Effect of Re addition on the crystallization,heat treatment and structure of the Cu–Ni–Si-Cr alloy

Differential scanning calorimetry (DSC) was used to investigate the thermal behavior and non-isothermal crystallization kinetics of the Fe₆₇Nb₅B₂₈ metallic glasses prepared by melt-spinning method. DSC traces exhibit that the crystallization takes place through a single exothermic reaction, and it processes a good thermal stability in thermodynamics. The activation energies for nucleation and grain growth processes were calculated to be 536 ± 22 and 559 ± 20 kJ mol^?1 by Kissinger equation, respectively, and 551 ± 24 and 574 ± 20 kJ mol^?1 by Ozawa equation, respectively. It means that the grain growth process is more difficult than the nucleation process. The variation of local Avrami exponent n(x) with crystallized fraction x demonstrates that the crystallization mechanism varies at different stages. The n(x) is larger than 2.5 at the initial stage of 0 < x < 0.3, implying a mechanism of diffusion-controlled three-dimensional growth with increasing nucleation rate. The n(x) decreases from 2.5 to 1.5 in the range of 0.3 < x < 0.65, suggesting that the crystallization belongs to three-dimensional nucleation and grain growth with decreasing nucleation rate. And n(x) lies between 1.0 and 1.5 in the range of 0.65 < x < 0.95, indicating that the crystallization corresponds to the growth of particles with an appreciable initial volume. Low-temperature annealing corresponds to the precipitation of α-Fe, Fe₂B, and Fe₂₃B₆ phases, and further annealing leads to the formation of α-Fe, Fe₂B, and FeNbB phases. The magnetic properties in relation to microstructure change of the Fe₆₇Nb₅B₂₈ metallic glasses are discussed.     

Natural extensions of holomorphic motions

We consider an arbitrary real analytic family X_z, , over the closed unit disc , of real analytic plane Jordan curves X_z. Ifj _e ^iθ ,e ^iθ ∋ ∂D, is an arbitrary real-analytic family of orientation-reversing homeomorphisms of fixingX _e ^iθ pointwise, we show that there is a unique holomorphic motion of extending the given motion of Jordan curves and consistent with the given family of involutions. If these generalized reflections are defined using the barycentric extension construction of Douady-Earle-Nag, then the resulting extension method for holomorphic motions of X is natural, that is Moebius-invariant and continuous with respect to variation of the given motion of X₀.     

Crystal and molecular structure of 1,4-S,S′-bis-isothiosemicarbazidebutane dihydrobromide

The synthesis and crystal structure of 1,4-S,S-isothiosemicarbazidebutane dihydrobromide have been presented. The crystals are monoclinic:P2₁/n, a=7.9910(10),b=10.979(2),c=8.9240(10)Å, =111.450(10)°,Z=2, room temp. The structure was solved by direct methods. and refined to R=0.0297 for 846 reflections. The title compound consists of the centrosymmetric [C₆H₁₈N₆S₂]²⁺ dication and two Br^– anions. Intramolecular N–H...N and intermolecular N–H...Br hydrogen bonds stabilizetrans conformation of the thiosemicarbazide moiety.     

Polynomial symplectomorphisms

Let be the field of real or complex numbers. Let (X ²ⁿ, )be a symplectic affine space. We study the group of polynomialsymplectomorphisms of X. We show that for an arbitrary k thegroup of polynomial symplectomorphisms acts k-transitively onX. Moreover, if 2 l 2n – 2 then elements of this groupcan be characterized by polynomial automorphisms which preservethe symplectic type of all algebraic l-dimensional subvarietiesof X.     

The exact asymptotic of the collision time tail distribution for independent Brownian particles with different drifts

In this note we consider the time of the collision τ for n independent Brownian motions X ¹ _t ,...,X _t ⁿ with drifts a ₁,...,a _n , each starting from x = (x ₁,...,x _n ), where x ₁ < ... < x _n . We show the exact asymptotics of ${\mathbb{P}}_{\bf x}(\tau > t) = Ch({\bf x})t^{-\alpha} {\rm e}^{-\gamma t}(1 + o(1))$ as t → ∞ and identify C, h(x), α, γ in terms of the drifts.     

Structural features of the Cu(II) complex with the rat Abeta(1-28) fragment

The interaction between Cu(II) and the rat amyloid beta (1-28) fragment in micellar solutions at pH 7.5 was investigated by CD and NMR spectroscopy; the proton-copper distances were used in restrained molecular dynamics simulations to obtain a structural model of the Cu(II) complex.     

Zn(II) ions bind very efficiently to tandem repeat region of "prion related protein" (PrP-rel-2) of zebra-fish. MS and potentiometric evidence

Multi-histidine peptide fragments of zebra-fish prion protein are effective ligands for Zn(II) ions. Moreover the formation of a dinuclear complex species with a longer peptide can suggest the existence of the cooperative effect in the metal ion binding.     

Enantioselective synthesis of (+)-trypargine and (+)-crispine E

Asymmetric transfer hydrogenation was used as a key step in the synthesis of two guanidine-derived alkaloids (+)-trypargine and (+)-crispine E. The enantiomeric compositions of key intermediates were established on the basis of ¹H NMR spectra with chiral solvating agents. The absolute stereochemistry was proven by X-ray crystallography.