cssi/SciSciGPT-SciSciNet huggingface dataset:
Surveying Graduate Students' Attitudes and Approaches to Problem Solving.

Students' attitudes and approaches to problem solving in physics can profoundly influence their motivation to learn and development of expertise. We developed and validated an Attitudes and Approaches to Problem Solving survey by expanding the Attitudes toward Problem Solving survey of Marx and Cummings and administered it to physics graduate students. Comparison of their responses to the survey questions about problem solving in their own graduate-level courses vs problem solving in the introductory physics courses provides insight into their expertise in introductory and graduate-level physics. The physics graduate students' responses to the survey questions were also compared with those of introductory physics and astronomy students and physics faculty. We find that, even for problem solving in introductory physics, graduate students' responses to some survey questions are less expertlike than those of the physics faculty. Comparison of survey responses of graduate students and introductory students for problem solving in introductory physics suggests that graduate students' responses are in general more expertlike than those of introductory students. However, survey responses suggest that graduate-level problem solving by graduate students on several measures has remarkably similar trends to introductory-level problem solving by introductory students.
Hopf algebras and invariants of the Johnson cokernel

We show that if H is a cocommutative Hopf algebra, then there is a natural action of Aut(F_n) on the nth tensor power of H which induces an Out(F_n) action on a quotient \overline{H^{\otimes n}}. In the case when H=T(V) is the tensor algebra, we show that the invariant Tr^C of the cokernel of the Johnson homomorphism studied in [J. Conant, The Johnson cokernel and the Enomoto-Satoh invariant, Algebraic and Geometric Topology, 15 (2015), no. 2, 801--821.] projects to take values in the top dimensional cohomology of Out(F_n) with coefficients in \overline{H^{\otimes n}}. We analyze the n=2 case, getting large families of obstructions generalizing the abelianization obstructions of [J. Conant, M. Kassabov, K. Vogtmann, Higher hairy graph homology, Journal of Topology, Geom. Dedicata 176 (2015), 345--374.].
A Langevin approach to multi-scale modeling

In plasmas, distribution functions often demonstrate long anisotropic tails or otherwise significant deviations from local Maxwellians. The tails, especially if they are pulled out from the bulk, pose a serious challenge for numerical simulations as resolving both the bulk and the tail on the same mesh is often challenging. A multi-scale approach, providing evolution equations for the bulk and the tail individually, could offer a resolution in the sense that both populations could be treated on separate meshes or different reduction techniques applied to the bulk and the tail population. In this letter, we propose a multi-scale method which allows us to split a distribution function into a bulk and a tail so that both populations remain genuine, non-negative distribution functions and may carry density, momentum, and energy. The proposed method is based on the observation that the motion of an individual test particle in a plasma obeys a stochastic differential equation, also referred to as a Langevin equ...
Property RD and the Classification of Traces on Reduced Group $C^*$-algebras of Hyperbolic Groups

In this paper, we show that if G is a non-elementary word hyperbolic group, a ∈ G is an element, and the conjugacy class of a is infinite, then all traces τ : Cred∗(G) → ℂ vanish on a. Moreover, we completely classify all traces by showing that traces θ : Cred∗(G) → ℂ are linear combinations of traces χg : Cred∗(G) → ℂ given by χg(h) = 1h ∈ C(g),0 else , where g is an element with finite conjugacy class, denoted C(g). We demonstrate these two statements by introducing a new method to study traces that uses Sobolev norms and the rapid decay property.
Tea: A High-level Language and Runtime System for Automating Statistical Analysis

Though statistical analyses are centered on research questions and hypotheses, current statistical analysis tools are not. Users must first translate their hypotheses into specific statistical tests and then perform API calls with functions and parameters. To do so accurately requires that users have statistical expertise. To lower this barrier to valid, replicable statistical analysis, we introduce Tea, a high-level declarative language and runtime system. In Tea, users express their study design, any parametric assumptions, and their hypotheses. Tea compiles these high-level specifications into a constraint satisfaction problem that determines the set of valid statistical tests and then executes them to test the hypothesis. We evaluate Tea using a suite of statistical analyses drawn from popular tutorials. We show that Tea generally matches the choices of experts while automatically switching to non-parametric tests when parametric assumptions are not met. We simulate the effect of mistakes made by non-expert users and show that Tea automatically avoids both false negatives and false positives that could be produced by the application of incorrect statistical tests.
QUANTUM SIMULATION OF SIMPLE MANY-BODY DYNAMICS

We describe a general quantum computational algorithm that simulates the time evolution of an arbitrary nonrelativistic, Coulombic many-body system in three dimensions, considering only spatial degrees of freedom. We use a simple discretized model of Schrodinger evolution in the coordinate representation and discuss detailed constructions of the operators necessary to realize the scheme of Wiesner and Zalka. The algorithm is simulated numerically for small test cases, and its outputs are found to be in good agreement with analytical solutions.
Opportunistic Synthesis in Reactive Games under Information Asymmetry

Reactive synthesis is a class of methods to construct a provably-correct control system, referred to as a robot, with respect to a temporal logic specification in the presence of a dynamic and uncontrollable environment. This is achieved by modeling the interaction between the robot and its environment as a two-player zero-sum game. However, existing reactive synthesis methods assume both players to have complete and symmetrical information, which is not the case in many strategic interactions. In this paper, we use a variant of hypergames to model the interaction between the robot and its environment; where the latter has incomplete information about the specification of the robot. We propose a novel method of opportunistic synthesis defined over the hypergame model to identify a subset of hypergame states from where the robot can leverage the asymmetrical information to achieve a better outcome, which is not possible if both players have symmetrical and complete information. By assuming the environment to play a stochastic strategy in its perceived sure-winning and sure-losing regions of the game, we show that by following the opportunistic strategy, the robot is ensured to only improve the outcome of the game—measured by satisfaction of sub-specifications—whenever an opportunity becomes available. We demonstrate the correctness and optimality of this method using a robot motion planning example in the presence of an adversary.
Hubble Parameter Measurement Constraints on the Redshift of the Deceleration–acceleration Transition, Dynamical Dark Energy, and Space Curvature

Citation: Farooq, O., Madiyar, F. R., Crandall, S., & Ratra, B. (2017). HUBBLE PARAMETER MEASUREMENT CONSTRAINTS ON THE REDSHIFT OF THE DECELERATION-ACCELERATION TRANSITION, DYNAMICAL DARK ENERGY, AND SPACE CURVATURE. Astrophysical Journal, 835(1), 11. doi:10.3847/1538-4357/835/1/26
Superconducting nanowire single-photon detector with integrated impedance-matching taper

Conventional readout of a superconducting nanowire single-photon detector (SNSPD) sets an upper bound on the output voltage to be the product of the bias current and the load impedance, IB × Zload, where Zload is limited to 50 Ω in standard r.f. electronics. Here, we break this limit by interfacing the 50 Ω load and the SNSPD using an integrated superconducting transmission line taper. The taper is a transformer that effectively loads the SNSPD with high impedance without latching. At the expense of reduced maximum counting rate, it increases the amplitude of the detector output while preserving the fast rising edge. Using a taper with a starting width of 500 nm, we experimentally observed a 3.6× higher pulse amplitude, 3.7× faster slew rate, and 25.1 ps smaller timing jitter. The results match our numerical simulation, which incorporates both the hotspot dynamics in the SNSPD and the distributed nature in the transmission line taper. The taper studied here may become a useful tool to interface high-impedance superconducting nanowire devices to conventional low-impedance circuits.
Scaling limits of a model for selection at two scales

The dynamics of a population undergoing selection is a central topic in evolutionary biology. This question is particularly intriguing in the case where selective forces act in opposing directions at two population scales. For example, a fast-replicating virus strain outcompetes slower-replicating strains at the within-host scale. However, if the fast-replicating strain causes host morbidity and is less frequently transmitted, it can be outcompeted by slower-replicating strains at the between-host scale. Here we consider a stochastic ball-and-urn process which models this type of phenomenon. We prove the weak convergence of this process under two natural scalings. The first scaling leads to a deterministic nonlinear integro-partial differential equation on the interval [0,1] with dependence on a single parameter, λ. We show that the fixed points of this differential equation are Beta distributions and that their stability depends on λ and the behavior of the initial data around 1. The second scaling leads to a measure-valued Fleming–Viot process, an infinite dimensional stochastic process that is frequently associated with a population genetics.
Marginally Trapped Tubes Generated from Nonlinear Scalar Field Initial Data

We show that the maximal future development of asymptotically flat spherically symmetric black hole initial data for a self-gravitating nonlinear scalar field, also called a Higgs field, contains a connected, achronal, spherically symmetric marginally trapped tube which is asymptotic to the event horizon of the black hole, provided the initial data is sufficiently small and decays like \({O(r^{-\frac{1}{2}})}\), and the potential function V is nonnegative with bounded second derivative. This result can be loosely interpreted as a statement about the stability of ‘nice’ asymptotic behavior of marginally trapped tubes under certain small perturbations of Schwarzschild.
Cyclohexane Vibrations: High-Resolution Spectra and Anharmonic Local Mode Calculations.

High-resolution infrared absorption spectra of cyclohexane have been recorded from 1100 to 4000 cm-1 at room temperature and 241 K. Cyclohexane is an oblate symmetric top with D3d symmetry. A rotational analysis was obtained for the ν27 (eu) and ν14 (a2u) CH2 scissor modes at 1452.9 and 1456.4 cm-1, respectively. Several combination modes were also assigned and rotationally analyzed. The C-H stretching modes are perturbed by overtone and combination modes of the CH2 scissor vibrations, and an anharmonic local mode calculation was needed to interpret the spectra. The four main strong allowed C-H stretching modes appear as two a2u eu pairs near at 2862 and 2933 cm-1. The Fermi-resonance local mode model coupling terms give physical insight into the effects that organize the cyclohexane vibrational energy levels. The unstrained cyclohexane molecule is a useful paradigm for six-membered rings in larger chemical and biological systems.
ESTIMATE OF THE TOTAL MECHANICAL FEEDBACK ENERGY FROM GALAXY CLUSTER-CENTERED BLACK HOLES: IMPLICATIONS FOR BLACK HOLE EVOLUTION, CLUSTER GAS FRACTION, AND ENTROPY

The total feedback energy injected into hot gas in galaxy clusters by central black holes can be estimated by comparing the potential energy of observed cluster gas profiles with the potential energy of non-radiating, feedback-free hot gas atmospheres resulting from gravitational collapse in clusters of the same total mass. Feedback energy from cluster-centered black holes expands the cluster gas, lowering the gas-to-dark-matter mass ratio below the cosmic value. Feedback energy is unnecessarily delivered by radio-emitting jets to distant gas far beyond the cooling radius where the cooling time equals the cluster lifetime. For clusters of mass (4-11) x 10{sup 14} M{sub sun}, estimates of the total feedback energy, (1-3) x 10{sup 63} erg, far exceed feedback energies estimated from observations of X-ray cavities and shocks in the cluster gas, energies gained from supernovae, and energies lost from cluster gas by radiation. The time-averaged mean feedback luminosity is comparable to those of powerful quasars, implying that some significant fraction of this energy may arise from the spin of the black hole. The universal entropy profile in feedback-free gaseous atmospheres in Navarro-Frenk-White cluster halos can be recovered by multiplying the observed gas entropy profile of any relaxed cluster by a factor involvingmore » the gas fraction profile. While the feedback energy and associated mass outflow in the clusters we consider far exceed that necessary to stop cooling inflow, the time-averaged mass outflow at the cooling radius almost exactly balances the mass that cools within this radius, an essential condition to shut down cluster cooling flows.« less
Big-Bang Nucleosynthesis after Planck

We assess the status of big-bang nucleosynthesis (BBN) in light of the final Planck data release and other recent developments, and in anticipation of future measurements. Planck data fix the cosmic baryon density to 0.9% precision, and determine the helium abundance and effective number of neutrinos with precision approaching that of astronomical and BBN determinations respectively. In addition, new high-redshift measurements give D/H to better precision than theoretical predictions, and new Li/H data reconfirm the lithium problem. We present new ${}^{7}{\rm Be}(n,p){}^{7}{\rm Li}$ rates using new neutron capture measurements; we have also examined the effect of proposed changes in the $d(p,\gamma){}^{3}{\rm He}$ rates. Using these results we perform a series of likelihood analyses. We assess BBN/CMB consistency, with attention to how our results depend on the choice of Planck data, as well as how the results depend on the choice of non-BBN, non-Planck data sets. Most importantly the lithium problem remains, and indeed is more acute given the very tight D/H observational constraints; new neutron capture data reveals systematics that somewhat increases uncertainty and thus slightly reduces but does not essentially change the problem. We confirm that $d(p,\gamma){}^{3}{\rm He}$ theoretical rates brings D/H out of agreement and slightly increases 7Li; new experimental data are needed at BBN energies. Setting the lithium problem aside, we find the effective number of neutrino species at BBN is $N_\nu = 2.86 \pm 0.15$. Future CMB Stage-4 measurements promise substantial improvements in BBN parameters: helium abundance determinations will be competitive with the best astronomical determinations, and $N_{\rm eff}$ will approach sensitivities capable of detecting the effects of Standard Model neutrino heating of the primordial plasma. (Abridged)
GMC Origins and Turbulent Motions in Spiral and Dwarf Galaxies

CO clouds can be non-self-gravitating in high pressure environments, while most should be strongly self-gravitating at low metallicities and ambient pressures. In the LMC, which is HI-rich, GMC formation and destruction should generally include molecule formation and destruction. In M51, which is CO-rich, GMCs grow by coalescence. The Milky Way is between these two situations. In all cases, large clouds form by accretion of gas and smaller clouds independently of the presence of molecules. GMCs in the Milky Way are analogous to dust lanes and spurs in other galaxies. The virial parameter alpha usually decreases monotonically with increasing cloud mass in surveys, which implies that small scale structure is formed by turbulence. Hierarchies of sequences with decreasing alpha should be present in cloud complexes from sub-solar masses up to the ambient Jeans mass (10^7 Msun).
NEUTRINO SCATTERING IN A NEWLY BORN NEUTRON STAR

We calculate neutrino cross sections from neutral-current reactions in the dense matter encountered in the evolution of a newly born neutron star. Effects of composition and of strong interactions in the deleptonization and cooling phases of the evolution are studied. The influence of the possible presence of strangeness-rich hyperons on the neutrino scattering cross sections is explored. Due to the large vector couplings of the Σ- and Ξ-, |CV| ~ 2, these particles, if present in protoneutron star matter, give significant contributions to neutrino scattering. In the deleptonization phase, the presence of strangeness leads to large neutrino energies, which results in large enhancements in the cross sections compared to those in matter with nucleons only. In the cooling phase, in which matter is nearly neutrino-free, the response of the Σ- hyperons to thermal neutrinos is the most significant. Neutrinos couple relatively weakly to the Λ hyperons and, hence, their contributions are significant only at high density.
Social goods dilemmas in heterogeneous societies

Prosocial behaviours are encountered in the donation game, the prisoner’s dilemma, relaxed social dilemmas and public goods games. Many studies assume that the population structure is homogeneous, meaning that all individuals have the same number of interaction partners or that the social good is of one particular type. Here, we explore general evolutionary dynamics for arbitrary spatial structures and social goods. We find that heterogeneous networks, in which some individuals have many more interaction partners than others, can enhance the evolution of prosocial behaviours. However, they often accumulate most of the benefits in the hands of a few highly connected individuals, while many others receive low or negative payoff. Surprisingly, selection can favour producers of social goods even if the total costs exceed the total benefits. In summary, heterogeneous structures have the ability to strongly promote the emergence of prosocial behaviours, but they also create the possibility of generating large inequality. Prosocial behaviours are ubiquitous in nature. These building blocks of cooperative societies can come in many forms, depending on how the underlying social good is produced and distributed. In this study, the authors show that heterogeneous populations can strongly promote the evolution of prosocial behaviours. However, this efficient evolution reveals a thorny side of prosocial behaviours: they generate the possibility of widespread wealth inequality, even to the point of being a detriment to the poorest in the population. The authors provide a general framework that can be used to understand when this harmful prosociality will emerge in a population. These findings suggest that institutional interventions are often essential for maintaining equitable outcomes in heterogeneous societies.
Spectral-based k-corrections and implications for the colour-magnitude relation of E/S0s and its evolution

We select a sample of 70 378 E/S0 (early-type) galaxies at 0 < z < 0.36 from the Sloan Digital Sky Survey (SDSS), excluding disc and star-forming galaxies. We estimate g and r magnitudes in the observer- and rest frames directly from the SDSS DR6 spectra; this provides an object-by-object estimate of the k-correction. Observer-frame colours can also be estimated from the imaging photometry. However, in this case, rest-frame colours, and hence k-corrections, must be inferred from fitting to data in other band passes as well as to stellar population synthesis models. There are small (a few 0.01 mag) discrepancies between the spectra and imaging photometry, particularly for galaxies with low signal-to-noise ratios in the spectra and more negative eclass spectral classifications. We correct for these, and then use the k-corrections from the spectra to study the evolution of the rest-frame colour-magnitude relation (CMR) and colour-σ relation CσR). Both the CMR and CσR evolve bluewards with increasing redshift, approximately in agreement with passive evolution models with age ~12 Gyr. The rate of evolution is sensitive to the k-corrections. Using k-corrections from the Coleman, Wu & Weedman (CWW) template spectrum, rather than the observed SDSS spectra, gives a CMR with much more evolution; k-corrections from Blanton & Roweis, which are based on fitting Bruzual & Charlot models with solar abundance ratios to the ugriz colours, give less/no evolution. However, the slope and zero-point of CMR depends on whether colours were defined in fixed physical or angular apertures, a consequence of the fact that the centres of these objects tend to be redder: the relation is steeper for fixed angular apertures. These colour gradients must be accounted for when estimating CMR evolution with fixed angular apertures. On the other hand, although the zero-point of the CσR depends on the aperture in which the colour was defined, the slope does not, suggesting that colour gradients are correlated with residuals from the σ-M r relation. Since these residuals are age indicators, our findings suggest that colour gradients depend on the age of the stellar population.
SKIFFS: Superconducting Kinetic Inductance Field-Frequency Sensors for sensitive magnetometry in moderate background magnetic fields

We describe sensitive magnetometry using lumped-element resonators fabricated from a superconducting thin film of NbTiN. Taking advantage of the large kinetic inductance of the superconductor, we demonstrate a continuous resonance frequency shift of 27 MHz for a change in the magnetic field of 1.8 μT within a perpendicular background field of 60 mT. By using phase-sensitive readout of microwaves transmitted through the sensors, we measure phase shifts in real time with a sensitivity of 1°/nT. We present measurements of the noise spectral density of the sensors and find that their field sensitivity is at least within one to two orders of magnitude of superconducting quantum interference devices operating with zero background field. Our superconducting kinetic inductance field-frequency sensors enable real-time magnetometry in the presence of moderate perpendicular background fields up to at least 0.2 T. Applications for our sensors include the stabilization of magnetic fields in long coherence electron spin resonance measurements and quantum computation.
Programmable multi-node quantum network design and simulation

Software-defined networking offers a device-agnostic programmable framework to encode new network functions. Externally centralized control plane intelligence allows programmers to write network applications and to build functional network designs. OpenFlow is a key protocol widely adopted to build programmable networks because of its programmability, flexibility and ability to interconnect heterogeneous network devices. We simulate the functional topology of a multi-node quantum network that uses programmable network principles to manage quantum metadata for protocols such as teleportation, superdense coding, and quantum key distribution. We first show how the OpenFlow protocol can manage the quantum metadata needed to control the quantum channel. We then use numerical simulation to demonstrate robust programmability of a quantum switch via the OpenFlow network controller while executing an application of superdense coding. We describe the software framework implemented to carry out these simulations and we discuss near-term efforts to realize these applications.
Ensemble estimation of multivariate f-divergence

f-divergence estimation is an important problem in the fields of information theory, machine learning, and statistics. While several divergence estimators exist, relatively few of their convergence rates are known. We derive the MSE convergence rate for a density plug-in estimator of f-divergence. Then by applying the theory of optimally weighted ensemble estimation, we derive a divergence estimator with a convergence rate of O(1/T) that is simple to implement and performs well in high dimensions. We validate our theoretical results with experiments.
Canonical measures on metric graphs and a Kazhdan’s theorem

We extend the notion of canonical measures to all (possibly non-compact) metric graphs. This will allow us to introduce a notion of “hyperbolic measures” on universal covers of metric graphs. Kazhdan’s theorem for Riemann surfaces describes the limiting behavior of canonical (Arakelov) measures on finite covers in relation to the hyperbolic measure. We will prove a generalized version of this theorem for metric graphs, allowing any infinite Galois cover to replace the universal cover. We will show all such limiting measures satisfy a version of Gauss–Bonnet formula which, using the theory of von Neumann dimensions, can be interpreted as a “trace formula”. In the special case where the infinite cover is the universal cover, we will provide explicit methods to compute the corresponding limiting (hyperbolic) measure. Our ideas are motivated by non-Archimedean analytic and tropical geometry.
Quantum criticality and novel phases: A panel discussion

In August 2009, physicists gathered in Dresden for a conference on "Quantum Criticality and Novel Phases." As one part of the meeting, nine panelists hosted an open and free-wheeling discussion on the topic of the meeting. This article outlines the discussions that took place during this panel-meeting on the afternoon of August 3, 2009.
Two-bit bit flipping decoding of LDPC codes

In this paper, we propose a new class of bit flipping algorithms for low-density parity-check (LDPC) codes over the binary symmetric channel (BSC). Compared to the regular (parallel or serial) bit flipping algorithms, the proposed algorithms employ one additional bit at a variable node to represent its “strength.” The introduction of this additional bit increases the guaranteed error correction capability by a factor of at least 2. An additional bit can also be employed at a check node to capture information which is beneficial to decoding. A framework for failure analysis of the proposed algorithms is described. These algorithms outperform the Gallager A/B algorithm and the min-sum algorithm at much lower complexity. Concatenation of two-bit bit flipping algorithms show a potential to approach the performance of belief propagation (BP) decoding in the error floor region, also at lower complexity.
Constant-Depth and Subcubic-Size Threshold Circuits for Matrix Multiplication

Boolean circuits of McCulloch-Pitts threshold gates are a classic model of neural computation studied heavily in the late 20th century as a model of general computation. Recent advances in large-scale neural computing hardware has made their practical implementation a near-term possibility. We describe a theoretical approach for multiplying two N by N matrices that integrates threshold gate logic with conventional fast matrix multiplication algorithms, that perform $O(N^omega)$ arithmetic operations for a positive constant $omega
Online data assimilation in distributionally robust optimization

This paper considers a class of real-time decision making problems to minimize the expected value of a function that depends on a random variable ξ under an unknown distribution P. In this process, samples of ξ are collected sequentially in real time, and the decisions are made, using the real-time data, to guarantee out-of-sample performance. We approach this problem in a distributionally robust optimization framework and propose a novel Online Data Assimilation Algorithm for this purpose. This algorithm guarantees the out-of-sample performance in high probability, and gradually improves the quality of the data-driven decisions by incorporating the streaming data. We show that the Online Data Assimilation Algorithm guarantees convergence under the streaming data, and a criteria for termination of the algorithm after certain number of data has been collected.
Nearest Neighbor Distances on a Circle: Multidimensional Case

We study the distances, called spacings, between pairs of neighboring energy levels for the quantum harmonic oscillator. Specifically, we consider all energy levels falling between E and E+1, and study how the spacings between these levels change for various choices of E, particularly when E goes to infinity. Primarily, we study the case in which the spring constant is a badly approximable vector. We first give the proof by Boshernitzan-Dyson that the number of distinct spacings has a uniform bound independent of E. Then, if the spring constant has components forming a basis of an algebraic number field, we show that, when normalized up to a unit, the spacings are from a finite set. Moreover, in the specific case that the field has one fundamental unit, the probability distribution of these spacings behaves quasiperiodically in logE. We conclude by studying the spacings in the case that the spring constant is not badly approximable, providing examples for which the number of distinct spacings is unbounded.
Synthesis from Probabilistic Components

Synthesis is the automatic construction of a system from its specification. In classical synthesis algorithms, it is always assumed that the system is "constructed from scratch" rather than composed from reusable components. This, of course, rarely happens in real life, where almost every non-trivial commercial software system relies heavily on using libraries of reusable components. Furthermore, other contexts, such as web-service orchestration, can be modeled as synthesis of a system from a library of components. Recently, Lustig and Vardi introduced dataflow and control-flow synthesis from libraries of reusable components. They proved that dataflow synthesis is undecidable, while control-flow synthesis is decidable. In this work, we consider the problem of control-flow synthesis from libraries of probabilistic components . We show that this more general problem is also decidable.
Phase tropical hypersurfaces

We prove a conjecture of Viro (Tr. Mat. Inst. Steklova 273 (2011) 271–303) that a smooth complex hypersurface in ( ℂ ∗ ) n is homeomorphic to the corresponding phase tropical hypersurface.
High-Resolution X-Ray Spectroscopy of the Accretion Disk Corona Source 4U 1822–37

We present a preliminary analysis of the X-ray spectrum of the accretion disk corona source 4U 1822-37 obtained with the High-Energy Transmission Grating Spectrometer on board the Chandra X-Ray Observatory. We detect discrete emission lines from photoionized iron, silicon, magnesium, neon, and oxygen as well as a bright iron fluorescent line. Phase-resolved spectroscopy suggests that the recombination emission comes from an X-ray-illuminated bulge located at the predicted point of impact between the disk and the accretion stream. The fluorescent emission originates in an extended region on the disk that is illuminated by light scattered from the corona.
Sensitivity Challenge of Steep Transistors

Steep transistors are crucial in lowering power consumption of the ICs. However, the difficulties in achieving steepness beyond the Boltzmann limit experimentally have hindered the fundamental challenges in application of these devices in ICs. From a sensitivity perspective, an ideal switch should have a high sensitivity to the gate voltage and lower sensitivity to the device design parameters such as oxide and body thicknesses. In this paper, conventional tunnel-FET (TFET) and negative capacitance FET are shown to suffer from high sensitivity to device design parameters using full-band atomistic quantum transport simulations and analytical analysis. Although dielectric-engineered (DE)-TFETs based on 2-D materials show smaller sensitivity compared with the conventional TFETs, they have leakage issue. To mitigate this challenge, a novel DE-TFET design has been proposed and studied.
Maximizing the sum of radii of disjoint balls or disks

Finding nonoverlapping balls with given centers in any metric space, maximizing the sum of radii of the balls, can be expressed as a linear program. Its dual linear program expresses the problem of finding a minimum-weight set of cycles (allowing 2-cycles) covering all vertices in a complete geometric graph. For points in a Euclidean space of any finite dimension $d$, with any convex distance function on this space, this graph can be replaced by a sparse subgraph obeying a separator theorem. This graph structure leads to an algorithm for finding the optimum set of balls in time $O(n^{2-1/d})$, improving the $O(n^3)$ time of a naive cycle cover algorithm. As a subroutine, we provide an algorithm for weighted bipartite matching in graphs with separators, which speeds up the best previous algorithm for this problem on planar bipartite graphs from $O(n^{3/2}\log n)$ to $O(n^{3/2})$ time.
Broadband circular polarization time-domain terahertz spectroscopy

Light-matter interactions are key in providing fundamental information about materials. Even in the linear-response regime, the spectroscopic response of a material encodes in it many properties of the ground state as well as of its excitations. This knowledge has been critical in our understanding of novel quantum materials, and the further improvement and extensions of linear spectroscopy will continue to be key in the exploration of novel states of matter. We report the development of broadband circular polarization spectroscopy in the terahertz range of the electromagnetic spectrum. We take advantage of a recent design of a broadband quarter wave plate, based on the Fresnel rhomb concept, and use it in conjunction with a polarization modulation technique to provide direct information of the response of a material to circularly polarized THz radiation. As an example of this technique we study the cyclotron resonance of a 2D electron gas from a AlGaAs-GaAs quantum well. We demonstrate the unique advantages that this technique will bring in the study of novel quantum materials.
Derrick's theorem beyond a potential

Scalar field theories with derivative interactions are known to possess solitonic excitations, but such solitons are generally unsatisfactory because the effective theory fails precisely where nonlinearities responsible for the solitons are important. A new class of theories possessing (internal) galilean invariance can in principle bypass this difficulty. Here, we show that these galileon theories do not possess stable solitonic solutions. As a by-product, we show that no stable solitons exist for a different class of derivatively coupled theories, describing for instance the infrared dynamics of superfluids, fluids, solids and some k-essence models.
Iron Emission in the z=6.4 Quasar SDSS J114816.64+525150.3

We present near-infrared J- and K-band spectra of the z = 6.4 quasar SDSS J114816.64+525150.3 obtained with the NIRSPEC spectrograph at the Keck II telescope, covering the rest-frame spectral regions surrounding the C IV λ1549 and Mg II λ2800 emission lines. The iron emission blend at rest wavelength 2900-3000 A is clearly detected, and its strength appears nearly indistinguishable from that of typical quasars at lower redshifts. The Fe II/Mg II ratio is also similar to values found for lower redshift quasars, demonstrating that there is no strong evolution in Fe/α broad-line emission ratios even out to z = 6.4. In the context of current models for iron enrichment from Type Ia supernovae (SNe Ia), this implies that the SN Ia progenitor stars formed at z 10. We apply the scaling relations of Vestergaard and of McLure & Jarvis to estimate the black hole mass from the widths of the C IV and Mg II emission lines and the ultraviolet continuum luminosity. The derived mass is in the range (2-6) × 109 M☉, with an additional uncertainty of a factor of 3 due to the intrinsic scatter in the scaling relations. This result is in agreement with the previous mass estimate of 3 × 109 M☉ by Willott, McLure, & Jarvis and supports their conclusion that the quasar is radiating close to its Eddington luminosity.
On Fiber Diameters of Continuous Maps

We present a surprisingly short proof that for any continuous map f: ℝn → ℝ;m, if n > m, then there exists no bound on the diameter of fibers of f. Moreover, we show that when m = 1, the union of s...
Morphological Statistics of the Cosmic Web

We report the first systematic study of the supercluster-void network in the ΛCDM concordance cosmology treating voids and superclusters on an equal footing. We study the dark matter density field in real space smoothed with the Ls = 5 h 1 Mpc Gaussian window. Super- clusters and voids are defined as individual members of over-dense and under-dense excursion sets respectively. We determine the morphological properties of the cosmic web at a large num- ber of dark matter density levels by computing Minkowski functionals for every supercluster and void. At the adopted smoothing scale individual superclusters totally occupy no more than about 5% of the total volume and contain no more than 20% of mass if the largest supercluster is excluded. Likewise, individual voids totally occupy no more than 14% of volume and contain no more than 4% of mass if the largest void is excluded. The genus of individual superclusters can be � 5 while the genus of individual voids reaches � 55, implying significant amount of substructure in superclusters and especially in voids. Large voids are typically distinctly non- spherical. � = const. At a given thresholdth regions hav- ing higher then threshold density (� > �th) will be called "superclusters", while regions with � < �th will be called "voids" We employ an elaborate surface modeling scheme, SURFGEN (short for 'surface generator'), that allows us to determine the geometry, mor- phology and topology of excursion sets defined on a density field in a very comprehensive manner (Sheth et al.2003). Working with the density field also permits us to determine the morphological properties of the full excursion set describing the supercluster-void network. More detailed information is then gleaned at one particular threshold (usually associated with percolation) at which shapes and sizes of individual superclusters and voids yield rich information about properties of the cosmic web to which we belong. We use dark matter distributions in a flat model with 0 = 0.3, � = 0.7, h = 0.7 ( LCDM). The initial spectrum was taken with the shape parameter Γ = 0.21. The amplitude (�8 = 0.9) of the power spectrum in the model is set so as to reproduce the observed abundance of rich galaxy clusters at the present epoch (see Jenkins et al.1998 for details). The study of mocked galaxy distributions was done by Sheth (2003). SURFGEN operates on three-dimensional pixelized maps. Therefore we first gener- ate the density field from the distribution of dark matter particles. This process was described in detail in Sheth et al.(2003); here we present a brief summary. The data consist of 256 3 particles in a box of size 239.5 h 1 Mpc. We fit a 128 3 grid to the box. We follow the smoothing technique used by Springel et al.(1998) which they adopted
Gravitational Tunneling Radiation

The isolated black hole radiation of both Hawking and Zel’dovich are idealized abstractions as there is always another body to distort the potential. This is considered with respect to both gravitational tunneling, and black hole “no-hair” theorems. The effects of a second body are to lower the gravitational barrier of a black hole and to give the barrier a finite rather than infinite width so that a particle can escape by tunneling (as in field emission) or over the top of the lowered barrier (as in Schottky emission). Thus radiation may be emitted from black holes in a process differing from that of Hawking radiation, PSH , which has been undetected for over 24 years. The radiated power from a black hole derived here is PR ∝ e PSH, where e-2∆γ is the transmission probability for radiation through the barrier. This is similar to electric field emission of electrons from a metal in that the emission can in principle be modulated and beamed. The temperature and entropy of black holes are reexamined. Miniscule black holes herein may help explain the missing mass of the universe, accelerated expansion of the universe, and anomalous rotation of spiral galaxies. A gravitational interference effect for black hole radiation similar to the Aharonov-Bohm effect is also examined.
Chern Class Identities from Tadpole Matching in Type IIB and F-Theory

In light of Sen's weak coupling limit of F-theory as a type IIB orientifold, the compatibility of the tadpole conditions leads to a non-trivial identity relating the Euler characteristics of an elliptically fibered Calabi-Yau fourfold and of certain related surfaces. We present the physical argument leading to the identity, and a mathematical derivation of a Chern class identity which confirms it, after taking into account singularities of the relevant loci. This identity of Chern classes holds in arbitrary dimension, and for varieties that are not necessarily Calabi-Yau. Singularities are essential in both the physics and the mathematics arguments: the tadpole relation may be interpreted as an identity involving stringy invariants of a singular hypersurface, and corrections for the presence of pinch-points. The mathematical discussion is streamlined by the use of Chern-Schwartz-MacPherson classes of singular varieties. We also show how the main identity may be obtained by applying `Verdier specialization' to suitable constructible functions.
A remark on T-duality and quantum volumes of zero-brane moduli spaces

T-duality (Fourier-Mukai duality) and properties of classical instanton moduli spaces can be used to deduce some properties of α'-corrected moduli spaces of branes for type-IIA string theory compactified on K3 or 4. Some interesting differences between the two compactifications are exhibited.
A Measurement of Radius Inflation in the Pleiades and Its Relation to Rotation and Lithium Depletion

Precise measurements of eclipsing binary parameters and statistical studies of young clusters have suggested that some magnetically active low-mass dwarfs possess radii inflated by $\sim$5-15% relative to theoretical expectations. If true, this effect should be pronounced in young open clusters, due to the rapid rotation and strong magnetic activity of their most extreme members. We explore this possibility by determining empirical radii for 83 members of the nearby Pleiades open cluster, using spectral energy distribution fitting to establish $\mathcal{F}_{bol}$ with a typical accuracy of $\approx$3\% together with color and spectro-photometric indices to determine $T_{\rm eff}$. We find several Pleiades members with radii inflated above radius-$T_{\rm eff}$ models from state-of-the-art calculations, and apparent dispersions in radii for the K-dwarfs of the cluster. Moreover, we demonstrate that this putative radius inflation correlates strongly with rotation rate, consistent with inflation of young stars by magnetic activity and/or starspots. We argue that this signal is not a consequence of starspot-induced color anomalies, binarity, or depth effects in the cluster, employing Gaia DR1 distances as a check. Finally, we consider the lithium abundances of these stars, demonstrating a triple correlation between rotation rate, radius inflation, and enhanced lithium abundance. Our result---already significant to $\sim$99.99% confidence---provides strong support for a magnetic origin of the inflated radii and lithium dispersion observed in young, low-mass stars.
Jet quenching in shock waves

We study the propagation of an ultrarelativistic light quark jet inside a shock wave using the holographic principle. The maximum stopping distance and its dependency on the energy of the jet is obtained.
A combinatorial approach to Voiculescu’s bi-free partial transforms

In this paper, we present a combinatorial approach to the 2-variable bi-free partial $S$- and $T$-transforms recently discovered by Voiculescu. This approach produces an alternate definition of said transforms using $(\ell, r)$-cumulants.
Enhanced Mobility With Connectivity and Automation: A Review of Shared Autonomous Vehicle Systems

Shared mobility can provide access to transportation on a custom basis without vehicle ownership. The advent of connected and automated vehicle technologies can further enhance the potential benefits of shared mobility systems. Although the implications of a system with shared autonomous vehicles have been investigated, the research reported in the literature has exhibited contradictory outcomes. In this paper, we present a summary of the research efforts in shared autonomous vehicle systems that have been reported in the literature to date and discuss potential future research directions.
Evidence for Proportionate Partition Between the Magnetic Field and Hot Gas in Turbulent Cassiopeia A

We present a deep X-ray observation of the young Galactic supernova remnant Cassiopeia A, acquired with the ROSAT High Resolution Imager. This high dynamic range (232 ks) image reveals low surface brightness X-ray structure that appears qualitatively similar to corresponding radio features. We consider the correlation between the X-ray and radio morphologies and its physical implications. After correcting for the inhomogeneous absorption across the remnant, we performed a point-by-point (4'' resolution) surface brightness comparison between the X-ray and radio images. We find a strong (r=0.75) log-log correlation, implying an overall relationship of log(ΣX-ray) ∝ (2.21 ± 0.05) × log(Σradio). This is consistent with proportionate partition (and possibly equipartition) between the local magnetic field and the hot gas—implying that Cas A's plasma is fully turbulent and continuously amplifying the magnetic field.
Bayesian forecasting of multivariate time series: scalability, structure uncertainty and decisions

I discuss recent research advances in Bayesian state-space modeling of multivariate time series. A main focus is on the “decouple/recouple” concept that enables application of state-space models to increasingly large-scale data, applying to continuous or discrete time series outcomes. Applied motivations come from areas such as financial and commercial forecasting and dynamic network studies. Explicit forecasting and decision goals are often paramount and should factor into model assessment and comparison, a perspective that is highlighted. The Akaike Memorial Lecture is a context to reflect on the contributions of Hirotugu Akaike and to promote new areas of research. In this spirit, this paper aims to promote new research on foundations of statistics and decision analysis, as well as on further modeling, algorithmic and computational innovation in dynamic models for increasingly complex and challenging problems in multivariate time series analysis and forecasting.
Stabilizing dilaton and moduli vacua in string and M-theory cosmology

Abstract We show how non-trivial form fields can induce an effective potential for the dilaton and metric moduli in compactifications of type II string theory and M-theory. For particular configurations, the potential can have a stable minimum. In cosmological compactifications of type II theories, we demonstrate that, if the metric moduli become fixed, this mechanism can then lead to the stabilization of the dilaton vacuum. Furthermore, we show that for certain cosmological M-theory solutions, non-trivial forms lead to the stabilization of moduli. We present a number of examples, including cosmological solutions with two solitonic forms and examples corresponding to the infinite throat of certain p-branes.