Correlating and predicting the air infiltration through the cracks of suspended timber floors

This paper shows that the visible gap length may be used as a physical parameter when correlating pressure difference to volume flow rate (or air velocity) through the cracks between floorboards and can be termed the Equivalent Crack Length. The crack widths, which previously have been determined separately from the edge effect coefficient and the laminar flow coefficient, were significantly different. When analysed graphically they can be shown to correlate by an empirical relationship. A generalised equation is proposed that, in conjunction with the empirical relationship, allows predictions to be made of the volume flow rate through the cracks between floorboards for a known pressure difference

How strong are the Rossby vortices?

The Rossby wave instability, associated with density bumps in differentially rotating discs, may arise in several different astrophysical contexts, such as galactic or protoplanetary discs. While the linear phase of the instability has been well studied, the nonlinear evolution and especially the saturation phase remain poorly understood. In this paper, we test the non-linear saturation mechanism analogous to that derived for wave-particle interaction in plasma physics. To this end we perform global numerical simulations of the evolution of the instability in a two-dimensional disc. We confirm the physical mechanism for the instability saturation and show that the maximum amplitude of vorticity can be estimated as twice the linear growth rate of the instability. We provide an empirical fitting formula for this growth rate for various parameters of the density bump. We also investigate the effects of the azimuthal mode number of the instability and the energy leakage in the spiral density waves. Finally, we show that our results can be extrapolated to 3D discs.Comment: Accepted for publication in MNRA

Spectrins in Axonal Cytoskeletons: Dynamics Revealed by Extensions and Fluctuations

The macroscopic properties, the properties of individual components and how those components interact with each other are three important aspects of a composited structure. An understanding of the interplay between them is essential in the study of complex systems. Using axonal cytoskeleton as an example system, here we perform a theoretical study of slender structures that can be coarse-grained as a simple smooth 3-dimensional curve. We first present a generic model for such systems based on the fundamental theorem of curves. We use this generic model to demonstrate the applicability of the well-known worm-like chain (WLC) model to the network level and investigate the situation when the system is stretched by strong forces (weakly bending limit). We specifically studied recent experimental observations that revealed the hitherto unknown periodic cytoskeleton structure of axons and measured the longitudinal fluctuations. Instead of focusing on single molecules, we apply analytical results from the WLC model to both single molecule and network levels and focus on the relations between extensions and fluctuations. We show how this approach introduces constraints to possible local dynamics of the spectrin tetramers in the axonal cytoskeleton and finally suggests simple but self-consistent dynamics of spectrins in which the spectrins in one spatial period of axons fluctuate in-sync.Comment: 18 pages, 4 figure

Cusp-scaling behavior in fractal dimension of chaotic scattering

A topological bifurcation in chaotic scattering is characterized by a sudden change in the topology of the infinite set of unstable periodic orbits embedded in the underlying chaotic invariant set. We uncover a scaling law for the fractal dimension of the chaotic set for such a bifurcation. Our analysis and numerical computations in both two- and three-degrees-of-freedom systems suggest a striking feature associated with these subtle bifurcations: the dimension typically exhibits a sharp, cusplike local minimum at the bifurcation.Comment: 4 pages, 4 figures, Revte

Comparison of 3D computation and experiment for non-axisymmetric nozzles

Three dimensional solutions of a single expansion ramp nozzle are computed with the existing PARC computer code by solving the full Navier-Stokes equations. The computations are performed to simulate the non-axisymmetric nozzle flowfield in both the internal/external expansion regions and the exhaust plume in a quiescent ambient environment. Two different configurations of the nozzle at a pressure ratio NPR = 10 are examined. Numerical results of laminar flows are presented, and the wall pressure distributions are compared with the experimental data

Sheath ionization model of beam emissions from large spacecraft

An analytical model of the charging of a spacecraft emitting electron and ion beams has been applied to the case of large spacecraft. In this model, ionization occurs in the sheath due to the return current. Charge neutralization of spherical space charge flow is examined by solving analytical equations numerically. Parametric studies of potential large spacecraft are performed. As in the case of small spacecraft, the ions created in the sheath by the returning current play a large role in determining spacecraft potential

USING THE MINNESOTA FARM RECORDS DATA BASE: 1977-82 DATA

Farm Management,

Two-dimensional viscous flow computations of hypersonic scramjet nozzle flowfields at design and off-design conditions

The PARC2D code has been selected to analyze the flowfields of a representative hypersonic scramjet nozzle over a range of flight conditions from Mach 3 to 20. The flowfields, wall pressures, wall skin friction values, heat transfer values and overall nozzle performance are presented