Eigenschaften der Lösungen der nichtlinearisierten Ginsburg-Landau-Gleichungen in Zylindersymmetrie

Solutions of the nonlinear Ginzburg-Landau equations in cylindrical symmetry have been computed for a type I superconductor. From these solutions the behaviour of a circular cylinder of infinite length in a magnetic field parallel to its axis has been deduced. For a series of values of the magnetic field solutions are given in two cases. The first case was calculated with the assumption of no fluxoid frozen in (fluxoid quantum number n=0), whereas in the second case a vortex with fluxoid quantum numbern=1 was assumed on the axis of the cylinder. For both series of solutions investigation of the thermodynamic stability was carried out. This and further thermodynamic considerations led to the result that in a gedankenexperiment the transition from the normal to the superconducting state and vice versa can be performed in a reversible manner. The expulsion of the magnetic field from the sample during the reversible transition to the superconducting state (Meissner-Effect) is also described by the solutions. Further results are the existence of a supercooled state down to a magnetic fieldH _c2=κ√2H_cb and of a superheated state up to a fieldH _c1>H _cb. The value ofH _c1 depends on the radius of the cylinder. If a condensation to the superconducting state takes place at a fieldH ₀ whereH _c2<H ₀<H _cb, condensation withn=0 seems to be preferred in comparison to that withn=1.     

Comparison of exchange mechanisms in πN → ϱN and pion photo- and electroproduction

Pho-, photo- and electroproduction are compared and contrasted from a t-channel exchange point of view. A common exchange mechanism is evident. Systematic differences associated with the variable mass of the vector particle are found - in particular, the mass dependence of the non-pole-like contributions is reminiscent of that seen in higher mass resonance production. Naive vector meson dominance arguments which do not allow for these mass-dependent effects are shown to disagree both qualitatively and quantitatively with the data. We emphasize the implications of this, and similar studies, for an understanding of absorption effects in two-body scattering.     

The Stark and Zeeman effects in methyl silane

The Stark and Zeeman effects in methyl silane in the ground vibronic state have been studied in detail using the molecular-beam electric-resonance method. For a symmetric rotor without internal rotation, the rotational dependence of the effective dipole moment for matrix elements diagonal in J has been shown by Watson, Takami, and Oka to have the form μ_Q = μ₀ + μ_JJ(J + 1) + μ_KK². It is shown here that, to this order, a complete characterization of the Stark effect requires only one more parameter, namely, the effective anisotropy (α_| - α_⊥)_eff in the polarizability. From Stark measurements alone, the true anisotropy cannot be separated from the additional dipole distortion constant shown by Aliev and Mikhaylov to enter dipole matrix elements off-diagonal in J. By studying nine different transitions (J, K, m_J) → (J, K, m_J ± 1) in CH₃²⁸SiH₃, values were obtained for the four Stark parameters: μ₀ = 0.7345600(33) D, μ_J = 8.83(35) μD, μ_K = ?32.82(37) μD, and (α_| - α_⊥)_eff = 1.99(16) × 10^?24 cm³. These errors reflect only the internal consistency in the data; the absolute error in μ₀ is 32 μD. The modification of the Stark effect by internal rotation is discussed; it is shown that the only significant effect here is to modify the interpretation of μ₀. The change in μ₀ upon isotopic substitution of ³⁰Si for ²⁸Si was determined: $\text{μ}{}_0\text{(}{}^{30}\text{Si) - μ}{}_0\text{(}{}^{28}\text{Si) = 67.0(2.0) μD}$. A study of molecular magnetic effects in CH₃²⁸SiH₃ has yielded the two molecular g factors, g_⊥ = ?0.036391(21) nm and g_| = ?0.10667(13) nm, as well as the anisotropy in the susceptibility $\text{(χ}{}_{\mathrm{|}}\text{- χ}{}_{\mathrm{\perp }}\text{) = ?44.9(2.3) × 10}{}^{\mathrm{?30}}\text{J}\text{T}{}^2$. The molecular quadrupole moment has been calculated.     

Jumping solitary waves in an autonomous reaction-diffusion system with subcritical wave instability

We describe a new type of solitary waves, which propagate in such a manner that the pulse periodically disappears from its original position and reemerges at a fixed distance. We find such jumping waves as solutions to a reaction-diffusion system with a subcritical short-wavelength instability. We demonstrate closely related solitary wave solutions in the quintic complex Ginzburg-Landau equation. We study the characteristics of and interactions between these solitary waves and the dynamics of related wave trains and standing waves.     

Diffusion on a self-assembled monolayer: molecular modeling of a bound + mobile lubricant

The diffusion of tricresyl phosphate molecules on an octadecyltrichlorosilane self-assembled monolayer (SAM) was characterized using molecular dynamics simulations. The simulations predict that when placed on the top of a close-packed SAM, the molecules remain mobile on the surface with an isotropic diffusion activation energy of approximately 9 kJ/mol. In contrast, an anisotropic barrier that results from chain tilt within the SAM is predicted for diffusion into a defect created by reducing the alkane chain length within a cylinderical region of the surface. Once in the defect, the molecules become trapped by embedding part of the molecule into the side of the SAM.     

The polymorphism of poly(vinylidene fluoride). I. The effect of head-to-head structure

The phenomenon of polymorphism in poly(vinylidene fluoride) has been observed recently by several authors. It has also been reported that high-resolution NMR measurements demonstrate the presence in this polymer of head-to-head linkages, resulting from the “backward” addition of from 5-6% of the monomer units. Since the van der Waals radii of fluorine (1.35 Å) and hydrogen (1.1-1.2 Å) are similar, the cocrystallization in a polymer chain of units that differ only by the substitution of fluorine atoms for hydrogen atoms is not unexpected. The two polymorphic forms of poly(vinylidene fluoride), examined in this investigation, have different chain conformations. Chains in phase I have a planar zigzag conformation, while chains in phase II are assumed to exhibit a 2₁ helical conformation. The incorporation into the polymer chain of small amounts of tetrafluoroethylene or trifluoroethylene comonomer favored the crystallization of phase I. This is in accord with the relative abilities, deduced from consideration of atomic size, of these comonomers to cocrystallize with vinylidene fluoride units in the two indicated chain conformations of the polymer. Since tetrafluoroethylene units are present in the head-to-head structure in the homopolymer, it can be concluded that the elimination of the head-to-head structure will eliminate or restrict crystallization in phase I.