5632 research outputs found
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Spatial extent of dust storm boundaries in the Mars Dust Activity Database
No full textThe Mars Dust Activity Database (MDAD) v1.1 is expanded to include all dust storm instance boundaries in MDAD v1.0 from the Mars Color Imager years (Mars Years 28–32). Dust storm boundaries are provided in two formats to ease adoption by the community: as netCDF masks and in comma separated value files. We demonstrate the utility of dust storm boundaries by showing how the frequency of dust storms evolves with season across the surface. The highest dust storm frequencies occur in the southern hemisphere around
L_s = 0° and L_s = 270° and in the northern hemisphere around L_s = 180° and L_s = 300°
Direct imaging and astrometric detection of a gas giant planet orbiting an accelerating star
No full textDirect imaging of gas giant exoplanets provides information on their atmospheres and the architectures of planetary systems. However, few planets have been detected in blind surveys with direct imaging. Using astrometry from the Gaia and Hipparcos spacecraft, we identified dynamical evidence for a gas giant planet around the nearby star HIP 99770. We confirmed the detection of this planet with direct imaging using the Subaru Coronagraphic Extreme Adaptive Optics instrument. The planet, HIP 99770 b, orbits 17 astronomical units from its host star, receiving an amount of light similar to that reaching Jupiter. Its dynamical mass is 13.9 to 16.1 Jupiter masses. The planet-to-star mass ratio [(7 to 8) × 10⁻³] is similar to that of other directly imaged planets. The planet’s atmospheric spectrum indicates an older, less cloudy analog of the previously imaged exoplanets around HR 8799
Lateral mammillary body neurons in mouse brain are disproportionately vulnerable in Alzheimer’s disease
No full textThe neural circuits governing the induction and progression of neurodegeneration and memory impairment in Alzheimer’s disease (AD) are incompletely understood. The mammillary body (MB), a subcortical node of the medial limbic circuit, is one of the first brain regions to exhibit amyloid deposition in the 5xFAD mouse model of AD. Amyloid burden in the MB correlates with pathological diagnosis of AD in human postmortem brain tissue. Whether and how MB neuronal circuitry contributes to neurodegeneration and memory deficits in AD are unknown. Using 5xFAD mice and postmortem MB samples from individuals with varying degrees of AD pathology, we identified two neuronal cell types in the MB harboring distinct electrophysiological properties and long-range projections: lateral neurons and medial neurons. lateral MB neurons harbored aberrant hyperactivity and exhibited early neurodegeneration in 5xFAD mice compared with lateral MB neurons in wild-type littermates. Inducing hyperactivity in lateral MB neurons in wild-type mice impaired performance on memory tasks, whereas attenuating aberrant hyperactivity in lateral MB neurons ameliorated memory deficits in 5xFAD mice. Our findings suggest that neurodegeneration may be a result of genetically distinct, projection-specific cellular dysfunction and that dysregulated lateral MB neurons may be causally linked to memory deficits in AD
A critical appraisal of fracture mechanics methods for self-healing and healable composites characterization
No full textSelf-healing and healable Fibre Reinforced Polymer composites (FRPs) have tremendous potential in reducing the weight and increasing the lifetime of aerospace structures. While several strategies have been developed to add healing functionality to composites, there is no generally accepted method for the evaluation of their healing efficiency. Most testing approaches are based on interlaminar fracture toughness evaluation which revolves around three widely recognised methods: double-cantilever beam (DCB), three-point end-notch flexure (3-ENF), and four-point end notch flexure (4-ENF) testing. Alternative tests also employed in literature are low-impact velocity, micro-cutting, and short-beam shear (SBS) testing. This paper introduces the advantages and disadvantages of each test method when applied to healing FRPs while highlighting and explaining the large inconsistencies found among investigations. Ultimately, this review provides the necessary tools in choosing the most adequate test method for the characterization of a novel mendable FRP
An in-vivo preclinical study assessing biocompatibility of Pd-based bulk metallic glass Pd₇₉Ag_(3.5)P₆Si_(9.5)Ge₂
No full textBackground: The bulk metallic glass (BMG), Pd₇₉Ag_(3.5)P₆Si_(9.5)Ge₂, has a high fracture toughness and has been found to accommodate post-yield stress, unlike most other BMG. Moreover, due to its greater noble gas composition it has a intrinsic corrosion resistance, ideal for dental and orthopedic implants.
Objective: This present study aimed to evaluate the in vivo application of Pd₇₉Ag_(3.5)P₆Si_(9.5)Ge₂ in a large translational sheep model to assess its efficacy to be utilized as an endosteal device.
Methods: Twelve implants in the form of cylindrical rods (3 mm in diameter) were produced through rapid quenching. Each sheep (n = 12) received one osteotomy in the mandibular region using rotary instrumentation, which was filled with Pd₇₉Ag_(3.5)P₆Si_(9.5)Ge₂. After 6- and 24-weeks the animals were euthanized, and samples collected en bloc to conduct histomorphometric analysis. The degree of osseointegration were assessed through bone-to-implant contact (BIC).
Results: All samples revealed favorable BIC along with with fibrous connective tissue layers at both 6- and 24-weeks. Bone along with interfacial remodeling was observed in proximity with the metallic glass surface at 6 weeks with higher degrees of bone organization being observed at the later healing time, 24 weeks.
Conclusions: The synthesized BMG, given its unique combination of toughness and strength, revealed potential to serve as an alternative to commonly used Ti alloys
Many-body cavity quantum electrodynamics with driven inhomogeneous emitters
No full textQuantum emitters coupled to optical resonators are quintessential systems for exploring fundamental phenomena in cavity quantum electrodynamics (cQED) and are commonly used in quantum devices acting as qubits, memories and transducers. Many previous experimental cQED studies have focused on regimes in which a small number of identical emitters interact with a weak external drive such that the system can be described with simple, effective models. However, the dynamics of a disordered, many-body quantum system subject to a strong drive have not been fully explored, despite its importance and potential in quantum applications. Here we study how a large, inhomogeneously broadened ensemble of solid-state emitters coupled with high cooperativity to a nanophotonic resonator behaves under strong excitation. We discover a sharp, collectively induced transparency (CIT) in the cavity reflection spectrum, resulting from quantum interference and collective response induced by the interplay between driven inhomogeneous emitters and cavity photons. Furthermore, coherent excitation within the CIT window leads to highly nonlinear optical emission, spanning from fast superradiance to slow subradiance. These phenomena in the many-body cQED regime enable new mechanisms for achieving slow light and frequency referencing, pave a way towards solid-state superradiant lasers and inform the development of ensemble-based quantum interconnects
Intermediate-state-trapped mutants pinpoint G protein-coupled receptor conformational allostery
No full textUnderstanding the roles of intermediate states in signaling is pivotal to unraveling the activation processes of G protein-coupled receptors (GPCRs). However, the field is still struggling to define these conformational states with sufficient resolution to study their individual functions. Here, we demonstrate the feasibility of enriching the populations of discrete states via conformation-biased mutants. These mutants adopt distinct distributions among five states that lie along the activation pathway of adenosine A2A receptor (A2AR), a class A GPCR. Our study reveals a structurally conserved cation-π lock between transmembrane helix VI (TM6) and Helix8 that regulates cytoplasmic cavity opening as a “gatekeeper” for G protein penetration. A GPCR activation process based on the well-discerned conformational states is thus proposed, allosterically micro-modulated by the cation-π lock and a previously well-defined ionic interaction between TM3 and TM6. Intermediate-state-trapped mutants will also provide useful information in relation to receptor-G protein signal transduction
The Plasmodium Falciparum Apicoplast Cysteine Desulfurase Provides Sulfur for Both Iron-Sulfur Cluster Assembly and tRNA Modification
No full textIron-sulfur clusters (FeS) are ancient and ubiquitous protein cofactors that play fundamental roles in many aspects of cell biology. These cofactors cannot be scavenged or trafficked within a cell and thus must be synthesized in any subcellular compartment where they are required. We examined the FeS synthesis proteins found in the relict plastid organelle, called the apicoplast, of the human malaria parasite Plasmodium falciparum. Using a chemical bypass method, we deleted four of the FeS pathway proteins involved in sulfur acquisition and cluster assembly and demonstrated that they are all essential for parasite survival. However, the effect that these deletions had on the apicoplast organelle differed. Deletion of the cysteine desulfurase SufS led to disruption of the apicoplast organelle and loss of the organellar genome, whereas the other deletions did not affect organelle maintenance. Ultimately, we discovered that the requirement of SufS for organelle maintenance is not driven by its role in FeS biosynthesis, but rather, by its function in generating sulfur for use by MnmA, a tRNA modifying enzyme that we localized to the apicoplast. Complementation of MnmA and SufS activity with a bacterial MnmA and its cognate cysteine desulfurase strongly suggests that the parasite SufS provides sulfur for both FeS biosynthesis and tRNA modification in the apicoplast. The dual role of parasite SufS is likely to be found in other plastid-containing organisms and highlights the central role of this enzyme in plastid biology
Vertical-Slice Ocean Tomography With Seismic Waves
No full textSeismically generated sound waves that propagate through the ocean are used to infer temperature anomalies and their vertical structure in the deep East Indian Ocean. These T waves are generated by earthquakes off Sumatra and received by hydrophone stations off Diego Garcia and Cape Leeuwin. Between repeating earthquakes, a T wave's travel time changes in response to temperature anomalies along the wave's path. What part of the water column the travel time is sensitive to depends on the frequency of the wave, so measuring travel time changes at a few low frequencies constrains the vertical structure of the inferred temperature anomalies. These measurements reveal anomalies due to equatorial waves, mesoscale eddies, and decadal warming trends. By providing direct constraints on basin-scale averages with dense sampling in time, these data complement previous point measurements that alias local and transient temperature anomalies
Single-shot photoacoustic imaging with single-element transducer through a spatiotemporal encoder
No full textSignificance. Current photoacoustic (PA) imaging modalities typically require either serial detection with a single-element transducer or parallel detections with an ultrasonic array, indicating a dilemma between system cost and imaging throughput. PA topography through ergodic relay (PATER) was recently developed to address this bottleneck. However, PATER requires object-specific calibration due to varied boundary condition and must be recalibrated through pointwise scanning for each object before measurements, which is time-consuming and severely limits practical application.
Aim. We aim to develop a new single-shot PA imaging technique that only requires a one-time calibration for imaging different objects using a single-element transducer.
Approach. We develop an imaging method, PA imaging through a spatiotemporal encoder (PAISE), to address the above issue. The spatial information is effectively coded into unique temporal features by the spatiotemporal encoder, which allows for compressive image reconstruction. An ultrasonic waveguide is proposed as a critical element to guide the PA waves from the object into the prism, which effectively accounts for the varied boundary condition of different objects. We further add irregular-shaped edges on the prism to introduce randomized internal reflections and further facilitate the scrambling of acoustic waves.
Results. The proposed technique is validated through comprehensive numerical simulations and experiments, and it is demonstrated that PAISE can successfully overcome the changed boundary condition and can image different samples given a single calibration.
Conclusions. The proposed PAISE technique is capable of single-shot widefield PA imaging with a single-element transducer and does not require sample-specific calibration, which successfully overcomes the major limitation of previous PATER technology