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排序方式: 共有77条查询结果,搜索用时 78 毫秒
1.
EI Rodriguez Martinez CI Barriga-Paulino MI Zapata CC Chinchilla AM López-Jiménez CM Gómez 《BMC neuroscience》2012,13(1):104-23
ABSTRACT: BACKGROUND: The peri-adolescent period is a crucial developmental moment of transition from childhood to emergent adulthood. The present report analyses the differences in Power Spectrum (PS) of the Electroencephalogram (EEG) between late childhood (24 children between 8 and 13 years old) and young adulthood (24 young adults between 18 and 23 years old). RESULTS: The narrow band analysis of the Electroencephalogram was computed in the frequency range of 0--20 Hz. The analysis of mean and variance suggested that six frequency ranges presented a different rate of maturation at these ages, namely: low delta, delta-theta, low alpha, high alpha, low beta and high beta. For most of these bands the maturation seems to occur later in anterior sites than posterior sites. Correlational analysis showed a lower pattern of correlation between different frequencies in children than in young adults, suggesting a certain asynchrony in the maturation of different rhythms. The topographical analysis revealed similar topographies of the different rhythms in children and young adults. Principal Component Analysis (PCA) demonstrated the same internal structure for the Electroencephalogram of both age groups. Principal Component Analysis allowed to separate four subcomponents in the alpha range. All these subcomponents peaked at a lower frequency in children than in young adults. CONCLUSIONS: The present approaches complement and solve some of the incertitudes when the classical brain broad rhythm analysis is applied. Children have a higher absolute power than young adults for frequency ranges between 0-20 Hz, the correlation of Power Spectrum (PS) with age and the variance age comparison showed that there are six ranges of frequencies that can distinguish the level of EEG maturation in children and adults. The establishment of maturational order of different frequencies and its possible maturational interdependence would require a complete series including all the different ages. 相似文献
2.
The temperature dependence of the switching frequency of a microwave-induced spontaneous electric field forming a domain structure and the conductance of a doping layer that provides electrons to the two-dimensional electron system have been measured on samples fabricated from the same GaAs/AlGaAs heterostructure. Both quantities have been found to obey the thermally activated dependence (Arrhenius law) with close activation energies. This result indicates a relation between the quantities and confirms a hypothesis that the observed dynamics of the domain structure originates from the dynamical screening of the spontaneous electric field of domains by charges in the doping layer. 相似文献
3.
Gribenyukov A. I. Dorozhkin K. V. Morozov A. N. Suslyaev V. I. 《Russian Physics Journal》2018,60(11):2000-2003
Russian Physics Journal - Results of investigations are presented of the THz spectra of the refractive index n(v) and of the extinction coefficient k(v) for ZnGeP2 single crystals with different... 相似文献
4.
Tamer Shoeib Junfang Zhao Houssain EI Aribi Alan C. Hopkinson K. W. Michael Siu 《Journal of the American Society for Mass Spectrometry》2013,24(1):38-48
The fragmentations of [AA + M]+ complexes, where AA = Phe, Tyr, Trp, or His, and M is a monovalent metal (Li, Na, or Ag), have been exhaustively studied through collision-induced dissociation (CID) and through deuterium labeling. Dissociations of the Li- and Ag-containing complexes gave a large number of fragment ions; by contrast, the sodium/amino acid complexes have lower binding energies, and dissociation resulted in much simpler spectra, with loss of the entire ligand dominating. Unambiguous assignments of these fragment ions were made and formation mechanisms are proposed. Of particular interest are fragmentations in which the charge was retained on the organic fragment and the metal was lost, either as a metal hydride (AgH) or hydroxide (LiOH) or as the silver atom (Ag?). Caption for Graphical Abstract
CID products of Li+, Na+, and Ag+ complexes of Phe, Tyr, Trp, and His are reported and mechanisms by which they are formed are proposed. 相似文献
5.
Journal of Experimental and Theoretical Physics - Equilibrium edge currents emerging due to the variation of occupation of individual Landau spin sublevels near the sample edge are calculated for... 相似文献
6.
The increase of the ratio of H0/Hc is experimentally foound to result in changing the configuration and motion of the normal and superconducting regions in the layer. 相似文献
7.
D. Golberg P.S. Dorozhkin Y. Bando Z.-C. Dong C.C. Tang Y. Uemura N. Grobert M. Reyes-Reyes H. Terrones M. Terrones 《Applied Physics A: Materials Science & Processing》2003,76(4):499-507
Transport and field-emission properties of as-synthesized CNx and BNCx (x<0.1) multi-walled nanotubes were compared in detail. Individual ropes made of these nanotubes and macrofilms of those
were tested. Before measurements, the nanotubes were thoroughly characterized using high-resolution and energy-filtered electron
microscopy, electron diffraction and electron-energy-loss spectroscopy. Individual ropes composed of dozens of CNx nanotubes displayed well-defined metallic behavior and low resistivities of ∼10–100 kΩ or less at room temperature, whereas
those made of BNCx nanotubes exhibited semiconducting properties and high resistivities of ∼50–300 MΩ. Both types of ropes revealed good field-emission
properties with emitting currents per rope reaching ∼4 μA(CNx) and ∼2 μA (BNCx), albeit the latter ropes se- verely deteriorated during the field emission. Macrofilms made of randomly oriented CNx or BNCx nanotubes displayed low and similar turn-on fields of ∼2–3 V/μm. 3 mA/cm2 (BNCx) and 5.5 mA/cm2 (CNx) current densities were reached at 5.5 V/μm macroscopic fields. At a current density of 0.2–0.4 mA/cm2 both types of compound nanotubes exhibited equally good emission stability over tens of minutes; by contrast, on increasing
the current density to 0.2–0.4 A/cm2, only CNx films continued to emit steadily, while the field emission from BNCx nanotube films was prone to fast degradation within several tens of seconds, likely due to arcing and/or resistive heating.
Received: 29 October 2002 / Accepted: 1 November 2002 / Published online: 10 March 2003
RID="*"
ID="*"Corresponding author. Fax: +81-298/51-6280, E-mail: golberg.dmitri@nims.go.jp 相似文献
8.
The photoresponse of magnetoresistance of a high-density two-dimensional electron system to microwave electromagnetic radiation is studied. The damping of the Shubnikov-de Haas oscillation by radiation with a non-monotonic dependence of this effect on the magnetic field and the radiation-induced oscillations of magnetoresistance are observed. The damping is most pronounced within isolated narrow magnetic field intervals that closely correspond to the expected positions of magnetoplasma resonances in the sample under study and also near the cyclotron resonance position. A “window” is observed in the photoresponse near the field value predicted on the basis of a single-particle electron spectrum consisting of broadened Landau levels. The radiation-induced oscillations, the window in the photoresponse, and the damping of the Shubnikov-de Haas oscillations near the cyclotron resonance are described in terms of the theory based on the concept of the nonequilibrium filling of single-electron states. Thus, it is demonstrated that the photoresponse pattern observed in the experiment is formed by both single-particle and collective (magnetoplasma) effects. 相似文献
9.
S. S. Kharintsev G. G. Hoffmann J. Loos G. de With P. S. Dorozhkin M. Kh. Salakhov 《Journal of Experimental and Theoretical Physics》2007,105(5):909-915
The resolution capabilities of near-field Raman spectroscopy based on a giant enhancement of the electric field near a nanosized metal probe are studied. As a test sample, bundles of single-walled carbon nanotubes deposited on glass substrates are used. It is shown that this method ensures a subwavelength spatial resolution of about 50 nm and demonstrates a Raman scattering enhancement of the order of 104. 相似文献
10.
The formation of regions of compressible and incompressible phases in the quantum Hall effect regime has been considered for a two-dimensional (2D) electron system that is created in a field-effect transistor. This effect arises from long-period fluctuations of the density of ionized donors supplying electrons to the 2D system. It is shown that the motion of these regions caused by variations of the average electron density gives rise to minima in the capacitance of the capacitor formed by the 2D electron system and the transistor gate. When the corrections to the capacitance are small, the shape of the minima reproduces the donor density distribution function. Experimental data are presented that demonstrate good agreement with the predictions of the model. 相似文献