Pervasive gaps in Amazonian ecological research

Biodiversity loss is one of the main challenges of our time, and attempts to address it require a clear understanding of how ecological communities respond to environmental change across time and space. While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes, vast areas of the tropics remain understudied. In the American tropics, Amazonia stands out as the world's most diverse rainforest and the primary source of Neotropical biodiversity, but it remains among the least known forests in America and is often underrepresented in biodiversity databases. To worsen this situation, human-induced modifications may eliminate pieces of the Amazon's biodiversity puzzle before we can use them to understand how ecological communities are responding. To increase generalization and applicability of biodiversity knowledge, it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple organism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region's vulnerability to environmental change. 15%–18% of the most neglected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lost

Theory of field ionization in the field ion microscope

Available from British Library Document Supply Centre- DSC:D58911/87 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

CONFORMAL MAPPING FOR SURFACE MODELLING

A conformal mapping method for obtaining electric potentials in a region close to a structured surface is developed. By neglecting one of the surface dimensions and assuming periodicity along the other, the resulting two-dimensional problem can be analytically treated. As examples of the method some arrays of monopoles and dipoles are calculated from which a surface model is proposed and exactly solved

IMAGING GAS ADSORPTION IN THE FIELD ION MICROSCOPE : DEPENDENCE IN TIP FIELD STRENGTH AND TIP TEMPERATURE

Les conditions pour la formation d'une couche de gaz "imageant" adsorbé sur la surface d'un échantillon au Microscope Ionique de Champ sont recherchées en utilisant un simple modèle théorique pour le mouvement des molécules du gaz. On conclue, alors, que la formation de cette couche n'est possible que pour une certaine gamme de valeurs d'intensité du champ et de température.The conditions for an imaging gas adsorbed layer in the Field Ion Microscope to be formed are investigated using a simple theoretical model for the imaging gas hopping motion. It is concluded that such a layer is formed just for a certain range of tip field (or voltage) values and tip temperatures

BEST IMAGE CONDITIONS IN FIELD ION MICROSCOPY

La qualité de l'image produite par le Microscope Ionique de Champ dépend de certains paramètres opérationnels qui peuvent être ajustés afin d'améliorer résolution et contraste. Les conditions optimales d'opération sont étudiées en vue de les établir de façon quantitative. À cette fin, la courbe de probabilité d'ionization est calculée à l'aide d'un modèle JWKB et une nouvelle interprétation des conditions optimales est suggérée. Ainsi sont calculées les valeurs approximatives du champ qui donnent lieu à la meilleure image pour les gaz inertes, de l'hélium au xénon.The Field Ion Microscope image quality is dependent on operational parameters which can be adjusted in order to improve resolution and contrast. The best image operation conditions are discussed with the aim to define them quantitatively. To do so, a JWKB calculation for the ionization distribution is used and a new interpretation of the best image conditions is proposed. An approximate range for the best image field values for the noble gases from He to Xe is established, based on this new interpretation

ENERGY DISTRIBUTION OF FREE SPACE FIELD IONIZATION : APPLICATION TO FIELD STRENGTH CALIBRATION

Nous discutons la méthode de calibration du champ électrique à la surface d'un émetteur à partir des mesures de la distribution d'énergie cinétique des ions qui sont formés par ionisation de champ loin de l'émetteur. Nous présentons une nouvelle approche de cette méthode qui permettrait une meilleure calibration.We discuss the method of field strength calibration from energy distributions measurements of free space field ionization. An alternative approach is considered and an improved calibration is suggested

Local Electric Field Variation in the Field Emission Process

Tunnelling probabilities in field emission processes are usually calculated assuming flat emitting surfaces. This corresponds to consider the electric field as a constant along the potential barrier. Previous work have shown the importance of taking into account image effects but neglecting local field variations. Even when the local field has been taken into account, a proper three dimensional calculation of the transmission coefficient was not performed. We discuss previous calculation models, their limitations and conclusions, comparing them with our model results. We have determined the transmission coefficient using a 3-D numerical integration process. Considering a completely planar surface and another one with an hemispherical protrusion superimposed on it, we could compare the relative influence of either the local field variation dong the potential barrier and image effects. These results lead to the conclusion that corrections due to the local field variation are of a magnitude that deserves to be considered, together as those resulting from the image potential

Electric Potential and Field Near Pointed Shaped Surfaces

The trajectories of charged particles, emitted from within or from the close vicinity of pointed shaped surfaces, requires the knowledge of the electric field resulting from the potential bias between surface and detector, or screen. Frequently it is necessary the use of numerical methods for solving Laplace's equation as a result of difficulties in obtaining an analytical expression. Recently we have shown that, when any two coordinate surfaces of an orthogonal system are kept at two different but constant potentials, it is possible to obtain an analytical solution for the potential in a relatively simple manner. Using this general property of orthogonal coordinate systems, we present the solution for the electric potential and field in the vicinity of pointed sudaces for several cases of practical interest in field emission, field ionisation, atomprobe field ion spectroscopy and related phenomena