The quantum-mechanical tunnelling effect allows charge transport across nanometre-scale gaps between conducting electrodes. Application of a voltage between these electrodes leads to a measurable ...tunnelling current, which is highly sensitive to the gap size, the voltage applied and the medium in the gap. Applied to liquid environments, this offers interesting prospects of using tunnelling currents as a sensitive tool to study fundamental interfacial processes, to probe chemical reactions at the single-molecule level and to analyse the composition of biopolymers such as DNA, RNA or proteins. This offers the possibility of a new class of sensor devices with unique capabilities.
Forest diversity-productivity relationships have been intensively investigated in recent decades. However, few studies have considered the interplay between species and structural diversity in ...driving productivity. We analyzed these factors using data from 52 permanent plots in southwestern Germany with more than 53,000 repeated tree measurements. We used basal area increment as a proxy for productivity and hypothesized that: (1) structural diversity would increase tree and stand productivity, (2) diversity-productivity relationships would be weaker for species diversity than for structural diversity, and (3) species diversity would also indirectly impact stand productivity via changes in size structure. We measured diversity using distance-independent indices indices. We fitted separate linear mixed-effects models for fir, spruce and beech at the tree level, whereas at the stand level we pooled all available data. We tested our third hypothesis using structural equation modeling. Structural and species diversity acted as direct and independent drivers of stand productivity, with structural diversity being a slightly better predictor. Structural diversity, but not species diversity, had a significant, albeit asymmetric, effect on tree productivity. The functioning of structurally diverse, mixed forests is influenced by both structural and species diversity. These sources of trait diversity contribute to increased vertical stratification and crown plasticity, which in turn diminish competitive interferences and lead to more densely packed canopies per unit area. Our research highlights the positive effects of species diversity and structural diversity on forest productivity and ecosystem dynamics.
To predict the future contributions of the Antarctic ice sheets to sea-level rise, numerical models use reconstructions of past ice-sheet retreat after the Last Glacial Maximum to tune model ...parameters
. Reconstructions of the West Antarctic Ice Sheet have assumed that it retreated progressively throughout the Holocene epoch (the past 11,500 years or so)
. Here we show, however, that over this period the grounding line of the West Antarctic Ice Sheet (which marks the point at which it is no longer in contact with the ground and becomes a floating ice shelf) retreated several hundred kilometres inland of today's grounding line, before isostatic rebound caused it to re-advance to its present position. Our evidence includes, first, radiocarbon dating of sediment cores recovered from beneath the ice streams of the Ross Sea sector, indicating widespread Holocene marine exposure; and second, ice-penetrating radar observations of englacial structure in the Weddell Sea sector, indicating ice-shelf grounding. We explore the implications of these findings with an ice-sheet model. Modelled re-advance of the grounding line in the Holocene requires ice-shelf grounding caused by isostatic rebound. Our findings overturn the assumption of progressive retreat of the grounding line during the Holocene in West Antarctica, and corroborate previous suggestions of ice-sheet re-advance
. Rebound-driven stabilizing processes were apparently able to halt and reverse climate-initiated ice loss. Whether these processes can reverse present-day ice loss
on millennial timescales will depend on bedrock topography and mantle viscosity-parameters that are difficult to measure and to incorporate into ice-sheet models.
Semtex enables direct numerical simulation (DNS) of the incompressible Navier–Stokes equations by coupling continuous-Galerkin nodal spectral element–Fourier spatial discretisation with semi-implicit ...temporal integration via a time-splitting scheme. Transport of a scalar quantity may be included. The analyst has a choice of Cartesian or cylindrical coordinate systems. Domain geometries and solutions may be two-dimensional with spectral element decomposition of arbitrary planar shapes, or made three-dimensional by extrusion along a spatially homogeneous direction in which Fourier expansions are employed. For three-dimensional solutions, MPI may be used to support parallel execution. Various body forces, including Boussinesq buoyancy and Coriolis terms may be added to the momentum equation to simulate e.g. the effects of stratification and thermal expansion or reference frame rotation. Parallel decomposition is performed in the Fourier dimension only, and two-dimensional elliptic systems in the plane are solved for the spectral element discretisation using direct (Cholesky) or iterative (conjugate-gradient) methods. Semtex includes a suite of additional tools for generating initial conditions and model configurations, for post processing and for analysis of model output.
Program Title: Semtex
Program Files doi:http://dx.doi.org/10.17632/65mz2szz5t.1
Code Ocean Capsule:https://doi.org/10.24433/CO.2589809.v1
Licensing provisions: GPLv2
Programming languages: C++, C, Fortran77
External routines: BLAS, LAPACK, yacc/bison, (optionally) MPI
Nature of problem: Two- or three-dimensional incompressible Navier–Stokes in cylindrical and periodic Cartesian geometries with optional body forces. Two- or three-component velocity fields.
Solution method: Continuous Galerkin nodal spectral element–Fourier spatial discretisation with semi-implicit time-splitting-based temporal integration of the nonlinear, viscous and pressure gradient terms in the Navier–Stokes equations via a projection method.
Reconstruction of lesions in the head and neck region must be both functionally and esthetically adequate, as the exposed anatomic position can easily lead to social stigmatization after injury. ...Distortion of symmetry, e.g., by a crooked nose, enophthalmos, or a (partial) amputation of the outer ear, is easily visible. On the other hand, limitations to nasal breathing and olfaction or diplopia may significantly reduce quality of life, and restoration of form and function continues to be challenging. This review discusses the treatment options for trauma of the external nose and the lateral midface, including the orbital floor and the auricle.
We present the Potsdam Parallel Ice Sheet Model (PISM-PIK), developed at the Potsdam Institute for Climate Impact Research to be used for simulations of large-scale ice sheet-shelf systems. It is ...derived from the Parallel Ice Sheet Model (Bueler and Brown, 2009). Velocities are calculated by superposition of two shallow stress balance approximations within the entire ice covered region: the shallow ice approximation (SIA) is dominant in grounded regions and accounts for shear deformation parallel to the geoid. The plug-flow type shallow shelf approximation (SSA) dominates the velocity field in ice shelf regions and serves as a basal sliding velocity in grounded regions. Ice streams can be identified diagnostically as regions with a significant contribution of membrane stresses to the local momentum balance. All lateral boundaries in PISM-PIK are free to evolve, including the grounding line and ice fronts. Ice shelf margins in particular are modeled using Neumann boundary conditions for the SSA equations, reflecting a hydrostatic stress imbalance along the vertical calving face. The ice front position is modeled using a subgrid-scale representation of calving front motion (Albrecht et al., 2011) and a physically-motivated calving law based on horizontal spreading rates. The model is tested in experiments from the Marine Ice Sheet Model Intercomparison Project (MISMIP). A dynamic equilibrium simulation of Antarctica under present-day conditions is presented in Martin et al. (2011).
Making confident statements about the evolution of an ice-sheet–shelf system with a numerical model requires the capability to reproduce the migration of the grounding line. Here we show that the ...shallow-ice approximation/shallow-shelf approximation hybrid-type Parallel Ice Sheet Model (PISM), with its recent improvements, is capable of modeling the grounding line motion in a perturbed ice-sheet–shelf system. The model is set up according to the three-dimensional Marine Ice-Sheet Model Intercomparison Project (MISMIP3d), and simulations are carried out across a broad range of spatial resolutions. Using (1) a linear interpolation of the grounding line with locally interpolated basal friction and (2) an improved driving-stress computation across the grounding line, the reversibility of the grounding line (i.e. its retreat after an advance forced by a local perturbation of basal resistance) is captured by the model even at medium and low resolutions (∆x > 10 km). The transient model response is qualitatively similar to that of higher-order models but reveals a higher initial sensitivity to perturbations on very short timescales. Our findings support the application of PISM to the Antarctic ice sheet from regional up to continental scales and on relatively low spatial resolutions.
Hydrometallurgical copper extraction from chalcopyrite is a slow and often incomplete process that relies on corrosive and environmentally unfriendly H2SO4-based leaching systems. Some ionic liquids ...(ILs), including imidazolium- and ammonium-based ILs, have previously been suggested as better performing alternatives, but at present it is not clear whether the leaching mechanism is different than in H2SO4-based lixiviants. Here, we study a range of different, structurally simple ILs using a robotic screening platform and other methods, to address this question. Indeed, we do find differences between ILs, in that IL-based lixiviants with more polar cations (NH4+, K+, C1Him+) appear to show better extraction than those with less polar cations (C2C1im+, C4C1im+). However, none performed better than aqueous H2SO4, when corrected for differences in pH. Notably, results are qualitatively very similar: three leaching stages were seen in all cases, presumably involving leaching of a Fe rich/Cu poor layer first, followed by leaching of bulk chalcopyrite and eventually passivation. During the second stage, the apparent activation energies in aqueous NH4HSO4, and H2SO4 are similar in that both rates are first order with respect to the proton concentration in both cases. The leaching rate increases with stirring, suggesting some degree of mass transport-control on the leaching process. The poorer leaching performance for C2C1imHSO4 and C4C1imHSO4 is consistent with physical blocking of the mineral surface, presumably by the IL cation, in accordance with contact angle data.
•EDAS is used for highly-sensitive automated multiplexed, 'combinatorial' monitoring of the leaching performance of ILs.•NH4HSO4 and C1HimHSO4 were identified as best performing ILs amongst a number of HSO4- and imidazolium based ILs.•In our study, no ionic liquid performed better than sulfuric acid at the same pH.•The IL cation appears to have a blocking effect, possibly via adsorption to the mineral surface.
Segmented thermoplastic polyurethanes (TPU) often show multiple endothermic signals during melting in conventional differential scanning calorimetry (DSC). Repeated reorganization during heating and ...separate crystal melting and phase mixing have been proposed as the origin of this phenomenon. We used fast scanning calorimetry on a series of TPUs with polyether soft segments and hard segments consisting of 4,4′-methylenediphenyl diisocyanate and 1,4-butanediol to differentiate between the two possibilities. Fast heating scans (>500 °C s–1) of isothermally crystallized samples exhibited only a single melting peak, while complementary experiments on quenched, fully amorphous samples showed a single glass transition step indicating a homogeneous mixed phase. These results prove that the multiple melting peaks observed in DSC are related to reorganization during heating, i.e., repeated melting and recrystallization. Phase separation during cooling of such TPUs is induced by crystallization. A comparison with conventional DSC scans shows the consistency of both calorimetric techniques in the limit of low heating rates.
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