• Energy Research
• QA close
• BH close

Structural, mechanical and electronic structure properties of Mg7NbH16 were investigated using the norm-conserving pseudo-potentials and plane waves (PP-PW) within the general gradient approximation (GGA) in the frame of density functional theory (DFT). The computed equilibrium lattice constants are in excellent agreement with the available experimental and theoretical data. The elastic constants Cij of Mg7NbH16 were calculated for the first time. The Mg7NbH16 compound is found to be mechanically stable. The bulk modulus of single crystals has been derived using elastic constants. The results are discussed and compared with the calculated bulk modulus reported in the literature. The polycrystalline elastic moduli (namely: the shear modulus, Young's modulus, Poisson's ratio, Lamé's coefficients, sound velocities and the Debye temperature) were derived from the obtained single-crystal elastic constants. According to the obtained results, Mg7NbH16 can be classified as ductile material. The shear anisotropic factors and the elastic anisotropy are also discussed. A Debye temperature of 619 K was also determined using theoretical elastic constants.

This publication was made possible by the NPRP grant (NPRP8-370-2-154) from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of author(s).

Abstract This article examines and conceptualizes the implications of the adoption of circular economy (CE) business models on operations management (OM) decision-making processes, in the areas of product design, production planning and control, and logistics/supply chains. A systematic literature review was conducted in order to identify and examine the following key areas: (1) the new demands faced by OM decision-making regarding changes in capability, work procedures, intra- and inter-organizational relationships and technologies; (2) the specific changes OM decision-making must make in order to support CE business models (based on the ReSOLVE framework); and (3) guidelines which will help designers and operations and logistics/supply chain managers develop the necessary skills to meet society and the global market's emerging demands. The findings of this research will allow operations managers to foresee the unfolding needs for capacity building in CE, and scholars can build on the results of this article to develop new research themes. Furthermore, this is the first article to describe the ways in which OM knowledge can support the transition towards the circular economy based on the perspective of dynamic capabilities.

In hot climatic conditions, the temperature inside a greenhouse is much higher than the ambient temperature and requires significant cooling to maintain the temperature in the optimal range. This study proposes a novel concept for a self‐sustaining greenhouse, which integrates evacuated tube collectors, a multistage flash desalination system, vapor absorption cooling system, and photovoltaic thermal (PV/T) system to produce freshwater, cooling, and electricity. The PV/T system uses spectrum selective nanofluid that is circulated over the roof of the greenhouse and absorbs solar radiation having wavelengths greater than 1400 nm to reduce cooling load inside the greenhouse and optimize the spectrum use. The performance of the proposed system is evaluated using energy and exergy analysis. The energy efficiencies of the evacuated tube collector, desalination unit, and PV/T system are obtained as 45.85%, 46.16%, and 51.25%, respectively. The absorption cooling system achieves an energetic coefficient of performance of 0.83. The overall energy and exergy efficiencies of the proposed system are found to be 30% and 5.88%, respectively. The application of spectrum selective nanofluid on the roof of the greenhouse yields about 26% reduction in the cooling load of the greenhouse.

AbstractStudies have shown that occupant satisfaction is a compelling factor affecting building energy consumption. Occupants' behavior has a direct relationship to their satisfaction, and it is cl...

Chronic, low intensity herbivory by invertebrates, termed background herbivory, has been understudied in tundra, yet its impacts are likely to increase in a warmer Arctic. The magnitude of these changes is however hard to predict as we know little about the drivers of current levels of invertebrate herbivory in tundra. We assessed the intensity of invertebrate herbivory on a common tundra plant, the dwarf birch (Betula glandulosa-nana complex), and investigated its relationship to latitude and climate across the tundra biome. Leaf damage by defoliating, mining and gall-forming invertebrates was measured in samples collected from 192 sites at 56 locations. Our results indicate that invertebrate herbivory is nearly ubiquitous across the tundra biome but occurs at low intensity. On average, invertebrates damaged 11.2% of the leaves and removed 1.4% of total leaf area. The damage was mainly caused by external leaf feeders, and most damaged leaves were only slightly affected (12% leaf area lost). Foliar damage was consistently positively correlated with mid-summer (July) temperature and, to a lesser extent, precipitation in the year of data collection, irrespective of latitude. Our models predict that, on average, foliar losses to invertebrates on dwarf birch are likely to increase by 6--7% over the current levels with a 1 textdegreeC increase in summer temperatures. Our results show that invertebrate herbivory on dwarf birch is small in magnitude but given its prevalence and dependence on climatic variables, background invertebrate herbivory should be included in predictions of climate change impacts on tundra ecosystems.

The purpose of this study was to determine, during an overground supra-threshold run, whether a change in the internal mechanical cost could occur during an exhaustive run and whether this change was related to the increase in the energy cost of running (C(r)).The Cr of 14 endurance runners was measured from pulmonary gas exchange using a breath-by-breath portable gas analyzer (Cosmed K4b, Rome, Italy), at the third and the last minute of an exhaustive exercise performed at their velocity corresponding to 95% of the maximal oxygen uptake (4.88 +/- 0.38 m.s(-1)). At the same time, potential, kinetic, and internal mechanical costs (C(pe), C(ke), and C(int)) were measured with a 3D motion analysis system (ANIMAN3D).C(int) and C(r) increased significantly within the third minute and the end of the supra-threshold exercise (respectively, 0.55 +/- 0.07 vs 0.60 +/- 0.07 J.kg(-1).m(-1) and 4.10 +/- 0.39 vs 4.32 +/- 0.42 J.kg(-1).m(-1); P < or = 0.03). However, the percentage of variation of C(int) and C(r) were not correlated (r = 0.06; P = 0.84). Contrary to C(int), C(ke) and C(pe) remained constant during the exercise (respectively, 1.33 +/- 0.33 vs 1.38 +/- 0.29 J.kg(-1).m(-1) P = 0.79 and 0.47 +/- 0.11 vs 0.48 +/- 0.10 J.kg(-1).m(-1); P = 0.67), but both parameters were significantly correlated with C(r) (r = 0.43; P = 0.03 and r = 0.40; P = 0.03).During overground running to exhaustion, a significant increase in C(int) occurred, but this did not account for the increase in C(r). Moreover, the increase in C(int) has yet to be explained.