5632 research outputs found
Sort by
Using Non-negative Matrix Factorization to Improve Calibration of the Keck OSIRIS Integral Field Spectrograph
No full textIntegral Field Spectrographs (IFS) often require non-trivial calibration techniques to process raw data. The OH Suppressing InfraRed Imaging Spectrograph at the W. M. Keck Observatory is a lenslet-based IFS that requires precise methods to associate the flux on the detector with both a wavelength and a position on the detector. During calibration scans, a single column lenslet mask is utilized to keep light from adjacent lenslet columns separate from the primary lenslet column, in order to uniquely determine spectral response of individual lenslets on the detector. Despite employing a single column lenslet mask, an issue associated with such calibration schemes may occur when light from adjacent masked lenslet columns leaks into the primary lenslet column. Incorrectly characterizing the flux due to additional light in the primary lenslet column results in one form of crosstalk between lenslet columns, which most clearly manifest as non-physical artifacts in the spectral dimension of the reduced data. We treat the problem of potentially blended calibration scans as a source separation problem and implement Non-negative Matrix Factorization (NMF) as a way to separate blended calibration scan spectra. After applying NMF to calibration scan data, extracted spectra from calibration scans show reduced crosstalk of up to 26.7% ± 0.5% while not adversely impacting the signal-to-noise ratio. Additionally, we determined the optimal number of calibration scans per lenslet column needed to create NMF factors, finding that greatest reduction crosstalk occurs when NMF factors are created using one calibration scan per lenslet column
Modularizable Liquid‐Crystal‐Based Open Surfaces Enable Programmable Chemical Transport and Feeding using Liquid Droplets
No full textDroplet-based miniature reactors have attracted interest in both fundamental studies, for the unique reaction kinetics they enable, and applications in bio-diagnosis and material synthesis. However, the precise and automatic feeding of chemicals, important for the delicate reactions in these miniaturized chemical reactors, either requires complex, high-cost microfluidic devices or lacks the capability to maintain a pinning-free droplet movement. Here, the design and synthesis of a new class of liquid crystal (LC)-based open surfaces, which enable a controlled chemical release via a programmable LC phase transition without sacrificing the free transport of the droplets, are reported. It is demonstrated that their intrinsic slipperiness and self-healing properties enable a modularizable assembly of LC surfaces that can be loaded with different chemicals to achieve a wide range of chemical reactions carried out within the droplets, including sequential and parallel chemical reactions, crystal growth, and polymer synthesis. Finally, an LC-based chemical feeding device is developed that can automatically control the release of chemicals to direct the simultaneous differentiation of human induced pluripotent stem cells into endothelial progenitor cells and cardiomyocytes. Overall, these LC surfaces exhibit desirable levels of automation, responsiveness, and controllability for use in miniature droplet carriers and reactors
Autonomous Real-Time Science-Driven Follow-up of Survey Transients
No full textAstronomical surveys continue to provide unprecedented insights into the time-variable Universe and will remain the source of groundbreaking discoveries for years to come. However, their data throughput has overwhelmed the ability to manually synthesize alerts for devising and coordinating necessary follow-up with limited resources. The advent of Rubin Observatory, with alert volumes an order of magnitude higher at otherwise sparse cadence, presents an urgent need to overhaul existing human-centered protocols in favor of machine-directed infrastructure for conducting science inference and optimally planning expensive follow-up observations.
We present the first implementation of autonomous real-time science-driven follow-up using value iteration to perform sequential experiment design. We demonstrate it for strategizing photometric augmentation of Zwicky Transient Facility Type Ia supernova light-curves given the goal of minimizing SALT2 parameter uncertainties. We find a median improvement of 2–6% for SALT2 parameters and 3–11% for photometric redshift with 2–7 additional data points in g, r and/or i compared to random augmentation. The augmentations are automatically strategized to complete gaps and for resolving phases with high constraining power (e.g. around peaks). We suggest that such a technique can deliver higher impact during the era of Rubin Observatory for precision cosmology at high redshift and can serve as the foundation for the development of general-purpose resource allocation systems
Probing neutron stars with the full premerger and postmerger gravitational wave signal from binary coalescences
No full textThe gravitational wave signal emitted during the coalescence of two neutron stars carries information about the stars’ internal structure. During the long inspiral phase the main matter observable is the tidal interaction between the binary components, an effect that can be parametrically modeled with compact-binary solutions to general relativity. After the binary merger the main observable is frequency modes of the remnant, most commonly giving rise to a short-duration signal accessible only through numerical simulations. The complicated morphology and the decreasing detector sensitivity in the relevant frequencies currently hinder detection of the postmerger signal and motivate separate analyses for the premerger and postmerger data. However, planned and ongoing detector improvements could soon put the postmerger signal within reach. In this study we target the whole premerger and postmerger signal without an artificial separation at the binary merger. We construct a hybrid analysis that models the inspiral with templates based on analytical calculations and calibrated to numerical relativity and the postmerger signal with a flexible morphology-independent analysis. Applying this analysis to GW170817 we find, as expected, that the postmerger signal remains undetected. We further study simulated signals and find that we can reconstruct the full signal and simultaneously estimate both the premerger tidal deformation and the postmerger signal frequency content. Our analysis allows us to study neutron star physics using all the data available and directly test the premerger and postmerger signal for consistency thus probing effects such as the onset of the hadron-quark phase transition
Enabling spatiotemporal regulation within biomaterials using DNA reaction- diffusion waveguides
No full textIn multicellular organisms, cells and tissues coordinate biochemical signal propagation across length scales spanning microns to meters. Endowing synthetic materials with similar capacities for coordinated signal propagation could allow these systems to adaptively regulate themselves across space and over time. Here we combine ideas from cell signaling and electronic circuitry to design a biochemical waveguide that transmits information in the form of a concentration of a DNA species on a directed path. The waveguide can be seamlessly integrated into a soft material because there is virtually no difference between the chemical or physical properties of the waveguide and the material it is embedded within. We propose the design of DNA strand displacement reactions to construct the system and, using reaction-diffusion models, identify kinetic and diffusive parameters that enable super-diffusive transport of DNA species via autocatalysis. Finally, to support experimental waveguide implementation, we show how a sink reaction could mitigate the spurious amplification of an autocatalyst within the waveguide, allowing for controlled waveguide triggering. Chemical waveguides could facilitate the design of synthetic biomaterials with distributed sensing machinery integrated throughout their structure and enable coordinated self-regulating programs triggered by changing environmental conditions
The role of concentrated solar power with thermal energy storage in least-cost highly reliable electricity systems fully powered by variable renewable energy
No full textPolicies in the US increasingly stipulate the use of variable renewable energy sources, which must be able to meet electricity demand reliably and affordably despite variability. The value of grid services provided by additional marginal capacity and storage in existing grids is likely very different than their value in a 100% variable renewable electricity system under such policies. Consequently, the role of concentrated solar power (CSP) and thermal energy storage (TES) relative to photovoltaics (PV) and batteries has not been clearly evaluated or established for such highly reliable, 100% renewable systems. Electricity generation by CSP is currently more costly than by PV, but TES is much less costly than chemical battery storage. Herein, we analyze the role of CSP and TES compared to PV and batteries in an idealized least-cost solar/wind/storage electricity system using a macro-scale energy model with real-world historical demand and hourly weather data across the contiguous United States. We find that CSP does not compete directly with PV. Instead, TES competes with short-duration storage from batteries, with the coupled CSP+TES system providing reliability in the absence of other grid flexibility mechanisms. Without TES, little CSP generation is built in this system because CSP and PV have similar generation profiles, but PV is currently cheaper on a dollar-per-kWh basis than CSP. However, CSP with TES can provide grid flexibility in the modeled least-cost system under some circumstances due to the low cost of TES compared to batteries. Cost-sensitivity analysis shows that penetration of CSP with TES is primarily limited by high CSP generation costs. These results provide a framework for researchers and decision-makers to assess the role of CSP with TES in future electricity systems
Very Low Frequency Earthquakes in Between the Seismogenic and Tremor Zones in Cascadia?
No full textMegathrust earthquakes and their associated tsunamis cause some of the worst natural disasters. In addition to earthquakes, a wide range of slip behaviors are present at subduction zones, including slow earthquakes that span multiple orders of spatial and temporal scales. Understanding these events may shed light on the stress or strength conditions of the megathrust fault. Out of all types of slow earthquakes, very low frequency earthquakes (VLFEs) are most enigmatic because they are difficult to detect reliably, and the physical nature of VLFEs are poorly understood. Here we show three VLFEs in Cascadia that were dynamically triggered by a 2009 Mw 6.9 Canal de Ballenas earthquake in the Gulf of California. The VLFEs likely locate in between the seismogenic zone and the Cascadia episodic tremor and slip (ETS) zone, including one event with a moment magnitude of 5.7. This is the largest VLFE reported to date, causing clear geodetic signals. Our results show that the Cascadia megathrust fault might slip rapidly at some spots in this gap zone, and such a permissible slip behavior has direct seismic hazard implications for coastal communities and perhaps further inland. Further, the observed seismic sources may represent a new class of slip events, whose characteristics do not fit current understandings of slow or regular earthquakes
Cesium carbonate mediated C–H functionalization of perhalogenated 12-vertex carborane anions
No full textC–H functionalization of undecahalogenated carborane anions, [HCB₁₁X₁₁⁻] (X = Cl, Br, I), is performed with Cs₂CO₃ in acetonitrile. We show that the requisite Cl, Br and I carborane dianions can all be efficiently accessed with Cs₂CO₃. The utilization of Cs₂CO₃ eliminates the complications associated with competing E2 elimination reactions providing an efficient, more functional group tolerant, and broader scope than previously reported. The ensuing functionalized cages provide potential synthons for constructing advanced materials and other molecular architectures for various applications
Co-evolution of the terrestrial and aquatic ecosystem in the Holocene Baltic Sea
No full textThe Baltic Sea experienced changes in marine input throughout the Holocene as substantial regional ice retreat led to isostatic adjustment, eustatic sea level change, and periodic isolation from the North Sea. Here, we determine the distributions and isotopic signatures of organic compounds preserved in a sediment record spanning the last ∼11 kyr to reconstruct environmental change under these dynamic conditions. Carbon and hydrogen isotope ratios of short-, mid-, and long-chain n-alkanes, along with long-chain diol and glycerol dialkyl glycerol tetraether abundances, were analyzed in sediments sampled from the Arkona Basin in the southwestern Baltic Sea. In the earlier part of the record (specifically 10–8.2 ka), hydrogen isotope values of higher plant-derived n-alkanes revealed a change in dominant water source from an ice-melt-derived to a precipitation-dominated hydrological regime. Following this shift in water source, carbon isotope values of n-alkanes suggest diversification of vegetation. Shifts in hydrology and vegetation did not coincide with established phase boundaries but instead occurred mid-phase or spanned phase transitions. For this reason, we suggest describing the Ancylus Lake in two phases: a meltwater phase (10.6 to 9.2 ka) and a precipitation phase (9.2 to 7.7 ka). Our results highlight the utility of using C and H isotope ratios in conjunction with other compound abundance proxies to better understand the complex environmental change recorded in paleoarchives
On the use of dissolved oxygen isotopologues as biogeochemical tracers in the Pacific Ocean
No full textThe isotopic composition of dissolved oxygen offers a family of potentially unique tracers of respiration and transport in the subsurface ocean. Uncertainties in transport parameters and isotopic fractionation factors, however, have limited the strength of the constraints offered by ¹⁸O/¹⁶O and ¹⁷O/¹⁶O ratios in dissolved oxygen. In particular, puzzlingly low ¹⁷O/¹⁶O ratios observed for some low-oxygen samples have been difficult to explain. To improve our understanding of oxygen cycling in the ocean’s interior, we investigated the systematics of oxygen isotopologues in the subsurface Pacific using new data and a 2-D isotopologue-enabled isopycnal reaction-transport model. We measured ¹⁸O/¹⁶O and ¹⁷O/¹⁶O ratios, as well as the “clumped” ¹⁸O¹⁸O isotopologue in the northeast Pacific, and compared the results to previously published data. We find that transport and respiration rates constrained by O₂ concentrations in the oligotrophic Pacific yield good measurement-model agreement across all O₂ isotopologues only when using a recently reported set of respiratory isotopologue fractionation factors that differ from those most often used for oxygen cycling in the ocean. These fractionation factors imply that an elevated proportion of ¹⁷O compared to ¹⁸O in dissolved oxygen―i.e., its triple-oxygen isotope composition―does not uniquely reflect gross primary productivity and mixing. For all oxygen isotopologues, transport, respiration, and photosynthesis comprise important parts of their respective budgets. Mechanisms of oxygen removal in the subsurface ocean are discussed