The University of Maryland University College is an American public university located in the unincorporated community of Adelphi in Prince George's County, Maryland in the United States. It is known primarily for its distance learning classes and programs, but UMUC also offers classes on campus at its Academic Center in Largo, and at satellite campuses across the Baltimore-Washington Metropolitan Area, throughout Maryland, as well as in Europe, the Middle East, and Asia. UMUC serves over 90,000 students worldwide and is one of the largest distance learning institutions in the world. UMUC is open to all applicants with a 100 percent acceptance rate for undergraduate programs. The university offers 120 academic programs in instructor-led and online classes, including bachelor, masters, and doctoral degrees as well as undergraduate and graduate certificates. UMUC is a member of the University System of Maryland, which includes eleven separate public universities in Maryland. Wikipedia.
Reynolds C.S.,University of Maryland University College
Space Science Reviews | Year: 2014
I review the current status of X-ray reflection (a.k.a. broad iron line) based black hole spin measurements. This is a powerful technique that allows us to measure robust black hole spins across the mass range, from the stellar-mass black holes in X-ray binaries to the supermassive black holes in active galactic nuclei. After describing the basic assumptions of this approach, I lay out the detailed methodology focusing on “best practices” that have been found necessary to obtain robust results. Reflecting my own biases, this review is slanted towards a discussion of supermassive black hole (SMBH) spin in active galactic nuclei (AGN). Pulling together all of the available XMM-Newton and Suzaku results from the literature that satisfy objective quality control criteria, it is clear that a large fraction of SMBHs are rapidly-spinning, although there are tentative hints of a more slowly spinning population at high (M>5×107 M⊙) and low (M<2×106 M⊙) mass. I also engage in a brief review of the spins of stellar-mass black holes in X-ray binaries. In general, reflection-based and continuum-fitting based spin measures are in agreement, although there remain two objects (GRO J1655–40 and 4U 1543–475) for which that is not true. I end this review by discussing the exciting frontier of relativistic reverberation, particularly the discovery of broad iron line reverberation in XMM-Newton data for the Seyfert galaxies NGC 4151, NGC 7314 and MCG–5-23-16. As well as confirming the basic paradigm of relativistic disk reflection, this detection of reverberation demonstrates that future large-area X-ray observatories such as LOFT will make tremendous progress in studies of strong gravity using relativistic reverberation in AGN. © 2013, Springer Science+Business Media Dordrecht.
A'Hearn M.F.,University of Maryland University College
Annual Review of Astronomy and Astrophysics | Year: 2011
Recent results, many but not all from flybys of comets by spacecraft, particularly the results from Deep Impact, have dramatically improved our understanding of the physical properties of cometary nuclei. Characteristic features are modest size (R<20 km), high porosity, low strength, and heterogeneity. There is also evidence that can be interpreted as showing the original cometesimals in a cometary nucleus and suggesting radial migration of macroscopic cometesimals during the aggregation of nuclei, which in turn aggregated into the cores of the giant planets. © 2011 by Annual Reviews. All rights reserved.
Levin M.,University of Maryland University College
Physical Review X | Year: 2013
We discuss the question of when a gapped two-dimensional electron system without any symmetry has a protected gapless edge mode. While it is well known that systems with a nonzero thermal Hall conductance, KH ≠ 0, support such modes, here we show that robust modes can also occur when KH = 0-if the system has quasiparticles with fractional statistics. We show that some types of fractional statistics are compatible with a gapped edge, while others are fundamentally incompatible. More generally, we give a criterion for when an electron system with Abelian statistics and KH = 0 can support a gapped edge: We show that a gapped edge is possible if and only if there exists a subset of quasiparticle typesMsuch that (1) all the quasiparticles inMhave trivial mutual statistics, and (2) every quasiparticle that is not in M has nontrivial mutual statistics with at least one quasiparticle in M. We derive this criterion using three different approaches: a microscopic analysis of the edge, a general argument based on braiding statistics, and finally a conformal field theory approach that uses constraints from modular invariance. We also discuss the analogous result for two-dimensional boson systems. © Published by the American Physical Society.
Isaacs L.,University of Maryland University College
Accounts of Chemical Research | Year: 2014
ConspectusThis Account focuses on stimuli responsive systems that function in aqueous solution using examples drawn from the work of the Isaacs group using cucurbit[n]uril (CB[n]) molecular containers as key recognition elements. Our entry into the area of stimuli responsive systems began with the preparation of glycoluril derived molecular clips that efficiently distinguish between self and nonself by H-bonds and π-π interactions even within complex mixtures and therefore undergo self-sorting. We concluded that the selectivity of a wide variety of H-bonded supramolecular assemblies was higher than previously appreciated and that self-sorting is not exceptional behavior. This lead us to examine self-sorting within the context of CB[n] host-guest chemistry in water.We discovered that CB[n] homologues (CB and CB) display remarkably high binding affinity (Ka up to 1017 M-1) and selectivity toward their guests, which renders CB[n]s prime components for the construction of stimuli responsive host-guest systems. The CB ·adamantaneammonium ion complex, which is particularly privileged (K a = 4.2 × 1012 M-1), was introduced by us as a stimulus to trigger constitutional changes in multicomponent self-sorting systems. For example, we describe how the free energy associated with the formation of host-guest complexes of CB[n]-type receptors can drive conformational changes of included guests like triazene-arylene foldamers and cationic calixarenes, as well as induced conformational changes (e.g., ammonium guest size dependent homotropic allostery, metal ion triggered folding, and heterochiral dimerization) of the hosts themselves.Many guests display large pKa shifts within their CB[n]-guest complexes, which we used to promote pH controlled guest swapping and thermal trans-to-cis isomerization of azobenzene derivatives. We also used the high affinity and selectivity of CB toward its guests to outcompete an enzyme (bovine carbonic anhydrase) for a two-faced inhibitor, which allowed stimuli responsive regulation of enzymatic activity. These results prompted us to examine the use of CB[n]-type receptors in both in vitro and in vivo biological systems. We demonstrated that adamantaneammonium ion can be used to intracellularly sequester CB from gold nanoparticles passivated with hexanediammonium ion·CB complexes and thereby trigger cytotoxicity. CB derivatives bearing a biotin targeting group enhance the cytotoxicity of encapsulated oxaliplatin toward L1210FR cells. Finally, acyclic CB[n]-type receptors function as solubilizing excipients for insoluble drugs for drug delivery purposes and as a broad spectrum reversal agent for the neuromuscular blocking agents rocuronium, vecuronium, and cis-atracurium in rats. The work highlights the great potential for integration of CB[n]-type receptors with biological systems. © 2014 American Chemical Society.
Cooper E.D.,University of Maryland University College
Trends in Plant Science | Year: 2014
Phylogenetic analysis is an increasingly common and valuable component of plant science. Knowledge of the phylogenetic relationships between plant groups is a prerequisite for understanding the origin and evolution of important plant features, and phylogenetic analysis of individual genes and gene families provides fundamental insights into how those genes and their functions evolved. However, despite an active research community exploring and improving phylogenetic methods, the analytical methods commonly used, and the phylogenetic results they produce, are accorded far more confidence than they warrant. In this opinion article, I emphasise that important parts of the green plant phylogeny are inconsistently resolved and I argue that the lack of consistency arises due to inadequate modelling of changes in the substitution process. © 2014 Elsevier Ltd.