La investigación del ADN antiguo: Directrices sobre las precauciones, controles y el tratamiento de las muestras

The young discipline of palaeogenetics has developed into a successful and expectant field of archaeobiological research within the last decade. Palaeogenetic investigation (e.g. PCR, DNA sequencing) of ancient specimens is, however, susceptible to falsification by the presence of contamination from more recent times. Contamination which can lead to amplification of non-authentic sequences is known to stem from several sources: (i) human biomolecules derived from the persons performing the genetic experiments, perhaps also from the archeologists and other persons who have previously handled the specimens or (ii) edaphic DNA sequences derived primarily from bacterial or fungal growth upon the specimen. A third source of contamination can arise from (iii) substances used for conservation of specimens. Here we give advice on the correct processing of prehistoric bone samples when further molecular biological examination is required. Along with the demonstration of necessary precautions and working conditions, we further explain how an unequivocal DNA contamination monitoring is performed.La paleogenética se ha convertido en los últimos años en una disciplina coronada de éxito que ofrece grandes expectativas para el desarrollo de la investigación arqueobiológica. No obstante, la investigación paleogenética (p. ej: PCR, secuenciación del ADN) de especímenes antiguos es susceptible de ser falsificada por la presencia de una contaminación más reciente. Actualmente sabemos que la contaminación que provoca la amplificación de secuencias ''no auténticas" procede de las siguientes fuentes: (i) las biomoléculas humanas provienen de la persona que realiza el experimento genético o incluso también del arqueólogo u otras personas que previamente hayan tenido contacto con el espécimen; (ii) de secuencias de ADN edáficas derivadas básicamente del crecimiento bacterial o fúngico en el seno del espécimen. La tercera fuente de contaminación puede surgir de las substancias (iii) empleadas para la conservación del espécimen. El objetivo de este artículo consiste en aportar una serie de consejos sobre el modo correcto para tratar las muestras de material óseo prehistórico, en el caso que se pretenda realizar ulteriores exámenes biomoleculares. Con esta finalidad presentamos detalladamente las precauciones y condiciones necesarias de trabajo, así como una explicación de cómo puede controlarse la contaminación del ADN. Resulta prometedora la introducción de las herramientas y de la metodología paleogenéticas en el marco de la investigación arqueológica. Tal y como se observa en la mayoría de las publicaciones recientes, existe un gran número de cuestiones que pueden beneficiarse del estudio paleogenético. Cabe citar, entre otras, por ejemplo, los métodos para la reconstrucción de las estructuras sociales en la Prehistoria (a saber, la determinación de las relaciones de parentesco), o ciertas aplicaciones de la investigación paleopatológica. Por otra parte, el repertorio de técnicas disponibles para el análisis del ADN fósil, incluso del que está altamente degradado, permite elucidar, y en algunos casos dar respuesta, a antiguas cuestiones de interés general sobre la evolución de la humanidad. Con la ayuda de métodos más extensos y de un conjunto de técnicas de ADNa optimizadas eficazmente, la paleogenética, en tanto que joven disciplina, se establecerá por sí misma como un instrumento importante de la investigación arqueológica y antropológica. Sin duda alguna, la colaboración científica internacional permitiría una mayor y mejor aceptación de estos métodos en el seno de las disciplinas implicadas, así como fuera de ellas y, en consecuencia, llevaría a una mejor cualidad de la investigación dentro de las ciencias paleo genéticas. Cabe desear que en un futuro próximo se intensifique el intercambio de conocimientos y experiencias entre los grupos de trabajo que estudian las sociedades antiguas

Detection of Bursts from FRB 121102 with the Effelsberg 100-m Radio Telescope at 5 GHz and the Role of Scintillation

FRB 121102, the only repeating fast radio burst (FRB) known to date, was discovered at 1.4 GHz and shortly after the discovery of its repeating nature, detected up to 2.4 GHz. Here we present three bursts detected with the 100-m Effelsberg radio telescope at 4.85 GHz. All three bursts exhibited frequency structure on broad and narrow frequency scales. Using an autocorrelation function analysis, we measured a characteristic bandwidth of the small-scale structure of 6.4$\pm$1.6 MHz, which is consistent with the diffractive scintillation bandwidth for this line of sight through the Galactic interstellar medium (ISM) predicted by the NE2001 model. These were the only detections in a campaign totaling 22 hours in 10 observing epochs spanning five months. The observed burst detection rate within this observation was inconsistent with a Poisson process with a constant average occurrence rate; three bursts arrived in the final 0.3 hr of a 2 hr observation on 2016 August 20. We therefore observed a change in the rate of detectable bursts during this observation, and we argue that boosting by diffractive interstellar scintillations may have played a role in the detectability. Understanding whether changes in the detection rate of bursts from FRB 121102 observed at other radio frequencies and epochs are also a product of propagation effects, such as scintillation boosting by the Galactic ISM or plasma lensing in the host galaxy, or an intrinsic property of the burst emission will require further observations.Comment: Accepted to ApJ. Minor typos correcte

Historical seismicity and rates of crustal deformation along the margins of the Ordos block, north China

Earthquakes in China show an empirical relation between seismic moment (M_0) and the areal distribution of Modified Mercalli intensities VI and VIII (log M_0 = 16.66 + 0.91 log A^(VIII) and log M_0 = 14.35 + 1.16 log A^(VI), where A and M_0 are measured in squared kilometers and Newton-meter, respectively). The empirical relations may be used to estimate M_0 for historical earthquakes in China to within a factor of three, on average, when sufficient isoseismal data exist. This observation and an extensive collection of isoseismal maps are used to estimate M_0 for large earthquakes that occurred along the margins of the Ordos block during the last 700 yr. Focal parameters of the historical events are inferred from the orientation and displacements across Quaternary faults. Average rates of crustal deformation are then estimated from the 700-yr historical record with formulas that relate the occurrence rate of seismic moment in a region to rates of crustal strain. The Shanxi and northern Ningxia graben systems are situated along the eastern and northwestern edges of the Ordos block, respectively. Normal faults in the two systems trend northeasterly and are characterized by a component of right-lateral slip. The deformation resulting from slip during earthquakes in each of the respective fault systems is estimated at about 0.5 to 1.0 mm/yr of both right-lateral shear and north by northwest extension. The Weihe graben system bounds the southern edge of the Ordos block, strikes easterly and conjugate to the Shanxi and northern Ningxia fault systems, and exhibits left-lateral normal fault displacements. The average rate of deformation across Weihe is described by about 1.0 mm/yr of north by northwest extension and 1.5 mm/yr left-lateral east-west shear. The Hetao fault system delineates the northern edge of the Ordos block and displays Quaternary faults similar in orientation and mechanism to that observed in Weihe. Although mapped faults in Hetao exhibit evidence of Quaternary displacement, crustal deformation rates are not estimated because there exists no historical record of large earthquakes in the area. In southern Ningxia, at the southwest boundary of the Ordos block, deformation occurs by slip on left-lateral strike-slip faults oriented in an easterly azimuth and thrust faults with strikes ranging from southeast to south. The average deformation rate in southern Ningxia is found to be about 4.0 mm/yr of east by northeast contraction and 10.0 mm/yr of left-lateral shear. Deformation of each of the fault systems is consistent with a regional compressive stress that trends northeast and results in an average of about 3.0 mm/yr each of contraction at N70°E and extension of N160°E across the entire region. Inasmuch as uncertainties in estimates of M0 for historical earthquakes are about a factor of three, a similar uncertainty is attached to rates of crustal strain determined in this manner

The large-scale disk fraction of brown dwarfs in the Taurus cloud as measured with Spitzer

Aims. The brown dwarf (BD) formation process has not yet been completely understood. To shed more light on the differences and similarities between star and BD formation processes, we study and compare the disk fraction among both kinds of objects over a large angular region in the Taurus cloud. In addition, we examine the spatial distribution of stars and BD relative to the underlying molecular gas Methods. In this paper, we present new and updated photometry data from the Infrared Array Camera (IRAC) aboard the Spitzer Space Telescope on 43 BDs in the Taurus cloud, and recalculate of the BD disk fraction in this region. We also useed recently available CO mm data to study the spatial distribution of stars and BDs relative to the cloud's molecular gas. Results. We find that the disk fraction among BDs in the Taurus cloud is 41 \pm 12%, a value statistically consistent with the one among TTS (58 \pm 9%). We find that BDs in transition from a state where they have a disk to a diskless state are rare, and we study one isolated example of a transitional disk with an inner radius of \approx 0.1 AU (CFHT BD Tau 12, found via its relatively small mid-IR excess compared to most members of Taurus that have disks. We find that BDs are statistically found in regions of similar molecular gas surface density to those associated with stars. Furthermore, we find that the gas column density distribution is almost identical for stellar and substellar objects with and without disks.Comment: 8 page, 6 figures, Accepted in Astronomy & Astrophysics

Twisted mass fermions: neutral pion masses from disconnected contributions

Twisted mass fermions allow light quarks to be explored but with the consequence that there are mass splittings, such as between the neutral and charged pion. Using a direct calculation of the connected neutral pion correlator and stochastic methods to evaluate the disconnected correlations, we determine the neutral pion mass. We explore the dependence on lattice spacing and quark mass in quenched QCD. For dynamical QCD, we determine the sign of the splitting which is linked, via chiral PT, to the nature of the phase transition at small quark mass.Comment: 6 pages, poster (hadron spectrum and quark masses) at Lattice 2005,Dublin, July 25-3

Stick-Slip Motion and Phase Transition in a Block-Spring System

We study numerically stick slip motions in a model of blocks and springs being pulled slowly. The sliding friction is assumed to change dynamically with a state variable. The transition from steady sliding to stick-slip is subcritical in a single block and spring system. However, we find that the transition is continuous in a long chain of blocks and springs. The size distribution of stick-slip motions exhibits a power law at the critical point.Comment: 8 figure

Conformal invariance: from Weyl to SO(2,d)

The present work deals with two different but subtilely related kinds of conformal mappings: Weyl rescaling in $d>2$ dimensional spaces and SO(2,d) transformations. We express how the difference between the two can be compensated by diffeomorphic transformations. This is well known in the framework of String Theory but in the particular case of $d=2$ spaces. Indeed, the Polyakov formalism describes world-sheets in terms of two-dimensional conformal field theory. On the other hand, B. Zumino had shown that a classical four-dimensional Weyl-invariant field theory restricted to live in Minkowski space leads to an SO(2,4)-invariant field theory. We extend Zumino's result to relate Weyl and SO(2,d) symmetries in arbitrary conformally flat spaces (CFS). This allows us to assert that a classical $SO(2,d)$-invariant field does not distinguish, at least locally, between two different $d$-dimensional CFSs.Comment: 5 pages, no figures. There are slight modifications to match with the published versio

Photometric Monitoring of the Gravitationally Lensed Ultraluminous BAL Quasar APM08279+5255

We report on one year of photometric monitoring of the ultraluminous BAL quasar APM 08279+5255. The temporal sampling reveals that this gravitationally lensed system has brightened by ~0.2 mag in 100 days. Two potential causes present themselves; either the variability is intrinsic to the quasar, or it is the result of microlensing by stars in a foreground system. The data is consistent with both hypotheses and further monitoring is required before either case can be conclusively confirmed. We demonstrate, however, that gravitational microlensing can not play a dominant role in explaining the phenomenal properties exhibited by APM 08279+5255. The identification of intrinsic variability, coupled with the simple gravitational lensing configuration, would suggest that APM 08279+5255 is a potential golden lens from which the cosmological parameters can be derived and is worthy of a monitoring program at high spatial resolution.Comment: 17 pages, with 2 figures. Accepted for publication in P.A.S.

GI2T/REGAIN spectro-interferometry with a new infrared beam combiner

We have built an infrared beam combiner for the GI2T/REGAIN interferometer of the Observatoire de la Cote d'Azur. The beam combiner allows us to record spectrally dispersed Michelson interference fringes in the near-infrared J-, H- or K-bands. The beam combiner has the advantage that Michelson interferograms can simultaneously be recorded in about 128 different spectral channels. The tilt of the spectrally dispersed fringes is a measure of the instantaneous optical path difference. We present the optical design of the beam combiner and GI2T/REGAIN observations of the Mira star R Cas with this beam combiner in the spectral range of 2.00 micron - 2.18 micron (observations on 22 and 25 August 1999; variability phase 0.08; V-magnitude approx. 6; seven baselines between 12m and 24m; reference stars Vega and Beta Peg). The spectrograph of the beam combiner consists of an anamorphotic cylindrical lens system, an image plane slit, and a grism. A system of digital signal processors calculates the ensemble average power spectrum of the spectrally dispersed Michelson interferograms and the instantaneous optical path difference error in real time. From the observed R Cas visibilities at baselines 12.0m, 13.8m and 13.9m, a 2.1 micron uniform-disk diameter of 25.3mas +/-3.3mas was derived. The unusually high visibility values at baselines >16m show that the stellar surface of R Cas is more complex than previously assumed. The visibility values at baselines >16m can be explained by high-contrast surface structure on the stellar surface of R Cas or other types of unexpected center-to-limb variations. The R Cas observations were compared with theoretical Mira star models yielding a linear Rosseland radius of 276Rsun +/-66Rsun and an effective temperature of 2685K+/-238K for R Cas at phase 0.08.Comment: 10 pages, 6 figures, see also http://www.mpifr-bonn.mpg.de/div/speckle, SPIE conf 4006 "Interferometry in Optical Astronomy", in pres