Spatial Period Research Articles

Non-Hermitian gravitational effects on Bose–Einstein condensate

We investigated the impact of Non-Hermitian gravitational potentials on the spatial distribution of Bose–Einstein condensate (BEC) wave functions. Through numerical solutions of the Gross–Pitaevskii (GP) equation, we observed that the imaginary component of Non-Hermitian gravitational potentials affects the spatial periodicity of the BEC wave function phase, resulting in spatial displacement of the wave function’s peak. By formulating equations describing the momentum of the BEC wave function with respect to Non-Hermitian gravitational potential parameters and solving and analyzing them under specific conditions, we provided a reasoned interpretation of the numerical results. Our results also can be simulated experimentally with the help of electron beam technique. Our findings contribute to exploring the physical essence of Non-Hermitian gravitational potentials and their impact on BEC, offering theoretical guidance for potential related experiments.

On-chip microresonator dispersion engineering via segmented sidewall modulation

Microresonator dispersion plays a crucial role in shaping the nonlinear dynamics of microcavity solitons. Here, we introduce and validate a method for dispersion engineering through modulating a portion of the inner edge of ring waveguides. We demonstrate that such partial modulation has a broadband effect on the dispersion profile, whereas modulation on the entire resonator’s inner circumference leads to mode splitting primarily affecting one optical mode. The impact of spatial modulation amplitude, period, and number of modulations on the mode splitting profile is also investigated. Through the integration of four modulated sections with different modulation amplitudes and periods, we achieve mode splitting across more than 50 modes over a spectral range exceeding 100 nm in silicon nitride resonators. These results highlight both the simplicity and efficacy of our method in achieving flatter dispersion profiles.

Controlling the Spatiotemporal Self-Organization of Stimuli-Responsive Nanocrystals under Out-of-Equilibrium Conditions.

Self-organization under out-of-equilibrium conditions is ubiquitous in natural systems for the generation of hierarchical solid-state patterns of complex structures with intricate properties. Efforts in applying this strategy to synthetic materials that mimic biological function have resulted in remarkable demonstrations of programmable self-healing and adaptive materials. However, the extension of these efforts to multifunctional stimuli-responsive solid-state materials across defined spatial distributions remains an unrealized technological opportunity. This paper describes the use of a nonequilibrium reaction-diffusion process to achieve the synthesis of a multifunctional stimuli-responsive electrically conductive metal-organic framework (cMOF) in a gelled medium with control over particle size and spatial periodicity on a macroscopic scale. Upon integration into chemiresistive devices, the resulting cMOF particles exhibit a size-dependent response toward hydrogen sulfide gas, as determined by their distinct surface-to-volume ratio, porosity, unique synthesis methodology, and unusual microcrystallite morphology compared to their counterparts obtained through bulk solution phase synthesis. Taken altogether, these achievements pave the way toward gaining access to functional nanomaterials with well-defined chemical composition, dimensions, and precisely tailored functions using far-from-equilibrium approaches.

Hydrodynamic moiré superlattice.

The structural periodicity in photonic crystals guarantees the crystal's effective energy band structure, which is the fundamental cornerstone of topological and moiré physics. However, the shear modulus in most fluids is close to zero, which makes it challenging for fluids to maintain spatial periodicity akin to photonic crystals. We realized periodic vortices in hydrodynamic metamaterials and created a bilayer moiré superlattice by stacking and twisting two such vortex fluids. We observed energy delocalization and localization when the twist angles, respectively, result in the Pythagorean and non-Pythagorean triples in the fluidic moiré superlattice. Anomalous localization was found even in commensurate moiré fluids with large lattice constants that satisfy Pythagorean triples. Our work reports the moiré phenomena in fluids and opens an unexpected door to controlling the energy transfer, mass transport, and particle navigation through the elaborate dynamics of vortices in fluidic moiré superlattices.

Analysis of Spatiotemporal Variation in Precipitation on the Loess Plateau from 1961 to 2016

This study utilized annual precipitation data collected from 76 meteorological stations located on the Loess Plateau and its adjacent regions. It employed empirical orthogonal function (EOF) analysis, the Mann–Kendall trend test (M-K), and continuous wavelet transform (CWT) to investigate the spatial distribution patterns, temporal trends, and periodicity of annual precipitation from 1961 to 2016. The results showed the following: (1) The long-term averages of annual rainfall on the Loess Plateau exhibited a general decline from the southeast to the northwest, with certain areas demonstrating a trend of reduction radiating outward from the central region. This precipitation regime was fundamentally governed by the interplay between geographic coordinates and topo-graphical characteristics. Nevertheless, this spatial distribution pattern is expected to undergo changes in the future. (2) Annual precipitation in the southern and eastern parts decreased significantly, while the western part reported the greatest increase, and thus the spatial variability of precipitation will decrease in the future. (3) Annual precipitation on the Loess Plateau generally has a period of about 4 years. The wavelet coherence analysis reveals that El Niño events, occurring over a brief 4-year interval, correlate with diminished precipitation patterns across the eastern and southern sectors of the Loess Plateau, consequently attenuating the precipitation’s spatial variability throughout the entire geographical domain. Therefore, in the future, when El Niño occurs, it is necessary to prevent droughts in the eastern and southern regions of the Loess Plateau.

Impaired spatial coding and neuronal hyperactivity in the medial entorhinal cortex of aged App NL-G-F mice.

The progressive accumulation of amyloid beta (Aβ) pathology in the brain has been associated with aberrant neuronal network activity and poor cognitive performance in preclinical mouse models of Alzheimer's disease (AD). Presently, our understanding of the mechanisms driving pathology-associated neuronal dysfunction and impaired information processing in the brain remains incomplete. Here, we assessed the impact of advanced Aβ pathology on spatial information processing in the medial entorhinal cortex (MEC) of 18-month App NL-G-F/NL- G-F knock-in (APP KI) mice as they explored contextually novel and familiar open field arenas in a two-day, four-session recording paradigm. We tracked single unit firing activity across all sessions and found that spatial information scores were decreased in MEC neurons from APP KI mice versus those in age-matched C57BL/6J controls. MEC single unit spatial representations were also impacted in APP KI mice. Border cell firing preferences were unstable across sessions and spatial periodicity in putative grid cells was disrupted. In contrast, MEC border cells and grid cells in Control mice were intact and stable across sessions. We then quantified the stability of MEC spatial maps across sessions by utilizing a metric based on the Earth Mover's Distance (EMD). We found evidence for increased instability in spatially-tuned APP KI MEC neurons versus Controls when mice were re-exposed to familiar environments and exposed to a novel environment. Additionally, spatial decoding analysis of MEC single units revealed deficits in position and speed coding in APP KI mice in all session comparisons. Finally, MEC single unit analysis revealed a mild hyperactive phenotype in APP KI mice that appeared to be driven by narrow-spiking units (putative interneurons). These findings tie Aβ-associated dysregulation in neuronal firing to disruptions in spatial information processing that may underlie certain cognitive deficits associated with AD.

Statistical modeling of soft magnetic composites’ permeability

Soft magnetic composites (SMC) also known as powder cores are widely used in many applications because of their linearity, controllable permeability and isotropy. Because of the distributed air gap, the permeability is governed by the inner demagnetizing fields. To model the permeability dependence on the filling fraction, essentially two approaches are used both based on spatial periodicity hypothesis: the non magnetic grain boundary model and the effective medium theory. Actually, the first one works only for dense materials and the second works at low concentration. Both need fitting of two parameters, the inner demagnetizing factor and the particle susceptibility, just because the periodicity hypothesis is never verified for magnetic filling factors larger than 20%. A breakaway model is proposed based on the computation of mathematical esperance of the statistical distribution of magnetic chains and the subsequent determination of demagnetizing coefficient of an ellipsoid of equivalent aspect ratio. The model is collated with permeability data from the literature for spherical or non-spherical particles based SMCs and shows a excellent agreement with only one or even without fitting parameter in the whole concentration range.

Direct Laser Interference Patterning of Fluorine‐Doped Tin Oxide as a Pathway to Higher Efficiency in Perovskite Solar Cells

AbstractImproving light‐trapping capabilities through surface microstructuring of transparent conductive oxides is a promising approach to enhance solar cell efficiency. This study focuses on treating fluorine‐doped tin oxide (FTO) thin films using four‐beam direct laser interference patterning (DLIP) to create dot‐like periodic surface microstructures. The surface analysis using scanning electron microscopy and confocal microscopy reveals the presence of a periodic square grid of microcraters with a spatial period of ≈700 nm and an average depth ranging between 4 and 18 nm. These structures enhance the dispersion of incoming light up to 1000% in the visible and NIR spectra. When integrated into metal halide perovskite solar cells, FTO films patterned using low fluence conditions lead to a notable increase in the power conversion efficiencies (PCEs) compared to those made using untreated FTO. Importantly, preliminary stability tests on devices based on patterned FTO substrates show significantly improved stability compared to those fabricated using reference unpatterned substrates. These findings demonstrate that a DLIP treatment of FTO substrates is a promising technique that can substantially enhance the efficiency and stability of perovskite photovoltaic devices.

Spatiotemporal pattern formation in parametrically driven two-dimensional Bose–Einstein condensates

We investigate spatiotemporal periodic patterns in harmonically trapped Bose–Einstein condensates (BECs) driven by a periodic modulation of the interaction. Resonant with the breathing mode, we show the emergence of a square lattice pattern containing two orthonormal stripes. We study the time evolutions of the lattice patterns for different driving strengths and dissipations. We find that its spatial periodicity and temporal oscillating frequency match the Bogoliubov dispersion, which is the intrinsic property of the system and relevant to the parametric amplification of elementary excitations. In the circumstances of strong driving strength and low dissipation, we further observe the triad interaction and the resulting superlattice state, which are well explained by the nonlinear amplitude equation for superimposed stripes. These results shed light on unexplored nonlinear spatiotemporal dynamics of two-dimensional patterns in harmonically trapped BECs that can pave the way for engineering exotic patterns by state-of-the-art experiments.

Phononic supercrystal as a highly absorbing metamaterial

We demonstrate analytically, numerically, and experimentally that a 2D supercrystal (SC)—an elastic structure of solid rods with two distinct spatial periods embedded in a viscous fluid—exhibits very high acoustic absorption. Smaller diameter rods arranged in a 2D lattice with a smaller period serve as an effective medium with high viscosity for a set of larger rods arranged in a lattice of much larger period. The enhancement of acoustic absorption is due to strong viscous friction within a narrow layer with high gradients of velocity formed around each scatterer. The SC as a whole is considered in the homogenization limit of frequencies where it behaves as a metafluid with an effective speed of sound and effective viscosity. Analytical results for the effective parameters are calculated for any Bravais lattices and arbitrary cross-sections of the rods. Experimental measurements of acoustic absorption in a supercrystal with hexagonal lattices for both types of rods are in a good agreement with analytical and numerical results. Published by the American Physical Society 2024

Vibration attenuation of dual periodic pipelines using interconnected vibration absorbers

Pipelines are crucial elements in various engineering applications. However, unexpected vibrations from different sources can jeopardize the operational performance and potentially damage the piping structures and other connected units. This study explores flexural wave propagation and attenuation characteristics of the pipes supported periodically on a rack. Also, a specific case of a rack with infinite stiffness (simple support) is investigated. The dispersion relations pertinent to pipe rack scenario is obtained through transfer matrix method (TMM) in conjunction with Floquet-Bloch’s theorem, and the accuracy of ensuing band gaps (BGs) are confirmed through finite element (FE) models. Following this, the modal analysis is performed to ascertain the minimum number of unit-cells necessary for the FE model to accurately mimic the attenuation and propagation characteristics of the corresponding infinite structure. The findings indicate that a pipe supported on rack displays resonance and Bragg-type BGs, arising from local resonance and spatial periodicity, respectively, while the pipe on simple support exhibits only Bragg-type BGs. To control low-frequency vibrations in dual pipelines placed on the rack, a novel configuration using interconnected dynamic vibration absorbers (DVAs) is proposed. The DVA consisting of two spring-damper units along with a mass is connected across the center of each span of the two pipelines. The proposed DVA is designed via genetic algorithm-based optimization. It was found that the designed DVA significantly reduces the vibration of the two pipelines. The performance of DVAs improves with an increase in the mass ratio. Additionally, the performance of pipes connected with conventional tuned mass damper (TMD) is evaluated and compared with the proposed DVA. The effectiveness of DVAs is also verified by employing a white Gaussian noise as input. The proposed DVAs are efficient in scenarios involving multiple pipes within a rack, leveraging other pipe’s mass, stiffness, and damping properties to mitigate vibrations in the considered pipes.

Multiple origins of freshwater invasion and parental care reflecting ancient vicariances in the bivalve family Cyrenidae (Mollusca)

Habitat transitions in living organisms are key innovations often coupled with species diversification after their successful adaptation to new environment. The Cyrenidae is among the most well-known heterodont bivalve groups that have successfully invaded freshwater systems from brackish water environments and display diverse lineage-specific developmental modes. Phylogenetic and molecular clock-based divergence time analyses using 12 complete mitochondrial genome sequences suggest that Cyrenidae species independently colonized freshwater habitats during three distinct spatial and geological periods: one from the American continents approximately in the Early Jurassic and the two others from Australasian/East Asian continents in the Early/Middle Cretaceous and the Paleogene-Neogene boundary, respectively. This study provides significant insight into the temporal and spatial patterns of multiple freshwater invasions, aligning with ancient vicariance events inferred from different geological timelines of plate tectonics. Additionally, mitogenome phylogeny confirms the earlier hypothesis of the repeated parallel evolution of parental care system within this bivalve group.

Mott Transition for a Lieb-Liniger Gas in a Shallow Quasiperiodic Potential: Delocalization Induced by Disorder.

Disorder or quasidisorder is known to favor localization in many-body Bose systems. Here, in contrast, we demonstrate an anomalous delocalization effect induced by incommensurability in quasiperiodic lattices. Loading ultracold atoms in two shallow periodic lattices with equal amplitude and either equal or incommensurate spatial periods, we show the onset of a Mott transition not only in the periodic case but also in the quasiperiodic case. Switching from periodic to quasiperiodic potential with the same amplitude, we find that the Mott insulator turns into a delocalized superfluid. Our experimental results agree with quantum MonteCarlo calculations, showing this anomalous delocalization induced by the interplay between the disorder and interaction.

Numerical Study of Low Engine Order Excitations due to Manufacturing Variability Part 1: Characterization of the Geometric Scatter and its Effect on Forced Response

Abstract The geometric scatter in the surfaces of blades and vanes due to manufacturing variability has an impact on the dynamics but also on the aerodynamics. The loss of the spatial periodicity of the flow due to the geometric variations generates an aerodynamic forcing with a wave number different from the airfoil count on the adjacent rows. In this paper, deviations from the nominal geometry are obtained from a set of scanned parts. The average manufactured geometry is computed through the point-by-point deviations between the scanned parts and the nominal geometry. Then, Principal Component Analysis is applied to the deviations from the average geometry to find a way to describe them in a simple manner. The cold geometries are reconstructed using the mean geometry and the PCA geometric modes; afterwards, a cold-to-hot process is applied to obtain the hot geometry, and finally the resulting aerodynamics are obtained using an in-house CFD solver. The described method is applied to a representative row constituted by packets of vanes. Firstly, the average packet geometry is used to analyze the aerodynamic forcing associated to the geometric variation of the airfoils inside the vane packet. After that, a conceptual study is carried out under some simplified assumptions in order to relate the geometric variability to random low engine order disturbances, using the geometric modes obtained from the PCA analysis. In both cases, the induced vibrations on the adjacent rotor row are comparable to the excitation due to the nominal blade-passing.

Arbuscular mycorrhizal fungal diversity in agricultural fields is explained by the historical proximity to natural habitats

Soil microbes are essential to maintain terrestrial ecosystem functionality. However, their diversity is threatened by land-use change, such as agricultural expansion and intensification. One important microbial group mediating the exchange of nutrients between plants and soil is arbuscular mycorrhizal (AM) fungi. The response of microorganism diversity to present and past habitat amount has been poorly studied. Here, we evaluate the potential role of current and historical natural habitat availability in explaining the diversity of AM fungi in arable fields. We conducted a spatially intensive sampling of three agricultural fields in Estonia. Soil AM fungal diversity was determined by soil DNA metabarcoding. We related AM fungal species richness, along with beta diversity components (turnover and nestedness), to abiotic conditions and natural habitat area availability at different spatial scales and time periods. Our findings showed a positive relationship between AM fungal richness and the amount of natural habitat area. Specifically, current AM fungal species richness was best explained by the amount of natural habitat from 130 years earlier, indicating a legacy effect of past land use on current soil biodiversity. The amount of past natural areas was negatively related to the beta diversity turnover component, indicating a replacement of AM fungal species in disturbed sites. While biodiversity-friendly farming is useful in promoting diverse soil biota, historical legacies can be persistent. Maintaining natural habitats around agricultural fields can further promote soil AM fungal diversity for future generations.

Complex-plane singularity dynamics for blow up in a nonlinear heat equation: analysis and computation

Abstract Blow-up solutions to a heat equation with spatial periodicity and a quadratic nonlinearity are studied through asymptotic analyses and a variety of numerical methods. The focus is on tracking the dynamics of the singularities in the complexified space domain all the way from the initial time until the blow-up time, which occurs when the singularities reach the real axis. This widely applicable approach gives forewarning of the possibility of blow up and an understanding of the influence of singularities on the solution behaviour on the real axis, aiding the (perhaps surprisingly involved) asymptotic analysis of the real-line behaviour. The analysis provides a distinction between small and large nonlinear effects, as well as insight into the various time scales over which blow up is approached. The solution to the nonlinear heat equation in the complex spatial plane is shown to be related asymptotically to a nonlinear ordinary differential equation. This latter equation is studied in detail, including its computation on multiple Riemann sheets, providing further insight into the singularities of blow-up solutions of the nonlinear heat equation when viewed as multivalued functions in the complex space domain and illustrating the potential intricacy of singularity dynamics in such (non-integrable) nonlinear contexts.

Dynamical decoding of the competition between charge density waves in a kagome superconductor

The kagome superconductor CsV3Sb5 hosts a variety of charge density wave (CDW) phases, which play a fundamental role in the formation of other exotic electronic instabilities. However, identifying the precise structure of these CDW phases and their intricate relationships remain the subject of intense debate, due to the lack of static probes that can distinguish the CDW phases with identical spatial periodicity. Here, we unveil the out-of-equilibrium competition between two coexisting 2 × 2 × 2 CDWs in CsV3Sb5 harnessing time-resolved X-ray diffraction. By analyzing the light-induced changes in the intensity of CDW superlattice peaks, we demonstrate the presence of both phases, each displaying a significantly different amount of melting upon excitation. The anomalous light-induced sharpening of peak width further shows that the phase that is more resistant to photo-excitation exhibits an increase in domain size at the expense of the other, thereby showcasing a hallmark of phase competition. Our results not only shed light on the interplay between the multiple CDW phases in CsV3Sb5, but also establish a non-equilibrium framework for comprehending complex phase relationships that are challenging to disentangle using static techniques.

Binding and unbinding of flexible surfactant bilayers

We have probed the influence of salt and temperature on the spatial periodicity (d) of the fluid lamellar (Lα) phase formed by two ionic amphiphiles, whose bilayer bending rigidity moduli are widely different. In the case of rigid 1,2-dimyristoyl-3-trimethylammonium-propane (chloride salt) (DMTAP) bilayers, d is found to decrease with increasing salt concentration (Cs) in the solution, in qualitative agreement with the DLVO theory. d depends only very weakly on temperature in this system. On the other hand, in the Lα phase formed by highly flexible didodecyldimethylammonium chloride (DDAC) bilayers, d is not set by the minimum of the DLVO potential over a wide range of Cs, due to inter-bilayer repulsion arising from thermal undulations of the bilayers. An abrupt transformation of this undulation stabilized swollen Lα phase into a collapsed Lα phase, where d is comparable to the bilayer thickness, is observed above a threshold value of Cs. At higher Cs an unbinding transition of the bilayers is observed on heating, where the collapsed Lα phase transforms into a dispersion of spatially uncorrelated bilayers. Our observations are consistent with this transition being first-order.

Generation of self-healing and sliding wear resistant titanium surfaces by different pico-second laser induced periodic surface structures

Selective and complete micro-patterning (μ-patterning) of α‑titanium surfaces were performed using a 1064 nm laser system. With a fluence of 0.6 J⋅cm−2 and a pulse duration of 10 ps, two different μ-patterns of laser induced periodic surface structures (LIPSS) were generated by mainly changing the number of pulses per spot and the spot-to-spot distance. A high number of pulses per spot and a large spot-to-spot distance of 60 μm gives selectively with LIPSS modified dimples. Their spatial period varies from 159 nm to a maximum of 620 nm inside the dimples. An increased fraction of TiO2 in the crystalline form of rutile gave improved wear resistance and a coefficient of friction COF of 0.20 ± 0.02. If the spot-to-spot distance is reduced to 6 μm and the number of pulses at one spot remains low, a completely rippled surface with slightly increased oxide fraction but still a metallic plastic behaviour was able to show volume expansion during sliding. The observed self-healing ability of this LIPSS pattern is correlated with the relief of compressive stresses in this study. As volume expansion operates against the sliding motion of the diamond tip, high COFs of 0.62 ± 0.11 for a normal load of 1.0 N and 0.45 ± 0.04 for a normal load of 0.5 N were measured. After further optimisation, such a tailored increase in COF and load stimulated volume expansion of the surface could be useful in order to act against implant loosening and undesired movements.

Signal generation in dynamic interferometric displacement detection.

Laser interferometry is a well-established and widely used technique for precise displacement measurements. In a non-contact atomic force microscope (NC-AFM), it facilitates the force measurement by recording the periodic displacement of an oscillating microcantilever. To understand signal generation in a NC-AFM-based Michelson-type interferometer, we evaluate the non-linear response of the interferometer to the harmonic displacement of the cantilever in the time domain. As the interferometer signal is limited in amplitude because of the spatial periodicity of the interferometer light field, an increasing cantilever oscillation amplitude creates an output signal with an increasingly complex temporal structure. By the fit of a model to the measured time-domain signal, all parameters governing the interferometric displacement signal can precisely be determined. It is demonstrated, that such an analysis specifically allows for the calibration of the cantilever oscillation amplitude with 2% accuracy.