函数的逼近及其在下半连续函数可微性中的应用

通过函数的下卷积函数列的逼近方法,在变分原理中从扰动最小值点集的“大小”入手,研究了下半连续函数的可微性。     

中国陆相油气的形成和运移(Ⅱ)

本文(Ⅰ)着重研究了中国陆相湖盆沉积物中有机质向油气演化的过程.本文(Ⅱ)阐明了现代青海湖沉积物埋藏初期及早期成岩作用过程中有机质的演化特征.其结果表明陆相有机质大量开始向石油转化的深度随不同地区、不同时代、不同类型的有机质而异.最后,运用特征有机化合物、稀有气体同位素等资料,结合构造发展史阐述我国陆相油气运移的类型、规模和途径.指出近油源短距离是陆相油气运移的基本特征.     

我国正负术历史

九章算术大約在公元一世紀編集成书,其中已著录正负术,这是我国古代数学上的光輝成就。正負术的产生有它在数学本身內在的发展,但为什么我国很早就熟悉了正負术,这和我国古代天文学的发展有关。东汉元和二年(85),我国天文学家创制的四分曆中,明白的記載了正負术的方法。它說: “強正弱负也。其強弱相減,同名相去;异名从之,从強进少为弱,从弱退少为強。”四分曆在計算太阳的視位置度数时,以不滿整度数部分用少、半、太来区别。少是1/4,半是2/4,太是3/4。比“少”多一些的叫少强,比“少”少一些的叫少弱。它們间的关系是:     

Chemical Oxidation of La2CuO4 Epitaxial Thin Films Grown by Pulsed Laser Deposition

Chemical oxidation is used to induce superconductivity in La2CuO4 expitaxial thin films fabricated by pulsed laser deposition technique. Details about the influence of oxidation time on structural, surface morphology, Raman spectra, and electrical properties have been investigated. The results convince that successful uptake of oxygen occurs in the oxidized films, and the content of the inserted oxygen increases with increasing oxidation interval. The possible mechanism for the excess oxygen insertion into the film is also discussed.     

A Base-Emitter Self-Aligned Multi-Finger Sil-xGex/Si Power Heterojunction Bipolar Transistor

With a crystal orientation dependent on the etch rate of Si in KOH-based solution, a base-emitter self-Migned large-area multi-finger configuration power SiGe heterojunction bipolar transistor （HBT） device （with an emitter area of about 880μm^2） is fabricated with 2μm double-mesa technology. The maximum dc current gain is 226.1. The collector-emitter junction breakdown voltage BVcEo is 10 V and the collector-base junction breakdown voltage BVcBo is 16 V with collector doping concentration of 1 × 10^17 cm^-3 and thickness of 400nm. The device exhibited a maximum oscillation frequency fmax of 35.5 GHz and a cut-off frequency fT of 24.9 GHz at a dc bias point of Ic = 70 mA and the voltage between collector and emitter is VCE = 3 V. Load pull measurements in class-A operation of the SiGe HBT are performed at 1.9 GHz with input power ranging from OdBm to 21 dBm. A maximum output power of 29.9dBm （about 977mW） is obtained at an input power of 18.SdBm with a gain of 11.47dB. Compared to a non-self-aligned SiGe HBT with the same heterostructure and process, fmax and fT are improved by about 83.9% and 38.3%, respectively.     

Measuring Grüneisen Parameter of Lead by High Pressure-Jump Method

Using the technology of pressure jump, variations of temperature associated with pressure from 2.4 GPa to 4.6 GPa are measured for lead. The Grfuneisen parameter is calculated from the thermodynamic relation γ =（Ks/T）（aT/aP）s, in which substitution of △T/△P for aT/aP at median pressure is strictly justified. The correction of temperature change is carried out by analysing the experimental data, which makes the process more approaching to an adiabatic condition. The calculated values of △T/ △ P and γ gradually decrease with the increasing pressure. The decrease trend is consistent with the previous work. The γ values in the range of 2-3 GPa are averagely higher than the results of Ramakrishnan et al., indicating the effect of temperature correction. The improved method is promising for measurements of Grfineisen parameter to higher pressure range.     

碳包覆铁纳米颗粒的气相爆轰合成北大核心CSCD

以粉末状与气态二茂铁为原料,以氢气和氧气混合气体为爆轰能源,采用气相爆轰法进行了合成碳包覆铁纳米颗粒实验。XRD和TEM实验结果表明,采用两种不同状态的二茂铁,均得到了纳米碳包覆铁颗粒。该包覆颗粒的组成核为铁或铁碳化合物,外层壳主要由石墨碳组成,大部分球形纳米颗粒尺寸分布于5-30 nm之间。通过对比发现,采用气态二茂铁爆轰时,所得到的碳包铁粒度分布较为集中,壳层厚度比较均匀,且粒子具有较好的球形状。最后结合铁碳合金相图,从热处理角度对气相爆轰合成碳包覆铁纳米颗粒的机理进行了分析,得出产物中α-Fe与Fe_3C的形成过程。分析了碳包覆铁纳米颗粒的磁滞回线,其表现出硬磁性与顺磁性双重性质。     

用于MOCVD的金属有机Ba源的制备及性质研究北大核心CSCD

金属有机化学气相沉积法(MOCVD)能够在长的柔性金属基带上连续、快速、均匀沉积YBa2Cu3O7-δ(YBCO)薄膜,因而极具开发价值.MOCVD制备YBCO涂层导体的关键技术之一在于金属有机源(MO)的制备.国外化学试剂公司在以2,2,6,6-4甲基-3,5庚二酮(thd)为配体的MO源上技术较为成熟,并已实现商业化生产,但是价格昂贵,其中Ba(thd)2价格约为700元/g.另外,与Y(thd)3和Cu(thd)2相比,Ba(thd)2挥发性、稳定性差且制备困难.本文对金属有机Ba源的制备、稳定性及真空下的蒸发特性进行了研究.通过引入助配体四乙烯基戊胺,该Ba源的蒸发温度比纯的Ba(thd)2更低,稳定性更高,且成本仅为30元/g,对于降低YBCO高温超导带材的制备成本具有重要意义.采用该Ba源制备的300nm厚YBCO薄膜的Jc达到2.0MA/cm2(77K,0T),表明其具有很好的实用性.     

Fe-N软磁薄膜的结构和性能

用RF溅射制备厚度为200 nm的Fe-N薄膜在250℃, 12000 A/m磁场下真空热处理后，当N含量在5%～7%(原子百分数)范围内形成α′+α″相时，4πM_S可达2.4 T, H_c＜80 A/m, 2～10 MHz下高频相对导磁率μ_r=1500，可满足针对10 Gb/in2存储密度的GMR/感应式复合读写磁头中写入磁头的需要. Fe-N系薄膜中α′相的形成机理和点阵常数与块状试样按Bain机理形成的α′相有明显的差别，得到了薄膜中α′相的a,c与Cα′_N之间的线性关系式.     

用气室法研究分子反应动力学的新进展

介绍了研究分子反应动力学的两大主要实验方法之一的气室法、在研究有热原子参与的反应所取得的新进展，讲述了此方法“新用”的理论依据及相应的实验条件，至此，可以获得对分子反应动力学更精细的信息，例如，态－态分辨的微分反应截面，并对两大方法进行了“现代”对比。还对两方法的发展前景作了适度的分析。