scholarly journals A Note on the Evolutionary Condition on Hydromagnetic Shocks

1962 ◽  
Vol 28 (4) ◽  
pp. 756-757 ◽  
Author(s):  
Tosiya Taniuti
Keyword(s):  
Evolutionary Condition

Genetic Differentiation in Isolated Populations of Hakea carinata (Proteaceae)

1998 ◽  
Vol 46 (6) ◽  
pp. 671 ◽  
Author(s):  
G. J. Starr ◽  
S. M. Carthew
Keyword(s):  
Gene Flow ◽  
Habitat Fragmentation ◽  
Gene Diversity ◽  
South Australia ◽  
Similar Species ◽  
Isolated Populations ◽  
Plant Populations ◽  
Evolutionary Condition ◽  
Private Alleles

Fragmentation of the landscape by human activity has created small, isolated plant populations. Hakea carinata F. Muell. ex Meissner, a sclerophyllous shrub, is common in isolated fragments of vegetation in South Australia. This study investigated whether habitat fragmentation has caused restrictions to gene flow between populations. Gene diversity (HT = 0.317) is average for similar species but little is held within populations (HS = 0.168) and 46.9% of gene diversity is accounted for between populations. Estimates of gene flow are NM = 0.270 (based on FST) and NM = 0.129 (based on private alleles). Populations are substantially selfing (t = 0.111). Small isolated populations appears to be a long-term evolutionary condition in this species rather than a consequence of habitat fragmentation; however, population extinctions are occurring. Conservation will require the reservation of many populations to represent the genetic variation present in the species.

On the stellar origin of low energy cosmic rays

1975 ◽  
Vol 277 (1270) ◽  
pp. 489-501 ◽  
Keyword(s):  
Cosmic Rays ◽  
Energy Release ◽  
Solar Flares ◽  
Cosmic Ray ◽  
Galactic Cosmic Rays ◽  
Optical Observations ◽  
Energy Estimates ◽  
The Sun ◽  
Dwarf Stars ◽  
Evolutionary Condition

The large solar flares associated with cosmic-ray events release total bolometric energies in the region 1024-1 0 25 J. This is of the order 10~5-10~6 of the normal bolometric energy emission of the Sun. The condition of the M and K type stars when they flare is entirely different; the rate of energy release during the flare is of the same order as the normal energy release of the star in the quiescent condition. Although these dwarf stars are in a markedly different evolutionary condition compared with the Sun recent simultaneous radio and optical observations of the flares have given decisive indications that the physical processes, involving magnetic field collapse of several hundredths of a tesla, must be similar to the flare mechanism in the Sun. Adopting the factor, which has been determined empirically in the case of the Sun, for the conversion of flare energy to cosmic-ray energy, estimates are made of the fraction of galactic cosmic rays which may be generated in the flares on the M and K type stars. It is shown that these stars may be the major source of the galactic cosmic rays for energies from 106-3 x 108 eV and that the K type stars may contribute one fifth of the total cosmic-ray energy up to 109 eV.

Structural diversity of fruits: conceptual reflexions and taxonomic implications / Diversidade estrutural de frutos: reflexões conceituais e implicações taxonômicas

2021 ◽  
Vol 7 (7) ◽  
pp. 69342-69354
Author(s):  
Luiz Antonio De Souza
Keyword(s):  
Structural Diversity ◽  
First Case ◽  
Inflorescence Axis ◽  
Paraffin Material ◽  
Taxonomic Implications ◽  
Fruit Evolution ◽  
Residual Tissue ◽  
Development Analysis ◽  
Evolutionary Condition ◽  
Made In

Fruit either originates solely from the ovary or ovary and other floral parts and inflorescence. Besides the ovary itself, the pedicle, bracteoles, receptacle, hypanthium, sepals, petals and inflorescence axis are included in the fruit development. Analysis was made in embedded historesin/paraffin material and sectioned in microtome. In the fruit ontogeny the pericarp either may be non-multiplicative or multiplicative. In the first case, the ovary wall differentiates in pericarp without the installation of meristem. Adaxial, middle or abaxial meristems can be installed in the multiplicative pericarp fruits from the periclinal cell divisions that occur in both the epidermis and the ovary mesophyll. Separation tissue takes place in the carpel margins and midrib in dehiscent fruits or it can remain as residual tissue in indehiscent fruits. Fruit classification is complex, and it may show divergence in nomenclature among fruit specialists. Structural fruit ontogeny can be a useful tool for its classification. Fruit structure has been used as diagnostic character of species, genera and tribes of angiosperms. Hypothesis about fruit evolution indicates that apocarpic fruit with follicles can be a basic evolutionary condition, at least among the sensu lato dicots. The Araucaria angustifolia pine seed is considered here as a fruit with protocarps/spermatocarps.

Self-Similar Reflection of Longitudinal Shock Wave from Free Boundary in Elastic Medium

2014 ◽  
Vol 1040 ◽  
pp. 652-657 ◽  
Author(s):  
Dmitrii A. Potyanikhin ◽  
Olga V. Dudko
Keyword(s):  
Shock Wave ◽  
Free Boundary ◽  
Elastic Medium ◽  
Second Law Of Thermodynamics ◽  
Elastic Half Space ◽  
Self Similar Solution ◽  
Wave Patterns ◽  
Self Similar ◽  
Wave Surfaces ◽  
Evolutionary Condition

Self-similar solution of two-dimensional problem of interaction between a plane longitudinal shock wave and free boundary of elastic half-space is considered. It is suggested that the intensity of this wave is constant. Feasible combinations of wave surfaces which may be generated in elastic medium as a result of such interaction are investigated. Choosing of unique physically admissible mode of deformation propagation from among mathematically possible wave patterns is related to shockwave evolutionary condition and the second law of thermodynamics.

scholarly journals Absolute Parameters of Young Stars: V Puppis

2021 ◽  
Author(s):  
E Budding ◽  
T Love ◽  
M G Blackford ◽  
T Banks ◽  
M J Rhodes
Keyword(s):  
Angular Momentum ◽  
Evolutionary Model ◽  
Young Stars ◽  
Close Binary ◽  
Spectrometric Data ◽  
Close Proximity ◽  
Low Amplitude ◽  
Absolute Parameters ◽  
Evolutionary Condition ◽  
Photometric Distance

Abstract New spectrometric data on V Pup are combined with satellite photometry (HIPPARCOS and recent TESS) to allow a revision of the absolute parameters with increased precision. We find: M1 = 14.0±0.5, M2 = 7.3±0.3 (M⊙); R1 = 5.48±0.18, R2 = 4.59±0.15 (R⊙); T1 26000±1000, T2 24000 ±1000 (K), age 5 ±1 (Myr), photometric distance 320 ±10 (pc). The TESS photometry reveals low-amplitude (∼0.002 mag) variations of the β Cep kind, consistent with the deduced evolutionary condition and age of the optical primary. This fact provides independent support to our understanding of the system as in a process of Case A type interactive evolution that can be compared with μ1 Sco. The ∼10 M⊙ amount of matter shed by the over-luminous present secondary must have been mostly ejected from the system rather than transferred, thus taking angular momentum out of the orbit and keeping the pair in relative close proximity. New times of minima for V Pup have been studied and the results compared with previous analyses. The implied variation of period is consistent with the Case A evolutionary model, though we offer only a tentative sketch of the original arrangement of this massive system. We are not able to confirm the previously reported cyclical variations having a 5.47 yr period with the new data, though a direct comparison between the HIPPARCOS and TESS photometry points to the presence of third light from a star that is cooler than those of the close binary, as mentioned in previous literature.

Shock waves and rarefaction waves in magnetohydrodynamics. Part 1. A model system

1997 ◽  
Vol 58 (3) ◽  
pp. 485-519 ◽  
Author(s):  
R. S. MYONG ◽  
P. L. ROE
Keyword(s):  
Shock Waves ◽  
Riemann Problem ◽  
Nonlinear Evolution ◽  
Rarefaction Waves ◽  
Planar Case ◽  
Model Set ◽  
The Stability ◽  
Mhd Shock Waves ◽  
Well Posed ◽  
Evolutionary Condition

The present study consists of two parts. Here in Part 1, a model set of conservation laws exactly preserving the MHD hyperbolic singularities is investigated to develop the general theory of the nonlinear evolution of MHD shock waves. Great emphasis is placed on shock admissibility conditions. By developing the viscosity admissibility condition, it is shown that the intermediate shocks are necessary to ensure that the planar Riemann problem is well-posed. In contrast, it turns out that the evolutionary condition is inappropriate for determining physically relevant MHD shocks. In the general non-planar case, by studying canonical cases, we show that the solution of the Riemann problem is not necessarily unique – in particular, that it depends not only on reference states but also on the associated internal structure. Finally, the stability of intermediate shocks is discussed, and a theory of their nonlinear evolution is proposed. In Part 2, the theory of nonlinear waves developed for the model is applied to the MHD problem. It is shown that the topology of the MHD Hugoniot and wave curves is identical to that of the model problem.

Evolutionary conditions for shock waves in collisionless plasma and stability of the associated flow

1968 ◽  
Vol 2 (3) ◽  
pp. 449-463 ◽  
Author(s):  
Shigeki Morioka ◽  
John R. Spreiter
Keyword(s):  
Magnetic Field ◽  
Shock Wave ◽  
Heat Flux ◽  
Mach Number ◽  
Shock Waves ◽  
Strong Magnetic Field ◽  
Collisionless Plasma ◽  
Shock Stability ◽  
The Magnetic Field ◽  
Evolutionary Condition

The evolutionary condition for transverse and normal shock waves, and the fire- hose and mirror instability conditions for the associated flow, in a collisionless, anisotropic plasma having a strong magnetic field are determined using the theoretical representation of Chew, Goldberger & Low (1956) for such a medium. The results are expressed in terms of the Mach number, Alfvén Mach number, and the ratio of the temperatures parallel and perpendicular to the magnetic field in the flow approaching the shock wave, and applied to ascertain in what range of these parameters various types of instabilities may occur. The effect of the heat flux, which does not vanish generally in a collisionless plasma, on the shock stability is discussed.

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