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  • Springer  (40)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of geodesy 73 (1999), S. 543-554 
    ISSN: 1432-1394
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. One of the most serious practical limitations of boundary element methods for gravity field determination is that they cannot make efficient use of existing satellite geopotential models. Three basic approaches to solving the problem are developed: (1) alternative representation formulas; (2) modified kernel functions of classical representation formulas; and (3) modified trial and test spaces. The three methods are tested and compared for the altimetry–gravimetry II boundary value problem. It is shown that there is in fact a significant improvement when compared to the pure boundary element solution. Most promising is the method of multiscale trial and test spaces which, in addition, yields sparse system matrices.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of geodesy 73 (1999), S. 491-500 
    ISSN: 1432-1394
    Keywords: Key words. Geodetic boundary value problems ; Altimetry ; gravimetry problems ; Vertical geodetic datum ; Gravitational boundary value problems ; Pseudo-boundary value problems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. A review of recent progress and current activities towards an improved formulation and solution of geodetic boundary value problems is given. Improvements stimulated and required by the dramatic changes of the real world of geodetic measurements are focused upon. Altimetry–gravimetry problems taking into account various scenarios of non-homogeneous data coverage are discussed in detail. Other problems are related to free geodetic datum parameters, most of all the vertical datum, overdetermination or additional constraints imposed by satellite geodetic observations or models. Some brief remarks are made on pseudo-boundary value problems for geoid determination and on purely gravitational boundary-value problems.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Colloid & polymer science 29 (1921), S. 250-260 
    ISSN: 1435-1536
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 8 (1975), S. 332-344 
    ISSN: 1436-4646
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Consequences of a general formulation of the theorem of the alternative are exploited.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Meteorology and atmospheric physics 52 (1993), S. 1-14 
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary Relaxation coefficients for Davies' lateral boundary scheme for limited-area numerical weather prediction models are constructed in such a way that, under idealized conditions, the unwanted partial reflection of outgoing waves (leaving the limited area) at the boundary is minimized.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-0827
    Keywords: Mobile bone densitometry ; Dual energy X-ray absorptiometry ; Peripheral QCT ; Long-term precision
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Irrespective of the method used for noninvasive bone mass determination, data comparison between different centers is a major problem as significant interunit variation may occur. We, therefore, have employed mobile densitometry units to reduce interunit variability in two large epidemiologic studies in Germany. Two cars were equipped with either two dual X-ray absorptiometry (DXA) instruments (QDR 1000 Hologic, USA) (car I) or a special purposed scanner for peripheral quantitative computed tomography (pQCT) (XCT 900, Stratec, FRG) (car II). The cars were moved across Germany 11,090 km and 1651 km during the studies over a period of 30 and 7 months, respectively. Precision in vitro was determined using hydroxyapatite phantoms. Forty-eight patients underwent duplicate measurements at the lumbar spine (n=22) and hip (n=26) for assessing reproducibility in vivo. Between the two series of scans, the car was moved 63 km. Long-term precision in vitro of the QDR 1000 instruments were 0.41% and 0.59% for BMD with no evidence of machine drift (rate of change per year 0.04% and 0.05%, respectively). Short-term reproductibility in vivo showed a coefficient of variation (cv) of 1.02% for spinal BMD (L2–L4) and 1.72% for femoral neck. Long-term precision in vitro of the pQCT scanner was 0.9%. Our study shows precision in vivo and in vitro and stability of the mobile densitometers similar to that achieved with stationary equipment. In conclusion, mobile densitometry may become a useful tool not only for epidemiologic surveys and clinical trials but also for routine evaluation in less densely populated areas.
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  • 7
    ISSN: 1432-0827
    Keywords: Bone mineral density ; Dual-energy X-ray absorptiometry ; Reference range ; Exclusion criteria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract A cross-sectional, population-based study of 238 randomly selected females and 224 males with German ethnic background (aged 20–80 years) was carried out to establish lumbar spine bone mineral density (BMD) values, using dual X-ray absorptiometry (DXA), for a German population. Comparison was made to the reference range provided by the manufacturer of the DXA equipment. No sex difference in peak spine BMD was found in our study (1.091±0.114 g/cm2 for males versus 1.070±0.113 g/cm2 for females, n.s.). Different patterns of bone loss could be detected in both sexes. In premenopausal women there was no significant correlation between age and BMD (y = 1.044 + 0.00047x, r=0.03, P=0.73) whereas reduction of female BMD at the spine was demonstrated in postmenopausal women (y = 1.189−0.0041x, r=-0.28, P=0.01), underscoring the important role of the menopause for later manifestation of spinal osteoporosis in women. In contrast, in males we found no significant change of BMD with aging (y = 1.071−0.0007x, r=-0.08, P=0.25). Employing commonly used exclusion criteria, BMD values of the study subjects were found mostly within the normal range of BMD. The major finding of our study was good concordance between female data of our study population and the reference data provided by the manufacturer. Clinically significant discrepancies between our data and the Hologic reference range for males could be detected. Our data on males (30–39 years of age) were up to 7% lower than those provided by the manufacturer, probably due to differences in sampling procedures.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Cellular and molecular life sciences 23 (1967), S. 210-211 
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The intermediate mesoderm (8th–12th somite) of early tailbuds ofTriturus alpestris was transplanted into the lateral body wall of 12 mm larvae. The differentiation of opisthonephros tubules, primordial gonad and a new coelom was observed in 21 mm larvae 23 days after implantation.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Journal of geodesy 71 (1997), S. 533-540 
    ISSN: 1432-1394
    Keywords: Key words. Geodetic surface integrals ; Numerical integration ; Parallel computer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. Geodetic surface integrals play an important role in the numerical solution of geodetic boundary-value problems. In many cases they can be evaluated using fast methods in the frequency domain (FFT). However, this is not possible in general, because the domain of integration may be non-trivial (as is the surface of the Earth), the kernel function may not be of convolution type, or the data distribution may be heterogeneous. Therefore, fast evaluation strategies are also required in the space domain. They are more difficult to design because only one property is left where a more or less fast evaluation strategy can be built upon: the potential type of the kernel function. Consequently, the idea is not to replace well-established frequency domain techniques, but to supplement them. Our approach to this problem goes in two directions: (1) we use advanced cubature methods where the integration nodes automatically densify in the vicinity of the evaluation points; (2) we use powerful computer hardware, namely MIMD computers with distributed memory. This enables us to evaluate geodetic surface integrals of any practical complexity in reasonable time and accuracy. This is shown in a numerical example.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of geodesy 72 (1998), S. 530-546 
    ISSN: 1432-1394
    Keywords: Key words. Hadamard finite part ; Cauchy principal values ; numerical integration ; Galerkin boundary element method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract. Efficient numerical computation of integrals defined on closed surfaces in ℝ3 with non-integrable point singularities that arise in physical geodesy is discussed. The method is based on the use of polar coordinates and the definition of integrals with non-integrable point singularities as Hadamard finite part integrals. First the behavior of singular integrals under smooth parameter transformations is studied, and then it is shown how they can be reduced to absolutely integrable functions over domains in ℝ2. The correction terms that usually arise if the substitution rule is formally applied, in contrast to absolutely integrable functions, are calculated. It is shown how to compute the regularized integrals efficiently, and, numerical efforts for various orders of singularity are compared. Finally, efficient numerical integration methods are discussed for integrals of functions that are defined as singular integrals, a task that typically arises in Galerkin boundary element methods.
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