Showing papers by "Technical University of Dortmund published in 2007"

Variable very high energy γ-ray emission from markarian 501

Abstract: The blazar Markarian 501 (Mrk 501) was observed at energies above 100 GeV with the MAGIC telescope from May through July 2005. The high sensitivity of the instrument enabled the determination of the flux and spectrum of the source on a night-by-night basis. Throughout our observational campaign, the flux from Mrk 501 was found to vary by an order of magnitude, and to be correlated with spectral changes. Intra-night flux variability with flux-doubling times down to 2 minutes was also observed. The strength of variability increased with the energy of the {gamma}-ray photons. The energy spectra were found to harden significantly with increasing flux, and a spectral peak clearly showed up during very active states. The position of the spectral peak seems to be correlated with the source luminosity.

Keeping a Quantum Bit Alive by Optimized π-Pulse Sequences

Abstract: A general strategy to maintain the coherence of a quantum bit is proposed. The analytical result is derived rigorously including all memory and backaction effects. It is based on an optimized $\ensuremath{\pi}$-pulse sequence for dynamic decoupling extending the Carr-Purcell-Meiboom-Gill cycle. The optimized sequence is very efficient, in particular, for strong couplings to the environment.

Molecular Dynamic Simulations of Ionic Liquids: A Reliable Description of Structure, Thermodynamics and Dynamics

Abstract: The parameterization of a new force-field and its validation for the liquid description of five imidazolium-based ionic liquids [C(n)mim][NTf2] (n=1,2,4,6,8) are described. The proposed force-field is derived to reproduce densities, self-diffusion coefficients for cations and ions as well as NMR rotational correlation times for cations and water molecules in [C(2)mim][NTf2]. The temperature dependence and the cation chain-length dependence of these properties is described well. Very good agreement between simulated and experimental values for the heats of vaporization, shear viscosities and NMR rotational correlation times is also achieved. All properties are crucial for understanding the nature and interaction of ionic liquids. The good performance of the new force-field suggests that the Lennard-Jones interactions previously were strongly overestimated. The given force-field now allows us to investigate other important properties of this class of ionic liquids such as the micro segregation of ionic liquids, ion pair formation, lifetimes of ion pairs and the solvent dependency of these properties.

Angular distributions of B̄ → Kl̄l decays

Abstract: We model-independently analyze the angular distributions of → Kl decays, l = e,μ, for low dilepton mass using QCD factorization. Besides the decay rate, we study the forward-backward asymmetry AlFB and a further observable, FlH, which gives rise to a flat term in the angular distribution. We find that in the Standard Model FlH∝ml2, hence vanishing FeH and FμH of around 2% (exact value depends on cuts) with a very small theoretical uncertainty of a few percent. We also give predictions for RK, the ratio of → Kμ to → Kēe decay rates. We analytically show using large recoil symmetry relations that in the Standard Model RK equals one up to lepton mass corrections of the order 10−4 including αs and subleading 1/E power corrections. The New Physics reach of the observables from the → Kl angular analysis is explored together with RK and the s → l and → Xsl branching ratios for both l = e and l = μ. We find substantial room for signals from (pseudo-) scalar and tensor interactions beyond the Standard Model. Experimental investigations of the → Kμ angular distributions are suitable for the LHC environment and high luminosity B factories, where also studies of the electron modes are promising.

Dijet cross sections and parton densities in diffractive DIS at HERA

Abstract: Differential dijet cross sections in diffractive deep-inelastic scattering are measured with the H1 detector at HERA using an integrated luminosity of 51.5 pb−1. The selected events are of the type ep → eXY , where the system X contains at least two jets and is well separated in rapidity from the low mass proton dissociation system Y . The dijet data are compared with QCD predictions at next-to-leading order based on diffractive parton distribution functions previously extracted from measurements of inclusive diffractive deepinelastic scattering. The prediction describes the dijet data well at low and intermediate zIP (the fraction of the momentum of the diffractive exchange carried by the parton entering the hard interaction) where the gluon density is well determined from the inclusive diffractive data, supporting QCD factorisation. A new set of diffractive parton distribution functions is obtained through a simultaneous fit to the diffractive inclusive and dijet cross sections. This allows for a precise determination of both the diffractive quark and gluon distributions in the range 0.05 < zIP < 0.9. In particular, the precision on the gluon density at high momentum fractions is improved compared to previous extractions.

Exciton-plasmon-photon conversion in plasmonic nanostructures.

Abstract: A silver-nanowire cavity is functionalized with CdSe nanocrystals and optimized towards cavity quantum electrodynamics by varying the nanocrystal-nanowire distance d and cavity length L. From the modulation of the nanocrystal emission by the cavity modes a plasmon group velocity of v (gr) approximately 0.5c is derived. Efficient exciton-plasmon-photon conversion and guiding is demonstrated along with a modification in the spontaneous emission rate of the coupled exciton-plasmon system.

Very high energy gamma-ray radiation from the stellar mass black hole binary cygnus X-1

Abstract: We report on the results from the observations in the very high energy band ( VHE; GeV) of the black E = 100 g hole X- ray binary ( BHXB) Cygnus X- 1. The observations were performed with the MAGIC telescope, for a total of 40 hr during 26 nights, spanning the period between 2006 June and November. Searches for steady gamma - ray signals yielded no positive result, and upper limits to the integral flux ranging between 1% and 2% of the Crab Nebula flux, depending on the energy, have been established. We also analyzed each observation night independently, obtaining evidence of gamma- ray signals at the 4.0 j significance level ( 3.2 j after trial correction) for 154 minutes of effective on- time ( EOT) on September 24 between 20: 58 and 23: 41 UTC, coinciding with an X- ray flare seen by RXTE, Swift, and INTEGRAL. A search for faster- varying signals within a night resulted in an excess with a significance of 4.9 j ( 4.1 j after trial correction) for 79 minutes EOT between 22: 17 and 23: 41 UTC. The measured excess is compatible with a pointlike source at the position of Cygnus X- 1 and excludes the nearby radio nebula powered by its relativistic jet. The differential energy spectrum is well fitted by an unbroken power law described as dN/(dA dt dE) = ( 2.3 +/- 0.6)* 10 ( E/1TeV). This is the first experimental evidence of VHE emission from a stellar mass black hole and therefore from a confirmed accreting X- ray binary.

Total nucleic acid analysis integrated on microfluidic devices

Abstract: The design and integration of microfluidic devices for on-chip amplification of nucleic acids from various biological samples has undergone extensive development The actual benefit to the biological community is far from clear, with a growing, but limited, number of application successes in terms of a full on-chip integrated analysis Several advances have been made, particularly with the integration of amplification and detection, where amplification is most often the polymerase chain reaction Full integration including sample preparation remains a major obstacle for achieving a quantitative analysis We review the recently described devices incorporating in vitro gene amplification and compare devices relative to each other and in terms of fully achieving a miniaturised total analysis system (μ-TAS)

Discovery of Very High Energy Gamma Radiation from IC 443 with the MAGIC Telescope

Abstract: We report the detection of a new source of very high energy (VHE; E-gamma >= 100 GeV) gamma- ray emission located close to the Galactic plane, MAGIC J0616 + 225, which is spatially coincident with supernova remnant IC 443. The observations were carried out with the MAGIC telescope in the periods 2005 December-2006 January and 2006 December-2007 January. Here we present results from this source, leading to a VHE gamma-ray signal with a statistical significance of 5.7 sigma in the 2006/2007 data and a measured differential gamma-ray flux consistent with a power law, described as dN(gamma)/(dA dt dE) = (1.0 +/- 0.2) x 10(-11) (E/0.4 TeV)(-3.1 +/- 0.3) cm(-2) s(-1) TeV-1. We briefly discuss the observational technique used and the procedure implemented for the data analysis. The results are placed in the context of the multiwavelength emission and the molecular environment found in the region of IC 443.

Towards a detailed understanding of bacterial metabolism--spectroscopic characterization of Staphylococcus epidermidis.

Abstract: Bacteria are a major cause of infection. To fight disease and growing resistance, research interest is focused on understanding bacterial metabolism. For a detailed evaluation of the involved mechanisms, a precise knowledge of the molecular composition of the bacteria is required. In this article, various vibrational spectroscopic techniques are applied to comprehensively characterize, on a molecular level, bacteria of the strain Staphylococcus epidermidis, an opportunistic pathogen which has evolved to become a major cause of nosocomial infections. IR absorption spectroscopy reflects the overall chemical composition of the cells, with major focus on the protein vibrations. Smaller sample volumes-down to a single cell-are sufficient to probe the overall chemical composition by means of micro-Raman spectroscopy. The nucleic-acid and aromatic amino-acid moieties are almost exclusively explored by UV resonance Raman spectroscopy. In combination with statistical evaluation methods [hierarchical cluster analysis (HCA), principal component analysis (PCA), linear discriminant analysis (LDA)], the protein and nucleic-acid components that change during the different bacterial growth phases can be identified from the in vivo vibrational spectra. Furthermore, tip-enhanced Raman spectroscopy (TERS) provides insight into the surface structures and follows the dynamics of the polysaccharide and peptide components on the bacterial cells with a spatial resolution below the diffraction limit. This might open new ways for the elucidation of host-bacteria and drug-bacteria interactions.

Quickest Flows Over Time

Abstract: Flows over time (also called dynamic flows) generalize standard network flows by introducing an element of time. They naturally model problems where travel and transmission are not instantaneous. Traditionally, flows over time are solved in time-expanded networks that contain one copy of the original network for each discrete time step. While this method makes available the whole algorithmic toolbox developed for static flows, its main and often fatal drawback is the enormous size of the time-expanded network. We present several approaches for coping with this difficulty. First, inspired by the work of Ford and Fulkerson on maximal $s$-$t$-flows over time (or “maximal dynamic $s$-$t$-flows”), we show that static length-bounded flows lead to provably good multicommodity flows over time. Second, we investigate “condensed” time-expanded networks which rely on a rougher discretization of time. We prove that a solution of arbitrary precision can be computed in polynomial time through an appropriate discretization leading to a condensed time-expanded network of polynomial size. In particular, our approach yields fully polynomial-time approximation schemes for the NP-hard quickest min-cost and multicommodity flow problems. For single commodity problems, we show that storage of flow at intermediate nodes is unnecessary, and our approximation schemes do not use any.

Detecting antigens by quantitative immuno-PCR.

Abstract: The quantitative immuno-PCR (qIPCR) technology combines the advantages of flexible and robust immunoassays with the exponential signal amplification power of PCR. The qIPCR allows one to detect antigens using specific antibodies labeled with double-stranded DNA. The label is used for signal generation by quantitative PCR. Because of the efficiency of nucleic acid amplification, qIPCR typically leads to a 10- to 1,000-fold increase in sensitivity compared to an analogous enzyme-amplified immunoassay. A standard protocol of a qIPCR assay to detect human interleukin 6 (IL-6) using a sandwich immunoassay combined with real-time PCR readout is described here. The protocol includes initial immobilization of the antigen, and coupling of this antigen with antibody-DNA conjugates is then carried out by (a) the stepwise assembly of biotinylated antibody, streptavidin and biotinylated DNA, (b) the use of a biotinylated antibody and an anti-biotin-DNA conjugate or (c) the employment of an anti-IL-6 antibody-DNA conjugate. Following the assembly of signal-generating immunocomplexes, real-time PCR is used to amplify and record the signal. Depending on the coupling strategy, the qIPCR assays require 4-7 h with only about 3 h hands-on-time. The use of qIPCR assays enables the detection of rare biomarkers in complex biological samples that are poorly accessible by conventional immunoassays. Therefore, qIPCR offers novel opportunities for the biomedical analysis of, for instance, neurodegenerative diseases and viral infections as well as new tools for the development of novel pharmaceuticals.

Performance and accuracy of hardware-oriented native-, emulated-and mixed-precision solvers in FEM simulations

Abstract: In this survey paper, we compare native double precision solvers with emulated-and mixed-precision solvers of linear systems of equations as they typically arise in finite element discretisations. The emulation utilises two single float numbers to achieve higher precision, while the mixed precision iterative refinement computes residuals and updates the solution vector in double precision but solves the residual systems in single precision. Both techniques have been known since the 1960s, but little attention has been devoted to their performance aspects. Motivated by changing paradigms in processor technology and the emergence of highly-parallel devices with outstanding single float performance, we adapt the emulation and mixed precision techniques to coupled hardware configurations, where the parallel devices serve as scientific co-processors. The performance advantages are examined with respect to speedups over a native double precision implementation (time aspect) and reduced area requirements for a chip (space aspect). The paper begins with an overview of the theoretical background, algorithmic approaches and suitable hardware architectures. We then employ several conjugate gradient (CG) and multigrid solvers and study their behaviour for different parameter settings of the iterative refinement technique. Concrete speedup factors are evaluated on the coupled hardware configuration of a general-purpose CPU and a graphics processor. The dual performance aspect of potential area savings is assessed on a field programmable gate array (FPGA). In the last part, we test the applicability of the proposed mixed precision schemes with ill-conditioned matrices. We conclude that the mixed precision approach works very well with the parallel co-processors gaining speedup factors of four to five, and area savings of three to four, while maintaining the same accuracy as a reference solver executing everything in double precision.

The Increased Forming Limits of Incremental Sheet Forming Processes

Abstract: Incremental sheet forming is known to give higher forming limits than conventional sheet forming processes, but investigation of this effect has been impeded by the computational cost of process models which include detailed predictions of through thickness behaviour. Here, a simplified process is used to gain insight into the mechanics of a broad class of incremental forming processes. The simplified process is described and shown to give increases in forming limits compared to a conventional process with the same geometry. A model of the process is set up with a commercial finite element package, validated, and used to trace the history of a ‘pin’ inserted perpendicularly into the workpiece. The history of the deformation of the ‘pin’ demonstrates significant through thickness shear occurring in the direction parallel to tool motion. This insight is used to modify an existing analysis used to predict forming limit curves. The analysis shows that for a sheet with uniform proportional loading, the forming limit is increased when through thickness shear is present, and this is proposed as an explanation for the increased forming limits of incremental sheet forming processes.

Observations of Markarian 421 with the MAGIC Telescope

Abstract: The MAGIC telescope took data of very high energy gamma-ray emission from the blazar Markarian 421 ( Mrk 421) between 2004 November and 2005 April. We present a combined analysis of data samples recorded under different observational conditions, down to gamma- ray energies of 100 GeV. The flux was found to vary between 0.5 and 2 crab ( integrated above 200 GeV), considered a low state when compared to known data. Although the flux varied day by day, no short-term variability was observed, although there is some indication that not all nights show an equally quiescent state. The results at higher energies were found to be consistent with previous observations. A clear correlation is observed between gamma-ray and X-ray fluxes, whereas no significant correlation between gamma-ray and optical data is seen. The spectral energy distribution between 100 GeVand 3 TeV shows a clear deviation from a power law, more clearly and at lower flux than previous observations at higher energies. The deviation persists after correcting for the effect of attenuation by the extragalactic background light, and most likely is source- inherent. There is a rather clear indication of an inverse Compton peak around 100 GeV. The spectral energy distribution of Mrk 421 can be fitted by a one-zone synchrotron self-Compton model, suggesting once again a leptonic origin of the very high energy gamma-ray emission from this blazar.

The e+e-→2(π+π-)π0, 2(π+π-)η, K+K-π+π-π0 and K+K-π+π-η cross sections measured with initial-state radiation

Abstract: We study the processes $e^+ e^-\to 2(\pi^+\pi^-)\pi^0\gamma$, $2(\pi^+\pi^-)\eta\gamma$, $K^+ K^-\pi^+\pi^-\pi^0\gamma$ and $K^+ K^-\pi^+\pi^-\eta\gamma$ with the hard photon radiated from the initial state. About 20000, 4300, 5500 and 375 fully reconstructed events, respectively, are selected from 232 fb$^{-1}$ of BaBar data. The invariant mass of the hadronic final state defines the effective $e^+ e^-$ center-of-mass energy, so that the obtained cross sections from the threshold to about 5 GeV can be compared with corresponding direct \epem measurements, currently available only for the $\eta\pi^+\pi^-$ and $\omega\pi^+\pi^-$ submodes of the $e^+ e^-\to 2(\pi^+\pi^-)\pi^0$ channel. Studying the structure of these events, we find contributions from a number of intermediate states, and we extract their cross sections where possible. In particular, we isolate the contribution from $e^+ e^-\to\omega(782)\pi^+\pi^-$ and study the $\omega(1420)$ and $\omega(1650)$ resonances. In the charmonium region, we observe the $J/\psi$ in all these final states and several intermediate states, as well as the $\psi(2S)$ in some modes, and we measure the corresponding branching fractions.

Modeling of Polar Systems Using PCP-SAFT: An Approach to Account for Induced-Association Interactions†

Abstract: The perturbed-chain polar statistical associating fluid theory (PCP-SAFT) equation of state is applied to mixtures containing polar as well as associating components where cross association may occur. In this work, we focus on mixtures in which at least one of the components does not self-associate but is able to form hydrogen bonds with other compounds, for example, water and alcohols. On the basis of the mixing rules from Wolbach and Sandler 1 for associating components, we propose a simple approach to account for this type of cross association (referred to as induced association) only from the knowledge of pure-component parameters. The application to vapor−liquid and liquid−liquid equilibria of numerous binary and ternary mixtures of polar components with alcohols and/or water revealed the strength of the proposed approach. It is confirmed that accounting for induced-association interactions improves the predictive capability as well as the ability of the model to correlate mixture phase equilibria qu...

Dynamical parton distributions of the nucleon and very small-x physics

Abstract: Utilizing recent DIS measurements (F_{2,L}) and data on dilepton and high-E_{T} jet production we determine the dynamical parton distributions of the nucleon generated radiatively from valence-like positive input distributions at optimally chosen low resolution scales. These are compared with `standard' distributions generated from positive input distributions at some fixed and higher resolution scale. It is shown that up to the next to leading order NLO(\bar{MS}, DIS) of perturbative QCD considered in this paper, the uncertainties of the dynamical distributions are, as expected, smaller than those of their standard counterparts. This holds true in particular in the presently unexplored extremely small-x region relevant for evaluating ultrahigh energy cross sections in astrophysical applications. It is noted that our new dynamical distributions are compatible, within the presently determined uncertainties, with previously determined dynamical parton distributions.

Capabilities of EMOA to detect and preserve equivalent pareto subsets

Abstract: Recent works in evolutionary multiobjective optimization suggest to shift the focus from solely evaluating optimization success in the objective space to also taking the decision space into account. They indicate that this may be a) necessary to express the users requirements of obtaining distinct solutions (distinct Pareto set parts or subsets) of similar quality (comparable locations on the Pareto front) in real-world applications, and b) a demanding task for the currently most commonly used algorithms.We investigate if standard EMOA are able to detect and preserve equivalent Pareto subsets and develop an own special purpose EMOA that meets these requirements reliably.

Tropical varieties for non-archimedean analytic spaces

Abstract: Generalizing the construction from tropical algebraic geometry, we associate to every (irreducible d-dimensional) closed analytic subvariety of $\mathbb{G}_{m}^{n}$ a tropical variety in ℝ n with respect to a complete non-archimedean place. By methods of analytic and formal geometry, we prove that the tropical variety is a totally concave locally finite union of d-dimensional polytopes. For an algebraic morphism f:X’→A to a totally degenerate abelian variety A, we give a bound for the dimension of f(X’) in terms of the singularities of a strictly semistable model of X’. A closed d-dimensional subvariety X of A induces a periodic tropical variety. A generalization of Mumford’s construction yields models of X and A which can be handled with the theory of toric varieties. For a canonically metrized line bundle L on A, the measures c 1(L| X )∧d are piecewise Haar measures on X. Using methods of convex geometry, we give an explicit description of these measures in terms of tropical geometry. In a subsequent paper, this is a key step in the proof of Bogomolov’s conjecture for totally degenerate abelian varieties over function fields.

Discovery of Very High Energy γ-Ray Emission from the Low-Frequency-peaked BL Lacertae Object BL Lacertae

Abstract: The MAGIC collaboration observed BL Lacertae for 22.2 hr during 2005 August to December and for 26 hr during 2006 July to September. The source is the historical prototype and eponym of a class of low-frequency-peaked BL Lacertae (LBL) objects. A very high energy (VHE) gamma-ray signal was discovered with a 5.1 sigma excess in the 2005 data. Above 200 GeV, an integral flux of (0.6 +/- 0.2) x 10(-11) cm(-2) S-1 was measured, corresponding to approximately 3% of the Crab flux. The differential spectrum between 150 and 900 GeV is rather steep with a photon index of -3.6 +/- 0.5. The light curve shows no significant variability during the observations in 2005. For the first time a clear detection of VHE gamma-ray emission from an LBL object was obtained with a signal below previous upper limits. The 2006 data show no significant excess. This drop in flux follows the observed trend in optical activity.

Discovery of very high energy γ-rays from 1ES 1011+496 at z = 0.212

Abstract: We report on the discovery of very high energy (VHE) gamma-ray emission from the BL Lacertae object 1ES 1011+496. The observation was triggered by an optical outburst in 2007 March and the source was observed with the MAGIC telescope from 2007 March to May. Observing for 18.7 hr, we find an excess of 6.2 sigma with an integrated flux above 200 GeV of ( 1.58 +/- 0.32) x 10(-11) photons cm(-2) s(-1). The VHE gamma-ray flux is > 40% higher than in 2006 March-April ( reported elsewhere), indicating that the VHE emission state may be related to the optical emission state. We have also determined the redshift of 1ES 1011+496 based on an optical spectrum that reveals the absorption lines of the host galaxy. The redshift of z = 0.212 makes 1ES 1011+496 the most distant source observed to emit VHE gamma-rays to date.

Femtosecond laser-induced breakdown spectroscopy: physics, applications, and perspectives.

Abstract: Progress in technology and society continually places new demands on analytical science and more powerful and informative methods need to be developed. One among them is laser-induced breakdown spectroscopy (LIBS), sometimes also referred to as LIPS (laserinduced plasma spectroscopy). Typically, LIBS measurements are conducted with nanosecond time scale lasers. A review by Song et al.1 and two recently published books by Miziolek et al.2 and Cremers et al.3 give a good overview of instrumental developments in this area. However, new developments in laser technology have made ultra-short lasers available4 and have stimulated an interest in LIBS with ultra-short pulses. There are fundamental differences between the ablation processes of ultra-short ( 1 ps) and short ( 1 ps) pulses that result in different mechanisms of energy dissipation in the sample. In the case of ultra-short laser pulses, at the end of the laser pulse, only a very hot electron gas and a practically undisturbed lattice are found, which subsequently interact. However, for longer pulses above a certain energy threshold, the material undergoes transient changes in the thermodynamic states from solid, through liquid, into a plasma state.5,6 Based on this difference, consequences for the analytical performance of the method can be expected that in the future should lead to new aspects in instrumentation and applications of LIBS. The goal of this review is to summarize current knowledge of the instrumentation and physics of laser ablation with femtosecond lasers and to draw some conclusions concerning new possible applications that rely on these specific new features. It seems clear that even if a better performance in terms of analytical figures of merit compared to standard LIBS applications7 is found, a replacement of current technology cannot be expected soon due to the cost and complexity of chirped pulse amplification (CPA) laser systems. However, current trends in other fields of application of these laser systems, e.g., medical laser applications or material processing,8 may change this picture in the near future.