Electroproduction of strangeness

Formalism for the electroproduction of strange particles based on the one photon exchange approximation and the Feynman diagrams representation of hadron current is reviewed. Different photoproduction models are compared with available photo and electroproduction data. New experiments are proposed that may resolve existing uncertainties and inconsistencies. The formation of hypernuclei via kaon electroproduction is investigated theoretically and compared with other reactions involving purely hadronic processes.     

Extrathermodynamic approach to the study of the adsorption of organic compounds by macromolecules

By using substituent constants and regression analysis, an analysis has been made of the binding of derivatives of aniline and acetanilide to nylon and rayon, the experimental data of Ward and Upchurch being used. The amount of organic compounds bound from an aqueous solution by these two types of synthetic macromolecules is shown to be related to the octanol–water partition coefficients P. In the case of the aniline derivatives, where the basicity of the compounds varied considerably, a good model describing binding results from the linear combination of the two parameters related to free energy, i.e., log P and ΔpK_a. The latter term is the difference between pK_a for aniline and a particular derivative. For the neutral acetanilides a simple linear free-energy relation between log P and log K is found. Of special note is the fact that the dependence of binding of these two classes of compounds to two classes of synthetic macromolecules as indicated by the coefficient with the log P term very closely parallels that found for a variety of biopolymers. The mechanism of hydrophobic binding seems to be the same in both the synthetic and natural polymers.     

UV-holographic gratings in TS-diacetylene single crystals

Holographic gratings with grating periods between 0.37 m and 4.4 m, respectively, were recorded on the surface of TS-diacetylene single crystals by two interfering 257 nm laser beams. Diffraction efficiencies of up to 35 % were obtained for readout with red light of = 633 nm. The main modulation mechanism was phase modulation. The spatial resolution was better than 1600 lines/mm. The upper limit of the polymer chain length was 0.6 m. The holographic sensitivity was 4.5 cm²/J for immediate read-out at 633 nm without processing after exposure. — A weakly exposed latent hologram may be developed simply by gentle annealing the crystal which increases the sensitivity by one order of magnitude.     

Development of a tunable mid-IR difference frequency laser source for highly sensitive airborne trace gas detection

The development of a compact tunable mid-IR laser system at 3.5 μm for quantitative airborne spectroscopic trace gas absorption measurements is reported. The mid-IR laser system is based on difference frequency generation (DFG) in periodically poled LiNbO₃ and utilizes optical fiber amplified near-IR diode and fiber lasers as pump sources operating at 1083 nm and 1562 nm, respectively. This paper describes the optical sensor architecture, performance characteristics of individual pump lasers and DFG, as well as its application to wavelength modulation spectroscopy employing an astigmatic Herriott multi-pass gas absorption cell. This compact system permits detection of formaldehyde with a minimal detectable concentration (1σ replicate precision) of 74 parts-per-trillion by volume (pptv) for 1 min of averaging time and was achieved using calibrated gas standards, zero air background and rapid dual-beam subtraction. This corresponds to a pathlength-normalized replicate fractional absorption sensitivity of 2.5×10^-10 cm^-1. Received: 29 April 2002 / Published online: 21 August 2002 RID="*" ID="*"Corresponding author. Fax: +1-303/497-1492, E-mail: dr@ucar.edu     

Total cross section for hadron production bye + e − annihilation between 9.4 and 9.5 GeV

The total cross section fore ⁺ e ^? annihilation into hadrons for center of mass energies from 9.4 to 9.5 GeV has been measured with the nonmagnetic DESY-Heidelberg detector at DORIS. A value ofR=σ_had/σ_µµ=3.8±0.7 for the continuum region around the Υ (9.46) resonance has been determined. The ratioΓ _ee Γ _had/Γ _tot of electronic, hadronic and total widths has been reevaluated to be (1.00±0.23) keV for the Υ resonance and (0.37±0.16) keV for the Υ′. In addition, a search for directly produced pohotons from Υ decays of the type Υ→γ+gluon+gluon has been performed. The Υ decay into muon pairs has also been searched for.     

High pressure-induced structural effects in plastic packaging

Today, flexible vacuum packages are predominantly used for products to be subjected to high pressure treatment. However, tray packages with a modified atmosphere are in demand, which provide a high failure rate with respect to gas and water vapour permeability and packaging integrity. Methods to follow permeation processes under high pressure were developed and used together with optical microscopy, confocal scanning laser microscopy, Raman spectroscopy and atomic force microscopy to identify the mechanisms for changes in permeability and damage to the packaging materials. Single film samples and pouch packages filled with model products were studied. Results indicate a reversible decrease in the coefficients of diffusion and permeation under the impact of high pressure, due to the compression of the polymeric bulk. Irreversible changes in the polymeric materials are associated with gases in the packaging head space, which cause high local temperatures and create damage due to rapid deliberation upon the pressure drop at the end of the high pressure cycle.