Genetic Transformation Among Azotobacter Species

Previous methods for genetic transformation in Azotobacter vinelandii have employed poorly defined genetic markers or crude DNA extracts. An improved transformation technique has been developed for use in Azotobacter. The technique was used to transform several strains of Azotobacter with DNA carrying a defined genetic marker. A method for isolating pure, high molecular weight, biologically active DNA from Azotobacter is also presented. Purity of the extracted DNA was determined by standard chemical assays. The molecular weight was determined by boundary sedimentation techniques to be 18.2 megadaltons. DNA was obtained from several mutant strains of Azotobacter. Biological activity of these samples was demonstrated by using them to accomplish both intra- and interstrain transformation. Thermal denaturation profiles of several DNA samples are presented, from which guanine plus cytosine content was determined. Among the Azotobacter species examined, GC content ranged from 65.1 to 67.8%. The use of the new transformation and DNA isolation methods in taxonomic and mapping studies is discussed

The highly excited C-H stretching states of CHD_3, CHT_3, and CH_3D

Unlike many other molecules having local modes, the highly excited C-H stretching states of CHD_3 show well resolved experimental spectra and simple Fermi resonance behavior. In this paper the local mode features in this prototype molecule are examined using a curvilinear coordinate approach. Theory and experiment are used to identify the vibrational state coupling. Both kinetic and potential terms are employed in order to characterize the coupling of the C-H stretch to various other vibrational modes, notably those including D-C-H bending. Predictions are also made for CHT_3 and the role of dynamical coupling on the vibrational states of CH_3D explored. Implications of these findings for mode-specific and other couplings are discussed

Passive directors in turbulence

In experiments and numerical simulations we measured angles between the symmetry axes of small spheroids advected in turbulence ("passive directors"). Since turbulent strains tend to align nearby spheroids, one might think that their relative angles are quite small. We show that this intuition fails in general because angles between the symmetry axes of nearby particles are anomalously large. We identify two mechanisms that cause this phenomenon. First, the dynamics evolves to a fractal attractor despite the fact that the fluid velocity is spatially smooth at small scales. Second, this fractal forms steps akin to scar lines observed in the director patterns for random or chaotic two-dimensional maps.Comment: 16 pages, 7 figures, revised versio

Local Variational Principle

A generalization of the Gibbs-Bogoliubov-Feynman inequality for spinless particles is proven and then illustrated for the simple model of a symmetric double-well quartic potential. The method gives a pointwise lower bound for the finite-temperature density matrix and it can be systematically improved by the Trotter composition rule. It is also shown to produce groundstate energies better than the ones given by the Rayleigh-Ritz principle as applied to the groundstate eigenfunctions of the reference potentials. Based on this observation, it is argued that the Local Variational Principle performs better than the equivalent methods based on the centroid path idea and on the Gibbs-Bogoliubov-Feynman variational principle, especially in the range of low temperatures.Comment: 15 pages, 5 figures, one more section adde

Ordered clusters and dynamical states of particles in a vibrated fluid

Fluid-mediated interactions between particles in a vibrating fluid lead to both long range attraction and short range repulsion. The resulting patterns include hexagonally ordered micro-crystallites, time-periodic structures, and chaotic fluctuating patterns with complex dynamics. A model based on streaming flow gives a good quantitative account of the attractive part of the interaction.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let

Effective interactions between inclusions in complex fluids driven out of equilibrium

The concept of fluctuation-induced effective interactions is extended to systems driven out of equilibrium. We compute the forces experienced by macroscopic objects immersed in a soft material driven by external shaking sources. We show that, in contrast with equilibrium Casimir forces induced by thermal fluctuations, their sign, range and amplitude depends on specifics of the shaking and can thus be tuned. We also comment upon the dispersion of these shaking-induced forces, and discuss their potential application to phase ordering in soft-materials.Comment: 10 pages, 8 figures, to appear in PR

Semiclassical time evolution of the density matrix and tunneling

The time dependent density matrix of a system with potential barrier is studied using path integrals. The characterization of the initial state, which is assumed to be restricted to one side of the barrier, and the time evolution of the density matrix lead to a three-fold path integral which is evaluated in the semiclassical limit. The semiclassical trajectories are found to move in the complex coordinate plane and barrier penetration only arises due to fluctuations. Both the form of the semiclassical paths and the relevant fluctuations change significantly as a function of temperature. The semiclassical analysis leads to a detailed picture of barrier penetration in the real time domain and the changeover from thermal activation to quantum tunneling. Deep tunneling is associated with quasi-zero modes in the fluctuation spectrum about the semiclassical orbits in the long time limit. The connection between this real time description of tunneling and the standard imaginary time instanton approach is established. Specific results are given for a double well potential and an Eckart barrier.Comment: 27 pages, 8 figures, to be published in Phys. Rev.

Theodore H. Voth to Dr. Silver, 12 March 1961

Personal correspondenc

Floquet-Markov description of the parametrically driven, dissipative harmonic quantum oscillator

Using the parametrically driven harmonic oscillator as a working example, we study two different Markovian approaches to the quantum dynamics of a periodically driven system with dissipation. In the simpler approach, the driving enters the master equation for the reduced density operator only in the Hamiltonian term. An improved master equation is achieved by treating the entire driven system within the Floquet formalism and coupling it to the reservoir as a whole. The different ensuing evolution equations are compared in various representations, particularly as Fokker-Planck equations for the Wigner function. On all levels of approximation, these evolution equations retain the periodicity of the driving, so that their solutions have Floquet form and represent eigenfunctions of a non-unitary propagator over a single period of the driving. We discuss asymptotic states in the long-time limit as well as the conservative and the high-temperature limits. Numerical results obtained within the different Markov approximations are compared with the exact path-integral solution. The application of the improved Floquet-Markov scheme becomes increasingly important when considering stronger driving and lower temperatures.Comment: 29 pages, 7 figure

Path lengths in turbulence

By tracking tracer particles at high speeds and for long times, we study the geometric statistics of Lagrangian trajectories in an intensely turbulent laboratory flow. In particular, we consider the distinction between the displacement of particles from their initial positions and the total distance they travel. The difference of these two quantities shows power-law scaling in the inertial range. By comparing them with simulations of a chaotic but non-turbulent flow and a Lagrangian Stochastic model, we suggest that our results are a signature of turbulence.Comment: accepted for publication in Journal of Statistical Physic