Local density of optical states calculated by the mode spectrum in stratified media

The local density of optical states(LDOS)is an important physical concept,which can characterize the spontaneous emission of microcavities.In order to calculate the LDOS,the relationship between the mode spectrum and the LDOS is established.Then,based on the transfer matrix method and the effective resonator model,the leaky loss of the leaky mode and the mode spectrum in the one-dimensional photonic bandgap crystal waveguide are calculated,results of which indicate that the mode spectrum can characterize the leaky loss of the leaky mode.At last,the density of optical states(DOS),and the LDOS in each layer are calculated.The partial DOS and the partial LDOS in the quantum well,related to the fundamental leaky mode,can be used to find out the optimal location of the quantum well in the defect layer to couple more useful photons into the lasing mode for lasers.

A background refinement method based on local density for hyperspectral anomaly detection

For anomaly detection,anomalies existing in the background will affect the detection performance.Accordingly,a background refinement method based on the local density is proposed to remove the anomalies from thebackground.In this work,the local density is measured by its spectral neighbors through a certain radius which is obtained by calculating the mean median of the distance matrix.Further,a two-step segmentation strategy is designed.The first segmentation step divides the original background into two subsets,a large subset composed by background pixels and a small subset containing both background pixels and anomalies.The second segmentation step employing Otsu method with an aim to obtain a discrimination threshold is conducted on the small subset.Then the pixels whose local densities are lower than the threshold are removed.Finally,to validate the effectiveness of the proposed method,it combines Reed-Xiaoli detector and collaborative-representation-based detector to detect anomalies.Experiments are conducted on two real hyperspectral datasets.Results show that the proposed method achieves better detection performance.

Spontaneous-emission control by local density of states of photonic crystal cavity

The local density of states （LDOS） of two-dimensional square lattice photonic crystal （PhC） defect cavity is studied. The results show that the LDOS in the centre is greatly reduced, while the LDOS at the point off the centre （for example, at the point （0.3a, 0.4a）, where a is the lattice constant） is extremely enhanced. Further, the disordered radii are introduced to imitate the real devices fabricated in our experiment, and then we study the LDOS of PhC cavity with configurations of different disordered radii. The results show that in the disordered cavity, the LDOS in the centre is still greatly reduced, while the LDOS at the point （0.3a, 0.4a） is still extremely enhanced. It shows that the LDOS analysis is useful. When a laser is designed on the basis of the square lattice PhC rod cavity, in order to enhance the spontaneous emission, the active materials should not be inserted in the centre of the cavity, but located at positions off the centre. So LDOS method gives a guide to design the positions of the active materials （quantum dots） in the lasers.

Local density of states of dc-biased superlattices with time-dependent imperfection

The single-particle Green＇s function for a dc-biased superlattices with single impurity potential varying harmonically with time has been obtained in the framework of U（t,t＇） method and Floquet-Green＇s function. The calculation of the local density of states shows that new states will emerge between the resonant Wannier-Stark states as a result of the intervention of time-dependent impurity potential, and the increase in electric field strength of impurity will result in the growing of the number of new states between the gaps of neighbouring Stark ladders.

Local density of states around two nonmagnetic impurities in cuprate superconductors

The local density of states （LDOS） around two nonmagnetic impurities which are located at different sites is studied within the two-dimensional t-J-U model. The order parameters are determined in a self-consistent way with the Gutzwiller projected mean-field approximation and the Bogoliubov-de Gennes theory. When the two impurities are located one or two sites away, we find the supercon- ductivity coherence peaks are more strongly suppressed and the zero-energy peak （ZEP） has split into two peaks. Whereas when the two impurities are located next to each other, the ZEP vanished, and LDOS does not change a lot compared with the case away from the impurities.

Electronic structures and optical properties of monoclinic ZrO2 studied by first-principles local density approximation plus U approach

The electronic structures and optical properties of the monoclinic ZrO2 (m-ZrO2) are investigated by means of first-principles local density approximation (LDA) + U approach.Without on-site Coulomb interactions,the band gap of m-ZrO2 is 3.60 eV,much lower than the experimental value (5.8 eV).By introducing the Coulomb interactions of 4d orbitals on Zr atom (Ud) and of 2p orbitals on O atom (Up),we can reproduce the experimental value of the band gap.The calculated dielectric function of m-ZrO2 exhibits a small shoulder at the edge of the band gap in its imaginary part,while in the tetragonal ZrO2 and cubic ZrO2 it is absent,which is consistent with the experimental observations.The origin of the shoulder is attributed to the difference of electronic structures near the edge of the valence and conduction bands.

Characteristics of local photonic state density in an infinite two-dimensional photonic crystal

The local density of photonic states （LDPS） of an infinite two-dimensional （2D） photonic crystal （PC） composed of rotated square-pillars in a 2D square lattice is calculated in terms of the plane-wave expansion method in a combination with the point group theory. The calculation results show that the LDPS strongly depends on the spatial positions. The variations of the LDPS as functions of the radial coordinate and frequency exhibit “mountain chain” structures with sharp peaks. The LDPS with large value spans a finite area and falls abruptly down to small value at the position corresponding to the interfaces between two different refractive index materials. The larger/lower LDPS occurs inward the lower/larger dielectric-constant medium. This feature can be well interpreted by the continuity of electricdisplacement vector at the interface. In the frequency range of the pseudo-PBG （photonic band gap）, the LDPS keeps very low value over the whole Wiger-Seitz cell. It indicates that the spontaneous emission in 2D PCs cannot be prohibited completely, but it can be inhibited intensively when the resonate frequency falls into the pseudo-PBG.

A local density optimization method based on a graph convolutional network

Success has been obtained using a semi-supervised graph analysis method based on a graph convolutional network(GCN).However,GCN ignores some local information at each node in the graph,so that data preprocessing is incomplete and the model generated is not accurate enough.Thus,in the case of numerous unsupervised models based on graph embedding technology,local node information is important.In this paper,we apply a local analysis method based on the similar neighbor hypothesis to a GCN,and propose a local density definition;we call this method LDGCN.The LDGCN algorithm processes the input data of GCN in two methods,i.e.,the unbalanced and balanced methods.Thus,the optimized input data contains detailed local node information,and then the model generated is accurate after training.We also introduce the implementation of the LDGCN algorithm through the principle of GCN,and use three mainstream datasets to verify the effectiveness of the LDGCN algorithm(i.e.,the Cora,Citeseer,and Pubmed datasets).Finally,we compare the performances of several mainstream graph analysis algorithms with that of the LDGCN algorithm.Experimental results show that the LDGCN algorithm has better performance in node classification tasks.

Anomalous Cell Detection with Kernel Density-Based Local Outlier Factor

Since data services are penetrating into our daily life rapidly, the mobile network becomes more complicated, and the amount of data transmission is more and more increasing. In this case, the traditional statistical methods for anomalous cell detection cannot adapt to the evolution of networks, and data mining becomes the mainstream. In this paper, we propose a novel kernel density-based local outlier factor(KLOF) to assign a degree of being an outlier to each object. Firstly, the notion of KLOF is introduced, which captures exactly the relative degree of isolation. Then, by analyzing its properties, including the tightness of upper and lower bounds, sensitivity of density perturbation, we find that KLOF is much greater than 1 for outliers. Lastly, KLOFis applied on a real-world dataset to detect anomalous cells with abnormal key performance indicators(KPIs) to verify its reliability. The experiment shows that KLOF can find outliers efficiently. It can be a guideline for the operators to perform faster and more efficient trouble shooting.

Design of Lattice Structures Using Local Relative Density Mapping Method

In order to solve the problem of substantial computational resources of lattice structure during optimization, a local relative density mapping(LRDM) method is proposed. The proposed method uses solid isotropic microstructures with penalization to optimize a model at the macroscopic scale. The local relative density information is obtained from the topology optimization result. The contour lines of an optimized model are extracted using a density contour approach, and the triangular mesh is generated using a mesh generator. A local mapping relationship between the elements’ relative density and the struts’ relative cross?sectional area is established to automatically determine the diameter of each individual strut in the lattice structures. The proposed LRDM method can be applied to local finite element meshes and local density elements, but it is also suitable for global ones. In addition, some cases are con?sidered in order to test the e ectiveness of the LRDM method. The results show that the solution time of the LRDM is lower than the RDM method by approximately 50%. The proposed method provides instructions for the design of more complex lattice structures.

Baroclinic pressure gradient difference schemes of subtracting the local averaged density stratification in sigma coordinates models

Much has been written of the error in computing the baroclinic pressure gradient (BPG) with sigma coordinates in ocean or atmospheric numerical models. The usual way to reduce the error is to subtract area-averaged density stratification of the whole computation region. But if there is great difference between the area-averaged and the local averaged density stratification, the error will be obvious. An example is given to show that the error from this method may be larger than that from no correction sometimes. The definition of local area is put forward. Then, four improved BPG difference schemes of subtracting the local averaged density stratification are designed to reduce the error. Two of them are for diagnostic calculation (density field is fixed), and the others are for prognostic calculation (density field is not fixed). The results show that the errors from these schemes all significantly decrease.

Estimation the Density of Localized State Glassy Se_(100-x)Zn_(x) Thin Films by Using Space Charge Limited Conduction Measurement

The dc conductivity in vacuum evaporated amorphous thin films of the glassy alloys Se100–xZnx(2 ≤ x ≤ 20) are meas-ured in the temperature range (308 - 388 K). The dc conductivity (σdc) is increases with increased of Zn concentration in the glassy alloys. The activation energy (ΔE) decreases with increase of Zn content. The conduction is explained on the basis of localized state in the mobility gap. To study the effect of electric field, a Current-Voltage characteristic has been measured at various fixed temperatures. The Current-Voltage data are fitted into the theory of space charge limited conduction in case of uniform distribution of traps in mobility gap at high electric fields (E ~104 V/cm) of these materials. The density of localized state (g0) are estimated by fitting in theory of space charge limited conduction (SCLC) at the temperature range of (352 - 372 K) in the glassy Se100–xZnx. The density of localized state (0) near the Fermi level are increases with increase of Zn concentration in the (Se100–xZnx) thin films and explain on the basis of increase of the Zn-Se bond.

Pressure Effect on the Local Composition SurroundingEthyl Acetoacetate in Supercritical CO_2 - Ethanol Mixture

The keto-enol tautomerization of ethyl acetoacetate (EAA) in supercritical CO2-ethanol mixture has been investigated at 308.15 K and at different pressures using UV-Visspectroscopy. A method for calculating the local composition about EAA has been developed based on the relationship between the equilibrium constant and dielectric property of the mixing solvent. The results indicate that the local concentration of ethanol surrounding EAA is much higher than that in the bulk.

Time-Dependent Density-Functional Calculations for Optical Spectra of Na2 and Na4 Clusters

With the frame of the time-dependent local density approximation, an efficient description of the optical response of clusters has been used to study the photo-absorption cross section of Na2 and Na4 clusters. It is shown that our calculated results are in good agreement with the experiment. In addition, our calculated spectrum for the Na4 cluster is in better agreement with experiment than the GW absorption spectrum.

Determination of Band Structure of Gallium-Arsenide and Aluminium-Arsenide Using Density Functional Theory

This research paper is on Density Functional Theory (DFT) within Local Density Approximation. The calculation was performed using Fritz Haber Institute Ab-initio Molecular Simulations (FHIAIMS) code based on numerical atomic-centered orbital basis sets. The electronic band structure, total density of state (DOS) and band gap energy were calculated for Gallium-Arsenide and Aluminium-Arsenide in diamond structures. The result of minimum total energy and computational time obtained from the experimental lattice constant 5.63 A for both Gallium Arsenide and Aluminium Arsenide is -114,915.7903 eV and 64.989 s, respectively. The electronic band structure analysis shows that Aluminium-Arsenide is an indirect band gap semiconductor while Gallium-Arsenide is a direct band gap semiconductor. The energy gap results obtained for GaAs is 0.37 eV and AlAs is 1.42 eV. The band gap in GaAs observed is very small when compared to AlAs. This indicates that GaAs can exhibit high transport property of the electron in the semiconductor which makes it suitable for optoelectronics devices while the wider band gap of AlAs indicates their potentials can be used in high temperature and strong electric fields device applications. The results reveal a good agreement within reasonable acceptable errors when compared with the theoretical and experimental values obtained in the work of Federico and Yin wang [1] [2].

Vortex bound states influenced by the Fermi surface anisotropy

The spatial distribution of vortex bound states is often anisotropic,which is correlated with the underlying property of materials.In this work,we examine the effects of Fermi surface anisotropy on vortex bound states.The large-scale calculation of vortex bound states is introduced in the presence of fourfold or twofold Fermi surface by solving the Bogoliubov–de Gennes(BdG)equations.Two kinds of quasiparticles’behaviors can be extracted from the local density of states(LDOS)around a vortex.The angle-dependent quasiparticles will move from high energy to low energy when the angle varies from curvature maxima to minima of the Fermi surface,while the angle-independent quasiparticles tend to stay at a relatively higher energy.In addition,the weight of angle-dependent quasiparticles can be enhanced by the increasing anisotropy degree of Fermi surface.

First-principles calculations of structural and thermodynamic properties of BeB2 compound

The lattice parameter bulk modulus and pressure derivative of BeB2 are calculated by using the Cambridge Serial Total Energy Package （CASTEP） program in the frame of density function theory. The calculated results agree well with the average experimental data and other theoretical results. Through the quasi-harmonic Debye model, the dependences of the normalized lattice parameters a/ao, c/c0 and the normalized primitive cell volume V/Vo on pressure P, the variation of the thermal expansion coefficient ~ with pressure P and temperature T, as well as the dependences of the heat capacity Cv on pressure P and temperature T are obtained systematically.

Feature Extraction of Acoustic/Seismic Signal of Target

A microphone and a seismic sensor always become a basic unit of UGS(unattended ground sensors) system. The mechanism of acoustic and seismic property of target and its propagation are described. The acoustic and seismic signals of targets are analyzed with time frequency distribution according to its non stationary property. Narrow band energy function (NEF) and local power spectral density (LPSD) are proposed to extract features for target identification. Experiment results show that local power spectral density indicates corresponding target clearly.

Elastic and thermodynamic properties of c-BN from first-principles calculations

The elastic constants and thermodynamic properties of c-BN are calculated using the first-principles plane wave method with the relativistic analytic pseudopotential of the Hartwigen, Goedecker and Hutter （HGH） type in the frame of local density approximation and using the quasi-harmonic Debye model, separately, Moreover, tbe dependences of the normalized volume V/V0 on pressure P, as well as the bulk modulus B, the thermal expansion α, and the heat capacity CV on pressure P and temperature T are also successfully obtained,

Phase transition and thermodynamic properties of TiO_2 from first-principles calculations

The pressure induced phase transitions of TiO2 from anatase to columbite structure and from rutile to columbite structure and the temperature induced phase transition from anatase to rutile structure and from columbite to rutile structure are investigated by ab initio plane-wave pseudopotential density functional theory method （DFT）, together with quasi-harmonic Debye model. It is found that the zero-temperature transition pressures from anatase to columbite and from rutile to columbite are 4.55 GPa and 19.92 GPa, respectively. The zero-pressure transition temperatures from anatase to rutile and from columbite to rutile are 950 K and 1500 K, respectively. Our results are consistent with the available experimental data and other theoretical results. Moreover, the dependence of the normalized primitive cell volume V/Vo on pressure and the dependences of thermal expansion coefficient α on temperature and pressure are also obtained successfully.