Effect of Stalling after Mismatches on the Error Catastrophe in Nonenzymatic Nucleic Acid Replication

The frequency of errors during genome replication limits the amount of functionally important information that can be passed on from generation to generation. During the origin of life, mutation rates are thought to have been quite high, raising a classic chicken-and-egg paradox: could nonenzymatic replication propagate sequences accurately enough to allow for the emergence of heritable function? Here we show that the theoretical limit on genomic information content may increase substantially as a consequence of dramatically slowed polymerization after mismatches. As a result of postmismatch stalling, accurate copies of a template tend to be completed more rapidly than mutant copies and the accurate copies can therefore begin a second round of replication more quickly. To quantify this effect, we characterized an experimental model of nonenzymatic, template-directed nucleic acid polymerization. We found that most mismatches decrease the rate of primer extension by more than 2 orders of magnitude relative to a matched (Watson-Crick) control. A chemical replication system with this property would be able to propagate sequences long enough to have function. Our study suggests that the emergence of functional sequences during the origin of life would be possible even in the face of the high intrinsic error rates of chemical replication

Growth and Characterization of lead free Multiferroic Ba0.85Ca0.15Zr0.10Ti0.90O3 –CoFe2O4 Nano Composite Thin Films

Multiferroic materials simultaneously possess more than one ferroic orders. The most important multiferroic materials are those that show simultaneous ferroelectric and ferromagnetic properties which is called magneto-electric materials. Magneto-electric materials manifest a change in polarization under external magnetic field or change in magnetization under an electric field. Magnetoelectricity can be found both in single phase and composite materials. Single phase materials have both electric and magnetic orders and the magnetoelectric effect originate from the coupling of ferroelectric and magnetic dipoles. In a magnetoelectric composite structure, a coupling is induced via an interfacial elastic interaction between magnetostrictive and piezoelectric materials enabling the control of the magnetization by an electric field and vice versa. Magneto- electric thin film nano composites have drawn significant interest because of the easy incorporation in to the integrated magnetic and electric devices, such as sensors, microelectromechanical system and spintronics devices which cannot be realized in the bulk counterpart. This dissertation focused on the growth and characterization of lead free multiferroic Ba0.85Ca0.15Zr0.10Ti0.90O3 (BCZT) – CoFe2O4 (CFO) nano composite thin films deposited on Pt substrate through pulsed laser deposition. BCZT thin film was chosen as piezoelectric materials because of recent development in lead-free piezoelectric ceramics in which piezoelectric properties are quite comparable to that of lead based PZT ceramics which is non-environment friendly due the toxicity of lead. Similarly, CFO thin films were preferred because of its high magnetostriction value among the oxide ferromagnetic materials. First, the piezoelectric thin film was systematically optimized for different oxygen pressures and substrate temperatures. The effect of these process parameter on structure, microstructure, ferroelectric and mechanical properties has been studied. The piezoelectric domains and the ferroelectric switching of dipoles with applied electric field were also studied. From the above experiments the optimum growth conditions were realized as O2 Pressure – 13.3 Pa and Substrate temperature 700°C to achieve high quality BCZT thin films. In the same way, the effect of different oxygen pressures on structure, microstructure, magnetic and mechanical properties were studied for CFO film. In addition, magnetic annealing was carried out to increase the magnetostriction and decrease the strain sensitivity in-order to enhance the total magnetoelectric coupling in the nano composites. Enhanced magnetostrictive properties and uniaxial anisotropy has been observed for magnetic annealed film compared to the nonmagnetic annealed and as deposited films. By using the above optimized conditions, multilayers of BCZT/CFO/BCZT nano composites were deposited for different thickness ratios to obtain growth control morphology at the interface since there is a continuous change in the morphology texture and surface topography as a function of film thickness. The interface between the piezoelectric and ferromagnetic layer plays a key role in transferring the stress and to achieve high magnetoelectric coupling. In general, the polycrystalline ferroelectric thin film was grown with columnar grains and spinel ferrite with granular grains. This difference in the morphology at the interface reduces the coupling between the two phases. Here we propose a new structure in the polycrystalline 2-2 multilayered structure which stacks in a single continuous column like a superlattice structure which provides more flexibility for strain transfer and reduces the substrate clamping effect by altering the deposition conditions within the frame work of Structure Zone Model (SZM). Morphologically coherent continuous columnar structure was obtained for the nanocomposite having thickness ratio of BCZT (900nm)/CFO (180nm)/BCZT (900). The grains between the BCZT/CFO and CFO/BCZT interface grew in a grain-over grain pattern with same crystallographic orientation such that the films are in local epitaxy registry over a wide spread of different orientation at the interface. The effect of thickness on the structure, ferroelectric, magnetic and magneto-dielectric properties were studied along with microstructure and Raman studies at the interface. A high dielectric constant change of 21% obtained by an induced applied magnetic field attained in continuous columnar growth indicating the high strain coupling

Effect of Magnetic Field Annealing on the Magnetostriction and Deflection Properties of CoFe2O4 Thin Films Grown by PLD

In this study, we investigate the effect of magnetic field annealing on the magnetostriction and deflection properties of polycrystalline CoFe2O4 thin films grown on Si(100) substrates by pulsed laser deposition. Prior to the field-annealing process, both structural and magnetic properties of the CoFe2O4 films were optimized through controlling the oxygen pressures from 7 to 13.3 Pa. A good combination of saturation magnetization (195 emu/cm3) and coercivity (690 Oe) was obtained for the CoFe2O4 films grown at 9.0 Pa. These films when subjected to field-annealing demonstrated improved magnetostriction (91 micro-strain) and deflection (730 nm) properties, as compared to the conventionally annealed counterparts. The observed enhancement in the magnetostriction and deflection in the CoFe2O4 films is hypothesized to both domain wall rotation and movement facilitated by the field-annealing process

COMPOSITIONAL AND ELECTRICAL RESISTIVITY STUDIES ON THERMAL EVAPORATION LEAD SELENIDE THIN FILMS

Lead selenide films are prepared by the vacuum evaporation technique on clean glass substrates held at room temperature in a vacuum 10 -6 torr. The thickness of the film is measured by employing quartz crystal monitor technique. EDAX analysis confirms the composition of constituent in the PbSe thin films. The electrical resistivity measurements as a function of temperature in the range 303 K -483 K, mostly are performed using FourProbe method. At temperature above 423 K, a sudden increase in resistivity is observed. Thermal activation energy is also calculated by varying the thickness of the films and no systematic variation of activation energy is observed

Grain to Grain Epitaxy-Like Nano Structures of (Ba,Ca)(ZrTi)O3/ CoFe2O4 for Magneto–Electric Based Devices

Multiferroic nanocomposites with grain to grain epitaxy-like feature comprising of Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT)/CoFe2O4 (CFO)/BCZT layers were deposited on Pt/TiO2/SiO2/Si substrates by pulsed laser deposition. To enhance strain coupling between the phases, vertically ordered continuous nanostructures with grain to grain epitaxy-like feature was achieved by careful choice of material and optimized growth conditions. The columnar grains between the BCZT/CFO and CFO/BCZT interface were optimized such that every column grew in an epitaxy-like growth with grain-over grain crystallographic relation even at nanoscale. Grain to grain epitaxy was evident from TEM analysis (inverse FFT analysis). Elastic strain coupling present between various vibrational modes of BCZT and CFO was confirmed by cross-sectional Raman studies. Ferroelectric polarization of 10 μC/cm2 and out-of-plane remnant magnetization (40emu/cc) was observed in the columnar structure. The morphologically coherent columnar structure of both the phases and the epitaxial registry at the interface of the composite significantly enhanced the strain coupling between the ferroelectric/ferromagnetic phases, which is evident from the magneto-dielectric studies with a 21% change in dielectric constant and the magneto-electric(ME) coefficients (620-840 mV/cm·Oe). The ME values indicate the existence of high elastic strain coupling in continuous columnar structures compared with granular structures with an incoherent interface. Enhanced magneto-electric coupling in these types of nanostructures can be of great potential in realizing devices like actuators and sensors

Origin of giant dielectric permittivity and weak ferromagnetic behavior in (1−x)LaFeO3−xBaTiO3 (0.0 ≤ x ≤ 0.25) solid solutions

The solid solutions of (1−x) LaFeO3–xBaTiO3 (0.0≤x≤0.25) have been synthesized successfully by the conventional solid-state reaction method. Room temperature (RT) X-ray diffraction studies reveal the stabilization of orthorhombic phase with Pbnm space group. Complete solubility in the perovskite series was demonstrated up to x=0.25. The dielectric permittivity shows colossal dielectric constant (CDC) at RT. The doping of BaTiO3 in LaFeO3 exhibit pronounced CDC up to a composition x=0.15, further it starts to decrease. The frequency-dependent dielectric loss exhibits polaronic conduction, which can attribute to presence of multiple valence of iron. The relaxation frequency and polaronic conduction mechanism was shifted towards RT as function of x. Moreover, large magnetic moment with weak ferromagnetic behavior is observed in doped LaFeO3 solid solution, which might be the destruction of spin cycloid structure due to insertion of Ti in Fe–O–Fe network of LaFeO3

Nanostructure-driven complex magnetic behavior of Sm2CoMnO6 double perovskite

Magnetic double perovskite oxides have steadily emerged as an important class of functional materials. A clear understanding of the complex interactions that govern the magnetic behavior, and thereby, the functionality in these mixed valence compounds, however, remains elusive. In this study, we show that the complex nanostructure that forms in these compounds is at the root of their magnetic behavior. Using complementary experimental and micromagnetic simulation results, we have uncovered the complex nanostructure of polycrystalline Sm2CoMnO6, a typical double perovskite oxide, and established how the nanostructure drives its magnetic behavior. Our results show that Sm2CoMnO6 exhibits a Griffiths phase with the formation of ferromagnetic clusters above the ordering temperature. The isothermal magnetization curves show no sign of saturation, even at the highest measured field (9 T), and irreversibility in the entire magnetic field range. Despite a very clear indication of the presence of antiferromagnetic antisite defects, surprisingly, no antisite defect-induced exchange bias occurs. This is explained from the micro magnetic simulations that confirm the presence of ferromagnetic nanoclusters and nanosized, random, and uncorrelated antisite defects, resulting in no exchange bias. This work provides a clear understanding of the role of antisite defects, in particular, on how their structure can lead to the presence/absence of exchange bias. The fundamental insight offered in this work fills an important knowledge gap in the field and will be of immense value in realizing the true potential of double perovskite oxides for future technological applications. (C)& nbsp;2022 The Author(s). Published by Elsevier B.V

Effect of Si/Ge ratio on resistivity and thermopower in Gd(5)Si(x)Ge(4-x) magnetocaloric compounds

The effect of Si/Ge ratio on resistivity and thermopower behavior has been investigated in the magnetocaloric ferromagnetic Gd(5)Si(x)Ge(4-x) compounds with x = 1.7-2.3. Microstructural studies reveal the presence of Gd(5)(Si, Ge)(4)-matrix phase (5:4-type) along with traces of secondary phases (5:5 or 5:3-type). The x = 1.7 and 2.0 samples display the presence of a first order structural transition from orthorhombic to monoclinic phase followed by a magnetic transition of the monoclinic phase. The alloys with x = 2.2 and 2.3 display only magnetic transitions of the orthorhombic phase. A low temperature feature apparent in the AC susceptibility and resistivity data below 100 K reflects an antiferromagnetic transition of secondary phase(s) present in these compounds. The resistivity behavior study correlates with microstructural studies. A large change in thermopower of -8 mu V/K was obtained at the magneto-structural transition for the x = 2 compound. (C) 2011 Elsevier B.V. All rights reserved