Pennsylvania, United States
Last year a team of physicists showed how to undo the “coffee-ring effect,” which occurs when drops of liquid with suspended particles dry, leaving a ring-shaped stain at the drop’s edges. The team discovered that different particles make smoother or rougher deposition profiles depending on their shape. The two deposition profiles of particular interest are “Poisson” and “Kardar-Parisi-Zhang” processes. Poisson processes arise when growth is random in space and time; the growth of one region is independent of neighboring regions. Kardar-Parisi-Zhang (KPZ) occurs when growth of an individual region depends on neighboring regions. A mathematical simulation of these growth processes might be a game of Tetris, but with single square blocks with the blocks falling at random into a series of adjacent columns, forming stacks. In a Poisson process a tall stack is just as likely to be next to a short stack as another tall stack. As such, Poisson processes produce a very rough surface, with large changes in surface height from one column to the next. On the other hand KPZ processes lead to blocks sticking to adjacent columns. When they fall into a column, they do not always fall all the way to the bottom but instead can stick to adjacent columns at their highest point. Thus short columns will catch up to their tall neighbors over time, and the resulting surfaces are smoother. There will be fewer abrupt changes in height from one column to the next.
The team’s experiment involved drying drops of water with differently shaped plastic particles under a microscope. They then measured the growth fronts of particles at the drying edge, especially their height fluctuations (the edge’s roughness) over time. When using spherical particles, they found their deposition at the edges of the drop exhibited a classic Poisson growth process. By changing the elongation of the particle they found that the growth process changed. Elliptical particles stretched by 20 percent produced KPZ growth and stretching the particles further (250 percent) produced another growth process known as Kardar-Parisi-Zhang with Quenched Disorder. This led to the surface’s growth being proportional the the local particle density so that particle-rich regions get richer and particle poor regions stay poor. The ability to control surface roughness is important for industrial and commercial applications, as rough films and coatings can lead to structural weakness or poor aesthetics. In the experiment surface roughness is controlled passively making this process an attractive alternative for more costly smoothing processes currently in use.
Scientists at Empa, the Swiss Federal Laboratories for Materials Science and Technology, developed thin film solar cells on flexible polymer foils with a new record efficiency of 20.4% for converting sunlight into electricity. The cells are based on copper indium gallium (di)selenide (CIGS) known for its potential to provide cost-effective solar electricity. The technology is currently awaiting scale-up for industrial applications. The team succeeded by modifying the properties of the CIGS layer that is grown at low temperatures and which absorbs light that contributes to the photo-current in solar cells. Thin film, lightweight and flexible high-performance solar cells are attractive for numerous applications and can be produced using manufacturing processes that offer further cost reductions when compared to silicon based solar cells.
Each cell has regulatory regions that control which genes are active at any time. Scientists at the Research Institute of Molecular Pathology (IMP) in Vienna recently developed a method that reliably detects these regions and measures their activity. Genes carry the instruction for proteins but they are a minority of the entire genome sequence (two percent in humans). The other 98 percent is known as “dark matter” and is often dismissed as its function has remained mostly unknown. Scientists found that “dark matter” or the non-coding part of DNA contains regulatory regions that determine when and where each gene is expressed. This regulation ensures that each gene is only active in appropriate cell-types and tissues, such as hemoglobin in red blood cells and digestive enzymes in the stomach. If gene regulation fails, cells express the wrong genes and often acquire inappropriate functions such as the ability to divide and proliferate, leading to diseases such as cancer. Despite the importance of “dark matter,” scientists were limited in their ability to study it due to identification relying on indirect means which were error prone.
Scientists at the IMP in Vienna developed a new technology called STARR-seq (self-transcribing active regulatory region sequencing). STARR-seq allows the direct identification of DNA sequences that function as regulatory regions and simultaneously measures their activity quantitatively in entire genomes. Applying this technology to Drosophila cells, the scientists found that the strongest regulators reside in both genes that determine cell-types and in genes that are required for basic cell survival. Furthermore, they found several regulators for each active gene, which might provide redundancy to ensure robustness of gene regulation.
The quantum law of entanglement may hold the key to the teleportation of quantum information. Researchers at Cambridge, University College London, and the University of Gdansk, worked out how entanglement could be recycled to increase the efficiency of these connections. Quantum teleportation involves transmitting particle-sized bites of information across vast distances. It uses the entanglement law where a pair of quantum particles (electrons or protons) are intrinsically bound together retaining synchronisation that holds whether the particles are next to each other or on opposing sides of a galaxy. Through this connection quantum bits of information (qubits) can be relayed. Previous teleportation techniques could only send scrambled information requiring correction by the receiver or teleportation that required an impractical amount of entanglement (each qubit sent would destroy the entangled state). The physicists developed a protocol to provide an optimal solution in which the entangled state is “recycled,” so that the gateway between particles holds for the teleportation of multiple objects or qubits.They also devised a protocol in which multiple qubits can be teleported simultaneously, but the entangled state degrades proportionally to the amount of qubits sent. While the physicists’ protocol is solely theoretical, last year a team of Chinese scientists reported teleporting photons over 143 km, breaking previous records. Teleportation of information carried by single atoms is feasible with current technologies, but teleportation of large objects such as people or Captain Kirk is still science fiction.
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