9 research outputs found
Improved resolution in fiber bundle inline holographic microscopy using multiple illumination sources
Recent work has shown that high-quality inline holographic microscopy images can be captured through fiber imaging bundles. Speckle patterns arising from modal interference within the bundle cores can be minimized by use of a partially-coherent optical source such as an LED delivered via a multimode fiber. This allows numerical refocusing of holograms from samples at working distances of up to approximately 1âmm from the fiber bundle before the finite coherence begins to degrade the lateral resolution. However, at short working distances the lateral resolution is limited not by coherence, but by sampling effects due to core-to-core spacing in the bundle. In this article we demonstrate that multiple shifted holograms can be combined to improve the resolution by a factor of two. The shifted holograms can be rapidly acquired by sequentially firing LEDs, which are each coupled to their own, mutually offset, illumination fiber. Following a one-time calibration, resolution-enhanced images are created in real-time at an equivalent net frame rate of up to 7.5âHz. The resolution improvement is demonstrated quantitatively using a resolution target and qualitatively using mounted biological slides. At longer working distances, beyond 0.6âmm, the improvement is reduced as resolution becomes limited by the source spatial and temporal coherence
Optical Polarimetry of the May 2022 Lunar Eclipse
The sunlight reflected from the Moon during a total lunar eclipse has been
transmitted through the Earth's atmosphere on the way to the Moon. The
combination of multiple scattering and inhomogeneous atmospheric
characteristics during that transmission can potentially polarize that light. A
similar (although much smaller) effect should also be observable from the
atmosphere of a transiting exoplanet. We present the results of polarization
observations during the first 15 minutes of totality of the lunar eclipse of
2022 May 16. We find degrees of polarization of 2.1 +/- 0.4 per cent in B, 1.2
+/- 0.3 per cent in V, 0.5 +/- 0.2 per cent in R and 0.2 +/- 0.2 per cent in I.
Our polarization values lie in the middle of the range of those reported for
previous eclipses, providing further evidence that the induced polarization can
change from event to event. We found no significant polarization difference
(<0.02 per cent) between a region of dark Mare and nearby bright uplands or
between the lunar limb and regions closer to the disk centre due to the
different angle of incidence. This further strengthens the interpretation of
the polarization's origin being due to scattering in the Earth's atmosphere
rather than by the lunar regolith.Comment: Accepted for publication in MNRA
Improved depth range and resolution of inline holographic microscopy through fiber imaging bundles
Inline holographic microscopy has recently been demonstrated through fiber imaging bundles, opening up the possibility of ultra-miniaturized microscopy probes. In order to minimize artefacts arising due to the multimode behaviour of the fiber bundle cores, a partially coherent light source was used: an LED coupled into a multimode fiber. However, partial coherence limits the maximum working distance between the bundle and the sample before the resolution begins to degrade. The resolution is also limited by the finite core spacing in the fiber bundle, leading to under-sampling of the finer details of the hologram. Here, we demonstrate and evaluate several techniques for improving the resolution and working range, including tailoring the source coherence and using multiple sources, demonstrating that we can achieve at least a two-fold improvement in performance
Optical Polarimetry of the May 2022 Lunar Eclipse
The sunlight reflected from the Moon during a total lunar eclipse has been
transmitted through the Earth's atmosphere on the way to the Moon. The
combination of multiple scattering and inhomogeneous atmospheric
characteristics during that transmission can potentially polarize that light. A
similar (although much smaller) effect should also be observable from the
atmosphere of a transiting exoplanet. We present the results of polarization
observations during the first 15 minutes of totality of the lunar eclipse of
2022 May 16. We find degrees of polarization of 2.1 +/- 0.4 per cent in B, 1.2
+/- 0.3 per cent in V, 0.5 +/- 0.2 per cent in R and 0.2 +/- 0.2 per cent in I.
Our polarization values lie in the middle of the range of those reported for
previous eclipses, providing further evidence that the induced polarization can
change from event to event. We found no significant polarization difference
(<0.02 per cent) between a region of dark Mare and nearby bright uplands or
between the lunar limb and regions closer to the disk centre due to the
different angle of incidence. This further strengthens the interpretation of
the polarization's origin being due to scattering in the Earth's atmosphere
rather than by the lunar regolith.Comment: Accepted for publication in MNRA
Refining the prediction for OJ 287 next impact flare arrival epoch
The bright blazar OJ~287 routinely parades high brightness bremsstrahlung
flares which are explained as being a result of a secondary supermassive black
hole (SMBH) impacting the accretion disk of a primary SMBH in a binary system.
We begin by showing that these flares occur at times predicted by a simple
analytical formula, based on the Kepler equation, which explains flares since
1888. The next impact flare, namely the flare number 26, is rather peculiar as
it breaks the typical pattern of two impact flares per 12 year cycle. This will
be the third bremsstrahlung flare of the current cycle that follows the already
observed 2015 and 2019 impact flares from OJ~287. Unfortunately, astrophysical
considerations make it difficult to predict the exact arrival epoch of the
flare number 26. In the second part of the paper, we describe our recent OJ~287
observations. They show that the pre-flare light curve of flare number 22,
observed in 2005, exhibits similar activity as the pre-flare light curve in
2022, preceding the expected flare number 26 in our model. We argue that the
pre-flare activity most likely arises in the primary jet whose activity is
modulated by the transit of the secondary SMBH through the accretion disk of
the primary. Observing the next impact flare of OJ~287 in October 2022 will
substantiate the theory of disk impacts in binary black hole systems.Comment: 16 pages, 2 figure
Demonstration of real-time resolution improvement in fiber bundle inline holographic microscopy using multiple illumination sources
The video demonstrates that resolution enhancement in fiber bundle inline holographic microscopy can be achieved during live imaging. The video shows a Python-based graphical user-interface which displays processed and refocusing holograms as they are streamed from the camera. A High Resolution USAF imaging target was imaged, initially at a distance of 140 microns from the bundle tip. The video initially shows the refocused hologram without resolution enhancement, at a frame rate of 30 fps. The exposure was set at 16 ms and kept constant throughout.
Resolution enhancement is then turned on, and the resolution visibly improves. With resolution enhancement turned on, raw frames are captured at 25 fps, giving a net enhanced-resolution frame rate of 3.1 fps. In principle a rate of 7.5 fps could be achieved using the camera and the python processing code, but the overheads of the python GUI and the screen recording software resulted in lagging at faster than 3.1 fps. When the sample is translated, motion artefacts are now seen, as expected from a multi-frame approach.
Finally, use of a calibration LUT to allow fast refocusing in the GUI is demonstrated. The calibration LUT was built from depths from 100 to 500 microns in steps of 20 microns. The USAF target is shown being moved away from the bundle using a translation stage, and the numerical refocusing then adjusted in the GUI to bring it back into focus, changing which calibration is used from the LUT in the process
A Bayesian reanalysis of the Standard versus Accelerated Initiation of Renal-Replacement Therapy in Acute Kidney Injury (STARRT-AKI) trial
Background
Timing of initiation of kidney-replacement therapy (KRT) in critically ill patients remains controversial. The Standard versus Accelerated Initiation of Renal-Replacement Therapy in Acute Kidney Injury (STARRT-AKI) trial compared two strategies of KRT initiation (accelerated versus standard) in critically ill patients with acute kidney injury and found neutral results for 90-day all-cause mortality. Probabilistic exploration of the trial endpoints may enable greater understanding of the trial findings. We aimed to perform a reanalysis using a Bayesian framework.
Methods
We performed a secondary analysis of all 2927 patients randomized in multi-national STARRT-AKI trial, performed at 168 centers in 15 countries. The primary endpoint, 90-day all-cause mortality, was evaluated using hierarchical Bayesian logistic regression. A spectrum of priors includes optimistic, neutral, and pessimistic priors, along with priors informed from earlier clinical trials. Secondary endpoints (KRT-free days and hospital-free days) were assessed using zeroâone inflated beta regression.
Results
The posterior probability of benefit comparing an accelerated versus a standard KRT initiation strategy for the primary endpoint suggested no important difference, regardless of the prior used (absolute difference of 0.13% [95% credible interval [CrI]âââ3.30%; 3.40%],âââ0.39% [95% CrIâââ3.46%; 3.00%], and 0.64% [95% CrIâââ2.53%; 3.88%] for neutral, optimistic, and pessimistic priors, respectively). There was a very low probability that the effect size was equal or larger than a consensus-defined minimal clinically important difference. Patients allocated to the accelerated strategy had a lower number of KRT-free days (median absolute difference ofâââ3.55 days [95% CrIâââ6.38;âââ0.48]), with a probability that the accelerated strategy was associated with more KRT-free days of 0.008. Hospital-free days were similar between strategies, with the accelerated strategy having a median absolute difference of 0.48 more hospital-free days (95% CrIâââ1.87; 2.72) compared with the standard strategy and the probability that the accelerated strategy had more hospital-free days was 0.66.
Conclusions
In a Bayesian reanalysis of the STARRT-AKI trial, we found very low probability that an accelerated strategy has clinically important benefits compared with the standard strategy. Patients receiving the accelerated strategy probably have fewer days alive and KRT-free. These findings do not support the adoption of an accelerated strategy of KRT initiation
Regional Practice Variation and Outcomes in the Standard Versus Accelerated Initiation of Renal Replacement Therapy in Acute Kidney Injury (STARRT-AKI) Trial: A Post Hoc Secondary Analysis.
ObjectivesAmong patients with severe acute kidney injury (AKI) admitted to the ICU in high-income countries, regional practice variations for fluid balance (FB) management, timing, and choice of renal replacement therapy (RRT) modality may be significant.DesignSecondary post hoc analysis of the STandard vs. Accelerated initiation of Renal Replacement Therapy in Acute Kidney Injury (STARRT-AKI) trial (ClinicalTrials.gov number NCT02568722).SettingOne hundred-fifty-three ICUs in 13 countries.PatientsAltogether 2693 critically ill patients with AKI, of whom 994 were North American, 1143 European, and 556 from Australia and New Zealand (ANZ).InterventionsNone.Measurements and main resultsTotal mean FB to a maximum of 14 days was +7199âmL in North America, +5641âmL in Europe, and +2211âmL in ANZ (p p p p p p p p = 0.007).ConclusionsAmong STARRT-AKI trial centers, significant regional practice variation exists regarding FB, timing of initiation of RRT, and initial use of continuous RRT. After adjustment, such practice variation was associated with lower ICU and hospital stay and 90-day mortality among ANZ patients compared with other regions