Tallo: A global tree allometry and crown architecture database

Data capturing multiple axes of tree size and shape, such as a tree's stem diameter, height and crown size, underpin a wide range of ecological research-from developing and testing theory on forest structure and dynamics, to estimating forest carbon stocks and their uncertainties, and integrating remote sensing imagery into forest monitoring programmes. However, these data can be surprisingly hard to come by, particularly for certain regions of the world and for specific taxonomic groups, posing a real barrier to progress in these fields. To overcome this challenge, we developed the Tallo database, a collection of 498,838 georeferenced and taxonomically standardized records of individual trees for which stem diameter, height and/or crown radius have been measured. These data were collected at 61,856 globally distributed sites, spanning all major forested and non-forested biomes. The majority of trees in the database are identified to species (88%), and collectively Tallo includes data for 5163 species distributed across 1453 genera and 187 plant families. The database is publicly archived under a CC-BY 4.0 licence and can be access from: https://doi.org/10.5281/zenodo.6637599. To demonstrate its value, here we present three case studies that highlight how the Tallo database can be used to address a range of theoretical and applied questions in ecology-from testing the predictions of metabolic scaling theory, to exploring the limits of tree allometric plasticity along environmental gradients and modelling global variation in maximum attainable tree height. In doing so, we provide a key resource for field ecologists, remote sensing researchers and the modelling community working together to better understand the role that trees play in regulating the terrestrial carbon cycle.

Near Velocity Field Downstream Prosthetic Valves in Aortic Position

Using a cardiovascular simulator to duplicate in vitro the flow conditions through valves in aortic position, bidimensional velocity maps very near the valve are reconstructed, from an ultrasonic 8 Mhz doppler system, in an elastic model of the ascending aortic arch. Three mechanical heart valves representative of the different types of commercial models (a tilting disc, a ball in cage and a two-leaflet valve) and a new bileaflet prototype were investigated. From examination of the velocity field, it is possible to define the main characteristics of the valve wake and to observe the development of negative velocities associated with regurgitant flows. From a comparison with tests in rigid tubes, the role played by the arch elasticity is analysed.

Near velocity field downstream prosthetic valves in aortic position

Using a cardiovascular simulator to duplicate in vitro the flow conditions through valves in aortic position, bidimensional velocity maps very near the valve are reconstructed, from an ultrasonic 8 Mhz doppler system, in an elastic model of the ascending aortic arch. Three mechanical heart valves representative of the different types of commercial models (a tilting disc, a ball in cage and a two-leaflet valve) and a new bileaflet prototype were investigated. From examination of the velocity field, it is possible to define the main characteristics of the valve wake and to observe the development of negative velocities associated with regurgitant flows. From a comparison with tests in rigid tubes, the role played by the arch elasticity is analysed.

In vitro study of a physiological type flow in a bifurcated vascular prosthesis

Using a cardiovascular simulator allowing the production of physiological conditions, velocity field and pressure-diameter relationship were determined in a bifurcated arterial graft for two geometric configurations of implantation. Velocity measurements give the surgeon attractive and useful information for finding out the best way to implant the graft. The study of the pressure-diameter relationship showed a particular behaviour of the graft; the wall motion of the graft, compared with the pressure wave, being different both in the mother branch at the upstream anastomosis and in the daughter branch.

Accuracy of the simplified Bernoulli relationship in measuring pressure gradients across stenosis

In order to test the validity of the modified Bernoulli equation in predicting pressure gradients across stenotic regions, we have constructed an in-vitro model and studied the influence of the length and of the severity of the stenosis. Under physiological conditions, simultaneous pressure gradients are estimated by both Doppler and direct pressure manometer techniques. Measurements of the pressure gradients (in the range 10-150 mmHg) by the two techniques show that the Doppler estimation using the modified Bernoulli equation underestimated the pressure transducer gradient measurements for every length of stenosis, this underestimation being greater than 45% for very severe stenosis.

Influence of the haemodynamic parameters on the repartition of the flow between an artery and its graft

The aim of this study was to investigate the repartition of the flow between an artery and its graft for several values of the geometric and dynamic parameters (length and severity of the stenosis, Reynolds number and frequency pulse value). The model, fabricated in silicone, was included in an hydrodynamic test bench, allowing to reproduce physiological conditions. Our study showed that the severity of the stenosis was the most influent parameter on the repartition of the flow; in particular, a 75% severity was necessary to obtain a repartition 70-30% between the graft and the artery.

Velocity field of a Björk-Shiley valve prosthesis: influence of the disc orientation

An experimental investigation was carried out on the development of physiological flows downstream of a Björk-Shiley valve prosthesis. The post-valvular velocity field was determined by an ultrasonic method in an elastic model of the aortic arch. The flow development in the ascending aorta was strongly dependent on the orientation of the tilting disc. The rotating direction of the vortices and the site of the maximum velocity were influenced by the orientation.

Velocity profiles in the wake of two prosthetic heart valves using a new cardiovascular simulator

In this paper we present a study of the post valvular flow field on a new cardiovascular simulator including an elastic model of the aortic arch. Transverse and vertical two-dimensional velocity measurements are performed with an ultrasonic velocimeter. Two prosthetic heart valves are tested in the aortic position. The behaviour of the velocity vectors patterns during one pulsatile cycle is one of the most striking features of the flow.

Velocity distribution along an elastic model of human arterial tree

An experimental investigation of an elastic model of the human arterial tree, has been performed for physiological type flow by pulsed Doppler ultrasonic velocimetry. The arterial tree model, fabricated in clear polyurethane, includes the aortic arch, with a Starr-Edwards ball valve mounted in the root of the aorta, the descending aorta and the iliac bifurcation. Our study showed that the velocity profile, a few centimeters beyond the valve, is skewed, with higher velocities towards the top and the inner wall (anatomically the posterior and left lateral wall). An inward shift of the maximum velocity and reverse flow are denoted along the inner wall of the aortic arch. The velocity profiles in the descending aorta are blunted. Downstream from the vertex of the iliac bifurcation, there is vorticity creation, but the branching effect is quickly damped by the pulsatility of the flow and the elasticity of the wall.

The effect of unsteadiness on the flow through stenoses and bifurcations

This paper is concerned with the influence of a stenosis or a bifurcation on the flow through a tube. In particular the effect of unsteadiness is investigated using simple pulsatile and physiological type flows (Fig. 1). The experimental investigations reported herein are concerned with velocity measurements and flow visualizations. (see formula in text) These measurements, performed in a 60 degrees bifurcation, have permitted the reconstruction of the three-dimensional velocity profiles. The importance of the secondary flow in the branching is analyzed for various values of the flow parameters. Results of tests show a strong influence of unsteadiness on flow characteristics and then on hemodynamic factors. One conclusion is the following: if hemodynamic factors play an important role in the problems of atherosclerosis, then, for macrocirculation studies, it is necessary to take into account unsteadiness and, in particular, the actual shape of the flow-time forcing function.

Simulation of blood flow by a hydrodynamic generator

Physiological flows are produced by a volumetric gear pump. The motor-pump group is controlled by an amplifying comparator, and produces a flow whose rate follows the control signal. This signal is delivered by a synthetizing generator and its shape, amplitude, and frequency are adjustable. This hydrodynamic generator supplies a test bench on which the modifications of flow patterns induced by models of vascular stenoses are studied. The study of the velocity distribution has been effected with a pulsed-Doppler ultrasonic velocimeter.