Redução de incertezas em radioterapia utilizando simulação Monte Carlo: análise espectral aplicada à correção de dose absorvida

OBJETIVO: Determinar, por simulação Monte Carlo, os espectros de feixes de cobaltoterapia em profundidade na água e fatores de correção para doses absorvidas em dosímetros termoluminescentes de fluoreto de lítio. MATERIAIS E MÉTODOS: As simulações dos espectros secundários da fonte clínica de cobalto-60 foram realizadas com o código Monte Carlo PENELOPE, em diversas profundidades na água. Medidas experimentais de dose profunda foram obtidas com dosímetros termoluminescentes e câmara de ionização em condições de referência em radioterapia. Os fatores de correção para os dosímetros termoluminescentes foram obtidos através da razão entre as absorções relativas ao espectro de baixa energia e ao espectro total. RESULTADOS: A análise espectral em profundidade revelou a existência de espectros secundários de baixa energia responsáveis por uma parcela significativa da deposição de dose. Foram observadas discrepâncias de 3,2% nas doses medidas experimentalmente com a câmara de ionização e com os dosímetros termoluminescentes. O uso dos fatores de correção nessas medidas permitiu diminuir a discrepância entre as doses absorvidas para, no máximo, 0,3%. CONCLUSÃO: Os espectros simulados permitem o cálculo de fatores de correção para as leituras de dosímetros termoluminescentes utilizados em medidas de dose profunda, contribuindo para a redução das incertezas associadas ao controle de qualidade de feixes clínicos em radioterapia.

La prima redazione della «Orazione scritta a Carlo V» di Giovanni della Casa

Nel contributo è pubblicata la prima redazione conosciuta dell'Orazione con cui Giovanni della Casa nel 1549 chiese all'imperatore Carlo V la restituzione di Piacenza ai Farnese, loro sottratta dopo l'uccisione di Pier Luigi nel 1547. L'edizione documenta l'elaborazione d'autore con un apparato evolutivo del testo trasmesso dal manoscritto Vaticano Chigiano O vi 80. This article provides an edition of the first known version of Giovanni della Casa's request to the Emperor Charles V (1549) for the restitution of Piacenza to the Farnese family after Pier Luigi's murder in 1547. This edition documents the Author's working out with an evolutional apparatus of the text transmitted by the manuscript Chigiano O vi 80.

Monte Carlo derivation of filtered tungsten anode X-ray spectra for dose computation in digital mammography

Abstract Objective: Derive filtered tungsten X-ray spectra used in digital mammography systems by means of Monte Carlo simulations. Materials and Methods: Filtered spectra for rhodium filter were obtained for tube potentials between 26 and 32 kV. The half-value layer (HVL) of simulated filtered spectra were compared with those obtained experimentally with a solid state detector Unfors model 8202031-H Xi R/F & MAM Detector Platinum and 8201023-C Xi Base unit Platinum Plus w mAs in a Hologic Selenia Dimensions system using a direct radiography mode. Results: Calculated HVL values showed good agreement as compared with those obtained experimentally. The greatest relative difference between the Monte Carlo calculated HVL values and experimental HVL values was 4%. Conclusion: The results show that the filtered tungsten anode X-ray spectra and the EGSnrc Monte Carlo code can be used for mean glandular dose determination in mammography.

Monte Carlo thermodynamic and structural properties of the TIP4P water model: dependence on the computational conditions

Classical Monte Carlo simulations were carried out on the NPT ensemble at 25°C and 1 atm, aiming to investigate the ability of the TIP4P water model [Jorgensen, Chandrasekhar, Madura, Impey and Klein; J. Chem. Phys., 79 (1983) 926] to reproduce the newest structural picture of liquid water. The results were compared with recent neutron diffraction data [Soper; Bruni and Ricci; J. Chem. Phys., 106 (1997) 247]. The influence of the computational conditions on the thermodynamic and structural results obtained with this model was also analyzed. The findings were compared with the original ones from Jorgensen et al [above-cited reference plus Mol. Phys., 56 (1985) 1381]. It is notice that the thermodynamic results are dependent on the boundary conditions used, whereas the usual radial distribution functions g(O/O(r)) and g(O/H(r)) do not depend on them.

Termodinâmica estatística de líquidos com o método de Monte Carlo. I. Metodologia

Statistical mechanics Monte Carlo simulation is reviewed as a formalism to study thermodynamic properties of liquids. Considering the importance of free energy changes in chemical processes, the thermodynamic perturbation theory implemented in the Monte Carlo method is discussed. The representation of molecular interaction by the Lennard-Jones and Coulomb potential functions is also discussed. Charges derived from quantum molecular electrostatic potential are also discussed as an useful methodology to generate an adequate set of partial charges to be used in liquid simulation.

Termodinâmica estatística de líquidos com o método de Monte Carlo. II. O líquido clorofórmio

Thermodynamic properties and radial distribution functions for liquid chloroform were calculated using the Monte Carlo method implemented with Metropolis algorithm in the NpT ensemble at 298 K and 1 atm. A five site model was developed to represent the chloroform molecules. A force field composed by Lennard-Jones and Coulomb potential functions was used to calculate the intermolecular energy. The partial charges needed to represent the Coulombic interactions were obtained from quantum chemical ab initio calculations. The Lennard-Jones parameters were adjusted to reproduce experimental values for density and enthalpy of vaporization for pure liquid. All thermodynamic results are in excelent agreement with experimental data. The correlation functions calculated are in good accordance with theoretical results avaliable in the literature. The free energy for solvating one chloroform molecule into its own liquid at 298 K and 1 atm was computed as an additional test of the potential model. The result obtained compares well with the experimental value. The medium effects on cis/trans convertion of a hypotetical solute in water TIP4P and chloroform solvents were also accomplished. The results obtained from this investigation are in agreement with estimates of the continuous theory of solvation.

Vacancy-assisted domain-growth in asymmetric binary alloys: A Monte Carlo Study

A Monte Carlo simulation study of the vacancy-assisted domain growth in asymmetric binary alloys is presented. The system is modeled using a three-state ABV Hamiltonian which includes an asymmetry term. Our simulated system is a stoichiometric two-dimensional binary alloy with a single vacancy which evolves according to the vacancy-atom exchange mechanism. We obtain that, compared to the symmetric case, the ordering process slows down dramatically. Concerning the asymptotic behavior it is algebraic and characterized by the Allen-Cahn growth exponent x51/2. The late stages of the evolution are preceded by a transient regime strongly affected by both the temperature and the degree of asymmetry of the alloy. The results are discussed and compared to those obtained for the symmetric case.

Monte Carlo simulation of x-ray emission by kilovolt electron bombardment

A physical model for the simulation of x-ray emission spectra from samples irradiated with kilovolt electron beams is proposed. Inner shell ionization by electron impact is described by means of total cross sections evaluated from an optical-data model. A double differential cross section is proposed for bremsstrahlung emission, which reproduces the radiative stopping powers derived from the partial wave calculations of Kissel, Quarles and Pratt [At. Data Nucl. Data Tables 28, 381 (1983)]. These ionization and radiative cross sections have been introduced into a general-purpose Monte Carlo code, which performs simulation of coupled electron and photon transport for arbitrary materials. To improve the efficiency of the simulation, interaction forcing, a variance reduction technique, has been applied for both ionizing collisions and radiative events. The reliability of simulated x-ray spectra is analyzed by comparing simulation results with electron probe measurements.

Monte Carlo simulation of x-ray spectra generated by kilo-electron-volt electrons

We present a general algorithm for the simulation of x-ray spectra emitted from targets of arbitrary composition bombarded with kilovolt electron beams. Electron and photon transport is simulated by means of the general-purpose Monte Carlo code PENELOPE, using the standard, detailed simulation scheme. Bremsstrahlung emission is described by using a recently proposed algorithm, in which the energy of emitted photons is sampled from numerical cross-section tables, while the angular distribution of the photons is represented by an analytical expression with parameters determined by fitting benchmark shape functions obtained from partial-wave calculations. Ionization of K and L shells by electron impact is accounted for by means of ionization cross sections calculated from the distorted-wave Born approximation. The relaxation of the excited atoms following the ionization of an inner shell, which proceeds through emission of characteristic x rays and Auger electrons, is simulated until all vacancies have migrated to M and outer shells. For comparison, measurements of x-ray emission spectra generated by 20 keV electrons impinging normally on multiple bulk targets of pure elements, which span the periodic system, have been performed using an electron microprobe. Simulation results are shown to be in close agreement with these measurements.

Bulletin monumental / publié sous les auspices de la Société française pour la conservation et la description des monuments historiques ; et dirigé par M. de Caumont

1869 (SER4,T5 = VOL35).

Ruukin koulussa. Lapset ja opettajat toimijoina Teijon tehtaankansakoulussa vuosina 1869–1909

Käsittelen tutkimuksessani lasten ja opettajien toimijuutta Teijon yksityisessä tehtaankansakoulussa vuosina 1869–1909. Tarkastelen heidän toimijuuteensa vaikuttaneita taustatekijöitä kuten koulun johtokuntaa, Teijon tehtaiden johtoa ja kouluylihallituksen ohjausta ja valvontaa. Kartoitan myös toimijoiden fyysistä ja sosiaalista toimintaympäristöä eli lasten ja opettajien asemaa yhteisössä ja koulutilaa. Tutkimukseni jakautuu viiteen lukuun. Johdantoluvussa määritän tutkimuskysymyksen ja käsittelen mikrohistoriallista tutkimusta. Selvitän keskeisimmät käyttämäni lähteet ja tutkimuskirjallisuuden. Toisessa luvussa pohdin koulun perustamiseen vaikuttaneita syitä, esittelen koulun johtokunnan, kouluhallituksen ja koulutarkastajien toimintaa ja sen merkitystä koulutyölle. Kolmannessa luvussa kuvaan Teijon kylää fyysisenä ja sosiaalisena ympäristönä, lasten sosiaalista taustaa ja koulumiljöötä. Oppilaiden ja opettajien toimijuus on vuorossa neljännessä luvussa. Viimeinen luku on yhteenveto tutkimuksen tuloksista. Tutkimus on mikrohistoriallinen. Mikrohistorian määrittelyssä käytän ensisijaisesti Carlo Ginzburgin, Matti Peltosen ja Anne Ollilan teoksia. Päälähteinäni ovat Teijon tehtaankansakoulun vuosikertomukset, koulun johtokunnan pöytäkirjat ja kansakouluntarkastajien tarkastuskertomukset. Tutkimuskirjallisuudesta kaikkein merkittävimpiä ovat Aimo Halilan Suomen kansakoululaitoksen historia, Eelis Aurolan Suomen tehtaankoulut 1636– 1881, M. A. Knaapisen Kansansivistystyö Perniössä ja Rauno Luttisen Perniön kansakoululaitos 1872–1972. Aikaisemmassa tutkimuksessa ei ole juurikaan käsitelty opettajien ja lasten toimijuutta, vaan siinä on keskitytty lähinnä koululaitoksen kehitykseen. Teijon tehtaankansakoulu perustettiin Teijon tehtaiden johdon aloitteesta tehtaan pedagogion tilalle vuonna 1869. Se oli yksityinen kansakoulu ja tehtaan omistajien johtama. Koska koulu sai valtionapua, se oli valtakunnallisen koululainsäädännön alainen ja kouluylihallitus valvoi ja ohjasi koulun toimintaa. Koulun alkuvuosikymmeninä opettajalla oli keskeisin rooli arjen koulutyössä. Opettajilla oli pitkään mahdollisuus muokata koulun opetusta ja toimintaa paikallisten tarpeiden ja mahdollisuuksien mukaan. Teijon tehtaankansakoulun opettajista varsinkin G. E. Marklund kehitti merkittävästi koulua ja vakiinnutti koulutyön muodot. Lasten tehtävänä oli kasvaa sivistyneiksi, moraalisiksi, isänmaallisiksi ja uskonnollisiksi kansalaisiksi. Koulussa opitut tiedot ja taidot olivat aluksi toissijaisia tämän päämäärän rinnalla, mutta niidenkin merkitys alettiin ymmärtää paremmin muun yhteiskunnan kehittyessä. Teijon tehtaankansakoulu muuttui kunnalliseksi kansakouluksi vuoden 1910 alusta. Tutkimukseni täydentää aikaisemman tutkimuksen antamaa kuvaa Teijon koulun vaiheista sekä kokoaa yhteen ja selkeyttää aikaisempia tutkimustuloksia. Teijon tehtaankansakoulun oppilaista, opettajista, oppiaineista, koulutyöstä ja koulutilasta ei ole ollut aikaisemmin yhtä kattavaa selvitystä. Jatkotutkimuksen kannalta kiinnostavia ovat Teijolla toimineet seurakunnan kiertokoulu ja kansakoulua edeltävä pientenlastenkoulu, Teijon vieressä olevien Mathildedalin ja Kirjakkalan ruukkikylien tehtaankoulut sekä näiden kaikkien koulujen oppilaiden myöhemmät opiskelu- ja työurat.

La Chanson illustrée (Paris. 1869)

Etat de collection : no. 1-78 (1869-1870) + spécimen

Simulação do equilíbrio: o método de Monte Carlo

We make several simulations using the Monte Carlo method in order to obtain the chemical equilibrium for several first-order reactions and one second-order reaction. We study several direct, reverse and consecutive reactions. These simulations show the fluctuations and relaxation time and help to understand the solution of the corresponding differential equations of chemical kinetics. This work was done in an undergraduate physical chemistry course at UNIFIEO.