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Search Results: 1 - 10 of 88 matches for " Frieder Boecker "
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Influenceable and Avoidable Risk Factors for Systemic Air Embolism due to Percutaneous CT-Guided Lung Biopsy: Patient Positioning and Coaxial Biopsy Technique—Case Report, Systematic Literature Review, and a Technical Note
Gernot Rott,Frieder Boecker
Radiology Research and Practice , 2014, DOI: 10.1155/2014/349062
Abstract: Following the first case of a systemic air embolism due to percutaneous CT-guided lung biopsy in our clinic we analysed the literature regarding this matter in view of influenceable or avoidable risk factors. A systematic review of literature reporting cases of systemic air embolism due to CT-guided lung biopsy was performed to find out whether prone positioning might be a risk factor regarding this issue. In addition, a technical note concerning coaxial biopsy practice is presented. Prone position seems to have relevance for the development and/or clinical manifestation of air embolism due to CT-guided lung biopsy and should be considered a risk factor, at least as far as lesions in the lower parts of the lung are concerned. Biopsies of small or cavitary lesions in coaxial technique should be performed using a hemostatic valve. 1. Introduction Percutaneous computed tomography- (CT-) guided lung biopsy, an everyday practice in many institutions, has well-known potential complications, in numbers, mainly occurring as pneumothorax and pulmonary bleeding with both of them normally requiring little or no further treatment. Systemic air embolism is a feared and potentially fatal complication but with very low reported incidences ranging from 0,001% to 0,003% according to publications dealing with greater series of biopsies [1, 2]. Statistically, most radiologists performing percutaneous lung biopsies will never have to deal with this complication. On the other hand one study with a smaller patient population recently reported an incidence of 3,8% [3]. Risk factors for systemic air embolism have been speculated, postulated, and reported; these include use of a coaxial biopsy system, number of biopsies, needle path through a longer distance of ventilated lung, coughing during the procedure, positive pressure ventilation, location of lesion in the lower lobes or lower parts of the lung, location of the lesion above the level of the left atrium, vasculitis, and small or cavitary lesions with some of these being influenceable or even avoidable and others not [2–9]. Prone positioning as a truly influenceable factor has been considered a risk factor [3] but to our knowledge has never been evaluated systematically in a literature review. Our very first case of systemic air embolism after CT-guided lung biopsy occurred at our institution after performing the procedure for much more than 10 years with a frequency of at least 50 cases per year. We are presenting this case, as we strongly believe that, in the light of the very low incidence of this complication, every
Impact of Hadronic Axions on Black Hole Accretion Discs and Neutron Stars
K. Boecker
Physics , 2000,
Abstract: We re-examine the possibility of an astrophysically allowed KSVZ-type axion that has a strongly suppressed coupling to photons. We then investigate the impact of such ''hadronic axions'' on two classes of astrophysical objects: black hole accretion disc (BHAD) based gamma-ray bursts and isolated neutron-stars. Although our results are sensitive to details of the underlying models, we show that hadronic axions could in principle play an important role in the evolution of gamma-ray bursts and in the cooling behaviour of neutron stars.
Topological Concepts in Gauge Theories
Frieder Lenz
Physics , 2004, DOI: 10.1007/978-3-540-31532-2_2
Abstract: In these lecture notes, an introduction to topological concepts and methods in studies of gauge field theories is presented. The three paradigms of topological objects, the Nielsen-Olesen vortex of the abelian Higgs model, the 't Hooft-Polyakov monopole of the non-abelian Higgs model and the instanton of Yang-Mills theory, are discussed. The common formal elements in their construction are emphasized and their different dynamical roles are exposed. The discussion of applications of topological methods to Quantum Chromodynamics focuses on confinement. An account is given of various attempts to relate this phenomenon to topological properties of Yang-Mills theory. The lecture notes also include an introduction to the underlying concept of homotopy with applications from various areas of physics.
Elements of a non-Hermitian quantum theory without Hermitian conjugation - scalar product and scattering
Frieder Kleefeld
Physics , 2015,
Abstract: The descripition of in a Hermitian setting seemingly nonlocal and nonperturbative phenomena like confinement or superconductivity is most conveniently performed by generalizing quantum theory to a non-Hermitian regime where these phenomena appear perturbative and local. The short presentation provides a clue how this can be done on the basis of Lorentz covariance while preserving the analyticity of the theory. After deriving with the help of Lorentz covariance a quantum scalar product without making any use of metric or complex conjugation we sketch how the formalism of scattering theory can be extended analytically to a non-Hermitian regime.
Character correspondences induced by magic representations
Frieder Ladisch
Mathematics , 2010,
Abstract: Let G be a finite group, K a normal subgroup of G and H a subgroup such that G = HK, and set L = H \cap K. Suppose \theta \in Irr K and \phi \in Irr L, and \phi\ occurs in \theta_L with multiplicity n > 0. A projective representation of degree n on H/L is defined in this situation; if this representation is ordinary, it yields a bijection between Irr(G | \theta) and Irr(H | \phi). The behavior of fields of values and Schur indices under this bijection is described. A modular version of the main result is proved. We show that the theory applies if n and the order of H/L are coprime. Finally, assume that P <= G is a p-group with P \cap K = 1 and PK normal in G, that H = N_G(P), and that \theta\ and \phi\ belong to blocks of p-defect zero which are Brauer correspondents with respect to the group P. Then every block of F_p[G] or Q_p[G] lying over \theta\ is Morita-equivalent to its Brauer correspondent with respect to P. This strengthens a result of Turull [Above the Glauberman correspondence, Advances in Math. 217 (2008), 2170--2205].
Character correspondences above fully ramified sections and Schur indices
Frieder Ladisch
Mathematics , 2011,
Abstract: Let N be a finite group of odd order and A a finite group that acts on N such that the orders of N and A are coprime. Isaacs constructed a natural correspondence between the set Irr_A(N) of irreducible complex characters invariant under the action of A, and the irreducible characters of the centralizer of A in N, Irr(C_N(A)). We show that this correspondence preserves Schur indices over the rational numbers. Moreover, suppose that the semidirect product AN is a normal subgroup of the finite group G and set U= N_G(A). Let \chi \in Irr_A(N) and \chi* \in Irr(C_N(A)) correspond. Then there is a canonical bijection between Irr(G | \chi) and Irr(U | \chi*) preserving Schur indices. We also give simplified and more conceptual proofs of (known) character correspondences above fully ramified sections.
The Schur-Clifford subgroup of the Brauer-Clifford group
Frieder Ladisch
Mathematics , 2014, DOI: 10.1016/j.jalgebra.2015.06.017
Abstract: We define a Schur-Clifford subgroup of Turull's Brauer-Clifford group, similar to the Schur subgroup of the Brauer group. The Schur-Clifford subgroup contains exactly the equivalence classes coming from the intended application to Clifford theory of finite groups. We show that the Schur-Clifford subgroup is indeed a subgroup of the Brauer-Clifford group, as are certain naturally defined subsets. We also show that this Schur-Clifford subgroup behaves well with respect to restriction and corestriction maps between Brauer-Clifford groups.
On Clifford theory with Galois action
Frieder Ladisch
Mathematics , 2014,
Abstract: Let $\widehat{G}$ be a finite group, $N $ a normal subgroup of $\widehat{G}$ and $\theta\in \operatorname{Irr}N$. Let $\mathbb{F}$ be a subfield of the complex numbers and assume that the Galois orbit of $\theta$ over $\mathbb{F}$ is invariant in $\widehat{G}$. We show that there is another triple $(\widehat{G}_1,N_1,\theta_1)$ of the same form, such that the character theories of $\widehat{G}$ over $\theta$ and of $\widehat{G}_1$ over $\theta_1$ are essentially "the same" over the field $\mathbb{F}$ and such that the following holds: $\widehat{G}_1$ has a cyclic normal subgroup $C$ contained in $N_1$, such that $\theta_1=\lambda^{N_1}$ for some linear character $\lambda$ of $C$, and such that $N_1/C$ is isomorphic to the (abelian) Galois group of the field extension $\mathbb{F}(\lambda)/\mathbb{F}(\theta_1)$. More precisely, "the same" means that both triples yield the same element of the Brauer-Clifford group $\operatorname{BrCliff}(G,\mathbb{F}(\theta))$ defined by A. Turull.
Corestriction for algebras with group action
Frieder Ladisch
Mathematics , 2014, DOI: 10.1016/j.jalgebra.2015.06.015
Abstract: We define a corestriction map for equivariant Brauer groups in the sense of Fr\"ohlich and Wall, which contain as a special case the Brauer-Clifford groups introduced by Turull. We show that this corestriction map has similar properties as the corestriction map in group cohomology (especially Galois cohomology). In particular, composing corestriction and restriction associated to a subgroup $H\leq G$ amounts to powering with the index $\lvert G:H \rvert$.
Harmony Perception by Periodicity Detection
Frieder Stolzenburg
Computer Science , 2013,
Abstract: The perception of consonance/dissonance of musical harmonies is strongly correlated to their periodicity. This is shown in this article by consistently applying recent results from psychophysics and neuroacoustics, namely that the just noticeable difference of human pitch perception is about 1% for the musically important low frequency range and that periodicities of complex chords can be detected in the human brain. The presented results correlate significantly to empirical investigations on the perception of chords. Even for scales, plausible results are obtained. For example, all classical church modes appear in the front ranks of all theoretically possible seven-tone scales.
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