Browsing by Subject "assimilation"

Now showing 1 - 6 of 6

Assimilation: A Study of North Indians in Bangalore by Vijaya B. Punekar
(The Journal of Asian Studies, 1977) Ullrich, Helen E.
Committed Retreat of Smith, Pope, and Kohler Glaciers Over the Next 30 Years Inferred by Transient Model Calibration
(2015-12) Goldberg, D. N.; Heimbach, P.; Joughin, I.; Smith, B.; Heimbach, P.
A glacial flow model of Smith, Pope and Kohler Glaciers is calibrated by means of control methods against time varying, annually resolved observations of ice height and velocities, covering the period 2002 to 2011. The inversion - termed "transient calibration" - produces an optimal set of time-mean, spatially varying parameters together with a time-evolving state that accounts for the transient nature of observations and the model dynamics. Serving as an optimal initial condition, the estimated state for 2011 is used, with no additional forcing, for predicting grounded ice volume loss and grounding line retreat over the ensuing 30 years. The transiently calibrated model predicts a near-steady loss of grounded ice volume of approximately 21 km(3) a(-1) over this period, as well as loss of 33 km(2) a(-1) grounded area. We contrast this prediction with one obtained following a commonly used "snapshot" or steady-state inversion, which does not consider time dependence and assumes all observations to be contemporaneous. Transient calibration is shown to achieve a better fit with observations of thinning and grounding line retreat histories, and yields a quantitatively different projection with respect to ice volume loss and ungrounding. Sensitivity studies suggest large near-future levels of unforced, i.e., committed sea level contribution from these ice streams under reasonable assumptions regarding uncertainties of the unknown parameters.
First Results from the GPS Atmosphere Sounding Experiment TOR Aboard the Terrasar-X Satellite
(2011) Beyerle, G.; Grunwaldt, L.; Heise, S.; Kohler, W.; Konig, R.; Michalak, G.; Rothacher, M.; Schmidt, T.; Wickert, J.; Tapley, B. D.; Giesinger, B.; Tapley, B. D.
GPS radio occultation events observed between 24 July and 17 November 2008 by the IGOR occultation receiver aboard the TerraSAR-X satellite are processed and analyzed. The comparison of 15 327 refractivity profiles with collocated ECMWF data yield a mean bias between zero and -0.30% at altitudes between 5 and 30 km. Standard deviations decrease from about 1.4% at 5 km to about 0.6% at 10 km altitude, however, increase significantly in the upper stratosphere. At low latitudes mean biases and standard deviations are larger, in particular in the lower troposphere. The results are consistent with 15 159 refractivity observations collected during the same time period by the BlackJack receiver aboard GRACE-A and processed by GFZ's operational processing system. The main difference between the two occultation instruments is the implementation of open-loop signal tracking in the IGOR (TerraSAR-X) receiver which improves the tropospheric penetration depth in terms of ray height by about 2 km compared to the conventional closed-loop data acquired by BlackJack (GRACE-A).
(Re)envisioning the Writing Center: Pragmatic Steps for Dismantling While Language Supremacy from Praxis: A Writing Center Journal vol.19 no.1
(Praxis, 2022) Basta, Hidy; Smith, Alexandra
Writing center work has long been haunted by the mandate to either fix the writing or fix the writer--both approaches share an assumption of a deficit model. As critical writing center scholarship has made clear, this is an assimilationist practice that re-enacts colonialist views of English. This paper expands the writing center work to reflect on effective strategies for interrupting this assimilationist methodology in order to create the kind of change that prioritizes making it make sense (Demand). We suggest making sense--true sense of writing center practices--means dispelling the myth of the superiority of standardized English and occupying braver spaces to hold honest conversations about languages and effective writing. These honest conversations are grounded in a critical examination of what we know of effective writing and what has long been taken for granted about the role of writing support and assessment. In this paper, we recount a brief history of the writing center as an institution--and our specific positionality within this history--to provide context for how our practices create and sustain change. We share the pragmatic steps of 1) revising tutor education curriculum to focus on antiracist approaches to writing, 2) facilitating conversations with faculty about antiracist writing assessment strategies, and 3) continuing professional development of writing center student staff. The writing center’s role in this broader communal work is essential, we argue, and necessary for dismantling white language supremacy in the ways we teach, mentor, and assess writing.
Xenolith constraints on the origin of low δ18O values in Mauna Kea basalts: The role of self-assimilation
(2018-05) Anderson, Danny W.
Several post-shield cones surrounding Mauna Kea volcano in Hawaii are marked by the presence of ultramafic and mafic cumulate xenoliths spanning a lithologic range from dunites to gabbros. These xenoliths offer a complimentary geochemical record to that provided by erupted lavas and may give insight into the dynamics of Hawaiian magma chambers and the effects of assimilation and fractional crystallization on the final melt compositions we observe at the surface. Trace-element concentrations measured in clinopyroxene suggest these xenoliths crystallized from similar parental magmas related to Mauna Kea volcanism; yet, isotopic variability precludes these samples from having formed from the same single parental magma. Compared with data from the HSDP-2 drillcore, the 87Sr/86Sr (0.70349 to 0.70357) and 208Pb/207Pb ratios (2.45 to 2.46) measured on these samples indicate they formed during the late shield stage to early post-shield transition in Mauna Kea’s volcanic history. Furthermore, a positive correlation between δ18O values measured in olivine (ranging from ~+3.3 to 4.8‰) and Mg# (ranging from ~0.73 to 0.90), in combination with Sr and Pb isotopic constraints, suggests that self-assimilation of hydrothermally altered, shallow edifice material has greatly lowered the δ18O values in Mauna Kea lavas from expected mantle olivine values (~+5.2‰). No clear correlation between radiogenic isotope values and Mg# suggests the Pb and Sr isotope ratios of the assimilant in this process are similar to those of the parental magma, preventing the assimilant from being an isotopically distinct material, such as lower oceanic crust (LOC). Additionally, Sr and Pb isotopes measured in samples of this study fall off of the expected mixing line between LOC and primitive Mauna Kea lavas. Additionally, the lack of anomalously high Sr isotope ratios, a typical signature of seawater interaction, rules out the possibility of submarine storage at intermediate depths. However, self-assimilation alone cannot account for the low- δ18O values (~+4.7 to 4.8‰) of the most primitive xenoliths (Mg# ~0.90). When applying a binary mixing model between Sr and O isotopic values of primitive Hawaiian basalt and extremely low assimilant estimates (δ18O ~0‰), assimilation of >10% edifice material would be required to lower the δ18O values. Energetically, this cannot be achieved, as assimilating this amount of material cannot be done without drawing down the Mg# to more evolved values through fractional crystallization. As a result, we propose that the low δ18O values in the high-Mg# xenoliths reflect the sampling of an isotopically light component of the Hawaiian plume.
Xenolith constraints on the origin of low δ18O values in Mauna Kea basalts: The role of self-assimilation
(2018-05) Amderson, Danny W.; Lassiter, John C.
Several post-shield cones surrounding Mauna Kea volcano in Hawaii are marked by the presence of ultramafic and mafic cumulate xenoliths spanning a lithologic range from dunites to gabbros. These xenoliths offer a complimentary geochemical record to that provided by erupted lavas and may give insight into the dynamics of Hawaiian magma chambers and the effects of assimilation and fractional crystallization on the final melt compositions we observe at the surface. Trace-element concentrations measured in clinopyroxene suggest these xenoliths crystallized from similar parental magmas related to Mauna Kea volcanism; yet, isotopic variability precludes these samples from having formed from the same single parental magma. Compared with data from the HSDP-2 drillcore, the 87Sr/86Sr (0.70349 to 0.70357) and 208Pb/207Pb ratios (2.45 to 2.46) measured on these samples indicate they formed during the late shield stage to early post-shield transition in Mauna Kea’s volcanic history. Furthermore, a positive correlation between δ18O values measured in olivine (ranging from ~+3.3 to 4.8‰) and Mg# (ranging from ~0.73 to 0.90), in combination with Sr and Pb isotopic constraints, suggests that self-assimilation of hydrothermally altered, shallow edifice material has greatly lowered the δ18O values in Mauna Kea lavas from expected mantle olivine values (~+5.2‰). No clear correlation between radiogenic isotope values and Mg# suggests the Pb and Sr isotope ratios of the assimilant in this process are similar to those of the parental magma, preventing the vi assimilant from being an isotopically distinct material, such as lower oceanic crust (LOC). Additionally, Sr and Pb isotopes measured in samples of this study fall off of the expected mixing line between LOC and primitive Mauna Kea lavas. Additionally, the lack of anomalously high Sr isotope ratios, a typical signature of seawater interaction, rules out the possibility of submarine storage at intermediate depths. However, self-assimilation alone cannot account for the low- δ18O values (~+4.7 to 4.8‰) of the most primitive xenoliths (Mg# ~0.90). When applying a binary mixing model between Sr and O isotopic values of primitive Hawaiian basalt and extremely low assimilant estimates (δ18O ~0‰), assimilation of >10% edifice material would be required to lower the δ18O values. Energetically, this cannot be achieved, as assimilating this amount of material cannot be done without drawing down the Mg# to more evolved values through fractional crystallization. As a result, we propose that the low δ18O values in the high-Mg# xenoliths reflect the sampling of an isotopically light component of the Hawaiian plume.