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81.
Application of continuous flow and alternative energy devices for 5-hydroxymethylfurfural production
Dehydration of fructose and glucose in dipolar, aprotic solvents leads to formation of 5-hydroxymethylfurfural. Conditions
for continuous flow reactions using a cartridge-based reactor system and a stop-flow microwave reactor were established showing
very good product yields and selectivity without the limitation of a batch process such as upscaling and precise temperature
monitoring and control. A maximum product HPLC yield of 90.3% under cartridge-based heating and 85.6% under microwave heating
could be achieved using mild and quick reaction conditions. Formation of levulinic acid as a by-product could not be detected
under the optimized reaction conditions. 相似文献
82.
We analyze the scaling properties of the ac conductivity spectra of ion-conducting polyelectrolyte complexes of different compositions. Spectra were taken at ambient temperature but at different relative humidities. For the first time, we report on a scaling principle for conductivity spectra termed "time-humidity-superposition principle" in analogy with the well-known time-temperature-superposition principle. This model-free scaling holds for different materials over several decades in frequency. It implies that the hydration is activating ion motion over short and long distances in a similar general way, a concept so far only established for thermal energy. 相似文献
83.
Schäfer J Schrupp D Rotenberg E Rossnagel K Koh H Blaha P Claessen R 《Physical review letters》2004,92(9):097205
High-resolution photoemission data of the (110) iron surface reveal the existence of well-defined metallic surface resonances in good correspondence to band calculations. Close to the Fermi level, their dispersion and momentum broadening display anomalies characteristic of quasiparticle renormalization due to coupling to bosonic excitations. Its energy scale exceeds that of phonons by far, and is in striking coincidence with that of the spin wave spectrum in iron. The self-energy behavior thus gives spectroscopic evidence of a quasiparticle mass enhancement due to electron-magnon coupling. 相似文献
84.
We report on a soft x-ray microscope using a gas-discharge plasma with pseudo spark-like electrode geometry as a light source. The source produces a radiant intensity of 4 x 10(13) photons/(sr pulse) for the 2.88 nm emission line of helium-like nitrogen. At a demonstrated 1 kHz repetition rate a brilliance of 4.3 x 10(9) photons/(microm2 sr s) is obtained for the 2.88 nm line. Ray-tracing simulations show that, employing an adequate grazing incidence collector, a photon flux of 1 x 10(7) photons/(microm2 s) can be achieved with the current source. The applicability of the presented pinch plasma concept to soft x-ray microscopy is demonstrated in a proof-of-principle experiment. 相似文献
85.
Benitez MJ Petracic O Salabas EL Radu F Tüysüz H Schüth F Zabel H 《Physical review letters》2008,101(9):097206
Employing magnetometry measurements, we have studied Co3O4 nanowires focusing on the core-shell behavior. We find two magnetic contributions, i.e., a regular antiferromagnetic and an additional irreversible one. The first contribution can be attributed to the antiferromagnetically ordered wire cores. The nature of the second one can be identified using thermoremanent and isothermoremanent magnetizaton curves as magnetic fingerprints of the irreversible magnetization. We conclude that the nanowire shell behaves like a two-dimensional diluted antiferromagnet in a field. 相似文献
86.
The possible build-up of the spin-isospin fluctuation strength in nuclear collisions is investigated. In lack of quantum mechanical methods we rely on assumptions usually applied for heavy ion collisions. Based on a fluid dynamical picture we present our ‘isospin coupling in a nucleon cascade’. Within this framework it is possible to describe the mean isospin value as a function of the number of participants in a heavy ion collision and it is possible to study the effect of neutron excess. Since the pion field couples to the spin-isospin density a substantial size of this quantity gives rise to pion bremsstrahlung, the dominant subthreshold pion production mechanism. 相似文献
87.
W. A. Schönfeldt P. H. Mokler D. H. H. Hoffmann A. Warczek 《Zeitschrift für Physik A Hadrons and Nuclei》1985,320(4):693-694
Resonance energies and widths of four resonances in the reaction25Mg(p,γ)26Al were measured with the high resolution proton beam of the new 500 kV accelerator IONAS. The previously given large width of the 389 keV resonance, Γ= 460±70 eV. (1), used in the interpretation of stellar26A1 production was shown to be incorrect and probably caused by target oxidation effects and insufficient energy resolution of the beam. The new value is Γ<4 eV. 相似文献
88.
G. Münzenberg S. Hofmann H. Folger F. P. Heßberger J. Keller K. Poppensieker B. Quint W. Reisdorf K. H. Schmidt H. J. Schött P. Armbruster M. E. Leino R. Hingmann 《Zeitschrift für Physik A Hadrons and Nuclei》1985,322(2):227-235
In irradiations of207Pb and208Pb, respectively, with54Cr theα-decay of the isotopes259106,260106, and261106 could be observed for the first time. For260106 a spontaneous fission branch of (50 ?20 +30 )% was observed. The isotopes were identified by genetic relationships of α-decay after separation in-flight with the velocity filter SHIP and implantation into a position-sensitive silicon surface-barrier detector. The measured partial fission halflife of the doubly even isotope260106 of (7.2 ?2.7 +4.8 )ms exceeds the predicted values by at least a factor of 40. This result could be explained by the high shell corrections of the ground state mass, derived from the measured α-decay energies. The experimental results show evidence for an island of purely shell stabilized nuclei in the region of deformed isotopes beyond the actinides. 相似文献
89.
We study a class of nonlinear Ito stochastic differential equations (with possibly state dependent diffusion coefficients), in which the variables can be divided into linearly damped (slaved) variables s and linearly undamped variablesu (order parameters). We devise a systematic and constructive procedure to eliminate the slaved variables. We take explicit time and chance dependence of the slaved variables into account, the latter via a family of diffusion processesZ
t
(v)
. These act as fluctuating coefficients of the Center Manifolds
t=s(u
t, t,Z
t
(v)
(v=2, 3, ...)) and appear explicitly in the elimination procedure. We show how in the Ito calculus fluctuating and deterministic coefficients of the Center Manifold are more completely separated than in the previously treated Stratonovich case [1]. The adiabatic approximation is defined as a partial summation of the elimination expansion and the stochastic generalization ofs=0 is derived. We show how thus ambiguity of stochastic calculi is removed. Closed form summations are given in two examples. We briefly indicate the potential use of perturbation theory techniques in the systematic elimination procedure. 相似文献
90.
Christophe Reutenauer Marcel-Paul Schützenberger 《Letters in Mathematical Physics》1987,13(4):299-302
We give a formula, involving circular words and symmetric functions of the eigenvalues, for the determinant of a sum of matrices. Theorem of Hamilton-Cayley is deduced from this formula.UQAM and LITPUniversité Paris 7 and LITP. 相似文献