122 research outputs found
Semileptonic form factors - a model-independent approach
We demonstrate that the B->D(*) l nu form factors can be accurately predicted
given the slope parameter rho^2 of the Isgur-Wise function. Only weak
assumptions, consistent with lattice results, on the wavefunction for the light
degrees of freedom are required to establish this result. We observe that the
QCD and 1/m_Q corrections can be systematically represented by an effective
Isgur-Wise function of shifted slope. This greatly simplifies the analysis of
semileptonic B decay. We also investigate what the available semileptonic data
can tell us about lattice QCD and Heavy Quark Effective Theory. A rigorous
identity relating the form factor slope difference rho_D^2-rho_A1^2 to a
combination of form factor intercepts is found. The identity provides a means
of checking theoretically evaluated intercepts with experiment.Comment: 18 pages, Revtex, 4 postscript figures, uses epsfig.st
Učinci UV zračenja visokog intenziteta na izdvojen i s dna interkaliran etidium bromid
High-intensity picosecond laser flash photolysis has been used for investigating ethidium bromide (EtBr). The quantum yield of primary photoproducts as a function of the laser intensity has been obtained. DNA intercalated EtBr and water solutions of EtBr have been investigated. The results have been compared. They show that two-photon processes are predominantly responsible for generation of hydrated electron (eaq-). The primary processes of DNA photosensitization have also been discussed.Istraživali smo etidium bromid (EtBr) pomoću pikosekundne bljeskovne fotolize velikog intenziteta. Određeni su kvantni prinosi fotoprodukata u ovisnosti o intenzitetu laserskog snopa. Istraživao se je EtBr u vodenoj otopini i interkalirani s DNA. Rezultati se uspoređuju i oni pokazuju da pretežno dvofotonski procesi tvore hidrirane elektrone eaq-. Raspravljaju se također primarni procesi fotosenzitiranja DNA
Učinci UV zračenja visokog intenziteta na izdvojen i s dna interkaliran etidium bromid
High-intensity picosecond laser flash photolysis has been used for investigating ethidium bromide (EtBr). The quantum yield of primary photoproducts as a function of the laser intensity has been obtained. DNA intercalated EtBr and water solutions of EtBr have been investigated. The results have been compared. They show that two-photon processes are predominantly responsible for generation of hydrated electron (eaq-). The primary processes of DNA photosensitization have also been discussed.Istraživali smo etidium bromid (EtBr) pomoću pikosekundne bljeskovne fotolize velikog intenziteta. Određeni su kvantni prinosi fotoprodukata u ovisnosti o intenzitetu laserskog snopa. Istraživao se je EtBr u vodenoj otopini i interkalirani s DNA. Rezultati se uspoređuju i oni pokazuju da pretežno dvofotonski procesi tvore hidrirane elektrone eaq-. Raspravljaju se također primarni procesi fotosenzitiranja DNA
Laserska izravna dvofotonska fotoliza guanina u DNK
Nanosecond laser-induced oxidative lesions at guanines within DNA were investigated using sequencing gel electrophoresis analysis. Strong sequence-specific lesions on guanines were revealed by either Fpg or piperidine treatments and assigned to 8-oxoG and oxazolone, respectively. It was shown that both the biphotonic ionization process and the chemical reactivity of the radical cation (G+) are dependent on the DNA sequence. The former were explained by the occurrence of energy and charge migration phenomena, while the latter in terms of local DNA hydration peculiarities.Istraživali smo lomove DNK izazvane nanosekundnim laserskim impulsima primjenom gel elektroforeze za određivanje nizova. Otkrili smo snažne nizovno specifične lomove kod guanina djelovanjem sa Fpg ili piperidinom i oni se pripisuju 8-oxoG odnosno oxazolonu. Pokazali smo da su i dvofotonski ionizacijski proces i kemijska reaktivnost radikala kationa (G+) nizovno ovisni. Prvi se objašnjava selenjem energije i naboja, a drugi kao posebnosti lokalnog hidriranja DNK
Distinguishing WH and WBBbar production at the Fermilab Tevatron
The production of a Higgs boson in association with a W-boson is the most
likely process for the discovery of a light Higgs at the Fermilab Tevatron.
Since it decays primarily to b-quark pairs, the principal background for this
associated Higgs production process is WBBbar, where the BBbar pair comes from
the splitting of an off mass shell gluon. In this paper we investigate whether
the spin angular correlations of the final state particles can be used to
separate the Higgs signal from the WBBbar background. We develop a general
numerical technique which allows one to find a spin basis optimized according
to a given criterion, and also give a new algorithm for reconstructing the W
longitudinal momentum which is suitable for the WH and WBBbar processes.Comment: latex, 12 pages, 19 postscript figure
Laserska izravna dvofotonska fotoliza guanina u DNK
Nanosecond laser-induced oxidative lesions at guanines within DNA were investigated using sequencing gel electrophoresis analysis. Strong sequence-specific lesions on guanines were revealed by either Fpg or piperidine treatments and assigned to 8-oxoG and oxazolone, respectively. It was shown that both the biphotonic ionization process and the chemical reactivity of the radical cation (G+) are dependent on the DNA sequence. The former were explained by the occurrence of energy and charge migration phenomena, while the latter in terms of local DNA hydration peculiarities.Istraživali smo lomove DNK izazvane nanosekundnim laserskim impulsima primjenom gel elektroforeze za određivanje nizova. Otkrili smo snažne nizovno specifične lomove kod guanina djelovanjem sa Fpg ili piperidinom i oni se pripisuju 8-oxoG odnosno oxazolonu. Pokazali smo da su i dvofotonski ionizacijski proces i kemijska reaktivnost radikala kationa (G+) nizovno ovisni. Prvi se objašnjava selenjem energije i naboja, a drugi kao posebnosti lokalnog hidriranja DNK
Direct experimental test of scalar confinement
The concept of Lorentz scalar quark confinement has a long history and is
still widely used despite its well-known theoretical faults. We point out here
that the predictions of scalar confinement also conflict directly with
experiment. We investigate the dependence of heavy-light meson mass differences
on the mass of the light quark. In particular, we examine the strange and
non-strange D mesons. We find that the predictions of scalar confinement are in
considerable conflict with measured values.Comment: REVTeX4, 7 pages, 4 EPS figure
Semiempirical versus ab Initio Calculations of Molecular Properties. I. Diamagnetic Susceptibilities and Quadrupole Moments in Some Medium Size Molecules
The self-consistent charge molecular orbital (SCC-MO) method
was applied to a number of medium size molecules involving atoms
exhibiting large differences in electronegativity and possessing one
or more lone pairs. The quality of the wave functions thus obtained
was applied to a number of medium size molecules involving atoms
calculated by a rigorous treatment of the operators x2, y2, and z2•
The SCC quadrupole moments can be favourably compared with the
ab initio results of Snyder and Basch obtained by the use of a
Gaussian double zeta basis set. The present results provide additional
justification of the sec method, which has apparent advantages
over the methods based on the ZDO approximation. Some difficulties
encountered in the treatment of pi-electrons are discussed and
suggestions for their remedy are given. The second moments
calculated by the application of a simple additivity formula (Z. B.
Maksic and J. E. Bloor, Chem. Phys. Lett., 13 (1972) 571; J. Phys.
Chem., 77 (1973) 1520) and the related diamagnetic susceptibilities
are in very good agreement with the ab initio values
On P-wave meson decay constants in the heavy quark limit of QCD
In previous work it has been shown that, either from a sum rule for the
subleading Isgur-Wise function or from a combination of Uraltsev and
Bjorken SR, one infers for -wave states . This implies, in the heavy quark limit of QCD, a hierarchy
for the {\it production} rates of -states that seems at
present to be contradicted by experiment. It was also shown that the decay
constants of -states vanish in the heavy quark limit of
QCD, . Assuming the {\it model} of factorization in the
decays , one expects the opposite hierarchy for
the {\it emission} rates , since
-states are coupled to vacuum. Moreover, using Bjorken SR and previously
discovered SR involving heavy-light meson decay constants and IW functions, one
can prove that the sums ,
(where and
are the decay constants of -states and
-states) are divergent. This situation seems to be realized in the
relativistic quark models \`a la Bakamjian and Thomas, that satisfy HQET and
predict decays constants and that do not decrease
with the radial quantum number .Comment: 7 pages, Late
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