Search Results (24)

We introduce a robust distributed collaborative beamforming (RDCB) approach for addressing channel estimation challenges in dual-hop transmissions within wireless sensor and actuator networks (WSANs) of K nodes. WSANs enhance wireless communication by reducing data transmission, latency, and energy consumption while optimizing network load through integrated sensing and actuation. The source S transmits signals to the WSAN, where nodes relay them to the destination D using beamforming weights to minimize noise and preserve signal integrity. These weights depend on channel state information (CSI), where estimation errors degrade performance. We develop RDCB solutions for three first-hop propagation scenarios—monochromatic [line-of-sight (LoS)] or “M”, bichromatic (moderately scattered) or “B”, and polychromatic (highly scattered) or “P”—while assuming a monochromatic LoS or “M” link for the second hop between the nodes and the far-field destination. Termed MM-RDCB, BM-RDCB, and PM-RDCB, respectively (“X” and “Y” in XY-RDCB—for X $\in \{\mathrm{M},\mathrm{B},\mathrm{P}\}$ and Y $\in \left\{\mathrm{M}\right\}$—refer to the chromatic natures of the first- and second-hop channels, respectively, to which a specific RDCB solution is tailored), these solutions leverage asymptotic approximations for large K values and the nodes’ geometric symmetries. Our distributed solutions allow local weight computation, enhancing spectral and power efficiency. Simulation results show significant improvements in the signal-to-noise ratio (SNR) and robustness versus WSAN node placement errors, making the solutions well suited for emerging 5G and future 5G+/6G and Internet of Things (IoT) applications for different challenging environments. Full article

Thyroid hormone receptor alpha (THRα) is a nuclear hormone receptor that binds triiodothyronine (T3) and acts as an important transcription factor in development, metabolism, and reproduction. The coding gene, THRA, has two major splicing isoforms in mammals, THRA1 and THRA2, which encode THRα1 and THRα1, respectively. The better characterized isoform, THRα1, is a transcriptional stimulator of genes involved in cell metabolism and growth. The less well-characterized isoform, THRα2, lacks the ligand-binding domain (LBD) and may act as an inhibitor of THRα1 activity. Thus, the ratio of THRα1 to THRα2 isoforms is critical for transcriptional regulation in various tissues and during development and may be abnormal in a number of thyroid hormone resistance syndromes. However, the complete characterization of the THRα isoform expression pattern in healthy human tissues, and especially the study of changes in the ratio of THRα1 to THRα2 in cultured patient cells, has been hampered by the lack of suitable tools to detect the isoform-specific expression patterns. Therefore, we developed a plasmid pCMV-THRA-RFP-EGFP splicing detector that allows the visualization and quantification of the differential expression of THRA1 and THRA2 splicing isoforms in living single cells during time-lapse and perturbation experiments. This tool enables experiments to further characterize the role of THRα2 and to perform high-throughput drug screening. Molecules that modify THRA splicing may be developed into drugs for the treatment of thyroid hormone resistance syndromes. Full article

Soliton crystal microcombs, as a new type of Kerr frequency comb, offer advantages such as higher energy conversion efficiency and a simpler generation mechanism compared to those of traditional soliton microcombs. They have a wide range of applications in fields like microwave photonics, ultra-high-speed optical communication, and photonic neural networks. In this review, we discuss the recent developments regarding soliton crystal microcombs and analyze the advantages and disadvantages of generating soliton crystal microcombs utilizing different mechanisms. First, we briefly introduce the numerical model of optical frequency combs. Then, we introduce the generation schemes for soliton crystal microcombs based on various mechanisms, such as utilizing an avoided mode crossing, harmonic modulation, bi-chromatic pumping, and the use of saturable absorbers. Finally, we discuss the progress of research on soliton crystal microcombs in the fields of microwave photonics, optical communication, and photonic neural networks. We also discuss the challenges and perspectives regarding soliton crystal microcombs. Full article

New systems and methods to access the temperature of the melt pool in welding processes have been developed to study phenomena, monitor behaviours, and even be used in closed-loop control strategies. Concerning arc welding processes, the arc radiation might impose a challenge to measure the temperature. However, heat input is the key point for welding quality. This work aims to evaluate the feasibility and detect potentialities of accessing the thermal field from the rear weld pool in the GTAW process by using in-house developed equipment. The original system was conceptualized based on a previous bichromatic method. Experiments were carried out with and without the wire feed addition, and welding parameters were varied to explore its impacts on the temperature measurement. A strategy to select the regions of interest (ROIs) within the weld pool was created, and the mean temperature was calculated and correlated to the weld bead features. This strategy was able to overcome the challenges imposed by the electrode/nozzle reflection and the arc radiation during the welding. The rear weld pool thermal field was shown to be an important source of data to provide hints of the weld bead features. The mean temperature can indicate geometrical changes in the weld bead. Furthermore, the technique has the potential to be used as a promising real-time process monitoring tool. Full article

In the paper we propose a method for characterizing VUV pulse(s) in a bichromatic ionization setup. The scheme is based on s-shell ionization by joint action of circularly polarized fundamental harmonic and linearly polarized second one. The advantage of the proposed approach is the existence of kinematic (geometrical) zeros of partial amplitudes which positions can be extracted with minimal number of theoretical (spectroscopic) assumptions and therefore they may serve as natural reference points in measuring the relative phase and amplitude of the harmonics. In the paper, we investigate a general possible geometry setup with more detailed consideration of the edge cases and present calculation and numerical stimulation for helium ionization as an illustrative example. Full article

Nonlinear interaction between the magnon mode and the mechanical mode in a magnomechanical system is treated analytically where the magnon mode is coherently driven by a bichromatic microwave drive field consisting of a strong pumping field and a weak probe field and that works within a perturbative regime. Using experimentally achievable parameters, we show that the magnonic second-order sideband is generated and can be considerably enhanced by increasing the power of the pumping field. The suppression of the magnonic second-order sideband generation at the resonance point is discussed. Furthermore, the efficiency of magnonic second-order sideband generation can be well controlled by adjusting the applied bias magnetic field strength, which is a particular feature compared to the optical second-order sideband. In addition to offering insights into the magnomechanical nonlinearity, the present results have the potential to pave the way for exploring practical applications for achieving high-precision measurement in magnonics. Full article

An important topic in the field of geometric optimization is finding the largest rectangle separating two different points sets, which has significant applications in circuit design and data science. We consider some extensions of the maximum bichromatic separating rectangle (MBSR) problem. In one of the extensions, the optimal rectangle may include up to k outliers, where k is given as part of the input. This extension and is called MBSR with outliers or MBSR-O. In this paper, we improve the current known time bounds for MBSR-O from $O(k^{7}m \log m+n)$ to $O(k^{3}m+km \log m+n)$ using a clever staircase sweep approach. We also propose another extension, which is named MBSR among circles or MBSR-C and asks for the largest rectangle separating red points from blue unit circles. Our solution to MBSR-C is an $O(m^2+n)$-time algorithm that involves an optimized scanning of all candidate circle arcs for locations of potential optimal solutions. Full article

Many symmetric properties are well-explored in graph theory, especially in graph coloring, such as symmetric graphs defined by the automorphism groups, symmetric drawing of planar graphs, and symmetric functions which are used to count the number of specific colorings of a graph. This paper is devoted to studying the star edge coloring of 1-planar graphs. The star chromatic index ${\chi }_{\mathrm{st}}^{\prime }\left(G\right)$ of a graph G is defined as the smallest k for which the edges of G can be colored by using k colors so that no two adjacent edges get the same color and no bichromatic paths or cycles of length four are produced. A graph G is called 1-planar if it can be drawn in the plane such that each edge crosses at most one other edge. In this paper, we prove that every 1-planar graph G satisfies ${\chi }_{\mathrm{st}}^{\prime }\left(G\right)\le 7.75\Delta +166$; and moreover ${\chi }_{\mathrm{st}}^{\prime }\left(G\right)\le \lfloor 1.5\Delta \rfloor +500$ if G contains no 4-cycles, and ${\chi }_{\mathrm{st}}^{\prime }\left(G\right)\le 2.75\Delta +116$ if G is 3-connected, or optimal, or NIC-planar. Full article

It is well-known that the bound long waves play an important role on beach morphology. The existence of the current will modify the intensity of the waves. To examine the more realistic problem where the current is non-uniform, a third-order analytical solution for bichromatic waves on currents with constant vorticity is derived using a perturbation method. Earlier derivations of theories for interactions between waves and currents have been limited to cases of bichromatic waves on depth-uniform currents and cases of monochromatic waves on linear shear currents. Unlike the derivations of monochromatic waves, the moving-frame method cannot be used in the case of bichromatic waves because there are multiple waves with different celerities, and the flow can in no way be treated as steady-state. Moreover, for shear currents where the flows are rotational, the velocity potential cannot be simply defined. For these reasons, it is difficult to carry out mathematical operations when the dynamic free surface boundary condition is applied. However, with the consideration of the wave part of the fluid motion remaining irrotational, some of the terms in the expanded boundary conditions can be ignored; thus, the derivations can be further processed. As a result, the third-order explicit expressions for the stream function, the velocity potential, and the surface elevation can be solved. The nonlinear dispersion relation is also derived to account for interacting wave components with different frequencies and amplitudes which can be used to solved for wavenumbers of both wave trains. The obtained solutions are verified by reducing to those of previous results for monochromatic waves and uniform currents. Furthermore, the influence of constant vorticity on the wave kinematics is illustrated. A comparison between following/opposing currents is also carried out. Finally, the effects of the shear current on the strength of the bound long waves are also illustrated. Full article

Squeezing light is a critical resource in both fundamental physics and precision measurement. Squeezing light has been generated through optical-parametric amplification inside an optical resonator. However, preparing the squeezing light in an optomechanical system is still a challenge for the thermal noise inevitably coupled to the system. We consider an optically levitated nano-particle in a bichromatic cavity, in which two cavity modes could be excited by the scattering photons of the dual tweezers, respectively. Based on the coherent scattering mechanism, the ultra-strong coupling between the cavity field and the torsional motion of nano-particle could be achieved for the current experimental conditions. With the back-action of the optically levitated nano-particle, the broad single-mode squeezing light can be realized in the bad cavity regime. Even at room temperature, the single-mode light can be squeezed for more than 17 dB, which is far beyond the 3 dB limit. The two-mode squeezing light can also be generated, if the optical tweezers contain two frequencies, one is on the red sideband of the cavity mode, the other is on the blue sideband. The two-mode squeezing can be maximized near the boundary of the system stable regime and is sensitive to both the cavity decay rate and the power of the optical tweezers. Full article

We address dynamics of Bose-Einstein condensates (BECs) loaded into a one-dimensional four-color optical lattice (FOL) potential with commensurate wavelengths and tunable intensities. This configuration lends system-specific symmetry properties. The analysis identifies specific multi-parameter forms of the FOL potential which admits exact solitary-wave solutions. This newly found class of potentials includes more particular species, such as frustrated double-well superlattices, and bichromatic and three-color lattices, which are subject to respective symmetry constraints. Our exact solutions provide options for controllable positioning of density maxima of the localized patterns, and tunable Anderson-like localization in the frustrated potential. A numerical analysis is performed to establish dynamical stability and structural stability of the obtained solutions, which makes them relevant for experimental realization. The newly found solutions offer applications to the design of schemes for quantum simulations and processing quantum information. Full article

A new validation campaign was conducted at the W2 Harold Alfond Ocean Engineering Laboratory at the University of Maine to investigate the hydrodynamic loading on floating offshore wind substructures, with a focus on the low-frequency contributions that tend to drive extreme and fatigue loading in semisubmersible designs. A component-level approach was taken to examine the hydrodynamic loads on individual parts of the semisubmersible in isolation and then in the presence of other members to assess the change in hydrodynamic loading. A variety of wave conditions were investigated, including bichromatic waves, to provide a direct assessment of difference-frequency wave loading. An assessment of the impact of wave uncertainty on the loading was performed, with the goal of enabling validation with this dataset of numerical models with different levels of fidelity. The dataset is openly available for public use and can be downloaded from the U.S. Department of Energy Data Archive and Portal. Full article

Ion–atom interactions are a comparatively recent field of research that has drawn considerable attention due to its applications in areas including quantum chemistry and quantum simulations. In first experiments, atomic ions and neutral atoms have been successfully overlapped by devising hybrid apparatuses combining established trapping methods, Paul traps for ions and optical or magneto-optical traps for neutral atoms, respectively. Since then, the field has seen considerable progress, but the inherent presence of radiofrequency (rf) fields in such hybrid traps was found to have a limiting impact on the achievable collision energies. Recently, it was shown that suitable combinations of optical dipole traps (ODTs) can be used for trapping both atoms and atomic ions alike, allowing to carry out experiments in absence of any rf fields. Here, we show that the expected cooling in such bichromatic traps is highly sensitive to relative position fluctuations between the two optical trapping beams, suggesting that this is the dominant mechanism limiting the currently observed cooling performance. We discuss strategies for mitigating these effects by using optimized setups featuring adapted ODT configurations. This includes proposed schemes that may mitigate three-body losses expected at very low temperatures, allowing to access the quantum dominated regime of interaction. Full article

A fundamental phenomenon of coherent control is investigated theoretically using the example of neon photoionization by the bichromatic field of a free-electron laser. A system exposed to coherent fields with commensurable frequencies loses some symmetry, which manifests itself in the angular distribution and spin polarization of the electron emission. We predict several such effects, for example, the violation of symmetry with respect to the plane perpendicular to the polarization vector of the second harmonic and the appearance of new components of spin polarization. Furthermore, we predict a very efficient control of spin polarization via manipulation of the phase between the harmonics. Experimental observation of these effects is accessible with modern free-electron lasers operating in the extreme ultraviolet wavelength regime. Full article

Current mid-fidelity modeling approaches for floating offshore wind turbines (FOWTs) have been found to underpredict the nonlinear, low-frequency wave excitation and the response of semisubmersible FOWTs. To examine the cause of this underprediction, the OC6 project is using computational fluid dynamics (CFD) tools to investigate the wave loads on the OC5-DeepCwind semisubmersible, with a focus on the nonlinear difference-frequency excitation. This paper focuses on assessing the uncertainty of the CFD predictions from simulations of the semisubmersible in a fixed condition under bichromatic wave loading and on establishing confidence in the results for use in improving mid-fidelity models. The uncertainty for the nonlinear wave excitation is found to be acceptable but larger than that for the wave-frequency excitation, with the spatial discretization error being the dominant contributor. Further, unwanted free waves at the difference frequency have been identified in the CFD solution. A wave-splitting and wave load-correction procedure are presented to remove the contamination from the free waves in the results. A preliminary comparison to second-order potential-flow theory shows that the CFD model predicted significantly higher difference-frequency wave excitations, especially in surge, suggesting that the CFD results can be used to better calibrate the mid-fidelity tools. Full article