On the Barzilai-Borwein basic scheme in FFT-based computational homogenization

Building upon the equivalence of the basic scheme in the work of Moulinec and Suquet with gradient descent methods, we investigate the effect of using the celebrated Barzilai-Borwein step size selection technique in this context. We provide an overview of recent convergence theory and present efficient implementations in the context of computational micromechanics, with and without globalization. In contrast to polarization schemes and fast gradient methods, no lower bound on the eigenvalues of the material tangent is necessary for the Barzilai-Borwein scheme. We demonstrate the power of the proposed method for linear elastic and inelastic large scale problems with finite and infinite material contrast.     

Lippmann-Schwinger solvers for the computational homogenization of materials with pores

We show that under suitable hypotheses on the nonporous material law and a geometric regularity condition on the pore space, Moulinec-Suquet's basic solution scheme converges linearly. We also discuss for which derived solvers a (super)linear convergence behavior may be obtained, and for which such results do not hold, in general. The key technical argument relies on a specific subspace on which the homogenization problem is nondegenerate, and which is preserved by iterations of the basic scheme. Our line of argument is based in the nondiscretized setting, and we draw conclusions on the convergence behavior for discretized solution schemes in FFT-based computational homogenization. Also, we see how the geometry of the pores' interface enters the convergence estimates. We provide computational experiments underlining our claims.     

Stretchable Composite Acoustic Transducer for Wearable Monitoring of Vital Signs

A highly flexible, stretchable, and mechanically robust low‐cost soft composite consisting of silicone polymers and water (or hydrogels) is reported. When combined with conventional acoustic transducers, the materials reported enable high performance real‐time monitoring of heart and respiratory patterns over layers of clothing (or furry skin of animals) without the need for direct contact with the skin. The approach enables an entirely new method of fabrication that involves encapsulation of water and hydrogels with silicones and exploits the ability of sound waves to travel through the body. The system proposed outperforms commercial, metal‐based stethoscopes for the auscultation of the heart when worn over clothing and is less susceptible to motion artefacts. The system both with human and furry animal subjects (i.e., dogs), primarily focusing on monitoring the heart, is tested; however, initial results on monitoring breathing are also presented. This work is especially important because it is the first demonstration of a stretchable sensor that is suitable for use with furry animals and does not require shaving of the animal for data acquisition.     

Correction to: Embrittlement Analysis of Σ5[210]/(-1-20) FeAl Grain Boundary in Presence of Defects: An Ab Initio Study

Metallurgical and Materials Transactions A -     

A Review of “Children & Their Urban Environment: Changing Worlds”

Problem: Information is often suppressed when public infrastructure is planned by design-build-finance-operate (DFBO) public/private partnerships, an increasingly popular strategy for procuring transportation facilities, hospitals, and schools.

Purpose: I aim to identify strategies to increase transparency and accountability in large infrastructure projects delivered through public/private partnerships.

Methods: I studied the case of an award winning public/private partnership to plan a rapid rail line in Vancouver by comparing confidential documents released after project approval to the information available while planning was underway.

Results and conclusions: I find that although this project followed many best practices for achieving accountable and transparent public/private partnerships, in some instances it kept unfavorable study results from public view, limiting the potential for meaningful public involvement in the planning process. Takeaway for practice: I identify the following strategies to increase transparency and accountability in large infrastructure projects, including those delivered through private-public partnerships: (1) using a clear and narrow standard for what information should be kept confidential; (2) ensuring that public officials with responsibility for project decisions and their staffs have full access to all project information, including that not made public; (3) appointing a watchdog to see that these standards are upheld; and (4) implementing a decision process that allows public input and places the burden for proving that information should remain confidential on the entity making the request.     

Examining the Relationship Between Black Carbon and Soot in Flames and Engine Exhaust

This article investigates the black carbon (BC) content of soot formed in premixed and diffusion flames and emitted by light duty gasoline and diesel vehicles. BC is measured photoacoustically and compared with particulate mass collected by filter and calculated from particle size distributions. The BC fraction of soot from rich premixed ethylene flames increases with height above the burner, but can remain well below unity in modestly sooting flames. The BC fraction produced by a propane diffusion flame soot generator (combustion aerosol standard, CAST) falls as the fuel is diluted with nitrogen, the principal means used to adjust the desired particle size. Thermally treating the soot to remove possible condensed semivolatile species does little to change these trends. Transmission electron microscopy (TEM) images show that despite low BC content, these particles display the characteristic fractal-like agglomerate morphology of soot. Particle mass spectra reveal polycyclic aromatic hydrocarbon (PAH) and fullerene fragments associated with low BC soot, which disappear as the BC fraction approaches unity. The results suggest that low BC content reflects immature solid soot that has not carbonized. Particulate matter (PM) measurements from current technology diesel and gasoline vehicles exhibit a high, >80% BC fraction. This is attributed to effective soot carbonization during the expansion and exhaust strokes of the engine, and to the substantial reductions of condensable hydrocarbons by catalytic aftertreatment. These results are discussed with respect to using light absorption-based instruments to monitor engine exhaust PM and using flame-generated soot for PM instrument calibration.     

A Highly Active and Selective Manganese Oxide Promoted Cobalt-on-Silica Fischer�CTropsch Catalyst

A highly active and selective manganese oxide-promoted silica-supported cobalt catalyst for the Fischer?CTropsch reaction is reported. Co/MnO/SiO₂ catalysts were prepared via impregnation of a cobalt nitrate and manganese nitrate precursor, followed by drying and calcination in an NO/He flow. The catalysts were studied with STEM?CEELS, infrared spectroscopy measurements of adsorbed CO and Steady-State Isotopic Transient Kinetic Analysis experiments. Based on those experiments, a relation between C₅₊-selectivity and surface-coverages of CH _x -intermediates on cobalt was found.