Study Of Field Effects Research Articles

Computer Simulation of the Linear and Nonlinear Optical Susceptibilities of p-Nitroaniline in Cyclohexane, 1,4-Dioxane, and Tetrahydrofuran in Quadrupolar Approximation. I. Molecular Polarizabilities and Hyperpolarizabilities

This is the first part of a study of the local field effects on (non)linear optical susceptibilities of solutions of para-nitroaniline (pNA) in three different solvents, cyclohexane (CH), 1,4-dioxane (DI), and tetrahydrofuran (THF), using a discrete molecular representation of the condensed phase. To account for dipolar and quadrupolar effects, the latter of which are especially important for DI solution, all the electric properties necessary to compute the local fields and local field gradients in quadrupolar approximation as well as the dipolar hyperpolarizabilities for the four molecules are computed, including frequency dispersion and vibrational contributions to the dipolar properties. The convergence of the perturbation treatment for the pure vibrational (PV) contributions is examined by comparison of the values obtained at the lowest order with those of partially computed second order in mechanical and electrical anharmonicity. For pNA, for which previous computations of the hyperpolarizabilities have generally found poor agreement with experimental results, a thorough investigation of the effects of solvent-induced geometry changes, dynamic and static correlation, frequency dispersion, and classical thermal averaging over the torsional modes of the substituent groups and the inversion mode of the amino group on the dipolar properties is carried out. Computations using self-consistent continuum reaction field models show that the amino group is substantially less pyramidalized in polar solvents than in the gas phase. With all the effects taken into account, reasonable agreement with the experimental electric-field induced second harmonic generation (EFISH) result on pNA vapor of Kaatz, Donley, and Shelton is obtained.

A Monte Carlo study of random surface field effect on layering transitions

The effect of a random surface field, within the bimodal distribution, on the layering transitions in a spin- 1 2 Ising thin film is investigated using Monte Carlo simulations. It is found that the layering transitions depend strongly on the concentration p of the disorder of the surface magnetic field, for a fixed temperature, surface and external magnetic fields. Indeed, the critical concentration p c ( k ) at which the magnetisation of each layer k changes the sign discontinuously, decreases with increase in applied surface magnetic field, for fixed values of the temperature T and the external magnetic field H. Moreover, the behaviour of the layer magnetisations as well as the distribution of positive and negative spins in each layer, are also established for specific values of H s , H, p and temperature T.

Magnetic field effect on N-ethylcarbazole–dimethylterephthalate and N-ethylcarbazole–1,4-dicyanobenzene: A comparitive study focusing on steric effect

This work is a comparative study of magnetic field effect (MFE) on photoinduced electron transfer between N-ethylcarbazole (ECZ)–dimethylterephthalate (DMT) pair and ECZ–1,4-dicyanobenzene (DCB) pair. Our aim was to see how a change in the steric bulk of the acceptor is manifested in the magnetic field behaviour of a system. The steric effect in DMT is responsible for maximization of MFE at a higher dielectric constant, ε; sustaining spin correlation to a larger extent so that the MFE vs. ε plot is broad and enhancing free ion formation so that the MFE is lower for ECZ–DMT compared to ECZ–DCB.

Effective generation lifetime depth profile in InAs quantum dots grown on InAlAs/InP(0 0 1)

Capacitance– and reverse current–voltage (C–V) measurements have been performed on a Schottky barrier structure incorporating InAs quantum dots (QDs) embedded in n-type InAlAs matrix. The electron confined energy level positions in the QDs have been deduced from a capacitance–voltage analysis. Three electron levels have been found at about 240 meV, 180 meV and 70 meV via the InAlAs conduction band edge, and were attributed to the s ground state, the first p excited state and the d state, respectively. The variation of the leakage current density as a function of the depletion layer width has revealed an additional reverse current in the plane containing the dots. It was attributed to the discharging of the InAs QDs through the InAlAs barrier. The effective generation lifetime depth profile was derived from the C–V and the reverse current–voltage measurements. The effective generation lifetime was found to be controlled by the confined states in the QDs. Electrical field effect studies lead us to suggest a mechanism of electrons injection and emission into/from the confined states in the QDs.

Study of the Magnetic Field Effect on Commercial Thermistors using a Water Triple Point

The effect of a magnetic field on commercial thermistors was precisely studied in detail using the water triple point. A thermistor with a code of 44004 manufactured by YSI Inc. was found to show a small correction. Its orientation effect and sensor dependence was found also to be small. The correction ΔT (mK) against magnetic field B(T) was found to be 0.069(B/T)2 (mK). The uncertainty of the correction function is estimated to be as small as 2 mK up to 15 T.

Theoretical Study of Internal Field Effects on Peptide Amide I Modes

Charged terminal groups or polar side chains of amino acids create spatially nonuniform electrostatic potential around intramolecular peptide bonds and induce amide I mode frequency shifts in polypeptides. By carrying out a series of quantum chemistry calculation studies of various ionic di- and tripeptides as well as dipeptides of 20 different amino acids, these internal field effects on vibrational properties are theoretically investigated. The amide I local and normal mode frequencies and dipole and rotational strengths determining IR and vibrational circular dichroism intensities, respectively, are found to depend on the polar nature of side chains, whereas the vibrational coupling strength weakly does so. The empirical correction and fragment analysis methods were used to theoretically calculate the amide I local mode frequencies and dipole and rotational strengths. These values were directly compared with ab initio and density functional theory calculation results, and the agreements were found to be quantitative.

Medium-dependent electron and H atom transfer between 2'-deoxyadenosine and menadione: a magnetic field effect study.

The interaction between 2'-deoxyadenosine and the model antitumor drug menadione has been studied in organic solvent and in micellar medium. The aim of the work is to elucidate the mechanism of this drug-nucleoside interaction and to determine the environmental effects. Laser flash photolysis and magnetic field effect are used to detect the transients and their spin states. The results indicate that H atom transfer and electron transfer are the operative mechanisms depending upon the medium.

A comparative study of large magnetic field effect on the radical pair generated by the photo-induced electron transfer from indoles to 2,4,6-triphenyl pyrylium tetrafluoroborate and its thia-analogue in aqueous SDS micellar medium

The effect of external magnetic field on the spin evolution of the radical pair (RP) generated by photo-induced electron transfer from indoles to 2,4,6-triphenyl pyrylium tetrafluoroborate and its thia-anologue for ring-sulfur in aqueous SDS micellar medium has been investigated. The transient signal observed at 555 nm at low fields was found to consist of a fast rise followed by decay; at high fields, an additional slow growth at the intermediate time delay was observed. The observed decay was explained in terms of a kinetic scheme involving multiple channels for radical formation. The yield of escape radicals increases gradually with increase of the field and ultimately reaches saturation. At low fields the magnetic field dependence of the escape yield is ascribed to competition between HFI and Zeeman effect and at higher fields, to the relaxation mechanism induced by anisotropic HFI [ δ ( hfi )]. Saturation in MFE is observed at high fields which is a consequence of the competition between the spin-re-phasing process and the fast escape process.

The effect of magnetic field on the stability of (18-crown-6) complexes with potassium ion

Macrocyclic polyethers are ligands with selectivity for metal ions. In order to understand the interactions between ligand, ion and solvent we resorting to study of magnetic field effect on ion-macrocyclic complexes. Therefore, we studied the complexation between 18-crown-6 and potassium ion in water through the conductometry technique (in 25+0.05 °C) by a nonlinear least-square program (Genplot) under magnetic field. We observed that stability constants of complexes in the presence of the magnetic field, were decreased. Like-wise, we observed that, magnetic field influenced on ion, solvent and ligand one by one.

Magnetic field effect on indole exciplexes: a comparative study

A comparative magnetic field effect (MFE) study was done on indole exciplexes with various acceptors, anthracene, pyrene, all-s- trans-1,4-diphenylbuta-1,3-diene and 9-cyanophenanthrene. A surprisingly low magnetic field effect was detected for the 9-cyanophenanthrene exciplexes and was correlated with exciplex geometry. The wavelength dependence of magnetic field effect confirms the presence of single charge-transfer complex for all the exciplexes with 1,2-dimethylindole.

A Study of Magnetic Field Effect on Nanofluid Stability of CuO

This study investigates the effect of additional magnetic field on the stability of CuO nanofluid. Experiments are conducted by imposing an additional magnetic field to the CuO nanofluid prepared by the self-developed Arc-Submerged Nanoparticle Synthesis System (ASNSS), so as to investigate the aggregation phenomenon and the stability of the nanoparticle suspension. It is subsequently known that the permeance strength, time and frequency of the additional magnetic field can affect the CuO nanofluid. Under the influence a strong magnetic field, the longer the permeance time, the more apparent the sedimentation phenomenon will be owing to the aggregation of the nanoparticles. However, the permeance frequency has a relatively slight effect on the CuO nanofluid.

The effect of vibration injection molding on mechanical properties of polyolefin parts

AbstractIn this paper an experimental study of vibration field effect on molded polymers specimens is carried out. A self‐made vibration injection device is employed to mold the experiment samples. In the experiment some polyolefin materials are investigated, and property tests for the specimens are carried out. The results show that the tensile strength of high‐density polyethylene (HDPE) and polypropylene (PP) have an obvious increase, but polystyrene (PS) does not. The effect of vibration on the strength is related to the temperature, pressure, and gate. Lastly, the test results are analyzed and conclusions are presented. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1514–1518, 2004

Raman study of magnetic field effects on surfacted and ionic ferrofluids

We report Raman spectroscopic measurements on surfacted (SFF) and ionic ferrofluids in magnetic fields up to 0.25 T. For the SFF Raman spectra display the characteristic broad bands associated with vibrations of surfactant and water molecules. With increasing magnetic field the overall Raman intensity decreases abruptly up to about 50 mT, leveling out above this field. In contrast, at high magnetic fields a broad peak which is attributed to a magnetic excitation becomes apparent in the spectra at frequencies in the range of 4000 cm −1 . Our results can be explained in terms of a local increase in magnetic-particle concentration and the formation of ordered structures in the presence of a magnetic field. The Raman spectra of the electrostatically stabilized ferrofluids, which are dominated by the H 2O stretching vibrations, exhibit a different magnetic-field behavior of their intensity probably indicating the incipient formation of large nanograin clusters.

Effect of electric field on the global and local reactivity indices

We present a comprehensive study of electric field effects on the global and local chemical reactivity indices. We use the effect of an applied uniform electric field on chosen molecules and stockholder population scheme to derive the local reactivity profiles. We find that the changes in the pattern of reactivity indices are strongly influenced when the electric field is applied to the system, this effect being more noticeable as the number of atoms in the molecule increases as well as the strength of the applied field. The field-induced polarization leads to changes in the global and local reactivity descriptors.

Impurity effects on energy levels and far-infrared spectra of nanorings

The effects of a positively charged impurity on the energy levels and far-infrared spectra ofone and two electrons in semiconductor nanorings under magnetic fields are studied. Theeffects of the nanoring size and the impurity position are also discussed. It is shown thatthe electron–electron interaction and electron–impurity one in nanorings are stronglydependent on the nanoring size and the impurity position. Based on the studies of theimpurity and field effects, the impurity-induced Aharonov–Bohm oscillations ofthe far-infrared spectra are found. The results predict a possibility of observingphenomena related to electron–impurity interaction in a nanoring in the future.

Magnetic field effect study of solvent hole deprotonation in X-irradiated liquid n-alkanes

Stationary magnetic field effects including MARY spectroscopy (radical ion pair level crossing technique) were employed to unequivocally establish primary radical cations of n-alkanes as targets for aliphatic alcohol attack, with indication of diffusion-controlled deprotonation of the radical cation. For n-alkanes C 6…C 16 and four alcohols from MeOH to t-BuOH the broadening of the zero field MARY line, attributed to the proton transfer reaction, was found to be independent of the proton affinity of the alcohol monomer and alkyl radical.

Time-Resolved Reflectivity Studies of Electric Field Effects in III-Nitride Semiconductors

ABSTRACTComparison of room temperature, frequency degenerate and nondegenerate femtosecond pump-probe reflectivity measurements reveal an additional component in the transient reflectivity (ΔR) decays for near bandgap probe in GaN that is attributed to a reduction of bandedge broadening due to screening of internal electric fields by photogenerated carriers. Pump-probe measurements with pulses spectrally centered at 363 nm show a ΔR component with a nanosecond decay time that is essentially absent from data obtained from nondegenerate experiments performed under identical pumping conditions, but with a probe at 385 nm far enough from the bandedges to minimize the electric field contribution and monitor primarily the carrier lifetime in the band states. The observation of significantly shorter decay times for 385 nm probe suggests that the carriers leave the band states on a picosecond time scale, but the slow decay of the field screening observed with 363 nm probe implies that they recombine from trap states at longer times. In addition, this field screening provides a mechanism for generation and detection of strain pulses in strained GaN and AlGaN epilayers that is used to measure the longitudinal sound velocity in bulk GaN and AlGaN with up to 0.4 Al content.

Magnetic field effects on intersubband transitions in a quantum nanostructure

We report on our theoretical studies of the magnetic field effects on intersubband transitions in quantum dots (QDs) embedded in a quantum cascade structure subjected to a strong magnetic field applied perpendicular to the QD plane. The peaks of the emission spectra calculated for QDs containing a few interacting electrons indicate that there is a correlation between the non-monotonic behavior of the maximum value of the emission spectrum as a function of the applied magnetic field and the field dependence of the low-lying energy spectra of the dots.

Laser flash photolysis of [3,n]paracyclophan-2-ones. Direct observation and chemical behavior of 4,4'-(1,n-alkanediyl)bisbenzyl biradicals.

The 4,4'-(1,n-alkanediyl)bisbenzyl biradicals (2b-d) have been generated from the Norrish type-I reaction of [3,n]paracyclophan-2-ones (1b-d) giving the paracyclophanes 3b-d as the only reaction products. The behavior of biradicals 2b-d has been studied in detail and compared with the previously reported biradical 2a. The lifetimes increase as the chain length decreases and are affected by the solvent viscosity, thus showing the effect of the length of the chain on the conformations of the biradicals. Quenching with persistent radicals such as TEMPO resulted in length-dependent rate constants. Finally, the study of the magnetic field effects on the biradical lifetimes suggest that ISC control determines biradical lifetimes for long-chain systems.

Near-surface deep-trap and bulk deep-trap states in In[sub x]Ga[sub 1−x]As/GaAs

Field-effect studies have been performed to investigate the near-surface deep-trap and bulk deep-trap states in molecular-beam epitaxy-grown InxGa1−xAs (where x=0.1) on n+ GaAs. We have measured the isothermal capacitance transients for the major trap levels in the range of 77–380 K in the reverse-bias field of −1 to −3.8 V/cm. The results of our investigation indicate a distinct effect on the deep level spectra due to the applied field, suggesting a definitive way to identify the near-surface deep traps from the bulk deep traps, and vice versa. The two major deep traps identified in the present investigation further display a transition from one state to another, from near-surface to bulk state in the high-field region, when the applied reverse-bias field is increased from −3.0 to −3.8 V/cm. “Field” means “normalized” field, F(norm)=F(appl)×10−5.