Ultrasonic diffraction technique for characterization of fatigue cracks

This paper describes an ultrasonic diffraction technique for characterizing fatigue cracks. The angular field of energy scattered from a crack tip was computed. Using the theoretically predicted and experimentally verified optimum range of angles, we measured the crack profiles by the ultrasonic diffraction technique. Ultrasonic measurements agreed very well with direct destructive measurements. In addition, fatigue crack closure was detected and information on crack surfaces was obtained.Oak Ridge National Laboratory; Oak Ridge National Laboratory is operated by Union Carbide Corporation under contract W-7405-eng-26 with the U.S. Department of Energy.     

Modal analysis and cut-off conditions of multichannel surface-acoustic-waveguide structures

Multichannel guides for surface acoustic waves can improve the efficiency of SAW (surface acoustic-wave) devices significantly. Focusing, steering, and modulating the propagating acoustical modes can be achieved similarly to optical waveguided devices. A general formulation is presented for the analysis of the lateral waveguiding properties of Rayleigh modes in surfaces loaded with deposited strips of different materials. General expressions are obtained for the number of modes and cutoff conditions in these structures. As examples of applications, a simple directional coupler and an electrically controlled coupler are proposed.     

Strategic Management of Religious Websites: The Case of Israel's Orthodox Communities

This study investigates how webmasters of sites affiliated with bounded communities manage tensions created by the open social affordances of the internet. We examine how webmasters strategically manage their respective websites to accommodate their assumed target audiences. Through in‐depth interviews with Orthodox webmasters in Israel, we uncover how they cultivate 3 unique strategies ‐‐ control, layering, and guiding ‐‐ to contain information flows. We thereby elucidate how web strategies reflect the relationships between community, religion and CMC.     

Cathodoluminescence study of micro-crack-induced stress relief for AlN films on Si(111)

Spatially, spectrally, and depth-resolved cathodoluminescence (CL) measurements were performed for high-quality thin AlN films grown on Si(111). Cl spectra exhibited a sharp peak at 5.960 eV, corresponding to the near-band-edge excitonic emission of AlN. Depth-resolved CL analysis showed that deep level oxygen and carbon impurities are localized primarily at the AlN/Si interface and AlN outer surface. Monochromatic CL imaging of the near-band-edge emission exhibits a spotty pattern, which corresponds to high concentrations of threading dislocations and thermally induced microcracks in the thin layers. We have examined relief of the thermal stress in close proximity to single microcracks and intersecting microcracks. Local CL spectra acquired with a focused e-beam show blue-shifts as large as ∼82 meV in the AlN near-band edge excitonic peaks, reflecting defect-induced reductions in the biaxial thermal stress, which has a maximum value of ∼47 kbar.     

Hot-Probe method for evaluation of impurities concentration in semiconductors

Electrical, optical, and mechanical properties of thin films significantly differ from those of bulk materials. Therefore, characterization methods for evaluation of thin film properties became highly important. A novel approach to the well known “Hot-Probe” method is proposed and applied in our work. The conventional Hot Probe characterization method enables only the definition of a semiconductor type, P or N, by identifying the majority charged carriers. According to the new Hot Probe technique, one can measure and calculate the majority charged carriers concentration and its dynamic parameters. Feasibility proof of the upgraded Hot Probe method was done in Si and Ge bulk, and in thin film semiconductor samples.     

Template Growth of Nanocrystalline PbS,CdS, and ZnS on a Polydiacetylene Langmuir Film: An In Situ Grazing Incidence X‐ray Diffraction Study

Chemical deposition of nanocrystalline PbS, CdS, and ZnS at the air/solution interface in the absence and presence of a polydiacetylene (PDA) Langmuir film is investigated in situ using grazing incidence X‐ray diffraction. In all cases, it is found that PDA has a pronounced effect on the incipient semiconductor nanocrystals (NCs). In the presence of PDA, PbS NCs showed a <111> orientation in addition to the commonly obtained <100> growth direction of the PbS rock salt structure while CdS and ZnS NCs crystallized in the zinc blende polymorph with a predominant <100> orientation. ZnS NCs were obtained only in the presence of PDA at the air/solution interface.     

Optical nanomanipulations of malignant cells: controlled cell damage and fusion

Specifically targeting and manipulating living cells is a key challenge in biomedicine and in cancer research in particular. Several studies have shown that nanoparticles irradiated by intense lasers are capable of conveying damage to nearby cells for various therapeutic and biological applications. In this work ultrashort laser pulses and gold nanospheres are used for the generation of localized, nanometric disruptions on the membranes of specifically targeted cells. The high structural stability of the nanospheres and the resonance pulse irradiation allow effective means for controlling the induced nanometric effects. The technique is demonstrated by inducing desired death mechanisms in epidermoid carcinoma and Burkitt lymphoma cells, and initiating efficient cell fusion between various cell types. Main advantages of the presented approach include low toxicity, high specificity, and high flexibility in the regulation of cell damage and cell fusion, which would allow it to play an important role in various future clinical and scientific applications.     

Receptor-regulated translocation of endothelial nitric-oxide synthase

The endothelial nitric-oxide synthase (eNOS) is activated by transient increases in intracellular Ca2+ elicited by stimulation of diverse receptors, including bradykinin B2 receptors on endothelial cells. eNOS and B2 receptors are targeted to specialized signal-transducing domains in the plasma membrane termed plasmalemmal caveolae. Targeting to caveolae facilitates eNOS activation following receptor stimulation, but in resting cells, eNOS is tonically inhibited by its interactions with caveolin, the scaffolding protein in caveolae. We used a quantitative approach exploiting immunofluorescence microscopy to investigate regulation of the subcellular distribution of eNOS in endothelial cells by bradykinin and Ca2+. In resting cells, most of the eNOS is localized at the cell membrane. However, within 5 min following addition of bradykinin, nearly all the eNOS translocates to structures in the cell cytosol; following more protracted incubations with bradykinin, most of the cytosolic enzyme subsequently translocates back to the cell membrane. The bradykinin-induced internalization of eNOS is completely abrogated by the intracellular Ca2+ chelator BAPTA; conversely, Ca2+-mobilizing drugs and agonists promote eNOS translocation. These results establish that eNOS targeting to the membrane is labile and is subject to receptor-regulated Ca2+-dependent reversible translocation, providing another point for regulation of NO-dependent signaling in the vascular endothelium.     

Recruitment of new sites of synaptic transmission during the cAMP-dependent late phase of LTP at CA3-CA1 synapses in the hippocampus

Long-term potentiation at CA3-CA1 hippocampal synapses exhibits an early phase and a late phase, which can be distinguished by their underlying molecular mechanisms. Unlike the early phase, the late phase is dependent on both cAMP and protein synthesis. Quantal analysis of unitary synaptic transmission between a single presynaptic CA3 neuron and a single postsynaptic CA1 neuron suggests that, under certain conditions, the early phase of LTP involves an increase in the probability of release of a single quantum of transmitter from a single presynaptic release site, with no change in the number of quanta that are released or in postsynaptic sensitivity to transmitter. Here, we show that the cAMP-induced late phase of LTP involves an increase in the number of quanta released in response to a single presynaptic action potential, possibly due to an increase in the number of sites of synaptic transmission between a single CA3 and a single CA1 neuron.