Random Motions at Finite Speed in Higher Dimensions

We present a general method of studying the transport process , t≥0, in the Euclidean space ℝ ^m , m≥2, based on the analysis of the integral transforms of its distributions. We show that the joint characteristic functions of are connected with each other by a convolution-type recurrent relation. This enables us to prove that the characteristic function (Fourier transform) of in any dimension m≥2 satisfies a convolution-type Volterra integral equation of second kind. We give its solution and obtain the characteristic function of in terms of the multiple convolutions of the kernel of the equation with itself. An explicit form of the Laplace transform of the characteristic function in any dimension is given. The complete solution of the problem of finding the initial conditions for the governing partial differential equations, is given. We also show that, under the standard Kac condition on the speed of the motion and on the intensity of the switching Poisson process, the transition density of the isotropic transport process converges to the transition density of the m-dimensional homogeneous Brownian motion with zero drift and diffusion coefficient depending on the dimension m. We give the conditional characteristic functions of the isotropic transport process in terms of the inverse Laplace transform of the powers of the Gauss hypergeometric function. Some important models of the isotropic transport processes in lower dimensions are considered and some known results are derived as the particular cases of our general model by means of the method developed.     

血液可见吸收光谱与血氧参数神经网络估算法

总血红蛋白浓度和血氧饱和度是两个基本的血氧参数。文章提出了利用内置双光纤微创探头在位测量大鼠脑组织血氧参数的新方法。首先,利用悬乳液(Intralipid)和全血配置不同总血红蛋白浓度的混合溶液,模拟生物组织模型,用光纤光谱仪测试系统测量组织模型在加氧和去氧时的实时吸收光谱,同时用血氧分析仪(OXI meter)对血氧参数定标,建立测试光谱和定标数据样本集。然后,利用人工神经网络建立血液吸收光谱与血氧参数的神经网络模型,训练后的网络模型能根据吸收光谱输出生物组织的血氧参数值,总血红蛋白浓度和血氧饱和度的平均输出误差分别为±4μmol·L-1和±5%。最后,利用神经网络模型对大鼠脑组织血氧参数进行了在位测试实验,测得脑灰质的血氧饱和度为0.60~0.70,脑白质血氧饱和度为0.45~0.55;总血红蛋白浓度在脑皮层(深度1mm)附近最高,平均110μmol·L-1,其余深度脑组织的总血红蛋白浓度为70~90μmol·L-1。这种方法对脑外科微创手术中实时在位测试脑组织血氧参数具有重要的参考意义。     

Electrochemical, morphological and microstructural characterization of carbon film resistor electrodes for application in electrochemical sensors

The electrochemical and microstructural properties of carbon film electrodes made from carbon film electrical resistors of 1.5, 15, 140 Ω and 2.0 kΩ nominal resistance have been investigated before and after electrochemical pre-treatment at +0.9 V vs SCE, in order to assess the potential use of these carbon film electrodes as electrochemical sensors and as substrates for sensors and biosensors. The results obtained are compared with those at electrodes made from previously investigated 2 Ω carbon film resistors. Cyclic voltammetry was performed in acetate buffer and phosphate buffer saline electrolytes and the kinetic parameters of the model redox system Fe(CN)₆^3−/4− obtained. The 1.5 Ω resistor electrodes show the best properties for sensor development with wide potential windows, similar electrochemical behaviour to those of 2 Ω and close-to-reversible kinetic parameters after electrochemical pre-treatment. The 15 and 140 Ω resistor electrodes show wide potential windows although with slower kinetics, whereas the 2.0 kΩ resistor electrodes show poor cyclic voltammetric profiles even after pre-treatment. Electrochemical impedance spectroscopy related these findings to the interfacial properties of the electrodes. Microstructural and morphological studies were carried out using contact mode Atomic Force Microscopy (AFM), Confocal Raman spectroscopy and X-ray diffraction. AFM showed more homogeneity of the films with lower nominal resistances, related to better electrochemical characteristics. X-ray diffraction and Confocal Raman spectroscopy indicate the existence of a graphitic structure in the carbon films.     

Photoinduced electron transfer between hen egg white lysozyme and anticancer drug menadione

The protein, hen egg white lysozyme, on photoexcitation undergoes electron transfer with menadione (2-methyl-1,4-naphthoquinone), a widely known anticancer drug. With the addition of menadione the fluorescence of lysozyme is quenched with the simultaneous formation of an excited state charge-transfer complex in the longer wavelength and a ground state complex. The former is further evident from laser flash photolysis studies, which indicate a tryptophan to menadione electron transfer. From fluorescence quenching studies the binding constant is found to be ∼1.7×10⁴ M⁻¹ with the corresponding changes in enthalpy (ΔH°) and entropy (ΔS°) as 12.24 kJ mol⁻¹ and 124.12 J mol⁻¹ K⁻¹, respectively, indicative of an entropy-driven process. The circular dichroism studies also show some structural changes with increase in α-helical content in the protein on interaction with menadione. Finally, docking studies give some insight into the role of Trp 108 of lysozyme in the interaction.     

Rate Constants for Reaction Between Hydroxyl Radical and Dimethyl Sulfide Under Real Atmospheric Condition

用相对速率方法分别考察了OH自由基与DMS在氮气、空气和氧气体系的反应速率常数. 发现使用HONO和CH3ONO作为OH自由基发生剂时,基态氧原子O(3P)对动力学的测定有很大的影响. H2O2为OH自由基的发生剂,室温下在氮气、空气及氧气体系下的速率常数分别为4.50×10-12,8.56×10-12和11.31×10-12 cm3/(molecule?s).在287～338 K,测得氮气和空气体系下的阿累尼乌斯表达式分别为:kair=(7.24±0.28)×10-13exp[(770.7±97.2)/T],kN2=(3.40±0.15)×10-11exp[-(590.3±165.9)/T     

Mechanical fabrication of metal nano-contacts showing conductance quantization under electrochemical potential control

We have mechanically fabricated Ni and Cu nano-constrictions in solution to study their quantized conductance behavior under electrochemical potential control. Conductance quantization was observed at both metals in solution at room temperature for the first time. The conductance of Cu nano-constriction was quantized in units of G₀(=2e²/h). A sharp 1G₀ peak was observed in the conductance histogram. For Ni, a rather broad peak at 1–1.5G₀ was observed in the histogram. The conductance quantization behavior was discussed by comparing previously documented results of nano-constrictions fabricated in air or ultra-high vacuum conditions, with those fabricated in solution.     

Diffusion and reaction in random media and models of evolution processes

A diffusion equation including source terms, representing randomly distributed sources and sinks is considered. For quasilinear growth rates the eigenvalue problem is equivalent to that of the quantum mechanical motion of electrons in random fields. Correspondingly there exist localized and extended density distributions dependent on the statistics of the random field and on the dimension of the space. Besides applications in physics (nonequilibrium processes in pumped disordered solid materials) a new evolution model is discussed which considers evolution as hill climbing in a random landscape.We dedicate this work to the memory of Ilya M. Lifshitz.     

Thermodynamics of natural selection

It is shown that biological-natural-selection-like behavior can occur, as a general type of time evolution, in a statistical system where detailed balance is violated owing to the presence of metastable energy states. A model of a non-equilibrium phase transition corresponding to the spontaneous origin of self-reproduction in the system is suggested. After a phase transition, the system passes from one quasistationary distribution of self-reproducing subsystems to another, with an increase in the total organization, as long as the growth of the energy flow through the system or a reduction of energy dissipation in the system is possible. The entropy production is calculated for this process in terms of selective values of Eigen's theory for self-organization in autocatalytic systems. Correspondence of the extremal principle of Eigen's theory with the criterion of evolution in Prigogine's thermodynamics is established.     

Half-plane diffraction of Gaussian beams carrying two vortices of equal charges

This paper derives explicit expressions for the propagation of Gaussian beams carrying two vortices of equal charges m=±1 diffracted at a half-plane screen, which enables the study of the dynamic evolution of vortices in the diffraction field. It shows that there may be no vortices, a pair or several pairs of vortices of opposite charges m=+1, -1 in the diffraction field. Pair creation, annihilation and motion of vortices may appear upon propagation. The off-axis distance additionally affects the evolutionary behaviour. In the process the total topological charge is equal to zero, which is unequal to that of the vortex beam at the source plane. A comparison with the free-space propagation of two vortices of equal charges and a further extension are made.     

Solution-combusting preparation of mono-dispersed Mn3O4 nanoparticles for electrochemical applications

Manganese oxide (Mn₃O₄) nanoparticles with average diameter of 15 nm were prepared using alcohol solution of manganese chloride as starting material via a facile solution-combusting method. The flame core zone was chosen to prepare mono-dispersed and high crystalline products, which were employed to modify glassy carbon electrode and detect dopamine via cyclic voltammetry. The results exhibited excellent electrochemical sensitivity. A linear relationship between the concentration of dopamine and its oxidation peak current was obtained by differential pulse voltammetry, which will find wide application in the biological detection.