Non-zero Parallel Research Articles

Shear Alfvén waves in a magnetic beach and the roles of electron and ion damping

Experiments are performed in the Large Plasma Device (LaPD) [Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)] at the University of California, Los Angeles to study the propagation of the shear Alfvén wave in a parallel gradient of the background magnetic field. The waves are excited by modulating a field-aligned electron current drawn to a disk antenna with a radius on the order of the electron skin-depth, δ=c/ωpe. The resulting shear waves have a nonzero parallel electric field and propagate both parallel and perpendicular to the background magnetic field. In this experiment, the wave is launched in a region where its frequency, ω equals one-half the local ion-cyclotron frequency, ωci and the local Alfvén speed, vA, is approximately equal to the electron thermal speed, v̄e. The wave propagates along a slowly decreasing background field to where ω=ωci and vA≈v̄e/2. The wave thus propagates from a region where Landau damping is significant to where ion-cyclotron damping dominates. Detailed two dimensional measurements of the wave magnetic field morphology are presented. The measured wavelength decreases in accord with WKB solutions of a modified wave equation. Wave damping is also observed and dissipation by both ions and electrons is required in the WKB model to fit the data. Suppression of the damping via electrons in the model results in a predicted wave magnetic field amplitude twenty times larger at the ion-cyclotron resonance point than observed.

Dissociation process of CH 4/H 2 gas mixture during EACVD

The dissociation process of CH 4/H 2 gas mixture during EACVD has been investigated using Monte Carlo simulation for the first time. The electron velocity distribution and H 2 dissociation were obtained over a wide range: 100< E/N<2000 Td. The variation of CH 4 dissociation with CH 4 concentration in the filling gas has been simulated. The electron velocity profile is asymmetric for the component parallel to the field. Most electrons possess non-zero velocity parallel to the substrate. The number of atomic H is a function of E/ N. There are two peaks at E/ N=177 Td and 460 Td. The appropriate E/N is suggested to be 500–800 Td for low temperature deposition. The main diamond growth precursor is proposed to be CH 3 and CH 3 +.

Constructing the Kähler and the symplectic structures from certain spinors on 4-manifolds

We show that, on an oriented Riemannian 4-manifold, existence of a non-zero parallel spinor with respect to a spinc^cstructure implies that the underlying smooth manifold admits a Kähler structure. A similar but weaker condition is obtained for the 4-manifold to admit a symplectic structure. We also show that thespincspin^cstructure in which the non-zero parallel spinor lives is equivalent to the canonical spinc^cstructure associated to the Kähler structure.

Polarization for pair annihilation in strong magnetic fields

We derive the cross-section for one-quantum annihilation of polarized electrons and positrons. The elec- tron and positron can occupy arbitrary Landau levels and have non-zero momentum parallel to the eld, and the cross-section is calculated for any polarization of the ra- diation. When we take zero parallel momentum for the electron and sum over photon polarization we obtain re- sults which agree with the existing calculation of Wunner et al. (1986).

Two‐Fluid Motion of Plasma in Alfven Waves and the Heating of Solar Coronal Loops

Taking the effect of two-fluid motion of plasma in Alfven waves into account, a nonzero parallel electric field can rise within the wave itself under collisionless conditions. This leads to a kinetic dissipation of Alfven waves by the wave-particle resonant interaction and electron heating along the ambient magnetic field lines. Employing the drift kinetic equation, we investigated this electron-heating mechanism under the cool ion approximation. The result shows that the damping rate and the heating rate obviously depend on the strength distribution of the ambient magnetic field, and that they reach their maximum values at B-0 = B-m and B-0 = (1 + 2 alpha)B-1/2(m), respectively, for the perturbed field of delta B proportional to B-0(alpha), where B-m is the ambient magnetic field strength when upsilon(A) = upsilon(Te). Finally, we propose that this heating mechanism can be applied to explain the brightness distribution of solar soft X-ray coronal loops.

Theory of the proximity effect in [formula omitted] magnetic field I

The Proximity Effect phenomenon in non-zero parallel magnetic field can be well explained by solving the complete L-G equation, including the cubic term. The L-G equation becomes the equation of the one-dimensional harmonic-oscillator. The energy eigenvalue equation naturally produces an explicit functional relation between the upper critical magnetic field H and the transition temperature T over a wide range of T near T c: T=T c{1− 4ed sξ 2 sB C n [ (k y− 2ed sB n ) 2+ 2eB n +(k y− 2ed sB n )]} Where B=μ oH, T c = T s for a single superconductor layer, T c = T csn for a S-N lamina, T c=T css for a S-S lamina, k y is the equivalent wave number, and C is a constant. The agreement between the theory and the experimental results is very good.

Angular distribution of the total cyclotron radiation of a relativistic particle with parallel velocity.

A closed-form formula is given for the mean power radiated per solid angle in a given direction by a relativistic particle in cyclotronic motion with a nonzero parallel velocity. The difference between emitted and received mean power for a nonclosed periodic motion is illustrated in this case.

Computing the Generalized Singular Value Decomposition

An algorithm is described for computing the generalized singular value decomposition of $A(m \times n)$ and $B(p \times n)$. Unitary matrices U, V and Q are developed so that $U^H AQ$ and $V^H BQ$ have as many nonzero parallel rows as possible, and these correspond to the common row space of the two matrices. The algorithm consists of an iterative sequence of cycles where each cycle is made up of the serial application of $2 \times 2$ generalized singular value decompositions. Convergence appears to be at least quadratic. With the correct choice of ordering the algorithm can be implemented using systolic array processors (Gentleman,personal communication). The algorithm can also be used to compute any CS decomposition of a unitary matrix.

TEM observations of defects in biotite and their relationship to polytypism

A dislocation model, based on Frank's screw dislocation model is proposed to explain transmission electron microscope (TEM) microstructures associated with growth defects in natural 1M and 2M1 metamorphic biotites. Burgers vectors have a non-zero component parallel to (001). Each rotation of the dislocation ledge repeats a stacking fault (R). By exercising control over the pitch of the screw dislocation and the component parallel to (001), the observed biotite crystal defects (stacking faults, superlattices and twins) and polytypes based on ± 120° rotations about c* can be generated. This model adds flexibility to Frank's spiral growth model as applied to mica by Baronnet (1975) by providing a means for changes of microstructures with changes in the growing environment.

X-ray rocking curve analysis of superlattices

We present detailed analyses of x-ray double-crystal rocking curve measurements of superlattices. The technique measures depth profiles of structure factor, and profiles of perpendicular and parallel strains relative to the underlying substrate. In addition to providing a detailed picture of the state of stress, the profiles are a direct measure of the composition modulation. The thickness of the period of modulation and the average strain are determined with a precision of ∼1%. The detailed structure of the period is determined to ∼5%. We obtain an expression relating the structure of the rocking curve to the structure of the period. This expression allows analytic determination of the structure without Fourier transformation or computer fitting. We show the influence of small random fluctuations in layer thicknesses and strains. The technique is applied to a 15-period GaAlAs/GaAs and a ten-period AlSb/GaSb superlattice grown on 〈100〉 GaAs and 〈100〉 GaSb substrates, respectively. In the former, the thickness of the period was 676 Å and the perpendicular strain varied between zero for the GaAs layer and 0.249% for the layer with peak (93%) Al concentration. Transition regions, ∼100 Å thick, with continuously varying composition, were found between the GaAs and the Ga0.07 Al0.93As layers. Fluctuations in structural properties were less than 5% of the average. The AlSb/GaSb superlattice had a period of 610 Å with sharp transition regions between the layers and negligible fluctuations from period to period. The perpendicular strains were −0.03% and 1.25%, respectively, for the GaSb and AlSb layers. A uniform parallel strain of 0.03% was found throughout the superlattice. Nonzero parallel strain indicates that a small fraction of the misfit between the superlattice and the substrate is plastically accommodated by net edge dislocations lying in a narrow region (a few hundred Å thick) at the interface with the substrate. The net number of edge dislocations was calculated to be ∼1×104/cm2. The measured perpendicular strains were in excellent agreement with the values calculated from bulk lattice parameters, elastic properties, and the parallel strain. For both superlattices, the standard deviation of random atomic displacements away from perfect crystal sites was below 0.1 Å, in agreement with reported ion channeling and electron diffraction measurements of superlattices. The rocking curve method is a major tool for quantitative analysis of superlattices.

Temperature effects on second harmonic generation in p-nitrophenylhydrazine

An increase of intensity of second harmonic generation is observed in p-nitrophenylhydrazine between room temperature and 77 K. The variation is present only when the applied laser field has a non-zero component parallel to the b edge of the unit cell.