Hydrodynamic interactions in active colloidal crystal microrheology

In dense colloids it is commonly assumed that hydrodynamic interactions do not play a role. However, a found theoretical quantification is often missing. We present computer simulations that are motivated by experiments where a large colloidal particle is dragged through a colloidal crystal. To qualify the influence of long-ranged hydrodynamics, we model the setup by conventional Langevin dynamics simulations and by an improved scheme with limited hydrodynamic interactions. This scheme significantly improves our results and allows to show that hydrodynamics strongly impacts on the development of defects, the crystal regeneration as well as on the jamming behavior.Comment: 5 pages, 4 figure

Purcell factor for point-like dipolar emitter coupling to 2D-plasmonic waveguides

We theoretically investigate the spontaneous emission of a point--like dipolar emitter located near a two--dimensional (2D) plasmonic waveguide of arbitrary form. We invoke an explicite link with the density of modes of the waveguide describing the electromagnetic channels into which the emitter can couple. We obtain a closed form expression for the coupling to propagative plasmon, extending thus the Purcell factor to plasmonic configurations. Radiative and non-radiative contributions to the spontaneous emission are also discussed in details

Polarization state of the optical near-field

The polarization state of the optical electromagnetic field lying several nanometers above complex dielectric structures reveals the intricate light-matter interaction that occurs in this near-field zone. This information can only be extracted from an analysis of the polarization state of the detected light in the near-field. These polarization states can be calculated by different numerical methods well-suited to near--field optics. In this paper, we apply two different techniques (Localized Green Function Method and Differential Theory of Gratings) to separate each polarisation component associated with both electric and magnetic optical near-fields produced by nanometer sized objects. The analysis is carried out in two stages: in the first stage, we use a simple dipolar model to achieve insight into the physical origin of the near-field polarization state. In the second stage, we calculate accurate numerical field maps, simulating experimental near-field light detection, to supplement the data produced by analytical models. We conclude this study by demonstrating the role played by the near-field polarization in the formation of the local density of states.Comment: 9 pages, 11 figures, accepted for publication in Phys. Rev.

Colloids dragged through a polymer solution: experiment, theory and simulation

We present micro-rheological measurments of the drag force on colloids pulled through a solution of lambda-DNA (used here as a monodisperse model polymer) with an optical tweezer. The experiments show a violation of the Stokes-Einstein relation based on the independently measured viscosity of the DNA solution: the drag force is larger than expected. We attribute this to the accumulation of DNA infront of the colloid and the reduced DNA density behind the colloid. This hypothesis is corroborated by a simple drift-diffusion model for the DNA molecules, which reproduces the experimental data surprisingly well, as well as by corresponding Brownian dynamics simulations.Comment: 9 pages, 13 figures, 3 table

Unfinished Business: a Review of the Implementation of the Provisions of United Nations General Assembly Resolutions 61/105 and 64/72, Related to the Management of Bottom Fisheries in Areas Beyond National Jurisdiction

In 2006 the General Assembly adopted resolution 61/105, based on a compromise proposal offered by deep-sea fishing nations, which committed States and regional fisheries management organisations [RFMOs] to take specific measures to protect vulnerable marine ecosystems [VMEs] from the adverse impacts of bottom fisheries in the high seas and to ensure the longterm sustainability of deep-sea fish stocks. These measures included conducting impact assessments to determine whether significant adverse impacts[SAIs] to VMEs would occur, managing fisheries to prevent SAIs on VMEs, and closing areas of the high seas to bottom fishing where VMEs are known or likely to occur, unless regulations are in place to prevent SAIs and to manage sustainably deep-sea fish stocks. Based on a review in 2009 of the actions taken by States and RFMOS, the UNGA adoptedresolution 64/72 that reaffirmed resolution 61/105 and strengthened the call for action through committing States, inter alia, to ensure that vessels do not engage in bottom fishing until impact assessments have been carried out and to not authorise bottom fishing activities until the measures in resolutions 64/72 and 61/105 have been adopted andimplemented

Similarities and differences in structure, expression, and functions of VLDLR and ApoER2

Very Low Density Lipoprotein Receptor (VLDLR) and Apolipoprotein E Receptor 2 (ApoER2) are important receptors in the brain for mediating the signaling effects of the extracellular matrix protein Reelin, affecting neuronal function in development and in the adult brain. VLDLR and ApoER2 are members of the low density lipoprotein family, which also mediates the effects of numerous other extracellular ligands, including apolipoprotein E. Although VLDLR and ApoER2 are highly homologous, they differ in a number of ways, including structural differences, expression patterns, alternative splicing, and binding of extracellular and intracellular proteins. This review aims to summarize important aspects of VLDLR and ApoER2 that may account for interesting recent findings that highlight the unique functions of each receptor

Altered hippocampus synaptic function in selenoprotein P deficient mice

Selenium is an essential micronutrient that function through selenoproteins. Selenium deficiency results in lower concentrations of selenium and selenoproteins. The brain maintains it's selenium better than other tissues under low-selenium conditions. Recently, the selenium-containing protein selenoprotein P (Sepp) has been identified as a possible transporter of selenium. The targeted disruption of the selenoprotein P gene (Sepp1) results in decreased brain selenium concentration and neurological dysfunction, unless selenium intake is excessive However, the effect of selenoprotein P deficiency on the processes of memory formation and synaptic plasticity is unknown. In the present studies Sepp1(-/-) mice and wild type littermate controls (Sepp1(+/+)) fed a high-selenium diet (1 mg Se/kg) were used to characterize activity, motor coordination, and anxiety as well as hippocampus-dependent learning and memory. Normal associative learning, but disrupted spatial learning was observed in Sepp1(-/-) mice. In addition, severe alterations were observed in synaptic transmission, short-term plasticity and long-term potentiation in hippocampus area CA1 synapses of Sepp1(-/-) mice on a 1 mg Se/kg diet and Sepp1(+/+) mice fed a selenium-deficient (0 mg Se/kg) diet. Taken together, these data suggest that selenoprotein P is required for normal synaptic function, either through presence of the protein or delivery of required selenium to the CNS

The generation and function of soluble apoE receptors in the CNS

More than a decade has passed since apolipoprotein E4 (APOE-ε4) was identified as a primary risk factor for Alzheimer 's disease (AD), yet researchers are even now struggling to understand how the apolipoprotein system integrates into the puzzle of AD etiology. The specific pathological actions of apoE4, methods of modulating apolipoprotein E4-associated risk, and possible roles of apoE in normal synaptic function are still being debated. These critical questions will never be fully answered without a complete understanding of the life cycle of the apolipoprotein receptors that mediate the uptake, signaling, and degradation of apoE. The present review will focus on apoE receptors as modulators of apoE actions and, in particular, explore the functions of soluble apoE receptors, a field almost entirely overlooked until now