MEVTV Workshop on Tectonic Features on Mars

The state of knowledge of tectonic features on Mars was determined and kinematic and mechanical models were assessed for their origin. Three sessions were held: wrinkle ridges and compressional structure; strike-slip faults; and extensional structures. Each session began with an overview of the features under discussion. In the case of wrinkle ridges and extensional structures, the overview was followed by keynote addresses by specialists working on similar structures on the Earth. The first session of the workshop focused on the controversy over the relative importance of folding, faulting, and intrusive volcanism in the origin of wrinkle ridges. The session ended with discussions of the origin of compressional flank structures associated with Martian volcanoes and the relationship between the volcanic complexes and the inferred regional stress field. The second day of the workshop began with the presentation and discussion of evidence for strike-slip faults on Mars at various scales. In the last session, the discussion of extensional structures ranged from the origin of grabens, tension cracks, and pit-crater chains to the origin of Valles Marineris canyons. Shear and tensile modes of brittle failure in the formation of extensional features and the role of these failure modes in the formation of pit-crater chains and the canyons of Valles Marineris were debated. The relationship of extensional features to other surface processes, such as carbonate dissolution (karst) were also discussed

A study of the influence of particle gradation in bonded assemblies

The discrete element method (DEM) has been used extensively to study soil, rock, and masonry behavior because of its ability to model the materials as individual particles or bonded clumps of particles. DEM allows for examination of the macro- and micro-scale response and provides a means to study the fundamental material behavior, but it is still considered computationally expensive in relation to other methods. To lower computational costs, the smallest particle sizes are often considered negligible and are left out of the model. Additionally, rock or intact materials are often modeled as a bonded assembly of uniform spheres. To date, few research studies have considered the influence of particle size and gradation on the strength and fracture behavior of bonded assemblies. This research aims to examine the influence of particle gradation in bonded assemblies through laboratory calibrated DEM simulations. Additionally, the role of the cement-sized particles will also be investigated. While the overall motivation for this study is related to the behavior of mortar in historic preservation applications, the preliminary studies can be directly applied to other geo-related materials such as cemented sands and rock specimens. This study addresses two critical questions associated with the computational efficiency of bonded assembly models (1) Does particle gradation influence the overall strength and fracture behavior, and (2) Do the smallest size particles influence the overall results enough to justify the additional computational cost? In this study two mortar materials, varying only in sand particle gradation, are subjected to physical laboratory compression strength tests to assess whether or not the influence is observed in physical experiments. Additionally, the compression test results act as a means of calibrating the simulations in DEM. These simulations will examine the macro- and micro-scale influence of particle gradation on the strength of bonded assemblies. Additional simulations are used to examine the effects of modeling the cement-sized particles in the bonded assembly. The results of the physical experiments and the development of the DEM simulations are discussed herein

Feasibility of Additive Manufactured Materials for Use in Geotechnical Laboratory Testing Applications

The factors affecting the positive volumetric strain, or dilatancy, typically observed in response to shearing of a dense granular material have long been investigated; however, there still lacks a direct relationship between particle shapes and the resulting dilatant response. The typical Mohr-Coulomb strength parameter associated with granular material is known as the effective friction angle (φ’). For a dense granular assemblage, the peak friction angle has been described as being comprised of a dilatant friction angle (φ’d) component and a critical state friction angle (φ’cv) component. While the topic of dilatancy and factors (both inherent and extrinsic) affecting its behavior are understood by researchers, added complexity exists due to the dependency of the dilatation angle on features such as density, confining stress, and stress path. With continuous innovation in additive manufacturing (AM), the technology has encompassed a broader spectrum of users including scientists and engineers. AM provides a new avenue for understanding the effect of particle shape on the dilatant response of granular material by providing the ability to change shape geometry while maintaining consistent material properties. It is hypothesized that an AM-fabricated analogue soil sample can then be used in a laboratory setting. A preliminary investigation was carried out to identify the various AM technologies available and their associated materials. After examining the strength and stiffness characteristics of the various materials, two separate AM technologies were selected. An analogue soil sample was fabricated using each device and was tested in consolidated drained triaxial compression. The analogue soils provided a shearing behavior similar to that of natural granular materials, thus indicating its feasibility for additional studies in geotechnical engineering

Establishing Reasonableness of Compensation Difficult in IRS Attackes

With this in mind, reasonable compensation determinations have developed a different twist for shareholder-employees of Subchapter S corporations. As the payroll tax burden continues to increase, it now appears that the respective positions of the taxpayer and the IRS in issues of reasonable compensation, at least in the case of S corporations, are being reversed. Thus the issue has turned to how small, rather than how large, a shareholder-employee\u27s salary may be and still be considered reasonable. The topic at hand centers around minimizing the payroll tax burden of the shareholder-employee. In recent years, payroll taxes have increased substantially in amount, both from an increasing tax rate and an increasing base. Annual payroll tax collections for social security amount to approximately $329 billion, of which$266 billion will be paid out in benefits. Recently, much debate has centered around these surpluses and the ever-growing payroll tax burden shouldered by America\u27s wage earners . However, although Congress appears to be considering a reduction in payroll taxes, to date, only increases in social security taxes have been legislated