The neurobiology of anxiety disorders

The use of pharmacologic challenges and the application of new brain imaging technologies in the study of patients with anxiety disorders have led to an improvement in the understanding of the neurobiologic basis of these disorders. Abnormal function of noradrenergic, serotonergic, GABAergic, and dopaminergic neural systems as well as abnormal chemoreceptor reactivity have all been implicated in the pathophysiology of anxiety. Functional imaging data have revealed abnormal patterns of cortical and subcortical activity in anxiety patients. These data have allowed significant improvements in the available anatomic models of the anxiety disorders. Further improvements in research technique and technology likely will lead in the near future to a significantly clearer image of the neurobiologic processes involved in anxiety disorders.     

Structural Design of Lunar Radio Telescope Using Interactive CAD

Some astronomers are considering the moon as an attractive location within the inner solar system for a variety of astronomical observatories, some of which could be operational early in the 21st century. This paper describes the computer‐aided structural design of a 122‐m diameter, fully steerable, parabolic radio telescope to be located on the moon. The loads acting on such a reflector differ substantially from those acting on a reflector that must operate in earth's environment. The moon has excellent advantages as a location for such an instrument. The absence of atmosphere completely eliminates the wind, snow, and ice loads. The gravity field is only one‐sixth that of earth's. The thermal changes from night to day are severe, but structural problems can be avoided by using a thermally stable composite material. Structural elements for the reflector dish have been analyzed and designed for static loads with a specially written interactive graphical computer program. The resulting structure has a mass nearly 40 times less than its earth's counterpart made of steel. The evaluation of the results of the design studies supports the possibility of building a large‐aperture parabolic radio telescope on the moon.     

Electron barrier height change and its influence on EEPROM cells

The effect of floating polysilicon doping on electron injection barrier height and therefore the PROGRAM/ERASE window of an electrically erasable programmable ROM (EEPROM) cell has been studied. The introduction of dopant and the concentration of electrically active sites at the floating-gate polysilicon/tunnel oxide interface influence the electron injection barrier height during cell ERASE operation. The electron injection barrier increases up to 250 meV upon degenerate doping of the floating-gate polysilicon electrode as measured by dark current-voltage characteristics. The application of these observations in this study is in the design and scaling of EEPROM cells     

Design and synthesis of amphipathic antimicrobial peptides

A large proportion of antimicrobial peptides share a common structural feature that is critical to their antimicrobial activity, i.e. amphipathic alpha-helices. The amphipathy of a polypeptide chain can be quantitated through the value of the hydrophobic moment. Generally, antimicrobial peptides are characterized by high hydrophobic moment and low hydrophobicity values. Using these criteria we have identified two short segments that possess hydrophobic moment properties associated with known antimicrobial peptides. Using in vitro assays the segment derived from the protein perforin displays no antifungal or antibacterial activity and, while showing no alpha-helicity in buffer or liposomes, exhibits a modest degree of alpha-helical structure in the presence of the alpha-helical inducer, 2,2,2-trifluoroethanol. However, rational modifications result in a derivative which assumes an alpha-helical conformation in the presence of liposomes, exhibits potent antifungal activity against plant fungal pathogens, has significant antibacterial activity, effects leakage of a fluorescent dye from acidic liposomes and is devoid of hemolytic activity. Results are also presented for a segment derived from the human immunodeficiency virus envelope protein. We suggest that the identification of putative amphipathic structures in proteins may provide a useful starting strategy in the design and synthesis of antimicrobial peptides.     

Gas-phase modeling of homogeneous boron/oxygen/hydrogen/carbon combustion

Boron has practical applications as an advanced fuel in propulsion systems due to its high energy content. The combustion of boron in the presence of hydrocarbon fuels is a complex problem involving heterogeneous particle oxidation followed by gas-phase kinetics of the volatilized boron species. In this study, we have modeled the high-temperature gas-phase combustion chemistry of the B/O/H/C system. We have examined the effects of recent experimental gas-phase kinetic measurements of several of the critical reaction rates and theoretical thermodynamic and transition state calculations on the previous model of boron combustion. Additional reactions that critically affect the combustion efficiency are identified for future experimental and theoretical study. The role of boron oxyhydrides, which are metastable species, is discussed.