Compact Configuration Research Articles

Aperture-encoded snapshot hyperspectral imaging with a lensless camera

We present a lensless snapshot hyperspectral camera that is capable of hyperspectral imaging over a broad spectrum using a compact and low-cost hardware configuration. We leverage the multiplexing capability of a lensless camera, a novel type of computational imaging device that replaces the lens with a thin mask. Our device utilizes a linear variable filter and a phase mask to encode spectral information onto a monochromatic image sensor, enabling recovery of hyperspectral image stacks from a single measurement by utilizing spectral information encoded in different parts of the 2D point spread function. We perform spectral calibration using a reference color chart and verify the prototype device’s spectral and spatial resolution, as well as its imaging field of view. We report on the design and construction of the device, the image reconstruction algorithm, and spectral calibration methods and present hyperspectral images ranging from 410 to 800 nm obtained with our prototype device.

New insights from modelling studies and molecular dynamics simulations of the DIS5-S6 extracellular linker of the skeletal muscle sodium channel NaV1.4.

In the CryoEM-structure of the hSkMNaV1.4 ion channel (PDB:6AGF), the 59-residue DIS5-S6 linker peptide was omitted due to absence of electron density. This peptide is intriguing - comprised of unique sequence and found only in mammalian skeletal muscle sodium ion channels. To probe potential physiological and evolutionary significance, we constructed an homology model of the complete hSkMNaV1.4 channel. Rather than a flexible random coil potentiating drift across the channel, the linker folds into a compact configuration through self-assembling secondary structural elements. Analogous sequences from 48 mammalian organisms show hypervariability with between 40% and 100% sequence similarity. To investigate structural implications, sequences from 14 representative organisms were additionally modelled. All showed highly conserved N-and C-terminal residues closely superimposed, suggesting a critical functional role. An optimally located asparagine residue within the conserved region was investigated for N-linked glycosylation and MD simulations carried out. Results suggest a complex glycan added at this site in the linker may form electrostatic interactions with the DIV voltage sensing domain and be mechanistically involved in channel gating. The relationship of unique sequence, compact configuration, potential glycosylation and MD simulations are discussed relative to SkMNaV1.4 structure and function.

A large depth-of-field virtual measurement network for non-cooperative 6DOF pose estimation in occlusion scenes

Six degrees of freedom (6DOF) measurement capable of determining the rigid transformation is a vital task in aerospace exploration and autonomous navigation. In this paper, a large depth-of-field virtual measurement network is proposed based on a moving rotating-prism-embedded camera to achieve 6DOF pose estimation for non-cooperative partially occluded targets. It includes stereo recovery using dense beam localization and accurate absolute orientation based on dual quaternions and adaptive scale factors. The former allows the three-dimensional (3D) extraction by multiview large-parallax imaging, while the latter enables the decoupling of translation and orientation without initial value estimation to avoid error accumulation. Compared to the mainstream methods, our method provides high-quality pose metrology, especially for depth extraction. The experiments show that the architecture allows the 3D reconstruction and non-cooperative 6DOF estimation with a large depth of field and object occlusion, solving the problem of difficult compromise between long-baseline imaging and compact configuration.

Time-dependent Hartree-Fock study of quasifission trajectories in reactions forming Og294

Background: Fission modes in superheavy nuclei are expected to be impacted by quantum shell effects. Similar shell effects may be present in quasifission reactions, acting to hinder the mass equilibration process in heavy-ion collisions.Purpose: To investigate quasifission mechanisms in five different reactions forming $^{294}\mathrm{Og}$ as a compound nucleus and compare quasifission trajectories with predicted fission modes.Methods: The potential energy surface (PES) of $^{294}\mathrm{Og}$ is calculated using the static Hartree-Fock approach with BCS pairing correlations. Quasifission trajectories for central collisions at various energies are studied with the time-dependent Hartree-Fock theory.Results: The exit channel strongly depends on initial mass asymmetry and orientation, but it only exhibits small dependencies in the reaction energy. The $^{48}\mathrm{Ca}+^{246}\mathrm{Cf}$ reaction is affected by the PES topography, leading to either fusion or asymmetric fission. $^{126}\mathrm{Sn}+^{168}\mathrm{Er}$ reactions exhibit large total kinetic energies and compact scission configurations, which could be interpreted as an effect of the $Z=50$ spherical magic gap.Conclusions: Quasifission trajectories can be interpreted in terms of the underlying PES for low excitation energies. Future investigations of quasifission with temperature- and angular-momentum-dependent PES could be considered.

Arbitrary wavefront modulation utilizing an aperiodic elastic metasurface

Metasurfaces have attracted much attention due to their much more compact configurations and their abilities to modulate wavefronts of propagating waves by abruptly shifting their phase and/or amplitude. Most current metasurfaces are usually composed of subunits with periodic unit cells, which limits their design freedom for arbitrary phase and amplitude modulation. To overcome this limitation, in this paper, we propose an aperiodic elastic metasurface where arbitrary phase and amplitude modulation can be achieved. The aperiodic elastic metasurface is composed of pillared resonators with different heights and an analytical model-based genetic algorithm (GA) inverse design method is employed to determine the heights of the pillared resonators. The underlying mechanism of the phase/amplitude shift and mechanism of full transmission are revealed. The proposed aperiodic elastic metasurface can steer and focus flexural waves with full transmission and can steer flexural waves into different directions with different amplitudes. The inverse design method and the aperiodic design in this paper can inspire the design of other types of functional metasurfaces for fascinating applications.

Formula omitted] optical parametric oscillator with wide temperature tuning

This paper investigated the output characteristics of ZGP optical parametric oscillator (OPO) with tuning over a wide temperature range. The temperature-dependent Sellmeier equation of the ZGP crystal was obtained, and the temperature-tuned curves of ZGP OPO at different phase matching angles were calculated. For temperatures ranging from 25 °C to 200 °C, a tunable long-wave laser at 7.08–7.50 μm, 7.40–7.95 μm, and 7.79–8.47 μm was obtained when the phase matching angles were 51.3°, 50.95°, and 50.6°, respectively. The total tuning range was 1.39 μm. When the idler wavelength was 8.348 μm, the output energy was 0.520 mJ with a pulse width of 15.5 ns, the corresponding slope efficiency and optical conversion efficiency were 10.22% and 8.15%, respectively. The laser has advantages of a wide tunable range and compact mechanical configuration, extending the tuning method of ZGP OPO, which is important in promoting the development of long-wave lasers with a wide tuning range.

Revisiting compact star in F(R) gravity: Roles of chameleon potential and energy conditions

We reexamine the static and spherical symmetric compact star configuration in the $R^2$ model of the $F(R)$ gravity theory. With asymptotic solutions for the additional scalar degrees of freedom, we refine analysis on the external geometry and settle the scalar-hair problem argued in previous works. Performing the numerical integration of the modified Tolman-Oppenheimer-Volkoff equations as a two-boundaries-value problem, we further discuss the scalar-field distribution inside the compact stars and its influence on the mass-radius relation. We show that the chameleon potential plays an essential role in determining the scalar-field profile inside the star. The scalar field often behaves as a quintessential field that effectively decreases the mass of compact stars with lower central energy density.

Recurrent 3He-rich solar energetic particle injections observed by Solar Orbiter at ∼0.5 au

We report Solar Orbiter observations of six recurrent solar energetic particle injections in 2022 March 3−6 at ∼0.5 au. All but one were associated with jets emanating from a plage near a large sunspot in active region 12 957. We saw large jets in injections with high 3He and Fe enrichments and minor jets in injections with no or lower enrichments. Furthermore, the event with the highest enrichment showed a more compact configuration of the underlying photospheric magnetic field. The higher fluences as well as harder spectra were seen in the event with a simultaneous jet and wider eruption. However, in this case, the energy buildup time in the source might be required to produce such spectra. Extreme-ultraviolet images from Solar Orbiter revealed a number of intersecting loops at the base of jets not seen from 1 au that might be a precondition for the recurrent events.

Stability analysis of axial geometry with anisotropic background in f(R,T) gravity

In this paper, we highlight the variables preserving stability of a very restricted class of anisotropic axial symmetrical compact geometry in the scenario of [Formula: see text] gravity, where [Formula: see text] stands for energy–momentum tensor’s trace and [Formula: see text] is invariant Ricci curvature. In the framework of [Formula: see text] gravity, we set up field equations as well as non-conservation equations. We use a perturbation technique for all variables involved in non-conservation equations, field equations, extra curvature terms of modified gravity as well as for considered gravity model (i.e. [Formula: see text]) to evaluate the collapse equation. We establish certain significant constraints for the stiffness parameter [Formula: see text] in Newtonian [Formula: see text] and post-Newtonian [Formula: see text] approximation to study the dynamical instability of a stellar compact configuration. In order to preserve the stability of an anisotropic self-gravitating axially symmetric configuration, we place certain restrictions on physical quantities. To examine the stable and unstable behavior of considered geometry via graphical approaches, we include schematic diagrams at the [Formula: see text] and [Formula: see text] eras.

Structural properties of anisotropic stars in modified teleparallel gravity: a brief study via an embedding approach

In this paper, we attempt to construct the anisotropic solution for compact stellar configurations using the observed mass and radius of compact stars from the literature under the influence of Rastall Teleparallel gravity. To investigate the crucial elements of spherically symmetric metric space, we employed the embedding class one spacetime paradigm with Karmarkar’s condition. The field equations have been computed under the gravitational action of Rastall Teleparallel gravity. However, the unknown constants were evaluated via junction conditions using the Schwarzschild metric as the outer geometry. The compact stars analysis’s crucial physical and mathematical requirements are all admitted and shared by the model, which is physically viable and supports the emergence of novel realistic stellar configurations in Rastall Teleparallel gravity. We fix the parameters of our model to compare with three compact stars (LMC X-4, Cen X-3, and EXO 1785-248) and find that it can be regular, robust, and stable.

Parametric Optimization of a Truncated Conical Metal Hydride Bed Surrounded by a Ring of PCM for Heat Recovery.

Metal hydride (MH) hydrogen storage needs an external heat source to release the stored hydrogen. To enhance the thermal performance of MHs, the incorporation of phase change materials (PCM) is a way to preserve reaction heat. This work proposes a new MH-PCM compact disk configuration (i.e., a truncated conical MH bed surrounded by a PCM ring). An optimization method is developed to find the optimal geometrical parameters of the MH truncated cone, which is then compared to a basic configuration (i.e., a cylindrical MH surrounded by a PCM ring). Moreover, a mathematical model is developed and used to optimize the heat transfer in a stack of MH-PCM disks. The optimum geometric parameters found (bottom radius of 0.2, top radius of 0.75 and tilt angle of 58.24) allow the truncated conical MH bed to reach a faster heat transfer rate and a large surface area of higher heat exchange. Compared to a cylindrical configuration, the optimized truncated cone shape enhances the heat transfer rate and the reaction rate in the MH bed by 37.68%.

Ultra-Flat Supercontinuum Generation in an All-Fiber Self-Q-Switched Er/Yb Laser

A supercontinuum source based on a self-Q-switched Er/Yb-codoped fiber laser has been experimentally demonstrated. At different pump powers, starting at a moderate value of 1.1 W, self-Q-switched pulses with a broad flat spectrum of ~ 560 nm width spanning over the range ~1600 – 2160 nm at −5 dB level (considering the Raman peak) are obtained. Such wide spectrum can be achieved directly at the output of the fiber laser resonator, making the structure compact and robust. With a maximum pump power of 4.9 W, the repetition rate, average output power, peak power and pulse energy are approximately 14.7 kHz, 465 mW, 66 kW and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$31~\mu \text{J}$ </tex-math></inline-formula> , respectively. This compact SC laser configuration has the merits of simple cavity design, low cost and good robustness, which provide a SC source that can be easily applied to numerous areas, such as spectroscopy, optical communications, metrology and biomedical applications.

A 3-D Printed Lightweight Miniaturized Dual-Band Dual-Polarized Feed Module for Advanced Millimeter-Wave and Microwave Shared-Aperture Wireless Backhaul System Applications

A 3-D-printed lightweight miniaturized dual-band dual-polarized feed module of wireless backhaul systems consisting of a dual-band air-filled waveguide orthomode transducer (OMT) and a shared-aperture conical horn radiator is investigated. The OMT operating in both Ku- and E-bands with a large frequency ratio is realized by combining the turnstile-junction-type and Bøifot-junction-type OMTs sharing a common-mode-composite coaxial port. A design method of the dual-band OMT considering the requirement for a self-supporting geometry in metallic 3-D printing is presented, so that its compact configuration that is difficult to fabricate by traditional milling technology can be fulfilled conveniently in a whole piece with the use of commercial 3-D printing facilities. A millimeter-wave horn with a small radiation aperture is embedded into a larger aperture of a microwave horn. A proper longitudinal offset between them is introduced to guarantee promising radiation characteristics of the shared-aperture scheme in the two bands. By connecting the OMT with the radiator, the proposed dual-band dual-polarized feed module with a weight of only 100 g is manufactured and measured. Excellent performance, involving the wide bandwidths of 46.7% and 31.2% at microwave and millimeter-wave frequencies, a high isolation of almost larger than 40 dB, a high radiation efficiency of about 90%, and stable dual-polarized radiation patterns with low cross polarizations, is confirmed experimentally. Benefitted from the geometric and operating merits, the feed module would be attractive for applications in advanced millimeter-wave and microwave shared-aperture wireless backhaul systems.

Computational-sampling-moiré-based on-machine alignment for freeform optics.

The manufacturing and characterization of freeform optical surfaces are influenced by their high sensitivity to misalignments. In this work, the computational sampling moiré technique combined with phase extraction is developed for the precise alignment of freeform optics during fabrication and in metrology applications. This novel, to the best of our knowledge, technique achieves near-interferometry-level precision in a simple and compact configuration. This robust technology can be applied to industrial manufacturing platforms (such as diamond turning machines, lithography, and other micro-nano-machining techniques) as well as their metrology equipment. In a demonstration of computational data processing and precision alignment using this method, iterative manufacturing of freeform optical surfaces with a final-form accuracy of about 180 nm was accomplished.

TIC 219006972: a compact, coplanar quadruple star system consisting of two eclipsing binaries with an outer period of 168 d

ABSTRACT We present the discovery of a new highly compact quadruple star system, TIC 219006972, consisting of two eclipsing binary stars with orbital periods of 8.3 and 13.7 d, and an outer orbital period of only 168 d. This period is a full factor of 2 shorter than the quadruple with the shortest outer period reported previously, VW LMi, where the two binary components orbit each other every 355 d. The target was observed by Transiting Exoplanet Survey Satellite in full-frame images in sectors 14–16, 21–23, 41, 48, and 49, and produced two sets of primary and secondary eclipses. These show strongly non-linear eclipse timing variations (ETVs) with an amplitude of ∼0.1 d, where the ETVs of the primary and secondary eclipses and of the two binaries are all largely positively correlated. This highlights the strong dynamical interactions between the two binaries and confirms the compact quadruple configuration of TIC 219006972. The two eclipsing binaries are nearly circular, whereas the quadruple system has an outer eccentricity of about 0.25. The entire system is nearly edge-on, with a mutual orbital inclination between the two eclipsing binary star systems of about 1 deg.

Study on a direct-coupling thermoacoustic refrigerator using time-domain acoustic-electrical analogy method

Thermoacoustic refrigeration is a clean cooling technology with high reliability. In this study, a time-domain acoustic–electrical analogy (TDAEA) method is proposed and improved, then applied to explore the performance of a high-efficiency 2-stage looped direct-coupling heat-driven thermoacoustic refrigerator. The effectiveness of the method is verified by experiments. Transient evolutions of oscillating pressure and volume flow rate are first presented. System performance under different working gases is explored, and helium is chosen due to its much larger cooling power. The influences of cooling and ambient temperatures and cavity parameters on system performance are then investigated. The results show that a rise in ambient temperature leads to a dramatic decline in cooling power. Moreover, the influences of cavity parameters are complicated. When the diameter and length of the cavity are respectively 95 mm and 440 mm, the cooling power achieves a maximum of 3.65 kW with COP of 0.76; while with diameter and length reaching 90 mm and 360 mm, respectively, a peak COP of 0.82 with cooling power of 1.47 kW is obtained. Furthermore, a comparison between the presented direct-coupling system and a series-connection system is performed. The results show better performance of the direct-coupling system, which achieves a cooling power of 5.08 kW under air-conditioning case, 22.4 % higher than that of the series-connection system, implying its superiority in air-conditioning field for larger cooling capacity and more compact configuration. This study provides a new perspective for understanding ofthermoacoustic refrigerators.

Light meson emissions of selected charmonium-like states within compact tetraquark configurations* *Supported by the National Natural Science Foundation of China (11705056, 12175037, 11947224, 11475192, 11975245, U1832173), the Key Project of Hunan Provincial Education Department under (21A0039), the State Scholarship Fund of China Scholarship Council (22006725011), the Sino-German CRC 110 “Symmetries and the Emergence of Structure in QCD” project by NSFC

We adopt the quark pair creation model to investigate the light meson emissions of several charmonium-like states. The quark pair creation model is applied to four-body systems, and we calculate the pion/kaon emissions of , , , , , and within compact tetraquark configurations. We find that the pion/kaon decay widths of and are relatively small, whereas the partial decay widths of the resonances , , , and are significant. We expect that our exploration of these decay behaviors will provide useful information for future experimental searches and theoretical interpretations.

Novel electrotactile brain-computer interface with somatosensory event-related potential based control.

A brain computer interface (BCI) allows users to control external devices using non-invasive brain recordings, such as electroencephalography (EEG). We developed and tested a novel electrotactile BCI prototype based on somatosensory event-related potentials (sERP) as control signals, paired with a tactile attention task as a control paradigm. A novel electrotactile BCI comprises commercial EEG device, an electrical stimulator and custom software for EEG recordings, electrical stimulation control, synchronization between devices, signal processing, feature extraction, selection, and classification. We tested a novel BCI control paradigm based on tactile attention on a sensation at a target stimulation location on the forearm. Tactile stimuli were electrical pulses delivered at two proximal locations on the user's forearm for stimulating branches of radial and median nerves, with equal probability of the target and distractor stimuli occurrence, unlike in any other ERP-based BCI design. We proposed a compact electrical stimulation electrodes configuration for delivering electrotactile stimuli (target and distractor) using 2 stimulation channels and 3 stimulation electrodes. We tested the feasibility of a single EEG channel BCI control, to determine pseudo-online BCI performance, in ten healthy subjects. For optimizing the BCI performance we compared the results for two classifiers, sERP averaging approaches, and novel dedicated feature extraction/selection methods via cross-validation procedures. We achieved a single EEG channel BCI classification accuracy in the range of 75.1 to 88.1% for all subjects. We have established an optimal combination of: single trial averaging to obtain sERP, feature extraction/selection methods and classification approach. The obtained results demonstrate that a novel electrotactile BCI paradigm with equal probability of attended (target) and unattended (distractor) stimuli and proximal stimulation sites is feasible. This method may be used to drive restorative BCIs for sensory retraining in stroke or brain injury, or assistive BCIs for communication in severely disabled users.

Seismic analysis of failure mechanisms in adjacent interacting stone masonry buildings via rigid block modeling

Groups of contiguous unreinforced stone masonry buildings are a common type of housing seen in old European downtowns. However, assessing their response to earthquakes poses several challenges to the analysts, especially when the housing units are laid out in compact configurations. In fact, in those circumstances a modeling technique that allows for the dynamic interaction of the units is required. The numerical study carried out in this paper makes use of a rigid block modeling approach implemented into in-house software tools to simulate the static behavior and dynamic response of an aggregate stone masonry building. Said approach is used to reproduce the results of bi-axial shake-table tests that were performed on a building prototype as part of the activities organized within the Adjacent Interacting Masonry Structures project, sponsored by the Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe. The experimental mock-up consisted of two adjacent interacting units with matching layout but different height. Two rigid block models are used to investigate the seismic response of the mock-up: a 3D model allowing for the limit analysis of the building on one hand, and a 2D model allowing for the non-linear static pushover and time-history analysis on the other. The 3D model was built for the blind prediction of the test results, as part of a competition organized to test different modeling approaches that are nowadays available to the analysts. The 2D model was implemented once the experimental data were made available, to deepen the investigation by non-linear static pushover and time-history analysis. In both models, the stonework is idealized into an assemblage of rigid blocks interacting via no-tension frictional interfaces, and mathematical programming is utilized to solve the optimization problems associated to the different types of analysis. Differences between numerical and experimental failure mechanisms, base shears, peak ground accelerations, and displacement histories are discussed. Potentialities and limitations of the adopted rigid block models for limit, pushover and time-history analyses are pointed out on the basis of their comparisons with the experimental results.

Stellar Model for Charged and Isotropic Rotating Neutron Stars in $$f(\mathcal {R},\mathcal {T})$$ Gravity

The modified theories of gravity have received a lot of attention in the last decade. These theories aim to describe the accelerated cosmic expansion by altering the theory of gravity, instead of introducing dark energy. The major goal of this research is to examine the spacetime surrounding charged compact star configurations in the context of $$f(\mathcal {R},\mathcal {T})$$ gravity and develop a workable model employing the Buchdahl metric potential (Phys. Rev. D 116, 1027 (1959)). We consider a simplified separable linear form for arbitrary function $$f(\mathcal {R},\mathcal {T})$$ given by, $$f(\mathcal {R},\mathcal {T})=\mathcal {R}+2\zeta \mathcal {T}$$ with the matter Lagrangian $$\mathcal {L}_\mathcal {M}=\rho$$ to depict the full solution of the modified field equations for the considered matter distribution. We assess various key characteristics, including effective energy density, effective pressure, sound velocities, relativistic adiabatic index, all energy conditions, and surface redshift, to determine the model’s physical viability and stability. For this investigation, we consider a rotating neutron star with isotropic configurations, namely Hercules X-1, as testing candidate. We also examine the effect of coupling constant $$\zeta$$ on the physical attributes of our model. The investigation illustrates that all our derived results lie within the physically accepted regime, demonstrating the model’s feasibility in $$f(\mathcal {R},\mathcal {T})$$ gravity.