• Carbon photochemical escape rates from the modern Mars atmosphere

      Lo, Daniel Y.; Yelle, Roger V.; Lillis, Robert J.; Deighan, Justin I.; Lunar and Planetary Laboratory, The University of Arizona (Academic Press Inc., 2021-02-14)
      We provide a comprehensive update of photochemical escape rates of atomic carbon from the present-day Martian atmosphere using a one-dimensional photochemical model and a Monte Carlo escape model. The photochemical model incorporates new results relevant to carbon photochemistry at Mars, including new cross sections for photodissociation of CO2 into C and O2 (Lu et al. 2014) and electron impact dissociation of CO (Ajello et al. 2019). We find the newly included channel of CO2 photodissociation to be the largest contributor to C escape, at 34%–58%. CO photodissociation and CO+ dissociative recombination, which have been discussed extensively in the literature, also show up as significant sources of hot C atoms, with respective contributions of 15%–23% and 7%–10%. Electron impact dissociation of CO2 (11%–15%) and photoionization of CO (6%–20%) are also important channels. Overall, escape rates vary over 3–11×1023 s−1, with an increase of 70% at perihelion compared to aphelion, and a much larger increase of 133% at solar maximum compared to solar minimum. While these present escape rates give a total integrated escape of only 1.3 mbar of CO2 when multiplied by 3.6 billion years, the better characterization of carbon photochemistry and escape from this study will enable us to more reliably extrapolate backwards in time to when conditions of the Martian atmosphere were significantly different from those of today.
    • Distinct and common neural coding of semantic and non-semantic control demands

      Gao, Zhiyao; Zheng, Li; Chiou, Rocco; Gouws, André; Krieger-Redwood, Katya; Wang, Xiuyi; Varga, Dominika; Ralph, Matthew A Lambon; Smallwood, Jonathan; Jefferies, Elizabeth; et al. (Academic Press Inc., 2021-06-02)
      The flexible retrieval of knowledge is critical in everyday situations involving problem solving, reasoning and social interaction. Current theories emphasise the importance of a left-lateralised semantic control network (SCN) in supporting flexible semantic behaviour, while a bilateral multiple-demand network (MDN) is implicated in executive functions across domains. No study, however, has examined whether semantic and non-semantic demands are reflected in a common neural code within regions specifically implicated in semantic control. Using functional MRI and univariate parametric modulation analysis as well as multivariate pattern analysis, we found that semantic and non-semantic demands gave rise to both similar and distinct neural responses across control-related networks. Though activity patterns in SCN and MDN could decode the difficulty of both semantic and verbal working memory decisions, there was no shared common neural coding of cognitive demands in SCN regions. In contrast, regions in MDN showed common patterns across manipulations of semantic and working memory control demands, with successful cross-classification of difficulty across tasks. Therefore, SCN and MDN can be dissociated according to the information they maintain about cognitive demands.
    • Evolving choice sets: The effect of dynamic (vs. static) choice sets on preferences

      Reich, Taly; Savary, Jennifer; Kupor, Daniella; Eller College of Management, University of Arizona (Academic Press Inc., 2021-04-07)
      Most decision-making research examines static choice sets, with fixed options presented all at once. In contrast, people often make decisions from dynamic choice sets, in which new alternatives arise during the decision process. We show that compared to a static choice set, a dynamic choice set can systematically affect preferences, even when the final choice is from an identical set of options. Moreover, dynamic presentation can have opposite effects on preferences. To explain these patterns we propose a unified theory based on perceived variance of the attribute distribution. When dynamic presentation increases the perceived variance of a focal attribute, preferences shift towards the option that is best on that attribute. In contrast, when dynamic presentation reduces perceived variance of a focal attribute, preferences shift towards the option that is best on a non-focal attribute. Five studies examine this proposal using asymmetrically dominated and compromise choice sets. © 2021 Elsevier Inc.
    • A general computational framework for the dynamics of single- and multi-phase vesicles and membranes

      Zhang, Tiankui; Wolgemuth, Charles W; Department of Physics, University of Arizona; Department of Molecular and Cellular Biology, University of Arizona (Academic Press Inc., 2021-11-08)
      The dynamics of thin, membrane-like structures are ubiquitous in nature. They play especially important roles in cell biology. Cell membranes separate the inside of a cell from the outside, and vesicles compartmentalize proteins into functional microregions, such as the lysosome. Proteins and/or lipid molecules also aggregate and deform membranes to carry out cellular functions. For example, some viral particles can induce the membrane to invaginate and form an endocytic vesicle that pulls the virus into the cell. While the physics of membranes has been extensively studied since the pioneering work of Helfrich in the 1970's, simulating the dynamics of large scale deformations remains challenging, especially for cases where the membrane composition is spatially heterogeneous. Here, we develop a general computational framework to simulate the overdamped dynamics of membranes and vesicles. We start by considering a membrane with an energy that is a generalized functional of the shape invariants and also includes line discontinuities that arise due to phase boundaries. Using this energy, we derive the internal restoring forces and construct a level set-based algorithm that can stably simulate the large-scale dynamics of these generalized membranes, including scenarios that lead to membrane fission. This method is applied to solve for shapes of single-phase vesicles using a range of reduced volumes, reduced area differences, and preferred curvatures. Our results match well the experimentally measured shapes of corresponding vesicles. The method is then applied to explore the dynamics of multiphase vesicles, predicting equilibrium shapes and conditions that lead to fission near phase boundaries.
    • Infrared neural stimulation with 7T fMRI: A rapid in vivo method for mapping cortical connections of primate amygdala

      Shi, Sunhang; Xu, Augix Guohua; Rui, Yun-Yun; Zhang, Xiaotong; Romanski, Lizabeth M; Gothard, Katalin M; Roe, Anna Wang; Dept of Physiology, University of Arizona (Academic Press Inc., 2021-02-04)
      We have previously shown that INS-fMRI is a rapid method for mapping mesoscale brain networks in the macaque monkey brain. Focal stimulation of single cortical sites led to the activation of connected cortical locations, resulting in a global connectivity map. Here, we have extended this method for mapping brainwide networks following stimulation of single subcortical sites. As a testbed, we focused on the basal nucleus of the amygdala in the macaque monkey. We describe methods to target basal nucleus locations with submillimeter precision, pulse train stimulation methods, and statistical tests for assessing non-random nature of activations. Using these methods, we report that stimulation of precisely targeted loci in the basal nucleus produced sparse and specific activations in the brain. Activations were observed in the insular and sensory association cortices as well as activations in the cingulate cortex, consistent with known anatomical connections. What is new here is that the activations were focal and, in some cases, exhibited shifting topography with millimeter shifts in stimulation site. The precision of the method enables networks mapped from different nearby sites in the basal nucleus to be distinguished. While further investigation is needed to improve the sensitivity of this method, our analyses do support the reproducibility and non-random nature of some of the activations. We suggest that INS-fMRI is a promising method for mapping large-scale cortical and subcortical networks at high spatial resolution. © 2021 The Author(s)
    • OSSOS: The eccentricity and inclination distributions of the stable Neptunian Trojans

      Lin, Hsing Wen; Chen, Ying-Tung; Volk, Kathryn; Gladman, Brett; Murray-Clay, Ruth; Alexandersen, Mike; Bannister, Michele T.; Lawler, Samantha M.; Ip, Wing-Huen; Lykawka, Patryk Sofia; et al. (Academic Press Inc., 2021-02-19)
      The minor planets on orbits that are dynamically stable in Neptune's 1:1 resonance on Gyr timescales were likely em:laced by Neptune's outward migration. We explore the intrinsic libration amplitude, eccentricity, and inclination distribution of Neptune's stable Trojans, using the detections and survey efficiency of the Outer Solar System Origins Survey (OSSOS) and Pan-STARRS1. We find that the libration amplitude of the stable Neptunian Trojan population can be well modeled as a Rayleigh distribution with a libration amplitude width σAϕ of 15°. When taken as a whole, the Neptune Trojan population can be acceptably modeled with a Rayleigh eccentricity distribution of width σe of 0.045 and a typical sin(i) × Gaussian inclination distribution with a width σi of 14±2∘; however, these distributions are only marginally acceptable. This is likely because, even after accounting for survey detection biases, the known large (Hr<8) and small (Hr≥8) Neptune Trojans appear to have markedly different eccentricities and inclinations. We propose that like the classical Kuiper belt, the stable intrinsic Neptunian Trojan population have dynamically ‘hot’ and dynamically ‘cold’ components to its eccentricity/inclination distribution, with σe−cold∼0.02/σi−cold∼6° and σe−hot∼0.05/σi−hot∼18°. In this scenario, the ‘cold’ L4 Neptunian Trojan population lacks the Hr≥8.0 members and has 13−6+11 ‘cold’ Trojans with Hr<8.0. On the other hand, the ‘hot’ L4 Neptunian Trojan population has 136−75+84 Trojans with Hr<10 — a population 2.4 times greater than that of the L4 Jovian Trojans in the same luminosity range.
    • Spectral signatures of L-DOPA-induced dyskinesia depend on L-DOPA dose and are suppressed by ketamine

      Ye, Tony; Bartlett, Mitchell J; Sherman, Scott J; Falk, Torsten; Cowen, Stephen L; Department of Neurology, University of Arizona College of Medicine; Department of Pharmacology, University of Arizona College of Medicine; Department of Psychology, University of Arizona College of Medicine (Academic Press Inc., 2021-03-02)
      L-DOPA-induced dyskinesias (LID) are debilitating motor symptoms of dopamine-replacement therapy for Parkinson's disease (PD) that emerge after years of L-DOPA treatment. While there is an abundance of research into the cellular and synaptic origins of LID, less is known about how LID impacts systems-level circuits and neural synchrony, how synchrony is affected by the dose and duration of L-DOPA exposure, or how potential novel treatments for LID, such as sub-anesthetic ketamine, alter this activity. Sub-anesthetic ketamine treatments have recently been shown to reduce LID, and ketamine is known to affect neural synchrony. To investigate these questions, we measured movement and local-field potential (LFP) activity from the motor cortex (M1) and the striatum of preclinical rodent models of PD and LID. In the first experiment, we investigated the effect of the LID priming procedures and L-DOPA dose on neural signatures of LID. Two common priming procedures were compared: a high-dose procedure that exposed unilateral 6-hydroxydopamine-lesioned rats to 12 mg/kg L-DOPA for 7 days, and a low-dose procedure that exposed rats to 7 mg/kg L-DOPA for 21 days. Consistent with reports from other groups, 12 mg/kg L-DOPA triggered LID and 80-Hz oscillations; however, these 80-Hz oscillations were not observed after 7 mg/kg administration despite clear evidence of LID, indicating that 80-Hz oscillations are not an exclusive signature of LID. We also found that weeks-long low-dose priming resulted in the emergence of non-oscillatory broadband gamma activity (> 30 Hz) in the striatum and theta-to-high-gamma cross-frequency coupling (CFC) in M1. In a second set of experiments, we investigated how ketamine exposure affects spectral signatures of low-dose L-DOPA priming. During each neural recording session, ketamine was delivered through 5 injections (20 mg/kg, i.p.) administered every 2 h. We found that ketamine exposure suppressed striatal broadband gamma associated with LID but enhanced M1 broadband activity. We also found that M1 theta-to-high-gamma CFC associated with the LID on-state was suppressed by ketamine. These results suggest that ketamine's therapeutic effects are region specific. Our findings also have clinical implications, as we are the first to report novel oscillatory signatures of the common low-dose LID priming procedure that more closely models dopamine replacement therapy in individuals with PD. We also identify neural correlates of the anti-dyskinetic activity of sub-anesthetic ketamine treatment.