How Does Cooking Time Scale with Size? A Numerical Modeling Approach

ABSTRACT:  A mathematical model for a spatially distributed mechanical property such as Young's modulus and texture inside solid food during the cooking process was developed by combining a numerical conduction heat transfer model with the kinetics of property changes. Using the distributed mechanical property obtained from the thermokinetic model, linear elastic stress analysis was performed to determine the effective material property and how it changes during cooking. Spatial variation in the mechanical property is found to be significant for commonly used food sizes in potato. When property varies spatially, volume average property, which is easier to compute than an effective property obtained from mechanical stress analysis, can be a substitute for the effective property. Cooking time based on volume average Young's modulus varies less strongly with size than how temperature varies with size. When activation energy for the property change kinetics is lower, cooking time varies less with size. The scaling of cooking time with size and kinetics and the extent of property variation in a sample during cooking should provide useful guidelines in automating cooking processes.     

Undernutrition among adult Dhimals of Naxalbari, West Bengal: comparison with other tribes of eastern India

BACKGROUND: The tribes of India comprise approximately 8% of the total population of the country, which probably has the largest number of tribal communities in the world. In general, the tribal populations are among the most underprivileged and undernourished people in India. OBJECTIVES: To determine the anthropometric characteristics and prevalence of undernutrition, based on body mass index (BMI), of adult Dhimals, a tribal population of Naxalbari, West Bengal, India, and to compare these results with those from four other tribes of Eastern India: the Bathudis, Kora Mudis, Santals, and Savars. METHODS: A total of 305 adult (18 years or older) Dhimals (159 men and 146 women) from three villages (Maniram, Hatighisa, and Buraganj) in the Mallabari area of Naxalbari were studied. These villages are located 5 km from Siliguri town, which is approximately 580 km from Kolkata, the provincial capital of West Bengal. Anthropometric measurements included height and weight. BMI was calculated by the standard equation. Undernutrition was evaluated according to World Health Organization (WHO) cutoff points. RESULTS: The overall prevalence of undernutrition (BMI < 18.5) was very high (36.4%). The prevalence was significantly higher in women than in men (46.4% vs. 27.0%; chi2 = 12.54; p < .001; odds ratio, 2.35). According to the WHO criterion, the prevalence of undernutrition was high and the situation was serious in men. Among women, the prevalence of undernutrition was very high and the situation was critical. However, in general, compared with other tribal people of eastern India except the Santals, adult Dhimals had better anthropometric and nutritional profiles. CONCLUSIONS: This study provides evidence that although the anthropometric and nutritional profiles of adult Dhimals are better than those of some of the other tribal populations of eastern India, immediate appropriate nutritional intervention programs are needed for implementation among this ethnic group.     

Nonlocal electronic distribution in metallic clusters: a critical examination of aromatic stabilization

All-metal clusters, such as Al(4)M(4) (M = alkali metal ion), exhibit interesting features of multi-fold aromaticity/antiaromaticity. Such characteristics arise particularly because of the poor sigma-pi separation in this class of systems. This Account presents computational strategies to unambiguously determine the aromaticity/antiaromaticity characteristics of such clusters. Computations of the linear and nonlinear optical responses show that all-metal clusters are orders of magnitude more polarized than the conventional pi-conjugated molecules. We also propose new strategies to stabilize all-metal antiaromatic systems through complexation to transition metals and discuss mechanisms for substitution reactions within the conventional organometallic systems by Al(4)M(4). Additionally, we find that these all-metal clusters form stacked superclusters that are extremely stable and aromatic.     

Stochastic Response and Stability of a Nonintegrable System

For determining the stochastic response and stability of a strongly nonlinear single-degree-of-freedom system using the stochastic averaging technique, the size of excitations should be small such that the response of the system converges weakly to a Markov process. This condition is not often met with practical problems, and therefore, application of this method for obtaining their responses becomes difficult. Further, for systems with nonlinearities that cannot be integrated in closed form, stability analysis by examining the conditions of the two boundaries of the problem is not possible. A semianalytical method along with a weighted residual technique is presented here to circumvent these difficulties and to determine the response and stability of a strongly nonlinear system subjected to sizable stochastic excitation. The weighted residual technique is employed to correct the errors in averaged drift and diffusion coefficients resulting due to the size of the stochastic excitation. Two example problems are solved as illustrations of the method.     

Age Hardening Behavior of Wrought Al-Mg-Sc Alloy

Ageing of Al-6Mg alloy doped with varying concentration of scandium ranging from 0.2 wt% to 0.6 wt% has been carried out. Cold-rolled alloy samples are isochronally aged for 60 minutes at different temperatures. The cast and hot-rolled samples are also aged isochronally for 90 minutes at different temperatures up to 450°C. Isothermal ageing of cold-rolled samples is conducted at various temperatures for different periods of time ranging from 30 to 480 minutes. Hardness values of the differently processed alloys have been measured to understand the ageing behavior of Al-6Mg alloy with scandium addition. The hot-rolled alloys after ageing do not show any hardening response due to ageing. Ageing of cold-rolled alloys envisaged precipitation of Al₃Sc which is not noted to be dislocation induced. The kinetics of precipitation of Al₃Sc in Al-6Mg-Sc alloys are found to be controlled by the diffusion of scandium in aluminum.     

Crystallographic etching of few-layer graphene

We demonstrate a method by which few-layer graphene samples can be etched along crystallographic axes by thermally activated metallic nanoparticles. The technique results in long (>1 microm) crystallographic edges etched through to the insulating substrate, making the process potentially useful for atomically precise graphene device fabrication. This advance could enable atomically precise construction of integrated circuits from single graphene sheets with a wide range of technological applications.     

Electrochemically active and robust cobalt doped copper phosphosulfide electro-catalysts for hydrogen evolution reaction in electrolytic and photoelectrochemical water splitting

The area of non-noble metals based electro-catalysts with electrochemical activity and stability similar or superior to that of noble metal electro-catalyst for efficient hydrogen production from electrolytic and photoelectrochemical (PEC) water splitting is a subject of intense research. In the current study, exploiting theoretical first principles study involving determination of hydrogen binding energy to the surface of the electro-catalyst, we have identified the (Cu_0.83Co_0.17)₃P: x at. % S system displaying excellent electrochemical activity for hydrogen evolution reaction (HER). Accordingly, we have experimentally synthesized (Cu_0.83Co_0.17)₃P: x at. % S (x = 10, 20, 30) demonstrating excellent electrochemical activity with an onset overpotential for HER similar to Pt/C in acidic, neutral as well as basic media. The highest electrochemical activity is exhibited by (Cu_0.83Co_0.17)₃P:30 at. % S nanoparticles (NPs) displaying overpotential to reach 100 mA cm^?2 in acidic, neutral and basic media similar to Pt/C. The (Cu_0.83Co_0.17)₃P:30 at. % S NPs also display excellent electrochemical stability in acidic media for long term electrolytic and PEC water splitting process [using our previously reported (Sn_0.95Nb_0.05) O₂: N-600 nanotubes (NTs) as the photoanode]. The applied bias photon-to-current efficiency obtained using (Cu_0.83Co_0.17)₃P:30 at. % S NPs as the cathode electro-catalyst for HER in an H-type PEC water splitting cell (～4%) is similar to that obtained using Pt/C (～4.1%) attesting to the promise of this exciting non-noble metal containing system.     

Active and robust novel bilayer photoanode architectures for hydrogen generation via direct non-electric bias induced photo-electrochemical water splitting

Photo-electrochemical (PEC) water splitting is a promising and environmentally benign approach for generation of hydrogen using solar energy with minimum greenhouse gas emissions. The development of semiconductor materials for photoanode with superior optoelectronic properties combined with excellent photoelectrochemical activity and stability is vital for the realization of viable commercial development of PEC water splitting systems. Herein, we report for the very first time, the study of nanoscale bilayer architecture of WO₃ and Nb and N co-doped SnO₂ nanotubes (NTs), wherein WO₃ NTs are coated with (Sn_0.95Nb_0.05)O₂:N-600 (annealed in NH₃ at 600 °C) layer of different thicknesses, as a potential semiconductor photoanode material for PEC water splitting. An excellent long term photoelectrochemical stability under illumination in the acidic electrolyte solution combined with a solar-to-hydrogen efficiency (STH) of ～3.83% (under zero applied potential) is obtained for the bilayer NTs, which is the highest STH obtained thus far, to the best of our knowledge compared to the other well studied semiconductor materials, such as TiO₂, ZnO and Fe₂O₃. These promising results demonstrate the excellent potential of bilayer NTs as a viable and promising photoanode in PEC water splitting.     

Multi-objective optimization of annular fin array with B-spline curve based fin profiles

The design of annular fin array with variable thickness fin profiles defined by B-spline curves is studied as a multi-objective optimization problem for simultaneously maximizing heat transfer rate and minimizing thermal stress. Maximization of surface e?ciency and augmentation factor as well as minimization of fin volume are considered as additional objective functions for further assessment of fin array performance. Evaluating the objective values through hybrid spline difference method, different cases are investigated by solving the optimization model by non-dominated sorting genetic algorithm II. The proposed scheme should aid designers in selecting compromise optimal solutions for practical problems.     

Modeling aspects of vapor bubble condensation in subcooled liquid using the VOF approach

Direct contact condensation of a vapor bubble during subcooled boiling flow scenario has diverse applications in many fields such as thermal, chemical, and nuclear energies. The present work aims at the exploration of the underlying physics of single vapor bubble condensation in subcooled water following the volume of fluid method approach using ANSYS FLUENT 14.5. This work emphasizes on the modeling of the mass transfer rate using interfacial jump conditions for investigating the effect of various parametric conditions on the collapse phenomenon. A comparative study is also performed between the interface jump approach and the models based on the proposed empirical correlations to assess the condensation heat transfer (in terms of the collapse rate and Nusselt number) and bubble shape. The mass transfer model based on the interfacial jump condition is found to be the more realistic among all models for capturing the collapse rate as well as its shape.