2,438 research outputs found

    Oceanographic features in the lee of the windward and leeward islands: ERTS and ship data

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    Analysis of the ERTS data in portions of the eastern Caribbean are presented for October 1972 showing features which are, as yet, not explained. Ground truth data obtained in that area during November 1972 are presented. These include vertical temperature structure in the mixed layer and thermocline, and surface measurements of salinity, temperature, and chlorophyll

    Mechanotransduction: Feeling the Squeeze in the C. elegans Reproductive System

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    SummaryA new study reports that the RhoGAP SPV-1 senses membrane curvature and cell stretch in the Caenorhabditis elegans spermatheca. Without SPV-1, the cells of the spermatheca are hypercontractile, leading to deformation and rapid ejection of the fertilized eggs. The spermatheca may provide a paradigm for understanding how cells detect mechanical stimuli in vivo

    Rhetoric, World-view, and Strategy in United States National Security Strategy Documents

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    Beginning in 1987, American Presidents have published a National Security Strategy (NSS), a public statement of their administration's grand strategy for the conduct of foreign policy. Despite breaking with a centuries-old tradition of secrecy, NSS documents have been routinely dismissed by scholars and experts as little more than an exercise in public relations or "mere rhetoric." In this dissertation, I argue that such a dismissive attitude is unproductive because it overlooks important linkages between the public expression of foreign policy, the influence that symbolism and rhetoric have on threat perception and policy choice, and the diverse (and continually shifting) array of audiences that such documents reach and influence. I engage in a close rhetorical analysis of the NSS documents of Presidents Ronald Reagan, George W. Bush, and Barack Obama in order to make this argument. Additionally, I demonstrate that NSS documents are an important resource for comparatively evaluating various administrations' foreign policies, thus facilitating better deliberation over grand strategy. While NSS documents may not function as "blueprints" for foreign policy, they are an important site for grounding public argument over the future of American foreign policy in an increasingly uncertain world

    "The Work of Generations": Tyranny and Democracy in the 2006 National Security Strategy

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    The 2006 National Security Strategy (NSS) of the George W. Bush administration has been neglected by rhetorical and policy scholars alike. In this study, I advance a rhetorical criticism of NSS 2006 and associated rhetoric of the Bush administration. Not only is NSS 2006 a rhetorical response to many of the challenges faced by the Bush administration's foreign policy during their first political term, it is also an exercise in symbolic action. The key rhetorical theme of this document is a constitutive agon centered on a dramatic clash between democracy (good) and tyranny (evil). Using narrative and Burkean methods of analysis, I argue that NSS 2006 substantially hinders open deliberation about foreign policy while simultaneously making the United States and the world less safe

    Wildland fire effects in silviculturally treated vs. untreated stands of New Mexico and Arizona

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    Stand-replacement fires, particularly in ponderosa pine (Pinus ponderosa) forests, have replaced high frequency, low-intensity historical fire regimes. We examined whether forest stands treated recently using silvicultural practices would be (1) less susceptible to stand-replacing crownfires, and (2) more ecologically and functionally resilient compared to untreated stands following extreme wildland fire. Reports detailing wildland fire behavior in treated stands remain largely anecdotal. We compared fire severity indices, fireline intensity (btu/ft/s), stand characteristics including canopy bulk density (kg/m3), and post-fire recovery indices in silviculturally treated vs. untreated forest stands in New Mexico and Arizona. Results indicated fire severity in pine-grassland forests was lowered when surface and aerial fuel loads were reduced. Specifically, as density (stems/ac) and basal area (ft2/ac) decreased and mean tree diameter (in) increased, fire severity and fireline intensity decreased. The more aggressive the treatment (i.e., where the canopy bulk density was reduced), the less susceptible forest stands were to crownfire. However, mechanical treatments where slash was scattered rendered stands susceptible to near stand-replacement type damage when wildfire occurred within 4 years of treatment. On our study sites, mechanical treatment followed by prescribed fire had the greatest impact toward mitigating fire severity (i.e., aerial and surface fuels were reduced). Treated stands were also more ecologically and functionally resilient than untreated forest stands following wildland fire

    The Phoenix Deep Survey: X-ray properties of faint radio sources

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    In this paper we use a 50ks XMM-Newton pointing overlapping with the Phoenix Deep Survey, a homogeneous radio survey reaching muJy sensitivities, to explore the X-ray properties and the evolution of star-forming galaxies. UV, optical and NIR photometry is available and is used to estimate photometric redshifts and spectral types for radio sources brighter than R=21.5mag (total of 82). Sources with R<21.5mag and spiral galaxy SEDs (34) are grouped into two redshift bins with a median of z=0.240 and 0.455 respectively. Stacking analysis for both the 0.5-2 and 2-8keV bands is performed on these subsamples. A high confidence level signal (>3.5sigma) is detected in the 0.5-2keV band corresponding to a mean flux of ~3e-16cgs for both subsamples. This flux translates to mean luminosities of ~5e40 and 1.5e41cgs for the z=0.240 and 0.455 subsamples respectively. Only a marginally significant signal (2.6sigma) is detected in the 2-8keV band for the z=0.455 subsample. We argue that the stacked signal above is dominated by star-formation. The mean L_X/L_B ratio and the mean L_X of the two subsamples are found to be higher than optically selected spirals and similar to starbursts. We also find that the mean L_X and L_1.4 of the faint radio sources studied here are consistent with the L_X-L_1.4 correlation of local star-forming galaxies. Moreover, the X-ray emissivity of sub-mJy sources to z~0.3 is found to be elevated compared to local HII galaxies. The observed increase is consistent with L_X evolution of the form (1+z)^3. Assuming that our sample is indeed dominated by starbursts this is direct evidence for evolution of such systems at X-ray wavelengths. Using an empirical L_X to SFR conversion we estimate a global SFR density at z~0.3 of \~0.029M_o/yr/Mpc in agreement with previous studies.Comment: 12 pages, 6 figures, accepted for publication in MNRA

    The Phoenix Deep Survey: spectroscopic catalog

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    The Phoenix Deep Survey is a multi-wavelength survey based on deep 1.4 GHz radio imaging, reaching well into the sub-100 microJy level. One of the aims of this survey is to characterize the sub-mJy radio population, exploring its nature and evolution. In this paper we present the catalog and results of the spectroscopic observations aimed at characterizing the optically ``bright'' (R<~ 21.5 mag) counterparts of faint radio sources. Out of 371 sources with redshift determination, 21% have absorption lines only, 11% show AGN signatures, 32% are star-forming galaxies, 34% show narrow emission lines that do not allow detailed spectral classification (due to poor signal-to-noise ratio and/or lack of diagnostic emission lines) and the remaining 2% are identified with stars. For the star-forming galaxies with a Balmer decrement measurement we find a median extinction of A(Ha)=1.9 mag, higher than that of optically selected samples. This is a result of the radio selection, which is not biased against dusty systems. Using the available spectroscopic information, we estimate the radio luminosity function of star-forming galaxies in two independent redshift bins at z~0.1 and 0.3 respectively. We find direct evidence for strong luminosity evolution of these systems consistent with L(1.4 GHz) ~ (1+z)^(2.7).Comment: 39 pages, 12 figures. References added, and minor changes to reflect published versio

    On the Determination of Star Formation Rates in Evolving Galaxy Populations

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    The redshift dependence of the luminosity density in certain wavebands (e.g. UV and H-alpha) can be used to infer the history of star formation in the populations of galaxies producing this luminosity. This history is a useful datum in studies of galaxy evolution. It is therefore important to understand the errors that attend the inference of star formation rate densities from luminosity densities. This paper explores the self-consistency of star formation rate diagnostics by reproducing commonly used observational procedures in a model with known galaxy populations, evolutionary histories and spectral emission properties. The study reveals a number of potential sources of error in the diagnostic processes arising from the differential evolution of different galaxy types. We argue that multi-wavelength observations can help to reduce these errors.Comment: 13 pages (including 5 encapsulated postscript figures), aastex, accepted for publication in Ap
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