What Actually Happened

This is the text of The Lindley Lecture for 1971, given by P.H. Nowell-Smith (1914-2006), a British philosopher

Animal proxies to characterize the strontium biosphere in the northeastern Nile Delta

Strontium (⁸⁷Sr/⁸⁶Sr) isotope analysis is a potent tool for reconstructing the residential mobility of humans and animals in the past but is reliant on knowledge of strontium isotope variation within the expanded physical environment. This paper aims to contribute to the isoscape in the northeastern Nile Delta with faunal samples from the site of Tell el-Dab‘a (Avaris), believed to be the capital of the so-called Hyksos kings. Mapping the available ⁸⁷Sr/⁸⁶Sr ratios from Egypt and the Sudan highlights major research gaps outside the Nile region. e current corpus of knowledge also shows that the Nile River region yields a homogenous range of isotopic values (median and IQR 0.7076 0.0003). Strontium isotope ratios from human dental enamel, which record childhood residence, will provide evidence of non-locals from outside the Nile area with confidence but these values suggest that identifying movement along the Nile River in the past will be difficult without the use of supplementary evidence (e.g. oxygen stable isotope analysis). We present ⁸⁷Sr/⁸⁶Sr ratios of archaeologically-derived faunal bone samples (n=6) from the site of Tell el-Dab‘a (Avaris) in the northeastern Nile Delta. e ⁸⁷Sr/⁸⁶Sr ratios fit within the expectations of the wider Nile values (mean 0.70769 0.00003) and serve as the first archaeologically-derived values reported for this area of Egypt

Commensurate lattice distortion in the layered titanium oxypnictides Na2_{2}Ti2Pn2_{2}Pn_{2}O (Pn=Pn = As, Sb) determined by X-ray diffraction

We report single crystal X-ray diffraction measurements on Na$_2$Ti$_{2}Pn_{2}$O ($Pn$ = As, Sb) which reveal a charge superstructure that appears below the density wave transitions previously observed in bulk data. From symmetry-constrained structure refinements we establish that the associated distortion mode can be described by two propagation vectors, ${\bf q}_{1} = (1/2, 0, l)$ and ${\bf q}_{2} = (0, 1/2, l)$, with $l=0$ (Sb) or $l = 1/2$ (As), and primarily involves in-plane displacements of the Ti atoms perpendicular to the Ti--O bonds. The results provide direct evidence for phonon-assisted charge density wave order in Na$_2$Ti$_{2}Pn_{2}$O and identify a proximate ordered phase that could compete with superconductivity in doped BaTi$_{2}$Sb$_{2}$O

Role of the iodide–methylammonium interaction in the ferroelectricity of CH3NH3PbI3

Excellent conversion efficiencies of over 20 % and facile cell production have placed hybrid perovskites at the forefront of novel solar cell materials, with CH3NH3PbI3 being an archetypal compound. The question why CH3NH3PbI3 has such extraordinary characteristics, particularly a very efficient power conversion from absorbed light to electrical power, is hotly debated, with ferroelectricity being a promising candidate. This does, however, require the crystal structure to be non‐centrosymmetric and we herein present crystallographic evidence as to how the symmetry breaking occurs on a crystallographic and, therefore, long‐range level. Although the molecular cation CH3NH3+ is intrinsically polar, it is heavily disordered and this cannot be the sole reason for the ferroelectricity. We show that it, nonetheless, plays an important role, as it distorts the neighboring iodide positions from their centrosymmetric positions

Understanding the Session Durability in Peer-to-Peer Storage System

This paper emphasizes that instead of long-term availability and reliability, the short-term session durability analysis will greatly impact the design of the real large-scale Peer-to-Peer storage system. In this paper, we use a Markov chain to model the session durability, and then derive the session durability probability distribution. Subsequently, we show the difference between our analysis and the traditional Mean Time to Failure (MTTF) analysis, from which we conclude that the misuse of MTTF analysis will greatly mislead our understanding of the session durability. We further show the impact of session durability analysis on the real system design. To our best knowledge, this is the first time ever to discuss the effects of session durability in large-scale Peer-to-Peer storage system.Computer Science, Theory & MethodsSCI(E)EICPCI-S(ISTP)

Fast matrix computations for pair-wise and column-wise commute times and Katz scores

We first explore methods for approximating the commute time and Katz score between a pair of nodes. These methods are based on the approach of matrices, moments, and quadrature developed in the numerical linear algebra community. They rely on the Lanczos process and provide upper and lower bounds on an estimate of the pair-wise scores. We also explore methods to approximate the commute times and Katz scores from a node to all other nodes in the graph. Here, our approach for the commute times is based on a variation of the conjugate gradient algorithm, and it provides an estimate of all the diagonals of the inverse of a matrix. Our technique for the Katz scores is based on exploiting an empirical localization property of the Katz matrix. We adopt algorithms used for personalized PageRank computing to these Katz scores and theoretically show that this approach is convergent. We evaluate these methods on 17 real world graphs ranging in size from 1000 to 1,000,000 nodes. Our results show that our pair-wise commute time method and column-wise Katz algorithm both have attractive theoretical properties and empirical performance.Comment: 35 pages, journal version of http://dx.doi.org/10.1007/978-3-642-18009-5_13 which has been submitted for publication. Please see http://www.cs.purdue.edu/homes/dgleich/publications/2011/codes/fast-katz/ for supplemental code

Navigability is a Robust Property

The Small World phenomenon has inspired researchers across a number of fields. A breakthrough in its understanding was made by Kleinberg who introduced Rank Based Augmentation (RBA): add to each vertex independently an arc to a random destination selected from a carefully crafted probability distribution. Kleinberg proved that RBA makes many networks navigable, i.e., it allows greedy routing to successfully deliver messages between any two vertices in a polylogarithmic number of steps. We prove that navigability is an inherent property of many random networks, arising without coordination, or even independence assumptions

Local corrugation and persistent charge density wave in ZrTe3 with Ni intercalation

The mechanism of emergent bulk superconductivity in t ransition-metal intercalated ZrTe3 is investigated by studying the effect of Ni doping on the band structure and charge density wave (CDW). The study reports theoretical and experimental results in the range of Ni0.01ZrTe3 to Ni0.05ZrTe3. In the highest doped samples, bulk superconductivity with Tc < TCDW is observed, with a reduced TCDW compared with pure ZrTe3. Relativistic ab initio calculations reveal that Ni incorporation occurs preferentially through intercalation in the van der Waals gap. Analysis of the structural and electronic effects of intercalation indicate buckling of the Te sheets adjacent to the Ni site akin to a locally stabilized CDW-like lattice distortion. In contrast to the changes of TCDW observed in resistivity, experiments with low-temperature x-ray diffraction, angle-resolved-photoemission spectroscopy, as well as temperature-dependent resistivity reveal the nearly unchanged persistence of the CDW into the regime of bulk superconductivity. The CDW gap is found to be unchanged in its extent in momentum space, with the gap size also unchanged or possibly slightly reduced upon Ni intercalation. Both experimental observations suggest that superconductivity coexists with the CDW in NixZrTe3