355 research outputs found
The Piola-Kirchhoff stress may depend linearly on the deformation gradient
No full textIt is shown that, whenever the residual stress does not vanish, the response function delivering the Piola-Kirchhoff stress in terms of the deformation gradient may be genuinely linear, and yet independent of the observer; moreover, an explicit representation formula for such a function is obtained
Exploring the feedback of asymmetric jets on the orbital motions in protoplanetary disks
No full textProtoplanetary disks are often associated with powerful bipolar jets. In most cases the two jet lobes carry a different amount of linear momentum. We investigate the dynamical feedback of such an asymmetric jet on its launch region in the disk. We adopt a Hamiltonian formulation and solve for the departures from the initial Keplerian orbits with a symplectic integrator. The back-reaction effect produces a shift in the position of the orbits toward the weaker jet lobe, deforming the shape of the inner disk. The loci of the orbits oscillate quasiperiodically, alternating radial and vertical displacements. The amplitude is a small fraction of the disk thickness, and is proportional to the momentum imbalance. Such motions can contribute to the onset of turbulence, and to the mixing of molecular material
A Deployable tensegrity structure, especially for space applications
No full textThe invention relates to a deployable tensegrity structure comprising, in the deployed state, a support structure (100) having a ring shape around a longitudinal axis and comprising : - a first flexible tension member (101 ) defining a first contour of said ring shape and a second flexible tension member (102) defining a second contour of said ring;
- a first plurality of rigid compression members (103, 103', 103") extending between said first and second contours (101, 102), one end (1030,1030') of each rigid compression member of the first plurality being mounted on the first contour (101 ) whereas the other end (1031,1031 ") is not mounted on a contour and; a second plurality of rigid compression members (104, 104') extending between said first and second contours (101, 102), one end (1040') of each rigid compression member of the second plurality being mounted on the second contour
(102) whereas the other end (1041, 1041 ') is not mounted on a contour; said first and second plurality of rigid compression members (103, 103', 103" 104, 104') being arranged with a repetitive crossing pattern around the ring; - a first plurality of flexible tension members (105, 106, 107, 110, 111 ) linking each end (1030, 1030',1040') of a compression member mounted on one of said contours (101,102) to an end of another compression member which is not mounted on one of said contours and, a second plurality of flexible tension members (108, 109, 112) linking each end (1031, 1031 ", 1041, 1041 ') of a compression member which is not mounted on a contour to an end of another compression member which is also not mounted on a contour
El tractadista Guillermus de Podio: bases per a la construcció d’una biografia
No full textTwo works of music theory from the endings of the 15th Century with the name of author Guillermus de Podio are preserved: the printed Ars musicorum (València, Hagenbach and Hutz, 1495) and the manuscript Enchiridion de principiis musice discipline contra negantes illa et destruentes. Despite the great influence that this musician exerted on Spanish theorists of the 16th Century, there are only few commonly accepted data about his biography. This article pretends to offer solid foundations to build his biography. In first place, verified from speculated data in the historiography of the musician will be distinguished. Finally, new documents will clarify his identity and will reveal his work as master of chant in the catedral of Valencia.Bajo el nombre de autor de Guillermus de Podio se conservan dos obras de teoría musical de finales del siglo XV: la impresa Ars musicorum (Valencia, Hagenbach y Hutz, 1495) y el manuscrito Enchiridion de principiis musice discipline contra negantes illa et destruentes. A pesar de la gran influencia que este músico ejerció sobre los teóricos españoles del siglo XVI, son mínimos los datos biográficos generalmente aceptados por la comunidad investigadora. El presente artículo pretende ofrecer unos cimientos sólidos sobre los cuales poder construir su biografía. Con esta finalidad, se distinguen primeramente los datos contrastados de los que forman parte de la especulación en la historiografía del músico. Finalmente se aportan nuevos documentos que resuelven las dudas sobre su identidad y desvelan su magisterio en la catedral de Valencia.
[ct] Sota el nom d’autor de Guillermus de Podio es conserven dues obres de teoria musical de finals del segle XV: l’impresa Ars musicorum (València, Hagenbach i Hutz, 1495) i el manuscrit Enchiridion de principiis musice discipline contra negantes illa et destruentes. Malgrat la gran influència que aquest músic va exercir sobre els teòrics espanyols del segle XVI, són mínimes les seues dades biogràfiques generalment acceptades per la comunitat investigadora. El present article pretén oferir uns fonaments sòlids sobre els quals poder construir la seua biografia. Amb aquesta fi nalitat, es distingeixen primerament les dades contrastades de les que formen part de l’especulació en la historiografia del músic. Finalment s’aporten nous documents que resolen els dubtes sobre la seua identitat i desvelen el seu magisteri en la seu de València
Evaluation of meiotic abnormalities and pollen viability in aposporous and sexual tetraploid Paspalum notatum (Poaceae)
No full textWe analyzed anaphase I configurations and pollen viability in aposporous and sexual tetraploid (2n = 4x = 40) cytotypes of Paspalum notatum. Five natural aposporous accessions and three experimentally obtained sexual individuals were used. In addition, 16 (8aposporous and 8 sexual) F1 hybrids, previously classified by their mode of reproduction, were analyzed. Cytogenetic observations revealed normal and abnormal anaphase I configurations in both aposporous and sexual genotypes. Anaphase I abnormalities were mainly laggard chromosomes, chromatin bridges, and micronuclei. On average, 44.36 % of aposporous meiocytes and 29.66 % of sexual ones showed abnormal anaphase I configurations. The total numbers of normal and abnormal anaphase I were highly significantly different between aposporous and sexual strains. The pollen viability test indicated that aposporous individuals had significantly more non-viable pollen than sexual ones; a positive correlation (r = 0.71; r2 = 0.50) between the variables was detected. Analysis of aposporous and sexual hybrids confirmed differences in the numbers of normal and abnormal anaphase I patterns in the aposporous and sexual parents. However, similar proportions of viable pollen were produced by both groups of hybrids. In this case, the variables were not correlated (r = 0.23; r2 = 0.05). Data from this study indicated that aposporous strains had a genetic rearrangement affecting meiosis that was absent in the experimentally obtained sexual individuals and that it was transmitted to the progeny. The possible association between meiotic abnormalities and the inheritance of apospory is discussed.Fil: Podio, Maricel. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias. Laboratorio de Biología Molecular; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; ArgentinaFil: Siena, Lorena Adelina. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias. Laboratorio de Biología Molecular; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Hojsgaard, Diego Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; Argentina. Universitat of Gottingen; AlemaniaFil: Stein, Juliana. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias. Laboratorio de Biología Molecular; ArgentinaFil: Quarin, Camilo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; ArgentinaFil: Ortiz, Juan Pablo Amelio. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias. Laboratorio de Biología Molecular; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; Argentin
ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT) : I. CO, CS, CN, and H2CO around DG Tau B
No full textThe chemical composition of planets is determined by the distribution of the various molecular species in the protoplanetary disk at the time of their formation. To date, only a handful of disks have been imaged in multiple spectral lines with high spatial resolution. As part of a small campaign devoted to the chemical characterization of disk-outflow sources in Taurus, we report on new ALMA Band 6 (~1.3 mm) observations with ~0.15′′ (20 au) resolution toward the embedded young star DG Tau B. Images of the continuum emission reveals a dust disk with rings and, putatively, a leading spiral arm. The disk, as well as the prominent outflow cavities, are detected in CO, H2CO, CS, and CN; instead, they remain undetected in SO2, HDO, and CH3OH. From the absorption of the back-side outflow, we inferred that the disk emission is optically thick in the inner 50 au. This morphology explains why no line emission is detected from this inner region and poses some limitations toward the calculation of the dust mass and the characterization of the inner gaseous disk. The H2CO and CS emission from the inner 200 au is mostly from the disk, and their morphology is very similar. The CN emission significantly differs from the other two molecules as it is observed only beyond 150 au. This ring-like morphology is consistent with previous observations and the predictions of thermochemical disk models. Finally, we constrained the disk-integrated column density of all molecules. In particular, we found that the CH3OH/H2CO ratio must be smaller than ~2, making the methanol non-detection still consistent with the only such ratio available from the literature (1.27 in TW Hya)
Physical properties of the jet from DG Tauri on sub-arcsecond scales with HST/STIS
No full textContext. Stellar jets are believed to play a key role in star formation, but the question of how they originate is still being debated. Aims. We derive the physical properties at the base of the jet from DG Tau both along and across the flow and as a function of velocity. Methods. We analysed seven optical spectra of the DG Tau jet, taken with the Hubble Space Telescope Imaging Spectrograph. The spectra were obtained by placing a long-slit parallel to the jet axis and stepping it across the jet width. The resulting position-velocity diagrams in optical forbidden emission lines allowed access to plasma conditions via calculation of emission line ratios. In this way, we produced a 3D map (2D in space and 1D in velocity) of the jet's physical parameters i.e. electron density ne, hydrogen ionisation fraction xe, and total hydrogen density nH. The method used is a new version of the BE-technique. Results. A fundamental improvement is that the new diagnostic method allows us to overcome the upper density limit of the standard [S≠ii] diagnostics. As a result, we find at the base of the jet high electron density, ne ~ 105, and very low ionisation, xe ~ 0.02-0.05, which combine to give a total density up to n H ~ 3 × 106. This analysis confirms previous reports of variations in plasma parameters along the jet, (i.e. decrease in density by several orders of magnitude, increase of xe from 0.05 to a plateau at 0.7 downstream at 2" from the star). Furthermore, a spatial coincidence is revealed between sharp gradients in the total density and supersonic velocity jumps. This strongly suggests that the emission is caused by shock excitation. No evidence was found of variations in the parameters across the jet, within a given velocity interval. The position-velocity diagrams indicate the presence of both fast accelerating gas and slower, less collimated material. We derive the mass outflow rate, Mj, in the blue-shifted lobe in different velocity channels, that contribute to a total of Mj ~ 8±4 × 10-9 M⊙yr-1. We estimate that a symmetric bipolar jet would transport at the low and intermediate velocities probed by rotation measurements, an angular momentum flux of L̇ j ~ 2.9 ± 1.5 × 10-6 M ⊙yr-1 AU km s-1. We discuss implications of these findings for jet launch theories. Conclusions. The derived properties of the DG Tau jet are demonstrated to be consistent with magneto-centrifugal theory. However, non-stationary modelling is required in order to explain all of the features revealed at high resolution
Tensegrity rings for deployable space antennas: Concept, design, analysis, and prototype testing
No full textIn this paper, an extended version of Zolesi et al. (Proceedings of the 42nd ICES (AIAA 2012-3601), San Diego, CA, 2012), we describe a tensegrity ring of innovative conception for deployable space antennas. Large deployable space structures are mission-critical technologies for which deployment failure cannot be an option. The difficulty to fully reproduce and test on ground the deployment of large systems dictates the need for extremely reliable architectural concepts. In 2010, ESA promoted a study focused on the pre-development of breakthrough architectural concepts offering superior reliability. This study, which was performed as an initiative of ESA Small Medium Enterprises Office by Kayser Italia at its premises in Livorno (Italy), with Università di Roma TorVergata (Rome, Italy) as sub-contractor and consultancy from KTH (Stockholm, Sweden), led to the identification of an innovative large deployable structure of tensegrity type, which achieves the required reliability because of a drastic reduction in the number of articulated joints in comparison with non-tensegrity architectures. The identified target application was in the field of large space antenna reflectors. The project focused on the overall architecture of a deployable system and the related design implications. With a view toward verifying experimentally the performance of the deployable structure, a reduced-scale breadboard model was designed and manufactured. A gravity off-loading system was designed and implemented, so as to check deployment functionality in a 1-g environment. Finally, a test campaign was conducted, to validate the main design assumptions as well as to ensure the concept’s suitability for the selected target application. The test activities demonstrated satisfactory stiffness, deployment repeatability, and geometric precision in the fully deployed configuration. The test data were also used to validate a finite element model, which predicts a good static and dynamic behavior of the full-scale deployable structure
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