The Cosmic Battery and the Inner Edge of the Accretion Disk

The Poynting-Robertson Cosmic Battery proposes that the innermost part of the accretion disk around a black hole is threaded by a large scale dipolar magnetic field generated in situ, and that the return part of the field diffuses outward through the accretion disk. This is different from the scenario that the field originates at large distances and is carried inward by the accretion flow. In view of the importance of large scale magnetic fields in regulating the processes of accretion and outflows, we study the stability of the inner edge of a magnetized disk in general relativity when the distribution of the magnetic field is the one predicted by the Poynting-Robertson Cosmic Battery. We found that as the field grows, the inner edge of the disk gradually moves outward. In a fast spinning black hole with a>0.8M the inner edge moves back in towards the black hole horizon as the field grows beyond some threshold value. In all cases, the inner part of the disk undergoes a dramatic structural change as the field approaches equipartition.Comment: 7 pages, 3 figures, accepted for publication in Monthly Notices of the RA

Equilibria of a Self-Gravitating, Rotating Disk Around a Magnetized Compact Object

We examine the effect of self-gravity in a rotating thick-disk equilibrium in the presence of a dipolar magnetic field. In the first part, we find a self-similar solution for non-self-gravitating disks. The solution that we have found shows that the pressure and density equilibrium profiles are strongly modified by a self-consistent toroidal magnetic field. We introduce 3 dimensionless variables $C_B$, $C_c$, $C_t$ that indicate the relative importance of toroidal component of magnetic field ($C_B$), centrifugal ($C_c$) and thermal ($C_t$) energy with respect to the gravitational potential energy of the central object. We study the effect of each of them on the structure of the disk. In the second part, we investigate the effect of self-gravity on the these disks; thus we introduce another dimensionless variable ($C_g$) that shows the importance of self-gravity. We find a self-similar solution for the equations of the system. Our solution shows that the structure of the disk is modified by the self-gravitation of the disk, the magnetic field of the central object, and the azimuthal velocity of the gas disk. We find that self-gravity and magnetism from the central object can change the thickness and the shape of the disk. We show that as the effect of self-gravity increases the disk becomes thinner. We also show that for different values of the star's magnetic field and of the disk's azimuthal velocity, the disk's shape and its density and pressure profiles are strongly modified.Comment: 7 page with 6 figures, Accepted for MNRA

Relativistic Expansion of Magnetic Loops at the Self-similar Stage II: Magnetized outflows interacting with the ambient plasma

We obtained self-similar solutions of relativistically expanding magnetic loops by assuming axisymmetry and a purely radial flow. The stellar rotation and the magnetic fields in the ambient plasma are neglected. We include the Newtonian gravity of the central star. These solutions are extended from those in our previous work (Takahashi, Asano, & Matsumoto 2009) by taking into account discontinuities such as the contact discontinuity and the shock. The global plasma flow consists of three regions, the outflowing region, the post shocked region, and the ambient plasma. They are divided by two discontinuities. The solutions are characterized by the radial velocity, which plays a role of the self-similar parameter in our solutions. The shock Lorentz factor gradually increases with radius. It can be approximately represented by the power of radius with the power law index of 0.25. We also carried out magnetohydrodynamic simulations of the evolution of magnetic loops to study the stability and the generality of our analytical solutions. We used the analytical solutions as the initial condition and the inner boundary conditions. We confirmed that our solutions are stable over the simulation time and that numerical results nicely recover the analytical solutions. We then carried out numerical simulations to study the generality of our solutions by changing the power law index \delta of the ambient plasma density \rho_0 \propto r^{-\delta}. We alter the power law index \delta from 3.5 in the analytical solutions. The analytical solutions are used as the initial conditions inside the shock in all simulations. We observed that the shock Lorentz factor increases with time when \delta is larger than 3, while it decreases with time when \delta is smaller than 3. The shock Lorentz factor is proportional to t^{(\delta-3)/2}. These results are consistent with the analytical studies by Shapiro (1979).Comment: 19 pages, 13 figures, Accepted for publication in MNRA

Nonradial and nonpolytropic astrophysical outflows VIII. A GRMHD generalization for relativistic jets

Steady axisymmetric outflows originating at the hot coronal magnetosphere of a Schwarzschild black hole and surrounding accretion disk are studied in the framework of general relativistic magnetohydrodynamics (GRMHD). The assumption of meridional self-similarity is adopted for the construction of semi-analytical solutions of the GRMHD equations describing outflows close to the polar axis. In addition, it is assumed that relativistic effects related to the rotation of the black hole and the plasma are negligible compared to the gravitational and other energetic terms. The constructed model allows us to extend previous MHD studies for coronal winds from young stars to spine jets from Active Galactic Nuclei surrounded by disk-driven outflows. The outflows are thermally driven and magnetically or thermally collimated. The collimation depends critically on an energetic integral measuring the efficiency of the magnetic rotator, similarly to the non relativistic case. It is also shown that relativistic effects affect quantitatively the depth of the gravitational well and the coronal temperature distribution in the launching region of the outflow. Similarly to previous analytical and numerical studies, relativistic effects tend to increase the efficiency of the thermal driving but reduce the effect of magnetic self-collimation.Comment: 20 page, Accepted in A&A 10/10/200

Patterns of genetic variation in native America

Journal ArticleAllele frequencies from seven polymorphic red cell antigen loci (ABO, Rh, MN, S, P, Duffy, and Diego) were examined in 144 Native American populations. Mean genetic distances (Nei's D) and the fixation index FST are approximately equal for the North and South American samples but are reduced in the Central American geographic area

Nitrifying and heterotrophic population dynamics in biofilm reactors: effects of hydraulic retention time and the presence of organic carbon

Two biofilmreactors operated with hydraulic retention times of 0.8 and 5.0 h were used to study the links between population dynamics and reactor operation performance during a shift in process operation from pure nitrification to combined nitrification and organic carbon removal. The ammonium and the organic carbon loads were identical for both reactors. The composition and dynamics of the microbial consortia were quantified by fluorescence in situ hybridization (FISH) with rRNA-targeted oligonucleotide probes combined with confocal laser scanning microscopy, and digital image analysis. In contrast to past research, after addition of acetate as organic carbon nitrification performance decreased more drastically in the reactor with longer hydraulic retention time. FISH analysis showed that this effect was caused by the unexpected formation of a heterotrophic microorganism layer on top of the nitrifying biofilm that limited nitrifiers oxygen supply. Our results demonstrate that extension of the hydraulic retention time might be insufficient to improve combined nitrification and organic carbon removal in biofilm reactors.Ministério da Ciência, Tecnologia e Ensino Superior. Fundação para a Ciência e a Tecnologia (FCT) - PRAXIS XXI BD/15943/98). Deutscher Akademischer Austauschdienst (A/99/06961). European Comission - T.M.R. BioToBio project. Deutsche Forschungsgemeinschaft

Comparative in silico analysis of PCR primers suited for diagnostics and cloning of ammonia monooxygenase genes from ammonia-oxidizing bacteria

Over recent years, several PCR primers have been described to amplify genes encoding the structural subunits of ammonia monooxygenase (AMO) from ammonia-oxidizing bacteria (AOB). Most of them target amoA, while amoB and amoC have been neglected so far. This study compared the nucleotide sequence of 33 primers that have been used to amplify different regions of the amoCAB operon with alignments of all available sequences in public databases. The advantages and disadvantages of these primers are discussed based on the original description and the spectrum of matching sequences obtained. Additionally, new primers to amplify the almost complete amoCAB operon of AOB belonging to Betaproteobacteria (betaproteobacterial AOB), a primer pair for DGGE analysis of amoA and specific primers for gammaproteobacterial AOB, are also described. The specificity of these new primers was also evaluated using the databases of the sequences created during this study

Gradient microfluidics enables rapid bacterial growth inhibition testing

Bacterial growth inhibition tests have become a standard measure of the adverse effects of inhibitors for a wide range of applications, such as toxicity testing in the medical and environmental sciences. However, conventional well-plate formats for these tests are laborious and provide limited information (often being restricted to an end-point assay). In this study, we have developed a microfluidic system that enables fast quantification of the effect of an inhibitor on bacteria growth and survival, within a single experiment. This format offers a unique combination of advantages, including long-term continuous flow culture, generation of concentration gradients, and single cell morphology tracking. Using Escherichia coli and the inhibitor amoxicillin as one model system, we show excellent agreement between an on-chip single cell-based assay and conventional methods to obtain quantitative measures of antibiotic inhibition (for example, minimum inhibition concentration). Furthermore, we show that our methods can provide additional information, over and above that of the standard well-plate assay, including kinetic information on growth inhibition and measurements of bacterial morphological dynamics over a wide range of inhibitor concentrations. Finally, using a second model system, we show that this chip-based systems does not require the bacteria to be labeled and is well suited for the study of naturally occurring species. We illustrate this using Nitrosomonas europaea, an environmentally important bacteria, and show that the chip system can lead to a significant reduction in the period required for growth and inhibition measurements (<4 days, compared to weeks in a culture flask)

Revision of the nonequilibrium thermal dissociation and stringent washing approaches for identification of mixed nucleic acid targets by microarrays

Microarray experiments typically involve washing steps that remove hybridized nonspecific targets with the purpose of improving the signal-to-noise ratio. The quality of washing ultimately affects downstream analysis of the microarray and interpretation. The paucity of fundamental studies directed towards understanding the dissociation of mixed targets from microarrays makes the development of meaningful washing/dissociation protocols difficult. To fill the void, we examined activation energies and preexponential coefficients of 47 perfect match (PM) and double-mismatch (MM) duplex pairs to discover that there was no statistical difference between the kinetics of the PM and MM duplexes. Based on these findings, we evaluated the nonequilibrium thermal dissociation (NTD) approach, which has been used to identify specific microbial targets in mixed target samples. We found that the major premises for various washing protocols and the NTD approach might be seriously compromised because: (i) nonspecific duplexes do not always dissociate before specific ones, and (ii) the relationship between dissociation rates of the PM and MM duplexes depends on temperature and duplex sequence. Specifically for the NTD, we show that previously suggested use of reference curves, indices of curves and temperature ramps lead to erroneous conclusions

Plasma sheet and (nonstorm) ring current formation from solar and polar wind sources

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95352/1/jgra17511.pd