Search for Galactic dark matter substructures with Cherenkov telescopes

Weakly interacting massive dark matter (DM) particles are expected to self-annihilate or decay, generating high-energy photons in these processes. This establishes the possibility for indirect detection of DM by \gamma-ray telescopes. For probing the secondary products of DM, accurate knowledge about the DM density distribution in potential astrophysical targets is crucial. In this contribution, the prospects for the detection of subhalos in the Galactic DM halo with present and future imaging atmospheric Cherenkov telescopes (IACT) are investigated. The source count distribution and angular power spectra for \gamma-rays originating from annihilating DM in subhalos are calculated from N-body simulation results. To study the systematic uncertainties coming from the modeling of the DM density distribution, parameters describing the \gamma-ray yield from subhalos are varied in 16 benchmark models. We conclude that Galactic subhalos of annihilating DM are probably too faint to be a promising target for IACT observations, even with the prospective Cherenkov Telescope Array (CTA).Comment: 8 pages, 5 figures. Included in Proceedings of the 34th International Cosmic Ray Conference, The Hague, The Netherlands (July 30 - August 6, 2015

Landau levels, edge states, and strained magnetic waveguides in graphene monolayers with enhanced spin-orbit interaction

The electronic properties of a graphene monolayer in a magnetic and a strain-induced pseudo-magnetic field are studied in the presence of spin-orbit interactions (SOI) that are artificially enhanced, e.g., by suitable adatom deposition. For the homogeneous case, we provide analytical results for the Landau level eigenstates for arbitrary intrinsic and Rashba SOI, including also the Zeeman field. The edge states in a semi-infinite geometry are studied in the absence of the Rashba term. For a critical value of the magnetic field, we find a quantum phase transition separating two phases with spin-filtered helical edge states at the Dirac point. These phases have opposite spin current direction. We also discuss strained magnetic waveguides with inhomogeneous field profiles that allow for chiral snake orbits. Such waveguides are practically immune to disorder-induced backscattering, and the SOI provides non-trivial spin texture to these modes.Comment: 12 pages, 7 figures; v2: minor modifications, published versio

The Auditor as Standard-setter – some US evidence and its implications

Cette étude fournit des exemples détaillés dans le cadre du GAAP américain de l'arrivée au niveau des préparateurs et des réviseurs de nouveaux réglements promulgués. Nous montrons que les réviseurs créent leur propre ‘sous-réglement' détaillé qu'ils imposent a leurs clients par la suite. Nous suggérons que de telles activitées pourraient être : • Hors de tout jugement « en bonne et due forme » et donc ne répondant pas aux exigences de la légitimité institutionnelle • Imposant la forme légaliste sur le contenu économique • Incompatible avec ce qui sont sensés être les exigences supérieures dans la hiérarchie du GAAP américain • Contradictoire avec la reconnaisance du FASB que la sélection des politiques convenables de comptabilité reste la responsabilité des préparateurs. • Soutenues par le FASB en dépit de la liste dressée ci-dessus, Nous généralisons les implications de ces déviances dans le contexte de l'harmonisation internationale puis nous suggérons que les réglements imposés par les auditeurs sont incompatibles avec une présentation juste des « économies implicites », bien que l'application et l'interprétation du GAAP promulguées au niveau de l'entreprise par le réviseur et le préprateur soient essentiels. Le soutien apparent , ou du moins l'acceptation, du FASB pour de tels réglements est problématique. Nous proposons ici des raisons pour lesquelles l'approche du FASB/SEC pourrait être condamnée si une plainte était déposée devant un tribunal américain. Les exemples de minutiae légaliste nécessaire que nous examinons sont incompatibles avec les exigences et la philosophie des Normes de Comptabilité Internationales, ce qui provoque des inquiétudes au sujet du processus de convergence des exigences de l'IASB et de la FASB.Légitimité institutionnelle; contenu prévalant sur la forme ; auditeur GAAP

Dark matter substructure modelling and sensitivity of the Cherenkov Telescope Array to Galactic dark halos

Hierarchical structure formation leads to a clumpy distribution of dark matter in the Milky Way. These clumps are possible targets to search for dark matter annihilation with present and future $\gamma$-ray instruments. Many uncertainties exist on the clump distribution, leading to disputed conclusions about the expected number of detectable clumps and the ensuing limits that can be obtained from non-detection. In this paper, we use the CLUMPY code to simulate thousands of skymaps for several clump distributions. This allows us to statistically assess the typical properties (mass, distance, angular size, luminosity) of the detectable clumps. Varying parameters of the clump distributions allows us to identify the key quantities to which the number of detectable clumps is the most sensitive. Focusing our analysis on two extreme clump configurations, yet consistent with results from numerical simulations, we revisit and compare various calculations made for the Fermi-LAT instrument, in terms of number of dark clumps expected and the angular power spectrum for the Galactic signal. We then focus on the prospects of detecting dark clumps with the future CTA instrument, for which we make a detailed sensitivity analysis using open-source CTA software. Based on a realistic scenario for the foreseen CTA extragalactic survey, and accounting for a post-trial sensitivity in the survey, we show that we obtain competitive and complementary limits to those based on long observation of a single bright dwarf spheroidal galaxy.Comment: 29 pages + appendix, 15 figures. V2: Sects. 3.3, 4, and 5.3 extended, results unchanged (matching accepted JCAP version

Identification and characterization of a cystatin-like effector protein from beet cyst nematode <em>Heterodera schachtii</em> and its role in plant-nematode interaction

Sedentary cyst nematodes are of high economic interest as they can cause substantial yield losses in important crop plants. Due to their complex soil-based life cycle and severe restrictions on the application of nematicides management strategies are rare. To date, resistant plants are the most effective and economically as well as environmentally reasonable alternative to chemical control agents. However, nematodes are evolutionarily able to overcome the resistance after some time, facing researchers with the challenge to breed new resistant lines. Therefore, knowing the details of the interaction between plant and pathogens is fundamentally. Cyst nematodes establish a highly complex long-term relationship with their hosts that requires massive cytological modifications of the host cell to form a syncytial feeding structure. Therefore, plant defence mechanisms need to be circumvented by the nematode. Using their stylet, cyst nematodes introduce a mixture of different effector proteins into the host cells that manipulate the activity of host derived proteins. Since enzymes are only functional in their active form, one objective of presented work was to visualize spezific proteins of the active proteome of syncytium induced by Heterodera schachtii in Arabidopsis roots. Using Activity-based Protein Profiling (ABPP) it could be shown that the activity of serine hydrolases are differently regulated, whereas the activity of vacuolar processing enzymes (VPEs) is supressed in syncytium. Furthermore Papain-like cysteine proteases (PLCPs) and all catalytic proteasomal subunits, both known to be involved in plant defence, are suppressed in case of successful parasitism. PLCPs are inhibited by cystatins, which guided to the second main objective of presented work: the identification and functional characterization of a putative cystatin-like effector protein in H. schachtii (HsCysL1). HsCysL1 shows involvement in plant defence and signalling by interacting with PTPLA (Protein tyrosine phosphatase-like A) and UBC19 (Ubiquitin-conjugating enzyme 19). Both proteins are known to play significant roles in various signalling and regulatory processes. Although these findings do not rudimentarily complete the understanding of the complex plant-nematode interaction, they definitely open an exciting chapter for researchers to find new management strategies against cyst nematodes.Sedentäre Zystnematoden sind von großer Bedeutung, da sie erhebliche Ertragsausfälle in landwirtschaftlichen Kulturen verursachen können. Aufgrund ihres bodenbürtigen Lebenszyklusses und strengen Auflagen bei der Anwendung von Nematiziden sind Bekämpfungsstrategien rar. Resistente Pflanzen stellen die effizienteste und ökonomisch wie auch ökologisch vertretbarste Alternative zur chemischen Bekämpfung dar, allerdings sind Nematoden nach einiger Zeit in der Lage, Resistenzen zu durchbrechen. Forscher benötigen daher detailliertes Wissen über die Interaktion zwischen Pflanze und Pathogen, um neue resistente Pflanzen züchten zu können. Zystnematoden entwickeln hochkomplexe Langzeitbeziehungen mit ihren Wirten, was die Bildung eines Nährzellensystems durch massive Veränderungen der Wirtszellen voraussetzt. Dazu muss die pflanzliche Abwehr vom Nematoden umgangen werden. Mittels ihres Mundstachels geben sie verschiedene Effektorproteine in die Wirtszelle ab, die die Aktivität von Proteinen beeinflussen. Da Enzyme nur in aktive Form funktionieren, war ein Ziel der vorgestellten Arbeit, das aktive Proteom eines Syncytiums darzustellen. Durch Activity-based Protein Profiling (ABPP) konnte gezeigt werden, dass die Aktivität von Serinhydrolasen unterschiedlich reguliert wird, während die von vakuolar verarbeitenden Enzymen (VPEs) im Syncytium runterreguliert ist. Des Weiteren sind Papain-ähnliche Cysteinproteasen (PLCPs) sowie alle katalytischen Untereinheiten des Proteasoms runterreguliert; beide Enzymgruppen sind wichtig für die pflanzliche Abwehr. PLCPs werden durch Cystatine gehemmt, was zum zweiten Hauptpunkt der vorliegenden Arbeit führte: die Identifizierung und funktionelle Charakterisierung eines cystatin-ähnlichen Effektorproteins in H. schachtii (HsCysL1). HsCysL1 zeigt eine Beteiligung an der pflanzlichen Abwehr und Signalwegen durch die Interaktion mit PTPLA und UBC19. Auch wenn diese Erkenntnisse nicht annähernd einen Gesamtüberblich über die komplexe Interaktion zwischen Nematoden und Pflanzen geben können, eröffnen sie dennoch spannende Möglichkeiten für Forscher, neue Bekämpfungsstrategien gegen Zystnematoden zu entwickeln

Landau Levels and Edge States in Graphene with Strong Spin-Orbit Coupling

We investigate the electronic properties of graphene in a magnetic and a strain-induced pseudo-magnetic field in the presence of strong spin-orbit interactions (SOI). For a homogeneous field we provide analytical results for the Landau level eigenstates for arbitrary intrinsic and Rashba SOI, including also the effect of a Zeeman field. We then study the edge states in a semi-infinite geometry in the absence of the Rashba term. We find that, for a critical value of the magnetic field, a quantum phase transition occurs, which separates two phases both with spin-filtered helical edge states but with opposite direction of the spin current. Finally,we discuss magnetic waveguides with inhomogeneous field profiles that allow for chiral snake orbits. Such waveguides are practically immune to disorder-induced backscattering, and the SOI provides non-trivial spin texture to these modes

High energy astroparticle physics for high school students

The questions about the origin and type of cosmic particles are not only fascinating for scientists in astrophysics, but also for young enthusiastic high school students. To familiarize them with research in astroparticle physics, the Pierre Auger Collaboration agreed to make 1% of its data publicly available. The Pierre Auger Observatory investigates cosmic rays at the highest energies and consists of more than 1600 water Cherenkov detectors, located near Malarg\"{u}e, Argentina. With publicly available data from the experiment, students can perform their own hands-on analysis. In the framework of a so-called Astroparticle Masterclass organized alongside the context of the German outreach network Netzwerk Teilchenwelt, students get a valuable insight into cosmic ray physics and scientific research concepts. We present the project and experiences with students.Comment: 8 pages, 5 figures, Proceedings of the 34th International Cosmic Ray Conference (ICRC2015), The Hague, The Netherlands, PoS(ICRC2015)30

On the direct employment of dipolar particle interaction in microfluidic systems

This review article will summarize recent developments in the employment of dipolar coupled magnetic particle structures. We will discuss the basics of magnetic dipolar particle interaction in static and rotating magnetic fields. In dependence on the magnetic fields employed, agglomerates of different dimensionality may form within the carrier liquid. The stability and formation dynamics of these particle structures will be presented. Furthermore, we will review recent microfluidic applications based on the interaction of magnetic particles and present methods for surface patterning with micron-sized and nano-sized particles which employ dipolar particle coupling.Alexander von Humboldt-StiftungBielefeld University. Research Group FOR 94