Thermal Conductivity and Viscosity Measurements of Water-Based TiO<Subscript>2</Subscript> Nanofluids

In this study, the thermal conductivity and viscosity of TiO₂ nanoparticles in deionized water were investigated up to a volume fraction of 3% of particles. The nanofluid was prepared by dispersing TiO₂ nanoparticles in deionized water by using ultrasonic equipment. The mean diameter of TiO₂ nanoparticles was 21 nm. While the thermal conductivity of nanofluids has been measured in general using conventional techniques such as the transient hot-wire method, this work presents the application of the 3ω method for measuring the thermal conductivity. The 3ω method was validated by measuring the thermal conductivity of pure fluids (water, methanol, ethanol, and ethylene glycol), yielding accurate values within 2%. Following this validation, the effective thermal conductivity of TiO₂ nanoparticles in deionized water was measured at temperatures of 13 °C, 23 °C, 40 °C, and 55 °C. The experimental results showed that the thermal conductivity increases with an increase of particle volume fraction, and the enhancement was observed to be 7.4% over the base fluid for a nanofluid with 3% volume fraction of TiO₂ nanoparticles at 13 °C. The increase in viscosity with the increase of particle volume fraction was much more than predicted by the Einstein model. From this research, it seems that the increase in the nanofluid viscosity is larger than the enhancement in the thermal conductivity.     

Optimal Twist and Polarization Angles for the Reflective Liquid Crystal Light Modulator

Abstract

We determine the twist angle and the input polarization angle that optimize the efficiency, modulation sensitivity, and contrast ratio for the reflective liquid crystal modulators (especially the liquid crystal light valve). If a monochromatic light source is used, and when the input polarization is parallel to the front molecular director of the liquid crystal, the conventionally used 45° twist has a theoretical maximum reflectance of only 81%. However, a 63·6° twist angle yields the highest efficiency (theoretical maximum reflectance of 100%) as well as a higher modulation sensitivity. When the input polarization is not parallel, different options that yield a high efficiency and an increased modulation sensitivity are available. If the light source is not monochromatic but has a narrow bandwidth, the dispersion effect tends to reduce the contrast ratio, so that a tradeoff between contrast and sensitivity must be made. We show that a configuration with 65–75° twist angle has an efficiency close to 100% with continuously increasing sensitivity but decreasing contrast as the input polarization changes from 0° to ?30°.     

Measurement of the amount of free and bound hydrogen in amorphous carbon

The effusion of hydrogen and other gases from an amorphous carbon a-C:H film annealed at temperatures of 100–1000°C was studied. A direct method was used to determine the amount of hydrogen in the material as 26 at.%. The amount of free hydrogen was determined as 4 at.%. The temperature curve for the release of free hydrogen gas has a maximum at 400 °C. A broad hydrogen effusion peak was observed above 400 °C. The amount of hydrogen released by breaking of weak C-H bonds was determined as 10 at.% and that released by breaking of strong C-H bonds was determined as 12 at.%. Pis’ma Zh. Tekh. Fiz. 23, 3–8 (January 12, 1997)     

Differential Thermal Analysis of Polyethylene Glycol and Glycerol Monostearate Suppository Bases Containing Theophylline

Abstract

Water soluble polyethylene glycol 4000 (PEG4) suppositories were prepared containing 4% (w/w) theophylline. Various concentrations of polyethylene glycol 1000 (PEG1) and glycerol monostearate (GMS) were also added. Differential thermal analysis (DTA) of the PEG4 and PEG1 combination suppositories showed no melting endotherm for theophylline. But when theophylline concentration in the base was 12% (w/w) and above, sharp endothermic peak of theophylline was obtained. In contrast, when GMS was added as a base material above 50% (w/w) with PEG4, the melting endotherm of theophylline (4%, w/w) appeared at 273-274°C. The melting endotherm of the suppository bases increased up to 2 to 4°C due to storage at 4°C for six months.     

A strategy for the optimization and economic evaluation of an ORC system for energy recovery

Abstract

A strategy for the performance prediction and economic evaluation of an ORC (organic Rankine cycle) system for power conversion is studied. Different assumptions and system boundaries are used to understand the constraints of the boundaries as well as their effects on the evaluation results. A series of methods, including cost estimation, operation’ research, sensitivity analysis and optimal design of heat exchangers, is employed in evaluating this thermal to power conversion system. It is found that the resultant variations in the economic evaluation, no matter what economic index is used, are mostly depending on the input parameters and the unpredictable variables at the preliminary design stage. The analysis strategy, the detailed procedures as well as the computer programs, is presented with a 400°F, 2.5 ×10⁷ Btu/hr flue gas recovery case as an illustration. This study shows a large variation of payback period ranging from 5 to 15 years, depending on different assumptions, operating conditions, and system boundaries. This analysis recommends a more conservative approach to evaluate an energy recovery project to avoid an inappropriate judgement of an engineering design project.     

The study of bridge phase conjugation in photorefractive Tb:Cu:KNSBN crystal

Abstract

Photorefractive bridge phase conjugation is studied theoretically by two-region coupled-wave theory. The dependence of phase conjugate reflectivity and transmissivity on the input intensity ratio is measured. When two incoherent beams symmetrically enter opposite Tb:Cu:KNSBN crystal faces, the maximum reflectivities are higher than 351%, 236% and 147% for incident angles of 17.5°, 27.5 and 39° respectively; we also obtain a transmissivity higher than 58% for an incident angle of 33.5°. A comparison between the experimental data and theoretical results is also given.     

Novel promising crosslinkable tricyanopyrroline polymeric electro-optic materials

A tricyanopyrroline chromophore with methacrylate reactive group was synthesized to fabricate the side chain (polymer 1) and crosslinkable (polymer 2) EO (electro optic) polymers with enhanced electrooptical tensor coefficients. These type of polymers have demonstrated the large EO coefficients with values of 29 pm/V and 25 pm/V at wavelength 1,310 nm, respectively. Compared with polymer 1, t polymer 2 had demonstrated a better stability of polar structure. The thermal stability of polar structure was improved for about 100 °C. The temperatures of poling and crosslinking processes were compatible in polymer 2, which allowed obtaining the EO films with improved features. The experimental results have been interpreted with the aid of quantum-chemical calculations.     

Measurement of Soft Elastic Gelatin Capsule Firmness with a Universal Testing Machine

Abstract

An indication of the firmness of Soft Elastic Gelatin (SEG) capsules was obtained by measurement in a universal testing machine (Instron, Model 1122). Capsules were packed in both glass and polystyrene containers and then exposed them in closed containers to 25°C and 75% RH, 35°C and 75% RH, and 45°C and 75% RH for a period of 21 weeks. At the end of 2, 12, and 21 week periods, samples were withdrawn from environmental chambers and evaluated them for firmness by subjective as well as objective techniques. The deformation of capsules measured by the universal testing machine appears to be a reliable and sensitive method for measuring firmness of SEG Capsules.     

Thermomechanical relaxation of residual stress in shot peened nickel base superalloy

Abstract

The thermal and thermomechanical behaviour of the relaxation of the residual stresses of a shot peened Astroloy superalloy under tensile cyclic loads has been evaluated by X-ray diffraction and investigated. The stress relaxation under purely thermal conditions (550 and 650°C) and thermomechanical conditions (pulsating tensile loading at 650°C) as afunction of the exposure time is presented. The purely thermal relaxation is interpreted by annihilation and reorganisation of the crystalline defects induced by shot peening, whereas the mechanical relaxation is linked to cyclic plasticity of materials. In consequence, the thermomechanical relaxation is essentially due to the complex mechanism of the concurrent thermal and mechanical effects. A model is used to predict the residual stresses induced by the specified shot peening conditions and their relaxation under the specified thermal/thermomechanical conditions.

MST/1963     

Statistical analysis of accurate prediction of local atmospheric optical attenuation with a new model according to weather together with beam wandering compensation system: a season-wise experimental investigation

Abstract

Atmospheric parameters strongly affect the performance of Free Space Optical Communication (FSOC) system when the optical wave is propagating through the inhomogeneous turbulent medium. Developing a model to get an accurate prediction of optical attenuation according to meteorological parameters becomes significant to understand the behaviour of FSOC channel during different seasons. A dedicated free space optical link experimental set-up is developed for the range of 0.5 km at an altitude of 15.25 m. The diurnal profile of received power and corresponding meteorological parameters are continuously measured using the developed optoelectronic assembly and weather station, respectively, and stored in a data logging computer. Measured meteorological parameters (as input factors) and optical attenuation (as response factor) of size [177147 × 4] are used for linear regression analysis and to design the mathematical model that is more suitable to predict the atmospheric optical attenuation at our test field. A model that exhibits the R² value of 98.76% and average percentage deviation of 1.59% is considered for practical implementation. The prediction accuracy of the proposed model is investigated along with the comparative results obtained from some of the existing models in terms of Root Mean Square Error (RMSE) during different local seasons in one-year period. The average RMSE value of 0.043-dB/km is obtained in the longer range dynamic of meteorological parameters variations.     

Thermal expansion behaviour of plasma sprayed Al–SiCp composites

Abstract

Al with 55 and 75 vol.-%SiC powders were free mechanically mixed or ball milled as feedstock. The powder feedstock was deposited onto a graphite substrate to form near net shape of Al/SiC composites by air plasma spraying. The pores and the gaps at the Al/SiC interface as well as at the boundary of Al grains exist extensively in the as sprayed composites. Coefficient of thermal expansion (CTE) of the sprayed composites was measured in the temperature range of 25–300°C. The composites plasma sprayed with Al–75SiC powder feedstock can reach a low CTE value of 8 × 10^?6 °C^?1. The effect of pore on the CTE of the composites has been discussed. The gap at Al/SiC interface has an influence on thermal expansion behaviour only at lower test temperatures. Reduction and elimination of the gap with temperature can offset the thermal expansion of the as sprayed composites, resulting in lower CTE at the beginning of the CTE test. Roughly quantitative consideration of the effect of the interfacial gaps between Al and SiC on CET was given. Linear rule of mixture (ROM), Turner and Kerner's models were used to estimate the CTE of the sprayed composites. It was found that ROM and Kerner's model give closer CTE prediction for the present composites.     

Constitutive equations that describe creep stress relaxation for 316H stainless steel at 550°C

Abstract

The prediction of the stress relaxation behaviour of welding induced residual stresses in thick section 316H austenitic stainless steel welded component provides an input for quantifying reheat crack initiation observed in the heat affected zone. The cracks occur after service at a temperature range from 490 to 520°C. The present work reviews some of the widely applied stress relaxation models. The relative strengths and weaknesses of these existing models are discussed. An improved constitutive equation derived from a forward uniaxial creep deformation law is proposed. The relative importance of the parameters selected in the new constitutive model, when compared with experimental data, is discussed. The importance of a better understanding of the role of the internal stress and its measurement is highlighted.     

The effect of microstructure on thermal expansion coefficients in powder-processed Al2Mo3O12

Orthorhombic Al₂Mo₃O₁₂ was investigated as a model anisotropic phase to understand the influence of powder preparation routes and bulk microstructure (mean grain size) on the bulk coefficient of thermal expansion (CTE) and to compare it to the intrinsic CTE of powder samples. A co-precipitation route was used for the synthesis of pure single-phase nanopowders, while a polyvinyl alcohol-assisted sol–gel method was utilized for the synthesis of micron-sized powders. Sintered samples prepared from both powders exhibited different microstructures in terms of mean crystal sizes and porosity. Bulk samples obtained from nanopowders were highly porous and contained crystals of approximately 100-nm diameter, while the bulk pieces produced from the micron-sized powders were denser, contained crystals larger than 5 μm, and showed occasional intergranular and transgranular microcracks. Such different microstructures hugely impact the bulk CTE: the nanometric sample possesses a bulk CTE (0.9 × 10^?6 °C^?1, from 200 to 700 °C) closer to the instrinsic CTE (2.4 × 10^?6 °C^?1) than for the micrometric sample, which showed a negative CTE (?2.2 × 10^?6 °C^?1) from 200 to 620 °C, and an even more negative CTE above 620 °C (?35 × 10^?6 °C^?1). A finite element analysis showed that the local maximum thermal tensile stresses could be as high as 220 MPa when simulating a temperature drop of 700 °C as an example of thermal treatment following sintering. This tensile stress is expected to exceed the tensile strength of Al₂Mo₃O₁₂, explaining the origin of microcracks in bulk samples prepared from the micron-sized powders. The thermal behavior of the microcracks leads to differences between the intrinsic and bulk thermal expansion; we show experimentally that such differences can be reduced by nanostructuring.     

Interfacial reaction mode and its influence on tensile strength in laser joining Al alloy to Ti alloy

Abstract

In order to obtain a robust dissimilar joint of Al/Ti alloys, a filler wire of Al–12 wt-%Si and 45° V shape groove on the base metal were used during CO₂ laser welding. Heat input had evident influence on the interfacial reaction mode. It was found that a dissolution mode for low heat input and a melting mode for high heat input exist at the joint interface, which was analysed from thermodynamic point of view. Tensile strength of the joints in the dissolution mode reached as high as 296 MPa, which was significantly higher than that in the melting mode.     

Effect of Environment on Crystallinity and Chemical Stability in Solid-State of Ground Cephalotin Sodium During Storage

Abstract

Effects of environmental conditions on the crystallinity and the decomposition point (Dp) of ground cephalotin sodium during storage were investigated by X-ray diffraction and differential thermal analysis (DTA). The X-ray diffraction peaks of ground products increased after storage at 0% and 75% relative humidity (R.H.), at 35° C. The crystallinity of ground product increased at 75% R.H. and 0% R.H., 35°C, but that of ground product at 0% R.H., -30°C was not changed. The Dp measured by DTA of the ground product increased from 189.5°C to 197°C after 4 days at 75% R.H., but the Dp of the ground product at 0% R.H., -30°C for 4 days was 190.1°C. Relation between the Dp and the crystal Unity of ground cefalotin sodium was a straight suggesting that the thermal stability of cefaiotin sodium in the solid-state depends on the degree of crystallinity.     

Hydroxyapatite nanospindles by biomimetic synthesis with chitosan as template

Abstract

Based on the principles of biomineralisation, spindle shaped hydroxyapatites (HA) were synthesised through the biomimetic method with chitosan (CS) as template. The microstructure, chemical composition and thermal behaviour were characterised by means of X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy and thermogravimetry differential thermal analysis (TGDTA) respectively. The results show that the spindle shaped nanoHA, 30–40 nm in length and 7–8 nm in width, were synthesised with 0·5 wt-%CS as template in 6% (v/v) hydrogen peroxide solution for 7 days. The crystallinity of samples increased with the aging time. TGDTA analyses show that the HA powders synthesised with CS as template contain CS molecules and have good thermal stability up to 800°C.     

Stability Prediction of cefazolin sodium and Cephaloridine in solid state

Abstract

The stability of commercially-available solid pharmaceutical preparations containing cephaloridine and cefazolin sodium was evaluated with an accelerated isothermal degradation method at three different temperatures (37°, 45° and 60°C). A specific and sensitive differential pulse polarographic method was used for cephalosporin determination. Data obtained from high-temperature studies were processed using Arrhenius relation to predict shelf-life. The greater thermal stability of cephaloridine than cefazolin sodium was found, in contrast to what can be deduced from official monographs. Differential scanning calorimetry and X-ray diffraction were used to characterize the solid state of cephalosporin antibiotics.     

Investigation of profiles of implanted Ti atoms over the depth of boron nitride nanocrystalline ceramic exposed to high radiation doses and fluxes with subsequent annealing

Results are presented of an investigation of distribution profiles of implanted Ti atoms at high implantation doses (fluence around 10¹⁷ cm⁻²) over the depth of boron nitride (BN) nanocrystalline ceramic. It is observed that the concentration maxima of implanted impurities are shifted into the substrate under post-implantation annealing in vacuum at 950 °C. This behavior of the implanted impurities in BN is directly the opposite of that observed in earlier studies of polycrystalline aluminum oxide ceramic exposed to similar ion thermal treatment. The effective diffusion coefficient of titanium atoms in BN under thermal annealing is estimated. The Ti/O concentration ratio in the layer modified as a result of implantation and subsequent annealing at 950 °C is close to stoichiometric TiO₂. A simultaneous increase in the concentration of carbon and nitrogen atoms in the surface layers of BN samples was observed as a result of annealing at 830 and 950 °C. Pis’ma Zh. Tekh. Fiz. 25, 53–57 (August 12, 1999)     

Pharmaceutical development of an amorphous solid dispersion formulation of elacridar hydrochloride for proof-of-concept clinical studies

Objective: A novel tablet formulation containing an amorphous solid dispersion (ASD) of elacridar hydrochloride was developed with the purpose to resolve the drug’s low solubility in water and to conduct proof-of-concept clinical studies.

Significance: Elacridar is highly demanded for proof-of-concept clinical trials that study the drug’s suitability to boost brain penetration and bioavailability of numerous anticancer agents. Previously, clinical trials with elacridar were performed with a tablet containing elacridar hydrochloride. However, this tablet formulation resulted in poor and unpredictable absorption which was caused by the low aqueous solubility of elacridar hydrochloride.

Methods: Twenty four different ASDs were produced and dissolution was compared to crystalline elacridar hydrochloride and a crystalline physical mixture. The formulation with highest dissolution was characterized for amorphicity. Subsequently, a tablet was developed and monitored for chemical/physical stability for 12 months at +15–25?°C, +2–8?°C and ?20?°C.

Results: The ASD powder was composed of freeze dried elacridar hydrochloride–povidone K30–sodium dodecyl sulfate (1:6:1, w/w/w), appeared fully amorphous and resulted in complete dissolution whereas crystalline elacridar hydrochloride resulted in only 1% dissolution. The ASD tablets contained 25?mg elacridar hydrochloride and were stable for at least 12 months at –20?°C.

Conclusions: The ASD tablet was considered feasible for proof-of-concept clinical studies and is now used as such.     

Experimental investigation and prediction of wear properties of Al/SiC metal matrix composites produced by thixomoulding method using Artificial Neural Networks

In this study, the wear properties of the SiC particle reinforced aluminium (A356) composite materials (MMCs), produced with thixomoulding method, were investigated both by experimental and Artificial Neural Network (ANN) model in order to determine the weight loss after the wear tests. Two different temperatures (590 °C and 600 °C) were used in production of the MMCs containing 5%, 10%, 15% and 20% SiC (vol%). The samples of MMC were tested at 2 ms⁻¹ constant sliding speed under 30 N and 60 N loads against four different sliding distances (500 m, 1000 m, 1500 m, and 2000 m). The results indicated that by increasing the production temperature increased the grain size of the MMCs was increased, but the hardness was decreased. The MMCs produced at 590 °C were found to have lower weight loss as compared with ones produced at 600 °C. In the theoretical prediction model of the MMCs, weight loss, SiC per cent, production temperature, applied weight and sliding distance were used as input values. After comparing the experimental results and the ANNs predicted data it was observed that R² was 0.9855. This shows that the developed prediction model has a high level of reliability.