Fracture parameter for thermoinelasticity

A path domain independent integral, S, that equals the energy release rate for an extending crack in a thermoinelastic field is presented. This paper develops the new parameter from its theoretical foundations in continuum mechanics, demonstrates that S can be calculated from finite element results and describes how S can be obtained from experiments.The S-integral is developed for simple uncoupled and linearized fully coupled quasi static thermoinelastic cases. Invoking thermoinelastic continuum mechanics linearized for small strain and small temperature changes, S emanates from a discrete Lagrangian describing the thermoinelastic system and Noether's theorem from classical field theory. S defines the force acting on an extending crack and represents a conservation law for a crack free body analogous to the Budiansky and Rice interpretation of the J-integral.The conservation law nature of S for a singularity free region is demonstrated by both computational and physical experiments. S can be calculated from finite element results via a two step postprocessing algorithm. Furthermore, S can be obtained from physical experiments. The S-integral offers a parameter to improve the understanding of the strength and reliability of materials subjected to thermomechanical loadings.     

化学链燃烧中Co掺杂改性Fe2O3（104）载氧体反应特性

基于密度泛函理论建立金属Co掺杂的铁基载氧体的微观模型,探究掺杂Co后模型表面的电子结构及反应特性的变化。首先,采用Material Studio软件中CASTEP模块构建并优化Fe₂O₃（104）的平板模型;其次,以Co原子分别替换模型表面不同配位数的Fe原子（Fe_5f,Fe_6f和Fe_7f）,构建Co在表面不同Fe原子位的掺杂模型（Co-Fe₂O₃（104））;最后,计算纯净模型和掺杂模型的表面能、掺杂结合能、态密度以及掺杂位点原子的键长、键角和原子间距离等参数,考察CO在Fe₂O₃（104）和Co掺杂的Fe₂O₃（104）表面的等温吸附特性,并以CO分子为探针测试Co掺杂模型和纯净模型表面的氧化反应特性,获取反应路径、过渡态和反应活化能等信息。几何优化结果得到Co掺杂模型的稳定性顺序是：Co_5f-Fe₂O₃（104）> Co_6f-Fe₂O₃（104）> Co_7f-Fe₂O₃（104）,对应的结合能分别为-0.399 eV、-0.215 eV和0.487 eV,Co在Fe_5f和Fe_6f位的掺杂是放热过程,并且在Fe_5f原子位的掺杂时放热较多,而在Fe_7f原子的掺杂属于是吸热反应;Co掺杂改变了掺杂位点相邻O原子的平均键长L_O-M（M代表Fe或Co）,其中Co替换Fe_7f后相邻O原子的L_O-M增加了0.004 4 nm;掺杂Co后模型的总态密度（DOS）均向费米能级（0 eV）方向移动,在-8 eV～0 eV能量范围内离域性增强,而且Co_5f-Fe₂O₃（104）模型体系靠近费米能级左边的填充态能量高于其他模型。等温吸附表明Co掺杂可以提高CO在模型表面的吸附量,并且存在吸附两种方式：-2.0 eV附近的峰为CO模型表面碱性位点的吸附峰,-0.75 eV附近的峰为CO在非碱性位点的吸附峰。CO在Co_5f-Fe₂O₃（104）表面的吸附能（-0.851 eV）最大,而在Co_7f-Fe₂O₃（104）表面的吸附需要外加能量（0.386 eV）,CO在Co_6f和Co_7f掺杂位吸附的键长（L_CO）比纯净模型表面的分别增加了0.000 4 nm和0.001 1 nm,表明Co掺杂表面对CO分子的活化作用较大;过渡态分析表明CO在Co掺杂表面氧化生成CO₂的反应活化能均明显下降,其中CO在Co_5f-Fe₂O₃（104）表面生成CO₂的活化能最低,比在Fe₂O₃（104）表面的减少了0.518 eV,且相应的反应能增加了0.445 eV。研究表明,Co与Fe在其氧化物中成键结构不同,导致掺杂后模型表面的悬键增多,表面能增大,态密度向费米能级方向移动,提高了Fe₂O₃（104）表面活性,并且Co在低配位数Fe原子位的掺杂更有利于降低氧化CO的反应活化能。因此,通过掺杂金属Co提高铁基载氧体反应活性是可行的,其改性效果与掺杂活性成分的特性和掺杂方式有密切的关系。     

One GHz class E RF power amplifier for a polar transmitter

This paper describes advantages and characteristics of a class E power amplifier when used in a polar transmitter system. Basic principles of class E operation and information about different nonlinearities are given. Also, modifying the transistor model for switch-mode use is discussed briefly. A 1 GHz, 0.5 W class E power amplifier was implemented for a polar transmitter. Performance measurements of a total transmitter system with and without predistortion are presented.     

Mobile Tracking in Mixed Line-of-Sight/Non-Line-of-Sight Conditions: Algorithm and Theoretical Lower Bound

The paper investigates the problem of mobile tracking in mixed line-of-sight (LOS)/non-line-of-sight (NLOS) conditions. The motion of mobile station is modeled by a dynamic white noise acceleration model, while the measurements are time of arrival (TOA). A first-order Markov model is employed to describe the dynamic transition of LOS/NLOS conditions. An improved Rao-Blackwellized particle filter (RBPF) is proposed, in which the LOS/NLOS sight conditions are estimated by particle filtering using the optimal trial distribution, and the mobile state is computed by applying approximated analytical methods. The theoretical error lower bound is further studied in the described problem. A new method is presented to compute the posterior Cramer-Rao lower bound (CRLB): the mobile state is first estimated by decentralized extended Kalman filter (EKF) method, then sigma point set and unscented transformation are applied to calculate Fisher information matrix (FIM). Simulation results show that the improved RBPF is more accurate than current methods, and its performance approaches to the theoretical bound.     

Fibre Optic Sensors for Long-Term Monitoring of Oil Film Pressure in Diesel Engine Main Bearing

The oil film pressure is one of the key parameters in journal bearings influencing the performance of the bearings. A fibre optic sensor was developed for online determination of actual oil film pressure under load without disturbing the actual tribological contact. Four optical sensors were integrated in a hydrodynamic journal bearing of a Wärtsilä Vasa 4R32 LN E medium-speed diesel engine with four cylinders, maximum power of 1,640 kW and rotating speed on 750 rpm. Online engine tests were carried out with different loads to study the sensor operation in real operating conditions. The engine tests were repeated six times over 4 years of operation reaching up to thousand hours of the engine use. The results showed differences in bearing pressure depending on the position of the sensor and on the operating cycle of the cylinders. The pressure peaks of all four cylinder work cycles could be identified in the measured pressure curves, and the pressure variations within the pressure curves fit well to the diesel engine’s work cycle and mass forces. The sensors had good repeatability over the whole test period.     

Availability and conversion to energy potentials of wood-based industry residues in Cameroon

The importance of biomass as the most accessible primary energy source in Cameroon is presented. The valorization of wood wastes and residues is seen as a way of implementing the sustainable use of biomass resources. A recent survey of wood-based industries in Cameroon reveals that large volumes of industrial wood residues are generated in the rain forest areas and are unefficiently used. Important quantities are lost in the form of burning in the four main forestry provinces, while other parts of the country suffer from fuelwood shortage. With the exception of the plywood factories, the wood industry is essentially dependent on commercial energy. An analysis made to show the economic and environmental benefits of converting wood residues to energy for industrial and domestic use is presented.     

Non-linear B-stability and symmetry preserving return mapping algorithms for plasticity and viscoplasticity

A class of second order accurate return mapping algorithms is presented which lead to symmetric algorithmic tangent moduli and contain the classical backward-Euler return maps as a particular case. More importantly, it is shown that this class of return maps is contractive relative to the natural norm defined by the complementary Helmholz free energy function (B-stability). Since the equations of classical plasticity and viscoplasticity are shown to be contractive relative to this natural norm, the requirement of B-stability furnishes the appropriate notion of unconditionally stable algorithms for plasticity and viscoplasticity. The analysis that follows depends critically on the assumption of convexity. In particular, the models of plasticity and viscoplasticity considered obey the principle of maximum plastic dissipation. The proposed algorithms obey the discrete counterpart of this classical principle.     

Direct tomography with chemical-bond contrast

Three-dimensional (3D) X-ray imaging methods have advanced tremendously during recent years. Traditional tomography uses absorption as the contrast mechanism, but for many purposes its sensitivity is limited. The introduction of diffraction, small-angle scattering, refraction, and phase contrasts has increased the sensitivity, especially in materials composed of light elements (for example, carbon and oxygen). X-ray spectroscopy, in principle, offers information on element composition and chemical environment. However, its application in 3D imaging over macroscopic length scales has not been possible for light elements. Here we introduce a new hard-X-ray spectroscopic tomography with a unique sensitivity to light elements. In this method, dark-field section images are obtained directly without any reconstruction algorithms. We apply the method to acquire the 3D structure and map the chemical bonding in selected samples relevant to materials science. The novel aspects make this technique a powerful new imaging tool, with an inherent access to the molecular-level chemical environment.     

An evaluation of corneal nerve morphology and function in moderate keratoconus.

PURPOSE: To investigate corneal nerve morphology and corneal sensitivity in keratoconus. METHODS: The central cornea of 13 subjects with keratoconus and 13 age-matched control subjects was assessed using in vivo confocal microscopy and corneal aesthesiometry. RESULTS: Significant differences in corneal nerve fibre density were found between the subjects with keratoconus and the control subjects (keratoconus versus control; 1018.3+/-489.6 microm versus 1820.7+/-789.5 microm; p = 0.006). The mean diameter of nerve fibres in the stroma was found to be greater in subjects with keratoconus compared to control subjects (keratoconus versus control; 10.2+/-4.6 microm versus 5.5+/-1.9 microm; p = 0.007). The orientation of corneal nerve fibres in the subjects with keratoconus appeared to be altered from the predominantly vertical orientation seen in the control subjects. Corneal touch threshold was found to be similar in the two groups, although the subjects with keratoconus using contact lens correction had reduced corneal sensitivity compared to the contact lens-wearing control subjects (keratoconus with contact lenses versus controls with contact lenses; 1.18+/-0.19 g/mm2 versus 0.98+/-0.05 g/mm2; p = 0.03). CONCLUSION: This study reveals significant reductions in nerve density in the keratoconic cornea. The thickened stromal nerve fibres observed in the keratoconic corneas may explain why prominent corneal nerves are often seen using slit lamp biomicroscopy in keratoconic patients.     

The effect of previous soft contact lens wear on corneal refractive surgery outcomes

Purpose

To examine the influence of previous soft contact lens (SCL) wear on corneal refractive surgery (CRS) outcomes when SCL wear is ceased for two weeks versus twenty-four hours, and also when compared to no wear, prior to CRS.