1,641 research outputs found
InfluĂȘncia de culturas antecessoras na disponibilidade de nitrogĂȘnio do solo para a cultura do algodĂŁo.
Um dos fatores importantes a ser considerado no manejo da adubação nitrogenada Ă© a cultura antecessora. O objetivo desse trabalho, conduzido em Santa Helena de GoiĂĄs, foi medir a influĂȘncia de culturas antecessoras na disponibilidade de nitrogĂȘnio (N) inorgĂąnico no solo e na resposta do algodoeiro Ă adubação nitrogenada. O experimento foi instalado em parcelas subdivididas com quatro repetiçÔes. Nas parcelas foram cultivadas as culturas antecessoras milho, soja, algodĂŁo e Brachiaria decumbens; e nas subparcelas foram aplicadas cinco doses de nitrogĂȘnio (0, 40, 80, 120 e 160 kg ha-1 de N) no algodoeiro cultivado em sucessĂŁo. O algodoeiro em sucessĂŁo Ă soja e ao algodĂŁo necessita de menor quantidade de fertilizante nitrogenado, em comparação com a sucessĂŁo Ă braquiĂĄria e ao milho. Durante o ciclo do algodoeiro a presença de resĂduos de soja favorece a mineralização lĂquida do nitrogĂȘnio do solo, tornando-o disponĂvel nos primeiros estĂĄdios de desenvolvimento da planta. Os resĂduos de B. decumbens favorecem a imobilização do N na biomassa microbiana do solo
Adubação NPK do algodoeiro em cultivo adensado de safrinha no Cerrado de Goiås - safra 2010/11.
O objetivo desse trabalho foi definir doses de NPK para adubação de manutenção do algodão de safrinha adensado, nas condiçÔes do Cerrado de Goiås, em função da fertilidade do solo, da expectativa de produtividade e das quantidades exportadas desses nutrientes pela cultura
Detrended Fluctuation Analysis of Systolic Blood Pressure Control Loop
We use detrended fluctuation analysis (DFA) to study the dynamics of blood
pressure oscillations and its feedback control in rats by analyzing systolic
pressure time series before and after a surgical procedure that interrupts its
control loop. We found, for each situation, a crossover between two scaling
regions characterized by exponents that reflect the nature of the feedback
control and its range of operation. In addition, we found evidences of
adaptation in the dynamics of blood pressure regulation a few days after
surgical disruption of its main feedback circuit. Based on the paradigm of
antagonistic, bipartite (vagal and sympathetic) action of the central nerve
system, we propose a simple model for pressure homeostasis as the balance
between two nonlinear opposing forces, successfully reproducing the crossover
observed in the DFA of actual pressure signals
A Unifying Theory of Biological Function
A new theory that naturalizes biological function is explained and compared with earlier etiological and causal role theories. Etiological theories explain functions from how they are caused over their evolutionary history. Causal role theories analyze how functional mechanisms serve the current capacities of their containing system. The new proposal unifies the key notions of both kinds of theories, but goes beyond them by explaining how functions in an organism can exist as factors with autonomous causal efficacy. The goal-directedness and normativity of functions exist in this strict sense as well. The theory depends on an internal physiological or neural process that mimics an organismâs fitness, and modulates the organismâs variability accordingly. The structure of the internal process can be subdivided into subprocesses that monitor specific functions in an organism. The theory matches well with each intuition on a previously published list of intuited ideas about biological functions, including intuitions that have posed difficulties for other theories
Cognitive appraisal of environmental stimuli induces emotion-like states in fish
The occurrence of emotions in non-human animals has been the focus of debate over the years. Recently, an interest in expanding this debate to non-tetrapod vertebrates and to invertebrates has emerged. Within vertebrates, the study of emotion in teleosts is particularly interesting since they represent a divergent evolutionary radiation from that of tetrapods, and thus they provide an insight into the evolution of the biological mechanisms of emotion. We report that Sea Bream exposed to stimuli that vary according to valence (positive, negative) and salience (predictable, unpredictable) exhibit different behavioural, physiological and neuromolecular states. Since according to the dimensional theory of emotion valence and salience define a two-dimensional affective space, our data can be interpreted as evidence for the occurrence of distinctive affective states in fish corresponding to each the four quadrants of the core affective space. Moreover, the fact that the same stimuli presented in a predictable vs. unpredictable way elicited different behavioural, physiological and neuromolecular states, suggests that stimulus appraisal by the individual, rather than an intrinsic characteristic of the stimulus, has triggered the observed responses. Therefore, our data supports the occurrence of emotion-like states in fish that are regulated by the individual's perception of environmental stimuli.European Commission [265957 Copewell]; Fundacao para a Ciencia e Tecnologia [SFRH/BD/80029/2011, SFRH/BPD/72952/2010]info:eu-repo/semantics/publishedVersio
TRANSIENT MODELING OF A SMALL HYDROKINETIC TURBINE
In recent years, great attention has been given to the study of hydrokinetic turbines for power generation. Such importance is due to the use of clean energy technology by using renewable sources. Therefore, this work aims to present a relevant methodology for the efficient design of horizontal-axis hydrokinetic turbines with variable rotational speed. This methodology includes the Blade Element Method (BEM) for determining the turbine power coefficient, since BEM is widely used in the hydrokinetic turbine design due to its good agreement with experimental data. In addition, the dynamic equation of the driveline is used, taking into account the BEM to provide the rotor hydrodynamic torque coupled with the drive train model, including the multiplier and the electric generator. In this case, the modeling of the whole system comprises the hydrodynamic information of the rotor, the mass-moment of inertia, frictional losses and electromagnetic torque imposed by the generator. The theoretical results were obtained for the transient rotational speed and compared with field data measured from small hydrokinetic turbine installed at the Arapiranga-Açu creek, which is located in the city of AcaraÌ, ParaÌ, Brazil
Cortisol coregulation in fish
Cortisol coregulation, which is the up- or down-regulation of partnersâ physiological stress responses, has been described for individuals with strong attachment bonds, e.g. parents and their children, and romantic relationship partners. Research into moderating effects on cortisol coregulation suggests stronger covariation among distressed partners. Whether cortisol coregulation is unique to humans or can also be found in other species that share universal features of the vertebrate stress response remains unexplored. Using a repeated measures approach and non-invasive waterborne hormone analysis, we test the hypothesis that dyads of three-spined stickleback fish (Gasterosteus aculeatus) coregulate their cortisol levels in shared environments. Dyadic cortisol levels were unrelated when cohabiting (home tank), but significantly covaried when sharing a more stressful (as indicated by higher cortisol levels) environment (open field). Time-lag analysis further revealed that open field cortisol levels were predicted by partnerâs cortisol levels prior to the shared experience. To our knowledge, this study provides the first evidence for coregulatory processes on cortisol responses in a non-human animal that lacks strong bonds and social attachment relationships, suggesting a shared evolutionary origin of cortisol coregulation in vertebrates. From an adaptive perspective, cortisol coregulation may serve to reduce risk in challenging, potentially threatening situations
Monotonicity of Fitness Landscapes and Mutation Rate Control
A common view in evolutionary biology is that mutation rates are minimised.
However, studies in combinatorial optimisation and search have shown a clear
advantage of using variable mutation rates as a control parameter to optimise
the performance of evolutionary algorithms. Much biological theory in this area
is based on Ronald Fisher's work, who used Euclidean geometry to study the
relation between mutation size and expected fitness of the offspring in
infinite phenotypic spaces. Here we reconsider this theory based on the
alternative geometry of discrete and finite spaces of DNA sequences. First, we
consider the geometric case of fitness being isomorphic to distance from an
optimum, and show how problems of optimal mutation rate control can be solved
exactly or approximately depending on additional constraints of the problem.
Then we consider the general case of fitness communicating only partial
information about the distance. We define weak monotonicity of fitness
landscapes and prove that this property holds in all landscapes that are
continuous and open at the optimum. This theoretical result motivates our
hypothesis that optimal mutation rate functions in such landscapes will
increase when fitness decreases in some neighbourhood of an optimum, resembling
the control functions derived in the geometric case. We test this hypothesis
experimentally by analysing approximately optimal mutation rate control
functions in 115 complete landscapes of binding scores between DNA sequences
and transcription factors. Our findings support the hypothesis and find that
the increase of mutation rate is more rapid in landscapes that are less
monotonic (more rugged). We discuss the relevance of these findings to living
organisms
Interplay between pleiotropy and secondary selection determines rise and fall of mutators in stress response
Dramatic rise of mutators has been found to accompany adaptation of bacteria
in response to many kinds of stress. Two views on the evolutionary origin of
this phenomenon emerged: the pleiotropic hypothesis positing that it is a
byproduct of environmental stress or other specific stress response mechanisms
and the second order selection which states that mutators hitchhike to fixation
with unrelated beneficial alleles. Conventional population genetics models
could not fully resolve this controversy because they are based on certain
assumptions about fitness landscape. Here we address this problem using a
microscopic multiscale model, which couples physically realistic molecular
descriptions of proteins and their interactions with population genetics of
carrier organisms without assuming any a priori fitness landscape. We found
that both pleiotropy and second order selection play a crucial role at
different stages of adaptation: the supply of mutators is provided through
destabilization of error correction complexes or fluctuations of production
levels of prototypic mismatch repair proteins (pleiotropic effects), while rise
and fixation of mutators occur when there is a sufficient supply of beneficial
mutations in replication-controlling genes. This general mechanism assures a
robust and reliable adaptation of organisms to unforeseen challenges. This
study highlights physical principles underlying physical biological mechanisms
of stress response and adaptation
Qualidade fisiolĂłgica de lotes comerciais de sementes de maracujazeiro-doce armazenadas por longo perĂodo.
O teste padrĂŁo de germinação fornece o potencial mĂĄximo para a formação de plĂąntulas normais, jĂĄ que, Ă© conduzido nas condiçÔes ideais. Para a disponibilidade de sementes durante todo o ano, se faz necessĂĄrio o armazenamento das mesmas. Ao longo do perĂodo de armazenamento das sementes, a qualidade fisiolĂłgica sofre redução, podendo ser maior ou menor dependendo da espĂ©cie, do genĂłtipo e das condiçÔes do armazenamento. A Embrapa e parceiros tĂȘm desenvolvido um programa de melhoramento genĂ©tico de diferentes espĂ©cies do gĂȘnero Passiflora com o lançamento de algumas cultivares. Entre as cultivares lançada pela Embrapa e parceiros estĂĄ a BRS Mel do Cerrado - BRS MC (Passiflora alata), (EMBRAPA, 2020). Com a oferta de mais cultivares de maracujazeiro, aumenta-se tambĂ©m a demanda por sementes com qualidade genĂ©tica, fisiolĂłgica e fitossanitĂĄria. E com isso, tambĂ©m, Ă© importante uma logĂstica adequada para a comercialização dessas sementes, alĂ©m de informaçÔes sobre a germinação, vigor e armazenamento. Trabalhos vem sendo realizados com diferentes espĂ©cies do gĂȘnero Passiflora tĂȘm mostrado o efeito do genĂłtipo sobre a viabilidade ou germinação de sementes (VIANA, et al., 2016; OLIVEIRA, et al., 2016; 2020). Desse modo, nĂŁo Ă© possĂvel generalizar as informaçÔes para a espĂ©cie, mas Ă© importante considerar o genĂłtipo que estĂĄ sendo analisado, bem como as condiçÔes e tempo de armazenamento. Neste contexto, objetivou-se avaliar a qualidade fisiolĂłgica de lotes de sementes e plĂąntulas da cultivar BRS Mel do Cerrado apĂłs longos perĂodos de armazenament
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