Output Stability and Semilinear Sets in Chemical Reaction Networks and Deciders

Abstract. We study the set of output stable configurations of chemical reaction deciders (CRDs). It turns out that CRDs with only bimolecular reactions (which are almost equivalent to population protocols) have a special structure that allows for an algorithm to efficiently calculate the (finite) set of minimal output stable configurations. As a consequence, a relatively large sequence of configurations may be efficiently checked for output stability. We also provide a number of observations regarding the semilinearity result of Angluin et al. [Distrib. Comput., 2007] from the context of population protocols (which is a central result for output stable CRDs). In particular, we observe that the computation-friendly class of totally stable CRDs has equal expressive power as the larger class of output stable CRDs.

HD 2685 b: A hot Jupiter orbiting an early F-type star detected by TESS

We report on the confirmation of a transiting giant planet around the relatively hot (Teff = 6801 ± 76 K) star HD 2685, whose transit signal was detected in Sector 1 data of NASA's TESS mission. We confirmed the planetary nature of the transit signal using Doppler velocimetric measurements with CHIRON, CORALIE, and FEROS, as well as using photometric data obtained with the Chilean-Hungarian Automated Telescope and the Las Cumbres Observatory. From the joint analysis of photometry and radial velocities, we derived the following parameters for HD 2685 b: P = 4.12688-0.00004+0.00005 days, e = 0.091-0.047+0.039, MP = 1.17 ± 0.12 MJ, and RP =1.44 ± 0.05 RJ. This system is a typical example of an inflated transiting hot Jupiter in a low-eccentricity orbit. Based on the apparent visual magnitude (V = 9.6 mag) of the host star, this is one of the brightest known stars hosting a transiting hot Jupiter, and it is a good example of the upcoming systems that will be detected by TESS during the two-year primary mission. This is also an excellent target for future ground- and space-based atmospheric characterization as well as a good candidate for measuring the projected spin-orbit misalignment angle through the Rossiter-McLaughlin effect

A giant planet candidate transiting a white dwarf

Astronomers have discovered thousands of planets outside the Solar System1, most of which orbit stars that will eventually evolve into red giants and then into white dwarfs. During the red giant phase, any close-orbiting planets will be engulfed by the star2, but more distant planets can survive this phase and remain in orbit around the white dwarf3,4. Some white dwarfs show evidence for rocky material floating in their atmospheres5, in warm debris disks6–9 or orbiting very closely10–12, which has been interpreted as the debris of rocky planets that were scattered inwards and tidally disrupted13. Recently, the discovery of a gaseous debris disk with a composition similar to that of ice giant planets14 demonstrated that massive planets might also find their way into tight orbits around white dwarfs, but it is unclear whether these planets can survive the journey. So far, no intact planets have been detected in close orbits around white dwarfs. Here we report the observation of a giant planet candidate transiting the white dwarf WD 1856+534 (TIC 267574918) every 1.4 days. We observed and modelled the periodic dimming of the white dwarf caused by the planet candidate passing in front of the star in its orbit. The planet candidate is roughly the same size as Jupiter and is no more than 14 times as massive (with 95 per cent confidence). Other cases of white dwarfs with close brown dwarf or stellar companions are explained as the consequence of common-envelope evolution, wherein the original orbit is enveloped during the red giant phase and shrinks owing to friction. In this case, however, the long orbital period (compared with other white dwarfs with close brown dwarf or stellar companions) and low mass of the planet candidate make common-envelope evolution less likely. Instead, our findings for the WD 1856+534 system indicate that giant planets can be scattered into tight orbits without being tidally disrupted, motivating the search for smaller transiting planets around white dwarfs

Enhanced Degradation of TCE on a Superfund Site Using Endophyte-Assisted Poplar Tree Phytoremediation

Trichloroethylene (TCE) is a widespread environmental pollutant common in groundwater plumes associated with industrial manufacturing areas. We had previously isolated and characterized a natural bacterial endophyte, Enterobacter sp. strain PDN3, of poplar trees, that rapidly metabolizes TCE, releasing chloride ion. We now report findings from a successful three-year field trial of endophyte-assisted phytoremediation on the Middlefield-Ellis-Whisman Superfund Study Area TCE plume in the Silicon Valley of California. The inoculated poplar trees exhibited increased growth and reduced TCE phytotoxic effects with a 32% increase in trunk diameter compared to mock-inoculated control poplar trees. The inoculated trees excreted 50% more chloride ion into the rhizosphere, indicative of increased TCE metabolism in planta. Data from tree core analysis of the tree tissues provided further supporting evidence of the enhanced rate of degradation of the chlorinated solvents in the inoculated trees. Test well groundwater analyses demonstrated a marked decrease in concentration of TCE and its derivatives from the tree-associated groundwater plume. The concentration of TCE decreased from 300 \u3bcg/L upstream of the planted area to less than 5 \u3bcg/L downstream of the planted area. TCE derivatives were similarly removed with cis-1,2-dichloroethene decreasing from 160 \u3bcg/L to less than 5 \u3bcg/L and trans-1,2-dichloroethene decreasing from 3.1 \u3bcg/L to less than 0.5 \u3bcg/L downstream of the planted trees. 1,1-dichloroethene and vinyl chloride both decreased from 6.8 and 0.77 \u3bcg/L, respectively, to below the reporting limit of 0.5 \u3bcg/L providing strong evidence of the ability of the endophytic inoculated trees to effectively remove TCE from affected groundwater. The combination of native pollutant-degrading endophytic bacteria and fast-growing poplar tree systems offers a readily deployable, cost-effective approach for the degradation of TCE, and may help mitigate potential transfer up the food chain, volatilization to the atmosphere, as well as direct phytotoxic impacts to plants used in this type of phytoremediation

An All-Feline Retroviral Packaging System for Transduction of Human Cells

Doty et al. in this technical report generate and characterize a helper-free, packaging system composed entirely of feline leukemia virus subgroup C (FeLV-C) components. Using this new packaging system, the authors demonstrate that they can produce higher titer vectors than existing gammaretroviral packaging systems