Electrochemical Tuning of the Dielectric Function of Au Nanoparticles

The tunable dielectric response of Au nanoparticles under electrochemical bias can be interpreted in terms of changes in the surface charge density, surface damping, and the near-surface volume fraction of the nanoparticles that experience a modified dielectric function, as well as changes in the index of refraction of the surrounding electrolyte medium. Using experimental bias-dependent extinction measurements, we derive a potential-dependent dielectric function for Au nanoparticles that accounts for changes in the physical properties contributing to the optical extinction

Quantum Magnetism with Polar Alkali Dimers

We show that dipolar interactions between ultracold polar alkali dimers in optical lattices can be used to realize a highly tunable generalization of the t-J model, which we refer to as the t-J-V-W model. The model features long-range spin-spin interactions J_z and J_perp of XXZ type, long-range density-density interaction V, and long-range density-spin interaction W, all of which can be controlled in both magnitude and sign independently of each other and of the tunneling t. The "spin" is encoded in the rotational degree of freedom of the molecules, while the interactions are controlled by applied static electric and continuous-wave microwave fields. Furthermore, we show that nuclear spins of the molecules can be used to implement an additional (orbital) degree of freedom that is coupled to the original rotational degree of freedom in a tunable way. The presented system is expected to exhibit exotic physics and to provide insights into strongly correlated phenomena in condensed matter systems. Realistic experimental imperfections are discussed.Comment: 24 pages, 8 figure

Ab initio phonon coupling and optical response of hot electrons in plasmonic metals

Ultrafast laser measurements probe the nonequilibrium dynamics of excited electrons in metals with increasing temporal resolution. Electronic structure calculations can provide a detailed microscopic understanding of hot electron dynamics, but a parameter-free description of pump-probe measurements has not yet been possible, despite intensive research, because of the phenomenological treatment of electron-phonon interactions. We present ab initio predictions of the electron-temperature dependent heat capacities and electron-phonon coupling coefficients of plasmonic metals. We find substantial differences from free-electron and semiempirical estimates, especially in noble metals above transient electron temperatures of 2000 K, because of the previously neglected strong dependence of electron-phonon matrix elements on electron energy. We also present first-principles calculations of the electron-temperature dependent dielectric response of hot electrons in plasmonic metals, including direct interband and phonon-assisted intraband transitions, facilitating complete theoretical predictions of the time-resolved optical probe signatures in ultrafast laser experiments

New compound sets identified from high throughput phenotypic screening against three kinetoplastid parasites:an open resource

Using whole-cell phenotypic assays, the GlaxoSmithKline high-throughput screening (HTS) diversity set of 1.8 million compounds was screened against the three kinetoplastids most relevant to human disease, i.e. Leishmania donovani, Trypanosoma cruzi and Trypanosoma brucei. Secondary confirmatory and orthogonal intracellular anti-parasiticidal assays were conducted, and the potential for non-specific cytotoxicity determined. Hit compounds were chemically clustered and triaged for desirable physicochemical properties. The hypothetical biological target space covered by these diversity sets was investigated through bioinformatics methodologies. Consequently, three anti-kinetoplastid chemical boxes of ~200 compounds each were assembled. Functional analyses of these compounds suggest a wide array of potential modes of action against kinetoplastid kinases, proteases and cytochromes as well as potential host–pathogen targets. This is the first published parallel high throughput screening of a pharma compound collection against kinetoplastids. The compound sets are provided as an open resource for future lead discovery programs, and to address important research questions.The support and funding of Tres Cantos Open Lab Foundation is gratefully acknowledgedPeer reviewe

Experimental and Ab Initio Ultrafast Carrier Dynamics in Plasmonic Nanoparticles

Ultrafast pump-probe measurements of plasmonic nanostructures probe the nonequilibrium behavior of excited carriers, which involves several competing effects obscured in typical empirical analyses. Here we present pump-probe measurements of plasmonic nanoparticles along with a complete theoretical description based on first-principles calculations of carrier dynamics and optical response, free of any fitting parameters. We account for detailed electronic-structure effects in the density of states, excited carrier distributions, electron-phonon coupling, and dielectric functions that allow us to avoid effective electron temperature approximations. Using this calculation method, we obtain excellent quantitative agreement with spectral and temporal features in transient-absorption measurements. In both our experiments and calculations, we identify the two major contributions of the initial response with distinct signatures: short-lived highly nonthermal excited carriers and longer-lived thermalizing carriers

Plasmoelectric potentials in metal nanostructures

The conversion of optical power to an electrical potential is of general interest for energy applications, and is typically obtained via optical excitation of semiconductor materials. Here, we introduce a new method using an all-metal geometry, based on the plasmon resonance in metal nanostructures. In arrays of Au nanoparticles on an indium-tin-oxide substrate and arrays of 100-nm-diameter holes in 20-nm-thick Au films on a glass substrate, we show negative and positive surface potentials during monochromatic irradiation at wavelengths below or above the plasmon resonance respectively. We observe such plasmoelectric surface potentials as large as 100 mV under 100 mW/cm^2 illumination. Plasmoelectric devices may enable development of entirely new types of all-metal optoelectronic devices that can convert light into electrical energy

Assessment of Noise and Associated Health Impacts at Selected Secondary Schools in Ibadan, Nigeria

Background. Most schools in Ibadan, Nigeria, are located near major roads (mobile line sources). We conducted an initial assessment of noise levels and adverse noise-related health and learning effects. Methods. For this descriptive, cross-sectional study, four schools were selected randomly from eight participating in overall project. We administered 200 questionnaires, 50 per school, assessing health and learning-related outcomes. Noise levels (A-weighted decibels, dBA) were measured with calibrated sound level meters. Traffic density was assessed for school with the highest measured dBA. Observational checklists assessed noise control parameters and building physical attributes. Results. Short-term, cross-sectional school-day noise levels ranged 68.3–84.7 dBA. Over 60% of respondents reported that vehicular traffic was major source of noise, and over 70% complained being disturbed by noise. Three schools reported tiredness, and one school lack of concentration, as the most prevalent noise-related health problems. Conclusion. Secondary school occupants in Ibadan, Nigeria were potentially affected by exposure to noise from mobile line sources

Formal Quantum Efficiencies for the Photocatalytic Reduction of CO2 in a Gas Phase Batch Reactor

The photocatalytic reduction of CO2 to fuels, or useful products, is an area of active research. In this work, nanoengineering and surface modification of titania were investigated as approaches for improving the CO2 reduction efficiency in a fixed-bed gas phase batch photoreactor under UV–vis irradiation. Titania nanotubes were prepared by a hydrothermal method, and TiO2 (P25) was surface modified with copper clusters. Unmodified TiO2 (P25) was used as the bench-mark comparison. The titania nanotubes and Cu-TiO2 materials showed higher efficiency for the photocatalytic reduction of CO2 to yield CH4 as compared to P25. Carbon monoxide yields were similar for all photocatalysts tested. The photocatalytic reduction of CO2 was observed on all photocatalyst tested, with the nanotubes proving to be the most efficient for the production of CH4. The product yields per mass of catalyst observed in this work are similar to those reported in the literature (with similar reactor parameters) but the calculated formal quantum efficiencies for CO2 reduction are very low (4.41 × 10−5 to 5.95 × 10-4)