Influence of the final extent of reaction on the structure of model polydimethylsiloxane networks obtained by the end-linking hydrosilation reaction

1995 ◽  
Vol 35 (3) ◽  
pp. 279-284 ◽  
Author(s):  
Marcelo A. Villar ◽  
Enrique M. Vall�s
Keyword(s):  
End Linking ◽  
Final Extent

Hydrogels prepared from polysiloxane chains by end linking them with trifunctional silanes containing hydrophilic groups

Polymer ◽  
2009 ◽  
Vol 50 (23) ◽  
pp. 5414-5421 ◽  
Author(s):  
Xiujuan Zhang ◽  
Gui Lin ◽  
Sai R. Kumar ◽  
James E. Mark
Keyword(s):  
End Linking

scholarly journals Rapid Acyl-Homoserine Lactone Quorum Signal Biodegradation in Diverse Soils

2005 ◽  
Vol 71 (3) ◽  
pp. 1291-1299 ◽  
Author(s):  
Ya-Juan Wang ◽  
Jared Renton Leadbetter
Keyword(s):  
Homoserine Lactone ◽  
Most Probable Number ◽  
Acyl Homoserine Lactone ◽  
Protein Synthesis Inhibitors ◽  
Probable Number ◽  
Signal Decay ◽  
Soil Activity ◽  
Final Extent ◽  
Termite Hindgut ◽  
Quorum Sensing Signals

ABSTRACT Signal degradation impacts all communications. Although acyl-homoserine lactone (acyl-HSL) quorum-sensing signals are known to be degraded by defined laboratory cultures, little is known about their stability in nature. Here, we show that acyl-HSLs are biodegraded in soils sampled from diverse U.S. sites and by termite hindgut contents. When amended to samples at physiologically relevant concentrations, 14C-labeled acyl-HSLs were mineralized to 14CO2 rapidly and, at most sites examined, without lag. A lag-free turf soil activity was characterized in further detail. Heating or irradiation of the soil prior to the addition of radiolabel abolished mineralization, whereas protein synthesis inhibitors did not. Mineralization exhibited an apparent Km of 1.5 μM acyl-HSL, ca. 1,000-fold lower than that reported for a purified acyl-HSL lactonase. Under optimal conditions, acyl-HSL degradation proceeded at a rate of 13.4 nmol · h−1 · g of fresh weight soil−1. Bioassays established that the final extent of signal inactivation was greater than for its full conversion to CO2 but that the two processes were well coupled kinetically. A most probable number of 4.6 × 105 cells · g of turf soil−1 degraded physiologically relevant amounts of hexanoyl-[1-14C]HSL to 14CO2. It would take chemical lactonolysis months to match the level of signal decay achieved in days by the observed biological activity. Rapid decay might serve either to quiet signal cross talk that might otherwise occur between spatially separated microbial aggregates or as a full system reset. Depending on the context, biological signal decay might either promote or complicate cellular communications and the accuracy of population density-based controls on gene expression in species-rich ecosystems.

Numerical Characterization of a HP Compressor Stage Equipped With a Closed Shrouded Stator Cavity

2020 ◽  
Author(s):  
Cedric Babin ◽  
Michel Dumas ◽  
Xavier Ottavy ◽  
Fabrizio Fontaneto
Keyword(s):  
Axial Compressor ◽  
Second Phase ◽  
Cavity Flows ◽  
Flow Topology ◽  
Closed Cavity ◽  
Axial Compressors ◽  
Numerical Characterization ◽  
Performance Effects ◽  
And Performance ◽  
Final Extent

Abstract In axial compressors, shrouded stator cavity flows are responsible for performance degradation due to their interaction with the power stream. The present paper aims at exploring the possibility of employing a single stage high pressure axial compressor as a test vehicle for cavity flows investigations. In a first step, the robustness of the adopted RANS approach is tested against experimental data on the closed-cavity baseline configuration (i.e. no downstream-to-upstream recirculation). In a second phase, the effect of different hub cavities layouts of different levels of realism is numerically investigated. The focus is set on the representativeness of a closed cavity configuration with injection. The cavity flow topology and impact on the overall performance are considered in the analysis. At its final extent, this paper provides numerical and experimental guidelines for the robust assessment of cavity flows topology and performance effects.

Dynamic viscoelasticity of end-linking α,ω-dimethyl silyl poly(propylene oxide) solutions near the gel point

Polymer ◽  
1994 ◽  
Vol 35 (14) ◽  
pp. 3005-3010 ◽  
Author(s):  
Akihiro Koike ◽  
Norio Nemoto ◽  
Masaoki Takahashi ◽  
Kunihiro Osaki
Keyword(s):  
Propylene Oxide ◽  
Gel Point ◽  
Dynamic Viscoelasticity ◽  
End Linking ◽  
Poly Propylene

Reinforcement from In-Situ Precipitated Silica in Polysiloxane Elastomers under Various Types of Deformation

1992 ◽  
Vol 274 ◽  
Author(s):  
James E. Mark ◽  
Shuhong Wang ◽  
Ping Xu ◽  
Jianye Wen
Keyword(s):  
Mechanical Properties ◽  
Uniaxial Elongation ◽  
Compression Set ◽  
Precipitated Silica ◽  
Equilibrium Swelling ◽  
Rupture Energy ◽  
End Linking ◽  
Reinforcing Effects

ABSTRACTElastomeric networks prepared by tetrafunctionally end linking hydroxyl-terminated poly(dimethylsiloxane) chains (PDMS) were filled by the in-situ precipitation of silica. The resulting networks were investigated under uniaxial elongation, biaxial extension, shear, and torsion in order to characterize the resulting changes in mechanical properties. Compared with the unfilled networks, the silica-filled materials showed large reinforcing effects. Specifically, their values of the modulus, ultimate strength, and rupture energy increased significantly. The results thus indicate that the PDMS networks filled by the in-situ precipitation of silica have very good mechanical properties in several, rather different deformations. Examples of other deformations of interest are equilibrium swelling, and dynamic cycling for characterization of compression set.

Myocardial bioenergetics during acute hibernation

1997 ◽  
Vol 273 (3) ◽  
pp. H1452-H1463 ◽  
Author(s):  
J. Zhang ◽  
Y. Ishibashi ◽  
Y. Zhang ◽  
M. H. Eijgelshoven ◽  
D. J. Duncker ◽  
...  
Keyword(s):  
Blood Flow ◽  
Contractile Function ◽  
Creatine Phosphate ◽  
Wall Thickening ◽  
Resonance Spectroscopy ◽  
Blood Flow Ratio ◽  
Ischemic Period ◽  
Myocardial O2 Consumption ◽  
Final Extent ◽  
Myocardial Bioenergetics

During moderate reductions of blood flow, the myocardium downregulates contractile function and ATP utilization to result in reduced but stable ATP levels, recovery or stability of (reduced) creatine phosphate (CP), and preservation of myocyte viability. The intent of this study was to determine the influence of the level of ischemic blood flow and the major determinants of myocardial O2 consumption (MVO2) (heart rate and systolic blood pressure) on recovery of CP during prolonged moderate myocardial hypoperfusion. 31P-nuclear magnetic resonance spectroscopy was used to measure CP, ATP, and Pi in the subepicardium (Epi) and subendocardium (Endo) of 13 open-chest dogs. Wall thickening was measured with sonomicrometry. A coronary stenosis reduced mean myocardial blood flow (microspheres) from 1.10 +/- 0.07 to 0.71 +/- 0.06 ml.g-1.min-1 (P < 0.01) and the Endo-to-Epi blood flow ratio from 1.12 +/- 0.07 to 0.59 +/- 0.06 (P < 0.01), and dyskinesis developed. Coronary blood flow and systolic wall thickening did not change significantly during 4 h of hypoperfusion. Epi CP and ATP fell to 80 +/- 4% (P < 0.05) and 93 +/- 3% of control, respectively, at 30 min. Epi CP then recovered to 87 +/- 5% while ATP decreased further to 83 +/- 5% of baseline by the end of the 240-min ischemic period. Endo CP and ATP fell to 53 +/- 4 and 77 +/- 5% of control, respectively, at 30 min; then Endo CP recovered to 85 +/- 6% while ATP decreased further to 68 +/- 6% of baseline at 240 min of hypoperfusion. ADP levels were significantly increased at 30 min but recovered to baseline by 240 min of hypoperfusion. delta Pi/CP increased significantly (Endo > Epi) at the onset of ischemia and then progressively decreased. At 30 min, mild myocardial acidosis was observed in some hearts with variable pH recovery during continuing hypoperfusion. The data demonstrate that variations in blood flow cannot account for the magnitude of the initial fall in CP or for the final extent of recovery. However, the rate at which CP recovered was significantly correlated with the level of blood flow. Variations in the determinants of MVO2 did not account for differences in CP recovery.

Model Polyelectrolyte Gels Synthesized by End-Linking of Tetra-Arm Polymers with Click Chemistry: Synthesis and Mechanical Properties

2014 ◽  
Vol 47 (21) ◽  
pp. 7573-7580 ◽  
Author(s):  
Kazuyuki Oshima ◽  
Taku Fujimoto ◽  
Erina Minami ◽  
Yoshiro Mitsukami
Keyword(s):  
Mechanical Properties ◽  
Click Chemistry ◽  
Polyelectrolyte Gels ◽  
End Linking
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