Constraints on scalar diffusion anomaly in three-dimensional flows having bounded velocity gradients

This study is concerned with the decay behaviour of a passive scalar $\theta$ in three-dimensional flows having bounded velocity gradients. Given an initially smooth scalar distribution, the decay rate $d/dt$ of the scalar variance $$ is found to be bounded in terms of controlled physical parameters. Furthermore, in the zero diffusivity limit, $\kappa\to0$, this rate vanishes as $\kappa^{\alpha_0}$ if there exists an $\alpha_0\in(0,1]$ independent of $\kappa$ such that $<\infty$ for $\alpha\le\alpha_0$. This condition is satisfied if in the limit $\kappa\to0$, the variance spectrum $\Theta(k)$ remains steeper than $k^{-1}$ for large wave numbers $k$. When no such positive $\alpha_0$ exists, the scalar field may be said to become virtually singular. A plausible scenario consistent with Batchelor's theory is that $\Theta(k)$ becomes increasingly shallower for smaller $\kappa$, approaching the Batchelor scaling $k^{-1}$ in the limit $\kappa\to0$. For this classical case, the decay rate also vanishes, albeit more slowly -- like $(\ln P_r)^{-1}$, where $P_r$ is the Prandtl or Schmidt number. Hence, diffusion anomaly is ruled out for a broad range of scalar distribution, including power-law spectra no shallower than $k^{-1}$. The implication is that in order to have a $\kappa$-independent and non-vanishing decay rate, the variance at small scales must necessarily be greater than that allowed by the Batchelor spectrum. These results are discussed in the light of existing literature on the asymptotic exponential decay $\sim e^{-\gamma t}$, where $\gamma>0$ is independent of $\kappa$.Comment: 6-7 journal pages, no figures. accepted for publication by Phys. Fluid

Vibrational Tamm states at the edges of graphene nanoribbons

We study vibrational states localized at the edges of graphene nanoribbons. Such surface oscillations can be considered as a phonon analog of Tamm states well known in the electronic theory. We consider both armchair and zigzag graphene stripes and demonstrate that surface modes correspond to phonons localized at the edges of the graphene nanoribbon, and they can be classified as in-plane and out-of-plane modes. In addition, in armchair nanoribbons anharmonic edge modes can experience longitudinal localization in the form of self-localized nonlinear modes, or surface breather solitons.Comment: 10 pages, 10 figure

The baboon endogenous virus genome. II. Provirus sequence variations in baboon cell DNA

Restriction analysis of the approximately 100 integrated baboon endogenous virus (BaEV) proviruses in baboon cells and tissues has revealed two major sequence variations, both in the gag gene region of the genome. One, a 150 nucleotide pair insert, is present in a small proportion of the proviral DNAs of some baboons, but is present in the majority of the proviral DNAs of other baboons. The second, a Bam HI recognition sequence located 2.25 kb from the proviral 5' end, is missing or modified in approximately one-half of the integrated genomes. We consider the possibility that accumulation of proviruses not containing the 0.15 kb insert is correlated with viral activation and expression since it is this form that is a replication intermediate in freshly infected permissive cells. It is evident from these initial studies that the organization of the multiple BaEV proviruses in baboon DNA has undergone modification during evolution

Calculation of nuclear-spin-dependent parity nonconservation in s-d transitions of Ba+^+, Yb+^+ and Ra+^+ ions

We use correlation potential and many-body perturbation theory techniques to calculate spin-independent and nuclear spin-dependent parts of the parity nonconserving amplitudes of the transitions between the $6s_{1/2}$ ground state and the $5d_{3/2}$ excited state of Ba$^+$ and Yb$^+$ and between the $7s_{1/2}$ ground state and the $6d_{3/2}$ excited state of Ra$^+$. The results are presented in a form convenient for extracting of the constants of nuclear-spin-dependent interaction (such as, e.g., anapole moment) from the measurements.Comment: 9 pages, 8 tables, no figure

The eta-photon transition form factor

The eta-photon transition form factor is evaluated in a formalism based on a phenomenological description at low values of the photon virtuality, and a QCD-based description at high photon virtualities, matching at a scale $Q_{0}^{2}$. The high photon virtuality description makes use of a Distribution Amplitude calculated in the Nambu-Jona-Lasinio model with Pauli-Villars regularization at the matching scale $Q_{0}^{2}$, and QCD evolution from $Q_{0}^{2}$ to higher values of $Q^{2}$. A good description of the available data is obtained. The analysis indicates that the recent data from the BaBar collaboration on pion and eta transition form factor can be well reproduced, if a small contribution of twist three at the matching scale $Q_{0}^{2}$ is included.Comment: 14 pages, 3 figures, revised version, minor corrections, references added, conclusions unchanged. Accepted for publication in Phys. Rev.

Photoionization and Photoelectric Loading of Barium Ion Traps

Simple and effective techniques for loading barium ions into linear Paul traps are demonstrated. Two-step photoionization of neutral barium is achieved using a weak intercombination line (6s2 1S0 6s6p 3P1, 791 nm) followed by excitation above the ionization threshold using a nitrogen gas laser (337 nm). Isotopic selectivity is achieved by using a near Doppler-free geometry for excitation of the triplet 6s6p 3P1 state. Additionally, we report a particularly simple and efficient trap loading technique that employs an in-expensive UV epoxy curing lamp to generate photoelectrons.Comment: 5 pages, Accepted to PRA 3/20/2007 -fixed typo -clarified figure 3 caption -added reference [15

Scotland, Catalonia and the “right” to self-determination: a comment suggested by Kathryn Crameri’s “Do Catalans Have the Right to Decide?

No abstract available

Nuclear collective motion with a coherent coupling interaction between quadrupole and octupole modes

A collective Hamiltonian for the rotation-vibration motion of nuclei is considered, in which the axial quadrupole and octupole degrees of freedom are coupled through the centrifugal interaction. The potential of the system depends on the two deformation variables $\beta_2$ and $\beta_3$. The system is considered to oscillate between positive and negative $\beta_3$-values, by rounding an infinite potential core in the $(\beta_2,\beta_3)$-plane with $\beta_2>0$. By assuming a coherent contribution of the quadrupole and octupole oscillation modes in the collective motion, the energy spectrum is derived in an explicit analytic form, providing specific parity shift effects. On this basis several possible ways in the evolution of quadrupole-octupole collectivity are outlined. A particular application of the model to the energy levels and electric transition probabilities in alternating parity spectra of the nuclei $^{150}$Nd, $^{152}$Sm, $^{154}$Gd and $^{156}$Dy is presented.Comment: 25 pages, 13 figures. Accepted in Phys. Rev.

Charged Higgs phenomenology in the flipped two Higgs doublet model

We study the phenomenology of the charged Higgs boson in the "flipped" two Higgs doublet model, in which one doublet gives mass to up-type quarks and charged leptons and the other gives mass to down-type quarks. We present the charged Higgs branching ratios and summarize the indirect constraints. We extrapolate existing LEP searches for H+H- and Tevatron searches for t tbar with t --> H+ b into the flipped model and extract constraints on MH+ and the parameter tan(beta). We finish by reviewing existing LHC charged Higgs searches and suggest that the LHC reach in this model could be extended for charged Higgs masses below the tb threshold by considering t tbar with t --> H+ b and H+ --> q qbar, as has been used in Tevatron searches.Comment: 23 pages, 7 figures. V2: added refs on H+W- associated productio

Baboon endogenous virus genome. I. Restriction enzyme map of the unintegrated DNA genome of a primate retrovirus

A detailed restriction map was deduced for the genome of an endogenous retrovirus of a higher primate, that of baboon. The cleavage sites for 12 restriction enzymes were mapped. The unintegrated linear viral DNA intermediate that is produced by infection of permissive cells with baboon endogenous virus was isolated. Hybridization with a strong-stop complementary DNA probe demonstrated presence of a terminal repetition in the linear viral DNA. The positions of restriction sites for two particular enzymes, SmaI and XhoI, near each end were consistent with this result and indicated that the length of the repetition is 0.55 +/- 0.01 kilobase. The linear viral DNA had a unique restriction map indicating that it is not a set of random circular permutations of the RNA genome. From hybridization with a 3'-specific probe, the DNA restriction map was aligned relative to the 5'-to-3' orientation of the viral RNA. We observed a minor heterogeneity in a BamHI recognition site 1.95 kilobases from the right end of the linear map