Laser-controlled fluorescence in two-level systems

The ability to modify the character of fluorescent emission by a laser-controlled, optically nonlinear process has recently been shown theoretically feasible, and several possible applications have already been identified. In operation, a pulse of off-resonant probe laser beam, of sufficient intensity, is applied to a system exhibiting fluorescence, during the interval of excited- state decay following the initial excitation. The result is a rate of decay that can be controllably modified, the associated changes in fluorescence behavior affording new, chemically specific information. In this paper, a two-level emission model is employed in the further analysis of this all-optical process; the results should prove especially relevant to the analysis and imaging of physical systems employing fluorescent markers, these ranging from quantum dots to green fluorescence protein. Expressions are presented for the laser-controlled fluorescence anisotropy exhibited by samples in which the fluorophores are randomly oriented. It is also shown that, in systems with suitably configured electronic levels and symmetry properties, fluorescence emission can be produced from energy levels that would normally decay nonradiatively. © 2010 American Chemical Society

Motivations for personal financial management: A Self-Determination Theory perspective

Financial knowledge and sound financial decision making are now broadly recognized to be important determinants of both personal and societal prosperity, but research has yet to examine how distinct qualities of motivation may be associated with the way people manage their money. In two studies we applied the framework of Self-Determination Theory (SDT) to examine people's autonomous (volitional) and controlled (pressured) motivation for understanding and managing their finances, as well as their amotivation (lack of motivation) for doing so, and the differential associations these motives have with financial knowledge and financial well-being. American participants (Study 1, N = 516; Study 2, N = 534) completed detailed demographic surveys and questionnaires assessing the financial variables of interest. As hypothesized, SDT's motivational constructs were associated with financial outcomes over and above participants' age, gender, income, household wealth, and educational attainment. Autonomous motivation was positively associated with a host of positive financial behaviors and characteristics (e.g., saving/investing and financial self-efficacy, well-being, and self-awareness). Controlled motivation was negatively associated with financial well-being. Amotivation was positively associated with overspending and negatively associated with financial self-efficacy and well-being. These findings support the relevance of SDT's framework in this domain and suggest that interventions aimed at promoting financial knowledge and wellness may benefit by adopting evidence-supported strategies for optimizing more autonomous motivations and addressing amotivations

Evolution of a mafic volcanic field in the central Great Basin, south central Nevada

This is the published version. Copyright 2012 American Geophysical Union. All Rights Reserved.Evolution of a mafic volcanic field is investigated through a study of Pliocene age rocks in the Reveille Range in south central Nevada. Pliocene activity began with the eruption of relatively abundant hawaiite (episode 1, 5–6 Ma), which was followed by trachytic volcanism (4.3 Ma) and by a second episode of lower-volume hawaiite and basanite (episode 2, 3.0–4.7 Ma). Incompatible elements indicate an asthenospheric source. Isotopically, episode 2 basalts cluster around 87Sr/86Sr = 0.7035 and εNd = +4.2, but episode 1 samples vary to high 87Si/86Sr (up to 0.7060) over a narrow range of εNd (+0.8 to +4.5). Trachytic rocks (MgO ∼ 0.5%) are isotopically akin to the episode 1 basalts. Geochemical variation requires the addition of a crustal component (high 87Sr/86Sr, Sr/Nd, Pb/La, low εNd) to the episode 1 hawaiites and trachytic samples, probably by assimilation of carbonate-rich sedimentary wall rock. The volcanic field developed in at least two eruptive cycles of approximately equal duration. Basanites (deeper and lower percentage melts) appear only in the younger episode. Eruptive episodes were apparently linked to separate melting events in the mantle. Through time, basalts were produced in diminishing volumes by lower percentage melting, magma generation and storage was at greater depths, and magma ascent was at higher velocities. Spatially, the melting anomalies were large in the Pliocene but progressively diminished in size so that by Pleistocene time, volcanism was restricted to a small area near the northern end of the initial outbreak

Sco X-1: The Evolution and Nature of the Twin Compact Radio Lobes

The radio components associated with the LMXB Sco X-1 have been monitored with extensive VLBI imaging at 1.7 and 5.0 GHz over four years, including a 56-hour continuous VLBI observation in 1999 June. We often detected one strong and one weak compact radio component, moving in opposite directions from the radio core. We suggest that the moving components are radio lobes generated by the disruption of energy flow in a twin-beam from the binary system. The average lifetime of a lobe-pair, the space motion of the lobes and the measured energy flow in the beam are discussed in arXiv:astro-ph/0104325. The lobe has a flux density that is variable over a time-scale of one hour, a measured minimum size of 1 mas (2.8 au), and is extended perpendicular to its motion. This short electron radiative lifetime may be caused by synchrotron losses if the lobe magnetic field is 300 G, or by adiabatic expansion of the electrons as soon as they are produced at the working surface. The lobes also show periods of slow expansion and a steepening radio spectrum, perhaps related to the characteristics of the beam energy flow. The radio morphology for Sco X-1 is more simple than for most other Galactic jet sources. The lobes of Sco X-1 are similar to hot-spots found in many extragalactic double sources. Scaling the phenomena observed in Sco X-1 to extragalactic sources implies hot-spot variability time-scales of 10^4 yr and hot-spot lifetimes of 10^5 yr. The recurrent formation of lobes in Sco X-1 probably does not occur for extragalactic radio sources.Comment: 22 pages of text + 16 figures. ApJ, in pres

Modelling the solar transition region using an adaptive conduction method

Funding: European Union Horizon 2020 research and innovation programme (grant agreement No. 647214); the UK Science and Technology Facilities Council through the consolidated grant ST/N000609/1.Modelling the solar Transition Region with the use of an Adaptive Conduction (TRAC) method permits fast and accurate numerical solutions of the field-aligned hydrodynamic equations, capturing the enthalpy exchange between the corona and transition region, when the corona undergoes impulsive heating. The TRAC method eliminates the need for highly resolved numerical grids in the transition region and the commensurate very short time steps that are required for numerical stability. When employed with coarse spatial resolutions, typically achieved in multi-dimensional magnetohydrodynamic codes, the errors at peak density are less than 5% and the computation time is three orders of magnitude faster than fully resolved field-aligned models. This paper presents further examples that demonstrate the versatility and robustness of the method over a range of heating events, including impulsive and quasi-steady footpoint heating. A detailed analytical assessment of the TRAC method is also presented, showing that the approach works through all phases of an impulsive heating event because (i) the total radiative losses and (ii) the total heating when integrated over the transition region are both preserved at all temperatures under the broadening modifications of the method. The results from the numerical simulations complement this conclusion.PostprintPeer reviewe

Structure of smectic defect cores: an X-ray study of 8CB liquid crystal ultra-thin films

We study the structure of very thin liquid crystal films frustrated by antagonistic anchorings in the smectic phase. In a cylindrical geometry, the structure is dominated by the defects for film thicknesses smaller than 150 nm and the detailed topology of the defects cores can be revealed by x-ray diffraction. They appear to be split in half tube-shaped Rotating Grain Boundaries (RGB). We determine the RGB spatial extension and evaluate its energy per unit line. Both are significantly larger than the ones usually proposed in the literatureComment: 4 page

Optically induced forces and torques:Interactions between nanoparticles in a laser beam

Distinctive optical forces and torques arise between nanoparticles irradiated by intense laser radiation. These forces, associated with a pairwise process of stimulated scattering, prove to enable the possibility of producing significant modifications to both the form and magnitude of interparticle forces, with additional contributions arising in the case of dipolar materials. Moreover, such forces have the capacity to generate unusual patterns of nanoscale response, entirely controlled by the input beam characteristics- principally the optical frequency, intensity, and polarization. Based on quantum electrodynamical theory, a general result is secured for the laser-induced force under arbitrary conditions, incorporating both static and dynamic coupling mechanisms. Specific features of the results are identified for pairs of particles with prolate cylindrical symmetry, e.g., carbon nanotubes, where it is shown that the laser-induced forces and torques are sensitive functions of the pair spacing and orientation, and the laser beam geometry; significantly, they can be either repulsive or attractive according to conditions. For nanoparticles trapped in a Laguerre-Gaussian laser beam the results also reveal additional and highly distinctive torques that suggest further possibilities for nanomanipulation with light. The paper concludes with a discussion on several potential applications of such forces. © 2005 The American Physical Society

Interparticle interactions:Energy potentials, energy transfer, and nanoscale mechanical motion in response to optical radiation

In the interactions between particles of material with slightly different electronic levels, unusually large shifts in the pair potential can result from photoexcitation, and on subsequent electronic excitation transfer. To elicit these phenomena, it is necessary to understand the fundamental differences between a variety of optical properties deriving from dispersion interactions, and processes such as resonance energy transfer that occur under laser irradiance. This helps dispel some confusion in the recent literature. By developing and interpreting the theory at a deeper level, one can anticipate that in suitable systems, light absorption and energy transfer will be accompanied by significant displacements in interparticle separation, leading to nanoscale mechanical motion

Asian Influence Over the Western North Pacific during the Fall Season: Inferences from Lead 210, Soluble Ionic Species and Ozone

Aerosol samples collected over the western Pacific during the NASA/Global Tropospheric Experiment Pacific Exploratory Mission (PEM-West A) expedition (September - October 1991) revealed mean Pb-210 concentrations in the free troposphere in the 5-10 fCi m(exp -3) STP range. Most soluble ionic aerosol-associated species were near detection limits [much less than 40 parts per trillion by volume (pptv)] in these same samples. The altitude distribution of O3 near Asia closely resembled that of Pb-210, while no relationship was found between the concentrations of O3 and Be-7. Free tropospheric air over the western Pacific was depleted in soluble aerosol-associated species but enriched in Pb-210 and O3, indicative of deep wet convection over the Asian continent. The influence of Asian air on the composition of the free troposphere over the western Pacific was evident on most of the PEM-West A flights. However, evidence of continental influence was largely restricted to those species that are relatively insoluble (or have insoluble precursors), hence escape scavenging during vertical transport from the boundary layer into the free troposphere by wet convective activity

"Driven to distraction?" Children's experiences of car travel

This is an Author's Accepted Manuscript of an article published in volume, 4, issue 1, pages 59-76 in Mobilities 2009. Copyright @ 2009 Taylor & Francis, available online at: http://www.tandfonline.com/doi/abs/10.1080/17450100802657962.Cars have become increasingly significant features in the lives of many children and adults in the UK and elsewhere. Whilst there is a growing body of research considering how adults experience automobility, that is the increasingly central role of cars within societies, there has been little equivalent research exploring children's perspectives. Drawing upon a variety of methods including personal diaries, photographs, in‐depth interviews and surveys amongst schools within Buckinghamshire and North London, the paper contributes to filling this gap in existing research through exploring how cars are not only journey spaces for children, but are also sites for play, relaxation, homework, companionship, technology and the consumption of commodities. Using a Foucauldian analysis of power, insights into wider familial processes relating to mobility are provided by exploring how cars are sites of conflicting power relations between parents and children. The paper also explores how children's everyday experiences of cars were framed by wider sets of power relations, including car corporations which design and manufacture these spaces, and the role of capital which commodifies everyday activities in cars. In doing so, the paper challenges existing research on automobility for only focusing upon adults' experiences of cars and begins to theorise a more inclusive account of automobility which incorporates children and young people