ÉTUDE DE LA RELAXATION DE VIBRATION DANS DES LIQUIDES POLYATOMIQUES PAR ANALYSE DES SPECTRES DE DIFFUSION BRILLOUIN

Nous avons mesuré les spectres de diffusion Brillouin de trois liquides polyatomiques (Dichlorométhane, Benzène et Toluène) a différentes températures et pour deux angles de diffusion (90° et 177° environ). Les spectres obtenus sont comparés à des spectres calculés dans l'hypothèse d'une relaxation à un ou deux temps de la chaleur spécifique de vibration. Les résultats sont discutés en termes de la théorie quantique de Slawsky, Schwartz et Herzfeld.Brillouin spectra have been measured in three polyatomic liquids (Dichloromethane, Benzene and Toluene) as a function of temperature and for two scattering angles (90° and backscattering). Experimental spectra have been compared with calculated ones assuming a single or double relaxation of the vibrational specific heat. Results are discussed in terms of the quantum theory developped by Slawsky, Schwartz and Herzfeld

Foraging efficiency and adjustment of energy expenditure in a pelagic seabird provisioning its chick

1. Foraging determines the intake of resources that are expended on fitness related activities, and allocation links foraging and life-history traits, but the extent to which individuals are able to adjust energy expenditure according to allocation decisions is still poorly studied. 2. To examine this, we studied for the first time the efficiency of foraging trips (defined as the ratio of energy gained over energy spent while foraging) in a pelagic seabird provisioning its chick by measuring simultaneously the energy flow to the chick, changes in adult body mass and foraging cost using doubly labelled water. The study was performed over two seasons. 3. Blue petrels (Halobaena caerulea ) alternate between short foraging trips (average 1.9 days, range 1-4 days) where they maximize food delivery to the chick but loose mass, and long foraging trips (7.3 days, 5-10 days) where they increase in mass. They expend 1.5-2.2 times more energy per unit of time during short trips (2561 kJ day(-1) kg(-1) , i.e. 3.2 times the resting metabolic rate) compared to long trips (1142-1676 kJ day(-1) kg(-1) , i.e. 1.4-2.1 the resting metabolic rate). 4. The currency during long trips is therefore to maximize efficiency, whereas during short trips the currency is to maximize rate of energy delivery to the chick. Maximum efficiency peaks for 6-day trips, i.e. when adult mass gain is highest, foraging costs are lowest and efficiency was extremely low during short trips. A duration of 6 days is therefore the optimal duration of long foraging trips but trips of 7 days were more common. 5. Our study shows that self-feeding during long trips is crucial for the success of short trips because most of the energy used during short trips is probably derived from the energy stored during long trips. Self-feeding during short trips is probably negligible. 6. The study indicates that surprisingly long distance foraging may not always result in higher foraging costs compared to shorter movements. It highlights the predominant role of body store usage as a mechanism for this animal to adjust energy expenditure and energetic efficiency during foraging for allocation purposes

Produção e partição da biomassa de Desmodium incanum em resposta à aplicação de fósforo Biomass production and partitioning of Desmodium incanum in response to phosphate application

Este trabalho teve o objetivo de analisar o efeito do tipo de solo e de doses de fósforo (P) sobre a produção e partição da biomassa de Desmodium incanum DC. Foram feitas quatro avaliações ao longo do tempo, visando determinar a evolução da biomassa total e sua partição em parte aérea e radicular. Os tratamentos consistiram de dois tipos de solo (Plintossolo e Latossolo) e quatro doses de P (0, 30, 60, 90 mg de P2O5/kg de solo). Foi utilizado o delineamento completamente casualizado, num fatorial 4 x 2, com quatro repetições. Determinou-se o teor total de N e P na matéria seca da parte aérea. Na ausência da adubação fosfatada, os dois solos apresentaram potencial semelhante para a produção de matéria seca. O Latossolo, quando adubado, foi superior ao Plintossolo. A deficiência de P e a menor fertilidade natural do solo alterou a partição da biomassa. A alocação de assimilados para a parte aérea foi prejudicada em favor do crescimento radicular. Modelos de diluição de P e N foram testados, propondo-se valores de parâmetros para plantas individuais.<br>This work had the objective of analysing the effect of soil type and phosphate (P) levels on production and biomass partition of Desmodium incanum DC. Four evaluations aiming at determining the evolution of total biomass and root and shoot biomass partition were made during the period. The treatments were two types of soil (Plinthaquult and Hapludox) and four levels of phosphate (0, 30, 60, 90 mg of P2O5/kg of soil) arranged in a completely randomized design, with four replications. The total N and P content was determined in the dry matter. In the absence of P fertilization both soils had a similar potential for dry matter production. When fertilized, the Hapludox was superior to the Plinthaquult. P deficiency and lower soil natural fertility altered biomass partition. The allocation of assimilates to plant aerial parts was smaller, favoring root growth. Models for P and N dilution were tested, and parameter values for individual plants were proposed

Curva crítica de diluição do nitrogênio para a cultura do melão Nitrogen critical dilution curve for the muskmelon crop

O objetivo do trabalho foi ajustar a curva crítica de diluição do nitrogênio da cultura do melão. O experimento foi conduzido em ambiente protegido na Universidade Federal de Santa Maria (UFSM), entre agosto de 2004 e janeiro de 2005. As mudas do híbrido Magellan foram plantadas em sacolas de polietileno contendo 4,5dm-3 de substrato comercial (Plantmax PXT®), na densidade de 3,3 plantas m-2 e fertirrigadas com solução nutritiva completa. As plantas foram conduzidas verticalmente com uma haste, deixando-se no máximo dois frutos por planta e foram podadas ao atingir a altura de 2m. Os tratamentos foram constituídos por concentrações de nitrogênio na solução nutritiva de 8; 11, 14; 17 e 20mmol L-1. O delineamento experimental utilizado foi o inteiramente casualizado com quatro repetições. Quatro plantas de cada tratamento foram coletadas semanalmente entre os 33 e 99 dias após o plantio para determinar o acúmulo de matéria seca (MS) e o teor de N nas folhas, haste e frutos. Foi constatada a diluição da concentração de N na matéria seca em todos os tratamentos e os dados ajustaram-se ao modelo potencial %N = aMS-b descrito na literatura. A curva crítica de diluição do N foi ajustada, com coeficientes a e b iguais a 5,16 e 0,63, respectivamente. Esse modelo poderá ser usado para estimar a quantidade de N extraída no decorrer do ciclo de crescimento e desenvolvimento dessa cultura, com base na análise do teor desse nutriente nas folhas.<br>The research was carried out to adjust the nitrogen critical dilution curve for the muskmelon crop, to be used in fertilization practices for this crop. The experiment was conducted in a greenhouse at Universidade Federal de Santa Maria, from August to January, 2005. Plantlets of the hybrid Magellan was grown in polyethylene bags with 4.5dm3 of the commercial substrate Plantmax PXT®, in a plant density of 3.3plants m-2, and fertigated with a complete nutrient solution. Plants were vertically trained with one stem and no more than two fruits per plant, and the main stem was cut at 2m height. Treatments were N concentrations in the nutrient solution of 8, 11, 14, 17, and 20mmol L-1, in a randomized experimental design with four replications. Four plants of each treatment were harvested at weekly intervals between 33 and 99 days after planting to determine dry mass (DM) accumulation and N concentration in leaves, stem and fruits. The N dilution in plant dry mass was confirmed in all treatments and data fitted the potential model %N = aMS-b described in the literature. The N dilution curve was adjusted, with values of 5.16 and 0.63 for a and b coefficients, respectively. This model could be used to estimate the N quantity absorbed during growth and development of this crop, based on the analysis of this element on leaf tissues