Anderson localization as position-dependent diffusion in disordered waveguides

We show that the recently developed self-consistent theory of Anderson localization with a position-dependent diffusion coefficient is in quantitative agreement with the supersymmetry approach up to terms of the order of $1/g_0^2$ (with $g_0$ the dimensionless conductance in the absence of interference effects) and with large-scale {\it ab-initio} simulations of the classical wave transport in disordered waveguides, at least for $g_0 \gtrsim 0.5$. In the latter case, agreement is found even in the presence of absorption. Our numerical results confirm that in open disordered media, the onset of Anderson localization can be viewed as position-dependent diffusion.Comment: 6 pages, 3 figure

Observation of the critical regime near Anderson localization of light

Diffusive transport is among the most common phenomena in nature [1]. However, as predicted by Anderson [2], diffusion may break down due to interference. This transition from diffusive transport to localization of waves should occur for any type of classical or quantum wave in any media as long as the wavelength becomes comparable to the transport mean free path $\ell^*$ [3]. The signatures of localization and those of absorption, or bound states, can however be similar, such that an unequivocal proof of the existence of wave localization in disordered bulk materials is still lacking. Here we present measurements of time resolved non-classical diffusion of visible light in strongly scattering samples, which cannot be explained by absorption, sample geometry or reduction in transport velocity. Deviations from classical diffusion increase strongly with decreasing $\ell^*$ as expected for a phase transition. This constitutes an experimental realization of the critical regime in the approach to Anderson localization.Comment: 5 pages, 4 figure

Vergleichende Untersuchungen zur circadianen Rhythmik des intraokularen Druckes (IOD) im Tagestensioprofil (TTP) und den Veränderungen der Druckwerte im Provokationstest "Wasserbelastungstest" (WBT) bei Patienten mit verschiedenen GLaukomformen

Ein wichtiges Verfahren in der Glaukomdiagnostik ist die Bestimmung des intraokularen Druckes (IOD). Dieser unterliegt einer circadianen Rhythmik, welche bei vielen Glaukompatienten gestört ist. Es wird vermutet, dass der maximale IOD und der Druckanstieg wichtig sind für das Fortschreiten der Erkrankung. Eine kompetente Diagnostik und Therapie erfordert deshalb in bestimmten Fällen die Erstellung eines Tagestensioprofils (TTP) über 24-Stunden. Um auch die nächtlichen Druckwerte erfassen zu können, erfolgt das TTP unter stationären Bedingungen, was die Untersuchungsmethode sehr aufwendig und kostenintensiv macht. Aus diesem Grund haben wir die Einsetzbarkeit und prognostische Bedeutung des Wasserbelastungstests als alternative Methode untersucht. Bei diesem Testverfahren wird durch das Trinken einer bestimmten Wassermenge eine erhöhte Drucksteigerung bei Glaukompatienten hervorgerufen. Es wurde von uns die Hypothese aufgestellt, dass die Durchführung des Wasserbelastungstests die gleichen maximalen Tagesdruckwerte und Druckschwankungen liefert wie das TTP. Dafür werteten wir retrospektiv 84 Augen von 44 Patienten aus, die innerhalb der Glaukomsprechstunde an der Augenklinik Marburg untersucht wurden. Die ausgewerteten Daten lassen folgende Schlussfolgerung zu: Die maximalen Druckwerte des Wasserbelastungstests fallen in unserer Studie im Durchschnitt höher aus als beim TTP, zeigen aber eine positive Korrelation zueinander. Im Durchschnitt fällt der WBT 2 mmHg höher aus, was klinisch gesehen schon durch zwei unterschiedliche Prüfer verursacht sein kann. Ein weiterer Grund für die Differenz der Messwerte in beiden Verfahren kann u. a. in der Hospitalisation der Patienten beim TTP gesucht werden. Bedingt durch den stationären Aufenthalt werden niedrigere Maximalwerte hervorgerufen, als sie im Alltag tatsächlich bestehen. Weitere Auslöser könnten verpasste Nachtmessungen und zu große Messabstände am Tage sein. Ob diese Faktoren die Hauptursache sind oder ob es noch weitere Gründe für die niedrigeren Druckwerte im TTP gibt, muss durch weitere Untersuchungen geklärt werden. Ähnliches gilt für den Druckanstieg. Hier konnte keine Korrelation für die Werte beider Testverfahren ermittelt werden, was u. a. an der Größe unseres Patientenkollektivs liegen kann. Weiterhin zeigte sich in unserer Studie, dass gerade der WBT effektiv zur Überprüfung von Normaldruckglaukomen eingesetzt werden kann. Diese Patienten weisen häufig normale Druckwerte während der Glaukomsprechstunde auf trotz fortschreitender Gesichtsfeldprogressionen. Die schnelle Durchführung eines WBT kann hier für Aufklärung sorgen, da durch den WBT meist deutlich höhere Druckwerte festgestellt werden können als beim TTP. Eine Erklärung könnte sein, dass das NDG Teil einer generalisierten Endotheliopathie ist. Bereits in einer früheren Studie wurde diskutiert, dass der erhöhte Augeninnendruck nach Durchführung des WBT Ursache einer Endothelstörung ist. Weitere Studien zu diesem Thema sollten folgen, da gerade diese Glaukomvariante im Zusammenhang mit der zunehmenden Alterskaskade ansteigt. In Anbetracht der ernormen Kostenexplosion im Gesundheitswesen sollte der WBT als kostengünstiges Testverfahren mit hohem Aussagewert wieder einen wichtigen Platz in der Glaukomdiagnostik einnehmen. TTPs dürfen aus diesem Grund nur für komplizierte Einzelfälle vorbehalten sein und auch hier ist immer eine kombinierte Durchführung eines TTP und WBT ratsam

Impact-Analyse für AspectJ - Eine kritische Analyse mit werkzeuggestütztem Ansatz

Aspect-Oriented Programming (AOP) has been promoted as a solution for modularization problems known as the tyranny of the dominant decomposition in literature. However, when analyzing AOP languages it can be doubted that uncontrolled AOP is indeed a silver bullet. The contributions of the work presented in this thesis are twofold. First, we critically analyze AOP language constructs and their effects on program semantics to sensitize programmers and researchers to resulting problems. We further demonstrate that AOP—as available in AspectJ and similar languages—can easily result in less understandable, less evolvable, and thus error prone code—quite opposite to its claims. Second, we examine how tools relying on both static and dynamic program analysis can help to detect problematical usage of aspect-oriented constructs. We propose to use change impact analysis techniques to both automatically determine the impact of aspects and to deal with AOP system evolution. We further introduce an analysis technique to detect potential semantical issues related to undefined advice precedence. The thesis concludes with an overview of available open source AspectJ systems and an assessment of aspect-oriented programming considering both fundamentals of software engineering and the contents of this thesis

Weshalb auf Mallorca wahrscheinlich alle Urlauber betrunken sind: Zur syntaktischen Position von Frameadverbialen und der Rolle der Informationsstruktur bei ihrer Verarbeitung

Die vorliegende psycholinguistisch ausgerichtete Dissertation befasst sich experimentell mit der Frage nach der syntaktischen Position von Frameadverbialen relativ zu Satzadverbialen. Es zeigt sich, dass es für die Positionierung von Framesettern einen Unterschied macht, ob sie referentiell sind oder nicht. Für nicht-referentielle Frameadverbiale ergibt sich eine deutliche Präferenz für die (Basis-)Position unterhalb von Satzadverbialen. Referentielle Frameadverbiale dagegen weisen in online-Studien keine präferierte Position auf; in offline-Experimenten zeigen sie andererseits eine klare Präferenz für die Position oberhalb von Satzadverbialen. Bei dieser Position handelt es sich mutmaßlich um eine in der Syntax reflektierte Position für (Aboutness-)Topiks, für deren Existenz durch diese Dissertation ebenfalls experimentelle Evidenz geliefert werden kann. Frameadverbiale werden in der Literatur häufig als auf irgendeine Weise topikal angesehen. Dass referentielle Frameadverbiale präferiert oberhalb von Satzadverbialen stehen, legt die Annahme nahe, dass ihre Topikalität der Grund dafür ist. In einem weiteren experimentellen Teil der Arbeit zeigt sich Evidenz für diese Auffassung: Frameadverbiale scheinen Topiks zu sein und aus diesem Grund offline präferiert oberhalb von Satzadverbialen zu stehen. Ihr topikaler Status geht allerdings erst in einem späteren Schritt in die Verarbeitung ein und steht der online-Verarbeitung daher noch nicht zur Verfügung.This psycholinguistic dissertation deals with the question in which syntactic position frame adverbials are positioned in relation to sentence adverbials. Experimental results show that referential vs. non-referential frame adverbials behave differently: Non-referential frame adverbials exhibit a clear preference for the (base) position below sentence adverbials. Referential frame adverbials, on the other hand, show no preference for any position in online experiments, but in offline studies they exhibit a preference for the position above sentence adverbials. This position is assumed to be a syntactic reflected position for (aboutness) topics. Experimental evidence for its existence is shown in this thesis. Since frame adverbials are often considered as topics, the assumption is that topicality is the reason for their positioning above sentence adverbials. A further experimental part of this dissertation provides evidence for this supposition: In offline experiments, referential frame adverbials seem to be topics, but their topical status is not yet available in online processing

Study of Photon Dominated Regions in Cepheus B

Aim: The aim of the paper is to understand the emission from the photon dominated regions in Cepheus B, estimate the column densities of neutral carbon in bulk of the gas in Cepheus B and to derive constraints on the factors which determine the abundance of neutral carbon relative to CO. Methods: This paper presents 15'x15' fully sampled maps of CI at 492 GHz and 12CO 4-3 observed with KOSMA at 1' resolution. The new observations have been combined with the FCRAO 12CO 1-0, IRAM-30m 13CO 2-1 and C18O 1-0 data, and far-infrared continuum data from HIRES/IRAS. The KOSMA-tau spherical PDR model has been used to understand the CI and CO emission from the PDRs in Cepheus B and to explain the observed variation of the relative abundances of both C^0 and CO. Results: The emission from the PDR associated with Cepheus B is primarily at V_LSR between -14 and -11 km s^-1. We estimate about 23% of the observed CII emission from the molecular hotspot is due to the ionized gas in the HII region. Over bulk of the material the C^0 column density does not change significantly, (2.0+-1.4)x10^17 cm^-2, although the CO column density changes by an order of magnitude. The observed \cbyco abundance ratio varies between 0.06 and 4 in Cepheus B. We find an anti-correlation of the observed C/CO abundance ratio with the observed hydrogen column density, which holds even when all previous observations providing C/CO ratios are included. Here we show that this observed variation of C/CO abundance with total column density can be explained only by clumpy PDRs consisting of an ensemble of clumps. At high H2 column densities high mass clumps, which exhibit low C/CO abundance, dominate, while at low column densities, low mass clumps with high C/CO abundance dominate.Comment: 12 pages, 10 figures, Accepted for publication in A&

Shocked and Scorched: The Tail of a Tadpole in an Interstellar Pond

We report multi-wavelength observations of the far-infrared source IRAS 20324+4057, including high-resolution optical imaging with HST, and ground-based near-infrared, millimeter-wave and radio observations. These data show an extended, limb-brightened, tadpole-shaped nebula with a bright, compact, cometary nebula located inside the tadpole head. Our molecular line observations indicate that the Tadpole is predominantly molecular, with a total gas mass exceeding 3.7 Msun. Our radio continuum imaging, and archival Spitzer IRAC images, show the presence of additional tadpole-shaped objects in the vicinity of IRAS 20324+4057 that share a common E-W head-tail orientation: we propose that these structures are small, dense molecular cores that originated in the Cygnus cloud and are now being (i) photoevaporated by the ultraviolet radiation field of the Cyg OB2 No. 8 cluster located to the North-West, and (ii) shaped by ram pressure of a distant wind source or sources located to the West, blowing ablated and photoevaporated material from their heads eastwards. The ripples in the tail of the Tadpole are interpreted in terms of instabilities at the interface between the ambient wind and the dense medium of the former.Comment: (accepted by the Astrophysical Journal

Disks around Hot Stars in the Trifid Nebula

We report on mid-IR observations of the central region in the Trifid nebula, carried out with ISOCAM in several broad-band infrared filters and in the low resolution spectroscopic mode provided by the circular variable filter. Analysis of the emission indicates the presence of a hot dust component (500 to 1000 K) and a warm dust component at lower temperatures (150-200 K) around several members of the cluster exciting the HII region, and other stars undetected at optical wavelengths. Complementary VLA observations suggest that the mid-IR emission could arise from a dust cocoon or a circumstellar disk, evaporated under the ionization of the central source and the exciting star of the nebula. In several sources the $9.7\mu m$ silicate band is seen in emission. One young stellar source shows indications of crystalline silicates in the circumstellar dust.Comment: 4 pages with 1 figur

Photodissociation chemistry footprints in the Starburst galaxy NGC 253

We report the first detection of PDR molecular tracers, namely HOC+, and CO+, and confirm the detection of the also PDR tracer HCO towards the starburst galaxy NGC 253, claimed to be mainly dominated by shock heating and in an earlier stage of evolution than M 82, the prototypical extragalactic PDR. Our CO+ detection suffers from significant blending to a group of transitions of 13CH3OH, tentatively detected for the first time in the extragalactic interstellar medium. These species are efficiently formed in the highly UV irradiated outer layers of molecular clouds, as observed in the late stage nuclear starburst in M 82. The molecular abundance ratios we derive for these molecules are very similar to those found in M 82. This strongly supports the idea that these molecules are tracing the PDR component associated with the starburst in the nuclear region of NGC 253. A comparison with the predictions of chemical models for PDRs shows that the observed molecular ratios are tracing the outer layers of UV illuminated clouds up to two magnitudes of visual extinction. Chemical models, which include grain formation and photodissociation of HNCO, support the scenario of a photo-dominated chemistry as an explanation to the abundances of the observed species. From this comparison we conclude that the molecular clouds in NGC 253 are more massive and with larger column densities than those in M 82, as expected from the evolutionary stage of the starbursts in both galaxies.Comment: 32 pages, 4 figures, Published in Ap

The Photon Dominated Region in the IC 348 molecular cloud

In this paper we discuss the physical conditions of clumpy nature in the IC 348 molecular cloud. We combine new observations of fully sampled maps in [C I] at 492 GHz and 12CO 4--3, taken with the KOSMA 3 m telescope at about 1' resolution, with FCRAO data of 12CO 1--0, 13CO 1--0 and far-infrared continuum data observed by HIRES/IRAS. To derive the physical parameters of the region we analyze the three different line ratios. A first rough estimate of abundance is obtained from an LTE analysis. To understand the [C I] and CO emission from the PDRs in IC 348, we use a clumpy PDR model. With an ensemble of identical clumps, we constrain the total mass from the observed absolute intensities. Then we apply a more realistic clump distribution model with a power law index of 1.8 for clump-mass spectrum and a power law index of 2.3 for mass-size relation. We provide detailed fits to observations at seven representative positions in the cloud, revealing clump densities between 4 10$^{4}$ cm$^{-3}$ and 4 10$^{5}$ cm$^{-3}$ and C/CO column density ratios between 0.02 and 0.26. The derived FUV flux from the model fit is consistent with the field calculated from FIR continuum data, varying between 2 and 100 Draine units across the cloud. We find that both an ensemble of identical clumps and an ensemble with a power law clump mass distribution produce line intensities which are in good agreement (within a factor ~ 2) with the observed intensities. The models confirm the anti-correlation between the C/CO abundance ratio and the hydrogen column density found in many regions.Comment: 11 pages, 8 figures, accepted by A&