Traditional shear design procedures for concrete structures rely on empirical equations derived from laboratory experiments and lack the type of adequate theory that forms the basis of flexural design. As shear resistance depends on so many variables and because laboratory tests do not cover the full practical range of parameters, empirical shear design equations can result in structures with inadequate shear strength. Recent failures of such structures have highlighted the need for shear design provisions solidly based on an adequate theory. This paper introduces such a theory and explains the simple design models derived from the theory, which include a strut-and-tie model for disturbed regions and a sectional model for flexural regions. These models form the basis of the shear provisions on the 2004 Canadian standard for the design of concrete structures. In the current paper, results from nine major experimental series are compared with predictions from the new shear provisions and with predictions from the shear provisions of the Eurocode and the American Concrete Institute code. It is demonstrated that the new shear design provisions are capable of predicting the shear strength of reinforced concrete members and prestressed concrete members with considerably greater reliability.

BackgroundTo determine the correlation between obesity in school-aged children and imbalance of gut microbes by examining the ratio change of intestinal Bifidobacteria and E.coli in obese children compared to non-obese controls.MethodsA hospital-based 1:1 case–control study was performed. Fecal samples of the subjects were collected for DNA extraction and analyzed by quantitative real-time PCR (qPCR) to determine the copy number of Bifidobacteria and E.coli. The ratio of two microbes (B/E) was then calculated and statistically analyzed.ResultsSubjects of the obesity group and control group showed no significant difference in age, gender or height (P > 0.05); whereas they had significant differences in body weight and BMI. Copy numbers of Bifidobacteria and E.coli per gram of wet fecal samples were first determined using qPCR in both obese and normal groups, which were further used for the calculation of B/E ratio. We found that B/E ration in the two groups showed significant difference (P < 0.05). Corrected χ2 test was performed for the two groups against B/E < 1, and it was found that there was a positive correlation (OR = 719.2, OR 95% C.I. = 81.57-6341.18) between B/E ratio decrease with childhood obesity.ConclusionsThe obese children have a lower amount of Bifidobacteria and higher amount of E.coli (smaller B/E ratio) compared to normal non-obese children. It was suggested that obesity in children may be associated with the imbalance of gut microbes.

We have compared the efficacy of daily injection of recomgiven as mean ± standard error of the mean.) Importantly, binant leptin protein (rh-leptin) with adenovirus-mediated rh-leptin and ex vivo-expressed Ad-leptin were equivalently delivery of the murine or human leptin gene (Ad-leptin) for active in a functional cell-based assay. The primary differtreatment of obesity in the obese (ob/ob) mouse model. ence in the two therapeutic approaches is the continuous We demonstrate an improved correction profile for obesity chronic secretion of leptin mediated by gene delivery, verand associated surrogate markers using the adenovirus sus the intermittent bolus delivery and rapid clearance of delivery method. Rate of weight loss and percentage satthe daily injection of rh-leptin protein. Thus, in vivo findings iety were significantly greater in the mice treated with Adsuggest that leptin effects are better achieved at lower leptin. These findings were associated with lower peak steady-state levels, a pharmacological feature attained serum leptin levels with Ad-leptin (22.9 ± 2.6 ng/ml for the here by gene therapy. These findings may have implihuman gene, and 48.9 ± 11.5 ng/ml for the murine gene) cations for the potential use of leptin in the treatment of compared to rh-leptin (385.2 ± 36.0 ng/ml). (Values are obesity.

With the improvement of living standards and dietary changes, childhood obesity has increased worldwide. This study aimed to understand the differences of intestinal flora structure between obese and normal children at school-age. Using the next generation sequencing platform, Illumina Miseq, 16S rDNA high-throughput sequencing technology, we analyzed the diversity and relative abundance of intestinal flora in 39 obese and 38 normal control school-age children. First, we categorized gut bacteria on the basis of their Operational taxonomic units (OTUs) using the RDP 16s rRNA database in RDP classifier. The alpha (α) diversity was used to measure the diversity within a sample and is calculated as a value for each sample. The beta (β) diversity was used to compare different samples and to measure the dissimilarity between each other sample. Our results indicated that intestinal flora in obese children showed lower diversity than normal controls. Significant differences of relative abundance of intestinal flora were detected at multiple levels of classifications. Identification of intestinal flora with significant difference between obese and normal children may provide important information to uncover the roles of these specific bacteria in the development of obesity and find new strategy to prevent and treat obesity through intervening the intestinal flora.

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In the design stage of mechanical components, the uncertainty in both the environmental load and the material parameters needs to be taken into consideration and a safety margin is required to guarantee the intrinsic reliability of mechanical components. The safety factor is comprehensively used in the practical design of mechanical components, which is industry specific and determined by the experience of engineers. However, the empirical safety factor cannot quantify the uncertainty and risk in mechanical design. Therefore, reliability analysis of mechanical products has gained more and more popularity [1] to [3].Reliability is defined as the probability that a product performs its intended functions without failure during a specified time period. For mechanical components, the load-strength interference (LSI) model is the most important analytical method in reliability assessment. The conventional LSI model is essentially a static reliability model. However, gradual failure of mechanical components commonly exists in practical engineering due to the strength degradation caused by corrosion, wear, erosion creep, etc. As pointed out by Martin, constructing reliability models considering strength degradation is an important issue for reliability estimation and further research on generalized methods for the dynamic reliability analysis of mechanical components is imperative [4].To overcome the shortcomings of conventional LSI models, reliability models based on stochastic process theory are investigated in which load and strength are modelled as two stochastic processes. Lewis [5] analysed the time-dependent behaviour of a 1-out-of-2: G redundant system by combining the LSI model with a Markov model. Geidl and Saunders [6] introduced time-dependent elements into the reliability equation to estimate the reliability. Somasundaram and Dhas [7] put forward a generalized formula to estimate the reliability of a dynamic parallel system, in which components equally shared the load. Noortwijk and Weide [8] developed a reliability model, in which load and strength are described as two stochastic processes. Labeau et al. proposed the framework of a dynamic reliability platform and identified its main constituents [9]. Zhang et al. analysed the main methods for dynamic reliability estimation of nuclear power plants, which include discrete dynamic event trees and Monte Carlo simulation [10]. Slak analysed production planning and scheduling, cutting tools and material flow process, and manufacturing capacities [11]. Barkallah et al. proposed a method for process planning to determine the tolerance for manufacturing with statistical tools [12].As a matter of fact, the reliability models based on stochastic process theory, such as the timedependent model, Markov model, etc, are the most important tools for dynamic reliability analysis. The Markov models are mainly used for dynamic reliability analysis of electronic elements and multi- Dynamic Reliability Analysis of Mechanical Components Based on Equivalent Strength Degradat...

This paper investigates the effect of stress gradient on the fatigue life of U‐notched specimens under multiaxial proportional loading by studying the shear stress gradient and normal stress gradient on the crack initiation plane separately. First, based on the energy method and critical plane method, an energy‐critical plane method for determining the direction of crack initiation is proposed. Second, with the help of the concept of stress field intensity, the shear stress gradient and normal stress gradient on the critical plane are studied. Finally, a multiaxial fatigue life prediction model is established by combining the equivalent stress field intensity, composed of the shear stress field intensity and normal stress field intensity, with the Manson–Coffin equation. Theoretical analysis is verified by the experiments of Q345 steel notched specimens, and the results show that the predicted accuracy of the proposed method is not conservative and is superior to the local stress–strain method.

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