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Global Trends in the Distribution of Biogenic Minerals in the Ocean
No full textThe cycling of marine particulate matter is critical for sequestering carbon in the deep ocean and in marine sediments. Biogenic minerals such as calcium carbonate (CaCO₃) and opal add density to more buoyant organic material, facilitating particle sinking and export. Here, we compile and analyze a global data set of particulate organic carbon (POC), particulate inorganic carbon (PIC, or CaCO₃), and biogenic silica (bSi, or opal) concentrations collected using large volume pumps (LVPs). We analyze the distribution of all three biogenic phases in the small (1–53 μm) and large (>53 μm) size classes. Over the entire water column 76% of POC exists in the small size fraction. Similarly, the small size class contains 82% of PIC, indicating the importance of small-sized coccolithophores to the PIC budget of the ocean. In contrast, 50% of bSi exists in the large size fraction, reflecting the larger size of diatoms and radiolarians compared with coccolithophores. We use PIC:POC and bSi:POC ratios in the upper ocean to document a consistent signal of shallow mineral dissolution, likely linked to biologically mediated processes. Sediment trap PIC:POC and bSi:POC are elevated with respect to LVP samples and increase strongly with depth, indicating the concentration of mineral phases and/or a deficit of POC in large sinking particles. We suggest that future sampling campaigns pair LVPs with sediment traps to capture the full particulate field, especially the large aggregates that contribute to mineral-rich deep ocean fluxes, and may be missed by LVPs
Emergent Spectral Fluxes of Hot Jupiters: An Abrupt Rise in Dayside Brightness Temperature Under Strong Irradiation
No full textWe study the emergent spectral fluxes of transiting hot Jupiters, using secondary eclipses from Spitzer. To achieve a large and uniform sample, we have reanalyzed all secondary eclipses for all hot Jupiters observed by Spitzer at 3.6 and/or 4.5 μm. Our sample comprises 457 eclipses of 122 planets, including eclipses of 13 planets not previously published. We use these eclipse depths to calculate the spectral fluxes emergent from the exoplanetary atmospheres, and thereby infer the temperatures and spectral properties of hot Jupiters. We find that an abrupt rise in brightness temperature, similar to a phase change, occurs on the dayside atmospheres of the population at an equilibrium temperature between 1714 and 1818 K (99% confidence limits). The amplitude of the rise is 291 ± 49 K, and two viable causes are the onset of magnetic drag that inhibits longitudinal heat redistribution, and/or the rapid dissipation of dayside clouds. We also study hot Jupiter spectral properties with respect to metallicity and temperature inversions. Models exhibiting 4.5 μm emission from temperature inversions reproduce our fluxes statistically for the hottest planets, but the transition to emission is gradual, not abrupt. The Spitzer fluxes are sensitive to metallicity for planets cooler than ∼1200 K, and most of the hot Jupiter population falls between model tracks having solar to 30× solar metallicity
Barrier-Based Test Synthesis for Safety-Critical Systems Subject to Timed Reach-Avoid Specifications
No full textWe propose an adversarial, time-varying test-synthesis procedure for safety-critical systems without requiring specific knowledge of the underlying controller steering the system. From a broader test and evaluation context, determination of difficult tests of system behavior is important as these tests would elucidate problematic system phenomena before these mistakes can engender problematic outcomes, e.g. loss of human life in autonomous cars, costly failures for airplane systems, etc. Our approach builds on existing, simulation-based work in the test and evaluation literature by offering a controller-agnostic test-synthesis procedure that provides a series of benchmark tests with which to determine controller reliability. To achieve this, our approach codifies the system objective as a timed reach-avoid specification. Then, by coupling control barrier functions with this class of specifications, we construct an instantaneous difficulty metric whose minimizer corresponds to the most difficult test at that system state. We use this instantaneous difficulty metric in a game-theoretic fashion, to produce an adversarial, time-varying test-synthesis procedure that does not require specific knowledge of the system's controller, but can still provably identify realizable and maximally difficult tests of system behavior. Finally, we develop this test-synthesis procedure for both continuous and discrete-time systems and showcase our test-synthesis procedure on simulated and hardware examples
Encoding of predictive associations in human prefrontal and medial temporal neurons during Pavlovian conditioning
No full textPavlovian conditioning is thought to involve the formation of learned associations between stimuli and values, and between stimuli and specific features of outcomes. Here we leveraged human single neuron recordings in ventromedial prefrontal, dorsomedial frontal, hippocampus and amygdala neurons while patients performed a sequential Pavlovian conditioning task containing both stimulus-value and stimulus-stimulus associations. Neurons in the ventromedial prefrontal cortex encoded predictive value along with the amygdala, but also encoded predictions about the identity of stimuli that would subsequently be presented, suggesting a role for neurons in this region in encoding predictive information beyond value. Unsigned error signals were found in dorsomedial prefrontal areas and hippocampus, potentially supporting learning of non-value related outcome features. Our findings implicate distinct human prefrontal and medial temporal neuronal populations in mediating predictive associations which could partially support model-based mechanisms during Pavlovian conditioning.Significance statementPavlovian conditioning is a fundamental form of learning, allowing organisms to associate stimuli and outcomes. Recent Pavlovian work suggests that phenomena such as devaluation sensitivity and sensory preconditioning can be explained by a model-based learning framework. How human neurons perform model-based learning during Pavlovian conditioning is still an open question. We recorded single neurons from epilepsy patients during a two-step Pavlovian conditioning task and found that ventromedial prefrontal neurons encoded expected rewards along with amygdala neurons, but also predicted the identity of upcoming stimuli as required for model-based cognition. Additionally, medial frontal neurons were found to encode error signals that could be used for stimulus-outcome learning. This is the first study mapping model-based computations during Pavlovian conditioning in human neurons
Functional gene delivery to and across brain vasculature of systemic AAVs with endothelial-specific tropism in rodents and broad tropism in primates
No full textDelivering genes to and across the brain vasculature efficiently and specifically across species remains a critical challenge for addressing neurological diseases. We have evolved adeno-associated virus (AAV9) capsids into vectors that transduce brain endothelial cells specifically and efficiently following systemic administration in wild-type mice with diverse genetic backgrounds and rats. These AAVs also exhibit superior transduction of the CNS across non-human primates (marmosets and rhesus macaques), andex vivohuman brain slices although the endothelial tropism is not conserved across species. The capsid modifications translate from AAV9 to other serotypes such as AAV1 and AAV-DJ, enabling serotype switching for sequential AAV administration in mice. We demonstrate that the endothelial specific mouse capsids can be used to genetically engineer the blood-brain barrier by transforming the mouse brain vasculature into a functional biofactory. Vasculature-secreted Hevin (a synaptogenic protein) rescued synaptic deficits in a mouse model
Strong Substrate Binding Modulates the Acoustic Quality Factors in Gold Nanodisks
No full textLithographically prepared plasmonic nanoparticles are ideal mechanical probes, as their vibrational behavior can be precisely tuned through particle size and shape. But these particles exhibit strong intrinsic and extrinsic damping that results in small vibrational quality (Q) factors. Here, we perform single-particle transient transmission microscopy to investigate the effect of substrate-particle binding strength on the vibrational Q-factor of lithographically prepared gold nanodisks on glass. Weak and strong binding is realized through titanium adhesion layers of variable thickness. We find that strong binding leads to the generation of several new acoustic modes with varying Q-factors that depend on the particle aspect ratio and substrate material. Our work proposes an approach to tune enhanced acoustic Q-factors of lithographically prepared nanoparticles and offers a comprehensive description of their damping mechanism
CRISPR mediated transactivation in the human disease vector Aedes aegypti
No full textAs a major insect vector of multiple arboviruses, Aedes aegypti poses a significant global health and economic burden. A number of genetic engineering tools have been exploited to understand its biology with the goal of reducing its impact. For example, current tools have focused on knocking-down RNA transcripts, inducing loss-of-function mutations, or expressing exogenous DNA. However, methods for transactivating endogenous genes have not been developed. To fill this void, here we developed a CRISPR activation (CRISPRa) system in Ae. aegypti to transactivate target gene expression. Gene expression is activated through pairing a catalytically-inactive (‘dead’) Cas9 (dCas9) with a highly-active tripartite activator, VP64-p65-Rta (VPR) and synthetic guide RNA (sgRNA) complementary to a user defined target-gene promoter region. As a proof of concept, we demonstrate that engineered Ae. aegypti mosquitoes harboring a binary CRISPRa system can be used to effectively overexpress two developmental genes, even-skipped (eve) and hedgehog (hh), resulting in observable morphological phenotypes. We also used this system to overexpress the positive transcriptional regulator of the Toll immune pathway known as AaRel1, which resulted in a significant suppression of dengue virus serotype 2 (DENV2) titers in the mosquito. This system provides a versatile tool for research pathways not previously possible in Ae. aegypti, such as programmed overexpression of endogenous genes, and may aid in gene characterization studies and the development of innovative vector control tools
Flexible parsing and preprocessing of technical sequences with splitcode
No full textNext-generation sequencing libraries are constructed with numerous synthetic constructs such as sequencing adapters, barcodes, and unique molecular identifiers. Such sequences can be essential for interpreting results of sequencing assays, and when they contain information pertinent to an experiment, they must be processed and analyzed. We present a tool called splitcode, that enables flexible and efficient preprocessing, parsing, and manipulation of sequencing reads. The splitcode program is free, open source, and available for download at http://github.com/pachterlab/splitcode. This versatile tool will facilitate simple, reproducible preprocessing of reads from libraries constructed for a large array of single-cell and bulk sequencing assays
UAS Flight Testing in Support of Research for Academia: Getting Started and Experiences from the Fields
No full textUninhabited Aerial Vehicles (UAVs) and miniaturized high-performance computing have enabled flight testing to become incredibly accessible, changing the status quo from an expensive, high-knowledge-barrier endeavour to a relatively low-cost exercise that is within the reach of small-scale research institutions and individuals. Due to this ease of entry, flight testing with UAVs is becoming increasingly commonplace as the technology allows cutting-edge research to leave the realm of simulation and enter real-world trials in very short time frames without the restrictions and costs of piloted, full-scale flight. Where traditional flight test engineers required many years of specialized training, budding UAV flight test engineers often start with little-to-no prior personal or in-house experience, and go through the same trail-and-error processes as those before them. This paper aims to document many years of experience flight testing at a university level, both to provide a basic understanding of the process for anyone getting started, and to share ideas with more experienced operators. It covers aspects such as instrumentation, flight controllers, airframes, bridging the sim-to-real gap and methodologies for conducting safe and efficient flight test campaigns
Design of a Lunar Architecture for Tree Traversal in Service of Cabled Exploration
No full textTraditional wheeled locomotion systems struggle to climb slopes greater than 20◦ and are unable to independently return samples from lunar regions of interest such as ISRU-enabling permanently shadowed polar craters. To reliably enable a diverse range of future robotic activities within lunar craters, this paper presents LATTICE, a lightweight, rapidly deploying, long-lived robotic infrastructure. Utilizing a novel, terrain agnostic, cabled locomotion modality, it is well equipped to repeatedly transport existing robotic systems and scientific hardware into and out of lunar craters and provide power for sustained activities within. LATTICE may be scaled indefinitely, providing a framework for unprecedented bulk transportation of volatile-containing regolith collected in permanently shadowed craters across the lunar surface and beyond