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.

Global Mammal Conservation: What Must We Manage?

Abstract: We present a global conservation analysis for an entire “flagship” taxon, land mammals. A combination of rarity, anthropogenic impacts, and political endemism has put about a quarter of terrestrial mammal species, and a larger fraction of their populations, at risk of extinction. A new global database and complementarity analysis for selecting priority areas for conservation shows that ∼11% of Earth's land surface should be managed for conservation to preserve at least 10% of terrestrial mammal geographic ranges. Different approaches, from protection (or establishment) of reserves to countryside biogeographic enhancement of human-dominated landscapes, will be required to approach this minimal goal.

Nanoscale Domain Control in Multiferroic BiFeO3 Thin Films

Abstract: With an ever-expanding demand for data storage, transducers, and microelectromechanical (MEMS) systems applications, materials with superior ferroelectric and piezoelectric responses are of great interest. The lead zirconate titanate (PZT) family of materials has served as the cornerstone for such applications up until now. A critical drawback of this material, however, is the presence of lead and the recent concerns about the toxicity of lead-containing devices. Recently, the lead-free ferroelectric BiFeO3 (BFO) has attracted a great deal of attention because of its superior thin-film ferroelectric properties, which are comparable to those of the tetragonal, Ti-rich PZT system; therefore, BFO provides an alternate choice as a “green” ferro/piezoelectric material. Another advantage of BFO is its high ferroelectric Curie temperature (Tc = 850 °C in single crystals), [3,4] which enables it to be used reliably at high temperatures. The ferroelectric domain structure of epitaxial BFO films are typically discussed in the context of the crystallographic model of Kubel and Schmid; however, by suppressing other structural variants in BFO, we can obtain periodic domain structures that may open additional application opportunities for this material. Ferroelectrics with periodic domain structures are of great interest for applications in photonic devices and nanolithography. Such a periodic polarization could be obtained by applying an external electric field while utilizing lithographically defined electrodes or by a direct writing process. To obtain sub-micrometer feature sizes, however, domain engineering using a scanning force microscope with an appropriate bias voltage must be used to fabricate the patterned domain structures. Unfortunately, this method works only on small areas and is limited by its slow scanning rate. Theoretical models predict the feasibility of controlling the domain architecture in thin films through suitable control over the heteroepitaxial constraints. In the case of BFO thin films, we have found that such a control is indeed possible, mainly through control over the growth of the underlying SrRuO3 electrode. Using this approach, we demonstrate the growth of highly ordered 1D ferroelectric domains in 120 nm thick BFO films. On the (001)C perovskite surface there are eight possible ferroelectric polarization directions corresponding to four structural variants of the rhombohedral ferroelectric thin film. (For simplicity, the c and o subscripts refer to the pseudocubic structures for BFO and orthorhombic structures of SrRuO3 (SRO) and DyScO3(110)O (DSO), respectively.) Domain patterns can develop with either {100}C or {101}C boundaries for (001)C-oriented rhombohedral films. [12] In both cases, the individual domains in the patterns are energetically degenerate and thus equal-width stripe patterns are theoretically predicted. When the spontaneous polarization is included in the analysis, the {100}C boundary patterns have no normal component of the net polarization, whereas the {101}C boundary patterns correspond to the fully poled state. The formation of domain patterns leads to the release of elastic energy at the expense of increased interfacial energy associated with the domain boundaries. Therefore, four possible polarization variants still exist when one examines large areas of the sample. If control over the ferroelectric domain structure is desired, one has to recourse to other approaches. In our work, we have used the constraints imposed by heteroepitaxy as well as filmgrowth mechanisms, shown in Figure 1a, to create long-range order in the domain structure of BFO. First, we use the fact that on the (110)O surface the DSO lattice is extremely closely matched to that of SRO. Further, the small structural anisotropy in DSO is used to pin the structure of the SRO layer C O M M U N IC A IO N S

Decline of monarch butterflies overwintering in Mexico: is the migratory phenomenon at risk?

Abstract: During the 2009-2010 overwintering season and following a 15-year downward trend, the total area in Mexico occupied by the eastern North American population of overwintering monarch butterflies reached an all-time low. Despite an increase, it remained low in 2010-2011. 2. Although the data set is small, the decline in abundance is statistically signifi- cant using both linear and exponential regression models. 3. Three factors appear to have contributed to reduce monarch abundance: degra- dation of the forest in the overwintering areas; the loss of breeding habitat in the Uni- ted States due to the expansion of GM herbicide-resistant crops, with consequent loss of milkweed host plants, as well as continued land development; and severe weather. 4. This decline calls into question the long-term survival of the monarchs' migra- tory phenomenon. Resumen. 1. Durante la temporada invernal 2009-2010, y siguiendo una tenden- cia a la baja de 15 anos, la superficie total ocupada por mariposas monarca en Mexico, provenientes del este America del Norte, llegoa su punto mas bajo. A pesar de su incremento, dicha superficie siguiosiendo baja en 2010-2011. 2. Aunque que el conjunto de datos disponibles es aun pequeno, esta disminucion de la abundancia de mariposas es estadisticamente significativa, tanto si se usan modelos de regresion lineales como exponenciales. 3. Hay tres factores que parecen haber contribuido con esta tendencia de reduc- ciond el numero de mariposas: la degradacion de bosque en las areas de invernacion en Mexico; la perdida de habitat de reproduccion en los Estados Unidos, debido a la expansiond e cultivos geneticamente modificados resistentes a herbicidas, con la consiguiente perdida de las plantas hospederas de algodoncillo, y por continuos cambios en el uso del suelo no favorables para ellas; y, las recientes condiciones cli- maticas severas. 4. Esta disminucion hace que nos cuestionemos sobre la posibilidad de superviven- cia a largo plazo del fenomeno migratorio de las mariposas monarca.

DNA Damage in Nasal and Brain Tissues of Canines Exposed to Air Pollutants Is Associated with Evidence of Chronic Brain Inflammation and Neurodegeneration

Abstract: Acute, subchronic, or chronic exposures to particulate matter (PM) and pollutant gases affect people in urban areas and those exposed to fires, disasters, and wars. Respiratory tract inflammation, production of mediators of inflammation capable of reaching the brain, systemic circulation of PM, and disruption of the nasal respiratory and olfactory barriers are likely in these populations. DNA damage is crucial in aging and in age-associated diseases such as Alzheimer's disease. We evaluated apurinic/apyrimidinic (AP) sites in nasal and brain genomic DNA, and explored by immunohistochemistry the expression of nuclear factor NFkappaB p65, inducible nitric oxide synthase (iNOS), cyclo-oxygenase 2 (COX2), metallothionein I and II, apolipoprotein E, amyloid precursor protein (APP), and beta-amyloid(1-42) in healthy dogs naturally exposed to urban pollution in Mexico City. Nickel (Ni) and vanadium (V) were measured by inductively coupled plasma mass spectrometry (ICP-MS). Forty mongrel dogs, ages 7 days-10 years were studied (14 controls from Tlaxcala and 26 exposed to urban pollution in South West Metropolitan Mexico City (SWMMC)). Nasal respiratory and olfactory epithelium were found to be early pollutant targets. Olfactory bulb and hippocampal AP sites were significantly higher in exposed than in control age matched animals. Ni and V were present in a gradient from olfactory mucosa > olfactory bulb > frontal cortex. Exposed dogs had (a) nuclear neuronal NFkappaB p65, (b) endothelial, glial and neuronal iNOS, (c) endothelial and glial COX2, (d) ApoE in neuronal, glial and vascular cells, and (e) APP and beta amyloid(1-42) in neurons, diffuse plaques (the earliest at age 11 months), and in subarachnoid blood vessels. Increased AP sites and the inflammatory and stress protein brain responses were early and significant in dogs exposed to urban pollution. Oil combustion PM-associated metals Ni and V were detected in the brain. There was an acceleration of Alzheimer's-type pathology in dogs chronically exposed to air pollutants. Respiratory tract inflammation and deteriorating olfactory and respiratory barriers may play a role in the observed neuropathology. These data suggest that Alzheimer's disease may be the sequela of air pollutant exposures and the resulting systemic inflammation.

Charged-Particle Multiplicity Density at Midrapidity in Central Pb-Pb Collisions at root s(NN)=2.76 TeV

Abstract: The first measurement of the charged-particle multiplicity density at midrapidity in Pb-Pb collisions at a center-of-mass energy per nucleon pair root s(NN) = 2.76 TeV is presented. For an event sample corresponding to the most central 5% of the hadronic cross section, the pseudorapidity density of primary charged particles at midrapidity is 1584 +/- 4(stat) +/- 76(syst), which corresponds to 8.3 +/- 0.4(syst) per participating nucleon pair. This represents an increase of about a factor 1.9 relative to pp collisions at similar collision energies, and about a factor 2.2 to central Au-Au collisions at root s(NN) = 0.2 TeV. This measurement provides the first experimental constraint for models of nucleus-nucleus collisions at LHC energies.