Agents and markets

Autonomous agents are intelligent software programs. Typically, agents are situated in an environment. Repeatedly, they sense their environment, engage in some decision making whereby they select actions, and execute their actions, which, in turn, impact their environment. Moreover, in most cases, the environment contains a number of such agents whose actions typically mutually affect one another. This interdependence arises because the different agents, with their own aims and objectives, must operate in a common environment that has finite resources and capabilities. Depending on the dependency's nature, several different types of social interaction occur between the agents, including cooperation, coordination, and negotiation. Autonomous agents are becoming active participants in marketplaces. We present a study on the interactions between autonomous agents and markets.     

Electron-Impact Cross Sections for Ground State to np Excitations of Sodium and Potassium

Cross sections for electron impact excitation of atoms are important for modeling of low temperature plasmas and gases. While there are many experimental and theoretical results for excitation to the first excited states, little information is available for excitation to higher states. We present here calculations of excitations from the ground state to the np levels of sodium (n = 3 through 11) and potassium (n = 4 through 12). We also present a calculation for a transition from the excited sodium level 3p to 3d to show the generality of the method. Scaling formulas developed earlier by Kim [Phys. Rev. A 64, 032713 (2001)] for plane-wave Born cross sections are used. These formulas have been shown to be remarkably accurate yet simple to use. We have used a core polarization potential in a Dirac-Fock wave function code to calculate target atom wave functions and a matching form of the dipole transition operator to calculate oscillator strengths and Born cross sections. The scaled Born results here for excitation to the first excited levels are in very good agreement with experimental and other theoretical data, and the results for excitation to the next few levels are in satisfactory agreement with the limited data available. The present results for excitation to the higher levels are believed to be the only data available.     

Phototoxicity and fluorotoxicity combine to alter the behavior of neutrophils in fluorescence microscopy based flow adhesion assays

The use of fluorescent probes that allow visualization of leukocyte-endothelial cell (EC) interactions has greatly informed our understanding of leukocyte recruitment. However, effects of these agents on the biological functions of leukocytes are poorly described, leading to concerns about the interpretation of such data. Here we used two flow-based neutrophil adhesion assays to compare the effects of phase contrast illumination (PCI) with high intensity illumination (HII) used for fluorescent microscopy, in the presence or absence of five commonly used fluorochromes. Isolated neutrophils were either (1) perfused across P-selectin to establish a population of rolling cells, which were subsequently activated with fMLP; or (2) perfused across EC activated with TNF-alpha. In the absence of fluorescent dyes, HII did not affect levels of leukocyte adhesion; however, subsequent neutrophil behavior was dramatically altered when compared with cells under PCI, for example, dramatically reducing their migration velocities. In the presence of fluorescent dyes, the effects of HII were exacerbated, although the precise nature of the biological effects of these probes was agent specific. Thus, for the first time, our experiments describe the effects of fluorescent microscopy on the separate stages of the neutrophil recruitment process and reveal a previously unsuspected effect of HII on neutrophil migration.     

High precision in-cylinder gas thermometry using Laser Induced Gratings: Quantitative measurement of evaporative cooling with gasoline/alcohol blends in a GDI optical engine

The first application of Laser Induced Thermal Gratings Spectroscopy (LITGS) for precision thermometry in a firing GDI optical engine is reported. Crank-angle resolved temperature values were derived from LITGS signals generated in fuel vapour with a pressure dependent precision in the range 0.1–1.0% allowing differences in evaporative or charge cooling effects arising from a variety of ethanol and methanol blends with a model gasoline fuel to be quantified. In addition, fluctuations in temperature arising from cyclic variations in compression were directly detected and measured.     

Key factors determining the energy rating of existing English houses

In the UK, the Standard Assessment Procedure (SAP) is used to rate the energy performance of existing dwellings whenever they are let or sold. This study investigates which of the inputs to SAP account for the most variance in energy rating across existing gas central heated houses in England. Data from the English Housing Survey (EHS) 2009 are used to generate a representative set of dwellings and variance-based global sensitivity analysis is then applied to assess each input's contribution to the variance in the calculated ratings. It is demonstrated that heating system efficiency, external wall U-value and dwelling geometry account for 75% of the variance of the energy rating of gas central heated houses in England. This suggests that improving heating system efficiencies and wall U-values of the worst performing dwellings will go a long way towards improving their energy rating and potentially reducing their energy consumption. It is also demonstrated that dwelling geometry has a much bigger influence on the calculated carbon emissions (accounting for 80% of the variance) than it does on the SAP energy rating (accounting for 30%), meaning that significant improvements in energy rating might not be accompanied by significant reductions in carbon emissions.     

Shear dispersion in dense granular flows

We formulate and solve a model problem of dispersion of dense granular materials in rapid shear flow down an incline. The effective dispersivity of the depth-averaged concentration of the dispersing powder is shown to vary as the Péclet number squared, as in classical Taylor–Aris dispersion of molecular solutes. An extension to generic shear profiles is presented, and possible applications to industrial and geological granular flows are noted.     

Biomechanics of fibrous proteins of the extracellular matrix studied by Brillouin scattering

Brillouin light scattering (BLS) spectroscopy is a technique that is able to detect thermally excited phonons within a material. The speed of propagation of these phonons can be determined from the magnitude of the Brillouin frequency shift between incident and scattered light, thereby providing a measure of the mechanical properties of the material in the gigahertz range. The mechanical properties of the extracellular matrices of biological tissues and their constituent biopolymers are important for normal tissue function and disturbances in these properties are widely implicated in disease. BLS offers the prospect of measuring mechanical properties on a microscopic scale in living tissues, thereby providing insights into structure–function relationships under normal and pathological conditions. In this study, we investigated BLS in collagen and elastin—the fibrous proteins of the extracellular matrix (ECM). Measurements were made on type I collagen in rat tail tendon, type II collagen in articular cartilage and nuchal ligament elastin. The dependence of the BLS spectrum on fibre orientation was investigated in a backscattering geometry using a reflective substrate. Two peaks, a bulk mode arising from phonon propagation along a quasi-radial direction to the fibre axis and a mode parallel to the surface, depending on sample orientation relative to the fibre axis, could be distinguished. The latter peak was fitted to a model of wave propagation through a hexagonally symmetric elastic solid, and the five components of the elasticity tensor were combined to give axial and transverse Young''s, shear and bulk moduli of the fibres. These were 10.2, 8.3, 3.2 and 10.9 GPa, and 6.1, 5.3, 1.9 and 8 GPa for dehydrated type I collagen and elastin, respectively. The former values are close to those previously reported. A microfocused BLS approach was also applied providing selection of single fibres. The moduli of collagen and elastin are much higher than those measured at lower frequency using macroscopic strains, and the difference between them is much less. We therefore believe, like previous investigators, that molecular-scale viscoelastic effects are responsible for the frequency dependence of the fibre biomechanics. Combining BLS with larger-scale mechanical testing methods therefore should, in the future, provide a means of following the evolution of mechanical properties in the formation of the complex structures found in the ECM.     

Boiling of binary mixtures—study of individual bubbles

Experiments are reported in which individual bubbles of vapour are grown at a plane wall in initially stagnant isothermal liquid. Such tests had already been done and satisfactorily analysed and understood for pure liquids, but here the liquids are binary mixtures of hexane and octane of varying composition.The chief result is that ciné observations of the general behaviour of such bubbles (rate of growth, change of shape, time and size at departure) presents no new problems; it is identical to behaviour in pure liquids, provided one change of parameter is made. That change is to substitute the correct temperature for the evaporating binary interface in place of the saturation temperature for the pure liquid. That interface temperature was determined by reference to recent analytic solutions for evaporation of semi-infinite binary liquid by diffusion of heat and mass.Detailed rapid thermometric observations were also made, of the temperatures at the wall below the bubble and inside the bubble. They showed some aspects which differ markedly from pure liquids (though not such as to affect general behaviour). Those aspects were explained by detailed analysis of diffusion of heat and mass in a thin layer of liquid (microlayer) left beneath the growing bubble.Implications for boiling heat transfer are also considered and it is shown that this analysis of individual bubbles does not, of itself, explain the known reduction in heat transfer coefficient between pure and binary liquids. Several existing methods of explaining that reduction are examined and shown to have a common basis close to that determined by our analysis of single bubbles. But on extending from that basis in a simple way, to predict boiling heat transfer rates, they fail, except where an additional pressure-dependent multiplier is introduced, on purely empirical grounds.