Rensselaer Polytechnic Institute

About: Rensselaer Polytechnic Institute is a education organization based out in Troy, New York, United States. It is known for research contribution in the topics: Terahertz radiation & Finite element method. The organization has 19024 authors who have published 39922 publications receiving 1414699 citations. The organization is also known as: RPI & Rensselaer Institute.

Zircon Saturation Thermometry

Abstract: The ability of crystalline zircon (ZrSiO4) to incorporate and retain trace element and isotopic information, due to sluggish diffusion, makes it an indispensable tool for geochemists and geochronologists (Valley, this volume; Cherniak and Watson, this volume) in deciphering the Earth’s geologic history. The stability of crystalline zircon over long periods of geologic time led researchers to prefer this mineral for geochronology (Heaman and Parrish 1991, Dickin 1995, Davis et al., this volume; Parrish and Noble, this volume). In fact, much of what is known about the timing of major geologic events has been accomplished through geochronology using U/Pb isotopic analyses of zircon (Froude et al. 1983, Bowring and Housch 1995, Buick et al. 1995, Bowring et al. 1998, Amelin et al. 1998, Amelin et al. 1999, Bowring and Williams 1999, Amelin et al. 2000, Mojzsis et al. 2001, Wilde et al. 2001, Peck et al. 2001, Bowring and Schmitz, this volume). Because of its durability, zircon has also been proposed as a potential storage material for weapons-grade plutonium from dismantled nuclear weapons (Ewing et al. 1995, Ewing 1999, Ewing et al., this volume). In addressing the petrogenesis of granitoid rocks, a thorough understanding of the role of accessory minerals is crucial for constraining the distribution of trace elements and isotopes that are hosted mainly by those minerals. In particular, in granitoid rocks that were derived from melting of preexisting crustal sediments or rocks, it is often desirable to understand the role of Zr (and Hf), which is primarily concentrated in zircon. This includes determining whether the zircon crystals are single generation growth having crystallized in the magma in which they were most recently found. Or, if preexisting zircon was entrained (i.e., did not dissolve) in …

Retrograde net transfer reaction insurance for pressure-temperature estimates

Abstract: Retrograde net transfer reactions significantly affect compositions of metamorphic minerals, yet are rarely considered when determining pressure-temperature (P-T) conditions. Two natural amphibolite facies metapelites from the central Himalaya of Nepal exhibit extremely common compositional patterns, including increases in Mn and Fe/(Fe + Mg) at the rims of garnets, which are the result of retrograde garnet dissolution and Fe-Mg exchange with biotite. However, typical thermobarometric approaches for these rocks result in errors of hundreds of degrees and 3–6 kbar compared with thermobarometry of nearby rocks and petrogenetic grids. These large errors result because dissolution of high-Fe garnet has strongly affected the Fe/Mg ratio of matrix biotite. X-ray maps help evaluate the extent and chemical effects of retrograde reactions in these samples by identifying mineral regions that retain highest-T compositions, or, through a new data-processing approach, by permitting correction of mineral compositions to original high-T values. These approaches ensure against retrograde net transfer reactions and should be applied routinely in thermobarometric studies—they ultimately yield P-T estimates that are more petrologically reasonable, and permit rapid screening of samples for those least affected by retrograde reactions. Reconsideration of thermobarometry in the central and eastern Himalaya indicates that retrograde net transfer reactions are extremely common. Therefore, previous thermobarometric studies based on garnet major element compositions from that region should be reevaluated.

Meeting report: The role of environmental lighting and circadian disruption in cancer and other diseases

Abstract: Light, including artificial light, has a range of effects on human physiology and behavior and can therefore alter human physiology when inappropriately timed. One example of potential lightinduced disruption is the effect of light on circadian organization, including the production of several hormone rhythms. Changes in light‐dark exposure (e.g., by nonday occupation or transmeridian travel) shift the timing of the circadian system such that internal rhythms can become desynchronized from both the external environment and internally with each other, impairing our ability to sleep and wake at the appropriate times and compromising physiologic and metabolic processes. Light can also have direct acute effects on neuroendocrine systems, for example, in suppressing melatonin synthesis or elevating cortisol production that may have untoward long-term consequences. For these reasons, the National Institute of Environmental Health Sciences convened a workshop of a diverse group of scientists to consider how best to conduct research on possible connections between lighting and health. According to the participants in the workshop, there are three broad areas of research effort that need to be addressed. First are the basic biophysical and molecular genetic mechanisms for phototransduction for circadian, neuroendocrine, and neurobehavioral regulation. Second are the possible physiologic consequences of disrupting these circadian regulatory processes such as on hormone production, particularly melatonin, and normal and neoplastic tissue growth dynamics. Third are effects of light-induced physiologic disruption on disease occurrence and prognosis, and how prevention and treatment could be improved by application of this knowledge.