An experimental study on mechanical properties of fiber-reinforced concrete of energy piles

The technology of energy piles for heat storage involves turning the concrete piles buried beneath the ground into a part of the ground-source heat pump system and burying the heat-transfer tubes in the foundation piles, which are regarded as heat transfer wells. The heat transfer tubes are embedded in the concrete foundation piles, destroying the mechanical bearing capacity of the piles and damaging the safety of the buildings. Thus, considering the structural stability and the degree of heat transfer of concrete piles, as well as the selection of material for the foundation piles, the mixing ratio of the material of the energy piles is experimentally studied by the orthogonal method. The optimum mixing ratio of the energy pile is thus obtained. A concrete test block is used to conduct a static load test and splitting test to verify the mixing ratio of the concrete of the energy pile. The results show that steel fiber can be used to enhance the bearing capacity of the storage pile as a reinforcement material. Under a reasonable ratio, the reinforced pile can absolutely meet the original design requirements. Ordinary Portland cement or composite Portland cement can be used as cementitious materials for energy piles. Through an experiment, it is proved that the composite Portland cement can better meet the requirements of the concrete foundation piles than the cementitious material. As thermal conductivity materials, the addition of industrial graphite and scrap copper slag can improve the thermal conductivity of the pile, but it can also reduce the mechanical properties of the pile. It is necessary to control it in a certain range and not to add a large amount of graphite just to improve the thermal conductivity

Single Fasting Plasma Glucose Versus 75-g Oral Glucose-Tolerance Test in Prediction of Adverse Perinatal Outcomes::A Cohort Study

Background: There remains uncertainty regarding whether a single fasting glucose measurement is sufficient to predict risk of adverse perinatal outcomes. Methods: We included 12,594 pregnant women who underwent a 75-g oral glucose-tolerance test (OGTT) at 22–28 weeks' gestation in the Born in Guangzhou Cohort Study, China. Outcomes were large for gestational age (LGA) baby, cesarean section, and spontaneous preterm birth. We calculated the area under the receiver operator characteristic curves (AUCs) to assess the capacity of OGTT glucose values to predict adverse outcomes, and compared the AUCs of different components of OGTT. Results: 1325 women had a LGA baby (10.5%). Glucose measurements were linearly associated with LGA, with strongest associations for fasting glucose (odds ratio 1.37, 95% confidence interval 1.30–1.45). Weaker associations were observed for cesarean section and spontaneous preterm birth. Fasting glucose have a comparable discriminative power for prediction of LGA to the combination of fasting, 1 h, and 2 h glucose values during OGTT (AUCs, 0.611 vs. 0.614, P = 0.166). The LGA risk was consistently increased in women with abnormal fasting glucose (≥5.1 mmol/l), irrespective of 1 h or 2 h glucose levels. Conclusions: A single fasting glucose measurement performs comparably to 75-g OGTT in predicting risk of having a LGA baby

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe

Numerical investigation on the prefabricated crack propagation of FV520B stainless steel

FV520B is a common stainless steel for manufacturing centrifugal compressor impeller and shaft. The internal metal flaw destroys the continuity of the material matrix, resulting in the crack propagation fracture of the component, which seriously reduces the service life of the equipment. In this paper, Abaqus software was used to simulate the prefabricated crack propagation of FV520B specimen with unilateral gap. The results of static crack propagation simulation results show that the maximum value of stress–strain located at the tip of the crack and symmetrical distributed like a butterfly along the prefabricated crack direction, the maximum stress is 1990 MPa and the maximum strain is 9.489 × 10−3. The Mises stress and stress intensity factor KI increases with the increase of the expansion step, the critical value of crack initiation is reached at the 6th extension step. The dynamic crack propagation simulation shows that the crack propagation path is perpendicular to the load loading direction. Similarly, the maximum Mises stress located at the crack tip and is symmetrically distributed along the crack propagation direction. The critical stress range of the crack propagation is 23.3–43.4 MPa. The maximum value of stress–strain curve located at the 8th extension step, that is, the crack initiation point, the maximum stress is 55.22 MPa, and the maximum strain is 2.26 × 10−4. On the crack tip, the stress changed as 32.24–40.16 MPa, the strain is at 1.292 × 10−4–1.897 × 10−4. Keywords: FV520B, Crack propagation, Mises stress, Stress–strain, Numerical investigatio

Numerical investigation on the stress corrosion cracking of FV520B based on the cohesive zone model

Tensile failure process of plane specimens and unilateral V-notched specimens is simulated basing on cohesive zone model (CZM). The internal stress in corrosion scales and film-induced stress in matrix increases with the increase of corrosion scale thickness. The thicker the corrosion scales are, the smaller the crack initiation strength is and the easier to initiate and propagate for stress corrosion cracks are. Meanwhile, with the thickness of corrosion scale increasing, the stress corrosion cracking (SCC) sensitivity of plane specimen increases and KISCC of unilateral V-notch specimens are reduced, making the stress corrosion cracks more likely to propagate. Simulation results show that the stress corrosion cracks nucleate on the surface of corrosion scale and propagate gradually until corrosion scale broke with the continuous tensile load. Finally, stress corrosion cracks propagate into the matrix. Keywords: FV520B stainless steel, Stress corrosion cracking, Slow strain rate tensile test, Cohesive zone mode

Analysis on the stress corrosion crack inception based on pit shape and size of the FV520B tensile specimen

The influence of pit shape and size on local stress concentration in the tensile specimen and the stress corrosion cracks inception was studied by employing the element remove technique. The maximum stress located in the bottom of pit on FV520B tensile specimen. The location of maximum strain was near the mouth of the pit or the shoulder and plastic strain existed in this region. Stress concentration factor and plastic deformation on four different geometrical shape pits of hemisphere, semi-ellipsoid, bullet and butterfly were numerically investigated, respectively. The simulation results showed that butterfly pit got the biggest stress concentration factor. The plastic strain rate during pit growth was in the sensitivity range of stress corrosion cracks inception, indicating that stress corrosion cracks were more likely to nucleate near the pit tip or the shoulder. Keywords: Stress corrosion crack, Pit shape, Stress concentration factor, FV520B, Element remove techniqu

Study on the solid solubility mechanism of Cr₂O₃ in Fe₃O₄ (γ-Fe₂O₃)

1317-1321XRD Rietveld analysis and Mössbauer spectra show that γ-Fe2O3 samples prepared by Fe3+(Cr3+)/Fe2+ mixed ions method (ions ratio 2:1), containing 0-14 wt% Cr2O3, have 20.56-49.58% amorphous iron oxide. The amorphous iron oxide is magnetic when the content of Cr2O3 is less than 4 wt%. Above 4 wt% Cr2O3, the non-magnetic phase appears and its content increases linearly with Cr2O3 concentration. During coprecipitating of Fe3+(Cr3+)/Fe2+ mixed ions, two different kinds of primary hydrous complex are formed : Fe3+ hydrous complex mixed with Cr3+ ions, with a maximum of 4 wt% Cr2O3 content, and, the Cr3+ hydrous complex mixed with Fe3+ ions with the Cr2O3 content above 4 wt%. The Cr3+ hydrous complexes incorporate into the Fe3+ hydrous complexes and hinder the crystallization and growth of the latter. These complexes dehydrate to form non-magnetic iron oxides containing chromium. The non-magnetic iron oxides affect the catalytic activity of Fe2O3-Cr2O3 catalysts. When Cr2O3 content is between 6-8 wt%, the catalysts have the highest water gas reaction activity for all samples

Study on different line gasoline blending with RJM via numerical investigation

The blending effect of gasoline is numerically simulated with different angles of nozzles and rotation speeds based on a rotary jet mixing (RJM) system. The outlet of the RJM system might destroy the components of gasoline, therefore an extra component is firstly added when the RJM system was established. In order to increase the accuracy of the simulation, sliding grid technology is applied and the meshes are divided into different sizes. The radial velocity attenuation curves and Center dynamic pressure attenuation curves of horizontal nozzles, the distribution curves of the cross-section velocity, and velocity nephograms of different blending flow fields were obtained. The results show that the jet property of nozzles and the mixing performance of the RJM system and it can effectively improve the mixing efficiency. Keywords: Gasoline blending, Numerical investigation, Rotary jet mixing system, Mixing time, Jet stirrin

Numerical Study on Entropy Generation of the Multi-Stage Centrifugal Pump

The energy loss of the multi-stage centrifugal pump was investigated by numerical analysis using the entropy generation method with the RNG k-ε turbulence model. Entropy generation due to time-averaged motion and velocity fluctuation was mainly considered. It was found that the entropy generation of guide vanes and impellers account for 71.2% and 23.3% of the total entropy generation under the designed flow condition. The guide vanes are the main hydraulic loss domains and their entropy generation is about 9 W/K, followed by impellers. There are vortices at the tongue of the guide vane inlet as well as flow separations in the impellers, which lead to entropy generation. The fluid impacts the outer surface of the guide vanes, resulting in the increase in entropy generation. There are refluxes near the guide vane tongues which also increase the entropy generation of this part. The entropy generation distribution of the guide vanes and impellers was investigated, which found that the positive guide vane has more entropy generation compared with the reverse guide. The entropy generation of the blade suction surface is higher compared with the pressure surface. This study indicated that the entropy generation method has distinct advantages in the assessment of hydraulic loss