Neutron-induced 2.2 MeV background in gamma ray telescopes

Neutron-induced gamma ray production is an important source of background in Compton scatter gamma ray telescopes where organic scintillator material is used. Most important is deuteron formation when atmospheric albedo and locally produced neutrons are thermalized and subsequently absorbed in the hydrogenous material. The resulting 2.2 MeV gamma ray line radiation essentially represents a continuous isotropic source within the scintillator itself. Interestingly, using a scintillator material with a high hydrogen-to-carbon ratio to minimize the scintillator material with a high hydrogen-to-carbon ratio to minimize the neutron-induced 4.4 MeV carbon line favors the np reaction. The full problem of neutron-induced background in Compton scatter telescopes has been previously discussed. Results are presented of observations with the University of California balloon-borne Compton scatter telescope where the 2.2 MeV induced line emission is prominently seen

The late Roman harbor temple of Berenike. Results of the 2010 season of excavations

Excavations in 2010 in the southwestern harbor at Berenike documented two distinct structures. One built of white gypsum/anhydrite ashlars was the earlier of the two. The later one, with walls composed mainly of extinct coral heads, but incorporating portions of the earlier ashlar structure, lay immediately southeast of the former. The later edifice, and the focus of this article, dated to the 4th and 5th centuries AD and clearly had a religious function. Excavations documented two major phases of this shrine and suggested that multiple creeds were venerated here, including one perhaps of South Arabian origin. Along with numerous cult objects made of metal, stone, terracotta, ostrich eggs and cowry shells there was ample floral and faunal evidence for offerings made or consumed by devotees.Iwona Zyc

Respuesta ecofisiológica de poblaciones de <i>Sorghum halepense</i> ante dosis reducidas de nicosulfurón

Las malezas constituyen una de las principales limitaciones en los sistemas de producción a escala mundial. Prueba de ello es la gran cantidad de herbicidas utilizados actualmente para mantener a las malezas en niveles que permitan la productividad de los cultivos. Los esfuerzos en reducir el uso de herbicidas, tanto por razones económicas como ambientales (Buhler, 1999), han introducido a la práctica el manejo integrado de malezas, como es el uso de dosis reducidas de herbicidas (Buhler et al., 1993; Prostko y Meade, 1993). Además las malezas presentan la capacidad de adaptarse rápidamente a los cambios ambientales y producir diferentes fenotipos. Dicha capacidad se denomina plasticidad fenotípica (Schmalhausen, 1949). Entre las malezas consideradas más perjudiciales del mundo para la agricultura se encuentra Sorghum halepense (sorgo de Alepo) (Holm et al., 1977 McWhorter, 1989), tiene importancia en 30 cultivos diferentes y en 53 países (Holm et al., 1977). La interferencia de Sorghum halepense con los cultivos se presenta tanto por la competencia por recursos limitantes (agua, luz y nutrientes), como por la incidencia alelopática hacia los cultivos. Son pocas las investigaciones realizadas sobre el uso de dosis reducidas de herbicidas para el control de Sorghum halepense, además, pocos trabajos han puesto su interés sobre la respuesta ecofisiológica (tasa fotosintética, conductancia estomática al vapor de agua, tasa transpiratoria y biomasa total) y el comportamiento del rebrote (biomasa aérea) de poblaciones de Sorghum halepense, cuando son tratadas con dosis reducidas de herbicidas. Teniendo en cuenta lo establecido, el objetivo primario de este estudio es evaluar la respuesta ecofisiológica de siete poblaciones de Sorghum halepense, de diferentes localidades argentinas, frente a dosis reducidas de nicosulfurón tratando de determinar si se modifica el rebrote de las mismas luego del tratamiento con nicosulfurón. Las poblaciones de regiones subhúmedas presentarían una mayor capacidad de rebrotar.Facultad de Ciencias Agrarias y Forestale

Inhomogeneity of donor doping in SrTiO3 substrates studied by fluorescence-lifetime imaging microscopy

Fluorescence-lifetime imaging microscopy (FLIM) was applied to investigate the donor distribution in SrTiO3 single crystals. On the surfaces of Nb- and La-doped SrTiO3, structures with different fluorescence intensities and lifetimes were found that could be related to different concentrations of Ti3+. Furthermore, the inhomogeneous distribution of donors caused a non-uniform conductivity of the surface, which complicates the production of potential electronic devices by the deposition of oxide thin films on top of doped single crystals. Hence, we propose FLIM as a convenient technique (length scale: 1 $\mu$m) for characterizing the quality of doped oxide surfaces, which could help to identify appropriate substrate materials

The “Square Feature” in the harbor: Excavations in Berenike 2010–2011

The Berenike Project team explored, as one of a number of objectives, a square feature situated on an island or promontory in the southwestern harbor bay of the Berenike port, directly to the northwest of the “Lotus Temple”. The report is a preliminary assessment of the results of excavations carried out in 2010 and 2011, which uncovered the inside of the structure as well as a continuous surface of melted gypsum anhydrite around it that was proved to be at least in part a tumble of large wall ashlars. A provisional dating of the remains suggests an early Roman origin for the structure, which may have been a sanctuary. The findings indicate that it was already abandoned in the 4th–5th centuries when the neighboring “Lotus Temple”, uncovered concurrently by the Polish–American team, was at its peak. Finds included an inscribed altar dedicated to Domitian(?), discovered among the tumble of a stone basin and unidentified installation, and some remains of bronze statuary, oil lamps, glass beads and other finds.Iwona Zyc

Testing the Universality of the Stellar IMF with Chandra and HST

The stellar initial mass function (IMF), which is often assumed to be universal across unresolved stellar populations, has recently been suggested to be "bottom-heavy" for massive ellipticals. In these galaxies, the prevalence of gravity-sensitive absorption lines (e.g. Na I and Ca II) in their near-IR spectra implies an excess of low-mass ($m <= 0.5$ $M_\odot$) stars over that expected from a canonical IMF observed in low-mass ellipticals. A direct extrapolation of such a bottom-heavy IMF to high stellar masses ($m >= 8$ $M_\odot$) would lead to a corresponding deficit of neutron stars and black holes, and therefore of low-mass X-ray binaries (LMXBs), per unit near-IR luminosity in these galaxies. Peacock et al. (2014) searched for evidence of this trend and found that the observed number of LMXBs per unit $K$-band luminosity ($N/L_K$) was nearly constant. We extend this work using new and archival Chandra X-ray Observatory (Chandra) and Hubble Space Telescope (HST) observations of seven low-mass ellipticals where $N/L_K$ is expected to be the largest and compare these data with a variety of IMF models to test which are consistent with the observed $N/L_K$. We reproduce the result of Peacock et al. (2014), strengthening the constraint that the slope of the IMF at $m >= 8$ $M_\odot$ must be consistent with a Kroupa-like IMF. We construct an IMF model that is a linear combination of a Milky Way-like IMF and a broken power-law IMF, with a steep slope ($\alpha_1=$ $3.84$) for stars < 0.5 $M_\odot$ (as suggested by near-IR indices), and that flattens out ($\alpha_2=$ $2.14$) for stars > 0.5 $M_\odot$, and discuss its wider ramifications and limitations.Comment: Accepted for publication in ApJ; 7 pages, 2 figures, 1 tabl

Evidence for Elevated X-ray Emission in Local Lyman Break Galaxy Analogs

In this paper, we study the relationship between the 2-10 keV X-ray luminosity (L_X), assumed to originate from X-ray binaries (XRBs), and star formation rate (SFR) in UV-selected z<0.1 Lyman break analogs (LBAs). We present Chandra observations for four new GALEX-selected LBAs. Including previously studied LBAs, Haro 11 and VV 114, we find that LBAs demonstrate L_X/SFR ratios that are elevated by ~1.5sigma compared to local galaxies, similar to the ratios found for stacked LBGs in the early Universe (z>2). We show that these LBAs are unlikely to harbor AGN, based on their optical and X-ray spectra and the spatial distribution of the X-rays in three spatially extended cases. We expect that high-mass X-ray binaries (HMXBs) dominate the X-ray emission in these galaxies, based on their high specific SFRs (sSFRs=SFR/M* > 10^{-9}/yr), which suggest the prevalence of young stellar populations. Since both LBAs and LBGs have lower dust attenuations and metallicities compared to similar samples of more typical local galaxies, we investigate the effects of dust extinction and metallicity on the L_X/SFR for the broader population of galaxies with high sSFRs (>10^{-10}/yr). The estimated dust extinctions (corresponding to column densities of N_H<10^{22}/cm^2) are expected to have insignificant effects on observed L_X/SFR ratio for the majority of galaxy samples. We find that the observed relationship between L_X/SFR and metallicity appears consistent with theoretical expectations from X-ray binary population synthesis models. Therefore, we conclude that lower metallicities, related to more luminous HMXBs such as ultraluminous X-ray sources (ULXs), drive the elevated L_X/SFR observed in our sample of z<0.1 LBAs. The relatively metal-poor, active mode of star formation in LBAs and distant z>2 LBGs may yield higher total HMXB luminosity than found in typical galaxies in the local Universe.Comment: 11 pages, 7 figures, Submitted to ApJ (references updated in v2