Magnetic and optical properties of cobalt nanowires fabricated in polycarbonate ion-track templates

Cobalt nanowires with diameter 75 nm were synthesized in ion track-etched membranes by electrochemical deposition. Scanning electron microscopy displays cylindrical wires with smooth and homogeneous contours. X-ray diffraction studies indicate that the wires possess a face centered cubic structure and a preferred growth orientation along the [1 1 0] direction. The wires exhibit magnetic anisotropy, which is observed and is ascribed to shape anisotropy. The optical extinction spectrum shows a band which probably originates from a surface plasmon resonance.     

Reliability analysis of in-situ stress measurement using circumferential velocity anisotropy

In-situ stress measurement for deep reservoir formation is difficult in terms of security, reliability and technique. Acoustic velocity anisotropy test is a basic method for stress measurement of rock cores, which is based on the distribution of acoustic velocity in different directions around rock cores. The heterogeneity of core samples, such as fractures and gravel contained, can also lead to wave velocity anisotropy. Therefore, the corresponding reliability evaluation method is established to exclude some other anisotropy factors caused by non-tectonic stresses. In this paper, the reliability of testing results is evaluated from three aspects, i.e. phase difference, anisotropy index and waveform, to remove the factors caused by non-tectonic stresses.     

Accelerated convergence for a normal state layered superconductor’s transverse resistance expression,measured with strip contacts

The expression of the transverse resistance for an ohmic parallelepipedic layered conductor, measured with strip contacts, extended along its width, is a slowly convergent series. This series is reworked and transformed to the sum of an analytical part and an exponentially convergent series, which reduces considerably the number of terms needed for the numerical evaluation. In addition, an asymptotic formula is obtained, valid for Γ < 2, Γ is the effective anisotropy. This formula is used to determine the room temperature resistivity anisotropy of two small Γ layered superconductors, which are 2H–NbSe₂ and 2H–TaSe₂.     

An experimental and theoretical study of the carbazole to carbazole intramolecular energy transfer in N‐vinylcarbazole/vinyl tert‐butyl‐benzoate copolymers of different molar compositions

Fluorescence depolarization and quenching measurements of N‐vinyl carbazole/vinyl tert‐butyl‐benzoate copolymers in dilute solution of several fluid solvents and in a rigid poly(methyl methacrylate) matrix were performed to study the effect of copolymer composition on the intramolecular energy transfer (IET) between carbazole groups (Cz) along the polymer chain. IET efficiency, as the amount of Cz? Cz intramolecular excimer formation, monotonically increases with Cz content up to a number average sequence length of carbazole of ca 12 (Cz molar content ≥ 90%). After this value, IET efficiency remains almost constant. Molecular dynamics simulations on isotactic and syndiotactic copolymer fragments of several monomer compositions were used for obtaining different parameters related to the efficiency for the IET process between Cz units along the polymer chain. Copyright © 2011 Society of Chemical Industry     

预应变对高钢级管线钢延性的影响

通过对X100管线钢原始状态和预应变状态钢材取光滑拉伸试样(ST)和缺口拉伸试样(NT),并分别在纵向(L)和横向(T)加载,研究了各试样应力-应变、应力-直径缩减量等的变化情况.结果表明,高钢级管线钢表现出了塑性的各向异性、各向同性和随动强化等特性.此外,通过数值模拟和分析,对不同加载状态下的试样建立了可以表现各向异...     

Modifying the structure and properties of polyethylene foams using thermal treatments

BACKGROUND: The physical properties of polymer foams depend on many factors: density, cellular structure, matrix polymer morphology, etc. Therefore, these properties can be adapted by appropriate control of the structure. However, this simple and attractive concept has some limitations because the cellular structure of foams cannot be fully controlled during manufacturing. Therefore, in order to make possible the control of properties, it is highly desirable to develop simple procedures, such as thermal treatments, to modify the cellular structure. In the work reported, low‐density polyethylene foams were thermally treated at temperatures below the melting temperature of the base polymer. The cellular structure, polymer base morphology and several thermal and mechanical properties were studied before and after the thermal treatments. RESULTS: It is shown that the anisotropy of the cellular structure is reduced by using adequate treatments. This modification of the structure influences physical properties that are sensitive to the cell shape, such as thermal expansion, elastic modulus and collapse stress. CONCLUSION: A simple procedure to allow further control of the structure and properties of polyethylene‐based foams has been presented. The use of adequate thermal treatments is able to modify the cellular structure and hence the physical properties of these materials. Copyright © 2009 Society of Chemical Industry     

金属薄板带应变硬化指数和厚向异性指数测定方法

介绍了应变硬化指数n值和厚向异性指r值的物理意义和几种不同的测定方法，具有一定的实践指导意义。     

Atomistic studies of stress effects on self-interstitial diffusion in α-titanium*

The diffusion anisotropy of intrinsic point defects is an important factor governing the behavior of the HCP metals bombarded by energetic particles. The effects of stress on the diffusion and its anisotropy, although known to be important, have not been well understood. In this paper, we use a combination of molecular dynamics and molecular statics methods to investigate energy states of a self-interstitial in α-titanium, a typical HCP metal. Our calculation shows that the most stable configuration of the self-interstitial is the basal-split dumbbell configuration on the basal plane. Compression along the [0001] or the [1ˉ100] directions leads to an insignificant change in the migration energies, while compression along the [11ˉ20] direction leads to a larger migration energy. A significant change of the diffusion anisotropy is observed when a uni-axial compressive stress of 200 MPa is applied along the [11ˉ20] direction. Similar stress along the other two directions does not produce substantial changes of the anisotropy. We also show that an applied hydrostatic stress can significantly change the diffusion anisotropy of HCP metals and alloys. Thus, under irradiation, a hydrostatic stress can produce a significant creep-like deformation (i.e., with a deviatoric strain rate) through a stress-dependent change of the growth rate. This revised version was published online in June 2006 with corrections to the Cover Date.     

Temperature dependence of single-crystal elastic constants of Mo(Si,Al)2

The temperature dependence of single-crystal elastic constants of Mo(Si,Al)₂ with the hexagonal C40 structure has been measured by the rectangular parallelepiped resonance method over the temperature range from room temperature to 1373 K. The silicide has the largest value of Poisson's ratio among transition-metal silicides with the C40 structure. This is interpreted in terms of the reduced directionality in atomic bonding due to the partial substitution of Al for Si atoms. The expression of the elastic constants on the basis of simple interatomic interactions cannot reproduce the elastic anisotropy of crystal with the C40 structure. The disagreement is considered to be a consequence of the occurrence of internal displacements during elastic deformation in crystals with the non-centrosymmetry.