FLUX EMERGENCE AND PROMINENCES: A NEW SCENARIO FOR 3-DIMENSIONAL FIELD GEOMETRY BASED ON OBSERVATIONS WITH THE ADVANCED STOKES POLARIMETER     

Lites  B.W.  Low  B.C. 《Solar physics》1997,174(1-2):91-98

This paper presents an interpretation of the evolution of the vector magnetic field at the photosphere based on measurements of the advanced Stokes polarimeter, along with chromospheric H from the Lockheed instrument operating on La Palma and X-ray images of the corona from Yohkoh. These measurements are consistent with the emergence of a nearly closed magnetic structure from the solar interior into the corona. The highly non-potential field topology inferred from the data suggests that strong field-aligned currents exist in the emergent magnetic structure as it buoyantly rises through the photosphere. Material trapped in this closed structure is pulled upward to later condense into a prominence. By analogy of this small active region evolution with the observed properties of large quiescent prominences, we speculate that this process might also be operative on a much larger scale. A 3-dimensional magnetostatic model is presented which has many topological features in common with the observations.  相似文献   

On the relationship between the topology of magnetic field lines and flux surfaces     

R. Rosner  B. C. Low  K. Tsinganos  M. A. Berger 《地球物理与天体物理流体动力学》2013,107(4):251-271

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Practical second‐order reliability analysis applied to foundation engineering     

Chin Loong Chan  Bak Kong Low 《国际地质力学数值与分析法杂志》2012,36(11):1387-1409

A practical and efficient approach of implementing second‐order reliability method (SORM) is presented and illustrated for cases related to foundation engineering involving explicit and implicit limit state functions. The proposed SORM procedure is based on an approximating paraboloid fitted to the limit state surface in the neighborhood of the design point and can be easily carried out in a spreadsheet. Complex mathematical operations are relegated to relatively simple user‐created functions. The failure probability is calculated automatically based on the reliability index and principal curvatures of the limit state surface using established closed‐form SORM formulas. Four common foundation engineering examples are analyzed using the proposed method and discussed: immediate settlement of a flexible rectangular foundation, bearing capacity of a shallow footing, axial capacity of a vertical single pile, and deflection of a pile under lateral load. Comparisons with Monte Carlo simulations are made. In the case of the laterally loaded pile, the friction angle of the soil is represented as a one‐dimensional random field, and pile deflections are computed based on finite element analysis on a stand‐alone computer package. The implicit limit state function is approximated via the response surface method using two quadratic models. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Hydrodynamical simulations of the decay of high-speed molecular turbulence – I. Dense molecular regions     

Georgi Pavlovski  Michael D. Smith  Mordecai-Mark Mac Low  Alexander Rosen 《Monthly notices of the Royal Astronomical Society》2002,337(2):477-487

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What controls the star formation rate in galaxies?     

Mordecai-Mark Mac Low 《Astrophysics and Space Science》2002,281(1-2):429-438

Summary of the third discussion of the conference. Topics covered include the mechanisms controlling the star formation rate ingalaxies, the source of the driving energy for interstellar turbulence, and the reasons for different star formation rates ingalaxies with similar masses. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

Non-axisymmetric magnetostatic equilibrium     

W. R. Hu  Y. Q. Hu  B. C. Low 《Solar physics》1983,83(2):195-205

This paper considers the structural properties of a sunspot-like magnetic flux tube which lacks perfect axisymmetry. The flux tube is taken to be in static equilibrium with an atmosphere in a uniform gravity. Assuming the departure from axisymmetry to be slight, the equations for the first order non-axisymmetric part of the equilibrium are derived in cylindrical coordinates. These first order equations reduce to a linear second order hyperbolic partial differential equation in the r-z plane. Whereas Cauchy type boundary conditions are appropriate for hyperbolic equations, physical considerations dictate the specification of boundary conditions on a closed surve for our problem of interest. The construction of solutions to this boundary value problem is illustrated with three analytically soluble cases, where the zero-order axisymmetric equilibria are chosen to have magnetic field geometry of different complexity. A physical discussion of the results is given.  相似文献   

A variational approach to the question of temporal stability of equilibrium models of solar prominences     

I. Lerche  B. C. Low 《Solar physics》1981,69(2):327-342

Using a Lagrangian approach to the equations describing small amplitude departures from equilibrium of solar prominences, we derive seven quantities which, by analogy to the concepts of energy, momentum and angular momentum, are conserved under circumstances corresponding to ignorable coordinates of classical mechanics. In a pragmatic sense it is expected that these conservation laws will be useful as criteria of accuracy in obtaining eigen-frequencies for the perturbation equations when numerical techniques are employed.We also demonstrate that: (i) the perturbation equations (which are not self-adjoint) follow from an external variation of a Lagrangian; (ii) the equations adjoint to the perturbation equations also follow from an extremal variation of the same Lagrangian; (iii) the Lagrangian approach automatically gives the conserved quantities, together with a variational principle for computing the eigen-frequencies of the perturbation equations.In view of the paucity of analytic solutions (and their eigen-frequencies) to the perturbation equations (due essentially to the complicated spatial dependence of thermodynamic quantities describing the equilibria) we believe that the technique developed here - which is capable of handling complicated spatial dependences and which has internal criteria for assessing accuracy of any given numerical convergence scheme - is a valuable addition to the arsenal of methods used for discussing the equilibria, and their stability, of models thought to represent the basic physical processes underlying the quiescent solar prominence phenomenon.  相似文献   

Legal aspects of conserving native oysters in Scotland     

Smith IP  Low PJ  Moore PG 《Marine pollution bulletin》2006,52(5):479-483

Native oysters (Ostrea edulis) historically supported valuable fisheries in Scotland, but are now absent from areas of former abundance on the east coast and occur mainly in isolated populations in west coast sea lochs. The main contemporary threat is from unauthorized gathering. In most places, the exclusive right to gather is retained by the Crown, as a remnant of the feudal system, but in some areas the right has been acquired by individuals or institutions. A temporary right to gather oysters may be obtained by permit from the proprietor, or through a Several or Regulating Order made under shellfish fisheries legislation. The right to gather oysters is separate from ownership of the foreshore or sea bed on which they are located. To receive the maximum legal protection, oyster beds must be marked out, or the rights to them otherwise adequately made known. Wild or formerly-cultivated oyster beds may not meet this criterion and, in any case, enforcement is difficult in remote locations. It has been proposed that there should be a statutory public right to gather oysters. Were this to be created, then strong conservation measures would need to be implemented to protect native oysters from eradication by uncontrolled gathering.  相似文献   

INTERPRETATION OF COPPER AND ZINC CONTAMINATION IN THE AQUATIC ENVIRONMENT OF PENINSULAR MALAYSIA WITH SPECIAL REFERENCE TO A POLLUTED RIVER, SEPANG RIVER   总被引：2，自引：0，他引：2  

Chee Kong Yap Ahmad Ismail Ching How Low Soon Guan Tan 《湿地科学》2007,5(4):311-321

Three different aquatic ecosystems(an urban pond,Kelana Jaya Pond;a polluted river,Sepang River;and the intertidal and offshore areas of the west coast of Peninsular Malaysia)with different sets of ecological backgrounds and human activities were reviewed and assessed for the levels of Cu and Zn contamination with special reference to those found in polluted sediments collected from the Sepang River.The discussion on the contamination levels of Cu and Zn in the aquatic environment of Peninsular Malaysia was based on a comparison of the metal contamination of 4 kinds of aquatic environments.The comparison of 4 different areas was based on ① total concentrations of 2 metals;② the concentrations and percentages of the nonresistant(EFLE,acid-reducible and oxidisable-organic)and resistant geochemical fractions;and ③ correlation coefficients(R-values)based on data of 4 areas separately and a combination of 4 areas.The Sepang River recorded nonresistant fractions of 63.1% for Zn and 55.8% for Cu in addition to slightly lower metal concentrations when compared to those(60%-70%)reported before the shutting down of the piggery activities in that area.These nonresistant metal percentages(55%-63%)indicated that the metal concentrations were still dominated by anthropogenic sources since nonresistant fraction of metals were mostly contributed by anthropogenic sources.The positive results from the four different aquatic environments assessed here provided strong evidence to show that Malaysia's aquatic environment had received anthropogenic Cu and Zn.The present study also showed that the percentage of the nonresistant fraction and the R-values based on correlation analysis of Cu and Zn could be used as indicators of Cu and Zn pollution in the Malaysian aquatic ecosystem.Based on the present data,the correlation coefficients(R-values)are potential indicators of EFLE Cu and acid-reducible Cu of the sediments.The use of R-values as indicators of metal pollution is suggested and it is applicable to other heavy metal data although it should be improved in future studies.  相似文献   

The energy of electric current sheets     

Low  B. C.  Hu  Y. Q. 《Solar physics》1983,84(1-2):83-98

Solar Physics - The free energy associated with current sheets formed by displacing magnetic dipoles in a highly conducting medium is discussed. Specific models are illustrated, based on the idea...  相似文献