Instability zones for isotropic and anisotropic multibladed rotor configurations

Helicopter ground resonance is an unstable dynamic phenomenon which can lead to the total destruction of the aircraft during take-off or landing phases. The earliest research in this domain was carried out by Coleman and Feingold during the decade of 60s. The instability was predicted by using classical procedures once the rotor was considered as isotropic, consequently, the periodic equations of motion could be simplified to a system with constant coefficients by introducing a change of variables, known as the Coleman Variable Transformation. The goal of the present work is to further comprehend the phenomenon and the influence of the anisotropic properties of rotors by analyzing the periodic set of equations of motion. For this, Floquet's Theory (Floquet's Method — FM) is used. The analysis for predicting the ground resonance phenomenon in isotropic and anisotropic rotor configurations is explored. The conclusions lead to verify the appearance of bifurcation points depending on the anisotropic characteristic present in the rotor. The temporal response analysis in the motion of helicopter with one asymmetric blade at unstable regions highlighted the presence of non symmetric rotor deformation shapes.     

Superhydrophobic/highly oleophobic surfaces based on poly(3,4-propylenedioxythiophene) surface <Emphasis Type="Italic">post</Emphasis>-functionalization

Here, we report for the first time the use of poly(3,4-propylenedioxythiophene) as platform for surface post-functionalization using the Staudinger-Vilarrasa reaction in order to covalently link perfluorinated chains and obtain various hydrophobic/oleophobic properties. 3,4-propylenedioxythiophene with one or two azido groups are prepared, in order to determine the impact of the number of functional groups on the surface morphology and wettability. Here, we show the possibility to prepare parahydrophobic (high water adhesion) or superhydrophobic (low water adhesion) surfaces with highly oleophilic to highly oleophobic properties.     

SRM 2460/2461 Standard Bullets and Casings Project

The National Institute of Standards and Technology Standard Reference Material (SRM) 2460/2461 standard bullets and casings project will provide support to firearms examiners and to the National Integrated Ballistics Information Network (NIBIN) in the United States. The SRM bullet is designed as both a virtual and a physical bullet profile signature standard. The virtual standard is a set of six digitized bullet profile signatures originally traced from six master bullets fired at the Bureau of Alcohol, Tobacco and Firearms (ATF) and the Federal Bureau of Investigation (FBI). By using the virtual signature standard to control the tool path on a numerically controlled diamond turning machine, 40 SRM bullets were produced. A profile signature measurement system was established for the SRM bullets. The profile signature differences are quantified by the maximum of the cross correlation function and by the signature difference between pairs of compared profile signatures measured on different SRM bullets. Initial measurement results showed high reproducibility for both the measurement system and production process of the SRM bullets. A traceability scheme has been proposed to establish the measurement traceability for nationwide bullet signature measurements to NIST, ATF and FBI. Prototype SRM casings have also been developed.     

Climate sensitivity of gaseous elemental mercury dry deposition to plants: impacts of temperature, light intensity, and plant species

Foliar accumulations of gaseous elemental mercury (GEM) were measured in three plant species between nominal temperatures of 10 and 30 °C and nominal irradiances of 0, 80, and 170 W m(-2) (300 nm-700 nm) in a 19 m(3) controlled environment chamber. The plants exposed were as follows: White Ash (Fraxinus americana; WA); White Spruce (Picea glauca; WS); and Kentucky Bluegrass (Poa partensis; KYBG). Foliar enrichments in the mercury stable isotope ((198)Hg) were used to measure mercury accumulation. Exposures lasted for 1 day after which the leaves were digested in hot acid and the extracted mercury was analyzed with ICPMS. Resistances to accumulative uptake by leaves were observed to be dependent on both light and temperature, reaching minima at optimal growing conditions (20 °C; 170 W m(-2) irradiance between 300-700 nm). Resistances typically increased at lower (10 °C) and higher (30 °C) temperatures and decreased with higher intensities of irradiance. Published models were modified and used to interpret the trends in stomatal and leaf interior resistances to GEM observed in WA. The model captured the experimental trends well and revealed that stomatal and internal resistances were both important across much of the temperature range. At high temperatures, however, stomatal resistance dominated due to increased water vapor pressure deficits. The resistances measured in this study were used to model foliar accumulations of GEM at a northern US deciduous forest using atmospheric mercury and climate measurements made over the 2003 growing season. The results were compared to modeled accumulations for GEM, RGM, and PHg using published deposition velocities. Predictions of foliar GEM accumulation were observed to be a factor of 5-10 lower when the temperature and irradiance dependent resistances determined in this study were used in place of previously published data. GEM uptake by leaves over the growing season was shown to be an important deposition pathway (2.3-3.7 μg m(-2) of one-sided leaf area; OSLA) when compared to total mercury wet deposition (1.2 μg m(-2) OSLA) and estimates of reactive mercury dry deposition (0.1-6 μg m(-2) OSLA). Resistance-Temperature-Irradiance relationships are provided for use in models.     

Characterization of ultrathin SOI film and application to short channel MOSFETs

In this study, a very dilute solution (NH(4)OH:H(2)O(2):H(2)O 1:8:64 mixture) was employed to reduce the thickness of commercially available SOI wafers down to 3?nm. The etch rate is precisely controlled at 0.11???s(-1) based on the self-limited etching speed of the solution. The thickness uniformity of the thin film, evaluated by spectroscopic ellipsometry and by high-resolution x-ray reflectivity, remains constant through the thinning process. Moreover, the film roughness, analyzed by atomic force microscopy, slightly improves during the thinning process. The residual stress in the thin film is much smaller than that obtained by sacrificial oxidation. Mobility, measured by means of a bridge-type Hall bar on 15?nm film, is not significantly reduced compared to the value of bulk silicon. Finally, the thinned SOI wafers were used to fabricate Schottky-barrier metal-oxide-semiconductor field-effect transistors with a gate length down to 30?nm, featuring state-of-the-art current drive performance.     

Microfluidic tools for cell biological research

Microfluidic technology is creating powerful tools for cell biologists to control the complete cellular microenvironment, leading to new questions and new discoveries. We review here the basic concepts and methodologies in designing microfluidic devices, and their diverse cell biological applications.     

Tailor-made morphologies for Pd/SiO2 catalysts through sol–gel process with various silylated ligands

With the aim of obtaining highly dispersed, immobilized and accessible catalytically active palladium nanoparticles in a silica support with a tailored morphology, a sol–gel cogelation method is developed. Pd/SiO₂ catalysts are synthesized in ethanol by concomitant hydrolysis and condensation, i.e. cogelation, of a Pd²⁺[L–X–Si(OR)₃]_n complex with Si(OC₂H₅)₄ (TEOS) as network-forming reagent followed by calcinations in air and by reductions of the resulting xerogel catalysts in hydrogen. By varying the nature of L, X and R in the Pd²⁺ complex, the purpose of the present work is to determine the influence of the nature of the L–X–Si(OR)₃ ligand on textural properties of silica and on palladium dispersion in Pd/SiO₂ catalysts.By changing the molecular weight of L–X– and thus its bulkiness of L and X, it is observed that with bulkier silylated ligand, the textural properties of resulting gels are strongly modified from micro- and macroporous materials to very highly micro- and mesoporous materials. In the latter ones, the size of silica particles is smaller and their void fraction is very high. In such a case, palladium particles are not trapped inside silica particles and are then able to migrate and to sinter. The Pd/SiO₂ xerogel catalysts were evaluated in the hydrodechlorination of 1,2-dichloroethane.