Infestations of the cypress bark beetles Phloeosinus rudis, P. bicolor and P. thujae in The Netherlands (Coleoptera: Curculionidae: Scolytinae).

In de zomer van 2004 trad er grote sterfte op bij coniferen in Rotterdam en nabijgelegen steden zoals Ridderkerk, Sleeuwijk, Maassluis, Nieuw-Lekkerland en Dordrecht. De sterfte trad op bij een solitaire 60-jarige Thuja maar ook bij coniferenhagen van Thuja, Chamaecyparis en Juniperus. Na 2004 werd de kever nog maar enkele malen waargenomen. Kleine populaties kunnen echter overleven in verzwakte bomen zoals in 2008 bleek uit de vondst van kevers in een door parasitaire schimmels verzwakte boom (Rotterdam) en gebroken takken (Wageningen en Renkum). Het zijn zwakteparasieten die zich alleen in verzwakte bomen kunnen ontwikkelen. 2003 was een zeer droog jaar met veel droogtestress verzwakte bomen en struiken waardoor de aantastingen konden plaatsvinden

The Effect of Diffusion on the Particle Spectra in Pulsar Wind Nebulae

A possible way to calculate particle spectra as a function of position in pulsar wind nebulae is to solve a Fokker-Planck transport equation. This paper presents numerical solutions to the transport equation with the processes of convection, diffusion, adiabatic losses, and synchrotron radiation included. In the first part of the paper the steady-state version of the transport equation is solved as a function of position and energy. This is done to distinguish the various effects of the aforementioned processes on the solutions to the transport equation. The second part of the paper deals with a time-dependent solution to the transport equation, specifically taking into account the effect of a moving outer boundary. The paper highlights the fact that diffusion can play a significant role in reducing the amount of synchrotron losses, leading to a modification in the expected particle spectra. These modified spectra can explain the change in the photon index of the synchrotron emission as a function of position. The solutions presented in this paper are not limited to pulsar wind nebulae, but can be applied to any similar central source system, e.g. globular clusters

Drift and Forbush decreases

Evidence is presented that the drift effect on the modulation of galactic cosmic rays can be seen on Forbush decreases observed by the Deep River and Hermanus neutron monitors

Proton Modulation Near Solar Minimum Periods in Consecutive Solar Cycles

Observations or the Pioneer/Voyager missions during 1985/1986/1987, together with observations at Earth in 1976/1977 and 1987, are compared with predictions of a steady-state modulation model. The qualitative features of the modulation are well understood, but to get quantitative agreement with observations, drastic modifications have to be made to the Parker spiral magnetic field above the solar poles

3D and Subtraction MR imaging in Multiple Sclerosis : Improved detection of spatiotemporal disease activity

Barkhof, F. [Promotor]Polman, C.H. [Promotor]Geurts, J.J.G. [Copromotor]Vrenken, H. [Copromotor

Cosmic Ray Perpendicular Diffusion Coefficient and Drift Velocity Calculated from Pioneer/Voyager Observations

The radial and latitudinal gradients measured by the Pioneer 10 and Voyager 1 and 2 spacecraft, reported by Cummings and Stone (1990), provide a unique opportunity to calculate the cosmic ray perpendicular diffusion coefficient and drift velocity

Aachen’s Policies on Air Pollution: A Law and Economics Analysis

This article compares the merits of two opposing air pollution policies in Aachen through a law and economics approach. Based on Cole’s property rights regimes, the current Aachener Approach and the soon to replace it Low Emission Zone (LEZ) are characterized as incentive-based and command-and-control regulation respectively, and subsequently evaluated on their efficiency and effectiveness using local government reports and legislation, and theoretical law and economics literature. This cost-benefit analysis shows the LEZ to be less efficient and of questionable effectivity in achieving reduction of air pollution levels compared to the current Aachener Approach.