Nickel: A micronutrient element for hydrogen-dependent growth of \u3ci\u3eRhizobium japonicum\u3c/i\u3e and for expression of urease activity in soybean leaves

Soybean plants and Rhizobium japonicum 122 DES, a hydrogen uptake-positive strain, were cultured in media purified to remove Ni. Supplemental Ni had no significant effect on the dry matter or total N content of plants. However, the addition of Ni to both nitrate-grown and symbiotically grown plants resulted in a 7- to 10-fold increase in urease activity (urea amidohydrolase, EC 3.5.1.5) in leaves and significantly increased the hydrogenase activity (EC 1.18.3.1) in isolated nodule bacteroids. When cultured under chemolithotrophic conditions, free-living R. japonicum required Ni for growth and for the expression of hydrogenase activity. Hydrogenase activity was minimal or not detectable in cells incubated either without Ni or with Ni and chloramphenicol. Ni is required for derepression of hydrogenase activity and apparently protein synthesis is necessary for the participation of Ni in hydrogenase expression. The addition of Cr, V, Sn, and Pb in place of Ni failed to stimulate the activity of hydrogenase in R. japonicum and urease in soybean leaves. The evidence indicates that Ni is an important micronutrient element in the biology of the soybean plant and R. japonicum

Near-Earth asteroid (3200) Phaethon. Characterization of its orbit, spin state, and thermophysical parameters

The near-Earth asteroid (3200) Phaethon is an intriguing object: its perihelion is at only 0.14 au and is associated with the Geminid meteor stream. We aim to use all available disk-integrated optical data to derive a reliable convex shape model of Phaethon. By interpreting the available space- and ground-based thermal infrared data and Spitzer spectra using a thermophysical model, we also aim to further constrain its size, thermal inertia, and visible geometric albedo. We applied the convex inversion method to the new optical data obtained by six instruments and to previous observations. The convex shape model was then used as input for the thermophysical modeling. We also studied the long-term stability of Phaethon's orbit and spin axis with a numerical orbital and rotation-state integrator. We present a new convex shape model and rotational state of Phaethon: a sidereal rotation period of 3.603958(2) h and ecliptic coordinates of the preferred pole orientation of (319$^{\circ}$, $-$39$^{\circ}$) with a 5$^{\circ}$ uncertainty. Moreover, we derive its size ($D$=5.1$\pm$0.2 km), thermal inertia ($\Gamma$=600$\pm$200 J m$^{-2}$ s$^{-1/2}$ K$^{-1}$), geometric visible albedo ($p_{\mathrm{V}}$=0.122$\pm$0.008), and estimate the macroscopic surface roughness. We also find that the Sun illumination at the perihelion passage during the past several thousand years is not connected to a specific area on the surface, which implies non-preferential heating.Comment: Astronomy and Astrophysics. In pres

YORP and Yarkovsky effects in asteroids (1685) Toro, (2100) Ra-Shalom, (3103) Eger, and (161989) Cacus

The rotation states of small asteroids are affected by a net torque arising from an anisotropic sunlight reflection and thermal radiation from the asteroids' surfaces. On long timescales, this so-called YORP effect can change asteroid spin directions and their rotation periods. We analyzed lightcurves of four selected near-Earth asteroids with the aim of detecting secular changes in their rotation rates that are caused by YORP. We use the lightcurve inversion method to model the observed lightcurves and include the change in the rotation rate $\mathrm{d} \omega / \mathrm{d} t$ as a free parameter of optimization. We collected more than 70 new lightcurves. For asteroids Toro and Cacus, we used thermal infrared data from the WISE spacecraft and estimated their size and thermal inertia. We also used the currently available optical and radar astrometry of Toro, Ra-Shalom, and Cacus to infer the Yarkovsky effect. We detected a YORP acceleration of $\mathrm{d}\omega / \mathrm{d} t = (1.9 \pm 0.3) \times 10^{-8}\,\mathrm{rad}\,\mathrm{d}^{-2}$ for asteroid Cacus. For Toro, we have a tentative ($2\sigma$) detection of YORP from a significant improvement of the lightcurve fit for a nonzero value of $\mathrm{d}\omega / \mathrm{d} t = 3.0 \times 10^{-9}\,\mathrm{rad}\,\mathrm{d}^{-2}$. For asteroid Eger, we confirmed the previously published YORP detection with more data and updated the YORP value to $(1.1 \pm 0.5) \times 10^{-8}\,\mathrm{rad}\,\mathrm{d}^{-2}$. We also updated the shape model of asteroid Ra-Shalom and put an upper limit for the change of the rotation rate to $|\mathrm{d}\omega / \mathrm{d} t| \lesssim 1.5 \times 10^{-8}\,\mathrm{rad}\,\mathrm{d}^{-2}$. Ra-Shalom has a greater than $3\sigma$ Yarkovsky detection with a theoretical value consistent with observations assuming its size and/or density is slightly larger than the nominally expected values

Enhanced ionization of acetylene in intense laser pulses is due to energy upshift and field coupling of multiple orbitals

Synopsis We describe a new enhanced ionization mechanism for polyatomic molecules. It works via a significant energy up-shift of valence orbitals for stretched bonds and a strong concomitant increase in the coupling between multiple molecular orbitals

Numerical study on the flexural behaviour of slim-floor beams with hollow core slabs at elevated temperature

[EN] Slim-floor beams are a novel typology of steel beams where the steel profile is fully embedded within the concrete floor depth. While the use of this system is increasing fast in the construction practice, the available investigations on its fire performance are still scarce. This paper focuses on analysing the fire behaviour of slim floor beams combined with hollow core slabs as flooring system. Two configurations are studied, namely Integrated Floor Beam (IFB) and Shallow Floor Beam (SFB). A finite element model is developed and validated by comparison with experimental results available in the literature as well as with thermal tests carried out by the authors. Subsequently, parametric studies are conducted with the aim of providing practical design recommendations. The influence of the composite beam configuration, concrete type, longitudinal reinforcement and steel plate thickness is studied. The conclusions drawn in this paper suggest that the SFB configuration may provide a significant enhancement in terms of fire resistance compared to IFB, provided that the appropriate combination of the parameters studied is used.The authors would like to express their sincere gratitude to the Spanish "Ministerio de Economia y Competitividad" for the help provided through the Project BIA2015-67192-R and to the European Union through the FEDER funds.Albero Gabarda, V.; Espinós Capilla, A.; Serra Mercé, E.; Romero, ML.; Hospitaler Pérez, A. (2019). Numerical study on the flexural behaviour of slim-floor beams with hollow core slabs at elevated temperature. Engineering Structures. 180:561-573. https://doi.org/10.1016/j.engstruct.2018.11.061S56157318

Microscopic observation of magnon bound states and their dynamics

More than eighty years ago, H. Bethe pointed out the existence of bound states of elementary spin waves in one-dimensional quantum magnets. To date, identifying signatures of such magnon bound states has remained a subject of intense theoretical research while their detection has proved challenging for experiments. Ultracold atoms offer an ideal setting to reveal such bound states by tracking the spin dynamics after a local quantum quench with single-spin and single-site resolution. Here we report on the direct observation of two-magnon bound states using in-situ correlation measurements in a one-dimensional Heisenberg spin chain realized with ultracold bosonic atoms in an optical lattice. We observe the quantum walk of free and bound magnon states through time-resolved measurements of the two spin impurities. The increased effective mass of the compound magnon state results in slower spin dynamics as compared to single magnon excitations. In our measurements, we also determine the decay time of bound magnons, which is most likely limited by scattering on thermal fluctuations in the system. Our results open a new pathway for studying fundamental properties of quantum magnets and, more generally, properties of interacting impurities in quantum many-body systems.Comment: 8 pages, 7 figure

The non-convex shape of (234) Barbara, the first Barbarian

Asteroid (234) Barbara is the prototype of a category of asteroids that has been shown to be extremely rich in refractory inclusions, the oldest material ever found in the Solar System. It exhibits several peculiar features, most notably its polarimetric behavior. In recent years other objects sharing the same property (collectively known as "Barbarians") have been discovered. Interferometric observations in the mid-infrared with the ESO VLTI suggested that (234) Barbara might have a bi-lobated shape or even a large companion satellite. We use a large set of 57 optical lightcurves acquired between 1979 and 2014, together with the timings of two stellar occultations in 2009, to determine the rotation period, spin-vector coordinates, and 3-D shape of (234) Barbara, using two different shape reconstruction algorithms. By using the lightcurves combined to the results obtained from stellar occultations, we are able to show that the shape of (234) Barbara exhibits large concave areas. Possible links of the shape to the polarimetric properties and the object evolution are discussed. We also show that VLTI data can be modeled without the presence of a satellite.Comment: 10 pages, 6 figure

Homeomorphic Embedding for Online Termination of Symbolic Methods

Well-quasi orders in general, and homeomorphic embedding in particular, have gained popularity to ensure the termination of techniques for program analysis, specialisation, transformation, and verification. In this paper we survey and discuss this use of homeomorphic embedding and clarify the advantages of such an approach over one using well-founded orders. We also discuss various extensions of the homeomorphic embedding relation. We conclude with a study of homeomorphic embedding in the context of metaprogramming, presenting some new (positive and negative) results and open problems