Discussion notes on “Computer simulation of interface potentials: Towards a first principle description of complex interfaces?”, by L.G. MacDowell

Comments are provided for [2].     

Towards a Resolution of Dilemma: Nonlocality or Nonobjectivity?

This paper discusses a possible resolution of the nonobjectivity-nonlocality dilemma in quantum mechanics in the light of experimental tests of the Bell inequality for two entangled photons and a Bell-like inequality for a single neutron. My conclusion is that these experiments show that quantum mechanics is nonobjective: that is, the values of physical observables cannot be assigned to a system before measurement. Bell’s assumption of nonlocality has to be rejected as having no direct experimental confirmation, at least thus far. I also consider the relationships between nonobjectivity and contextuality. Specifically, I analyze the impact of the Kochen-Specker theorem on the problem of contextuality of quantum observables. I argue that, just as von Neumann’s “no-go” theorem, the Kochen-Specker theorem is based on assumptions that do not correspond to the real physical situation. Finally, I present a theory of measurement based on a classical, purely wave model (pre-quantum classical statistical field theory), a model that reproduces quantum probabilities. In this model continuous fields are transformed into discrete clicks of detectors. While this model is classical, it is nonobjective. In this case, nonobjectivity is the result of the dependence of experimental outcomes on the context of measurement, in accordance with Bohr’s view.     

Dynamic surface tension of complex fluid-fluid interfaces: A useful concept, or not?

Dilatational moduli are typically determined by subjecting interfaces to oscillatory area deformations, and are often defined in terms of the difference between the dynamic or transient surface tension of the interface (the surface tension in its deformed state), and the surface tension of the interface in its non-deformed state. Here we will discuss the usefulness of the dynamic surface tension concept in the characterization of dilatational properties of complex fluid-fluid interfaces. Complex fluid-fluid interfaces are interfaces stabilized by components which form mesophases (two-dimensionional gels, glasses, or (liquid) crystalline phases), as a result of in-plane interactions between the components. We will show that for such interfaces dilatational properties are not exclusively determined by the exchange of surface active components between interface and adjoining bulk phases, but also by in-plane viscoelastic stresses. The separation of these contributions remains a challenging problem which remains to be solved.     

Does a Computer Have an Arrow of Time?

Schulman (Entropy 7(4):221–233, 2005) has argued that Boltzmann’s intuition, that the psychological arrow of time is necessarily aligned with the thermodynamic arrow, is correct. Schulman gives an explicit physical mechanism for this connection, based on the brain being representable as a computer, together with certain thermodynamic properties of computational processes. Hawking (Physical Origins of Time Asymmetry, Cambridge University Press, Cambridge, 1994) presents similar, if briefer, arguments. The purpose of this paper is to critically examine the support for the link between thermodynamics and an arrow of time for computers. The principal arguments put forward by Schulman and Hawking will be shown to fail. It will be shown that any computational process that can take place in an entropy increasing universe, can equally take place in an entropy decreasing universe. This conclusion does not automatically imply a psychological arrow can run counter to the thermodynamic arrow. Some alternative possible explanations for the alignment of the two arrows will be briefly discussed.     

Is a classical description of stable non-BPS D-branes possible?

We study the classical geometry produced by a stack of stable (i.e., tachyon-free) non-BPS D-branes present in K3 compactifications of type II string theory. This classical representation is derived by solving the equations of motion describing the low-energy dynamics of the supergravity fields which couple to the non-BPS state. Differently from what expected, this configuration displays a singular behaviour: the space–time geometry has a repulson-like singularity. This fact suggests that the simplest setting, namely a set of coinciding non-interacting D-branes, is not acceptable. We finally discuss the possible existence of other acceptable configurations corresponding to more complicated bound states of these non-BPS branes.     

Does roughening of rock-fluid-rock interfaces emerge from a stress-induced instability?

Non-planar solid-fluid-solid interfaces under stress are very common in many industrial and natural materials. For example, in the Earth’s crust, many rough and wavy interfaces can be observed in rocks in a wide range of spatial scales, from undulate grain boundaries at the micrometer scale, to stylolite dissolution planes at the meter scale. It is proposed here that these initially flat solid-fluid-solid interfaces become rough by a morphological instability triggered by elastic stress. A model for the formation of these unstable patterns at all scales is thus presented. It is shown that such instability is inherently present due to the uniaxial stress that promotes them, owing to the gain in the total elastic energy: the intrinsic elastic energy plus the work of the external forces. This is shown explicitly by solving the elastic problem in a linear stability analysis, and proved more generally without having resort to the computation of the elastic field.     

Multi-step magnetization of the Ising model on a Shastry-Sutherland lattice: a Monte?Carlo simulation

The magnetization behaviors and spin configurations of the classical Ising model on a Shastry-Sutherland lattice are investigated using Monte Carlo simulations, in order to understand the fascinating magnetization plateaus observed in TmB(4) and other rare-earth tetraborides. The simulations reproduce the 1/2 magnetization plateau by taking into account the dipole-dipole interaction. In addition, a narrow 2/3 magnetization step at low temperature is predicted in our simulation. The multi-step magnetization can be understood as the consequence of the competitions among the spin-exchange interaction, the dipole-dipole interaction, and the static magnetic energy.     

Computer simulation of the thermodynamics of the B → Z-DNA transition: effect of the ionic size and charge

The B- to Z-DNA transition free energy as a function of the size and charge of added ions is investigated by Monte Carlo simulation for simple grooved B- and Z-DNA models. It is shown that the electrostatic contribution to the free energy depends almost linearly on the logarithm of the salt concentration for all the systems. The effect of increasing the size of the ions is to make the curves steeper, although its influence on the transition midpoint is more complex. Divalent cations markedly reduce both the slope and the transition midpoint with respect to monovalent ions. These conclusions are in agreement with the experimental findings. The effect of increasing the charge of the anions—not yet experimentally studied—is less pronounced.     

Computer simulation study of a two-dimensional nematogenic lattice model based on the Gruhn–Hess interaction potential

We consider a nematogenic lattice model, associated with a 2-dimensional lattice; the nearest-neighbour interaction potential, proposed by Gruhn and Hess [Z. Naturforsch. A 51 (1996) 1], is defined via an approximate mapping from the elastic free-energy density, and has already been studied by simulation in 3 dimensions [S. Romano, Int. J. Mod. Phys. B 12 (1998) 2305]. The present simulation results show that the model produces homeotropic anchoring, and a weaker uniaxial orientational order, now surviving up to temperatures higher than the transition temperature of the 3-dimensional counterpart, possibly at all finite temperatures.     

Goos–H?nchen shift at an interface of a composite material: effects of particulate clustering

The Goos–H?nchen (GH) shift of a p-polarized light beam reflected from an interface of a composite material of particulate metals in a dielectric host is studied theoretically using effective medium approaches, with focus on the effects due to the clustering of the metal particles. With application of a fractal-clustering model, it is shown that the composite can have optically metallic behavior even for relatively low volume fraction of metal when clustering takes place, with appreciable negative GH shifts to take place for light of long wavelengths close to grazing incident angles. Furthermore, we confirm that large reflectance is always accompanied with this metal behavior, thus rendering these shifts easily observable.     

How many kinds of sclerite? Towards a morphometric classification of gorgoniid microskeletal components

Gorgoniid octocorals constitute a diverse group of organisms that inhabit a wide range of marine environments. The group is currently defined by the presence of calcareous sclerites that are less than 0.3 mm in length with regularly arranged warts. Generic and specific classification schemes are based on the presence/absence of different sclerite classes in the sampled specimen as well as the frequency in which each class occurs in the sample. Sclerite classification typically has been difficult because a continuum of sclerite forms is found within and between species. Thus, the use of sclerites for phylogenetic inference and classification is problematic. Herein, we present a methodology to obtain quantitative measurements of large numbers of sclerites and used finite mixture modeling to assess the number of statistically different sclerite classes present in the eastern Pacific octocoral genus Pacifigorgia. We also test the ability of simple neural classifiers (perceptrons) to sort sclerites into the classes traditionally used in octocoral taxonomy. This methodology can be used for other gorgoniids and can be further extended to include shape quantifiers for groups other than those studied here.     

Computer simulation of a diatomic molecule dissolved in a monatomic fluid—Correlation functions,band shapes,and relaxation times

Four N₂-Ar ‘solute-solvent’ systems representing different temperatures and densities were simulated on a computer by the molecular dynamics technique. From the data for each system, the dipole, angular velocity, force-on-the-bond, and P ₂ correlation functions were calculated. These functions were used to determine rovibrational infra-red and Raman band-shapes, and N.M.R. relaxation times for quadrupolar, magnetic dipole-dipole and spin-rotation relaxation mechanisms. The P ₂ and dipole correlation functions were compared with those calculated by Gordon from experimental data. The lack of agreement was examined to determine restrictions on the application of Gordon's method for obtaining these correlation functions. Also, the band shapes were compared with the experimental data to help determine these restrictions. The N.M.R. relaxation times were examined for temperature dependence and for dominant contributions to the total relaxation time. The force-on-the-bond correlation function was found to require an extra term that takes into account the average force field to which the N₂ molecule is subjected. A three-parameter model for rotational diffusion of a diatomic molecule is tested and compared with existing models.     

Femtosecond laser ablation of metals:a molecular dynamics simulation study

Using molecular dynamics (MD) methods combining with two-step radiation heating model, the mechanisms of ablation and the thermodynamic states at Ni surface under femtosecond laser irradiation are investigated. Simulation results show that the main mechanisms of ablation are evaporation and tensile stresses generated inside the target. The velocity of stress wave is predicted to be nearly equal to sound velocity. The rates of ablation at different fluences obtained from simulations are in good agreement with experimental data.     

Numerical simulation of the soliton solutions for a complex modified Korteweg—de Vries equation by a finite difference method

In this paper,a Crank-Nicolson-type finite difference method is proposed for computing the soliton solutions of a complex modifed Korteweg de Vries(MKdV)equation(which is equivalent to the Sasa-Satsuma equation)with the vanishing boundary condition.It is proved that such a numerical scheme has the second order accuracy both in space and time,and conserves the mass in the discrete level.Meanwhile,the resuling scheme is shown to be unconditionally stable via the von Nuemann analysis.In addition,an iterative method and the Thomas algorithm are used together to enhance the computational efficiency.In numerical experiments,this method is used to simulate the single-soliton propagation and two-soliton collisions in the complex MKdV equation.The numerical accuracy,mass conservation and linear stability are tested to assess the scheme's performance.     

PIXE–RBS survey of a Meissen porcelain snuff box: first version or not?

Non‐destructive materials analysis provided essential knowledge for deciding on the complete authenticity of a unique work of art made from porcelain, rich of delicate painting. The combination of ion‐beam based methods proton‐induced X‐ray emission (PIXE) and Rutherford‐backscattering spectrometry (RBS) was able to make simultaneously available both bulk composition and surface characterization. Potential differences in glazing and painting materials were verified when examining the base body and the lid of the box. In particular, RBS from Pb atoms in the near‐surface depth region could identify lead‐glazing for the shaded porcelain of the bottom. The chemical composition of the brilliant glaze of the lid was proved by PIXE to conform to the typical Meissen recipe. Consequently, a later completed or restored object was deduced. Copyright © 2012 John Wiley & Sons, Ltd.