11,288 research outputs found
Late Quaternary Mediterranean Outflow Water: implications from radiogenic Nd, Sr, Pb isotopes and clay minerals
Mediterranean Outflow Water (MOW) is characterised by higher temperatures and salinities than other ambient water masses. MOW spreads at water depths between 500 and 1500 m into the eastern North Atlantic and has been a source of salinity for the Atlantic Meridional Overturning Circulation. We used high-resolution Nd and Pb isotope records of past ambient seawater obtained from authigenic ferromanganese coatings of sediments in three gravity cores at 577, 1745 and 1974 m water depths in the Gulf of Cadiz and along the Portuguese margin complemented by a selection of surface sediments to reconstruct the extent and pathways of MOW over the past 23 000 years. In addition, radiogenic Nd, Pb and Sr isotope ratios obtained from total digestion of the residual clay fraction of the leached samples were used to evaluate any changes in the endmember compositions. The surface and downcore seawater Nd isotope data from all water depths exhibit only a very small variability close to the present day composition of MOW but do not reflect the present day Nd isotopic stratification of the water column as determined from a nearby open ocean hydrographic station, which is most likely the consequence of downslope sediment transport in the nepheloid boundary layer as well as the small variations in the Nd endmember compositions. In contrast, the seawater Pb isotope records show significant and systematic variations, which provide evidence for a significantly different pattern of the MOW pathways between 20 000 and 12 000 years ago compared with the subsequent period of time. A deeper situated MOW during the Last Glacial Maximum (LGM) raised during the early deglaciation with its shallowest position around Heinrich event H1, followed by a moderate deepening and the establishment of present-day MOW hydrography. The radiogenic isotope signatures of the residual clay fractions document a pulse of sediment input from the north during Heinrich event H1 around 14.8 ka, but other than that exhibit little varibility over time suggesting surprisingly constant sedimentary endmember compositions and mixing ratios since the LGM
Irradiation effect at cryogenic temperature on tensile properties of titanium and titanium- base alloys
Irradiation effects on tensile behavior of titanium alloys and titanium at cryogenic temperature
Extending Continuum Models for Atom Probe Simulation
This work describes extensions to existing level-set algorithms developed for
application within the field of Atom Probe Tomography (APT). We present a new
simulation tool for the simulation of 3D tomographic volumes, using advanced
level set methods. By combining narrow-band, B-Tree and particle-tracing
approaches from level-set methods, we demonstrate a practical tool for
simulating shape changes to APT samples under applied electrostatic fields, in
three dimensions. This work builds upon our previous studies by allowing for
non-axially symmetric solutions, with minimal loss in computational speed,
whilst retaining numerical accuracy
Plio-Pleistocene changes in water mass exchange and erosional inputs in the Fram Strait
We determined the isotopic composition of neodymium (Nd) and lead (Pb) of past seawater to reconstruct water mass exchange and erosional input between the Arctic Ocean and the Norwegian-Greenland Seas over the past 5 Ma. For this purpose, sediments of ODP site 911 (leg 151) located at 900 m water depth on the Yermak Plateau in the Fram Strait were used. The paleo-seawater variability of Nd and Pb isotopes was extracted from the sea water-derived metal oxide coatings on the sediment particles following the leaching method of Gutjahr et al. (2007). All radiogenic isotope data were acquired by Multi-Collector (MC) ICP-MS. The site 911 stratigraphy of Knies et al. (2009) was applied. Surface sediment Sr and Nd isotope data, as well as downcore Sr isotope data obtained on the same leaches are close to seawater and confirm the seawater origin of the Nd and Pb isotope signatures. The deep water Nd isotope time series extracted from site 911 was in general more radiogenic ("Nd = -7.5 to -10) than present day deep water ("Nd = -9.8 to -11.8) in the area of the Fram Strait (Andersson et al., 2008) and does not show a systematic trend with time. In contrast, the radiogenic isotope composition of Pb evolved from 206Pb/204Pb ratios around 18.7 to more radiogenic values around 19.2 between 2 Ma and today.
The data indicate that mixing of water masses from the Arctic Ocean and the Norwegian-Greenland Seas has controlled the Nd isotope signatures of deep waters on the Yermak Plateau over the past 5 Ma. Prior to 1.7 Ma the Nd isotope signatures on the Yermak Plateau were less radiogenic than waters from the same depth in the central Arctic Ocean (Haley et al., 2008) pointing to a greater influence from the Norwegian-Greenland Seas. After 1.7 Ma the central Arctic and Yermak Plateau data have varied around similar values indicating water mass mixing overall similar to today.
In contrast, the Pb isotope composition of deep waters in the Fram Strait appears to have been dominated by weathering inputs from glacially weathering old continental landmasses, such as Greenland or parts of Svalbard since 2 Ma. A similar control over the Pb isotope evolution of seawater since the onset of Northern Hemisphere Glaciation was recorded by ferromanganese crusts that grew from North Atlantic DeepWater in the western North Atlantic.
References:
Gutjahr, M., Frank, M., Stirling, C.H., Klemm, V., van de Flierdt, T. and Halliday, A.N. (2007): Reliable extraction of a deepwater trace metal isotope signal from Fe-Mn oxyhydroxide coatings of marine sediments.- Chemical Geology 242, 351-370
Haley B. A., M. Frank, R.F. Spielhagen and A. Eisenhauer (2008): Influence of brine formation on Arctic Ocean circulation over the past 15 million years. Nature Geoscience 1, 68â72
Andersson, P.S., Porcelli, D., Frank, M., Björk, G., Dahlqvist, R. and Gustafsson, Ă. (2008): Neodymium isotopes in seawater from the Barents Sea and Fram Strait Arctic- Atlantic gateways.- Geochim. Cosmochim. Acta 72, 2854-2867
Knies, J., J. Matthiessen, C. Vogt, J.S. Laberg, B.O. Hjelstuen, M.Smelror, E. Larsen, K. Andreassen, T. Eidvin and T.O. Vorren (2009): The Plio-Pleistocene glaciation of the Barents SeaâSvalbard region: a new model based on revised chronostratigraphy - Quaternary Science Reviews 28, 9-10, 812-82
A comparison of scores of kindergarten children and nonkindergarten children in specific background abilities at first grade entrance
Thesis (Ed.M.)--Boston Universit
The Impact of Community Based Adventure Therapy on Stress and Coping Skills in Adults.
Stress and coping skills are among the most essential components of the mental health counseling field. The use of coping skills (e.g., meditation, physical activities, appropriate uses of leisure) has been identified as an effective strategy for stress management. Adventure therapy has emerged as a modality that can positively augment other therapeutic approaches by improving coping skills and assisting clients in managing stress. As with all therapies, a positive working alliance has been found to be important toward achieving clinical outcomes. This study explored how adventure therapy enhanced learned coping strategies for stress and improved therapeutic alliance. Outcomes from this exploratory research highlighted the potential of adventure therapy to decrease stress, increase coping skills, and build therapeutic rapport with the therapist
Classroom Realities: Teaching Students with Disabilities as a Traditionally or Alternatively Certified Secondary Science Teacher in Maine
This study aimed to determine the characteristics of effective pre-service instruction and in-service professional development based on certification route that affect Maine secondary science teachersâ preparedness to accommodate students with disabilities. Traditional and alternative certification routes differ in fundamental elements such as length, course requirements, and format, leading to teachers who have different strengths and weaknesses, and consequently, different professional development needs. Effective preparation for instructing students with disabilities is an important issue because the trend toward full educational inclusion increasingly will require that classroom teachers have the skills to make appropriate accommodations. A survey sent to Maine secondary science teachers gathered information about their pre-service training, professional development needs and experiences, and current situations teaching students with disabilities. The results show that alternatively trained teachers feel more prepared than traditionally trained teachers to make accommodations, but that most teachers, regardless of certification route, were not confident in their special needs skills during their first year of teaching. To improve secondary science teachersâ skills for including students with disabilities, they should have more extensive pre-service training that includes special education field experiences. Professional development should be science-related and based on the needs within a school
Ordinary Women: Female Perpetrators of the Nazi Final Solution
This Thesis, by examining the roles of three Nazi women, Herta Oberheuser, Irma Grese, and Ilse Koch, as well as understanding the various womenâs programs that helped to cultivate and further racism and violence against Jews and others âunworthy of life,â aims to paint a more complete picture of the true role played by Nazi women during the second world war, as well as argue that women were not only victims of the Nazi regime, nor were they solely bystanders. Rather, this thesis will demonstrate that women were not only complicit, but were also accomplices, aiding German men in facilitating the Nazi Final Solution. The few women who were tried were not really exceptional, nor did they lack âinnate feminine virtues,â classically assigned to women at the time, but rather they were excited about the new opportunities made available to them, resulting from a sort of sadistic feminism. Operating within the intrusively patriarchal society, many Nazi women felt the need to prove that they were just as capable as Nazi men, and found a way to do so under the very system that murdered their victims and oppressed German men and women alike
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