739 research outputs found
Modelling understorey dynamics in temperate forests under global change : challenges and perspectives
The understorey harbours a substantial part of vascular plant diversity in temperate forests and plays an important functional role, affecting ecosystem processes such as nutrient cycling and overstorey regeneration. Global change, however, is putting these understorey communities on trajectories of change, potentially altering and reducing their functioning in the future. Developing mitigation strategies to safeguard the diversity and functioning of temperate forests in the future is challenging and requires improved predictive capacity. Process-based models that predict understorey community composition over time, based on first principles of ecology, have the potential to guide mitigation endeavours but such approaches are rare. Here, we review fourteen understorey modelling approaches that have been proposed during the last three decades. We evaluate their inclusion of mechanisms that are required to predict the impact of global change on understorey communities. We conclude that none of the currently existing models fully accounts for all processes that we deem important based on empirical and experimental evidence. Based on this review, we contend new models are needed to project the complex impacts of global change on forest understoreys. Plant functional traits should be central to such future model developments, as they drive community assembly processes and provide valuable information on the functioning of the understorey. Given the important role of the overstorey, a coupling of understorey models to overstorey models will be essential to predict the impact of global change on understorey composition and structure, and how it will affect the functioning of temperate forests in the future
Atomic resolution mapping of phonon excitations in STEM-EELS experiments
Atomically resolved electron energy-loss spectroscopy experiments are
commonplace in modern aberrationcorrected transmission electron microscopes.
Energy resolution has also been increasing steadily with the continuous
improvement of electron monochromators. Electronic excitations however are
known to be delocalised due to the long range interaction of the charged
accelerated electrons with the electrons in a sample. This has made several
scientists question the value of combined high spatial and energy resolution
for mapping interband transitions and possibly phonon excitation in crystals.
In this paper we demonstrate experimentally that atomic resolution information
is indeed available at very low energy losses around 100 meV expressed as a
modulation of the broadening of the zero loss peak. Careful data analysis
allows us to get a glimpse of what are likely phonon excitations with both an
energy loss and gain part. These experiments confirm recent theoretical
predictions on the strong localisation of phonon excitations as opposed to
electronic excitations and show that a combination of atomic resolution and
recent developments in increased energy resolution will offer great benefit for
mapping phonon modes in real space
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
Generic substitution: the use of medicinal products containing different salts and implications for safety and efficacy
In their quest to gain early entry of new generic products into the market prior to patent expiration, one of the strategies pursued by generic drug product manufacturers is to incorporate different salts of an approved active pharmaceutical ingredient (API) in a brand company's marketed dosage form and subject such dosage forms to bioequivalence assessment. These initiatives present challenges to regulatory authorities where the decision to approve bioequivalent products containing such pharmaceutical alternatives must be considered in the light of safety and efficacy, and more particularly, with respect to their substitutability. This article describes the various issues and contentions associated with the concept of pharmaceutical alternatives, specifically with respect to the uses of different salts and the implications for safety, efficacy and generic substitution
Nine Principles of Semantic Harmonization
Medical data is routinely collected, stored and recorded across different institutions and in a range of different formats. Semantic harmonization is the process of collating this data into a singular consistent logical view, with many approaches to harmonizing both possible and valid. The broad scope of possibilities for undertaking semantic harmonization do lead however to the development of bespoke and ad-hoc systems; this is particularly the case when it comes to cohort data, the format of which is often specific to a cohort's area of focus. Guided by work we have undertaken in developing the 'EMIF Knowledge Object Library', a semantic harmonization framework underpinning the collation of pan-European Alzheimer's cohort data, we have developed a set of nine generic guiding principles for developing semantic harmonization frameworks, the application of which will establish a solid base for constructing similar frameworks
Theory and applications of free-electron vortex states
Both classical and quantum waves can form vortices: with helical phase fronts
and azimuthal current densities. These features determine the intrinsic orbital
angular momentum carried by localized vortex states. In the past 25 years,
optical vortex beams have become an inherent part of modern optics, with many
remarkable achievements and applications. In the past decade, it has been
realized and demonstrated that such vortex beams or wavepackets can also appear
in free electron waves, in particular, in electron microscopy. Interest in
free-electron vortex states quickly spread over different areas of physics:
from basic aspects of quantum mechanics, via applications for fine probing of
matter (including individual atoms), to high-energy particle collision and
radiation processes. Here we provide a comprehensive review of theoretical and
experimental studies in this emerging field of research. We describe the main
properties of electron vortex states, experimental achievements and possible
applications within transmission electron microscopy, as well as the possible
role of vortex electrons in relativistic and high-energy processes. We aim to
provide a balanced description including a pedagogical introduction, solid
theoretical basis, and a wide range of practical details. Special attention is
paid to translate theoretical insights into suggestions for future experiments,
in electron microscopy and beyond, in any situation where free electrons occur.Comment: 87 pages, 34 figure
Experimental validation of flexibility provision by highly distributed demand portfolio
The wide scale deployment and utilization of demand side management for the provision of frequency balancing service provision is hindered by the lack of proof of performance evaluation of such mechanisms. In this paper, the pre-qualification testing approaches for performance evaluation of frequency balancing service provision by highly distributed demand portfolio are discussed. Preliminary experimental results and challenges that arise of the pre-qualification tests conducted on a highly distributed flexible resource portfolio being managed by a multi-agent based demand side management technology are presented and the need for expansion of present day testing procedures discussed
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
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