High‐rejection wide‐stopband lowpass filters using signal interference technique

A design of compact, sharp rejection microstrip lowpass filters (LPF) with wide‐stopband is presented by using signal interference technique. The filter parameters can be easily controlled by the characteristic impedances of the configuration. Explicit design equations with graphs are presented. To validate the theoretical prediction, two prototype LPFs are fabricated. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.     

Adsorption density of spherical cetyltrimethylammonium bromide (CTAB) micelles at a silica/silicon surface

In situ Fourier transform infrared internal reflection spectroscopy (FT-IR/IRS) was used to calculate the adsorption density values for spherical cetyltrimethylammonium bromide (CTAB) micelles at the silica/silicon (SiO2/Si) surface based on a previously developed adsorption density equation. Recent advances in atomic force microscopy (AFM) imaging methodology have led to the ability to image surface micelles, which was not possible previously. These AFM images have been used to independently calculate adsorption density values through offline fast Fourier transform (FFT) analysis. The adsorption density values measured from in situ FT-IR/IRS spectra and from AFM images showed good agreement and provide further validation of the FT-IR/IRS adsorption density equation in the low concentration range.     

A survey on MAC protocols in OSA networks

Opportunistic spectrum access (OSA) networks have emerged as a hot research topic following the publication of Mitola’s seminal paper on cognitive radio network. Success of such networks will depend on efficient spectrum sensing techniques as well as effective medium access control protocols that will offer efficient mechanisms for dynamic spectrum allocation, coordination and management of spectrum heterogeneity. Work on such issues have just started and is still in a rudimentary stage. The main purpose of this paper is to provide a comprehensive review of the research done at the MAC layer of the OSA networks, especially with reference to ad hoc network design and spark more research in this area. A classification of the MAC layer protocols used in OSA networks is provided, and the essential features of the different MAC layer protocols for OSA networks are thoroughly analyzed and compared. Finally, open research issues for the MAC layer are discussed.     

A new way of information storage using red, green, blue and black color imprints

Herein we report the development of a new way of information storage using a scheme based on four colors, namely red, green, blue and black. This provided the advantage of not only storing information in four-color bits, but also in terms of transition from one color to another also representing information storage. The practical demonstration of the method was achieved using a photolithographic principle with colored films as the medium of storage. A CCD camera fitted to an optical microscope was used to retrieve the stored information. The present method provides not only an alternative but also the possibility of higher information storage capacity in comparison to compact disc, digital versatile disc and blu-ray disc technology.     

A Thermal‐Reflow‐Based Low‐Temperature,High‐Pressure Sintering of Lyophilized Silk Fibroin for the Fast Fabrication of Biosubstrates

Solid fibroin is a bulk nonporous material that can be prepared with two methods: a liquid–gel–solid transition from a fibroin solution or a sintering procedure starting from silk powder. Both methods have their own disadvantages: the first requires several weeks and the process is size dependent; the second requires high temperatures. To overcome these limitations, a low‐temperature sintering procedure based on a thermal‐reflow is proposed in this work to produce in fast‐fashion monoliths of solid fibroin. Thermal‐reflow is a well‐known mechanism that takes place when the glass transition temperature of the material is lower than the temperature used to process it. Water plays an important role decreasing the glass transition temperature down to 40 °C. For the first time, a thermal reflow is conducted on lyophilized silk fibroin at 40 °C, associating to the water addition a high‐pressure compression. To optimize the process, a full factorial design of experiment is used. The material is then studied in the crucial phases by digital scanning calorimetry, Fourier‐transform infrared spectroscopy, and scanning electron microscopy. Finally, a mechanical characterization and a preliminary in vitro test are conducted.     

Phase Transformation Temperatures, γ–γ′ Lattice Parameter Misfit,and γ′ Precipitate Morphology in Co–Ti–V Alloys

In the context of developing tungsten free cobalt alloys, the physical metallurgical properties of γ′ precipitate strengthened Co–Ti–V alloys were investigated. In this study, few alloys were cast and heat treated to study systematic effects on the properties. The addition of V to the Co–Ti system decreases γ′ solvus temperature, whereas it increases solidus temperature. The γ–γ′ lattice parameter misfit decreases with V addition. The γ′ precipitates have cuboidal with round corners morphology, and the extent of roundedness of corners increases with V addition. Density functional theory calculations were performed to understand the experimental observation of phase transformation temperatures, lattice misfit, and γ′ precipitate morphology. The calculations indicate that magnitude of the heat of formation of Co₃(Ti,V) in the L1₂ crystal structure decreases with V addition. The γ–γ′ interfacial energy at 0 K is predicted to increase with V addition to the Co–Ti system.

     

Formation of lubricant “moguls” at the head/disk interface

In a typical head/disk interface of a rigid disk drive, the motion and redistribution of a 14 Å thick lubricant film on the disk under a flying slider is analyzed with an optical surface analyzer. At short times (seconds to a few minutes), the film is rearranged in an isotropic manner, creating a pattern of moguls¹ of 100 m in lateral size and a few angstroms in height. A strong correlation is demonstrated between the resulting distribution of the lubricant film and the underlying substrate topography. Surprisingly, lubricant becomes thicker on the peaks of the micro-waviness, and thinner in the valleys. Possible mechanisms for this unexpected behavior will be discussed, as well as its tribological implications. At longer times, the lubricant film is pushed away from underneath the slider, creating the previously reported circumferentially depleted tracks beneath the slider rails. In the timeframe of our experiment, no significant net lubricant loss was observed.     

Quasi-static Torsional Deformation Behavior of Porous Ti6Al4V alloy

Laser processed Ti6Al4V alloy samples with total porosities of 0%, 10% and 20% have been subjected to torsional loading to determine mechanical properties and to understand the deformation behavior. The torsional yield strength and modulus of porous Ti alloy samples was found to be in the range of 185-332 MPa and 5.7-11 GPa, respectively. With an increase in the porosity both the strength and the modulus decreased, and at 20% porosity the torsional modulus of Ti6Al4V alloy was found to be very close to that of human cortical bone. Further, the experiments revealed clear strain hardening and ductile deformation in all the samples, which suggests that the inherent brittleness associated solid-state sintered porous materials can be completely eliminated via laser processing for load bearing metal implant applications.     

Adaptive backbone protocol for heterogeneous wireless networks

We propose Adaptive Backbone Protocol ABP, a lightweight protocol for distributed formation of a backbone over Heterogeneous Wireless Networks. ABP does not require any neighborhood information and consequently scales well with the number of nodes and network size. We present an analytical framework to study the performance of ABP. By making the nodes rotate the role of backbone nodes, we extend the life of the network.     

Engineered porous metals for implants

Interest is significant in patient-specific implants with the possibility of guided tissue regeneration, particularly for load-bearing implants. For such implants to succeed, novel design approaches and fabrication technologies that can achieve balanced mechanical and functional performance in the implants are necessary. This article is focused on porous load-bearing implants with tailored micro-as well as macrostructures using laser-engineered net shaping (LENS™), a solid freeform fabrication or rapid prototyping technique that can be used to manufacture patient-specific implants. This review provides an insight into LENS, some properties of porous metals, and the potential applications of this process to fabricate unitized structures which can eliminate longstanding challenges in load-bearing implants to increase their in-vivo lifetime, such as in a total hip prosthesis.