cssi/SciSciGPT-SciSciNet huggingface dataset:
Microscopic Structure of Metal Whiskers

After more than 70 years of research and billions of dollars in losses to multiple industries, the physics of metal whiskers remains mysterious. The authors investigate a tin whisker's structure at the nanoscale with transmission electron microscopy. A rich, nontrivial morphology is revealed, suggesting that metal whiskers consist of many filaments grown side by side. An electrostatic theory of field-induced nucleation explains such multifilament growth, bringing us a step closer to understanding, and possibly preventing, the formation of these nanostructure that can be so deleterious to electronics.
Inference Strategies for Machine Translation with Conditional Masking

Conditional masked language model (CMLM) training has proven successful for non-autoregressive and semi-autoregressive sequence generation tasks, such as machine translation. Given a trained CMLM, however, it is not clear what the best inference strategy is. We formulate masked inference as a factorization of conditional probabilities of partial sequences, show that this does not harm performance, and investigate a number of simple heuristics motivated by this perspective. We identify a thresholding strategy that has advantages over the standard ``mask-predict'' algorithm, and provide analyses of its behavior on machine translation tasks.
Arithmeticity of the monodromy of some Kodaira fibrations

A question of Griffiths–Schmid asks when the monodromy group of an algebraic family of complex varieties is arithmetic. We resolve this in the affirmative for a class of algebraic surfaces known as Atiyah–Kodaira manifolds, which have base and fibers equal to complete algebraic curves. Our methods are topological in nature and involve an analysis of the ‘geometric’ monodromy, valued in the mapping class group of the fiber.
On the Nature of the Compact Dark Mass at the Galactic Center

We consider a model in which Sgr A*, the 3.7 × 106 M☉ supermassive black hole candidate at the Galactic center, is a compact object with a thermally emitting surface. For very compact surfaces within the photon orbit, the thermal assumption is likely to be a good approximation because of the large number of rays that are strongly gravitationally lensed back onto the surface. Given the very low quiescent luminosity of Sgr A* in the near-infrared, the existence of a hard surface, even in the limit in which the radius approaches the horizon, places a severe constraint on the steady mass accretion rate onto the source: 10-12 M☉ yr-1. This limit is well below the minimum accretion rate needed to power the observed submillimeter luminosity of Sgr A*: > 10-10 M☉ yr-1. We thus argue that Sgr A* does not have a surface, i.e., that it must have an event horizon. The argument could be made more restrictive by an order of magnitude with microarcsecond resolution imaging, e.g., with submillimeter very long baseline interferometry.
Indicators of Tambara–Yamagami categories and Gauss sums

We prove that the higher Frobenius–Schur indicators, introduced by Ng and Schauenburg, give a strong-enough invariant to distinguish between any two Tambara–Yamagami fusion categories. Our proofs are based on computation of the higher indicators in terms of Gauss sums for certain quadratic forms on finite abelian groups and rely on the classification of quadratic forms on finite abelian groups, due to Wall. As a corollary to our work, we show that the state-sum invariants of a Tambara–Yamagami category determine the category as long as we restrict to Tambara–Yamagami categories coming from groups G whose order is not a power of 2. Turaev and Vainerman proved this result under the assumption that G has odd order, and they conjectured that a similar result should hold for groups of even order. We also give an example to show that the assumption that |G| is not a power of 2 cannot be completely relaxed.
On the number of ends of rank one locally symmetric spaces

Let Y be a noncompact rank one locally symmetric space of finite volume. Then Y has a finite number e.Y/ > 0 of topological ends. In this paper, we show that for any n2 N , the Y with e.Y/ n that are arithmetic fall into finitely many commensurability classes. In particular, there is a constant cn such that n‐cusped arithmetic orbifolds do not exist in dimension greater than cn . We make this explicit for one-cusped arithmetic hyperbolic n‐orbifolds and prove that none exist for n 30. 11F06, 20H10, 22E40
Inf-VAE: A Variational Autoencoder Framework to Integrate Homophily and Influence in Diffusion Prediction

Recent years have witnessed tremendous interest in understanding and predicting information spread on social media platforms such as Twitter, Facebook, etc. Existing diffusion prediction methods primarily exploit the sequential order of influenced users by projecting diffusion cascades onto their local social neighborhoods. However, this fails to capture global social structures that do not explicitly manifest in any of the cascades, resulting in poor performance for inactive users with limited historical activities. In this paper, we present a novel variational autoencoder framework (Inf-VAE) to jointly embed homophily and influence through proximity-preserving social and position-encoded temporal latent variables. To model social homophily, Inf-VAE utilizes powerful graph neural network architectures to learn social variables that selectively exploit the social connections of users. Given a sequence of seed user activations, Inf-VAE uses a novel expressive co-attentive fusion network that jointly attends over their social and temporal variables to predict the set of all influenced users. Our experimental results on multiple real-world social network datasets, including Digg, Weibo, and Stack-Exchanges demonstrate significant gains (22% MAP@10) for Inf-VAE over state-of-the-art diffusion prediction models; we achieve massive gains for users with sparse activities, and users who lack direct social neighbors in seed sets.
Existence and uniqueness of Arrow-Debreu equilibria with consumptions in $\mathbf{L}^0_+$

We consider an economy where agents' consumption sets are given by the cone ${\bf L}^0_+$ of nonnegative measurable functions and whose preferences are defined by additive utilities satisfying the Inada conditions. We extend to this setting the results of Dana [J. Math. Econom., 22 (1993), pp. 563--579; Econometrica, 61 (1993), pp. 953--957] on the existence and uniqueness of Arrow--Debreu equilibria. In the case of existence, our conditions are necessary and sufficient.
Ferromagnetism and spin-dependent transport at a complex oxide interface

Complex oxide interfaces are a promising platform for studying a wide array of correlated electron phenomena in low dimensions, including magnetism and superconductivity. The microscopic origin of these phenomena in complex oxide interfaces remains an open question. Here we investigate the magnetic properties of semi-insulating $\mathrm{NdTi}{\mathrm{O}}_{3}\text{/}\mathrm{SrTi}{\mathrm{O}}_{3}$ (NTO/STO) interfaces and present the first millikelvin study of NTO/STO. The magnetoresistance (MR) reveals signatures of local ferromagnetic order and of spin-dependent thermally activated transport, which are described quantitatively by a simple phenomenological model. We discuss possible origins of the interfacial ferromagnetism. In addition, the MR also shows transient hysteretic features on a time scale of $\ensuremath{\sim}10\ensuremath{-}100\phantom{\rule{0.16em}{0ex}}\mathrm{s}$. We demonstrate that these are consistent with an extrinsic magnetothermal origin, which may have been misinterpreted in previous reports of magnetism in STO-based oxide interfaces. The existence of these two MR regimes (steady-state and transient) highlights the importance of time-dependent measurements for distinguishing signatures of ferromagnetism from other effects that can produce hysteresis at low temperatures.
Multi-phonon-assisted absorption and emission in semiconductors and its potential for laser refrigeration

Laser cooling of semiconductors has been an elusive goal for many years, and while attempts to cool the narrow gap semiconductors such as GaAs are yet to succeed, recently, net cooling has been attained in a wider gap CdS. This raises the question of whether wider gap semiconductors with higher phonon energies and stronger electron-phonon coupling are better suitable for laser cooling. In this work, we develop a straightforward theory of phonon-assisted absorption and photoluminescence of semiconductors that involves more than one phonon and use to examine wide gap materials, such as GaN and CdS and compare them with GaAs. The results indicate that while strong electron-phonon coupling in both GaN and CdS definitely improves the prospects of laser cooling, large phonon energy in GaN may be a limitation, which makes CdS a better prospect for laser cooling.
Interpolation in model spaces

In this paper we consider interpolation in model spaces, $H^2 \ominus B H^2$ with $B$ a Blaschke product. We study unions of interpolating sequences for two sequences that are far from each other in the pseudohyperbolic metric as well as two sequences that are close to each other in the pseudohyperbolic metric. The paper concludes with a discussion of the behavior of Frostman sequences under perturbations.
Siegel paramodular forms of weight 2 and squarefree level

We compute the space S2(K(N)) of weight 2 Siegel paramodular cusp forms of squarefree level N < 300. In conformance with the paramodular conjecture of Brumer and Kramer, the space is only the addit...
Influence of fake news in Twitter during the 2016 US presidential election

The dynamics and influence of fake news on Twitter during the 2016 US presidential election remains to be clarified. Here, we use a dataset of 171 million tweets in the five months preceding the election day to identify 30 million tweets, from 2.2 million users, which contain a link to news outlets. Based on a classification of news outlets curated by www.opensources.co , we find that 25% of these tweets spread either fake or extremely biased news. We characterize the networks of information flow to find the most influential spreaders of fake and traditional news and use causal modeling to uncover how fake news influenced the presidential election. We find that, while top influencers spreading traditional center and left leaning news largely influence the activity of Clinton supporters, this causality is reversed for the fake news: the activity of Trump supporters influences the dynamics of the top fake news spreaders.
APPROACH TO EQUILIBRIUM IN THE CALDEIRA–LEGGETT MODEL

The Caldeira–Leggett (CL) model describes a microscopic quantum system, represented by a harmonic oscillator, in interaction with a heat bath, represented by a large number of harmonic oscillators with a range of frequencies. We consider the case when the system oscillator starts out in the ground state and then thermalizes due to interactions with the heat bath, which is at temperature θ. We calculate the position autocorrelation function 〈x(t')x(t)〉 of the system oscillator at two different times and study its behavior in the small and large time limits. Our results show that the system oscillator thermalizes as expected. We also confirm by explicit calculation that the position autocorrelation function exhibits periodicity for imaginary values of the time difference t'-t = iτ at late-(real) times t.
Testing split supersymmetry with inflation

Split supersymmetry (SUSY) — in which SUSY is relevant to our universe but largely inaccessible at current accelerators — has become increasingly plausible given the absence of new physics at the LHC, the success of gauge coupling unification, and the observed Higgs mass. Indirect probes of split SUSY such as electric dipole moments (EDMs) and flavor violation offer hope for further evidence but are ultimately limited in their reach. Inflation offers an alternate window into SUSY through the direct production of superpartners during inflation. These particles are capable of leaving imprints in future cosmological probes of primordial non-gaussianity. Given the recent observations of BICEP2, the scale of inflation is likely high enough to probe the full range of split SUSY scenarios and therefore offers a unique advantage over low energy probes. The key observable for future experiments is equilateral non-gaussianity, which will be probed by both cosmic microwave background (CMB) and large scale structure (LSS) surveys. In the event of a detection, we forecast our ability to find evidence for superpartners through the scaling behavior in the squeezed limit of the bispectrum.
ON MAGNETOCONDUCTIVITY OF METALLIC MANGANITE PHASES AND HETEROSTRUCTURES

We use the double exchange (DE) model via degenerate orbitals and tight-binding approximation to study the magnetoconductivity of a canted A-phase of pseudo-cubic manganites. It is argued that the model is applicable in a broad concentration range for manganites A1 - xBxMnO3 with the tolerance factor t close to one. As for the substitutional disorder, scattering on random Jahn–Teller distortions of MnO6 octahedra is chosen. We emphasize an intimate correlation between the carrier concentration and resistivity value of metallic manganites. Magnetoresistance as a function of magnetization is calculated for a canted A-phase for both in-plane and out-of-plane current directions. A contact between two manganite phases is considered and structure of the transition region near the contact is discussed. Numerical calculations show charge re-distribution near the contact and a large screening length of the order of five inter-atomic distances. We employed our results to interpret data obtained in recent experiments on La0.4Sr0.6MnO3/La0.55Sr0.45MnO3 superlattices. We also briefly discuss the relative importance of the cooperative Jahn–Teller distortions, double exchange mechanism and super-exchange interactions for the formation of the A-phase at increasing Sr concentrations x > 0.45 in La1 - xSrxMnO3 which suggest that the Jahn–Teller contraction of octahedra, c/a < 1, plays a prevailing role.
The Extended IRTF Spectral Library: Expanded Coverage in Metallicity, Temperature, and Surface Gravity

We present a $0.7-2.5\mu m$ spectral library of 284 stars observed with the medium-resolution infrared spectrograph, SpeX, at the 3.0 meter NASA Infrared Telescope Facility (IRTF) on Maunakea, Hawaii. This library extends the metallicity range of the IRTF Cool Star library beyond solar metallicity to $-1.7 <$ [Fe/H] $< 0.6$. All of the observed stars are also in the MILES optical stellar library, providing continuous spectral coverage for each star from $0.35-2.5\mu m$. The spectra are absolute flux calibrated using Two Micron All Sky Survey photometry and the continuum shape of the spectra is preserved during the data reduction process. Synthesized $JHK_S$ colors agree with observed colors at the $1-2\%$ level, on average. We also present a spectral interpolator that uses the library to create a data-driven model of spectra as a function of $teff$, $logg$, and [Fe/H]. We use the library and interpolator to compare empirical trends with theoretical predictions of spectral feature behavior as a function of stellar parameters. These comparisons extend to the previously difficult to access low-metallicity and cool dwarf regimes, as well as the previously poorly sampled super-solar metallicity regime. The library and interpolator are publicly available.
Long wavelength observations of high galactic latitude dust

Abstract The properties of high latitude dust are of great interest to extragalactic astronomers and cosmologists. It is proposed here that essentially all high galactic latitude interstellar dust is at a typical temperature of about 20 K (i.e. it is warm dust) and that if any cold interstellar dust exists. its emission at mm wavelengths is less than 5%, of that from the primary component of warm dust observed by IRAS. Thus. the IRAS maps reveal the high latitude dust of import. The crucial issue is how the emissivity of the dust scales with wavelength. The mm wavelength emission in this warm dust-only model is consistent with roughly a wavelength-dependent emissivity ϵ(λ)∞λ−1.5. Such a dependence has been observed previously in the IR. What is new here is the proposal that this extends to the mm wavelength region.
M Dwarf Metallicities and Giant Planet Occurrence: Ironing Out Uncertainties and Systematics

Comparisons between the planet populations around solar-type stars and those orbiting M dwarfs shed light on the possible dependence of planet formation and evolution on stellar mass. However, such analyses must control for other factors, i.e., metallicity, a stellar parameter that strongly influences the occurrence of gas giant planets. We obtained infrared spectra of 121 M dwarfs stars monitored by the California Planet Search and determined metallicities with an accuracy of 0.08 dex. The mean and standard deviation of the sample are –0.05 and 0.20 dex, respectively. We parameterized the metallicity dependence of the occurrence of giant planets on orbits with a period less than two years around solar-type stars and applied this to our M dwarf sample to estimate the expected number of giant planets. The number of detected planets (3) is lower than the predicted number (6.4), but the difference is not very significant (12% probability of finding as many or fewer planets). The three M dwarf planet hosts are not especially metal rich and the most likely value of the power-law index relating planet occurrence to metallicity is 1.06 dex per dex for M dwarfs compared to 1.80 for solar-type stars; this difference, however, is comparable to more » uncertainties. Giant planet occurrence around both types of stars allows, but does not necessarily require, a mass dependence of ∼1 dex per dex. The actual planet-mass-metallicity relation may be complex, and elucidating it will require larger surveys like those to be conducted by ground-based infrared spectrographs and the Gaia space astrometry mission. « less
Knot Floer homology and Seifert surfaces

Let K be a knot in S3 of genus g and let n>0. We show that if rkHFK(K,g)<2n+1 (where HFK denotes knot Floer homology), in particular if K is an alternating knot such that the leading coefficient ag of its Alexander polynomial satisfies |ag|<2n+1, then K has at most n pairwise disjoint nonisotopic genus g Seifert surfaces. For n=1 this implies that K has a unique minimal genus Seifert surface up to isotopy.
A Comparative Study of Long and Short GRBs. I. Overlapping Properties

Gamma-ray bursts (GRBs) are classified into long and short categories based on their durations. Broadband studies suggest that these two categories of objects roughly correspond to two different classes of progenitor systems, i.e., compact star mergers (Type I) versus massive star core collapse (Type II). However, the duration criterion sometimes leads to mis-identification of the progenitor systems. We perform a comprehensive multi-wavelength comparative study between duration-defined long GRBs and short GRBs as well as the so-called "consensus" long GRBs and short GRBs (which are believed to be more closely related to the two types of progenitor systems). The parameters we study include two parts: the prompt emission properties including duration (T90), spectral peak energy (), low energy photon index (α), isotropic γ-ray energy (), isotropic peak luminosity (), and the amplitude parameters (f and ); and the host galaxy properties including stellar mass (), star formation rate, metallicity ([X/H]), half light radius (R50), angular and physical () offset of the afterglow from the center of the host galaxy, the normalized offset (), and the brightness fraction . For most parameters, we find interesting overlapping properties between the two populations in both one-dimensional (1D) and 2D distribution plots. The three best parameters for the purpose of classification are T90, , and . However, no single parameter alone is good enough to place a particular burst into the right physical category, suggesting the need for multiple criteria for physical classification.
Minority-carrier dynamics in semiconductors probed by two-photon microscopy

Two-photon time-resolved photoluminescence has been recently applied to various semiconductor devices to determine carrier lifetime and surface recombination velocities. So far the theoretical modeling activity has been mainly limited to the commonly used one-photon counterpart of the technique. Here we provide the analytical solution to a 3D diffusion equation that describes two-photon microscopy in the low-injection regime. We focus on a system with a single buried interface with enhanced recombination, and analyze how transport, bulk and surface recombinations influence photoluminescence decays. We find that bulk measurements are dominated by diffusion at short times and by bulk recombination at long times. Surface recombination modifies bulk signals when the optical spot is less than a diffusion length away from the probed interface. In addition, the resolution is increased as the spot size is reduced, which however makes the signal more sensitive to diffusion.
Completeness for Sparse Potential Scattering

The present paper is devoted to the scattering theory of a class of continuum Schrodinger operators with deterministic sparse potentials. We first establish the limiting absorption principle for both modified free resolvents and modified perturbed resolvents. This actually is a weak form of the classical limiting absorption principle. We then prove the existence and completeness of local wave operators, which, in particular, imply the existence of wave operators. Under additional assumptions on the sparse potential, we prove the completeness of wave operators. In the context of continuum Schrodinger operators with sparse potentials, this paper gives the first proof of the completeness of wave operators.
Dirac's classical-quantum analogy for the harmonic oscillator: Classical aspects in thermal radiation including zero-point radiation

Dirac's Poisson-bracket-to-commutator analogy for the transition from classical to quantum mechanics assures that for many systems, the classical and quantum systems share the same algebraic structure. The quantum side of the analogy (involving operators on Hilbert space with commutators scaled by Planck's constant ℏ ) not only gives the algebraic structure but also dictates the average values of physical quantities in the quantum ground state. On the other hand, the Poisson brackets of nonrelativistic mechanics, which give only the classical canonical transformations, do not give any values for physical quantities. Rather, one must go outside nonrelativistic classical mechanics in order to obtain a fundamental phase space distribution for classical physics. We assume that the values of physical quantities in classical theory at any temperature depend on the phase space probability distribution that arises from thermal radiation equilibrium including classical zero-point radiation with the scale set by Planck's constant ℏ . All mechanical systems in thermal radiation will inherit the constant ℏ from thermal radiation. Here, we note the connections between classical and quantum theories (agreement and contrasts) at all temperatures for the harmonic oscillator in one and three spatial dimensions.
Optical phase-space-time-frequency tomography

We present a new approach for constructing optical phase-space-time-frequency tomography (OPSTFT) of an optical wave field. This tomography can be measured by using a novel four-window optical imaging system based on two local oscillator fields balanced heterodyne detection. The OPSTFT is a Wigner distribution function of two independent Fourier Transform pairs, i.e., phase-space and time-frequency. From its theoretical and experimental aspects, it can provide information of position, momentum, time and frequency of a spatial light field with precision beyond the uncertainty principle. Besides the distributions of x – p and t – ω, the OPSTFT can provide four other distributions such as x – t, p – t, x – ω and p – ω. We simulate the OPSTFT for a light field obscured by a wire and a single-line absorption filter. We believe that the four-window system can provide spatial and temporal properties of a wave field for quantum image processing and biophotonics.
A BANACH SPACE DETERMINED BY THE WEIL HEIGHT

The absolute logarithmic Weil height is well defined on the quo- tient group Q ◊ /Tor Q ◊ and induces a metric topology in this group. We show that the completion of this metric space is a Banach space over the field R of real numbers. We further show that this Banach space is isometrically isomorphic to a co-dimension one subspace of L 1 (Y,B, ), where Y is a certain totally disconnected, locally compact space, B is the -algebra of Borel subsets of Y , and is a certain measure satisfying an invariance property with respect to the absolute Galois group Aut(Q/Q).
Does self-replication imply evolvability?

The most prominent property of life on Earth is its ability to evolve. It is often taken for granted that self-replication--the characteristic that makes life possible--implies evolvability, but many examples such as the lack of evolvability in computer viruses seem to challenge this view. Is evolvability itself a property that needs to evolve, or is it automatically present within any chemistry that supports sequences that can evolve in principle? Here, we study evolvability in the digital life system Avida, where self-replicating sequences written by hand are used to seed evolutionary experiments. We use 170 self-replicators that we found in a search through 3 billion randomly generated sequences (at three different sequence lengths) to study the evolvability of generic rather than hand-designed self-replicators. We find that most can evolve but some are evolutionarily sterile. From this limited data set we are led to conclude that evolvability is a likely--but not a guaranteed-- property of random replicators in a digital chemistry.
Gamma-Ray Burst Prompt Emission

The origin of gamma-ray burst (GRB) prompt emission, bursts of γ-rays lasting from shorter than one second to thousands of seconds, remains not fully understood after more than 40 years of observations. The uncertainties lie in several open questions in the GRB physics, including jet composition, energy dissipation mechanism, particle acceleration mechanism and radiation mechanism. Recent broad-band observations of prompt emission with Fermi sharpen the debates in these areas, which stimulated intense theoretical investigations invoking very different ideas. I will review these debates, and argue that the current data suggest the following picture: A quasi-thermal spectral component originating from the photosphere of the relativistic ejecta has been detected in some GRBs. Even though in some cases (e.g. GRB 090902B) this component dominates the spectrum, in most GRBs, this component either forms a sub-dominant "shoulder" spectral component in the low energy spectral regime of the more dominant "Band" component, or is not detectable at all. The main "Band" spectral component likely originates from the optically thin region due to synchrotron radiation. The diverse magnetization in the GRB central engine is likely the origin of the observed diverse prompt emission properties among bursts.
The Impact of a Reentry and Aftercare Program on Recidivism

In this article, we explore the impact of a reentry and aftercare service program on the likelihood of returning to prison by ex-offenders. Using administrative data within a difference-in-differen...
Strongly Convex Divergences

We consider a sub-class of the f-divergences satisfying a stronger convexity property, which we refer to as strongly convex, or κ-convex divergences. We derive new and old relationships, based on convexity arguments, between popular f-divergences.
Supersymmetric Euclidean field theories and K-theory

Abstract We construct spaces of 1-dimensional supersymmetric Euclidean field theories and show that they represent real or complex K-theory. This is done without prescribing the space of states in the definition of field theory.
Noninteracting electrons in a prototypical one-dimensional sinusoidal potential

A prototypical model of a one-dimensional metallic monatomic solid containing noninteracting electrons is studied, where the argument of the cosine potential energy, periodic with the lattice, contains the first reciprocal lattice vector G 1 = 2 π / a, where a is the lattice constant. The time-independent Schrodinger equation can be written in reduced variables as a Mathieu equation for which numerically exact solutions for the band structure and wave functions are obtained. The band structure has band gaps that increase with increasing amplitude q of the cosine potential. In the extended-zone scheme, the energy gaps decrease with increasing index n of the Brillouin-zone boundary k a = n π, where k is the crystal momentum of the electron. The wave functions of the band electron are derived for various combinations of k and q as complex combinations of the real Mathieu functions with even and odd parity, and the normalization factor is discussed. The wave functions at the bottoms and tops of the bands are found to be real or imaginary, respectively, corresponding to standing waves at these energies. Irrespective of the wave vector k within the first Brillouin zone, the electron probability density is found to be periodic with the lattice. The Fourier components of the wave functions are derived versus q, which reveal multiple reciprocal-lattice-vector components with variable amplitudes in the wave functions unless q = 0. The magnitudes of the Fourier components are found to decrease exponentially as a power of n for n ∼ 3 to 45 for k a = π / 2 and q = 2, and a precise fit is obtained to the data. The probability densities and probability currents obtained from the wave functions are also discussed. The probability currents are found to be zero for crystal momenta at the tops and bottoms of the energy bands, because the wave functions for these crystal momenta are standing waves. Finally, the band structure is calculated from the central equation and compared to the numerically exact band structure.
Pulsed Laser Mixing of Ni-Au Surface Films on Nickel Substrates

The melt phase alloying of Ni-Au films on Ni substrates has been studied for rapid quenches following 35 nano-second Q switched ruby laser pulses (0.69μ wavelength) in the energy regime of 0.5 to 3.0 j/cm 2 . The Ni and Au films were each 200 A in thickness having been deposited on a polished Ni substrate by standard hot ribbon vapor deposition methods. Data was obtained on pre and post alloyed surface layers using Rutherford backscattering, transmission electron microscopy, and STEM energy dispersive X-ray analysis. The melting and resolidification dynamics of the liquid-solid interface was monitored through finite difference integration of the non-linear heat conduction equation to give temperature profiles, depth of melting and melt front velocities associated with the liquid-solid phase change. Resolidification velocities were typically 15 meters/second with melt depths extending to a few thousand angstroms depending on pulse energy. RBS data confirms that liquid phase diffusion of gold in nickel has occured. TEM analysis reveals the presence of a two phase mixture being composed of nickel rich and gold rich material. Microbeam energy dispersive X-ray analysis indicates the presence of a relatively uniform mixing of these two Phases. Pronounced one dimensional solute segregation was not observed in these specimens, however, overall penetration depths of the gold was somewhat larger for the lower energy densities than for the larger ones. Also, unusual circular cell patterns were observed in the resolidified material, their contrast being enhanced by preferential etching during the TEM specimen polishing procedure.
Power Network Regulation Benchmark for Switched-Mode Optimal Control

Abstract Power network regulation is presented as a benchmark problem for assessing and developing switched-mode optimal control approaches like mode scheduling, sliding window scheduling and modal design. Power network evolution modeled by the swing equations and coupled with controllable switching components is a nonlinear, high-dimensional problem. The proposed benchmark problem is the 54 generator IEEE 118 Bus Test Case composed of 106 states. Open questions include scalability in state and number of modes of operation, as well as real-time implementation, reliability, hysteresis, and timing constraints. Can the entire North American power network be regulated? Can every transmission line have independent switching control authority?
Hardness of Reconfiguring Robot Swarms with Uniform External Control in Limited Directions

Motivated by advances is nanoscale applications and simplistic robot agents, we look at problems based on using a global signal to move all agents when given a limited number of directional signals and immovable geometry. We study a model where unit square particles move within a 2D grid based on uniform external forces. Movement is based on a sequence of uniform commands which cause all particles to move 1 step in a specific direction. The 2D grid board additionally contains "blocked" spaces which prevent particles from entry. Within this model, we investigate the complexity of deciding 1) whether a target location on the board can be occupied (by any) particle (\emph{occupancy problem}), 2) whether a specific particle can be relocated to another specific position in the board (\emph{relocation problem}), and 3) whether a board configuration can be transformed into another configuration (\emph{reconfiguration problem}). We prove that while occupancy is solvable in polynomial time, the relocation and reconfiguration problems are both NP-Complete even when restricted to only 2 or 3 movement directions. We further define a hierarchy of board geometries and show that this hardness holds for even very restricted classes of board geometry.
On the delta function broadening in the Kubo–Greenwood equation

Abstract Understanding DC electrical conductivity is crucial for the study of materials. Macroscopic DC conductivity can be calculated from first principles using the Kubo–Greenwood equation. The procedure involves finding the thermodynamic limit of the current response to an electric field that is slowly switched on, and then taking the limit of the switching rate to zero. We introduce a nonlinear extrapolation procedure executed in systems with periodic boundary conditions, which predicts conductivity close to the thermodynamic limit even for very small systems. The scheme also overcomes a large part of the usual ambiguities of the DC conductivity definition for finite systems. We numerically compare our method to the Landauer equation-based approach and find both techniques to be consistent with each other.
$\aleph_k$-free cogenerators

We prove in ZFC that an abelian group $C$ is cotorsion if and only if $\operatorname{Ext}(F,C) = 0$ for every $\aleph_k$-free group $F$, and discuss some consequences and related results. This short note includes a condensed overview of the $\bar\lambda$-Black Box for $\aleph_k$-free constructions in ZFC.
A Signal Theory Model for Continuous Monitoring and Intelligence Systems

Continuous monitoring and intelligence systems analyze data and text from various sources and use that information to monitor risk, controls, reputations, companies, people, opportunities, competition, and other concerns. We summarize some of the previous literature for such systems and the capabilities of existing continuous monitoring systems. Unfortunately, there has been limited theoretical development for such systems. We view the monitored information sources as providing information signals relating to events, activities, issues, etc. Systems must choose which information sources to monitor and gather information from. Unfortunately, choice of such source systems is not a straightforward problem, but must account for time, cost, redundancy, reliability, relevance, information asymmetries, weak signals, and other issues. Further, analytics must be generated to monitor signals created from the information sources to gather the information needed for the system. Accordingly, this paper generates and applies a signal theory model to address these issues. This allows us to elicit several issues of potential importance associated with the design and implementation of such systems.
Design of 18 nm Doxorubicin-Loaded 3-Helix Micelles: Cellular Uptake and Cytotoxicity in Patient-Derived GBM6 Cells.

The fate of nanocarrier materials at the cellular level constitutes a critical checkpoint in the development of effective nanomedicines, determining whether tissue level accumulation results in therapeutic benefit. The cytotoxicity and cell internalization of ∼18 nm 3-helix micelle (3HM) loaded with doxorubicin (DOX) were analyzed in patient-derived glioblastoma (GBM) cells in vitro. The half-maximal inhibitory concentration (IC50) of 3HM-DOX increased to 6.2 μg/mL from <0.5 μg/mL for free DOX in patient-derived GBM6 cells, to 15.0 μg/mL from 6.5 μg/mL in U87MG cells, and to 21.5 μg/mL from ∼0.5 μg/mL in LN229 cells. Modeling analysis of previous 3HM biodistribution results predicts that these cytotoxic concentrations are achievable with intravenous injection in rodent GBM models. 3HM-DOX formulations were internalized intact and underwent intracellular trafficking distinct from free DOX. 3HM was quantified to have an internalization half-life of 12.6 h in GBM6 cells, significantly longer than that reported for some liposome and polymer systems. 3HM was found to traffic through active endocytic processes, with clathrin-mediated endocytosis being the most involved of the pathways studied. Inhibition studies suggest substantial involvement of receptor recognition in 3HM uptake. As the 3HM surface is PEG-ylated with no targeting functionalities, protein corona-cell surface interactions, such as the apolipoprotein-low-density lipoprotein receptor, are expected to initiate internalization. The present work gives insights into the cytotoxicity, pharmacodynamics, and cellular interactions of 3HM and 3HM-DOX relevant for ongoing preclinical studies. This work also contributes to efforts to develop predictive mathematical models tracking the accumulation and biodistribution kinetics at a systemic level.
Tight Distributed Sketching Lower Bound for Connectivity

In this paper, we study the distributed sketching complexity of connectivity. In distributed graph sketching, an $n$-node graph $G$ is distributed to $n$ players such that each player sees the neighborhood of one vertex. The players then simultaneously send one message to the referee, who must compute some function of $G$ with high probability. For connectivity, the referee must output whether $G$ is connected. The goal is to minimize the message lengths. Such sketching schemes are equivalent to one-round protocols in the broadcast congested clique model. We prove that the expected average message length must be at least $\Omega(\log^3 n)$ bits, if the error probability is at most $1/4$. It matches the upper bound obtained by the AGM sketch [AGM12], which even allows the referee to output a spanning forest of $G$ with probability $1-1/\mathrm{poly}\, n$. Our lower bound strengthens the previous $\Omega(\log^3 n)$ lower bound for spanning forest computation [NY19]. Hence, it implies that connectivity, a decision problem, is as hard as its "search" version in this model.
The costs and benefits of a modified biomedical science workforce

Analyses of the biomedical research workforce, the biomedical research enterprise, and its sustainability have identified a number of threats and offered many solutions to alleviate the problems. While a number of these solutions have been implemented, one solution that has not been broadly adopted, despite being widely recommended, is to increase the number of staff scientists and reduce dependency on trainees. The perceived impediment of this is the cost. This paper explores the costs associated with laboratory personnel and the benefits, in terms of productivity, associated with different positions in the workforce. The results of this cost-benefit analysis depend upon the values assigned to different metrics of productivity by individuals and institutions. If first and senior author publications are the most important metrics of productivity, a trainee-dependent workforce is much more cost effective. If total publications are the most valued metric of productivity, the cost effectiveness of trainee and staff scientists is reasonably equitable. This analysis provides data for consideration when making personnel decisions and for the continued discussion of modification of the biomedical research workforce. It also provides insight into the incentives for modification of the workforce at the grass roots, which must be considered by institutions genuinely committed to workforce modification to sustain the biomedical research enterprise.
Path-dependent course of epidemic: Are two phases of quarantine better than one?

The importance of a strict quarantine has been widely debated during the COVID-19 epidemic even from the purely epidemiological point of view One argument against strict lockdown measures is that once the strict quarantine is lifted, the epidemic comes back, and so the cumulative number of infected individuals during the entire epidemic will stay the same We consider an SIR model on a network and follow the disease dynamics, modeling the phases of quarantine by changing the node degree distribution We show that the system reaches different steady states based on the history: the outcome of the epidemic is path-dependent despite the same final node degree distribution The results indicate that the two-phase route to the final node degree distribution (a strict phase followed by a soft phase) is always better than one phase (the same soft one) unless all the individuals have the same number of connections at the end (the same degree);in the latter case, the overall number of infected is indeed history-independent The modeling also suggests that the optimal procedure of lifting the quarantine consists of releasing nodes in the order of their degree - highest first © Copyright2020 EPLA
Model-free Reinforcement Learning for Non-stationary Mean Field Games

In this paper, we consider a finite horizon, non-stationary, mean field game (MFG) with a large population of homogeneous players, sequentially making strategic decisions, where each player is affected by other players through an aggregate population state termed as mean field state. Each player has a private type that only it can observe, and a mean field population state representing the empirical distribution of other players’ types, which is shared among all of them. Recently, authors in [1] provided a sequential decomposition algorithm to compute mean field equilibrium (MFE) for such games which allows for the computation of equilibrium policies for them in linear time than exponential, as before. In this paper, we extend it for the case when state transitions are not known, to propose a reinforcement learning algorithm based on Expected Sarsa with a policy gradient approach that learns the MFE policy by learning the dynamics of the game simultaneously. We illustrate our results using cyber-physical security example.
Evolutionary NAS with Gene Expression Programming of Cellular Encoding

The renaissance of neural architecture search (NAS) has seen classical methods such as genetic algorithms (GA) and genetic programming (GP) being exploited for convolutional neural network (CNN) architectures. While recent work have achieved promising performance on visual perception tasks, the direct encoding scheme of both GA and GP has functional complexity deficiency and does not scale well on large architectures like CNN. To address this, we present a new generative encoding scheme—symbolic linear generative encoding (SLGE)—simple, yet a powerful scheme which embeds local graph transformations in chromosomes of linear fixed-length string to develop CNN architectures of variant shapes and sizes via an evolutionary process of gene expression programming. In experiments, the effectiveness of SLGE is shown in discovering architectures that improve the performance of the state-of-the-art handcrafted CNN architectures on CIFAR-10 and CFAR-100 image classification tasks; and achieves a competitive classification error rate with the existing NAS methods using fewer GPU resources.
Do We Really Need Gold Samples for Sample Weighting under Label Noise

Learning with labels noise has gained significant traction recently due to the sensitivity of deep neural networks under label noise under common loss functions. Losses that are theoretically robust to label noise, however, often makes training difficult. Consequently, several recently proposed methods, such as Meta-Weight-Net (MW-Net), use a small number of unbiased, clean samples to learn a weighting function that downweights samples that are likely to have corrupted labels under the meta-learning framework. However, obtaining such a set of clean samples is not always feasible in practice. In this paper, we analytically show that one can easily train MW-Net without access to clean samples simply by using a loss function that is robust to label noise, such as mean absolute error, as the meta objective to train the weighting network. We experimentally show that our method beats all existing methods that do not use clean samples and performs on-par with methods that use gold samples on benchmark datasets across various noise types and noise rates.
Effective forms of the Sato--Tate conjecture

We prove effective forms of the Sato–Tate conjecture for holomorphic cuspidal newforms which improve on the author’s previous work (solo and joint with Lemke Oliver). We also prove an effective form of the joint Sato–Tate distribution for two twist-inequivalent newforms. Our results are unconditional because of recent work of Newton and Thorne.
Moving and housing expenditure: Transaction costs and disequilibrium

Abstract This paper specifies and estimates a model of rental housing expenditure that explicitly incorporates moving transaction costs. Parameter estimates reveal low income elasticities and substantial moving costs which vary considerably among families. The model is employed to evaluate the effects of proposed subsidy schemes. Simulated responses indicate that high moving costs deter many families from adjusting current rental expenditure to higher levels in response to subsidies. An additional dollar of unconstrained subsidy payment will, on average, increase rental expenditures by only 2–7 cents. Schemes with minimum rent requirements are also quite ineffective and involve substantial deadweight loss. Comparisons of the model predictions with estimated program effects based on experimental data are also included.
COVID and crime: An early empirical look

Abstract Data from 25 large U.S. cities is assembled to estimate the impact of the onset of the COVID-19 pandemic on crime. There is a widespread immediate drop in both criminal incidents and arrests most heavily pronounced among drug crimes, theft, residential burglaries, and most violent crimes. The decline appears to precede stay-at-home orders, and arrests follow a similar pattern as reports. There is no decline in homicides and shootings, and an increase in non-residential burglary and car theft in most cities, suggesting that criminal activity was displaced to locations with fewer people. Pittsburgh, New York City, San Francisco, Philadelphia, Washington DC and Chicago each saw overall crime drops of at least 35%. Evidence from police-initiated reports and geographic variation in crime change suggests that most of the observed changes are not due to changes in crime reporting.