Magnetic properties and giant magnetoresistance in electrodeposited Co–Ag granular films

Small cobalt particles embedded in a silver matrix have been prepared using the electrodeposition technique. The size of the clusters is controlled by the deposition potential and the Co growth time. Structural, magnetic and magneto-transport properties of Co–Ag samples have been investigated as a function of the Co concentration between 2 and 40 at% cobalt. Superparamagnetic behavior is evidenced for the low contents of cobalt while long-range magnetic order appears at higher Co concentrations. The particles size has been determined from magnetic properties and from the X-ray diffraction technique, and varies between 3.5 and 9 nm. Magnetoresistance passes through a maximum as a function of the cobalt concentration. A maximum of ∼4% GMR is obtained at room temperature while GMR reaches a value of 14% at 10 K.     

Fixation of advantageous mutations in an off-equilibrium population

We investigate the evolution of asexual populations subject to a large supply of deleterious mutations such that Muller's ratchet operates. In this regime, the accumulation of deleterious mutations takes place continuously with the resulting loss of the least-loaded class of individuals. In the current work, we study the effect of the supply of beneficial mutations on the ratchet's speed. We also examine how the rate of substitution of favorable mutations as well as the mean selective effect of favorable mutations that reach fixation is compared to those assuming a population at equilibrium. We observe that under Muller's ratchet, the rate of fixation of advantageous mutations is higher than that predicted for an equilibrium population. The difference between the rate supposing an equilibrium regime and that for the non-equilibrium case becomes larger as we increase the rate of deleterious mutations. On the other hand, the mean selective effect of beneficial mutations that reach fixation is smaller than the expected value for the equilibrium situation.     

Preparation and properties of ZnO nanostructures by electrochemical anodization method

ZnO thin films with diverse nanostructures, including nanodot, nanowire and nanoflower, have been fabricated on zinc foils by a simple and rapid electrochemical anodization method. The ZnO thin films reveal very strong visible emission that is ascribed to the transition between V_OZn_i and valence band. Under the dc or ac electric field, the electroinduced surface wettability conversion from the superhydrophobic to hydrophilic state was observed and the generation of surface defective sites on ZnO films under electric field was used to explain the transition mechanism. This work provides a simple and rapid method for synthesizing different ZnO nanostructures in large scale, and electric field can be used to modulate the wettability of ZnO nanostructures.     

Synthesis and characterization of cadmium selenide nanostructures on porous aluminum oxide templates by high frequency alternating current electrolysis

We have successfully deposited nanostructured cadmium selenide (CdSe) inside anodic aluminum oxide (AAO) templates from aqueous electrolyte containing cadmium sulfate, selenium oxide and mercuric chloride by using high frequency alternating current (19 V_rms, 200 Hz). Addition of mercury ions aids in the deposition of CdSe inside anodic oxide pores. Scanning and transmission electron microscopy studies of the deposit etched in phosphoric acid showed the presence of end standing nanostrips. Energy dispersive X-ray analysis of the deposit confirmed the presence of cadmium and selenium in the deposit. X-ray diffraction (XRD) studies of the deposit showed small but broad diffraction peaks consistent with the presence of hexagonal CdSe. Optical studies revealed blue shift in band gap energy due to quantum confinement.     

On size and shape of the average meson fields in the semibosonized Nambu & Jona-Lasinio model

We consider the bosonized form of a two-flavor Nambu & Jona-Lasinio model involving scalar-isoscalar and pseudoscalar-isovector quark-quark interaction. Solitonic meson fields are obtained by minimizing the effective Euclidean action. In dependence on the constituent quark mass, which is the only free parameter in the model, we evaluate a series of meson profiles and compare them with a properly parameterized reference profile. We show that the self-consistent fields do in fact practically not depend on the constituent quark mass. Their shape can be very well approximated by this reference profile which interpolates between the correct asymptotic behavior for small and large radii. To demonstrate the accuracy of the approximation we evaluate several static properties like energy, mean square radius, axial-vector constant and delta-nucleon mass splitting using both self-consistent and reference profiles. The agreement is found to be very well in the physically relevant mass region.     

Dynamical Analysis of Protein Regulatory Network in Budding Yeast Nucleus

Recent progresses in the protein regulatory network of budding yeast Saccharomyces cerevisiae have provided a global picture of its protein network for further dynamical research. We simplify and modularize the protein regulatory networks in yeast nucleus, and study the dynamical properties of the core 37-node network by a Boolean network model, especially the evolution steps and final fixed points. Our simulation results show that the number of fixed points N（k） for a given size of the attraction basin k obeys a power-law distribution N（k） χ k^-2.024. The yeast network is more similar to a scale-free network than a random network in the above dynamical properties.     

The effect of inactive impurities on a surface in NO-CO reaction: A Monte Carlo simulation

The interaction among the reacting species in the NO-CO reaction on a metal catalytic surface that proceeds according to the Langmuir-Hinshelwood thermal mechanism is studied by means of Monte Carlo simulations. The study of this system is essential for the understanding of the influence of impurities on the catalytic oxidation of NO by CO. It is found that this complex system exhibits irreversible phase transitions between active states with sustained reaction and poisoned states without reaction. The same system has also been investigated by non-thermal (Eley-Rideal) mechanism. Both the phase diagrams of the surface coverage and the steady state production of CO₂ and N₂ are evaluated as a function of the partial pressures of the reactants in the gas phase. From this study, it is observed that with the increase of impurities, the production rate reduces and the reaction stops at a certain point. Moreover, the first order transition in the phase diagram converts into second order phase transition that is in accordance with the experimental findings. Therefore, the first order phase transition, which is a characteristic of such catalytic reactions, is eliminated.     

Surface morphology characterization of pentacene thin film and its substrate with under-layers by power spectral density using fast Fourier transform algorithms

Surface morphology of pentacene thin films and their substrates with under-layers is characterized by using atomic force microscopy (AFM). The power values of power spectral density (PSD) for the AFM digital data were determined by the fast Fourier transform (FFT) algorithms instead of the root-mean-square (rms) and peak-to-valley value. The PSD plots of pentacene films on glass substrate are successfully approximated by the k-correlation model. The pentacene film growth is interpreted the intermediation of the bulk and surface diffusion by parameter C of k-correlation model. The PSD plots of pentacene film on Au under-layer is approximated by using the linear continuum model (LCM) instead of the combination model of the k-correlation model and Gaussian function. The PSD plots of SiO₂ layer on Au under-layer as a gate insulator on a gate electrode of organic thin film transistors (OTFTs) have three power values of PSD. It is interpreted that the specific three PSD power values are caused by the planarization of the smooth SiO₂ layer to rough Au under-layer.     

Active Control of Cellular Orientation through In-Situ Stress in the Substrate

We investigate the orientation of cells on substrates to find possible methods for controlling the cellular orientation. The force dipole model is employed in our modelling and simulation. The elastic interaction between cells as well as the elastic interaction between the cell and in-situ stress field in the substrate are found to be the two main physical mechanisms to control the cellular orientation. The former interaction dominates the cellular orientation when the in-situ stress is small, while the later dominates when the in-situ stress is large enough. Two cells tend to align perpendicularly on a free substrate, but the cellular orientation varies with the increasing in-situ stress. Two cells tendto align in parallel when the normal stress is large enough. Their direction is perpendicular to the extension stress direction or parallel to the compression stress direction. When the positive in-situ shear stress is large enough, the two cells tend to align at -45°. Based on this theoretical simulation, it is believed that the cellular orientation on substrates can be controlled by thein-situ stresses.     

A Coarse Estimation of Cell Size Region from a Mesoscopic Stochastic Cell Cycle Model

Based on a deterministic cell cycle model of fission yeast, the effects of the finite cell size on the cell cycle regulation in wee1- cdc25△ double mutant type are numerically studied by using of the chemical Langevin equations. It is found that at a certain region of cell size, our numerical results from the chemical Langevin equations are in good qualitative agreement with the experimental observations. The two resettings to the G2 phase from early stages of mitosis can be induced under the moderate cell size. The quantized cycle times can be observed during such a cell size region. Therefore, a coarse estimation of cell size is obtained from the mesoscopic stochastic cell cycle model.