•La0.7Ca0.3Mn0.9Co0.1O3: locating at the threshold of the first- and second-order phase transitions.•Coexistence of MR and MCE effects.•The relationship between electrical and magnetic ...properties.•High magnetic entropy change under low applied field.
In this work, a polycrystalline sample of La0.7Ca0.3Mn0.9Co0.1O3 was prepared by solid-state reaction method. The room-temperature X-ray diffraction analysis using Rietveld refinement technique confirms that the sample has a single-phase state with the orthorhombic structure (space group Pbnm). Based on the temperature dependences of the resistance and magnetization, the magnetoresistance and the magnetocaloric effects of the sample have been investigated. Our results pointed out that La0.7Ca0.3Mn0.9Co0.1O3 compound exhibits the maximum magnetoresistance MR = 100% × ρ(0) − ρ(H)/ρ(H) = 14.3% near the metal–semiconductor transition with TP = 155 K and the maximum magnetic entropy change |ΔSmax| = 1.45 J/kg·K around the ferromagnetic–paramagnetic phase transition with TC = 188 K under an applied magnetic field change ΔH = 4 kOe. Besides, the changes of the specific heat ΔCP(T, H) for ΔH = 1–4 kOe have been also calculated.
Polycrystalline orthorhombic samples La0.7Ca0.3−xNaxMnO3 (x = 0–0.09) were prepared by solid-state reaction. The study of magnetic properties revealed that the ferromagnetic-paramagnetic (FM-PM) ...transition temperature (TC) increases from 255 to about 271 K with increasing Na-doping content (x) from 0 to 0.09, respectively. Around the TC, we have found the samples showing a large magnetocaloric (MC) effect with maximum values of magnetic entropy change (|ΔSmax|) of 7–8 J kg−1 K−1 and relative cooling power RCP = 232–236 J/kg for the samples x = 0.03–0.09 in a magnetic-field interval ΔH = 40 kOe. Detailed analyses of isothermal magnetization data M(T, H) based on Banerjee's criteria indicated a first-to-second-order magnetic-phase transformation taking place at a threshold Na-doping concentration xc ≈ 0.06. This could also be observed clearly from the feature of entropy universal curves. An assessment of the magnetic-ordering exponent N = dLn|ΔSm|/dLnH demonstrates an existence of short-range magnetic order in the samples. We believe that the changes of the magnetic properties and MC effect in La0.7Ca0.3−xNaxMnO3 caused by Na doping are related to the changes in the structural parameters and Mn4+/Mn3+ ratio, which are confirmed by the geometrical and electronic analyses based on X-ray diffraction and X-ray absorption fine structure.
•Geometrical and electronic structures of La0.7Ca0.3−xNaxMnO3.•Threshold of first-to-second-order phase transformation in La0.7Ca0.3−xNaxMnO3.•Large magneto-caloric effect with |ΔSmax|≈7–8 J kg−1 K−1, and RCP = 232–236 J/kg.•Universal curve of magnetic-entropy change.
In the design of large-scale data centres, CFD is used widely but very time-consuming with intensive computational resource requirement. When it comes to near real-time thermal control or optimizing ...multiple design parameters of data centres, this method becomes impractical. In this paper, response surface methodology (RSM) based on radial basis function (RBF) is used to significantly reduce the running time while maintaining a good accuracy. In the first application, by using 5%, 10%, and 20% of the original CFD data, the temperature profiles of the three corresponding cases are reconstructed based on RSM. Three reconstructed temperature profiles are then compared to the full temperature profile of a data centre model. The method shows good agreement with the CFD simulation result, especially for the case of 20% utilization of the original CFD data points. In the later application, RSM is used for generating a large set of generations during a two-objective optimization process which uses the genetic algorithm as its main engine. With three investigated design parameters including mass flow inlet, inlet temperature, and server heat load, the goal is to minimize both the temperature difference and the maximum temperature inside the data centre. The outcome shows a desirable range of design input parameters for a data centre.
Highlights
Response surface model is trained using high fidelity CFD simulation data
Radial basis function is found to show superior advantages in constructing response surface
Rapid thermal profile reconstruction for data centre using response surface method is illustrated
CFD-based response surface method for data centre optimization process is investigated
The vapour chamber is a two-phase heat transfer device that is able to effectively spread heat from concentrated heat sources to much larger heat sinks. This paper presents an experimental ...investigation into a copper-water vapour chamber heat spreader with hybrid wick structures. The vapour chamber had sintered powder and screen mesh wicks on the evaporator, and a screen mesh wick on the condenser. Its overall dimensions were 123 mm × 140 mm × 3 mm. The spreading resistance of the vapour chamber was explored for a non-central heating scenario. It was determined that spreading resistance of 0.08 K/W could be achieved with this vapour chamber, which was around half what would be achieved with an equivalent copper heat spreader. At low heat inputs, the vapour chamber experienced start-up difficulties. Furthermore, temperature drops through the vapour chamber and copper spreader were explored and some weaknesses of current vapour chamber designs were highlighted. Even with these weaknesses, the hybrid wick vapour chamber was able to spread heat more effectively than a copper spreader.
•Spreading thermal resistance of vapour chamber was experimentally found.•A hybrid wick structure consisting of both sintered powder and mesh was used.•The resistance of the vapour chamber was half that of a copper spreader.•Axial temperature drops were larger in the vapour chamber than for copper.
The present work of this study involves an advanced analytical procedure that allows direct and fast determining the specific activity of
238
U and
235
U using the gamma-rays of 63.3 keV and ...185.7 keV after subtraction of the contribution of overlapping peaks. This procedure also included MCNP-CP code in order to calculate the coincidence summing and the self-absorption correction factor. Validation of the developed procedure was confirmed by the IAEA proficiency test to calculate the activities of radionuclides in various types of samples such as rich thorium, secular equilibrium, and disequilibrium of uranium. The final scores were received “acceptable” for all radionuclides.
Naturally occurring and recombinant protein-based materials are frequently employed for the study of fundamental biological processes and are often leveraged for applications in areas as diverse as ...electronics, optics, bioengineering, medicine, and even fashion. Within this context, unique structural proteins known as reflectins have recently attracted substantial attention due to their key roles in the fascinating color-changing capabilities of cephalopods and their technological potential as biophotonic and bioelectronic materials. However, progress toward understanding reflectins has been hindered by their atypical aromatic and charged residue-enriched sequences, extreme sensitivities to subtle changes in environmental conditions, and well-known propensities for aggregation. Herein, we elucidate the structure of a reflectin variant at the molecular level, demonstrate a straightforward mechanical agitation-based methodology for controlling this variant’s hierarchical assembly, and establish a direct correlation between the protein’s structural characteristics and intrinsic optical properties. Altogether, our findings address multiple challenges associated with the development of reflectins as materials, furnish molecular-level insight into the mechanistic underpinnings of cephalopod skin cells’ color-changing functionalities, and may inform new research directions across biochemistry, cellular biology, bioengineering, and optics.
Purpose
This study aims to explore the intention–action relationship of small and medium-sized (SMEs) firms with knowledge capital that declare their intention to internationalize from their ...inception.
Design/methodology/approach
The authors apply the theory of planned behavior and hand-collect a database of Chinese born globals, purely domestic firms and traditional exporting firms. The authors’ hypothesis is that Chinese born globals or young aspiring globals (YAGs) will strive to acquire domestic and international patents at an early stage to institutionally protect their knowledge-capital via intellectual property rights as they enter the competitive global marketplace.
Findings
The results confirm that knowledge-focused YAGs apply for patents at an earlier stage than purely domestic and traditional exporting firms. However, in the long run, these firms are neither demonstrating increased knowledge capital by being more innovative nor producing more valuable innovations than their counterparts.
Originality/value
This study tests the intention–action relationship in the context of SMEs internationalization. It contributes to the internationalization literature by identifying the internationalization pattern of born globals (YAGs) from emerging markets and providing an explanation for what happens to these firms as they mature.
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