6,333 research outputs found
Dynamical Models of Extreme Rolling of Vessels in Head Waves
Rolling of a ship is a swinging motion around its length axis. In particular vessels transporting containers may show large amplitude roll when sailing in seas with large head waves. The dynamics of the ship is such that rolling interacts with heave being the motion of the mass point of the ship in vertical direction. Due to the shape of the hull of the vessel its heave is influenced considerably by the phase of the wave as it passes the ship. The interaction of heave and roll can be modeled by a mass-spring-pendulum system. The effect of waves is then included in the system by a periodic forcing term. In first instance the damping of the spring can be taken infinitely large making the system a pendulum with an in vertical direction periodically moving suspension. For a small angular deflection the roll motion is then described by the Mathieu equation containing a periodic forcing. If the period of the solution of the equation without forcing is about twice the period of the forcing then the oscillation gets unstable and the amplitude starts to grow. After describing this model we turn to situation that the ship is not anymore statically fixed at the fluctuating water level. It may move up and down showing a motion
modeled by a damped spring. One step further we also allow for pitch, a swinging motion around a horizontal axis perpendicular to the ship. It is recommended to investigate the way waves may directly drive this mode and to determine the amount of energy that flows along this path towards the roll mode. Since at sea waves are a superposition of waves with different wavelengths, we also pay attention to the properties of such a type of forcing containing stochastic elements. It is recommended that as a measure for the
occurrence of large deflections of the roll angle one should take the expected time for which a given large deflection may occur instead of the mean amplitude of the deflection
Solidification in soft-core fluids: disordered solids from fast solidification fronts
Using dynamical density functional theory we calculate the speed of
solidification fronts advancing into a quenched two-dimensional model fluid of
soft-core particles. We find that solidification fronts can advance via two
different mechanisms, depending on the depth of the quench. For shallow
quenches, the front propagation is via a nonlinear mechanism. For deep
quenches, front propagation is governed by a linear mechanism and in this
regime we are able to determine the front speed via a marginal stability
analysis. We find that the density modulations generated behind the advancing
front have a characteristic scale that differs from the wavelength of the
density modulation in thermodynamic equilibrium, i.e., the spacing between the
crystal planes in an equilibrium crystal. This leads to the subsequent
development of disorder in the solids that are formed. For the one-component
fluid, the particles are able to rearrange to form a well-ordered crystal, with
few defects. However, solidification fronts in a binary mixture exhibiting
crystalline phases with square and hexagonal ordering generate solids that are
unable to rearrange after the passage of the solidification front and a
significant amount of disorder remains in the system.Comment: 18 pages, 14 fig
Criticality and phase separation in a two-dimensional binary colloidal fluid induced by the solvent critical behavior
We present an experimental and theoretical study of the phase behavior of a
binary mixture of colloids with opposite adsorption preferences in a critical
solvent. As a result of the attractive and repulsive critical Casimir forces,
the critical fluctuations of the solvent lead to a further critical point in
the colloidal system, i.e. to a critical colloidal-liquid--colloidal-liquid
demixing phase transition which is controlled by the solvent temperature. Our
experimental findings are in good agreement with calculations based on a simple
approximation for the free energy of the system.Comment: 5 pages, 5 figures, to be published in Europhysics Letter
Colonic Protein Fermentation and Promotion of Colon Carcinogenesis by Thermolyzed Casein
Thermolyzed casein is known to promote the growth of aberrant crypt foci (ACF) and colon cancer when it is fed to rats that have been initiated with azoxymethane. We speculated that the promotion was a consequence of increased colonic protein fermentation (i.e., that the thermolysis of the casein decreases its digestibility, increases the amount of protein reaching the colon, and increases colonic protein fermentation and that the potentially toxic products of this fermentation promote colon carcinogenesis). We found that the thermolysis of casein reduces its digestibility and increases colonic protein fermentation, as assessed by fecal ammonium and urinary phenol, cresol, and indol-3-ol. Thermolysis of two other proteins, soy and egg white protein, also increases colonic protein fermentation with increased fecal ammonia and urinary phenols, and thermolysis of all three proteins increases the levels of ammonia and butyric, valeric, and i-valeric acids in the cecal contents. We found, however, that the increased protein fermentation observed with thermolysis is not associated with pro-motion of colon carcinogenesis. With casein, the kinetics of protein fermentation with increasing thermolysis time are clearly different from the kinetics of promotion of ACF growth. The formation of the fermentation products was highest when the protein was thermolyzed for one hour, whereas promotion was highest for protein that had been thermolyzed for two or more hours. With soy and egg white, thermolysis increased colonic protein fermentation but did not promote colon carcinogenesis. Thus, although thermolysis of dietary casein increases colonic protein fermentation, products of this fermentation do not appear to be responsible for the promotion of colon carcinogenesis. Indeed, the results suggest that protein fermentation products do not play an important role in colon cancer promotion
Effect of Growth Arrestment Disease on the Anatomy and Ultrastructure of Vitis vinifera L. var. sultana
The anatomical and ultrastructural changes caused by the so called Growth Arrestment Disease (G.A.D.) in Vitis vinifera L. var. sultana were investigated by means of scanning and transmitted electron microscopy as well as light microscopy. Important morphological symptoms are described. Anatomical abnormalities were found, especially in the leaves and Hower clusters of the affected vines. Heat and moisture stress may induce abnormal physiological changes, and this may give rise to G.A.D.-symptoms
Static and Dynamic Properties of Type-II Composite Fermion Wigner Crystals
The Wigner crystal of composite fermions is a strongly correlated state of
complex emergent particles, and therefore its unambiguous detection would be of
significant importance. Recent observation of optical resonances in the
vicinity of filling factor {\nu} = 1/3 has been interpreted as evidence for a
pinned Wigner crystal of composite fermions [Zhu et al., Phys. Rev. Lett. 105,
126803 (2010)]. We evaluate in a microscopic theory the shear modulus and the
magnetophonon and magnetoplasmon dispersions of the composite fermion Wigner
crystal in the vicinity of filling factors 1/3, 2/5, and 3/7. We determine the
region of stability of the crystal phase, and also relate the frequency of its
pinning mode to that of the corresponding electron crystal near integer
fillings. These results are in good semiquantitative agreement with experiment,
and therefore support the identification of the optical resonance as the
pinning mode of the composite fermions Wigner crystal. Our calculations also
bring out certain puzzling features, such as a relatively small melting
temperature for the composite fermion Wigner crystal, and also suggest a higher
asymmetry between Wigner crystals of composite fermion particles and holes than
that observed experimentally.Comment: Composite Fermion Wigner Crystal; 14 pages, 9 figure
Density functional approach for inhomogeneous star polymers
We propose microscopic density functional theory for inhomogeneous star
polymers. Our approach is based on fundamental measure theory for hard spheres,
and on Wertheim's first- and second-order perturbation theory for the
interparticle connectivity. For simplicity we consider a model in which all the
arms are of the same length, but our approach can be easily extended to the
case of stars with arms of arbitrary lengths.Comment: 4 pages, 3 figures, submitte
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