Sublimation pit distribution indicates convection cell surface velocities of ∼10 cm per year in Sputnik Planitia, Pluto

The ∼10^6 km^2 Sputnik Planitia, Pluto is the upper surface of a vast basin of nitrogen ice. Cellular landforms in Sputnik Planitia with areas in the range of a few × 10^2–10^3 km^2 are likely the surface manifestation of convective overturn in the nitrogen ice. The cells have sublimation pits on them, with smaller pits near their centers and larger pits near their edges. We map pits on seven cells and find that the pit radii increase by between 2.1 ± 0.4 × 10^(−3) and 5.9 ± 0.8 × 10^(−3) m m^(−1) away from the cell center, depending on the cell. This is a lower bound on the size increase because of the finite resolution of the data. Accounting for resolution yields upper bounds on the size vs. distance distribution of between 4.2 ± 0.2 × 10^(−3) and 23.4 ± 1.5 × 10^(−3)m m^(−1). We then use an analytic model to calculate that pit radii grow via sublimation at a rate of 3.6_(−0.6)^(+2.1)×10^(−4) m yr^(−1), which allows us to convert the pit size vs. distance distribution into a pit age vs. distance distribution. This yields surface velocities between 1.5_(−0.2)^(+1.0) and 6.2_(−1.4)^(+3.4) cm yr^(−1) for the slowest cell and surface velocities between 8.1_(−1.0)^(+5.5) and 17.9_(−5.1)^(+8.9) cm yr^(−1) for the fastest cell. These convection rates imply that the surface ages at the edge of cells reach ∼4.2–8.9 × 10^5 yr. The rates are comparable to rates of ∼6 cm yr^(−1) that were previously obtained from modeling of the convective overturn in Sputnik Planitia (McKinnon et al., 2016). Finally, we investigate the surface rheology of the convection cells and estimate that the minimum ice viscosity necessary to support the geometry of the observed pits is of order 10^(16)–10^(17) Pa s, based on the argument that pits would relax away before growing to their observed radii of several hundred meters if the viscosity were lower than this value

Sublimation pit distribution indicates convection cell surface velocities of ∼10 cm per year in Sputnik Planitia, Pluto

The ∼10^6 km^2 Sputnik Planitia, Pluto is the upper surface of a vast basin of nitrogen ice. Cellular landforms in Sputnik Planitia with areas in the range of a few × 10^2–10^3 km^2 are likely the surface manifestation of convective overturn in the nitrogen ice. The cells have sublimation pits on them, with smaller pits near their centers and larger pits near their edges. We map pits on seven cells and find that the pit radii increase by between 2.1 ± 0.4 × 10^(−3) and 5.9 ± 0.8 × 10^(−3) m m^(−1) away from the cell center, depending on the cell. This is a lower bound on the size increase because of the finite resolution of the data. Accounting for resolution yields upper bounds on the size vs. distance distribution of between 4.2 ± 0.2 × 10^(−3) and 23.4 ± 1.5 × 10^(−3)m m^(−1). We then use an analytic model to calculate that pit radii grow via sublimation at a rate of 3.6_(−0.6)^(+2.1)×10^(−4) m yr^(−1), which allows us to convert the pit size vs. distance distribution into a pit age vs. distance distribution. This yields surface velocities between 1.5_(−0.2)^(+1.0) and 6.2_(−1.4)^(+3.4) cm yr^(−1) for the slowest cell and surface velocities between 8.1_(−1.0)^(+5.5) and 17.9_(−5.1)^(+8.9) cm yr^(−1) for the fastest cell. These convection rates imply that the surface ages at the edge of cells reach ∼4.2–8.9 × 10^5 yr. The rates are comparable to rates of ∼6 cm yr^(−1) that were previously obtained from modeling of the convective overturn in Sputnik Planitia (McKinnon et al., 2016). Finally, we investigate the surface rheology of the convection cells and estimate that the minimum ice viscosity necessary to support the geometry of the observed pits is of order 10^(16)–10^(17) Pa s, based on the argument that pits would relax away before growing to their observed radii of several hundred meters if the viscosity were lower than this value

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Temperature-controlled interlayer exchange coupling in strong/weak ferromagnetic multilayers: a thermo-magnetic Curie-switch

We investigate a novel type of interlayer exchange coupling based on driving a strong/weak/strong ferromagnetic tri-layer through the Curie point of the weakly ferromagnetic spacer, with the exchange coupling between the strongly ferromagnetic outer layers that can be switched, on and off, or varied continuously in magnitude by controlling the temperature of the material. We use Ni-Cu alloy of varied composition as the spacer material and model the effects of proximity-induced magnetism and the interlayer exchange coupling through the spacer from first principles, taking into account not only thermal spin-disorder but also the dependence of the atomic moment of Ni on the nearest-neighbor concentration of the non-magnetic Cu. We propose and demonstrate a gradient-composition spacer, with a lower Ni-concentration at the interfaces, for greatly improved effective-exchange uniformity and significantly improved thermo-magnetic switching in the structure. The reported magnetic multilayer materials can form the base for a variety of novel magnetic devices, such as sensors, oscillators, and memory elements based on thermo-magnetic Curie-switching in the device.Comment: 15 pages, 5 figure

A unifying framework for seed sensitivity and its application to subset seeds

We propose a general approach to compute the seed sensitivity, that can be applied to different definitions of seeds. It treats separately three components of the seed sensitivity problem -- a set of target alignments, an associated probability distribution, and a seed model -- that are specified by distinct finite automata. The approach is then applied to a new concept of subset seeds for which we propose an efficient automaton construction. Experimental results confirm that sensitive subset seeds can be efficiently designed using our approach, and can then be used in similarity search producing better results than ordinary spaced seeds

Entropic phase separation of linked beads

We study theoretically a model system of a transient network of microemulsion droplets connected by telechelic polymers and explain recent experimental findings. Despite the absence of any specific interactions between either the droplets or polymer chains, we predict that as the number of polymers per drop is increased, the system undergoes a first order phase separation into a dense, highly connected phase, in equilibrium with dilute droplets, decorated by polymer loops. The phase transition is purely entropic and is driven by the interplay between the translational entropy of the drops and the configurational entropy of the polymer connections between them. Because it is dominated by entropic effects, the phase separation mechanism of the system is extremely robust and does not depend on the particlular physical realization of the network. The discussed model applies as well to other polymer linked particle aggregates, such as nano-particles connected with short DNA linkers

Sublimation pit distribution indicates convection cell surface velocities of ∼10 cm per year in Sputnik Planitia, Pluto

The ∼10^6 km^2 Sputnik Planitia, Pluto is the upper surface of a vast basin of nitrogen ice. Cellular landforms in Sputnik Planitia with areas in the range of a few × 10^2–10^3 km^2 are likely the surface manifestation of convective overturn in the nitrogen ice. The cells have sublimation pits on them, with smaller pits near their centers and larger pits near their edges. We map pits on seven cells and find that the pit radii increase by between 2.1 ± 0.4 × 10^(−3) and 5.9 ± 0.8 × 10^(−3) m m^(−1) away from the cell center, depending on the cell. This is a lower bound on the size increase because of the finite resolution of the data. Accounting for resolution yields upper bounds on the size vs. distance distribution of between 4.2 ± 0.2 × 10^(−3) and 23.4 ± 1.5 × 10^(−3)m m^(−1). We then use an analytic model to calculate that pit radii grow via sublimation at a rate of 3.6_(−0.6)^(+2.1)×10^(−4) m yr^(−1), which allows us to convert the pit size vs. distance distribution into a pit age vs. distance distribution. This yields surface velocities between 1.5_(−0.2)^(+1.0) and 6.2_(−1.4)^(+3.4) cm yr^(−1) for the slowest cell and surface velocities between 8.1_(−1.0)^(+5.5) and 17.9_(−5.1)^(+8.9) cm yr^(−1) for the fastest cell. These convection rates imply that the surface ages at the edge of cells reach ∼4.2–8.9 × 10^5 yr. The rates are comparable to rates of ∼6 cm yr^(−1) that were previously obtained from modeling of the convective overturn in Sputnik Planitia (McKinnon et al., 2016). Finally, we investigate the surface rheology of the convection cells and estimate that the minimum ice viscosity necessary to support the geometry of the observed pits is of order 10^(16)–10^(17) Pa s, based on the argument that pits would relax away before growing to their observed radii of several hundred meters if the viscosity were lower than this value

Effect of Non-Magnetic Impurities (Zn,Li) in a Hole Doped Spin-Fermion Model for Cuprates

The effect of adding non-magnetic impurities (NMI), such as Zn or Li, to high-Tc cuprates is studied applying Monte Carlo techniques to a spin-fermion model. It is observed that adding Li is qualitatively similar to doping with equal percentages of Sr and Zn. The mobile holes (MH) are trapped by the NMI and the system remains insulating and commensurate with antiferromagnetic (AF) correlations. This behavior persists in the region %NMI > %MH. On the other hand, when %NMI < %MH magnetic and charge incommensurabilities are observed. The vertical or horizontal hole-rich stripes, present when % NMI=0 upon hole doping, are pinned by the NMI and tend to become diagonal, surrounding finite AF domains. The %MH-%NMI plane is investigated. Good agreement with experimental results is found in the small portion of this diagram where experimental data are available. Predictions about the expected behavior in the remaining regions are made.Comment: Four pages with four figures embedded in tex

Comparative Effects of Haemodialysis and Haemofiltration on Plasma Atrial Natriuretic Peptide

The effects of 4 h haemodialysis (15 patients) or 4 h haemofiltration (five patients) on plasma concentrations of atrial natriuretic peptide (ANP) were compared by means of a sensitive radioreceptor binding assay, and related to accompanying changes in body weight, blood pressure and plasma renin activity. Before dialysis, plasma ANP concentrations were considerably elevated: haemodialysis group 10-484 pmol/l (mean 156 pmol/l); haemofiltration group 72-320 pmol/l (mean 170 pmol/l). Although plasma concentrations of ANP fell markedly with treatment in both groups: post-haemodialysis 2-187 pmol/l (mean 67 pmol/l); post-haemofiltration 47-135 pmol/l (mean 79 pmol/l), after treatment it remained above the normal range in 14 of the 20 patients. Pretreatment plasma ANP was related to systolic blood pressure (r=0.459; P<0.05) but bore no relationship to mean or diastolic blood pressure, or plasma renin activity. The fall in plasma ANP concentration during treatment correlated with the postural blood pressure drop after dialysis (r=0.505; P<0.05), but was unrelated to changes in weight or plasma renin activity with haemodialysis or haemofiltration. Plasma ANP concentrations rose rapidly again in the 60 min after dialysis treatment, without change in body weight. These results show that high levels of biologically active ANP circulate in end-stage renal disease. The fact that these are not reduced to normal by haemodialysis or haemofiltration, despite restoration to normovolaemic or hypovolaemic state, suggests that the increased levels of ANP in end-stage renal failure are due to both hypervolaemia and other factors, which may include occult cardiac dysfunction and loss of renal clearanc

Anura, Hylidae, <i>Dendropsophus nahdereri</i> (Lutz and Bokermann, 1963): Distribution extension and new state record.

Dendropsophus nahdereri is included in the Dendropsophus marmoratus group. Its distribution is known fromthe Brazilian states of Paraná and Santa Catarina. Here we report new records of this species and briefly describe the habitatof calling males. We found new localities of occurrence of D. nahdereri in Brazilian states of Santa Catarina and Rio Grandedo Sul. We collected calling males in temporary lentic water bodies surrounded by arboreal vegetation, inside and on theborder of native forest, and inside Pinus plantations near native forest