[en] In this thesis, hadron structure was explored by studying three problems. In each case some underlying hard process, or a characteristic hard momentum, yielded important physical information such as structure and fragmentation functions describing hadrons. This provided a test of QCD predictions. In the first problem, spin dependent quark structure functions were estimated for nuclei. The multipole L=2 structure function, measurable in deeply inelastic scattering of unpolarized leptons off a polarized J_> 1 nuclear target, is a good indicator of exotic quark gluon components in the nucleus. I estimated this structure function for two different classes of nuclei light nuclei describable in an independent particle model approach, as well as for heavy nuclei described by slowly rotating collective variables. In the second problem, spin dependent gluonic structure functions in a transversely polarized proton were identified and the classification according to twist was discussed. I found that there were two twist three transverse spin gluonic structure functions, called herein H1(x,Q2) and H2(x,Q2). Cross section formulae were calculated for a variety of polarization states, assuming a simple effective interaction for X2 production from gluon fusion. In the third, and final problem, the emphasis shifted from spin dependent structure functions of polarised hadrons to the formulation of an effective, low energy, field theory of s wave quarkonia, constituent heavy quarks, and gluons. and radiative transitions were shown to be easily recovered. The light-cone gluon momentum distribution at very small x was calculated and shown to be uniquely determined by the non relativistic wave function. I found that the emission of low momentum gluons made this process quite sensitive to assumptions about the binding energy of heavy quarks in quarkonia. This gauge invariant theory is extend able to p-wave quarkonia where the non locality of the meson state is enhanced by the centrifugal barrier, thereby making a gauge invariant description still more important. A framework to study quarkonia with spin is provided in this part of the thesis. (Orig./A.B.)

[en] Ultraviolet radiation of 254 nm was found to cause a dose dependent, essentially irreversible inactivation of mushroom tyrosinase (EC1.14.18.1). Photoinactivation, tryptophan destruction and fluorescence loss obeyed first order kinetics and the apparent first order rate constants being 17.9 x 10^-2 min^-1, 3.7 x 10^-2 min^-1 and 6.3 x 10^-2 min^-1, respectively. In contrast to native tyrosinase, photoinactivated enzyme was found to be sensitive towards tryptic attack. The kinetics of tryptic hydrolysis suggested partial unfolding of tyrosinase by UV light. Fluorescence difference spectral studies indicated loss in transfer of excitation energy between tyrosine and tryptophan residues in photoinactivated tyrosinase. The influence of varying radiation dose on tryptic digestibility, intrinsic fluorescence and UV absorption are altogether consistent with the conformational changes associated with photoinactivation of tyrosinase. (author)

[en] The Kansas State CRYEBIS facility was used to study the collisional dynamics for the collisional system of Ar¹⁵⁺ with a cold gas jet argon atom target. This system is studied over the collisional velocity range of 0.2 a.u. ≤ v_p ≤ 2.0 a.u. Up to eight target electrons become molecular during the collision leading to multiply-excited states in the projectile which then Auger and radiative decay to a ground state configuration. The final charge states of the projectile and target are measured on position sensitive detectors, thereby enabling the determination of the momentum transfer to the target. This angular scattering (transverse momentum transfer) and the Q-values (longitudinal momentum transfer) are compared with the predictions from the extended over-barrier model for ion-atom collisions

[en] We have analyzed the decrease in synthesis of individual size classes of heterogeneous nuclear RNA (hnRNA) in ultraviolet (uv)-irradiated Merwin plasmacytoma (MPC-11) cells at various times of postirradiation incubation. HnRNA from nonirradiated control cells is distributed over a wide range from approximately 60S to 5S, with 42S RNA carrying more label than any other size class. HnRNA from uv-irradiated cells shows a dose-dependent shift in size distribution toward lower molecular weight. The size distribution of hnRNA synthesized after prolonged times of postirradiation incubation is restored toward normal, i.e., synthesis of long RNA molecules increases relative to the synthesis of short ones. Analysis of the total number of hnRNA chains synthesized during a 20-min [³H]uridine pulse shows a considerable eduction in their number with increasing uv dose. Murine cell lines are excision-repair-deficient but capable of post replication repair inhibited by caffeine. HnRNA transcripts of cells incubated in its presence were studied. The caffeine, which has no effect on hnRNA size in control cells, inhibits to a considerable extent the restoration of full-length transcripts during postirradiation incubation. The lack of excision repair in MPC-11 was confirmed by the analysis of pyrimidine dimers in trichloracetic acid-insoluble and soluble fractions within 8 h of postirradiation incubation. The size of parental and daughter strand DNA in uv-irradiated cells was correlated with RNA transcript size. The parental DNA in these experiments does not change its size as a consequence of uv exposure and postirradiation incubation. In contrast, daughter DNA strands are short in uv-irradiated cells and they increase in size during postirradiation incubation to reach the size of parental strands after 8 h

[en] The 2 ¹S₀ state in helium-like ions is forbidden to decay to the ground state by the emission of a single photon so the dominant decay mode is emission of two E1 photons. The energies of the individual photons have a continuous distribution with a broad peak at half the transition energy and the sum of the energies of the two photons is equal to the transition energy. The shape of the continuum single-photon spectrum provides a sensitive probe of the calculation of the transition probability for this decay and we have started a program to make a precision measurement of the spectral shape of the decay of the 2 ¹S₀ level in He-like krypton in order to test the calculations

[en] Ionization and fragmentation have been measured for C₆₀ molecules bombarded by highly charged (up to 35+) xenon ions with energies ranging up to 625 MeV. The observed mass distribution of positively charged fragments is explained in terms of a theoretical model indicating that the total interaction cross section contains roughly equal contributions from (a) excitation of the giant plasmon resonance, and (b) large-energy-transfer processes that lead to multiple fragmentation of the molecule. Preliminary results of measurements on VUV photons emitted in these interactions are also presented

[en] In 1985, Robert Curl and Richard Smalley discovered a new form of carbon, the fullerene, C₆₀, which consists of 60 carbon atoms in a closed cage resembling a soccer ball. In 1990, Kritschmer et al. were able to make macroscopic quantities of fullerenes. This has generated intense activity to study the properties of fullerenes. One area of research involves collisions between fullerenes and atoms, ions or electrons. In this paper we describe experiments involving interactions between fullerenes and highly charged ions in which the center-of-mass energies exceed those used in other work by several orders of magnitude. The high values of projectile velocity and charge state result in excitation and decay processes differing significantly from those seen in studies 3 at lower energies. Our results are discussed in terms of theoretical models analogous to those used in nuclear physics and this provides an interesting demonstration of the unity of physics

[en] Ultraviolet irradiation of tyrosinase rapidly decreased the dopa oxidase activity of the enzyme. Hydrodynamic, kinetic and thermodynamic parameters revealed gross differences in the native and photoinactivated states of the enzyme. The native state of tyrosinase was characterized as a tetramer with a compact, globular and rigid conformation. However, the photoinactivated state of tyrosinase was thermodynamically less stable and unusually sensitive to temperatures as low as 35 ⁰C. From the dose dependent loss in conformational integrity, thermodynamic stability and catalytic activity of tyrosinase, it is speculated that there are various structural segments distributed throughout the enzyme molecule. These structural segments act as centres of major molecular forces which hold the tetrameric enzyme into a compact and globular conformation. UV modification of these segments triggers a series of conformational changes leading to formation of a partially unfolded and catalytically inactive form of tyrosinase. (author)

[en] Ionization and fragmentation were measured for C₆₀ molecules bombarded in the vapor phase by Xe³⁵⁺ and Xe¹⁸⁺ ions with energies in the range 420-625 MeV. The CM energies exceeded those used in previous studies by several orders of magnitude. The mass distribution for the resulting positively charged fragments was determined and we studied the dependence of the fragment yields on the energy and charge of the projectiles. We developed a theoretical model that indicates the total interaction cross section contains roughly equal contributions from (1) excitation of the giant plasmon resonance, and (2) large-energy-transfer processes leading to multiple fragmentation of the molecule

[en] Unequivocal evidence for significant target outer-shell excitation accompanying multiple-electron capture, in slow collisions of highly charged ions with many-electron atoms, has been obtained by means of simultaneous Auger-electron and cold-target recoil-ion momentum spectroscopic measurements. For the 28 keV ¹⁵N⁷⁺+Ar collision system, it is found that target excitation accompanies about 40% of all double-electron capture collisions. The evidence supports the predictions of the molecular classical overbarrier model by Niehaus [A. Niehaus, J. Phys. B 19, 2925 (1986)]. (c) 1999 The American Physical Society