175,211 research outputs found
Systematics of a Kleptoplastidal Dinoflagellate, Gymnodinium eucyaneum Hu (Dinophyceae), and Its Cryptomonad Endosymbiont
No full textNew specimens of the kleptoplastidal dinoflagellate Gymnodinium eucyaneum Hu were collected in China. We investigated the systematics of the dinoflagellate and the origin of its endosymbiont based on light morphology and phylogenetic analyses using multiple DNA sequences. Cells were dorsoventrally flattened with a sharply acute hypocone and a hemispherical epicone. The confusion between G. eucyaneum and G. acidotum Nygaard still needs to be resolved. We found that the hypocone was conspicuously larger than the epicone in most G. eucyaneum cells, which differed from G. acidotum, but there were a few cells whose hypocone and epicone were of nearly the same size. In addition, there was only one site difference in the partial nuclear LSU rDNA sequences of a sample from Japan given the name G. acidotum and G. eucyaneum in the present study, which suggest that G. eucyaneum may be a synonym of G. acidotum. Spectroscopic analyses and phylogenetic analyses based on nucleomorph SSU rDNA sequences and chloroplast 23 s rDNA sequences suggested that the endosymbiont of G. eucyaneum was derived from Chroomonas (Cryptophyta), and that it was most closely related to C. coerulea Skuja. Moreover, the newly reported kleptoplastidal dinoflagellates G. myriopyrenoides and G. eucyaneum in our study were very similar, and the taxonomy of kleptoplastidal dinoflagellates was discussed.New specimens of the kleptoplastidal dinoflagellate Gymnodinium eucyaneum Hu were collected in China. We investigated the systematics of the dinoflagellate and the origin of its endosymbiont based on light morphology and phylogenetic analyses using multiple DNA sequences. Cells were dorsoventrally flattened with a sharply acute hypocone and a hemispherical epicone. The confusion between G. eucyaneum and G. acidotum Nygaard still needs to be resolved. We found that the hypocone was conspicuously larger than the epicone in most G. eucyaneum cells, which differed from G. acidotum, but there were a few cells whose hypocone and epicone were of nearly the same size. In addition, there was only one site difference in the partial nuclear LSU rDNA sequences of a sample from Japan given the name G. acidotum and G. eucyaneum in the present study, which suggest that G. eucyaneum may be a synonym of G. acidotum. Spectroscopic analyses and phylogenetic analyses based on nucleomorph SSU rDNA sequences and chloroplast 23 s rDNA sequences suggested that the endosymbiont of G. eucyaneum was derived from Chroomonas (Cryptophyta), and that it was most closely related to C. coerulea Skuja. Moreover, the newly reported kleptoplastidal dinoflagellates G. myriopyrenoides and G. eucyaneum in our study were very similar, and the taxonomy of kleptoplastidal dinoflagellates was discussed
Signature of solar g modes in first-order p-mode frequency shifts
No full textContext. Solar gravity modes (g modes) are buoyancy waves that are trapped in the solar radiative zone and have been very difficult to detect at the surface. Solar g modes would complement solar pressure modes (p modes) in probing the central regions of the Sun, for example the rotation rate of the core.
Aims. A detection of g modes using changes in the large frequency separation of p modes has recently been reported. However, it is unclear how p and g modes interact. The aim of this study is to evaluate to what extent g modes can perturb the frequencies of p modes.
Methods. We computed the first-order perturbation to global p-mode frequencies due to a flow field and perturbations to solar structure (e.g. density and sound speed) caused by a g mode. We focused on long-period g modes and assumed that the g-mode perturbations are constant in time. The surface amplitude of g modes is assumed to be 1 mm s−1, which is close to the observational limit set by Doppler observations.
Results. Gravity modes do perturb p-mode frequencies to first order if the harmonic degree of the g mode is even and if its azimuthal order is zero. The effect is extremely small. For dipole and quadrupole p modes, all frequency shifts are smaller than 0.1 nHz, or 2 × 10−8 in relative numbers. This is because the relative perturbation to solar structure quantities caused by a g mode of realistic amplitude is of the order of 10−6–10−5. Additionally, we find that structural changes dominate over advection. Surprisingly, the interaction of g and p modes takes place to a large part near the surface, where p modes spend most of their propagation times and g modes generate the largest relative changes to solar structure. This is due to the steep density stratification, which compensates the evanescent behaviour of g modes in the convection zone.
Conclusions. It appears to be impossible to detect g modes solely through their signature in p-mode frequency shifts. Whether g modes leave a detectable signature in p-mode travel times under a given observational setup remains an open question
A hygro-thermal stress finite element analysis of laminated beam structures by hierarchical one-dimensional modelling
No full textA hygro-thermal stress finite element analysis of laminated beam structures by hierarchical one-dimensional modelling Composite structure operating under severe temperature conditions and/or wet environments are very common is several engineering fields such as aeronautics, space and transportation. Hygro-thermal solicitation of beam-like structures results in a three- dimensional response that classical one-dimensional models are not always capable of describe effectively. An accurate prediction calls, then, for refined higher-order theories making this subject of research relevant and up-to-date. In this work, laminated composite Several beam models are hierarchically derived by means of a unified formulation [1, 2] that allows for atheoretical derivation of the finite elements independent from the displacements polynomial approximation order over the cross-section as well as the number of nodes per element. Elements stiffness matrix are derived in a compact form ("fundamental nucleus") via the Principle of Virtual Displacements. As a result, a family of several one-dimensional finite elements accounting for transverse shear deformations and cross section in- and out-of-plane warping can be obtained. Temperature and humid-ity profiles are obtained by directly solving the corresponding diffusion equation(Fourier's heat conduction equation for temperature and Fick's law for moisture). These fields are, then, accounted as sources terms in the elastic analysis through Hooke's law. Simply supported and cantilever configurations are considered. Numerical results in terms of temperature, moisture, displacement and stress distributions are provided for different beam slenderness ratios. Three-dimensional finite element solutions developed within the commercial code Ansys are presented for validation. The numerical investigations show that the hygro-thermo-elastic problem presents a complex three-dimensional stress state that can be efficiently obtained by a suitable choice of approximation order over the cross section: the accuracy is comparable to the reference solutions whereas the computational costs can beconsiderably reduce
A Novel FE2 Method Based Fourier Macroscopic Model for Instability Phenomena of Long Fiber Reinforced Composites
No full textA multi-scale model of fibre reinforced beams using hierarchical one-dimensional finite elements
No full textA multi-scale model of fibre reinforced beams using hierarchical one-dimensional finite elements A multi-scale analysis of fibre reinforced composite beams was proposed by this presentation. At structural level, several higher-order refined beam theories can be easily implemented on the basis of Carrera's unified formulation (CUF) by deriving a fundamental nucleus that does not depend upon the approximation order nor the number of nodes per element (they are free parameters of the formulation). Under the framework of FE2 method, the effective properties of the fibre-reinforced composite material are found by numerical homogenization over representative volume elements, that is, the unknown constitutive relationship at the macro-scale is obtained by solving a local finite element problem at the micro-scale. Consequently, a coupled two-scale problem is obtained for linear cases. Results are validated in terms of accuracy and computational costs towards FEM solutions. Numerical investigations show that accurate results can be obtained with reduced computational costs
Differential role of r-met-hu G-CSF on male reproductive function and development in prepubertal domestic mammals
No full textThe understanding of mammalian spermatogenesis niche factors active during sexual development may be leveraged to impact reproduction in farm animals. The aim of this study was to evaluate the effects of r-met-hu/G-CSF (filgrastim) on prepubertal sexual development of guinea pigs (Cavia porcellus) and ram lambs (Ovis aries). Individuals of both species were administered r-met-hu/G-CSF daily for 4 days. During and after administration protocols, testicular function and development were assessed through hematological responses, hormonal profiles (gonadotropins, testosterone and cortisol) testicular morphometry and germ cell kinetics. As expected, r-met-hu/G-CSF acutely mobilized white-lineage blood cells in both species. LH was increased by r-met-hu/G-CSF in guinea pigs (P0.05). In guinea pigs there were no differences in testicular weights and volumes 2-mo after r-met-hu/G-CSF application (P>0.05). However, ram lambs showed a dose-response effect regarding testis weight (P</div
Summary of germ cell kinetics results during r-met-hu G-CSF experiments.
No full textSummary of germ cell kinetics results during r-met-hu G-CSF experiments.</p
Performance Evaluation of Distributed-Antenna Communications Systems Using Beam-Hopping
No full textDigital beamforming (DBF) techniques are capable of improving the performance of communications systems significantly. However, if the transmitted signals are conflicted with strong interference, especially, in the direction of the transmitted beams , these directional jamming signals will severely degrade the system performance. In order to efficiently mitigate the interference of the directional jammers, in this contribution a beam-hopping (BH) communications scheme is proposed. In the proposed BH communications scheme, only one pair of the beams is used for transmission and it hops from one to the next according to an assigned BH pattern. In this contribution a range of expressions in terms of the average SINR performance have been derived, when both the uplink and downlink are considered. The average SINR performance of the proposed BH scheme and that of the conventional single-beam (SB) as well as multiple-beam (MB) assisted beam-processing schemes have been investigated. Our analysis and results show that the proposed BH scheme is capable of efficiently combating the directional jamming, with the aid of utilizing the directional gain of the beams generated by both the transmitter and the receiver. Furthermore, the BH scheme is capable of reducing the intercept probability of the communications. Therefore, the proposed BH scheme is suitable for communications, when several distributed antenna arrays are available around a mobile
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