Hadron diffractive processes: the structure of soft pomeron and colour screening

On the basis of the experimental data on diffractive processes in πp, pp and pˉp collisions at intermediate, moderately high and high energies, we restore the scattering amplitude related to the t-channel exchange by vacuum quantum numbers by taking account of the diffractive s-channel rescatterings. At intermediate and moderately high energies, the t-channel exchange amplitude turns, with a good accuracy, into an effective pomeron which renders the results of the additive quark model. At superhigh energies the scattering amplitude provides a Froissart-type behaviour, with an asymptotic universality of cross sections such as σ^tot _πp/σ^tot _pp→ 1 at s→∞. The quark structure of hadrons being taken into account at the level of constituent quarks, the cross sections of pion and proton (antiproton) in the impact parameter space of quarks, σ_π(r _1⊥, r _2⊥; s) and σ_p(r _1⊥, r _2⊥, r _3⊥; s), are found as functions of s. These cross sections implicate the phenomenon of colour screening: they tend to zero at |r _i⊥−r _k⊥|→ 0. The effective colour screening radius for pion (proton) is found for different s. The predictions for the diffractive cross sections at superhigh energies are presented. Received: 15 December 1998     

Dipole traps with mode-locked lasers

We investigate the properties of two separate dipole traps, realised using a cw mode-locked Ti:sapphire laser and a cw mode-locked Nd:YVO₄ laser, red-detuned by 25 nm and 284 nm, respectively. Approximately 10³ laser-cooled ⁸⁵Rb atoms were confined in the traps at ≈50 μK, with no observable heating after initial loading. The lifetimes of the traps were consistent with limitations imposed by wavelength-dependent photoassociation losses and collisions with background vapour. Determination of the ac Stark shift of the 780 nm cooling transition using a weak probe beam showed no observable difference between using narrow-bandwidth or mode-locked trapping light. Techniques for trapping and focusing of atoms based on the dipole force of blue and uv light become much more accessible through efficient doubling, tripling and quadrupling of mode-locked sources. This opens up the possibility of manipulating more technologically interesting species. Received: 30 September 1999 / Revised version: 21 December 1999 / Published online: 24 March 2000     

Interaction of 157-nm excimer laser radiation with fluorocarbon polymers

Two important fluoropolymers, polytetrafluoroethylene [PTFE—(C₂F₄)_N] and polyvinylidene fluoride [PVDF—(C₂H₂F₂)_N], respond to 157-nm laser radiation in dramatically different ways. At fluences sufficient to produce rapid etching, the volatile emissions from PTFE are dominated by (CF₂)_N fragments. The velocities of the fastest (CF₂)_N molecules at each mass are consistent with kinetic energies on the order of an electron volt—and change little with fluence. This fluence independence suggests that the velocities are not affected by collisions after emission. To account for the high kinetic energies and the unusual, half-monomer mass distribution, we propose that these fragments are produced by photochemical scission of the polymer backbone, and that a fraction of the excitation energy is delivered to each fragment as kinetic energy. In contrast, the principle neutral species from PVDF is HF. HF is produced by the scission of C-F bonds, followed by chemical reactions with nearby hydrogen. This process is accompanied by the conjugation of backbone C-C bonds. The photochemical cleavage of C-C bonds in PTFE and C-F bonds in PVDF is consistent with the lower C-C bond energy of PTFE.     

Influence of processing parameters on atmospheric pressure plasma etching of polyamide 6 films

This study is designed to systematically investigate how various factors, such as treatment duration, output power, oxygen gas flux, jet to substrate distance, and moisture regain, influence atmospheric pressure plasma etching rate of polyamide 6 (PA 6) films. The etching rate increased as the output power, oxygen gas flux, and moisture regain increased. As the treatment time increased, the etching rate increased first and then decreased. When the substrate was too close or too far from the nozzle, the etching rate was almost not measurable. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) show an increased surface roughness after the plasma treatment. X-ray photoelectron spectroscopy (XPS) shows a decreased carbon content and an increased oxygen content after the plasma treatment. T-peel strength shows an improved bonding strength between the PA 6 films and an adhesive tape after the plasma treatment.     

All-optical confinement of ultracold plasma with resonant ions

The solution of the problem of all-optical (nonmagnetic) confinement of ultracold electron-ion neutral plasma based on selective action on plasma ions with quantum transition J=1→J=0 of so-called rectified radiation forces in a strong nonmonochromatic light field is suggested. The presented scheme of the three-dimensional dissipative optical trap for plasma allows one to obtain long-lived ultracold plasma with controlled characteristics. The lifetime of the ultracold plasma in such a trap may exceed considerably (by orders of magnitude) the time of free plasma expansion and the lifetime in the (earlier proposed) optical molasses for the ultracold plasma.     

A Light-Cone QCD Inspired Effective Hamiltonian Model with SU（3） Flavor Mixing

The effective light-cone Harniltonian is extended to include the SU（3） flavor mixing interaction besides the confining potential. Solving the coupled J = 0 mass eigen equations for the up, down, and strange quark components numerically, the masses of π^0 and η, their radial wave functions, and rms radii are obtained in agreement with the experimental data.     

Deciphering triply heavy baryons in terms of QCD sum rules

The mass spectra of ground-state triply heavy baryons are systematically unscrambled and computed in QCD sum rules. With a tentative (QQ)–(Q^′)$(\mathit{QQ})\text{–}(Q^{\prime })$ configuration for QQQ^′${\mathit{QQQ}}^{\prime }$, the interpolating currents representing the triply heavy baryons are proposed. Technically, contributions of the operators up to dimension six are included in operator product expansion (OPE). The numerical results are presented in comparison with other theoretical predictions.     

Novel 1D optical molasses composed of two elliptical Gaussian beams with an ultrahigh orbital angular-momentum

We propose a novel scheme to form a 1D optical molasses by using two counter-propagating red-detuned elliptical Gaussian beams possessing an ultrahigh orbital angular-momentum. In this optical molasses, atoms will suffer both an axial and an azimuthal Doppler cooling, and their temperature can be far below the conventional Doppler cooling limit, which provides a new opportunity for the laser cooling of the most abundant bosonic isotopes of alkaline-earth atoms. Because these atoms lack the hyperfine structure, they cannot be cooled by the well-known sub-Doppler cooling schemes.     

Mechanical, chemical and acoustic properties of new hybrid ceramic-polymer varnishes for musical instruments

Novel ceramic-polymer hybrid varnishes were designed to protect the wood surface of musical instruments. These hybrid coatings consist of chemically functionalized silica nanoparticles and synthetic solvent-based acrylic- and alkyd-polyurethanes. The nanoparticles were added to increase the abrasion resistance. An alkoxide was used to increase the number and reactivity of OH’s groups on the wood surface improving the adhesion with the coating through a chemical link between them. The properties of the synthetic coatings were compared with those of a traditional varnish (based on alcohol and natural resins) to obtain a better performance. Two types of woods were used: maple and spruce. The samples were characterized by UV-Vis, mechanical and abrasion tests, water’s absorption, acoustic properties, chemical resistance and SEM.