Second-order Effects Research Articles

Observation of nonlinear thermoelectric effect in MoGe/Y3Fe5O12

Thermoelectric effects refer to the voltage generation from temperature gradients in condensed matter. Although various power generators are made from them, all the known effects, such as Seebeck effect, require macroscopic temperature gradients; since the sign of the generated voltage is reversed by reversing the temperature gradient, the net voltage disappears when the temperature distribution fluctuates temporarily or spatially with a macroscopic temperature gradient of zero. It is impossible to utilize such temperature fluctuations in the conventional thermoelectric effects, a situation which limits their application. Here we report the observation of a second-order nonlinear thermoelectric effect; we develop a method to measure nonlinear thermoelectricity and observe that a superconducting MoGe film on Y3Fe5O12 generates a voltage proportional to the square of the applied temperature gradient. The nonlinear thermoelectric generation demonstrated here provides a way for making power generators that produce electric power from temperature fluctuations.

Scalar field solutions and energy bounds for modeling spatial oscillations in Schwarzschild black holes based on the Regge–Wheeler equation

This text discusses the behavior of solutions and the energy stability within Schwarzschild spacetimes, with a particular emphasis on the behavior of massless scalar fields under the influence of a non-rotating and spherically symmetric black hole. The stability of solutions in the proximity of the event horizon of black holes in general relativity remains an open question, especially given the difficulties introduced by minor perturbations that may resemble Kerr solutions. To address this, this work explores a simplified model, including massless scalar fields, to better understand perturbation behaviors around black holes under the Schwarzschild approach. We depart from Richard Price’s work in connection with how scalar, electromagnetic, and gravitational fields behave. The tortoise coordinate transformation is considered to set the stage for numerical solutions to the wave equations. Afterward, we explore energy estimates, which are used to gauge stability and wave behavior over time. Our analysis reveals that the time evolution of the energy does not exceed twice its initial value. Further and under the assumption of initial conditions in L2−spaces, we obtain an exponential decreasing behavior in the energy time evolution. A question to continue exploring is how perturbations in L2 in the initial conditions that introduce Kerr solutions as a second-order effect in the linearized equations perturb this obtained exponential decay.

Second harmonic generation enhancement based on quasi-BICs in centrosymmetric materials

In centrosymmetric optical materials, the second-order nonlinear polarization of the bulk electric dipolar contribution is zero. More effective utilization of the contribution of the surface term is one of the key methods to efficiently obtain second-order nonlinear responses on these materials. Herein, a design of densely packed slotted nanopillar arrays based on quasi-bound states in the continuum (quasi-BICs) is proposed. The quasi-BICs are analyzed by using the finite element method as an example of silicon and the second harmonic generation (SHG) process is simulated. In the structure, normal-incidence linearly polarized light excites magnetic dipole-like quasi-BICs with a high quality factor which effectively promotes light-matter interactions. Increasing the nanopillar radius or decreasing the lattice constant within a certain range can cause the distribution of quality factors in k-space of the ky direction to contract toward the Γ point, which leads to a quasi-BIC with higher quality factors at the Γ point. By conjunctively adjusting the nanopillar radius and lattice constant or changing the slot azimuth, the resonance wavelength can be adjusted over a wide range (about several hundred nanometers) or finely (within about one nanometer) while maintaining high quality factors. When the symmetry perturbation introduced by the slot is small, it is calculated that the SHG conversion efficiency is about 10−6∼10−5 at an incident light power density of 1 MW/m2, and the SHG power is about 107∼108 times enhancement compared with the structure without slots. As the slot width decreases, higher SHG conversion efficiency with more significant SHG enhancement can be achieved at a specific slot length. The results provide new insights into the modulation of the resonant wavelength and quality factor of quasi-BICs, as well as the control of second-order nonlinear effects in centrosymmetric materials.

Victim’s identification and social categorization: first- and second-order effects on altruistic behavior

We explore in laboratory how donations to a charity can be influenced by the identifiability and the social categorization of the recipients. We find that donors give more, on average, to unidentified than to identified beneficiaries, since the latter are more likely to receive small donations than the former. Average donations are the same for in- and out-group beneficiaries; however, an in-group recipient is more likely to receive a top donation than an out-group one, whereas the latter is more likely than the former to receive an intermediate donation. Both first- and second-order effects are associated to the Dynamic Identity Fusion Index elicited from participants toward the ‘Multicultural World’.

Coupling parameter analysis of photovoltaic double skin façade targeting photovoltaic etching ratio and cavity depth

The photovoltaic double skin façade (PV-DSF) represents the frontier of the advanced building envelope, whereas the prior parameter analysis had predominantly focused on the influence of individual factors. As two essential factors of PV-DSF, the photovoltaic etching ratio ϑ and cavity depth Dcav have garnered considerable academic attention, with little of them focusing on their coupling effect to energy performance. This paper investigates the impact of ϑ and Dcav using a spectrum-resolution numerical model, incorporating the concept of elementary effects derived from Morris method to quantify their interaction. The findings reveal that ϑ exhibits a non-monotonic impact, whereas the influence of Dcav is monotonic but non-linear. The optimal ϑ is found to be within the range of 30–50 %, while the lowest Dcav mostly outperforms other values, contrary to previous studies. This deviation is speculated to arise from the consideration of hot air generation energy. Furthermore, the variation of one factor can potentially alter the optimal value of the other. The second-order elementary effect between them demonstrates that their coupling effect is also non-linear and non-monotonic, with an impact as significant as that of Dcav alone. Overall, the correlations between ϑ and Dcav should be thoroughly considered during the design period.

Enhanced vertical second harmonic generation from layered GaSe coupled to photonic crystal circular Bragg resonators

Abstract Two-dimensional (2D) layered materials without centrosymmetry, such as GaSe, have emerged as promising novel optical materials due to large second-order nonlinear susceptibilities. However, their nonlinear responses are severely limited by the short interaction between the 2D materials and light, which should be improved by coupling them with photonic structures with strong field confinement. Here, we theoretically design photonic crystal circular Bragg gratings (CBG) based on hole gratings with a quality factor as high as Q = 8 × 103, a mode volume as small as V = 1.18 (λ/n)3, and vertical emission of light field in silicon nitride thin film platform. Experimentally, we achieved a Q value up to nearly 4 × 103, resulting in a 1,200-fold enhancement of second harmonic generation from GaSe flakes with a thickness of 50 nm coupling to the CBG structures under continuous-wave excitation. Our work endows silicon-based photonic platforms with significant second-order nonlinear effect, which is potentially applied in on-chip quantum light sources and nonlinear frequency conversion.

Critical Policy Analysis of the Second Round of the Double First-Class Project in China

Purpose This critical policy analysis aims to comprehensively examine the second round of China's first-class discipline development project, commonly known as the “Double First-Class Project” (DFC Project or Shuang Yi Liu Project). Design/Approach/Methods We conducted desk research between May 2022 and December 2023 using relevant policy documents, academic literature, news sources, and commentaries that specifically focused on the second round of the DFC Project in China. Employing a critical policy analysis approach, we analyzed the gathered data from three key perspectives: policy as text, policy as discourse, and policy effects (including both first- and second-order effects). Findings The second round of the DFC Project was implemented within the context of strengthened state regulation, prevalent managerialism, and an emphasis on promoting education equality in China's higher education development. A notable shift in structural dynamics occurred between the first and second round. These include the possibility of universities being added to or removed from the official list, increased academic autonomy for selected universities, and the promotion of interdisciplinary research within specific institutions. The implementation of the second round of the DFC Project reflects China's commitment to developing an internationalization strategy with Chinese characteristics. This strategy aims to align with China's national strategic needs and position the country as a cooperative partner, promoter, competitor, and potential leader in global scholarship. Originality/Value By employing a critical policy analysis approach, this study offers a comprehensive examination of the second round of the DFC project in China, contributing to existing knowledge on the development of world-class university policies in the country.

What causes social class disparities in education? The role of the mismatches between academic contexts and working-class socialization contexts and how the effects of these mismatches are explained.

Within psychology, the underachievement of students from working-class backgrounds has often been explained as a product of individual characteristics such as a lack of intelligence or motivation. Here, we propose an integrated model illustrating how educational contexts contribute to social class disparities in education over and beyond individual characteristics. According to this new Social Class-Academic Contexts Mismatch model, social class disparities in education are due to several mismatches between the experiences that students from working-class backgrounds bring with them to the classroom and those valued in academic contexts-specifically, mismatches between (a) academic contexts' culture of independence and the working-class orientation to interdependence, (b) academic contexts' culture of competition and the working-class orientation toward cooperation, (c) the knowledge valued in academic contexts and the knowledge developed through working-class socialization, and (d) the social identities valued in academic contexts and the negatively stereotyped social identities of students from working-class backgrounds. Because of these mismatches, students from working-class backgrounds are likely to experience discomfort and difficulty in the classroom. We further propose that, when attempting to make sense of these first-order effects, students and teachers rely on inherent characteristics (e.g., ability, motivation) more often than warranted; conversely, they overlook extrinsic, contextual factors. In turn, this explanatory bias toward inherent features leads (a) students from working-class backgrounds to experience self-threat and (b) their teachers to treat them unfairly. These second-order effects magnify social class disparities in education. This integrated model has the potential to reshape research and discourse on social class and education. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Post-Fire Vegetation (Non-)Recovery across the Edges of a Wildfire: An Unexplored Theme

Wildfires have a significant influence on ecosystems globally, shaping vegetation, biodiversity, landscapes, soil properties, and other ecosystem processes. Despite extensive research on different aspects of wildfires, the edges of burned areas remain understudied, even though they involve complex dynamics. In this study, we analyzed the post-fire vegetation recovery across the edges of a large wildfire in a Mediterranean area. The investigations were focused on patches of woodlands that, in a previous study, showed a normalized burn ratio (NBR) decline one year after the fire. Field vegetation surveys were carried out in areas characterized by different NBR recovery rates and in areas outside the burned area as controls. Five hypotheses were tested, identifying delayed tree mortality as a key factor linked to NBR decline, particularly in low-severity fire zones in proximity to the fire edges. Delayed mortality, observed predominantly near the edges, may also affect unburned or less severely burned patches within the main fire perimeter, highlighting the need for ongoing monitoring. As these areas play a crucial role in the post-fire succession and vegetation dynamics, understanding the second-order effects of a fire is imperative for effective ecosystem management. This study underscores the importance of the long-term assessment of fire impacts, emphasizing the necessity of field surveys alongside remote sensing. Continued observation is essential to elucidate the enduring impacts of wildfires and to facilitate informed restoration strategies.

Group Theory on Quasisymmetry and Protected Near Degeneracy.

In solid state systems, group representation theory is powerful in characterizing the behavior of quasiparticles, notably the energy degeneracy. While conventional group theory is effective in answering yes-or-no questions related to symmetry breaking, its application to determining the magnitude of energy splitting resulting from symmetry lowering is limited. Here, we propose a theory on quasisymmetry and near degeneracy, thereby expanding the applicability of group theory to address questions regarding large-or-small energy splitting. Defined within the degenerate subspace of an unperturbed Hamiltonian, quasisymmetries form an enlarged symmetry group eliminating the first-order splitting. This framework ensures that the magnitude of splitting arises as a second-order effect of symmetry-lowering perturbations, such as external fields and spin-orbit coupling. We systematically tabulate the quasisymmetry groups within 32 crystallographic point groups and find all the possible unitary quasisymmetry group structures regarding double degeneracy. Applying our theory to the realistic material AgLa, we predict a "quasi-Dirac semimetal" phase characterized by two tiny-gap band anticrossings.

Giant nonlinear Hall and wireless rectification effects at room temperature in the elemental semiconductor tellurium

The second-order nonlinear Hall effect (NLHE) in non-centrosymmetric materials has recently drawn intense interest, since its inherent rectification could enable various device applications such as energy harvesting and wireless charging. However, previously reported NLHE systems normally suffer from relatively small Hall voltage outputs and/or low working temperatures. In this study, we report the observation of a pronounced NLHE in tellurium (Te) thin flakes at room temperature. Benefiting from the semiconductor nature of Te, the obtained nonlinear response can be readily enhanced through electrostatic gating, leading to a second-harmonic output at 300 K up to 2.8 mV. By utilizing such a giant NLHE, we further demonstrate the potential of Te as a wireless Hall rectifier within the radiofrequency range, which is manifested by the remarkable and tunable rectification effect also at room temperature. Extrinsic scattering is then revealed to be the dominant mechanism for the NLHE in Te, with symmetry breaking on the surface playing a key role. As a simple elemental semiconductor, Te provides an appealing platform to advance our understanding of nonlinear transport in solids and to develop NLHE-based electronic devices.

Parametric Study on the Buckling of Unbraced Steel Frames under Fire Situation

A parametric investigation of several unbraced steel frames with regular and irregular geometry subjected to elevated temperatures is carried out in this study to determine the most accurate procedure and buckling lengths to be considered during the structural design under a fire situation. In such conditions, the stiffness and strength of steel decrease considerably due to high temperatures, and uncertainty remains in the application of the fire design rules of Eurocode 3 Part 1-2 (EN 1993-1-2) for unbraced frames as no information is given regarding the treatment of the deformed geometry (the so-called second-order effects). More precisely, it is unclear in the norm whether the verification based on the buckling length concept could be used or if a second-order analysis to calculate the internal forces is sufficient to ensure the stability of the frame in case of fire. Based on the linear buckling analysis of the steel frames accounting for the temperature development during a fire, recommendations for the appropriate buckling lengths to be used are given. Finally, it is demonstrated that using the recommended buckling lengths together with the design rules of EN 1993-1-2 leads to results in favor of safety when compared to the results obtained with the finite element method. On the other hand, it is concluded that using second-order internal forces and the real length of the columns as the buckling length, as suggested for room temperature design, yielded results outside safety when compared with the finite element method, and this analysis and verification procedure should not be used for the case of fire.

On the energetic particle-induced geodesic acoustic modes with finite-orbit-width effects

This study presents an analytical investigation of energetic particle-induced geodesic acoustic modes (EGAMs) within a gyro-kinetic model, incorporating finite-orbit-width (FOW) effects up to the second order. The inclusion of second-order FOW effects introduces two distinct types of energetic particle-wave resonances, occurring at ω=ωth and ω=2ωth , respectively, where ωth denotes the transit frequency of energetic particles (EPs). It is found that two unstable EGAM branches coexist: a low frequency branch (LFB) characterized by 0<ωLFB<ωt,maxh , and a high frequency branch (HFB) marked by ωt,maxh<ωHFB<2ωt,maxh . The instability of LFB primarily arises from the resonance ω=ωth , mainly introduced by first-order FOW effects. As a result, the instability of LFB always exists regardless of the presence or absence of second-order FOW effects, and is barely modified by these effects. In contrast, the instability of HFB is exclusively attributed to the resonance ω=2ωth induced by second-order FOW effects. Consequently, the HFB exhibits instability in the presence of these effects.

Input costs’ pass-through to output prices: a cross-country empirical analysis

ABSTRACT This article decodes the pass-through behaviour from input prices to output prices, which is a key component in assessing second-order effects of cost-push pressures. Using panel GMM model, this paper has tried to empirically test the degree of pass-through of Purchasing Managers Index (PMI) input prices to output prices in a cross-country framework for 28 countries for the period 2011–2023. Empirical results support modest pass through with the sensitivity of output prices to input prices being lower for advanced nations and inflation targeting countries and higher for manufacturing sector with signs of non-linearity.

Optimizing off-axis fields for two-axis magnetometry with point defects

Vector magnetometry is an essential tool for characterizing the distribution of currents and magnetization in a broad range of systems. Point defect sensors, like the nitrogen vacancy center in diamond, have demonstrated impressive sensitivity and spatial resolution for detecting these fields. Measuring the vector field at a single point in space using single defects, however, remains an outstanding challenge. We demonstrate that careful optimization of the static bias field can enable simultaneous measurement of multiple magnetic field components with enhanced sensitivity by leveraging the nonlinear Zeeman shift from transverse magnetic fields, realizing an improvement in transverse sensitivity from &amp;gt;200 μT/Hz (no bias field) to 30 μT/Hz. This work quantifies the trade-off between the increased frequency shift from second-order Zeeman effects with decreasing contrast as off-axis field components increase, demonstrating the measurement of multiple components of the magnetic field from an exemplar antiferromagnet with a complex magnetic texture.

Multiphase riveting structure constructed by slight molybdenum for enhanced P3/O3 layer-structured oxide cathode material

Phase engineering has been efficiently employed to improve the performance of transition metal oxide cathode materials by alleviating the Jahn-Teller effects and optimizing the ions diffusion pathway. The second-order Jahn-Teller effects by slight molybdenum substitution was confirmed to activate a new phase formation and to construct a multiphase riveting structure. A P3/O3 riveting-structured NaNi0.3Mn0.52Mo0.03Cu0.1Ti0.05O2 cathode material was successfully synthesized for sodium ion batteries, which undergoes a reversible phase transition from P3/O3 → P3 → Hex.O3′ when charged to 4.25 V and most of the materials will transform into P3 phase after the first charge–discharge cycle. Due to the high reversibility and crystal structure stability, it indicates 155.0 mAh g−1 discharge capacity with a high up to 99.65 % initial Coulomb efficiency. This P3/O3 riveting structure can alleviate the rigid failure caused by phase transition. Meanwhile, O3/P3 phases provide the main storage sites for Na+ as skeletons and the existence of P3 phase provides a better diffusion pathway for ion transport.

Eccentric compression behavior of partially CFRP wrapped seawater sea-sand concrete columns reinforced with epoxy-coated rebars

The combined use of seawater sea-sand concrete (SSC), epoxy-coated rebar (ECR) and fiber-reinforced polymer (FRP) can achieve significant economic and environmental benefits in coastal infrastructure constructions. Thus, this paper first presents an experimental and analytical study on the eccentric compression behavior of partially carbon FRP (CFRP) wrapped SSC columns reinforced with ECR. The effects of load eccentricities, thickness of CFRP strips, clear spacing ratios, and slenderness ratios were comprehensively analyzed. Test results show that as the eccentricity increased from 60 mm to 120 mm, the increment of load capacity of partially CFRP wrapped columns reduced by 27.6 % to 17.1 %. Moreover, a larger lateral deflection was detected for the specimens with a relatively high slenderness ratio, which results in an obvious second-order effect and further aggravates the nonlinearity of axial load-bending curves, especially for the specimens under a small eccentricity. In addition, an eccentricity-dependent stress-strain model for concrete was developed under FRP strip-steel hoop composite confinement, and the lateral deflection formula of eccentrically loaded columns was also derived based on force equilibrium analysis. Finally, a new theoretical formula incorporating the effect of the slenderness ratio was also presented for the determination of load and moment capacity of the partially CFRP wrapped columns based on section analysis. By comparing with the test results, the developed model exhibits satisfactory accuracy.

2019 European Elections in Cyprus: An Empirical Exploration of Second-Order Election Effects and Europe Salience

Abstract By focusing on Cyprus’ constitutional and political system in light of the most recent European elections, this article explores and empirically analyses the second-order election theory and the European salience theory. The study applies these theories to identify key trends in Cypriot voters’ electoral behavior, including their attitudes toward European integration. The contribution starts with a brief preliminary section on the country’s historical background, geopolitical profile, and political landscape. It then provides insights on Cyprus’ electoral system, the political parties’ campaigns, and election results. The findings seek to unveil voter attitudes and political trends in Cyprus, feeding public discussion and academic dialogue on the issue in anticipation of the upcoming 2024 European election. The article aims to clarify the European South’s attitudes toward voting and what to expect in the upcoming 2024 elections, considering challenges, threats, and volatility.1

Vector dark matter, inflation, and non-minimal couplings with gravity

We propose a cosmological dark matter production mechanism in the form of a longitudinal massive vector boson. We build upon the work [1] including non-minimal couplings of the massive vector with gravity, developing a well motivated set-up from an effective field theory perspective. We carefully track the dynamics of vector field in passing from inflation to radiation dominated universe to show that the late time abundance of longitudinal modes — excited initially by the quantum fluctuations during inflation — can provide the observed dark matter abundance for sufficiently weak non-minimal coupling and wide range of vector masses 5 × 10-7 ≲ m [eV] ≲ 5 × 103. The final abundance of dark matter depends on two parameter, the vector mass and its non-minimal coupling with gravity. We discuss experimental venues to probe this framework, including the production of a stochastic gravitational wave background. The latter is especially interesting, as the same mechanism that generates dark matter can potentially lead to the production of gravitational waves in the LISA frequency band, through the second-order effects of large dark matter iso-curvature perturbations at small scales. We take a first step in this direction, identifying the potential information that gravitational wave experiments can provide on the parameter space of dark matter within this scenario.

Eccentrically compressed behavior of UHPC columns considering the P-delta effect

Eccentric compression is a critical behavior observed in arches and columns, particularly in structures constructed with ultra-high performance concrete (UHPC). Compared to normal concrete structures, those made with UHPC exhibit distinct behaviors that need to be clearly investigated. This study comprehensively investigates UHPC columns under eccentric compression load through experimental study and theoretical analysis. Various experimental parameters, including slenderness ratio, eccentricity distance, fiber content, and stirrup ratio, were examined across 26 UHPC columns. Failure modes were evaluated using digital image correlation (DIC) methods. The load-displacement responses indicated that slender columns subjected to significant eccentricity exhibited load decreases during yielding stages, whereas short columns experienced load increases. This discrepancy in yielding stages was attributed to P-delta effects. In addition, theoretical models were developed to determine the ultimate bearing capacity of columns experiencing compression-controlled and tension-controlled failures, considering the P-delta effect caused by the different slenderness ratios. The moment magnifying coefficients for UHPC were calibrated based on theoretical analyses of the limit curvature of eccentric compression members. The proposed theoretical models agreed well with the experimental results, with an average ratio of 1.02. The second-order effect for the case of UHPC short column with a slenderness ratio of 5 can be ignored as per Eurocode 2, which is less than 10 % of the corresponding first-order effect.