DES中一种新的搜索密钥空间的方法

本文根据DES中生成内部密钥的左移次数,给出了一种搜索密钥空间的新方法。就搜索时间来看,此方法把密钥空间的大小由2^(56)下降到2^(54)。

关于McEliece-Sarwate密钥共享方案的几点注记

本文分析了McEliece与Sarwate提出的两个密钥共享方案,即MSTS1与MSTS2。指出了MSTS1是不安全的,而MSTS2实际上是(l,k,n)Ramp方案,不是(k,n)门限方案。

Multimodal background model with noise and shadow suppression for moving object detection

A statistical multimodal background model was described for moving object detection in video surveillance. The solution to some of the problems such as illumination changes, initialization of model with moving objects, and shadows suppression was provided. The background samples were chosen by thresholding inter-frame differences, and the Gaussian kernel density estimation was used to estimate the probability density function of background intensity. Pixel's neighbor information was considered to remove noise due to camera jitter and small motion in the scene. The hue-max-min-diff color information was used to detect and suppress moving cast shadows. The effectiveness of the proposed method in the foreground segmentation was demonstrated in the traffic surveillance application.

Experimental and Theoretical Study of Hydrogen Atom Abstraction from C2H6 and C4H10 by Zirconium Oxide Clusters Anions

The reactions of anionic zirconium oxide clusters ZrxOy- with C2H6 and C4H10 are investi-gated by a time of flight mass spectrometer coupled with a laser vaporization cluster source.Hydrogen containing products Zr2O5H- and Zr3O7H- are observed after the reaction. Den-sity functional theory calculations indicate that the hydrogen abstraction is favorable in the reaction of Zr2O5- with C2H6, which supports that the observed Zr2O5H- and Zr3O7H- are due to hydrogen atom abstraction from the alkane molecules. This work shows a newpossible pathway in the reaction of zirconium oxide cluster anions with alkane molecules.

Interactions of Anionic and Neutral Serine with Pure and Metal-doped Graphene Studied by Density Functional Theory

We present a theoretical study of interactions of anionic and neutral serine （Ser） on pure or metal-doped graphene surfaces using density functional theory calculations. Interactions of both types of Ser with the pure graphene surface show weak non-covalent interactions due to the formation of-COOH…π, -COO^-…π, and -OH…π interactions. On metal- doped graphene, covalent interactions to the surface dominate, due to the formation of strong metal-O and O-metal-O interactions. Furthermore, the doped Fe, Cr, Mn, A1, or Ti enhances the ability of graphene to attract both types of Ser by a combination of the adsorption energy, the density of states, the Mulliken atomic charges, and differences of electron density. At the same time, the interaction strengths of anionic Ser on various graphene surfaces are stronger than those of neutral Ser. These results provide useful insights for the rational design and development of graphene-based sensors for the two forms of Ser by introducing appropriate doped atoms. Ti and Fe are suggested to be the best choices among all doped atoms for the anionic Ser and neutral Ser, respectively.

MULTI-WATERMARKING SCHEME FOR GROUP USERS BASED ON VISUAL CRYPTOGRAPHY

All watermarks are shared into shadow images using VCS(Visual Cryptography Scheme). Only one specific shadow (as a new watermark) is embedded into the host signal and the other ones are distributed to every user in each group as a key. In the watermarking extraction procedure, users in different group can obtain different watermark by combining their shadows with the extracted one from the watermarked signal. Analysis and experimental results show that the new watermarking method is novel, secure and robust.

H2 Dissociation by Au1-Doped Closed-Shell Titanium Oxide Cluster Anions

Dissociation of molecular hydrogen （H2） is extensively studied to understand the mechanism of hydrogenation reactions. In this study, H2 dissociation by Aul-doped closed-shell titanium oxide cluster anions AuTi3O7 and AuTi3O8 has been identified by mass spectrometry and quantum chemistry calculations. The clusters were generated by laser ablation and mass- selected to react with H2 in art ion trap reactor. In the reaction of AuTi3O8 with H2, the ion pair Au＋-O22 rather than Au＋-O2 is the active site to promote H2 dissociation. This finding is in contrast with the previous result that the lattice oxygen is usually the reactive oxygen species in H2 dissociation. The higher reactivity of the peroxide species is further supported by frontier molecular orbital analysis. This study provides new insights into gold catalysis involving H2 activation and dissociation.

Study of the Influence of the Electrolysis Parameters on Mn-Zn, Mn-Cu and Mn-Cu-Zn Alloys Coatings from Electrolytes Containing Complexing Ligands

The process of obtaining of high quality Mn-Zn, Mn-Cu and Mn-Cu-Zn alloy coatings from complexing ligands--citrate, EDTA （ethylene diaminetetra acetic acid） and nitrilotriacetic acid solutions was studied. Factors affecting stability of solutions containing ligand or ligands and influence of electrolysis parameters： electrolyte composition, pH, cathodic current density on chemical composition of the obtained coatings, on their current efficiency, morphology and structure were investigated.

Synthesis of VIB Group Metals Silicides Dispersed Powders by Electrolysis of Halide-Oxide Melts

Study of electrochemical behavior of chromium （molybdenum, tungsten） and silicon containing melts allowed defining conditions for synthesis of silicides of chromium, molybdenum and tungsten in the form of fine powders by electrolysis of halide-oxide melts. Sequence of stages of electrosynthesis of silicides of molybdenum and tungsten was found as follows： deposition of more electroposifve metal （molybdenum or tungsten）, deposition of the second component （silicon） on the surface of metal deposited previously, and reaction diffusion of silicon into the deep of the metal-salt ＂pear＂ with the formation of silicide phases of different compositions up to the higher silicides. In contrast, during the electrodeposition of chromium silicides, one of the components （chromium） is deposited not in elemental form, but in oxide form, and the other （silicon） acts as a reducing agent for this oxide to form binary compounds. Duration of the synthesis first stage （deposition of refractory metal or of its oxide） depends on the refractory metal compound content in the system and on the cathode current density. Synthesis of silicides is possible due to retention of powders of molybdenum （tungsten） or chromium oxide at the cathode without scaling. Optimal values of concentrations ratio, current density, temperature, and duration of electrosynthesis were found. Phase composition of products were obtained, as well as their chemical and thermal stability, were studied.

An efficient approach for shadow detection based on Gaussian mixture model

An efficient approach was proposed for discriminating shadows from moving objects. In the background subtraction stage, moving objects were extracted. Then, the initial classification for moving shadow pixels and foreground object pixels was performed by using color invariant features. In the shadow model learning stage, instead of a single Gaussian distribution, it was assumed that the density function computed on the values of chromaticity difference or bright difference, can be modeled as a mixture of Gaussian consisting of two density functions. Meanwhile, the Gaussian parameter estimation was performed by using EM algorithm. The estimates were used to obtain shadow mask according to two constraints. Finally, experiments were carried out. The visual experiment results confirm the effectiveness of proposed method. Quantitative results in terms of the shadow detection rate and the shadow discrimination rate(the maximum values are 85.79% and 97.56%, respectively) show that the proposed approach achieves a satisfying result with post-processing step.

Cyclic M（S02） （M=Zn, Cd） and its Anions： Matrix Infrared Spectra and DFT Calculations

Reaction of laser ablated zinc and cadmium atoms with SO2 molecules was studied by low temperature matrix isolation infrared spectroscopy. Cyclic M（SO2） and anion M（SO2）-（M=Zn, Cd） were produced in excess argon and neon, which were identified by 34SO2 and S18O2 isotopic substitutions. The observed infrared spectra and molecular structures were confirmed by density functional theoretical calculations. Natural charge distributions indicated significant electron transfer from s orbitals of zinc or cadmium metal atom to S02 ligand and cyclic M（SO2） complexes favored ＂ion pair＂ M＋（SO2）-formation, which were trapped in low temperature matrices. In addition Zn-O or Cd-O bond in M（SO2） exhibited strong polarized covalent character. Reaction of Hg atom with SO2 was also investigated, but no reaction product was observed, due to the relativistic effect that resulted in the contraction of 6s valence shell and high ionization potential of Hg atom.

DFT Study on Structural Distortion and Vibronic Coupling of Vanadyl Porphyrin Anion and Cation

The geometries of one-electron reduced/oxidized species （[TOP]-/[VOP] ＋） of vanadyl por- phyrin （VOP） have been calculated with PBE1PBE method. The results show that for both [VOP]- and [VOP]＋ the ground states are triplet, in which one of the two unpaired electron occupies the dxy orbital of the V atom while the other occupies the n-orbital of porphyrin ring. Thus both [VOP]- and [VOP]＋ can be considered as n-radicals. The ground state of neutral VOP molecule is doublet with the unpaired electron occupying dxy orbital of V atom. In contract to the C4v symmetry of neutral VOP molecule, [VOP]- anion has a ＂rectangular＂ distorted C2v structure due to Jahn-Teller effect. The linear vibronic coupling constants for the Jahn-Teller active modes of [TOP]- were evaluated and the node patterns of frontier KS orbitals are used to explain the reason why the distortion occurs along specific modes. The ground state [VOP]＋ has a porphyrin ring with pronounced bond length alternation due to pseudo-Jahn-Teller effect, causing its symmetry declined from C4v to Ca. The bond length alternation is well explained with the node patterns of re-constructed frontier KS orbitals.

Influence of Cathode Plasma on Breakdown Formation in Plasma-Anode Explosive-Emission Source

Breakdown formation in an explosive-emission electron source is related to the interelectrode gap filling with plasma propagating from the cathode and formed at the anode and in the interelectrode gap under the electron beam action. Plasma anode is used to increase the beam current density. Preliminary interelectrode gap filling with plasma in the explosive-emission source decreases the influence of uncontrolled plasma arrival from the anode on the diode processes, promotes current density increase and duration of generated electron beams. The paper considers the influence of the cathode geometry on the breakdown formation in the plasma-anode explosive-emission electron source. The data on obtaining of microsecond electron beams with current density of 30 A/cm^2 and 1.5-2 kA/cm^2 are presented.

Effect of indium addition on corrosion of AP65 magnesium alloy

The effect of indium addition on the corrosion behavior of AP65 Mg alloy was examined. The indium modified AP65 exhibits accelerated pitting corrosion and overall corrosion, but there is almost no incubation period at the onset of corrosion. Polarization curve measurements indicate that the indium modified AP65 has more negative corrosion potential, which is an improvement aspect of the electrochemical activation. The corrosion current density increases from 0.126 to 0.868 mA/cm2 with and without 2.0% (mass fraction) indium addition. The mean potentials of AP65 negatively shift from -1.491 V to -1.584 V by adding 2.0% indium. The effect of indium addition on the corrosion performance of AP65 seems to be associated with the decrease of cathode-to-anode area ratio of the alloy, which may change the electrochemical anode and cathode polarization behavior of the alloy.

Large Area Thermionic Cathode and Its Prilimiary Experimental Results

A 2MeV thermionic cathode test stand was established to meet the requirement of the large area thermionic cathode system.A 100ram in diameter type'B'thermionic dispenser cathode was developed.A 1000A emission current was produced at the voltage of the diode about 1.8MV,the pulse width about 90ns(FWHM),and the cathode temperature about 1350℃.The emission current density is 12A/cm^2.The results indicate that a large area thermionic cathode which produces high quality and high current electron beams is visible.The results also indicate that the ability of cathode emission relies on the diode-vacuum and cathode-temperature.

Facile microwave approach towards high performance MoS2/graphene nanocomposite for hydrogen evolution reaction

Low-cost, highly efficient catalysts for hydrogen evolution reaction(HER) are very important to advance energy economy based on clean hydrogen gas. Intensive studies on two-dimensional molybdenum disulfides(2 D Mo S2) have been conducted due to their remarkable catalytic properties.However, most of the reported syntheses are time consuming,complicated and less efficient. The present work demonstrates the production of Mo S2/graphene catalyst via an ultra-fast(60 s) microwave-initiated approach. High specific surface area and conductivity of graphene delivers a favorable conductive network for the growth of Mo S2 nanosheets, along with rapid charge transfer kinetics. As-produced Mo S2/graphene nanocomposites exhibit superior electrocatalytic activity for the HER in acidic medium, with a low onset potential of62 m V, high cathodic currents and a Tafel slope of43.3 m V/decade. Beyond excellent catalytic activity, Mo S2/graphene reveals long cycling stability with a very high cathodic current density of around 1000 m A cm^-2 at an overpotential of 250 m V. Moreover, the Mo S2/graphene-catalyst exhibits outstanding HER activities in a temperature range of 30 to 120°C with low activation energy of36.51 k J mol^-1, providing the opportunity of practical scalable processing.

Mesoporous Fe_(3)O_(4)@C nanoarrays as high-performance anode for rechargeable Ni/Fe battery

Rechargeable aqueous batteries with high power density and energy density are highly desired for electrochemical energy storage.Despite the recent reports of various cathode materials with ultrahigh pseudocapacitance exceeding3000 F g^(-1)(or 800 mA h g^(-1)),the development of anode materials is relatively insufficient,which limits the whole performance of the devices far from practical applications.Herein,we report the preparation of mesoporous Fe_(3)O_(4)@C nanoarrays as high-performance anode for rechargeable Ni/Fe battery by a self-generated sacrificial template method.Zn O/Fe_(3)O_(4)composite was first synthesized by a co-deposition process,and Zn O was subsequently removed by alkali etching to construct the mesoporous structure.A thin carbon film was introduced onto the surface of the electrode by the carbonization of glucose to increase the structural stability of the electrode.The unique mesoporous nanoarray architecture endows the electrode with larger specific surface area,faster charge/mass transport and higher utilization of Fe_(3)O_(4),which shows an ultrahigh specific capacity (292.4 mA h g^(-1)at a current density of 5 mA cm^(-2)) and superior stability in aqueous electrolyte (capacitance retention of 90.8%after 5000cycles).After assembled with hierarchical mesoporous Ni O nanoarray as a cathode,an optimized rechargeable Ni/Fe battery with double mesoporous nanoarray electrodes was fabricated,which provided high energy/power densities(213.3 W h kg^(-1)at 0.658 kW kg^(-1)and 20.7 kW kg^(-1)at113.9 W h kg^(-1),based on the total mass of the active materials)in the potential window of 1.5 V with excellent cyclability(81.7%retention after 5000 charge/discharge cycles).

Large field emission current and density from robust carbon nanotube cathodes for continuous and pulsed electron sources

Highly adhesive cold cathodes with high field emission performance are fabricated by using a screen-print- ing method. The emission density of carbon nanotube （CNT） cold cathode reaches 207.0 mA cm-2 at an electric field of 4.5 Vμm-1 under continuous driving mode, and high peak current emission of 315.8 mA corresponding to 4.5 A cm 2 at the electric field of 10.3 V μm-1 under pulsed driving mode. The emission patterns of the cold cathodes are of excellent uniformity that was revealed by vivid luminescent patterns of phosphor coated transparent indium tin oxide （ITO） an- ode. The cold cathodes also exhibit highly stable emission under continuous and pulsed driving modes. The high adhe- sion of CNTs to molybdenum substrates results in robust cold cathodes and is responsible for the high field emission performance. This robust CNT emitter could meet the operating requirements of continuous and pulsed electron sources, and it provides promising applications in various vacuum- micro/nanoelectronic devices.

Density Functional Study of Cationic and Anionic Ag_mCu_n (m + n ≤ 5) Clusters

Abstract The structural and energetic properties of bimetallic AgmCun （m ＋n ≤ 5） in the cationic and anionic charged states have been investigated by density functional theory with relativistic effective core potentails. The stable cationic pentamers have three-dimensional structures in contrast to anionic clusters assume planar structures. For the given cluster size the electron affinities decrease as the Cu content increases, while no clear trend can be found in adiabatic ionization potentials. The binding energy per atom also increases with the increasing Cu content and follows the order anion 〈 cation. The most probable dissociation channels of the clusters considered are also discussed.

Field Emission from Carbon Nanotube/Tin Composite

Powder metallurgy was used to fabricate carbon nanotube(CNT) field emission cathodes.CNTs and tin(Sn) powder were blended,compacted and sintered.After polishing and etching,CNTs were exposed and protruded from the metal surface.CNTs were embedded into the Sn matrix,which acted as stable field emitters. The J-E curves show excellent field emission properties,such as low turn-on field of 2.8 V/μm,high emission current density and good current stability.