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1.
B. P. Tritakis 《Astrophysics and Space Science》1979,66(2):385-390
A study of all the observed and well-defined sector boundaries from January 1957 to February 1975, published by Svalgaard (1974, 1975a, b), indicated that sector boundary key-dates, transformed into Bartels' days, have a significant preference to occur on certain days of the solar rotation. The eclectic distribution of these sector boundaries give some Bartels' days that are empty of cases, while on other days there is a significant excess over the average. Using this effect, we can predict, in high levels of significance, the possible occurrence of a (+,–) or (–,+) boundary within particular days of the solar rotation. 相似文献
2.
Basil P. Tritakis 《Astrophysics and Space Science》1983,93(1):141-147
Correlation studies between various solar activity indices and a long time series of annual sums of the maximum value of solar
magnetic field intensity, observed for each group of sunspots during each passage of it over the visible solar hemisphere,
have pointed out a couple of interesting points. First, the faculae have a significant contribution to the numerical representation
of the small scale solar magnetic coefficients and low standard errors of estimation to the above mentioned maximum values
of the solar magnetic field. These properties give to the area index an important physical meaning which is a first approximation
to the small scale solar magnetic fields expressed by the above-mentioned maximum values of it. Finally, the main point which
comes out is that long term studies of the solar magnetic fields, especially extrapolated studies to the past, could be supported
by photospheric indices of the solar activity.
This paper constitutes the expanded version of a report presented to theIAU Symposium No. 102 ‘Solar and Stellar magnetic fields: Origins and coronal effects’, held in Zürich 2–6 August, 1982. 相似文献
3.
临界转换的早期预警信号 总被引：1，自引：0，他引：1
Marten Scheffer George Sugihara Jordi Bascompte Victor Brovkin Vasilis Dakos Hermann Held Max Rietkerk 李迎春 闫伟 蒋长胜 《国际地震动态》2009,(9):1-14
从生态系统到金融市场和气候在内的很多复杂动力系统,都会有临界点,在这样的点上系统可能会发生突变,从而演变到一个对立的动力模式上。在这样的临界点到达之前对其进行预测极为困难,但是现在,不同科学领域的研究工作表明,普遍性的早期预警信号有迹可循。对一系列不同类型的系统来说,这些信号会指示是否正在趋近一个临界阈值。 相似文献
4.
5.
A study of the predominant interplanetary magnetic field (IMF) polarity is made, for the time period 1957–1977. The examination of the mean positive and negative sector width for time periods (semesters) for which the Earth was in northern and southern heliolatitudes shows that the predominant polarity for every semester follows, up to a certain extent, the Rosenberg-Coleman effect. However, the statistical support is not satisfactory. The same conclusion was pointed out by a similar study of data grouped over various phases of the solar cycle.Additionally the relative frequency of positive (negative) IMF polarity days, appeared over a mean solar rotation, shows that the general pattern of the mean IMF has a tendency to reoccur in the homologous (corresponding) phases of different solar cycles. 相似文献
6.
Basil P. Tritakis 《Solar physics》1979,63(1):207-215
The representation of the sector boundaries, published by Svalgaard (1974, 1975) in a superposed 27-days Bartels format showed that they have a significant preference to occur in certain days of the solar rotation. Further study of these data, as well as of the polarized days in the vicinity of them, pointed out that during the epoch of extrema of the 11-year cycle there is a well-established 2-sector structure, on the average. On the contrary, a mean 4-sector structure is more prominent during the intermediate years. 相似文献
7.
Antonietta Rosso Rossana Sanfilippo Adriano Guido Vasilis Gerovasileiou Emma Taddei Ruggiero Genuario Belmonte 《Marine Ecology》2021,42(1):e12634
Metazoan/microbial bioconstructions, or biostalactites (BSTs), discovered in submarine caves of Apulia c. 20 years ago—and later found in several shallow‐water Mediterranean caves—are receiving increasing attention in the last years. Examination of a single BST from the “lu Lampiùne” cave (Apulia), at the limit between the Adriatic and the Ionian seas, has been addressed for the first time in this paper. The BST started growing at c. 6,000 years ago with a rapid accretion of large‐sized serpulids (Protula), slowing down since about 3,000–4,000 years ago with a shift in main bioconstructors, probably caused by environmental changes. The present‐day community on the outer BST surface is dominated by skeletonised epibionts, mostly small‐sized serpulids, bryozoans and foraminifers, which contribute carbonate to the BST growth, by encrusting sponges, and by a few endobionts, including boring bivalves and insinuating sponges. New data remarkably increase biodiversity known for the “lu Lampiùne” cave and the cave habitat in the region. Thirty‐five taxa (16 bryozoans, 10 serpulids, 3 brachiopods, 2 foraminifers, 2 sponges, 1 bivalve and 1 cirriped) are recorded for the first time from Apulian marine caves, highlighting the need for further research in the area. In addition, the BST‐associated community seems to differ from those of individual BSTs from other Mediterranean caves, revealing the individuality of these communities. 相似文献
8.
Nikolaos Skliris Sarantis Sofianos Athanasios Gkanasos Anneta Mantziafou Vasilis Vervatis Panagiotis Axaopoulos Alex Lascaratos 《Ocean Dynamics》2012,62(1):13-30
Twenty-four years of AVHRR-derived sea surface temperature (SST) data (1985–2008) and 35 years of NOCS (V.2) in situ-based
SST data (1973–2008) were used to investigate the decadal scale variability of this parameter in the Mediterranean Sea in
relation to local air–sea interaction and large-scale atmospheric variability. Satellite and in situ-derived data indicate
a strong eastward increasing sea surface warming trend from the early 1990s onwards. The satellite-derived mean annual warming
rate is about 0.037°C year–1 for the whole basin, about 0.026°C year–1 for the western sub-basin and about 0.042°C year–1 for the eastern sub-basin over 1985–2008. NOCS-derived data indicate similar variability but with lower warming trends for
both sub-basins over the same period. The long-term Mediterranean SST spatiotemporal variability is mainly associated with
horizontal heat advection variations and an increasing warming of the Atlantic inflow. Analysis of SST and net heat flux inter-annual
variations indicates a negative correlation, with the long-term SST increase, driving a net air–sea heat flux decrease in
the Mediterranean Sea through a large increase in the latent heat loss. Empirical orthogonal function (EOF) analysis of the
monthly average anomaly satellite-derived time series showed that the first EOF mode is associated with a long-term warming
trend throughout the whole Mediterranean surface and it is highly correlated with both the Eastern Atlantic (EA) pattern and
the Atlantic Multidecadal Oscillation (AMO) index. On the other hand, SST basin-average yearly anomaly and NAO variations
show low and not statistically significant correlations of opposite sign for the eastern (negative correlation) and western
(positive correlation) sub-basins. However, there seems to be a link between NAO and SST decadal-scale variations that is
particularly evidenced in the second EOF mode of SST anomalies. NOCS SST time series show a significant SST rise in the western
basin from 1973 to the late 1980s following a large warming of the inflowing surface Atlantic waters and a long-term increase
of the NAO index, whereas SST slowly increased in the eastern basin. In the early 1990s, there is an abrupt change from a
very high positive to a low NAO phase which coincides with a large change in the SST spatiotemporal variability pattern. This
pronounced variability shift is followed by an acceleration of the warming rate in the Mediterranean Sea and a change in the
direction (from westward to eastward) of its spatial increasing tendency. 相似文献
9.
Accurate reproduction of time series with diverse frequency characteristics is a central issue in structural testing. This is true not only for simple experimental tests performed by reaction walls or shaking tables but also for more sophisticated ones, such as hybrid testing. Especially in the latter case, where actual feedback from an ongoing test is used in the calculation of the next excitation value, any possible mismatch may be fatal for both the validity of the test and the safety. The objective of this study is to propose a framework for the adaptive inverse control of shaking tables, which succeeds in this matching to a certain degree. By formulating a critical set of design specifications that correspond to safety, implementation, robustness and ease of use, the conducted research results in a design that is based on a modified version of the filtered‐X algorithm with very competitive features. These are the following: (i) default operation in hard real‐time and acceleration mode; (ii) very low hardware requirements; (iii) effective cancelation of the shaking table's dynamics; and (iv) robustness against specimen dynamics. For its practical evaluation, the method is applied to shaking table waveform replication tests under the installation of an approximately linear specimen of sufficiently high mass and complex geometry. The results are promising and suggest further research toward this field, especially in conjunction with hybrid testing, as the method retains certain global applicability attributes and it can be easily extended to other transfer systems, apart from shaking tables. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
10.
H. Mavromichalaki V. Tritakis B. Petropoulos E. Marmatsouri A. Vassilaki A. Belehaki X. Raphios J. C. Noëns B. Pech 《Astrophysics and Space Science》1994,218(1):35-57
The analysis of the daily measurements of the coronal green and red line intensities as well as the K-corona brightness, which have been collected by the Pic-du-Midi Observatory, for the time period 1944–1974, has revealed some very interesting features. North-South (N-S) asymmetries for all these coronal intensities are confirmed again for this time period. The main point of this analysis is a strong evidence of longitudinal distribution of the coronal intensities as derived from the data record. In our effort to confirm this asymmetry, we have examined the yearly and monthly distribution of the asymmetry coefficient in each solar quadrant showing that the northeast (NE) quadrant appears the most active of all. We have also examined the intensity ratios measured at the East and West solar limbs which is continuously greater than the unit.A seasonal variation of this ratio has also been reported with a maximum during the winter period and a minimum during the summer period. 相似文献