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Structure and Assembly of the Proteus mirabilis Flagellar Motor by Cryo-Electron Tomography
No full textProteus mirabilis is a Gram-negative Gammaproteobacterium and a major causative agent of urinary tract infections in humans. It is characterized by its ability to switch between swimming motility in liquid media and swarming on solid surfaces. Here, we used cryo-electron tomography and subtomogram averaging to reveal the structure of the flagellar motor of P. mirabilis at nanometer resolution in intact cells. We found that P. mirabilis has a motor that is structurally similar to those of Escherichia coli and Salmonella enterica, lacking the periplasmic elaborations that characterize other more specialized gammaproteobacterial motors. In addition, no density corresponding to stators was present in the subtomogram average suggesting that the stators are dynamic. Finally, several assembly intermediates of the motor were seen that support the inside-out assembly pathway
3D-patterned inverse-designed mid-infrared metaoptics
No full textModern imaging systems can be enhanced in efficiency, compactness, and application through the introduction of multilayer nanopatterned structures for manipulation of light based on its fundamental properties. High transmission multispectral imaging is elusive due to the commonplace use of filter arrays which discard most of the incident light. Further, given the challenges of miniaturizing optical systems, most cameras do not leverage the wealth of information in polarization and spatial degrees of freedom. Optical metamaterials can respond to these electromagnetic properties but have been explored primarily in single-layer geometries, limiting their performance and multifunctional capacity. Here we use advanced two-photon lithography to realize multilayer scattering structures that achieve highly nontrivial optical transformations intended to process light just before it reaches a focal plane array. Computationally optimized multispectral and polarimetric sorting devices are fabricated with submicron feature sizes and experimentally validated in the mid-infrared. A final structure shown in simulation redirects light based on its angular momentum. These devices demonstrate that with precise 3-dimensional nanopatterning, one can directly modify the scattering properties of a sensor array to create advanced imaging systems
Spatially resolved imaging of the inner Fomalhaut disk using JWST/MIRI
No full textPlanetary debris disks around other stars are analogous to the Asteroid and Kuiper belts in the Solar System. Their structure reveals the configuration of small bodies and provides hints for the presence of planets. The nearby star Fomalhaut hosts one of the most prominent debris disks, resolved by HST, Spitzer, Herschel, and ALMA. Images of this system at mid-infrared wavelengths using JWST/MIRI not only show the narrow Kuiper-Belt-analog outer ring, but also that (1) what was thought from indirect evidence to be an asteroid-analog structure is instead broad, extending outward into the outer system; (2) there is an intermediate belt, probably shepherded by an unseen planet. The newly discovered belt is demarcated by an inner gap, located at ~ 78 au, and it is misaligned relative to the outer belt. The previously known collisionally generated dust cloud, Fomalhaut b, could have originated from this belt, suggesting increased dynamical stirring and collision rates there. We also discovered a large dust cloud within the outer ring, possible evidence of another dust-creating collision. Taken together with previous observations, Fomalhaut appears to be the site of a complex and possibly dynamically active planetary system
The Cell Tracking Challenge: 10 years of objective benchmarking
No full textThe Cell Tracking Challenge is an ongoing benchmarking initiative that has become a reference in cell segmentation and tracking algorithm development. Here, we present a significant number of improvements introduced in the challenge since our 2017 report. These include the creation of a new segmentation-only benchmark, the enrichment of the dataset repository with new datasets that increase its diversity and complexity, and the creation of a silver standard reference corpus based on the most competitive results, which will be of particular interest for data-hungry deep learning-based strategies. Furthermore, we present the up-to-date cell segmentation and tracking leaderboards, an in-depth analysis of the relationship between the performance of the state-of-the-art methods and the properties of the datasets and annotations, and two novel, insightful studies about the generalizability and the reusability of top-performing methods. These studies provide critical practical conclusions for both developers and users of traditional and machine learning-based cell segmentation and tracking algorithms
Revisiting the coupling reaction between 4-aminoantipyrine and phenols: a potential one-pot reaction pathway to 4,11- and 5,12-naphthoxazepine isomers
No full textA while ago, this journal (Canadian Journal of Chemistry) published a set of seminal studies that revealed the underlying mechanism supporting the widely used 4-aminoantipyrine (4-AAP)-based analytical technique for detecting phenols at low levels in domestic water supplies. The current paper revisits these studies, but with a primary focus on an aspect of the mechanism that synthesizes a 6- and a 7-membered heterocyclic ring containing both N and O in a single step. Here we report a rather unusual outcome of this aspect in which, while the same naphthoquinonimide product is produced in the oxidative coupling of 4-AAP to 1-naphthol in aqueous solution and in the condensation of 4-AAP with 1,4-naphthoquinone in chloroform, a similar pair of reactions with 2-naphthol and 1,2-naphthoquinone produces two oxazepine isomers instead. In one isomer, the 4-AAP/naphthol C–N and C–O linkages are at positions 1 and 2 of the naphthyl ring, respectively; in the other isomer, these linkages are at positions 2 and 1, respectively. This unexpected difference in a one-pot reaction at ambient temperature is potentially the flexibility needed to synthesize families of pharmaceutically relevant oxazepines. Spectroscopic features useful for identifying 12 heterocyclic compounds synthesized here, nine of which are new, are also provided
System Level Availability Budget for the Multi-Vehicle Sun Radio Interferometer Space Experiment
No full textThe Sun Radio Interferometer Space Experiment (SunRISE) will be the first space-based radio interferometer. Comprised of six identical 6U vehicles carrying decametric-hectometric radio and GNSS receiver payloads, the SunRISE Observatory orbits Earth slightly above GEO to measure solar radio bursts associated with solar coronal mass ejections (CMEs) and solar flares. Because the solar radio bursts that SunRISE will observe are inherently unpredictable, the SunRISE Observatory must have a long enough observing time in order to observe a sufficient number of solar radio bursts to satisfy the Level 1 Science requirements. The observing time is the product of two factors, the total duration of the prime science mission and the fraction of that time that can be used for science or the “Observatory availability”. In practice, solar radio bursts associated with CMEs, so-called Type II bursts, are less frequent, and the requirement to observe a sufficient number of them drives the resulting set of lower-level requirements. The “Observatory availability budget” is a mission-unique system-level budget that aims to guarantee science closure by synthesizing various, apparently disjoint, factors. The factors considered range from typical to more exotic. Typical considerations include time spent downlinking data or conducting orbital maneuvers, considerations of reliability and infant mortality, and expectations for spacecraft and payload hardware and software. Special considerations include the three-dimensional geometric arrangement of the vehicles in space and the extent to which they are in a configuration and with separation sufficient to form an interferometer with the required performance. This paper describes these factors and shows how we have assessed the Observatory availability budget to ensure that the Observatory is online greater than 90% of the time in order to observe a sufficient number of Type II radio bursts. The relevant requirements decomposed from this budget pertain to upset frequencies and durations, planned outage limits, mission duration, and fault protection/management and autonomy needs for the vehicles. This Observatory availability budget also informs mission plans for downlink/uplink and maneuver durations and cadences. This paper provides background on how the 90% availability requirement was developed, and focus on how the Observatory availability budget factors were identified and estimated, the statistical Monte Carlo-based model built to synthesize them, and the philosophy developed for how to interpret the results and evaluate compliance and margin. Of particular interest, we will discuss how SunRISE's architecture of six identical vehicles provides on-orbit redundancy, which is critical to the resiliency of this budget, allowing it to degrade gracefully with anomalies. At current, the SunRISE team is working to close this analysis and verify the related requirements in preparation for launch. SunRISE is a PI-led NASA science mission with PI and science data system at University of Michigan, managed by and with payloads, mission operations, and systems engineering provided by NASA's Jet Propulsion Laboratory, and spacecraft buses, assembly/integration/test from Space Dynamics Laboratory. SunRISE is in Phase D and currently preparing for hardware delivery to launch storage
Wireless Power Transfer at Distance
No full textWireless revolution in communication systems over the last several decades is beginning to move to the realm of energy transfer. Continuous energy transmission using proximity inductive charging is already available in many of our portable device [1]. Although it is technically wireless, the source and recipient of the energy still need to be within immediate proximity of each other, which leaves most of the wireless power application space unaddressed. This need drives the development of wireless power transfer at distance (WPT-AD) [2]
Astrophysics with the Laser Interferometer Space Antenna
No full textThe Laser Interferometer Space Antenna (LISA) will be a transformative experiment for gravitational wave astronomy, and, as such, it will offer unique opportunities to address many key astrophysical questions in a completely novel way. The synergy with ground-based and space-born instruments in the electromagnetic domain, by enabling multi-messenger observations, will add further to the discovery potential of LISA. The next decade is crucial to prepare the astrophysical community for LISA’s first observations. This review outlines the extensive landscape of astrophysical theory, numerical simulations, and astronomical observations that are instrumental for modeling and interpreting the upcoming LISA datastream. To this aim, the current knowledge in three main source classes for LISA is reviewed; ultra-compact stellar-mass binaries, massive black hole binaries, and extreme or interme-diate mass ratio inspirals. The relevant astrophysical processes and the established modeling techniques are summarized. Likewise, open issues and gaps in our understanding of these sources are highlighted, along with an indication of how LISA could help making progress in the different areas. New research avenues that LISA itself, or its joint exploitation with upcoming studies in the electromagnetic domain, will enable, are also illustrated. Improvements in modeling and analysis approaches, such as the combination of numerical simulations and modern data science techniques, are discussed. This review is intended to be a starting point for using LISA as a new discovery tool for understanding our Universe
Pseudoplane-wave gravitational calibrator for gravitational wave observatories
No full textThe precisions of existing gravitational calibrators for gravitational wave observatories are limited by their dependence on the relative position between the calibrators and the observatory’s test masses. Here we present a novel geometry consisting of four quadrupole rotors placed at the vertices of a rectangle centered on the test mass. The phases and rotation directions are selected to produce a pseudoplane-wave sinusoidal gravitational acceleration with amplitude of ∼100 fm/s². We show that this acceleration only has minimal dependence on the test mass position relative to the rotor array and can yield 0.15% acceleration amplitude uncertainty while tolerating a 1-cm test mass position uncertainty. The acceleration can be directed precisely along the optical axis of the interferometer arm and applies no torque on the test mass. In addition, the small size of the rotors has significant engineering and safety benefits
Conditional moment methods for polydisperse cavitating flows
No full textThe dynamics of cavitation bubbles are important in many flows, but their small sizes and high number densities often preclude direct numerical simulation. We present a computational model that averages their effect on the flow over larger spatiotemporal scales. The model is based on solving a generalized population balance equation (PBE) for nonlinear bubble dynamics and explicitly represents the evolving probability density of bubble radii and radial velocities. Conditional quadrature-based moment methods (QBMMs) are adapted to solve this PBE. A one-way-coupled bubble dynamics problem demonstrates the efficacy of different QBMMs for the evolving bubble statistics. Results show that enforcing hyperbolicity during moment inversion (CHyQMOM) provides comparable model-form accuracy to the traditional conditional method of moments and decreases computational costs by about ten times for a broad range of test cases. The CHyQMOM-based computational model is implemented in MFC, an open-source multi-phase and high-order-accurate flow solver. We assess the effect of the model and its parameters on a two-way coupled bubble screen flow problem