اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدTracking of supergranules - Does it make any sense?
40
0
0.0
(
0
)
تأليف
M. Svanda
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
The motions of the plasma and structures in and below the solar photosphere is not well understood. The results obtained using various methods cannot be in general considered as consistent, especially in details. In this contribution we show a summary of the results obtained by the method we have developed recently. To study the photospheric dynamics we apply the local correlation tracking algorithm to the series of full-disc Dopplergrams obtained by Michelson Doppler Imager (MDI) aboard the SOHO satelite. The dominant structure recorded in Dopplergrams is the supergranulation. Under the assumtion that the supergranules are carried by the flow field of the larger scale, we study properties of this underlying velocity field. We perform comparative tests with synthetic data with known properties and with results of the time-distance helioseismology with a great success. A few case studies are shown to demonstrate the performance of the method. We believe that tracking of supergranules makes a perfect sense when studying the large-scale flows in the solar photosphere. The method we demonstrate is suitable to detect large-scale velocity field with effective resolution of 60 and random error of 15 m/s. We believe that our method may provide a powerful tool for studies related to the dynamic behaviour of plasmas in the solar photosphere.
قيم البحث
اقرأ أيضاً
While feedback is important in theoretical models, we do not really know if it works in reality. Feedback from jets appears to be sufficient to keep the cooling flows in clusters from cooling too much and it may be sufficient to regulate black hole g
rowth in dominant cluster galaxies. Only about 10% of all quasars, however, have powerful radio jets, so jet-related feedback cannot be generic. The outflows could potentially be a more common form of AGN feedback, but measuring mass and energy outflow rates is a challenging task, the main unknown being the location and geometry of the absorbing medium. Using a novel technique, we made first such measurement in NGC 4051 using XMM data and found the mass and energy outflow rates to be 4 to 5 orders of magnitude below those required for efficient feedback. To test whether the outflow velocity in NGC 4051 is unusually low, we compared the ratio of outflow velocity to escape velocity in a sample of AGNs and found it to be generally less than one. It is thus possible that in most Seyferts the feedback is not sufficient and may not be necessary.
The ionization constant of water Kw is currently determined on the proton conductivity sigma1 which is measured at frequencies lower than 10^7 Hz. Here, we develop the idea that the high frequency conductivity sigma2 (~10^11 Hz), rather than sigma1 r
epresents a net proton dynamics in water, to evaluate the actual concentration c of H3O+ and OH- ions from sigma2. We find c to be not dependent on temperature to conclude that i) water electrodynamics is due to a proton exchange between H3O+ (or OH-) ions and neutral H2O molecules rather than spontaneous ionization of H2O molecules, ii) the common Kw (or pH) reflects the thermoactivation of the H3O+ and OH- ions from the potential of their interaction, iii) the lifetime of a target water molecule does not exceed parts of nanosecond.
There is a longstanding discrepancy between the observed Galactic classical nova rate of $sim 10$ yr$^{-1}$ and the predicted rate from Galactic models of $sim 30$--50 yr$^{-1}$. One explanation for this discrepancy is that many novae are hidden by i
nterstellar extinction, but the degree to which dust can obscure novae is poorly constrained. We use newly available all-sky three-dimensional dust maps to compare the brightness and spatial distribution of known novae to that predicted from relatively simple models in which novae trace Galactic stellar mass. We find that only half ($sim 48$%) of novae are expected to be easily detectable ($g lesssim 15$) with current all-sky optical surveys such as the All-Sky Automated Survey for Supernovae (ASAS-SN). This fraction is much lower than previously estimated, showing that dust does substantially affect nova detection in the optical. By comparing complementary survey results from ASAS-SN, OGLE-IV, and the Palomar Gattini IR-survey in the context of our modeling, we find a tentative Galactic nova rate of $sim 40$ yr$^{-1}$, though this could decrease to as low as $sim 30$ yr$^{-1}$ depending on the assumed distribution of novae within the Galaxy. These preliminary estimates will be improved in future work through more sophisticated modeling of nova detection in ASAS-SN and other surveys.
The software program BAMM has been widely used to study the dynamics of speciation, extinction, and phenotypic evolution on phylogenetic trees. The program implements a model-based clustering algorithm to identify clades that share common macroevolut
ionary rate dynamics and to estimate rate parameters. A recent simulation study published in Evolution (2017) by Meyer and Wiens (M&W) claimed that (i) simple (MS) estimators of diversification rates perform much better than BAMM, and (ii) evolutionary rates inferred with BAMM are weakly correlated with the true rates in the generating model. I demonstrate that their assessment suffers from two major conceptual errors that invalidate both primary conclusions. These statistical considerations are not specific to BAMM and apply to all methods for estimating parameters from empirical data where the true grouping structure of the data is unknown. First, M&Ws comparisons between BAMM and MS estimators suffer from false equivalency because the MS estimators are given perfect prior knowledge of the locations of rate shifts on the simulated phylogenies. BAMM is given no such information and must simultaneously estimate the number and location of rate shifts from the data, thus resulting in a massive degrees-of-freedom advantage for the MS estimators.When both methods are given equivalent information, BAMM dramatically outperforms the MS estimators. Second, M&Ws experimental design is unable to assess parameter reliability because their analyses conflate small effect sizes across treatment groups with error in parameter estimates. Nearly all model-based frameworks for partitioning data are susceptible to the statistical mistakes in M&W, including popular clustering algorithms in population genetics, phylogenetics, and comparative methods.
In order to stabilize the behavior of noisy systems, confining it around a desirable state, an effort is required to suppress the intrinsic noise. This noise suppression task entails a cost. For the important case of thermal noise in an overdamped sy
stem, we show that the minimum cost is achieved when the system control parameters are held constant: any additional deterministic or random modulation produces an increase of the cost. We discuss the implications of this phenomenon for those overdamped systems whose control parameters are intrinsically noisy, presenting a case study based on the example of a Brownian particle optically trapped in an oscillating potential.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
