The phase behavior of a molecular brush-C18 grafted to the surface of both a silicon wafer and SiO2 nanoparticles was investigated as a function of temperature using neutron reflectometry (NR) and ...small-angle neutron scattering (SANS), respectively. The experiments demonstrate a phase change in the brush layer characterized by a straightening of the molecular configuration, increase in shell thickness, and increase in solvent concentration with decreasing temperature that corresponds to gelation in the nanoparticle dispersion.
Striatal D2/D3 dopaminergic receptors have been proposed to play a role in cataplexy. The authors studied the striatal presynaptic dopamine transporter and postsynaptic D2-receptors in seven patients ...with narcolepsy and seven control subjects using 123I(N)-(3-iodopropene-2-yl)-2beta-carbomethoxy-3beta-(4-chlorophenyl)tropane and 123I(S)-2-hydroxy-3-iodo-6-methoxy-(1-ethyl-2-pyrrolidinylmethyl)benzamide SPECT. D2-receptor binding was elevated in narcolepsy (p = 0.017) and correlated with the frequency of cataplectic and sleep attacks (R > or = 0.844, p < or = 0.017). The human striatal dopaminergic system is altered in vivo in narcolepsy/cataplexy.
The three basic surgical approaches used most commonly in total hip arthroplasty are transtrochanteric, posterior, and anterolateral. Complications related to each of these surgical approaches have ...been reported including dislocation, trochanteric nonunion, heterotopic ossification, neurovascular damage, postoperative limp, and implant malalignment. The anterolateral abductor split approach previously has been reported to allow ease of access into the hip joint, optimum joint visualization, protection of neurovascular structures of the hip, and predictable results for postoperative hip function restoration. Reviewing a large consecutive series of primary total hip arthroplasty cases (1518), the authors report an overall dislocation rate less than 1% (12:1518; 0.79%). Stratified by preoperative diagnosis, patients undergoing total hip arthroplasty after trauma, or presenting with congenital dysplastic hip are at the highest risk for postoperative dislocation. Primary total hip arthroplasty using the anterolateral, abductor split approach can minimize the rate of postoperative dislocation in the prevailing preoperative diagnostic categories.
Changes in the crystalline and mesoscale lamellar structure during plastic deformation of semicrystalline polymers have been extensively studied by X-ray diffraction techniques. However, direct ...measurements of single chain conformations during stretching have not been realized, although they are key to fully understand the structural transitions during cold drawing and their relation with the state of uniaxial stress. We report direct measurements of molecular alignment of a semicrystalline polymer during cold drawing by combining in-situ small-angle neutron scattering (SANS) and polarized Raman spectroscopy. The sample investigated is a linear low-density polyethylene (LLDPE) with density of 918 kg/m3 and melt index of 1.0 g/10 min. A multifaceted protocol consisting of hydrogen–deuterium exchange, followed by fractionation (by molecular weight, MW) and blending of selected deuterated fractions with protonated LLDPE, was used to elucidate, via SANS measurements, the response of the different fractions to uniaxial deformation. Under tensile deformation significant chain stretching occurs in the initial elastic regime. Further plastic deformation causes additional chain stretching, but to a lesser degree, that eventually plateaus in the strain hardening regime. Concurrently, the fraction of trans conformers increases linearly, as measured by in-situ Raman spectroscopy. The total orientation, quantified using an alignment factor, is lower for the lower MW fractions. We hypothesize through simple geometric arguments that this is directly related to the probability of forming intercrystal tie chains.
The role of gravity in gelation of adhesive hard spheres is studied and a critical criterion developed for homogeneous gelation within the gas-liquid binodal. We hypothesize that gelation by Brownian ...diffusion competes with phase separation enhanced by gravitational settling. This competition is characterized by the gravitational Péclet number Pe(g), which is a function of particle size, volume fraction, and gravitational acceleration. Through a systematic variation of the parameters, we observe the critical Pe(g) of ∼ 0.01 can predict the stability of gels composed of adhesive hard spheres.
Monkey B virus (Macacine herpesvirus 1; BV) is an α-herpesvirus of macaques that causes serious infections in humans. A spontaneous mutant resistant to penciclovir (PCV) was isolated. Several genes ...were sequenced to identify mutations potentially responsible for PCV resistance. A single nucleotide deletion in the thymidine kinase (TK) gene was identified. To confirm its role in PCV resistance, several TK recombinants were constructed. A TK-deletion virus and a recombinant carrying the mutation were both resistant to PCV, while a revertant was PCV-sensitive. These results demonstrate that spontaneous drug-resistant mutants of BV do occur and that the BV TK is responsible for sensitivity to PCV.
Eleven rhesus monkeys developed multifocal erythematous and a vesicular rash. Most recovered spontaneously, but a 21-year-old female became moribund and was euthanized. Findings were of vesicular ...dermatitis and widespread multifocal hemorrhagic necrosis of the lungs and other viscera, with intralesional intranuclear inclusions. Simian varicella virus was identified as the cause by polymerase chain reaction analysis and serologic testing.
The strand-specific in situ hybridization technique of CO-FISH was used to probe telomeres of human mitotic cells in order to determine the spontaneous frequency of crossover. This approach allowed ...the detection of recombinational crossovers occurring anywhere along the length of individual chromosomes, including reciprocal events taking place between sister chromatids. Although the process of sister chromatid exchange (SCE) is the most prominent type of recombination in somatic mammalian cells, our results show that SCEs accounted for less than a third of the recombinational events revealed by CO-FISH. It is concluded that chromosomal regions near the termini of chromosome arms undergo extraordinarily high rates of spontaneous recombination, producing terminal crossovers whose small size precludes detection by standard cytogenetic methods. That similar results were observed for transformed epithelial cells, as well as primary fibroblasts, suggests that the phenomenon is a common characteristic of human cells. These findings are noteworthy because, although telomeric and subtelomeric DNA is known to be preferentially involved in certain types of recombination, the tips of somatic mammalian chromosomes have not previously been identified as preferred sites for crossover. Implications of these results are discussed in terms of limitations imposed on CO-FISH for its proposed use in directional hybridization mapping.
Small-angle neutron scattering (SANS) is a powerful method for probing the structural properties of polymeric materials. Contrast between polymer chains can be obtained by labeling with deuterium, ...which provides an opportunity for analyzing individual chain behavior in bulk. A transition metal (Pt/Re)-catalyzed reaction in isooctane was used to exchange deuterium for hydrogen in various saturated hydrocarbon polymers, including a commercial polyethylene. We have investigated the role of two forms of molecular heterogeneity on the labeling reaction using narrow dispersity hydrogenated polybutadiene (hPBD) samples with controlled molecular weight and ethyl branch content (short chain branching). These materials were prepared by anionic polymerization, followed by catalytic hydrogenation. A monotonic increase of deuterium labeling from 65% to 84% was observed when molecular weight was increased from 4000 to 216 000. Increasing the molecular weight to 635 000, however, resulted in almost no exchange, which is possibly due to the existence of a lower critical solution temperature (LCST) in isooctane. A similar trend with molecular weight was found for an isotope-labeled commercial linear low-density polyethylene material with 2.5% butyl branches and molecular weight ranging between 1000 and 1 000 000. Variation of ethyl branches from 2 to 50 ethyl branches per 100 backbone carbons in hPBDs reduced the level of exchange from 78% to 34%, with deuterons preferentially entering the pendant methyl groups at higher levels of branching. The materials generated from this isotope exchange reaction proved to be viable materials for SANS, providing consistent single chain statistics through proper analysis strategies, which take into account the inhomogeneous distribution of deuterium along and among individual chains caused by partial labeling and the molecular weight dependence of exchange. These results suggest that for a given chain, isotope exchange occurs on the metal catalyst surface during relatively few adsorption steps.
► We study the transient shear rheology of a long glass fiber melt. ► The sliding plate rheometer showed consistency with a cone-and-donut rheometer. ► Behavior is highly dependent on the initial ...fiber orientation. ► Orientation measurements show all fiber samples evolve in the direction of flow.
In order to eventually predict the behavior of long fiber suspensions in complex flows commonly found in processing operations, it is necessary to understand their rheology and its connection to the evolution of fiber orientation and configuration in well defined flows. In this paper we report the transient behavior at the startup of shear flow of a polymer melt containing long glass fibers with a length (
L) >1
mm, using a sliding plate rheometer (SPR). The operation of the SPR was confirmed by comparing the transient shear viscosity (
η
+) for a polymer melt and a melt containing short glass fibers (
L
<
1
mm) with measurements obtained from a cone-and-plate device, using a modified sample geometry that was designed to avoid wall effects. For the long fiber systems, measurements could only be obtained in the SPR because these systems would not stay within the gap of the rotational rheometer. Transient stress growth behavior of the long fiber systems was obtained as a function of shear rate and fiber concentration for samples prepared with three different initial orientations. Results showed that, unlike short fiber systems (with a random planar initial orientation) that usually exhibit a single overshoot peak followed by a steady state,
η
+ of the long fiber suspensions often passed through multiple transient regions, depending on the fiber concentration and applied shear rate. Additionally,
η
+ of the long fiber suspensions was found to be highly dependent on the initial orientation of the sheared samples. Finally, the initial and final fiber orientations of the long glass fiber samples were measured and used to initiate an explanation of the viscosity behavior. The results obtained in this research will be useful for future assessment of a quantitative correlation between transient rheology and the evolution of fiber orientation.
PDF
