Ribozyme-catalyzed transcription of an active ribozyme

A critical event in the origin of life is thought to have been the emergence of an RNA molecule capable of replicating a primordial RNA "genome." Here we describe the evolution and engineering of an RNA polymerase ribozyme capable of synthesizing RNAs of up to 95 nucleotides in length. To overcome its sequence dependence, we recombined traits evolved separately in different ribozyme lineages. This yielded a more general polymerase ribozyme that was able to synthesize a wider spectrum of RNA sequences, as we demonstrate by the accurate synthesis of an enzymatically active RNA, a hammerhead endonuclease ribozyme. This recapitulates a central aspect of an RNA-based genetic system: the RNA-catalyzed synthesis of an active ribozyme from an RNA template.     

Measurements of the equation of state of deuterium at the fluid insulator-metal transition

A high-intensity laser was used to shock-compress liquid deuterium to pressures from 22 to 340 gigapascals. In this regime deuterium is predicted to transform from an insulating molecular fluid to an atomic metallic fluid. Shock densities and pressures, determined by radiography, revealed an increase in compressibility near 100 gigapascals indicative of such a transition. Velocity interferometry measurements, obtained by reflecting a laser probe directly off the shock front in flight, demonstrated that deuterium shocked above 55 gigapascals has an electrical conductivity characteristic of a liquid metal and independently confirmed the radiography.     

Oxygen-mediated diffusion of oxygen vacancies on the TiO2(110) surface

Defects such as oxygen vacancies play a crucial role in the surface properties of transition metal oxides. By means of time-resolved, high-resolution scanning tunneling microscopy, we unraveled an adsorbate-mediated diffusion mechanism of oxygen vacancies on rutile TiO2(110). Adsorbed oxygen molecules mediate vacancy diffusion through the loss of an oxygen atom to a vacancy and the sequential capture of an oxygen atom from a neighboring bridging oxygen row, leading to an anisotropic oxygen vacancy diffusion pathway perpendicular to the bridging oxygen rows.     

Optomechanically induced transparency

Electromagnetically induced transparency is a quantum interference effect observed in atoms and molecules, in which the optical response of an atomic medium is controlled by an electromagnetic field. We demonstrated a form of induced transparency enabled by radiation-pressure coupling of an optical and a mechanical mode. A control optical beam tuned to a sideband transition of a micro-optomechanical system leads to destructive interference for the excitation of an intracavity probe field, inducing a tunable transparency window for the probe beam. Optomechanically induced transparency may be used for slowing and on-chip storage of light pulses via microfabricated optomechanical arrays.     

Serial-choice reaction time: inadequacies of the information hypothesis

The results of an experiment on serial-choice reaction time, specifically designed as a critical test of the Information Hypothesis, lead to rejection of the hypothesis; information is found to be neither a necessary nor a sufficient condition to account for the data. Where previously information had been interpreted as a determinant of reaction time, it was usually confounded with the probability of nonrepetition of a signal. Thus, to the extent that this confounding is present in previous experiments, the inference attributing an increase in reaction time to an increase in information is logically invalid.     

Electrochromic nanocrystal quantum dots

Incorporating nanocrystals into future electronic or optoelectronic devices will require a means of controlling charge-injection processes and an understanding of how the injected charges affect the properties of nanocrystals. We show that the optical properties of colloidal semiconductor nanocrystal quantum dots can be tuned by an electrochemical potential. The injection of electrons into the quantum-confined states of the nanocrystal leads to an electrochromic response, including a strong, size-tunable, midinfrared absorption corresponding to an intraband transition, a bleach of the visible interband exciton transitions, and a quench of the narrow band-edge photoluminescence.     

Creation of liquid crystal waveguides with scanning force microscopy

The rubbing of a polymer layer, a commonly applied process, leads to an anisotropic surface morphology, aligning liquid crystal molecules. Scanning force microscopy can be used to intentionally create areas with a similar anisotropy by operating the instrument at loads in the range of 10(-7) to 10(-5) newtons. These areas have an orientation effect on liquid crystals indistinguishable from the rubbing process, which allows a systematic investigation of the orientation properties of an alignment layer as a function of its nanometer-scale morphology. Refractive index patterns can be tailored with this method by scratching a suitable area, as demonstrated by fabrication of an optical waveguide 6 micrometers wide and 5 millimeters long.     

企业内部控制的现状与对策

企业内部控制的有效性是一个企业是否建立现代法人治理结构的标志。内部控制制度的建立和施行使企业各种资源的效用达到最大化。但是目前我国企业的内部控制却存在着诸多问题 ,形成了现有企业向现代企业制度跨越的瓶颈。     

Inverse temperature dependence of toughness in an ultrafine grain-structure steel

Materials are typically ductile at higher temperatures and become brittle at lower temperatures. In contrast to the typical ductile-to-brittle transition behavior of body-centered cubic (bcc) steels, we observed an inverse temperature dependence of toughness in an ultrahigh-strength bcc steel with an ultrafine elongated ferrite grain structure that was processed by a thermomechanical treatment without the addition of a large amount of an alloying element. The enhanced toughness is attributed to a delamination that was a result of crack branching on the aligned {100} cleavage planes in the bundles of the ultrafine elongated ferrite grains strengthened by nanometer-sized carbides. In the temperature range from 60 degrees to -60 degrees C, the yield strength was greater, leading to the enhancement of the toughness.     

西安市旅游目的地旅游形象感知与评价研究（英文）

[目的]探讨旅游目的地形象测量的方法,并以西安市为例进行实证研究。[方法]运用非结构化和结构化方法设计调查问卷,运用SPSS软件进行评价分析西安市旅游形象的感知特征与存在问题。[结果]西安的旅游形象显著表现为文物历史古迹氛围,以兵马俑、城墙、大雁塔、华清池等为主要载体,总体上呈积极性。旅游传播、旅游基础设施建设、旅游交通、旅游服务等方面对西安旅游形象的塑造具有一定的负面影响。[结论]游客对旅游资源评价高于景区评价,表明西安的旅游资源虽具有较高知名度,但缺乏形成强有力的核心竞争力和完整的旅游产业链,需要采取正确的营销策略以提高旅游者对西安的熟悉度,西安旅游景区的发展须要关注旅游者需求变化,注重新的旅游产品和项目开发,增强游者满意度。     

Synthesis and application of modulated polymer gels

A class of environmentally responsive materials based on the spatial modulation of the chemical nature of gels is proposed and demonstrated here. The modulation was achieved by limiting the interpenetration of part of one gel network with another gel network. The gels so produced have an internally heterogeneous or modulated structure. Three simple applications based on the modulated gels are described here: a bigel strip, a shape memory gel, and a gel "hand." The bigel strip bends almost to a circle in response to a temperature increase or an increase in solvent concentration. The shape memory gel changes its shape from a straight line to a pentagon to a quadrangle as the temperature increases. These transitions from one shape to another are reversible. The gel "hand" in water can grasp or release an object simply by an adjustment of the temperature.     

Receptive field mechanism in the vertebrate retina

In the catfish retina there are two types of ganglion cells: in one type (type A cell) a spot of light at the center of its receptive field gives rise to a sustained discharge whereas an annulus gives rise to a transient response, and in the other type (type B cell) the response pattern is reversed for a spot and an annulus. Current injected into the horizontal cell induces spike discharges of the ganglion cell very similar to that elicited by a spot of light or by an annulus. In both types of receptive fields, depolarization of the horizontal cell gives rise to a response of the ganglion cell similar to that elicited by a spot of light, whereas hyperpolarization of the cell gives rise to a response of the ganglion cell similar to that elicited by an annulus. Current through a single injecting electrode could drive two types of cells simultaneously. Interaction between a spot of light and an annulus can also be simulated by replacing one light stimulus by current of the proper polarization injected into the horizontal cells. Results suggest that interactions among three neuronal structures, the receptor, the horizontal cell, and the bipolar cell, produce the basic receptive field organization in the channel catfish.     

Microbial dehalorespiration with 1,1,1-trichloroethane

1,1,1-Trichloroethane (TCA) is a ubiquitous environmental pollutant because of its widespread use as an industrial solvent, its improper disposal, and its substantial emission to the atmosphere. We report the isolation of an anaerobic bacterium, strain TCA1, that reductively dechlorinates TCA to 1,1-dichloroethane and chloroethane. Strain TCA1 required H2 as an electron donor and TCA as an electron acceptor for growth, indicating that dechlorination is a respiratory process. Phylogenetic analysis indicated that strain TCA1 is related to gram-positive bacteria with low DNA G+C content and that its closest relative is Dehalobacter restrictus, an obligate H2-oxidizing, chloroethene-respiring bacterium.     

Atomic-resolution electrochemistry with the atomic force microscope: copper deposition on gold

The atomic force microscope (AFM) was used to image an electrode surface at atomic resolution while the electrode was under potential control in a fluid electrolyte. A new level of subtlety was observed for each step of a complete electrochemical cycle that started with an Au(111) surface onto which bulk Cu was electrodeposited. The Cu was stripped down to an underpotential-deposited monolayer and finally returned to a bare Au(111) surface. The images revealed that the underpotential-deposited monolayer has different structures in different electrolytes. Specifically, for a perchloric acid electrolyte the Cu atoms are in a close-packed lattice with a spacing of 0.29 +/- 0.02 nanometer (nm). For a sulfate electrolyte they are in a more open lattice with a spacing of 0.49 +/- 0.02 nm. As the deposited Cu layer grew thicker, the Cu atoms converged to a (111)-oriented layer with a lattice spacing of 0.26 +/- 0.02 nm for both electrolytes. A terrace pattern was observed during dissolution of bulk Cu. Images were obtained of an atomically resolved Cu monolayer in one region and an atomically resolved Au substrate in another in which a 30 degrees rotation of the Cu monolayer lattice from the Au lattice is clearly visible.     

Correction

An article reporting a congressional hearing on the National Cancer Institute (NCI) (News and Comment, 20 Nov., p. 887) incorrectly states that the institute allowed an unnamed individual to produce a preparation called "Jim's Juice" under what is known as a "compassionate investigational new drug" permit. The NCI, which does not have authority to issue such IND's, was not involved in the matter. The article also refers to an internal memo written by an NCI researcher about the alleged misuse of an experimental drug called Mitoxantrone. The drug in question was one known as M-AMSA, a new agent against acute leukemia.     

Quantum conversion and image detection by a bacteriorhodopsin-based artificial photoreceptor

A thin film (50 to 500 angstroms thick) comprising fragments of bacteriorhodopsin (bR)-containing purple membrane was formed on an SnO(2) conductive electrode by the Langmuir-Blodgett method. The film was put into contact with a thin, aqueous electrolyte gel to construct an electrochemical sandwich-type photocell with a junction structure SnO(2)/bR/electrolyte/Au electrode. Under visible light irradiation, the bR-based photocell produced an efficient rectified photocurrent that proved to have unique differential responsivity to light intensity, which is characteristic of in vivo biological photoreceptors. An artificial photoreceptor comprising a pixel network of the bR photocell was fabricated in an attempt to study image-detecting and processing abilities of bR.     

发挥基层林业站在集体林权改革中的重要作用

作为一个职能部门,基层林业站在集体林权改革中充当着一个举足轻重的角色,如何充分发挥作用基层林业站在集体林权制度改革中的作用至关重要。     

试论传统耻感文化的内涵、价值及启示

传统文化中的耻感对个人道德自身修养的提高和国家治理都曾发挥重要作用。对个人而言,耻感的树立是立人之本,耻感的养护是其道德安身之路,而对于国家治理来说,耻感的推行,是正民导俗之源,更是安邦之基。     

Infant responses to impending collision: optical and real

Twenty-four infants ranging in age from 2 to 11 weeks responded to symmetrically expanding shadows, which optically specify an approaching object, with an integrated avoidance response and upset. This response did not occur for asymmetrically expanding shadows nor for contracting shadows that specify an object on a miss path and a receding object. The response was observed in all the infants regardless of age, and the addition of kinetic depth information to the displays did not increase the intensity or likelihood of the response. In a second experiment, seven infants defensively reacted to the approach of a real object except when it was on a miss path.