524 research outputs found
Setting up a general data collection system integrating different types of oceanographic survey data
Flux Jumps Driven by a Pulsed Magnetic Field
The understanding of flux jumps in the high temperature superconductors is of
importance since the occurrence of these jumps may limit the perspectives of
the practical use of these materials. In this work we present the experimental
study of the role of heavy ion irradiation in stabilizing the HTSC against flux
jumps by comparing un-irradiated and 7.5 10^10 Kr-ion/cm2 irradiated
(YxTm1-x)Ba2Cu3O7 single crystals. Using pulsed field magnetization
measurements, we have applied a broad range of field sweep rates from 0.1T/s up
to 1800 T/s to investigate the behavior of the flux jumps. The observed flux
jumps, which may be attributed to thermal instabilities, are incomplete and
have different amplitudes. The flux jumps strongly depend on the magnetic
field, on the magneto-thermal history of the sample, on the magnetic field
sweep rate, on the critical current density jc, on the temperature and on the
thermal contact with the bath in which the sample is immersed.Comment: 5 pages, PDF-fil
Axion-Dilaton Domain Walls and Fake Supergravity
Dynamical systems methods are used to investigate domain-wall solutions of a
two-parameter family of models in which gravity is coupled to an axion, and to
a dilaton with an exponential potential of either sign. A complete global
analysis is presented for (i) constant axion and (ii) flat walls, including a
study of bifurcations and a new exact domain-wall solution with non-constant
axion. We reconsider `fake supergravity' issues in light of these results. We
show, by example, how domain walls determine multi-valued superpotentials that
branch at stationary points that are not stationary points of the potential,
and we apply this result to potentials with anti-de Sitter vacua. We also show
by example that `adapted' truncation to a single-scalar model is sometimes
inconsistent, and we propose a `generalized' fake supergravity formalism that
applies in some such cases.Comment: 43pp, 19 figures; minor corrections and extensions; one additional
figur
Upgrading the OMES database: online access to OMES monitoring data using the IMERS web interface
The OMES collection is a database that holds a huge amount of measurement data on stations along the Zeeschelde and Westerschelde. The data collection consists in three main types of data: historical data (1904-1991) derived from literature, more recent data (1995-2007) generated during the OMES monitoring campaigns and some additional data from incidental measurements in the same study area. The measurements vary from water quality and suspended matter to biological data.The OMES project started in 1995 and is a multidisciplinary study on the estuarine environment of the Belgian part of the Scheldt. The main aim of OMES is to create a tool for the Flemish government that can be used as scientific support for the policy on water management of the Scheldt Estuary.In the summer of 2007 the OMES data collection has been integrated as a separate context in the IMERS data system. The Flanders Marine Institute is now responsible for centralizing and management of the newly gathered OMES data and for redistributing the data towards the OMES partners and extern users.The user that is interested in access to and use of the data is presented with a web interface on the OMES website that allows querying the database based on specific search criteria. Search criteria include parameters measured and taxonomic, spatial and temporal scope. The user can visualize the resulting data in tables and export the data to The whole dataset is made available to the project partners on the restricted pages of the OMES website: http://www.vliz.be/projects/omes
Shapiro steps in a superconducting film with an antidot lattice
Shapiro voltage steps at voltages V_n=nV_0 (n integer) have been observed in
the voltage-current characteristics of a superconducting film with a square
lattice of perforating microholes (antidots)in the presence of radiofrequent
radiation. These equidistant steps appear at the second matching field H_2 when
the flow of the interstitial vortex lattice in the periodic potential created
by the antidots and the vortices trapped by them, is in phase with the applied
rf frequency. Therefore, the observation of Shapiro steps clearly reveals the
presence of mobile intersitial vortices in superconducting films with regular
pinning arrays. The interstitial vortices, moved by the driving current,
coexist with immobile vortices strongly pinned at the antidots.Comment: 6 pages text, 3 EPS figures, RevTeX, accepted for publication in PRB
Rapid Communication
The Dutch version of the Child Posttraumatic Cognitions Inventory:validation in a clinical sample and a school sample
With the inclusion of trauma-related cognitions in the DSM-5 criteria for posttraumatic stress disorder (PTSD), the assessment of these cognitions has become essential. Therefore, valid tools for the assessment of these cognitions are warranted
Generalized Newton-Cartan geometries for particles and strings
We discuss the generalized Newton-Cartan geometries that can serve as gravitational background fields for particles and strings. In order to enable us to define affine connections that are invariant under all the symmetries of the structure group, we describe torsionful geometries with independent torsion tensors. A characteristic feature of the non-Lorentzian geometries we consider is that some of the torsion tensors are so-called ‘intrinsic torsion’ tensors. Setting some components of these intrinsic torsion tensors to zero leads to constraints on the geometry. For both particles and strings, we discuss various such constraints that can be imposed consistently with the structure group symmetries. In this way, we reproduce several results in the literature.</p
Critical Currents, Pinning Forces and Irreversibility Fields in (YxTml-x)Ba2Cu3O7 Single Crystals with Columnar Defects in Fields up to 50 T
We have studied the influence of columnar defects, created by heavy-ion (Kr)
irradiation with doses up to 6 10^11 Kr-ions/cm2, on the superconducting
critical parameters of single crystalline (YxTm1-x)Ba2Cu3O7. Magnetisation
measurements in pulsed fields up to 50 T in the temperature range 4.2 - 90 K
revealed that: (i) in fields up to T the critical current Jc(H,T) is
considerably enhanced and (ii) down to temperatures T ~ 40 K the
irreversibility field Hirr(T) is strongly increased. The field range and
magnitude of the Jc(H,T) and Hirr(T) enhancement increase with increasing
irradiation dose. To interpret these observations, an effective matching field
was defined. Moreover, introducing columnar defects also changes the pinning
force fp qualitatively. Due to stronger pinning of flux lines by the amorphous
defects, the superconducting critical parameters largely exceed those
associated with the defect structures in the unirradiated as-grown material:
Jc,irrad(77 K, 5 T) ^3 10* Jc,ref(77 K, 5 T).Comment: 11 pages, all PDF, contribution to Physica
Study of electrically active defects in epitaxial layers on silicon
Electrically active defects in silicon-based epitaxial layers on silicon substrates have been studied by Deep-Level Transient Spectroscopy (DLTS). Several aspects have been investigated, like, the impact of the pre-epi cleaning conditions and the effect of a post-deposition anneal on the deep-level properties. It is shown that the pre-cleaning thermal budget has a strong influence on the defects at the substrate/epi layer interface. At the same time, a post-deposition Forming Gas Anneal can passivate to a large extent the active defect states. Finally, it is shown that application of a post-deposition anneal increases the out-diffusion of carbon from a Si:C stressor layer into the p-type CZ substrate
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