cssi/SciSciGPT-SciSciNet huggingface dataset:
Perigee: Efficient Peer-to-Peer Network Design for Blockchains

A key performance metric in blockchains is the latency between when a transaction is broadcast and when it is confirmed (the so-called, confirmation latency). While improvements in consensus techniques can lead to lower confirmation latency, a fundamental lower bound on confirmation latency is the propagation latency of messages through the underlying peer-to-peer (p2p) network (in Bitcoin, the propagation latency is several tens of seconds). The de facto p2p protocol used by Bitcoin and other blockchains is based on random connectivity: each node connects to a random subset of nodes. The induced p2p network topology can be highly suboptimal since it neglects geographical distance, differences in bandwidth, hash-power and computational abilities across peers. We present Perigee, a decentralized algorithm that automatically learns an efficient p2p topology tuned to the aforementioned network heterogeneities, purely based on peers' interactions with their neighbors. Motivated by the literature on the multi-armed bandit problem, Perigee optimally balances the tradeoff between retaining connections to known well-connected neighbors, and exploring new connections to previously-unseen neighbors. Experimental evaluations show that Perigee reduces the latency to broadcast by 33%. Lastly Perigee is simple, computationally lightweight, adversary-resistant, and compatible with the selfish interests of peers, making it an attractive p2p protocol for blockchains.
Regulating Jurisdiction Collisions in International Law: The Case of the European Court of Justice's Exclusive Jurisdiction in Law of the Sea Disputes

Is it meaningful to call on the jurisdiction of one international tribunal over another? And if so, how do you decide which one should hear your case? In responding to this question, on one side, claimants often aspire to bring complex disputes to more than one international court under the jurisdiction of more than one branch of international law and, on the other, regional organizations seek to prioritize their respective judicial bodies above the rest. The combination of these two factors poses a challenge to the cohesion of international adjudication in terms of the profound differences between the interpretation that competing international tribunals could give to the same rule. It raises what this note calls a jurisdiction collision. Concentrating on the classical roots of international law and its changing significance over time and within different contexts, this note confronts incentives to exclusive litigation at the European Court of Justice of international disputes involving EU Member States that potentially raise issues of Community law. In specific, it addresses how the exclusive jurisdiction system institutionalized by the European Court has affected litigation of law of the sea disputes as a case study, and, in a more practical vein, encourages a relatively coherent system of principles to deal with jurisdiction collisions in international adjudication. This system is based on three main elements: the determination of proper jurisdiction over international legal disputes should be analyzed in light of the importance and urgency of the rights at stake to the relevant community; the degree to which each court can provide meaningful remedies; and whether the claims either have been previously decided or are being simultaneously heard at another court.
Flow-firing processes

Abstract We consider a discrete non-deterministic flow-firing process for rerouting flow on the edges of a planar complex. The process is an instance of higher-dimensional chip-firing. In the flow-firing process, flow on the edges of a complex is repeatedly diverted across the faces of the complex. For non-conservative initial configurations we show this process never terminates. For conservative initial flows we show the process terminates after a finite number of rerouting steps, but there are many possible final configurations reachable from a single initial state. Finally, for conservative initial flows around a topological hole we show the process terminates at a unique final configuration. In this case the process exhibits global confluence despite not satisfying local confluence.
High energy modular bootstrap, global symmetries and defects

We derive Cardy-like formulas for the growth of operators in different sectors of unitary 2 dimensional CFT in the presence of topological defect lines by putting an upper and lower bound on the number of states with scaling dimension in the interval [∆ − δ, ∆ + δ] for large ∆ at fixed δ. Consequently we prove that given any unitary modular invariant 2D CFT symmetric under finite global symmetry G (acting faithfully), all the irreducible representations of G appear in the spectra of the untwisted sector; the growth of states is Cardy like and proportional to the “square” of the dimension of the irrep. In the Schwarzian limit, the result matches onto that of JT gravity with a bulk gauge theory. If the symmetry is non-anomalous, the result applies to any sector twisted by a group element. For c > 1, the statements are true for Virasoro primaries. Furthermore, the results are applicable to large c CFTs. We also extend our results for the continuous U(1) group.
The political economy of feudalism in medieval Europe

Why did enduring traditions of economic and political liberty arise in Western Europe? An answer to this question must be sought at the constitutional level. Within the medieval constitutional order, traditions of representative and limited government developed through patterns of constitutional bargaining. The politically fragmented landscape that emerged following the decline of the Western Roman Empire and the barbarian migrations was conducive to those patterns. In particular, that landscape was characterized by polycentric and hierarchical governance structures; within those structures, political property rights holders were sovereign and residual claimants to governance returns. I elaborate on why this environment of polycentric sovereignty promoted constitutional bargaining in the direction of good governance and greater liberty.
A Real-Time Receding Horizon Sequence Planner for Disassembly in a Human-Robot Collaboration Setting

Product disassembly is a labor-intensive process and is far from being automated. Typically, disassembly is not robust enough to handle product varieties from different shapes, models, and physical uncertainties due to component imperfections, damage throughout component usage, or insufficient product information. To overcome these difficulties and to automate the disassembly procedure through human-robot collaboration without excessive computational cost, this paper proposes a real-time receding horizon sequence planner that distributes tasks between robot and human operator while taking real-time human motion into consideration. The sequence planner aims to address several issues in the disassembly line, such as varying orientations, safety constraints of human operators, uncertainty of human operation, and the computational cost of large number of disassembly tasks. The proposed disassembly sequence planner identifies both the positions and orientations of the to-be-disassembled items, as well as the locations of human operator, and obtains an optimal disassembly sequence that follows disassembly rules and safety constraints for human operation. Experimental tests have been conducted to validate the proposed planner: the robot can locate and disassemble the components following the optimal sequence, and consider explicitly human operator's real-time motion, and collaborate with the human operator without violating safety constraints.
Host immune response driving SARS-CoV-2 evolution

The transmission and evolution of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are of paramount importance in controlling and combating the coronavirus disease 2019 (COVID-19) pandemic. Currently, over 15,000 SARS-CoV-2 single mutations have been recorded, which have a great impact on the development of diagnostics, vaccines, antibody therapies, and drugs. However, little is known about SARS-CoV-2’s evolutionary characteristics and general trend. In this work, we present a comprehensive genotyping analysis of existing SARS-CoV-2 mutations. We reveal that host immune response via APOBEC and ADAR gene editing gives rise to near 65% of recorded mutations. Additionally, we show that children under age five and the elderly may be at high risk from COVID-19 because of their overreaction to the viral infection. Moreover, we uncover that populations of Oceania and Africa react significantly more intensively to SARS-CoV-2 infection than those of Europe and Asia, which may explain why African Americans were shown to be at increased risk of dying from COVID-19, in addition to their high risk of COVID-19 infection caused by systemic health and social inequities. Finally, our study indicates that for two viral genome sequences of the same origin, their evolution order may be determined from the ratio of mutation type, C > T over T > C.
Semi-bandit Optimization in the Dispersed Setting.

In this work, we study the problem of online optimization of piecewise Lipschitz functions with semi-bandit feedback. This challenging class of non-convex optimization problems often arises in algorithm selection problems for combinatorial settings, where the goal is to find the best algorithm from a large algorithm family for a specific application domain. In these settings, each evaluation of the loss functions in the optimization problem can be computationally expensive, often requiring the learner to run a combinatorial algorithm to measure its performance. Combined with the fact that small differences between similar algorithms in the family can lead to cascading changes in algorithm behavior, efficient online optimization in these settings is a challenging problem. However, we show that in many applications, evaluating the loss function for one algorithm choice can sometimes reveal the loss for a range of similar algorithms, essentially for free. We develop online optimization algorithms capable of using this kind of extra information by working in the semi-bandit feedback setting. Our algorithms achieve regret bounds that are essentially as good as algorithms under full-information feedback and are significantly more computationally efficient. We apply our semi-bandit optimization results to obtain online algorithm selection procedures for two rich families of combinatorial algorithms. We provide the first provable guarantees for online algorithm selection for clustering problems using a family of clustering algorithms containing classic linkage procedures. We also show how to select algorithms from a family of greedy knapsack algorithms with simultaneously lower computational complexity and stronger regret bounds than the best algorithm selection procedures from prior work.
A Conversational Digital Assistant for Intelligent Process Automation

Robotic process automation (RPA) has emerged as the leading approach to automate tasks in business processes. Moving away from back-end automation, RPA automated the mouse-click on user interfaces; this outside-in approach reduced the overhead of updating legacy software. However, its many shortcomings, namely its lack of accessibility to business users, have prevented its widespread adoption in highly regulated industries. In this work, we explore interactive automation in the form of a conversational digital assistant. It allows business users to interact with and customize their automation solutions through natural language. The framework, which creates such assistants, relies on a multi-agent orchestration model and conversational wrappers for autonomous agents including RPAs. We demonstrate the effectiveness of our proposed approach on a loan approval business process and a travel preapproval business process.
Physical limits to sensing material properties

All materials respond heterogeneously at small scales, which limits what a sensor can learn. Although previous studies have characterized measurement noise arising from thermal fluctuations, the limits imposed by structural heterogeneity have remained unclear. In this paper, we find that the least fractional uncertainty with which a sensor can determine a material constant λ0 of an elastic medium is approximately $$\delta {\lambda }_{0}/{\lambda }_{0} \sim ({\Delta }_{\lambda }^{1/2}/{\lambda }_{0}){(d/a)}^{D/2}{(\xi /a)}^{D/2}$$ for a ≫ d ≫ ξ, $${\lambda }_{0}\gg {\Delta }_{\lambda }^{1/2}$$ , and D > 1, where a is the size of the sensor, d is its spatial resolution, ξ is the correlation length of fluctuations in λ0, Δλ is the local variability of λ0, and D is the dimension of the medium. Our results reveal how one can construct devices capable of sensing near these limits, e.g. for medical diagnostics. We use our theoretical framework to estimate the limits of mechanosensing in a biopolymer network, a sensory process involved in cellular behavior, medical diagnostics, and material fabrication. At small scales, structural heterogeneities limit what a sensor can learn about the properties of a material. Here, the authors quantify these limits and determine the optimal measurement protocols, which depend on both the spatial resolution of the sensor and the number of probes.
Chromosome-Level Assembly of the Atlantic Silverside Genome Reveals Extreme Levels of Sequence Diversity and Structural Genetic Variation.

The levels and distribution of standing genetic variation in a genome can provide a wealth of insights about the adaptive potential, demographic history, and genome structure of a population or species. As structural variants are increasingly associated with traits important for adaptation and speciation, investigating both sequence and structural variation is essential for wholly tapping this potential. Using a combination of shotgun sequencing, 10X Genomics linked reads and proximity-ligation data (Chicago and Hi-C), we produced and annotated a chromosome-level genome assembly for the Atlantic silverside (Menidia menidia) - an established ecological model for studying the phenotypic effects of natural and artificial selection - and examined patterns of genomic variation across two individuals sampled from different populations with divergent local adaptations. Levels of diversity varied substantially across each chromosome, consistently being highly elevated near the ends (presumably near telomeric regions) and dipping to near zero around putative centromeres. Overall, our estimate of the genome-wide average heterozygosity in the Atlantic silverside is among the highest reported for a fish, or any vertebrate (1.32-1.76% depending on inference method and sample). Furthermore, we also found extreme levels of structural variation, affecting ∼23% of the total genome sequence, including multiple large inversions (> 1 Mb and up to 12.6 Mb) associated with previously identified haploblocks showing strong differentiation between locally adapted populations. These extreme levels of standing genetic variation are likely associated with large effective population sizes and may help explain the remarkable adaptive divergence among populations of the Atlantic silverside.
A Birman-Series type result for geodesics with infinitely many self-intersections

Given a hyperbolic surface $\S$, a classic result of Birman and Series states that for each $K$, all complete geodesics with at most $K$ self-intersections can only pass through a certain nowhere dense, Hausdorff dimension 1 subset of $\S$. We define a self-intersection function for each complete geodesic, which bounds the number of self-intersections in finite length subarcs. We then extend the Birman-Series result to sets of complete geodesics with certain bounds on their self-intersection functions. In fact, we get the same conclusion as the Birman-Series result for sets of complete geodesics whose self-intersection functions are in $o(l^2)$, where $l$ measures arclength.
Emergent super-Virasoro on magnetic branes

The low energy limit of the stress tensor, gauge current, and supercurrent twopoint correlators are calculated in the background of the supersymmetric magnetic brane solution to gauged five-dimensional supergravity constructed by Almuhairi and Polchinski. The resulting correlators provide evidence for the emergence of an $$ \mathcal{N}=2 $$ super-Virasoro algebra of right-movers, in addition to a bosonic Virasoro algebra and a U(1) ⊕U(1)-current algebra of left-movers (or the parity transform of left- and right-movers depending on the sign of the magnetic field), in the holographically dual strongly interacting two-dimensional effective field theory of the lowest Landau level.
Modulational Instability in Equations of KdV Type

It is a matter of experience that nonlinear waves in a dispersive medium, propagating primarily in one direction, may appear periodic in small space and time scales, but their characteristics—the amplitude, the phase, the wave number, etc.—slowly vary in large space and time scales. In the 1960s, Whitham developed an asymptotic (WKB) method to study the effects of small “modulations” on nonlinear dispersive waves. Since then, there has been a great deal of work aiming at rigorously justifying the predictions from Whitham’s formal theory. We discuss some recent advances in the mathematical understanding of the dynamics, in particular, the instability, of slowly modulated waves for equations of KdV type.
Quantum Group as Semi-infinite Cohomology

We obtain the quantum group SLq(2) as semi-infinite cohomology of the Virasoro algebra with values in a tensor product of two braided vertex operator algebras with complementary central charges \({c+\bar{c}=26}\). Each braided VOA is constructed from the free Fock space realization of the Virasoro algebra with an additional q-deformed harmonic oscillator degree of freedom. The braided VOA structure arises from the theory of local systems over configuration spaces and it yields an associative algebra structure on the cohomology. We explicitly provide the four cohomology classes that serve as the generators of SLq(2) and verify their relations. We also discuss the possible extensions of our construction and its connection to the Liouville model and minimal string theory.
$C^{*}$-algebras isomorphically representable on $l^{p}$

Let p ∈ ( 1 , ∞ ) ∖ { 2 } . We show that every homomorphism from a C ∗ -algebra 𝒜 into B ( l p ( J ) ) satisfies a compactness property where J is any set. As a consequence, we show that a C ∗ -algebra 𝒜 is isomorphic to a subalgebra of B ( l p ( J ) ) , for some set J , if and only if 𝒜 is residually finite-dimensional.
Block Model Guided Unsupervised Feature Selection

Feature selection is a core area of data mining with a recent innovation of graph-driven unsupervised feature selection for linked data. In this setting we have a dataset Y consisting of n instances each with m features and a corresponding n node graph (whose adjacency matrix is A) with an edge indicating that the two instances are similar. Existing efforts for unsupervised feature selection on attributed networks have explored either directly regenerating the links by solving for f such that f(yi,yj) ~ Ai,j or finding community structure in A and using the features in Y to predict these communities. However, graph-driven unsupervised feature selection remains an understudied area with respect to exploring more complex guidance. Here we take the novel approach of first building a block model on the graph and then using the block model for feature selection. That is, we discover FMFT ~ A and then find a subset of features S that induces another graph to preserve both F and M. We call our approach Block Model Guided Unsupervised Feature Selection (BMGUFS). Experimental results show that our method outperforms the state of the art on several real-world public datasets in finding high-quality features for clustering.
Torus actions and tensor products of intersection cohomology

Given certain intersection cohomology sheaves on a projective variety with a torus action, we relate the cohomology groups of their tensor product to the cohomology groups of the individual sheaves. We also prove a similar result in the case of equivariant cohomology.
Synthetic Radio Imaging for Quiescent and CME-flare Scenarios

Radio observations grant access to a wide range of physical processes through different emission mechanisms. These processes range from thermal and quiescent to eruptive phenomena, such as shock waves and particle beams. We present a new synthetic radio imaging tool that calculates and visualizes the Bremsstrahlung radio emission. This tool works concurrently with state-of-the-art Magnetohydrodynamic (MHD) simulations of the solar corona using the code BATS-R-US. Our model produces results that are in good agreement with both high and low frequency observations of the solar disk. In this study, a ray-tracing algorithm is used and the radio intensity is computed along the actual curved ray trajectories. We illustrate the importance of refraction in locating the radio emitting source by comparison of the radio imaging illustrations when the line-of-sight instead of the refracted paths are considered. We are planning to incorporate non-thermal radio emission mechanisms in a future version of the radio imaging tool.
Mechanical Search: Multi-Step Retrieval of a Target Object Occluded by Clutter

When operating in unstructured environments such as warehouses, homes, and retail centers, robots are frequently required to interactively search for and retrieve specific objects from cluttered bins, shelves, or tables. Mechanical Search describes the class of tasks where the goal is to locate and extract a known target object. In this paper, we formalize Mechanical Search and study a version where distractor objects are heaped over the target object in a bin. The robot uses an RGBD perception system and control policies to iteratively select, parameterize, and perform one of 3 actions – push, suction, grasp – until the target object is extracted, or either a time limit is exceeded, or no high confidence push or grasp is available. We present a study of 5 algorithmic policies for mechanical search, with 15,000 simulated trials and 300 physical trials for heaps ranging from 10 to 20 objects. Results suggest that success can be achieved in this long-horizon task with algorithmic policies in over 95% of instances and that the number of actions required scales approximately linearly with the size of the heap. Code and supplementary material can be found at http://ai.stanford.edu/mech-search.
Extended Linear Response for Bioanalytical Applications Using Multiple Enzymes

We develop a framework for optimizing a novel approach to extending the linear range of bioanalytical systems and biosensors by utilizing two enzymes with different kinetic responses to the input chemical as their substrate. Data for the flow injection amperometric system devised for detection of lysine based on the function of l-lysine-alpha-oxidase and lysine-2-monooxygenase are analyzed. Lysine is a homotropic substrate for the latter enzyme. We elucidate the mechanism for extending the linear response range and develop optimization techniques for future applications of such systems.
A Prime Ideal Principle for Two-Sided Ideals

Many classical ring-theoretic results state that an ideal that is maximal with respect to satisfying a special property must be prime. We present a “Prime Ideal Principle” that gives a uniform method of proving such facts, generalizing the Prime Ideal Principle for commutative rings due to T. Y. Lam and the author. Old and new “maximal implies prime” results are presented, with results touching on annihilator ideals, polynomial identity rings, the Artin–Rees property, Dedekind-finite rings, principal ideals generated by normal elements, strongly noetherian algebras, and just infinite algebras.
Infima of length functions and dual cube complexes

In the presence of certain topological conditions, we provide lower bounds for the infimum of the length function associated to a collection of curves on Teichmuller space that depend on the dual cube complex associated to the collection, a concept due to Sageev. As an application of our bounds, we obtain estimates for the ‘longest’ curve with k self-intersections, complementing work of Basmajian [Bas]. Let Σ be an oriented topological surface of finite type. We denote the Teichmuller space of Σ by T(Σ), which we interpret as the deformation space of marked hyperbolic structures on Σ. Given X ∈ T(Σ) and a free homotopy class (or closed curve) γ on Σ, we denote the length of the geodesic representative of γ, in the hyperbolic structure determined by X, by `(γ,X). If Γ = {γi} is a collection of closed curves, then we define `(Γ, X) = ∑ `(γi, X). In this note, we obtain quantitative information about the length function `(Γ, ·) : T(Σ)→ R from topological information of Γ. In particular, we develop tools to estimate the infimum of `(Γ, ·) over T(Σ). This work naturally complements [Bas], where such estimates are obtained that depend on the number of self-intersections of Γ. Here we consider a finer topological invariant than the self-intersection number. A construction of Sageev [Sag1] associates to a curve system Γ an isometric action of π1Σ on a finite-dimensional cube complex, or the dual cube complex C(Γ) of Γ. In what follows we connect geometric properties of the dual cube complex C(Γ) to the length of the collection of curves Γ on any hyperbolic surface. Indeed, [AG, Thm. 3] suggests that any such information is implicitly contained in the combinatorics of C(Γ). We have: Theorem A. Suppose that the action of π1Σ on C(Γ) has a set of cubes C1, . . . , Cm, of dimensions n1, . . . , nk, respectively, in distinct π1Σ-orbits, and so that the union of orbits ⋃ i π1Σ · Ci is hyperplane separated. Then inf X∈T(Σ) `(Γ, X) ≥ m ∑ i=1 ni log ( 1 + cos π ni 1− cos π ni )
ON THE MECHANISM OF HARD X-RAY EMISSION FROM MAGNETARS

Persistent activity of magnetars is associated with electric discharge that continually injects relativistic particles into the magnetosphere. Large active magnetic loops around magnetars must be filled with outflowing particles that interact with radiation via resonant scattering and spawn electron-positron pairs. The outflow energy is processed into copious e ± until the plasma enters outer parts of the loop where the magnetic field is reduced below 1013 G. In the outer zone, photons scattered by the outflow do not convert to e ± pairs and the outflow radiates its energy away. The escaping radiation forms a distinct hard X-ray peak in the magnetar spectrum. It has the following features: (1) its luminosity L = 1035-1036 erg s–1 can easily exceed the thermal luminosity from the magnetar surface, (2) its spectrum extends from 10 keV to the MeV band with a hard spectral slope, which depends on the object inclination to the line of sight, (3) the anisotropic hard X-ray emission exhibits strong pulsations as the magnetar spins, (4) the emission spectrum typically peaks around 1 MeV, but the peak position significantly oscillates with the spin period, (5) the emission is dominated by the extraordinary polarization mode at photon energies below ~1 MeV, and (6) the decelerated pairs accumulate and annihilate at the top of the magnetic loop, and emit the 511 keV line with luminosity L ann ~ 0.1 L. Features (1)-(3) agree with available data; (4)-(6) can be tested by future observations.
Toward computer-assisted discovery and automated proofs of cutting plane theorems

Using a metaprogramming technique and semialgebraic computations, we provide computer-based proofs for old and new cutting-plane theorems in Gomory–Johnson’s model of cut generating functions.
MOST Space Telescope Photometry of the 2010 January Transit of Extrasolar Planet HD80606b

We present observations of the full 2010 January transit of HD80606b from the Canadian microsatellite, Microvariability and Oscillations of Stars. By employing a space-based telescope, we monitor the entire transit, thus limiting systematic errors that result from ground observations. We determine measurements for the planetary radius (Rp = 0.987 ± 0.061 R Jup) and inclination (i = 89.°283 ± 0.024) by constraining our fits with the observed parameters of different groups. Our measured mid-transit time of 2455210.6449 ± 0.0034 HJD is consistent with the 2010 Spitzer results and is 20 minutes earlier than predicted by groups who observed the 2009 June transit.
Few-layer Phosphorene: An Ideal 2D Material For Tunnel Transistors

2D transition metal dichalcogenides (TMDs) have attracted a lot of attention recently for energy-efficient tunneling-field-effect transistor (TFET) applications due to their excellent gate control resulting from their atomically thin dimensions. However, most TMDs have bandgaps (Eg) and effective masses (m(*)) outside the optimum range needed for high performance. It is shown here that the newly discovered 2D material, few-layer phosphorene, has several properties ideally suited for TFET applications: 1) direct Eg in the optimum range ~1.0-0.4 eV, 2) light transport m(*) (0.15 m0), 3) anisotropic m(*) which increases the density of states near the band edges, and 4) a high mobility. These properties combine to provide phosphorene TFET outstanding ION ~ 1 mA/um, ON/OFF ratio ~ 10(6) for a 15 nm channel and 0.5 V supply voltage, thereby significantly outperforming the best TMD-TFETs and CMOS in many aspects such as ON/OFF current ratio and energy-delay products. Furthermore, phosphorene TFETS can scale down to 6 nm channel length and 0.2 V supply voltage within acceptable range in deterioration of the performance metrics. Full-band atomistic quantum transport simulations establish phosphorene TFETs as serious candidates for energy-efficient and scalable replacements of MOSFETs.
Prediction for the cosmological constant and constraints on SUSY GUTs in resummed quantum gravity

Working in the context of the Planck scale cosmology formulation of Bonanno and Reuter, we use our resummed quantum gravity approach to Einstein’s general theory of relativity to estimate the value...
Hunting the most distant stars in the milky way: Methods and initial results

We present a new catalog of 404 M giant candidates found in the UKIRT Infrared Deep Sky Survey (UKIDSS). The 2400 deg2 available in the UKIDSS Large Area Survey Data Release 8 resolve M giants through a volume four times larger than that of the entire Two Micron All Sky Survey. Combining near-infrared photometry with optical photometry and proper motions from the Sloan Digital Sky Survey yields an M giant candidate catalog with less M dwarf and quasar contamination than previous searches for similarly distant M giants. Extensive follow-up spectroscopy of this sample will yield the first map of our Galaxy's outermost reaches over a large area of sky. Our initial spectroscopic follow-up of ~30 bright candidates yielded the positive identification of five M giants at distances ~20-90 kpc. Each of these confirmed M giants have positions and velocities consistent with the Sagittarius stream. The fainter M giant candidates in our sample have estimated photometric distances ~200 kpc (assuming [Fe/H] = 0.0), but require further spectroscopic verification. The photometric distance estimates extend beyond the Milky Way's virial radius, and increase by ~50% for each 0.5 dex decrease in assumed [Fe/H]. Given the number of M giant candidates, initial selection efficiency, and volume surveyed, we loosely estimate that at least one additional Sagittarius-like accretion event could have contributed to the hierarchical build-up of the Milky Way's outer halo.
Quantum Groups, Property (T), and Weak Mixing

For second countable discrete quantum groups, and more generally second countable locally compact quantum groups with trivial scaling group, we show that property (T) is equivalent to every weakly mixing unitary representation not having almost invariant vectors. This is a generalization of a theorem of Bekka and Valette from the group setting and was previously established in the case of low dual by Daws, Skalski, and Viselter. Our approach uses spectral techniques and is completely different from those of Bekka–Valette and Daws–Skalski–Viselter. By a separate argument we furthermore extend the result to second countable nonunimodular locally compact quantum groups, which are shown in particular not to have property (T), generalizing a theorem of Fima from the discrete setting. We also obtain quantum group versions of characterizations of property (T) of Kerr and Pichot in terms of the Baire category theory of weak mixing representations and of Connes and Weiss in terms of the prevalence of strongly ergodic actions.
Contact angle selection for interfaces in growing domains

We study interfaces in an Allen-Cahn equation, separating two metastable states. Our focus is on a directional quenching scenario, where a parameter renders the system bistable in a half plane and monostable in its complement, with the region of bistability expanding at a fixed speed. We show that the growth mechanism selects a contact angle between the boundary of the region of bistability and the interface separating the two metastable states. Technically, we focus on a perturbative setting in a vicinity of a symmetric situation with perpendicular contact. The main difficulty stems from the lack of Fredholm properties for the linearization in translation invariant norms. We overcome those difficulties establishing Fredholm properties in weighted spaces and farfield-core decompositions to compensate for negative Fredholm indices.
Automotive Radar Interference Mitigation Using Adaptive Noise Canceller

Interference among frequency modulated continues wave automotive radars can either increase the noise floor, which occurs in the most cases, or generate a ghost target in rare situations. To address the increment of noise floor due to interference, we proposed a low calculation cost method using adaptive noise canceller to increase the signal-to-interference ratio. In a quadrature receiver, the interference in the positive half of frequency spectrum is correlated to that in the negative half of frequency spectrum, whereas the beat frequencies from real targets are always present in the positive frequency. Thus, we estimated the power of the negative frequency as an indication of interference, and fed the positive frequency and negative frequency components into the primary and reference channel of an adaptive noise canceller, respectively. The least mean square algorithm was used to solve for the optimum filter solution. As a result, both the simulation and experiment showed a good interference mitigation performance.
Coherent Two-Dimensional Multiphoton Photoelectron Spectroscopy of Metal Surfaces

A new technique for studying interactions between light and metals provides insight into how some electrons are excited by incoming photons, overturning a more than 20-year-old accepted model.
Unitary Thermodynamics from Thermodynamic Geometry

Degenerate Fermi gases of atoms near a Feshbach resonance show universal thermodynamic properties, which are here calculated with the geometry of thermodynamics, and the thermodynamic curvature R. Unitary thermodynamics is expressed as the solution to a pair of ordinary differential equations, a “superfluid” one valid for small entropy per atom z≡S/Nk B , and a “normal” one valid for high z. These two solutions are joined at a second-order phase transition at z=z c . Define the internal energy per atom, in units of the Fermi energy, as Y=Y(z). For small z, Y(z)=y 0+y 1 z α +y 2 z 2α +⋯, where α is a constant exponent, y 0 and y 1 are scaling factors, and the series coefficients y i (i≥2) are determined uniquely in terms of (α,y 0,y 1). For large z the solution follows if we also specify z c , with Y(z) diverging as z 5/3 for high z. The four undetermined parameters (α,y 0,y 1,z c ) were determined by fitting the theory to experimental data taken by a Duke University group on 6Li in an optical trap with a Gaussian potential. The very best fit of this theory to the data had α=2.1, z c =4.7, y 0=0.277, and y 1=0.0735, with χ 2=0.95. The corresponding Bertsch parameter is ξ B =0.462(40).
Gravity Dual of a Quantum Hall Plateau Transition

We show how to model the transition between distinct quantum Hall plateaus in terms of D-branes in string theory. A low energy theory of 2 + 1 dimensional fermions is obtained by considering the D3-D7 system, and the plateau transition corresponds to moving the branes through one another. We study the transition at strong coupling using gauge/gravity duality and the probe approximation. Strong coupling leads to a novel kind of plateau transition: at low temperatures the transition remains discontinuous due to the effects of dynamical symmetry breaking and mass generation, and at high temperatures is only partially smoothed out.
The minimal volume orientable hyperbolic 2-cusped 3-manifolds

We prove that the Whitehead link complement and the pretzel link complement are the minimal volume orientable hyperbolic 3-manifolds with two cusps, with volume = 4 Catalan's constant. We use topological arguments to establish the existence of an essential surface which provides a lower bound on volume and strong constraints on the manifolds that realize that lower bound.
Continuum percolation in the intrinsically secure communications graph

The intrinsically secure communications graph (iS-graph) is a random graph which captures the connections that can be securely established over a large-scale network, in the presence of eavesdroppers. It is based on principles of information-theoretic security, widely accepted as the strictest notion of security. In this paper, we are interested in characterizing the global properties of the iS-graph in terms of percolation on the infinite plane. We prove the existence of a phase transition in the Poisson iS-graph, whereby an unbounded component of securely connected nodes suddenly arises as we increase the density of legitimate nodes. Our work shows that long-range communication in a wireless network is still possible when a secrecy constraint is present.
Contextual and Granular Policy Enforcement in Database-backed Applications

Database-backed applications rely on inlined policy checks to process users' private and confidential data in a policy-compliant manner as traditional database access control mechanisms cannot enforce complex policies. However, application bugs due to missed checks are common in such applications, which result in data breaches. While separating policy from code is a natural solution, many data protection policies specify restrictions based on the context in which data is accessed and how the data is used. Enforcing these restrictions automatically presents significant challenges, as the information needed to determine context requires a tight coupling between policy enforcement and an application's implementation. We present Estrela, a framework for enforcing contextual and granular data access policies. Working from the observation that API endpoints can be associated with salient contextual information in most database-backed applications, Estrela allows developers to specify API-specific restrictions on data access and use. Estrela provides a clean separation between policy specification and the application's implementation, which facilitates easier auditing and maintenance of policies. Policies in Estrela consist of pre-evaluation and post-evaluation conditions, which provide the means to modulate database access before a query is issued, and to impose finer-grained constraints on information release after the evaluation of query, respectively. We build a prototype of Estrela and apply it to retrofit several real world applications (from 1000-80k LOC) to enforce different contextual policies. Our evaluation shows that Estrela can enforce policies with minimal overheads.
Maximizing the Probability of Detecting an Electromagnetic Counterpart of Gravitational-wave Events

Compact binary coalescences are a promising source of gravitational waves for second-generation interferometric gravitational-wave detectors such as advanced LIGO and advanced Virgo. These are among the most promising sources for joint detection of electromagnetic (EM) and gravitational-wave (GW) emission. To maximize the science performed with these objects, it is essential to undertake a followup observing strategy that maximizes the likelihood of detecting the EM counterpart. We present a follow-up strategy that maximizes the counterpart detection probability, given a fixed investment of telescope time. We show how the prior assumption on the luminosity function of the electro-magnetic counterpart impacts the optimized followup strategy. Our results suggest that if the goal is to detect an EM counterpart from among a succession of GW triggers, the optimal strategy is to perform long integrations in the highest likelihood regions. For certain assumptions about source luminosity and mass distributions, we find that an optimal time investment that is proportional to the 2/3 power of the surface density of the GW location probability on the sky. In the future, this analysis framework will benefit significantly from the 3-dimensional localization probability.
Analysis of the Laplacian and spectral operators on the Vicsek set

We study the spectral decomposition of the Laplacian on a family of fractals $\mathcal{VS}_n$ that includes the Vicsek set for $n=2$, extending earlier research on the Sierpinski Gasket. We implement an algorithm [23] for spectral decimation of eigenfunctions of the Laplacian, and explicitly compute these eigenfunctions and some of their properties. We give an algorithm for computing inner products of eigenfunctions. We explicitly compute solutions to the heat equation and wave equation for Neumann boundary conditions. We study gaps in the ratios of eigenvalues and eigenvalue clusters. We give an explicit formula for the Green's function on $\mathcal{VS}_n$. Finally, we explain how the spectrum of the Laplacian on $\mathcal{VS}_n$ converges as $n \to \infty$ to the spectrum of the Laplacian on two crossed lines (the limit of the sets $\mathcal{VS}_n$.)
Age Determinations of the Hyades, Praesepe, and Pleiades via MESA Models with Rotation

The Hyades, Praesepe, and Pleiades are well studied stellar clusters that anchor important secondary stellar age indicators. Recent studies have shown that main sequence turn off-based ages for these clusters may depend on the degree of rotation in the underlying stellar models. Rotation induces structural instabilities that can enhance the chemical mixing of a star, extending its fuel supply. In addition, rotation introduces a modulation of the star's observed magnitude and color due to the effects of gravity darkening. We aim to investigate the extent to which stellar rotation affects the age determination of star clusters. We utilize the MESA stellar evolution code to create models that cover a range of rotation rates corresponding to $\Omega/\Omega_c=0.0$ to $0.6$ in $0.1$ dex steps, allowing the assessment of variations in this dimension. The statistical analysis package, MATCH, is employed to derive ages and metallicities by fitting our MESA models to Tycho $B_T$, $V_T$ and 2MASS $J$, $K_s$ color-magnitude diagrams. We find that the derived ages are relatively insensitive to the effects of rotation. For the Hyades, Praesepe, and Pleiades, we derive ages based on synthetic populations that model a distribution of rotation rates or a fixed rate. Across each case, derived ages tend to agree roughly within errors, near $680$, $590$, and $110-160$ Myr for the Hyades, Praesepe, and Pleiades, respectively. These ages are in agreement with Li depletion boundary-based ages and previous analyses that used non-rotating isochrones. Our methods do not provide a strong constraint on the metallicities of these clusters.
Role of direct laser acceleration in energy gained by electrons in a laser wakefield accelerator with ionization injection

We have investigated the role that the transverse electric field of the laser plays in the acceleration of electrons in a laser wakefield accelerator operating in the quasi-blowout regime through particle-in-cell code simulations. In order to ensure that longitudinal compression and/or transverse focusing of the laser pulse is not needed before the wake can self-trap the plasma electrons, we have employed the ionization injection technique. Furthermore, the plasma density is varied such that at the lowest densities, the laser pulse occupies only a fraction of the first wavelength of the wake oscillation (the accelerating bucket), whereas at the highest density, the same duration laser pulse fills the entire first bucket. Although the trapped electrons execute betatron oscillations due to the ion column in all cases, at the lowest plasma density they do not interact with the laser field and the energy gain is all due to the longitudinal wakefield. However, as the density is increased, there can be a significant contribution to the maximum energy due to direct laser acceleration (DLA) of those electrons that undergo betatron motion in the plane of the polarization of the laser pulse. Eventually, DLA can be the dominant energy gain mechanism over acceleration due to the longitudinal field at the highest densities.
Dirac magnetic monopole production from photon fusion in proton collisions

We calculate the lowest-order cross-section for Dirac magnetic monopole production from photon fusion ( \( \gamma\)\( \gamma\)in p\( \bar{{p}}\) collisions at \( \sqrt{{s}}\) = 1.96 TeV, pp collisions at \( \sqrt{{s}}\) = 14 TeV, and we compare \( \gamma\)\( \gamma\) with Drell-Yan (DY) production. We find the total \( \gamma\)\( \gamma\) cross-section is comparable with DY at \( \sqrt{{s}}\) = 1.96 TeV and dominates DY by a factor > 50 at \( \sqrt{{s}}\) = 14 TeV. We conclude that both the \( \gamma\)\( \gamma\) and DY processes allow for a monopole mass limit m > 370 GeV based upon the null results of the recent monopole search at the Collider Detector at Fermilab (CDF). We also conclude that \( \gamma\)\( \gamma\) production is the leading mechanism to be considered for direct monopole searches at the Large Hadron Collider (LHC).
Semisupervised Clustering by Queries and Locally Encodable Source Coding

Source coding is the canonical problem of data compression in information theory. In a locally encodable source coding, each compressed bit depends on only few bits of the input. In this paper, we show that a recently popular model of semisupervised clustering is equivalent to locally encodable source coding. In this model, the task is to perform multiclass labeling of unlabeled elements. At the beginning, we can ask in parallel a set of simple queries to an oracle who provides (possibly erroneous) binary answers to the queries. The queries cannot involve more than two (or a fixed constant number of) elements. Now the labeling of all the elements (or clustering) must be performed based on the noisy query answers. The goal is to recover all the correct labelings while minimizing the number of such queries. The equivalence to locally encodable source codes leads us to find lower bounds on the number of queries required in variety of scenarios. We provide querying schemes based on pairwise ‘same cluster’ queries - and pairwise AND queries, and show provable performance guarantees for each of the schemes.
Waves in Solar Coronal Loops

Recent observations have revealed the ubiquitous presence of magnetohydrodynamic (MHD) waves and oscillations in the solar corona. The aim of this review is to present recent progress in the observational study of four types of wave (or oscillation) phenomena mainly occurring in active region coronal loops, including (i) flare-induced slow mode oscillations, (ii) fast kink mode oscillations, (iii) propagating slow magnetoacoustic waves, and (iv) ubiquitous propagating kink (Alfvenic) waves. This review not only comprehensively outlines various aspects of these waves and coronal seismology, but also highlights the topics that are newly emerging or hotly debated, thus can provide readers a useful guidance on further studies of their interested topics.