Oxidation Dynamics of a Chain of Aluminum Nanoparticles

2013 ◽  
Vol 1521 ◽  
Author(s):  
Adarsh Shekhar ◽  
Weiqiang Wang ◽  
Richard Clark ◽  
Rajiv K. Kalia ◽  
Aiichiro Nakano ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Pure Aluminum ◽  
Aluminum Nanoparticles ◽  
Oxidation Reactions ◽  
The Third ◽  
The Core ◽  
Burning Behavior ◽  
A Chain ◽  
Dynamics Simulations ◽  
Exothermic Oxidation

ABSTRACTMultimillion-atom molecular dynamics simulations are used to investigate burning behavior of a chain of three alumina-coated aluminum nanoparticles (ANPs), where particles one and three are heated above the melting temperature of pure aluminum. The mode and mechanism behind the heat and mass transfer from the hot ANPs (particles one and three) to the middle, cold ANP (particle two) are studied. The hot nanoparticles oxidize first, after which hot Al atoms penetrate into the cold nanoparticle. It is also found that due to the penetration of hot Al atoms, the cold nanoparticle oxidizes at a faster rate than in the initially heated nanoparticles. The calculated speed of penetration is found to be 54 m/s, which is within the range of experimentally measured flame propagation rates. As the atoms penetrate into the central ANP, they maintain their relative positions. The atoms from the shell of the central ANP form the first layer, which is followed by the atoms from the shell of the outer ANP making the second layer and lastly the atoms from the core of the outer ANPs form the third layer. In addition to heating the central ANP by convection, the ejected hot Al atoms from the outer ANPs initiate exothermic oxidation reactions inside the central ANP, leading to further heating within the central ANP. During 1 ns, all three ANPs fuse together, forming a single ellipsoidal aggregate.

Heat-Initiated Oxidation of an Aluminum Nanoparticle

2012 ◽  
Vol 1405 ◽  
Author(s):  
Richard Clark ◽  
Weiqiang Wang ◽  
Ken-ichi Nomura ◽  
Rajiv K. Kalia ◽  
Aiichiro Nakano ◽  
...  
Keyword(s):  
Energetic Materials ◽  
Particle Temperature ◽  
Local Heating ◽  
Oxidation Reactions ◽  
Reactive Molecular Dynamics ◽  
The Core ◽  
Underlying Mechanisms ◽  
Shell Boundary ◽  
Dynamics Simulations ◽  
Visualization Techniques

ABSTRACTMultimillion-atom reactive molecular dynamics simulations were used to investigate the mechanisms which control heat-initiated oxidation in aluminum nanoparticles. The simulation results reveal three stages: (1) confined burning, (2) onset of deformation, and (3) onset of small cluster ejections. The first stage of the reaction is localized primarily at the core-shell boundary, where oxidation reactions result in strong local heating and the increased migration of oxygen from the shell into the core. When the local temperature rises above the melting point of alumina (T=2330K), the melting of the shell allows deformation of the overall particle and an increase in heat production. Finally, once the particle temperature exceeds 2800-3000 K, small aluminum-rich clusters are ejected from the outside of the shell. The underlying mechanisms were explored using global and radial statistical analysis, as well as developed visualization techniques and localized fragment analysis.The three-stage reaction mechanism found here provides insight into the controlling factors of aluminum nanoparticle oxidation, a topic of considerable importance in the energetic materials community.

scholarly journals Cryptochrome magnetoreception: four tryptophans could be better than three

2021 ◽  
Vol 18 (184) ◽  
Author(s):  
Siu Ying Wong ◽  
Yujing Wei ◽  
Henrik Mouritsen ◽  
Ilia A. Solov'yov ◽  
P. J. Hore
Keyword(s):  
Dynamic Equilibrium ◽  
Radical Pair ◽  
Spin Dynamics ◽  
Photoreceptor Cells ◽  
Kinetic Properties ◽  
Radical Pairs ◽  
Magnetic Sensing ◽  
The Third ◽  
A Chain ◽  
Dynamics Simulations

The biophysical mechanism of the magnetic compass sensor in migratory songbirds is thought to involve photo-induced radical pairs formed in cryptochrome (Cry) flavoproteins located in photoreceptor cells in the eyes. In Cry4a—the most likely of the six known avian Crys to have a magnetic sensing function—four radical pair states are formed sequentially by the stepwise transfer of an electron along a chain of four tryptophan residues to the photo-excited flavin. In purified Cry4a from the migratory European robin, the third of these flavin–tryptophan radical pairs is more magnetically sensitive than the fourth, consistent with the smaller separation of the radicals in the former. Here, we explore the idea that these two radical pair states of Cry4a could exist in rapid dynamic equilibrium such that the key magnetic and kinetic properties are weighted averages. Spin dynamics simulations suggest that the third radical pair is largely responsible for magnetic sensing while the fourth may be better placed to initiate magnetic signalling particularly if the terminal tryptophan radical can be reduced by a nearby tyrosine. Such an arrangement could have allowed independent optimization of the essential sensing and signalling functions of the protein. It might also rationalize why avian Cry4a has four tryptophans while Crys from plants have only three.

Consent

2018 ◽  
Author(s):  
Martin Krzywdzinski
Keyword(s):  
Production Systems ◽  
Employee Behavior ◽  
Labor Disputes ◽  
Performance Expectations ◽  
The Third ◽  
The Core ◽  
Core Requirements ◽  
High Level

This chapter deals with the dependent variable of the study: consent. It analyses workplace consent in Russia and China using three indicators that refer to the core requirements of the production systems in automotive companies regarding employee behavior: first, standardized work; and second, compliance with expectations in terms of flexibility, cooperation, and a commitment to improving processes. The third indicator of consent (or the lack of it) is the absence or presence of open criticism, resistance, and labor disputes. The chapter reveals significant and unexpected differences between the Chinese and Russian sites on all three indicators. While the Chinese factories exhibit (with some variance between the companies), a relatively high level of consent, the Russian plants have problems with standardized work, the acceptance of performance expectations, and to some extent with labor disputes.

Duoethnography: A Polytheoretical Approach to (Re)Storing, (Re)Storying the Meanings That One Gives

2020 ◽  
pp. 396-423
Author(s):  
John Joseph Norris ◽  
Richard D. Sawyer
Keyword(s):  
Social Justice ◽  
Critical Theory ◽  
Third Space ◽  
The Third ◽  
The Core ◽  
Wide Range ◽  
Core Elements ◽  
Feminist Inquiry

This chapter summarizes the advancement of duoethnography throughout its fifteen-year history, employing examples from a variety of topics in education and social justice to provide a wide range of approaches that one may take when conducting a duoethnography. A checklist articulates what its cofounders consider the core elements of duoethnographies, additional features that may or may not be employed and how some studies purporting to be duoethnographies may not be so. The chapter indicates connections between duoethnography and a number of methodological concepts including the third space, the problematics of representation, feminist inquiry, and critical theory using published examples by several duoethnographers.

scholarly journals Spatial segregation of mixed-sized counterions in dendritic polyelectrolytes

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
J. S. Kłos ◽  
J. Paturej
Keyword(s):  
Electrostatic Interactions ◽  
Spatial Separation ◽  
Excluded Volume ◽  
The Core ◽  
Bjerrum Length ◽  
Two Component ◽  
Conformational Properties ◽  
Dynamics Simulations ◽  
Two Parameters ◽  
Swelling Factor

AbstractLangevin dynamics simulations are utilized to study the structure of a dendritic polyelectrolyte embedded in two component mixtures comprised of conventional (small) and bulky counterions. We vary two parameters that trigger conformational properties of the dendrimer: the reduced Bjerrum length, $$\lambda _B^*$$ λ B ∗ , which controls the strength of electrostatic interactions and the number fraction of the bulky counterions, $$f_b$$ f b , which impacts on their steric repulsion. We find that the interplay between the electrostatic and the counterion excluded volume interactions affects the swelling behavior of the molecule. As compared to its neutral counterpart, for weak electrostatic couplings the charged dendrimer exists in swollen conformations whose size remains unaffected by $$f_b$$ f b . For intermediate couplings, the absorption of counterions into the pervaded volume of the dendrimer starts to influence its conformation. Here, the swelling factor exhibits a maximum which can be shifted by increasing $$f_b$$ f b . For strong electrostatic couplings the dendrimer deswells correspondingly to $$f_b$$ f b . In this regime a spatial separation of the counterions into core–shell microstructures is observed. The core of the dendrimer cage is preferentially occupied by the conventional ions, whereas its periphery contains the bulky counterions.

scholarly journals Costa, cancer and coronavirus: contractualism as a guide to the ethics of lockdown

2021 ◽  
pp. medethics-2020-107103
Author(s):  
Stephen David John ◽  
Emma J Curran
Keyword(s):  
Moral Theory ◽  
Cost Benefit Analysis ◽  
Cost Benefit ◽  
Benefit Analysis ◽  
Life And Death ◽  
The Third ◽  
The Core ◽  
Key Issues ◽  
Moral Distinction ◽  
Self Defence

Lockdown measures in response to the COVID-19 pandemic involve placing huge burdens on some members of society for the sake of benefiting other members of society. How should we decide when these policies are permissible? Many writers propose we should address this question using cost-benefit analysis (CBA), a broadly consequentialist approach. We argue for an alternative non-consequentialist approach, grounded in contractualist moral theorising. The first section sets up key issues in the ethics of lockdown, and sketches the apparent appeal of addressing these problems in a CBA frame. The second section argues that CBA fundamentally distorts the normative landscape in two ways: first, in principle, it allows very many morally trivial preferences—say, for a coffee—might outweigh morally weighty life-and-death concerns; second, it is insensitive to the core moral distinction between victims and vectors of disease. The third section sketches our non-consequentialist alternative, grounded in Thomas Scanlon’s contractualist moral theory. On this account, the ethics of self-defence implies a strong default presumption in favour of a highly restrictive, universal lockdown policy: we then ask whether there are alternatives to such a policy which are justifiable to all affected parties, paying particular attention to the complaints of those most burdened by policy. In the fourth section, we defend our contractualist approach against the charge that it is impractical or counterintuitive, noting that actual CBAs face similar, or worse, challenges.

Desire for Self-healing

2017 ◽  
Vol 12 (1-2) ◽  
pp. 317-335
Author(s):  
Ngar-sze Lau
Keyword(s):  
Theravada Buddhism ◽  
Self Healing ◽  
Core Knowledge ◽  
The Third ◽  
The Core ◽  
Physical Suffering ◽  
Mind And Body ◽  
Core Practice ◽  
The Relationship ◽  
Contemporary Chinese

Abstract This practice report describes how Chinese meditators understand the “four foundations of mindfulness” (satipaṭṭhāna, sinianzhu 四念住) as a remedy for both mental and physical suffering. In the tradition of Theravāda Buddhism, satipaṭṭhāna is particularly recognized as the core knowledge for understanding the relationship between mind and body, and the core practice leading to liberation from suffering. Based on interviews with Chinese meditation practitioners, this study develops three main themes concerning how they have alleviated afflictions through the practice of satipaṭṭhāna. The first theme highlights how practitioners learn to overcome meditation difficulties with “right attitude.” The second theme is about practicing awareness with “six sense doors” open in order to facilitate the balance of the “five faculties.” The third theme explores how practitioners cultivate daily life practice through an understanding of the nature of mind and body as impermanent and as not-self. This paper details how these themes and embodied practices of satipaṭṭhāna constitute ways of self-healing for urban educated Buddhists in the contemporary Chinese context.

Measured Film Cooling Effectiveness of Three Multihole Patterns

2005 ◽  
Vol 128 (2) ◽  
pp. 192-197 ◽  
Author(s):  
Yuzhen Lin ◽  
Bo Song ◽  
Bin Li ◽  
Gaoen Liu
Keyword(s):  
Experimental Data ◽  
Mass Transfer ◽  
Film Cooling ◽  
Row Spacing ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Analogy Method ◽  
Blowing Ratio ◽  
The Third ◽  
Coolant Injection

As an advanced cooling scheme to meet increasingly stringent combustor cooling requirements, multihole film cooling has received considerable attention. Experimental data of this cooling scheme are limited in the open literature in terms of different hole patterns and blowing ratios. The heat-mass transfer analogy method was employed to measure adiabatic film cooling effectiveness of three multihole patterns. Three hole patterns differed in streamwise row spacing (S), spanwise hole pitch (P), and hole inclination angle (α), with the first pattern S∕P=2 and α=30°, the second S∕P=1 and α=30°, and the third S∕P=2 and α=150°. Measurements were performed at different blow ratios (M=1-4). Streamwise coolant injection offers high cooling protection for downstream rows. Reverse coolant injection provides superior cooling protection for initial rows. The effect of blowing ratio on cooling effectiveness is small for streamwise injection but significant for reversion injection.

scholarly journals Efficient Nanoporous Silicon Membranes for Integrated Microfluidic Separation and Sensing Systems

2009 ◽  
Vol 1191 ◽  
Author(s):  
Nazar Ileri ◽  
Sonia E. Létant ◽  
Jerald Britten ◽  
Hoang Nguyen ◽  
Cindy Larson ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Processing System ◽  
Molecular Transport ◽  
Superior Performance ◽  
Electron Conduction ◽  
Microfluidic Separation ◽  
Planar Arrays ◽  
Molecular Separation ◽  
Silicon Membranes ◽  
Dynamics Simulations

AbstractNanoporous devices constitute emerging platforms for selective molecule separation and sensing, with great potential for high throughput and economy in manufacturing and operation. Acting as mass transfer diodes similar to a solid-state device based on electron conduction, conical pores are shown to have superior performance characteristics compared to traditional cylindrical pores. Such phenomena, however, remain to be exploited for molecular separation. Here we present performance results from silicon membranes created by a new synthesis technique based on interferometric lithography. This method creates millimeter sized planar arrays of uniformly tapered nanopores in silicon with pore diameter 100 nm or smaller, ideally-suited for integration into a multi-scale microfluidic processing system. Molecular transport properties of these devices are compared against state-of-the-art polycarbonate track etched (PCTE) membranes. Mass transfer rates of up to fifteen-fold greater than commercial sieve technology are obtained. Complementary results from molecular dynamics simulations on molecular transport are reported.

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