2,548 research outputs found
Design and simulation of a testing fixture for planar magnetic levitation system control using switched reluctance actuator
Author name used in this publication: Norbert C. CheungRefereed conference paper2008-2009 > Academic research: refereed > Refereed conference paperVersion of RecordPublishe
Integral sliding mode control with integral switching gain for magnetic levitation apparatus
Author name used in this publication: Norbert C. CheungRefereed conference paper2008-2009 > Academic research: refereed > Refereed conference paperVersion of RecordPublishe
Nonlinear effects in superconducting thin film microwave resonators
We discuss how reactive and dissipative non-linearities affect the intrinsic
response of superconducting thin-film resonators. We explain how most, if not
all, of the complex phenomena commonly seen can be described by a model in
which the underlying resonance is a single-pole Lorentzian, but whose centre
frequency and quality factor change as external parameters, such as readout
power and frequency, are varied. What is seen during a vector-network-analyser
measurement is series of samples taken from an ideal Lorentzian that is
shifting and spreading as the readout frequency is changed. According to this
model, it is perfectly proper to refer to, and measure, the resonant frequency
and quality factor of the underlying resonance, even though the swept-frequency
curves appear highly distorted and hysteretic. In those cases where the
resonance curve is highly distorted, the specific shape of the trajectory in
the Argand plane gives valuable insights into the second-order physical
processes present. We discuss the formulation and consequences of this approach
in the case of non-linear kinetic inductance, two-level-system loss,
quasiparticle generation, and a generic model based on a power-law form. The
generic model captures the key features of specific dissipative
non-linearities, but additionally leads to insights into how general
dissipative processes create characteristic forms in the Argand plane. We
provide detailed formulations in each case, and indicate how they lead to the
wide variety of phenomena commonly seen in experimental data. We also explain
how the properties of the underlying resonance can be extracted from this data.
Overall, our paper provides a self-contained compendium of behaviour that will
help practitioners interpret and determine important parameters from distorted
swept-frequency measurements
Recommended from our members
Demonstration of Machine Learning-Based Model-Independent Stabilization of Source Properties in Synchrotron Light Sources.
Synchrotron light sources, arguably among the most powerful tools of modern scientific discovery, are presently undergoing a major transformation to provide orders of magnitude higher brightness and transverse coherence enabling the most demanding experiments. In these experiments, overall source stability will soon be limited by achievable levels of electron beam size stability, presently on the order of several microns, which is still 1-2 orders of magnitude larger than already demonstrated stability of source position and current. Until now source size stabilization has been achieved through corrections based on a combination of static predetermined physics models and lengthy calibration measurements, periodically repeated to counteract drift in the accelerator and instrumentation. We now demonstrate for the first time how the application of machine learning allows for a physics- and model-independent stabilization of source size relying only on previously existing instrumentation. Such feed-forward correction based on a neural network that can be continuously online retrained achieves source size stability as low as 0.2 μm (0.4%) rms, which results in overall source stability approaching the subpercent noise floor of the most sensitive experiments
Initial growth of the Northern Lhasaplano, Tibetan Plateau in the early Late Cretaceous (ca. 92 Ma)
Constraining the growth of the Tibetan Plateau in time and space is critical for testing geodynamic models and climatic changes at the regional and global scale. The Lhasa block is a key region for unraveling the early history of the Tibetan Plateau. Distinct from the underlying shallow-marine limestones, the Jingzhushan and Daxiong formations consist of conglomerate and sandstone deposited in alluvial-fan and braided-river systems. Both units were deposited at ca. 92 Ma, as constrained by interbedded tuff layers, detrital zircons, and micropaleontological data. Provenance and paleocurrent analyses indicate that both units were derived from the same elevated source area located in the central-northern Lhasa block. These two parallel belts of coeval conglomerates record a major change in paleogeography of the source region from a shallow seaway to a continental highland, implying initial topographic growth of an area over 160,000 km2, named here the Northern Lhasaplano. The early Late Cretaceous topographic growth of the Northern Lhasaplano was associated with the demise of Tethyan seaways, thrust-belt development, and crustal thickening. The same paleogeographic and paleotectonic changes were recorded earlier in the Northern Lhasaplano than in the Southern Lhasaplano, indicating progressive topographic growth from north to south across the Bangong-Nujiang suture and Lhasa block during the Cretaceous. Similar to the Central Andean Plateau, the Northern Lhasaplano developed by plate convergence above the oceanic Neo-Tethyan subduction zone before the onset of the India-Asia collision
Topological semimetal in a fermionic optical lattice
Optical lattices play a versatile role in advancing our understanding of
correlated quantum matter. The recent implementation of orbital degrees of
freedom in chequerboard and hexagonal optical lattices opens up a new thrust
towards discovering novel quantum states of matter, which have no prior analogs
in solid state electronic materials. Here, we demonstrate that an exotic
topological semimetal emerges as a parity-protected gapless state in the
orbital bands of a two-dimensional fermionic optical lattice. The new quantum
state is characterized by a parabolic band-degeneracy point with Berry flux
, in sharp contrast to the flux of Dirac points as in graphene. We
prove that the appearance of this topological liquid is universal for all
lattices with D point group symmetry as long as orbitals with opposite
parities hybridize strongly with each other and the band degeneracy is
protected by odd parity. Turning on inter-particle repulsive interactions, the
system undergoes a phase transition to a topological insulator whose
experimental signature includes chiral gapless domain-wall modes, reminiscent
of quantum Hall edge states.Comment: 6 pages, 3 figures and Supplementary Informatio
Glucose lowering effect of transgenic human insulin-like growth factor-I from rice: in vitro and in vivo studies
<p>Abstract</p> <p>Background</p> <p>Human insulin-like growth factor-I (hIGF-I) is a growth factor which is highly resemble to insulin. It is essential for cell proliferation and has been proposed for treatment of various endocrine-associated diseases including growth hormone insensitivity syndrome and diabetes mellitus. In the present study, an efficient plant expression system was developed to produce biologically active recombinant hIGF-I (rhIGF-I) in transgenic rice grains.</p> <p>Results</p> <p>The plant-codon-optimized hIGF-I was introduced into rice via <it>Agrobacterium</it>-mediated transformation. To enhance the stability and yield of rhIGF-I, the endoplasmic reticulum-retention signal and glutelin signal peptide were used to deliver rhIGF-I to endoplasmic reticulum for stable accumulation. We found that only glutelin signal peptide could lead to successful expression of hIGF-I and one gram of hIGF-I rice grain possessed the maximum activity level equivalent to 3.2 micro molar of commercial rhIGF-I. <it>In vitro </it>functional analysis showed that the rice-derived rhIGF-I was effective in inducing membrane ruffling and glucose uptake on rat skeletal muscle cells. Oral meal test with rice-containing rhIGF-I acutely reduced blood glucose levels in streptozotocin-induced and Zucker diabetic rats, whereas it had no effect in normal rats.</p> <p>Conclusion</p> <p>Our findings provided an alternative expression system to produce large quantities of biologically active rhIGF-I. The provision of large quantity of recombinant proteins will promote further research on the therapeutic potential of rhIGF-I.</p
Topological orbital ladders
We unveil a topological phase of interacting fermions on a two-leg ladder of
unequal parity orbitals, derived from the experimentally realized double-well
lattices by dimension reduction. topological invariant originates simply
from the staggered phases of -orbital quantum tunneling, requiring none of
the previously known mechanisms such as spin-orbit coupling or artificial gauge
field. Another unique feature is that upon crossing over to two dimensions with
coupled ladders, the edge modes from each ladder form a parity-protected flat
band at zero energy, opening the route to strongly correlated states controlled
by interactions. Experimental signatures are found in density correlations and
phase transitions to trivial band and Mott insulators.Comment: 12 pages, 5 figures, Revised title, abstract, and the discussion on
Majorana numbe
ARPES: A probe of electronic correlations
Angle-resolved photoemission spectroscopy (ARPES) is one of the most direct
methods of studying the electronic structure of solids. By measuring the
kinetic energy and angular distribution of the electrons photoemitted from a
sample illuminated with sufficiently high-energy radiation, one can gain
information on both the energy and momentum of the electrons propagating inside
a material. This is of vital importance in elucidating the connection between
electronic, magnetic, and chemical structure of solids, in particular for those
complex systems which cannot be appropriately described within the
independent-particle picture. Among the various classes of complex systems, of
great interest are the transition metal oxides, which have been at the center
stage in condensed matter physics for the last four decades. Following a
general introduction to the topic, we will lay the theoretical basis needed to
understand the pivotal role of ARPES in the study of such systems. After a
brief overview on the state-of-the-art capabilities of the technique, we will
review some of the most interesting and relevant case studies of the novel
physics revealed by ARPES in 3d-, 4d- and 5d-based oxides.Comment: Chapter to appear in "Strongly Correlated Systems: Experimental
Techniques", edited by A. Avella and F. Mancini, Springer Series in
Solid-State Sciences (2013). A high-resolution version can be found at:
http://www.phas.ubc.ca/~quantmat/ARPES/PUBLICATIONS/Reviews/ARPES_Springer.pdf.
arXiv admin note: text overlap with arXiv:cond-mat/0307085,
arXiv:cond-mat/020850
- …