The behaviour of a flexible anionic chain of 150 univalent and negatively charged beads connected by a harmonic-like potential with each other in the presence of an equal number of positive and free counterions, is studied in molecular dynamics simulations with Langevin thermostat in a wide range of temperatures. Simulations were carried out for several values of the bending parameter, corresponding to fully flexible polyion, moderately and strongly stiff polyion as well as for the case when bend conformation is preferable to the straight one. We have found that in all cases three regimes can be distinguished, which can be characterized as "random coil", observed at high temperatures; "extended conformation" observed at moderate temperatures (of the order of 1 in reduced units), and compact "globular conformation" attained at low temperatures. While the transition between high-temperature random and extended conformations is gradual, the transition from the extended coil to the globular state, taking place at a temperature of about 0.2 in reduced units, is of abrupt character resembling a phase transition.
The present study is dedicated to analyze the dual-nature solutions of the axisymmetric flow of a magneto-hydrodynamics (MHD) nanofluid over a permeable shrinking sheet. In those phenomena where the fluid flow is due to the shrinking surface, some reverse behaviors of the flow arise because of vorticity effects. Despite of heat transfer analysis, the main purpose of the present study is to attain the solutions of the complex nature problem that appear in reverse flow phenomena. Thermophysical properties of both base fluid (water) and nanoparticles (copper) are also taken into account. By means of similarity transformation, partial differential equations are converted into a system of coupled nonlinear ordinary differential equations and then solved via the Runge-Kutta method. These results are divided separately into two cases: the first one is the unidirectional shrinking along the surface (m = 1) and the other one is for axisymmetric shrinking phenomena (m = 2) . To enhance the thermal conductivity of base fluid, nanoparticle volume fractions ([Formula: see text]) are incorporated within the base fluid. The numerical investigation explores the condition of existence, non-existence and the duality of similarity solution depends upon the range of suction parameter (S) and Hartmann number (M). The reduced skin friction coefficient and local Nusselt number are plotted to analyze the fluid flow and heat transfer at the surface of the shrinking sheet. Streamlines and isotherms are also plotted against the engineering control parameters to analyze the flow behavior and heat transfer within the whole domain. Throughout this analysis it is found that both nanoparticle volume fraction and Hartmann number are increasing functions of both skin friction coefficient and Nusselt number.
We have performed computational molecular modelling to study the polarization switching and hysteresis loop behaviours of DNA and RNA nucleobases using the PM3 semi-empirical quantum mechanical approaches. All the nucleobases: adenine (A), thymine (T), guanine (G), cytosine (C), and uracil (U) were modelled. Our study indicates that all the nucleobases exhibit a zero-field polarization due to the presence of polar atoms or molecules such as amidogen and carbonyl. The shape of polarization P versus an applied electric field E hysteresis loop is square, implying typical ferroelectrics behaviour. The total energy U as a function of an applied electric field E exhibits a butterfly-like loop. The presence of zero-field polarization and ferroelectrics hysteresis loop behaviours in nucleobases may support the hypothesis of the existence of bioferroelectricity in DNA and RNA. We also found an interesting relationship between the minimum electric field required for switching [Formula: see text] and the ratio of the topological polar surface area (TPSA) to the total surface area (TSA) of a nucleobase. In particular, the [Formula: see text] of a nucleobase is inversely proportional to the TPSA/TSA ratio. This work may provide useful information for understanding the possible existence of ferroelectricity in biomaterials.
Understanding the charge transfer mechanism through deoxyribonucleic acid (DNA) molecules remains a challenge for numerous theoretical and experimental studies in order to be utilized in nanoelectronic devices. Various methods have attempted to investigate the conductivity of double-stranded (ds-) and single-stranded DNA (ssDNA) molecules. However, different electronic behaviors of these molecules are not clearly understood due to the complexity and lack of accuracy of the methods applied in these studies. In this work however, we demonstrated an electronic method to study the electrical behavior of synthetic ssDNA or dsDNA integrated within printed circuit board (PCB)-based metal (gold)-semiconductor (DNA) Schottky junctions. The results obtained in this work are in agreement with other studies reporting dsDNA as having higher conductivity than ssDNA as observed by us in the range of 4-6μA for the former and 2-3μA for the latter at an applied bias of 3V. Selected solid-state parameters such as turn-on voltage, series resistance, shunt resistance, ideality factor, and saturation current were also calculated for the specifically designed ss- and dsDNA sequences using the thermionic emission model. The results also showed that the highest conductance was observed for dsDNA with guanine and cytosine base pairs, while the lowest conductance was for ssDNA with adenine and thymine bases. We believe the results of this preliminary work involving the gold-DNA Schottky junction may allow the interrogation of DNA charge transfer mechanisms and contribute to better understanding its elusive electronic properties.