Controlling surface statistical properties using bias voltage: Atomic force microscopy and stochastic analysis

The effect of bias voltages on the statistical properties of rough surfaces has been studied using atomic force microscopy technique and its stochastic analysis. We have characterized the complexity of the height fluctuation of a rough surface by the stochastic parameters such as roughness exponent, level crossing, and drift and diffusion coefficients as a function of the applied bias voltage. It is shown that these statistical as well as microstructural parameters can also explain the macroscopic property of a surface. Furthermore, the tip convolution effect on the stochastic parameters has been examined.Comment: 8 pages, 11 figures

The phosphomimetic mutation of syndecan-4 binds and inhibits Tiam1 modulating Rac1 activity in PDZ interaction-dependent manner

The small GTPases of the Rho family comprising RhoA, Rac1 and Cdc42 function as molecular switches controlling several essential biochemical pathways in eukaryotic cells. Their activity is cycling between an active GTP-bound and an inactive GDP-bound conformation. The exchange of GDP to GTP is catalyzed by guanine nucleotide exchange factors (GEFs). Here we report a novel regulatory mechanism of Rac1 activity, which is controlled by a phosphomimetic (Ser179Glu) mutant of syndecan-4 (SDC4). SDC4 is a ubiquitously expressed transmembrane, heparan sulfate proteoglycan. In this study we show that the Ser179Glu mutant binds strongly Tiam1, a Rac1-GEF reducing Rac1-GTP by 3-fold in MCF-7 breast adenocarcinoma cells. Mutational analysis unravels the PDZ interaction between SDC4 and Tiam1 is indispensable for the suppression of the Rac1 activity. Neither of the SDC4 interactions is effective alone to block the Rac1 activity, on the contrary, lack of either of interactions can increase the activity of Rac1, therefore the Rac1 activity is the resultant of the inhibitory and stimulatory effects. In addition, SDC4 can bind and tether RhoGDI1 (GDP-dissociation inhibitor 1) to the membrane. Expression of the phosphomimetic SDC4 results in the accumulation of the Rac1-RhoGDI1 complex. Co-immunoprecipitation assays (co-IP-s) reveal that SDC4 can form complexes with RhoGDI1. Together, the regulation of the basal activity of Rac1 is fine tuned and SDC4 is implicated in multiple ways

Synthesis of Well-Defined, Surfactant-Free Co₃O₄ Nanoparticles:The Impact of Size and Manganese Promotion on Co₃O₄ Reduction and Water Oxidation Activity

Abstract: A surfactant-free synthetic route has been developed to produce size-controlled, cube-like cobalt oxide nanoparticles of three different sizes in high yields. It was found that by using sodium nitrite as salt-mediating agent, near-quantitative yields could be obtained. The size of the nanoparticles could be altered from 11 to 22 nm by changing the cobalt concentration and reaction time. These surfactant-free nanoparticles form ideal substrates for facile deposition of further elements such as manganese. The effect of size of the cobalt oxide nanoparticles and the presence of manganese on the reducibility of cobalt oxide to metallic cobalt was investigated. Similarly, the effect of these parameters was investigated with a visible light promoted water oxidation system with cobalt oxide as catalyst, together with [Ru(bpy) 3] 2+ light harvester dye and an electron acceptor. Graphical Abstract: A novel surfactant-free synthetic route has been developed to produce size-controlled, cube shaped cobalt oxide nanoparticles in high yields. [Figure not available: see fulltext.]. </p

Everything you always wanted to know about SDPD⋆ (⋆but were afraid to ask)

An overview of the smoothed dissipative particle dynamics (SDPD) method is presented in a format that tries to quickly answer questions that often arise among users and newcomers. It is hoped that the status of SDPD is clarified as a mesoscopic particle model and its potentials and limitations are highlighted, as compared with other methods

Kinetics and mechanism of NH3 synthesis over Fe(100) and K/Fe(100) model catalysts

  In this investigation kinetics and mechanism of NH3 synthesis over Fe(100) and K/Fe(100) model catalysts have been studied. In this context, adsorption kinetics of both N2/Fe (100) and H2/Fe (100)systems is initially investigated. By using statistical mechanic approach, we have determined the adsorption coefficient for N2 and H2 molecules as well as transition probability of different states of adsorption and dissociation of the reactants molecules. The effect of surface catalyst temperature on the reaction rate (TOF) is studied under different reactant partial pressures. The mechanism of NH3 synthesis is suggested based on LH surface reactions model. According to the obtained results, activation energy for the reaction over Fe (100) and K/Fe(100) (for θk=0.1ML) was determined 19.6 and 11.1 kcal/mole, respectively. The order of reaction on both catalysts with respect to PN2 and PH2 was unity and negative, respectively. Based on our data analysis, the NH3 synthesis obeys Temkin isotherm

Synthesis and characterization of porous BiVO4 thin films: the effect of structural defects on photoelectrochemical properties

BiVO4 thin films with thickness of ~ 1.3 μm were deposited on ITO substrate via pulsed-spray pyrolysis deposition. X-ray diffraction pattern revealed that BiVO4 layers have been crystallized in tetragonal scheelite phase with average crystallite size of ~ 16 nm. According to UV-visible absorption spectra, a band gap energy of ~2.47 eV was determined for the synthesized layers. Scanning electron microscopy observations indicated that a porous BiVO4 structure with average pore diameter of ~ 162 nm and worm-like fine particle diameter of ~ 208 nm has been synthesized. Oxygen vacancies have been induced into the layers via an electrochemical reduction treatment (ET). This employed process increased the surface-related capacitance by about 6 times. A double charge transport resistance and half capacitance for Helmholtz layer was determined after ET, indicating electron transfer from space charge layer to Helmholtz layer upon ET. Using electrochemical impedance spectroscopy, it was found that effective charge carrier life time inside the BiVO4 thin films increased to ~25 ms which is 2-fold longer than the time before electrochemical reduction treatment