Clay exfoliation and organic modification on wear of nylon 6 nanocomposites processed by different routes

The role of nanoclay on the wear characteristics of nylon 6 nanocomposites processed via different routes is examined in this paper. Pristine clay and organoclay were used in melt-extrusion with the matrix resulting in a largely aggregated and a highly exfoliated morphology, respectively. High exfoliation of pristine clay was also achieved by a water-assist process in melt compounding. Nylon 6/pristine clay composite had the worst wear resistance due to the large aggregated clay particles. For the two nylon 6/exfoliated clay nanocomposites, the one with the organically modified clay outperformed that with the pristine clay exfoliated by water. Detailed study on the wear track and subsurface below of the nylon 6/clay composites using both transmission and scanning electron microscopy provided new insight into the differences in their deformation and damage mechanisms. It was revealed that the interfacial adhesion of clay to matrix, and not the exfoliated morphology of clay, played a critical role in wear. However, exfoliated clay morphology is preferred to aggregate morphology. Hence, the superior wear-performance of nylon 6/organoclay nanocomposite is brought about by a combined effect of fine dispersion of clay platelets in nylon 6, high interfacial interaction between nylon 6 and clay layers, and effective constraint on surrounding nylon 6 material exerted by the clay platelets.     

Opportunistic large array concentric routing algorithm (OLACRA) for upstream routing in wireless sensor networks

An opportunistic large array (OLA) is a form of cooperative diversity in which a large group of relays or forwarding nodes operate without any mutual coordination, but naturally fire together in response to energy received from a single source or another OLA. When used for broadcast, OLAs form concentric rings around the source, and have been shown to use less transmit energy than conventional multi-hop protocols during broadcasting. The OLA concentric routing algorithm (OLACRA) and its variants, the main contributions of this paper, leverage the concentric ring structure of the OLAs during the initialization phase to limit the node participation on the upstream connection. For the simulation scenarios considered in this paper, OLACRA is shown to save over 80% of the transmit energy relative to other OLA-based schemes. This paper analyzes the performance of OLACRA over ‘deterministic channels’ or non-faded orthogonal channels and on ‘diversity’ or Rayleigh flat-fading channels with limited orthogonality. Enhancements to OLACRA to further improve its energy efficiency by limited broadcasting in the initial upstream level and limiting the downlink ‘step-sizes’ are also considered. A simple contention avoidance scheme for WSNs with multiple flows is also proposed. In addition to this, the robustness of OLACRA over mobile channels is also studied. The protocols are tested using Monte Carlo evaluation.     

Using OpenFlow to provide cut-through switching in MobilityFirst

Mobile devices are expected to become the Internet’s predominant technology. Current protocols such as TCP/IP were not originally designed with mobility as a key consideration, and therefore underperform under challenging mobile and wireless conditions. MobilityFirst, a clean slate architecture proposal, embraces several key concepts centered around secure identifiers that inherently support mobility and trustworthiness as key requirements of the network architecture. This includes a hop-by-hop segmented data transport based on a globally unique identifier. This allows late and dynamic rebinding of end-point addresses to support mobility. While this provides critical gains in wireless segments, some overheads are incurred even in stable segments such as in the core. Bypassing routing-layer decisions in these cases, with lower layer cut-through forwarding, can improve said gains. In this work, we introduce a general bypass capability within the MobilityFirst architecture that provides better performance and enables both individual and aggregate flow-level traffic control. Furthermore, we present an OpenFlow-based proof-of-concept implementation of the bypass function using layer 2 VLAN tagging. We run experiments on the ORBIT and Global Environment for Network Innovations (GENI) testbeds to evaluate the performance and scalability of the solution. By implementing the bypass functionality, we are able to significantly reduce the number of messages processed by the controller as well as the number of flow rules that need to be pushed into the switches.     

Angstrom Scale Wear of the Air-Bearing Sliders in Hard Disk Drives

We utilize thermal fly-height control (TFC) technology to perform in situ measurements of carbon overcoat wear at the angstrom level at the read–write area of magnetic recording heads. We also study the durability of the molecularly thin lubricated disk surface. Experimental findings reveal a linear relationship between the quantified carbon wear depth on the flying head versus the head–disk contact level produced by the TFC power. It is demonstrated that this method can serve as a measurement and probing technique of wear resistance for different types of lubricants. Lubricants possessing more polar hydroxyl end-groups and less mobility tend to show a superior surface stability under head–disk contacts, but raise concerns on head carbon overcoat wear.     

Constrained Sintering of Low-Temperature Co-Fired Ceramics

This paper discusses the effect of uniaxial compressive stress and pressureless constraint on the microstructure, density, and shrinkage anisotropy during the sintering of two commercial low-temperature co-fired ceramic (LTCC) systems, i.e., Heraeus CT2000 (CT) and DuPont 951Tape (DU). Under uniaxial compression, the ratio of axial to transverse shrinkage of DU is significantly higher than that of CT. A simple linear viscous theory was used to estimate the change in the strain rates produced by the external stress and the stress required to produce zero shrinkage. The theory was found to overestimate the measured stress-induced strain rates. The uniaxial compressive stress required for zero overall shrinkage was estimated to be ∼60 kPa for DU and 80 kPa for CT. The estimate for the DU materials was in good agreement with the experimental data, but there was significant deviation for the CT material. Higher viscosity and higher constraining stresses led to lower densities in pressure-less constrained CT specimens compared with DU.     

Roles of graphite oxide, clay and POSS during the combustion of polyamide 6

Two contrasting approaches have been adopted in the current study to obtain environmental benign and superior flame retardant polymer nanocomposites. In the first approach, polyhedral oligomeric silsesquioxane (POSS) is incorporated as an additional filler in polyamide 6/clay nanocomposite to improve the homogeneity of the ‘physical’ barrier, since POSS transforms to a glassy material upon fire and enhances the coupling of silicate layers to each other. In the second approach, fire response of an intumescent system, polyamide 6/graphite oxide (GO), is compared to polyamide 6/clay systems. The intention of using GO as a flame retardant is to benefit from its layered structure (‘physical’ barrier mechanism) and intumescent/blowing effect (‘chemical’ mechanism). Considerable insight and physical knowledge on the roles of different fillers in the combustion process have been obtained, which would provide useful guidance for the development of a new generation of nanocomposites. Besides the obvious contrasting differences in the flame properties of different materials, the incorporation of various fillers, depending on their nature, has both advantages and disadvantages from the viewpoint of flame retardancy.     

Analysis of Surface Textured Air Bearing Sliders with Rarefaction Effects

A numerical model is developed to study the effect of texture on air bearing sliders for large Knudsen numbers. The effect of texture location, texture size, and density on the pressure generation is studied. First, a textured plane slider parallel to the disk surface is investigated, and the texture parameters are determined that result in optimum pressure generation. Then, a plane inclined slider is studied using optimum texture parameters found in the parallel slider case. Thereafter, the effect of texture on the steady state flying characteristics of an actual magnetic recording slider is investigated. Finally, the flying height modulation, pitch, and roll motion of a textured slider (pico and femto form factors) are determined numerically by exciting the slider using a step on the disk. Comparison of the results for textured and untextured sliders is made. It is found that textured sliders show better dynamic performance compared to the untextured sliders in terms of stiffness and damping.