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Search Results: 1 - 10 of 1503 matches for " Claus; "
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Simultaneous Echo Refocused Magnetization Transfer Imaging  [PDF]
Claus Kiefer
Open Journal of Medical Imaging (OJMI) , 2014, DOI: 10.4236/ojmi.2014.43021
Abstract: Purpose: To increase the efficiency of densely encoded magnetization transfer imaging of the brain, we time-multiplex multiple slices within the same readout using simultaneous echo refocusing FLASH imaging with magnetization transfer (MT) preparation (MT-SER-FLASH). Materials and Methods: Inefficiency in total scan time results from the number of frequency samples needed for sufficient quality of quantitative parameter maps for a binary spin bath model. We present a highly efficient multiplexing method, simultaneous echo refocused magnetization transfer imaging (MT-SER-FLASH) for reducing the total scan time of MT imaging by one-third. The specific absorption rate (SAR) was also reduced by reducing the number of MT-pulses per volume. Results: 2D-MT-SER-FLASH is performed in 19 minutes rather than 1 hour, acceptable for routine clinical application. The SAR could be reduced to 69% instead of more than 100% with a standard 2D or 3D-FLASH with MT-preparation. Conclusion: The net reduction of scan time and SAR enables the use of quantitative model based magnetization transfer imaging within a clinical environment.
Modelling Magnetization Transfer Considering Spin-Locking Effects  [PDF]
Claus Kiefer
Open Journal of Medical Imaging (OJMI) , 2014, DOI: 10.4236/ojmi.2014.44027
Abstract: Purpose: Recently it was demonstrated that spin-locking (SL) effects can manifest as pseudo magnetization transfer (MT). To our best knowledge the MT models proposed so far cannot distinguish between saturation effects caused by the MT preparation pulses and SL phenomena. Therefore a new MT model is proposed. Materials and Methods: A binary spin-bath model for magnetization transfer was extended in that sense that SL effects are considered. The new modified spin bath model was tested for a phantom with different agar concentrates (2%, 4%, 8%) and a MnCl2 (0.3 mM) solution. Results: The mean fitting error is 3.2 times lower for the modified model compared to the original model. Especially the parameter F for the fractional part of the bounded proton pool describes the situation for the MnCl2 (F = 0) better than the original model (F = 0.004). Conclusion: The proposed mathematical modifications of the binary spin-bath model considering SL seem to be a step in the right direction in that sense that the effects associated with SL are not interpreted as magnetization transfer.
Diversity and abundance of orchid bees (Hymenoptera: Apidae, Euglossini) in a tropical rainforest succession
Rasmussen, Claus;
Neotropical Entomology , 2009, DOI: 10.1590/S1519-566X2009000100006
Abstract: euglossine bee males are easily lured to chemical baits imitating natural fragrances gathered by bees, providing a widely applied measure for estimating the diversity and abundance of euglossines. in here, i report the composition of euglossine bees in three lowland rainforest habitats of peru, a primary old forest, a reforested and managed forest, and a very disturbed forest. a total of 2,072 males of euglossine were collected, belonging to 33 species and four genera. although a comparable diversity relative to other studies from the amazonian region was found, no significant differences among the sampled areas were detected. perhaps, the short time and low intensity surveys here used (< 3 months) were not good enough indicators of forest disturbance without additional data. compared to other major studies on the euglossine bee fauna, loreto is most similar to the species assemblage reported from lowland rainforest in brazil (manaus), central peru (panguana) and southern peru (tambopata).
Quantum cosmology and the arrow of time
Kiefer, Claus;
Brazilian Journal of Physics , 2005, DOI: 10.1590/S0103-97332005000200014
Abstract: although most fundamental laws are invariant under time reversal, experience exhibits the presence of irreversible phenomena - the arrows of time. their origin lies in cosmology, and i argue that only quantum cosmology can provide the appropriate formal framework. after briefly reviewing the formalism, i discuss how a simple and natural boundary condition can lead to the observed arrows of time. this yields at the same time interesting consequences for black holes.
A new solution algorithm for skip-free processes to the left
Cubo (Temuco) , 2010, DOI: 10.4067/S0719-06462010000200011
Abstract: this paper proposes a new solution algorithm for steady state models describing skip-free processes to the left where each level has one phase. the computational complexity of the algorithm is independent of the number of levels of the system. if the skip parameter of the skip-free process is significantly smaller than the number of levels of the system, our algorithm numerically outperforms existing algorithms for skip-free processes. the proposed algorithm is based on a novel method for applying generalized fibonacci series to the solution of steady state models.
Russia and the OSCE - The Influence of Interested Third and Disinterested Fourth Parties on the Conflicts in Estonia and Moldova
Claus Neukirch
Journal on Ethnopolitics and Minority Issues in Europe , 2001,
Abstract: This article aims to analyse the influence of external actors on the domestic conditions surrounding the conflicts in Estonia and Moldova. It attempts to answer the question why the Moldovan conflict turned violent while the Estonian conflict remained peaceful.
Die Geschichtlichkeit des Rechts in der Methodologie der Rechtsphilosophie K.C.F. Krauses
Claus Dierksmeier
Forum Historiae Iuris , 2002,
Delphine Bellis, Le visible et l’invisible dans la pensée cartésienne. Figuration, imaginatio et vision dans la philosophie naturelle de René Descartes (2010)
Claus Zittel
Studium : Tijdschrift voor Wetenschaps- en Universiteits-Geschiedenis , 2011,
Aspects of Complexity in Life and Science.
Claus Emmeche
Philosophica , 1997,
Analysis and Synthesis. Interdependent Operations in Chemical Language and Practice
Claus Jacob
Hyle : International Journal for Philosophy of Chemistry , 2001,
Abstract: Chemical symbolism provides the linguistic representations for experimental research. It is based on an empirical set of formal (syntactic) rules that allows operations on formulas and reaction equations. The semantic interpretation of formulas and reaction equations links these operations to experimental analysis and synthesis. These syntactic and semantic aspects of chemical symbolism guide as well as limit chemical research. A better understanding of these aspects of chemical language allows chemists to rationalize novel approaches to chemical research (e.g. combinatorial chemistry) and possibly exploit the vast area of 'surprise discoveries'.
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