Xingfei Zhou

The PLATO Dome A site-testing observatory: Power generation and control systems

The atmospheric conditions above Dome A, a currently unmanned location at the highest point on the Antarctic plateau, are uniquely suited to astronomy. For certain types of astronomy Dome A is likely to be the best location on the planet, and this has motivated the development of the Plateau Observatory (PLATO). PLATO was deployed to Dome A in early 2008. It houses a suite of purpose-built site-testing instruments designed to quantify the benefits of Dome A site for astronomy, and science instruments designed to take advantage of the observing conditions. The PLATO power generation and control system is designed to provide continuous power and heat, and a high-reliability command and communications platform for these instruments. PLATO has run and collected data throughout the winter 2008 season completely unattended. Here we present a detailed description of the power generation, power control, thermal management, instrument interface, and communications systems for PLATO, and an overview of the system performance for 2008.

The PLATO Antarctic site testing observatory

Over a decade of site testing in Antarctica has shown that both South Pole and Dome C are exceptional sites for astronomy, with certain atmospheric conditions superior to those at existing mid-latitude sites. However, the highest point on the Antarctic plateau, Dome A, is expected to experience colder atmospheric temperatures, lower wind speeds, and a turbulent boundary layer that is confined closer to the ground. The Polar Research Institute of China, who were the first to visit the Dome A site in January 2005, plan to establish a permanently manned station there within the next decade. As part of this process they conducted a second expedition to Dome A, arriving via overland traverse in January 2008. This traverse involved the delivery and installation of the PLATeau Observatory (PLATO). PLATO is an automated self-powered astrophysical site testing observatory, developed by the University of New South Wales. A number of international institutions have contributed site testing instruments measuring turbulence, optical sky background, and sub-millimetre transparency. In addition, a set of science instruments are providing wide-field high time resolution optical photometry and terahertz imaging of the Galaxy. We present here an overview of the PLATO system design and instrumentation suite.

Thickness of the Atmospheric Boundary Layer Above Dome A, Antarctica, during 2009

The domes, or local elevation maxima, on the Antarctic plateau provide a unique opportunity for ground-based astronomy in that the turbulent boundary layer is so thin that a telescope on a small tower can be in the free atmosphere, i.e., the portion of the atmosphere in which the turbulence is decoupled from the effect of the Earths surface. There, it can enjoy a free atmosphere which itself appears to offer superior conditions to that of temperate sites. This breaks the problem of characterizing the turbulence at Antarctic plateau sites into two separate tasks: determining the variability, distribution and thickness of the boundary layer, and characterizing the free atmosphere. In this article we tackle the first of these tasks using a high-resolution, low minimum sample height sonic radar (SODAR) called Snodar that has been specifically designed to characterize the Antarctic bound- ary thickness and structure. Snodar delivers a vertical resolution of 0.9 m, with a minimum sampling height of 8 m. Snodar sampled the first 180 m of the atmosphere with 0.9 m resolution every 10 s at Dome A, Antarctica between 2009 February 4 and 2009 August 18. The median thickness of the boundary layer over this period was 13.9 m, with the 25th and 75th percentiles at 9.7 m and 19.7 m, respectively. The data collected from Dome A also show that, while the boundary layer can be stable for several hundred hours at a time, it can also be highly variable and must be sampled on the time scale of minutes to properly characterize its thickness.

Controllable synthesis of activated graphene and its application in supercapacitors

Activated graphene has been considered as an ideal electrode material for supercapacitors. In order to reveal the relationship between activated graphene and its precursor and controllably synthesize activated graphene, the structural parameters of the precursor (reduced graphene oxide, RGO) such as crystallinity and attached oxygen-functional groups were controllably adjusted during the synthesis of activated graphene and the effects of the precursor structure on the microstructure of activated graphene were investigated. The activation results reveal that the structure of RGO obviously affects the porous structure of activated graphene. Specifically, the crystallinity and oxygen-functional groups play an important role in the porosity development of activated graphene. By combining the simplified Brodie method and the subsequent post-oxidation process, porous activated graphene with a specific surface area of as high as 2406 m2 g−1 and high pore volume has been successfully prepared. The as-prepared activated graphene exhibits good capacitive characteristics and delivers high energy density (55.7 W h kg−1) when measured in a two-electrode cell with the EMIMBF4 ionic liquid as the electrolyte. The results demonstrate that the obtained activated graphene can be considered as a candidate for advanced electrode materials for supercapacitors.

Edge-enriched porous graphene nanoribbons for high energy density supercapacitors

A simple solution-based oxidative process and subsequent chemical activation combination method has been developed to prepare edge-enriched porous graphene nanoribbons (GNRs) as a high-performance electrode material for supercapacitors. The precursor aligned carbon nanotubes are cut longitudinally and unzipped by a modified Brodie method to form tube-like GNRs with abundant edges. The intermediate GNRs were subsequently chemically activated using KOH to generate a suitable porosity and create more edge sites. These edge sites contribute a larger capacitance than the basal plane of graphene and the nanopores facilitate the fast immigration of ions. As a result, the edge-enriched GNRs exhibit a capacitance uptake per specific surface area almost two times higher than that of conventional activated graphene sheets, which gives rise to the high energy density of the porous GNR electrode. The highly efficient utilization of the edge planes and easy, low-cost scale-up production will make porous GNRs potentially applicable to high-performance supercapacitors.

Nitrogen-doped porous graphene–activated carbon composite derived from “bucky gels” for supercapacitors

A simple method has been developed to prepare nitrogen-doped porous graphene–activated carbon (AC) composites as high-performance electrode materials for supercapacitors. The graphene-based “bucky gels”, prepared by simple mixing and grinding of graphene in ionic liquids (ILs), are carbonized to form an “untractable char” intermediate product, and finally converted to the nitrogen-doped porous graphene–AC composite by chemical activation using KOH. Results demonstrate that the introduction of graphene sheets into the composite not only effectively enhance the specific surface area and conductivity of graphene–AC composite, but also enlarge the pore size in the electrode material compared with pure AC. In addition, the nitrogen-doping can further improve the kinetics for both charge transfer and ion transport throughout the electrode. Its found that the composite has a large specific surface area of 2375.2 m2 g−1, and also contains plenty of mesopores and appreciable nitrogen-doping amount. It exhibits a specific capacitance up to 145 F g−1 at 20 mV s−1 in 6 M KOH electrolyte, and the specific capacitance decreases by only 1.6% after 5000 cycles. This kind of nitrogen-doped composite represents an alternative promising candidate as electrode material for supercapacitors.

Hierarchical ordering of amyloid fibrils on the mica surface

The aggregation of amyloid peptides into ordered fibrils is closely associated with many neurodegenerative diseases. The surfaces of cell membranes and biomolecules are believed to play important roles in modulation of peptide aggregation under physiological conditions. Experimental studies of fibrillogenesis at the molecular level in vivo, however, are inherently challenging, and the molecular mechanisms of how surface affects the structure and ordering of amyloid fibrils still remain elusive. Herein we have investigated the aggregation behavior of insulin peptides within water films adsorbed on the mica surface. AFM measurements revealed that the structure and orientation of fibrils were significantly affected by the mica lattice and the peptide concentration. At low peptide concentration (~0.05 mg mL(-1)), there appeared a single layer of short and well oriented fibrils with a mean height of 1.6 nm. With an increase of concentration to a range of 0.2-2.0 mg mL(-1), a different type of fibrils with a mean height of 3.8 nm was present. Interestingly, when the concentration was above 2.0 mg mL(-1), the thicker fibrils exhibited two-dimensional liquid-crystal-like ordering probably caused by the combination of entropic and electrostatic forces. These results could help us gain better insight into the effects of the substrate on amyloid fibrillation.

Height measurement of dsDNA and antibodies adsorbed on solid substrates in air by vibrating mode scanning polarization force microscopy

A method of height measurement based on vibrating mode scanning polarization force microscopy is developed and applied to soft molecules such as dsDNA and antibodies. In the experiment, a bias voltage is applied to a conductive atomic force microscopy (AFM) tip to maintain it farther from the surface during imaging in vibrating mode. By changing amplitude setpoint (A(sp)) the tip can be lowered from the top of a molecule to the substrate, and the displacement of the tip in the z direction (D-Z) approximates the true height of this molecule. This method is first applied to rigid colloidal gold particles and then to dsDNA and antibodies. The measured heights of gold particles are consistent with those in normal tapping mode AFM (TM-AFM). However, the measured heights of dsDNA molecules and antibodies CA125 are much larger than the results in TM-AFM. We deduce that tip pressure might have caused large deformation on soft biomolecules when imaging is performed in ITM-AFM

Assembly of glucagon (proto)fibrils by longitudinal addition of oligomers

The process of glucagon peptide aggregation was studied with high resolution atomic force microscopy (AFM). The statistical analysis of ex situ AFM images in combination with in situ AFM observation suggests that it is more likely that (proto)fibrils are formed via direct longitudinal growth of oligomers, instead of the lateral association of two or more filaments.

Combined-dynamic mode "dip-pen" nanolithography and physically nanopatterning along single DNA molecules

Atomic force micriscope (AFM)-based dip-pen nanolithography (DPN) is an emerging approach for constructing nanostructures on material surfaces such as gold, silicon and silicon oxide. Although DPN is a powerful technique, it has not shown its ability of direct-writing and patterning of nanostructures on surfaces of soft materials, for example biomacromolecules. Direct depositing on soft surfaces becomes possible with the introduction of a combined-dynamic mode DPN rather than mostly used contact mode DPN or tapping mode DPN. In this report, the combined dynamic mode DPN is used for direct depositing protein ink on DNA molecules at the nanometer scale.