Search

To determine the relationship between blood flow in the fetal descending aorta and discordant umbilical arteries (UAs). Pulsed wave Doppler of both UAs and the descending aorta was performed at 4‐weekly intervals between 14 and 40 weeks of gestation in 209 pregnant women. In datasets with discordant UAs, a linear mixed effects model was used to determine the categorical relationship between the UA pulsatility index (PI) (high, low and average) and the descending aorta PI. Of the 209 cases, 81 had a discordance of greater than 25% in UA PI during one of their visits. There were no differences in birth outcomes between the groups with concordant and discordant UA PIs. In the cases with discordant UA PIs, the descending aorta PI was most strongly associated with both the average UA PI (P= .008), and with the UA with the lower PI (P= .008). The relationship between blood flow in the descending aorta and UAs is consistent with the law for combining resistances in parallel. Measurements of the descending aorta PI, particularly in a scenario with discordant UAs, may inform the stability of the feto‐placental circulation where discordant UA PIs are found.

A concise review of fatigue of fiber-reinforced composites, covering fatigue life and damage development and how the properties of constituents, orientations and other parameters affect fatigue life, is presented. The subject broadly covers polymer, metal, and ceramic matrix composites, by including specific examples of fatigue data from literature. Studies of composite fatigue have mostly evolved over the last 60 years, largely driven by aerospace applications of composites. The field is very vast in terms of accumulated technical literature and fatigue data. Therefore, only some iconic examples, each with good experimental data, have been considered in this review to illustrate the behavior and the trends as clearly as possible. First, the general nature of tensile deformation of fiber composites under various combinations of fiber and matrix failure strains are reviewed to provide a background with which the more complicated fatigue behavior can be easily understood. Second, examples of S–N fatigue data of glass (GFRP) and carbon (CFRP) fiber-reinforced plastics are provided, illustrating the effects of reinforcement, constituent properties, temperature, and orientation effects on fatigue failure. These analyses are also modeled by S–N curve calculations using exponential S–N fatigue constitutive equations proposed by author. These calculations helped to easily rationalize the trends in S–N data, as influenced by strength and failure strains of fiber and matrix. Next, stiffness degradation behavior in fiber composites are reviewed, with specific examples including CFRP (polymer matrix) and SiC/SiC (ceramic matrix) composites. The nature of stiffness degradation is also modeled using a semi-empirical equation that relates the fractional remaining stiffness to fractional remaining fatigue life in the composite. Finally, a few examples of fatigue behavior of laminated composites that are typically used in real-world applications are reviewed.

Abstract

Silicon electrodes with the columnar macroporous structure were investigated to determine the effect of variations in the columnar pore morphology on lithiation and energy storage capacity in Li-ion cells. Several variants of macroporous Si columnar electrodes were electrochemically cycled against the Li reference electrode. The changes in macro-pore size and Si wall thickness of the columnar architecture greatly affected the cyclic Li storage and discharge capacities. A strong correlation of the Li-storage capacity with the ratio of Si wall thickness to pore diameter is found to exist. Specifically, one columnar Si electrode with an optimum macroporous structure exhibited a very high reversible specific capacity of ~1250 mAh/g (total capacity 1.2 mAh/cm2) for over 200 cycles. Electron microscopy revealed that the high reversible Li-storage capacity is due to the macropores accommodating the change in volume of lithiation and providing nearly complete reconstruction of Si walls upon delithiation. The present observations can lead to practical, high-capacity, and damage-resistant Si electrodes for Li-ion batteries.

Since the last decade, the collective intelligent behavior of groups of animals, birds or insects have attracted the attention of researchers. Swarm intelligence is the branch of artificial intelligence that deals with the implementation of intelligent systems by taking inspiration from the collective behavior of social insects and other societies of animals. Many meta-heuristic algorithms based on aggregative conduct of swarms through complex interactions with no supervision have been used to solve complex optimization problems. Data clustering organizes data into groups called clusters, such that each cluster has similar data. It also produces clusters that could be disjoint. Accuracy and efficiency are the important measures in data clustering. Several recent studies describe bio-inspired systems as information processing systems capable of some cognitive ability. However, existing popular bio-inspired algorithms for data clustering ignored good balance between exploration and exploitation for producing better clustering results. In this article, we propose a bio-inspired algorithm, namely social spider optimization (SSO), for clustering that maintains a good balance between exploration and exploitation using female and male spiders, respectively. We compare results of the proposed algorithm SSO with K means and other nature-inspired algorithms such as particle swarm optimization (PSO), ant colony optimization (ACO) and improved bee colony optimization (IBCO). We find it to be more robust as it produces better clustering results. Although SSO solves the problem of getting stuck in the local optimum, it needs to be modified for locating the best solution in the proximity of the generated global solution. Hence, we hybridize SSO with K means, which produces good results in local searches. We compare proposed hybrid algorithms SSO+K means (SSOKC), integrated SSOKC (ISSOKC), and interleaved SSOKC (ILSSOKC) with K means+PSO (KPSO), K means+genetic algorithm (KGA), K means+artificial bee colony (KABC) and interleaved K means+IBCO (IKIBCO) and find better clustering results. We use sum of intra-cluster distances (SICD), average cosine similarity, accuracy and inter-cluster distance to measure and validate the performance and efficiency of the proposed clustering techniques.

Abstract: The study demonstrates an effective method to synthesize titanium-titanium boride (Ti-TiB) functionally graded material (FGM) tiles by exploiting the simultaneous TiB whisker formation in situ and the densification occurring during the reaction sintering process. The macrostructure of the graded material was designed to have a beta-titanium (β-Ti) layer on one side with the composite layers of Ti-TiB mixture having increasing volume fraction of the TiB through the thickness. The approach used an optimized tri-modal powder mixture consisting of α-Ti powder, a master alloy of the β-stabilizing-element powders (Fe-Mo), and TiB2. The structure and properties of both of these FGMs were systematically characterized by X-ray diffraction, electron microscopy, and microhardness measurements. Interestingly, it has been found that two different kinds of TiB whisker morphologies were observed in the FGMs. The Ti-rich layers were found to have large and pristine TiB whiskers uniformly distributed in the Ti matrix. On the other hand, the TiB-rich layer was found to have a network of interconnected and relatively smaller TiB whiskers appearing as clusters. The layers of intermediate TiB volume fractions were found to consist of both the morphologies of TiB. The effectiveness of the X-ray direct comparison method for the determination of volume fractions of phases in the FGM layers was also demonstrated. The Vickers microhardness level was found to increase dramatically from 420 kgf/mm2 in the β-Ti layer to 1600 kgf/mm2 in the TiB-rich layer. The elastic residual stresses retained in the graded layers after fabrication were determined based on an elastic multilayer model. The nature of microstructure, the hardness variation, and the distribution of residual stresses in these novel FGMs are discussed.

The study focused on the in-situsynthesis of titanium (Ti)-titanium boride (TiB) composites with βphase in the matrix by reaction sintering of TiB2with Ti and alloying element powders. The goal was to examine the nature of TiB whisker formation in three different kinds of powder mixtures: (1) β-Ti alloy powders and TiB2; (2) α-Ti powder, a master alloy (Fe-Mo) powder containing the β-stabilizing elements, and TiB2; and (3) α-Ti powder, a β-stabilizing elemental powder (Mo or Nb), and TiB2. The effects of powder packing and the relative locations of powder particles on the morphological changes in TiB whisker formation and their growth were studied at processing temperatures ranging from 1100°C to 1300°C. The morphology, size, and distribution of whiskers were found to be influenced by the powder-packing conditions. A large particle-size ratio in bimodally packed mixtures led to the formation of a TiB monolithic layer around βgrains. With a relatively finer starting powder, smaller size ratio, and trimodal packing arrangement, the TiB whiskers were found to be distributed more homogeneously in the matrix. The study also used the X-ray direct comparison method and the structure factor for the βphase to determine the volume fraction of TiB phase from X-ray data. Tensile tests and fractographic investigations were carried out on selected composites. The evolution of the composite microstructure, the influence of powder-packing variables, and the morphology and growth of TiB whiskers and their effect on mechanical properties are discussed.

Abstract: The study demonstrates the feasibility of synthesizing TiB whiskers on titanium (Ti) surfaces by solid-state diffusion to form a hard and wear-resistant coating. The microstructural and mechanical properties of the TiB coating layer have also been investigated. The TiB coating was formed by the solid-state diffusion of boron (B) from a powder mixture containing amorphous boron, Na2CO3 powder, and charcoal (activated) powder. The diffusion process was carried out at various temperatures ranging from 800 C to 1000 C for various periods of time ranging from 1 to 24 hours. The amount of Na2CO3 in the mixture was also varied. It has been found that pristine and extremely fine TiB whiskers form on the surfaces of titanium, with the whiskers growing more or less normal to the surface. A maximum coating thickness of about 218 m was observed for the pack diffusion conditions at 850 C for 24 hours with 15 pct Na2CO3. The kinetics of TiB formation was found to follow the growth rates in bulk composites. The X-ray diffraction (XRD) patterns of the coatings revealed the dominant TiB peaks with a very few TiB2 peaks, with small intensity at higher temperature and time. The surface hardness of the coated layer increased to a Vickers hardness of about 550 kgf/mm2 due to the presence of TiB whiskers in the coating. It is shown that pack diffusion of boron in the solid state is a simple and very effective means of generating hard and wear-resistant coatings on titanium.

When blood was drawn from the brachial vein of the dog upon infusion of buprenorphine hydrochloride in saline through a plastic catheter into the jugular vein, the post-infusion jugular vein plasma concentrations observed during the first 15 min of the post-infusion distributive phase were significantly higher than the highest observed brachial vein plasma concentrations at the time of cessation of infusion. When blood was drawn from the jugular vein following infusion of buprenorphine hydrochloride into the left brachial vein, the post-infusion left brachial plasma concentrations during the first 15 min of the post-infusion distributive phase were significantly higher than the highest jugular and contralateral brachial vein concentrations observed just before and after the cessation of infusion. Dependent on whether the plasma concentrations sampled from the infused catheter or another catheter were used, the apparent calculated total body clearances differed by 25–39%. These results demonstrated that the observed differences in the post-infusion buprenorphine concentrations in plasma obtained from different veins were not due to any drug-induced changes in the circulatory physiology of the dog. Evidence is presented to show that the discrepancies were due to the repartitioning of the catheter-bound drug into the blood drawn through the catheter for assay, which significantly increased the apparent blood concentration of drug, not-withstanding the fact that only an extremely small fraction (0.004–0.009) of a simulated 1–3-h infused dose partitioned into the plastic catheter. When buprenorphine hydrochloride was administered by a bolus injection, there was no significant partitioning of drug into the infusion catheter. When buprenorphine glucuronide solution was infused through the jugular catheter, post-infusion plasma concentrations from both the jugular and brachial veins were the same, indicating no significant binding of the glucuronide to the plastic catheter. In general, caution must be exercised in interpreting pharmacokinetic data obtained from plasma samples that were drawn through the same plastic catheter as was used in the prolonged infusion of lipophilic drugs.