HF单边带解调器

图1所示电路用于补充“设计实例(Design Idea)”栏目以前的一篇文章渗考文献1)。图中的调制器使用了一个移相网络,把一个低频的(声频)信号分成同相和90°相差(正交)的两个分量。这里的移相网络比其他移相电路优越之处在于,它产生的移相误     

Solid state N.M.R. relaxation study of liquid crystal polymers employing a two dimensional technique

Molecular motions of liquid crystal polymers in the solid state cover a broad dynamic range, extending from the fast rotational to the ultra slow motional regime. Two dimensional N.M.R. relaxation spectroscopy is designed to follow these motions and to differentiate the various motional modes. In addition, different types of molecular order, modulated by these regions, are also discriminated. The solid state dynamics of the polyesters studied depends sensitively upon their thermal history. Annealed samples show a typical semicrystalline behaviour, manifested by two different motional components. The molecular order is characterized by a high degree of conformational and orientational order of the polymer chains, which is strongly correlated with the exceptional mechanical properties of these systems.     

Catalytic Addition of Simple Alkenes to Carbonyl Compounds Using Group 10 Metals

Recent advances using nickel complexes in the activation of unactivated monosubstituted olefins for catalytic intermolecular carbon-carbon bond-forming reactions with carbonyl compounds, such as simple aldehydes, isocyanates, and conjugated aldehydes and ketones, are discussed. In these reactions, the olefins function as vinyl- and allylmetal equivalents, providing a new strategy for organic synthesis. Current limitations and the outlook for this new strategy are also discussed.     

On biaccessible points in the Julia set of a Cremer quadratic polynomial

We prove that the only possible biaccessible points in the Julia set of a Cremer quadratic polynomial are the Cremer fixed point and its preimages. This gives a partial answer to a question posed by C. McMullen on whether such a Julia set can contain any biaccessible point at all.

     

Sera from healthy and diabetic subjects contain autoantibodies against various species-specific proteins

Conclusions Our results confirm those of others [4, 5] suggesting the presence of natural antibodies (autoantibodies) in the serum of nearly 100% of apparently healthy subjects as well in sera from IDDM patients. Since overlapping of the values found for both groups is common for the antigens tested here, none of the specific autoantibody populations can serve as a diabetes-specific disease marker.

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Autoantikörper gegen verschiedene Spezies-spezifische Proteine in Seren von Gesunden und Diabetes-Patienten

     

Unexpected electron transfer in cryptochrome identified by time-resolved EPR spectroscopy

Subtle differences in the local sequence and conformation of amino acids can result in diversity and specificity in electron transfer (ET) in proteins, despite structural conservation of the redox partners. For individual ET steps, distance is not necessarily the decisive parameter; orientation and solvent accessibility of the ET partners, and thus the stabilization of the charge-separated states, contribute substantially.