Velocity anisotropy induced by MHD turbulence is investigated using computational simulations and molecular line observations of the Taurus molecular cloud. A new analysis method is presented to evaluate the degree and angle of velocity anisotropy using spectroscopic imaging data of interstellar clouds. The efficacy of this method is demonstrated on model observations derived from three dimensional velocity and density fields from the set of numerical MHD simulations that span a range of magnetic field strengths. The analysis is applied to 12CO J=1-0 imaging of a sub-field within the Taurus molecular cloud. Velocity anisotropy is identified that is aligned within 10 degrees of the mean local magnetic field direction derived from optical polarization measurements. Estimated values of the field strength based on velocity anisotropy are consistent with results from other methods. When combined with new column density measurements for Taurus, our magnetic field strength estimate indicates that the envelope of the cloud is magnetically subcritical. These observations favor strong MHD turbulence within the low density, sub-critical, molecular gas substrate of the Taurus cloud.Comment: Accepted for publication in ApJ

We use numerical hydrodynamic simulations to investigate prestellar core formation in the dynamic environment of giant molecular clouds (GMCs), focusing on planar post-shock layers produced by colliding turbulent flows. A key goal is to test how core evolution and properties depend on the velocity dispersion in the parent cloud; our simulation suite consists of 180 models with inflow Mach numbers M ≡ v/c s = 1.1 − 9. At all Mach numbers, our models show that turbulence and self-gravity collect gas within post-shock regions into filaments at the same time as overdense areas within these filaments condense into cores. This morphology, together with the subsonic velocities we find inside cores, is similar to observations. We extend previous results showing that core collapse develops in an "outside-in" manner, with density and velocity approaching the Larson-Penston asymptotic solution. The time for the first core to collapse depends on Mach number as t coll ∝ M −1/2 ρ −1/2 0

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We present a unified model for molecular core formation and evolution, based on numerical simulations of converging, supersonic flows. Our model applies to star formation in GMCs dominated by large-scale turbulence, and contains four main stages: core building, core collapse, envelope infall, and late accretion. During the building stage, cores form out of dense, post-shock gas, and become increasingly centrally stratified as the mass grows over time. Even for highly-supersonic converging flows, the dense gas is subsonic, consistent with observations showing quiescent cores. When the shock radius defining the core boundary exceeds R ≈ 4a(4πGρ mean ) −1/2 , where a is the isothermal sound speed, a wave of collapse propagates from the edge to the center. During the building and collapse stages, density profiles can be fit by Bonnor-Ebert profiles with temperature 1.2 -2.9 times the true value, similar to many observed cores. As found previously for initially static equilibria, outside-in collapse leads to a Larson-Penston density profile ρ ≈ 8.86a 2 /(4πGr 2 ). The third stage, consisting of an inside-out wave of gravitational rarefaction leading to ρ ∝ r −3/2 , v ∝ r −1/2 , is also similar to that for initially-static spheres, as originally described by Shu. We find that the collapse and infall stages have comparable duration, ∼ t f f , consistent with estimates for observed prestellar and protostellar (Class 0/I) cores. Core building takes longer, but does not produce high-contrast objects until shortly before collapse. The time to reach core collapse, and the core mass at collapse, decrease with increasing inflow Mach number. For all cases the accretion rate is ≫ a 3 /G early on but sharply drops off; the final system mass depends on the duration of late-stage accretion, set by large-scale conditions in a cloud.

• Synthesis strategies of layered double hydroxides (LDHs) were summarized with classifications of traditional coprecipitation, homogeneous precipitation, and newly developed topochemical oxidation. • Diverse approaches of structural modulation and hybridization to enhance the electrocatalytic activity of LDHs were systematically reviewed.

We describe implementation and tests of sink particle algorithms in the Eulerian grid-based code Athena. Introduction of sink particles enables long-term evolution of systems in which localized collapse occurs, and it is impractical (or unnecessary) to resolve the accretion shocks at the centers of collapsing regions. We discuss similarities and differences of our methods compared to other implementations of sink particles. Our criteria for sink creation are motivated by the properties of the Larson-Penston collapse solution. We use standard particlemesh methods to compute particle and gas gravity together. Accretion of mass and momenta onto sinks is computed using fluxes returned by the Riemann solver. A series of tests based on previous analytic and numerical collapse solutions is used to validate our method and implementation. We demonstrate use of our code for applications with a simulation of planar converging supersonic turbulent flow, in which multiple cores form and collapse to create sinks; these sinks continue to interact and accrete from their surroundings over several Myr.

Novel two-dimensional Ceria@Co, N-doped leaf-like porous carbon nanosheets (Ce-HPCNs) were fabricated using an efficient aqueous solution-mediated method. More importantly, the prepared Ce-HPCNs demonstrate even better electrocatalytic performance than the commercial Pt/C due to the synergistic effect of the oxygen buffer CeO with Co-N, and exhibit a new direction and impact in the development of new catalysts for energy applications.

Tin oxide nanoparticles (SnO2 NPs) have been encapsulated in situ in a three-dimensional ordered space structure. Within this composite, ordered mesoporous carbon (OMC) acts as a carbon framework showing a desirable ordered mesoporous structure with an average pore size (≈6 nm) and a high surface area (470.3 m(2) g(-1)), and the SnO2 NPs (≈10 nm) are highly loaded (up to 80 wt %) and homogeneously distributed within the OMC matrix. As an anode material for lithium-ion batteries, a SnO2 @OMC composite material can deliver an initial charge capacity of 943 mAh g(-1) and retain 68.9 % of the initial capacity after 50 cycles at a current density of 50 mA g(-1), even exhibit a capacity of 503 mA h g(-1) after 100 cycles at 160 mA g(-1). In situ encapsulation of the SnO2 NPs within an OMC framework contributes to a higher capacity and a better cycling stability and rate capability in comparison with bare OMC and OMC ex situ loaded with SnO2 particles (SnO2/OMC). The significantly improved electrochemical performance of the SnO2@OMC composite can be attributed to the multifunctional OMC matrix, which can facilitate electrolyte infiltration, accelerate charge transfer, and lithium-ion diffusion, and act as a favorable buffer to release reaction strains for lithiation/delithiation of the SnO2 NPs.