734 research outputs found
Sobre «la impresión del grifo». El trasfondo de unos pasajes quevedianos
Repeatedley (up to four times), Francisco de Quevedo uses, somewhat enigmatically, the sentence «the impression of griffin». For example, he says that an old woman had «a face of the impression of the griffin»; also he wrote of a go-between that «she made a gesture of the impression of the griphon». This expression was rightly explained by Luisa López Grigera as a reference to the image of the griffin which appeared engraved on the title page of the books printed in Lyon by Sébastien Griphe, and whose face was similar in ugliness to the one of an old woman. This article carefully searches the trajectory of this sentence, which was close to becoming lexicalized in our language, and adds to the Quevedo’s examples others unknown.En varias ocasiones (hasta cuatro) utiliza Francisco de Quevedo, un tanto enigmáticamente, la frase «la impresión del grifo». Por ejemplo, dice de una vieja que tenía «una cara de la impresión del grifo»; de una alcahueta, que «hizo un gesto de la impresión del grifo», etcétera. La expresión ya fue acertadamente explicada por Luisa López Grigera como una referencia a la imagen de un grifo que aparecía grabada en las portadas de los libros salidos de la imprenta lionesa de Sébastien Griphe, y cuya cabeza resultaba equiparable por su fealdad a la de una mujer vieja. El presente estudio rastrea detenidamente la trayectoria de dicha frase, que estuvo próxima a lexicalizarse en nuestra lengua, y se añaden a los quevedianos otros testimonios no conocidos
DNA-based biosensor for the electrocatalytic determination of antioxidant capacity in beverages
Reactive oxygen species (ROS) are produced as a consequence of normal aerobic metabolism and are
able to induce DNA oxidative damage. At the cellular level, the evaluation of the protective effect of
antioxidants can be achieved by examining the integrity of the DNA nucleobases using electrochemical
techniques. Herein, the use of an adenine-rich oligonucleotide (dA21) adsorbed on carbon paste electrodes
for the assessment of the antioxidant capacity is proposed. The method was based on the partial damage
of a DNA layer adsorbed on the electrode surface by OH• radicals generated by Fenton reaction and
the subsequent electrochemical oxidation of the intact adenine bases to generate an oxidation product
that was able to catalyze the oxidation of NADH. The presence of antioxidant compounds scavenged
hydroxyl radicals leaving more adenines unoxidized, and thus, increasing the electrocatalytic current of
NADHmeasured by differential pulse voltammetry (DPV). Using ascorbic acid (AA) as a model antioxidant
species, the detection of as low as 50nMof AA in aqueous solution was possible. The protection efficiency
was evaluated for several antioxidant compounds. The biosensor was applied to the determination of the
total antioxidant capacity (TAC) in beverages
Electrocatalytic evaluation of DNA damage by superoxide radical for antioxidant capacity assessment
The integrity of DNA purine bases was herein used to evaluate the antioxidant capacity. Unlike other
DNA-based antioxidant sensors reported so far, the damaging agent chosen was the O
2 radical enzymatically
generated by the xanthine/xanthine oxidase system. An adenine-rich oligonucleotide was adsorbed
on carbon paste electrodes and subjected to radical damage in the presence/absence of several antioxidant
compounds. As a result, partial damage on DNA was observed. A minor product of the radical oxidation
was identified by cyclic voltammetry as a diimine adenine derivative also formed during the
electrochemical oxidation of adenine/guanine bases. The protective efficiency of several antioxidant compounds
was evaluated after electrochemical oxidation of the remaining unoxidized adenine bases, by
measuring the electrocatalytic current of NADH mediated by the adsorbed catalyst species generated.
A comparison between O
2 and OH radicals as a source of DNA lesions and the scavenging efficiency
of various antioxidant compounds against both of them is discussed. Finally, the antioxidant capacity
of beverages was evaluated and compared with the results obtained with an optical method
Observation of the Crab Nebula with the HAWC Gamma-Ray Observatory
The Crab Nebula is the brightest TeV gamma-ray source in the sky and has been
used for the past 25 years as a reference source in TeV astronomy, for
calibration and verification of new TeV instruments. The High Altitude Water
Cherenkov Observatory (HAWC), completed in early 2015, has been used to observe
the Crab Nebula at high significance across nearly the full spectrum of
energies to which HAWC is sensitive. HAWC is unique for its wide field-of-view,
nearly 2 sr at any instant, and its high-energy reach, up to 100 TeV. HAWC's
sensitivity improves with the gamma-ray energy. Above 1 TeV the
sensitivity is driven by the best background rejection and angular resolution
ever achieved for a wide-field ground array.
We present a time-integrated analysis of the Crab using 507 live days of HAWC
data from 2014 November to 2016 June. The spectrum of the Crab is fit to a
function of the form . The data is well-fit with values of
, , and
log when
is fixed at 7 TeV and the fit applies between 1 and 37 TeV. Study of the
systematic errors in this HAWC measurement is discussed and estimated to be
50\% in the photon flux between 1 and 37 TeV.
Confirmation of the Crab flux serves to establish the HAWC instrument's
sensitivity for surveys of the sky. The HAWC survey will exceed sensitivity of
current-generation observatories and open a new view of 2/3 of the sky above 10
TeV.Comment: Submitted 2017/01/06 to the Astrophysical Journa
Daily monitoring of TeV gamma-ray emission from Mrk 421, Mrk 501, and the Crab Nebula with HAWC
We present results from daily monitoring of gamma rays in the energy range
to TeV with the first 17 months of data from the High
Altitude Water Cherenkov (HAWC) Observatory. Its wide field of view of 2
steradians and duty cycle of % are unique features compared to other TeV
observatories that allow us to observe every source that transits over HAWC for
up to hours each sidereal day. This regular sampling yields
unprecedented light curves from unbiased measurements that are independent of
seasons or weather conditions. For the Crab Nebula as a reference source we
find no variability in the TeV band. Our main focus is the study of the TeV
blazars Markarian (Mrk) 421 and Mrk 501. A spectral fit for Mrk 421 yields a
power law index and
an exponential cut-off
TeV. For Mrk 501, we find an index and exponential cut-off TeV. The light curves for both sources show clear
variability and a Bayesian analysis is applied to identify changes between flux
states. The highest per-transit fluxes observed from Mrk 421 exceed the Crab
Nebula flux by a factor of approximately five. For Mrk 501, several transits
show fluxes in excess of three times the Crab Nebula flux. In a comparison to
lower energy gamma-ray and X-ray monitoring data with comparable sampling we
cannot identify clear counterparts for the most significant flaring features
observed by HAWC.Comment: 18 pages, 10 figures, accepted for publication in The Astrophysical
Journa
All-particle cosmic ray energy spectrum measured by the HAWC experiment from 10 to 500 TeV
We report on the measurement of the all-particle cosmic ray energy spectrum
with the High Altitude Water Cherenkov (HAWC) Observatory in the energy range
10 to 500 TeV. HAWC is a ground based air-shower array deployed on the slopes
of Volcan Sierra Negra in the state of Puebla, Mexico, and is sensitive to
gamma rays and cosmic rays at TeV energies. The data used in this work were
taken from 234 days between June 2016 to February 2017. The primary cosmic-ray
energy is determined with a maximum likelihood approach using the particle
density as a function of distance to the shower core. Introducing quality cuts
to isolate events with shower cores landing on the array, the reconstructed
energy distribution is unfolded iteratively. The measured all-particle spectrum
is consistent with a broken power law with an index of prior to
a break at ) TeV, followed by an index of . The
spectrum also respresents a single measurement that spans the energy range
between direct detection and ground based experiments. As a verification of the
detector response, the energy scale and angular resolution are validated by
observation of the cosmic ray Moon shadow's dependence on energy.Comment: 16 pages, 11 figures, 4 tables, submission to Physical Review
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