Nickel nanoparticles obtained by a modified polyol process: synthesis, characterization, and magnetic properties

The synthesis of nickel nanoparticles using poly(N-vinilpyrrolidone) (PVP) as protective agent was studied. The nanoparticles were prepared in air according to a modified polyol route, using nickel chloride as precursor and sodium borohydride as reducing agent. Samples with different nickel/PVP ratio were obtained. The X-ray diffraction and transmission electron microscopy (TEM) measurements indicate the occurrence of face-centered cubic metallic nickel nanoparticles with a medium diameter of 3.8 nm and good size dispersion. Fourier transformed infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) data show an effective interaction between the nickel nanoparticles surface and the carboxyl oxygen atoms of PVP. Magnetic measurements show single-domain nonideal superparamagnetism behavior due to dipolar magnetic coupling between particles.     

Modulated noisy biological dynamics: Three examples

Three examples of noisy biological dynamics modulated by a periodic signal are discussed. A minimal neuron model driven by stochastic noise and small periodic force show a firing statistic comparable with stochastic resonance as demonstrated in bistable systems. Similar results are obtained from responses to periodic vibrotactile stimulation on higher-order neuronal units of the somatosensory pathway. Finally, results from a bistable visual perception task exhibiting stochastic resonance are reported.     

Dynamic Electrical-Mechanical Energy Coupling in Electrolyte-Mineral Systems

Electrical-mechanical and mechanical-electrical coupling phenomena have been observed in geo-materials. Underlying internal phenomena are not always clear. In this paper, we identify potential microscale processes on the bases of previously published research; fundamental physical principles and analytical models are included. Second, we notice important inconsistencies between theoretically predicted values or high-frequency laboratory data with respect to low-frequency field observations. To explore these differences, we conduct a laboratory experimental study that simulates field conditions, placing emphasis on low frequency coupling, that is, less than 10 kHz. Both, mechanical-electrical and electrical-mechanical effects are observed. Finally, hypotheses are presented in an attempt to explain observed differences.     

The first structurally characterized aluminum compound with two SH groups: [LAl(SH)(2)] (L = N(Ar)C(Me)CHC(Me)N(Ar), Ar = 2,6-i-Pr(2)C(6)H(3)) and the catalytic properties of the sulfur P(NMe(2))(3) system

Surprisingly stable is the bis(hydrogen sulfide) of aluminum LAl(SH)(2) with two terminal arranged SH groups. The insertion of sulfur into the Al-H bonds is catalyzed by SP(NMe(2))(3). A possible mechanism is discussed.     

Bonding Capabilities of the Biochemical Buffer TRIS toward Copper(II) Ion. Structure and Magnetic Properties of Binuclear and Tetranuclear Systems

Following X-ray crystal structure studies, the products of the reaction between Cu(II) halides and tris(hydroxymethyl)methylamine (TRIS) can be formulated as [Cu(TRISH_?1)(TRIS)]₂X₂ and [Cu(TRISH_?1)X]₄ (X ? Cl, Br). TRISH_?1 is the deprotonated ligand. Initial metal-ligand stoichiometric ratios of 1:2 and 1:1 are required to obtain the former and the latter species, respectively. Relevant crystal data for the dimeric compound with X ? Br are: monoclinic, a = 11.39(2), b = 10.049(2), c = 12.149(2) Å, β = 95.83(2)°, space group P2₁/c, Z = 2. The tetramer with X ? Cl crystallizes in teh triclinic space group P 1 with a 9.182(1), b = 9.120(2), c = 8.817(1) Å, α = 88.95(1), β = 87.01(1), γ = 84.13(1), Z = 1. In the dimer, two square planar Cu(II)-units are held together by two H-bonds of the type O? H …? O, which involve the O-atoms coordinated to the metals. The formation of an eight-membered cycle containing two metal ons ensues. The tetramer contains two dinuclear units formed by two metal centers, square planar in first approximation, which share one edge; the arrangement is significantly puckered at this vector. One of these bridging O-atoms has μ₃ character as it serves as a weak apical donor for a Cu-atom of another binuclear unit. Thus a step-like geometry of the central core is obtained. Both compounds have constant magnetic moments at least down to the liquid N₂ temperature. In this respect, they differ from other complexes of Cu(II) having comparable geometries, but temperature-dependent magnetic moments.