Ray-optical negative refraction and pseudoscopic imaging with Dove-prism arrays

A sheet consisting of an array of small, aligned Dove prisms can locally (on the scale of the width of the prisms) invert one component of the ray direction. A sandwich of two such Dove-prism sheets that inverts both transverse components of the ray direction is a ray-optical approximation to the interface between two media with refractive indices +n and –n. We demonstrate the simulated imaging properties of such a Dove-prism-sheet sandwich, including a demonstration of pseudoscopic imaging

Effect of anions on dispersion of a kaolinitic soil clay: A combined study of dynamic light scattering and test tube experiments

Dispersion is an important issue for clay leaching in soils. In this study, effects of various anions (Cl-, SO42-, acetate, oxalate and citrate) on dispersion of a kaolinitic soil clay were determined at different pH values and ionic strengths by dynamic light scattering and test tube experiments. Adsorption of anions on clay samples was characterized by the zeta potential (ζ) in a pH range of 2 to 11. At a pH range between 2 and 6, the effects of different anions on decreasing ζ were obvious and followed the order oxalate>citrate>SO42->Cl->acetate, while fluctuated changes in ζ were observed at pH>6. Based on a comparison of hydrodynamic radii (rh) obtained from dynamic light scattering and of transmission of 50% (T50 values) from the test tube experiments, the ability of anions to facilitate the dispersion of the clay fraction followed the sequence of oxalate>citrate>acetate>SO42->Cl-. It implies that adsorption of anions on positively charged edge sites of kaolinite resulting in a decrease in ζ is a key factor for dispersion of the clay fraction. Also, the results suggested that the dynamic light scattering can be used in combination with the test tube experiments in order to evaluate the effect of anions on dispersion at broader ranges of pH, ionic strength and clay concentration.Vietnam National Foundation for Science & Technology Development/105.09-2010.0

Interferon-free antiviral combination therapies without nucleosidic polymerase inhibitors

SummaryThe establishment of robust HCV cell culture systems and characterization of the viral life cycle provided the molecular basis for highly innovative, successful years in HCV drug development. With the identification of direct-acting antiviral agents (DAAs), such as NS3/4A protease inhibitors, NS5A replication complex inhibitors, nucleotide and non-nucleoside polymerase inhibitors, as well as host cell targeting agents, novel therapeutic strategies were established and competitively entered clinical testing. The first-in-class NS3/4A protease inhibitors telaprevir and boceprevir, approved in 2011, were recently outpaced by the pan-genotypic nucleotide polymerase inhibitor sofosbuvir that in combination with pegylated interferon and ribavirin, further shortens therapy durations and also offers the first interferon-free HCV treatment option. In the challenging race towards the goal of interferon-free HCV therapies, however, several oral DAA regimens without nucleotide polymerase inhibitors that combine a NS3/4A protease inhibitor, a NS5A inhibitor and/or a non-nucleoside polymerase inhibitor yielded competitive results. Second generation NS3/4A protease and NS5A inhibitors promise an improved genotypic coverage and a high resistance barrier. Results of novel DAA combination therapies without the backbone of a nucleotide polymerase inhibitor, as well as treatment strategies involving host targeting agents are reviewed herein

Not all nuclear pores created equal

Pore-making process isn't identical in interphase and mitosis

The Nuclear Pore Complex: Birth, Life, and Death of a Cellular Behemoth

Nuclear pore complexes (NPCs) are the only transport channels that cross the nuclear envelope. Constructed from ~500–1000 nucleoporin proteins each, they are among the largest macromolecular assemblies in eukaryotic cells. Thanks to advances in structural analysis approaches, the construction principles and architecture of the NPC have recently been revealed at submolecular resolution. Although the overall structure and inventory of nucleoporins are conserved, NPCs exhibit significant compositional and functional plasticity even within single cells and surprising variability in their assembly pathways. Once assembled, NPCs remain seemingly unexchangeable in post-mitotic cells. There are a number of as yet unresolved questions about how the versatility of NPC assembly and composition is established, how cells monitor the functional state of NPCs or how they could be renewed. Here, we review current progress in our understanding of the key aspects of NPC architecture and lifecycle.publishedVersio

Compressibility of a two-dimensional hole gas in tilted magnetic field

We have measured compressibility of a two-dimensional hole gas in p-GaAs/AlGaAs heterostructure, grown on a (100) surface, in the presence of a tilted magnetic field. It turns out that the parallel component of magnetic field affects neither the spin splitting nor the density of states. We conclude that: (a) g-factor in the parallel magnetic field is nearly zero in this system; and (b) the level of the disorder potential is not sensitive to the parallel component of the magnetic field

Particle size as controlling factor of soil microaggregate formation

Aggregates are formed when soil particles connect to larger secondary units. Stable microaggregates in soils are supposed to consist of close associations of Fe-oxides and clay minerals with both components being attracted by electrostatic forces between the oppositely charged particles. However, the geometric preconditions for the formation of stable associations between Fe oxides and clay minerals are poorly known. Therefore, our goal was to determine geometrical constraints resulting from particle size and morphology likely impeding optimum arrangement of particles for shielding of charges during aggregate formation. Aggregation kinetics was determined for nine combinations of each three particle size fractions of goethite and mica in a Zetasizer at pH 6. Experiments were conducted using needle-shape goethites synthesized at 4, 20, and 60°C (lengths of 0.42, 0.46 and 0.84 µm, specific surface areas (SSA) of 87, 75, and 60 m²/g, respectively) and ground platy muscovite separated in fine, medium and coarse clay (diameters of 0.16, 0.80, and 2.9 µm, SSA of 182, 100, and 27 m²/g, respectively). For five combinations even smallest additions of goethite to muscovite facilitated aggregation. By further additions of goethite maximum aggregate sizes up to 5.6 µm were obtained, the respective mixing ratio strongly depending on the type of combination. After that sizes declined. For medium and coarse-sized muscovite, goethite amendments >18% did not facilitate aggregation, indicating the dominance of repulsive forces. In contrast, for fine-sized muscovite aggregation was facilitated up to an addition of 63% fine-sized goethite and of 90% coarse-sized goethite. Here also biggest aggregate sizes were obtained. Based on all examined size fraction combinations, our results suggest a strong impact of particle size on aggregation. Whereas all combinations with fine-sized muscovite facilitated aggregation at very different mixing ratios, the amendment of the finest fraction of goethite to medium- and coarse-sized muscovite facilitated aggregation at small additions only. Aggregation was favored for evenly sized combinations. The quantification of surface charge density of minerals and calculation of charge balances of the combinations is in progress and will help interpreting the observed aggregation patterns. For soils it is likely that aggregation by electrostatic interactions occurs only at certain mineral mixing ratios highly depending on particle morphology

Live imaging of single nuclear pores reveals unique assembly kinetics and mechanism in interphase

Recruitment of nuclear pore complex (NPC) components during interphase occurs in a different order and with slower kinetics than during postmitotic NPC assembly, suggesting the two processes are regulated by distinct mechanisms