Results for "Noah Goodman"

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Overtwisted open books from sobering arcsJul 24 2004Oct 11 2005We study open books on three manifolds which are compatible with an overtwisted contact structure. We show that the existence of certain arcs, called sobering arcs, is a sufficient condition for an open book to be overtwisted, and is necessary up to stabilization ... More
Bias and Generalization in Deep Generative Models: An Empirical StudyNov 08 2018In high dimensional settings, density estimation algorithms rely crucially on their inductive bias. Despite recent empirical success, the inductive bias of deep generative models is not well understood. In this paper we propose a framework to systematically ... More
On the stable equivalence of open books in three-manifoldsSep 23 2005Mar 03 2009We show that two open books in a given closed, oriented three-manifold admit isotopic stabilizations, where the stabilization is made by successive plumbings with Hopf bands, if and only if their associated plane fields are homologous. Since this condition ... More
Multimodal Generative Models for Scalable Weakly-Supervised LearningFeb 14 2018Nov 12 2018Multiple modalities often co-occur when describing natural phenomena. Learning a joint representation of these modalities should yield deeper and more useful representations. Previous generative approaches to multi-modal input either do not learn a joint ... More
A Dynamic Programming Algorithm for Inference in Recursive Probabilistic ProgramsJun 15 2012Sep 10 2012We describe a dynamic programming algorithm for computing the marginal distribution of discrete probabilistic programs. This algorithm takes a functional interpreter for an arbitrary probabilistic programming language and turns it into an efficient marginalizer. ... More
Inducing Probabilistic Programs by Bayesian Program MergingOct 25 2011This report outlines an approach to learning generative models from data. We express models as probabilistic programs, which allows us to capture abstract patterns within the examples. By choosing our language for programs to be an extension of the algebraic ... More
Inducing Interpretable Representations with Variational AutoencodersNov 22 2016We develop a framework for incorporating structured graphical models in the \emph{encoders} of variational autoencoders (VAEs) that allows us to induce interpretable representations through approximate variational inference. This allows us to both perform ... More
A pragmatic theory of generic languageAug 09 2016Aug 26 2016Generalizations about categories are central to human understanding, and generic language (e.g. "Dogs bark.") provides a simple and ubiquitous way to communicate these generalizations. Yet the meaning of generic language is philosophically puzzling and ... More
Deep Amortized Inference for Probabilistic ProgramsOct 18 2016Probabilistic programming languages (PPLs) are a powerful modeling tool, able to represent any computable probability distribution. Unfortunately, probabilistic program inference is often intractable, and existing PPLs mostly rely on expensive, approximate ... More
Learning to Generate Compositional Color DescriptionsJun 13 2016Oct 18 2016The production of color language is essential for grounded language generation. Color descriptions have many challenging properties: they can be vague, compositionally complex, and denotationally rich. We present an effective approach to generating color ... More
Learning the Preferences of Ignorant, Inconsistent AgentsDec 18 2015An important use of machine learning is to learn what people value. What posts or photos should a user be shown? Which jobs or activities would a person find rewarding? In each case, observations of people's past choices can inform our inferences about ... More
Differentiable Antithetic Sampling for Variance Reduction in Stochastic Variational InferenceOct 05 2018Stochastic optimization techniques are standard in variational inference algorithms. These methods estimate gradients by approximating expectations with independent Monte Carlo samples. In this paper, we explore a technique that uses correlated, but more ... More
C3: Lightweight Incrementalized MCMC for Probabilistic Programs using Continuations and Callsite CachingSep 07 2015Sep 08 2015Lightweight, source-to-source transformation approaches to implementing MCMC for probabilistic programming languages are popular for their simplicity, support of existing deterministic code, and ability to execute on existing fast runtimes. However, they ... More
Mass-structure of weighted real treesJan 08 2018Rooted, weighted continuum random trees are used to describe limits of sequences of random discrete trees. Formally, they are random quadruples $(\mathcal{T},d,r,p)$, where $(\mathcal{T},d)$ is a tree-like metric space, $r\in\mathcal{T}$ is a distinguished ... More
Electromagnetic Casimir Forces in Elliptic Cylinder GeometriesMar 26 2013The scattering theory approach makes it possible to carry out exact calculations of Casimir energies in any geometry for which the scattering T-matrix and a partial wave expansion of the free Green's function are available. We implement this program for ... More
Schwarzschild Quantum Fluctuations from Regge-Wheeler ScatteringOct 17 2018Jan 08 2019We apply a multichannel variable phase method to scattering from Regge-Wheeler potentials. Using a reduced version of the WKB subtraction developed by Candelas and Howard, this approach allows for efficient numerical calculations of scattering data for ... More
The m-Degenerate Chromatic Number of a DigraphSep 26 2014Dec 04 2018The digraph chromatic number of a directed graph $D$, denoted $\chi_A(D)$, is the minimum positive integer $k$ such that there exists a partition of the vertices of $D$ into $k$ disjoint sets, each of which induces an acyclic subgraph. For any $m \geq ... More
Casimir Energies of Periodic Dielectric GratingsJul 17 2014Sep 23 2014Reflection of electromagnetic waves from a periodic grating can be described in terms of a discrete coupled multichannel scattering problem. By modeling the grating as a space- and frequency-dependent dielectric, it is possible to use a variable phase ... More
Mednykh's Formula via Lattice Topological Quantum Field TheoriesMar 05 2007Aug 28 2008Mednykh proved that for any finite group G and any orientable surface S, there is a formula for #Hom(pi_1(S), G) in terms of the Euler characteristic of S and the dimensions of the irreducible representations of G. A similar formula in the nonorientable ... More
Resolving a Conjecture on Degree of Regularity of Linear Homogeneous EquationsApr 13 2014A linear equation is $r$-regular, if, for every $r$-coloring of the positive integers, there exist positive integers of the same color which satisfy the equation. In 2005, Fox and Radoicic conjectured that the equation $x_1 + 2x_2 + \cdots + 2^{n-2}x_{n-1} ... More
The dual complex of $\bar{M}_{0,n}$ via phylogeneticsDec 01 2015May 09 2016The moduli space $\bar{M}_{0,n}$ of stable rational n-pointed curves has divisorial boundary with simple normal crossings. In this brief note I observe that the dual complex is a flag complex; that is, a collection of irreducible boundary divisors has ... More
Brownian bricklayer: a random space-filling curveAug 23 2017Let $(B(t),\,t\ge0)$ denote the standard, one-dimensional Wiener process and $(\ell(y,t);\, y\in\mathbb{R},\, t\ge0)$ its local time at level $y$ up to time $t$. Then $\big( (B(t),\, \ell(B(t),t)),\; t\ge0 \big)$ is a random path that fills the upper ... More
Practical optimal experiment design with probabilistic programsAug 17 2016Scientists often run experiments to distinguish competing theories. This requires patience, rigor, and ingenuity - there is often a large space of possible experiments one could run. But we need not comb this space by hand - if we represent our theories ... More
Meta-Amortized Variational Inference and LearningFeb 05 2019How can we learn to do probabilistic inference in a way that generalizes between models? Amortized variational inference learns for a single model, sharing statistical strength across observations. This benefits scalability and model learning, but does ... More
Zero Shot Learning for Code Education: Rubric Sampling with Deep Learning InferenceSep 05 2018Dec 17 2018In modern computer science education, massive open online courses (MOOCs) log thousands of hours of data about how students solve coding challenges. Being so rich in data, these platforms have garnered the interest of the machine learning community, with ... More
Neurally-Guided Procedural Models: Amortized Inference for Procedural Graphics Programs using Neural NetworksMar 19 2016Oct 13 2016Probabilistic inference algorithms such as Sequential Monte Carlo (SMC) provide powerful tools for constraining procedural models in computer graphics, but they require many samples to produce desirable results. In this paper, we show how to create procedural ... More
The Infinite Latent Events ModelMay 09 2012We present the Infinite Latent Events Model, a nonparametric hierarchical Bayesian distribution over infinite dimensional Dynamic Bayesian Networks with binary state representations and noisy-OR-like transitions. The distribution can be used to learn ... More
Classes for Fast Maximum Entropy TrainingAug 09 2001Maximum entropy models are considered by many to be one of the most promising avenues of language modeling research. Unfortunately, long training times make maximum entropy research difficult. We present a novel speedup technique: we change the form of ... More
Parsing Inside-OutMay 19 1998The inside-outside probabilities are typically used for reestimating Probabilistic Context Free Grammars (PCFGs), just as the forward-backward probabilities are typically used for reestimating HMMs. I show several novel uses, including improving parser ... More
Radio scintillation of gamma-ray-burst afterglowsJun 09 1997Stars twinkle to the eye through atmospheric turbulence, but planets, because of their larger angular size, do not. Similarly, scintillation due to the local interstellar medium will modulate the radio flux of gamma-ray-burst afterglows and may permit ... More
Detectors for New Neutrino ExperimentsMar 11 2004There has been great progress in understanding the neutrino sector in the last few years. One mixing angle has not yet been measured, theta-13. Detectors for the current round of long-baseline neutrino oscillation experiments, for future long-baseline ... More
The Maximum Detectable Momentum for cosmic ray muons in the MINOS far detectorJun 04 2007A magnetic detector such as MINOS which is measuring the sign of muons has to deal with issues of bending, which depend on the magnetic field configuration, and multiple scattering, which depends on the amount of material which is traversed. Above some ... More
Megaton Water Cerenkov Detectors and Astrophysical NeutrinosJan 21 2005Although formal proposals have not yet been made, the UNO and Hyper-Kamiokande projects are being developed to follow-up the tremendously successful program at Super-Kamiokande using a detector that is 20-50 times larger. The potential of such a detector ... More
Restrictions on endomorphism rings of jacobians and their minimal fields of definitionJan 17 2019We use tools from representation theory to give simple, easy to verify weak conditions for `upper bounds' on endomorphism rings of certain jacobians defined over a number field $K$. For example, we provide easy to check conditions for such a jacobian ... More
Brownian Super-exponentsDec 06 2006We introduce a transform on the class of stochastic exponentials for d-dimensional Brownian motions. Each stochastic exponential generates another stochastic exponential under the transform. The new exponential process is often merely a supermartingale ... More
Concerning thermal tides on hot JupitersJan 21 2009By analogy with a mechanism proposed by Gold and Soter to explain the retrograde rotation of Venus, Arras and Socrates suggest that thermal tides may excite hot jovian exoplanets into nonsynchronous rotation, and perhaps also noncircular orbits. It is ... More
Extended Comment on Language Trees and ZippingFeb 21 2002This is the extended version of a Comment submitted to Physical Review Letters. I first point out the inappropriateness of publishing a Letter unrelated to physics. Next, I give experimental results showing that the technique used in the Letter is 3 times ... More
A Bit of Progress in Language ModelingAug 09 2001In the past several years, a number of different language modeling improvements over simple trigram models have been found, including caching, higher-order n-grams, skipping, interpolated Kneser-Ney smoothing, and clustering. We present explorations of ... More
Global Thresholding and Multiple Pass ParsingAug 13 1997Aug 15 1997We present a variation on classic beam thresholding techniques that is up to an order of magnitude faster than the traditional method, at the same performance level. We also present a new thresholding technique, global thresholding, which, combined with ... More
New Projects in Underground PhysicsJul 08 2003A large fraction of neutrino research is taking place in facilities underground. In this paper, I review the underground facilities for neutrino research. I discuss ideas for future reactor experiments being considered to measure theta_13 and the UNO ... More
Seeing ScienceNov 17 2009The ability to represent scientific data and concepts visually is becoming increasingly important due to the unprecedented exponential growth of computational power during the present digital age. The data sets and simulations scientists in all fields ... More
Selfgravity and QSO disksJan 01 2002It is well known that the outer parts of QSO accretion disks are prone to selfgravity if heated solely by orbital dissipation. Such disks might be expected to form stars rather than accrete onto the black hole. The arguments leading to this conclusion ... More
Geocentrism reexaminedJun 09 1995The universe is nearly isotropic on very large scales. It is much more difficult to show that the universe is radially homogeneous (independent of distance), or equivalently, that it is isotropic about distant points. This taken as an axiom, since if ... More
Searching for the Neutrino Mixing Angle Theta-13 at ReactorsJun 04 2007Two neutrino mixing angles have been measured, and much of the neutrino community is turning its attention to the unmeasured mixing angle, $\quq$, whose best limit comes from the reactor neutrino experiment CHOOZ.\cite{bib:chooz} New two detector reactor ... More
Other Atmospheric Neutrino ExperimentsOct 23 2002The history and recent progress of atmospheric neutrinos are reviewed. An emphasis is placed on results from experiments other than Super-Kamiokande.
Neutrino Physics in 2020Feb 25 2014Many talks at the 16th Lomonosov Conference, dedicated to Bruno Pontecorvo, detail the remarkable progress in neutrino physics over the last two decades. In this paper, I give an opinionated, and therefore likely inaccurate, review of the future, with ... More
Reduction of Maximum Entropy Models to Hidden Markov ModelsDec 12 2012We show that maximum entropy (maxent) models can be modeled with certain kinds of HMMs, allowing us to construct maxent models with hidden variables, hidden state sequences, or other characteristics. The models can be trained using the forward-backward ... More
Repulsive Dark MatterMar 02 2000It seems necessary to suppress, at least partially, the formation of structure on subgalactic scales. As an alternative to warm or collisional dark matter, I postulate a condensate of massive bosons interacting via a repulsive interparticle potential, ... More
Efficient Algorithms for Parsing the DOP ModelApr 22 1996Excellent results have been reported for Data-Oriented Parsing (DOP) of natural language texts (Bod, 1993). Unfortunately, existing algorithms are both computationally intensive and difficult to implement. Previous algorithms are expensive due to two ... More
Exact Electromagnetic Casimir Energy of a Disk Opposite a PlaneJun 03 2016Sep 08 2016Building on work of Meixner [J. Meixner, Z. Naturforschung 3a, 506 (1948)], we show how to compute the exact scattering amplitude (or $T$-matrix) for electromagnetic scattering from a perfectly conducting disk. This calculation is a rare example of a ... More
Good dynamics versus bad kinematics. Is entanglement needed for quantum computation?Jun 01 1999Jun 03 1999We consider quantum computing with pseudo-pure states. This framework arises in certain implementations of quantum computing using NMR. We analyze quantum computational protocols which aim to solve exponential classical problems with polynomial resources ... More
On the role of entanglement in quantum computational speed-upJan 30 2002Mar 08 2002For any quantum algorithm operating on pure states we prove that the presence of multi-partite entanglement, with a number of parties that increases unboundedly with input size, is necessary if the quantum algorithm is to offer an exponential speed-up ... More
The Halting Problem for Quantum ComputersJun 16 1998Jun 29 1998We argue that the halting problem for quantum computers which was first raised by Myers, is by no means solved, as has been claimed recently. We explicitly demonstrate the difficulties that arise in a quantum computer when different branches of the computation ... More
The Chen-Gibney-Krashen moduli space as a Chow quotientSep 11 2015The space of n distinct points and a disjoint parameterized hyperplane in projective d-space up to projectivity---equivalently, configurations of n distinct points in affine d-space up to translation and homothety---has a beautiful compactification introduced ... More
Variable Phase S-Matrix Calculations for Asymmetric Potentials and DielectricsOct 02 2012Dec 23 2012Motivated by recently developed techniques making it possible to compute Casimir energies for any object whose scattering S-matrix (or, equivalently, T-matrix) is available, we develop a variable phase method to compute the S-matrix for localized but ... More
The NGC 672 and NGC 784 Galaxy Groups: Evidence for Galaxy Formation and Growth Along a Nearby Dark Matter FilamentAug 13 2008(Abridged): We present U, B, V, R, I, H-alpha and NUV photometry of 14 galaxies in the very local Universe (within 10 Mpc that are dwarf irregular galaxies (dIrr), are at low redshift (51<v<610 km/s), and appear as a six degree long linear filament.. ... More
Path Intergals and Perturbative Expansions for Non-Compact Symmetric SpacesFeb 05 1992We show how to construct path integrals for quantum mechanical systems where the space of configurations is a general non-compact symmetric space. Associated with this path integral is a perturbation theory which respects the global structure of the system. ... More
Inhomogeneous Quantum WalksJun 19 2009We study a natural construction of a general class of inhomogeneous quantum walks (namely walks whose transition probabilities depend on position). Within the class we analyze walks that are periodic in position and show that, depending on the period, ... More
Measurement entropy in Generalized Non-Signalling Theory cannot detect bipartite non-localityJul 13 2012Nov 13 2012We consider entropy in Generalized Non-Signalling Theory (also known as box world) where the most common definition of entropy is the measurement entropy. In this setting, we completely characterize the set of allowed entropies for a bipartite state. ... More
Transition To Order After Hilltop InflationJan 24 2014We investigate the rich nonlinear dynamics during the end of hilltop inflation by numerically solving the coupled Klein-Gordon-Friedmann equations in a expanding universe. In particular, we search for coherent, nonperturbative configurations that may ... More
Radiatively induced symmetry breaking and the conformally coupled magnetic monopole in AdS spaceOct 29 2013We implement quantum corrections for a magnetic monopole in a classically conformally invariant theory containing gravity. This yields the trace (conformal) anomaly and introduces a length scale in a natural fashion via the process of renormalization. ... More
Modeling dynamical scalarization with a resummed post-Newtonian expansionMar 10 2016Mar 13 2016Despite stringent constraints set by astrophysical observations, there remain viable scalar-tensor theories that could be distinguished from general relativity with gravitational-wave detectors. A promising signal predicted in these alternative theories ... More
Rank conditional coverage and confidence intervals in high dimensional problemsFeb 22 2017Confidence interval procedures used in low dimensional settings are often inappropriate for high dimensional applications. When a large number of parameters are estimated, marginal confidence intervals associated with the most significant estimates have ... More
Sparse-Input Neural Networks for High-dimensional Nonparametric Regression and ClassificationNov 21 2017Neural networks are usually not the tool of choice for nonparametric high-dimensional problems where the number of input features is much larger than the number of observations. Though neural networks can approximate complex multivariate functions, they ... More
The cone of type A, level one conformal blocks divisorsMay 16 2011May 17 2011We prove that the type A, level one, conformal blocks divisors on $\bar{M}_{0,n}$ span a finitely generated, full-dimensional subcone of the nef cone. Each such divisor induces a morphism from $\bar{M}_{0,n}$, and we identify its image as a GIT quotient ... More
Remote Homology Detection in Proteins Using Graphical ModelsApr 24 2013Given the amino acid sequence of a protein, researchers often infer its structure and function by finding homologous, or evolutionarily-related, proteins of known structure and function. Since structure is typically more conserved than sequence over long ... More
The shape of the LoTr 5 planetary nebulaOct 18 1998We observed the large and faint planetary nebula (PN) around IN Com in H-alpha and [NII] light with a coronagraphic CCD device on the Wise Observatory reflector blocking the light from the central star. Our goal was to provide a second image of the object ... More
Non-cyclotomic fusion categoriesFeb 01 2010May 02 2010Etingof, Nikshych and Ostrik ask in arXiv:math.QA/0203060 if every fusion category can be completely defined over a cyclotomic field. We show that this is not the case: in particular one of the fusion categories coming from the Haagerup subfactor arXiv:math.OA/9803044 ... More
The universal tropicalization and the Berkovich analytificationOct 16 2014Jan 01 2016Given an integral scheme X over a non-archimedean valued field k, we construct a universal closed embedding of X into a k-scheme equipped with a model over the field with one element (a generalization of a toric variety). An embedding into such an ambient ... More
Contextual Word Representations: A Contextual IntroductionFeb 15 2019This introduction aims to tell the story of how we put words into computers. It is part of the story of the field of natural language processing (NLP), a branch of artificial intelligence. It targets a wide audience with a basic understanding of computer ... More
Evaluating Compositionality in Sentence EmbeddingsFeb 12 2018May 17 2018An important challenge for human-like AI is compositional semantics. Recent research has attempted to address this by using deep neural networks to learn vector space embeddings of sentences, which then serve as input to other tasks. We present a new ... More
Coarse-to-Fine Sequential Monte Carlo for Probabilistic ProgramsSep 09 2015Many practical techniques for probabilistic inference require a sequence of distributions that interpolate between a tractable distribution and an intractable distribution of interest. Usually, the sequences used are simple, e.g., based on geometric averages ... More
Tensor Variable Elimination for Plated Factor GraphsFeb 08 2019A wide class of machine learning algorithms can be reduced to variable elimination on factor graphs. While factor graphs provide a unifying notation for these algorithms, they do not provide a compact way to express repeated structure when compared to ... More
Church: a language for generative modelsJun 13 2012Jul 15 2014We introduce Church, a universal language for describing stochastic generative processes. Church is based on the Lisp model of lambda calculus, containing a pure Lisp as its deterministic subset. The semantics of Church is defined in terms of evaluation ... More
Joint Mapping and Calibration via Differentiable Sensor FusionNov 21 2018Dec 20 2018We leverage automatic differentiation (AD) and probabilistic programming to develop an end-to-end optimization algorithm for batch triangulation of a large number of unknown objects. Given noisy detections extracted from noisily geo-located street level ... More
Chance and Chandra (and repulsive dark matter)Apr 13 2011A few examples are given of Chandra's work on statistical and stochastic problems that relate to open questions in astrophysics, in particular his theory of dynamical relaxation in systems with inverse-square interparticle forces. The roles of chaos and ... More
Nonlinear Damping of Oscillations in Tidal-Capture BinariesSep 21 1995We calculate the damping of quadrupole f and low order g modes (primary modes) by nonlinear coupling to other modes of the star. This damping is orders of magnitude more rapid than direct radiative damping when the primary amplitude is large, as in tidal ... More
Fitting Formula for Flux Scintillation of Compact Radio SourcesSep 07 2005We present a fitting function to describe the statistics of flux modulations caused by interstellar scintillation. The function models a very general quantity: the cross-correlation of the flux observed from a compact radio source of finite angular size ... More
The algebra of K-invariant vector fields on a symmetric space G/KJul 19 2002Mar 31 2003When $G$ is a complex reductive algebraic group and $G/K$ is a reductive symmetric space, the decomposition of $\C[G/K]$ as a $K$-module was obtained (in a non-constructive way) by Richardson, generalizing the celebrated result of Kostant-Rallis for the ... More
Market Price of Risk and Random Field Driven Models of Term Structure: A Space-Time Change of Measure LookMay 20 2010No-arbitrage models of term structure have the feature that the return on zero-coupon bonds is the sum of the short rate and the product of volatility and market price of risk. Well known models restrict the behavior of the market price of risk so that ... More
On obliquely magnetized and differentially rotating starsJan 17 2015Apr 30 2015We investigate the interaction of differential rotation and a misaligned magnetic field. The incompressible magnetohydrodynamic equations are solved numerically for a free-decay problem. In the kinematic limit, differential rotation annihilates the non-axisymmetric ... More
Acceleration of Type 2 Spicules in the Solar Chromosphere - 2: Viscous Braking and Upper Bounds on Coronal Energy InputMar 11 2014A magnetohydrodynamic model is used to determine conditions under which the Lorentz force accelerates plasma to type 2 spicule speeds in the chromosphere. The model generalizes a previous model to include a more realistic pre-spicule state, and the vertical ... More
Interpretation of the atmospheric muon charge ratio in MINOSJun 04 2007MINOS is the first large magnetic detector deep underground and is the first to measure the muon charge ratio with high statistics in the region near 1 TeV.\cite{bib:adamson} An approximate formula for the muon charge ratio can be expressed in terms of ... More
The Effect of Noise on the Propagating Speed of Pre-mixed Laminar Flame FrontsOct 24 2016We study the effect of thermal noise on the propagation speed of a planar flame. We show that this out of equilibrium greatly amplifies the effect of thermal noise to yield macroscopic reductions in the flame speed over what is predicted by the noise-free ... More
Femtolensing: Beyond the Semi-Classical ApproximationJun 13 1994Jun 16 1994Femtolensing is a gravitational lensing effect in which the magnification is a function not only of the positions and sizes of the source and lens, but also of the wavelength of light. Femtolensing is the only known effect of $(10^{-13}-10^{-16} M_{\sun})$ ... More
TessellationsJun 14 2016A survey of tessellations, which appeared in Italian in La Matematica vol 3 in 2010. The Tiling Lemma appears for the first time.
Statistical Description of a Magnetized Corona above a Turbulent Accretion DiskMar 04 2008We present a physics-based statistical theory of a force-free magnetic field in the corona above a turbulent accretion disk. The field is represented by a statistical ensemble of loops tied to the disk. Each loop evolves under several physical processes: ... More
The Pegasus Tiles: an aperiodic pair of tilesAug 25 2016The Pegasus tiles are an aperiodic pair of tiles with "tip to tip" matching rules, first drawn in 1996. We present them here.
Matching Rules for the Sphinx Tiling SubstitutionAug 25 2016We give a set of tiles that enforces the sphinx tiling substitution system; the tiles are thus aperiodic.
On a generalization of Dehn's algorithmJun 20 2007Jan 15 2008Viewing Dehn's algorithm as a rewriting system, we generalise to allow an alphabet containing letters which do not necessarily represent group elements. This extends the class of groups for which the algorithm solves the word problem to include nilpotent ... More
Comparison of Admissibility Conditions for Cyclotomic Birman--Wenzl--Murakami AlgebrasMay 26 2009Jan 22 2010We show the equivalence of admissibility conditions proposed by Wilcox and Yu and by Rui and Xu for the parameters of cyclotomic BMW algebras.
Stochastic Coagulation and the Timescale for Runaway GrowthApr 05 2000We study the stochastic coagulation equation using simplified models and efficient Monte Carlo simulations. It is known that (i) runaway growth occurs if the two-body coalescence kernel rises faster than linearly in the mass of the heavier particle; and ... More
Secular Instability and Planetesimal Formation in the Dust LayerDec 28 1999Late in the gaseous phase of a protostellar disk, centimeter-sized bodies probably settle into a thin ``dust layer'' at the midplane. A velocity difference between the dust layer and the gas gives rise to turbulence, which prevents further settling and ... More
Ruling Out Bosonic Repulsive Dark Matter in Thermal EquilibriumSep 18 2011Aug 21 2012Self-interacting dark matter (SIDM), especially bosonic, has been considered a promising candidate to replace cold dark matter (CDM) as it resolves some of the problems associated with CDM. Here, we rule out the possibility that dark matter is a repulsive ... More
On the nature of the S stars in the Galactic CenterApr 04 2005Davies and King have suggested that the bright stars observed on short-period orbits about Sgr A* (``S stars'') are old, low-mass stripped AGB stars rather than young, high-mass main-sequence stars. If the observationally inferred effective temperatures ... More
Conditions for Photospherically Driven Alfvenic Oscillations to Heat the Solar Chromosphere by Pedersen Current DissipationOct 30 2014A magnetohydrodynamic model that includes a complete electrical conductivity tensor is used to estimate conditions for photospherically driven, linear, non-plane Alfvenic oscillations extending from the photosphere to the lower corona to drive a chromospheric ... More
Principles of High-Dimensional Data Visualization in AstronomyMay 21 2012Astronomical researchers often think of analysis and visualization as separate tasks. In the case of high-dimensional data sets, though, interactive exploratory data visualization can give far more insight than an approach where data processing and statistical ... More
A Guide to Comparisons of Star Formation Simulations with ObservationsJul 14 2011We review an approach to observation-theory comparisons we call "Taste-Testing." In this approach, synthetic observations are made of numerical simulations, and then both real and synthetic observations are "tasted" (compared) using a variety of statistical ... More
The COMPLETE Survey of Star-Forming Regions on its Second BirthdayMay 27 2004Jun 01 2004At age two, humans are just learning to speak, and they see the world in an unbiased way. At age two, the COMPLETE (COordinated Molecular Probe Line Extinction Thermal Emission) Survey of Star-Forming Regions is just beginning to hint at what it will ... More
Restricted Roots and Restricted Form of Weyl Dimension Formula for Spherical VarietiesSep 13 2012We study in this paper the restricted roots for a class of spherical homogeneous spaces of semisimple groups which includes simply connected symmetric spaces. For these spaces we give a detailed description (case by case) of the set of roots of the group ... More