Harmonic oscillators of carbon nanotube arrays

The harmonic properties of single-walled carbon nanotube (10, 10) arrays in cantilever geometry of lengths, L = 1,000 to 10,000 nm and diameters, D = 15 to 70 nm have been measured recently, and a linear relationship between the first natural frequency and the ratio of array diameter and the square of the span length, D/L2 was postulated. In the present work the authors show that this relationship is highly nonlinear, especially for large values of the ratio, D/L2. In addition, for a given array length, L = 1000 nm, the first natural frequency of the cantilever is shown to vary little with diameters more than 30 nm and to become asymptotic to a value of 22 MHz as it is further increased. The present study is based on earlier work of the authors wherein the flexural stiffness of the single-walled carbon nanotube (CNT) array of hexagonal symmetry and of non-covalent bonding, due to van der Waals interactions, was predicted in terms of the chirality of the nanotubes and the shearing transfer efficiency between nanotubes when subjected to flexural deformation. In addition, predictions are shown to be in agreement with the experimental evidence wherein the flexural modulus of the CNT array decreases with an increase in array diameter.     

Free-edge singularities meet the microstructure: Important considerations

The significance of the free-edge singularities in angle–ply laminates and due to fiber terminations is explored and results are compared to that of a singularity due to the presence of a crack in the same region. A new dimensionless ratio, Δ is defined to compare the intensity of the singularities and the ratio shows that the stress field due to a crack of finite size is approximately twice that generated by free-edge singularities and 1.5 times as intense as the field generated by fiber terminations. For a range of material properties studied, it was found that the free-edge singularity was shown to effectively disappear as the ply angles decrease below ±15° or increase above ±85° and the fiber termination singularity was surprisingly insensitive to material properties. The results of this study suggest that singularities due to cracks dominate the stress field in the free-edge as compared to singularities at lamina discontinuities in equivalent media and fiber terminations.     

Rethinking the concept of acculturation: Implications for theory and research.

This article presents an expanded model of acculturation among international migrants and their immediate descendants. Acculturation is proposed as a multidimensional process consisting of the confluence among heritage-cultural and receiving-cultural practices, values, and identifications. The implications of this reconceptualization for the acculturation construct, as well as for its relationship to psychosocial and health outcomes, are discussed. In particular, an expanded operationalization of acculturation is needed to address the “immigrant paradox,” whereby international migrants with more exposure to the receiving cultural context report poorer mental and physical health outcomes. We discuss the role of ethnicity, cultural similarity, and discrimination in the acculturation process, offer an operational definition for context of reception, and call for studies on the role that context of reception plays in the acculturation process. The new perspective on acculturation presented in this article is intended to yield a fuller understanding of complex acculturation processes and their relationships to contextual and individual functioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Retrogradation—Digestibility Relationship of Selected Glutinous and Non-Glutinous Fresh and Stale Cooked Rice

This study examined the retrogradation and digestibility relationship of fresh and stale cooked rice of three rice varieties: glutinous (TDK11) and non-glutinous (Doongara and floating rice). The effect of rice variety, degree of milling and retrogradation (staling) of cooked rice on the estimated glycaemic index was determined. Although high-glycaemic index values were obtained for fresh cooked rice of all varieties, staling rice at 4^oC for 24 h showed positive effect on floating rice only, yielding intermediate-glycaemic index. The effect of staling on retrogradation rates was corroborated by changes in x-ray diffraction peaks. The thermal and textural properties of rice samples showed higher pasting temperature, final viscosity, and hardness, and lower peak viscosity and adhesiveness for fresh cooked non-glutinous varieties, which were also significantly affected by degree of milling, in terms of hardness, after retrogradation.     

Small Worlds in Networks of Inventors and the Role of Academics: An Analysis of France

Using data on patent applications at the European Patent Office, we examine the structural properties of networks of inventors in France in different technologies. We find that the higher the presence of inventors from universities and public research organizations (PROs), the more likely the networks are to exhibit small world properties. University and PRO inventors contribute to reduce average path length insofar they are more mobile (across applicants) than other inventors, thus linking up otherwise disconnected cliques. We achieve these results by implementing an original methodology for detecting small world properties in one-mode projections of two-mode graphs.     

Microstructural Effects on the Mechanical Integrity of a TRIP-800 Steel Welded by Laser-CO2 Process

In this study, a TRIP-800 steel was welded using a Laser CO₂ process, and the resultant microstructures were characterized by optical, scanning, and transmission electron microscopy (TEM) means. It was found that the microstructure of the steel in the as-received condition consisted of ferrite, bainite, and retained austenite (RA), including some martensite. In particular, TEM observations indicated that the developed martensites were high carbon twinned martensites. It was found that laser beam welding (LBW) promoted the development of up to 23% martensite in the fusion zone (FZ) and up to 30% in the heat-affected zone (HAZ). In addition, determinations of RA using x-ray diffraction indicated that the amount of RA developed in the FZ was relatively small (<6%). Confirmation for the relatively large amounts of martensite in both the FZ and HAZ was indirectly made by the shape of microhardness profiles, which resembled a “top hat.” Tensile testing in welded strips indicated a loss of strength and ductility. An examination of the fracture surfaces indicated that the steel fractured in a brittle fashion at the HAZ-BM interface. Apparently, the development of relatively large amounts of martensite in the HAZ reduced the steel toughness. In turn, this indicated that LBW leads to martensite embrittlement in the HAZ regions, but not at the parting line of the FZ.     

Alkaline Corrosion-Resistant Sealant for Anodized Aluminum Alloys

Corrosion resistance of anodized aluminum sealed with conventional and a new sealant was tested against the alkaline, acid and neutral chloride salt solutions. The results show that the conventional water based sealants have good acid and Neutral Salt Fog resistance; however, they do not possess the necessary alkaline corrosion resistance to be used for decorative and automotive exterior applications. A new anodic coating sealant was developed to provide the necessary alkaline corrosion resistance along with the acid and neutral salt attack resistance. Acid Dissolution Test (ADT) Rating, Alkaline Corrosion Resistance, Neutral Salt Fog, Heat Resistance and Alkaline Car Wash Detergent tests were done in accordance with General Motors Spec GMW 14665. Results revealed that this novel sealant is significantly capable of meeting the rigorous GMW 14665 specification and can be used for sealing the anodic coatings used in automotive exterior applications.     

Model development and validation of a solar cooling plant

This paper describes the dynamic model of a solar cooling plant that has been built for demonstration purposes using market-available technology and has been successfully operational since 2001. The plant uses hot water coming from a field of solar flat collectors which feed a single-effect absorption chiller of 35 kW nominal cooling capacity. The work includes model development based on first principles and model validation with a set of experiments carried out on the real plant. The simulation model has been done in a modular way, and can be adapted to other solar cooling-plants since the main modules (solar field, absorption machine, accumulators and auxiliary heater) can be easily replaced. This simulator is a powerful tool for solar cooling systems both during the design phase, when it can be used for component selection, and also for the development and testing of control strategies.     

CFD analysis of water gas shift membrane reactor

Fuel cell based modular power generation can be achieved by miniaturization and process intensification of equipments in the process. Fuel cells require hydrogen rich gas which can be generated through reforming and water gas shift reaction. The water gas shift reactor being kinetically limited occupies more volume to achieve the required CO conversion. A membrane reactor integrates the reaction and hydrogen separation stages and hence reduces the volume requirement. Computational Fluid Dynamics offers virtual prototyping of the reactor and thus helps in design, optimization and scale up of reactors. In this study customized User Defined Functions (UDFs) were developed to analyze the performance of low temperature water gas shift membrane reactor. The models were validated using literature data for the parameters – synthesis gas compositions, time factor, sweep flow rate and steam to CO ratio. The effect of all these parameters on the reactor was analyzed for CO conversion, H₂ recovery, DaPe, concentration polarization, concentration profiles and conversion index. The simulations have showed that the UDFs developed were capable of simulating the membrane reactor and this can be used for the design and optimization of the membrane reactor for any process conditions.     

Effect of heat treatment of carbon nanofibers on the electromagnetic shielding effectiveness of linear low density polyethylene nanocomposites

The electrical properties and electromagnetic shielding effectiveness (EM SE) of nanocomposites consisting of heat‐treated carbon nanofibers (Pyrograf® III PR‐19, CNF) in a linear low density polyethylene (LLDPE) matrix were assessed. Heat treatment (HT) of carbon nanofibers at 2500°C significantly improved their graphitic crystallinity and intrinsic transport properties, thereby increasing the EM SE of the nanocomposites. Nanocomposites containing 11 vol% (20 wt%) PR‐19 HT displayed a DC electrical conductivity of about 1.0 ± 0.1 × 10¹ S/m (n = 4), about 10 orders of magnitude better than that of as‐received PR‐19 CNF nanocomposites. Over a frequency range of 30 MHz to 1.5 GHz, nanocomposites (2.5 mm thick) containing PR‐19 HT displayed EM SE average values of about 14 ± 2 dB (n = 4). Absorption was determined to be the main EM SE mechanism for the heat‐treated CNF nanocomposites. The nanocomposites possessed a modulus of 632 ± 36 MPa (n = 6) (nominally twice that of pure LLDPE) and a strain‐to‐failure of 180 ± 98% (n = 6), indicating that a significant ductility is retained in the nanocomposites. Such nanocomposites display potential as absorptive electromagnetic interference shielding materials for thin films and micromolding. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers