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Search Results: 1 - 10 of 17225 matches for " Christian Becker "
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On the Riemannian geometry of Seiberg-Witten moduli spaces
Christian Becker
Mathematics , 2007, DOI: 10.1016/j.geomphys.2008.05.005
Abstract: We construct natural Riemannian metrics on Seiberg-Witten moduli spaces and study their geometry.
Cheeger-Chern-Simons theory and differential String classes
Christian Becker
Mathematics , 2014,
Abstract: We introduce certain relative differential characters which we call Cheeger-Chern-Simons characters. These combine the well-known Cheeger-Simons characters with Chern-Simons forms. In the same way as the Cheeger-Simons characters generalize Chern-Simons invariants of oriented closed manifolds, the Cheeger-Chern-Simons characters generalize Chern-Simons invariants of oriented manifolds with boundary. Using Cheeger-Chern-Simons characters, we introduce the notion of differential trivializations of universal characteristic classes. Specializing to the class 1/2 $p_1 \in H^4(B\mathrm{Spin}_n;\mathbb Z)$ this yields a notion of differential String classes. Differential String classes turn out to be stable isomorphism classes of geometric String structures.
Relative differential cohomology
Christian Becker
Mathematics , 2013,
Abstract: We study two notions of relative differential cohomology, using the model of differential characters. The two notions arise from the two options to construct relative homology, either by cycles of a quotient complex or of a mapping cone complex. We discuss the relation of the two notions of relative differential cohomology to each other. We discuss long exact sequences for both notions, thereby clarifying their relation to absolute differential cohomology. We construct the external and internal product of relative and absolute characters and show that relative differential cohomology is a right module over the absolute differential cohomology ring. Finally we construct fiber integration and transgression for relative differential characters.
Differential Characters and Geometric Chains
Christian Baer,Christian Becker
Mathematics , 2013,
Abstract: We study Cheeger-Simons differential characters and provide geometric descriptions of the ring structure and of the fiber integration map. The uniqueness of differential cohomology (up to unique natural transformation) is proved by deriving an explicit formula for any natural transformation between a differential cohomology theory and the model given by differential characters. Fiber integration for fibers with boundary is treated in the context of relative differential characters. As applications we treat higher-dimensional holonomy, parallel transport, and transgression.
Acute Cholecystitis Caused by Ceftriaxone Stones in an Adult
Christian D. Becker,Robert A. Fischer
Case Reports in Medicine , 2009, DOI: 10.1155/2009/132452
Abstract: Acute cholecystitis is a major health problem. There are multiple etiologies to be considered and early recognition of the condition is important to optimize management and outcome. We report the first case in the medical literature of symptomatic acute cholecystitis triggered by ceftriaxone-associated gallbladder sludge formation and, importantly, solid ceftriaxone gallstone formation in an adult patient with underlying mineral and pigment cholecystolithiasis, necessitating cholecystectomy. This case serves as a reminder for physicians to keep this uncommon cause of cholecystolithiasis and cholecystitis in mind in patients who receive prolonged ceftriaxone therapy. These patients should be cautioned to promptly report to their physicians any signs or symptoms of cholecystitis in order to ensure timely and appropriate evaluation.
An Interface for a Decentralized 2D Reconfiguration on Xilinx Virtex-FPGAs for Organic Computing
Christian Schuck,Bastian Haetzer,Jürgen Becker
International Journal of Reconfigurable Computing , 2009, DOI: 10.1155/2009/273791
Abstract: Partial and dynamic online reconfiguration of Field Programmable Gate Arrays (FPGAs) is a promising approach to design high adaptive systems with lower power consumption, higher task specific performance, and even build-in fault tolerance. Different techniques and tool flows have been successfully developed. One of them, the two-dimensional partial reconfiguration, based on the Readback-Modify-Writeback method implemented on Xilinx Virtex devices, makes them ideally suited to be used as a hardware platform in future organic computing systems, where a highly adaptive hardware is necessary. In turn, decentralisation, the key property of an organic computing system, is in contradiction with the central nature of the FPGAs configuration port. Therefore, this paper presents an approach that connects the single ICAP port to a network on chip (NoC) to provide access for all clients of the network. Through this a virtual decentralisation of the ICAP is achieved. Further true 2-dimensional partial reconfiguration is raised to a higher level of abstraction through a lightweight Readback-Modify-Writeback hardware module with different configuration and addressing modes. Results show that configuration data as well as reconfiguration times could be significantly reduced.
Reconfiguration Techniques for Self-X Power and Performance Management on Xilinx Virtex-II/Virtex-II-Pro FPGAs
Christian Schuck,Bastian Haetzer,Jürgen Becker
International Journal of Reconfigurable Computing , 2011, DOI: 10.1155/2011/671546
Abstract: Xilinx Virtex-II family FPGAs support an advanced low-skew clock distribution network with numerous global clock nets to support high-speed mixed frequency designs. Digital Clock Managers in combination with Global Clock Buffers are already in place to generate the desired frequency and to drive the clock networks with different sources, respectively. Currently, almost all designs run at a fixed clock frequency determined statically during design time. Such systems cannot take the full advantage of partial and dynamic self-reconfiguration. Therefore, we introduce a new methodology that allows the implemented hardware to dynamically self-adopt the clock frequency during runtime by reconfiguring the Digital Clock Managers. We also present a method for online speed monitoring which is based on a two-dimensional online routing. The created speed maps of the FPGA area can be used as an input for the dynamic frequency scaling. Figures for reconfiguration performance and power savings are given. Further, the tradeoffs for reconfiguration effort using this method are evaluated. Results show the high potential and importance of the distributed dynamic frequency scaling method with little additional overhead. 1. Introduction Xilinx Virtex FPGAs have been designed with high-performance applications in mind. They feature several dedicated Digital Clock Managers (DCMs) and Digital Clock Buffers for solving high-speed clock distribution problems. Multiple clock nets are supported to enable highly heterogeneous mixed frequency designs. Usually all clock frequencies for the single clock nets and the parameters for the DCMs are determined during design time through static timing analysis. Targeting maximum performance these parameters strongly depend on the longest combinatorial path (critical path) between two storage elements. For minimum power the required throughput of the design unit determines the lower boundary of the possible clock frequency. In both cases nonadjusted clock frequencies lead to waste of either processing power or energy [1, 2]. Considering the feature of partial and dynamic self-reconfiguration of Xilinx Virtex FPGAs, during runtime a high dynamic and flexibility arises. Static analysis methods are no longer able to sufficiently determine an adjusted clock frequency during design time. At the same time a new partial module is reconfigured onto the FPGA grid, its critical path changes, and in turn the clock frequency has to be adjusted as well during runtime to fit the new critical path. On the other side the throughput requirement of the
Dosage compensation and the global re-balancing of aneuploid genomes
Matthias Prestel, Christian Feller, Peter B Becker
Genome Biology , 2010, DOI: 10.1186/gb-2010-11-8-216
Abstract: Complex genomes are more than just the sum of their genes, but are rather complex regulatory systems in which the expression of each individual gene is a function of the activity of many other genes, so that the levels of their protein products are maintained within a narrow range. Such homeostasis favors the maintenance of the appropriate stoichiometry of subunits in multiprotein complexes or of components in signal transduction pathways, and defines the 'ground state' of a cell [1]. In diploid genomes, both alleles of a gene are usually active and this 'double dose' of each gene is figured into the equation. Thus, deviations from diploidy, such as the deletion or duplication of genes or of larger chromosomal fragments (aneuploidy), unbalance the finely tuned expression of the genome. Segmental aneuploidies of this kind can arise from failed or faulty repair of chromosomal damage due to irradiation, chemical insult or perturbation of replication, or from illegitimate recombination during meiosis. Loss or duplication of entire chromosomes (monosomy or trisomy, respectively) can arise from non-disjunction during cell division. Depending on the extent of the aneuploidy and on the genes affected, the fine balance of trans-acting factors and their chromosomal binding sites that define the gene-expression system is disturbed, and the fitness of the cell or organism challenged.Often, aneuploidies have been associated with a variety of developmental defects and malignant aberrations, such as Down syndrome or certain breast cancers (reviewed in [2,3]). The phenotypes associated with changes in gene copy number can not only be the result of the deregulation of the affected gene(s), but may also reflect trans-acting effects on other chromosomal loci or even more global alterations of the entire regulatory system. This is particularly true if genes coding for regulatory factors, such as transcription factors, are affected (reviewed in [4,5]).Genome-wide studies in different or
HIV/AIDS, conflict and security in Africa: rethinking relationships
Becker Joseph U,Theodosis Christian,Kulkarni Rick
Journal of the International AIDS Society , 2008, DOI: 10.1186/1758-2652-11-3
Abstract: The effect of conflict on HIV transmission and regional and global security has been the subject of much recent discussion and debate. Many long held assumptions regarding these relationships are being reconsidered. Conflict has long been assumed to contribute significantly to the spread of HIV infection. However, new research is casting doubt on this assumption. Studies from Africa suggest that conflict does not necessarily predispose to HIV transmission and indeed, there is evidence to suggest that recovery in the "post-conflict" state is potentially dangerous from the standpoint of HIV transmission. As well, refugee populations have been previously considered as highly infected vectors of HIV transmission. But in light of new investigation this belief is also being reconsidered. There has additionally been concern that high rates of HIV infection among many of the militaries of sub-Saharan Africa poses a threat to regional security. However, data is lacking on both dramatically elevated prevalence amongst soldiers and a possible negative effect on regional security. Nevertheless, HIV/AIDS remain a serious threat to population health and economic well being in this region. These issues are of vital importance for HIV programming and health sector development in conflict and "post-conflict" societies and will constitute formidable challenges to the international community. Further research is required to better inform the discussion of HIV, conflict, and security in sub-Saharan Africa.
Simulation study of the impact of AGIPD design choices on X-ray Photon Correlation Spectroscopy utilizing the intensity autocorrelation technique
Julian Becker,Christian Gutt,Heinz Graafsma
Physics , 2011, DOI: 10.1088/1748-0221/6/11/P11005
Abstract: The European XFEL, currently under construction, will produce a coherent X-ray pulse every 222 ns in pulse trains of up to 2700 pulses. In conjunction with the fast 2D area detectors currently under development, it will be possible to perform X-ray Photon Correlation Spectroscopy (XPCS) experiments on sub-microsecond timescales with non-ergodic systems. A case study for the Adaptive Gain Integrating Pixel Detector (AGIPD) at the European XFEL employing the intensity autocorrelation technique was performed using the detector simulation tool HORUS. As optimum results from XPCS experiments are obtained when the pixel size approximates the (small) speckle size, the presented study compares the AGIPD (pixel size of (200 $\upmu$m)$^2$) to a possible apertured version of the detector and to a hypothetical system with (100 $\upmu$m)$^2$ pixel size and investigates the influence of intensity fluctuations and incoherent noise on the quality of the acquired data. The intuitive conclusion that aperturing is not beneficial as data is 'thrown away' was proven to be correct for low intensities. For intensities larger than approximately 1 photon per (100 $\upmu$m)$^2$ aperturing was found to be beneficial, as charge sharing effects were excluded by it. It was shown that for the investigated case (100 $\upmu$m)$^2$ pixels produced significantly better results than (200 $\upmu$m)$^2$ pixels when the average intensity exceeded approximately 0.05 photons per (100 $\upmu$m)$^2$. Although the systems were quite different in design they varied in the signal to noise ratio only by a factor of 2-3, and even less in the relative error of the extracted correlation constants. However the dependence on intensity showed distinctively different features for the different systems.
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