Influence of drying conditions on the rheological properties of prunes

Rheological properties of rehydrated prunes were obtained applying compression-relaxation tests by using a Texture Analyzer TAXT2i. A mathematical development was adopted to determine the stress and area, along the deformation. Experimental data of stress versus time was fitted by using three different rheological models: generalized Maxwell, Normand & Peleg and Maxwell. Results showed that generalized Maxwell model can be used to describe the viscoelastic behavior of the samples. The rheological parameters obtained indicated that prunes exhibited elastic behavior more pronounced at low moisture content and drying air temperature. At high moisture content and temperature the sample became a more viscous and less rigid.

Viscoelastic behavior of persimmons dried at constant air temperature

The viscoelastic behavior of dried persimmons at different air-drying temperatures and velocities was evaluated. Air temperatures and velocities were varied according to a second-order central composite design, with temperature ranging from 40degreesC to 70degreesC and air velocity from 0.8 to 2.0 m/s. After drying, persimmons were equilibrated at four different water activities: 0.432, 0.576, 0.625 and 0.751. The rheological behavior of dried and conditioned persimmons was studied under uniaxial compression-relaxation tests. Three different rheological models were fitted to the experimental relaxation curves: Maxwell, Generalized Maxwell and Peleg and Normand. Based on the root mean square of residuals, the Generalized Maxwell model showed the best fit and a regression analysis was applied to obtain response surfaces for the model parameters. The dependence of the rheological properties on water activity was also analysed. Results showed that only the linear effect of air temperature was significant at a 5% level on the equilibrium stress and relaxation times. In a general way, these parameters increased with increasing air temperature and decreasing water activity. (C) 2004 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved.

Prediction and spatial variability of soil dynamic properties in sugar cane fields of São Paulo State Brazil

The objective of this work was to model and diagnose the spatial variability of soil load support capacity (SLSC) in sugar cane crop fields, as well as to evaluate the management impact on São Paulo State soil structure. The investigated variables were: pressure preconsolidation (sigma(p)), apparent cohesion () and internal friction angle (). The conclusions from the results were that the models and spatial dependence maps constitute important tools in the prediction and location of the mechanical internal strength of soils cultivated with sugar cane. They will help future soil management decisions so that soil structure sustainability will not be compromised.

The effect of the ocean water immersion and UV ageing on the dynamic mechanical properties of the PPS/glass fiber composites

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

Morphological, mechanical properties and biodegradability of biocomposite thermoplastic starch and polycaprolactone reinforced with sisal fibers

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

Dielectric and ferroelectric properties of PZT and PT thin films for saw sensors applications

It is very important for the building of the SAW devices to study dielectric and ferroelectrics properties because every SAW device is based in piezoelectric effect that it is made up to transform an electric sign in the mechanical or acoustic sign and a mechanical or acoustic sign in an electric sign. Thus, the purpose of the present work is to prepare PbZr 0,53Ti0.47O3 (PZT) and PbTiO3 (PT) thin films on the Si (100) substrates across spin-coating using a chemical method based in polymeric precursors. After conventional treatment in the furnace, the films were characterized by impedance spectroscopy and hysteresis loops to know its dielectric and ferroelectric properties.

Effect of lithium doping on the evolution of rheological and structural properties during gelation of siloxane-poly(oxypropylene) nanocomposites

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

Influence of temperature and concentration on thermophysical properties of yellow mombin (Spondias mombin, L.)

Thermal conductivity, thermal diffusivity, and density of yellow mombin juice were determined at 8.8-49.4 °Brix and at temperature from 0.4 to 77.1 °C. Apparent viscosity was also measured between 7.8 and 30 °Brix and at temperature from 0 to 60 °C. Yellow mombin juice was produced from fruits of two different batches and the concentration process was performed using a roto evaporator or a rising film evaporator, single effect, with recirculation, under vacuum, to obtain concentrated juice. In order to obtain different concentrations, concentrated juice was diluted with distilled water. Multiple regression analysis was performed to fit thermal conductivity, thermal diffusivity and density experimental data obtaining a good fit. Arrhenius and power law relationships were proposed to fit apparent viscosity as a function of temperature and juice concentration at typical shear rates found during processing. The rheological parameters together with experimental values of pressure loss in tube flow were used to calculate friction factors, which were compared to those resulting from theoretical equation.

Simultaneous effects of total solids content, milk base, heat treatment temperature and sample temperature on the rheological properties of plain stirred yogurt

Response surface methodology was used to establish a relationship between total solids content, milk base, heat treatment temperature, and sample temperature, and consistency index, flow behaviour index, and apparent viscosity of plain stirred yogurts. Statistical treatments resulted in developments of mathematical models. All samples presented shear thinning fluid behaviour. The increase of the content of total solids (9.3-22.7 %) and milk base heat treatment temperature (81.6-98.4°C) resulted in a significant increase in consistency index and a decrease in flow behaviour index. Increase in the sample temperature (1.6-18.4°C) caused a decrease in consistency index and increase in flow behaviour index. Apparent viscosity was directly related to the content of total solids. Rheological properties of yogurt were highly dependent on the content of total solids in milk.

Study of cutting forces on machinability properties of gray cast iron using new ceramics cutting tools

During gray cast iron cutting, the great rate of mechanical energy from cutting forces is converted into heat. Considerable heat is generated, principally in three areas: the shear zone, rake face and at the clearance side of the cutting edge. Excessive heat will cause undesirable high temperature in the tool which leads to softening of the tool and its accelerated wear and breakage. Nowadays the advanced ceramics are widely used in cutting tools. In this paper a composition special of Si3N4 was sintering, characterized, cut and ground to make SNGN120408 and applyed in machining gray cast iron with hardness equal 205 HB in dry cutting conditions by using digital controlled computer lathe. The tool performance was analysed in function of cutting forces, flank wear, temperature and roughness. Therefore metal removing process is carried out for three different cutting speeds (300 m/min, 600 m/min, and 800 m/min), while a cutting depth of 1 mm and a feed rate of 0.33 mm/rev are kept constant. As a result of the experiments, the lowest main cutting force, which depends on cutting speed, is obtained as 264 N at 600 m/min while the highest main cutting force is recorded as 294 N at 300 m/min.

Comparison of the shear bond strengths of conventional mesh bases and sandblasted orthodontic bracket bases

This study aimed to compare in vitro the shear bond strength between metallic brackets (Abzil) with conventional mesh bases and metallic brackets with bases industrially sandblasted with aluminum oxide using three adhesive systems, in order to assess the influence of sandblasting on adhesiveness and to compare 3 different bonding systems. Two hundred and forty bovine incisors were used and randomly divided into 6 groups (40 teeth in each group), according to the bracket base and to the bonding system. The brackets were direct-bonded in bovine teeth with 3 adhesive systems: System A - conventional Transbond™ XT (3M -Unitek); System B - Transbond™ Plus Self Etching Primer + Transbond™ XT (3M - Unitek) and System C - Fuji ORTHO LC resin-reinforced glass ionomer cement in capsules (GC Corp.). Shear bond strength tests were performed 24 hours after bonding, in a DL-3000 universal testing machine (EMIC), using a load cell of 200 kgf and a speed of 1 mm/min. The results were submitted to statistical analysis and showed no significant difference between conventional and sandblasted bracket bases. However, comparison between the bonding systems presented significantly different results. System A (14.92 MPa) and system C (13.24 MPa) presented statistically greater shear bond strength when compared to system B (10.66 MPa). There was no statistically significant difference between system A and system C.

Shear bond strength of orthodontic brackets bonded using halogen light and light-emitting diode at different debond times

The aim of this in vitro study was to compare the photoactivation effects of QTH (Quartz-Tungsten-Halogen) and LED (Light-Emitting Diode) on the SBS (Shear Bond Strength) of orthodontic brackets at different debond times. Seventy-two bovine lower incisors were randomly divided into two groups according to the photoactivation system used (QTH or LED). The enamel surfaces were conditioned with Transbond self-etching primer, and APC (Adhesive Pre-Coated) brackets were used in all specimens. Group I was cured with QTH for 20 s and Group II with LED for 10 s. Both groups were subdivided according to the different experimental times after bonding (immediately, 24 h and 7 days). The specimens were tested for SBS and the enamel surfaces were analyzed according to the Adhesive Remnant Index (ARI). The statistical analysis included the Tukey's test to evaluate the main effects of photoactivation and debond time on SBS. The Chi-square test was used to compare the ARI values found for each group, and no statistically significant difference was observed. The debond time of 7 days for QTH photoactivation showed statistically greater values of SBS when compared to the immediate and 24 h periods. There was no statistically significant difference between the QTH and LED groups immediately and after the 24 h period. In conclusion, bonding orthodontic brackets with LED photoactivation for 10 s is suggested because it requires a reduced clinical chair time.

Shear bond strength of resin cement bonded to alumina ceramic after treatment by aluminum oxide sandblasting or silica coating

Purpose: To evaluate the shear bond strength and bond durability between a dual-cured resin cement (RC) and a high alumina ceramic (In-Ceram Alumina), subjected to two surface treatments. Materials and Methods: Forty disc-shaped specimens (sp) (4-mm diameter, 5-mm thick) were fabricated from In-Ceram Alumina and divided into two groups (n = 20) in accordance with surface treatment: (1) sandblasting by aluminum oxide particles (50 μm Al 2O 3) (SB) and (2) silica coating (30 μm SiO x) using the CoJet system (SC). After the 40 sp were bonded to the dual-cured RC, they were stored in distilled water at 37°C for 24 hours. After this period, the sp from each group were divided into two conditions of storage (n = 10): (a) 24 h-shear bond test 24 hours after cementation; (b) Aging-thermocycling (TC) (12,000 times, 5 to 55°C) and water storage (150 days). The shear test was performed in a universal test machine (1 mm/min). Results: ANOVA and Tukey (5%) tests noted no statistically significant difference in the bond strength values between the two surface treatments (p= 0.7897). The bond strengths (MPa) for both surface treatments reduced significantly after aging (SB-24: 8.2 ± 4.6; SB-Aging: 3.7 ± 2.5; SC-24: 8.6 ± 2.2; SC-Aging: 3.5 ± 3.1). Conclusion: Surface conditioning using airborne particle abrasion with either 50 μm alumina or 30 μm silica particles exhibited similar bond strength values and decreased after long-term TC and water storage for both methods. © 2011 by The American College of Prosthodontists.

Numerical assessment of mass conservation on a MAC-type method for viscoelastic free surface flows

A numerical study of mass conservation of MAC-type methods is presented, for viscoelastic free-surface flows. We use an implicit formulation which allows for greater time steps, and therefore time marching schemes for advecting the free surface marker particles have to be accurate in order to preserve the good mass conservation properties of this methodology. We then present an improvement by using a Runge-Kutta scheme coupled with a local linear extrapolation on the free surface. A thorough study of the viscoelastic impacting drop problem, for both Oldroyd-B and XPP fluid models, is presented, investigating the influence of timestep, grid spacing and other model parameters to the overall mass conservation of the method. Furthermore, an unsteady fountain flow is also simulated to illustrate the low mass conservation error obtained.

Atmospheric plasma treatment of carbon fibers for enhancement of their adhesion properties

Plasma processing of carbon fibers (CFs) is aimed to provide better contact and adhesion between individual plies without decrease in the CF mechanical resistance. This paper deals with surface modification of CFs by an atmospheric pressure dielectric barrier discharge (DBD) for enhancing the adhesion between the CF and the polymeric matrix. The scanning electron microscopy of the treated samples revealed many small particles distributed over entire surface of the fiber. These particles are product of the fiber surface etching during the DBD treatment that removes the epoxy layer covering as-received samples. The alteration of the CF surface morphology was also confirmed by the Atomic force microscopy (AFM), which indicated that the CF roughness increased as a result of the plasma treatment. The analysis of the surface chemical composition provided by X-ray photoelectron spectroscopy showed that oxygen and nitrogen atoms are incorporated onto the surface. The polar oxygen groups formed on the surface lead to the increasing of the CF surface energy. The results of interlaminar shear strength test (short beam) of CFs/polypropylene composites demonstrated a greater shear resistance of the composites made with CFs treated by DBD than the one with untreated fibers. Both the increase in surface roughness and the surface oxidation contribute for the enhancement of CF adhesion properties. © 2012 IEEE.