2,406 research outputs found
Conservation genetic assessment of savannah elephants (Loxodonta africana) in the Greater Kruger Biosphere, South Africa
Savannah elephant populations have been severely reduced and fragmented throughout its remaining range. In general, however, there is limited information regarding their genetic status, which is essential knowledge for conservation. We investigated patterns of genetic variation in savannah elephants from the Greater Kruger Biosphere, with a focus on those in previously unstudied nature reserves adjacent to Kruger National Park, using dung samples from 294 individuals and 18 microsatellites. The results of genetic structure analyses using several different methods of ordination and Bayesian clustering strongly suggest that elephants throughout the Greater Kruger National Park (GKNP) constitute a single population. No evidence of a recent genetic bottleneck was detected using three moment-based approaches and two coalescent likelihood methods. The apparent absence of a recent genetic bottleneck associated with the known early 1900s demographic bottleneck may result from a combination of rapid post-bottleneck population growth, immigration and long generation time. Point estimates of contemporary effective population size (Ne) for the GKNP were ~ 500â700, that is, at the low end of the range of Ne values that have been proposed for maintaining evolutionary potential and the current ratio of Ne to census population size (Nc) may be quite low (<0.1). This study illustrates the difficulties in assessing the impacts on Ne in populations that have suffered demographic crashes but have recovered rapidly and received gene flow, particularly in species with long generation times in which genetic time lags are longer. This work provides a starting point and baseline information for genetic monitoring of the GKNP elephants
A comparison of load cell and pressure sensors to measure in-water force in young competitive swimmers
The purpose of this study was to compare the in-water force of young competitive swimmers using tethered
swimming and differential pressure sensors. Thirty-one swimmers (16 girls and 15 boys) were randomly assigned
to perform two in-water tests. Swimmers completed two maximum bouts of 25 m front crawl with a differential
pressure system and a 30 s maximum bout with an attached load cell (tethered-swimming). The peak force
(FPEAK, in N) of dominant and non-dominant upper limbs was retrieved for further analysis. Comparison between
methods revealed significant differences in all force variables (p †0.05) and the biases (mean differences) were
large in girls (FPEAK dominant, 45.89 N; FPEAK non-dominant, 43.79 N) and boys (FPEAK dominant, 67.26 N; FPEAK
non-dominant, 61.78 N). Despite that, simple linear regression models between the two methods showed significant
relationships with a moderate effect in all variables for girls, whereas in boys a high and moderate effect
was verified for FPEAK of dominant and non-dominant limbs (respectively). It seems that using pressure sensors
and tethered swimming leads to different FPEAK values in young competitive, where correction factors are needed
to compare data between both methods.The authors would like to thank all swimming coaches for their
voluntary support as well as all the swimmers involved. This project was
supported by the Portuguese Foundation for Science and Technology
(FCT), I.P., under Grants 2020.08326.BD and UID 04045/2020.info:eu-repo/semantics/publishedVersio
Conservation genetic assessment of savannah elephants (Loxodonta africana) in the Greater Kruger Biosphere, South Africa
Savannah elephant populations have been severely reduced and fragmented throughout its remaining range. In general, however, there is limited information regarding their genetic status, which is essential knowledge for conservation. We investigated patterns of genetic variation in savannah elephants from the Greater Kruger Biosphere, with a focus on those in previously unstudied nature reserves adjacent to Kruger National Park, using dung samples from 294 individuals and 18 microsatellites. The results of genetic structure analyses using several different methods of ordination and Bayesian clustering strongly suggest that elephants throughout the Greater Kruger National Park (GKNP) constitute a single population. No evidence of a recent genetic bottleneck was detected using three moment-based approaches and two coalescent likelihood methods. The apparent absence of a recent genetic bottleneck associated with the known early 1900s demographic bottleneck may result from a combination of rapid post-bottleneck population growth, immigration and long generation time. Point estimates of contemporary effective population size (Ne) for the GKNP were ~ 500â700, that is, at the low end of the range of Ne values that have been proposed for maintaining evolutionary potential and the current ratio of Ne to census population size (Nc) may be quite low (<0.1). This study illustrates the difficulties in assessing the impacts on Ne in populations that have suffered demographic crashes but have recovered rapidly and received gene flow, particularly in species with long generation times in which genetic time lags are longer. This work provides a starting point and baseline information for genetic monitoring of the GKNP elephants
Metal-insulator transition at B=0 in an ultra-low density () two dimensional GaAs/AlGaAs hole gas
We have observed a metal-insulator transition in an ultra-low density two
dimensional hole gas formed in a high quality GaAs-AlGaAs heterostructure at
B=0. At the highest carrier density studied () the hole gas is strongly metallic, with an exceptional mobility of
. The low disorder and strength of the many-body
interactions in this sample are highlighted by the observation of re-entrant
metal insulator transitions in both the fractional () and integer
() quantum Hall regimes. On reducing the carrier density the
temperature and electric field dependence of the resistivity show that the
sample is still metallic at (), becoming
insulating at . Our results indicate that
electron-electron interactions are dominant at these low densities, pointing to
the many body origins of this metal-insulator transition. We note that the
value of at the transition () is large enough to allow
the formation of a weakly pinned Wigner crystal, and is approaching the value
calculated for the condensation of a pure Wigner crystal.Comment: 4 pages, latex, 4 postscript figures, submitted to EP2DS-12 on 21st
August 1997, to appear in Physica
Modelling the 200 m front-crawl performance predictors at the winter season peak
This study aimed to identify potential predictors of 200 m front crawl performance at the winter season peak based on the anthropometric, physiological and biomechanical domains. Twelve expert male swimmers completed an incremental 7 Ă 200 m step test immediately after their most important winter competitions. Measurements were made of: (i) height, body mass and arm span as anthropometrical parameters; (ii) velocity at a 4 mmol·L-1 lactate concentration (V4), maximal oxygen uptake (VO2mĂĄx) and energy cost (C), as physiological parameters; (iii) stroke frequency (SF), stroke length (SL), stroke index (SI) and propelling efficiency (Æp) as biomechanical indicators; and (iv) 200 m front crawl race time in official long course competitions. Spearman correlation coefficients identified V4 as the single factor having significant relationship with performance. Simple regression analysis determined V4, SI and arm span as the most relevant variables of each group. Multiple linear regression models showed that physiological factors explained better (59%) the variation in performance at this stage of the season, followed by the biomechanical (14%) ones. Therefore, V4 can be one important aspect for training control and diagnosis for those who want to achieve success in the 200 m front crawl at the winter season peakThis research was funded by the Portuguese Science and Technology Foundation, under the project UID04045/2020info:eu-repo/semantics/publishedVersio
Role Of Disorder In The Conduction Mechanism In Polyanilines
We present the first theoretical calculations of the electronic structure of long (200 rings) linear chains of polyaniline, ranging in composition from leucoemeraldine to emeraldine, allowing for compositional disorder in that the sequence of quinoid-benzenoid groups is random. We show that random protonation of the disordered polymers may induce p-type conductivity: This process pulls the Fermi energy down into the valence band, past localized band tails, to extended states. The effect is only seen if disorder is taken into account. © 1989 The American Physical Society.63778678
Kinetic analysis of water fitness exercises: contributions for strength development
The evaluation of propulsive forces in water allows the selection of the most appropriate
strategies to develop strength during water fitness sessions. The aim of this study was threefold: (i)
to analyze the rate of force production; (ii) to analyze the rate of force variation; and (iii) to compare
limbsâ symmetry in two water fitness exercises. Twentyâtwo young health subjects (age: 21.23 ± 1.51
years old, body mass: 67.04 ± 9.31 kg, and height: 166.36 ± 8.01 cm) performed incremental protocols
of horizontal adduction (HA) and rocking horse (RHadd), from 105 until 150 bâminâ1. Data acquisition
required an isokinetic dynamometer and a differential pressure system that allowed the assessment
of (a) isometric peak force of dominant upper limb (IsometricFD); (b) propulsive peak force of
dominant upper limb (PropulsiveFD); and (c) propulsive peak force of nondominant upper limb
(PropulsiveFND). Significant differences were found in the rate of force production (RateFD) between
the majority cadences in both exercises. The RateFD reached ~68% of the force in dryâland conditions,
and lower cadences promoted a higher rate of force variation (ÎForce). Most actions were
asymmetric, except for the HA at 135 bâminâ1. In conclusion, the musical cadence of 135 bâminâ1
seems to elicit a desired rate of force production with a symmetric motion in both exercises.This work was supported by national funding through the Portuguese Foundation for Science and Technology, I.P., under project UID/DTP/04045/2019info:eu-repo/semantics/publishedVersio
Resistive and propulsive forces in wheelchair racing: a brief review
Wheelchair racing is one of the most important sports in the Paralympics. The detailed analysis of all parameters is of great importance to achieve sporting excellence in this modality. In wheelchair racing, resistive and propulsive forces determine the movement of the athlete-wheelchair system. Most of propulsive forces are generated by the strength of individuals. As a result, strength levels play an important role in propelling the athlete-wheelchair system. Thus, the main objective of this study is to provide a set of methodologies to assess propulsive and resistive forces. The manuscript presents different methods and procedures, based on previous studies, that can be used for wheelchair racing athletes. Resistive forces in wheelchair racing can be evaluated by analytical procedures, experimental tests, and numerical simulations. Moreover, the strength of athletes' upper limbs to generate propulsion in wheelchair races can be assessed by dynamometry, one-repetition maximum, and medicine ball throw test. It may be that the tests presented may be useful to predict the strength and endurance of athletes' upper limbs. However, this competitive sport still presents a considerable gap in the Paralympics research. Currently, in Paralympic sport, evidence-based methodologies are lacking, making it an issue for athletes, coaches and researchers to support their work on scientific evidences.This research is supported by the Portuguese Foundation for Science and Technology, I.P. (project UIDB04045/2020) and The APC. It has been funded by the Research Center in Sports Health and Human Development, CovilhA, Portugal.info:eu-repo/semantics/publishedVersio
Critical temperature for the two-dimensional attractive Hubbard Model
The critical temperature for the attractive Hubbard model on a square lattice
is determined from the analysis of two independent quantities, the helicity
modulus, , and the pairing correlation function, . These
quantities have been calculated through Quantum Monte Carlo simulations for
lattices up to , and for several densities, in the
intermediate-coupling regime. Imposing the universal-jump condition for an
accurately calculated , together with thorough finite-size scaling
analyses (in the spirit of the phenomenological renormalization group) of
, suggests that is considerably higher than hitherto assumed.Comment: 5 pages, 6 figures. Accepted for publication in Phys. Rev.
The Hahn Quantum Variational Calculus
We introduce the Hahn quantum variational calculus. Necessary and sufficient
optimality conditions for the basic, isoperimetric, and Hahn quantum Lagrange
problems, are studied. We also show the validity of Leitmann's direct method
for the Hahn quantum variational calculus, and give explicit solutions to some
concrete problems. To illustrate the results, we provide several examples and
discuss a quantum version of the well known Ramsey model of economics.Comment: Submitted: 3/March/2010; 4th revision: 9/June/2010; accepted:
18/June/2010; for publication in Journal of Optimization Theory and
Application
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