Double-diffusive magnetic buoyancy instability in a quasi-two-dimensional Cartesian geometry

Magnetic buoyancy, believed to occur in the solar tachocline, is both an important part of large-scale solar dynamo models and the picture of how sunspots are formed. Given that in the tachocline region the ratio of magnetic diffusivity to thermal diffusivity is small it is important, for both the dynamo and sunspot formation pictures, to understand magnetic buoyancy in this regime. Furthermore, the tachocline is a region of strong shear and such investigations must involve structures that become buoyant in the double-diffusive regime which are generated entirely from a shear flow. In a previous study, we have illustrated that shear-generated doublediffusive magnetic buoyancy instability is possible in the tachocline. However, this study was severely limited due to the computational requirements of running three-dimensional magnetohydrodynamic simulations over diffusive time-scales. A more comprehensive investigation is required to fully understand the double-diffusive magnetic buoyancy instability and its dependency on a number of key parameters; such an investigation requires the consideration of a reduced model. Here we consider a quasi-two-dimensional model where all gradients in the x direction are set to zero. We show how the instability is sensitive to changes in the thermal diffusivity and also show how different initial configurations of the forced shear flow affect the behaviour of the instability. Finally, we conclude that if the tachocline is thinner than currently stated then the double-diffusive magnetic buoyancy instability can more easily occur

Alpha effect due to buoyancy instability of a magnetic layer

A strong toroidal field can exist in form of a magnetic layer in the overshoot region below the solar convection zone. This motivates a more detailed study of the magnetic buoyancy instability with rotation. We calculate the alpha effect due to helical motions caused by a disintegrating magnetic layer in a rotating density-stratified system with angular velocity Omega making an angle theta with the vertical. We also study the dependence of the alpha effect on theta and the strength of the initial magnetic field. We carry out three-dimensional hydromagnetic simulations in Cartesian geometry. A turbulent EMF due to the correlations of the small scale velocity and magnetic field is generated. We use the test-field method to calculate the transport coefficients of the inhomogeneous turbulence produced by the layer. We show that the growth rate of the instability and the twist of the magnetic field vary monotonically with the ratio of thermal conductivity to magnetic diffusivity. The resulting alpha effect is inhomogeneous and increases with the strength of the initial magnetic field. It is thus an example of an "anti-quenched" alpha effect. The alpha effect is nonlocal, requiring around 8--16 Fourier modes to reconstruct the actual EMF based on the actual mean field.Comment: 14 pages, 19 figures 3 tables (submitted to A & A

19F-labeling of the adenine H2-site to study large RNAs by NMR spectroscopy

In comparison to proteins and protein complexes, the size of RNA amenable to NMR studies is limited despite the development of new isotopic labeling strategies including deuteration and ligation of differentially labeled RNAs. Due to the restricted chemical shift dispersion in only four different nucleotides spectral resolution remains limited in larger RNAs. Labeling RNAs with the NMR-active nucleus [superscript 19]F has previously been introduced for small RNAs up to 40 nucleotides (nt). In the presented work, we study the natural occurring RNA aptamer domain of the guanine-sensing riboswitch comprising 73 nucleotides from Bacillus subtilis. The work includes protocols for improved in vitro transcription of 2-fluoroadenosine-5′-triphosphat (2F-ATP) using the mutant P266L of the T7 RNA polymerase. Our NMR analysis shows that the secondary and tertiary structure of the riboswitch is fully maintained and that the specific binding of the cognate ligand hypoxanthine is not impaired by the introduction of the [superscript 19]F isotope. The thermal stability of the [superscript 19]F-labeled riboswitch is not altered compared to the unmodified sequence, but local base pair stabilities, as measured by hydrogen exchange experiments, are modulated. The characteristic change in the chemical shift of the imino resonances detected in a 1H,15N-HSQC allow the identification of Watson–Crick base paired uridine signals and the [superscript 19]F resonances can be used as reporters for tertiary and secondary structure transitions, confirming the potential of [superscript 19]F-labeling even for sizeable RNAs in the range of 70 nucleotides.Deutsche Forschungsgemeinschaft (collaborative research center: SFB902

Age-related differences in emotional reactivity, regulation, and rejection sensitivity in adolescence

Although adolescents’ emotional lives are thought to be more turbulent than those of adults, it is unknown whether this difference is attributable to developmental changes in emotional reactivity or emotion regulation. Study 1 addressed this question by presenting healthy individuals aged 10–23 with negative and neutral pictures and asking them to respond naturally or use cognitive reappraisal to down-regulate their responses on a trial-by-trial basis. Results indicated that age exerted both linear and quadratic effects on regulation success but was unrelated to emotional reactivity. Study 2 replicated and extended these findings using a different reappraisal task and further showed that situational (i.e., social vs. nonsocial stimuli) and dispositional (i.e., level of rejection sensitivity) social factors interacted with age to predict regulation success: young adolescents were less successful at regulating responses to social than to nonsocial stimuli, particularly if the adolescents were high in rejection sensitivity. Taken together, these results have important implications for the inclusion of emotion regulation in models of emotional and cognitive development.National Science Foundation (U.S.) (Award BCS-0224342)National Institutes of Health (U.S.) (Award MH076137)National Institutes of Health (U.S.) (Award HD069178)National Institutes of Health (U.S.) (Award MH094056

Photo collage-based photograph display system on mobile computing platform

In the last few decades, mobile computing platform technology has grown rapidly, as observed from smart phones that have quickly become ubiquitous. The mobile computing platform is the most widely used platform in our life today, and digital photographs captured through these devices have become routine for most people. In this study, we propose a novel artistic method for displaying photographs in mobile devices as a photo collage. Using our system, users can view a representative photograph as a collage of photographs associated with a certain event and access each of photographs individually. To implement this, we employ centroidal Voronoi diagram to obtain an even distribution of tiles, and use the sites as the location of tiles. We use the edge avoidance technique to prevent tiles from being located across the edges. To obtain the direction of tiles that follow near a strong edge, we employ the Edge tangent Flow field and use the field as the directions of tiles. Finally, we search for photographs that best match the tiles calculated above by using a thumbnail difference metric

Search for the standard model Higgs boson in the H to ZZ to 2l 2nu channel in pp collisions at sqrt(s) = 7 TeV

A search for the standard model Higgs boson in the H to ZZ to 2l 2nu decay channel, where l = e or mu, in pp collisions at a center-of-mass energy of 7 TeV is presented. The data were collected at the LHC, with the CMS detector, and correspond to an integrated luminosity of 4.6 inverse femtobarns. No significant excess is observed above the background expectation, and upper limits are set on the Higgs boson production cross section. The presence of the standard model Higgs boson with a mass in the 270-440 GeV range is excluded at 95% confidence level.Comment: Submitted to JHE

Combined search for the quarks of a sequential fourth generation

Results are presented from a search for a fourth generation of quarks produced singly or in pairs in a data set corresponding to an integrated luminosity of 5 inverse femtobarns recorded by the CMS experiment at the LHC in 2011. A novel strategy has been developed for a combined search for quarks of the up and down type in decay channels with at least one isolated muon or electron. Limits on the mass of the fourth-generation quarks and the relevant Cabibbo-Kobayashi-Maskawa matrix elements are derived in the context of a simple extension of the standard model with a sequential fourth generation of fermions. The existence of mass-degenerate fourth-generation quarks with masses below 685 GeV is excluded at 95% confidence level for minimal off-diagonal mixing between the third- and the fourth-generation quarks. With a mass difference of 25 GeV between the quark masses, the obtained limit on the masses of the fourth-generation quarks shifts by about +/- 20 GeV. These results significantly reduce the allowed parameter space for a fourth generation of fermions.Comment: Replaced with published version. Added journal reference and DO

A Search for Dark Higgs Bosons

Recent astrophysical and terrestrial experiments have motivated the proposal of a dark sector with GeV-scale gauge boson force carriers and new Higgs bosons. We present a search for a dark Higgs boson using 516 fb-1 of data collected with the BABAR detector. We do not observe a significant signal and we set 90% confidence level upper limits on the product of the Standard Model-dark sector mixing angle and the dark sector coupling constant.Comment: 7 pages, 5 postscript figures, published version with improved plots for b/w printin

Performance of CMS muon reconstruction in pp collision events at sqrt(s) = 7 TeV

The performance of muon reconstruction, identification, and triggering in CMS has been studied using 40 inverse picobarns of data collected in pp collisions at sqrt(s) = 7 TeV at the LHC in 2010. A few benchmark sets of selection criteria covering a wide range of physics analysis needs have been examined. For all considered selections, the efficiency to reconstruct and identify a muon with a transverse momentum pT larger than a few GeV is above 95% over the whole region of pseudorapidity covered by the CMS muon system, abs(eta) < 2.4, while the probability to misidentify a hadron as a muon is well below 1%. The efficiency to trigger on single muons with pT above a few GeV is higher than 90% over the full eta range, and typically substantially better. The overall momentum scale is measured to a precision of 0.2% with muons from Z decays. The transverse momentum resolution varies from 1% to 6% depending on pseudorapidity for muons with pT below 100 GeV and, using cosmic rays, it is shown to be better than 10% in the central region up to pT = 1 TeV. Observed distributions of all quantities are well reproduced by the Monte Carlo simulation.Comment: Replaced with published version. Added journal reference and DO