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Institution

National Autonomous University of Mexico

EducationMexico City, Distrito Federal, 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.


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Journal ArticleDOI
TL;DR: In this article, the authors studied the mid-infrared spectra of T Tauri stars in the Taurus star-forming region obtained with the Spitzer Infrared Spectrograph (IRS).
Abstract: We present mid-infrared spectra of T Tauri stars in the Taurus star-forming region obtained with the Spitzer Infrared Spectrograph (IRS). For the first time, the 5–36 � m spectra of a large sample of T Tauri stars belonging to the same star-forming region is studied, revealing details of the midinfrared excess due to dust in circumstellar disks. We analyze common features and differences in the mid-IR spectra based on disk structure, dust grain properties, and the presence of companions. Our analysis encompasses spectral energy distributions from the optical to the far-infrared, a morphological sequence based on the IRS spectra, and spectral indices in IRS wave bands representative of continuum emission. By comparing the observed spectra to a grid of accretion disk models, we infer some basic disk properties for our sample of T Tauri stars, and find additional evidence for dust settling. Subject headings: circumstellar matter — planetary systems: protoplanetary disks — stars: pre-main sequence — infrared: stars

477 citations

Journal ArticleDOI
TL;DR: In this article, the authors used the Hubble Space Telescope ultraviolet spectra and supporting ground-based data for a sample of nine intermediate-mass T T Tauri stars (IMTTSs; 1.5-4 M⊙).
Abstract: We present Hubble Space Telescope ultraviolet spectra and supporting ground-based data for a sample of nine intermediate-mass T Tauri stars (IMTTSs; 1.5–4 M⊙). The targets belong to three star-forming regions: T Tau, SU Aur, and RY Tau in the Taurus clouds; EZ Ori, P2441, and V1044 Ori in the Ori OB1c association surrounding the Orion Nebula cluster; and CO Ori, GW Ori, and GX Ori in the ring around λ Ori. The supporting ground-based observations include nearly simultaneous UBV(R I)C photometry, 6 A resolution spectra covering the range 3900–7000 A, optical echelle observations in the range 5800–8600 A, and K-band near-infrared spectra. We use these data to determine improved spectral types and reddening corrections and to obtain physical parameters of the targets. We find that an extinction law with a weak 2175 A feature but high values of AUV/AV is required to explain the simultaneous optical-UV data; the reddening laws for two B-type stars located behind the Taurus clouds, HD 29647 and HD 283809, meet these properties. We argue that reddening laws with these characteristics may well be representative of cold, dense molecular clouds. Spectral energy distributions and emission-line profiles of the IMTTSs are consistent with expectations from magnetospheric accretion models. We compare our simultaneous optical-UV data with predictions from accretion shock models to get accretion luminosities and mass accretion rates () for the targets. We find that the average mass accretion rate for IMTTSs is ~3 × 10-8 M⊙ yr-1, a factor of ~5 higher than that for their low-mass counterparts. The new data extend the correlation between and stellar mass to the intermediate-mass range. Since the IMTTSs are evolutionary descendants of the Herbig Ae/Be stars, our results put limits to the mass accretion rates of their disks. We present luminosities of the UV lines of highly ionized metals and show that they are well above the saturation limit for magnetically active cool stars but correlate strongly with accretion luminosity, indicating that they are powered by accretion, in agreement with previous claims but using a sample in which reddening and accretion luminosities have been determined self-consistently. Finally, we find that the relation between accretion luminosity and Brγ luminosity found for low-mass T Tauri stars extends to the intermediate-mass regime.

476 citations

Journal ArticleDOI
TL;DR: In this article, an Arabidopsis thaliana miR159 precursor was modified to express artificial miRNAs (amiRNAs) targeting viral mRNA sequences encoding two gene silencing suppressors, P69 of turnip yellow mosaic virus (TYMV) and HC-Pro of TuMV (TuMV).
Abstract: Plant microRNAs (miRNAs) regulate the abundance of target mRNAs by guiding their cleavage at the sequence complementary region. We have modified an Arabidopsis thaliana miR159 precursor to express artificial miRNAs (amiRNAs) targeting viral mRNA sequences encoding two gene silencing suppressors, P69 of turnip yellow mosaic virus (TYMV) and HC-Pro of turnip mosaic virus (TuMV). Production of these amiRNAs requires A. thaliana DICER-like protein 1. Transgenic A. thaliana plants expressing amiR-P69159 and amiR-HC-Pro159 are specifically resistant to TYMV and TuMV, respectively. Expression of amiR-TuCP159 targeting TuMV coat protein sequences also confers specific TuMV resistance. However, transgenic plants that express both amiR-P69159 and amiR-HC-Pro159 from a dimeric pre-amiR-P69159/amiR-HC-Pro159 transgene are resistant to both viruses. The virus resistance trait is displayed at the cell level and is hereditable. More important, the resistance trait is maintained at 15 °C, a temperature that compromises small interfering RNA–mediated gene silencing. The amiRNA-mediated approach should have broad applicability for engineering multiple virus resistance in crop plants.

476 citations

Journal ArticleDOI
Paul R. Mahaffy1, Chris Webster2, Michel Cabane3, Pamela G. Conrad1, Patrice Coll4, Sushil K. Atreya5, Robert Arvey1, Michael Barciniak1, Mehdi Benna1, L. Bleacher1, William B. Brinckerhoff1, Jennifer L. Eigenbrode1, Daniel Carignan1, Mark Cascia1, Robert A. Chalmers1, Jason P. Dworkin1, Therese Errigo1, Paula Everson1, Heather B. Franz1, Rodger Farley1, Steven Feng1, Gregory Frazier1, Caroline Freissinet1, Daniel P. Glavin1, D. N. Harpold1, Douglas L. Hawk1, Vincent Holmes1, Christopher S. Johnson1, Andrea Jones1, Patrick R. Jordan1, James W. Kellogg1, Jesse Lewis1, Eric Lyness1, Charles Malespin1, David Martin1, John Maurer1, Amy McAdam1, Douglas McLennan1, T. Nolan1, Marvin Noriega1, Alexander A. Pavlov1, B. D. Prats1, E. Raaen1, Oren E. Sheinman1, D. Sheppard1, James Smith1, Jennifer C. Stern1, Florence Tan1, Melissa G. Trainer1, Douglas W. Ming, Richard V. Morris, John H. Jones, Cindy Gundersen, Andrew Steele6, James J. Wray7, Oliver Botta, Laurie A. Leshin8, Tobias Owen9, Steve Battel, Bruce M. Jakosky10, H. L. K. Manning11, Steven W. Squyres12, Rafael Navarro-González13, Christopher P. McKay14, François Raulin3, Robert Sternberg3, Arnaud Buch15, Paul Sorensen, Robert Kline-Schoder, David Coscia3, Cyril Szopa3, Samuel Teinturier3, Curt Baffes2, Jason Feldman2, Greg Flesch2, Siamak Forouhar2, Ray Garcia2, Didier Keymeulen2, Steve Woodward2, Bruce P. Block5, Ken Arnett5, Ryan M. Miller5, Charles Edmonson5, Stephen Gorevan16, E. Mumm16 
TL;DR: The Sample Analysis at Mars (SAM) investigation of the Mars Science Laboratory (MSL) addresses the chemical and isotopic composition of the atmosphere and volatiles extracted from solid samples.
Abstract: The Sample Analysis at Mars (SAM) investigation of the Mars Science Laboratory (MSL) addresses the chemical and isotopic composition of the atmosphere and volatiles extracted from solid samples. The SAM investigation is designed to contribute substantially to the mission goal of quantitatively assessing the habitability of Mars as an essential step in the search for past or present life on Mars. SAM is a 40 kg instrument suite located in the interior of MSL’s Curiosity rover. The SAM instruments are a quadrupole mass spectrometer, a tunable laser spectrometer, and a 6-column gas chromatograph all coupled through solid and gas processing systems to provide complementary information on the same samples. The SAM suite is able to measure a suite of light isotopes and to analyze volatiles directly from the atmosphere or thermally released from solid samples. In addition to measurements of simple inorganic compounds and noble gases SAM will conduct a sensitive search for organic compounds with either thermal or chemical extraction from sieved samples delivered by the sample processing system on the Curiosity rover’s robotic arm.

475 citations

Journal ArticleDOI
TL;DR: BT is a useful, inexpensive, simple and safe diagnostic test in the evaluation of common gastroenterology problems and should help to standardize the indications, preparation, performance and interpretation of BT in clinical practice and research.

475 citations


Authors

Showing all 73617 results

NameH-indexPapersCitations
Richard Peto183683231434
Anton M. Koekemoer1681127106796
Rory Collins162489193407
Timothy C. Beers156934102581
Vivek Sharma1503030136228
Kjell Fuxe142147989846
Prashant V. Kamat14072579259
Carmen García139150396925
Harold A. Mooney135450100404
Efe Yazgan12898679041
Roberto Maiolino12781661724
Peter Nugent12775492988
William R. Miller12560172570
Nicholas A. Kotov12357455210
John C. Wingfield12250952291
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Performance
Metrics
No. of papers from the Institution in previous years
YearPapers
20241
2023311
2022967
20217,481
20207,906
20197,107