The dosimetry of neutron fields of therapeutic complex based on the U-120 cyclotron

In this work, the characteristics of the treat beam's dosimetry of fast neutrons of the U-120 cyclotron have been analyzed with the help of the ionizing method. The fast neutrons with 6, 3 MeV as medium energy have been obtained in coordination of deuterons with the target made of beryllium and are meant to be used for treating the patients with malignant neoplasms. The capacity of the dose in the beam of fast neutrons has been measured by ionization chambers of different types. The research has been done with the consideration of co-occurring gamma rays. The monitoring indices needed for calculation the duration of therapy session at given therapy dose have also been specified

Spectroscopic assessment of the UV laser removal of varnishes on paint substrates

TECHNART 2015 − Catania, April 27 - 30, 2015; http://technart2015.lns.infn.it/The removal/thinning of aged varnishes from easel paintings is a very complex issue, which involves the need of finely-optimized conservation treatments for preserving both the pictorial substrates and the remaining varnish film. To this goal, cleaning techniques based on laser ablation may satisfy these requirements, especially when wavelengths and pulse durations are accurately selected. Recently, with the aim of minimizing photo-thermal, photo-mechanical and photo-chemical phenomena, ultra-short lasers operating in picosecond and femtosecond regimes have been introduced in the field [1-2]. Processing of fresh mastic and dammar varnishes with 248 nm, 500 fs laser pulses results in an improved etched morphology as compared with ns pulses of the same wavelength [1]. Irradiation of shellac at 213 nm with pulses of 15 ns of photo-sensitive tempera paint models covered with shellac allows controlled micrometric removal without affecting the surface morphology and chemical composition of the remaining varnish film and underlying paint layers. However, fs multiple pulse Ti:Sapphire irradiation of films of this varnish at 795, 398 and 265 nm has turned out to be ineffective for removing shellac varnish from egg-yolk based tempera paints [2]. Taking advantage from the latest findings, in the present work we focus on the assessment of the chemical and physical modifications induced by laser irradiation of varnish samples (i.e. dammar, mastic, shellac, mastic-oil) after natural and artificial ageing by using confocal ¿-Raman and laser induced fluorescence spectroscopies. We irradiated the varnish films with the fifth (213 nm) and fourth (266 nm) harmonics of a pulsed nanosecond (15 ns) Q-switched Nd:YAG laser. Together with systematic microscopy inspection of the irradiated areas, a significant effort was devoted to the study of the optical properties of the varnish films by means of UV-Vis absorption spectroscopy, which allowed the determination of linear absorption coefficients at the laser irradiation wavelengths used. Single-pulse laser ablation thresholds were measured by applying the spot regression method and processing of the films was carried out using three different scanning speeds that resulted in 1, 5 and 10 laser pulses on each irradiated area. The obtained results, using fluences well above the single-pulse ablation threshold of the treated varnishes, depend crucially on the irradiation wavelength, the considered varnish and its degree of polymerization. In contrast with the induced modifications resulting from irradiation at 266 nm, that lead to a whitish appearance (indicative of bubble formation) and discoloration of pigments, the promising results achieved at 213 nm emphasize the importance of using a highly absorbed wavelength to finely remove the oxidized uppermost layer of different types of aged varnishes. [1] Pouli, P., Paun, I. A., Bounos, G., Georgiou, S., Fotakis, C., Applied Surface Science, 254(21), 2008, 6875-6879. [2] Oujja, M., García, A., Romero, C., de Aldana, J. R. V., Moreno, P., Castillejo, M., Physical Chemistry Chemical Physics, 13(10), 2011, 4625-4631.Peer Reviewe

Optical properties of the dibenzothiazolylphenol molecular crystals through ONIOM calculations: the effect of the electrostatic embedding scheme

Periodic density functional theory (DFT) and hybrid ONIOM time-dependent DFT/MM cluster calculations have been carried out to investigate the ground- and excited-state properties of the crystalline structures of the enolic and ketonic tautomeric forms of a propoxy-substituted dibenzothiazolylphenol molecule (OPr), a prototype for systems undergoing the excited-state intramolecular proton transfer process. The crystalline structures of the tautomeric forms are well reproduced and, as expected, at the ground state, the enol polymorph is predicted to be more stable than the keto one. At the excited state, the effect of the environment on time-dependent DFT calculations has been accounted for by including a charge embedding scheme, and the influence of different kinds of point charges (Mulliken, CM5, RESP and QEq) in determining the optical properties of the central molecule has been investigated. The results reveal that, in fair agreement with experimental data, the absorption (emission) energies of the enol (keto) OPr molecule is red-shifted of about 3 (3) nm going from the gas phase to chloroform and blue-shifted of 10 (23) nm going from the gas to the crystal phase when the electronic embedding with Mulliken charges is employed. The electrostatic embedding influences the excited-state properties more severely than the ground-state properties, and apart the QEq charges, all other models provide Stokes shifts in reasonable agreement with experimental data

Current status of the research on transparent YAG ceramics as laser hosts from an Italian network

This work describes the results obtained using two different processing systems for the production of YAG based ceramics. One involves the use of commercially available oxide powders (Yb2O3, Y2O3, Al2O3) The other involves the use of Yb-doped Y2O3 (Yb, 9.8%) powders obtained by microwave assisted co-precipitation from salts solution and a commercial alumina (Al2O3). Both systems are processed by wet mechanical mixing of starting oxides and reactive sintering of the obtained mixtur

Experimental study of the delayed threshold phenomenon in a semiconductor laser

An experimental study of the delayed threshold phenomenon in a Vertical Extended Cavity Semiconductor Emitting Laser is carried out. Under modulation of the pump power, the laser intensity exhibits a hysteresis behavior in the vicinity of the threshold. The temporal width of this hysteresis is measured as a function of the modulation frequency, and is proved to follow the predicted scaling law. A model based on the rate equations is derived and used to analyze the experimental observations. A frequency variation of the laser around the delayed threshold and induced by the phase-amplitude coupling is predicted and estimated

Mouse aortic muscle cells respond to oxygen following cytochrome P450 3A13 gene transfer

We have previously shown that a cytochrome P450 (CYP450) hemoprotein from the 3A subfamily CYP3A13 for the mouse, serves as the sensor in the contraction of the ductus arteriosus in response to increased oxygen tension. In addition, we have identified endothelin-1 (ET-1) as the effector for this response. Here, we examined whether Cyp3a13 gene transfer confers oxygen sensitivity to cultured muscle cells from mouse aorta. Coincidentally, we determined whether the same hemoprotein is normally present in the vessel. Cyp3a13-transfected aortic cells responded to oxygen, whereas no significant response was seen in native cells or in cells transfected with an empty vector. Furthermore, this oxygen effect was curtailed by the ET-1/ETA receptor antagonist BQ-123. We also found that CYP3A13 occurs naturally in aortic tissue and its isolated muscle cells in culture. We conclude that CYP3A13 is involved in oxygen sensing, and its action in the transfected muscle cells of the aorta, as in the native cells of the ductus, takes place through a linkage to ET-1. However, the response of aortic muscle to oxygen, conceivably entailing the presence of CYP3A13 at some special site, is not seen in the native situation, and may instead unfold upon transfection of the parent gene

Delayed Self-Synchronization in Homoclinic Chaos

The chaotic spike train of a homoclinic dynamical system is self-synchronized by re-inserting a small fraction of the delayed output. Due to the sensitive nature of the homoclinic chaos to external perturbations, stabilization of very long periodic orbits is possible. On these orbits, the dynamics appears chaotic over a finite time, but then it repeats with a recurrence time that is slightly longer than the delay time. The effect, called delayed self-synchronization (DSS), displays analogies with neurodynamic events which occur in the build-up of long term memories.Comment: Submitted to Phys. Rev. Lett., 13 pages, 7 figure