Hipparcos-VLBI: the way towards an ideal primary celestial system

The astrometric satellite HIPPARCOS of the European Space Agency (ESA) was launched in August 1989. As a consequence of a technical defect, the satellite could not reach the operational geostationary orbit, and it is now in an extremely elliptical orbit around the Earth. Despite the bad observing conditions, HIPPARCOS began to develop the new observing program, and its results promise to be of a higher quality than those expected for the nominal mission. The celestial frame of HIPPARCOS satellite will be materialized by the positions and proper motions of about 120000 stars relative to arbitrary origins. The astrometric precision of its frame will be one order of magnitude higher than that of the optical astronomy from Earth. The precision expected for HIPPARCOS nominal mission is 0.002" for the positions, yearly proper motion and parallaxes, decreasing towards the limit magnitude of the satellite (m=13). However, this precision will be intrinsic to HIPPARCOS sphere, and it will be completely achieved only if its reference frame becomes inertial by means of its link to another stable, non-rotating frame of similar quality. The technique of VLBI determines the coordinates at the level of 0.001" (see Arias, this volume). The quasars and the galactic nuclei are not affected by apparent proper motions, and therefore they constitute the most stable celestial reference frame available at present. The link between the VLBI and HIPPARCOS reference frames will: a) stop the rotation of the reference frame produced by the satellite, b) densify the extragalactic reference frame in optical frequencies, c) unify the radio and optical coordinate systems and allow direct comparison of the images of the celestial objects obtained with radio and optical techniques with the same angular resolution. In absence of regional deformations, the link between two frames with the same origin can be mathematically expressed by a simple rotation. If the relative orientation of the frames evolve linearly with time, the link is given by a global rotation at an arbitrary epoch, and by the components of the angular velocity of rotation of one frame relative to the other. The method to link the VLBI and HIPPARCOS frames has been developed by Arias (1990). We have studied the link between HIPPARCOS and VLBI frames on the basis of observations of radio stars. We have simulated HIPPARCOS observations in a realistic way. Lastrade et al. (1988) and White et al. (1990) provided the VLBI positions and proper motions of 14 stars between +62° and -75° in declination. The relative orientation at the initial epoch is determined with a precision at the level of 0.001". The precision of the components of the angular velocity is in the range 0.0007" - 0.0009". Concerning the distribution of objects, the inclusion of radio stars at negative declination, with uncertainties several times greater than those in the North, does not improve the link and introduces a bias in the angles of orientation of the frames.Asociación Argentina de Astronomí

Determinación de las componentes principales del movimiento polar

El desplazamiento del eje de rotación terrestre se produce como consecuencia de la superposición de movimientos de distintos períodos provocados por diferentes causas, siendo los principales el período de Chandler (14 meses) y el período anual. Se analizaron las periodicidades en las coordenadas x, y del polo y en la incógnita z. Habiendo sido éstas calculadas a partir de observaciones realizadas en Punta Indio, Mount Stromlo, San Juan y Santiago de Chile. Los valores calculados del período anual y de Chandler, como así también sus amplitudes, concuerdan con los obtenidos mediante otros procedimientos.Asociación Argentina de Astronomí

Population, Land Use and Deforestation in the Pan Amazon Basin: a Comparison of Brazil, Bolivia, Colombia, Ecuador, Perú and Venezuela

This paper discusses the linkages between population change, land use, and deforestation in the Amazon regions of Brazil, Bolivia, Colombia, Ecuador, Perú, and Venezuela. We begin with a brief discussion of theories of population–environment linkages, and then focus on the case of deforestation in the PanAmazon. The core of the paper reviews available data on deforestation, population growth, migration and land use in order to see how well land cover change reflects demographic and agricultural change. The data indicate that population dynamics and net migration exhibit to deforestation in some states of the basin but not others. We then discuss other explanatory factors for deforestation, and find a close correspondence between land use and deforestation, which suggests that land use is loosely tied to demographic dynamics and mediates the influence of population on deforestation. We also consider national political economic contexts of Amazon change in the six countries, and find contrasting contexts, which also helps to explain the limited demographic-deforestation correspondence. The paper closes by noting general conclusions based on the data, topics in need of further research and recent policy proposals.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42720/1/10668_2003_Article_6977.pd

Whole-genome sequencing reveals host factors underlying critical COVID-19

Critical COVID-19 is caused by immune-mediated inflammatory lung injury. Host genetic variation influences the development of illness requiring critical care1 or hospitalization2,3,4 after infection with SARS-CoV-2. The GenOMICC (Genetics of Mortality in Critical Care) study enables the comparison of genomes from individuals who are critically ill with those of population controls to find underlying disease mechanisms. Here we use whole-genome sequencing in 7,491 critically ill individuals compared with 48,400 controls to discover and replicate 23 independent variants that significantly predispose to critical COVID-19. We identify 16 new independent associations, including variants within genes that are involved in interferon signalling (IL10RB and PLSCR1), leucocyte differentiation (BCL11A) and blood-type antigen secretor status (FUT2). Using transcriptome-wide association and colocalization to infer the effect of gene expression on disease severity, we find evidence that implicates multiple genes—including reduced expression of a membrane flippase (ATP11A), and increased expression of a mucin (MUC1)—in critical disease. Mendelian randomization provides evidence in support of causal roles for myeloid cell adhesion molecules (SELE, ICAM5 and CD209) and the coagulation factor F8, all of which are potentially druggable targets. Our results are broadly consistent with a multi-component model of COVID-19 pathophysiology, in which at least two distinct mechanisms can predispose to life-threatening disease: failure to control viral replication; or an enhanced tendency towards pulmonary inflammation and intravascular coagulation. We show that comparison between cases of critical illness and population controls is highly efficient for the detection of therapeutically relevant mechanisms of disease

Bovine and human lactoferricin peptides: chimeras and new cyclic analogs

Lactoferrin (LF) is an important antimicrobial and immune regulatory protein present in neutrophils and most exocrine secretions of mammals. The antimicrobial activity of LF has been related to the presence of an antimicrobial peptide sequence, called lactoferricin (LFcin), located in the N-terminal region of the protein. The antimicrobial activity of bovine LFcin is considerably stronger than the human version. In this work, chimera peptides combining segments of bovine and human LFcin were generated in order to study their antimicrobial activity and mechanism of action. In addition, the relevance of the conserved disulfide bridge and the resulting cyclic structure of both LFcins were analyzed by using "click chemistry" and sortase A-catalyzed cyclization of the peptides. The N-terminal region of bovine LFcin (residues 17-25 of bovine LF) proved to be very important for the antimicrobial activity of the chimera peptides against E. coli, when combined with the C-terminal region of human LFcin. Similarly the cyclic bovine LFcin analogs generated by "click chemistry" and sortase A preserved the antimicrobial activity of the original peptide, showing the significance of these two techniques in the design of cyclic antimicrobial peptides. The mechanism of action of bovine LFcin and its active derived peptides was strongly correlated with membrane leakage in E. coli and up to some extent with the ability to induce vesicle aggregation. This mechanism was also preserved under conditions of high ionic strength (150 mM NaCl) illustrating the importance of these peptides in a more physiologically relevant system