9,595 research outputs found
Yield and yield components of upland rice as influenced by nitrogen sources.
Ammonium sulfate and urea are main sources of nitrogen (N) for annual crop production in developing countries. Two greenhouse experiments were conducted using ammonium sulfate and urea as N sources for upland rice grown on a Brazilian Oxisol. The N rates used were 0, 50, 100, 150, 3000, and 400 kg N kg?1 of soil. Yield and yield components were significantly increased in a quadratic fashion with increasing N rate. Ammonium sulfate X urea interaction was significant for grain yield, shoot dry matter yield, panicle number, plant height and root dry weight, indicating a different response magnitude of these plant parameters to two sources of N. Based on regression equation, maximum grain yield was achieved with the application of 380 mg N kg?1 by ammonium sulfate and 271 mg N kg?1 by urea. Grain yield and yield components were reduced at higher rates of urea (>300 mg kg N) but these plant parameters? responses to ammonium sulfate at higher rates was constant. In the intermediate N rate range (125 to 275 mg kg?1), urea was slightly better compared to ammonium sulfate for grain yield. Grain yield was significantly related with plant height, shoot dry weight, panicle number, grain harvest index and root dry weight. Hence, improving these plant characteristics by using appropriate soil and plant management practices can improve upland rice yield
Robustness of bipartite Gaussian entangled beams propagating in lossy channels
Subtle quantum properties offer exciting new prospects in optical
communications. Quantum entanglement enables the secure exchange of
cryptographic keys and the distribution of quantum information by
teleportation. Entangled bright beams of light attract increasing interest for
such tasks, since they enable the employment of well-established classical
communications techniques. However, quantum resources are fragile and undergo
decoherence by interaction with the environment. The unavoidable losses in the
communication channel can lead to a complete destruction of useful quantum
properties -- the so-called "entanglement sudden death". We investigate the
precise conditions under which this phenomenon takes place for the simplest
case of two light beams and demonstrate how to produce states which are robust
against losses. Our study sheds new light on the intriguing properties of
quantum entanglement and how they may be tamed for future applications.Comment: To be published - Nature Photonic
Frequencias de alternancia no molhamento parcial do sistema radicular do limoeiro no Norte de Minas Gerais.
No Brasil, 61% da água é consumida pela agricultura irrigada (Santos & Anjos, 2001). Uma dessas evidencias ocorre nos perímetros irrigados onde as irrigações são geralmente realizadas em excesso. Além do maior gasto de água, regas excessivas acarretam prejuízos à produção, maior incidência de doenças e impacto ambiental (Lopes et al., 2006). Em plantas cítricas, tem-se demonstrado que a produção e qualidade dos frutos são muito afetadas pela qualidade da irrigação nos períodos de floração e ?pegamento? de frutos (Fase I) e de crescimento rápido do fruto (Fase II) (Domingo et al., 1996). O molhamento parcial do sistema radicular (MPSR) tem sido uma tecbica usada recomendada para diferentes culturas com objetivo de racionalização do uso de água sem redução significativa da produtividade potencial da cultura. Consiste na alternância da irrigação em dois lados de uma planta, a freqüência definida, sendo que as mais usadas tem sido 7, 14 e 21 dias (Kang & Zang, 2004). O secamento do solo de um lado acarreta redução da transpiração da planta, sem que a mesma manifeste sintomas de estresse acentuado. Essa tecnologia tem sido avaliada principalmente na Austrália e África do Sul com aumento de até 80% na eficiência de uso de água. Este trabalho objetiva definir a freqüência de alternância do lado irrigado da planta e a percentagem de redução da lamina aplicada na técnica do molhamento parcial do sistema radicular da lima ácida Tahiti nas condições do Norte de Minas em solo de textura arenosa.pdf 165
Disentanglement in Bipartite Continuous-Variable Systems
Entanglement in bipartite continuous-variable systems is investigated in the
presence of partial losses, such as those introduced by a realistic quantum
communication channel, e.g. by propagation in an optical fiber. We find that
entanglement can vanish completely for partial losses, in a situa- tion
reminiscent of so-called entanglement sudden death. Even states with extreme
squeezing may become separable after propagation in lossy channels. Having in
mind the potential applications of such entangled light beams to optical
communications, we investigate the conditions under which entanglement can
survive for all partial losses. Different loss scenarios are examined and we
derive criteria to test the robustness of entangled states. These criteria are
necessary and sufficient for Gaussian states. Our study provides a framework to
investigate the robustness of continuous-variable entanglement in more complex
multipartite systems.Comment: Phys. Rev. A (in press
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