1,457 research outputs found
A submillimeter interference spectrometer - Characteristics, performance and measurements
Performance characteristics of interference spectrometer using submillimeter wave
Spontaneous Fluxoid Formation in Superconducting Loops
We report on the first experimental verification of the Zurek-Kibble scenario
in an isolated superconducting ring over a wide parameter range. The
probability of creating a single flux quantum spontaneously during the fast
normal-superconducting phase transition of a wide Nb loop clearly follows an
allometric dependence on the quenching time , as one would expect if
the transition took place as fast as causality permits. However, the observed
Zurek-Kibble scaling exponent is two times larger than
anticipated for large loops. Assuming Gaussian winding number densities we show
that this doubling is well-founded for small annuli.Comment: 10 pages, 2 figures, submitted to Phys. Rev. Lett
Fluxoid formation: size effects and non-equilibrium universality
Simple causal arguments put forward by Kibble and Zurek suggest that the
scaling behaviour of condensed matter at continuous transitions is related to
the familiar universality classes of the systems at quasi-equilibrium. Although
proposed 25 years ago or more, it is only in the last few years that it has
been possible to devise experiments from which scaling exponents can be
determined and in which this scenario can be tested. In previous work, an
unusually high Kibble-Zurek scaling exponent was reported for spontaneous
fluxoid production in a single isolated superconducting Nb loop, albeit with
low density. Using analytic approximations backed up by Langevin simulations,
we argue that densities as small as these are too low to be attributable to
scaling, and are conditioned by the small size of the loop. We also reflect on
the physical differences between slow quenches and small rings, and derive some
criteria for these differences, noting that recent work on slow quenches does
not adequately explain the anomalous behaviour seen here.Comment: 7 pages, 4 figures, presentation given at CMMP 201
The Creation of Defects with Core Condensation
Defects in superfluid 3He, high-Tc superconductors, QCD colour superfluids
and cosmic vortons can possess (anti)ferromagnetic cores, and their
generalisations. In each case there is a second order parameter whose value is
zero in the bulk which does not vanish in the core. We examine the production
of defects in the simplest 1+1 dimensional scalar theory in which a second
order parameter can take non-zero values in a defect core. We study in detail
the effects of core condensation on the defect production mechanism.Comment: 9 pages, 7 figures, small corrections, 2 references added, final
version to be published in PR
Zurek-Kibble Mechanism for the Spontaneous Vortex Formation in Josephson Tunnel Junctions: New Theory and Experiment
New scaling behavior has been both predicted and observed in the spontaneous
production of fluxons in quenched annular Josephson tunnel
junctions as a function of the quench time, . The probability
to trap a single defect during the N-S phase transition clearly follows an
allometric dependence on with a scaling exponent , as
predicted from the Zurek-Kibble mechanism for {\it realistic} JTJs formed by
strongly coupled superconductors. This definitive experiment replaces one
reported by us earlier, in which an idealised model was used that predicted
, commensurate with the then much poorer data. Our experiment
remains the only condensed matter experiment to date to have measured a scaling
exponent with any reliability.Comment: Four pages, one figur
Shared Governance at Virginia Commonwealth University: Increasing Awareness of Shared Governance Among Faculty
Abstract
SHARED GOVERNANCE AT VIRGINIA COMMONWEALTH UNIVERSITY: INCREASING AWARENESS OF SHARED GOVERNANCE AMONG FACULTY
By Andrea H. Becker, Carlton H. Goode, Jennifer C. Rivers, Melissa W. Tyler
A capstone project submitted in partial fulfillment of the requirements for the degree of Doctor of Education in the Department of Educational Leadership at Virginia Commonwealth University
Virginia Commonwealth University, 2022.
Capstone Chair: Jonathan D. Becker, Ph.D., Department of Educational Leadership
The primary focus of this study is to understand and define the concept of shared governance as practiced at Virginia Commonwealth University (VCU). The researchers approached the study through three guiding questions: What is shared governance as understood through relevant literature and practice; What are the current faculty perceptions of shared governance at VCU; How can awareness of shared governance be increased at the institution? A naturalistic study was conducted including a thorough literature review and narrative data collection from focus groups, individual interviews, and a modified charrette. Participants included faculty across the institution from a variety of ranks, units, and demographics. The study found faculty perceptions and literature speak to two overarching ways to experience shared governance at VCU: structure and culture. Structural components included the lack of standardized systems, workflow, and communication methods between university stakeholders. Cultural components encompassed decreased trust, engagement, and value of engaging in shared governance. Using the information collected, this paper offers recommendations for a collective definition of shared governance and strategies for increasing awareness.
Keywords: shared governance, faculty governance, participatory governance, structure, communication, recognition, trust, transparenc
Zurek-Kibble domain structures: The Dynamics of Spontaneous Vortex formation in Annular Josephson Tunnel Junctions
Phase transitions executed in a finite time show a domain structure with
defects, that has been argued by Zurek and Kibble to depend in a characteristic
way on the quench rate. In this letter we present an experiment to measure the
Zurek-Kibble scaling exponent sigma. Using symmetric and long Josephson Tunnel
Junctions, for which the predicted index is sigma = 0.25, we find sigma = 0.27
+/- 0.05. Further, there is agreement with the ZK prediction for the overall
normalisation.Comment: To be published in Phys. Rev. Lett
Testing the Kibble-Zurek Scenario with Annular Josephson Tunnel Junctions
In parallel with Kibble's description of the onset of phase transitions in
the early universe, Zurek has provided a simple picture for the onset of phase
transitions in condensed matter systems, strongly supported by agreement with
experiments in He3. In this letter we show how experiments with annular
Josephson tunnel Junctions can and do provide further support for this
scenario.Comment: Revised version with correct formula for the Swihart velocity. The
results are qualitatively the same as with the previous version but differ
quantitatively. 4 pages, RevTe
Spontaneous Fluxon Production in Annular Josephson Tunnel Junctions in the Presence of a Magnetic Field
We report on the spontaneous production of fluxons in the presence of a
symmetry-breaking magnetic field for annular Josephson tunnel junctions during
a thermal quench. The dependence on field intensity of the probability
to trap a single defect during the N-S phase transition drastically
depends on the sample circumferences. We show that the data can be understood
in the framework of the Kibble-Zurek picture of spontaneous defect formation
controlled by causal bounds.Comment: Submitted to Phys. Rev. B with 5 figures on Nov. 15, 200
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