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1.
In this paper, one of the distribution-free tests — randomization test, is briefly described. It doesn’t need any distribution
assumption and its related parameter estimation and is applicable to random and nonrandom sample. Then it is used to the test
of migration of strong earthquakes on the Xianshuihe Fault Belt and “immunity” of large earthquakes in the large northern
reigon of China. The test results show that there is 98.7% confidence degree for the migration of strong earthqueks on the
Xianshuihe Fault Belt and “immunity” of earthqueks withM
S⩾8 toM
S⩾7 is significant in the large northern region of China. The obtained test results and the test method itself have certain
application in the practice.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 484–489, 1993. 相似文献
2.
A seismic index method for vulnerability assessment of existing frames: application to RC structures with wide beams in spain 总被引:1,自引:1,他引:0
A. Benavent-Climent 《Bulletin of Earthquake Engineering》2011,9(2):491-517
A method for assessing the vulnerability of existing frames in terms of an energy-based seismic index is proposed. The ground
motion is characterized by the so-called Seismic Hazard Energy Factor AE
I
, and the susceptibility of the frame to damage is a function of two counterpart energy factors, AE
IS
and AE
IU
. AE
IS
represents the level of the “maximum earthquake” that the frame can sustain within the elastic range. AE
IU
characterizes the level of the “ultimate earthquake” associated with the collapse of the structure. The procedure takes into
account the relation between the dynamic properties of the existing frame and the spectral shape of the ground motion expected
at the site. The seismic index used by the method has a transparent and direct physical meaning; thus, it is useful not only
for screening existing buildings but also to design a seismic retrofit solution, if needed. The method is applied to reinforced
concrete frames with wide beam-column connections built in the southern part of Spain during the 1970’s, 1980’s and 1990’s. 相似文献
3.
Properties of wave velocity for two types of granitoids at high pressure and temperature and their geological meaning 总被引:1,自引:0,他引:1
Shufeng Yang Hanlin Chen Jishuang Jiang Guoqiang Zhu Hongshen Xie Wei Hou Yueming Zhang Huigang Xu 《中国科学D辑(英文版)》1997,40(5):470-476
The wave velocity for two types of granitoids was measured using the analytic method of full-wave vibration at high pressure
and high temperature. The laws of velocity changes for them differ with the pressure boost and temperature rise, and the velocity
change of S-type is more violent than that of I-type. The “softening point” of compressional wave velocity (V μ) is also revealed
during the measurement for two types of granitoids imitating the pressure and temperature at a certain depth. But the depth
of “softening”, Vp after “softening” and the percentage of Vp’s drop around the “sofrening point” for two types of granitoids are obviously different. The depth of “softening” is 15 km
approximately and Vp after “softening” is 5.62 km/s for S-type granitoid. But for I-type granitoid the depth of “softening” is 26 km approximately
and Vp after “softening” is 6. 08 km/s. Through careful analysis of rock slices after the experiment, it was found that the “softening”
of elastic-wave velocity is caused by the partial melting of granite. Combined with the results of geophysical prospecting,
these results suggest that the low-velocity layers developing in the interior of Earth crust are related to thc partial melting
of different types of granitoids. The formation of the low-velocity layer in the upper-middle Earth crust is closely related
to the development of S-type granitoid, but that in the lower Earth crust is closely related to the development of I-type
granitoid. 相似文献
4.
Werner Stumm 《Aquatic Sciences - Research Across Boundaries》1984,46(2):291-296
Frevert deserves credit for proposing—for equilibrium systems—a distinction between a conceptually defined redox intensity,
pε, and an operationally defined redox condition under stationary states, pe, as given by the response of a sensor electrode,
and for pointing out that pε need not relate to pe.
We would like to re-emphasize (1, 2, 3) that in defining a redox intensity, pε=−log{e}, we have treated the electron conceptually
as a basic redox component which, as a species in aqueous solution, does not have an existence of its own. Morel (4) has elaborated
on the use of the electron as a (phase rule) component in redox reactions. As he shows, it obviously can be treated equivalent
to O2, i.e. O2=(H+)−4(e−)−4(H2O)2. We define (3) pε as “the hypothetical electron activity at equilibrium which measures the relative tendency of a solution
to accept or transfer electrons”. This free energy change ΔG can be expressed as a redox potential (electrode potential) in
volts (i.e., as a free energy change per mole of electrons associated with a given reduction). Electron activities may be
defined in any equilibrium systems where the free activities of reductants {Red}, and oxidants {Ox}, are defined. Thus, pε
(like pH) is a derivative form of free energy.
Using electrons in redox reactions and as components does not at all imply that such electrons exist as species in waters.
In the compilation of “Stability Constants” of the Chemical Society (London), Sillén and Martell (1964) treat the electron
as an inorganic ligand and establish an electron activity scale that corresponds to the definition given. 相似文献
5.
William D. Taylor 《Aquatic Sciences - Research Across Boundaries》2010,72(1):13-20
Techniques recently developed for measuring P regeneration, particulate P turnover, and PO4
3− concentration in lakewater assume that dissolved 32P (D32P) released by plankton is PO4
3−. To test this assumption, I obtained samples of D32P regenerated from whole plankton communities by labeling the communities with 32P-PO4
3− then blocking re-uptake and transformation of regenerated D32P with two competitive inhibitors, unlabeled 31P-PO4
3− and pyrophosphate. Under these conditions, regenerated D32P accumulated and could be examined by gel chromatography to discern how much of it was 32P-PO4
3− versus higher molecular weight P compounds. I estimated that most or all of the D32P released was 32P-PO4
3−. I also observed that the amount of DP observed on filtration of lakewater depended on the method employed to obtain the
filtrate. Therefore, I also separated particulate 32P from D32P with dialysis membrane (100,000 MW cutoff) without pressure. There was little DP larger than PO4
3− and no DP >5,000 MW in the dialysate, leading me to conclude that DP <100,000 MW was a minor component of both regenerated
and total P. I suggest that under P-limited conditions that most dissolved P observed in lakewater filtrates may be intact
viruses and cell constituents liberated in the filtration process. These results are mostly congruent with Lean’s (J Fish
Res Board Can 30:1525–1536, 1973) model of P-cycling in lake plankton, although the nature of “colloidal P” in Lean’s model should be further investigated. 相似文献
6.
Jan Wiszniowski Marian Hościłowicz Andrzej Skrzyński Jerzy Suchcicki Krzysztof P. Teisseyre 《Acta Geophysica》2008,56(2):391-407
A method of correcting the seismometers’ responses discrepancy for differential measurements of strains and rotations in the
seismic far field is proposed. The method concerns differential calibration of the whole seismometers’ array by electric current.
A model of corrective filtering of the obtained differential signals in the Z domain is given. Two methods of the filter parameters’
estimation are introduced; they are based on the seismometers response to the calibration.
A practical test of the methods — an analysis of a recorded seismic event — is added. Significant reduction of differences
between simultaneous seismic recordings was obtained, which is interpreted as cleaning of differential signal from spurious
elements. 相似文献
7.
Nitrogen uptake and denitrification in restored and unrestored streams in urban Maryland, USA 总被引:2,自引:0,他引:2
Carolyn A. Klocker Sujay S. Kaushal Peter M. Groffman Paul M. Mayer Raymond P. Morgan 《Aquatic Sciences - Research Across Boundaries》2009,71(4):411-424
There is growing interest in rates of nitrate uptake and denitrification in restored streams to better understand the effects
of restoration on nitrogen processing. This study quantified nitrate uptake in two restored and two unrestored streams in
Baltimore, Maryland, USA using nitrate additions, denitrification enzyme assays, and a 15N isotope tracer addition in one of the urban restored streams, Minebank Run. Restoration included either incorporation of
stormwater ponds below a storm drain and catch basins to attenuate flow or hydrologic “reconnection” of a stream channel to
its floodplain. Stream restoration was conducted for restoring aging sanitary and bridge infrastructure and introducing some
stormwater management in watersheds developed prior to current regulations. Denitrification potential in sediments was variable
across streams, whereas nitrate uptake length appeared to be significantly correlated to surface water velocity, which was
low in the restored streams during summer baseflow conditions. Uptake length of NO3
−–N in Minebank Run estimated by 15N tracer addition was 556 m. Whole stream denitrification rates in Minebank Run were 153 mg NO3
−–N m−2 day−1, and approximately 40% of the daily load of nitrate was estimated to be removed via denitrification over a distance of 220.5 m
in a stream reach designed to be hydrologically “connected” to its floodplain. Increased hydrologic residence time in Minebank
Run during baseflow likely influenced rates of whole stream denitrification, suggesting that hydrologic residence time may
be a key factor influencing N uptake and denitrification. Restoration approaches that increase hydrologic “connectivity” with
hyporheic sediments and increase hydrologic residence time may be useful for stimulating denitrification. More work is necessary,
however, to examine changes in denitrification rates in restored streams across different seasons, variable N loads, and in
response to the “flashy” hydrologic flow conditions during storms common in urban streams. 相似文献
8.
O. K. Kedrov E. O. Kedrov N. A. Sergeyeva L. P. Zabarinskaya V. R. Gordon A. B. Chulkov 《Izvestiya Physics of the Solid Earth》2010,46(11):974-999
The Method of Dynamic Calibration (MDC) of stations of the International Monitoring System (IMS) was developed for calibrating
regions where no underground nuclear explosions were carried out, with the purpose of providing conditions for implementation
of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) in nontrivial cases. Initially, the MDC had been presented in [Kedrov,
2001; Kedrov et al., 2001; Kedrov O.K. and Kedrov E.O., 2003] and then considered in detail in [Kedrov et al., 2008]. The
core of MDC relates to adapting diagnostic parameters for the identification of underground nuclear explosions (UNE) and earthquakes
elaborated for the region of Eurasia, taken as a basic region (BR), for other researched regions that differ from BR in the
character of the attenuation of seismic waves. The unique characteristic of this method lies in the fact that calibration
of diagnostic parameters with the help of attenuation coefficients b
Δ at varied source-station traces is implemented using only natural seismicity data within the limits of an explored region
and does not require special underground chemical explosions. The MDC algorithm is implemented in the research program ”Kalibr”,
which was tested by using the experimental data from Eurasia region. It is shown in this work that MDC can be used for calibration
of regions where a very low level of natural seismicity is observed. According to the results of the calibration of diagnostic
parameters at IMS stations in several regions of North America, Africa, and Asia, the approximate classification of propagation
conditions for seismic signals at source-station traces in platform and tectonically active regions is made. The results for
the development of two research programs, “Spektr” and “Signal”, are presented; this software is intended for automation of
calculation procedures for spectral diagnostic parameters of UNEs’ and earthquakes’ identification by amplitude spectra of
P waves and by the maximal amplitudes of P, S, and LR signals. The application of these programs allowed us to accelerate the whole calibration procedure for a particular source-station
trace using the ”Kalibr” program. 相似文献
9.
赵和云 《地震学报(英文版)》1994,7(3):465-474
ThepatterncharacteristicsofthetendencyvariationsofearthresistivityanditsrelationtoearthquakesHe-YunZHAO(赵和云)(EarthquakeResear... 相似文献
10.
Early Paleozoic subduction of the Paleo-Asian Ocean: Geochronological and geochemical evidence from the Dashizhai basalts,Inner Mongolia 总被引:10,自引:0,他引:10
Zircon U-Pb results of basalt from the Dashizhai Town in Inner Mongolia, NE China, shows that the basaltic lava was erupted
at 439±3 Ma, much older than the “Permian basalts” as previously thought. These rocks show arc-type trace element patterns
(i.e., Nb-Ta depletion and light REE and large ion lithophile element enrichment) and unradiogenic Sr and highly radiogenic
Nd and Hf isotope compositions. They can be subdivided into two petrogenetic groups: Group 1 basalts have relatively high
TiO2, MgO and compatible elements and low Sr and Th, characterized by mid-oceanic ridge basalt (MORB)-type Sr-Nd-Hf isotope compositions
(87Sr/86Sr(i)=0.7028−0.7032, εNd(t)=+9.8−+11.2, εHf(t)=+16.1−+18.4). Group 2 has lower TiO2, MgO and compatible elements and higher Sr and Th, and relatively evolved Sr-Nd-Hf isotope compositions (87Sr/86Sr(i)=0.7037−0.7038, εNd(t)=+5.7−+7.3, εHf(t)=+12.6−+13.0). Both groups were interpreted as melts derived from a metasomatized mantle wedge formed during the subduction
of Paleo-Asian Ocean. The mantle source for Group 1 was probably a highly isotopically depleted oceanic mantle modified by
predominant slab fluids; whereas subducted sediments had an important contribution to the melting source for Group 2. The
petrogenesis of the Dashizhai basalts provides clear evidence for early Paleozoic subduction of the Paleo-Asian Ocean, and
the highly radiogenic Nd and Hf compositions in these rocks suggest that these lavas and their possible intrusive counterparts
were one of the important components for Phanerozoic crustal growth. Our and previous studies on the “Dashizhai Formation”
volcanic rocks yield an unrealistic eruption range of 440-270 Ma for different rock types, we thus advise to disassemble the
previously defined “Dashizhai Formation” into multiple lithologic units and to reinterpret the spatial and temporal distributions
of different volcano-sedimentary associations.
Supported by National Basic Research Program of China (Grant No. 2006CB403504) 相似文献
11.
Sediment characteristics and wind-induced sediment dynamics in shallow Lake Markermeer, the Netherlands 总被引:2,自引:1,他引:1
P. Kelderman R. O. Ang’weya P. De Rozari T. Vijverberg 《Aquatic Sciences - Research Across Boundaries》2012,74(2):301-313
In 2007/08, a study was undertaken on the sediment dynamics in shallow Lake Markermeer (the Netherlands). Firstly, sediment
characteristics were determined at 49 sites in the lake. Parameters such as median grain size and loss on ignition showed
a spatial as well as water depth related pattern, indicating wind-induced sediment transport. Highly significant correlations
were found between all sediment parameters. Lake Markermeer sediment dynamics were investigated in a sediment trap field survey
at two permanent stations in the lake. Sediment yields, virtually all coming from sediment resuspension, were significantly
correlated with average wind speeds, though periods of extreme winds also played a role. Sediment resuspension rates for Lake
Markermeer were high, viz. on average ca. 1,000 g m−2 day−1. The highly dynamic nature of Lake Markermeer sediments must be due to the overall shallowness of the lake, together with
its large surface area (dynamic ratio = [√(area)]/[average depth] = 7.5); wind-induced waves and currents will impact most
of the lake’s sediment bed. Indeed, near-bed currents can easily reach values >10 cm/s. Measurements of the thickness of the
settled “mud” layer, as well as 137Cs dating, showed that long-term deposition only takes place in the deeper SE area of the lake. Finally, lake sediment dynamics
were investigated in preliminary laboratory experiments in a small “micro-flume”, applying increasing water currents onto
five Lake Markermeer sediments. Sediment resuspension started off at 0.5–0.7 cm/s and showed a strongly exponential behaviour
with respect to these currents. 相似文献
12.
Cadet Héloïse Anne-Marie Duval Etienne Bertrand 《Bulletin of Earthquake Engineering》2012,10(2):451-489
This paper presents empirical correlations between amplification factors and simple site parameters derived from a large subset
of the KiK-net data. The amplification factor is estimated from the ratios between the surface and down-hole horizontal response
spectra, corrected for the varying depths and impedance of the down-hole sites (Cadet et al. in Site effect assessment using
KiK-net data—part 1—a simple correction procedure for surface/downhole spectral ratios, 2011). Several site parameters are selected on the basis of their simplicity and availability at relatively low cost. They are
the shallow time-average velocities VSZ, with z equal to 5, 10, 20 and 30 m, and the fundamental frequency f0. The amplification factors are then correlated with each of the individual site parameters; four other “twin-parameter”—couples
(f0, VSZ)—are also considered and the correlation with amplification factors is performed through a normalization of the frequencies
by each site fundamental frequency. The quality of the correlations is given by a misfit compared with the original data variance.
The largest variance reduction is obtained with twin-parameter characterizations, out of which the couple (f0, VS30) proves to provide the lower misfit. The performance of single parameter correlations is relatively lower; however, the best
single parameter proves to be the fundamental frequency, which provides smaller misfit than the Vsz parameters. A comparison
is also performed with the amplification factors recommended in European regulations, showing that it is possible right now
to significantly improve both the site characterization criteria and the associated amplification factors, for use in building
codes and microzonation studies. 相似文献
13.
GuoLiang Zhang ZhiGang Zeng XueBo Yin DaiGeng Chen XiaoYuan Wang XiaoMei Wang 《中国科学D辑(英文版)》2008,51(12):1786-1801
Thirty-six basalt samples from near East Pacific Rise 13°N are analyzed for major and trace elements. Different types of zoned plagioclase phenocrysts in basalts are also backscatter imaged, and major element profiles scanned and analyzed for microprobe. Basalts dredged from a restricted area have evolved to different extents (MgO=9.38wt%—6.76wt%). High MgO basalts are modeled for crystalliza-tion to MgO of about 7wt%, and resulted in the Ni contents (≈28 ppm) that are generally lower than that in observed basalts (>60 ppm). It suggests that low MgO basalts may have experienced more intensive magma mixing. High MgO (9.38wt%) basalt is modeled for self-"mixing-crystallization", and the high Ni contents in low MgO basalts can be generated in small scale and periodical self-mixing of new magma (high MgO). "Mixing-crystallization" processes that low MgO magmas experienced accord with recent 226Ra/230Th disequilibria studies for magma residence time, in which low MgO magmas have experi-enced more circles of "mixing-crystallization" in relatively longer residence time. Magma mixing is not homogeneous in magma chamber, however, low MgO magmas are closer to stable composition pro-duced by periodical "mixing-crystallization", which is also an important reason for magma diversity in East Pacific Rise. Zoned plagioclase phenocrysts can be divided into two types: with and without high An# cores, both of which have multiple reversed An# zones, suggesting periodical mixing of their host magmas. Cores of zoned plagioclase in low MgO (7.45wt%) basalt differ significantly with their mantle in An#, but are similar in An# with microlite cores (products of equilibrium crystallization) in high MgO (9.38wt%) basalt, which further shows that plagioclase phenocryst cores in low MgO basalts may have formed in their parental magmas before entering into the magma chamber. 相似文献
14.
Quaternary biogenic opal records in the South China Sea: Linkages to East Asian monsoon, global ice volume and orbital forcing 总被引:3,自引:0,他引:3
WANG RuJian JIAN ZhiMin XIAO WenShen TIAN Jun LI JianRu CHEN RongHua ZHENG YuLong & CHEN JianFang State Key Laboratory of Marine Geology Tongji University Shanghai China The Key Laboratory of Submarine Geoscience State Oceanic Administration Hangzhou China 《中国科学D辑(英文版)》2007,50(5):710-724
Particulate fluxes investigated in the central South China Sea (SCS) during 1993―1996 indicate that opal flux can be used to show primary productivity change, which provides a foundation for tracing the evolutionary relationship between the surface productivity and East Asian monsoon in the SCS during the late Quaternary glacial and interglacial periods. Based on the studies of opal % and their mass accumulation rates (MAR) at the six sites recovered from the SCS during the “Resolution” ODP Leg 184 and “Sonne” 95 cruise of the Sino-Germany cooperation, opal % and their MARs increased evidently in the northern sites since 470―900 ka, and they enhanced and reduced, respectively, during the glacial and interglacial periods. Whereas they increased obviously in the southern sites since 420―450 ka, and they augmented and declined, respectively, during the interglacial and glacial periods. The vari- ability in opal % and their MARs in the late Quaternary glacial cyclicity indicate the “seesaw” pattern of surface productivity in the SCS. The winter monsoon intensified during the glacial periods, surface productivity increased and decreased, respectively, in the northern and southern SCS. The summer monsoon strengthened during the interglacial periods, surface productivity increased and decreased, respectively, in the southern and northern SCS. The cross spectral analyses between the opal % in the northern and southern SCS during the Quaternary and global ice volume (δ 18O) and orbital forcing (ETP) indicate that the East Asian winter and summer monsoons could be ascribed to the different drive mechanisms. On the orbital time scale, the global ice volume change could be a dominant factor for the winter monsoon intension and temporal variations. As compared with the winter monsoon, the correlative summer solar radiation with the obliquity and precession in the Northern Hemisphere could be a mostly controlling factor for the summer monsoon intension and temporal variations. 相似文献
15.
Based on satellite observation data, using dynamics equation, the ionospheric O+ ion’s distribution in the synchronous altitude region for different geomagnetic activity indexK
p is studied by theoretical modeling and numerical analyzing, and semi-empirical models for the O+ ion’s density and flux versus longitude in the synchronous altitude region for differentK
p
are given. The main results show that in the synchronous altitude region: (i) The O+ ion’s density and flux in day-side are larger than those in nightside. (ii) With longitude changing, the higher the geomagnetic
activity indexK
p
is, the higher the O+ ion’s density and flux, and their variation amplitude will be. The O+ ion’s density and flux whenK
p ≥ 6 will be about ten times as great as that whenK
p
= 0. (iii) WhenK
p
= 0 orK
p ≥ 6, the O+ ion’s density reaches maximum at longitudes 120° and 240° respectively, and minimum in the magnetotail. WhenK
p
= 3−5, the O+ ion’s density gets to maximum at longitude 0°, and minimum in the magnetotail. However, the O+ ion’s flux reaches maximum at longitude 120° and 240° respectively, and minimum in the magnetotail for anyK
p
value. 相似文献
16.
The source parameters of the Bohai Sea earthquake, July 18, 1969 and Yongshan, Yunnan earthquake, May 11, 1974 were determined
by full — wave theory synthetic seismograms of teleseismic P waves. P+pP+sP wereform were calculated with WKBJ approximation
and real integral paths. One — dimensional unilateral, finite propagation source was also considered. By trail — and — error
in comparing the theoretical seismograms with the observational ones of WWSSN stations, the source parameters were obtained
as follow: for Bohai earthquake, φ=195°, δ=85°, λ=65°,M
o=0.9×1019Nm,L=59.9km.V
R=3.5km/s, ∧
R
=160°; for Yongshan earthquake, φ=240°, δ=80°, ∧=150°,M
o=1.3×1018Nm,L=48.8km,V
R=3km/s, ∧
R
=−10°, where φ is strike, δ dip angle, λ slip angle,M
o seismic moment,L rupture length,V
R rupture propagation speed. As III type fractures the faulting propagated along the fault planes, and ∧
R
is the angle from the strike to the propagation direction. Yongshan earthquake showed complexity in its focal process, having
four sub—ruptures during the first 60 seconds.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 1–8, 1991. 相似文献
17.
Conclusion Based on the analysis about the law of deformation rate, the concepts of the deformation rate of precursor, and its stress
drop, and the stress drop of instability are discussed. According to the obtained deformationu
0 corresponding to the maximum stress, the unstable pointu
1 and the stable pointu
2 of equilibrium, the complete process of rock failure can be divided into four stages quantitatively, corresponding to “the
steady stage I”, “the precursor stage II”, “the unstable stage III” and “the later stage IV” of rock failure respectively,
which can be used to simulate the complete course of earthquake. This kind of similarity between the complete process of rock
failure and the complete course of earthquake suggests clearly the direction to reveal the law being of universal significance
for the simulation of the earthquake in the laboratory experiments.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 517–521, 1991. 相似文献
18.
GUO Zeng-Jian 《地震学报(英文版)》2000,13(4):477-480
IntroductionIn the book Future CataS~ologr published in 1992, we proposed a viewpoiflt on using the"criterion of activity in quiescence" to predict big eathquake (MsZ7) (GUO, et al, 1992), and predicted in the book that in futore several years or in ten years a big earthquake (Ms27) will be possible to occur in the Zhongdian and nearby in Yunnan Province. In the 1994 nation-wide earthquake tendency consultation meeting we pointed out, once more, in the Zhongdian region of Yunnan Province… 相似文献
19.
Gerhard Neumann 《Ocean Dynamics》1951,4(1-2):6-13
Zusammenfassung Aus Windprofilmessungen in feststehenden H?hen über den Wellenk?mmen lassen sich keine zuverl?ssigen Schlüsse über die effektive
Schubkraft des Windes an der Meeresoberfl?che ziehen. Der Grund liegt im wesentlichen in der verschiedenartigen vertikalen
Windgeschwindigkeitsverteilung über Wellenbergen und Wellent?lern und in der Tatsache, da? die Windprofilmessungen im wesentlichen
nur das Windprofil über den Bergen widerspiegeln. Der Versuch, die Windprofilmessungen zu „reduzieren“, ist mit zu gro?en
Fehlern behaftet, zeigt aber qualitativ eine systematische Erh?hung der aus Windmessungen berechneten Reibungsfaktoren an.
Damit kann der Anschlu? an die aus Windstaubeobachtungen ermittelten Reibungsfaktoren gewonnen werden, so da? der vermeintliche
„Sprung“ von einer „glatten“ zu einer „rauhen“ Grenzfl?che verschwindet, und eine „kritische Windgeschwindigkeit“, die diesen
Sprung angeben soll, gar nicht existiert.
On the problem of the “critical wind velocity” at the air — sea boundary surface
Summary From the measurements of wind profiles at fixed heights above the wave crests no reliable conclusions can be drawn with regard to the wind's effective shearing force at the sea surface. This is essentially due to the diversified vertical distribution of the wind speed above the waves' crests and troughs as well as to the fact that when measuring wind profiles above the waves it is mainly the profiles above the wave crests that are obtained. Attempts to “reduce” wind profiles have proved to be subject to considerable errors; however, they show qualitatively a systematic increase of the frictional factors as computed from wind measurements. This links up with the frictional factors ascertained from observations of the wind effect so that the supposed “leap” from a “smooth” to a “rough” boundary surface and the “critical wind speed” corresponding to this leap do not exist at all.相似文献
20.
Jean-Claude Tanguy Michel Condomines Maxime Le Goff Vito Chillemi Santo La Delfa Giuseppe Patanè 《Bulletin of Volcanology》2007,70(1):55-83
A careful re-examination of the well-known written documents pertaining to the 2,750-year-long historical period of Mount
Etna was carried out and their interpretation checked through the high-accuracy archeomagnetic method (>1,200 large samples),
combined with the 226Ra-230Th radiochronology. The magnetic dating is based upon secular variation of the direction of the geomagnetic field (DGF) and
estimated to reach a precision of ±40 years for the last 1,200 years, and ±100 to 200 years up to circa 150 B.C. Although
less precise, the 226Ra-230Th method provides a unique tool for distinguishing between historic and prehistoric lavas, which in some cases might have
similar DGFs. We show that despite the abundance of details on ancient historical eruptions, the primary sources of information
are often too imprecise to identify their lava flows and eruptive systems. Most of the ages of these lavas, which are today
accepted on the geological maps and catalogues, were attributed in the 1800s on the basis of their morphology and without
any stratigraphical control. In fact, we found that 80% of the “historically dated” flows and cones prior to the 1700s are
usually several hundreds of years older than recorded, the discrepancies sometimes exceeding a millennium. This is proper
the case for volcanics presumed of the “1651 east” (actually ∼1020), “1595” (actually two distinct flows, respectively, ∼1200
and ∼1060), “1566” (∼1180), “1536” (two branches dated ∼1250 and ∼950), “1444” (a branch dated ∼1270), “1408” (lower branches
dated ∼450 and ∼350), “1381” (∼1160), “1329” (∼1030), “1284” (∼1450 and ∼700), “1169 or 812” (∼1000) eruptions. Conversely,
well-preserved cones and flows that are undated on the maps were produced by recent eruptions that went unnoticed in historical
accounts, especially during the Middle Ages. For the few eruptions that are recorded between A.D. 252 and 750 B.C., none of
their presumed lava flows shows a DGF in agreement with that existing at their respective dates of occurrence, most of these
flows being in fact prehistoric. The cinder cones of Monpeloso (presumed “A.D. 252”) and Mt. Gorna (“394 B.C.”), although
roughly consistent magnetically and radiochronologically with their respective epochs, remain of unspecified age because of
a lack of precision of the DGF reference curve at the time. It is concluded that at the time scale of the last millennia,
Mount Etna does not provide evidence of a steady-state behavior. Periods of voluminous eruptions lasting 50 to 150 years (e.g.,
A.D. 300–450, 950–1060, 1607–1669) are followed by centuries of less productive activity, although at any time a violent outburst
may occur. Such a revised history should be taken into account for eruptive models, magma output, internal plumbing of the
volcano, petrological evolution, volcano mapping and civil protection. 相似文献