Instituto Politécnico Nacional

About: Instituto Politécnico Nacional is a education organization based out in Mexico City, Mexico. It is known for research contribution in the topics: Population & Control theory. The organization has 43351 authors who have published 63315 publications receiving 938532 citations. The organization is also known as: Instituto Politécnico Nacional & Instituto Politecnico Nacional.

Insight into the Trophic Ecology of Yellowfin Tuna, Thunnus albacares, from Compound‐Specific Nitrogen Isotope Analysis of Proteinaceous Amino Acids

Abstract: Publisher Summary This chapter tests the premise that a single sample from an upper trophic level pelagic predator fish could provide information on both the trophic level of the fish and the δ15N value at the base of the food web. This chapter analyzes the nitrogen isotopic composition of individual amino acids in white muscle tissue (WMT) of yellowfin tuna (Thunnus albacares) from the eastern tropical Pacific (ETP) to determine if the observed variations in the δ15N values of WMT are primarily controlled by the nitrogen isotopic composition at the base of the food web or the trophic level of the tuna. The difference between the δ15N values of source and trophic amino acids is used to estimate the trophic level of yellowfin, and this is compared to the estimates based on two independent methods, stomach content analysis and the isotopic difference between the δ15N values of mesozooplankton and yellowfin tuna in the ETP. It is found that nitrogen isotopic analyses of individual amino acids in tuna can be used to distinguish between nutrient and trophic dynamics in pelagic ecosystems, and the implications of these results are discussed for investigating the long-term impact of commercial fishing on the food web structure of marine ecosystems.

Fermi GBM Observations of LIGO Gravitational Wave event GW150914

Abstract: With an instantaneous view of 70% of the sky, the Fermi Gamma-ray Burst Monitor (GBM) is an excellent partner in the search for electromagnetic counterparts to gravitational-wave (GW) events. GBM observations at the time of the Laser Interferometer Gravitational-wave Observatory (LIGO) event GW150914 reveal the presence of a weak transient above 50 keV, 0.4 s after the GW event, with a false-alarm probability of 0.0022 (2.9(sigma)). This weak transient lasting 1 s was not detected by any other instrument and does not appear to be connected with other previously known astrophysical, solar, terrestrial, or magnetospheric activity. Its localization is ill-constrained but consistent with the direction of GW150914. The duration and spectrum of the transient event are consistent with a weak short gamma-ray burst (GRB) arriving at a large angle to the direction in which Fermi was pointing where the GBM detector response is not optimal. If the GBM transient is associated with GW150914, then this electromagnetic signal from a stellar mass black hole binary merger is unexpected. We calculate a luminosity in hard X-ray emission between 1 keV and 10 MeV of 1.8(sup +1.5, sub -1.0) x 10(exp 49) erg/s. Future joint observations of GW events by LIGO/Virgo and Fermi GBM could reveal whether the weak transient reported here is a plausible counterpart to GW150914 or a chance coincidence, and will further probe the connection between compact binary mergers and short GRBs.

Cohen-macaulay graphs

Abstract: For a graph G we consider its associated ideal I(G). We uncover large classes of Cohen-Macaulay (=CM) graphs, in particular the full subclass of CM trees is presented. A formula for the Krull dimension of the symmetric algebra of I(G) is given along with a description of when this algebra is a domain. The first Koszul homology module of a CM tree is also studied.