Region Of Field Strength Research Articles

Electric birefringence of segmentally flexible macromolecules with two subunits at arbitrary field strengths

We first present the general treatment of the steady-state orientational distribution of a segmentally flexible macromolecule with two subunits in an electric field E. The orientation-dependent property that we consider is the electric birefringence Δn, although other electro-optical properties can be derived in the same way. In the low-field region linear in E2 we obtain the Kerr constant of macromolecules with a partially flexible joint, and explicit results are presented for a broken rod. A theory recently proposed by Yoshioka is used for the region of intermediate field strength, where Δn is quadratic in E2. The quadratic constant is also evaluated for hinged rods. For electric field of arbitrary strenght we have devised a Monte Carlo simulation procedure which has been checked using analytical results for straight rods. We have determined the extension of the E2 and E4 regions as a function of flexibility, using Yoshioka’s formulas and the simulation results. Finally, we have used literature data for the Kerr constant of myosin rod and its subfragments to obtain a value of the flexibility parameter that is in agreement with those for other properties.

EXO 033319-2554.2: an Eclipsing AM Herculis System Showing Cyclotron Emission Features

view Abstract Citations (68) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS EXO 033319-2554.2: an Eclipsing AM Herculis System Showing Cyclotron Emission Features Ferrario, Lilia ; Wickramasinghe, D. T. ; Bailey, Jeremy ; Tuohy, I. R. ; Hough, J. H. Abstract We report spectroscopic and circular polarization observations of the soft X-ray binary EXO 033319 - 2554.2 which confirm it as a member of the AM Herculis class with properties similar to VV Puppis. Circular polarization reaching 10% in the blue and less than or equal to 2% in the I band is seen during the bright phase which lasts for 70 minutes of the 126.5 minute orbital cycle. The optical light curve exhibits a narrow eclipse due to the companion star, lasting about 8 minutes and occurring toward the end of the bright phase. The radial velocity curves show a sharp discontinuity due to an eclipse of the line-forming region by the accretion funnel and the white dwarf. Broad resolvable and variable cyclotron harmonics are seen during the bright phase. At the center of the bright phase, the emission peaks are located near 4200 Å, 5200 Å, and 6550 Å, corresponding to a magnetic field B 5.6 × 107 gauss and a temperature T = 20 keV. Detailed theoretical models suggest the presence of a second emission region of field strength B ∼ 2.8 × 107 gauss which can be seen toward the end of the bright phase. We deduce a mass ratio of ∼0.1 and estimate an orbital inclination of ∼88° and a colatitude of ∼14° for the main emission region, assuming that it is a point source and that the duration of the bright phase is Δφ ∼ 0.55. Publication: The Astrophysical Journal Pub Date: February 1989 DOI: 10.1086/167153 Bibcode: 1989ApJ...337..832F Keywords: STARS: ECLIPSING BINARIES; POLARIZATION; STARS: INDIVIDUAL ALPHANUMERIC: EXO 033319-2554.2; STARS: MAGNETIC; STARS: WHITE DWARFS; X-RAYS: BINARIES full text sources ADS | data products SIMBAD (2)

Evidence of Complex Field Structure in the Magnetic White Dwarf in EXO 033319–2554.2

AbstractWe present detailed theoretical models for polarisation and spectroscopic data from EXO 033319–2554.2 that suggest the presence of two cyclotron emission regions of field strengths B ∼ 5.6 × 107 G and B ∼ 2.8 × 107 G, and which are separated by about 90° on the surface of the white dwarf. The large difference in magnetic field strength and the proximity of the two regions imply a more complex field structure than that of a centred dipole field distribution if it is assumed that the regions are connected by closed field lines.

Mobility of deoxyribonucleic acid in a fine-pore gel in a constant electric field

A reptation model of the motion of a persistent charged deoxyribonucleic acid macromolecule in a fine-pore gel in a constant electric field is proposed, and the chain mobility is calculated on its basis. In some field strength regions chains of length L< l( l/ λ) 4 (where l is the persistence length, λ is the distance between entanglements) can fall into random “traps”, which significantly affect the macromolecule mobility.

An in-the-lens spectrometer for high performance E-beam testing

In-the-lens spectrometers using the properties of an adiabatically decreasing magnetic field have demonstrated superior performance over a number of other detectors, particularly in terms of rejection of errors due to local field effects. Traditionally, however, this has involved placing the sample in a strong magnetic field which can have deleterious effects, particularly on imaging resolution. We present a design of spectrometer which uses adiabatic electron straightening to minimize local field errors but in which the sample is maintained in a region of low magnetic field strength. The design offers all the previous advantages but with imaging capabilities approaching those attainable with a conventional SEM at short working distance.

The derivation of vector magnetic fields from stokes profiles: Integral versus least squares fitting techniques

We compare the results of two distinct methods for deriving photospheric vector magnetic fields from the Zeeman effect as observed in the Fe I line at 6302.5 A at high spectral resolution (45 mA.). One method ignores magneto-optical effects but allows for an absolute determination of B from the integral properties of the Stokes profiles, under the assumption of weak field strength. The other method is an iterative least-squares fitting technique developed by Lites and Skumanich which fits the observed Stokes profiles to the profiles predicted by the Unno-Rachkovsky solution to the radiative transfer equation. We find empirically that for sunspot fields above ≈ 1500 gauss the two methods agree in derived azimuthal and inclination angles to within ≈ ± 20 degs., Furthermore, for such fields, the estimate of the line of sight field and the transverse field derived using the two methods agree to within ≈ ± 500 gauss. In weak field strength regions the integral method can be used with little error and computational load in the estimation of the line of sight field, the transverse field and the inclination angle but the disagreement in derived azimuthal angle is considerable (≈ ± 90 degs.).

Multidipole confinement of argon and potassium plasmas

Multidipole confinement of an argon discharge plasma and a potassium plasma produced by surface ionization was investigated. In both cases, a large volume of uniform density quiescent plasma was produced in the central region of low magnetic field strength. Measurements of electron and ion densities and space potentials suggest that self-consistent electrostatic fields resulted in crossfield (to B) ion confinement and that the cusp leak widths were determined by a noncollisional mechanism (e.g., Bohm diffusion). A comparison of the nondischarge potassium plasmas produced with and without multidipole confinement indicates that the ion confinement time was improved by a factor of ∼15 by the multidipole magnetic field.

Potential probing of a thyristor cross-cut during turn-on

On a cross-cut of a thyristor with a particularly wide n-base, the dynamic change in voltage at the surface was probed during turn-on. Furthermore, the infrared recombination radiation emitted from the regions of carrier storage was observed time-resolved. The results show that during the turn-on delay phase, the load current flows in a channel that widens significantly from the n-emitter towards the p-emitter. Compensation of the stationary charge in the space charge region by free electrons results in a movement of the space charge region towards the p-emitter. Concurrently, the particular distribution of electrons causes the region of maximum fieldstrength to move away from the junction.

Radial diffusion in magnetodiscs

We consider further the orbits of charged particles in magnetodiscs. The bounce motion is assumed adiabatic except for transits of a small equatorial region of weak magnetic field strength and high field curvature. Previous theory and modeling have shown that particles scatter randomly in pitch angle with each passage through the equator. A peaked distribution thus diffuses in pitch angle on the time scale of many bounces. We argue in this paper that spatial diffusion is a further consequence when the magnetodisc has a longitudinal asymmetry. A general expression for DLL, the diffusion of equatorial crossing radii, is derived. DLL is evaluated explicitly for ions in Jupiter's 20–35 RJ magnetodisc, assumed to be represented by Connerney et al.'s Voyager model plus a small image dipole asymmetry. Rates are energy, species, and space dependent but can average as much as a few tenths of a planetary radius per bounce period.

Reversing-Pulse Electric Birefringence of Poly(γ-methyl l-glutamate) in Hexafluoro-2-propanol

Abstract Reversing-pulse electric birefringence (RPEB) signals of poly(γ-methyl l-glutamate) (PMLG) were measured, for the first time, in hexafluoro-2-propanol at 25 °C and at 535 nm. Quantitative analyses were carried out on the steady-state birefringence and the field-free decay time (&amp;lt;τ&amp;gt;EB) in the wide field strength region and also on the rise, reverse, and decay portions in the low field strength region by taking into account the continuous molecular length distribution of a fractionated PMLG sample. The weight-average length (lw), permanent dipole moment (μw), polarizability anisotropy (Δαw), and the degree of polydispersity (lw/ln) were evaluated by two procedures: one from the analysis of the reverse-transient portion and the other from the field-free decay portion of RPEB signals. These two sets of the parameters should be identical with each other, if the electrooptical and hydrodynamic properties of PMLG do not change during the field-on and field-off processes. However, the length of the PMLG helix is shorter by about 18% in the presence of an electric field than that in the absence of the field. In order to explain this discrepancy, a new concept of reversible conformational transition under the external electric field is introduced.

Symmetric hysteresis curves of rare earth-cobalt magnets measured by high magnetic fields

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On the distribution of By in the geomagnetic tail

The distribution of B y in the geomagnetic tail associated with a net cross-tail magnetic flux, recently experimentally discovered, is here investigated within the framework of two-dimensional but non-planar field adiabatic time-independent equilbria. It is found that the flux distribution is controlled by the pressure anisotropy of the plasma, B y being enhanced at the current sheet centre relative to that in the lobes for P ∥> P ⊥ and vice-versa for P ⊥> P ∥. For P ⊥> P ∥ a broad region of depressed field strength is found across the centre plane of the current sheet, terminated at its outer boundaries by spikes in the perpendicular current, across which B y and B x are “switched on” and rapidly increase towards their values in the low-β lobes. For P ∥> P ⊥ a thin high-current density layer forms at the sheet centre if the marginal firehose condition is approached, across which the B x field reverses by rotation at nearly constant magnitude about the z-axis. The field magnitude in this thin layer depends upon the pressure anisotropy, such that the plasma remains just firehose stable within it, and may approach an appreciable fraction of the lobe field strength even for moderate anisotropies. Such structures have been observed in the geomagnetic tail, but do not appear to be a common feature of the quiet-time plasmasheet, where the field strength at the centre plane can reach small values with little obvious enhancement of B y. In terms of the present model these observations require that either P ⊥> P ∥ in the quiet-time tail or that the plasma is within one or two per cent of isotropy if P ∥> P ⊥. These results then indicate that the production of plasma pressure anisotropy during adiabatic inward transport towards the Earth, which is generally expected to lead to P ∥> P ⊥ and its destruction by either macroscopic or microscopic processes, requires further study.

Formal approach to various properties of antiferromagnets

The formal representation of thermal and magnetic properties of moderately anisotropic antiferromagnets in the presence and absence of a constant, uniform external magnetic field is discussed both in selective ordered configurations and in the paramagnetic phase. The mean-field-theoretical formalism is shown to give a satisfactory account of the magnetic properties of a class of two-sublattice antiferromagnets in those ordered configurations where the applied magnetic field is at a right angle to the direction of the spontaneously evolving sublattice magnetic moments. Predictions of mean-field theory on the linearity of the magnetic moment in the applied field strength and the attendant invariant molar susceptibility throughout the relevant portions of the configuration phase diagrams, phase-boundary lines included, are seen to be well satisfied. This is verified in detail on the typical antiferromagnet MnCl2 · 4H2O, where the Mn2+ ions in their6S5/2 ground state determine the magnetic properties and for which numerous magnetic and thermal measurements have been accumulated in both the ordered and paramagnetic phases. The experimentally explored low-temperature properties of this antiferromagnet refer to the liquid3He and4He and liquid H2 bath-temperature intervals 0.3≤T≤4.2 K and 15≤T≤21 K, respectively. In contrast with the magnetic properties, mean-field theory is less successful in accounting for the thermal properties of antiferromagnets, but its qualitative predictions agree well with the observations. In the paramagnetic phase, the isotropic nearest-neighbor exchange-coupled model system is used, wherein the data on the manganese compound are assigned approximately to an effective simple-cubic distribution of the Mn2+ ions, with an effective empirical exchange-energy parameter,J<0, derived from magnetic and heat capacity data at asymptotically high temperatures. Here the formal approach corresponds to a series expansion of the various properties in ascending powers of ‖J‖/kT, in the absence of magnetic field, with an additional magnetic-field-exchange double series in the presence of an external field. In those temperature and field-strength regions where convergence is satisfactory, the above approach is shown to give a good account of the observed thermal properties of the manganese compound in the absence of magnetic field, as well as of the low-field paramagnetic susceptibility. The hitherto observed field-dependent properties are confined to a much too narrow temperature interval outside the region of convergence of the series-expansion formalism. Experimental control of this approach requires acquisition of new data in the appropriate temperature range of convergence of the model formalism.

Klein-Gordon equation with discontinuous mass: An instructive nonlinear classical field theory

The Klein-Gordon equation with a discontinuous field-dependent mass term provides an example of a simple nonlinear classical field theory. This theory is studied to determine if it exhibits a behavior hypothesized in a recently proposed picture of multimeson production. As expected, it turns out that (with a small additional decay term in the equation) the space-time average of the field strength generated by a delta-function source can be made insensitive to the source strength, once it exceeds a certain threshold. When two space-time- separated delta-function sources are present, their independence (or dependence) in producing slow mesons is determined by the ratio of decay time to source separation. If the mass in the region of low field strength is imaginary, then there are stable sourceless ''kink'' solutions in one space dimension. (AIP)

Dielectrophoresis of macromolecules

AbstractDilute solutions of rigid helical macromolecules with permanent dipole moments have been studied with dielectrophoresis. The polymers used were poly‐γ‐benzyl‐L‐glutmate and poly‐n‐butyl isocyanate, both fractions of average molecular weight 120,000. In this phenomenon dipolar molecules migrate in an inhomogeneous electric field towards the region of maximum field strength. The field gradient is produced by a 10‐μm diameter Pt wire serving as the inner electrode of a cell, and a 2.5‐mm diameter cylinder as the outer electrode. An equilibrium exponential concentration gradient is achieved within a few wire radii of the inner electrode in a matter of minutes, making both kinetic and equilibrium measurements feasible. The concentration gradient is monitored by measuring the change in capacitance ΔC of the cell from its value for a uniform solute concentration. The time dependences of ΔC for the build‐up of the concentration gradient towards the equilibrium value, and the decay to a uniform concentration after the field is removed have been calculated, using a frictional coefficient and a Boltzmann factor, β1, as the sole adjustable parameters.For low voltages (β1 small), the measured build‐up and decay are completely symmetrical, in agreement with theory, and yield the same frictional coefficient. For larger β1, the build‐up is faster, reflecting a reduced frictional coefficient due to partial alignment of the long axes of the polymers in the direction of migration. In either case, the decay determines a diffusion constant of randomly aligned molecules, identical to classical diffusion measurement.The value of ΔC at equilibrium, for β1 small, determines μ2F2, where μ is the dipole moment and F is the internal field at the polymer. Combined with a classical dielectric constant measurement, which gives μ2F, both μ and F may be determined, independent of assumptions about cavity shapes.Dielectrophoresis works in alternating as well as constant fields, provided the dipolar orientation can follow the field reversals. The dispersion of dielectrophoresis with frequency is a sensitive measure of the molecular‐weight distribution of a given sample.

Injection of Electrons into p‐Chloranil Crystals via Exciton Decay at Metal and Aqueous Electrodes

AbstractIn weakly or non‐luminescing molecular crystals like p‐chloranil, information concerning the exciton dynamics can be derived from injection currents when charge carriers are formed during electron transfer between excitons and an appropriate electron donor‐ or acceptor species in aqueous electrolyte. Due to the slow orientation polarization of water molecules as compared to the hopping frequency of injected charge carriers, image forces can be neglected when aqueous electrodes are applied. Consequently, at external field strengths of 10+ V/cm, steady state saturation currents and space‐charge‐free transients are observed which may yield information as to the kinetics of the electron transfer reaction and the diffusion of excitons (lifetime, diffusion length). In the same field strength region, photocurrents originating from exciton decay at a metal contact are still determined by the action of image forces and by surface recombination of charges. Secondary effects like enhanced trapping of charge carriers within the image potential barrier influence the current rise in space‐charge‐free transients.

Dielectrophoresis of Cells

Dielectrophoresis, the motion produced by the action of nonuniform electric field upon a neutral object, is shown to be a simple and useful technique for the study of cellular organisms. In the present study of yeast (Saccharomyces cerevisiae) using a simple pin-pin electrode system of platinum and high-frequency alternating fields, one observes that the collectability of cells at the electrode tip, i.e. at the region of highest field strength, depends upon physical parameters such as field strength, field uniformity, frequency, cell concentration, suspension conductivity, and time of collection. The yield of cells collected is also observed to depend upon biological factors such as colony age, thermal treatment of the cells, and chemical poisons, but not upon irradiation with ultraviolet light. Several interesting side effect phenomena coincident with nonuniform electric field conditions were observed, including stirring (related to "jet" effects at localized electrode sites), discontinuous repulsions, and cellular rotation which was found to be frequency dependent.

The influence of magnetic reversal on the magnetic stiffness of polycrystalline barium ferrite

The magnetic stiffness of polycrystalline isotropic barium ferrite has been measured in the region of negative field strength. It is found that the Stoner-Wohlfarth model describes magnetic reversal only for small field strength. Irreversible magnetization processes known from magnetization measurements have strong influence on the field dependence of the magnetic stiffness. The domain splitting of 90° crystallites which was found in previous investigations proves to be essentially independent of the magnetic history of the sample.

Statistics of electron multiplication in proportional counters

Pulse spectra produced by the release of single primary electrons in a proportional counter have been determined for a variety of gas fillings. The spectra were recorded with sufficient statistical accuracy to define their logarithmic derivatives in order to investigate deviations from the approximately exponential distributions. Two main effects were observed: (1) at small pulse heights there may be a reduced number of pulses compared with the exponential distribution if the electron multiplication commences in a region of low field strength; (2) at large pulse heights there may be an excess of pulses owing to the occurrence of secondary successor avalanches initiated by photoelectric effects. A theoretical distribution has been derived which describes both these effects in terms of two parameters, one of which is characteristic of the ionizing efficiency of the electron at the commencement of the multiplication process while the other is a measure of the mean number of successors per avalanche. These parameters have been determined for each of the observed spectra.

Electrically Induced Convection in Dielectric Liquids

IF a non-uniform electric field is applied to an inhomogeneous dielectric medium, regions of lower dielectric constant will experience a force directed towards regions of lower field strength. This force is proportional to the difference in dielectric constants and to the gradient of the square of the electric field strength. If there is a decrease in the dielectric constant as a result of heating, and if this occurs in a region of high field strength, the heated fluid will be forced into regions of lower field strength. Watson1 has demonstrated the effect of this force on the natural convection process from a horizontal wire. In all cases the effect of the field was to increase heat transfer rates from the wire, the results being virtually identical for d.c. fields of negative and positive polarity. Unfortunately, results using a.c. fields were not reported.