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| 2. |
- Chen, Chuchu, et al.
(author)
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Conservative methods for stochastic differential equations with a conserved quantity
- 2016
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In: International Journal of Numerical Analysis and Modeling. - Edmonton, Alberta, Canada. - 1923-2942. ; 13:3, s. 435-456
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Journal article (peer-reviewed)abstract
- This paper proposes a novel conservative method for the numerical approximation of general stochastic differential equations in the Stratonovich sense with a conserved quantity. We show that the mean-square order of the method is 1 if noises are commutative and that the weak order is 1 in the general case. Since the proposed method may need the computation of a deterministic integral, we analyse the effect of the use of quadrature formulas on the convergence orders. Furthermore, based on the splitting technique of stochastic vector fields, we construct conservative composition methods with similar orders as the above method. Finally, numerical experiments are presented to support our theoretical results.
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| 4. |
- Hazy, James K., et al.
(author)
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Notes on the Complexity of Corruption
- 2017
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Conference paper (peer-reviewed)abstract
- This article is intended to spark discussion about how complexity thinking might help researchers and practitioners better understand and prevent corruption. Moral and ethical arguments can be problematic because individuals vary in their underlying values. Complex systems theory offers a less values-laden interpretation of the phenomenon, its mechanisms, and its solutions. We describe an emergent condition in organizing dynamics that exploits an externality of a larger system such that certain individuals or groups benefit at the expense of others in that larger system. They do this by creating a “value sink” that captures resources that would otherwise continue to circulate within the system. A value sink is “corrupt” when it is actively maintained by some who enforce conditions that either limit transparency or constrain the autonomy of others in violation of the rules of interaction within the larger system. It follows that institutionalized corruption is a dynamically stable cooperative regime that sustains a corrupt value sink.
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| 5. |
- Kanninen, Petri, et al.
(author)
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Activation of commercial Pt/C catalyst toward glucose electro-oxidation by irreversible Bi adsorption
- 2018
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In: Journal of Energy Challenges and Mechanics. - : Elsevier. - 2056-9386. ; 27:5, s. 1446-1452
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Journal article (peer-reviewed)abstract
- The effect of irreversibly adsorbed Bi on commercial Pt/C catalyst toward glucose electro-oxidation reaction (GOR) in different electrolytes (acidic, neutral, alkaline) is studied. Bi is successfully deposited on Pt/C from Bi3+ containing acidic solution from 0 to 90% coverage degree. The stability of the Bi layer in acid and alkaline corresponded to previous studies and started to dissolve at 0.7 V and 0.8 V versus reversible hydrogen electrode (RHE), respectively. However, in neutral phosphate buffer the layer showed remarkable stability to at least 1.2 V versus RHE. Bi modification at low (20%) and high (80%) coverage showed the highest increase in the activity of Pt/C toward GOR by a factor up to 7 due to the increased poisoning resistance of the modified catalyst. The effect of poisoning was especially reduced at high Bi coverage (80%), which shows that adsorbate blocked by Bi through the third-body effect is effective. Finally, with or without Bi modification GOR on Pt/C was most active in alkaline conditions.
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| 6. |
- Krishnan, U., et al.
(author)
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The International Network on Oesophageal Atresia (INoEA) consensus guidelines on the transition of patients with oesophageal atresia-tracheoesophageal fistula
- 2023
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In: Nature Reviews Gastroenterology & Hepatology. - 1759-5045. ; 20, s. 735-755
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Journal article (peer-reviewed)abstract
- Oesophageal atresia-tracheoesophageal fistula (EA-TEF) is a common congenital digestive disease. Patients with EA-TEF face gastrointestinal, surgical, respiratory, otolaryngological, nutritional, psychological and quality of life issues in childhood, adolescence and adulthood. Although consensus guidelines exist for the management of gastrointestinal, nutritional, surgical and respiratory problems in childhood, a systematic approach to the care of these patients in adolescence, during transition to adulthood and in adulthood is currently lacking. The Transition Working Group of the International Network on Oesophageal Atresia (INoEA) was charged with the task of developing uniform evidence-based guidelines for the management of complications through the transition from adolescence into adulthood. Forty-two questions addressing the diagnosis, treatment and prognosis of gastrointestinal, surgical, respiratory, otolaryngological, nutritional, psychological and quality of life complications that patients with EA-TEF face during adolescence and after the transition to adulthood were formulated. A systematic literature search was performed based on which recommendations were made. All recommendations were discussed and finalized during consensus meetings, and the group members voted on each recommendation. Expert opinion was used when no randomized controlled trials were available to support the recommendation. The list of the 42 statements, all based on expert opinion, was voted on and agreed upon. Currently, systematic care for adults and adolescents with oesophageal atresia-tracheoesophageal fistula (EA-TEF) as they transition into adulthood is lacking. A multidisciplinary group of experts structured this Consensus Statement offering guidelines for the care of adolescents and adults with EA-TEF during transition.
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| 7. |
- Lennström, David, et al.
(author)
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The influence of the acoustic transfer functions on the estimated interior noise from an electric rear axle drive
- 2014
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In: SAE International Journal of Passenger Cars - Mechanical Systems. - : SAE International. - 1946-3995 .- 1946-4002. ; 7:1, s. 413-422
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Journal article (peer-reviewed)abstract
- In the vehicle development process, targets are defined to fulfill customers' expectations on acoustic comfort. The interior complete vehicle acoustic targets can be cascaded down to system and component targets, e.g. insulation properties and source strengths. The acoustic transfer functions (ATFs) from components radiating airborne noise play a central role for the interior sound pressure levels. For hybrid vehicles fitted with an electric traction motor, the contribution of high frequency tonal components radiated from the motor housing needs to be controlled. The interior sound pressure due to an airborne motor order can be estimated by surface velocities and ATFs. This study addresses the ATFs measured from a large number of positions located around an electric rear axle drive (ERAD) and their influence on estimated interior noise. First, the magnitude variation between the individual ATFs and how it clearly can be visualized was presented. Displaying all ATFs in a color map revealed the magnitude at each geometrical location of the respective microphone. Secondly, the influence of the ATF's spatial resolution on estimated interior sound pressure was investigated. This was done for theoretical models of the stator shell source shape and also for measured surface velocities. By reducing the spatial resolution from 0.05 to 0.10 m between each microphone, the difference in noise contribution is typically within three decibels with a 12th octave smoothing filter applied to the narrow-band data. The findings from this work provide insight in the risks of compromising with the number of ATF's needed for contribution analysis.
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| 8. |
- Wang, Ruoqi, 1992-, et al.
(author)
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Comparison of simulation methods applied to steel bridge reliability evaluations
- 2019
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In: 13th International Conference on Applications of Statistics and Probability in Civil Engineering, ICASP 2019.
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Conference paper (peer-reviewed)abstract
- Steel bridges are in general subjected to fatigue deterioration and the structural reliability of bridges will thus reduce over time. There are multiple simulation-based procedures available to perform structural probabilistic studies with several classes of uncertainty taken into account. Since the crack propagation is highly nonlinear and the limit state function (LSF) is multi-dimensional, it imposes specific demands on the simulation methods. Monte Carlo simulation (MCS) has been widely applied in various of fields, however, it requires a great amount of samples and long computation time to reach a high level of accuracy. A more advanced method, Subset Simulation (SS), compensates this shortage. It calculates the product of conditional probabilities of several chosen intermediate failure events. In this paper, the performance of each method was evaluated and compared against fatigue deterioration for aselected bridge detail. A probabilistic model was defined and both prior and updated reliability estimation were performed. The results showed that SS is a good option to deal with fatigue problem with high nonlinearity and multi-dimensional LSF, and shows outstanding time efficiency compared to MCS to reach a comparable accuracy.
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| 9. |
- Zhang, Qing
(author)
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Mechanical properties of semi-solid Al castings : Role of stirring
- 2023
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Doctoral thesis (other academic/artistic)abstract
- Aluminum castings have been widely used in the automotive industry to reduce the vehicle's weight. However, the existence of casting defects significantly limits its application. The most common and detrimental defects in aluminum castings are porosity and oxides. The formation of the pores comes from the solute hydrogen and volumetric reduction during the solidification process, resulting in the gas and shrinkage pores, respectively. The oxides can be introduced by either the operation during the process or the originally existing oxides in the melt. To reduce these defects, optimizing the casting process and controlling the melt quality is essential.In this work, the Semisolid Metal (SSM) process was used as it can significantly reduce the formation of shrinkage pores. The main focuses were on the influence of stirring intensity on the formation of casting defects and, thus, the resultant mechanical properties. In addition, to control the original melt quality, particularly the amount of oxides, efforts were made to develop proper methods for the melt quality assessment.The results show that the slurry-making process, mainly through stirring intensity, can affect the casting defects significantly. On the one hand, the increasing stirring intensity can distribute the primary Al particles more homogeneously, reducing the pores in terms of size and number by increasing the permeability during the solidification process. On the other hand, the increasing stirring intensity can affect the size of oxides differently, depending on the composition, for instance, the Mg content.For the alloys with sufficient Mg, the oxides would be MgAl2O4, which are small films with numerous cracks. Under intensive stirring, the oxides can break down into small oxide particles. As a result, intensive stirring can improve ductility by reducing the formation of big pores. However, the oxides would mainly be Al2O3 films for alloys with low Mg content. In this case, the current stirring intensity is insufficient to break the oxide films. Instead, the increased stirring has introduced more oxide films into the melt. Consequently, in the casting with intensive stirring, the increasing oxide films dominated the ductility rather than the reduced porosity.The SSM castings exhibit better bending fatigue properties than the casting using the traditional high-pressure die casting (HPDC) process. This improvement is mainly due to the formation of the harder surface liquid segregation (SLS) layer on the SSM casting surface. Furthermore, compared with the standard SSM process, the castings using intensive stirring (hereinafter referred to as the modified SSM process) show similar but more reliable fatigue properties. This reliable fatigue property can be attributed to eliminating the big internal pores through intensive stirring, which results in local stress concentration and significantly reduces fatigue performance. Besides, due to the gradient stress distribution in the bending loading, the surface defects play a significant role in the fatigue properties. With the increase of the specimens’ thickness, the failure mechanisms changed.The shrinkage pores in the reduced pressure test (RPT) test play a significant role in the accuracy of melt quality assessment. A good correlation between the bifilm index (BI)/ density index (DI) and hydrogen content is observed for the RPT samples without significant shrinkage pores. In addition, the correlation between the BI and elongation is also strongly affected by the clusters of shrinkage pores due to the conflict between the definition of the BI and the influence of clusters of shrinkage pores on the ductility. Based on this, we proposed an optimized BI where the clusters of shrinkage pores were treated as single pores, increasing the reliability of the correlation between the BI and elongation.
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| 10. |
- Huang, Yongming, et al.
(author)
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Constant Envelope Hybrid Precoding for Directional Millimeter-Wave Communications
- 2018
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In: IEEE Journal on Selected Areas in Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 0733-8716 .- 1558-0008. ; 36:4, s. 845-859
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Journal article (peer-reviewed)abstract
- Millimeter wave (mmwave) communication has attracted increasing attention owing to its abundant spectrum resource. The short wavelength at mmwave frequencies facilitates placing a large number of antennas in a small space, and the mmwave channels are likely to be sparse in the directions. These two new features promise enhanced security by directional precoding. To explore this potential, we investigate the design of directional hybrid digital and analog precoding for the multiuser mmwave communication system with multiple eavesdroppers. Particularly, we consider two cost-efficient sub-connected hybrid architectures, i.e., multi-subarray architecture and switched phased- array architecture, and optimize the hybrid precoding under per-antenna constant envelope (CE) constraints. The goal of our design is to guarantee the receive quality of the legitimate users while minimizing the power leaked to the eavesdroppers, so as to realize a directional transmission for a general mmwave channel. The resulting problems are very challenging due to the nonlinear CE constraints and binary integer constraint from antenna selection. To address them, we leverage exact penalty function methods to find efficient solutions to the CE hybrid directional precoding. Our analysis shows that the proposed algorithm is able to converge to a stationary point under some mild conditions. Simulation results are finally provided to confirm the effectiveness of the proposed schemes and their superiority over the existing schemes under both single-path and multi-path mmwave channels.
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