Influence on the resolution of target detection with defective NR-PC flat lens incorporating Al,Cu by dynamic scanning scheme

Based on the defective NR-PC flat lens incorporating Al or Cu, the effects on the resolution for target detection and imaging are studied with dynamic scanning scheme. We use the finite-difference-time-domain method to do this research. Firstly, by using the NR-PC flat lens may improve the refocusing resolution by four times, if compared to the directly backscattered lightwave without using the NR-PC lens. Then, incorporating Al or Cu into the NR-PC flat lens, we find that the dope modes with very high quality factors will occur in the photonic forbidden band. Also the stimulated radiation is enhanced for the character of energy localization of defective photonic crystal. Further studies show that different kinds of metal and structures will result in different dopped modes in the photonic forbidden band, which will lead to the change of the corresponding resolution. Due to the displacement field redistribution, the photonic crystal containing metal ingredients may take on the typical qualities of all-directional reflection, and the resonant tunneling effect may effectively reduce the loss, which provides greatly improvement on the refocusing resolution when using the defective NR-PC flat lens. In conclusion, our investigation provided the basis for converting an idealized LHM lens into a physically realizable NR-PC flat lens. Meanwhile, by impregnating metallic defect into the NR-PC lens, a new method is found out for the improvement of the refocusing resolution, which further optimizes the performance of a detecting and imaging system.     

On the cylinder air holes of NR-PC double flats lens group with active impurities for lightwave target detection and imaging

In the paper, the influence of the cylinder air holes of negative-refraction photonic crystal (NR-PC) double flats lens group with active impurities on the performance of lightwave target detection and imaging are studied with finite-difference time-domain (FDTD) method. Firstly, we conclude the focusing imaging circuit diagram of NR-PC flat lens with the Snell extension law and geometrical optics principle. Then we use NR-PC flat lens to detect target with dynamic scanning system according to that. Numerical simulations indicate that significant enhancement of the scattering signal can be obtained due to the use of the NR-PC flat lens. We further research the influence of active impurities on target detecting by using NR-PC double flats lens group with cylinder air holes. We use NR-PC flat with active impurities instead of the perfect ones. By using dynamic scanning scheme, we find that it could improve the lateral resolution of target scanning through introducing appropriate active impurities. In conclusion, our investigation optimized the performance of the small target detection and imaging system, and provided the basis for converting an idealized LHM lens into a physically realizable NR-PC double flats lens group.     

Numerical research on properties of optical-wave target detection and imaging from NR-PC flat lens

The characteristics of optical-wave target detection and imaging from a negative-refraction photonic crystal (NR-PC) flat lens are studied with a two-dimensional (2D) finite-difference time-domain (FDTD) method in the paper. The results show that there exists a transmission peak, with a value far greater than unit, resulting from the influence of the mini-forbidden bands and resonance excitation effect at resonance frequency. Also, the refocusing of backscattered optical wave from the target leads to its image with a sub-wavelength lateral resolution and great amplitude as long as the target is placed at the focus of the NR-PC flat lens. Therefore, the NR-PC flat lens will find many implications in optical area, especially in the detection and imaging of small targets.     

On the use of NR-PC flat lens for square target detection and imaging by lens-combined scanning scheme

In the paper, target detection and imaging from refraction photonic crystal (NR-PC) slab lens is studied by the finite-difference time-domain (FDTD) method. Numerical simulation shows that, there is a transmission peak with a value far greater than unit, resulting from the mini-forbidden bands and resonance excitation at the resonance frequency of 0.3068 (a/λ). When a target is placed at the focus point (F₂) of the NR-PC lens, its image and great amplitude could be formed in the vicinity of the point source through the focusing of backscattered optical wave from the target. Further investigation demonstrates that the lens-combined scanning scheme provides higher refocusing resolution than lens-fixed and non-dynamic scanning scheme for square target detection and imaging.     

Two-square target detection and imaging using NR-PC flat lens

The characteristics of two-target detection and imaging from negative-refraction photonic crystal (NR-PC) flat lens are studied by using the two-dimensional finite-difference time-domain method. It is demonstrated that due to the influence of the mini-forbidden band and resonance excitation effect, high transmissivity will appear at the normalized resonance frequency of 0.3068 when the lightwave goes through the NR-PC lens. Meanwhile, the use of the NR-PC lens may introduce at least fourfold improvement of the refocusing resolution, if compared to the directly backscattered lightwave without using the NR-PC lens. In addition, by giving a defination for two-target minimum distinguishable distance, we further investigate the performance of two-target detection and imaging system using the proposed focus-scanning scheme. The results show that the smaller the size of the target pair is, the weeker the interference between the two targets will be, which results in a better performance in the minimum distinguishable distance.     

Image resolution and the properties of optical-wave target detection and imaging by using the NR-PC flat lens

We used the method of two-dimensional (2D) finite-difference time-domain (FDTD) to study the characteristics of optical-wave target detection and imaging from negative-refraction photonic crystal (NR-PC) flat lens in the paper. The theory of image resolution was introduced. The results show that there exists a transmission peak, with a value far greater than unit, resulting from the influence of the mini-forbidden bands and resonance excitation effect at resonance frequency. And, the refocusing of backscattered optical wave from the target leads to its image with a sub-wavelength lateral resolution and great amplitude as long as the target is placed at the focus of the NR-PC flat lens. And the application of NR-PC flat lens can be extended in optical area, especially in the detection and imaging of small target.     

Critical condition of inner cylinder radius for sustaining rotating detonation waves in rotating detonation engine thruster

We describe the critical condition necessary for the inner cylinder radius of a rotating detonation engine (RDE) used for in-space rocket propulsion to sustain adequate thruster performance. Using gaseous C₂H₄ and O₂ as the propellant, we measured thrust and impulse of the RDE experimentally, varying in the inner cylinder radius r_i from 31 mm (typical annular configuration) to 0 (no-inner-cylinder configuration), while keeping the outer cylinder radius (r_o = 39 mm) and propellant injector position (r_inj = 35 mm) constant. In the experiments, we also performed high-speed imaging of self-luminescence in the combustion chamber and engine plume. In the case of relatively large inner cylinder radii (r_i = 23 and 31 mm), rotating detonation waves in the combustion chamber attached to the inner cylinder surface, whereas for relatively small inner cylinder radii (r_i = 0, 9, and 15 mm), rotating detonation waves were observed to detach from the inner cylinder surface. In these small inner radii cases, strong chemical luminescence was observed in the plume, probably due to the existence of soot. On the other hand, for cases where r_i = 15, 23, and 31 mm, the specific impulses were greater than 80% of the ideal value at correct expansion. Meanwhile, for cases r_i = 0 and 9 mm, the specific impulses were below 80% of the ideal expansion value. This was considered to be due to the imperfect detonation combustion (deflagration combustion) observed in small inner cylinder radius cases. Our results suggest that in our experimental conditions, r_i = 15 mm was close to the critical condition for sustaining rotating detonation in a suitable state for efficient thrust generation. This condition in the inner cylinder radius corresponds to a condition in the reduced unburned layer height of 4.5–6.5.     

A theoretical deduction of the shape and size of nanocarbons suitable for hydrogen storage

We evaluated the adsorption energy of a hydrogen molecule in nanocarbons consisting of graphene sheets. The nanocarbon shapes were a pair of disks with separation 2d, a cylinder with radius d, and a truncated sphere with radius d. We obtained the adsorption energy in the form of a 10–4 Lennard–Jones function with respect to 1/d. The values of the potential depth (D) and equilibrium distance (d _e), respectively, were 94 meV and 2.89 Å for the disk pair, 158 meV and 3.14 Å for the cylinder, and 203 meV and 3.37 Å for the sphere. When d=d _e, the adsorption energy of the disk pair (cylinder) became deeper than ?0.9D, and it approached ?D when the radius (length) increased to more than twice its separation (radius). The adsorption energy of the sphere was increased from ?D to ?0.5D when the radius of the opening increased from 0 to d _e. These results suggest that porous carbon materials can increase the adsorption energy by up to ～200 meV if the carbon atoms are arranged on a spherical-like surface with ～7 Å separation. This may lead to practical hydrogen storage for fuel cells.     

Impacts of Refraction Index Mismatch on Performance of Target Detection and Imaging by Using Flat LHM Lens

Refraction index mismatch between flat left-handed metamaterial (LHM) lens and its surrounding medium generally destroys the focusing of flat LHM lens and degrades the performance of near-field target detection by using flat LHM lens. For LHM lens of refraction index mismatch within ±30%, numerical simulations demonstrate that lenses with large refraction index may suffer less resolution degradation than lenses with small refraction index, and the enhancement of refocused microwave backscattered from target can be subsided by up to approximately 5.5dB. The refraction index mismatch will also shift the target position in the reconstructed image so that theoretical prediction of target position needs to be modified.     

Analysis of signal-to-noise ratio and heterodyne efficiency for reference-beam laser Doppler velocimeter

Heterodyne efficiency is a very important factor in a laser Doppler velocimeter (LDV). Gaussian-Airy mode is put forward to analyze the heterodyne efficiency. By studying the distribution of the optical field, the mathematic expression and simulation results of heterodyne efficiency are given under the conditions of both exact match and mismatch. The results of numerical analysis show that heterodyne efficiency of LDV depends on Gaussian beam's parameter Q, detector's parameter X₀, angle of collimation mismatching θ_a, parameter of offset mismatching X_a and the radius of curvature of the reference beam on the detector R(z). Heterodyne efficiency can reach 83.39% when Q=4.15×10^?7, X₀=6.1×10^?7, θ_a=X_a=0, R(z)=∞. But it declines to 0.5 when Fθ_a enhances to 0.28. It decreases with the increment of the offset X_a and the diminishment of the radius of curvature R(z). Results of experiment are in good accordance with the theoretical analysis.     

Measurement of the pH value in pork meat early postmortem by Raman spectroscopy

The pH of a muscle is an accepted parameter to identify normal and deviating meat qualities. In this work, Raman spectroscopy is shown to be suitable for the non-invasive measurement of the early postmortem pH of meat. Raman spectra of ten pork semimembranosus muscles were recorded with a portable handheld device 0.5–24 h postmortem. The spectra were correlated with pH and lactate kinetics measured in parallel. Seven of the muscles were normal, two exhibited accelerated glycolysis and one showed absence of acidification. The pH decline with time could be calculated from the Raman spectra with the Henderson–Hasselbalch equation using only two signals of phosphate vibrations at 980 and 1,080 cm^?1 with a close correlation for each muscle, but larger variations between animals. More robust and better correlations for all muscles were obtained with a linear model based on 11 signals from lactate, lactic acid, phosphate, a carbonyl band and nucleotides resulting in R ² = 0.78 and RMSECV = 0.2 or a partial least-square model using the complete spectrum (R ² = 0.94 and RMSECV = 0.2). These results show the potential of Raman spectroscopy for an online detection of the pH and thus meat qualities during meat processing.     

Pressure-dependent phase transition in the ordered BaBi0.7Nb0.3O3 perovskite

BaBi_0.7Nb_0.3O₃, an ordered perovskite, crystallizes in a centrosymmetric rhombohedral structure with the space group R3¯. The refined cell parameters obtained from synchrotron powder X-ray diffraction data for the rhombohedral phase at ambient pressure are a=6.109 (2) Å and α=60.3 (1)°. The pressure-dependent synchrotron powder X-ray diffraction studies show a phase transition around 8.44±1 GPa, where it transforms from rhombohedral structure to a monoclinic structure. The lattice parameters obtained for the monoclinic phase at a pressure of 15±1 GPa are a=5.91 (2) Å, b=6.25 (3) Å and c=8.22 (1) Å with monoclinic angle, β=88 (1)°.     

Measuring of the hardly measurable: adhesion properties of anti-adhesive surfaces

Adhesion is a universal phenomenon influencing many processes in natural and technical systems. To elucidate these influences, reliable measurements of adhesion forces are of high importance. In the present study, by using a microforce tester combined with a compliant sticky probe, we introduce a newly established method allowing adhesion measurements on surfaces with low adhesive capabilities. Four quality control tests revealed a high reproducibility and reliability of data obtained. Further advantages of the method are (1) defined geometry of the probe, (2) ease attachment of the probe to the cantilever, (3) its applicability for time consuming experiments, (4) as well as a low price of components and a minimum of required equipment. We present the first results obtained by using this method in a case study with six epoxy resin replicas having various roughness (R _a =0.007–3.515 μm). Interestingly, the highest pull-off force values were obtained not on the smooth sample, but on the surface with the finest microroughness (R _a =0.150 μm). With a further increase in the surface microroughness, pull-off forces continuously decreased. These results are in accordance with previously reported theoretical predictions.     

Focusing of a Flat Left-Handed Metamaterial Lens in a Heterogeneous and Lossy Medium

For applications such as near-field target detection and tumor hyperthermia with a fiat left-handed metamaterial （LHM） lens, a microwave will be focused in the heterogeneous and lossy medium. Different from the focusing of a fiat LHM lens in vacuum as reported in most previous studies, the medium loss and heterogeneity will affect the focusing performance of the LHM lens. Numerical simulations indicate that the medium loss will degrade the focusing resolution, while the heterogeneity of random variability within ±30% will affect the focusing resolution to a limited extent. Both the loss and heterogeneity of the medium will shift the focal point away from the image plane. When focusing in a medium with different permittivity values, an LHM lens will also have different focusing resolutions due to different electric thicknesses.     

Energy dependence of the elastic scattering 40Ca(3He, 3He) in the energy range 10.0 to 18.0 MeV

Differential cross sections for the elastic scattering of 18, 16, 14, 12 and 10 MeV ³He particles by ⁴⁰Ca were measured and analyzed in terms of the optical model with volume imaginary and real spin-orbit potentials. Angular distributions have been measured in 5° steps between 25° and 175°. Four sets of optical model parameters were established and in two of these, sets A and B, systematic variations with energy of the real, volume imaginary and spin-orbit potentials were obtained. The geometrical parameters were not varied as a function of energy. The effect of the matching radius R_M on the optical model calculations, was investigated. It was found that the matching radius should be calculated using the geometrical parameters of the potential that yields the largest value for R_M according to the receipe R_M = R + 7a where R is the nuclear radius and a is the diffuseness.     

Synthesis and characterization of Ce-doped Sm<Subscript>2</Subscript>CuO<Subscript>4 + <Emphasis Type="Italic">δ</Emphasis></Subscript> cathode for IT-SOFC applications

Single-phase solid solutions of Sm_2 ? x Ce _x CuO_4 + δ (0.05 ≤ x ≤ 0.20) with tetragonal structure are synthesized using acetate combustion followed by sintering at 1373 K for 10 h. X-ray powder diffraction and transmission electron microscopy studies confirmed the formation of solid solution in a single phase. Maximum conductivity (σ = 96.0 ± 0.5 S cm^?1 at 973 K) giving composition Sm_1.90Ce_0.10CuO₄ offers the minimum activation energy (E _a = 0.32 ± 0.004 eV) among all prepared compositions. Lowest cathode polarization resistance (R _p = 3.92 ± 0.07 Ω cm² at 973 K) and activation energy (E _a = 1.12 ± 0.03 eV) values across the measured temperature range are obtained for Sm_1.90Ce_0.10CuO₄. The impedance data fitted well to the Gerischer model indicates that a chemical-electrochemical-chemical-type reaction occurred at the mixed electronic-ionic conducting cathode.     

Study on the structure and luminescence properties of the coordinated ZnO crystallites

The coordinated ZnO nanoparticles and crystallites have been produced by focused pulsed laser ablation of ZnO target submerged in the ethanol solution of 8-hydroxyquinoline. The structure of the nanoparticles was characterized by high-resolution transmission electron microscopy (HRTEM). The ZnO crystallites properties were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis coupled to differential scanning calorimetry (TG/DSC), X-ray photoelectron spectroscopy (XPS) and luminescence spectrometry. The results show the surface Zn²⁺ ions of the ZnO nanoparticles are coordinated by the 8-hydroxyquinoline. The crystal class and the space group of the coordinated ZnO crystallites are triclinic and P-1(2), respectively. The lattice parameters are refined to a=1.1904 nm, b=1.2135 nm, c=0.8586 nm, α=108.28^°,β=100.27^° and γ=85.50^°, respectively. The coordinated ZnO crystallites have better thermo stability than bis(8-hydroxyquinoline)zinc and can emit yellow-green light under UV and visible radiations.     

Elasticp+12C scattering between 0.3 and 2 MeV

Absolute differential cross-sections ofp+¹²C elastic scattering have been measured atθ _cm=89.1°, 118.7°, 146.9° for bombarding energies between 0.3 and 2.0 MeV. Revised level parameters of the first three excited states in¹³N have been extracted with aR-matrix analysis. It is shown that the influence of the bound ground-state of¹³N has an appreciable effect on low-energy scattering. Recent predictions concerning Mott-Schwinger polarization are also discussed.     

1×4光子晶体波导分束器的特性

在完整的二维光子晶体中引入线缺陷,形成了光子晶体波导,光子晶体波导分束器是集成化光学电路的重要组成元件。我们设计了一种线缺陷1×4光子晶体分束器,并且用有限时域差分法研究了它的特性。研究表明,输出端的透射传输特性与入射光的波长和分支的几何形状有关,并且入射波分别相等地流入四个输出端口。为了减少1×4分束器在三个Y型分支区的反射,可以通过调节在分支区的可调介质柱的半径R,使每个输出端口具有很高的透射率。     

An Exact Solution of Perfect Fluid in Isotropic Coordinates, Compatible with Relativistic Modeling of Star

We present a spherically symmetric solution of the general relativistic field equations in isotropic coordinates for perfect fluid, compatible with a super dense star modeling. The solution is well behaved for all the values of u lying in the range 0<u≤0.12. Further, we have constructed a super-dense star model with all degree of suitability and by assuming the surface density ρ _b =2×10¹⁴ g/cm³. Corresponding to u=0.12, the resulting well behaved model has maximum mass M=0.912M _Θ with radius R _b ≈11.27 km and Moment of inertia 0.97×10⁴⁵ gm?cm². The good matching of our results for Vela pulsars show the stoutness of our model.