Search results for "Fluctuations"

Climate fluctuations and trajectories to complexity in the neolithic: towards a theory:

2009

Theories about the emergence and spread of farming in western Eurasia have a long research history. Occasionally, climate fluctuations have served as explanations for short-term culture change. However, the entire Holocene climate fluctuation sequence has so far not been regarded. First steps towards a theory which combines the successive stages in Neolithization and early to Mid-Holocene climate fluctuations are described.

Self-assembly of bioelastomeric structures from solutions: Mean-field critical behavior and Flory-Huggins free energy of interactions

1993

Elastic and quasi-elastic light scattering studies were performed on aqueous solutions of poly (Val-Pro-Gly-Gly), a representative synthetic bioelastomer that differs from the previously studied poly (Val-Pro-Gly-Val-Gly) by the deletion of the hydrophobic Val in position four. When the spinodal line was approached from the region of thermodynamic stability, the intensity of light scattered by fluctuations, and the related lifetime and correlation length, were observed to diverge with mean-field critical exponents for both systems. Fitting of the experimental data allowed determining the spinodal and binodal (coexistence) lines that characterize the phase diagrams of the two systems, and it…

Casimir-Polder force density between an atom and a conducting wall

2007

In this paper we calculate the Casimir-Polder force density (force per unit area acting on the elements of the surface) on a metallic plate placed in front of a neutral atom. To obtain the force density we use the quantum operator associated to the electromagnetic stress tensor. We explicitly show that the integral of this force density over the plate reproduces the total force acting on the plate. This result shows that, although the force is obtained as a sum of surface element-atom contributions, the stress-tensor method includes also nonadditive components of Casimir-Polder forces in the evaluation of the force acting on a macroscopic object.

(no title)

1999

We propose hereafter that the signature of the Space-Time metric (+++-) is not anymore frozen at the Planck scale and presents quantum fluctuations (+++±) untill 0 scale where it becomes Euclidean (++++). (i) At the albraic level we suggest an oscillation path (3,1) (4,0) exluding (2,2). We built the quotient topological space describing the superposition of the Lorentzian and the Riemanian metrics. In terms of quantum groups we evidence a relation between q-deformation and deformation of the signature. We have obtained a new algebraic construction ( a new cocycle bicross products by twisting) which allowed us to unify the Lorentzian and the Euclidean signatures within a unique quantum grou…

Capillary Waves in a Colloid-Polymer Interface

2004

The structure and the statistical fluctuations of interfaces between coexisting phases in the Asakura-Oosawa (AO) model for a colloid--polymer mixture are analyzed by extensive Monte Carlo simulations. We make use of a recently developed grand canonical cluster move with an additional constraint stabilizing the existence of two interfaces in the (rectangular) box that is simulated. Choosing very large systems, of size LxLxD with L=60 and D=120, measured in units of the colloid radius, the spectrum of capillary wave-type interfacial excitations is analyzed in detail. The local position of the interface is defined in terms of a (local) Gibbs surface concept. For small wavevectors capillary wa…

A microscopic approach to Casimir forces between metal bodies

2014

We consider the Casimir interaction between macroscopic metallic objects in terms of the dispersion interactions (Casimir-Polder and van der Waals) between their constituents. Expressions for two- and three-body dispersion interactions between the microscopic parts of a metal are obtained, both in the retarded and non-retarded limits. They are then used to evaluate two- and three-body contributions of the Casimir force between two flat ideal metallic slabs. Our results show the non-applicability of the Hamaker approximation in this geometry. It is further seen that the three-body contributions give an overall repulsive contribution to the force, which is of the same order of magnitude as th…

Dynamical Casimir-Polder forces between an atom and a conducting wall

2008

The promise of spintronics for unconventional computing

2021

Novel computational paradigms may provide the blueprint to help solving the time and energy limitations that we face with our modern computers, and provide solutions to complex problems more efficiently (with reduced time, power consumption and/or less device footprint) than is currently possible with standard approaches. Spintronics offers a promising basis for the development of efficient devices and unconventional operations for at least three main reasons: (i) the low-power requirements of spin-based devices, i.e., requiring no standby power for operation and the possibility to write information with small dynamic energy dissipation, (ii) the strong nonlinearity, time nonlocality, and/o…

Disorder and dephasing effects on electron transport through conjugated molecular wires in molecular junctions

2012

Understanding electron transport processes in molecular wires connected between contacts is a central focus in the field of molecular electronics. Especially, the dephasing effect causing tunneling-to-hopping transition has great importance from both applicational and fundamental points of view. We analyzed coherent and incoherent electron transmission through conjugated molecular wires by means of density-functional tight-binding theory within the D'Amato-Pastawski model. Our approach can study explicitly the structure/transport relationship in molecular junctions in a dephasing environmental condition using only single dephasing parameter. We investigated the length dependence and the inf…

Effects of a uniform acceleration on atom–field interactions

2014

We review some quantum electrodynamical effects related to the uniform acceleration of atoms in vacuum. After discussing the energy level shifts of a uniformly accelerated atom in vacuum, we investigate the atom-wall Casimir-Polder force for accelerated atoms, and the van der Waals/Casimir-Polder interaction between two accelerated atoms. The possibility of detecting the Unruh effect through these phenomena is also discussed in detail.