Tuning and Switching a Plasmonic Quantum Dot Sandwich in a Nematic Line Defect

We study the quantum-mechanical effects arising in a single semiconductor core/shell quantum dot controllably sandwiched between two plasmonic nanorods. Control over the position and the sandwich confinement structure is achieved by the use of a linear-trap, liquid-crystal line defect and laser tweezers that push the sandwich together. This arrangement allows for the study of exciton plasmon interactions in a single structure, unaltered by ensemble effects or the complexity of dielectric interfaces. We demonstrate the effect of plasmonic confinement on the photon-antibunching behavior of the quantum dot and its luminescence lifetime. The quantum dot behaves as a single emitter when nanorods are far away from the quantum dot but shows possible multiexciton emission and a significantly decreased lifetime when tightly confined in a plasmonic sandwich. These findings demonstrate that liquid crystal defects, combined with laser tweezers, enable a versatile platform to study plasmonic coupling phenomena in a nanoscale laboratory, where all elements can be arranged almost at will.Comment: Supporting information at the en

Comparison of Dye-Sensitized Rutile- and Anatase-Based TiO2 Solar Cells

The objective of this work is to develop and optimize the new dye-sensitized solar cell technology. In view of the infancy of rutile material development for solar cells, the PV response of the dye-sensitized rutile-based solar cell is remarkably close to that of the anatase-based cell

A critical reappraisal of paleomagnetic evidence for Philippine Sea Plate rotation

The kinematic history of the Philippine Sea Plate (PSP) is crucial for interpreting its geological record related to subduction initiation processes and the paleogeography of the junction between the Paleo-Pacific and Tethyan oceanic realms. However, reconstructing PSP's kinematic history is difficult because the plate has been surrounded by subduction zones for most of its history. In absence of marine magnetic anomalies to constrain PSP's motion relative to its neighboring plates, paleomagnetic data may be used as quantitative constraints on its motion. Previous paleomagnetic studies interpreted easterly deflected declinations to infer clockwise rotations of up to 90° since the Eocene. However, rotations inferred from these datasets may also reflect local block rotations related to plate margin deformation. We here re-evaluate to what extent paleomagnetic data from the PSP unequivocally demonstrate plate motion rather than local rotation. To this end, we provide new data from Guam, in the Mariana forearc, and reassess published paleomagnetic data. Our new data from Guam come from two localities in the Eocene, two in the Oligocene, and two in the Miocene. Our compilation assesses data quality against recently defined criteria. Our new results demonstrate that in Guam, declination differences of up to 35° exist in rocks of Eocene age, indicating local rotations. Our compilation identifies both clockwise and counterclockwise rotations from the plate margins, with little confidence which of these would reflect plate-wide rotation. We compiled paleolatitude data from igneous rocks, which we correct for microplate rotation constrained by intra-PSP marine magnetic anomalies and show a northward drift of the PSP of ∼15° since the Eocene, but without a paleomagnetic necessity for major vertical axis rotation. Hence, with the currently available data, rotations of the PSP may be permitted, but are not required. Plate motion is currently better reconstructed from geological constraints contained in circum-PSP orogenic belts

Determining the Locus for Photocarrier Recombination in Dye-Sensitized Solar Cells

We present intensity-modulated photocurrent and infrared transmittance measurements on dye-sensitized solar cells based on a mesoporous titania (TiO2) matrix immersed in an iodine-based electrolyte. Under short-circuit conditions, we show that an elementary analysis accurately relates the two measurements. Under open-circuit conditions, infrared transmittance, and photovoltage measurements yield information on the characteristic depth at which electrons recombine with ions (the ‘‘locus of recombination’’). For one particular series of samples recombination occurred near the substrate supporting the titania film, as opposed to homogeneously throughout the film

A Comparison of the Adaptive Response of Staphylococcus aureus vs. Streptococcus mutans and the Development of Chlorhexidine Resistance

Antimicrobials with nonselective antibacterial efficacy such as chlorhexidine can be effective in reducing biofilm, but bear the risk of inducing resistance in specific bacteria. In clinical practice, bacteria such as Staphylococcus aureus have been found resistant to chlorhexidine, but other bacteria, including Streptococcus mutans, have largely remained susceptible to chlorhexidine despite its widespread use in oral healthcare. Here, we aim to forward a possible reason as to why S. aureus can acquire resistance against chlorhexidine, while S. mutans remains susceptible to chlorhexidine. Measurement of surface-enhanced fluorescence indicated that chlorhexidine caused gradual, but irreversible deformation to adhering green fluorescent S. aureus due to irreparable damage to the cell wall. Concurrently, the metabolic activity of adhering staphylococci was higher than of planktonic bacteria, suggesting efflux mechanisms may have been activated upon cell wall deformation, impeding the buildup of a high chlorhexidine concentration in the cytoplasm and therewith stimulating the development of chlorhexidine resistance in S. aureus. Exposure of S. mutans to chlorhexidine caused immediate, but reversible deformation in adhering streptococci, indicative of rapid self-repair of cell wall damage done by chlorhexidine. Due to cell wall self-repair, S. mutans will be unable to effectively reduce the chlorhexidine concentration in the cytoplasm causing solidification of the cytoplasm. In line, no increased metabolic activity was observed in S. mutans during exposure to chlorhexidine. Therewith, self-repair is suicidal and prevents the development of a chlorhexidine-resistant progeny in S. mutans

In situ interface engineering for probing the limit of quantum dot photovoltaic devices.

Quantum dot (QD) photovoltaic devices are attractive for their low-cost synthesis, tunable band gap and potentially high power conversion efficiency (PCE). However, the experimentally achieved efficiency to date remains far from ideal. Here, we report an in-situ fabrication and investigation of single TiO2-nanowire/CdSe-QD heterojunction solar cell (QDHSC) using a custom-designed photoelectric transmission electron microscope (TEM) holder. A mobile counter electrode is used to precisely tune the interface area for in situ photoelectrical measurements, which reveals a strong interface area dependent PCE. Theoretical simulations show that the simplified single nanowire solar cell structure can minimize the interface area and associated charge scattering to enable an efficient charge collection. Additionally, the optical antenna effect of nanowire-based QDHSCs can further enhance the absorption and boost the PCE. This study establishes a robust 'nanolab' platform in a TEM for in situ photoelectrical studies and provides valuable insight into the interfacial effects in nanoscale solar cells

The Effect of Transposable Element Insertions on Gene Expression Evolution in Rodents

Background:Many genomes contain a substantial number of transposable elements (TEs), a few of which are known to be involved in regulating gene expression. However, recent observations suggest that TEs may have played a very important role in the evolution of gene expression because many conserved non-genic sequences, some of which are know to be involved in gene regulation, resemble TEs. Results:Here we investigate whether new TE insertions affect gene expression profiles by testing whether gene expression divergence between mouse and rat is correlated to the numbers of new transposable elements inserted near genes. We show that expression divergence is significantly correlated to the number of new LTR and SINE elements, but not to the numbers of LINEs. We also show that expression divergence is not significantly correlated to the numbers of ancestral TEs in most cases, which suggests that the correlations between expression divergence and the numbers of new TEs are causal in nature. We quantify the effect and estimate that TE insertion has accounted for ~20% (95% confidence interval: 12% to 26%) of all expression profile divergence in rodents. Conclusions:We conclude that TE insertions may have had a major impact on the evolution of gene expression levels in rodents