Search

This paper examines the time-varying conditional correlations among new deaths because of covid-19, new tests for covid-19 and new vaccination for covid-19. We apply a trivariate dynamic conditional correlation (DCC) EGARCH model to capture potential contagion effects between the markets for the period 2020-2022. Empirical results reveal contagion. Findings have crucial implications for policymakers who provide regulations for the above derivative markets and for investors, who apply massive strategies to convince the general public to be vaccinated.

This empirical study examines the time-varying spillover and contagion effects between one major future market, one major FOREX market and six major Islamic CDS markets. We use daily data for crude oil future, SAR/EUR and Saudi Arabia CDS markets. The data spans from February 15, 2011 to August 27, 2020, which entails major economic events. In this paper, we deploy DCC-FIGARCH process. The empirical findings indicate volatility effects spilling over from crude oil future returns to SAR/EUR returns and CDS market returns. Dynamic Conditional Correlations provide empirical evidence of strong contagion effects between the market returns. Conclusions of this paper are of interest to investors diversifying their portfolios of the above markets and to financial derivative markets regulators providing regulations for the under investigation derivative markets.

Laser powder bed fusion (L-PBF) was utilized to produce specimens in Ti-6Al-4V, which were subjected to a bi-lamellar heat treatment, which produces microstructures consisting of primary α-lamellae and a fine secondary α-phase inside the inter-lamellar β-regions. The bi-lamellar microstructure was obtained as (i) a direct bi-lamellar heat treatment from the asbuilt condition or (ii) a bi-lamellar heat treatment preceded by a β-homogenization. For the bi-lamellar treatment with β-homogenization, cooling rates in the range 1−500 K/min were applied after homogenization in β-region followed by inter-critical annealing in the α + β region at various temperatures in the range 850-950 °C. The microstructures were characterized using various microscopical techniques. Mechanical testing with Vickers hardness indentation and tensile testing was performed. The bi-lamellar microstructure was harder when compared to a soft fully lamellar microstructure, because of the presence of fine α-platelets inside the β-lamellae. Final low temperature ageing provided an additional hardness increase by precipitation hardening of the primary α-regions. The age hardened bi-lamellar microstructure shows a similar hardness as the very fine, as-built martensitic microstructure. The bi-lamellar microstructure has more favorable mechanical properties than the as-built condition, which has high strength, but poor ductility. After the bi-lamellar heat treatment, the elongation was improved by more than 250 %. Due to the very high strength of the as-built condition, loss of tensile strength is unavoidable, resulting in a reduction of tensile strength of ∼18 %.

Medical devices are required to feature a unique device identification marking to enable traceability. These identification tags are extensively applied directly onto metallic devices. Universally, the technology utilized to apply such markings is laser marking, where the device is heated locally in atmospheric air to form a dark oxide layer and generate contrast. Despite the wide application, the consequences of laser marking on materials performance are largely unknown. In this study, the effect of laser marking on the most common titanium alloys in the medical industry, i.e., commercially pure titanium and Ti6Al4V, is investigated. The morphology and composition of the generated oxide layer were investigated, along with a characterization of the heat affected zone. Additionally, the effect on fatigue strength is investigated in relation to the application of laser marked titanium in a dental implant. Morphologically the laser marked titanium surfaces exhibited signs of melting on the very surface and the generation of an abundance of cracks which formed upon cooling. Scanning electron microscopy shows that these cracks are perpendicular to the surface and reach deep into the HAZ. Evidence of substantial oxygen ingress was demonstrated: various titanium-based oxides were identified via X-ray diffraction, as well as oxygen stabilized α-phase. The fatigue analysis showed a severe reduction in endurance limit for all investigated parameters and materials of up to 80%. This was attributed the notch effect resulting from crack formation during laser marking. The fractured surfaces were investigated and showed a clear crack propagation from the entire laser-marked surface.

This work evaluates and revisits elements from the depth-sensing indentation literature by means of carefully chosen practical indentation cases, simulated numerically and compared to experiments. The aim is not to provide a comprehensive study, but to close a series of debated subjects, which constitute major sources of inaccuracies in the evaluation of depth-sensing indentation data in practice, with the help of illustrative examples. First, own examples and references from the literature are presented in order to demonstrate how crucial self-similarity detection and blunting distance compensation are, for establishing a rigorous link between experiments and simple sharp indenter models. Moreover, it is demonstrated, once again, in terms of clear and practical examples, that no more than two parameters are necessary to achieve an excellent match between a sharp indenter finite element simulation and experimental force–displacement data. The clear conclusion is that reverse analysis methods promising to deliver a set of three unique material parameters from depth-sensing indentation cannot be reliable. Lastly, in light of the broad availability of modern finite element software, we also suggest to avoid the rigid indenter approximation, as it is shown to lead to unnecessary inaccuracies. All conclusions from the critical literature review performed lead to a new semi-analytical reverse analysis method, based on available dimensionless functions from the literature and a calibration against case specific finite element simulations. Implementations of the finite element model employed are released as supplementary material, for two major finite element software packages.

The aim of the paper is to propose the construction of an index that captures the economic complexity of cities over the globe, as well as to explore whether it is a good predictor for a range of city-level economic outcomes. This index aspires to mitigate data scarcity for cities and to provide policy makers with the tools for monitoring the evolving role of cities in the global economy. Analytically, we implement the economic complexity methodology on data for the ownership, location and economic activities of the world’s 3,000 largest firms and their subsidiaries to propose a new indicator that quantifies the network of the largest cities worldwide and the economic activities of their globalized firms. We first show that complex cities are the highly diversified cities that host non-ubiquitous economic activities of firms with global presence. Then, in a sample of EU cities, we show that complex cities tend to be more prosperous, have higher population, and are associated with more jobs, human capital, innovation, technology and transport infrastructure. Last, using OLS methodology and accounting for several other confounders, we show that a higher ECI, at the city level, enhances the resilience of cities to negative economic shocks, i.e., their ability to bounce back after a shock. Specifically, we find that the expected increase of the ratio of employment in 2012 over 2006 is 0.01 (mean: 0.992; standard deviation: 0.081) when the ECI increases by 1 unit (mean: 0.371; standard deviation: 1.094), i.e., a satisfactory pace of recovery, in terms of employment. The ability to diversify in the presence of a shock, the reallocation of factors of production to other sectors and the ability to extract rents associated with those diversified activities, uncovers the mechanics of the ECI index.

We present a novel optical beam steering technique for fiber to free-space to fiber-coupling schemes on optical breadboards, which is based on a glass plate and a pair of glass wedges. Our approach permits much finer adjustments of the beam direction and position when compared to conventional beam steering techniques that use adjusting elements of the same mechanical precision. This results in a much increased precision, accuracy, and stability. Furthermore, the presence of a beam steering element in proximity to the fiber coupler allows a great simplification of the design of this element which is typically considered as the most complex and sensitive element on an optical fiber breadboard. Overall, a beam steering precision of better than $$5\,\upmu $$rad and $$5\,\upmu $$m is demonstrated, resulting in a resolution in coupling efficiency of 0.1%. Likewise, we demonstrate a fiber-to-fiber-coupling efficiency of more than 89.8%, with a stability of 0.2% in a stable temperature environment and 2% fluctuations over a temperature range from 10 to 40 °C over a measurement time of 14 h. Finally, we observe no non-reversible change in the coupling efficiency after performing a series of tests over large temperature variations ($$\varDelta T > 30$$ K). This technique can find direct application in proposed missions for quantum experiments in space (Bongs et al. in STE-QUEST space–time explorer and quantum equivalence principle space test, Technical report STE-QUEST, European Space Agency, 2013; Kaltenbaek et al. in EPJ Quantum Technol 3(1):5, 2016; Carraz et al. in Microgravity Sci Technol 26:139, 2014), e.g., in space-based quantum sensing, where precisely controlled laser light is used to cool and manipulate atoms, or in inter-satellite quantum key distribution.

This work demonstrates numerically how microplasticity, i.e. the yielding behavior below the conventional 0.2% plastic strain threshold, can lead to initiation of cracks at subsurface defects, in rolling contact applications operating under realistic loads. A 3D elasto-plastic finite element model is employed to perform shakedown analysis of the bearing steel around a small spherical void with two different approximations of the steel constitutive behavior at the plastic micro-strain regime. When non-linear kinematic hardening is used to model a fast but smooth onset of plasticity, the fields of plastic strains and micro-residual stresses around the void evolve very distinctly to the case where a sharp transition is assumed. To further investigate the role of the tensile micro-residual stresses occurring in the former case on crack initiation, a planar circular crack is inserted at the equator of the void and an entire overrolling cycle is investigated by means of linear elastic fracture mechanics (LEFM). This analysis is repeated for different crack sizes and the respective stress intensity factors and their amplitudes, relevant for crack growth, are reported. The work also reports implementation details for the coupling of a 3D elasto-plastic model for shakedown analysis to a subsequent LEFM analysis model.

This work investigates plastic deformation around non-metallic inclusions in rolling contact fatigue applications. Subsurface stresses from Hertzian theory are applied in form of far-field loading on an elasto-plastic micro-mechanical model of an isolated inclusion. Initial and cyclic micro-scale plasticity are quantified, assuming linear kinematic hardening for the steel matrix and elastic or elastic perfectly plastic behavior for the inclusion. The accumulated plastic strain and cyclic plasticity are evaluated in the matrix. The effect of the yield strength on the elasto-plastic behavior of the matrix around the inclusions is investigated along with the effect of superimposed macro-residual stresses.

This paper demonstrates gradient driven density based topology optimization of transient impact problems with friction. The sensitivities are obtained using the semidiscrete adjoint approach in which the temporal components are obtained by the "differentiate then discretize" whereas the spatial part is determined discretely. In this work, the sensitivity analysis method is extended to a mixed formulation involving both displacements, velocities, accelerations and contact forces. The proposed formulation allows to account for frictional impacts during the structural optimization process. A first simple example demonstrates the effects of including frictional impacts into the transient design problem. As a second example, a drop test is considered and a casing for protecting a falling object during a frictional impact, is designed. Solid-void designs are obtained by application of the robust design formulation combined with a parameter continuation scheme.

This paper proposes a numerical method for determining the evolution of lubricant film thickness and pressure in partially and fully flooded regions of a hydrodynamic contact between two non-conformal rigid surfaces. The proposed method accounts for the classical Reynolds equation within the fully flooded region and for film separation with surface tension driven flow in the partially flooded region, while at the same time it resolves the a priori unknown boundary between the two regions. Additionally it deals with transitions between wetted, partially flooded regions to dry regions, where the film thickness is zero. Both pressure and film thickness fields are considered as unknowns to solve for in each time step and they are approximated through quadratic B-spline finite elements. The geometry of the gap between the rigid surfaces delimiting the lubricant is accounted for in the form of a unilateral contact condition. Appropriate complementarity conditions with respect to separation or no penetration and no slip between the lubricant and the rigid surfaces are enforced by means of a weighted residual formulation.

This paper concerns density-based topology optimization of linear elastic contact problems, aiming to present robust and practically realizable designs for different objective functions. First we revisit a compliance minimization with frictionless contact problem from the literature and present crisp solid–void designs, based on the so-called modified robust topology optimization formulation. An adaptation of this problem to frictional contact is then solved for various friction coefficients and it is checked that the optimization algorithm indeed exploits the presence of friction for lowering the objective further. Secondly, we propose and demonstrate the use of a p -norm based objective function to control the distribution and variation of contact pressure, on an a priori unknown area of contact, between a body of unknown topology and an obstacle. To have control over the contact pressure, a Lagrange multiplier based contact formulation is used within a coupled Newton solution, for imposing impenetrability, friction, and the corresponding complementarity conditions. The adjoint method is employed for deriving consistent design sensitivities for the mixed formulation involving both displacements and contact Lagrange multipliers. Through a series of numerical examples, it is demonstrated how an even distribution of contact pressure and crisp solid–void designs can be obtained for problems with and without friction.

A framework is introduced for benchmarking periodic microstructures in terms of their ability to maintain their stiffness under large deformations, accounting in a unified manner both for buckling and softening due to geometric and material nonlinearities. The proposed framework is applied to three classical 2D lattice microstructures at different volume fractions as well as to an optimized hierarchical microstructure from the literature. The high slenderness of the structure members, often assumed in analyses, is demonstrated not to be valid at volume fractions of 10% and above, with the infinitesimal volume fraction solutions underestimating the actual buckling resistance considerably. The performed analyses provide useful and quantitative insight regarding the compressive load carrying capacity of materials with a moderately dense periodic microstructure, in a rather universal and practical form.

We present the theoretical analysis of a novel optical beam steering technique (OBST) for fiber to free-space to fiber coupling schemes on optical breadboards. This technique uses glass wedges and plates to correct misalignments in the position and angle of beams on the breadboard. It can be used in any application where stable and robust coupling of light from an input to an output fiber is required, such as laser distribution boards for cold atom experiments in space. We examine the optical performance in terms of coupling efficiency (CE) for a number of different OBST systems and compare the results. Coupling efficiencies above 95% and positional and angular resolution of smaller than 5 μm and 5 μrad can be achieved using this technology.

We present a novel optical beam steering technique (OBST) for fiber to free-space to fiber coupling schemes on optical breadboards, which uses glass wedge pairs and plates to correct for angular and translational misalignments respectively. This technique finds application in proposed missions for atom quantum experiments in space, e.g. where laser beams are used to cool and manipulate atomic clouds. The key advantage compared to the conventional beam steering is that OBST permits extremely fine adjustments whilst being far less sensitive to alignment errors and mechanical drifts. Beam steering resolutions of better than 5 μrad and 2 μm are achieved, resulting in a resolution in coupling efficiency (CE) of 0.1%. The inclusion of OBST on an optical breadboard reduces the requirements on the pointing and position precision adjustment of the fiber couplers, leading to a much-simplified design. The simpler construction of the couplers combined with the reduced sensitivity to drifts increases the stability-reliability of the breadboard and reduces the production duration and cost. We demonstrate CE of up to 90%, with a stability of 0.2% in a stable temperature environment and 2% over a temperature range from 10-40 degrees Celsius. We do not observe any change in the performance after large temperature changes.

We study the hyperfine spectrum of atoms of $^{87}$Rb dressed by a radio-frequency field, and present experimental results in three different situations: freely falling atoms, atoms trapped in an optical dipole trap and atoms in an adiabatic radio-frequency dressed shell trap. In all cases, we observe several resonant side bands spaced (in frequency) at intervals equal to the dressing frequency, corresponding to transitions enabled by the dressing field. We theoretically explain the main features of the microwave spectrum, using a semi-classical model in the low field limit and the Rotating Wave Approximation for alkali-like species in general and $^{87}$Rb atoms in particular. As a proof of concept, we demonstrate how the spectral signal of a dressed atomic ensemble enables an accurate determination of the dressing configuration and the probing microwave field., 17 pages, 14 figures, 3 tables

Under longitudinal compressive loading, periodically layered composites are prone to micro-buckling, which is often the decisive mechanism determining their strength. This paper is concerned with the load carrying capacity of structures made of layered composites with respect to micro-buckling related failure in regions of stress concentrations. A series of parametric studies show the effect of non-uniform stress distributions due to bending loads and the presence of geometrical features such as notches and holes on the initiation of micro-buckling. The contribution of the bending stiffness of the reinforcing layers on the resistance against micro-buckling introduces a dependence on the layer thickness, resulting in size-scale dependent strength limits. Therefore, both the shape and dimensions of the considered geometrical features and the layering thickness of the micro-structure are varied as part of the parametric studies. Moreover, the impact of imperfections in the composite micro-structure on the strength of the considered specimens is investigated.

This paper presents a homogenization method, which accounts for intrinsic size effects related to the fiber diameter in long fiber reinforced composite materials with two independent constitutive models for the matrix and fiber materials. A new choice of internal kinematic variables allows to maintain the kinematics of the two material phases independent from the assumed constitutive models, so that stress–deformation relationships, can be expressed in the framework of hyper-elasticity and hyper-elastoplasticity for the fiber and the matrix materials respectively. The bending stiffness of the reinforcing fibers is captured by higher order strain terms, resulting in an accurate representation of the micro-mechanical behavior of the composite. Numerical examples show that the accuracy of the proposed model is very close to a non-homogenized finite-element model with an explicit discretization of the matrix and the fibers.

A semi-analytical framework is introduced for the evaluation of favorable residual stresses for delaying rolling contact fatigue initiation. Subsurface stress histories are applied to a micro-scale model accounting for isolated inclusions of different types and geometries. Micro-scale von Mises stresses are calculated based on Eshelby’s method and considered as an estimator of crack initiation due to plastic deformation. The most critical cases in terms of micro-scale plasticity are identified, and the effect of macro-scale compressive residual stresses is considered. Finally, optimized residual stresses are determined that minimize the maximum attained micro-scale von Mises stress at different depths.

A theoretical framework is developed for the evaluation of favorable residual stress profiles, suppressing fatigue damage initiation in rolling contact fatigue. Non-metallic inclusions at the microstructure of bearings are one of the most important reasons for fatigue damage initiation since they act as stress risers. In order to evaluate the stress state around such inclusions at the micro-scale, macroscopic stress histories are determined by Hertzian contact theory at different depths below the raceway for a typical roller bearing. These stress distributions are then used as far-field stresses for a micro-scale model accounting for single inclusions of different geometries and orientations. Eshelby’s method is used to relate far-field and local stresses in the vicinity of inclusions. The von Mises stress criterion is then used as a conservative estimator of crack initiation due to micro-scale plasticity. The effect of compressive residual stresses added to the axial and circumferential normal stress components at different depths is analyzed. The von Mises stress field around different inclusions at different depths is investigated in order to determine the most critical case in terms of micro-scale plastic deformation. Finally, an optimization process is carried out in order to determine the residual stresses that minimize the maximum observed von Mises stress as a function of depth.

Some of the most sensitive and precise measurements to date are based on matterwave interferometry with freely falling atomic clouds. Examples include high-precision measurements of inertia, gravity and rotation. In order to achieve these very high sensitivities, the interrogation time has to be very long and consequently the experimental apparatus has to be very tall, in some cases reaching ten or even one hundred meters. Cancelling gravitational acceleration, e.g. in atomtronic circuits6,7 and matterwave guides, will result in compact devices having much extended interrogation times and thus much increased sensitivity both for fundamental and practical measurements. In this letter, we demonstrate extremely smooth and controllable matterwave guides by transporting Bose-Einstein condensates (BEC) over macroscopic distances: We use a novel neutral-atom accelerator ring to bring BECs to very high speeds (16x their velocity of sound) and transport them in a magnetic matterwave guide for 15 cm whilst fully preserving their internal coherence. The high angular momentum of more than 40000h per atom gives access to the higher Landau levels of quantum Hall states. The hypersonic velocities combined with our ability to control the potentials with pico-Kelvin precision open new perspectives in the study of superfluidity and give rise to new regimes of tunnelling and transport. Coherent matterwave guides are expected to enable interaction times of several seconds in highly compact devices. These developments will result in portable guided-atom interferometers for applications such as inertial navigation and gravity mapping., Comment: 11 pages, 3 figures

Inequality constraints converted to non-smooth equalities before discretization.Method resulting to very low fluctuations of friction forces in numerical examples.Reporting number of full Newton iterations for a series of well documented examples.Proposing the term "raytracing" for avoiding ambiguity between projection strategies. A new integral approximation of frictional contact problems under large deformations is presented. Impenetrability, friction and the relevant complementarity conditions are expressed through a non-smooth equation, considered in the continuous setting. A weak formulation of this non-smooth complementarity equation is discretized through a standard Galerkin procedure, is linearized consistently and incorporated in a generalized Newton solution process. The resulting integral handling of contact and friction complementarity conditions, previously implemented for small deformations only, is extended in the present paper to large deformations. In total, the proposed method is relatively simple to implement, while its robustness is illustrated through numerical examples.

This research focuses on establishing the relationship between the SLM process parameters, microstructure and mechanical properties in 3D printed ti-6Al-4V. To this end modelling of the thermal history, reflecting the applied process parameters, is linked to the as-printed microstructure, which, in turn, is linked to experimentally determined mechanical properties. The very high cooling rates in the centre of the specimen, as predicted by modelling, lead to a fine, martensitic microstructure, while the slower cooling rates close to the support structure lead to a fine lamellar α+β microstructure. The tensile properties, in particular the ductility, were found to depend on the printing orientation and surface finish.

This paper refers to testing of friction materials for holding brakes. In contrast to the more typical case of high energy brakes, holding brakes operate usually in a reciprocating sense, at very low sliding speeds and allow significantly higher clamping pressures. The design of a reciprocating pin-on-plate test-rig for studying the evolution of wear by monitoring the pin height reduction using Eddy-current proximity sensors is presented. Moreover, a new mechanism for recording the friction force is suggested. Apart from the design of the test-rig, friction force and wear rate measurements for two different friction materials running against an unhardened steel surface are presented as a usage case. © 2014 Elsevier B.V.

The paper concerns measurement of pin height for the determination of wear in a pin-on-plate (POP) or pin-on-disc (POD) test, where a pin is mounted on a holder that can be fixed on the test rig and removed for measurements. The amount of wear is assessed as difference of pin height before and after the test, using the distance between holder plane and pin friction plane as measurand. A series of measurements were performed in connection with POP testing of different friction material pins mounted on an aluminium holder. Pin height measurements were carried out on a coordinate measuring machine (CMM), achieving an expanded measurement uncertainty (k = 2) better than 1 μm. A simple dedicated fixture adaptable to workshop environment was developed and its metrological capability investigated, estimating an average uncertainty of measurement in the order of 5 μm (k = 2). Fixture measurements were compared with CMM measurements using the normalised En value. Acceptable En values (En < 1) were obtained in 58% of the measurements, showing a discrepancy which was explained in terms of different probing patterns on CMM and fixture.

We explore the relationship between human migration and OECD's foreign direct investment (FDI) using a gravity equation enriched with variables that account for complex-network effects. Based on a panel data analysis, we find a strong positive correlation between the migration network and the FDI network, which can be mostly explained by countries' economic/demographic sizes and geographical distance. We highlight the existence of a stronger positive FDI relationship in pairs of countries that are more central in the migration network. Both intensive and extensive forms of centrality are FDI enhancing. Illuminating this result, we show that bilateral FDI between any two countries is further affected positively by the complex web of "third party" corridors/migration stocks of the international migration network (IMN). Our findings are consistent whether we consider bilateral FDI and bilateral migration figures, or we focus on the outward FDI and the respective inward migration of the OECD countries., 26 pages, 3 figures, 4 tables

Friction materials for typical brake applications are normally designed considering thermal stability as the major performance criterion. There are, however, brake applications with very limited sliding velocities, where the generated heat is insignificant. In such cases it is possible that friction materials which are untypical for brake applications, like thermoplastics and fibre composites, can offer superior performance in terms of braking torque, wear resistance and cost than typical brake linings. In this paper coefficient of friction measurements for various thermoplastic and fibre composite materials running against a steel surface are presented. All tests were carried out on a pin-on-disc test-rig in reciprocating operation at a fixed sliding speed and various pressure levels for both dry and grease lubricated conditions. Moreover, a generic theoretical framework is introduced in order to interpret the changes of friction observed during the running-in phase.

We discuss a scheme to implement a gyroscopic atom sensor with magnetically trapped ultra-cold atoms. Unlike standard light or matter wave Sagnac interferometers no free wave propagation is used. Interferometer operation is controlled only with static, radio-frequency and microwave magnetic fields, which removes the need for interferometric stability of optical laser beams. Due to the confinement of atoms, the scheme may allow the construction of small scale portable sensors. We discuss the main elements of the scheme and report on recent results and efforts towards its experimental realization.

Often journal bearings have to support shafts that run misaligned into the bushing bore because of the combined effect of elastic deformations and manufacturing tolerances. In such cases, the thermo-hydrodynamic behaviour of the bearing needs to be investigated in detail in order to ensure the safe operation of the device, or, in other words, to avoid asperities contact. The difficulties to model the thermal phenomena comprise one of the main reasons for the limited contribution of theoretical models to the designing efforts. In this article an accurate thermo-hydrodynamic simulation of journal bearings operating under misalignment conditions is introduced at first. Then, the computed film thickness, pressure and temperature distribution, as well as the friction coefficient are shown for several variations of hour-glass profiled bearings operating under a misalignment of up to 5′. From the results shown it can be concluded that the load-carrying capacity of journal bearings can be greatly enhanced if a properly selected hour-glass design is applied. The results show further that a three-dimensional thermo-hydrodynamic analysis, as the one shown here, should always be carried out in order to verify the bushing design.

Limiting heat losses during ventilation of indoor building spaces has become a basic aim for architects, particularly since the oil crisis of 1970. Much experience has been gained in terms of ventilation of indoor spaces. Nevertheless, due to the complex applications, attempts to create a theoretical base for solving the problems related to the issue are limited, especially determining the minimum ventilation period required within a designated space. In this paper we have approached this matter, both theoretically and experimentally. The conclusion we reached was that controlled ventilation of spaces through vent holes that successively open and close at regular time intervals can limit the excessive circulation of air masses, which in turn limits heat losses.

We demonstrate quantum walks of correlated photons in a 2D network of directly laser written waveguides coupled in a 'swiss cross' arrangement. The correlated detection events show high-visibility quantum interference and unique composite behaviour: strong correlation and independence of the quantum walkers, between and within the planes of the cross. Violations of a classically defined inequality, for photons injected in the same plane and in orthogonal planes, reveal non-classical behaviour in a non-planar structure., 5 pages, 5 figures

Multiphoton quantum walks in integrated optics comprise an attractive controlled quantum system, that can mimic less readily accessible quantum systems and exhibit behavior that cannot in general be accurately replicated by classical light without an exponential overhead in resources. The ability to observe the time evolution of such systems is important for characterizing multiparticle quantum dynamics—notably this includes the effects of boundary conditions for walks in spaces of finite size. Here we demonstrate the coherent evolution of quantum walks of two indistinguishable photons using planar arrays of 21 evanescently coupled waveguides fabricated in silicon oxynitride technology. We compare three time evolutions, that follow closely a model assuming unitary evolution, corresponding to three different lengths of the array—in each case we observe quantum interference features that violate classical predictions. The longest array includes reflecting boundary conditions

Quantum mechanics defines two classes of particles-bosons and fermions-whose exchange statistics fundamentally dictate quantum dynamics. Here we develop a scheme that uses entanglement to directly observe the correlated detection statistics of any number of fermions in any physical process. This approach relies on sending each of the entangled particles through identical copies of the process and by controlling a single phase parameter in the entangled state, the correlated detection statistics can be continuously tuned between bosonic and fermionic statistics. We implement this scheme via two entangled photons shared across the polarisation modes of a single photonic chip to directly mimic the fermion, boson and intermediate behaviour of two-particles undergoing a continuous time quantum walk. The ability to simulate fermions with photons is likely to have applications for verifying boson scattering and for observing particle correlations in analogue simulation using any physical platform that can prepare the entangled state prescribed here.

Quantum mechanics defines two classes of particles-bosons and fermions-whose exchange statistics fundamentally dictate quantum dynamics. Here we develop a scheme that uses entanglement to directly observe the correlated detection statistics of any number of fermions in any physical process. This approach relies on sending each of the entangled particles through identical copies of the process and by controlling a single phase parameter in the entangled state, the correlated detection statistics can be continuously tuned between bosonic and fermionic statistics. We implement this scheme via two entangled photons shared across the polarisation modes of a single photonic chip to directly mimic the fermion, boson and intermediate behaviour of two-particles undergoing a continuous time quantum walk. The ability to simulate fermions with photons is likely to have applications for verifying boson scattering and for observing particle correlations in analogue simulation using any physical platform that can prepare the entangled state prescribed here.

Due to the rough nature of real mechanical surfaces, the contact between elastic bodies occurs at several size-scales. Statistical and fractal contact models can take a wide range of roughness wavelengths into account, without additional computational cost. However, deterministic models are more straightforward to understand and easier to extend to more complex cases like contacting bodies that demonstrate elasto-plastic behavior. This paper presents a finite-element model for studying the frictionless contact between nominally flat rough surfaces. Apart from a description of the model implementation, results from a series of calculations corresponding to theoretical and real life applications are included. Numerically generated surface topographies but also roughness measurements from a stylus instrument are used as input for the model. Elastic and perfectly elastic-plastic materials are included in the examples. Among the presented results one can find the distribution of the contact pressure at the interface and diagrams of the real area of contact as a function of the nominal contact pressure. © 2013 Elsevier B.V.

The compressive strength of unidirectionally or layer-wise reinforced composite materials in direction parallel to their reinforcement is limited by micro-buckling instabilities. Although the inherent compressive strength of a given material micro-structure can easily be determined by assessing its stability under a uniform compressive load, this is often not sufficient for predicting failure initiation within a larger structure. In cases, where the composite material micro-structure is locally subjected to strongly non-uniform loadings, compressive instabilities depend not only on the maximum compressive stress but also on spatial stress or strain gradients, rendering failure initiation size scale dependent. The present work demonstrates and investigates the aforementioned effect through numerical simulations of periodically layered structures with notches and holes under bending and compressive loads, respectively. The presented results emphasize the importance of the reinforcing layer thickness on the load carrying capacity of the investigated structures, at a constant volumetric fraction of the reinforcement. The observed strengthening at higher values of the relative layer thickness is attributed to the bending stiffness of the reinforcing layers.

Quantum information science aims to harness uniquely quantum mechanical properties to enhance measurement and information technologies, and to explore fundamental aspects of quantum physics. Of the various approaches to quantum computing [1], photons are particularly appealing for their low-noise properties and ease of manipulation at the single qubit level [2,3]. Encoding quantum information in photons is also an appealing approach to quantum communication, metrology (eg. [4]), measurement (eg. [5]) and other quantum technologies [6]. However, the implementation of optical quantum circuits with bulk optics has reached practical limits. We have developed an integrated waveguide approach to photonic quantum circuits for high performance, miniaturization and scalability [7]. Here we report high-fidelity silica-on-silicon integrated optical realizations of key quantum photonic circuits, including two-photon quantum interference and a controlled-NOT logic gate [8]. We have demonstrated controlled manipulation of up to four photons on-chip, including highfidelity single qubit operations, using a lithographically patterned resistive phase shifter [9]. We have used this architecture to implement a small-scale compiled version of Shor's quantum factoring algorithm [10], demonstrated heralded generation of tunable four photon entangled states from a six photon input [11], a reconfigurable two-qubit circuit [12], and combined waveguide photonic circuits with superconducting single photon detectors [13]. We describe complex quantum interference behavior in multi-mode interference devices with up to eight inputs and outputs [14], and quantum walks of correlated particles in arrays of coupled waveguides [15]. Finally, we give an overview of our recent work on fundamental aspects of quantum measurement [16,17] and diamond [18,19] and nonlinear [20,21] photon sources.

Integrated photonics is required to fully exploit the capabilities of Optical Quantum Information science. We demonstrate new components that take full advantage of the integrated architecture; we show quantum interference in MMI couplers and two-particle quantum walks in coupled waveguides.

A Correlated Quantum Walk Random walks are powerful tools for modeling statistical events. The analogous quantum walk involves particles tunneling between available sites. Peruzzo et al. (p. 1500 ; see the Perspective by Hillery ) now report on the quantum walk of a correlated pair of photons propagating through a coupled waveguide array. The output pattern resulting from the injection of two correlated photons possess quantum features, indicating that the photons retain their correlations as they walk randomly through the waveguide array, allowing scale-up and parallel searches over many possible paths.

New components are required to take full advantage of the integrated photonic architecture for Quantum Information science. We demonstrate quantum interference in MMI couplers and two-particle quantum walks in coupled waveguides, showing unique quantum behaviour.