Viscosity estimation of triacylglycerols and of some vegetable oils, based on their triacylglycerol composition

The experimentally determined kinematic viscosities of simple triacylglycerols [trilaurin, trimyristin (MMM), tripalmitin (PPP), tristearin (SSS), triolein (OOO), and trilinolein (LiLiLi) were correlated to a modified Andrade-type equation. The constants for the modified equation were derived for each simple triacylglycerol. The method was also used to estimate the viscosity of mixed triacylglycerols [1,2-dimyristoyl-3-palmitoyl (MMP), 1,2-dioleoyl-3-palmitoyl (OOP), 1,2-dimyristoyl-3-oleoyl (MMO), and 1,2-dipalmitoyl-3-oleoyl (PPO)], binary triacylglycerol mixtures (PPO/OOP, PPP/SSS, and OOO/SSS of different portions), and three types of vegetable oils [refined, bleached, and deodorized palm oil; cocoa butter; and canola oil] by applying modified Kay’s rule utilizing the simple triacylglycerol constants derived earlier. In all cases, the estimated values for liquid viscosity were compared with experimental values determined in this work and with previous work from the literature. When applied to vegetable oils, the method requires knowledge of their triacylglycerol composition. Despite its simplicity, the method gives a reasonable estimate. The method may be used to predict the viscosity of different blends of vegetable oils, and the accuracy is expected to increase when more experimental data on simple triacylglycerols become available.     

Preparation of presintered zirconia blocks for dental restorations through colloidal dispersion and cold isostatic pressing

This work proposes an effective method for dispersion of zirconia suspension for dental block preparation and optimizes the cold isostatic pressing (CIP) pressure to improve the densification of slip-casted zirconia blocks. Two batches of 44 wt% zirconia suspension were prepared using distilled water in a pH 2 medium containing 0.5 wt% polyethyleneimine as dispersant. The first batch was sonicated for different durations (from 5 min to 30 min), and the second batch was dispersed through ball milling at rotational speeds of 200, 300, and 400 rpm for 60, 90, and 120 min. All suspensions were subjected to sedimentation test and particle size measurement. Results revealed that the optimum ultrasonication duration was 10 min, which yielded the smallest particle size of 133 nm. Ball milling at 300 rpm for 120 min achieved the maximum dispersion of particles, with an average size of 75 nm. Under the optimum conditions of ultrasonication duration, ball milling duration, and ball milling speed, the particle size decreased to 48 nm, which is close to the primary particle size. These dispersion techniques and parameters were selected for preparing a suspension to be consolidated into blocks through slip casting and were enhanced through CIP at pressure ranging from 100 MPa to 300 MPa. CIP compaction at 250 MPa significantly increased the shrinkage percentage of green zirconia blocks, with pore radius decreased to 18 nm. The density of zirconia pressed at 250 MPa and presintered at a low temperature of 950 °C was 59% of the theoretical density and was higher than that of commercial presintered blocks. Thus, CIP should be conducted under a compaction pressure of 250 MPa to produce dense and homogeneous zirconia blocks.     

Analysis of a turbulent boundary layer subjected to a strong adverse pressure gradient

We define two non-dimensional parameters $\text{Λ =}\text{τ}{}_{\mathrm{w}}\text{p}{}_{\mathrm{x}}\text{δ}$ and $\text{R}{}_{\mathrm{p}}\text{=}\text{U}{}_{\mathrm{p}}\text{δ}\text{ν}$ where τ_w is the wall stress, p_x(?0) is the pressure gradient to which the turbulent boundary layer (of thickness δ) is subjected, ν is the kinematic viscosity, $\text{U}{}_{\mathrm{p}}\text{= (}\text{νp}{}_{\mathrm{x}}\text{p}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$ is a characteristic velocity and p is the density. The limit corresponding to the strong adverse pressure gradient is formulated as Λ → 0, R_p → ∞, ΛR_p finite. Using appropriate inner and outer asympcotic expansions, both above a wall layer possibly scaling with τ_w and ν, it is found by an application of Millikan's argument that there is an inertial sublayer where the streamwise velocity distribution obeys a half-power law, whose slope depends on Λ, and intercept on ΛR_p. Indeed comparison with available experimental data shows the inner law to be well represented by $\text{u}\text{Up}\text{= (3.5 + 19Λ)(}\text{yU}{}_{\mathrm{p}}\text{ν}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{+ 2.5ΛR}{}_{\mathrm{p}}$. The outer flow obeys a generalized defect law; use of constant eddy viscosity closure yields results in good agreement with experiment.     

Tracing post-limit-point paths with reduced basis technique

A reduced basis technique and a problem-adaptive computational algorithm are presented for predicting the post-limit-point paths of structures. In the proposed approach the structure is discretized by using displacement finite element models. The nodal displacement vector is expressed as a linear combination of a small number of vectors and a Rayleigh-Ritz technique is used to approximate the finite element equations by a small system of nonlinear algebraic equations.To circumvent the difficulties associated with the singularity of the stiffness matrix at limit points, a constraint equation, defining a generalized arc-length in the solution space, is added to the system of nonlinear algebraic equations and the Rayleigh-Ritz approximation functions (or basis vectors) are chosen to consist of a nonlinear solution of the discretized structure and its various order derivatives with respect to the generalized arc-length. The potential of the proposed approach and its advantages over the reduced basis-load control technique are outlined. The effectiveness of the proposed approach is demonstrated by means of numerical examples of structural problems with snap-through and snap-back phenomena.     

Recombination effects with high-pressure Langmuir probes

With increasing ion density, the ion current collected by a negatively biased electric probe is eventually dominated by ions produced by reactive processes in the vicinity of the probe. Here, we derive an expression for the probe current to a cylindrical probe when all the ions collected to the probe are assumed to be generated within the sheath which surrounds the probe. Measurements of probe current in a seeded atmospheric-pressure flame are in good agreement with the theory. The significance of reaction processes is reinforced by the fact that the maximum probe current is found to be approximately three times the total current that the flame would produce with frozen chemistry, i.e. the saturation current.     

Alkyl amides and nitriles as novel tracers for biomass burning

The occurrence of n-alkanoic acids, amides, and nitriles in samples of aerosol particulate matter from Kuala Lumpur and Santiago suggests that emissions from cooking and biomass burning are the primary sources of these organic markers in the atmosphere. It is proposed that fatty acids react with ammonia during biomass burning or combustion to produce amides and nitriles, which can be applied as useful biomarker tracers. To test this hypothesis, nonadecanoic acid and hexadecanamide were used as reactants in hydrous pyrolysis experiments. These experiments produced amides and nitriles and indicated that ammonia is an essential agent in their formation. Thus amides and nitriles are of utility as indicators for input from combustion and biomass burning in the ambient atmosphere.     

Islam and Online Imagery on Malaysian Tourist Destination Websites

In December 1996, TIME magazine published an article titled "Finding God on the Web," which projected how the Internet would shape information seeking on faith and religion. A decade later, the Web has become a popular tool for gathering religious information as well as information and imagery related to religious travel. Yet there is little research on religious destination imagery online. Imagery—positive or negative, pictographic or narrative—influences the selection of tourism destinations. This study explored online Muslim images in Malaysia via interviews and content analyses of pictures and text on tourism destination websites' homepages. The results reveal minimal portrayal of Muslim images by Malaysian tourism destination organizations. This study adds to the small body of research, especially in Muslim countries, on online religious imagery and suggests avenues for tourism operators in Malaysia and elsewhere to improve their online image with both Muslim and non-Muslim travelers.     

Power Law Velocity Profile in Fully Developed Turbulent Pipe and Channel Flows

The power law velocity profile has been analyzed in terms of the envelope of the friction factor which gives the friction factor log law. The power law index α and prefactor C are shown as the function of the friction Reynolds number, as well as the function of the alternate variable the nondimensional friction velocity. The fully developed turbulent superpipe flow data of McKeon et al. and fully developed channel flow data of Zanoun et al. have been analyzed and the power law index α and prefactor C data have been estimated, first as a function of the friction Reynolds number and second as function of the nondimensional friction velocity. Based on analysis, several correlations have been proposed that have been supported by the data.     

A Carrier-Based Unipolar PWM Current Controller That Minimizes the PWM-Cycle Average Current-Error Using Internal Feedback of the PWM Signals

A carrier-based unipolar pulsewidth modulation (PWM) current controller is described using a one-phase PWM rectifier bridge as a test circuit. The controller PWM signal generator uses a sawtooth carrier signal to obtain both synchronized PWM waveforms and a constant switching frequency. A current-error signal and an amplitude modulation depth signal are used to create the input reference signal to the PWM signal generator. The amplitude modulation depth signal is obtained from the PWM-cycle average of the PWM signal generator output signals. This internal feedback is illustrated using a second-order low pass Butterworth filter. With an appropriately designed low-pass filter, the current-error signal is forced to be centered on zero over a PWM cycle. The maximum peak-peak magnitude of the current-error signal is used as a design guideline for deciding an appropriate gain constant in the controller current feedback loop. The low pass filter design is examined to determine a suitable gain and 20-dB attenuation frequency to minimize the current-error signal. The steady-state and transient operation of the proposed current controller is compared with a proportional-integral controller and an average current-error controller. SPICE simulations and experimental results are used to demonstrate the characteristics of the controller.