Decentralized Spectrum Access Amongst Cognitive Radios—An Interacting Multivariate Global Game-Theoretic Approach

This paper studies decentralized dynamic spectrum access using the theory of multivariate global games. We consider a network of cognitive radios (CRs) where each CR obtains noisy multivariate measurements of the quality of several logical channels and needs to decide which channel to access. Assuming the CRs are rational devices, each CR determines which channel to access, based on its expected throughput and Bayesian estimate of the intention of other CRs. We formulate conditions for which the Bayesian Nash equilibrium (BNE) of the resulting global game is monotonically increasing in the quality of the logical channel. This leads to a simple characterization of the competitive optimal behavior of the system as a function of the prior probability distribution of spectrum hole occupancy, channel quality and observation noise. In obtaining the characterization of the BNE, we extend recent results in univariate global games to the multivariate case.     

Tuning radio resource in an overlay cognitive radio network for TCP: greed isn't good [Accepted from Open Call]

In this article we illustrate the performance of Transmission Control Protocol in an overlay cognitive radio network under dynamic spectrum access. We show that the performance of TCP in overlay CR networks that implement DSA to be quite different from its performance in conventional networks, which do not allow DSA. The key difference is that secondary users in an overlay CR network have to cope with a new type of loss called service interruption loss, due to the existence of primary users. We demonstrate on an NS2 simulation testbed the surprising result: Excessive radio resource usage leads to a decrease in aggregate TCP throughput. This behavior is in contrast to the behavior of TCP in conventional networks, where throughput increases monotonically with the available radio resource.     

Optimal Adaptive Modulation and Coding with Switching Costs

We present an optimal adaptive modulation and coding policy that minimizes the transmission latency and modulation/coding switching cost across a finite-state Markovian fading channel. We formulate the optimal tradeoff between transmission latency and modulation/coding switching cost as a discounted infinite horizon Markov Decision Problem (MDP). By exploiting special structures of the formulated MDP and under certain sufficient conditions, we show that optimal modulation and coding selection policies are monotone in the state variables. These monotone optimal policies are computationally inexpensive to implement and are scalable in terms of channel and switching cost parameters. Numerical results confirm the monotonicity and threshold-based structure of the optimal Modulation and Coding Scheme (MCS) selection policies under the proposed sufficient conditions.     

Allylic disulfide rearrangement and desulfurization: mild, electrophile-free thioether formation from thiols

[reaction: see text] Secondary and tertiary allylic 2-pyridyl and 2-benzothiazolyl disulfides react with thiol groups at room temperature to give secondary and tertiary allyl alkyl disulfides. On the addition of a phosphine, a desulfurative sigmatropic rearrangement takes place at room temperature to give thioethers.     

Magnetization and Mössbauer study of double layer perovskites La1.5Ca1.5Mn2 − x Fe x O7 prepared by sol–gel method

Magnetization and Mössbauer studies have been made for understanding magnetic behavior of three double perovskite systems La_1.5Ca_1.5Mn_2???x Fe _x O₇ corresponding to x = 0.05, 0.10 and 0.50. These have been prepared following sol–gel route. Substitution of Fe does not lead to any major change in the tetragonal cell but increased iron leads to greater distortion in octahedral site. The three samples undergo paramagnetic–ferromagnetic transition. Curie temperature (T _c) for the system with 0.05 Fe is ～150 K which is lower than (190 K) for the system without iron; with 0.50 Fe T _c goes below 50 K. Iron goes as Fe^3?+? and replaces Mn in ab plane. With increasing Fe the valence states of Mn get re-distributed in a way that number of the Jahn–Teller ions Mn^3?+? increases and that of the pairs of Mn^3?+?–O–Mn^4?+? experiencing double exchange decreases.     

Evolution and Impact of Wi-Fi Technology and Applications: A Historical Perspective

International Journal of Wireless Information Networks - The IEEE 802.11 standard for wireless local area networking (WLAN), commercially known as Wi-Fi, has become a necessity in our day-to-day...     

Topologically-Interlocked Minicircles as Probes of DNA Topology and DNA-Protein Interactions

DNA minicircles exist in biological contexts, such as kinetoplast DNA, and are promising components for creating functional nanodevices. They have been used to mimic the topological features of nucleosomal DNA and to probe DNA-protein interactions such as HIV-1 and PFV integrases, and DNA gyrase. Here, we synthesized the topologically-interlocked minicircle rotaxane and catenane inside a frame-shaped DNA origami. These minicircles are 183 bp in length, constitute six individual single-stranded DNAs that are ligated to realize duplex interlocking, and adopt temporary base pairing of single strands for interlocking. To probe the DNA-protein interactions, restriction reactions were carried out on DNAs with different topologies such as free linear duplex or duplex constrained inside origami and free or topologically-interlocked minicircles. Except the free linear duplex, all tested structures were resistant to restriction digestion, indicating that the topological features of DNA, such as flexibility, curvature, and groove orientation, play a major role in DNA-protein interactions.     

Bimetallic Co–Ni/TiO<Subscript>2</Subscript> catalysts for selective hydrogenation of cinnamaldehyde

Bimetallic Co–Ni catalysts in the composition range Co_(1?x)Ni_x with x?=?0.0, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8 and 1.0, with total metal loading of 15% w/w and supported on TiO₂-P25, have been prepared by chemical reduction of the metal acetates by glucose in aqueous alkaline medium and characterized by XRD, TEM, TPR, XPS and H₂-TPD techniques. Selective hydrogenation of cinnamaldhyde (CAL) to hydrocinnamaldehyde (HCAL), cinnamyl alcohol (COL) and hydrocinnamyl alcohol (HCOL) has been investigated at 20 bar pressure, in the temperature range 120–140 °C. Co/Ni crystallite sizes in the range 6.0?±?1 nm are observed by TEM. TPR and XPS results indicate the formation of nanoscale Co–Ni alloys, which tend to weaken M–H bond strength, as revealed by H₂-TPD measurements. Ni/TiO₂ displays very high conversion of CAL (86.9%) with high selectivity (78.7%) towards HCAL formation at 140 °C. Co/TiO₂, on the other hand, exhibits relatively lower CAL conversion (55%) and higher selectivity (61.3%) for COL formation at the same temperature. However, bi-metallic Co–Ni catalysts in the composition range x?=?0.3–0.6 display very high conversion (>?98%) due to alloy formation and weakening of M–H bonds. Bimetallic Co_0.7Ni_0.3 catalyst displays high conversion of CAL (98.1%) and high selectivity (82.9%) towards HCOL. Overall CAL hydrogenation activity at 140 °C, when expressed as TOF, displays a maximum value at the composition Co_0.5Ni_0.5. Activity and selectivity patterns have been rationalized based on the reaction pathways observed on the catalysts and the influence of Co–Ni alloy formation and M–H bond strength. Thus, a synergetic effect, originating from an appropriate composition of base metal catalysts and reaction conditions, could result in hydrogenation activity comparable with noble metal based catalysts.     

Binary Cellulose Nanocrystal Blends for Bioinspired Damage Tolerant Photonic Films

Most attempts to emulate the mechanical properties of strong and tough natural composites using helicoidal films of wood‐derived cellulose nanocrystals (w‐CNCs) fall short in mechanical performance due to the limited shear transfer ability between the w‐CNCs. This shortcoming is ascribed to the small w‐CNC‐w‐CNC overlap lengths that lower the shear transfer efficiency. Herein, we present a simple strategy to fabricate superior helicoidal CNC films with mechanical properties that rival those of the best natural materials and are some of the best reported for photonic CNC materials thus far. Assembling the short w‐CNCs with a minority fraction of high aspect ratio CNCs derived from tunicates (t‐CNCs), we report remarkable simultaneous enhancement of all in‐plane mechanical properties and out‐of‐plane flexibility. The important role of t‐CNCs is revealed by coarse grained molecular dynamics simulations where the property enhancement are due to increased interaction lengths and the activation of additional toughening mechanisms. At t‐CNC contents greater than 5% by mass the mixed films also display UV reflecting behaviour. These damage tolerant optically active materials hold great promise for application as protective coatings. More broadly, we expect the strategy of using length‐bidispersity to be adaptable to mechanically enhancing other matrix‐free nanoparticle ensembles.