Reduction of mercury(II) by tropical river humic substances (Rio Negro) - Part II. Influence of structural features (molecular size, aromaticity, phenolic groups, organically bound sulfur)

The influence of structural features of tropical river humic substances (HS) on their capability to reduce mercury(II) in aqueous solutions was studied. The HS investigated were conventionally isolated from Rio Negro water-Amazonas State/Brazil by means of the collector XAD 8. In addition, the isolated HS were on-line fractionated by tangential-flow multistage ultrafiltration (nominal molecular-weight cut-offs: 100, 50, 30, 10, 5 kDa) and characterized by potentiometry and UV/VIS spectroscopy. The reduction of Hg(II) ions to elemental Hg by size-fractions of Rio Negro HS was assessed by cold-vapor AAS (CVAAS). UV/VIS spectrometry revealed that the fractions of high molecular-size (F-1 > 100 kDa and F-2: 50-100 kDa) have a higher aromaticity compared to the fractions of small molecular-size (F-5: 5-10 kDa, F-6: < 5 kDa). In contrast, the potentiometric study showed different concentration of functional groups in the studied HS fractions. The reduction of Hg(II) by aquatic HS fractions at pH 5 proceeded in two steps (I, II) of slow first order kinetics (t(1/2) of I: 160 min, t(1/2) of II: 300 min) weakly influenced by the molecular-size, in contrast to the differing degree of Hg(II) reduction (F-5 > F-2 > > F-1 > F-3 > F-4 > > F-6). Accordingly, Hg(II) ions were preferably reduced by HS molecules having a relatively high ratio of phenolic/carboxylic groups and a small concentration of sulfur. From these results a complex 'competition' between reduction and complexation of mercury(II) by aquatic HS occurring in tropical rivers such as the Rio Negro can be suggested. (C) 2003 Elsevier B.V. All rights reserved.

Reduction of mercury(II) by tropical river humic substances (Rio Negro) - A possible process of the mercury cycle in Brazil

The evolution of elemental Hg from its environmental compounds has already been supposed to be an important process within the global mercury cycle. The present study characterizes the abiotic reduction of Hg(II) ions by typical river humic substances (HS) conventionally pre-isolated by the adsorbent XAD 8 from the Rio Negro near Manaus, Brazil. For the investigation of this reduction process a special reaction and Hg(0) trapping unit combined with cold-vapor atomic absorption spectrometry (CVAAS) was developed. Preconcentration of traces of mercury(II), if required, was obtained by a home-made FIA system using microcolumns filled with the Hg(II)-selective collector CheliteS(R) (Serva Company). The effect of environmentally relevant parameters such as the pH value, the Hg(II)/HS ratio and the HS concentration on the I-IE;(II) reduction process was studied as a function of the time. The Hg(0) production was highest at pH 8.0 and in the case of decreasing HS amounts (0.5 mg) when about 65% of initially 1.0 mug Hg(H) was reduced within 50 h. Moreover, the reduction efficiency of HS towards HE;(II) strongly depended on the HS concentration but hardly on the Hg(II)/HS ratio. The reduction kinetics followed a relatively slow two-step first-order mechanism with formal rate constants of about 0.1 and 0.02 h(-1), respectively. Based on these findings the possible relevance of the abiotic evolution of mercury in humic-rich aquatic environments is considered. (C) 2000 Elsevier B.V. B.V. All rights reserved.

Productive and reproductive performance of heifers fed different levels of urea in the diet

The objective of the present study was to evaluate the nutrient intake, blood parameters, follicular diameter and performance of pre-puberty crossbred heifers fed isoproteic diets (14.1%CP) containing 0.0; 0.44; 0.88 and 1.32% urea on the total dry matter (DM) of the diet, with a 77:23 roughage:concentrate ratio. Twenty-four 18- month old heifers (Holstein x Zebu), 277.9 kg mean live weight (LW) were used, distributed in four treatments and six replications in a randomized complete design. The following were evaluated: dry matter intake (DM), crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), ether extract (EE), hemicellulose (HEM), plasmatic ureic nitrogen (PUN), plasmatic glucose, plasmatic total cholesterol, follicular diameter and daily weight gain (DWG). No influence of the urea levels in the diet was observed on NDF and HEM intake. A maximum intake was obtained of DM (8.75 kg day(-1)), CP (0.88 kg day(-1)), ADF (2.5 kg day(-1)) and EE (0.17 kg day(-1)) respectively for the levels 0.7, 0.8, 0.7 and 0.7% urea in total DM. The 0.6%; 0.77% and 0.6% urea levels in diet were the critical points for obtaining maximum response for the PUN (10.96 mg dL(-1)) and plasmatic glucose (84.97 mg dL(-1)) concentrations and, for follicular diameter (11.08 mm) on the 40(th); 24(th) and 31(st) day, respectively. The plasmatic total cholesterol concentration and DWG were not influenced by the urea added to the diet, with averages of 119.39 mg dL(-1) and 1.66 kg day(-1), respectively. It was concluded that urea can be added up to 1.32% on the total DM of the diet for pre-puberty crossbred heifers.

Use of the Normalized Absorbance Ratio as an Internal Standardization Approach To Minimize Measurement Error in Enzyme-Linked Immunosorbent Assays for Diagnosis of Human Papillomavirus Infection

The serological detection of antibodies against human papillomavirus (HPV) antigens is a useful tool to determine exposure to genital HPV infection and in predicting the risk of infection persistence and associated lesions. Enzyme-linked immunosorbent assays (ELISAs) are commonly used for seroepidemiological studies of HPV infection but are not standardized. Intra-and interassay performance variation is difficult to control, especially in cohort studies that require the testing of specimens over extended periods. We propose the use of normalized absorbance ratios (NARs) as a standardization procedure to control for such variations and minimize measurement error. We compared NAR and ELISA optical density (OD) values for the strength of the correlation between serological results for paired visits 4 months apart and HPV-16 DNA positivity in cervical specimens from a cohort investigation of 2,048 women tested with an ELISA using HPV-16 virus-like particles. NARs were calculated by dividing the mean blank-subtracted (net) ODs by the equivalent values of a control serum pool included in the same plate in triplicate, using different dilutions. Stronger correlations were observed with NAR values than with net ODs at every dilution, with an overall reduction in nonexplained regression variability of 39%. Using logistic regression, the ranges of odds ratios of HPV-16 DNA positivity contrasting upper and lower quintiles at different dilutions and their averages were 4.73 to 5.47 for NARs and 2.78 to 3.28 for net ODs, with corresponding significant improvements in seroreactivity-risk trends across quintiles when NARs were used. The NAR standardization is a simple procedure to reduce measurement error in seroepidemiological studies of HPV infection.

Noise reduction in speech signals using a TMS320C31 digital signal processor

This paper describes a speech enhancement system (SES) based on a TMS320C31 digital signal processor (DSP) for real-time application. The SES algorithm is based on a modified spectral subtraction method and a new speech activity detector (SAD) is used. The system presents a medium computational load and a sampling rate up to 18 kHz can be used. The goal is load and a sampling rate up to 18 kHz can be used. The goal is to use it to reduce noise in an analog telephone line.

Coordination of Eu3+ ions in siliceous nanohybrids containing short polyether chains and bridging urea cross-links

Infrared and photoluminescence spectroscopies have been used to investigate the local environment of the Eu3+ ions in luminescent sol-gel derived materials-di-ureasils-based on a hybrid framework represented by U(600). This host is composed of a siliceous backbone grafted, through urea cross-links, to both ends of polymer segments incorporating 8.5 oxyethylene repeat units. The active centers have been introduced as europium perchlorate, Eu(ClO4)3. Samples with compositions n = 232, 62, 23, 12, and 6 (where n denotes the ratio of (OCH2CH2) moieties per lanthanide ion) have been examined. The combination of the information retrieved from the analysis of characteristic bands of the FTIR spectra-the perchlorate and the Amide I/Amide II features-with that obtained from the photoluminescence data demonstrates that at compositions n = 232 and 62 the anions are free, whereas the Eu3+ ions are complexed by the heteroatoms of the polyether chains. At higher salt concentration, the cations are bonded, not only to the ClO4 - ions, but also to the ether oxygen atoms of the organic segments and to the carbonyl oxygen atoms of the urea linkages. The dual behavior of U(600) with respect to cation coordination has been attributed to the presence in this nanohybrid of strong hydrogen-bonded urea-urea structures, which, at low salt content, cannot be disrupted, thus inhibiting the formation of Eu3+-O=C(urea) contacts and promoting the interaction between the lanthanide ions and the (OCH2CH2) moieties. The present work substantiates the claim that the activation of the coordinating sites of the di-ureasil framework can be tuned by varying either the guest salt concentration at constant chain length or the length of the.organic segments at constant salt concentration. This relevant property opens challenging new prospects in the fields of application of this class of hybrids. © 2001 American Chemical Society.

Multipath reduction from GPS double differences using wavelets: How far can we go?

Wavelets are being extensively used in Geodetic applications. In this paper, the Multi-Resolution Analysis (MRA) using wavelets is applied to pseudorange and carrier phase GPS double differences (DDs) in order to reduce multipath effects. The wavelets were already applied to GPS carrier phase DDs, but some questions remain: How good can be the results, and are all multipath effects reduced? The answers to these questions are discussed in this paper. Thus, the wavelet transform is used to decompose the DD signals, splitting them in lower resolution components. After the decomposition process, the wavelet shrinkage is performed by thresholding to eliminate the components relative to multipath effects. Then, the DD observation can be reconstructed. This new DD signal is used to perform the baseline processing. The daily multipath repeatability was verified. With the application of the proposed approach, the results showed that the reliability of the ambiguity resolution and accuracy of the results improved when compared with the standard procedure. Furthermore, the method showed to be very efficient computationally, because, it is not noticed, at practical level, difference in the time span between the processing with and without application of the proposed method. However, only the high frequency multipath was eliminated.

Structural control of photoluminescence of four poly(urethane-urea-co-1,3,5-triazine)s: Synthesis and characterization

A series of segmented poly(urethane-urea)s containing 1,3,5 triazine in the hard block and hexamethylene spacers in the soft block was prepared. The hard to soft segment ratio was varied systematically, to afford a series of polymers in which the chromophore concentration varied from 4.2% to 18.1%. Although triazine emission is located in the UV region, the films with higher content of the chromophore emitted a visible blue light (425 nm) when excited at the very red-edge of the absorption band. The photophysical properties of the materials were strongly dependent on the relative amount of triazine moieties along the main chain. Isolated moieties emit in copolymers with small amount of triazine groups, indicating that even though in solid state, these moieties tend to be apart. Two photophysical consequences were observed when the amount of triazine increases: there is some energy transfer process involving isolated moieties with consequent decrease of the lifetime and an additional red-edge emission attributed to aggregated lumophores. The mono-exponential decay observed for the isolated form is substituted by a bi-exponential decay of the aggregated species. The materials were not strong emitters, but since the N-containing triazine moieties are good electron transport groups, the polymers have potential application as electron transport enhancers in various applications. © 2006 Elsevier B.V. All rights reserved.

Ultrassonografia Doppler na avaliação renal de cadelas diagnosticadas com piometra antes e após tratamento com ovariosalpingohisterectomia

The aim of this study was evaluate the renal hemodynamics of bitches with pyometra by means of laboratory tests, ultrasound B mode and Doppler, before and after treatment with ovariohysterectomy (OSH). This study evaluated 30 bitches with pyometra, all were subjected to OSH (moment 1) and 20 were evaluated after 7 days (moment 2). The renal perfusion, the resistivity index (RI) of the main renal artery and the interlobar arteries (cranial, middle and caudal) were statistically different between times 1 and 2 (p<0,05). There was no statistical difference for renal perfusion between the left and the right kidney at the time 1 and 2. The correlations between the IR of the main artery and the variables used to determine renal function were stablished at the time 1. For the correlated variables: urea, creatinine, proteinuria, ratio GGT/creatinine and protein/creatinine were curvilinear and positive associations with the resistivity index of the main renal artery (p<0,05), however these correlations were considered medium and weak. Comparing the RI of the main renal artery with different scores of dehydration and renal perfusion, there was statistical difference, and show increased of resistance renal in bitches with moderate reduction in renal perfusion as well as in dehydrated bitches. Were evaluated several features of renal morphology in ultrasound B mode, however, only the presence of pelvic dilatation, medullary signal and other changes as infarcts areas and diffuse hyperechoic spots in the renal cortical and medullary were statistically different from one moment to the other, most frequently at the time 2. The results of this study show that the Doppler ultrasound can identify changes of reduction in renal perfusion by color Doppler and the increasing of the resistivity index of the renal arteries in some bitches with pyometra. As well as, the ultrasound B mode, although has non-specific changes, can detect progressive renal disorders in bitches with pyometra.

Avaliação da proporção áurea em radiografias cefalométricas laterais de indivíduos edêntulos antes e depois do tratamento por próteses totais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Verificação da proporção áurea em indivíduos dolicofaciais e mesofaciais, por meio de radiografias cefalométricas laterais

Pós-graduação em Biopatologia Bucal - ICT

Estudo da proporção áurea em indivíduos edêntulos antes e depois do tratamento por próteses totais por meio de radiografias cefalométricas laterais e fotografias

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Verificação da relação entre proporção áurea e estética facial, antes e depois do tratamento ortodôntico, utilizando radiografias cefalométricas laterais e fotograficas

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Verificação da proporção áurea de indivíduos com alteração de perfil facial antes e depois do tratamento ortodôntico em radiografias cefalométricas laterais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Verificação da proporção áurea em medidas cefalométricas laterais de indivíduos com síndrome de Down

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)