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Worcester, MA, United States

Fabian A.C.,Institute of Astronomy | Ross R.R.,College of the Holy Cross, Worcester
Space Science Reviews | Year: 2010

Material irradiated by X-rays produces backscattered radiation which is commonly known as the Reflection Spectrum. It consists of a structured continuum, due at high energies to the competition between photoelectric absorption and electron scattering enhanced at low energies by emission from the material itself, together with a complex line spectrum. We briefly review the history of X-ray reflection in astronomy and discuss various methods for computing the reflection spectrum from cold and ionized gas, illustrated with results from our own work reflionx. We discuss how the reflection spectrum can be used to obtain the geometry of the accretion flow, particularly the inner regions around black holes and neutron stars. © 2010 Springer Science+Business Media B.V. Source


Topilina N.I.,Albany State University | Mills K.V.,College of the Holy Cross, Worcester
Mobile DNA | Year: 2014

Intein-mediated protein splicing has become an essential tool in modern biotechnology. Fundamental progress in the structure and catalytic strategies of cis- and trans-splicing inteins has led to the development of modified inteins that promote efficient protein purification, ligation, modification and cyclization. Recent work has extended these in vitro applications to the cell or to whole organisms. We review recent advances in intein-mediated protein expression and modification, post-translational processing and labeling, protein regulation by conditional protein splicing, biosensors, and expression of trans-genes. © 2014 Topilina and Mills; licensee BioMed Central Ltd. Source


Mitchell S.G.,College of the Holy Cross, Worcester | Humphries E.E.,University of North Carolina at Chapel Hill
Geology | Year: 2015

A global GIS- and literature-based analysis of the altitude and relief of more than 14,000 ice-free glacial cirques in 56 study areas ranging from 69°N to 77°S shows that average cirque floor altitudes vary with latitude in a zone centered on the Quaternary average equilibrium line altitude (QA-ELA). In addition, relief above cirque floors averages 346 ± 107 m, and is rarely >600 m. In regions where ice-free cirques are abundant, cirque relief is independent of modern precipitation rates, tectonic regime, and relative peak height, limiting peaks to within a fixed distance above the QA-ELA and thus causing them to also parallel the ELA. We propose a physical process model where, under suitable geologic and tectonic conditions, climate exerts a first-order control on mountain range height. In this model, glacial erosion excavates a zone of cirques with floors centered on the QA-ELA, while climate-driven weathering processes on adjacent slopes limit the peaks to within a few hundred meters above this zone. © 2014 Geological Society of America. Source


Anders A.M.,Urbana University | Mitchell S.G.,College of the Holy Cross, Worcester | Tomkin J.H.,Urbana University
Geology | Year: 2010

Glacial erosion, a process influenced by climate, has been implicated in limiting the relief of mountain ranges. However, climate itself is sensitive to large-scale topography, suggesting that climate, topography, and glacial processes form a coupled system. Large spatial gradients in precipitation exist in the southern Swiss Alps, allowing us to study this coupling in a region of climate variability. More than 500 cirques were identified, and neighboring peaks were found to co-vary in elevation with cirque floors (R2 0.64). Cirque headwall relief does not vary with precipitation or cirque floor altitude. These relationships confirm the hypothesis that cirque formation restricts peak altitudes via slope processes that limit the relief of cirque headwalls. We compared the position of the regional equilibrium line altitude (ELA) estimated from modern climate to a surface defined by the cirque floors. The modern ELA and cirque floor surfaces are similar in shape, illustrating the impact of spatial variability in precipitation on glacial processes and topography. Precipitation variability in this region is partially dictated by large-scale topography. Therefore, precipitation patterns, glacial process domains, and topography must evolve together. © 2010 Geological Society of America. Source


Kain B.,College of the Holy Cross, Worcester | Ling H.Y.,Rowan University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

We consider the growth of cosmological perturbations to the energy density of dark matter during matter domination when dark matter is a scalar field that has undergone Bose-Einstein condensation. We study these inhomogeneities within the framework of both Newtonian gravity, where the calculation and results are more transparent, and General Relativity. The direction we take is to derive analytical expressions, which can be obtained in the small pressure limit. Throughout we compare our results to those of the standard cosmology, where dark matter is assumed pressureless, using our analytical expressions to showcase precise differences. We find, compared to the standard cosmology, that Bose-Einstein condensate dark matter leads to a scale factor, gravitational potential and density contrast that increase at faster rates. © 2012 American Physical Society. Source

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