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T Stumpf

Publications and source records attributed to T Stumpf.

5 recordsLinked to original sources
PubMed2006

Structural characterization of Am incorporated into calcite: a TRLFS and EXAFS study.

Calcite homogeneously doped with Am(III) and Cm(III) was synthesized in a mixed-flow reactor. The mechanism of incorporation of these actinides (An) into calcite was investigated by time-resolved laser fluorescence spectroscopy. Two different An(III)/calcite species were found. One has been identified as ions bonded onto the calcite surface. The second An(III) species has lost its complete hydration sphere and is incorporated into the calcite bulk structure. Both Cm(III)/calcite and Am(III)/calcite complexes have been characterized by their fluorescence emission spectra and lifetimes. Structural parameters of the incorporated Am(III) species determined by EXAFS indicate a coordination number of 6.3+/-0.6 and distances of 2.40+/-0.01 A for the first AmO shell.

Journal Article↗
PubMed2001

Time-resolved laser fluorescence spectroscopy study of the sorption of Cm(III) onto smectite and kaolinite.

For long-term performance assessment of nuclear waste repositories knowledge concerning interactions of actinides with mineral surfaces is imperative. The mobility and bioavailability of released radionuclides is strongly dependent on sorption/desorption processes onto mineral surfaces. Therefore it is necessary to characterize the surface species formed and to elucidate the reaction mechanisms involved. The high fluorescence spectroscopic sensitivity of Cm(III) has attracted our interest regarding the complexation process of Cm(III) onto smectite and kaolinite as a model system for the sorption of trivalent actinides in the trace concentration range. We conclude that at low pH Cm(III) is sorbed onto kaolinite and smectite as an outer-sphere complex and retains its complete primary hydration sphere. With increasing pH inner-sphere adsorption onto kaolinite and smectite occurs via the aluminol edge sites. The same evolution of the Cm(III)-clay surface species as a function of pH was observed for both minerals. Starting at a pH > or = 5 we observe the formation of a [triple bond]Al-O-Cm2+(H2O)5 surface complex, which is replaced by a second species at higher pH. The second surface complex may be a monodentate [triple bond]Al-O-Cm+(OH)(H2O)4 species or bidentate [triple bond](Al-O)2-Cm+(H2O)5 species. The Cm(III)/clay surface complexes are characterized bytheir emission spectra (peak maxima at 598.8 and 603.3 nm) and their fluorescence lifetime (both 110 +/- 7 micros). An important result in view of the mobility and bioavailability of radionuclides is that no incorporation of Cm(III) into the bulk clay structure was observed.

Adsorption↗
PubMed1998

[Time perception and time estimation in depressive patients].

Subjective time-experience and objective time-estimation were examined in 20 endogenous, 20 neurotic depressives, and 15 healthy volunteers. Subjective experience of past and anticipated future time was more extended in both depressive groups than in healthy controls. Objective time estimation differed between depressives and controls concerning relatively long time spans whereas very short time spans were correctly estimated also by depressives. There were no significant differences between endogenous and neurotic depressives. The perception of extended time normalized during treatment. The depressives' time perception, differences correlated with the extent of depressive psychopathological symptoms and--to a lesser degree--with retardation. The findings support the hypotheses of anthropological phenomenology concerning disturbed time perception and estimation in depressives. Amelioration of experienced time-extension in intentionally structured time spans compared to empty time spans suggests psychotherapeutic consequences in the sense of Lewinsohn.

Adult↗
PubMed1987

Luteinizing hormone and progesterone concentrations in serum of heifers administered a short half-life prostaglandin (PGF(2alpha)) or long half-life prostaglandin analogue (fenprostalene) on days six or eleven of the estrous cycle.

Two trials were conducted to measure the progesterone (P(4)) decline and luteinizing hormone (LH) surge in serum subsequent to administration of a short half-life (short t (1 2 )) prostaglandin (PGF(2alpha)) or a long half-life (long t (1 2 )) prostaglandin analogue (fenprostalene) on Days 6 or 11 of the estrous cycle. Twenty-five crossbred Shorthorn and five Hereford heifers with a mean weight of 331.4 +/- 29.8 kg were used in both trials. The heifers were randomly allotted to receive either a short t (1 2 ) or long t (1 2 ) prostaglandin treatment on Day 6 or 11 of the estrous cycle. A crossover design for the main effect, treatment (type of prostaglandin), was conducted. Heifers that received PGF(2alpha) in Trial I were given fenprostalene in Trial II and vice versa. Stage of the estrous cycle (day) was the same for each heifer in both trials. Stage of estrous cycle was standardized to either Day 6 or 11 by administering Syncro-Mate B (SMB). Blood was collected every hour for 80 h post injection to quantify LH and P(4) concentrations. There were no significant differences (P > 0.05) between the short t (1 2 ) or long t (1 2 ) for either P(4) or LH profiles. In addition, no differences were detected between stages of the estrous cycle for the timing of the preovulatory surge of LH after prostaglandin administration.

Journal Article↗