醋酸乙烯酯-丙烯酸丁酯乳液聚合成核机理

本工作研究了醋酸乙烯酯(VA)和丙烯酸丁酯(BA)乳液共聚合.通过对不同共聚单体配比下共聚合时胶乳粒径及胶粒数密度随转化率变化的分析,对VA/BA乳液共聚合成核及粒增长机理进行了探讨,指出水相成核是高VA含量时胶粒数密度较大的主要原因并解释了胶粒数密度及胶乳粒径与单体转化率的关系,同时也讨论了该共聚体系一步法聚合时反应机理与胶粒形态的关系.

A two variable refined plate theory for the bending analysis of functionally graded plates

Bending analysis of functionally graded plates using the two variable refined plate theory is presented in this paper.The number of unknown functions involved is reduced to merely four,as against five in other shear deformation theories. The variationally consistent theory presented here has, in many respects,strong similarity to the classical plate theory. It does not require shear correction factors,and gives rise to such transverse shear stress variation that the transverse shear stresses vary parabolically across the thickness and satisfy shear stress free surface conditions.Material properties of the plate are assumed to be graded in the thickness direction with their distributions following a simple power-law in terms of the volume fractions of the constituents.Governing equations are derived from the principle of virtual displacements, and a closed-form solution is found for a simply supported rectangular plate subjected to sinusoidal loading by using the Navier method.Numerical results obtained by the present theory are compared with available solutions,from which it can be concluded that the proposed theory is accurate and simple in analyzing the static bending behavior of functionally graded plates.

Structural and Electronic Properties of Bixo₃(X = Mn, Fe, Cr)

The candidate multiferroic BiCrO3 and its chemical neighbors BiMnO3 and BiFeO3 are known to be ferromagnetic and ferroelectric respectively. With structural distortions driven by the strongly polarizable Bi ions, we present results of the first-principles density functional calculations using the (FP-LMTO) method with the spin-orbit coupling for those materials in the pseudo-cubic perovskite phase. The results showed that the valence bands in these compounds are formed by the 6p orbitals of bismuth and 3d orbital’s of the transition metals. Our results indicate that these materials have metallic behavior for spin-up polarization but being a clear tandance for semiconductor spin-down BiMnO3.

Ground state parameters,electronic properties and elastic constants of CaMg3:DFT study

The present study aims to investigate the equation of state(EOS)parameters of CaMg3 in aReCh(D09),AIFR(DO3),CU3A11(LI2)and CuTi3(L60)structures,using full potential linear muffin-tin orbitals(FP-LMTO)approach based on the density functional theory(DFT).The local density approximation(LDA)and the generalized gradient approximation(GGA)were both applied for the exchange-correlation potential term.The calculated equation of slate parameters at equilibrium,in general,agreed well with the available data of the literature.The calculations showed that under compression CaMg3 transforms from DO3 to DO9 at about 29.96GPa,and 25.1 GPa using LDA and GGA,respectively.The elastic constants C,y,aggregate moduli,Vickers hardness,sound velocity,and Debye temperature of CaMg3 in D03 structure were also reported,discussed and analyzed.Using LDA(GGA),the calculated values of Hv andθD were found at around 5.80GPa(5.93GPa)and 393.44 K(389.91 K),respectively.Electronic band structure,total density of states(TDOS)as well as the partial density of states(PDOS)have been also obtained.The electronic band structure confirms the metallic behavior of CaMg3 in DO3 phase,the valence bands are dominated by the maximum contribution of‘d’like states of Ca in the energy ranging from 2 to 3 eV for GGA,and from 4.5 to 5 eV for LDA,respectively.

Preparation and Characterization of Hybrid Luminescence Mesoporous MCM-48 Doped with Eu( Ⅲ ) Complex

The preparation of hybrid mesoporous MCM-48 grafted by vinyl group via post-grafting process was reported and studied by X-ray diffraction, BET and 29Si solid MAS NMR.An organic β-diketonate Europium complex the corresponding luminescence property was characterized.

Li(2p←2s)+Na(3s)pressure broadening in the far-wing and line-core profiles

This work reports pressure-broadening line-wing and line-core of the lithium Li(2p←2s)resonance line perturbed by ground sodium Na(3s)atoms.In far-wing regions,the calculations are performed quantum-mechanically and are intended to examine the photoabsorption coefficients at diverse temperatures.The results show the existence of three satellites,in the blue wing near the wavelengths 470 nm and in the red wing around 862 nm and 1070 nm.For the line-core region,by adopting the simplified Baranger model,the line-width and line-shift rates are determined,and their variation law with temperature is examined.No published data were found to compare these results with.

Effect of Strontium on Structure and Superficial Area of La_(2)O_(3)

Recently, lanthanum oxide doped by group IIA elements may strongly influence solid state reaction. A series of samples, noted LaSrX (where X = % atomic of strontium) have been prepared by hydrolysis, in neutral medium from La2O3 and SrCO3. These samples were calcined under air at 450?C and 1150?C then characterized by specific surface area (BET), X-ray diffraction, scanning electron microscopy (SEM), thermogravimetry (TG) and differential thermal analysis (DTA). Obtained results show that after calcinations at: 1) 450?C, the addition of strontium is without effect on surface of La2O3 and the XRD analysis revealed no interaction between lanthanum oxide and strontium carbonate;2) 1150?C, the sintering of the samples is very important, reduction of 70% of surfaces compared to the samples calcined at 450?C;XRD results show that LaSrX are formed principally by two oxides: SrLa2O4 and La2O3, which is confirmed by SEM method. The reaction between La2O3 and SrCO3 showed three endothermic weight losses;elimination of water, a partial dehydroxylation of La(OH)3 and formation of La2O2CO3 and La2(CO3)3.

Sodium-Modified Fluorapatite: A Mild and Efficient Reusable Catalyst for the Synthesis of <i>α,α</i>’-Bis(Substituted Benzylidene) Cycloalkanones under Conventional Heating and Microwave Irradiation

A versatile and environmentally friendly method for α,α’-bis(substituted ben-zylidene) cycloalkanones has been developed using a heterogeneous catalysis technology. We have synthesized a series of the α,α’-bis(substituted benzylidene) cycloalkanones, a biologically important class of compounds, via the cross aldol condensation between arylaldehydes and cycloketones using sodium-modified fluorapatite (Na/FAP) as a highly efficient solid catalyst under conventional heating in aqueous media and solventless conditions under microwave. Catalyst reuse, ease of separation of the pure product, and high yields are some of the unique features of this process. Shorter reaction times (4 - 7 min) and higher yields (80% - 94%) were achieved under microwave irradiation conditions.

Effect of Initial Size and Shape Importance on Masse Transfer during Convective Drying

In this paper the influence of sample initial size on their convective drying at 80°C using convective dryer is determined. Results prove that initial size must be taken into account when drying process was estimated. This influence is limited by its form of cut. Comparing cubic form and parallelepiped (slice) one;results seem to show that thickness is the most important parameter governing the transfer phenomena during foodstuff convective drying. Three slices with thickness of 0.5 cm and surface area of 17, 82 and 112 cm2 respectively, dry better than cubic sample with a = 1 cm or a = 2 cm of arrest and having respectively 6 and 24 cm2 of surface area. All things seem to show that initial surface is not only the essential parameter;but also the thickness of the sample must be taken into account. Indeed, all of the samples with equal thickness (0.5 cm) and different exchange surfaces dry at the same time, about 210 min, comparing with cubic form 1 cm of arrest and 6 cm2 of surface and drying time of 230 min. A new parameter noted Dc called characteristic diameter is so considered to bridge the gaps. It is defined to be the diameter of the biggest sphere we can cut into a sample. This parameter is independent of form of the sample, and time increase with characteristic diameter increasing.

foF2 Diurnal Variability at African Equatorial Stations:Dip Equator Secular Displacement Effect

The paper goal is to analyze the variability of foF2 at African equatorial stations and the effect of dip angle on this variability. The gap between the dip angle of Dakar and Ouagadougou is superior to that between Djibouti and Ouagadougou. The trend of the dip angle at Ouagadougou and Dakar decreases while that of Djibouti increases. The relative position of the station with respect to the equator and the trend sign explains the difference observed in foF2 variability at Dakar station and at the two other stations. At Djibouti and Ouagadougou, foF2 exhibits noon bite out profile during all solar cycle phases while at Dakar observed profile is dome or plateau during the maximum and the predominance afternoon peak for the other solar cycle phases.

Statistical Study of foF2 Diurnal Variation at Dakar Station from 1971 to 1996:Effect of Geomagnetic Classes of Activity on Seasonal Variation at Solar Minimum and Maximum

The statistical study of F2 layer critical frequency at Dakar station from 1971 to 1996 is carried out. This paper shows foF2 statistical diurnal for all geomagnetic activities and all seasons and that during solar maximum and minimum phases. It emerges that foF2 diurnal variation graphs at Dakar station exhibits the different types of foF2 profiles in African EIA regions. The type of profile depends on solar activity, season and solar phase. During solar minimum and under quiet time condition, data show?the signature of a strength electrojet that is coupled with intense counter electrojet in the afternoon. Under disturbed conditions,?mean intense electrojet is observed in winter?during fluctuating and recurrent activities. Intense counter electrojet is seen under fluctuating and shock activities in all seasons coupled with strength electrojet in autumn. In summer?and spring under all geomagnetic activity condition, there is intense counter electrojet. During solar maximum, in summer and spring there is no electrojet under geomagnetic activity conditions.?Winter shows a mean intense electrojet. Winter and autumn are marked by the signature of the reversal electric field.

Field-effect passivation on silicon nanowire solar cells

表面再结合为高效率的太阳能电池代表一个缺陷。这为 nanowire 数组太阳能电池是特别重要的，在 surface-to-volume 比率极大地被提高的地方。这里，有效再结合上并且在设备表演上的不同钝化材料的效果试验性地被分析。我们的太阳能电池是自顶向下的轴的 n-p 连接硅 nanowires 借助于近地的阶段移动平版印刷术(NF-PSL ) 制作了的大区域。我们为最好的房间报导 9.9% 的效率，与 SiO 使钝化 < 潜水艇 class= “ a-plus-plus ” > 2 /SiN x 栈。表面的存在的影响在硅 / 氧化物接口修理了费用密度被学习。

Positron Characteristics in Cadmium and Zinc Chalcogenides

Electron energy levels and positron states have been calculated for cadmium and zinc chalcogenide compounds within the pseudo-potential approach and the independent particle model.Furthermore,the present contribution deals with the electron and positron chemical potentials allowing the calculation of the positron affinity to different materials of interest and hetero-structures formed by these materials.Besides,we here determine the positron diffusion constant by means of the positron deformation potential.An attempt has been made to scale positron affinity and diffusion constant with the lattice constant and the band gap energy,respectively.Such scaling is found to be not possible.The information gathered by the present study is of prime importance for a better understanding of positron trapping at interfaces and precipitates and should be useful in slow positron beam experiments.

Beat note analysis and spectral modulation of terahertz quantum cascade lasers with radio frequency injection

We demonstrate the electrical beat note analysis and radio frequency （RF） injection locking of a continuous wave （cw） terahertz quantum cascade laser （QCL） emitting around 3 THz （-100 μm）. In free running the beat note frequency of the QCL shows a shift of ~180 MHz with increasing drive current. The beat note, modulation response, injection pulling, and terahertz emission spectral characteristics in the different current regimes Ⅰ, Ⅱ, and Ⅲ are investigated. The results show that in the current regime I close to the laser threshold we obtain a narrower beat note and flat response to the RF modulation at the cavity round trip frequency. The pulling effect and spectral modulation measurements verify that in the current regime I the RF injection locking is more ef- ficient and a robust tool to modulate the mode number and mode frequency of terahertz QCLs.

Accurate surface potential determination in Schottky diodes by the use of a correlated current and capacitance voltage measurements.Application to n-InP

Based on current voltage（I-Vg） and capacitance voltage（C-Vg） measurements,a reliable procedure is proposed to determine the effective surface potential Vd（Vg） in Schottky diodes.In the framework of thermionic emission,our analysis includes both the effect of the series resistance and the ideality factor,even voltage dependent. This technique is applied to n-type indium phosphide（n-InP） Schottky diodes with and without an interfacial layer and allows us to provide an interpretation of the observed peak on the C-Vg measurements.The study clearly shows that the depletion width and the flat band barrier height deduced from C-Vg,which are important parameters directly related to the surface potential in the semiconductor,should be estimated within our approach to obtain more reliable information.

Very-high-frequency probes for atomic force microscopy with silicon optomechanics

Atomic force microscopy(AFM)has been consistently supporting nanosciences and nanotechnologies for over 30 years and is used in many fields from condensed matter physics to biology.It enables the measurement of very weak forces at the nanoscale,thus elucidating the interactions at play in fundamental processes.Here,we leverage the combined benefits of micro/nanoelectromechanical systems and cavity optomechanics to fabricate a sensor for dynamic mode AFM at a frequency above 100 MHz.This frequency is two decades above the fastest commercial AFM probes,suggesting an opportunity for measuring forces at timescales unexplored thus far.The fabrication is achieved using very-large-scale integration technologies derived from photonic silicon circuits.The probe's optomechanical ring cavity is coupled to a 1.55 pm laser light and features a 130 MHz mechanical resonance mode with a quality factor of 900 in air.A limit of detection in the displacement of 3×10^(-16)m/VHz is obtained,enabling the detection of the Brownian motion of the probe and paving the way for force sensing experiments in the dynamic mode with a working vibration amplitude in the picometer range.When inserted in a custom AFM instrument embodiment,this optomechanical sensor demonstrates the capacity to perform force-distance measurements and to maintain a constant interaction strength between the tip and sample,an essential requirement for AFM applications.Experiments indeed show a stable closed-loop operation with a setpoint of 4 nN/nm for an unprecedented subpicometer vibration amplitude,where the tip-sample interaction is mediated by a stretched water meniscus.

High Temperature Stability of Platinum Nanoparticles on Few-Layer Graphene Investigated by In Situ High Resolution Transmission Electron Microscopy

eterogeneous 催化反应在热地稳定的支持上包含象金属，金属氧化物，或金属硫醚 nanoparticles 那样的高度驱散的活跃阶段的使用。反应温度的变化能在反应期间导致粒子的 sintering。如此的小粒子的稳定性在许多域里与高活动在催化剂的新家庭的开发代表一个关键参数。这里，我们在很少层 graphene (FLG ) 上报导铂 nanoparticles (23 nm ) 的稳定性学习了由的表面在 situ 高温度传播电子显微镜学。

Vasarely painting at the nanoscale on sapphire crystals

We demonstrate that convenient thermal treatment of a specific sapphire vicinal surface can induce the formation of a fully two-dimensional(2D)ordered surface made of a periodic assembly of(006)facets.The simiarity between the resuting surface topography and pattemns represented in the hexagon series"of paintings by Vasarely is really striking!We thus propose to call these surfaces as"nanoscaled Vasarely surfaces".We also show that the self-organization process,which is driven by the minimization of the free energy of a closed system,results in a quasi-linear isothermal growth of the facets'surface area over time.