206 research outputs found
The FastMap Algorithm for Shortest Path Computations
We present a new preprocessing algorithm for embedding the nodes of a given
edge-weighted undirected graph into a Euclidean space. The Euclidean distance
between any two nodes in this space approximates the length of the shortest
path between them in the given graph. Later, at runtime, a shortest path
between any two nodes can be computed with A* search using the Euclidean
distances as heuristic. Our preprocessing algorithm, called FastMap, is
inspired by the data mining algorithm of the same name and runs in near-linear
time. Hence, FastMap is orders of magnitude faster than competing approaches
that produce a Euclidean embedding using Semidefinite Programming. FastMap also
produces admissible and consistent heuristics and therefore guarantees the
generation of shortest paths. Moreover, FastMap applies to general undirected
graphs for which many traditional heuristics, such as the Manhattan Distance
heuristic, are not well defined. Empirically, we demonstrate that A* search
using the FastMap heuristic is competitive with A* search using other
state-of-the-art heuristics, such as the Differential heuristic
Embedding Directed Graphs in Potential Fields Using FastMap-D
Embedding undirected graphs in a Euclidean space has many computational
benefits. FastMap is an efficient embedding algorithm that facilitates a
geometric interpretation of problems posed on undirected graphs. However,
Euclidean distances are inherently symmetric and, thus, Euclidean embeddings
cannot be used for directed graphs. In this paper, we present FastMap-D, an
efficient generalization of FastMap to directed graphs. FastMap-D embeds
vertices using a potential field to capture the asymmetry between the pairwise
distances in directed graphs. FastMap-D learns a potential function to define
the potential field using a machine learning module. In experiments on various
kinds of directed graphs, we demonstrate the advantage of FastMap-D over other
approaches.Comment: 9 pages, Published in Symposium on Combinatorial Search(SoCS-2020).
Erratum with updated Result
Active and driven hydrodynamic crystals
Motivated by the experimental ability to produce monodisperse particles in
microfluidic devices, we study theoretically the hydrodynamic stability of
driven and active crystals. We first recall the theoretical tools allowing to
quantify the dynamics of elongated particles in a confined fluid. In this
regime hydrodynamic interactions between particles arise from a superposition
of potential dipolar singularities. We exploit this feature to derive the
equations of motion for the particle positions and orientations. After showing
that all five planar Bravais lattices are stationary solutions of the equations
of motion, we consider separately the case where the particles are passively
driven by an external force, and the situation where they are self-propelling.
We first demonstrate that phonon modes propagate in driven crystals, which are
always marginally stable. The spatial structure of the eigenmodes depend solely
on the symmetries of the lattices, and on the orientation of the driving force.
For active crystals, the stability of the particle positions and orientations
depends not only on the symmetry of the crystals but also on the perturbation
wavelengths and on the crystal density. Unlike unconfined fluids, the stability
of active crystals is independent of the nature of the propulsion mechanism at
the single particle level. The square and rectangular lattices are found to be
linearly unstable at short wavelengths provided the volume fraction of the
crystals is high enough. Differently, hexagonal, oblique, and face-centered
crystals are always unstable. Our work provides a theoretical basis for future
experimental work on flowing microfluidic crystals.Comment: 10 pages, 10 figure
The long-time dynamics of two hydrodynamically-coupled swimming cells
Swimming micro-organisms such as bacteria or spermatozoa are typically found
in dense suspensions, and exhibit collective modes of locomotion qualitatively
different from that displayed by isolated cells. In the dilute limit where
fluid-mediated interactions can be treated rigorously, the long-time
hydrodynamics of a collection of cells result from interactions with many other
cells, and as such typically eludes an analytical approach. Here we consider
the only case where such problem can be treated rigorously analytically, namely
when the cells have spatially confined trajectories, such as the spermatozoa of
some marine invertebrates. We consider two spherical cells swimming, when
isolated, with arbitrary circular trajectories, and derive the long-time
kinematics of their relative locomotion. We show that in the dilute limit where
the cells are much further away than their size, and the size of their circular
motion, a separation of time scale occurs between a fast (intrinsic) swimming
time, and a slow time where hydrodynamic interactions lead to change in the
relative position and orientation of the swimmers. We perform a multiple-scale
analysis and derive the effective dynamical system - of dimension two -
describing the long-time behavior of the pair of cells. We show that the system
displays one type of equilibrium, and two types of rotational equilibrium, all
of which are found to be unstable. A detailed mathematical analysis of the
dynamical systems further allows us to show that only two cell-cell behaviors
are possible in the limit of , either the cells are attracted to
each other (possibly monotonically), or they are repelled (possibly
monotonically as well), which we confirm with numerical computations
Design of a conservation program assited by genetic markers in a herd of Yacumeño cattle in Santa Cruz – Bolivia
La Facultad de Ciencias Veterinarias de la UAGRM consolido un programa de conservación del ganado Bovino Criollo Yacumeño a partir del año 2004. La conservación de recursos zoogenéticos generalmente se realiza en poblaciones pequeñas, las cuales tienen un tamaño poblacional efectivo muy reducido. En estos casos es importante realizar apareamientos que mantengan la variabilidad genética alta y los niveles de consanguinidad bajos. El objetivo del presente trabajo consistió en determinar las paternidades y los linajes paternos mediante el uso de marcadores moleculares. El ADN se extrajo partir de muestras de sangre de los 149 animales del hato y se procedió a genotipificar todos los individuos utilizando 18 microsatélites y 7 marcadores del cromosoma Y. Los resultados obtenidos permitieron identificar dos grandes grupos de vacas y 3 linajes paternos. Esta información servirá para diseñar un programa reproductivo que evite en lo posible la perdida de la variabilidad genética y mantenga niveles aceptables de consaguinidad en el hato a conservar.The Faculty of Veterinary Science of the UAGRM consolidated a conservation program of the Yacumeño Creole cattle. The conservation of zoogenetic resources is performed generally in small populations, which usually has a reduced effective population size. In those cases it is important to keep high genetic variability and low levels of consanguinity by performing specific mating among the animals. The main objective of this research consisted in determine the paternity and male lines by using molecular markers. The DNA was extracted from blood sample of 149 animals and were genotyped all the individuals using 18 microsatellites and 7 markers of the Y chromosome. The results obtained allowed to identify two groups of cows and 3 male lines. This information will be useful to design a reproductive program that avoids to a certain degree the lost of genetic variability and will keep acceptable levels of consanguinity among the herd.Fil: Pereira, J. A. C.. Universidad Autónoma Gabriel René Moreno; BoliviaFil: Carino, M. H.. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico La Plata. Instituto de Genética Veterinaria "Ingeniero Fernando Noel Dulout"; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias; ArgentinaFil: Hoyos, R.. Universidad Autónoma Gabriel René Moreno; BoliviaFil: Rogberg Muñoz, Andres. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico La Plata. Instituto de Genética Veterinaria "Ingeniero Fernando Noel Dulout"; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias; ArgentinaFil: Loza, A.. Universidad Autónoma Gabriel René Moreno; BoliviaFil: Liron, Juan Pedro. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico La Plata. Instituto de Genética Veterinaria "Ingeniero Fernando Noel Dulout"; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias; ArgentinaFil: Mamani, T.. Universidad Autónoma Gabriel René Moreno; BoliviaFil: Ripoli, MarÃa Verónica. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico La Plata. Instituto de Genética Veterinaria "Ingeniero Fernando Noel Dulout"; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias; ArgentinaFil: Giovambattista, Guillermo. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico La Plata. Instituto de Genética Veterinaria "Ingeniero Fernando Noel Dulout"; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias; Argentin
The effectiveness of acellular nerve allografts compared to autografts in animal models:A systematic review and meta-analysis
Background Treatment of nerve injuries proves to be a worldwide clinical challenge. Acellular nerve allografts are suggested to be a promising alternative for bridging a nerve gap to the current gold standard, an autologous nerve graft. Objective To systematically review the efficacy of the acellular nerve allograft, its difference from the gold standard (the nerve autograft) and to discuss its possible indications. Material and methods PubMed, Embase and Web of Science were systematically searched until the 4th of January 2022. Original peer reviewed paper that presented 1) distinctive data; 2) a clear comparison between not immunologically processed acellular allografts and autologous nerve transfers; 3) was performed in laboratory animals of all species and sex. Meta analyses and subgroup analyses (for graft length and species) were conducted for muscle weight, sciatic function index, ankle angle, nerve conduction velocity, axon count diameter, tetanic contraction and amplitude using a Random effects model. Subgroup analyses were conducted on graft length and species. Results Fifty articles were included in this review and all were included in the meta-analyses. An acellular allograft resulted in a significantly lower muscle weight, sciatic function index, ankle angle, nerve conduction velocity, axon count and smaller diameter, tetanic contraction compared to an autologous nerve graft. No difference was found in amplitude between acellular allografts and autologous nerve transfers. Post hoc subgroup analyses of graft length showed a significant reduced muscle weight in long grafts versus small and medium length grafts. All included studies showed a large variance in methodological design. Conclusion Our review shows that the included studies, investigating the use of acellular allografts, showed a large variance in methodological design and are as a consequence difficult to compare. Nevertheless, our results indicate that treating a nerve gap with an allograft results in an inferior nerve recovery compared to an autograft in seven out of eight outcomes assessed in experimental animals. In addition, based on our preliminary post hoc subgroup analyses we suggest that when an allograft is being used an allograft in short and medium (0-1cm, > 1-2cm) nerve gaps is preferred over an allograft in long (> 2cm) nerve gaps.</p
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