Where nanotechnology meets quantum computation

Since the invention of the scanning tunnelling microscope (STM) in the early 1980s atomic level microscopy has taken on a new dimension. The STM and the atomic force microscope (AFM) have become key instruments in the study of phenomena in the smallest dimensions ranging from magnetism in ultra-thin films, through the understanding of how atoms and molecules organise themselves, to insights into the propagation of electron waves. A good understanding of these issues will facilitate the manufacture of components or devices that are a few atomic dimensions in size and this will have far-reaching implications in fields ranging from medicine through to consumer electronics. As early as the 1970s, the scientific community was discussing the possibility of embedding a few molecules, or even a single molecule, between electrodes to perform the basic switching function. This is now possible in the case of individual components but key challenges lie with the economic commercial fabrication of whole devices. A key challenge lies in determining whether such quantum computers will work and how quantum effects can be used to perform variety of previously unsuspected and potentially useful schemes of information processing     

When green marketing meets reality: selected facts about sustainable house building

Since 2012, Life Cycle Engineering Experts (LCEE) have carried out a series of comprehensive studies into the sustainability of market‐relevant (also potentially) construction methods in German housing ([1] to [4]). The methodical basis was a systematic application of the sustainability assessment approach of the Deutsches Gütesiegel Nachhaltiges Bauen (DGNB) applied to representative model buildings from the detached house and apartment building sectors (see Figs. 1 and 2). The key findings have been compressed into themed fact sheets intended to ensure appropriate knowledge and information transfer to various recipients. As a contribution to less marketing and more reality, the following paper outlines the lessons learnt from selected example fact sheets concerning sustainable housing.     

Multiscale simulations of carbon nanotube nucleation and growth: mesoscopic continuum calculations

As part of a focused computational effort on the multiscale simulations of carbon nanotube nucleation and growth, we have developed computer programs for coupled heat and mass flow in one and two dimensions. In the tip-growth mode, the sample is divided into three main regions, each of which can be further subdivided as required. In region 1, carbon is supplied to the catalytic particle from an ambient gas of carbon-containing compounds. The chemistry and thermodynamics of the decomposition of these compounds can be included in region 1, but the capability has not yet been implemented. The carbon diffuses through the catalytic particle in region 2 under concentration and temperature gradients and with a diffusion coefficient that can depend on both concentration and temperature. Region 3 consists of the interfacial region between the catalytic particle and the growing nanotube. Results to date demonstrate the key roles played by the size and shape of the catalytic particle in conjunction with the concentration and temperature gradients at the gas/solid interface and in region 2. Results also suggest how the growth of a single wall may interfere with, but not necessarily prevent, the growth of additional walls in a multi-walled nanotube. Again, the carbon concentration profile in the catalytic particle at the different growth sites is a key factor.     

Multiscale simulations: application to the heat transfer simulation of sliding solids

Molecular dynamics is a powerful tool allowing the simulation of matter behaviour at the atomic scale. Due to computation time, it is clearly not possible to use molecular dynamics to simulate a forming process. However, atomistic simulations can be used to study and understand the physical phenomena that occur during matter deformation. As an example, heat transfer between the contacting solids in forming processes is one of the important physics phenomena that have to be taken into account in order to do realistic simulations. A multiscale analysis of heat transfer is presented. This analysis leads to two kinds of models: a macroscopic model which can be used for the simulation of the process itself and a microscopic model that is used to determine the parameters of the macroscopic model. In this microscopic model, the friction heat generation phenomena has to be described quite accurately. Friction heat is mainly due to plastic and elastic deformation and adhesion. Thus, to understand the underlying friction heat generation phenomena, atomistic simulations using molecular dynamics are carried out. It is shown that friction heat is the transformation of mechanical work given to the system at the macroscopic scale into potential energy during elastic deformation. This potential energy which is stored in the system is finally transformed into atomic kinetic energy (friction heat) during plastic transformation.     

Multiscale simulations of carbon nanotube nucleation and growth: electronic structure calculations

Several first-principles surface and bulk electronic structure calculations relating to the nucleation and growth of single-wall carbon nanotubes are described. Density-functional theory in various forms is used throughout. In the surface-related calculations, a 38-atom Ni cluster and several low-index Ni surfaces are investigated using pseudopotentials and plane-wave expansions. The energetic ordering of the sites for C atom adsorption is found to be the same, with the Ni(100) facet favored. The bulk diffusion coefficient of C in Ni as a function of cluster size and temperature is calculated from various molecular dynamics approaches. In another group of bulk-related calculations, Gaussian orbital basis sets are used to study a cluster or "flake" containing 14 C atoms. The flake is a segment of three hexagons from an "unrolled" carbon nanotube, with an armchair termination. The binding energies of C, Ni, Co, Fe, Cu, and Au atoms to it were calculated in an effort to gain insight into the mechanism for the high catalytic activity of Ni, Co, and Fe and the lack of it in Cu and Au. The binding energies of Cu and Au are about 1 eV less than those of the three catalytic elements. Similar methods are used to study the initial stages of nanotube growth within the context of classical nucleation theory. Finally, issues relating to the establishment of a fundamental catalytic mechanism are addressed.     

On the computation of sound by large-eddy simulations

The effect of the small scales on the source term in Lighthill's acoustic analogy is investigated, with the objective of determining the accuracy of large-eddy simulations when applied to studies of flow-generated sound. The distribution of the turbulent quadrupole is predicted accurately, if models that take into account the trace of the SGS stresses are used. Its spatial distribution is also correct, indicating that the low-wave-number (or frequency) part of the sound spectrum can be predicted well by LES. Filtering, however, removes the small-scale fluctuations that contribute significantly to the higher derivatives in space and time of Lighthill's stress tensor T _ij. The rms fluctuations of the filtered derivatives are substantially lower than those of the unfiltered quantities. The small scales, however, are not strongly correlated, and are not expected to contribute significantly to the far-field sound; separate modeling of the subgrid-scale density fluctuations might, however, be required in some configurations.     

Multiscale stochastic simulations for tensile testing of nanotube-based macroscopic cables

Thousands of multiscale stochastic simulations are carried out in order to perform the first in-silico tensile tests of carbon nanotube (CNT)-based macroscopic cables with varying length. The longest treated cable is the space-elevator megacable but more realistic shorter cables are also considered in this bottom-up investigation. Different sizes, shapes, and concentrations of defects are simulated, resulting in cable macrostrengths not larger than approximately 10 GPa, which is much smaller than the theoretical nanotube strength (approximately 100 GPa). No best-fit parameters are present in the multiscale simulations: the input at level 1 is directly estimated from nanotensile tests of CNTs, whereas its output is considered as the input for the level 2, and so on up to level 5, corresponding to the megacable. Thus, five hierarchical levels are used to span lengths from that of a single nanotube (approximately 100 nm) to that of the space-elevator megacable (approximately 100 Mm).     

Multiscale complex moments of the local power spectrum

Complex moments of the local power spectrum (CMP) are investigated in a multiscale context. The multiscale CMPs are shown to approximate well the 1D angular Fourier transform of the band in question. This observation is used to derive further properties of the power spectrum in terms of texture orientations or n-folded symmetry patterns. A method is presented to approximate the power spectrum using only separable filtering in the spatial domain. Interesting implications to the Gabor decomposition are shown. The number of orientations in the filter bank is related to the order of n-folded symmetry detectable. Furthermore, the multiscale CMPs can be estimated incrementally in the spatial domain, which is both fast and reliable. Experiments on power spectrum estimation, orientation estimation, and texture segmentation are presented.     

Fast computation of multi-scale combustion systems

In the present work, we illustrate the process of constructing a simplified model for complex multi-scale combustion systems. To this end, reduced models of homogeneous ideal gas mixtures of methane and air are first obtained by the novel relaxation redistribution method, and thereafter used for the extraction of all the missing variables in a reactive flow simulation with a global reaction model.     

Digital computation of the complex linear canonical transform

An efficient algorithm for the accurate computation of the linear canonical transform with complex transform parameters and with complex output variable is presented. Sampling issues are discussed and the requirements for different cases given. Simulations are provided to validate the results.     

Techniques to accelerate BEM computation to provide virtual reality update of stress solutions

We address the problem of rapid re-analysis of small problems in elasticity, in which the aim is to enable updated stress contours to be displayed in real time as a design geometry is dynamically modified. For the small to medium sized problems that are the focus of the work, it cannot be assumed that the solution phase dominates, and so the evaluation of boundary integrals is considered as well as the equation solution. Two strategies are employed for acceleration of boundary element integrals: the use of look-up tables (LUTs) containing pre-computed integrals and the use of approximate analytical expressions derived from surface fits. These may be used in the matrix assembly and internal point calculations. This paper concentrates on the extension of the LUT technique presented earlier [Trevelyan J, Wang P. Interactive re-analysis in mechanical design evolution. Part 2: rapid evaluation of boundary element integrals. Comput Struct 2001;79:939–51 [1]] to consider circular arc elements as well as extending the method to the derivative kernels to allow the use of LUTs with the stress boundary integral equation. Further details are provided on suitable LUT refinement and the approach is benchmarked against conventional Gauss–Legendre integration. The surface fit approach is presented as an alternative to LUTs that does not incur the considerable memory cost associated with LUTs. The equation solution is cast in a re-solution framework, in which we use a GMRES algorithm. Convergence is greatly accelerated by using an approximate complete LU preconditioner updated periodically using multi-threading. The resulting system achieves the aim of providing real-time update of contours for small to medium sized problems on a PC. This development is expected to allow a qualitative change in the way engineers might use computer aided engineering tools, in which design ideas may rapidly be assessed immediately as a change is made.     

Integral floating display systems for augmented reality

Novel integral floating three-dimensional (3D) display methods are proposed for implementing an augmented reality (AR) system. The 3D display for AR requires a long-range focus depth and a see-though property. A system that adopts a concave lens instead of a convex lens is proposed for realizing the integral floating system with a long working distance using a reduced pixel pitch of the elemental image. An investigation that reveals that the location of the central depth plane is restricted by the pixel pitch of the display device is presented. An optical see-through system using a convex half mirror is also proposed for providing 3D images with a proper accommodation response. The concepts of the proposed methods are explained and the validity of system is proved by the experimental results.     

面向异构多核并行系统的层次化计算模型HmPlogP

在参数化LogP模型(PLogP模型)的基础上,针对异构多核并行系统通用核和加速核的异构性、存储的层次化、并行执行的层次化特征,提出了新的层次化计算模型Hm-PlogP.该模型对异构多核并行系统的通信和访存进行了抽象,采用向量化参数表达并行系统不同层次的特征,能够预测加速核的执行开销并以此指导并行程序的设计和优化.实验...     

Brute force meets Bruno force in parameter optimisation: introduction of novel constraints for parameter accuracy improvement by symbolic computation

Recent remarkable advances in computer performance have enabled us to estimate parameter values by the huge power of numerical computation, the so-called 'Brute force', resulting in the high-speed simultaneous estimation of a large number of parameter values. However, these advancements have not been fully utilised to improve the accuracy of parameter estimation. Here the authors review a novel method for parameter estimation using symbolic computation power, 'Bruno force', named after Bruno Buchberger, who found the Gro?bner base. In the method, the objective functions combining the symbolic computation techniques are formulated. First, the authors utilise a symbolic computation technique, differential elimination, which symbolically reduces an equivalent system of differential equations to a system in a given model. Second, since its equivalent system is frequently composed of large equations, the system is further simplified by another symbolic computation. The performance of the authors' method for parameter accuracy improvement is illustrated by two representative models in biology, a simple cascade model and a negative feedback model in comparison with the previous numerical methods. Finally, the limits and extensions of the authors' method are discussed, in terms of the possible power of 'Bruno force' for the development of a new horizon in parameter estimation.     

Multiscale and hysteresis effects in vortex pattern simulations for Ginzburg–Landau problems

The behavior and properties of vortex pattern solutions to a benchmark Ginzburg–Landau model are investigated using hybrid continuation algorithms in conjunction with parallel adaptive mesh refinement (AMR) schemes to resolve the local vortices. The model is related to phase transition models arising in superconductivity and superfluids. The approach is based on a coupled variational formulation and finite element approximation scheme for the complex‐valued solution. The associated algorithms implement continuation treatments based on the vortex scale coherence parameter and the winding number parameter in this model. Simulation results demonstrate the behavior of non‐unique solutions, as characterized by different vortex configurations, and energy plots are used to display hysteresis effects. The complex‐valued nature of the solution also serves to illustrate some interesting open questions related to AMR strategies and error indicators for complex‐valued solution fields as well as other implications for such coupled systems. Copyright © 2009 John Wiley & Sons, Ltd.     

When quantitative meets qualitative: enhancing OPM conceptual systems modeling with MATLAB computational capabilities

Conceptual modeling is an important initial stage in the life cycle of engineered systems. It is also highly instrumental in studying existing unfamiliar systems—the focus of scientific inquiry. Conceptual modeling methodologies convey key qualitative system aspects, often at the expense of suppressing quantitative ones. We present and assess two approaches for solving this computational simplification problem by combining Object-Process Methodology (OPM), the new ISO/PAS 19450 standard, with MATLAB or Simulink without compromising the holism and simplicity of the OPM conceptual model. The first approach, AUTOMATLAB, expands the OPM model to a full-fledged MATLAB-based simulation. In the second approach, OPM computational subcontractor, computation-enhanced functions replace low-level processes of the OPM model with MATLAB or Simulink models. We demonstrate the OPM computational subcontractor on a radar system computation. Experimenting with students on a model of an online shopping system with and without AUTOMATLAB has indicated important benefits of employing this computation layer on top of the native conceptual OPM model.