A spatial statistics approach to characterizing and modeling the structure of cognitive wireless networks

The performance of cognitive wireless networks (CWNs) depends heavily on their spatial structure. However, highly simplified models are still routinely used for performance evaluation of CWNs and other wireless networks, with node locations often being assumed to be uniformly and randomly distributed in a given region. In this paper we apply techniques from spatial statistics literature to show that this assumption is not valid for a wide variety of existing networks, and neither can it be expected to hold for future cognitive wireless networks. We also develop improved models of the spatial structure of the network for a variety of wireless network types. In particular, we construct models of television and radio transmitter distributions as well as different types of cellular and Wi-Fi networks that have direct applications in cognitive wireless networks research. We use a stochastic approach based on fitting parametric location models to empirical data. Our results strongly indicate that the so-called Geyer saturation model can accurately reproduce the spatial structure of a large variety of wireless network types, arising from both planned or chaotic deployments. The resulting models can be used in simulations or as basis of analytical calculations to study different network properties. They can be also used within CWNs for on-line reasoning about the surrounding radio environment.     

Promoter effect of BaO on CO oxidation on PdO surfaces

The effect of bulk BaO promoter on CO oxidation activity of palladium oxide phase was studied by density functional calculations. A series of BaO(100) supported Pd(x)O(y) thin layer models were constructed, and energy profiles for CO oxidation on the films were calculated and compared with corresponding profiles for the most stable PdO bulk surfaces PdO(100) and PdO(101). The most stable of the thin films typically exhibit the same PdO(100) and PdO(101) surface planes; the PdO(100) dominates already with double layer thickness. The supporting promoter improves the CO oxidation activity of the Pd(x)O(y) phase via a direct electronic effect and introduced structural strain and corrugation. Changes in CO adsorption strength are reflected in oxidation energy barriers, and the promoting effect of even 0.3 eV can be seen locally. Easier oxygen vacancy formation may partially facilitate the reaction.     

Top-down mass spectrometry reveals new sequence variants of the major bovine seminal plasma protein PDC-109

The major protein of bovine seminal plasma, PDC-109, is a 109-residue polypeptide that exists as a polydisperse aggregate under native conditions. The oligomeric state of this aggregate varies with ionic strength and the presence of lipids. Binding of PDC-109 to choline phospholipids on the sperm plasma membrane results in an efflux of cholesterol and choline phospholipids, which is an important step in sperm capacitation. In this study, Fourier transform ion cyclotron resonance mass spectrometry was used to analyze PDC-109 purified from bovine seminal plasma. In addition to the previously known PDC-109 variants, four new sequence variants were identified by top-down mass spectrometry. For example, a protein variant containing point mutations P10L and G14R was identified along with another form having a 14-residue truncation in the N-terminal region. Two other minor variants could also be identified from the affinity-purified PDC-109. These results demonstrate that PDC-109 is naturally produced as a mixture of several protein forms, most of which have not been detected in previous studies. Native mass spectrometry revealed that PDC-109 is exclusively monomeric at low protein concentrations, suggesting that the protein oligomers are weakly bound and can easily be disrupted. Ligand binding to PDC-109 was also investigated, and it was observed that two molecules of O-phosphorylcholine bind to each PDC-109 monomer, consistent with previous reports.     

Hybrid waveguide-surface plasmon polariton modes in a guided-mode resonance grating

We analyze the coupling between surface plasmon polaritons in a metal grating and the guided modes of a dielectric waveguide. Our model structure is a gold wire grating on a slab waveguide made of silicon nitride on silica wafer. The excitation of guided-mode resonances, surface plasmon polariton modes and hybrid waveguide-plasmon modes are observed in numerical simulations. Our experiments verify the existence of the predicted modes. These hybrid modes add significant degrees of freedom in designing structures for plasmonic applications.     

Formation of stable Ag-nanoparticle aggregates induced by dithiol cross-linking

Aggregation of thiol-stabilized silver nanoparticles induced by 1,6-hexane dithiol was studied in situ by dynamic light scattering. The aggregates were observed to reach a finite size in the 100-200 nm range depending on the applied conditions. Growth kinetics were shown to be linked to the dynamics of the thiol-exchange reaction. A model for the aggregation process was developed on the basis of a simple diffusion-kinetic approach assuming an elementary kinetic reaction at the surfaces and a spherical diffusion field surrounding the aggregates. The rate constant for the thiol exchange reaction was found to vary between 0.6 and 4.0 x 10(-4) s(-1), and the activation energy was 46 +/- 10 kJ mol(-1).     

Comparative study of the Kumada, Negishi, Stille, and Suzuki-Miyaura reactions in the synthesis of the indole alkaloids hippadine and pratosine

The total synthesis of hippadine by a tandem metalation/cross-coupling/lactamization strategy was investigated starting from either 7-bromoindole or a 6-halogenated methyl piperonate. The Kumada and Negishi cross-coupling reactions failed to provide any of the desired product. However, the Stille and Suzuki reactions furnished hippadine in low yields starting from the electron-deficient methyl 6-iodo- and 6-bromopiperonate, respectively. Starting from the metalated indole, only the Suzuki reaction occurred, affording hippadine in 67-74% and pratosine in 62% isolated yield.     

Dipeptide analogues containing 4-ethoxy-3-pyrrolin-2-ones

[reaction: see text] Pyrrolidine-2,4-diones (1) are naturally occurring analogues of amino acids. We herein present a facile synthesis of N-acylated, O-alkylated pyrrolin-2-ones (2) in high yield and excellent enantiopurity. Molecular mechanics calculations suggest that the resulting dipeptide analogues adopt a linear, extended conformation.     

Microstructure, creep properties, and failure mechanism of SnAgCu solder joints

The effect of microstructure on the creep properties and the failure mechanism of SnAgCu solder joints was studied. Single overlap shear specimens made of FR-4 printed circuit boards (PCBs) with organic solderability preservative (OSP), NiAu, and immersion Sn surface finish were reflow-soldered with hypoeutectic, eutectic, and hypereutectic SnAgCu solder paste. Creep tests of the solder joints were performed at 85°C and 105°C under constant load. The effect of microstructure on the creep behavior of the joints was studied by examining the fracture surfaces and cross-sectional samples of the tested joints. Results show that the intermetallic compound at the interface between the PCB and solder affects the fracture behavior of SnAgCu solder joints, thus creating a significant difference in the creep properties of solder joints on different surface finishes. Composition of SnAgCu solder was also found to affect the creep properties of the joints.     

New way to quantify multiple steroidal compounds in wastewater by comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry

The applicability of comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry to the screening of steroidal compounds in wastewater is demonstrated. Advanced software was utilized to identify unknown compounds in complex two-dimensional chromatograms exploiting retention indices and two different mass spectral databases. Response factors calculated as a function of the individual mass spectra of six commercial standards at different concentrations were used to develop a model allowing the quantitation of all steroidal compounds identified in the sample. The model, based on partial least squares regression equations, provided good accuracy (prediction error < 16%) in the quantitation of steroidal compounds, so offering a valuable alternative to conventional quantitation methods where reference compounds are required for the verification of analytical measurements. Special attention was paid to the development of an exhaustive sample preparation method for the separate analysis of conjugated and free steroids in both water phase and suspended solid particles. The method, including the exploitation of chemometrics, was successfully applied to the determination of steroidal compounds in effluent and influent waters collected at a local wastewater treatment plant.     

Combined synthesis and in situ coating of nanoparticles in the gas phase

Ga₂O₃ was-synthesized by doping a premixed H₂/O₂/Ar flat flame with diluted trimethyl gallium Ga(CH₃)₃ in a low-pressure reactor. The mean particle diameter d _p of the resulting metal oxide was characterized in-situ with a particle mass spectrometer (PMS), and was observed to range between 2.5 nm ≤ d _p ≤ 6.5 nm. XRD results show that the as-synthesized Ga₂O₃ nanoparticles are mostly amorphous, although, a few broad reflexes were observed that indicate the presence of some degree of crystallinity. Thermal annealing of the as-synthesized material at 1000 °C for 5 min yielded β-Ga₂O₃ with a monoclinic structure. UV–VIS measurements indicate strong absorption in the UV range (4.8 eV), which corresponds quite well to the direct band gap of bulk Ga₂O₃. Photoluminescence (PL) measurements of the as-synthesized metal oxide show a broad emission ranging from 350 nm to 600 nm with a maximum at 460 nm. Crystalline β-Ga₂O₃ exhibited stronger luminescence than as-synthesized particles.