• Atmospheric oxidation in the presence of clouds during the Deep Convective Clouds and Chemistry (DC3) study

      Brune, William H.; Ren, Xinrong; Zhang, Li; Mao, Jingqiu; Miller, David O.; Anderson, Bruce E.; Blake, Donald R.; Cohen, Ronald C.; Diskin, Glenn S.; Hall, Samuel R.; et al. (COPERNICUS GESELLSCHAFT MBH, 2018-10-10)
      Deep convective clouds are critically important to the distribution of atmospheric constituents throughout the troposphere but are difficult environments to study. The Deep Convective Clouds and Chemistry (DC3) study in 2012 provided the environment, platforms, and instrumentation to test oxidation chemistry around deep convective clouds and their impacts downwind. Measurements on the NASA DC-8 air-craft included those of the radicals hydroxyl (OH) and hydroperoxyl (HO2), OH reactivity, and more than 100 other chemical species and atmospheric properties. OH, HO2, and OH reactivity were compared to photochemical models, some with and some without simplified heterogeneous chemistry, to test the understanding of atmospheric oxidation as encoded in the model. In general, the agreement between the observed and modeled OH, HO2, and OH reactivity was within the combined uncertainties for the model without heterogeneous chemistry and the model including heterogeneous chemistry with small OH and HO2 uptake consistent with laboratory studies. This agreement is generally independent of the altitude, ozone photolysis rate, nitric oxide and ozone abundances, modeled OH reactivity, and aerosol and ice surface area. For a sunrise to midday flight downwind of a nighttime mesoscale convective system, the observed ozone increase is consistent with the calculated ozone production rate. Even with some observed-to-modeled discrepancies, these results provide evidence that a current measurement constrained photochemical model can simulate observed atmospheric oxidation processes to within combined uncertainties, even around convective clouds. For this DC3 study, reduction in the combined uncertainties would be needed to confidently unmask errors or omissions in the model chemical mechanism.
    • Atmospheric Structure and Radiation Pattern for Neutron-star Polar Caps Heated by Magnetospheric Return Currents

      Bauböck, Michi; Psaltis, Dimitrios; Özel, Feryal; Univ Arizona, Dept Astron (IOP PUBLISHING LTD, 2019-02-20)
      The Neutron-star Interior Composition ExploreR (NICER) is collecting data to measure the radii of neutron stars by observing the pulsed emission from their surfaces. The primary targets are isolated, rotation-powered pulsars, in which the surface polar caps are heated by bombardment from magnetospheric currents of electrons and positrons. We investigate various stopping mechanisms for the beams of particles that bombard the atmosphere and calculate the heat deposition, the atmospheric temperature profiles, and the energy spectra and beaming of the emerging radiation. We find that low-energy particles with gamma similar to 2-10 deposit most of their energy in the upper regions of the atmosphere, at low optical depth, resulting in beaming patterns that are substantially different from those of deep-heated, radiative equilibrium models. Only particles with energies gamma greater than or similar to 50 penetrate to high optical depths and fulfill the conditions necessary for a deep-heating approximation. We discuss the implications of our work for modeling the pulse profiles from rotation-powered pulsars and for the inference of their radii with NICER observations.
    • Atmospheric teleconnection influence on North American land surface phenology

      Dannenberg, Matthew P; Wise, Erika K; Janko, Mark; Hwang, Taehee; Smith, W Kolby; Univ Arizona, Sch Nat Resources & Environm (IOP PUBLISHING LTD, 2018-03)
      Short-term forecasts of vegetation activity are currently not well constrained due largely to our lack of understanding of coupled climate-vegetation dynamics mediated by complex interactions between atmospheric teleconnection patterns. Using ecoregion-scale estimates of North American vegetation activity inferred from remote sensing (1982-2015), we examined seasonal and spatial relationships between land surface phenology and the atmospheric components of five teleconnection patterns over the tropical Pacific, north Pacific, and north Atlantic. Using a set of regression experiments, we also tested for interactions among these teleconnection patterns and assessed predictability of vegetation activity solely based on knowledge of atmospheric teleconnection indices. Autumn-to-winter composites of the Southern Oscillation Index (SOI) were strongly correlated with start of growing season timing, especially in the Pacific Northwest. The two leading modes of north Pacific variability (the Pacific-North American, PNA, and West Pacific patterns) were significantly correlated with start of growing season timing across much of southern Canada and the upper Great Lakes. Regression models based on these Pacific teleconnections were skillful predictors of spring phenology across an east-west swath of temperate and boreal North America, between 40 degrees N-60 degrees N. While the North Atlantic Oscillation (NAO) was not strongly correlated with start of growing season timing on its own, we found compelling evidence of widespread NAO-SOI and NAO-PNA interaction effects. These results suggest that knowledge of atmospheric conditions over the Pacific and Atlantic Oceans increases the predictability of North American spring phenology. A more robust consideration of the complexity of the atmospheric circulation system, including interactions across multiple ocean basins, is an important step towards accurate forecasts of vegetation activity.
    • Atmospheric Turbulence-Controlled Cryptosystems

      Djordjevic, Ivan B.; ECE Dept., College of Engineering, University of Arizona (Institute of Electrical and Electronics Engineers Inc., 2021-01-22)
      To overcome the limitations of QKD, post-quantum cryptography, and computational security-based cryptography protocols in this paper, an atmospheric turbulence-controlled cryptosystem is proposed. The proposed encryption scheme employs the traditional scheme to utilize the atmospheric turbulence as the common source of randomness only in the initialization stage to determine the common parameters to be used in the proposed encryption scheme. To overcome low secret-key rates of traditional scheme, dictated by the long coherence time Tc of turbulence channel, the proposed encryption scheme updates the parameters of gamma-gamma distribution, used to generate irradiance samples for cumulative distribution function-based determination of the key, every Tc seconds and as such the final key is shaped by the atmospheric turbulence channel. We also describe a scheme that randomly selects one of several available paths in which the simultaneously measured irradiance samples, after interleaving, are used to generate the raw key. The secret-key rates of the proposed schemes are orders of magnitude higher compared to corresponding traditional QKD and source type physical-layer security schemes and are comparable with the state-of-the-art optical communication data rates.
    • Atmospheric Variability Driven by Radiative Cloud Feedback in Brown Dwarfs and Directly Imaged Extrasolar Giant Planets

      Tan, Xianyu; Showman, Adam P.; Univ Arizona, Lunar & Planetary Lab (IOP PUBLISHING LTD, 2019-03-28)
      Growing observational evidence has suggested active meteorology in the atmospheres of brown dwarfs (BDs) and directly imaged extrasolar giant planets (EGPs). In particular, a number of surveys have shown that near-infrared brightness variability is common among L and T dwarfs. Despite the likelihood from previous studies that atmospheric dynamics is the major cause of the variability, the detailed mechanism of the variability remains elusive, and we need to seek a natural, self-consistent mechanism. Clouds are important in shaping the thermal structure and spectral properties of these atmospheres via their opacity, and we expect the same for inducing atmospheric variability. In this work, using a time-dependent one-dimensional model that incorporates a self-consistent coupling between the thermal structure, convective mixing, cloud radiative heating/cooling, and condensation/evaporation of clouds, we show that radiative cloud feedback can drive spontaneous atmospheric variability in both temperature and cloud structure under conditions appropriate for BDs and directly imaged EGPs. The typical periods of variability are 1 to tens of hr, with a typical amplitude of the variability up to hundreds of K in effective temperature. The existence of variability is robust over a wide range of parameter space, but the detailed evolution of the variability is sensitive to model parameters. Our novel, self-consistent mechanism has important implications for the observed flux variability of BDs and directly imaged EGPs, especially for objects whose variability evolves on short timescales. It is also a promising mechanism for cloud breaking, which has been proposed to explain the L/T transition of BDs.
    • Atmospheric Waves and Their Possible Effect on the Thermal Structure of Saturn's Thermosphere

      Müller‐Wodarg, I. C. F.; Koskinen, T. T.; Moore, L.; Serigano, J.; Yelle, R. V.; Hörst, S.; Waite, J. H.; Mendillo, M.; Univ Arizona, Lunar & Planetary Lab (AMER GEOPHYSICAL UNION, 2019-03-11)
      Atmospheric waves have been discovered for the first time in Saturn's neutral upper atmosphere (thermosphere). Waves may be generated from instabilities, convective storms or other atmospheric phenomena. The inferred wave amplitudes change little with height within the sampled region, raising the possibility of the waves being damped, which in turn may enhance the eddy friction within the thermosphere. Using our Saturn Thermosphere Ionosphere General Circulation Model, we explore the parameter space of how an enhanced Rayleigh drag in different latitude regimes would affect the global circulation pattern within the thermosphere and, in turn, its global thermal structure. We find that Rayleigh drag of sufficient magnitude at midlatitudes may reduce the otherwise dominant Coriolis forces and enhance equatorward winds to transport energy from poles toward the equator, raising the temperatures there to observed values. Without this Rayleigh drag, energy supplied into the polar upper atmosphere by magnetosphere-atmosphere coupling processes remains trapped at high latitudes and causes low-latitude thermosphere temperatures to remain well below the observed levels. Our simulations thus suggest that giant planet upper atmosphere global circulation models need to include additional Rayleigh drag in order to capture the effects of physical processes otherwise not resolved by the codes. Plain Language Summary Atmospheric waves have been discovered for the first time in Saturn's neutral upper atmosphere (thermosphere) with typical vertical wavelengths ranging from 100-200 km and density amplitudes reaching around 10%. Amplitudes are roughly constant over this height range, implying that wave damping occurs, which in turn is expected to enhance eddy friction (Rayleigh drag) within the thermosphere. Using the Saturn Thermosphere Ionosphere General Circulation Model (STIM), we explore the response of Saturn's thermosphere to a range of possible Rayleigh drag profiles. We find that the introduction of momentum dissipation equatorward of 60 degrees latitude will slow down the zonal winds on Saturn sufficiently to enhance equatorward winds and thereby allow energy propagation from the poles toward the equator. Under the assumption that sufficiently strong Rayleigh drag is present in Saturn's thermosphere, large temperatures at low latitudes may result from wind-driven global redistribution of energy from the polar regions.
    • Atomic Embeddability, Clustered Planarity, and Thickenability

      Fulek, Radoslav; Tóth, Csaba D.; Univ Arizona, Dept Comp Sci (Society for Industrial and Applied Mathematics, 2020-12-23)
      We study the atomic embeddability testing problem, which is a common generalization of clustered planarity (c-planarity, for short) and thickenability testing, and present a polynomial time algorithm for this problem, thereby giving the first polynomial time algorithm for c-planarity. C-planarity was introduced in 1995 by Feng, Cohen, and Eades as a variant of graph planarity, in which the vertex set of the input graph is endowed with a hierarchical clustering and we seek an embedding (crossing free drawing) of the graph in the plane that respects the clustering in a certain natural sense. Until now, it has been an open problem whether c-planarity can be tested efficiently, despite relentless efforts. The thickenability problem for simplicial complexes emerged in the topology of manifolds in the 1960s. A 2-dimensional simplicial complex is thickenable if it embeds in some orientable 3-dimensional manifold. Recently, Carmesin announced that thickenability can be tested in polynomial time. Our algorithm for atomic embeddability combines ideas from Carmesin's work with algorithmic tools previously developed for weak embeddability testing. We express our results purely in terms of graphs on surfaces, and rely on the machinery of topological graph theory. Finally we give a polynomial-time reduction from c-planarity to thickenability and show that a slight generalization of atomic embeddability to the setting in which clusters are toroidal graphs is NP-complete.
    • Atomic-scale evidence for open-system thermodynamics in the early solar nebula

      Zega, T.J.; Manga, V.R.; Ciesla, F.; Muralidharan, K.; Watanabe, K.; Inada, H.; Lunar and Planetary Laboratory, University of Arizona; Department of Materials Science and Engineering, University of Arizona (IOP Publishing, 2021)
      We report a new integrated framework that combines atomic-length-scale characterization via aberration-corrected scanning transmission electron microscopy with first-principles-driven thermodynamic modeling and dusttransport models to probe the origins of some of the first-formed solids in the solar system. We find that within one of the first solids that formed in our solar system, spinel, nominally MgAl2O4, occurs as a twinned inclusion within perovskite, CaTiO3, and contains vanadium segregated to its twin boundary as atomic columns. Our results support a scenario in which spinel condensed at 1435 K in the midplane of the solar protoplanetary disk and was later transported inward to a hotter region where perovskite condensed around it at 1681 K. The spinel became twinned as a result of a displacive phase transition in the perovskite after which it was later transported to cooler regions of the disk and incorporated into its parent asteroid. The condensation, transport, and phase transformation can all be explained within the developed self-consistent framework that reproduces the observed phase assemblage and atomic-scale structure. This framework suggests that planetary materials evolved within a thermodynamically open system and, moving forward, motivates such an approach in order to understand the thermodynamic landscape on which planetary materials formed. © 2021 The Author(s).
    • Atomistic simulation of shape memory effect (SME) and superelasticity (SE) in nano-porous NiTi shape memory alloy (SMA)

      Gur, Sourav; Frantziskonis, George N.; Muralidharan, Krishna; Univ Arizona, Civil Engn & Engn Mech; Univ Arizona, Mat Sci & Engn (ELSEVIER SCIENCE BV, 2018-09)
      Porosity can play an important role in altering the phase transformation characteristics of NiTi shape memory alloys (SMA), thus changing its shape memory as well as its superelasticity properties. This work, based on atomistic simulations of binary NiTi SMA, documents the effects of porosity at the nanometer length scale on phase fraction evolution kinetics, transformation temperatures, and stress-strain response. Classical molecular dynamics simulations are performed using a well-examined and verified Finnis-Sinclair type embedded-atom method interatomic potential. Simulation results for the nano-porous NiTi with various porosity configurations are compared to non-porous NiTi. The martensite phase fraction and transformation temperatures increase noticeably with increasing porosity, and the stress-strain response shows noticeable variation with porosity. The residual strain and hysteretic energy dissipation capacity increase significantly with increasing porosity.
    • The Atoxigenic Biocontrol Product Aflasafe SN01 Is a Valuable Tool to Mitigate Aflatoxin Contamination of Both Maize and Groundnut Cultivated in Senegal

      Senghor, L. A.; Ortega-Beltran, A.; Atehnkeng, J.; Callicott, K. A.; Cotty, P. J.; Bandyopadhyay, R.; Univ Arizona, Sch Plant Sci, USDA ARS (AMER PHYTOPATHOLOGICAL SOC, 2020-02)
      Aflatoxin contamination of groundnut and maize infected by Aspergillus section Flavi fungi is common throughout Senegal. The use of biocontrol products containing atoxigenic Aspergillus flavus strains to reduce crop aflatoxin content has been successful in several regions, but no such products are available in Senegal. The biocontrol product Aflasafe SN01 was developed for use in Senegal. The four active ingredients of Aflasafe SN01 are atoxigenic A. flavus genotypes native to Senegal and distinct from active ingredients used in other biocontrol products. Efficacy tests on groundnut and maize in farmers' fields were carried out in Senegal during the course of 5 years. Active ingredients were monitored with vegetative compatibility analyses. Significant (P < 0.05) displacement of aflatoxin producers occurred in all years, districts, and crops. In addition, crops from Aflasafe SN01-treated fields contained significantly (P < 0.05) fewer aflatoxins both at harvest and after storage. Most crops from treated fields contained aflatoxin concentrations permissible in both local and international markets. Results suggest that Aflasafe SN01 is an effective tool for aflatoxin mitigation in groundnut and maize. Large-scale use of Aflasafe SN01 should provide health, trade, and economic benefits for Senegal.
    • ATP-competitive, marine derived natural products that target the DEAD box helicase, eIF4A

      Tillotson, Joseph; Kedzior, Magdalena; Guimarães, Larissa; Ross, Alison B.; Peters, Tara L.; Ambrose, Andrew J.; Schmidlin, Cody J.; Zhang, Donna D.; Costa-Lotufo, Letícia V.; Rodríguez, Abimael D.; et al. (PERGAMON-ELSEVIER SCIENCE LTD, 2017-09-01)
      Activation of translation initiation is a common trait of cancer cells. Formation of the heterotrimeric eukaryotic initiation factor F (eIF4F) complex is the rate-limiting step in 5' m7GpppN cap-dependent translation. This trimeric complex includes the eIF4E cap binding protein, the eIF4G scaffolding protein, and the DEAD box RNA helicase eIF4A. eIF4A is an ATP-dependent helicase and because it is the only enzyme in the eIF4F complex, it has been shown to be a potential therapeutic target for a variety of malignancies. To this end, we have used a simple ATPase biochemical screen to survey several hundred marine and terrestrial derived natural products. Herein, we report the discovery of two natural products from marine sources, elisabatin A (1) and allolaurinterol (2), which show low mu M inhibition of eIF4A ATPase activity. Enzymological analyses revealed 1 and 2 to be ATP-competitive, and cellular evaluations showed reasonable cytotoxicity against A549 (lung cancer) and MDA-MA-468 (breast cancer) cell lines. However, only compound 2 showed potent inhibition of helicase activity congruent with its ATPase inhibitory activity. (C) 2017 Elsevier Ltd. All rights reserved.
    • AtPIG-S, a predicted Glycosylphosphatidylinositol Transamidase subunit, is critical for pollen tube growth in Arabidopsis

      Desnoyer, Nicholas; Howard, Gregory; Jong, Emma; Palanivelu, Ravishankar; Univ Arizona, Sch Plant Sci (BMC, 2020-08)
      Background Glycosylphosphatidylinositol (GPI) addition is one of the several post-translational modifications to proteins that increase their affinity for membranes. In eukaryotes, the GPI transamidase complex (GPI-T) catalyzes the attachment of pre-assembled GPI anchors to GPI-anchored proteins (GAPs) through a transamidation reaction. A mutation inAtGPI8(gpi8-2), the putative catalytic subunit of GPI-T in Arabidopsis,is transmitted normally through the female gametophyte (FG), indicating the FG tolerates loss of GPI transamidation. In contrast,gpi8-2almost completely abolishes male gametophyte (MG) function. Still, the unexpected finding thatgpi8-2FGs function normally requires further investigation. Additionally, specific developmental defects in the MG caused by loss of GPI transamidation remain poorly characterized. Results Here we investigated the effect of loss ofAtPIG-S,another GPI-T subunit, in both gametophytes. Likegpi8-2, we showed that a mutation inAtPIG-S(pigs-1) disrupted synergid localization of LORELEI (LRE), a putative GAP critical for pollen tube reception by the FG. Still,pigs-1is transmitted normally through the FG. Conversely,pigs-1severely impaired male gametophyte (MG) function during pollen tube emergence and growth in the pistil. ApPIGS:GFP-PIGStransgene complemented these MG defects and enabled generation ofpigs-1/pigs-1seedlings. However, thepPIGS:GFP-PIGStransgene seemingly failed to rescue the function of AtPIG-S in the sporophyte, aspigs-1/pigs-1, pPIGS:GFP-PIGSseedlings died soon after germination. Conclusions Characterization ofpigs-1provided further evidence that the FG tolerates loss of GPI transamidation more than the MG and that the MG compared to the FG may be a better haploid system to study the role of GPI-anchoring.Pigs-1pollen develops normally and thus represent a tool in which GPI anchor biosynthesis and transamidation of GAPs have been uncoupled, offering a potential way to study free GPI in plant development. While previously reported male fertility defects of GPI biosynthesis mutants could have been due either to loss of GPI or GAPs lacking the GPI anchor, our results clarified that the loss of mature GAPs underlie male fertility defects of GPI-deficient pollen grains, aspigs-1is defective only in the downstream transamidation step.
    • Atrial Septal Defect with Eisenmenger Syndrome: A Rare Presentation

      Forlemu, Arnold Nongmoh; Ajmal, Muhammad; Saririan, Mehrdad; Univ Arizona, Coll Med Tucson, Sarver Heart Ctr, Dept Cardiol (HINDAWI LTD, 2020-03-09)
      Atrial septal defects (ASDs) are common congenital heart defects (CHD). The clinical course in patients without closure of the ASD is associated with significant morbidity and mortality in advanced age. A small percentage of patients may develop pulmonary arterial hypertension (PAH) due to left to right shunting that impacts morbidity and mortality. Advances in prenatal screening and fetal echocardiography have allowed timely interventions. Nonetheless, some patients still may be diagnosed with ASD in adulthood as an incidental finding or presenting with clinical symptoms such as shortness of breath from right heart failure. We report a case of an adult female presenting with shortness of breath due to ASD causing PAH with Eisenmenger physiology.
    • Attack Transferability Against Information-Theoretic Feature Selection

      Gupta, S.; Golota, R.; Ditzler, G.; Department of Electrical & Computer Engineering, University of Arizona (Institute of Electrical and Electronics Engineers Inc., 2021)
      Machine learning (ML) is vital to many application-driven fields, such as image and signal classification, cyber-security, and health sciences. Unfortunately, many of these fields can easily have their training data tampered with by an adversary to thwart an ML algorithm&#x2019;s objective. Further, the adversary can impact any stage in an ML pipeline (e.g., preprocessing, learning, and classification). Recent work has shown that many models can be attacked by poisoning the training data, and the impact of the poisoned data can be quite significant. Prior works on adversarial feature selection have shown that the attacks can damage feature selection (FS). Filter FS algorithms, a type of FS, are widely used for their ability to model nonlinear relationships, classifier independence and lower computational requirements. One important question from the security perspective of these widely used approaches is, whether filter FS algorithms are robust against other FS attacks. In this work, we focus on the task of information-theoretic filter FS such MIM, MIFS, and mRMR, and the impact that gradient-based attack can have on these selections. The experiments on five benchmark datasets demonstrate that the stability of different information-theoretic algorithms can be significantly degraded by injecting poisonous data into the training dataset. CCBY
    • Attaining quantum limited precision of localizing an object in passive imaging

      Sajjad, A.; Grace, M.R.; Zhuang, Q.; Guha, S.; James C. Wyant College of Optical Sciences, University of Arizona; Department of Electrical and Computer Engineering, University of Arizona (American Physical Society, 2021)
      We investigate our ability to determine the mean position, or centroid, of a linear array of equally bright incoherent point sources of light whose continuum limit is the problem of estimating the center of a uniformly radiating object. We consider two receivers, an image-plane ideal direct-detection imager and a receiver that employs Hermite-Gaussian (HG) spatial-mode demultiplexing in the image plane, prior to shot-noise-limited photon detection. We compare the Fisher information (FI) for estimating the centroid achieved by these two receivers, which quantifies the information-accrual rate per photon, and compare those with the quantum Fisher information (QFI): the maximum attainable FI by any choice of measurement on the collected light allowed by physics. We find that focal-plane direct imaging is strictly suboptimal, although not by a large margin. We also find that not only is the HG mode sorter, which is the optimal measurement for estimating the separation between point sources (or the length of a line object), suboptimal, but it performs worse than direct imaging. We study the scaling behavior of the QFI and direct imaging's FI for a continuous uniformly bright object in terms of its length and find that both are inversely proportional to the object's length when it is sufficiently larger than the Rayleigh length. Finally, we propose a two-stage adaptive modal receiver design that attains the QFI for centroid estimation. © 2021 American Physical Society.
    • Attaining the quantum limit of superresolution in imaging an object's length via predetection spatial-mode sorting

      Dutton, Zachary; Kerviche, Ronan; Ashok, Amit; Guha, Saikat; Univ Arizona, Coll Opt Sci (AMER PHYSICAL SOC, 2019-03-25)
      We consider estimating the length of an incoherently radiating quasimonochromatic extended object of length much smaller than the traditional diffraction limit, the Rayleigh length. This is the simplest abstraction of the problems of estimating the diameter of a star in astronomical imaging or the dimensions of a cellular feature in biological imaging. We find, as expected by the Rayleigh criterion, that the Fisher information (FI) of the object's length, per integrated photon, vanishes in the limit of small sub-Rayleigh length for an ideal image-plane direct-detection receiver. With an image-plane Hermite-Gaussian (HG) mode sorter followed by direct detection, we show that this normalized FI does not diminish with decreasing object length. The FI per photon of both detection strategies gradually decreases as the object length greatly exceeds the Rayleigh limit, due to the relative inefficiency of information provided by photons emanating from near the center of the object about its length. We evaluate the quantum Fisher information per unit integrated photon and find that the HG mode sorter exactly achieves this limit at all values of the object length. Further, a simple binary mode sorter maintains the advantage of the full mode sorter at highly sub-Rayleigh lengths. In addition to this FI analysis, we quantify improvement in terms of the actual mean-square error of the length estimate using predetection mode sorting. We consider the effect of imperfect mode sorting and show that the performance improvement over direct detection is robust over a range of sub-Rayleigh lengths.
    • An Attempt to Probe the Radio Jet Collimation Regions in NGC 4278, NGC 4374 (M84), and NGC 6166

      Ly, C.; Walker, R. C.; Wrobel, J. M.; Univ Arizona, Steward Observ (IOP Publishing, 2004-01)
      NRAO Very Long Baseline Array (VLBA) observations of NGC 4278, NGC 4374 (M84), NGC 6166, and M87 (NGC 4486) have been made at 43 GHz in an effort to image the jet collimation region. This is the first attempt to image the first three sources at 43 GHz using very long baseline interferometry (VLBI) techniques. These three sources were chosen because their estimated black hole mass and distance implied a Schwarzschild radius with large angular size, giving hope that the jet collimation regions could be studied. Phase referencing was utilized for the three sources because of their expected low flux densities. M87 was chosen as the calibrator for NGC 4374 because it satisfied the phase-referencing requirements: near the source and sufficiently strong. Having observed M87 for a long integration time, we have detected its subparsec jet, allowing us to confirm previous high-resolution observations made by Junor, Biretta, & Livio, who have indicated that a wide opening angle was seen near the base of the jet. Phase referencing successfully improved our image sensitivity, yielding detections and providing accurate positions for NGC 4278, NGC 4374, and NGC 6166. These sources are point dominated but show suggestions of extended structure in the direction of the large-scale jets. However, higher sensitivity will be required to study their subparsec jet structure.
    • Attenuated Activity across Multiple Cell Types and Reduced Monosynaptic Connectivity in the Aged Perirhinal Cortex

      Maurer, Andrew P.; Burke, Sara N.; Diba, Kamran; Barnes, Carol A.; Univ Arizona, Evelyn F McKnight Brain Inst; Univ Arizona, Div Neural Syst Memory & Aging; Univ Arizona, Dept Psychol; Univ Arizona, Dept Neurol; Univ Arizona, Dept Neurosci (SOC NEUROSCIENCE, 2017-09-13)
      The perirhinal cortex (PER), which is critical for associative memory and stimulus discrimination, has been described as a wall of inhibition between the neocortex and hippocampus. With advanced age, rats show deficits on PER-dependent behavioral tasks and fewer PER principal neurons are activated by stimuli, but the role of PER interneurons in these altered circuit properties in old age has not been characterized. In the present study, PER neurons were recorded while rats traversed a circular track bidirectionally in which the track was either empty or contained eight novel objects evenly spaced around the track. Putative interneurons were discriminated from principal cells based on the autocorrelogram, waveform parameters, and firing rate. While object modulation of interneuron firing was observed in both young and aged rats, PER interneurons recorded from old animals had lower firing rates compared with those from young animals. This difference could not be accounted for by differences in running speed, as the firing rates of PER interneurons did not show significant velocity modulation. Finally, in the aged rats, relative to young rats, there was a significant reduction in detected excitatory and inhibitory monosynaptic connections. Together these data suggest that with advanced age there may be reduced afferent drive from excitatory cells onto interneurons that may compromise the wall of inhibition between the hippocampus and cortex. This circuit dysfunction could erode the function of temporal lobe networks and ultimately contribute to cognitive aging.
    • Attenuated Late-Phase Arc Transcription in the Dentate Gyrus of Mice Lacking Egr3

      Maple, Amanda; Lackie, Rachel E.; Elizalde, Diana I.; Grella, Stephanie L.; Damphousse, Chelsey C.; Xa, Collin; Gallitano, Amelia L.; Marrone, Diano F.; Univ Arizona, Dept Basic Med Sci; Univ Arizona, McKnight Brain Inst; et al. (HINDAWI LTD, 2017)
      The dentate gyrus (DG) engages in sustained Arc transcription for at least 8 hours following behavioral induction, and this time course may be functionally coupled to the unique role of the DG in hippocampus-dependent learning and memory. The factors that regulate long-term DG Arc expression, however, remain poorly understood. Animals lacking Egr(3) show less Arc expression following convulsive stimulation, but the effect of Egr3 ablation on behaviorally induced Arc remains unknown. To address this, Egr3(-/-) and wild-type (WT) mice explored novel spatial environments and were sacrificed either immediately or after 5, 60, 240, or 480 minutes, and Arc expression was quantified by fluorescence in situ hybridization. Although short-term (i.e., within 60 min) Arc expression was equivalent across genotypes, DG Arc expression was selectively reduced at 240 and 480 minutes in mice lacking Egr3. These data demonstrate the involvement of Egr3 in regulating the late protein-dependent phase of Arc expression in the DG.
    • Attenuation of cGAS/STING activity during mitosis

      Uhlorn, Brittany L; Gamez, Eduardo R; Li, Shuaizhi; Campos, Samuel K; Univ Arizona, Canc Biol Grad Interdisciplinary Program; Univ Arizona, Dept Physiol; Univ Arizona, Dept Immunobiol; Univ Arizona, BIO5 Inst; Univ Arizona, Dept Mol & Cellular Biol (LIFE SCIENCE ALLIANCE LLC, 2020-07-13)
      The innate immune system recognizes cytosolic DNA associated with microbial infections and cellular stress via the cGAS/STING pathway, leading to activation of phospho-IRF3 and downstream IFN-I and senescence responses. To prevent hyperactivation, cGAS/ STING is presumed to be nonresponsive to chromosomal self-DNA during open mitosis, although specific regulatory mechanisms are lacking. Given a role for the Golgi in STING activation, we investigated the state of the cGAS/STING pathway in interphase cells with artificially vesiculated Golgi and in cells arrested in mitosis. We find that whereas cGAS activity is impaired through interaction with mitotic chromosomes, Golgi integrity has little effect on the enzyme's production of cGAMP. In contrast, STING activation in response to either foreign DNA (cGAS-dependent) or exogenous cGAMP is impaired by a vesiculated Golgi. Overall, our data suggest a secondary means for cells to limit potentially harmful cGAS/ STING responses during open mitosis via natural Golgi vesiculation.