Should Pediatric Patients Wait for HLA-DR-Matched Renal Transplants?

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74900/1/j.1600-6143.2008.02320.x.pd

Surface Wavefield Tomography of the Alpine Region to Constrain Slab Geometries, Lithospheric Deformation and Asthenospheric Flow

Surface waves radiated by teleseismic earthquakes are ideally suited to constrain isotropic and anisotropic elastic properties of the upper mantle down to about 300 km depth beneath dense networks of broad-band stations. Rayleigh wave phase velocities were automatically determined in a broad period range from 8 s to 300 s and a very strict quality control was applied. This resulted in a data set of more than 200,000 inter-station phase velocity curves. Local dispersion curves, extracted from phase velocity maps were inverted for a 3D shear-wave velocity model (MeRE2020) using a newly developed stochastic inversion algorithm based on particle swarm optimization. It was shown that the presence of small and highly segmented slabs can be resolved by surface wave tomography in case of a high station density. In the western Alps, a short Eurasian slab was imaged down to about 150 km depth, whereas at larger depths a pronounced low velocity anomaly indicates slab break-off. In the northern Apennines, a nearly vertical south-dipping slab connected to the Adriatic mantle lithosphere beneath the Po Basin is observed. In the central Alps, the presence of Eurasian mantle lithosphere is found down to the bottom of the model at 300 km depth. Whereas in the eastern Alps, a short Eurasian nearly vertical dipping slab is found down to only 150 km depth. The presence of a short slab consisting of Adriatic mantle lithosphere is also indicated beneath the northern Dinarides extending towards the Alps east of the Giudicaria fault. Anisotropic phase velocity maps show at 25 s period (lower crustal depth) mostly fast orogen parallel directions, whereas in the western Alps azimuthal anisotropy is more inclined with respect to the Alpine arc. At 100 s period, azimuthal anisotropy beneath the western Alps indicates asthenospheric flow towards the Ligurian Sea and beneath the northern Dinarides towards the Pannonian Basin through slab gaps. Moreover, seismic wavefields were analysed using AlpArray and Swath-D data. Wavefield animations illustrate the considerable spatio-temporal variability of the wavefield's properties at a lateral resolution down to about 100km. Within denser station distributions like those provided by Swath-D, even shorter period body and surface wave features can be recovered. Considerable amplifications of the Rayleigh wave in the Alpine area are observed for several earthquakes. To analyse Rayleigh wave quantitatively, an algorithm has been developed to extract their phase and amplitude fields using cross correlation between synthetic waveforms and recordings of a dense array. Phase fields are unwrapped by solving a linear system of equations. Phase and amplitude fields are quality controlled and interpolated to determine structural phase velocity fields using Helmholtz tomography. It is shown that the observed amplitude fields depend heavily on lateral heterogeneity outside the array. Often, linear amplifications in the propagation direction are observed. In order to model the observed wavefields, the AxiSEM-SPECFEM Coupling algorithm has been improved and adapted concerning flexibility and efficiency, reducing the necessary wavefield interpolation significantly and allowing topography as well as existing 3D Models of the Alpine region to be easily implemented

Depressive symptoms and perceived burdens related to being a student: Survey in three European countries

Mikolajczyk RT, Maxwell AE, Naydenova V, Meier S, El Ansari W. Depressive symptoms and perceived burdens related to being a student: survey in three European countries. Clinical Practice and Epidemiology in Mental Health. 2008;4(1): 19.Background: Despite a high prevalence of depressive symptoms among university students, few studies have examined how this mental health problem is associated with perceived stress and perceived burdens related to being a student. Methods: We conducted a cross-sectional study of 2,103 first year students from one western (Germany), one central (Poland), and one south-eastern European country (Bulgaria). The self-administered questionnaires included the modified Beck Depression Inventory and Cohen's Perceived Stress Scale. A 13 item scale measured perceived burdens related to being a student with four subscales: ''Course work'', ''Relationships'', ''Isolation'', and ''Future''. Results: Depressive symptoms were highly prevalent in all three countries (M-BDI ≥35: 34% in Poland, 39% in Bulgaria, and 23% in Germany). Students felt more burdened by course work and bad job prospects (''Future'') than by relationship problems or by feelings of isolation. The perceived burdens subscales ''Future'', ''Relationship'' and ''Isolation'' remained associated with depressive symptoms after adjusting for perceived stress, which displayed a strong association with depressive symptoms. The association between perceived stress and depressive symptoms differed by gender. These findings were similar in all three countries. Conclusion: Perceived burdens related to studying are positively associated with higher depression scores among students, not only by mediation through perceived stress but also directly. While the strong association between perceived stress and depressive symptoms suggests the need for interventions that improve stress management, perceived burdens should also be addressed

Electromagnetic and weak hyperon properties in the Skyrme model

We report on the result of some investigations concerning the radiative decays of decuplet baryons and the non-leptonic weak decays of the octet baryons in the context of topological chiral soliton models. Our results are compared with those of alternative baryon models. For the radiative decays we find that the predictions are similar to those of quark models. In the case of the non-leptonic weak decays, we find that although the predicted S-wave amplitudes are in rather good agreement with the observed values, the model is not able to reproduce the empirical P-wave amplitudes. Thus, in contrast to previous expectations, the Skyrme model does not seem to provide a solution to the long-standing 'S-wave/P-wave puzzle'.Comment: 7 pages, 1 fig. Cont. to the Proc. of the "School on Electromagnetic probes and the structure of hadrons and nuclei". Erice, Italy. September 17- 24, 1999 to be published in Progress in Particle and Nuclear Physic

Identifying Main Lithospheric Structures in the Eastern Alpine Domain by Joint Inversion of Receiver Function and Surface Wave Measurements for Seismic Anisotropy

Rayleigh-wave phase velocity measurements from both earthquakes and ambient noise were combined to image the 3-D shear-wave velocity structure beneath the eastern Alps and in the transitions towards the Pannonian Basin and the Dinarides. This allows us to resolve crust and upper mantle structures down to 300 km including the Moho topography. Continuous waveforms were collected from 1254 stations within a 9° radius for the time period from 2006 to 2018. More than 164,464 inter-station Rayleigh wave phase-velocity curves were automatically extracted after applying a strict quality control. Using the combined dataset, a period and distance dependence correction was applied to account for the bias observed between phase velocities from both datasets that amounts to ~1 % and increases towards longer periods. 2-D anisotropic phase velocity maps were then constructed spanning periods from 5 s to 250 s. 33,981 local dispersion curves were extracted and inverted for a 3-D shear-wave velocity model (PanREA2023) encompassing crust and mantle using a non-linear stochastic particle swarm optimization. At shallower crustal depths, the horst and graben structure of the Pannonian Basin is imaged, characterized by two NE-SW trending horsts and three graben systems. A pronounced crustal low-velocity anomaly extending to the Moho is found beneath the surrounding Carpathian orogen. A shallow south-dipping Eurasian slab was imaged beneath the eastern Alps down to only 150 km depth. Adriatic lithosphere is near-vertically dipping beneath the northern Apennines and northern Dinarides. The Adriatic slab is short reaching depths of around 150 km. Seismic discontinuities down to the mantle transition zone are analysed using S-to-P converted phases from teleseismic earthquakes. We stack broadband teleseismic S waveform data to retrieve S-to-P converted signals from below the seismic stations. In order to avoid processing artefacts, no deconvolution or filtering is applied. The Moho signals are always seen very clearly. In addition, a negative velocity gradient below the Moho depth is evident in many regions. A Moho depression is visible along larger parts of the Alpine chain reaching its largest depth of 60 km beneath the Tauern Window. The Moho depression ends abruptly near about 13°E below the eastern Tauern Window. East of 13°E the Moho shallows all the way to the Pannonian Basin. A prominent along-strike change was also detected in the upper mantle structure at about 14°E. There, the lateral disappearance of a zone of negative S-wave velocity gradient in the uppermost mantle is interpreted to indicate that the S-dipping European slab laterally terminates east of the Tauern Window. Joint inversion of surface wave dispersion curves and Moho travel times inferred from S-to-P converted phases allows to determine shear-wave velocity models consistent with both measurements. The uncertainty of the Moho depth estimates decreases from about 5 to 10 km considerably to 2 to 5 km depending on the depth of the Moho. The joint inversion further enables the determination of the sharpness of the negative discontinuity associated with the lithosphere-asthenosphere boundary. It appears to be rather sharp in the northern Alpine foreland and the Pannonian Basin

Could magnetic properties be used to image a grouted rock volume?

In this study, the feasibility to develop a detectable permeation grouting system is tested, based on the addition of magnetic materials to the grout, specifically, magnetite. A magnetic-based detection system is selected for development because unlike other previously trialled detection methods, magnetic fields are detectable over large distances within the subsurface, and importantly, attenuation of the magnetic field is not strongly dependent on the material properties of the surrounding rock. To test the conceptual feasibility of such a system, a finite element based numerical model is developed to simulate the magnetic field anomaly that can be achieved by the addition of magnetic materials to a cement grout. The model is verified against an analytical solution and then used to predict the magnetic field generated by a grouted cylinder of rock, assuming a fixed percentage of uniformly distributed magnetic minerals, and a central injection borehole. Two field trials are conducted to verify the detectable grouting concept, the first using a walkover survey that allowed mapping of the magnetic signal in 2D. The second is designed to mimic magnetic field measurements from a borehole monitoring array, with a single central magnetic grout block (representing the grout close to the injection point). Results of the two field trials show that the magnetic cement is detectable, even when the background magnetic noise within the surrounding soils/rocks is significant. A good agreement is obtained between the measured and the modelled magnetic anomaly. This research opens the door to the development of a ‘detectable’ magnetic grouting system, that can increase confidence in the integrity of grouted rock volumes and reduce the inefficiencies currently present in the grouting industry, enabling in-situ real-time optimisation of grouting campaigns

Slabs in the Alpine region: inferences down to 300 km depth from surface wave tomography and receiver functions

Mountain building in the Alps is driven by a complex interplay between (i) subduction of oceanic lithosphere and/or continental mantle lithosphere and (ii) exhumation of crustal material. A major challenge represents passive seismic imaging of the various slab segments crucial for shaping the Alpine orogen. AlpArray and Swath-D provide the necessary dense station distribution for high-resolution surface wave tomography using earthquake and ambient noise data as well as for detailed P-to-S and S-to-P receiver function analyses. Absolute shear-wave velocity models of the crust and upper mantle down to 300 km depth have been obtained from stochastic particle‐swarm‐optimization inversion of a large data set of more than 200,000 Rayleigh wave phase velocity curves (4 -300 s period). This allows for imaging the slabs and their connection to the forelands with a lateral resolution of about 50 km to 75 km in the Alpine area. Moreover, about 300,000 P-to-S and about 80.000 S-to-P receiver functions have been obtained for the wider Alpine area. The common conversion point stacks of the P-to-S and S-to-P waveforms, concentrated in the Eastern Alps, provide high resolution images of the crustal structure as well as velocity discontinuities in the mantle at the interface between the European, Adriatic, and Pannonian domains. Moho topography indicating the tops of slabs as well as negative velocity gradients in the mantle beneath the Moho have been imaged. Thermochemical modelling provides evidence that the bottom of the negative velocity gradient causing S-to-P conversions is located close to the lithosphere-asthenosphere boundary. These conversions are thus hinting at the geometry of the bottom of mantle lithosphere and slabs, respectively. Beneath the northern Apennines, Adriatic lithosphere is subducting nearly vertically southwards down to at least 200 km depth as supported by the spatial distribution of a few intermediate-depth earthquakes. A short Eurasian slab subducting eastwards down to about 150 km depth and a slab gap beneath are present beneath the western Alps. Interestingly, the Eurasian slab is almost colliding with the east-west oriented Adriatic slab beneath the southwestern Po Basin. An attached Eurasian slab subducting to at least 250 km depth is imaged beneath the central Alps, whereas beneath the eastern Alps a short Eurasian slab is found down to only about 150 km depth. A short slab of continental mantle lithosphere is also present beneath the northern Dinarides. It is extending towards the Alps east of the Guidicaria fault. Broken-off Eurasian or Adriatic lithosphere may be indicated by high-velocity anomalies at depth larger than 250 km beneath the south-eastern Alps and the Adriatic Sea. Next, digital slab interface models are to be set up accounting for the various geophysical observations in order to create realistic input models for numerical geodynamic forward modelling of observed deformation rates

Neue Aspekte in der Chemie von Übergangsmetallpolysulfidkomplexen: Synthese und Kristallstrukturen von Cp′3Nb3S12 und Cp′3Nb3S10O (Cp′ = t-BuC5H4)

Thermolysis of a mixture of Cp′4Nb2Sn (Cp′ = t-BuC5H4; n = 8, 9) results in the formation of the new niobium polysulfide complexes: Cp′3Nb3S12 (2), Cp′3Nb3S10O (3), Cp′3Nb3S10O (4) and Cp′4Nb4S13 (5). The structures of 2 and 3 have been established by X-ray diffraction studies. The complexes are characterized by an unusual variety of different sulfur ligands (up to five in 2), which is responsible for the absence of any metal-metal interaction

On the Production of π+π+\pi^+\pi^+ Pairs in pp Collisions at 0.8 GeV

Data accumulated recently for the exclusive measurement of the $pp\to pp\pi^+\pi^-$ reaction at a beam energy of 0.793 GeV using the COSY-TOF spectrometer have been analyzed with respect to possible events from the $pp \to nn\pi^+\pi^+$ reaction channel. The latter is expected to be the only $\pi\pi$ production channel, which contains no major contributions from resonance excitation close to threshold and hence should be a good testing ground for chiral dynamics in the $\pi\pi$ production process. No single event has been found, which meets all conditions for being a candidate for the $pp \to nn \pi^+\pi^+$ reaction. This gives an upper limit for the cross section of 0.16 $\mu$b (90% C.L.), which is more than an order of magnitude smaller than the cross sections of the other two-pion production channels at the same incident energy

Probing shells against buckling: a non-destructive technique for laboratory testing

This paper addresses testing of compressed structures, such as shells, that exhibit catastrophic buckling and notorious imperfection sensitivity. The central concept is the probing of a loaded structural specimen by a controlled lateral displacement to gain quantitative insight into its buckling behaviour and to measure the energy barrier against buckling. This can provide design information about a structure's stiffness and robustness against buckling in terms of energy and force landscapes. Developments in this area are relatively new but have proceeded rapidly with encouraging progress. Recent experimental tests on uniformly compressed spherical shells, and axially loaded cylinders, show excellent agreement with theoretical solutions. The probing technique could be a valuable experimental procedure for testing prototype structures, but before it can be used a range of potential problems must be examined and solved. The probing response is highly nonlinear and a variety of complications can occur. Here, we make a careful assessment of unexpected limit points and bifurcations, that could accompany probing, causing complications and possibly even collapse of a test specimen. First, a limit point in the probe displacement (associated with a cusp instability and fold) can result in dynamic buckling as probing progresses, as demonstrated in the buckling of a spherical shell under volume control. Second, various types of bifurcations which can occur on the probing path which result in the probing response becoming unstable are also discussed. To overcome these problems, we outline the extra controls over the entire structure that may be needed to stabilize the response.Comment: as accepted in International Journal of Bifurcation and Chaos (18 pages