cssi/SciSciGPT-SciSciNet huggingface dataset:
Compressed Underwater Acoustic Communications for Dynamic Interaction with Underwater Vehicles

Underwater vehicles are utilized in various applications including underwater data-collection missions. The tethered connection constrains the mission both in distance traveled and number of vehicles that can run in the same area, while the addition of acoustic communications onto the vehicles grants them several functionalities. However, due to the low bandwidth of the underwater acoustic channel---which leads to low data rates---and the time overhead imposed by both the channel propagation delay and the processing delay by the acoustic modems, efficient protocols are required. In this paper, an implicit data-compression and transmission protocol is proposed to carry out environmental monitoring missions such as adaptive sampling of physical and chemical parameters in the water. In a semi-autonomous manner between the vehicle and the control center, both sides keep silent in data transmission as long as they can estimate and predict the actions of the other side, unless environmental data and/or kinematic data are found to be unpredictable. Our design puts the human in the loop to send high-level control commands. Experiments were conducted using an autonomous vehicle with WHOI micro-modems in the Raritan River, Somerset, Carnegie Lake in Princeton, and in the Marine Park in Red Bank, all in New Jersey.
Almost pure phase mass matrices from six dimensions

Abstract A model of quark masses and mixing angles is constructed within the framework of two large extra compact dimensions. A “democratic” almost pure phase mass matrix arises in a rather interesting way. This type of mass matrix has often been used as a phenomenologically viable ansatz, albeit one which had very little dynamical justification. It turns out that the idea of large extra dimensions provides a fresh look at this interesting phenomenological ansatz as presented in this paper. Some possible interesting connections to the strong CP problem will also be presented.
Combinatorial complexity in O-minimal geometry

In this paper we prove tight bounds on the combinatorial and topological complexity of sets defined in terms of $n$ definable sets belonging to some fixed definable family of sets in an o-minimal structure. This generalizes the combinatorial parts of similar bounds known in the case of semi-algebraic and semi-Pfaffian sets, and as a result vastly increases the applicability of results on combinatorial and topological complexity of arrangements studied in discrete and computational geometry. As a sample application, we extend a Ramsey-type theorem due to Alon et al., originally proved for semi-algebraic sets of fixed description complexity to this more general setting.
Effect of Inclination of Galaxies on Photometric Redshift

The inclination of galaxies induces both reddening and extinction to their observed spectral energy distribution, which in turn impact the derived properties of the galaxies. Here we report a significant dependence of the error in photometric redshift (photo-z) on the inclination of disk galaxies from the Sloan Digital Sky Survey. The bias in the photo-z based on the template-fitting approach increases from ?0.015 in face-on to 0.021 in edge-on galaxies. A Principal Component Analysis on the full sample of photometry reveals the inclination of the galaxies to be represented by the second mode. The corresponding eigenspectrum resembles an extinction curve. The isolation of the inclination effect in a low-order mode demonstrates the significant reddening induced on the observed colors, leading to the over-estimated photo-z in galaxies of high inclinations. We present approaches to correct the photo-z and the other properties of the disk galaxies against the inclination effect.
Electronic Hybridization of Large-Area Stacked Graphene Films

Direct, tunable coupling between individually assembled graphene layers is a next step toward designer two-dimensional (2D) crystal systems, with relevance for fundamental studies and technological applications. Here we describe the fabrication and characterization of large-area (>cm2), coupled bilayer graphene on SiO2/Si substrates. Stacking two graphene films leads to direct electronic interactions between layers, where the resulting film properties are determined by the local twist angle. Polycrystalline bilayer films have a “stained-glass window” appearance explained by the emergence of a narrow absorption band in the visible spectrum that depends on twist angle. Direct measurement of layer orientation via electron diffraction, together with Raman and optical spectroscopy, confirms the persistence of clean interfaces over large areas. Finally, we demonstrate that interlayer coupling can be reversibly turned off through chemical modification, enabling optical-based chemical detection schemes. Together,...
SPIN RESPONSE OF THE NUCLEON IN THE RESONANCE REGION

I discuss recent results from CLAS and Hall A at Jefferson Lab on the measurement of inclusive spin structure functions in the nucleon resonance region using polarized electron beams and polarized targets. Results on the first moment of the spin structure function for protons and neutrons will be discussed, as well as the Bjorken integral. I will argue that the helicity structure of individual resonances plays a vital role in understanding the nucleon's spin response in the domain of strong interaction QCD, and must be considered in any analysis of the nucleon spin structure at low and intermediate photon virtuality.
DYNAMICAL EVOLUTION OF MULTI-RESONANT SYSTEMS: THE CASE OF GJ876

The GJ 876 system was among the earliest multi-planetary detections outside of the Solar System, and has long been known to harbor a resonant pair of giant planets. Subsequent characterization of the system revealed the presence of an additional Neptune mass object on an external orbit, locked in a three body Laplace mean motion resonance with the previously known planets. While this system is currently the only known extrasolar example of a Laplace resonance, it differs from the Galilean satellites in that the orbital motion of the planets is known to be chaotic. In this work, we present a simple perturbative model that illuminates the origins of stochasticity inherent to this system and derive analytic estimates of the Lyapunov time as well as the chaotic diffusion coefficient. We then address the formation of the multi-resonant structure within a protoplanetary disk and show that modest turbulent forcing in addition to dissipative effects is required to reproduce the observed chaotic configuration. Accordingly, this work places important constraints on the typical formation environments of planetary systems and informs the attributes of representative orbital architectures that arise from extended disk-driven evolution.
CONFIGURATIONS OF EXTREMAL EVEN UNIMODULAR LATTICES

We extend the results of Ozeki on the configurations of extremal even unimodular lattices. Specifically, we show that if L is such a lattice of rank 56, 72, or 96, then L is generated by its minimal-norm vectors.
Maximum Entropy Approach to a Mean Field Theory for Fluids

Making statistical predictions requires tackling two problems: one must assign appropriate probability distributions and then one must calculate a variety of expected values. The method of maximum entropy is commonly used to address the first problem. Here we explore its use to tackle the second problem. We show how this use of maximum entropy leads to the Bogoliuvob variational principle which we generalize, apply to density functional theory, and use it to develop a mean field theory for classical fluids. Numerical calculations for Argon gas are compared with experimental data.
Accelerated Electrons in Cassiopeia A: An Explanation for the Hard X-Ray Tail

We propose a model for the hard X-ray (>10 keV) emission observed from the supernova remnant Cas A. Lower hybrid waves are generated in strong (mG) magnetic fields, generally believed to reside in this remnant, by shocks reflected from density inhomogeneities. These then accelerate electrons to energies of several tens of keV. Around 4% of the X-ray-emitting plasma electrons need to be in this accelerated distribution, which extends up to electron velocities of order the electron Alfven speed and is directed along magnetic field lines. Bremsstrahlung from these electrons produces the observed hard X-ray emission. Such waves and accelerated electrons have been observed in situ at comet Halley, and we discuss the viability of the extrapolation from this case to the parameters relevant to Cas A.
Rational group ring elements with kernels having irrational dimension

We prove that there are examples of finitely generated groups G together with group ring elements Q \in \bbQ G for which the von Neumann dimension \dim_{LG}\ker Q is irrational, so (in conjunction with other known results) answering a question of Atiyah.
Fast and Flexible ADMM Algorithms for Trend Filtering

This article presents a fast and robust algorithm for trend filtering, a recently developed nonparametric regression tool. It has been shown that, for estimating functions whose derivatives are of bounded variation, trend filtering achieves the minimax optimal error rate, while other popular methods like smoothing splines and kernels do not. Standing in the way of a more widespread practical adoption, however, is a lack of scalable and numerically stable algorithms for fitting trend filtering estimates. This article presents a highly efficient, specialized alternating direction method of multipliers (ADMM) routine for trend filtering. Our algorithm is competitive with the specialized interior point methods that are currently in use, and yet is far more numerically robust. Furthermore, the proposed ADMM implementation is very simple, and, importantly, it is flexible enough to extend to many interesting related problems, such as sparse trend filtering and isotonic trend filtering. Software for our method is...
Trajectory-free approximation of phase space structures using the trajectory divergence rate

This paper introduces the trajectory divergence rate, a scalar field which locally gives the instantaneous attraction or repulsion of adjacent trajectories. This scalar field may be used to find highly attracting or repelling invariant manifolds, such as slow manifolds, to rapidly approximate hyperbolic Lagrangian coherent structures, or to provide the local stability of invariant manifolds. This work presents the derivation of the trajectory divergence rate and the related trajectory divergence ratio for two-dimensional systems, investigates their properties, shows their application to several example systems, and presents their extension to higher dimensions.
A Bayesian network model of the bit error rate for cognitive radio networks

In addition to serve as platforms for dynamic spectrum access, cognitive radios can also serve as a method for improving the performance of wireless communication systems by smartly adjusting their operating parameters according to the environment and requirements. The uncertainty always present in the environment makes the practical implementation of the latter application difficult. In this paper, we propose a probabilistic graphical model, Bayesian network that captures the causal relationships among the variables bit energy to noise spectral density ratio (EbN0), carrier to interference ratio (C/I), modulation scheme (MOD), Doppler phase shift (Dop_Phi), and bit error rate (BER). BER indicates how the communication link is performing. The goal of our proposed Bayesian network is to use the BER as evidence in order to infer the behavior of the other variables, so the cognitive radio can learn how the conditions of the environment are, and based on that knowledge make better informed decisions. This model along with the method used to build it are described in this paper.
Renormalization and quantum field theory

The aim of this paper is to describe how to use regularization and renormalization to construct a perturbative quantum field theory from a Lagrangian. We first define renormalizations and Feynman measures, and show that although there need not exist a canonical Feynman measure, there is a canonical orbit of Feynman measures under renormalization. We then construct a perturbative quantum field theory from a Lagrangian and a Feynman measure, and show that it satisfies perturbative analogues of the Wightman axioms, extended to allow time-ordered composite operators over curved spacetimes.
Noncomputable Functions in the Blum-Shub-Smale Model

Working in the Blum-Shub-Smale model of computation on the real numbers, we answer several questions of Meer and Ziegler. First, we show that, for each natural number d, an oracle for the set of algebraic real numbers of degree at most d is insufficient to allow an oracle BSS-machine to decide membership in the set of algebraic numbers of degree d + 1. We add a number of further results on relative computability of these sets and their unions. Then we show that the halting problem for BSS-computation is not decidable below any countable oracle set, and give a more specific condition, related to the cardinalities of the sets, necessary for relative BSS-computability. Most of our results involve the technique of using as input a tuple of real numbers which is algebraically independent over both the parameters and the oracle of the machine.
First-Order Methods for Large-Scale Market Equilibrium Computation

Market equilibrium is a solution concept with many applications such as digital ad markets, fair division, and resource sharing. For many classes of utility functions, equilibria can be captured by convex programs. We develop simple first-order methods suitable for solving these convex programs for large-scale markets. We focus on three practically-relevant utility classes: linear, quasilinear, and Leontief utilities. Using structural properties of market equilibria under each utility class, we show that the corresponding convex programs can be reformulated as optimization of a structured smooth convex function over a polyhedral set, for which projected gradient achieves linear convergence. To do so, we utilize recent linear convergence results under weakened strong-convexity conditions, and further refine the relevant constants in existing convergence results. Then, we show that proximal gradient (a generalization of projected gradient) with a practical linesearch scheme achieves linear convergence under the Proximal-PL condition, a recently developed error bound condition for convex composite problems. For quasilinear utilities, we show that Mirror Descent applied to a new convex program achieves sublinear last-iterate convergence and yields a form of Proportional Response dynamics, an elegant, interpretable algorithm for computing market equilibria originally developed for linear utilities. Numerical experiments show that Proportional Response dynamics is highly efficient for computing approximate market equilibria, while projected gradient with linesearch can be much faster when higher-accuracy solutions are needed.
GLOBULAR CLUSTER ABUNDANCES FROM HIGH-RESOLUTION, INTEGRATED-LIGHT SPECTROSCOPY. III. THE LARGE MAGELLANIC CLOUD: Fe AND AGES*

In this paper, we refine our method for the abundance analysis of high-resolution spectroscopy of the integrated light of unresolved globular clusters (GCs). This method was previously demonstrated for the analysis of old (>10 Gyr) Milky Way (MW) GCs. Here, we extend the technique to young clusters using a training set of nine GCs in the Large Magellanic Cloud. Depending on the signal-to-noise ratio of the data, we use 20-100 Fe lines per cluster to successfully constrain the ages of old clusters to within a {approx}5 Gyr range, the ages of {approx}2 Gyr clusters to a 1-2 Gyr range, and the ages of the youngest clusters (0.05-1 Gyr) to a {approx}200 Myr range. We also demonstrate that we can measure [Fe/H] in clusters with any age less than 12 Gyr with similar or only slightly larger uncertainties (0.1-0.25 dex) than those obtained for old MW GCs (0.1 dex); the slightly larger uncertainties are due to the rapid evolution in stellar populations at these ages. In this paper, we present only Fe abundances and ages. In the next paper in this series, we present our complete analysis of {approx}20 elements for which we are able to measure abundances. For several ofmore » the clusters in this sample, there are no high-resolution abundances in the literature from individual member stars; our results are the first detailed chemical abundances available. The spectra used in this paper were obtained at Las Campanas with the echelle on the du Pont Telescope and with the MIKE spectrograph on the Magellan Clay Telescope.« less
Helimagnons in a chiral ground state of the pyrochlore antiferromagnets

The Goldstone mode in a helical magnetic phase, also known as the helimagnon, is a propagating mode with a highly anisotropic dispersion relation. Here we study theoretically the magnetic excitations in a complex chiral ground state of pyrochlore antiferromagnets such as spinel CdCr2O4 and itinerant magnet YMn2. We show that the effective theory of the soft modes in the helical state possesses a symmetry similar to that of smectic liquid crystals. An overall agreement is obtained between experiments and our dynamics simulations with realistic model parameters. By exactly diagonalizing the linearized Landu-Lifshitz equation in various commensurate limits of the spiral order, we find a low-energy dispersion relation characteristic of the helimagnons. Our calculation thus reveals the first example of helimagnon excitations in geometrically frustrated spin systems.
Self-crumpling elastomers: bending induced by the drying stimulus of a nanoparticle suspension

We report an experimental study of the drying-induced peeling of a bilayer, consisting of an elastomeric disk coated with a suspension of nanoparticles. We show that although capillary forces associated with the scale of the droplet cannot compete with the adhesion of the elastomer on a surface, large tensile stresses develop in the coating, which results in a moment bending the bilayer. We attribute this stress to the nano-menisci in the pores of the colloidal material and we propose a model that describes successfully the early-stage curvature of the bilayer. Thus, we show that the peeling can be conveniently controlled by the particle size and the coating thickness.
Primordial fluctuations in extended Liouville theory

Liouville gravity can be used to precisely model features of 3+1 dimensional cosmology in a simplified 1+1d setting. We study primordial fluctuations in a generally covariant extension of Liouville theory, in the context of single field inflation. The scale invariant spectrum of scalar curvature perturbations is exhibited, and their three-point correlation function is computed in the slow roll approximation. We recover Maldacena’s consistency relation for the three-point function, which in this context depends on a global shift symmetry of extended Liouville theory.
Black holes in the quantum universe.

A succinct summary is given of the problem of reconciling observation of black hole-like objects with quantum mechanics. If quantum black holes behave like subsystems, and also decay, their informa...
Pseudogap and time reversal breaking in a holographic superconductor

Classical SU(2) Yang-Mills theory in 3+1 dimensional anti-de Sitter space is known to provide a holographic dual to a 2+1 system that undergoes a superconducting phase transition. We study the electrical conductivity and spectral density of an isotropic superconducting phase. We show that the theory exhibits a pseudogap at low temperatures and a nonzero Hall conductivity. The Hall conductivity is possible because of spontaneous breaking of time reversal symmetry.
D-sphalerons and the topology of string configuration space

We show that unstable D-branes play the role of ``D-sphalerons'' in string theory. Their existence implies that the configuration space of type-II string theory has a complicated homotopy structure, similar to that of an infinite grassmannian. In particular, the configuration space of type-IIA (-IIB) string theory on Bbb R10 has non-trivial homotopy groups πk for all k even (odd).
Baryonic sources of thermal photons

Thermal radiation of photons and dileptons from hadronic matter plays an essential role in understanding electromagnetic emission spectra in high-energy heavy-ion collisions. In particular, baryons and anti-baryons have been found to be strong catalysts for electromagnetic radiation, even at collider energies where the baryon chemical potential is small. Here, we conduct a systematic analysis of $$\pi $$ - and $$\omega $$ -meson-induced reactions off a large set of baryon states. The interactions are based on effective hadronic Lagrangians where the parameters are quantitatively constrained by empirical information from vacuum decay branchings and scattering data, and gauge invariance is maintained by suitable regularization procedures. The thermal emission rates are computed using kinetic theory but can be directly compared to previous calculations using hadronic many-body theory. The comparison to existing calculations in the literature reveals our newly identified contributions to be rather significant.
MONODROMY OF THE p-RANK STRATA OF THE MODULI SPACE OF CURVES

We determine the -monodromy and -monodromy of every irreducible component of the stratum of curves of genus g and p-rank f in characteristic p. In particular, we prove that the -monodromy of every component of is the symplectic group if and if is a prime distinct from p. The method involves results on the intersection of with the boundary of . We give applications to the generic behavior of automorphism groups, Jacobians, class groups, and zeta functions of curves of given genus and p-rank.
Can the slow-rotation approximation be used in electromagnetic observations of black holes?

Future electromagnetic observations of black holes may allow us to test General Relativity in the strong-field regime. Such tests, however, require knowledge of rotating black hole solutions in modified gravity theories, a class of which does not admit the Kerr metric as a solution. Several rotating black hole solutions in modified theories have only been found in the slow-rotation approximation (i.e. assuming the spin angular momentum is much smaller than the mass squared). We here investigate whether the systematic error due to the approximate nature of these black hole metrics is small enough relative to the observational error to allow their use in electromagnetic observations to constrain deviations from General Relativity. We address this by considering whether electromagnetic observables constructed from a slow-rotation approximation to the Kerr metric can fit observables constructed from the full Kerr metric with systematic errors smaller than current observational errors. We focus on black hole shadow and continuum spectrum observations, as these are the least influenced by accretion disk physics, with current observational errors of about 10%. We find that the fractional systematic error introduced by using a second-order, slowly-rotating Kerr metric is at most 2% for shadows created by black holes with dimensionless spins $\chi\leq0.6$. We also find that the systematic error introduced by using the slowly-rotating Kerr metric as an exact metric when constructing continuum spectrum observables is negligible for black holes with dimensionless spins of $\chi \lesssim 0.9$. Our results suggest that the modified gravity solutions found in the slow-rotation approximation may be used to constrain realistic deviations from General Relativity with continuum spectrum and black hole shadow observations.
Online User Assessment for Minimal Intervention During Task-Based Robotic Assistance

We propose a novel criterion for evaluating user input for human-robot interfaces for known tasks. We use the mode insertion gradient (MIG)---a tool from hybrid control theory---as a filtering criterion that instantaneously assesses the impact of user actions on a dynamic system over a time window into the future. As a result, the filter is permissive to many chosen strategies, minimally engaging, and skill-sensitive---qualities desired when evaluating human actions. Through a human study with 28 healthy volunteers, we show that the criterion exhibits a low, but significant, negative correlation between skill level, as estimated from task-specific measures in unassisted trials, and the rate of controller intervention during assistance. Moreover, a MIG-based filter can be utilized to create a shared control scheme for training or assistance. In the human study, we observe a substantial training effect when using a MIG-based filter to perform cart-pendulum inversion, particularly when comparing improvement via the RMS error measure. Using simulation of a controlled spring-loaded inverted pendulum (SLIP) as a test case, we observe that the MIG criterion could be used for assistance to guarantee either task completion or safety of a joint human-robot system, while maintaining the system's flexibility with respect to user-chosen strategies.
Vertical Shear Instability in the Solar Nebula

We quantify the thermodynamic requirement for the Vertical Shear Instability and evaluate its relevance to realistic protoplanetary disks as a potential route to hydrodynamic turbulence.
DYNAMICAL MODEL OF AN EXPANDING SHELL

Expanding blast waves are ubiquitous in many astronomical sources, such as supernova remnants, X-ray emitting binaries, and gamma-ray bursts. I consider here the dynamics of such an expanding blast wave, both in the adiabatic and the radiative regimes. As the blast wave collects material from its surroundings, it decelerates. A full description of the temporal evolution of the blast wave requires consideration of both the energy density and the pressure of the shocked material. The obtained equation is different from earlier works in which only the energy was considered. The solution converges to the familiar results in both the ultrarelativistic and the sub-relativistic (Newtonian) regimes.
The Holographic Entropy Arrangement

Author(s): Hubeny, VE; Rangamani, M; Rota, M | Abstract: We develop a convenient framework for characterizing multipartite entanglement in composite systems, based on relations between entropies of various subsystems. This continues the program initiated in [1], of using holography to effectively recast the geometric problem into an algebraic one. We prove that, for an arbitrary number of parties, our procedure identifies a finite set of entropic information quantities that we conveniently represent geometrically in the form of an arrangement of hyperplanes. This leads us to define the holographic entropy arrangement, whose algebraic and combinatorial aspects we explore in detail. Using the framework, we derive three new information quantities for four parties, as well as a new infinite family for any number of parties. A natural construct from the arrangement is the holographic entropy polyhedron which captures holographic entropy inequalities describing the physically allowed region of entropy space. We illustrate how to obtain the polyhedron by winnowing down the arrangement through a sieve to pick out candidate sign-definite information quantities. Comparing the polyhedron with the holographic entropy cone, we find perfect agreement for 4 parties and corroborating evidence for the conjectured 5-party entropy cone. We work with explicit configurations in arbitrary (time-dependent) states leading to both simple derivations and an intuitive picture of the entanglementnpattern.
The Spinning Particle with Curved Target

We extend our previous calculation of the BV cohomology of the spinning particle with a flat target to the general case, in which the target carries a non-trivial pseudo-Riemannian metric and a magnetic field.
Collecting data with a mobile phone: Studies of mechanical laws such as energy and momentum conservation

We use videos taken with a mobile phone to study conservation of energy, conservation of momentum, and the work-energy theorem by analyzing the collision of a cue ball and the eight ball. A video of the full time sequence, starting from before the cue ball is struck until well after the collision, is recorded with a mobile phone. The video is imported into Origin (free to teachers and students taking a class) [OriginLab Corporation, Origin, Version 2020 (OriginLab Corporation, Northampton, MA, USA, 2020)], where the coordinates of the balls are digitized frame-by-frame using the free Video Extractor app. From these data, the velocities are determined as a function of time and used to determine the energy and momentum of each ball. The data suggest that the balls slip through part of their motion when rotating at an angular velocity different than the rolling angular velocity, so angular momentum and frictional torque must be considered. Such experiments require no specialized equipment other than a device to take a video, and the act of digitizing the data provides the student with visual reinforcement of the physics. Experimentation by students outside of campus can be fun for them and provides a useful alternative to classes when in-lab experiments are not practical. Use of a mobile phone in this way is generally applicable to any other mechanical phenomena that involve motion.
Spontaneous mass generation due to phonons in a two-dimensional Dirac fermion system

Abstract Fermions with one and two Dirac nodes are coupled to in-plane phonons to study a spontaneous transition into the Hall insulating phase. At sufficiently strong electron–phonon interaction a gap appears in the spectrum of fermions, signaling a transition into a phase with spontaneously broken parity and time-reversal symmetry. The structure of elementary excitations above the gap in the corresponding phase reveals the presence of scale invariant parity breaking terms which resemble Chern–Simons excitations. Evaluating the Kubo formula for both models we find quantized Hall plateaux in each case, with conductance of binodal model exactly twice as large as of the mononodal model.
Hydrogen–water mixtures in giant planet interiors studied with ab initio simulations

Abstract We study water–hydrogen mixtures under planetary interior conditions using ab initio molecular dynamics simulations. We determine the thermodynamic properties of various water–hydrogen mixing ratios at temperatures of 2000 and 6000 K for pressures of a few tens of GPa. These conditions are relevant for ice giant planets and for the outer envelope of the gas giants. We find that at 2000 K the mixture is in a molecular regime, while at 6000 K the dissociation of hydrogen and water is important and affects the thermodynamic properties. We study the structure of the liquid and analyze the radial distribution function. We provide estimates for the transport properties, diffusion and viscosity, based on autocorrelation functions. We obtained viscosity estimates of the order of a few tenths of mPa s for the conditions under consideration. These results are relevant for dynamo simulations of ice giant planets.
Nearly defect-free dynamical models of disordered solids: The case of amorphous silicon

It is widely accepted in the materials modeling community that defect-free realistic networks of amorphous silicon cannot be prepared by quenching from a molten state of silicon using classical or ab initio molecular-dynamics (MD) simulations. In this work, we address this long-standing problem by producing nearly defect-free ultra-large models of amorphous silicon, consisting of up to half a million atoms, using classical MD simulations. The structural, topological, electronic, and vibrational properties of the models are presented and compared with experimental data. A comparison of the models with those obtained from using the modified Wooten-Winer-Weaire bond-switching algorithm shows that the models are on par with the latter, which were generated via event-based total-energy relaxations of atomistic networks in the configuration space. The MD models produced in this work represent the highest quality of amorphous-silicon networks so far reported in the literature using MD simulations.
TRACES ON SEMIGROUP RINGS AND LEAVITT PATH ALGEBRAS

The trace on matrix rings, along with the augmentation map and Kaplansky trace on group rings, are some of the many examples of linear functions on algebras that vanish on all commutators. We generalize and unify these examples by studying traces on (contracted) semigroup rings over commutative rings. We show that every such ring admits a minimal trace (i.e., one that vanishes only on sums of commutators), classify all minimal traces on these rings, and give applications to various classes of semigroup rings and quotients thereof. We then study traces on Leavitt path algebras (which are quotients of contracted semigroup rings), where we describe all linear traces in terms of central maps on graph inverse semigroups and, under mild assumptions, those Leavitt path algebras that admit faithful traces.
Breaking the zero lower bound period: The shift across two unconventional policies

Abstract The impact of unconventional monetary policies on asset prices can be broken into two distinct time periods in the US. While the impact of large-scale asset purchases was substantial on stock prices and the exchange rate before September 2011, their impact almost fully disappears afterward. On the contrary, the effects of forward guidance on asset prices grow substantially after this date. This shift could be explained by the severe illiquidity in financial markets before September 2011 and the Federal Reserve’s explicit communication regarding the initial policy rate hike afterward.
Mapping spatially distributed material properties in finite element models of plant tissue using computed tomography

Plant tissues are often heterogeneous. To accurately investigate these tissues, methods to spatially map these tissue stiffness values onto finite element models are required. The aim was to study the feasibility of using specimen-specific computed tomography data to inform the spatial mapping of Young's modulus values on finite element models. Specimen-specific finite element models with mapped elastic moduli values were developed. The validation models predicted the structural response of the specimen tests within 11.0% of the physical test data. The ability of the models to accurately predict the force-displacement response of the specimen in a different test configuration was considered to be positive validation of the mapping approach. The existence of a model with accurate spatial distribution of material stiffnesses allows for investigations into the stress patterns within the rind and pith tissues. Typically, structural failure in transverse compression manifests as a crack that propagates in the pith along the line of load. In building detailed FEM analyses, we are able to investigate in more detail how the stress is distributed through the pith, and further investigate the causes of the stress concentrations that ultimately lead to the structural failure of the specimen. A method was developed for determining the relationship between computed-tomography intensity and the transverse elastic modulus in maize stalks. The mapping was used to accurately predict the response of each specimen thus indicating that the mapping relationship is appropriate for modelling and stress analysis activities.
Impaired Glutamate Receptor Function Underlies Early Activity Loss of Ipsilesional Motor Cortex after Closed-Head Mild Traumatic Brain Injury.

Although mild traumatic brain injury (mTBI) accounts for the majority of TBI patients, the effects and cellular and molecular mechanisms of mTBI on cortical neural circuits are still not well under...
Deep learning the sound of light to guide surgeries

Photoacoustic imaging utilizes light and sound to make images by transmitting laser pulses that illuminate regions of interest, which subsequently absorb the light, causing thermal expansion and the generation of sound waves that are detected with conventional ultrasound transducers. The Photoacoustic and Ultrasonic Systems Engineering (PULSE) Lab is developing novel methods that use photoacoustic imaging to guide surgeries with the ultimate goal of eliminating surgical complications caused by injury to important structures like major blood vessels and nerves that are otherwise hidden from a surgeons immediate view. This invited presentation will summarize our recent work to learn from the physics of sound propagation in tissue and develop acoustic beamforming algorithms that improve image quality, using state-of-the-art deep learning methods. These deep learning methods hold promise for robotic tracking tasks, visualization and visual servoing of surgical tool tips, and assessment of relative distances between the surgical tool and nearby critical structures (e.g., major blood vessels and nerves that if injured will cause severe complications, paralysis, or patient death). Impacted surgeries and procedures include neurosurgery, spinal fusion surgery, hysterectomies, cardiac interventions, and biopsies.
A Tale of Two Types of Schools: An Exploration of How School Working Conditions Influence Black Male Teacher Turnover.

ContextOngoing teacher diversity campaigns will not increase the net number of teachers of color if policymakers fail to address the disproportionate rate at which teachers of color leave the profe...
Maximally Algebraic potentially irrational Cubic Fourfolds

A well known conjecture asserts that a cubic fourfold $X$ whose transcendental cohomology $T_X$ can not be realized as the transcendental cohomology of a $K3$ surface is irrational. Since the geometry of cubic fourfolds is intricately related to the existence of algebraic $2$-cycles on them, it is natural to ask for the most algebraic cubic fourfolds $X$ to which this conjecture is still applicable. In this paper, we show that for an appropriate `algebraicity index' $\kappa_X$, there exists a unique class of cubics maximizing $\kappa_X$, not having an associated $K3$ surface; namely, the cubic fourfolds with an Eckardt point (previously investigated in [LPZ17]). Arguably, they are the most algebraic potentially irrational cubic fourfolds, and thus a good testing ground for the Harris, Hassett, Kuznetsov conjectures.
Efficient Market Managers

We examine the effect of the Efficient Market Hypothesis (EMH) on the investment behavior of mutual fund managers. We show that managers who are more likely to be exposed to the ideas of EMH throug...
Prioritization of PMU Location and Signal Selection for Monitoring Critical Power System Oscillations

This paper proposes a method of selecting and/or locating phasor measurement unit (PMU) signals for monitoring critical oscillation modes in large power systems. A robust indicator, modal participation ratio, is introduced to identify critical PMU locations and signal channels, in order to monitor modes of interest to power system operators. This indicator is easy to compute in practice, and is theoretically rigorous based on linear control theory and spectral analysis. This indicator can suggest location and/or selection of PMUs in order to most effectively observe modes of interest to power system operators. The effectiveness and robustness of the algorithm is illustrated in both modified 68-bus system and 140-bus system.
Centralized model predictive control with distributed adaptation

A centralized model predictive controller (MPC), which is unaware of local uncertainties, for an affine discrete time nonlinear system is presented. The local uncertainties are assumed to be matched, bounded and structured. In order to encounter disturbances and to improve performance, an adaptive control mechanism is employed locally. The proposed approach ensures input-to-state stability of closed-loop states and convergence to the equilibrium point. Moreover, uncertainties are learnt in terms of the given feature basis by using adaptive control mechanism. In addition, hard constraints on state and control are satisfied.
Dark initial state radiation and the kinetic mixing portal

Data from Planck measurements of the cosmic microwave background (CMB) place important constraints on models with light dark matter (DM) and light mediators especially when both lie in the mass range below ∼ 1 GeV. In models involving kinetic mixing where the dark photon acts as the mediator, these constraints are easily satisfied and the appropriate DM relic density achievable if the DM is, e.g., a complex scalar, where p-wave annihilation occurs, or is the lighter component of a split pseudo-Dirac state where co-annihilation dominates. In both of these cases, although higher order in the dark gauge coupling, gD, the corresponding annihilation processes including dark photon initial state radiation (ISR) will be dominantly s-wave with essentially temperature independent cross sections. The rates for these dark ISR associated processes, though not yielding cross sections large enough to contribute to the relic density, can still run into possible conflicts with the bounds arising from the CMB. In this paper we perform a preliminary study of the present and potential future constraints that the CMB imposes on the parameter spaces for both of these scenarios due to the existence of this dark ISR. Further analyses of the effects of dark ISR in DM annihilation is clearly warranted.
How do migration and remittances affect inequality? A case study of Mexico

The poverty‐reducing effects of remittances have been well documented; however, their effects on inequality are less clear. This paper examines the impact of remittances on inequality in Mexico using household‐level information on the receiving side. It hopes to speak to their insurance role by examining how remittances are affected by domestic and external crises: the 1994 Mexican peso crisis and the global financial crisis. We find that remittances lower inequality and that they become more pro‐poor over time. This also strengthens their insurance effects, mitigating some of the negative impact of shocks on the poorest.
Copyright Law's Theory of the Consumer

Copyright law has a rather well-developed theory of the author, but it has no similarly well-developed conception of the consumer. This exploratory Article is an attempt to begin piecing together a coherent image of the copyright consumer. The author argues that copyright law currently conceives of consumers in one of two ways, either as passive consumers of copyrighted works or as active authors in their own right. This binary conception of the consumer, however, is incomplete, as it neglects important and complex consumer interests in autonomy, communication, and creative self-expression. By examining these additional interests, it is possible to begin constructing a richer and more complex image of the copyright consumer. This image, in turn, can help shed light on some of the current debates over the proper shape and scope of copyright law.
The collateral channel: Evidence on leverage and asset tangibility

Abstract We examine how asset structure is related to leverage in different institutional environments, using tens of thousands of firm-level observations from small, privately held, emerging market firms that are likely to face financing constraints. Our empirical analysis indicates that the linkage between asset tangibility (fixed assets as a portion of total assets) and leverage (measured as long-term debt over total assets) varies, such that in countries with fewer restrictions on collateral (land transferability), the relationship between these variables is much tighter. This also applies to the linkage between tangibility and debt maturity structure (measured as long-term debt over total debt). We find no evidence that industry concentration in different countries or changing composition of firms over time is driving our findings. The results are robust to using firm-level fixed effects specifications, to clustering error terms at the country level, and to using an alternative proxy for collateral law regime.
The Importance of Negotiated Rulemaking to the No Child Left Behind Act

The No Child Left Behind Act of 2001 is failing both in theory and execution. NCLB has been called “the most sweeping reform of the Elementary and Secondary Education Act since it was enacted in 1965” and was intended to “redefine the federal role in K-12 education so it can be used to improve the academic achievement of all American students.” The stated purpose of the NCLBA is to “ensure that all children have a fair, equal and significant opportunity to obtain a high-quality education.” This article takes a new approach to examining the failure of NCLB. Much of the criticism of NCLB focuses on the Act’s substantive requirements, but this Article examines the administrative process for enacting regulations under NCLB. I argue that the substantive failures of NCLB are magnified and exacerbated in the negotiated rulemaking process. Negotiated rulemaking offers the promise of collaboration between the Department of Education, state education officials, local school boards, teachers, parents, and students to achieve the goals of the statute. Instead, the voices of the non-Department of Education officials are being ignored during the negotiated rulemaking process. The valid critiques of many aspects of the statute, such as the burdens on state resources, are left unaddressed during the rulemaking process. Instead of the administrative process leading to the best practices to achieve statutory goals, it becomes another roadblock to success for NCLB.
Corporate Cash Reserves and Acquisitions

Cash-rich firms are more likely than other firms to attempt acquisitions. Stock return evidence shows that acquisitions by cash-rich firms are value decreasing. Cash-rich bidders destroy seven cents in value for every excess dollar of cash reserves held. Cash-rich firms are more likely to make diversifying acquisitions and their targets are less likely to attract other bidders. Consistent with the stock return evidence, mergers in which the bidder is cash-rich are followed by abnormal declines in operating performance. Overall, the evidence supports the agency costs of free cash flow explanation for acquisitions by cash-rich firms. DESPITE THE IMPORTANCE OF CASH RESERVES to theories in corporate finance, corporate holdings of cash have received relatively little direct attention in the academic literature. Much of the literature on cash reserves is older and either descriptive or concerned with corporate transaction demand for cash.' However, the role of cash in the corporation is much broader. In the presence of capital market imperfections deriving from asymmetric information between managers and capital providers, liquidity can take on a strategic role. Managers can increase firm value by managing their cash balances as buffer stocks. These buffer stocks allow the firm to maintain the ability to finance investments even when current cash flows are insufficient to meet the firm's investment demands. Thus, cash reserves provide benefits to equity holders by reducing the underinvestment problem. Managers wishing to avoid the costs associated with external financing in an imperfect information environment find it optimal to maintain sufficient internal financial flexibility to allow them to reduce the underinvestment problem. Further, since the equity holders suffer the loss from underinvestment, they find it value increasing for managers to maintain the buffer stock of cash.