Oxygen-induced p(2x3) reconstruction on Mo(112) studied by LEED and STM

The open trough-and-row Mo(112) surface serves as substrate for the epitaxial growth of MoO2. In the early stage of oxygen exposure, oxygen chemisorption induces a p(2x3) surface reconstruction of the missing row type on Mo(112). The surface structure of this reconstructed surface has been studied in detail by low-energy electron diffraction and scanning tunneling microscope. The experimental findings can be explained based on the effective medium theory for oxygen adsorption on transition-metal surfaces, providing a structure model for the oxygen-modified Mo(112) surface. The structure model allows the discussion of the oxygen-chemisorbed surface phase as a possible precursor state fo

Descendants of the first stars: the distinct chemical signature of second generation stars

Extremely metal-poor (EMP) stars in the Milky Way (MW) allow us to infer the properties of their progenitors by comparing their chemical composition to the metal yields of the first supernovae. This method is most powerful when applied to mono-enriched stars, i.e. stars that formed from gas that was enriched by only one previous supernova. We present a novel diagnostic to identify this subclass of EMP stars. We model the first generations of star formation semi-analytically, based on dark matter halo merger trees that yield MW-like halos at the present day. Radiative and chemical feedback are included self-consistently and we trace all elements up to zinc. Mono-enriched stars account for only $\sim 1\%$ of second generation stars in our fiducial model and we provide an analytical formula for this probability. We also present a novel analytical diagnostic to identify mono-enriched stars, based on the metal yields of the first supernovae. This new diagnostic allows us to derive our main results independently from the specific assumptions made regarding Pop III star formation, and we apply it to a set of observed EMP stars to demonstrate its strengths and limitations. Our results may provide selection criteria for current and future surveys and therefore contribute to a deeper understanding of EMP stars and their progenitors.Comment: 18 pages, 20 figures, published in MNRA

The leukemogenic fusion gene MLL-AF9 alters microRNA expression pattern and inhibits monoblastic differentiation via miR-511 repression

BACKGROUND: In this study we explored the role of microRNAs (miRNAs) as mediators of leukemogenic effects of the fusion gene MLL-AF9, which results from a frequent chromosomal translocation in infant and monoblastic acute myeloid leukemia (AML). METHODS: We performed a specific and efficient knockdown of endogenous MLL-AF9 in the human monoblastic AML cell line THP1. RESULTS: The knockdown associated miRNA expression profile revealed 21 MLL-AF9 dependently expressed miRNAs. Gene ontology analyses of target genes suggested an impact of these miRNAs on downstream gene regulation via targeting of transcriptional modulators as well as involvement in many functions important for leukemia maintenance as e.g. myeloid differentiation, cell cycle and stem cell maintenance. Furthermore, we identified one of the most intensely repressed miRNAs, miR-511, to raise CCL2 expression (a chemokine ligand important for immunosurveillance), directly target cyclin D1, inhibit cell cycle progression, increase cellular migration and promote monoblastic differentiation. With these effects, miR-511 may have a therapeutic potential as a pro-differentiation agent as well as in leukemia vaccination approaches. CONCLUSIONS: Our study provides new insights into the understanding of miRNAs as functional mediators of the leukemogenic fusion gene MLL-AF9 and opens new opportunities to further investigate specific therapeutic options for AML via the miRNA level. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s13046-016-0283-5) contains supplementary material, which is available to authorized users

Bounds on neutrino masses from leptogenesis in type-II see-saw models

The presence of the triplet $\Delta_{L}$ in left-right symmetric theories leads to type-II see-saw mechanism for the neutrino masses. In these models, assuming a normal mass hierarchy for the heavy Majorana neutrinos, we derive a lower bound on the mass of the lightest of heavy Majorana neutrino from the leptogenesis constraint. From this bound we establish a consistent picture for the hierarchy of heavy Majorana neutrinos in a class of left right symmetric models in which we identify the neutrino Dirac mass matrix with that of Fritzsch type charged lepton mass matrix. It is shown that these values are compatible with the current neutrino oscillation data.Comment: minor typos corrected, references added, match with published versio

The chemical composition of globular clusters in the Local Group

We present detailed abundance measurements for 45 globular clusters (GCs) in galaxies in (and, in one case, beyond) the Local Group. The measurements are based on new high-resolution integrated-light spectra of GCs in NGC 185, NGC 205, M31, M33, and NGC 2403, combined with reanalysis of previous observations of GCs in the Fornax dSph, WLM, NGC 147, NGC 6822, and the Milky Way. The GCs cover the range -2.8 < [Fe/H] < -0.1 and we determined abundances for Fe, Na, Mg, Si, Ca, Sc, Ti, Cr, Mn, Ni, Cu, Zn, Zr, Ba, and Eu. Corrections for non local thermodynamic equilibrium effects are included for Na, Mg, Ca, Ti, Mn, Fe, Ni, and Ba. For several of the galaxies, our measurements provide the first quantitative constraints on the detailed composition of their metal-poor stellar populations. Overall, the GCs in different galaxies exhibit remarkably uniform abundance patterns of the alpha-, iron-peak, and neutron-capture elements, with a dispersion of less than 0.1 dex in [alpha/Fe] for the full sample. There is a hint that GCs in dwarf galaxies are slightly less alpha-enhanced (by about 0.04 dex on average) than those in larger galaxies. One GC in M33 (HM33-B) resembles the most metal-rich GCs in the Fornax dSph (Fornax 4) and NGC 6822 (SC7) by having alpha-element abundances closer to scaled-solar values, possibly hinting at an accretion origin. We find that the alpha-element abundances strongly correlate with those of Na, Sc, Ni, and Zn. Several GCs with [Fe/H]<-1.5 are deficient in Mg compared to other alpha-elements. We find no GCs with strongly enhanced r-process abundances as reported for metal-poor stars in some ultra-faint dwarfs and the Magellanic Clouds. The similarity of the abundance patterns for metal-poor GCs in different environments points to similar early enrichment histories and only allow for minor variations in the initial mass function.Comment: 34 pages + 6 appendices. Accepted for publication in Astronomy & Astrophysic

Leptogenesis Bound on Spontaneous Symmetry Breaking of Global Lepton Number

We propose a new class of leptogenesis bounds on the spontaneous symmetry breaking of global lepton number. These models have a generic feature of inducing new lepton number violating interactions, due to the presence of the Majorons. We analyzed the singlet Majoron model with right-handed neutrinos and find that the lepton number should be broken above 10^5 GeV to realize a successful leptogenesis because the annihilations of the right-handed neutrinos into the massless Majorons and into the standard model Higgs should go out of equilibrium before the sphaleron process is over. We then argue that this type of leptogenesis constraint should exist in the singlet-triplet Majoron models as well as in a class of R-parity violating supersymmetric Majoron models.Comment: 4 pages, 2 figure

Population III X-ray Binaries and their Impact on the Early Universe

The first population of X-ray binaries (XRBs) is expected to affect the thermal and ionization states of the gas in the early Universe. Although these X-ray sources are predicted to have important implications for high-redshift observable signals, such as the hydrogen 21-cm signal from cosmic dawn and the cosmic X-ray background, their properties are poorly explored, leaving theoretical models largely uninformed. In this paper we model a population of X-ray binaries arising from zero metallicity stars. We explore how their properties depend on the adopted initial mass function (IMF) of primordial stars, finding a strong effect on their number and X-ray production efficiency. We also present scaling relations between XRBs and their X-ray emission with the local star formation rate, which can be used in sub-grid models in numerical simulations to improve the X-ray feedback prescriptions. Specifically, we find that the uniformity and strength of the X-ray feedback in the intergalactic medium is strongly dependant on the IMF. Bottom-heavy IMFs result in a smoother distribution of XRBs, but have a luminosity orders of magnitude lower than more top-heavy IMFs. Top-heavy IMFs lead to more spatially uneven, albeit strong, X-ray emission. An intermediate IMF has a strong X-ray feedback while sustaining an even emission across the intergalactic medium. These differences in X-ray feedback could be probed in the future with measurements of the cosmic dawn 21-cm line of neutral hydrogen, which offers us a new way of constraining population III IMF.Comment: Accepted for publication in MNRAS, 17 pages, 9 figure