Mines Repository (Colorado School of Mines)
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Manganite
No full textPhotographed by Ron Wolf.Spiky grey black prisms of manganite, Ilfeld, Nordhausen, Thuringia, Germany
Steel wars: the surface strikes back
No full textMetals are widely used to repair, restore, and augment the function of human bone and other tissues. They are also used extensively in surgical tools and appliances. One challenge of metals contacting human tissues is ensuring their biocompatibility. The human immune system rejects substances that are not native to our bodies. Some individuals may experience allergic reactions to specific metals. This research evaluated the risks of human soft tissues being exposed to cast martensitic stainless steel during surgery. The devices, called spinal retractor blades and retractor hooks, are used by surgeons to spread fatty and muscular tissues on a patient’s back, often for hours during spinal surgery. The retractors are removed after surgery, cleaned, and sterilized to be used repeatedly. The biocompatibility risks from repeated contact of metals with tissue are categorized by international standards, including ISO 10993, ISO 5832, and ISO 7153. Undesirable interactions between metals and tissues due to several effects such as cytotoxicity, genotoxicity, carcinogenicity, reproductive toxicity, immunotoxicity, systemic toxicity, metal degradation products or leachable products causing undesirable reactions. We assessed the biocompatibility of cast 420 stainless steel spinal retractors in the newly fabricated condition and after hospital use. Our evaluation included Laser Confocal Raman and Energy Dispersive Spectroscopy to identify elements and compounds that could pose risks. Surprisingly, we discovered degradation products in both pristine unused and hospital-used retractors. Iron oxide and hydroxide corrosion products were present on new and used retractors alike. Furthermore, used retractors showed evidence of pitting corrosion, likely associated with repeated steam sterilization treatments
Galena with calcite
No full textPhotographed by Ron Wolf.Metallic grey blocky galena crystals with small translucent white calcite crystal
Mimetite
No full textPhotographed by Ron Wolf.Greasy orange-tan cluster of tabular mimetite, San Carlos, Chihuahua, Mexico
Dioptase with cerussite
No full textPhotographed by Ron Wolf.Needle-like crystals of blue dioptase with cerussite, near Mammoth, Pinal County, Arizona
Conichalcite with calcite
No full textPhotographed by Ron Wolf.Dark green botryoidal clusters of small conichalcite crystals with glassy blades of white calcite
Arsenian pyromorphite
No full textPhotographed by Ron Wolf.Botryoidal mass of orange arsenian pyromorphite
Seismic imaging by nonlinear inversion
No full textIncludes bibliographical references.2024 Spring.Imaging aims to create representations of internal object structures through indirect external physical measurements. In seismic exploration, for instance, seismic reflections on the Earth’s surface are mapped into discontinuities in physical properties, revealing geological structures. Various seismic imaging techniques exist, differing in their approach to wave propagation (acoustic or elastic; isotropic or anisotropic), wave equation type (one-way or all-way), application domain (post-stack or pre-stack), numerical implementation (frequency or time domain; integral or differential forms), and other factors.
Migrations usually assume a linear relationship between data and image based on the Born approximation, and the image consists of a scalar parameter that describes the spatial distribution of subsurface reflectors. Since seismic data includes not only primary reflections but also multiples that do not satisfy the Born approximation, imaging is normally preceded by multiple attenuation to meet the linear assumption and avoid creating fake reflectors and crosstalk noise. However, multiples provide additional illumination and resolution because they can sample subsurface image points at angles different from those of the primary waves. Therefore, multiple attenuation ignores additional information that could be used to improve the image.
In this thesis, I introduce an acoustic nonlinear inversion imaging method, based on a parameterization of the wave equation that preserves the nonlinearity between data and image, defined as a vector instead of a scalar function. This parameterization separates propagation and dynamic effects. Wave propagation is ruled by a background velocity model, lacking sharp contrasts, while the dynamics of reflections is controlled by the image vector parameter I seek to invert. The vectorial nature of the image reflects the directional dependence of the reflectivity and its nonlinear dependence to the data enables multiple-scattering modeling to fit unprocessed data, containing multiples and ghots in addition to primaries