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In case-hardened steel components, fine-grain stability is one of the most important properties of the microstructure, since a single coarse grain in a fine-grain matrix is often sufficient to cause premature failure of the component under appropriate loading. In order to better understand the influence of heat treatments on cold formed components, the case hardened microstructure of 16 different heat treatment combinations was investigated on the case hardening steel 20MnCr5 (1.7168). The process chain influences grain growth inhibiting precipitations, which in turn influence the fine grain stability. For this reason, aluminium nitrides in size ranges from approx. 15 to 250 nm were analysed in two samples using high-resolution scanning electron microscopy in both fine and coarse-grained areas. The respective areas examined had an average area of 1,250−2,000 μm2. The statistical analysis showed that within the samples no significant difference in morphology and density between aluminium nitrides in fine and coarse-grained areas could be found. On the other hand, more clusters appear in larger grains. Furthermore, a significant influence of the heat treatments on the aluminium nitrides could be detected.

We present a comparison of the computer simulation data of gyroid nanostructures with optical measurements (reflectivity spectra and scattering diagrams) of ventral wing scales of the Green Hairstreak butterfly, Callophrys rubi. We demonstrate that the omnidirectional green colour arises from the gyroid cuticular structure grown in the domains of different orientation. We also show that this three-dimensional structure, operating as a biophotonic crystal, gives rise to various polarization effects. We briefly discuss the possible biological utility of the green coloration and polarization effects.

Starting from the data gathering and analysis procedures used in Einstein–Podolsky–Rosen–Bohm experiments with photons, we construct a simulation algorithm that satisfies Einstein''s criteria of local causality and realism and generates the same type of data as recorded in these idealized experiments. The simulation data is analyzed according to the experimental procedure to count coincidences, that is by using an expression for the coincidence counts that, besides depending on the settings of the variable polarizers, explicitly depends on the difference of the time tags of the detection signals in both observation stations and on an adjustable time window. We demonstrate that the simulation algorithm produces data that agrees with the two-particle correlation for the singlet state. [Copyright &y& Elsevier]

Abstract: We study the relation between the acquisition and analysis of data and quantum theory using a probabilistic and deterministic model for photon polarizers. We introduce criteria for efficient processing of data and then use these criteria to demonstrate that efficient processing of the data contained in single events is equivalent to the observation that Malus'' law holds. A strictly deterministic process that also yields Malus'' law is analyzed in detail. We present a performance analysis of the probabilistic and deterministic model of the photon polarizer. The latter is an adaptive dynamical system that has primitive learning capabilities. This additional feature has recently been shown to be sufficient to perform event-by-event simulations of interference phenomena, without using concepts of wave mechanics. We illustrate this by presenting results for a system of two chained Mach–Zehnder interferometers, suggesting that systems that perform efficient data processing and have learning capability are able to exhibit behavior that is usually attributed to quantum systems only. [Copyright &y& Elsevier]

Abstract: We propose and analyse simple deterministic algorithms that can be used to construct machines that have primitive learning capabilities. We demonstrate that locally connected networks of these machines can be used to perform blind classification on an event-by-event basis, without storing the information of the individual events. We also demonstrate that properly designed networks of these machines exhibit behavior that is usually only attributed to quantum systems. We present networks that simulate quantum interference on an event-by-event basis. In particular we show that by using simple geometry and the learning capabilities of the machines it is possible to simulate single-photon interference in a Mach–Zehnder interferometer. The interference pattern generated by the network of deterministic learning machines is in perfect agreement with the quantum theoretical result for the single-photon Mach–Zehnder interferometer. To illustrate that networks of these machines are indeed capable of simulating quantum interference we simulate, event-by-event, a setup involving two chained Mach–Zehnder interferometers, and demonstrate that also in this case the simulation results agree with quantum theory. [Copyright &y& Elsevier]

We present a comparative study of numerical algorithms to solve the time-dependent Maxwell equations for systems with spatially varying permittivity and permeability. We show that the Lie–Trotter–Suzuki product-formula approach can be used to construct a family of unconditionally stable algorithms, the conventional Yee algorithm, and two new variants of the Yee algorithm that do not require the use of the staggered-in-time grid. We also consider a one-step algorithm, based on the Chebyshev polynomial expansion, and compare the computational efficiency of the one-step, the Yee-type, the alternating-direction-implicit, and the unconditionally stable algorithms. For applications where the long-time behavior is of main interest, we find that the one-step algorithm may be orders of magnitude more efficient than present multiple time-step, finite-difference time-domain algorithms. [Copyright &y& Elsevier]

Abstract:: We study effects of the physical realization of quantum computers on their logical operation. Through simulation of physical models of quantum computer hardware, we analyze the difficulties that are encountered in programming physical realizations of quantum computers. Examples of logically identical implementations of the controlled-NOT operation and Grover's database search algorithm are used to demonstrate that the results of a quantum computation are unstable with respect to the physical realization of the quantum computer. We discuss the origin of these instabilities and discuss possibilities to overcome this, for practical purposes, fundamental limitation of quantum computers.

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A numerical method is presented to solve exactly the time-dependent diffusion equation that describes light transport in turbid media. The simulation takes into account spatial variations of the scattering and absorption factors of the medium and the objects as well as random fluctuations of these quantities. The technique is employed to explore the possibility of locating millimeter-sized objects immersed in turbid media from time-gated measurements of the transmitted or reflected (near-infrared) light. The simulation results for tissuelike phantoms are compared with experimental transillumination data, and excellent agreement is found. Simulations of time-gated reflection experiments indicate that it may be possible to detect objects of 1-mm radius.

We investigate the transition temperature of layered superconductors by considering a stack ofLz superconducting layers, separated by insulating material. We adopt a pairing Hamiltonian, invoke the variational principle and solve the resulting gap equations numerically. Our results confirm previous weak coupling and Ginzburg-Landau treatments and reveal a rise ofTc withLz and saturation at the bulk transition temperature. Thus, the rise ofTc is traced back to a finite size effect, corresponding to a crossover from 2-d to 3-d superconductivity. The results also reveal a sizeable variation of the gap along the stack with pronounced variation at the ends.

We explore the consequences of coupling between repulsive Hubbard models and Bosonic or spin degrees of freedom. In the regime where the characteristic energy of the non-fermionic part is large compared to the characteristic energy of the Fermions, the effective Hamiltonian corresponds to a generalized attractive Hubbard model. Superconducting properties are then calculated within the BCS scheme including the finite size dependence of correlation functions functions characterizings-wave pairing.

We report on the quantum-mechanical displacement form factor in quasiperiodic and random heterostructures. A one-dimensional treatment is adopted to describe the longitudinal displacement along the growth axis. Elastic properties are assumed to be homogeneous, while the inhomogeneous mass density characterizes the heterostructure. In the low-frequency limit, the peak structure can be attributed to acoustic phonons, whereas for higher frequencies the quasiperiodic and random cases differ markedly. In the quasiperiodic case and constant momentum transfer, resonances separated by gaps occur and their number depends on the resolution in the frequency domain. The random case is dominated by an acoustic resonance becoming broader with increasing frequency.

We investigate the importance of local anharmonic vibrations of the bridging oxygen in the copper oxide high-Tc materials in the context of superconductivity. For the numerical simulation we employ the projector quantum Monte Carlo method to study the ground state properties of the coupled electron-phonon system. The quantum Monte Carlo simulation allows an accurate treatment of electronic interactions which investigates the influence of strong correlations on superconductivity mediated by additional quantum degrees of freedom. As a generic model for such a system, we study the two-dimensional single band Hubbard model coupled to local pseudo spins (bridging oxygen), which mediate an effective attractive electron-electron interaction leading to superconductivity. The results are compared to those of an effective negativeU model.

Quantum Monte Carlo techniques often suffer from the so-called minus-sign problem. This paper explores a possibility to circumvent this fundamental problem by combining the Projector Quantum Monte Carlo method with the variational principle. Results are presented for the two-dimensional Hubbard model.

Assuming that charge carriers form a Fermi liquid state, we study a model for layered high-temperature superconductors with unretarded intralayer and interlayer pairing. Guided by band structure calculations and inverse photoemission experiments, we adopt a tight binding band with nearest and next-nearest neighbors hopping within the sheets and weak interlayer hopping. The gap equations are solved numerically, without imposing a cutoff energy, characteristic to phonon mediated superconductivity. On this basis we calculate the gap parameters,Tc, the tunneling conductance, infrared absorption and the coherence length for various band fillings ?=1/2-x by introducing excess holes of concentrationx. Assuming the interlayer coupling strength to be smaller than the intralayer one, our main results are as follows:Tc is dominated by the intralayer properties, reaching a maximum atx˜0.3, where strong coupling features appear. In the presence of interlayer pairing, the gap becomes anisotropic perpendicular to the layers, and standard BCS-behavior is modified. In particular the BCS-square root singularity in the density of states and in the tunneling conductance is replaced by van Hove singularities characterizing the anisotropic gap. In particular, we investigate the anisotropy of the tunneling conductance for specular and diffuse tunneling for a junction parallel or perpendicular to the layers, infrared absorption, as well as the coherence length, parallel and perpendicular to the layers.

Monte Carlo computer simulation techniques are used to study the formation of bipolarons on a lattice. The transition between the three possible states, extended, twopolaron, and bipolaron is studied. The phase diagram as a function of the strengths of the electron-phonon coupling and repulsive interaction is determined.

The neuroimaging technique three-dimensional polarized light imaging (3D-PLI) provides a high-resolution reconstruction of nerve fibres in human post-mortem brains. The orientations of the fibres are derived from birefringence measurements of histological brain sections assuming that the nerve fibres—consisting of an axon and a surrounding myelin sheath—are uniaxial birefringent and that the measured optic axis is oriented in the direction of the nerve fibres (macroscopic model). Although experimental studies support this assumption, the molecular structure of the myelin sheath suggests that the birefringence of a nerve fibre can be described more precisely by multiple optic axes oriented radially around the fibre axis (microscopic model). In this paper, we compare the use of the macroscopic and the microscopic model for simulating 3D-PLI by means of the Jones matrix formalism. The simulations show that the macroscopic model ensures a reliable estimation of the fibre orientations as long as the polarimeter does not resolve structures smaller than the diameter of single fibres. In the case of fibre bundles, polarimeters with even higher resolutions can be used without losing reliability. When taking the myelin density into account, the derived fibre orientations are considerably improved.

We discuss the impact of the physical implementation of a quantum computer on its computational efficiency, using computer simulations of physical models of quantum computer hardware. We address the computational efficiency of practical procedures to extract the results of a quantum computation from the wave function respresenting the final state of the quantum computer.

We describe a morphological image analysis method to characterize spatial patterns in terms of geometry and topology. This involves the calculation of the Minkowski functionals and the analysis of these functionals as a function of control parameters. The method is applied to triply periodic minimal surfaces and to three-dimensional structures formed in polymer solutions.

We describe a quantum algorithm to compute the density of states and thermal equilibrium properties of quantum many-body systems. We present results obtained by running this algorithm on a software implementation of a 21-qubit quantum computer for the case of an antiferromagnetic Heisenberg model on triangular lattices of different size.

We propose a modified single-particle Mach-Zehnder interferometer experiment in which the path length of one arm may change (randomly or systematically) according to the value of an external two-valued variable x, for each passage of a particle through the interferometer. Quantum theory predicts an interference pattern that is independent of the sequence of the values of x. On the other hand, corpuscular models that reproduce the results of quantum optics experiments carried out up to this date show a reduced visibility and a shift of the interference pattern depending on the details of the sequence of the values of x. The key question to be answered in a real laboratory experiment is: Which interference pattern is observed? Despite the general believe that quantum theory might be used to describe all single particle experiments, this is an interesting question to be answered since in the proposed experiment the experimental conditions not only continuously change but they might also have causal effects on the passage of the photons through the interferometer. The proposed experiment can be used to determine to what extent quantum theory provides a description of observed events beyond the usual statistical level.

We discuss an event-based corpuscular model of optical phenomena that does not require the knowledge of the solution of a wave equation of the whole system and reproduces the results of Maxwell's theory through a series of cause-and-effect processes, starting with the emission and ending with the detection of a particle. Event-based models of a single-photon detector and of light propagation through an interface of two dielectrics are used as modular building blocks to give a unified, corpuscular description of many optical phenomena. The approach is illustrated by applications to Wheeler's delayed choice, Einstein-Podolsky-Rosen-Bohm and Hanbury Brown-Twiss experiments.

Abstract: We describe portable software to simulate universal quantum computers on massive parallel computers. We illustrate the use of the simulation software by running various quantum algorithms on different computer architectures, such as a IBM BlueGene/L, a IBM Regatta p690+, a Hitachi SR11000/J1, a Cray X1E, a SGI Altix 3700 and clusters of PCs running Windows XP. We study the performance of the software by simulating quantum computers containing up to 36 qubits, using up to 4096 processors and up to 1 TB of memory. Our results demonstrate that the simulator exhibits nearly ideal scaling as a function of the number of processors and suggest that the simulation software described in this paper may also serve as benchmark for testing high-end parallel computers. [Copyright &y& Elsevier]

Kernel-based support vector machines (SVMs) are supervised machine learning algorithms for classification and regression problems. We introduce a method to train SVMs on a D-Wave 2000Q quantum annealer and study its performance in comparison to SVMs trained on conventional computers. The method is applied to both synthetic data and real data obtained from biology experiments. We find that the quantum annealer produces an ensemble of different solutions that often generalizes better to unseen data than the single global minimum of an SVM trained on a conventional computer, especially in cases where only limited training data is available. For cases with more training data than currently fits on the quantum annealer, we show that a combination of classifiers for subsets of the data almost always produces stronger joint classifiers than the conventional SVM for the same parameters. [ABSTRACT FROM AUTHOR]

We determine the classical and quantum complexities of a specific ensemble of three-satisfiability problems with a unique satisfying assignment for up to N=100 and 80 variables, respectively. In the classical limit, we employ generalized ensemble techniques and measure the time that a Markovian Monte Carlo process spends in searching classical ground states. In the quantum limit, we determine the maximum finite correlation length along a quantum adiabatic trajectory determined by the linear sweep of the adiabatic control parameter in the Hamiltonian composed of the problem Hamiltonian and the constant transverse field Hamiltonian. In the median of our ensemble, both complexities diverge exponentially with the number of variables. Hence, standard, conventional adiabatic quantum computation fails to reduce the computational complexity to polynomial. Moreover, the growth-rate constant in the quantum limit is 3.8 times as large as the one in the classical limit, making classical fluctuations more beneficial than quantum fluctuations in ground-state searches. [ABSTRACT FROM AUTHOR]

We study measures of decoherence and thermalization of a quantum system S in the presence of a quantum environment (bath) E. The entirety S+E is prepared in a canonical-thermal state at a finite temperature; that is, the entirety is in a steady state. Both our numerical results and theoretical predictions show that measures of the decoherence and the thermalization of S are generally finite, even in the thermodynamic limit, when the entirety S+E is at finite temperature. Notably, applying perturbation theory with respect to the system-environment coupling strength, we find that under common Hamiltonian symmetries, up to first order in the coupling strength it is sufficient to consider S uncoupled from E, but entangled with E, to predict decoherence and thermalization measures of S. This decoupling allows closed-form expressions for perturbative expansions for the measures of decoherence and thermalization in terms of the free energies of S and of E. Large-scale numerical results for both coupled and uncoupled entireties with up to 40 quantum spins support these findings. [ABSTRACT FROM AUTHOR]