390 research outputs found
Superconductivity for Magnets
The present state of development of a series of industrial superconductors is
reviewed in consideration of their future applications in high field
accelerator magnets, with particular attention on the material aspect. The
discussion is centred on Nb3Sn and MgB2, which are industrially available in a
round wire configuration in kilometre lengths and are already envisaged for use
in the LHC Upgrade (HL-LHC). The two systems Bi-2212 and R.E.123 may be used in
magnets with even higher fields in future accelerators: they are briefly
described.Comment: 21 pages, contribution to the CAS-CERN Accelerator School:
Superconductivity for Accelerators, Erice, Italy, 24 April - 4 May 2013,
edited by R. Baile
Transport Properties and Exponential n-values of Fe/MgB2 Tapes With Various MgB2 Particle Sizes
Fe/MgB2 tapes have been prepared starting with pre-reacted binary MgB2
powders. As shown by resistive and inductive measurements, the reduction of
particle size to a few microns by ball milling has little influence on Bc2,
while the superconducting properties of the individual MgB2 grains are
essentially unchanged. Reducing the particle size causes an enhancement of Birr
from 14 to 16 T, while Jc has considerably increased at high fields, its slope
Jc(B) being reduced. At 4.2K, values of 5.3*10^4 and 1.2*10^3 A/cm^2 were
measured at 3.5 and 10 T, respectively, suggesting a dominant role of the
conditions at the grain interfaces. A systematic variation of these conditions
at the interfaces is undertaken in order to determine the limit of transport
properties for Fe/MgB2 tapes. The addition of 5% Mg to MgB2 powder was found to
affect neither Jc nor Bc2. For the tapes with the highest Jc values, very high
exponential n factors were measured: n = 148, 89 and 17 at 3.5, 5 and 10T,
respectively and measurements of critical current versus applied strain have
been performed. The mechanism leading to high transport critical current
densities of filamentary Fe/MgB2 tapes based on MgB2 particles is discussed.Comment: Presented at ICMC 2003, 25-28 May 200
Kognitive Verhaltenstherapie : Ein möglicher Behandlungsansatz des Symptoms Fatigue beim Post-Polio-Syndrom?
Hintergrund: Das Post-Polio-Syndrom (PPS) ist von geringer Bekanntheit, trotz dessen Aktualität und der beträchtlichen Anzahl Betroffener in der Schweiz. Fatigue gilt für die Mehrheit aller PPS-Erkrankten als die grösste Beeinträchtigung. Studien belegen, dass Fatigue in anderen Krankheitsbildern durch die kognitive Verhaltenstherapie (Cognitive Behavioral Therapy, CBT) verringert werden kann.
Ziel: In dieser Arbeit wird aufgezeigt, ob CBT Fatigue bei neuromuskulären Erkrankungen vermindert und inwiefern diese Resultate auf das PPS übertragbar sind. Ebenfalls werden Hypothesen aufgestellt, welche Relevanz die Behandlung von Fatigue mittels CBT für die Physiotherapie hat.
Methode: Von März bis November 2015 wurden in den Datenbanken CINAHL, Pubmed, Medline und PsycINFO anhand spezifischer Keywords Studien zur Beantwortung der Fragestellung gesucht. Die gefundenen Studien wurden mittels PEDro und AICA ausgewertet.
Resultate: Drei Studien bestätigen, dass CBT zur Verminderung von Fatigue bei neuromuskulären Erkrankungen führt. Eine Studie widerlegt jedoch diese Annahme.
Schlussfolgerung: Es bedarf sowohl im Bereich der genauen Ursachen für die Fatigue bei neuromuskulären Erkrankungen, insbesondere bei PPS, als auch bei der Effektivität von CBT weitere Forschung.
Patientenedukation, strukturierte Behandlungen mit klaren Zielen und die Eigenverantwortung des Patienten sehen die Autorinnen als einen Ansatz, CBT auf Fatigue bei PPS in der Physiotherapie anzuwenden
Effects of Neutron Irradiation on Pinning Force Scaling in State-of-the-Art Nb3Sn Wires
We present an extensive irradiation study involving five state-of-the-art
Nb3Sn wires which were subjected to sequential neutron irradiation up to a fast
neutron fluence of 1.6 * 10^22 m^-2 (E > 0.1 MeV). The volume pinning force of
short wire samples was assessed in the temperature range from 4.2 to 15 K in
applied fields of up to 7 T by means of SQUID magnetometry in the unirradiated
state and after each irradiation step. Pinning force scaling computations
revealed that the exponents in the pinning force function differ significantly
from those expected for pure grain boundary pinning, and that fast neutron
irradiation causes a substantial change in the functional dependence of the
volume pinning force. A model is presented, which describes the pinning force
function of irradiated wires using a two-component ansatz involving a
point-pinning contribution stemming from radiation induced pinning centers. The
dependence of this point-pinning contribution on fast neutron fluence appears
to be a universal function for all examined wire types.Comment: 8 page
Surface impedance measurements on NbSn at high magnetic fields
NbSn is a superconductor of great relevance for perspective RF
applications. We present for the first time surface impedance
measurements at 15 GHz and low RF field amplitude on NbSn in high
magnetic fields up to 12 T, with the aim of increasing the knowledge of
NbSn behavior in such conditions. is a fundamental material
parameter that directly gives useful information about the dissipative and
reactive phenomena when the superconductor is subjected to high-frequency
excitations. Therefore, we present an analysis of the measured with the
aim of extracting interesting data about pinning in NbSn at high
frequencies. From we extract the vortex motion complex resistivity to
obtain the -parameter and the depinning frequency in high magnetic
fields. The comparison of the results with the literature shows that the
measured on bulk NbSn is several times greater than that of pure
Nb. This demonstrates how NbSn can be a good candidate for RF
technological applications, also in high magnetic fields.Comment: ASC 2018 conference, accepted in IEEE Trans Appl Supercon
A Review of the Properties of Nb3Sn and Their Variation with A15 Composition, Morphology and Strain State
This article gives an overview of the available literature on simplified,
well defined (quasi-)homogeneous laboratory samples. After more than 50 years
of research on superconductivity in Nb3Sn, a significant amount of results are
available, but these are scattered over a multitude of publications. Two
reviews exist on the basic properties of A15 materials in general, but no
specific review for Nb3Sn is available. This article is intended to provide
such an overview. It starts with a basic description of the Niobium-Tin
intermetallic. After this it maps the influence of Sn content on the the
electron-phonon interaction strength and on the field-temperature phase
boundary. The literature on the influence of Cu, Ti and Ta additions will then
be briefly summarized. This is followed by a review on the effects of grain
size and strain. The article is concluded with a summary of the main results.Comment: Invited Topical Review for Superconductor, Science and Technology.
Provisionally scheduled for July 200
Phase coexistence and critical temperatures of the (Bi, Pb)2Sr2Ca2Cu3Ox phase under partial pressures of oxygen between 10−3 and 0.21 bar with and without additions of silver
We have investigated the stability of the (Bi, Pb)2Sr2Ca2Cu3Ox phase for the stoichiometry (Bi: Pb: Sr:Ca: Cu = 1.72: 0.34: 1.83: 1.97: 3.13), subjecting it to temperatures between 700 and 850 °C under various oxygen partial pressures. A narrow region was found in which Bi, Pb(2223) was the only superconducting phase. This region follows closely the thermal decomposition line. X-ray pure Bi, Pb(2223) will partially decompose if treated outside of the stability region. For a given oxygen partial pressure, the Bi, Pb(2223) phase tends to coexist with the 2201 phase for temperatures above, and the 2212 phase for temperatures below this region. At even lower temperatures an additional lead-rich phase appears. Critical temperatures Tc vary little with treatment and range between 108.5 K and 110.8 K. If 10% silver is added to the starting powder, the phase coexistence regions shift. Silver does not seem to have a significant effect on the absolute values of the critical temperature. The Bi, Pb(2223) thermal decomposition temperature for a given oxygen pressure is lowered by at least 10 K by the presence of A
Bewegungsalltag im Homeoffice vs. Arbeit im Betrieb : eine Mixed-Methods-Studie während der Covid-19- Pandemie
Ausgangslage: Personen, die Schreibtischarbeit im Büro, insbesondere auch im Homeoffice verrichten,
verbringen einen Grossteil ihres Alltags sitzend und bewegen sich zu wenig. Dadurch stellen sie eine Risikopopulation für ein erhöhtes Mass an nicht übertragbaren Krankheiten dar. Die Arbeit von zu Hause verringert einerseits die Alltagsbewegung, andererseits kann die im Homeoffice gewonnene Zeit für mehr körperliche Aktivität genutzt werden.
Ziel: Diese Bachelorarbeit hat das Ziel, den Bewegungsalltag im Homeoffice mit dem im Betrieb zu vergleichen und darzulegen, welche Faktoren zum Bewegungsverhalten im Homeoffice beitragen und welche Bedürfnisse die Erwerbstätigen haben.
Methode: Für die Datenerhebung wurde ein exploratives Mixed-Method-Design angewendet. Zuerst wurde eine quantitative Befragung mit 65 Erwerbstätigen durchgeführt. Anhand der Ergebnisse konnten sechs Erwerbstätige für qualitative Interviews rekrutiert werden.
Ergebnisse: 50 % der Befragten bewegen sich im Homeoffice allgemein weniger als im Büro, ein Viertel bewegt sich mehr. Wiederum macht die Mehrheit im Homeoffice mehr Sport, längere Unterbrüche und ist mehr in der Natur im Gegensatz zum Betrieb. Das soziale Umfeld, das Wohlbefinden und der Workload sind wichtige Einflussfaktoren auf die Bewegung.
Schlussfolgerung: Der Bewegungsalltag ist sehr individuell. Aufgrund der Eigenverantwortung im Homeoffice muss die Bewegung bewusst in den Alltag integriert werden. Die Unterstützung von gesundheitsförderlichen Verhaltensweisen erfordert das Verständnis der verschiedenen Faktoren, welche die körperliche Aktivität beeinflussen
The upper critical field of filamentary Nb3Sn conductors
We have examined the upper critical field of a large and representative set
of present multi-filamentary Nb3Sn wires and one bulk sample over a temperature
range from 1.4 K up to the zero field critical temperature. Since all present
wires use a solid-state diffusion reaction to form the A15 layers,
inhomogeneities with respect to Sn content are inevitable, in contrast to some
previously studied homogeneous samples. Our study emphasizes the effects that
these inevitable inhomogeneities have on the field-temperature phase boundary.
The property inhomogeneities are extracted from field-dependent resistive
transitions which we find broaden with increasing inhomogeneity. The upper
90-99 % of the transitions clearly separates alloyed and binary wires but a
pure, Cu-free binary bulk sample also exhibits a zero temperature critical
field that is comparable to the ternary wires. The highest mu0Hc2 detected in
the ternary wires are remarkably constant: The highest zero temperature upper
critical fields and zero field critical temperatures fall within 29.5 +/- 0.3 T
and 17.8 +/- 0.3 K respectively, independent of the wire layout. The complete
field-temperature phase boundary can be described very well with the relatively
simple Maki-DeGennes model using a two parameter fit, independent of
composition, strain state, sample layout or applied critical state criterion.Comment: Accepted Journal of Applied Physics Few changes to shorten document,
replaced eq. 7-
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