Cooperative Access in Cognitive Radio Networks: Stable Throughput and Delay Tradeoffs

In this paper, we study and analyze fundamental throughput-delay tradeoffs in cooperative multiple access for cognitive radio systems. We focus on the class of randomized cooperative policies, whereby the secondary user (SU) serves either the queue of its own data or the queue of the primary user (PU) relayed data with certain service probabilities. The proposed policy opens room for trading the PU delay for enhanced SU delay. Towards this objective, stability conditions for the queues involved in the system are derived. Furthermore, a moment generating function approach is employed to derive closed-form expressions for the average delay encountered by the packets of both users. Results reveal that cooperation expands the stable throughput region of the system and significantly reduces the delay at both users. Moreover, we quantify the gain obtained in terms of the SU delay under the proposed policy, over conventional relaying that gives strict priority to the relay queue.Comment: accepted for publication in IEEE 12th Intl. Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks (WiOpt), 201

A New Generating Family of Distributions: Properties and Applications to the Weibull Exponential Model

A new method for generating family of distributions was proposed. Some fundamental properties of the new proposed family include the quantile, survival function, hazard rate function, reversed hazard and cumulative hazard rate functions are provided. This family contains several new models as sub models, such as the Weibull exponential model which was defined and discussed its properties. The maximum likelihood method of estimation is using to estimate the model parameters of the new proposed family. The flexibility and the importance of the Weibull-exponential model is assessed by applying it to a real data set and comparing it with other known models

Polyvinylpyrrolidone - Reduced Graphene Oxide - Pd Nanoparticles as an Efficient Nanocomposite for Catalysis Applications in Cross-Coupling Reactions

This paper reported a scientific approach adopting microwave-assisted synthesis as a synthetic route for preparing highly active palladium nanoparticles stabilized by polyvinylpyrrolidone (Pd/PVP) and supported on reduced Graphene oxide (rGO) as a highly active catalyst used for Suzuki, Heck, and Sonogashira cross coupling reactions with remarkable turnover number (6500) and turnover frequency of 78000 h-1. Pd/PVP nanoparticles supported on reduced Graphene oxide nanosheets (Pd-PVP/rGO) showed an outstanding performance through high catalytic activity towards cross coupling reactions. A simple, reproducible, and reliable method was used to prepare this efficient catalyst using microwave irradiation synthetic conditions. The synthesis approach requires simultaneous reduction of palladium and in the presence of Gaphene oxide (GO) nanosheets using ethylene glycol as a solvent and also as a strong reducing agent. The highly active and recyclable catalyst has so many advantages including the use of mild reaction conditions, short reaction times in an environmentally benign solvent system. Moreover, the prepared catalyst could be recycled for up to five times with nearly the same high catalytic activity. Furthermore, the high catalytic activity and recyclability of the prepared catalyst are due to the strong catalyst-support interaction. The defect sites in the reduced Graphene oxide (rGO) act as nucleation centers that enable anchoring of both Pd/PVP nanoparticles and hence, minimize the possibility of agglomeration which leads to a severe decrease in the catalytic activity.

Optimization Of The Catalytic Performance Of Pd/Fe 3 O 4 Nanoparticles Prepared Via Microwave-assisted Synthesis For Pharmaceutical And Catalysis Applications

Microwave assisted synthesis technique was used to prepare palladium supported on iron oxide nanoparticles. The advantage of using microwave irradiation as a synthetic tool is due to its unique features as a one step, simple, versatile, and rapid process. The reactants are added simply at room temperature without using high-temperature injection. Hydrazine hydrate was added by the following ratios (0.1, 0.2, 0.3, 0.4, 0.6, 0.8, 1, 1.6, and 3) ml to the different prepared samples at room temperature in order to investigate its effect on the catalytic performance of the prepared catalysts. The prepared catalyst could be used as an ideal candidate not only for pharmaceutical industry through cross-coupling reactions but also for low temperature oxidation catalysis of carbon monoxide and pharmaceutical applications as well. The experimental results showed that Pd/Fe3O4 catalyst has a remarkable catalytic activity for carbon monoxide oxidation catalysis due to the strong interaction between palladium and iron oxide nanoparticles. This may be due to the small particle size (7-14 nm) and concentration ratio of the Pd nanoparticles dispersed on the surface of magnetite (Fe3O4). Those nanoparticles were characterized by various spectroscopic techniques including; X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Vibrating Sample Magnetometer (VSM) and transmission electron microscopy (TEM)

Laparoscopic Thal versus laparoscopic Nissen fundoplication in children: Comparative study regarding outcome and patient satisfaction

Introduction Gastroesophageal reflux disease is a common condition in pediatric age group. Many surgeons believe that complete fundoplication provides better reflux control, yet it results in more dysphagia and gas-bloat symptoms. On the other hand, a partial wrap is reported to have fewer adverse effects but a higher failure rate in controlling reflux. Until now, there is no agreement and little evidence as to whether complete or partial  fundoplication is the optimal procedure in this age group.Patients and methods This is a prospective singleblinded randomized comparative study that included 30 patients who were admitted in the time period from May 2013 to May 2015 and were treated laparoscopically byeither Nissen or Thal fundoplication.Results Operative time (minutes) was significantly longer in the Thal group (186 ± 52) when compared with the Nissen group (150 ±48) (P =0.031). Intraoperative complications showed no significant difference when comparing the two groups. Although the incidence of postoperative dysphagia was statistically insignificant, the duration of dysphagia did  show significantly shorter duration in the Thal group (median: 6 days), when compared with the Nissen group (median: 17 days). There was no recurrence in the Thal group, whereas there was one recurrence in the Nissen group.Conclusion This study suggests that Thal fundoplication offers an effective alternative to Nissen fundoplication with apparently shorter duration of dysphagia and thus earlier return to the normal eating pattern. Level of evidence

Facile Synthesis Of Reduced Graphene Oxide-supported Pd/Cuo Nanoparticles As An Efficient Catalyst For Cross-coupling Reactions

The present communication reports a scientific investigation of a simple and versatile synthetic route for the synthesis of palladium nanoparticles decorated with copper oxide and supported on reduced graphene oxide (rGO). They are used as a highly active catalyst of Suzuki, Heck, and Sonogashira cross coupling reactions with a remarkable turnover number of 7000 and a turnover frequency of 85000 h-1. The Pd-CuO nanoparticles supported on reduced graphene oxide nanosheets (Pd-CuO/rGO) exhibit an outstanding performance through a high catalytic activity towards cross coupling reactions. A simple, reproducible, and reliable method is used to prepare this efficient catalyst using microwave irradiation synthetic conditions. The synthesis approach requires a simultaneous reduction of palladium and copper nitrates in presence of graphene oxide (GO) nanosheets using hydrazine hydrate as a strong reducing agent. The highly active and recyclable catalyst has many advantages including mild reaction conditions and short reaction durations in an environmentally benign solvent system. Moreover, the catalyst prepared can be recycled for up to five times with nearly identical high catalytic activity. Furthermore, the high catalytic activity and the recyclability of the catalyst prepared are due to the strong catalyst-support interaction. The defect sites of the reduced graphene oxide (rGO) act as nucleation centers that enable anchoring of both Pd and CuO nanoparticles and hence, minimize the possibility of agglomeration which leads to a severe decrease of the catalytic activity

Microwave-assisted Synthesis Of Palladium Nanoparticles Supported On Copper Oxide In Aqueous Medium As An Efficient Catalyst For Suzuki Cross-coupling Reaction

We report here a reliable green method for the synthesis of palladium nanoparticles supported on copper oxide as a highly active and efficient catalyst for Suzuki cross-coupling reaction. The experimental synthetic approach is based on microwave-assisted chemical reduction of an aqueous mixture of palladium and copper salt simultaneously using hydrazine hydrate as reducing agent. The catalyst was fully characterized using various techniques showing well-dispersed palladium nanoparticles. The catalytic activity and recyclability of the prepared catalyst were experimentally explored in the ligand-free Suzuki cross-coupling reaction with a diverse series of functionalized substrates. The synthesized Pd/CuO catalyst shows many advantages beside its high catalytic efficiency such as the recyclability of up to five times with negligible loss of catalytic activity, short reaction times, use of environmentally benign solvent systems, and mild reaction conditions