Effect of Particle Packing on Flow Property and Strength of Concrete Mortar

Optimum particle packing is a key for designing a dense, strong, and durable cement-based material. By optimizing cement and aggregate particle size distribution, the voids among the particles can be significantly minimized, thus increasing packing density, reducing the amount of binder required for filling pores, and improving the material strength, impermeability, and volume stability of the resulting products. Dense particle packing is generally formed by particles with varying particle size distributions, where voids can be successively filled up with smaller particles. Various models have been developed for achieving maximum density, or optimal packing, of aggregate particles in concrete, among which is the Andreasen and Andersen (A&A) model. In concrete practice, groups of aggregate particles with a specific particle size distributions (PSD) are often combined in such a way that the PSD of the blended aggregate is getting as close as possible to a modeled PSD curve. In this study, modified A&A model is used for achieving optimum packing density of mortars made with various cementitious materials (cement, limestone fines, fly ash, and silica fume) and river sand. The influences of the mortar material proportion on the packing density, flow property, and strength of concrete mortar were investigated. According to the A&A model theory, optimum packing can be achieved when the cumulative PSD obeys equation: P(D) = (Dq-Dq min)/(Dq max-Dq min), where D represents the size of the sieve used for analyzing the particles studied. D min and D max are accounting for the minimum and maximum particle size in the mix, respectively. The distribution modulus q is related to the fineness of the aggregate particles. (Generally, a high q value (\u3e0.50) results in a coarse mixture, whereas a small q value (q\u3c0.25) results in a mixture that is rich in fine particles. The study consists of two parts, as written of two research papers. In paper one, a fixed distribution modulus (q) value was used, and the PSD of a given mixture was modified by different amount of limestone fines (LFs) and river sand addition. The effects of the LF and sand addition on the particle packing as well as on flow property and strength of concrete mortar were examined. The results indicate that enhanced particle packing improves mortar density and increases viscosity, but it had minimal effect on heat of hydration and yield stress of the mortar mixture. In paper two, various distribution modulus values (q = 0.25, 0.35, and 0.45) were used to evaluate the particle packing quality of a given high performance mortar (HPM). Single sized sand was selected and added to the HPM mixture so as to make the PSD of the modified HPM mixture to the A&A model curve. The minimum sum of squares of the residuals (RSS) was used to assess the quality of the PSD modification. Dry density, rheology, and compressive strength tests were performed for the both original mortar mix and sand-modified mixes. The results show that the increasing q value decreased mortar density, viscosity, and early age strength but had little/no effect on 28-day mortar strength

Can Team Resilience Boost Team Creativity Among Undergraduate Students? A Sequential Mediation Model of Team Creative Efficacy and Team Trust

Although recent literature has highlighted the critical role of resilience in creativity literature, existing findings have failed to indicate the processes through which resilience contributes to creativity at the graduate level. The current study fills this gap by hypothesizing the influence of team resilience on team creativity through a sequential mediating mechanism. A time lagged research study was conducted, and a sample of 201 undergraduate students and their teacher filled out questionnaires at three different time points (with 2-week intervals). After aggregating the data at the team level, we employed the PROCESS macro in SPSS to analyze data and test all the hypotheses through performing a sequential mediation analysis. We found that (a) team resilience would predict team creativity; and (b) team efficacy and team trust sequentially mediated the relation between team resilience and team creativity. The results in our study advance the emergent literature on linking resilience and creativity for the practical applications of resilience and creativity in education settings

Effect of empowering leadership on employees’ workplace loneliness: a moderated mediation model

BackgroundWorkplace loneliness has become a prevalent experience among employees in organizations; however, there is limited empirical research on how leaders can address and mitigate this issue. Drawing upon self-determination theory and empowering leadership theory, this study examines the impact of empowering leadership on workplace loneliness by exploring the mediator of role breadth self-efficacy and the moderator of leader–member conversational quality.MethodsA time-lagged research design was used, collecting data through a two-wave online survey involving 531 employees in Chinese public sectors. The participants consisted of 321 males and 210 females, with an average age of 35 years (SD = 7.36).ResultsOur findings indicate that empowering leadership positively influences employees’ role breadth self-efficacy, reducing their workplace loneliness. Moreover, leader–member conversational quality strengthens this indirect effect, suggesting that empowering leadership is more effective in reducing workplace loneliness when leader–member conversational quality is high.ConclusionThis study expands and enriches research on the antecedents of workplace loneliness from the leadership approach, providing valuable insights for organizations to implement interventions that effectively alleviate employees’ workplace loneliness

A double-distribution-function lattice Boltzmann method for bed-load sediment transport

The governing equations of bed-load sediment transport are the shallow water equations and the Exner equation. To embody the advantages of the lattice Boltzmann method (e.g., simplicity, efficiency), the three-velocity (D1Q3) and five-velocity (D1Q5) double-distribution-function lattice Boltzmann models (DDF-LBMs), which can present the numerical solution for one-dimensional bed-load sediment transport, are proposed here based on the quasi-steady approach. The so-called DDF-LBM means we use two distribution functions to describe the movement of the two components, respectively. By using the Chapman–Enskog expansion, the governing equations can be recovered correctly from the DDF-LBMs. To illustrate the efficiency of these, two benchmark tests are used, and excellent agreements between the numerical and analytical solutions are demonstrated. In addition, we show that the D1Q5 DDF-LBM has better accuracy compared to the Hudson’s method

Linking visionary leadership to creativity at multiple levels:The role of goal-related processes

Conceptualizing visionary leadership as a multilevel phenomenon that is manifested as dual-level (i.e., team and individual level) visionary leadership, we explore how it influences multilevel creativity through multilevel goal-related processes. Using two-wave data collected from 272 employees and 75 corresponding supervisors, we find that visionary leadership affects creativity through multilevel pathways. Specifically, team-level visionary leadership influences team creativity via team goal commitment, while individual-level visionary leadership influences employee creativity by fostering leader-follower goal congruence. The results also support two cross-level effects, i.e., team-level visionary leadership strengthens the relationship between individual-level visionary leadership and leader-follower congruence, and team goal commitment amplifies the effects of leader-follower goal congruence on employee creativity. This study thus sets the stage for further theoretical research on dual-level visionary leadership and how it functions at multiple levels to increase creativity.</p

Monotonic loading behavior of calcareous sands with increasing particle crushing

Calcareous sediment, comprising higher than 50% calcium carbonate by weight, are mostly located between latitudes 30 ͦ S and 30 ͦ N in coastal areas, such as Florida, India, Puerto Rico, and Australia. Lots of researches have been focused on the loading behavior and the particle breakage subjected to loading. It has been reported that in offshore construction, the measured capacities in calcareous were approximately 20% lower than predicted capacities. Therefore, it is necessary to investigate the loading behavior of calcareous sand with the scenario of post-construction. Calcareous sands from Puerto Rico and Western Australia are selected as the tested materials for this study. The primary objective is to investigate the static loading behavior of calcareous sand with increasing particle crushing. To accomplish this, the physical properties are determined firstly. Calcareous sand is found to have high carbonate content, high specific gravity, and porous particle structures. Triaxial undrained tests are performed with various confining pressures to investigate the static stress-strain behavior of uncrushed calcareous sand. Then, calcareous samples, prepared with different particle crushing contents, are tested by triaxial undrained tests. Various particle crushing contents are obtained by compression loading (one-dimensional consolidation test) and shear loading (triaxial consolidated drained test and TruePath test). The effect of the loading mechanism on particle breakage is evaluated as well. Results obtained from the tests for Puerto Rico and Western Australia sand are analyzed and compared with each other

Servant Leadership and Innovative Work Behavior in Chinese High-Tech Firms: A Moderated Mediation Model of Meaningful Work and Job Autonomy

Scholars acknowledge the critical role of employee innovative work behavior (IWB) in facilitating organizational innovation in high-tech industries. However, the current knowledge is far from complete to paint a clear picture of how to evoke employee IWB in the Chinese high-tech industry. Many Chinese high-tech firms face a challenge moving from hierarchy-based leadership toward more employee-centered leadership styles, as the styles have different effects on employees’ IWB. This perspective may complement and sharpen the incomplete picture. Drawing on a dynamic componential model of creativity and innovation, this study proposes and tests a moderated mediation model that examines the hypothesized positive influence of servant leadership on employee IWB via meaningful work as well as the moderating role of job autonomy in this process. We collected data (N = 288) from three Chinese high-tech firms and found that employees’ perceptions of meaningful work mediate the relationship between servant leaders and IWB. We also found that this mediating relationship is conditional on the moderating role of job autonomy in the path from servant leadership to meaningful work. The results further show that the indirect effect of servant leadership on employee IWB via meaningful work exists only when job autonomy is high

MiR-20a-5p represses multi-drug resistance in osteosarcoma by targeting the KIF26B gene

BACKGROUND: Chemoresistance hinders curative cancer chemotherapy in osteosarcoma (OS), resulting in only an approximately 20 % survival rate in patients with metastatic disease at diagnosis. Identifying the mechanisms responsible for regulating chemotherapy resistance is crucial for improving OS treatment. METHODS: This study was performed in two human OS cell lines (the multi-chemosensitive OS cell line G-292 and the multi-chemoresistant OS cell line SJSA-1). The levels of miR-20a-5p and KIF26B mRNA expression were determined by quantitative real-time PCR. KIF26B protein levels were determined by western blot analysis. Cell viability was assessed by MTT assay. Apoptosis was evaluated by flow cytometry. RESULTS: We found that miR-20a-5p was more highly expressed in G-292 cells than in SJSA-1 cells. Forced expression of miR-20a-5p counteracted OS cell chemoresistance in both cell culture and tumor xenografts in nude mice. One of miR-20a-5p's targets, kinesin family member 26B (KIF26B), was found to mediate the miR-20a-5p-induced reduction in OS chemoresistance by modulating the activities of the MAPK/ERK and cAMP/PKA signaling pathways. CONCLUSIONS: In addition to providing mechanistic insights, our study revealed that miR-20a-5p and KIF26B contribute to OS chemoresistance and determined the roles of these genes in this process, which may be critical for characterizing drug responsiveness and overcoming chemoresistance in OS patients

MiR-34a-5p promotes the multi-drug resistance of osteosarcoma by targeting the CD117 gene.

An association has been reported between miR-34a-5p and several types of cancer. Specifically, in this study, using systematic observations of multi-drug sensitive (G-292 and MG63.2) and resistant (SJSA-1 and MNNG/HOS) osteosarcoma (OS) cell lines, we showed that miR-34a-5p promotes the multi-drug resistance of OS through the receptor tyrosine kinase CD117, a direct target of miR-34a-5p. Consistently, the siRNA-mediated repression of CD117 in G-292 and MG63.2 cells led to a similar phenotype that exhibited all of the miR-34a-5p mimic-triggered changes. In addition, the activity of the MEF2 signaling pathway was drastically altered by the forced changes in the miR-34a-5p or CD117 level in OS cells. Furthermore, si-CD117 suppressed the enhanced colony and sphere formation, which is in agreement with the characteristics of a cancer stem marker. Taken together, our data established CD117 as a direct target of miR-34-5p and demonstrated that this regulation interferes with several CD117-mediated effects on OS cells. In addition to providing new mechanistic insights, our results will provide an approach for diagnosing and chemotherapeutically treating OS

Safety and efficacy of early radiofrequency catheter ablation in patients with paroxysmal atrial fibrillation complicated with amiodarone-induced thyrotoxicosis

Background: Amiodarone is an antiarrhythmic drug that is frequently used to control atrial fibrillation (AF). Many patients with AF are afraid of the risk of ablation and take amiodar­one, some patients develop amiodarone-induced thyrotoxicosis (AIT). The purpose of the study was to investigate the safety and efficacy of early radiofrequency catheter ablation in patients with paroxysmal AF complicated with AIT. Methods: From the 146 consecutive patients with paroxysmal AF who had been treated with amiodarone and underwent 3-dimensional mapping system guided circumferential pulmonary vein isolation (PVI) at our center from January 2013 to June 2014, 20 had developed AIT. Thirty controls with normal thyroid function and matched for baseline characteristics were selected. Results: Pulmonary vein isolation was completed in all patients without serious complications and with similar procedural (170.60 ± 14.80 vs. 158.18 ± 9.06 min; p = 0.062) and X-ray exposure (16.48 ± 2.15 vs. 15.36 ± 1.57 min; p = 0.058) time in AIT vs. control groups; however, upon coronary sinus catheter pacing (from 300 ms to 200 ms) after intrave­nous isoproterenol administration 30 min post PVI, rates of induction of AF (35% vs. 3.33%; p = 0.005) and of non-pulmonary vein-related atrial tachyarrhythmias (50% vs. 6.67%; p = 0.01) were higher, while those for atrial flutter (15% vs. 3.33%; p = 0.17) and atrial tachycardia (15% vs. 6.67%; p = 0.31) were similar, as was the recovery of conduction of pulmonary vein potential (15% vs. 30%; p = 0.191). In AIT vs. control group, atrial tachyarrhythmia recurrence rate was higher at 3 months (45% vs. 16.67%, p = 0.032) but not between 3 and 12 months (30% vs. 23.33%; p = 0.418) follow-up. Conclusions: Early catheter ablation for paroxysmal AF in patients with AIT appeared safe and effective albeit with higher atrial tachyarrhythmia recurrence rate up to 3 months but not beyond 12 months after PVI relative to controls.