Helicity and alpha-effect by current-driven instabilities of helical magnetic fields

Helical magnetic background fields with adjustable pitch angle are imposed on a conducting fluid in a differentially rotating cylindrical container. The small-scale kinetic and current helicities are calculated for various field geometries, and shown to have the opposite sign as the helicity of the large-scale field. These helicities and also the corresponding $\alpha$-effect scale with the current helicity of the background field. The $\alpha$-tensor is highly anisotropic as the components $\alpha_{\phi\phi}$ and $\alpha_{zz}$ have opposite signs. The amplitudes of the azimuthal $\alpha$-effect computed with the cylindrical 3D MHD code are so small that the operation of an $\alpha\Omega$ dynamo on the basis of the current-driven, kink-type instabilities of toroidal fields is highly questionable. In any case the low value of the $\alpha$-effect would lead to very long growth times of a dynamo in the radiation zone of the Sun and early-type stars of the order of mega-years.Comment: 6 pages, 7 figures, submitted to MNRA

Nonaxisymmetric MHD instabilities of Chandrasekhar states in Taylor-Couette geometry

We consider axially periodic Taylor-Couette geometry with insulating boundary conditions. The imposed basic states are so-called Chandrasekhar states, where the azimuthal flow $U_\phi$ and magnetic field $B_\phi$ have the same radial profiles. Mainly three particular profiles are considered: the Rayleigh limit, quasi-Keplerian, and solid-body rotation. In each case we begin by computing linear instability curves and their dependence on the magnetic Prandtl number Pm. For the azimuthal wavenumber m=1 modes, the instability curves always scale with the Reynolds number and the Hartmann number. For sufficiently small Pm these modes therefore only become unstable for magnetic Mach numbers less than unity, and are thus not relevant for most astrophysical applications. However, modes with m>10 can behave very differently. For sufficiently flat profiles, they scale with the magnetic Reynolds number and the Lundquist number, thereby allowing instability also for the large magnetic Mach numbers of astrophysical objects. We further compute fully nonlinear, three-dimensional equilibration of these instabilities, and investigate how the energy is distributed among the azimuthal (m) and axial (k) wavenumbers. In comparison spectra become steeper for large m, reflecting the smoothing action of shear. On the other hand kinetic and magnetic energy spectra exhibit similar behavior: if several azimuthal modes are already linearly unstable they are relatively flat, but for the rigidly rotating case where m=1 is the only unstable mode they are so steep that neither Kolmogorov nor Iroshnikov-Kraichnan spectra fit the results. The total magnetic energy exceeds the kinetic energy only for large magnetic Reynolds numbers Rm>100.Comment: 12 pages, 14 figures, submitted to Ap

Zbrinjavanje dišnog puta u jedinici intenzivnog liječenja

Airway management in the intensive care unit (ICU) is a challenging procedure and is frequently associated with life threatening complications. The incidence of difficult intubations ranges from 10% to 22%, depending on the setting and the patients in need of endotracheal intubation. Multiple attempts are often needed to secure the airway. Despite the high risk for patients in the ICU setting, the equipment for airway management such as capnometry or alternative devices is not always available. The novel technique of video laryngoscopy has been recently introduced into clinical practice in the operating room. First results from larger studies are very promising, suggesting these new devices to be helpful for successful intubation with fewer attempts in difficult intubation scenarios. At the same time, several reports show that successful use of video laryngoscopes in emergency situations need substantial practical training and expertise in airway management. The use of a protocol for airway management has been shown to decrease complications. Parts of this protocol are appropriate staffing, pre-oxygenation and strategies to avoid cardiovascular complications. In conclusion, high practical skill of airway management is needed in critically ill patients. Monitoring such as capnography and alternative equipment for securing the airway is not just mandatory in the operating room but also in the ICU.Zbrinjavanje dišnog puta u jedinici intenzivnog liječenja (JIL) je izazovan postupak i često se povezuje sa životno opasnim komplikacijama. Incidencija otežane intubacije varira od 10% do 22%, ovisno o uvjetima i bolesnicima kojima je potrebna endotrahealna intubacija. Obično je potrebno više pokušaja kako bi se osigurao dišni put. Unatoč visokom riziku za bolesnika u okruženju JIL oprema za osiguravanje dišnih putova kao što su kapnometrija i alternativna pomagala često nije dostupna. Nova tehnika video laringoskopije je nedavno uvedena u kliničku praksu u operacijskoj dvorani. Prvi rezultati većih studija su vrlo obećavajući, jer pokazuju da su ti novi uređaji korisni za uspješnu intubaciju s manje pokušaja kod otežane inubacije. Istodobno je nekoliko izvješća pokazalo da uspješna uporaba video laringoskopa u hitnim situacijama zahtijeva stalnu praktičnu uvježbanost i stručnost u osiguranju dišnog puta. Primjena protokola za zbrinjavanje dišnih putova je smanjila komplikacije. Dio ovoga protokola čine odgovorajuće osoblje, pred-oksigenacija i strategije za izbjegavanje kardiovaskularnih komplikacija. Ukratko, kod bolesnika u JIL potrebna je visoka praktična vještina zbrinjavanja dišnog puta. Praćenje kao što je kapnografija i alternativna pomagala za osiguravanje dišnog puta nisu obvezna samo u operacijskoj dvorani, nego i u JIL

Shared and unique patterns of embryo development in extremophile poeciliids

Background: Closely related lineages of livebearing fishes have independently adapted to two extreme environmental factors: toxic hydrogen sulphide (H2S) and perpetual darkness. Previous work has demonstrated in adult specimens that fish from these extreme habitats convergently evolved drastically increased head and offspring size, while cave fish are further characterized by reduced pigmentation and eye size. Here, we traced the development of these (and other) divergent traits in embryos of Poecilia mexicana from benign surface habitats (“surface mollies”) and a sulphidic cave (“cave mollies”), as well as in embryos of the sister taxon, Poecilia sulphuraria from a sulphidic surface spring (“sulphur mollies”). We asked at which points during development changes in the timing of the involved processes (i.e., heterochrony) would be detectible. Methods and Results: Data were extracted from digital photographs taken of representative embryos for each stage of development and each type of molly. Embryo mass decreased in convergent fashion, but we found patterns of embryonic fat content and ovum/embryo diameter to be divergent among all three types of mollies. The intensity of yellow colouration of the yolk (a proxy for carotenoid content) was significantly lower in cave mollies throughout development. Moreover, while relative head size decreased through development in surface mollies, it increased in both types of extremophile mollies, and eye growth was arrested in mid-stage embryos of cave mollies but not in surface or sulphur mollies. Conclusion: Our results clearly demonstrate that even among sister taxa convergence in phenotypic traits is not always achieved by the same processes during embryo development. Furthermore, teleost development is crucially dependent on sufficient carotenoid stores in the yolk, and so we discuss how the apparent ability of cave mollies to overcome this carotenoid-dependency may represent another potential mechanism explaining the lack of gene flow between surface and cave mollies

Bistability and hysteresis of dipolar dynamos generated by turbulent convection in rotating spherical shells

Bistability and hysteresis of magnetohydrodynamic dipolar dynamos generated by turbulent convection in rotating spherical fluid shells is demonstrated. Hysteresis appears as a transition between two distinct regimes of dipolar dynamos with rather different properties including a pronounced difference in the amplitude of the axisymmetric poloidal field component and in the form of the differential rotation. The bistability occurs from the onset of dynamo action up to about 9 times the critical value of the Rayleigh number for onset of convection and over a wide range of values of the ordinary and the magnetic Prandtl numbers including the value unity

The cross helicity at the solar surface by simulations and observations

The quasilinear mean-field theory for driven MHD turbulence leads to the result that the observed cross helicity may directly yield the magnetic eddy diffusivity \eta_{T} of the quiet Sun. In order to model the cross helicity at the solar surface, magnetoconvection under the presence of a vertical large-scale magnetic field is simulated with the nonlinear MHD code NIRVANA. The very robust result of the calculations is that \simeq 2 independent of the applied magnetic field amplitude. The correlation coefficient for the cross helicity is about 10%. Of similar robustness is the finding that the rms value of the magnetic perturbations exceeds the mean-field amplitude (only) by a factor of five. The characteristic helicity speed u_{\eta} as the ratio of the eddy diffusivity and the density scale height for an isothermal sound velocity of 6.6 km/s proves to be 1 km/s for weak fields. This value well coincides with empirical results obtained from the data of the HINODE satellite and the Swedish 1-m Solar Telescope (SST) providing the cross helicity component . Both simulations and observations thus lead to a numerical value of \eta_{T} \simeq 10^12 cm^2 /s as characteristic for the surface of the quiet Sun.Comment: 6 pages, 6 figure

The Causal Link Between Financial Incentives and Weight Loss – An Evidence-based Survey of the Literature

Obesity and overweight are linked to diseases that cost society a significant amount of resources. While behavior modification can reduce the problem, instigating such lifestyle changes is an uneasy task. One potential way to reduce the problem is through the use of financial incentives. In this survey, we review the available evidence with a significant emphasis on studies that yield credible estimates of the effect of financial incentives on weight loss. We find that the scientific literature on the subject has not yet satisfactorily settled whether such a mechanism is effective at eliciting the desired behavioral and health outcomes. We therefore advocate a rigorous large-scale randomized experiment to provide reliable estimates of the effect.Financial incentives; weight loss; obesity; randomized experiment; survey

ZZE-Configuration of chromophore ß-153 in C-phycocyanin from Mastigocladus laminosus

The photochemistry of C-phycocyanin has been studied after denaturation in the dark. It shows an irreversible reaction which has characteristics of a Ζ,Ζ,Ε- to Z,Z,Z-isomerization of dihydrobilins. Its amplitude depends on the reaction conditions, with a maximum corresponding to 15% conversion of one of the three PC chromophores. This chromophore is suggested to be ß-153, for which recent X-ray data T. Schirmer, W. Bode, and R. Huber, J. Mol. Biol., submitted, show ring D being highly twisted out of the plane of the other rings. During unfolding, there is thus a probability of falling into the photochemically labile Z,Z,^-configuration

A Simple Algorithm for Local Conversion of Pure States

We describe an algorithm for converting one bipartite quantum state into another using only local operations and classical communication, which is much simpler than the original algorithm given by Nielsen [Phys. Rev. Lett. 83, 436 (1999)]. Our algorithm uses only a single measurement by one of the parties, followed by local unitary operations which are permutations in the local Schmidt bases.Comment: 5 pages, LaTeX, reference adde