Generation of stable, low-divergence electron beams by laser-wakefield acceleration in a steady-state-flow gas cell

Laser-driven, quasimonoenergetic electron beams of up to approximately 200 MeV in energy have been observed from steady-state-flow gas cells. These beams emitted within a low-divergence cone of 2.1+/-0.5 mrad FWHM display unprecedented shot-to-shot stability in energy (2.5% rms), pointing (1.4 mrad rms), and charge (16% rms) owing to a highly reproducible gas-density profile within the interaction volume. Laser-wakefield acceleration in gas cells of this type provides a simple and reliable source of relativistic electrons suitable for applications such as the production of extreme-ultraviolet undulator radiation.     

Characteristic fragmentation patterns of the trimethylsilyl and trimethylsilyl-oxime derivatives of various saccharides as obtained by gas chromatography coupled to ion-trap mass spectrometry

The fragmentation patterns of selected glycosidic linkage containing non-reducing (methylmannoside, methylgalactoside, lactitol, sucrose, trehalose, raffinose, erlose, melezitose) and reducing saccharides (maltose, cellobiose, lactose, melibiose, palatinose, primeverose, rutinose) have been compared as their trimethylsilyl and as their trimethylsilyl-oxime derivatives. Fragmentation characteristics of the glycosidic linkage containing trimethylsilyl-oxime derivatives have been investigated at the first time: these spectra are not available in the official libraries (NIST, Wiley). Applying gas chromatography-ion trap mass spectrometry, informative fragments of high masses with high intensities have been obtained. Results confirmed characteristic differences between the simple trimethylsilyl derivative providing non-reducing glycosides and the trimethylsilyl, syn and antioxime species. Fragmentation starts at the glycosidic linkage resulting in the case of the non-reducing di- and trisaccharides in two, identical fragments of ring structure, with the abundant selective fragment ion at m/z=361. In the case of reducing disaccharides fragmentation provides two different moieties: one moiety of ring structure at m/z=361, and one of the open chain trimethylsilyl-oxime moiety with two special fragment ions at m/z=361 and at m/z=538. These fragmentation patterns proved to be independent on the position of the glycosidic linkage. Distribution of the selective fragment ions, obtained from their total ion current elutions, was evaluated on a quantitative basis, expressed in percentages of the total of ions formed. Reproducibility in the formation of these selective fragment ions, depending on their amount to be fragmented, proved to be proper for identification and quantitation purposes, equally. On this basis, in addition to the authentic ones, also two reducing disaccharides (primeverose and rutinose), as authentic compounds not available on the market, were identified and quantified in natural matrices.     

Gas chromatographic-mass spectrometric fragmentation study of flavonoids as their trimethylsilyl derivatives: analysis of flavonoids, sugars, carboxylic and amino acids in model systems and in citrus fruits

The fragmentation patterns and quantitation possibilities of three anthocyanidins (pelargonidin, cyanidin, malvidin), one flavonol (quercetin), two flavones (apigenin, luteolin) and two flavanones (naringenin, hesperetin) have been investigated as trimethylsilyl and as trimethylsilyl (oxime) derivatives by gas chromatography-mass spectrometry. Results proved that anthocyanidins and flavanones form trimethylsilyl (oximes), while flavonol and flavones provide simple trimethylsilyl derivatives. In all cases, characteristic fragments of high masses are formed proper for quantitation purposes. Hydrolysis conditions for naringin, hesperidin and rutin have been optimized, resulting in the quantitative release of naringenin, hesperetin and quercetin together with their corresponding saccharides. These basic studies made possible the identification and quantification of the flavonoid, carboxylic-/amino acid and sugar constituents of citrus fruit juices and albedos, without any extraction/enrichment procedure. In total 33 compounds have been determined in hydrolyzed samples, such as 2 flavonoids (naringenin and hesperetin), 6 phenolic acids (trimethoxybenzoic, 4-hydroxybenzoic, vanillic, quinic, chlorogenic and rosmarinic acids), 3 aliphatic carboxylic acids (levulinic, malic, citric acids), phosphoric acid, 4 amino acids (aspartic, glutamic acids, alanine, proline), 9 monosaccharides (xylose, arabinose, rhamnose, fucose, fructose, galactose, glucose, galacturonic acid, sedoheptulose), inositol, sugarphosphate, 5 disaccharides and tocopherol. Measurements were carried out as the trimethylsilyl (oxime) ether/ester derivatives of constituents, in the concentration range of 2 x 10(-3) to 49.9%. Identification level of samples varied between 26.4 and 77.5%, expressed in dry matter content of juices and albedos.     

Analytical Calculation of Sensitivity for Capacitive Pressure Transducers

Calculation of sensitivity for capacitive pressure transducers requires the integration of the deflection function of a clamped‐edge thin diaphragm. For typical square‐formed diaphragms we integrated analytically a closed form deflection function obtained by the Ritz‐method. This exact integration enables fast and accurate simulation.     

The specific grain-boundary electrical resistivity of Ni

The purpose of the present study was to provide a reliable value for the specific grain-boundary resistivity ρ_SGBR of Ni metal. New results are presented on the room-temperature electrical resistivity of nanocrystalline (nc) Ni metal samples produced by electrodeposition with various grain sizes. These resistivity data were compared with previous reports on nc-Ni and all results were analysed according to the procedure of Andrews [Phys. Lett. 19, 558 (1965)] who found that the resistivity increment due to grain boundaries is proportional to the grain-boundary surface area per unit volume which is, on the other hand, inversely proportional to the grain size. It is pointed out that the grain size directly accessible by transmission electron microscopy imaging is the relevant parameter for the evaluation of ρ_SGBR whereas the crystallite size deduced from X-ray diffraction line broadening leads to an underestimation of ρ_SGBR because coherency-breaking intragrain defects not contributing significantly to the resistivity also cause a line broadening. From the evaluation of the nc-Ni resistivity data at room temperature, we find that 4.45·10^?16?Ω·m²?ρ_SGBR(Ni)??16?Ω·m² and our upper bound agrees exactly with the most recent calculated value in the literature.     

Generation of frequency-chirped laser pulses by an electro-optic amplitude modulator

We propose a single electro-optic amplitude modulator to modulate both the intensity and the phase of the light of a diode laser to produce frequency-chirped light pulses in the nanosecond time range. The two-in-one property of the Mach–Zehnder type electro-optic amplitude modulator is used to create a specific device available for experiments with cooled atoms. The phase induced in each optical path of the Mach–Zehnder interferometer and the phase-to-intensity modulation ratio, the intrinsic chirp parameter of the device is determined by generating high order optical harmonics.