Synthesis and characterization of polypropiolate sodium (PPNa)-Fe3O4 nanocomposite

Polypropiolate sodium (PPNa)-Fe₃O₄ nanocomposites were successfully synthesized by the precipitation of Fe₃O₄ in the presence of sodium polypropiolate and followed by reflux route. Structural, morphological, electrical and magnetic properties evaluation of the nanocomposite were performed by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), vibrating scanning magnetometry (VSM) and conductivity measurements. Crystalline phase was identified as magnetite with an average crystallite size of 7 ± 3 nm as estimated from X-ray line profile fitting. Particle size estimated from TEM, by log-normal fitting, is ∼9 ± 1 nm. FT-IR analysis shows that the binding of PPNa on the surface of iron oxide is through bidentate linkage of carboxyl group. TGA analysis showed the presence of 20% PPNa around 80% magnetic core (Fe₃O₄)…PPNa-Fe₃O₄ nanocomposite show superparamagnetic characteristics at room temperature. It is found that the a.c. conductivity of the nanocomposites obeys the well-known power law of frequency in which it also depends on temperature. Additionally, its d.c. conductivity showed that two operating regions of the activation energy. Both real and imaginary parts of either permittivity exhibit almost the same attitudes which are the indication of the same ability in the stored energy, and dissipation of energy within the PPNa and PPNa-Fe₃O₄ nanocomposites.     

Bailout forward contracts for edge-to-edge internet services

Despite the huge success of the Internet in providing basic communication services, its economic architecture needs to be upgraded so as to provide end-to-end guaranteed or more reliable services to its customers. Currently, a user or an enterprise that needs end-to-end bandwidth guarantees between two arbitrary points in the Internet for a short period of time has no way of expressing its needs. To allow these much needed basic services, we propose a single-domain edge-to-edge (g2g) dynamic capacity contracting mechanism, where a network customer can enter into a bandwidth contract on a g2g path at a future time, at a predetermined price. For practical and economic viability, such forward contracts must involve a bailout option to account for bandwidth becoming unavailable at service delivery time, and must be priced appropriately to enable Internet Service Providers (ISPs) manage risks in their contracting and investments. Our design allows ISPs to advertise point-to-point different prices for each of their g2g paths instead of the current point-to-anywhere prices, allowing discovery of better end-to-end paths, temporal flexibility and efficiency of bandwidth usage. We compute the risk-neutral prices for these g2g bailout forward contracts (BFCs), taking into account correlations between different contracts due to correlated demand patterns and overlapping paths. We apply this multiple g2g BFC framework on network models with Rocketfuel topologies. We evaluate our contracting mechanism in terms of key network performance metrics like fraction of bailouts, revenue earned by the provider, and adaptability to link failures. We also explore the tradeoffs between complexity of pricing and performance benefits of our BFC mechanism.     

Investigations on the variation of corrosion and contact resistance characteristics of metallic bipolar plates manufactured under long-run conditions

Tribological variations, surface conditions (roughness, hardness, coating) and surface interactions between micro-stamping dies and bipolar plate blanks play a critical role in determining the surface quality, channel formation and precision of bipolar plates. This study is aimed to understand the cause, mechanism and consequences of interactions between micro-stamping process conditions and bipolar plate quality. A total of 2000 repeated micro-stamping of 51 μm-thick uncoated and 1 μm-thick ZrN coated SS316L sheet blanks into an array of 750 μm micro-channels were performed using 175-220 kN force levels with constant stamping speed of 1 mm/s. Microscopic examinations were conducted periodically on both die and coated & uncoated plate surfaces to observe topographic variations. In addition, corrosion and contact resistance tests were carried out in the same intervals. Analysis of variance (ANOVA) technique was used to determine the significance of the process parameters on channel height, roughness, corrosion and contact resistance differences. The results revealed similar roughness trends for die and plate surfaces during 2000 micro-stampings. ZrN coating with 1 μm thickness dramatically improved corrosion and contact resistance behavior of plates.     

Analytical performance of soft clustering protocols

The success of a mobile ad hoc network (MANET) is strongly related to the protocol used at the medium access control (MAC) layer. Depending on the requirements and the specific network under concern, the protocol parameters at the MAC layer can be arbitrated to make best use of the channel resources. Typically, extensive simulation studies are used to find the best values for these variables. The problem with this approach is the need for excessive amounts of processing power and time. As the dimensions of the decision space increase, the need for processing power grows exponentially. This paper addresses this problem by developing an analytical model that reflects the relationships between protocol parameters and the overall performance of the protocol under various network conditions. Specifically, we model the MH-TRACE cluster-based protocol, which is capable of supporting real-time data transmission. The model is capable of estimating performance measures such as energy consumption and number of receptions while being simple enough to be run for a large set of parameters. The model can be used to optimize parameters of the protocol (such as the number of frames per superframe) as well as to predict the performance variations as the external conditions (such as data generation rate) vary.     

Application of ANN techniques for estimating backwater through bridge constrictions in Mississippi River basin

Bridge backwater data were collected for 92 different floods at 35 bridge sites in the Mississippi River basin in 1960s [Neely BL. Hydraulic performance of bridges, hydraulic efficiency of bridges—analysis of field data. Unpublished Report Conducted by US Geological Survey, June 30; 1966]. This major field data showed that the backwater computed both by the United States Geological Survey’s method (USGS) and the United States Bureau of Public Roads’ method (USBPR) averaged approximately 50% less than the measured backwater. Therefore, in the current work, a new bridge backwater formula based on the three different artificial neural network approaches (ANNs), namely FFBP (Feed-Forward Back Propagation), RBNN (Radial Basis Function-Based Neural Network), and GRNN (Generalized Regression Neural Networks) are proposed and compared with the methods mentioned above. The results showed that the FFBP produced slightly better estimations than those of the RBNN and these two was significantly superior to the GRNN, USGS and USBPR methods when applied to Neely’s field data.     

CoFe2O4–Pd (0) Nanocomposite: Magnetically Recyclable Catalyst

This study reports on the fabrication and characterization of magnetically recyclable catalysts of CoFe₂O₄–Pd (0) nanocomposite as highly effective catalysts for reduction reactions (hydrogenation reactions) in liquid phase. The CoFe₂O₄ nanoparticles were prepared by a sonochemical method, and the reduction of Pd²⁺ was accomplished with polyethylene glycol 400 (PEG-400). The formation of CoFe₂O₄–Pd (0) magnetically recyclable catalysts (MRCs) was confirmed by X-ray diffraction, Fourier transform infrared spectroscopy, and inductively coupled plasma. Vibrating sample magnetometer showed the ferromagnetic property of the product. The crystallite size (16 ± 4 nm) obtained from XRD was consistent with the particle size (15 ± 5 nm) from TEM. Thus, formed CoFe₂O₄–Pd (0) MRCs showed a very high activity in reduction reactions of 4-nitroaniline and 1,3-dinitrobenzene in liquid phase. Magnetic character of this system allowed recovery and multiple uses without significant loss of its catalytic activity. Graphical Abstract

?Preparation steps for fabricating CoFe₂O₄–Pd (0) MRCs     

XAFS Investigation of Platinum Impurities in Phosphate Glasses

The coordination environments of Pt impurities in a ternary K-aluminophosphate (KAP) glass and commercial K,Mg-aluminophosphate (KMAP) laser glasses have been investigated by Pt L _III-edge X-ray absorption fine structure (XAFS) spectroscopy. Pt valence in the KAP glass depends on the melt preparation atmosphere. Pt⁴⁺ ions form in melts that are bubbled with oxygen, whereas metallic Pt particles form when these same samples are remelted in air. Residual chlorine in KMAP glasses has an effect on Pt bonding. In chlorine-free samples, Pt⁴⁺ ions are coordinated with ∼5.4 (8) oxygen atoms with an average distance of 2.02 (1) Å. For glasses with low chlorine contents (<200 ppm Cl), the Pt⁴⁺ ions have both O and Cl atoms in the first coordination shell. As the Cl concentration increases, the number of O nearest neighbors decreases and for Cl:Pt > 5, only Cl nearest neighbors are observed. Pt⁴⁺ ions in these latter glasses are coordinated by ∼5.5 (8) Cl atoms at an average distance of 2.27 (2) Å.