Creation of hot radiation environments in laser-driven targets

A hot radiation environment, produced by maximizing laser-energy deposition into a small, high- "can," is a platform being developed for investigations of material properties under extreme conditions. In such small targets, almost doubling the laser energy results in only an incremental increase in the x-radiation flux, and almost no increase in the maximum achieved radiation temperature. That most of this additional laser energy is not deposited within the target is a direct consequence of laser-plasma interactions (LPI) outside of the target, which result in high-angle beams never entering the target late in the laser pulse. Accounting for these processes in the modeling results in quantitative agreement for the first time with experiments using very small cans. These findings have provided the scientific foundation for modifying the target geometry to mitigate the LPI and to achieve higher radiation temperatures.     

DNA-templated covalent coupling of G4 PAMAM dendrimers

Generation-4 polyamidoamine (PAMAM) dendrimers were surface-functionalized with azides or alkynes and conjugated to one DNA strand. DNA-controlled self-assembly of alternating azide and alkyne dendrimers on a DNA template enabled the coupling of the dendrimers by the azide-alkyne "click" reaction to form covalently coupled dimers, trimers, and tetramers. Polymerization of the DNA-dendrimer conjugates was also demonstrated, as well as assembly in a circular structure on DNA origami and imaging by atomic force microscopy.     

Natural Products as Probes of Cellular Function: Studies of Immunophilins

One of the great mysteries of cell biology remains the mechanism of information transfer, or signaling, through the cytoplasm of the cell. Natural products that inhibit this process offer a unique window into fundamental aspects of cytoplasmic signal transduction, the means by which extracellular molecules influence intracellular events. Thus, natural products chemistry, including organic synthesis, conformational analysis, and methods of structure elucidation, is a powerful tool in the study of cell function. This article traces our understanding of a group of natural products from the finding that they inhibit cytoplasmic signaling to their current recognition as mediators of the interaction between widely distributed protein targets. The emphasis of the discussion is primarily structural. The interactions between the natural-product ligands and their protein receptors are analyzed at a molecular level in order to shed light on the molecular mechanisms of the biological functions of these compounds. In the process we hope to illustrate the power of chemical analysis as applied to biological systems. Through chemistry we can understand the molecular basis of biological phenomena.     

Is quantized electric charge a purely electromagnetic phenomenon?

It is observed that the manifestly covariant Feynman path integral formulation for quantum electromagnetism admits a physically interesting extended definition for the sum-over-histories measure. From an equal-weighting condition and the postulate that the functional integration is to be free of renormalization, it follows that point singularies in the electromagnetic field have an electric charge associated with the fine-structure value = (137.032 41)^–1.     

Approach to a theory for the masses of the electron,muon, and heavier charged leptons

The electron mass valuem=9.093 × 10^–28 g is shown to be obtainable from the QED self-energy formula amended to include gravitational selfenergy and restricted by the space-time equipartition lawm/n ₀=4/3. Held together by gravity, the electron has a radiusr _e =8Gm/9e ² c=2.588 × 10^–53 cm. An extension of the analysis yields the theoretical muon-electron mass ratio of 206.241 and predicts heavier charged leptons with mass values of 1.915 GeV, 15.67 GeV, and above.     

Bimetric gravitation theory on a cosmological basis

In the bimetric theory of gravitation the background metric tensor , previously taken as describing flat space-time, is now chosen on the basis of a model of the universe. In accordance with the perfect cosmological principle, it is taken as describing a space-time of constant curvature. There are three possible forms, corresponding tok=0, 1, –1. Only fork=1 (a closed universe) does the model not go through a singular state; hence this is the appropriate choice. The isotropic solution of the field equations can be chosen to agree with the present cosmological observations. For small systems like the solar system the theory gives the same results as before, in agreement with those of general relativity.