138 research outputs found
An Image Compression Method Based on Wavelet Transform and Neural Network
Image compression is to compress the redundancy between the pixels as much as possible by using the correlation between the neighborhood pixels so as to reduce the transmission bandwidth and the storage space. This paper applies the integration of wavelet analysis and artificial neural network in the image compression, discusses its performance in the image compression theoretically, analyzes the multi-resolution analysis thought, constructs a wavelet neural network model which is used in the improved image compression and gives the corresponding algorithm. Only the weight in the output layer of the wavelet neural network needs training while the weight of the input layer can be determined according to the relationship between the interval of the sampling points and the interval of the compactly-supported intervals. Once determined, training is unnecessary, in this way, it accelerates the training speed of the wavelet neural network and solves the problem that it is difficult to determine the nodes of the hidden layer in the traditional neural network. The computer simulation experiment shows that the algorithm of this paper has more excellent compression effect than the traditional neural network method
Photon-assistant Fano resonance in coupled multiple quantum dots
Based on calculations of the electronic structure of coupled multiple quantum
dots, we study systemically the transport properties of the system driven by an
ac electric field. We find qualitative difference between transport properties
of double coupled quantum dots (DQDs) and triple quantum dots. For both
symmetrical and asymmetrical configurations of coupled DQDs, the field can
induce the photon-assisted Fano resonances in current-AC frequency curve in
parallel DQDs, and a symmetric resonance in serial DQDs. For serially coupled
triple quantum dots(STQDs), it is found that the -type energy level
has remarkable impact on the transport properties. For an asymmetric (between
left and right dots) configuration, there is a symmetric peak due to resonant
photon induced mixing between left/right dot and middle dot. In the symmetric
configuration, a Fano asymmetric line shape appears with the help of ``trapping
dark state". Here the interesting coherent trapping phenomena, which usual
appear in quantum optics, play an essential role in quantum electronic
transport. We provide a clear physics picture for the Fano resonance and
convenient ways to tune the Fano effects.Comment: 7 pages, 5 figure
STUDY ON EQUIPMENT FOR SHOT PUT SOUND SIGNAL FEEDBACK
There are not many articles about the structure of putting, especially on the dynamic study. At present nobody applies instruments and equipments to measure dynamic parameters in the course of putting. The result of this study is to make an electronic pressure device fixed inside a shot. According to non-electric measuring principles, a computer is used to analyze the acquired signals after their amplification, taking sample and NO transmission so as to measure the dynamic parameters that shot-putters have strength on their arms. They may work as theoretical basis of teaching and training. In the meantime they can also help coaches to give technological diagnosis of shot-putters and make a scientific plan of training. Only in this way can shot-putters in China catch the advanced level of the world and win good scores at the Olympic Games
Optical properties of coupled metal-semiconductor and metal-molecule nanocrystal complexes: the role of multipole effects
We investigate theoretically the effects of interaction between an optical
dipole (semiconductor quantum dot or molecule) and metal nanoparticles. The
calculated absorption spectra of hybrid structures demonstrate strong effects
of interference coming from the exciton-plasmon coupling. In particular, the
absorption spectra acquire characteristic asymmetric lineshapes and strong
anti-resonances. We present here an exact solution of the problem beyond the
dipole approximation and find that the multipole treatment of the interaction
is crucial for the understanding of strongly-interacting exciton-plasmon
nano-systems. Interestingly, the visibility of the exciton resonance becomes
greatly enhanced for small inter-particle distances due to the interference
phenomenon, multipole effects, and electromagnetic enhancement. We find that
the destructive interference is particularly strong. Using our exact theory, we
show that the interference effects can be observed experimentally even in the
exciting systems at room temperature.Comment: 9 page
Atomic oxygen adsorption and incipient oxidation of the Pb(111) surface: A density-functional theory study
We study the atomic oxygen adsorption on Pb(111) surface by using
density-functional theory within the generalized gradient approximation and a
supercell approach. The atomic and energetic properties of purely on-surface
and subsurface oxygen structures at the Pb(111) surface are systematically
investigated for a wide range of coverages and adsorption sites. The fcc and
tetra-II sites (see the text for definition) are found to be energetically
preferred for the on-surface and subsurface adsorption, respectively, in the
whole range of coverage considered. The on-surface and subsurface oxygen
binding energies monotonically increase with the coverage, and the latter is
always higher than the former, thus indicating the tendency to the formation of
oxygen islands (clusters) and the higher stability of subsurface adsorption.
The on-surface and subsurface diffusion-path energetics of atomic oxygen, and
the activation barriers for the O penetration from the on-surface to the
subsurface sites are presented at low and high coverages. In particular, it is
shown that the penetration barrier from the on-surface hcp to the subsurface
tetra-I site is as small as 65 meV at low coverage (=0.25). The other
properties of the O/Pb(111) system, including the charge distribution, the
lattice relaxation, the work function, and the electronic density of states,
are also studied and discussed in detail, which consistently show the gradually
stabilizing ionic O-Pb bond with increase of the oxygen coverage.Comment: 31 pages, 16 figure
Critical parameters for the one-dimensional systems with long-range correlated disorder
We study the metal-insulator transition in a tight-binding one-dimensional
(1D) model with long-range correlated disorder. In the case of diagonal
disorder with site energy within and having a
power-law spectral density , we investigate the
competition between the disorder and correlation. Using the transfer-matrix
method and finite-size scaling analysis, we find out that there is a finite
range of extended eigenstates for , and the mobility edges are at
. Furthermore, we find the critical exponent of
localization length () to be
. Thus our results indicate that the disorder strength
determines the mobility edges and the degree of correlation
determines the critical exponents.Comment: 6 pages, 6 figure
Multiple processes affecting surface seawater N2O saturation anomalies in tropical oceans and Prydz Bay, Antarctica
We analyzed the N2O content of surface seawater sampled from Prydz Bay, Antarctica, on a cruise track between 30°S and 30°N during the twenty-second Chinese National Antarctic Research Expedition during austral summer, 2006. The surface water showed an average pN2O value of 311.9±7.6 nL·L-1 (14.1±0.4 nmol·L-1), which was slightly undersaturated. The air-sea N2O flux in the region was -0.3±0.8 μmol·m-2·d-1; however, N2O in the surface water was oversaturated in most stations along the cruise track. Saturation anomalies were greater than 10%, with a maximum of 54.7% being observed at the Equator, followed by 31% at 10°N in the Sulu Sea. The air-sea fluxes at these locations were 12.4 and 4 μmol·m-2·d-1, respectively. Overall, the results indicated that surface water in Prydz Bay was near equilibrium with atmospheric N2O, and that ocean waters in lower latitudes acted as a N2O source. Physical processes such as stratification, ice-melt water dilution, and solar radiation dominate the factors leading to N2O saturation of surface water of Prydz Bay, while biological production and upwelling are primarily responsible for the N2O oversaturation of surface water observed in subtropical and tropical regions along the cruise track
Quantum blockade and loop current induced by a single lattice defect in graphene nanoribbons
We investigate theoretically the electronic transport properties in narrow
graphene ribbons with an adatom-induced defect. It is found that the lowest
conductance step of a metallic graphene nanoribbon may develop a dip even down
to zero at certain values of the Fermi energy due to the defect. Accompanying
the occurrence of the conductance dip, a loop current develops around the
defect. We show how the properties of the conductance dip depend on the
parameters of the defect, such as the relative position and severity of the
defect as well as the width and edges of the graphene ribbons. In particular,
for metallic armchair-edges graphene nanoribbons, whether the conductance dip
appears or not, they can be controlled by choosing the position of the single
defect.Comment: 6 pages, 6 figure
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