cssi/SciSciGPT-SciSciNet huggingface dataset:
Rate equation analysis and non-Hermiticity in coupled semiconductor laser arrays

Optically coupled semiconductor laser arrays are described by coupled rate equations. The coupled mode equations and carrier densities are included in the analysis, which inherently incorporate the carrier-induced nonlinearities including gain saturation and amplitude-phase coupling. We solve the steady-state coupled rate equations and consider the cavity frequency detuning and the individual laser pump rates as the experimentally controlled variables. We show that the carrier-induced nonlinearities play a critical role in the mode control, and we identify gain contrast induced by cavity frequency detuning as a unique mechanism for mode control. Photon-mediated energy transfer between cavities is also discussed. Parity-time symmetry and exceptional points in this system are studied. Unbroken parity-time symmetry can be achieved by judiciously combining cavity detuning and unequal pump rates, while broken symmetry lies on the boundary of the optical locking region. Exceptional points are identified at the intersection between broken symmetry and unbroken parity-time symmetry.
Investigations of metastable Ca2IrO4 epitaxial thin-films: systematic comparison with Sr2IrO4 and Ba2IrO4

We have synthesized thermodynamically metastable Ca2IrO4 thin-films on YAlO3 (110) substrates by pulsed laser deposition. The epitaxial Ca2IrO4 thin-films are of K2NiF4-type tetragonal structure. Transport and optical spectroscopy measurements indicate that the electronic structure of the Ca2IrO4 thin-films is similar to that of Jeff = 1/2 spin-orbit-coupled Mott insulator Sr2IrO4 and Ba2IrO4, with the exception of an increased gap energy. The gap increase is to be expected in Ca2IrO4 due to its increased octahedral rotation and tilting, which results in enhanced electron-correlation, U/W. Our results suggest that the epitaxial stabilization growth of metastable-phase thin-films can be used effectively for investigating layered iridates and various complex-oxide systems.
No “Maunder Minimum” Candidates in M67: Mitigating Interstellar Contamination of Chromospheric Emission Lines

The solar analogs of M67 let us glimpse the probable behavior of the Sun on time scales surpassing the duration of human civilization. M67 can serve as a solar proxy because its stars share a similar age and composition with the Sun. Previous surveys of M67 observed that 15% of its Sun-like stars exhibited chromospheric activity levels below solar minimum, which suggest that these stars might be in activity-minimum states analogous to the Maunder Minimum. The activity diagnostic used, the HK index (relative intensities of the Ca II H&K lines integrated over 1 Ang. bandpasses), was measured from low-resolution spectra ($R\approx 5000$), as is traditional and suitable for nearby, bright stars. However, for stars beyond the Local Bubble, the interstellar medium (ISM) imprints absorption lines in spectra at Ca II H&K, which negatively bias activity measurements when these lines fall within the HK index bandpass. I model the ISM clouds in the M67 foreground with high-resolution spectra of blue stragglers and solar analogs. I demonstrate that ISM absorption varies across the cluster and must be accounted for on a star-by-star basis. I then apply the ISM model to a solar spectrum and broaden it to the lower spectral resolution employed by prior surveys. Comparing HK indices measured from ISM-free and ISM-contaminated spectra, I find that all stars observed below solar minimum can be explained by this ISM bias. I conclude that there is no compelling evidence for Maunder minimum candidates in M67 at this time.
A SIZE-DURATION TREND FOR GAMMA-RAY BURST PROGENITORS

Gamma-ray bursts (GRBs) show a bimodal distribution of durations, separated at a duration of ∼2 s. Observations have confirmed the association of long GRBs with the collapse of massive stars. The origin of short GRBs is still being explored. We examine constraints on the size of emission regions in short and long GRBs detected by Fermi/GBM. We find that the transverse extent of emission regions during the prompt phase, R, and the burst duration, T {sub 90}, are consistent with the relation R ∼ c × T {sub 90}, for both long and short GRBs. We find the characteristic transverse extent for the prompt emission region to be ∼2 × 10{sup 10} cm and ∼4 × 10{sup 11} cm for short and long GRBs, respectively.
Stellar absorption lines in the spectra of Seyfert galaxies

Abstract We have measured the strengths of Ca II triplet and Mgb stellar absorption lines in the nuclear and off-nuclear spectra of Seyfert galaxies. These features are diluted to varying degrees by continuum emission from the active nucleus and from young stars. Ca II triplet strengths can be enhanced if late-type supergiant stars dominate the near-IR light. Thus, objects with strong Ca II triplet and weak Mgb lines may be objects with strong bursts of star formation. We find that for most of our sample the line strengths are at least consistent with dilution of a normal galaxy spectrum by a power law continuum, in accord with the standard model for AGN. However, for several Seyferts in our sample, it appears that dilution by a power law continuum cannot simultaneously explain strong Ca II triplet and relatively weak Mgb. Also, these objects occupy the region of the IRAS color-color diagram characteristic of starburst galaxies. In these objects it appears that the optical to near-IR emission is dominated by late-type supergiants produced in a circumnuclear burst of star formation.
Rigidity and curvature estimates for graphical self-shrinkers

Self-shrinkers are hypersurfaces that shrink homothetically under mean curvature flow; these solitons model the singularities of the flow. It is presently known that an entire self-shrinking graph must be a hyperplane. In this paper we show that the hyperplane is rigid in an even stronger sense, namely: for $$2\le n \le 6$$ , any smooth, complete self-shrinker $$\Sigma ^n\subset \mathbf {R}^{n+1}$$ that is graphical inside a large, but compact, set must be a hyperplane. In fact, this rigidity holds within a larger class of almost stable self-shrinkers. A key component of this paper is the procurement of linear curvature estimates for almost stable shrinkers, and it is this step that is responsible for the restriction on n. Our methods also yield uniform curvature bounds for translating solitons of the mean curvature flow.
Enriching a Linear/Non-linear Lambda Calculus: A Programming Language for String Diagrams

Linear/non-linear (LNL) models, as described by Benton, soundly model a LNL term calculus and LNL logic closely related to intuitionistic linear logic. Every such model induces a canonical enrichment that we show soundly models a LNL lambda calculus for string diagrams, introduced by Rios and Selinger (with primary application in quantum computing). Our abstract treatment of this language leads to simpler concrete models compared to those presented so far. We also extend the language with general recursion and prove soundness. Finally, we present an adequacy result for the diagram-free fragment of the language which corresponds to a modified version of Benton and Wadler's adjoint calculus with recursion.
Comparison of hand-held WEMI target detection algorithms

Wide-band Electromagnetic Induction Sensors (WEMI) have been used for a number of years in subsurface detection of explosive hazards. While WEMI sensors have proven effective at localizing objects exhibiting large magnetic responses, detecting objects lacking or containing very low amounts of conductive materials can be challenging. In this paper, we compare a number of target detection algorithms in the literature in terms of detection performance. In the comparison, methods are tested on two real-world data sets: one containing relatively low amounts of ground noise pollution, and the other demonstrating highly-magnetic soil interference. Results are quantitatively evaluated through receiver-operator characteristic (ROC) curves and are used to highlight the strengths and weaknesses of the compared approaches in hand-held explosive hazard detection.
MATRIX RICCATI EQUATION SOLUTION of the 1D RADIATIVE TRANSFER EQUATION

In recent years, the first author has developed three successful numerical methods to solve the 1D radiative transport equation yielding highly precise benchmarks. The second author has shown a kee...
CONSTRAINING THE ISM PROPERTIES OF THE CLOVERLEAF QUASAR HOST GALAXY WITH HERSCHEL SPECTROSCOPY

We present Herschel observations of the far-infrared (FIR) fine-structure (FS) lines [C II]158 μm, [O I]63 μm, [O III]52 μm, and [Si II]35 μm in the z = 2.56 Cloverleaf quasar, and combine them with published data in an analysis of the dense interstellar medium (ISM) in this system. Observed [C II]158 μm, [O I]63 μm, and FIR continuum flux ratios are reproduced with photodissociation region (PDR) models characterized by moderate far-ultraviolet (FUV) radiation fields with G_0 = 0.3–1 × 10^3 and atomic gas densities n_H = 3–5 × 10^3 cm^(−3), depending on contributions to [C II]158 μm from ionized gas. We assess the contribution to the [C II]158 μm flux from an active galactic nucleus (AGN) narrow line region (NLR) using ground-based measurements of the [N II]122 μm transition, finding that the NLR can contribute at most 20%–30% of the observed [C II]158 μm flux. The PDR density and far-UV radiation fields inferred from the atomic lines are not consistent with the CO emission, indicating that the molecular gas excitation is not solely provided via UV heating from local star formation (SF), but requires an additional heating source. X-ray heating from the AGN is explored, and we find that X-ray-dominated region (XDR) models, in combination with PDR models, can match the CO cooling without overproducing the observed FS line emission. While this XDR/PDR solution is favored given the evidence for both X-rays and SF in the Cloverleaf, we also investigate alternatives for the warm molecular gas, finding that either mechanical heating via low-velocity shocks or an enhanced cosmic-ray ionization rate may also contribute. Finally, we include upper limits on two other measurements attempted in the Herschel program: [C II]158 μm in FSC 10214 and [O I]63 μm in APM 08279+5255.
Thermionic Emission and Negative dI/dV in Photoactive Graphene Heterostructures

Transport in photoactive graphene heterostructures, originating from the dynamics of photogenerated hot carriers, is governed by the processes of thermionic emission, electron–lattice thermal imbalance, and cooling. These processes give rise to interesting photoresponse effects, in particular negative differential resistance (NDR) arising in the hot-carrier regime. The NDR effect stems from a strong dependence of electron–lattice cooling on the carrier density, which results in the carrier temperature dropping precipitously upon increasing bias. The ON–OFF switching between the NDR regime and the conventional cold emission regime, as well as the gate-controlled closed-circuit current that is present at zero bias voltage, can serve as signatures of hot-carrier dominated transport.
Understanding Bulk Defects in Topological Insulators from Nuclear-Spin Interactions

Non-invasive local probes are needed to characterize bulk defects in binary and ternary chalcogenides. These defects contribute to the non-ideal behavior of topological insulators. The bulk electronic properties are studied via 125Te NMR in Bi2Te3, Sb2Te3, Bi0.5Sb1.5Te3, Bi2Te2Se, and Bi2Te2S. A distribution of defects gives rise to asymmetry in the powder lineshapes. The Knight shift, line shape, and spin-lattice relaxation are investigated in terms of how they affect carrier density, spin-orbit coupling, and phase separation in the bulk. The present study confirms that the ordered ternary compound Bi2Te2Se is the best topological insulator candidate material at the present time. These results, which are in good agreement with transport and angle-resolved photoemission spectroscopy studies, help establish the NMR probe as a valuable method to characterize the bulk properties of these materials.
Effective field theory approach to Casimir interactions on soft matter surfaces

We utilize an effective field theory approach to calculate Casimir interactions between objects bound to thermally fluctuating fluid surfaces or interfaces. This approach circumvents the complicated constraints imposed by such objects on the functional integration measure by reverting to a point particle representation. To capture the finite-size effects, we augment the Hamiltonian by a term Δ that encapsulates the particles' response to external fields. Δ is systematically expanded in a series of terms, each of which scales homogeneously in the two power counting parameters: λ≡R/r , the ratio of the typical object size (R) to the typical distance between them (r), and δ≡kBT/k, where k is the modulus characterizing the surface energy. The coefficients of the terms in Δ correspond to generalized polarizabilities and thus the formalism applies to rigid as well as deformable objects. We first illustrate and verify our approach by re-deriving known pair forces between circular objects bound to films or membranes. To demonstrate its efficiency and versatility, we then derive a number of new results, among them the triplet interactions present in these systems, a higher-order correction to the film interaction, and general scaling laws for the leading-order interaction valid for objects of arbitrary shape and internal flexibility.
Thermal Comptonization and Disk Thermal Reprocessing in NGC 3516

We present an application of the thermal Comptonization/disk reprocessing model recently proposed by Zdziarski, Lubiniski, and Smith. We show that the absence of strong optical variations in the presence of strong concurrent X-ray variations, similar to those found by Hubble Space Telescope (HST)/Rossi X-Ray Timing Explorer (RXTE) monitoring observations of NGC 3516, can be explained by changing the geometry of the Comptonizing plasma rather than the accretion disk itself. The total X-ray luminosity of the Comptonizing plasma must decrease as its spatial extent increases. In contrast, the disk inner radius must be roughly fixed in order not to produce optical/ultraviolet color variations stronger than observed. By including emission due to internal viscous dissipation in the disk, we can roughly match the optical and X-ray flux levels and variability amplitudes seen from NGC 3516 during the HST/RXTE campaign.
On the sign problem in dense QCD

We investigate the Euclidean path integral formulation of QCD at finite baryon density and temperature. We show that the partition function Z can be written as a difference between two sums Z+ and Z-, each of which defines a partition function with positive weights. We call the sign problem severe if the ratio Z-/Z+ is nonzero in the infinite volume limit. This occurs only if, and generically always if, the associated free energy densities F± are equal in this limit. We present strong evidence here that the sign problem is severe at almost all points in the phase diagram, with the exception of special cases like exactly zero chemical potential (ordinary QCD), which requires a particular order of limits. Part of our reasoning is based on the analyticity of free energy densities within their open phase regions. Finally, we describe a Monte Carlo technique to simulate finite-density QCD in regions where Z-/Z+ is small.
Monotonicity of Quantum Ground State Energies: Bosonic Atoms and Stars

The N-dependence of the non-relativistic bosonic ground state energy ℰB(N) is studied for quantum N-body systems with either Coulomb or Newton interactions. The Coulomb systems are “bosonic atoms,” with their nucleus fixed, and it is shown that \(\mathcal {E}_{{C}}^{{B}}(N)/\mathcal {P}_{{C}}(N)\) grows monotonically in N>1, where ℘C(N)=N2(N−1). The Newton systems are “bosonic stars,” and it is shown that when the Bosons are centrally attracted to a fixed gravitational “grain” of mass M>0, and N>2, then \(\mathcal {E}_{{N}}^{{B}}(N;M)/\mathcal {P}_{\!{N}}(N)\) grows monotonically in N, where ℘N(N)=N(N−1)(N−2); in the translation-invariant problem (M=0), it is shown that when N>1 then \(\mathcal {E}_{{N}}^{{B}}(N;0)/\mathcal {P}_{{C}}(N)\) grows monotonically in N, with ℘C(N) from the Coulomb problem. Some applications of the new monotonicity results are discussed.
Division polynomials and intersection of projective torsion points

Given two elliptic curves, each of which is associated with a projection map that identifies opposite elements with respect to the natural group structure, we investigate how their corresponding projective images of torsion points intersect.
On the ‘simple’ form of the gravitational action and the self-interacting graviton

The so-called ΓΓ-form of the gravitational Lagrangian, long known to provide its most compact expression as well as the most efficient generation of the graviton vertices, is taken as the starting point for discussing General Relativity as a theory of the self-interacting graviton. A straightforward but general method of converting to a covariant formulation by the introduction of a reference metric is given. It is used to recast the Einstein field equation as the equation of motion of a spin-2 particle interacting with the canonical energy-momentum tensor symmetrized by the standard Belinfante method applicable to any field carrying nonzero spin. This represents the graviton field equation in a form complying with the precepts of standard field theory. It is then shown how representations based on other, at face value completely unrelated definitions of energy-momentum (pseudo)tensors are all related by the addition of appropriate superpotential terms. Specifically, the superpotentials are explicitly constructed which connect to: i) the common definition consisting simply of the nonlinear part of the Einstein tensor; ii) the Landau-Lifshitz definition.
Low-power object counting with hierarchical neural networks

Deep Neural Networks (DNNs) achieve state-of-the-art accuracy in many computer vision tasks, such as object counting. Object counting takes two inputs: an image and an object query and reports the number of occurrences of the queried object. To achieve high accuracy, DNNs require billions of operations, making them difficult to deploy on resource-constrained, low-power devices. Prior work shows that a significant number of DNN operations are redundant and can be eliminated without affecting the accuracy. To reduce these redundancies, we propose a hierarchical DNN architecture for object counting. This architecture uses a Region Proposal Network (RPN) to propose regions-of-interest (RoIs) that may contain the queried objects. A hierarchical classifier then efficiently finds the RoIs that actually contain the queried objects. The hierarchy contains groups of visually similar object categories. Small DNNs at each node of the hierarchy classify between these groups. The RoIs are incrementally processed by the hierarchical classifier. If the object in an RoI is in the same group as the queried object, then the next DNN in the hierarchy processes the RoI further; otherwise, the RoI is discarded. By using a few small DNNs to process each image, this method reduces the memory requirement, inference time, energy consumption, and number of operations with negligible accuracy loss when compared with the existing techniques.
Condensation of SiC Stardust in CO Nova Outbursts

This study on presolar grains compares high-precision isotopic compositions of individual SiC grains with low 12C/13C ratios, low 14N/15N ratios, large 30Si excesses, and high 26Al/27Al ratios, all available in the presolar grain database, to new CO nova models with white dwarf (WD) masses from 0.6 to 1.35 M ⊙. The models were designed to match the Large Binocular Telescope high-dispersion spectra acquired for nova V5668 Sgr. These CO nova models provide elemental abundances up to calcium and include mixing of WD material into the accreted material in a binary star system under several scenarios, including one where mixing occurs only after temperatures >7 × 107 K are achieved during a thermonuclear runaway (TNR). The 0.8–1.35 M ⊙ simulations where 25% of the WD core matter mixes with 75% of the accreted material (assumed solar) from its binary companion after the TNR has begun provide the best fits to the measured isotopic data in four presolar grains. One grain matches the 50% accreted 50% solar 1.35 M ⊙ simulation. For these five presolar grains, less than 25% of solar system material is required to be mixed with the CO nova ejecta to account for the grains' compositions. Thus, our study reports evidence of pure CO nova ejecta material in meteorites. Finally, we speculate that SiC grains can form in the winds of cool and dense CO novae, where the criterion C > O may not be locally imposed, and thus nova winds can be chemically inhomogeneous.
The development of magnetic field line wander by plasma turbulence

Plasma turbulence occurs ubiquitously in space and astrophysical plasmas, mediating the nonlinear transfer of energy from large-scale electromagnetic fields and plasma flows to small scales at which the energy may be ultimately converted to plasma heat. But plasma turbulence also generically leads to a tangling of the magnetic field that threads through the plasma. The resulting wander of the magnetic field lines may significantly impact a number of important physical processes, including the propagation of cosmic rays and energetic particles, confinement in magnetic fusion devices and the fundamental processes of turbulence, magnetic reconnection and particle acceleration. The various potential impacts of magnetic field line wander are reviewed in detail, and a number of important theoretical considerations are identified that may influence the development and saturation of magnetic field line wander in astrophysical plasma turbulence. The results of nonlinear gyrokinetic simulations of kinetic Alfven wave turbulence of sub-ion length scales are evaluated to understand the development and saturation of the turbulent magnetic energy spectrum and of the magnetic field line wander. It is found that turbulent space and astrophysical plasmas are generally expected to contain a stochastic magnetic field due to the tangling of the field by strong plasma turbulence. Future work will explore how the saturated magnetic field line wander varies as a function of the amplitude of the plasma turbulence and the ratio of the thermal to magnetic pressure, known as the plasma beta.
The universal character ring of some families of one-relator groups

We study the universal character ring of some families of one-relator groups. As an application, we calculate the universal character ring of two-generator one-relator groups whose relators are palindromic and, in particular, of the . 2; 2mC1; 2nC1/– pretzel knot for all integers m and n . For the . 2; 3; 2nC1/–pretzel knot, we give a simple proof of a result in [8] on its universal character ring, and an elementary proof of a result in [10] on the number of irreducible components of its character variety.
Little Blue Dots in the Hubble Space Telescope Frontier Fields: Precursors to Globular Clusters?

Galaxies with stellar masses and specific star formation rates yr−1 were examined on images of the Hubble Space Telescope Frontier Field Parallels for Abell 2744 and MACS J0416.1-02403. They appear as unresolved "Little Blue Dots" (LBDs). They are less massive and have higher specific star formation rates (sSFRs) than "blueberries" studied by Yang et al. and higher sSFRs than "Blue Nuggets" studied by Tacchella et al. We divided the LBDs into three redshift bins and, for each, stacked the B435, V606, and I814 images convolved to the same stellar point-spread function (PSF). Their radii were determined from PSF deconvolution to be ~80 to ~180 pc. The high sSFRs suggest that their entire stellar mass has formed in only 1% of the local age of the universe. The sSFRs at similar epochs in local dwarf galaxies are lower by a factor of ~100. Assuming that the star formation rate is for efficiency , gas mass M gas, and free-fall time, t ff, the gas mass and gas-to-star mass ratio are determined. This ratio exceeds 1 for reasonable efficiencies, and is likely to be ~5 even with a high of 0.1. We consider whether these regions are forming today's globular clusters. With their observed stellar masses, the maximum likely cluster mass is , but if star formation continues at the current rate for before feedback and gas exhaustion stop it, then the maximum cluster mass could become .
WHERE CAN WE REALLY FIND THE FIRST STARS' REMNANTS TODAY?

A number of recent numerical investigations concluded that the remnants of rare structures formed at very high redshift, such as the very first stars and bright redshift z ≈ 6 QSOs, are preferentially located at the center of the most massive galaxy clusters at redshift z = 0. In this paper we readdress this question using a combination of cosmological simulations of structure formation and extended Press-Schechter formalism, and we show that the typical remnants of Population III stars are instead more likely to be found in a group environment, that is, in dark matter halos of mass 2 × 1013 h−1 M☉. Similarly, the descendants of the brightest z ≈ 6 QSOs are expected to be in medium-sized clusters (mass of a few 1014 h−1 M☉), rather than in the most massive superclusters (M > 1015 h−1 M☉) found within the typical 1 Gpc3 cosmic volume where a bright z ≈ 6 QSO lives. The origin of past claims that the most massive clusters preferentially host these remnants is rooted in the numerical method used to initialize their numerical simulations: Only a small region of the cosmological volume of interest was simulated with sufficient resolution to identify low-mass halos at early times, and this region was chosen to host the most massive halo in the cosmological volume at late times. The conclusion that the earliest structures formed in the entire cosmological volume evolve into the most massive halo at late times was thus arrived at by construction. We demonstrate that, to the contrary, the first structures to form in a cosmological region evolve into relatively typical objects at later times. We propose alternative numerical methods for simulating the earliest structures in cosmological volumes.
A note on spectral properties of Hermite subdivision operators

Abstract In this paper we study the connection between the spectral condition of an Hermite subdivision operator and polynomial reproduction properties of the associated subdivision scheme. While it is known that in general the spectral condition does not imply the reproduction of polynomials, we here prove that a special spectral condition (defined by shifted monomials) is actually equivalent to the reproduction of polynomials. We further put into evidence that the sum rule of order l > d associated with an Hermite subdivision operator of order d does not imply that the spectral condition of order l is satisfied, while it is known that these two concepts are equivalent in the case l = d .
Bulk Locality and Quantum Error Correction in AdS/CFT

We point out a connection between the emergence of bulk locality in AdS/CFT and the theory of quantum error correction. Bulk notions such as Bogoliubov transformations, location in the radial direction, and the holographic entropy bound all have natural CFT interpretations in the language of quantum error correction. We also show that the question of whether bulk operator reconstruction works only in the causal wedge or all the way to the extremal surface is related to the question of whether or not the quantum error correcting code realized by AdS/CFT is also a “quantum secret sharing scheme”, and suggest a tensor network calculation that may settle the issue. Interestingly, the version of quantum error correction which is best suited to our analysis is the somewhat nonstandard “operator algebra quantum error correction” of Beny, Kempf, and Kribs. Our proposal gives a precise formulation of the idea of “subregion-subregion” duality in AdS/CFT, and clarifies the limits of its validity.
Core Formation in Galactic Nuclei due to Recoiling Black Holes

Anisotropic gravitational radiation from a coalescing black hole binary can impart a recoil velocity of up to several hundred kilometers per second to the remnant black hole. We examine the effects of recoiling massive black holes on their host stellar bulges, both for holes that escape their host and for those that return to the galactic center via dynamical friction. We show that removal of a black hole via radiation recoil generally results in a rapidly formed central core in the stellar system, with the effect being largest when the hole stays bound to the bulge and the recoil velocity is comparable to the bulge velocity dispersion. Black hole recoil therefore provides a mechanism for producing cores in some early-type galaxies, but it is expected to be most efficient in faint elliptical galaxies that are known to have steep density profiles. We argue that these results may hint at a significant role for gas in facilitating the coalescence of binary black holes in faint (power-law) early-type galaxies.
Higher-Order Signature Cocycles for Subgroups of Mapping Class Groups and Homology Cylinders

We define families of invariants for elements of the mapping class group of S, a compact orientable surface. Fix any characteristic subgroup H of pi_1(S) and restrict to J(H), any subgroup of mapping classes that induce the identity modulo H. To any unitary representation, r of pi_1(S)/H we associate a higher-order rho_r-invariant and a signature 2-cocycle sigma_r. These signature cocycles are shown to be generalizations of the Meyer cocycle. In particular each rho_r is a quasimorphism and each sigma_r is a bounded 2-cocycle on J(H). In one of the simplest non-trivial cases, by varying r, we exhibit infinite families of linearly independent quasimorphisms and signature cocycles. We show that the rho_r restrict to homomorphisms on certain interesting subgroups. Many of these invariants extend naturally to the full mapping class group and some extend to the monoid of homology cylinders based on S.
Coarse-grained entropy and causal holographic information in AdS/CFT

We propose bulk duals for certain coarse-grained entropies of boundary regions. The ‘one-point entropy’ is defined in the conformal field theory by maximizing the entropy in a domain of dependence while fixing the one-point functions. We conjecture that this is dual to the area of the edge of the region causally accessible to the domain of dependence (i.e. the ‘causal holographic information’ of Hubeny and Rangamani). The ‘future onepoint entropy’ is defined by generalizing this conjecture to future domains of dependence and their corresponding bulk regions. We show that the future one-point entropy obeys a nontrivial second law. If our conjecture is true, this answers the question “What is the field theory dual of Hawking’s area theorem?”
Multiple Collimated Outflows in the Proto-Planetary Nebula GL 618

We present narrowband Hα, [S II], and [O I] Hubble Space Telescope images of the young planetary nebula GL 618. This object is a compact, bipolar nebula that is currently undergoing the transition from asymptotic giant branch star to planetary nebula. Our images confirm the presence of at least three highly collimated outflows emanating from the central regions of GL 618. We also detect Hα emission close to the central dust lane and in an extended scattered light halo. The three outflows are occurring simultaneously in this object as opposed to being the result of a precessing jet. We derive an inclination for the brightest outflow in the east lobe of 39° ± 4°. This differs from the previous estimate of 45°. In addition, our results indicate that the outflows seen in GL 618 are probably not coplanar. Line strengths derived from the narrowband images indicate a shock velocity in the range of 40-100 km s-1. Based on the shock velocity, we estimate that the age of the outflows is less than 500 yr. The outflows seen in the optical images of GL 618 are related to features seen in near-IR, CO, and CS maps of this object. This relationship indicates that the outflows are playing a major role in the morphological evolution of this young planetary nebula, interacting with and shaping the neutral envelope surrounding GL 618. We discuss the implications of these jets and their interaction with the neutral envelope in the context of current models of planetary nebula formation.
Context-aware path ranking for knowledge base completion

Knowledge base (KB) completion aims to infer missing facts from existing ones in a KB. Among various approaches, path ranking (PR) algorithms have received increasing attention in recent years. PR algorithms enumerate paths between entity pairs in a KB and use those paths as features to train a model for missing fact prediction. Due to their good performances and high model interpretability, several methods have been proposed. However, most existing methods suffer from scalability (high RAM consumption) and feature explosion (trains on an exponentially large number of features) problems. This paper proposes a Context-aware Path Ranking (C-PR) algorithm to solve these problems by introducing a selective path exploration strategy. C-PR learns global semantics of entities in the KB using word embedding and leverages the knowledge of entity semantics to enumerate contextually relevant paths using bidirectional random walk. Experimental results on three large KBs show that the path features (fewer in number) discovered by C-PR not only improve predictive performance but also are more interpretable than existing baselines.
Do Employer-Sponsored Immigrants Fare Better in Labor Markets Than Family-Sponsored Immigrants?

Debates about revising U.S. legal immigration policies tend to question the economic value of immigrants sponsored by family members rather than by employers. To date, little evidence has been cited. This article uses the latest data to measure legal immigrants’ characteristics and economic outcomes by class of entry, comparing employment rates, self-employment rates, and occupational outcomes of family-sponsored immigrants, humanitarian migrants, and diversity visa immigrants with those of employer-sponsored immigrants. It finds that most legal, permanent immigrants to the United States show high employment rates relative to the overall U.S. population after several years in the country, but that employment-sponsored immigrants and their spouses bring the highest education and English proficiency and work in the most highly skilled occupations both initially and over time.
Measuring the frequency response of optically pumped metal-clad nanolasers

We report on our initial attempt to characterize the intrinsic frequency response of metal-clad nanolasers. The probed nanolaser is optically biased and modulated, allowing the emitted signal to be detected using a high-speed photodiode at each modulation frequency. Based on this technique, the prospect of high-speed operation of nanolasers is evaluated by measuring the D-factor, which is the ratio of the resonance frequency to the square root of its output power(fR/Pout1/2). Our measurements show that for nanolasers, this factor is an order of magnitude greater than that of other state-of-the-art directly modulated semiconductor lasers. The theoretical analysis, based on the rate equation model and finite element method simulations of the cavity is in full agreement with the measurement results.
Electronic structure of carbon nanotubes on graphene substrates

The authors investigate the electronic properties of a carbon nanotube deposited on a graphene sheet. They derive a low-energy theory that is able to account both for rotations and rigid displacements of the nanotube with respect to the underlying graphene layer, and use it to calculate nanotube electronic spectra.
Surgery on closed 4-manifolds with free fundamental group

Even though the disk embedding theorem is not available in dimension 4 for free fundamental groups, some surgery problems may be shown to have topological solutions. We prove that surgery problems may be solved if one considers closed 4-manifolds and the intersection pairing is extended from the integers, and prove a related splitting result.
In situ models for planet assembly around cool stars

We present a model for the in situ assembly of planetary systems around a 0.5 M⊙ star, and compare the resulting statistics with the observed sample of cool Kepler planet candidates. We are able to reproduce the distribution of planetary periods and period ratios, although we once again find an underabundance of single transit systems relative to the observations. We also demonstrate that almost every planetary system assembled in this fashion contains at least one planet in the habitable zone, and that water delivery to these planets can potentially produce water content comparable to that of Earth. Our results broadly support the notion that habitable planets are plentiful around M dwarfs in the solar neighbourhood.
A cryogenic-helium pipe flow facility with unique double-line molecular tagging velocimetry capability.

Cryogenic helium-4 has extremely small kinetic viscosity, which makes it a promising material for high Reynolds (Re) number turbulence research in compact laboratory apparatus. In its superfluid phase (He II), helium has an extraordinary heat transfer capability and has been utilized in various scientific and engineering applications. In order to unlock the full potential of helium in turbulence research and to improve our understanding of the heat transfer mechanism in He II, a flow facility that allows quantitative study of helium heat-and-mass transfer processes is needed. Here, we report our work in assembling and testing a unique helium pipe-flow facility that incorporates a novel double-line molecular tagging velocimetry (DL-MTV) system. This flow facility allows us to generate turbulent pipe flows with Re above 107, and it can also be adapted to produce heat-induced counterflow in He II. The DL-MTV system, which is based on the generation and tracking of two parallel thin He2* molecular tracer lines with an adjustable separation distance, allows us to measure not only the velocity profile but also both the transverse and longitudinal spatial velocity structure functions. We have also installed a differential pressure sensor on the flow pipe for pressure drop measurements. The testing results of the flow facility and the measuring instruments are presented. We discuss how this facility will allow us to solve some outstanding problems in the helium heat-and-mass transfer topic area.
Finite-temperature entanglement negativity of free fermions

The entanglement entropy of free fermions with a Fermi surface is known to obey a logarithmic scaling and violate the area law in all dimensions. Here, we would like to see how temperature affects the logarithmic scaling behavior. To this end, we compute the entanglement negativity of free fermions using the fermionic partial transpose developed in our earlier paper (Shapourian et al 2017 Phys. Rev. B 95 165101). In one dimension, we analytically derive the leading order term in the finite-temperature entanglement negativity and show how the entanglement negativity indicates a crossover from a quantum entangled state to a classical thermal state, where the entanglement is completely lost. We explain how the one-dimensional result can be generalized to codimension-one Fermi surface of arbitrary shape in higher dimensions. In both one and two dimensions, we check that our analytical results agree with the numerical simulation of free fermions on a lattice.
Structure of sets which are well approximated by zero sets of harmonic polynomials

The zero sets of harmonic polynomials play a crucial role in the study of the free boundary regularity problem for harmonic measure. In order to understand the fine structure of these free boundaries a detailed study of the singular points of these zero sets is required. In this paper we study how “degree k points” sit inside zero sets of harmonic polynomials in R of degree d (for all n ≥ 2 and 1 ≤ k ≤ d) and inside sets that admit arbitrarily good local approximations by zero sets of harmonic polynomials. We obtain a general structure theorem for the latter type of sets, including sharp Hausdorff and Minkowski dimension estimates on the singular set of “degree k points” (k ≥ 2) without proving uniqueness of blowups or aid of PDE methods such as monotonicity formulas. In addition, we show that in the presence of a certain topological separation condition, the sharp dimension estimates improve and depend on the parity of k. An application is given to the two-phase free boundary regularity problem for harmonic measure below the continuous threshold introduced by Kenig and Toro.
Radio-quiet quasars in the direction of the northern Hubble Deep Field

We match quasars discovered in a multicolor survey centered on the northern Hubble Deep Field (HDF) with radio sources from an ultradeep radio survey. Although three out of 12 quasars are detected at a level below 0.2 mJy at 1.4 GHz, all of the quasars in the search area are radio quiet by the criterion Lr < 1025 h W Hz-1. We combine this information with other radio surveys of quasars so as to break the degeneracy between redshift and luminosity. In the redshift range 0.02 < z < 3.64, the radio-loud fraction increases with increasing optical luminosity, consistent with some degree of correlation between the nonthermal optical and radio emissions. More tentatively, for low-luminosity quasars in the range -22.5 < MB < -25, the radio-loud fraction decreases with increasing redshift. We can infer from this that the radio luminosity function evolves more slowly than the optical luminosity function. The mechanism that leads to strong radio emission in only a small fraction of quasars at any epoch is still unknown.
Fundamental parameters from precision tests

I review how electroweak precision observables can be used to constrain the Higgs boson mass and the strong coupling constant. Implications for physics beyond the standard model are also addressed.
Entropic representation and estimation of diversity indices

This paper serves a twofold purpose. First, a unified perspective on diversity indices is introduced based on an entropic basis. It is shown that the class of all linear combinations of the entropi...
Geometric Sensitivity Measures for Bayesian Nonparametric Density Estimation Models

We propose a geometric framework to assess global sensitivity in Bayesian nonparametric models for density estimation. We study sensitivity of nonparametric Bayesian models for density estimation, based on Dirichlet-type priors, to perturbations of either the precision parameter or the base probability measure. To quantify the different effects of the perturbations of the parameters and hyperparameters in these models on the posterior, we define three geometrically-motivated global sensitivity measures based on geodesic paths and distances computed under the nonparametric Fisher-Rao Riemannian metric on the space of densities, applied to posterior samples of densities: (1) the Fisher-Rao distance between density averages of posterior samples, (2) the log-ratio of Karcher variances of posterior samples, and (3) the norm of the difference of scaled cumulative eigenvalues of empirical covariance operators obtained from posterior samples. We validate our approach using multiple simulation studies, and consider the problem of sensitivity analysis for Bayesian density estimation models in the context of three real datasets that have previously been studied.
Formal Synthesis of Control Strategies for Positive Monotone Systems

We design controllers from formal specifications for positive discrete-time monotone systems that are subject to bounded disturbances. Such systems are widely used to model the dynamics of transportation and biological networks. The specifications are described using signal temporal logic (STL), which can express a broad range of temporal properties. We formulate the problem as a mixed-integer linear program (MILP) and show that under the assumptions made in this paper, which are not restrictive for traffic applications, the existence of open-loop control policies is sufficient and almost necessary to ensure the satisfaction of STL formulas. We establish a relation between satisfaction of STL formulas in infinite time and set-invariance theories and provide an efficient method to compute robust control invariant sets in high dimensions. We also develop a robust model predictive framework to plan controls optimally while ensuring the satisfaction of the specification. Illustrative examples and a traffic management case study are included.
Nature abhors a horizon

The information paradox can be resolved if we recognize that the wave functional in gravity Ψ[g] should be considered on the whole of superspace, the space of possible g. The largeness of the Bekenstein entropy implies a vast space of gravitational solutions, which are conjectured to be fuzzball configurations. In the WKB approximation, the wave functional for a collapsing shell is oscillatory in a small region of superspace, and the classical approximation picks out this part. But the wave functional will be damped (“under the barrier”) in the remainder of this vast superspace. We perform a simple computation to show that at the threshold of black hole formation, the barrier is lowered enough to make the latter part oscillatory; this alters the classical evolution and avoids horizon formation.
PARTICLE ACCELERATION IN RELATIVISTIC MAGNETIZED COLLISIONLESS ELECTRON-ION SHOCKS

We investigate shock structure and particle acceleration in relativistic magnetized collisionless electron-ion shocks by means of 2.5-dimensional particle-in-cell simulations with ion-to-electron mass ratios (m i /m e ) ranging from 16 to 1000. We explore a range of inclination angles between the pre-shock magnetic field and the shock normal. In "subluminal" shocks, where relativistic particles can escape ahead of the shock along the magnetic field lines, ions are efficiently accelerated via the first-order Fermi process. The downstream ion spectrum consists of a relativistic Maxwellian and a high-energy power-law tail, which contains ~5% of ions and ~30% of ion energy. Its slope is -2.1 ± 0.1. The scattering is provided by short-wavelength non-resonant modes produced by Bell's instability, whose growth is seeded by the current of shock-accelerated ions that propagate ahead of the shock. Upstream electrons enter the shock with lower energy than ions (albeit by only a factor of ~5 << m i /m e ), so they are more strongly tied to the field. As a result, only ~ 1% of the incoming electrons are accelerated at the shock before being advected downstream, where they populate a steep power-law tail (with slope -3.5 ± 0.1). For "superluminal" shocks, where relativistic particles cannot outrun the shock along the field, the self-generated turbulence is not strong enough to permit efficient Fermi acceleration, and the ion and electron downstream spectra are consistent with thermal distributions. The incoming electrons are heated up to equipartition with ions, due to strong electromagnetic waves emitted by the shock into the upstream. Thus, efficient electron heating (≳15% of the upstream ion energy) is the universal property of relativistic electron-ion shocks, but significant nonthermal acceleration of electrons (≳2% by number, ≳10% by energy, with slope flatter than -2.5) is hard to achieve in magnetized flows and requires weakly magnetized shocks (magnetization σ ≲ 10- 3 ), where magnetic fields self-generated via the Weibel instability are stronger than the background field. These findings place important constraints on the models of gamma-ray bursts and jets from active galactic nuclei that invoke particle acceleration in relativistic magnetized electron-ion shocks.