Mode Spacing Research Articles

Rethinking Sexuality: A Reading of Ismat Chughtai’s “Lihaaf”

This research paper seeks to reinterpret sexuality keeping in mind its fictional depiction in Ismat Chughtai’s phenomenal story “Lihaaf.” An attempt will be made to challenge “heterosexual normativity” ὰ la Monique Wittig and Judith Butler to eventually clear space for alternate sexual modes of life namely homosexual and lesbian. Chughtai’s courage to deal with taboo subjects such as homosexuality and lesbianism at one level offended the conservative society, and at another voiced the actual prevalence of sexual practices that are still denounced and undermined. Several other issues about Butler’s and Wittig’s theorization will be examined through rigorous textual analysis of this story which is narrated from the perspective of a teenage girl who can be considered a symbol of the homophobic social and cultural milieu. The story brings to light the subject of female sexuality and the presence of repressed sexual desires of females in a heteronormative marriage which paves the way to homosexuality and breaks the patriarchal barriers of a claustrophobic society. Through the characters of Nawab Saheb and Begum Jaan, Chughtai foregrounds “the distinction between the “naturally given, normative ‘self’ of heterosexuality and the rejected ‘other’ of homosexuality” as well as dismantles the conventional notion of marriage.

Application of the Constrained Formulation to the Nonlinear Sloshing Problem Based on the Arbitrary Lagrangian–Eulerian Method

Abstract This study deals with an application of constrained formulation to a nonlinear sloshing problem based on the arbitrary Lagrangian–Eulerian finite element method (ALE). The ALE method incorporates a discretized form of equations of motion with mesh updating algorithms in order to prevent a problem of mesh distortion. This paper focuses on an analytical aspect of such treatments as constrained systems in the formulation of the ALE method. Since the mesh updating algorithms give algebraic relations for nodal coordinates, this study treats these relations as constraints. Then, we introduce formulation for constrained systems based on the method of Lagrange multipliers. As a result of this formulation, equations of motion are given by differential algebraic equations (DAEs) consisting of differential equations for time evolution of physical quantities and algebraic equations (constraints). The present method can be classified into a kind of augmented formulation. Moreover, we present a size-reduction technique used in the Newton–Raphson method in order to remove a part of the redundant degrees-of-freedom in the iterative procedures, because the resulting set of DAEs involves a larger number of unknowns than the minimal number of degrees-of-freedom due to the introduction of the constrained formulation. The derived reduced system still holds the physically essential part of equations of motion for the sloshing problem. Even though it is not reduced to the minimal degrees-of-freedom, it does not involve algebraically complicated and inefficient procedures in computation. In addition, this study presents a method to introduce damping effects defined in the modal space into the FEM models. The proposed approach is validated by comparisons with experimental data in the time domain analysis.

Detection accuracy of target accelerations based on vortex electromagnetic wave in keyhole space

The influence of the longitudinal acceleration and the angular acceleration of detecting target based on vortex electromagnetic waves in keyhole space are analyzed. The spectrum spreads of different orbital angular momentum (OAM) modes in different non-line-of-sight situations are simulated. The errors of target accelerations in detection are calculated and compared based on the OAM spectra spreading by using two combinations of composite OAM modes in the keyhole space. According to the research, the effects about spectrum spreads of higher OAM modes are more obvious. The error in detection is mainly affected by OAM spectrum spreading, which can be reduced by reasonably using different combinations of OAM modes in different practical situations. The above results provide a reference idea for investigating keyhole effect when vortex electromagnetic wave is used to detect accelerations.

A versatile platform for gas-phase molecular polaritonics.

Cavity coupling of gas-phase molecules will enable studies of benchmark chemical processes under strong light-matter interactions with a high level of experimental control and no solvent effects. We recently demonstrated the formation of gas-phase molecular polaritons by strongly coupling bright ν3, J = 3 → 4 rovibrational transitions of methane (CH4) to a Fabry-Pérot optical cavity mode inside a cryogenic buffer gas cell. Here, we further explore the flexible capabilities of this infrastructure. We show that we can greatly increase the collective coupling strength of the molecular ensemble to the cavity by increasing the intracavity CH4 number density. In doing so, we can tune from the single-mode coupling regime to a multimode coupling regime in which many nested polaritonic states arise as the Rabi splitting approaches the cavity mode spacing. We explore polariton formation for cavity geometries of varying length, finesse, and mirror radius of curvature. We also report a proof-of-principle demonstration of rovibrational gas-phase polariton formation at room temperature. This experimental flexibility affords a great degree of control over the properties of molecular polaritons and opens up a wider range of simple molecular processes to future interrogation under strong cavity-coupling. We anticipate that ongoing work in gas-phase polaritonics will facilitate convergence between experimental results and theoretical models of cavity-altered chemistry and physics.

Complex mode superposition method of non-classically damped systems based on hysteretic damping model with frequency-dependent loss factors

For non-classically damped systems, it is easy to construct a damping matrix based on a hysteretic damping model. However, the damped natural frequency is non-physical, and the frequency response function is non-causal. These two drawbacks can be overcome by the hysteretic damping model with frequency-dependent loss factors. In this paper, a complex mode superposition method for non-classically damped systems based on the hysteretic damping model with frequency-dependent loss factors is proposed. Frequency-dependent loss factors of the natural frequencies are considered in the transient vibration response, while frequency-dependent loss factors of the external excitation frequencies are considered in the steady state vibration response. By decoupling complex modes in state space and physical space, non-proportional damping characteristics of hybrid structures can be effectively considered. Therefore, the proposed method can be used to calculate the time-domain dynamic responses of hybrid structures, whose loss factors are sensitive to frequency variation and have strong non-proportional damping characteristics. The time-domain dynamic responses of numerical examples are compared based on different mode superposition methods. Shaking table tests are performed on cantilever plates with different damping characteristics. The numerical and test results validate the proposed method. Moreover, the proposed method has a wide range of applications.

Random matrix theory for description of sound scattering on background internal waves in a shallow sea

The problem of propagation of low-frequency sound in a shallow waveguide with random hydrological inhomogeneity caused by background internal waves is considered. A new approach to statistical modeling of acoustic fields, based on the application of the random matrix theory and previously successfully used for deep-water acoustic waveguides, is used to the case of shallow-water waveguides. In this approach, sound scattering on random inhomogeneity is described using an ensemble of random propagator matrices which describe the transformation of the acoustic field in the space of normal waveguide modes. A study of the effect of sound “escaping” from a waveguide was carried out. The term “escaping” here means energy transfer to modes with stronger attenuation due to scattering on internal waves. A model of an underwater sound channel with an axis at a depth of about 45 meters is considered. It is shown that the first few modes propagating inside the water column are very little subject to losses due to the “escaping”. The strongest impact of the leakage scattering is experienced by the middle group of modes capable of reaching the sea surface. It is revealed as significant increasing of losses as compared to a horizontally homogeneous waveguide. On the other hand, the existence of linear mode combinations for which loss enhancement is practically absent has been revealed. These linear combinations correspond to the eigenfunctions of an inhomogeneous waveguide. Statistical analysis of propagator eigenfunctions indicates on qualitative differences of mechanisms of scattering for frequencies of 100 and 500 Hz.

Impacts of parking and accessibility on retail-oriented city centres

Growing e-commerce, the aftermath of the COVID-19 pandemic, the need for greater sustainability, and increasing competition between different uses for scarce space pose increasing challenges to city centres. Most city centres in high-income countries are strongly characterized by retail. To create space for other mobility modes, outdoor dining, or greening, reducing on-street parking is a controversially discussed measure that is feared especially by retailers. However, the impact of parking infrastructure and accessibility on the performance of retail in city centres is not yet clearly explored in the literature. This paper contributes to closing this research gap by analysing the impact of on- and off-street parking capacity and accessibility on the rents for retail properties in city centres. The applied database consists of nearly 400 retail rental offers in the city centre of Aachen, Germany, published between 2015 and 2022. As the data cover the period of the COVID-19 pandemic, we also consider the impact of the pandemic on retail rents.Results of a spatial regression indicate that public transport stops, pedestrian zones, and public parking garages nearby increase the attractiveness of retail locations. On the contrary, much on-street parking capacity in the immediate vicinity reduces retail rents. However, sufficient parking capacity should be accessible within a comfortable walking distance. This finding supports the approach of reducing on-street parking in city centres while concentrating stationary car traffic in multi-storey car parks.

Регулярна та складна поведінка маятникової системи у магнітному полі

This paper considers the dynamics of an oscillatory dissipative system of two coupled pendulums in a magnetic field. The pendulums are coupled via an elastic element. The inertial components of the pendulums vary over a wide range, and in the analytical study the mass ratio is chosen as a small parameter. The magnetic forces are calculated using the Pade approximation, which best agrees with the experiment. This approximation describes the magnetic excitation to good accuracy. The presence of external inputs in the form of magnetic forces and various types of loads that exist in many engineering systems significantly complicates the mode shape analysis of nonlinear system. Nonlinear normal modes of this system are studied, one mode being coupled and the other being local. The modes are constructed by the multiple-scale method. Both regular and compound behavior is studied as a function of the system parameters: the pendulum mass ratio, the coupling coefficient, the magnetic intensity coefficient, and the distance between the axis of rotation and the center of gravity. The effect of these parameters is studied both at small and at sizeable initial pendulum inclination angles. The analytical solution is compared with the results of a numerical simulation based on the fourth-order Runge?Kutta method where the modes are calculated using the initial values of the variables found in the analytical solution. The numerical simulation, which includes the construction of phase diagrams and trajectories in the configuration space, allows one to assess the dynamics of the system, which may be both regular and compound. The stability of the coupled mode is studied using a numerical-analytical test, which is an implementation of the Lyapunov stability criterion. In doing so, the stability of a mode is determined by assessing the vertical off-trajectory deviation of the mode in the configuration space.

High-power and high-quality Gaussian beam in VCSEL via anisotropic modes control

Gaussian beam in the vertical cavity surface emitting laser (VCSEL) hasimportantapplicationin 3D sensing and optical communications, due to its concentrate energy at center and long propagation distance. However, its beam quality under high power tends to be serious degradation and become annular hollow distribution, severely limiting the use of VCSEL. Here, the anisotropic elliptical oxide aperture VCSEL (AEOA-VCSEL) was designed to achieve high-power Gaussian beam with high-quality via anisotropic modes control. The saturation output power reached up to 8.2 mW under low injection current, to our best knowledge, which was the highest power generated in single VCSEL device. Moreover, the AEOA-VCSEL can control the output beam profile only by adjusting injection current, and could also homogenize the mode spacing among adjacent high-order modes. The facile preparation process and low cost makes the device present great potential in augmented and virtual reality (AR/VR), 3D sensing and optical communications.

A hybrid Bloch mode synthesis method based on the free interface component mode synthesis method

For band-structure computation, the Bloch mode synthesis (BMS) or the generalized Bloch mode synthesis (GBMS) method is a series of model-reduction computational algorithms based on the Craig-Bampton method. A hybrid Bloch mode synthesis (HBMS) method with a hybrid Floquet-Bloch periodic boundary condition is proposed in this paper. A force-based Floquet-Bloch periodic boundary condition is derived and combined with the default displacement-based Floquet-Bloch periodic boundary condition to form the hybrid Floquet-Bloch periodic boundary condition. The hybrid BMS method has been developed by combining the hybrid Floquet-Bloch periodic boundary conditions with the free-interface component mode synthesis method. The HBMS method considers the influence of higher-order modes on periodic boundary structures so that the hybrid Floquet-Bloch periodic boundary conditions can be applied to the reduced-order modal space without introducing errors, which improves the computational efficiency. According to different truncation errors, the HBMS method has been developed into three algorithms, and they each have a different precision-efficiency ratio. Numerical experiments demonstrate that the developed method outperforms in accuracy and computational efficiency compared to the default BMS/GBMS method.

Urban space distribution: The case for a more equitable mobility system

Cities everywhere are struggling to establish more sustainable transport systems to reduce accidents, congestion, pollution and improve overall urban environments for human well-being. Due to increased mobility, particularly with private motorized vehicles, there is pressure and conflicts over space allocation in limited city roads and open spaces. There is also evidence that different transport modes are favoured over others in the allocation of and access to space. In urban planning, there are increasing efforts to allocate more space to the car, promoting rapid urbanisation at the expense of the space for more sustainable modes of transport. This process is leading to negative externalities, making the road environment unsafe for those outside the car. This space distribution is also dynamic and responsive to political agendas that change over time and geography. This research provides a comparative of urban space allocation in three cities, distinguishing between motorized (private and public transport) spaces and spaces allocated to non-motorized modes (walking and cycling). The research builds on analysis across different geographies of development taking examples from Europe, South America and Africa as case studies. We approach the cities of Bogotá (Colombia), Valletta (Malta) and Freetown (Sierra Leone) as examples of high density urban areas from both the global south and global north. The methodology entails the use of high-resolution satellite images and the application of geographic information systems to derive the necessary measurements in each city. Results show how space is unevenly distributed in many parts of the case study cities in the context of their own social, economic and political contexts, reflecting on the distribution of space in relation to other inequalities that might manifest in the urban space. Such inequalities lead to inequities in the transport system and the availability and use of open and public space. The study hopes to raise awareness of the equity issues surrounding urban transport systems, and the need for more sustainable urban designs for public and open spaces, identify commonalities and structural drivers of spatial inequalities, as well as context-specific determinants of urban space distribution.

Multi-channel chaotic signal generation using a weak resonant cavity Fabry–Perot laser diode subject to self-phase-modulated feedback

We propose and experimentally demonstrate a wideband multi-channel chaotic source using a weak resonant cavity Fabry–Perot laser diode with self-phase modulated optical feedback. In this configuration, self-phase modulation is incorporated into the external optical feedback loop to enhance bandwidth of the generated multi-channel chaos and suppress time delay signature (TDS). The experimental results indicate that, with appropriate optical feedback intensity, 86 lasing modes within the wavelength range of 1530–1570 nm and with the mode spacing of 0.47 nm can be simultaneously driven into a state of chaos, and the generated multi-channel chaos have an enhanced bandwidth and suppressed TDS.

Jahn–Teller distortion in Sr2FeO4: group-theoretical analysis and hybrid DFT calculations

We present theoretical justification for distorted Ruddlesden–Popper (RP) phases of the first-order by using hybrid density functional theory (DFT) calculations and group-theoretical analysis. We, thus, demonstrate the existence of the Jahn–Teller effect around an Fe^{4texttt {+}} ion in Sr_{2}FeO_{4}. On the calculation side, we have established a combination of Wu–Cohen (WC) exchange and Perdew-Wang (PW) correlation in a three-parameter functional WC3PW, giving the most accurate description of Sr_{2}FeO_{4} from the comparison of three hybrid DFT functionals. Self-consistently obtained Hartree–Fock exact exchange of 0.16 demonstrates consistent results with the experimental literature data. Importantly, we explain conditions for co-existing proper and pseudo-Jahn–Teller effects from the crystalline orbitals, symmetry-mode analysis and irreps products. Moreover, phonon frequency calculations support and confirm the results of symmetry-mode analysis. In particular, the symmetry-mode analysis identifies a dominating irreducible representation of the Jahn-Teller mode (X2+) and corresponding space group (SG) of ground state structure (SG Cmce model). Therefore, the usually suggested high-symmetry tetragonal crystal structure (SG I4/mmm model) is higher in energy by 121 meV/f.u. (equivalent to the Jahn-Teller stabilization energy) compared with the distorted low-symmetry structure (SG Cmce model). We also present diffraction patterns for the two crystal symmetries to discuss the differences. Therefore, our results shed light on the existence of low-symmetry RP phases and make possible direct comparisons with future experiments.

Geometric Phase in Twisted Topological Complementary Pair.

Geometric phase enabled by spin-orbit coupling has attracted enormous interest in optics over the past few decades. However, it is only applicable to circularly-polarized light and encounters substantial challenges when applied to wave fields lacking the intrinsic spin degree of freedom. Here, a new paradigm is presented for achieving geometric phase by elucidating the concept of topological complementary pair (TCP), which arises from the combination of two compact phase elements possessing opposite intrinsic topological charge. Twisting the TCP leads to the generation of a linearly-varying geometric phase of arbitrary order, which is quantified by the intrinsic topological charge. Notably distinct from the conventional spin-orbit coupling-based theories, the proposed geometric phase is the direct result of the cyclic evolution of orbital-angular-momentum transformation in mode space, thereby exhibiting universality across classical wave systems. As a proof of concept, the existence of this geometric phase is experimentally demonstrated using scalar acoustic waves, showcasing the remarkable ability in the precise manipulation of acoustic waves at subwavelength scales. These findings engender a fresh understanding of wave-matter interaction in compact structures and establish a promising platform for exploring geometric phase, offering significant opportunities for diverse applications in wave systems.

Optimization as generator of structural instability: Koiter’s worst imperfection

This paper is focused on the interaction of local modes in pin-jointed structures, with the aim to present an algorithm for the appraisal of the lowest critical load characterizing the structure under the effect of small imperfections. This interaction phenomenon is framed within Koiter’s theory of elastic instability as a quartic system. First of all, the paper discusses the theoretical results of Koiter’s theorem about the determination of the worst imperfection with respect to the critical load. In doing this, the characterization of the fold lines in the modal space is recalled and used for the purposes of the reformulation of the theorem. Then, a FEM code aimed at the determination of the most dangerous shape of the imperfection, and at performing the related sensitivity analysis, is presented. The basis of the code is a nonlinear model of a 3D rod equipped with a planar flexural deformation, within the context of Eulerian instability. Some numerical results having a practical interest are discussed.

Multibeam Metasurface Antenna Enabled by Orbital Angular Momentum Demultiplexing Feeding for IoT Communication

Multibeam antenna radiations provide linkages to multiple nodes and can bring enhanced communication quality with reduced power consumption for Internet of Things (IoT) applications. In this paper, a novel method providing a low-cost and flexible multibeam antenna solution is proposed. Multiple orbital angular momentum (OAM) modes are used as internal excitations of the antenna, and the generated multiple beams are pencil beams with no OAM mode, which is convenient for IoT nodes connection. First, aperture phase distributions that convert incident vortex beams with different and orthogonal topological orders into designated directional pencil beams are acquired and superimposed to form a metasurface aperture that, under excitations of vortex beams with multiple orders, produces multibeam each with a predefined direction. The proposed multibeam method is then illustrated with a transmissive metasurface design, with four beams pointing at arbitrary half space directions. Techniques such as OAM modes spacing and aperture partitioning are utilized for reducing sidelobe levels (SLLs). Furthermore, a similar multibeam metasurface antenna with additional linear-to-circular polarization conversion function is demonstrated, which opens the possibility of utilizing different polarizations on top of the OAM based multibeam. This paper successfully explores and achieves a novel antenna system with multiple radiations suited for multiple IoT nodes accessing with low cost and low energy consumption, and also provides a new degree-of-freedom for OAM applications.

Unveiling arc deflection instability in narrow gap laser-arc hybrid welding of thick Ti-6Al-4V plate

Unveiling the mechanism behind arc deflection under narrow gap laser arc hybrid welding (NGLAHW) is of paramount significance in mitigating laser-arc coupling failure and welding porosity for thick Ti-6Al-4V plate structure. This paper utilizes high-speed camera technology, data statistics and model prediction to comprehensively study the influence of constrained groove space and droplet transfer mode on arc deflection. The results demonstrate that narrowing groove gap exerts a substantial compressive effect on welding arc behavior, particularly rendering it more susceptible to arc deflection when the groove gap is smaller than the arc length. The small droplet transfer mode is characterized by stable arc behavior, whereas the large droplet transfer mode tends to be susceptible to arc instability due to the droplet deviation induced by turbulent metal vapor. Particularly noteworthy is the emergence of substantial arc deflection when the droplet deviation exceeds the critical threshold of 0.51 mm, which diminishes the driving force for droplet transfer and subsequently leading to potential short-circuiting explosions and unstable welding process. Moreover, the lateral force induced by arc deflection drives a deviation in arc heat source with accelerated solidification of molten pool, consequently resulting in an elevation in welding porosity. This paper has provided a comprehensive insight into the mechanism driving arc deflection in NGLAHW, which holds paramount importance in enabling effective strategies to regulate the arc behavior.

An orthogonal subspace method for source depth discrimination in shallow water using a horizontal line array

Source depth discrimination with a horizontal line array in a shallow water environment generally involves mode filtering. Since a limited horizontal aperture can make the observation matrix an ill-conditioned matrix, which affects the mode filtering, the application of the Schmidt Orthogonalization to the problem of source depth discrimination with a horizontal line array is investigated. It aims to construct orthogonal trapped and non-trapped component subspaces while preserving an almost complete mode space and reducing energy loss. An orthogonal subspace discriminator is proposed, and the corresponding decision metric relies on estimating the proportion of the trapped component. The performance of each method is predicted by receiver operating characteristic curves obtained by simulation, enabling one to compare the proposed method with the comparison methods. The impact of horizontal aperture, frequency, signal-to-noise ratio, and environmental mismatch on performance is numerically studied. The results show that the proposed method performs better than comparison methods at smaller apertures and is more robust against environmental mismatch at lower frequencies. Finally, the method is demonstrated on experimental data acquired with a bottom-mounted horizontal line array deployed in the South China Sea.

Nonlinear mode decomposition via physics-assimilated convolutional autoencoder for unsteady flows over an airfoil

I have developed a physics-assimilated convolutional autoencoder (CAE) neural network, namely, PhyAENet, to carry out nonlinear mode decomposition of the unsteady flow field around a National Advisory Committee for Aeronautics 4412 airfoil near stall conditions. The flow field snapshots are mapped into latent modes by the encoder part of the well-trained CAE, which are used for dynamic mode decomposition (DMD) analysis. The computed DMD modes are split into modes covering different frequency ranges. These high and low-frequency DMD modes are used to form reconstructed encoded sequences, which are then mapped back to generate the nonlinear decomposed spatiotemporal modes by the decoder of the CAE. As such, physics is assimilated into the neural network by incorporating the frequencies of the DMD modes into the latent modes in the latent space. The proposed PhyAENet is capable of extracting the dominant features of the flow fields, accounting for the nonlinearity of the underlying dynamics. Furthermore, the extracted nonlinear modes are evolving with time and physically interpretable. It is revealed that the nonlinear modes can be well represented when using more DMD modes for reconstruction of the encoded sequences. The energy spectrum of the nonlinear modes are obtained by ranking the Frobenius norm of the mode vector.

Exploring the spatial hole burning effect on the mode-locking characteristics of self-mode-locked Nd:YVO4 lasers

The spatial hole burning (SHB) effect on the mode-locking characteristics of Nd:YVO4 self-mode-locked (SML) lasers are investigated. By varying the cavity length, pump power, and crystal temperature, we manipulate the SHB effect on the longitudinal mode distributions and the temporal waveforms of the SML lasers. The experimental results indicate that, at a pump power of 3395 mW and a cavity length of 23 mm, the SHB effect is minimal, the temporal waveform remains stable and the longitudinal mode spacing equals the fundamental longitudinal mode interval (FLMI). As increasing the cavity length to 75 mm, the experimental longitudinal mode spacing becomes 1 to 5 times the FLMI and the temporal waveforms are then multi-pulse mode-locked state, indicating an aggravation in the SHB effect of the SML laser. With the cavity length of 23 mm, as the pump power increases from 3.4 W to 9.7 W, the SHB effect on the mode-locking characteristics gradually also aggravates. The laser gradually changes from the fundamental mode-locked state to the spaced mode-locked state. By adjusting the crystal temperature from 25 °C to 35 °C, the aggravated SHB effect caused by the increase in pump power is counteracted.