ABSTRACT
We report on 400 nm broadband type I frequency doubling in a noncollinear geometry with pulse-front-tilted and chirped femtosecond pulses (λ =800 nm; Fourier transform limited pulse duration, 45 fs). With moderate power densities (2 to 10 GW/cm2) thus avoiding higher-order nonlinear phenomena, the energy conversion efficiency was up to 65%. Second-harmonic pulses of Fourier transform limited pulse duration shorter than the fundamental wave were generated, exhibiting good beam quality and no pulse-front tilt. High energy (20 mJ/pulse) was produced in a 40 mm diameter and 6 mm thick LBO crystal. To the best of our knowledge, this is the first demonstration of this optical configuration with sub-100-fs pulses. Good agreement between experimental results and simulations is obtained.
ABSTRACT
Iron oxides are present in many occupational atmospheres mainly in iron ore mines and in steel industry. Among these workers, epidemiological studies indicated an excess of lung cancer deaths. In mines, it was difficult to involve iron oxides exposure because there are other possible causes as radon, polycyclic aromatic hydrocarbon (PAH) present in diesel exhausts, silicosis or siderosis. The contradictory results of these studies are due to the differences of exposure levels or to the presence or not of these cofactors or of a sufficient prevention. But generally the results agree with an interaction of iron oxide dusts and smoking habits. It is unclear if this interaction supports an additive or multiplicative risk of lung cancer. Experimental studies with Fe2O3 showed that these particles are able to induce lung cancers only in the presence of PAH when administered to animals. In vitro studies permitted to observe an interaction in the metabolism of benzo(a)pyrene (BaP) leading to a higher level of precursors of the ultimate carcinogen. As this metabolism of BaP is known to be enhanced during lipoperoxidation, it is possible to involve this mechanism with Fe2O3. After phagocytosis and dissolution with production of ferric ions, Fe2O3 can enhance the production of reactive oxygen species responsible of damaging both lipidic constituents and DNA. Fe3O4 and mainly FeO may be more toxic, introducing directly ferrous ions in the cells after dissolution, but the cancerogenicity of the these compounds is unknown, making necessary to develop research.
Subject(s)
Ferric Compounds/metabolism , Lung Neoplasms/chemically induced , Mining , Occupational Diseases/chemically induced , Occupational Exposure , Polycyclic Aromatic Hydrocarbons , Animals , Benzo(a)pyrene/metabolism , Ferric Compounds/adverse effects , Ferrous Compounds/metabolism , Humans , Lipid Peroxidation , Lung Neoplasms/epidemiology , Occupational Diseases/epidemiology , Oxidative Stress , Polycyclic Aromatic Hydrocarbons/adverse effects , Polycyclic Aromatic Hydrocarbons/metabolismABSTRACT
The DNA of gametes of the water fern, Marsilea vestita, has been radioactively labelled during gemetogenesis. The distribution of the originally present paternal and maternal genomes could thus be followed during the development of the embryo. It has been found that the maternal chromatin is uniformly distributed among the daughter cells of the several successive cell generations. However, the paternal chromatin divides equally only during the first three embryonic divisions. From this stage on, the partition varies according to the different areas of the embryo. Only the organogenic cells retain a high degree of radioactivity. This pattern of inheritance concerns chiefly the apical cells of shoots and roots. This peculiar behaviour of the paternal genome can be explained in different ways. At present, a non-random distribution of paternal chromatids, i. e. a selective segregation of old and new strands of DNA to opposite poles of embryonic mitoses, appears most likely.
