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melting-temperature
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Calculation of melting temperature and transition curve for dickerson DNA dodecamer on the basis of configurational entropy, hydrogen bonding energy, and heat capacity: A molecular dynamics simulation study
, Article Journal of the Iranian Chemical Society ; Volume 8, Issue 3 , 2011 , Pages 708-716 ; 1735207X (ISSN) ; Parsafar, G. A ; Abroshan, H ; Akbarzade, H ; Sharif University of Technology
Abstract
A familiarity with denaturation process is highly significant in understanding the DNA replication, manipulation, and interactions involving DNA double helix stability. We have performed molecular dynamics simulation on B-DNA duplex (CGCGAATTGCGC) at different temperatures. At each temperature, configurational entropy was estimated using the covariance matrix of atom-positional fluctuations. By plotting the configuration entropy versus temperature, we calculated the melting temperature which was found to be 329.7 K. We also calculated the hydrogen bonding energy and heat capacity for the atoms participating in the hydrogen bonding between two strands of DNA. Moreover, their temperature...
Analytical model based on cohesive energy to indicate the edge and corner effects on melting temperature of metallic nanoparticles
, Article Chemical Physics ; Volume 378, Issue 1-3 , 2010 , Pages 14-18 ; 03010104 (ISSN) ; Delavari H. H ; Vossoughi, M ; Sharif University of Technology
2010
Abstract
An analytical model based on cohesive energy has been conducted to study the effects of edge, corner, and inward surface relaxation as varying parameters on melting temperature of nanoparticles. It is shown that taking into account the edge and corner (EC) atoms of nanoparticle, causes to drop melting temperature more, when compared to consider them the same as only surface atoms. This reduction is significant especially when the size of nanoparticle is below 10 nm. The results are supported by available experimental results of tin, lead and gold melting temperature (Tm). Finally, it is shown that inward relaxation increases melting temperature slightly
An Investigation on the Effects of Experimental Variables on Silver Nano Particles Produced by Electromagnetic Levitation Technique
, Article Journal of Cluster Science ; Volume 24, Issue 3 , 2013 , Pages 635-642 ; 10407278 (ISSN) ; Malekzadeh, M ; Sharif University of Technology
2013
Abstract
In this study the effects of melt temperature and flow rate of cooling gas on the characteristics of silver nanoparticles have been studied. Transmission electron microscopy and dynamic light scattering techniques have been employed to monitor morphology and particle size of the product. Measurements reveal that higher melt temperatures and higher cooling gas flow rates can decrease particle size. Silver nanoparticles with an average particle size of 35 nm and specific surface of 18.489 m2/g have been obtained at a melt temperature of 1,130 °C with argon flow rate of 20 liters per minute
Investigation of I the Stability of B-DNA Molecule: A Molecular Dynamics Simulation
, Ph.D. Dissertation Sharif University of Technology ; Parsafar, Gholam Abbas (Supervisor)
Abstract
In this thesis, the molecular dynamics simulation is used to investigate the melting transition of B-DNA molecule, via of configurational entropy, the fraction of broken hydrogen bonds (f-curve) and hydrogen bonding energy.We have performed molecular dynamics simulation on Drew-Dickerson oligomer with sequence of (CGCGAATTGCGC) at different temperatures, within the range of 280-400 K with the 20 K intervals. The simulation was done in two different mediums (pure water and 1 M NaCl), to see influences of water and salt in stabilizing the DNA molecule. At each temperature, configurational entropy is calculated by the Schlitter’s formula, using the Cartesian coordinate of all atoms. So, in each...
Denaturation of Drew-Dickerson DNA in a high salt concentration medium: Molecular dynamics simulations
, Article Journal of Computational Chemistry ; Volume 32, Issue 16 , September , 2011 , Pages 3354-3361 ; 01928651 (ISSN) ; Parsafar, G. A ; Abroshan, H ; Akbarzadeh, H ; Sharif University of Technology
2011
Abstract
We have performed molecular dynamics simulation on B-DNA duplex (CGCGAATTGCGC) at different temperatures. The DNA was immerged in a salt-water medium with 1 M NaCl concentration to investigate salt effect on the denaturation process. At each temperature, configurational entropy is estimated using the covariance matrix of atom-positional fluctuations, from which the melting temperature (T m) was found to be 349 K. The calculated configuration entropy for different bases shows that the melting process involves more peeling (including fraying from the ends) conformations, and therefore the untwisting of the duplex and peeling states form the transition state of the denaturation process. There...
A molecular-dynamics study of thermal and physical properties of platinum nanoclusters
, Article Fluid Phase Equilibria ; Volume 280, Issue 1-2 , 2009 , Pages 16-21 ; 03783812 (ISSN) ; Parsafar, G. A ; Sharif University of Technology
2009
Abstract
Metallic nanoclusters are interesting because of their utility in catalysis and sensors. The thermal and physical characteristics of metallic Pt nanoclusters with different sizes were investigated via molecular-dynamics simulations using Quantum Sutton-Chen (QSC) potential. This force field accurately predicts solid and liquid states properties as well as melting of the bulk platinum. Molecular dynamic simulations of Pt nanoclusters with 256, 456, 500, 864, 1372, 2048, 2916, 4000, 5324, 6912, 8788 atoms have been carried out at various temperatures. The Pt-Pt radial distribution function, internal energy, heat capacity, enthalpy, entropy of the nanoclusters were calculated at some...
Design and manufacture of a wax injection tool for investment casting using rapid tooling
, Article Tsinghua Science and Technology ; Volume 14, Issue SUPPL. 1 , 2009 , Pages 108-115 ; 10070214 (ISSN) ; Rezaei, M. R ; Akbari, J ; Sharif University of Technology
2009
Abstract
A rapid wax injection tool of a gearbox shift fork was designed, simulated, and manufactured using rapid prototyping and rapid tooling technology to save time and cost of producing wax models used for the investment casting process. CAE simulation softwares, in particular, MoldFlow, are used to get wax injection moulding parameters such as filling parameters, temperature profiles, freeze time, speed, and pressure. The results of this research were compared with conventional wax model production methods. The criteria of such comparison were based upon parameters such as time, cost, and other related characteristics, which resulted in saving of 50% in time and 60% in cost. In this research,...
Solid state and liquid phase sintering of mechanically activated W-20 wt.% Cu powder mixture
, Article Journal of Alloys and Compounds ; Volume 463, Issue 1-2 , 8 September , 2008 , Pages 153-159 ; 09258388 (ISSN) ; Simchi, A ; Sharif University of Technology
2008
Abstract
W-20 wt.% Cu powder mixture was mechanically alloyed by high-energy ball milling for various times and the effect of mechanical alloying (MA) on the sintering response of the composite compacts was investigated. The densification, microstructure, hardness and electrical conductivity after solid phase sintering (SPS) and liquid phase sintering (LPS) were examined. It was shown that the microstructure of mechanically alloyed powder profoundly influence the sintering response, i.e. a meaningful relationship between the sintering kinetics and the milling time was observed. It is suggested that MA disintegrates the W-W particle networks and increases the contribution of solid phase sintering...