Experimental Evidence of Time Delay Induced Death in Coupled Limit Cycle Oscillators

Experimental observations of time delay induced amplitude death in a pair of coupled nonlinear electronic circuits that are individually capable of exhibiting limit cycle oscillations are described. In particular, the existence of multiply connected death islands in the parameter space of the coupling strength and the time delay parameter for coupled identical oscillators is established. The existence of such regions was predicted earlier on theoretical grounds in [Phys. Rev. Lett. 80, 5109 (1998); Physica 129D, 15 (1999)]. The experiments also reveal the occurrence of multiple frequency states, frequency suppression of oscillations with increased time delay and the onset of both in-phase and anti-phase collective oscillations.Comment: 4 aps formatted RevTeX pages; 6 figures; to appear in Phys. Rev. Let

Electronic screening and damping in magnetars

We calculate the screening of the ion-ion potential due to electrons in the presence of a large background magnetic field, at densities of relevance to neutron star crusts. Using the standard approach to incorporate electron screening through the one-loop polarization function, we show that the magnetic field produces important corrections both at short and long distances. In extreme fields, realized in highly magnetized neutron stars called magnetars, electrons occupy only the lowest Landau levels in the relatively low density region of the crust. Here our results show that the screening length for Coulomb interactions between ions can be smaller than the inter-ion spacing. More interestingly, we find that the screening is anisotropic and the screened potential between two static charges exhibits long range Friedel oscillations parallel to the magnetic field. This long-range oscillatory behavior is likely to affect the lattice structure of ions, and can possibly create rod-like structures in the magnetar crusts. We also calculate the imaginary part of the electron polarization function which determines the spectrum of electron-hole excitations and plays a role in damping lattice phonon excitations. We demonstrate that even for modest magnetic fields this damping is highly anisotropic and will likely lead to anisotropic phonon heat transport in the outer neutron star crust.Comment: 14 pages, 5 Figure

Bacterial removal of toxic phenols from an industrial effluent

Chlorinated phenols, widely used in industries, are of growing concern owing to their high toxicity, carcinogenicity and wide distribution in industrial wastes. In the present study, one Pseudomonasisolate, identified as Pseudomonas fluorescens, was obtained using the enrichment process with 2,4,6-trichlorophenol (2,4,6-TCP) as a sole carbon source. This isolate was found to be able to degrade various highly chlorinated phenolic compounds such as pentachlorophenol, 2,4,5-TCP, 2,4,6-TCP as well as phenol, 2,4-dibromophenol and 2,4-dichlorophenol (2,4-DCP). The ability of P. fluorescensisolate to remove phenol from a resin producing industrial effluent was tested by scanning the spectrum with a UV-VIS spectrophotometer. The results indicated that this isolate metabolized phenol in the meta-pathway. The optimal phenol degradation conditions of P. fluorescens isolate were at pH 7 and 30oC. At the 480 mg/l of phenol concentration, the highest specific degradation rate of wasobserved. Further increases in phenol concentration slowed down the degradation ability of the isolate. However, P. fluorescens isolate still has the ability of degrading phenol at the concentration of 3.2 g/L.The supplementation of 1% glucose stimulated the growth of P. fluorescens isolate and enhanced the ability to utilize phenol from the effluent sample. GC-MS results show that 85.4% of phenol in theeffluent sample was metabolized after 40 days. In conclusion, P. fluorescens isolated in this study has the ability of utilizing various chlorophenolic compounds and demonstrates its potentials of degradinghigh concentration of phenol in industrial effluents

Effect of an electric field on superfluid helium scintillation produced by alpha-particle sources

We report a study of the intensity and time dependence of scintillation produced by weak alpha particle sources in superfluid helium in the presence of an electric field (0 - 45 kV/cm) in the temperature range of 0.2 K to 1.1 K at the saturated vapor pressure. Both the prompt and the delayed components of the scintillation exhibit a reduction in intensity with the application of an electric field. The reduction in the intensity of the prompt component is well approximated by a linear dependence on the electric field strength with a reduction of 15% at 45 kV/cm. When analyzed using the Kramers theory of columnar recombination, this electric field dependence leads to the conclusion that roughly 40% of the scintillation results from species formed from atoms originally promoted to excited states and 60% from excimers created by ionization and subsequent recombination with the charges initially having a cylindrical Gaussian distribution about the alpha track of 60 nm radius. The intensity of the delayed component of the scintillation has a stronger dependence on the electric field strength and on temperature. The implications of these data on the mechanisms affecting scintillation in liquid helium are discussed.Comment: 17 pages, 23 figure

Spin-lattice coupling mediated giant magnetodielectricity across the spin reorientation in Ca2FeCoO5

The structural, phonon, magnetic, dielectric, and magneto dielectric responses of the pure bulk Brownmillerite compound Ca2FeCoO5 are reported. This compound showed giant magneto dielectric response (10%-24%) induced by strong spin-lattice coupling across its spin reorientation transition (150-250 K). The role of two Debye temperatures pertaining to differently coordinated sites in the dielectric relaxations is established. The positive giant magneto-dielectricity is shown to be a direct consequence of the modulations in the lattice degrees of freedom through applied external field across the spin reorientation transition. Our study illustrates novel control of magneto-dielectricity by tuning the spin reorientation transition in a material that possess strong spin lattice coupling.Comment: 7 pages, 12 figure

Effect of Nonlinear Thermal Radiation on MHD Chemically Reacting Maxwell Fluid Flow Past a Linearly Stretching Sheet

This communication addresses the influence of nonlinear thermal radiation on magneto hydrodynamic Maxwell fluid flow past a linearly stretching surface with heat and mass transfer. The effects of heat generation/absorption and chemical reaction are taken into account. At first, we converted the governing partial differential equations into nonlinear ordinary differential equations with the help of suitable similarity transformations and solved by using Runge-Kutta based shooting technique. Further, the effects of various physical parameters on velocity, temperature and concentration fields were discussed thoroughly with the help of graphs obtained by using bvp5c MATLAB package. In view of many engineering applications we also computed the friction factor, heat and mass transfer coefficients and presented them in tables. Results indicate that an increase in thermal buoyancy parameter enhances the fluid velocity but suppresses the temperature. Deborah number have tendency to reduce the fluid velocity and mass transfer rate. It is also perceived that temperature ratio parameter has the propensity to enrich the fluid temperature

Strangelet dwarfs

If the surface tension of quark matter is low enough, quark matter is not self bound. At sufficiently low pressure and temperature, it will take the form of a crystal of positively charged strangelets in a neutralizing background of electrons. In this case there will exist, in addition to the usual family of strange stars, a family of low-mass large-radius objects analogous to white dwarfs, which we call "strangelet dwarfs". Using a generic parametrization of the equation of state of quark matter, we calculate the mass-radius relationship of these objects.Comment: 10 pages, LaTeX, added discussion of CFL phase and strangelet pollution, version to appear in journal. arXiv admin note: text overlap with arXiv:0808.067

Three Li-rich K giants: IRAS 12327-6523, IRAS 13539-4153, and IRAS 17596-3952

We report on spectroscopic analyses of three K giants previously suggested to be Li-rich: IRAS 12327-6523, IRAS 13539-4153, and IRAS 17596-3952. High-resolution optical spectra and the LTE model atmospheres are used to derive the stellar parameters: ($T_{\rm eff}$, log $g$, [Fe/H]), elemental abundances, and the isotopic ratio $^{12}$C/$^{13}$C. IRAS 13539-4153 shows an extremely high Li abundance of $\log\epsilon$(Li) $\approx$ 4.2, a value ten times more than the present Li abundance in the local interstellar medium. This is the third highest Li abundance yet reported for a K giant. IRAS 12327-6523 shows a Li abundances of $\log\epsilon$(Li)$\approx$ 1.4. IRAS 17596-3952 is a rapidly rotating ($V{\sin i}$ $\approx$ 35 km s$^{-1}$) K giant with $\log\epsilon$(Li) $\approx$ 2.2. Infrared photometry which shows the presence of an IR excess suggesting mass-loss. A comparison is made between these three stars and previously recognized Li-rich giants.Comment: 17 pages, 6 figures, accepted for A

New Spectroscopic Observations of the Post-AGB Star V354Lac=IRAS22272+5435

The strongest absorption features with the lower-level excitation potentials $\chi_{\rm low}<1$ eV are found to be split in the high-resolution optical spectra of the post-AGB star V354 Lac taken in 2007--2008. Main parameters, T$_{eff}$=5650 K, $\log g$=0.2, $\xi_t$=5.0 km/s, and the abundances of 22 chemical elements in the star's atmosphere are found. The overabundance of the $s$-process chemical elements (Ba, La, Ce, Nd) in the star's atmosphere is partly due to the splitting of strong lines of the ions of these metals. The peculiarities of the spectrum in the wavelength interval containing the LiI $\lambda$ 6707 \AA{} line can be naturally explained only by taking the overabundances of the CeII and SmII heavy-metal ions into account. The best agreement with the synthetic spectrum is achieved assuming $\epsilon$(LiI)=2.0, $\epsilon$(CeII)=3.2, and $\epsilon$(SmII)=2.7. The velocity field both in the atmosphere and in the circumstellar envelope of V354 Lac remained stationary throughout the last 15 years of our observations.Comment: 16 pages, 6 figures, 2 table