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41.
A considerable depletion of sodium was observed in Geminid meteoroids. To explain this phenomenon, we developed a quantitative model of sodium loss from meteoroids due to solar heating. We found that sodium can be lost completely from Geminid meteoroids after several thousands of years when they are composed of grains with sizes up to ∼100 μm. The observed variations of sodium abundances in Geminid meteor spectra can be explained by differences in the grain sizes among these meteoroids. Sodium depletions are also to be expected for other meteoroid streams with perihelion distances smaller than ∼0.2 AU. In our model, the meteoroids were represented by spherical dust-balls of spherical grains with an interconnected pore space system. The grains have no porosity and contain usual minerals known from meteorites and IDP's, including small amount of Na-bearing minerals. We modeled the sequence of three consecutive processes for sodium loss in Geminid meteoroids: (i) solid-state diffusion of Na atoms from Na-bearing minerals to the surface of grains, (ii) thermal desorption from grain surfaces and (iii) diffusion through the pore system to the space. The unknown material parameters were approximated by terrestrial analogs; the solid-state diffusion of Na in the grains was approximated by the diffusion rates for albite and orthoclase. 相似文献
42.
A bright fireball appeared on the sky during the spectrophotometric observations with the 2.2-m telescope at the Calar Alto Observatory. The CCD spectrum of the scattered light of the fireball has been recorded. The spectrum is typical for a very bright, slowly moving fireball. For the first time, the spectral region 6600 – 7150 Å could be studied in such a case. Six spectral lines were identified here, the most remarkable being the lithium line at 6708 Å. The estimated lithium abundance proved to be consistent with meteoritic values. 相似文献
43.
The first results of the television observations of meteors at the Ondejov Observatory are presented. It is shown that three spectral components may be distinguished in meteors: cool meteoric, hot meteoric and hot atmospheric. The intensity ratio of these components varies strongly even in meteors of the same velocity and within the records of single meteors. This is evidence for variations in the ablation process and in the formation of the shock wave. The so called calcium anomaly is in fact only a demonstration of these variations. 相似文献
44.
In biological wastewater treatment, bacteria tend to aggregate by forming flocs, biofilms and even granules. A large part of the floc structure in activated sludge is composed of extracellular polymers. The extracellular polymeric substances (EPS) are mainly responsible for the structural and functional integrity of biofilms/flocs and they are considered to be important for the physico‐chemical properties of activated sludge. This review considers the composition of EPS and proportion between the constituents. Moreover it includes the relationship between the EPS constituents and sludge properties such as sludge retention time, hydrophobicity and surface charge. 相似文献
45.
Two seismic agencies reported a very low double-couple percentage (DC%) of the Amfilochia earthquake, of about 30% and 60%,
by Schweizerischer Erdbebendienst and Mediterranean Very Broadband Seismographic Network, respectively. Near-regional waveforms,
carefully analyzed in this paper for the DC%, suggested a higher DC%, ranging from 75 to 100, dependent on the uncertainty
of the source position (optimum value DC% = 93). Using a statistical F test, forward modeling of the near-regional data with a single-event low-DC% source yields a significantly worse waveform
match. The fit of near-regional data can be further improved (although at the 90% significance level only) when considering
a speculative two-event model. The same model, when viewed at the very-low frequency range, reaches the very low DC% values.
However, two features make the two-event model unlikely: The two subevents strongly differ in their focal mechanism, and their
mutual separation (3.5 s) is larger than the expected duration of this earthquake. Therefore, the two-source model appears
to be nothing but an interesting equivalent representation of the non-DC model, providing some insight into the possible origin
of the apparently low DC%. Preference is given to the simple interpretation, most clearly supported by the near-regional data,
that the Amfilochia earthquake was an almost pure-shear event. 相似文献
46.
Pavel Koten Jiří Borovička Pavel Spurný Stephen Evans Rostislav Štork Andrew Elliott 《Earth, Moon, and Planets》2008,102(1-4):151-156
We carried out double station observations of the Leonid meteor shower outburst, which occurred in the morning hours of November
19, 2006. Using image-intensified cameras we recorded approximately 100 Leonid meteors. As predicted, the outburst was rich
especially in fainter meteors. The activity profile shows that the peak of the outburst occurred at 4:40 ± 0:05 UT. The maximum
reached flux was 0.03 meteoroids km−2 hod−1 for meteors brighter than +6.5 magnitude. 相似文献
47.
Lucie Novakova Milan Broz Jiri Zaruba Karel Sosna Jan Najser Lenka Rukavickova Jan Franek Vladimir Rudajev 《应用地球物理》2016,13(2):315-325
Underground storage systems are currently being used worldwide for the geological storage of natural gas (CH4), the geological disposal of CO2, in geothermal energy, or radioactive waste disposal. We introduce a complex approach to the risks posed by induced bedrock instabilities in deep geological underground storage sites. Bedrock instability owing to underground openings has been studied and discussed for many years. The Bohemian Massif in the Czech Republic (Central Europe) is geologically and tectonically complex. However, this setting is ideal for learning about the instability state of rock masses. Longterm geological and mining studies, natural and induced seismicity, radon emanations, and granite properties as potential storage sites for disposal of radioactive waste in the Czech Republic have provided useful information. In addition, the Czech Republic, with an average concentration radon of 140 Bq m?3, has the highest average radon concentrations in the world. Bedrock instabilities might emerge from microscale features, such as grain size and mineral orientation, and microfracturing. Any underground storage facility construction has to consider the stored substance and the geological settings. In the Czech Republic, granites and granitoids are the best underground storage sites. Microcrack networks and migration properties are rock specific and vary considerably. Moreover, the matrix porosity also affects the mechanical properties of the rocks. Any underground storage site has to be selected carefully. The authors suggest to study the complex set of parameters from micro to macroscale for a particular place and type of rock to ensure that the storage remains safe and stable during construction, operation, and after closure. 相似文献
48.
Glaciers around the world retreated as the climate warmed substantially. For the majority of alpine and arctic areas, however, the lack of meteorological data over a long period makes it difficult to build long-term climate and glacial fluctuation relationships, emphasizing the importance of natural proxy archives. Here we use the 230-year record of stem radial growth of birch trees (Betula ermanii) from the treeline forests above the receding glaciers in eastern maritime Kamchatka to analyse temporal variations of climate as well as glacial advance and retreat. Glaciers in Kamchatka Peninsula represent the southern limit of glaciation in far eastern Eurasia, which makes them prone to global warming. Using instrumental climate data (1930–1996) from local meteorological stations, we find that the July temperature had most prominent positive impact on birch growth. On the contrary, smaller ring increments are associated with the positive summer and net annual ice mass balance of Koryto Glacier. The prevailing trend of higher summer temperatures and lower snowfall over the past 70 years has enhanced tree growth while causing the glacier’s surface to lower by about 35 m and its front to retreat by about 490 m. Assuming these same relationships between climate, tree growth, and glacier mass balance also existed in the past, we use tree rings as a proxy record of climatically induced temporary halts in the glacier’s retreat over the past two centuries, which in total was over 1,000 m. Both direct observations and tree ring proxies indicate several prolonged warm periods (1990s, 1960s, 1930–1940s, 1880–1900s) interspersed with cooler periods (1984–1985, 1970–1976, 1953–1957, 1912–1926, 1855–1875, 1830–1845, 1805–1820 and 1770–1780) when the glacier re-advanced, creating several consecutive terminal moraine ridges. We conclude that birch tree-rings are suitable for assessing tree growth/climate/glacial relationships over a longer timescale in maritime Kamchatka. 相似文献
49.
The Krusné hory (Erzgebirge or Ore Mountains) has been heavily affected by high atmospheric pollutant deposition caused by fossil fuel combustion in an adjacent Tertiary coal basin. Long‐term routine sampling of bulk precipitation (1977–1996) and stream water (1977–1998) in a forested area on the south‐eastern slope of the mountains were used to evaluate trends and patterns in solute concentration and flux with respect to controlling processes. From 1977 to 1996, the annual volume‐weighted Ca2+ and SOconcentrations decreased in bulk precipitation. However, after 1989, when a pronounced and continuous decrease occurred in coal production, annual volume‐weighted concentrations decreased for most solutes, except H+. The concentration decreases were marked, with 1996 levels at or below 50% of those in 1989. The lack of a trend in H+ is attributed to similar decreases in both acid anions and neutralizing base cations. Stream water concentrations of most solutes, i.e. H+, Ca2+, Mg2+, SONOwere highest at the onset of sampling in 1977, decreased markedly from 1977 to 1983 and decreased more gradually from 1983 to 1998. The spruce forest die‐back and removal reduced dry deposition of these solutes by reducing the filtering action, which was provided by the forest canopy. A notable decrease in stream water Ca2+ concentrations occurred after 1995 and may be due to the depletion of Ca2+, which was provided by catchment liming in 1986, 1988 and 1989. Solute flux trends in bulk atmospheric deposition and stream water generally were not significant and the lack of trend is attributed to the large interannual variability in precipitation quantity and runoff, respectively. All solutes except Na+ varied seasonally. The average seasonal concentrations varied between the solutes, but for most solutes were highest in winter and spring and lowest in summer, correlating with the seasonal trend in runoff. For Ca2+, Mg2+ and SOthe concentration minimum occurs in September and the maximum occurs in February or March, correlating with the seasonal baseflow. These solutes are primarily controlled by the contribution of soil water and groundwater to stream flow. During snowmelt, the meltwater generally causes concentrations to decrease as soil water and groundwater are diluted. For NO3 , average minimum concentrations occur in August at the end of the growing season concurrent with the lowest stream flow, and the maximum occurs in February and March with high stream flow during snowmelt. Seasonal stream water NOconcentration variations are large compared with the long‐term decrease. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献