Joining, with microwaves

Pure rotational spectroscopy in the microwave or far IR regions joins electron diffraction as one of the two principal methods for the accurate determination of structural parameters of molecules in the gas phase. The relative merits of the two techniques should therefore be summarised. Microwave spectroscopy usually requires sample partial pressures some two orders of magnitude greater than those needed for electron diffraction, which limits its applicability where substances of low volatility are under scrutiny. Compared with electron diffraction, microwave spectra yield fewer experimental parameters more parameters can be obtained by resort to isotopic substitution, because the replacement of, say, 160 by lsO will affect the rotational constants (unless the O atom is at the centre of the molecule, where the rotational axes coincide) without significantly changing the structural parameters. The microwave spectrum of a very complex molecule of low symmetry may defy complete analysis. But the microwave lines are much sharper than the peaks in the radial distribution function obtained by electron diffraction, so that for a fairly simple molecule whose structure can be determined completely, microwave spectroscopy yields more accurate parameters. Thus internuclear distances can often be measured with uncertainties of the order of 0.001 pm, compared with (at best) 0.1 pm with electron diffraction. If the sample is a mixture of gaseous species (perhaps two or more isomers in equilibrium), it may be possible to unravel the lines due to the different components in the microwave spectrum, but such resolution is more difficult to accomplish with electron diffraction. 

The microwave spectrum of CSFg observed by Kisliuk and Silvey (2 ) shows that the molecule is a symmetric rotor comprised of CFg and SFg groups joined by a C-S bond. The infrared ( i 4) and Raman (4) spectra obey the selection rules predicted for the point group We estimate all structural data except for the C-S bond length by analogy with the CF structure in CgFg... 

Fig. 8 A scanning electron microscope micrograph of microwave-joined MaCor and hydroxyapatite, joined at 1020°C for 20 min in a single-mode 2.45 GHz microwave cavity. (MaCor is a mica-platelet reinforced glass ceramic and HAP is a bioceramic material.) (From Ref. f Reprinted with permission of The American Ceramic Society, www. ceramics.org. Copyright 2003. All rights reserved.)...

As is the case with ceramic sintering, joining, and powder synthesis, microwave-assisted fabrication of ceramic coatings can offer unique benefits. To expose the material surfaces for reaction with a gas phase, fibers or powder particles may be suspended by the flow of gas in the fluidized bed. In addition to the flow of the fluidizing gas, low frequency mechanical vibrations (for example, 10-15 Hz) may be applied to the container to reduce the tendency for the powders or fibers to sinter together to form clumps. As the powder size decreases, the powder s sinterability increases. While vibration may not be necessary for particles as large as, say, 50 pm, it may be beneficial for powder particles that are a few microns in diameter. 

In September 2007, following my nomination as a university lecturer at the University of Strasbourg, I joined the laboratory of Dr. Andre Mann in the faculty of pharmacy at Strasbourg. The recent work of this laboratory concerned the reaction of hydroformylation. They had just published an article on the synthesis of derivatives of kainic acid by cyclohydrocarbonylation (CHC) in collaboration with Professor Ojima, and another on olefin hydroa minomethylations assisted by microwave irradiation with Professor Taddei. One year before my arrival, a research student had the role of continuing... 

Looking back, that is exactly what happened. I later joined a small start-up company called AFx, Inc., in California, where we developed a minimally invasive microwave-based surgical ablation system used to treat atrial fibrillation. The company was then acquired by Guidant in 2004 for about 110 million. There is a point to be made here. Opportunities are everywhere At one point, you will find a good opportunity, ora good opportunity will find you. To be successful, you need to have a clear vision of what you want, why you want it, and put all of the elements of your life in place in such a way that, when the opportunity comes, you can see it, take it, and run with it. In any success story, there are also elements of luck. To me, luck is related to the level of your natural talents, and the potential of the opportunities that will come to you. For the rest, it is up to you. Note that there is an element of pro-activeness in put all elements of your life in place. Some of those elements are associated with your mental and physical health, well-being, education, skills and empathy. Do not wait for the elements of your life to be put in place for you. If you take the latter approach, opportunities will still be present, and will still come to you, but you will not see them, nor be capable of exploiting them. 

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