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The conduction characteristics of SnF2 from room temperature (300 K) to 463 K have been investigated by using impedance spectroscopy. The temperature dependent conductivity plot shows a break in conductivity around 443 K corresponding to the ? ? ? phase transition temperature. The electrical properties of SnF2 are also investigated by extracting dielectric and modulus data from impedance values. The frequency dependent plots of M? and Z? show that the conductivity relaxation is non-Debye in nature. The activation energy responsible for relaxation has been calculated from the modulus spectra and is found to be almost the same as that from the temperature dependent dc conductivity data. The real part of conductivity and permittivity in addition to the modulus spectra of the present system show scaling behavior, which means ??(?), ??(?) and M?(?) isotherms successfully collapse to a single master curve indicating that the relaxation mechanism is temperature independent. Different scaling approaches have been applied to arrive at a correlation between the scaling parameters. � 2009 Elsevier B.V. All rights reserved.

Polycrystalline samples of BaSn1-xMnxO3 with x = 0, 0.01, 0.02, 0.03, 0.04 and 0.05 were prepared by solid state reaction method. Using the powder X-ray diffraction patterns, these samples were found to be free of secondary phases. The substitution of Mn for Sn is also evidenced by the gradual disappearance of the characteristic optical band gap absorption (at 3.1 eV) and disappearance of Raman modes (centered around 835�cm-1, 1157�cm-1 and 1473�cm-1) of the host BaSnO3 with increasing Mn-content. The field dependent magnetization data collected at 300 K show that the undoped BaSnO3 is diamagnetic; upon doping Mn, the diamagnetic character of BaSnO3 diminishes and the ferromagnetic character evolves gradually with increasing Mn-content. The presence of F-centers in the samples is witnessed by the electron spin resonance (ESR) spectrum and the first order Raman spectrum of BaSnO3. At room temperature, the electrical resistivity of Mn-doped BaSnO3 is of the order of 108�?�m. These results suggest that the ferromagnetism in these systems is due to F-center exchange interaction. The observed ferromagnetism in these samples is also supported by ESR spectra. � 2009 Elsevier Ltd. All rights reserved.

Al-based metal matrix composites consisting of pure Al reinforced with different amounts of mechanically alloyed Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5 glassy powder were produced by powder metallurgy, and their mechanical properties were investigated by room temperature compression tests. The samples were consolidated into highly dense bulk specimens at temperatures within the supercooled liquid region in order to take advantage of the viscous flow behavior of the glassy powder. Compression tests show that the addition of the glass reinforcement increases the strength of pure Al from 155 to 250 MPa, while retaining appreciable plastic deformation with a fracture strain ranging between 70% and 40%. The yield strength and the elastoplastic deformation of such composites containing a high volume fraction of glassy particles were accurately modeled using a shear lag model and a self-consistent effective medium approach. Finally, the fracture characteristics of the reinforcing particles were rationalized using a proposed fracture criterion. � 2009 Acta Materialia Inc.

Polycrystalline bulk samples of BaSn1-xFexO3, with x = 0.03, 0.04 and 0.05 were prepared by solid-state reaction method. These Fe-doped BaSnO3 systems exhibit ferromagnetism at room temperature with an average magnetic moment of 0.047, 0.038 and 0.025?B/Fe and Curie temperature of 510, 462 and 446 K, respectively. The observed magnetic properties are not attributed to any of the known impurity phases or clusters. The presence of ferromagnetic interaction at room temperature is supported by the ferromagnetic resonance (FMR) signals observed in the electron spin resonance spectra. The ferromagnetic order between Fe-ions is expected to be mediated by an electron trapped at the oxygen anion vacancy, called the F-centre exchange (FCE) interaction. � 2008 Elsevier B.V. All rights reserved.

Au and Au-Pt alloy nanoparticles are prepared and patterned at room temperature within the PMMA polymer matrix by the action of 254 nm UV light or X-rays. The polymer matrix enables us to entangle the kinetics of the photochemical reduction from the nucleation and growth processes, when monitored by UV-vis spectroscopy. Accordingly, increase of the temperature to 50 degrees C of the reaction medium increases the nucleation and growth rates of the nanoparticle formation by more than one order of magnitude, due to enhanced diffusion and nucleation at the higher temperature, but has no effect on the photochemical reduction process. Presence of Pt ions also increases the same rate, but by a factor two only. Similar photochemical reduction and particle growth take also place within the PMMA matrix, when these metal ions are subjected to prolonged exposure to X-rays, as evidenced by XPS analysis. Both angle-resolved and charge-contrast measurements using XPS reveal that the resultant Au and Pt species are in close proximity to each other, indicating the Au-Pt alloy formation to be the most likely case. (C) 2008 Elsevier Ltd. All rights reserved.

Design against fatigue requires thorough understanding of the underlying fatigue mechanisms and factors influencing them. The objective of the present work is to study the effect of nanoclay addition on the temperature rise and modulus drop during cyclic loading in polyamide-6 and polyamide-6 base nanocomposite. Isocyclic stress strain curves were used to understand the deformation characteristics of test materials. Polyamide-6 samples exhibited necking and continuous temperature rise until fracture at high stress levels investigated. Addition of nanoclay improved the modulus retention compared to pristine polymers. Nanocomposite samples sustained more than 105 cycles at all stress levels investigated. The performance improvement due to the addition of nanoclay is attributed to decrease in the cyclic strain amplitude at a given stress level which results in reduced hysteresis heating compared to polyamide-6. � 2008 Elsevier Ltd. All rights reserved.

Potassium p-nitrophenolate dihydrate, a potential semiorganic nonlinear optical material, has been synthesized and grown by slow evaporation technique at room temperature. Single crystal X-ray analysis presents an unprecedented bonding between ions in the crystal with acentric structure. In the new structural investigation, p-nitrophenolate instead of producing bond between phenolic O- and K+, it seems to put nitro group in bonding with the metal ion. Optical absorption shows excellent transmission in the entire visible and near-infrared region. Room temperature photocurrent, transport properties are carried out in order to enhance the application for second harmonic generation and opto-electronic devices. Dielectric constant is found to be independent at higher frequencies. The crystal possesses prominent positive photoconduction in the presence of photoactive centers formed with trap energy level. The nonlinear optical activity is confirmed by Kurtz powder test. � 2008 Elsevier Ltd. All rights reserved.

Dry sliding wear behavior of 8090Al alloy and its composites reinforced with 8, 12 and 18 vol% SiC particles was studied in as-extruded and peak-aged conditions using a pin-on-disc machine. Tests were done at room temperature in air under loads of 10, 20 and 50 N at a constant sliding speed of 1 m s-1. The unreinforced alloy and composites show mild wear upto 20 N. Transition from mild to severe wear takes place beyond 20 N. Composites exhibit better wear resistance compared to the unreinforced alloy in as-extruded condition. Effect of heat treatment (artificial ageing) on wear behavior has also been studied. The unreinforced alloy exhibits better wear resistance at all the three loads used here in peak-aged condition compared to the as-extruded condition. Composites on the other hand, show better wear resistance upto 20 N, however, they show lower wear resistance in peak-aged condition compared to as-extruded condition beyond 20 N. This can be attributed to higher surface and subsurface deformation in peak-aged condition at higher load. � 2008 Elsevier B.V. All rights reserved.

The electrochromic and photocatalytic properties of vanadium-doped tungsten trioxide thin films prepared at room temperature (300 K) by the electron beam evaporation technique are reported in this paper. The vanadium to tungsten ratio (V/W) in these films are 0.003, 0.019, 0.029 and 0.047. The optical band gap of the vanadium-doped tungsten oxide (WO3) thin film initially increases from 3.16 to 3.28 eV for V/W ratio 0.003 then decreases to 3.15 eV for V/W ratio 0.047. These vanadium-doped films switch between neutral gray and transparent states. The coloration efficiency (CE) decreases from 82 cm2 C-1 (pure WO3) to 27 cm2 C-1 for the film containing V/W ratio 0.047. The photocatalytic activity has enhanced with vanadium doping and maximum activity of 15% (percentage change in optical density of methylene blue due to photo degradation) has been observed for the film containing V/W ratio of 0.019. The Kelvin probe measurements show that the work function of pure WO3 films is 4.07 eV and vanadium doping initially increases the work function to 4.19 eV for V/W ratio 0.019 and then decreases it to 3.97 eV for film with V/W ratio 0.047. � 2008 Elsevier B.V. All rights reserved.

A series of meso-tetraarylporphyrins bearing electron-donor or electron-withdrawing substituents at the meso-phenyl groups were examined for antipodal ?-pyrrole tetrabromination using different brominating agents. Porphyrins bearing electron-donor substituents undergo bromination at moderate temperatures with N-bromosuccinimide as the brominating agent while the electron-deficient porphyrins require Hq. Br2 at room temperature. The brominated porphyrins were isolated in moderate to very good yields. Synthesized compounds were characterized by electronic absorption, 1HNMR, and mass spectroscopic methods. Regioselectivity of an electron-deficient porphyrin, 2,3,12,13-tetrabromo-5,10,15,20-tetrakis(4- methoxycarbonylphenyl)porphyrin was examined by single-crystal X-ray structure analysis and showed antipodal ?-pyrrole bromo substitution. � 2008 The Chemical Society of Japan.

In this work, we have employed spectroscopic ellipsometry technique to study the optical properties of polymer/carbon nanotube (CN) composites as a function of nanotube concentration. Using a two-layer structural model based on Airy rigorous equations, the optical constants in various CN concentrations have been extracted. In the optical absorption spectra, we have observed a tuning of the excitonic transitions with the addition of single wall CN concentration. Based on theoretical calculations for the interaction of CNs with the surrounding effective media, the spectral evolution of the binding energy of optically active excitonic transitions with the addition of CNs suggests that the effective dielectric function of surrounding media decreases. Furthermore, using an oscillator Lorentz model, the absorption peaks, oscillator strengths and energy broadenings of the excitonic transitions have been extracted. © 2008 Elsevier B.V. All rights reserved. 17 7-10 1600 1603

Magnetic, magnetoresistive, and magnetocaloric properties of a novel double perovskite oxide, namely, LaCaMnCo O6 have been studied. Polycrystalline sample of LaCaMnCo O6 has been synthesized by sol-gel technique. It has cubic crystal structure (space group Fm 3- m) at room temperature. The temperature variation in magnetization reveals a steep increase in magnetization around 168 K (TC). The magnetization does not even saturate at 5 K and a magnetic moment of 0.7 ?B f.u. is obtained at 5 K in an applied field of 50 kOe. The electrical resistivity measurement indicates that the material is semiconducting-like in the temperature range of ?300-50 K and below ?50 K the sample becomes insulating. A maximum magnetoresistance (MR) of about 8% is found at 200 K in an applied field of 7 T and MR has a negative sign. The magnetocaloric effect is calculated from the magnetization versus temperature data and a maximum magnetic entropy change of 3.1 Jkg K for a field change of 11 kOe is obtained near TC. Thus a moderate magnetocaloric effect is achieved in rather low magnetic fields. � 2009 American Institute of Physics.

Indium nitride films have been grown using modified activated reactive evaporation (MARE). The films were grown on glass and silicon substrates at room temperatures, i.e. without any intentional substrate heating. In this technique, the substrates were kept on the cathode instead of the grounded electrode and hence subjected to low energy nitrogen ion bombardment leading to highly c-axis oriented films. The photoluminescence (PL) and Raman spectrum shows significant improvement in the quality of the films compared with conventional activated reactive evaporation. The band gap measured from the room temperature PL was found to be 1.9 eV. Very high growth rates can be achieved in the MARE growth technique. The modification in the activated reactive evaporation technique may have a large impact on the growth of various compounds such as metal oxides. � 2008 IOP Publishing Ltd.

An energy cost allocation system records the energy consumption of a building and divides the overall energy costs between the flats. Because the indoor temperatures of rooms are usually not equal, static heat flows between flats cannot be avoided. Hence, in order to ensure fair energy costs per flat the system should be able to determine the static heat flows, preferably without utilising design data or in-situ measurements. This paper presents a new method for estimating static heat flows between neighbouring rooms. It also outlines the instrumentation and technical properties of the energy allocation system (EAS), needed in implementation. The approach is strictly technical, focusing only on heat transfer issues. Energy cost allocation is not considered. The approach is based on the proposed control techniques and the ARMAX-model describing dynamic behaviour of heating power. The model is created for each room/flat of a building. Parameter values are identified using real-time measurements collected from each room/flat and its environment. Only ordinary instrumentation is required. The tuning of parameters takes a few days using a fifteen-minute sampling time. A prerequisite for successful estimation is the overall control and the precise adjustment of the room temperatures at specified level. This is accomplished by the suggested set point control. All test runs are performed in a simulated office hotel using the TRNSYS simulation program. Realistic inner and outer heating loads, and their daily schedules and variations are included. The results are encouraging, but further research is needed, especially in a real building environment.