Matching Conditions Research Articles

Dynamic interplay of anisotropy and matter-geometry coupling in stellar structures: A comprehensive study on the stability of pulsars 4U 1820-30 and LMC X-4

This study investigates the behavior of dense celestial objects within the context of f(R,Lm,T) theory. We develop modified Einstein field equations that account for the anisotropic configured static interior spacetime. By applying two specific constraints associated with the radial metric function and anisotropic pressure, we find a couple of solutions to these highly non-linear gravitational equations. For both models, we encounter differential equations whose integration yield constants which are determined through matching conditions. Additionally, the requirement of vanishing radial pressure at the hypersurface also plays an important role in this context. Furthermore, we graphically evaluate certain conditions whose fulfillment ensures the model’s feasibility under different parametric values. For this, we take into account the observational data of two compact stars 4U 1820-30 and LMC X-4. We conclude both our models to be well-aligned with the required viability and stability criteria. We must highlight here that our study advances the understanding of how f(R,Lm,T) gravity affects the internal structure of compact stars, providing valuable insights for future explorations.

The Effect of Cue Probe Interval on Internal Attention: Evidence from Event-related Potentials.

Compelling evidence indicated shared cognitive mechanisms underpinning attention in both the external and internal domains. Typically, both external attention and internal attention are vulnerable to biases from intended goals and stimulus features. However, it is still unclear whether the temporal characteristics of the relationship between goal-directed and stimulus-driven external attention could be observed in internal attention. This study aimed to fill this gap by examining whether the lengths of time interval before a recalling probe influenced goal-directed and stimulus-driven internal attention. We manipulated the cue probe interval (CPI) before the probe in a working memory change detection task with a retrospective cue. In addition to behavioral performance, we also traced two electrophysiological signals of the event-related potential (ERP) components of N450 and P300 to represent goal-directed and stimulus-driven internal attention respectively. The results suggested that CPI modulated goal-directed attention with more pronounced N450 amplitudes when CPI was 2000ms than those when CPI was 500ms during the informative condition. Meanwhile, more pronounced P300 amplitudes were observed when CPI was 500ms than those when CPI was 2000ms for both the matching and nonmatching conditions. Such results lead to the conclusion that internal attention was goal-directed when CPI was as long as 2000ms, whereas stimulus-driven when CPI is as short as 500ms. Findings from this study contribute to the common points shared between internal and external attention.

Terahertz electro-optic Kerr effect in LaAlO3.

In this Letter, we investigate the terahertz (THz) electro-optic Kerr effect (KE) dynamics in LaAlO3 (LAO), a widely used substrate for thin-film preparation. We show that the KE dynamics strongly depend on the material anisotropy due to interference between THz field-induced and strain-induced optical birefringence. Such interference leads to quasi-phase matching conditions of the KE, which becomes strongly frequency dependent. Depending on the THz frequency, the KE exhibits a uni- and bipolar shape of the quadratic response. The demonstrated effects will be present in a wide variety of materials used as substrates in different THz pump laser-probe experiments and need to be considered in order to disentangle the different contributions to the measured ultrafast dynamic signals.

Gamma and theta/alpha-band oscillations in the electroencephalogram distinguish the content of inner speech.

Inner speech refers to the silent production of language in one's mind. As a purely mental action without obvious physical manifestations, inner speech has been notoriously difficult to quantify. Inner speech is thought to be closely related to overt speech. Overt speech has been consistently shown to elicit reduced auditory-evoked potentials compared to externally-generated speech (a phenomenon known as speaking-induced suppression), as well as changes in oscillatory activity in the gamma and theta frequency bands. Given the functional similarities between inner and overt speech, the present study used a novel experimental protocol to investigate whether these metrics can be used to distinguish the content of a person's inner speech. Healthy control participants (n = 129) produced an inner syllable at a precisely specified time. An audible syllable was concurrently presented which either matched or mismatched the content of the inner syllable. The N1 component of the auditory evoked potential was suppressed in the Match condition while the P2 component was suppressed in the Mismatch condition, replicating our previous findings. A novel finding was that the Match and Mismatch conditions could be differentiated on the basis of their evoked gamma and theta / alpha oscillations. There was a single gamma-band oscillation in the vicinity of the P2 that differed in spectral power between the Match and Mismatch conditions, which provides support for the idea that 'late' gamma-band activity may index consciously-perceived expectancy violations, or cognitive prediction errors. The Match and Mismatch conditions also differed in terms of their evoked power in a temporally-extended cluster which spanned the theta and alpha bands. The results of this study provide support for the phenomenon of 'inner speaking-induced suppression', and demonstrate that inner syllables can be differentiated using scalp electroencephalography (evoked potentials and oscillations) based on whether their content matches that of a simultaneously-presented audible syllable.Significance statement Inner speech refers to the silent production of language in one's mind. As a purely mental action without obvious physical manifestations, inner speech has been notoriously difficult to quantify empirically. The aim of the present study was to develop an objective, electroencephalography-based marker of inner speech that was sensitive to its content. The results of this study demonstrate that it is possible to distinguish between two syllables produced in inner speech on the basis of their auditory-evoked activity and evoked oscillations in the gamma and theta/alpha bands in the electroencephalogram. The gamma-band oscillation may represent a 'cognitive' prediction error. The ability to determine the content of a person's inner speech on the basis of a non-invasive biometric signal could have significant commercial, industrial, and clinical applications.

Efficient Second Harmonic Generation via Plasmonic-Photonic Mode Matching in Hybrid Waveguide.

Hybrid nonlinear plasmonic waveguides, characterized by a small mode area and large nonlinear susceptibility, present an intriguing and practical platform for the minimization of nonlinear photonic devices. Nevertheless, the intrinsic Ohmic loss associated with surface plasmon polaritons (SPPs) and modal dispersion imposes constraints on the effective interaction length and, consequently, the ultimate efficiency of nonlinear processes. In this study, we demonstrate an efficient second harmonic generation (SHG) within a hybrid plasmonic waveguide by leveraging SPP-like modes at the fundamental wave and photonic-like modes at the SHG under phase matching conditions. The presence of photonic-like modes significantly reduces the SHG losses, while the SPP-like modes improve the modal overlap, resulting in SHG conversion efficiency up to 8.5% W-1 cm-2 in a 55 μm-long waveguide. Our findings offer new avenues for the minimization of nonlinear photonic devices on a chip.

Impact of Charge on Strange Compact Stars in Rastall Theory

Within the framework of Rastall theory, we investigate the impact of charge on the structural development of different types of spherically symmetric anisotropic stars. To do so, we present modified field equations based upon the Finch–Skea metric potentials expressed in terms of three parameters (A,B,C). These constants are determined using suitable matching conditions and observational data for compact objects which include Her X-1, SAX J 1808.4-3658, PSR J038-0842, LMC X-4 and SMC X-1. The equation of state offered by the MIT bag model for quark–gluon plasma is used to investigate the inner structure and other characteristics of these compact objects. For a fixed bag constant, B=60MeV/fm3, and two sets of the Rastall and charge parameters, ζ=0.255,0.259 and Q˜=0.2,0.7, respectively, we analyze the consistency of the matter variables in the model and other physical parameters such as energy conditions, stellar mass, compactness, and surface redshift. In addition, we assess the stability of the constructed model through two different approaches. It is found that the obtained model is physically viable and stable.

Flow of a Viscous Fluid Past a Porous Oblate Spheroid at Small Reynolds Number

This study deals with the uniform motion of an adhesive, incompressible fluid flowing over a porous oblate spheroid at tiny values of the Reynolds number. These types of problems have been considered by dividing fluid flow into three regions, namely, zone I, zone II, and zone III. In the zone I, which is completely filled with viscous fluid, is the region of the porous oblate spheroid, and in this region fluid flow is governed by the equation suggested by Brinkman. The zone II and the zone III, where the clear fluid flows, are the regions outside the porous oblate spheroid. The fluid flow in these two zones has been discussed using the perturbation method given by Proudman and Pearson in which the Stokes stream function is expanded in terms of Reynolds number. This solution is then matched with the Oseen solution, At the interface of zone II and zone I, the matching conditions suggested by Ochoa-Tapia and Whitaker are applied for matching the stream function of the clear fluid region with that of the porous region at the surface of the oblate spheroid. It has been found that the drag on the oblate spheroid reduces with that of the departure from the spherical shape. Similar effects of the drag on the spheroid are obtained when the permeability of the porous medium increases. Also, the drag experienced on the porous oblate spheroid is directly proportional to Reynolds number and the ratio of effective viscosity of the porous medium to the real viscosity of the fluid. The application of a viscous fluid flow past a porous oblate at low Reynolds number is to calculate the friction factor and drag in internal and external flow, hydraulics study, aerofoil design, filtration technology, geothermal energy, and precipitation.

Optical properties of barium borate crystal in the THz range revisited.

Low-temperature phase (β-form) barium borate (BBO) is one of the most important nonlinear crystals that has been widely used for optical second-harmonic generation (SHG), especially with femtosecond sources. There was growing interest in its applications in the direct generation of terahertz (THz) radiations, but it was hindered by the lack of knowledge of its basic properties in the THz range. In a recent study based on first-principles quantum chemistry calculation, we found that the theoretically calculated refractive indices of β-BBO in the THz frequency range do not agree with the previously reported values. To explore the discrepancy between measured and calculated results, we grew and cut β-BBO crystals and performed independent experimental measurements on the refractive indices of BBO crystals. The new data show that the order of ordinary and extraordinary index of β-BBO in the THz range is opposite, contrary to several papers previously reported. Based on the newly acquired material properties, simple geometries fulfilling phase matching (PM) conditions with n o(THz)=n o g r(800nm) for efficient generation of THz radiation through optical rectification in β-BBO are proposed.

In Ukrainian

Due to its excellent electrical, mechanical, thermal and optical properties, graphene has attracted much interest since it was discovered in 2004. Its two-dimensional nature and other remarkable properties meet the needs of surface plasmons and have greatly enriched the field of plasmonics. The paper will review recent advances and applications of graphene in plasmonic, including theoretical mechanisms, experimental observations, and meaningful applications. Due to its flexibility and good tunability, graphene can be a promising plasmonic material as an alternative to noble metals. Optical conversion, plasmonic metamaterials, light harvesting, etc. have already been realized in graphene-based devices, which are useful for applications in electronics, optics, energy storage, THz technology, etc. In addition, the excellent biocompatibility of graphene makes it a very good candidate for applications in biotechnology and medical science. Surface plasmons in graphene offer a compelling route to many useful photonic technologies. As a plasmonic material, graphene offers several intriguing properties, such as excellent electro-optic tunability, crystal stability, large optical nonlinearity, and extremely high electromagnetic field concentration. Thus, recent demonstrations of surface plasmon excitation in graphene using near-infrared light scattering] have attracted great interest. Here we present an all-optical plasmonic coupling scheme that takes advantage of the intrinsic nonlinear optical response of graphene. To generate plasmons, pulses of visible light in a free in-plane graphene sheet are used using difference frequency mixing of the waves to match both the wave vector and the energy of the surface wave. By carefully controlling the phase with matching conditions, we show that it is possible to excite surface plasmons with a defined wave vector and direction in a wide frequency range with high photon efficiency. Prospects for the practical use of graphene in plasmonics are discussed.

Nonlinear Raman-Nath diffraction in submicron-thick periodically poled lithium niobate thin film

Nonlinear Raman-Nath diffraction (NRND) is a unique diffraction pattern formed when a high-intensity laser interacts with a nonlinear microstructure bulky medium relying only on the transverse phase matching condition. Here, we report on the first experimental observation of NRND in a submicron-thick periodically poled lithium niobate thin film (PPLNTF) by geometric reflection pumped via a near-infrared femtosecond pulse laser. We further observe the evolution of the diffracted signals after broadening of the pump laser via a fused silica plate. We systematically analyze the spectral properties of multi-order second harmonic generation (SHG) diffracted signals exhibiting asymmetric distributions and explicitly clarify their phase matching conditions, simultaneously considering the impacts of the incident pump wavelength, the sample poling period, and the incident angle on the properties of the angular distribution diffracted beams. The realization of NRND phenomena with appreciable on-chip efficiency at a submicron interaction length is mainly attributed to the significant contribution of domain walls to enhance the nonlinear effects along with the modulation of second-order nonlinear susceptibilities χ(2). This NRND scheme provides a high-resolution, non-destructive on-chip microstructure diagnostic method, and even has the potential to develop novel on-chip integrated optoelectronic devices for applications such as precision metrology, biosensing, and spectral analysis.

A novel design method for dual-band Wilkinson power dividers with different power split ratios on each band based on extended pi-shaped microstrip line

This paper proposes a novel method for designing a dual-band Wilkinson power divider with different power split ratios on each band. The circuit is designed based on the proposed dual-band matching impedance circuit, with input and output impedances varying according to the working band. The isolation resistor of the circuit is calculated using exact building formulas to ensure output matching and isolation conditions between output ports at two operating bands. A design procedure with analytical design equations is described in the paper. To validate the proposed design method, a dual-band Wilkinson power divider operating at 1 and 2.2 GHz with power split ratios on each band are 1:1 and 2:1, respectively was designed, simulated, fabricated, and tested. The agreement between simulated and measured results has validated the proposed design concept.

Biomimetic Linkage Mechanism Robust Control for Variable Stator Vanes in Aero-Engine.

This work addresses the position tracking control design of the stator vane driven by electro-hydrostatic actuators facing uncertain aerodynamic disturbances. Rapidly changing aerodynamic conditions impose complex disturbance torques on the guide vanes. Consequently, a challenging task is to enhance control precision in complex uncertain environments. Inspired by the principles of mammalian muscle movement, a novel robust control strategy based on the backstepping method has been proposed. Using backstepping, virtual rotational speed and virtual pressure difference force are designed, which decompose the high-order position closed-loop control problem into three lower-order parts, eliminating the need for matching conditions. Subsequently, robust controllers were designed, and stability proofs and performance analyses of the controllers were provided. This control strategy was tested through numerical hydraulic simulation. The results show that compared to other control methods, this approach significantly improves tracking accuracy and robustness. Therefore, it is believed that this method has the potential to become a new generation solution for such problems.

Role of the Radical Character in Singlet Fission: An Ab Initio and Quantum Chemical Topology Analysis.

The radical character of molecules exhibiting singlet fission is related to the energy level matching relationships that facilitate this process. Using a linear H4 model molecule, we employ quantum chemical topology descriptors based on full configuration interaction calculations to rationalize singlet fission. In this context, the influence of the closed-shell to diradical and diradical to tetraradical character on the singlet fission energy matching conditions is analyzed. We find that in the diradical limit the singlet fission efficiency can be manipulated considering the active molecule coupled to an excited diradical, while in the diradical to tetraradical limit, the efficiency is dependent only on the gap between the lowest-lying excited singlet and triplet state. Furthermore, our results reveal possible design strategies for molecules with radical character exhibiting efficient singlet fission.

Wheel profile optimization of high-speed locomotive to improve railway line adaptability

Aiming at the low-frequency carbody swaying phenomenon of the locomotive belonging to the power concentrated electric multiple unit (EMU) for high-speed passenger transport, which operated in the early stage after the wheel profile is repaired as the JM3-32 thin flange profile according to the standard, the profile is optimized to improve the locomotive’s dynamic performance. The optimization objective is to improve the equivalent conicity and its distribution concentration of the wheel profile under various rail profiles and rail cants conditions, as well as to improve its wear performance. The mapping relationship between the design variables and the objective functions is realized by constructing the radial basis function neural network (RBFNN) surrogate model. The Nondominated Sorting Genetic Algorithm II (NSGA-II) is used to optimize the position and size of the four arcs in the rolling circle contact area of the wheel profile. The wheel-rail contact characteristics and vehicle dynamics simulation of the wheel profile before and after optimization are compared to reveal the optimization effects. The results show that under different wheel-rail matching conditions, the equivalent conicity of the optimized wheel profile is significantly improved compared with the original wheel profile, and the dispersion degree of its distribution is significantly reduced at the same time. The nominal equivalent conicities corresponding to the 3 mm lateral displacement of the wheelset are all about 0.1. The nonlinear critical velocity is increased by more than 290 km/h under the condition of 1/20 rail cant. Under the four wheel-rail matching conditions, the Locomotive will not have the problem of lateral ride comfort deterioration and vehicle swaying when running at high speed. The curve passing performance and wear performance are also improved.

Transverse momentum dependent PDFs in chiral effective theory

We develop a theoretical framework to match transverse momentum dependent parton distribution functions (TMD PDFs) onto chiral effective theory operators. In this framework the TMD PDF is expressed as a convolution of TMD hadronic distribution functions, which describe fluctuations of initial states into intermediate hadrons in chiral perturbation theory, and short distance matching coefficients, which are the TMD PDFs of intermediate hadrons in the chiral limit. The various limits of the matching condition are explored and an operator product expansion is applied to the high energy TMD matching coefficients, allowing them to be written in terms of the collinear valence PDFs of intermediate hadrons. As an example, we calculate the isovector TMD hadronic distribution functions for the proton at leading order in the chiral expansion. Published by the American Physical Society 2024

Nocturnal camouflage through background matching against moonlight

Camouflage is often considered a daytime phenomenon based on light and shade. Nocturnal camouflage can also occur, but its mechanistic basis remains unclear. Here, we analyze the conditions for background matching (BM) of avian predators against the night sky. Such concealment is achieved when the contrast between the predator and the sky is smaller than the contrast detection threshold of prey. This condition cannot be fulfilled under isotropic skies, as in fully overcast or moonless nights. However, on clear moonlit nights, the isotropy of the sky radiance is broken due to the presence of the Moon, and the conditions for BM can be met for a wide range of sky directions. This effect is mainly dependent on the altitude of the Moon above the horizon, rather than on Moon phase. We have modeled the feasibility of concealment through BM of a typically white barn owl (Tyto alba) when hunting rodents, based on its contrast against the moonlit sky. We considered the radiometric quantities of the sky, the ground, and the bird's undersides. Our results show that a barn owl with highly reflecting underparts may approach a rodent from broad regions of the moonlit sky while keeping itself below the contrast detection threshold of the mouse M-cones and rods. S-cones, in turn, remain below their excitation threshold for most of the lunar cycle. Our results demonstrate that the white color of barn owls serves as camouflage tailored to the moonlit sky background, providing a mechanistic basis for understanding nocturnal camouflage.

Mechanistic study on the utilisation and mineral formation of incineration fly ash in sintering

Fly ash, a significant byproduct of municipal solid waste incineration, garners attention for its harmless treatment and resource utilisation. Existing research has demonstrated the viability of incorporating fly ash into the sintering process and explored its influence on the sintering bonding phase. In the context of co-disposal of municipal solid waste incineration residues through sintering, it is imperative to consider the mineralisation characteristics, necessitating a comprehensive evaluation of sinter strength and metallurgical performance. In this investigation, the process is validated on an expanded scale using sintering cup experiments. The results indicate that the experimental group with a basicity of 2 and the inclusion of fly ash exhibits sinter strength in line with actual production requirements, its drop index is 76.03%, and its drum index is 77.2%. Additionally, the reduction velocity index is recorded at 0.573% min−1, the reduction degradation index for RDI+3.15 at 92% and the total characteristic value of melting properties ( S) at 99.175 KPa·°C—nearly equivalent to the control group with matching alkali conditions. The technology roadmap was verified by sintering cup experiment, offering vital theoretical support for the development of sintering process in the collaborative treatment of incineration fly ash.

A log story short: running contributions to radiative Higgs decays in the SMEFT

We investigate the renormalization of the radiative decays of the Higgs to two gauge bosons in the Standard Model Effective Field Theory at mass dimension eight. Given that these are loop-level processes, their one-loop renormalization can be phenomenologically important when triggered by operators generated through the tree-level exchange of heavy particles (assuming a weakly coupled UV model). By computing the tree-level matching conditions of all relevant extensions of the Standard Model, we demonstrate that this effect is indeed present in the h → γZ decay at dimension eight, even though it is absent at dimension six. In contrast, the h → gg and h → γγ decays can only be renormalized by operators generated by one-loop processes. For UV models with heavy vectors, this conclusion hinges on the specific form of their interaction with massless gauge bosons which is required for perturbative unitarity. We study the quantitative impact of the possible logarithmic enhancement of h → γZ, and we propose an observable to boost the sensitivity to this effect. Given the expected increased precision of next-generation high-energy experiments, this dimension-eight contribution could be large enough to be probed and could therefore give valuable clues about new physics by revealing some of its structural features manifesting first at dimension eight.

Optical properties and phase matching conditions of KTiOPO4 crystals at terahertz frequencies in the temperature range of 5.8 to 300 K

In this paper, the optical properties and phase matching (PM) conditions of KTiOPO4 (KTP) crystals in the temperature range of 5.8–300 K are studied by terahertz (THz) time-domain spectroscopy. It is found that the absorption coefficient of KTP decreases with the decrease of temperature, and that of the Z axis at 1.2 THz decreases from 19.56cm−1 at 300 K to 7.83cm−1 at 5.8 K. Along the Z axis, the refractive index decreases with the decrease of temperature and changes the most, while along the X and Y axes the refractive index is relatively stable with temperature. The optical properties along the Z axis are sensitive to temperature, mainly because the movement of K+ is located in the Z axis and slows down with the decrease of temperature. KTP crystals are found to have obvious birefringence characteristics in the frequency range of 0.3–1.6 THz, with the birefringence of approximately 0.67 at 300 K and 0.58 at 5.8 K. The PM angle is calculated using the refractive index dispersion equation to satisfy the PM condition of frequency transformation. When the temperature is lowered from 300 K to 5.8 K, the maximum change in PM angle is 1.08°, while the minimum change is 0.10° at the same output wavelength. Due to the small absorption coefficient and the birefringence characteristics at low temperatures, and the relatively stable change of PM angle with temperature, the potential of KTP crystals to efficiently generate THz radiation at low temperatures can be fully realized.

Digging deep

Beach volleyball (BVB) tournaments often require elite athletes to compete in multiple matches per day over several consecutive days with limited rest, potentially leading to neuromuscular fatigue (NMF) and reduced performance. This study aimed to evaluate such fatigue. Twelve adult national team BVB players (8 males, 4 females) completed countermovement jump (CMJ) and 8-meter sprint tests before and after two simulated BVB matches, separated by a 2-hour rest period. No statistically significant changes were observed in performance measures at any time point. However, individual variations in CMJ height, which either increased or decreased beyond the smallest worthwhile change and typical error, were noted. These findings suggest that CMJ height alone may not be a reliable indicator of NMF, or that significant NMF does not occur following two BVB matches. Additionally, the validity of using sprint performance on sand to assess post-exercise NMF remains unverified. Future research should aim to include larger samples of elite athletes, address the limitations of simulated match conditions, and utilize more sensitive tools to evaluate NMF.