Exact Boundary Conditions at an Artificial Boundary for Partial Differential Equations in Cylinders

The numerical solution of partial differential equations in unbounded domains requires a finite computational domain. Often one obtains a finite domain by introducing an artificial boundary and imposing boundary conditions there. This paper derives exact boundary conditions at an artificial boundary for partial differential equations in cylinders. An abstract theory is developed to analyze the general linear problem. Solvability requirements and estimates of the solution of the resulting finite problem are obtained by use of the notions of exponential and ordinary dichotomies. Useful representations of the boundary conditions are derived using separation of variables for problems with constant tails. The constant tail results are extended to problems whose coefficients obtain limits at infinity by use of an abstract perturbation theory. The perturbation theory approach is also applied to a class of nonlinear problems. General asymptotic formulas for the boundary conditions are derived and displayed in detail

The Numerical Calculation of Traveling Wave Solutions of Nonlinear Parabolic Equations

Traveling wave solutions have been studied for a variety of nonlinear parabolic problems. In the initial value approach to such problems the initial data at infinity determines the wave that propagates. The numerical simulation of such problems is thus quite difficult. If the domain is replaced by a finite one, to facilitate numerical computations, then appropriate boundary conditions on the "artificial" boundaries must depend upon the initial data in the discarded region. In this work we derive such boundary conditions, based on the Laplace transform of the linearized problems at ±∞, and illustrate their utility by presenting a numerical solution of Fisher’s equation which has been proposed as a model in genetics

Loss of the Surface Layers of Comet Nuclei

The Deep Impact observations of low thermal inertia for comet 9P/Tempel 1 are of profound importance for the observations to be made by the Rosetta spacecraft at comet 67P/Churyumov-Gerasimenko. While sub-surface sublimation is necessary to explain the observations, the depth at which this occurs is no more than 2-3cm and possibly less. The low thermal conductivity when combined with local surface roughness (also observed with Deep Impact) implies that local variations in outgassing rates can be substantial. These variations are likely to be on scales smaller than the resolution limits of all experiments on the Rosetta orbiter. The observed physico-chemical inhomogeneity further suggests that the Rosetta lander will only provide a local snapshot of conditions in the nucleus laye

Natural and managed soil structure: On the fragile scaffolding for soil functioning

Soil structure in natural systems is a product of complex interactions between biological activity, climate and soil minerals that promote aggregation and accumulation of biopores. In arable lands, the management of soil structure often requires the mechanical fragmentation of hardened soil to improve seedbed, control weeds and bury plant residue. Despite difficulties in defining and quantifying soil structure, its critical role is evidenced by loss of productivity when natural structure is perturbed (e.g. compaction) and the long history of tillage in agriculture. To overcome persistent ambiguities among scientific disciplines regarding definition and function of soil structure, we propose a framework for distinguishing managed and natural soil structure based on their different formation processes and functions. Natural soil structure preserves ecological order and legacy that promotes biopore reuse, stabilizes foodwebs and protects soil organic carbon (SOC). The contribution of net primary productivity of natural lands to soil structure forming processes makes it a useful (surrogate) metric of soil structure. The benefits of managed soil structure for crops are quantified indirectly via comparisons with no-till farming under similar conditions. The levels and trends of SOC are useful metrics for the status of natural and managed soil structure. The systematic consideration of soil structure state in natural and arable lands using suitable metrics is a prerequisite for rational decisions related to land management and ensuring sustainable functioning of a fragile and central resource such as soil

Die Messung der Patientenzufriedenheit

Die Wettbewerbsintensivierung auf dem Markt für Krankenhausdienstleistungen erfordert patientenorientierte Führungskonzepte. Durch das Ausscheiden des Preises als Wettbewerbsinstrument sowie den eingeschränkten kommunikationspolitischen Möglichkeiten eines Krankenhauses im deutschsprachigen Raum kommen der Konzentration auf die Zielgruppen und deren Zufriedenstellung eine herausragende ökonomische Bedeutung zu. Die aus der subjektiv wahrgenommenen Dienstleistungsqualität resultierende Patientenzufriedenheit wird somit zum entscheidenden Wettbewerbsfaktor. An dieser Stelle setzt die vorliegende Arbeit an. Ziel ist es, ein Messinstrument zur Erfassung der Dienstleistungsqualität in Krankenhäusern zu entwickeln. Das vorgeschlagene Modell basiert auf der subjektiven Wahrnehmung der Patientenzufriedenheit und beschränkt sich auf den stationären Krankenhausaufenthalt auf Normalstationen. Die aufgestellte Hypothesenstruktur wird mit Hilfe eines linearen Strukturgleichungsmodells überprüft und mit zwei weiteren Modellen zur Messung der Dienstleistungsqualität verglichen. Das entwickelte Basismodul ermöglicht im Sinne eines Früherkennungssystems eine permanente, multiattributive Messung der Patientenzufriedenheit zur kontinuierlichen Überprüfung der eigenen Versorgungsleistungen und zum rechtzeitigen Ergreifen von Korrekturmaßnahmen

Evaluating multiple causes of persistent low microwave backscatter from Amazon forests after the 2005 drought

Amazonia has experienced large-scale regional droughts that affect forest productivity and biomass stocks. Space-borne remote sensing provides basin-wide data on impacts of meteorological anomalies, an important complement to relatively limited ground observations across the Amazon’s vast and remote humid tropical forests. Morning overpass QuikScat Ku-band microwave backscatter from the forest canopy was anomalously low during the 2005 drought, relative to the full instrument record of 1999–2009, and low morning backscatter persisted for 2006–2009, after which the instrument failed. The persistent low backscatter has been suggested to be indicative of increased forest vulnerability to future drought. To better ascribe the cause of the low post-drought backscatter, we analyzed multiyear, gridded remote sensing data sets of precipitation, land surface temperature, forest cover and forest cover loss, and microwave backscatter over the 2005 drought region in the southwestern Amazon Basin (4°-12°S, 66°-76°W) and in adjacent 8°x10° regions to the north and east. We found moderate to weak correlations with the spatial distribution of persistent low backscatter for variables related to three groups of forest impacts: the 2005 drought itself, loss of forest cover, and warmer and drier dry seasons in the post-drought vs. the pre-drought years. However, these variables explained only about one quarter of the variability in depressed backscatter across the southwestern drought region. Our findings indicate that drought impact is a complex phenomenon and that better understanding can only come from more extensive ground data and/or analysis of frequent, spatially-comprehensive, high-resolution data or imagery before and after droughts

Quantum Fluctuations in Josephson Junction Comparators

We have developed a method for calculation of quantum fluctuation effects, in particular of the uncertainty zone developing at the potential curvature sign inversion, for a damped harmonic oscillator with arbitrary time dependence of frequency and for arbitrary temperature, within the Caldeira-Leggett model. The method has been applied to the calculation of the gray zone width Delta Ix of Josephson-junction balanced comparators driven by a specially designed low-impedance RSFQ circuit. The calculated temperature dependence of Delta Ix in the range 1.5 to 4.2K is in a virtually perfect agreement with experimental data for Nb-trilayer comparators with critical current densities of 1.0 and 5.5 kA/cm^2, without any fitting parameters.Comment: 4 pages, 4 figures, submitted to Physical Review Letter

Cross-calibration of the Siemens mMR:easily acquired accurate PET phantom measurements, long-term stability and reproducibility

BACKGROUND: We present a quick and easy method to perform quantitatively accurate PET scans of typical water-filled PET plastic shell phantoms on the Siemens Biograph mMR PET/MR system. We perform regular cross-calibrations (Xcal) of our PET systems, including the PET/MR, using a Siemens mCT water phantom. LONG-TERM STABILITY: The mMR calibration stability was evaluated over a 3-year period where 54 cross-calibrations were acquired, showing that the mMR on average underestimated the concentration by 16 %, consistently due to the use of MR-based μ-maps. The mMR produced the narrowest calibration ratio range with the lowest standard deviation, implying it is the most stable of the six systems in the study over a 3-year period. MMR ACCURACY WITH PREDEFINED μ-MAPS: With the latest mMR software version, VB20P, it is possible to utilize predefined phantom μ-maps. We evaluated both the system-integrated, predefined μ-map of the long mMR water phantom and our own user-defined CT-based μ-map of the mCT water phantom, which is used for cross-calibration. For seven scans, which were reconstructed with correctly segmented μ-maps, the mMR produced cross-calibration ratios of 1.00–1.02, well within the acceptance range [0.95–1.05], showing high accuracy. CONCLUSIONS: The mMR is the most stable PET system in this study, and the mean underestimation is no longer an issue with the easily accessible μ-map, which resulted in correct cross-calibration ratios in all seven tests. We will share the user-defined μ-map of the mCT phantom and the protocol with interested mMR users

The Beagle 2 microscope

The Beagle 2 microscope provides optical images of the Martian surface at a resolution 5x higher than any other experiment currently planned. By using a novel illumination system it images in three colors and can also detect fluorescent materials