1,204 research outputs found
Miniaturised all-optical ultrasound probe for thrombus imaging
All-Optical Ultrasound (OpUS) has emerged as an imaging paradigm well-suited for minimally invasive procedures. In particular, OpUS has demonstrated potential in endovascular imaging due to its high degree of miniaturization and mechanical flexibility, high imaging resolution and immunity to electromagnetic interference. Here, we present the first human thrombus imaging using an OpUS device, which was performed on an extracted clot. The results demonstrate the feasibility of using OpUS for thrombus imaging, with the ultimate goal of guiding minimally invasive endovascular clot retrieval procedures
The Square-Lattice Heisenberg Antiferromagnet at Very Large Correlation Lengths
The correlation length of the square-lattice spin-1/2 Heisenberg
antiferromagnet is studied in the low-temperature (asymptotic-scaling) regime.
Our novel approach combines a very efficient loop cluster algorithm --
operating directly in the Euclidean time continuum -- with finite-size scaling.
This enables us to probe correlation lengths up to
lattice spacings -- more than three orders of magnitude larger than any
previous study. We resolve a conundrum concerning the applicability of
asymptotic-scaling formulae to experimentally- and numerically-determined
correlation lengths, and arrive at a very precise determination of the
low-energy observables. Our results have direct implications for the
zero-temperature behavior of spin-1/2 ladders.Comment: 12 pages, RevTeX, plus two Postscript figures. Some minor
modifications for final submission to Physical Review Letters. (accepted by
PRL
Correlation Lengths in Quantum Spin Ladders
Analytic expressions for the correlation length temperature dependences are
given for antiferromagnetic spin-1/2 Heisenberg ladders using a finite-size
non-linear sigma-model approach. These calculations rely on identifying three
successive crossover regimes as a function of temperature. In each of these
regimes, precise and controlled approximations are formulated. The analytical
results are found to be in excellent agreement with Monte Carlo simulations for
the Heisenberg Hamiltonian.Comment: 5 pages LaTeX using RevTeX, 3 encapsulated postscript figure
Fluctuating Elastic Rings: Statics and Dynamics
We study the effects of thermal fluctuations on elastic rings. Analytical
expressions are derived for correlation functions of Euler angles, mean square
distance between points on the ring contour, radius of gyration, and
probability distribution of writhe fluctuations. Since fluctuation amplitudes
diverge in the limit of vanishing twist rigidity, twist elasticity is essential
for the description of fluctuating rings. We find a crossover from a small
scale regime in which the filament behaves as a straight rod, to a large scale
regime in which spontaneous curvature is important and twist rigidity affects
the spatial configurations of the ring. The fluctuation-dissipation relation
between correlation functions of Euler angles and response functions, is used
to study the deformation of the ring by external forces. The effects of inertia
and dissipation on the relaxation of temporal correlations of writhe
fluctuations, are analyzed using Langevin dynamics.Comment: 43 pages, 9 Figure
Quantum magnetism in the stripe phase: bond- versus site order
It is argued that the spin dynamics in the charge-ordered stripe phase might
be revealing with regards to the nature of the anomalous spin dynamics in
cuprate superconductors. Specifically, if the stripes are bond ordered much of
the spin fluctuation will originate in the spin sector itself, while site
ordered stripes require the charge sector as the driving force for the strong
quantum spin fluctuations.Comment: 4 pages, 3 figures, LaTe
Spin orthogonality catastrophe in two-dimensional antiferromagnets and superconductors
We compute the spectral function of a spin S hole injected into a
two-dimensional antiferromagnet or superconductor in the vicinity of a magnetic
quantum critical point. We show that, near van Hove singularities, the problem
maps onto that of a static vacancy carrying excess spin S. The hole creation
operator is characterized by a new boundary anomalous dimension and a vanishing
quasiparticle residue at the critical point. We discuss possible relevance to
photoemission spectra of cuprate superconductors near the anti-nodal points.Comment: (v1) 4 pages, 2 figures; field theory afficionados - see also
cond-mat/0011233; (v2) added figure of Monte Carlo data; (v3) corrected typo
The treatment of segmental tibial fractures: does patient preference differ from surgeon choice?
INTRODUCTION: Segmental tibial fractures are complex injuries with a prolonged recovery time. Current definitive treatment options include intramedullary fixation or a circular external fixator. However, there is uncertainty as to which surgical option is preferable and there are no sufficiently rigorous multi-centre trials that have answered this question. The objective of this study was to determine whether patient and surgeon opinion was permissive for a randomised controlled trial (RCT) comparing intramedullary nailing to the application of a circular external fixator. MATERIALS AND METHODS: A convenience questionnaire survey of attending surgeons was conducted during the United Kingdom's Orthopaedic Trauma Society annual meeting 2017 to determine the treatment modalities used for a segmental tibial fracture (n=63). Patient opinion was obtained from clinical patients who had been treated for a segmental tibial fracture as part of a patient and public involvement focus group with questions covering the domains of surgical preference, treatment expectations, outcome, the consent process and follow-up regime (n=5). RESULTS: Based on the surgeon survey, 39% routinely use circular frame fixation following segmental tibial fracture compared to 61% who use nail fixation. Nail fixation was reported as the treatment of choice for a closed injury in a healthy patient in 81% of surgeons, and by 86% for a patient with a closed fracture who was obese. Twenty-one percent reported that they would use a nail for an open segmental tibia fracture in diabetics who smoked, whilst 57% would opt for a nail for a closed injury with compartment syndrome, and only 27% would use a nail for an open segmental injury in a young fit sports person. The patient and public preference exercise identified that sleep, early functional outcomes and psychosocial measures of outcomes are important. CONCLUSION: We concluded that a RCT comparing definitive fixation with an intramedullary nail and a circular external fixator is justified as there remains uncertainty on the optimal surgical management for segmental tibial fractures. Furthermore, psychosocial factors and early post-operative outcomes should be reported as core outcome measures as part of such a trial
Ultrasensitive plano-concave optical microresonators for ultrasound sensing
Highly sensitive broadband ultrasound detectors are needed to expand the capabilities of biomedical ultrasound, photoacoustic imaging and industrial ultrasonic non-destructive testing techniques. Here, a generic optical ultrasound sensing concept based on a novel plano-concave polymer microresonator is described. This achieves strong optical confinement (Q-factors > 105) resulting in very high sensitivity with excellent broadband acoustic frequency response and wide directivity. The concept is highly scalable in terms of bandwidth and sensitivity. To illustrate this, a family of microresonator sensors with broadband acoustic responses up to 40 MHz and noise-equivalent pressures as low as 1.6 mPa per √Hz have been fabricated and comprehensively characterized in terms of their acoustic performance. In addition, their practical application to high-resolution photoacoustic and ultrasound imaging is demonstrated. The favourable acoustic performance and design flexibility of the technology offers new opportunities to advance biomedical and industrial ultrasound-based techniques
Single hole dynamics in the t-J model on a square lattice
We present quantum Monte Carlo (QMC) simulations for a single hole in a t-J
model from J=0.4t to J=4t on square lattices with up to 24 x 24 sites. The
lower edge of the spectrum is directly extracted from the imaginary time
Green's function. In agreement with earlier calculations, we find flat bands
around , and the minimum of the dispersion at
. For small J both self-consistent Born approximation and
series expansions give a bandwidth for the lower edge of the spectrum in
agreement with the simulations, whereas for J/t > 1, only series expansions
agree quantitatively with our QMC results. This band corresponds to a coherent
quasiparticle. This is shown by a finite size scaling of the quasiparticle
weight that leads to a finite result in the thermodynamic limit for
the considered values of . The spectral function is
obtained from the imaginary time Green's function via the maximum entropy
method. Resonances above the lowest edge of the spectrum are identified, whose
J-dependence is quantitatively described by string excitations up to J/t=2
- …