102 research outputs found
Few-body hydrodynamic interactions probed by optical trap pulling experiment
We study the hydrodynamic coupling of neighboring micro-beads placed in a
dual optical trap setup allowing us to precisely control the degree of coupling
and directly measure time-dependent trajectories of the entrained beads.
Average experimental trajectories of a probe bead entrained by the motion of a
neighboring scan bead are compared with theoretical computation, illustrating
the role of viscous coupling and setting timescales for probe bead relaxation.
The findings provide direct experimental corroborations of hydrodynamic
coupling at larger, micron spatial scales and millisecond timescales, of
relevance to hydrodynamic-assisted colloidal assembly as well as improving the
resolution of optical tweezers. We repeat the experiments for three bead
setups
Image Segmentation Using Frequency Locking of Coupled Oscillators
Synchronization of coupled oscillators is observed at multiple levels of
neural systems, and has been shown to play an important function in visual
perception. We propose a computing system based on locally coupled oscillator
networks for image segmentation. The system can serve as the preprocessing
front-end of an image processing pipeline where the common frequencies of
clusters of oscillators reflect the segmentation results. To demonstrate the
feasibility of our design, the system is simulated and tested on a human face
image dataset and its performance is compared with traditional intensity
threshold based algorithms. Our system shows both better performance and higher
noise tolerance than traditional methods.Comment: 7 pages, 14 figures, the 51th Design Automation Conference 2014, Work
in Progress Poster Sessio
Hydro-morphodynamics 2D modelling using a discontinuous Galerkin discretisation
The development of morphodynamic models to simulate sediment transport accurately is a challenging process that is becoming ever more important because of our increasing exploitation of the coastal zone, as well as sea-level rise and the potential increase in strength and frequency of storms due to a changing climate. Morphodynamic models are highly complex given the non-linear and coupled nature of the sediment transport problem. Here we implement a new depth-averaged coupled hydrodynamic and sediment transport model within the coastal ocean model Thetis, built using the code generating framework Firedrake which facilitates code flexibility and optimisation benefits. To the best of our knowledge, this represents the first full morphodynamic model including both bedload and suspended sediment transport which uses a discontinuous Galerkin based finite element discretisation. We implement new functionalities within Thetis extending its existing capacity to model scalar transport to modelling suspended sediment transport, incorporating within Thetis options to model bedload transport and bedlevel changes. We apply our model to problems with non-cohesive sediment and account for effects of gravity and helical flow by adding slope gradient terms and parametrising secondary currents. For validation purposes and in demonstrating model capability, we present results from test cases of a migrating trench and a meandering channel comparing against experimental data and the widely-used model Telemac-Mascaret
Hybridised multigrid preconditioners for a compatible finite element dynamical core
Compatible finite element discretisations for the atmospheric equations of
motion have recently attracted considerable interest. Semi-implicit
timestepping methods require the repeated solution of a large saddle-point
system of linear equations. Preconditioning this system is challenging since
the velocity mass matrix is non-diagonal, leading to a dense Schur complement.
Hybridisable discretisations overcome this issue: weakly enforcing continuity
of the velocity field with Lagrange multipliers leads to a sparse system of
equations, which has a similar structure to the pressure Schur complement in
traditional approaches. We describe how the hybridised sparse system can be
preconditioned with a non-nested two-level preconditioner. To solve the coarse
system, we use the multigrid pressure solver that is employed in the
approximate Schur complement method previously proposed by the some of the
authors. Our approach significantly reduces the number of solver iterations.
The method shows excellent performance and scales to large numbers of cores in
the Met Office next-generation climate- and weather prediction model LFRic.Comment: 24 pages, 13 figures, 5 tables; accepted for publication in Quarterly
Journal of the Royal Meteorological Societ
Multi-scale hydro-morphodynamic modelling using mesh movement methods
Abstract: Hydro-morphodynamic modelling is an important tool that can be used in the protection of coastal zones. The models can be required to resolve spatial scales ranging from sub-metre to hundreds of kilometres and are computationally expensive. In this work, we apply mesh movement methods to a depth-averaged hydro-morphodynamic model for the first time, in order to tackle both these issues. Mesh movement methods are particularly well-suited to coastal problems as they allow the mesh to move in response to evolving flow and morphology structures. This new capability is demonstrated using test cases that exhibit complex evolving bathymetries and have moving wet-dry interfaces. In order to be able to simulate sediment transport in wet-dry domains, a new conservative discretisation approach has been developed as part of this work, as well as a sediment slide mechanism. For all test cases, we demonstrate how mesh movement methods can be used to reduce discretisation error and computational cost. We also show that the optimum parameter choices in the mesh movement monitor functions are fairly predictable based upon the physical characteristics of the test case, facilitating the use of mesh movement methods on further problems
Blazars in the Fermi Era: The OVRO 40-m Telescope Monitoring Program
The Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope
provides an unprecedented opportunity to study gamma-ray blazars. To capitalize
on this opportunity, beginning in late 2007, about a year before the start of
LAT science operations, we began a large-scale, fast-cadence 15 GHz radio
monitoring program with the 40-m telescope at the Owens Valley Radio
Observatory (OVRO). This program began with the 1158 northern (declination>-20
deg) sources from the Candidate Gamma-ray Blazar Survey (CGRaBS) and now
encompasses over 1500 sources, each observed twice per week with a ~4 mJy
(minimum) and 3% (typical) uncertainty. Here, we describe this monitoring
program and our methods, and present radio light curves from the first two
years (2008 and 2009). As a first application, we combine these data with a
novel measure of light curve variability amplitude, the intrinsic modulation
index, through a likelihood analysis to examine the variability properties of
subpopulations of our sample. We demonstrate that, with high significance
(7-sigma), gamma-ray-loud blazars detected by the LAT during its first 11
months of operation vary with about a factor of two greater amplitude than do
the gamma-ray-quiet blazars in our sample. We also find a significant (3-sigma)
difference between variability amplitude in BL Lacertae objects and
flat-spectrum radio quasars (FSRQs), with the former exhibiting larger
variability amplitudes. Finally, low-redshift (z<1) FSRQs are found to vary
more strongly than high-redshift FSRQs, with 3-sigma significance. These
findings represent an important step toward understanding why some blazars emit
gamma-rays while others, with apparently similar properties, remain silent.Comment: 23 pages, 24 figures. Submitted to ApJ
A Phase I trial of talazoparib in patients with advanced hematologic malignancies
Aim: The objective of this study was to establish the maximum tolerated dose (MTD), safety, pharmacokinetics, and anti-leukemic activity of talazoparib.
Patients & methods: This Phase I, two-cohort, dose-escalation trial evaluated talazoparib monotherapy in advanced hematologic malignancies (cohort 1: acute myeloid leukemia/myelodysplastic syndrome; cohort 2: chronic lymphocytic leukemia/mantle cell lymphoma).
Results: Thirty-three (cohort 1: n = 25; cohort 2: n = 8) patients received talazoparib (0.1-2.0 mg once daily). The MTD was exceeded at 2.0 mg/day in cohort 1 and at 0.9 mg/day in cohort 2. Grade ≥3 adverse events were primarily hematologic. Eighteen (54.5%) patients reported stable disease.
Conclusion: Talazoparib is relatively well tolerated in hematologic malignancies, with a similar MTD as in solid tumors, and shows preliminary anti leukemic activity.Clinical trial registration: NCT01399840 (ClinicalTrials.gov).
Keywords: BRCA1/2 mutations; DNA damage response; hematologic malignancy; poly(ADP-ribose) polymerase inhibition; talazoparib
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