462 research outputs found
Importing into the EU - Council Regulation (EEC) No 1991/2006
Report on the presentation held at BioFach, 23.02.2008, by Herman Van Boxem (European Commission, Agriculture and rural development Directorate-General Unit F5 - Organic farming)
compiled by Beate Huber, FiB
Inelastic electron-vortex-beam scattering
Recent theoretical and experimental developments in the field of electron
vortex beam physics have raised questions on what exactly this novelty in the
field of electron microscopy (and other fields, such as particle physics)
really provides. An important part in the answer to those questions lies in
scattering theory. The present investigation explores various aspects of
inelastic quantum scattering theory for cylindrically symmetric beams with
orbital angular momentum. The model system of Coulomb scattering on a hydrogen
atom provides the setting to address various open questions: How is momentum
transferred? Do vortex beams selectively excite atoms, and how can one employ
vortex beams to detect magnetic transitions? The analytical approach presented
here provides answers to these questions. OAM transfer is possible, but not
through selective excitation; rather, by pre- and post-selection one can filter
out the relevant contributions to a specific signal
Rutherford scattering of electron vortices
By considering a cylindrically symmetric generalization of a plane wave, the
first Born approximation of screened Coulomb scattering unfolds two new
dimensions in the scattering problem: transverse momentum and orbital angular
momentum of the incoming beam. In this paper, the elastic Coulomb scattering
amplitude is calculated analytically for incoming Bessel beams. This reveals
novel features occurring for wide angle scattering when the incoming beam is
correctly prepared. The result successfully generalizes the well known
Rutherford formula, incorporating transverse and orbital angular momentum into
the formalism.Comment: 9 pages, 5 figure
Injection therapy and denervation procedures for chronic low back pain: a systematic reviewâclinical value?
Exporting to Europe
What will change under the revised EU Regulation? Impacts for traders and certification bodies in third countries
Exploiting lens aberrations to create electron vortex beams
A model for a new electron vortex beam production method is proposed and
experimentally demonstrated. The technique calls on the controlled manipulation
of the degrees of freedom of the lens aberrations to achieve a helical phase
front. These degrees of freedom are accessible by using the corrector lenses of
a transmission electron microscope. The vortex beam is produced through a
particular alignment of these lenses into a specifically designed astigmatic
state and applying an annular aperture in the condensor plane. Experimental
results are found to be in good agreement with simulations.Comment: 5 pages, 4 figure
Prospects for versatile phase manipulation in the TEM: beyond aberration correction
In this paper we explore the desirability of a transmission electron
microscope in which the phase of the electron wave can be freely controlled. We
discuss different existing methods to manipulate the phase of the electron wave
and their limitations. We show how with the help of current techniques the
electron wave can already be crafted into specific classes of waves each having
their own peculiar properties. Assuming a versatile phase modulation device is
feasible, we explore possible benefits and methods that could come into
existence borrowing from light optics where so-called spatial light modulators
provide programmable phase plates for quite some time now. We demonstrate that
a fully controllable phase plate building on Harald Rose's legacy in aberration
correction and electron optics in general would open an exciting field of
research and applications.Comment: 9 pages, 4 figures, special Ultramicroscopy issue for PICO2015
conferenc
Magnetic monopole field exposed by electrons
Magnetic monopoles have provided a rich field of study, leading to a wide
area of research in particle physics, solid state physics, ultra-cold gases,
superconductors, cosmology, and gauge theory. So far, no true magnetic
monopoles were found experimentally. Using the Aharonov-Bohm effect, one of the
central results of quantum physics, shows however, that an effective monopole
field can be produced. Understanding the effects of such a monopole field on
its surroundings is crucial to its observation and provides a better grasp of
fundamental physical theory. We realize the diffraction of fast electrons at a
magnetic monopole field generated by a nanoscopic magnetized ferromagnetic
needle. Previous studies have been limited to theoretical semiclassical optical
calculations of the motion of electrons in such a monopole field. Solid state
systems like the recently studied 'spin ice' provide a constrained system to
study similar fields, but make it impossible to separate the monopole from the
material. Free space diffraction helps to understand the dynamics of the
electron-monopole system without the complexity of a solid state system. The
use of a simple object such as a magnetized needle will allow various areas of
physics to use the general dynamical effects of monopole fields without
requiring a monopole particle or specific solids which have internal
monopole-like properties. The experiment performed here shows that even without
a true magnetic monopole particle, the theoretical background on monopoles
serves as a basis for experiments and can be applied to efficiently create
electron vortices. Various predictions about angular momentum and general field
effects can readily be studied using the available equipment. This realization
provides insights for the scientific community on how to detect magnetic
monopoles in high energy collisions, cosmological processes, or novel
materials.Comment: 5 pages, 3 figures + 7 pages of supplementary information, 8 figure
Shaping electron beams for the generation of innovative measurements in the (S)TEM
In TEM, a typical goal consists of making a small electron probe in the
sample plane in order to obtain high spatial resolution in scanning
transmission electron microscopy. In order to do so, the phase of the electron
wave is corrected to resemble a spherical wave compensating for aberrations in
the magnetic lenses. In this contribution we discuss the advantage of changing
the phase of an electron wave in a specific way in order to obtain
fundamentally different electron probes opening up new application in the
(S)TEM. We focus on electron vortex states as a specific family of waves with
an azimuthal phase signature and discuss their properties, production and
applications. The concepts presented here are rather general and also different
classes of probes can be obtained in a similar fashion showing that electron
probes can be tuned to optimise a specific measurement or interaction
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