Results for "D. B. Jess"

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MHD wave modes resolved in fine-scale chromospheric magnetic structuresMay 05 2015Within the last decade, due to significant improvements in the spatial and temporal resolution of chromospheric data, magnetohydrodynamic (MHD) wave studies in this fascinating region of the Sun's atmosphere have risen to the forefront of solar physics ... More
TRACE Observations of Driven Loop OscillationsAug 12 2011Aims: On 13 June 1998, the TRACE satellite was fortuitously well placed to observe the effects of a flare-induced EIT wave in the corona, and its subsequent interaction with coronal magnetic loops. In this study, we use these TRACE observations to corroborate ... More
A photospheric bright point modelMar 08 2010A magneto-hydrostatic model is constructed with spectropolarimetric properties close to those of solar photospheric magnetic bright points. Results of solar radiative magneto-convection simulations are used to produce the spatial structure of the vertical ... More
Nanoflare Activity in the Solar ChromosphereSep 23 2014We use ground-based images of high spatial and temporal resolution to search for evidence of nanoflare activity in the solar chromosphere. Through close examination of more than 10^9 pixels in the immediate vicinity of an active region, we show that the ... More
Observations of sausage modes in magnetic poresNov 10 2010We present here evidence for the observation of the magneto-hydrodynamic (MHD) sausage modes in magnetic pores in the solar photosphere. Further evidence for the omnipresent nature of acoustic global modes is also found. The empirical decomposition method ... More
On the Source of Propagating Slow Magneto-acoustic Waves in SunspotsOct 12 2015Recent high-resolution observations of sunspot oscillations using simultaneously operated ground- and space-based telescopes reveal the intrinsic connection between different layers of the solar atmosphere. However, it is not clear whether these oscillations ... More
Ultra-high-resolution Observations of MHD Waves in Photospheric Magnetic StructuresFeb 24 2015Here we review the recent progress made in the detection, examination, characterisation and interpretation of oscillations manifesting in small-scale magnetic elements in the solar photosphere. This region of the Sun's atmosphere is especially dynamic, ... More
The periodic variations of a white-light flare observed with ULTRACAMMay 08 2006High time resolution observations of a white--light flare on the active star EQ PegB show evidence of intensity variations with a period of approximately 10 s. The period drifts to longer values during the decay phase of the flare. If the oscillation ... More
Alfven Waves in the Lower Solar AtmosphereMar 20 2009We report the detection of oscillatory phenomena associated with a large bright-point group that is 430,000 square kilometers in area and located near the solar disk center. Wavelet analysis reveals full-width half-maximum oscillations with periodicities ... More
Propagating Wave Phenomena Detected in Observations and Simulations of the Lower Solar AtmosphereJan 10 2012We present high-cadence observations and simulations of the solar photosphere, obtained using the Rapid Oscillations in the Solar Atmosphere imaging system and the MuRAM magneto-hydrodynamic code, respectively. Each dataset demonstrates a wealth of magneto-acoustic ... More
Rapid Fluctuations in the Lower Solar AtmosphereNov 18 2011The Rapid Oscillations in the Solar Atmosphere (ROSA) instrument reveals solar atmospheric fluctuations at high frequencies. Spectra of variations of the G-band intensity (IG) and CaII K-line intensity (IK) show correlated fluctuations above white noise ... More
Multiwavelength studies of MHD waves in the solar chromosphere: An overview of recent resultsMar 05 2015Mar 11 2015The chromosphere is a thin layer of the solar atmosphere that bridges the relatively cool photosphere and the intensely heated transition region and corona. Compressible and incompressible waves propagating through the chromosphere can supply significant ... More
Tracking Magnetic Bright Point Motions Through the Solar AtmosphereOct 22 2012High cadence, multi-wavelength observations and simulations are employed for the analysis of solar photospheric magnetic bright points (MBPs) in the quiet Sun. The observations were obtained with the Rapid Oscillations in the Solar Atmosphere (ROSA) imager ... More
Heating Mechanisms for Intermittent Loops in Active Region Cores from AIA/SDO EUV ObservationsApr 30 2014Sep 05 2014We investigate intensity variations and energy deposition in five coronal loops in active region cores. These were selected for their strong variability in the AIA/SDO 94 {\AA} intensity channel. We isolate the hot Fe XVIII and Fe XXI components of the ... More
High-Frequency Oscillations in a Solar Active Region observed with the Rapid Dual ImagerJul 18 2007Oct 01 2007High-cadence, synchronized, multiwavelength optical observations of a solar active region (NOAA 10794) are presented. The data were obtained with the Dunn Solar Telescope at the National Solar Observatory/Sacramento Peak using a newly developed camera ... More
The Influence of the Magnetic Field on Running Penumbral Waves in the Solar ChromosphereOct 29 2013We use images of high spatial and temporal resolution, obtained using both ground- and space-based instrumentation, to investigate the role magnetic field inclination angles play in the propagation characteristics of running penumbral waves in the solar ... More
Unravelling the components of a multi-thermal coronal loop using magnetohydrodynamic seismologyNov 12 2016Coronal loops, constituting the basic building blocks of the active Sun, serve as primary targets to help understand the mechanisms responsible for maintaining multi-million Kelvin temperatures in the solar and stellar coronae. Despite significant advances ... More
A study of Magnetic Bright Points in the Na I D1 lineJul 15 2010High cadence, multiwavelength, optical observations of solar magnetic bright points, captured at disk center using the ROSA and IBIS imaging systems on the Dunn Solar Telescope, are presented. Magnetic bright points manifesting in the Na I D1 core are ... More
The Area Distribution of Solar Magnetic Bright PointsSep 13 2010Magnetic Bright Points (MBPs) are among the smallest observable objects on the solar photosphere. A combination of G-band observations and numerical simulations is used to determine their area distribution. An automatic detection algorithm, employing ... More
Automated Detection and Tracking of Solar Magnetic Bright PointsMay 19 2009Magnetic Bright Points (MBPs) in the internetwork are among the smallest objects in the solar photosphere and appear bright against the ambient environment. An algorithm is presented that can be used for the automated detection of the MBPs in the spatial ... More
Ultraviolet and extreme-ultraviolet line ratio diagnostics for O IVJan 15 2009Aims: We generate theoretical ultraviolet and extreme-ultraviolet emission line ratios for O IV and show their strong versatility as electron temperature and density diagnostics for astrophysical plasmas. Methods: Recent fully relativistic calculations ... More
The polytropic index of solar coronal plasma in sunspot fan loops and its temperature dependenceOct 19 2018Observations of slow magneto-acoustic waves have been demonstrated to possess a number of applications in coronal seismology. Determination of the polytropic index ($\gamma$) is one such important application. Analysing the amplitudes of oscillations ... More
The Changing Face of $α$ Centauri B: Probing plage and stellar activity in K-dwarfsFeb 06 2017A detailed knowledge of stellar activity is crucial for understanding stellar dynamos, as well as pushing exoplanet radial-velocity detection limits towards Earth analogue confirmation. We directly compare archival HARPS spectra taken at the minimum in ... More
Do all Flares have White Light Emission?Oct 08 2008High-cadence, multiwavelength optical observations of a solar active region (NOAA 10969), obtained with the Swedish Solar Telescope, are presented. Difference imaging of white light continuum data reveals a white light brightening, 2 min in duration, ... More
Discovery of Spatial Periodicities in a Coronal Loop using Automated Edge-Tracking AlgorithmsFeb 14 2008A new method for automated coronal loop tracking, in both spatial and temporal domains, is presented. Applying this technique to TRACE data, obtained using the 171 Angstrom filter on 1998 July 14, we detect a coronal loop undergoing a 270s kink-mode oscillation, ... More
Microflare Activity driven by Forced Magnetic ReconnectionFeb 19 2010High cadence, multiwavelength, optical observations of a solar active region are presented, obtained with the Swedish Solar Telescope. Two magnetic bright points are seen to separate in opposite directions at a constant velocity of 2.8km/s. After a separation ... More
Time-dependent suppression of oscillatory power in evolving solar magnetic fieldsApr 19 2016Oscillation amplitudes are generally smaller within magnetically active regions like sunspots and plage, when compared to their surroundings. Such magnetic features, when viewed in spatially-resolved powermaps, appear as regions of suppressed power due ... More
Adjusting the melting point of a model system via Gibbs-Duhem integration: application to a model of AluminumJun 26 2000Model interaction potentials for real materials are generally optimized with respect to only those experimental properties that are easily evaluated as mechanical averages (e.g., elastic constants (at T=0 K), static lattice energies and liquid structure). ... More
Symplectic algorithm for constant-pressure molecular dynamics using a Nose-Poincare thermostatMar 04 1999We present a new algorithm for isothermal-isobaric molecular-dynamics simulation. The method uses an extended Hamiltonian with an Andersen piston combined with the Nos'e-Poincar'e thermostat, recently developed by Bond, Leimkuhler and Laird [J. Comp. ... More
Characteristics of transverse waves in chromospheric mottlesOct 14 2013Using data obtained by the high temporal and spatial resolution Rapid Oscillations in the Solar Atmosphere (ROSA) instrument on the Dunn Solar Telescope, we investigate at an unprecedented level of detail transverse oscillations in chromospheric fine ... More
The Origin of Type I Spicule OscillationsNov 23 2011We use images of high spatial and temporal resolution, obtained with the Rapid Oscillations in the Solar Atmosphere instrument at the Dunn Solar Telescope, to reveal how the generation of transverse waves in Type I spicules is a direct result of longitudinal ... More
Transverse oscillations in chromospheric mottlesFeb 25 2012A number of recent investigations have revealed that transverse waves are ubiquitous in the solar chromosphere. The vast majority of these have been reported in limb spicules and active region fibrils. We investigate long-lived, quiet Sun, on-disk features ... More
Small-scale Hα Jets in the Solar ChromosphereAug 04 2011High temporal and spatial resolution observations from the Rapid Oscillations in the Solar Atmosphere (ROSA) multiwavelength imager on the Dunn Solar Telescope are used to study the velocities of small-scale H{\alpha} jets in an emerging solar active ... More
Twisting Flux Tubes as a cause of Micro-Flaring ActivitySep 14 2007High-cadence optical observations of an H-alpha blue-wing bright point near solar AR NOAA 10794 are presented. The data were obtained with the Dunn Solar Telescope at the National Solar Observatory/Sacramento Peak using a newly developed camera system, ... More
Tracing the Chromospheric and Coronal Magnetic Field with AIA, IRIS, IBIS, and ROSA DataFeb 05 2016The aim of this study is to explore the suitability of chromospheric images for magnetic modeling of active regions. We use high-resolution images (0.1") from the Interferometric Bidimensional Spectrometer (IBIS) in the Ca II 8542 A line, the Rapid Oscillations ... More
ROSA: a high cadence, synchronized multi-camera solar imaging systemDec 21 2009Rapid Oscillations in the Solar Atmosphere (ROSA) is a synchronized, six camera high cadence solar imaging instrument developed by Queen's University Belfast. The system is available on the Dunn Solar Telescope at the National Solar Observatory in Sunspot, ... More
Transition-Region Velocity Oscillations Observed by EUNIS-06Apr 10 2008Spectroscopic measurements of AR NOAA 10871, obtained with the Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS) sounding rocket instrument on 2006 April 12, reveal velocity oscillations in the He II 303.8 Angstrom emission line formed at T ~ ... More
Observations of ubiquitous compressive waves in the Sun's chromosphereJun 18 2013The details of the mechanism(s) responsible for the observed heating and dynamics of the solar atmosphere still remain a mystery. Magnetohydrodynamic (MHD) waves are thought to play a vital role in this process. Although it has been shown that incompressible ... More
The Source of Three-minute Magneto-acoustic Oscillations in Coronal FansAug 15 2012We use images of high spatial, spectral and temporal resolution, obtained using both ground- and space-based instrumentation, to investigate the coupling between wave phenomena observed at numerous heights in the solar atmosphere. Intensity oscillations ... More
A failed filament eruption inside a coronal mass ejection in active region 11121Feb 24 2013We study the formation and evolution of a failed filament eruption observed in NOAA active region 11121 near the southeast limb on November 6, 2010. We use a time series of SDO/AIA 304, 171, 131, 193, 335, 94 {\AA} images, SDO/HMI magnetograms, plus ROSA ... More
A Search for High-Frequency Coronal Brightness Variations in the 21 August 2017 Total Solar EclipseMar 14 2019We report on a search for short-period intensity variations in the green-line FeXIV 530.3 nm emission from the solar corona during the 21 August 2017 total eclipse viewed from Idaho in the United States. Our experiment was performed with a much more sensitive ... More
Emission lines of Fe X in active region spectra obtained with the Solar Extreme-ultraviolet Research Telescope and SpectrographJun 20 2008Fully relativistic calculations of radiative rates and electron impact excitation cross sections for Fe X are used to derive theoretical emission-line ratios involving transitions in the 174-366 A wavelength range. A comparison of these with solar active ... More
Fe XIII emission lines in active region spectra obtained with the Solar Extreme-Ultraviolet Research Telescope and SpectrographDec 18 2006Recent fully relativistic calculations of radiative rates and electron impact excitation cross sections for Fe {\sc xiii} are used to generate emission-line ratios involving 3s$^{2}$3p$^{2}$--3s3p$^{3}$ and 3s$^{2}$3p$^{2}$--3s$^{2}$3p3d transitions in ... More
The Magnetic Response of the Solar Atmosphere to Umbral FlashesFeb 28 2018Chromospheric observations of sunspot umbrae offer an exceptional view of magneto-acoustic shock phenomena and the impact they have on the surrounding magnetically-dominated plasma. We employ simultaneous slit-based spectro-polarimetry and spectral imaging ... More
The Frequency-dependent Damping of Slow Magnetoacoustic Waves in a Sunspot Umbral AtmosphereAug 16 2017High spatial and temporal resolution images of a sunspot, obtained simultaneously in multiple optical and UV wavelengths, are employed to study the propagation and damping characteristics of slow magnetoacoustic waves up to transition region heights. ... More
Propagating Spectropolarimetric Disturbances in a Large SunspotOct 30 2018We present results derived from the analysis of spectropolarimetric measurements of active region AR12546, which represents one of the largest sunspots to have emerged onto the solar surface over the last $20$ years. The region was observed with full-Stokes ... More
Emission lines of Fe XI in the 257--407 A wavelength region observed in solar spectra from EIS/Hinode and SERTSJan 20 2010Theoretical emission-line ratios involving Fe XI transitions in the 257-407 A wavelength range are derived using fully relativistic calculations of radiative rates and electron impact excitation cross sections. These are subsequently compared with both ... More
Departure of high temperature iron lines from the equilibrium state in flaring solar plasmasJun 07 2016The aim of this study is to clarify if the assumption of ionization equilibrium and a Maxwellian electron energy distribution is valid in flaring solar plasmas. We analyze the 2014 December 20 X1.8 flare, in which the \ion{Fe}{xxi} 187~\AA, \ion{Fe}{xxii} ... More
Void Nucleation, Growth, and Coalescence in Irradiated MetalsMar 26 2008A novel computational treatment of dense, stiff, coupled reaction rate equations is introduced to study the nucleation, growth, and possible coalescence of cavities during neutron irradiation of metals. Radiation damage is modeled by the creation of Frenkel ... More
An Inside Look at Sunspot Oscillations with Higher Azimuthal WavenumbersMay 17 2017Solar chromospheric observations of sunspot umbrae offer an exceptional view of magneto-hydrodynamic wave phenomena. In recent years, a wealth of wave signatures related to propagating magneto-acoustic modes have been presented, which demonstrate complex ... More
H$α$ and EUV observations of a partial CMEMar 13 2015We have obtained H$\alpha$ high spatial and time resolution observations of the upper solar chromosphere and supplemented these with multi-wavelength observations from the Solar Dynamic Observatory (SDO) and the {\it Hinode} ExtremeUltraviolet Imaging ... More
Solar coronal magnetic fields derived using seismology techniques applied to omnipresent sunspot wavesMay 19 2016Sunspots on the surface of the Sun are the observational signatures of intense manifestations of tightly packed magnetic field lines, with near-vertical field strengths exceeding 6,000 G in extreme cases. It is well accepted that both the plasma density ... More
Observations and simulations of the Na I D1 line profiles in an M-class solar flareSep 26 2016We study the temporal evolution of the Na I D1 line profiles in the M3.9 flare SOL2014-06-11T21:03 UT, using high spectral resolution observations obtained with the IBIS instrument on the Dunn Solar Telescope combined with radiative hydrodynamic simulations. ... More
Alfvén Wave Dissipation in the Solar ChromosphereOct 17 2018Magneto-hydrodynamic (MHD) Alfv\'en waves have been a focus of laboratory plasma physics and astrophysics for over half a century. Their unique nature makes them ideal energy transporters, and while the solar atmosphere provides preferential conditions ... More
Wave Damping Observed in Upwardly Propagating Sausage-mode Oscillations contained within a Magnetic PoreMay 06 2015May 11 2015We present observational evidence of compressible magnetohydrodynamic wave modes propagating from the solar photosphere through to the base of the transition region in a solar magnetic pore. High cadence images were obtained simultaneously across four ... More
Homogeneous Solutions of Pluriclosed Flow on Closed Complex SurfacesApr 28 2014Jul 15 2014Streets and Tian introduced a parabolic flow of pluriclosed metrics. We classify the long time behavior of homogeneous solutions of this flow on closed complex surfaces including minimal Hopf, Inoue, Kodaira, and non-Kahler, properly elliptic surfaces. ... More
$\bar{\partial}$-Harmonic Maps Between Almost Hermitian ManifoldsJul 06 2015Aug 05 2015In this paper we study an energy of maps between almost Hermitian manifolds for which pseudo-holomorphic maps are global minimizers. We derive its Euler-Lagrange equation, the $\bar{\partial}$-harmonic map equation, and show that it coincides with the ... More
Statistical Signatures of Nanoflare Activity. I. Monte Carlo Simulations and Parameter Space ExplorationDec 17 2018Small-scale magnetic reconnection processes, in the form of nanoflares, have become increasingly hypothesized as important mechanisms for the heating of the solar atmosphere, for driving propagating disturbances along magnetic field lines in the Sun's ... More
Photospheric observations of surface and body modes in solar magnetic poresMar 05 2018Over the past number of years, great strides have been made in identifying the various low-order magnetohydrodynamic wave modes observable in a number of magnetic structures found within the solar atmosphere. However, one aspect of these modes that has ... More
Statistical Signatures of Nanoflare Activity. I. Monte Carlo Simulations and Parameter-space ExplorationDec 17 2018Feb 27 2019Small-scale magnetic reconnection processes, in the form of nanoflares, have become increasingly hypothesized as important mechanisms for the heating of the solar atmosphere, for driving propagating disturbances along magnetic field lines in the Sun's ... More
Chromospheric Velocities of a C-class FlareMar 22 2011We use high spatial and temporal resolution observations from the Swedish Solar Telescope to study the chromospheric velocities of a C-class flare originating from active region NOAA 10969. A time-distance analysis is employed to estimate directional ... More
The Search for Super-saturation in Chromospheric EmissionJul 09 2011We investigate if the super-saturation phenomenon observed at X-ray wavelengths for the corona, exists in the chromosphere for rapidly rotating late-type stars. Moderate resolution optical spectra of fast rotating EUV- and X-ray- selected late-type stars ... More
Multi-wavelength observations of the 2014 June 11 M3.9 flare: temporal and spatial characteristicsNov 17 2018We present multi-wavelength observations of an M-class flare (M3.9) that occurred on 2014 June 11. Our observations were conducted with the Dunn Solar Telescope (DST), adaptive optics, the multi-camera system ROSA (Rapid Oscillations in Solar Atmosphere) ... More
Multi-wavelength observations of the 2014 June 11 M3.9 flare: temporal and spatial characteristicsNov 17 2018Feb 19 2019We present multi-wavelength observations of an M-class flare (M3.9) that occurred on 2014 June 11. Our observations were conducted with the Dunn Solar Telescope (DST), adaptive optics, the multi-camera system ROSA (Rapid Oscillations in Solar Atmosphere) ... More
Steps on Rutile TiO2(110): Active Sites for Water and Methanol DissociationNov 02 2011We present a detailed investigation of the structure and activity of extended defects namely monoatomic steps on (1x1)-TiO2(110). Specifically, the two most stable <001> and <1-11> step edges are considered. Employing an automated genetic algorithm that ... More
Dynamic properties of bright points in an active regionMay 15 2014Context. Bright points (BPs) are small-scale, magnetic features ubiquitous across the solar surface. Previously, we have observed and noted their properties for quiet Sun regions. Here, we determine the dynamic properties of BPs using simultaneous quiet ... More
Local Records and Global Entanglement: A Unique Multi-Partite Generalization of the Schmidt DecompositionOct 16 2013We show that there is a unique maximal decomposition of a pure multi-partite (N>2) quantum state into a sum of states which are "locally orthogonal" in the sense that the local reduced state for a term in the sum lives in its own orthogonal subspace for ... More
The effects of transients on photospheric and chromospheric power distributionsApr 21 2016We have observed a quiet Sun region with the Swedish 1-meter Solar Telescope (SST) equipped with CRISP Imaging SpectroPolarimeter. High-resolution, high-cadence, H$\alpha$ line scanning images were taken to observe different layers of the solar atmosphere ... More
Classical branch structure from spatial redundancy in a many-body wavefunctionAug 18 2016Apr 03 2017When the wavefunction of a large quantum system unitarily evolves away from a low-entropy initial state, there is strong circumstantial evidence it develops "branches": a decomposition into orthogonal components that is indistinguishable from the corresponding ... More
Evidence for gravitons from decoherence by bremsstrahlungOct 23 2013It is thought that gravitons are impossible to detect, even with the technological ability to construct experiments larger than Jupiter. However, in principle it is possible to detect the emission of single gravitons through the decoherence of relativistic ... More
Detecting Classically Undetectable Particles through Quantum DecoherenceMay 14 2012Jul 31 2013Some hypothetical particles are considered essentially undetectable because they are far too light and slow-moving to transfer appreciable energy or momentum to the normal matter that composes a detector. I propose instead directly detecting such feeble ... More
The Velocity Distribution of Solar Photospheric Magnetic Bright PointsSep 16 2011We use high spatial resolution observations and numerical simulations to study the velocity distribution of solar photospheric magnetic bright points. The observations were obtained with the Rapid Oscillations in the Solar Atmosphere instrument at the ... More
Classical branch structure from spatial redundancy in a many-body wavefunctionAug 18 2016There is good circumstantial evidence that when the wavefunction of a large system unitarily evolves from a low-entropy initial state, it should develop "branches", i.e., a decomposition into orthogonal components that can't be distinguished from the ... More
Decoherence from classically undetectable sources: A standard quantum limit for diffusionApr 13 2015Dec 09 2015In the pursuit of speculative new particles, forces, and dimensions with vanishingly small influence on normal matter, understanding the ultimate physical limits of experimental sensitivity is essential. Here, I show that quantum decoherence offers a ... More
Quantum Brownian motion as an iterated entanglement-breaking measurement by the environmentJul 15 2015Feb 03 2016Einstein-Smoluchowski diffusion, damped harmonic oscillations, and spatial decoherence are special cases of an elegant class of Markovian quantum Brownian motion models that is invariant under linear symplectic transformations. Here we prove that for ... More
Direct Detection of Classically Undetectable Dark Matter through Quantum DecoherenceDec 13 2012Nov 19 2013Although various pieces of indirect evidence about the nature of dark matter have been collected, its direct detection has eluded experimental searches despite extensive effort. If the mass of dark matter is below 1 MeV, it is essentially imperceptible ... More
Information-theoretic thresholds for community detection in sparse networksJan 11 2016Apr 21 2016We give upper and lower bounds on the information-theoretic threshold for community detection in the stochastic block model. Specifically, let $k$ be the number of groups, $d$ be the average degree, the probability of edges between vertices within and ... More
Bulk measurement of copper and sodium content in CuIn(0.7)Ga(0.3)Se(2) (CIGS) solar cells with nanosecond pulse length laser induced breakdown spectroscopy (LIBS)Jan 07 2013In this work, we show that laser induced breakdown spectroscopy (LIBS) with a nanosecond pulse laser can be used to measure the copper and sodium content of CuIn(0.7)Ga(0.3)Se(2) (CIGS) thin film solar cells on molybdenum. This method has four significant ... More
Classical branches and entanglement structure in the wavefunction of cosmological fluctuationsNov 15 2017The emergence of preferred classical variables within a many-body wavefunction is encoded in its entanglement structure in the form of redundant classical information shared between many spatially local subsystems. We show how such structure can be generated ... More
Decoherence as a way to measure extremely soft collisions with dark matterSep 14 2016Jul 31 2017A new frontier in the search for dark matter (DM) is based on the idea of detecting the decoherence caused by DM scattering against a mesoscopic superposition of normal matter. Such superpositions are uniquely sensitive to very small momentum transfers ... More
Decoherence as a way to measure extremely soft collisions with Dark MatterSep 14 2016A new frontier in the search for dark matter (DM) is based on the idea of detecting the decoherence caused by DM scattering against a mesoscopic superposition of normal matter. Such superpositions are uniquely sensitive to very small momentum transfers ... More
Classical Entanglement Structure in the Wavefunction of Inflationary FluctuationsApr 03 2017Dec 11 2017We argue that the preferred classical variables that emerge from a pure quantum state are determined by its entanglement structure in the form of redundant records: information shared between many subsystems. Focusing on the early universe, we ask how ... More
Signatures of New $d$-Wave Vortex Physics in Overdoped Tl$_2$Ba$_2$CuO$_{6+x}$ Revealed by TF-$μ^+$SRApr 18 2014Aug 26 2015The spontaneous expulsion of applied magnetic field, the Meissner effect, is a defining feature of superconductors; in Type-II superconductors above the lower critical field, this screening takes the form of a lattice of magnetic flux vortices. Using ... More
Magnetic moment of rare earth elements in R2Fe14B estimated with μ^+SRMay 01 2019The ferromagnetic (FM) nature of Nd2Fe14B has been investigated with muon spin rotation and relaxation ({\mu}^+SR) measurements on an aligned, sintered plate-shaped sample. A clear muon spin precession frequency (f_{FM}) corresponding to the static internal ... More
The Lovász Theta Function for Random Regular Graphs and Community Detection in the Hard RegimeMay 02 2017Aug 28 2017We derive upper and lower bounds on the degree $d$ for which the Lov\'asz $\vartheta$ function, or equivalently sum-of-squares proofs with degree two, can refute the existence of a $k$-coloring in random regular graphs $G_{n,d}$. We show that this type ... More
On the security of key distribution based on Johnson-Nyquist noiseMar 29 2013We point out that arguments for the security of Kish's noise-based cryptographic protocol have relied on an unphysical no-wave limit, which if taken seriously would prevent any correlation from developing between the users. We introduce a noiseless version ... More
Alfven Waves in the Solar AtmosphereOct 12 2012Alfven waves are considered to be viable transporters of the non-thermal energy required to heat the Sun's quiescent atmosphere. An abundance of recent observations, from state-of-the-art facilities, have reported the existence of Alfven waves in a range ... More
Redundant Information from Thermal Illumination: Quantum Darwinism in Scattered PhotonsFeb 15 2011Sep 19 2011We study quantum Darwinism, the redundant recording of information about the preferred states of a decohering system by its environment, for an object illuminated by a blackbody. We calculate the quantum mutual information between the object and its photon ... More
Entropy, stability, and harmonic map flowJun 24 2015Inspired by work of Colding-Minicozzi on mean curvature flow, Zhang introduced a notion of entropy stability for harmonic map flow. We build further upon this work in several directions. First we prove the equivalence of entropy stability with a more ... More
DizzyRNN: Reparameterizing Recurrent Neural Networks for Norm-Preserving BackpropagationDec 13 2016The vanishing and exploding gradient problems are well-studied obstacles that make it difficult for recurrent neural networks to learn long-term time dependencies. We propose a reparameterization of standard recurrent neural networks to update linear ... More
Quantum Darwinism in an Everyday Environment: Huge Redundancy in Scattered PhotonsJan 19 2010Jul 09 2010We study quantum Darwinism--the redundant recording of information about the preferred states of a decohering system by its environment--for an object illuminated by a black body. In the cases of point-source and isotropic illumination, we calculate the ... More
Information-theoretic thresholds for community detection in sparse networksJul 06 2016We give upper and lower bounds on the information-theoretic threshold for community detection in the stochastic block model. Specifically, consider the symmetric stochastic block model with $q$ groups, average degree $d$, and connection probabilities ... More
Comment on 'The aestivation hypothesis for resolving Fermi's paradox'Feb 18 2019In their article [arXiv:1705.03394], 'That is not dead which can eternal lie: the aestivation hypothesis for resolving Fermi's paradox', Sandberg et al. try to explain the Fermi paradox (we see no aliens) by claiming that Landauer's principle implies ... More
Radio lobes and X-ray hot spots of the extraordinary microquasar in NGC 7793Dec 14 2009We have studied the newly-discovered microquasar in NGC 7793 in radio, optical and X-ray bands. This system comprises a large (250 x 120 pc) line-emitting optical nebula, detected in H-alpha and HeII 4686. The optical nebula coincides with a synchrotron-emitting ... More
Viruses and Fullerenes - Symmetry as a Common Thread?Feb 18 2014We apply here the principle of affine symmetry to the nested fullerene cages (carbon onions) that arise in the context of carbon chemistry. Previous work on affine extensions of the icosahedral group has revealed a new organisational principle in virus ... More
Information-theoretic bounds and phase transitions in clustering, sparse PCA, and submatrix localizationJul 18 2016We study the problem of detecting a structured, low-rank signal matrix corrupted with additive Gaussian noise. This includes clustering in a Gaussian mixture model, sparse PCA, and submatrix localization. Each of these problems is conjectured to exhibit ... More
Amplification, Decoherence, and the Acquisition of Information by Spin EnvironmentsMar 07 2016Quantum Darwinism recognizes the role of the environment as a communication channel: Decoherence can selectively amplify information about the pointer states of a system of interest (preventing access to complementary information about their superpositions) ... More
Amplification, Redundancy, and the Quantum Chernoff InformationDec 18 2013Apr 12 2014Amplification was regarded, since the early days of quantum theory, as a mysterious ingredient that endows quantum microstates with macroscopic consequences, key to the "collapse of the wavepacket", and a way to avoid embarrassing problems exemplified ... More
Information-theoretic bounds and phase transitions in clustering, sparse PCA, and submatrix localizationJul 18 2016Jan 23 2017We study the problem of detecting a structured, low-rank signal matrix corrupted with additive Gaussian noise. This includes clustering in a Gaussian mixture model, sparse PCA, and submatrix localization. Each of these problems is conjectured to exhibit ... More
The Objective Past of a Quantum Universe: Redundant Records of Consistent HistoriesDec 02 2013Apr 14 2016Motivated by the advances of quantum Darwinism and recognizing the role played by redundancy in identifying the small subset of quantum states with resilience characteristic of objective classical reality, we explore the implications of redundant records ... More