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41.
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 σtot
πp/σtot
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, σπ(r
1⊥, r
2⊥; s) and σp(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 相似文献
42.
43.
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 相似文献
44.
Sharon R. George 《Applied Surface Science》2009,255(24):9558-9561
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. 相似文献
45.
Zhiqiang Gao Shujing Peng Jie Sun Lan Yao Yiping Qiu 《Applied Surface Science》2009,255(17):7683-7688
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. 相似文献
46.
I.V. Krasnov 《Physics letters. A》2009,373(26):2291-2297
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. 相似文献
47.
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. 相似文献
48.
The mass spectra of ground-state triply heavy baryons are systematically unscrambled and computed in QCD sum rules. With a tentative (QQ)–(Q′) configuration for QQQ′, 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. 相似文献
49.
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. 相似文献
50.
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. 相似文献