1,610 research outputs found
Dispersal in Mastomys natalensis mice: use of fine-scale genetic analyses for pest management
Mastomys natalensis is the major pest rodent in sub-Saharan Africa. In this study, population genetic techniques were used to gain new insights into its dispersal behaviour, a critical parameter in pest management. Using 11 microsatellites, 272 individuals from a 300 ha area in Tanzania were genotyped. Genetic diversity was high, with no isolation by distance and little differentiation between field plots far apart, indicating a large effective population size and high dispersal rates in agreement with ecological observations. On the other hand, genetic differentiation between nearby field plots, isolation by distance within a single field plot and kin clustering were also observed. This apparent contradiction may be explained by yearly founder effects of a small number of breeding individuals per square area, which is consistent with the presence of linkage disequilibrium. An alternative, not mutually exclusive explanation is that there are both dispersing and sedentary animals in the population. The low-density field plots were characterized by low relatedness and small genetic distances to other field plots, indicating a high turnover rate and negative density-dependent dispersal. In one field plot female-biased dispersal was observed, which may be related to inbreeding avoidance or female competition for resources. Most juveniles appeared to be local recruits, but they did not seem to stay in their native area for more than two months. Finally, possible implications for pest management are discusse
Adaptive neural network control of fes-induced cyclical lower leg movements
As a first step to the control of paraplegic gait by functional electrical stimulation (FES), the control of the swinging lower leg is being studied. This paper deals with a neural control system, that has been developed for this case. The control system has been tested for a model of the swinging lower leg using computer simulations. The neural controller was trained by supervised learning (SL) and by backpropagation through time (BTT). The performance of the controller with random initial weights was poor after training with BTT and fair after SL. BTT training of the neural controller with weights, which had been initialized by SL, resulted in good control. Training with BTT thus improved the performance of the controller that initially had been trained by SL. An adaptive neural control system based on BTT has been proposed and partially tested. The controller adapted relatively fast to the change of an important model parameter
Team Achievement Goals and Sports Team Performance
This study focuses on team achievement goals and performance outcomes in interdependent sports teams. Team achievement goals reflect shared motivational states that exist exclusively at the team level. In a survey among 310 members of 29 premier-league field-hockey teams, team-level performance-approach, performance-avoidance, mastery-approach, and mastery-avoidance achievement goals explained 69% of the overall variance in team performance and 16% after controlling for previous performance. Teams performed better to the extent they were more approach- and less avoidance oriented in terms of both mastery and performance, although mastery-approach goals related to early-season team performance rather than predicting later changes in team performance
Construct validity of multi-source performance ratings: An examination of the relationship of self-, supervisor-, and peer-ratings with cognitive and personality measures
Although more and more organizations prefer using multi-source performance ratings or 3601 feedback over traditional performance appraisals, researchers have been rather
skeptical regarding the reliability and validity of such ratings. The present study examined the validity of self-, supervisor-, and peer-ratings of 195 employees in a Dutch public organization, using scores on an In-Basket exercise, an intelligence test, and a personality questionnaire as external criterion measures. Interrater agreement ranged from .28 to .38. Variance in the ratings was explained by both method and content factors. Support for the external construct validity was rather weak. Supervisor-ratings were not found to be superior to self- and peer-ratings in predicting the scores on the external measures
Hard X-ray lags in GRO J1719-24
We have used the Fourier cross spectra of GRO J1719-24, as obtained with
BATSE, to estimate the phase lags between the X-ray flux variations in the
20--50 and 50--100 keV energy bands as a function of Fourier frequency in the
interval 0.002--0.488 Hz. Our analysis covers the entire ~80 day X-ray outburst
of this black-hole candidate, following the first X-ray detection on 1993
September 25. The X-ray variations in the 50--100 keV band lag those in the
20--50 keV energy band by an approximately constant phase difference of 0.072
+/- 0.010 rad in the frequency interval 0.02--0.20 Hz. The peak phase lags in
the interval 0.02--0.20 Hz are about twice those of Cyg X-1 and GRO
J0422+32.These results are consistent with models for Comptonization regions
composed of extended non-uniform clouds around the central source.Comment: 10 pages, including 4 postscript figures, AASTEX. Accepted for
publication by Ap
Probing spacetime foam with extragalactic sources
Due to quantum fluctuations, spacetime is probably ``foamy'' on very small
scales. We propose to detect this texture of spacetime foam by looking for
core-halo structures in the images of distant quasars. We find that the Very
Large Telescope interferometer will be on the verge of being able to probe the
fabric of spacetime when it reaches its design performance. Our method also
allows us to use spacetime foam physics and physics of computation to infer the
existence of dark energy/matter, independent of the evidence from recent
cosmological observations.Comment: LaTeX, 11 pages, 1 figure; version submitted to PRL; several
references added; very useful comments and suggestions by Eric Perlman
incorporate
Chiral symmetry restoration in linear sigma models with different numbers of quark flavors
Chiral symmetry restoration at nonzero temperature is studied in the
framework of the O(4) linear sigma model and the U(N_f)_r x U(N_f)_l linear
sigma model with N_f=2,3, and 4 quark flavors. We investigate the temperature
dependence of the masses of the scalar and pseudoscalar mesons, and the
non-strange, strange, and charm condensates within the Hartree approximation as
derived from the Cornwall-Jackiw-Tomboulis formalism. We find that the masses
of the non-strange and strange mesons at nonzero temperature depend sensitively
on the particular symmetry of the model and the number of light quark flavors
N_f. On the other hand, due to the large charm quark mass, neither do charmed
mesons significantly affect the properties of the other mesons, nor do their
masses change appreciably in the temperature range around the chiral symmetry
restoration temperature. In the chiral limit, the transition temperatures for
chiral symmetry restoration are surprisingly close to those found in lattice
QCD.Comment: 28 pages, 8 figure
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