Main Types Of Interactions Research Articles

Molecular Plasmonics for Biology and Nanomedicine

The optical excitation of surface plasmons in metal nanoparticles leads to nanoscale spatial confinement of electromagnetic fields. The confined electromagnetic fields can generate intense, localized thermal energy and large near-field optical forces. The interaction between these effects and nearby molecules has led to the emerging field known as molecular plasmonics. Recent advances in molecular plasmonics have enabled novel optical materials and devices with applications in biology and nanomedicine. In this article, we categorize three main types of interactions between molecules and surface plasmons: optical, thermal and mechanical. Within the scope of each type of interaction, we will review applications of molecular plasmonics in biology and nanomedicine. We include a wide range of applications that involve sensing, spectral analysis, imaging, delivery, manipulation and heating of molecules, biomolecules or cells using plasmonic effects. We also briefly describe the physical principles of molecular plasmonics and progress in the nanofabrication, surface functionalization and bioconjugation of metal nanoparticles.

Interparticle interactions in concentrated suspensions and their bulk (Rheological) properties

The interparticle interactions in concentrated suspensions are described. Four main types of interactions can be distinguished: (i) “Hard-sphere” interactions whereby repulsive and attractive forces are screened. (ii) “Soft” or electrostatic interactions determined by double layer repulsion. (iii) Steric repulsion produced by interaction between adsorbed or grafted surfactant and polymer layers. (iv)and van der Waals attraction mainly due to London dispersion forces. Combination of these interaction energies results in three main energy-distance curves: (i) A DLVO type energy-distance curves produced by combination of double layer repulsion and van der Waals attraction. For a stable suspension the energy-distance curve shows a “barrier” (energy maximum) whose height must exceed 25 kT (where k is the Boltzmann constant and T is the absolute temperature). (ii) An energy-distance curve characterized by a shallow attractive minimum at twice the adsorbed layer thickness 2δ and when the interparticle-distance h becomes smaller than 2δ the energy shows a sharp increase with further decrease of h and this is the origin of steric stabilization. (iii) an energy-distance curve characterized by a shallow attractive minimum, an energy maximum of the DLVO type and a sharp increase in energy with further decrease of h due to steric repulsion. This is referred to as electrosteric repulsion. The flocculation of electrostatically and sterically stabilized suspensions is briefly described. A section is devoted to charge neutralization by polyelectrolytes and bridging flocculation by polymers. A distinction could be made between “dilute”, “concentrated” and “solid suspensions” in terms of the balance between the Brownian motion and interparticle interaction. The states of suspension on standing are described in terms of interaction forces and the effect of gravity. The bulk properties (rheology) of concentrated suspensions are described starting with the case of very dilute suspensions (the Einstein limit with volume fraction ϕ ≤ 0.01), moderately concentrated suspensions (0.2 > ϕ ≥ 0.1) taking into account the hydrodynamic interaction and concentrated suspensions (ϕ > 0.2) where semi-empirical theories are available. The rheological behavior of the above four main types of interactions is described starting with “hard-sphere” systems where the relative viscosity–volume fraction relationship could be described. The rheology of electrostatically stabilized suspensions was described with particular reference to the effect of electrolyte that controls the double layer extension. The rheology of sterically stabilized systems is described using model polystyrene suspensions with grafter poly(ethylene oxide) layers. Finally the rheology of flocculated suspensions was described and a distinction could be made between weakly and strongly flocculated systems.

Asymmetric vortex-chain domain walls in triaxial magnetic (110) films

Vortex-like structures of domain walls in triaxial magnetic (110) films are studied within a strict micromagnetic approach and a two-dimensional magnetization distribution approximation by numerically minimizing the total energy functional that includes all main types of interactions, among them the exchange, magnetic-anisotropy, and dipole-dipole (in the continuum approximation) interactions. It is demonstrated that, because of the unusual anisotropy, chains of asymmetric vortex structures can arise in this type of films and that the vortices in the structures increase in number with the film thickness.

Coevolution of economic and ecological systems

This paper analyzes a model of economy–environment coevolution in which economic activities induce the genetic evolution of a biological species. This model is applied to the problem of pesticide resistance management. Just as in Munro (Environ Resour Econ, 9:429–449, 1997), we consider three main types of interactions: (1) a large pest population reduces economic revenues, (2) economic activities select for resistant genes and (3) the spread of resistant genes affects the size of the pest population. The model differs from Munro in that it includes evolutionary modeling of economic strategies. Economic agents are assumed to be boundedly rational, i.e they cannot compute the optimal level of pesticide use that minimizes resistance among pests. Economic evolution represents the change in the distribution of pesticide strategies in the population of economic agents and is modeled by a replicator dynamics equation. The interactions between economic evolution of pesticide strategies, pest population dynamics and genetic evolution of resistance of pests are studied in a system of three differential equations. We explore the dynamics and stability properties of the system using numerical simulations.

Gas phase interaction of L‐proline with Be2+, Mg2+ and Ca2+ ions: a computational study

AbstractGeometry optimisation and metal ion affinities (MIAs) of the binding configurations of Be2+, Mg2+ and Ca2+ to L‐proline were calculated using the hybrid Density Functional Theory (DFT‐B3LYP) and second order Møllet−Plesset perturbation theory (MP2) methods. Be2+ was found to bind preferentially in a charge transfer type arrangement through the carbonyl oxygen (CO) and the lone pair of the imino‐group nitrogen atom (NH). On the contrary Mg2+ and Ca2+ were found to prefer binding in a bi‐dentate manner through the carboxylate group of L‐proline (OCO) in a zwitterion form. The main types of interactions found to influence the binding preference of M2+ ions to L‐proline were (i) charge transfer in the case of Be2+ ions and (ii) electrostatic interactions in the case of Mg2+ and Ca2+ ions. Inspection of the IR stretching of the NH and the OH groups of L‐proline with M2+ ions in a chelating configuration (to both O and N atoms) indicated a considerable shift to higher frequency with decreasing MIA. On the other hand, the MIA for the zwitterion L‐proline with M2+ tracks the reciprocal distance of the M2+OCO bond further confirming that the nature of the bond is mainly electrostatic. Comparison with other molecules containing the carboxylic function is also included in order to gain more insight on the types of interaction of this amino acid with metal ions in general. Copyright © 2007 John Wiley & Sons, Ltd.

Subtidal Underwater Rock Communities of the White Sea: Structure and Interaction with Bottom Flow

The taxonomic composition and quantitative characteristics of typical subtidal rock communities of the White Sea (biocenosis of Laminaria and biocenosis of Lithothamnion and the sponges Polymastia arctica) were studied. The hydrodynamic activity of the near-bottom water layer within and beyond the communities was estimated using the plaster structures technique. A comparative analysis of our results and the literature data revealed three main types of interactions between the benthic community and the water flow: turbulation of the water flow (mussel banks), smoothing of turbulent pulsations (Laminaria community), and an insignificant effect on the water flow (community of Lithothamnion and sponges).

On the success and failure of mixed-species tree plantations: lessons learned from a model system of Eucalyptus globulus and Acacia mearnsii

Mixed plantations of a Eucalyptus species with a nitrogen-fixing tree species can produce significantly higher quantities of aboveground biomass than monocultures. However, if species or sites are not chosen correctly, one species may suppress the growth of the other and mixtures may be less productive than monocultures. Based on a study of Eucalyptus globulus and Acacia mearnsii, this paper discusses the species attributes and site factors that should be considered to improve the probability of increasing biomass production using mixed-species plantations. In an 11-year-old mixed-species trial of E. globulus and A. mearnsii in southeastern Australia aboveground biomass production was twice as high in mixtures containing 50% E. globulus and 50% A. mearnsii than in E. globulus monocultures. There are three main types of interactions that led to this growth outcome: competition, competitive reduction and facilitation. Facilitation occurred as A. mearnsii fixed significant quantities of N, both in monoculture and when mixed with E. globulus. In addition, not only rates of N but also those of P cycling through litterfall were significantly higher in mixed stands than E. globulus monocultures, pointing to the importance of selecting a nitrogen-fixing species that is capable of N fixation and subsequent fast nutrient cycling through litterfall. Mixed stands developed stratified canopies, such that E. globulus eventually overtopped A. mearnsii after 9 years. This resulted in an increase in light capture at the stand level and a reduction in competition for light for E. globulus, a relatively shade intolerant species. This illustrates the importance of selecting species based on their height growth dynamics and relative shade tolerances, to ensure that neither species is suppressed by the other and that the less tolerant species is not overtopped by the more shade tolerant species. In addition to species attributes, site factors, such as soil nitrogen, phosphorus and water availability, play an important role in the interactions and processes occurring in mixtures. In a pot trial containing monocultures and mixtures of E. globulus and A. mearnsii, mixtures produced more biomass than monocultures of either species at low levels of N fertiliser. However, at high levels of N fertiliser E. globulus suppressed A. mearnsii and the biomass production of mixtures was not significantly different to that of E. globulus monocultures. This suggests that mixtures should only be planted on sites where the processes and interactions between species will increase the availability of, or reduce competition for, a major limiting resource for growth at that site. The accurate prediction of successful mixed-species combinations and sites is difficult due to the limited number of studies on mixtures. A mechanistic approach is required to examine the interactions and processes that occur in mixtures and to demonstrate why certain combinations are successful on some sites and not others.

Factors Ruling Protein Adsorption

Abstract In this short review an introduction to the phenomenon of protein adsorption will be given. Protein adsorption often plays the central role in a wide variety of processes occurring in medicine, biochemistry, biotechnology and daily life. The main types of interactions ruling protein adsorption are summarized in this review and the principles of a few powerful experimental techniques to characterize protein adsorbates are outlined. Taking the silica/water interface as an example, the driving forces for protein adsorption are discussed on the basis of recent experimental results. Finally, the interactions of proteins with polyelectrolyte brushes are described. These brushes combine favourable properties of other interfaces and permit a controlled immobilization of protein molecules.

Penetration of beta rays through gold absorbers

The linear transport equation for electrons has been solved adopting the P1 approximation and assuming two main types of interactions with matter: elastic scattering and soft inelastic collisions. The differential cross-section for elastic scattering is calculated using the screened Mott formula. For inelastic processes the differential cross-section is obtained from a simple oscillator strength model. Comparisons are made between the attenuation coefficients for beta rays obtained by solution of the linear transport equation and those obtained experimentally, obtaining a fairly good result.

Calcul des distributions d'amplitude dans les mesures de spectrometrie gamma faites a l'aide de detecteurs au germanium

Taking advantage of the good energy resolution and linearity of germanium lithium drift detectors, we describe a method for the calculation of pulse height distributions observed with these spectrometers for monoenergetic γ rays. This discussion includes the main types of interactions: photoelectric, single and double Compton effects for incident photons and for radiations scattered from surrounding materials. The resulting calculated gamma ray shapes are compared with experimental spectra, the detector considered was a coaxial device with a sensitive volume of 20 cm 3.