Small-scale Components Research Articles

From the street to the metropolitan region: Pedestrian perspective in urban fabric analysis

The urban fabric is a fundamental small-scale component of urban form. Its quantitative analysis has so far been limited either in its geographical extent or in the diversity of components analysed. Moreover, the planning approach has traditionally privileged an aerial perspective. A new approach integrating the pedestrian point of view is proposed. Spatial analysis procedures are implemented with a twofold objective: identifying urban fabrics and studying their spatial organization within a large metropolitan area. The former is achieved through multiple fabric assessment, a three-step protocol using a network-based partition of urban space: (i) a set of skeletal streetscape indicators is implemented on each spatial unit, considering different constituents of the urban fabric; (ii) spatial patterns on the street network are identified, applying geostatistical analysis to each indicator; and (iii) spatial patterns with Bayesian clustering are recombined, allowing the identification and characterization of urban fabric types and subspaces within the city. This methodology is tested on the French Riviera metropolitan area, where nine families of urban fabric are identified. Disentangling the spatial organization of urban fabrics represents the second objective of this paper: the geographical distribution of urban fabrics is investigated, applying mathematical morphology and variography while considering network-constrained topological contiguities.

Research on Free Jet Test Technology

Aerodynamic thermal ground test can not completely simulate flight conditions, and there is no simple and clear similarity criterion as aerodynamic test. In practical application, it is often to grasp the local flow characteristics of materials or structures and use ground test equipment to simulate their main thermal environment parameters. Therefore, according to the thermal environment characteristics of different parts of the aircraft, a variety of arc heating test techniques have been developed. For example, free jet test technology has been developed for material test of simplified model and assessment test of small-scale components. It effectively solves some problems of thermal protection test examination.

Study on Multi-Scale Coupled Ecological Dispatching Model Based on the Decomposition-Coordination Principle

Studies on environmental flow have developed into a flow management strategy that includes flow magnitude, duration, frequency, and timing from a flat line minimum flow requirement. Furthermore, it has been suggested that the degree of hydrologic alteration be employed as an evaluation method of river ecological health. However, few studies have used it as an objective function of the deterministic reservoir optimal dispatching model. In this work, a multi-scale coupled ecological dispatching model was built, based on the decomposition-coordination principle, and considers multi-scale features of ecological water demand. It is composed of both small-scale model and large-scale model components. The small-scale model uses a daily scale and is formulated to minimize the degree of hydrologic alteration. The large-scale model uses a monthly scale and is formulated to minimize the uneven distribution of water resources. In order to avoid dimensionality, the decomposition coordination algorithm is utilized for the coordination among subsystems; and the adaptive genetic algorithm (AGA) is utilized for the solution of subsystems. The entire model—which is in effect a large, complex system—was divided into several subsystems by time and space. The subsystems, which include large-scale and small-scale subsystems, were correlated by coordinating variables. The lower reaches of the Yellow River were selected as the study area. The calculation results show that the degree of hydrologic alteration of small-scale ecological flow regimes and the daily stream flow can be obtained by the model. Furthermore, the model demonstrates the impact of considering the degree of hydrologic alteration on the reliability of water supply. Thus, we conclude that the operation rules extracted from the calculation results of the model contain more serviceable information than that provided by other models thus far. However, model optimization results were compared with results from the POF approach and current scheduling. The comparison shows that further reduction in hydrologic alteration is possible and there are still inherent limitations within the model that need to be resolved.

Analytical study of micro-rotating disks with angular acceleration on the basis of the strain gradient elasticity

The small-scale effects on the mechanical responses of micro-rotating disks with angular acceleration are investigated based on the strain gradient theory, as one of the powerful non-classical continuum theories which have been developed to justify the empirical observations of mechanical behavior in small-scale structures and components. The differential equations governing motion of the micro-disk elements in radial and circumferential direction together with the corresponding boundary conditions are derived. Then, an analytical solution is presented for the components of the displacement field which can be used as a base for determination of the components of the stress field. In a numerical case study, the distribution of stress components as well as of the displacement components is investigated, and the obtained results are compared with those of the classical continuum theories.

Development of a small-diameter and high-resolution industrial endoscope with CMOS image sensor

In the industrial field, an endoscope is typically employed for the observation and inspection of internal defect and corrosion of an engine and chemical plant. Current industrial optical endoscopes normally use CMOS sensor which offers best performance as an image pickup device. Here we report experimental demonstration of an industrial endoscope modality consisting of a 5 mm diameter rigid tube and 1280 × 960 pixels CMOS camera, which enables accurate diagnosis of small-scale industrial components with hollow shape. As a proof of concept, we successfully perform arc-surface imaging at a resolution of 57 lp/mm and ± 30° field of view. Finally, potentially applying the wave-front coding method to extend the depth of field of endoscopic system is comprehensively discussed.

Stochastic flow approach to model the mean velocity profile of wall-bounded flows.

There is no satisfactory model to explain the mean velocity profile of the whole turbulent layer in canonical wall-bounded flows. In this paper, a mean velocity profile expression is proposed for wall-bounded turbulent flows based on a recently proposed stochastic representation of fluid flows dynamics. This original approach, called modeling under location uncertainty, introduces in a rigorous way a subgrid term generalizing the eddy-viscosity assumption and an eddy-induced advection term resulting from turbulence inhomogeneity. This latter term gives rise to a theoretically well-grounded model for the transitional zone between the viscous sublayer and the turbulent sublayer. An expression of the small-scale velocity component is also provided in the viscous zone. Numerical assessments of the results are provided for turbulent boundary layer flows, pipe flows and channel flows at various Reynolds numbers.

Evolution of Magnetic Helicity in Solar Cycle 24

Abstract We propose a novel approach to reconstruct the surface magnetic helicity density on the Sun or Sun-like stars. The magnetic vector potential is determined via decomposition of vector magnetic-field measurements into toroidal and poloidal components. The method is verified using data from a non-axisymmetric dynamo model. We apply the method to vector field synoptic maps from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory to study the evolution of the magnetic helicity density during solar cycle 24. It is found that the mean helicity density of the non-axisymmetric magnetic field of the Sun evolves in a way similar to that reported for the current helicity density of the solar active regions. It predominantly has a negative sign in the northern hemisphere, while it is mainly positive in the southern hemisphere. Also, the hemispheric helicity rule for the non-axisymmetric magnetic field showed the sign inversion at the end of cycle 24. The evolution of the magnetic helicity density of a large-scale axisymmetric magnetic field is different from what is predicted by dynamo theory. On one hand, the mean large- and small-scale components of magnetic helicity density display the hemispheric helicity rule of opposite signs at the beginning of cycle 24. However, later in the cycle, the two helicities exhibit the same sign, in contrast with theoretical expectations.

Collapse mechanism analysis of historic masonry structures subjected to lateral loads: A comparison between continuous and discrete models

The aim of this paper is to show to what extent a simple constitutive model can adequately describe the collapse mechanisms of historic masonry structures under horizontal seismic loads. Referring to block masonry, the paper presents the formulation and the numerical implementation of a constitutive relationship for modeling masonry structures regarded at a macroscopic scale as homogenized anisotropic continuum. The macroscopic model is shown to retain memory of the mechanical characteristics of the joints and of the shape of the blocks. The overall mechanical properties display anisotropy and singularities in the yield surface, arising from the discrete nature of the block structure and the geometrical arrangement of the units. The model is formulated in the framework of multi-surface plasticity. It is implemented in a FE code by means of a minimization algorithm directly derived from the Haar-Karman principle.A sensitivity analysis to mechanical and geometrical parameters was carried out to show the influence on the predicted response of small-scale wall components from the literature. The model is then used for the analysis of a numerical case study which is representative of a masonry church subjected to horizontal seismic action.The result of the model will be compared with those obtained by a rigid block model (RBM) of the same small-scale masonry prototypes and of the church building. In the paper, the results of the two models are discussed and analyzed in the way to highlight the weakness and the potentiality of the two different approaches.

High-temperature bulk metallic glasses developed by combinatorial methods.

Since their discovery in 19601, metallic glasses based on a wide range of elements have been developed2. However, the theoretical prediction of glass-forming compositions is challenging and the discovery of alloys with specific properties has so far largely been the result of trial and error3-8. Bulk metallic glasses can exhibit strength and elasticity surpassing those of conventional structural alloys9-11, but the mechanical properties of these glasses are critically dependent on the glass transition temperature. At temperatures approaching the glass transition, bulk metallic glasses undergo plastic flow, resulting in a substantial decrease in quasi-static strength. Bulk metallic glasses with glass transition temperatures greater than 1,000kelvin have been developed, but the supercooled liquid region (between the glass transition and the crystallization temperature) is narrow, resulting in very little thermoplastic formability, which limits their practical applicability. Here we report the design of iridium/nickel/tantalum metallic glasses (and others also containing boron) with a glass transition temperature of up to 1,162kelvin and a supercooled liquid region of 136kelvin that is wider than that of most existing metallic glasses12. Our Ir-Ni-Ta-(B) glasses exhibit high strength at high temperatures compared to existing alloys: 3.7 gigapascals at 1,000kelvin9,13. Their glass-forming ability is characterized by a critical casting thickness of three millimetres, suggesting that small-scale components for applications at high temperatures or in harsh environments can readily be obtained by thermoplastic forming14. To identify alloys of interest, we used a simplified combinatorial approach6-8 harnessing a previously reported correlation between glass-forming ability and electrical resistivity15-17. This method is non-destructive, allowing subsequent testing of a range of physical properties on the same library of samples. The practicality of our design and discovery approach, exemplified by the identification of high-strength, high-temperature bulk metallic glasses, bodes well for enabling the discovery of other glassy alloys with exciting properties.

Mechanism of suppression of vortex-induced vibrations of a streamlined closed-box girder using additional small-scale components

VIV (vortex-induced vibration) suppression using aerodynamic countermeasures are critical for design of long-span bridges. Strong vertical VIVs were observed in a streamlined closed-box bridge girder subject to wind at an initial attack angle of +3°. CFD simulation, and pressures and displacements measured in wind tunnel tests on a large-scale model (approximately 1:20) were analyzed to reveal the VIV-triggering mechanism for a bridge girder, as well as the VIV-suppression mechanism for bridge girders modified with typical small-scale additional components such as spoilers on crash barriers or guide vanes near maintenance traces. Spoilers can almost eliminate VIVs, while guide vanes can moderately mitigate them. Large-scale vortexes generated from flow separation at leading barriers and leading maintenance trails, referred to as separated vortexes and secondary vortexes, respectively, and called "double vortex mode" together, are responsible for VIVs of an unmodified girder. When spoilers were set on the barriers, the separated vortexes, and then the "double vortex mode" observed on the unmodified bridge girder, could be broken. This greatly reduced the correlation between local aerodynamic forces and general vortex-excited forces (VEFs), and thus the contribution of local aerodynamic forces to general VEFs on the model surface, which caused the VIVs to disappear. As for the unmodified girder, the "double vortex mode" is also responsible for vertical VIVs of a girder modified with guide vanes. This is due to the strong correlation between local aerodynamic forces and general VEFs. However, the phase lags between them have an overall offset of approximately 90° from the approximate synchronous action. Furthermore, a significant decrease in RMS values of pressure coefficients on the model surface dramatically reduce the direct contribution of local aerodynamic forces to general VEFs, especially in the downstream region of the upper surface, thus clearly mitigating VIVs.

Inverse identification of tungsten static recrystallization kinetics under high thermal flux

Understanding of recrystallization phenomenon is essential to apprehend damage process of tungsten armored plasma facing components and to optimize their use in tokamak environment. In ITER, plasma facing components will reach extreme surface temperature value up to 2000 °C. Up to now, recrystallization kinetics of ITER tungsten grade were investigated from 1150 °C to 1350 °C. In order to understand tungsten recrystallization process on the wider relevant temperature range, kinetics have to be investigated at higher temperature and on several tungsten grades. Usually, kinetics are investigated by performing successive isothermal annealings on tungsten samples. Due to number of ITER tungsten grades and large temperature range (from 500 °C to 2000 °C), an important amount of tungsten samples have to be prepared to investigate recrystallization kinetics on ITER representative conditions. In this paper, an innovative way is proposed to obtain recrystallization kinetics of ITER tungsten grade based on the use of small-scale plasma facing component tested under high heat flux. Thanks to the use of this inverse method, tungsten recrystallization kinetics are identified at 1348 °C±29, 1480 °C±29, 1586 °C±28 and 1696 °C±27 by using experimental measurements and Johnson–Mehl–Avrami–Kolmogorov model. Then, obtained kinetics are used as input data in numerical post-treatments to obtain tungsten recrystallization gradients after 500 thermal cycles at 20 MW/m2.

Numerical investigation of the two-scale model for rough surface scattering

The two-scale approximation for rough surface scattering assumes that a rough surface can be divided into two components: a large-scale and small-scale component, using a cutoff wavenumber to partition the wavenumber domain. This approach is attractive for multi-scale roughness such as the air-ocean and ocean-seafloor interfaces. Traditionally, the small roughness perturbation approximation is used for the small-scale component, and the Kirchhoff, or tangent-plane approximation is used for the large-scale component. Typically, the high-frequency approximation is used when propagating the surface fields to the far field, resulting in the physical interpretation of the large-scale surface modulating the local grazing angle of the small-scale surface. Using these approximations, the incoherent scattered power exhibits a dependence on the cutoff frequency, which is undesirable from a theoretical point of view. In this work, the validity of the approximations used on the small-scale surface, and large scale surface is examined through the use of numerical solution of the governing integral equations. This investigation is performed with the goal of testing the hypothesis that if each approximation on the component surfaces is demonstrated to be accurate, then the two-scale model should be independent of the cutoff frequency.

Study on the Construction of Initial Condition Perturbations for the Regional Ensemble Prediction System of North China

The regional ensemble prediction system (REPS) of North China is currently under development at the Institute of Urban Meteorology, China Meteorological Administration, with initial condition perturbations provided by global ensemble dynamical downscaling. To improve the performance of the REPS, a comparison of two initial condition perturbation methods is conducted in this paper: (i) Breeding, which was specifically designed for the REPS, and (ii) Dynamical downscaling. Consecutive tests were implemented to evaluate the performances of both methods in the operational REPS environment. The perturbation characteristics were analyzed, and ensemble forecast verifications were conducted. Furthermore, a heavy precipitation case was investigated. The main conclusions are as follows: the Breeding perturbations were more powerful at small scales, while the downscaling perturbations were more powerful at large scales; the difference between the two perturbation types gradually decreased with the forecast lead time. The downscaling perturbation growth was more remarkable than that of the Breeding perturbations at short forecast lead times, while the perturbation magnitudes of both schemes were similar for long-range forecasts. However, the Breeding perturbations contained more abundant small-scale components than downscaling for the short-range forecasts. The ensemble forecast verification indicated a slightly better downscaling ensemble performance than that of the Breeding ensemble. A precipitation case study indicated that the Breeding ensemble performance was better than that of downscaling, particularly in terms of location and strength of the precipitation forecast.

Pedestrian-to-Vehicle Communications in an Urban Environment: Channel Measurements and Modeling

As wireless connectivity becomes increasingly ubiquitous, a greater emphasis will be placed upon the seamless integration of dissimilar networking technologies. One such example of this will occur in urban environments, where wearable devices and vehicular networks will operate in close proximity to one another. Clearly, a natural extension to both types of network is their interconnectivity through vehicle-to-pedestrian (V2P) or equivalently pedestrian-to-vehicle (P2V) communications as part of a much greater vehicle-to-X (V2X)-based intelligent transportation system. To this end, we empirically investigate the P2V communications channel at 5.8 GHz for the case of a moving vehicle when a person positioned by the edge of a road was either stationary or walking parallel to the side of the highway. The measurements considered a chest-mounted transmitter and four receiver locations on the vehicle covering the front wing mirrors and two positions on the roof, which simultaneously recorded the received signal power. To characterize the propagation mechanisms which are responsible for shaping the received signal in the P2V channel, we decomposed it into its path loss (PL), large-scale, and small-scale fading components. We first show that although there was evidence of interference caused by multiple rays interacting with one another, the popular two-ray ground-reflection PL model was unable to adequately describe the compounded effects of the vehicle and pedestrian’s body on the signal attenuation in the majority of the considered scenarios. Instead, we found that the overall PL was well characterized using a dual-slope log-distance model, with lognormal large-scale fading. Due to the often severe small-scale fading that was observed in the P2V channel, we have been able to utilize the $\kappa $ - $\mu $ extreme distribution with considerable success to characterize the worse than Rayleigh fading conditions which were encountered.

Investigation on the Material Failure in a Small Scale Automotive Camera Module via Root Cause Analysis and Experimental Validation

Automotive camera modules are critical components for vision, detection, and recognition in an advanced driver assistance system. They usually consist of housing, a lens, a lens holder, a harness, seals, and printed circuit boards, which are assembled through screws, adhesive, and connectors. Due to a small and complex geometry of the components, the component material failure is a critical issue. In this paper, the lens holder material failure is investigated using the root cause analysis and experimental validation. First, a fishbone diagram model is created to analyze the potential causes and an action checklist is employed to identify the root cause. Second, the structure of the lens holder is optimized according to the finite-element analysis result. The numerical results show that the strength of the optimized lens holder is improved by nearly 35%. Finally, the torque test is carried out to validate the optimized structure experimentally. The presented analysis and validation procedure can be used to solve material failure issues for small-scale automotive components effectively.

Product Channeling in an O2O Supply Chain Management as Power Transmission in Electric Power Distribution Systems

With the aim of delivering goods and services to customers, optimal delivery channel selection is a significant part of supply chain management. Several heuristics have been developed to solve the variants of distribution center allocation and vehicle routing problems. In reality, small-scale suppliers cannot afford research and development departments to optimize their distribution networks. In this context, this research work develops a model for an online to offline (O2O) supply chain management network of a small-scale household electric components manufacturer for delivering goods to its distribution centers and retailers. Retailers are acquired by the company through investment in the O2O channel of e-commerce. Electric power transmission and distribution is considered as representative of the product distribution network. A model is developed using a combination of the supply chain management technique and power transmission terminologies. The constrained linear programming model is solved through the linear programming tool of the LINGO optimization software and the global optimum results for the proposed quantity allocation problem are achieved. A numerical experiment is provided to illustrate the practical applicability of the model and the optimal results are analyzed for model robustness.

Evolution of galactic magnetic fields

ABSTRACTWe study the cosmic evolution of the magnetic fields of a large sample of spiral galaxies in a cosmologically representative volume by employing a semi-analytic galaxy formation model and numerical dynamo solver in tandem. We start by deriving time- and radius-dependent galaxy properties using the galform galaxy formation model, which are then fed into the non-linear mean-field dynamo equations. These are solved to give the large-scale (mean) field as a function of time and galactocentric radius for a thin disc, assuming axial symmetry. A simple prescription for the evolution of the small-scale (random) magnetic field component is also adopted. We find that, while most massive galaxies are predicted to have large-scale magnetic fields at redshift $z$ = 0, a significant fraction of them is expected to contain negligible large-scale field. Our model indicates that, for most of the galaxies containing large-scale magnetic fields today, the mean-field dynamo becomes active at $z$ < 3. Moreover, the typical magnetic field strength at any given galactic stellar mass is predicted to decline with time up until the present epoch, in agreement with our earlier results. We compute the radial profiles of pitch angle, and find broad agreement with observational data for nearby galaxies.

Photodiodes embedded within electronic textiles

A novel photodiode-embedded yarn has been presented and characterized for the first time, offering new possibilities for applications including monitoring body vital signs (including heart rate, blood oxygen and skin temperature) and environmental conditions (light, humidity and ultraviolet radiation). To create an E-Textile integrated with electronic devices that is comfortable, conformal, aesthetically pleasing and washable, electronic components are best integrated within the structure of a textile fabric in yarn form. The device is first encapsulated within a protective clear resin micro-pod before being covered in a fibrous sheath. The resin micro-pod and covering fibres have a significant effect on the nature of light received by the photoactive region of the device. This work characterised the effects of both encapsulating photodiodes within resin micro-pods and covering the micro-pod with a fibrous sheath on the opto-electronic parameters. A theoretical model is presented to provide an estimate for these effects and validated experimentally using two photodiode types and a range of different resin micro-pods. This knowledge may have wider applications to other devices with small-scale opto-electronic components. Wash tests confirmed that the yarns could survive multiple machine wash and drying cycles without deterioration in performance.

Material selection for automated dry fiber placement using the analytical hierarchy process

Dry fiber tapes have become an alternative to pre-impregnated tapes for automated fiber placement. However, their industrial adoption is inhibited by high upfront research and development cost. To reduce the cost of material selection as part of such an investment, this work presents the application of the analytical hierarchy process (AHP) to material selection with a focus on material processability and manufacturing quality. The selection is based on procurement, material and its performance throughout the manufacturing process, and some laminate quality indicators. Criteria and sub-criteria were identified and implemented into the AHP. This established decision making tool was compared to a more efficient derivative using the chain of interaction method. Two materials, including the selected material, were used to manufacture a small-scale L-section composite component. This demonstrates that the proposed material selection method predicted the more preferable material for manufacturing quality when applied to a complex geometry.

On the Helical MHD Mode in a Finite-Conductivity Tokamak Plasma

A helical MHD perturbation in a finite-conductivity tokamak plasma has been considered in the straight-cylinder model in a situation where there is no resonance surface q = m/n in plasma. The radial eigenfunction of the helical mode, in addition to the large-scale component described at σ||→ ∞ by the ideal MHD equation, contains a small-scale component localized near the wall and near discontinuities in the radial profiles of the unperturbed quantities. At smooth profiles, the small-scale component is attached to the wall and is smaller in magnitude than the large-scale component. Therefore, beyond a thin near-wall plasma layer, the mode is close to the large-scale ideal MHD mode. The presence of the small-scale component is necessary to satisfy the boundary conditions for the perturbed field on the wall.