390 research outputs found
Improvement of the old reductions of irregular satellites using the first publications of the data
Program available at: http://www.imcce.fr/hosted_sites/naroo/program.htmlInternational audienceThe use of long-exposure photographic plates made the discovery of additional natural satellites possible. The first satellite to be discovered in this manner, Phoebe, was found in 1899 by W.H. Pickering. A reliable model of satellite motion must be constructed with high accurate observations and with data spreading over a period as long as possible. Some old literatures have given the positions of the natural satellites and the reference stars for determining its positions. At that time, the catalogue they used did not contain enough stars, so there were not many catalogue stars on the plates. Because of the unsatisfactory precision of the old catalogue at the epoch and the imprecise measurements on the plate, the positions of the reference stars were not very precise. At present, although we have no plates, we can reduce the positions of the natural satellites from the row data provided in these literatures with modern precise astrometric catalogues, such as PPM and UCAC2. The purpose of this work is to reduce the old observations of Phoebe (Saturn IX), in order to improve its orbit
A dynamical description of neutron star crusts
Neutron Stars are natural laboratories where fundamental properties of matter
under extreme conditions can be explored. Modern nuclear physics input as well
as many-body theories are valuable tools which may allow us to improve our
understanding of the physics of those compact objects.
In this work the occurrence of exotic structures in the outermost layers of
neutron stars is investigated within the framework of a microscopic model. In
this approach the nucleonic dynamics is described by a time-dependent mean
field approach at around zero temperature. Starting from an initial crystalline
lattice of nuclei at subnuclear densities the system evolves toward a manifold
of self-organized structures with different shapes and similar energies. These
structures are studied in terms of a phase diagram in density and the
corresponding sensitivity to the isospin-dependent part of the equation of
state and to the isotopic composition is investigated.Comment: 8 pages, 5 figures, conference NN201
Assessment of 50%-Propagation-Delay for Cascaded PCB Non-Linear Interconnect Lines for the High-Rate Signal Integrity Analysis
This paper presents an enlarged study about the 50-% propagation-time assessment of cascaded transmission lines (TLs). First and foremost, the accurate modeling and measurement technique of signal integrity (SI) for high-rate microelectronic interconnection is recalled. This model is based on the reduced transfer function extracted from the electromagnetic (EM) behavior of the interconnect line RLCG-parameters. So, the transfer function established takes into account both the frequency dispersion effects and the different propagation modes. In addition, the transfer function includes also the load and source impedance effects. Then, the SI analysis is proposed for high-speed digital signals through the developed model. To validate the model understudy, a prototype of microstrip interconnection with w = 500 µm and length d = 33 mm was designed, simulated, fabricated and tested. Then, comparisons between the frequency and time domain results from the model and from measurements are performed. As expected, good agreement between the S-parameters form measurements and the model proposed is obtained from DC to 8 GHz. Furthermore, a de-embedding method enabling to cancel out the connectors and the probe effects are also presented. In addition, an innovative time-domain characterization is proposed in order to validate the concept with a 2.38 Gbit/s-input data signal. Afterwards, the 50-% propagation-time assessment problem is clearly exposed. Consequently an extracting theory of this propagation-time with first order RC-circuits is presented. Finally, to show the relevance of this calculation, propagation-time simulations and an application to signal integrity issues are offered
Dynamical approach to spectator fragmentation in Au+Au reactions at 35 MeV/A
The characteristics of fragment emission in peripheral Au+Au
collisions 35 MeV/A are studied using the two clusterization approaches within
framework of \emph{quantum molecular dynamics} model. Our model calculations
using \emph{minimum spanning tree} (MST) algorithm and advanced clusterization
method namely \emph{simulated annealing clusterization algorithm} (SACA) showed
that fragment structure can be realized at an earlier time when spectators
contribute significantly toward the fragment production even at such a low
incident energy. Comparison of model predictions with experimental data reveals
that SACA method can nicely reproduce the fragment charge yields and mean
charge of the heaviest fragment. This reflects suitability of SACA method over
conventional clusterization techniques to investigate spectator matter
fragmentation in low energy domain.Comment: 6 pages, 5 figures, accepte
A Quasi-Classical Model of Intermediate Velocity Particle Production in Asymmetric Heavy Ion Reactions
The particle emission at intermediate velocities in mass asymmetric reactions
is studied within the framework of classical molecular dynamics. Two reactions
in the Fermi energy domain were modelized, Ni+C and Ni+Au at 34.5
MeV/nucleon. The availability of microscopic correlations at all times allowed
a detailed study of the fragment formation process. Special attention was paid
to the physical origin of fragments and emission timescales, which allowed us
to disentangle the different processes involved in the mid-rapidity particle
production. Consequently, a clear distinction between a prompt pre- equilibrium
emission and a delayed aligned asymmetric breakup of the heavier partner of the
reaction was achieved.Comment: 8 pages, 7 figures. Final version: figures were redesigned, and a new
section discussing the role of Coulomb in IMF production was include
Formação continuada em leitura: o olhar do professor para o uso de estratégias de pré-leitura na sala de aula
This article presents the Pre-Reading Activities Workshop, one of the actions of the Ler & Educar (Read & Educate) Project: in service education for teachers in Santa Catarina (OBEDUC / CAPES), developed by three universities, UFSC (FlorianĂłpolis), UFFS (ChapecĂł) and UNESC (CriciĂşma). The proposal presented in this article, based on the assumptions of Psycholinguistics, was offered to teachers who were in the schools of Ler & Educar in ChapecĂł. The aim of it was to teach the participants based on metacognitive processes involved in reading, how to use pre-reading strategies for preparing during classes as a resource to the process of reading comprehension. The methodology comprised the direct teaching of pre-reading metacognitive strategies, in the format of workshops, using audiovisual tools and interactive activities that facilitate the action / reflection on the metacognitive processes involved in reading comprehension. The meetings were an important time for pedagogical reflection on practices of those groups. The outcomes were evaluated through a questionnaire, which answers pointed to the participants' recognition of the contemporaneity, relevance and contribution of the proposal and its content to their pedagogical practices.Este artigo apresenta a Oficina de PrĂ©-leitura, uma das ações do Projeto Ler & Educar: formação continuada de professores de Santa Catarina (OBEDUC/CAPES), desenvolvido em rede pela UFSC (FlorianĂłpolis), UFFS (ChapecĂł) e UNESC (CriciĂşma). A ação apresentada neste artigo, fundamentada nos pressupostos da PsicolinguĂstica, foi oferecida aos docentes das escolas participantes do projeto, em ChapecĂł, com o objetivo de ensiná-los, a partir dos processos metacognitivos envolvidos na leitura, a utilizar estratĂ©gias de prĂ©-leitura durante as aulas, como recursos para auxiliar os alunos ao longo do processo de compreensĂŁo leitora. A metodologia compreendeu o ensino direto de estratĂ©gias metacognitivas na prĂ©-leitura, no formato de oficinas, com o uso de ferramentas audiovisuais e atividades interativas que favoreceram a ação/reflexĂŁo sobre os processos metacognitivos envolvidos na compreensĂŁo leitora. A ação se constituiu em um momento importante para a reflexĂŁo da prática docente daquele grupo. O resultado foi avaliado por meio de um questionário, cujas respostas apontaram para o reconhecimento dos participantes da contemporaneidade, pertinĂŞncia e contribuição do conteĂşdo proposto para suas práticas pedagĂłgicas
Nucleon-induced reactions at intermediate energies: New data at 96 MeV and theoretical status
Double-differential cross sections for light charged particle production (up
to A=4) were measured in 96 MeV neutron-induced reactions, at TSL laboratory
cyclotron in Uppsala (Sweden). Measurements for three targets, Fe, Pb, and U,
were performed using two independent devices, SCANDAL and MEDLEY. The data were
recorded with low energy thresholds and for a wide angular range (20-160
degrees). The normalization procedure used to extract the cross sections is
based on the np elastic scattering reaction that we measured and for which we
present experimental results. A good control of the systematic uncertainties
affecting the results is achieved. Calculations using the exciton model are
reported. Two different theoretical approches proposed to improve its
predictive power regarding the complex particle emission are tested. The
capabilities of each approach is illustrated by comparison with the 96 MeV data
that we measured, and with other experimental results available in the
literature.Comment: 21 pages, 28 figure
Study of intermediate velocity products in the Ar+Ni collisions between 52 and 95 A.MeV
Intermediate velocity products in Ar+Ni collisions from 52 to 95 A.MeV are
studied in an experiment performed at the GANIL facility with the 4
multidetector INDRA. It is shown that these emissions cannot be explained by
statistical decays of the quasi-projectile and the quasi-target in complete
equilibrium. Three methods are used to isolate and characterize intermediate
velocity products. The total mass of these products increases with the violence
of the collision and reaches a large fraction of the system mass in mid-central
collisions. This mass is found independent of the incident energy, but strongly
dependent on the geometry of the collision. Finally it is shown that the
kinematical characteristics of intermediate velocity products are weakly
dependent on the experimental impact parameter, but strongly dependent on the
incident energy. The observed trends are consistent with a
participant-spectator like scenario or with neck emissions and/or break-up.Comment: 37 pages, 13 figure
Hydrogen-bonding interactions in T-2 toxin studies using solution and solid-state NMR
Open accessThe structure of T-2 toxin in the solid-state is limited to X-ray crystallographic
studies, which lack sufficient resolution to provide direct evidence for hydrogen-bonding
interactions. Furthermore, its solution-structure, despite extensive Nuclear Magnetic
Resonance (NMR) studies, has provided little insight into its hydrogen-bonding behavior,
thus far. Hydrogen-bonding interactions are often an important part of biological activity.
In order to study these interactions, the structure of T-2 toxin was compared in both the
solution- and solid-state using NMR Spectroscopy. It was determined that the solution- and
solid-state structure differ dramatically, as indicated by differences in their carbon
chemical shifts, these observations are further supported by solution proton spectral
parameters and exchange behavior. The slow chemical exchange process and
cross-relaxation dynamics with water observed between the hydroxyl hydrogen on C-3 and
water supports the existence of a preferential hydrogen bonding interaction on the opposite
side of the molecule from the epoxide ring, which is known to be essential for
trichothecene toxicity. This result implies that these hydrogen-bonding interactions could
play an important role in the biological function of T-2 toxin and posits towards a possible interaction for the trichothecene class of toxins and the ribosome. These findings clearly
illustrate the importance of utilizing solid-state NMR for the study of biological
compounds, and suggest that a more detailed study of this whole class of toxins, namely
trichothecenes, should be pursued using this methodology.Ye
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