Structural analysis of polyethene prepared with rac‐dimethylsilylbis(indenyl)zirconium dichloride/methylaluminoxane in a high‐temperature,continuously stirred tank reactor

A study of ethene solution polymerization with the rac‐dimethylsilylbis(indenyl)‐zirconium dichloride/methylaluminoxane catalyst system in a high‐temperature (140 °C), continuously stirred tank reactor system was carried out. ¹³C NMR, gel permeation chromatography, Fourier transform infrared, and rheological measurements were used for polymer analyses. Polyethylenes with low molecular weights (weight‐average molecular weight ≈ 35–55 kg/mol) and small amounts of methyl, ethyl, and long‐chain branching were produced. ¹³C NMR measurements showed that the long‐chain and methyl branches increased and that the ethyl branch contents decreased with decreasing monomer concentrations. At high monomer concentrations, the chain transfer to the coordinated monomer was concluded to be the predominant chain termination mechanism, whereas the chain transfer to aluminum was dominant at low monomer concentrations, which was evidenced by the fact that the selectivity of end groups was reduced to about 50%. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3292–3301, 2002     

Modification of surface properties of polyethylene by perfluoropolyether blending

The preparation of a stabile blend from thermoplastic polymer and lubricating additive was studied with high density polyethylene (HDPE) and perfluoropolyether (PFPE). PFPE was melt blended within HDPE by injection molding. The chemical composition of the mixtures, the relative amount of PFPE on the surface, and the nature of the surface were studied by three surface sensitive methods: attenuated total reflectance infrared (ATR‐IR) spectroscopy, secondary ion mass spectroscopy (SIMS), and contact angle (CA) measurement. All the blends exhibited improved hydrophobicity. CA and SIMS gave a maximum response when about 2.0 wt % PFPE was added, whereas ATR‐IR spectroscopy gave maximum response for an addition of about 3.0 wt %. No changes in surface properties were observed when samples were reanalyzed about 1–4 months after preparation. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2252–2258, 2005     

Theoretical description of low divergence Gaussian fields in self-defocusing photorefractive media

Experimental evidence is presented that shows that low intensity optical fields preserve their Gaussian transverse amplitude distribution as they propagate through self-defocusing Ce:BaTiO₃ photorefractive media. The Gaussian nature of the field is used in a theoretical treatment to derive conditions under which bright solitons are formed in photorefractive media that have a light induced refractive index that is approximately quadratic. This analysis shows that while it is not possible to produce a single bright soliton in self-defocusing media that it is possible to minimize the field’s divergence such that the change in beam radius is small (<1%) over large propagation distances (∼1 m). An imaginary light induced refractive index component is necessary to generate the low divergence fields in both self-focusing and self-defocusing media when illuminated with Gaussian fields that have a non-planar wavefront.     

Elimination and rearrangement reactions in the electron impact ionization mass spectrometry of 2,4,5,5-tetrasubstituted 1,2,4-triazolidine-3-thiones

The electron impact mass spectra of 2,4,5,5-tetrasubstituted l,2,4-triazolidine-3-thiones exhibited, in addition to four main routes of fragmentation, a reaction leading to the formation of 5-alkyl-l,2,4-triazoline-3-thiones via an elimination of HR⁴ (R³ ≤ R⁴ are the substituents at C(5)) or via a McLafferty-type reaction from the rearranged molecular ion in the case of the 5,5-spiro derivatives. Substitution at N(2), N(4) and/or C(5) had a decisive effect on the contribution of the alternative reaction routes. Some fragments via the triazoline-thione structure were also formed.     

Local dimensions of sliced measures and stability of packing dimensions of sections of sets

Let m and n be integers with 0<m<n. We relate the absolutely continuous and singular parts of a measure μ on to certain properties of plane sections of μ. This leads us to prove, among other things, that the lower local dimension of (n−m)-plane sections of μ is typically constant provided that the Hausdorff dimension of μ is greater than m. The analogous result holds for the upper local dimension if μ has finite t-energy for some t>m. We also give a sufficient condition for stability of packing dimensions of section of sets.     

An evaluation of some sodium ion-selective glass electrodes in aqueous solution: Part I. Electrode calibration characteristics and selectivity with respect to hydrogen ions

Some properties of a series of commercial sodium ion-selective electrodes have been investigated and the results compared. In general the potential response of the electrodes was found to approach Nernstian with aging.An improved method for investigating the selectivity of ion-selective electrodes with respect to hydrogen ions is based on the mixed solution method utilizing tris buffers. The selectivity of the sodium ion electrodes with respect to hydrogen ions was also found to depend on the ratio of the primary to interfering ion activity. Some other improvements in technique are also reported.     

UWB radio module design for wireless sensor networks

In this paper, we describe an impulse-based ultra wideband (UWB) radio system for wireless sensor network (WSN) applications. Different architectures have been studied for base station and sensor nodes. The base station node uses coherent UWB architecture because of the high performance and good sensitivity requirements. However, to meet complexity, power and cost constraints, the sensor module uses a novel non-coherent architecture that can autonomously detect the UWB signals. The radio modules include a transceiver block, a baseband processing unit and a power management block. The transceiver block includes a Gaussian pulse generator, a multiplier, an integrator and timing circuits. For long range applications, a wideband low noise amplifier (LNA) is included in the transceiver of the sensor module, whereas in short range applications it is simply eliminated to further reduce the power consumption. In order to verify the proposed system concept, circuit level implementation is studied using 1.5 V 0.18 μm CMOS technology. Finally, the UWB radio modules have been designed for implementation in liquid-crystal-polymer (LCP) based System-on-Package (SoP) technology for low power, low cost and small size integration. A small low cost, double-slotted, Knight’s helm antenna is embedded in the LCP substrate, which shows stable characterization and a return loss better than ?10 dB over the UWB band.     

Analysis of S2QA- charge recombination with the Arrhenius, Eyring and Marcus theories

The Q band of photosynthetic thermoluminescence, measured in the presence of a herbicide that blocks electron transfer from PSII, is associated with recombination of the S(2)Q(A)(-) charge pair. The same charge recombination reaction can be monitored with chlorophyll fluorescence. It has been shown that the recombination occurs via three competing routes of which one produces luminescence. In the present study, we measured the thermoluminescence Q band and the decay of chlorophyll fluorescence yield after a single turnover flash at different temperatures from spinach thylakoids. The data were analyzed using the commonly used Arrhenius theory, the Eyring rate theory and the Marcus theory of electron transfer. The fitting error was minimized for both thermoluminescence and fluorescence by adjusting the global, phenomenological constants obtained when the reaction rate theories were applied to the multi-step recombination reaction. For chlorophyll fluorescence, all three theories give decent fits. The peak position of the thermoluminescence Q band is correct by all theories but the form of the Q band is somewhat different in curves predicted by the three theories. The Eyring and Marcus theories give good fits for the decreasing part of the thermoluminescence curve and Marcus theory gives the closest fit for the rising part.     

The Effect of Pure Component Characteristic Parameters on Sanchez–Lacombe Equation‐of‐State Predictive Capabilities

The dependence of predictive capabilities of SL EOS on the pure characteristic parameters of monomers and polymers is investigated. A sensitivity analysis study is carried out to understand the effect of these parameters on the predictive capability of SL EOS for different α‐olefin/polyolefins systems. Among all pure component characteristic parameters, the monomer characteristic temperature (T*_monomer) has the largest impact on SL EOS predictive capability; whereas the polymer characteristic density (ρ*_polymer) is found to have the smallest impact.

     

An acoustically enhanced gold film Raman sensor on a lithium niobate substrate

The surface enhanced Raman scattering effect has shown immense potential for detecting trace amounts of explosive vapor molecules. To date, efforts to produce a commercially available, reliable SERS sensor have been impeded by an inability to separate the electromagnetic enhancement produced by the metallic nanostructure from other signal enhancing effects. Here, we show a new Raman sensor that uses surface acoustic waves (SAWs) to produce controllable surface structures on gold films deposited on LiNbO₃ substrates that modulate the Raman signal of a target compound (thiophenol) adsorbed on the films. We demonstrate that this sensor can dynamically control the Raman signal simply by changing the SAW's amplitude, allowing the Raman signal enhancement factor to be directly measured with no variation in the concentration of the target compound. The physically adsorbed molecules can be removed from the sensor without physical cleaning or damage, making it possible to reuse it for real‐time Raman detection. Copyright © 2014 John Wiley & Sons, Ltd.