Admittance and dielectric spectroscopy of polycrystalline semiconductors

This text discusses about advantageous, powerful and limitations of admittance and dielectric spectroscopy in the characterization of polycrystalline semiconductors. In the context of polycrystalline semiconductors or dielectric materials, the admittance or dielectric frequency response analyses are shown to be sometimes more useful than impedance spectra analysis, mainly because information on the capacitances or deep trap states are possible to be monitored from admittance or dielectric spectra as a function of dopant concentration or annealing effects. The majority of examples of the application of admittance or dielectric analysis approach were here based on SnO2- and ZnO-based polycrystalline semiconductors devices presenting nonohmic properties. Examples of how to perform the characterization of Schottky barrier in such devices are clearly depicted. The approach is based on findings of the true Mott-Schottky pattern of the barrier by extracting the grain boundary capacitance value from complex capacitance diagram analysis. The equivalent circuit of such kind of devices is mainly consistent with the existence of three parallel elements: the high-frequency limit related to grain boundary capacitances, the complex incremental capacitance at intermediate frequency related to the deep trap relaxation and finally at low frequency region the manifestation of the conductance term representing the dc conductance of the multi-junction device. (c) 2007 Elsevier Ltd. All rights reserved.

FTY720 in combination with cyclosporine - an analysis of skin allograft survival and renal function

Acute and chronic nephrotoxicity caused by CsA Continuous administration impair kidney allograft survival. Several clinical and experimental protocols have shown benefits to the kidney after decreasing CsA dose, withdrawing the drug or delaying its introduction after transplantation.FTY720 is a new Compound that has immunosuppressive characteristics and increase allograft survival in animal models without causing the side effects of calcineurin inhibitors (CNIs). FTY720 described mechanism of action that consists to alter the lymphocyte migration pattern without impairment of the immune system response against pathogens.In our mice model, FTY720 administered alone or in combination with CsA during 21 days increased skin allograft survival in a fully mismatched strain combination and did not cause significant changes in renal function. Moreover, renal structure was normal in all groups suggesting that at low doses (10 mg/kg/day) CsA can be associated during short-term period to other immunosuppressive drugs, i.e. FTY720 without affecting the kidney.Combination of immunosuppressive compounds with FTY720 and/or delayed introduction of low cyclosporine dose Could prevent graft rejection and avoid nephrotoxicity. (c) 2006 Elsevier B.V. All rights reserved.

Synthesis of SnO2 by chemical routes and its use in varistors production

Tin oxide, SnO2. is a very used compound in industry and one of its uses is as varistor. For the current requirements of the technology is necessary a strict control of the chemical purity and the particle size of the raw material; for that reason the great interest that exists at the moment to develop synthesis methods that allow to get these requirements. In this work, ceramic powders of the Sn-Co-Nb-Ti-Al system using the controlled precipitation and polymeric precursor (Pechini) methods were synthesized. The raw material obtained was characterized using X-ray diffraction (XRD), thermal analysis (DTA/FG) and scanning electron microscopy (SEM). The sintering samples shown a good varistor behavior with non-linear coefficient (alpha) values similar to 22, and Er 2083 V/cm(2). (c) 2007 Elsevier Ltd. All rights reserved.

Screen printed PLZT thick films prepared from nanopowders

The gap between the bulk materials and thin films can be filled with thick films suitably designed and appropriate processed. Thick films of complex system like lead-lanthanum-zirconium titanate (PLZT) is difficult to produce by simple solid-state reaction keeping compositional homogeneity and optimal grain size distribution. In the present work, PLZT thick films were fabricated by screen-printing technique from nanosized powders obtained through soft chemistry by polymeric precursor method. Thick film paste was obtained by mixing PLZT fine powders and organic vehicle. The upper and bottom electrodes based on Ag-Pd and functional component based on PLZT were screen-printed on alumina substrate and after that annealed in air atmosphere. The powder morphology, microstructure, dielectric and ferroelectric properties of 9.5/65/35 PLZT thick films were analysed. (c) 2007 Elsevier Ltd. All rights reserved.

Laser weld: microstructure and corrosion study of Ag-Pd-Au-Cu alloy of the dental application

The laser Welding process was introduced into dentistry by the end of the 1980s, resulting on a great impulse to that area with the development of cheaper and smaller equipment, using simpler technique. This allowed greater use of that process on the confection of prostheses compared to the brazing process since the heat source for that process is a concentrated light beam of high power, which minimizes distortion problems on the prosthetic pieces. Ag-Pd-Au-Cu alloy used on the confection of dental implant prostheses was observed before and after subjection to the laser welding process. The microstructure was analyzed with the. use of optic microscopy and the corrosion resistance was studied by the traditional electrochemical techniques and by electrochemical impedance, under environmental conditions simulating the aggressiveness found in the mouth cavity. A structural change was detected on the weld area, which presented a refined microstructure deriving from the high-speed cooling. The base metal out of the weld area presented a fusion coarse microstructure. The electrochemical essays showed differences on the potentiodynamic polarization behavior in both weld and metal base areas, indicating superior corrosion resistance in the weld area. The impedance spectra were characterized by capacitive distorted components, presenting linear impedance in the low frequencies area. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Barium strontium titanate nanocrystalline thin films prepared by soft chemical method

Barium strontium titanate (Ba0.65Sr0.35TiO3) nanocrystalline thin films, which were produced by the soft chemical method, were crystallized at low temperature using a domestic microwave oven. A SiC susceptor were used to absorb the microwave energy and rapidly transfer the heat to the film. Low microwave power and short time have been used. The films obtained are crack-free, well-adhered, and fully crystallized. The microstructure displayed a polycrystalline nature with nanograin size. The metal-BST-metal structure of the thin films treated at 700 degrees C show food electric properties. The ferroelectric nature of the BST35 thin film was indicated by buttertly- shaped C-V curves. The capacitance-frequency curves reveal that the dielectric constant may reach a value up to 800 at 100kHz. The dissipation factor was 0.01 at 100kHz. The charge storage density as function of applied voltage graph showed that the charge storage densities are suitable for use in trench type 64 Mb ( 1-5 mu C/cm(2) and 265 Mb (2-11 mu C/cm(2)) DRAMs. (C) 2007 Elsevier Ltd. All rights reserved.

EXAFS investigation on Sb incorporation effects to electrical transport in SnO2 thin films deposited by sot-gel

The effect of Sb doping in SnO2 thin films prepared by the sol-gel dip-coating (SGDC) process is investigated. Electronic and structural properties are evaluated through synchrotron radiation measurements by EXAFS and XANES. These data indicate that antimony is in the oxidation state W, and replaces tin atoms (Sn4+), at a grain surface site. Although the substitution yields net free carrier concentration, the electrical conductivity is increased only slightly, because it is reduced by the high grain boundary scattering. The overall picture leads to a shortening of the grain boundary potential, where oxygen vacancies compensate for oxygen adsorbed species, decreasing the trapped charge at grain boundary. (c) 2007 Elsevier Ltd. All rights reserved.

Electron trapping of laser-induced carriers in Er-doped SnO2 thin films

In order to investigate optically excited electronic transport in Er-doped SnO2, thin films are excited with the fourth harmonic of an Nd:YAG laser (266nm) at low temperature, yielding conductivity decay when the illumination is removed. Inspection of these electrical characteristics aims knowledge for electroluminescent devices operation. Based on a proposed model where trapping defects present thermally activated cross section, the capture barrier is evaluated as 140, 108, 100 and 148 meV for doped SnO2, thin films with 0.0, 0.05, 0. 10 and 4.0 at% of Er, respectively. The undoped film has vacancy levels as dominating, whereas for doped films. there are two distinct trapping centers: Er3+ substitutional at Sn lattice sites and Er3+ located at grain boundary. (C) 2007 Elsevier Ltd. All rights reserved.

A Simple Method Based on ICP-MS for Estimation of Background Levels of Arsenic, Cadmium, Copper, Manganese, Nickel, Lead, and Selenium in Blood of the Brazilian Population

Throughout the world, biomonitoring has become the standard for assessing exposure of individuals to toxic elements as well as for responding to serious environmental public health problems. However, extensive biomonitoring surveys require rapid and simple analytical methods. Thus, a simple and high-throughput method is proposed for the determination of arsenic (As), cadmium (Cd), copper (Cu), manganese (Mn), nickel (Ni), lead (Pb), and selenium (Se) in blood samples by using inductively coupled plasma-mass spectrometry (ICP-MS). Prior to analysis, 200 l of blood samples was mixed with 500 l of 10% v/v tetramethylammonium hydroxide (TMAH) solution, incubated for 10 min, and subsequently diluted to 10 ml with a solution containing 0.05% w/v ethylenediamine tetraacetic acid (EDTA) + 0.005% v/v Triton X-100. After that, samples were directly analyzed by ICP-MS (ELAN DRC II). Rhodium was selected as an internal standard with matrix-matching calibration. Method detection limits were 0.08, 0.04, 0.5, 0.09, 0.12, 0.04, and 0.1 g//L for As, Cd, Cu, Mn, Ni, Pb, and Se, respectively. Validation data are provided based on the analysis of blood samples from the trace elements inter-\comparison program operated by the Institut National de Sante Publique du Quebec, Canada. Additional validation was provided by the analysis of human blood samples by the proposed method and by using electrothermal atomic absorption spectrometry (ETAAS). The method was subsequently applied for the estimation of background metal blood values in the Brazilian population. In general, the mean concentrations of As, Cd, Cu, Mn, Ni, Pb, and Se in blood were 1.1, 0.4, 890, 9.6, 2.1, 65.4, and 89.3 g/L, respectively, and are in agreement with other global populations. Influences of age, gender, smoking habits, alcohol consumption, and geographical variation on the values were also considered. Smoking habits influenced the levels of Cd in blood. The levels of Cu, Mn, and Pb were significantly correlated with gender, whereas Cu and Pb were significantly correlated with age. There were also interesting differences in Mn and Se levels in the population living in the north of Brazil compared to the south.

Dissociated time course recovery between rate of force development and peak torque after eccentric exercise

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

REDUCAO DA CONCENTRACAO ALVEOLAR MINIMA DO ISOFLURANO E DO SEVOFLURANO PELO SUFENTANIL

Background and Objectives - Inhalational anesthetics have a mild analgesic effect. The reduction of alveolar concentration (MAC) of potent volatile anesthesics by increasing plasma concentrations of opioids is desired in inhalational anesthesia. The purpose of this study was to determine the role of sufentanil in reducing sevoflurane and isoflurane MAC. Methods - Thirty eight adult patients of both genders, physical status ASA I or II, submitted to major abdominal procedures were randomly allocated into two groups. Group I (n = 24) received inahalational anesthesia with sevoflurane and Group II (n = 14) received inhalational anesthesia with isoflurane, both diluted in a mixture of N2O (1 liter) and O2 (0.5 liter). A semi-closed system with CO2 absorber and partial reinhalation was used. Ventilation was mechanically controlled. Sufentanil infusion was administered aiming at obtaining 0.5 ng.ml-1 of plasma concentration. Sufentanil plasma concentration was previously calculated by a computer software. End-tidal concentrations were obtained through a gas analyzer and measured at 15 minutes (M1), 30 minutes (M2), 60 minutes (M3), 90 minutes (M4) and 120 minutes (M5). Systolic and diastolic blood pressure (SBP and DBP) and heart rate (RR) were measured during the same periods with the addition of M0 (pre-anesthetic period). Hourly consumption of the inhalational anesthetic agent (IAC), extubation time (ET = time between admission to the recovery room and extubation) and stay in the post anesthesia recovery room (PA-RR) were also measured. Results - Type and duration of surgeries were similar for both groups. There were no statistically significant differences in MAC, SBP, DBP, RR, IAC, TE and PA-RR between groups. Systolic blood pressure in group I (sevoflurane) showed differences among periods F = 3.82 p < O.05; (M2 = M3)(M4 = M5) and M1 had a intermediate value. MAC in group I showed differences among periods F = 9.0 p < 0.05; M1 < M3. MAC in group II also showed differences among periods F = 13.03 p < O.05; M1 < (M2,M3,M4,M5). Conclusions - Both groups had similar behavior when associated to sufentanil in major abdominal surgeries. Group II showed a higher cardiac and circulatory stability.

β-Carotene supplementation results in adverse ventricular remodeling after acute myocardial infarction

Objective: We studied the effects of β-carotene (BC) on ventricular remodeling after myocardial infarction. Methods: Myocardial infarction was induced in Wistar rats that were then treated with a BC diet (500 mg/kg of diet per day; MI-BC; n = 27) or a regular diet (MI; n = 27). Hearts were analyzed in vivo and in vitro after 6 mo. Results: BC caused decreased left ventricular wall thickness (MI = 1.49 ± 0.3 mm, MI-BC = 1.23 ± 0.2 mm, P = 0.027) and increased diastolic (MI = 0.83 ± 0.15 cm2, MI-BC = 0.98 ± 0.14 cm2, P = 0.020) and systolic (MI = 0.56 ± 0.12 cm2, MI-BC = 0.75 ± 0.13 cm2, P = 0.002) left ventricular chamber areas. With respect to systolic function, the BC group presented less change in fractional area than did controls (MI = 32.35 ± 6.67, MI-BC = 23.77 ± 6.06, P = 0.004). There was no difference in transmitral diastolic flow velocities between groups. In vitro results showed decreased maximal isovolumetric systolic pressure (MI = 125.5 ± 24.1 mmHg, MI-BC = 95.2 ± 28.4 mmHg, P = 0.019) and increased interstitial myocardial collagen concentration (MI = 3.3 ± 1.2%, MI-BC = 5.8 ± 1.7%, P = 0.004) in BC-treated animals. Infarct sizes were similar between groups (MI = 45.0 ± 6.6%, MI-BC = 48.0 ± 5.8%, P = 0.246). Conclusion: Taken together, these data suggest that BC has adverse effects on ventricular remodeling after myocardial infarction. © 2006 Elsevier Inc. All rights reserved.

Agronomic effectiveness of cationic phosphate impurities present in superphosphate fertilizers as affected by soil pH

The general concept that low-water-soluble phosphorus (P) fertilizers should be more agronomically effective when applied to acidic soils was developed based on sources containing mainly calcium (Ca)-P compounds, but it may not hold true for sources with different chemical composition. To obtain information related to this issue, two important iron (Fe)-potassium (K)-P compounds present in superphosphates [Fe 3 KH 8 (PO 4 ) 6·6H 2 O, H8, and Fe 3 KH 14 (PO 4 ) 8·4H 2 O, H14] were prepared and characterized. These P sources were used to provide 30 and 60 mg P kg -1 as neutral ammonium citrate (NAC)+H 2 O-soluble P. Reagent-grade monocalcium phosphate (MCP) was used as a standard P source with high water solubility with an additional rate of 120 mg P kg -1 included. Also, mixtures of both Fe-K-P compounds and MCP were prepared to provide 0, 25, 50, 75, and 100% of the total P as MCP. All sources were applied to a clayey loamy acid soil (pH 5.3) classified as Rhodic Kanhapludult. The soil was incubated at two rates (0 and 10 g kg -1 ) of lime, which resulted in pH 5.4 and 6.8. Upland rice was cultivated to maturity. The H14 compound confirmed to be a highly effective source of P for the rice plants at both soil pH, as opposed to the H8, which was poorly effective when applied alone. When mixed with water-soluble P (WSP), the H8 was able to provide P to the plants with the maximum yield of upland rice reached with 54.8 and 80.5% of WSP for pH 5.4 and 6.8, respectively. The high agronomic performance of the H14 compound clearly indicates that this low-water-soluble P source cannot be deemed as ineffective at high soil pH. Copyright © Taylor & Francis Group, LLC.

Comparison of the population biology of Epialtus bituberculatus from two rocky shores with distinct hydrodynamic patterns

The population biology of Epialtus bituberculatus was compared between two different intertidal localities with differing levels of wave exposure. Sampling was conducted monthly between January and December, 2001 on seaweed banks of Sargassum cymosum in the intertidal zone of the rocky shores Grande (GR) (23°23′S-45°03′W) and Domingas Dias (DD) (23°29′S-45°08′W). Four hundred and twenty-eight crabs were captured at the GR site: 111 juvenile males, 106 adult males, 57 juvenile females, 17 adult females and 137 ovigerous females; while 455 specimens were obtained at the DD site: 76 juvenile males, 113 adult males, 37 juvenile females, 40 adult females and 189 ovigerous females. The population from GR showed a non-normal distribution and from DD a normal distribution. The sex-ratio (female/male) was 1:0.97 at GR (χ2 = 0.77, P = 0.084), whereas it was 1:1.41 at DD (χ2 = 13.03, P < 0.001). The largest individuals occurred at DD (U = 78249.0, P < 0.001). The estimated size at sexual maturity was 6.3 and 5.0 mm carapace width (CW) for males, and 5.4 and 5.2 mm CW for females, from GR and DD, respectively. The observed differences in E. bituberculatus between the studied localities might be explained by the different degrees of wave exposure between sites. However, other factors that might also explain the observed differences (e.g. temperature, salinity and food availability) cannot be discarded as relevant in influencing the population structure between sites herein studied. © 2012 Marine Biological Association of the United Kingdom.

Genomic Signatures Predict Poor Outcome in Undifferentiated Pleomorphic Sarcomas and Leiomyosarcomas

Undifferentiated high-grade pleomorphic sarcomas (UPSs) display aggressive clinical behavior and frequently develop local recurrence and distant metastasis. Because these sarcomas often share similar morphological patterns with other tumors, particularly leiomyosarcomas (LMSs), classification by exclusion is frequently used. In this study, array-based comparative genomic hybridization (array CGH) was used to analyze 20 UPS and 17 LMS samples from untreated patients. The LMS samples presented a lower frequency of genomic alterations compared with the UPS samples. The most frequently altered UPS regions involved gains at 20q13.33 and 7q22.1 and losses at 3p26.3. Gains at 8q24.3 and 19q13.12 and losses at 9p21.3 were frequently detected in the LMS samples. Of these regions, gains at 1q21.3, 11q12.2-q12.3, 16p11.2, and 19q13.12 were significantly associated with reduced overall survival times in LMS patients. A multivariate analysis revealed that gains at 1q21.3 were an independent prognostic marker of shorter survival times in LMS patients (HR = 13.76; P = 0.019). Although the copy number profiles of the UPS and LMS samples could not be distinguished using unsupervised hierarchical clustering analysis, one of the three clusters presented cases associated with poor prognostic outcome (P = 0.022). A relative copy number analysis for the ARNT, SLC27A3, and PBXIP1 genes was performed using quantitative real-time PCR in 11 LMS and 16 UPS samples. Gains at 1q21-q22 were observed in both tumor types, particularly in the UPS samples. These findings provide strong evidence for the existence of a genomic signature to predict poor outcome in a subset of UPS and LMS patients. © 2013 Silveira et al.