Redox reactions with empirical potentials: Atomistic battery discharge simulations

Batteries are pivotal components in overcoming some of today's greatest technological challenges. Yet to date there is no self-consistent atomistic description of a complete battery. We take first steps toward modeling of a battery as a whole microscopically. Our focus lies on phenomena occurring at the electrode-electrolyte interface which are not easily studied with other methods. We use the redox split-charge equilibration (redoxSQE) method that assigns a discrete ionization state to each atom. Along with exchanging partial charges across bonds, atoms can swap integer charges. With redoxSQE we study the discharge behavior of a nano-battery, and demonstrate that this reproduces the generic properties of a macroscopic battery qualitatively. Examples are the dependence of the battery's capacity on temperature and discharge rate, as well as performance degradation upon recharge.Comment: 14 pages, 10 figure

Volunteer Angling and Technology-Based Solutions Provide the First Estimate of Sea Lice Infections for Wild Coastal Cutthroat Trout (Oncorhynchus Clarkii Clarkii)

Anadromous Coastal Cutthroat Trout Oncorhynchus clarkii clarkii are one of the least studied salmonids but are a highly prized target in sport fisheries in coastal waters of the Pacific Northwest. Despite an observed high prevalence of ectoparasite infections, described by sport anglers as "sea lice," there is a paucity of data available on the spatial and temporal occurrence of infections on Coastal Cutthroat Trout. We collaborated with the angling community through social media engagement and an online application to report ectoparasites observed on sport catch. In 2018, we received voluntary reports for 1,493 Cutthroat Trout and 416 salmon catch events in marine waters from the province of British Columbia and the states of Washington, Oregon, and California. These data demonstrated that the number of argulids and copepods per trout varied according to body size, capture month, and area. To evaluate accuracy of voluntary parasite counts, we compared results to parasite counts on cutthroat from sampling events conducted by trained biologists. For both voluntary angler reports and those of biologists, spring months had a lower prevalence of argulids and copepods, argulids were common on trout, but absent on salmon, and larger trout were associated with an increased number of argulid and copepod infections

Using Logbook Data to Determine the Immediate Mortality of Blue Sharks (Prionace glauca) and Tiger Sharks (Galeocerdo cuvier) Caught in the Commercial U.S. Pelagic Longline Fishery

Commercial fisheries are recognized as one of the greatest threats to shark populations worldwide, but factors affecting the likelihood of shark mortality during fishery capture are poorly understood. We used the U.S. pelagic fishery logbook data from 1992 through 2008 to quantify the effects of several variables (fisheries regulatory periods, geographic zone, target catch, and sea surface temperature) on mortality of blue sharks (Prionace glauca) and tiger sharks (Galeocerdo cuvier). Mortality rates and trends in both species closely matched those recorded from other sources, and therefore indicated that the data on sharks discarded dead and discarded alive in the U.S. pelagic fishery logbook are accurate. The introduction of fisheries management regulations (fin weight to carcass weight ratios in 1993 [to prevent finning] and the prohibition of J-hooks in 2004) presumably decreased the immediate mortality rate of captured blue and tiger sharks (by 8.0% in blue sharks after 2004 and 4.4% in tiger sharks after 1993). Other factors that we examined had a statistically significant effect on mortality, but additional variables should be recorded or made available in logbook data to enable the determination of other causes of mortality. Our results show that the U.S. pelagic fishery logbook data can be used as a powerful tool in future studies of the immediate mortality of longline-caught animals

Disc formation in turbulent massive cores: Circumventing the magnetic braking catastrophe

We present collapse simulations of 100 M_{\sun}, turbulent cloud cores threaded by a strong magnetic field. During the initial collapse phase filaments are generated which fragment quickly and form several protostars. Around these protostars Keplerian discs with typical sizes of up to 100 AU build up in contrast to previous simulations neglecting turbulence. We examine three mechanisms potentially responsible for lowering the magnetic braking efficiency and therefore allowing for the formation of Keplerian discs. Analysing the condensations in which the discs form, we show that the build-up of Keplerian discs is neither caused by magnetic flux loss due to turbulent reconnection nor by the misalignment of the magnetic field and the angular momentum. It is rather a consequence of the turbulent surroundings of the disc which exhibit no coherent rotation structure while strong local shear flows carry large amounts of angular momentum. We suggest that the "magnetic braking catastrophe", i.e. the formation of sub-Keplerian discs only, is an artefact of the idealised non-turbulent initial conditions and that turbulence provides a natural mechanism to circumvent this problem.Comment: 6 pages, 5 figures, accepted by MNRAS Letters, updated to final versio

Magnetic fields during the early stages of massive star formation - I. Accretion and disk evolution

We present simulations of collapsing 100 M_\sun mass cores in the context of massive star formation. The effect of variable initial rotational and magnetic energies on the formation of massive stars is studied in detail. We focus on accretion rates and on the question under which conditions massive Keplerian disks can form in the very early evolutionary stage of massive protostars. For this purpose, we perform 12 simulations with different initial conditions extending over a wide range in parameter space. The equations of magnetohydrodynamics (MHD) are solved under the assumption of ideal MHD. We find that the formation of Keplerian disks in the very early stages is suppressed for a mass-to-flux ratio normalised to the critical value \mu below 10, in agreement with a series of low-mass star formation simulations. This is caused by very efficient magnetic braking resulting in a nearly instantaneous removal of angular momentum from the disk. For weak magnetic fields, corresponding to \mu > 10, large-scale, centrifugally supported disks build up with radii exceeding 100 AU. A stability analysis reveals that the disks are supported against gravitationally induced perturbations by the magnetic field and tend to form single stars rather than multiple objects. We find protostellar accretion rates of the order of a few 10^-4 M_\sun yr^-1 which, considering the large range covered by the initial conditions, vary only by a factor of ~ 3 between the different simulations. We attribute this fact to two competing effects of magnetic fields. On the one hand, magnetic braking enhances accretion by removing angular momentum from the disk thus lowering the centrifugal support against gravity. On the other hand, the combined effect of magnetic pressure and magnetic tension counteracts gravity by exerting an outward directed force on the gas in the disk thus reducing the accretion onto the protostars.Comment: 22 pages, 17 figures, accepted for publication in MNRAS, updated to final versio