Radioactive Iron Rain: Transporting 60^{60}Fe in Supernova Dust to the Ocean Floor

Several searches have found evidence of $^{60}$Fe deposition, presumably from a near-Earth supernova (SN), with concentrations that vary in different locations on Earth. This paper examines various influences on the path of interstellar dust carrying $^{60}$Fe from a SN through the heliosphere, with the aim of estimating the final global distribution on the ocean floor. We study the influences of magnetic fields, angle of arrival, wind and ocean cycling of SN material on the concentrations at different locations. We find that the passage of SN material through the mesosphere/lower thermosphere (MLT) is the greatest influence on the final global distribution, with ocean cycling causing lesser alteration as the SN material sinks to the ocean floor. SN distance estimates in previous works that assumed a uniform distribution are a good approximation. Including the effects on surface distributions, we estimate a distance of $46^{+10}_{-6}$ pc for a $8-10 \ M_{\odot}$ SN progenitor. This is consistent with a SN occurring within the Tuc-Hor stellar group $\sim$2.8 Myr ago with SN material arriving on Earth $\sim$2.2 Myr ago. We note that the SN dust retains directional information to within $1^{\circ}$ through its arrival in the inner Solar System, so that SN debris deposition on inert bodies such as the Moon will be anisotropic, and thus could in principle be used to infer directional information. In particular, we predict that existing lunar samples should show measurable $^{60}$Fe differences.Comment: 18 pages, 8 figures. Comments welcom

Astrophysical Shrapnel: Discriminating Among Near-Earth Stellar Explosion Sources of Live Radioactive Isotopes

We consider the production and deposition on Earth of isotopes with half-lives in the range 10$^{5}$ to 10$^{8}$ years that might provide signatures of nearby stellar explosions, extending previous analyses of Core-Collapse Supernovae (CCSNe) to include Electron-Capture Supernovae (ECSNe), Super-Asymptotic Giant Branch (SAGBs) stars, Thermonuclear/Type Ia Supernovae (TNSNe), and Kilonovae/Neutron Star Mergers (KNe). We revisit previous estimates of the $^{60}$Fe and $^{26}$Al signatures, and extend these estimates to include $^{244}$Pu and $^{53}$Mn. We discuss interpretations of the $^{60}$Fe signals in terrestrial and lunar reservoirs in terms of a nearby stellar ejection ~2.2 Myr ago, showing that (i) the $^{60}$Fe yield rules out the TNSN and KN interpretations, (ii) the $^{60}$Fe signals highly constrain a SAGB interpretation but do not completely them rule out, (iii) are consistent with a CCSN origin, and (iv) are highly compatible with an ECSN interpretation. Future measurements could resolve the radioisotope deposition over time, and we use the Sedov blast wave solution to illustrate possible time-resolved profiles. Measuring such profiles would independently probe the blast properties including distance, and would provide additional constraints the nature of the explosion.Comment: 38 pages, 6 figures. Comments welcom

Spinal cord pathology in chronic traumatic encephalopathy with motor neuron disease

Chronic Traumatic Encephalopathy (CTE) is a neurodegenerative disease caused by repetitive head trauma and mild traumatic brain injuries (mTBIs) and has been associated with contact sports such as football, boxing, and ice hockey. CTE is a slowly progressing neurological disease that is often clinically associated with symptoms of memory loss, decline in cognitive function, behavioral changes such as increased impulsivity and aggression, and/or suicidal thoughts. Advanced stages of the disease present with more severe neurological changes such as dementia, speech and gait abnormalities, and parkinsonism. Amyotrophic Lateral Sclerosis (ALS, also known as Lou Gehrig Disease) is a progressive and fatal neurodegenerative disease characterized by motor neuron loss and corticospinal tract degeneration. While 90-95% of ALS cases are sporadic in nature, many genetic mutations have been identified that contribute to familial forms of the disease. The etiology of sporadic ALS is unknown but it is likely caused by a complex interaction of various genetic and environmental risk factors. Epidemiological evidence suggests that one such risk factor is brain trauma, the main risk factor associated with the development of CTE. In this study the spinal cord tissue of twelve athletes diagnosed with CTE who also developed a progressive motor neuron disease and showed symptoms of profound muscle weakness, atrophy, spasticity, and fasciculations several years before death was examined. The spinal cord tissue from these 12 CTE cases with motor neuron disease (CTE+MND) was compared to the spinal cord tissue of 10 sporadic ALS control cases. Results showed a difference in frequency of tau pathology between the two disease cohorts, as one-third of CTE+MND cases and none of the ALS cases showed tau immunoreactivity. In addition, TDP-43 immunoreactivity was present in every CTE+MND case but one and was present in all ALS cases. Motor neuron inclusions were positive for both FUS and p62 in both cohorts, and no distinct differences were observed cystatin C pathology. Overall, this suggests that the spinal cord inclusions in CTE+MND have a similar composition to sporadic ALS. However, there is an increased frequency of tau pathology in CTE+MND though this result did not reach statistical significance in this study

Rotational spectrum of cis–cis HOONO

The pure rotational spectrum of cis-cis peroxynitrous acid, HOONO, has been observed. Over 220 transitions, sampling states up to J(')=67 and K-a(')=31, have been fitted with an rms uncertainty of 48.4 kHz. The experimentally determined rotational constants agree well with ab initio values for the cis-cis conformer, a five-membered ring formed by intramolecular hydrogen bonding. The small, positive inertial defect Delta=0.075667(60) amu A(2) and lack of any observable torsional splittings in the spectrum indicate that cis-cis HOONO exists in a well-defined planar structure at room temperature

Rotational spectroscopy and dipole moment of cis-cis HOONO and DOONO

The rotational spectrum of cis-cis HOONO has been studied over a broad range of frequencies, 13–840 GHz, using pulsed beam Fourier-transform microwave spectroscopy and room-temperature flow cell submillimeter spectroscopy. The rotational spectrum of the deuterated isotopomer, cis-cis DOONO, has been studied over a subset of this range, 84–640 GHz. Improved spectroscopic constants have been determined for HOONO, and the DOONO spectrum is analyzed for the first time. Weak-field Stark effect measurements in the region of 84–110 GHz have been employed to determine the molecular dipole moments of cis-cis HOONO [µa=0.542(8) D,µb=0.918(15) D,µ=1.07(2) D] and DOONO [µa=0.517(9) D,µb=0.930(15) D,µ=1.06(2) D]. The quadrupole coupling tensor in the principal inertial axis system for the 14N nucleus has been determined to be chiaa=1.4907(25) MHz,chibb=–4.5990(59) MHz,chiab=3.17(147) MHz, and chicc=3.1082(59) MHz. Coordinates of the H atom in the center-of-mass frame have been determined with use of the Kraitchman equations, |aH|=0.516 Å and |bH|=1.171 Å. The inertial defects of HOONO and DOONO are consistent with a planar equilibrium structure with significant out-of-plane H atom torsional motion. Comparisons of the present results are made to ab initio calculations

Superior lentiviral vectors designed for BSL-0 environment abolish vector mobilization.

Lentiviral vector mobilization following HIV-1 infection of vector-transduced cells poses biosafety risks to vector-treated patients and their communities. The self-inactivating (SIN) vector design has reduced, however, not abolished mobilization of integrated vector genomes. Furthermore, an earlier study demonstrated the ability of the major product of reverse transcription, a circular SIN HIV-1 vector comprising a single- long terminal repeat (LTR) to support production of high vector titers. Here, we demonstrate that configuring the internal vector expression cassette in opposite orientation to the LTRs abolishes mobilization of SIN vectors. This additional SIN mechanism is in part premised on induction of host PKR response to double-stranded RNAs comprised of mRNAs transcribed from cryptic transcription initiation sites around 3'SIN-LTR's and the vector internal promoter. As anticipated, PKR response following transfection of opposite orientation vectors, negatively affects their titers. Importantly, shRNA-mediated knockdown of PKR rendered titers of SIN HIV-1 vectors comprising opposite orientation expression cassettes comparable to titers of conventional SIN vectors. High-titer vectors carrying an expression cassette in opposite orientation to the LTRs efficiently delivered and maintained high levels of transgene expression in mouse livers. This study establishes opposite orientation expression cassettes as an additional PKR-dependent SIN mechanism that abolishes vector mobilization from integrated and episomal SIN lentiviral vectors

Supernova shrapnel: nearby supernovae and dust transport in the ISM

The last 2 decades have seen the proposal, detection, and confirmation of live ^60Fe radioisotopes from an extra-solar source on Earth, showing an event outside the Solar System directly delivered material to the Earth since its formation. This work examines the possible sources for the ^60Fe and models the passage of the material from its source through the Solar System to the ocean floor. We consider the production and deposition on Earth of isotopes with half-lives in the range 10^5 to 10^8 years that might provide signatures of nearby stellar explosions, extending previous analyses of Core-Collapse Supernovae (CCSNe) to include Electron-Capture Supernovae (ECSNe), Super-Asymptotic Giant Branch (SAGBs) stars, Thermonuclear/Type Ia Supernovae (TNSNe), and Kilonovae/Neutron Star Mergers (KNe). We revisit previous estimates of the ^60Fe and ^26Al signatures, and extend these estimates to include ^244Pu and ^53Mn. We show that (i) the ^60Fe yield rules out the TNSN and KN interpretations, (ii) the ^60Fe signals highly constrain a SAGB interpretation but do not completely them rule out, (iii) are consistent with a CCSN origin, and (iv) are highly compatible with an ECSN interpretation. We also examine various influences on the path of interstellar dust carrying ^60Fe from a SN through the Heliosphere, with the aim of estimating the final global distribution on the ocean floor. We study the influences of magnetic fields, angle of arrival, wind and ocean cycling of SN material on the concentrations at different locations. We find that the passage of SN material through the mesosphere/lower thermosphere (MLT) is the greatest influence on the final global distribution, with ocean cycling causing lesser alteration as the SN material sinks to the ocean floor. SN distance estimates in previous works that assumed a uniform distribution are a good approximation. Including the effects on surface distributions, we estimate a distance of 46^(+10)_(-6) pc for an ECSN progenitor. We note that the SN dust retains directional information to within 1^(circ) through its arrival in the inner Solar System, so that SN debris deposition on inert bodies such as the Moon will be anisotropic, and thus could in principle be used to infer directional information. Lastly, we examine the various influences on the path of dust within a SN remnant (SNR) to determine when/if the dust decouples from the plasma, how much it is sputtered, and where within the ejecta the dust is located. We find that the inclusion of Rayleigh-Taylor (R-T) instabilities are important in studying dust survival as R-T instabilities influence the location of the SN's reverse shock. We also find the presence of a magnetic field within the shocked ISM material will limit the passage of SN dust grains reflecting them or trapping within the heart of the SNR