Results for "Nathaniel J. Fisch"

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Reducing parametric backscattering by polarization rotationJun 27 2016Sep 20 2016When a laser passes through underdense plasmas, Raman and Brillouin Backscattering can reflect a substantial portion of the incident laser energy. This is a major loss mechanism, for example, in employing lasers in inertial confinement fusion. However, ... More
Radiation in equilibrium with plasma and plasma effects on cosmic microwave backgroundMar 13 2019The spectrum of the radiation of a body in equilibrium is given by Planck's law. In plasma, however, waves below the plasma frequency cannot propagate, consequently, the equilibrium radiation inside plasma is necessary different from the Planck spectrum. ... More
Ladder Climbing and Autoresonant Acceleration of Plasma WavesApr 01 2015Jul 21 2015When the background density in a bounded plasma is modulated in time, discrete modes become coupled. Interestingly, for appropriately chosen modulations, the average plasmon energy might be made to grow in a ladder-like manner, achieving up-conversion ... More
Do pulsars rotate clockwise or counterclockwise?Mar 04 2019Pulsars are rotating neutron stars which emit lighthouse-like beams. Owing to their unique properties, pulsars are a unique astrophysical tool to test general relativity, inform on matter at extreme densities, and probe galactic magnetic fields. Understanding ... More
Practicality of magnetic compression for plasma density controlJan 26 2016Plasma densification through magnetic compression has been suggested for time-resolved control of the wave properties in plasma-based accelerators. Using particle in cell simulations with real mass ratio, the practicality of large magnetic compression ... More
Compressing turbulence and sudden viscous dissipation with compression-dependent ionization stateMay 10 2016Jun 14 2016Turbulent plasma flow, amplified by rapid 3D compression, can be suddenly dissipated under continuing compression. This effect relies on the sensitivity of the plasma viscosity to the temperature, $\mu \sim T^{5/2}$. The plasma viscosity is also sensitive ... More
Compressing turbulence and sudden viscous dissipation with compression-dependent ionization stateMay 10 2016Oct 27 2016Turbulent plasma flow, amplified by rapid 3D compression, can be suddenly dissipated under continuing compression. This effect relies on the sensitivity of the plasma viscosity to the temperature, $\mu \sim T^{5/2}$. The plasma viscosity is also sensitive ... More
A lower bound on adiabatic heating of compressed turbulence for simulation and model validationNov 30 2016The energy in turbulent flow can be amplified by compression, when the compression occurs on a timescale shorter than the turbulent dissipation time. This mechanism may play a part in sustaining turbulence in various astrophysical systems, including molecular ... More
Ignition threshold for non-Maxwellian plasmasSep 08 2015Sep 09 2015An optically thin $p$-$^{11}$B plasma loses more energy to bremsstrahlung than it gains from fusion reactions, unless the ion temperature can be elevated above the electron temperature. In thermal plasmas, the temperature differences required are possible ... More
Laser Pulse Compression Using Magnetized PlasmasDec 29 2016Proposals to reach the next generation of laser intensities through Raman or Brillouin backscattering have centered on optical frequencies. Higher frequencies are beyond the range of such methods mainly due to the wave damping that accompanies the higher ... More
Efficiency of Current Drive by Fast WavesJan 12 2005The Rosenbluth form for the collision operator for a weakly relativistic plasma is derived. The formalism adopted by Antonsen and Chu can then be used to calculate the efficiency of current drive by fast waves in a relativistic plasma. Accurate numerical ... More
Effective action approach to wave propagation in scalar QED plasmasMar 12 2016A relativistic quantum field theory with nontrivial background fields is developed and applied to study waves in plasmas. The effective action of the electromagnetic 4-potential is calculated ab initio from the standard action of scalar QED using path ... More
Alpha Channeling in a Rotating PlasmaAug 28 2008The wave-particle alpha-channeling effect is generalized to include rotating plasma. Specifically, radio frequency waves can resonate with alpha particles in a mirror machine with ExB rotation to diffuse the alpha particles along constrained paths in ... More
Current in Wave Driven PlasmasJan 12 2005A theory for the generation of current in a toroidal plasma by radio-frequency waves is presented. The effect of an opposing electric field is included, allowing the case of time varying currents to be studied. The key quantities that characterize this ... More
Current limiting effects on laser compression by resonant backward Raman scatteringJan 05 2011Through resonant backward Raman scattering, the plasma wave mediates the energy transfer between long pump and short seed laser pulses. These mediation can result in pulse compression at extraordinarily high powers. However, both the overall efficiency ... More
Three-wave scattering in magnetized plasmas: from cold fluid to quantized LagrangianMay 27 2017Large amplitude waves in magnetized plasmas, generated either by external pumps or internal instabilities, can scatter via three-waves interactions. While three-wave scatterings in either forward or backward geometry are well-known, what happens when ... More
Laser-plasma interaction in magnetized environmentDec 01 2017Propagation and scattering of lasers present new phenomena and applications when the plasma medium becomes strongly magnetized. With mega-Gauss magnetic fields, scattering of optical lasers already becomes manifestly anisotropic. Special angles exist ... More
Green's function for rf-driven current in a toroidal plasmaFeb 01 2004The Green's function for rf-driven currents in a toroidal plasma is calculated in the long mean-free-path limit.
Plasma filtering techniques for nuclear waste remediationApr 27 2015Nuclear waste cleanup is challenged by the handling of feed stocks that are both unknown and complex. Plasma filtering, operating on dissociated elements, offers advantages over chemical methods in processing such wastes. The costs incurred by plasma ... More
X-Ray Amplification by Stimulated Brillouin ScatteringMay 24 2017Jul 23 2017Plasma-based parametric amplification using stimulated Brillouin scattering offers a route to coherent x-ray pulses orders-of-magnitude more intense than those of the brightest available sources. Brillouin amplification permits amplification of shorter ... More
Coupling of alpha-channeling to parallel wavenumber upshift in lower hybrid current driveAug 29 2014Feb 08 2016Although lower hybrid waves have been shown to be effective in driving plasma current in present-day tokamaks, they are predicted to strongly interact with the energetic alpha particles born from fusion reactions in eventual tokamak reactors. However, ... More
Alpha Channeling with High-field Launch of Lower Hybrid WavesAug 10 2015Oct 02 2015Although lower hybrid waves are effective at driving currents in present-day tokamaks, they are expected to interact strongly with high-energy particles in extrapolating to reactors. In the presence of a radial alpha particle birth gradient, this interaction ... More
Maximal energy extraction under discrete diffusive exchangeAug 14 2015Waves propagating through a bounded plasma can rearrange the densities of states in the six-dimensional velocity-configuration phase space. Depending on the rearrangement, the wave energy can either increase or decrease, with the difference taken up by ... More
Beyond nonlinear saturation of backward Raman amplifiersJan 21 2016Backward Raman amplification is limited by relativistic nonlinear dephasing resulting in saturation of the leading spike of the amplified pulse. Pump detuning is employed to mitigate the relativistic phase mismatch and to overcome the associated saturation. ... More
Strongly Enhanced Stimulated Brillouin Backscattering in an Electron-Positron PlasmaDec 02 2015Jan 07 2016Stimulated Brillouin backscattering of light is shown to be drastically enhanced in electron-positron plasmas, in contrast to the suppression of stimulated Raman scattering. A generalized theory of three-wave coupling between electromagnetic and plasma ... More
Simulations of relativistic-quantum plasmas using real-time lattice scalar QEDFeb 02 2018Real-time lattice quantum electrodynamics (QED) provides a unique tool for simulating plasmas in the strong-field regime, where collective plasma scales are not well-separated from relativistic-quantum scales. As a toy model, we study scalar QED, which ... More
Statistical Mechanics of an Optical Phase Space CompressorFeb 10 2005We describe the statistical mechanics of a new method to produce very cold atoms or molecules. The method results from trapping a gas in a potential well, and sweeping through the well a semi-permeable barrier, one that allows particles to leave but not ... More
What is the fate of runaway positrons in tokamaks?Apr 17 2015Massive runaway positrons are generated by runaway electrons in tokamaks. The fate of these positrons encodes valuable information about the runaway dynamics. The phase space dynamics of a runaway position is investigated using a Lagrangian that incorporates ... More
Short-Pulse Amplification by Strongly-Coupled Stimulated Brillouin ScatteringJul 01 2016Sep 07 2016We examine the feasibility of strongly-coupled stimulated Brillouin scattering as a mechanism for the plasma-based amplification of sub-picosecond pulses. In particular, we use fluid theory and particle-in-cell simulations to compare the relative advantages ... More
Laser Amplification in Strongly-Magnetized PlasmaDec 22 2018We consider backscattering of laser pulses in strongly-magnetized plasma mediated by kinetic magnetohydrodynamic waves. Magnetized low-frequency scattering, which can occur when the external magnetic field is neither perpendicular nor parallel to the ... More
Non-Positive Partial Transpose Subspaces Can be as Large as Any Entangled SubspaceMay 01 2013Jun 19 2013It is known that, in an $(m \otimes n)$-dimensional quantum system, the maximum dimension of a subspace that contains only entangled states is (m-1)(n-1). We show that the exact same bound is tight if we require the stronger condition that every state ... More
Norms and Cones in the Theory of Quantum EntanglementJul 05 2012There are various notions of positivity for matrices and linear matrix-valued maps that play important roles in quantum information theory. The cones of positive semidefinite matrices and completely positive linear maps, which represent quantum states ... More
The Complexity of the Puzzles of Final Fantasy XIII-2Mar 07 2012We analyze the computational complexity of solving the three "temporal rift" puzzles in the recent popular video game Final Fantasy XIII-2. We show that the Tile Trial puzzle is NP-hard and we provide an efficient algorithm for solving the Crystal Bonds ... More
Explicit constructions of quilts with seam condition coming from symplectic reductionAug 22 2018Associated to a symplectic quotient $M/\!/G$ is a Lagrangian correspondence $\Lambda_G$ from $M/\!/G$ to $M$. In this note, we construct in two examples quilts with seam condition on such a correspondence, in the case of $S^1$ acting on $\mathbb{CP}^2$ ... More
Strong hypercontractivity and strong logarithmic Sobolev inequalities for log-subharmonic functions on stratified Lie groupsJun 22 2017Jun 26 2017On a stratified Lie group $G$ equipped with hypoelliptic heat kernel measure, we study the behavior of the dilation semigroup on $L^p$ spaces of log-subharmonic functions. We consider a notion of strong hypercontractivity and a strong logarithmic Sobolev ... More
Electron-Beam Driven Relaxation Oscillations in Ferroelectric NanodisksMay 09 2015Using a combination of computational simulations, atomic-scale resolution imaging and phenomenological modelling, we examine the underlying mechanism for nanodomain restructuring in lead zirconate titanate (PZT) nanodisks driven by electron beams. The ... More
Synthesis of High-Quality Visible Faces from Polarimetric Thermal Faces using Generative Adversarial NetworksDec 12 2018The large domain discrepancy between faces captured in polarimetric (or conventional) thermal and visible domain makes cross-domain face verification a highly challenging problem for human examiners as well as computer vision algorithms. Previous approaches ... More
A Geometric Perspective on First-Passage CompetitionDec 26 2012We study the macroscopic geometry of first-passage competition on the integer lattice $Z^d$, with a particular interest in describing the behavior when one species initially occupies the exterior of a cone. First-passage competition is a stochastic process ... More
Monte Carlo Radiation Hydrodynamics with Implicit MethodsApr 17 2014Jan 28 2015We explore the application of Monte Carlo transport methods to solving coupled radiation-hydrodynamics problems. We use a time-dependent, frequency-dependent, 3-dimensional radiation transport code, that is special relativistic and includes some detailed ... More
Doubling down on naturalness with a supersymmetric twin HiggsDec 04 2013We show that naturalness of the weak scale can be comfortably reconciled with both LHC null results and observed Higgs properties provided the double protection of supersymmetry and the twin Higgs mechanism. This double protection radically alters conventional ... More
Pattern groups and a poset based Hopf monoidOct 03 2018The supercharacter theory of algebra groups gave us a representation theoretic realization of the Hopf algebra of symmetric functions in noncommuting variables. The underlying representation theoretic framework comes equipped with two canonical bases, ... More
First passage percolation and competition modelsMay 04 2010This paper is a survey of various results and techniques in first passage percolation, a random process modeling a spreading fluid on an infinite graph. The latter half of the paper focuses on the connection between first passage percolation and a certain ... More
The structure of normal lattice supercharacter theoriesOct 02 2018The character theory of finite groups has numerous basic questions that are often already quite involved: enumerating of irreducible characters, their character formulas, point-wise product decompositions, and restriction/induction between groups. A supercharacter ... More
Collapse of an ecological network in Ancient EgyptSep 24 2014The dynamics of ecosystem collapse are fundamental to determining how and why biological communities change through time, as well as the potential effects of extinctions on ecosystems. Here we integrate depictions of mammals from Egyptian antiquity with ... More
Testing Split Supersymmetry with InflationMar 27 2014Split supersymmetry (SUSY) -- in which SUSY is relevant to our universe but largely inaccessible at current accelerators -- has become increasingly plausible given the absence of new physics at the LHC, the success of gauge coupling unification, and the ... More
Excellent rings in transchromatic homotopy theoryJun 01 2017The purpose of this note is to verify that several basic rings appearing in transchromatic homotopy theory are Noetherian excellent normal domains and thus amenable to standard techniques from commutative algebra. In particular, we show that the coefficients ... More
Widespread Excess Ice in Arcadia Planitia, MarsSep 10 2015The distribution of subsurface water ice on Mars is a key constraint on past climate, while the volumetric concentration of buried ice (pore-filling versus excess) provides information about the process that led to its deposition. We investigate the subsurface ... More
Sudden viscous dissipation of compressing turbulenceOct 28 2015Feb 23 2016Compression of turbulent plasma can amplify the turbulent kinetic energy, if the compression is fast compared to the viscous dissipation time of the turbulent eddies. A sudden viscous dissipation mechanism is demonstrated, whereby this amplified turbulent ... More
X-ray Hardness Variations as an Internal/External Shock DiagnosticFeb 23 2007Jun 22 2007The early, highly time-variable X-ray emission immediately following GRBs exhibits strong spectral variations that are unlike the temporally smoother emission which dominates after $t\sim 10^3$ s. The ratio of hard channel (1.3-10.0 keV) to soft channel ... More
The Evolution of Stellar Velocity Dispersion During Dissipationless Galaxy MergersJan 22 2012Using N-body simulations, we studied the detailed evolution of central stellar velocity dispersion, {\sigma}, during dissipationless binary mergers of galaxies. Stellar velocity dispersion was measured using the common mass-weighting method as well as ... More
Excitation of Large-ktheta Ion-Berstein Waves in TokamaksFeb 28 1995The mode-converted ion-Bernstein wave excited in tokamaks is shown to exhibit certain very interesting behavior, including the attainment of very small poloidal phase velocities, the reversal of poloidal direction, and up-down asymmetries in propagation ... More
Algorithms and error bounds for noisy phase retrieval with low-redundancy framesDec 20 2014The main objective of this paper is to find algorithms accompanied by explicit error bounds for phase retrieval from noisy magnitudes of frame coefficients when the underlying frame has a low redundancy. We achieve these goals with frames consisting of ... More
Are perytons signatures of ball lightning?May 15 2014Aug 18 2014The enigmatic downchirped signals, called "perytons", that are detected by radio telescopes in the GHz frequency range may be produced by an atmospheric phenomenon known as ball lightning (BL). If BLs act as nonstationary radiofrequency cavities, their ... More
Ponderomotive forces on waves in modulated mediaFeb 24 2014Nonlinear interactions of waves via instantaneous cross-phase modulation can be cast in the same way as ponderomotive wave-particle interactions in high-frequency electromagnetic field. The ponderomotive effect arises when rays of a probe wave scatter ... More
Positive and negative effective mass of classical particles in oscillatory and static fieldsNov 28 2007A classical particle oscillating in an arbitrary high-frequency or static field effectively exhibits a modified rest mass m_eff derived from the particle averaged Lagrangian. Relativistic ponderomotive and diamagnetic forces, as well as magnetic drifts, ... More
Diagnostic Setup for Characterization of Near-Anode Processes in Hall ThrustersOct 16 2003A diagnostic setup for characterization of near-anode processes in Hall-current plasma thrusters consisting of biased and emissive electrostatic probes, high-precision positioning system and low-noise electronic circuitry was developed and tested. Experimental ... More
Axiomatic geometrical optics, Abraham-Minkowski controversy, and photon properties derived classicallyMar 27 2012Nov 21 2012By restating geometrical optics within the field-theoretical approach, the classical concept of a photon (and, more generally, any elementary excitation) in arbitrary dispersive medium is introduced, and photon properties are calculated unambiguously. ... More
Adiabatic nonlinear waves with trapped particles: II. Wave dispersionJul 15 2011Nov 12 2011A general nonlinear dispersion relation is derived in a nondifferential form for an adiabatic sinusoidal Langmuir wave in collisionless plasma, allowing for an arbitrary distribution of trapped electrons. The linear dielectric function is generalized, ... More
Vlasov equation and collisionless hydrodynamics adapted to curved spacetimeJun 18 2010Sep 16 2010The modification of the Vlasov equation, in its standard form describing a charged particle distribution in the six-dimensional phase space, is derived explicitly within a formal Hamiltonian approach for arbitrarily curved spacetime. The equation accounts ... More
On the nature of kinetic electrostatic electron nonlinear (KEEN) wavesFeb 25 2014An analytical theory is proposed for the kinetic electrostatic electron nonlinear (KEEN) waves originally found in simulations by Afeyan et al [arXiv:1210.8105]. We suggest that KEEN waves represent saturated states of the negative mass instability (NMI) ... More
Non-equilibrium piezo-thermal effect in spinning gasApr 01 2016A spinning gas, heated adiabatically through axial compression, is known to exhibit a rotation-dependent heat capacity. However, as equilibrium is approached, a new effect is identified here wherein the temperature does not grow homogeneously in the radial ... More
Surfatron acceleration along magnetic field by oblique electrostatic wavesNov 20 2011Charged particles can be accelerated via surfatron mechanism along dc magnetic field by obliquely propagating electrostatic waves. In plasma, this mechanism can, in principle, produce an average parallel current, even when the wave frequency is much larger ... More
Nonlinear dispersion of stationary waves in collisionless plasmasMay 01 2011A nonlinear dispersion of a general stationary wave in collisionless plasma is obtained in a non-differential form from a single-particle oscillation-center Hamiltonian. For electrostatic oscillations in nonmagnetized plasma, considered as a paradigmatic ... More
Extended propagation of powerful laser pulses in focusing Kerr mediaJun 01 2016Powerful incoherent laser pulses can propagate in focusing Kerr media much longer distances than can coherent pulses, due to the fast phase mixing that prevents transverse filamentation. This distance is limited by 4-wave scattering, which accumulates ... More
Motility at the origin of life: Its characterization and a modelNov 11 2013Due to recent advances in synthetic biology and artificial life, the origin of life is currently a hot topic of research. We review the literature and argue that the two traditionally competing "replicator-first" and "metabolism-first" approaches are ... More
Adiabatic nonlinear waves with trapped particles: I. General formalismJul 15 2011Nov 12 2011A Lagrangian formalism is developed for a general nondissipative quasiperiodic nonlinear wave with trapped particles in collisionless plasma. The adiabatic time-averaged Lagrangian density $\mcc{L}$ is expressed in terms of the single-particle oscillation-center ... More
Adiabatic nonlinear waves with trapped particles: III. Wave dynamicsJul 15 2011Nov 12 2011The evolution of adiabatic waves with autoresonant trapped particles is described within the Lagrangian model developed in Paper I, under the assumption that the action distribution of these particles is conserved, and, in particular, that their number ... More
Dressed-particle approach in the nonrelativistic classical limitNov 12 2008For a nonrelativistic classical particle undergoing arbitrary oscillations, the generalized effective potential Y is derived from nonlinear eigenfrequencies of the particle-field system. Specifically, the ponderomotive potential is extended to a nonlinear ... More
Optimal Time-Series Selection of QuasarsAug 18 2010Jan 04 2011We present a novel method for the optimal selection of quasars using time-series observations in a single photometric bandpass. Utilizing the damped random walk model of Kelly et al. (2009), we parameterize the ensemble quasar structure function in Sloan ... More
PSpectRe: A Pseudo-Spectral Code for (P)reheatingMay 11 2010Aug 20 2010PSpectRe is a C++ program that uses Fourier-space pseudo-spectral methods to evolve interacting scalar fields in an expanding universe. PSpectRe is optimized for the analysis of parametric resonance in the post-inflationary universe, and provides an alternative ... More
Hypoelliptic heat kernels on infinite-dimensional Heisenberg groupsOct 30 2013Dec 12 2013We study the law of a hypoelliptic Brownian motion on an infinite-dimensional Heisenberg group based on an abstract Wiener space. We show that the endpoint distribution, which can be seen as a heat kernel measure, is absolutely continuous with respect ... More
On Convergence to Essential SingularitiesJan 05 2018An iterative optimization method applied to a function $f$ on $\mathbb{R}^n$ will produce a sequence of arguments $\{\mathbf{x}_k\}_{k \in \mathbb{N}}$; this sequence is often constrained such that $\{f(\mathbf{x}_k)\}_{k \in \mathbb{N}}$ is monotonic. ... More
Strong hypercontractivity and logarithmic Sobolev inequalities on stratified complex Lie groupsOct 17 2015Sep 13 2017We show that for a hypoelliptic Dirichlet form operator A on a stratified complex Lie group, if the logarithmic Sobolev inequality holds, then a holomorphic projection of A is strongly hypercontractive in the sense of Janson. This extends previous results ... More
Gravitational Waves from Supersymmetry BreakingFeb 11 2009In theories of supersymmetry breaking, it is often the case that there is more than one metastable vacuum. First-order phase transitions among such metastable vacua may generate a stochastic background of gravitational waves, the observation of which ... More
Computing with voting treesNov 02 2012The classical paradox of social choice theory asserts that there is no fair way to deterministically select a winner in an election among more than two candidates; the only definite collective preferences are between individual pairs of candidates. Combinatorially, ... More
Chromatic homotopy theory is asymptotically algebraicNov 02 2017Oct 24 2018Inspired by the Ax--Kochen isomorphism theorem, we develop a notion of categorical ultraproducts to capture the generic behavior of an infinite collection of mathematical objects. We employ this theory to give an asymptotic solution to the approximation ... More
Searching for Signs of the Second Higgs DoubletMay 10 2013The search for evidence of extended electroweak symmetry breaking has entered a new phase with the discovery of a Standard Model (SM)-like Higgs at the LHC. The measurement of Higgs couplings and direct searches for additional scalars provide complementary ... More
Anharmonic Effects in the Low-Frequency Vibrational Modes of Aspirin and Paracetamol CrystalsJan 29 2019The low-frequency range of vibrational spectra is sensitive to collective vibrations of the lattice. In molecular crystals, it can be decisive to identify the structure of different polymorphs, and in addition, it plays an important role on the magnitude ... More
The electrical response matrix of a regular 2n-gonMar 28 2007Jun 17 2008Consider a unit-resistive plate in the shape of a regular polygon with 2n sides, in which even-numbered sides are wired to electrodes and odd-numbered sides are insulated. The response matrix, or Dirichlet-to-Neumann map, allows one to compute the currents ... More
Transchromatic generalized character mapsOct 14 2011Sep 07 2012In "Generalized Group Characters and Complex Oriented Cohomology Theories", Hopkins, Kuhn, and Ravenel develop a way to study cohomology rings of the form E^*(BG) in terms of a character map. The character map can be interpreted as a map of cohomology ... More
ISS-flationJan 14 2008Inflation may occur while rolling into the metastable supersymmetry-breaking vacuum of massive supersymmetric QCD. We explore the range of parameters in which slow-roll inflation and long-lived metastable supersymmetry breaking may be simultaneously realized. ... More
Electron quantum metamaterials in van der Waals heterostructuresNov 08 2018In recent decades, scientists have developed the means to engineer synthetic periodic arrays with feature sizes below the wavelength of light. When such features are appropriately structured, electromagnetic radiation can be manipulated in unusual ways, ... More
Reactors as a source of antineutrinos: the effect of fuel loading and burnup for mixed oxide fuelsDec 02 2016Dec 05 2016In a conventional light water reactor loaded with a range of uranium and plutonium-based fuel mixtures, the variation in antineutrino production over the cycle reflects both the initial core fissile inventory and its evolution. Under the assumption of ... More
Trapped-Electron Runaway EffectApr 01 2015In a tokamak, trapped electrons subject to a strong electric field cannot run away immediately, because their parallel velocity does not increase over a bounce period. However, they do pinch towards the tokamak center. As they pinch towards the center, ... More
Strategies for Advantageous Differential Transport of Ions in Magnetic Fusion DevicesJan 19 2018In a variety of magnetized plasma geometries, it has long been known that highly charged impurities tend to accumulate in regions of higher density. Here, we examine how this "collisional pinch" changes in the presence of additional forces, such as might ... More
Key-Value Memory Networks for Directly Reading DocumentsJun 09 2016Directly reading documents and being able to answer questions from them is a key problem. To avoid its inherent difficulty, question answering (QA) has been directed towards using Knowledge Bases (KBs) instead, which has proven effective. Unfortunately ... More
Effect of Anode Dielectric Coating on Hall Thruster OperationOct 16 2003An interesting phenomenon observed in the near-anode region of a Hall thruster is that the anode fall changes from positive to negative upon removal of the dielectric coating, which is produced on the anode surface during the normal course of Hall thruster ... More
Limits on Radioactive-Powered Emission Associated With a Short-Hard GRB 070724A in a Star-Forming GalaxyAug 01 2009We present results of an extensive observing campaign of the short duration, hard spectrum gamma-ray burst (GRB) 070724A, aimed at detecting the radioactively-powered emission that might follow from a binary merger or collapse involving compact objects. ... More
Exceeding the leading spike intensity and fluence limits in backward Raman amplifiersSep 18 2014The leading amplified spike in backward Raman amplifiers can reach nearly relativistic intensities before the saturation by the relativistic electron nonlinearity, which sets an upper limit to the largest achievable leading spike intensity. It is shown ... More
Backward Raman amplification in the Langmuir wavebreaking regimeSep 17 2014In plasma-based backward Raman amplifiers, the output pulse intensity increases with the input pump pulse intensity, as long as the Langmuir wave mediating energy transfer from the pump to the seed pulse remains intact. However, at high pump intensity, ... More
Available free energy under local phase space diffusionApr 28 2016The free energy associated with the birth distribution of alpha particles in DT fusion reactors is an enormous resource that can be tapped with waves. An interesting academic question is the maximum energy that can be extracted from the alpha particle ... More
Building a Better mSUGRA: WIMP Dark Matter Without Flavor ViolationJun 10 2009The appearance of a natural dark matter candidate, the neutralino, is among the principal successes of minimal supergravity (mSUGRA) and its descendents. In lieu of a suitable ultraviolet completion, however, theories of gravity-mediated supersymmetry ... More
On the Phenomenology of Strongly Coupled Hidden SectorsMay 25 2009In models of supersymmetry (SUSY) breaking and mediation, strongly coupled SUSY-breaking sectors can play a significant role in determining the low-energy spectrum of the model. For example, strong dynamics may provide a natural solution to both the SUSY ... More
Efficiency of Wave-Driven Rigid Body Rotation Toroidal ConfinementNov 13 2016The compensation of vertical drifts in toroidal magnetic fields through a wave-driven poloidal rotation is compared to compensation through the wave driven toroidal current generation to support the classical magnetic rotational transform. The advantages ... More
Saturation of the leading spike growth in backward Raman amplifiersSep 18 2014Backward Raman amplification of laser pulses in plasmas can produce nearly relativistic unfocused output intensities and multi-exawatt powers in compact devices. The largest achievable intensity depends on which of major competitive processes sets this ... More
The possibility of a Hall thruster operation in the absence of the anode sheathMay 11 2002A method of determining boundary conditions for quasi 1-D modeling of steady-state operation of a Hall Thruster with ceramic channel is presented. For a given mass flow rate and magnetic field profile the imposed condition of a smooth sonic transition ... More
Sequestering the Gravitino: Neutralino Dark Matter in Gauge MediationAug 07 2008Sep 03 2008In conventional models of gauge-mediated supersymmetry breaking, the lightest supersymmetric particle (LSP) is invariably the gravitino. However, if the supersymmetry breaking sector is strongly coupled, conformal sequestering may raise the mass of the ... More
Modulino Dark Matter and the INTEGRAL 511 keV LineAug 13 2009Aug 21 2009In this paper we present a simple extension of the minimal supersymmetric standard model [MSSM] which "naturally" produces the INTEGRAL photon signal. The model can be embedded in an SU(5) grand unified theory [GUT] with gauge mediated SUSY breaking. ... More
Evidence of Long Range Order in the Riemann Zeta FunctionOct 14 2012We have done a statistical analysis of some properties of the contour lines Im$(\zeta (s))$ = 0 of the Riemann zeta function. We find that this function is broken up into strips whose average width on the critical line does not appear to vary with height. ... More
Beyond the Imry-Ma Length: Scaling Behavior in the 3D Random Field $XY$ ModelDec 13 2018We have performed studies of the 3D random field $XY$ model on $L \times L \times L$ simple cubic lattices with periodic boundary conditions, with a random field strength of $h_r$ = 1.875, for $L =$ 64, 96 and 128, using a parallelized Monte Carlo algorithm. ... More