Flux expulsion by inhomogeneous turbulence     

L. Tao  M. R. E. Proctor  & N. O. Weiss 《Monthly notices of the Royal Astronomical Society》1998,300(3):907-914

Flux expulsion is an important consequence of the interaction of magnetic fields with fluid convection and has been well studied for particular cases of steady, single-cell flows. Here we examine a related phenomenon in inhomogeneous turbulence using direct numerical simulations. To understand our numerical results, we analyse average properties of our model, and obtain mean transport coefficients which can be used to describe the approach of the system to its final state. For the kinematic problem these transport coefficients give an excellent prediction of the expulsion process; however, the enhanced transport is suppressed by dynamical back-reaction of the Lorentz force. Finally, we discuss the astrophysical implications for magnetic fields in stellar convection zones. Segregation of magnetic fields from turbulent motion not only allows strong toroidal fields to accumulate in regions of convective overshoot but also permits significant poloidal fields to be maintained by dynamo action in stars like the Sun.  相似文献   

Simulation of Ground-Water Flow in a Mined Watershed in Eastern Ohioa     

Jonathan S. Weiss  Allan C. Razem 《Ground water》1984,22(5):549-560

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Discovery of rapid radial velocity variations in the roAp star 10 Aql and possible pulsations of β CrB     

O. Kochukhov  J. D. Landstreet  T. Ryabchikova  W. W. Weiss  F. Kupka 《Monthly notices of the Royal Astronomical Society》2002,337(2):L1-L5

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On the magnetic field in pores     

G. W. Simon  N. O. Weiss 《Solar physics》1970,13(1):85-103

The magnetic field in an axisymmetric pore is current free and can be represented by a flux tube with a magnetic potential of the formAJ ₀(kr)e ^-kz. For a given magnetic flux the field in this pore model is uniquely defined if the magnetic pressure balances the gas pressure at two levels. For models with fluxes of 0.5–3.0 × 10²⁰ mx the surface radius varies from 1100–2700 km (diameters of 3–8 arc-sec) and the Wilson depression is estimated at 200 km. As the flux increases, the field becomes nearly horizontal at the edge of the pore and eventually a penumbra is formed. The distinction between pores and sunspots is investigated; the critical flux is about 10²⁰ Mx, corresponding to a radius of 1500 km.Visitor, as a member of the High Altitude Observatory Solar Project, at Sacramento Peak Observatory, Sunspot, N.M., U.S.A.  相似文献   

Ship motion measurement filter design     

Weiss  I. DeVries  T. 《Oceanic Engineering, IEEE Journal of》1977,2(4):325-330

A procedure is presented for designing Kalman filters to measure linear and angular ship motion parameters using realistic models of the ship motion dynamics. The design is based on the state space modeling of ship motion dynamics. The designed filters exhibited significant accuracy improvement (order of magnitude) over filters which do not model ship dynamics. The sensitivity of the filter mechanization to mismodeling of dynamics is investigated. Bounding filter design techniques are used to minimize the effects of mismodeling. The particular measurement system investigated consisted of linear and angular accelerometers in a strapdown mode. The design techniques are also applicable to inertial instruments in a stable inertial platform mode.  相似文献   

Recent developments and goals in texture research of geological materials     

B. Leiss  K. Ullemeyer  K. Weber  H. G. Brokmeier  H. -J. Bunge  M. Drury  U. Faul  F. Fueten  A. Frischbutter  H. Klein  W. Kuhs  P. Launeau  G. E. Lloyd  D. J. Prior  Ch. Scheffzük  T. Weiss  K. Walther  H. -R. Wenk 《Journal of Structural Geology》2000,22(11-12)

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An evaluation of solar radiation pressure strategies for the GPS constellation     

Ant Sibthorpe  Willy Bertiger  Shailen D. Desai  Bruce Haines  Nate Harvey  Jan P. Weiss 《Journal of Geodesy》2011,85(8):505-517

The subtle effects of different Global Positioning System (GPS) satellite force models are becoming apparent now that mature processing strategies are reaching new levels of accuracy and precision. For this paper, we tested several approaches to solar radiation pressure (SRP) modeling that are commonly used by International GNSS Service (IGS) analysis centers. These include the GPS Solar Pressure Model (GSPM; Bar-Sever and Kuang in The Interplanetary Network Progress Report 42-160, 2005) and variants of the so-called DYB model (Springer et al. in Adv Space Res 23:673–676, 1999). Our results show that currently observed differences between GPS orbit solutions from the various IGS analysis centers are in large part explained by differences between their respective approaches to modeling SRP. DYB-based strategies typically generate orbit solutions that have the smallest differences with respect to the IGS final combined solution, largely because the DYB approach is most commonly used by the contributing analysis centers. However, various internal and external metrics, including ambiguity resolution statistics and satellite laser ranging observations, support continued use of the GSPM-based approach for precise orbit determination of the GPS constellation, at least when using the GIPSY-OASIS software.  相似文献   

The null result of a search for pulsational variations of the surface magnetic field in the roAp star γ Equulei     

O. Kochukhov  T. Ryabchikova  J. D. Landstreet  W. W. Weiss 《Monthly notices of the Royal Astronomical Society》2004,351(2):L34-L38

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Simple models for magnetic flux tubes     

G. W. Simon  N. O. Weiss  A. H. Nye 《Solar physics》1983,87(1):65-75

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New constraints on elemental and Pb and Nd isotope compositions of South American and Southern African aerosol sources to the South Atlantic Ocean     

R. Khondoker  D. Weiss  T. van de Flierdt  M. Rehkämper  K. Kreissig  B.J. Coles  S. Strekopytov  E. Humphreys-Williams  S. Dong  A. Bory  V. Bout-Roumazeilles  P. Smichowski  P. Cid-Agüero  M. Babinski  R. Losno  F. Monna 《Chemie der Erde / Geochemistry》2018,78(3):372-384

Improving the geochemical database available for characterising potential natural and anthropogenic aerosol sources from South America and Southern Africa is a critical precondition for studies aimed at understanding trace metal controls on the marine biogeochemical cycles of the South Atlantic Ocean. We here present new elemental and isotopic data for a wide range of sample types from South America and Southern Africa that are potentially important aerosol sources. This includes road dust from Buenos Aires and lichen samples from Johannesburg, soil dust from Patagonia, volcanic ash from the Andean volcanic belt, and aerosol samples from São Paulo. All samples were investigated for major (Al, Ca, Fe, Mg, Na, K, Mn) and trace element (Cd, Co, Cr, Cu, Ni, Pb, REE, Sc, Th, Y, V, Zn) concentrations and Nd and Pb isotopic compositions. We show that diagrams of ²⁰⁸Pb/²⁰⁷Pb vs. ε_Nd, ²⁰⁸Pb/²⁰⁷Pb vs. Pb/Al, 1/[Pb], Zn/Al, Cd/Al, Cu/Al, and ε_Nd vs. Pb/Al, and 1/[Nd] are best suited to separate South American and South African source regions as well as natural and anthropogenic sources. A subset of samples from Patagonia and the Andes was additionally subjected to separation of a fine (<5?μm) fraction and compared to the composition of the bulk sample. We show that differences in the geochemical signature of bulk samples between individual regions and source types are significantly larger than between grain sizes. Jointly, these findings present an important step forward towards a quantitative assessment of aeolian trace metal inputs to the South Atlantic Ocean.  相似文献