4,320 research outputs found
Correlated transport through junction arrays in the small Josephson energy limit: incoherent Cooper-pairs and hot electrons
We study correlated transport in a Josephson junction array for small
Josephson energies. In this regime transport is dominated by Cooper-pair
hopping, although we observe that quasiparticles can not be neglected. We
assume that the energy dissipated by a Cooper-pair is absorbed by the intrinsic
impedance of the array. This allows us to formulate explicit Cooper-pair
hopping rates without adding any parameters to the system. We show that the
current is correlated and crucially, these correlations rely fundamentally on
the interplay between the Cooper-pairs and equilibrium quasiparticles.Comment: 11 pages, 9 figures - Published Versio
Influence of two-level fluctuators on adiabatic passage techniques
We study the process of Stimulated Raman Adiabatic Passage (STIRAP) under the
influence of a non-trivial solid-state environment, particularly the effect of
two-level fluctuators (TLFs) as they are frequently present in solid-state
devices. When the amplitudes of the driving-pulses used in STIRAP are in
resonance with the level spacing of the fluctuators the quality of the
protocol, i.e., the transferred population decreases sharply. In general the
effect can not be reduced by speeding up the STIRAP process. We also discuss
the effect of a structured noise environment on the process of Coherent
Tunneling by Adiabatic Passage (CTAP). The effect of a weakly structured
environment or TLFs with short coherence times on STIRAP and CTAP can be
described by the Bloch-Redfield theory. For a strongly structured environment a
higher-dimensional approach must be used, where the TLFs are treated as part of
the system.Comment: 8 pages, 8 figure
The parity effect in Josephson junction arrays
We study the parity effect and transport due to quasiparticles in circuits
comprised of many superconducting islands. We develop a general approach and
show that it is equivalent to previous methods for describing the parity effect
in their more limited regimes of validity. As an example we study transport
through linear arrays of Josephson junctions in the limit of negligible
Josephson energy and observe the emergence of the parity effect with decreasing
number of non-equilibrium quasiparticles. Due to the exponential increase in
the number of relevant charge states with increasing length, in multi-junction
arrays the parity effect manifests in qualitatively different ways to the two
junction case. The role of charge disorder is also studied as this hides much
of the parity physics which would otherwise be observed. Nonetheless, we see
that the current through a multi-junction array at low bias is limited by the
formation of meta-stable even-parity states.Comment: 8 pages, 5 figure
Emission characteristics of laser-driven dissipative coupled-cavity systems
We consider a laser-driven and dissipative system of two coupled cavities
with Jaynes-Cummings nonlinearity. In particular, we investigate both
incoherent and coherent laser driving, corresponding to different experimental
situations. We employ Arnoldi time evolution as a numerical tool to solve
exactly the many-body master equation describing the non-equilibrium quantum
system. We evaluate the fluorescence spectrum and the spectrum of the
second-order correlation function of the emitted light field. Finally, we
relate the measured spectra of the dissipative quantum system to excitations of
the corresponding non-dissipative quantum system. Our results demonstrate how
to interpret spectra obtained from dissipative quantum systems and specify what
information is contained therein.Comment: 12 pages, 8 figure
Gait characteristics and falls in Parkinson's disease: A systematic review and meta-analysis
Introduction: Given the high rate of falls during walking in people with idiopathic Parkinson's disease (PD), identifying at risk individuals and developing targeted interventions to reduce falls incidence is paramount. Numerous studies have investigated gait-related risk factors for falls in PD, however findings are inconsistent across studies, and thus a synthesis of the current evidence is needed to guide clinical practice and the development of interventions to reduce falls risk. The objective of this study was to systematically review the literature regarding the association between walking biomechanics and falls in people with PD, and where possible, perform meta-analyses. Methods: The study was performed in accordance with the PRISMA guidelines. Databases were searched until January 2018 to identify articles that reported on the association between walking biomechanics and prospective or retrospective falls in people with PD. Results: Twenty-six articles were included (15 prospective studies, 11 retrospective studies). Articles reported on spatiotemporal and kinematic characteristics, and muscle activation patterns. Meta-analyses revealed slower walking speed, lower cadence, shorter strides and more mediolateral head and pelvis motion in those at higher risk of future falls. Findings from prospective and retrospective articles were largely consistent. Conclusion: Our findings identify spatiotemporal and kinematic characteristics of gait that are risk factors for falls in PD. Modification of these characteristics may have the potential to mediate falls risk, and future research to investigate this possibility is merited. The influence of body and ground reaction forces, and muscle activation patterns on falls risk in PD is currently under-researched
Proposal for an IMLS Collection Registry and Metadata Repository
The University of Illinois at Urbana-Champaign proposes to design, implement, and research a collection-level registry and item-level metadata repository service that will aggregate information about digital collections and items of digital content created using funds from Institute of Museum and Library Services (IMLS) National Leadership Grants. This work will be a collaboration by the University Library and the Graduate School of Library and Information Science. All extant digital collections initiated or augmented under IMLS aegis from 1998 through September 30, 2005 will be included in the proposed collection registry. Item-level metadata will be harvested from collections making such content available using the Open Archives Initiative Protocol for Metadata Harvesting (OAI PMH). As part of this work, project personnel, in cooperation with IMLS staff and grantees, will define and document appropriate metadata schemas, help create and maintain collection-level metadata records, assist in implementing OAI compliant metadata provider services for dissemination of item-level metadata records, and research potential benefits and issues associated with these activities. The immediate outcomes of this work will be the practical demonstration of technologies that have the potential to enhance the visibility of IMLS funded online exhibits and digital library collections and improve discoverability of items contained in these resources. Experience gained and research conducted during this project will make clearer both the costs and the potential benefits associated with such services. Metadata provider and harvesting service implementations will be appropriately instrumented (e.g., customized anonymous transaction logs, online questionnaires for targeted user groups, performance monitors). At the conclusion of this project we will submit a final report that discusses tasks performed and lessons learned, presents business plans for sustaining registry and repository services, enumerates and summarizes potential benefits of these services, and makes recommendations regarding future implementations of these and related intermediary and end user interoperability services by IMLS projects.unpublishednot peer reviewe
Dual-probe decoherence microscopy: Probing pockets of coherence in a decohering environment
We study the use of a pair of qubits as a decoherence probe of a non-trivial
environment. This dual-probe configuration is modelled by three
two-level-systems which are coupled in a chain in which the middle system
represents an environmental two-level-system (TLS). This TLS resides within the
environment of the qubits and therefore its coupling to perturbing fluctuations
(i.e. its decoherence) is assumed much stronger than the decoherence acting on
the probe qubits. We study the evolution of such a tripartite system including
the appearance of a decoherence-free state (dark state) and non-Markovian
behaviour. We find that all parameters of this TLS can be obtained from
measurements of one of the probe qubits. Furthermore we show the advantages of
two qubits in probing environments and the new dynamics imposed by a TLS which
couples to two qubits at once.Comment: 29 pages, 10 figure
Digging Deeper into Hardin\u27s Pasture: The Complex Institutional Structure of The Tragedy of the Commons
The institutional and ecological structure of Hardin’s “tragedy of the commons” appears deceptively simple: the open-access pasture eventually will be overexploited and degraded unless (i) it is privatized, (ii) the government regulates access and use, or (iii) the users themselves impose a common-property regime to regulate their own access and use. In this paper, we argue that the institutional structure of the “Herder Problem” (as it is known to game theorists) is far more complicated than it is usually portrayed. Specifically, it is not just about the pasture. It is equally about the grass that grows on the pasture and the cattle that consume the grass. Even Elinor Ostrom — a scholar known for embracing complexity — presented an overly simplistic portrayal of Hardin’s open-access pasture when she described its governance system as a null set of institutions. A more careful assessment of the situation, employing Ostrom’s Social-Ecological System (SES) framework, broadens the focus from the res communes omnium pasture to incorporate the res nullius grass that grows upon it and the res private cattle grazing there. The “tragedy” arises from the combination and interactions of the resources and their governing institutions, not just from the absence of property in the pasture. If the grass was not subject to appropriation, the cattle were not privately owned, or if property- and contract-enforcement institutions supporting market exchange were absent, the “tragedy of the commons” probably would not arise regardless of the pasture’s open-access status
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