基于子集模拟的建设工程项目多资源均衡优化算法

为高效、稳定地求解建设工程项目管理过程中的多资源均衡问题,提出一种基于子集模拟的优化算法.多资源均衡问题中,如直接采用工序计划开始时间作为决策变量,在优化算法的实现时易违反工序间的逻辑关系.为避免该问题,本文采用工序计划开始时间的间隔率变量表示(在二者的映射中考虑工序间的逻辑关系),并据此建立间隔率变量表示的建设工程项目多资源均衡优化模型,以简化基于子集模拟的优化算法的操作流程.通过算例验证,与目前应用较广的遗传算法相比,本文提出的优化算法在最优解的获取稳定性上有较大改进.     

高端口隔离度的太赫兹基波上混频器设计

介绍了一种基于IHP 0.13 μm SiGe BiCMOS工艺,具有高本振（Local Oscillator, LO）/射频（Radio Frequency, RF）及本振/中频（Intermediate Frequency, IF）端口隔离度的太赫兹基波上混频器.该混频器采用了吉尔伯特双平衡结构,本振信号通过共面波导（Coplanar Waveguide, CPW）传输来抑制其在传输过程中由于强寄生耦合效应造成的传输不对称性,削弱了由该不对称性造成的LO/RF端口隔离度恶化的特性.通过采用非对称性的开关互联结构降低本振信号在开关晶体管集电极端寄生耦合的不平衡性,提升本振信号在开关晶体管集电极端的对消效率,通过在版图中合理布局跨导级晶体管的位置来抑制本振信号在中频端口的泄露.后仿真结果表明：在2.2 V电源电压下,本振信号为230 GHz,中频信号为2 ~ 12 GHz,该上混频器工作在218 ~ 228 GHz时,LO/RF端口隔离度大于24 dB, LO/IF端口隔离度大于20 dB,转换增益为-4 ~ -3.5 dB.当中频信号为10 GHz时,输出1 dB压缩点为-14.8dBm.电路直流功耗为42.4 mW,芯片的核心面积为0.079 mm2.该上混频器可应用于采用高阶正交幅度调制（Quadrature Amplitude Modulation, QAM）方式的无线发射系统.     

预言现代神经科学的文学教授

21世纪见证了神经科学的发展,我们更加深入地理解了脑,不再局限于脑的解剖学基础,而是转向了认知的角度.每年都会涌现出对记忆和想象力的新认识,同时让人惊讶于这一学科与人类学和哲学等学科的深度交叉.不到一个世纪之前,在二战的余波中,一位剑桥大学的文学教授率先提出了他对认知的看法,这一看法如今仍然相当现代.而直到最近,我们才...     

一次不可思议的跨洋漂流造就了人类起源的可能

人类同猩猩、猿、猴一样发源于非洲.但从现有研究来看,更早的祖先在进入非洲之前起源于非洲之外,比如亚洲.在大约5000万年前,非洲是一片被海水与世界隔绝的孤岛.那么这些祖先是如何到达非洲的呢? 最容易想到的是这些祖先通过陆桥进入非洲,但是目前已有的地理学证据不支持这一理论.相反,地理学证据提示了我们一种看起来最不可能的方...     

脑让人每日耳目一新

脑的"可塑性"是现代科学的伟大发现之一,但神经科学家大卫?伊戈曼(David Eagleman)认为这种描述具有一定误导性."塑料"通过模具固定为一种特定的形状,而脑的物质结构却处在不断变化之中.但伊戈曼无法摆脱这个词:"所有的文献都在用这个词,我只能尽量避免."伊戈曼对脑的"计算机类比"也有所质疑.他创造出了"活体连...     

此号错误

隐约响起的隆隆声如同打雷一般,将沉睡的我吵醒.我翻转身,望向窗外——夜空清澈又静谧,满是明亮的星星,视野之内见不到半片云朵.我叹息了一声,闭上眼睛,渴望能有一晚不受打搅的好眠. 一声古怪的轻鸣长驱直入,传进我的耳朵,开始变得越来越响,害得我背上的汗毛都竖立得笔直.窗外有个暗影在移动,随着它从夜空中逐渐下降,星星一颗又一...     

人类进化故事如何继续开枝散叶

我们人类不再是过去的模样.在过去20年里,基因组学、古DNA学和古人类学齐心协力,彻底修订了我们对于人类起源的理解.在最近几十万年里,人类进化的多样性和复杂性甚至超越了我们最无稽的想象.然而,我们对人类起源的了解越来越清楚,对于人类进化的叙述却越来越混乱,越来越不简练.事实证明,人类这个物种的身份纷繁复杂.     

科学和灵性 ——寻找火星上的生命

在西方长期的科学和宗教斗争中,某些角色并非一成不变.起初,宗教领袖坚信神创万物,他们谴责(经常是处死)那些质疑圣经中关于地球起源以及天堂美好故事之人.而科学家则不断对此提出挑战.如今,科学家反而成了确定论者,以理查德?道金斯(Richard Dawkins)为代表的新无神论者认为,宗教人士既软弱又愚蠢,因为他们无法接受...     

Sperm viability in the reproductive tract of females in a population of Sceloporus mucronatus exhibiting asynchronous reproduction

Asynchronous reproduction is a common phenomenon in high-elevation populations of lizards from Central México. Sperm storage in the reproductive tract of females is the mechanism for making oocyte fertilization possible. Our study addresses questions related to functional oviductal sperm storage of females mating on different dates throughout the reproductive season. A population of Sceloporus mucronatus with copulation in the summer and ovulation in the fall was chosen for this experiment. Eleven females that copulated in the field during June and 13 females that copulated in captivity during August were maintained in the laboratory until parturition. The number of pregnant females and the litter sizes produced in each experimental group were indicative of the viability of the stored sperm. Sperm stored in the reproductive tract of females were able to fertilize eggs after 4 months. No significant differences were found in the number of pregnant females between the 2 experimental groups nor in the litter sizes that they produced. We found that the amount of time sperm were held in the female reproductive tract (ca. 3 months) had no effect on the capacity of sperm to fertilize eggs. Histological examination of 8 oviducts collected before the mating season eliminated the possibility of sperm storage from one year to the next. In this system, sperm retention could have evolved as a response mechanism to deal with the asynchrony between sexes in the reproductive cycles. However, we cannot rule out alternative hypotheses.     

New testing methodology for the quantification of rock crushability: Compressive crushing value (CCV)

Crushing is a size reduction process that plays a key role in both mineral processing and crushing-screening plant design. Investigations on rock crushability have become an important issue in mining operations and the manufacture of industrial crusher equipment. The main objective of this research is to quantify the crushability of hard rocks based on their mineralogical and mechanical properties. For this purpose, the mineralogical, physical, and mechanical properties of various hard rocks were determined. A new compressive crushing value (CCV) testing methodology was proposed. The results obtained from CCV tests were compared with those from mineralogical inspections, rock strength as well as mechanical aggregate tests. Strong correlations were found between CCV and several rock and aggregate properties such as uniaxial compressive strength (UCS), the brittleness index (S₂₀), and aggregate impact value (AIV). Furthermore, the relationship between the mineralogical properties of the rocks and their CCVs were established. It is concluded that the proposed testing methodology is simple and highly repeatable and could be utilized as a pre-design tool in the design stage of the crushing process for rock quarries.