3)3]+, and [N(CH3)4]+) were used to synthesize four cyclo-N5− containing energetic salts, and the contribution of crystal stacking mode, hydrogen bonding, C–H···π and π-stacking interactions in the stabilization of cyclo-N5− salts has been investigated by geometrical and Hirshfeld surface analyses as well as theoretical calculations. All salts have been thoroughly characterized by single-crystal X-ray diffraction, infrared (IR), multinuclear NMR (1H and 13C) spectroscopy, and elemental analysis. The decomposition temperatures of all salts are higher than 75 °C, as measured by thermogravimetric (TG). These compounds all show low sensitivities (IS ≥ 35 J, FS > 360 N) measured by standard BAM methods. Their heats of formation and detonation performances were calculated using the Born–Haber energy cycle and K-J method (“Pilem” program), respectively. This study has great significance for future design and synthesis of cyclo-N5− containing energetic materials.

Multimodal Sentiment Analysis Method Based on Hierarchical Adaptive Feature Fusion Network

The traditional multi-modal sentiment analysis (MSA) method usually considers the multi-modal characteristics to be equally important and ignores the contribution of different modes to the final MSA result. Therefore, an MSA method based on hierarchical adaptive feature fusion network is proposed. Firstly, RoBERTa, ResViT, and LibROSA are used to extract different modal features and construct a layered adaptive multi-modal fusion network. Then, the multi-modal feature extraction module and cross-modal feature interaction module are combined to realize the interactive fusion of information between modes. Finally, an adaptive gating mechanism is introduced to design a global multi-modal feature interaction module to learn the unique features of different modes. The experimental results on three public data sets show that the proposed method can make full use of multi-modal information, outperform other advanced comparison methods, improve the accuracy and robustness of sentiment analysis, and is expected to achieve better results in the field of sentiment analysis.

Impact of nanoparticle agglomeration on thermal conductivity of molten salt based nanofluids: Insights from molecular dynamics and lattice Boltzmann methods

The nanoparticle aggregation has significant influence on heat transfer properties. The contradictions between different researches exist and the underlying mechanisms of heat conduction remain unclear. To address these issues, the thermal conductivity of solar salt-SiO2 nanofluids in the non-aggregated and aggregated states was investigated, based on the combination of the advantages of molecular dynamics (MD) in revealing physical insights and lattice Boltzmann method (LBM) in simulating properties for complex structures. LBM models were simplified on the basic of MD results. Different heat transfer physics in nanofluids at nanoscale and mesoscale were compared. The results show that the thermal conductivity of aggregated nanofluid is higher than the non-aggregated nanofluid. By analyzing the diffusion coefficient, number density and vibrational density of states, we found that the previous hypotheses (such as Brownian motion, interfacial layer and interfacial thermal resistance) cannot explain the enhanced thermal conductivity induced by the nanoparticle agglomeration. The heat transfer mechanisms of aggregated nanofluid were further analyzed from new perspectives, i.e., the contributions of different material components and fluctuation modes to heat flux. It is found that the nanoparticle aggregation leads to the nanoparticle contribution increase, indicating the formation of low thermal resistance channels within the aggregates. The heat conduction contributed by collision decreases in the aggregated state, while that contributed by potential energy increases. Moreover, the thermal conductivity of aggregated nanofluid is negatively correlated with temperature, aggregate size and fractal dimension of agglomerates, and positively correlated with mass fraction of nanoparticles, degree of agglomeration, and backbone length of each aggregate.

Precise predictions for boosted Higgs production

Inclusive Higgs boson production at large transverse momentum is induced by different production channels. We focus on the leading production mechanism through gluon fusion, and perform a consistent combination of the state of the art calculations obtained in the infinite-top-mass effective theory at next-to-next-to-leading order (NNLO) and in the full Standard Model (SM) at next-to-leading order (NLO). We thus present approximate QCD predictions for this process at NNLO, and a study of the corresponding perturbative uncertainties. This calculation is then compared with those obtained with commonly used event generators, and we observe that the description of the considered kinematic regime provided by these tools is in good agreement with state of the art calculations. Finally, we present accurate predictions for other production channels such as vector boson fusion, and associated production with a gauge boson, and with a t\bar{t}tt‾ pair. We find that, at large transverse momentum, the contribution of other production modes is substantial, and therefore must be included for a precise theory prediction of this observable.

Closed-form optimal design of the tuned inerter damper (TID) connecting adjacent flexible buildings

The tuned inerter damper (TID) is a viable solution for addressing the vibration issue of the adjacent-building system. However, the conventional optimal calibration of the TID is conducted based on the classic 3-degree-of-freedom (3-DOF) model with one resonant DOF for each structure, which ignored the background flexibility contribution that comes from non-resonant modes of each one, and thus leads to non-optimal control performance. This paper developed a novel analogue 3-DOF model, in which the background flexibility contribution of each flexible building at the damper attachment location is represented by an equivalent stiffness element. An enhanced formula for the TID optimal frequency is developed accordingly (targeting the fundamental mode of the taller building) using the ‘root-locus’ method, where the background flexibility as well as the resonant mode contributions that come from both buildings are accounted for. For completeness, the optimal frequency formula that ignores the background flexibility contribution is derived based on the classic 3-DOF model. A robust approach is adopted to determine the optimal damping ratio based on the classic model. Numerical analysis is conducted based on a 25-15 floors adjacent-building system. Results demonstrate that when the enhanced frequency-tuning formula is used, a much more balanced frequency response curve of the taller building is achieved. Further, time-domain seismic analysis indicates that the TID performance is consistently improved when background flexibility is accounted for in the design formulas.

Quantum torque on a non-reciprocal body out of thermal equilibrium and induced by a magnetic field of arbitrary strength

AbstractA stationary body that is out of thermal equilibrium with its environment, and for which the electric susceptibility is non-reciprocal, experiences a quantum torque. This arises from the spatially non-symmetric electrical response of the body to its interaction with the non-equilibrium thermal fluctuations of the electromagnetic field: the non-equilibrium nature of the thermal field fluctuations results in a net energy flow through the body, and the spatially non-symmetric nature of the electrical response of the body to its interaction with these field fluctuations causes that energy flow to be transformed into a rotational motion. We establish an exact, closed-form, analytical expression for this torque in the case that the environment is the vacuum and the material of the body is described by a damped oscillator model, where the non-reciprocal nature of the electric susceptibility is induced by an external magnetic field, as for magneto-optical media. We also generalise this expression to the context in which the body is slowly rotating. By exploring the high-temperature expansion of the torque, we are able to identify the separate contributions from the continuous spectral distribution of the non-reciprocal electric susceptibility, and from the resonance modes. In particular, we find that the torque persists in the limiting case of zero damping parameter, due to the contribution of the resonance modes. We also consider the low-temperature expansion of the torque. This work extends our previous consideration of this model to an external magnetic field of arbitrary strength, thereby including non-linear magnetic field effects.

Quantitative descriptor of lattice anharmonicity in crystal

<sec>Anharmonic effect is often one of the physical root causes of some special material properties, such as soft mode phase transition, negative thermal expansion, multiferroicity, and ultra-low thermal conductivity. However, the existing methods of quantifying the anharmonicity of material do not give a clear and accurate anharmonicity descriptor. The calculation of the anharmonic effect requires extremely time-consuming molecular dynamics simulation, the calculation process is complex and costly. Therefore, a quantitative descriptor is urgently needed, which can be used to implement quick calculation so as to understand, evaluate, design, and screen functional materials with strong anharmonicity.</sec><sec>In this paper, we propose a method to quantify the anharmonicity of materials by only phonon spectrum and static self-consistent calculation through calculating and analyzing the material composed of germanium and its surrounding elements. In this method, the lattice anharmonicity is decomposed into the anharmonic contribution of independent phonon vibration modes, and the quantitative anharmonicity descriptor <inline-formula><tex-math id="M3">\begin{document}$ {\sigma }_{\boldsymbol{q},j}^{A} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231428_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231428_M3.png"/></alternatives></inline-formula> of phonons is proposed. Combining it with the Bose-Einstein distribution, the quantitative descriptor <inline-formula><tex-math id="M4">\begin{document}$ {A}_{{\mathrm{p}}{\mathrm{h}}}\left(T\right) $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231428_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231428_M4.png"/></alternatives></inline-formula> of temperature-dependent material anharmonicity is proposed. We calculate the bulk moduli and lattice thermal conductivities at 300 K of nine widely representative materials. There is a clear linear trend between them and our proposed quantitative descriptor <inline-formula><tex-math id="M5">\begin{document}$ {A}_{{\mathrm{p}}{\mathrm{h}}}\left(T\right) $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231428_M5.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231428_M5.png"/></alternatives></inline-formula>, which verifies the accuracy of our proposed descriptor. The results show that the descriptor has the following functions. i) It can systematically and quantitatively classify materials as the strength of anharmonicity; ii) it intuitively shows the distribution of the anharmonic effect of the material on the phonon spectrum, and realizes the separate analysis of the phonon anharmonicity that affects the specific properties of the material; iii) it is cost-effective in first-principles molecular dynamics calculations and lays a foundation for screening and designing materials based on anharmonicity.</sec><sec>This study provides an example for the high-throughput study of functional materials driven by anharmonic effect in the future, and opens up new possibilities for material design and application. In addition, for strongly anharmonic materials such as CsPbI<sub>3</sub>, the equilibrium position of the atoms is not fixed at high temperatures, resulting in a decrease in the accuracy of quantifying anharmonicity using our proposed descriptor. In order to get rid of this limitation, our future research will focus on the distribution of atomic equilibrium positions in strongly anharmonic materials at high temperatures, so as to propose a more accurate theoretical method to quantify the anharmonicity in strongly anharmonic materials.</sec>

Excitation energy dependency of the low-energy fission dynamics: Probing through prompt gamma-ray spectroscopy

Fission Fragment Spectroscopy (FFS) technique has been utilized to make simultaneous measurements of both the relative charge and mass yield distributions of even-even fission fragments produced from the fission of 236U at two different excitation energies, Eex. The necessary analysis has been carried out on the measured yield distributions by employing the Multimodal Random Neck Rupture Model (MM-RNRM). The relative contribution of two different types of asymmetric mode of fission – Standard I and Standard II has been extracted at Eex = 6.5 and 21.5 MeV. An attempt has been made to study the evolution of these two asymmetric fission modes with respect to the values of Eex of the concerned fissioning system at low-excitation regime. The probable evidence, although at the primitive stage, for an oscillatory behavior of the relative contributions of different low-energy fission modes with increasing values of Eex has been presented.

Measurements of flow-induced vibration of a flexible splitter plate mounted on a cylinder in free stream flow

We experimentally study flow-induced vibration (FIV) of a thin, cantilevered, flexible plate attached on the lee side of a circular cylinder in a free stream airflow. The Reynolds number (ReD) based on the diameter of the cylinder was varied in the range of (4 × 103, 5×104). The plates of different lengths and the same span were tested with varying airflow velocities (U) in a wind tunnel. The reduced velocity (UR) based on the length and the second natural frequency of the plate was in the range of (1, 11). We describe the plate dynamics showing displacement, frequency, phase plane, amplitude spectral density (ASD), oscillation envelope, modal energy contribution, and flow structures. Based on the motion of the plate, three FIV regimes are observed, namely, initial excitation, transition, and lock-in. During lock-in, the plate attains self-sustained limit cycle oscillation. We observe the presence of small-amplitude higher harmonics in the ASD plot. The second mode is dominant around the onset of lock-in, while the first mode is dominant later in the lock-in regime. The dimensionless displacement increases with an increase in mass ratio (Ms) in the lock-in regime. With a decrease in Ms, the slope of the dimensionless frequency with UR increases. To explain measurements, we develop a wake oscillator model (WOM) in which the plate and fluctuating lift force are modeled as an Euler–Bernoulli cantilever beam and van der Pol oscillator, respectively. The coupled WOM qualitatively and quantitatively predict the measured amplitude and frequency response, respectively, in the lock-in regime.

The radiation from railway wheel modes and their effect on loudness, sharpness, and equivalent pressure level

The noise of railway wheels is one of the main contributors to railway rolling noise. Auralization, the rendering of sound fields from virtual sources, is a promising tool for studying rolling noise, as it enables the study of perceptual qualities of noise. Generating such sound fields based on physical models requires knowledge of the structural vibrations and radiation characteristics of the wheels. The vibration and radiation of a railway wheel are typically dominated by highly undamped modes. The amplitudes of the various modes depend on the roughness excitation and the contact position of the wheel on the rail. For auralization, it is relevant to investigate which modes are significant in reproducing the equivalent sound pressure level (SPL), as well as psychoacoustic quantities. Identifying significant modes can also help simplify the physical model. This article explores the influence of lateral contact positions on wheel radiation and analyzes the modal contributions to pass-by SPLs. Using a timedomain prediction model for the sound pressure produced by one wheel as it passes a stationary track side position, the psychoacoustic quantities loudness and sharpness were investigated. The smallest number of modes required to reproduce equivalent pressure levels and psychoacoustic quantities is identified for two contact positions. For simplicity, the discussion is limited to one wheel, surface roughness, and vehicle speed. The results show possible simplifications in auralization models and can enable noise mitigation with a focus on psychoacoustic parameters.

Determining the key vibrations for spin relaxation in ruffled Cu(ii) porphyrins via resonance Raman spectroscopy.

Pinpointing vibrational mode contributions to electron spin relaxation (T1) constitutes a key goal for developing molecular quantum bits (qubits) with long room-temperature coherence times. However, there remains no consensus to date as to the energy and symmetry of the relevant modes that drive relaxation. Here, we analyze a series of three geometrically-tunable S = ½ Cu(ii) porphyrins with varying degrees of ruffling distortion in the ground state. Theoretical calculations predict that increased distortion should activate low-energy ruffling modes (∼50 cm-1) for spin-phonon coupling, thereby causing faster spin relaxation in distorted porphyrins. However, experimental T1 times do not follow the degree of ruffling, with the highly distorted copper tetraisopropylporphyrin (CuTiPP) even displaying room-temperature coherence. Local mode fitting indicates that the true vibrations dominating T1 lie in the energy regime of bond stretches (∼200-300 cm-1), which are comparatively insensitive to the degree of ruffling. We employ resonance Raman (rR) spectroscopy to determine vibrational modes possessing both the correct energy and symmetry to drive spin-phonon coupling. The rR spectra uncover a set of mixed symmetric stretch vibrations from 200-250 cm-1 that explain the trends in temperature-dependent T1. These results indicate that molecular spin-phonon coupling models systematically overestimate the contribution of ultra-low-energy distortion modes to T1, pointing out a key deficiency of existing theory. Furthermore, this work highlights the untapped power of rR spectroscopy as a tool for building spin dynamics structure-property relationships in molecular quantum information science.

Role of phonon scattering and bonding in resolving lattice thermal conductivity ambiguities of β-Ga2O3.

Understanding the lattice thermal conductivity (κl) of β-Ga2O3 is very intriguing owing to its advantages in high-voltage and high-temperature applications. Despite several attempts, the underlying mechanism and causes of the notable discrepancies found in the κl values of β-Ga2O3 along [100] and [001] directions calculated using first principles remained unresolved. We demonstrate that the understanding of the nature of chemical bonding is crucial to overcome the inconsistency in theoretically reported κl values. In low-symmetry structures such as β-Ga2O3, the nature of the interactions is primarily long-range; therefore, a sufficiently large supercell inclusive of various bonding characteristics is required to capture relevant phonon wavelengths. Bonding nature-aware structure modeling allows precise estimation of acoustic and optical mode contributions towards κl. Additionally, phonon mean free path analysis confirms that considering only third-order interaction terms is adequate to determine the κl of β-Ga2O3. The calculated κl values are in excellent agreement with experimentally reported values in all three directions. Our results establish that the bonding nature and its influence on phonon scattering are essential to consider in calculating κl accurately.

Influence of torsional effects in seismic retrofit of RC buildings

The nonlinear static procedures are very popular for the design and assessment of buildings subjected to earthquake ground motion in current structural engineering practice. Their application and relative accuracy are very relevant issues, especially in the case of seismic retrofit of irregular and/or high-rise buildings. Many retrofit design procedures are valid for low-rise buildings and/or neglect torsional effects and higher modes contribution. Often, the vibration properties are considered unchanged after retrofit, and the higher modes are neglected. Other ones are based on the proportional stiffness criterion (i.e., lateral story stiffness due to the additive structures is considered proportional to that of the original main structure). Still others rely on the hypothesis that the main structure remains elastic. Often, they neglect the interaction between the main structure and the additive structures used for retrofit. These are very significant drawbacks in the case of plan-asymmetric buildings, where torsional effects are important. In this case, the seismic response is dominated by harmful torsional effects and, thus, the retrofit strategy should significantly modify the dynamic response. To overcome such drawbacks but still keep the simplicity of using equivalent pushover analysis, this paper develops a “two-step” pushover procedure for seismic retrofit of plan-asymmetric buildings using buckling restrained braces based on steel hysteretic dampers (HBF). To this aim, a real case-study school building has been considered in the analyses. A design method has been implemented to size buckling restrained braces to be placed on selected spans and stories of the building. The effectiveness of the retrofit strategy has been finally demonstrated by nonlinear time-history analyses under different sets of earthquake-strong ground motions.

Sound radiation control of an unbaffled long enclosure using wavy micro-perforated panel absorbers

The sound radiation control of an unbaffled long enclosure using wavy micro-perforated panel absorbers (WMPPAs) was numerically and experimentally investigated. First, a hybrid model based on the finite element method (FEM) and the Wiener-Hopf (W-H) technique was established to calculate the sound pressure level (SPL) radiated from an unbaffled long enclosure lined with MPPAs. Then, the hybrid model was validated, and the sound suppression performance of a single WMPPA was evaluated. The results demonstrate that the WMPPA exhibits better sound absorption properties than the flat and corrugated micro-perforated panel absorber (FMPPA and CMPPA), especially in the middle- to high-frequency range. To further enhance the sound attenuation performance, an array of WMPPAs was subsequently proposed to absorb higher-order acoustic modes inside the long enclosure so that broadband-radiated noise could be suppressed. The comparison results demonstrate that the WMPPAs can reduce the radiated SPL within a wide frequency range which is favourable for the suppression of environmental noise. In addition, the WMPPA array shifts the sound reduction curve towards a low-frequency range by approximately 500 Hz compared with that of a single WMPPA, which is promising for the reduction of broadband noise. After that, a mechanistic study was conducted to explain the sound reduction performance of WMPPAs from the perspective of modal contributions. In addition, the diffraction effect of sound waves at the sharp edge of a long enclosure was illustrated. Besides, the contribution of the wavy structure's scattering effect to the sound reduction performance of WMPPAs was analysed. Finally, the sound absorption abilities of the WMPPAs were examined using a quasi-two-dimensional (quasi-2D) experiment. The results show that the WMPPAs exhibit good sound reduction performance in the middle- to high-frequency range, which verifies the feasibility of applying WMPPAs to suppress the broadband noise radiated from long enclosures.

Research on Electromagnetic Scattering Influence of Transmission Towers on Medium Wave Antenna Based on the Characteristic Mode Theory

Electromagnetic scattering from UHV transmission towers is a major factor affecting the safety and stability of the surrounding antenna signal system. In this paper, the electromagnetic scattering effect of ±800 kV UHV DC transmission tower on the medium-wave antenna is investigated based on the characteristic mode theory (CMT). The simulation model of the tower and antenna is established, and the mode selection is carried out according to the percentage of the contribution of the characteristic mode to the total electromagnetic scattering. The effects of electromagnetic scattering under three conditions, namely, the number of towers, the distance between towers and antennas, and different frequencies, are investigated separately. The simulation results show that as the number of towers increases from 1 to 3, it leads to an increase in the electromagnetic scattering impact by about 49.5%. The shape distortion of the antenna’s directional map becomes more pronounced and is accompanied by the extension with the direction of the power line. The distance between the tower and the antenna is shortened from 500 m to 125 m, resulting in the growth of the influence of electromagnetic scattering by about 36.4%, and the directional gain of the antenna increases along the direction of the transmission line. As the frequency increases from 600 kHz to 1400 kHz, it leads to the rise of electromagnetic scattering effect of about 32.7% and the antenna directional map becomes more complicated. The research results will provide technical support for developing protective measures against electromagnetic scattering from UHV DC transmission towers to medium-wave antennas.