Three dimensional numerical modeling of flow around bridge piers using LES and RANS

River hydrodynamicsTurbulent open channel flow and transport phenomen

Effect Of Internal Curing And Shrinkage-mitigating Materials On Microstructural Characteristics Of Fiber-reinforced Mortar

Internal curing (IC) and other shrinkage mitigating materials are employed to reduce shrinkage and risk of cracking. This study investigates the efficiency of individual versus combined use of IC and shrinkage mitigating materials on key characteristics of fiber-reinforced mortar (FRM). The investigated mixtures include a 25% pre-saturated lightweight sand (LWS) that is added individually and combined with 10% CaO-based expansive agent (EA) and 2% shrinkage reducing admixture (SRA). This elucidates the synergistic effect of high content IC and EA/SRA on macro- and micro-mechanical characteristics of FRM, especially at the interface of the matrix with fibers. Mechanical properties, microstructural characteristics, and fiber–matrix bonding of FRM made with 0.5% steel fibers are investigated. The results show that the use of IC with EA and SRA completely compensates for shrinkage at 56 days. The highest compressive and fiber pull out strengths are observed for FRM with IC and without EA/SRA due to the densification of the interfacial transition zone (ITZ) confirmed by microstructural analysis. Such improvement is associated with the lower porosity of the cement paste and longer silicate chain—higher Si/Ca—obtained by FRM made with LWS. Although the combination of both EA and SRA with IC leads to 180 μstrain expansion after 56 days, the corresponding mixture presents the weakest ITZ and inferior mechanical properties

Fluidization of cohesive nanoparticles with a new pulsation technique

The nanoparticles are building block of many advanced materials that are developed for a variety of industries. Fluidization of the nanoparticles can improve dramatically quality of the final material in processes such as coating, drying and crystallization because of enhanced mixing conductions in a fluidized bed. However, due to severe presence of interparticle forces, the nanoparticles are very cohesive, and thus their fluidization is impossible with conventional methods. Authors developed a novel pulsation-assisted technic to effectively fluidize the nanoparticles of different types. The developed fluidization technic was primarily investigated inside a transparent tube with 2.5 cm diameter and 20 cm height. A solenoid valve was located in the reactor outlet to switch between ON and OFF positions to intermittently pressurize the gas inside the reactor and then let it exit. Two differential pressure transducers and a high-speed camera recorded the pressure fluctuations of the bed. Superficial gas velocity and intermittence frequency of the solenoid valve were varied to investigate fluidization quality. An experimental procedure was developed to estimate the maximum amount of interparticle forces between the nanoparticles in the bed. Investigations showed under optimum conditions when the solenoid valve was open an upward lift force was generated that helped fluidize the bed. The lift force was greater than sum of the bed weight and the maximum interparticle forces minus the drag force. Bed fluctuations were examined at temperatures 650, 700 and 750 °C, and it was revealed that the developed technique could be optimized to work at such temperatures

Design And Performance Of Fiber-reinforced Shrinkage Compensating Eco-friendly Concrete

Eco-Crete is an ecological and economical concrete that benefits from high packing density of solid materials and reduced paste. Eco-Crete can enhance the service life of structures by reducing the risk of shrinkage cracking. In this study, shrinkage mitigating materials included an expansive agent (EA), a shrinkage reducing admixture (SRA), and a lightweight sand (LWS), as well as steel and synthetic fibers were used to minimize the risk of cracking. A total of 35 fiber-reinforced Eco-Crete mixtures were prepared with 350 kg/m3 of cementitious materials and 55 % substitution of fly ash and slag. Key fresh and mechanical properties in addition to plastic, restrained, and drying shrinkage were evaluated. Results showed that 32-week drying shrinkage of Eco-Crete made with shrinkage mitigating strategies was limited to 400 µstrain, and none of the selected Eco-Crete mixtures experienced cracking up to 112 d under restrained shrinkage testing. Mixtures incorporating only EA and synthetic fibers exhibited excessive initial expansion and minor plastic shrinkage cracking. Eco-Crete mixtures developed at least 40 MPa compressive strength after 56 d. Mixtures made with EA and SRA presented the highest flowability and mechanical properties and the lowest drying shrinkage. The use of synthetic fibers exhibited a better flexural pre-cracking performance than steel fibers. However, steel fiber-reinforced mixtures showed 250 % greater flexural toughness. The use of steel fibers was more effective than synthetic fibers in reducing long-term shrinkage and limiting initial expansion caused by the high content of EA. Statistical analysis and embodied carbon assessment revealed the advantages of using Eco-Crete made with 5 % EA and 0.5 % SRA and 0.5 % synthetic fibers to secure low-shrinkage Eco-Crete

Breastfeeding and timing of pubertal onset in girls: a multiethnic population-based prospective cohort study.

BackgroundEarly puberty is associated with higher risk of adverse health and behavioral outcomes throughout adolescence and adulthood. US girls are experiencing earlier puberty with substantial racial/ethnic differences. We examined the association between breastfeeding and pubertal timing to identify modifiable risk factors of early puberty and potential sources of racial/ethnic differences in the timing of pubertal development.MethodsA prospective cohort study of 3331 racially/ethnically diverse girls born at Kaiser Permanente Northern California (KPNC) between 2004 and 06. All data were obtained from KPNC electronic clinical and administrative datasets. Mother-reported duration of breastfeeding was obtained from questionnaires administered at each 'well-baby' check-up exam throughout the baby's first year and categorized as 'Not breastfed', 'Breastfed < 6 months', and 'Breastfed ≥ 6 months'. Pubertal development data used Tanner stages assessed by pediatricians during routine pediatric checkups starting at age 6. Pubertal onset was defined as transition from Tanner Stage 1 to Tanner Stage 2+ for breast (thelarche) and pubic hair (pubarche). Weibull regression models accommodating for left, right, and interval censoring were used in all analyses. Models were adjusted for maternal age, education, race/ethnicity, parity and prepubertal body mass index (BMI). We also examined race/ethnicity as a potential effect modifier of these associations.ResultsNot breastfeeding was associated with earlier onset of breast and pubic hair development compared to breastfeeding ≥6 months (adjusted hazard ratio [HR]: 1.25; 95% confidence interval [CI]: 1.07-1.46; HR: 1.24; 95% CI: 1.05-1.46, respectively). Breastfeeding for < 6 months was also associated with the risk of earlier pubic hair development (HR: 1.14; 95% CI: 1.00-1.30, compared to breastfeeding ≥6 months). Inclusion of girls' prepubertal BMI slightly attenuated the association between breastfeeding and timing of breast onset but remained significant. The association between not breastfeeding and early breast development may be stronger among African American girls (HR: 1.92; 95% CI: 1.01-3.66, no breastfeeding vs. ≥6 months) than other racial/ethnic groups.ConclusionsBreastfeeding is an independent predictor of pubertal onset in girls, and the strength of the association may vary by race/ethnicity. Providing breastfeeding support and lactation education for high risk mothers may help prevent earlier pubertal onset and promote positive health outcomes later in life

Impact of COVID-19 pandemic crisis and food safety system: a literature review

The new outbreak as unknown pneumonia that occurred in Wuhan province of China in December 2019, is a new coronavirus from Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), and has been termed Coronavirus Disease 2019 (COVID-19). Coronaviruses are a family of viruses that usually cause respiratory illness. Since food plays an essential role in human health as an integral part of human life, food safety is critical in such cases. It is essential to adopt practical strategies in controlling the COVID-19 crisis. Also, extreme economic consequences and threats to human health were imposed in the COVID-19 pandemic in 2019-2021. Some studies have been published by World Health Organization (WHO), Environmental Protection Agency (EPA), and Food and Drug Administration (FDA); however, there is little information about food safety and COVID-19. Although COVID-19 transmission routes through food are not currently known, contamination through contaminated food and environmental surfaces cannot be ignored, especially in manufacturing companies, restaurants, and communities that are unsanitary. Nevertheless, World Health Organization precautions on good hygiene when preparing food, and recommends effective management of food safety during COVID-19. In food safety, COVID-19 is known as a potential risk through food especially in restaurants and industrial areas. There have been very few studies on the relationship between food safety and COVID- 19. Studies have shown that COVID-19 can survive longer than MERS-CoV in food stored at 4 °C. In the current situation, several methods are used to disinfect and control the spread of COVID-19 disease, some of which are not effective and can also have problems and limitations. Heat treatment, pasteurization, UV light-based, and chemical disinfectants can be ways to prevent COVID-19 probable transmission. The temperatures (30 or 40 °C) reduced the survival time of HCoVs on the inanimate surfaces. The cooking processes (70 °C) are effective in inactivating the virus in food. SARS-CoVs were inactivated by exposure to ultraviolet (254 nm) for 1 to 6 min with an increase of up to 400-fold. Also, usage of disinfectants can be effective for inanimate surfaces. This review summarizes the available data related to some topics and methods to inactivate COVID-19 and the role and importance of the food industry and food supply chain during the pandemic