Mode Of Energy Transfer Research Articles

Prospects for applications of lanthanide-based upconverting surfaces to bioassay and detection

Biological assays to detect binding interactions are often conducted using fluorescence resonance energy transfer (FRET) but this has several disadvantages that markedly reduce the dynamic range of measurements. The very short range of FRET interactions also causes difficulties when large analytes such as viruses or spores are to be detected. Conventional FRET-based assays can in principle be improved using infrared-excited upconverting lanthanide-based energy donors but this does not address the short range of the FRET process. Here we investigate an alternative mode of energy transfer based on evanescent wave coupling from an erbium-doped waveguide to an absorbed fluorophore and characterise the luminescence from the dopant. The upconverted erbium emission is highly structured with well-separated bands in the violet, green and red spectral regions and very little detectable signal between the peaks. The relative intensity of these bands depends on power-density of infrared excitation. Green emission predominates at low power-density and red emission increases more rapidly as power-density increases, with a smaller violet peak also emerging. The temporal response of the upconverting material to pulsed infrared excitation was investigated and was shown to vary markedly with emission wavelength with the red component being particularly sensitive to the duration of the excitation pulse. A surface monolayer of the fluorescent protein R-phycoerythrin was very easily detected on binding to an upconverting waveguide. The potential advantages and limitations of the evanescent wave excitation technique for fluorescence detection are discussed and avenues for further development are considered.

Microstructural modifications of Ni–Ti shape memory alloy thin films induced by electronic stopping of high-energy heavy ions

The current study is part of an overarching goal to develop an ion implantation process for producing cyclic actuating elements used in microelectromechanical systems. The damage produced by high-energy ions can be used as a means to selectively suppress the martensitic transformation and bias the motion of shape memory alloy thin films Ni–Ti. In order to optimize the performance of these devices, detailed knowledge of the influence of ion implantation on the microstructure is needed. Recent experiments have shown that complex microstructures are formed after 5 MeV Ni ion implantation. In particular, the extensive surface amorphization and the depth distributions of the irradiation induced phase transformations, which were more prominent at shallower depths than expected, did not correlate with ion transport theories involving nuclear stopping damage distributions. Although electronic stopping effects are normally neglected in metals in these energy regimes, they may explain the unexpected surface amorphization since electronic stopping is the prevalent mode of ion energy transfer at shallow depths. Therefore, swift ion irradiation experiments were conducted to assess the effects of electronic stopping on the damage production. Microstructural observations showed that significant damage was produced from ions possessing low electronic stopping powers (<9 keV/nm) near those of 5 MeV Ni ions (3 keV/nm), confirming, in part, that electronic stopping effects contribute to the damage processes.

Fluorescence enhancement and cofluorescence in complexes of terbium(III) with trimellitic acid

The fluorescence of terbium (III) was enhanced by about three orders of magnitude in the presence of trimellitic acid (benzene-1, 2, 4-tricarboxylic acid (TLA)) in aqueous solution at pH 6. The fluorescence intensity could be greatly increased when the system of Tb 3+-TLA was treated with La 3+(or Gd 3+) and TritonX-100. The addition of La 3+(or Gd 3+) enhances the fluorescence of the system by about two orders of magnitude due to cofluorescence, and the TritonX-100 micellar medium plays an important role for stabilization of the system. Both the intermolecular energy transfer mode and intramolecular energy transfer mode are responsible for the mechanism of fluorescence enhancement. In the optimum conditions, the fluorescence intensity is a linear function of Tb 3+ concentration in the range of 7.8 × 10 −9-3.6 × 10 −6 mol/L for the system Tb 3+-La 3+-TLA and 1.0 × 10 −8-4.7 × 10 −6 mol/L for the system Tb 3+-Gd 3+-TLA, and the limits of detection are 4.6 × 10 −10 mol/L and 6.0 × 10 −10 mol/L, respectively.

Management of singlet and triplet excitons for efficient white organic light-emitting devices

Lighting accounts for approximately 22 per cent of the electricity consumed in buildings in the United States, with 40 per cent of that amount consumed by inefficient (approximately 15 lm W(-1)) incandescent lamps. This has generated increased interest in the use of white electroluminescent organic light-emitting devices, owing to their potential for significantly improved efficiency over incandescent sources combined with low-cost, high-throughput manufacturability. The most impressive characteristics of such devices reported to date have been achieved in all-phosphor-doped devices, which have the potential for 100 per cent internal quantum efficiency: the phosphorescent molecules harness the triplet excitons that constitute three-quarters of the bound electron-hole pairs that form during charge injection, and which (unlike the remaining singlet excitons) would otherwise recombine non-radiatively. Here we introduce a different device concept that exploits a blue fluorescent molecule in exchange for a phosphorescent dopant, in combination with green and red phosphor dopants, to yield high power efficiency and stable colour balance, while maintaining the potential for unity internal quantum efficiency. Two distinct modes of energy transfer within this device serve to channel nearly all of the triplet energy to the phosphorescent dopants, retaining the singlet energy exclusively on the blue fluorescent dopant. Additionally, eliminating the exchange energy loss to the blue fluorophore allows for roughly 20 per cent increased power efficiency compared to a fully phosphorescent device. Our device challenges incandescent sources by exhibiting total external quantum and power efficiencies that peak at 18.7 +/- 0.5 per cent and 37.6 +/- 0.6 lm W(-1), respectively, decreasing to 18.4 +/- 0.5 per cent and 23.8 +/- 0.5 lm W(-1) at a high luminance of 500 cd m(-2).

A limit on the energy transfer rate from the human fat store in hypophagia

A limit on the maximum energy transfer rate from the human fat store in hypophagia is deduced from experimental data of underfed subjects maintaining moderate activity levels and is found to have a value of (290±25) kJ/kg d. A dietary restriction which exceeds the limited capability of the fat store to compensate for the energy deficiency results in an immediate decrease in the fat free mass (FFM). In cases of a less severe dietary deficiency, the FFM will not be depleted. The transition between these two dietary regions is developed and a criterion to distinguish the regions is defined. An exact mathematical solution for the decrease of the FFM is derived for the case where the fat mass (FM) is in its limited energy transfer mode. The solution shows a steady-state term which is in agreement with conventional ideas, a term indicating a slow decrease of much of the FFM moderated by the limited energy transferred from the fat store, and a final term showing an unprotected rapid decrease of the remaining part of the FFM. The average resting metabolic rate of subjects undergoing hypophagia is shown to decrease linearly as a function of the FFM with a slope of (249±25) kJ/kg d. This value disagrees with the results of other observers who have measured metabolic rates of diverse groups. The disagreement is explained in terms of individual metabolic properties as opposed to those of the larger population.

Mechanisms of VUV Damage in BaMgAl10O17:Eu2+

We have studied vacuum ultraviolet (VUV)-induced damage processes in BaMgAl10O17:Eu2+ using a unique accelerated life-testing device. Emission, excitation, and reflectance spectra of doped and undoped samples before and after VUV damage reveal two independent mechanisms of degradation. The observed color shift in damaged materials is due to the migration of Eu2+ ions to metastable sites in the lattice. The observed loss of brightness is due in part to the formation of color centers in the spinel layer that act as energy traps and also absorb the exciton emission of the host lattice, thus interrupting the transfer of energy from the host to the activator. Several modes of energy transfer to Eu2+ are available depending on the excitation energy.

Full spectrum k-distribution correlations for CO 2 from the CDSD-1000 spectroscopic databank

Radiative heat transfer through molecular gases is a very important mode of energy transfer when dealing with combustion systems or modelling atmospheric processes. The most accurate radiative transfer results are obtained through line-by-line (LBL) calculations, which require, however, a prohibitively large computational effort. Consequently a number of global and band models have been proposed. Presently, the most accurate global models are the Full-Spectrum k-distributions (FSK) by Modest and coworkers [1, 2]. Earlier, somewhat less refined, related methods include the Spectral-Line-Based WeightedSum-of-Gray-Gases [3–5] or SLW and Absorption-Distribution-Function(ADF) [6, 7] models. All of these methods are orders-of-magnitude more efficient than LBL calculations, and they all use full-spectrum kdistributions, which, in general, need to be calculated from high-resolution databases, such as HITRAN [8], HITEMP [9] or —for CO2— the new CDSD-1000 [10, 11]. Both the SLW and ADF methods use simplified k-distributions reducing them to step-functions (gray gases), whereas the full-spectrum k-distribution method uses Gaussian quadrature to integrate over g-space resulting in better accuracy. Assembling such k-distributions is a rather tedious task and, therefore, to make simple engineering calculations feasible, Denison and Webb [12, 13] have proposed several simple full-spectrum k-distribution correlations for CO2 and H2O, based on the outdated HITRAN92 [8] database, combined with some extrapolations of their own for high temperatures. Recently, Zhang and Modest [14] provided an updated correlation for CO2 based on the newer HITEMP database which is purported to be accurate to at least 1000K. Unfortunately, it appears that the HITEMP database shows some erroneous behavior for temperatures beyond 1200K, as seen by comparison with experimental data [10,15]. The new CDSD-1000 databank [10,11], on the other hand, follows experimental data much more closely. Thus, it is the purpose of this note to provide a simple engineering correlation for full-spectrum k-distributions evaluated from the CDSD-1000 databank. ∗To whom all correspondence should be addressed. Fax: (814)863-8682; Email: mfm6@psu.edu

INCORPORATION OF A TWO-FLUX MODEL FOR RADIATIVE HEAT TRANSFER IN A COMPREHENSIVE FLUIDIZED BED SIMULATOR PART I: PRELIMINARY THEORETICAL INVESTIGATIONS

Over the last two decades, a comprehensive mathematical model and its corresponding computational program, aimed to simulate steady-state operations of bubbling fluidized bed equipments, has been continuously improved and tested. Despite its success, the simulator has employed a simple approach for radiative heat transfers. In cases of high temperatures, thermal radiation becomes an important energy transfer mode and the original model could lead to deviations above acceptable levels. The purpose of the present work was to improve the model for thermal radiation heat transfer between all solid particles in the bed section by applying a two-flux method to a non-homogeneous polydispersed particulate media in radiative equilibrium. Gases in the emulsion and in the bubbles were assumed transparent to thermal radiation. This first part of the paper presents and discusses the basic structure of the former mathematical model and of the new one.

INCORPORATION OF A TWO-FLUX MODEL FOR RADIATIVE HEAT TRANSFER IN A COMPREHENSIVE FLUIDIZED BED SIMULATOR PART I: PRELIMINARY THEORETICAL INVESTIGATIONS

Over the last two decades, a comprehensive mathematical model and its corresponding computational program, aimed to simulate steady-state operations of bubbling fluidized bed equipments, has been continuously improved and tested. Despite its success, the simulator has employed a simple approach for radiative heat transfers. In cases of high temperatures, thermal radiation becomes an important energy transfer mode and the original model could lead to deviations above acceptable levels. The purpose of the present work was to improve the model for thermal radiation heat transfer between all solid particles in the bed section by applying a two-flux method to a non-homogeneous polydispersed particulate media in radiative equilibrium. Gases in the emulsion and in the bubbles were assumed transparent to thermal radiation. This first part of the paper presents and discusses the basic structure of the former mathematical model and of the new one.

Modes of energy transfer from the solar wind to the inner magnetosphere

Energy transport from the interplanetary plasma to Earth’s inner magnetosphere occurs in a range of time scales and efficiencies. It is often hypothesized that this range is smoothly varying with radial geocentric distance, indicating the transport involves many processes, whose ranges overlap. Here we report evidence from observations, and time series analysis, and other data-based modeling which indicates that the coupling of magnetospheric relativistic electron fluxes to solar wind variables occurs in specific ranges of radial distance (L shell). These findings probably have important consequences for the understanding of physical mechanisms responsible for the acceleration in each region. We identify three distinct regions: P0 at approximately 3&amp;lt;L&amp;lt;4 RE, P1 at 4&amp;lt;L&amp;lt;7 RE, and P2 at L&amp;gt;7 RE. Each one responds to a different combination of solar wind variables, and couples to the main driver variable, the solar wind speed VSW, in a different way. Mode P1 is the prototypical response of the inner magnetosphere. The electron flux responds more slowly than the other two regions to VSW (2–3 days): high-speed streams are the most geoeffective structures for that region. Mode P0 responds significantly faster (&amp;lt;1 day) and seems to be more affected by the negative Bz component of the interplanetary field (probably through magnetic reconnection) and the magnitude of the field, rather than by variations in solar wind plasma variables. Region P2 contains much lower fluxes of trapped particles than the other two, and responds rapidly (∼1 day) to positive Bz and to lower solar wind speed. The interpretation is that these regions are representative of different modes of energy transfer from the interplanetary medium to the inner magnetosphere with implications for very different particle acceleration mechanisms.

Simultaneous time resolution of the emission spectra of fluorescent proteins and zooxanthellar chlorophyll in reef-building corals.

Light is absorbed by photosynthetic algal symbionts (i.e. zooxanthellae) and by chromophoric fluorescent proteins (FP) in reef-building coral tissue. We used a streak-camera spectrograph equipped with a pulsed, blue laser diode (50 ps, 405 nm) to simultaneously resolve the fluorescence spectra and kinetics for both the FP and the zooxanthellae. Shallow water (<9 m)-dwelling Acropora spp. and Plesiastrea versipora specimens were collected from Okinawa, Japan, and Sydney, Australia, respectively. The main FP emitted light in the blue, blue-green and green emission regions with each species exhibiting distinct color morphs and spectra. All corals showed rapidly decaying species and reciprocal rises in greener emission components indicating Förster resonance energy transfer (FRET) between FP populations. The energy transfer modes were around 250 ps, and the main decay modes of the acceptor FP were typically 1900-2800 ps. All zooxanthellae emitted similar spectra and kinetics with peak emission (approximately 683 nm) mainly from photosystem II (PSII) chlorophyll (chl) a. Compared with the FP, the PSII emission exhibited similar rise times but much faster decay times, typically around 640-760 ps. The fluorescence kinetics and excitation versus emission mapping indicated that the FP emission played only a minor role, if any, in chl excitation. We thus suggest the FP could only indirectly act to absorb, screen and scatter light to protect PSII and underlying and surrounding animal tissue from excess visible and UV light. We conclude that our time-resolved spectral analysis and simulation revealed new FP emission components that would not be easily resolved at steady state because of their relatively rapid decays due to efficient FRET. We believe the methods show promise for future studies of coral bleaching and for potentially identifying FP species for use as genetic markers and FRET partners, like the related green FP from Aequorea spp.

6] Photophysics of green and red fluorescent proteins: Implications for quantitative microscopy

This chapter describes the implications for quantitative microscopy. The green fluorescent protein (GFP) from the jellyfish Aequorea victoria and its mutants constitute a class of fluorophores that has revolutionized the evaluation of molecular interactions and visualization of biological systems. When fused to proteins of interest and expressed in vivo, fluorescent proteins (FPs) act as versatile indicators of structure and function within cells and can be imaged with the full repertoire of fluorescence microscopy techniques. FPs and their constructs are finding increasing use in fluorescence lifetime imaging microscopy (FLIM) and fluorescence resonance energy transfer (FRET) modes of microspectroscopy for the elucidation of protein-protein interactions, signaling, and trafficking in cellular systems. The simple and the most common, application of FPs is as a passive marker fused to a target protein of interest for visualizing its spatiotemporal distribution. Mutations in and around the chromophore have systematic effects on the spectra. Green and red fluorescent proteins exhibit photophysical properties that are generally more complex than those of traditional fluorophores, for example, fluorescein and rhodamine.

Two‐dimensional structure of auroral poleward boundary intensifications

We investigate the two‐dimensional structure of auroral poleward boundary intensifications (PBIs). PBIs are a nightside auroral intensification that has been studied primarily with ground‐based meridian scanning photometers (MSPs). They have a signature that in the MSP data, appears as an increase in intensity at or near the magnetic separatrix and is often seen to extend equatorward. They are also associated with fast flows in the tail and are thus important to the dynamics of the plasma sheet. MSP data provide information about the temporal evolution of the aurora in one spatial dimension, in this case roughly along a magnetic meridian. This paper is motivated by a desire to determine the physics of PBIs that is revealed by their two‐dimensional structure. To do this, we have identified a number of PBI events in the CANOPUS Rankin Inlet and Gillam MSPs that occurred at times when high‐resolution, two‐dimensional images of the aurora over the same region were also available. The two‐dimensional images used in this study were obtained by the Freja UV imager, from October 1992 to January 1993, and by the CANOPUS Gillam all‐sky imager during the winter viewing season of 1996–1997. We find that PBIs, as observed by the MSPs, are either equatorward extending or non‐equatorward extending. Equatorward extending PBIs are either north‐south aligned structures or east‐west arcs propagating mostly equatorward, but we were not able to determine without doubt which type is the most prevalent. We suggest that equatorward extending PBIs may be the auroral footprint of two major modes of energy transfer in the plasma sheet: multiple, narrow, earthward fast‐flow channels in the plasma sheet and sequences of azimuthally broad and primarily earthward propagating phase fronts initiating near the separatrix. Nonequatorward extending PBIs are found to mostly be a series of multiple bead‐like intensifications along the poleward boundary of the aurora zone. Such PBIs may be evidence for shear instabilities at the separatrix boundary on the flanks of the magnetotail.

Classical theory for scattering of rigid molecules from surfaces

A theoretical model is presented for the scattering of molecules from surfaces under conditions in which the major modes of energy transfer are multiple phonon excitation at the surface and rotational excitations of the molecule. Beginning from a completely quantum mechanical formalism, the classical limit is obtained for large mass molecules and large energies and in this limit the result is a closed-form expression for the scattering intensities. Results of calculations are compared with recent measurements for the scattering of hyperthermal beams of C 2H 2 from a LiF(0 0 1) surface. The results of these comparisons indicate that a classical theoretical treatment of translational and rotational motion is adequate for describing this system.

Hypervelocity penetration modeling: momentum vs. energy and energy transfer mechanisms

Analytic penetration modeling usually relies on either a momentum balance or an energy-rate balance to predict depth of penetration by a penetrator based on initial geometry and impact velocity. In recent years, fairly sophisticated models of penetration have arisen that develop the three-dimensional flow field within a target. Based on the flow field and constitutive assumptions, it is then possible to derive a momentum or an energy-rate balance. This paper examines the use of assumed flow fields within a target created by impact and then examines the resulting predicted behavior based on either momentum conservation or energy conservation. It is shown that for the energy-rate balance to work, the details of the energy transfer mechanisms must be included in the model. In particular, how the projectile energy is initially transferred into target kinetic energy and elastic compression energy must be included. As impact velocity increases, more and more energy during the penetration event is temporarily deposited within the target as elastic compression and target kinetic energy. This energy will be dissipated by the target at a later time, but at the time of penetration it is this transfer of energy that defines the forces acting on the projectile. Thus, for an energy rate balance approach to successfully model penetration, it must include the transfer of energy into kinetic energy within the target and the storage of energy by elastic compression. Understanding the role of energy dissipation in the target clarifies the various terms in analytic models and identifies their origin in terms of the fundamental physics. Understanding the modes of energy transfer also assists in understanding the hypervelocity result that penetration depth only slowly increases with increasing velocity even though the kinetic energy increases as the square of the velocity.

Plume Dynamics in Natural Convection in a Horizontal Cylindrical Annulus

Measurements of the unsteady temperature fluctuations in the plume region between differentially heated horizontal concentric cylinders are reported. In particular, power spectral density estimates of the temperature fluctuations within the plume show the development and breakdown of the oscillatory plume structure at high Rayleigh number, Rad, by two relatively independent processes: (1) the development of harmonic oscillations related to the dominant plume oscillation frequency, and (2) interactions between the oscillating plume and the adjacent relatively stagnant core flow (shear and entrainment). The harmonic oscillations are shown to be the dominant energy transfer mode at moderate Rad (up to Rad = 108), acting to disperse the plume energy without generating a broadband spectrum. The spectral density estimates show that while a distinct plume oscillation is still present near the inner cylinder at Rad = 109, the plume becomes increasingly turbulent as the outer cylinder is approached. A new correlation for the plume oscillation frequency, which is found to be proportional to Rad0.5, is also presented.

Energetic components of the allosteric machinery in hemoglobin measured by hydrogen exchange

A hydrogen exchange (HX) functional labeling method was used to study allosterically active segments in human hemoglobin (Hb) at the α-chain N terminus and the β-chain C terminus. Allosterically important interactions that contact these segments were removed one or more at a time by mutation (Hbs Cowtown, Bunbury, Barcelona, Kariya), proteolysis (desArg141α, desHis146β), chemical modification (N-ethylsuccinimidyl-Cys93β), and the withdrawal of extrinsic effectors (phosphate groups, chloride). The effects of each modification on HX rate at the local and the remote position were measured in the deoxy Hb T-state and translated into change in structural free energy at each position.The removal of individual salt links destabilizes local structure by 0.4 to 0.75 kcal/mol (pH 7.4, 0°C, 0.35 M ionic strength) and often produces cross-subunit effects while hemoglobin remains in the T-state. In doubly modified hemoglobins, different changes that break the same links produce identical destabilization, changes that are structurally independent show energetic additivity, and changes that intersect show energetic overlap. For the overall T-state to R-state transition and for some but not all modifications within the T-state, the summed loss in stabilization free energy measured at the two chain termini matches the total loss in allosteric free energy measured by global methods. These observations illustrate the importance of evaluating the detailed energetics and the modes of energy transfer that define the allosteric machinery.

On assessing and enhancing the energy efficiency of comminution processes

This paper shows how the efficiencies of size-reduction processes depend on the mode of particle constraint and energy transfer within the comminution device: namely, whether the process consists of single-particle loading, confined-particle-bed comminution or loose- (unconstrained-) particle grinding. The relative efficiency of single-particle comminution, ball mill grinding and particle-bed comminution in the recently invented high-pressure roll mill is evaluated by making use of the self-preserving nature of the size distributions of comminuted products. The highest energy efficiency can be achieved by utilizing a hybrid two-stage system in which the material is first ground in the high-pressure roll mill and then the ball mill.

The enigma of microtubules and their self-organizing behavior in the cytoskeleton

The cytoskeleton of eukaryotic cells contains networks of protein polymers called microtubules which structurally and functionally organize their interiors. Both in vivo and in vitro microtubules exhibit a fascinating and yet poorly understood array of important functions involving complex self-organization phenomena which are very sensitive to physiological and laboratory conditions, respectively. In this paper we discuss the main physical characteristics of microtubules focusing our attention on four particular aspects: (a) the dynamics of their assembly and disassembly processes (b) the types and the range of existence of ordered dipolar phases and (c) modes of energy transfer and (d) information processing capabilities.

Supernova neutrino scattering rates reduced by nucleon spin fluctuations: Perturbative limit.

In a nuclear medium, spin-dependent forces cause the nucleon spins to fluctuate with a rate $\Gamma_\sigma$. We have previously shown that as a consequence the effective axial-current neutrino-nucleon scattering cross section is reduced. Here, we calculate this reduction explicitly in the perturbative limit $\Gamma_\sigma\ll T$. By virtue of an exact sum rule of the spin-density structure function, we express the modified cross section in terms of the matrix element for neutrino-nucleon scattering in the presence of a spin-dependent nuclear potential. This representation allows for a direct comparison with and confirmation of Sawyer's related perturbative result. In a supernova core with a typical temperature $T=10\,\rm MeV$, the perturbative limit is relevant for densities $\rho\alt10^{13}\,\rm g\,cm^{-3}$ and thus applies around the neutrino sphere. There, the cross-section reduction is of order a few percent and thus not large; however, a new mode of energy transfer between neutrinos and nucleons is enabled which may be important for neutrino spectra formation. We derive an analytic perturbative expression for the rate of energy transfer.