Ring opening polymerization of ε‐caprolactone initiated by decamolybdate anion: Determination of kinetic and thermodynamic parameters by DSC and 1H‐NMR

The aim of this work is the kinetic and thermodynamic study (by differential scanning calorimetry (DSC) and proton nuclear magnetic resonance (¹H‐NMR)) of the polymerization of ε‐caprolactone initiated by ammonium decamolybdate. By means of isothermal kinetics, enthalpies of reaction in the range 150–160°C, as well as constant rates of polymerization (using an nth‐order kinetics function model), were determined. From an Arrhenius plot, activation energy (E_a = 85.3 kJ/mol) and preexponential factor (A = 1.78 × 10⁸ min^?1) were estimated. Using dynamic methods, crystallization and melting temperatures for the polymer obtained in situ were derived. Kinetic data for polymerization (obtained by ¹H‐NMR) were fitted to 13 different model reaction functions. It was found that power law equations represent better the conversion versus time plots for this system. On the basis of experimental facts, a coordination‐insertion mechanism involving molybdenum(V) species is proposed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Impact and dynamic response of high-density structural foams used as filler inside circular steel tube

Structural foams have good energy absorption properties and are effective in reducing the vulnerability of sandwich structures. This research investigated the impact and dynamic response of three different high-density polymeric structural foams; designated A, B and C for proprietary reasons. Foam-C had the lowest density out of the three; density of foam-B was approximately twice the density of foam-C, while the density of foam-A was about three times the density of foam-C. The cylindrical foam samples were initially impacted at different velocities in a DYNATUP Model 8250 instrumented impact test machine and their energy absorption was characterized from the resulting load–deflection data. Each of the three foams was then modeled as filler inside a circular steel tube of 0.8 mm thickness. Non-linear finite element analysis was performed under displacement controlled quasi-static compressive monotonic loading using PATRAN as pre-processor and ABAQUS Standard commercial software. The area under the load–deflection curve was calculated to obtain the absorbed energy and the crush loads for the three foam fillers were compared. Results indicate that foam-A having the highest density was more effective as filler inside the circular steel tube, with the intermediate density foam-B performing equally well under uni-axial compressive loading. Foam-C, which had the lowest density, was found to be ineffective as filler in this application due to large differences in stiffness between this foam and the enclosed steel tube.

A TA Instruments Model 983 DMA (dynamic mechanical analyzer) was used for obtaining the storage and loss modulus along with the damping and glass transition properties of the different density structural foams. Frequency multiplexing was also used in conjunction with the time–temperature superposition principle for characterizing the long-term behavior of these viscoelastic foams.     

A Sensor for Acid Concentration Based on Cellulose Paper Sheets Modified with Polyaniline Nanoparticles

Sheets of cellulosic paper were modified with PAni nanoparticles through a chromatographic process. When exposed to acidic conditions, strips of the modified paper sheets are subject to RGB color changes that can be detected by a scanner (and similar devices used for image analyses). As a consequence, cellulosic paper sheets modified with PAni can be used for analyses of acid concentrations in liquid and gaseous streams. Aqueous solutions of hydrochloric acid were used for modeling purposes and it was observed that color changes were most significant when the HCl content was between 0–500 ppm range. Materials were characterized by FT‐IR spectroscopy, optical microscopy, AFM, and SAXS techniques, in order to reveal the main characteristics of the produced materials.

     

Detection of bioconjugated quantum dots passivated with different ligands for bio-applications

Bioconjugation of quantum dots has resulted in a significant increase in resolution of biological fluorescent labeling. This intrinsic property of quantum dots can be utilized for sensitive detection of target analytes with high sensitivity; including pathogenic bacteria and cancer monitoring. The quantum dots and quantum dot doped silica nanoparticles exhibit prominent emission peaks when excited at 400 nm but on conjugation to model rabbit antigoat antibodies exhibit diminished intensity of emission peak at 600 nm. It shows that photoluminescence intensity of conjugated quantum dots and quantum dot doped silica nanoparticles could permit the detection of bioconjugation. Samples of conjugated and unconjugated quantum dots and quantum dot doped silica nanoparticles were subjected to enzyme linked immunosorbent assay for further confirmation of bioconjugation. In the present study ligand exchange, bioconjugation, fluorescence detection of bioconjugated quantum dots and quantum dot doped silica nanoparticles and further confirmation of bioconjugation by enzyme linked immunosorbent assay has been described.     

Geometrical confinement of gadolinium-based contrast agents in nanoporous particles enhances T1 contrast

Magnetic resonance imaging contrast agents are currently designed by modifying their structural and physiochemical properties to improve relaxivity and to enhance image contrast. Here, we show a general method for increasing relaxivity by confining contrast agents inside the nanoporous structure of silicon particles. Magnevist, gadofullerenes and gadonanotubes were loaded inside the pores of quasi-hemispherical and discoidal particles. For all combinations of nanoconstructs, a boost in longitudinal proton relaxivity r(1) was observed: Magnevist, r(1) ≈ 14 mM(-1) s(-1)/Gd(3+) ion (～ 8.15 × 10(+7) mM(-1) s(-1)/construct); gadofullerenes, r(1) ≈ 200 mM(-1) s(-1)/Gd(3+) ion (～ 7 × 10(+9) mM(-1) s(-1)/construct); gadonanotubes, r(1) ≈ 150 mM(-1) s(-1)/Gd(3+) ion (～ 2 × 10(+9) mM(-1) s(-1)/construct). These relaxivity values are about 4 to 50 times larger than those of clinically available gadolinium-based agents (～ 4 mM(-1) s(-1)/Gd(3+) ion). The enhancement in contrast is attributed to the geometrical confinement of the agents, which influences the paramagnetic behaviour of the Gd(3+) ions. Thus, nanoscale confinement offers a new and general strategy for enhancing the contrast of gadolinium-based contrast agents.     

Remnant lipoprotein density profiling by CsBiEDTA density gradient ultracentrifugation

Remnant lipoproteins (RLPs) are now considered a strong marker of the triglyceride-rich lipoprotein (TRL) class for cardiovascular heart disease. The purpose of this research is to demonstrate the efficacy of a novel method that combines an established immunoseparation assay used to measure the RLP class in human serum with ultracentrifugal density gradient separation. These two methods are combined to obtain an RLP density profile. The immunoseparation effectively removes the non-RLP lipoproteins from serum. The RLPs obtained from the immunoseparation are separated into two density-distinct fractions by ultracentrifugal density gradient separation in CsBiEDTA. It is now clear that IDL is distinct in density and immunoreactivity from the two RLP classes isolated by the immunoseparation and ultracentrifugation. This methodology defines the RLP by density and measures their relative prevalence in the TRL class. When applied to clinical samples, variations in the RLP subclasses in different patients are examined. The differences in the RLP density profile are also examined in fasting and postprandial samples. The RLP density profile significantly increases in the postprandial state versus the fasting state. However, the overall quantity of TRL does not appreciably increase in the postprandial state. This work demonstrates the feasibility of measuring the postprandial state in clinical samples to provide insight into the clearance of RLP by the liver as well as the general atherogenicity of these particles. The major outcome of this research is a novel analytical method that couples immunoseparation and density gradient ultracentrifugation to separate and differentially profile the RLP subclass against its nascent counterparts in the TRL class.     

Variations in normal color vision. III. Unique hues in Indian and United States observers

Basic color categories are thought to share a common pattern across linguistic groups, yet the focal colors defining those categories can vary substantially within any single group. We asked whether focal colors can also differ systematically across different groups of individuals living in potentially different color environments, by measuring focal and unique hues for observers in India and the United States. Differences between groups were generally small relative to the within-group variations, consistent with a strong common basis for color naming across diverse contexts. However, for most hues the average settings differed significantly across subpopulations. These differences persisted across testing conditions and thus probably reflect longer-term contextual influences on color appearance judgments. They suggest that while color categories may be qualitatively similar, precisely how the hue spectrum is parsed may differ quantitatively across different populations of observers. Both the between-group and the within-group differences are inconsistent with the differences predicted by common peripheral sources of variation in color vision (e.g., in lens or macular pigment) and may reflect an influence of environmental or cultural differences in focal color choices.     

Approximation Algorithms for the Mobile Piercing Set Problem with Applications to Clustering in Ad-Hoc Networks

The main contributions of this paper are two-fold. First, we present a simple, general framework for obtaining efficient constant-factor approximation algorithms for the mobile piercing set (MPS) problem on unit-disks for standard metrics in fixed dimension vector spaces. More specifically, we provide low constant approximations for L ₁ and L norms on a d-dimensional space, for any fixed d>0, and for the L ₂ norm on two- and three-dimensional spaces. Our framework provides a family of fully-distributed and decentralized algorithms, which adapt (asymptotically) optimally to the mobility of disks, at the expense of a low degradation on the best known approximation factors of the respective centralized algorithms: Our algorithms take O(1) time to update the piercing set maintained, per movement of a disk. We also present a family of fully-distributed algorithms for the MPS problem which either match or improve the best known approximation bounds of centralized algorithms for the respective norms and space dimensions.Second, we show how the proposed algorithms can be directly applied to provide theoretical performance analyses for two popular 1-hop clustering algorithms in ad-hoc networks: the lowest-id algorithm and the Least Cluster Change (LCC) algorithm. More specifically, we formally prove that the LCC algorithm adapts in constant time to the mobility of the network nodes, and minimizes (up to low constant factors) the number of 1-hop clusters maintained. While there is a vast literature on simulation results for the LCC and the lowest-id algorithms, these had not been formally analyzed prior to this work.We also present an O(logn)-approximation algorithm for the mobile piercing set problem for nonuniform disks (i.e., disks that may have different radii), with constant update time.