1,155 research outputs found
Three-dimensional imaging of direct-written photonic structures
Third harmonic generation microscopy has been used to analyze the morphology
of photonic structures created using the femtosecond laser direct-write
technique. Three dimensional waveguide arrays and waveguide-Bragg gratings
written in fused-silica and doped phosphate glass were investigated. A
sensorless adaptive optical system was used to correct the optical aberrations
occurring in the sample and microscope system, which had a lateral resolution
of less than 500 nm. This non-destructive testing method creates volume
reconstructions of photonic devices and reveals details invisible to other
linear microscopy and index profilometry techniques.Comment: 8 pages, 3 color figures, 2 hyper-linked animation
Uncertainty in multitask learning: joint representations for probabilistic MR-only radiotherapy planning
Multi-task neural network architectures provide a mechanism that jointly
integrates information from distinct sources. It is ideal in the context of
MR-only radiotherapy planning as it can jointly regress a synthetic CT (synCT)
scan and segment organs-at-risk (OAR) from MRI. We propose a probabilistic
multi-task network that estimates: 1) intrinsic uncertainty through a
heteroscedastic noise model for spatially-adaptive task loss weighting and 2)
parameter uncertainty through approximate Bayesian inference. This allows
sampling of multiple segmentations and synCTs that share their network
representation. We test our model on prostate cancer scans and show that it
produces more accurate and consistent synCTs with a better estimation in the
variance of the errors, state of the art results in OAR segmentation and a
methodology for quality assurance in radiotherapy treatment planning.Comment: Early-accept at MICCAI 2018, 8 pages, 4 figure
Beyond Ethics: Considerations for Centering Equity-Minded Data Science
In this paper, we utilize duoethnography - a research method in which practitioners discursively interrogate the relationships between culture, context, and the mechanisms which shape individual autobiographical experiences - to explore what may be beyond ethics in the context of data science. Although ethical frameworks have the ability to reflect cultural priorities, a singular view of ethics, as we explore, often fails to speak to the multiple and diverse priorities held both within and across institutional spaces. To that end, this paper explores multiple perspectives, epistemologies, and worldviews that can collectively push researchers towards considerations of a data science education that is equity-minded both in concept and practice. Through a set of dialogues which examine our positionalities, journeys, ethics, local cultures, and accountabilities, this paper explores the contextual realities rooted in the authors’ educational settings. These conversations focus on the humanity of our students, the communities from which we come from and serve, as well as the unintentional harms and possibilities associated with the development of data science programs across institutional types. We take a set of five core questions to examine how we made, and continue to make, sense of our diverse cultural perspectives on data science education and equity with/in relation to others’ realities. Broadly, this paper seeks to offer reflections on the related but differing functions of ethics and equity in data science education
Mathematical retroreflectors
Retroreflectors are optical devices that reverse the direction of incident
beams of light. Here we present a collection of billiard type retroreflectors
consisting of four objects; three of them are asymptotically perfect
retroreflectors, and the fourth one is a retroreflector which is very close to
perfect. Three objects of the collection have recently been discovered and
published or submitted for publication. The fourth object - notched angle - is
a new one; a proof of its retroreflectivity is given.Comment: 32 pages, 19 figure
Validation of Immersed Boundary Simulations of Heart Valve Hemodynamics against In Vitro 4D Flow MRI Data
The immersed boundary (IB) method is a mathematical framework for
fluid-structure interaction problems (FSI) that was originally developed to
simulate flows around heart valves. Validation of FSI simulations around heart
valves against experimental data is challenging, however, due to the difficulty
of performing robust and effective simulations, the complications of modeling a
specific physical experiment, and the need to acquire experimental data that is
directly comparable to simulation data. In this work, we performed physical
experiments of flow through a pulmonary valve in an in vitro pulse duplicator,
and measured the corresponding velocity field using 4D flow MRI (4-dimensional
flow magnetic resonance imaging). We constructed a computer model of this
pulmonary artery setup, including modeling valve geometry and material
properties via a technique called design-based elasticity, and simulated flow
through it with the IB method. The simulated flow fields showed excellent
qualitative agreement with experiments, excellent agreement on integral
metrics, and reasonable relative error in the entire flow domain and on slices
of interest. These results validate our design-based valve model construction,
the IB solvers used and the immersed boundary method for flows around heart
valves
Contractile force is enhanced in Aortas from pendrin null mice due to stimulation of angiotensin II-dependent signaling.
Pendrin is a Cl-/HCO3- exchanger expressed in the apical regions of renal intercalated cells. Following pendrin gene ablation, blood pressure falls, in part, from reduced renal NaCl absorption. We asked if pendrin is expressed in vascular tissue and if the lower blood pressure observed in pendrin null mice is accompanied by reduced vascular reactivity. Thus, the contractile responses to KCl and phenylephrine (PE) were examined in isometrically mounted thoracic aortas from wild-type and pendrin null mice. Although pendrin expression was not detected in the aorta, pendrin gene ablation changed contractile protein abundance and increased the maximal contractile response to PE when normalized to cross sectional area (CSA). However, the contractile sensitivity to this agent was unchanged. The increase in contractile force/cross sectional area observed in pendrin null mice was due to reduced cross sectional area of the aorta and not from increased contractile force per vessel. The pendrin-dependent increase in maximal contractile response was endothelium- and nitric oxide-independent and did not occur from changes in Ca2+ sensitivity or chronic changes in catecholamine production. However, application of 100 nM angiotensin II increased force/CSA more in aortas from pendrin null than from wild type mice. Moreover, angiotensin type 1 receptor inhibitor (candesartan) treatment in vivo eliminated the pendrin-dependent changes contractile protein abundance and changes in the contractile force/cross sectional area in response to PE. In conclusion, pendrin gene ablation increases aorta contractile force per cross sectional area in response to angiotensin II and PE due to stimulation of angiotensin type 1 receptor-dependent signaling. The angiotensin type 1 receptor-dependent increase in vascular reactivity may mitigate the fall in blood pressure observed with pendrin gene ablation
Nanoparticle transport in epithelial cells: pathway switching through bioconjugation
The understanding and control of nanoparticle transport into and through cellular compartments is central to biomedical applications of nanotechnology. Here, it is shown that the transport pathway of 50 nm polystyrene nanoparticles decorated with vitamin B12 in epithelial cells is different compared to both soluble B12 ligand and unmodified nanoparticles, and this is not attributable to B12 recognition alone. Importantly, the study indicates that vitamin B12-conjugated nanoparticles circumnavigate the lysosomal compartment, the destination of soluble vitamin B12 ligand. Whereas cellular trafficking of soluble B12 is confirmed to occur via the clathrin-mediated pathway, transport of B12-conjugated nanoparticles appears to predominantly take place by a route that is perturbed by caveolae-specific inhibitors. This data suggests that, following its conjugation to nanoparticles, in addition to dramatically increasing the cellular uptake of nanoparticles, the normal cell trafficking of B12 is switched to an alternative pathway, omitting the lysosomal stage: a result with important implications for oral delivery of nanoparticulate diagnostics and therapeutics
The evolution of the premaxillary protrusion system in some teleostean fish groups
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74874/1/j.1469-7998.1981.tb01487.x.pd
Integrated photonic building blocks for next-generation astronomical instrumentation I: the multimode waveguide
We report on the fabrication and characterization of composite multimode
waveguide structures that consist of a stack of single-mode waveguides
fabricated by ultrafast laser inscription. We explore 2 types of composite
structures; those that consist of overlapping single-mode waveguides which
offer the maximum effective index contrast and non overlapped structures which
support multiple modes via strong evanescent coupling. We demonstrate that both
types of waveguides have negligible propagation losses (to within experimental
uncertainty) for light injected with focal ratios >8, which corresponds to the
cutoff of the waveguides. We also show that right below cutoff, there is a
narrow region where the injected focal ratio is preserved (to within
experimental uncertainty) at the output. Finally, we outline the major
application of these highly efficient waveguides; in a device that is used to
reformat the light in the focal plane of a telescope to a slit, in order to
feed a diffraction-limited spectrograph.Comment: 15 pages, 11 figures, accepted to Optics Expres
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