Search Results (658)

The systematic design of ruthenium-based electrocatalysts for the hydrogen evolution reaction (HER) is crucial for sustainable hydrogen production via electrocatalytic water splitting in an alkaline medium. However, the mismatch between water dissociation and hydrogen adsorption kinetics limits its HER activity. Herein, we present a phase engineering-modulated strategy to develop an ultrasmall ZnRu bimetallic metal–organic framework electrocatalyst (ZnRu₃₀-ZIF) for catalyzing alkaline HER. Experimental results and density functional theory calculations indicate that the incorporation of Ru atoms modifies the crystal structure of the ZIF-8 phase, resulting in enlarged facet spacing and smaller nanocrystals (45 ± 3 nm). This optimization of the crystal structure regulates the electronic properties of the ZnRu₃₀-ZIF, forming a higher d-band center (−5.91 eV), which reduces the water dissociation energy (0.19 eV) and facilitates hydrogen desorption (ΔG_H* = 1.09 eV). The prepared ZnRu₃₀-ZIF exhibits a low overpotential of 48 mV at 10 mA cm⁻² and an excellent mass activity of 2.9 A mg_Ru⁻¹ at 0.1 V (vs. RHE). This work establishes a phase-engineering strategy for the preparation of high-performance Ru-based MOF electrocatalysts for HER. Full article

A frequency-reconfigurable MIMO antenna with high gain, low mutual coupling and highly suppressed side lobe level (SLL) for applications in 24 GHz ISM band sensing and automotive radar systems was designed, modeled, and simulated. The reconfigurability feature was modeled with the implementation of a varactor diode in the model to alter the frequency in a wide band around 24 GHz. The design features 2- and 4-port MIMO antenna each comprising a 1 × 8 microstrip patch array. At the core of achieving both a high gain of 16 dBi and high isolation of 38.4 dB at a resonance frequency of 24.120 GHz lies the integration of a metamaterial absorber, comprising an optimized split-ring unit cell to effectively mitigate interference among the MIMO elements. Noteworthy impedance bandwidths of the sensor antenna span from 23.8 to 24.3 GHz, catering to diverse frequency requirements. The proposed sensor antenna feature a half-power beamwidth of 74° in the E-plane and 11° in the H-plane and an SLL of −24 dB at 24.120 GHz showing its robust performance characteristics across multiple operational dimensions. Full article

We propose herein a metamaterial (MM) dual-band THz sensor for various biomedical sensing applications. An MM is a material engineered to have a particular property that is rarely observed in naturally occurring materials with an aperiodic subwavelength arrangement. MM properties across a wide range of frequencies, like high sensitivity and quality factors, remain challenging to obtain. MM-based sensors are useful for the in vitro, non-destructive testing (NDT) of samples. The challenge lies in designing a narrow band resonator such that higher sensitivities can be achieved, which in turn allow for the sensing of ultra-low quantities. We propose a compact structure, consisting of a basic single-square split ring resonator (SRR) with an integrated inverted Z-shaped unit cell. The projected structure provides dual-band frequencies resonating at 0.75 THz and 1.01 THz with unity absorption at resonant peaks. The proposed structure exhibits a narrow bandwidth of 0.022 THz and 0.036 THz at resonances. The resonant frequency exhibits a shift in response to variations in the refractive index of the surrounding medium. This enables the detection of various biomolecules, including cancer cells, glucose, HIV-1, and M13 viruses. The refractive index varies between 1.35 and 1.40. Furthermore, the sensor is characterized by its performance, with an average sensitivity of 2.075 THz and a quality factor of 24.35, making it suitable for various biomedical sensing applications. Full article

Semiconductor polymeric graphitic carbon nitride (g-C₃N₄) photocatalysts have garnered significant and rapidly increasing interest in the realm of visible light-driven hydrogen evolution reactions. This interest stems from their straightforward synthesis, ease of functionalization, appealing electronic band structure, high physicochemical and thermal stability, and robust photocatalytic activity. This review starts with the basic principle of photocatalysis and the development history, synthetic strategy, and structural properties of g-C₃N₄ materials, followed by the rational design and engineering of g-C₃N₄ from the perspectives of nano-morphological control and electronic band tailoring. Some representative results, including experimental and theoretical calculations, are listed to show the advantages of optimizing the above two characteristics for performance improvement in photocatalytic hydrogen evolution from water splitting. The existing opportunities and challenges of g-C₃N₄ photocatalysts are outlined to illuminate the developmental trajectory of this field. This paper provides guidance for the preparation of g-C₃N₄ and to better understand the current state of the art for future research directions. Full article

We propose an observation system based on the Lagrange L1 point of the Earth–Moon system to observe solar spectral radiation reflected from the Earth, enabling continuous hyperspectral observation of the Earth’s hemisphere. The system can observe the solar spectral radiation reflected by the Moon, with its data applicable to on-orbit spectral radiation calibration. In this paper, the spectral irradiance at the entrance pupil of the Earth spectral radiation observation system (ESROS) is analyzed, and the optical design of the ESROS is introduced. An off-axis two-mirror telescope system, a coupling system of a microlens array and a fiber bundle, and an optical splitting system based on concave grating are used to achieve the full field of view hyperspectral splitting and miniaturization of the instrument. Finally, the stray radiation suppression of the instrument is introduced. The results show that the spectral resolution of the system is better than 5 nm in the 380–1000 nm band, and the spectral resolution is better than 10 nm in the 1000–1700 nm band. When observing the Earth, the signal-to-noise ratio is greater than 200. The external stray radiation suppression reaches the order of 10⁻⁹. The ESROS will provide crucial data support for researching global energy balance, climate change, and the spectral characteristics of exoplanets, facilitating planetary science and the exploration of extraterrestrial life. Full article

Silicocarnotite, Ca₅[(PO₄)(SiO₄)](PO₄), was first described from slag over 140 years ago. In 2013, it was officially recognised as a mineral after being discovered in the larnite–gehlenite hornfels of the pyrometamorphic Hatrurim Complex. This paper describes the composition and structure of V-bearing silicocarnotite, crystals of which were found in a thin paralava vein cutting through the gehlenite hornfels. A network of thin paralava veins a few centimetres thick is widespread in the gehlenite hornfels of the Hatrurim Basin, Negev Desert, Israel. These veins, typically coarse crystalline rock and traditionally referred to as paralava, have a symmetrical structure and do not contain glass. Silicocarnotite in the paralava, whose primary rock-forming minerals are gehlenite, flamite, Ti-bearing andradite, rankinite and pseudowollastonite, was a relatively late-stage high-temperature mineral, crystallising at temperatures above 1100 °C. It formed from the reaction of a Si-rich residual melt with pre-existing fluorapatite. A single-crystal structural study of silicocarnotite (Pnma, a = 6.72970(12) Å, b = 15.5109(3) Å, c = 10.1147(2) Å) suggests that the phenomenon of Ca1 position splitting observed in this mineral is most likely related to the partial ordering of Si and P in the T2O₄ tetrahedrons. Raman studies of silicocarnotite with varying vanadium content have shown that phases with V₂O₅ content of 3–5 wt.% exhibit additional bands at approximately 864 cm⁻¹, corresponding to vibrations of ν₁(VO₄)³⁻. Full article

Among the reported photocatalysts, ZnIn₂S₄ has garnered significant research interest due to its advantageous layered structure and appropriate band gap. However, achieving rational design and effective interfacial regulation in heterojunctions remains challenging. In this study, we designed two novel heterojunctions: SrTiO₃@ZnIn₂S₄ and SrCrO₃@ZnIn₂S₄. The photocatalytic hydrogen evolution performance of prepared heterojunctions was systematically investigated under different single-wavelength light sources. Without a cocatalyst, the optimized hydrogen evolution efficiency of SrTiO₃@ZnIn₂S₄ and SrCrO₃@ZnIn₂S₄ reached 3.27 and 4.6 mmol g⁻¹. The enhanced photocatalytic performance can be attributed to the formation of a type-II heterojunction, which improves light absorption capabilities and promotes the separation and transfer of photoinduced carriers. This study provides valuable insights into the strategic construction of heterojunctions for photocatalytic water splitting. Full article

Accurate crop type mapping using satellite imagery is crucial for food security, yet accurately distinguishing between crops with similar spectral signatures is challenging. This study assessed the performance of Sentinel-2 (S2) time series (spectral bands and vegetation indices), Sentinel-1 (S1) time series (backscattering coefficients and polarimetric parameters), alongside phenological features derived from both S1 and S2 time series (harmonic coefficients and median features), for classifying sunflower, soybean, and maize. Random Forest (RF), Multi-Layer Perceptron (MLP), and XGBoost classifiers were applied across various dataset configurations and train-test splits over two study sites and years in France. Additionally, the InceptionTime classifier, specifically designed for time series data, was tested exclusively with time series datasets to compare its performance against the three general machine learning algorithms (RF, XGBoost, and MLP). The results showed that XGBoost outperformed RF and MLP in classifying the three crops. The optimal dataset for mapping all three crops combined S1 backscattering coefficients with S2 vegetation indices, with comparable results between phenological features and time series data (mean F1 scores of 89.9% for sunflower, 76.6% for soybean, and 91.1% for maize). However, when using individual satellite sensors, S1 phenological features and time series outperformed S2 for sunflower, while S2 was superior for soybean and maize. Both phenological features and time series data produced close mean F1 scores across spatial, temporal, and spatiotemporal transfer scenarios, though median features dataset was the best choice for spatiotemporal transfer. Polarimetric S1 data did not yield effective results. The InceptionTime classifier further improved classification accuracy over XGBoost for all crops, with the degree of improvement varying by crop and dataset (the highest mean F1 scores of 90.6% for sunflower, 86.0% for soybean, and 93.5% for maize). Full article

This study examined the effects of heat treatment on the microstructure and dynamic deformation characteristics of AA2519 aluminum alloy in T4, T6, and T8 tempers under high strain rates of 1000–4000 s⁻¹. A Split Hopkinson pressure bar (SHPB) was utilized to characterize the mechanical response, and microstructural analysis was performed to examine the material’s microstructure. The findings indicated varied deformation across all three temper conditions. The dynamic behavior of each temper is influenced by its strength properties, which are determined by the aging type and the subsequent transformation of strengthening precipitates, along with the initial microstructure. At a strain rate of 1500 s⁻¹, AA2519-T6 demonstrated a peak dynamic yield strength of 509 MPa and a flow stress of 667 MPa. These values are comparable to those recorded for AA2519-T8 at a strain rate of 3500 s⁻¹. AA2519-T4 exhibited the lowest strength and flow stress characteristics. The T6 temper demonstrated initial stress collapse, dynamic strain aging, and an increased tendency for shear band formation and fracture within the defined strain rate range. The strain rates all showed similar trends in terms of strain hardening rate. The damage evolution of the alloy primarily involved the nucleation, shearing, and cracking of dispersoid particles. Full article

Outlined is a proposal designed to culminate in the foundry fabrication of arrays of singly addressable quantum dot sources deterministically emitting single pairs of energy-time entangled photons at C-band wavelengths, each pair having negligible spin-orbit fine structure splitting, each pair being channeled into single mode pig-tail optical fibers. Entangled photons carry quantum state information among distributed quantum servers via I/O ports having two functions: the unconditionally secure distribution of decryption keys to decrypt publicly distributed, encrypted classical bit streams as input to generate corresponding qubit excitations and to convert a stream of quantum nondemolition measurements of qubit states into a classical bit stream. Outlined are key steps necessary to fabricate arrays of on-demand quantum dot sources of entangled photon pairs; the principles are (1) foundry fabrication of arrays of isolated quantum dots, (2) generation of localized sub-surface shear strain in a semiconductor stack, (3) a cryogenic anvil cell, (4) channeling entangled photons into single-mode optical fibers, (5) unconditionally secure decryption key distribution over the fiber network, (6) resonant excitation of a Josephson tunnel junction qubits from classical bits, and (7) conversion of quantum nondemolition measurements of qubit states into a classical bit. Full article

This study explores the enhancement of α-Fe₂O₃ (hematite) nanorod arrays for photoelec-trochemical applications by constructing a Cu₂ZnSnS₄ (CZTS) heterojunction. While α-Fe₂O₃ offers good stability, a low cost, and environmental benefits, its efficiency is limited by slow oxygen evolution kinetics, high carrier recombination rates, and low conductivity. By introducing CZTS, a material with strong light absorption and charge transport properties, we enhance the separation of photogenerated charge carriers, reduce charge transfer resistance, and increase the carrier concentration, thereby boosting the overall photoelectrochemical performance. The experimental results show that a modified FC-15 photoanode achieves a photocurrent density of 3.40 mA/cm² at 1.60 V vs. RHE, a substantial increase compared to 0.40 mA/cm² for unmodified α-Fe₂O₃. Band gap analysis reveals a reduced band gap in the FC-15 material, enhancing light absorption and boosting the photoelectrocatalytic performance. In photoelectrochemical water-splitting tests, the FC-15 photoanode achieves a hydrogen production rate of 41.6 μmol/cm²/h, which is significantly improved over the unmodified sample at 5.64 μmol/cm²/h. These findings indicate that the CZTS/α-Fe₂O₃ heterojunction effectively promotes charge separation, enhances charge transport, and improves light absorption, substantially increasing photocatalytic efficiency. This heterojunction approach offers new insights and technical strategies for developing photocatalytic materials with potential applications in renewable energy. Full article

To enhance the anti-interference capabilities and increase flexibility in frequency allocation between the lower and upper sidebands of the navigation signal, we introduce frequency-hopping binary offset carrier modulation with independent frequency-hopping patterns in lower and upper sidebands (IFH-BOC). This novel modulation is classified as a constant-envelope multiplexing (CEM) method, with independent frequency-hopping patterns for the lower and upper sidebands, in contrast with frequency-hopping binary offset carrier (FH-BOC) and binary offset carrier (BOC) modulations, which share the same patterns. IFH-BOC represents a generalized modulation that incorporates FH-BOC and BOC, thus retaining their advantages while introducing new characteristics, such as independent frequency-hopping pattern design and flexible spectral splitting. The results indicate that IFH-BOC maintains the same time–frequency characteristics and measurement accuracy as FH-BOC when using identical modulation parameters, yet it demonstrates superior anti-interference performance due to its varied frequency-hopping patterns. Furthermore, IFH-BOC provides enhanced flexibility in spectral splitting compared with BOC modulation, potentially allowing for increased availability of L-band frequencies for satellite navigation. With these benefits, IFH-BOC is poised to be a promising modulation for the signal design of next-generation global navigation satellite systems. Full article

Two new 2p–3d complexes, (Et₃NH)[ML(hfac)₂], have been obtained using the nitronyl-nitroxide radical (HL) derived from 2-hydroxy-3-methoxy-5-nitrobenzaldehyde (M = Mn 1; Co 2). The two compounds are isomorphous and their structures consist of anionic mononuclear species, [M(hfac)₂L]⁻, M = Mn 1; Co 2, and triethylammonium cations, Et₃NH⁺. The metal ions adopt an octahedral geometry, being coordinated by phenoxido and aminoxyl oxygen atoms from the ligand and four oxygen atoms from the hexafluoroacetylacetonato (hfac⁻) ligand. The cryomagnetic behaviors of the two compounds reveal relatively strong antiferromagnetic M(II)-Rad interactions (J_MnRad = −191 cm⁻¹, J_CoRad = −166 cm⁻¹ with H = −JS_MS_Rad). The EPR spectra (X- and Q-band) of compound 1 below 70 K show the characteristical features of a S = 2 spin system with zero field splitting terms of D = 0.26 cm⁻¹ and E = 0.031 cm⁻¹. Full article

Research on the production of field crops in semi-arid regions mainly focuses on irrigation and climate change adaptation because these are emphasized as the practices determining yields of field crops in these regions. The need to evolve research in this direction is important because general crop production systems in all regions can adopt the findings from this kind of research during unforeseen drought conditions. Research on fertilizers is usually treated as a secondary factor or neglected despite it being an important practice for crops growing in semi-arid regions. Fertilization affects parameters that are responsible for metabolism, physiology, morphology, and subsequent crop yields under drought conditions. This literature review focused on dual-yield crops’ response to fertilization and the potential for researchers to employ these responses for the improvement of cultivations and yields in semi-arid regions. These findings indicated that the application of various nitrogen (N), phosphorus (P), or potassium (K) fertilizers is common and based on broadcasting and banding techniques. The split application of N, P, and K fertilizers is mostly employed to adjust the metabolism, physiology, and morphology of crops at different growth stages so that the crops can be exposed to water shortages. These adjustments can be used to increase or decrease the water use efficiency of the crops, which is highly associated with biological and economic yields. Research on micro-elements in dual-yield crops is currently very limited. Multidimensional future research based on the effects of micro-elements on the metabolism, physiology, and morphology of dual-yield crops is recommended. This research must be conducted with the aim of enhancing water use efficiency. Full article

A new dual-band low-noise amplifier (LNA) operating at L1/E1 1.575 GHz and L5/E5 1.192 GHz center frequencies for global navigation satellite system receivers is proposed. A doubled common-source amplifier architecture is used with a single input, shared gate inductor, and two outputs to split the RF signal into separate RX channels. The main advantage of the proposed circuit is compatibility with widespread multi-band antennas with single RF connectors dedicated to high-precision applications, as well as the possibility to use cheap SAW filters with small footprints to build low-cost, highly accurate GNSS receiver modules. The input and both outputs are well matched to 50 Ω impedance. The LNA is designed with a 110 nm CMOS process, consuming 6.13 mA current from a 1.5 V supply. The measured noise figures and voltage gains of the dual-band LNA are, respectively, NF1/NF5 = 3.23/3.5 dB and G1/G5 = 21.22/18.2 dB in the band of interest for each channel. The measured impedance matching at the input (S11) and output (S22) of the dual-band low-frequency amplifier is as follows: S11_L1 = −23.89, S11_L5 = −8.42, S22_L1 = −12.65, S22_L5 = −15.08. The one-decibel compression points are L1 band PdB1 = −37.71 dBm and L5 band PdB5 = −34.72 dBm, respectively. Full article