Charge carrier transport in Cu(COOH)2 organic molecular single crystal

The temperature dependences of the d.c. electrical conductivity (σ) and thermoelectric power (TEP) of low-dimensional Cu(COOH)₂ single crystal have been studied. The electrical conductivity is highly anisotropic (σ_‡/σ = 3.0 × 10²) and the crystal undergoes a Peierls transition at 208 K and two polymorphous phase transitions, namely → β and β → at 327 and 377 K respectively. The conductivity in this crystal is found to be mainly due to a non-adiabatic hopping mechanism. TEP measurements carried out at various temperatures show that the conductivity is due to the mobility of holes.     

Microstructure evolution during annealing of an amorphous TiAl sheet

An amorphous, 150 μm thick freestanding sheet of a TiAl-based alloy was produced by physical vapor deposition (PVD). The following phase transformations were observed after different stages of crystallization of the amorphous sheet and analyzed using differential thermal analysis, X-ray diffraction, and transmission electron microscopy: amorphous→body centered cubic (β)→hexagonal close-packed ()?→tetragonal (γ)+ordered ₂. The β phase was formed as near-spherical particles that were evenly distributed in the amorphous phase and the size of these particles was approximately 90 nm. Formation of the phase by decomposition of β and the remaining amorphous phases led to a very fine feathery-like microstructure arranged in colonies of approximately 100 nm in size. Interface boundaries between the phase particles were poorly defined. The transformation of the metastable phase into a mixture of the γ and ₂ phases led to formation of an equiaxed γ-grain structure with the grain size of approximately 150 nm.     

The electric and dielectric properties of a coal tar epoxy coating

The dielectric properties of a coal tar epoxy coating on a steel surface in a dry dielectric layer, metal/organic coating/metal (MOCM) structures, as well as in electrochemical systems, metal/organic coating/electrolyte (MOCE), have been investigated by means of impedance spectroscopy. The influence of temperature and chemically-different contacting electrolytes on the electrical properties of the organic coating are discussed on the basis of the frequency-dependent impedance modulus ωZ(ω)ω and the phase angle Θ(ω) which are both accessible through measurements. The results are presented in the form of Bode plots. It was possible to model the measured values of the modulus by the linear relation lnωZ(ω)ω = K−n ln ω and in terms of Kramers-Kronig (KK) relations. It was shown that the poles and residues of the KK integrand [lnωZ(ω)ω/(ω²−ω²_c)] suffice to establish Θ(ω) uniquely. This means that if the modulus in the Bode plot can be represented by a linear relation with a slope -n, the phase angle is frequency-independent. The experimental results for Θ(ω) are in good agreement with this prediction for a dry (MOCM) and an electrochemical system (MOCE).     

Effect of ferroic domain pattern changes on the Raman spectra of some ferroic crystals

The influence of changes in the pattern of ferroic domain structure on the Raman spectra of β-LiNH₄SO₄ and (NH₄)₃H(SO₄)₂ single crystals were studied. It was shown that the Raman spectra of β-LiNH₄SO₄ passed from the ferroelastic phase differ from those of “as-grown” crystal and those of the crystal, which was in the paraelectric phase. Significant changes could be observed in the Raman bands related to triply degenerated ν₃ and ν₄ vibrations of the SO₄ tetrahedron. Detailed temperature studies of the Raman spectra of β-LiNH₄SO₄ close to the paraelectric–ferroelectric phase transition, exhibit anomaly of some internal vibrations of SO₄ in the temperature range where a regular large-scale structure is observed. Different types of evolution of the ferroelastic domain structure and temperature behaviour of the donor and acceptor vibrations were shown while heating and cooling the (NH₄)₃H(SO₄)₂ crystal. Different values of temperature hysteresis were found in temperature studies of the ferroelastic domain structure (ΔT_S  3–5 K) and in Raman spectra studies (ΔT_S  12 K). No changes were observed in the pattern of ferroelastic domain structure at the temperature T_II–III  265 K, at which C2/c → P2/n structural phase transition takes place. On the other hand, at T_III–IV  135 K additional domains with W′-type of domain wall orientation were found.     

The dependence of penetration velocity on impact velocity

Recent experimental measurements show that eroding long-rod penetration velocity is a linear function of impact velocity over a very wide range of impact velocities and for an interesting range of rod–target material combinations. These experiments all show that U=a+bV, where U and V are the penetration and impact velocity, respectively, and “a” and “b” are constants for given projectile and target materials. Numerical simulations also show that U=a+bV. The accumulation of these results suggests that a linear relationship between penetration and impact velocity may be fundamental over a very large range of impact velocities. A linear relationship between penetration and impact velocity has a number of implications. Some implications of this result for the Tate–Alekseevskii model are briefly examined in this paper.     

Computer simulation of martensitic textures

We consider a Ginzburg-Landau model free energy F(ε, e₁, e₂) for a (2D) martensitic transition, that provides a unified understanding of varied twin/tweed textures. Here F is a triple well potential in the rectangular strain (ε) order parameter and quadratic e₁², e₂² in the compressional and shear strains, respectively. Random compositional fluctuations η(r) (e.g. in an alloy) are gradient-coupled to ε, ˜ − ∑_rε(r)[(Δ_x² − Δ_y²)η(r)] in a “local-stress” model. We find that the compatibility condition (linking tensor components ε(r) and e₁(r), e₂(r)), together with local variations such as interfaces or η(r) fluctuations, can drive the formation of global elastic textures, through long-range and anisotropic effective ε-ε interactions. We have carried out extensive relaxational computer simulations using the time-dependent Ginzburg-Landau (TDGL) equation that supports our analytic work and shows the spontaneous formation of parallel twins, and chequer-board tweed. The observed microstructure in NiAl and Fe_xPd_{1 − x} alloys can be explained on the basis of our analysis and simulations.     

M-subshell ionization of U by light-ion bombardment

M X-rays of U were produced by proton, deuteron and alpha-particle bombardment in the energy range of 0.20–1.00 MeV/u. N_6,7 → M₅ (M), N₆ → M₄ (M_β), N₅ → M₃ (M_γ), N₄ → M₂ and N₂ → M₁ line yields were obtained from a least-squares fit to the spectra and used to convert M X-ray production into M-subshell ionization cross sections. The uncertainty induced by the atomic parameters (X-ray fluorescence yields, Coster-Kronig and radiative transition rates) used in the conversion is discussed. The subshell ionization cross sections are then compared to PWBA values corrected for Coulomb deflection and energy loss according to Brandt and Lapicki, to the semiclassical theoretical values of Kocbach and to relativistic PWBA results, corrected for Coulomb and binding effects, of Chen et al. Intrashell transitions induced by the projectile and multiple ionization are suggested as causes of disagreement between theory and experiment, especially for alpha-particles. It is concluded that theory must go beyond the simple picture of the first-order perturbation approximation to explain M-subshell results and that care must be taken in the choice of wave functions.     

Inference of critical cod from Charpy V test result

Correlation between the Charpy absorbed energy and critical COD is investigated to obtain a useful method for estimating critical COD from Charpy V data. The round bar tension test, Charpy V-notch test and static 3-point bend test with fatigue notched specimen are carried out using mild steel, 785 MPa grade high strength steel and A5083 aluminum alloy. Correlation is found between W'_c/σ_Y and δ_c as well as between EW'_c/σ_Y² and Eδ_c/σ_Y, where W'_c is the Charpy absorbed energy obtained by considering temperature difference between the Charpy transition temperature and COD transition temperature. The symbols σ_Y, δ_c and E are yield strength, critical COD and Young's modulus, respectively. The correlations are established for various kinds of metals and over a wide temperature range including not only upper shelf range but also the transition range.     

Microstructural changes inside the lamellar structures of alloy ZA27

The microstructural changes inside the lamellar structure of the cast and aged alloy ZA27 were studied using TEM, XRD and SEM techniques. Using TEM, the network of transitional phase η_m^′ was determined to be of an fcc crystal structure inside the lamellae η phase during ageing at 150 °C. The mechanism of the decomposition of the η phase lamellae can be summarized as follows: η → η_m^′ + η′ →  + η. The adjacent co-existence of the ε phase and the T′ phase inside the phase lamellae confirmed that a four phase transformation,  + ε → T′ + η, had occurred during the prolonged ageing.     

(1-x)K0.48Na0.52NbO3-xBi0.45Nd0.05(Na0.92Li0.08)0.5ZrO3无铅压电陶瓷相结构及压电性能

为了在获得较高压电性能的同时又不大大降低陶瓷的居里温度(T_C), 设计和制备了Bi_0.45Nd_0.05(Na_0.92Li_0.08)_0.5ZrO₃改性的K_0.48Na_0.52NbO₃系无铅压电陶瓷((1-x)KNN-xBNNLZ), 研究了BNNLZ含量对KNN基无铅压电陶瓷相结构和电学性能的影响。研究结果表明, 所有陶瓷样品均具有较高的居里温度T_C(>300℃)。随着BNNLZ含量的增加, 陶瓷的正交-四方相变温度(T_O-T)不断向低温方向移动, 而三方-正交相变温度(T_R-O)不断向高温方向移动, 最终在陶瓷中形成了三方-四方(R-T)共存相, R-T共存相处于0.05<x<0.07范围。BNNLZ的加入引起陶瓷相结构的演化改变导致压电常数(d₃₃ )、介电常数(ε_r )、剩余极化强度 (P_r )和机电耦合系数(k_p )都先增大后减小, 当x=0.06时陶瓷具有最佳压电性能: d₃₃=313 pC/N, k_p=42%, P_r=25.48 μC/cm², ε_r=1353, tanδ=2.5%, T_C=327℃。     

Infrared absorption and Zeeman effect in Nd doped YVO4

Low temperature infrared transmission studies of Nd³⁺ doped YVO₄ were performed, under a magnetic field B c, in the 1800–8000 cm⁻¹ range of the ⁴I_9/2→⁴I_11/2, ⁴I_13/2, and ⁴I_15/2 Nd³⁺ crystal-field transitions. Good agreement is obtained between the experimental and calculated g-factors. Frequencies of the satellites in the ⁴I_9/2→⁴F_3/2 transitions of the Nd³⁺ isolated ion confirm the presence of ferromagnetic interactions between pairs of coupled Nd³⁺ ions that lift the Kramers doublet degeneracies of their ground state and excited multiplets.     

Characterization, Processing, and Alloy Design of NiAl-Based Shape Memory Alloys

The microstructures and phase transformations in binary Ni-al, ternary Ni-Al-Fe, and quaternary Ni-Al-Fe-Mn shape memory alloys (SMAs) were investigated by light and electron microscopy, electron and X-ray diffraction, and differential scanning calorimetry. The effects of alloying additions (B, Fe, and Mn) on martensite stability, shape recovery, and tensile ductility were also studied. NiAl-based SMAs can be made ductile by alloying with B for enhanced grain boundary cohesion and Fe for improved bulk properties. Iron has the undesirable effect that it decreases the martensite → austenite transformation temperatures (A_p). Fortunately, A_p can be increased by decreasing the “equivalent” Al content of the alloy. In this way, a high A_p temperature of 190°C has been obtained without sacrificing ductility. Recoverable strains of 0.7% have been obtained in a Ni-Al-Fe alloy with A_p temperature of 140°C. Manganese additions (2–10%) lower A_p, degrade hot workability, and decrease room temperature ductility. Good-quality, ductile SMA ribbons have been produced by melt spinning. However, additional alloy design is required to suppress the aging-induced embrittlement caused by Ni₅Al₃ formation.     

N-particle dynamics of the Euler equations for planar diffeomorphisms

The Euler equations associated with diffeomorphism groups have received much recent study because of their links with fluid dynamics, computer vision, and mechanics. In this article, we consider the dynamics of N point particles or “blobs” moving under the action of the Euler equations associated with the group of diffeomorphisms of the plane in a variety of different metrics. This dynamical system is already in widespread use in the field of image registration, where the point particles correspond to image landmarks, but its dynamical behavior has not previously been studied. The 2-body problem is always integrable, and we analyze its phase portrait under different metrics. In particular, we show that 2-body capturing orbits (in which the distances between the particles tend to 0 as t  → ∞) can occur when the kernel is sufficiently smooth and the relative initial velocity of the particles is sufficiently large. We compute the dynamics of these “dipoles” with respect to other test particles, and supplement the calculations with simulations for larger N that illustrate the different regimes.     

The resistance of silicon carbide to static and impact local loading

The physical nature of the resistance of SiC crystals to static and local impact loading has been examined. Investigation of the temperature dependence of hardness for SiC crystals allows the determination of the characteristic deformation temperature (T* ≈ 1600 K), the parameter that characterizes the degree of covalence in interatomic bonds ( ≈ 6) and the temperature range in which a phase transition under pressure during indentation is possible (T < 800 K). Indentation technique gives possibility to construct stress-strain curves for brittle materials and to determine Hugoniot Elastic Limit. During dynamic penetration of a kinetic projectile into a SiC target the phase transition takes place.     

Heat pump cycles based on the AF–F transition in Fe–Rh alloys induced by tensile stress

The heat-pumping scheme based on the 1st order antiferromagnetism–ferromagnetism transition induced in FeRh alloy by one-dimensional tensile stress is proposed. Using the model S–T diagram for this alloy, the heat-pump cycles are drawn up based both on the transition latent heat absorption and emission when the transition is induced isothermally and on the change in alloy's temperature when the transition is induced adiabatically by applying tensile stress. The calculated values of heat coefficient φ for the cycles are 30 at ΔT=5 К and 20 at ΔT=10 К, where ΔT is the difference between the temperature surrounding and that of the heat receiver. These values are achieved using the tensile stress of 1·10⁹ Pa. The high values of φ make it possible to consider Fe–Rh alloys near the equiatomic composition as an effective refrigerant for elastocaloric heat-pumping near the room temperature.     

Influence of stress ratio at baseline loading on delayed retardation phenomena of fatigue crack growth in A553 steel and A5083 aluminium alloy

The delayed retardation phenomena of fatigue crack growth following a single application of tensile overload were investigated under the baseline loading with the stress ratio, R = σ_min/σ_max, ranging from −1 to 0.5 for A553 steel and A5083 aluminium alloy. Two different overload cycles were applied; the one is the case that the ratio of peak stress range to baseline stress range, r = Δσ₂/Δσ₁, is equal to two and the other is the case that the ratio of maximum peak stress to maximum baseline stress, σ_2max/σ_1max, is equal to two. The retardation took place stronger in aluminium than in steel. Under the condition of r = 2 the normalized number of cycles, N_D/N_C, (N_D: the number of cycles during retardation, N_C: the number of cycles required for propagation through the overload-affected-zone size) decreased slightly as the R ratio increased from −1 to 0.5, while under the condition of σ_2max/σ_1max = 2 the N_D/N_C-values increased drastically as the R ratio increased from −1 to 0 (or the overload ratio, r, increased from 1.5 to 2) in both the materials. These retardation behaviors were expressed theoretically according to the model proposed by Matsuoka and Tanaka [1, 3] by using four parameters: the overload ratio, r, the exponent in Paris equation, m, the overload-affected-zone size, ω_D, and the distance at the inflection point, ω_B.     

Oscillatory and chaotic wakes behind moving boundaries in reaction-diffusion systems

Oscillatory wakes occur in a wide range of reaction-diffusion systems, consisting of either periodic travelling waves or irregular spatiotemporal oscillations, behind a moving transition front. In this paper, the use of a finite boundary moving with an imposed speed to mimic the transition front is considered. For both λ-ω systems and standard predator-prey models, the solutions behind these moving boundaries agree very closely with the behaviour behind transition fronts, provided suitable end conditions are used on the moving boundary. This confirms that the transition front can be regarded as determining the solution, by forcing a particular periodic wave at the boundary of the wake region. In the case of λ-ω systems, a detailed numerical study of solutions on a fixed-length finite domain with a periodic wave solution forced at the boundaries is performed. As the domain length is varied as a parameter, the long-term temporal behaviour undergoes bifurcation sequences that are well known as routes to chaos in ordinary differential equations. This suggests that irregular wakes actually have the form of a perpetual transient in a progression towards chaos. Finally, the way in which the moving boundary results can be used to design an experimental verification of the oscillatory wakes phenomenon in a chemical system is discussed.     

The CPLEAR electromagnetic calorimeter

A large-acceptance lead/gas sampling electromagnetic calorimeter (ECAL) was constructed for the CPLEAR experiment to detect photons from decays of π⁰s with momentum p_π⁰ ≤ 800 MeV/c. The main purpose of the ECAL is to determine the decay vertex of neutral-kaon decays K⁰ → π⁰π⁰ → 4γ and K⁰ → π⁰π⁰π⁰ → 6γ. This requires a position-sensitive photon detector with high spatial granularity in r−, −, and z−coordinates. The ECAL - a barrel without end-caps located inside a magnetic field of 0.44 T - consists of 18 identical concentric layers. Each layer of 1/3 radiation length (X₀) contains a converter plate followed by small cross-section high-gain tubes of 2640 mm active length which are sandwiched by passive pick-up strip plates. The ECAL, with a total of 6X₀ has an energy resolution of and a position resolution of 4.5 mm for the shower foot. The shower topology allows separation of electrons from pions. The design, construction, read-out electronics, and performance of the detector are described.     

Analysis of the temperature dependence of the fracture stress of sharp notched bending specimens of a structural steel with respect to intermediate transitions

The flow and fracture stresses, σ_y^g and σ_f^g (δ = crack tip displacement), of sharply notched bending specimens of a structural steel U St 37-1 are measured in the temperature range from full scale to small scale yielding. The best adaption of the experimental results for σ_f^g is obtained by a curve which exhibits an intermediate transition, i.e. which follows in a temperature range between an upper, T_tM¹ and a lower, T_tl¹, transition temperature to the curve σ_y^g(T) for the flow stress with a constant δ = δ₁. This transition corresponds to that of the slip to the twin nucleated fracture. Two analyses [3,5] according to the local fracture stress, σ_f^*, concept show that the amount and the temperature dependence of σ_f^* are somewhat different for both methods, but that both exhibit an increase of σ_f^* in the transition range. It is concluded that each transition in the nucleation mode of the fracture is connected with such a transition in the fracture stress. It may, however, become indistinct or even be covered by the scatter of the experimental points.     

Optical absorption and emission properties of Er doped mixed alkali borosilicate glasses

This paper presents the optical absorption and luminescence properties of Er³⁺ doped mixed alkali borosilicate glasses: 59.5SiO₂ · 20B₂O₃ · xLi₂O · (20 − x)Na₂O · 0.5Er₂O₃ and 59.5SiO₂ · 20B₂O₃ · xLi₂O · (20 − x)K₂O · 0.5Er₂O₃, with x = 0, 4, 8, 12, 16 and 20 mol%. The variations of Judd–Ofelt intensity parameters (Ω₂, Ω₄, and Ω₆), hypersensitive transition intensities, total radiative transition probability (A_T), radiative lifetimes (τ_R), integrated absorption cross-sections (Σ) and stimulated emission cross-sections (σ_p) as a function of x are discussed in detail. The changes in Ω₂ and intensities of hypersensitive transitions are attributed to optical basicity changes in the host glass matrix, which leads to variations in the covalency of the Er–O bond. The luminescence properties are reported for certain transitions, and the emission cross-section is high at x = 8–12 in the case of lithium sodium glass, whereas in lithium potassium glass it is high at x = 8.