Biblioteca Digital

As a contribution towards detecting the genetic effects of low doses of genotoxic physical agents, this paper deals with the consequences of low-dose X-rays in the Aspergillus nidulans genome. The irradiation doses studied were those commonly used in dental clinics (1-5 cGy). Even very low doses promoted increased mitotic crossing-over frequencies in diploid strains heterozygous for several genetic markers including the ones involved in DNA repair and recombination mechanisms. Genetic markers of several heterozygous strains were individu`ally analyzed disclosing that some markers were especially sensitive to the treatments. These markers should be chosen as bio-indicators in the homozygotization index assay to better detect the recombinogenic/carcinogenic genomic effects of low-dose X-rays.

As injúrias mecânicas, com efeitos imediatos e latentes, se caracterizam por causarem problemas para a produção de sementes de soja. O objetivo dessa pesquisa foi verificar a ocorrência de injúrias mecânicas, pelo teste de raios X em sementes de soja, colhidas com diferentes teores de água, determinar as possíveis alterações do potencial fisiológico das sementes, provocada por injúrias, logo após as colheitas e após seis meses de armazenamento, e comparar a utilização dos raios X e dos testes de hipoclorito de sódio e de tetrazólio, para detectar a ocorrência de diferentes graus de injúrias mecânicas nas sementes de soja. Para a pesquisa, foram utilizadas sementes de soja dos cultivares Embrapa 48 e FTS Águia que têm diferenças no teor de lignina do tegumento. As sementes foram produzidas e colhidas, manual e mecanicamente, com 18%, 15% e 12% de água e, imediatamente após a colheita, avaliadas quanto ao teor de água e às injúrias mecânicas. Após a secagem, a qualidade das sementes foi determinada pelos testes de germinação, emergência da plântula, tetrazólio (viabilidade e vigor), envelhecimento acelerado, hipoclorito de sódio e sanidade. Após a avaliação inicial, as sementes foram armazenadas (20°C e 45% UR) e analisadas após seis meses. Os resultados obtidos indicam que a utilização dos raios X possibilita a identificação das injúrias mecânicas...

O recente medo de atos terroristas provocou um aumento do número de atrasos e cancelamentos do transporte de radioisótopos. Isto representa uma verdadeira ameaça aos projetos de produção de insetos estéreis ao redor do mundo. Visando validar o uso de um novo tipo de irradiador de raios-X de baixa energia, foram conduzidos uma série de estudos de radiobiologia para moscamed, Ceratitis capitata (linhagem tsl-VIENNA 8) (Wied., 1824) (Diptera: Tephritidae), e uma linhagem argentina de Anastrepha fraterculus (Wied., 1830) (Diptera: Tephritidae), também calculando-se a eficiência biológica relativa (RBE) entre raios-X e a tradicional radiação de 60Co. Pupas 48-24 h antes da emergência do adulto de machos de moscamed e de ambos os sexos de A. fraterculus foram irradiadas com doses variando de 15 a 120 Gy e 10 a 70 Gy respectivamente. As doses que induzem 50, 90 e 99% de esterilidade foram estimadas e a hipótese de paralelismo para as equações de Probit foram testadas. Doses de 82,7 Gy de raios-X e 128,2 Gy de raios (portanto, uma RBE=1,5) induziram 99% de esterilidade em machos de moscamed. A fertilidade de fêmeas férteis de A. fraterculus cruzadas com machos irradiados com 41 Gy de raios-X e 62,7 Gy de raios foi reduzida em 99% comparando-se com a testemunha (RBE=1...

Um contador a gás, com multifios, sensível à posição, para a detecção de raios X foi construído utilizando linhas de atraso integradas para leitura da posição. Seis linhas de atraso (50ns de atraso cada, frequência de corte de 40MHz) cobrem um comprimento sensível total de 150mm, possuindo uma razão do atraso total pelo tempo de subida dos sinais na linha adequadas para a detecção em posição raios X de 5,9keV do ANTIPOT. 55 Fe com alta resolução. Testes usando a forneceram uma não-linearidade linha de integral máxima menor que 0,1% e não-linearidade diferencial máxima de ±4,0%, com o detector utilizando a mistura 700torr. Testes similares foram feitos usando de Ar-CH IND 4 (90%-10%) a a linha de 8,04keV de um tubo de raios X de Cu. Uma resolução total de 330m, e as mesmas não-linearidades integral e diferencial foram obtidas. Com a finalidade de t.est.ar o comportamento do detector sob condições experimentais reais, duas diferentes amostras foram analisadas na região de espalhamento em baixo ângulo. As amostras analisadas foram o carvão vítreo e o dodecil sulfato de sódio (SLS). O feixe de raios X foi colimado por um conjunto de fendas, com 50,um cada uma delas e separadas de 98mm. A distância entre a amostra e o detector era de 404...

O glioblastoma (GBM) é um tumor extremamente agressivo e resistente aos tratamentos convencionais. Os agentes utilizados na quimio- e radioterapia são indutores de danos no DNA, por induzirem quebras de fita simples (SSBs) e quebras de fita dupla (DSBs), as quais são letais para as células, mas quando eficientemente reparadas pelas células tumorais tornam estas resistentes. As principais vias de reparo de DSBs são: a via por recombinação homológa (Homologous Recombination HR) e por recombinação não- homóloga (Non-homologous end joining NHEJ). As proteínas de reparo participantes dessas vias têm sido estudadas como potenciais alvos moleculares na terapia contra o câncer. A estratégia empregada no presente trabalho foi a de inibir a via de reparo HR em células já comprometidas para a via NHEJ. Para isso foi utilizado o inibidor de RAD51 (uma das principais proteínas da via HR), 3-chloro-1-(3,4-dichlorophenyl)-4- morpholinylo-1H-pyrrole-2,5-dione, conhecido como RI-1(Calbiochem), testado em células de glioma M059J e M059K (deficientes e proficientes para DNA-PK, respectivamente), irradiadas com raios-X. Diferentes ensaios foram realizados para o teste com o inibidor RI-1 em células irradiadas ou não e comparados ao controle sem tratamento. Os resultados dos ensaios de sobrevivência clonogênica mostraram que a concentração de 40 M do inibidor RI-1 exerceu um maior efeito inibitório sobre a capacidade de as células se dividirem e formarem colônias. O RI-1 induziu alterações significativas na cinética do ciclo celular predominantemente na linhagem selvagem M059K...

As a contribution towards detecting the genetic effects of low doses of genotoxic physical agents, this paper deals with the consequences of low-dose X-rays in the Aspergillus nidulans genome. The irradiation doses studied were those commonly used in dental clinics (1-5 cGy). Even very low doses promoted increased mitotic crossing-over frequencies in diploid strains heterozygous for several genetic markers including the ones involved in DNA repair and recombination mechanisms. Genetic markers of several heterozygous strains were individually analyzed disclosing that some markers were especially sensitive to the treatments. These markers should be chosen as bio-indicators in the homozygotization index assay to better detect the recombinogenic/ carcinogenic genomic effects of low-dose X-rays. ©FUNPEC-RP.

Neste trabalho estudamos o comportamento magnético do composto Eu8Ga16Ge30, o único clatrato conhecido atualmente cujas posições hóspedes são completamente preenchidas por um elemento terra-rara. Este composto cristaliza-se em uma estrutura cúbica (grupo espacial Pm_3n), apresentando duas diferentes gaiolas formadas pelos átomos Ga-Ge (uma gaiola menor formada por 20 átomos e uma gaiola maior, formada por 24 átomos) que englobam em seu interior íons divalentes Eu+2. Os momentos magnéticos desses íons ordenam-se ferromagneticamente abaixo de TC = 36 K através da interação RKKY. O objetivo deste trabalho foi investigar o comportamento magnético local dos sítios cristalográficos ocupados pelos íons de Eu, que no interior das gaiolas maiores, situam-se em posições fora do centro destas, contidas em planos perpendiculares às faces da célula unitária cúbica. Nesta dissertação descrevemos a síntese do composto Eu8Ga16Ge30 pelo método do fluxo metálico, a caracterização da amostra através da difração de raios X de alta resolução (verificação da qualidade cristalina) e da difração de pó de raios X (determinação do parâmetro de rede). Medidas de resistividade elétrica em função da temperatura mostraram a existência de saltos relacionados ao aumento da resistividade...

Nesta tese foram investigados as propriedades eletrônicas e magnéticas de diversos compostos que apresentam suas estruturas formadas por gaiolas na qual estas apresentam átomos hospedes no seu interior. Os compostos estudados foram o clatrato tipo-I Eu8Ga16Ge30, o composto fase cúbica de Remeika Eu3Ir4Sn13 e por m os compostos de GdT2Zn20 com T = Fe e Co. As propriedades destes materiais foram investigadas através do uso de medidas macroscópicas como resistividade elétrica, susceptibilidade magnética e também por medidas microscópicas como técnicas de absorção e espalhamento de raios-X e difração de nêutrons. O clarão Eu8Ga16Ge30, formado por dois tipos de gaiolas (X20 - dodecaedral e X24 - tetrakaidecaedral), foi principalmente investigado por difração e absorção de raios-X. Essas técnicas foram conciliadas com a aplicação de altas pressões na qual observou-se uma transição de fase irreversível cristalina-amorfa ao redor de Pa = 18 GPa. Concomitantemente a mudança estrutural, observou-se também através do dicroísmo circular magnético um colapso do ordenamento ferromagnético (FM) sob pressão. A diminuição do sinal magnético em altas pressões pode ser explicado por um estado paramagnético ou de "spin glass"...

This paper describes a pixel imaging array consisting in 400µm x 400µm photodiodes fabricated in CMOS technology. An array of scintillating CsI:Tl crystals is placed above the photodiodes. These crystals are encapsulated in aluminum walls, forming a light path that guides the visible light produced by the scintillating crystal into the photodiodes. In This way, the x-ray energy is first converted into visible light which is then detected by the photodiode at the end of each light guide. The scintillator is 800 µm thick, absorbing almost all 20keV x-ray photons. Usually, the spatial resolution of the scintillating x-ray detectors is identical to the scintillator thickness. By using the light guides, the scintillator thickness can be increased without decreasing the spatial resolution. The increase of the scintillator thickness is desirable in order to increase the x-rays absorption efficiency. Tests carried out on the system show very promising results near 20keV.

This paper describes a pixel imaging array consisting in 400 um x 400 um photodiodes fabricated in CMOS technology. Above the photodiodes, an array of scintillating CsI:Tl crystals are placed. The scintillating crystals are encapsulated in aluminum walls forming a light path to guide the produced visible light into the photodiodes. So, the x-ray energy is first converted into visible light which is then detected by the photodiode at the end of each light guide. The scintillator is 800 um thick, absorbing almost all of 20 keV x-ray photons. Usually, the spatial resolution of the scintillating x-rays detectors is identical to the scintillator thickness. By using the light guides, the scintillator thickness can be increased, without decreasing the spatial resolution. The increase of the scintillator thickness is desirable in order to increase the x-rays absorption efficiency. Tests carried out on the system show very promising results near 20 keV.; This work was supported by The Foundation of Science and Technology, Portugal, FCT-CTM/POCTI/33751/1999; Grant-BD SFRH/BD/1296/2000.

Bombardment of pyrene-doped n-heneicosane (C21H44) in its orthorhombic solid phase with <1.3> MeV broadband X-rays results in the formation of both mono- and di-heneicosylpyrenes, whereas the same dose in liquid cyclohexane yields only monosubstituted pyrene. In both cases, the reaction efficiency decreases as pyrene concentration is increased from 10-5 to 10-2 M. Qualitatively, the overall attachment efficiency is higher in orthorhombic n-heneicosane than in liquid cyclohexane, but the selectivity of attachment is greater in cyclohexane. Differences between these results and those from irradiations of the same samples with eV range photons are discussed.

One hundred years after its discovery, one can hardly conceive the medical practice without the existence of X rays. A brief account of X rays discovery and about its notable discoverer is presented.

The crystallization processes for the amorphous metallic alloys Fe74B17Si2Ni4Mo3 and Fe86B6Zr7Cu1 (at. %) were investigated using X-rays diffraction measurements performed in-situ during Joule-heating, with simultaneous monitoring of the electrical resistance. We determined the main structural transitions and crystalline phases formed during heating, and correlated these results to the observed resistance variations. As the annealing current is increased, the resistance shows an initial decrease due to stress relaxation, followed by a drop to a minimum value due to massive nucleation and growth of alpha-Fe nanocrystals. Further annealing causes the formation of small fractions of Fe-B, B2Zr or ZrO2, while the resistance increases due to temperature enhancement. In situ XRD measurements allowed the identification of metastable phases, as the gamma-Fe phase which occurs at high temperatures. The exothermal peaks observed in the differential scanning calorimetry (DSC) for each alloy corroborate the results. We also have performed DSC measurements with several heating rates, which allowed the determination of the Avrami exponent and crystallization activation energy for each alloy. The obtained activation energies (362 and 301 kJ/mol for Fe-B-Zr-Cu; 323 kJ/mol for Fe-B-Si-Ni-Mo) are comparable to reported values for amorphous iron alloys...

A dentist reviewing X-Rays with his patient.

A dental hygienists is developing dental x-rays at the Rochester Dental Dispensary.

Die Arbeit untersucht die Entstehung der harten Röntgenstrahlung galaktischer Schwarzlochkandidaten. Der wahrscheinlichste physikalische Prozeß, der dieses Spektrum erzeugt, ist die Comptonisierung weicher Strahlung in einem heißen Elektronenplasma, einer Akkretionsscheibenkorona. Diese entsteht wahrscheinlich als Folge hydrodynamischer Instabilitäten in einer Akkretionsscheibe. Unter Comptonisierung versteht man hierbei die Erzeugung harter Photonen durch inverse Comptonstöße an heißen Elektronen. Dabei können Photonendichten entstehen, die so groß sind, daß Photon-Photon-Paarbildungsprozesse eintreten können. Unter Verwendung nichtlinearer Monte Carlo Methoden wird das Strahlungstransportproblem in solchen Akkretionsscheibenkoronen selbstkonsistent für verschiedene Geometrien gelöst. Um genaue Parameter für die Koronen in Schwarzen Löchern zu erhalten, müssen die aus den theoretischen Rechnungen erhaltenen Spektren direkt mit Beobachtungsdaten verglichen werden. Hierzu sind Beobachtungen im Energiebereich von 1 bis 300 keV notwendig. Die Arbeit geht besonders auf eine Rossi X-ray Timing Explorer Beobachtung des galaktischen Schwarzen Loches Cygnus X-1 ein. Hier zeigt sich, daß die Akkretionsscheiben- modelle tatsächlich das Röntgenspektrum beschreiben können. Die optische Tiefe der Korona beträgt tau=2.1+/-0.1...

In order to improve the reliability of children's models, the aim of this study was to determine the subject-specific masses and 3D locations of the centres of mass (CoM) of body segments using biplanar X-rays. Previous methods, validated on upper leg segments, were applied to the whole body. Six children and six adults were studied. The low-dose X-ray system EOS® was used to simultaneously get head-to-foot biplanar X-rays in the upright position. Specific methods were used to get 3D reconstructions of bones and body shape. The densities from the literature were used to define the masses. To assess the accuracy of the reconstructions, a force plate was used to compare the mass and the projection of the CoM. A mean distance of 4.5 mm between the measured and the calculated projections of the CoM was found. The mean error between the estimated and the actual body mass was 2.6%. Such a method will be useful in obtaining the body segment parameters in children, hard to obtain using direct measurement techniques.; Baptiste Sandoz, Sébastien Laporte, Wafa Skalli and David Mitton

Version éditeur : http://www.tandfonline.com/toc/gcmb20/13/6; In order to improve the reliability of children’s models, the aim of this study was to determine the subject-specific masses and 3D locations of the centres of mass (CoM) of body segments using biplanar X-rays. Previous methods, validated on upper leg segments, were applied to the whole body. Six children and six adults were studied. The low-dose X-ray system EOS was used to simultaneously get head-to-foot biplanar X-rays in the upright position. Specific methods were used to get 3D reconstructions of bones and body shape. The densities from the literature were used to define the masses. To assess the accuracy of the reconstructions, a force plate was used to compare the mass and the projection of the CoM. A mean distance of 4.5mm between the measured and the calculated projections of the CoM was found. The mean error between the estimated and the actual body mass was 2.6%. Such a method will be useful in obtaining the body segment parameters in children, hard to obtain using direct measurement techniques.; ANR (SECUR_ENFANT_06_0385)

We present the results of XMM-Newton X-ray observations of the Mira AB binary system, which consists of a pulsating, asymptotic giant branch primary and nearby (~0.6′′ separation) secondary of uncertain nature. The EPIC CCD (MOS and pn) X-ray spectra of Mira AB are relatively soft, peaking at ~1 keV, with only very weak emission at energies >3 keV; lines of Ne ix, Ne x, and O viii are apparent. Spectral modeling indicates a characteristic temperature TX ~10^7 K and intrinsic luminosity LX ~5×10^29 erg s^−1, and suggests enhanced abundances of O and, possibly, Ne and Si in the X-ray-emitting plasma. Overall, the X-ray spectrum and luminosity of the Mira AB system more closely resemble those of late-type, pre-main sequence stars or late-type, magnetically active main sequence stars than those of accreting white dwarfs. We conclude that Mira B is most likely a late-type, magnetically active, main-sequence dwarf, and that X-rays from the Mira AB system arise either from magnetospheric accretion of wind material from Mira A onto Mira B, or from coronal activity associated with Mira B itself, as a consequence of accretion-driven spin-up. One (or both) of these mechanisms also could be responsible for the recently discovered, point-like X-ray sources within planetary nebulae (Refer to PDF file for exact formulas).; Also archived in: arXiv :astro-ph/0408329 v2 27 Aug 2004; We acknowledge support for this research provided by NASA/GSFC XMM-Newton General Observer grant NAG5–13158 to RIT. N.S. acknowledges support from the Israel Science Foundation. We thank Falk Herwig and Norbert Schulz for useful comments and suggestions.

Exposure to X-rays (ionizing radiation) may cause chromosomal aberrations (CA) in somatic or germinative cells in exposed individuals, and may lead to manifestations of diseases such as cancer. This study was carried out to assess the CA frequency in lymphocytes obtained by means of temporary culture of peripheral blood from dentists in Londrina, Paraná, Brazil, who have worked for more than ten years with X-rays. The results obtained from the experimental group were compared with a matched negative control group, which had never been exposed to X-rays. All individuals, dentists and controls, answered a personal questionnaire, from which a profile of each group was obtained. Slides, prepared after the cultures, were stained with Giemsa, and 100 to 200 metaphase cells were analyzed per individual. CA frequencies and types were registered and statistical tests were not necessary to evaluate the obtained data. The analysis of mitotic index (MI) did not indicate significant differences (p < 0.05) between the group of individuals exposed to X-rays and the control group. The analyzed confounding factors did not influence the results of MI and CA frequencies.; A exposição à radiação ionizante pode causar aberrações cromossômicas (AC) em células somáticas ou germinativas dos indivíduos expostos...