Modeling and simulation of the background light in underwater imaging under different illumination conditions
The underwater visibility is very important in underwater vision research and target detection. However, most underwater vision systems cannot guarantee to possess the performance under complex water conditions. This is because underwater images are usually degraded by light-water interactions of absorption and scattering. The ambient light is scattered into the camera’s line of sight by water molecules and suspended particles in the water medium, which adds a layer of haze to the image and reduces the contrast of the image. This part of scattered light is usually called background light, which is the main reason for underwater image degradation. In this paper, the formations of background light in underwater imaging under two different lighting conditions: natural illumination and artificial lighting, are analyzed by setting up physical models. The models developed include the parameters such as camera parameters, light source parameters, inherent optical properties, and camera-source-object geometry. Based on the models, the relationship between the background light and the above parameters is studied. Computer analysis shows that the global background light under two illumination conditions has a close relationship between the inherent optical properties of water medium and camera parameters. The global background light under natural illumination is proportional to the scattering coefficient and inversely proportional to the attenuation coefficient. The background light under the two illumination conditions both can be described in simple exponential falloff expressions of the global background light. The simple expression greatly reduces the computational complexity of simulations. The intensity of background light mainly depends on the inherent optical properties, camera-scene distance, camera-source distance and camera’s imaging angle. The relationship between the global background light and the inherent optical properties can be used to estimate the attenuation coefficient, scattering coefficient and scene depth information. The result of this paper can be very useful for designing and improving the underwater imaging systems.
Anisotropy of melting of Ag nanocrystal with different crystallographic planes at high temperature
Torsional mechanical properties of (n, n)-(2n, 0) carbon nanotubes heterojunction
A coaxial cylindrical heterojunction of carbon tubes, which consists of alternant bands of 5- and 7-membered rings, can be formed by one armchair (n, n) carbon nanotube and one zigzag (2n, 0) carbon nanotube. The torsional mechanical properties of this kind of (n, n)-(2n, 0) heterojunction constructed by the same length of armchair and zigzag nanotubes are studied by using molecular dynamics method. In order to make a comparison, the relations of the torque and axial stress to torsional angle of (n, n) and (2n, 0) carbon tubes are also systemically calculated. Moreover, the transfer process of torsional stress in the (n, n)-(2n, 0) heterojunction is analyzed. Some important conclusions are obtained. Firstly, the torsional angle corresponding to the buckling point of carbon nanotubes is closely related to their torsional stiffness. The buckling angle decreases monotonically with torsional stiffness. Secondly, as the torsion develops, the torsional stress appears from the joint position due to the fact that the junction part in the (n, n)-(2n, 0) heterojunction has the smallest torsional stiffness and then transfers from the joint position to both ends. The propagation velocity of the torsional stress in (n, n) nanotube which has smaller stiffness is faster than that in (2n, 0) nanotube with bigger stiffness. Finally, for the process of torsion within the elastic limit, no axial stress is produced in (n, n)-(2n, 0) heterojunction during the torsion. This effect is of great significance for designing the carbon nanotube-based nano-oscillator devices.
Fabrication and microstucture of spray formed powder metallurgy superalloy FGH4095M
Phase-field-crystal simulation of edge dislocation climbing and gliding under shear strain
Phase field crystal simulation of grain boundary annihilation under strain strain at high temperature
Sound velocity and phase transition for low porosity tin at high pressure
Phase diagram of the one-dimensional extended ionic Hubbard model
Effect of electronic correlations on magnetotransport through a parallel double quantum dot
We theoretically investigate the effects of electronic correlations (including spin and Coulomb correlations) on the magnetotransport through a parallel double quantum dot (DQD) coupled to ferromagnetic leads. Two dots couple coherently through electron correlations, rather than tunneling directly between two dots, and each dot is coupled to two semi-infinite ferromagnetic leads. We assume that the intradot Coulomb repulsion is much larger than the interdot Coulomb repulsion U. Thus, only the zero, one and two-particle DQD states are relevant to transport. Because of interdot electron correlation, the I-V characteristics of each dot is sensitive to the change in the state of the other dot. This work focuses on the effects of electron spin correlation and electron Coulomb correlation on magnetotransport through this system. In order to determine the transport properties of the system, we use the generalized master equation method. This method is based on the reduced density operator defined by averaging the statistical operator of the total system over the states of all leads. With the framework of the generalized master equation and the sequential tunneling approximation, we calculate the current, differential conductance and tunnel magnetoresistance (TMR) in the dot 1 as a function of bias for different spin correlations and Coulomb correlations. Our results reveal that the magnetotransport through this system is more sensitive to Coulomb correlation than to spin correlation; when Coulomb correlation equals zero, the spin correlation can induce a giant tunnel magnetoresistance, which is further larger than the Julliere’s value of TMR; when Coulomb correlation occurs, the giant tunnel magnetoresistance disappears; when Coulomb correlation is equal to or larger than spin correlation, Coulomb correlation can suppress spin correlation; while the coexistence of Coulomb correlation and asymmetry of the DQD system can result in dynamical channel blockade, which can lead to the occurrence of negative tunnel magetoresistance and negative differential conductance. These novel properties lead to the potential applications in nanoelectronics, and relevant underlying physics of this problem is discussed.
First-principles study on the uniaxial pressure induced topological quantum phase transitions of Ge2X2Te5 (X =Sb, Bi) thin films
Electronic Tamm states of metamaterial-like semiconductor composite structures
First-principles calculation of doped GaN/AlN superlattices
Spin-wave band gaps created by rotating square rods in triangular lattice magnonic crystals
Study on magnetic properties of strontium ferrite based on the technology of electron paramagnetic resonance
In order to study how the ingredient, sintering temperature, oxygen, doping and other conditions affect magnetic properties of strontium ferrite powder, a strontium ferrite powder is prepared by sol-gel method, and a new method of studying magnetic properties of strontium ferrite powder based on an electron paramagnetic resonance (EPR) is established in this paper. The sintered samples are tested by electron paramagnetic resonance spectrometer. Results show that α-Fe2O3, a paramagnetic intermediate, is most compared with other ratios under calcined at 400 ℃ and the strontium iron mole ratio of 1:9; while at the other temperatures it decreases and the ferromagnetic phase increases; the optimum calcination temperature is between 800 ℃ and 900 ℃. These facts are caused by both external magnetic field and other magnetic fields, thus resulting in some new stronger magnetic moment interactions. Results also show that a large quantity of paramagnetic α-Fe2O3 is found under hypoxic annealing environment, which is not conducible to generating the ferrimagnetic phase; X-ray diffraction (XRD) analysis shows that the others are paramagnetic and ferrimagnetic phase except a bit of other phases; both EPR spectra and XRD spectra show that the paramagnetic phase is least, and ferrimagnetic phase is most in the sintering sample when strontium iron mole ratio is 1:9, so the sample owns the strongest magnetism. The sample remanence experiment by milli-tesla meter also confirms these results. It is also found that paramagnetic phase can effectively decrease and ferrimagnetism is enhanced when samples are doped by lanthanum ion accounting for 20%-30% of the total number of moles of strontium lanthanum.
Effect of thermal annealing on the structure and properties of plasma enhanced chemical vapor deposited SiCOH film
Influences of p-type layer structure and doping profile on the temperature dependence of the foward voltage characteristic of GaInN light-emitting diode
Design and optimization of integrated micro optical gyroscope based on a planar ring resonator
Luminescence properties of Eu3+ doped CaMoO4 micron phosphors
Effects of growth angle and solidification rate on crystal growth of precious metal prepared by electron beam floating zone method
Three-dimensional numerical analysis of interaction between arc and pool by considering the behavior of the metal vapor in tungsten inert gas welding
Microstructural evolution of laser surface remelting remolten Ni-28 wt%Sn alloy under liquid nitrogen cooling
Multiple heat sources with multi-parameter inversion of nondestructive infrared detection
Fluorescence resonance energy transfer in a aqueous system of CdTe quantum dots and Rhodamine B with two-photon excitation
Modeling and failure monitor of Li-ion battery based on single particle model and partial difference equations
Li-ion battery is a complicated distributed parameter system that can be described precisely by field theory and partial differential equations. In order to reduce the calculation amount and the solution difficulty, a distributed parameter system is often described by ordinary differential equation model during the design and the analysis. As a result, systemic error is caused, and the reliability of the system model is reduced. The rechargeable Li-ion batteries are widely used in many fields because of their excellent properties. The research on the modeling and failure monitor of Li-ion battery can evaluate its working state, and improve the security during its servicing. Li-ion battery system is regarded as a distributed parameter system in this paper. Single particle model is a simplification of a Li-ion battery under a few assumptions. According to the measured data, single particle model can be used for estimating the parameter at a fast simulation speed. Li-ion battery model based on partial difference equations and single particle model is proposed to detect the failure and evaluate the working state of Li-ion battery system. Lithium ion concentration is an unmeasurable distributed variable in the anode of Li-ion battery. The failure monitor system can track the real-time Li ion concentration in the anode of Li-ion battery, calculate the residual which is the difference between the measured value and the ideal value. A failure can be judged when the residual is beyond a predefined failure threshold. A simulation example verifies that the accuracy and the effectiveness of Li-ion battery failure monitor system based on parabolic partial difference equations and single particle model is reliable.
Characteristics of spherical stress wave propagation in the standard linear solid material
The study of energy model and multi-period of discrete phase shift control technique for full-bridge DC-DC converter
Tooth-shaped plasmonic filter based on graphene nanoribbon
Spectrum handoff model based on preemptive queuing theory in cognitive radio networks
Analysis and design of a Ka-band sheet beam relativistic extended interaction klystron amplifier
Low frequency noise behaviors in the partially depleted silicon-on-insulator device
Influence of length parameter on the characteristics of nanoscale titanium oxide memristor
Low-voltage pentacene photodetector based on a vertical transistor configuration
Dynamical balance between excitation and inhibition of feedback neural circuit via inhibitory synaptic plasticity
Effects of bathocuproine/Ag composite anode on the performances of stability polymer photovoltaic devices
Carrier transport mechanism of GaAs/Ge solar cells under electrons irradiation
Optical properties of graphene plasmons and their potential applications
Graphene plasmons have aroused a great deal of research interest in recent years due to their unique features such as electrical tunability, ultra-strong field confinement and relatively low intrinsic damping. In this review paper, we summarize the fundamental optical properties of localized and propagating plasmons supported by graphene, and the experimental techniques for excitation and detection of them, with focusing on their dispersion relations and plasmon-phonon coupling mechanism. In general, the dispersion of graphene plasmons is affected by the Fermi level of graphene and the dielectric environment. The graphene plasmons can exist in a broad spectrum range from mid-infrared to terahertz. This has been experimentally verified for both the localized and propagation plasmons in graphene. On the one hand, the excitation frequency and confinement of localized plasmons supported by graphene micro/nano-structures are constrained by the structural geometry. Additionally, influenced from the tunability of the optical conductivity of graphene, the excitation frequency of graphene plasmons can be tuned by electrostatic or chemical doping. On the other hand, propagating plasmons have been launched and detected by using scattering-type scanning near-field optical microscopy. This technique provides the real-space imaging of the electromagnetic fields of plasmons, thereby directly confirming the existence of the graphene plasmons and verifying their properties predicted theoretically. In a similar regime, the launching and controlling of the propagating plasmons have also been demonstrated by using resonant metal antennas. Compared to metal plasmons, graphene plasmons are much more easily affected by the surroundings due to their scattering from impurity charges and coupling with substrate phonons. In particular, graphene plasmons can hybridize strongly with substrate phonons and there are a series of effects on plasmon properties such as resonance frequency, intensity and plasmon lifetime. The designing of the dielectric surrounding can effectively manipulate the graphene plasmons. Finally, we review the emerging applications of graphene plasmon in the mid-infrared and terahertz, such as electro-optical modulators and enhanced mid-infrared spectroscopy.
Harmonic signal extraction from chaotic interference based on synchrosqueezed wavelet transform
Macroscopic stable mechanism of autonomous cooperative system
Sensitivity analysis of sample number on the drought descriptive model built by Copula function in southwest China
Interpolating particle method for mechanical analysis of space axisymmetric components
A numerical study of effects on detection height of a radio acoustic sounding system influenced by atmospheric wind and temperature
Canonical quantization of classical fields in finite volume
Mechanism for the coexistence phenomenon of random phase suppressing chaos and stochastic resonance in Duffing system
Multispectral image enhancement based on irradiation-reflection model and bounded operation
Optimal calculation of detection efficiency for thermal neutron sensitive microchannel plate
Heat transfer analysis of rotating tritium target of deuterium-tritium fusion neutron generator
Construction of Lennard-Jones pair potential and pairwise many-body potential for crystal α-boron
Collision dynamic behaviors of CO(X1Σ+) molecule with Mg atom in cold and ultracold temperatures
Experimental study on breakdown voltage between parallel plates in high-pressure helium
Plasma density effect on backward Raman laser amplification
Shock wave amplification by shock wave self-generated magnetic field driven by laser and the external magnetic field
Shock wave is a common phenomenon in astrophysics. Shock wave acceleration has been regarded as a source of high-energy cosmic rays. Very strong magnetic field exists in the surrounding of the shock wave at the edge of the supernova remnants. But the mechanisms of generation and amplification of such a strong magnetic field are not clear yet. In this paper, the properties of shock wave driven by the laser irradiating on un-magnetized and magnetized plasmas are investigated using two-dimensional particle-in-cell (PIC) simulations. It is found that very strong spontaneous magnetic field can be generated around the laser-driven shock front in the un-magnetized plasma. The spontaneous magnetic field can store energy and accelerate electrons further. When an external magnetic field is introduced, the electrons and ions are accelerated more efficiently by the shock wave than in the un-magnetized plasma. The external magnetic field can transfer its energy to electrons and ions, and strengthen the shock wave. In simulations, the introduced external magnetic field has three different strengths: 1072 MG, 107.2 MG and 10.72 MG, which determine the shock structures through the driven currents. There are two single-polar magnetic arcs that constitute the shock structure when the external magnetic field is 1072 MG, i.e., one is the shock itself and the other is actually the reverse shock, whereas only one magnetic arc is produced but with a bipolar structure in the direction perpendicular to the shock propagation when the externally added magnetic fields are much lower (107.2 MG and 10.72 MG). The two bipolar magnetic structures will evolve into a single-polar arc when the externally added magnetic field is 107.2 MG, but they are kept for all the time when the external magnetic field is 10.72 MG. It can be explained by taking the Larmor radius into the consideration. That the amplification ratio of the magnetic field decreases as the introduced external magnetic field increases implies that the magnetic amplification in the space is possibly due to the local field generation rather than the field compression. An amplification ratio of tens of the external magnetic field is achieved due to the pseudo Rayleigh-Taylor instability, but still much smaller than that around the astrophysical shock front, indicating that other efficient mechanisms are responsible for the observed magnetic amplification around shocks in the supernova remnants.
Interaction between low energy proton ring-beam and plasma with one-dimentional hybrid simulations
Theoretical and experimental study of thrust produced by corona discharge exciter in wire-aluminum foil electrode configration
Numerical simulation of positive glow corona discharge initiated from long ground wire under thundercloud field
Effect of gas bubble on acoustic characteristic of sediment: taking sediment from East China Sea for example
The effect of gas bubble on acoustic characteristic of sediment is important for ocean science, ocean geology, ocean geophysics, etc. Twenty five samples of ocean bottom sediments are extracted through gravity sampling equipment from the East China Sea and are sealed in PVC pipes for storage in order to study the effect of gas bubble on acoustic characteristic of sediment. In order to obtain the gas content of sediment, in this the paper the Micro-CT scanning technology is introduced into sediment measuring method. The different X ray absorption rates of water, gas and solid particles in sediment samples are obtained through Micro-CT scanning using Siemens’ Micro-CT scanner. The gas volume content and water volume content in sediment can be obtained according to CT number distribution. The acoustic measurement is carried out in laboratory using intelligent nonmetal ultrasonic detector and the 40 kHz waves are launched from one side of the sediment sample and obtained from another side. The acoustic attenuation can be obtained according to the amplitudes of launched and received waves and the acoustic velocity can be obtained according to travelling time when acoustic wave goes through the sediment. The attenuation of sediment sample is about a few to twenty and the velocity is about 1100 to 1700 m·-1. By mean of analysis of regression, the correlations are obtained among gas content, fluid content, acoustic velocity, attenuation and power function, which better match the measuring data. The result of study indicates that slight augment of gas content can cause sharp decrease of acoustic velocity and rapid increase of acoustic attenuation. The increment and decrement decrease obviously when the gas content exceeds 10%. The result in this paper is useful to explore oil and gas seismic.