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121.
Exploring the feasibility of simultaneous electroencephalography/functional magnetic resonance imaging at 7 T 总被引:1,自引:0,他引:1
The increased blood oxygenation level-dependent contrast available at high field makes the implementation of combined EEG/fMRI experiments at 7 T highly worthwhile from the point of view of fMRI data quality, but the higher field poses greater technical challenges for achieving good quality EEG data. A study of the feasibility of recording EEG signals from human subjects at 7 T using a commercially available, MR-compatible EEG system has therefore been carried out. This involved systematic measurement of the sources of noise in EEG recordings made in the 7 T scanner and measurement of RF heating effects on a gel phantom in the presence of a 32-electrode EEG cap. Having found no significant safety concerns and identified a set-up (involving switching off the magnet's cryo-cooler pumps and mounting the EEG amplifier on a cantilever) that limited scanner-induced noise, combined EEG/fMRI experiments employing visual stimulation were then successfully carried out on two human subjects. With the use of beamformer-based analysis of the EEG data, driven responses and alpha-band, event-related desynchronisation were identified in both subjects. 相似文献
122.
Mario Ficker Søren W. Svenningsen Thomas Larribeau Jørn B. Christensen 《Tetrahedron letters》2018,59(12):1125-1129
The simple reduction of a number of alkenes and alkynes was performed with a typical reaction time of 20?min using a copper-cobalt catalytic system. The reduction did not cleave benzyl protecting groups which are usually vulnerable to catalytic hydrogenation reactions. The catalyst can be prepared in situ by reduction of the inexpensive precursor salts CuSO4 and CoCl2 with NaBH4. Sodium borohydride was also used as an easily handled hydrogen source for the catalytic reductions. No pressure, heating or inert atmosphere is required and purification/catalyst removal is achieved using extraction procedures, making this approach simple and efficient. 相似文献
123.
Ricardo A. Luna-Mora Ángeles Torres-Reyes Oscar A. González-Cruz Fernando Ortega-Jiménez Hulme Ríos-Guerra Jessica V. González-Carrillo 《Green Chemistry Letters and Reviews》2018,11(4):371-378
The efficiency of conventional heating energy source compared with Infrared (IR), Ultrasound (US), Microwave and the simultaneous combination US–IR eco-friendly approaches for preparation of new N-(5-R1 -amino-2-nitrophenyl)acetamides and 5-R1-amino-2-nitroaniline by Nucleophilic Aromatic Substitution (SNAr) via addition–elimination reactions on the halogens F, Cl, Br, I, employing amines as nucleophiles were explored. Moreover, phenyldiazenyl derivatives in good yields by an oxidative one-pot SNAr-based amination reaction from an unusual oxidation of 2-phenylhydrazinyl derivatives in DMSO was prepared. 相似文献
124.
《Mendeleev Communications》2023,33(1):130-132
A glass with CdS nanoparticles was used simultaneously as a matrix for Ce-doped garnet and a yellow-red phosphor to prepare luminescent glass ceramics for the sources of white light. CdS nanoparticles compensate for the unbalanced Ce3+ emission spectrum of the composite material due to the addition of a red component. The synthesized composite material can be a tunable light converter due to altered luminescence spectra by changing the sintering conditions and excitation wavelength 相似文献
125.
Reflection of cold atoms from an array of current-carrying wires 总被引:1,自引:0,他引:1
D.C. Lau A.I. Sidorov G.I. Opat R.J. McLean W.J. Rowlands P. Hannaford 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,5(2):193-199
We report the realization of a new type of magnetostatic mirror for slowly moving atoms which comprises a planar array of
parallel wires alternately carrying electric current in opposite directions. One of the features of this atomic mirror is
that the magnetic field may be readily varied, switched or modulated by altering the current in the wires. Reflection signals
close to 100% at a pulsed current of 3 A are demonstrated for a beam of free-falling laser-cooled cesium atoms at normal incidence.
The current dependence of the reflection signals exhibits structure which is associated with the sequential onset of reflection
of cesium 62
S
1/2
, F=4 atoms in the m=+4, +3, +2 and +1 magnetic states. Measurements of the spatial distribution of the reflected atoms indicate the reflection
is predominantly specular at currents of 3 A.
Received: 31 August 1998 / Accepted: 6 October 1998 相似文献
126.
《Particuology》2023
Amines are important nitrogen-containing compounds in fine particles (PM2.5) in the atmosphere. Observations are necessary for in-depth understanding on the characteristics, sources and atmospheric processes of aminiums. In this study, the observation of ten C1–C4 aminiums in PM2.5 was conducted in January and March of 2021 in suburban Guangzhou. The concentration and composition of aminiums showed significant differences between the pollution episodes and non-episode periods. Seasonal difference was also observed between winter and spring. The influence of meteorological factors (i.e., wind speed, atmospheric pressure, temperature and relative humidity) was investigated. The variations of aminiums were also affected by different sources. Anthropogenic sources were suggested to be major contributor to aminiums in the pollution episodes, while biological sources were important sources to aminiums in the non-episode periods, especially in spring. Positive matrix factorization receptor model was applied to investigate the source contributions, and four major sources were identified. The results show that vehicular emission, industrial production, biological emission and soil/dust were the major sources of aminiums. This study emphasizes the importance of source contribution and meteorological conditions on the variations of aminiums, which provides further understanding of organic nitrogen in the atmosphere. 相似文献
127.
Valeria Ferrari 《Annalen der Physik》2000,9(1):3-17
Stars and black holes are sources of gravitational radiation in many phases of their life, and the signals they emit exhibit features that are characteristic of the generating process. Emitted since the beginning of star formation, these signals also contribute to create a stochastic background of gravitational waves. We shall show how the spectral properties of this background can be estimated in terms of the energy spectrum of each single event and of the star formation rate history, which is now deducible from astronomical observations. We shall further discuss the process of scattering of masses by stars and black holes, showing that, unlike black holes, stars emit signals that carry a clear signature of the nature of the source. 相似文献
128.
Driss Laraqui Olivier Allgaier Cornelius Schönnenbeck Gontrand Leyssens Jean-François Brilhac Ricardo Lomba Clément Dumand Olivier Guézet 《Proceedings of the Combustion Institute》2019,37(3):3175-3184
This work presents a study of a magnesium/air combustion process in the context of innovative zero carbon dioxide (CO2) energy carriers for reducing global warming effects. In order to analyze more deeply the confined combustion of magnesium under fluctuating overpressure conditions (0 to 24 hPa) and the generated gaseous by-products, magnesium/air flames have been realized in a combustion chamber with a conical bluff-body as flame holder and different contraction ratios diaphragms at the exit duct. Sieved magnesium samples with two size-fractions were tested: 20–50?µm and 50–70?µm. The gaseous emissions of nitrogen oxides (NOx) and dioxygen (O2) were analyzed with on-line infrared, ultraviolet and paramagnetic analyzers. A flame pulsating behavior was clearly observed from light emission intensity (monitored by a photodiode) and pressure fluctuations (monitored by a pressure sensor); the frequencies obtained ranged between 3 and 10?Hz. The frequency of the pulsation exhibited strong dependence on the geometric configuration of the chamber: a contraction diaphragm divided by two the frequency level of the fluctuations in the studied range of maximum overpressure. Such fluctuations may probably be the consequence of periodic perturbations of the recirculation zone behind the bluff-body. These periodic perturbations are themselves caused by strong periodic overpressure variations due to stiff contraction downstream responding to gas velocity fluctuations. This feed-back-loop mechanism was considered in this study. NOx emissions produced through the thermal pathway were analyzed for equivalence ratios ranging from 0.29 to 1. The representation of NOx versus equivalence ratio exhibited a parabolic shape with a maximum for an equivalence ratio of 0.4. Moreover, NOx emissions of this metal combustor have shown a similar order of magnitude than current internal combustion engines. 相似文献
129.
How to construct new super integrable equation hierarchy is an important problem. In this paper, a new Lax pair is proposed and the super D-Kaup-Newell hierarchy is generated, then a nonlinear integrable coupling of the super D-Kaup-Newell hierarchy is constructed. The super Hamiltonian structures of coupling equation hierarchy is derived with the aid of the super variational identity. Finally, the self-consistent sources of super integrable coupling hierarchy is established. It is indicated that this method is a straight- forward and efficient way to construct the super integrable equation hierarchy. 相似文献
130.
《Wave Motion》2017
This paper presents a simulation-based analysis of the effect of a reflecting surface on aeroacoustic Time-Reversal (TR) source localization/characterization and compares the results of TR with those obtained using cross-spectral Conventional Beamforming (CB). The TR technique is shown to require the use of at least two line arrays of microphones to accurately characterize the nature of aeroacoustic sources. This work, however, shows that in the presence of a rigid surface, only one line array of microphones is sufficient to accurately localize and characterize idealized aeroacoustic sources. Forward simulations were carried out using the 2-D Linearized Euler Equations on a rectangular domain with a rigid bottom boundary (modeling a 2-D semi-infinite space) for the test-cases of stationary idealized tonal aeroacoustic (monopole, dipole and lateral quadrupole) sources located in a fully-developed mean shear flow field wherein the acoustic pressure time–history was stored at the computational boundaries. A set of TR simulations are implemented that show for each test-case that only the top line array is required to accurately characterize the idealized aeroacoustic sources in the presence of a reflecting bottom boundary, thereby suggesting the redundancy of acoustic pressure measurement at the rigid surface. The test-case of convecting (moving) idealized aeroacoustic source was also considered and the TR simulation using only the top line array in the presence of reflecting bottom boundary was able to accurately retrieve the source trajectory and simultaneously characterize its nature. This numerical experiment demonstrates in principle that when a rigid surface is mounted on the floor of an Anechoic Wind Tunnel, the use of only one (top) line array of microphones should be sufficient to characterize the nature and location of experimental flow-induced noise source. Acoustic source maps were also obtained using the CB method based on the Method of Images (to model the reflecting surface) and incorporation of the Ray-Tracing algorithm necessary to account for the effect of mean flow. The CB results were found to be highly comparable to those obtained using TR for the test-cases of non-convecting sources; thereby demonstrating the conceptual equivalence of the Method of Images and directly implementing the rigid-wall condition during TR for source localization/characterization. 相似文献