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This Account reviews two procedures for controlling the flow of fluids in microchannels. The first procedure involves patterning the density of charge on the inner surfaces of a channel. These patterns generate recirculating electroosmotic flows in the presence of a steady electric field. The second procedure involves patterning topography on an inner surface of a channel. These patterns generate recirculation in the cross-section of steady, pressure-driven flows. This Account summarizes applications of these flow to mixing and to controlling dispersion (band broadening).
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTmeso-2,5-Dimercapto-N,N,N',N'-tetramethyladipamide: a readily available, kinetically rapid reagent for the reduction of disulfides in aqueous solutionWatson J. Lees, Rajeeva Singh, and George M. WhitesidesCite this: J. Org. Chem. 1991, 56, 26, 7328–7331Publication Date (Print):December 1, 1991Publication History Published online1 May 2002Published inissue 1 December 1991https://pubs.acs.org/doi/10.1021/jo00026a026https://doi.org/10.1021/jo00026a026research-articleACS PublicationsRequest reuse permissionsArticle Views822Altmetric-Citations35LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
A constitutive model for the elastic-plastic behavior of plastically compressible orthotropic materi- als is proposed based on an ellipsoidalyield surface with evolving ellipticity to accommodate non-uniform hard- ening or softening associated with stressing in different directions. Themodel incorporatesrate-dependencearis- ing from material rate-dependence and micro-inertial ef- fects. The basic inputs are the stress-strain responses under the six fundamental stress histories in the or- thotropicaxes. Special limitsofthemodel includeclassi- cal isotropichardening theory, the Hill model for incom- pressible orthotropic solids, and the Deshpande-Fleck model for highly porous isotropic foam metals. A pri- mary motivation is application to metal core structure in sandwich plates wherein the core is modeled by a con- tinuumconstitutivemodel. The constitutivemodel is im- plemented withinafinite element framework to represent the behavior of square honeycomb metal cores of sand- wich plates subject to quasi-static and dynamic loads. Input identification is illustrated for numerical formula- tionsthatemployoneelement throughthecorethickness. Representationsof the core with oneelement through the thickness are shown to be able to capture most of the im- portant influences of nonlinear core behavior on overall response of sandwich plates under both quasi-static and dynamic loadings. a general class of plastically compressible, orthotropic solids based on an ellipsoidal yield surface which incor- porates non-uniform hardening. The constitutive model has considerable flexibility. Limits of the model include many of the important phenomenologicalconstitutivere- lations for elastic-plastic solids: classical isotropic plas- ticity, Hill's theory for incompressible orthotropic plas- ticity, and the Deshpande-Fleck theory for highly com- pressible isotropic metal foams. A salient feature of the formulation is its ability to model distinct hardening or softening behaviors under different stressing conditions, with applicationto both plasticallyincompressiblesolids and highly compressible materials. For application to metal sandwich cores, the approach requires inputsspecifyingthe stress-strainbehaviorchar- acterizing single component stressing in orthotropicaxes for each of the six components of stress. These basic inputs can be obtained from theoretical models, exper- imental data or numerical simulations, or combinations of all three. Once the inputs are characterized, the con- stitutive model can be used to represent the core in con- nection with standard finite element codes. In this paper, the commercial code ABAQUS Explicithas been used in connection with a user-supplied subroutinethat has been constructed based on the constitutive model. The pa- per illustrates the process of identifying the input stress- strain data for square honeycomb cores. It also demon- strates that representing the core by elements extending all the way through the core can be accurate and highly efficient in the analysis of sandwich plates deformed un- der quasi-static and dynamic loads to large deflections. Simulations based on full three-dimensional meshing of the core demonstrate the validity of the approach. The present paper continues the effort underway for sev- eral years by a number of groups to develop contin- uum constitutiverelations to characterize a range of core structures and to validate them for structural applica- tions (Deshpande, Fleck and Ashby (2001); Hanssen, Langseth and Hopperstad (2002); Mohr and Doyoyo
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Two new tris-melamine derivatives, triazine-thio-M3 (5) (C3N3-2,4,6-[SCH2C6H4-3-N(CH2C6H4-4-C(CH3)3)COC6N3-2-NHC3N3(NH2)(NHCH2CH2C(CH3)3)-5-Br]3) and benzene-thio-M3 (6) (C6H3-1,3,5-[SCH2C6H4-3-N(CH2C6H4-4-C(CH3)3)COC6H3-2-NHC3N3(NH2)(NHCH2CH2C(CH3)3)-5-Br]3), were synthesized by reactions of 2,4,6-trithiocyanuric acid and 1,3,5-trimercaptobenzene with a bromobenzyl melamine derivative 19 (BrCH2C6H4-3-N(CH2C6H4-4-C(CH3)3)COC6H3-2-NHC3N3(NH2)(NHCH2CH2C(CH3)3)-5-Br). These two compounds formed stable and structurally well-defined 1 + 3 supramolecular aggregates with neohexyl isocyanurate (R'CA) (9) as shown by NMR spectroscopy and gel permeation chromatography. 1H NMR competition experiments indicated that the stability of triazine-thio-M3·(R'CA)3 (1) was similar to that of benzene-thio-M3·(R'CA)3 (2). The order of stabilities of tris-melamine-based 1 + 3 complexes was hubM3·(R'CA)3 (3) > triazine-thio-M3·(R'CA)3 (1) ∼ benzene-thio-M3·(R'CA)3 (2) > flexM3·(R'CA)3 (4). Computational simulations were also carried out on triazine-thio-M3·(R'CA)3 and hubM3·(R'CA)3 fully solvated in CHCl3. Values of DP (the deviation from planarity of the cyanuric acid and melamine rosette) obtained from these simulations correlated correctly with the observed stabilities and suggested a structural reason why triazine-thio-M3·(R'CA)3 was less stable than hubM3·(R'CA)3.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThermal decomposition of vinylic copper(I) and silver(I) organometallic compoundsGeorge M. Whitesides, Charles P. Casey, and Jeanne K. KriegerCite this: J. Am. Chem. Soc. 1971, 93, 6, 1379–1389Publication Date (Print):March 1, 1971Publication History Published online1 May 2002Published inissue 1 March 1971https://pubs.acs.org/doi/10.1021/ja00735a011https://doi.org/10.1021/ja00735a011research-articleACS PublicationsRequest reuse permissionsArticle Views1588Altmetric-Citations213LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
The activation energy for dislocation nucleation from a stressed crack tip is calculated within the Peierls framework, in which a periodic shear stress vs displacement relation is assumed to hold on a slip plane emanating from the crack tip. Previous results have revealed that the critical G (energy release rate corresponding to the “screened” crack tip stress field) for dislocation nucleation scales with γus (the unstable stacking energy), in an analysis which neglects any coupling between tension and shear along the slip plane. That analysis represents instantaneous nucleation and takes thermal effects into account only via the weak temperature dependence of the elastic constants. In this work, the energy required to thermally activate a stable, incipient dislocation into its unstable “saddle-point” configuration is directly calculated for loads less than that critical value. We do so only with the simplest case, for which the slip plane is a prolongation of the crack plane. A first calculation reported is 2D in nature, and hence reveals an activation energy per unit length. A more realistic scheme for thermal activation involves the emission of a dislocation loop, an inherently 3D phenomenon. Asymptotic calculations of the activation energy for loads close to the critical load are performed in 2D and in 3D. It is found that the 3D activation energy generally corresponds to the 2D activation energy per unit length multiplied by about 5–10 Burgers vectors (but by as many as 17 very near to the critical loading). Implications for the emission of dislocations in copper, α-iron, and silicon at elevated temperature are discussed. The effects of thermal activation are very significant in lowering the load for emission. Also, the appropriate activation energy to correspond to molecular dynamics simulations of crack tips is discussed. Such simulations, as typically carried out with only a few atomic planes in a periodic repeat direction parallel to the crack tip, are shown to greatly exaggerate the (already large) effects of temperature on dislocation nucleation.
As = stiff eiier area b = postbuckling coefficient (see Fig. 2) D = shell bending stiffness {=Et*/[l2(l *>)]} E = Young's modulus H = spherical cap rise (see Fig. 10) Is = stiffener moment of inertia Kij KZ = foundation moduli (see Fig. 7) k = parameter in imperfection spectrum (see Fig. 8) L = shell length Z = I/TT (buckle length) lc = critical value of / NC = classical buckling load per unit length n = circumferential wave number in spherical cap buckling P = load PC = classical buckling load PS = static buckling load of imperfect structure PD = dynamic buckling load PC = classical buckling pressure R = shell radius (cylinder, sphere, toroidal-segment boundary); correlation function (see Fig. 7) Rx . = meridional radius of curvature of toroidal segment s = stiff ener eccentricity (see Fig. 6) S = power spectral density of imperfection (see Fig. 7) W = deflection of column W = initial deflection of column Z = curvature parameter { =(L/Rt)(l j/)/} S = buckling displacement amplitude d_ — initial displacement amplitude A = rms initial displacement v = Poisson's ratio
