969 resultados para groups of elements
Resumo:
Chemical investigations of superheavy elements in the gas-phase, i.e. elements with Z≥104Z≥104, allow assessing the influence of relativistic effects on their chemical properties. Furthermore, for some superheavy elements and their compounds quite unique gas-phase chemical properties were predicted. The experimental verification of these properties yields supporting evidence for a firm assignment of the atomic number. Prominent examples are the high volatility observed for HsO4 or the very weak interaction of Cn with gold surfaces. The unique properties of HsO4 were exploited to discover the doubly-magic even–even nucleus 270Hs and the new isotope 271Hs. The combination of kinematic pre-separation and gas-phase chemistry allowed gaining access to a new class of relatively fragile compounds, the carbonyl complexes of elements Sg through Mt. A not yet resolved issue concerns the interaction of Fl with gold surfaces. While competing experiments agree on the fact that Fl is a volatile element, there are discrepancies concerning its adsorption on gold surfaces with respect to its daughter Cn. The elucidation of these and other questions amounts to the fascination that gas-phase chemical investigations exert on current research at the extreme limits of chemistry today.
Resumo:
Limited research has addressed reunification of runaway youths with their families following an emergency shelter stay; however, recent studies have shown that those who reunify with their families following a shelter stay have more positive outcomes than those relocated to other residences. This study evaluated differences between two samples of runaway youth utilizing youth emergency shelters in New York (n = 155) and Texas (n = 195) and identified factors associated with reunification among these two groups of adolescents. Less than half (43.7%) of the youths were reunited with their families. Among New York runaway youths, those who had lived primarily with someone other than a parent before shelter admission, were physically abused, or neglected were less likely to return home. Among youths admitted to emergency shelter services in Texas, those with longer shelter stays, living primarily with someone other than a parent before shelter admission, or being pregnant or a parent were less likely to reunify. This study provides valuable information concerning family reunification following shelter service use; however, additional research is needed to delineate youth, family, and shelter system factors that distinguish successful from unsuccessful reunification over an extended period of time.
Resumo:
Geochemical data are presented for samples from strata, mainly of Miocene age, in the Cape Roberts-1 core (western McMurdo Sound, Antarctica) to assess the sediment provenance. Bulk (major and trace element) chemistry together with bulk mineralogy of fine-grained sandstones, siltstones, mudstones, and diamictites indicate that chemical alteration of source materials, fractionation due to sedimentary sorting, and diagenetic effects were not significant in the Cape Roberts sediment history. Relevant geochemical parameters are consistent with the Cape Roberts sediments being derived mainly from the crystalline basement and the Beacon Supergroup. On the basis of element distributions, an additional contribution from the Ferrar Dolerite and, mainly above about 60 m, influxes of detritus derived from basanitic to intermediate members of the McMurdo Volcanic Group are recognised.
Resumo:
Findings made in 31 catches with an Isaacs-Kidd midwater trawl in the light (09.00-16.00) and dark (21.00-04.00) periods of a day within a survey area of about 100 sq. miles with approximate center coordinates of 13°S and 78°E have been used to investigate vertical distribution of the main groups of sound-scattering fishes (35 species of the family Myctophidae and 16 species of other families). It has been shown that during daylight hours all fishes sink to depths deeper than 400 m. Data are presented concerning the fish population of night-time sound-scattering layers at depths of 70-150 m and about 400 m and of the daytime ones at depths of about 450 m.