Tunneling through a fluctuating barrier in the presence of a periodically driving field

The zero and finite temperature tunneling dynamics of a periodically driven particle moving in a bistable potential with a fluctuating barrier is studied. We have focused on the influence of barrier fluctuation and thermal modulation on the tunneling processes in the presence of a driving field. At zero temperature, for a fixed strength of the driving field, both the tunneling probability and rate passes through a well-defined minimum when plotted as a function of fluctuation frequency while it reveals a clear maximum as a function of driving frequency. However, at T > 0 the tunneling probability and rate show two maxima as a function of both fluctuation frequency and driving frequency. In both zero and finite temperature, the tunneling rate constant decreases with increasing fluctuation strength. So, the barrier fluctuation may enhance the stability of a periodically driven system. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Tunneling dynamics of a double‐well oscillator: Effects of barrier fluctuation and thermal modulation

The tunneling dynamics of a particle moving in a bistable potential with fluctuating barrier is studied. For barriers fluctuating randomly in time we show by exact numerical calculation the significant effect of barrier fluctuation on the tunneling behavior of the particle. At nonzero temperatures the computed tunneling rate constant passes through a maximum when plotted against fluctuation frequency. The resonant frequency (at which the maximum appears) slowly decreases with increase in temperature and attains a constant value at higher temperature and it increases linearly with increase in barrier height of the potential. Another important observation is that in presence of barrier fluctuation the dependence of tunneling rate constant on temperature is strongly guided by the barrier fluctuation frequency. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 280–285, 2003     

Photodetachment dynamics from closed‐shell anions in the presence of a bichromatic field

I have studied the dynamics of photodetachment from closed‐shell anions in the presence of a two‐color (bichromatic) laser field. The electronic states of halide ions are modeled by a 1‐D Hamiltonian with a potential V(x) = ?V₀e. The two parameters V₀ and σ are fixed by requiring V(x) to reproduce the experimentally observed ground‐state ionization energy of the halide ions concerned. The potentials so generated are shown to support only one bound state in each case. The time‐dependent Fourier grid Hamiltonian method is used to follow the detachment dynamics with fairly high intensities of light. The environmental effects on the dynamics are sought to be modeled by allowing the well depth (V₀) to fluctuate randomly (V₀(t) = V₀[1 + ΔVR(t)]; R(t) randomly fluctuates between +1 and ?1 with time, when ΔV is fixed). The average detachment rate constants k_av are seen to increase with increase in the intensities of used bichromatic field. An alternative model potential, V(x) = ?V₀e^?σx, is also shown to yield similar results. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

The effect of stochastic barrier fluctuation on semiclassical transmission probability and Shannon entropy of a symmetric double well potential

Stochastic fluctuation of barrier height and width of a symmetric double well plays a very significant role in the corresponding dynamics by increasing the semiclassical transmission probability and Shannon entropy of the system. The population of the system has been observed to be spread into several under barrier states starting from the or [, where and are the wave functions describing the two lowest degenerate states] in presence of the stochastic fluctuation. This distribution over several states is manifested by steady increase in Shannon entropy. However, any arbitrary value of the stochastic fluctuation cannot increase the populations of the upper energy states and consequently no gain in the net value of Shannon entropy results. There is an optimum frequency for which the Shannon entropy passes through a maximum, which is also found out in this work. We have also calculated the semiclassical WKB like transmission probability as a function of time and it is clear that the random fluctuation of barrier causes the transmission probability to increase to a significant amount. As the total energy of the system remains below the potential barrier, this transmission probability is equivalent to tunneling probability. It has been clearly shown that if the fluctuation is made to be periodic (without changing the frequency and magnitude of the fluctuation) it cannot effect any significant change in the overall dynamics.     

Isothermal oxidation behavior of a thermal barrier coating prepared using EB‐PVD

A novel two‐layer structural thermal barrier coating (TBC) system with a ~150‐µm‐thick CoCrAlY bond coat (BC) and a ~60‐µm‐thick yttria stabilized zirconia (YSZ) ceramic top coat (TC) was prepared on superalloy K444 matrix using electron beam physical vapor deposition (EB‐PVD). This deposited coating was characterized using isothermal oxidation tests (1000 °C × 200 h). The results indicated that the deposited coating had a dense structure and close bonding between the layers. The thermally grown oxide (TGO) layer (predominantly alumina) that formed at the interface between the TC and the BC as a consequence of the oxidation process was effective in preventing the further oxidation of the BC. In the later stages of the oxidation process, embedded oxides of chromium/cobalt were observed among the TC's columnar grains, and the TGO underwent densification thinning. Through observations of the growth behavior of the TGO, the element diffusion, displacement reaction, and volatilization of the oxides were found to be related to the weight loss in the coating and the densification thinning of the TGO. These coatings displayed superior high‐temperature oxidation resistance properties. Copyright © 2014 John Wiley & Sons, Ltd.     

Effects of additive gases on dimethyl ether conversion through dielectric barrier discharge

Effects of additive gases on dimethyl ether (DME) conversion through dielectric barrier discharge (DBD) were investigated. Most of the additive gases tested in this work increased the conversion of DME, but decreased the yield of liquid product. However, the addition of O2 markedly increased both the conversion of DME and the yield of liquid product. The results show that when O2 volume fraction was 39.95%, the conversion of DME was close to 100% and the yield of liquid product reached 34.43%. Different additive gases resulted in different mass fractions variation of components in liquid products.     

Enhanced modulation of magnetic field on surface plasmon coupled emission (SPCE) by magnetic nanoparticles

This article demonstrates the enhancement of magnetic nanoparticles on magnetic field modulation of surface plasmon coupled emission (SPCE), and this method is designed as a biosensor to prove the feasibility of magnetic field modulated SPCE to be employed in the field of biosensing and biodetection.     

Enhanced modulation of magnetic field on surface plasmon coupled emission (SPCE) by magnetic nanoparticles

The obvious enhancement effect of magnetic nanoparticles (MNPs) introduced in Cr/Co/Cr/Au substrate on the pulsed magnetic field-modulated surface plasmon coupled emission (SPCE) was investigated, and the observed enhancement factor was 4 comparing with the magnetic field modulated SPCE without MNPs. This is the new observation for the magnetic field modulated SPCE, and this method was designed as a biosensor, which to our knowledge, is the first application of magnetic field-modulated SPCE in biosensing and detection field. This strategy is a universal approach to increase the fluorescence signal and helps to build the new SPCE based stimulus-response system.     

Thermodynamic study of the thermal denaturation of a globular protein in the presence of different ligands

By means of difference UV-Vis spectra, the thermal denaturation of catalase has been studied in the presence of different surfactants: sodium perfluorooctanoate, sodium octanoate and sodium dodecanoate. These results indicate that hydrogenated surfactants play two opposite roles in the folding and stability of catalase, they act as a structure stabiliser at a low molar concentrations (enhancing T _m) and as a destabilizer at a higher concentrations (diminishing T _m). Meanwhile sodium perfluorooctanoate enhances T _m in the whole concentration range. An approach for the determination of the heat capacity, enthalpy and entropy has been made, finding that for the three studied surfactants, at all concentrations, the enthalpy term dominates the entropy term.     

Forces at the nuclei of a molecule in the presence of non-uniform electric field

The interaction Hamiltonian within the Bloch gauge for the potentials of the electric field has been used to define electric multipole moment operators. Perturbation theory has been applied to evaluate the induced electronic moments and electric field at the nuclei in the presence of spatially non-uniform electric fields of high intensity. Multipole nuclear electric shielding tensors have been defined to describe the contributions arising from a non-homogeneous electric field. These quantities are useful to rationalize linear and non-linear responses of a molecule in the presence of intense external electric perturbations.     

Reactivity dynamics of a confined molecule in presence of an external magnetic field

Reactivity dynamics and stability of a confined hydrogen molecule in presence of an external magnetic field has been studied using quantum fluid density functional theory. Dynamic profiles of various reactivity parameters such as hardness, electrophilicity, magnetizability, phase volume, entropy, etc. have been studied within a confined environment. Responses in the reactivity parameters as well as the associated electronic structure principles validate the stability of the confined H₂ molecule in ground and excited states in presence of an external magnetic field. Confinement to the system has been imposed by the Dirichlet type boundary condition. Confinement and excitation act in opposite directions. Ground state type dynamics is obtained on simultaneous electronic excitation and confinement. © 2014 Wiley Periodicals, Inc.     

Simultaneous stochastic effects of a thermal reservoir and an electromagnetic field on the optical susceptibility of a two-level system

In this paper we derive analytical expressions for the optical susceptibility of a two-level system immersed in a thermal bath and interacting with an external electromagnetic field, where both of them are considered as noise sources. The dynamics of the system is described by a set of optical stochastic Bloch equations. The noise sources are modeled as Ornstein-Uhlenbeck processes. The optical stochastic Bloch equations are perturbatively solved up to second order in the external field. We found that each noise affects the dynamics in a different manner. Thus, at first order, the bath modifies the transverse relaxation time, whereas the effect of a random field can only be appreciated if the expansion is calculated up to second order, where correlations begin to be important.     

Curing and thermal behaviour of epoxy resin in the presence of a mixture of imide-amines

The curing behaviour of diglycidyl ether of bisphenol-A (DGEBA) was investigated by the dynamic differential scanning calorimetry using varying molar ratios of aromatic imide-amines and 4,4′-diaminodiphenylsulfone (DDS). The imide-amines were prepared by reacting 1 mole of naphthalene 1,4,5,8-tetracarboxylic dianhydride (N) and 4,4′-oxodiphthalic anhydride (O) with 2.5 moles of 4,4′-diaminodiphenyl ether (E) or 4,4′-diaminodiphenyl methane (M) or 4,4′-diaminodiphenylsulfone (S) and designated as NE/OE or NM/OM or NS/OS. The mixture of the imide-amines and DDS at ratio of 0:1, 0.25:0.75, 0.5:0.5, 0.75:0.25 and 1:0 were used to investigate the curing behaviour of DGEBA. A single exotherm was observed on curing with mixture of imide-amines and DDS. This clearly shows that the two amines act as co-curing agents. Curing temperatures were higher with imide-amines having sulfone linkage irrespective of anhydride. Curing of DGEBA with mixture of imide-amines and or DDS resulted in a decrease in characteristic curing temperatures. The thermal stability of the isothermally cured resins was also evaluated using dynamic thermogravimetry in a nitrogen atmosphere. The char yield was higher in case of resins cured imide-amines based on N and E. The activation energy of decomposition and integral procedural decomposition temperature were also calculated from the TG data.     

Improving barrier properties of polyethylene/Fe2O3-modified nanographene nanocomposites in a magnetic field

The present work aims at improving the barrier properties of high molecular weight Polyethylene/ graphene nanoplatelets (HMWPE/GnP) nanocomposites by aligning the embedded modified graphene nanoparticles in a magnetic field. Graphene nanoplatelets (GnP) were modified by magnetic Fe₂O₃ to produce Fe₂O₃-modified Graphene, GnP-mFe₂O₃. The magnetic properties of Fe₂O₃ were previously characterized by the vibrating sample magnetometer (VSM) method and resulting GnP-mFe₂O₃ nanoparticles were characterized by Fourier transform infrared (FTIR) analysis. HMWPE/GnP nanocomposites were prepared via melt mixing. The prepared nanocomposites were sheeted at high temperatures in a magnetic field using a hot press. The barrier properties of prepared films, HMWPE/GnP and HMWPE/GnP-mFe₂O₃ were characterized by carrying out a permeation to oxygen experiment as a function of GnP and GnP-mFe₂O₃ contents. A decrease in gas transmission rate (GTR) was observed for the samples after being subjected to the magnetic field compared to the non-treated sample. The results of differential scanning calorimetry (DSC) and field emission electron microscopy (FESEM) experiments confirmed the orientation of GnP-mFe₂O₃ nanoparticles in nanocomposites.     

Effects of external electromagnetic fields on the conformational sampling of a short alanine peptide

Non‐equilibrium molecular dynamics simulations of a solvated 21‐residue polyalanine (A21) peptide, featuring a high propensity for helix formation, have been performed at 300 K and 1 bar in the presence of external electromagnetic (e/m) fields in the microwave region (2.45 GHz) and an r.m.s. electric field intensity range of 0.01–0.05 V/Å. To investigate how the field presence affects transitions between the conformational states of a protein, we report 16 independent 40 ns‐trajectories of A21 starting from both extended and fully folded states. We observe folding‐behavior of the peptide consistent with prior simulation and experimental studies. The peptide displays a natural tendency to form stable elements of secondary structure which are stabilized by tertiary interactions with proximate regions of the peptide. Consistent with our earlier work, the presence of external e/m fields disrupts this behavior, involving a mechanism of localized dipolar alignment which serves to enhance intra‐protein perturbations in hydrogen bonds (English, et al., J. Chem. Phys. 2010 , 133, 091105), leading to more frequent transitions between shorter‐lifetime states. © 2012 Wiley Periodicals, Inc.     

Cell-sorption of paramagnetic metal ions on a cell-immobilized micro-column in the presence of an external magnetic field

The cell-sorption of paramagnetic ions of Mn²⁺ and Cr³⁺ onto a Chlorella vulgaris(C. vulgaris) cell-immobilized micro-column was significantly improved in the presence of an external magnetic field generated in a finite solenoid, by placing the micro-column in the center of the solenoid in a sequential injection system. Magnetic field creates an opposite drift velocity on the hydrated paramagnetic ions against the flow of the sample zone, retards the moving velocity of the metal ions and provides extra contacting time with the cells on the micro-column and offers more chances for the paramagnetic ions to interact with the various functional groups or binding sites on the cell surface, which significantly facilitates cell-sorption of the paramagnetic ions. The sorption efficiencies of Mn²⁺ and Cr³⁺ at the 20 μg L⁻¹ level were improved from 45 to 80% and 60 to 90%, respectively, in a magnetic field of 240 mT.The system was applied for the separation/preconcentration of ultra-trace level of manganese. The presence of an external magnetic field significantly alleviated the interfering effects from coexisting metal ions. Within a liner range of 0.025-0.5 μg L⁻¹ and a sampling volume of 500 μL, an enrichment factor of 21.2, a limit of detection of 0.008 μg L⁻¹, along with a sampling frequency of 20 h⁻¹ was attained, achieving a precision of 2.1% R.S.D. (0.2 μg L⁻¹). Manganese contents in a certified reference material of riverine water and a snow water were analyzed.     

Expression of ornithine decarboxylase during the transport of saquinavir across the blood-brain barrier using composite polymeric nanocarriers under an electromagnetic field

The expression of human ornithine decarboxylase (ODC) and permeability of saquinavir (SQV) across the blood-brain barrier were studied using nanoparticles (NPs) composed of poly(lactide-co-glycolide) (PLGA), poly-(γ-glutamic acid) (γ-PGA), and polyethyleneimine (PEI). SQV was encapsulated in the particle core to traverse a monolayer of human brain-microvascular endothelial cells (HBMECs) with the regulation of human astrocytes under an electromagnetic field (EMF). An increase in the weight percentage of PEI enhanced the particle size, zeta potential, and permeability of SQV. However, the viability of HBMECs reduced when the weight percentage of PEI increased. In addition, an increment in the molecular weight of γ-PGA enhanced the particle size and viability of HBMECs, and reduced the zeta potential. The permeability of SQV and expression of ODC were in the order: an EMF with amplitude modulation (AM)>an EMF with frequency modulation>no EMF. At 0.04% PEI, the AM EMF increased 2.38 times the uptake of NPs and 2.72 times the expression of ODC. The combination of PEI/γ-PGA/PLGA NPs and EMF can be an innovative strategy for delivering SQV into the brain.     

Effect of aspect ratio of vertically aligned copper nanowires in the presence of cellulose nanofibers on the thermal conductivity of epoxy composites

The composites comprising vertically aligned network of copper nanowires (CuNWs) in the presence of cellulose nanofibers were fabricated by using the freeze‐templating method and the effect of aspect ratio (A/R) of CuNWs on the thermal conductivity of epoxy composites was investigated. The thermal conductivity of epoxy composites increased to 0.79 W m^?1 K^?1 at 1.12 vol% of high A/R CuNWs loading, corresponding to the thermal conductivity enhancement of 365% as compared to the pure epoxy. The thermal conductivity of vertically aligned higher A/R CuNWs/epoxy, which is 38.5% and 51.9% higher than those of the lower A/R CuNWs and the randomly aligned CuNWs, respectively. The application of the epoxy composites in heat dissipation was demonstrated by the temperature changes of composites on a hot plate with the increase of heating time. These results indicate that the thermally conductive composites in this study could be applied for thermal dissipating materials in electronic devices.     

The kinetics of reaction of 4-nitrophenylnitromethane with N’-Propyl-N,N-dipropylbenzimidamide in aprotic solvents. a steric effect on tunneling

Thermodynamic and kinetic parameters have been established for the reaction between the carbon acid, 4-nitrophenylnitromethane, (4-NPNM), and the base N’-n-propyl-N,N-di-n-propylbenzimidamide, (N’PDPBA), in mesitylene and in chlorobenzene. In some cases deuteron transfer from 4-(D₂)NPNM to the base has also been studied. In addition, some results for the proton transfer reaction in tetrahydrofuran have been collected. Spectrophotometric methods have been employed to monitor the ion-pair product, which is solvatochromic. In general the solvent dependence of the parameters is as expected, but there is some indication of specific solvation. The kinetic isotope effects of 11 and 8 in mesitylene and chlorobenzene, respectively, are larger than those predicted classically. However, as is discussed the n-propyl group on the secondary nitrogen of the base may serve to reduce the extent of tunneling compared to that in an unsubstituted analogue by a steric effect.     

Effect of transverse magnetic field on the laser-blow-off plasma plume emission in the presence of ambient gas

In the present paper we report the effect of variable magnetic field in the range of 0.04-0.2 T on the emission of two neutral Lithium lines Li I 670.8 nm and Li I 610.3 nm and one ionic line Li II 548.4 nm in the presence of ambient gas on the laser-blow-off plasma plume. Enhancement in the intensity associated with structures was observed in the temporal profile of neutrals, which is strongly dependent on the magnetic field intensity, distance from the target and background gas pressure. At 6 mm distance and 1.33 Pa argon pressure, apart from overall enhancement in the intensity of both the neutral lines, the results reveal some interesting features, e.g. disappearance of structures and narrowing of the temporal extent of 670.8 nm line at higher magnetic fields. On the other hand, the 610.3 nm line exhibits a significant enhancement in the intensity at the trailing part as the field is increased. At a shorter distance (2 mm) and for relatively higher pressures (133.3 Pa), the effect of field is not much prominent. Interestingly, the ionic spectral line does not exhibit any significant change with both, magnetic field and ambient gas.We explain the results by considering the role of various atomic processes viz. electron impact excitation, recombination and diffusion of ambient gas into plume in collisional and hydrodynamical regimes.