Functional characterization of the diatom cyclin-dependent kinase A2 as a mitotic regulator reveals plant-like properties in a non-green lineage

Background: Cyclin-dependent kinases (CDKs) are crucial regulators of cell cycle progression in eukaryotes. The diatom CDKA2 was originally assigned to the classical A-type CDKs, but its cell cycle phase-specific transcription at the G2-to-M phase transition is typical for plant-specific B-type CDKs. Results: Here, we report the functional characterization of CDKA2 from the diatom Phaeodactylum tricornutum. Through a yeast two-hybrid library screen, CDKA2 was found to interact with the G2/M-specific CDK scaffolding factor CKS1. Localization of CDKA2 was found to be nuclear in interphase cells, while in cells undergoing cytokinesis, the signal extended to the cell division plane. In addition, overexpression of CDKA2 induced an overall reduction in the cell growth rate. Expression analysis of cell cycle marker genes in the overexpression lines indicates that this growth reduction is primarily due to a prolongation of the mitotic phase. Conclusions: Our study indicates a role for CDKA2 during cell division in diatoms. The functional characterization of a CDK with clear CDKB properties in a non-green organism questions whether the current definition of B-type CDKs being plant-specific might need revision

Charmed and Bottom Baryons: a Variational Approach based on Heavy Quark Symmetry

The use of Heavy Quark Symmetry to study bottom and charmed baryons leads to important simplifications of the non-relativistic three body problem, which turns out to be easily solved by a simple variational ansatz. Our simple scheme reproduces previous results (baryon masses, charge and mass radii, $...$) obtained by solving the Faddeev equations with simple non-relativistic quark--quark potentials, adjusted to the light and heavy--light meson spectra. Wave functions, parameterized in a simple manner, are also given and thus they can be easily used to compute further observables. Our method has been also used to find the predictions for strangeness-less baryons of the SU(2) chirally inspired quark-quark interactions. We find that the one pion exchange term of the chirally inspired interactions leads to relative changes of the $\Lambda_b$ and $\Lambda_c$ binding energies as large as 90%.Comment: 20 pages, 5 figures. Revised version to be published in Nucl. Phys.

Ginsparg-Wilson Pions Scattering in a Sea of Staggered Quarks

We calculate isospin 2 pion-pion scattering in chiral perturbation theory for a partially quenched, mixed action theory with Ginsparg-Wilson valence quarks and staggered sea quarks. We point out that for some scattering channels, the power-law volume dependence of two pion states in nonunitary theories such as partially quenched or mixed action QCD is identical to that of QCD. Thus one can extract infinite volume scattering parameters from mixed action simulations. We then determine the scattering length for both 2 and 2+1 sea quarks in the isospin limit. The scattering length, when expressed in terms of the pion mass and the decay constant measured on the lattice, has no contributions from mixed valence-sea mesons, thus it does not depend upon the parameter, C_Mix, that appears in the chiral Lagrangian of the mixed theory. In addition, the contributions which nominally arise from operators appearing in the mixed action O(a^2 m_q) Lagrangian exactly cancel when the scattering length is written in this form. This is in contrast to the scattering length expressed in terms of the bare parameters of the chiral Lagrangian, which explicitly exhibits all the sicknesses and lattice spacing dependence allowed by a partially quenched mixed action theory. These results hold for both 2 and 2+1 flavors of sea quarks.Comment: 27 pages, 3 figures. Mistakes corrected in Eqs. (37), (42). Improved discussion in section 4 and related results in Eqs. (33), (37), (40) and (42). Added references. Version to be published in PR

Youth beyond borders: Methodological challenges in youth information interaction

The pace of technological change is rapid and the impact of this acceleration on the information behavior of youth from diverse backgrounds is multifaceted. Most young people have online access in some form, but the uses and quality of access vary tremendously (Madden, Lenhart, Duggan, Cortesi & Gasser, 2013). With the growth and variation of information behaviors among youth in social media and the mobile Web, keeping pace with research methods used to capture these behaviors and phenomena continues to be a discussion among scholars. Adding to the complications of research in this area, youth are increasingly using information and communications technologies (ICT) across platforms for a variety of information behaviors, including academic and social reasons (Agosto & Abbas, 2010). It is often not enough to solely examine a young person's Twitter feed-we need to see how that conversation carries from Twitter, to direct messages, to texting, to a Facebook post and so on. This variation suggests a need for greater nuance in research (Madden, Lenhart, Duggan, Cortesi & Gasser, 2013; Gasser, Cortesi, Malik & Lee, 2012). This panel will bring together several researchers experienced in studying youth information practices to discuss their methodologies and strategies in dealing with these intricate issues. This panel will be conducted in a roundtable style-encouraging deep conversation between the researchers and the audience. This will be followed by a small group discussions with the audience and conclude by sharing back best practices uncovered through the group discussions. Through attending this panel, attendees will engage with current developments in diverse youth, ICT and research methodologies, and identify priorities and approaches for future work in these areas

Low-lying spectrum of the Y-string three-quark potential using hyper-spherical coordinates

We calculate the energies of three-quark states with definite permutation symmetry (i.e. of SU(6) multiplets) in the N=0,1,2 shells, confined by the Y-string three-quark potential. The exact Y-string potential consists of one, so-called three-string term, and three angle-dependent two-string terms. Due to this technical complication we treat the problem at three increasingly accurate levels of approximation: 1) the (approximate) three-string potential expanded to first order in trigonometric functions of hyper-spherical angles; 2) the (approximate) three-string potential to all orders in the power expansion in hyper-spherical harmonics, but without taking into account the transition(s) to two-string potentials; 3) the exact minimal-length string potential to all orders in power expansion in hyper-spherical harmonics, and taking into account the transition(s) to two-string potentials. We show the general trend of improvement %convergence of these approximations: The exact non-perturbative corrections to the total energy are of the order of one per cent, as compared with approximation 2), yet the exact energy differences between the $[20,1^{+}], [70,2^{+}], [56,2^{+}], [70,0^{+}]$-plets are shifted to 2:2:0.9, from the Bowler and Tynemouth separation rule 2:2:1, which is obeyed by approximation 2) at the one per cent level. The precise value of the energy separation of the first radial excitation ("Roper") $[56^{\prime},0^{+}]$-plet from the $[70,1^{-}]$-plet depends on the approximation, but does not become negative, i.e. the "Roper" remains heavier than the odd-parity $[70,1^{-}]$-plet in all of our approximations.Comment: 19 pages, 6 figure

Structure and Magnetic Fields in the Precessing Jet System SS 433 II. Intrinsic Brightness of the Jets

Deep Very Large Array imaging of the binary X-ray source SS 433, sometimes classified as a microquasar, has been used to study the intrinsic brightness distribution and evolution of its radio jets. The intrinsic brightness of the jets as a function of age at emission of the jet material tau is recovered by removal of the Doppler boosting and projection effects. We find that intrinsically the two jets are remarkably similar when compared for equal tau, and that they are best described by Doppler boosting of the form D^{2+alpha}, as expected for continuous jets. The intrinsic brightnesses of the jets as functions of age behave in complex ways. In the age range 60 < tau < 150 days, the jet decays are best represented by exponential functions of tau, but linear or power law functions are not statistically excluded. This is followed by a region out to tau ~ 250 days during which the intrinsic brightness is essentially constant. At later times the jet decay can be fit roughly as exponential or power law functions of tau.Comment: 30 Pages, 11 Figures, Submitted to Ap

Lattice 2001: Reflections

A few subjects which strongly intertwine our field are discussed: K --> Pi Pi decay, chiral symmetry on the lattice and a few other selected topics. Open questions are touched also on perturbation theory, locality, Gribov copies, CP symmetry in chiral gauge theories and cut-off effects.Comment: 12 pages, Lattice 2001 (plenary), corrected typos in reference

Isgur--Wise function in a relativistic model of constituent quarks

The integral representation for Isgur -- Wise function (IWF) is obtained in the framework of instant--form relativistic Hamiltonian dynamics for mesons with one heavy quark. The upper and lower limits are calculated for the slope parameter of IWF $\rho^2$ by the model independent way. IWF is calculated for different wave functions of quarks in the meson. The difference between the limits of $\rho^2$ equals 1/3. The constraint on the slope parameter is in a good agreement with experiments. The weak dependence of IWF on the choice of wave functions is found.Comment: 10 pages, latex, 1 figure as eps-fil

A Disk Around the Planetary-Mass Companion GSC 06214-00210 b: Clues About the Formation of Gas Giants on Wide Orbits

We present Keck/OSIRIS 1.1-1.8 um adaptive optics integral field spectroscopy of the planetary-mass companion to GSC 06214-00210, a member of the ~5 Myr Upper Scorpius OB association. We infer a spectral type of L0+/-1, and our spectrum exhibits multiple signs of youth. The most notable feature is exceptionally strong PaBeta emission (EW=-11.4 +/- 0.3 A) which signals the presence of a circumplanetary accretion disk. The luminosity of GSC 06214-00210 b combined with its age yields a model-dependent mass of 14 +/- 2 MJup, making it the lowest-mass companion to show evidence of a disk. With a projected separation of 320 AU, the formation of GSC 06214-00210 b and other very low-mass companions on similarly wide orbits is unclear. One proposed mechanism is formation at close separations followed by planet-planet scattering to much larger orbits. Since that scenario involves a close encounter with another massive body, which is probably destructive to circumplanetary disks, it is unlikely that GSC 06214-00210 b underwent a scattering event in the past. This implies that planet-planet scattering is not solely responsible for the population of gas giants on wide orbits. More generally, the identification of disks around young planetary companions on wide orbits offers a novel method to constrain the formation pathway of these objects, which is otherwise notoriously difficult to do for individual systems. We also refine the spectral type of the primary from M1 to K7 and detect a mild (2-sigma) excess at 22 um using WISE photometry.Comment: 25 pages, 13 figures; Accepted by Ap