Non-classical light generated by quantum-noise-driven cavity optomechanics

Optomechanical systems, in which light drives and is affected by the motion of a massive object, will comprise a new framework for nonlinear quantum optics, with applications ranging from the storage and transduction of quantum information to enhanced detection sensitivity in gravitational wave detectors. However, quantum optical effects in optomechanical systems have remained obscure, because their detection requires the object’s motion to be dominated by vacuum fluctuations in the optical radiation pressure; so far, direct observations have been stymied by technical and thermal noise. Here we report an implementation of cavity optomechanics using ultracold atoms in which the collective atomic motion is dominantly driven by quantum fluctuations in radiation pressure. The back-action of this motion onto the cavity light field produces ponderomotive squeezing. We detect this quantum phenomenon by measuring sub-shot-noise optical squeezing. Furthermore, the system acts as a low-power, high-gain, nonlinear parametric amplifier for optical fluctuations, demonstrating a gain of 20?dB with a pump corresponding to an average of only seven intracavity photons. These findings may pave the way for low-power quantum optical devices, surpassing quantum limits on position and force sensing, and the control and measurement of motion in quantum gases.     

摇蚊见证气候变化

对于蠓虫,大家再也熟悉不过了。这些纠缠不休的小不点,常常令人生厌。可是,你知道吗？有些蠓虫非但不叮咬人畜,还能告诉我们一些有关气候变化的秘密呢!这类蠓虫有着另外一个名字——摇蚊。     

动物思维和人类思维——结论

思维是一个词,而不是一件东西。我们可以按照我们喜欢的方式使用这个词。如果我们用它指有了人类的语言能力才能产生的心理过程,那么,动物思维这一提法不过是动物与思维两个词的组合而已,并无实际意义;但是,如果我们认为,不借助言词也能进行某种思维,并且认为,思维可以是一种意向、一种想象、一种意图,或一种期望,那么,“这种思维除了见之于我们人     

Structure of the E. coli protein-conducting channel bound to a translating ribosome

Secreted and membrane proteins are translocated across or into cell membranes through a protein-conducting channel (PCC). Here we present a cryo-electron microscopy reconstruction of the Escherichia coli PCC, SecYEG, complexed with the ribosome and a nascent chain containing a signal anchor. This reconstruction shows a messenger RNA, three transfer RNAs, the nascent chain, and detailed features of both a translocating PCC and a second, non-translocating PCC bound to mRNA hairpins. The translocating PCC forms connections with ribosomal RNA hairpins on two sides and ribosomal proteins at the back, leaving a frontal opening. Normal mode-based flexible fitting of the archaeal SecYEbeta structure into the PCC electron microscopy densities favours a front-to-front arrangement of two SecYEG complexes in the PCC, and supports channel formation by the opening of two linked SecY halves during polypeptide translocation. On the basis of our observation in the translocating PCC of two segregated pores with different degrees of access to bulk lipid, we propose a model for co-translational protein translocation.     

治病的新武器

满装杭休的美膜囊在治疗人类疾病中,也许将触发一场医学革命。如果患癌症,将来医生会将病人的血样送交单克隆抗体制造室.药室将用血样中的白细胞产生的相应抗体去抗击病人所患的癌症。这一治疗的全部诀窍在于微型荚膜内成药。     

生态系统机能障碍的鉴定与分类

虽然在全球范围内，生态系统受胁迫的案例正在呈上升趋势，但是研究对同样情况有参考价值的行之有效的方法还未引起足够重视。在环境管理中采用更加系统的方法来作有效的分析是很有必要的。本文提出一个鉴定生态系统机能障碍的框架结构和以压力与反应为基础的分类系统，此法不需要了解由于偶然原因而导致环境恶化的作用机理。通过引入人类医学的分类技术，把生态系统看作一名病人。不论是人类医学还是生态系统，区分病理反应和自然反应必需以环境背景为基础。对于一个特定的病人来说，考虑其所处的特定状况及采用合适的治疗方法是很重要的。…     

概 率 逻 辑 学 习 概 述

在归纳逻辑编程研究的基础上, 给出了概率逻辑学习的一种形式化定义框架. 根据不同概率逻辑学习方法在实例表示和概率定义上的不同, 讨论了3种概率逻辑学习框架： 解释学习、 证明学习和蕴涵学习; 并据此对现有的典型概率逻辑学习方法和系统进行了分析和概述.