115 research outputs found
The Chimalapas Region, Oaxaca, Mexico: a high-priority region for bird conservation in Mesoamerica
The Chimalapas region, in eastern Oaxaca, Mexico, holds lowland rainforests, tropical dry
forests, and cloud forests typical of the Neotropics, as well as montane pine and pine-oak
forests more typical of the Nearctic. Totaling more than 600,000 ha, much of the region is
forested, and in a good state of preservation. The Chimalapas avifauna is by far the most
diverse for any region of comparable size in the country, totalling at least 464 species in
the region as a whole (with more than 300 species in the lowland rainforest) representing
44% of the bird species known from Mexico. Within the region, the humid Atlantic
lowlands hold 317 species, the montane regions 113 species, and the southern dry forested
lowlands 216 species. Important species present in the region include Harpy Eagle Harpia
harpyja and several other large eagles, Black Penelopina nigra and probably Horned
Oreophasis derbianus Guans, Scarlet Macaw Ara macao, Cinnamon-tailed Sparrow Aimophila
sumichrasti, Rose-bellied Bunting Passerina rositae, and Resplendent Quetzal Pharomachrus
mocinno. The area holds immense lowland rainforests and cloud forests that rank among
the largest and best preserved in all of Mesoamerica, including a complete
lowland-to-highland continuum, with entire watersheds preserved more or less intact
Magnetic Field Measurement with Ground State Alignment
Observational studies of magnetic fields are crucial. We introduce a process
"ground state alignment" as a new way to determine the magnetic field direction
in diffuse medium. The alignment is due to anisotropic radiation impinging on
the atom/ion. The consequence of the process is the polarization of spectral
lines resulting from scattering and absorption from aligned atomic/ionic
species with fine or hyperfine structure. The magnetic field induces precession
and realign the atom/ion and therefore the polarization of the emitted or
absorbed radiation reflects the direction of the magnetic field. The atoms get
aligned at their low levels and, as the life-time of the atoms/ions we deal
with is long, the alignment induced by anisotropic radiation is susceptible to
extremely weak magnetic fields (G). In fact,
the effects of atomic/ionic alignment were studied in the laboratory decades
ago, mostly in relation to the maser research. Recently, the atomic effect has
been already detected in observations from circumstellar medium and this is a
harbinger of future extensive magnetic field studies. A unique feature of the
atomic realignment is that they can reveal the 3D orientation of magnetic
field. In this article, we shall review the basic physical processes involved
in atomic realignment. We shall also discuss its applications to
interplanetary, circumstellar and interstellar magnetic fields. In addition,
our research reveals that the polarization of the radiation arising from the
transitions between fine and hyperfine states of the ground level can provide a
unique diagnostics of magnetic fields in the Epoch of Reionization.Comment: 30 pages, 12 figures, chapter in Lecture Notes in Physics "Magnetic
Fields in Diffuse Media". arXiv admin note: substantial text overlap with
arXiv:1203.557
Nitrogen uptake and internal recycling in Zostera marina exposed to oyster farming: eelgrass potential as a natural biofilter
Oyster farming in estuaries and coastal lagoons frequently overlaps with the distribution of seagrass meadows, yet there are few studies on how this aquaculture practice affects seagrass physiology. We compared in situ nitrogen uptake and the productivity of Zostera marina shoots growing near off-bottom longlines and at a site not affected by oyster farming in San Quintin Bay, a coastal lagoon in Baja California, Mexico. We used benthic chambers to measure leaf NH4 (+) uptake capacities by pulse labeling with (NH4)-N-15 (+) and plant photosynthesis and respiration. The internal N-15 resorption/recycling was measured in shoots 2 weeks after incubations. The natural isotopic composition of eelgrass tissues and vegetative descriptors were also examined. Plants growing at the oyster farming site showed a higher leaf NH4 (+) uptake rate (33.1 mmol NH4 (+) m(-2) day(-1)) relative to those not exposed to oyster cultures (25.6 mmol NH4 (+) m(-2) day(-1)). We calculated that an eelgrass meadow of 15-16 ha (which represents only about 3-4 % of the subtidal eelgrass meadow cover in the western arm of the lagoon) can potentially incorporate the total amount of NH4 (+) excreted by oysters (similar to 5.2 x 10(6) mmol NH4 (+) day(-1)). This highlights the potential of eelgrass to act as a natural biofilter for the NH4 (+) produced by oyster farming. Shoots exposed to oysters were more efficient in re-utilizing the internal N-15 into the growth of new leaf tissues or to translocate it to belowground tissues. Photosynthetic rates were greater in shoots exposed to oysters, which is consistent with higher NH4 (+) uptake and less negative delta C-13 values. Vegetative production (shoot size, leaf growth) was also higher in these shoots. Aboveground/belowground biomass ratio was lower in eelgrass beds not directly influenced by oyster farms, likely related to the higher investment in belowground biomass to incorporate sedimentary nutrients
Minimum requirements for publishing hydrogen, carbon, nitrogen, oxygen and sulfur stable-isotope delta results (IUPAC Technical Report)
Minimum requirements for publishing hydrogen, carbon, nitrogen, oxygen and sulfur stable-isotope delta results (IUPAC Technical Report)
Stable hydrogen, carbon, nitrogen, oxygen and sulfur (HCNOS) isotope compositions expressed as isotope-delta values are typically reported relative to international standards such as Vienna Standard Mean Ocean Water (VSMOW), Vienna Peedee belemnite (VPDB) or Vienna Cañon Diablo Troilite (VCDT). These international standards are chosen by convention and the calibration methods used to realise them in practice undergo occasional changes. To ensure longevity and reusability of published data, a comprehensive description of (1) analytical procedure, (2) traceability, (3) data processing, and (4) uncertainty evaluation is required. Following earlier International Union of Pure and Applied Chemistry documents on terminology and notations, this paper proposes minimum requirements for publishing HCNOS stable-isotope delta results. Each of the requirements are presented with illustrative example
Relationship between gender, income and education and self-perceived oral health among elderly Mexicans. An exploratory study
Saberes digitales: una aproximación desde las voces de los estudiantes
The second decade of the new century is about to end. In educational matters, it could be affirmed that many learning has left us the insertion of technologies in the classroom in these years, at all levels schoolchildren without exception. However, it could also be ensured that challenges in the short term arising from the current revolution social and technological, which on many occasions has left us without Enough spaces to reflect on its progress and implications It is interesting and challenging how the training processes in these last 20 years, when technologies of information and communications (ICT) have evolved step by step accelerated. Interesting, on the one hand, since one of the most important contributions important of the ICT is to act as large portals with access to the world, which both students, teachers and researchers open daily to understand the progress of their areas of knowledge and use tools that allow establishing better connectivity networks for the learning. Challenging, on the other hand, due to changes in paradigm that is being built around what has been understood for years regarding what the training process requires in terms of planning, didactic strategies, use of learning resources and the evaluation, to mention the main
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