Acyclic orientations with path constraints

Many well-known combinatorial optimization problems can be stated over the set of acyclic orientations of an undirected graph. For example, acyclic orientations with certain diameter constraints are closely related to the optimal solutions of the vertex coloring and frequency assignment problems. In this paper we introduce a linear programming formulation of acyclic orientations with path constraints, and discuss its use in the solution of the vertex coloring problem and some versions of the frequency assignment problem. A study of the polytope associated with the formulation is presented, including proofs of which constraints of the formulation are facet-defining and the introduction of new classes of valid inequalities

Stellar population gradients in Seyfert 2 galaxies. Northern sample

We use high signal-to-noise ratio long-slit spectra in the 3600-4700A range of the twenty brightest northern Seyfert 2 galaxies to study the variation of the stellar population properties as a function of distance from the nucleus. In order to characterize the stellar population and other continuum sources (e.g. featureless continuum FC) we have measured equivalent widths Ws of six absorption features, four continuum colours and their radial variations, and performed spectral population synthesis as a function of distance from the nucleus. About half the sample has CaIIK and G-band W values smaller at the nucleus than at 1 kpc from it, due to a younger population and/or FC. The stellar population synthesis shows that, while at the nucleus, 75% of the galaxies present contribution > 20% of ages younger or equal than 100Myr and/or of a FC, this proportion decreases to 45% at 3 kpc. In particular, 55% of the galaxies have contribution > 10% of the 3 Myr/FC component (a degenerate component in which one cannot separate what is due to a FC or to a 3 Myr stellar population) at the nucleus, but only 25% of them have this contribution at 3 kpc. As reference, the stellar population of 10 non-Seyfert galaxies, spanning the Hubble types of the Seyfert (from S0 to Sc) was also studied. A comparison between the stellar population of the Seyferts and that of the non-Seyferts shows systematic differences: the contribution of ages younger than 1 Gyr is in most cases larger in the Seyfert galaxies than in non-Seyferts, not only at the nucleus but up to 1 kpc from it.Comment: 23 pages, 18 figures, MNRAS in pres

Publicidad contextual: Una alternativa de la eficacia en Internet

Proponemos analizar la “publicidad interactiva” en España y, de forma particular del formato denominado “publicidad contextual” o de “enlaces patrocinados” (entre otros, sus aspectos funcionales y operativos). La velocidad de los procesos de esta nueva forma de comunicación y la falta de estudios relacionados con el tema, invita a discutir y profundizar en los aspectos singulares que pudiera aportar Internet como herramienta en la gestión del marketing, en esa búsqueda constante por contactar con el público objetivo determinado. La accesibilidad que caracteriza a este formato -se le podría denominar como “democrático”, ya que no necesita grandes inversiones para alcanzar una elevada efectividad-, y su transparencia y rapidez en la evaluación de los resultados lo hacen interesante para cualquier organización que considere estratégica la utilización de Internet como medio para sus comunicaciones comerciales. La inclusión del desarrollo de un proyecto real, además de ser un apoyo explicativo a nuestro discurso, permite evaluar en sus aspectos cuantitativos y cualitativos las características de nuestro objeto de estudio.We aim to analyse “interactive advertising” in Spain, particularly the format known as “contextual advertising” or “sponsored links” (including their functional and operative aspects). The speed of processes in this new form of communication and the absence of studies on the matter invite discussion, examining the special features that Internet could contribute as a marketing management tool, in that constant striving to contact a given target public. The accessibility that characterises this format -it could be called “democratic” since it can be highly effective without requiring heavy investment- and its transparency and speed in assessing results make it interesting for any organisation that considers Internet a strategic medium for commercial communication. By including the development of a real project, apart from backing up our dissertation, we are able to assess the quantitative and qualitative aspects of our subject matter

Leaf Blade Selection by Sheep in Kleingrass (\u3ci\u3ePanicum coloratum\u3c/i\u3e L.) Pastures with Different Deferment Periods

The winter use of standing dead biomass produced by warm season grasses during the previous growing season may be an alternative to grazing systems in the semi-arid Pampean Region of Argentina. This study evaluated: 1) the effect of different deferment periods on the leaf blade percentage and quality of ‘kleingrass’ (Panicum coloratum L.), a warm season specie recently introduced to that region, and 2) whether rams grazing the vegetation accumulated during these different periods are able to select leaf blades to maintain the quality of their diets. It was generated three treatments by deferment of the forage produced after harvesting in mid December 1987 (T1), and in early January (T2) and early February (T3), 1998. Length of the deferment reduced (P\u3c 0.05) the percentages of leaf blade from 42.2±0.01 % to 30.5±2.40%. However, the percentage of blades in ram diets remained stable (62±5.4%; P\u3e 0.05). The percentage of crude protein (CP) in the vegetation was not affected by the length of the deferment period (P\u3e 0.05), however CP contents in the blades were twice higher than in the rest of the vegetation (4.13±0.9 vs 1.82±0.34). Rams actively selected leaf blades in all the treatments (P\u3e 0.05), but selection effort was stronger in those with longer deferment. These results indicated that rams are able to made an effort to select the plant part of highest quality, and suggest that this effort is restricted by the vegetation structure

Microhistological Estimation of Leaf Blade Percentage in Diets from Monoespecific Pastures

Although a decrease in the leaf-stem ratio affects the nutritive value of pastures, herbivores can reinforce selection for leaf blades to maintain the quality of their diets. This study evaluated whether the percentage of fragments with furrows in blades could be used to estimate the relative intake of this part of the leaves by herbivores grazing monoespecific pastures. It was worked with vegetation of kleingrass (Panicum coloratum L.) from paddocks with three deferment periods. Blade samples, and different plant part mixtures hand compounded were in vitro digested. The digestion residues were microhistological analyzed determining the number of fragment with furrows (#FWF), and the total number of fragments (T#F). The blade percentages in mixtures was computed as: Estimated %Blademixtures = ((#FWFmixtures*100/ %FWFblades)/ T#Fmixtures))*100. The %FWF in blade samples (19+ 1.5%) was not affected (P\u3e 0.05) by changes in plant maturity determined by the length of the deferment period. The relationship between the actual blade percentages (y), and those determined by microanalysis (x) in mixtures was 1:1. This suggests that the microanalysis of feces or digestive contents could be used to estimate the percentages of blades in the diet of herbivores grazing monoespecific pastures

Slowly and non-digestible tissues in Elytrigia scabrifolia y E. Scabriglumis

The estimation of the percentages of slowly and non-digestible tissues allows the prediction 01the nutritive value of forages. In this study, the percentages of tissues in sheaths and blades of two species natives of the Salado Basin and abundant in the Pampas range pastures (Elytrigia scabrifolia y E. scabriglumis) were determined as a primary evaluation of their forage qualily. The estimations were done in the vegetative and reproductive stages. A split-plots design in space and time, with species as main plot, plant part (sheath or blade) as secondary plots, and three replications was used. Percentages of all leaf tissues were estimated by microscopic analysis of cross section and were grouped in rapidly and slowly plus non-digestible tissues. The variation of all leaf tissues between species, plant parts and growth stage, and the percentages variation of slowly and non-digestible tissues were analysed by principal components and by ANOVA, respectively. In all cases, the percentages of sclerenchyma were lower than 10% and those of slowly plus non-digestible tissues were lower than 45%. The percentages of slowly and non-digestible tissues did not differ (P<0.05) either between species (P<0.05) or plant parts, but increased 34% with the advancement of growth from the vegetativa to the reproductive stage. Although the percentage of slowly and nondigestible tissues suggest that both species have an acceptable nutritive value, this rating could be altered by the degree of forage lignification.Resúmenes de Trabajos presentados en otras publicaciones (por docentes de la UNLPam.) Publicado en Archivos latinoamericanos de producción animal, 5(Supl. 1): 118-121, 1997

Bibliografia sobre artrópodes associados ao cajueiro (Anacardium occidentale L.) na literatura brasileira.

Foi efetuada uma revisão visando recuperar a bibliografia nacional sobre antrópodes associados ao cajueiro, referente ao período compreendido entre 1922 e 1995. Foram recuperados dois trabalhos da década de 20; três trabalhos da década de 50; seis trabalhos da decada de 60; 63 trabalhos da decada de 70; 20 trabalhos da decada de 80; e 26 trabalhos nos cinco anos da decada de 90. A grande maioria dos trabalhos foram relativos a ocorrencia de antropodes (43,44%). Em segundo lugar figuram os trabalhos sobre controle quimico (30,32%). Neste caso, foram agrupados os realizados em campo e em confinamento. Os trabalhos sobre biologia parcial ou total representaram 8,19%; o restante da bibliografia encontra-se distribuido em outros 16 assuntos. Os trabalhos publicados a partir de 1990 foram, na sua totalidade, desenvolvidos no Centro Nacional de Pesquisa de Caju, hoje, CNPAT.bitstream/CNPAT-2010/4788/1/Dc-026.pd

Slowly and non-digestible tissues in Elytrigia scabrifolia y E. Scabriglumis

The estimation of the percentages of slowly and non-digestible tissues allows the prediction 01the nutritive value of forages. In this study, the percentages of tissues in sheaths and blades of two species natives of the Salado Basin and abundant in the Pampas range pastures (Elytrigia scabrifolia y E. scabriglumis) were determined as a primary evaluation of their forage qualily. The estimations were done in the vegetative and reproductive stages. A split-plots design in space and time, with species as main plot, plant part (sheath or blade) as secondary plots, and three replications was used. Percentages of all leaf tissues were estimated by microscopic analysis of cross section and were grouped in rapidly and slowly plus non-digestible tissues. The variation of all leaf tissues between species, plant parts and growth stage, and the percentages variation of slowly and non-digestible tissues were analysed by principal components and by ANOVA, respectively. In all cases, the percentages of sclerenchyma were lower than 10% and those of slowly plus non-digestible tissues were lower than 45%. The percentages of slowly and non-digestible tissues did not differ (P<0.05) either between species (P<0.05) or plant parts, but increased 34% with the advancement of growth from the vegetativa to the reproductive stage. Although the percentage of slowly and nondigestible tissues suggest that both species have an acceptable nutritive value, this rating could be altered by the degree of forage lignification.Resúmenes de Trabajos presentados en otras publicaciones (por docentes de la UNLPam.) Publicado en Archivos latinoamericanos de producción animal, 5(Supl. 1): 118-121, 1997