Pseudoseisuropsis nehuen

Fotografía del cráneo de Pseudoseisuropsis nehuen Noriega 1991, un ave fósil, pariente lejano de los chincheros, de la Formación Miramar (Buenos Aires, Argentina), de aproximadamente 2,3 millones de años atrás (arriba). Modelo 3D del cráneo y sus estructuras internas realizado a partir de microtomografías de rayos X del ejemplar (abajo). Celeste: cerebro; rosa: oído interno; rojo: carótidas; amarillo: nervios. Escala: 5 mm

Additively Manufactured Carbon Fiber- Reinforced Thermoplastic Composite Mold Plates For Injection Molding Process

Polymer injection molding processes have been used to create high-volume parts quickly and efficiently. Injection molding uses mold plates that are traditionally made of very hard tool steels, such as P20 steel, which is extremely heavy and has very long lead times to build new molds. In this study, composite-based additive manufacturing (CBAM) was used to create mold plates using long-fiber carbon fiber and polyether ether ketone (PEEK). These mold plates were installed in an injection molding machine, and rectangular flat plates were produced using Lustran 348 acrylonitrile butadiene styrene (ABS). Tensile and flexural testing was performed on these parts as well as parts produced using traditional P20 steel mold plates with the same geometry to compare the performance of the different mold plates. The parts produced using the carbon fiber mold plates were within 5% of the tensile strength and 10% of the flexural strength of the traditionally manufactured parts. However, the parts produced using the carbon fiber mold plates required additional cooling time due to the lower conductivity of the carbon fiber composite compared to the P20 steel. This allows additively manufactured composite molds to be a good substitute for conventional molds in low-volume injection molding production

Neo and paleo virtual ornithology

La visualización y análisis de los fósiles asistido por computadoras ha revolucionado el estudio de los organismos extintos. Técnicas novedosas permiten caracterizar los restos en tres dimensiones y acceder a detalles sin precedentes. Esto ha permitido a los paleontólogos ganar importantes conocimientos sobre la anatomía, el desarrollo, la función y hasta la conservación. Las reconstrucciones digitales se pueden utilizar en análisis funcionales y en la puesta a prueba rigurosa de hipótesis sobre la paleobiología de los organismos extintos. Estos enfoques están transformando nuestra comprensión de la vida en el pasado y también de los organismos vivientes en general. El empleo de técnicas no invasivas permite la captura de grandes cantidades de datos útiles sin dañar los especímenes que se están estudiando. Debido a que los datos digitales se pueden compartir de forma instantánea y global, equipos de científicos pueden trabajar en para­lelo, acelerando el ritmo de las investigaciones. En este trabajo se ejemplifican casos en los cuales a partir de modelos virtuales se pueden abordar problemas morfológicos en aves.Visualization and analysis of fossils assisted by computers have revolutionized the study of extinct organisms. Innovative techniques allow to characterize the remains in three dimensions with unprecedented detail, allowing paleontologists to gain important knowledge about anatomy, development, function and even conservation. Digital reconstructions can be used in functional analysis and rigorous testing of hypotheses on the paleobiology of extinct organisms. These approaches are transforming our understanding about life in the past and also of living organisms in general. The use of non-invasive techniques enables capturing large amounts of data without damaging the specimens under study. As digital data can be shared instantly and globally, teams of scientists can work in parallel, accelerating research time. In this paper, cases in which virtual models were used to assess morphological problems are shown

Jaw myology and bite force of the monk parakeet (Aves, Psittaciformes)

Psittaciform birds exhibit novelties in jaw bone structure and musculature that are associated with strong bite forces. These features include an ossified arcus suborbitalis and the muscles ethmomandibularis and pseudomasseter. We analyse the jaw musculature of the monk parakeet (Myiopsitta monachus) to enable future studies aimed at understanding craniofacial development, morphology, function and evolution. We estimate bite force based on muscle dissections, physiological cross-sectional area and skull biomechanical modelling. We also compare our results with available data for other birds and traced the evolutionary origin of the three novel diagnostic traits. Our results indicate that, in Myiopsitta, (i) the arcus suborbitalis is absent and the orbit is ventrally closed by an elongate processus orbitalis and a short ligamentum suborbitale; (ii) the ethmomandibularis muscle is a conspicuous muscle with two bellies, with its origin on the anterior portion of the septum interorbitale and insertion on the medial aspect of the mandible; (iii) the pseudomasseter muscle consists of some fibers arising from the m. adductor mandibulae externus superficialis, covering the lateral surface of the arcus jugalis and attaches by an aponeurotic sheet on the processus orbitalis; (iv) a well-developed adductor mandibulae complex is present; (v) the bite force estimation relative to body mass is higher than that calculated for other non-psittaciform species; and (vi) character evolution analysis revealed that the absence of the arcus suborbitalis and the presence of the m. pseudomassseter are the ancestral conditions, and mapping is inconclusive about presence of one or two bellies of the m. ethmomandibularis.Facultad de Ciencias Naturales y Muse

Complex Spectral Variability from Intensive Multi-wavelength Monitoring of Mrk421 in 1998

We conducted a multi-frequency campaign for the TeV blazar Mrk~421 in 1998 April. The campaign started from a pronounced high amplitude flare recorded by SAX and Whipple; ASCA observation started three days later. In the X-ray data, we detected multiple flares, occuring on time scales of about one day. ASCA data clearly reveal spectral variability. The comparison of the data from ASCA, EUVE and RXTE indicates that the variability amplitudes in the low energy synchrotron component are larger at higher photon energies. In TeV Gamma-rays, large intra-day variations -- which were correlated with the X-ray flux -- were observed when results from three Cherenkov telescopes are combined. The RMS variability of TeV Gamma--rays was similar to that observed in hard X-rays, above 10 keV. The X-ray light curve reveals flares which are almost symmetric for most of cases, implying the dominant time scale is the light crossing time through the emitting region. The structure function analysis based on the continuous X-ray light curve of seven days indicates that the characteristic time scale is ~0.5 day. The analysis of ASCA light curves in various energy bands appears to show both soft (positive) and hard (negative) lags. These may not be real, as systematic effects could also produce these lags, which are all much smaller than an orbit. If the lags of both signs are real, these imply that the particle acceleration and X-ray cooling time scales are similar.Comment: 10 pages, 4 figures, accepted for publication in ApJ Letter

Flexibility along the Neck of the Neogene Terror Bird Andalgalornis steulleti (Aves Phorusrhacidae)

BACKGROUND: Andalgalornis steulleti from the upper Miocene-lower Pliocene (≈6 million years ago) of Argentina is a medium-sized patagornithine phorusrhacid. It was a member of the predominantly South American radiation of 'terror birds' (Phorusrhacidae) that were apex predators throughout much of the Cenozoic. A previous biomechanical study suggests that the skull would be prepared to make sudden movements in the sagittal plane to subdue prey. METHODOLOGY/PRINCIPAL FINDINGS: We analyze the flexion patterns of the neck of Andalgalornis based on the neck vertebrae morphology and biometrics. The transitional cervical vertebrae 5th and 9th clearly separate regions 1-2 and 2-3 respectively. Bifurcate neural spines are developed in the cervical vertebrae 7th to 12th suggesting the presence of a very intricate ligamentary system and of a very well developed epaxial musculature. The presence of the lig. elasticum interespinale is inferred. High neural spines of R3 suggest that this region concentrates the major stresses during downstrokes. CONCLUSIONS/SIGNIFICANCE: The musculoskeletal system of Andalgalornis seems to be prepared (1) to support a particularly big head during normal stance, and (2) to help the neck (and the head) rising after the maximum ventroflexion during a strike. The study herein is the first interpretation of the potential performance of the neck of Andalgalornis in its entirety and we considered this an important starting point to understand and reconstruct the flexion pattern of other phorusrhacids from which the neck is unknown

Spectrum and Variability of Mrk501 as observed by the CAT Imaging Telescope

The CAT Imaging Telescope has observed the BL Lac object Markarian 501 between March and August 1997. We report here on the variability over this time including several large flares. We present also preliminary spectra for all these data, for the low emission state, and for the largest flare.Comment: 4 pages, 4 figures, Late

Searching for TeV dark matter by atmospheric Cerenkov techniques

There is a growing interest in the possibility that dark matter could be formed of weakly interacting particles with a mass in the 100 GeV - 2 TeV range, and supersymmetric particles are favorite candidates. If they constitute the dark halo of our Galaxy, their mutual annihilations produce energetic gamma rays that could be detected using existing atmospheric \u{C}erenkov techniques.Comment: 10 pp, LaTex (3 figures available by e-mail) PAR-LPTHE 92X

Detection of Vhe Gamma-Rays from MRK 501 with the Cat Imaging Telescope

The CAT imaging telescope on the site on the former solar plant Themis has been observing gamma-rays from Mrk501 above 220 GeV in March and April 1997. This source is shown to be highly variable and the light curve is presented. The detected gamma-ray rate for the most intense flare is in excess of 10 per minute.Comment: 5 pages, 4 figures, Tex, contribution to 25th ICRC Durba