On line, Real-Time Densimeter-Theory and Optimization

The speed of a torsional stress wave transmitted in a solid waveguide, that has a non-circular cross-section and is submerged in a liquid, is inversely proportional to the density of the liquid. Thus, by measuring the speed of the torsional stress wave, one can obtain information about the liquid\u27s density or density-related characteristics such as liquid level and the mass composition of bi-phase mixtures. A predictive theory is developed to correlate the speed of the wave with the liquid\u27s density and the shape of the waveguide\u27s cross-section. The theory is used to optimize the waveguide\u27s geometry so as to increase the sensor\u27s sensitivity. The theoretical results are compared and found to favorably agree with experimental observations

Instrument for Simultaneous Measurement of Density and Viscosity

The speed of torsional stress waves transmitted in solid waveguides submerged in a liquid depends, among other things, on the liquid\u27s density and viscosity and the waveguides\u27 cross-sectional geometry. By measuring the speed of torsional stress waves in two waveguides of different cross-sectional geometries, one can obtain both the liquid\u27s density and viscosity. An online, real-time sensor for the simultaneous measurement of density and viscosity is described. The article details the sensor\u27s principles of operation and reports experimental results conducted using viscosity standard calibration liquids with wen-known thermophysical properties. For fluids with density ρf \u3e 1 X 103 kg/m3 , it is estimated that the instrument can measure density with a precision better than 0.5%. For fluids with the product shear viscosity (µ) and density, ρfµ\u3e 100 kg2/(m4s), it can measure the shear viscosity with a precision better than 1%

Translocation of a Single Stranded DNA Through a Conformationally Changing Nanopore

We investigate the translocation of a single stranded DNA through a pore which fluctuates between two conformations, using coupled master equations. The probability density function of the first passage times (FPT) of the translocation process is calculated, displaying a triple, double or mono peaked behavior, depending on the interconversion rates between the conformations, the applied electric field, and the initial conditions. The cumulative probability function of the FPT, in a field-free environment, is shown to have two regimes, characterized by fast and slow timescales. An analytical expression for the mean first passage time of the translocation process is derived, and provides, in addition to the interconversion rates, an extensive characterization of the translocation process. Relationships to experimental observations are discussed.Comment: 8 pages, 5 figures, Biophys. J., in pres

The Effect of an Adjacent Viscous Fluid on the Transmission of Torsional Stress Waves in a Submerged Waveguide

The effects of an adjacent fluid\u27s viscosity and density on the characteristics of torsional stress waves transmitted in a waveguide with a circular cross section are studied theoretically and experimentally. Expressions for the torsional waves speed, dispersion relations, and attenuation are obtained as functions of the adjacent fluid\u27s viscosity and density. The theoretical results are compared with experimental observations. It is demonstrated that a devices similar to the one described herein can be used as a rugged, real-time, on-lines sensor for measuring the viscosity of a fluid with a known density. Such a sensor can measure the viscosity of fluids with a density viscosity product (ρfμ) greater than 100kg2/m4s to a precision of 1% or bette

Single Stranded DNA Translocation Through A Nanopore: A Master Equation Approach

We study voltage driven translocation of a single stranded (ss) DNA through a membrane channel. Our model, based on a master equation (ME) approach, investigates the probability density function (pdf) of the translocation times, and shows that it can be either double or mono-peaked, depending on the system parameters. We show that the most probable translocation time is proportional to the polymer length, and inversely proportional to the first or second power of the voltage, depending on the initial conditions. The model recovers experimental observations on hetro-polymers when using their properties inside the pore, such as stiffness and polymer-pore interaction.Comment: 7 pages submitted to PR

On the joint residence time of N independent two-dimensional Brownian motions

We study the behavior of several joint residence times of N independent Brownian particles in a disc of radius $R$ in two dimensions. We consider: (i) the time T_N(t) spent by all N particles simultaneously in the disc within the time interval [0,t]; (ii) the time T_N^{(m)}(t) which at least m out of N particles spend together in the disc within the time interval [0,t]; and (iii) the time {\tilde T}_N^{(m)}(t) which exactly m out of N particles spend together in the disc within the time interval [0,t]. We obtain very simple exact expressions for the expectations of these three residence times in the limit t\to\infty.Comment: 8 page