Holographic field theory models of dark energy in interaction with dark matter

We discuss two lagrangian interacting dark energy models in the context of the holographic principle. The potentials of the interacting fields are constructed. The models are compared with CMB distance information, baryonic acoustic oscilations, lookback time and the Constitution supernovae sample. For both models the results are consistent with a non vanishing interaction between dark sectors - with more than three standard deviations of confidence for one of them. Moreover, in both cases, the sign of coupling is consistent with dark energy decaying into dark matter, alleviating the coincidence problem.Comment: arXiv admin note: substantial text overlap with arXiv:0912.399

How to fold intricately: using theory and experiments to unravel the properties of knotted proteins

Over the years, advances in experimental and computational methods have helped us to understand the role of thermodynamic, kinetic and active (chaperone-aided) effects in coordinating the folding steps required to achieving a knotted native state. Here, we review such developments by paying particular attention to the complementarity of experimental and computational studies. Key open issues that could be tackled with either or both approaches are finally pointed out

Anharmonicity and self-similarity of the free energy landscape of protein G

The near-native free energy landscape of protein G is investigated through 0.4 microseconds-long atomistic molecular dynamics simulations in explicit solvent. A theoretical and computational framework is used to assess the time-dependence of salient thermodynamical features. While the quasi-harmonic character of the free energy is found to degrade in a few ns, the slow modes display a very mild dependence on the trajectory duration. This property originates from a striking self-similarity of the free energy landscape embodied by the consistency of the principal directions of the local minima, where the system dwells for several ns, and of the virtual jumps connecting them.Comment: revtex, 6 pages, 5 figure

A complete devil's staircase in the Falicov-Kimball model

We consider the neutral, one-dimensional Falicov-Kimball model at zero temperature in the limit of a large electron--ion attractive potential, U. By calculating the general n-ion interaction terms to leading order in 1/U we argue that the ground-state of the model exhibits the behavior of a complete devil's staircase.Comment: 6 pages, RevTeX, 3 Postscript figure

Role of Secondary Motifs in Fast Folding Polymers: A Dynamical Variational Principle

A fascinating and open question challenging biochemistry, physics and even geometry is the presence of highly regular motifs such as alpha-helices in the folded state of biopolymers and proteins. Stimulating explanations ranging from chemical propensity to simple geometrical reasoning have been invoked to rationalize the existence of such secondary structures. We formulate a dynamical variational principle for selection in conformation space based on the requirement that the backbone of the native state of biologically viable polymers be rapidly accessible from the denatured state. The variational principle is shown to result in the emergence of helical order in compact structures.Comment: 4 pages, RevTex, 4 eps figure

Topological Friction and Relaxation Dynamics of Spatially Confined Catenated Polymers

We study catenated ring polymers confined inside channels and slits with Langevin dynamics simulations and address how the contour position and size of the interlocked or physically linked region evolve with time. We show that the catenation constraints generate a drag, or topological friction, that couples the contour motion of the interlocked regions. Notably, the coupling strength decreases as the interlocking is made tighter, but also shorter, by confinement. Though the coupling strength differs for channel and slit confinement, the data outline a single universal curve when plotted against the size of the linked region. Finally, we study how the relaxation kinetics changes after one of the rings is cut open and conclude that considering interlocked circular polymers is key for isolating the manifestations of topological friction. The results ought to be relevant for linked biomolecules in experimental or biological confining conditions

Body composition symmetry in long-term active middle-aged and older individuals

This study aimed to analyze body composition and strength symmetry in a sample of 165 middle-aged and elderly Italian volunteers, which included 97 active (67 men and 30 women; 61.17 ± 7.56 years) individuals regularly engaged in Tai Chi Chuan, tennis, or running, and a control group of 59 age-matched sedentary (27 men and 32 women) individuals. Anthropometric and bioelectrical measurements and hand grip strength of both sides were collected. Segmental body composition was analyzed through specific bioelectrical impedance vector analysis. The body composition of the right and left limbs was similar among active individuals (arms: T2 = 6.3, n.s.; legs: T2 = 5.0, n.s.), with a similar pattern in the three different disciplines. By contrast, the control group showed bilateral asymmetry (arms: T2 = 6.8, p < 0.001; legs: T2 = 8.8, p < 0.001), mainly because of the higher values of specific reactance (t = 2.4; p = 0.018) and phase angle (t = 2.0; p = 0.054) in the dominant arm, and the higher specific vector length (t = −3.0; p = 0.027) in the left leg. All of the groups showed a higher hand grip strength in the dominant arm (active: t = 7.0, p < 0.001; control: t = 2.9; p < 0.01). In conclusion, the active individuals showed stronger body composition symmetry than the controls, thus indicating a previously undetected positive effect of sport in middle-aged and older adults