Nano‐ice on Boron Nitride Nanomesh: Accessing Proton Disorder

Water was investigated on a h‐BN/Rh(111) nanomesh template using variable temperature scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. Below 52 K, two distinct phases self‐assemble within the 3.2 nm unit cell of the nanomesh that consists of “holes” and “wires”. In the 2 nm holes, an ordered phase of nano‐ice crystals with about 40 molecules is found. The ice crystals arrange in a bilayer honeycomb lattice, where hydrogen atoms of the lower layer point to the substrate. The phase on the 1 nm wires is a low density gas phase. Tunneling barrier height dI/dz spectroscopy measurements reveal the dipoles of individual molecules in the nano‐ice clusters and access proton disorder.     

Robust automated three-dimensional segmentation of secondary ion mass spectrometry image sets

Three-dimensional (3-D) element distributions generated by scanning secondary ion mass spectrometry (SIMS) are usually noisy and blurred and contain objects which do not usually have sharp edges or may have noise induced boundaries. Additionally, there are local intensity differences due to sensitivity differences of the channelplate. As a result, traditional segmentation techniques become difficult and yield rather poor results. We present a novel methodology which combines a restoration process (using a combination of channelplate sensitivity compensation with a 3-D de-noising technique based on the wavelet transform) with a fuzzy logic 3-D gray level segmentation which can be used to successfully segment 3-D SIMS image sets. The restoration algorithm removes the artifacts produced by the channelplate inhomogeneities as well as noise aberrations from the image sets and the gray level thresholding algorithm segments their features. The algorithm is designed for minimal user interaction to achieve a high automation level. The methodology is discussed and experimental results using real 3-D images are presented.     

Quantitative investigation of boron incorporation in polycrystalline CVD diamond films by SIMS

Polycrystalline diamond films have been produced on pre-treated silicon substrate by CVD hot filament method, with B(C₂H₅)₃ added to the gas phase. However, under identical surface conditions, boron incorporation is not homogeneous. In {111} growth sectors, the boron concentration is found to be about 5 times higher than in {100} growth sectors. Moreover, a marked increase in contaminating elements such as aluminium and sodium in regions with higher boron concentrations is detected. Under SIMS fine focus conditions it can be shown that the interface between these two different facet regions is smaller than 0.5?μm. With 3D-depth profile images it can also be shown that the carbon distribution in the diamond layer is not totally homogeneous.     

Evolution of plane disturbances in hypoplastic granular materials

Received July 5, 2000 / Published online February 14, 2001     

A solid-fluid mixture model allowing for solid dilatation under external pressure

Received January 26, 2000 / Published online August 16, 2001     

A Nonlocal Zero-Equation Turbulence Model and a Deficit-Power Law of the Wall with a Dynamical Critical Phenomenon

This article supports a deficit power law for ‘wall’ turbulent shear flows. For infinite Reynolds number flow the model predicts a power, which is a quadratic irrationality in good agreement with experiments (relative error less than one percent). (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A thermo-mechanical continuum theory with internal length for cohesionless granular materials

A thermodynamically consistent continuum theory for single-phase, single-constituent cohesionless granular materials is presented. The theory is motivated by dimensional inconsistencies of the original Goodman-Cowin theory [1–3]; it is constructed by removing these inconsistencies through the introduction of an internal length ℓ. Four constitutive models are proposed and discussed in which ℓ is (i) a material constant (Model I), (ii) an independent constitutive variable (Model II), (iii) an independent dynamic field quantity (Model III) and (iv) an independent kinematic field quantity (Model IV). Expressions of the constitutive variables emerging in the systems of the balance equations in these four models in thermodynamic equilibrium are deduced by use of a thermodynamic analysis based on the Müller-Liu entropy principle. Comments on the validity of these four models are given and discussed; the results presented in the current study show a more general formulation for the constitutive quantities and can be used as a basis for further continuum-based theoretical investigations on the behaviour of flowing granular materials. Numerical results regarding simple plane shear flows will be discussed and compared in Part II of this work.     

Induced anisotropy in large ice shields: theory and its homogenization

For polycrystalline ice, an isothermal flow law is derived from microscopic considerations concerning constitutive equations and kinematic assumptions. On the basis of an elasto-plastic decomposition of the deformation gradient on the grain level and by assuming a continuous distribution of different orientated grains in the vicinity of each material point the classical macroscopic field quantities are obtained by calculating the weighted mean values of the associated microscopic quantities. The weighting function is represented by a so called Orientation Distribution Function (ODF). For the general two dimensional (plane and rotationally symmetric) flow regime analytical representations of the ODF are derived under the assumption of a uniform stress distribution over all polycrystals (Sachs-Condition) and a plane or rotationally symmetric orientation distribution. Additionally, the influence of the macroscopic constitutive relations on the microscopic level is restricted to isotropic parts only. Simple examples are used to demonstrate the ability of the ODF to perform the evolving texture. The microscopic constitutive relation for the dissipation potential is assumed to be an objective function of the stress deviator and is expressed as a polynomial law up to the power , as proposed by Lliboutry (1993). A second order structure tensor which depends on the ODF is introduced to consider induced anisotropy. The resulting macro fluidities (inverse viscosities) are then calculated from the analytical representation of the ODF for the case of uniaxial loading underlying linear and nonlinear material behaviour. Received March 30, 1998     

Anisotropic damage mechanics for viscoelastic ice

We present a formulation of continuum damage in glacier ice that incorporates the induced anisotropy of the damage effects but restricts these formally to orthotropy. Damage is modeled by a symmetric second rank tensor that structurally plays the role of an internal variable. It may be interpreted as a texture measure that quantifies the effective specific areas over which internal stresses can be transmitted. The evolution equation for the damage tensor is motivated in the reference configuration and pushed forward to the present configuration. A spatially objective constitutive form of the evolution equation for the damage tensor is obtained. The rheology of the damaged ice presumes no volume conservation. Its constitutive relations are derived from the free enthalpy and a dissipation potential, and extends the classical isotropic power law by elastic and damage tensor dependent terms. All constitutive relations are in conformity with the second law of thermodynamics.PACS 83.60.Df, 62.20.Mk