二层交换机转发帧的原理与实现

介绍了二层交换机转发帧的原理及其具体的硬件和软件实现.着重讲解了其软件实现的过程中,在各种端口上设置MAC地址的处理方法.     

高分辨率影像城市植被自动提取算法

近十几年来,随着城市化进程加剧,准确获取城市植被的分布信息,是城市气候和地表能量平衡研究的重要内容。高空间分辨率遥感影像数据,为精确获取和动态监测城市植被提供了重要资料。本研究利用资源三号数据对长江三角洲地区城市植被进行光谱特征分析与提取,提出一种城市植被的自动化信息提取算法—分离面法（Hyperplanes for Plant Extraction Methodology,HPEM）。结果表明：在假彩色反射率空间,植被与NDVI值低的背景有很好的分离性,而在真彩色反射率空间,植被与NDVI值高的背景有很好的分离性;HPEM能很好地避免NDVI最佳阈值法中将建筑物误分为植被的问题,其精度明显优于NDVI最佳阈值法,Kappa系数从0.85提高到0.90,总的错分与漏分误差从21.15%降低到14.18%。可见,本文的HPEM方法能有效提高城市植被信息自动提取的精度。     

珠江口盆地惠州21-1构造二氧化碳地质封存数值模拟

二氧化碳(CO2)地质封存是减少温室气体向大气排放的有效措施之一,而CO2海上地质封存是其中的一个重要领域。以距离广东沿海约179 km的珠江口盆地惠州凹陷惠州21-1构造为例,建立三维地质模型,利用TOUGH2程序模块开展了CO2注入咸水层地质封存模拟研究;分析了CO2注入咸水层后的运移分布和溶解扩散情况以及地层压力变化特征;并且通过设置8个对比方案,进行了渗透率纵横比、盐度、渗透率、孔隙度等4个参数的敏感性分析。结果表明,所建的惠州21-1构造三维地质模型能够较好地描述CO2在注入层中的运移过程和分布状况;珠江组下部的局部盖层由于泥岩厚度较小且渗透率相对较高,存在局部封盖效果不佳现象;渗透率纵横比、储层孔隙度、渗透率等取值变化对封存效果影响较大,而地层水盐度在33~39范围变化,对CO2注入运移分布与溶解没有明显影响。     

高速公路交通事故与气象条件的关系研究

选取2013—2017年河北高速公路逐日发生的一般等级以上交通事故起数、伤亡人数、经济损失及同期气象要素资料,基于序关系分析法将事故量及等级量化为事故指数,分析了对高速通行高影响的雾天、雨天和雪天事故的年际、月际及日变化特征,并构建日均交通事故指数与气象要素的非线性回归模型。研究表明：（1）交通事故发生时不利天气条件下交通事故总起数、死亡事故起数及人数、经济损失为雾天>雨天>雪天,而伤人事故及人数为雨天>雾天>雪天。（2）雨天、雪天交通事故峰值与当年雨雪极端天气事件有关,雾天单起交通事故的直接经济损失呈上升趋势;事故月、日分布有显著性差异,表现为雾天事故高发月份在9月至翌年2月、雨天事故多发于在5—10月、雪天事故多发于1—2月、12月;05—08时和00时为事故高发时段。（3）分别针对不同等级日雨量和能见度与日均交通事故指数建立了一般等级以上交通事故模型,非线性回归效果显著。

     

改进型反褶积分层解释法——一种应用PC～1500计算机处理γ测井资料的新方法

本文吸取了现行Υ测井资料解释方法的合理部分,提出了改进型反褶积分层解释法。叙述了方法的原理及设置判别因子的原则。作者以PC-1500微机为例给出了改进后的反褶积分层解释法程序流程图。通过对模型钻孔和实际钻孔测井资料的解释,证实了方法的合理性和可行性,克服了目前平均强度法中存在的人为影响,扩大了一般分层解释法的应用范围,该法可在现场及时取得结果,提高了解释速度和质量。     

Propagation and Damping of a Localized Impulsive Longitudinal Perturbation in Coronal Loops

We use linear analysis to simulate the evolution of a coronal loop in response to a localized impulsive event. The disturbance is modeled by injecting a narrow Gaussian velocity pulse near one footpoint of a loop in equilibrium. Three different damping mechanisms, namely viscosity, thermal conduction, and optically thin radiation, are included in the loop calculations. We consider homogeneous and gravitationally stratified, isothermal loops of varying length (50≤L≤400 Mm) and temperature (2≤T≤10 MK). We find that a localized pulse can effectively excite slow magnetoacoustic waves that propagate up along the loop. The amplitudes of the oscillations increase with decreasing loop temperature and increasing loop length and size of the pulse width. At T≥4 MK, the waves are dissipated by the combined effects of viscosity and thermal conduction, whereas at temperatures of 2 MK, or lower, wave dissipation is governed by radiative cooling. We predict periods in the range of 4.6?–?41.6 minutes. The wave periods remain unaltered by variations of the pulse size, decrease with the loop temperature, and increase almost linearly with the loop length. In addition, gravitational stratification results in a small reduction of the periods and amplification of the waves as they propagate up along the loop.     

The potential of FAST in detecting celestial hydroxyl masers and related science topics

The Five-hundred-meter Aperture Spherical radio Telescope(FAST) will make contributions to studies of Galactic and extragalactic masers. This telescope, with construction finished and now undergoing commissioning, has an innovative design that leads to the highest sensitivity of any single dish radio telescope in the world. FAST's potential for OH megamaser research is discussed, including the sky density of masers detectable in surveys. The scientific impact expected from FAST maser studies is also discussed.     

肺黏膜相关淋巴组织淋巴瘤合并肺鳞癌一例并文献复习

目的：探讨肺黏膜相关淋巴组织（MALT）淋巴瘤MSCT影像学特点。方法：回顾性分析2014年2月至2022年7月经病理证实的8例肺MALT淋巴瘤的临床资料及MSCT表现,分析误诊原因。结果：5例行胸部平扫及增强检查,3例仅行胸部平扫,8例患者中单发病灶、多发病灶各4例,表现为大片状高密度影7例,均见支气管充气征,1例表现为混杂密度结片灶;CT增强4例中度强化,1例轻度强化,4例可见血管造影征。结论：肺原发性MALT淋巴瘤是一种低度恶性的惰性肿瘤,MSCT表现具有一定特征性,应及时获取病变组织行病理学检查并结合免疫组化明确诊断。

     

Multi-risk governance for natural hazards in Naples and Guadeloupe

Technical and institutional capacities are strongly related and must be jointly developed to guarantee effective natural risk governance. Indeed, the available technical solutions and decision support tools influence the development of institutional frameworks and disaster policies. This paper analyses technical and institutional capacities, by providing a comparative evaluation of governance systems in Italy and France. The focus is on two case studies: Naples and Guadeloupe. Both areas are exposed to multiple hazards, including earthquakes, volcanic eruptions, landslides, floods, tsunamis, fires, cyclones, and marine inundations Cascade and conjoint effects such as seismic swarms triggered by volcanic activity have also been taken into account. The research design is based on a documentary analysis of laws and policy documents informed by semi-structured interviews and focus groups with stakeholders at the local level. This leads to the identification of three sets of governance characteristics that cover the key issues of: (1) stakeholders and governance level; (2) decision support tools and mitigation measures; and (3) stakeholder cooperation and communication. The results provide an overview of the similarities and differences as well as the strengths and weaknesses of the governance systems across risks. Both case studies have developed adequate decision support tools for most of the hazards of concern. Warning systems, and the assessment of hazards and exposure are the main strengths. While technical/scientific capacities are very well developed, the main weaknesses involve the interagency communication and cooperation, and the use and dissemination of scientific knowledge when developing policies and practices. The consequences for multi-risk governance are outlined in the discussion.     

Remote sensing of Mercury's magnetospheric plasma environment via energetic neutral atoms imaging

The potentiality of exploring the plasma dynamical behavior of Mercury via energetic neutral atom (ENA) analysis is briefly discussed. The analysis of the Hermean ENA would give clues to the global magnetospheric configuration, clarifying crucial issues like the existence of radiation belts. In order to demonstrate the feasibility of ENA imaging in the Hermean environment, an empirical model of the equatorial proton distributions, originally developed for the Earth's magnetosphere, is here modified in order to be applicable to the expected conditions, according to the present knowledge of the planet. Simulations of the ENA radiation are then presented and discussed. It is shown that the simulated radiation is significantly high, especially when pointing the field of view towards the Hermean surface. The way of determining the proton flux distributions and the cross-tail electric field characteristics by using the ENA signal is discussed. Finally, a preliminary design of an ENA detector suitable for the ESA mission to Mercury ‘BepiColombo’ is proposed and discussed.