Publications

Peer-to-Peer Systems III: Third International Workshop, IPTPS 2004, La Jolla, CA, USA, February 26-27, 2004, Revised Selected Papers (Lecture Notes in Computer Science)

Influence of Pore Size and Pore Size Distribution of Polymer-Based Packing Materials on Chromatographic Separation of Carbon Clusters

Abstract Size monodispersed poly(styrene-divinylbenzene) particles with a variety of pore size and pore size distribution were prepared by a multi-step swelling and polymerization method and utilized as packing materials in high performance liquid chromatography (HPLC). As an application of these packing materials, separation of carbon clusters C60 and C70 were examined in a mixture of hexane and benzene and an influence of the pore size and the pore size distribution of the polymer-based packing materials on the separation was investigated. Although carbon clusters are sterically bulky molecules, packing materials with smaller pores showed better separation than those with larger pores. Completely separated peaks and the good peak shape suggest possible isolation of carbon clusters on relatively cheap polymer-based packing materials.

Design of photoresists with reduced environmental impact. II. Water-soluble resists based on photocrosslinking of poly(2-isopropenyl-2-oxazoline)

The performance of water- and solvent-cast, two-component photoresist films containing poly(2-isopropenyl-2-oxazoline) or poly(2-isopropenyl-2-oxazoline-co-styrene) with a photoacid generator has been investigated. These materials afford negative-tone images after deep-UV exposure and development in a suitable medium (water or toluene). Resist solutions prepared from polymers containing at least 80 mol % 2-isopropenyl-2-oxazoline may be cast from and developed in pure water. Features of higher quality can be obtained when the resist is cast from 2-methoxyethanol, probably because side reactions such as partial hydrolysis of the pendant oxazoline rings in aqueous environments are avoided. It was possible to resolve micrometer scale patterns using ca. 200 mJ/cm2 of irradiation at 254 nm, followed by heating 2 min at 130°C and development in water alone. Image quality and etch resistance were improved using copolymers containing up to 20 mol % of styrene repeat units. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1225–1236, 1999

Treatment Adherence Rating Scale

Incorporation of Furan into Low Band-Gap Polymers for Efficient Solar Cells

The design, synthesis, and characterization of the first examples of furan-containing low band-gap polymers, PDPP2FT and PDPP3F, with substantial power conversion efficiencies in organic solar cells are reported. Inserting furan moieties in the backbone of the conjugated polymers enables the use of relatively small solubilizing side chains because of the significant contribution of the furan rings to overall polymer solubility in common organic solvents. Bulk heterojunction solar cells fabricated from furan-containing polymers and PC(71)BM as the acceptor showed power conversion efficiencies reaching 5.0%.

Tailoring the Morphology of LiCoO₂: A First Principles Study

Surface energies of several low-index surfaces of layered LiCoO2 are investigated as a function of the external lithium and oxygen chemical potentials by means of First Principles calculations in the generalized gradient approximation (GGA) to density functional theory (DFT), treating on-site electron correlation within the DFT+U framework. We find the set of surfaces contained in the equilibrium shape to be depending on environment. The(0001)and (10 (1) over bar4) surfaces are present for all reasonable values of the Li and O chemical potentials. The (01 (1) over bar2) surface, however, is stable only under oxidizing conditions. The equilibrium shape is sensitive to the equilibration environment because the thermodynamically favorable surface terminations and surface energies of the polar (0001) and (01 (1) over bar2) surfaces are a function of environment. This provides a lever to tailor the crystal shape according to application requirements (e.g., as active material in lithium-ion batteries).

Kinetics of hydrogenation and hydrogenolysis of 2,5-dimethylfuran over noble metals catalysts under mild conditions

An extremely soft and weak fast X-ray transient associated with a luminous supernova

Long gamma-ray bursts (LGRBs), including their subclasses of low-luminosity GRBs (LL-GRBs) and X-ray flashes (XRFs) characterized by low spectral peak energies, are known to be associated with broad-lined Type Ic supernovae (SNe Ic-BL), which result from the core collapse of massive stars that lose their outer hydrogen and helium envelopes. However, the soft and weak end of the GRB/XRF population remains largely unexplored, due to the limited sensitivity to soft X-ray emission. Here we report the discovery of a fast X-ray transient, EP250108a, detected by the Einstein Probe (EP) in the soft X-ray band at redshift $z = 0.176$, which was followed up by extensive multiband observations. EP250108a shares similar X-ray luminosity as XRF\,060218, the prototype of XRFs, but it extends GRBs/XRFs down to the unprecedentedly soft and weak regimes, with its $E_{\rm peak} \lesssim 1.8\,\mathrm{keV}$ and $E_{\rm iso} \lesssim 10^{49}\, \mathrm{erg}$, respectively. Meanwhile, EP250108a is found to be associated with SN\,2025kg, one of the most luminous and possibly magnetar-powered SNe Ic-BL detected so far. Modeling of the well-sampled optical light curves favors a mildly relativistic outflow as the origin of this event. This discovery demonstrates that EP, with its unique capability, is opening a new observational window into the diverse outcomes of death of massive stars.

An architecture for the future internet

The Internet is the hottest interconnection in town. The number of Internet users, and the variety of resources available over the Internet, are growing at an astounding rate. The Internet is clearly this year's technology media darling, and it is rapidly becoming a social institution of some import. However, behind all the superficial glamour lies a technical edifice in serious need of fundamental repair.

Self-Assembly and Photomechanical Switching of an Azobenzene Derivative on GaAs(110): Scanning Tunneling Microscopy Study

Self-assembly and light-induced mechanical switching of azobenzene derivatives deposited on GaAs(110) were explored at the single molecule level using scanning tunneling microscopy (STM). 3,3′,5,5′-Tetra-tert-butylazobenzene (TTB-AB) molecules in the trans isomer configuration were found to form well-ordered islands on GaAs(110). After exposure to ultraviolet (UV) light, the TTB-AB molecules exhibited conformational changes attributed to trans to cis photoisomerization. Photoisomerization of TTB-AB/GaAs is observed to occur preferentially in one-dimensional (1D) stripes. This 1D cascade behavior differs significantly from optically induced switching behavior observed when TTB-AB molecules are placed on a gold surface.

Comparing nocturnal eddy covariance measurements to estimates of ecosystem respiration made by scaling chamber measurements at six coniferous boreal sites

During the growing season, nighttime ecosystem respiration emits 30–100% of the daytime net photosynthetic uptake of carbon, and therefore measurements of rates and understanding of its control by the environment are important for understanding net ecosystem exchange. Ecosystem respiration can be measured at night by eddy covariance methods, but the data may not be reliable because of low turbulence or other methodological problems. We used relationships between woody tissue, foliage, and soil respiration rates and temperature, with temperature records collected on site to estimate ecosystem respiration rates at six coniferous BOREAS sites at half‐hour or 1‐hour intervals, and then compared these estimates to nocturnal measurements of CO 2 exchange by eddy covariance. Soil surface respiration was the largest source of CO 2 at all sites (48–71%), and foliar respiration made a large contribution to ecosystem respiration at all sites (25–43%). Woody tissue respiration contributed only 5–15% to ecosystem respiration. We estimated error for the scaled chamber predictions of ecosystem respiration by using the uncertainty associated with each respiration parameter and respiring biomass value. There was substantial uncertainty in estimates of foliar and soil respiration because of the spatial variability of specific respiration rates. In addition, more attention needs to be paid to estimating foliar respiration during the early part of the growing season, when new foliage is growing, and to determining seasonal trends of soil surface respiration. Nocturnal eddy covariance measurements were poorly correlated to scaled chamber estimates of ecosystem respiration ( r 2 =0.06–0.27) and were consistently lower than scaled chamber predictions (by 27% on average for the six sites). The bias in eddy covariance estimates of ecosystem respiration will alter estimates of gross assimilation in the light and of net ecosystem exchange rates over extended periods.

Continuous observation of tree leaf area index at ecosystem scale using upward-pointing digital cameras

Confinement-Induced Berry Phase and Helicity-Dependent Photocurrents

The photocurrent in an optically active metal is known to contain a component that switches sign with the helicity of the incident radiation. At low frequencies, this current depends on the orbital Berry phase of the Bloch electrons via the "anomalous velocity" of Karplus and Luttinger. We consider quantum wells in which the parent material, such as GaAs, is not optically active and the relevant Berry phase only arises as a result of quantum confinement. Using an envelope approximation that is supported by numerical tight-binding results, it is shown that the Berry-phase contribution is determined for realistic wells by a cubic Berry phase intrinsic to the bulk material, the well width, and the well direction. These results for the Berry-phase effect suggest that it may already have been observed in quantum well experiments.

Isotopomer Distributions in Amino Acids from a Highly Expressed Protein as a Proxy for Those from Total Protein

13C-Based metabolic flux analysis provides valuable information about bacterial physiology. Though many biological processes rely on the synergistic functions of microbial communities, study of individual organisms in a mixed culture using existing flux analysis methods is difficult. Isotopomer-based flux analysis typically relies on hydrolyzed amino acids from a homogeneous biomass. Thus, metabolic flux analysis of a given organism in a mixed culture requires its separation from the mixed culture. Swift and efficient cell separation is difficult and a major hurdle for isotopomer-based flux analysis of mixed cultures. Here we demonstrate the use of a single highly expressed protein to analyze the isotopomer distribution of amino acids from one organism. Using the model organism Escherichia coli expressing a plasmid-borne, His-tagged green fluorescent protein (GFP), we show that induction of GFP does not affect E. coli growth kinetics or the isotopomer distribution in nine key metabolites. Further, the isotopomer labeling patterns of amino acids derived from purified GFP and total cell protein are indistinguishable, indicating that amino acids from a purified protein can be used to infer metabolic fluxes of targeted organisms in a mixed culture. This study provides the foundation to extend isotopomer-based flux analysis to study metabolism of individual strains in microbial communities.

China and the Exports of Other Asian Countries

Gold(i)-catalyzed enantioselective bromocyclization reactions of allenes

The enantioselective bromocyclization of allenes is accomplished through the use of a chiral dinuclear gold complex and/or chiral phosphate anions in the presence of an N-bromolactam as an electrophilic bromine source. This method provides access to heterocyclic vinyl bromides with an allylic stereocenter in excellent yield and enantioselectivity. These enantioenriched vinyl bromides may serve as a handle for further derivatization via cross-coupling reactions.

NMR Studies on the Diffusion of Hydrocarbons on the Metal‐Organic Framework Material MOF‐5

On the move: High intracrystalline mobilities and fast exchange between the crystal and the surrounding gas phase were found in NMR studies on the diffusion of methane, ethane, n-hexane, and benzene in large crystals of the metal-organic framework MOF-5 (see SEM image). The results support future use of metal-organic framework materials as tailorable sorbents for fast gas processing and gas-storage materials in industry.

Gated proton transport in aligned mesoporous silica films