我们生活在一碗汤面里吗?——光和电子的统一与起源

光和物质的起源是物理学中一个非常基本的问题,对该问题的探究贯穿了整个物理学的发展史.文章首先从最早的光微粒说和波动理论讲起,详细介绍了为什么光的波动学说可以成功地解释光的折射和干涉现象.然后以光的横波特性为基础,论述了是否存在可以承载光传播的媒介物质.通过对电荷和磁场的研究,人们认识到光是一种电磁波.最后从凝聚态物理学的演生原理出发,作者论述了弦网液体中的弦密度波对应于电磁波,弦的端点对应于电子,进而给出了光和电子起源的统一解释.     

地球磁场的物理问题

地磁学的发展经历了两千多年的历史，文章回顾了这一漫长历史的四个主要阶段，对每一阶段研究的基本物理问题和主要进展做了简要概述．地磁场的空间分布、地磁场起源、地磁场长期变化和西向漂移、磁极移动和极性倒转、地磁场与人类生存环境等，是地磁学的基本物理问题．文章还从物理概念、研究现状和地磁学以及相关学科当前存在的问题等几个方面对地磁学未来的发展趋势做了简要的说明．     

三维荧光光谱在蓝宝石成因及产地指示作用中的研究——以斯里兰卡和老挝蓝宝石为例

判别蓝宝石成因及产地是宝石学研究中的重要内容,区分蓝宝石属于变质岩型或玄武岩型通常需要使用光谱学分析、内含物分析、化学成分分析结合的方法.选取斯里兰卡变质岩型蓝宝石和老挝玄武岩型蓝宝石进行研究.两地蓝宝石的紫外-可见-近红外吸收光谱测试、化学成分分析结果分别符合变质岩型和玄武岩型蓝宝石的基本特征.三维荧光光谱测试表明,...     

Neutron- and muon-induced background in underground physics experiments

Background induced by neutrons in deep underground laboratories is a critical issue for all experiments looking for rare events, such as dark matter interactions or neutrinoless ββ decay. Neutrons can be produced either by natural radioactivity, via spontaneous fission or (α, n) reactions, or by interactions initiated by high-energy cosmic rays. In all underground experiments, Monte Carlo simulations of neutron background play a crucial role for the evaluation of the total background rate and for the optimization of rejection strategies. The Monte Carlo methods that are commonly employed to evaluate neutron-induced background and to optimize the experimental setup, are reviewed and discussed. Focus is given to the issue of reliability of Monte Carlo background estimates. We dedicate this work to the memory of our friend and colleague Nicola Ferrari, who prematurely passed away in July 2006.     

A new method to determine the projected coordinate origin of a cone-beam CT system using elliptical projection

In order to determine the projected coordinate origin in the cone-beam CT scanning system with respect to the Feldkamp-Davis-Kress(FDK)algorithm,we propose a simple yet feasible method to accurately measure the projected coordinate origin.This method was established on the basis of the theory that the projection of a spherical object in the cone-beam field is an ellipse.We first utilized image processing and the least square estimation method to get each major axis of the elliptical Digital Radiography(DR)projections of a group of spherical objects.Then we determined the intersection point of the group of major axis by solving an over-determined equation set that was composed by the major axis equations of all the elliptical projections.Based on the experimental results,this new method was proved to be easy to implement in practical scanning systems with high accuracy and anti-noise capability.     

基于卷积神经网络和近红外光谱的太平猴魁茶产地鉴别分析

太平猴魁茶因其特有的“喉韵”深受广大消费者喜爱,不同产地太平猴魁茶市场价格相差较大,如何实现产地精准鉴别是目前促进绿茶产业发展的关键因素。依赖于人工经验的感官评审方法主观性强、稳定性差,无法应用于实际生产检测过程。作为目前主要的检测分析方法,化学分析方法周期长、检测成本高,而且目前没有用于茶叶产地鉴别的统一标准。近红外光谱（NIR）作为一种无损检测分析方法,具有快速、非破坏性、无污染等特点,但是不同产地太平猴魁茶主要内含成分及其含量基本相同,不同产地样本光谱特征峰分布相似,导致常规分析方法无法有效选择特征变量。卷积神经网络（CNN）作为经典深度学习网络模型之一,具有强特征提取和模型表达能力。采用太平猴魁茶产地光谱特征分析,利用一维卷积神经网络模型（1-D CNN）提取太平猴魁茶NIR特征,提出一种基于1-D CNN和NIR的太平猴魁茶产地鉴别分析方法。试验以6个不同产地共120个样本为研究对象,分析10 000~4 000 cm-1范围内的光谱信息;将样本随机划分为训练集（84,占70%）和测试集（36,占30%）,分别讨论不同间隔采样、网络结构、卷积核大小及激活函数对产地鉴别结果的影响,并引入Dropout方法对比分析模型过拟合现象;最终建立一个具有9层结构的1-D CNN模型。蒙特卡罗试验结果表明,相比于基于原始光谱数据（40.57%,7.06）和PCA方法（31.93%,6.96）的太平猴魁茶产地预测模型准确率和标准差,基于1-D CNN的太平猴魁茶产地鉴别模型预测精度和稳定性更高,其测试集预测准确率平均值和标准差分别为97.73%和3.47。因此,1-D CNN可有效提取太平猴魁茶不同产地NIR特征,提高太平猴魁茶产地鉴别精度,为太平猴魁茶精准产地鉴别及溯源分析提供参考。     

基于能量色散X射线荧光光谱的鱼粉产地溯源方法研究

鱼粉是一种在养殖业中占有重要地位的高蛋白饲料原料.我国对鱼粉的市场需求很大,但不同产地的鱼粉存在品质差异的问题.为保证鱼粉品质安全,建立鱼粉产地溯源系统具有非常重要的意义.能量色散X射线荧光光谱根据元素辐射X射线荧光光子能量不同,能够检测样品矿物质元素种类和含量.鱼粉所含矿物质元素种类和含量会因鱼粉产地不同而存在差异,...     

Study on the separation of 100 TeV γ-rays from cosmic rays for the Tibet ASγ experiment

A γ/hadron separation analysis is described for the observed air shower events with primary energy above 100 TeV based on the Tibet AST detector configuration. The shower age and size parameters are fitted from the measured lateral density distribution and used as discrimination variables. According to the MC simulation while taking into account the systematic uncertainty estimated from data and MC comparison,it is found that 70% of the cosmic ray (CR) background can be rejected while more than 78% of the γ-rays can be retained. Sensitivity for 100 TeV γ-rays observation can thus be improved by at least 40%.     

Searching for protostars

Summary We present molecular-line observations of young stellar objects (YSOs) suspected to be protostars in the main accretion phase. The aim of this work is to define a list of the best protostellar candidates to be observed in the near future with the ISO spectrometers with the precise scope of searching for the final proof of the infall, theHoly Grail of astrophysics. The sources were mapped in the CS 3?2 and CO 3?2 lines; our data were used to investigate the presence of clumps of materials around these objects and the amount of this material, as well as to detect outflows associated with these objects that would enormously complicate the interpretation of further dynamics studies. Only one of our sources suspected to be protostars resulted to have a good chance of being in the accretion phase and to deserve further spectroscopic measurements. Paper presented at the 6th Cosmic Physics National Conference, Palermo, 3–7 November 1992.     

塔里木盆地植物区系的研究

塔里木盆地位于欧亚大陆腹地．该区自然环境独特，植被呈紧缩型分布．植物区系组成贫乏，种子植物１０５属１６５种。分隶３５科，多属于温带成分．特有成分比例较高．生活型以地面芽植物占优势，植被具有温带荒漠的特殊属性．本地区植物区系形成于第三纪．主要来源于华夏植物区系，是华夏植物区系向本地区发展，并在独特环境中蜕变的结果，其中有部分是从本地的荒漠环境中发展起来的．同时还存在古地中海及安哥拉区系成分．区系植物中既有第三纪的种，也有第四纪的种，即在第三纪形成荒漠植物区系，第四纪由于气候进一步变干燥，植物的耐旱适应又有新的发展．