On localizations of quasi-simple groups with given countable center

A group homomorphism $i: H \to G$ is a localization of $H$ if for every homomorphism $\varphi: H\rightarrow G$ there exists a unique endomorphism $\psi: G\rightarrow G$, such that $i \psi=\varphi$ (maps are acting on the right). G\"{o}bel and Trlifaj asked in \cite[Problem 30.4(4), p. 831]{GT12} which abelian groups are centers of localizations of simple groups. Approaching this question we show that every countable abelian group is indeed the center of some localization of a quasi-simple group, i.e. a central extension of a simple group. The proof uses Obraztsov and Ol'shanskii's construction of infinite simple groups with a special subgroup lattice and also extensions of results on localizations of finite simple groups by the second author and Scherer, Th\'{e}venaz and Viruel.Comment: 21 page

Generators and closed classes of groups

We show that in the category of groups, every singly-generated class which is closed under isomorphisms, direct limits and extensions is also singly-generated under isomorphisms and direct limits, and in particular is co-reflective. We also establish several new relations between singly-generated closed classes.Comment: 22 page

PATTERNS OF OCCURRENCE AND ABUNDANCE IN COLONY COMPLEXES OF THE MEXICAN PRAIRIE DOG (CYNOMYS MEXICANUS) IN PRODUCTIVE AND UNPRODUCTIVE GRASSLANDS

The Mexican prairie dog lives in a small (500-600 km2) area of northeastern Mexico. The species is listed as endangered due to habitat fragmentation from recent large-scale agricultural development in the northern part of its limited geographical range and from shrub encroachment in the south. In this work we aim to study the role of Mexican prairie dog in the ecology of grasslands in the southern Chihuahuan Desert. Most of the species’ colonies, particularly in the far south of its range, occur today in short grasslands that grow on low productivity, gypsum-derived soils where the rate of such shrub encroachment is reduced. A survey of the region surrounding these southern colonies indicated that this has not always been the case as evidence of the species’ occurrence on more productive alluvial soils in the past is apparent. Biomass production and seasonal prairie dog densities were measured on these low productivity soils in the south of its range and on richer and deeper alluvial soils to the north. Total biomass production was seven times greater and densities were three-and-one-half times greater on the deeper alluvial soils. Adult seasonal densities were not significantly different within a soil type during the period monitored while juvenile densities increased significantly in the summer censuses due to the birth of young. The similar seasonal densities at each site suggest that the Mexican prairie dog is resource limited. An inferential study of the development of one isolated colony on the more productive alluvial soils in the north of the species’ range showed lower prairie dog densities in the center of the colony and at the edge of the colony in the zone of recent expansion than in the area peripheral to the center. Vegetation coverage was too scarce in the center of the colony to quantify. The areas peripheral to the center and in the zone of expansion were reduced in coverage of grasses and sedges in comparison to the unutilized surrounding grassland while the palatable grass, Bouteloua gracilis, was absent in the center and periphery of the colony and increased significantly in coverage from the zone of expansion to the adjoining grassland.Such low productivity grasslands may have served as refuges for the species during previous episodes of shrub encroachment in the Holocene. In addition, the natural fragmentation of such grasslands suggested that the Mexican prairie dog might function as a metapopulation. Colonizations and extinctions were recorded at monitored areas on each soil type. The major difference between the two complexes was due to the greater productivity of the alluvial soils in the north. Consequently, three times as many young per hectare are produced on these soils, greatly increasing the probability of the species maintaining an extant colony or successfully founding new colonies there. The probability of extinction of the Mexican prairie dog is higher in the south of its range due to these lower densities and conservation of the species there should involve the systematic transplantation of individuals from colonies on the richer alluvial soils to the north.El perro llanero mexicano (Cynomys mexicanus) vive en una pequeña área (500-600 km2) del noreste de México. La especie está considerada en peligro de extinción debido principalmente a la fragmentación del hábitat, al reciente desarrollo y expansión agrícola en la porción norte de su limitada distribución geográfica y a la invasión de arbustos en el sur de su área de distribución. En este trabajo estudiamos el papel ecológico del perro llanero mexicano en la ecología de los pastizales en el sur del desierto Chihuahuense. Muchas colonias de esta especie, particularmente en la parte más sur de su área de distribución, están actualmente asentadas en pastizales cortos que se desarrollan en suelos de productividad baja derivados de yeso, donde la tasa de invasión de los arbustos es reducida. Un estudio de la región de los alrededores de las colonias sureñas indicó que esto no siempre ha sido el caso y hay evidencias de que en el pasado estuvo presente en los suelos aluviales profundos más productivos. Se evaluaron la producción de biomasa y las densidades estacionales de la especie en suelos baja productividad del sur de su área de distribución actual y sobre suelos aluviales ricos y profundos en la parte norte. En los suelos aluviales profundos la producción de biomasa total fue siete veces mayor y las densidades de los perros llaneros fueron tres veces y media más grandes. Las densidades estacionales de adultos no fueron significativamente diferentes por tipo de suelo durante el período del monitoreo, en cambio las densidades de juveniles aumentaron significativamente en los censos de verano debido al nacimiento de las crías. La similitud en densidades estacionales por sitio sugiere que la especie está limitada por alimento. Un estudio inferencial del desarrollo de una colonia aislada sobre los suelos aluviales más productivos en el norte del área de distribución de la especie, mostró densidades bajas en el centro y en el borde de la colonia de reciente expansión, en comparación con la zona periférica al centro. La cobertura vegetal también fue escasa en el centro de esa colonia. Las áreas periféricas al centro y la zona de expansión de la colonia mostraron menor cobertura de pastos y juncias en comparación con el pastizal aledaño no utilizado por la colonia, mientras que la especie de pasto Bouteloua gracilis estuvo ausente en el centro y periferia de la colonia, y aumentó significativamente en cobertura desde la zona de expansión de la colonia hacia el pastizal que la circunda.Los pastizales de productividad baja pudieron haber funcionado como refugios para el perro llanero durante episodios previos de invasión de arbustos en el Holoceno. La fragmentación natural de esos pastizales, sugiere que el perro llanero mexicano puede estar funcionando como una metapoblación. Se registraron colonizaciones y extinciones en áreas monitoreadas en cada tipo de suelo. La diferencia principal entre los dos complejos se debió a la productividad mayor de los suelos aluviales de la porción norte. En consecuencia, se producen tres veces mas juveniles por hectárea en esos suelos, lo que aumenta mucho la probabilidad de que la especie mantenga una colonia establecida o de fundar con éxito nuevas colonias en esos suelos. La probabilidad de extinción del perro llanero mexicano es mas alta en el sur de su área de distribución debido a estas densidades mas bajas y su conservación ahí deberá de incluir el trasplante sistemático de individuos desde las colonias de los suelos aluviales productivos de la parte norte

Prediction of a novel monoclinic carbon allotrope

A novel allotrope of carbon with $P2/m$ symmetry was identified during an \emph{ab-initio} minima-hopping structural search which we call $M10$-carbon. This structure is predicted to be more stable than graphite at pressures above 14.4 GPa and consists purely of $sp^3$ bonds. It has a high bulk modulus and is almost as hard as diamond. A comparison of the simulated X-ray diffraction pattern shows a good agreement with experimental results from cold compressed graphite.Comment: 3 pages, 3 figure

Combined use of the GGSFT data base and on Board Marine Collected Data to Model the Moho Beneath the Powell Basin, Antarctica

The Powell Basin is a small oceanic basin located at the NE end of the Antarctic Peninsula developed during the Early Miocene and mostly surrounded by the continental crusts of the South Orkney Microcontinent, South Scotia Ridge and Antarctic Peninsula margins. Gravity data from the SCAN 97 cruise obtained with the R/V Hespérides and data from the Global Gravity Grid and Sea Floor Topography (GGSFT) database (Sandwell and Smith, 1997) are used to determine the 3D geometry of the crustal-mantle interface (CMI) by numerical inversion methods. Water layer contribution and sedimentary effects were eliminated from the Free Air anomaly to obtain the total anomaly. Sedimentary effects were obtained from the analysis of existing and new SCAN 97 multichannel seismic profiles (MCS). The regional anomaly was obtained after spectral and filtering processes. The smooth 3D geometry of the crustal mantle interface obtained after inversion of the regional anomaly shows an increase in the thickness of the crust towards the continental margins and a NW-SE oriented axis of symmetry coinciding with the position of an older oceanic spreading axis. This interface shows a moderate uplift towards the western part and depicts two main uplifts to the northern and eastern sectors

Enhancing the superconducting transition temperature of BaSi2 by structural tuning

We present a joint experimental and theoretical study of the superconducting phase of the layered binary silicide BaSi2. Compared with the layered AlB2 structure of graphite or diboride-like superconductors, in the hexagonal structure of binary silicides the sp3 arrangement of silicon atoms leads to corrugated sheets. Through a high-pressure synthesis procedure we are able to modify the buckling of these sheets, obtaining the enhancement of the superconducting transition temperature from 4 K to 8.7 K when the silicon planes flatten out. By performing ab-initio calculations based on density functional theory we explain how the electronic and phononic properties of the system are strongly affected by changes in the buckling. This mechanism is likely present in other intercalated layered superconductors, opening the way to the tuning of superconductivity through the control of internal structural parameters.Comment: Submitte

The c-completion of Lorentzian metric spaces

Inspired by some Lorentzian versions of the notion of metric and length space introduced by Kunzinger and Sämman [24], and more recently, by Müller [31], and Minguzzi and Sühr [30], we revisit the notion of Lorentzian metric space in order to later construct the c-completion of these general objects. We not only prove that this construction is feasible in great generality for these objects, including spacetimes of low regularity, but also endow the c-completion with a structure of Lorentzian metric space by itself. We also prove that the c-completion constitutes a well-suited extension of the original space, which really completes it in a precise sense and becomes sensible to certain causal properties of that space.Project PID2020-116126GB-I00 (funded by MCIN/AEI/10.13039/501100011033)IMAG-María de Maeztu grant CEX2020- 001105-M (funded by MCIN/AEI/10.13039/50110001103)Grants PID2020-118452GBI00 and PID2021-126217NBI00 (Spanish MICINN)PY20-01391 (PAIDI 2020, Junta de Andalucía-FEDER