2,638 research outputs found
Analysis of pressure blips in aft-finocyl solid rocket motor
Ballistic anomalies have frequently occurred during the firing of several solid rocket motors (SRMs) (Inertial Upper Stage, Space Shuttle Redesigned SRM (RSRM) and Titan IV SRM Upgrade (SRMU)), producing even relevant and unexpected variations of the SRM pressure trace from its nominal profile. This paper has the purpose to provide a numerical analysis of the following possible causes of ballistic anomalies in SRMs: an inert object discharge, a slag ejection, and an unexpected increase in the propellant burning rate or in the combustion surface. The SRM configuration under investigation is an aft-finocyl SRM with a first-stage/small booster design. The numerical simulations are performed with a quasi-one-dimensional (Q1D) unsteady model of the SRM internal ballistics, properly tailored to model each possible cause of the ballistic anomalies. The results have shown that a classification based on the head-end pressure (HEP) signature, relating each other the HEP shape and the ballistic anomaly cause, can be made. For each cause of ballistic anomalies, a deepened discussion of the parameters driving the HEP signatures is provided, as well as qualitative and quantitative assessments of the resultant pressure signals
Elastic moduli approximation of higher symmetry for the acoustical properties of an anisotropic material
The issue of how to define and determine an optimal acoustical fit to a set
of anisotropic elastic constants is addressed. The optimal moduli are defined
as those which minimize the mean squared difference in the acoustical tensors
between the given moduli and all possible moduli of a chosen higher material
symmetry. The solution is shown to be identical to minimizing a Euclidean
distance function, or equivalently, projecting the tensor of elastic stiffness
onto the appropriate symmetry. This has implications for how to best select
anisotropic constants to acoustically model complex materials.Comment: 20 page
Revealing the nature of magnetic shadows with numerical 3D-MHD simulations
We investigate the interaction of magneto-acoustic waves with magnetic
network elements with the aim of finding possible signatures of the magnetic
shadow phenomenon in the vicinity of network elements. We carried out
three-dimensional numerical simulations of magneto-acoustic wave propagation in
a model solar atmosphere that is threaded by a complexly structured magnetic
field, resembling that of a typical magnetic network element and of
internetwork regions. High-frequency waves of 10 mHz are excited at the bottom
of the simulation domain. On their way through the upper convection zone and
through the photosphere and the chromosphere they become perturbed, refracted,
and converted into different mode types. We applied a standard Fourier analysis
to produce oscillatory power-maps of the line-of-sight velocity. In the power
maps of the upper photosphere and the lower chromosphere, we clearly see the
magnetic shadow: a seam of suppressed power surrounding the magnetic network
elements. We demonstrate that this shadow is linked to the mode conversion
process and that power maps at these height levels show the signature of three
different magneto-acoustic wave modes.Comment: Astronomy & Astrophysics Letters, in print 4 pages, 4 figure
Radiative transfer effects on Doppler measurements as sources of surface effects in sunspot seismology
We show that the use of Doppler shifts of Zeeman sensitive spectral lines to
observe wavesn in sunspots is subject to measurement specific phase shifts
arising from, (i) altered height range of spectral line formation and the
propagating character of p mode waves in penumbrae, and (ii) Zeeman broadening
and splitting. We also show that these phase shifts depend on wave frequencies,
strengths and line of sight inclination of magnetic field, and the polarization
state used for Doppler measurements. We discuss how these phase shifts could
contribute to local helioseismic measurements of 'surface effects' in sunspot
seismology.Comment: 12 pages, 4 figures, Accepted for publication in the Astrophysical
Journal Letter
Fluxos, Encontros e Dispersões: Agenciamento Entre Arte e Clínica
Buscamos cartografar os fluxos artísticos que povoaram um CAPS para
cuidados referentes ao uso de álcool e outras drogas de um município do
Espírito Santo entre os anos de 2006 e 2016 e, com eles, delinear uma
paisagem coletiva, relacionando-os com alguns momentos da arte e da
clínica a partir do século XIX até os dias de hoje. Esta relação, por sua vez,
visa apontar, ainda que de maneira circunscrita, a política de saúde mental
que se fez tangenciando a arte ao longo dos anos, colocando em evidência
as forças manicomiais que se fazem ainda presentes, assim como as
resistências que são criadas para enfrentá-las. Evidencia
alguns momentos
de ampliação da clínica e seus agenciamentos com as artes moderna e
contemporânea, com a construção e regulamentação das oficinas artísticas
nos serviços de saúde mental, procurando tornar visíveis fluxos emergentes
que apontam, por sua vez, para uma necessidade de desinstitucionalização
da arte, assim como a territorialização de outros caminhos.
Palavras chave: Arte - saúde mental. Álcool e outras drogas - CAPS
Numerical test of the Schoemberg-Muir theory
The Schoenberg-Muir theory states that an equivalent, homogeneous and anisotropic medium can be constructed from a layered medium composed of several thin layers, each anisotropic, under the assumption of stationarity. To test the theory we considered single transversely isotropic layers with different orientations of the symmetry axis and performed numerical simulations of wave propagation with a full-wave solver. The equivalent media have orthorhombic and monoclinic symmetries, respectively. The theory performed very well from the kinematical and dynamical points of view, even for strong anisotropy and layers described by media whose symmetry axes have different orientations.Fil: Carcione, José M.. Istituto Nazionale di Oceanografia e di Geofisica Sperimentale; ItaliaFil: Picotti, Stefano. Istituto Nazionale di Oceanografia e di Geofisica Sperimentale; ItaliaFil: Cavallini, Fabio. Istituto Nazionale di Oceanografia e di Geofisica Sperimentale; ItaliaFil: Santos, Juan Enrique. Universidad de Buenos Aires. Facultad de Ingeniería. Instituto del Gas y del Petróleo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
Genome-wide analysis of LTR retrotransposon diversity and its impact on the evolution of the genus Helianthus (L.)
Background: Genome divergence by mobile elements activity and recombination is a continuous process that plays a key role in the evolution of species. Nevertheless, knowledge on retrotransposon-related variability among species belonging to the same genus is still limited. Considering the importance of the genus Helianthus, a model system for studying the ecological genetics of speciation and adaptation, we performed a comparative analysis of the repetitive genome fraction across ten species and one subspecies of sunflower, focusing on long terminal repeat retrotransposons at superfamily, lineage and sublineage levels. Results: After determining the relative genome size of each species, genomic DNA was isolated and subjected to Illumina sequencing. Then, different assembling and clustering approaches allowed exploring the repetitive component of all genomes. On average, repetitive DNA in Helianthus species represented more than 75% of the genome, being composed mostly by long terminal repeat retrotransposons. Also, the prevalence of Gypsy over Copia superfamily was observed and, among lineages, Chromovirus was by far the most represented. Although nearly all the same sublineages are present in all species, we found considerable variability in the abundance of diverse retrotransposon lineages and sublineages, especially between annual and perennial species. Conclusions: This large variability should indicate that different events of amplification or loss related to these elements occurred following species separation and should have been involved in species differentiation. Our data allowed us inferring on the extent of interspecific repetitive DNA variation related to LTR-RE abundance, investigating the relationship between changes of LTR-RE abundance and the evolution of the genus, and determining the degree of coevolution of different LTR-RE lineages or sublineages between and within species. Moreover, the data suggested that LTR-RE abundance in a species was affected by the annual or perennial habit of that species
Technical characteristics can make the difference in a surgical linear stapler. or not?
Background Anastomotic leak (AL) after gastrointestinal surgery is a severe complication associated with relevant short- and long-term sequelae. Most of the anastomosis are currently performed with a surgical stapler that is required to have appropriate characteristics to guarantee good performances. The aim of our study was to evaluate, in the laboratory, pressure resistance and tensile strength of anastomosis performed with different surgical linear staplers, available in the market. Materials and methods We have been studying three linear staplers, with diverse cartridges and staple heights, of three different companies, used for gastrointestinal anastomosis and gastric or intestinal closure. We performed 50 anastomosis for each device, with the pertinent different cartridges, on fresh pig intestine, for a total of 350 anastomosis, then injected saline solution and recorded the pressure that provokes a leak on the staple line. There were no statistically significant differences between the mean pressure necessary to induce an AL in the various instruments (P > 0.05). For studying the tensile strength, we performed a total of 350 anastomosis with the different linear staplers on a special strong paper (Tyvek), then recorded the maximal tensile force that could open the anastomosis. Results There were no statistically significant differences between the different staplers about the strength necessary to open the staple line (P > 0.05). Conclusions we demonstrated that different linear staplers of three companies available in the market give comparable anastomotic pressure resistance and tensile strength. This might suggest that small dissimilarities between different devices are not involved, at least as major parameters, in AL etiology
Nonlinear response of single-molecule nanomagnets: equilibrium and dynamical
We present an experimental study of the {\em nonlinear} susceptibility of
Mn single-molecule magnets. We investigate both their
thermal-equilibrium and dynamical nonlinear responses. The equilibrium results
show the sensitivity of the nonlinear susceptibility to the magnetic
anisotropy, which is nearly absent in the linear response for axes distributed
at random. The nonlinear dynamic response of Mn was recently found to be
very large and displaying peaks reversed with respect to classical
superparamagnets [F. Luis {\em et al.}, Phys. Rev. Lett. {\bf 92}, 107201
(2004)]. Here we corroborate the proposed explanation -- strong field
dependence of the relaxation rate due to the detuning of tunnel energy levels.
This is done by studying the orientational dependence of the nonlinear
susceptibility, which permits to isolate the quantum detuning contribution.
Besides, from the analysis of the longitudinal and transverse contributions we
estimate a bound for the decoherence time due to the coupling to the phonon
bath.Comment: 13 pages, 8 figures, resubmitted to Phys. Rev. B with minor change
- …