scholarly journals Modelling the Melting of Gallium Clusters: A Path to Understanding Molecular Solids

2021 ◽  
Author(s):  
◽  
Krista Grace Steenbergen
Keyword(s):  
Melting Temperature ◽  
Correlation Energy ◽  
Single Atom ◽  
Metallic Surface ◽  
Molecular Solids ◽  
The Difference ◽  
Dynamics Simulations ◽  
Measured Specific Heat ◽  
Small Clusters ◽  
Relationship Of

<p>Gallium is a molecular solid with many unique properties. Comprised of Ga2 dimers but exhibiting metal-like electronic characteristics, gallium may be deemed a molecular metal. The role of this dual covalent-metallic nature may explain gallium’s fascinating thermodynamic behaviour. While bulk gallium melts at 303 K, clusters with only 10’s of atoms melt at temperatures between 500 and 800 K, according to experiment. The measured specific heat curves exhibit a strong size-sensitivity, where the addition of a single atom can alter the melting temperature by up to 100 K. This research addresses the relationship of electronic structure to the melting behaviour in small gallium clusters through a parallel tempering implementation of first-principles molecular dynamics simulations. These simulations cover 11 cluster sizes and two charge states, including neutral clusters sized 7-12 atoms and cationic clusters sized 32-35 atoms. The modelling of small clusters sets a lower size limit for melting and illustrates that greater-than-bulk melting is not universal for small gallium clusters. The larger cluster sizes allow for a direct comparison to experimental data. Each simulation reveals that the clusters have a non-covalent nature more similar to the metallic surface structure of bulk gallium than its covalently bonded interior. The dramatic lowering of melting temperatures and cluster stabilities with single atom additions supports the conclusion that the difference in the nature of bonding between bulk and clusters accounts for the melting temperature discrepancy. Finally, in order to gain additional insight into the nature of bonding in molecular solids, the cohesive energies of the solid halogens are calculated by the method of increments. These calculations investigate the relative N-body correlation energy contributions to the total cohesive energy for solid Cl2, Br2 and I2.</p>

scholarly journals Modelling the Melting of Gallium Clusters: A Path to Understanding Molecular Solids

2021 ◽  
Author(s):  
◽  
Krista Grace Steenbergen
Keyword(s):  
Melting Temperature ◽  
Correlation Energy ◽  
Single Atom ◽  
Metallic Surface ◽  
Molecular Solids ◽  
The Difference ◽  
Dynamics Simulations ◽  
Measured Specific Heat ◽  
Small Clusters ◽  
Relationship Of

<p>Gallium is a molecular solid with many unique properties. Comprised of Ga2 dimers but exhibiting metal-like electronic characteristics, gallium may be deemed a molecular metal. The role of this dual covalent-metallic nature may explain gallium’s fascinating thermodynamic behaviour. While bulk gallium melts at 303 K, clusters with only 10’s of atoms melt at temperatures between 500 and 800 K, according to experiment. The measured specific heat curves exhibit a strong size-sensitivity, where the addition of a single atom can alter the melting temperature by up to 100 K. This research addresses the relationship of electronic structure to the melting behaviour in small gallium clusters through a parallel tempering implementation of first-principles molecular dynamics simulations. These simulations cover 11 cluster sizes and two charge states, including neutral clusters sized 7-12 atoms and cationic clusters sized 32-35 atoms. The modelling of small clusters sets a lower size limit for melting and illustrates that greater-than-bulk melting is not universal for small gallium clusters. The larger cluster sizes allow for a direct comparison to experimental data. Each simulation reveals that the clusters have a non-covalent nature more similar to the metallic surface structure of bulk gallium than its covalently bonded interior. The dramatic lowering of melting temperatures and cluster stabilities with single atom additions supports the conclusion that the difference in the nature of bonding between bulk and clusters accounts for the melting temperature discrepancy. Finally, in order to gain additional insight into the nature of bonding in molecular solids, the cohesive energies of the solid halogens are calculated by the method of increments. These calculations investigate the relative N-body correlation energy contributions to the total cohesive energy for solid Cl2, Br2 and I2.</p>

The relationship of IGE receptor topography to signaling activity in RBL-2H3 mast cells

1991 ◽  
Vol 49 ◽  
pp. 236-237
Author(s):  
J.R. Pfeiffer ◽  
J.C. Seagrave ◽  
C. Wofsy ◽  
J.M. Oliver
Keyword(s):  
Mast Cells ◽  
Protein A ◽  
Scattered Electron ◽  
Ige Receptor ◽  
Receptor Complexes ◽  
Ige Binding ◽  
Electron Imaging ◽  
Small Clusters ◽  
Relationship Of ◽  
The Relationship

In RBL-2H3 rat leukemic mast cells, crosslinking IgE-receptor complexes with anti-IgE antibody leads to degranulation. Receptor crosslinking also stimulates the redistribution of receptors on the cell surface, a process that can be observed by labeling the anti-IgE with 15 nm protein A-gold particles as described in Stump et al. (1989), followed by back-scattered electron imaging (BEI) in the scanning electron microscope. We report that anti-IgE binding stimulates the redistribution of IgE-receptor complexes at 37“C from a dispersed topography (singlets and doublets; S/D) to distributions dominated sequentially by short chains, small clusters and large aggregates of crosslinked receptors. These patterns can be observed (Figure 1), quantified (Figure 2) and analyzed statistically. Cells incubated with 1 μg/ml anti-IgE, a concentration that stimulates maximum net secretion, redistribute receptors as far as chains and small clusters during a 15 min incubation period. At 3 and 10 μg/ml anti-IgE, net secretion is reduced and the majority of receptors redistribute rapidly into clusters and large aggregates.

Data-Driven Many-Body Models with Chemical Accuracy for CH4/H2O Mixtures

2020 ◽  
Author(s):  
Marc Riera ◽  
Alan Hirales ◽  
Raja Ghosh ◽  
Francesco Paesani
Keyword(s):  
Liquid Phase ◽  
Quantitative Description ◽  
Liquid Mixtures ◽  
Many Body ◽  
Energy Functions ◽  
Potential Energy Functions ◽  
Dynamics Simulations ◽  
Body Potential ◽  
Small Clusters ◽  
Many Body Interactions

<div> <div> <div> <p>Many-body potential energy functions (PEFs) based on the TTM-nrg and MB-nrg theoretical/computational frameworks are developed from coupled cluster reference data for neat methane and mixed methane/water systems. It is shown that that the MB-nrg PEFs achieve subchemical accuracy in the representation of individual many-body effects in small clusters and enables predictive simulations from the gas to the liquid phase. Analysis of structural properties calculated from molecular dynamics simulations of liquid methane and methane/water mixtures using both TTM-nrg and MB-nrg PEFs indicates that, while accounting for polarization effects is important for a correct description of many-body interactions in the liquid phase, an accurate representation of short-range interactions, as provided by the MB-nrg PEFs, is necessary for a quantitative description of the local solvation structure in liquid mixtures. </p> </div> </div> </div>

It Keeps Me Seeking

2018 ◽  
Author(s):  
Andrew Briggs ◽  
Hans Halvorson ◽  
Andrew Steane
Keyword(s):  
Evolutionary Biology ◽  
Quantum Physics ◽  
Natural World ◽  
Theological Reflection ◽  
Fine Tuning ◽  
Good Argument ◽  
The Difference ◽  
Argument From Design ◽  
Relationship Of

Two scientists and a philosopher aim to show how science both enriches and is enriched by Christian faith. The text is written around four themes: 1. God is a being to be known, not a hypothesis to be tested; 2. We set a high bar on what constitutes good argument; 3. Uncertainty is OK; 4. We are allowed to open up the window that the natural world offers us. This is not a work of apologetics. Rather, the text takes an overview of various themes and gives reactions and responses, intended to place science correctly as a valued component of the life of faith. The difference between philosophical analysis and theological reflection is expounded. Questions of human identity are addressed from philosophy, computer science, quantum physics, evolutionary biology and theological reflection. Contemporary physics reveals the subtle and open nature of physical existence, and offers lessons in how to learn and how to live with incomplete knowledge. The nature and role of miracles is considered. The ‘argument from design’ is critiqued, especially arguments from fine-tuning. Logical derivation from impersonal facts is not an appropriate route to a relationship of mutual trust. Mainstream evolutionary biology is assessed to be a valuable component of our understanding, but no exploratory process can itself fully account for the nature of what is discovered. To engage deeply in science is to seek truth and to seek a better future; it is also an activity of appreciation, as one may appreciate a work of art.

Dynamic network intelligent hybrid recommendation algorithm and its application in online shopping platform

2021 ◽  
pp. 1-13
Author(s):  
Yuxuan Gao ◽  
Haiming Liang ◽  
Bingzhen Sun
Keyword(s):  
Online Shopping ◽  
Rapid Development ◽  
Dynamic Network ◽  
Topsis Method ◽  
Recommendation Algorithm ◽  
Time Periods ◽  
The Difference ◽  
Relationship Of ◽  
Hybrid Recommendation ◽  
Novel Model

With the rapid development of e-commerce, whether network intelligent recommendation can attract customers has become a measure of customer retention on online shopping platforms. In the literature about network intelligent recommendation, there are few studies that consider the difference preference of customers in different time periods. This paper proposes the dynamic network intelligent hybrid recommendation algorithm distinguishing time periods (DIHR), it is a integrated novel model combined with the DEMATEL and TOPSIS method to solved the problem of network intelligent recommendation considering time periods. The proposed method makes use of the DEMATEL method for evaluating the preference relationship of customers for indexes of merchandises, and adopt the TOPSIS method combined with intuitionistic fuzzy number (IFN) for assessing and ranking the merchandises according to the indexes. We specifically introduce the calculation steps of the proposed method, and then calculate its application in the online shopping platform.

scholarly journals A diffusion anisotropy descriptor links morphology effects of H-ZSM-5 zeolites to their catalytic cracking performance

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Xiaoliang Liu ◽  
Jing Shi ◽  
Guang Yang ◽  
Jian Zhou ◽  
Chuanming Wang ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Catalytic Cracking ◽  
Catalytic Performance ◽  
Zeolite Catalysts ◽  
Time Resolved ◽  
Cracking Performance ◽  
Morphology Effect ◽  
Ft Ir ◽  
The Difference ◽  
Dynamics Simulations

AbstractZeolite morphology is crucial in determining their catalytic activity, selectivity and stability, but quantitative descriptors of such a morphology effect are challenging to define. Here we introduce a descriptor that accounts for the morphology effect in the catalytic performances of H-ZSM-5 zeolite for C4 olefin catalytic cracking. A series of H-ZSM-5 zeolites with similar sheet-like morphology but different c-axis lengths were synthesized. We found that the catalytic activity and stability is improved in samples with longer c-axis. Combining time-resolved in-situ FT-IR spectroscopy with molecular dynamics simulations, we show that the difference in catalytic performance can be attributed to the anisotropy of the intracrystalline diffusive propensity of the olefins in different channels. Our descriptor offers mechanistic insight for the design of highly effective zeolite catalysts for olefin cracking.

scholarly journals Modeled 3D-Structures of Proteobacterial Transglycosylases from Glycoside Hydrolase Family 17 Give Insight in Ligand Interactions Explaining Differences in Transglycosylation Products

2021 ◽  
Vol 11 (9) ◽  
pp. 4048
Author(s):  
Javier A. Linares-Pastén ◽  
Lilja Björk Jonsdottir ◽  
Gudmundur O. Hreggvidsson ◽  
Olafur H. Fridjonsson ◽  
Hildegard Watzlawick ◽  
...  
Keyword(s):  
Glycoside Hydrolase ◽  
Ligand Docking ◽  
Glycoside Hydrolase Family ◽  
Ligand Interactions ◽  
Tim Barrel ◽  
Branching Point ◽  
The Difference ◽  
Dynamics Simulations ◽  
And Function ◽  
Hydrolase Family

The structures of glycoside hydrolase family 17 (GH17) catalytic modules from modular proteins in the ndvB loci in Pseudomonas aeruginosa (Glt1), P. putida (Glt3) and Bradyrhizobium diazoefficiens (previously B. japonicum) (Glt20) were modeled to shed light on reported differences between these homologous transglycosylases concerning substrate size, preferred cleavage site (from reducing end (Glt20: DP2 product) or non-reducing end (Glt1, Glt3: DP4 products)), branching (Glt20) and linkage formed (1,3-linkage in Glt1, Glt3 and 1,6-linkage in Glt20). Hybrid models were built and stability of the resulting TIM-barrel structures was supported by molecular dynamics simulations. Catalytic amino acids were identified by superimposition of GH17 structures, and function was verified by mutagenesis using Glt20 as template (i.e., E120 and E209). Ligand docking revealed six putative subsites (−4, −3, −2, −1, +1 and +2), and the conserved interacting residues suggest substrate binding in the same orientation in all three transglycosylases, despite release of the donor oligosaccharide product from either the reducing (Glt20) or non-reducing end (Glt1, Gl3). Subsites +1 and +2 are most conserved and the difference in release is likely due to changes in loop structures, leading to loss of hydrogen bonds in Glt20. Substrate docking in Glt20 indicate that presence of covalently bound donor in glycone subsites −4 to −1 creates space to accommodate acceptor oligosaccharide in alternative subsites in the catalytic cleft, promoting a branching point and formation of a 1,6-linkage. The minimum donor size of DP5, can be explained assuming preferred binding of DP4 substrates in subsite −4 to −1, preventing catalysis.

scholarly journals Shifting the scaling relations of single-atom catalysts for facile methane activation by tuning the coordination number

2021 ◽  
Author(s):  
Changhyeok Choi ◽  
Sungho Yoon ◽  
Yousung Jung
Keyword(s):  
Transition State ◽  
Coordination Number ◽  
Active Sites ◽  
Methane Activation ◽  
Single Atom ◽  
Scaling Relations ◽  
Scaling Relationship ◽  
Relationship Of

The scaling relationship of methane activation via a radical-like transition state shifts toward a more reactive region with decreasing coordination number of the active sites.

Computational studies of ice defects

2003 ◽  
Vol 81 (1-2) ◽  
pp. 325-332 ◽  
Author(s):  
P LM Plummer
Keyword(s):  
Defect Formation ◽  
Structural Evolution ◽  
Energy Difference ◽  
Electronic Energy ◽  
Energy Structure ◽  
Defect Site ◽  
And Migration ◽  
Dynamics Simulations ◽  
Small Clusters ◽  
Structure Calculations

Continuing our investigations of the energetics associated with defect formation and migration, both ab initio energy-structure calculations and molecular dynamics simulations are carried out on small clusters of water molecules containing one or more defects in hydrogen bonding. Previous studies in this series have identified structures containing defects that are stable at 0 K or that are transition states between such structures. However, results from this laboratory and elsewhere have shown that the energy required for the production or migration of a defect is more complex than merely the energy difference between the static structures. Cooperative motion of neighbors to the defect site can either increase or decrease the energy involved to produce or annihilate the defect. Thus, experimental measurements associated with the energy of defects in ice can differ substantially from those calculated using static models. By increasing the complexity of the model, the studies described in this report attempt to more realistically simulate a defect-containing ice system. The types of defects studied include ion and ion-pair defects. The initial structures are energetically stable — minima on the electronic energy surface — and contain one or more kinds of defects. Since the means and amount of energy injection can alter the migration path, the energy is introduced into the system in a variety of ways. The structural evolution of the ice system is then monitored as a function of time. PACS Nos.: 82.20Wt, 82.20Kh, 82.30Rs

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