The physics of particle acceleration by collisionless shocks

Using analytic theory, test-particle simulations, and self-consistent hybrid simulations, we show that quasi-perpendicular shocks—those which propagate nearly perpendicular to the upstream magnetic field—accelerate particles directly out of the incident thermal population to energies much higher than the upstream ram energy of the plasma. It has already been established that quasi-parallel shocks—those which propagate nearly in the same direction as the upstream magnetic field—efficiently accelerate particles directly out of the incident thermal population; however, this has not yet been established for quasi-perpendicular shocks. Our results can be understood within the framework of the diffusive shock acceleration theory. We find that the accelerated-particle spectrum obtained from a more-general self-consistent hybrid plasma simulation are quantitatively consistent with a less-sophisticated test-particle simulation. The implications of this are discussed.     

Wide Field Imaging of Ion Tail of Comet C/Hale–Bopp

A sequential imaging observation of the ion tail of Comet C/Hale-Bopp 1995O1 was carried out in February–March 1997 with a wide-field CCD imaging camera using narrow band filters for two ion species; CO⁺ and H₂O⁺ along with those for blue and red continuum. From the surface photometry of the ion tail of two species, we derived a relationship between plasma density and distance from the nucleus. The local velocity of the ion flow as a function of the distance from the nucleus was also estimated on the basis of some assumptions. We report preliminary results of our analysis, and discuss some characteristics of cometary plasma and its interaction with interplanetary magnetic field (IMF). May the source be with you! This revised version was published online in July 2006 with corrections to the Cover Date.     

Molecular shocks in star forming regions

The role of excited molecular hydrogen as a powerful observational tool is examined in the context of shock phenomena in molecular clouds, particularly in star forming regions. Conclusions that may be drawn from line intensities and line profiles, and the properties of J and C shocks in a bow shock structure are discussed.     

Large earthquakes initiate by the acceleration of slips on the downward extensions of seismogenic faults

In order to examine the relationship between anomalous crustal deformations and subsequent large earthquakes, we compiled and examined data on preseismic anomalous crustal deformations for two earthquakes that occurred in and around the Japanese Islands in recent years. We found that the slip on a downward extension of a seismogenic fault accelerates before the main shock and that the average slip velocity is inversely proportional to the time remaining until the main shock occurs.     

A Physical Method of Analyzing theMechanism of Continental StrongShocks from Crustal Movement

In order to analyze the mechanism of continental strong shocks from the angle of crustal movement using the data of repeated geodetic survey, this paper has proposed a physical method; it analyzes the mechanism of density change due to the occurrence of strong shocks by use of the physical quantity that reflects the time change of crustal density. ( 1 ) The general theory of the time change of density in the earth‘ s interior and the theory of the time change of single layer density have been introduced, and an algorithm of stepwise iteration has been proposed; (2) The effect of the change of single layer density caused by fault dislocation has been analyzed in brief; (3) The characteristics of the time change of crustal density in the south of the seismogenic region before the 1996 Lijiang earthquake with ML = 7.0 have been studied; (4) The precursor model or causal mechanism of strong shocks possibly existing in the time change of crustal density has been investigated preliminarily.     

Earthquake recurrence of a particular type

The recurrence relation for Turkish earthquakes, expressed as the single-frequency versus magnitude dependence, exhibits significant maxima and minima, reflecting true physical conditions. Various mathematical formulations are developed to fit the observed data for the single or the cumulative frequency and are compared with each other as regards their accuracy and simplicity. The results may be applicable to regions with high seismicity.     

Energy time dispersion of a new class of magnetospheric ion events observed near the Earth’s bow shock

We have analyzed high time resolution (6 s) data during the onset and the decay phase of several energetic (35 keV) ion events observed near the Earths bow shock by the CCE/AMPTE and IMP-7/8 spacecraft, during times of intense substorm/geomagnetic activity. We found that forward energy dispersion at the onset of events (earlier increase of middle energy ions) and/or a delayed fall of the middle energy ion fluxes at the end of events are often evident in high time resolution data. The energy spectra at the onset and the decay of this kind of events show a characteristic hump at middle (50–120 keV) energies and the angular distributions display either anisotropic or broad forms. The time scale of energy dispersion in the ion events examined was found to range from several seconds to 1 h depending on the ion energies compared and on the rate of variation of the Interplanetary Magnetic Field (IMF) direction. Several canditate processes are discussed to explain the observations and it is suggested that a rigidity dependent transport process of magnetospheric particles within the magnetosheath is most probably responsible for the detection of this new type of near bow shock magnetospheric ion events. The new class of ion events was observed within both the magnetosheath and the upstream region.     

Climate variability and individual motivations for participating in political violence

Climate shocks are argued to affect the likelihood of conflict through individual economic outcomes that change the individual opportunity costs of participation in violent activities. Studies testing this proposition, however, either fail to answer convincingly because they use aggregated data, because they rely on observed controls and strong assumptions about variable independence, or because their study sample is restricted to particular conflicts. This article uses two rounds in Afrobarometer where respondents were asked about participation in politically motivated violence as well as how their living conditions had changed in the last year. To get around endogeneity problems, perceived changes in living conditions are instrumented using a standardized precipitation-evapotranspiration index (SPEI). The study finds that participation in violence would, on average, have been more likely if an individual experienced a deterioration of living conditions than if it had not, in the subpopulation in Africa whose living conditions are affected by droughts.     

云南水汞的远震和近震前兆异常特征分析

本通过对云南西部７个水汞观测站,１９９０年￣１９９６年９月省内及邻区２６次Ｍ≥５．０级地震的水汞资料进行异常时空强及其形态的分析研究,总结出云南水汞在远震和近震前的前兆异常特征,用这些前兆异常特征对１９９６年９月后１年内各观测站的水汞异常与所发生的地震进行检验,结果很好。此项研究,有助于对未来发震区的判定。     

Submillimeter CO spectroscopy of low mass young stellar objects

We report submillimeter CO(6-5) observations around 15 nearby young stellar objects of low mass. The correlation between linewidth and peak temperature indicates shock heating of dense gas, presumably at the origin of molecular outflows.