Surfaces

Landau, Luiz; Lifshitz, E.M.

doi:10.1016/b978-0-08-023039-9.50021-4

Cited by 52 publications

(70 citation statements)

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“…In this context, structural phase transitions of lipids are subjects of particular interest (for reviews, see Laggner, 1988;Caffrey, 1989). Their mechanisms are widely discussed in the theoretical framework of statistical and non-equilibrium thermodynamics (Haken, 1983;Landau & Lifshitz, 1980; cf. Sugar, 1989), and they bear interesting practical implications in important fields, such as membrane biophysics and new materials design based on Langmuir-Blodgett film technology (Tieke, 1990).…”

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confidence: 99%

Structural intermediates in phospholipid phase transitions

Laggner¹,

Kriechbaum²,

Rapp³

1991

J Appl Cryst

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I. IntroductionA new experimental tecFnique to investigate the structural rearrangements associated with thermal phase transitions of phospholipids is outlined. The method utilizes the changes in small-angle X-ray powder diffraction patterns, monitored with a time resolution of down to 1 ms, following fast temperature jumps of about 10 K height in 1-2 ms. This heating rate, effected by an erbium infrared laser pulse, provides a synchronous disequilibration of the lipid samples and the ensuing structural relaxation processes are observed by using the high-flux X-ray beam from a synchrotron source in combination with a rapid position-sensitive-detection and dataacquisition system. For the two symmetryheterologous phase transitions, the lamellar (Ltv)-tomonoclinic (Pt3') 'pretransition' of synthetic phosphatidylcholines and the lamellar (L,,)-to-inverted hexagonal (H.) transition of phosphatidylethanolamines, this method provides the first evidence for the existence of transient intermediate ordered structures. In the pretransition, the first step is the rapid (< 2 ms) formation of a second lamellar lattice, with a decreased repeat distance, which coexists for up to about lOOms with the original L o, lattice. In a second, slower, process, these two lattices merge and transform to the Po" structure within several seconds. In the L,~-Hn transition, the first rapid step (r-5 ms) consists of a uniform shrinkage of the lamellar lattice; this is followed after about 20 ms by the first appearance of a distorted hexagonal lattice and a slow transformation into the final H. lattice. Comparison of these results with X-ray diffraction data obtained under near-equilibrium conditions, where these intermediates cannot be detected, shows that the systems respond to the high thermodynamic driving force which exists under non-linear nonequilibrium conditions by formation of correlated intermediate structures which provide efficient pathways for relaxation.

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confidence: 99%

Structural intermediates in phospholipid phase transitions

Laggner¹,

Kriechbaum²,

Rapp³

1991

J Appl Cryst

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“…(Online version in colour.) 42]. For active systems, the common order parameter is the particle velocity, so that equation (3.1) resembles Newton's second law, where the left-hand side gives the acceleration and the right-hand side the sum of forces acting on the particles.…”

Section: Hysteresis Of the Average Velocity In A Model Swarmmentioning

confidence: 99%

Hysteretic dynamics of active particles in a periodic orienting field

Romensky

Scholz

Lobaskin

2015

J. R. Soc. Interface.

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Active motion of living organisms and artificial self-propelling particles has been an area of intense research at the interface of biology, chemistry and physics. Significant progress in understanding these phenomena has been related to the observation that dynamic self-organization in active systems has much in common with ordering in equilibrium condensed matter such as spontaneous magnetization in ferromagnets. The velocities of active particles may behave similar to magnetic dipoles and develop global alignment, although interactions between the individuals might be completely different. In this work, we show that the dynamics of active particles in external fields can also be described in a way that resembles equilibrium condensed matter. It follows simple general laws, which are independent of the microscopic details of the system. The dynamics is revealed through hysteresis of the mean velocity of active particles subjected to a periodic orienting field. The hysteresis is measured in computer simulations and experiments on unicellular organisms. We find that the ability of the particles to follow the field scales with the ratio of the field variation period to the particles' orientational relaxation time, which, in turn, is related to the particle self-propulsion power and the energy dissipation rate. The collective behaviour of the particles due to aligning interactions manifests itself at low frequencies via increased persistence of the swarm motion when compared with motion of an individual. By contrast, at high field frequencies, the active group fails to develop the alignment and tends to behave like a set of independent individuals even in the presence of interactions. We also report on asymptotic laws for the hysteretic dynamics of active particles, which resemble those in magnetic systems. The generality of the assumptions in the underlying model suggests that the observed laws might apply to a variety of dynamic phenomena from the motion of synthetic active particles to crowd or opinion dynamics.

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“…Consider a self-gravitating fluid governed by the NavierStokes and continuity equations, together with the equation of state of an ideal gas (for example, see Landau & Lifshitz 1987):…”

Section: Basic Equations Of the Dynamical Approachmentioning

confidence: 99%

Gravothermal catastrophe: The dynamical stability of a fluid model

Sormani

Bertin

2013

A&A

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A re-investigation of the gravothermal catastrophe is presented. By means of a linear perturbation analysis, we study the dynamical stability of a spherical self-gravitating isothermal fluid of finite volume and find that the conditions for the onset of the gravothermal catastrophe, under different external conditions, coincide with those obtained from thermodynamical arguments. This suggests that the gravothermal catastrophe may reduce to Jeans instability, rediscovered in an inhomogeneous framework. We find normal modes and frequencies for the fluid system and show that instability develops on the dynamical time scale. We then discuss several related issues. In particular, (1) for perturbations at constant total energy and constant volume, we introduce a simple heuristic term in the energy budget to mimic the role of binaries. (2) We outline the analysis of the two-component case and show how linear perturbation analysis can also be carried out in this more complex context in a relatively straightforward way. (3) We compare the behavior of the fluid model with that of the collisionless sphere. In the collisionless case the instability seems to disappear, which is at variance with the linear Jeans stability analysis in the homogeneous case. We argue that a key ingredient for understanding the difference lies in the role of the detailed angular momentum in a collisionless system. A spherical stellar system is expected to undergo the gravothermal catastrophe only in the presence of some collisionality, which suggests that the instability is dissipative and not dynamical. Finally, we briefly comment on the meaning of the Boltzmann entropy and its applicability to the study of the dynamics of selfgravitating inhomogeneous gaseous systems.

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Surfaces

Cited by 52 publications

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Structural intermediates in phospholipid phase transitions

Structural intermediates in phospholipid phase transitions

Hysteretic dynamics of active particles in a periodic orienting field

Gravothermal catastrophe: The dynamical stability of a fluid model

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