Hygroscopicity and ammonia volatilization losses from nitrogen sources in coated urea

Hygroscopic fertilizers tend to absorb moisture from the air and may have undesirable characteristics such as moistness, clumping and lower fluidity, hampering the application. The increasing use of urea is due to its numerous advantages, although this nitrogen (N) source is highly susceptible to volatilization losses, particularly when applied to the soil surface of management systems with conservation of crop residues. The volatilization losses can be minimized by slow or controlled-release fertilizers, with controlled water solubility of the urea-coating materials; and by stabilized fertilizers, which prolong the period during which N remains in the amide or ammonia forms by urease inhibitors. This study evaluated the hygroscopicity of and ammonia volatilization from urea coated with boric acid and copper sulfate or with sulfur. The hygroscopicity of the sources was evaluated over time after exposure to five levels of relative humidity (RH) and volatilization evaluated after application to the soil surface covered with sugarcane trash. Ammonium nitrate has a low potential for volatilization losses, but is highly hygroscopic. Although coating with boric acid and copper sulfate or elemental sulfur reduced the critical humidity level of urea, the delay in the volatilization process is a potential positive factor.

Quantum tunneling of magnetization in single domain particles

We present a study of the magnetic relaxation of several ferrofluids composed of particles of about 40 Å in diameter (Fe3O4FeC, CoFe2O4). Our key observation is a nonthermal character of the relaxation below 3 K for the CoFe2O4 ferrofluid and below 1 K for the FeC ferrofluid. The crossover temperature from thermal to nonthermal (quantum) regime is in accordance with theoretical suggestions of macroscopic quantum tunneling of magnetization in single doma in particles

"O amor dos começos": por uma história das relações com a escola

Este texto explicita e discute peculiaridades das relações que os indivíduos, homens e mulheres (alunos e professores), mantêm com a escola e com as diferentes disciplinas e os significados dessas relações em histórias de escolarização, com base em depoimentos presentes na literatura, nas autobiografias e nos relatos de formação intelectual de alunos e professores já atuantes. Pretende-se, com a análise, propor novas modalidades de formação favoráveis ao conhecimentos e, assim, ultrapassar concepções de que essas relações são contaminadas por vagos atributos como o interesse ou o desinteresse dos alunos.

Desempenho de dois sistemas distribuidores de sementes utilizados em semeadoras de milho

O tratamento de sementes de milho (Zea mays L.) com inseticidas altera a rugosidade da superfície das sementes, afetando o desempenho da semeadora, pela dificuldade de movimentá-las no depósito e também nos sistemas distribuidores, e a densidade de plantio. Determinou-se o efeito do tratamento com inseticidas ou grafite sobre o ângulo de repouso de sementes de milho, e avaliou-se o efeito da velocidade de deslocamento, do tratamento químico e com grafite das sementes, além da classificação por peneiras, no desempenho de dois sistemas distribuidores, de disco e de dedos prensores. Os testes foram realizados em uma bancada montada em laboratório com sementes classificadas em diferentes peneiras e submetidas a seis tratamentos, testadas em duas velocidades de deslocamento e em dois sistemas de distribuição de sementes. O delineamento utilizado foi em blocos casualizados, com três repetições. No sistema de dedos prensores, o uso do inseticida melhorou significativamente o desempenho da semeadora, ao contrário do verificado no sistema de disco. Com a adição de grafite, na dose de 4 g/kg de sementes, o desempenho voltou a ser o mesmo de antes do tratamento com a utilização de Semevin, e ligeiramente inferior com Furadan.

Percutaneous endoscopic gastrostomy in head and neck cancer patients: indications, techniques, complications and results.

The aim of this study was to review our experience in percutaneous endoscopic gastrostomy (PEG) performed in patients with cancer of the upper aerodigestive tract. Descriptive retrospective study of 142 patients (115 males, 27 females), mean age 62.4 years (25-84 years), with head and neck or esophageal cancer, who underwent PEG tube insertion between January 2006 and December 2008. The studied parameters were indications, success rate, rate and type of complications, and their management. Percutaneous endoscopic gastrostomy was inserted before chemoradiation therapy in 80% and during or after cancer treatment in 20% of the patients. PEG placement was possible in 137 patients (96%). Major complications were observed in 9 (7%) and minor complications in 22 (17%) of the 137 patients. Seven of the 9 patients with a major complication needed revision surgery. The mortality directly related to the procedure was 0.7%. Percutaneous endoscopic gastrostomy tube insertion has a high success rate. In patients with upper aerodigestive tract cancer, PEG should be the first choice for enteral nutrition when sufficient oral intake is not possible. Although apparently easy, the procedure may occasionally lead to severe complications. Therefore, a strict technique and knowledge of clinical signs of possible complications are mandatory.