Experimental study on multi-point autoignition characteristics and influence factors of diesel spray in a controllable active thermo-atmosphere

Auto-ignition characteristics of high-pressure diesel spray in the controllable active thermo-atmos-phere (CATA) were studied with a high-speed camera video system. Multi-point autoignition phe-nomenon of diesel spray in the CATA was observed and the influence factors of the autoignition were analyzed. The stabilization mechanisms of the spray flame in different coflow temperatures were also discussed. The stabilization of the flames was controlled by different factors: autoignition phenomenon in low coflow temperature and flame spread in high coflow temperature. The test results also show that the autoignition delay depends strongly on the coflow temperature and has nonlinear relationship with the temperature. Autoignition delay decreases by almost 10 ms from 16.9 to 7.1 ms when the coflow temperature increases from 996 to 1048 K and only 4 ms from 1048 to 1101 K. The injection parameters in terms of nozzle diameter, injection pressure and pump speed, have some effects on autoignition delay while these effects depend on the coflow temperature. The significant effect lies in low coflow temperature. The injection parameters influence the autoignition delay because it can shorten the physical delay by improving the spray quality and enlarging the spray angle or penetration rate to im-prove mixture quality.     

Characterization of MoO<Subscript>3</Subscript> nanobelt cathode for Li-battery applications

Molybdenum trioxide (MoO₃) and PPy_xMoO₃ (x=0.5 and 1) nanobelts were obtained by the simple hydrothermal process from MoO₃ sol. The morphology and structure of the samples were characterized using X-ray diffractometry (XRD), Fourier transformation infrared spectroscopy (FTIR), Raman spectra, SEM and AFM. The results show that the H atoms in polypyrrole are H-bonded with the O atoms in the Mo=O bonds of MoO₃ nanobelts. Using the electrolyte, we fabricated electrochemical cells with a configuration of Li/(LiPF₆+EC+DMC)/(MoO₃+acetyleneblack+PTFE) and studied discharge profiles. PACS 81.07.BC; 81.05.Je; 82.47.Aa; 82.45.Fk; 82.45.Gj     

Darboux transformations for the isospectral and nonisospectral mKP equation

Darboux transformations for the isospectral and nonisospectral modified Kadomtsev-Petviashvili (mKP) equations are investigated. In the isospectral case it is an auto-Darboux transformation; however, in the nonisospectral case it is not auto-Darboux tranformation.     

Dependence of critical pitting temperature on the concentration of sulphate ion in chloride-containing solutions

Effects of varying concentration of sulphate (SO₄²⁻) ion on the pitting behavior of 316SS have been investigated using potentiostatic critical pitting temperature (CPT) measurements, potentiostatic current transient technique and scanning electron microscopy in NaCl solution containing 0.5% Cl⁻ ions. The results demonstrated that when the concentration of SO₄²⁻ ion is less than 0.42%, the CPT is surprisingly lower than that without SO₄²⁻ ion, showing an accelerating effect of the SO₄²⁻ ion on pit initiation, which is different from the traditional concept. As the concentration of SO₄²⁻ ion increases beyond 0.42%, the CPT is higher than that without SO₄²⁻ ion, displaying an inhibiting effect of the SO₄²⁻ ion on pit initiation. Based on the above results, a qualitative model is proposed to explain the inhibiting and accelerating effect of SO₄²⁻ ion on the pit initiation using the mechanism of ions-competitive adsorption between SO₄²⁻ and Cl⁻ ions. The electric charges calculated in the process of pitting corrosion indicated that the pit morphology and its dimension are dependent on the content of SO₄²⁻ ion in chloride-containing solutions. The higher the concentration of SO₄²⁻ ion, the larger the dimension of the pit, reflecting an accelerating effect on pit growth.     

First-principles study for the atomic structures and electronic properties of PbTiO3 oxygen-vacancies (0 0 1) surface

The structural and electronic properties of fully-relaxed PbTiO₃ (0 0 1) oxygen-vacancy surface with PbO and TiO₂ terminations are investigated by first-principles calculations. In contrast to the perfect surface, the smaller surface rumples and interlayer distances have been found. The largest relaxation occurs on the second layer atoms not on the surface layer ones, and some in-gap Ti 3d states at about −1.1 eV below the Fermi-level are observed in the TiO₂-terminated surface caused by oxygen-vacancies. For the PbO-terminated surface, some in-gap Ti 3d states and Pb 6p states also move into the bulk midgap region to become partially occupied, and two different chemical states of the Pb 6s states were found. One is attributed to the bulk perovskite Pb atoms and another one is caused by the relaxation of surface Pb atoms. These theoretical results would give a good reference for the future experimental studies.     

Surface luminescence in ZnO nanoparticles

Spectral and time-resolved photoluminescence (TRPL) measurements were performed on ZnO nanoparticles of different sizes (17-300 nm). Under a low photon energy excitation of 2.33 eV, the time-integrated PL spectra (TIPL) clearly exhibit broad emission in the range of 1.2-2.3 eV. Upon increase of the particle size, a red-shift in the PL peak position was observed. Gaussian analysis indicates that this red-shift corresponds to the increased relative magnitude of the Gaussian combination in the low energy region. In addition, TRPL demonstrates a clear relationship between the particle diameters and the PL decay times. The shortening of the PL lifetime could be explained by a surface states model.     

A cheap and practical FBG temperature sensor utilizing a long-period grating in a photonic crystal fiber

A whole temperature sensor in one package utilizing a fiber Bragg grating (FBG) made in a conventional single-mode fiber and which uses a long-period grating (LPG) made in a photonic crystal fiber is proposed and experimentally demonstrated. The function of the interrogation is that the wavelength change of the FBG with environmental temperature is transferred to the intensity of the output via the LPG. Utilizing the temperature-insensitivity of the LPG in the PCF, the interrogation is stable and enables a cheap and practical temperature measurement system with a wide dynamic range.     

Propagation properties of beams generated by Gaussian mirror resonator in uniaxial crystals

Based on the paraxial vectorial theory of beams propagating in uniaxially anisotropic media, we have derived the analytical propagation equations of beams generated by Gaussian mirror resonator (GMR) in uniaxial crystals, and given the typical numerical example to illustrate our analytical results. Due to the anisotropy crystals, the ordinary and extraordinary beams originated by incident beams generated by GMR propagate with different diffraction lengths, thus the linear polarization state and axial symmetry of the incident beams generated by GMR do not remain during propagating in crystals.     

Watermarks encrypted in the cascaded Fresnel digital hologram

A cascaded Fresnel digital hologram (CFDH) is proposed, together with its mathematical derivation. Its application to watermarking has been demonstrated by a simulation procedure, in which the watermark image to be hidden is encoded into the phase of the host image. The watermark image can be deciphered by the CFDH setup, the reconstructed image shows good quality and the error is almost closed to zeros. Compared with previous technique, this is a lensless architecture, which minimizes the hardware requirement.     

Quantum secure direct communication and deterministic secure quantum communication

In this review article, we review the recent development of quantum secure direct communication (QSDC) and deterministic secure quantum communication (DSQC) which both are used to transmit secret message, including the criteria for QSDC, some interesting QSDC protocols, the DSQC protocols and QSDC network, etc. The difference between these two branches of quantum communication is that DSQC requires the two parties exchange at least one bit of classical information for reading out the message in each qubit, and QSDC does not. They are attractive because they are deterministic, in particular, the QSDC protocol is fully quantum mechanical. With sophisticated quantum technology in the future, the QSDC may become more and more popular. For ensuring the safety of QSDC with single photons and quantum information sharing of single qubit in a noisy channel, a quantum privacy amplification protocol has been proposed. It involves very simple CHC operations and reduces the information leakage to a negligible small level. Moreover, with the one-party quantum error correction, a relation has been established between classical linear codes and quantum one-party codes, hence it is convenient to transfer many good classical error correction codes to the quantum world. The one-party quantum error correction codes are especially designed for quantum dense coding and related QSDC protocols based on dense coding.