Matsuoka T.,University of Michigan |
McGuffey C.,University of Michigan |
Cummings P.G.,University of Michigan |
Horovitz Y.,University of Michigan |
And 10 more authors.
Physical Review Letters | Year: 2010
Stimulated Raman side scattering of an ultrashort high power laser pulse is studied in experiments on laser wakefield acceleration. Experiments and simulations reveal that stimulated Raman side scattering occurs at the beginning of the interaction, that it contributes to the evolution of the pulse prior to wakefield formation, and also that it affects the quality of electron beams generated. The relativistic shift of the plasma frequency is measured. © 2010 The American Physical Society.
Banks B.A.,NASA |
Banks B.A.,Alphaport Inc. |
Edwards D.L.,NASA |
Gouzman I.,Soreq NRC |
And 13 more authors.
MRS Bulletin | Year: 2010
To explore higher, farther, and faster, scientists and engineers have developed advanced materials for manned spacecraft and satellites for a range of sophisticated applications in transportation, global positioning, exploration, and communication. Materials used in space are exposed to vacuum, intense ultraviolet radiation from the sun, and ionizing radiation that results in material damage as well as charging (electrostatic discharge effects), micrometeoroids and debris impacts, and thermal cycling (typically from -175 to 160°C). In terms of materials degradation in space, the low Earth orbit (LEO), where LEO is defined as 200-1000 km above the Earth's surface, is a particularly challenging synergistic environment, since atomic oxygen (AO) is present along with all other environmental elements. Hence, this special issue focuses primarily on the materials issues experienced in LEO by space environmental exposure, such as on the exterior of the International Space Station and the Hubble Space Telescope, and the challenges and opportunities of ground-based laboratory sources to mimic LEO. The combination and comparison of both in-flight and ground-based experiments are needed for the development of predictive understanding of the materials degradation and AO passivation mechanisms in LEO. Such insights are essential for the development of advanced materials and coatings to ensure the longterm durability and performance of vehicles employed in space.
Pokrass M.,NRC Group |
Burshtein Z.,Ben - Gurion University of the Negev |
Gvishi R.,NRC Group
Optical Materials | Year: 2010
We have investigated the effect of organic content in hybrid organic/inorganic glasses prepared by the sol-gel process on the thermo-optic coefficient dn/dT. The organic phase consisted of homogeneously dispersed methyl groups within an inorganic silica matrix. Analysis of Fresnel reflectance temperature dependence of an optically polished sample-surface yielded the desired value, with an accuracy of 10 5/°C. A negative linear dependence of the thermo-optic coefficient on the volumetric thermal expansion coefficient β was obtained, dn/dT[10 4/°C] = -1.1-0.45β[10 4/°C]. Using Prod'homme's model, a negative value was derived for the electronic polarizability coefficient Φ = (-1.8 ± 0.3) × 10 4/°C. The negative sign of Φ is attributed to isolation of the silica matrix sections by the methyl groups, causing the sections to distance upon increase in temperature. © 2010 Elsevier B.V. All rights reserved.
Berkovic G.,NRC Group |
Shafir E.,NRC Group
Advances in Optics and Photonics | Year: 2012
This tutorial reviews various noncontact optical sensing techniques that can be used to measure distances to objects, and related parameters such as displacements, surface profiles, velocities and vibrations. The techniques that are discussed and compared include intensity-based sensing, triangulation, time-of-flight sensing, confocal sensing, Doppler sensing, and various kinds of interferometric sensing with both high- and low-coherence sources. © 2012 Optical Society of America.
Pokrass M.,NRC Group |
Pokrass M.,Tel Aviv University |
Azulay D.,Hebrew University of Jerusalem |
Balberg I.,Hebrew University of Jerusalem |
And 4 more authors.
Journal of Sol-Gel Science and Technology | Year: 2014
Electrical properties of multi-walled carbon nanotubes (MWNTs)/hybrid-glass nanocomposites prepared by the fast-sol-gel reaction were investigated in light of percolation theory. A good correlation was found between the experimental results and the theory. We obtained a percolation threshold c = 0.22 wt%, and a critical exponent of t = 1.73. These values are reported for the first time for a silica-based system. The highest conductivity measured on the MWNT/hybrid-glass nanocomposites was σ ≈ 10-3(Ω cm)-1 for 2 wt% carbon nanotube (CNT) loading. The electrical conductivity was at least 12 orders of magnitude higher than that of pure silica. Electrostatic force microscopy and conductive-mode atomic force microscopy studies demonstrated conductivity at the micro-level, which was attributed to the CNT dispersed in the matrix. It appears that the dispersion in our MWNT/hybrid-glass system yields a particularly low percolation threshold compared with that of a MWNT/silica-glass system. Materials with electrical conductivities described in this work can be exploited for anti-static coating. © 2014 Springer Science+Business Media New York.