DNA‐Mediated Stabilization of Self‐Assembling Bead Monolayers for Microfluidic Applications

Forming ordered 2D or 3D arrays of colloidal particles on the micro‐ or nanometer scale in a bottom‐up process is a challenging task. In previous works by various groups, hybridization between DNA strands localized on the particle surface is used to create crystalline arrays. However, this method requires an annealing process with a duration of one day or more and usually yields agglomerates of only a few dozen particles. In this work, a method for the rapid formation of highly‐ordered 2D agglomerates of superparamagnetic microparticles (beads) is presented. Dipolar coupling between the beads under the influence of a rotating magnetic field leads to the formation of a dense monolayer. The monolayer is then stabilized through DNA hybridization between DNA strands immobilized on the bead surface and a linker strand in solution. The whole self‐assembly process requires less than an hour and is therefore significantly faster than comparable methods.     

A study of second-order interference for pions produced in various hadronic interactions

Second-order interference of pion pairs of equal charge is observed in good statistics samples of 16 GeV/cπ⁺p and K^?p interactions (2 × 10⁶ and 10⁶ pion pair combinations, respectively) and in a smaller sample of $\text{p}\text{p}$ annihilations at rest. The effective radius R of the pion source is found to be approximately 1.4 fm for all three types of interaction. The interference does not appear to be “total”, about 60–80% of the like pairs interfering. It is shown that the numerical results for the radius R, for the depth cτ of the source “photosphere” and for the fraction λ of the interfering pairs are sensitive to any dynamical correlation in the background, and hence depend on the background chosen. It is argued that further refinements in the theoretical formulation of the phenomenon and in the experimental approach are needed for truly quantitative results.     

Simplicity of “transverse energy” spectra of hadrons

Using data from a 16 GeV/cπ⁺p bubble chamber experiment, we have studied the production of pions and meson resonances in the central region. Transverse spectra have been analysed in terms of the transverse energy variable E_t=√p_t²+M². We find that the E_t spectra of “stable” particles, of resonances like ?, ω and f, and of corresponding non-resonant two- and three-pion systems all follow one simple exponential in E_t over several orders of magnitude in cross section. All spectra are consistent with one common slope parameter of approximately (120 MeV)^?1.     

Production of charged kaons in proton-nucleus and nucleus-nucleus collisions at 200 GeV/nucleon

Production of charged kaons in proton-sulphur, proton-gold, sulphur-sulphur and oxygen-gold collisions at 200 GeV/nucleon has been studied in the NA35 Streamer Chamber experiment. Rapidity and transverse mass distributions as well as mean multiplicities were obtained. The results are compared with nucleon-nucleon data and with model predictions.Deceased     

New Applications of the CD Exciton Chirality Method. Stereochemical Assignment of Organic Compounds Containing Carboxylic Acid Groups

Summary. CD exciton chirality methods are described for the stereochemical assignment of organic compounds containing carboxylic acid groups. Using the chromophoric combination 2-naphthoate or 2-anthroate and 9-anthrylmethyl group the absolute stereochemistry of - and -hydroxy carboxylic acids can be deduced from a single CD measurement. Furthermore, as demonstrated with cyclic and acylic dicarboxylic acids, the direct esterification of sterically hindered carboxyl groups with 2-naphthol also allows the stereochemical assignment via CD spectroscopy.     

Strange particle production in nuclear collisions at 200 GeV per nucleon

Multiplicities and spectra of strange particles ( andK ^– produced in central³²S+S,³²S+Ag and³²S+Au collisions at 200 GeV per nucleon are presented and compared with data on strange particle production in protonnucleus and nucleon-nucleon interactions. It is shown that strangeness production in³²S+Ag collisions is enhanced by a factor of two, similar to that found previously in central³²S+S collisions.     

Estimation of Kinetic Parameters for the Polar-Modified Anionic Solution Copolymerization of 1,3-Butadiene and Styrene

Summary : The application of the terminal copolymerization model to polar modified anionic initiated 1,3-butadiene/styrene systems in hydrocarbon solvent requires the determination of twelve kinetic model parameters. These include frequency factors (k_xY,∞), activation energies (E_xY) and live chain end association numbers (n_xY) for all four possible combinations of live chain end termini and free monomer. The individual determination of all twelve parameters requires an enormous numerical effort and a large number of experiments. A method for estimating parameters with a minimum number of kinetic batch experiments in an industrial environment will be demonstrated.     

Sorption and Diffusion of Propylene and Ethylene in Heterophasic Polypropylene Copolymers

Summary: Sorption experiments of ethylene and propylene in different polypropylene powder samples, both homopolymer and heterophasic copolymers with different rubber content, have been carried out in a high-pressure magnetic suspension balance at 10 bars pressure and 70 °C. The gross solubilities measured can be well correlated with the rubber content of the polymer samples. Solubility of ethylene and propylene in the rubber phase differ from solubility in the amorphous fraction of the homopolymer, especially the concentration ratio of propylene to ethylene differs significantly between rubber phase and amorphous fraction of the homopolymer. From the slope of monomer uptake, information on kinetics of mass-transfer can be gained. No significant differences were observed in terms of mass-transfer for ethylene and propylene. With increasing rubber content, effective diffusion coefficients increased slightly. By combined sorption studies with powder samples and compressed films, information about both effective diffusion coefficients and the effective length scale of diffusion could be gained. It could be shown, that the particle radius is not the characteristic length of diffusion in the studied powder samples. Mass transfer of nearly all samples could be described by a constant diffusion length of 120 to 130 µm, independently on particle size. This indicates that the effective scale of diffusion in polymer particles is in between microparticle and macroparticle scale used in classical particle modeling.     

Lambda and lambda production in central Pb-Pb collisions at 40, 80, and 158A GeV

Production of Lambda and Antilambda hyperons was measured in central Pb-Pb collisions at 40, 80, and 158A GeV beam energy on a fixed target. Transverse mass spectra and rapidity distributions are given for all three energies. The Lambda/pi ratio at midrapidity and in full phase space shows a pronounced maximum between the highest BNL Alternating Gradient Synchrotron and 40A GeV CERN Super Proton Synchrotron energies, whereas the Lambda/pi ratio exhibits a monotonic increase.