分类： 工程与技术科学 >> 物理学相关工程与技术 分类： 工程与技术科学 >> 仪器仪表技术 分类： 电子与通信技术 >> 电子技术 分类： 物理学 >> 交叉学科物理及相关领域的科学与技术 提交时间： 2024-05-02
摘要： 本文提出了一种用于低温扫描隧道显微镜(CryoSTM)的跨阻放大器(TIA)设计方案。在CryoSTM中带有尖端样品成分的TIA称为CryoSTM-TIA。该CryoSTM-TIA的跨阻增益在1Gohm，而其带宽大于300kHz。所提出的CryoSTM-TIA的独特特点是其前置放大器由单个低温高电子迁移率晶体管(HEMT)制成，因此在100kHz时仪器等效输入噪声电流功率谱密度低于4(fA)2/Hz。此外，应用“偏置冷却法”可用于原位控制HEMT掺杂区冻结DX-中心的密度，改变其结构以降低器件噪声。利用该仪器，可以进行高能量分辨率的快速扫描隧道光谱测量。并且，它能够测量各种量子系统在原子尺度上的扫描隧道散粒噪声谱(STSNS)，即使散粒噪声非常低。它为通过测量STSNS来研究新的量子态提供了一个强大的工具，例如检测拓扑量子系统中马约拉纳束缚态的存在。
分类： 电子与通信技术 >> 电子技术 分类： 工程与技术科学 >> 仪器仪表技术 分类： 物理学 >> 交叉学科物理及相关领域的科学与技术 分类： 物理学 >> 凝聚态:电子结构、电、磁和光学性质 提交时间： 2024-05-01
摘要： In this work, we design and fabricate the transimpedance Amplifier (TIA) following the design mentioned in Ref. cite{Liang2024}. In the TIA, the preamplifier (Pre-Amp) is made of a junction field effect transistor (JFET) that can work at 77 K. The post-amplifier is made of an operational amplifier (OPA). Cascade Pre-Amp and Post-Amp to form the inverting-amplifier (Inv-Amp). The gain-bandwidth product of Inv-Amp with the gain about 50,000 is higher than 10 GHz. With a 1.13 Gohm feedback network, the gain of TIA is 1.13 Gohm and its bandwidth is about 97 kHz. The equivalent input noise voltage power spectral density of TIA is not more than 9 (nV)2/Hz at 10 kHz and 4 (nV)2/Hz at 50kHz, and its equivalent input noise current power spectral density is about 26 (fA)2/Hz at 10 kHz and 240(fA)2/Hz at 50 kHz. The measured transport performances and noise performances of TIA are consistent with the simulations and calculations, verifying the feasibility for the design of low-noise large-bandwidth TIA proposed in Ref. 1 . And, TIA with various performances that meet various needs can be designed according to the design methods in Ref. 1,2 . With the same gain, the bandwidth of the TIA in this work is much larger than the present TIA and its noises are much lower than those of present ones. The TIA in this work is perfect for the cryogenic STM working at 77 K (i.e. liquid nitrogen temperature).
分类： 物理学 >> 核物理学 分类： 核科学技术 >> 核探测技术与核电子学 提交时间： 2024-04-28
摘要： A charged particle array, named MATE-PA, which serves as an auxiliary detec#2;tor system to the Multi-purpose Active-target Time projection chamber for nuclear astrophysical and exotic beam Experiments (MATE) has been con#2;structed. The array is composed of twenty single-sided strip-silicon detectors, covering around 10% of the solid angle. It is dedicated for the detection of reaction-induced charged particles which penetrate the MATE active volume. The performance of MATE-PA has been experimentally studied using an alpha source, and a 36-MeV 14N beam injected into the chamber of MATE, filled with a mixture gas of 95% 4He and 5% CO2 under the pressure of 500 mbar, at the Radioactive Ion Beam Line in Lanzhou (RIBLL). The results demonstrate good separation of light charged particles with the forward double-layer silicon detectors of MATE-PA. The energy resolution of the Si detectors was deduced to be about 1% (σ) for an energy loss of about 10 MeV by the α particles. The inclusion of MATE-PA helps improve particle identification, and increases the dynamic range for the kinetic energy of charged particles, in particular that of α particles up to about 15 MeV.
分类： 医学、药学 >> 预防医学与公共卫生学 分类： 统计学 >> 生物与医学统计学 提交时间： 2024-04-25
摘要： 极端不平衡数据定义为自变量或因变量指标的取值呈现严重比例失衡的数据，例如病例-对照极度不平衡、疾病发病率极低、生存数据大量删失以及遗传位点为低频或罕见变异等。在此情境下，logistic回归模型、Cox比例风险模型等参数假设检验的经典统计量偏离正态分布，难以控制一类错误。近年来，随着超大型人群队列全基因组关联研究资源的日益共享与深度挖掘，高效准确处理独立或非独立样本极端不平衡数据的统计需求日益突出。为此，本文系统地进行了方法学概述。首先，综述常见经典统计量理论推导的原理；其次，阐述极端不平衡数据对统计量分布的影响；然后，介绍遗传统计学中常用的两种统计量校正方法：Firth校正和鞍点近似方法；最后，简介极端不平衡基因组学数据常用软件。本文为极端不平衡数据的统计分析提供理论参考和应用推荐。
分类： 其他 分类： 其他 提交时间： 2024-04-25
摘要： The Australia Telescope Large Area Survey (ATLAS) and the VLA survey in the XMM-LSS/VIDEO deep field provide deep ($\approx 15$ ${\mu}$Jybeam$^{-1}$) and high-resolution ($\approx$ 4.5--8 arcsec) radio coverage of the three XMM-SERVS fields (W-CDF-S, ELAIS-S1, and XMM-LSS). These data cover a total sky area of 11.3 deg$^2$ and contain $\approx 11000$ radio components. Furthermore, about 3~deg$^2$ of the XMM-LSS field also has deeper MIGHTEE data that achieve a median RMS of 5.6 ${\mu}$Jy beam$^{-1}$ and detect more than 20000 radio sources. We analyze all these radio data and find source counterparts at other wavebands utilizing deep optical and IR surveys. The nature of these radio sources is studied using radio-band properties (spectral slope and morphology), and the IR-radio correlation. %and spectral energy distribution. Radio AGNs are selected and compared with those selected using other methods (e.g. X-ray). We found 1656 new AGNs that were not selected using X-ray and/or MIR methods. We constrain the FIR-to-UV SEDs of radio AGNs using {\sc cigale} and investigate the dependence of radio AGN fraction upon galaxy stellar mass and star-formation rate.
分类： 其他 分类： 其他 提交时间： 2024-04-25
摘要： We present X-ray spectral and long-term variability analyses of an unbiased sample of 361 optically selected radio-loud quasars (RLQs) utilizing sensitive serendipitous X-ray data from the Chandra and XMM-Newton archives. The spectral and temporal properties of RLQs are compared with those of radio-quiet quasars (RQQs) matched in $L_\mathrm{2500A}$ and $z$. The median power-law photon index ($\Gamma$) of RLQs is $1.84^{+0.01}_{-0.01}$, which is close to that of matched RQQs ($1.90^{+0.02}_{-0.01}$). No significant correlations between $\Gamma$ and radio-loudness, $L_\mathrm{x}/L_\mathrm{x,rqq}$ (the X-ray luminosity over that expected from the $L_\mathrm{x}$-$L_\mathrm{uv}$ relation for RQQs), redshift, or Eddington ratio are found for our RLQs. The stacked X-ray spectra of our RLQs show strong iron-line emission and a possible Compton-reflection hump. The intrinsic X-ray variability amplitude is $\approx40$% for RLQs on timescales of months-to-years in the rest frame, which is somewhat smaller than for the matched RQQs ($\approx60$%) on similar timescales, perhaps due to the larger black-hole masses and lower Eddington ratios in our RLQ sample. The X-ray spectral and variability results for our RLQs generally support the idea that the X-ray emission of typical RLQs is dominated by the disk/corona, as is also indicated by a recent luminosity correlation study.
分类： 其他 分类： 其他 提交时间： 2024-04-25
摘要： Radio-loud quasars (RLQs) are known to produce excess X-ray emission, compared to radio-quiet quasars (RQQs) of the same luminosity, commonly attributed to jet-related emission. Recently, we found that the HeII EW and $\alpha_{\rm{ox}}$ in RQQs are strongly correlated, which suggests that their extreme-ultraviolet (EUV) and X-ray emission mechanisms are tightly related. Using 48 RLQs, we show that steep-spectrum radio quasars (SSRQs) and low radio-luminosity ($L_{\rm R}$) flat-spectrum radio quasars (FSRQs) follow the $\alpha_{\rm ox}$--HeII EW relation of RQQs. This suggests that the X-ray and EUV emission mechanisms in these types of RLQs is the same as in RQQs, and is not jet related. High-$L_{\rm R}$ FSRQs show excess X-ray emission given their HeII EW by a factor of $\approx$ 3.5, which suggests that only in this type of RLQ is the X-ray production likely jet related.
分类： 其他 分类： 其他 提交时间： 2024-04-25
摘要： Radio-loud quasars (RLQs) are more X-ray luminous than predicted by the X-ray-optical/UV relation (i.e. $L_\mathrm{x}\propto L_\mathrm{uv}^\gamma$) for radio-quiet quasars (RQQs). The excess X-ray emission depends on the radio-loudness parameter ($R$) and radio spectral slope ($\alpha_\mathrm{r}$). We construct a uniform sample of 729 optically selected RLQs with high fractions of X-ray detections and $\alpha_\mathrm{r}$ measurements.We find that steep-spectrum radio quasars (SSRQs; $\alpha_\mathrm{r}\le-0.5$) follow a quantitatively similar $L_\mathrm{x}\propto L_\mathrm{uv}^\gamma$ relation as that for RQQs, suggesting a common coronal origin for the X-ray emission of both SSRQs and RQQs. However, the corresponding intercept of SSRQs is larger than that for RQQs and increases with $R$, suggesting a connection between the radio jets and the configuration of the accretion flow. Flat-spectrum radio quasars (FSRQs; $\alpha_\mathrm{r}>-0.5$) are generally more X-ray luminous than SSRQs at given $L_\mathrm{uv}$ and $R$, likely involving more physical processes. The emergent picture is different from that commonly assumed where the excess X-ray emission of RLQs is attributed to the jets. We thus perform model selection to comparecritically these different interpretations, which prefers the coronal scenario with a corona-jet connection. A distinct jet component is likely important for only a small portion of FSRQs.The corona-jet, disk-corona, and disk-jet connections of RLQs are likely driven by independent physical processes. Furthermore, the corona-jet connection implies that small-scale processesin the vicinity of SMBHs, probably associated with the magnetic flux/topology instead of black-hole spin, are controlling the radio-loudness of quasars.
分类： 其他 分类： 其他 分类： 其他 提交时间： 2024-04-25
摘要： Fluxes emitted at different wavebands from active galactic nuclei (AGNs) fluctuate at both long and short timescales. The variation can typically be characterized by a broadband power spectrum, which exhibits a red-noise process at high frequencies. The standard method of estimating power spectral density (PSD) of AGN variability is easily affected by systematic biases such as red-noise leakage and aliasing, in particular, when the observation spans a relatively short period and is gapped. Focusing on the high-frequency PSD that is strongly distorted due to red-noise leakage and usually not significantly affected by aliasing, we develop a novel and observable normalized leakage spectrum (NLS), which describes sensitively the effects of leaked red-noise power on the PSD at different temporal frequencies. Using Monte Carlo simulations, we demonstrate how an AGN underlying PSD sensitively determines the NLS when there is severe red-noise leakage and thereby how the NLS can be used to effectively constrain the underlying PSD.
分类： 心理学 >> 发展心理学 分类： 心理学 >> 教育心理学 提交时间： 2024-04-23
摘要： 对185名二年级儿童进行历时20个月的两波次追踪，考察了二年级的家庭社会经济地位对二、三年级数学运算能力、逻辑思维能力和空间想象能力的预测作用，以及干扰抑制、反应抑制和工作记忆在其中的中介作用。研究发现：(1)二年级的家庭社会经济地位仅对二年级时的三种数学能力具有直接预测作用。(2)家庭社会经济地位可以通过工作记忆的中介作用间接预测二年级的数学运算能力和三年级的逻辑思维能力。这表明执行功能在家庭社会经济地位与数学能力关系中的作用会随执行功能成分类型、数学能力类型及测试时间点而发生变化。
分类： 计算机科学 >> 信息安全 分类： 计算机科学 >> 计算机应用技术 提交时间： 2024-04-23
摘要： Image steganography has become a focal point of interest for researchers due to its capacity for the covert transmission of sensitive data. Traditional diffusion models often struggle with image steganography tasks involving paired data, as their core principle of gradually removing noise is not directly suited for maintaining the correspondence between carrier and secret information. To address this challenge, this paper conducts an in-depth analysis of the principles behind diffusion models and proposes a novel framework for an image steganography diffusion model. The study begins by mathematically representing the steganography tasks of paired images, introducing two optimization objectives: minimizing the secrecy leakage function and embedding distortion function. Subsequently, it identifies three key issues that need to be addressed in paired image steganography tasks and, through specific constraint mechanisms and optimization strategies, enables the diffusion model to effectively handle paired data. This enhances the quality of the generated stego-images and resolves issues such as image clarity. Finally, on public datasets like CelebA, the proposed model is compared with existing generation model-based image steganography techniques, analyzing its implementation effects and performance parameters. Experimental results indicate that, compared to current technologies, the model framework proposed in this study not only improves image quality but also achieves significant enhancements in multiple performance metrics, including the imperceptibility and anti-detection capabilities of the images. Specifically, the PSNR of its stego-images reaches 93.14dB, and the extracted images’ PSNR reaches 91.23dB, an approximate improvement of 30% over existing technologies; the attack success rate is reduced to 2.4x10-38. These experimental outcomes validate the efficacy and superiority of the method in image steganography tasks.
分类： 计算机科学 >> 计算机软件 分类： 语言学及应用语言学 >> 语言学及应用语言学 提交时间： 2024-04-21
摘要： 此幻灯片从背景、动机、方法、效果、展望和致谢六方面讲述了《引导大语言模型生成计算机可解析内容》的研究。全文请参考：https://arxiv.org/abs/2404.05499
分类： 天文学 >> 天体力学 分类： 物理学 >> 地球物理学、天文学和天体物理学 提交时间： 2024-04-20
摘要： 本文简要介绍新的对称形式的质点动力学方程对天体动力学理论的系统性改进。 首先，对于开放的多体系统，无法找到近似程度非常高的惯性系，在传统理论中不得不引入惯性系的近似，而对称新方程因为可以直接适用于任意的平动参考系而避免了惯性系的近似，从而可以提高理论预言的精度。其次，对于束缚的多体系统，传统理论的动力学应用是先引入质心参考系，在质心参考系中应用牛顿第二定律，然后通过坐标变换再转化到实体参考系，比如太阳系的行星摄动方程。 但是，应用对称新方程则可以一步到位推导得到行星摄动方程。最后，如果进一步考虑行星受到临时推力或者冲击力，甚至为了进一步提高计算精度进而考虑来自束缚系统外的作用力，则一个可以叠加非微扰作用力的行星摄动的修正方程在本文得到了确立。
分类： 心理学 >> 实验心理学 分类： 心理学 >> 社会心理学 提交时间： 2024-04-20
摘要： 情绪能够强化记忆编码且对后续记忆编码也有增强效果。本研究探索复杂社会情绪（即民族危机感和自豪感）唤醒如何影响后续的记忆编码。在问卷调查的基础上，研究利用两个实验探索民族情绪唤醒如何选择性地增强记忆编码。实验2采用被试间设计，参与者被随机分配到危机感、自豪感及中性情绪组进行情绪唤醒，随后进行记忆编码。结果显示，民族危机感和自豪感的唤醒显著增强了记忆编码，但对同一时间窗内与民族情绪无关图片记忆无显著影响。实验3采用相同的设计，但更换记忆材料为数学统计概念，结果发现民族情绪唤醒不影响数学统计记忆编码。本研究深化了我们对复杂社会情绪与记忆交互作用的理解，同时为优化高校思想政治教育提供了实证基础。
分类： 图书馆学、情报学 >> 各种文献工作 分类： 图书馆学、情报学 >> 图书馆学 提交时间： 2024-04-18
摘要： 目的 知识可视化设计研究综述反映了人们对知识新形式的探索路径。 文献范围 国外文献来自Web of Science的核心合集数据库论文1377篇。国内文献来自知网518篇论文数据。 方法 研究借助文献计量分析工具Vosview、Citespace 以及自主梳理方法，以“知识可视化设计”为关键词对1985-2022年间国内外文献进行检索和分析，解析了知识可视化设计研究的辩证发展路径。 结果 发现目前可视化定义研究的局限，研究对知识可视化设计的本体论和认识论上缺乏思考，以及过于依赖单一的研究视角缺乏辩证思维。 局限 由于国内外数据库不统一较难用同种方法进行统一分析。 结论 中国知识可视化设计者和研究者应用唯物辩证法把握知识可视化设计领域研究脉络和规律，了解其辩证发展过程，找到中国知识可视化领域的发展道路。
分类： 心理学 >> 认知心理学 分类： 心理学 >> 心理统计 提交时间： 2024-04-17
摘要： 认知建模近年来在科学心理学获得广泛应用，而模型比较是认知建模中关键的一环：研究者需要通过模型比较来选择出最优模型，才能进行后续的假设检验或潜变量推断。模型比较不仅要考虑模型对数据的拟合（平衡过拟合与欠拟合），也需要考虑参数数据和数学形式的复杂度。然而，模型比较指标众多，纷繁复杂。将认知建模常用的模型比较的指标分为三大类，并介绍了其计算方法及优劣，包括拟合优度指标（包括均方误差、决定系数、ROC曲线等）、基于交叉验证的指标（包括AIC、DIC等）和基于边际似然的指标。结合正交Go /No-Go范式下的模拟数据和真实数据，展示各指标在R语言中如何实现。在此基础上，探讨各指标的适用情境，介绍模型平均等模型比较的新思路。
分类： 生物学 >> 生物物理学 分类： 化学 >> 物理化学 分类： 生物学 >> 生物物理学 提交时间： 2024-04-16
摘要： Transcription factor (TF) are proteins that regulates the transcription of genetic information from DNA to messenger RNA by binding to a specific DNA sequence.Nucleic acid-protein interactions are crucial in regulating transcription in biological systems. This work presents a quick and convenient method for constructing tight-binding models and offers physical insights into the electronic structure properties of transcription factor complexes and DNA motifs. The tight binding Hamiltonian parameters are generated using the random forest regression algorithm, which reproduces the given ab-initiolevel calculations with reasonable accuracy. We present a library of residue-level parameters derived from extensive electronic structure calculations over various possible combinations of nucleobases and amino acid side chains from high-quality DNA-protein complex structures. As an example, our approach can reasonably generate the subtle electronic structure details for the orthologous transcription factors human AP-1 and Epstein-Barr virus Zta within a few seconds on a laptop. This method potentially enhances our understanding of the electronic structure variationsof gene-protein interaction complexes, even those involving dozens of proteins and genes. We hope this study offers a powerful tool for analyzing transcription regulation mechanisms at an electronic structural level.
分类： 物理学 >> 核物理学 分类： 物理学 >> 基本粒子与场物理学 提交时间： 2024-04-15
摘要： 在相对论重离子碰撞中寻找手征磁效应（CME）有助于我们理解强相互作用中的CP对称性破缺和量子色动力学（QCD）真空的拓扑性质。基于CME的背景和信号相对于旁观者平面和参与者平面有不同的相关性，实验上提出了一种双平面方法提取CME信号。利用具有不同强度CME的多相输运模型，我们在质心碰撞能量为200 GeV的同质异位素碰撞中重新探讨了双平面方法，发现相对于两个不同平面的CME信号和背景效应的比值系数是不同的，这与目前实验测量中的假设不一致。这种差异来自于相对于旁观者和参与者平面的CME的退关联，它源于末态的相互作用。我们的发现表明，目前的实验测量可能高估了在相对论性重离子碰撞中观测到的末态CME信号的比例。
分类： 信息科学与系统科学 >> 信息科学与系统科学基础学科 分类： 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 分类： 天文学 >> 天文学 提交时间： 2024-04-11
摘要： The electromagnetic fields of point sources with time varying charges moving in the vacuum are derived using the Liénard-Wiechert potentials. The properties of the propagation velocities and the Doppler effect are discussed based on their far fields. The results show that the velocity of the electromagnetic waves and the velocity of the sources cannot be added like vectors; the velocity of electromagnetic waves of moving sources are anisotropic in the vacuum; the transverse Doppler shift is intrinsically included in the fields of the moving sources and is not a pure relativity effect caused by time dilation. Since the fields are rigorous solutions of the Maxwell’s equations, the findings can help us to abort the long-standing misinterpretations concerning about the classic mechanics and the classic electromagnetic theory. Although it may violate the theory of the special relativity, we show mathematically that, when the sources move faster than the light in the vacuum, the electromagnetic barriers and the electromagnetic shock waves can be clearly predicted using the exact solutions. Since they cannot be detected by observers in the region outside their shock wave zones, an intuitive and reasonable hypothesis can be made that the superluminal sources may be considered as a kind of electromagnetic blackholes.
分类： 图书馆学、情报学 >> 图书馆学 分类： 图书馆学、情报学 >> 情报学 提交时间： 2024-04-11
摘要： 摘要： 研究目的 随着生成式人工智能在网络空间的广泛应用，围绕其产业链的内容安全风险逐渐凸显，从模型层到应用层，它不断冲击着原有的内容供给安全和内容生成生态，并从内容域进一步扩散，逐步影响到政治、法律以及伦理等诸多领域，使得网络空间的内容安全面临传统风险、新型风险以及生成式人工智能带来的潜在风险等多重挑战。因此，针对生成式人工智能内容治理显得尤为重要。 研究方法 基于行动者网络理论中对人与技术的异质建构，现阶段，应当构建面向内容安全风险的治理行动者网络，着重强调政府部门在事前风险防范、风险常态化监管、事中即时处置以及事后有效重建中的核心决策者地位，并发挥算法、制度文本等异质行动者的治理效用。 研究结论 在具体治理路径上，形成以政府部门为主导力量，以文本协同为路径支撑、以风险识别为行为导向、以情境建构为重建原则，以生成式人工智能的内容安全风险为治理主线的可执行多重行动者网络体系，共同应对生成式人工智能带来的内容安全挑战。
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