Showing papers by "Lawrence Berkeley National Laboratory published in 1996"
TL;DR: This biennial Review summarizes much of particle physics, using data from previous editions.
12,798 citations
TL;DR: In this article, the authors focus on the properties of quantum dots and their ability to join the dots into complex assemblies creates many opportunities for scientific discovery, such as the ability of joining the dots to complex assemblies.
Abstract: Current research into semiconductor clusters is focused on the properties of quantum dots-fragments of semiconductor consisting of hundreds to many thousands of atoms-with the bulk bonding geometry and with surface states eliminated by enclosure in a material that has a larger band gap. Quantum dots exhibit strongly size-dependent optical and electrical properties. The ability to join the dots into complex assemblies creates many opportunities for scientific discovery.
10,737 citations
TL;DR: In this paper, the present status and new opportunities for research in this area of materials physical chemistry are reviewed, as well as a review of the present state and opportunities in this field.
Abstract: Semiconductor nanocrystals exhibit a wide range of size-dependent properties. Variations in fundamental characteristics ranging from phase transitions to electrical conductivity can be induced by controlling the size of the crystals. The present status and new opportunities for research in this area of materials physical chemistry are reviewed.
3,493 citations
TL;DR: A strategy for the synthesis of 'nanocrystal molecules', in which discrete numbers of gold nanocrystals are organized into spatially defined structures based on Watson-Crick base-pairing interactions is described.
Abstract: PATTERNING matter on the nanometre scale is an important objective of current materials chemistry and physics. It is driven by both the need to further miniaturize electronic components and the fact that at the nanometre scale, materials properties are strongly size-dependent and thus can be tuned sensitively1. In nanoscale crystals, quantum size effects and the large number of surface atoms influence the, chemical, electronic, magnetic and optical behaviour2—4. 'Top-down' (for example, lithographic) methods for nanoscale manipulation reach only to the upper end of the nanometre regime5; but whereas 'bottom-up' wet chemical techniques allow for the preparation of mono-disperse, defect-free crystallites just 1–10 nm in size6–10, ways to control the structure of nanocrystal assemblies are scarce. Here we describe a strategy for the synthesis of'nanocrystal molecules', in which discrete numbers of gold nanocrystals are organized into spatially defined structures based on Watson-Crick base-pairing interactions. We attach single-stranded DNA oligonucleotides of defined length and sequence to individual nanocrystals, and these assemble into dimers and trimers on addition of a complementary single-stranded DNA template. We anticipate that this approach should allow the construction of more complex two-and three-dimensional assemblies.
2,864 citations
TL;DR: A simple model is described to explain the recombination in these devices, and how the absorption, charge separation, and transport properties of the composites can be controlled by changing the size, material, and surface ligands of the nanocrystals.
Abstract: We study the processes of charge separation and transport in composite materials formed by mixing cadmium selenide or cadmium sulfide nanocrystals with the conjugated polymer poly(2-methoxy,5-(2\ensuremath{'}-ethyl)-hexyloxy-$p$-phenylenevinylene) (MEH-PPV). When the surface of the nanocrystals is treated so as to remove the surface ligand, we find that the polymer photoluminescence is quenched, consistent with rapid charge separation at the polymer/nanocrystal interface. Transmission electron microscopy of these quantum-dot/conjugated-polymer composites shows clear evidence for phase segregation with length scales in the range 10-200 nm, providing a large area of interface for charge separation to occur. Thin-film photovoltaic devices using the composite materials show quantum efficiencies that are significantly improved over those for pure polymer devices, consistent with improved charge separation. At high concentrations of nanocrystals, where both the nanocrystal and polymer components provide continuous pathways to the electrodes, we find quantum efficiencies of up to 12%. We describe a simple model to explain the recombination in these devices, and show how the absorption, charge separation, and transport properties of the composites can be controlled by changing the size, material, and surface ligands of the nanocrystals.
1,517 citations
28 Aug 1996
TL;DR: The RLM protocol is described, its performance is evaluated with a preliminary simulation study that characterizes user-perceived quality by assessing loss rates over multiple time scales, and the implementation of a software-based Internet video codec is discussed.
Abstract: State of the art, real-time, rate-adaptive, multimedia applications adjust their transmission rate to match the available network capacity. Unfortunately, this source-based rate-adaptation performs poorly in a heterogeneous multicast environment because there is no single target rate --- the conflicting bandwidth requirements of all receivers cannot be simultaneously satisfied with one transmission rate. If the burden of rate-adaption is moved from the source to the receivers, heterogeneity is accommodated. One approach to receiver-driven adaptation is to combine a layered source coding algorithm with a layered transmission system. By selectively forwarding subsets of layers at constrained network links, each user receives the best quality signal that the network can deliver. We and others have proposed that selective-forwarding be carried out using multiple IP-Multicast groups where each receiver specifies its level of subscription by joining a subset of the groups. In this paper, we extend the multiple group framework with a rate-adaptation protocol called Receiver-driven Layered Multicast, or RLM. Under RLM, multicast receivers adapt to both the static heterogeneity of link bandwidths as well as dynamic variations in network capacity (i.e., congestion). We describe the RLM protocol and evaluate its performance with a preliminary simulation study that characterizes user-perceived quality by assessing loss rates over multiple time scales. For the configurations we simulated, RLM results in good throughput with transient short-term loss rates on the order of a few percent and long-term loss rates on the order of one percent. Finally, we discuss our implementation of a software-based Internet video codec and its integration with RLM.
1,284 citations
01 Jul 1996
TL;DR: The congestion control algorithms in the simulated implementation of SACK TCP are described and it is shown that while selective acknowledgments are not required to solve Reno TCP's performance problems when multiple packets are dropped, the absence of selective acknowledgements does impose limits to TCP's ultimate performance.
Abstract: This paper uses simulations to explore the benefits of adding selective acknowledgments (SACK) and selective repeat to TCP. We compare Tahoe and Reno TCP, the two most common reference implementations for TCP, with two modified versions of Reno TCP. The first version is New-Reno TCP, a modified version of TCP without SACK that avoids some of Reno TCP's performance problems when multiple packets are dropped from a window of data. The second version is SACK TCP, a conservative extension of Reno TCP modified to use the SACK option being proposed in the Internet Engineering Task Force (IETF). We describe the congestion control algorithms in our simulated implementation of SACK TCP and show that while selective acknowledgments are not required to solve Reno TCP's performance problems when multiple packets are dropped, the absence of selective acknowledgments does impose limits to TCP's ultimate performance. In particular, we show that without selective acknowledgments, TCP implementations are constrained to either retransmit at most one dropped packet per round-trip time, or to retransmit packets that might have already been successfully delivered.
1,228 citations
TL;DR: In this article, the sensitivity of fluorescence resonance energy transfer (FRET) was extended to the single molecule level by measuring energy transfer between a single donor and a single acceptor fluorophore.
Abstract: We extend the sensitivity of fluorescence resonance energy transfer (FRET) to the single molecule level by measuring energy transfer between a single donor fluorophore and a single acceptor fluorophore. Near-field scanning optical microscopy (NSOM) is used to obtain simultaneous dual color images and emission spectra from donor and acceptor fluorophores linked by a short DNA molecule. Photodestruction dynamics of the donor or acceptor are used to determine the presence and efficiency of energy transfer. The classical equations used to measure energy transfer on ensembles of fluorophores are modified for single-molecule measurements. In contrast to ensemble measurements, dynamic events on a molecular scale are observable in single pair FRET measurements because they are not canceled out by random averaging. Monitoring conformational changes, such as rotations and distance changes on a nanometer scale, within single biological macromolecules, may be possible with single pair FRET.
1,172 citations
TL;DR: In this article, the authors derived the cubic law of the Navier-Stokes equations for flow between smooth, parallel plates and showed that the effective hydraulic aperture is less than the mean aperture, by a factor that depends on the ratio of the mean value of the aperture to its standard deviation.
Abstract: The flow of a single-phase fluid through a rough-walled rock fracture is discussed within the context of fluid mechanics. The derivation of the ‘cubic law’ is given as the solution to the Navier-Stokes equations for flow between smooth, parallel plates - the only fracture geometry that is amenable to exact treatment. The various geometric and kinematic conditions that are necessary in order for the Navier-Stokes equations to be replaced by the more tractable lubrication or Hele-Shaw equations are studied and quantified. In general, this requires a sufficiently low flow rate, and some restrictions on the spatial rate of change of the aperture profile. Various analytical and numerical results are reviewed pertaining to the problem of relating the effective hydraulic aperture to the statistics of the aperture distribution. These studies all lead to the conclusion that the effective hydraulic aperture is less than the mean aperture, by a factor that depends on the ratio of the mean value of the aperture to its standard deviation. The tortuosity effect caused by regions where the rock walls are in contact with each other is studied using the Hele-Shaw equations, leading to a simple correction factor that depends on the area fraction occupied by the contact regions. Finally, the predicted hydraulic apertures are compared to measured values for eight data sets from the literature for which aperture and conductivity data were available on the same fracture. It is found that reasonably accurate predictions of hydraulic conductivity can be made based solely on the first two moments of the aperture distribution function, and the proportion of contact area.
1,003 citations
TL;DR: Mn is well suited for the redox role with accessible oxidation states of II, III, and IV, and possibly V: oxidation states that have all been proposed to explain the mechanisms of the Mn redox enzymes.
Abstract: The essential involvement of manganese in photosynthetic water oxidation was implicit in the observation by Pirson in 1937 that plants and algae deprived of Mn in their growth medium lost the ability to evolve O{sub 2}. Addition of this essential element to the growth medium resulted in the restoration of water oxidation within 30 min. There is increased interest in the study of Mn in biological chemistry and dioxygen metabolism in the last two decades with the discovery of several Mn redox enzymes. The list of enzymes where Mn is required for redox activity includes a Mn superoxide dismutase, a binuclear Mn-containing catalase, a binuclear Mn-containing ribonucleotide reductase, a proposed binuclear Mn site in thiosulfate oxidase, a Mn peroxidase that is capable of oxidative degradation of lignin, and perhaps the most complex and important, the tetranuclear Mn-containing oxygen-evolving complex in photosystem II (Mn-OEC). Mn is well suited for the redox role with accessible oxidation states of II, III, and IV, and possibly V: oxidation states that have all been proposed to explain the mechanisms of the Mn redox enzymes.
974 citations
TL;DR: Using electron diffraction data corrected for diffuse scattering together with additional phase information from 30 new images of tilted specimens, an improved experimental density map has been calculated for bacteriorhodopsin and the overall accuracy of the co-ordinates of residues in the other six helices has been improved.
TL;DR: The protocol independent multicast (PIM) architecture maintains the traditional IP multicast service model of receiver-initiated membership, supports both shared and source-specific (shortest-path) distribution trees, and uses soft-state mechanisms to adapt to underlying network conditions and group dynamics.
Abstract: The purpose of multicast routing is to reduce the communication costs for applications that send the same data to multiple recipients. Existing multicast routing mechanisms were intended for use within regions where a group is widely represented or bandwidth is universally plentiful. When group members, and senders to those group members, are distributed sparsely across a wide area, these schemes are not efficient; data packets or membership report information are occasionally sent over many links that do not lead to receivers or senders, respectively. We have developed a multicast routing architecture that efficiently establishes distribution trees across wide area internets, where many groups will be sparsely represented. Efficiency is measured in terms of the router state, control message processing, and data packet processing, required across the entire network in order to deliver data packets to the members of the group. Our protocol independent multicast (PIM) architecture: (a) maintains the traditional IP multicast service model of receiver-initiated membership, (b) supports both shared and source-specific (shortest-path) distribution trees, (c) is not dependent on a specific unicast routing protocol, and (d) uses soft-state mechanisms to adapt to underlying network conditions and group dynamics. The robustness, flexibility, and scaling properties of this architecture make it well-suited to large heterogeneous internetworks.
TL;DR: Stochichiometric variations in the GaN thin films together with the design of specific buffer layers can be utilized to strain engineer the material to an extent that greatly exceeds the possibilities known from other semiconductor systems because of the largely different covalent radii of the Ga and the N atom.
Abstract: Photoluminescence (PL), Raman spectroscopy, and x-ray diffraction are employed to demonstrate the co-existence of a biaxial and a hydrostatic strain that can be present in GaN thin films. The biaxial strain originates from growth on lattice-mismatched substrates and from post-growth cooling. An additional hydrostatic strain is shown to be introduced by the presence of point defects. A consistent description of the experimental results is derived within the limits of the linear and isotropic elastic theory using a Poisson ratio $\ensuremath{
u}=0.23\ifmmode\pm\else\textpm\fi{}0.06$ and a bulk modulus $B=200\ifmmode\pm\else\textpm\fi{}20$ GPa. These isotropic elastic constants help to judge the validity of published anisotropic elastic constants that vary greatly. Calibration constants for strain-induced shifts of the near-band-edge PL lines with respect to the ${E}_{2}$ Raman mode are given for strain-free, biaxially strained, and hydrostatically contracted or expanded thin films. They allow us to extract differences between hydrostatic and biaxial stress components if present. In particular, we determine that a biaxial stress of one GPa would shift the near-band-edge PL lines by 27\ifmmode\pm\else\textpm\fi{}2 meV and the ${E}_{2}$ Raman mode by 4.2\ifmmode\pm\else\textpm\fi{}0.3 ${\mathrm{cm}}^{\ensuremath{-}1}$ by use of the listed isotropic elastic constants. It is expected from the analyses that stoichiometric variations in the GaN thin films together with the design of specific buffer layers can be utilized to strain engineer the material to an extent that greatly exceeds the possibilities known from other semiconductor systems because of the largely different covalent radii of the Ga and the N atom.
TL;DR: The interface between the unit cells of the (8,0) and (5,3) half tubes contains three heptagons, three pentagons, and two hexagons, which are studied to study the configuration in which the hexagons are separated from each other.
Abstract: heptagon pair. The interface between the unit cells of the (8,0) and (5,3) half tubes contains three heptagons, three pentagons, and two hexagons. Two different matching orientations are possible: one with the two hexagons adjacent, the other without. We choose to study the configuration in which the hexagons are separated from each other. The sequence of n-fold rings around the circumference is then 6-7-5-6-7-5-7-5. In the tight-binding p-electron approximation [8], the (8,0) tube has a 1.2 eV gap [1] and the (7,1) tube is a semimetal. Within tight binding, these tubes form an
TL;DR: During channel activation, a stretch of at least seven amino acids of the putative transmembrane segment S4 moved from a buried position into the extracellular environment, providing physical evidence in support of the hypothesis that S4 is the voltage sensor of voltage-gated ion channels.
Abstract: In response to membrane depolarization, voltage-gated ion channels undergo a structural rearrangement that moves charges or dipoles in the membrane electric field and opens the channel-conducting pathway. By combination of site-specific fluorescent labeling of the Shaker potassium channel protein with voltage clamping, this gating conformational change was measured in real time. During channel activation, a stretch of at least seven amino acids of the putative transmembrane segment S4 moved from a buried position into the extracellular environment. This movement correlated with the displacement of the gating charge, providing physical evidence in support of the hypothesis that S4 is the voltage sensor of voltage-gated ion channels.
TL;DR: In this article, the muon anomalous magnetic dipole moment (MDM) is calculated in the framework of the minimal supersymmetric standard model (MSSM), and the contribution of the superparticle loop becomes significant especially when $tan\ensuremath{\beta}$ is large.
Abstract: The muon anomalous magnetic dipole moment (MDM) is calculated in the framework of the minimal supersymmetric standard model (MSSM). In this paper, we discuss how the muon MDM depends on the parameters in the MSSM in detail. We show that the contribution of the superparticle loop becomes significant especially when $tan\ensuremath{\beta}$ is large. Numerically, it becomes of order ${10}^{\ensuremath{-}8}$-${10}^{\ensuremath{-}9}$ in a wide parameter space, which is within the reach of the new Brookhaven E821 experiment.
TL;DR: Oxidative activation offers a novel route for the involvement of TGF beta in tissue processes in which ROS are implicated and endows LTGF beta with the ability to act as a sensor of oxidative stress and to function as a signal for orchestrating the response of multiple cell types.
Abstract: Transforming growth factor beta 1 (TGF beta) is a multifunctional cytokine that orchestrates response to injury via ubiquitous cell surface receptors. The biological activity of TGF beta is restrained by its secretion as a latent complex (LTGF beta) such that activation determines the extent of TGF beta activity during physiological and pathological events. TGF beta action has been implicated in a variety of reactive oxygen-mediated tissue processes, particularly inflammation, and in pathologies such as reperfusion injury, rheumatoid arthritis, and atherosclerosis. It was recently shown to be rapidly activated after in vivo radiation exposure, which also generates reactive oxygen species (ROS). In the present studies, the potential for redox-mediated LTGF beta activation was investigated using a cell-free system in which ROS were generated in solution by ionizing radiation or metal ion-catalyzed ascorbate reaction. Irradiation (100 Gray) of recombinant human LTGF beta in solution induced 26% activation compared with that elicited by standard thermal activation. Metal-catalyzed ascorbate oxidation elicited extremely efficient recombinant LTGF beta activation that matched or exceeded thermal activation. The efficiency of ascorbate activation depended on ascorbate concentrations and the presence of transition metal ions. We postulate that oxidation of specific amino acids in the latency-conferring peptide leads to a conformation change in the latent complex that allows release of TGF beta. Oxidative activation offers a novel route for the involvement of TGF beta in tissue processes in which ROS are implicated and endows LTGF beta with the ability to act as a sensor of oxidative stress and, by releasing TGF beta, to function as a signal for orchestrating the response of multiple cell types. LTGF beta redox sensitivity is presumably directed toward recovery of homeostasis; however, oxidation may also be a mechanism of LTGF beta activation that can be deleterious during disease mechanisms involving chronic ROS production.
TL;DR: When Totem delivers multicast messages, it invokes operations in the same total order throughout the distributed system, resulting in consistency of replicated data and simpli ed programming of applications.
TL;DR: In this paper, the degenerating limits of superconformal theories for compactifications on singular K3 and Calabi-Yau threefolds were studied and the degeneration involves creating an Euclidean two-dimensional black hole coupled weakly to the rest of the system.
TL;DR: In this paper, the boundary states of D-branes wrapped around supersymmetric cycles in a general Calabi-Yau manifold were studied and the geometric data on the cycles were encoded in the boundary state.
TL;DR: The one-dimensional to two-dimensional crossover in these systems is examined and the existence of metallic tube junctions in which the conductance is suppressed for symmetry reasons is shown.
Abstract: We study the conductance of metallic carbon nanotubes with vacancies and pentagon-heptagon pair defects within the Landauer formalism. Using a tight-binding model and a Green's function technique to calculate the scattering matrix, we examine the one-dimensional to two-dimensional crossover in these systems and show the existence of metallic tube junctions in which the conductance is suppressed for symmetry reasons. \textcopyright{} 1996 The American Physical Society.
TL;DR: In this paper, a femtosecond x-ray burst is determined by the transit time of the laser pulse across the ∼ 90-micrometer waist of the focused electron beam.
Abstract: Pulses of x-rays 300 femtoseconds in duration at a wavelength of 04 angstroms (30,000 electron volts) have been generated by 90° Thomson scattering between infrared terawatt laser pulses and highly relativistic electrons from an accelerator In the right-angle scattering geometry, the duration of the x-ray burst is determined by the transit time of the laser pulse across the ∼ 90-micrometer waist of the focused electron beam The x-rays are highly directed (∼ 06° divergence) and can be tuned in energy This source of femtosecond x-rays will make it possible to combine x-ray techniques with ultrafast time resolution to investigate structural dynamics in condensed matter
TL;DR: The results suggest that the general‐stress‐induced transcription of acrAB is primarily mediated by global regulatory pathway(s), and that one major role of AcrR is to function as a specific secondary modulator to fine tune the level of acRAB transcription and to prevent the unwanted overexpression of ac rAB.
Abstract: Summary
Genes acrAB encode a multidrug efflux pump in Escherichia coli. We have previously reported that transcription of acrAB is increased under general stress conditions (i.e. 4% ethanol, 0.5 M NaCl, and the stationary phase in Luria-Bertanl medium). In this study, lacZ transcriptional fusions and an in vitro gel mobility shift assay have been utilized to study the mechanisms governing the regulation of acrAB. We found that a closely linked gene, acrR, encoded a repressor of acrAB. Nevertheless, the general stress conditions increased transcription of acrAB in the absence of functional AcrR, and such conditions surprisingly increased the transcription of acrR even more strongly than that of acrAB. These results suggest that the general-stress-induced transcription of acrAB is primarily mediated by global regulatory pathway(s), and that one major role of AcrR is to function as a specific secondary modulator to fine tune the level of acrAB transcription and to prevent the unwanted overexpression of acrAB. To our knowledge, this represents a novel mechanism of regulating gene expression in E. coli. Evidence also suggests that the up-regulation of acrAB expression under general stress conditions is not likely to be mediated by the known global regulators, such as MarA or SoxS, although elevated levels of these proteins were shown to increase the transcription of acrAB.
28 Aug 1996
TL;DR: It is found that Internet paths are heavily dominated by a single prevalent route, but that the time periods over which routes persist show wide variation, ranging from seconds up to days.
Abstract: The large-scale behavior of routing in the Internet has gone virtually without any formal study, the exception being Chinoy's analysis of the dynamics of Internet routing information [Ch93]. We report on an analysis of 40,000 end-to-end route measurements conducted using repeated "traceroutes" between 37 Internet sites. We analyze the routing behavior for pathological conditions, routing stability, and routing symmetry. For pathologies, we characterize the prevalence of routing loops, erroneous routing, infrastructure failures, and temporary outages. We find that the likelihood of encountering a major routing pathology more than doubled between the end of 1994 and the end of 1995, rising from 1.5% to 3.4%. For routing stability, we define two separate types of stability, "prevalence" meaning the overall likelihood that a particular route is encountered, and "persistence," the likelihood that a route remains unchanged over a long period of time. We find that Internet paths are heavily dominated by a single prevalent route, but that the time periods over which routes persist show wide variation, ranging from seconds up to days. About 2/3's of the Internet paths had routes persisting for either days or weeks. For routing symmetry, we look at the likelihood that a path through the Internet visits at least one different city in the two directions. At the end of 1995, this was the case half the time, and at least one different autonomous system was visited 30% of the time.
TL;DR: A general approach using Bayesian analysis for the estimation of parameters in physiological pharmacokinetic models is described, which includes hierarchical population modeling and informative prior distributions for population parameters.
Abstract: We describe a general approach using Bayesian analysis for the estimation of parameters in physiological pharmacokinetic models. The chief statistical difficulty in estimation with these models is that any physiological model that is even approximately realistic will have a large number of parameters, often comparable to the number of observations in a typical pharmacokinetic experiment (e.g., 28 measurements and 15 parameters for each subject). In addition, the parameters are generally poorly identified, akin to the well-known ill-conditioned problem of estimating a mixture of declining exponentials. Our modeling includes (a) hierarchical population modeling, which allows partial pooling of information among different experimental subjects; (b) a pharmacokinetic model including compartments for well-perfused tissues, poorly perfused tissues, fat, and the liver; and (c) informative prior distributions for population parameters, which is possible because the parameters represent real physiological...
TL;DR: Real time biospecific interaction analysis (surface plasmon resonance, SPR) shows that cholera toxin preferably binds to gangliosides in the following sequence: GM1 > GM2 > GD1A > GM3 > GT1B • GD1B > asialo-GM1.
Abstract: The present study determines the affinity of cholera toxin for the ganglioside series GM1, GM2, GM3, GD1A, GD1B, GT1B, asialo GM1, globotriosyl ceramide, and lactosyl ceramide using real time biospecific interaction analysis (surface plasmon resonance, SPR). SPR shows that cholera toxin preferably binds to gangliosides in the following sequence: GM1 > GM2 > GD1A > GM3 > GT1B > GD1B > asialo-GM1. The measured binding affinity of cholera toxin for the ganglioside sequence ranges from 4.61 x 10-12 M for GM1 to 1.88 x 10-10 M for asialo GM1. The picomolar values obtained by surface plasmon resonance are similar to Kd values determined with whole-cell binding assays. Both whole-cell assays and SPR measurements on synthetic membranes are higher than free solution measurements by several orders of magnitude. This difference may be caused by the effects of avidity and charged lipid head-groups, which may play a major role in the binding between cholera toxin, the receptor, and the membrane surface. The primary difference between free solution binding studies and surface plasmon resonance studies is that the latter technique is performed on surfaces resembling the cell membrane. Surface plasmon resonance has the further advantage of measuring apparent kinetic association and dissociation rates in real time, providing direct information about binding events at the membrane surface.
TL;DR: The study observed and made unambiguous distinctions between abrupt photophysical events of single molecules: a rotational jump of a single dipole, a transition to a dark state (reversible and irreversible photobleaching), and a spectral jump.
Abstract: We observed and made unambiguous distinctions between abrupt photophysical events of single molecules: a rotational jump of a single dipole, a transition to a dark state (reversible and irreversible photobleaching), and a spectral jump. The study was performed in the far field by modulating the excitation polarization and monitoring the fluorescence in time. This technique also allowed us to measure the in-plane dipole orientation of stationary single molecular dipoles with subdegree accuracy and to resolve desorption and readsorption of fluorophores from and onto a glass surface. In one case, clear evidence was obtained for rapid rotation of the dipole after a desorption process. {copyright} {ital 1996 The American Physical Society.}
TL;DR: In this article, it was observed that a significant fraction of COads is oxidized at a much lower (<400 mV) potential than the rest of the COads, a phenomenon that does not occur on any other Pt and Pt-alloy surfaces examined in the same way.
TL;DR: In this paper, a time-dependent departure of the proton spin polarization from its thermal equilibrium is observed, which is an unexpected manifestation of the nuclear Overhauser effect, a consequence of cross-relaxation between the spins of solution protons and dissolved xenon-129.
Abstract: Optical pumping with laser light can be used to polarize the nuclear spins of gaseous xenon-129. When hyperpolarized xenon-129 is dissolved in liquids, a time-dependent departure of the proton spin polarization from its thermal equilibrium is observed. The variation of the magnetization is an unexpected manifestation of the nuclear Overhauser effect, a consequence of cross-relaxation between the spins of solution protons and dissolved xenon-129. Time-resolved magnetic resonance images of both nuclei in solution show that the proton magnetization is selectively perturbed in regions containing spin-polarized xenon-129. This effect could find use in nuclear magnetic resonance spectroscopy of surfaces and proteins and in magnetic resonance imaging.
TL;DR: In this article, a thermal analysis of lithium-ion batteries during charge/discharge and thermal runaway has been carried out with a mathematical model with the main concern with the thermal behavior of the room temperature batteries is the possible significant temperature increase which may cause thermal runaway.
Abstract: A thermal analysis of lithium-ion batteries during charge/discharge and thermal runaway has been carried out with a mathematical model The main concern with the thermal behavior of the room temperature batteries is the possible significant temperature increase which may cause thermal runaway The emphases of this work include the examination of the effects of battery design parameters and operating conditions on temperature rise/profile during normal battery operation and the evaluation of the possibility of the occurrence of thermal runaway due to battery abuse