Intra mode decision and frame layer Lagrange multiplier adjustment scheme for H.264 based on structural similarity

H.264 takes rate distortion optimisation (RDO) technique to perform intra and inter mode decision and achieves higher coding efficiency, but the objective distortion metric such as mean square error (MSE) is employed in traditional RDO framework, which cannot acquire optimal subjective quality. In this paper, structural similarity (SSIM)-based subjective distortion is applied to RDO-based intra mode decision in H.264 I frame video coding, and a linear SSIM distortion model is firstly proposed and SSIM-based rate distortion cost function for intra mode decision is defined. Furthermore, a content adaptive frame layer Lagrange multiplier adjustment scheme is proposed to balance the tradeoff between rate and SSIM distortion better. Experimental results show that, the proposed method encodes image structural information more effectively and thus acquires better perceptual quality and subjective RDO performance compared with objective distortion-based RDO method. Under the same perceptual quality, our scheme achieves about 8·03% I frame bit rate reduction on average for various sequences over MSE-based RDO employed in JM reference software.     

Fracture behavior of stitched warp-knit fabric composites

Pilot studies are conducted to characterize the macroscopic fracture resistance behavior using linear elastic fracture mechanics and attempt to quantify the fracture parameters in which may govern the fracture and failure patterns of stitched warp-knit fabric composites. Methods based on the J-integral method and Betti's reciprocal theorem in extracting the fracture parameters, critical stress intensity factors, T-stress, and the second term of _y(r,0) near the crack tip prior to fracture initiation are formulated. Two fracture criteria, [_c,r _c] and [_c,r _c] are attempted to characterize the failure initiation for the fiber-dominated failure mode and self-similar crack extension in a given thickness of the laminate. Based on linear elastic fracture mechanics principle, these criteria are transformed into crack-driving forces [K _Q,T] and [K _Q,g ₃₂]. The two-parameter fracture criteria, [K _Q,T] and [K _Q,g ₃₂] provide a good correlation for the CCT and SENT specimens, but not for the high constraint CT specimens. With the limited experimental data, the results tend to show that the large tensile T-stress and large magnitude of negative g ₃₂ may inhibit the crack extension in the same crack plane and promote crack kinking.     

Microstructure and microwave dielectric properties of Ba(Mg1/3Nb2/3)O3–MgO composite ceramics with nano-silica added

Ba(Mg_1/3Nb_2/3)O₃–MgO composite ceramics were prepared by solid-phase method. The ceramic exhibited the 1:2 ordered structure. By adding a proper amount of MgO, the permittivity decreased rapidly compared with other Ba(Mg_1/3Nb_2/3)O₃-based ceramics. The Q?×?f values of the samples were greatly improved by nano-silica. Raman spectra showed that the permittivity and Q?×?f value showed a strong correlation with Raman shift and full width at half maximum of the A_1g(O) phonon mode, respectively. The Raman shift of A_1g(O) was consistent with the variation trend of permittivity. And the full width at half maximum of the A_1g(O) phonon mode had a negative correlation with the Q?×?f value. The results showed that upon adding 1.5 wt% nano-silica to the ceramics, the ceramics sintered at 1550 °C for 5 h had the lowest Raman shift and the narrowest full width at half maximum, achieving the best microwave dielectric properties: ε_r?=?22.22, Q?×?f?=?80,436 GHz, τ_f?=?–?5.89 ppm/°C.

     

Quality of beam in the integer resonances crossing in a cyclotron

It is shown that the crossing of the integer resonance Q_r = 2 in an isochronous cyclotron is accompanied by the distortion of the closed orbit only. The amplitude of free radial oscillations of a beam is attenuated adiabatically and the radial emittance is constant in the course of acceleration.     

Constraint‐corrected J–R curve based on three‐dimensional finite element analyses

Three‐dimensional (3D) finite element analyses are carried out on single‐edge bend [SE(B)] specimens for which the J‐integral resistance curves (J–R curves) have been experimentally determined to develop the constraint‐corrected J–R curves for the X80 grade pipe steel. The constraint parameters considered in this study include Q_HRR, Q_SSY, Q_{SSY_m}, Q_LM, Q_BM1, Q_BM2, A₂, h and T_z. The constraint‐corrected J–R curves were developed on the basis of the constraint parameters obtained from finite element analysis and experimentally determined J–R curves associated with deeply cracked and medium‐cracked SE(B) specimens and validated against shallow‐cracked SE(B) specimens. The analysis results indicate that all the constraint parameters considered in this study except Q_HRR, Q_SSY, Q_{SSY_m} and Q_LM lead to reasonably accurate constraint‐corrected J–R curves if the crack extensions are relatively small (≤0.7 mm). For larger crack extensions (≤1.5 mm), the Q_BM1‐based constraint‐corrected J–R curve leads to the most accurate predictions of J among all the constraint parameters considered.     

X-ray diffraction study of amorphous Al77.5Mn22.5 and Al56Si30Mn14 alloys

The structure of amorphous sputtered Al_77.5Mn_22.5 and as-spun Al₅₆Si₃₀Mn₁₄ alloys is investigated by X-ray diffraction. Some distinct features are observed in the intensity profile, i.e. a pronounced prepeak atQ = 16 nm^–1 in both the alloys and a shoulder at the low-Q side in Al-Si-Mn. Also in the radial distribution functions, the first peak has a shoulder at the high-r side. This experimental evidence suggests the presence of a strong chemical short-range order persisting in the phase.     

Higher‐order extensions of a discontinuous Galerkin method for mid‐frequency Helmholtz problems

Recently, a discontinuous Galerkin method with plane wave basis functions and Lagrange multiplier degrees of freedom was proposed for the efficient solution of Helmholtz problems in the mid‐frequency regime. In this paper, this method is extended to higher‐order elements. Performance results obtained for various two‐dimensional problems highlight the advantages of these elements over classical higher‐order Galerkin elements such as Q₂ and Q₄ for the discretization of interior and exterior Helmholtz problems. Copyright © 2004 John Wiley & Sons, Ltd.     

Intrinsic Electron Paramagnetic Resonance in La2?xSrxCuO4: Manifestation of Three Spin Polarons

Electron-Paramagnetic-Resonance (EPR) measurements on La_2–x Sr _x CuO₄single crystals provide experimental evidence of a three-spin polaron of twoCu²⁺ ions and one p hole. The symmetry properties and the peculiartemperature dependence of the g-value of the EPR line indicate the presenceof a dynamical Jahn–Teller distortion (Q ₂-mode) and formation of acollective mode of polarons and surrounding strongly correlated Cu ions(bottleneck regime).     

Ultrahigh-temperature deformation of high-purity HIPed Si3N4

High-temperature tensile deformation behavior of high-purity HIPed silicon nitride material was investigated in the temperature range between 1600°C and 1750°C. Recoverable anelastic and non-recoverable deformation was observed in high-purity HIPed silicon nitride. A power-law deformation model analogous to rheological models was used to distinguish the different deformation components. A stress exponent n = 1.64 and an activation energy Q ₁ = 708 kJ/mol was determined for the non-recoverable deformation. For the anelastic deformation a stress exponent p = 4 and an activation energy Q ₃ = 619 kJ/mol was observed. Diffusional creep and grain boundary sliding with the accomodation process responsible for the anelastic component are discussed as deformation mechanisms.     

Exceedingly Small Gadolinium Oxide Nanoparticles with Remarkable Relaxivities for Magnetic Resonance Imaging of Tumors

Gd chelates have occupied most of the market of magnetic resonance imaging (MRI) contrast agents for decades. However, there have been some problems (nephrotoxicity, non‐specificity, and low r₁) that limit their applications. Herein, a wet‐chemical method is proposed for facile synthesis of poly(acrylic acid) (PAA) stabilized exceedingly small gadolinium oxide nanoparticles (ES‐GON‐PAA) with an excellent water dispersibility and a size smaller than 2.0 nm, which is a powerful T₁‐weighted MRI contrast agent for diagnosis of diseases due to its remarkable relaxivities (r₁ = 70.2 ± 1.8 mM^?1 s^?1, and r₂/r₁ = 1.02 ± 0.03, at 1.5 T). The r₁ is much higher and the r₂/r₁ is lower than that of the commercial Gd chelates and reported gadolinium oxide nanoparticles (GONs). Further ES‐GON‐PAA is developed with conjugation of RGD2 (RGD dimer) (i.e., ES‐GON‐PAA@RGD2) for T₁‐weighted MRI of tumors that overexpress RGD receptors (i.e., integrin α_vβ₃). The maximum signal enhancement (ΔSNR) for T₁‐weighted MRI of tumors reaches up to 372 ± 56% at 2 h post‐injection of ES‐GON‐PAA@RGD2, which is much higher than commercial Gd‐chelates (<80%). Due to the high biocompatibility and high tumor accumulation, ES‐GON‐PAA@RGD2 with remarkable relaxivities is a promising and powerful T₁‐weighted MRI contrast agent.     

Crack-tip constraint in mode II deformation

Studies of cracked specimens loaded in mode I have shown that the stresses near the crack tip depend significantly on the level of constraint. The stresses can be determined near the crack tip using the HRR solution, but only for high constraint specimens. For other levels of constraint, O'Dowd and Shih's Q parameter may be used to adjust the stresses derived from the HRR solution. Only limited research has been carried out to study the effect of constraint in mode II. In this paper a mode II boundary layer formulation is used to study the effect of far field elastic stresses on the size and shape of the plastic zone around the crack tip and on the stresses inside the plastic zone. It is shown that in mode II, both positive and negative values of remote T-stress influence the tangential stress along the direction of maximum tangential stress. In the spirit of O'Dowd and Shih, a dimensionless parameter Q _II is introduced to quantify the constraint for mode II specimens failing by brittle fracture. The relation between Q _II and T/₀ is determined for different values of the strain hardening coefficient n. To investigate the range of validity of the Q–T diagram for real specimens, the constraint parameter Q _II is calculated directly from finite element analysis for three mode II specimens and compared with the evaluation using the Q–T diagram.     

Fabry–Pérot Oscillation and Room Temperature Lasing in Perovskite Cube‐Corner Pyramid Cavities

Recently, organometal halide perovskite‐based optoelectronics, particularly lasers, have attracted intensive attentions because of its outstanding spectral coherence, low threshold, and wideband tunability. In this work, high‐quality CH₃NH₃PbBr₃ single crystals with a unique shape of cube‐corner pyramids are synthesized on mica substrates using chemical vapor deposition method. These micropyramids naturally form cube‐corner cavities, which are eminent candidates for small‐sized resonators and retroreflectors. The as‐grown perovskites show strong emission ≈530 nm in the vertical direction at room temperature. A special Fabry–Pérot (F–P) mode is employed to interpret the light confinement in the cavity. Lasing from the perovskite pyramids is observed from 80 to 200 K, with threshold ranging from ≈92 µJ cm^?2 to 2.2 mJ cm^?2, yielding a characteristic temperature of T₀ = 35 K. By coating a thin layer of Ag film, the threshold is reduced from ≈92 to 26 µJ cm^?2, which is accompanied by room temperature lasing with a threshold of ≈75 µJ cm^?2. This work advocates the prospect of shape‐engineered perovskite crystals toward developing micro‐sized optoelectronic devices and potentially investigating light–matter coupling in quantum optics.     

Threshold and growth mechanism of fatigue cracks under mode II and III loadings

ABSTRACT The fatigue crack growth behaviour of 0.47% carbon steel was studied under mode II and III loadings. Mode II fatigue crack growth tests were carried out using specially designed double cantilever (DC) type specimens in order to measure the mode II threshold stress intensity factor range, ΔK_IIth. The relationship ΔK_IIth > ΔK_Ith caused crack branching from mode II to I after a crack reached the mode II threshold. Torsion fatigue tests on circumferentially cracked specimens were carried out to study the mechanisms of both mode III crack growth and of the formation of the factory‐roof crack surface morphology. A change in microstructure occurred at a crack tip during crack growth in both mode II and mode III shear cracks. It is presumed that the crack growth mechanisms in mode II and in mode III are essentially the same. Detailed fractographic investigation showed that factory‐roofs were formed by crack branching into mode I. Crack branching started from small semi‐elliptical cracks nucleated by shear at the tip of the original circumferential crack.     

Study on creep deformation mechanism of 316LN stainless steel from impression creep tests

Abstract

Impression creep tests were carried out on 316LN stainless steel (SS) at various temperatures in the range 898–973 K. The stress dependence of the steady state impression velocity followed the power-law with stress exponent n?=?6. The temperature dependence of the steady state impression velocity obeyed Arrhenius type rate equation. The apparent activation energy for creep deformation (Q_c) was estimated to be 500 kJ mol^?1. Based on the n and Q_c values, it is concluded that the rate controlling mechanism is dislocation creep.     

Grain boundary sliding behaviour of copper and alpha brass at intermediate temperatures

The role of grain boundary sliding in copper and Cu-30% Zn in the temperature range 0.50 to 0.72T _m, whereT _m is the absolute melting point of the material, is examined. First, sliding data obtained on these materials are presented. These results indicate that the stress exponent for sliding,n _gbs, is similar to that for lattice deformation, while the activation energy for sliding,Q _gbs, varies between about 0·5Q _c and 1.6Q _c, whereQ _c is the activation energy for creep. Next, a comparison of the published values ofQ _gbs for bicrystals and polycrystals suggests that grain boundary sliding in polycrystalline materials requires the accommodation of the sliding process, whereas in bicrystals, the absence of triple points and other grain boundaries results in intrinsic sliding. Finally, several models proposed for grain boundary sliding are discussed, and it is shown that they do not account for the observed results on copper and alpha brass. A phenomenological model is proposed, where it is assumed that grain boundary sliding results from the glide of dislocations on secondary slip planes.     

A direct estimate of JIc from the load versus load-line displacement record

The purpose of this study is to examine the current standard fracture toughness test procedure to determine if there could be an easier method to get a J_Ic value from the test record. The current method for determining J_Ic involves a detailed computational and construction procedure. The objective in this study is to simplify the analysis for the determination of J_Ic. The results of this study show that the load and displacement record for a fracture toughness test can be used to directly estimate a J_Q value, a provisional value for fracture toughness, J_Ic. The J value taken at the maximum load point can be used along with an adjustment factor to estimate a J_Q value. This J_Q estimate is close to the one obtained from the construction procedure of ASTM Standard E 1820. When a unit‐sized specimen is tested, that is, a specimen with a width of 50 mm and a thickness of 25 mm the maximum load point provides a direct estimate of J_Q. Other sizes require a size adjustment factor, which is simply a square root relationship between the width of the test specimen and a unit width. The proposed new method of estimating J_Q is simple in concept and requires a minimum number of calculations. It appears to produce values of J_Q which are comparable to those obtained from the ASTM E1820 construction procedure and may produce less scatter.     

Near‐threshold behaviour of shear‐mode fatigue cracks in metallic materials

This review paper presents a brief state‐of‐the art of the research on long fatigue shear‐mode cracks and describes some recent results on effective crack growth thresholds and mode I branching conditions achieved by the authors for ARMCO iron, titanium with two different microstructures, nickel and stainless steel. A special technique for preparation of fatigue precracks enabled us to substantially suppress the crack closure (friction) effects at the beginning of the experiment, and the measured threshold values could be considered to be very close to the effective ones. In all investigated materials, the effective thresholds under the remote mode II loading were found to be about 1.7 times lower than those under the remote mode III loading. Effective thresholds under mode II loading of investigated materials were found to follow a simple formula assembled by the shear modulus G, the magnitude of Burgers vector b and a goniometrical function n_α of the mean deflection angle that depends on the number of available crystallographic slip systems. These quantities determine the intrinsic material resistance to mode II crack propagation at the threshold. A simple criterion for mode I branching in terms of effective threshold values well reflects a transition from the shear‐mode to the opening‐mode controlled crack propagation at the threshold. The associated transition deflection angle of 40° is a material independent constant.     

Study of influence of gamma prime and eta phases on corrosion behaviour of A286 superalloy by using electrochemical potentiokinetic techniques

This work studies the influence of gamma prime and eta phases, resulting from precipitation hardening, on the corrosion behaviour of A286 superalloy by using electrochemical potentiokinetic reactivation (EPR) and double loop electrochemical potentiokinetic reactivation (DLEPR). The general trend is that I_r, Q_r, I_r/I_a and Q_r/Q_a increase with aging temperature and, for a given aging temperature, with aging time, which is consistent with the fact that gamma prime precipitate may cause discontinuities in the passive layer. I_r, Q_r, I_r/I_a and Q_r/Q_a reach a peak, which alters the general trend, for both aging temperatures (670 and 720 °C), at the aging time from which there is evidence of the presence of eta phase at grain boundary (GB). Gamma prime and eta precipitates can cause the passive layer that forms on them to become more unstable and, consequently, cause the current density through the passive layer and the susceptibility to localized corrosion attack to increase.     

Reduction in sintering temperature and tunable microwave dielectric properties in NaCa4V5O17 via compositional engineering

Some Li⁺-substituted NaCa₄V₅O₁₇ ceramics were designed and fabricated by the solid-state reaction method. Effects of cation doping on the sintering behavior, crystal structure, microstructure, and dielectric properties were systematically studied. As expected, Li⁺ substitution effectively reduced the densification temperature of NaCa₄V₅O₁₇ ceramics and lower the relative permittivity (ε_r), but surprisingly increased the quality factor (Q×f). A composition with 20?mol% Li⁺ dopants exhibits the highest Q×f?=?66,000?±?124?GHz coupled with an ε_r of 10.4?±?0.1 and a τ_f of ? 81.3?±?1.4?ppm/°C. Such compositional dependence in dielectric properties was analyzed in terms of ionic polarization and packing fraction.