[N_2]_2二聚物激光介质研究

理论上通过从头算法 (abinitio)计算强相互作用的N2 分子二聚物可能存在的 6种点群构型的势能曲线 ,证明N2 分子二聚物以D2h 对称群构型存在 ,且存在电偶极允许的类准分子跃迁a1B2 g →a1B3u,并计算了a1B2 g →a1B3u 跃迁的荧光谱。估算了N2 分子二聚物 ( 3 3 6 2 1nm)的小信号增益系数。利用微波 ( 2 45GHz)激励高纯氮 ,实验观测了N2 分子二聚物的系列荧光谱带 ,并利用放大自发辐射 (ASE)法测量N2 分子二聚物 ( 3 3 6 2 1nm)的小信号增益系数 ,在误差范围内与理论估算基本一致。最后从理论上估算了N2 分子二聚物激光振荡的输出功率。     

Personal identification using feature and score level fusion of palm- and fingerprints

The ever increasing demand of security has resulted in wide use of Biometric systems. Despite overcoming the traditional verification problems, the unimodal systems suffer from various challenges like intra class variation, noise in the sensor data etc, affecting the system performance. These problems are effectively handled by multimodal systems. In this paper, we present multimodal approach for palm- and fingerprints by feature level and score level fusions (sum and product rules). The proposed multi-modal systems are tested on a developed database consisting of 440 palm- and fingerprints each of 55 individuals. In feature level fusion, directional energy-based feature vectors of palm- and fingerprint identifiers are combined to form joint feature vector that is subsequently used to identify the individual using a distance classifier. In score level fusion, the matching scores of individual classifiers are fused by sum and product rules. Receiver operating characteristics curves are formed for unimodal and multimodal systems. Equal Error Rate (EER) of 0.538% for feature level fusion shows best performance compared to score level fusion of 0.6141 and 0.5482% of sum and product rules, respectively. Multimodal systems, however, significantly outperform unimodal palm- and fingerprints identifiers with EER of 2.822 and 2.553%, respectively.     

An Efficient,Scalable Key Transport Scheme (ESKTS) for Delay/Disruption Tolerant Networks

In the past, security protocols including key transport protocols are designed with the assumption that there are two parties communication with each other and an adversary tries to intercept this communication. In Delay/Disruption Tolerant Networking (DTN), packet delivery relies on intermediate parties in the communication path to store and forward the packets. DTN security architecture requires that integrity and authentication should be verified at intermediate nodes as well as at end nodes and confidentiality should be maintained for end communicating parties. This requires new security protocols and key management to be defined for DTN as traditional end-to-end security protocols will not work with DTN. To contribute towards solving this problem, we propose a novel Efficient and Scalable Key Transport Scheme (ESKTS) to transport the symmetric key generated at a DTN node to other communicating body securely using public key cryptography and proxy signatures. It is unique effort to design a key transport protocol in compliance with DTN architecture. ESKTS ensures that integrity and authentication is achieved at hop-by-hop level as well as end-to-end level. It also ensures end-to-end confidentiality and freshness for end communicating parties. This scheme provides a secure symmetric key transport mechanism based on public key cryptography to exploit the unique bundle buffering characteristics of DTN to reduce communication and computation cost .     

Cathodic behaviour of CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> spinel electrodes in alkaline medium

Spinel type CoFe₂O₄ thin films have been prepared, on stainless steel supports, by thermal decomposition of aqueous solutions of mixed cobalt and iron nitrates in 1:2 molar ratio at 400 °C. The electrochemical behaviour of the CoFe₂O₄/1 M KOH interface was investigated by cyclic voltammetry, chronoamperometry and impedance techniques. The studies allowed finding out the redox reactions occurring at the oxide surface. The results were compared with colloidal electrodes prepared by alkaline precipitation of Fe(II) or Fe(III) hydrous oxi-hydroxides on platinum electrodes. In addition, it has been concluded that the processes are diffusion-controlled and the diffusion of the hydroxide ion, through the oxide, acts as the rate-determining step. The diffusion coefficient of OH⁻ through the oxide film was determined using cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy techniques.     

Infrared absorption spectroscopy and fluctuations induced conductivity (FIC) analysis of Be-doped TlBa2Ca2Cu3O10−δ superconductor

Be-doped TlBa₂(Ca_2−yBe_y)Cu₃O_10−δ (y=0, 0.25, 0.5, 0.75, and 1.0) superconductor bulk samples were synthesized by solid state reaction and characterized by X-ray diffraction (XRD), dc-resistivity {ρ (Ω cm)}, and Fourier Transform Infrared (FTIR) absorption spectroscopy. Fluctuations induced conductivity (FIC) analysis is carried out on temperature dependent dc-resistivity data of as-prepared and oxygen post-annealed TlBa₂(Ca_2−yBe_y)Cu₃O_10−δ superconductor samples by using Aslamazov–Larkin (AL) and Lawrence–Doniach (LD) models for excess conductivity. Different microscopic parameters such as zero temperature coherence length along c-axis {ξ_c(0)}, inter-layer coupling (J), inter-grain coupling (α), critical exponent (λ_D) and dimensionality of fluctuations are calculated for understanding the role of Be-doping on superconducting properties of TlBa₂(Ca_2−yBe_y)Cu₃O_10−δ samples. The cross-over temperature (T_o) is shifted towards higher temperature values with the increase of Be contents in TlBa₂(Ca_2−yBe_y)Cu₃O_10−δ samples. The increase in ξ_c(0) and J after Be-doping at Ca sites shows the improvement of inter-plane coupling in TlBa₂(Ca_2−yBe_y)Cu₃O_10−δ samples. The increase in zero resistivity critical temperature {T_c(R=0) (K)} up to y=0.5 and then decrease for y=0.75, 1.00 fixed the Be-doping level for optimum increase of superconducting properties of TlBa₂(Ca_2−yBe_y)Cu₃O_10−δ samples. The appreciable changes in all the microscopic parameters extracted from the FIC analysis and the increase in relative intensity of almost all the oxygen phonon modes indicate the oxygen diffusion in the unit cell after oxygen post-annealing the samples. The oxygen diffusion can take place at both inter-granular and intra-granular sites, which increase the superconducting volume fraction by improving the grains size, inter-grain connectivity and carrier density.     

Poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐co‐HFP) hollow fiber membranes prepared from PVDF‐co‐HFP/PEG‐600Mw/DMAC solution for membrane distillation

Poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐co‐HFP) hollow fiber membranes were prepared by using the phase inversion method. The effect of polyethylene glycol (PEG‐600Mw) with different concentrations (i.e., 0, 5, 7, 10, 12, 15, 18, and 20 wt %) as a pore former on the preparation and characterization of PVDF‐co‐HFP hollow fibers was investigated. The hollow fiber membranes were characterized using scanning electron microscopy, atomic force microscopy, and porosity measurement. It was found that there is no significant effect of the PEG concentration on the dimensions of the hollow fibers, whereas the porosity of the hollow fibers increases with increase of PEG concentration. The cross‐sectional structure changed from a sponge‐like structure of the hollow fiber prepared from pure PVDF‐co‐HFP to a finger‐like structure with small sponge‐like layer in the middle of the cross section with increase of PEG concentration. A remarkable undescribed shape of the nodules with different sizes in the outer surfaces, which are denoted as “twisted rope nodules,” was observed. The mean surface roughness of the hollow fiber membranes decreased with an increase of PEG concentration in the polymer solution. The mean pore size of the hollow fibers gradually increased from 99.12 to 368.91 nm with increase of PEG concentration in polymer solution. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Uncoupling Proteins and Regulated Proton Leak in Mitochondria

Higher concentration of protons in the mitochondrial intermembrane space compared to the matrix results in an electrochemical potential causing the back flux of protons to the matrix. This proton transport can take place through ATP synthase complex (leading to formation of ATP) or can occur via proton transporters of the mitochondrial carrier superfamily and/or membrane lipids. Some mitochondrial proton transporters, such as uncoupling proteins (UCPs), transport protons as their general regulating function; while others are symporters or antiporters, which use the proton gradient as a driving force to co-transport other substrates across the mitochondrial inner membrane (such as phosphate carrier, a symporter; or aspartate/glutamate transporter, an antiporter). Passage (or leakage) of protons across the inner membrane to matrix from any route other than ATP synthase negatively impacts ATP synthesis. The focus of this review is on regulated proton transport by UCPs. Recent findings on the structure and function of UCPs, and the related research methodologies, are also critically reviewed. Due to structural similarity of members of the mitochondrial carrier superfamily, several of the known structural features are potentially expandable to all members. Overall, this report provides a brief, yet comprehensive, overview of the current knowledge in the field.     

Proton exchange membranes prepared by simultaneous radiation grafting of styrene onto poly(tetrafluoroethylene‐co‐hexafluoropropylene) films. II. Properties of sulfonated membranes

Proton exchange membranes were prepared by radiation‐induced grafting of styrene onto commercial poly(tetrafluoroethylene‐co‐hexafluoropropylene) films using a simultaneous irradiation technique followed by a sulfonation reaction. The resulting membranes were characterized by measuring their physicochemical properties such as water uptake, ion exchange capacity, hydration number, and proton conductivity as a function of the degree of grafting. The thermal properties (melting and glass transition temperatures) and thermal stability of the membrane were also investigated using differential scanning calorimetry and thermal gravimetric analysis, respectively. Membranes having degrees of grafting of 16% and above showed proton conductivity of the magnitude of 10⁻² Ω⁻¹ cm⁻¹ at room temperature, as well as thermal stability at up to 290°C under an oxygen atmosphere. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2443–2453, 2000     

Proton exchange membranes prepared by simultaneous radiation grafting of styrene onto poly(tetrafluoroethylene‐co‐hexafluoropropylene) films. I. Effect of grafting conditions

The simultaneous radiation grafting of styrene onto poly(tetrafluoroethylene‐co‐hexafluoropropylene) (FEP) films was studied at room temperature. The effects of grafting conditions (type of solvent, irradiation dose, dose rate, and monomer concentration) were investigated. The degree of grafting was found to be dependent on the investigated grafting conditions. The dependence of the initial rate of grafting on the dose rate and the monomer concentration was found to be of 0.5 and 1.3 orders, respectively. The results suggest that grafting proceeds by the so‐called front mechanism in which the grafting front starts at the surface of the film and moves internally toward the middle of the film by successive diffusion of styrene through the grafted layers. Some selected properties of the grafted films were evaluated in correlation with the degree of grafting. We found that the grafted FEP films possess good mechanical stability, which encourages their use for the preparation of proton exchange membranes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 220–227, 2000