14 research outputs found
Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
We review HB stars in a broad astrophysical context, including both variable
and non-variable stars. A reassessment of the Oosterhoff dichotomy is
presented, which provides unprecedented detail regarding its origin and
systematics. We show that the Oosterhoff dichotomy and the distribution of
globular clusters (GCs) in the HB morphology-metallicity plane both exclude,
with high statistical significance, the possibility that the Galactic halo may
have formed from the accretion of dwarf galaxies resembling present-day Milky
Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the
second-parameter problem is presented. A technique is proposed to estimate the
HB types of extragalactic GCs on the basis of integrated far-UV photometry. The
relationship between the absolute V magnitude of the HB at the RR Lyrae level
and metallicity, as obtained on the basis of trigonometric parallax
measurements for the star RR Lyrae, is also revisited, giving a distance
modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are
studied. Finally, the conductive opacities used in evolutionary calculations of
low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and
Space Scienc
Conceito de ideotipo e seu uso no aumento do rendimento potencial de cereais The ideotipe concept and its use to increase cereal's yield potential
A presente revisĂŁo tem por objetivo apresentar algumas caracterĂsticas consideradas interessantes de serem incorporadas em plantas de cereais quando cultivadas em comunidade, atravĂ©s da integração de conhecimentos de fisiologia, bioquĂmica e melhoramento. No melhoramento de diferentes espĂ©cies verifica-se que várias caracterĂsticas de planta foram modificadas no processo de seleção para rendimento de grĂŁos. Neste enfoque, propõe-se discutir a validade de incorporar estas caracterĂsticas em cultivares e perguntar se as cultivares antigas tivessem sido melhoradas atravĂ©s destas caracterĂsticas qual resultado teria sido alcançado. A discussĂŁo de ideotipo aumenta de importância com a rápida evolução das tĂ©cnicas de avaliação da variabilidade genĂ©tica, pois caso nĂŁo seja definido um modelo de planta para aumentar o rendimento potencial estas tĂ©cnicas podem ter uma utilização restrita. Na discussĂŁo de ideotipo para aumentar o rendimento potencial, Ă© necessário formular um novo modelo baseado em algumas caracterĂsticas já amplamente analisadas deforma isolada. As principais, sĂŁo o maior crescimento inicial e maior fitomassa da comunidade, o que lhe permite aumentar a capacidade de aproveitamento da radiação, principalmente no inĂcio do ciclo da cultura. Somado a isto, o aumento da capacidade fotossintĂ©tica atravĂ©s do aumento da força de demanda, com provável efeito sobre o Ăndice de colheita. A ação conjunta das caracterĂsticas individuais necessita ser testada quando incorporadas sobre um mesmo genĂłtipo, para analisar o seu grau de resposta.<br>This review has the purpose of presenting some important traits to be incorporated in cereals through the integration of physiology, biochemistry and plant breeding. Several plant attributes were modified during the selection process to improve grain yield of different plant species. This paper intends to discuss the validity of aggregating some of the se traits in new cultivars and to pinpoint the possible consequences of using those individual characteristics rather than grain yield per se to bred the old genotypes. Discussion about crop ideotipes grows in importance with the fast evolution of genetic variability techniques because if a model plant to increase grain yield is not defined all the new genetic technology available may have a narrow practical utilization. This ideotipe was formulated integrating severa! characteristics that have been analyzed individually in the past. Its main proposed features are: (a) higher initial growth and greater communal phytomass, which are both important to improve solar radiation use, particularly during early stages of development, (b) an increase in photosynthetic capacity through the enhancement of sink strength with a probable effèct on harvest index. The collective influence of the suggested traits must be evaluated on different genotypes to analyze the response level obtained