New Constraints on the Timing and Pattern of Deglaciation in the Húnaflói Bay Region of Northwest Iceland Using Cosmogenic 36CA Dating and Geomorphic Mapping

Understanding the evolution and timing of changes in ice sheet geometry and extent in Iceland during the Last Glacial Maximum (LGM) and subsequent deglaciation continues to stimulate much active research. Though many previous studies have advanced our knowledge of Icelandic ice sheet history preserved in marine and terrestrial settings (e.g., Andrews et al., 2000; Norðdahl et al., 2008), the timing of ice margin retreat remains largely unknown in several key regions. Recently published 36Cl surface exposure ages of bedrock surfaces and moraines in the West Fjords (Brynjólfsson et al., 2015) contribute important progress in establishing more precise age control of ice recession in northwest Iceland. In another recent study, the spatial pattern and style of deglaciation in northern Iceland have been revealed through geomorphic mapping and GIS analyses of glacial landforms (Principato et al., 2016). Additional insight comes from updated numerical modeling reconstructions, which now provide a series of glaciologically plausible Icelandic ice sheet configurations from the LGM through the last deglaciation (Patton et al., 2017). However, the optimization of ice sheet model simulations relies on critical comparisons with the available empirical record of glacial-geologic evidence and chronological control, which remains relatively limited and sparsely distributed throughout Iceland. Our investigation is motivated by the need for more accurate constraints on the deglacial history in northern Iceland, where dated terrestrial records of ice margin retreat are particularly scarce. (excerpt

Takayasu arteritis presenting as cerebral aneurysms in an 18 month old: A case report

<p>Abstract</p> <p>Background</p> <p>Central nervous system involvement occurs in as many as twenty percent of Takayasu arteritis cases. When central nervous system disease is present, it typically manifests as cerebral ischemia or stroke. There are rare reports of intracranial aneurysms in adults with Takayasu arteritis, but none in children.</p> <p>Case presentation</p> <p>We describe a case of Takayasu arteritis in an 18 month old girl who presented with a ruptured cerebral aneurysm. Full body magnetic resonance angiography revealed bilateral iliac, pelvic and intragluteal aneurysms, irregular terminal aorta, and stenotic renal arteries. Iliac vessel biopsy showed a lymphocytic infiltrate and giant cells localized to the internal elastica.</p> <p>Conclusion</p> <p>This case highlights cerebral aneurysm as a highly unusual initial manifestation of Takayasu arteritis and demonstrates the challenges of diagnosis, treatment, and assessment of response to therapy in TA in children.</p

Structure of isobaric analog states in 91Nb populated by the 90Zr(a,t) reaction

Decay via proton emission of isobaric analog states (IAS's) in $^{91}{Nb}$ was studied using the $^{90}{Zr}(\alpha,t)$ reaction at $E_\alpha$=180 MeV. This study provides information about the damping mechanism of these states. Decay to the ground state and low-lying phonon states in $^{90}{Zr}$ was observed. The experimental data are compared with theoretical predictions wherein the IAS `single-particle' proton escape widths are calculated in a continuum RPA approach. The branching ratios for decay to the phonon states are explained using a simple model.Comment: 3 figures. submitted to Phys. Lett.

Phase Transition in a Random Fragmentation Problem with Applications to Computer Science

We study a fragmentation problem where an initial object of size x is broken into m random pieces provided x>x_0 where x_0 is an atomic cut-off. Subsequently the fragmentation process continues for each of those daughter pieces whose sizes are bigger than x_0. The process stops when all the fragments have sizes smaller than x_0. We show that the fluctuation of the total number of splitting events, characterized by the variance, generically undergoes a nontrivial phase transition as one tunes the branching number m through a critical value m=m_c. For m<m_c, the fluctuations are Gaussian where as for m>m_c they are anomalously large and non-Gaussian. We apply this general result to analyze two different search algorithms in computer science.Comment: 5 pages RevTeX, 3 figures (.eps

Understanding Search Trees via Statistical Physics

We study the random m-ary search tree model (where m stands for the number of branches of a search tree), an important problem for data storage in computer science, using a variety of statistical physics techniques that allow us to obtain exact asymptotic results. In particular, we show that the probability distributions of extreme observables associated with a random search tree such as the height and the balanced height of a tree have a traveling front structure. In addition, the variance of the number of nodes needed to store a data string of a given size N is shown to undergo a striking phase transition at a critical value of the branching ratio m_c=26. We identify the mechanism of this phase transition, show that it is generic and occurs in various other problems as well. New results are obtained when each element of the data string is a D-dimensional vector. We show that this problem also has a phase transition at a critical dimension, D_c= \pi/\sin^{-1}(1/\sqrt{8})=8.69363...Comment: 11 pages, 8 .eps figures included. Invited contribution to STATPHYS-22 held at Bangalore (India) in July 2004. To appear in the proceedings of STATPHYS-2

Crime in Maine 2014

Automata over infinite alphabets have recently come to be studied extensively as potentially useful tools for solving problems in verification and database theory. One popular model of automata studied is the Class Memory Automata (CMA), for which the emptiness problem is equivalent to Petri Net Reachability. We identify a restriction - which we call weakness - of CMA, and show that their emptiness problem is equivalent to Petri Net Coverability. Further, we show that in the deterministic case they are closed under all Boolean operations. We clarify the connections between weak CMA and existing automata over data languages. We also extend CMA to operate over multiple levels of nested data values, and show that while these have undecidable emptiness in general, adding the weakness constraint recovers decidability of emptiness, via reduction to coverability in well-structured transition systems. We also examine connections with existing automata over nested data.Comment: Preprint of LATA'15 pape

Tracing Noble Gas Radionuclides in the Environment

Trace analysis of radionuclides is an essential and versatile tool in modern science and technology. Due to their ideal geophysical and geochemical properties, long-lived noble gas radionuclides, in particular, 39Ar (t1/2 = 269 yr), 81Kr (t1/2 = 2.3x10^5 yr) and 85Kr (t1/2 = 10.8 yr), have long been recognized to have a wide range of important applications in Earth sciences. In recent years, significant progress has been made in the development of practical analytical methods, and has led to applications of these isotopes in the hydrosphere (tracing the flow of groundwater and ocean water). In this article, we introduce the applications of these isotopes and review three leading analytical methods: Low-Level Counting (LLC), Accelerator Mass Spectrometry (AMS) and Atom Trap Trace Analysis (ATTA)

Homeomorphic Embedding for Online Termination of Symbolic Methods

Well-quasi orders in general, and homeomorphic embedding in particular, have gained popularity to ensure the termination of techniques for program analysis, specialisation, transformation, and verification. In this paper we survey and discuss this use of homeomorphic embedding and clarify the advantages of such an approach over one using well-founded orders. We also discuss various extensions of the homeomorphic embedding relation. We conclude with a study of homeomorphic embedding in the context of metaprogramming, presenting some new (positive and negative) results and open problems

Calogero-Moser models with noncommutative spin interactions

We construct integrable generalizations of the elliptic Calogero-Sutherland-Moser model of particles with spin, involving noncommutative spin interactions. The spin coupling potential is a modular function and, generically, breaks the global spin symmetry of the model down to a product of U(1) phase symmetries. Previously known models are recovered as special cases.Comment: Version to appear in Phys. Rev. Let

On the families of orthogonal polynomials associated to the Razavy potential

We show that there are two different families of (weakly) orthogonal polynomials associated to the quasi-exactly solvable Razavy potential V(x)=(\z \cosh 2x-M)^2 (\z>0, $M\in\mathbf N$). One of these families encompasses the four sets of orthogonal polynomials recently found by Khare and Mandal, while the other one is new. These results are extended to the related periodic potential U(x)=-(\z \cos 2x -M)^2, for which we also construct two different families of weakly orthogonal polynomials. We prove that either of these two families yields the ground state (when $M$ is odd) and the lowest lying gaps in the energy spectrum of the latter periodic potential up to and including the $(M-1)^{\rm th}$ gap and having the same parity as $M-1$. Moreover, we show that the algebraic eigenfunctions obtained in this way are the well-known finite solutions of the Whittaker--Hill (or Hill's three-term) periodic differential equation. Thus, the foregoing results provide a Lie-algebraic justification of the fact that the Whittaker--Hill equation (unlike, for instance, Mathieu's equation) admits finite solutions.Comment: Typeset in LaTeX2e using amsmath, amssymb, epic, epsfig, float (24 pages, 1 figure