343 research outputs found
Study of loss in superconducting coplanar waveguide resonators
Superconducting coplanar waveguide (SCPW) resonators have a wide range of
applications due to the combination of their planar geometry and high quality
factors relative to normal metals. However, their performance is sensitive to
both the details of their geometry and the materials and processes that are
used in their fabrication. In this paper, we study the dependence of SCPW
resonator performance on materials and geometry as a function of temperature
and excitation power. We measure quality factors greater than at
high excitation power and at a power comparable to that generated
by a single microwave photon circulating in the resonator. We examine the
limits to the high excitation power performance of the resonators and find it
to be consistent with a model of radiation loss. We further observe that while
in all cases the quality factors are degraded as the temperature and power are
reduced due to dielectric loss, the size of this effect is dependent on
resonator materials and geometry. Finally, we demonstrate that the dielectric
loss can be controlled in principle using a separate excitation near the
resonance frequencies of the resonator.Comment: Replacing original version. Changes made based on referee comments.
Fixed typo in equation (3) and added appendi
Reduced leakage current in Josephson tunnel junctions with codeposited barriers
Josephson junctions were fabricated using two different methods of barrier
formation. The trilayers employed were Nb/Al-AlOx/Nb on sapphire, where the
first two layers were epitaxial. The oxide barrier was formed either by
exposing the Al surface to O2 or by codepositing Al in an O2 background. The
codeposition process yielded junctions that showed the theoretically predicted
subgap current and no measurable shunt conductance. In contrast, devices with
barriers formed by thermal oxidation showed a small shunt conductance in
addition to the predicted subgap current.Comment: 3 pages, 4 figure
Migraine and gastrointestinal disorders in middle and old age: A UK Biobank study
Introduction: Migraine is a prevalent condition causing a substantial level of disability worldwide. Despite this, the pathophysiological mechanisms are not fully understood. Migraine often co-occurs with gastrointestinal disorders, but the direction of a potential causal link is unclear. The aim of this project was to investigate the associations between migraine and several gastrointestinal disorders in the same cohort in order to determine the relative strengths of these associations. Methods: This cross-sectional study examined whether migraine is associated with irritable bowel syndrome (IBS), peptic ulcers, Helicobacter pylori (HP) infections, celiac disease, Crohn's disease and ulcerative colitis. Baseline data covering 489,753 UK Biobank participants (migraine group: n = 14,180) were analyzed using Pearson's chi-square tests and adjusted binary logistic regression models. Results: Migraine was significantly associated with IBS (odds ratio [OR] 2.24, 95% confidence interval [CI] 2.08â2.40, p <.001) and peptic ulcers (OR 1.55, 95% CI 1.35â1.77, p <.001). Migraine was not associated with HP infection (OR 1.34, 95% CI 1.04â1.73, p =.024), celiac disease (OR 1.29, 95% CI 1.04â1.60, p =.023), Crohn's disease (OR 1.08, 95% CI 0.80â1.45, p =.617) or ulcerative colitis (OR 1.00, 95% CI 0.79â1.27, p =.979) after adjusting for multiple testing. Conclusions: Migraine was associated with IBS and peptic ulcers in this large population-based cohort. The associations with HP infection, celiac disease, Crohn's disease, and ulcerative colitis did not reach significance, suggesting a weaker link between migraine and autoimmune gastrointestinal conditions or HP infection
T-cell intracellular antigens in health and disease
T-cell intracellular antigen 1 (TIA1) and TIA1-related/like protein (TIAR/TIAL1) are 2 proteins discovered in 1991 as components of cytotoxic T lymphocyte granules. They act in the nucleus as regulators of transcription and pre-mRNA splicing. In the cytoplasm, TIA1 and TIAR regulate and/or modulate the location, stability and/or translation of mRNAs. As knowledge of the different genes regulated by these proteins and the cellular/biological programs in which they are involved increases, it is evident that these antigens are key players in human physiology and pathology. This review will discuss the latest developments in the field, with physiopathological relevance, that point to novel roles for these regulators in the molecular and cell biology of higher eukaryotes.Ministry Economic Affairs and Competitiveness through FEDER funds (BFU2008â00354, BFU2011â29653 and BFU2014â57735-R). The CBMSO receives an institutional grant from FundaciĂłn RamĂłn Areces.Peer Reviewe
A general theorem on angular-momentum changes due to potential vorticity mixing and on potential-energy changes due to buoyancy mixing
An initial zonally symmetric quasigeostrophic potential-vorticity (PV)
distribution q_i(y) is subjected to complete or partial mixing within some
finite zone |y| < L, where y is latitude. The change in M, the total absolute
angular momentum, between the initial and any later time is considered. For
standard quasigeostrophic shallow-water beta-channel dynamics it is proved
that, for any q_i(y) such that dq_i/dy > 0 throughout |y| < L, the change in M
is always negative. This theorem holds even when "mixing" is understood in the
most general possible sense. Arbitrary stirring or advective rearrangement is
included, combined to an arbitrary extent with spatially inhomogeneous
diffusion. The theorem holds whether or not the PV distribution is zonally
symmetric at the later time. The same theorem governs Boussinesq
potential-energy changes due to buoyancy mixing in the vertical. For the
standard quasigeostrophic beta-channel dynamics to be valid the Rossby
deformation length L_D >> \epsilon L where \epsilon is the Rossby number; when
L_D = \infty the theorem applies not only to the beta-channel, but also to a
single barotropic layer on the full sphere, as considered in the recent work of
Dunkerton and Scott on "PV staircases". It follows that the M-conserving PV
reconfigurations studied by those authors must involve processes describable as
PV unmixing, or anti-diffusion, in the sense of time-reversed diffusion.
Ordinary jet self-sharpening and jet-core acceleration do not, by contrast,
require unmixing, as is shown here by detailed analysis. Mixing in the jet
flanks suffices. The theorem extends to multiple layers and continuous
stratification. A corollary is a new nonlinear stability theorem for shear
flows.Comment: 14 pages, 4 figures; Final version, accepted by J. Atmos. Sci, in
pres
Driven dynamics and rotary echo of a qubit tunably coupled to a harmonic oscillator
We have investigated the driven dynamics of a superconducting flux qubit that
is tunably coupled to a microwave resonator. We find that the qubit experiences
an oscillating field mediated by off-resonant driving of the resonator, leading
to strong modifications of the qubit Rabi frequency. This opens an additional
noise channel, and we find that low-frequency noise in the coupling parameter
causes a reduction of the coherence time during driven evolution. The noise can
be mitigated with the rotary-echo pulse sequence, which, for driven systems, is
analogous to the Hahn-echo sequence
Development and Characterization of Nbân/Alâ0â Superconducting Multilayers for Particle Accelerators
Superconducting radio-frequency (SRF) resonator cavities provide extremely high quality factorsâ\u3eâ1010 at 1-2 GHz and 2 K in large linear accelerators of high-energy particles. The maximum accelerating field of SRF cavities is limited by penetration of vortices into the superconductor. Present state-of-the-art Nb cavities can withstand up to 50 MV/m accelerating gradients and magnetic fields of 200-240 mT which destroy the low-dissipative Meissner state. Achieving higher accelerating gradients requires superconductors with higher thermodynamic critical fields, of which Nb3Sn has emerged as a leading material for the next generation accelerators. To overcome the problem of low vortex penetration field in Nb3Sn, it has been proposed to coat Nb cavities with thin film Nb3Sn multilayers with dielectric interlayers. Here, we report the growth and multi-technique characterization of stoichiometric Nb3Sn/Al2O3 multilayers with good superconducting and RF properties. We developed an adsorption-controlled growth process by co-sputtering Nb and Sn at high temperatures with a high overpressure of Sn. The cross-sectional scanning electron transmission microscope images show no interdiffusion between Al2O3 and Nb3Sn. Low-field RF measurements suggest that our multilayers have quality factor comparable with cavity-grade Nb at 4.2 K. These results provide a materials platform for the development and optimization of high-performance SIS multilayers which could overcome the intrinsic limits of the Nb cavity technology
The Politics of Exhaustion and the Externalization of British Border Control. An Articulation of a Strategy Designed to Deter, Control and Exclude
In response to contemporary forms of human mobility, there has been a continued hardening of borders seeking to deter, control and exclude certain groups of people from entering nation states in Europe, North America and Australasia. Within this context, a disconcerting evolution of new and increasingly sophisticated forms of border control measures have emerged, which often play out within bilateral arrangements of âexternalisedâ or âoffshoreâ border controls. Drawing on extensive firstâhand field research among displaced people in Calais, Paris and Brussels in 2016â2019, this paper argues that the externalization of the British border to France is contingent upon a harmful strategy, which can be understood as the âpolitics of exhaustion.â This is a raft of (micro) practices and methods strategically aimed to deter, control and exclude certain groups of people on the move who have been profiled as âundesirable,â with a detrimental (un)intended impact on human lives
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