•Proposed input calibration method for intra-/interlaminar failure behavior enabled favorable results on structural level.•Strong validation of the simulation approach was achieved based on a ...comprehensive experimental data base.•Applied FE mesh modifications significantly reduced mesh-dependencies.
This paper deals with the investigation of a numerical simulation method to appropriately represent relevant failure mechanisms of carbon fiber reinforced plastic (CFRP) components subjected to dynamic crash loads. The presented work considers the stacked shell approach, using a stack of continuum shell elements and cohesive elements, and focuses on the calibration of simulation input parameters. Furthermore, modeling aspects are discussed to reduce mesh-dependencies for the simulation of progressive crushing.
The validation of the numerical approach is performed on the basis of an extensive test program of CFRP crush absorbers on the structural level. The capability of current state-of-the-art technologies for the simulation of progressive crushing is identified. The simulations capture general failure effects and force-displacement characteristics for different designs and loading conditions. Drawbacks are identified in the definition of cohesive input parameters to obtain numerical stability for complex loading conditions.
The numerical simulations were performed using the commercial finite element software Abaqus/Explicit.
Due to their inherently brittle behaviour, carbon fibre reinforced plastics (CFRP) structures demand for a specific design to achieve appropriate crash energy absorption compared to classical ...metallic fuselage designs. In this paper, experimental as well as numerical studies on two different crashworthy designs are presented. The first concept aims to absorb the crash energy by crushing of CFRP components below a reinforced cargo cross beam in combination with further energy absorbing devices in the lower side shell. The feasibility of this concept was in the meantime proven by tests at the coupon and structural element level. An alternative crash concept making use of energy absorption in so-called tension absorbers in the passenger and cargo floor structure was developed and assessed with the focus on a reduction of structural mass in combination with improved concept robustness. This paper provides a summary of the performed research work and discusses the context of the concept development. Details on the individual research tasks can be found in further publications which are given in the references.
In this study, the osteoinductive and cell-binding properties of three different resorbable polymers were evaluated by human mesenchymal stem cells (MSCs). MSCs were isolated, expanded, and ...cultivated onto resorbable D,D,L,L-polylactide (PLLA), collagen I/III, and polygalactin-910/polydioxanone (PGPD) scaffolds in vitro. To evaluate the influence of dexamethasone, ascorbic acid, and beta-glycerolphosphate (DAG) on osteoblast differentiation, MSCs were incubated in a DAG-enriched medium. After a 28-day period in vitro, the cellular loaded polymers were digested enzymatically by papain and HCl. The Ca(2+) content of the biomembranes was evaluated by an o-kresolphthalein-complexon reaction via photometer. A PicoGreen assay was performed for dsDNA quantification. Significant differences between the number of adherent MSCs were documented (collagen > PLLA > PGPD). Compared to the initial number of adherent cells, all biomaterials induced a significant decrease in cellular adherence after 28 days in vitro. The presence of DAG-enriched culture medium stimulated the cellular proliferation for PLLA and slightly for PGPD, whereas cell proliferation was inhibited when MSCs were cultivated onto collagen I/III. In comparison with the control groups, all biomaterials (PLLA, PGPD, and collagen I/III) showed a significant increase in local Ca(2+) accumulation under DAG stimulation after 28 days in vitro. Furthermore, collagen I/III and PLLA scaffolds showed osteoinductive properties without DAG stimulation. These results were verified by immunocytochemical stainings against osteoblast-typical markers (osteopontin and alkaline phosphatase) and completed by calcified matrix detection (von Kossa staining). MSCs were identified by CD105 and CD13 antigen expression. Corresponding to an absence of CD34, CD45, and collagen II expression, we found no chondrogenic or hematopoietic cell differentiation. The results indicate significant differences for the proliferation, differentiation, adherence, and Ca(2+) accumulation between the tested polymers in a MSC culture.
The first sensors of the IceCube neutrino observatory were deployed at the South Pole during the austral summer of 2004–2005 and have been producing data since February 2005. One string of 60 sensors ...buried in the ice and a surface array of eight ice Cherenkov tanks took data until December 2005 when deployment of the next set of strings and tanks began. We have analyzed these data, demonstrating that the performance of the system meets or exceeds design requirements. Times are determined across the whole array to a relative precision of better than 3
ns, allowing reconstruction of muon tracks and light bursts in the ice, of air-showers in the surface array and of events seen in coincidence by surface and deep-ice detectors separated by up to 2.5
km.
We have remotely mapped optical scattering and absorption in glacial ice at the South Pole for wavelengths between 313 and 560 nm and depths between 1100 and 2350 m. We used pulsed and continuous ...light sources embedded with the AMANDA neutrino telescope, an array of more than six hundred photomultiplier tubes buried deep in the ice. At depths greater than 1300 m, both the scattering coefficient and absorptivity follow vertical variations in concentration of dust impurities, which are seen in ice cores from other Antarctic sites and which track climatological changes. The scattering coefficient varies by a factor of seven, and absorptivity (for wavelengths less than ∼450 nm) varies by a factor of three in the depth range between 1300 and 2300 m, where four dust peaks due to stadials in the late Pleistocene have been identified. In our absorption data, we also identify a broad peak due to the Last Glacial Maximum around 1300 m. In the scattering data, this peak is partially masked by scattering on residual air bubbles, whose contribution dominates the scattering coefficient in shallower ice but vanishes at ∼1350 m where all bubbles have converted to nonscattering air hydrates. The wavelength dependence of scattering by dust is described by a power law with exponent −0.90 ± 0.03, independent of depth. The wavelength dependence of absorptivity in the studied wavelength range is described by the sum of two components: a power law due to absorption by dust, with exponent −1.08 ± 0.01 and a normalization proportional to dust concentration that varies with depth; and a rising exponential due to intrinsic ice absorption which dominates at wavelengths greater than ∼500 nm.
Muon track reconstruction and data selection techniques in AMANDA Ahrens, J.; Bai, X.; Bay, R. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/2004, Letnik:
524, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The Antarctic Muon And Neutrino Detector
Array (AMANDA) is a high-energy neutrino telescope operating at the geographic South Pole. It is a lattice of photo-multiplier tubes buried deep in the polar ...ice between 1500 and
2000
m
. The primary goal of this detector is to discover astrophysical sources of high-energy neutrinos. A high-energy muon neutrino coming through the earth from the Northern Hemisphere can be identified by the secondary muon moving upward through the detector.
The muon tracks are reconstructed with a maximum likelihood method. It models the arrival times and amplitudes of Cherenkov photons registered by the photo-multipliers. This paper describes the different methods of reconstruction, which have been successfully implemented within
AMANDA. Strategies for optimizing the reconstruction performance and rejecting background are presented. For a typical analysis procedure the direction of tracks are reconstructed with about 2° accuracy.
Neutrinos are elementary particles that carry no electric charge and have little mass. As they interact only weakly with other particles, they can penetrate enormous amounts of matter, and therefore ...have the potential to directly convey astrophysical information from the edge of the Universe and from deep inside the most cataclysmic high-energy regions. The neutrino's great penetrating power, however, also makes this particle difficult to detect. Underground detectors have observed low-energy neutrinos from the Sun and a nearby supernova, as well as neutrinos generated in the Earth's atmosphere. But the very low fluxes of high-energy neutrinos from cosmic sources can be observed only by much larger, expandable detectors in, for example, deep water or ice. Here we report the detection of upwardly propagating atmospheric neutrinos by the ice-based Antarctic muon and neutrino detector array (AMANDA). These results establish a technology with which to build a kilometre-scale neutrino observatory necessary for astrophysical observations.
We show new results from both the older and newer incarnations of AMANDA (AMANDA-B10 and AMANDA-II, respectively). These results demonstrate that AMANDA is a functioning, multipurpose detector with ...significant physics and astrophysics reach. They include a new higher-statistics measurement of the atmospheric muon neutrino flux and preliminary results from searches for a variety of sources of ultrahigh energy neutrinos: generic point sources, gamma-ray bursters and diffuse sources producing muons in the detector, and diffuse sources producing electromagnetic or hadronic showers in or near the detector.
We present new data taken with the AMANDA-II neutrino telescope array. The AMANDA-II upgrade was completed at the beginning of 2000. It significantly extends the sensitivity of the 10-string ...AMANDA-B10 detector to high- and ultrahigh-energy neutrino fluxes into regions of interest for probing current astrophysical models which remain unexplored by other experiments.
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