Analyses of factors influencing the population dynamics of cereal aphids and their relevance to model extensions

Aphids annually infest winter wheat, Triticum aestivum L., in late spring and early summer in Central Europe, but densities leading to strong yield losses are reached only occasionally (Basedow et al., 1994). Three aphid species, Sitobion avenae Fabr., Metopolophium dirhodum Walk. and R. padi L., usually occur in cereal crops with increasing densities from late spring onwards (Basedow et al., 1994). Modelling population levels of cereal aphids is a key tool in integrated pest management for winter wheat. Over the last 30 years, considerable efforts have been made to investigate the population dynamics of aphids (DeWit and Rabbinge, 1979; Entwistle and Dixon, 1987). In Central Europe to date, two models have attained greater importance in late spring: LAUS (Friesland, 1986) and GETLAUS01 (Gosselke et al., 2001). The first one estimates the population level of S. avenae in spring in winter wheat fields and has obtained regional significance in practical plant protection. In contrast, the model GETLAUS01 is a scientific model, not designed for practical plant protection. It describes in great detail the population dynamics of S. avenae, R. padi and M. dirhodum. Both models have been improved over time and extended with several factors, e.g. by including the effects of antagonists, fertilisation, crop density, plant protection agents and meteorological parameters on population development. The objective of this study was to analyse the following three factors in terms of their impact on population and migration characteristics: cultivar, proximity between winter and summer hosts and migration (according to meteorological parameters).Getreideblattläuse (Hemiptera: Aphididae) sind die bedeutendsten Schädlinge von Winterweizen im Frühjahr und Sommer. Sie führen jedoch nur zu signifikanten Ertragsausfällen, wenn biotische und abiotische Faktoren ein optimales Populationswachstum erlauben. Einige dieser Faktoren sind bereits in Simulationsmodellen berücksichtigt. In der vorliegenden Arbeit wurden Sorteneinflüsse, die Nähe von Winter- zu Sommerwirten und meteorologische Parameter bezüglich der Migrations- und Populationsentwicklung als weitere mögliche Faktoren im Hinblick auf Modellerweiterungen untersucht. 8 Winterweizensorten zeigten weder bezüglich der Entwicklung von Nachkommen (in Klippkäfigen, BBCH-Stadium 32 und 69), noch während der Erstbesiedelungsphase von geflügelten Getreideblattläusen (Ende Mai, Anfang Juni) bedeutende Unterschiede. Die Nähe von Winter- zu Sommerwirten beeinflusste in unterschiedlicher Weise den Populationsaufbau der wirtswechselnden Arten im Winterweizen. In Jahren mit hoher Populationsentwicklung auf den Winterwirten konnte nur für Rhopalosiphum padi L. signifikant erhöhte Populationsdichten im Winterweizen in nächster Nähe zu Prunus padus L. festgestellt werden. Die frühe Migration wurde anhand von Saugfallendaten verschiedener Standorte der letzten Jahre untersucht. Das Erstauftreten von R. padi (1. Fänge in Saugfallen) zeigte sich dabei recht konstant am 13. Mai eines Jahres. Die Beziehungen zwischen den weiteren Migrationsereignissen und meteorologischen Parametern waren jedoch eher schwach ausgeprägt (R²<0,21, p=0,01); wobei hier Globalstrahlung (R²=0,21), Temperatur (R²=0,18) und Windgeschwindigkeit (R²=0,14) die deutlichsten Beziehungen zeigten

Creation of long-term coherent optical memory via controlled nonlinear interactions in Bose-Einstein condensates

A Bose-Einstein condensate confined in an optical dipole trap is used to generate long-term coherent memory for light, and storage times of more than one second are observed. Phase coherence of the condensate as well as controlled manipulations of elastic and inelastic atomic scattering processes are utilized to increase the storage fidelity by several orders of magnitude over previous schemes. The results have important applications for creation of long-distance quantum networks and for generation of entangled states of light and matter.Comment: published version of the pape

An Observational Limit on the Dwarf Galaxy Population of the Local Group

We present the results of an all-sky, deep optical survey for faint Local Group dwarf galaxies. Candidate objects were selected from the second Palomar survey (POSS-II) and ESO/SRC survey plates and follow-up observations performed to determine whether they were indeed overlooked members of the Local Group. Only two galaxies (Antlia and Cetus) were discovered this way out of 206 candidates. Based on internal and external comparisons, we estimate that our visual survey is more than 77% complete for objects larger than one arc minute in size and with a surface brightness greater than an extremely faint limit over the 72% of the sky not obstructed by the Milky Way. Our limit of sensitivity cannot be calculated exactly, but is certainly fainter than 25 magnitudes per square arc second in R, probably 25.5 and possibly approaching 26. We conclude that there are at most one or two Local Group dwarf galaxies fitting our observational criteria still undiscovered in the clear part of the sky, and a roughly a dozen hidden behind the Milky Way. Our work places the "missing satellite problem" on a firm quantitative observational basis. We present detailed data on all our candidates, including surface brightness measurements.Comment: 58 pages in AJ manuscript format; some figures at slightly reduced quality; accepted by the Astronomical Journa

Biomolecular imaging and electronic damage using X-ray free-electron lasers

Proposals to determine biomolecular structures from diffraction experiments using femtosecond X-ray free-electron laser (XFEL) pulses involve a conflict between the incident brightness required to achieve diffraction-limited atomic resolution and the electronic and structural damage induced by the illumination. Here we show that previous estimates of the conditions under which biomolecular structures may be obtained in this manner are unduly restrictive, because they are based on a coherent diffraction model that is not appropriate to the proposed interaction conditions. A more detailed imaging model derived from optical coherence theory and quantum electrodynamics is shown to be far more tolerant of electronic damage. The nuclear density is employed as the principal descriptor of molecular structure. The foundations of the approach may also be used to characterize electrodynamical processes by performing scattering experiments on complex molecules of known structure.Comment: 16 pages, 2 figure

Financial panic and emerging market funds

This article studies equity investment of emerging-market funds based on the 2003–2009 weekly data and compares the dynamics of flow and return between tranquil period and financial panic based on the experience of the latest 2008–2009 global financial crisis. First, we find that the well-documented positive feedback trading is a tranquil-period phenomenon such that it is more difficult in general for emerging-market funds to attract new investment in financial panic. Second, the predictive power of flow on return is driven by a combination of price pressure and information effects in tranquil period, while the information effect dominates in financial panic. Third, the underlying co-movements or contagion of flow across the emerging-market funds influence the association between flow and return. Overall, the findings highlight the importance of accounting for state-dependent dynamics as well as cross-regional co-movements in the analysis of flow and return

Float zone experiments in space

The molten zone/freezing crystal interface system and all the mechanisms were examined. If Marangoni convection produces oscillatory flows in the float zone of semiconductor materials, such as silicon, then it is unlikely that superior quality crystals can be grown in space using this process. The major goals were: (1) to determine the conditions for the onset of Marangoni flows in molten tin, a model system for low Prandtl number molten semiconductor materials; (2) to determine whether the flows can be suppressed by a thin oxide layer; and (3) based on experimental and mathematical analysis, to predict whether oscillatory flows will occur in the float zone silicon geometry in space, and if so, could it be suppressed by thin oxide or nitride films. Techniques were developed to analyze molten tin surfaces in a UHV system in a disk float zone geometry to minimize buoyancy flows. The critical Marangoni number for onset of oscillatory flows was determined to be greater than 4300 on atomically clean molten tin surfaces

An iterative warping and clustering algorithm to estimate multiple wave-shape functions from a nonstationary oscillatory signal

Nonsinusoidal oscillatory signals are everywhere. In practice, the nonsinusoidal oscillatory pattern, modeled as a 1-periodic wave-shape function (WSF), might vary from cycle to cycle. When there are finite different WSFs, $s_1,\ldots,s_K$, so that the WSF jumps from one to another suddenly, the different WSFs and jumps encode useful information. We present an iterative warping and clustering algorithm to estimate $s_1,\ldots,s_K$ from a nonstationary oscillatory signal with time-varying amplitude and frequency, and hence the change points of the WSFs. The algorithm is a novel combination of time-frequency analysis, singular value decomposition entropy and vector spectral clustering. We demonstrate the efficiency of the proposed algorithm with simulated and real signals, including the voice signal, arterial blood pressure, electrocardiogram and accelerometer signal. Moreover, we provide a mathematical justification of the algorithm under the assumption that the amplitude and frequency of the signal are slowly time-varying and there are finite change points that model sudden changes from one wave-shape function to another one.Comment: 39 pages, 11 figure