A single transition state may lead to multiple intermediates or products if there is a post-transition-state reaction pathway bifurcation. These bifurcations arise when there are sequential ...transition states with no intervening energy minimum. For such systems, the shape of the potential energy surface and dynamic effects, rather than transition-state energetics, control selectivity. This Minireview covers recent investigations of organic reactions exhibiting reaction pathway bifurcations. Such phenomena are surprisingly general and affect experimental observables such as kinetic isotope effects and product distributions.
•Compressive strength was improved by elevating curing temperature and adding slag.•High temperature curing has a slight improvement on the freeze-thaw resistance.•The freeze-thaw resistance ...increases with the increase of slag content.•An inflection point of freeze-thaw resistance of GPC-50.
A set of Class F fly ash-based geopolymer concrete with slag gradient, namely, GPC-10 (10% slag content), GPC-30 (30% slag content) and GPC-50 (50% slag content), was prepared to study its freeze-thaw resistance. GPC-10 was wrapped in aluminum foil and cured at 80 °C for 24 h to accelerate strength development. The others were cured under standard conditions (20 ± 2 °C, relative humidity ≥95%). Rapid freeze-thaw cycle testing was carried out according to ASTM C666, and an ordinary Portland cement concrete (OPCC) sample was used as the control. The freeze-thaw resistance was evaluated by mass loss, relative dynamic elasticity modulus and compressive strength loss. In addition, the microstructure and mineralogy were characterized using scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), energy dispersive X-ray spectrosocpy (EDS) and X-ray diffraction (XRD). The results show that GPC-10 is damaged after five freeze-thaw cycles, although high temperature curing improves its freeze-thaw resistance. GPC-30 is damaged in 50 freeze-thaw cycles, while GPC-50 can withstand 225 freeze-thaw cycles, which is comparable to the freeze-thaw resistance of the OPCC. Also, 125 freeze-thaw cycles marks an inflection point for the freeze-thaw resistance of GPC-50, which is verified by the SEM and MIP results. The effect of adding slag on the enhanced freeze-thaw resistance was analyzed by EDS and XRD.
•Zeotropic mixtures presented higher CHF than that of pure components.•The three-stage model of nucleate pool boiling process of zeotropic mixtures was proposed.•An analytical model for the heat ...transfer degradation factor at P-DB point was established.
In the present study, the nucleate pool boiling heat transfer characteristics of zeotropic binary mixtures (R134a/R245fa) with different blending ratios, as well as their pure components, were experimentally investigated in a visualized pressure vessel. For each test refrigerant, the experiments were performed on a horizontal plain copper surface (10 mm × 10 mm) at the same evaporating temperature of 26 °C with the heat flux ranging from 1.2 kW/m2 to 360 kW/m2. The boiling curves of test refrigerants were subdivided into up to four zones from natural convection region to bubble column region according to the visualization results. The slope of the boiling curve in bubble coalescence region was greater than that in isolated bubble region. The onset of nucleate boiling (ONB) point of zeotropic mixtures obviously lagged behind that of pure components, namely, the higher wall superheat was required, which presented the consistent variation with the temperature glide. The boiling heat transfer coefficient of zeotropic mixtures, although increasing with the increase of heat flux, was degraded compared to the corresponding ideal heat transfer coefficient, except for some specific cases with high heat flux. Based on the analysis of heat transfer degradation factors and additional mass transfer resistance, the nucleate pool boiling process of zeotropic mixtures was identified as three stages due to the presence of two inflection points, pseudo fully developed nucleate boiling (P-FDNB) point and pseudo double boiling (P-DB) point. The wall superheat of test mixtures at P-DB point was stable at a certain value and did not vary with the blending ratio. The thermodynamic fluctuation theory was introduced to describe the effect of mass transfer resistance for zeotropic mixtures at P-DB point and the calculation results showed good agreement with the experimental data.
An improved Dijkstra algorithm based on adaptive resolution grid (ARG) is proposed to assist manual transmission line planning, shorten the construction period and achieve lower cost and higher ...efficiency of line selection. Firstly, the semantic segmentation network is used to change the remote sensing image into a ground object-identification image and the grayscale image of the ground object-identification image is rasterized. The ARG map model is introduced to greatly reduce the number of redundant grids, which can effectively reduce the time required to traverse the grids. Then, the Dijkstra algorithm is combined with the ARG and the neighborhood structure of the grid is a multi-center neighborhood. An improved method of bidirectional search mechanism based on ARG and inflection point-correction is adopted to greatly increase the running speed. The inflection point-correction reduces the number of inflection points and reduces the cost. Finally, according to the results of the search, the lowest-cost transmission line is determined. The experimental results show that this method aids manual planning by providing a route for reference, improving planning efficiency while shortening the duration, and reducing the time spent on algorithm debugging. Compared with the comparison algorithm, this method is faster in running speed and better in cost saving and has a broader application prospect.
Improving urban resilience (UR) and natural capital utilization are critical for supporting regional sustainable development. However, most of the previous studies have separately assessed them, and ...their coupling mechanism is still unclear. This study develops a cloud model-based urban resilience (UR) assessment framework to explore the dynamic evolution of UR in the three typical urban agglomerations of the Yangtze River Economic Belt (YREB). Natural capital utilization is analyzed by an improved ecological footprint (EF3D) model. Coupling Coordination Degree (CCD) and Environmental Kuznets Theory (EKC) are integrated for revealing the relationship between UR and natural capital utilization. Results show that UR in the YREB shows an increasing trend with an average annual rate of 1.33%, and there is a significant difference in the sub-dimensions of UR. Water system resilience generally has a positive impact on UR in the early periods, but its impact later becomes negative, with over 45% of all cities' UR being negatively affected by water system resilience. The spatial distribution of EF3D shows a decentralized trend in the YREB. The consumption of resource stocks represented by ecological footprint depth increases during the period from 2000 to 2015, with increase rates of 1.09%, 4.73%, and 3.42% for the upstream, midstream, and downstream urban agglomerations, respectively. The CCD between UR and natural capital utilization increases from an intermediate coordination stage to a well-coordinated stage. The EKC analysis discloses that UR and natural capital utilization present inverted U-shaped curves in three urban agglomerations with spatial differences. The inflection point of UR in the upstream is earlier (in 2008) than that in the midstream (in 2014) and downstream (in 2015) urban agglomerations. Findings can help quantify the development space for each city to enter into coordinated development in the future.
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•A comprehensive evaluation framework of urban resilience (UR) is developed based on a cloud model.•Dynamic evolution of natural capital utilization (NCU) is illustrated through an improved ecological footprint model.•The coupling mechanism between UR and NCU in the Yangtze river Economic Belt is revealed.•Effects of water resource system resilience on UR are displayed.•Policy implications are given for improving the regional environmental performance.
Nursing is the largest health profession, with nearly 4 million providers practicing across acute, primary, and public health care settings. In response to the pandemic, nursing schools halted ...on-site course delivery and redesigned programs to attenuate risks to students and faculty. Key challenges faced by schools included financial cutbacks, rapid increases in online learning technology, maintaining student academic progression, disruption to clinical learning opportunities, and meeting accreditation standards, while addressing the stress and loss experienced by faculty, staff, and students. Despite challenges, nursing organizations provided guidance for decision making, new learning resources, and faculty development opportunities. Schools of nursing leveraged their resources to redesign nursing curricula, strengthen partnerships for student clinical experiences, and address needs of the community. Nursing education will look different from its prepandemic profile in the future. Lessons learned during the pandemic point to gaps in nursing education, particularly related to disaster and public health preparedness, health equity, and technology. The American Association of Colleges of Nursing's new Essentials-standards for professional nursing education-were finalized during the pandemic and reflect these lessons. The need for nurse scientists to conduct emergency response research was made evident. The importance of strong academic-practice partnerships was highlighted for rapid communication, flexibility, and responses to dynamic environments. For the future, nursing education and practice must collaborate to ensure that students and practicing nurses are prepared to address emergencies and pandemics, as well as the needs of vulnerable populations.
The kinetics of hydrogen oxidation reaction (HOR) declines with orders of magnitude when the electrolyte varies from acid to base. Therefore, unveiling the mechanism of pH-dependent HOR and narrowing ...the acid-base kinetic gap are indispensable and challenging. Here, the HOR behaviors of palladium phosphides and their counterpart (PdP
2
/C, Pd
5
P
2
/C, Pd
3
P/C, and Pd/C) in the whole pH region (from pH 1 to 13) are explored. Unexpectedly, there are non-monotonous relationships between their HOR kinetics and varied pHs, showing distinct inflection-point behaviors (inflection points and acid-base kinetic gaps). We find the inflection-point behaviors can be explained by the discrepant role of pH-dependent hydroxyl binding energy (OHBE) and hydrogen binding energy (HBE) induced HOR kinetics under the entire pH range. We further reveal that the strengthened OHBE is responsible for the earlier appearance of the inflection point and much narrower acid-base kinetic gap. These findings are conducive to understanding the mechanism of the pH-targeted HOR process, and provide a new strategy for rational designing advanced HOR electrocatalysts under alkaline electrolyte.
•The modified cycloid reducer has cycloid gearing mechanism like a planocentric reducer.•Various tooth profiles of a cycloid gear can designed according tooth thickness ratio and the height of the ...teeth.•The effect of pressure angle on gear performance of cycloid gear.•A dynamic model is proposed considering friction coefficient.•The stress results of the cycloid gear shows the higher rigidity than in the involute gear.
This study proposes a design method for a modified cycloid reducer with an epitrochoid tooth profile. The reducer used here has one contact pattern and non-pin rollers like a planocentric reducer. This feature makes the designed reducer easier to be manufactured compared to conventional cycloid reducers, which are difficult to manufacture due to tolerances. The tooth profile characteristics for nine different design scenarios for the cycloid reducer were analyzed with respect to the tooth thickness ratio and the distance from the center of the rolling circle. It was observed that the inflection point, which was calculated from the radius of curvature, was a major factor influencing the design of the cycloidal tooth profiles. A mathematical model for the force analysis of the designed reducer was developed, and variations in force distribution between the internal and external gears as well as the efficiency of the cycloid reducer were calculated according to different coefficients of friction. Involute and cycloid gears with a difference of one tooth between the internal and external gears were designed and manufactured, and finite element analysis showed that the cycloid gear had higher rigidity than the involute gear.
Soil–water characteristic curve (SWCC) contains the fundamental information needed for describing the mechanical behavior of unsaturated soil. Some parameters such as air-entry value, slope at the ...inflection point, residual water content and residual suction are commonly used to describe the SWCC and other associated properties such as shear strength and permeability. Currently these parameters are determined using the graphical method which can be subjective and time consuming. Equations for determining these parameters are proposed and the relationships between SWCC parameters and fitting parameters are discussed in this paper. These equations can be used for computational analyses to replace the conventional graphical method in providing consistent results.
The constitutive relationship between stress and strain for titanium alloy Ti6Al4V has been investigated using tensile tests at four different temperatures that is room temperature, 200 °C, 400 °C, ...and 550 °C. Detail observations on the variation of nature of flow curves in the work hardening regime have been reported at different test temperatures. At room temperature and 550 °C, the flow curves are found to be linear in nature and follow the Hollomon relationship. The flow curves at 200 and 400 °C exhibit non-linear nature and demonstrate Ludwigson relationship. The various constant parameters of above relationships influence the overall strength and ductility of the alloy at different temperatures. The alloy shows presence of premature plastic instability or inflection points in the early period of flow curves and displays a fast decrease in work hardening rate at room temperature and 550 °C, which in turn results in lower values of strain to fracture.
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