Showing papers by "Universidade Federal de Santa Maria published in 2006"

Micropower System Modeling with Homer

Abstract: This chapter contains sections titled: Introduction Simulation Optimization Sensitivity Analysis Physical Modeling Economic Modeling References Glossary

Integration of alternative sources of energy

Abstract: This chapter contains sections titled: Introduction Principles of Power Injection Instantaneous Active and Reactive Power Control Approach Integration of Multiple Renewable Energy Sources Islanding and Interconnection Control DG Control and Power Injection References

Counting triangles in data streams

Abstract: We present two space bounded random sampling algorithms that compute an approximation of the number of triangles in an undirected graph given as a stream of edges. Our first algorithm does not make any assumptions on the order of edges in the stream. It uses space that is inversely related to the ratio between the number of triangles and the number of triples with at least one edge in the induced subgraph, and constant expected update time per edge. Our second algorithm is designed for incidence streams (all edges incident to the same vertex appear consecutively). It uses space that is inversely related to the ratio between the number of triangles and length 2 paths in the graph and expected update time O(log|V|⋅(1+s⋅|V|/|E|)), where s is the space requirement of the algorithm. These results significantly improve over previous work [20, 8]. Since the space complexity depends only on the structure of the input graph and not on the number of nodes, our algorithms scale very well with increasing graph size and so they provide a basic tool to analyze the structure of large graphs. They have many applications, for example, in the discovery of Web communities, the computation of clustering and transitivity coefficient, and discovery of frequent patterns in large graphs.We have implemented both algorithms and evaluated their performance on networks from different application domains. The sizes of the considered graphs varied from about 8,000 nodes and 40,000 edges to 135 million nodes and more than 1 billion edges. For both algorithms we run experiments with parameter s=1,000, 10,000, 100,000, 1,000,000 to evaluate running time and approximation guarantee. Both algorithms appear to be time efficient for these sample sizes. The approximation quality of the first algorithm was varying significantly and even for s=1,000,000 we had more than 10% deviation for more than half of the instances. The second algorithm performed much better and even for s=10,000 we had an average deviation of less than 6% (taken over all but the largest instance for which we could not compute the number of triangles exactly).

Taking stock of the Brazilian "zero-till revolution": a review of landmark research and farmers' practice

Abstract: Two decades of extensive research and experimentation with zero‐till methods has allowed “ideal” zero‐till systems to emerge in Brazil, involving no soil turning, maintenance of a permanent vegetative cover, and rotations of both cash and cover crops. By exploiting rapid successions of suitable crops, for example, as well as through careful temporal and spatial planning, Brazilian examples show that it is possible to continuously cover soil, gradually increase soil organic matter (SOM) stocks, integrate livestock, move surface‐applied lime through the soil profile, break compact soil layers, and reduce reliance on agrochemicals in zero‐till, all under a variety of edaphic and climatic conditions, and levels of mechanization/farm sizes. Various such technologies and systems are reviewed in this chapter. However, we also note that among smallholder zero‐till farmers, for example, the adaptations of “ideal” zero‐till systems are manifold and complex, partial adoption of certain components and technologies rather than full adoption of zero‐till systems being the norm. By examining farmers' experiences and practice, we ascertain that in many cases there is perhaps a divorce between the ideal, originating mainly from individual technology research on agricultural research stations, and farmers' reality, given the complexity of socioeconomical constraints facing the latter. We conclude that although there is a wealth of valuable zero‐till experience and technologies precipitating from the Brazilian zero‐till “revolution,” numerous challenges in zero‐till research, especially in respect to resource‐poor smallholder farmers, still remain, and perhaps more holistic, participatory and adaptive on farm‐research is necessary in future. © 2006, Elsevier Inc.

Bond strength of a resin cement to high-alumina and zirconia-reinforced ceramics: The effect of surface conditioning

Abstract: Purpose: The aim of this study was to evaluate the effect of two surface conditioning methods on the microtensile bond strength of a resin cement to three high-strength core ceramics: high alumina-based (In-Ceram Alumina, Procera AllCeram) and zirconia-reinforced alumina-based (in-Ceram Zirconia) ceramics. Materials and Methods: Ten blocks (5 x 6 x 8 mm) of In-Ceram Alumina (AL), In-Ceram Zirconia (ZR), and Procera (PR) ceramics were fabricated according to each manufacturer's instructions and duplicated in composite. The specimens were assigned to one of the two following treatment conditions: (1) airborne particle abrasion with 110-mu m Al(2)O(3) particles + silanization, (2) silica coating with 30 lam SiO(x) particles (CoJet, 3M ESPE) + silanization. Each ceramic block was duplicated in composite resin (W3D-Master, Wilcos, Petropolis, RJ, Brazil) using a mold made out of silicon impression material. Composite resin layers were incrementally condensed into the mold to fill up the mold and each layer was light polymerized for 40 s. The composite blocks were bonded to the surface-conditioned ceramic blocks using a resin cement system (Panavia F, Kuraray, Okayama, Japan). One composite resin block was fabricated for each ceramic block. The ceramic-composite was stored at 37 degrees C in distilled water for 7 days prior to bond tests. The blocks were cut under water cooling to produce bar specimens (n = 30) with a bonding area of approximately 0.6 mm(2). The bond strength tests were performed in a universal testing machine (crosshead speed: 1 mm/min). Bond strength values were statistically analyzed using two-way ANOVA and Tukey's test ( Results: Silica coating with silanization increased the bond strength significantly for all three high-strength ceramics (18.5 to 31.2 MPa) compared to that of airborne particle abrasion with 110-mu m Al(2)O(3) (12.7-17.3 MPa) (ANOVA, p <0.05). PR exhibited the lowest bond strengths after both Al(2)O(3) and silica coating (12.7 and 18.5 MPa, respectively). Conclusion: Conditioning the high-strength ceramic surfaces with silica coating and silanization provided higher bond strengths of the resin cement than with airborne particle abrasion with 110- mu m Al(2)O(3) and silanization.

Analysis of the antinociceptive effect of the flavonoid myricitrin: evidence for a role of the L-arginine-nitric oxide and protein kinase C pathways.

Abstract: The present study investigated the antinociceptive effects of the flavonoid myricitrin in chemical behavioral models of pain in mice and rats. Myricitrin given by i.p. or p.o. routes produced dose-related antinociception when assessed on acetic acid-induced visceral pain in mice. In addition, the i.p. administration of myricitrin exhibited significant inhibition of the neurogenic pain induced by intraplantar (i.pl.) injection of capsaicin. Like-wise, myricitrin given by i.p. route reduced the nociception produced by i.pl. injection of glutamate and phorbol myristate acetate (PMA). Western blot analysis revealed that myricitrin treatment fully prevented the protein kinase C (PKC) alpha and PKCepsilon activation by PMA in mice hind paws. Myricitrin given i.p. also inhibited the mechanical hyperalgesia induced by bradykinin, without affecting similar responses caused by epinephrine and prostaglandin E(2). The antinociception caused by myricitrin in the acetic acid test was significantly attenuated by i.p. treatment of mice with the nitric oxide precursor, L-arginine. In contrast, myricitrin antinociception was not affected by naloxone (opioid receptor antagonist) or neonatal pretreatment of mice with capsaicin and myricitrin antinociceptive effects is not related to muscle relaxant or sedative action. Together, these results indicate that myricitrin produces pronounced antinociception against chemical and mechanical models of pain in rodents. The mechanisms involved in their actions are not completely understood but seem to involve an interaction with nitric oxide-L-arginine and protein kinase C pathways.

Potential of carbon accumulation in no-till soils with intensive use and cover crops in southern Brazil.

Abstract: The area under no-till (NT) in Brazil reached 22 million ha in 2004-2005, of which approximately 45% was located in the southern states. From the 1970s to the mid-1980s, this region was a source of carbon dioxide to the atmosphere due to decrease of soil carbon (C) stocks and high consumption of fuel by intensive tillage. Since then, NT has partially restored the soil C lost and reduced the consumption of fossil fuels. To assess the potential of C accumulation in NT soils, four long-term experiments (7-19 yr) in subtropical soils (Paleudult, Paleudalf, and Hapludox) varying in soil texture (87-760 g kg -1 of clay) in agroecologic southern Brazil zones (central region, northwest basaltic plateau in Rio Grande Sul, and west basaltic plateau in Santa Catarina) and with different cropping systems (soybean and maize) were investigated. The lability of soil organic matter (SOM) was calculated as the ratio of total organic carbon (TOC) to particulate organic carbon (POC), and the role of physical protection on stability of SOM was evaluated. In general, TOC and POC stocks in native grass correlated closely with clay content. Conversely, there was no clear effect of soil texture on C accumulation rates in NT soils, which ranged from 0.12 to 0.59 Mg ha -1 yr -1 . The C accumulation was higher in NT than in conventional-till (CT) soils. The legume cover crops pigeon pea [Cajanus cajan (L.) Millsp] and velvet beans (Stizolobium cinereum Piper & Tracy) in NT maize cropping systems had the highest C accumulation rates (0.38-0.59 Mg ha -1 yr -1 ). The intensive cropping systems also were effective in increasing the C accumulation rates in NT soils (0.25-0.34 Mg ha -1 yr -1 ) when compared to the double-crop system used by farmers. These results stress the role of N fixation in improving the tropical and subtropical cropping systems. The physical protection of SOM within soil aggregates was an important mechanism of C accumulation in the sandy clay loam Paleudult under NT. The cropping system and NT effects on C stocks were attributed to an increase in the lability of SOM, as evidenced by the higher POC to TOC ratio, which is very important to C and energy flux through the soil.

Resíduos vegetais na superfície e carbono orgânico do solo e suas relações com a densidade máxima obtida no ensaio proctor

Abstract: The susceptibility of soils to compaction, measured by the Proctor test, decreases with increasing soil organic matter (SOM) content. For a given energy level, with increasing SOM contents the maximum obtained density decreases and the corresponding critical moisture content increases. Due to its low density, elasticity and deformation susceptibility, straw is potentially able to dissipate applied loads. This study was conducted to evaluate the SOM effect on the soil compaction curve and to evaluate the ability that mulch has to absorb compactive energy in the Proctor test. The compaction test was carried out using soil surface samples (0 to 0.05 m) of a Hapludalf, with sandy loam texture at its soil surface, and an Oxisol, with clayey texture at its soil surface, both with variations in the SOM content. The maximum density, the critical moisture content, the liquid and plastic limits, and the soil organic carbon content were determined. A second test was performed to evaluate the ability of mulch to absorb compactive energy, by compacting Hapludalf samples with the presence of a straw layer on the soil surface, inside a Proctor cylinder, at amounts corresponding to 2, 4, 8 and 12 Mg ha-1. SOM accumulation reduced the maximum density and increased the critical moisture content, suggesting an increased resistance to soil compaction. In the Proctor test the straw on the soil surface dissipated up to 30 % of the compactive energy and reduced the bulk density, confirming the hypothesis that mulch can absorb part of the compactive energy caused by machine traffic and by animals.

Analysis and Design of a New High-Efficiency Bidirectional Integrated ZVT PWM Converter for DC-Bus and Battery-Bank Interface

Abstract: This paper proposes a high-efficiency bidirectional integrated zero-voltage transition (iZVT) pulsewidth-modulation (PWM) converter for dc-bus and battery-bank interface. The proposed converter can operate as battery charger when the utility is within its acceptable voltage range and can supply energy to critical loads when the utility fails. The converter practically eliminates both low- and high-frequency current ripple on the batteries, thus maximizing battery life without penalizing the volume of the converter. Moreover, soft switching of all switches is achieved using the proposed integrated auxiliary commutation circuit (iACC). Just one iACC is used to provide soft-switching conditions for the three converters that compose the system: the preregulator (boost), the battery charger (bidirectional converter operating as a buck), and the backup converter (bidirectional converter operating as a boost). This auxiliary circuit has few components and low reactive energy, increasing the system's overall efficiency. Experimental results based on a 580-W prototype are presented to validate the analysis and the proposed design procedure and to demonstrate the performance of the proposed approach

Azapirones for generalized anxiety disorder

Abstract: Background Azapirones are a group of drugs that work at the 5-HT1A receptor and are used to treat patients suffering from generalized anxiety disorder (GAD). However, several studies have shown conflicting results. Whether azapirones are useful as first line treatment in general anxiety disorders still needs to be answered. Objectives To assess the efficacy and the acceptability of azapirones for the treatment of GAD. Search methods Initiallyt the Cochrane Collaboration Depression, Anxiety and Neurosis Controlled Trials Register (CCDANCTR) and The Cochrane Central Register of Controlled Trials (CENTRAL) were searched, incorporating results of group searches of MEDLINE (1966 to June 2005), EMBASE (1980 to June 2005), CINAHL (1982 to June 2005), PsycLIT (1974 to June 2005), PSYNDEX (1977 to June 2005), and LILACS (1982 to June 2005). Subsequently the revised Cochrane Collaboration Depression, Anxiety and Neurosis Controlled Trials Registers (CCDANCTR-Studies and CCDANCTR-References) were searched on 21-10-2005. Reference lists of relevant papers and major text books of anxiety disorder were examined. Authors, other experts in the field and pharmaceutical companies were contacted for knowledge of suitable trials, published or unpublished. Specialist journals concerning azapirones were handsearched. Selection criteria Randomized controlled trials of azapirones, including buspirone versus placebo and/or other medication and/or psychological treatment, were included. Participants were males and females of all ages with a diagnosis of generalized anxiety disorder. Data collection and analysis Data were extracted from the original reports independently by CC, MA and MT. The main outcomes studied were related to the objectives stated above. Data were analysed for generalized anxiety disorder versus placebo, versus other medication and versus psychological treatment separately. Data were analysed using Review Manager Version 4.2.7. Main results Thirty six trials were included in the review, reporting on 5908 participants randomly allocated to azapirones and/or placebo, benzodiazepines, antidepressants, psychotherapy or kava kava. Azapirones, including buspirone, were superior to placebo in treating GAD. The calculated number needed to treat for azapirones using the Clinical Global Impression scale was 4.4 (95% confidence interval (CI) 2.16 to 15.4). Azapirones may be less effective than benzodiazepines and we were unable to conclude if azapirones were superior to antidepressants, kava kava or psychotherapy. Azapirones appeared to be well tolerated. Fewer participants stopped taking benzodiazepines compared to azapirones. The length of studies ranged from four to nine weeks, with one study lasting 14 weeks. Authors' conclusions Azapirones appeared to be useful in the treatment of GAD, particularly for those participants who had not been on a benzodiazepine. Azapirones may not be superior to benzodiazepines and do not appear as acceptable as benzodiazepines. Side effects appeared mild and non serious in the azapirone treated group. Longer term studies are needed to show that azapirones are effective in treating GAD, which is a chronic long-term illness.

A method for estimating coefficients of soil organic matter dynamics based on long-term experiments

Abstract: The one-compartment C model C t = C 0 e − k 2 t + k 1 A / k 2 ( 1 − e − k 2 t ) is being long used to simulate soil organic C (SOC) stocks. C t is the SOC stock at the time t ; C 0 , the initial SOC stock; k 2 , the annual rate of SOC loss (mainly mineralization and erosion); k 1 , the annual rate to which the added C is incorporated into SOC; and A , the annual C addition. The component C 0 e − k 2 t expresses the decay of C 0 and, for a time t , corresponds to the remains of C 0 ( C 0 remains ). The component k 1 A / k 2 ( 1 − e − k 2 t ) refers, at time t , to the stock of SOC derived from C crops ( C crop ). We herein propose a simple method to estimate k 1 and k 2 coefficients for tillage systems conducted in long-term experiments under several cropping systems with a wide range of annual C additions ( A ) and SOC stocks. We estimated k 1 and k 2 for conventional tillage (CT) and no-till (NT), which has been conducted under three cropping systems (oat/maize −O/M, vetch/maize −V/M and oat + vetch/maize + cowpea −OV/MC) and two N -urea rates (0 kg N ha −1 −0 N and 180 kg N ha −1 −180 N) in a long-term experiment established in a subtropical Acrisol with C 0 = 32.55 Mg C ha −1 in the 0–17.5 cm layer. A linear equation ( C t = a + bA ) between the SOC stocks measured at the 13th year (0–17.5 cm) and the mean annual C additions was fitted for CT and NT. This equation is equivalent to the equation of the model C t = C 0 e − k 2 t + k 1 A / k 2 ( 1 − e − k 2 t ) , so that a = C 0 e − k 2 t and b A = k 1 A / k 2 ( 1 − e − k 2 t ) . Such equivalences thus allow the calculation of k 1 and k 2 . NT soil had a lower rate of C loss ( k 2 = 0.019 year −1 ) than CT soil ( k 2 = 0.040 year −1 ), while k 1 was not affected by tillage (0.148 year −1 under CT and 0.146 year −1 under NT). Despite that only three treatments had lack of fit (LOFIT) value lower than the critical 5% F value, all treatments showed root mean square error (RMSE) lower than RMSE 95% indicating that simulated values fall within 95% confidence interval of the measurements. The estimated SOC stocks at steady state ( C e ) in the 0–17.5 cm layer ranged from 15.65 Mg ha −1 in CT O/M 0 N to 60.17 Mg ha −1 in NT OV/MC 180 N. The SOC half-life ( t 1/2 = ln 2/ k 2 ) was 36 years in NT and 17 years in CT, reflecting the slower C turnover in NT. The effects of NT on the SOC stocks relates to the maintenance of the initial C stocks (higher C 0 remais ), while increments in C crop are imparted mainly by crop additions.

Influence of ceramic surface conditioning and resin cements on microtensile bond strength to a glass ceramic

Abstract: Statement of problem It is not clear how different glass ceramic surface pretreatments influence the bonding capacity of various luting agents to these surfaces. Purpose The purpose of this study was to evaluate the microtensile bond strength (μTBS) of 3 resin cements to a lithia disilicate–based ceramic submitted to 2 surface conditioning treatments. Material and methods Eighteen 5 × 6 × 8-mm ceramic (IPS Empress 2) blocks were fabricated according to manufacturer's instructions and duplicated in composite resin (Tetric Ceram). Ceramic blocks were polished and divided into 2 groups (n=9/treatment): no conditioning (no-conditioning/control), or 5% hydrofluoric acid etching for 20 seconds and silanization for 1 minute (HF + SIL). Ceramic blocks were cemented to the composite resin blocks with 1 self-adhesive universal resin cement (RelyX Unicem) or 1 of 2 resin-based luting agents (Multilink or Panavia F), according to the manufacturer's instructions. The composite resin–ceramic blocks were stored in humidity at 37°C for 7 days and serially sectioned to produce 25 beam specimens per group with a 1.0-mm 2 cross-sectional area. Specimens were thermal cycled (5000 cycles, 5°C-55°C) and tested in tension at 1 mm/min. Microtensile bond strength data (MPa) were analyzed by 2-way analysis of variance and Tukey multiple comparisons tests (α=.05). Fractured specimens were examined with a stereomicroscope (×40) and classified as adhesive, mixed, or cohesive. Results The surface conditioning factor was significant (HF+SIL > no-conditioning) ( P Conclusion Etching and silanization treatments appear to be crucial for resin bonding to a lithia disilicate–based ceramic, regardless of the resin cement used.

Coluna de areia para medir a retenção de água no solo: protótipos e teste

Abstract: Soil water retention curve (SWRC) has been built using several strategies and methodologies. For low tension the use of tension tables has predominated. This paper presents prototypes and test the use of sand suction columns to measure soil water retention from 0 to 100hPa tension. An initial test was set up in a sand column instrumented with tensiometers every 0.1m from top to 1.0m depth. The column was set in a plastic tube 0.25m diameter with devices to have water inlet and to allow water table level. The column was filled with sieved sand, saturated and drained till a given water table depth. The total water potential distribution inside of column and water tension variation at sand surface indicated that, after hydrostatic equilibrium, the depth of water table regulates the potential distribution and the water tension at sand surface is equal to depth of water table. Sand column models (low and high cost) were set up and tested. In these columns a tensiometer was installed at sand surface and saturated soil samples in cylinders with tensiometers inside were set on top of sand and on top of filter paper laid on sand. Tensiometers located at sand surface and inside of soil samples indicated that tension targets were achieved from 8 to 12 hours at both, sand surface or inside of soil samples.

Hydrogen Adsorption on Carbon-Doped Boron Nitride Nanotube

Abstract: The adsorption of atomic and molecular hydrogen on carbon-doped boron nitride nanotubes is investigated within the ab initio density functional theory. The binding energy of adsorbed hydrogen on carbon-doped boron nitride nanotube is substantially increased when compared with hydrogen on nondoped nanotube. These results are in agreement with experimental results for boron nitride nanotubes (BNNT) where dangling bonds are present. The atomic hydrogen makes a chemical covalent bond with carbon substitution, while a physisorption occurs for the molecular hydrogen. For the H(2) molecule adsorbed on the top of a carbon atom in a boron site (BNNT + C(B)-H(2)), a donor defect level is present, while for the H(2) molecule adsorbed on the top of a carbon atom in a nitrogen site (BNNT + C(N)-H(2)), an acceptor defect level is present. The binding energies of H(2) molecules absorbed on carbon-doped boron nitride nanotubes are in the optimal range to work as a hydrogen storage medium.

Hydrogen adsorption on carbon-doped boron nitride nanotube

Abstract: The adsorption of atomic and molecular hydrogen on carbon-doped boron nitride nanotubes is investigated within the ab initio density functional theory. The binding energy of adsorbed hydrogen on carbon-doped boron nitride nanotube is substantially increased when compared with hydrogen on nondoped nanotube. These results are in agreement with experimental results for boron nitride nanotubes (BNNT) where dangling bonds are present. The atomic hydrogen makes a chemical covalent bond with carbon substitution, while a physisorption occurs for the molecular hydrogen. For the H(2) molecule adsorbed on the top of a carbon atom in a boron site (BNNT + C(B)-H(2)), a donor defect level is present, while for the H(2) molecule adsorbed on the top of a carbon atom in a nitrogen site (BNNT + C(N)-H(2)), an acceptor defect level is present. The binding energies of H(2) molecules absorbed on carbon-doped boron nitride nanotubes are in the optimal range to work as a hydrogen storage medium.