4,160 research outputs found
Attitude Determination from Single-Antenna Carrier-Phase Measurements
A model of carrier phase measurement (as carried out by a satellite
navigation receiver) is formulated based on electromagnetic theory. The model
shows that the phase of the open-circuit voltage induced in the receiver
antenna with respect to a local oscillator (in the receiver) depends on the
relative orientation of the receiving and transmitting antennas. The model
shows that using a {\it single} receiving antenna, and making carrier phase
measurements to seven satellites, the 3-axis attitude of a user platform (in
addition to its position and time) can be computed relative to an initial
point. This measurement model can also be used to create high-fidelity
satellite signal simulators that take into account the effect of platform
rotation as well as translation.Comment: 12 pages, and one figure. Published in J. Appl. Phys. vol. 91, No. 7,
April 1, 200
Progress on a spherical TPC for low energy neutrino detection
The new concept of the spherical TPC aims at relatively large target masses
with low threshold and background, keeping an extremely simple and robust
operation. Such a device would open the way to detect the neutrino-nucleus
interaction, which, although a standard process, remains undetected due to the
low energy of the neutrino-induced nuclear recoils. The progress in the
development of the fist 1 m prototype at Saclay is presented. Other physics
goals of such a device could include supernova detection, low energy neutrino
oscillations and study of non-standard properties of the neutrino, among
others.Comment: 3 pages, talk given at the 9th Workshop on Topics in Astroparticle
and Underground Physics, Zaragoza, September 10-1
Blue light absorption enhancement based on vertically channelling modes in nano-holes arrays
We investigate the specific optical regime occurring at short wavelengths, in
the high absorption regime, in silicon thin-films patterned by periodically
arranged nano-holes. Near-field scanning optical microscopy indicates that the
incoming light is coupled to vertically channelling modes. Optical modelling
and simulations show that the light, travelling inside the low-index regions,
is absorbed at the direct vicinity of the nano-holes sidewalls. This
channelling regime should be taken into account for light management in
optoelectronic devices
Electromagnetic Fields Produced by Moving Sources in a Curved Beam Pipe
A new geometrical perturbation scheme is developed in order to calculate the
electromagnetic fields produced by charged sources in prescribed motion moving
in a non-straight perfectly conducting beam pipe. The pipe is regarded as a
perturbed infinitely long hollow right-circular cylinder. The perturbation
maintains the pipe's circular cross-section while deforming its axis into a
planar space-curve with, in general, non-constant curvature. Various charged
source models are considered including a charged bunch and an off-axis point
particle. In the ultra-relativistic limit this permits a calculation of the
longitudinal wake potential in terms of powers of the product of the pipe
radius and the arbitrarily varying curvature of the axial space-curve. Analytic
expressions to leading order are presented for beam pipes with piecewise
defined constant curvature modelling pipes with straight segments linked by
circular arcs of finite length. The language of differential forms is used
throughout and to illustrate the power of this formalism a pedagogical
introduction is developed by deriving the theory ab-initio from Maxwell's
equations expressed intrinsically as a differential system on (Minkowski)
spacetime.Comment: 43pages, 7figure
Design and implementation of an instrumented pedal for cycling biomechanics research
Cycling is a common, low-impact activity used for recreation, exercise, and rehabilitation. Knee joint loading can be predicted using inverse dynamic analyses of pedal load cell and kinematic data measured during cycling biomechanics experiments. Several studies have successfully measured foot loading at the pedals, e.g. by using custom instrumented pedal spindles outfitted with strain gauges and a potentiometer to measure crank angle [1-3]. Such designs are relatively complex, requiring difficult machining and component fabrication, and require post-processing of strain gauge data.
The long-term goal of this study is to calculate knee joint loading and, ultimately, cartilage tissue stress to provide evidence-based prescriptions for rehabilitative and fitness sustainment exercises for those who are at high risk for knee osteoarthritis. The objective of this project was to design, fabricate, and implement an instrumented pedal system using existing load cells for use in cycling biomechanics research. Measured data retrieved from the load cells during cycling experiments will be compared to similar studies to verify that this project was successful
Metagenome-based diversity analyses suggest a significant contribution of non-cyanobacterial lineages to carbonate precipitation in modern microbialites
Frontiers in Microbiology 6 (2015): 797 This Document is Protected by copyright and was first published by Frontiers. All rights reserved. It is reproduced with permissionCyanobacteria are thought to play a key role in carbonate formation due to their metabolic activity, but other organisms carrying out oxygenic photosynthesis (photosynthetic eukaryotes) or other metabolisms (e.g., anoxygenic photosynthesis, sulfate reduction), may also contribute to carbonate formation. To obtain more quantitative information than that provided by more classical PCR-dependent methods, we studied the microbial diversity of microbialites from the Alchichica crater lake (Mexico) by mining for 16S/18S rRNA genes in metagenomes obtained by direct sequencing of environmental DNA. We studied samples collected at the Western (AL-W) and Northern (AL-N) shores of the lake and, at the latter site, along a depth gradient (1, 5, 10, and 15 m depth). The associated microbial communities were mainly composed of bacteria, most of which seemed heterotrophic, whereas archaea were negligible. Eukaryotes composed a relatively minor fraction dominated by photosynthetic lineages, diatoms in AL-W, influenced by Si-rich seepage waters, and green algae in AL-N samples. Members of the Gammaproteobacteria and Alphaproteobacteria classes of Proteobacteria, Cyanobacteria, and Bacteroidetes were the most abundant bacterial taxa, followed by Planctomycetes, Deltaproteobacteria (Proteobacteria), Verrucomicrobia, Actinobacteria, Firmicutes, and Chloroflexi. Community composition varied among sites and with depth. Although cyanobacteria were the most important bacterial group contributing to the carbonate precipitation potential, photosynthetic eukaryotes, anoxygenic photosynthesizers and sulfate reducers were also very abundant. Cyanobacteria affiliated to Pleurocapsales largely increased with depth. Scanning electron microscopy (SEM) observations showed considerable areas of aragonite-encrusted Pleurocapsa-like cyanobacteria at microscale. Multivariate statistical analyses showed a strong positive correlation of Pleurocapsales and Chroococcales with aragonite formation at macroscale, and suggest a potential causal link. Despite the previous identification of intracellularly calcifying cyanobacteria in Alchichica microbialites, most carbonate precipitation seems extracellular in this systemWe are grateful to Eleonor Cortés for help and good company during the field trip and to Eberto Novelo for helpful discussions at the UNAM lab. This research was funded by
the European Research Council Grants ProtistWorld (PI PL-G., Grant Agreement no. 322669) and CALCYAN (PI KB, Grant Agreement no. 307110) under the European Union’s Seventh Framework Program and the RTP Génomique environnementale of the CNRS (project MetaStrom, PI DM
Intermediate snowpack melt-out dates guarantee the highest seasonal grasslands greening in the Pyrenees
In mountain areas, the phenology and productivity of grassland are closely related to snow dynamics. However, the influence that snow melt timing has on grassland growing still needs further attention for a full understanding, particularly at high spatial resolution. Aiming to reduce this knowledge gap, this work exploits 1 m resolution snow depth and Normalized Difference Vegetation Index observations acquired with an Unmanned Aerial Vehicle at a sub-alpine site in the Pyrenees. During two snow seasons (2019–2020 and 2020–2021), 14 NDVI and 17 snow depth distributions were acquired over 48 ha. Despite the snow dynamics being different in the two seasons, the response of grasslands greening to snow melt-out exhibited a very similar pattern in both. The NDVI temporal evolution in areas with distinct melt-out dates reveals that sectors where the melt-out date occurs in late April or early May (optimum melt-out) reach the maximum vegetation productivity. Zones with an earlier or a later melt-out rarely reach peak NDVI values. The results obtained in this study area, suggest that knowledge about snow depth distribution is not needed to understand NDVI grassland dynamics. The analysis did not reveal a clear link between the spatial variability in snow duration and the diversity and richness of grassland communities within the study area
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