6,459 research outputs found
Modulated spin and charge densities in cuprate superconductors
Neutron scattering experiments have played a crucial role in characterizing
the spin and charge correlations in copper-oxide superconductors. While the
data are often interpreted with respect to specific theories of the cuprates,
an attempt is made here to distinguish those facts that can be extracted
empirically, and the connections that can be made with minimal assumptions.Comment: 6 pp., LaTeX, 2 col., uses espcrc2.sty + psfig.sty, 2 eps figures;
Proc. of the International Conf. on Neutron Scattering, Toronto, Aug. 1997,
to be published in Physica
Cell Model of In-cloud Scavenging of Highly Soluble Gases
We investigate mass transfer during absorption of highly soluble gases such
as HNO_{3}, H_{2}O_{2} by stagnant cloud droplets in the presence of inert
admixtures. Thermophysical properties of the gases and liquids are assumed to
be constant. Diffusion interactions between droplets, caused by the overlap of
depleted of soluble gas regions around the neighboring droplets, are taken into
account in the approximation of a cellular model of a gas-droplet suspension
whereby a suspension is viewed as a periodic structure consisting of the
identical spherical cells with periodic boundary conditions at the cell
boundary. Using this model we determined temporal and spatial dependencies of
the concentration of the soluble trace gas in a gaseous phase and in a droplet
and calculated the dependence of the scavenging coefficient on time. It is
shown that scavenging of highly soluble gases by cloud droplets leads to
essential decrease of soluble trace gas concentration in the interstitial air.
We found that scavenging coefficient for gas absorption by cloud droplets
remains constant and sharply decreases only at the final stage of absorption.
In the calculations we employed gamma size distribution of cloud droplets. It
was shown that despite of the comparable values of Henry's law constants for
the hydrogen peroxide (H2O2) and the nitric acid (HNO3), the nitric acid is
scavenged more effectively by cloud than the hydrogen peroxide due to a major
affect of the dissociation reaction on HNO3 scavenging.Comment: 28 pages, including 11 Figures, 1 Tabl
A Two-level Prediction Model for Deep Reactive Ion Etch (DRIE)
We contribute a quantitative and systematic model to capture etch non-uniformity in deep reactive ion etch of microelectromechanical systems (MEMS) devices. Deep reactive ion etch is commonly used in MEMS fabrication where high-aspect ratio features are to be produced in silicon. It is typical for many supposedly identical devices, perhaps of diameter 10 mm, to be etched simultaneously into one silicon wafer of diameter 150 mm. Etch non-uniformity depends on uneven distributions of ion and neutral species at the wafer level, and on local consumption of those species at the device, or die, level. An ion–neutral synergism model is constructed from data obtained from etching several layouts of differing pattern opening densities. Such a model is used to predict wafer-level variation with an r.m.s. error below 3%. This model is combined with a die-level model, which we have reported previously, on a MEMS layout. The two-level model is shown to enable prediction of both within-die and wafer-scale etch rate variation for arbitrary wafer loadings.Singapore-MIT Alliance (SMA
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Shoot yield drives phosphorus use efficiency in Brassica oleracea and correlates with root architecture traits
The environmental and financial costs of using inorganic phosphate fertilizers to maintain crop yield and quality are high. Breeding crops that acquire and use phosphorus (P) more efficiently could reduce these costs. The variation in shoot P concentration (shoot-P) and various measures of P use efficiency (PUE) were quantified among 355 Brassica oleracea L. accessions, 74 current commercial cultivars, and 90 doubled haploid (DH) mapping lines from a reference genetic mapping population. Accessions were grown at two or more external P concentrations in glasshouse experiments; commercial and DH accessions were also grown in replicated field experiments. Within the substantial species-wide diversity observed for shoot-P and various measures of PUE in B. oleracea, current commercial cultivars have greater PUE than would be expected by chance. This may be a consequence of breeding for increased yield, which is a significant component of most measures of PUE, or early establishment. Root development and architecture correlate with PUE; in particular, lateral root number, length, and growth rate. Significant quantitative trait loci associated with shoot-P and PUE occur on chromosomes C3 and C7. These data provide information to initiate breeding programmes to improve PUE in B. oleracea
Human security and the rise of the social
As the concept of human security has become part of the mainstream discourse of international politics it should be no surprise that both realist and critical approaches to international theory have found the agenda wanting. This article seeks to go beyond both the realist and biopolitical critiques by situating all three – political realism, biopolitics and human security – within the history and theory of the modern rise of the social realm from late eighteenth and nineteenth century Europe. Human security is the further expansion of social forms of governance under capitalism, more specifically a form of socialpolitik than realpolitik or biopolitics. Drawing on the work of historical sociologist Robert Castel and political theorist Hannah Arendt, the article develops an alternative framework with which to question the extent to which ‘life’ has become the subject of global intervention through the human security agenda
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