Line Tension

The effects of waves with a uniform current on marine aquaculture gravity-type cages were analyzed using a numerical model previously validated by physical model tests. The present analysis employs a numerical algorithm to study the dynamic behaviors of the net-cage system when impinged upon by surface waves from various angles over a uniform current. The maximum tension of the mooring lines and the minimum volume reduction coefficients of the rearing system were analyzed. We found that the current-induced effects on the net-cage system were more important than those due to waves only. We conclude that farming sites should not be situated in areas where the current speed exceeds 1 m/s, unless technological devices are available to overcome serious net-cage volume deformation. Furthermore, we recommend that, whenever possible, the combined effects of various oblique waves and currents be carefully examined before a system is installed. Finally, the ideal range of water depth for net-cage implementation in the open sea is between 30 and 50 m.

This paper presents a theoretical model for the electromagnetic radiation (EMR) emissions during plastic deformation and crack propagation in metallic materials. It is shown that under an externally applied stress, edge dislocations within the plastic zone ahead of a crack tip form accelerated electric line dipoles which give rise to the EMR emissions. The dynamic motion of these dislocations becomes overdamped, underdamped or critically damped, depending upon the material/microstructural properties such as mass per unit length of dislocation, line tension, damping coefficient, and distance between the dislocation pinning points. The nature of the EMR signals, viz. exponential decay or damped sinusoidal, is decided essentially by these damping characteristics. The EMR emissions are followed by crack propagation in metallic materials. The EMR has a continuous frequency spectrum with a frequency bandwidth ranging from 108 to 1012 radians s−1, depending upon the properties of the metals. Screw dislocations do not contribute to the EMR emissions. The paper also presents some experimental results on the EMR emissions in ASTM B265 grade 2 titanium sheets. The nature (damped sinusoidal and exponential decay), amplitude and frequency of the observed EMR emissions are in conformity with the predictions of the theoretical model.

We study the effect of critical fluctuations on the $(B,T)$ phase diagram in extreme type-II superconductors in zero and finite magnetic field using large-scale Monte Carlo simulations on the Ginzburg-Landau model in a frozen gauge approximation. We show that a vortex-loop unbinding gives a correct picture of the zero field superconducting-normal transition even in the presence of amplitude fluctuations, which are far from being critical at $T_c$. We extract critical exponents of the dual model by studying the topological excitations of the original model. From the vortex-loop distribution function we extract the anomalous dimension of the dual field $\eta \simeq -0.18$, and conclude that the charged Ginzburg-Landau model and the neutral 3DXY model belong to different universality classes. We find are two distinct scaling regimes for the vortex-line lattice melting line: a high-field scaling regime and a distinct low-field 3DXY critical scaling regime. We also find indications of an abrupt change in the connectivity of the vortex-tangle in the vortex liquid along a line $T_L \geq T_M$. This is the finite field counter-part of the zero-field vortex-loop blowout. Which at low enough fields appears to coincide with $T_M$. Here, a description of the vortex system only in terms of field induced vortex lines is inadequate at and above the VLL melting temperature.

Lung surfactant, a mixture of dipalmitoylphosphatidylcholine, phosphatidylglycerols, fatty acids and four lung surfactant specific proteins, forms tightly packed monolayers at the alveolar interface which are capable of lowering the normal air-water surface tension to almost zero. Isolating the roles of the individual components of lung surfactant is essential to understanding the biophysics of surfactant functioning and to developing new low-cost replacement surfactants. We have used fluorescence microscopy to show that both the full length lung surfactant specific protein SP-B1–78 and a shorter model peptide SP-B1–25 alter the phase behavior and surface morphology of palmitic acid (PA) monolayers. PA is an important component of both natural and replacement lung surfactants. Both the protein and the peptide inhibit the formation of condensed phase in monolayers of PA, resulting in a new fluid PA-protein phase. This fluid phase forms a network that separates condensed phase domains at coexistence. The network persists to high surface pressures, altering the nucleation, growth and morphology of monolayer collapse structures, leading to lower surface tensions on compression and more reversible respreading on expansion, factors essential to the in vivo performance of both natural and replacement lung surfactants. The network is stabilized by the low line tension between the fluid phase and the condensed phase as confirmed by the formation of extended linear domains or “stripe” phases. Similar stripes are found in monolayers of fluorescein-labeled SP-B1–25, suggesting that the reduction in line tension is due to the protein. The peptide retains many of the essential functions of the full length protein and may be a lower cost substitute in replacement surfactants.

We report on theoretical studies of molecularly thin Langmuir films on the surface of a quiescent subfluid and qualitatively compare the results to both new and previous experiments. The film covers the entire fluid surface, but domains of di!erent phases are observed. In the absence of external forcing, the compact domains tend to relax to circles, driven by a line

We analyze in detail the fluctuations and correlations of the (spatial) Fourier modes of nano-scale single-layer islands on (111) fcc crystal surfaces. We analytically show that the Fourier modes of the fluctuations couple due to the anisotropy of the crystal, changing the power spectrum of the fluctuations, and that the actual eigenmodes of the fluctuations are the appropriate linear combinations of the Fourier modes. Using kinetic Monte Carlo simulations with bond-counting parameters that best match realistic energy barriers for hopping rates, we deduce absolute line tensions as a function of azimuthal orientation from the analyses of the fluctuation of each individual mode. The autocorrelation functions of these modes give the scaling of the correlation times with wavelength, providing us with the rate-limiting kinetics driving the fluctuations, here step-edge diffusion. The results for the energetic parameters are in reasonable agreement with available experimental data for Pb(111) surfaces, and we compare the correlation times of island-edge fluctuations to relaxation times of quenched Pb crystallites.

We discuss three topologically different methods for calculating the surface tension between a flat solid and a liquid from theoretical and computer simulation viewpoints. The first method, commonly used in experiments, measures the contact angle at which a static droplet of liquid rests on a solid surface. We present a new analysis algorithm for this method and explore the effects of line tension on the contact angle. The second method, commonly used computer simulations, uses the pressure tensor through the virial in a system where a thick, infinitely extended slab of liquid rests on a solid surface. The third method, which is original to this paper and is closest to the thermodynamic definition of surface tension, applies to a spherical solid in contact with liquid in which the flat solid is recovered by extrapolating the sphere radius to infinity. We find that the second and third methods agree with each other, while the first method systematically underestimates surface tension values.

We report on theoretical studies of molecularly thin Langmuir films on the surface of a quiescent subfluid and qualitatively compare the results to both new and previous experiments. The film covers the entire fluid surface, but domains of different phases are observed. In the absence of external forcing, the compact domains tend to relax to circles, driven by a line tension at the phase boundaries. When stretched (by a transient applied stagnation-point flow or by stirring), a compact domain elongates, creating a bola consisting of two roughly circular reservoirs connected by a thin tether. This shape will then relax slowly to the minimum-energy configuration of a circular domain. The tether is never observed to rupture, even when it is more than a hundred times as long as it is wide. We model these experiments by taking previous descriptions of the full hydrodynamics, identifying the dominant effects via dimensional analysis, and reducing the system to a more tractable form. The r...

... 10:37 AM–10:49 AM. Preview Abstract. Authors: Lu Zou (Kent State University). Jacob M. Pugh (Harvey Mudd College). Elizabeth K. Mann (Kent State University). Andrew J. Bernoff (Harvey Mudd College). James C. Alexander J. Adin Mann, Jr. (Case Western Reserve University ...