Browse Articles

Low-radar cross section wideband circularly polarized patch antennas by controlling scattering and surface wave propagation with a coding metasurface

A new method using a 1-bit coding metasurface to reach a low radar cross section (RCS) for a wideband circularly polarized (CP) patch antenna is proposed. The essence of the technique is to simultaneously control phase cancelation and surface wave propagation with the coding metasurface. The metasurface cell is a simple rectangular patch with a 180° phase difference between x- and y-directions. In terms of radiation performance, owing to the propagated surface waves, two TM10 and TM30 modes are excited and the wideband CP radiation is achieved. In terms of scattering performance, owing to the phase cancelation of the sequential-rotated pattern, the backward RCS of the proposed antenna is reduced for both in-band and out-band frequencies compared to that of the conventional antenna. A prototype operating at C-band is fabricated and measured. Experimental and simulation results are in good agreement. The CP bandwidth (both |S11| < −10 dB and AR < 3 dB) is extended to 10.0%, and the peak gain is enhanced to 8.90 dBi.

Probing water-electrified electrode interfaces: Insights from Au and Pd

The water/electrode interface under an applied bias potential is a challenging out-of-equilibrium phenomenon, which is difficult to accurately model at the atomic scale. In this study, we employ a combined approach of density functional theory and non-equilibrium Green’s function methods to analyze the influence of an external bias on the properties of water adsorbed on Au(111) and Pd(111) metallic electrodes. Our results demonstrate that while both Au and Pd-electrodes induce qualitatively similar structural responses in adsorbed water molecules, the quantitative differences are substantial, driven by the distinct nature of water–metal bonding. Our findings underscore the necessity of quantum-mechanical modeling for accurately describing electrochemical interfaces.

Thermo-responsive jamming by particle shape change

Insights into nitrogen-incorporated nano silicon oxide on the passivation performance of <i>p</i>-type tunneling oxide passivating contact structures

Although n-type tunneling oxide passivating contact (TOPCon) solar cells dominate the mainstream crystalline silicon (c-Si) technologies in the photovoltaic market, p-type TOPCon solar cells also hold great potential to advance TOPCon technology and may achieve efficiencies comparable to heterojunction solar cells in the future due to their unique passivation method. In this study, we investigate a method for introducing nitrogen (N) atoms into the SiOx layer using N2O/NH3 mixture gas, aiming to reduce B diffusion and activation at the SiOx/poly-Si interface and within the c-Si substrate. Our findings indicate that while incorporating N atoms into SiOx layers prepared with the N2O/NH3 gas mixture significantly suppresses B diffusion within the c-Si substrate and reduces B activation at both the SiOx/poly-Si interface and within the c-Si substrate, the passivation performance of p-type TOPCon with N-doped SiOx remains relatively low. In contrast, p-type TOPCon with SiOx prepared using pure N2O demonstrates significantly higher passivation, achieving an implied open-circuit voltage (iVoc) of 723 mV and a low single-sided recombination current density (J0,s) of 9.6 fA/cm2. This disparity is attributed to the presence of N in SiOx, which leads to a thinner SiOx layer, reduced Si4+ content, and increased surface defects, thereby counteracting the beneficial effects of N doping. This study provides comprehensive insights into the impact of N-doped SiOx on the passivation performance of p-type TOPCon, along with the underlying mechanisms, providing valuable insights for enhancing p-type TOPCon passivation.

Deepening bis-(thio)carbohydrazones conformational dynamics and hydrogen bond interactions in a non-protic solvent: DFT, molecular dynamics, NMR, and Raman investigations

Despite the capability of bis-(thio)carbohydrazones to coordinate metals and the remarkable biological properties of the resulting complexes, no general information is known about their individual behavior in solution. This study is focused on two recently synthesized compounds, a bis-thiocarbohydrazone (bis-TCH) and a bis-carbohydrazone (bis-CH) isolated as sodium salts, that have shown chelating properties toward copper(II) and zinc(II) metal ions along with promising cytotoxic activity. In this work, an integrated theoretical–computational, nuclear magnetic resonance (NMR), and vibrational characterization of both bis-TCH and bis-CH anions in a non-protic solvent (dimethylsulfoxide) is presented to better elucidate their properties. Their protonic NMR spectra underline the presence of cis–trans, EE isomers, characterized by a significant conformational freedom at room temperature. The presence of oxygen or sulfur heteroatoms can tune the molecular conformational dynamics driving a different interaction with the solvent, as highlighted by density functional theory calculations and atomistic molecular dynamics simulations. Our results demonstrate that a quantitative agreement with the NMR and Raman signals is achieved only when an explicit solvent description is included. The insights achieved by this study can contribute to a better understanding of the behavior of bis-carbohydrazones and bis-thiocarbohydrazones in solution, a crucial and mandatory step to improve the design of novel, more potent analogs.

Post-modulation of layer-by-layer assemblies coordinated by a catalytic dose of fullerene derivatives without external fields

Zero-group velocity combined-harmonic generation through counter-directional mixing and application for internal damage localization in composites

This paper investigates the generation of zero-group velocity (ZGV) combined-harmonic modes through the interaction of counter-directional mixing of guided waves in carbon fiber reinforced polymer (CFRP) laminated plates. The internal resonance conditions for generating ZGV combined harmonics in transversely isotropic materials are derived in detail through theoretical analysis. The ZGV mode in a [90/45/−45/0]s layered CFRP plate is calculated using the semi-analytical finite element method. Based on this analysis, a primary mode pair is selected for generating the ZGV combined-harmonic mode. The generation of the ZGV combined-harmonic mode is successfully validated via a three-dimensional finite element model simulation, which also reveals the local resonance effect of the generated S1-ZGV combined harmonic. Subsequently, the feasibility of multi-internal damage localization is validated by the use of the generated ZGV combined-harmonic mode. A B-scan approach is implemented by locally generating the ZGV combined-harmonic mode through adjusting the excitation time delay of the primary waves. The results demonstrate that the S1-ZGV combined harmonic exhibits greater sensitivity and effectiveness for accurate localization of internal damage in composites.

Incorporating multiscale methylation effects into nucleosome-resolution chromatin models for simulating mesoscale fibers

Histone modifications play a crucial role in regulating chromatin architecture and gene expression. Here we develop a multiscale model for incorporating methylation in our nucleosome-resolution physics-based chromatin model to investigate the mechanisms by which H3K9 and H3K27 trimethylation (H3K9me3 and H3K27me3) influence chromatin structure and gene regulation. We apply three types of energy terms for this purpose: short-range potentials are derived from all-atom molecular dynamics simulations of wildtype and methylated chromatosomes, which revealed subtle local changes; medium-range potentials are derived by incorporating contacts between HP1 and nucleosomes modified by H3K9me3, to incorporate experimental results of enhanced contacts for short chromatin fibers (12 nucleosomes); for long-range interactions we identify H3K9me3- and H3K27me3-associated contacts based on Hi-C maps with a machine learning approach. These combined multiscale effects can model methylation as a first approximation in our mesoscale chromatin model, and applications to gene systems offer new insights into the epigenetic regulation of genomes mediated by H3K9me3 and H3K27me3.

Copper is essential for cyclin B1-mediated CDK1 activation

Role of ion milling angle in determining conducting and insulating states on SrTiO3 surfaces

SrTiO3 (STO), a promising wide-bandgap semiconductor for high-k capacitors and photocatalysis, requires precise surface control for device fabrication. This study investigates the impact of ion milling on STO’s surface conductivity. We find that ion milling at incident angles below 10° preserves the insulating state, while ion milling at larger angles induces a conducting surface with high electron mobility (5000–11 000 cm²/Vs). This transition is attributed to the milling penetration depth exceeding the STO lattice constant (3.905 Å). Our results provide valuable insights for optimizing STO-based device fabrication, enabling precise control over surface properties while maintaining the desired insulating characteristics.

Enhancing half-integer quadrupolar solid-state NMR signals via steady states: A double frequency sweep-based approach

We introduce a novel signal enhancement technique, termed steadyDFS, for quadrupolar solid-state nuclear magnetic resonance spectroscopy. It can substantially increase the performance of double frequency sweeps (DFSs) for all half-integer quadrupolar spins (I = 3/2, 5/2, 7/2, and 9/2). In steadyDFS, the DFS and readout pulse are repeated multiple times with a repetition time of TR,DFS to generate a steady state that provides substantial sensitivity enhancement. Using a series of simulations, we show that steadyDFS can outperform conventional DFS methods, and enhancements per unit time of ∼5 to 21 can be achieved depending on the value of I. The sensitivity of steadyDFS is robust toward changes in repetition times and quadrupolar relaxation rates of the system. Moreover, steadyDFS is highly modular and can be combined with quadrupolar Carr–Purcell–Meiboom–Gill (QCPMG) detection. Using 39K (I = 3/2), 17O (I = 5/2), and 49Ti (I = 7/2) as representative challenging nuclei, we show that enhancements up to 46× can be realized experimentally via steadyDFS-QCPMG, translating to a 20× enhancement per unit time. We applied steadyDFS-QCPMG to protonated and deprotonated samples, as well as to samples with a diverse range of transverse relaxation times (i.e., T2/T2*), where steadyDFS-QCPMG can provide an enhancement per unit time of at least 7. For samples that are not amendable to QCPMG, we explored the use of steady-state free precession (SSFP). Although SSFP is fundamentally incompatible with steadyDFS, we show that beneficial results can be obtained when DFSs are combined with SSFP in an interruptive manner.

Spatiotemporally resolved transcriptomics reveals the cellular dynamics of human retinal development

Modulation of magnetic phase transition and magnetic anisotropy in CrSe2 monolayer under biaxial strain

The discovery of two-dimensional magnetic materials paves the way for novel research directions and expands the applications of spintronics. In this study, we investigated the electronic structure and magnetic properties of the CrSe2 monolayer under different biaxial strains using first-principles calculations. Our results suggest that the ground state of the CrSe2 monolayer is both antiferromagnetic and metallic, with a Curie temperature of 76 K. Under a 6% tensile biaxial strain, the CrSe2 monolayer transitions from an antiferromagnetic ground state to a ferromagnetic state. Furthermore, the magnetization direction of the magnetic anisotropy energy transitions from the in-plane direction to the out-of-plane direction. Remarkably, the CrSe₂ monolayer exhibits a Curie temperature of 336 K at 12% tensile biaxial strain. Our study advances the understanding of the magnetic properties of the CrSe2 monolayer, highlighting its potential for future nanoelectronic applications.

Influence of topology on rheological properties of polymer ring melts

We investigate with numerical simulations the influence of topology and stiffness on macroscopic rheological properties of polymer melts consisting of unknotted, knotted, or concatenated rings. While melts of flexible, knotted oligomer rings tend to be significantly more viscous than their unknotted counterparts, differences vanish in a low shear rate scenario with increasing degree of polymerization. Melts of catenanes consisting of two rings on the other hand are consistently more viscous than their unconcatenated counterparts. These topology-based differences in rheological properties can be exploited to segregate mixtures of otherwise chemically similar polymers, e.g., in microfluidic devices, which is demonstrated by exposing a blend of flexible knotted and unknotted oligomer rings to channel flow.

Fiber-based angular demultiplexer using nanoprinted periodic structures on single-mode multicore fibers

Abstract Precise analysis of light beams is critical for modern applications, especially in integrated photonics, with traditional methods often struggling with efficient angular demultiplexing in compact environments. Here, we present a novel fiber-based approach that achieves angular demultiplexing through angle-sensitive coupling in nanostructure-enhanced multicore fibers. Our device uses axially symmetric nanoprinted structures to distribute the angular power spectrum of incident light over different fiber cores through higher diffraction orders. By implementing algorithmically optimized nanostructures on a seven-core single-mode fiber facet via 3D nanoprinting, we demonstrate unprecedented in-coupling efficiency over wide incident angle ranges. Our theoretical and experimental results confirm the ability of the device to function as both an angular demultiplexer and a highly efficient remote light collector. The presented approach to remotely collect and analyze light, and the combination of multicore fibers and fiber-based nanostructures, opens new possibilities for high-capacity telecommunications, environmental monitoring, bioanalytical sensing, and integrated photonic applications.

Electromechanical coupling induced multiple excitation mechanisms in conical dielectric elastomer resonators

Resonant actuation of the dielectric elastomer resonators (DERs) allows them to achieve outstanding output performance comparable to biological muscles and facilitates numerous applications of the DERs in robotics. However, the electromechanical coupling mechanism of the DERs introduces complicated nonlinear correlations between the input signals, system states, and excitation forces at resonances, which are overlooked in previous studies. In this paper, we adopt a conical DER (CDER) configuration, and by decomposing the electromechanical coupling term in this nonlinear dynamic system, we reveal that the resonances in this system are excited both externally and parametrically and at two frequencies. The forcing mechanisms include four excitation components: The external excitation components with the frequencies of 1:1 and 2:1 to the actuation frequency (fe_ext1 and fe_ext2, respectively) and parametric excitation components with the frequencies of 1:1 and 2:1 to the actuation frequency (fe_par1 and fe_par2, respectively). Using an energy balance approach, we theoretically investigate the contributions of these four excitation components to the resonances in the CDER. We show that the primary resonance is mainly excited by fe_ext1 and fe_par2, the super-harmonic resonance is mainly excited by fe_ext2, and the subharmonic resonance is excited by fe_par1. We reveal that the strengths of these excitation components are strongly influenced by the out-of-plane deformation of the membrane and the ratios of the voltage components. Power studies suggest that parametric excitation is heavily affected by damping, while the super-harmonic and primary resonances excited by the external excitation components show good robustness against the increasing payload.

Space-local memory in generalized master equations: Reaching the thermodynamic limit for the cost of a small lattice simulation

The exact quantum dynamics of lattice models can be computationally intensive, especially when aiming for large system sizes and extended simulation times necessary to converge transport coefficients. By leveraging finite memory times to access long-time dynamics using only short-time data, generalized master equations can offer a route to simulating the dynamics of lattice problems efficiently. However, such simulations are limited to small lattices whose dynamics exhibit finite-size artifacts that contaminate transport coefficient predictions. To address this problem, we introduce a novel approach that exploits finite memory in both time and space to efficiently predict the many-body dynamics of dissipative lattice problems involving short-range interactions. This advance enables one to leverage the short-time dynamics of small lattices to nonperturbatively and exactly simulate arbitrarily large systems over long times. We demonstrate the strengths of this method by focusing on nonequilibrium polaron relaxation and transport in the dispersive Holstein model, successfully simulating lattice dynamics in one and two dimensions free from finite-size effects, thereby reducing the computational expense of such simulations by multiple orders of magnitude. Our method is broadly applicable and provides an accurate and efficient means to investigate nonequilibrium relaxation with microscopic resolution over mesoscopic length and time scales that are relevant to experiments.

Engineering the reversible redox electrochemistry on cuprous oxide for efficient chloride ion uptake

Modeling glasses from first principles using random structure sampling

We present an approach to approximating static properties of glasses without experimental inputs rooted in the first-principles random structure sampling. In our approach, the glassy system is represented by a collection (composite) of periodic, small-cell (few 10 s of atoms) local minima on the potential energy surface. These are obtained by generating a set of periodic structures with random lattice parameters and random atomic positions, which are then relaxed to their closest local minima on the potential energy surface using the first-principles methods. Using vitreous SiO2 as an example, we illustrate and discuss how well various atomic and electronic structure properties calculated as averages over the set of such local minima reproduce experimental data. The practical benefit of our approach, which can be rigorously thought of as representing an infinitely quickly quenched liquid, is in that it transfers the computational burden to linear scaling and easy to converge averages of properties computed on small-cell structures, rather than simulation cells with 100 s if not 1000 s of atoms while retaining a good overall predictive accuracy. Because of this, it enables the future use of high-cost/high-accuracy electronic structure methods, thereby bringing the modeling of glasses and amorphous phases closer to the state of modeling of crystalline solids.

Line shape parameters of the first pure rotational R lines of CO in helium baths down to a few kelvins

Close coupling calculations of line shape parameters have been performed for the first pure rotational R0(j = 0–4) lines of CO in helium baths at various temperatures. Besides the usual Lorentzian widths and shifts, we provide the complex Dicke parameters as well as the double power law temperature representation of all four parameters. In addition, we study the speed dependence of these parameters. The R0(0) and R0(1) theoretical thermally averaged collisional widths and shifts between 500 and about 15 K are in excellent agreement with the values reported in the literature. Below this temperature range, we confirm the persistent substantial disagreement that exists since 1985 between experimental and theoretical values. We thus focus on this regime, which is important for astrophysical applications, and we discuss various beyond-Voigt effects at low temperatures to try to understand this mismatch. We show that such mechanisms do not allow experimental widths and shifts to be reconciled with those from theory.