3,179 research outputs found
Two Gap State Density in MgB: A True Bulk Property or A Proximity Effect?
We report on the temperature dependence of the quasiparticle density of
states (DOS) in the simple binary compound MgB2 directly measured using
scanning tunneling microscope (STM). To achieve high quality tunneling
conditions, a small crystal of MgB2 is used as a tip in the STM experiment. The
``sample'' is chosen to be a 2H-NbSe2 single crystal presenting an atomically
flat surface. At low temperature the tunneling conductance spectra show a gap
at the Fermi energy followed by two well-pronounced conductance peaks on each
side. They appear at voltages V mV and V mV. With rising temperature both peaks disappear at the Tc of the bulk
MgB2, a behavior consistent with the model of two-gap superconductivity. The
explanation of the double-peak structure in terms of a particular proximity
effect is also discussed.Comment: 4 pages, 3 figure
Weighted Sobolev spaces of radially symmetric functions
We prove dilation invariant inequalities involving radial functions,
poliharmonic operators and weights that are powers of the distance from the
origin. Then we discuss the existence of extremals and in some cases we compute
the best constants.Comment: 38 page
Computer model validation with functional output
A key question in evaluation of computer models is Does the computer model
adequately represent reality? A six-step process for computer model validation
is set out in Bayarri et al. [Technometrics 49 (2007) 138--154] (and briefly
summarized below), based on comparison of computer model runs with field data
of the process being modeled. The methodology is particularly suited to
treating the major issues associated with the validation process: quantifying
multiple sources of error and uncertainty in computer models; combining
multiple sources of information; and being able to adapt to different, but
related scenarios. Two complications that frequently arise in practice are the
need to deal with highly irregular functional data and the need to acknowledge
and incorporate uncertainty in the inputs. We develop methodology to deal with
both complications. A key part of the approach utilizes a wavelet
representation of the functional data, applies a hierarchical version of the
scalar validation methodology to the wavelet coefficients, and transforms back,
to ultimately compare computer model output with field output. The generality
of the methodology is only limited by the capability of a combination of
computational tools and the appropriateness of decompositions of the sort
(wavelets) employed here. The methods and analyses we present are illustrated
with a test bed dynamic stress analysis for a particular engineering system.Comment: Published in at http://dx.doi.org/10.1214/009053607000000163 the
Annals of Statistics (http://www.imstat.org/aos/) by the Institute of
Mathematical Statistics (http://www.imstat.org
A threshold phenomenon for embeddings of into Orlicz spaces
We consider a sequence of positive smooth critical points of the
Adams-Moser-Trudinger embedding of into Orlicz spaces. We study its
concentration-compactness behavior and show that if the sequence is not
precompact, then the liminf of the -norms of the functions is greater
than or equal to a positive geometric constant.Comment: 14 Page
What happens when the inflaton stops during inflation
The spectrum of adiabatic density perturbation generated during inflation is
studied in the case the time derivative of an inflation-driving scalar field
(inflaton) vanishes at some time during inflation. It is shown that the
nondecaying mode of perturbation has a finite value even in this case and that
its amplitude is given by the standard formula with the time derivation of the
scalar field replaced by the potential gradient using the slow-roll equation
Null Models of Economic Networks: The Case of the World Trade Web
In all empirical-network studies, the observed properties of economic
networks are informative only if compared with a well-defined null model that
can quantitatively predict the behavior of such properties in constrained
graphs. However, predictions of the available null-model methods can be derived
analytically only under assumptions (e.g., sparseness of the network) that are
unrealistic for most economic networks like the World Trade Web (WTW). In this
paper we study the evolution of the WTW using a recently-proposed family of
null network models. The method allows to analytically obtain the expected
value of any network statistic across the ensemble of networks that preserve on
average some local properties, and are otherwise fully random. We compare
expected and observed properties of the WTW in the period 1950-2000, when
either the expected number of trade partners or total country trade is kept
fixed and equal to observed quantities. We show that, in the binary WTW,
node-degree sequences are sufficient to explain higher-order network properties
such as disassortativity and clustering-degree correlation, especially in the
last part of the sample. Conversely, in the weighted WTW, the observed sequence
of total country imports and exports are not sufficient to predict higher-order
patterns of the WTW. We discuss some important implications of these findings
for international-trade models.Comment: 39 pages, 46 figures, 2 table
Education policy as an act of white supremacy: whiteness, critical race theory and education reform
The paper presents an empirical analysis of education policy in England that is informed by recent developments in US critical theory. In particular, I draw on ‘whiteness studies’ and the application of Critical Race Theory (CRT). These perspectives offer a new and radical way of conceptualising the role of racism in education. Although the US literature has paid little or no regard to issues outside North America, I argue that a similar understanding of racism (as a multifaceted, deeply embedded, often taken-for-granted aspect of power relations) lies at the heart of recent attempts to understand institutional racism in the UK. Having set out the conceptual terrain in the first half of the paper, I then apply this approach to recent changes in the English education system to reveal the central role accorded the defence (and extension) of race inequity. Finally, the paper touches on the question of racism and intentionality: although race inequity may not be a planned and deliberate goal of education policy neither is it accidental. The patterning of racial advantage and inequity is structured in domination and its continuation represents a form of tacit intentionality on the part of white powerholders and policy makers. It is in this sense that education policy is an act of white supremacy. Following others in the CRT tradition, therefore, the paper’s analysis concludes that the most dangerous form of ‘white supremacy’ is not the obvious and extreme fascistic posturing of small neonazi groups, but rather the taken-for-granted routine privileging of white interests that goes unremarked in the political mainstream
Seismological monitoring of the February 2007 effusive eruption of the Stromboli volcano
On February 27, 2007, the Stromboli volcano, which has usually been characterized by moderate explosive activity,
started an effusive eruption with a small lava flow down the NW flank. The permanent broadband network
installed on the island allowed the revealing of anomalies in the seismicity before the effusive eruption and for
the phenomena to be followed over time, thus obtaining meaningful information about the eruption dynamics.
During the effusive phase, a major explosion occurred on March 15, 2007. On that occasion, two strainmeters
deployed on the volcano in the previous year recorded a strain increment before the blast. After this explosion,
which further destabilized the upper part of the edifice, swarms of Long-Period (LP) and hybrid events were
recorded. The characteristics and locations of these events suggest that they were associated with the fracturing
processes that affected the summit area of the cone. During the effusive phase, changes in the Very Long Period
(VLP) event location were recorded. This type of events accompanied the change in the eruptive style, providing
information about the magmatic conduit involved in their seismogenetic processes. The effusive phase
stopped on April 2, 2007, and the typical Strombolian activity restarted some months later
Synesthesia and Migraine: Case Report
<p>Abstract</p> <p>Background</p> <p>Synesthesia is, as visual migraine aura, a common and fascinating perceptual phenomenon. Here we present a unique case with synesthesias exclusively during visual migraine auras.</p> <p>Case presentation</p> <p>A 40-year-old woman with a cyclic mood disorder had suffered from migraine with visual aura for several years. On several occasions she had experienced "mixing of senses" during the aura phase. Staring at strong bright light she could experience intense taste of lemon with flow from the salivary glands.</p> <p>Conclusion</p> <p>Acquired synesthesia, exclusively coincident with migraine aura, gives support to the idea of an anomalous cortical processing underlying the phenomenon.</p
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