Controlling material structure and its electromagnetic properties, including complex permittivity and permeability, could enhance the microwave absorption performance of the material in terms of ...reflection loss and effective absorption bandwidth. In this study, La‐substituted barium hexaferrite, Ba3−xLaxCo2Fe24O41 (x = 0, 0.1, 0.3, and 0.5) compounds were successfully prepared using the solid‐state reaction method, and their corresponding microstructures, static magnetic properties, and electromagnetic features in 2–18 GHz were investigated. The doping of La content increased saturation magnetization, coercivity, and remnant magnetization. The Ba2.7La0.3Co2Fe24O41 epoxied sample with 3.5 mm thickness possessed an excellent microwave absorption of −47.3 dB at 3.52 GHz, and its corresponding effective absorption bandwidths were 3.75 GHz (2.25–6 GHz) and 0.57 GHz (17.43–18 GHz). It is shown that doping with various La concentrations on Ba3Co2Fe24O41 can be used as an effective technique to tune the performance of microwave absorbers based on barium hexaferrite.
•A 3D CFD-based reduced order model for a new data center model with hot/cold aisles is investigated.•The effects of three different design parameters on the temperature difference between POD & CFD ...are discussed.•The effects of the number of parameters on basis functions in POD and their outcomes are investigated.•Simulation speed is found to be greatly enhanced by POD with accuracy little compromised.
Although full-field simulations using computational fluid dynamics and heat transfer (CFD/HT) tools can be applied to predict the flow and temperature fields inside data centers, their running time remain the biggest challenge to most modelers. In this paper, a reduced order modeling method is used to drastically reduce the running time (up to 600 times faster) while still acceptably preserving the accuracy of the model. The results obtained from Proper Orthogonal Decomposition (POD) method are in good agreement with the results obtained from CFD/HT model simulation. The sensitivity analysis of some of the design parameters in the POD model is evaluated. In addition, a 3-D temperature profile of the data center model constructed from 2D slices are generated with a linear interpolation technique. Tradeoff between accuracy and running time is observed and discussed.
Polycrystalline Ca2Fe2−xAlxO5 (x = 0‐1.4) samples were prepared by conventional solid‐state reactions. Their crystalline/electronic structures and magnetic properties were characterized in detail. ...Powder X‐ray diffraction analyses revealed that the samples crystallized in orthorhombic brownmillerite‐type structures with the occurrence of the Pcmn‐Ibm2 phase separation in the region between x = 0.4 and 0.6. The results obtained from analyzing Raman scattering and X‐ray‐absorption fine‐structure spectra also indicated this phase separation. Although x in Ca2Fe2−xAlxO5 varies in a wide range from 0 to 1.4, the +3 oxidation state of Fe remained almost unchanged. Magnetization measurements revealed that all Ca2Fe2−xAlxO5 samples have weak ferromagnetic order, and both the saturation magnetization and coercive force are dependent on the temperature, x, and structure phases.
Research examining the antecedents of recalls, instead of their consequences, is relatively sparse and has not considered whether firms’ likelihood to recall products is influenced by legal changes ...that could induce managerial opportunism, such as those reducing shareholder litigation risk. To examine this question, the authors exploit the staggered adoption of universal demand (UD) laws across several U.S. states as a quasi-natural experiment. UD laws aim to prevent frivolous litigation from disrupting a firm's normal business operations by making it more difficult for shareholders to sue managers for neglecting their fiduciary duties and hold them personally liable. Although UD laws are well-intended, the reduced threat of shareholder litigation disciplining a firm's managers could have unintended negative consequences. Indeed, using a difference-in-differences analysis, the authors find that following the adoption of UD laws, affected firms become less likely to recall products. This effect is weaker in the presence of organizational mechanisms constraining managers’ self-interest-seeking behavior, such as a corporate culture focused on customer needs and interests or the exercise of normative control through monitoring by institutional investors. The authors do not find support for a potential alternative explanation of operational improvement and therefore higher product quality driving their findings.
PurposeDrawing on the conservation of resources theory, this study aims to apply a mixed-method to enrich the literature by investigating interrelationships among training, environmental triggers ...(environmental knowledge, awareness and concern) and employees' intention to carry out environmental activities.Design/methodology/approachThis research applied a mixed-method carried out in Vietnam. By using the time-lagged data, Study 1 (quantitative research) was employed to test hypotheses. With Study 2 (qualitative research), four in-depth interviews were conducted to gain insight into a few unexpected findings from Study 1.FindingsStudy 1 indicates that environmental training is critical to directly boost not only the three environmental triggers but also employees' intention to engage in environmental activities. The findings further point out that environmental concern and awareness mediate the relationship between environmental training and employees' intention to engage in environmental activities. Unexpectedly, connections from environmental concern and awareness to employees' intentions were not moderated by environmental knowledge. The findings of Study 2 shed light on the role of environmental knowledge.Originality/valueBased on the conservation of resources and social exchange theories, the research contributes to the existing literature by providing a better understanding of how environmental training stimulates employees' intention to implement environmental activities. The findings may be helpful for managers to encourage employees to contribute to organizations' green objectives.
Results of an experimental study, which measured thermally-induced pore pressure and corresponding concrete temperatures in high-strength concrete (HSC) and normal strength concrete (NSC), to ...quantify the effects of factors influencing pore pressure buildup and potential for explosive spalling in HSC and NSC are presented. The specimens are 100 × 200 × 200 mm concrete blocks, heated to a maximum temperature of 600°C (1,112°F) at 5°C/min (41°F/min) and 25°C/min (77°F/min). The complex heat-induced moisture transport process, which varied with specific levels of concrete temperature and significantly influenced the developments of pore pressure and concrete temperature, is explained. Pore pressure developments are shown to be directly related to the moisture transport process and have a significant influence on occurrence of explosive spalling. Effects of water-to-cementitious materials ratios (
w/cm
), curing conditions, heating rates, and polypropylene (PP) fibers on pore pressure buildup and explosive spalling are quantified and described.
Acidic groundwaters enriched with heavy metals are frequently observed in the coastal plain aquifers. The acidic pHs are observed even in the deep confined aquifers in southern Vietnam. This study ...geochemically explores the causes of these acidic groundwaters by investigating 41 groundwater samples, 4 soil samples and a 54 m long sediment core and the long-term monitoring data (4189 observations) obtained from 178 wells of the National Groundwater Monitoring Network for the South of Vietnam (NGMNS). The groundwater data show elevated Fe, Mn, Al, Pb, and Zn concentrations as the pH becomes acidic and suggest pyrite oxidation be the major cause for the groundwater acidification. This is further confirmed by pyrite framboids observed in the sediment or soil samples taken from the sites where strongly acidic groundwaters were observed. Results of leaching experiments using sediment and soil samples indicate that high metal concentrations in the acidic pH are associated with the increased metal solubility and mineral dissolution kinetics. The acidification of deep groundwaters is revealed to be associated with well installation, indicating the importance of proper well-installation techniques to protect water quality of deep confined aquifers.
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•Metal-rich, acidic groundwaters are commonly observed in Mekong Delta area.•Pyrite oxidation is the major reason for groundwater acidification in the area.•The pyrite oxidation in deep confined aquifer was induced by well installation.•Well installation techniques minimizing aquifer disturbance are required.
•A multi-zone modeling strategy is developed for a data center with hot and cold aisles.•Data center energy performances in hot (Miami) and cold (Chicago) climates are compared.•Temperature ...variations in different zones of the data center are investigated.•Effects of wall exposure conditions on the energy performance of data center are investigated.•Effects of supply air temperatures and flow rates on data center performance are investigated.
In this paper, a building energy simulation code, EnergyPlus, was used to study the effects of wall boundary conditions, climatic locations, supply air temperatures, and volumetric flow rates, on the energy consumption and thermal performance of a popular data center model. The data center model having 1120 servers distributed in four rows of rack was investigated under two major climatic conditions–hot and humid (Miami, FL), and cool and humid (Chicago, IL). A multi-zone modeling approach was proposed to resolve the hot and cold aisles in the data center, and was compared to existing well-mixed single-zone model. Using the multi-zone approach that is believed more reasonable, both monthly and annual overall energy consumptions as well as cooling load were analyzed under various boundary conditions. In addition, monthly thermal behavior in the zones for hot and cold aisles within the data center was analyzed. The simulation results show that thermal performance of the data center is significantly affected by locations or climatic conditions. The effects of location and wall boundary conditions are particularly appreciable during the summer and winter seasons. An optimal supply temperature of 11.8°C, and air flow rate of 2.5m3/s were found to be most preferred selections for the data center model.
In recent decades, computational tool is popularly used for thermal management of large data centers to meet the high demand of IT services which causes an increase in thermal load density. In this ...study, an evaluation of various available tile models at different tile-to-rack airflow rate ratios is carefully conducted using experimental data for one single server rack in a dada center laboratory from the available literature. In addition, several turbulence models are thoroughly studied, and recommendations are provided for the most accurate and less time-consuming turbulence models depending on targeting purposes when applying to a single rack model. A proposed composite performance index is introduced and used for evaluating various tile and turbulence models. It is an interesting finding that the zero-equation produces a very decent result when compared to the widely used standard k-ε. As for the tile model investigated, it is found that the body force and modified body force model are the best candidates for tile modelling applications. The use of zero equation with either body force or modified body force tile model yields either an equivalent or better results in terms of time and accuracy compared to the standard k-ε case combined with the same tile models.
•New performance indexes based on time and accuracy are proposed for model assessment.•Body force and modified body force tile models are found to the best tile models among several investigated.•Zero-equation model reduces the computing time while yielding good accuracy among other turbulence models.•The combination of zero-equation model with either body force or modified body force model is preferred.
We have prepared polycrystalline samples La0.7Ca0.3-xBaxMnO3 (x = 0, 0.025, 0.05, 0.075 and 0.1) by solid-state reaction, and then studied their magnetic properties and magnetocaloric (MC) effect ...based on magnetization versus temperature and magnetic-field (M–H–T) measurements. Experimental results reveal the easiness in tuning the Curie temperature (TC) from 260 to about 300 K by increasing Ba-doping concentration (x) from 0 to 0.1. Under an applied field H = 50 kOe, maximum magnetic-entropy changes around TC of the samples can be tuned in the range between 6 and 11 J kg−1 K−1, corresponding to refrigerant-capacity values ranging from 190 to 250 J kg−1. These values are comparable to those of some conventional MC materials, and reveal the applicability of La0.7Ca0.3-xBaxMnO3 materials in magnetic refrigeration. Analyses of the critical behavior based on the Banerjee criteria, Arrott plots and scaling hypothesis for M–H–T data prove a magnetic-phase separation when Ba-doping concentration changes. In the doping region x = 0.05–0.075, the samples exhibits the crossover of first- and second-order phase transitions with the values of critical exponents β and γ close to those expected for the tricritical mean-field theory. The samples with x < 0.05 and x > 0.075 exhibit first- and second-order transitions, respectively. More detailed analyses related to the Griffiths singularity, the critical behavior for different magnetic-field intervals started from 10 kOe, and the magnetic-ordering parameter n = dLn|ΔSm|/dLnH (where ΔSm is the magnetic-entropy change) demonstrate magnetic inhomogeneities and multicritical phenomena existing in the samples.
•Threshold of first-to-second-order phase transformation in La0.7Ca0.3-xBaxMnO3.•Giant magneto-caloric effect with magnetic-entropy changes of 6–11 J kg−1 K−1.•Detailed analyses of critical behavior in comparison with previous studies.•Magnetic phase-transition theories and universal curves of magnetic-entropy change.
