Charge Variations in Cuprate Superconductors from Nuclear Magnetic Resonance

Charge inhomogeneities in the cuprates were reported early on and have been in the focus of much research recently. Nuclear magnetic resonance (NMR) is very sensitive to local charge symmetry through the electric quadrupole interaction that must detect any static charge density variation. Recent experiments in high magnetic fields that seem to induce charge density waves in some systems have rekindled the interest in static inhomogeneities. It has long been known that excessive NMR linewidths can be observed in all cuprates, but with the exception of a few materials. However, the relation of the quadrupolar linewidths with respect to variations of the charge density in the cuprates is not understood. Here, we investigate YBa₂Cu₃O₇ and we find even in a moderate magnetic field that below about 200 K, i.e., well above T _c, a temperature dependent NMR linewidth appears that must be related to incipient static charge density variations. We argue that this establishes field induced charge density variation as a more general phenomenon in the cuprates. In view of the very recent understanding of the relation between the hole distribution in the CuO₂ plane and T _c, it is argued that charge density variations are ubiquitous, but appear not related to the maximum T _c.     

SQUID-Detected Magnetic Resonance Imaging in Microtesla Magnetic Fields

We describe studies of nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) of liquid samples at room temperature in microtesla magnetic fields. The nuclear spins are prepolarized in a strong transient field. The magnetic signals generated by the precessing spins, which range in frequency from tens of Hz to several kHz, are detected by a low-transition temperature dc SQUID (Superconducting QUantum Interference Device) coupled to an untuned, superconducting flux transformer configured as an axial gradiometer. The combination of prepolarization and frequency-independent detector sensitivity results in a high signal-to-noise ratio and high spectral resolution (～1 Hz) even in grossly inhomogeneous magnetic fields. In the NMR experiments, the high spectral resolution enables us to detect the 10-Hz splitting of the spectrum of protons due to their scalar coupling to a ³¹P nucleus. Furthermore, the broadband detection scheme combined with a non-resonant field-reversal spin echo allows the simultaneous observation of signals from protons and ³¹P nuclei, even though their NMR resonance frequencies differ by a factor of 2.5. We extend our methodology to MRI in microtesla fields, where the high spectral resolution translates into high spatial resolution. We demonstrate two-dimensional images of a mineral oil phantom and slices of peppers, with a spatial resolution of about 1 mm. We also image an intact pepper using slice selection, again with 1-mm resolution. In further experiments we demonstrate T₁-contrast imaging of a water phantom, some parts of which were doped with a paramagnetic salt to reduce the longitudinal relaxation time T₁. Possible applications of this MRI technique include screening for tumors and integration with existing multichannel SQUID systems for brain imaging.     

Residual U-Network for Breast Tumor Segmentation from Magnetic Resonance Images

Breast cancer positions as the most well-known threat and the main source of malignant growth-related morbidity and mortality throughout the world. It is apical of all new cancer incidences analyzed among females. Two features substantially influence the classification accuracy of malignancy and benignity in automated cancer diagnostics. These are the precision of tumor segmentation and appropriateness of extracted attributes required for the diagnosis. In this research, the authors have proposed a ResU-Net (Residual U-Network) model for breast tumor segmentation. The proposed methodology renders augmented, and precise identification of tumor regions and produces accurate breast tumor segmentation in contrast-enhanced MR images. Furthermore, the proposed framework also encompasses the residual network technique, which subsequently enhances the performance and displays the improved training process. Over and above, the performance of ResU-Net has experimentally been analyzed with conventional U-Net, FCN8, FCN32. Algorithm performance is evaluated in the form of dice coefficient and MIoU (Mean Intersection of Union), accuracy, loss, sensitivity, specificity, F1score. Experimental results show that ResU-Net achieved validation accuracy & dice coefficient value of 73.22% & 85.32% respectively on the Rider Breast MRI dataset and outperformed as compared to the other algorithms used in experimentation.     

磁共振成像的3D头面部模型的标准化处理

通过磁共振成像技术获取人体头部的系列二维图像,分别提取其边界坐标数据,并采用傅里叶级数拟合各层的外形轮廓,建立了一种分层描述的3D头部参数化模型。然后根据人类面部主要特征定义了若干特征层,并基于面部特征相匹配的原则,对多个样本进行了平均处理,构造出3D标准头面部模型,能够反映特定人群的综合特点。作为实例,用558个样本计算构造了圆高标准头型,可作为头面部装备设计的依据。     

Magnetic Resonance Force Microscopy of a Permalloy Microstrip Array

The ferromagnetic resonance in an array of permalloy microstrips 3000 × 500 × 30 nm in size ordered on a rectangular grid 3.5 × 6 μm in size has been investigated by magnetic resonance force microscopy. The dependences of magnetic resonance force microscopy spectra of a sample on the probe–sample distance are analyzed. The possibility of detection of a ferromagnetic resonance spectrum of a single microstrip is demonstrated.     

Nuclear Magnetic Resonance and the BCS Theory

The author describes the inspiration for the experiment by Hebel and Slichter to measure the nuclear spin–lattice relaxation time in superconductors, the design considerations for the experiment, the surprising experimental results, their theoretical treatment using the Bardeen-Cooper–Schrieffer theory, and how comparing the nuclear relaxation results with those for ultrasound absorption confirmed the central idea of the BCS theory, the BCS pair wave function. An erratum to this article can be found at     

Features of a Silver-Beam Magnetic Resonance Apparatus as a Frequency Standard

Silver has two stable isotopes Ag107 and Ag109 with nearly equal populations (51.35 percent and 48.65 percent). A microwave magnetic resonance apparatus employing a silver beam and simultaneous magnetic resonance of both isotopes was built and a so-called superposition line was measured. The possibility of using such an apparatus as a frequency standard is discussed.     

地域文化视角下国内城市家具研究探析

目的 系统呈现并分析我国近23年来地域文化视角下城市家具研究进展。方法 以中国知网（CNKI）全文数据库收录的2000-2023年度地域文化和城市家具研究文献为数据来源,采用文献计量方法,运用COOC软件对城市家具研究文献进行计量分析与可视化呈现。结果 结合文献分析发文特点及时间分布、研究热点和知识演进脉络。结论 该主题下总体发文量呈现逐年稳定增长的趋势,但逐年所占研究比重呈下降趋势;从宏观、中观、微观三个层面提出既有研究关注的主要内容;传统城市家具的功能将会受智能技术大热背景的影响迎来大量创新与植入;未来研究的趋势将会在城市家具的功能智能性、信息集成性,以及对心理的正面导向性方面提高研究投入,还将涉及人文关怀、可持续性、交互性等多重维度的研究。     

区域视角下的包装文化创意产业竞争力初探

利用Porter的钻石理论模型作为分析包装文化创意产业竞争力的理论基础,并以云南发展现状为例,分析了包装文化创意产业对区域经济增长、相关产业成长和城市竞争力水平提升的重大影响;依据国内外文化创意产业竞争力的研究成果,提出从推动创意产业同传统产业融合互动协同发展、完善产业链条、优化产业发展环境、拓宽投融资渠道、加快园区集聚发展、构筑人才高地等方面推动该产业做大做强,打造具有核心竞争力的包装文化创意产业集群。     

磁共振成像系统图像均匀性的检测

医用磁共振成像(MRI)系统是大型医用影像诊断设备,如何对磁共振影像进行评价,图像均匀性是一项重要指标.本文根据医用磁共振成像(MRI)系统的技术特性,参考国际标准和国家标准,验证、推荐了一种图像均匀性检测方法,该方法科学性、适用性强,可作为计量检测、医院质量控制的技术依据.     

基于区域视角的单位内部安全防范标准研制探讨

本文介绍了区域性单位内部安全防范标准的研究背景。以广州市为例,探讨了基于区域视角的单位内部安全防范标准边界和概念内涵,分析标准研制过程的重点和难点,提出了区域性单位内部安全防范标准的基本框架和主要内容。     

人性化视角下的疫情防护用品设计

2019年12月,湖北省武汉市发生了新型冠状病毒肺炎疫情,随着疫情的蔓延,全国都进入了紧急防护阶段。同时,各医院医生护士也投入到紧张的疫情防护工作中。而在此期间,医用防护用品也暴露出了许多问题。为了改良当前疫情防护用品设计,使疫情防护产品更人性化,提高医护人员使用时的舒适性、安全性和有效性,在分析使用者的行为特征以及当前疫情防护用品的设计痛点后,从人机工程、CMF考虑,产品功能、造型设计、产品安全、用户心理等方面进行探讨,得到了从人性化视角考虑的疫情防护用品设计的指导措施。该设计研究可为人性化疫情医用防护产品设计提供理论依据和应用参考。     

科学知识图谱视角下国际绿色包装科研中的合作性分析

深度剖析国际期刊刊载的与绿色包装相关的文献,探讨科研合作在团队中的重要性,追踪绿色包装的研究动态,为绿色包装领域的科研人员提供一定理论参考。对Web of Science核心合集2007—2015年收录的1 252篇以"green package"或"green packaging"为关键词的文献进行梳理和分析;利用Citespace Ⅲ软件,挖掘国际绿色包装领域的核心作者、研究机构、国家地区之间的合作关系,并对关键点进行详尽阐述。研究结果表明:在国际绿色包装研究中文献合著率维持在较高水平;高产作者合著团队众多,形成了比较稳定的合著研究结构;大部分具有重要学术影响力的文献合著人数为2以上,因此合作团队人数以3~6最佳;国际机构间合作的宽度和广度不断加大,美国处于所有合作国家(地区)中心,中心度为0.56,几乎所有的国家(地区)与其都建立了合作关系。     

问题求解视角下工程机械产品的体验设计研究

目的 从问题求解的角度出发,构建工程机械产品的体验设计层级,探讨各层级对应的问题求解内涵。方法 通过文献研究法,梳理设计问题求解的研究脉络,奠定理论出发点,即设计问题求解方式已经从产品拓展到了体验设计。基于工程机械产品及行业的特殊性,分别从工程性思考和B2B行业视角分析工程机械问题求解的特点。借助实证案例分析方法,结合工程机械行业所涉及到的众多利益相关者,提出由用户体验(UX)、客户体验(CX)、品牌体验(BX)构成的工程机械体验设计层级,并对各层级问题求解内容及方式进行了阐释。结论 用户体验涉及到物理层的可用性问题和行为层的交互问题;客户体验关系到服务层的价值问题;品牌体验主要关注系统层的整合问题。未来工程机械产品问题求解的核心思路将是以“体验设计目标”为整体出发点。     

Proton Magnetic Resonance Imaging of Specimens in Simulated Microgravity

In situ proton stray-field (STRAFI) nuclear magnetic resonance (NMR) imaging of diamagnetic samples in simulated microgravity is described. The magnetic field gradient at the edge of the superconductive coil in the magnet of a NMR spectrometer is exploited to levitate diamagnetic samples and, at the same time, obtain their corresponding one-dimensional NMR images. Proton T ₂ (spin-spin relaxation time)/ diffusion-weighted profiles of samples under simulated microgravity conditions are acquired with a solid-echo radiofrequency pulse sequence. Since water is a diamagnetic main constituent substance of living systems, the methodology described could be useful to monitor non-destructively changes in the NMR properties of water protons induced by simulated microgravity and magnetic forces. Furthermore, this approach may be used to observe other NMR-sensitive nuclei of interest, e.g., fluor-19, phosphorous-31, carbon-13, etc.     

低场核磁共振技术在水泥基材料中的应用

近年来,核磁共振技术已经成为表征水泥基材料水化进程、非化学结合水量和孔结构的一种重要手段。简单介绍了核磁共振基本原理和低场核磁共振主要参数;阐述了低场核磁共振技术在水泥基材料测试中的应用,主要包括水化进程、孔结构、水分迁移和扩散等方面的内容;展望了低场核磁共振技术在水泥基材料研究中的应用前景。