Electrokinetic flow of aqueous electrolyte in amorphous silica nanotubes

We study the pressure-driven flow of aqueous NaCl in amorphous silica nanotubes using nonequilibrium molecular dynamics simulations featuring both polarizable and non-polarizable molecular models. Different pressures, electrolyte concentrations and pore sizes are examined. Our results indicate a flow that deviates considerably from the predictions of Poiseuille fluid mechanics. Due to preferential adsorption of the different ionic species by surface SiO! or SiOH groups, we find that a significant electric current is generated, but with opposite polarities using polarizable vs. fixed charge models for water and ions, emphasizing the need for careful parameterization in such complex systems. We also examine the influence of partial deprotonation of the silica surface, and we find that much more current is generated in a dehydrogenated nanopore, even though the overall efficiency remains low. These findings indicate that different methods of nanopore preparation, which can produce a range of surface properties, should be examined more closely in the related experimental methods to generate electrokinetic current

Effect of Field Direction on Electrowetting in a Nanopore

We manifest a significant influence of field direction and polarity on surface wetting, when the latter is tuned by application of an external electric field. Thermodynamics of field-induced filling of hydrocarbon-like nanopores with water is studied by open ensemble molecular simulation. Increased field strength consistently results in water-filling and electrostriction in hydrophobic nanopores. A threshold field commensurate with surface charge density of about one elementary charge per 10 nm2 suffices to render prototypical paraffin surfaces hydrophilic. When a field is applied in the direction perpendicular to the confining walls, the competition between orientational polarization and angle preferences of interfacial water molecules relative to the walls results in an asymmetric wettability of opposing surfaces (Janus interface). Reduction of surface free energy observed upon alignment of confinement walls with field direction suggests a novel mechanism whereby the applied electric field can operate selectively on water-filled nanotubes while empty ones remain unaffected

After Recess: Historical Practice, Textual Ambiguity, and Constitutional Adverse Possession

The Supreme Court’s interpretation of the Recess Appointments Clause in NLRB v. Noel Canning stands as one of the Supreme Court’s most significant endorsements of the relevance of “historical gloss” to the interpretation of the separation of powers. This Article uses the decision as a vehicle for examining the relationship between interpretive methodology and historical practice, and between historical practice and textual ambiguity. As the Article explains, Noel Canning exemplifies how the constitutional text, perceptions about clarity or ambiguity, and “extra-textual” considerations such as historical practice operate interactively rather than as separate elements of interpretation. The decision also provides a useful entry point into critically analyzing the concept of constitutional “liquidation,” which the majority in Noel Canning seemed to conflate with historical gloss but which seems more consistent with the approach to historical practice reflected in Justice Scalia’s concurrence in the judgment. Finally, this Article argues that the historical gloss approach, when applied cautiously and with sensitivity to the potential concerns raised by Justice Scalia and others, is not vulnerable to the charge of licensing executive aggrandizement by “adverse possession.

Transcriptome sequencing of Mycosphaerella fijiensis during association with Musa acuminata reveals candidate pathogenicity genes

Figure S4. Phylogenetic tree of fusicoccadiene synthase protein sequences. A maximum likelihood tree was created of the M. fijiensis fusicoccadiene synthase sequence and its top 50 hits using blastp with the non-redundant protein sequence database on NCBI. Bootstrap values are indicated on the tree, and the scale bar of branch lengths indicate substitutions per site. A description of each blast hit is shown, along with an abbreviation for species. Ab = Alternaria brassicicola; Ac = Acremonium chrysogenum; Af = Aspergillus flavus; Ak = Aspergillus kawachii; An = Aspergillus niger; Ao = Aspergillus oryzae; Ar = Aspergillus ruber; Bm = Bipolaris maydis; Bo = Bipolaris oryzae; Bp = Baudoinia panamericana; Bs = Bipolaris sorokiniana; Bv = Bipolaris victoriae; Bz = Bipolaris zeicola; Cg = Chaetomium globosum; Ci = Coccidioides immitis; Cp = Coccidioides posadasii; Da = Diaporthe amygdali; Fg = Fusarium graminearum; Fp = Fusarium pseudograminearum; Gl = Gymnopus luxurians; Mo = Magnaporthe oryzae; Mp = Macrophomina phaseolina; Nf = Neosartorya fischeri; Nu = Neosartorya udagawae; Om = Oidiodendron maius; Pp = Pseudogymnoascus pannorum; Ptt = Pyrenophora teres f. teres; Tc = Talaromyces cellulolyticus; Ti = Talaromyces islandicus; Tm = Talaromyces marneffei; To = Tolypocladium ophioglossoides; Ts = Talaromyces stipitatus; Tt = Thielavia terrestris. (TIF 303 kb

Ab Initio Molecular Dynamics Simulations of the Influence of Lithium Bromide on the Structure of the Aqueous Solution-Air Interface

We present the results of ab initio molecular dynamics simulations of the solution-air interface of aqueous lithium bromide (LiBr). We find that, in agreement with the experimental data and previous simulation results with empirical polarizable force field models, Br- anions prefer to accumulate just below the first molecular water layer near the interface, whereas Li+ cations remain deeply buried several molecular layers from the interface, even at very high concentration. The separation of ions has a profound effect on the average orientation of water molecules in the vicinity of the interface. We also find that the hydration number of Li+ cations in the center of the slab Na-c,Na-Li+-H2O approximate to 4.7 +/- 0.3, regardless of the salt concentration. This estimate is consistent with the recent experimental neutron scattering data, confirming that results from nonpolarizable empirical models, which consistently predict tetrahedral coordination of Li+ to four solvent molecules, are incorrect. Consequently, disruption of the hydrogen bond network caused by Li+ may be overestimated in nonpolarizable empirical models. Overall, our results suggest that empirical models, in particular nonpolarizable models, may not capture all of the properties of the solution-air interface necessary to fully understand the interfacial chemistry.Peer reviewe

Rate dependent shear bands in a shear transformation zone model of amorphous solids

We use Shear Transformation Zone (STZ) theory to develop a deformation map for amorphous solids as a function of the imposed shear rate and initial material preparation. The STZ formulation incorporates recent simulation results [Haxton and Liu, PRL 99 195701 (2007)] showing that the steady state effective temperature is rate dependent. The resulting model predicts a wide range of deformation behavior as a function of the initial conditions, including homogeneous deformation, broad shear bands, extremely thin shear bands, and the onset of material failure. In particular, the STZ model predicts homogeneous deformation for shorter quench times and lower strain rates, and inhomogeneous deformation for longer quench times and higher strain rates. The location of the transition between homogeneous and inhomogeneous flow on the deformation map is determined in part by the steady state effective temperature, which is likely material dependent. This model also suggests that material failure occurs due to a runaway feedback between shear heating and the local disorder, and provides an explanation for the thickness of shear bands near the onset of material failure. We find that this model, which resolves dynamics within a sheared material interface, predicts that the stress weakens with strain much more rapidly than a similar model which uses a single state variable to specify internal dynamics on the interface.Comment: 10 pages, 13 figures, corrected typos, added section on rate strengthening vs. rate weakening material

Electrowetting at the nanoscale

Using molecular simulations of nano-sized aqueous droplets on a model graphite surface we demonstrate remarkable sensitivity of water contact angles to the applied electric field polarity and direction relative to the liquid/solid interface. The effect is explained by analyzing the influence of the field on interfacial hydrogen bonding in the nanodrop, which in turn affects the interfacial tensions. The observed anisotropy in droplet wetting is a new nanoscale phenomenon that has so far been elusive as, in current experimental setups, surface molecules represent a very low fraction of the total number affected by the field. Our findings may have important implications for the design of electrowetting techniques in fabrication and property tuning of nanomaterials

Microscopic Dynamics of the Orientation of a Hydrated Nanoparticle in an Electric Field

We use atomistic simulations to study the orientational dynamics of a nonpolar nanoparticle suspended in water and subject to an electric field. Due to molecular-level effects we describe, the torque exerted on the nanoparticle exceeds continuum-electrostatics based estimates by about a factor of two. The reorientation time of a 16.2×16.2×3.35 ̊A3 nanoparticle in a field E \u3e 0.015V/ ̊A is an order of magnitude less than the field-free orientational time (∼ 1 ns). Surprisingly, the alignment speed is nearly independent of the nanoparticle size in this regime. These findings are relevant for design of novel nanostructures and sensors and development of nanoengineering methods