A unified model for multi-turn closed-loop pulsating heat pipe

Numerical modeling of  the multi-turn closed-loop pulsating heat pipe (CLPHP) in the bottom, horizontal, and top heat mode is presented in this paper, with water as working fluid. Modeling is carried out for 2-mm ID CLPHP having 5, 16, and 32 turns at different orientations for 10 different cases. Momentum and heat transfer variations with time are investigated by numerically solving the one-dimensional governing equations for vapor bubble and liquid plugs. Instead of considering all the vapor bubble at saturation temperature, vapor bubbles are allowed to remain in super-heated condition. Film thickness is found using a correlation. Two-phase heat transfer coefficient is calculated by considering conduction through the thin film at liquid–vapor interface. Liquid plug merging and splitting result in continuous variation in the number of liquid plugs and vapor bubble with time, which is also considered in the code. During the merging of liquid plugs, a time step-adaptive scheme is implemented and this minimum time step was found to be 10⁻⁷ s. Model results are compared with the experimental results from literature for heat transfer and the maximum variation in heat transfer for all these cases is below ±39%.     

Studies on effect of ethyl 4-amino cinnamate functionalized multiwall carbon nanotubes (f-MWCNTs) on properties of millable polyurethane rubber (MPU) nanocomposites

Multiwall carbon nanotubes (MWCNTs) were prepared using chemical vapor deposition (CVD) technique in presence of nano Co/Mo-MgO as an efficient catalyst. Further the as-synthesized MWCNTs were functionalized using ethyl 4-amino cinnamate (f-MWCNTs) to improve its wettability or compatibility with the chains of polymer. The as-synthesized MWCNTs and f-MWCNTs were subjected to various characterization techniques Raman spectroscopy, X-ray diffraction, FTIR, FESEM and TGA to investigate its size, presence of functional groups and stability. It was observed that diameter of f-MWCNTs were found to be ~ 45 nm with thermally more stable. Further, f-MWCNTs (0 to 1 %) were reinforced in MPU rubber using two roll mill and molded on compression molding machine. The dumbbell shape specimens were then subjected to mechanical and thermal study. It was observed that both the tensile strength and % elongation at break of MPU nanocomposites increases significantly up to 0.8 wt loading and decreases thereafter. This improvement in properties was due to uniform dispersion of f-MWCNTs into the chains of MPU rubber with homogeneity in bonding, while the decrement in properties at 1wt % loading was due to agglomeration of f-MWCNTs at some places. Also the functionalization using ethyl 4-amino cinnamate increases the compatibility of MWCNTs with MPU rubber chains. Besides this, functionalization makes the surface of MWCNTs smooth with enhancement in bonding between the two surfaces that is filler as well as matrix counterpart. Significant improvement in mechanical and thermal properties are achieved due to modification MPU with functionalized MWCNT.     

The Problem of Expensive Chunks and its Solution by Restricting Expressiveness

Soar is an architecture for a system that is intended to be capable of general intelligence. Chunking, a simple experience-based learning mechanism, is Soar's only learning mechanism. Chunking creates new items of information, called chunks, based on the results of problem-solving and stores them in the knowledge base. These chunks are accessed and used in appropriate later situations to avoid the problem-solving required to determine them. It is already well-established that chunking improves performance in Soar when viewed in terms of the subproblems required and the number of steps within a subproblem. However, despite the reduction in number of steps, sometimes there may be a severe degradation in the total run time. This problem arises due to expensive chunks, i.e., chunks that require a large amount of effort in accessing them from the knowledge base. They pose a major problem for Soar, since in their presence, no guarantees can be given about Soar's performance.In this article, we establish that expensive chunks exist and analyze their causes. We use this analysis to propose a solution for expensive chunks. The solution is based on the notion of restricting the expressiveness of the representational language to guarantee that the chunks formed will require only a limited amount of accessing effort. We analyze the tradeoffs involved in restricting expressiveness and present some empirical evidence to support our analysis.     

Modifications of Tapioca Starch Properties by Polyethylene Glycol (4000) and Polyethylene Glycol (4000) Stearate Additives

Changes in crystallinity, iodine binding capacity and infrared spectral characteristics of tapioca starch on incorporation of polyethylene glycol (4000) and polyethylene glycol (4000) distearate additives into gelatinised starch have been investigated. A plausible explanation for the appearance of crystallinity for gelatinised starch on incorporation of the additives is given. The additives were also shown to influence the gelatinisation temperature of native tapioca starch. The DSC studies indicating this effect are discussed in detail.     

Structure–property relationship studies in amine functionalized multiwall carbon nanotubes filled polypropylene composite fiber

Amine functionalized multiwalled carbon nanotubes (a‐MWNT) based polypropylene (PP) composite fibers were prepared in the presence of polypropylene‐g‐maleic anhydride (PP‐g‐MA) by melt‐mixing followed by melt‐spinning with subsequent post‐drawing of the as‐spun fibers of varying draw ratio (DR). In order to enhance the interfacial interaction, a‐MWNT were utilized in combination with PP‐g‐MA during melt‐mixing. Fourier transform infrared spectroscopic analysis revealed the formation of imide bonds between MA functionality of PP‐g‐MA and amine functional group of a‐MWNT. Higher tensile properties of PP/a‐MWNT/PP‐g‐MA composite fibers were registered with varying DR of the as‐spun fiber. Orientation factors of a‐MWNT and PP chains along the fiber axis were correlated with the higher tensile modulus and tensile strength of PP/a‐MWNT/PP‐g‐MA composite fiber of varying DR. Crystallization studies indicated the role of hetero‐nucleating action of a‐MWNT in PP/a‐MWNT/PP‐g‐MA composite fiber. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

High-Performance Photodetector and Angular-Dependent Random Lasing from Long-Chain Organic Diammonium Sandwiched 2D Hybrid Perovskite Non-Linear Optical Single Crystal

3D organic-inorganic metal halide perovskites are excellent materials for optoelectronic applications due to their exceptional properties, solution processability, and cost-effectiveness. However, the lack of environmental stability highly restricts them from practical applications. Herein, a stable centimeter-long 2D hybrid perovskite (N-MPDA)[PbBr₄] single crystal using divalent N1-methylpropane-1,3-diammonium (N-MPDA) cation as an organic spacer, is reported. The as-grown single crystal exhibits stable optoelectronic performance, low threshold random lasing, and multi-photon luminescence/multi-harmonic generation. A photoconductive device fabricated using (N-MPDA)[PbBr₄] single crystal exhibits an excellent photoresponsivity (≈124 AW⁻¹ at 405 nm) that is ≈4 orders of magnitudes higher than that of monovalent organic spacer-assisted 2D perovskites, such as (BA)₂PbBr₄ and (PEA)₂PbBr₄, and large specific detectivity (≈10¹² Jones). As an optical gain media, the (N-MPDA)[PbBr₄] single crystal exhibits a low threshold random lasing (≈6.5 µJ cm⁻²) with angular dependent narrow linewidth (≈0.1 nm) and high-quality factor (Q ≈ 2673). Based on these results, the outstanding optoelectronic merits of (N-MPDA)[PbBr₄] single crystal will offer a high-performance device and act as a dynamic material to construct stable future electronics and optoelectronic-based applications.     

Compact high-gain composite horn antenna for space-borne beacon application

ABSTRACT

The growing interest in higher capacity communications satellite necessitates the development of compact and lightweight other antennas (such as beacon horn antenna) at Earth-viewing deck due to crowded accommodation and weight limitation. In this article, we describe an innovative and compact high-gain composite horn antenna for space-borne beacon application. We have designed, manufactured and measured beacon horn antenna operating from 10.7 GHz to 12.5 GHz. The beacon horn antenna is devised by combining stepped section at input, axial corrugated in mid and finally radial corrugated sections. This engineered multiple sections provide extra flexibility of optimisation, leading to high edge of coverage (EoC) gain for Indian mainland, Lakshadweep Islands and Andaman & Nicobar Islands. The radial corrugated section is specially profiled using multi-profile subsections. The mode-matching technique (MMT)-based software CHAMP and ‘minimax optimiser’ have been used to analyse and optimise the Beacon horn antenna. Manufacturing of the horn using a turning machine over aluminium alloy helps to reduce its cost. Characterisation of the beacon antenna confirm predicted electrical results (return loss> 17 dB, cross-polarisation discrimination < ?40 dB, EoC gain > 24 dB). The Accommodation of the Ku-Beacon antenna on spacecraft is discussed with help of its near field from the scattering point of view and its tilt.     

The development of risk assessment models for carpal tunnel syndrome: a case-referent study

The present study developed risk assessment models for carpal tunnel syndrome (CTS) which can provide information of the likelihood of developing CTS for an individual having certain personal characteristics and occupational risks. A case-referent study was conducted consisting of two case groups and one referent group: (1) 22 work-related CTS patients (W-CTS), (2) 25 non-work related CTS patients (NW-CTS), and (3) 50 healthy workers (HEALTHY) having had no CTS history. The classification of CTS patients into one of the case groups was determined according to the type of insurance covering their medical costs. Personal characteristics, psychosocial stresses at work, and physical work conditions were surveyed by using a questionnaire tailor-designed to CTS (reliability of each scale > or = 0.7). By contrasting the risk information of each case group to that of the referent group, three logistic regression models were developed: W-CTS/HEALTHY, NW-CTS/HEALTHY, and C-CTS/HEALTHY (C-CTS, the combined group of W-CTS and NW-CTS). ROC analysis indicated that the models have satisfactory discriminability (d' = 1.91 to 2.51) and high classification accuracy (overall accuracy = 83-89%). Both W-CTS/HEALTHY and C-CTS/HEALTHY include personal and physical factors, while NW-CTS/HEALTHY involves only personal factors. This suggests that the injury causation of NW-CTS patients should be attributable mainly to their 'high' personal susceptibility to the disorder rather than exposure to adverse work conditions, while that of W-CTS patients be attributable to improper work conditions and CTS-prone personal characteristics in combination.     

Controlled growth of ternary alloy nanowires using metalorganic chemical vapor deposition

We report the growth and characterization of ternary AlxGa1- xAs nanowires by metalorganic chemical vapor deposition as a function of temperature and V/III ratio. Transmission electron microscopy and energy dispersive X-ray spectroscopy show that, at high temperatures and high V/III ratios, the nanowires form a core-shell structure with higher Al composition in the nanowire core than in the shell. We develop a growth model that takes into account diffusion of reactants and decomposition rates at the nanowire catalyst and stem to describe the compositional difference and the shell growth rate. Utilizing this model, we have successfully grown compositionally uniform Al0.16Ga0.84As nanowires. The ability to rationally tune the composition of ternary alloy nanowires broadens the application range of nanowires by enabling more complex nanowire heterostructures.