Study of the energy flow in sulphur-and oxygen-nucleus collisions at 60 and 200 GeV/nucleon

Data on multiplicities of charged particles produced in proton-nucleus and nucleus-nucleus collisions at 200 GeV per nucleon are presented. It is shown that the mean multiplicity of negative particles is proportional to the mean number of nucleons participating in the collision both for nucleus-nucleus and proton-nucleus collisions. The apparent consistency of pion multiplicity data with the assumption of an incoherent superposition of nucleon-nucleon collisions is critically discussed.     

Synthesis, crystal structures, and photophysical properties of electron-accepting diethynylindenofluorenediones

A series of 6,12-bis[(trialkylsilyl)ethynyl]indeno[1,2-b]fluorene-5,11-diones has been synthesized. X-ray crystallographic analysis of these compounds reveals that triisopropylsilyl (TIPS) substitution on the alkyne terminus affords the largest number of intermolecular π-π interactions in the solid state. Conversely, use of trialkylsilyl groups smaller or larger than TIPS furnishes a variety of crystal-packing motifs that contain fewer π-π interactions. Electrochemical and photophysical data suggest that these molecules are excellent electron-accepting materials.     

Matrix Fabry-Perot resonance mechanism in high-contrast gratings

We present a simple analytic formalism to explain the unique resonance phenomenon in subwavelength high-contrast gratings (HCG). We show that the resonances are due to strong coupling between two surface-normal waveguide array modes resulting from abrupt and large index contrast. Simple expression for HCG quality factor is derived that agrees with spectral-fitting approaches reported in literature.     

Off-resonance saturation MRI of superparamagnetic nanoprobes: theoretical models and experimental validations

Off-resonance saturation (ORS) is a new magnetic resonance imaging (MRI) method that has shown greatly improved contrast sensitivity for the detection of cancer-specific biomarkers by superparamagnetic nanoprobes in vivo. However, quantitative understanding of the ORS contrast mechanism and its dependence on the structural parameters of superparamagnetic nanoprobes are still lacking. Here we propose a quantitative model of ORS contrast and its experimental validation by superparamagnetic polymeric micelles (SPPM) with precisely controlled structural properties. Size selected, monodisperse Fe?O? nanoparticles (6.1 ± 0.2 nm) were used to form a series of SPPM nanoprobes with specifically controlled corona thickness using 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-methoxypoly(ethylene glycol) (DSPE-PEG) with different PEG molecular weights. Transmission electron microscopy and dynamic light scattering showed that SPPM were uniform in size. The average hydrodynamic diameters of SPPM with PEG lengths of 0.55, 1, 2, and 5 kD were 16.6 ± 2.8, 18.4 ± 2.9, 24.1 ± 3.4, and 28.9 ± 3.4 nm, respectively. MRI experiments at 7 T determined that r? values of SPPM with 0.55, 1, 2, and 5 kD PEG as corona were 201 ± 3, 136 ± 8, 107 ± 5, and 108 ± 8 FemM?1s?1, respectively. ORS intensity from Z-spectra of SPPM showed a significant correlation with the inverse of T? relaxation rates (1/T?, s?1) of the SPPM nanoprobes regardless of the PEG corona thickness. These data provide the fundamental understanding of the structure-property relationships between the SPPM nanostructures and ORS sensitivity, which offers useful mechanistic insights for the future improvement of SPPM nanoprobes in cancer molecular imaging applications.     

Characterization and evaluation of a macroporous adsorbent for possible use in the expanded bed adsorption of flavonoids from Ginkgo biloba L.

The suitability of the use of macroporous adsorbent Amberlite XAD7HP in expanded bed adsorption processes for the isolation of flavonoids from crude extracts of Ginkgo biloba L. has been assessed. The expansion and hydrodynamic properties of expanded beds were investigated and analyzed. The bed expansion as a function of operational fluid velocity was measured and correlated with the Richardson–Zaki equation. Theoretical predictions of the correlation parameters (the terminal settling velocity u_t and exponent n) were improved by modifying equations in the literature. Residence time distributions (RTDs) were studied using acetone as a tracer. Three measures of liquid phase dispersion (the height equivalent of theoretical plate, Bodenstein number and axial distribution coefficient) were investigated and compared to values previously obtained with commercial EBA adsorbents developed for protein purification. A suitable bed expansion ratio was found to be 1.25 times the settled bed height, which occurred at a corresponding flow velocity of 183 cm/h. For an initial settled bed height of 42 cm, the mean residence time of liquid in the expanded bed was around 28 min. Under these flow conditions, the axial mixing coefficient D_ax was 7.54 × 10⁻⁶ m²/s and the Bodenstein number was 28; the number of theoretical plates (N) was 19 and the height equivalent of a theoretical plate (HETP) was 2.77 cm. Rutin trihydrate was used as a model flavonoid for the characterization of the adsorption properties of Amberlite XAD7HP. Adsorption was observed to reach equilibrium within 3 h with 70% of the adsorption capacity being achieved within 30 min. The estimated maximum equilibrium adsorption capacity for rutin was estimated to be 43.0 mg/(g resin) when the results were fitted to Langmuir isotherms. The adsorption performance was not seriously impaired by the physical presence of G. biloba leaf powders. Assessment of the kinetics of the adsorption of rutin revealed that the rate constant for adsorption was only reduced by 15% in the presence of leaf powders at a concentration of 50 mg/mL. The results demonstrated that Amberlite XAD7HP should be suitable for expanded bed adsorption of flavonoids from crude extracts of G. biloba L.     

Selective assembly and alignment of actin filaments with desired polarity on solid substrates

We report a new strategy to selectively assemble and align filamentous actin (F-actin) onto desired locations on a solid substrate with a specific structural polarity. In this strategy, biotinylated gelsolin caps the structural minus end of F-actin so that the F-actin binds onto a streptavidin pattern with a specific structural polarity. We also demonstrate that an electric field can be utilized to align bound F-actin along a desired direction. This can be one of the major technical breakthroughs toward the assembly of nanomechanical systems based on myosin biomotors.     

Observation of backward η production

The production of η mesons has been observed at high momentum transfer in the reaction π⁻p → nη. The ratio between this cross-section and that for backward charge exchange yields a value for the relative couplings g²_ηNN/g²_πNN.     

Mechanical and optical properties of an anelastic polymer at intermediate strain rates and large strains

The mechanical and optical properties of a polyester–styrene copolymer have been investigated by means of drop tests at strain rates from 38 to 113 sec^?1 for strains less than 50%. Over this range of rates, the optical behavior was found to be linear with strain and independent of strain rate while the elastic–plastic mechanical behavior was only slightly dependent on strain rate. Comparison with the results of similar experiments at lower strain rates achieved by means of an Instron tester reveals that both mechanical and optical properties vary significantly with strain rate. The variation of flow stress with strain rate was found to obey a power law.     

The Q2 evolution of flavour singlet wave functions in QCD

We calculate the Q² evolution of the quark-antiquark and gluon-gluon components of helicity-zero, flavour and colour singlet wave functions by summing diagrams to all orders in axial gauge QCD perturbation theory in the leading logarithm approximation. We find that Gegenbauer moments of these components have exactly the same scale-breaking behaviour as moments of singlet quark and gluon distribution functions in leptoproduction. The resulting singlet wave function is used to calculate the amplitudes for quark-antiquark and gluon-gluon jet production in off-shell photon-photon collisions.