On-Line Optical and Morphological Studies of Silver Nanoparticles Growth Formed by Nanosecond Laser Irradiation of Silver-Exchanged Silicate Glass

Silver-exchanged silicate glass has been irradiated by 532-nm pulsed Nd:YAG laser in order to locally form metallic nanoparticles. The particular interest of this process is to locally control the silver nanoparticles (NPs) growth. Silver ions are exchanged with sodium ions near the glass surface after dumping of a silicate glass few minutes in silver and sodium nitrates molten salt. A low-energy density laser exposure (0.239 J/cm²) chosen at the ablation threshold allows to observe the kinetics of the silver NPs growth according to the increasing shots number. An on-line optical measurement is carried out after each shot to identify the most important steps during the irradiation process. According to this measurement, we have determined four steps highlighted by UV/Visible spectrophotometry and we have identified the influence of located surface plasmon resonance. Three combined material analysis methods were used to understand the glass/laser interaction mechanism: we outlined the material volume variations by profilometric method, the element distribution by scanning electron microscopy and finally the structural distribution of the irradiated region by a local infrared investigation. The trend for NPs formation revealed by the UV/Visible spectrophotometry is thus explained by the formation of a ring expelled from a central hole. We highlight that the on-line extinction measurement can be used to data process the NPs evolution.     

The timing of sexual maturation among boys and girls in eastern Poland, 1980–2000: A rural–urban comparison

The aim of this study was to determine secular changes in the sexual maturation of children and adolescents from Eastern regions of Poland between 1980 and 2000, with special attention paid to rural–urban differences. Our sample comprised 34,055 girls and 28,100 boys from 9 to 18 years of age. The age at which each gender reached each stage of sexual maturation was examined, along with menarcheal age in girls. An increase in the rate of sexual maturation was observed over the 20-year period of this study. Menarcheal age in girls decreased by 0.59 years. The length of sexual maturation decreased: from 6.58 years to 3.85 years in girls and from 5.84 years to 3.65 years in boys. A significantly faster rate of sexual maturation was observed between 1990 and 2000. Over the entire 20-year period, adolescents living in rural settings experienced a slower rate of sexual maturation than did their urban peers.     

Distribution of Recombination Hotspots in the Human Genome – A Comparison of Computer Simulations with Real Data

Recombination is the main cause of genetic diversity. Thus, errors in this process can lead to chromosomal abnormalities. Recombination events are confined to narrow chromosome regions called hotspots in which characteristic DNA motifs are found. Genomic analyses have shown that both recombination hotspots and DNA motifs are distributed unevenly along human chromosomes and are much more frequent in the subtelomeric regions of chromosomes than in their central parts. Clusters of motifs roughly follow the distribution of recombination hotspots whereas single motifs show a negative correlation with the hotspot distribution. To model the phenomena related to recombination, we carried out computer Monte Carlo simulations of genome evolution. Computer simulations generated uneven distribution of hotspots with their domination in the subtelomeric regions of chromosomes. They also revealed that purifying selection eliminating defective alleles is strong enough to cause such hotspot distribution. After sufficiently long time of simulations, the structure of chromosomes reached a dynamic equilibrium, in which number and global distribution of both hotspots and defective alleles remained statistically unchanged, while their precise positions were shifted. This resembles the dynamic structure of human and chimpanzee genomes, where hotspots change their exact locations but the global distributions of recombination events are very similar.