Mechanical properties in the initial stage of sintering

Silicon nitride-based ceramics with different compositions were sintered in the 60%–90% range of theoretical density. Linear correlations between the apparent density and the modulus of elasticity, the three- and four-point bend strengths or the Vickers hardness, were observed. The slopes of the straight lines were nearly the same for all compositions. Furthermore, the modulus of elasticity, hardness, fracture toughness and strength were calculated as functions of density by modelling the structure as a random arrangement of spheres as suggested by Fischmeister and Arzt. The relationships obtained have been compared with the measured ones.Nomenclature a average contact area - a _c increase of the area of a crack - A area of the reference plane - b size of the critical defect - c constant in Equation 4 - D density - D ₀ density before shrinkage - D _T theoretical density - e direction of macroscopic strain - E modulus of elasticity - E ₀ modulus of elasticity of the dense material - f force loading a contact - f() projection of force f to e - F force loading the reference plane - g geometry parameter in the Griffiths relationship - H hardness - K _IC fracture toughness - N number of particles in unit volume - N() the fraction of N in a given spherical angle - n() number of particles in the volume around the reference plane - P porosity - R initial particle radius - R particle radius after fictitious growth - R particle radius after redistribution of material - R _SQ shared correlation coefficient - S surface energy of the defect - vector connecting the centres of neighbouring particles - W work necessary for increase the area of a crack - Z average coordination number - Z ₀ initial coordination number - strain - _T strain at theoretical strength - strength - _T theoretical strength (limit of elasticity) - angle between v and e     

Behavior of square concrete columns reinforced with Prefabricated Cage System

Behavior of normal strength concrete columns reinforced with a new reinforcement, termed Prefabricated Cage System (PCS) is investigated. A total of 16 small-scale PCS and rebar reinforced column specimens were constructed and tested under monotonic axial displacement. The experimental results indicate that the overall behavior of rebar and PCS reinforced specimens are comparable prior to achieving the peak column load. In general, PCS specimens are more ductile and absorb more energy than similar rebar specimens after the peak load is reached. The effect of different parameters, such as the steel tube thickness, number of longitudinal reinforcements, transverse steel spacing, and crossties on the specimens’ strength and deformation capacity are investigated. A confined concrete model is proposed and used to predict the load–displacement response. The theoretical load–displacement relations obtained from the proposed model are compared with those obtained from the Mander et al. (J Struct Eng 114(8):1804–1826, 1988) confinement model.     

PET纤维纺丝中采用纳米微粒添加剂的相关问题

在许多市场和用途中采用尺寸更小的微粒材料的趋势正明显增长。在纤维纺丝中加入整个范围的添加剂（包含纳米微粒）开发具有特殊性能纺织品时存在着一些争论。纤维纺丝中的主要问题是开发低含量的添加剂。     

Seismic Performance of Industrial Facilities Affected by the 1999 Turkey Earthquake

Approximately 40% of the heavy industry in Turkey was located in the region affected by the 1999 Mw 7.4 Kocaeli earthquake. Twenty-four facilities representing different industries in the epicentral region were surveyed after the earthquake. Structural and nonstructural damage to these facilities is summarized and performance is reported using a damage classification scheme. Information on typical industrial-facility construction practice in Turkey is presented. Earthquake damage to the most common structural framing systems is highlighted. The structural performance of a small number of the facilities visited by the reconnaissance team is investigated.     

Finding optimal hardware/software partitions

Most previous approaches to hardware/software partitioning considered heuristic solutions. In contrast, this paper presents an exact algorithm for the problem based on branch-and-bound. Several techniques are investigated to speed up the algorithm, including bounds based on linear programming, a custom inference engine to make the most out of the inferred information, advanced necessary conditions for partial solutions, and different heuristics to obtain high-quality initial solutions. It is demonstrated with empirical measurements that the resulting algorithm can solve highly complex partitioning problems in reasonable time. Moreover, it is about ten times faster than a previous exact algorithm based on integer linear programming. The presented methods can also be useful in other related optimization problems.     

Value prediction in hls allocation problems using intellectual properties

A value approximation-based global search algorithm is suggested to solve resource-constrained allocation in high level synthesis problems. Value approximation is preferred, because it can start by using expert heuristics, can estimate the global structure of the search problem, and can optimize heuristics. We are concerned by those allocation problems that have hidden global structure that value approximation may unravel. The value approximation applied here computes the cost of the actual solution and estimates the cost of the solution that could be achieved upon performing a global search on the hidden structure starting from the actual solution. We transcribed the allocation problem into a special form of weighted CNF formulae to suit our approach. We also extended the formalism to pipeline operations. Comparisons are made with expert heuristics. Scaling of computation time and performance are compared.     

Effect of flow on solutions of rod-coil block co-polymers

An elongational flow field is imposed on a solution of block copolymers consisting of semirigid macromolecules with rigid, rodlike sequences of units in combination with random coil (flexible) units. The problem is formulated according to the lattice treatment of Matheson and Flory. In this formulation, the system consists of rigid blocks whose lengths and locations are fixed by the structure within each macromolecule. These blocks are separated by random coiled units. An excess free energy other than the equilibrium Gibbs free energy of the quiescent solution has to be considered due to the flow field that tends to align the rods. This excess free energy is calculated from the potential energy of rods when a steady-state, homogeneous and irrotational flow field is applied to the solution. The effects of composition, polymer-solvent interaction, size of the co-polymer and flow rates are investigated. Depending on the size and number of rods, some of the chains studied exhibit a biphasic region at equilibrium that shifts to lower concentrations with increasing flow. Longer chains with shorter rods that are isotropic at equilibrium, exhibit a biphasic region at finite values of flow. The degree of orientation increases sharply when the system is biphasic. For larger flows, the orientation function is very close to unity which is perfect orientation.     

A deep eutectic solvent based liquid phase microextraction for the determination of caffeine in Turkish coffee samples by HPLC-UV

ABSTRACT

A novel liquid-phase microextraction procedure for the determination and extraction of caffeine using a deep eutectic solvent based liquid-phase microextraction method (DES-LPME) was developed. A deep eutectic solvent consisting of choline chloride-phenol (1:3) and tetrahydrofuran as a dilution solvent were used for the extraction of caffeine from Turkish coffee samples. The quantitative recoveries were obtained when the DES volume was 400 µL, and the volume of tetrahydrofuran that was used as an emulsifier solvent was 800 µL. The limit of detection and the limit of quantification were found to be 0.12 and 0.40 µg mL^?1, respectively. Linear dynamic range was 0.5–100 µg mL^?1, and coefficient of determination (R²) was 0.9998. The relative standard deviation (RSD) was 2.20% when the standard solution concentration was 1.0 µg mL^?1. The fact that the determination coefficient obtained from the calibration curve was greater than 0.9998 gives information about the accuracy of the method. Also, in order to determine the accuracy of the developed method, selected coffee samples were spiked with 25 and 50 µg mL^?1 caffeine.     

Relationship between retinal lesions and axial length, age and sex in high myopia

Questionnaires (3426; 72.8%) and blood samples (3890; 82.6%) were analysed from 4704 women post-natally. The answers to the questionnaire confirmed that those patients living in areas with the highest percentage employed in agriculture were most likely to be in direct or indirect contact with sheep or sheep products. When the 788 (20.3%) of the sera with group specific antibody were examined for type-specific antibody, 291 (7.5%) reacted with Chlamydia trachomatis, 153 (3.9%) with Chlamydia pneumoniae, but only one (0.03%) with Chlamydia psittaci. Thus, it would appear that C. psittaci was not an important pathogen in this survey, despite the largest proportion of blood samples being submitted from those most likely to be employed in agriculture. However, in the course of this survey the three patients who had previously suffered chlamydia-associated abortion had successful pregnancies and submitted blood specimens. Serological studies on the serial bloods from these patients showed that, despite developing antibody to the C. psittaci pool and the ovine abortion strain of C. psittaci following abortion, this antibody waned. At the time of the subsequent successful pregnancy, serological results would not have detected a previous C. psittaci infection, but one due to C. pneumoniae. Thus, the results of a survey such as this must be interpreted with caution.