11,580 research outputs found
Magnetic flux density and the critical field in the intermediate state of type-I superconductors
To address unsolved fundamental problems of the intermediate state (IS), the
equilibrium magnetic flux structure and the critical field in a high purity
type-I superconductor (indium film) are investigated using magneto-optical
imaging with a 3D vector magnet and electrical transport measurements. The
least expected observation is that the critical field in the IS can be as small
as nearly 40% of the thermodynamic critical field . This indicates that
the flux density in the \textit{bulk} of normal domains can be
\textit{considerably} less than , in apparent contradiction with the long
established paradigm, stating that the normal phase is unstable below .
Here we present a novel theoretical model consistently describing this and
\textit{all} other properties of the IS. Moreover, our model, based the
rigorous thermodynamic treatment of observed laminar flux structure in a tilted
field, allows for a \textit{quantitative} determination of the domain-wall
parameter and the coherence length, and provides new insight into the
properties of all superconductors.Comment: 5 pages, 5 figure
COVID-19 and the difficulty of inferring epidemiological parameters from clinical data
Knowing the infection fatality ratio (IFR) is of crucial importance for
evidence-based epidemic management: for immediate planning; for balancing the
life years saved against the life years lost due to the consequences of
management; and for evaluating the ethical issues associated with the tacit
willingness to pay substantially more for life years lost to the epidemic, than
for those to other diseases. Against this background Verity et al. (2020,
Lancet Infections Diseases) have rapidly assembled case data and used
statistical modelling to infer the IFR for COVID-19. We have attempted an
in-depth statistical review of their approach, to identify to what extent the
data are sufficiently informative about the IFR to play a greater role than the
modelling assumptions, and have tried to identify those assumptions that appear
to play a key role. Given the difficulties with other data sources, we provide
a crude alternative analysis based on the Diamond Princess Cruise ship data and
case data from China, and argue that, given the data problems, modelling of
clinical data to obtain the IFR can only be a stop-gap measure. What is needed
is near direct measurement of epidemic size by PCR and/or antibody testing of
random samples of the at risk population.Comment: Version accepted by the Lancet Infectious Diseases. See previous
version for less terse presentatio
The Tensor Hierarchies of Pure N=2,d=4,5,6 Supergravities
We study the supersymmetric tensor hierarchy of pure (gauged) N=2,d=4,5,6
supergravity and compare them with those of the pure, ungauged, theories
(worked out by Gomis and Roest for d=5) and the predictions of the Kac-Moody
approach made by Kleinschmidt and Roest. We find complete agreement in the
ungauged case but we also find that, after gauging, new Stueckelberg symmetries
reduce the number of independent "physical" top-forms. The analysis has to be
performed to all orders in fermion fields.
We discuss the construction of the worldvolume effective actions for the
p-branes which are charged with respect to the (p+1)-form potentials and the
relations between the tensor hierarchies and p-branes upon dimensional
reduction.Comment: LaTeX2e file, 20 pages, 1 figure Results refined by extension of the
analysis to all orders in fermion
A Massive S-duality in 4 dimensions
We reduce the Type IIA supergravity theory with a generalized Scherk-Schwarz
ansatz that exploits the scaling symmetry of the dilaton, the metric and the NS
2-form field. The resulting theory is a new massive, gauged supergravity theory
in four dimensions with a massive 2-form field and a massive 1-form field. We
show that this theory is S-dual to a theory with a massive vector field and a
massive 2-form field, which are dual to the massive 2-form and 1-form fields in
the original theory, respectively. The S-dual theory is shown to arise from a
Scherk-Schwarz reduction of the heterotic theory. Hence we establish a massive,
S-duality type relation between the IIA theory and the heterotic theory in four
dimensions. We also show that the Lagrangian for the new four dimensional
theory can be put in the most general form of a D=4, N=4 gauged Lagrangian
found by Schon and Weidner, in which (part of) the SL(2) group has been gauged.Comment: 20 pages, references adde
Strong Couplings of X(3872)_{J=1,2} and a New Look at J/psi Suppression in Heavy Ion Collisions
We define and compute from data the strong couplings of the X(3872) with both
of the possible quantum numbers assignments J^{PC}=1^{++},2^{-+}. We use these
to compute cross sections for J/psi resonance scattering into D Dbar*. As an
application of the results obtained we revise the calculation of the J/psi
absorption in a hot hadron gas to confront with recent RHIC observations in
Au-Au collisions.Comment: 23 pages, 18 figures, 4 table
Taxonomic description of fossil wood from Cainozoic Sak River terraces, near Brandvlei, Bushmanland, South Africa
Seven pieces of silicified wood are described from two sites near the Sak River, Bushmanland. The Miocene deposit yielded five specimens which can be assigned to the Dipterocarpaceae, Fagaceae, Myrtaceae, Oleaceae and Rutaceae. Of the two logs recovered from the Plio-Pleistocene deposit, only one was well enough preserved to be assigned to the Polygalaceae. All the woods indicate that the palaeoenvironment in that region was tropical to subtropical based on the wood structure, growth rings and from their modem counterparts.De Beer
Stikstof- en fosfaatexcretie van gangbaar en biologisch gehouden landbouwhuisdieren. Herziening excretieforfaits Meststoffenwet 2015.
Om de hoeveelheden stikstof en fosfaat in dierlijke mest te berekenen die op een bedrijf worden geproduceerd, kunnen veehouders gebruik maken van de zogenoemde excretieforfaits in de Uitvoeringsregeling van de Meststoffenwet. Deze excretieforfaits geven weer hoeveel stikstof en fosfaat in mest per dier en per diercategorie op jaarbasis wordt geproduceerd. Op verzoek van het Ministerie van Economische Zaken heeft de Commissie Deskundigen Meststoffenwet (CDM) een voorstel gemaakt voor herziening van de diercategorieën en de excretieforfaits van de Uitvoeringsregeling Meststoffenwet. Dit rapport beschrijft het voorstel voor de herziening van de excretieforfaits voor de eerder aangepaste lijst vandiercategorieën. Bij de excretieforfaits wordt onderscheid gemaakt tussen gangbare en biologische dierhouderijsystemen. De bruto stikstof- en fosfaatexcreties voor dieren in gangbare dierhouderijsystemen zijn gebaseerd op de resultaten van de Werkgroep Uniformering berekening Mest- en mineralencijfers (WUM) voor de jaren 2011, 2012 en 2013. De WUM berekent per jaar de gemiddelde excreties per diercategorie op basis van statistieken over veevoergebruik en dierlijke productie. De bruto stikstof- en fosfaatexcreties voor dieren in biologische dierhouderijsystemen zijn gebaseerd op die van gangbare dierhouderijsystemen en een diercategorie-specifieke correctiefactor. De bruto stikstofexcreties zijn vervolgens gecorrigeerd voor gasvormige stikstofverliezen op basis van gegevens van de werkgroep National Emission Model for Agriculture (NEMA)
VLTI/MIDI 10 micron interferometry of the forming massive star W33A
We report on resolved interferometric observations with VLTI/MIDI of the
massive young stellar object (MYSO) W33A. The MIDI observations deliver
spectrally dispersed visibilities with values between 0.03 and 0.06, for a
baseline of 45m over the wavelength range 8-13 micron. The visibilities
indicate that W33A has a FWHM size of approximately 120AU (0.030'') at 8 micron
which increases to 240AU at 13 micron, scales previously unexplored among
MYSOs. This observed trend is consistent with the temperature falling off with
distance. 1D dust radiative transfer models are simultaneously fit to the
visibility spectrum, the strong silicate feature and the shape of the mid
infrared spectral energy distribution (SED). For any powerlaw density
distribution, we find that the sizes (as implied by the visibilities) and the
stellar luminosity are incompatible. A reduction to a third of W33A's
previously adopted luminosity is required to match the visibilities; such a
reduction is consistent with new high resolution 70 micron data from Spitzer's
MIPSGAL survey. We obtain best fits for models with shallow dust density
distributions of r^(-0.5) and r^(-1.0) and for increased optical depth in the
silicate feature produced by decreasing the ISM ratio of graphite to silicates
and using optical grain properties by Ossenkopf et al. (1992).Comment: 4 pages, 4 figures. Accepted for ApJ letter
N=2 supergravity in five dimensions revisited
We construct matter-coupled N=2 supergravity in five dimensions, using the
superconformal approach. For the matter sector we take an arbitrary number of
vector-, tensor- and hyper-multiplets. By allowing off-diagonal vector-tensor
couplings we find more general results than currently known in the literature.
Our results provide the appropriate starting point for a systematic search for
BPS solutions, and for applications of M-theory compactifications on Calabi-Yau
manifolds with fluxes.Comment: 35 pages; v.2: A sign changed in a bilinear fermion term in (5.7
- …