1,068 research outputs found
Crossing the \u27Color Bar\u27: African American Soldiers in Britain and Australia During the Second World War
During the Second World War, African American soldiers were stationed all over the world as part of the American war effort. During these deployments, African Americans encountered a number of white societies, such as those in Britain and Australia, which they generally interacted with cordially. Good relations between African American soldiers and the local white populations angered many white servicemembers, who saw the lack of Jim Crow style segregation as a threat to the racial status quo, and attempted to enforce segregation overseas themselves. These attempts were often resisted fiercely by African American soldiers and the local white populations, both of whom despised such rules being forced upon them. This thesis examines the interactions between American forces and the British and Australian populations during the Second World War through the lens of race. It argues that the deployment of African Americans soldiers overseas left not only an impression on those African Americans who served, but also on Britons and Australians who encountered them. For those African Americans who were deployed in places like Britain and Australia, their experiences with these relatively friendly white societies and the white American soldiers who attempted to enforce segregation outside the United States highlighted the racial inequalities inherent in American society, and strengthened their resolve to fight against inequality. For the Britons and Australians who interacted with African Americans, racial discrimination by white Americans in their own countries lead many to reevaluate their opinions on both racism in the United States and in their own societies. Thus, this thesis expands the boundaries of the wartime struggle for civil rights by bringing the fight for equality into a larger multinational conversation
Emission-Line Properties of z > 4 Quasars
We present results of a program of high signal-to-noise spectroscopy for 44
QSOs at redshifts > 4 using the MMT and Keck observatories. The quasar spectra
cover 1100 -- 1700 A in the rest frame for sources spanning a luminosity range
of approximately 2 orders of magnitude. Comparisons between these data and
spectra of lower redshift quasars reveal a high degree of similarity, although
differences are present in the profiles and the strengths of some emission
features. An examination of the luminosity dependence of the emission lines
reveals evidence for a weak or absent Baldwin effect among z > 4 QSOs. We
compare measurements for objects in our sample with results from other high
redshift surveys characterized by different selection techniques. Distributions
of equivalent widths for these different ensembles are consistent with a common
parent population, suggesting that our sample is not strongly biased, or in any
case, subject to selection effects that are not significantly different from
other surveys, including the Sloan Digital Sky Survey. Based on this
comparison, we tentatively conclude that the trends identified here are
representative of high z QSOs. In particular, the data bolster indications of
supersolar metallicities in these luminous, high-z sources, which support
scenarios that assume substantial star formation at epochs preceding or
concurrent with the QSO phenomena.Comment: 26 pages (incl. 9 figures), AASTeX v5.0, to appear in The
Astrophysical Journa
The nearest extreme starburst: bubbles, young star clusters, and outflow in NGC 3256
In this Work we report, for the extreme starburst in the IR merger NGC 3256:
(i) The detection of 4 galactic bubbles, associated with SN explosions.(ii) The
first analysis of the spatial distribution of young star clusters (YSC)
candidates.(iii) The kinematic study of the ionized gas in the core of of the
main optical nucleus, performed with HST STIS spectra. The shape of the
rotation curve and the emission line profile could be explained by the presence
in the core of YSC with outflow.Comment: 5 pages, 5 figures, Contect Replac., accepted MN-RA
Key Science Goals for the Next Generation Very Large Array (ngVLA): Report from the ngVLA Science Advisory Council
This document describes some of the fundamental astrophysical problems that
require observing capabilities at millimeter- and centimeter wavelengths well
beyond those of existing, or already planned, telescopes. The results
summarized in this report follow a solicitation from the National Radio
Astronomy Observatory to develop key science cases for a future U. S.-led radio
telescope, the "next generation Very Large Array" (ngVLA). The ngVLA will have
roughly 10 times the collecting area of the Jansky VLA, operate at frequencies
from 1 GHz to 116 GHz with up to 20 GHz of bandwidth, possess a compact core
for high surface-brightness sensitivity, and extended baselines of at least
hundreds of kilometers and ultimately across the continent to provide
high-resolution imaging. The ngVLA builds on the scientific and technical
legacy of the Jansky VLA and ALMA, and will be designed to provide the next
leap forward in our understanding of planets, galaxies, and black holes.Comment: ngVLA memo 1
Nitrogen Controls on Climate Model Evapotranspiration
Most evapotranspiration over land occurs through vegetation. The fraction of net radiation balanced by evapotranspiration depends on stomatal controls. Stomates transpire water for the leaf to assimilate carbon, depending on the canopy carbon demand, and on root uptake, if it is limiting. Canopy carbon demand in turn depends on the balancing between visible photon-driven and enzyme-driven steps in the leaf carbon physiology. The enzyme-driven component is here represented by a Rubisco-related nitrogen reservoir that interacts with plantâsoil nitrogen cycling and other components of a climate model. Previous canopy carbon models included in GCMs have assumed either fixed leaf nitrogen, that is, prescribed photosynthetic capacities, or an optimization between leaf nitrogen and light levels so that in either case stomatal conductance varied only with light levels and temperature.A nitrogen model is coupled to a previously derived but here modified carbon model and includes, besides the enzyme reservoir, additional plant stores for leaf structure and roots. It also includes organic and mineral reservoirs in the soil; the latter are generated, exchanged, and lost by biological fixation, deposition and fertilization, mineralization, nitrification, root uptake, denitrification, and leaching. The root nutrient uptake model is a novel and simple, but rigorous, treatment of soil transport and root physiological uptake. The other soil components are largely derived from previously published parameterizations and global budget constraints.The feasibility of applying the derived biogeochemical cycling model to climate model calculations of evapotranspiration is demonstrated through its incorporation in the BiosphereâAtmosphere Transfer Scheme land model and a 17-yr Atmospheric Model Inter comparison Project II integration with the NCAR CCM3 GCM. The derived global budgets show land net primary production (NPP), fine root carbon, and various aspects of the nitrogen cycling are reasonably consistent with past studies. Time series for monthly statistics averaged over model grid points for the Amazon evergreen forest and lower Colorado basin demonstrate the coupled interannual variability of modeled precipitation, evapotranspiration, NPP, and canopy Rubisco enzymes
Superhumps in Cataclysmic Binaries. XXIII. V442 Ophiuchi and RX J1643.7+3402
We report the results of long observing campaigns on two novalike variables:
V442 Ophiuchi and RX J1643.7+3402. These stars have high-excitation spectra,
complex line profiles signifying mass loss at particular orbital phases, and
similar orbital periods (respectively 0.12433 and 0.12056 d). They are
well-credentialed members of the SW Sex class of cataclysmic variables. Their
light curves are also quite complex. V442 Oph shows periodic signals with
periods of 0.12090(8) and 4.37(15) days, and RX J1643.7+3402 shows similar
signals at 0.11696(8) d and 4.05(12) d. We interpret these short and long
periods respectively as a "negative superhump" and the wobble period of the
accretion disk. The superhump could then possibly arise from the heating of the
secondary (and structures fixed in the orbital frame) by inner-disk radiation,
which reaches the secondary relatively unimpeded since the disk is not
coplanar.
At higher frequencies, both stars show another type of variability:
quasi-periodic oscillations (QPOs) with a period near 1000 seconds. Underlying
these strong signals of low stability may be weak signals of higher stability.
Similar QPOs, and negative superhumps, are quite common features in SW Sex
stars. Both can in principle be explained by ascribing strong magnetism to the
white dwarf member of the binary; and we suggest that SW Sex stars are
borderline AM Herculis binaries, usually drowned by a high accretion rate. This
would provide an ancestor channel for AM Hers, whose origin is still
mysterious.Comment: PDF, 41 pages, 4 tables, 16 figures; accepted, in press, to appear
December 2002, PASP; more info at http://cba.phys.columbia.edu
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