基于Android平台的一种保护隐私的即时通讯工具的设计与实现

在移动互联网飞速发展的今天,即时通讯工具已经成为人们生活和工作中不可或缺的工具。但是,国内外主流的即时通讯工具依然面临着两大主要问题。一个是基于不同协议的软件的互联互通问题,另一个是日益严峻的即时通讯的安全性与隐私性问题。为了从根本上解决问题,针对即时通讯工具的特点进行了深入分析,最终设计并实现了一款基于安卓平台上更具安全性、更实用、用户体验更好的即时通讯工具SecretChat。本工具采用开放的XMPP通讯协议,并在XMPP上实现OTR安全协议。经过系统测试,系统具备稳定性并且具有良好的互联互通性能和隐私保护功能。     

稳定性同位素的分离

近年来同位素越来越广泛地被应用于科学研究和生产技术中,因此同位素的制备和浓集的技术也得到了很大的发展。对于稳定性同位素,它們都是天然存在的,因此没有人工制备的过程,只需对它們进行分离(或称浓集)。到目前为止,稳定性同位素的分离技术已经相当完善,方法很多,其規模可以从示踪量的制备到工业規模的大量生产,而且可以应用于所有元素的同位素,有些产品的浓度可以达99％以上。本文就是要对这些被广泛采用的各种分离方法作简要的論述和介紹。有些天然的放射性同位素(如U~(235),U~(238))和长寿命的人工放射性同位紊、(如H~3)的浓集也属于这些方法。     

基于改进集的带约束集值向量均衡问题的最优性条件

在局部凸空间中,研究了带约束集值向量均衡问题的最优性条件.首先,利用改进集引进了带约束集值向量均衡问题的E-Henig真有效解和E-超有效解的概念.其次,在邻近E-次似凸的假设下,建立了带约束集值向量均衡问题的E-Henig真有效解的充分必要性条件.最后,在邻近E-次似凸的假设下,建立了带约束集值向量均衡问题的E-超有效解的必要性条件.     

Observation of multiple charge density wave phases in epitaxial monolayer 1T-VSe2 film

As a special order of electronic correlation induced by spatial modulation, the charge density wave (CDW) phenomena in condensed matters attract enormous research interests. Here, using scanning—tunneling microscopy in various temperatures, we discover a hidden incommensurate stripe-like CDW order besides the ($sqrt{7}$ × $sqrt{3}$) CDW phase at low-temperature of 4 K in the epitaxial monolayer 1T-VSe₂} film. Combining the variable-temperature angle-resolved photoemission spectroscopic (ARPES) measurements, we discover a two-step transition of an anisotropic CDW gap structure that consists of two parts Δ₁ and Δ₂. The gap part Δ₁ that closes around ～ 150 K is accompanied with the vanish of the ($sqrt{7}$ × $sqrt{3}$) CDW phase. While another momentum-dependent gap part Δ₂ can survive up to ～ 340 K, and is suggested to the result of the incommensurate CDW phase. This two-step transition with anisotropic gap opening and the resulted evolution in ARPES spectra are corroborated by our theoretical calculation based on a phenomenological form for the self-energy containing a two-gap structure Δ₁ + Δ₂, which suggests different forming mechanisms between the ($sqrt{7}$ × $sqrt{3}$) and the incommensurate CDW phases. Our findings provide significant information and deep understandings on the CDW phases in monolayer 1T-VSe₂} film as a two-dimensional (2D) material.