A method to evaluate the relative weights of structural and functional constraints on a genome

Summary A method that numerically evaluates the relative influence of structural or functional constraints on the codon composition of a gene is presented. The method applies to any constraint provided that it can be translated intoa priori probability table of codon usage. The method is very easy to apply to different constraints and to different pools of sequences. Theoretical codon usage obtained from a linear combination of the various constraints was compared with experimental codon frequencies of several classes of genes taxonomically homogeneous and, applying a minimization tecnique, the relative weights of the examined constraints have been evaluated. The results show that a common strategy exists for all coding sequences even though most of the constraints are represented by different probability tables for different pools of genes. We also demonstrate that the method is reliable when it is applied to a single gene, so that it can also be used as a tool to predict the characteristics of a gene from its sequence.     

Secondary structure of T2 intraphage DNA: a spectrophotometric study

Summary Relevant differences in the spectral properties (in the (230÷320) nm range) between intraphage and free T₂ DNA are reported in this work. These differences are very similar to the variation in absorption obtained for a native DNA solution when thepH is lowered starting from the neutral value. On this basis, cytosine protonation in intraphage DNA is hypothesized. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

甾族化合物的仿生选择性卤化

甾族化合物的选择性卤化可以仿生的模拟方式进行,使用“模板导向”,可进攻甾族化合物的特定部位。     

Water concentration and dielectric permittivity in molecular crevices

Summary The behaviour of electric dipoles (water molecules) under the action of a high and nonuniform electric field is investigated. The model incorporates all the features of Clausius-Mossotti’s Debye’s, Onsager’s and Kirkwood’s approaches, and assumes, as a novel feature, that the dielectrophoretic drift of dipoles is balanced by dipole diffusion. A new relationship among local permittivity, electric field and water density is found that could explain why water molecules are rejected by charged molecular crevices which can engineer the binding of ionized ligands at very high rates as compared to bulk water. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Thermodynamic optimality in some biochemical reactions

Summary In this short communication we discuss the possibility that anaerobic glycolisis and (aerobic) respiration, both for adenosine triphosphate (ATP) production, be chemical reactions that follow different thermodynamic-optimization criteria. The former reaction maximizing power output and the latter maximizing a function that represents an advantageous compromise between high power output and low entropy production. Our approach is by means of finite-time thermodynamics (FTT).     

Isotopic biology

Summary A model of genetic code based on isotopic combinations of a single chemical element is discussed as a possible alternative to the ?usual? heteroatomic biology.

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Riassunto Si discute un modello di codice genetico basato su combinazioni isotopiche di un singolo elemento chimico come possibile alternativa all' ?usuale? biologia eteroatomica.

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Резюме Обсуждена модель генетического кода основанная на изотопических комбинациях одного и того же химического злемента. Данная модель представляет собой альтернативу ?обычной? гетероатомной биологии.

     

Information flow in sensory neurons

Summary Recent experiments show that the neural codes at work in a wide range of creatures share some common features. At first sight, these observations seem unrelated. However, we show that all of these features of the code arise naturally in a simple threshold crossing model when we choose the threshold to maximize the transmitted information. This maximization process requires neural adaptation to not only the d.c. signal level, as in conventional light and dark adaptation (for example), but also to the statistical structure of the signal and noise distributions. Interestingly, if we fix the threshold level, we can observe a peak in the transmitted information at a finite value of the input signal-to-noise ratio. However, when we allow the threshold to adapt to the statistical structure of the signal and noise, the transmitted information is always monotonically increasing with increasing input signal-to-noise ratio. Paper presented at the International Workshop ?Fluctuations in Physics and Biology: Stochastic Resonance, Signal Processing and Related Phenomena?, Elba, 5–10 June 1994.     

基于昆虫视觉原理的角速度测量系统

为了解决以往表征法模型中存在的边缘检测同步性问题,参考昆虫视觉中利用相邻小眼信号提取边缘运动的原理,提出了一种角速度测量系统。系统通过对相邻两个探测器的信号进行二值化处理和运算,得到物体不同边缘的运动方向和触发时刻,并通过不同计时器对这些边缘的运动分别计时,能有效地解决物体边缘触发脉冲不同步的问题。在利用硬件电路构建该系统后,实际测量了2种不同角宽度物体的运动角速度,得到系统的角速度测量不确定度为0.55°/s。该结果证明在物体绕系统做圆周运动的情况下,系统可以很好地解决同步性问题。     

仿生阻尼缓冲结构建模及应用研究

对动物运动肢体的结构、缓冲机理进行了分析,建立起其数学模型。通过对模型参数特性的分析,提出了一种新颖的、应用于工程车辆的仿生阻尼缓冲悬挂机构。分析及试用表明,该悬挂机构可同时提高车辆的平顺性、动力性和作业生产率。     

Development of Bionic Polymers

Bionics, an artificial imitation of natural products, has always been a forever dream in the fairy tale or scientific fiction when we were childhood and children live now. However, the development of science in molecular scale makes this dream of childhood and manhood realize today.Bionics, a branch of science concerned with application the data about the functioning of biological system to the solution of engineering problems, become top-priority of science in the 21st century.However, few examples are given in molecular-level or nano-scale controlling lotus-like surface (a bionic surface for vast potential application). In the same time, such a typical bionic surface (as well known, so called "Lotus-effect") is a symbol or a totem that scientists can develop a novel approach to prepare desired surface and to control its microstructure or morphology at one's pleasure.In general, a film with a water contact angle (CA) higher than 150° can be defined as a superhydrophobic surface. The Langmuir-Blodgett film prepared by using CF3(CF2)10COOH possesses the lowest surface tension, which is 6 mJ/m2 (1). However, the water CA on a smooth surface with regularly aligned C20F42 with close-hexagonal packed -CF3 groups is only 119° (2).Obviously, only adjusting chemical composition is not enough to produce a superhydrophobic surface. Wenzel et al (3) suggested that the contact angle θ' of a liquid droplet on a rough solid surface should be written as:cosθ, =γcosθ = γ(γs-γsl)/γl, here γ is a roughness factor and γsl, γs and γl denote the interfacial tensions of the solid-liquid, the solid-gas, and the liquid-gas interfaces,respectively. This γ is always larger than 1 and a rough surface will be more water-repellent or more wettable to a liquid when intrinsic contact angle θ is bigger or smaller than 90°, respectively.Therefore, a general approach to obtain superhydrophobic surfaces is using a combination of depressing surface energy and enhancing surface roughness (4-17).Super-hydrophobic polymeric surface has been prepared in this case with a mixture of low-cost fluorine-end-capped polyurethane(FPU) and commonly available polymethyarylates(PMA) under ambient conditions. No obvious structures were observed by SEM for the pure FPU coated surface.The surface morphology is uniformly smooth at both low and high magnifications. The CA on the surface is about 95°, which indicates that FPU film has better hydrophobicity than pure polyurethane without fluorine-group, whose CA is about 65°. However, the hydrophobicity of polymer surface changes dramatically as the film is directly prepared through a one-step coating of a FPU/PMA solution between 10-30℃. The CA is up to 166 . The result shows that the SA can be dramatically decreased with small amount of FPU, and the SA reached a limiting value of 3.4 ± 2.0 ° when the FPU content in the FPU/PMA mixture is between 20 ～ 60 wt%. The water drop is unstable on these surfaces, and with a very small tilt-angle, the water drop will roll off the surface.It means that such a polymeric surface exhibits an excellent superhydrophobicity. In addition, the polymer surface possesses not only a better hydrophobicity than that of natural lotus leaf (CA measured is about 160°), but also a lypophobic property: the oil contact angle on the same surface is 140°, while the surface of lotus is lypophilic. Most interestingly, we have found that the coated film prepared by FPU/PMA mixture has a two-length scaled rough micro-nano-binary structure, that is, every micro-papilla (300-700nm) on the polymeric surface is also covered by nano-papillae ranging from 30-40nm. These MNBs is very much the same as the natural lotus-leaf surface in micro- and nano-scales. Compared with lotus surface structure, the NMBs structure on this bionic polymeric surface prepared is in less scale. The results clearly demonstrated that a bionic polymeric surface similar to the natural lotus-leaf surface can be obtained by a one-step coating process. The results showed also that such a bionic polymeric surface possess of some "self-repairing" properties similar to that of natural surfaces and the effects of preparation temperature and concentration as well as substrate made no obvious difference on the hydrophobicity of the bionic polymeric surfaces..In conclusion, we demonstrated that the MNBs of a bionic polymeric film has been one-step obtained with the use of the self-aggregation of PMA combining with a nano-scaled phase separation of amphiphilic copolymer during the drying process in ambient atmosphere. This remarkable result provides many potential possibilities, including coating, hygienic, medical,environmental, and industrial processing applications.