Pearling instability of nanoscale fluid flow confined to a chemical channel

We investigate the flow of a nano-scale incompressible ridge of low-volatility liquid along a "chemical channel": a long, straight, and completely wetting stripe embedded in a planar substrate, and sandwiched between two extended less wetting solid regions. Molecular dynamics simulations, a simple long-wavelength approximation, and a full stability analysis based on the Stokes equations are used, and give qualitatively consistent results. While thin liquid ridges are stable both statically and during flow, a (linear) pearling instability develops if the thickness of the ridge exceeds half of the width of the channel. In the flowing case periodic bulges propagate along the channel and subsequently merge due to nonlinear effects. However, the ridge does not break up even when the flow is unstable, and the qualitative behavior is unchanged even when the fluid can spill over onto a partially wetting exterior solid region.Comment: 17 pages, 12 figures, submitted to Physics of Fluids, fixed equation numbering after Eq. (17

Shear flow pumping in open microfluidic systems

We propose to drive open microfluidic systems by shear in a covering fluid layer, e.g., oil covering water-filled chemical channels. The advantages as compared to other means of pumping are simpler forcing and prevention of evaporation of volatile components. We calculate the expected throughput for straight channels and show that devices can be built with off-the-shelf technology. Molecular dynamics simulations suggest that this concept is scalable down to the nanoscale.Comment: 4 pages, 4 figure, submitted to Phys. Rev. Let

The Influence of Smoking, Gender, and Family History on Colorectal Adenomas

Evidence independently links smoking, family history, and gender with increased risk of adenomatous polyps. Using data from the New Hampshire Colonoscopy Registry (2004–2006), we examined the relation of combined risk factors with adenoma occurrence in 5,395 individuals undergoing screening colonoscopy. Self-reported data on smoking, family history and other factors were linked to pathology reports identifying adenomatous polyps and modeled with multiple logistic regression. In adjusted models a >15 pack-year smoking history increased the likelihood of an adenoma (OR = 1.54, 95% CI 1.28–1.86), although ≤15 pack-years did not (OR = 1.07, 95% CI 0.87–1.32). Gender-stratified models showed a significantly increased risk of adenoma at lower smoking exposure even for men (OR = 1.32; 95% CI:1.00–1.76), but not for women (OR = 0.85; 95% CI:0.61–1.14). An ordered logistic regression model of adenoma occurrence showed a smoking history of ≥15 pack-years associated with 61% higher odds of adenoma at successively larger size categories (95% CI 1.34–1.93). For individuals with a family history of colorectal cancer, smoking does not further increase the risk of adenomas. Smoking duration is linked to occurrence and size of adenoma, especially for men

Depression Care Management: Can Employers Purchase Improved Outcomes?

Fourteen vendors are currently selling depression care management products to US employers after randomized trials demonstrate improved work outcomes. The research team interviewed 10 (71.4%) of these vendors to compare their products to four key components of interventions demonstrated to improve work outcomes. Five of 10 depression products incorporate all four key components, three of which are sold by health maintenance organizations (HMOs); however, HMOs did not deliver these components at the recommended intensity and/or duration. Only one product delivered by a disease management company delivered all four components of care at the recommended intensity and duration. This “voltage drop,” which we anticipate will increase with product implementation, suggests that every delivery system should carefully evaluate the design of its depression product before implementation for its capacity to deliver evidence-based care, repeating these evaluations as new evidence emerges

Wall-liquid and wall-crystal interfacial free energies via thermodynamic integration: A molecular dynamics simulation study

A method is proposed to compute the interfacial free energy of a Lennard-Jones system in contact with a structured wall by molecular dynamics simulation. Both the bulk liquid and bulk face-centered-cubic crystal phase along the (111) orientation are considered. Our approach is based on a thermodynamic integration scheme where first the bulk Lennard-Jones system is reversibly transformed to a state where it interacts with a structureless flat wall. In a second step, the flat structureless wall is reversibly transformed into an atomistic wall with crystalline structure. The dependence of the interfacial free energy on various parameters such as the wall potential, the density and orientation of the wall is investigated. The conditions are indicated under which a Lennard-Jones crystal partially wets a flat wall.Comment: 15 pages, 11 figure

Nonlinear dielectric effect of dipolar fluids

The nonlinear dielectric effect for dipolar fluids is studied within the framework of the mean spherical approximation (MSA) of hard core dipolar Yukawa fluids. Based on earlier results for the electric field dependence of the polarization our analytical results show so-called normal saturation effects which are in good agreement with corresponding NVT ensemble Monte Carlo simulation data. The linear and the nonlinear dielectric permittivities obtained from MC simulations are determined from the fluctuations of the total dipole moment of the system in the absence of an applied electric field. We compare the MSA based theoretical results with the corresponding Langevin and Debye-Weiss behaviors.Comment: 10 pages including 4 figure

A filament of dark matter between two clusters of galaxies

It is a firm prediction of the concordance Cold Dark Matter (CDM) cosmological model that galaxy clusters live at the intersection of large-scale structure filaments. The thread-like structure of this "cosmic web" has been traced by galaxy redshift surveys for decades. More recently the Warm-Hot Intergalactic Medium (WHIM) residing in low redshift filaments has been observed in emission and absorption. However, a reliable direct detection of the underlying Dark Matter skeleton, which should contain more than half of all matter, remained elusive, as earlier candidates for such detections were either falsified or suffered from low signal-to-noise ratios and unphysical misalignements of dark and luminous matter. Here we report the detection of a dark matter filament connecting the two main components of the Abell 222/223 supercluster system from its weak gravitational lensing signal, both in a non-parametric mass reconstruction and in parametric model fits. This filament is coincident with an overdensity of galaxies and diffuse, soft X-ray emission and contributes mass comparable to that of an additional galaxy cluster to the total mass of the supercluster. Combined with X-ray observations, we place an upper limit of 0.09 on the hot gas fraction, the mass of X-ray emitting gas divided by the total mass, in the filament.Comment: Nature, in pres

Mean-field dynamical density functional theory

We examine the out-of-equilibrium dynamical evolution of density profiles of ultrasoft particles under time-varying external confining potentials in three spatial dimensions. The theoretical formalism employed is the dynamical density functional theory (DDFT) of Marini Bettolo Marconi and Tarazona [J. Chem. Phys. {\bf 110}, 8032 (1999)], supplied by an equilibrium excess free energy functional that is essentially exact. We complement our theoretical analysis by carrying out extensive Brownian Dynamics simulations. We find excellent agreement between theory and simulations for the whole time evolution of density profiles, demonstrating thereby the validity of the DDFT when an accurate equilibrium free energy functional is employed.Comment: 8 pagers, 4 figure

PYR/PYL/RCAR abscisic acid receptors regulate K⁺ and Cl^- channels through reactive oxygen species-mediated activation of Ca²⁺ channels at the plasma membrane of intact Arabidopsis guard cells.

The discovery of the START family of abscisic acid (ABA) receptors places these proteins at the front of a protein kinase/phosphatase signal cascade that promotes stomatal closure. The connection of these receptors to Ca<sup>2+</sup> signals evoked by ABA has proven more difficult to resolve, although it has been implicated by studies of the pyrbactin-insensitive <i>pyr1/pyl1/pyl2/pyl4</i> quadruple mutant. One difficulty is that flux through plasma membrane Ca<sup>2+</sup> channels and Ca<sup>2+</sup> release from endomembrane stores coordinately elevate cytosolic free Ca<sup>2+</sup> concentration ([Ca<sup>2+</sup>]<sub>i</sub>) in guard cells, and both processes are facilitated by ABA. Here, we describe a method for recording Ca<sup>2+</sup> channels at the plasma membrane of intact guard cells of Arabidopsis (Arabidopsis thaliana). We have used this method to resolve the loss of ABA-evoked Ca<sup>2+</sup> channel activity at the plasma membrane in the <i>pyr1/pyl1/pyl2/pyl4</i> mutant and show the consequent suppression of [Ca<sup>2+</sup>]<sub>i</sub> increases in vivo. The basal activity of Ca<sup>2+</sup> channels was not affected in the mutant; raising the concentration of Ca<sup>2+</sup> outside was sufficient to promote Ca<sup>2+</sup> entry, to inactivate current carried by inward-rectifying K<sup>+</sup> channels and to activate current carried by the anion channels, both of which are sensitive to [Ca<sup>2+</sup>]<sub>i</sub> elevations. However, the ABA-dependent increase in reactive oxygen species (ROS) was impaired. Adding the ROS hydrogen peroxide was sufficient to activate the Ca<sup>2+</sup> channels and trigger stomatal closure in the mutant. These results offer direct evidence of PYR/PYL/RCAR receptor coupling to the activation by ABA of plasma membrane Ca<sup>2+</sup> channels through ROS, thus affecting [Ca<sup>2+</sup>]<sub>i</sub> and its regulation of stomatal closure

Convergent Evolution of Chromosomal Sex-Determining Regions in the Animal and Fungal Kingdoms

Sexual identity is governed by sex chromosomes in plants and animals, and by mating type (MAT) loci in fungi. Comparative analysis of the MAT locus from a species cluster of the human fungal pathogen Cryptococcus revealed sequential evolutionary events that fashioned this large, highly unusual region. We hypothesize that MAT evolved via four main steps, beginning with acquisition of genes into two unlinked sex-determining regions, forming independent gene clusters that then fused via chromosomal translocation. A transitional tripolar intermediate state then converted to a bipolar system via gene conversion or recombination between the linked and unlinked sex-determining regions. MAT was subsequently subjected to intra- and interallelic gene conversion and inversions that suppress recombination. These events resemble those that shaped mammalian sex chromosomes, illustrating convergent evolution in sex-determining structures in the animal and fungal kingdoms