On the Analysis of the Bluetooth Time Division Duplex Mechanism

Efficient communication in Bluetooth networks requires design of intra and inter-piconet scheduling algorithms, and therefore, numerous algorithms have been proposed. However, due to complexities of the Bluetooth MAC, the performance of these algorithms has been analyzed mostly via simulation. We present analytic results regarding the exhaustive, gated, and limited (pure round robin) scheduling algorithms in piconets with bidirectional and unidirectional traffic. We show that a piconet operated according to the limited scheduling algorithm is equivalent to a 1-limited polling system and present exact results regarding symmetric piconets with bidirectional traffic. Then, the difficulties in analyzing the performance of the exhaustive and gated algorithms in a piconet with bidirectional traffic are demonstrated. In addition, we present exact analytic results for piconets with unidirectional traffic. We show that, surprisingly, in symmetrical piconets with only uplink traffic, the mean waiting time is the same for the exhaustive and limited algorithms. This observation results from the differences between piconets and traditional polling systems and can be extended for time-division-duplex systems with arbitrary packet lengths. Furthermore, we show that the mean waiting time in a piconet with only uplink traffic is significantly higher than its corresponding value in a piconet with only downlink traffic. Finally, we numerically compare the exact results to approximate results, presented in the past.     

YBCO nanofibers synthesized by electrospinning a solution of poly(acrylic acid) and metal nitrates

A versatile approach to the synthesis of YBCO (high temperature superconductor ceramics) nanofibers via electrospinning a polymer precursor solution is reported. The aqueous polymer precursor solution consists of poly(acrylic acid) (PAAc) and a mixture of yttrium nitrate, barium nitrate, and copper nitrate, henceforth termed (Y,Ba,Cu)–N. The conductivity of the polymer precursor solution at 27.1 °C was 14.70 mS/cm, its zero shear viscosity was 52.00 cP, and its pH was 1.88. Typical YBCO nanofibers were 50–100 nm in diameter and around of 10 μm length. The nanofibers also contain relatively small amounts of yttrium oxide and copper yttrium oxide.     

Upward needleless electrospinning of multiple nanofibers

A new approach to electrospinning of polymer nanofibers is proposed. A two-layer system, with the lower layer being a ferromagnetic suspension and the upper layer a polymer solution, is subject to a normal magnetic field provided by a permanent magnet or a coil. As a result, steady vertical spikes of magnetic suspension perturbed the interlayer interface, as well as the free surface of the uppermost polymer layer. When a normal electric field is applied in addition to the system, the perturbations of the free surface become sites of jetting directed upward. Multiple electrified jets undergo strong stretching by the electric field and bending instability, solvent evaporates and solidified nanofibers deposit on the upper counter-electrode, as in an ordinary electrospinning process. However, the production rate is shown to be higher.     

Relationship of demographic factors to parental discipline techniques.

Interviewed 44 5th graders and their mothers about parental discipline practices. Responses were coded as indicating parental use of power assertion, love withdrawal, or induction. Boys received more power assertion and love withdrawal and less induction than did girls. Indicators of social status (parent education and parent occupation) related negatively to use of power assertion. Larger family size was associated with increased use of power assertion and decreased use of induction with boys, but with girls both relationships were reversed. (5 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of embedded carbon nanotubes on the morphological evolution during the carbonization of poly(acrylonitrile) nanofibers

Hybrid nanofibers with different concentrations of multi-walled carbon nanotubes (MWCNTs) in polyacrylonitrile (PAN) were fabricated using the electrospinning technique and subsequently carbonized. The morphology of the fabricated carbon nanofibers (CNFs) at different stages of the carbonization process was characterized by transmission electron microscopy and Raman spectroscopy. The polycrystalline nature of the CNFs was shown, with increasing content of ordered crystalline regions having enhanced orientation with increasing content of MWCNTs. The results indicate that embedded MWCNTs in the PAN nanofibers nucleate the growth of carbon crystals during PAN carbonization.     

Effect of supramolecular structure on polymer nanofibre elasticity

Polymer materials of reduced size and dimensionality, such as thin films, polymer nanofibres and nanotubes, exhibit exceptional mechanical properties compared with those of their macroscopic counterparts. We discuss here the abrupt increase in Young's modulus in polymer nanofibres. Using scaling estimation we show that this effect occurs when, in the amorphous (non-crystalline) part of the nanofibres, the transversal size of regions consisting of orientation-correlated macromolecules is comparable to the nanofibre diameter, thereby resulting in confinement of the supramolecular structure. We suggest that in polymer nanofibres the resulting supramolecular microstructure plays a more dominant role in the deformation process than previously thought, challenging the commonly held view that surface effects are most significant. The concept we develop also provides a way to interpret the observed--but not yet understood--temperature dependence of Young's modulus in nanofibres of different diameters.     

Encapsulation of bacteria and viruses in electrospun nanofibres

Bacteria and viruses were encapsulated in electrospun polymer nanofibres. The bacteria and viruses were suspended in a solution of poly(vinyl alcohol) (PVA) in water and subjected to an electrostatic field of the order of 1?kV?cm(-1). Encapsulated bacteria in this work, (Escherichia coli, Staphylococcus albus) and bacterial viruses (T7, T4, λ) managed to survive the electrospinning process while maintaining their viability at fairly high levels. Subsequently the bacteria and viruses remain viable during three months at -20 and -55?°C without a further decrease in number. The present results demonstrate the potential of the electrospinning process for the encapsulation and immobilization of living biological material.     

Analysis of bandwidth allocation algorithms for wireless personal area networks

A major issue in the design and operation of ad hoc networks is sharing the common spectrum among links in the same geographic area. Bandwidth allocation, to optimize the performance of networks in which each station can converse with at most a single neighbor at a time, has been recently studied in the context of Bluetooth Personal Area Networks. There, centralized and distributed, capacity assignment heuristics were developed, with applicability to a variety of ad hoc networks. Yet, no guarantees on the performance of these heuristics have been provided. In this paper, we extend these heuristics such that they can operate with general convex objective functions. Then, we present our analytic results regarding these heuristics. Specifically, we show that they are β-approximation (β<2) algorithms. Moreover, we show that even though the distributed and centralized algorithms allocate capacity in a different manner, both algorithms converge to the same results. Finally, we present numerical results that demonstrate the performance of the algorithms. Randeep Bhatia received the Ph.D. degree in Computer Science from University of Maryland, the M.S. degree in Mathematics and Computer Science from University of Illinois at Chicago and the B.Tech. degree in Computer Science and Engineering from Indian Institute of Technology, Delhi. He is currently with the High Speed Networks Research Department at Bell Labs, Lucent technologies, working on network design, traffic engineering and scheduling algorithms. His current research interests are in the area of QoS for multimedia services in wireless data networks. Adrian Segall received the B.Sc. and M.Sc. degrees in electrical engineering from the Technion, Israel Institute of Technology in 1965 and 1971, respectively, and the Ph.D. degree in electrical engineering with a minor in statistics from Stanford University in 1973. After serving active duty in the Israel Defense Forces, he joined in 1968 the Scientific Department of Israel’s Ministry of Defense. From 1973 to 1974 he was a Research Engineer at System Control Inc., Palo Alto, CA and a Lecturer at Stanford University. From 1974 to 1976 he was an Assistant Professor of Electrical Engineering and Computer Science at the Massachusetts Institute of Technology. From 1987 to 1998 he was on the faculty of the Department of Computer Science at the Technion. He is presently Benjamin Professor of Computer-Communication Networks in the Department of Electrical Engineering, Technion, Israel Institute of Technology. From 1982 to 1984 he was on leave with the IBM T.J.Watson Research Center, Yorktown Heights, NY. He held visiting positions with IBM, AT&T and Lucent Bell Labs. His current research interests are in the area of optical networks, wireless, sensor and ad-hoc networks. Dr. Segall is an IEEE Fellow and has served in the past as Editor for Computer Communication Theory of the IEEE Transactions on Communications, Editor for the IEEE Information Theory Society Newsletter and Senior Editor for the IEEE Journal on Selected Areas in Communications. He was selected as an IEEE delegate to the 1975 IEEE-USSR Information Theory Workshop, and is the recipient of the 1981 Miriam and Ray Klein Award for Outstanding Research and of the 1990 Taub Award in Computer Science. Gil Zussman received the B.Sc. degree in Industrial Engineering and Management and the B.A. degree in Economics (both summa cum laude) from the Technion—Israel Institute of Technology in 1995. He received the M.Sc. degree (summa cum laude) in Operations Research from Tel-Aviv University in 1999 and the Ph.D. degree in Electrical Engineering from the Technion—Israel Institute of Technology in 2004. Between 1995 and 1998, he served as an engineer in the Israel Defense Forces. He is currently a Postdoctoral Associate in the Laboratory for Information and Decision Systems in MIT. His current research interests are in the area of ad hoc and sensor networks. In particular, he is interested in energy efficient protocols, medium access control protocols, and personal area networks. Gil received the Knesset (Israeli Parliament) Award for distinguished students, the Best Student Paper Award at the IFIP-TC6 Networking 2002 Conference, and the IEEE Communications Magazine Best Paper Award at the OPNETWORK 2002 Conference. In 2004 he received the Marie Curie Outgoing International Fellowship and the Fulbright Fellowship.