Results for "G. G. Howes"

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Inertial range turbulence in kinetic plasmasNov 27 2007The transfer of turbulent energy through an inertial range from the driving scale to dissipative scales in a kinetic plasma followed by the conversion of this energy into heat is a fundamental plasma physics process. A theoretical foundation for the study ... More
Prediction of the Proton-to-Total Turbulent Heating in the Solar WindJun 21 2011This paper employs a recent turbulent heating prescription to predict the ratio of proton-to-total heating due to the kinetic dissipation of Alfvenic turbulence as a function of heliocentric distance. Comparing to a recent empirical estimate for this ... More
A Dynamical Model of Plasma Turbulence in the Solar WindFeb 13 2015A dynamical approach, rather than the usual statistical approach, is taken to explore the physical mechanisms underlying the nonlinear transfer of energy, the damping of the turbulent fluctuations, and the development of coherent structures in kinetic ... More
Kinetic TurbulenceFeb 13 2015The weak collisionality typical of turbulence in many diffuse astrophysical plasmas invalidates an MHD description of the turbulent dynamics, motivating the development of a more comprehensive theory of kinetic turbulence. In particular, a kinetic approach ... More
A prescription for the turbulent heating of astrophysical plasmasSep 21 2010The ratio of ion to electron heating due to the dissipation of Alfvenic turbulence in astrophysical plasmas is calculated based on a cascade model for turbulence in weakly collisional plasmas. Conditions for validity of this model are discussed, a prescription ... More
Limitations of Hall MHD as a model for turbulence in weakly collisional plasmasMar 24 2009The limitations of Hall MHD as a model for turbulence in weakly collisional plasmas are explored using quantitative comparisons to Vlasov-Maxwell kinetic theory over a wide range of parameter space. The validity of Hall MHD in the cold ion limit is shown, ... More
The Dynamical Generation of Current Sheets in Astrophysical Plasma TurbulenceJul 25 2016Turbulence profoundly affects particle transport and plasma heating in many astrophysical plasma environments, from galaxy clusters to the solar corona and solar wind to Earth's magnetosphere. Both fluid and kinetic simulations of plasma turbulence ubiquitously ... More
The Inherently Three-Dimensional Nature of Magnetized Plasma TurbulenceJun 19 2013Jun 02 2014It is often asserted or implicitly assumed, without justification, that the results of two-dimensional investigations of plasma turbulence are applicable to the three-dimensional plasma environments of interest. A projection method is applied to derive ... More
Twistor spaces for HKT manifoldsFeb 20 1996We construct the twistor space associated with an HKT manifold, that is, a hyper-K\"ahler manifold with torsion, a type of geometry that arises as the target space geometry in two-dimensional sigma models with (4,0) supersymmetry. We show that this twistor ... More
Holonomy groups and W-symmetriesFeb 12 1992Feb 14 1992Irreducible sigma models, i.e. those for which the partition function does not factorise, are defined on Riemannian spaces with irreducible holonomy groups. These special geometries are characterised by the existence of covariantly constant forms which ... More
On the Interpretation of Magnetic Helicity Signatures in the Dissipation Range of Solar Wind TurbulenceOct 27 2009Measurements of small-scale turbulent fluctuations in the solar wind find a non-zero right-handed magnetic helicity. This has been interpreted as evidence for ion cyclotron damping. However, theoretical and empirical evidence suggests that the majority ... More
Patching DFT, T-duality and GerbesDec 23 2016Feb 27 2017We clarify the role of the dual coordinates as described from the perspectives of the Buscher T-duality rules and Double Field Theory. We show that the T-duality angular dual coordinates cannot be identified with Double Field Theory dual coordinates in ... More
Finiteness and anomalies in (4,0) supersymmetric sigma modelsMar 25 1992Power-counting arguments based on extended superfields have been used to argue that two-dimensional supersymmetric sigma models with (4,0) supersymmetry are finite. This result is confirmed up to three loop order in pertubation theory by an explicit calculation ... More
Predicted Impacts of Proton Temperature Anisotropy on Solar Wind TurbulenceMar 02 2015Mar 13 2015Particle velocity distributions measured in the weakly collisional solar wind are frequently found to be non-Maxwellian, but how these non-Maxwellian distributions impact the physics of plasma turbulence in the solar wind remains unanswered. Using numerical ... More
Evidence of Critical Balance in Kinetic Alfven Wave Turbulence SimulationsDec 30 2011A numerical simulation of kinetic plasma turbulence is performed to assess the applicability of critical balance to kinetic, dissipation scale turbulence. The analysis is performed in the frequency domain to obviate complications inherent in performing ... More
(N,p,q) Harmonic SuperspaceDec 16 1994Jan 19 1995A family of harmonic superspaces associated with four-dimensional spacetime is described. Some applications to supersymmetric field theories, including supergravity, are given.
Measuring Collisionless Damping in Heliospheric Plasmas using Field-Particle CorrelationsJul 06 2016An innovative field-particle correlation technique is proposed that uses single-point measurements of the electromagnetic fields and particle velocity distribution functions to investigate the net transfer of energy from fields to particles associated ... More
Current Sheets and Collisionless Damping in Kinetic Plasma TurbulenceApr 10 2013Jun 07 2013We present the first study of the formation and dissipation of current sheets at electron scales in a wave-driven, weakly collisional, 3D kinetic turbulence simulation. We investigate the relative importance of dissipation associated with collisionless ... More
Alfven Wave Collisions, The Fundamental Building Block of Plasma Turbulence I: Asymptotic SolutionJun 06 2013The nonlinear interaction between counterpropagating Alfven waves is the physical mechanism underlying the cascade of energy to small scales in astrophysical plasma turbulence. Beginning with the equations for incompressible MHD, an asymptotic analytical ... More
Twistor Spaces for QKT ManifoldsOct 08 1997We find that the target space of two-dimensional (4,0) supersymmetric sigma models with torsion coupled to (4,0) supergravity is a QKT manifold, that is, a quaternionic K\"ahler manifold with torsion. We give four examples of geodesically complete QKT ... More
Gradient Particle MagnetohydrodynamicsJul 24 2001We introduce Gradient Particle Magnetohydrodynamics (GPM), a new Lagrangian method for magnetohydrodynamics based on gradients corrected for the locally disordered particle distribution. The development of a numerical code for MHD simulation using the ... More
Evidence for Electron Landau Damping in Space Plasma TurbulenceFeb 15 2019How turbulent energy is dissipated in weakly collisional space and astrophysical plasmas is a major open question. Here, we present the application of a field-particle correlation technique to directly measure the transfer of energy between the turbulent ... More
Validity of the Taylor Hypothesis for Linear Kinetic Waves in the Weakly Collisional Solar WindMay 21 2014The interpretation of single-point spacecraft measurements of solar wind turbulence is complicated by the fact that the measurements are made in a frame of reference in relative motion with respect to the turbulent plasma. The Taylor hypothesis---that ... More
A Weakened Cascade Model for Turbulence in Astrophysical PlasmasSep 19 2011A refined cascade model for kinetic turbulence in weakly collisional astrophysical plasmas is presented that includes both the transition between weak and strong turbulence and the effect of nonlocal interactions on the nonlinear transfer of energy. The ... More
The Quasilinear Premise for the Modeling of Plasma TurbulenceApr 10 2014The quasilinear premise is a hypothesis for the modeling of plasma turbulence in which the turbulent fluctuations are represented by a superposition of randomly-phased linear wave modes, and energy is transferred among these wave modes via nonlinear interactions. ... More
Alfven Wave Collisions, The Fundamental Building Block of Plasma Turbulence II: Numerical SolutionJun 06 2013This paper presents the numerical verification of an asymptotic analytical solution for the nonlinear interaction between counterpropagating Alfven waves, the fundamental building block of astrophysical plasma turbulence. The analytical solution, derived ... More
Invariants and divergences in half-maximal supergravity theoriesApr 29 2013The invariants in half-maximal supergravity theories in D=4,5 are discussed in detail up to dimension eight (e.g. R^4). In D=4, owing to the anomaly in the rigid SL(2,R) duality symmetry, the restrictions on divergences need careful treatment. In pure ... More
The vanishing volume of D=4 superspaceMay 30 2011Aug 25 2011The volume of on-shell D=4, N=8 superspace is shown to vanish. Despite this, it is shown that there is a fully supersymmetric and duality-invariant candidate d^8 R^4 counterterm corresponding to an anticipated seven-loop logarithmic divergence in D=4. ... More
Local Gravitational Instability of Magnetized Shear FlowsFeb 22 2001The effect of magnetic shear and shear flow on local gravitationally induced instabilities is investigated. A simple model is constructed allowing for an arbitrary entropy gradient and a shear plasma flow in the Boussinesq approximation. A transformation ... More
The ultra-violet question in maximally supersymmetric field theoriesJan 29 2009Feb 11 2009We discuss various approaches to the problem of determining which supersymmetric invariants are permitted as counterterms in maximally supersymmetric super Yang--Mills and supergravity theories in various dimensions. We review the superspace non-renormalisation ... More
A note on the UV behaviour of maximally supersymmetric Yang-Mills theoriesAug 26 2009Oct 05 2009The question of whether BPS invariants are protected in maximally supersymmetric Yang-Mills theories is investigated from the point of view of algebraic renormalisation theory. The protected invariants are those whose cohomology type differs from that ... More
Freely decaying turbulence in two-dimensional electrostatic gyrokineticsAug 07 2012Dec 12 2012In magnetized plasmas, a turbulent cascade occurs in phase space at scales smaller than the thermal Larmor radius ("sub-Larmor scales") [Phys. Rev. Lett. 103, 015003 (2009)]. When the turbulence is restricted to two spatial dimensions perpendicular to ... More
Anomalies and divergences in N=4 supergravityDec 04 2012Feb 28 2013The invariants in D=4, N=4 supergravity are discussed up to the three-loop order (where one expects a general R^4 structure). Because there is an anomaly in the rigid SL(2,R) symmetry of this theory, the analysis of possible restrictions on three-loop ... More
On duality symmetries of supergravity invariantsSep 03 2010Nov 08 2010The role of duality symmetries in the construction of counterterms for maximal supergravity theories is discussed in a field-theoretic context from different points of view. These are: dimensional reduction, the question of whether appropriate superspace ... More
Impact of low-frequency p modes on the inversions of the internal rotation of the SunNov 11 2008We used the m-averaged spectrum technique ("collapsogram") to extract the low-frequency solar p-mode parameters of low- and intermediate-angular degrees (l \leq 35) in long time series of GONG and MDI observations. Rotational splittings and central frequencies ... More
Free Fermions and Extended Conformal AlgebrasJul 27 1994Oct 07 1994A class of algebras is constructed using free fermions and the invariant antisymmetric tensors associated with irreducible holonomy groups. (This version contains minor typographical corrections and some additional references. )
An Oscillating Langevin Antenna for Driving Plasma Turbulence SimulationsMay 09 2013Oct 21 2013A unique method of driving Alfvenic turbulence via an oscillating Langevin antenna is presented. This method of driving is motivated by a desire to inject energy into a finite domain numerical simulation in a manner that models the nonlinear transfer ... More
Interpreting Magnetic Variance Anisotropy Measurements in the Solar WindMay 03 2012The magnetic variance anisotropy ($\mathcal{A}_m$) of the solar wind has been used widely as a method to identify the nature of solar wind turbulent fluctuations; however, a thorough discussion of the meaning and interpretation of the $\mathcal{A}_m$ ... More
Multiscale nature of the dissipation range in gyrokinetic simulations of Alfvénic turbulenceMay 08 2015Jul 09 2015Nonlinear energy transfer and dissipation in Alfv\'en wave turbulence are analyzed in the first gyrokinetic simulation spanning all scales from the tail of the MHD range to the electron gyroradius scale. For typical solar wind parameters at 1 AU, about ... More
Magnetic fluctuation power near proton temperature anisotropy instability thresholds in the solar windAug 10 2009The proton temperature anisotropy in the solar wind is known to be constrained by the theoretical thresholds for pressure anisotropy-driven instabilities. Here we use approximately 1 million independent measurements of gyroscale magnetic fluctuations ... More
Physical Interpretation of the Angle Dependent Magnetic Helicity Spectrum in the Solar Wind: The Nature of Turbulent Fluctuations near the Proton Gyroradius ScaleMar 10 2014Motivated by recent observations of distinct parallel and perpendicular signatures in magnetic helicity measurements segregated by wave period and angle between the local magnetic field and the solar wind velocity, this paper undertakes a comparison of ... More
Collisionless Reconnection in the Large Guide Field Regime: Gyrokinetic Versus Particle-in-Cell SimulationsDec 18 2013Feb 18 2014Results of the first validation of large guide field, $B_g / \delta B_0 \gg 1$, gyrokinetic simulations of magnetic reconnection at a fusion and solar corona relevant $\beta_i = 0.01$ and solar wind relevant $\beta_i = 1$ are presented, where $\delta ... More
The Turbulent Heating Rate in Strong MHD Turbulence with Nonzero Cross HelicityMay 20 2009Different results for the cascade power in strong, incompressible MHD turbulence with nonzero cross helicity appear in the literature. In this paper, we discuss the conditions under which these different results are valid. We define z+ to be the rms amplitude ... More
Gyrokinetic simulations of the tearing instabilityJul 28 2011Linear gyrokinetic simulations covering the collisional -- collisionless transitional regime of the tearing instability are performed. It is shown that the growth rate scaling with collisionality agrees well with that predicted by a two-fluid theory for ... More
Constraining Low-Frequency Alfvenic Turbulence in the Solar Wind Using Density Fluctuation MeasurementsAug 05 2009One proposed mechanism for heating the solar wind, from close to the sun to beyond 10 AU, invokes low-frequency, oblique, Alfven-wave turbulence. Because small-scale oblique Alfven waves (kinetic Alfven waves) are compressive, the measured density fluctuations ... More
Collisionless Energy Transfer in Kinetic Turbulence: Field-Particle Correlations in Fourier SpaceApr 18 2019Turbulence is commonly observed in nearly collisionless heliospheric plasmas, including the solar wind and corona and the Earth's magnetosphere. Understanding the collisionless mechanisms responsible for the energy transfer from the turbulent fluctuations ... More
Dissipation via Landau Damping in Two- and Three-Dimensional Plasma TurbulenceOct 09 2015Plasma turbulence is ubiquitous in space and astrophysical plasmas, playing an important role in plasma energization, but the physical mechanisms that lead to dissipation of the turbulent energy remain to be definitively identified. This work addresses ... More
Gyrokinetic simulation of entropy cascade in two-dimensional electrostatic turbulenceMar 20 2010Aug 16 2010Two-dimensional electrostatic turbulence in magnetized weakly-collisional plasmas exhibits a cascade of entropy in phase space [Phys. Rev. Lett. 103, 015003 (2009)]. At scales smaller than the gyroradius, this cascade is characterized by the dimensionless ... More
Nonlinear phase mixing and phase-space cascade of entropy in gyrokinetic plasma turbulenceNov 16 2008Jun 30 2009Electrostatic turbulence in weakly collisional, magnetized plasma can be interpreted as a cascade of entropy in phase space, which is proposed as a universal mechanism for dissipation of energy in magnetized plasma turbulence. When the nonlinear decorrelation ... More
The slow-mode nature of compressible wave power in solar wind turbulenceJun 21 2011We use a large, statistical set of measurements from the Wind spacecraft at 1 AU, and supporting synthetic spacecraft data based on kinetic plasma theory, to show that the compressible component of inertial range solar wind turbulence is primarily in ... More
Astrophysical gyrokinetics: kinetic and fluid turbulent cascades in magnetized weakly collisional plasmasMar 31 2007May 09 2009We present a theoretical framework for plasma turbulence in astrophysical plasmas (solar wind, interstellar medium, galaxy clusters, accretion disks). The key assumptions are that the turbulence is anisotropic with respect to the mean magnetic field and ... More
Using Synthetic Spacecraft Data to Interpret Compressible Fluctuations in Solar Wind TurbulenceJun 28 2012Kinetic plasma theory is used to generate synthetic spacecraft data to analyze and interpret the compressible fluctuations in the inertial range of solar wind turbulence. The kinetic counterparts of the three familiar linear MHD wave modes---the fast, ... More
Howes et al. ReplyDec 12 2008Howes et al. Reply to Comment on "Kinetic Simulations of Magnetized Turbulence in Astrophysical Plasmas" arXiv:0711.4355
Kinetic Scale Density Fluctuations in the Solar WindSep 29 2012We motivate the importance of studying kinetic scale turbulence for understanding the macroscopic properties of the heliosphere, such as the heating of the solar wind. We then discuss the technique by which kinetic scale density fluctuations can be measured ... More
Kinetic Simulations of Magnetized Turbulence in Astrophysical PlasmasNov 27 2007This letter presents the first ab initio, fully electromagnetic, kinetic simulations of magnetized turbulence in a homogeneous, weakly collisional plasma at the scale of the ion Larmor radius (ion gyroscale). Magnetic and electric-field energy spectra ... More
Integral invariants in maximally supersymmetric Yang-Mills theoriesDec 14 2010Integral invariants in maximally supersymmetric Yang-Mills theories are discussed in spacetime dimensions $4\leq D\leq 10$ for $SU(k)$ gauge groups. It is shown that, in addition to the action, there are three special invariants in all dimensions. Two ... More
Performance of the Birmingham Solar-Oscillations Network (BiSON)Oct 23 2015Dec 27 2015The Birmingham Solar-Oscillations Network (BiSON) has been operating with a full complement of six stations since 1992. Over 20 years later, we look back on the network history. The meta-data from the sites have been analysed to assess performance in ... More
Validation of solar-cycle changes in low-degree helioseismic parameters from the Birmingham Solar-Oscillations NetworkSep 23 2015We present a new and up-to-date analysis of the solar low-degree $p$-mode parameter shifts from the Birmingham Solar-Oscillations Network (BiSON) over the past 22 years, up to the end of 2014. We aim to demonstrate that they are not dominated by changes ... More
New supergravities with central charges and Killing spinors in 2+1 dimensionsMay 05 1995Dec 20 1995We construct a new class of $(p,q)$-extended Poincar\'e supergravity theories in 2+1 dimensions as Chern-Simons theories of supersymmetry algebras with both central and automorphism charges. The new theories have the advantage that they are limits of ... More
A Model of Turbulence in Magnetized Plasmas: Implications for the Dissipation Range in the Solar WindJul 20 2007Dec 12 2008This paper studies the turbulent cascade of magnetic energy in weakly collisional magnetized plasmas. A cascade model is presented, based on the assumptions of local nonlinear energy transfer in wavenumber space, critical balance between linear propagation ... More
Astrophysical Gyrokinetics: Basic Equations and Linear TheoryNov 30 2005May 04 2006Magnetohydrodynamic (MHD) turbulence is encountered in a wide variety of astrophysical plasmas, including accretion disks, the solar wind, and the interstellar and intracluster medium. On small scales, this turbulence is often expected to consist of highly ... More
Yb- and Er-doped fiber laser Q-switched with an optically uniform, broadband WS2 saturable absorberJul 12 2015We demonstrate a ytterbium (Yb) and an erbium (Er)-doped fiber laser Q-switched by a solution processed, optically uniform, few-layer tungsten disulfide saturable absorber (WS2-SA). Nonlinear optical absorption of the WS2-SA in the sub-bandgap region, ... More
Ectoplasm with an EdgeApr 22 2011The construction of supersymmetric invariant actions on a spacetime manifold with a boundary is carried out using the "ectoplasm" formalism for the construction of closed forms in superspace. Non-trivial actions are obtained from the pull-backs to the ... More
Changes in the sensitivity of solar p-mode frequency shifts to activity over three solar cyclesJul 04 2018Low-degree solar p-mode observations from the long-lived Birmingham Solar Oscillations Network (BiSON) stretch back further than any other single helioseismic data set. Results from BiSON have suggested that the response of the mode frequency to solar ... More
pMSSM Dark Matter Searches on IceMay 06 2011We explore the capability of the IceCube/Deepcore array to discover signal neutrinos resulting from the annihilations of Supersymmetric WIMPS that may be captured in the solar core. In this analysis, we use a previously generated set of /sim 70k model ... More
AstroGK: Astrophysical Gyrokinetics CodeApr 02 2010Oct 15 2010The gyrokinetic simulation code AstroGK is developed to study fundamental aspects of kinetic plasmas and for applications mainly to astrophysical problems. AstroGK is an Eulerian slab code that solves the electromagnetic Gyrokinetic-Maxwell equations ... More
Bayesian changepoint analysis for atomic force microscopy and soft material indentationSep 29 2009Material indentation studies, in which a probe is brought into controlled physical contact with an experimental sample, have long been a primary means by which scientists characterize the mechanical properties of materials. More recently, the advent of ... More
Dissipation-Scale Turbulence in the Solar WindJul 20 2007We present a cascade model for turbulence in weakly collisional plasmas that follows the nonlinear cascade of energy from the large scales of driving in the MHD regime to the small scales of the kinetic Alfven wave regime where the turbulence is dissipated ... More
Gyrokinetic turbulence: a nonlinear route to dissipation through phase spaceJun 05 2008Nov 04 2008This paper describes a conceptual framework for understanding kinetic plasma turbulence as a generalized form of energy cascade in phase space. It is emphasized that conversion of turbulent energy into thermodynamic heat is only achievable in the presence ... More
Toward Astrophysical Turbulence in the LaboratoryOct 16 2012Turbulence is a ubiquitous phenomenon in space and astrophysical plasmas, driving a cascade of energy from large to small scales and strongly influencing the plasma heating resulting from the dissipation of the turbulence. Modern theories of plasma turbulence ... More
Extended Co(7-6) Emission from Warm Gas in OrionJan 18 1993We mapped quiescent 807 GHz CO(7-6) emission from Orion along a strip in RA extending from 0.7 pc west to 1.2 pc east of Ori theta 1C. The lines arise in warm gas with T > 40 K. The line brightness temperature is > 160 K in the di- rection of theta 1C, ... More
Gyrokinetic Simulations of Solar Wind Turbulence from Ion to Electron ScalesApr 05 2011The first three-dimensional, nonlinear gyrokinetic simulation of plasma turbulence resolving scales from the ion to electron gyroradius with a realistic mass ratio is presented, where all damping is provided by resolved physical mechanisms. The resulting ... More
SUSY Simplified Models at 14, 33, and 100 TeV Proton CollidersNov 25 2013May 14 2014Results are presented for a variety of SUSY Simplified Models at the 14 TeV LHC as well as a 33 and 100 TeV proton collider. Our focus is on models whose signals are driven by colored production. We present projections of the upper limit and discovery ... More
A Comparison of Future Proton Colliders Using SUSY Simplified Models: A Snowmass WhitepaperSep 30 2013Dec 01 2013We present a summary of results for SUSY Simplified Model searches at future proton colliders: the 14 TeV LHC as well as a 33 TeV proton collider and a 100 TeV proton collider. Upper limits and discovery significances are provided for the gluino-neutralino ... More
Wideband saturable absorption in few-layer molybdenum diselenide (MoSe2) for Q-switching Yb-, Er- and Tm-doped fiber lasersMar 27 2015Jun 12 2015We fabricate a free-standing molybdenum diselenide (MoSe2) saturable absorber by embedding liquid-phase exfoliated few-layer MoSe2 flakes into a polymer film. The MoSe2-polymer composite is used to Q-switch fiber lasers based on ytterbium (Yb), erbium ... More
Assembling large, complex environmental metagenomesDec 12 2012Dec 28 2012The large volumes of sequencing data required to sample complex environments deeply pose new challenges to sequence analysis approaches. De novo metagenomic assembly effectively reduces the total amount of data to be analyzed but requires significant ... More
Parametrizing the time-variation of the "surface term" of stellar p-mode frequencies: application to helioseismic dataOct 13 2016The solar-cyle variation of acoustic mode frequencies has a frequency dependence related to the inverse mode inertia. The discrepancy between model predictions and measured oscillation frequencies for solar and solar-type stellar acoustic modes includes ... More
Alfven Wave Collisions, The Fundamental Building Block of Plasma Turbulence IV: Laboratory ExperimentJun 05 2013Turbulence is a phenomenon found throughout space and astrophysical plasmas. It plays an important role in solar coronal heating, acceleration of the solar wind, and heating of the interstellar medium. Turbulence in these regimes is dominated by Alfven ... More
Alfven Wave Collisions, The Fundamental Building Block of Plasma Turbulence III: Theory for Experimental DesignJun 06 2013Jun 11 2013Turbulence in space and astrophysical plasmas is governed by the nonlinear interactions between counterpropagating Alfven waves. Here we present the theoretical considerations behind the design of the first laboratory measurement of an Alfven wave collision, ... More
Gap Anisotropy, Spin Fluctuations and Normal-State Properties of the Electron Doped Superconductor Sr0.9La0.1CuO2Nov 22 2001Dec 24 2001We report the results from a thermopower and a Cu nuclear magnetic resonance (NMR) study of the infinite CuO2 layer electron doped high temperature superconducting cuprate (HTSC), Sr0.9La0.1CuO2. We find that the temperature dependence of the thermopower, ... More
A Revised Collection of Sunspot Group NumbersSep 15 2016We describe a revised collection of the number of sunspot groups from 1610 to the present. This new collection is based on the work of Hoyt and Schatten (Solar Phys. 179, 189, 1998). The main changes are the elimination of a considerable number of observations ... More
Quantification of the spin-Hall anti-damping torque with a resonance spectrometerNov 22 2014We present a simple technique using a cavity-based resonance spectrometer to quantify the anti-damping torque due to the spin Hall effect. Modification of ferromagnetic resonance is observed as a function of small DC current in sub-mm-wide strips of bilayers, ... More
Analysis of Magnetic Fields in Inertial Alfven Wave CollisionsJun 12 2014Turbulence in astrophysical and space plasmas is dominated by the nonlinear interaction of counterpropagating Alfven waves. Most Alfven wave turbulence theories have been based on ideal plasma models, such as incompressible MHD, for Alfven waves at large ... More
Comparison of spin-orbit torques and spin pumping across NiFe/Pt and NiFe/Cu/Pt interfacesMar 13 2015Feb 12 2016We experimentally investigate spin-orbit torques and spin pumping in NiFe/Pt bilayers with direct and interrupted interfaces. The damping-like and field-like torques are simultaneously measured with spin-torque ferromagnetic resonance tuned by a dc bias ... More
Methods and Results for Standard Model Event Generation at $\sqrt{s}$ = 14 TeV, 33 TeV and 100 TeV Proton Colliders (A Snowmass Whitepaper)Aug 07 2013Oct 02 2013This document describes the novel techniques used to simulate the common Snowmass 2013 Energy Frontier Standard Model backgrounds for future hadron colliders. The purpose of many Energy Frontier studies is to explore the reach of high luminosity data ... More
The Sun in transition? Persistence of near-surface structural changes through Cycle 24May 25 2017We examine the frequency shifts in low-degree helioseismic modes from the Birmingham Solar-Oscillations Network (BiSON) covering the period from 1985 - 2016, and compare them with a number of global activity proxies well as a latitudinally-resolved magnetic ... More
Asteroseismic constraints on active latitudes of solar-type stars: HD173701 has active bands at higher latitudes than the SunMar 12 2019We present a new method for determining the location of active bands of latitude on solar-type stars, which uses stellar-cycle-induced frequency shifts of detectable solar-like oscillations. When near-surface activity is distributed in a non-homogeneous ... More
Signatures of magnetic activity in the seismic data of solar-type stars observed by KeplerMay 31 2018In the Sun, the frequencies of the acoustic modes are observed to vary in phase with the magnetic activity level. These frequency variations are expected to be common in solar-type stars and contain information about the activity-related changes that ... More
Oscillation mode linewidths and heights of 23 main-sequence stars observed by KeplerMar 27 2014Solar-like oscillations have been observed by Kepler and CoRoT in many solar-type stars, thereby providing a way to probe the stars using asteroseismology. We provide the mode linewidths and mode heights of the oscillations of various stars as a function ... More
Seismic signatures of magnetic activity in solar-type stars observed by KeplerJun 11 2018The properties of the acoustic modes are sensitive to magnetic activity. The unprecedented long-term Kepler photometry, thus, allows stellar magnetic cycles to be studied through asteroseismology. We search for signatures of magnetic cycles in the seismic ... More
An integrated low phase noise radiation-pressure-driven optomechanical oscillator chipsetOct 21 2014High-quality frequency references are the cornerstones in position, navigation and timing applications of both scientific and commercial domains. Optomechanical oscillators, with direct coupling to continuous-wave light and non-material-limited f Q product, ... More
Motivic random variables and representation stability I: Configuration spacesOct 18 2016We prove a motivic stabilization result for the cohomology of the local systems on configuration spaces of varieties over $\mathbb{C}$ attached to character polynomials. Our approach interprets the stabilization as a probabilistic phenomenon based on ... More
The $p$-adic Jacquet-Langlands correspondence and a question of SerreJun 18 2018We show that the completed Hecke algebra of $p$-adic modular forms is isomorphic to the completed Hecke algebra of continuous $p$-adic automorphic forms for the units of the quaternion algebra ramified at $p$ and $\infty$. This gives an affirmative answer ... More
Motivic random variables and representation stability II: Hypersurface sectionsOct 18 2016We prove geometric and cohomological stabilization results for the universal smooth degree $d$ hypersurface section of a fixed smooth projective variety as $d$ goes to infinity. We show that relative configuration spaces of the universal smooth hypersurface ... More
The Log-Convex Density Conjecture and vertical surface area in warped productsJul 22 2011Dec 22 2014We examine the vertical component of surface area in the warped product of a Euclidean interval and a fiber manifold with product density. We determine general conditions under which vertical fibers minimize vertical surface area among regions bounding ... More
Transcendence of the Hodge-Tate filtrationOct 17 2016For $C$ a complete algebraically closed extension of $\mathbb{Q}_p$, we show that a one-dimensional $p$-divisible group $G/ \mathcal{O}_C$ can be defined over a complete discretely valued subfield $L \subset C$ with Hodge-Tate period ratios contained ... More
Extended [C I] and ^{13}CO(5-4) Emission in M17SWOct 19 2000We mapped a 13 by 22 pc region in emission from 492 GHz [C I] and, for the first time, 551 GHz ^{13}CO(5-4) in the giant molecular cloud M17SW, using the Submillimeter Wave Astronomy Satellite. The morphologies of the [C I] and ^{13}CO emission are strikingly ... More
Water Abundance in Molecular Cloud CoresOct 19 2000We present Submillimeter Wave Astronomy Satellite (SWAS) observations of the 1_{10}-1_{01} transition of ortho-water at 557 GHz toward 12 molecular cloud cores. The water emission was detected in NGC 7538, Rho Oph A, NGC 2024, CRL 2591, W3, W3(OH), Mon ... More
Atmospheric extinction coefficients in the $\mathrm{I_c}$ band for several major international observatories: Results from the BiSON telescopes, 1984 to 2016Jul 20 2017Over 30 years of solar data have been acquired by the Birmingham Solar Oscillations Network (BiSON), an international network of telescopes used to study oscillations of the Sun. Five of the six BiSON telescopes are located at major observatories. The ... More
Spin-orbit torque and spin pumping in YIG/Pt with interfacial insertion layersFeb 12 2018Apr 29 2018We experimentally investigate spin-orbit torque and spin pumping in Y$_3$Fe$_5$O$_{12}$(YIG)/Pt bilayers with ultrathin insertion layers at the interface. An insertion layer of Cu suppresses both spin-orbit torque and spin pumping, whereas an insertion ... More