Alterations in the odor profile of plants in cultivar mixtures affect aphid host-location behavior

The effect of cultivar mixtures on aphid control is attributed to the masking or alteration of host-preferred cultivar odor cues. However, the underlying physiological mechanism remains unclear. This study assessed alterations in the volatile emissions of wheat cultivars grown together (Florence-Aurora and Forment; Florence-Aurora and Montcada) and the consequences for the olfactory preference of aphids. Volatile organic compounds were collected from wheat plants grown in a laboratory under mixed or monoculture conditions and subsequently analyzed. The odor profiles of Florence-Aurora and Montcada were indistinguishable from each other. However, the odors of Florence-Aurora and Forment grown in monocultures differed significantly from those emitted by their mixture. The Florence-Aurora and Forment mixture induced plant physiological responses that affected the emission of single volatile compounds and, consequently, altered volatile organic compound ratios. English grain aphids (Sitobion avenae) were less attracted to the odors of Florence-Aurora and Forment when grown as a mixture than the combination of the odors from Florence-Aurora and Forment monocultures. Moreover, aphids preferred clean air over the odor from the Florence-Aurora and Forment mixture but preferred the odor from the Florence-Aurora and Montcada mixture over clean air. This study highlights the beneficial effects of intraspecific plant diversity on aphid control by altering plant odors in response to plant-plant interactions. The emission of less attractive odor cues consequently affects plant-aphid interactions; hence, less attractive odors are likely to impair aphid host-locating behavior. This effect was exclusive to certain cultivar mixtures, which supports the "right neighbor" concept

Entropic uncertainty relations for electromagnetic beams

The symplectic tomograms of 2D Hermite--Gauss beams are found and expressed in terms of the Hermite polynomials squared. It is shown that measurements of optical-field intensities may be used to determine the tomograms of electromagnetic-radiation modes. Furthermore, entropic uncertainty relations associated with these tomograms are found and applied to establish the compatibility conditions of the the field profile properties with Hermite--Gauss beam description. Numerical evaluations for some Hermite--Gauss modes illustrating the corresponding entropic uncertainty relations are finally given.Comment: Invited talk at the XV Central European Workshop on Quantum Optics (Belgrade, Serbia, 30 May -- 3 June 2008), to appear in Physica Scripta

Stochastic collective dynamics of charged--particle beams in the stability regime

We introduce a description of the collective transverse dynamics of charged (proton) beams in the stability regime by suitable classical stochastic fluctuations. In this scheme, the collective beam dynamics is described by time--reversal invariant diffusion processes deduced by stochastic variational principles (Nelson processes). By general arguments, we show that the diffusion coefficient, expressed in units of length, is given by $\lambda_c\sqrt{N}$, where $N$ is the number of particles in the beam and $\lambda_c$ the Compton wavelength of a single constituent. This diffusion coefficient represents an effective unit of beam emittance. The hydrodynamic equations of the stochastic dynamics can be easily recast in the form of a Schr\"odinger equation, with the unit of emittance replacing the Planck action constant. This fact provides a natural connection to the so--called ``quantum--like approaches'' to beam dynamics. The transition probabilities associated to Nelson processes can be exploited to model evolutions suitable to control the transverse beam dynamics. In particular we show how to control, in the quadrupole approximation to the beam--field interaction, both the focusing and the transverse oscillations of the beam, either together or independently.Comment: 15 pages, 9 figure

Default Risk and Equity Returns: A Comparison of the Bank-Based German and the U.S. Financial System

In this paper, we address the question whether the impact of default risk on equity returns depends on the financial system firms operate in. Using an implementation of Merton's option-pricing model for the value of equity to estimate firms' default risk, we construct a factor that measures the excess return of firms with low default risk over firms with high default risk. We then compare results from asset pricing tests for the German and the U.S. stock markets. Since Germany is the prime example of a bank-based financial system, where debt is supposedly a major instrument of corporate governance, we expect that a systematic default risk effect on equity returns should be more pronounced for German rather than U.S. firms. Our evidence suggests that a higher firm default risk systematically leads to lower returns in both capital markets. This contradicts some previous results for the U.S. by Vassalou/Xing (2004), but we show that their default risk factor looses its explanatory power if one includes a default risk factor measured as a factor mimicking portfolio. It further turns out that the composition of corporate debt affects equity returns in Germany. Firms' default risk sensitivities are attenuated the more a firm depends on bank debt financing

Epicardium-derived cells are important for correct development of the Purkinje fibers in the avian heart

During embryonic development, the proepicardial organ (PEO) grows out over the heart surface to form the epicardium. Following epithelial-mesenchymal transformation, epicardium-derived cells (EPDCs) migrate into the heart and contribute to the developing coronary arteries, to the valves, and to the myocardium. The peripheral Purkinje fiber network develops from differentiating cardiomyocytes in the ventricular myocardium. Intrigued by the close spatial relationship between the final destinations of migrating EPDCs and Purkinje fiber differentiation in the avian heart, that is, surrounding the coronary arteries and at subendocardial sites, we investigated whether inhibition of epicardial outgrowth would disturb cardiomyocyte differentiation into Purkinje fibers. To this end, epicardial development was inhibited mechanically with a membrane, or genetically, by suppressing epicardial epithelial-to-mesenchymal transformation with antisense retroviral vectors affecting Ets transcription factor levels (n = 4, HH39-41). In both epicardial inhibition models, we evaluated Purkinje fiber development by EAP-300 immunohistochemistry and found that restraints on EPDC development resulted in morphologically aberrant differentiation of Purkinje fibers. Purkinje fiber hypoplasia was observed both periarterially and at subendocardial positions. Furthermore, the cells were morphologically abnormal and not aligned in orderly Purkinje fibers. We conclude that EPDCs are instrumental in Purkinje fiber differentiation, and we hypothesize that they coo

Study of Zγ events and limits on anomalous ZZγ and Zγγ couplings in pp̄ collisions at s=1.96TeV

We present a measurement of the Zγ production cross section and limits on anomalous ZZγ and Zγγ couplings for form-factor scales of Λ=750 and 1000 GeV. The measurement is based on 138 (152) candidates in the eeγ (μμγ) final state using 320(290)pb-1 of pp̄ collisions at s=1.96TeV. The 95% C.L. limits on real and imaginary parts of individual anomalous couplings are |h10,30Z|<0.23, |h20,40Z|<0.020, |h10,30γ|<0.23, and |h20,40γ|<0.019 for Λ=1000GeV. © 2005 The American Physical Society