Shaping point- and mirror-symmetric proto-planetary nebulae by the orbital motion of the central binary system

We present 3D hydrodynamical simulations of a jet launched from the secondary star of a binary system inside a proto-planetary nebula. The secondary star moves around the primary in a close eccentric orbit. From the gasdynamic simulations we compute synthetic [NII] 6583 emission maps. Different jet axis inclinations with respect to the orbital plane, as well as different orientations of the flow with respect to the observer are considered. For some parameter combinations, we obtain structures that show point- or mirror-symmetric morphologies depending on the orientation of the flow with respect to the observer. Furthermore, our models can explain some of the emission distribution asymmetries that are summarized in the classification given by Soker & hadar (2002).Comment: 15 pages, 3 figures, 2 tables, Accepted in Apj Letter

The X chromosome and male infertility

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Vacancy patterning and patterning vacancies: controlled self-assembly of fullerenes on metal surfaces

A density functional theory study accounting for van der Waals interactions reveals the potential of metal surface vacancies as anchor points for the construction of user-defined 2D patterns of adsorbate molecules via a controlled self-assembly process. Vice versa, energetic criteria indicate the formation of regular adsorbate-induced vacancies after adsorbate self-assembly on clean surfaces. These processes are exemplified by adsorbing C60 fullerene on Al(111), Au(111), and Be(0001) surfaces with and without single, triple, and septuple atom pits. An analysis of vacancy-adatom formation energetics precedes the study of the adsorption processes

Hypersonic Buckshot: Astrophysical Jets as Heterogeneous Collimated Plasmoids

Herbig-Haro (HH) jets are commonly thought of as homogeneous beams of plasma traveling at hypersonic velocities. Structure within jet beams is often attributed to periodic or ``pulsed'' variations of conditions at the jet source. Simulations based on this scenario result in knots extending across the jet diameter. Observations and recent high energy density laboratory experiments shed new light on structures below this scale and indicate they may be important for understanding the fundamentals of jet dynamics. In this paper we offer an alternative to ``pulsed'' models of protostellar jets. Using direct numerical simulations we explore the possibility that jets are chains of sub-radial clumps propagating through a moving inter-clump medium. Our models explore an idealization of this scenario by injecting small ($r<r_{jet}$), dense ($\rho>\rho_{jet}$) spheres embedded in an otherwise smooth inter-clump jet flow. The spheres are initialized with velocities differing from the jet velocity by $\sim15$%. We find the consequences of shifting from homogeneous to heterogeneous flows are significant as clumps interact with each other and with the inter-clump medium in a variety of ways. Structures which mimic what is expected from pulsed-jet models can form, as can previously unseen ``sub-radial'' behaviors including backward facing bow shocks and off-axis working surfaces. While these small-scale structures have not been seen before in simulation studies, they are found in high resolution jet observations. We discuss implications of our simulations for the interpretation of protostellar jets with regard to characterization of knots by a ``lifetime'' or ``velocity history'' approach as well as linking observed structures with central engines which produce the jets.Comment: 15 pages, 3 figures (1 color), submitted to Ap

The lower mass function of the young open cluster Blanco 1: from 30 Mjup to 3 Mo

We performed a deep wide field optical survey of the young (~100-150 Myr) open cluster Blanco1 to study its low mass population well down into the brown dwarf regime and estimate its mass function over the whole cluster mass range.The survey covers 2.3 square degrees in the I and z-bands down to I ~ z ~ 24 with the CFH12K camera. Considering two different cluster ages (100 and 150 Myr), we selected cluster member candidates on the basis of their location in the (I,I-z) CMD relative to the isochrones, and estimated the contamination by foreground late-type field dwarfs using statistical arguments, infrared photometry and low-resolution optical spectroscopy. We find that our survey should contain about 57% of the cluster members in the 0.03-0.6 Mo mass range, including 30-40 brown dwarfs. The candidate's radial distribution presents evidence that mass segregation has already occured in the cluster. We took it into account to estimate the cluster mass function across the stellar/substellar boundary. We find that, between 0.03Mo and 0.6Mo, the cluster mass distribution does not depend much on its exact age, and is well represented by a single power-law, with an index alpha=0.69 +/- 0.15. Over the whole mass domain, from 0.03Mo to 3Mo, the mass function is better fitted by a log-normal function with m0=0.36 +/- 0.07Mo and sigma=0.58 +/- 0.06. Comparison between the Blanco1 mass function, other young open clusters' MF, and the galactic disc MF suggests that the IMF, from the substellar domain to the higher mass part, does not depend much on initial conditions. We discuss the implications of this result on theories developed to date to explain the origin of the mass distribution.Comment: 18 pages, 15 figures and 5 tables accepted in A&

Congenital short QT syndrome: Landmarks of the newest arrhythmogenic cardiac channelopathy

Congenital or familial short QT syndrome is a genetically heterogeneous cardiac channelopathy without structural heart disease that has a dominant autosomal or sporadic pattern of transmission affecting the electric system of the heart. Patients present clinically with a spectrum of signs and symptoms including irregular palpitations due to episodes of paroxysmal atrialfibrillation, dizziness and fainting (syncope) and/or sudden cardiac death due to polymorphic ventricular tachycardia and ventricular fibrillation. Electrocardiographic (ECG) findings include extremely short QTc intervals (QTc interval ≤ 330 ms) not significantly modified with heart rate changes and T waves of great voltage witha narrow base. Electrophysiologic studies are characterized by significant shortening of atrial and ventricular refractory periods and arrhythmias induced by programmed stimulation. A few families have been identified with specific genotypes: 3 with mutations in potassium channels called SQT1 (Iks), SQT2 (Ikr) and SQT3 (Ik1). These 3 potassium channel variants are the “genetic mirror image” of long QT syndrome type 2, type 1 and Andersen-Tawil syndrome respectively because they exert opposite gain-of-function effects on the potassium channels in contrast to the loss-of-function of the potassium channels in the long QT syndromes. Three new variants with overlapping phenotypes affecting the slow inward calcium channels havealso been described. Finally, another variant with mixed phenotype affecting the sodium channel was reported. This review focuses the landmarks of this newest arrhythmogenic cardiac channelopathy on the main clinical, genetic, and proposed ECG mechanisms. In addition therapeutic options and the molecular autopsy of this fascinating primary electrical heart disease are discussed

Hole pairing and phonon dynamics in generalized 2D t−J−t-J-Holstein models

The formation of hole pairs in the planar t-J model is studied in the presence of independent {\it dynamic} vibrations of the in-plane oxygen atoms. In-plane (breathing modes) and out-of-plane (buckling modes) displacements are considered. We find strong evidences in favor of a stabilization of the two hole bound pair by out-of-plane vibrations of the in-plane oxygens. On the contrary, the breathing modes weaken the binding energy of the hole pair. These results are discussed in the context of the superconducting cuprates.Comment: 4 pages LaTeX and 6 PostScript figures in uuencoded for

Laboratory Experiments, Numerical Simulations, and Astronomical Observations of Deflected Supersonic Jets: Application to HH 110

Collimated supersonic flows in laboratory experiments behave in a similar manner to astrophysical jets provided that radiation, viscosity, and thermal conductivity are unimportant in the laboratory jets, and that the experimental and astrophysical jets share similar dimensionless parameters such as the Mach number and the ratio of the density between the jet and the ambient medium. Laboratory jets can be studied for a variety of initial conditions, arbitrary viewing angles, and different times, attributes especially helpful for interpreting astronomical images where the viewing angle and initial conditions are fixed and the time domain is limited. Experiments are also a powerful way to test numerical fluid codes in a parameter range where the codes must perform well. In this paper we combine images from a series of laboratory experiments of deflected supersonic jets with numerical simulations and new spectral observations of an astrophysical example, the young stellar jet HH 110. The experiments provide key insights into how deflected jets evolve in 3-D, particularly within working surfaces where multiple subsonic shells and filaments form, and along the interface where shocked jet material penetrates into and destroys the obstacle along its path. The experiments also underscore the importance of the viewing angle in determining what an observer will see. The simulations match the experiments so well that we can use the simulated velocity maps to compare the dynamics in the experiment with those implied by the astronomical spectra. The experiments support a model where the observed shock structures in HH 110 form as a result of a pulsed driving source rather than from weak shocks that may arise in the supersonic shear layer between the Mach disk and bow shock of the jet's working surface.Comment: Full resolution figures available at http://sparky.rice.edu/~hartigan/pub.html To appear in Ap

Birth and early evolution of a planetary nebula

The final expulsion of gas by a star as it forms a planetary nebula --- the ionized shell of gas often observed surrounding a young white dwarf --- is one of the most poorly understood stages of stellar evolution. Such nebulae form extremely rapidly (about 100 years for the ionization) and so the formation process is inherently difficult to observe. Particularly puzzling is how a spherical star can produce a highly asymmetric nebula with collimated outflows. Here we report optical observations of the Stingray Nebula which has become an ionized planetary nebula within the past few decades. We find that the collimated outflows are already evident, and we have identified the nebular structure that focuses the outflows. We have also found a companion star, reinforcing previous suspicions that binary companions play an important role in shaping planetary nebulae and changing the direction of successive outflows.Comment: 9 pages + 3 figures. To appear in Nature, 2 April 199

Double exchange magnets: Spin-dynamics in the paramagnetic phase

The electronic structure of perovskite manganese oxides is investigated in terms of a Kondo lattice model with ferromagnetic Hund coupling and antiferromagnetic exchange between $t_{2g}$-spins using a finite temperature diagonalization technique. Results for the dynamic structure factor are consistent with recent neutron scattering experiments for the bilayer manganite La$_{1.2}$Sr$_{1.8}$Mn$_2$O$_7$ . The susceptibility shows Curie-Weiss behaviour and is used to derive a phase diagram. In the paramagnetic phase carriers are characterized as ferromagnetic polarons in an antiferromagnetic spin liquid.Comment: Revtex, 4 pages with 5 postscript figures include