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    Competing role of catalysis-coagulation and catalysis-fragmentation in kinetic aggregation behaviours
    Li Xiao-Dong(李晓东), Lin Zhen-Quan(林振权), Song Mei-Xia(宋美霞), and Ke Jian-Hong(柯见洪)
    Chin. Phys. B, 2010, 19 (12): 128201.   DOI: 10.1088/1674-1056/19/12/128201
    Abstract1170)      PDF (225KB)(389)      
    We propose a kinetic aggregation model where species A aggregates evolve by the catalysis-coagulation and the catalysis-fragmentation, while the catalyst aggregates of the same species B or C perform self-coagulation processes. By means of the generalized Smoluchowski rate equation based on the mean-field assumption, we study the kinetic behaviours of the system with the catalysis-coagulation rate kernel $K(i,j;l)\propto l^{\nu}$ and the catalysis-fragmentation rate kernel $F(i,j;l)\propto l^{\mu}$ , where l is the size of the catalyst aggregate, and $\nu$ and $\mu$ are two parameters reflecting the dependence of the catalysis reaction on the size of the catalyst aggregate. The relation between the values of parameters $\nu$ and $\mu$ reflects the competing roles between the two catalysis processes in the kinetic evolution of species A. It is found that the competing roles of the catalysis-coagulation and catalysis-fragmentation in the kinetic aggregation behaviours are not determined simply by the relation between the two parameters $\nu$ and $\mu$, but also depend on the values of these two parameters. When $\nu> \mu$ and $\nu\geqslant 0$, the kinetic evolution of species A is dominated by the catalysis-coagulation and its aggregate size distribution ak(t) obeys the conventional or generalized scaling law; when $\nu<\mu$ and $\nu \geqslant 0$ or $\nu>0$ but $\mu \geqslant 0$, the catalysis-fragmentation process may play a dominating role and ak(t) approaches the scale-free form; and in other cases, a balance is established between the two competing processes at large times and ak(t) obeys a modified scaling law.
    Relative energy dissipation-induced effective attraction in granular mixture
    Jia Yan(贾燕), Yang Xian-Qing(杨先清), Deng Min(邓敏), Guo Hai-Ping(郭海萍), and Ye Jian-Lan(叶见兰)
    Chin. Phys. B, 2010, 19 (12): 128202.   DOI: 10.1088/1674-1056/19/12/128202
    Abstract1174)      PDF (295KB)(510)      
    This paper presents the investigation of the clustering of the intruders in a vertically vibrated granular bed by means of event-driven simulations. The results indicate that the position of intruders in the vertical direction is not a key factor for their aggregation. Energy dissipation of the intruders and host particles are calculated in the process of intruder-host and host–host collisions. The relative energy dissipation of the intruders to that of the host particles is obtained. We find that clustering of the intruders happens when the relative energy dissipation is negative. The conclusion is verified when the restitution coefficient, density and diameter of the intruders are varied.
    Critical volume fraction and size for a colloidal cluster to nucleate
    Zhao Dan-Dan(赵丹丹), Long Lian-Feng(龙联丰), and Xiao Chang-Ming(肖长明)
    Chin. Phys. B, 2010, 19 (12): 128203.   DOI: 10.1088/1674-1056/19/12/128203
    Abstract1189)      PDF (186KB)(699)      
    With the aid of the critical size of colloidal cluster, the critical volume fraction of phase transition of colloidal system is determined by the principle of entropy maximum and Carnahan–Starling (CS) state equation in this paper. In our discussion, no parameter is introduced externally, and our results are in good agreement with the experimental results.
    Thermal stability of HfO2/Si (001) films prepared by electron beam evaporation in ultrahigh vacuum using atomic oxygen
    Xu Run(徐闰), Gong Wei-Ming(贡伟明), Yan Zhi-Jun(阎志军), Wang Lin-Jun(王林军), and Xia Yi-Ben(夏义本)
    Chin. Phys. B, 2010, 19 (12): 128204.   DOI: 10.1088/1674-1056/19/12/128204
    Abstract1152)      PDF (224KB)(665)      
    HfO2 films on silicon substrates have been prepared by electron beam evaporation in ultrahigh vacuum using atomic oxygen. Synchrotron radiation photon–electron spectroscopy was used to investigate the thermal stability of HfO2 films under an ultrahigh vacuum environment. At the temperature of 750 $^\circ$C, HfO2 films begin to decompose. After being further annealed at 850 $^\circ$C for 3 min, HfO2 films decomposes completely, partially to form Hf-silicide and partially to form gaseous HfO. Two chemical reactions are responsible for this decomposition process. A small amount of Hf-silicide, which is formed at the very beginning of growth, may result in the films grown subsequently to be loosened, and thereby leads to a relatively low decomposition temperature.
    Multi-grid simulation of pedestrian counter flow with topological interaction
    Ma Jian(马剑), Song Wei-Guo(宋卫国), and Liao Guang-Xuan(廖光煊)
    Chin. Phys. B, 2010, 19 (12): 128901.   DOI: 10.1088/1674-1056/19/12/128901
    Abstract1262)      PDF (518KB)(938)      
    We investigate the dynamics of pedestrian counter flow by using a multi-grid topological pedestrian counter flow model. In the model, each pedestrian occupies multi- rather than only one grid, and interacts with others in the form of topological interaction, which means that a moving pedestrian interacts with a fixed number of those nearest neighbours coming from the opposite direction to determine his/her own moving direction. Thus the discretization of space and time are much finer, the decision making process of the pedestrian is more reliable, which all together makes the moving behaviour and boundary conditions much more realistic. When compared with field observations, it can be found that the modified model is able to reproduce well fitted pedestrian collective behaviour such as dynamical variation of lane formation, clustering of pedestrians in the same direction, etc. The fundamental diagram produced by the model fits also well with field data in the free flow region. Further analyses indicate that with the increase of the size of pedestrian counter flow system, it becomes harder for the system to transit into a jamming state, while the increase of interaction range does not change the transition point from free flow to jamming flow in the multi-grid topological counter flow model. It is also found that the asymmetry of the injection rate of pedestrians on the boundaries has direct influence on the process of transition from free flow to jamming flow, i.e., a symmetric injection makes it easier for the system to transit into jamming flow.
    Synthesis of large diamond crystals containing high-nitrogen concentration at high pressure and high temperature using Ni-based solvent by temperature gradient method
    Huang Guo-Feng(黄国锋), Jia Xiao-Peng(贾晓鹏), Li Shang-Sheng(李尚升), Zhang Ya-Fei(张亚飞), Li Yong(李勇), Zhao Ming(赵明), and Ma Hong-An(马红安)
    Chin. Phys. B, 2010, 19 (11): 118101.   DOI: 10.1088/1674-1056/19/11/118101
    Abstract1181)      PDF (795KB)(1972)      
    This paper reprots that with Ni-based catalyst/solvent and with a dopant of NaN3, large green single crystal diamonds with perfect shape are successfully synthesized by temperature gradient method under high pressure and high temperature in a China-type cubic anvil high-pressure apparatus (SPD-6×1200), and the highest nitrogen concentration reaches approximately 1214-1257 ppm calculated by infrared absorption spectra. The synthesis conditions are about 5.5 GPa and 1240-1300 ℃. The growth behaviour of diamond with high-nitrogen concentration is investigated in detail. The results show that, with increasing the content of NaN3 added in synthesis system, the width of synthesis temperature region for growth high-quality diamonds becomes narrower, and the morphology of diamond crystal is changed from cube-octahedral to octahedral at same temperature and pressure, the crystal growth rate is slowed down, nevertheless, the nitrogen concentration doped in synthetic diamond increases.
    Structure, room-temperature magnetic and optical properties of Mn-doped TiO2 nano powders prepared by the sol–gel process
    Ding Peng(丁芃),Liu Fa-Min(刘发民),Zhou Chuang-Cang(周传仓), Zhong Wen-Wu(钟文武), Zhang Huan(张嬛), Cai Lu-Gang(蔡鲁刚), and Zeng Le-Gui(曾乐贵)
    Chin. Phys. B, 2010, 19 (11): 118102.   DOI: 10.1088/1674-1056/19/11/118102
    Abstract1251)      PDF (4128KB)(2070)      
    TiO2 nano powders with Mn concentration of 0 at%-12 at% were synthesized by the sol–gel process, and were annealed at 500 ℃ and 800 ℃ in air for 2 hrs. X-ray diffraction (XRD) measurements indicate that the Mn–TiO2 nano powders with Mn concentration of 1 at% and 2 at% annealed at 500 and 800 ℃ are of pure anatase and rutile, respectively. The scanning electron microscope (SEM) observations reveal that the crystal grain size increases with the annealing temperature, and the high resolution transmission electron microscopy (HRTEM) investigations further indicate that the samples are well crystallized, confirming that Mn has doped into the TiO2 crystal lattice effectively. The room temperature ferromagnetism, which could be explained within the scope of the bound magnetic polaron (BMP) theory, is detected in the Mn–TiO2 samples with Mn concentration of 2 at%, and the magnetization of the powders annealed at 500 ℃ is stronger than that of the sample treated at 800 ℃. The UV–VIS diffuse reflectance spectra results demonstrate that the absorption of the TiO2 powders could be enlarged by the enhanced trapped electron absorption caused by Mn doping.
    Thermal diffusivity of light-emitting diode packaging material determined by photoacoustic piezoelectric technique
    Sun Qi-Ming(孙启明), Gao Chun-Ming(高椿明), Zhao Bin-Xing(赵斌兴), and Rao Hai-Bo(饶海波)
    Chin. Phys. B, 2010, 19 (11): 118103.   DOI: 10.1088/1674-1056/19/11/118103
    Abstract992)      PDF (519KB)(721)      
    Thermal property is one of the most important properties of light-emitting diode (LED). Thermal property of LED packaging material determines the heat dissipations of the phosphor and the chip surface, accordingly having an influence on the light-emitting efficiency and the life-span of the device. In this paper, photoacoustic piezoelectric (PAPE) technique has been employed to investigate the thermal properties of polyvinyl alcohol (PVA) and silicon dioxide, which are the new and the traditional packaging materials in white LED, respectively. Firstly, the theory of PAPE technique has been developed for two-layer model in order to investigate soft materials; secondly, the experimental system has been set up and adjusted by measuring the reference sample; thirdly, the thermal diffusivities of PVA and silicon dioxide are measured and analysed. The experimental results show that PVA has a higher thermal diffusivity than silicon dioxide and is a better packaging material in the sense of thermal diffusivity for white LED.
    Finite element modeling of heating phenomena of cracks excited by high-intensity ultrasonic pulses
    Chen Zhao-Jiang(陈赵江), Zheng Jiang(郑江), Zhang Shu-Yi(张淑仪), Mi Xiao-Bing(米小兵), and Zheng Kai(郑凯)
    Chin. Phys. B, 2010, 19 (11): 118104.   DOI: 10.1088/1674-1056/19/11/118104
    Abstract1290)      PDF (5627KB)(1675)      
    A three-dimensional thermo-mechanical coupled finite element model is built up to simulate the phenomena of dynamical contact and frictional heating of crack faces when the plate containing the crack is excited by high-intensity ultrasonic pulses. In the finite element model, the high-power ultrasonic transducer is modeled by using a piezoelectric thermal-analogy method, and the dynamical interaction between both crack faces is modeled using a contact-impact theory. In the simulations, the frictional heating taking place at the crack faces is quantitatively calculated by using finite element thermal-structural coupling analysis, especially, the influences of acoustic chaos to plate vibration and crack heating are calculated and analysed in detail. Meanwhile, the related ultrasonic infrared images are also obtained experimentally, and the theoretical simulation results are in agreement with that of the experiments. The results show that, by using the theoretical method, a good simulation of dynamic interaction and friction heating process of the crack faces under non-chaotic or chaotic sound excitation can be obtained.
    Influence of small-molecule material on performance of polymer solar cells based on MEH-PPV:PCBM blend
    Liu Xiao-Dong(刘晓东), Xu Zheng(徐征), Zhang Fu-Jun(张福俊), Zhao Su-Ling(赵谡玲), Zhang Tian-Hui(张天慧), Gong Wei(龚伟), Song Jing-Lu (宋晶路), Kong Chao(孔超), Yan Guang(闫光), and Xu Xu-Rong(徐叙瑢)
    Chin. Phys. B, 2010, 19 (11): 118601.   DOI: 10.1088/1674-1056/19/11/118601
    Abstract1430)      PDF (318KB)(884)      
    In this work, the influence of a small-molecule material, tris(8-hydroxyquinoline) aluminum (Alq3), on bulk heterojunction (BHJ) polymer solar cells (PSCs) is investigated in devices based on the blend of poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). By doping Alq3 into MEH-PPV:PCBM solution, the number of MEH-PPV excitons can be effectively increased due to the energy transfer from Alq3 to MEH-PPV, which probably induces the increase of photocurrent generated by excitons dissociation. However, the low carrier mobility of Alq3 is detrimental to the efficient charge transport, thereby blocking the charge collection by the respective electrodes. The balance between photon absorption and charge transport in the active layer plays a key role in the performance of PSCs. For the case of 5 wt.% Alq3 doping, the device performance is deteriorated rather than improved as compared with that of the undoped device. On the other hand, we adopt Alq3 as a buffer layer instead of commonly used LiF. All the photovoltaic parameters are improved, yielding an 80% increase in power conversion efficiency (PCE) at the optimum thickness (1 nm) as compared with that of the device without any buffer layer. Even for the 5 wt.% Alq3 doped device, the PCE has a slight enhancement compared with that of the standard device after modification with 1 nm (or 2 nm) thermally evaporated Alq3. The performance deterioration of Alq3-doped devices can be explained by the low solubility of Alq3, which probably deteriorates the bicontinuous D-A network morphology; while the performance improvement of the devices with Alq_3 as a buffer layer is attributed to the increased light harvesting, as well as blocking the hole leakage from MEH-PPV to the aluminum (Al) electrode due to the lower highest occupied molecular orbital (HOMO) level of Alq3 compared with that of MEH-PPV.
    Effect of physical disturbance on the structure of needle coke
    Zhao Shi-Gui(赵世贵), Wang Bao-Cheng(王保成), and Sun Quan(孙权)
    Chin. Phys. B, 2010, 19 (10): 108101.   DOI: 10.1088/1674-1056/19/10/108101
    Abstract1291)      PDF (1292KB)(2315)      
    Through different preparation technology, this paper reports that the needle coke is prepared with coal-tar pitch under the effect of magnetic field and ultrasonic cavitation. It studies the effect of physical disturbance on the structure of needle coke. The structure of needle coke is characterized by scanning electron microscope and x-ray diffractometer, and the influence mechanism is analysed. Results showed that the structure and property of needle coke could be effectively improved by magnetic field and ultrasonic cavitations, such as degree of order, degree of graphitization and crystallization. Comparatively speaking, the effect of magnetic field was greater. The graphitization degree of needle coke prepared under the effect of magnetic field is up to 45.35%.
    Preparation of size controllable copper nanocrystals for nonvolatile memory applications
    Wang Li(王利), Sun Hong-Fang(孙红芳), Zhou Hui-Hua(周惠华), and Zhu Jing(朱静)
    Chin. Phys. B, 2010, 19 (10): 108102.   DOI: 10.1088/1674-1056/19/10/108102
    Abstract1386)      PDF (3061KB)(597)      
    A method of fabricating Cu nanocrystals embedded in SiO2 dielectric film for nonvolatile memory applications by magnetron sputtering is introduced in this paper. The average size and distribution density of Cu nanocrystal grains are controlled by adjusting experimental parameters. The relationship between nanocrystal floating gate micro-structure and its charge storage capability is also discussed theoretically.
    Non-equilibrium statistical theory about microscopic fatigue cracks of metal in magnetic field
    Liu Zhao-Long(刘兆龙), Hu Hai-Yun(胡海云), Fan Tian-You(范天佑), and Xing Xiu-San(邢修三)
    Chin. Phys. B, 2010, 19 (10): 108103.   DOI: 10.1088/1674-1056/19/10/108103
    Abstract1272)      PDF (164KB)(502)      
    This paper develops the non-equilibrium statistical fatigue damage theory to study the statistical behaviour of micro-crack for metals in magnetic field. The one-dimensional homogeneous crack system is chosen for study. To investigate the effect caused by magnetic field on the statistical distribution of micro-crack in the system, the theoretical analysis on microcrack evolution equation, the average length of micro-crack, density distribution function of micro-crack and fatigue fracture probability have been performed. The derived results relate the changes of some quantities, such as average length, density distribution function and fatigue fracture probability, to the applied magnetic field, the magnetic and mechanical properties of metals. It gives a theoretical explanation on the change of fatigue damage due to magnetic fields observed by experiments, and presents an analytic approach on studying the fatigue damage of metal in magnetic field.
    Influence of Pb adatom on adsorption of oxygen molecules on Pb(111) surface: a first-principles study
    Yang Yu(杨宇)
    Chin. Phys. B, 2010, 19 (10): 108201.   DOI: 10.1088/1674-1056/19/10/108201
    Abstract1079)      PDF (2449KB)(553)      
    Using first-principles calculations, we systematically study the influence of Pb adatom on the adsorption and the dissociation of oxygen molecules on Pb(111) surface, to explore the effect of a point defect on the oxidation of the Pb(111) surface. We find that when an oxygen molecule is adsorbed near an adatom on the Pb surface, the molecule will be dissociated without any obvious barriers, and the dissociated O atoms bond with both the adatom and the surface Pb atoms. The adsorption energy in this situation is much larger than that on a clean Pb surface. Besides, for an adsorbed oxygen molecule on a clean Pb surface, a diffusing Pb adatom can also change its adsorption state and enlarge the adsorption energy for O, but it does not make the oxygen molecule dissociated. And in this situation, there is a molecule-like PbO2 cluster formed on the Pb surface.
    Intrinsic noise analysis and stochastic simulation on transforming growth factor beta signal pathway
    Wang Lu(王路) and Ouyang Qi(欧阳颀)
    Chin. Phys. B, 2010, 19 (10): 108202.   DOI: 10.1088/1674-1056/19/10/108202
    Abstract1136)      PDF (280KB)(503)      
    A typical biological cell lives in a small volume at room temperature; the noise effect on the cell signal transduction pathway may play an important role in its dynamics. Here, using the transforming growth factor-β signal transduction pathway as an example, we report our stochastic simulations of the dynamics of the pathway and introduce a linear noise approximation method to calculate the transient intrinsic noise of pathway components. We compare the numerical solutions of the linear noise approximation with the statistic results of chemical Langevin equations, and find that they are quantitatively in agreement with the other. When transforming growth factor-β dose decreases to a low level, the time evolution of noise fluctuation of nuclear Smad2–Smad4 complex indicates the abnormal enhancement in the transient signal activation process.
    Effect of number density on velocity distributions in a driven quasi-two-dimensional granular gas
    Sajjad Hussain Shah, Li Yin-Chang(李寅阊), and Hou Mei-Ying (厚美瑛)
    Chin. Phys. B, 2010, 19 (10): 108203.   DOI: 10.1088/1674-1056/19/10/108203
    Abstract1230)      PDF (241KB)(428)      
    The motion of mono-disperse spherical steel particles in a vibration driven quasi-two-dimensional (2D) square cell is studied. The cell is horizontally vibrated to eliminate the effect of gravity compaction. The velocity distributions at different particle number densities are studied and found to obey the form $\exp[-\beta(|v_y|/\sigma_y)^{\alpha}]$, in which $v_y$ and $\sigma_y$ are velocity and its variance in the transverse direction, and $\alpha$ and $\beta$ are fitting parameters. The value of $\alpha$ is found to decrease with the number density of particles increasing. To investigate the effect of the bottom plate, the molecular dynamics simulation without considering any bottom friction is performed. The accordance between the simulation result and the experimental result shows that the influence of bottom plate friction force on the high energy tail of the velocity distribution can be neglected.
    Depletion interactions in binary mixtures of repulsive colloids
    Li Wei-Hua(李卫华) and Qiu Feng(邱枫)
    Chin. Phys. B, 2010, 19 (10): 108204.   DOI: 10.1088/1674-1056/19/10/108204
    Abstract1180)      PDF (1062KB)(426)      
    Acceptance ratio method, which has been used to calculate the depletion potential in binary hard-sphere mixtures, is extended to the computation of the depletion potential of non-rigid particle systems. The repulsive part of the Lennard–Jones pair potential is used as the direct pair potential between the non-rigid particles. The depletion potential between two big spheres immersed in a suspension of small spheres is determined with the acceptance ratio method through the application of Monte Carlo simulation. In order to check the validity of this method, our results are compared with those obtained by the Asakura–Oosawa approximation, and by Varial expansion approach, and by molecular dynamics simulation. The total effective potential and the depth of its potential well are computed for various softness parameters of the direct pair potential.
    Effects of fractal gating of potassium channels on neuronal behaviours
    Zhao De-Jiang(赵德江), Zeng Shang-You(曾上游), and Zhang Zheng-Zhen(张争珍)
    Chin. Phys. B, 2010, 19 (10): 108701.   DOI: 10.1088/1674-1056/19/10/108701
    Abstract1100)      PDF (198KB)(528)      
    The classical model of voltage-gated ion channels assumes that according to a Markov process ion channels switch among a small number of states without memory, but a bunch of experimental papers show that some ion channels exhibit significant memory effects, and this memory effects can take the form of kinetic rate constant that is fractal. Obviously the gating character of ion channels will affect generation and propagation of action potentials, furthermore, affect generation, coding and propagation of neural information. However, there is little previous research on this series of interesting issues. This paper investigates effects of fractal gating of potassium channel subunits switching from closed state to open state on neuronal behaviours. The obtained results show that fractal gating of potassium channel subunits switching from closed state to open state has important effects on neuronal behaviours, increases excitability, rest potential and spiking frequency of the neuronal membrane, and decreases threshold voltage and threshold injected current of the neuronal membrane. So fractal gating of potassium channel subunits switching from closed state to open state can improve the sensitivity of the neuronal membrane, and enlarge the encoded strength of neural information.
    Research on the response model of microbolometer
    Sui Xiu-Bao(隋修宝), Chen Qian(陈钱), Gu Guo-Hua(顾国华) and Liu Ning(刘宁)
    Chin. Phys. B, 2010, 19 (10): 108702.   DOI: 10.1088/1674-1056/19/10/108702
    Abstract1130)      PDF (1717KB)(1331)      
    There are certain limitations in the application of uncooled focal plane array (FPA) detector due to the lack of an effective response model which reliably transforms the target temperature to analog output voltage. This paper establishes the response model of microbolometer through researching the detection theory of microbolometer and the heat balance equation under the condition of the pulsed voltage bias. In the establishing process, we simplified the heat balance equation to acquire a simple answer. The experimental data show that, in the temperature dynamic range of 30 K, the biggest tolerance between the model data and the experiment data is 0.2 K; while in the temperature dynamic range of 100 K, it is 1 K. This model can reflect the real response of the microbolometer with only small differences which are acceptable in engineering applications.
    Structures and magnetic behaviours of TiO2–Mn–TiO2 multilayers
    Liu Fa-Min(刘发民), Ding Peng(丁芃), and Li Jian-Qi(李建奇)
    Chin. Phys. B, 2010, 19 (9): 098101.   DOI: 10.1088/1674-1056/19/9/098101
    Abstract1091)      PDF (6089KB)(824)      
    The TiO2–Mn–TiO2 multilayers are successfully grown on glass and silicon substrates by alternately using radio frequency reactive magnetron sputtering and direct current magnetron sputtering. The structures and the magnetic behaviours of these films are characterised with x-ray diffraction, transmission electron microscope (TEM), vibrating sample magnetometer, and superconducting quantum interference device (SQUID). It is shown that the multi-film consists of a mixture of anatase and rutile TiO2 with an embedded Mn nano-film. It is found that there are two turning points from ferromagnetic phase to antiferromagnetic phase. One is at 42 K attributed to interface coupling between ferromagnetic Mn3O4 and antiferromagnetic Mn2O3, and the other is at 97 K owing to the interface coupling between ferromagnetic Mn and antiferromagnetic MnO. The samples are shown to have ferromagnetic behaviours at room temperature from hysteresis in the MH loops, and their ferromagnetism is found to vary with the thickness of Mn nano-film. Moreover, the Mn nano-film has a critical thickness of about 18.5 nm, which makes the coercivity of the multi-film reach a maximum of about 3.965times 10 - 2 T.
ISSN 1674-1056   CN 11-5639/O4

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