National Autonomous University of Mexico

About: National Autonomous University of Mexico is a education organization based out in Mexico City, Distrito Federal, Mexico. It is known for research contribution in the topics: Population & Galaxy. The organization has 72868 authors who have published 127797 publications receiving 2285543 citations. The organization is also known as: UNAM & Universidad Nacional Autónoma de México.

Informal Exchange Networks in Formal Systems: A Theoretical Model

Abstract: some degree from access to services provided by the modern state. Networks of reciprocity and patron-client relations have been shown to play an important role within these disadvantaged sectors, in articulating their members to the formal market system and in creating an informal social security system to survive (Lomnitz 1977, 1978, 1982). The present article proposes to examine a different aspect of "informality": the pervasive utilization of informal modes of exchange within the formal sector itself. These exchanges include various forms of trading influence and bureaucratic favors for equivalent services or cash. Depending on the political system, some forms of informal exchange may be tolerated while others may be severely repressed. Even in the latter case, however, illicit economic activities ("economic crimes") in the state bureaucracy are often seen as inevitable (if not actually useful) by members of elite groups within the formal system. I show that these activities are not random or chaotic but are based on informal networks following principles similar to those in shantytown networks: patronage, loyalty, and confianza (trust). Often the networks run underneath and parallel to the formal hierarchy. Weberian analysis of the rationality of bureaucratic systems ignored the informal activities that sprang up within formal organizations as a response to the malfunctionings of bureaucracies. Political science and anthropology, however, based on first-hand observations in underdeveloped, non-Western societies, have developed an extensive literature focusing on the discrepancies between the goals and structures of organizations and the historical and cultural specificities of the social systems in which those organizations are embedded. The main consequences of this conflict appear to be inefficiencies resulting from rigidity and corruption (arising from inefficiency). Personalistic, culturally determined loyalties to kin and local groups often defy the more nationalistic ideologies that underlie bureaucratic rationality. (For a review of this literature, see Britan and Cohen 1980; Scott 1972.) This article is generally in line with the literature mentioned above, but goes a step further in that it sees "informality" not only as a residue of traditionalism, but as an intrinsic element of "formality" insofar as it is a response to the inadequacies of formal

Magnetospheres and Disk Accretion in Herbig Ae/Be Stars

Abstract: We present evidence of magnetically mediated disk accretion in Herbig Ae/Be stars. Magnetospheric accretion models of Balmer and sodium profiles calculated with appropriate stellar and rotational parameters are in qualitative agreement with the observed profiles of the Herbig Ae star UX Ori and yield a mass accretion rate of ~10-8?M??yr-1. If more recent indications of an extremely large rotation rate for this object are correct, the magnetic field geometry must deviate from that of a standard dipole in order to produce line emission consistent with observed flux levels. Models of the associated accretion shock qualitatively explain the observed distribution of excess fluxes in the Balmer discontinuity for a large ensemble of Herbig Ae/Be stars and imply typically small mass accretion rates, 10-7?M??yr-1. In order for accretion to proceed onto the star, significant amounts of gas must exist inside the dust destruction radius, which is potentially problematic for recently advocated scenarios of puffed inner dust wall geometries. However, our models of the inner gas disk show that for the typical accretion rates we have derived, the gas should generally be optically thin, thus allowing direct stellar irradiation of the inner dust edge of the disk.

Technical design report for the upgrade of the ALICE inner tracking system

Abstract: ALICE (A Large Ion Collider Experiment) is studying the physics of strongly interacting matter, and in particular the properties of the Quark–Gluon Plasma (QGP), using proton–proton, proton–nucleus and nucleus–nucleus collisions at the CERN LHC (Large Hadron Collider). The ALICE Collaboration is preparing a major upgrade of the experimental apparatus, planned for installation in the second long LHC shutdown in the years 2018–2019. A key element of the ALICE upgrade is the construction of a new, ultra-light, high- resolution Inner Tracking System (ITS) based on monolithic CMOS pixel detectors. The primary focus of the ITS upgrade is on improving the performance for detection of heavy-flavour hadrons, and of thermal photons and low-mass di- electrons emitted by the QGP. With respect to the current detector, the new Inner Tracking System will significantly enhance the determination of the distance of closest approach to the primary vertex, the tracking efficiency at low transverse momenta, and the read-out rate capabilities. This will be obtained by seven concentric detector layers based on a 50 μm thick CMOS pixel sensor with a pixel pitch of about 30×30 μm2. This document, submitted to the LHCC (LHC experiments Committee) in September 2013, presents the design goals, a summary of the R&D activities, with focus on the technical implementation of the main detector components, and the projected detector and physics performance.

Oaxaquia, a Proterozoic microcontinent accreted to North America during the late Paleozoic

Abstract: Grenville-age granulite facies rocks in southern, central, and northeastern Mexico have distinctive geologic features that suggest a common tectonic evolution. The similarities include northwest-trending structural grain from Oaxaca to Tamaulipas, massif-type anorthosite-charnockite complexes, protoliths rich in sedimentary rocks of shallow-marine platform or continental rift-related facies devoid of calc-alkaline volcanic rocks, common metamorphism under granulite facies conditions, U-Pb zircon ages of about 1.0 Ga., and an apparently common history of uplift and cooling. Altogether, this evidence strongly suggests a coherent geologic history for this block. Paleontologic data from the overlying sedimentary sequences indicate that Oaxaquia was not part of Laurentia during most of the Paleozoic. This precludes emplacement of Oaxaquia in its present position by simple lateral displacement from the southern United States as well as a Taconic time of emplacement. Oaxaquia was probably emplaced to its present position during late Paleozoic time. The concept of a Mesoproterozoic “Oaxaquia” microcontinent extending for about 1000 km in Mexico needs to be considered in the reconstruction of the Grenville orogen as a whole and for the Paleozoic tectonic interactions between eastern Laurentia and western Gondwana.

Pet, an Autotransporter Enterotoxin from Enteroaggregative Escherichia coli

Abstract: Enteroaggregative Escherichia coli (EAEC) is an emerging cause of diarrheal illness. Clinical data suggest that diarrhea caused by EAEC is predominantly secretory in nature, but the responsible enterotoxin has not been described. Work from our laboratories has implicated a ca. 108-kDa protein as a heat-labile enterotoxin and cytotoxin, as evidenced by rises in short-circuit current and falls in tissue resistance in rat jejunal tissue mounted in an Ussing chamber. Here we report the genetic cloning, sequencing, and characterization of this high-molecular-weight heat-labile toxin. The toxin (designated the plasmid-encoded toxin [Pet]) is encoded on the 65-MDa adherence-related plasmid of EAEC strain 042. Nucleotide sequence analysis suggests that the toxin is a member of the autotransporter class of proteins, characterized by the presence of a conserved C-terminal domain which forms a β-barrel pore in the bacterial outer membrane and through which the mature protein is transported. The Pet toxin is highly homologous to the EspP protease of enterohemorrhagic E. coli and to EspC of enteropathogenic E. coli, an as yet cryptic protein. In addition to its potential role in EAEC infection, Pet represents the first enterotoxin within the autotransporter class of secreted proteins. We hypothesize that other closely related members of this class may also produce enterotoxic effects.