High-resolution thermal expansion measurements under helium-gas pressure

We report on the realization of a capacitive dilatometer, designed for high-resolution measurements of length changes of a material for temperatures 1.4K ≤ T ≤ 300K and hydrostatic pressure P ≤ 250MPa. Helium ( 4He) is used as a pressure-transmitting medium, ensuring hydrostatic-pressure conditions. Special emphasis has been given to guarantee, to a good approximation, constant-pressure conditions during temperature sweeps. The performance of the dilatometer is demonstrated by measurements of the coefficient of thermal expansion at pressures P ≃ 0.1MPa (ambient pressure) and 104MPa on a single crystal of azurite, Cu 3(CO 3) 2(OH) 2, a quasi-one-dimensional spin S = 1/2 Heisenberg antiferromagnet. The results indicate a strong effect of pressure on the magnetic interactions in this system. © 2012 American Institute of Physics.

Chemical stability and electrical properties of Nb doped BaCe 0.9Y 0.1O 3-δ as a high temperature proton conducting electrolyte for IT-SOFC

BaCe 0.9-xNb xY 0.1O 3-δ (where x=0, 0.01, 0.03 and 0.05) powders were synthesized by solid-state reaction to investigate the influence of Nb concentration on chemical stability and electrical properties of the sintered samples. The dense electrolyte pellets were formed from the powders after being uniaxially pressed and sintered at 1550 °C. The electrical conductivities determined by impedance measurements in temperature range of 550-750 °C in different atmospheres (dry argon and wet hydrogen) showed a decreasing trend with an increase of Nb content. For all samples higher conductivities were observed in the wet hydrogen than in dry argon atmosphere. The chemical stability was enhanced with increasing of Nb concentration. It was found that BaCe 0.87Nb 0.03Y 0.1O 3-δ is the optimal composition that satisfies the opposite demands for electrical conductivity and chemical stability, reaching 0.8×10 -2 S cm -1 in wet hydrogen at 650 °C compared to 1.01×10 -2 S cm -1 for undoped electrolyte. © 2012 Elsevier Ltd and Techna Group S.r.l.

Enhanced stability in CO2 of Ta doped BaCe0.9Y 0.1O3-δ electrolyte for intermediate temperature SOFCs

The influence of Ta concentration on the stability of BaCe 0.9-xTaxY0.1O3-δ (where x=0.01, 0.03 and 0.05) powders and sintered samples in CO2, their microstructure and electrical properties were investigated. The ceramic powders were synthesized by the method of solid state reaction, uniaxially pressed and sintered at 1550 °C to form dense electrolyte pellets. A significant stability in CO2 indicated by the X-ray analysis performed was observed for the samples with x≥0.03. The electrical conductivities determined by impedance measurements in the temperature range of 550-750 °C and in various atmospheres (dry argon, wet argon and wet hydrogen) increased with temperature but decreased with Ta concentration. The highest conductivities were observed in the wet hydrogen atmosphere, followed by those in wet argon, while the lowest were obtained in the dry argon atmosphere for each dopant concentration. The composition with Ta content of 3 mol% showed satisfactory characteristics: good resistance to CO2 in extreme testing conditions, while a somewhat reduced electrical conductivity is still comparable with that of BaCe0.9Y0.1O3-δ. © 2012 Elsevier Ltd and Techna Group S.r.l.

Intense photoluminescence emission at room temperature in calcium copper titanate powders

A study was undertaken about the structural and photoluminescent properties at room temperature of CaCu3Ti4O12 (CCTO) powders synthesized by a soft chemical method and heat treated between 300 and 800 °C. The decomposition of precursor powder was followed by thermogravimetric analysis (TG-DTA), X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Fourier transform Raman (FT-Raman) and photoluminescence (PL) measurements. XRD analyses revealed that the powders annealed at 800 °C are becoming ordered and crystallize in the cubic structure. The most intense PL emission was obtained for the sample calcined at 700 °C, which is not highly disordered (300-500 °C) and neither completely ordered (800 °C). From the spectrum it is clearly visible that the lowest wavelength peak is placed around 480 nm and the highest wavelength peak at about 590 nm. The UV/vis absorption spectroscopy measurements showed the presence of intermediate energy levels in the band gap of structurally disordered powders. © 2012 Elsevier Ltd and Techna Group S.r.l.

Low-temperature structural effects in the (TMTSF)2PF6 and AsF6 Bechgaard salts

We present a detailed low-temperature investigation of the statics and dynamics of the anions and methyl groups in the organic conductors (TMTSF) 2PF6 and (TMTSF)2AsF6 (TMTSF: tetramethyl-tetraselenafulvalene). The 4 K neutron-scattering structure refinement of the fully deuterated (TMTSF)2PF6-D12 salt allows locating precisely the methyl groups at 4 K. This structure is compared to the one of the fully hydrogenated (TMTSF)2PF6-H12 salt previously determined at the same temperature. Surprisingly, it is found that deuteration corresponds to the application of a negative pressure of 5×102 MPa to the H12 salt. Accurate measurements of the Bragg intensity show anomalous thermal variations at low temperature both in the deuterated PF 6 and AsF6 salts. Two different thermal behaviors have been distinguished. Small Bragg-angle measurements reflect the presence of low-frequency modes at characteristic energies θE = 8.3 K and θE = 6.7 K for the PF6-D12 and AsF6-D12 salts, respectively. These modes correspond to the low-temperature methyl group motion. Large Bragg-angle measurements evidence an unexpected structural change around 55 K, which probably corresponds to the linkage of the anions to the methyl groups via the formation of F...D-CD2 bonds observed in the 4 K structural refinement. Finally we show that the thermal expansion coefficient of (TMTSF)2PF6 is dominated by the librational motion of the PF6 units. We quantitatively analyze the low-temperature variation of the lattice expansion via the contribution of Einstein oscillators, which allows us to determine for the first time the characteristic frequency of the PF6 librations: θE ≈ 50 K and θE = 76 K for the PF6-D12 and PF6-H12 salts, respectively. © 2013 American Physical Society.

Investigation of the effect of movement and irrigation systems on temperature in the conventional drilling of cortical bone

We have compared the results of the external irrigation technique with those of a double irrigation technique with continuous intermittent movement. Maximum thermal measurements were made in the cortical part of 10 samples of bovine ribs during osteotomy to simulate the preparation of a surgical bed for the installation of dental implants at a depth of 10 mm Twenty specimens were drilled for each group: external irrigation and continuous movement (control group 1, CG1); external irrigation and intermittent movement (control group 2, CG2); double irrigation and continuous movement (test group 1, TG1); and double irrigation and intermittent movement (test group 2, TG2). The double irrigation technique gave significantly better results regardless of the drilling movement used. Thermal increases between samples was 19.2% in group CG1, 10.4% in CG2, 5.4% in TG1, and 3.4% in TG2. The double irrigation technique produced a significantly smaller increase in temperature in the cortical bone during both types of drilling (p = 0.001), which illustrated its greater efficiency compared with that of the external irrigation technique. (C) 2013 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.

Phase transitions and interface phenomena in the cryogenic temperature domain of a niobate nanostructured ceramic

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

Temperature and thermal regime effects on the specific dynamic action of Bothrops alternatus (Serpentes, Viperidae)

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

Rheological behavior of Peruvian carrot starch gels as affected by temperature and concentration

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

New method to assess the pozzolanic reactivity of mineral admixtures by means of pH and electrical conductivity measurements in lime:pozzolan suspensions

A very simple method based on electrical conductivity and pH measurements was proposed for assessing reactivity of pozzolans. Calcium hydroxide: pozzolan water suspensions were monitored by means of measurements of electrical conductivity and pH values. In these suspensions, Ca(OH)(2) in solid state was initially present, being them, thus, saturated in this reagent. Three testing temperatures were selected (40, 50 and 60 degrees C). In the experiments carried out, calcium hydroxide was suspended in deionized water for yielding a lime saturated suspension. The addition of siliceous pozzolan (two types of rice husk ash RHA and two types of densified silica fume DSF were tested) to the saturated lime suspension can produce the unsaturation of the system, depending on the testing time, testing temperature and reactivity of pozzolan. When unsaturation was reached, the loss of electrical conductivity was higher than 30% and the variation of pH was higher than 0.15 units. These threshold values were selected for characterizing the reactivity of pozzolans by means of a proposed template, classifying the pozzolan in three different reactivity levels.

Evaluation of measurement errors of temperature and relative humidity from HOBO data logger under different conditions of exposure to solar radiation

This study aimed to assess measurements of temperature and relative humidity obtained with HOBO a data logger, under various conditions of exposure to solar radiation, comparing them with those obtained through the use of a temperature/relative humidity probe and a copper-constantan thermocouple psychrometer, which are considered the standards for obtaining such measurements. Data were collected over a 6-day period (from 25 March to 1 April, 2010), during which the equipment was monitored continuously and simultaneously. We employed the following combinations of equipment and conditions: a HOBO data logger in full sunlight; a HOBO data logger shielded within a white plastic cup with windows for air circulation; a HOBO data logger shielded within a gill-type shelter (multi-plate prototype plastic); a copper-constantan thermocouple psychrometer exposed to natural ventilation and protected from sunlight; and a temperature/relative humidity probe under a commercial, multi-plate radiation shield. Comparisons between the measurements obtained with the various devices were made on the basis of statistical indicators: linear regression, with coefficient of determination; index of agreement; maximum absolute error; and mean absolute error. The prototype multi-plate shelter (gill-type) used in order to protect the HOBO data logger was found to provide the best protection against the effects of solar radiation on measurements of temperature and relative humidity. The precision and accuracy of a device that measures temperature and relative humidity depend on an efficient shelter that minimizes the interference caused by solar radiation, thereby avoiding erroneous analysis of the data obtained.

c ̂-Axis resistivity in graphite-AlCl3 as found by CESR measurements

We report the absolute values of the c ̂-axis resistivity obtained from conduction electron spin resonance (CESR) experiments at various temperatures for a graphite-AlCl3 stage 2 compound. The agreement with d.c. measurements is quite good. The temperature dependence of the c ̂-axis resistivity previously obtained from CESR for graphite-AlCl3 is revised. © 1990.

Temperature Dependent Luminescence Spectra of Synthetic and Natural Alexandrite

Results of photoluminescence measurements for natural and synthetic alexandrite (BeAl2O4:Cr3+) are presented, where the samples are excited by the 488 nm line of an Ar+ laser, at different temperatures. The main issue is the analysis of the Cr3+ transition in the chrysoberyl matrix (BeAl2O4), with major technological application as active media for laser action. Results indicate anomalous behavior of Cr3+ transition depending on the measurement temperature. A simple model to explain the phenomena is suggested.

Development of technologies and methods for monitoring the spatial variability of air temperature in greenhouse environment

Climatic factors directly influence growth and productivity of plants inside greenhouses, where temperature can be considered one of the major parameter in this context. Thus, the aim of this research was to develop a low cost device for thermal sensing and data acquisition, and use it in data collection and analysis of spatial variability of temperature inside a greenhouse with tropical climate. The developed equipment for thermal measurements showed a high degree of accuracy and fast responses in measurements, proving its efficiency. The data analysis interpretations were made from the elaborations of variograms and of tridimensional maps generated by a geostatistical software. The processed data analysis presented that a greenhouse without thermal control has spatial variations of air temperature, both in the sampled horizontals layers as in the three analyzed vertical columns, presenting variations of up to 3.6 ºC in certain times.

Analysis of simple hardware efficiency for temperature measurement in agriculture and environment

This work focuses basically on the design and analysis of simple and low cost hardware systems efficiency for temperature measurement in agricultural area. The main objective is to prove quantitatively, through statistical data analysis, to what extent a simple hardware designed with inexpensive components can be used safely in the indoor temperature measurement in farm buildings, such as greenhouses, warehouse or silos. To verify the of simple hardware efficiency, its data were compared with data from measurements with a high performance LabVIEW platform. This work proved that a simple hardware based on a microcontroller and the LM35 sensor can perform well. It presented a good accuracy but a relatively low precision that can be improved when performed some consecutive signal sampling and then used its average value. Although there are many papers that explain these components, this work has the distinction of presenting a data analysis in numerical form and using high performance systems to ensure critical data comparison.