Uranium(III) coordination chemistry and oxidation in a flexible small-cavity macrocycle

U(III) complexes of the conformationally flexible, small-cavity macrocycle trans-calix[2]benzene[2]pyrrolide (L)2–, [U(L)X] (X = O-2,6-tBu2C6H3, N(SiMe3)2), have been synthesized from [U(L)BH4] and structurally characterized. These complexes show binding of the U(III) center in the bis(arene) pocket of the macrocycle, which flexes to accommodate the increase in the steric bulk of X, resulting in long U–X bonds to the ancillary ligands. Oxidation to the cationic U(IV) complex [U(L)X][B(C6F5)4] (X = BH4) results in ligand rearrangement to bind the smaller, harder cation in the bis(pyrrolide) pocket, in a conformation that has not been previously observed for (L)2–, with X located between the two ligand arene rings

Node synchronization schemes for the Big Viterbi Decoder

The Big Viterbi Decoder (BVD), currently under development for the DSN, includes three separate algorithms to acquire and maintain node and frame synchronization. The first measures the number of decoded bits between two consecutive renormalization operations (renorm rate), the second detects the presence of the frame marker in the decoded bit stream (bit correlation), while the third searches for an encoded version of the frame marker in the encoded input stream (symbol correlation). A detailed account of the operation is given, as well as performance comparison, of the three methods

Bs Mixing and Electric Dipole Moments in MFV

We analyze the general structure of four-fermion operators capable of introducing CP-violation preferentially in Bs mixing within the framework of Minimal Flavor Violation. The effect requires a minimum of O(Yu^4 Yd^4) Yukawa insertions, and at this order we find a total of six operators with different Lorentz, color, and flavor contractions that lead to enhanced Bs mixing. We then estimate the impact of these operators and of their close relatives on the possible sizes of electric dipole moments (EDMs) of neutrons and heavy atoms. We identify two broad classes of such operators: those that give EDMs in the limit of vanishing CKM angles, and those that require quark mixing for the existence of non-zero EDMs. The natural value for EDMs from the operators in the first category is up to an order of magnitude above the experimental upper bounds, while the second group predicts EDMs well below the current sensitivity level. Finally, we discuss plausible UV-completions for each type of operator.Comment: 11 pages; v2: references adde

Pesin's Formula for Random Dynamical Systems on RdR^d

Pesin's formula relates the entropy of a dynamical system with its positive Lyapunov exponents. It is well known, that this formula holds true for random dynamical systems on a compact Riemannian manifold with invariant probability measure which is absolutely continuous with respect to the Lebesgue measure. We will show that this formula remains true for random dynamical systems on $R^d$ which have an invariant probability measure absolutely continuous to the Lebesgue measure on $R^d$. Finally we will show that a broad class of stochastic flows on $R^d$ of a Kunita type satisfies Pesin's formula.Comment: 35 page

Surface magnetic canting in a ferromagnet

The surface magnetic canting (SMC) of a semi-infinite film with ferromagnetic exchange interaction and competing bulk and surface anisotropies is investigated via a nonlinear mapping formulation of mean-field theory previously developed by our group [L. Trallori et al., Int. J. Mod. Phys. B 10, 1935-1988 (1996)], and extended to the case where an external magnetic field is applied to the system. When the field H is parallel to the film plane, the condition for SMC is found to be the same as that recently reported by Popov and Pappas [Phys. Rev. B 64, 184401 (2001)]. The case of a field H applied perpendicularly to the film plane is also investigated. In both cases, the zero-temperature equilibrium configuration is easily determined by our theoretical approach.Comment: 4 pages, 3 figure

Real-time Chern-Simons term for hypermagnetic fields

If non-vanishing chemical potentials are assigned to chiral fermions, then a Chern-Simons term is induced for the corresponding gauge fields. In thermal equilibrium anomalous processes adjust the chemical potentials such that the coefficient of the Chern-Simons term vanishes, but it has been argued that there are non-equilibrium epochs in cosmology where this is not the case and that, consequently, certain fermionic number densities and large-scale (hypermagnetic) field strengths get coupled to each other. We generalise the Chern-Simons term to a real-time situation relevant for dynamical considerations, by deriving the anomalous Hard Thermal Loop effective action for the hypermagnetic fields, write down the corresponding equations of motion, and discuss some exponentially growing solutions thereof.Comment: 13 page

Criteria for strong and weak random attractors

The theory of random attractors has different notions of attraction, amongst them pullback attraction and weak attraction. We investigate necessary and sufficient conditions for the existence of pullback attractors as well as of weak attractors

Low-lying bifurcations in cavity quantum electrodynamics

The interplay of quantum fluctuations with nonlinear dynamics is a central topic in the study of open quantum systems, connected to fundamental issues (such as decoherence and the quantum-classical transition) and practical applications (such as coherent information processing and the development of mesoscopic sensors/amplifiers). With this context in mind, we here present a computational study of some elementary bifurcations that occur in a driven and damped cavity quantum electrodynamics (cavity QED) model at low intracavity photon number. In particular, we utilize the single-atom cavity QED Master Equation and associated Stochastic Schrodinger Equations to characterize the equilibrium distribution and dynamical behavior of the quantized intracavity optical field in parameter regimes near points in the semiclassical (mean-field, Maxwell-Bloch) bifurcation set. Our numerical results show that the semiclassical limit sets are qualitatively preserved in the quantum stationary states, although quantum fluctuations apparently induce phase diffusion within periodic orbits and stochastic transitions between attractors. We restrict our attention to an experimentally realistic parameter regime.Comment: 13 pages, 10 figures, submitted to PR

High-energy gluon bremsstrahlung in a finite medium: harmonic oscillator versus single scattering approximation

A particle produced in a hard collision can lose energy through bremsstrahlung. It has long been of interest to calculate the effect on bremsstrahlung if the particle is produced inside a finite-size QCD medium such as a quark-gluon plasma. For the case of very high-energy particles traveling through the background of a weakly-coupled quark-gluon plasma, it is known how to reduce this problem to an equivalent problem in non-relativistic two-dimensional quantum mechanics. Analytic solutions, however, have always resorted to further approximations. One is a harmonic oscillator approximation to the corresponding quantum mechanics problem, which is appropriate for sufficiently thick media. Another is to formally treat the particle as having only a single significant scattering from the plasma (known as the N=1 term of the opacity expansion), which is appropriate for sufficiently thin media. In a broad range of intermediate cases, these two very different approximations give surprisingly similar but slightly differing results if one works to leading logarithmic order in the particle energy, and there has been confusion about the range of validity of each approximation. In this paper, I sort out in detail the parametric range of validity of these two approximations at leading logarithmic order. For simplicity, I study the problem for small alpha_s and large logarithms but alpha_s log << 1.Comment: 40 pages, 23 figures [Primary change since v1: addition of new appendix reviewing transverse momentum distribution from multiple scattering