溶剂热法制备翠玉状Fe3O4微晶及表征

采用溶剂热法合成粒径为1～2 μm的翠玉状的Fe3O4晶粒.样品物相用X射线衍射(XRD)仪表征,形貌通过电子扫描显微镜(SEM)观测.所得样品的磁性用振动样品磁强计(VSM)测试,结果显示出铁磁性:饱和磁化强度Ms为89.7 emu/g,剩余磁化强度Mr为6.7 emu/g,矫顽力Hc为107.1 Oe.     

CARBONATE EOLIANITES IN PUTIAN, FUJIAN (Ⅰ)——SEDIMENTARY STRUCTURES AND PALEOWINDS

Carbonate eolianites in Houshijing, Putian, Fujian, consist of three sand ridges. The geometry and sedimentary structures of these ridges are described here, and their paleodune types and the paleowind directions are reconstructed on the basis of discussion of genesis. The authors consider that they were vegetated longitudinal dunes or sand drifts and wind shadow dunes or sand shadows which were formed by reworking of adjacent beach sand by prevailing northeast monsoon during the latest Middle Holocene. The wind directions in the past and at present do not appear to have obviously changed.     

彩票里的学问

这天,我和爸爸一起去买彩票.来到彩票销售点,我一眼就瞅见挂在门前的牌子上写着:彩票2元一张,中奖率1％.特等奖30000元,一等奖6000元,二等奖1000元,三等奖200元,鼓励奖10元.看完我心中不免一阵狂喜:哈哈,中奖率是1％,也就是说买100张彩票就会有一张彩票中奖,如果中了特等奖,就能赚28000元,中一、二等奖都能稳赚不赔呀.最次中个鼓励奖,多买几次肯定能中大奖呢!     

水浮莲（Pistia stratiotes L．）在极端环境中的生存能力检测

检测水浮莲（Pistia　stratiotes　L．）在不同pH和不同温度条件下的生长能力以及对NaCl的敏感性，结果表明．水浮莲最适合的生长繁殖温度条件为20-35℃．低于10℃时不能够正常生长繁殖，低于5℃时难以保持生存能力；最适pH范围在pH6～10之间；水浮莲对NaCl非常敏感，10mM·L^-1NaCl影响水浮莲的正常生长，高于此浓度的NaCl会导致水浮莲的黄化以及死亡．     

对一个错误的再修正

文[1],文[3]对同一问题的讨论得到的结论均是错误.现收到连云港市教育局研究室寇恒清,湖南常德市一中朱纯刚,石家庄外国语学校郝红宾等给出的正确结论,本刊根据来稿的先后刊出下文,由此造成的不便在此深表歉意.     

Electric gating of the multichannel conduction in LaAlO_3/SrTiO_3 superlattices

The electric gating on the transport properties of two-dimensional electron gas(2DEG) at the interface of LaAlO₃/SrTiO₃(LAO/STO) heterostructure has attracted great research interest due to its potential application in fieldeffect devices. Most of previous works of gate effect were focused on the LAO/STO heterostructure containing only one conductive interface. Here, we systematically investigated the gate effect on high-quality LAO/STO superlattices(SLs)fabricated on the TiO₂-terminated(001) STO substrates. In addition to the good metallicity of all SLs, we found that there are two types of charge carriers, the majority carriers and the minority carriers, coexisting in the SLs. The sheet resistance of the SLs with a fixed thickness of the LAO layer increases monotonically as the thickness of the STO layer increases. This is derived from the dependence of the minority carrier density on the thickness of STO. Unlike the LAO/STO heterostructure in which minority and majority carriers are simultaneously modulated by the gate effect, the minority carriers in the SLs can be tuned more significantly by the electric gating while the density of majority carriers is almost invariable. Thus, we consider that the minority carriers may mainly exist in the first interface near the STO substrate that is more sensitive to the back-gate voltage, and the majority carriers exist in the post-deposited STO layers. The SL structure provides the space separation for the multichannel conduction in the 2 DEG, which opens an avenue for the design of field-effect devices based on LAO/STO heterostructure.     

基于实测光谱和国产高分五号高光谱卫星的铁尾矿表层含水率遥感反演方法研究

尾矿库作为高势能的人造泥石流危险源,在尾砂含水量过高时有溃坝风险,低含水量状态下产生扬尘则会危害周围环境。尾砂含水量实时、动态监测对于尾矿库安全状况及矿区环境保护具有重要意义。相比传统采样化验手段,高光谱遥感拥有观测面积大、数据实时易获取、光谱信息丰富的特点,为快速、高精度尾矿水分监测提供了手段。以鞍山-本溪铁矿群中的高硅型铁尾矿为研究区,实地采集尾砂样品77个,利用可见光-近红外(350～2 500 nm)光谱仪获取其光谱数据,分析不同含水率尾砂光谱特征及机理;引入竞争性自适应加权重采样法(CARS)筛选水分敏感波段,并基于敏感波段建立三维波段光谱指数(TBI),结合随机森林(RF)、粒子群优化的极限学习机(PSO-ELM)及卷积神经网络(CNN)算法建立尾砂水分反演模型,以国产高分五号高光谱卫星为数据源进行模型应用,获取尾矿库表层含水时空分布特征。结果表明：(1)尾砂光谱反射率随含水率升高明显下降,在1 455和1 930 nm处出现O—H吸收特征,吸收深度随含水率减小而逐渐减小;(2)基于CARS方法能够对高光谱数据(305波段)有效降维,筛选出18个水分敏感波段,进一步利用敏感...     

NEPE固体推进剂含损伤的黏弹性本构研究

作为一种新型高能固体推进剂,NEPE推进剂在固体火箭发动机中得到了越来越多的应用.本文首先对NEPE固体推进剂进行了松弛试验和单轴等速拉伸试验,在试验结果的基础上,对积分型本构进行了修正,增加了率的影响函数.考虑到颗粒大小的分布,借用Weibull分布函数形式构建了受损面积比与伸长比、应变率的变化关系,建立了一个损伤函数,较好地描述了推进剂拉伸过程中的损伤.综合修正积分本构与损伤函数,给出了NEPE固体推进剂含损伤的黏弹性本构,并用多个速率的拉伸试验曲线进行了验证,结果显示试验值与理论值吻合较好.     

源于非晶合金的透明磁性半导体

磁性半导体兼具磁性和半导体特性,通过操控电子自旋,有望实现接近完全的电子极化,提供一种全新的导电方式和器件概念.目前磁性半导体的研究对象主要为稀磁半导体,采用在非磁性半导体中添加过渡族磁性元素使半导体获得内禀磁性的方法进行制备.但大部分稀磁半导体仅具有低温磁性,成为限制其在室温可操控电子器件中应用的瓶颈.针对这一关键科学问题,本文提出与传统稀磁半导体制备方法相反的合成思路,在磁性非晶合金中引入非金属元素诱发金属-半导体转变,使磁性非晶获得半导体电性,研制出具有新奇磁、光、电耦合特性的非晶态浓磁半导体,揭示其载流子调制磁性的内禀机理,发展出可在室温下工作的p-n结及电控磁器件.