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The detection and extraction of weak signals are crucial in various engineering and scientific fields, yet current acoustic sensing technologies are restricted by fundamental pressure detection methods. This paper proposes gradient-equivalent medium-coupled metamaterials (GEMCMs) utilizing strong wave compression and an equivalent medium mechanism to capture weak signals in complex environments and enhance target acoustic signals. Overcoming shape and impedance mismatch limitations of traditional gradient structures, GEMCMs significantly improve control performance. Experimental and numerical simulations indicate that GEMCMs can effectively enhance specific frequency components in acoustic signals, outperforming traditional gradient structures. This enhancement of specific frequency components relies on the resonance effect of the unit cell structure. By introducing acoustic resonance within a spatially wound acoustic channel, a significant amplification of weak acoustic signals is achieved. This provides a new research direction for acoustic wave manipulation and enhancement, and holds significant importance in fields such as mechanical fault diagnosis and medical diagnostics.

Acoustic sensing systems play a critical role in identifying and determining weak sound sources in various fields. In many fault warning and environmental monitoring processes, sound-based sensing techniques are highly valued for their information-rich and non-contact advantages. However, noise signals from the environment reduce the signal-to-noise ratio (SNR) of conventional acoustic sensing systems. Therefore, we proposed novel nonlinear gradient-coiling metamaterials (NGCMs) to sense weak effective signals from complex environments using the strong wave compression effect coupled with the equivalent medium mechanism. Theoretical derivations and finite element simulations of NGCMs were executed to verify the properties of the designed metamaterials. Compared with nonlinear gradient acoustic metamaterials (Nonlinear-GAMs) without coiling structures, NGCMs exhibit far superior performance in terms of acoustic enhancement, and the structures capture lower frequencies and possess a wider angle acoustic response. Additionally, experiments were constructed and conducted using set Gaussian pulse and harmonic acoustic signals as emission sources to simulate real application scenarios. It is unanimously shown that NGCMs have unique advantages and broad application prospects in the application of weak acoustic signal sensing, enhancement and localization.

Jupiter’s upper atmosphere is considerably hotter than expected from the amount of sunlight that it receives 1 – 3 . Processes that couple the magnetosphere to the atmosphere give rise to intense auroral emissions and enormous deposition of energy in the magnetic polar regions, so it has been presumed that redistribution of this energy could heat the rest of the planet 4 – 6 . Instead, most thermospheric global circulation models demonstrate that auroral energy is trapped at high latitudes by the strong winds on this rapidly rotating planet 3 , 5 , 7 – 10 . Consequently, other possible heat sources have continued to be studied, such as heating by gravity waves and acoustic waves emanating from the lower atmosphere 2 , 11 – 13 . Each mechanism would imprint a unique signature on the global Jovian temperature gradients, thus revealing the dominant heat source, but a lack of planet-wide, high-resolution data has meant that these gradients have not been determined. Here we report infrared spectroscopy of Jupiter with a spatial resolution of 2 degrees in longitude and latitude, extending from pole to equator. We find that temperatures decrease steadily from the auroral polar regions to the equator. Furthermore, during a period of enhanced activity possibly driven by a solar wind compression, a high-temperature planetary-scale structure was observed that may be propagating from the aurora. These observations indicate that Jupiter’s upper atmosphere is predominantly heated by the redistribution of auroral energy. High-resolution observations confirm that Jupiter’s global upper atmosphere is heated by transport of energy from the polar aurora.

The evolution of the wave pattern in a multimodulus elastic half-space with a boundary moving in nonstationary uniaxial piecewise linear “tension–compression–stop” mode is studied. The solution of the boundary value problem includes all cases of interaction between plane one-dimensional strain waves, including reflected weak-intensity fronts. A number of new features of one-dimensional elastic deformation dynamics in a multimodulus medium are revealed, some of which (e.g., the appearance of a reflected shock wave at a distance from the loaded boundary, cyclic transitions of a narrow moving zone from a compressed to rigid state and back, and a stepwise decrease in the tensile strain level in the near-boundary zone after the boundary is stopped) can be obtained with a given boundary loading only taking into account reflection effects.

Quantum states of light can improve imaging whenever the image quality and resolution are limited by the quantum noise of the illumination. In the case of a bright illumination, quantum enhancement is obtained for a light field composed of many squeezed transverse modes. A possible realization of such a multi-spatial-mode squeezed state is a field which contains a transverse plane in which the local electric field displays reduced quantum fluctuations at all locations, on any one quadrature. Using a traveling-wave amplifier, we have generated a multi-spatial-mode squeezed state and showed that it exhibits localized quadrature squeezing at any point of its transverse profile, in regions much smaller than its size. We observe 75 independently squeezed regions. The amplification relies on nondegenerate four-wave mixing in a hot vapor and produces a bichromatic squeezed state. The result confirms the potential of this technique for producing illumination suitable for practical quantum imaging.

We consider the effect of concentric pulse impact (an abrupt increase in liquid pressure at some distance from a collapsing bubble surface) on the collapse of a spherical cavitation bubble in water. The vapor dynamics within the bubble and movement of the surrounding liquid are described by gasdynamic equations, closed by wide-range state equations. The thermal conductivity of both phases and heat and mass transfer on the surface of the bubble are taken into account. The calculation technique involves moving grids converging toward the bubble’s explicitly defined surface. The modified high-accuracy Godunov method is used. It has been found that the pulse impact accelerates the bubble collapse, and the bubble’s radius and pressure within its cavity increase at the end of the collapse. Under pulse impact, collapse of the bubble is accompanied by the periodic focusing of radially converging compression waves in the center of the bubble. At moments of focusing, the pressure in the small vicinity of the bubble center significantly increases. These noted features intensify with an increase in the amplitude of the impulse impact.

The active tectonics of northern Central Mongolia is studied between two largest W–E-trending left lateral fault zones: the Khangai Fault and the Tunka–Mondy. These strike-slip zones are part of a single ensemble of active faults in the Mongol–Baikal region, formed under conditions of maximum northeastern compression and maximum northwestern extension. Their ENE-trending Erzin–Agardag and Tsetserleg faults with a dominant sinistral component extend between these zones. A series of the N-trending graben basins (Busiyngol, Darkhat, and Khubsugul) are located between the eastern end of the Erzin–Agardag strike-slip fault and the western part of the Tunka–Mondy strike-slip zone. The basins form a sinistral deformation zone, which is kinematically similar with the strike-slip faults, which follow the latter. In contrast to the largest boundary strike-slip faults, this structural paragenesis formed under conditions of N–S-trending relative compression and N–S-trending extension. A change in the orientation of the axes of the principal normal stress may be caused by the rotation of the block between the boundary faults. The area of graben-shaped basins is located above the top of a vast volume of low-velocity mantle, which we have identified as the Khangai plume. The lithospheric mantle above this rise is reduced; the remaining part of the lithosphere is heated and softened. The large active strike-slip faults are located above areas of subsidence of the low-velocity top of the mantle. Our trenching of the active faults showed that strong earthquakes repeated in the area of graben-shaped basins more often than in the large strike-slip zones, but they were characterized by lower magnitudes.

Nowadays, most of the site classifications schemes are based on the predominant period of the site as determined from the average horizontal to vertical spectral ratios of seismic motion or microtremor. However, the difficulty lies in the identification of the predominant period in particular if the observed average response spectral ratio does not present a clear peak but rather a broadband amplification or multiple peaks. In this work, based on the Eurocode-8 (2004) site classification, and assuming bounded random fields for both shear and compression waves-velocities, damping coefficient, natural period and depth of soil profile, one propose a new site-classification approach, based on “target” simulated average \\[ H/V \\] spectral ratios, defined for each soil class. Taking advantage of the relationship of Kawase et al. (Bull Seismol Soc Am 101:2001–2014, 2011), which link the \\[ H/V \\] spectral ratio to the horizontal (\\[ HTF \\]) over the vertical (\\[ VTF \\]) transfer functions, statistics of \\[ H/V \\] spectral ratio via deterministic visco-elastic seismic analysis using the wave propagation theory are computed for the 4 soil classes. The obtained results show that \\[ H/V \\] and \\[ HTF \\] have amplitudes and shapes remarkably different among the four soil classes and exhibit fundamental peaks in the period ranges remarkably similar. Moreover, the “target” simulated average \\[ H/V \\] spectral ratios for the 4 soil classes are in good agreement with the experimental ones obtained by Zhao et al. (Bull Seismol Soc Am 96:914–925, 2006) from the abundant and reliable Japanese strong motions database Kik-net, Ghasemi et al. (Soil Dyn Earthq Eng 29:121–132, 2009) from the Iranian strong motion data, and Di Alessandro et al. (Bull Sesismol Soc Am 106:2, 2011. https://doi.org/10.1785/0120110084) from the Italian strong motion data. In addition to the 4 EC-8 standard soil classes (A, B, C and D), the superposition of the 4 target \\[ H/V \\] reveals 3 new boundary site classes; AB, BC and CD, for overlapping \\[ V_{s,30} \\] ranges when the predominant peak is not clearly consistent with any of the 4 proposed classes. Finally, one proposes a site classification index based on the ratio between the cross-correlation and the mean quadratic error between the in situ \\[ H/V \\] spectral ratio and the “target” one. In order to test the reliability of the proposed approach, data from 139 sites were used, 132 collected from the Kik-net network database from Japan and 7 from Algeria. The site classification success rate per site class are around 93, 82, 89 and 100% for rock, hard soil, medium soil and soft soil, respectively. Zhao et al. (2006) found an average success for the 4 classes of soil close to 60%, similar to what one found in the present study (63%) without considering the new soil classes, but much smaller if one considers them (86%). In the absence of \\[ V_{s,30} \\] data, the proposed approach can be an alternative to site classification.

We present a systematic study of the phenomena of number squeezing and fragmentation for a repulsive Bose-Einstein condensate (BEC) in a three dimensional double well potential over a range of interaction strengths and barrier heights, including geometries that exhibit appreciable overlap in the one-body wavefunctions localized in the left and right wells. We compute the properties of the condensate with numerically exact, full dimensional path integral ground state (PIGS) Quantum Monte Carlo simulations and compare with results obtained from using two- and eight-mode truncated basis models. The truncated basis models are found to agree with the numerically exact PIGS simulations for weak interactions, but fail to correctly predict the amount of number squeezing and fragmentation exhibited by the PIGS simulations for strong interactions. We find that both number squeezing and fragmentation of the BEC show non-monotonic behavior at large values of interaction strength a. The number squeezing shows a universal scaling with the product of number of particles and interaction strength (Na) but no such universal behavior is found for fragmentation. Detailed analysis shows that the introduction of repulsive interactions not only suppresses number fluctuations to enhance number squeezing, but can also enhance delocalization across wells and tunneling between wells, each of which may suppress number squeezing. This results in a dynamical competition whose resolution shows a complex dependence on all three physical parameters defining the system: interaction strength, number of particles, and barrier height.