New mechanism and exact theory of superconductivity from strong repulsive interaction
A mechanism for pairing in purely repulsive Fermi systems is developed, leading to unconventional superconducting behaviors.
36 MATERIALS SCIENCE↗
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Interaction of strong shock wave with turbulent boundary layer
The reported investigation represents an extension of the time-dependent solution of separated laminar flows based on the complete Navier-Stokes equations reported by MacCormack (1971) and Carter (1973). The current study includes turbulence models in conjunction with the compressible flow equations. The calculations start with a uniform flow except for values imposed along the upstream and outer boundaries. The basic numerical method is discussed along with questions concerning the exponential accuracy and the resolution of the viscous sublayer in a compressed region.
Baldwin, B. S.↗
The Echo 4 electron beam experiment - Television observation of artificial auroral streaks indicating strong beam interactions in the high-latitude magnetosphere
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Hallinan, T. J.↗
Navier-Stokes simulations of blade-vortex interaction using high-order accurate upwind schemes
Conventional, spatially second-order-accurate, finite-difference schemes are much too dissipative for calculations involving vortices that travel large distances (relative to some measure of the size of the vortex). This study presents a fifth-order-accurate upwind-biased scheme that preserves vortex structure for much longer times than existing second-order-accurate central and upwind difference schemes. Vortex calculations demonstrating this aspect of the fifth-order scheme are also presented. The method is then applied to the blade-vortex interaction problem. Results for strong interactions wherein the vortex impinges directly on the airfoil or a shock associated with the airfoil are presented. None of these calculations required any modeling of the shape, size, and trajectory of the interacting vortex.
Rai, Man Mohan↗
The strong nonlinear interaction of Tollmien-Schlichting waves and Taylor-Goertler vortices in curved channel flow
Viscous fluid flows with curved streamlines can support both centrifugal and viscous traveling wave instabilities. Here the interaction of these instabilities in the context of the fully developed flow in a curved channel is discussed. The viscous (Tollmein-Schlichting) instability is described asymptotically at high Reynolds numbers and it is found that it can induce a Taylor-Goertler flow even at extremely small amplitudes. In this interaction, the Tollmein-Schlichting wave can drive a vortex state with wavelength either comparable with the channel width or the wavelength of lower branch viscous modes. The nonlinear equations which describe these interactions are solved for nonlinear equilibrium states.
Bennett, J.↗
More accurate predictions with transonic Navier-Stokes methods through improved turbulence modeling
Significant improvements in predictive accuracies for off-design conditions are achievable through better turbulence modeling; and, without necessarily adding any significant complication to the numerics. One well established fact about turbulence is it is slow to respond to changes in the mean strain field. With the 'equilibrium' algebraic turbulence models no attempt is made to model this characteristic and as a consequence these turbulence models exaggerate the turbulent boundary layer's ability to produce turbulent Reynolds shear stresses in regions of adverse pressure gradient. As a consequence, too little momentum loss within the boundary layer is predicted in the region of the shock wave and along the aft part of the airfoil where the surface pressure undergoes further increases. Recently, a 'nonequilibrium' algebraic turbulence model was formulated which attempts to capture this important characteristic of turbulence. This 'nonequilibrium' algebraic model employs an ordinary differential equation to model the slow response of the turbulence to changes in local flow conditions. In its original form, there was some question as to whether this 'nonequilibrium' model performed as well as the 'equilibrium' models for weak interaction cases. However, this turbulence model has since been further improved wherein it now appears that this turbulence model performs at least as well as the 'equilibrium' models for weak interaction cases and for strong interaction cases represents a very significant improvement. The performance of this turbulence model relative to popular 'equilibrium' models is illustrated for three airfoil test cases of the 1987 AIAA Viscous Transonic Airfoil Workshop, Reno, Nevada. A form of this 'nonequilibrium' turbulence model is currently being applied to wing flows for which similar improvements in predictive accuracy are being realized.
Johnson, Dennis A.↗
Plasma Flow Past Cometary and Planetary Satellite Atmospheres
The tenuous atmospheres and ionospheres of comets and outer planet satellites share many common properties and features. Such similarities include a strong interaction with their outer radiation, fields and particles environs. For comets the interaction is with the magnetized solar wind plasma, whereas for satellites the interaction is with the strongly magnetized and corotating planetary magnetospheric plasma. For this reason there are many common or analogous physical regimes, and many of the same modeling techniques are used to interpret remote sensing and in situ measurements in order to study the important underlying physical phenomena responsible for their appearances. We present here a review of various modeling approaches which are used to elucidate the basic properties and processes shaping the energetics and dynamics of these systems which are similar in many respects.
Combi, Michael R.↗
A Generalized Weizsacker-Williams Method Applied to Pion Production in Proton-Proton Collisions
A new "Generalized" Weizsacker-Williams method (GWWM) is used to calculate approximate cross sections for relativistic peripheral proton-proton collisions. Instead of a mass less photon mediator, the method allows for the mediator to have mass for short range interactions. This method generalizes the Weizsacker-Williams method (WWM) from Coulomb interactions to GWWM for strong interactions. An elastic proton-proton cross section is calculated using GWWM with experimental data for the elastic p+p interaction, where the mass p+ is now the mediator. The resulting calculated cross sections is compared to existing data for the elastic proton-proton interaction. A good approximate fit is found between the data and the calculation.
Ahern, Sean C.↗
Interaction of Strong Transient Interplanetary Disturbances with the Dayside Magnetosphere
The objective of the investigation was to gain an understanding of the complex response of the magnetosphere to strong transient interplanetary disturbances. Because the project was only funded for a year, the investigation focused on only one of the three topics proposed in the original three year proposal. We investigated the response of the dayside auroral region to strong transient interplanetary disturbances. The method of the investigation was to use three-dimensional magnetohydrodynamic (MHD) simulations that employ measurements of the solar wind conditions upstream the bow shock to model actual events and then to compare the simulation results with observations from spacecraft located at downstream locations. We modeled an event that occurred on July 14,2000, for which both CLUSTER and IMAGE simultaneous observations were available. The event was marked by high solar wind dynamic pressure and a strong IMF By component. Comparisons showed a very good agreement between intensifications in the auroral emissions measured by IMAGE
Berchem, Jean↗
DO WEAK INTERACTIONS BECOME STRONG AT 10-TEV?
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Singleton, R.↗
Strong WW Interaction at LHC
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Dobado, A.↗
Role of Capping Agents in the Synthesis of Salicylate-Capped Zinc Oxide Nanoparticles
Capping agents are often used for controlling the size, aggregation, and properties of nanoparticles. To guide the design of improved nanomaterials for targeted performance, one can use mechanistic insights into the interactions between capping agents and nanoparticles. Here, we employ density functional theory (DFT), reactive force-field molecular dynamics (ReaxFF MD) simulations, and optical spectroscopy to study the interactions between salicylate, as a model capping agent, and zinc oxide (ZnO) nanoparticles. In this work, we find that salicylate strongly interacts with the nanoparticle via the formation of O–Zn bonds in a distorted six-membered coordination ring structure. We describe the mechanisms of capping of ZnO nanoparticles by salicylate via three different binding modes. Simulations indicate that salicylate undergoes dissociative adsorption at the highly active surface Zn sites via a hydrogen-transfer process, thereby forming a tridentate configuration. The water-mediated interaction also facilitates the dissociative adsorption, leading to two salicylate O atoms coordinating with a surface Zn atom, while the other salicylate O atom bonds with another surface Zn atom. For molecular adsorption, binding free energies indicate that salicylate binds more strongly to ZnO, often in a bidentate configuration, than water does. The formation of the salicylate–ZnO complex is substantiated by UV–visible and Fourier transform infrared spectra. We find that the C=O stretching mode of salicylate becomes softened when it interacts with the nanoparticle, suggesting chemisorption of salicylate on ZnO. Although DFT predicts strong interaction between salicylate and ZnO, ReaxFF MD simulation indicates the moderate interaction between these two components in aqueous solution. Water molecules in close contact with the nanoparticle surface undergo dissociation, thus resulting in a surface hydroxyl, a reactive oxygen species that may influence the nanoparticle’s catalytic properties. Overall, the atomic-level information provided here can guide the selection process of salicylate as an appropriate agent for ZnO nanoparticle synthesis when strong interactions of particles with capping agents are required.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
User's guide for ENSAERO: A multidisciplinary program for fluid/structural/control interaction studies of aircraft (release 1)
Strong interactions can occur between the flow about an aerospace vehicle and its structural components resulting in several important aeroelastic phenomena. These aeroelastic phenomena can significantly influence the performance of the vehicle. At present, closed-form solutions are available for aeroelastic computations when flows are in either the linear subsonic or supersonic range. However, for aeroelasticity involving complex nonlinear flows with shock waves, vortices, flow separations, and aerodynamic heating, computational methods are still under development. These complex aeroelastic interactions can be dangerous and limit the performance of aircraft. Examples of these detrimental effects are aircraft with highly swept wings experiencing vortex-induced aeroelastic oscillations, transonic regime at which the flutter speed is low, aerothermoelastic loads that play a critical role in the design of high-speed vehicles, and flow separations that often lead to buffeting with undesirable structural oscillations. The simulation of these complex aeroelastic phenomena requires an integrated analysis of fluids and structures. This report presents a summary of the development, applications, and procedures to use the multidisciplinary computer code ENSAERO. This code is based on the Euler/Navier-Stokes flow equations and modal/finite-element structural equations.
Guruswamy, Guru P.↗
Magnetoresistance effect in Fe{sub 20}Ni{sub 80}/graphene/Fe{sub 20}Ni{sub 80} vertical spin valves
Vertical spin valve devices with junctions of single- and bi-layer graphene interlayers sandwiched with Fe{sub 20}Ni{sub 80} (Permalloy) electrodes were fabricated by exploiting the direct growth of graphene on the Permalloy. The linear current-voltage characteristics indicated that ohmic contacts were realized at the interfaces. The systematic characterization revealed the significant modification of the electronic state of the interfacial graphene layer on the Permalloy surface, which indicates the strong interactions at the interface. The ohmic transport was attributable to the strong interface-interaction. The vertical resistivity of the graphene interlayer and the spin asymmetry coefficient at the graphene/Permalloy interface were obtained to be 0.13 Ω cm and 0.06, respectively. It was found that the strong interface interaction modifies the electronic structure and metallic properties in the vertical spin valve devices with bi-layer graphene as well as single-layer graphene.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
I Would Like to Know... [Slides]
Problems of High-Energy Physics (NAL Design Report, January 1968) We would like to have answers to many questions. Among them are the following: Which, if any, of the particles that have so far been discovered, is, in fact, elementary, and is there any validity in the concept of “elementary” particles? What new particles can be made at energies that have not yet been reached? Is there some set of building blocks that is still more fundamental than the neutron and the proton? Is there a law that correctly predicts the existence and nature of all the particles, and if so, what is that law? Will the characteristics of some of the very short-lived particles appear to be different when they are produced at such higher velocities that they no longer spend their entire lives within the strong influence of the particle from which they are produced? Do new symmetries appear or old ones disappear for high momentum-transfer events? What is the connection, if any, of electromagnetism and strong interactions? Do the laws of electromagnetic radiation, which are now known to hold over an enormous range of lengths and frequencies, continue to hold in the wavelength domain characteristic of the subnuclear particles? What is the connection between the weak interaction that is associated with the massless neutrino and the strong one that acts between neutron and proton? Is there some new particle underlying the action of the “weak” forces, just as, in the case of the nuclear force, there are mesons, and, in the case of the electromagnetic force, there are photons? If there is not, why not? In more technical terms: Is local field theory valid? A failure in locality may imply a failure in our concept of space. What are the fields relevant to a correct local field theory? What are the form factors of the particles? What exactly is the explanation of the electromagnetic mass difference? Do “weak” interactions become strong at sufficiently small distances? Is the Pomeranchuk theorem true? Do the total cross sections become constant at high energy? Will new symmetries appear, or old ones disappear, at higher energy?
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Selective Kondo strong coupling in magnetic impurity flat-band lattices
The periodic Anderson impurity model on the Lieb lattice is studied by the slave-boson mean-field approximation in the strong interaction limit. The electron structure of conduction electrons on the Lieb lattice features both the band flatness and soft gap at low energy. With these features conduction electrons can form both the soft-gap and the molecular Kondo singlets with the magnetic impurities, and this leads to a competition between the soft-gap and the molecular Kondo effects in the lattice. We find a selective Kondo strong coupling, where at selected sites the magnetic impurities are strongly coupled to conduction electrons, and at the remaining sites they are decoupled from the lattice. The selective Kondo strong coupling occurs between the full local moment and the full strong coupling regimes, and it yields an effective lattice depletion. At low temperature the selection of the Kondo strong coupling is dominant at those lattice sites, where the local density of states of conduction electrons exhibits the flat-band feature, independently of the impurity parameters. Rich phase diagrams for different model parameters are obtained.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Production of dark-matter bound states in the early universe by three-body recombination
The small-scale structure problems of the universe can be solved by self-interacting dark matter that becomes strongly interacting at low energy. A particularly predictive model for the self-interactions is resonant short-range interactions with an S-wave scattering length that is much larger than the range. The velocity dependence of the cross section in such a model provides an excellent fit to self-interaction cross sections inferred from dark-matter halos of galaxies and clusters of galaxies if the dark-matter mass is about 19 GeV and the scattering length is about 17 fm. Such a model makes definite predictions for the few-body physics of weakly bound clusters of the dark-matter particles. The formation of the two-body bound cluster is a bottleneck for the formation of larger bound clusters. We calculate the production of two-body bound clusters by three-body recombination in the early universe under the assumption that the dark matter particles are identical bosons, which is the most favorable case. If the dark-matter mass is 19 GeV and the scattering length is 17 fm, the fraction of dark matter in the form of two-body bound clusters can increase by as much as 4 orders of magnitude when the dark-matter temperature falls below the binding energy, but its present value remains less than 10 -6 . The present fraction can be increased to as large as 10 -3 by relaxing the constraints from small-scale structure and decreasing the mass of the dark matter particle.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DarkNESS: A skipper-CCD nanosatellite for dark matter searches
The Dark matter Nanosatellite Equipped with Skipper Sensors (DarkNESS) deploys a recently developed skipper-CCD architecture with sub-electron readout noise in low Earth orbit (LEO) to investigate potential signatures of dark matter (DM). The mission addresses two interaction channels: electron recoils from strongly interacting sub-GeV DM and X-rays produced through decaying DM. Orbital observations avoid attenuation that limits ground-based measurements, extending sensitivity reach for both channels. The mission proceeds toward launch following laboratory validation of the instrument. A launch opportunity has been secured through Firefly Aerospace’s DREAM 2.0 program, awarded to the University of Illinois Urbana-Champaign (UIUC). As a result, this will constitute the first use of skipper-CCDs in space and evaluate their suitability for low-noise X-ray and single-photon detection in future space observatories.
Alpine, Phoenix [University of Illinois, Urbana-Ch↗