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231.
S. Withington G. Yassin M. Buffey C. Norden 《International Journal of Infrared and Millimeter Waves》1997,18(2):341-358
We have developed an antenna for high-performance submillimetrewave imaging arrays. The antenna comprises a corrugated horn
with an off-axis paraboloidal reflector at its aperture. The corrugated horn is machined directly into two halves of a split
aluminium block. This approach avoids electroforming and is compatible with E-plane circuit technology. The resulting antenna
is light weight and is ideal for space applications. For compatibility with submillimetre-wave optics, the the behaviour has
been calculated by using Gaussian-Hermite modes, and the integrity of the theory has been verified by modelling the behaviour
of a 17GHz antenna. The manufacturing procedure has been investigated by machining and testing a horn-reflector antenna for
450–500GHz. Our next step is to extend the technique to 1THz. 相似文献
232.
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234.
P. Verdonck M. ArestiA. Ferchichi E. Van BesienB. Stafford C. TrompoukisD. De Roest M. Baklanov 《Microelectronic Engineering》2011,88(5):627-630
The use of low-k materials is essential for improving the quality of integrated circuits. Subsequent process steps may however modify this film to the extent that the final result is unacceptable. Organosilicate-based low-k films, with a nominal k-value of 2.3, were exposed to different post-CMP cleaning plasmas used for copper reduction. The resulting plasma damage was investigated and is reported in this paper. All the studied plasmas increased the density of the low-k film. TOFSIMS and FTIR analyses showed that they all removed CH3 groups from the bulk, leading to water incorporation. The carbon depletion was more pronounced and deeper (100 nm) from a NH3 plasma than from any other investigated plasma. N2 + H2 plasma removed somewhat less carbon from the low-k film (83 nm deep). The N2 plasma removed carbon down to a depth of 60 nm into the film, while a pure H2 plasma removed the least carbon of all the investigated plasmas, to a depth of only 35 nm. The combination of TOFSIMS and XPS indicated the incorporation of a significant amount of N in the films treated with the pure N2 plasma. C-V measurements showed an increase of the dielectric constant, again mostly for the NH3 plasmas. There was an intermediate and approximately equal increase of the dielectric constant for all N2 containing plasmas, and the least increase was for the H2 plasma. This increase of the dielectric constant was caused by the increase of density of the film, incorporation of water, and in the case of the N2 plasma also the incorporation of N. This shows that the presence of N2 in plasma may significantly damage low-k materials, and it should not therefore be treated as a mere carrier gas. 相似文献
235.
Jason Stafford Ed Walsh Vanessa Egan 《International Journal of Heat and Fluid Flow》2011,32(6):1160-1172
Scaled versions of fan designs are often chosen to address thermal management issues in space constrained applications. Using velocity field and local heat transfer measurement techniques, the thermal performance characteristics of a range of geometrically scaled centrifugal fan designs have been investigated. Complex fluid flow structures and surface heat transfer trends due to centrifugal fans were found to be common over a wide range of fan aspect ratios (blade height to fan diameter). The limiting aspect ratio for heat transfer enhancement was 0.3, as larger aspect ratios were shown to result in a reduction in overall thermal performance. Over the range of fans examined, the low profile centrifugal designs produced significant enhancement in thermal performance when compared to that predicted using classical laminar flow theory. The limiting non-dimensional distance from the fan, where this enhancement is no longer apparent, has also been determined. Using the fundamental information inferred from local velocity field and heat transfer measurements, selection criteria can be determined for both low and high power practical applications where space restrictions exist. 相似文献
236.
Osmotic coefficients were measured for tetra-n-butylammonium hexafluorophosphate (TBA PF6) and tetra-n-butylammonium tetrakis(pentafluorophenyl)borate (TBABARF) in tetrahydrofuran and in acetonitrile. These osmotic coefficients
were fit using equations first derived by Pitzer. Mean ionic activity coefficients were determined using the integrated form
of the Pitzer equations. Densities were measured for each of the solutions and the results were used to convert mean ionic
activity coefficients on the molal scale to the molar scale. Remarkably, over concentrations ranging from 0.1 to 1.0 m in acetonitrile, the behavior of TBABARF is consistent with the simple Debye-Hückel equation.
Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 1, pp. 66–73.
The text was submitted by the authors in English. 相似文献
237.
Girod M Dagany X Boutou V Broyer M Antoine R Dugourd P Mordehai A Love C Werlich M Fjeldsted J Stafford G 《Physical chemistry chemical physics : PCCP》2012,14(26):9389-9396
We investigated how physico-chemical properties of charged droplets are affected by the electrospray process, using simultaneous in situ measurements by laser-induced fluorescence (LIF), Fraunhofer diffraction and mass spectrometry. For this purpose, we implemented a laser-induced-fluorescence profiling setup in conjunction with a fast, high-resolution particle sizing scheme on a modified Agilent Jet Stream electrospray source coupled to a single quadrupole mass analyser. The optical setup permits us to profile the solvent fractionation and the size of the droplets as they evaporate in an electrospray plume by measuring both the angular scattering pattern and emission spectra of a solvatochromic fluorescent dye. Mass spectra are recorded simultaneously. These mass spectrometry and optical spectroscopy investigations allow us to study the relation between the observed charge-state distributions of protein anions and physico-chemical properties of evaporating droplets in the spray plume. By mixing water with methanol, a refolding of cytochrome C is observed as the water percentage increases in the plume due to the preponderant evaporation of volatile methanol. 相似文献
238.
This paper discusses the experience of a preservice secondary mathematics teacher during lesson study. Although the preservice teacher was a strong undergraduate mathematics student, she used compensation “moves” to deflect attention away from her insecurities about her conceptual understanding of secondary mathematics. She feared being labeled as “dumb” and redirected conversations in order to protect her identity as a knower of mathematics. This paper investigates the culture in which preservice teachers develop confidence in their personal mathematics knowledge and how that confidence may influence behavior. 相似文献