We analytically investigate the prospect of using electrokinetic phenomena to transfer hydrostatic energy to electrical power with high energy transfer efficiencies, by exploiting time periodic pressure-driven flows in narrow fluidic confinements. An expression for the energy transfer efficiency for such pulsating pressure-driven flows is derived by considering wall-slip effects due to hydrophobic interactions, strong electrical double layer interactions in the confined flow passages, possibilities of exploring the regimes of large wall potentials, and the adverse consequences of the finite conductance of the Stern layer. It is revealed from our studies that high-frequency pressure pulsations may be employed in practice to improve the concerned energy transfer efficiency to a considerable extent, instead of using a steady-state pressure field. Such favorable effects are found to be best exploited by utilizing "slipping" electro-hydrodynamics in thick electrical double layers in the presence of high surface potentials.

Fish-mint (Houttuynia cordataThunb.), belonging to family Saururaceae, has long been used as food and traditional herbal medicine. The present study was framed to assess the changes occurring in the essential-oil composition of H. cordata during annual growth and to evaluate allelopathic, antibacterial, antifungal, and antiacetylcholinesterase activities. The essential-oil content ranged from 0.06 - 0.14% and 0.08 - 0.16% in aerial parts and underground stem, respectively. The essential oils were analysed by GC-FID, GC/MS, and NMR ( H and C). Major constituents of aerial-parts oil was 2-undecanone (19.4 - 56.3%), myrcene (2.6 - 44.3%), ethyl decanoate (0.0 - 10.6%), ethyl dodecanoate (1.1 - 8.6%), 2-tridecanone (0.5 - 8.3%), and decanal (1.1 - 6.9%). However, major constituents of underground-stem oil were 2-undecanone (29.5 - 42.3%), myrcene (14.4 - 20.8%), sabinene (6.0 - 11.1%), 2-tridecanone (1.8 - 10.5%), β-pinene (5.3 - 10.0%), and ethyl dodecanoate (0.8 - 7.3%). Cluster analysis revealed that essential-oil composition varied substantially due to the plant parts and season of collection. The oils exhibited significant allelopathic (inhibition: 77.8 - 88.8%; LD : 2.45 - 3.05 μl/plate), antibacterial (MIC: 0.52 - 2.08 μl/ml; MBC: bacteriostatic) and antifungal (MIC: 2.08 - 33.33 μl/ml; MFC: 4.16 - 33.33 μl/ml) activities. The results indicate that the essential oil from H. cordata has a significant potential to allow future exploration and exploitation as a natural antimicrobial and allelopathic agent.

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In this article, we investigate the implications of electroosmosis with interfacial slip on electrohydrodynamic transport in microchannels having complex (yet symmetric) cross-sectional shapes, by employing a generic semi-analytical approach. We also devise an approximate technique of flow rate prediction under these conditions, using a combined consideration of electroosmotic slip (under thin electrical double layer limits) and Navier slip conditions (originating out of confinement-induced hydrophobic interactions) at the fluid-solid interface. We further assess the effectiveness of the approximate solutions in perspective of the exact solutions, as a parametric function of the relative thickness of the electrical double layer with respect to the channel hydraulic diameter. We illustrate the underlying consequences through examples of elliptic, polygonal, point star-shaped, and annular microchannel cross sections. List of symbolsA Area of the channel cross section (m 2 ) b Slip length (m) D h Hydraulic diameter of the channel (m) E Electric field (V m -1 ) e Charge of a proton (C) e Eccentricity of ellipse g Channel boundary I m Modified 1st kind Bessel functions of order m K Non-dimensional EDL thickness K m Modified 2nd kind Bessel functions of order m k B Boltzmann constant (J K -1 ) n Normal distance from the surface (m) n 0 Bulk ionic concentration (m -3 ) n ? Concentration of cations (m -3 ) nConcentration of anions (m -3 ) Q Volume flow rate in actual situation Q app Volume flow rate in approximate situation T Absolute temperature (K) U HS Helmholtz-Smoluchowski velocity (m s -1 ) u Velocity in actual situation (m s -1 ) u app Velocity in approximate situation (m s -1 ) z ValanceGreek symbols q Fluid density (kg m -3 ) l Dynamic viscosity (kg m -1 s -1 ) q e Ionic charge density (C m -3 ) e Permittivity of the medium (C V -1 m -1 ) w EDL potential (V) f Zeta potential (V) j Reciprocal of EDL thickness (m -1 ) kEigen value b Angle of symmetry (rad.)

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