Correlation between hardness and bond orientation of vanadium borides

RSC Advances ◽  
2014 ◽  
Vol 4 (88) ◽  
pp. 47377-47382 ◽  
Author(s):  
Y. Pan ◽  
Y. H. Lin ◽  
J. M. Guo ◽  
M. Wen
Keyword(s):  
First Principles ◽  
The Relationship ◽  
Bond Characteristic

The relationship between hardness and bond characteristic of vanadium borides was investigated by first-principles approach.

Phase stability, Debye temperature and hardness of semiconducting manganese tetraboride MnB4: First-principles investigations

2017 ◽  
Vol 31 (20) ◽  
pp. 1750131 ◽  
Author(s):  
Ming-Min Zhong ◽  
Cheng Huang ◽  
Chun-Ling Tian
Keyword(s):  
Debye Temperature ◽  
Phase Stability ◽  
First Principles ◽  
Formation Enthalpy ◽  
Structural Features ◽  
High Melting Point ◽  
Fundamental Understanding ◽  
New Perspective ◽  
The Relationship ◽  
Good Agreement

First-principles investigations are employed to provide a fundamental understanding of the structural features, phase stability, mechanical properties, Debye temperature, and hardness of manganese tetraboride. Eight candidate structures of known transition-metal tetraborides are chosen to probe. The calculated lattice parameters, elastic properties, Poisson’s ratio, and [Formula: see text] ratio are derived. It is observed that the monoclinic structure with [Formula: see text] symmetry (MnB4–MnB4) is the most stable in energy. The mechanical and thermodynamic stabilities of seven possible phases are confirmed by the calculated elastic constants and formation enthalpy. Moreover, the analysis on density of states demonstrates semiconducting behavior of MnB4–MnB4 and different metallic behaviors of other phases. The estimated hardness of MnB4–MnB4 is 38.3 GPa, which is in good agreement with experimental value. Furthermore, the relationship between hardness and Debye temperature is investigated and verifies that MnB4–MnB4 is a newly potential semiconducting ultrahard material with high melting point. It provides a new perspective of searching for semiconducting superhard materials to be applied in extreme conditions.

Mathematical Background

1993 ◽  
Author(s):  
Greg M. Anderson ◽  
David A. Crerar
Keyword(s):  
Free Energy ◽  
Real World ◽  
First Principles ◽  
Mathematical Language ◽  
Integral Calculus ◽  
The Road ◽  
Mathematical Background ◽  
The Subject ◽  
The Relationship ◽  
Theoretical Side

Thermodynamics, like other sciences, has a theoretical side, expressed in mathematical language, and a practical side, in which experiments are performed to produce the physical data required and interpreted by the theoretical side. The mathematical side of thermodynamics is simple and elegant and is easily derived from first principles. This might lead to the conclusion that thermodynamics is a simple subject, one that can be easily absorbed early in one's education before going on to more challenging and interesting topics. This is true, if by learning thermodynamics one means learning to manipulate its equations and variables and showing their interrelationships. But for most students the subject is actually far from simple, and for professors it is a considerable challenge to present the necessary material intelligibly. The equations and the variables are somehow related to the real world of beakers and solutions, fuels and engines, rocks and minerals, and it is this interface that provides most of the difficulties. What do variables such as entropy and free energy really mean, and what physical processes do the equations describe? The difficulty in understanding and using thermodynamics is conceptual, not mathematical. We will attempt to explain the relationship between the mathematical and the physical sides of thermodynamics, but it is advisable first to review the mathematics involved and subsequently to define the terms used in thermodynamics. The mathematics required for thermodynamics consists for the most part of nothing more complex than differential and integral calculus. However, several aspects of the subject can be presented in various ways that are either more or less mathematically based, and the "best" way for various individuals depends on their mathematical background. The more mathematical treatments are elegant, concise, and satisfying to some people, and too abstract and divorced from reality for others. In this book we attempt to steer a middle-of-the-road course. We review in the first part of this chapter those aspects of mathematics that are absolutely essential to an understanding of thermodynamics. The chapter closes with mathematical topics that, although not essential, do help in understanding certain aspects of thermodynamics.

scholarly journals Effect of Defects on Spontaneous Polarization in Pure and Doped LiNbO3: First-Principles Calculations

Materials ◽  
2018 ◽  
Vol 12 (1) ◽  
pp. 100 ◽  
Author(s):  
Weiwei Wang ◽  
Dahuai Zheng ◽  
Mengyuan Hu ◽  
Shahzad Saeed ◽  
Hongde Liu ◽  
...  
Keyword(s):  
Spontaneous Polarization ◽  
First Principles ◽  
Density Functional ◽  
Lattice Distortion ◽  
Stable Structure ◽  
First Principles Calculations ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Specific Configuration ◽  
The Relationship

Numerous studies have indicated that intrinsic defects in lithium niobate (LN) dominate its physical properties. In an Nb-rich environment, the structure that consists of a niobium anti-site with four lithium vacancies is considered the most stable structure. Based on the density functional theory (DFT), the specific configuration of the four lithium vacancies of LN were explored. The results indicated the most stable structure consisted of two lithium vacancies as the first neighbors and the other two as the second nearest neighbors of Nb anti-site in pure LN, and a similar stable structure was found in the doped LN. We found that the defects dipole moment has no direct contribution to the crystal polarization. Spontaneous polarization is more likely due to the lattice distortion of the crystal. This was verified in the defects structure of Mg2+, Sc3+, and Zr4+ doped LN. The conclusion provides a new understanding about the relationship between defect clusters and crystal polarization.

Offender Mobility and Crime Pattern Formation from First Principles

2011 ◽  
pp. 193-208 ◽  
Author(s):  
P. Jeffrey Brantingham ◽  
George Tita
Keyword(s):  
Pattern Formation ◽  
First Principles ◽  
Two Dimensional ◽  
Agent Based ◽  
Crime Patterns ◽  
Movement Strategies ◽  
Criminal Opportunity ◽  
The Relationship ◽  
Basic Movement ◽  
Crime Pattern

Criminal opportunity in most cases is constrained by the fact that motivated offenders and potential targets or victims are not found at the same place at the same time. This ecological fact necessitates that offenders, potential victims, or both move into spatial positions that make crimes physically possible. This chapter develops a series of simple mathematical and agent-based models looking at the relationship between basic movement decisions and emergent crime patterns in two-dimensional environments. It is shown that there may be substantial regularities to crime patterns, including the tendency for crime to form discrete hotspots that arise solely from different movement strategies deployed by offenders.

scholarly journals First-principles study of organic molecule for corrosion inhibition

2019 ◽  
Vol 116 ◽  
pp. 00007
Author(s):  
Rachid Belkada ◽  
Dalila Hammoutène ◽  
Rahma Tibigui ◽  
Ikram Hadj-Said
Keyword(s):  
First Principles ◽  
Global Economy ◽  
Density Functional ◽  
Corrosion Inhibitors ◽  
Computational Techniques ◽  
Corrosion Properties ◽  
Functional Theory ◽  
Fundamental Level ◽  
Organic Inhibitors ◽  
The Relationship

The widespread use of steel in various industries, especially in the transportation of hydrocarbons and gas, has recently gained a potential interest to explore eco-friendly solutions against corrosion. In fact, the highly aggressive environment generates considerable losses that affect global economy of countries that are mainly depending on the production and transport of energy. In the field of corrosion inhibitors, most common method so far available for protection against corrosion relies on synthetic one. These are unfortunately harmful to the environment as well to the human health, however they remain the most popular and the most effective due to their cost, and their ease of application. One of the most challenging issues in this area is the accurate understanding and measure of the degree of the passivation of corrosion inhibitors, which is complex and depend on many factors such as the nature of the metal, the fluid, the electronic structure of the inhibitor, the temperature, the exposure time, and so on. Recently, organic inhibitors have become increasingly attractive due to their competitive character as compared to the synthetic ones. With the use of advanced computational techniques enhanced by the development of density functional theory (DFT), it becomes possible to identify and design at the fundamental level, novel corrosion inhibitor molecules as complementary well established tool beside to the experimental techniques, which are often very expensive and time-consuming. In this work, we explore by mean of DFT, the anti-corrosion effect of the Lawsone molecule (2-hydroxy-1,4-naphthoquinone) and some of its derivatives to clarify and understand the relationship at the fundamental level between the anti-corrosion properties and the structure of the molecule in contact with the iron.

scholarly journals Multiscale modelling for tokamak pedestals

2018 ◽  
Vol 84 (2) ◽  
Author(s):  
I. G. Abel ◽  
A. Hallenbert
Keyword(s):  
First Principles ◽  
Detailed Comparison ◽  
Multiscale Approach ◽  
Systems Of Equations ◽  
Line Region ◽  
Open Field Line ◽  
Small Parameters ◽  
The Relationship ◽  
Kinetic Physics ◽  
Current Modelling

Pedestal modelling is crucial to predict the performance of future fusion devices. Current modelling efforts suffer either from a lack of kinetic physics, or an excess of computational complexity. To ameliorate these problems, we take a first-principles multiscale approach to the pedestal. We will present three separate sets of equations, covering the dynamics of edge localised modes (ELMs), the inter-ELM pedestal and pedestal turbulence, respectively. Precisely how these equations should be coupled to each other is covered in detail. This framework is completely self-consistent; it is derived from first principles by means of an asymptotic expansion of the fundamental Vlasov–Landau–Maxwell system in appropriate small parameters. The derivation exploits the narrowness of the pedestal region, the smallness of the thermal gyroradius and the low plasma$\unicode[STIX]{x1D6FD}$(the ratio of thermal to magnetic pressures) typical of current pedestal operation to achieve its simplifications. The relationship between this framework and gyrokinetics is analysed, and possibilities to directly match our systems of equations onto multiscale gyrokinetics are explored. A detailed comparison between our model and other models in the literature is performed. Finally, the potential for matching this framework onto an open-field-line region is briefly discussed.

scholarly journals What People Really Think About Safety around Horses: The Relationship between Risk Perception, Values and Safety Behaviours

Animals ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 2222
Author(s):  
Meredith Chapman ◽  
Matthew Thomas ◽  
Kirrilly Thompson
Keyword(s):  
Risk Perception ◽  
First Principles ◽  
Risk Perceptions ◽  
Risk Mitigation ◽  
Perceptions Of Risk ◽  
General Acceptance ◽  
Related Risk ◽  
Serious Injuries ◽  
The Relationship ◽  
Safety First

The equestrian industry reports high rates of serious injuries, illness and fatalities when compared to other high-risk sports and work environments. To address these ongoing safety concerns, a greater understanding of the relationship between human risk perception, values and safety behaviours is required. This paper presents results from an international survey that explored relationships between a respondents’ willingness to take risk during daily activities along with, their perceptions of risk and behaviours during horse-related interactions. Respondents’ comments around risk management principles and safety-first inspirations were also analysed. We examined what humans think about hazardous situations or activities and how they managed risk with suitable controls. Analysis identified three important findings. First, safe behaviours around horses were associated with safety training (formal and/or informal). Second, unsafe behaviours around horses were associated with higher levels of equestrian experience as well as income from horse-related work. Finally, findings revealed a general acceptance of danger and imminent injury during horse interactions. This may explain why some respondents de-emphasised or ‘talked-down’ the importance of safety-first principles. In this paper we predominantly reported quantitative findings of respondents self-reported safety behaviours, general and horse-related risk perceptions despite injury or illness. We discussed the benefits of improved safety-first principles like training, risk assessments, rider-horse match with enriched safety communications to enhance risk-mitigation during human–horse interactions.

Deconstructing RTK: How to explicate a theory of implicit knowledge

1999 ◽  
Vol 22 (5) ◽  
pp. 790-801 ◽  
Author(s):  
Josef Perner ◽  
Zoltan Dienes
Keyword(s):  
Executive Control ◽  
First Principles ◽  
Explicit Knowledge ◽  
Implicit Knowledge ◽  
Theory Of Knowledge ◽  
Memory Development ◽  
Target Article ◽  
Linguistic Representations ◽  
Implicit And Explicit ◽  
The Relationship

In this response, we start from first principles, building up our theory to show more precisely what assumptions we do and do not make about the representational nature of implicit and explicit knowledge (in contrast to the target article, where we started our exposition with a description of a fully fledged representational theory of knowledge (RTK). Along the way, we indicate how our analysis does not rely on linguistic representations but it implies that implicit knowledge is causally efficacious; we discuss the relationship between property structure implicitness and conceptual and nonconceptual content; then we consider the factual, fictional, and functional uses of representations and how we go from there to consciousness. Having shown how the basic theory deals with foundational criticisms, we indicate how the theory can elucidate issues that commentators raised in the particular application areas of explicitation, voluntary control, visual perception, memory, development (with discussion on infancy, theory of mind [TOM] and executive control, gestures), and finally models of learning.

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