基于光学相关的红外目标检测

光学图像处理技术能以复振幅、并行、高速度和巨量互连来处理信号。利用光学方法的半色调网屏技术实现了红外图像的假彩色编码,提高了红外图像的可识别性;利用光学相关识别技术构造了一种基于4f系统的光学图像实时相关识别系统,以实现对红外图像的实时处理和识别。     

Scales in nuclear matter: Chiral dynamics with pion nucleon form factors<Superscript>⋆</Superscript>

A systematic calculation of nuclear matter is performed which includes the long-range correlations between nucleons arising from one- and two-pion exchange. Three-body effects from 2π exchange with excitations of virtual Δ(1232)-isobars are also taken into account in our diagrammatic calculation of the energy per particle ˉ(k _f). In order to eliminate possible high-momentum components from the interactions we introduce at each pion-baryon vertex a form factor of monopole type. The empirical nuclear matter saturation point, ρ₀ ≃ 0.16fm^-3, ˉ₀ ≃ - 16MeV, is well reproduced with a monopole mass of Λ ≃ 4πf _π ≃ 1.16GeV. As in the recent approach based on the universal low-momentum NN potential V _low-k, the inclusion of three-body effects is crucial in order to achieve saturation of nuclear matter. We demonstrate that the dependence of the pion exchange contributions to ˉ(k _f) on the “resolution” scale Λ can be compensated over a wide range of Λ by counterterms with two “running” contact couplings. As a further application we study the in-medium chiral condensate 〈ˉq〉(ρ) beyond the linear density approximation. For ρ ⩽ 1.5ρ₀ we find small corrections from the derivative dˉ(k _f)/dm _π, which are stable against variations of the monopole regulator mass Λ.     

Superfluidity in many fermion systems: Exact renormalisation group treatment

The application of the exact renormalisation group to symmetric as well as asymmetric many-fermion systems with a short-range attractive force is studied. Assuming an ansatz for the effective action with effective bosons, describing pairing effects, a set of approximate flow equations for the effective coupling including boson and fermionic fluctuations has been derived. The phase transition to a phase with broken symmetry is found at a critical value of the running scale. The mean-field results are recovered if boson-loop effects are omitted. The calculations with two different forms of the regulator are shown to lead to similar results. We find that, being quite small in the case of the symmetric many-fermion system the corrections to mean-field approximation become more important with increasing mass asymmetry.     

Correlations in hypernuclear matter

We investigate short-range correlations in nuclear and hypernuclear matter. Self-energies due to short-range correlations and their influence on the nucleon and Λ -hyperon spectral functions are described in an approach accounting for a realistic treatment of mean-field dynamics and a self-consistently derived quasi-particle interaction. Landau-Migdal theory is used to derived the short-range interaction from a phenomenological Skyrme energy density functional, subtracting the long-range pionic contributions to the nucleonic spectral functions. We discuss our results for different hyperon-baryon ratios to show the influence of strangeness on the correlations in hypernuclear matter.     

On the geometry of reduced cotangent bundles at zero momentum

We consider the problem of cotangent bundle reduction for proper non-free group actions at zero momentum. We show that in this context the symplectic stratification obtained by Sjamaar and Lerman refines in two ways: (i) each symplectic stratum admits a stratification which we call the secondary stratification with two distinct types of pieces, one of which is open and dense and symplectomorphic to a cotangent bundle; (ii) the reduced space at zero momentum admits a finer stratification than the symplectic one into pieces that are coisotropic in their respective symplectic strata.     

Thermoelectric properties of CoSb3 with maize‐like structure

Maize‐like CoSb₃ powders were obtained via the chemical alloying method. After the consolidation of the nanopowder using hot press, the CoSb₃ compact shows a higher Seebeck coefficient and lower thermal conductivity. For the investigated CoSb₃, a ZT of 0.15 at 673 K is shown. Though the achieved ZT does not reach the optimal value (0.17 to 0.18) for pure CoSb₃, due to its lower electrical conductivity, the novel structure fabrication provides an interesting and promising approach to enhancing the thermoelectric performance. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermoelectric properties of p‐type Mg2Si0.6Ge0.4 fabricated by bulk mechanical alloying and hot pressing

Bulk mechanical alloying (BMA) followed by hot pressing (HP) was used to prepare Mg₂Si_0.6Ge_0.4 thermoelectric material with high densification. Starting from the elemental power mixture, the Mg₂Si_0.6Ge_0.4 solid solution was solid‐state synthesized via BMA. In fact, the peaks for the cubic‐structured Mg₂Si_0.6Ge_0.4 solid solution phase were detected after 300 cycles in BMA. The single phase of Mg₂Si_0.6Ge_0.4 was synthesized at 600 cycles in BMA. Mg₂Si_0.6Ge_0.4 showed p‐type semiconduction without doping. Effects of hot pressing conditions on thermoelectric properties were investigated. With increasing hot pressing temperature from 673 to 773 K and pressure from 500 MPa to 1 GPa, the electrical conductivity increased and the Seebeck coefficient decreased. The maximum figure of merit was obtained with the processing parameter of 600 cycles BMA and hot pressing at 773 K, 1 GPa for 1 h. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spin asymmetry and s-electron itinerancy in Co/X (X=Co,Cu, V and Ta) multilayers: their dependence on the electronegativity of non-magnetic layers

The electronic structure and magnetic properties of the Co at the Co/X (X=Co, Cu, V and Ta) interfaces have been studied by first-principle discrete variational method. We have found that the spin asymmetry and the s-electron itinerancy of the Co interface layer in the Co/X systems are strongly dependent on the electronegativity of the non-magnetic layers. A large difference in the electronegativity between the non-magnetic and Co layers is unfavorable both for s-electron itinerancy and for the spin exchange split of DOS at the Fermi level. Further study on charge density has revealed that a bond is formed across the Co/V and Co/Ta interfaces.     

Laser synthesis of semiconductor nanostructures with narrow band gap

Semiconductor nanostructures with narrow band gap were synthesized by means of laser chemical vapor deposition (LCVD) of elements from iron carbonyl vapors [Fe(CO)₅] under the action of Ar⁺ laser radiation (λ_L = 488 nm) on the Si substrate surface. The temperature dependence of the specific conductivity of these nanostructures in the form of thin films demonstrated typical semiconductor tendency and gave the possibility to calculate the band gap for intrinsic conductivity (E_g) and the band gap assigned for impurities (E_i), which were depended upon film thickness and applied electrical field. Analysis of deposited films with scanning electron microscopy (SEM) and atomic force microscopy (AFM) demonstrated their cluster structure with average size not more than 100 nm. Semiconductor properties of deposited nanostructures were stipulated with iron oxides in different oxidized phases according to X-ray photoelectron spectroscopy (XPS) analysis.These deposited nanostructures were irradiated with Q-switched YAG laser (λ_L = 1064 nm) at power density about 6 × 10⁷ W/cm². This irradiation resulted in the crystallization process of deposited films on the Si substrate surface. The crystallization process resulted in the synthesis of iron carbide-silicide (FeSi_2−xC_x) layer with semiconductor properties too. The width of the band gap E_g of the synthesized layer of iron carbide-silicide was less than for deposited films based on iron oxides Fe₂O_3−x (0 ≤ x ≤ 1).     

Electrochemically decorated carbon nanotubes for hydrogen sensing

Low-density networks of single-wall carbon nanotubes have been modified by palladium nanoparticles using an electrochemical method. A major advantage of this approach is that it allows for selective metal deposition on the electrically contacted nanotubes, whereas the remaining substrate surface and the non-contacted tubes remain essentially unaffected. The Pd-decorated networks function as effective hydrogen sensors enabling the detection of hydrogen concentrations as low as 10 ppm at room temperature. The electrochemical metal deposition scheme is promising for the development of sensor arrays suitable for analysing gas mixtures.