光学非球面反射镜轻量化制造技术

新一代的空间相机一般通过采用轻质大尺寸的非球面光学元件来提高系统的成像质量，以降低系统复杂性。而空间相机中的结构件主要是用来支撑和定位主镜，如果主镜制作得更轻，则系统的其它结构将会设计得更加轻巧。受此趋势影响，大口径非球面镜的轻量化问题成为一个研究热点。     

Complex genetic evolution of artificial self‐replicators in cellular automata

It is widely believed that evolutionary dynamics of artificial self‐replicators realized in cellular automata (CA) are limited in diversity and adaptation. Contrary to this view, we show that complex genetic evolution may occur within simple CA. The evolving self‐replicating loops (“evoloops”) we investigate exhibit significant diversity in macro‐scale morphologies and mutational biases, undergoing nontrivial genetic adaptation by maximizing colony density and enhancing sustainability against other species. Nonmutable subsequences enable genetic operations that alter fitness differentials and promote long‐term evolutionary exploration. These results demonstrate a unique example of genetic evolution hierarchically emerging from local interactions between elements much smaller than individual replicators. © 2004 Wiley Periodicals, Inc. Complexity 10: 33–39, 2004     

Structural and dynamic variations in DNA hexamers containing T-T and F-F single and tandem internal mispairs

Molecular dynamics simulations of double-helical DNA oligomers have been performed to investigate differences in the structure, dynamics, and hydration of F-F and T-T mispairs. Hexamers containing F-F pairs were found to be more dynamic, especially in the region of the mispair itself. This dynamic variability derives from greater flexibility of F-F pairs. The T-T mispairs, on the other hand, were found to be comparatively tightly bound as wobble pairs. The major and minor groove edges of the T-T pairs were observed to be solvated at exposed carbonyl positions by at least one water molecule, while F-F pairs lacked solvating waters. Stacking interactions were nearly identical for T-T and F-F pairs, leading to similar average structures, even though F stacking was more dynamically variable. Solvation differences between F-F and T-T therefore support the steric exclusion model for nucleotide incorporation in DNA replication. Large differences in the orientation of minor groove functional groups, in addition to differences in solvation, further rationalize why F bases present during DNA extension events induce stalls. Two novel nucleotides are proposed to further elucidate minor groove interactions of DNA with polymerase molecules.Electronic Supplementary Material This Material consists of equilibration protocol, plots of center-of-mass stacking, water radial distribution functions, helical parameter dynamics, and dynamics data for a control AT sequence. Supplementary material is available in the online version of this article at Contribution to the Jacopo Tomasi Honorary Issue     

Tuning single nucleotide discrimination in polymerase chain reactions (PCRs): synthesis of primer probes bearing polar 4'-C-modifications and their application in allele-specific PCR

There are many methods available for the detection of nucleotide variations in genetic material. Most of these methods are applied after amplification of the target genome sequence by the polymerase chain reaction (PCR). Many efforts are currently underway to develop techniques that can detect single nucleotide variations in genes either by means of, or without the need for, PCR. Allele-specific PCR (asPCR), which reports nucleotide variations based on either the presence or absence of a PCR-amplified DNA product, has the potential to combine target amplification and analysis in one single step. The principle of asPCR is based on the formation of matched or mismatched primer-target complexes by using allele-specific primer probes. PCR amplification by a DNA polymerase from matched 3'-primer termini proceeds, whereas a mismatch should obviate amplification. Given the recent advancements in real-time PCR, this technique should, in principle, allow single nucleotide variations to be detected online. However, this method is hampered by low selectivity, which necessitates tedious and costly manipulations. Recently, we reported that the selectivity of asPCR can be significantly increased through the employment of chemically modified primer probes. Here we report further significant advances in this area. We describe the synthesis of various primer probes that bear polar 4'-C-modified nucleotide residues at their 3' termini, and their evaluation in real-time asPCR. We found that primer probes bearing a 4'-C-methoxymethylene modification have superior properties in the discrimination of single nucleotide variations by PCR.     

Effect of DNA and bivalent metal ions on the interaction of thermostable DNA polymerase <Emphasis Type="Italic">Tte</Emphasis> with dNTPs

The interaction of DNA polymerase Tte from Thermus thermophilus B35 with dUTP analog containing a fluorescein residue bound to C(5) of the base (Flu-dUTP) was studied by fluorescence titration. The dissociation constants of the enzyme—substrate complexes in the absence and in the presence of a DNA duplex containing an extended template and bivalent metal ions and the kinetic parameters of polymerization by DNA polymerase Tte in the presence of Flu-dUTP were determined. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1268–1272, May, 2005.     

Artificial Genetic Sets Composed of Size‐Expanded Base Pairs

We describe in this Minireview the synthesis, properties, and applications of artificial genetic sets built from base pairs that are larger than the natural Watson–Crick architecture. Such designed systems are being explored by several research groups to investigate basic chemical questions regarding the functions of the genetic information storage systems and thus of the origin and evolution of life. For example, is the terrestrial DNA structure the only viable one, or can other architectures function as well? Working outside the constraints of purine–pyrimidine geometry provides more chemical flexibility in design, and the added size confers useful properties such as high binding affinity and helix stability as well as fluorescence. These features are useful for the investigation of fundamental biochemical questions as well as in the development of new biotechnological, biomedical, and nanostructural tools and methods.     

Controlled fabrication of hierarchically microstructured surfaces via surface wrinkling combined with template replication

In this paper,we present a simple method by combining surface wrinkling and template replication to create a series of hierarchical structures on polydimethylsiloxane(PDMS) elastomer.The primary stable lined patterns are formed by duplicating commercialized compact disk and digital versatile disk with PDMS.The secondary microscale patterns are from surface wrinkling,which is elicited by oxygen plasma(OP) treatment of the prestrained PDMS stamp followed with the prestrain release.By systematically varying the OP exposure duration,the prestrain,and the angle(θ) between the primary pattern orientation and the prestrain direction,we obtain highly ordered well-organized composite patterns from different patterning techniques and with different length scales and mechanical stabilities.     

Mechanisms of Autocatalysis

Self‐replication is a fundamental concept. The idea of an entity that can repeatedly create more of itself has captured the imagination of many thinkers from von Neumann to Vonnegut. Beyond the sciences and science fiction, autocatalysis has found currency in economics and language theory, and has raised ethical fears memorably summed up by the “gray goo” trope. Autocatalysis is central to the propagation of life and intrinsic to many other biological processes. This includes the modern conception of evolution, which has radically altered humanity’s image of itself. Organisms can be thought of as imperfect self‐replicators which produce closely‐related species, allowing for selection and evolution. Hence, any consideration of self‐replication raises one of the most profound questions of all: what is life? Minimal self‐replicating systems have been studied with the aim of understanding the principles underlying living systems, allowing us to refine our concepts of biological fitness and chemical stability, self‐organization and emergence, and ultimately to discover how chemistry may become biology.     

Template‐Directed Copying of RNA by Non‐enzymatic Ligation

The non‐enzymatic replication of the primordial genetic material is thought to have enabled the evolution of early forms of RNA‐based life. However, the replication of oligonucleotides long enough to encode catalytic functions is problematic due to the low efficiency of template copying with mononucleotides. We show that template‐directed ligation can assemble long RNAs from shorter oligonucleotides, which would be easier to replicate. The rate of ligation can be greatly enhanced by employing a 3′‐amino group at the 3′‐end of each oligonucleotide, in combination with an N‐alkyl imidazole organocatalyst. These modifications enable the copying of RNA templates by the multistep ligation of tetranucleotide building blocks, as well as the assembly of long oligonucleotides using short splint oligonucleotides. We also demonstrate the formation of long oligonucleotides inside model prebiotic vesicles, which suggests a potential route to the assembly of artificial cells capable of evolution.