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131.
Partha Majumdar Bret Mayo Jongsoo Kim Christy Gallagher-Lein Elizabeth Lee Nathan Gubbins Bret J. Chisholm 《Journal of Coatings Technology and Research》2010,7(2):239-252
Moisture-curable polysiloxanes were modified with ionic groups to enable specific interactions between the polysiloxane matrix
and silica nanoparticle reinforcement. A trimethoxysilane-functional quaternary ammonium salt (QAS) was used to modify the
polysiloxane matrix. A comparison of the mechanical properties of coatings containing QAS modification to analogous coatings
without QAS modification showed that QAS modification resulted in a dramatic improvement in mechanical properties of silica
nanoparticle-reinforced coatings. QAS modification provided major enhancements in both tensile modulus and toughness. The
coatings were characterized using positron annihilation spectroscopy, photo-acoustic FT-IR, differential scanning calorimetry,
transmission electron microscope, and atomic force microscopy. The characterization results suggested that the QAS moieties
present in the polysiloxane matrix undergo specific interactions with the surface of silica nanoparticles enabling an enhancement
in interfacial adhesion between the polymer matrix and the nanoparticles. Most likely, the specific interaction that provided
the enhanced mechanical properties was an ion–dipole interaction involving silanol groups present on the surface of the silica
nanoparticles. The enhanced modulus and toughness of these polysiloxane materials may enable their application as a fouling-release
coating for ship hulls, since current polysiloxane-based fouling release coatings suffer from poor mechanical properties and
durability. 相似文献
132.
An array of quaternary ammonium-functionalized POSS (Q-POSS) compounds were synthesized and their antimicrobial properties toward the Gram-negative bacterium, Escherichia coli, and the Gram-positive bacterium, Staphylococcus aureus, determined in aqueous solution. Using Q-POSS compositions that exhibited broad spectrum antimicrobial activity in solution, the utility of the Q-POSS compounds as an antimicrobial additive for polysiloxane coatings was determined. The results of the investigation showed that Q-POSSs possessing a relatively low extent of quaternization and longer alkyl chain lengths provided the highest antimicrobial activity in solution. For polysiloxane coatings containing Q-POSS molecules as an antimicrobial additive, coating surface energy, surface morphology, and antimicrobial properties were found to be strongly dependent on Q-POSS composition. Coatings based on Q-POSSs possessing the lowest extent of quaternization displayed antimicrobial activity while analogous coatings produced using Q-POSSs possessing the highest extent of quaternization showed no antimicrobial activity. The lack of antimicrobial activity exhibited by coatings possessing Q-POSSs with a relatively high extent of quaternization was attributed to agglomeration of Q-POSS molecules through the formation of intermolecular interactions involving the quaternary ammonium moieties. Agglomeration would be expected to reduce diffusivity and inhibit interaction of the Q-POSS molecules with microbial cells. 相似文献
133.
Partha P. Sarkar Luca Caracoglia Frederick L. Haan Hiroshi Sato Jun Murakoshi 《Engineering Structures》2009,31(1):158-169
Aeroelastic coefficients (flutter derivatives) of bridge decks are routinely extracted from wind tunnel section model experiments for the assessment of performance against wind loading. Two distinct methods, developed over the years, are usually employed for this purpose (free or forced vibration). Even though advantages and disadvantages of each technique have been highlighted by numerous researchers, few examples of a systematic comparison of the experimental results are available in the literature. The significance of this study is related to the evaluation of an extended set of experimental data on flutter derivatives, and includes the analysis and interpretation of the differences recorded through the two methods.The motivation for this work emerged from the United States–Japan Benchmark Study on Bridge Flutter Derivatives that Iowa State University (ISU) in the United States and the Public Works Research Institute (PWRI) in Japan, initiated in 2002. Tests were designed to cover a wide range of solid cross sections, from bluff (rectangular prisms) to streamlined, in particular considering the current trend of engineers to use aerodynamically-designed girders for bridges with longer spans. In this paper, a systematic analysis and a comparison of laboratory results of flutter derivatives obtained at both institutions were performed. In a companion paper, a sensitivity study was performed to examine the implications of the perceived dissimilarities among flutter-derivative data sets on the aeroelastic instability of long-span bridges (single-mode and coupled-mode). 相似文献
134.
With the help of extensive simulations, we systematically investigated the effects of varying tilt angle of halo implant in sub 100 nm lateral asymmetric channel (LAC) MOSFETs on the reverse short channel effects, the on current and the hot carrier immunity. The devices with large angle tilt implants also show the substantial reduction in the subthreshold swing, improvement in ION/IOFF ratio and significantly the lower junction capacitance as compared to the devices with low angle tilt implant. It is also observed that the subthreshold characteristics do not change as the channel length decreases for such devices. These devices, known as lateral asymmetric channel with large angle tilt implant (LACLATI), will therefore have much improved performance in comparison to a low angle tilt implant LAC devices for digital applications. 相似文献
135.
Molecular dynamics simulation is utilized to investigate the ionic transport of NaCl in solution through a graphene nanopore under an applied electric field. Results show the formation of concentration polarization layers in the vicinity of the graphene sheet. The nonuniformity of the ion distribution gives rise to an electric pressure which drives vortical motions in the fluid if the electric field is sufficiently strong to overcome the influence of viscosity and thermal fluctuations. The relative importance of hydrodynamic transport and thermal fluctuations in determining the pore conductivity is investigated. A second important effect that is observed is the mass transport of water through the nanopore, with an average velocity proportional to the applied voltage and independent of the pore diameter. The flux arises as a consequence of the asymmetry in the ion distribution which can be attributed to differing mobilities of the sodium and chlorine ions and to the polarity of water molecules. The accumulation of liquid molecules in the vicinity of the nanopore due to re-orientation of the water dipoles by the local electric field is seen to result in a local increase in the liquid density. Results confirm that the electric conductance is proportional to the nanopore diameter for the parameter regimes that we simulated. The occurrence of fluid vortices is found to result in an increase in the effective electrical conductance. 相似文献
136.
Krishanu Sarkar Koushik Dhara Mahasweta Nandi Partha Roy Asim Bhaumik Pradyot Banerjee 《Advanced functional materials》2009,19(2):223-234
A highly ordered 2D‐hexagonal mesoporous silica material is functionalized with 3‐aminopropyltriethoxysilane. This organically modified mesoporous material is grafted with a dialdehyde fluorescent chromophore, 4‐methyl‐2,6‐diformyl phenol. Powder X‐ray diffraction, transmission electron microscopy, N2 sorption, Fourier transform infrared spectroscopy, and UV‐visible absorption and emission have been employed to characterize the material. This material shows excellent selective Zn2+ sensing, which is due to the fluorophore moiety present at its surface. Fluorescence measurements reveal that the emission intensity of the Zn2+‐bound mesoporous material increases significantly upon addition of various concentrations of Zn2+, while the introduction of other biologically relevant (Ca2+, Mg2+, Na+, and K+) and environmentally hazardous transition‐metal ions results in either unchanged or weakened intensity. The enhancement of fluorescence is attributed to the strong covalent binding of Zn2+, evident from the large binding constant value (0.87 × 104 M ?1). Thus, this functionalized mesoporous material grafted with the fluorescent chromophore could monitor or recognize Zn2+ from a mixture of ions that contains Zn2+ even in trace amounts and can be considered as a selective fluorescent probe. We have examined the application of this mesoporous zinc(II) sensor to cultured living cells (A375 human melanoma and human cervical cancer cell, HeLa) by fluorescence microscopy. 相似文献
137.
Vijoy Pandey Dipak Ghosal Biswanath Mukherjee Xiaoxin Wu 《Wireless Personal Communications》2007,43(3):857-878
In this paper, we investigate a call-admission and handoff-control framework for multi-tier cellular networks. We first propose
and compare Call-Admission Control (CAC) algorithms based on the cell-dwelling time, by studying their impact on the handoff-call
dropping and new-call blocking probabilities and the channel partitioning between the two tiers. Our results show that a simple,
cell-dwelling-time-insensitive algorithm performs better under various mixes of user mobilities and call types. Moreover,
there is an optimal channel partition of the overall spectrum between the tiers which minimizes the dropping and blocking
probabilities for the two different CAC algorithms studied in this paper. Once the call is admitted into the network, we propose
and compare various handoff- queuing strategies to reduce the call dropping probability. We show that implementing a queuing
framework in one of the tiers (especially the upper, i.e., macrocellular, tier), results in a significant reduction in the
dropping probability. 相似文献
138.
V.K. Chandravanshi R. Sarkar P. Ghosal S.V. Kamat T.K. Nandy 《Metallurgical and Materials Transactions A》2010,41(4):936-946
This work investigates the effect of boron addition on the microstructure and mechanical properties of a near alpha Ti alloy,
Timetal 685 in as-cast plus heat-treated condition. While significant refinement of the prior β grain size is seen with small
additions of boron, the thickness of α lath (in transformed β structure) increases with increasing boron. At room temperature (RT), tensile yield strength increases
marginally, but the ductility drops significantly possibly because of the cracking of TiB phase. At elevated temperature,
significant strengthening is observed in the boron containing alloys especially at higher plastic strains. Additionally, the
creep resistance shows significant enhancement with boron addition. 相似文献
139.
Partha Majumdar Shane Stafslien Justin Daniels Dean C. Webster 《Journal of Coatings Technology and Research》2007,4(2):131-138
High throughput combinatorial characterization was performed on thermosetting siloxane–urethane coatings in order to find
a correlation between the characterization techniques, surface topography, and adhesion strength of barnacles. A series of
coatings having microtopographical surfaces with different domain sizes were prepared based on a thermosetting siloxane–urethane
system. This microtopography was formed spontaneously during the film-formation process. These surfaces were characterized
by atomic force microscopy (AFM), surface energy, dynamic contact angle, and pseudo barnacle pull-off adhesion and were compared
to pure polyurethane (PU) and silicone rubber control. Surface energy and dynamic contact angles were measured by an automated
surface energy measurement system and pull-off adhesion values were obtained from a high throughput pull-off adhesion measurement
unit. The results were compared with the adhesion strength of barnacles.
Presented at the 2006 FutureCoat! conference, sponsored by the Federation of Societies for Coatings Technology, in New Orleans,
LA, on November 1–3, 2006. 相似文献
140.
Ghosal S 《Analytical chemistry》2002,74(16):4198-4203
In capillary zone electrophoresis (CZE), adsorption of charged analytes to walls has been observed to cause significant band broadening. The effect is believed to be due to modification of the flow pattern and the consequent Taylor dispersion caused by the alteration of the wall charge by the adsorbed analytes. Experiments using neutral (nonadsorbing) analytes in capillaries in which the zeta-potential has been deliberately altered in a controlled way by chemically coating a segment of the capillary have been performed by Towns and Regnier (Anal. Chem. 1992, 64, 2473) in an effort to understand the mechanism of the band broadening. In this paper, the Taylor dispersion due to electroosmotic flow in such a partially coated capillary is calculated and compared to the experimental data. The theoretical predictions are found to be in excellent agreement with the data, thus supporting the hypothesis that the decreased resolution can be attributed to Taylor dispersion due to the induced pressure gradient brought about by the nonuniformity of the zeta-potential. 相似文献