Dynamics of water evaporation from porous asphalt

The dynamics of water evaporation from porous asphalt mixture, with porosity ranging from 15% to 12 29%, have been investigated in this article. In order to test the same samples under different conditions, the pore structure of asphalt was quantified using X-ray Computed Tomography (CT) scans and 3D printed in transparent resin blocks. 3D printed transparent resin samples were tested under controlled laboratory conditions to understand the effect of pore space topology on the water retention and drying dynamics. The macroporosity, pore size distribution, air void tortuosity, water conductivity, and water retention curves of the 3D printed porous asphalt samples were quantified by means of image analysis. Moreover, a model was developed and tested experimentally to estimate the evaporation rates from porous asphalt materials under a wide range of porosities. Within the range of asphalt mixtures studied in the present work, the evaporation rate is related predominantly to the porosity, pore size distribution and tortuosity. It was found that the period over which water evaporation occurs at the surface is relatively short during drying of porous asphalt materials due to their relatively large pores weakening the capillary forces. This results in significantly shortening the so-called stage-1 evaporation (when the drying rate is controlled by liquid vaporisation at the surface) and early onset of the transition period (when both surface water evaporation and vapour diffusion inside porous asphalt play a comparable role in supplying the 26 evaporative demand). The transition period is followed by the stage-2 evaporation when the process is limited by the vapour diffusion inside the porous asphalt. Our results illustrate that the beginning of the stage-2 evaporation depends on the porosity and tortuosity of the porous asphalt material among other parameters. Our results and analysis provide new insights into the dynamics of water evaporation from asphalt materials

Dynamics of water evaporation from porous asphalt

The dynamics of water evaporation from porous asphalt mixture, with porosity ranging from 15% to 29%, have been investigated in this article. In order to test the same samples under different conditions, the pore structure of asphalt was quantified using X-ray Computed Tomography (CT) scans and 3D printed in transparent resin blocks. 3D printed transparent resin samples were tested under controlled laboratory conditions to understand the effect of pore space topology on the water retention and drying dynamics. The macroporosity, pore size distribution, air void tortuosity, water conductivity, and water retention curves of the 3D printed porous asphalt samples were quantified by means of image analysis. Moreover, a model was developed and tested experimentally to estimate the evaporation rates from porous asphalt materials under a wide range of porosities. Within the range of asphalt mixtures studied in the present work, the evaporation rate is related predominantly to the porosity, pore size distribution and tortuosity. It was found that the period over which water evaporation occurs at the surface is relatively short during drying of porous asphalt materials due to their relatively large pores weakening the capillary forces. This results in significantly shortening the so-called stage-1 evaporation (when the drying rate is controlled by liquid vaporisation at the surface) and early onset of the transition period (when both surface water evaporation and vapour diffusion inside porous asphalt play a comparable role in supplying the evaporative demand). The transition period is followed by the stage-2 evaporation when the process is limited by the vapour diffusion inside the porous asphalt. Our results illustrate that the beginning of the stage-2 evaporation depends on the porosity and tortuosity of the porous asphalt material among other parameters. Our results and analysis provide new insights into the dynamics of water evaporation from asphalt materials

Study of aircraft in intraurban transportation systems, volume 1

An analysis of an effective short range, high density computer transportation system for intraurban systems is presented. The seven county Detroit, Michigan, metropolitan area, was chosen as the scenario for the analysis. The study consisted of an analysis and forecast of the Detroit market through 1985, a parametric analysis of appropriate short haul aircraft concepts and associated ground systems, and a preliminary overall economic analysis of a simplified total system designed to evaluate the candidate vehicles and select the most promising VTOL and STOL aircraft. Data are also included on the impact of advanced technology on the system, the sensitivity of mission performance to changes in aircraft characteristics and system operations, and identification of key problem areas that may be improved by additional research. The approach, logic, and computer models used are adaptable to other intraurban or interurban areas

Diffusion mechanism of Zn in InP and GaP from first principles

The diffusion mechanism of Zn in GaP and InP has been investigated using first-principles computational methods. It is found that the kickout mechanism is the favored diffusion process under all doping conditions for InP, and under all except n-type conditions for GaP. In n-type GaP the dissociative mechanism is probable. In both p-type GaP and InP, the diffusing species is found to be Zni+2. The activation energy for the kickout process is 2.49 eV in GaP and 1.60 eV in InP, and therefore unintentional diffusion of Zn should be a larger concern in InP than in GaP. The dependence of the activation energy both on the doping conditions of the material and on the stoichiometry is explained, and found to be in qualitative agreement with the experimentally observed dependencies. The calculated activation energies agree reasonably with experimental data, assuming that the region from which Zn diffuses is p type. Explanations are also found as to why Zn tends to accumulate at pn junctions in InP and to why a relatively low fraction of Zn is found on substitutional sites in InP

A Hybrid Algorithm for Topology Optimization of Additive Manufactured Structures

Most topology (TO) algorithms involve the penalization of intricate structural features to eliminate manufacturing difficulties. Since additive manufacturing is less dependent on manufacturing constraints, it becomes necessary to adapt these algorithms for AM. We propose a hybrid algorithm consisting of an adaptive meshing strategy (AMS) and a modified form of the bidirectional evolutionary structural optimization (BESO) method. By solving a standard cantilever problem, we show that the hybrid method offers improved performance over the standard BESO method. It is proposed that the new method is more suitable for optimizing structures for AM in a computational efficient manner.Mechanical Engineerin

Residual disorder and diffusion in thin Heusler alloy films

Co2FeSi/GaAs(110) and Co2FeSi/GaAs(111)B hybrid structures were grown by molecular-beam epitaxy and characterized by transmission electron microscopy (TEM) and X-ray diffraction. The films contained inhomogeneous distributions of ordered L2_1 and B2 phases. The average stoichiometry was controlled by lattice parameter measurements, however diffusion processes lead to inhomogeneities of the atomic concentrations and the degradation of the interface, influencing long-range order. An average long-range order of 30-60% was measured by grazing-incidence X-ray diffraction, i.e. the as-grown Co2FeSi films were highly but not fully ordered. Lateral inhomogeneities of the spatial distribution of long-range order in Co2FeSi were found using dark-field TEM images taken with superlattice reflections

Predicting phase resetting due to multiple stimuli

We generalized the phase resetting curve (PRC) to a more realistic case of neural oscillators receiving two or more inputs per cycle. The PRC tabulates the transient change in the firing period of a neuron due to an external perturbation, such as a presynaptic stimulus. We used a conductance-based model neuron to estimate experimentally the two-stimulus PRC and compared the results against our mathematical prediction based on the assumption of instantaneous recurrent stimulation. Within the limits of the recurrent stimulation assumptions, we found that the newly introduced prediction for the two-stimulus PRC matched experimental measurements. Our new results open the possibility of a more realistic approach to predicting phase-locked modes in neural networks, such as the synchronous activity of large networks during epileptic seizures

Fractal scan strategies for selective laser melting of ‘unweldable’ nickel superalloys

The high thermal gradients experienced during manufacture via selective laser melting commonly result in cracking of high γ/γ′ Nickel based superalloys. Such defects cannot be tolerated in applications where component integrity is of paramount importance. To overcome this, many industrial practitioners make use of hot isostatic pressing to ‘heal’ these defects. The possibility of such defects re-opening during the component life necessitates optimisation of SLM processing parameters in order to produce the highest bulk density and integrity in the as-built state. In this paper, novel fractal scanning strategies based upon mathematical fill curves, namely the Hilbert and Peano-Gosper curve, are explored in which the use of short vector length scans, in the order of 100 μm, is used as a method of reducing residual stresses. The effect on cracking observed in CM247LC superalloy samples was analysed using image processing, comparing the novel fractal scan strategies to more conventional ‘island’ scans. Scanning electron microscopy and energy dispersive X-ray spectroscopy was utilised to determine the cracking mechanisms. Results show that cracking occurs via two mechanisms, solidification and liquation, with a strong dependence on the laser scan vectors. Through the use of fractal scan strategies, bulk density can be increased by 2 ± 0.7% when compared to the ‘island’ scanning, demonstrating the potential of fractal scan strategies in the manufacture of typically ‘unweldable’ nickel superalloys

Femoral Neck Shaft Angle in Men with Fragility Fractures

Introduction. Femoral neck shaft angle (NSA) has been reported to be an independent predictor of hip fracture risk in men. We aimed to assess the role of NSA in UK men. Methods. The NSA was measured manually from the DXA scan printout in men with hip (62, 31 femoral neck and 31 trochanteric), symptomatic vertebral (91), and distal forearm (67) fractures and 389 age-matched control subjects. Age, height, weight, and BMD (g/cm2: lumbar spine, femoral neck, and total femur) measurements were performed. Results. There was no significant difference in mean NSA between men with femoral neck and trochanteric hip fractures, so all further analyses of hip fractures utilised the combined data. There was no difference in NSA between those with hip fractures and those without (either using the combined data or analysing trochanteric and femoral neck shaft fractures separately), nor between fracture subjects as a whole and controls. Mean NSA was smaller in those with vertebral fractures (129.2° versus 131°: P = 0.001), but larger in those with distal forearm fractures (129.8° versus 128.5°: P = 0.01). Conclusions. The conflicting results suggest that femoral NSA is not an important determinant of hip fracture risk in UK men