Monitoring the statistics of turbulence: Fried parameter estimation from the wavefront sensor measurements

Near-the-ground laser communication systems must operate in the presence of strong atmospheric turbulence. The effects of atmospheric turbulence on the laser beam that are relevant to optical communications are a broadening of the laser footprint, random jitter of the laser beam, and high spatial frequency intensity fluctuations referred to as scintillation. The overall goal of our program is to improve the performance and extend the range of optical communications systems by exploring the use of adaptive optics and channel coding. Knowledge of the turbulence conditions and the ability to describe its properties are the key aspects to make these improvements effective. The developed multiphase approach is directed to statistically describe atmospheric turbulence based on results derived from experimentally collected data. Statistics of Fried parameter r(0) is derived from 6 TB of data collected over 50 days, and under various day and night atmospheric conditions. Significant fluctuations of r(0) are found with the values ranging from 2 mm and up to 15 cm, corresponding to the significant structure function Cn2 fluctuations from 7.4×10(-14) to 8.1×10(-16).     

Inhibition of hIAPP Amyloid Aggregation and Pancreatic β‐Cell Toxicity by OH‐Terminated PAMAM Dendrimer

Human islet amyloid polypeptide (hIAPP, or amylin) forms amyloid deposits in the islets of Langerhans, a phenomenon that is associated with type‐2 diabetes impacting millions of people worldwide. Accordingly, strategies against hIAPP aggregation are essential for the prevention and eventual treatment of the disease. Here, it is shown that generation‐3 OH‐terminated poly(amidoamine) dendrimer, a polymeric nanoparticle, can effectively halt the aggregation of hIAPP and shut down hIAPP toxicity in pancreatic MIN6 and NIT‐1 cells as well as in mouse islets. This finding is supported by high‐throughput dynamic light scattering experiment and thioflavin T assay, where the rapid evolution of hIAPP nucleation and elongation processes is halted by the addition of the dendrimer up to 8 h. Discrete molecular dynamics simulations further reveal that hIAPP residues bound strongly with the dendrimer near the c‐terminal portion of the peptide, where the amyloidogenic sequence (residues 22–29) locates. Furthermore, simulations of hIAPP dimerization reveal that binding with the dendrimer significantly reduces formation of interpeptide contacts and hydrogen bonds, thereby prohibiting peptide self‐association and amyloidosis. This study points to a promising nanomedicinal strategy for combating type‐2 diabetes and may have broader implications for targeting neurological disorders whose distinct hallmark is also amyloid fibrillation.     

Computer-based engineering of thermostabilized antibody fragments

We used the molecular modeling program Rosetta to identify clusters of amino acid substitutions in antibody fragments (scFvs and scAbs) that improve global protein stability and resistance to thermal deactivation. Using this methodology, we increased the melting temperature (T_m) and resistance to heat treatment of an antibody fragment that binds to the Clostridium botulinum hemagglutinin protein (anti-HA33). Two designed antibody fragment variants with two amino acid replacement clusters, designed to stabilize local regions, were shown to have both higher T_m compared to the parental scFv and importantly to retain full antigen binding activity after 2 hr of incubation at 70°C. The crystal structure of one thermostabilized scFv variants was solved at 1.6 Å and shown to be in close agreement with the RosettaAntibody model prediction.     

Possibilities for Producing Radionuclides in Nuclear Power Plants with RBMK Reactors

It is shown that radiation doping of silicon and the production of medical and industrial radioisotopes in the reactors at the Leningrad nuclear power plant are possible and safe. The production of cobalt with specific activity ~100 Ci/g in an RBMK-1000 reactor is studied. Some promising developments for improving the quality of the radioisotopes produced are described. It is shown that the production volumes can be increased by linking up other nuclear power plants with RBMK reactors into the production chain.     

Formation of submicrocrystalline structure in titanium and titanium alloys and their mechanical properties

The effect of deformation temperature on the grain size in titanium VT1-0 and double-phase titanium alloy VT6 is studied. The temperature-and-rate modes of formation of submicrocrystalline structure are determined. The mechanical behavior and the evolution of the microstructure in the course of warm severe deformation is investigated by means of successive compression of specimens over three orthogonal directions at a temperature of 400°C for titanium and 550°C for alloy VT6. The mechanisms of grain refinement in severe deformation are determined. It is shown that they differ depending on the composition of the alloy. The method of “abc”-deformation is used for fabricating large-mass preforms from titanium VT1-0 and alloy VT6 with submicrocrystalline structure; large-size sheets are produced from alloy VT6. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 19–26, February, 2006. Grant of Russian foundation for fundamental research No. 05-08-65396-a.     

Changes in the thermoresistance of the isolated ciliated epithelium of the frog palate under the influence of heavy metals

The resistance to 36 and 38 degrees C of isolated ciliated epithelium of the frog palate has been investigated, in relation to the following concentrations of some heavy metals in Ringer solution: 3CdSO4.8H2O (0.001-250.000 mg/l), CuSO4.5H2O (0.01-250.00 mg/l), Zn(NO3)2.6H2O (100-250 mg/l), Pb(NO3)2 (50-100 mg/l), Pb(CH3COO)2.3H2O (1-250 mg/l). In general, the epithelium heat resistance decreased as the concentration of heavy metal increased. The most toxic to the investigated object appeared Cd and Cu. A dependence was revealed between the toxicity of heavy metals and the testing temperatures.     

Regulation of constitutive exocytic transport by membrane receptors. A biochemical and morphometric study

Biochemical and morphometric approaches were combined to examine whether constitutive secretory transport might be controlled by plasma membrane receptors, as this possibility would have significant physiological implications. Indeed, IgE receptor stimulation in rat basophilic leukemia cells potently increased the rate of transport of soluble pulse-labeled 35S-sulfated glycosaminoglycans from distal Golgi compartments to the cell surface. This effect was largely protein kinase C (PKC)-dependent. Direct activation of PKC also stimulated constitutive transport of glycosaminoglycans, as indicated by the use of agonistic and antagonistic PKC ligands. PKC ligands also had potent, but different, effects on the exocytic transport from distal Golgi compartments to the plasma membrane of a membrane-bound protein (vesicular stomatitis virus glycoprotein), which was slightly stimulated by activators and profoundly suppressed by inhibitors of PKC. Morphological analysis showed impressive changes of the organelles of the secretory pathway in response to IgE receptor stimulation and to direct PKC activation (enhanced number of buds and vesicles originating from the endoplasmic reticulum and Golgi and increase in surface and volume of Golgi compartments), suggestive of an overall activation of exocytic movements. These results show that rapid and large changes in constitutive transport fluxes and in the morphology of the exocytic apparatus can be induced by membrane receptors (as well as by direct PKC stimulation).     

Summation of random and residual systematic components of errors in direct measurements

Some universally adopted procedures for summation of errors in direct measurements are discussed. Conditions under which the methods applied yield noncontradictory results are stated. Practical recommendations for summation of random and residual systematic error components of direct measurements are provided. Translanted from Izmeritel'naya Tekhnika, No. 6, pp. 9‐11, June, 1998.