船舶自动识别系统（AIS）VHF接收机的设计

VHF接收机是船载自动识别系统(AIS)的关键部件之一,其性能直接影响到AIS系统自组织组网的优劣、接收船舶的数目多少及所能接收到最远船只的距离远近。本文根据国际海事组织(IMO)有关标准,给出了一种船舶自动识别系统中VHF接收机的设计方案。文中简介了接收机的工作原理,给出了基于MAX2306的VHF接收机的硬件和软件设计。实验测试和实际应用表明该接收机的接收灵敏度、邻信道选择性等都已达到规定的要求,并且该接收机结构简单、性能稳定,易于批量化生产。     

用于提高水泥浆封固能力的树脂体系性能评价

为获得较好的封固效果,室内制备了一种带有特殊亲水基团的环氧树脂,并与相应的固化剂混合制备了树脂体系,分析了该树脂体系的固化温度、热稳定性等物理性能,研究了该树脂体系对水泥浆封固能力的影响,并使用扫描电镜和能谱分析仪研究了树脂水泥浆的微观结构。研究表明,所合成的环氧树脂与相应的固化剂混合后的固化效果好,固化温度在39.9℃至164.6℃之间,在243.9℃以下固化物热稳定性较好。将树脂体系掺入油井水泥浆中,能显著提高水泥石的封固能力。与空白水泥浆相比,含15%树脂体系的水泥浆所形成的水泥石,渗透率由空白组的 0.037×10-3 μm2降至 0.023×10-3 μm2,降低了 37.8%;胶结强度由 1.8 MPa 增至 3.2 MPa,提高了77.8%;弹性模量由9.86 GPa降至4.08 GPa,降低了58.6%。水泥石的微观结构表明,树脂与水泥浆固化后,树脂的固化产物与水化产物混合形成整体,未反应的树脂聚合物颗粒填充在水泥石内部形成柔性结构中心,两种作用共同提高水泥浆封隔能力。     

纺织纤维拉曼光谱定性分析法

针对当前纤维定性鉴别方法存在的不足,采用拉曼光谱分析法定性鉴别.通过对纺织纤维原始拉曼谱图的特性分析,经过光谱预处理得到信噪比更高的标准拉曼谱图,建立了拉曼谱图特征表数据库,实现了纺织纤维的定性鉴别.实验结果表明:拉曼光谱定性分析法可快速定性鉴别纺织纤维,尤其适合于合成纤维及其混纺织物.对环境温湿度无特殊要求,样品无需...     

锡量子点制备及其电催化还原二氧化碳产甲酸性能

锡基材料在自然界含量丰富、价格低廉, 在电催化还原CO₂制液体燃料反应中具有巨大潜力。但是较低的产物选择性和较差的稳定性限制了其应用。本工作制备的锡量子点电催化剂(Sn-QDs), 具有高效、高稳定性和高选择性的电催化还原CO₂产HCOOH活性。Sn-QDs的平均颗粒尺寸仅为2~3 nm, 结晶性良好。小的颗粒尺寸增大了电化学活性面积(ECSA), Sn-QDs的ECSA约为锡颗粒的4.4倍。ECSA增大以及CO₂还原反应动力学加速, 促进了CO₂电化学转化。在-1.0 V (vs RHE)下, Sn-QDs/CN催化剂的HCOOH法拉第效率(FE_HCOOH)达到95%, 并且在宽约0.5 V的电势范围内能够保持在83%以上。此外, Sn-QDs/CN可以在24 h内保持良好的电化学稳定性。     

Tibetan Multi-Dialect Speech and Dialect Identity Recognition

Tibetan language has very limited resource for conventional automatic speech recognition so far. It lacks of enough data, sub-word unit, lexicons and word inventories for some dialects. And speech content recognition and dialect classification have been treated as two independent tasks and modeled respectively in most prior works. But the two tasks are highly correlated. In this paper, we present a multi-task WaveNet model to perform simultaneous Tibetan multi-dialect speech recognition and dialect identification. It avoids processing the pronunciation dictionary and word segmentation for new dialects, while, in the meantime, allows training speech recognition and dialect identification in a single model. The experimental results show our method can simultaneously recognize speech content for different Tibetan dialects and identify the dialect with high accuracy using a unified model. The dialect information used in output for training can improve multi-dialect speech recognition accuracy, and the low-resource dialects got higher speech content recognition rate and dialect classification accuracy by multi-dialect and multi-task recognition model than task-specific models.     

Surface homogenizing heterostructure coatings induced by Ti3C2Tx MXene for enhanced cycle performance of lithium-rich cathode materials

The layered lithium-rich manganese-based cathode material (Li_1.2Mn_0.54Co_0.13Ni_0.13) has the significant advantage of high specific capacity, but this material also suffers serious defects, including severe capacity attenuation and voltage attenuation during the cycle. At present, most researchers have been working to optimize the cycle performance of lithium-rich materials. In this work, we propose a surface homogenizing heterostructure coating induced by MXene modification to reduce capacity reduction and voltage decay. It can be found that the initial Coulombic efficiency (ICE) increases from 77.2% for the bare electrode Li_1.2Mn_0.54Co_0.13Ni_0.13 (LMO) to 85.5% for 1.4 wt% MXene (Ti₃C₂T_x, T_x represents the surface terminations: OH, O, F) modified lithium-rich (TO2). Furthermore, the discharge specific capacity of the electrode at 5 C rate increased from 160.7 mAh g⁻¹ for LMO to 200.6 mAh g⁻¹ for TO2. More prominently, the outstanding cycle stability with capacity retention rate is 82.1% for TO2 after 200 cycles, while only 64.7% for LMO, and the average discharge voltage dropped from 0.788 to 0.468 V. In addition, the mechanism for improving the electrochemical performance is systematically studied.     

Damage formation and suppression in rotary ultrasonic machining of hard and brittle materials: A critical review

Rotary ultrasonic machining (RUM) combines diamond grinding with small-amplitude tool vibration, to improve machining processes of hard and brittle materials. It has been successfully applied to the machining of a number of brittle materials from optical glasses to advanced ceramics as well as ceramic matrix composites. The emphasis of this literature review was on formation mechanism and suppression methods of machining induced damages that truly limit RUM machining efficiency improvement of brittle materials. In this review paper, material removal mechanism and cutting force modeling of RUM of brittle materials were presented, as well as all corresponding roles in the damage formation process. The critical processing capacity of RUM machine tools was described, which guarantees the RUM effectiveness and consequently constitutes the boundary condition of processing parameters determination. Formation mechanisms of edge chipping, tearing defects, subsurface damages, and their interactive effects were summarized. Advances in damage suppression methods were also described, including optimization of processing parameters, tool design of low damage, and other methods such as rotary ultrasonic elliptical machining.     

Metal–Organic Frameworks and Their Derived Materials: Emerging Catalysts for a Sulfate Radicals‐Based Advanced Oxidation Process in Water Purification

With the ever‐growing environmental issues, sulfate radical (SO₄^??)‐based advanced oxidation processes (SR‐AOPs) have been attracting widespread attention due to their high selectivity and oxidative potential in water purification. Among various methods generating SO₄^??, employing heterogeneous catalysts for activation of peroxymonosulfate or persulfate has been demonstrated as an effective strategy. Therefore, the future advances of SR‐AOPs depend on the development of adequate catalysts with high activity and stability. Metal–organic frameworks (MOFs) with large surface area, ultrahigh porosity, and diversity of material design have been extensively used in heterogeneous catalysts, and more recently, enormous effort has been made to utilize MOFs‐based materials for SR‐AOPs applications. In this work, the state‐of‐the‐art research on pristine MOFs, MOFs composites, and their derivatives, such as oxides, metal/carbon hybrids, and carbon materials for SR‐AOPs, is summarized. The mechanisms, including radical and nonradical pathways, are also detailed in the discussion. This work will hopefully promote the future development of MOFs‐based materials toward SR‐AOPs applications.     

Mesoporous Silica Thin Membranes with Large Vertical Mesochannels for Nanosize‐Based Separation

Membrane separation technologies are of great interest in industrial processes such as water purification, gas separation, and materials synthesis. However, commercial filtration membranes have broad pore size distributions, leading to poor size cutoff properties. In this work, mesoporous silica thin membranes with uniform and large vertical mesochannels are synthesized via a simple biphase stratification growth method, which possess an intact structure over centimeter size, ultrathin thickness (≤50 nm), high surface areas (up to 1420 m² g^?1), and tunable pore sizes from ≈2.8 to 11.8 nm by adjusting the micelle parameters. The nanofilter devices based on the free‐standing mesoporous silica thin membranes show excellent performances in separating differently sized gold nanoparticles (>91.8%) and proteins (>93.1%) due to the uniform pore channels. This work paves a promising way to develop new membranes with well‐defined pore diameters for highly efficient nanosize‐based separation at the macroscale.