56,408 research outputs found
Adhesion and non-linear rheology of adhesives with supramolecular crosslinking points
Soft supramolecular materials are promising for the design of innovative and
highly tunable adhesives. These materials are composed of polymer chains
functionalized by strongly interacting moieties, sometimes called "stickers".
In order to systematically investigate the effect of the presence of
associative groups on the debonding properties of a supramolecular adhesive, a
series of supramolecular model systems has been characterized by probe-tack
tests. These model materials, composed of linear and low dispersity
poly(butylacrylate) chains functionalized in the middle by a single tri-urea
sticker, are able to self-associate by six hydrogen bonds and range in
molecular weight (M n) between 5 and 85 kg/mol. The linear rheology and the
nanostructure of the same materials (called "PnBA3U") was the object of a
previous study 1,2. At room temperature, the association of polymers via
hydrogen bonds induces the formation of rod-like aggregates structured into
bundles for M n \textless{} 40kg/mol and the behavior of a soft elastic
material was observed (G'\textgreater{}\textgreater{}G "and G'~ 0). For
higher M n , the filaments were randomly oriented and polymers displayed a
crossover towards viscous behavior although terminal relaxation was not reached
in the experimental frequency window. All these materials show however similar
adhesive properties characterized by a cohesive mode of failure and low
debonding energies (W adh \textless{}40J/m 2 for a debonding speed of
100m/s). The debonding mechanisms observed during the adhesion tests have
been investigated in detail with an Image tools analysis developed by our group
3. The measure of the projected area covered by cavities growing in the
adhesive layer during debonding can be used to estimate the true stress in the
walls of the cavities and thus, to characterize the in-situ large strain
deformation of the thin layer during the adhesion test itself. This analysis
revealed in particular that the PnBA3U materials with M n \textless{} 40 kg/mol
soften very markedly at large deformation like yield stress fluids, explaining
the low adhesion energies measured for these viscoelastic gels.
Attribution of injury in the shrimp antidumping case: A simultaneous equations approach
We apply a simultaneous equations framework, similar to that of Prusa and Sharp (2001), to the recent shrimp antidumping investigation in order to determine how much injury to the domestic industry—proxied by deterioration in domestic shrimp prices—is attributable to subject imports versus other market factors. We construct an econometric model then estimated with three-stage least squares (3SLS). We then apply the movements of each explanatory variable over the period of investigation (POI) to its respective coefficient in order to determine how much injury is attributable to that particular market factor. We find that subject and non-subject imports were essentially equal causes of injury to the domestic industry.3SLS
Wind tunnel evaluation of a truncated NACA 64-621 airfoil for wind turbine applications
An experimental program to measure the aerodynamic performance of a NACA 64-621 airfoil with a truncated trailing edge for wind turbine applications has been conducted in the Ohio State University Aeronautical and Astronautical Research Laboratory 6 in. by 21 in. pressurized wind tunnel. The blunted or trailing edge truncated (TET) airfoil has an advantage over similar trailing edge airfoils because it is able to streamline a larger spar structure, while also providing aerodynamic properties that are quite good. Surface pressures were measured and integrated to determine the lift, pressure drag, and moment coefficients over angles of attack ranging from -14 to +90 deg at Mach 0.2 and Reynolds numbers of 1,000,000 and 600,000. Results are compared to the NACA 0025, 0030, and 0035 thick airfoils with sharp trailing edges. Comparison shows that the 30 percent thick NACA 64-621-TET airfoil has higher maximum lift, higher lift curve slope, lower drag at higher lift coefficients, and higher chordwise force coefficient than similar thick airfoils with sharp trailing edges
Effects of angle of attack and bluntness on the shock-layer properties of a 15 deg cone at a Mach number of 10.6
Effects of angle of attack and bluntness on shock layer properties of cones at supersonic speed
Application of the vortex-lattice technique to the analysis of thin wings with vortex separation and thick multi-element wings
Two techniques for extending the range of applicability of the basic vortex-lattice method are discussed. The first improves the computation of aerodynamic forces on thin, low-aspect-ratio wings of arbitrary planforms at subsonic Mach numbers by including the effects of leading-edge and tip vortex separation, characteristic of this type wing, through use of the well-known suction-analogy method of E. C. Polhamus. Comparisons with experimental data for a variety of planforms are presented. The second consists of the use of the vortex-lattice method to predict pressure distributions over thick multi-element wings (wings with leading- and trailing-edge devices). A method of laying out the lattice is described which gives accurate pressures on the top and part of the bottom surface of the wing. Limited comparisons between the result predicted by this method, the conventional lattice arrangement method, experimental data, and 2-D potential flow analysis techniques are presented
Quantitative analysis of the debonding structure of soft adhesives
We experimentally investigate the growth dynamics of cavities nucleating
during the first stages of debonding of three different model adhesives. The
material properties of these adhesives range from a more liquid-like material
to a soft viscoelastic solid and are carefully characterized by small strain
oscillatory shear rheology as well as large strain uniaxial extension. The
debonding experiments are performed on a probe tack set-up. Using high contrast
images of the debonding process and precise image analysis tools we quantify
the total projected area of the cavities, the average cavity shape and growth
rate and link these observations to the material properties. These measurements
are then used to access corrected effective stress and strain curves that can
be directly compared to the results from the uniaxial extension
Simulation Analysis of Medium Access Techniques
This paper presents comparison of Access Techniques used in Medium Access
Control (MAC) protocol for Wireless Body Area Networks (WBANs). Comparison is
performed between Time Division Multiple Access (TDMA), Frequency Division
Multiple Access (FDMA), Carrier Sense Multiple Access with Collision Avoidance
(CSMA/CA), Pure ALOHA and Slotted ALOHA (S-ALOHA). Performance metrics used for
comparison are throughput (T), delay (D) and offered load (G). The main goal
for comparison is to show which technique gives highest Throughput and lowest
Delay with increase in Load. Energy efficiency is major issue in WBAN that is
why there is need to know which technique performs best for energy conservation
and also gives minimum delay.Comment: NGWMN with 7th IEEE International Conference on Broadband and
Wireless Computing, Com- munication and Applications (BWCCA 2012), Victoria,
Canada, 201
A simple microscopic model for the dynamics of adhesive failure
We consider a microscopic model for the failure of soft adhesives in tension
based on ideas of bond rupture under dynamic loading. Focusing on adhesive
failure under loading at constant velocity, we demonstrate that bi-modal curves
of stress against strain may occur due to effects of finite polymer chain or
bond length and characterise the loading conditions under which such bi-modal
behaviour is observed. The results of this analysis are in qualitative
agreement with experiments performed on unconfined adhesives in which failure
does not occur by cavitation.Comment: 11 pages, 5 figure
On issues concerning flow separation and vortical flows in 3 dimensions
This review provides an illustrated introduction laying the knowledge base for vortical flows about three dimensional configurations that are of typical interest to aerodynamicists and researchers in fluid mechanics. The paper then compiles a list of ten issues, again in illustrative format, that the authors deem important to the understanding of complex vortical flows. These issues and our responses to them provide, it is hoped, a skeletal framework on which to hang the ensuing conference proceedings
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