Aplicação da espectroscopia de ressonância magnética nuclear para estudos de difusão molecular em líquidos: a técnica DOSY

Diffusion coefficients provide uniquely detailed and easily interpreted information on molecular organization and phase structure. They are quite sensitive to structural changes, and to binding and association phenomena, in particular for liquid colloidal or macromolecular systems. This paper describes the principles of diffusion measurements in liquids by pulsed magnetic field gradient spin-echo (PFG-SE) NMR spectroscopy. The important PFG-SE technique known as DOSY is presented and discussed. This is a noninvasive technique that can provide individual multicomponent translational diffusion coefficients with good precision in a few minutes, without the need for radioactive isotopic labelling.

Novos materiais à base de nanofibras de carbono como suporte de catalisador na decomposição da hidrazina

Today satellites propulsion is based on the use of monopropellant and/or bipropellant chemical systems. The maneuvering of satellite is based on the hydrazine decomposition micropropulsors catalyzed by metallic iridium supported on g-alumina. This reaction is a surface reaction and is strongly exothermic and implies that the operation of the micropropulsor is controlled by the mass and heat diffusions. For this reason and for the fact that the propulsor operation is frequently in pulsed regime, the catalyst should support high pressure and temperature variations within a short time period. The performance and the durability of the commercial catalyst are jeopardized by the low thermal conductivity of the alumina. The low thermal conductivity of the alumina support restricts the heat diffusion and leads to the formation of hot spots on the catalyst surface causing the metal sintering and/or fractures of the support, resulting in loss of the activity and catalyst destruction. This work presents the synthesis and characterization of new carbon composite support for the active element iridium, in substitution of the commercial catalysts alumina based support. These supports are constituted of carbon nanofibers (30 to 40 nm diameter) supported on a macroscopic carbon felt. These materials present high thermal conductivity and mechanical resistance, as well as the easiness to be shaped with different macroscopic shapes. The mechanical stability and the performance of the iridium supported on the carbon composite support, evaluated in a laboratory scale test in hydrazine decomposition reaction, are superior compared to the commercial catalyst.

Irradiação de polímeros com feixe de elétrons: caracterização de íons positivos através da técnica de tempo-de-vôo

With the aim of studying the interaction of fast electrons with solid surfaces we have developed an experimental set-up based on electron stimulated desorption (ESD) coupled to time-of-flight (TOF) mass spectrometry. Poly(methyl methacrylate) and poly(vynil chloride) samples have been irradiated by a pulsed electron beam of 1.2 keV and 0.18 µs FWHM. The results show that H+ is the main ionic species to desorb after electron bombardment. In addition, other ionic fragments were also observed and assigned. These results show the potentiality of this technique in the study of ESD of polymers.

Butyltin speciation in sediments from Todos os Santos Bay (Bahia, Brazil) by GC-PFPD

Butyltin compounds were investigated in surface sediments from 17 stations in Todos os Santos Bay. Analytical conditions for organotin determination in marine sediments were optimized for GC with pulsed flame photometric detection. Detection limits were: 5.4 µg kg-1 for TBT; 0.2 µg kg-1 for DBT; and 2.1 µg kg-1 for MBT, using a 610-nm filter. In general, TBT concentrations were low and in the range of

Implementação computacional do modelo carga-fluxo de carga-fluxo de dipolo para cálculo e interpretação das intensidades do espectro infravermelho

The first computational implementation that automates the procedures involved in the calculation of infrared intensities using the charge-charge flux-dipole flux model is presented. The atomic charges and dipoles from the Quantum Theory of Atoms in Molecules (QTAIM) model was programmed for Morphy98, Gaussian98 and Gaussian03 programs outputs, but for the ChelpG parameters only the Gaussian programs are supported. Results of illustrative but new calculations for the water, ammonia and methane molecules at the MP2/6-311++G(3d,3p) theoretical level, using the ChelpG and QTAIM/Morphy charges and dipoles are presented. These results showed excellent agreement with analytical results obtained directly at the MP2/6-311++G(3d,3p) level of theory.

Simulation of the energy performance of maize production integrated to pig farming

The study evaluated the energy performance of pig farming integrated with maize production in mechanized no-tillage system. In this proposed conception of integration, the swine excrement is used as fertilizers in the maize crop. The system was designed involving the activities associated to the pig management and maize production (soil management, cultivation and harvest). A one-year period of analysis was considered, enabling the production of three batches of pigs and two crops of maize. To evaluate the energy performance, three indicators were created: energy efficiency, use of non-renewable resources efficiency and cost of non-renewable energy to produce protein. The energy inputs are composed by the inputs and infrastructure used by the breeding of pigs and maize production, as well as the solar energy incident on the agroecosystem. The energy outputs are represented by the products (finished pigs and maize). The results obtained in the simulation indicates that the integration improves the energy performance of pig farms, with an increase in the energy efficiency (186%) as well as in the use of the non-renewable energy resources efficiency (352%), while reducing the cost of non-renewable energy to produce protein (‑58%).

Groundwater recharge estimate at Alto Rio Grande - MG watershed

Springs are outcrops of aquifers surface, and the water cycle in this environment pass through the recharge, generally defined as the amount of water added to the aquifer, which may occur locally from rainwater infiltration. This study uses the Water Table Fluctuation (WTF) method to estimate the direct recharge and a groundwater balance to estimate the deep recharge on unconfined aquifers. The WTF method employs data of the aquifer water levels and its specific yield to estimate the direct recharge. The groundwater balance considers the direct recharge estimated by the WTF method, as the water input in the system and outputs as the base flow and deep recharge. The recharge was estimated at four areas at the watershed of Alto Rio Grande city, Minas Gerais (MG) state, in Brazil. The direct recharge estimate was 121.11; 64.62; 83.99; 152.46 (mm/year) for the L1, L2, M1 and M2 areas. The effect of the presence of forest in the recharge area can prevail over slope of relief, allowing more direct recharge, even in sources with steeper relief. The runoff from the springs in the study period exceeded the direct recharge, indicating a situation in which the saturated zone feeds the vadose zone. The annual flow was above the direct recharge pointing a situation of over exploitation of the aquifer, a non sustainable situation. The specific yield of the aquifers could also have been underestimated.

Ultrasonografic changes in the axillary vein of patients with lymphedema after mastectomy

OBJECTIVE: To determine the prevalence of sonographic abnormalities (SA) in the axillary vein of patients with and without post-mastectomy lymphedema. METHODS: We studied a sample of 80 women, divided into two equal groups, with and without lymphedema, with B mode ultrasound, color and pulsed Doppler. The primary variable, SA, is defined as change in the venous diameter, parietal thickening, intraluminal images, compressibility, parietal collapse at inspiration and feature of the axillary venous flow on the operated side. Secondary variables were: stage of lymphedema, surgical technique, number of radio and chemotherapy sessions, limb volume, weight and age. The differences between the proportions in the groups were determined using the Chi-square test and / or Fisher's test. For continuous variables, we used the Mann-Whitney Test. To estimate the magnitude of the associations, we used the prevalence rate of SA in both groups as a measure of frequency, and as a measure of association, the prevalence ratio (PR) obtained as a function of relative risk (RR) and estimated by the test Mantel-Haenszel homogeneity test. We adopted the statistical significance level of 5% (p < 0.05). RESULTS: only the criterion "parietal thickening" was strongly associated with the lymphedema group (p = 0.001). The prevalence of SA was 55% in patients with lymphedema and 17.5% in the group without it, with difference in prevalence of 37.5%. CONCLUSION: the prevalence of SA was higher in patients undergoing mastectomy with lymphedema than in those without lymphedema.

Reference range of uterine artery Doppler parameters between the 11th and 14th pregnancy weeks in a population sample from Northeast Brazil

PURPOSE: To establish reference values for the first trimester uterine artery resistance index (UtA-RI) and pulsatility index (UtA-PI) in healthy singleton pregnant women from Northeast Brazil. METHODS: A prospective observational cohort study including 409 consecutive singleton pregnancies undergoing routine early ultrasound screening at 11 - 14 weeks of gestation was performed. The patients responded to a questionnaire to assess maternal epidemiological characteristics. The left and right UtA-PI and UtA-RI were examined by color and pulsed Doppler by transabdominal technique and the mean UtA-PI, mean UtA-RI and the presence of bilateral protodiastolic notching were recorded. Quartile regression was used to estimate reference values. RESULTS: The mean±standard deviation UtA-RI and UtA-PI were 0.7±0.1 and 1.5±0.5, respectively. When segregated for gestation age, mean UtA-PI was 1.6±0.5 at 11 weeks, 1.5±0.6 at 12 weeks, 1.4±0.4 at 13 weeks and 1.3±0.4 at 14 weeks' gestation and mean UtA-RI was 0.7±0.1 at 11 weeks, 0.7±0.1 at 12 weeks, 0.6±0.1 at 13 weeks and 0.6±0.1 at 14 weeks' gestation. Uterine artery bilateral notch was present in 261 (63.8%) patients. We observed that the 5th and 95th percentiles of the UtA-PI and UtA-RI uterine arteries were 0.7 and 2.3 and, 0.5 and 0.8, respectively. CONCLUSION: Normal reference range of uterine artery Doppler in healthy singleton pregnancies from Northeast Brazil was established. The 95th percentile of UtA-PI and UtA-RI values may serve as a cut-off for future prediction of pregnancy complications studies (i.e., pre-eclampsia) in Northeast Brazil.

Molecular epidemiology and extended-spectrum β-lactamases production of Klebsiella pneumoniae isolated from three dairy herds

The objectives of this study were to isolate Klebsiella pneumoniae from different sources in three dairy cattle herds, to use the pulsed-field gel electrophoresis (PFGE) to measure genotypic similarities between isolates within a dairy herd, to verify the production of extended-spectrum β-lactamases (ESBLs) by the double-disk synergy test (DDST), and to use the PCR to detect the main ESBLs subgroups genes. Three dairy farms were selected based on previous mastitis outbreaks caused by K. pneumoniae. Milk samples were collected from lactating cows and from the bulk tank. Swabs were performed in different locations, including milking parlors, waiting room, soil, animal's hind limbs and rectum. K. pneumoniae was isolated from 27 cases of intramammary infections (IMI) and from 41 swabs. For farm A isolates from IMI and bulk tank were considered of the same PGFE subtype. One isolate from a bulk tank, three from IMI cases and four from environmental samples were positive in the DDST test. All eight DDST positive isolates harbored the bla shv gene, one harbored the bla tem gene, and three harbored the bla ctx-m gene, including the bulk tank isolate. Our study confirms that ESBL producing bacteria is present in different locations in dairy farms, and may be responsible for IMI. The detection of ESBLs on dairy herds could be a major concern for both public and animal health.

Pulse response based control for positive definite systems

Pulse Response Based Control (PRBC) is a recently developed minimum time control method for flexible structures. The flexible behavior of the structure is represented through a set of discrete time sequences, which are the responses of the structure due to rectangular force pulses. The rectangular force pulses are given by the actuators that control the structure. The set of pulse responses, desired outputs, and force bounds form a numerical optimization problem. The solution of the optimization problem is a minimum time piecewise constant control sequence for driving the system to a desired final state. The method was developed for driving positive semi-definite systems. In case the system is positive definite, some final states of the system may not be reachable. Necessary conditions for reachability of the final states are derived for systems with a finite number of degrees of freedom. Numerical results are presented that confirm the derived analytical conditions. Numerical simulations of maneuvers of distributed parameter systems have shown a relationship between the error in the estimated minimum control time and sampling interval

A quality and cost approach for welding process selection

The aim of this work was to propose, apply and evaluate a methodical approach to select welding processes in a productive environment based on market requirements of Quality and Costs. A case study was used. The welds were carried out in laboratory, simulating the joint conditions of a manufacturer and using several welding processes: SMAW, GTAW, pulsed GTAW, GMAW with CO2 and Ar based shielding gases and pulsed GMAW. For Quality analysis geometrical aspects of the beads were considered and for Cost analysis, welding parameters and consumable prices. Quantitative indices were proposed and evaluated. After that, evaluation of both Quality and Costs was done, showing to be possible to select the most suitable welding process to a specific application, taking into account the market conditions of a company.

On-site calibration of a phase fraction meter by an inverse technique

The formal calibration procedure of a phase fraction meter is based on registering the outputs resulting from imposed phase fractions at known flow regimes. This can be straightforwardly done in laboratory conditions, but is rarely the case in industrial conditions, and particularly for on-site applications. Thus, there is a clear need for less restrictive calibration methods regarding to the prior knowledge of the complete set of inlet conditions. A new procedure is proposed in this work for the on-site construction of the calibration curve from total flown mass values of the homogeneous dispersed phase. The solution is obtained by minimizing a convenient error functional, assembled with data from redundant tests to handle the intrinsic ill-conditioned nature of the problem. Numerical simulations performed for increasing error levels demonstrate that acceptable calibration curves can be reconstructed, even from total mass measured within a precision of up to 2%. Consequently, the method can readily be applied, especially in on-site calibration problems in which classical procedures fail due to the impossibility of having a strict control of all the input/output parameters.

Factors affecting Cyperus difformis seed germination and seedling emergence

Specific knowledge about the dormancy, germination, and emergence patterns of weed species aids the development of integrated management strategies. Laboratory studies were conducted to determine the effect of several environmental factors on seed germination and seedling emergence of Cyperus difformis. Germination of freshly harvested seeds was inhibited by darkness; however, when seeds were subsequently transferred to complete light they germinated readily. Our results showed that 2 wk of cold stratification overcome the light requirement for germination. Seeds of C. difformis were able to germinate over a broad range of temperatures (25/15, 30/20, 35/25, and 40/30 ºC day/night). The response of germination rate to temperature was described as a non-linear function. Based on model outputs, the base, the optimum and the ceiling temperatures were estimated as 14.81, 37.72 and 45 ºC, respectively. A temperature of 120 ºC for a 5 min was required to inhibit 50% of maximum germination. The osmotic potential and salinity required for 50% inhibition of maximum germination were -0.47 MPa and 135.57 mM, respectively. High percentage of seed germination (89%) was observed at pH=6 and decreased to 12% at alkaline medium (pH 9) pH. Seeds sown on the soil surface gave the greatest percentage of seedling emergence, and no seedlings emerged from seeds buried in soil at depths of 1 cm.

Biologia reprodutiva de Rourea induta Planch. (Connaraceae), uma espécie heterostílica de cerrado do Brasil Central

A heterostilia é um polimorfismo floral geralmente associado a sistemas genéticos de intramorfo incompatibilidade. Nós avaliamos aspectos reprodutivos da heterostilia de uma população de Rourea induta Planch. em uma área de cerrado de Brasília, DF. Foram conduzidos estudos sobre sua biologia floral, sistema reprodutivo, produção e maturação de frutos, germinação de sementes, fenologia reprodutiva e visitantes florais. As flores são pequenas (11 mm de diâmetro), com morfologia simples e possuem dois grupos de cinco estames de comprimentos diferentes e cinco pistilos. O comprimento médio de estames e pistilos diferiu significativamente entre o morfo brevistilo e o longistilo. No entanto, não houve hercogamia recíproca completa entre os dois morfos florais. Os dois morfos são intramorfo incompatíveis, mas o morfo brevistilo é completamente auto-incompatível enquanto o longistilo é parcialmente autocompatível. Apesar das diferenças na morfologia floral e no sistema reprodutivo entre os morfos, estes apresentam igual sucesso reprodutivo em condições naturais, uma vez que a produção e a maturação de frutos por planta e a taxa de germinação das sementes não diferiram significativamente. A população de R. induta apresentou floração tipo "pulsed bang" com alta sincronia intra-individual e inter-individual de floração. Grande variedade de insetos, principalmente pequenas abelhas sociais, foi observada visitando as flores. Nossos resultados sugerem que a auto-incompatibilidade parcial, a incompatibilidade intramorfo e as diferenças nas alturas dos verticilos reprodutivos entre os dois morfos reduzem os níveis de autogamia em R. induta. Em última análise, a maior produção de frutos por polinização intermorfo, promoveu a razão isoplética na população estudada e indicou que R. induta é dependente dos polinizadores para a reprodução sexuada.