Collective phenomena

An example of electronic collectivity may also be the electronic bistability effect expected to occur in a rigid donor-acceptor oligomer (DA)n, composed of suitable electron donors (D) and acceptors (A) at a proper DA distance and orientation, Fig. 15.5. 

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In favourable contrast to molecular dynamics, BD allows molecular movements of realistically long duration to be simulated. Nevertheless, the practical number of protein molecules which can be simulated is only two since collective phenomena are often of crucial importance in detennining the course of interaction events, other simulation teclmiques, such as cellular automata [115], need to be used to capture the behaviour of large numbers of particles. 

The computation of quantum many-body effects requires additional effort compared to classical cases. This holds in particular if strong collective phenomena such as phase transitions are considered. The path integral approach to critical phenomena allows the computation of collective phenomena at constant temperature — a condition which is preferred experimentally. Due to the link of path integrals to the partition function in statistical physics, methods from the latter — such as Monte Carlo simulation techniques — can be used for efficient computation of quantum effects. 

Biology is presently going through an important phase, as the importance of collective phenomena is becoming very clear (as is the case in other areas). The above-mentioned important and highly complex questions will perhaps only be solved using statistical mechanics and/or dynamic system theory (N. Goldenfeld and C. Woese, 2007). 

Popp F A, Ruth B, Bahr W, Bohm J, Grass P, Grolig G, Rattenmeyer M, Schmidt H G and Wulle P (1981), Emission of visible and ultraviolet radiation by active biological systems , Collective Phenomena, 3, 187-214. 

The typical person is influenced by both an optimistic bias and an illusion of control (Frewer et al., 1994). When these are lost or compromised, panic can occur. While panic disorder can afflict an individual, panic also occurs as a collective phenomena. While it has been thought that emotional instability will lead some people to be more likely to panic, this is not always found. However, people who are emotionally unstable are more likely to attach importance to information provided during the crises than more emotionally stable individuals (Verbeke and Van Kenhove, 2002). Furthermore, some people are more likely to believe they are sick or affected than others. Feldman et al. (1999) examined the panic predisposition of people based on their classification by the big five personality factors. People were inoculated with a common cold virus, and those who were classified as neurotic were more likely to report unfounded illness and more symptoms than other groups. In contrast to this, openness to experience was associated with reporting unfounded symptoms in those with verifiable colds, whereas conscientiousness was associated with reporting unfounded illness in those who were not ill (Feldman et al, 1999). 

One important point is whether narrow bands would display permanent magnetic moments and undergo magnetic collective phenomena. This depends clearly upon their bandwidth and will lead again to the problem localization vs itineracy. In band calculations, new ways have to be looked for, since the set of hypotheses examined previously, which hold for non-magnetic solids, must be corrected for spin-polarization. 

A Fermion dynamical symmetry model which can account for both the low as well as high spin nuclear collective phenomena is presented. 

For a comprehensive discussion, see R. Bengtsson and J. D. Garrett in COLLECTIVE PHENOMENA IN ATOMIC NUCLEI, edited by T. Engeland,... 

Since the molecule is thermalized it does not possess sufficient energy to penetrate the surface of water. This requires energy on the order of the surface tension of the liquid. Therefore, the entry of the molecule into the liquid phase depends on collective phenomena wherein an opening sufficiently large to accommodate the molecule is created at the surface site of the gas molecule. Designating p as the rate at which sufficiently large holes are formed at the surface per unit area per unit time and Am as the area of the molecular site, then the mass accommodation coefficient can be written as... 

The confinement of a relatively large number of dye molecules in the small volume of a nanoparticle may trigger collective phenomena otherwise not observable in bulk solution. This has been demonstrated by Prasad and coworkers in the case of an ORMOSIL pH sensor.69 The PEBBLEs contain a naphthalenylvinylpyridine derivative (NVP) as pH-sensitive fluorescent dye which has been functionalized with a triethoxysilane anchor by reaction with an excess of (3-isocyanatopropyl)triethoxysi-lane (ICTES). The sol-gel polymerization in aqueous micellar solution of the NVP-ICTES derivative with VTES gives spherically shaped 33 nm silica nanoparticles in which the dye is covalently linked to the silica matrix and uniformly distributed in the nanoparticle volume. The NVP dye responds ratiometrically to protons, with a... 

Under high vacuum conditions, i.e., pressure p < 10 2 mbar, the material transfer can be described using Monte Carlo simulations. Usually, inelastic collisions and collective phenomena as shock waves cannot be considered here. The so called Direct Simulation Monte Carlo method allows extension to slightly higher gas pressures. 

For the investigation of collective phenomena it is simplest (although not necessary), with regard to translational symmetry and boundary conditions, to deal with a 3D infinite molecular crystal, the positions and the orientations of the constitutive molecules being given with high precision by X-ray... 

In the first part of this introductory section, we summarize the main collective phenomena acquired by the dipolar exciton from the lattice-symmetry collectivization of molecular properties. The crystal is considered as an assembly of electrically neutral systems, the molecules, physically separated from each other and in electromagnetic interaction. This /V-body problem will be treated quantum-mechanically in the limit of low exciton densities. We redemonstrate the complete equivalence of this treatment with the theories of Lorentz and Ewald, as well as with the semiclassical approximation. In Section I.A, in a more compact but still gradual way, we establish the model of the rigid lattice of dipoles and the general theory of low-exciton-density systems in interaction with the radiation field. Coulombic excitons, photons,... 

The pore formation mechanism presented in Fig. 7 (45) is appealing for many reasons. It illustrates the significance of thermal fluctuations, because the pore is indeed induced by fluctuations in spontaneous salt ion concentrations in the vicinity of the membrane. Furthermore, the pore mediated ion leakage mechanism is very rapid, and it occurs in a collective manner through redistribution and diffusion of lipids around the pore. Also, recent data indicate that the pores also mediate flip-flop events across a membrane (46), which provides one plausible mechanism for lipid translocation, which in turn is of central importance in processes such as programmed cell death. Other dynamic processes in lipid systems are expected to be equally complex, which highlights the importance to understand the interplay between thermal fluctuations, physiologic conditions, and collective phenomena. 

Quantum theory of collective phenomena G. L. Sewell Experimental high-resolution electron microscopy (Second edition)... 

G. L. Sewell, Quantum Theory of Collective Phenomena. Clarendon, Qxford, 1986. 

The impact of bath molecules on the atoms of the molecule of interest cannot be treated as impulsive because the strong binding forces of chemical bonds places a significant fraction of the vibrational sjjectrum of the molecule above the collisional bandwidth, broadly defined as the reciprocal of the duration of a collision. Thus collisional vibrational relaxation and excitation are inefficient relative to rotational relaxation. Binary collision theory is well develojjed at the microcanonical level because of the its importance in chemical reactions. The relationship to the friction is of interest, " primarily because stochastic treatments have the potential of bridging the gas-phase limit of resolved binary collisions and the liquid phase where collective phenomena of the solvent can preclude interpretation in terms of binary collisions. 

M. Muller, K. Katsov, and M. Schick (2003) Coarse-grained models and collective phenomena in membranes Computer simulation of membrane fusion. J. Polym. Sci. B 41, pp. 1441-1450... 

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