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1.
Burkhard Fuchs 《Astrophysics and Space Science》2003,284(2):719-722
An update of the set of low surface brightness galaxies is presented which can be used to set constraints on the otherwise
ambiguous decompositions of their rotation curves into contributions due to the various components of the galaxies. The selected
galaxies show all clear spiral structure and arguments of density wave theory of galactic spiral arms are used to estimate
the masses of the galactic disks. Again these estimates seem to indicate that the disks of low surface brightness galaxies
might be much more massive than currently thought. This puzzling result contradicts stellar population synthesis models. This
would mean also that low surface brightness galaxies are not dominated by dark matter in their inner parts.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
2.
On the multivariate total least-squares approach to empirical coordinate transformations. Three algorithms 总被引:2,自引:1,他引:1
The multivariate total least-squares (MTLS) approach aims at estimating a matrix of parameters, Ξ, from a linear model (Y−E
Y
= (X−E
X
) · Ξ) that includes an observation matrix, Y, another observation matrix, X, and matrices of randomly distributed errors, E
Y
and E
X
. Two special cases of the MTLS approach include the standard multivariate least-squares approach where only the observation
matrix, Y, is perturbed by random errors and, on the other hand, the data least-squares approach where only the coefficient matrix
X is affected by random errors. In a previous contribution, the authors derived an iterative algorithm to solve the MTLS problem
by using the nonlinear Euler–Lagrange conditions. In this contribution, new lemmas are developed to analyze the iterative
algorithm, modify it, and compare it with a new ‘closed form’ solution that is based on the singular-value decomposition.
For an application, the total least-squares approach is used to estimate the affine transformation parameters that convert
cadastral data from the old to the new Israeli datum. Technical aspects of this approach, such as scaling the data and fixing
the columns in the coefficient matrix are investigated. This case study illuminates the issue of “symmetry” in the treatment
of two sets of coordinates for identical point fields, a topic that had already been emphasized by Teunissen (1989, Festschrift
to Torben Krarup, Geodetic Institute Bull no. 58, Copenhagen, Denmark, pp 335–342). The differences between the standard least-squares
and the TLS approach are analyzed in terms of the estimated variance component and a first-order approximation of the dispersion
matrix of the estimated parameters. 相似文献
3.
Biocrusts abound in southern Israel, covering the Hallamish dune field near Nizzana (NIZ) in the Negev (mean annual precipitation of 95 mm) and the coast of Nizzanim (NIM) near Ashdod (mean annual precipitation of 500 mm). While the hydrological response of the NIZ crust to natural rain events was thoroughly investigated, no data is available on the hydrological response of the NIM crust. Runoff was monitored in runoff plots during the years 2005–2008, and in addition, sprinkling experiments were carried out on NIM and NIZ crusts. For the evaluation of the possible factors that may control runoff initiation, fine content of the parent material, crust thickness, compressional strength, hydrophobicity, surface microrelief, organic matter, biomass (chlorophyll a and total carbohydrates) and the crust's species composition of NIM were studied and compared to that of NIZ. The data showed that in comparison to the NIZ crust that readily generated runoff, no runoff was produced by the NIM crust. This was so despite the fact that (1) Microculeus vaginatus predominated in both crusts, (2) the substantially higher rain intensities in NIM, (3) the greater thickness and higher chlorophyll content and (4) the lower microrelief at NIM in comparison to NIZ. The lack of runoff in NIM was explained by its low amounts of exopolysaccharides that did not suffice to affectively clog the surface and in turn to facilitate runoff initiation. The absence of runoff and its consequences on the NIM ecosystem are discussed. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
4.
Burkhard Schaffrin 《Journal of Geodesy》1989,63(4):395-404
The now classical collocation method in geodesy has been derived byH. Moritz (1970; 1973) within an appropriate Mixed Linear Model. According toB. Schaffrin (1985; 1986) even a generalized form of the collocation solution can be proved to represent a combined estimation/prediction
procedure of typeBLUUE (Best Linear Uniformly Unbiased Estimation) for the fixed parameters, and of type inhomBLIP (Best inhomogeneously LInear Prediction) for the random effects with not necessarily zero expectation. Moreover, “robust collocation” has been introduced by means of homBLUP (Best homogeneously Linear weakly Unbiased Prediction) for the random effects together with a suitableLUUE for the fixed parameters. Here we present anequivalence theorem which states that the robust collocation solution in theoriginal Mixed Linear Model can identically be derived as traditionalLESS (LEast Squares Solution) in amodified Mixed Linear Model without using artifacts like “pseudo-observations”. This allows us a nice interpretation of “robust collocation”
as an adjustment technique in the presence of “weak prior information”. 相似文献
5.
Burkhard Schaffrin 《Journal of Geodesy》1987,61(3):276-280
The Bayesian estimates
b of the standard deviation σ in a linear model—as needed for the evaluation of reliability—is well known to be proportional
to the square root of the Bayesian estimate (s
2)
b
of the variance component σ2 by a proportionality factor
involving the ratio of Gamma functions. However, in analogy to the case of the respective unbiased estimates, the troublesome
exact computation ofa
b may be avoided by a simple approximation which turns out to be good enough for most applications even if the degree of freedom
ν is rather small.
Paper presented to the Int. Conf. on “Practical Bayesian Statistics”, Cambridge (U.K.), 8.–11. July 1986. 相似文献
6.
Doreen E. AMES Ingrid M. KJARSGAARD Kevin O. POPE Burkhard DRESSLER Mark PILKINGTON 《Meteoritics & planetary science》2004,39(7):1145-1167
Abstract The 65 Ma Chicxulub impact crater formed in the shallow coastal marine shelf of the Yucatán Platform in Mexico. Impacts into water‐rich environments provide heat and geological structures that generate and focus sub‐seafloor convective hydrothermal systems. Core from the Yaxcopoil‐1 (Yax‐1) hole, drilled by the Chicxulub Scientific Drilling Project (CSDP), allowed testing for the presence of an impact‐induced hydrothermal system by: a) characterizing the secondary alteration of the 100 m‐thick impactite sequence; and b) testing for a chemical input into the lower Tertiary sediments that would reflect aquagene hydrothermal plume deposition. Interaction of the Yax‐1 impactites with seawater is evident through redeposition of the suevites (unit 1), secondary alteration mineral assemblages, and the subaqueous depositional environment for the lower Tertiary carbonates immediately overlying the impactites. The least‐altered silicate melt composition intersected in Yax‐1 is that of a calc‐alkaline basaltic andesite with 53.4–56 wt% SiO2(volatile‐free). The primary mineralogy consists of fine microlites of diopside, plagioclase (mainly Ab 47), ternary feldspar (Ab 37 to 77), and trace apatite, titanite, and zircon. The overprinting alteration mineral assemblage is characterized by Mg‐saponite, K‐montmorillonite, celadonite, K‐feldspar, albite, Fe‐oxides, and late Ca and Mg carbonates. Mg and K metasomatism resulted from seawater interaction with the suevitic rocks producing smectite‐K‐feldspar assemblages in the absence of any mixed layer clay minerals, illite, or chlorite. Rare pyrite, sphalerite, galena, and chalcopyrite occur near the base of the impactites. These secondary alteration minerals formed by low temperature (0–150°C) oxidation and fixation of alkalis due to the interaction of glass‐rich suevite with down‐welling seawater in the outer annular trough intersected at Yax‐1. The alteration represents a cold, Mg‐K‐rich seawater recharge zone, possibly recharging higher temperature hydrothermal activity proposed in the central impact basin. Hydrothermal metal input into the Tertiary ocean is shown by elevated Ni, Ag, Au, Bi, and Te concentrations in marcasite and Cd and Ga in sphalerite in the basal 25 m of the Tertiary carbonates in Yax‐1. The lower Tertiary trace element signature reflects hydrothermal metal remobilization from a mafic source rock and is indicative of hydrothermal venting of evolved seawater into the Tertiary ocean from an impact‐generated hydrothermal convective system. 相似文献
7.
8.
Franz E. Schunck Burkhard Fuchs Eckehard W. Mielke 《Monthly notices of the Royal Astronomical Society》2006,369(1):485-491
A non-topological soliton model with a repulsive scalar self-interaction of the Emden type provides a constant-density core, similarly as the empirical Burkert profile of dark matter (DM) haloes. As a further test, we derive the gravitational lens properties of our model, in particular, the demarcation curves between 'weak' and 'strong' lensing. Accordingly, strong lensing with typically three images is almost three times more probable for our solitonic model than for the Burkert fit. Moreover, some prospective consequences of a possible flattening of DM haloes are indicated. 相似文献
9.
Over a century ago Pearson solved the problem of fitting lines in 2D space to points with noisy coordinates in both dimensions. Surprisingly, however, the case of fitting lines in 3D space has seen little attention, though Adcock long ago published a brief (one page) article claiming that the solution that minimized orthogonal distances is the most probable. We solve this problem using a new algorithm for the Total Least-Squares (TLS) solution within an Errors-In-Variables Model, respectively an equivalent nonlinear Gauss-Helmert Model. Following Roberts, only four parameters are estimated, thereby avoiding over-parametrization that may lead to unnecessary singularities and, hence, require the introduction of constraints to the model. The current pervasiveness of Global Navigation Satellite Systems, robotic total stations, and digital laser scanners as sources of geodetic observations means that geodetic engineers and scientists now commonly work with observational models in 3D space as opposed to classical geodetic methods that often separated horizontal and vertical observational models. And while several papers have been written describing a TLS solution for line fitting problems in 2D space, the extension to 3D space is not readily apparent from these works. This further motivates the treatment of the 3D problem in some detail in this contribution. 相似文献
10.
We measured the thickness and the dry weight of recently deposited sediment along several transects across Lake Arendsee in order to quantify the sedimentation rate and its local variability. As a time marker, we used an artificial marl layer that was deposited by a remediation program in the year 1995. A portion of the sediment deposited during the year was transported from the littoral and the top of the submerged hills to the foot of the slope, where we found the greatest deposition. Within the same lake, the deposited sediment layer varied by a factor of 4 between minimal and maximal values over the same time periods. Lake Arendsee is a holomictic and eutrophic lake with depletion of oxygen in summer time. 相似文献