The effect of retardation on the stability of current filaments

We investigate the influence of the finite Alfvén velocity on the evolution of an active region filament. In general, variations of a current result in variations of the magnetic fields which spread around with the Alfvén velocity. As a consequence of the fact that a magnetic field can only change with the Alfvén velocity, a filament will experience the photospheric boundary conditions as these were at an Alfvén travel time back in time. The inclusion of this retardation effect in the momentum equation of a filament leads effectively to an extra force term. This force contribution acts in the direction in which the filament moves and has therefore a destabilizing effect on the filament. Because a moving filament acts as an antenna of Alfvén waves, the filament loses energy by the emission process. This leads to a radiative damping term in the equation of motion of the filament. In general, the radiative damping will be sufficiently strong to counteract the retardation instability. Numerical simulations show that during the energy build-up phase a filament follows the van Tend-Kuperus equilibrium curve. After the van Tend-Kuperus equilibrium has disappeared the filament goes through a transient phase moving with a sub-Alfvénic velocity upward. At greater heights the repulsive Lorentz force of the photospheric surface current magnetic field is balanced by the radiative damping, resulting in a decreasing filament velocity.Parts of this paper were presented at the 4th CESRA Workshop in Ouranopolis (Greece) in 1991.     

海河口地区全新世海侵层的相变与海面波动的对应关系

B_2孔揭示海河口地区全新世海侵层厚达19.2m,自下往上依次出现潮间滩、近岸浅海、前三角洲、三角洲湾、河口砂坝及河口边滩六个亚相,下部两个亚相呈海进层序,上部四个亚相呈海退层序。除河口边滩亚相底界外,其他所有亚相间的界面均为不连续面,显示海侵层为不连续沉积。研究表明该不连续沉积与海面波动有关.在全新世海侵高峰后,海面一直处于幅度不大(约1m 左右)的振荡运动状态,一次振荡波就在海岸线上留下一道贝壳堤,近5000余年来发生了5次振荡波,在海退平原中就有5道贝克堤与之对应。B_2孔海退层序中曲不连续面与贝壳堤基底侵蚀面相对应,也与振荡波的上升坡段相对应。海退层序所表现出来的海岸向海推进现象不是海面大幅度下降的反映,而主要是河口区沉积物迅速加积的结果。     

A finite element model of circulation in shallow water with moving boundary on tidal-flat

To examine the circulation in shallow water with tidal flat, a finite element model for the numerical solution of the shallow water equations was developed by means of standard Galerkin's method. The domain computed was covered with triangular finite elements, and water elevation and velocity were approximated by linear interpolation functions, and the lumped coefficients were used to substitute for solving the high order algebraic equation system. The time-dependent land-water boundary changes are treated mathematically by interrelating the location of the land-water boundary with the instantaneous tidal level. The implicit scheme was adopted for the terms of the bottom friction and the Coriolis effect in the motion equation so that the numerical stability of the model has been improved.The model was applied to the tidal current on shoaling water with large tidal flat off Pikou, and a comparison between observed and calculated values showed good agreement, the flow pattern being reproduced. The result     

Profiles and Source Apportionment of Nonmethane Volatile Organic Compounds in Winter and Summer in Xi’an,China, based on the Hybrid Environmental Receptor Model

Summer and winter campaigns for the chemical compositions and sources of nonmethane hydrocarbons(NMHCs)and oxygenated volatile organic compounds(OVOCs)were conducted in Xi’an.Data from 57 photochemical assessment monitoring stations for NMHCs and 20 OVOC species were analyzed.Significant seasonal differences were noted for total VOC(TVOC,NMHCs and OVOCs)concentrations and compositions.The campaign-average TVOC concentrations in winter(85.3±60.6 ppbv)were almost twice those in summer(47.2±31.6 ppbv).Alkanes and OVOCs were the most abundant category in winter and summer,respectively.NMHCs,but not OVOCs,had significantly higher levels on weekends than on weekdays.Total ozone formation potential was higher in summer than in winter(by 50%)because of the high concentrations of alkenes(particularly isoprene),high temperature,and high solar radiation levels in summer.The Hybrid Environmental Receptor Model(HERM)was used to conduct source apportionment for atmospheric TVOCs in winter and summer,with excellent accuracy.HERM demonstrated its suitability in a situation where only partial source profile data were available.The HERM results indicated significantly different seasonal source contributions to TVOCs in Xi’an.In particular,coal and biomass burning had contributions greater than half in winter(53.4%),whereas traffic sources were prevalent in summer(53.1%).This study’s results highlight the need for targeted and adjustable VOC control measures that account for seasonal differences in Xi’an;such measures should target not only the severe problem with VOC pollution but also the problem of consequent secondary pollution(e.g.,from ozone and secondary organic aerosols).     

Multi-gas Emissions Pathways to Meet Climate Targets

So far, climate change mitigation pathways focus mostly on CO₂ and a limited number of climate targets. Comprehensive studies of emission implications have been hindered by the absence of a flexible method to generate multi-gas emissions pathways, user-definable in shape and the climate target. The presented method ‘Equal Quantile Walk’ (EQW) is intended to fill this gap, building upon and complementing existing multi-gas emission scenarios. The EQW method generates new mitigation pathways by ‘walking along equal quantile paths’ of the emission distributions derived from existing multi-gas IPCC baseline and stabilization scenarios. Considered emissions include those of CO₂ and all other major radiative forcing agents (greenhouse gases, ozone precursors and sulphur aerosols). Sample EQW pathways are derived for stabilization at 350 ppm to 750 ppm CO₂ concentrations and compared to WRE profiles. Furthermore, the ability of the method to analyze emission implications in a probabilistic multi-gas framework is demonstrated. The probability of overshooting a 2 ^∘C climate target is derived by using different sets of EQW radiative forcing peaking pathways. If the probability shall not be increased above 30%, it seems necessary to peak CO₂ equivalence concentrations around 475 ppm and return to lower levels after peaking (below 400 ppm). EQW emissions pathways can be applied in studies relating to Article 2 of the UNFCCC, for the analysis of climate impacts, adaptation and emission control implications associated with certain climate targets. See for EQW-software and data.     

Identification of the Major Allergen in Greasy-Back Shrimp （Metapenaeus ensis） by MALDI-TOF-MS

In order to better understand shrimp allergen,some basic characters of the major allergen of greasy-back shrimp (Metapenaeus ensis)were investigated.The major allergen was extracted and separated,and its peptide mass fingerprint(PMF) was analyzed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry(MALDI-TOF-MS).After screening in the NCBI database with Mascot searching engine,the results indicated that the major allergen of greasy-back shirmp was muscle tropomyosin.Database matching search showed that the top protein matched,i.e.the tropomyosin from giant tiger prawn(Penaeus monodon),had a Mowse value of 268.In addition,there were 27 queries matched with the allergen in greasy-back shirmp with an amino acid sequence coverage value of 65%.The matching scores and the sequence coverage values were also high with tropomyosins of other invertebrates,including Tyrophagus putrescentiae and Lepisma saccharina.These results indicated that the allergen of Metapenaeus ensis had high homology with other crustacean allergens,and provided molecular explanations for the high cross-reactivity of the major allergens between crustaceans and some other invertebrates.     

The role of algae in the stabilization of coastal dune blowouts

A number of mechanisms prevent blowouts in the dunes along the Dutch-coast from growing beyond a certain length. Plants play an important role in the stabilization process. Algae are the first plants to colonize the blowouts. Their filaments are surrounded by mucilaginous sheaths which adhere to the sand grains and increase the resistance of the sand to entrainment by wind. This suggests that artificially induced algal growths might be used in cheap, and ecologically justifiable, stabilization measures.     

Regions of primary energy release of solar flares associated with singularities in the magnetic field

The locations of sites of primary energy release of solar flares are studied. Magnetic singularities revealed earlier—self-intersections (reconnections) of F = 0 surfaces, where F is a differential factor determining the structural singularity in a potential magnetic field—are considered as possible sites of energy release. Six flare events demonstrating paired sources of non-thermal hard X-rays emission observed on March 17, 2002, July 17, 2002, April 6, 2004, November 4, 2004, November 6, 2004, and December 1, 2004 are analyzed for probable singularities. In each event analyzed, each source of non-thermal hard X-rays emission can be associated with an individual magnetic singularity; in other words, there is a magnetic-field line passing near the singularity and ending near (i.e. within about 10″) the source located on the photosphere (in the chromosphere). For the homologous flares observed on November 4 and 6, 2004, the same magnetic singularity is responsible for the source of non-thermal hard X-rays emission observed in the eastern sector of the flare region on November 4 and the source observed in the western part on November 6. A proposed interpretation associates these observations with a reversal of the electric field generated in the magnetic singularity on November 6, compared with the electric field generated on November 4, attributed to corresponding changes occurring in the photospheric magnetic field.     

湖南砂矿金刚石的颜色

研究表明,湖南砂矿金刚石中存在着两类决定金刚石颜色(主要指黄、褐和绿色)的色心。一类是氮原子中心,有孤氮原子和N3中心。另一类是辐射损伤中心,有GR1、637、595、H3、H4和3H中心。文中还讨论了这些色心的地质意义。