Effective linearization technique for amplifiers operating close to saturation

The linearization technique that uses simultaneous injection of the second harmonics into the amplifier input and their feedforwarding to the amplifier output is suggested. This technique reduces the third‐order intermodulation products in multichannel amplifiers when amplifiers operate closer to saturation. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007.     

Energy Crisis ?Fact or Fiction

SOME political pundits suggest that the energy crisis is a political conspiracy to cover up the other difficulties confronting the administration. Others suggest that it is a business conspiracy to drive up prices. There are still others who believe it to be the natural evolution of our affluent society. With headlines screaming of gasoline shortages natural gas restrictions, and heating oil allocations, is there any doubt that an energy crisis exists?     

A 1H-NMR study of the permeation of glycolic acid through phospholipid membranes

The transmembrane permeability coefficient of the alpha-hydroxyacid, glycolic acid, has been measured for egg phosphatidylcholine large unilamellar vesicles. The determination of the vesicle concentration independent first-order rate constant for membrane transport and the permeability coefficient were made using an NMR technique employing shift agents. Both the temperature dependence and the dependence on cholesterol content were investigated. The activation energy and the Arrhenius pre-exponential factor were found to be dependent on the cholesterol content. A marked increase in both parameters was observed up to 20 mol% cholesterol, with a further, small increase up to 50%. The pH dependence of permeability was also investigated. An increase in permeability is observed with a decrease in pH, providing a possible explanation for the effectiveness of glycolic acid in skin treatment.     

A Bioengineering-Regenerative Medicine Approach for Ocular Surface Reconstruction Using a Functionalized Native Cornea-Derived Bio-Scaffold

Limbal stem cell deficiency (LSCD) is characterized by the loss of limbal epithelial stem cells (LESCs) which compromises corneal transparency, leading to blindness. It cannot be treated with pharmacological or corneal transplantation interventions, instead a specialized stem cell (SC) therapy is needed to restore eye health and sight. Herein, a native cornea-derived biomaterial, a by-product of a laser refractive surgical procedure called small incision lenticule extraction is identified as a new cell delivery matrix. Culture conditions are optimized to facilitate LESC attachment, expansion and stratification, and their identity is immunophenotyped. Using electron microscopy, bio-constructs display stratification, similar to the architectural and cellular organization of a native mammalian cornea with formation of a basement membrane and an orderly array of collagen fibrils. Neuronal growth and depleted CD45⁺/CD14⁺ leukocytes on lenticules are also shown, suggesting that in transplantation experiments, they will re-innervate and not trigger a host-mediated immune response. Finally, human lenticules are geometrically customized to successfully fit them over a LSCD murine cornea ex vivo, during which they maintain curvature. The authors are poised to conduced similar studies in live mice using these and other carriers currently used in the clinic to compare SC therapy outcomes.     

Structure,Function and Mechanism of N-Glycan Processing Enzymes: endo-α-1,2-Mannanase and endo-α-1,2-Mannosidase

While most glycosidases that act on N-linked glycans remove a single sugar residue at a time, endo-α-1,2-mannosidases and endo-α-1,2-mannanases of glycoside hydrolase family GH99 cut within a chain and remove two or more sugar residues. They are stereochemically retaining enzymes that use an enzymatic mechanism involving an epoxide intermediate. Human endo-α-1,2-mannosidase (MANEA) trims glucosylated mannose residues; the endomannosidase pathway provides a glucosidase-independent pathway for glycoprotein maturation. Cell-active MANEA inhibitors alter N-glycan processing and reduce infectivity of dengue virus, demonstrating that MANEA has potential as a host-directed antiviral target. Sequence-related enzymes from gut Bacteroides spp. exhibit endo-α-1,2-mannosidase activity and are a fruitful test bed for structure-guided inhibitor development. The genes encoding the Bacteroides spp. enzymes sit within polysaccharide utilization loci and are preferential endo-α-1,2-mannanases.