Analytical Models for Single-Hop and Multi-Hop Ad Hoc Networks

There is considerable interest in modeling the performance of ad hoc networks analytically. This paper presents approximate analytical models for the throughput performance of single-hop and multi-hop ad hoc networks. The inherent complexity of analysis of a multi-hop ad hoc network together with the fact that the behavior of a node is dependent not only on its neighbors' behavior, but also on the behavior of other unseen nodes makes multi-hop network analysis extremely difficult. However, our approach in this paper to analyze multi-hop networks offers an accurate approximation with moderate complexity. Our approach is based on characterizing the behavior of a node by its state and the state of the channel it sees. This approach is used to carry out an analysis of single-hop and multi-hop ad hoc networks in which different nodes may have different traffic loads. In order to validate the model, it is applied to IEEE 802.11-based networks, and it is shown through extensive simulations that the model is very accurate. Farshid Alizadeh-Shabdiz received his B.Sc. in 1989 at University of Science and Technology, M.Sc. in 1991 at Tehran University, Iran, and D.Sc. in 2004 at the George Washington University. He is a senior research engineer in Advanced Solution Group, part of Cross Country Automotive Services, and he is also a part time faculty member at Boston University. Dr. Alizadeh-Shabdiz was part of the design and implementation team of the three first satellite-based mobile networks: ICO global medium orbit satellite network voice and data services, Thuraya GEO satellite network, and the first phase of Inmarsat high speed data network. His research interests include MAC layer, physical layer and network layer of wireless and satellite networks. Suresh Subramaniam received the Ph.D. degree in electrical engineering from the University of Washington, Seattle, in 1997. He is an Associate Professor in the Department of Electrical and Computer Engineering at the George Washington University, Washington, DC. His research interests are in the architectural, algorithmic, and performance aspects of communication networks, with particular emphasis on optical and wireless ad hoc networks. Dr. Subramaniam is a co-editor of the books “Optical WDM Networks – Principles and Practice” and “Emerging Optical Network Technologies: Architectures, Protocols, and Performance”. He has been on the program committees of several conferences including Infocom, ICC, Globecom, and Broadnets, and served as TPC Co-Chair for the 2004 Broadband Optical Networking Symposium. He currently serves on the editorial boards of Journal of Communications and Networks and IEEE Communications Surveys and Tutorials. He is a co-recipient of the Best Paper Award at the 1997 SPIE Conference on All-Optical Communication Systems.     

Synthesis and characterization of calcium aluminum silicate hydroxide (CASH) mineral

The synthesis of calcium aluminum silicate hydroxide (CASH) has been carried out under mild hydrothermal and solvothermal conditions. Different mineralizers such as HCOOH, HNO₃, CH₃COOH, HCl, mixed acids, NaOH and non-aqueous solvents like C₂H₅OH, n-butanol, glycol, methanol, etc., were employed in the synthesis of CASH. The crystals obtained were characterized by X-ray powder diffraction and FTIR spectroscopic techniques.     

Effect of cardanol diol on the synthesis,characterization, and film properties of aqueous polyurethane dispersions

This article reports on the effect of a diol prepared from a renewable resource, cardanol, on the synthesis, film formation and film properties of aqueous polyurethane dispersions. The PU dispersions were prepared by the acetone process from poly(tetramethylene ether)glycol (PTMEG) and isophorone diisocyanate (IPDI) prepolymer at constant NCO/OH ratio of 1:1.1. Dispersions with two different concentrations of cardanol diol (OH value 140 mg KOH/g) were prepared through chain extension and characterized for solid content, particle size, and particle-size distribution (PSD). Free films were prepared by casting and were studied for their thermal, mechanical, viscoelastic, and hydrophobic properties. Due to the broad PSD, the dispersions containing cardanol diol exhibit better film formation property in comparison to the butane diol chain-extended PU. Soft and flexible films were obtained using cardanol diol as chain extender, whereas brittle film was obtained with butane diol chain extender. Morphological characterization using atomic force microscopy (AFM) and scanning electron microscopy (SEM) suggests a heterogeneous and amorphous nature of the polyurethanes-containing cardanol diol. The thermomechanical and viscoelastic properties show that incorporation of cardanol diol decreases the glass transition temperature and modulus of the films but enhances the properties like thermal stability, hydrophobicity, elongation, etc., of the polyurethane films.     

Design of polymeric materials for culturing human pluripotent stem cells: Progress toward feeder-free and xeno-free culturing

This review describes recent developments regarding the use of natural and synthetic polymers to support the propagation of human pluripotent stem cells (hPSCs), human embryonic stem cells (hESCs), and induced pluripotent stem cells (hiPSCs) while maintaining pluripotency in feeder-free and xeno-free cultures. The development of methods for culturing these cells without using mouse embryonic fibroblasts (MEFs) as a feeder layer will enable more reproducible culture conditions and reduce the risk of xenogenic contaminants, thus increasing the potential clinical applications of differentiated hPSCs. Human or recombinant fibronectin, laminin-511, and vitronectin, which are components of the extracellular matrix (ECM), have been used instead of Matrigel for the feeder-free growth of undifferentiated hPSCs. Successful hPSC cultures have been described for the following conditions: on oligopeptide-immobilized surfaces derived from vitronectin, on microcarriers prepared from synthetic polymers, and encapsulated within three-dimensional (3D) hydrogels composed of alginate and other hydrophilic natural polymers. Recently, synthetic biomaterials that allow hPSCs to maintain pluripotency by secreting endogenous ECM components have been designed. The combination of human ECM proteins or cell adhesion molecules (e.g., oligopeptides and poly-d-lysine) and synthetic biomaterials with well-designed surfaces and/or structures (e.g., scaffolds, hydrogels, microcarriers, microcapsules, or microfibers) in the presence of a chemically defined medium containing recombinant growth factors would offer a xeno-free alternative to feeder cells for culturing hPSCs and maintaining their pluripotency.     

Ink‐Jet Printed CMOS Electronics from Oxide Semiconductors

Complementary metal oxide semiconductor (CMOS) technology with high transconductance and signal gain is mandatory for practicable digital/analog logic electronics. However, high performance all‐oxide CMOS logics are scarcely reported in the literature; specifically, not at all for solution‐processed/printed transistors. As a major step toward solution‐processed all‐oxide electronics, here it is shown that using a highly efficient electrolyte‐gating approach one can obtain printed and low‐voltage operated oxide CMOS logics with high signal gain (≈21 at a supply voltage of only 1.5 V) and low static power dissipation.