The order-disorder phenomenon of the cation sub-lattice is of substantial interests recently. However, randomness of the disordered local atomic structures poses great challenges for the modeling of ...ordering at larger size/time scales. In this work, a cation-pair model is developed to simulate the order-disorder of layered Li2TiO3. The configurational order of the lattice is simplified by the number of cation pairs at ordered/disordered state. Simulated x-ray diffraction of lattice models is performed to allow comparison with experimental observations. The configuration dependent activation energy is obtained by the simulated evolution of order-disorder based on density functional total energies. The cation-pair simplification enables fast estimation of ordering by tracking the number of pairs with rate theory. The model successfully reproduces the inhibition of ordering from increasing Zr/Ti in the Li2Ti1-xZrxO3 solid solution. Different stages of order-disorder have distinct features of ordering rates, which is explained by the coupling between ordering rates and degree of disorder. In addition, the model predicts stage-specific equilibrium conditions at various Zr/Ti and temperatures.
Display omitted
A taxonomy for sp2 carbon allotropes in two dimensions (2D) is proposed where single-layer structures are assigned a unique symbol associated with the geometry of each allotrope. The naming scheme is ...demonstrated for structures described in the literature and is further illustrated for a number of other topology-allowed sp2 carbon systems. The symbol is easy to use and gives a direct access to geometrical features such as the number of polygons and their arrangement. It facilitates the classification of structures reported in the literature, where many such structures are found to have been assigned a name based on each author’s somewhat arbitrary choice. This naming scheme will help rationalize future studies on this class of systems. A comparative study of the energetics of the structures is also performed, using a consistent set of numerical parameters. The naming scheme can be expanded to carbon systems with mixed hybridizations and to other non-carbon 2D systems.
Display omitted
Slow Component of V˙O2 Kinetics JONES, ANDREW M.; GRASSI, BRUNO; CHRISTENSEN, PETER M. ...
Medicine and science in sports and exercise,
11/2011, Letnik:
43, Številka:
11
Journal Article
We demonstrate the use of nanosecond pulse transient plasma (NPTP) to improve the control (and acceleration) of the combustion of solid rocket propellants. Here, we fabricate end-burning propellant ...samples (i.e., grains) with a co-axial center wire electrode using hydroxyl terminated polybutadiene (HTPB), isodecyl pelargonate (IDP), modified diphenyl diisocyanate (MDI), and ammonium perchlorate (AP) as the fuel, plasticizer, curative, and oxidizer, respectively. High voltage (20 kV) nanosecond pulses (20 nsec) produce a streamer discharge that provides electronic throttling of the solid rocket propellant. These studies are carried out over a wide range of oxidizer mass fractions, including those considered insensitive munitions (IM). In addition, real time imaging is performed characterizing the plasma-formation, evolution of the ignition process, and plasma enhanced flame-fuel coupling. We believe the plasma-based mechanisms of enhancement are 3-fold: 1.) The plasma provides highly energetic electrons that drive new chemical reaction pathways via highly reactive atomic species such as H, O, and Cl, 2.) The plasma sputters chunks of the solid fuel material up into the flame where it is combusted, producing an agitated flame profile. 3.) The plasma provides increased turbulence and multi-scale mixing due to hydrodynamic effects (i.e., ionic winds), which further improves the combustion process. Having electronic control of the burn rate introduces the ability to “throttle” solid rocket motors and introduce new flight profile options beyond a pre-selected profile such as the typical boost-sustain profile. While we are unable to quantify the burn rate or thrust from these relatively simple observations, we observe clear evidence of the effect of the plasma on the combustion of these solid rocket fuels even at high oxidizer content.
Abstract
Context
Metabolic syndrome and elevated high-sensitivity C-reactive protein (hsCRP) levels are associated with risk of cardiovascular diseases. A reduced myocardial mechano-energetic ...efficiency (MEE) has been found to be an independent predictor of cardiovascular disease.
Objective
To evaluate the association between metabolic syndrome and hsCRP levels with impaired MEE.
Methods
Myocardial MEE was assessed by a validated echocardiography-derived measure in 1975 nondiabetic and prediabetic individuals subdivided into 2 groups according to the presence of metabolic syndrome.
Results
Individuals with metabolic syndrome exhibited increased stroke work and myocardial oxygen consumption estimated by rate pressure product, and a reduced MEE per gram of left ventricular mass (MEEi) compared with subjects without metabolic syndrome, after adjusting for age and sex. Myocardial MEEi progressively decreased in parallel with the increase in the number of metabolic syndrome components. In a multivariable regression analysis, both metabolic syndrome and hsCRP contributed to reduced myocardial MEEi independently of sex, total cholesterol, high-density lipoprotein, triglycerides, fasting, and 2-hour postload glucose levels. When the study population was divided into 4 groups by the presence or absence of metabolic syndrome and by hsCRP levels above and below 3 mg/L, hsCRP levels ≥3 mg/L were associated with reduced myocardial MEEi both in subjects with metabolic syndrome and in those without the syndrome.
Conclusion
Nondiabetic and prediabetic individuals with metabolic syndrome exhibit increased stroke work and myocardial oxygen consumption, and an impaired MEEi, an established predictor of adverse cardiovascular events, and elevated hsCRP levels in combination with metabolic syndrome aggravate the myocardial MEEi impairment.
A plane wave periodic density functional theory study of a representative hexagonal shaped MoS2 nanoparticle is conducted to compute the site-dependent energetics of the catalyst under different ...operating conditions. It is shown that the (1) energy for vacancy formation and the associated free energy profile of the reaction steps involved in creating the vacancy and (2) the binding energy of hydrogen and other probe atoms such as CO and lutidine, are all dependent on the location of the associated sulfur or molybdenum atom and the edge type (i.e. metal or sulfur edge). In particular, sulfur atoms near the corner are more strongly bound than those in the interior of the metal edge. Further, a larger metal-sulfur bond strength results in lower binding energy of hydrogen on that sulfur atom which in turn implies that this hydrogen is more Brønsted acidic in nature. These results indicate that the nature and the location of active sites on MoS2 is heavily dependent on the nature of the reaction that is being catalyzed and the corresponding operating conditions.
Display omitted
•Site-dependent energetic properties of MoS2 nanoparticles were investigated.•Vacancy formation difficult on corner sites & progressively easier away from them.•H binding energy is negative on some S atoms but otherwise usually endothermic.•CO prefers Mo atoms and vacancies while lutidine gets protonated on SH groups.•Scaling relations between vacancy formation, H binding, and lutidine protonation.
First principles study within the density functional theory is addressed to study the energetic and electronic properties of β12 borophene nanosheet with adsorbed platinum (Pt). In addition, the ...potential use of Pt-decorated borophene as a catalytic material and molecular sensor is also studied. We observed that the most stable configuration (lower binding energy) for Pt be adsorbed on the β12 borophene nanosheet is on the center of a hexagon (Eb=−4.473 eV). The presence of Pt adsorbed does not modify the metallic properties of β12 borophene but gives rise to new electronic levels resonant with the conduction band (around 2.0 eV above the Fermi energy). The calculated Bader charge show a charge transference of 0.567 electrons from borophene to the Pt atom. When molecules are adsorbed on the Pt atom, the calculated adsorption energies, electronic density of states (DOS), work function, and charge transference show that there is a strong interaction between hazardous molecules and Pt-decorated β12 borophene. The only exception is CO2, which interact with Pt-decorated borophene via van der Waals forces. The comparative analysis of the DOS before and after the molecular adsorption shows that the Pt levels are spread out and shifted to the Fermi energy after the molecular adsorption. The results of the DOS, charge transference, as well as the change in the work function allow us to infer that Pt-decorated β12 borophene is a potential material to be used as catalyst and gas sensing.
Display omitted
•Understanding the energetics of Pt-decorated on β12 borophene.•Effects of molecular adsorption on Pt-decorated β12 borophene.•Use Pt-decorated β12 borophene for gas sensing.
Researchers from diverse disciplines, including organismal and cellular physiology, sports science, human nutrition, evolution and ecology, have sought to understand the causes and consequences of ...the surprising variation in metabolic rate found among and within individual animals of the same species. Research in this area has been hampered by differences in approach, terminology and methodology, and the context in which measurements are made. Recent advances provide important opportunities to identify and address the key questions in the field. By bringing together researchers from different areas of biology and biomedicine, we describe and evaluate these developments and the insights they could yield, highlighting the need for more standardisation across disciplines. We conclude with a list of important questions that can now be addressed by developing a common conceptual and methodological toolkit for studies on metabolic variation in animals.
New technologies and methods, drawn from across biomedicine and the biosciences, are allowing quantification of metabolic rates at both whole‐animal and cellular (mitochondrial) levels and in a broad range of species and contexts, so allowing insights into why both maximal and minimal metabolic rates show such marked intraspecific variation.
PDF
