An impact theory for Doppler and pressure broadening—I. General theory

A quantum-mechanical impact theory for the combined effects of Doppler and pressure broadening is developed from quantum radiation theory. The results are compared with other semiclassical theories and certain simplifying approximations relevant to cases of experimental and theoretical interest are discussed.     

Pion pair production in photon-photon collisions at spear

We report a measurement of the cross section for the process γγ→π⁺π^? at invariant masses 500 MeV/c² < m_ππ<2000 MeV/c². A value for the radiative width of the f(1270) tensor meson Γ_f→γγ = 3.6 ± 0.3 ± 0.5 KeV (helicity λ = 2) has been obtained from a fit to the observed ππ mass spectrum.     

Electronic energy band parameters of graphite and their dependence on pressure,temperature and acceptor concentration

An analysis has been made of experimental data on the dependence of electronic properties of graphite on pressure and acceptor concentration, using the Slonczewski-Weiss dispersion relationship for the free carriers. It is shown that such experiments cannot be interpreted adequately without taking into account all of the band-overlap parameters in this theory. Previous workers had particularly neglected the influence of the parameter γ₃, which trigonally warps the constant energy surfaces. The results presented will also be useful for interpreting new experiments in which either the band overlap parameters or the Fermi-energy are changed. A discussion of possible changes in band parameters with temperature is included.     

Galvanomagnetic effects in graphite—III: The effect of neutron irradiation on the quantum limit Shubnikov-de Haas oscillations

Galvanomagnetic effects have been studied for a range of highly oriented, neutron-irradiated samples of graphite at 1.2–7K, in fields up to 9 Tesla. Irradiation doses were in the range $\text{0}\text{?}\text{?3× 10}{}^{17}\text{nvt}\text{(E> 1}\text{MeV}$). Asymptotic values of σ_xyB were used to obtain independent values of the carrier density difference (P-N). Shubnikov-de Haas frequencies, effective masses, Dingle temperatures and coincidence fields in the quantum limit were measured. Theoretical values for the variation of these quantities with the Fermi energy, (P-N) and with band overlap parameters were also obtained. The results could not be fitted to a simple model in which reasonable changes were allowed in ?_F and the band parameters.     

The clinical significance of stage 2 meniscal abnormalities on magnetic resonance knee images

The Stage 2 meniscal abnormality was subdivided into Stage 2A--linear abnormal signal not contacting an articular surface, Stage 2B--abnormal signal in contact with the articular surface on a single image, Stage 2C--extensive wedge-shaped signal abnormality not in contact with an articular surface. Arthroscopy showed tears in 2A 3%, 2B 0%, 2C 50%. Complete tears should only be diagnosed if contact is seen on more than one image. Many Stage 2C menisci may have tears.     

A kinetic theory of spectral line shapes

The methods of kinetic theory are used to describe the radiation from an atom immersed in a gas of perturbing particles. It is shown that the line shape can be expressed in terms of a one-particle distribution function. The appropriate BBGKY hierarchy of equations is derived. This hierarchy is then truncated by assuming that only two-body collisions are important. The resulting equations are solved to obtain a non-Markovian kinetic equation which describes the combined effects of Doppler and pressure broadening. When the Markovian assumption is applied, a generalized linear Boltzmann equation is obtained which describes the line shape in the region where the impact limit is valid and which also describes the phenomenon of collisional narrowing.This research was supported in part by the Advanced Research Projects Agency of the Department of Defense, monitored by Army Research Office-Durham under Contract No. DA-31-124-ARO-D-139.     

Reaction of a cyclic triphosphenium ion with triflic acid and SnX2 (X = Br or Cl): A 31P NMR study

The di‐ium dication formed by triflic acid protonation of the cyclic triphosphenium ion derived from 1,4‐bis‐diphenylphosphinobutane, (dppb), and P₃(X = Br or Cl) decomposes via an acyclic dication bearing a  PHX group; this intermediate is reduced by SnX₂ in the presence of HX to yield a dication with a  PH₂ primary phosphane terminal group, which is comparatively stable. The structure of this species has been unequivocally confirmed by ³¹P solution‐state NMR spectroscopy. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:609–612, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20302     

Facile, fast, and inexpensive synthesis of monodisperse amorphous nickel-phosphide nanoparticles of predefined size

Monodisperse, size-controlled Ni-P nanoparticles were synthesised in a single step process using triphenyl-phosphane (TPP), oleylamine (OA), and Ni(II)acetyl-acetonate. The nanoparticles were amorphous, contained ~30 at% P and their size was controlled between 7-21 nm simply by varying the amount of TPP. They are catalytically active for tailored carbon nanotube growth.     

FRET detection of proteins using fluorescently doped electrospun nanofibers and pattern recognition

This paper reports the fabrication of solid-state nanofiber sensor arrays and their use for detection of multiple proteins using principal component analysis (PCA). Four cationic and anionic fluorescently embedded nanofibers are generated by an electrospinning method, yielding unique patterns of fluorescence change upon interaction with protein samples. Five metal and nonmetal containing proteins, i.e., hemoglobin, myoglobin, cytochrome c, BSA, and avidin, have been investigated; and the results show that distinct fluorescent patterns can be formed upon the addition of protein samples to the array of solid nanofiber substrates, allowing their unambiguous identification. The nanofiber films are highly repeatable with a batch-to-batch variation of approximately 5% and demonstrated outstanding reusability with less than a 15% loss of fluorescence intensity signal after 5 regenerations of test cycles. For a more practical visualization, a cluster map was generated using PCA of the change-in-fluorescence (ΔI) composite patterns, demonstrating the potential of the method for diagnostic applications.     

Polarization switching without domain formation at the intrinsic coercive field in ultrathin ferroelectric PbTiO₃

Polarization switching in ferroelectrics has been thought to occur only through the nucleation and growth of new domains. Here we use in situ synchrotron x-ray scattering to monitor switching controlled by applied chemical potential. In sufficiently thin PbTiO? films, nucleation is suppressed and switching occurs by a continuous mechanism, i.e., by uniform decrease and inversion of the polarization without domain formation. The observed lattice parameter shows that the electric field in the film during switching reaches the theoretical intrinsic coercive field.