cometadata/datacite-rtg-text-other-reclassification-records huggingface dataset:
Blueprints for Medieval hydroclimate
Creators: Seager, Richard
Graham, Nicholas E.
Herweijer, Celine
Gordon, Arnold L.
Kushnir, Yochanan
Cook, Edward R.
Publisher: name: Columbia University
Year: 2007
Subjects: Hydrology
Paleoclimatology
Dendroclimatology

description: According to tree ring and other records, a series of severe droughts that lasted for decades afflicted western North America during the Medieval period resulting in a more arid climate than in subsequent centuries. A review of proxy evidence from around the world indicates that North American megadroughts were part of a global pattern of Medieval hydroclimate that was distinct from that of today. In particular, the Medieval hydroclimate was wet in northern South America, dry in mid-latitude South America, dry in eastern Africa but with strong Nile River floods and a strong Indian monsoon. This pattern is similar to that accompanying persistent North American droughts in the instrumental era. This pattern is compared to that associated with familiar climate phenomena. The best fit comes from a persistently La Nin ̃ a-like tropical Pacific and the warm phase of the so-called Atlantic Multidecadal Oscillation. A positive North Atlantic Oscillation (NAO) also helps to explain the Medieval hydroclimate pattern. Limited sea surface temperature reconstructions support the contention that the tropical Pacific was cold and the subtropical North Atlantic was warm, ideal conditions for North American drought. Tentative modeling results indicate that a multi-century La Nina-like state could have arisen as a coupled atmosphere–ocean response to high irradiance and weak volcanism during the Medieval period and that this could in turn have induced a persistently positive NAO state. A La Nina-like state could also induce a strengthening of the North Atlantic meridional overturning circulation, and hence warming of the North Atlantic Ocean, by (i) the ocean response to the positive NAO and by shifting the southern mid-latitude westerlies poleward which (ii) will increase the salt flux from the Indian Ocean into the South Atlantic and (iii) drive stronger Southern Ocean upwelling.
A double bootstrap approach to Superposed Epoch Analysis to evaluate response uncertainty
Creators: Rao, Mukund Palat
Cook, Edward R.
Cook, Benjamin I.
Anchukaitis, Kevin
D'Arrigo, Rosanne Dorothy
Krusic, Paul
LeGrande, Allegra N.
Publisher: name: Columbia University
Year: 2019
Subjects: Climatic changes
Paleoclimatology
Dendroclimatology
Dendrochronology
Volcanic eruptions

description: The association between climate variability and episodic events, such as the antecedent moisture conditions prior to wildfire or the cooling following volcanic eruptions, is commonly assessed using Superposed Epoch Analysis (SEA). In SEA the epochal response is typically calculated as the average climate conditions prior to and following all event years or their deviation from climatology. However, the magnitude and significance of the inferred climate association may be sensitive to the selection or omission of individual key years, potentially resulting in a biased assessment of the relationship between these events and climate. Here we describe and test a modified double-bootstrap SEA that generates multiple unique draws of the key years and evaluates the sign, magnitude, and significance of event-climate relationships within a probabilistic framework. This multiple resampling helps quantify multiple uncertainties inherent in conventional applications of SEA within dendrochronology and paleoclimatology. We demonstrate our modified SEA by evaluating the volcanic cooling signal in a Northern Hemisphere tree-ring temperature reconstruction and the link between drought and wildfire events in the western United States. Finally, we make our Matlab and R code available to be adapted for future SEA applications.
A Tree-Ring-Based Reconstruction of Delaware River Basin Streamflow Using Hierarchical Bayesian Regression
Creators: Devineni, Naresh
Lall, Upmanu
Pederson, Neil
Cook, Edward R.
Publisher: name: Columbia University
Year: 2013
Subjects: Paleoclimatology
Meteorology

description: A hierarchical Bayesian regression model is presented for reconstructing the average summer streamflow at five gauges in the Delaware River basin using eight regional tree-ring chronologies. The model provides estimates of the posterior probability distribution of each reconstructed streamflow series considering parameter uncertainty. The vectors of regression coefficients are modeled as draws from a common multivariate normal distribution with unknown parameters estimated as part of the analysis. This leads to a multilevel structure. The covariance structure of the streamflow residuals across sites is explicitly modeled. The resulting partial pooling of information across multiple stations leads to a reduction in parameter uncertainty. The effect of no pooling and full pooling of station information, as end points of the method, is explored. The no-pooling model considers independent estimation of the regression coefficients for each streamflow gauge with respect to each tree-ring chronology. The full-pooling model considers that the same regression coefficients apply across all streamflow sites for a particular tree-ring chronology. The cross-site correlation of residuals is modeled in all cases. Performance on metrics typically used by tree-ring reconstruction experts, such as reduction of error, coefficient of efficiency, and coverage rates under credible intervals is comparable to, or better, for the partial-pooling model relative to the no-pooling model, and streamflow estimation uncertainty is reduced. Long record simulations from reconstructions are used to develop estimates of the probability of duration and severity of droughts in the region. Analysis of monotonic trends in the reconstructed drought events do not reject the null hypothesis of no trend at the 90% significance over 1754–2000.
The use of conditional lethals in the analysis of development of Drosophila melanogaster
Creators: name: Tarasoff, Mary Somerville
Publisher: name: University of British Columbia
Year: 2011

description: Conditional lethals which survive under "permissive" conditions but die under "restrictive" conditions have greatly facilitated genetic and biochemical analyses in micro-organisms. One class of conditional lethals, the so-called temperature-sensitives, has been recovered from ethyl methanesulfonate-induced lethals in Drosophila melanogaster. Such mutants survive at 17°C or 22°C but die at 29°C and appear to map genetically as point mutants. These mutants may be useful in identifying previously undetected loci and in studying mitotic, meiotic and developmental processes. In Drosophila gross developmental studies indicate that recessive temperature-sensitive (ts) lethals may have specific developmental effects. By means of shifting different cultures from one temperature to the other at successive intervals, the period during which the restrictive temperature (29°C) prevented survival could be ascertained. Each ts lethal could be classified with respect to its effective lethal phase(s), its period(s) of temperature-sensitivity and any effect on visible morphological characteristics. Four sex-linked recessive ts lethals were studied extensively with respect to their genetic and developmental action. Each of these mutants is representative of a different class of lethals with specific properties: pupal lethality, indispensability, sexual dimorphism, and parental influence. The potential use of these and other ts lethals in genetic and developmental analyses is discussed.
Computational rheology of liquid crystalline composite and active materials
Creators: name: Mackay, Fraser
Publisher: name: The University of Edinburgh
Year: 2021
Subjects: liquid crystals
active matter
composite liquid crystal
Rheology
lattice Boltzmann method
computational fluid dynamics
nematic liquid crystals

description: Liquid crystals are a type of soft matter that exists as a mesophase between the solid and liquid phase. As a result, they are observed to exhibit some properties which are characteristic of each of these phases. For example, a liquid crystalline material can flow and be poured as can a liquid, and display long-range orientational, but not positional, order as observed in a solid. Examples of liquid crystals can be found in many technological devices, in particular they are used in electronic displays. Additionally, the molecules in a wide variety of soaps and detergents can form liquid crystalline phases. The simplest type of liquid crystal molecule can be modelled as a thin, long rod. Active matter refers to a system of particles which can take in energy, either from an external or an internal fuel source and dissipate this energy. This can lead to, for example, self-motility, growth or replication of the particles. Examples of active matter include suspensions of swimming bacteria and collections of cytoskeletal filaments, such as actin or microtubules, and molecular motors, such as myosin or kinesin. We model active materials as liquid crystal rods which exert a force dipole along their primary axis, either outwards or inwards. These are known as extensile and contractile materials respectively. In this thesis we present computational simulation results investigating the rheological properties of active and liquid crystalline composite materials. Starting with the rheology of active nematic fluids under Poiseuille flow in a channel, we show that there exists a regime in which contractile materials exhibit a plug like flow and permeation-like behaviour as observed in cholesterics. Additionally, specific to extensile materials, we have carried out simulations seeking to answer the questions posed by the existence of a near-zero, or negative shear viscosity, measured in experiments. Presented in this thesis, we show that for a fully three-dimensional extensile material, the viscosity is not a state function, and is related to the microstate of the system. Furthermore, we have investigated two different models for liquid crystal composite emulsions, consisting of isotropic droplets dispersed within a continuous nematic solvent. In these simulations the two dimensional emulsions were subjected to a Poiseuille flow and the viscosity was measured. Interestingly, we observe a yield stress response and discontinuous shear thinning of the fluid not seen in the case of a typical, isotropic emulsion.
Harmonic measures for distributions with finite support on the mapping class group are singular
Creators: name: Gadre, Vaibhav S
Publisher: name: arXiv
Year: 2009
Subjects: subject: Geometric Topology (math.GT)
subject: Dynamical Systems (math.DS)
subject: FOS: Mathematics
subject: 37E30; 32G15; 20F65

description: Kaimanovich and Masur showed that a random walk on the mapping class group for an initial distribution with finite first moment and whose support generates a non-elementary subgroup, converges almost surely to a point in the space PMF of projective measured foliations on the surface. This defines a harmonic measure on PMF. Here, we show that when the initial distribution has finite support, the corresponding harmonic measure is singular with respect to the natural Lebesgue measure on PMF.
description: 43 pages, 16 figures. Minor improvements overall, specifically Section 12. Added references
A multispecies tree ring reconstruction of Potomac River streamflow (950–2001)
Creators: Maxwell, R. Stockton
Hessl, Amy E.
Cook, Edward R.
Pederson, Neil
Publisher: name: Columbia University
Year: 2011
Subjects: Paleoclimatology
Meteorology
Hydrology

description: Mean May–September Potomac River streamflow was reconstructed from 950–2001 using a network of tree ring chronologies (n = 27) representing multiple species. We chose a nested principal components reconstruction method to maximize use of available chronologies backward in time. Explained variance during the period of calibration ranged from 20% to 53% depending on the number and species of chronologies available in each 25 year time step. The model was verified by two goodness of fit tests, the coefficient of efficiency (CE) and the reduction of error statistic (RE). The RE and CE never fell below zero, suggesting the model had explanatory power over the entire period of reconstruction. Beta weights indicated a loss of explained variance during the 1550–1700 period that we hypothesize was caused by the reduction in total number of predictor chronologies and loss of important predictor species. Thus, the reconstruction is strongest from 1700–2001. Frequency, intensity, and duration of drought and pluvial events were examined to aid water resource managers. We found that the instrumental period did not represent adequately the full range of annual to multidecadal variability present in the reconstruction. Our reconstruction of mean May–September Potomac River streamflow was a significant improvement over the Cook and Jacoby (1983) reconstruction because it expanded the seasonal window, lengthened the record by 780 years, and better replicated the mean and variance of the instrumental record. By capitalizing on variable phenologies and tree growth responses to climate, multispecies reconstructions may provide significantly more information about past hydroclimate, especially in regions with low aridity and high tree species diversity.
Strong Double Higgs Production at the LHC
Creators: name: Contino, Roberto
name: Grojean, Christophe
name: Moretti, Mauro
name: Piccinini, Fulvio
name: Rattazzi, Riccardo
Publisher: name: arXiv
Year: 2010
Subjects: subject: High Energy Physics - Phenomenology (hep-ph)
subject: FOS: Physical sciences

description: The hierarchy problem and the electroweak data, together, provide a plausible motivation for considering a light Higgs emerging as a pseudo-Goldstone boson from a strongly-coupled sector. In that scenario, the rates for Higgs production and decay differ significantly from those in the Standard Model. However, one genuine strong coupling signature is the growth with energy of the scattering amplitudes among the Goldstone bosons, the longitudinally polarized vector bosons as well as the Higgs boson itself. The rate for double Higgs production in vector boson fusion is thus enhanced with respect to its negligible rate in the SM. We study that reaction in pp collisions, where the production of two Higgs bosons at high pT is associated with the emission of two forward jets. We concentrate on the decay mode hh -> WW^(*)WW^(*) and study the semi-leptonic decay chains of the W's with 2, 3 or 4 leptons in the final states. While the 3 lepton final states are the most relevant and can lead to a 3 sigma signal significance with 300 fb^{-1} collected at a 14 TeV LHC, the two same-sign lepton final states provide complementary information. We also comment on the prospects for improving the detectability of double Higgs production at the foreseen LHC energy and luminosity upgrades.
description: 54 pages, 26 figures. v2: typos corrected, a few comments and one table added. Version published in JHEP
A quantitative hydroclimatic context for the European Great Famine of 1315-17
Creators: Baek, Seung Hun
Smerdon, Jason E.
Dobrin, George-Costin
Naimark, Jacob Genek
Cook, Edward R.
Cook, Benjamin I.
Seager, Richard
Cane, Mark A.
Scholz, Serena R.
Publisher: name: Columbia University
Year: 2020
Subjects: Hydrology
Paleoclimatology
Dendrochronology
Famines

description: The European Great Famine of 1315–1317 triggered one of the worst population collapses in European history and ranks as the single worst European famine in mortality as a proportion of population. Historical records point to torrential rainfall, land saturation, crop failure, and prolonged flooding as important causes of the famine. Here we use the tree-ring based Old World Drought Atlas (OWDA) to show that the average of each growing season preceding the Great Famine years (1314–1316) was the fifth wettest over Europe from 1300 to 2012 C.E. The spatial and temporal characteristics of our OWDA-estimated anomalies are in excellent agreement with available historical accounts. We also characterize a mode of European hydroclimate variability that is associated with the Great Famine, which we term the “Great Famine mode.” This mode emerges as the leading mode of European hydroclimate variability from 1300–2012 and is strongly associated with extreme wet and dry events in Europe over the last millennium.
On number-ratio fluctuations in high-energy particle-production
Creators: name: Christiansen, P.
name: Haslum, E.
name: Stenlund, E.
Publisher: name: arXiv
Year: 2009
Subjects: subject: High Energy Physics - Experiment (hep-ex)
subject: FOS: Physical sciences

description: In this paper we will discuss the previously proposed quantity nu_dyn[1], as a measure of the number-ratio fluctuations in high-energy particle-production. We will show that nu_dyn has pleasing mathematical properties making it ideal for the purpose. We will demonstrate its relation to two-particle correlations and how this measure can be generalized to higher order correlations.
description: 14 pages with 4 figures
Far-infrared absorption in single-electron transistors: Theoretical results and experiment proposal
Creators: name: Baldea, Ioan
name: Koeppel, Horst
Publisher: name: arXiv
Year: 2009
Subjects: subject: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
subject: Strongly Correlated Electrons (cond-mat.str-el)
subject: FOS: Physical sciences

description: We present theoretical results on far-infrared (FIR) absorption of single-electron transistors. Based on them, we propose and explain how to conduct combined FIR--dc-transport experiments to determine the charging energy and other relevant parameters, without measuring FIR intensities.
Bridging Past and Future Climate across Paleoclimatic Reconstructions, Observations, and Models: A Hydroclimate Case Study
Creators: Smerdon, Jason E.
Cook, Benjamin I.
Cook, Edward R.
Seager, Richard
Publisher: name: Columbia University
Year: 2015
Subjects: Soil moisture
Dendroclimatology
Climatic changes
Paleoclimatology

description: Potential biases in tree-ring reconstructed Palmer drought severity index (PDSI) are evaluated using Thornthwaite (TH), Penman–Monteith (PM), and self-calibrating Penman–Monteith (SC) PDSI in three diverse regions of the United States and tree-ring chronologies from the North American drought atlas (NADA). Minimal differences are found between the three PDSI reconstructions and all compare favorably to independently reconstructed Thornthwaite-based PDSI from the NADA. Reconstructions are bridged with model-derived PDSI_TH and PDSI_PM, which both closely track modeled soil moisture (near surface and full column) during the twentieth century. Differences between modeled moisture-balance metrics only emerge in twenty-first-century projections. These differences confirm the tendency of PDSI_TH to overestimate drying when temperatures exceed the range of the normalization interval; the more physical accounting of PDSI_PM compares well with modeled soil moisture in the projection interval. Remaining regional differences in the secular behavior of projected soil moisture and PDSI_PM are interpreted in terms of underlying physical processes and temporal sampling. Results demonstrate the continued utility of PDSI as a metric of surface moisture balance while additionally providing two recommendations for future work: 1) PDSI_PM (or similar moisture-balance metrics) compare well to modeled soil moisture and are an appropriate means of representing soil-moisture balance in model simulations and 2) although PDSI_PM is more physically appropriate than PDSI_TH, the latter metric does not bias tree-ring reconstructions of past hydroclimate variability and, as such, reconstructions targeting PDSI_TH can be used with confidence in data–model comparisons. These recommendations and the collective results of this study thus provide a framework for comparing hydroclimate variability within paleoclimatic, observational, and modeled data.
Invariant theory and the W_{1+\infty} algebra with negative integral central charge
Creators: name: Linshaw, Andrew R.
Publisher: name: arXiv
Year: 2008
Subjects: subject: Representation Theory (math.RT)
subject: Quantum Algebra (math.QA)
subject: FOS: Mathematics

description: The vertex algebra W_{1+\infty,c} with central charge c may be defined as a module over the universal central extension of the Lie algebra of differential operators on the circle. For an integer n\geq 1, it was conjectured in the physics literature that W_{1+\infty,-n} should have a minimal strong generating set consisting of n^2+2n elements. Using a free field realization of W_{1+\infty,-n} due to Kac-Radul, together with a deformed version of Weyl's first and second fundamental theorems of invariant theory for the standard representation of GL_n, we prove this conjecture. A consequence is that the irreducible, highest-weight representations of W_{1+\infty,-n} are parametrized by a closed subvariety of C^{n^2+2n}.
description: Minor corrections, final version
A long-term context (931–2005 C.E.) for rapid warming over Central Asia
Creators: Davi, Nicole K.
D'Arrigo, Rosanne Dorothy
Jacoby, G. C.
Cook, Edward R.
Anchukaitis, Kevin
Nachin, Baatarbileg
Rao, Mukund Palat
Leland, Caroline Wogan
Publisher: name: Columbia University
Year: 2015
Subjects: Paleoclimatology
Global warming
Dendrochronology
Climatic changes

description: Warming over Mongolia and Central Asia has been unusually rapid over the past few decades, particularly in the summer, with surface temperature anomalies higher than for much of the globe. With few temperature station records available in this remote region prior to the 1950s, paleoclimatic data must be used to understand annual-to-centennial scale climate variability, local response to large-scale forcing mechanisms, and the significance of major features of the past millennium such as the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA) both of which can vary globally. Here we use an extensive collection of living and subfossil wood samples from temperature-sensitive trees to produce a millennial-length, validated reconstruction of summer temperatures for Mongolia and Central Asia from 931 to 2005 CE. This tree-ring reconstruction shows general agreement with the MCA (warming) and LIA (cooling) trends, a significant volcanic signature, and warming in the 20th and 21st Century. Recent warming (2000–2005) exceeds that from any other time and is concurrent with, and likely exacerbated, the impact of extreme drought (1999–2002) that resulted in massive livestock loss across Mongolia.
Constant-work-space algorithms for geometric problems
Creators: name: Asano, Tetsuo
name: Mulzer, Wolfgang
name: Rote, Günter
name: Wang, Yajun
Publisher: name: Journal of Computational Geometry
Year: 2011

description: Constant-work-space algorithms may use only constantly many cells of storage in addition to their input, which is provided as a read-only array. We show how to construct several geometric structures efficiently in the constant-work-space model. Traditional algorithms process the input into a suitable data structure (like a doubly-connected edge list) that allows efficient traversal of the structure at hand. In the constant-work-space setting, however, we cannot afford to do this. Instead, we provide operations that compute the desired features on the fly by accessing the input with no extra space. The whole geometric structure can be obtained by using these operations to enumerate all the features. Of course, we must pay for the space savings by slower running times. While the standard data structure allows us to implement traversal operations in constant time, our schemes typically take linear time to read the input data in each step. We begin with two simple problems: triangulating a planar point set and finding the trapezoidal decomposition of a simple polygon. In both cases adjacent features can be enumerated in linear time per step, resulting in total quadratic running time to output the whole structure. Actually, we show that the former result carries over to the Delaunay triangulation, and hence the Voronoi diagram. This also means that we can compute the largest empty circle of a planar point set in quadratic time and constant work-space. As another application, we demonstrate how to enumerate the features of an Euclidean minimum spanning tree (EMST) in quadratic time per step, so that the whole EMST can be found in cubic time using constant work-space. Finally, we describe how to compute a shortest geodesic path between two points in a simple polygon. Although the shortest path problem in general graphs is NL-complete (Jakoby and Tantau 2003), this constrained problem can be solved in quadratic time using only constant work-space.
description: Journal of Computational Geometry, Vol 2, No 1 (2011)
Nonlinear stochastic equations with multiplicative Lévy noise
Creators: name: Srokowski, Tomasz
Publisher: name: arXiv
Year: 2010
Subjects: subject: Statistical Mechanics (cond-mat.stat-mech)
subject: FOS: Physical sciences

description: The Langevin equation with a multiplicative Lévy white noise is solved. The noise amplitude and the drift coefficient have a power-law form. A validity of ordinary rules of the calculus for the Stratonovich interpretation is discussed. The solution has the algebraic asymptotic form and the variance may assume a finite value for the case of the Stratonovich interpretation. The problem of escaping from a potential well is analysed numerically; predictions of different interpretations of the stochastic integral are compared.
description: 10 pages, 7 figures
Changing hydroclimate dynamics and the 19th to 20th century wetting trend in the English Channel region of northwest Europe
Creators: Scholz, Serena R.
Seager, Richard
Ting, Mingfang
Kushnir, Yochanan
Smerdon, Jason E.
Cook, Benjamin I.
Cook, Edward R.
Baek, Seung Hun
Publisher: name: Columbia University
Year: 2021
Subjects: Paleoclimatology
Hydrology
Droughts
Precipitation (Meteorology)

description: Northwestern Europe has experienced a trend of increasingly wet winters over the past 150 years, with few explanations for what may have driven this hydroclimatic change. Here we use the Old World Drought Atlas (OWDA), a tree-ring based reconstruction of the self-calibrating Palmer Drought Severity Index (scPDSI), to examine this wetting trend and place it in a longer hydroclimatic context. We find that scPDSI variability in northwestern Europe is strongly correlated with the leading mode of the OWDA during the last millennium (1000–2012). This leading mode, here named the ‘English Channel’ (EC) mode, has pronounced variability on interannual to centennial timescales and has an expression in scPDSI similar to that of the East Atlantic teleconnection pattern. A shift in the EC mode from a prolonged negative phase to more neutral conditions during the 19th and 20th centuries is associated with the wetting trend over its area of influence in England, Wales, and much of northern continental Europe. The EC mode is the dominant scPDSI mode from approximately 1000–1850, after which its dominance waned in favor of the secondary ‘North–South’ (NS) mode, which has an expression in scPDSI similar to that of the winter North Atlantic Oscillation (NAO). We examine the dynamical nature of both of these modes and how they vary on interannual to centennial timescales. Our results provide insight into the nature of hydroclimate variability in Europe before the widespread availability of instrumental observations.
Euclidean Epstein-Glaser Renormalization
Creators: name: Keller, Kai Johannes
Publisher: name: arXiv
Year: 2009
Subjects: subject: Mathematical Physics (math-ph)
subject: High Energy Physics - Theory (hep-th)
subject: FOS: Physical sciences

description: In the framework of perturbative Algebraic Quantum Field Theory (pAQFT), recently introduced by Brunetti, Duetsch and Fredenhagen, I give a general construction of so-called "Euclidean time-ordered products", i.e. algebraic versions of the Schwinger functions, for scalar quantum field theories on spaces of Euclidean signature. This is done by generalizing the recursive construction of time-ordered products by Epstein and Glaser, originally formulated for quantum field theories on Minkowski space (MQFT). An essential input of Epstein-Glaser renormalization is the causal structure of Minkowski space. The absence of this causal structure in the Euclidean framework makes it necessary to modify the original construction of Epstein and Glaser at two points. First, the whole construction has to be performed with an only partially defined product on (interaction-) functionals. This is due to the fact that the fundamental solutions of the Helmholtz operator of EQFT have a unique singularity structure, i.e. they are unique up to a smooth part. Second, one needs to (re-)introduce a (rather natural) "Euclidean causality" condition for the recursion of Epstein and Glaser to be applicable.
description: 30 pages, 1 figure, to be published in JMP, relation to standard approach added, appendix added, proofs enhanced, typos corrected
Climate and the Global Famine of 1876-78
Creators: Singh, Deepti
Seager, Richard
Cook, Benjamin I.
Cane, Mark A.
Ting, Mingfang
Cook, Edward R.
Davis, Michael
Publisher: name: Columbia University
Year: 2018
Subjects: Climatic changes
Droughts
Famines

description: From 1875-78, concurrent multi-year droughts in Asia, Brazil, and Africa, referred to as the Great Drought, caused widespread crop failures, catalyzing the Global Famine, which had fatalities exceeding 50 million people and long-lasting societal consequences. Observations, paleoclimate reconstructions, and climate model simulations are used to 1) demonstrate the severity and characterize the evolution of drought across different regions, and 2) investigate the underlying mechanisms driving its multi-year persistence. Severe or record-setting droughts occurred on continents in both hemispheres and in multiple seasons, with Monsoon Asia the hardest hit, which experienced the single most intense and the second most expansive drought in the last 800 years. The extreme severity, duration, and extent of this global event is associated with an extraordinary combination of preceding cool tropical Pacific conditions (1870-76), a record breaking El Niño (1877-78), record strong Indian Ocean Dipole (1877) and record warm North Atlantic Ocean (1878) conditions. Composites of historical analogues and two sets of ensemble simulations – one forced with global sea-surface temperatures (SSTs) and another forced with tropical Pacific SSTs - were used to distinguish the role of the extreme conditions in different ocean basins. While the drought in most regions was largely driven by the tropical Pacific SST conditions, an extreme positive phase of the Indian Ocean Dipole and warm North Atlantic SSTs, both likely aided by the strong El Niño in 1877-78, intensified and prolonged droughts in Brazil and Australia respectively and extended the impact to northern and southeastern Africa. Climatic conditions that caused the Great Drought and Global Famine arose from natural variability, and their recurrence, with hydrological impacts intensified by global warming, could again potentially undermine global food security.
Easy data, same old platforms? A systematic review of digital activism methodologies
Creators: name: Özkula, Suay M.
name: Reilly, Paul J.
name: Hayes, Jenny
Publisher: name: Taylor & Francis
Year: 2022
Subjects: Cell Biology
Science Policy

description: Burgess and Bruns (2015) have linked the computational turn in social media research to an increase in the number of studies focussing exclusively on ‘easy data’, such as the ‘low hanging fruit’ provided by Twitter hashtags. This paper explores whether there is a preponderance of such easy data in digital activism research through a systematic review of relevant journal articles published between 2011 and 2018 (N = 315). Specifically, it examines whether computational digital methods have become increasingly prominent in digital activism research during this period. A key focus of the paper is the extent to which digital activism research focused on easily accessible Twitter data, and whether these were obtained via standard API services. Results indicate that (1) traditional research methodologies were more commonly deployed in these articles than digital methods, but (2) Twitter was the most researched platform in the corpus, and (3) single-platform hashtag studies were an archetype of digital activism research alongside single-platform Facebook studies and holistic approaches (hybrid, multi-method & multi-sited, e.g., ethnography). The paper concludes by advocating for greater diversity in terms of the methodological approaches adopted in digital activism research.
Hamiltonian light-front field theory in a basis function approach
Creators: name: Vary, J. P.
name: Honkanen, H.
name: Li, Jun
name: Maris, P.
name: Brodsky, S. J.
name: Harindranath, A.
name: de Teramond, G. F.
name: Sternberg, P.
name: Ng, E. G.
name: Yang, C.
Publisher: name: arXiv
Year: 2009
Subjects: subject: Nuclear Theory (nucl-th)
subject: High Energy Physics - Theory (hep-th)
subject: FOS: Physical sciences

description: Hamiltonian light-front quantum field theory constitutes a framework for the non-perturbative solution of invariant masses and correlated parton amplitudes of self-bound systems. By choosing the light-front gauge and adopting a basis function representation, we obtain a large, sparse, Hamiltonian matrix for mass eigenstates of gauge theories that is solvable by adapting the ab initio no-core methods of nuclear many-body theory. Full covariance is recovered in the continuum limit, the infinite matrix limit. There is considerable freedom in the choice of the orthonormal and complete set of basis functions with convenience and convergence rates providing key considerations. Here, we use a two-dimensional harmonic oscillator basis for transverse modes that corresponds with eigensolutions of the soft-wall AdS/QCD model obtained from light-front holography. We outline our approach and present illustrative features of some non-interacting systems in a cavity. We illustrate the first steps towards solving QED by obtaining the mass eigenstates of an electron in a cavity in small basis spaces and discuss the computational challenges.
description: 35 pages, 15 figures, Revised to correct Fig. 7 and add new Fig. 15 with spectral results for electron in a transverse cavity
Climate as a contributing factor in the demise of Angkor, Cambodia
Creators: Buckley, Brendan M.
Anchukaitis, Kevin
Penny, Daniel
Fletcher, Roland
Cook, Edward R.
Sano, Masaki
Nam, Le Canh
Wichienkeeo, Aroonrut
Minh, Ton That
Hong, Truong Mai
Publisher: name: Columbia University
Year: 2010
Subjects: Paleoclimatology
Droughts
Dendrochronology

description: The “hydraulic city” of Angkor, the capitol of the Khmer Empire in Cambodia, experienced decades-long drought interspersed with intense monsoons in the fourteenth and fifteenth centuries that, in combination with other factors, contributed to its eventual demise. The climatic evidence comes from a seven-and-a-half century robust hydroclimate reconstruction from tropical southern Vietnamese tree rings. The Angkor droughts were of a duration and severity that would have impacted the sprawling city’s water supply and agricultural productivity, while high-magnitude monsoon years damaged its water control infrastructure. Hydroclimate variability for this region is strongly and inversely correlated with tropical Pacific sea surface temperature, indicating that a warm Pacific and El Niño events induce drought at interannual and interdecadal time scales, and that low-frequency variations of tropical Pacific climate can exert significant influence over Southeast Asian climate and society.
Zeta_tau Particle
Creators: name: Riley, Spencer
Publisher: name: figshare
Year: 2017
Subjects: subject: Quantum Mechanics
subject: 20203 Particle Physics
subject: FOS: Physical sciences

description: Emission of a particular Zeta Particle, also called the "Now" Photon, from Tachyon - Anti-Tachyon Collision.
The sharing of disinformation in cross-national comparison: analyzing patterns of resilience
Creators: name: Humprecht, Edda
name: Esser, Frank
name: Van Aelst, Peter
name: Staender, Anna
name: Morosoli, Sophie
Publisher: name: Taylor & Francis
Year: 2021
Subjects: subject: 59999 Environmental Sciences not elsewhere classified
subject: FOS: Earth and related environmental sciences
subject: Ecology
subject: FOS: Biological sciences
subject: Sociology
subject: FOS: Sociology
subject: 69999 Biological Sciences not elsewhere classified
subject: Marine Biology
subject: Science Policy

description: Although the problem of disinformation is on the rise across the globe, previous research has found that countries differ in the extent of widespread disinformation. In this study, we examine the willingness to disseminate disinformation across six countries (Belgium, France, Germany, Switzerland, the U.K. and the U.S.). We use a model by Humprecht et al. (2020) to study to what degree various systemic-structural factors influence individual behavior and contribute to resilience to disinformation. We draw on uniformly collected primary survey data and use regression analyses to examine which factors may explain citizens’ decisions to not further propagate disinformation. The results of our cross-national study show that resilience factors are country-specific and are highly dependent on the respective political and information environments. While in some countries extreme ideology weakens resilience, in others low education can have such an effect. Cross-national resilience factors include heavy social media use, the use of alternative media, and populist party support. We discuss what kind of tailored measures in combating online disinformation are needed to improve social resilience across different countries.
A comprehensive connection between the basic results and properties derived from two kinds of topologies for a random locally convex module
Creators: name: Guo, Tiexin
Publisher: name: arXiv
Year: 2009
Subjects: subject: Functional Analysis (math.FA)
subject: Probability (math.PR)
subject: FOS: Mathematics
subject: 46A22, 46A16, 46A25, 46H25, 46H05, 46B10, 60H25

description: The purpose of this paper is to make a comprehensive connection between the basic results and properties derived from the two kinds of topologies (namely the $(ε,λ)-$topology introduced by the author and the stronger locally $L^{0}-$convex topology recently introduced by Filipovi$\acute{c}$ et. al) for a random locally convex module. First, we give an extremely simple proof of the known Hahn-Banach extension theorem of $L^{0}-$linear functions as well as its continuous variants. Then we give the essential relations between the hyperplane separation theorems in [Filipovi$\acute{c}$ et. al, J. Funct. Anal.256(2009)3996--4029] and a basic strict separation theorem in [Guo et. al, Nonlinear Anal. 71(2009)3794--3804]: in the process obtain a useful and surprising fact that a random locally convex module with the countable concatenation property must have the same completeness under the two topologies! Based on the relation between the two kinds of completeness, we go on to present the central part of this paper: we prove that most of the previously established deep results of random conjugate spaces of random normed modules under the $(ε,λ)-$topology are still valid under the locally $L^{0}-$convex topology, which considerably enriches financial applications of random normed modules.
description: 32 pages
Spatially resolved study of the physical properties of the ionized gas in NGC 595
Creators: name: Relano, M.
name: Monreal-Ibero, A.
name: Vilchez, J. M.
name: Kennicutt, R. C.
Publisher: name: arXiv
Year: 2009
Subjects: subject: Cosmology and Nongalactic Astrophysics (astro-ph.CO)
subject: FOS: Physical sciences

description: We present Integral Field Spectroscopy (IFS) of NGC 595, one of the most luminous HII regions in M33. This type of observations allows studying the variation of the principal emission-line ratios across the surface of the nebula. At each position of the field of view, we fit the main emission-line features of the spectrum within the spectral range 3650-6990A, and create maps of the principal emission-line ratios for the total surface of the region. The extinction map derived from the Balmer decrement and the absorbed H-alpha luminosity show good spatial correlation with the 24 micron emission from Spitzer. We also show here the capability of the IFS to study the existence of Wolf-Rayet (WR) stars, identifying the previously catalogued WR stars and detecting a new candidate towards the north of the region. The ionization structure of the region nicely follows the H-alpha shell morphology and is clearly related to the location of the central ionizing stars. The electron density distribution does not show strong variations within the HII region nor any trend with the H-alpha emission distribution. We study the behaviour within the HII region of several classical emission-line ratios proposed as metallicity calibrators: while [NII]/Ha and [NII]/[OIII] show important variations, the R23 index is substantially constant across the surface of the nebula, despite the strong variation of the ionization parameter as a function of the radial distance from the ionizing stars. These results show the reliability in using the R23 index to characterize the metallicity of HII regions even when only a fraction of the total area is covered by the observations.
description: 16 pages, 12 figures, published in MNRAS (replaced to match the journal version). Based on observations collected at the German-Spanish Astronomical Center, Calar Alto, (MPIA and IAA-CSIC)
Evaluación por competencias en campos de conocimiento, una mirada hacia el currículo
Creators: name: Mosquera Rodas, Jhon  Jairo
Publisher: name: figshare
Year: 2021
Subjects: subject: Education
subject: 170103 Educational Psychology
subject: FOS: Psychology

description: La investigación examina el problema de evaluar a través del modelo por competencias empleando la teoría de Biggs, teniendo en cuenta tres campos de conocimiento desde el enfoque crítico, presentando finalmente un tercero, que muestra los resultados de la investigación desde la configuración evaluativa e interpretativa del proceso evaluativo por competencias. Luego de lo anterior, se aplica el método hermenéutico, empleando la perspectiva Gademariana, partiendo de la adaptación propuesta por (Noriega, 2002, pp. 1-8), centrada en el análisis textual desde el aspecto educativo, a través de los tres campos de conocimiento relacionados con el contexto, presentando resultados de índole teórico y analítico, para la solución del problema planteado. Los resultados presentan una mirada de la evaluación para el currículo por competencias, centrada en la importancia del proceso educativo, y no en el profesor o el estudiante, como se viene investigando actualmente, permitiendo así un proceso de enseñaza-aprendizaje más equilibrado. El resultado didáctico presenta una plantilla para facilitar la construcción de las preguntas propuestas en la taxonomía SOLO, junto al desarrollo del paso a paso de la metodología del círculo hermenéutico.
Good quality virtual realization of unit disk graphs
Creators: name: Pemmaraju, Sriram
name: Pirwani, Imran
Publisher: name: Journal of Computational Geometry
Year: 2011

description: We consider the problem of finding a realization of an n-vertex unit disk graph (UDG) expressed in general form, say, as an adjacency matrix. The problem is to construct an embedding of the graph in low-dimensional Euclidean space so that the ratio of the length of the longest edge under the embedding to the length of the shortest non-edge under the embedding is as small as possible; the measure is known as the quality of the realization. Thus, an optimum quality realization has quality between 1/2 and 1. Kuhn et al. gave aO(log3.5 n (loglog n)1/2}) quality realization that requires solving a linear program with exponentially many constraints by using the ellipsoid algorithm. In this article, we give a combinatorial algorithm that achieves an O(log3 n) quality realization of an n-vertex UDG expressed in general form. Thus, not only is our algorithm an improvement, it also bypasses the standard and costly technique of solving a linear program with exponentially many “spreading constraints.” As a side effect of our construction, we get the first constant-factor approximation to the minimum clique partition problem for UDGs expressed in general form. Such a clique partition also represents our key technical contribution. If the embedding is allowed to reside in higher dimensional space, we obtain improved results: a quality-2 embedding in constant dimensional Euclidean space.
description: Journal of Computational Geometry, Vol 2, No 1 (2011)
Superconducting triplet spin valve
Creators: name: Fominov, Ya. V.
name: Golubov, A. A.
name: Karminskaya, T. Yu.
name: Kupriyanov, M. Yu.
name: Deminov, R. G.
name: Tagirov, L. R.
Publisher: name: arXiv
Year: 2010
Subjects: subject: Superconductivity (cond-mat.supr-con)
subject: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
subject: FOS: Physical sciences

description: We study the critical temperature T_c of SFF trilayers (S is a singlet superconductor, F is a ferromagnetic metal), where the long-range triplet superconducting component is generated at noncollinear magnetizations of the F layers. We demonstrate that T_c can be a nonmonotonic function of the angle αbetween the magnetizations of the two F layers. The minimum is achieved at an intermediate α, lying between the parallel (P, α=0) and antiparallel (AP, α=π) cases. This implies a possibility of a "triplet" spin-valve effect: at temperatures above the minimum T_c^{Tr} but below T_c^{P} and T_c^{AP}, the system is superconducting only in the vicinity of the collinear orientations. At certain parameters, we predict a reentrant T_c(α) behavior. At the same time, considering only the P and AP orientations, we find that both the "standard" (T_c^{P} < T_c^{AP}) and "inverse" (T_c^{P} > T_c^{AP}) switching effects are possible depending on parameters of the system.
description: 5 pages (including 4 EPS figures)
Probing CP violation with the electric dipole moment of atomic mercury
Creators: name: Latha, K. V. P.
name: Angom, D.
name: Das, B. P.
name: Mukherjee, D.
Publisher: name: arXiv
Year: 2009
Subjects: subject: Atomic Physics (physics.atom-ph)
subject: High Energy Physics - Phenomenology (hep-ph)
subject: Chemical Physics (physics.chem-ph)
subject: Computational Physics (physics.comp-ph)
subject: FOS: Physical sciences

description: The electric dipole moment of atomic $^{199}$Hg induced by the nuclear Schiff moment and tensor-pseudotensor electron-nucleus interactions has been calculated. For this, we have developed and employed a novel method based on the relativistic coupled-cluster theory. The results of our theoretical calculations combined with the latest experimental result of $^{199}$Hg electric dipole moment, provide new bounds on the T reversal or CP violation parameters $θ_{\rm QCD}$, the tensor-pseudotensor coupling constant $C_T$ and $(\widetilde{d}_u - \widetilde{d}_d)$. This is the most accurate calculation of these parameters to date. We highlight the the crucial role of electron correlation effects in their interplay with the P,T violating interactions. Our results demonstrate substantial changes in the results of earlier calculations of these parameters which can be attributed to the more accurate inclusion of important correlation effects in the present work.
description: 4 pages and 1 figure