Medium range ordering and some magnetic properties of amorphous Fe90Zr7B3 alloy

High-resolution electron microscopy (HREM) reveals in the as-quenched Fe₉₀Zr₇B₃ alloy the existence of medium range ordered (MRO) regions 1-2 nm in size. Transmission Mössbauer spectroscopy confirms that these regions are α-Fe MRO ones. Above the Curie point of the amorphous phase (T_C=(257±2)K) they behave like non-interacting superparamagnetic particles with the magnetization decreasing linearly with the temperature. For these particles the average magnetic moment of 390μ_B and the average size of 1.7 nm, in excellent agreement with HREM observations, were estimated. The maximum of the isothermal magnetic entropy change at the maximum magnetizing field induction of 2 T occurs at the Curie temperature of the amorphous phase and equals to 1.05 Jkg⁻¹ K⁻¹. The magnetic entropy changes exhibit the linear dependence on the maximum magnetizing field induction in the range 0.5-2 T below, near and above T_C. Such correlations are attributed to superparamagnetic behavior of α-Fe MRO regions.     

Phase transitions in solid-liquid-gas systems with applications to alkali metal generators

Motivated by physical applications we consider a mathematical model describing the evaporation process in solid-liquid-gas systems with two moving boundaries of the phase transition. An alkali metal generator with a working substance in the form of an intermetallic compound and the evaporation of a volatile component into a vacuum is considered. Explicit analytical solutions of the problem under consideration are constructed in three different geometries of the process. We demonstrate that the evaporation boundary moves much more slowly than the dissolution boundary and the liquid layer thickness increases with time. The role of the evaporation coefficient on the evaporation stream and the nonlinear dynamics of the process is studied. An approach developed in the present study can be used for solutions of mathematical models describing similar Stefan-type processes met in other areas of applied physics.     

Regenerated silk fibroin nanofibers: water vapor-induced structural changes and their effects on the behavior of normal human cells

Nanofibrous non-woven matrices were prepared by electrospinning a regenerated silk fibroin (SF) solution, and the structural changes of SF nanofibers treated with water vapor were investigated using time-resolved IR and (13)C CP/MAS NMR spectroscopy. Conformational transitions of SF from random coil to beta-sheet structures were induced by water vapor treatment and were strongly dependent on the treatment time and temperature. Water vapor treatment provided a useful means of stabilizing the SF nanofiber matrices, resulting in the formation of matrices with a decreased solubility in water and increased mechanical strength. The adhesion and spreading of both normal human keratinocytes and fibroblasts onto the SF nanofiber matrices were also investigated, and the water vapor-treated SF nanofiber matrices showed good cellular compatibility, in comparison with traditional methanol-treated ones. This approach to controlling the conformational changes of SF nanofibers by water vapor treatment may be useful in the design and tailoring of novel materials for biomedical applications, including wound dressings and scaffolds for tissue engineering.     

四川产业结构与就业结构变动关系的实证研究

四川省是农业人口大省,而在西部十二省中四川的经济发展水平处于前列。因此,对四川省产业结构和就业结构的研究对西部乃至全国经济的发展有着重要的意义。为了使四川省产业结构和就业结构之间的关系更加明确,本文运用Granger因果关系检验得出,四川省产业结构变动是引起就业结构变动的原因。在此基础上利用Johansen协整关系检验、线性回归等方法测算出产业结构对就业结构影响程度、做出各产业对就业贡献率的折线图并分析了产业结构与就业结构的偏离度。最后得出结论:第一产业产值的增长不仅无法拉动就业而且对业已存在的剩余劳动力还具有一定的挤出效应,第三产业具有较大的发展空间和吸纳就业的能力,第二产业次之。     

The velocity of sound and compressibility in the melts of Hg-Te system

Liquid Hg-Te system has been investigated as a function of composition and temperature by measuring the velocity of sound. A minimum in the sound velocity as a function of temperature observed for Te persists up to 50 at.% Hg, of which the position increases rather steeply between 20 and 30 at.% Hg. This suggests that the molten HgTe and alloys in the Te-rich side undergo structural changes involving the change in coordination number with increasing temperature, and the crossover of the nature of the chemical bond from p-p to sp³ covalent bond takes place with changing composition. It is concluded that the structural change in liquid HgTe is due to intrinsic nature of bonding of HgTe as a compound. Received 2 September 1998 and Received in final form 16 March 1999     

N-o-tolyl-2-hydroxy-1-naphthaldimine and its NiII complex. Conformational changes of free ligand by chelatation

The main scope of the paper deals with keto/amine-enol/imine tautomerism in the solid state of an N-aryl substituted naphthaldimine and conformational changes of this ligand after coordinating to the nickel atom. The N-o-tolyl-2-hydroxy-1-naphthaldimine (I) crystallizes in the orthorhombic space group P 2₁2₁2₁ with cell dimensions a = 7.8641(4), b = 12.712(1), c = 13.853(1) Å and corresponding bis-bidentate nickel complex (II) in the monoclinic space group P 2₁/c and unit cell dimensions a = 7.436(3), b = 22.050(5), c = 8.643(4) Å, = 95.05(6)°. In the nonplanar molecule of (I) the presence of the enol tautomer is found. In (II) the metal atom has the characteristic square-planar coordination with Ni^II on crystallographically imposed inversion centers. Two naphthaldimine moieties are not coplanar showing stepped conformation with step height 1.034 Å.     

Infrared and Raman spectra of 2,4-dimethylaniline

The infrared spectra of 2,4 dimethylaniline have been recorded in the region 3600-100 cm⁻¹. The Raman spectra with polarization measurements have been recorded and investigated for the first time in the region 3500-100 cm⁻¹. New frequency assignments have been proposed assuming the molecule to possess an approximateC ₂ symmetry. Fifty normal modes of the molecule, out of a possible fifty four modes, have actually been observed and assigned including twenty seven hitherto unreported frequencies. The observed spectral changes give evidence of the presence of an intermolecular hydrogen bonding of an N−H...N type, and suggest a solid-solid phase transition between 223 and 123 K in the molecule.     

The effects of stretching on wool fibres as monitored by FT-Raman spectroscopy

FT-Raman spectroscopy coupled with amide I band deconvolution was used to monitor the conformational changes of the peptide backbone of sulphite pre-treated wool fibres during stretching. The spectral changes observed are consistent with the transition of -helical to β-pleated sheet structure. These changes, which are most rapid during the early stages of stretching, can be related to protein secondary structure at both the crystalline and molecular levels. Analysis of the amide III region of the spectra reveals that a very small amount of additional disorder is imparted to the peptide backbone as a result of stretching. The consistency in the widths at half-height of the amide I band components implies that stretching does not significantly change the distribution of peptide chain conformations. From the Raman analysis of cells isolated from the stretched fibres, it is evident that conformational changes occur in both the cuticle and cortex. The most evident change, however, is in the cortical cells.