Molecular conformations in polyethylene after recrystallization or annealing at high pressures

Information on molecular conformations inside polyethylene lamellas following high pressure treatments is obtained by comparing observed and predicted length distributions of nitrated samples. Three types of conformation are inferred. The commonest is that molecules are folded with chain ends included in lamellas, except that ends are not turned in by less than ～600 Å from a surface. This situation accounts in detail for the previously observed agreement between the number fracture-surface distribution of crystal thicknesses and the gel permeation chromatography (GPC) weight distribution following nitration. The second conformation, found especially for samples of low polydispersity, is also of folded molecules but with chain ends excluded from lamellas. This particular case justifies rigorously the initial assumption of folding. Finally there are examples where the molecular length distribution is substantially lower than the crystal thickness distribution, implying that molecular length is not the upper limit of crystal thickness and that molecules can be fully extended inside lamellas.     

Model-independent dark energy differentiation with the integrated Sachs-Wolfe effect

We study the integrated Sachs-Wolfe effect using a model-independent parametrization of the dark energy equation of state, w(z). Cosmic variance severely restricts the class of models distinguishable from one based on cold dark matter and a cosmological constant unless w(z) currently satisfies w(o)(Q)>-0.8, or exhibits a rapid, late-time, transition at redshifts z<3. Because of the degeneracy with other cosmological parameters, models with a slowly varying w(z) cannot be differentiated from each other or from a cosmological constant. This may place a fundamental limit on our understanding of the origin of the currently observed acceleration.     

Analytic Results for Gaussian Wave Packets in Four Model Systems: I. Visualization of the Kinetic Energy

Using Gaussian wave packet solutions, we examine how the kinetic energy is distributed in time-dependent solutions of the Schrödinger equation corresponding to the cases of a free particle, a particle under-going uniform acceleration, a particle in a harmonic oscillator potential, and a system corresponding to all unstable equilibrium. We find, for specific choices of initial parameters, that as much as 90° of the kinetic energy can be localized (at least conceptually) in the front half of such Gaussian wave packets, and we visualize these effects.     

Search for disoriented chiral condensate in 158<Emphasis Type="Italic">A</Emphasis> GeV Pb+Pb collisions in WA98 experiment

The current status of the search for localized domains of disoriented chiral condensates (DCC) in Pb+Pb collisions at 158A GeV/c are presented. A new method based on the discrete wavelet transformation (DWT) technique along with an analysis of correlation between charged and neutral particles has been used for the search of localized DCC domains. We show that both the methods indicate the presence of non-statistical fluctuations in data.     

Rheological and microcalorimetric studies of a model alkali‐soluble associative polymer (HASE) in nonionic surfactant solutions

Rheological experiments were carried out on a 1 wt % hydrophobically modified alkali‐soluble emulsion (HASE) solutions at pH ∼ 9 in the presence of nonionic polyoxyethylene ether type surfactant (C₁₂EO₂₃). The low shear viscosity and dynamic moduli increases at c > cmc until they reach a maximum at a critical concentration, c^m of approximately 1 mM (∼17 times the cmc of free surfactant) and then decrease. The dominant mechanism at cmc < c < c^m is an increase in the number of intermolecular hydrophobic junctions and a strengthening of the overall associative network structure. Above c^m, the disruption of the associative network causes a reduction in the number of junctions and strength of the overall network structure. The influence of C₁₂EO₂₃ on HASE before cmc could not be detected macroscopically by the rheological technique. However, isothermal titration calorimetry enables the determination of complex binding of surfactant to the polymer. Isothermal titration of C₁₂EO₂₃ into 0.1 wt % HASE indicates that the C₁₂EO₂₃ aggregation in water and 0.1 wt % HASE polymer solutions is entropically driven. A reduction in the critical aggregation concentration (cac) confirms the existence of polymer–surfactant interactions. The hydrophobic micellar junctions cause a decrease in the ΔH and ΔS of aggregation of the nonionic surfactant. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2019–2032, 2000     

A laser extraction/combustion technique for in situ delta(13)C analysis of organic and inorganic materials

A CO(2) laser extraction system is described for in situ delta(13)C analysis of organic and inorganic materials. Carbonaceous compounds volatilized by the laser are quantitatively converted to CO(2) gas by a combustion furnace mounted after the sample chamber. Gases produced by the laser and combustion processes are swept by helium carrier gas and separated by a packed gas chromatography column prior to their introduction to an isotope ratio monitoring mass spectrometer. A sample of lentil bean was analyzed at a spatial resolution of 200 μm and yielded delta(13)C values with precision of +/- 0.3 per thousand. The accuracy of delta(13)C measurements was better than +/- 0.5 per thousand from NBS 22 (mineral oil), USGS 24 (graphite), and IAEA CO-1 (calcium carbonate). Copyright 1999 John Wiley & Sons, Ltd.     

Conspicuity of bone metastases on fast Dixon-based multisequence whole-body MRI: Clinical utility per sequence

Purpose

The purpose of the study was to evaluate the conspicuity of bone metastases on each of the numerous sequences produced by fast Dixon-based multisequence whole-body (WB) magnetic resonance imaging (MRI) scanning in order to determine the most clinically useful sequences overall and per anatomic region.

Materials and Methods

Twenty-seven breast cancer patients with bone metastases were prospectively studied with fast Dixon-based WB MRI including head/neck, chest, abdominal, pelvic, thigh, calf/feet and either cervical, thoracic and lumbar or cervical/thoracic and thoracic/lumbar regions. Sequences included coronal T2, axial T1 without and with intravenous gadolinium (+ C), sagittal T1 spine + C, each associated fat-only (FO) and fat-saturated (FS) sequence, axial diffusion-weighted imaging (DWI) and short tau inversion recovery (STIR). Blinded reviewers evaluated lesion conspicuity, a surrogate of clinical utility, on a five-point scale per anatomic region. Sequences were compared using analysis of variance, differences were detected with Tukey's honestly significant difference test, and the four sequences with highest mean conspicuity were compared to the remainder overall and per anatomic region.

Results

Overall, a significant lesion conspicuity difference was found (P < .0001), and lesion conspicuity was significantly higher on FS T1 + C, FO T1 + C, T1 + C sagittal and FS T1 + C axial sequences (P < .0001). Per-region results were the same in the head/neck. Other sequences overlapped with these and included the following: chest/abdomen — FO T2, DWI; pelvis — DWI, FO T2; thigh — FS T2, FO T2, FO T1 + C; calf/feet — FS T2, DWI, FO T2, STIR.

Conclusion

Overall, bone lesions were most conspicuous on FS T1 + C sagittal, FO T1 + C sagittal, T1 + C sagittal and FS T1 + C axial fast Dixon WB MRI sequences.     

Diamond anvil cell, 50th birthday

The year 2008 marked the fiftieth birthday of the diamond anvil cell. Its birth took place when Alvin Van Valkenburg, while working with his colleagues, Charles E. Weir, Ellis R. Lippincott, and Elmer N. Bunting, first realized that he could look right through one of the diamond anvils and see a sample while it was at high pressure. In the following years, these scientists and many others adapted the diamond anvil cell to a wide variety of analytical techniques that have provided an impressive amount of information about materials at high pressures and high temperatures. But, virtually all of those techniques start with looking into the diamond anvil cell.     

Head-to-Head Polymers

Head-to-head polymers of α-olef ins, vinyl and acrylic monomers synthesized by indirect methods have shown similarities and differences in some of their behavior when compared to their counterparts of the common head to tail polymers. Head-to-head polyole-fins, such as polystyrene or polypropylene, were prepared by 1,4-polymerization of the corresponding 2,3-disubstituted butadienes-1,3 followed by hydrogenation of the remaining double bonds, polyacrylates by alternating copolymerization of ethylene and maleic anhydride, followed by esterification of the polymer. Head-to-head polyacrylates were reduced to poly(allyl alcohols) which were then acrylated to the acetates and benzoates. Head-to-head polyvinyl halides) were obtained from 1,4-polybutadiene by chlorination or bromination. The head-to-head polymers were characterized by spectroscopic analysis, some molecular weight characterization was done, and their thermal behavior was studied. The blending behavior with the corresponding head-to-tail polymers was studied in some cases; in others (head-to-head polystyrene), the blending with other polymers was investigated and the codegradation of the polymers was evaluated.     

A Diselenide Turn‐On Fluorescent Probe for the Detection of Thioredoxin Reductase

We report the first diselenide‐based probe for the selective detection of thioredoxin reductase (TrxR), an enzyme commonly overexpressed in melanomas. The probe design involves conjugation of a seminaphthorhodafluor dye with a diselenide moiety. TrxR reduces the diselenide bond, triggering a fluorescence turn‐on response of the probe. Kinetic studies reveal favorable binding of the probe with TrxR with a Michaelis–Menten constant (K_m) of 15.89 μm . Computational docking simulations predict a greater binding affinity to the TrxR active site in comparison to its disulfide analogue. In vitro imaging studies further confirmed the diselenide probe exhibited improved signaling of TrxR activity compared to the disulfide analogue.