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61.
62.
Crow J. T. Forrester A. T. Goebel D. M. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1978,6(4):535-538
An ion accelerator system using one or two fine mesh tungsten grids has been used in a magnetic multipole containment ion source to produce a continuous positive ion beam variable over a wide range of beam currents and accelerator voltages. The ion source plasma is low noise and uniform to ± 1% density variation over 9 cm diameter. Beams up to 4 cm × 4 cm have been extracted which have low divergence (±1%), uniform current density (±2%), small ion energy speed, beam ion energy variable from 200V to several thousand volts, and current densities variable from ?A per cm2 to tens of milliamperes per cm2, limited only by acceleration grid power loading or sputtering. 相似文献
63.
Efficiency enhancement in high power backward-wave oscillators 总被引:1,自引:0,他引:1
Goebel D.M. Adler E.A. Ponti E.S. Feicht J.R. Eisenhart R.L. Lemke R.W. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1999,27(3):800-809
High power microwave (HPM) sources based on the backward-wave oscillator (BWO) have been investigated for the past two decades primarily because of their potential for very high efficiency (15 to 40%) operation. Several different effects have been proposed to explain this high efficiency compared to conventional BWOs. One of the major contributors to the high efficiency of the plasma-filled Pasotron HPM BWO source is the presence of optimally phased end reflections. The Pasotron uses a long-pulse (⩾100 μs) plasma-cathode electron-gun and plasma filled slow-wave structure to produce microwave pulses in the range of 1 to 10 MW without the use of externally produced magnetic fields. The efficiency of the Pasotron can be enhanced by up to a factor of two when the device is configured as a standing-wave oscillator in which properly phased reflections from the downstream collector end of the finite length SWS constructively interfere with the fundamental backward-wave modes and improve the coupling of the beam to the circuit. Operation in this configuration increases the efficiency up to 30% but causes the frequency to vary in discrete steps and the output power to change strongly with beam parameters and oscillation frequency 相似文献
64.
Karl Goebel 《Fresenius' Journal of Analytical Chemistry》1914,53(2):118
Ohne Zusammenfassung 相似文献
65.
66.
Thorsten Goebel Alim Ormeci Oliver Pecher Prof. Dr. Frank Haarmann 《无机化学与普通化学杂志》2012,638(10):1437-1445
The Zintl phases M4Si4 with M = Na, K, Rb, Cs, and Ba2Si4 feature a common structural unit, the Si44– anion. The coordination of the anions by the cations varies significantly. This allows a systematic investigation of the bonding situation of the anions by 29Si NMR spectroscopy. The compounds were characterized by powder X‐ray diffraction, differential thermal analysis, magnetic susceptibility measurements, 23Na, 29Si, 87Rb, 133Cs NMR spectroscopy, and quantum mechanical calculation of the NMR coupling parameter. The chemical bonding was investigated by quantum mechanical calculations of the electron localizability indicator (ELI). Synthesis of the compounds results for all of them in single phase material. A systematic increase of the isotropic 29Si NMR signal shift with increasing atomic number of the cations is observed by NMR experiments and quantum mechanical calculation of the NMR coupling parameter. The agreement of experimental and theoretical results is very good allowing an unambiguous assignment of the NMR signals to the atomic sites. Quantum mechanical modelling of the NMR shift parameter indicates a dominant influence of the cations on the isotropic 29Si NMR signal shift. In contrast to this a negligible influence of the geometry of the anions on the NMR signal shift is obtained by these model calculations. The origin of the systematic variation of the isotropic NMR signal shift is not yet clear although an influence of the charge transfer estimated by calculation using the QTAIM approach is indicated. 相似文献
67.
Esposito F Aragri A Pesaresi I Cirillo S Tedeschi G Marciano E Goebel R Di Salle F 《Magnetic resonance imaging》2008,26(7):905-913
Resting-state functional magnetic resonance imaging (RS-fMRI) is a technique used to investigate the spontaneous correlations of blood-oxygen-level-dependent signals across different regions of the brain. Using functional connectivity tools, it is possible to investigate a specific RS-fMRI network, referred to as "default-mode" (DM) network, that involves cortical regions deactivated in fMRI experiments with cognitive tasks. Previous works have reported a significant effect of aging on DM regions activity. Independent component analysis (ICA) is often used for generating spatially distributed DM functional connectivity patterns from RS-fMRI data without the need for a reference region. This aspect and the relatively easy setup of an RS-fMRI experiment even in clinical trials have boosted the combined use of RS-fMRI and ICA-based DM analysis for noninvasive research of brain disorders. In this work, we considered different strategies for combining ICA results from individual-level and population-level analyses and used them to evaluate and predict the effect of aging on the DM component. Using RS-fMRI data from 20 normal subjects and a previously developed group-level ICA methodology, we generated group DM maps and showed that the overall ICA-DM connectivity is negatively correlated with age. A negative correlation of the ICA voxel weights with age existed in all DM regions at a variable degree. As an alternative approach, we generated a distributed DM spatial template and evaluated the correlation of each individual DM component fit to this template with age. Using a "leave-one-out" procedure, we discuss the importance of removing the bias from the DM template-generation process. 相似文献
68.
This paper deals with a Dirichlet boundary value problem for a linear second order ordinary differential operator, whose coefficients belong to certainLp-spaces. Its solution is to be understood in the sense of Sobolev, so that the Fredholm alternative holds. The main purpose of this paper is, in case of unique solvability, to introduce a Green's function by means of which the solution can be given explicitly by integrals. We give the precise definition of the Green's function via Riesz' Representation Theorem and establish some of its basic properties. As a preliminary tool the Cauchy initial value problem is considered. 相似文献
69.
Timothy S. Goebel Kevin J. McInnes Scott A. Senseman Robert J. Lascano Lucas S. Marchand Todd A. Davis 《Tetrahedron letters》2011,52(41):5241-5244
Due to strong hydrogen bonding interactions, thiourea has been shown to have a high affinity for anions such as inorganic phosphate. The interaction between phosphate and thiourea has been used to develop technologies that can detect and even remove phosphate from water. This research investigates the use of thiourea derivatized polymer flocculants for the sequestering of inorganic phosphate from water. The study presented herein describes the development of a thiourea based monomer that was used to create a bi-functional polymer that flocculates suspended solid material as well as sorbs phosphate, removing both from water. The new polymer removed more than 60% of the phosphate from a simulated wastewater sample. The addition of a thiourea trapping group to the polymer more than doubled the amount of phosphate removed from solution compared to control polymers. 相似文献
70.
An optimal feedback mapping, leading to necessary and sufficient conditions for optimality in terms of a closed-loop differential inclusion, is derived in the setting of fully convex generalized problems of Bolza. Results are translated to the format of control problems with linear dynamics and convex costs. Properties of the feedback mapping, with focus on single-valuedness and continuity, are analyzed through those of the value function and of the Hamiltonian. Conditions guaranteeing differentiability of the value function are obtained through the analysis of its subdifferential as a maximal monotone operator and of the generalized Hamiltonian dynamics. 相似文献