Search

Od srpnja 2018. godine, zakonski je propisano da se u sklopu obvezne kontrole kvalitete dentalnih panoramskih rendgenskih i CBCT uređaja moraju provoditi mjerenja kerme i površine (KAP)za panoramske rendgenske uređaje te umjeravanje KAP metara za dentalne CBCT uređaje. Započeli smo projekt uspostave baze podataka panoramskih rendgenskih uređaja i CBCT uređaja u dentalnoj medicini u uporabi u Republici Hrvatskoj kako bi omogućili usporedbu modela i proizvođača te pratili kako se njihova svojstva mijenjaju s vremenom i korištenjem. U ovom radu predstavljena su naša prva mjerenja te raspravljeni problemi koji su se pojavili tijekom implementacije EFOMP CBCT protokola u hrvatskoj regulativi, a posljedično i tijekom provedbe godišnje provjere kvalitete

We propose a simple formula for multichannel resonant scattering with parameters related to physical resonant properties. It can be used to predict residue phase from other resonant parameters and describe the shape of scattering amplitudes close to the resonance without any background contributions or fitting. It works well even for overlapping resonances. Imposing unitarity to the proposed formula enabled us to explain some puzzling features of much more advanced models., 5 pages, 3 figures, 2 tables

Usvajanjem i daljnjim usavršavanjem Carnegie-Melon-Berkeley analitične, unitarne više-kanalne analize parcijalnih valova koje je zagrebačka grupa započela još daleke 1994 godine, uočena je mogućnost da se kompletnost metode iskoristi kao sredstvo ostvarivanja novog uvida u problematiku prirode nukleonskih rezonancija. Zagrebačka grupa je uočila da se svjetski tek naznačena moguća različitost između dva tipa rezonancija, standardnih i dinamički generiranih, u zagrebačkoj verziji CMB modela može konkretizirati na vezu između postojanje golog i obučenog pola Greenove funkcije. U literaturi je pokazano da osim standardnih nukleonskih rezonancija, čiji se nastanak veže uz postojanje pola elementarne amplitude raspršenja, postoji i druga klasa rezonancija kod kojih uzrok rezonantnog ponašanje parcijalno-valnih matrica raspršenja ne leži u postojanju elementarnog singulariteta, već se rezonirajuće ponašanje stvara kolektivnim djelovanjem svih mogućih čestičnih među-stanja. Ta različitost se u zagrebačkoj verziji CMB modela konkretizira i operacionalizira. Kao što je u svjetskoj literaturi istaknuto, neobična svojstva N(1440) P11 – tzv. Roperove rezonancije, ističu je kao kandidata da se njena priroda detaljnije istraži, i ustvrdi da li je ona mogući kandidat za jedno od rijetkih dinamičkih rezonantnih stanja. Osim što se potvrđuju ove spekulacije o prirodi Roperove rezonancije, dodatno se pronalazi još jedno stanje koje se po svojem ponašanju ističe kao slijedeći prirodni kandidat za dinamičko rezonantno stanje, a to je rezonancija u G17 parcijalnom valu. Pokazuje se da priroda tog rezonantnog stanja N(2190) G17 u našem modelu ovisi o tome da li se kao analizirani podaci uzmu Karlsruhe-Helsinki (KH80) ili George Washington University (GWU) parcijalni valovi. Konačan odgovor nije, i ne može biti dan bez uzimanja u obzir i eksperimentalnih podataka u drugim, za sada još nemjerenim kanalima. Stoga se samo ukazuje na tu mogućnost, ali ostavlja da se konačni odgovor donese u budućem znanstvenom istraživanju.

Eta meson production in the proton– proton scattering is dominated by the low-mass meson exchange. We present a brief study on how the type of the exchanged mesons within coupled-channel and multi-resonance model influences the scattering observables. We show under which circumstances the eta exchange may explain the shape of the observed cross-sections, and present a few selected results: total cross-section in the full energy range, and the proton– proton energy distribution at 15.5 MeV.

It is argued in [1] that when the strong coupling to the K Lambda channel is considered, Breit-Wigner mass of the lightest orbital excitation of the nucleon N(1535) shifts to a lower value. The new value turned out to be smaller than the mass of the lightest radial excitation N(1440), which effectively solved the long-standing problem of conventional constituent quark models. In this Comment we show that it is not the Breit-Wigner mass of N(1535) that is decreased, but its bare mass. [1] B. C. Liu and B. S. Zou, Phys. Rev. Lett. 96, 042002 (2006).

Partial wave scattering matrix poles, representing a link between experimental data and quark-model resonant states, contain two sources of ambiguities and uncertainties: fundamental (continuum ambiguities) and factual (quality of input data). Furthermore, two types of scattering matrix singularities are identifed when energy dependence of partial wave data is implemented through a coupled-channel model: bare and dressed Green function poles. Both types of uncertainties, for both type of poles, are strongly reduced by extending the data base in the direction of increasing the number of accessible and utilized channels. As we strongly suspect that the quality of data in one channel is of less importance then the overall number of used channels, new measurements in inelastic meson-nucleon sector are recommended, and recognized as a task of prime importance.

The method of avoiding continuum ambiguities in a pion-nucleon partial wave analysis in the inelastic region by using the coupled channel formalism is discussed. The very number of poles of the analytic partial wave T-matrix, their position in the complex energy plane and their residues depend strongly on the number of channels used for constraining the free parameters of the model. The criteria for determining the minimal number of poles needed to describe the given input are discussed, and the procedure of increasing the number of poles necessary for simultaneously describing additional channels is introduced. The interplay of the pole structure and the number of inelastic channels is demonstrated for the P11 partial wave for the case of inclusion of pi N -> eta N channel into the coupled channel partial wave analysis in addition to the full pi N elastic data base. The N(1710) P11 resonance is a clear example when the continuum ambiguity, present when solely the pi N elastic scattering data are analyzed, is spontaneously eliminated by increasing the number of resonant states when the piN -> eta N channel data are included in the framework of coupled channel partial wave analysis formalism.

The pole structure of the P11 pion-nucleon partial wave is examined with the emphasis on the 1700 MeV energy domain. The mechanism of eliminating continuum ambiguities in pion-nucleon partial wave analyses by using the coupled channel formalism, presented elsewhere for the piN -> etaN channel, is applied for the piN -> K Lambda channel, with the aim to clarify the issue whether physical reality requires none (VPI/GWU), one (KH80, CMB, Kent, Pittsburgh/ANL, Giessen), or possibly two (Zagreb) poles of the partial wave T-matrix in the 1700 MeV range. The role of second inelastic channel for resolving the dilemma is demonstrated. It is pointed out that the experiments for the piN -> K Lambda and piN -> K Sigma channel, extremely important for the 1700 MeV range, are old and inconclusive so an urgent need for remeasuring that channel is stressed., 4 pages, 5 figures; talk held at NSTAR 2005 in Tallahassee, FL

In spite of prolonged polemics, the agreement on the existence of N(1710) P11 resonance has not until now been reached, and the Particle Data Group declares it as a 3-star resonance only. We show that the proper inclusion of inelastic channels in the coupled-channel formalism indisputably demands the existence of N(1710) P11 state, and that it presumably stays "hidden" within the continuum ambiguity of any typical single channel partial wave analyses. Consequently, its Particle Data Group confidence rating should be raised to a 4-star resonance.

given on the link.

The new and improved treatment of eta meson exchange diagrams turns out to be essential in order to fully describe both total cross-sections and, in particular, the challenging pp invariant mass distributions. Contrary to other approaches, the eta meson contribution in our model is comparable with the leading pi meson exchange term, and using the phenomenological final state interaction we have no need to include other mesons, like rho and omega, in order to obtain good agreement with experiment.

The partial wave T-matrices for the piN, etaN and pi^2N channels have been obtained within the framework of the coupled channel model using the piN elastic and piN - etaN data base as input. It has been shown that for the P11partial wave an equally good representation of the experimental data (namely the T_{; ; ; pi N, pi N}; ; ; and T_{; ; ; pi N, eta N}; ; ; T-matrices) can be obtained using either three, or four poles for the Green function propagator. However, the three Green function pole solution is not acceptable due to the structure of the extracted resonances. The two out of four P11 resonances, those lying in the energy range 1700 MeV < M_R < 1800 MeV, are poorly determined, but they seem to be strongly inelastic. The inclusion of other inelastic channels is needed to determine masses and widths of missing resonances with greater precision.

The OPERA experiment foresees the use of about 3000 m^2 of RPCs, that will be tested before the installation in a dedicated cosmic ray test facility. The test facility is composed of 2 triggering walls selecting horizontal cosmic rays muons. Each wall houses 64 glass RPCs equipped with 128 horizontal Flat Cable Strips. The z-coordinate is measured with a standard digital chain, while the x-coordinate is obtained by measuring the propagation time of the signals along the strips. In this paper the performance of the trigger walls and the first results of the RPC debug are presented.

Vrijednosti parametara nukleonskih rezonancija dobivenih u višekanalnom, višerezonantnom i unitarnom modelu, korištene su za opis inelasticnog raspršenja piona na protonu za kanal KL. Uz pretpostavku da se proces može dobro opisati koristeci koherentni zbroj jedno-rezonantnih dijagrama za S_11, P_11 i P_13 parcijalne valove pokazano je da proracun zasnovan na standardnim parametrima iznesenim u [3] ne daje dobro slaganje posebno s oblikom diferencijalnog udarnog presjeka [4, 5]. Slaganje ukupnog udarnog presjeka s mjerenim vrijednostima je dobro. Korištenje novopredloženih parametara, a i u potpunosti otklanja neslaganje. Potrebno je, stoga, vrijednost standardno prihvacenih parametara S_11, P_11 i P_13 rezonancija uskladiti s novim saznanjima.

Prikazana je geometrija crvotočina. Raspravljena je mogućnost pretvaranja crvotočina u vremeplove. Diskutirani su vremenski paradoksi.

Dvočestične amplitude raspršenja dobivene u višekanalnom, višerezonantnom i unitarnom modelu primjenjene su u analizi višečestičnih procesa.