37 research outputs found
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
A Matrix Model for Baryons and Nuclear Forces
We propose a new matrix model describing multi-baryon systems. We derive the
action from open string theory on the wrapped baryon vertex D-branes embedded
in the D4-D8 model of large N holographic QCD. The positions of k baryons are
unified into k x k matrices, with spin/isospin of the baryons encoded in a set
of k-vectors. Holographic baryons are known to be very small in the large 't
Hooft coupling limit, and our model offers a better systematic approach to
dynamics of such baryons at short distances. We compute energetics and spectra
(k=1), and also short-distance nuclear force (k=2). In particular, we obtain a
new size of the holographic baryon and find a precise form of the repulsive
core of nucleons. This matrix model complements the instanton soliton picture
of holographic baryons, whose small size turned out to be well below the
natural length scale of the approximation involved there. Our results show
that, nevertheless, the basic properties of holographic baryons obtained there
are robust under stringy corrections within a few percents.Comment: 30 pages. v3: more comments added, published versio
Skyrmions, Skyrme stars and black holes with Skyrme hair in five spacetime dimension
We consider a class of generalizations of the Skyrme model to five spacetime dimensions (d = 5), which is de fined in terms of an O (5) sigma model. A special ansatz for the Skyrme field allows angular momentum to be present and equations of motion with a radial dependence only. Using it, we obtain: 1) everywhere regular solutions describing localised energy lumps (Skyrmions); 2) Self-gravitating, asymptotically flat, everywhere non-singular solitonic solutions (Skyrme stars), upon minimally coupling the model to Einstein's gravity; 3) both static and spinning black holes with Skyrme hair, the latter with rotation in two orthogonal planes, with both angular momenta of equal magnitude. In the absence of gravity we present an analytic solution that satisfies a BPS-type bound and explore numerically some of the non-BPS solutions. In the presence of gravity, we contrast the solutions to this model with solutions to a complex scalar field model, namely boson stars and black holes with synchronised hair. Remarkably, even though the two models present key differences, and in particular the Skyrme model allows static hairy black holes, when introducing rotation, the synchronisation condition becomes mandatory, providing further evidence for its generality in obtaining rotating hairy black holes
Baryonic Popcorn
In the large N limit cold dense nuclear matter must be in a lattice phase.
This applies also to holographic models of hadron physics. In a class of such
models, like the generalized Sakai-Sugimoto model, baryons take the form of
instantons of the effective flavor gauge theory that resides on probe flavor
branes. In this paper we study the phase structure of baryonic crystals by
analyzing discrete periodic configurations of such instantons. We find that
instanton configurations exhibit a series of "popcorn" transitions upon
increasing the density. Through these transitions normal (3D) lattices expand
into the transverse dimension, eventually becoming a higher dimensional (4D)
multi-layer lattice at large densities.
We consider 3D lattices of zero size instantons as well as 1D periodic chains
of finite size instantons, which serve as toy models of the full holographic
systems. In particular, for the finite-size case we determine solutions of the
corresponding ADHM equations for both a straight chain and for a 2D zigzag
configuration where instantons pop up into the holographic dimension. At low
density the system takes the form of an "abelian anti-ferromagnetic" straight
periodic chain. Above a critical density there is a second order phase
transition into a zigzag structure. An even higher density yields a rich phase
space characterized by the formation of multi-layer zigzag structures. The
finite size of the lattices in the transverse dimension is a signal of an
emerging Fermi sea of quarks. We thus propose that the popcorn transitions
indicate the onset of the "quarkyonic" phase of the cold dense nuclear matter.Comment: v3, 80 pages, 18 figures, footnotes 5 and 7 added, version to appear
in the JHE
The effect of type of femoral component fixation on mortality and morbidity after hip hemiarthroplasty:A systematic review and meta-analysis
Background: Hip hemiarthroplasty is a well-established treatment of displaced femoral neck fracture, although debate exists over whether cemented or uncemented fixation is superior. Uncemented prostheses have typically been used in younger, healthier patients and cemented prostheses in older patients with less-stable bone. Also, earlier research has suggested that bone cement has cytotoxic effects and may trigger cardiovascular and respiratory adverse events. Questions/Purposes: The aim of this systematic review and meta-analysis was to compare morbidity and mortality rates after cemented and uncemented hemiarthroplasty for the treatment of displaced femoral neck fractures in elderly patients. Methods: Using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, we searched seven medical databases for randomized clinical trials and observational studies. We compared cemented and uncemented hemiarthroplasty using the Harris Hip Score (HHS), as well as measures of postoperative pain, mortality, and complications. Data were extracted and pooled as risk ratios or standardized mean difference with their corresponding 95% confidence intervals in a meta-analysis model. Results: The meta-analysis included 34 studies (12 randomized trials and 22 observational studies), with a total of 42,411 patients. In the pooled estimate, cemented hemiarthroplasty was associated with less risk of postoperative pain than uncemented hemiarthroplasty. There were no significant differences between groups regarding HHS or rates of postoperative mortality, pulmonary embolism, cardiac arrest, myocardial infarction, acute cardiac arrhythmia, or deep venous thrombosis. Conclusions: While we found that cemented hemiarthroplasty results in less postoperative pain than uncemented hemiarthroplasty in older patients with femoral neck fracture, the lack of significant differences in functional hip scores, mortality, and complications was surprising. Further high-level research is needed