Browse Articles

Determination of microwave material properties at cryogenic temperatures

Quantum information processing systems rely on cryogenic microwave electronics, and printed circuit board (PCB) laminates play an essential role, including integrating quantum chips and connecting microwave circuit elements. In this Letter, we report a method for accurately determining the microwave conductivity and complex permittivity of PCB laminates over a wide temperature range, from 4 to 300 K. The use of higher-order resonant modes of a balanced-type circular disk resonator (BCDR) enables broadband measurements ranging from below 5 GHz to above 20 GHz. Furthermore, a temperature-independent determination scheme is achieved by employing a pair of BCDRs and a cryogenic calibration technique. This method is demonstrated by measuring two commercially available PCB laminates. The results indicate that while dielectric loss is monotonically reduced at cryogenic temperatures, the reduction in conductor loss is strongly suppressed by the surface roughness of the copper foil. Additionally, the obtained conductivity as a function of frequency and temperature fits well with the Gradient Model, allowing for the evaluation of the root mean square roughness parameter.

A comparative study of LQU and LQFI in general qubit-qutrit axially symmetric states

Abstract We derive the compact closed forms of local quantum uncertainty (LQU) and local quantum Fisher information (LQFI) for hybrid qubit-qutrit axially symmetric (AS) states. This allows us to study the quantum correlations in detail and present some essentially novel results for spin-(1/2, 1) systems, the Hamiltonian of which contains ten independent types of physically important parameters. As an application of the derived formulas, we study the behavior of these two quantum correlation measures at thermal equilibrium. New features are observed in their behavior that are important for quantum information processing. Specifically, cascades of sudden changes in the behavior of LQU and LQFI are found with a smooth change in temperature or interaction parameters. Interestingly, in some cases, sudden transitions are observed in the behavior of LQU but not in LQFI, and vice versa. Moreover, our compact formulas open a way to apply them to other problems, for instance, when investigating the environmental effects on quantum correlations in open systems.

A phononic crystal waveguide using surface waves below the sound cone

Surface acoustic waves are commonly used in a variety of radio-frequency electrical devices as a result of their operation at high frequencies and robust nature. For devices based on Rayleigh-like plane waves, functionality is based on the fact that the Rayleigh wave mode is confined at the solid–air interface. However, to create advanced functionality through the use of phononic crystal structures, standard cylindrical inclusions have been shown to couple Rayleigh modes to the shear horizontal bulk modes and provide a significant pathway to energy loss. We introduce alternative inclusion shapes with a reduced two-fold symmetry that lowers the speed of the Rayleigh-like surface acoustic wave to below that of the shear horizontal mode. With an eigenfrequency below the sound line, the mode is confined to the surface with limited coupling and loss to the bulk. Based on these inclusions, an acoustic waveguide design is proposed, which demonstrates a strong confinement of wave energy both at the surface and within the waveguide.

Effects of environmental factors on the phenotypic traits and seed element accumulation of wild Elymus nutans in Tibet

Shared-aperture full-duplex Janus meta-lens for asymmetric focusing of electromagnetic waves

Janus metasurfaces have provided a platform for multiplexing diverse electromagnetic (EM) wave functionalities, which are determined by the intrinsic propagation direction of the EM wave. However, most existing approaches only utilize half of the metasurface aperture for each EM functionality. Here, we propose a method that employs receiver–transmitter Janus meta-atom to accomplish high-efficiency transmission and asymmetric phase responses. By fully implementing the direction-duplex strategy through these meta-atoms, we can directly assign asymmetric phase profiles to the Janus meta-lens in order to achieve a direction-selective focusing configuration, thereby effectively improving aperture utilization. Experimental validation is conducted in the microwave region to demonstrate the feasibility of the proposed method, showcasing potential applications of shared-aperture Janus metasurfaces in asymmetric imaging and multichannel information processing.

Dust removal on solar panels of exploration rovers using Chladni patterns

Recent progress on quantum Hall effect in unconventional material systems

The quantum Hall effect (QHE) is an elegant macroscopic manifestation of quantum mechanical behavior on the microscopic scale, and its discovery is a major triumph in condensed matter physics. While QHE has been predominantly observed in two-dimensional electron gas (2DEG) systems, recently, many efforts have been devoted to searching for the QHE in unconventional materials platforms beyond the classical framework to extend the horizon of the QHE. In this Perspective, we highlight recent important experimental discoveries and progress on the QHE material platforms beyond 2DEG platforms, such as three-dimensional QHE, Weyl-orbit-based QHE, and QHE in two-dimensional insulators. In addition, novel phenomena arising from incorporating QHE with other exotic quantum states, such as topological band structures and superconductivity, will be discussed. We also present the emerging field-free version of QHE–quantum anomalous Hall effect on its transport characteristics, working principles as well as potential applications in quantum metrology and quantum computing. With the exploration of these unconventional QHE hosts and the development of the understanding of new physics arising from the interplay between QHE and other physical systems, QHE will continue to play a critical role in both advancing fundamental physics and developing next-generation quantum technologies.

Exploring behavioral determinants of residents’ ecological conservation in rural tourism development

Highly sensitive UV detector based on the transverse Dember effect of 4H-SiC single crystal

In this work, voltage-mode passive ultraviolet (UV) detectors have been designed and fabricated based on the transverse Dember effect of c-axis tilted n-type 4H-SiC single crystals, which may solve the disadvantages of traditional UV detectors with inadequate sensitivity and stability. A sensitivity as high as 96 000 μV/W has been identified in such 4H-SiC detectors via the transverse Dember effect under the illumination of UV light with a wavelength of 365 nm, which significantly exceeds those of traditional UV detectors based on the transverse thermoelectric effect. In addition, the rise time and decay time of 1.0 and 10.2 ms have been determined in these 4H-SiC detectors, respectively, which are much smaller than those of the current-mode detectors. These results may provide an approach to fabricate the high-performance UV detectors with low cost.

Angle-controlled strong and weak coupling in photon molecules

Quantum secure direct communication based on quantum error correction code

Quantum secure direct communication (QSDC) enables the message sender to directly transmit messages to the message receiver through quantum channel without keys. Environmental noise is the main obstacle for QSDC's practicality. For enhancing QSDC's noise robustness, we introduce the quantum error correction (QEC) code into QSDC and propose the QSDC protocol based on the redundancy code. This QSDC protocol correlates atomic state with the electron–photon entangled pairs and transmits photons in quantum channels for two rounds. The parties can construct the remote atomic logical entanglement channel and decode messages with the heralded photonic Bell state measurement (BSM) and single electron measurement. This QSDC protocol is unconditionally secure in theory and has some advantages. First, benefiting from the heralded photonic BSM, it can eliminate the influence from photon transmission loss and has the potential to realize long-distance secure message transmission. Second, taking use of the error correction function of the repetition code, the error rate caused by the decoherence during the second round of photon transmission can be reduced, which can reduce the message error and increase the secret message capacity. Third, the whole protocol is feasible under current experimental condition. Our QSDC protocol can be extended to use other stronger QEC code. It provides a promising method to promote QSDC's practicality in the future.

MLP Enhanced CO2 Emission Prediction Model with LWSSA Nature Inspired Optimization

Abstract Environmental degradation due to the rapid increase in CO₂ emissions is a pressing global challenge, necessitating innovative solutions for accurate prediction and policy development. Machine learning (ML) techniques offer a robust approach to modeling complex relationships between various factors influencing emissions. Furthermore, ML models can learn and interpret the significance of each factor’s contribution to the rise of CO2. This study proposes a novel hybrid framework combining a Multi-Layer Perceptron (MLP) with an enhanced Locally Weighted Salp Swarm Algorithm (LWSSA) to address the limitations of traditional optimization techniques, such as premature convergence and stagnation in locally optimal solutions. The LWSSA improves the standard Salp Swarm Algorithm (SSA) by incorporating a Locally Weighted Mechanism (LWM) and a Mutation Mechanism (MM) for greater exploration and exploitation. The LWSSA-MLP framework achieved a prediction accuracy of 97% and outperformed traditional optimizer-based MLP models across several evaluation metrics. A permutation feature significance analysis identified global trade, coal energy, export levels, urbanization, and natural resources as the most influential factors in CO₂ emissions, offering valuable insights for targeted interventions. The study provides a reliable and scalable framework for CO₂ emission prediction, contributing to actionable strategies for sustainable development and environmental resilience.

The band structure and carrier recombination mechanism of α/β-phase tellurium homojunction investigated by infrared photoluminescence

During the synthesis of tellurium (Te) crystals, the coexistence of multiple crystalline phases (α-Te, β-Te, and γ-Te) with diverse structures commonly occurs, leading to instability and complexity in the performance of Te-based optoelectronic devices. This study employs physical vapor deposition to synthesize Te crystals of various sizes and morphologies, followed by spatially and temperature-dependent evaluation using Raman mapping and infrared photoluminescence (PL) spectroscopy. Spatially resolved results reveal that the size and morphology of Te crystals significantly influence the energy and peak profiles of Raman and PL spectra. Statistical analysis of spatially random sampling indicates the PL peak energies of Te crystals follow a lognormal distribution in terms of their occurrence frequencies, reflecting the complex interplay of multiple factors during crystal growth. This results in the coexistence of α-Te and β-Te phases, forming α/β-Te heterophase homojunction (HPHJ). Meanwhile, temperature-dependent PL results, obtained for the range of 3–290 K, reveal multi-peak competitive behavior in the PL spectra, accompanied by S-shaped shifts in peak energy. These features can be rationally explained by an interface transition-recombination mechanism based on the I-type α/β-Te HPHJ model. It also confirms infrared PL spectroscopy is an effective method for identifying the crystalline phase composition of Te crystals.

Antisense mediated blockade of Dickkopf 1 attenuates tumor survival, metastases and bone damage in experimental osteosarcoma

Realization of p-type MA-based perovskite solar cells based on exposure of the (002) facet

The crystallographic orientation of perovskite crystals significantly influences their photoelectric performance and associated photovoltaic devices. The classic perovskite (MAPbI3) films based on solution processing usually suffer from chaotic orientations. The impact of preferential crystallographic orientation of MAPbI3 thin films on the carrier transport is still far from being well understood. In comparison with the (011) and (111) facets, our density functional theory results revealed that the hole carrier in the (001) facet exhibits superior carrier transport properties. Herein, the highly oriented (001) FAPbI3 could serve as growth templates and promote the (002) orientations of MAPbI3 perovskite. Furthermore, the p-type doping in MAPbI3 was obtained by controlling the amount of MAI. The (002)-dominated MAPbI3 perovskite with p-type characteristics exhibits exceptional carrier transport properties, thereby enhancing device performance.

Assessment of upper respiratory and gut bacterial microbiomes during COVID-19 infection in adults: potential aerodigestive transmission

Defect-mediated electron–phonon coupling in halide double perovskite

Optically active defects often play a crucial role in governing the light emission as well as the electronic properties of materials. Moreover, defect-mediated states in the midgap region can trap electrons, thus opening a path for the recombination of electrons and holes in lower energy states that may require phonons in the process. Considering this, we have probed electron–phonon interaction in halide perovskite systems with the introduction of defects and investigated the thermal effect on this interaction. Here, we report Raman spectroscopic study of the thermal evolution of electron–phonon coupling, which is tunable with the crystal growth conditions, in the halide perovskite systems Cs2AgInCl6 and Cs2NaInCl6. The signature of electron–phonon coupling is observed as a Fano anomaly in the lowest frequency phonon mode (51 cm−1), which evolves with temperature. In addition, we observe a broad band in the photoluminescence (PL) measurements for the defect-mediated systems, which is otherwise absent in defect-free halide perovskite. The simultaneous observation of the Fano anomaly in the Raman spectrum and the emergence of the PL band suggests the defect-mediated midgap states and the consequent existence of electron–phonon coupling in the double perovskite.

Probabilistic nested model selection in pharmacokinetic analysis of DCE-MRI data in animal model of cerebral tumor

Abstract Best current practice in the analysis of dynamic contrast enhanced (DCE)-MRI is to employ a voxel-by-voxel model selection from a hierarchy of nested models. This nested model selection (NMS) assumes that the observed time-trace of contrast-agent (CA) concentration within a voxel, corresponds to a singular physiologically nested model. However, admixtures of different models may exist within a voxel’s CA time-trace. This study introduces an unsupervised feature engineering technique (Kohonen-Self-Organizing-Map (K-SOM)) to estimate the voxel-wise probability of each nested model. Sixty-six immune-compromised-RNU rats were implanted with human U-251 N cancer cells, and DCE-MRI data were acquired from all the rat brains. The time-trace of change in the longitudinal-relaxivity (ΔR 1 ) for all animals’ brain voxels was calculated. DCE-MRI pharmacokinetic (PK) analysis was performed using NMS to estimate three model regions: Model-1: normal vasculature without leakage, Model-2: tumor tissues with leakage without back-flux to the vasculature, Model-3: tumor vessels with leakage and back-flux. Approximately two hundred thirty thousand (229,314) normalized ΔR 1 profiles of animals’ brain voxels along with their NMS results were used to build a K-SOM (topology-size: 8 × 8, with competitive-learning algorithm) and probability map of each model. K -fold nested-cross-validation (NCV, k = 10) was used to evaluate the performance of the K-SOM probabilistic-NMS (PNMS) technique against the NMS technique. The K-SOM PNMS’s estimation for the leaky tumor regions were strongly similar (Dice-Similarity-Coefficient, DSC = 0.774 [CI: 0.731–0.823], and 0.866 [CI: 0.828–0.912] for Models 2 and 3, respectively) to their respective NMS regions. The mean-percent-differences (MPDs, NCV, k = 10) for the estimated permeability parameters by the two techniques were: -28%, + 18%, and + 24%, for v p , K trans , and v e , respectively. The KSOM-PNMS technique produced microvasculature parameters and NMS regions less impacted by the arterial-input-function dispersion effect. This study introduces an unsupervised model-averaging technique (K-SOM) to estimate the contribution of different nested-models in PK analysis and provides a faster estimate of permeability parameters.

Dynamic manipulation of ultrasonic beams by coding Moiré metasurfaces

Dynamic acoustic beam manipulation via tunable acoustic metasurfaces (AMs) has attracted significant attention. However, most current tunable AMs are primarily designed for airborne sound, feature complex structural components, and serve a singular purpose. This study proposes a coding Moiré metasurface (CMM) consisting of two cascaded acoustic coding metasurfaces (ACMs) to dynamically manipulate ultrasonic beams in water. The CMM merges the characteristics of Moiré AMs and coding and can achieve different ultrasonic beam manipulations by rotating the ACM and changing the coding sequence. This is demonstrated by presenting CMMs with stripe and checkerboard coding patterns: the former split an ultrasonic beam into two dynamically omnidirectional scanning beams, while the latter divided it into four sections. Finally, two coding bits are employed to construct the CMM samples: a water unit for bit “0” and a photosensitive resin unit for bit “1.” Experimental results demonstrate that the CMM can dynamically manipulate ultrasonic beams. The proposed CMMs hold substantial potential for acoustic communication and dynamic detection applications.

Mind the leaf anatomy while taking ground truth with portable chlorophyll meters

Abstract A wide range of portable chlorophyll meters are increasingly being used to measure leaf chlorophyll content as an indicator of plant performance, providing reference data for remote sensing studies. We tested the effect of leaf anatomy on the relationship between optical assessments of chlorophyll (Chl) against biochemically determined Chl content as a reference. Optical Chl assessments included measurements taken by four chlorophyll meters: three transmittance-based (SPAD-502, Dualex-4 Scientific, and MultispeQ 2.0), one fluorescence-based (CCM-300), and vegetation indices calculated from the 400–2500 nm leaf reflectance acquired using an ASD FieldSpec and a contact plant probe. Three leaf types with different anatomy were included: dorsiventral laminar leaves, grass leaves, and needles. On laminar leaves, all instruments performed well for chlorophyll content estimation (R2 > 0.80, nRMSE < 15%), regardless of the variation in their specific internal structure (mesomorphic, scleromorphic, or scleromorphic with hypodermis), similarly to the performance of four reflectance indices (R2 > 0.90, nRMSE < 16%). For grasses, the model to predict chlorophyll content across multiple species had low performance with CCM-300 (R2 = 0.45, nRMSE = 11%) and failed for SPAD. For Norway spruce needles, the relation of CCM-300 values to chlorophyll content was also weak (R2 = 0.45, nRMSE = 11%). To improve the accuracy of data used for remote sensing algorithm development, we recommend calibration of chlorophyll meter measurements with biochemical assessments, especially for species with anatomy other than laminar dicot leaves. The take-home message is that portable chlorophyll meters perform well for laminar leaves and grasses with wider leaves, however, their accuracy is limited for conifer needles and narrow grass leaves. Species-specific calibrations are necessary to account for anatomical variations, and adjustments in sampling protocols may be required to improve measurement reliability.