7,285 research outputs found
Experimental investigation of orangutans’ lithic percussive and sharp stone tool behaviours
Early stone tools, and in particular sharp stone tools, arguably represent one of the most important technological milestones in human evolution. The production and use of sharp stone tools significantly widened the ecological niche of our ancestors, allowing them to exploit novel food resources. However, despite their importance, it is still unclear how these early lithic technologies emerged and which behaviours served as stepping-stones for the development of systematic lithic production in our lineage. One approach to answer this question is to collect comparative data on the stone tool making and using abilities of our closest living relatives, the great apes, to reconstruct the potential stone-related behaviours of early hominins. To this end, we tested both the individual and the social learning abilities of five orangutans to make and use stone tools. Although the orangutans did not make sharp stone tools initially, three individuals spontaneously engaged in lithic percussion, and sharp stone pieces were produced under later experimental conditions. Furthermore, when provided with a human-made sharp stone, one orangutan spontaneously used it as a cutting tool. Contrary to previous experiments, social demonstrations did not considerably improve the stone tool making and using abilities of orangutans. Our study is the first to systematically investigate the stone tool making and using abilities of untrained, unenculturated orangutans showing that two proposed pre-requisites for the emergence of early lithic technologies–lithic percussion and the recognition of sharp-edged stones as cutting tools–are present in this species. We discuss the implications that ours and previous great ape stone tool experiments have for understanding the initial stages of lithic technologies in our lineage
The Influence of Habitat and Fishing on Reef Fish Assemblages in Cuba
The abundance of selected fish species was estimated using the stationary visual census technique in the northwestern region of the Cuban shelf. A total of 26,809 individuals of 32 species were counted in 1,172 stationary point censuses made at 10 reef sites along the coast. We found that the abundance patterns were most probably the consequence of the presence/absence of mangroves and seagrass beds in adjacent lagoon areas. A second factor influencing the spatial variation appeared to be overfishing on an east-west gradient, with lower abundances of commercially targeted species near Havana City in the east
Environment shapes sleep patterns in a wild nocturnal primate
Among primates, the suborder Haplorhini is considered to have evolved a consolidated monophasic sleep pattern, with diurnal species requiring a shorter sleep duration than nocturnal species. Only a few primate species have been systematically studied in their natural habitat where environmental variables, including temperature and light, have a major influence on sleep and activity patterns. Here we report the first sleep study on a nocturnal primate performed in the wild. We fitted seven wild Javan slow lorises (Nycticebus javanicus) in West Java, Indonesia with accelerometers that collected activity data, and installed climate loggers in each individual's home range to collect ambient temperature readings (over 321 days in total). All individuals showed a strictly nocturnal pattern of activity and displayed a striking synchronisation of onset and cessation of activity in relation to sunset and sunrise. The longest consolidated rest episodes were typically clustered near the beginning and towards the end of the light period, and this pattern was inversely related to daily fluctuations of the ambient temperature. The striking relationship between daily activity patterns, light levels and temperature suggests a major role of the environment in shaping the daily architecture of waking and sleep. We concluded that well-known phenotypic variability in daily sleep amount and architecture across species may represent an adaptation to changes in the environment. Our data suggest that the consolidated monophasic sleep patterns shaped by environmental pressures observed in slow lorises represent phylogenetic inertia in the evolution of sleep patterns in humans
Review of tau lifetime measurements
The measurements of the mean lifetime of the tau lepton are reviewed. The
conditions for measuring the lifetime at various e+e- colliders are compared
and the analysis methods are briefly described. The new developments since the
previous Workshop on Tau Lepton Physics are listed. The world average is
tau_tau = 290.5 +- 1.0 fs. The LEP experiments dominate this average and have
analyzed nearly all of their data. In anticipation of the next era of precision
measurements at CLEO and the b factories, the important sources of systematic
errors and the treatment of systematic biases are discussed.Comment: Invited talk presented at the Fifth International Workshop on Tau
Lepton Physics, Santander, Spain, 14-17 September 1998; 10 pages, 8 figure
Spitzer Imaging of the Nearby Rich Young Cluster, Cep OB3b
We map the full extent of a rich massive young cluster in the Cep OB3b
association with the IRAC and MIPS instruments aboard the {\it Spitzer} Space
Telescope and the ACIS instrument aboard the X-Ray Observatory.
At 700 pc, it is revealed to be the second nearest large ( member),
young ( Myr) cluster known. In contrast to the nearest large cluster, the
Orion Nebula Cluster, Cep OB3b is only lightly obscured and is mostly located
in a large cavity carved out of the surrounding molecular cloud. Our infrared
and X-ray datasets, as well as visible photometry from the literature, are used
to take a census of the young stars in Cep OB3b. We find that the young stars
within the cluster are concentrated in two sub-clusters; an eastern
sub-cluster, near the Cep B molecular clump, and a western sub-cluster, near
the Cep F molecular clump. Using our census of young stars, we examine the
fraction of young stars with infrared excesses indicative of circumstellar
disks. We create a map of the disk fraction throughout the cluster and find
that it is spatially variable. Due to these spatial variations, the two
sub-clusters exhibit substantially different average disk fractions from each
other: and . We discuss whether the discrepant disk
fractions are due to the photodestruction of disks by the high mass members of
the cluster or whether they result from differences in the ages of the
sub-clusters. We conclude that the discrepant disk fractions are most likely
due to differences in the ages.Comment: 48 Pages, 12 figures, 6 table
Collective Action and Decision Making: An Analysis of Economic Modeling and Environmental Free-Riding
It is hypothesized that tool-assisted excavation of plant underground storage organs (USOs) played an adaptive role in hominin evolution and was also once considered a uniquely human behavior. Recent data indicate that savanna chimpanzees also use tools to excavate edible USOs. However, those chimpanzees remain largely unhabituated and we lack direct observations of this behavior in the wild. To fill this gap in our knowledge of hominoid USO extractive foraging, we conducted tool-mediated excavation experiments with captive chimpanzees naive to this behavior. We presented the chimpanzees with the opportunity to use tools in order to excavate artificially-placed underground foods in their naturally forested outdoor enclosure. No guidance or demonstration was given to the chimpanzees at any time. The chimpanzees used tools spontaneously in order to excavate the underground foods. They exhibited six different tool use behaviors in the context of excavation: probe, perforate, dig, pound, enlarge and shovel. However, they still excavated manually more often than they did with tools. Chimpanzees were selective in their choice of tools that we provided, preferring longer tools for excavation. They also obtained their own tools mainly from naturally occurring vegetation and transported them to the excavation site. They reused some tools throughout the study. Our new data provide a direction for the study of variables relevant to modeling USO extractive foraging by early hominins.Funding Agencies|La Caixa Foundation Spain [LCF/BQ/EU15/10350002]; University of Oslo, Department of Biosciences, Norway</p
Magnetism of small V clusters embedded in a Cu fcc matrix: an ab initio study
We present extensive first principles density functional theory (DFT)
calculations dedicated to analyze the magnetic and electronic properties of
small V clusters (n=1,2,3,4,5,6) embedded in a Cu fcc matrix. We consider
different cluster structures such as: i) a single V impurity, ii) several
V dimers having different interatomic distance and varying local atomic
environment, iii) V and iv) V clusters for which we assume compact
as well as 2- and 1-dimensional atomic configurations and finally, in the case
of the v) V and vi) V structures we consider a square pyramid and a
square bipyramid together with linear arrays, respectively. In all cases, the V
atoms are embedded as substitutional impurities in the Cu network. In general,
and as in the free standing case, we have found that the V clusters tend to
form compact atomic arrays within the cooper matrix. Our calculated non
spin-polarized density of states at the V sites shows a complex peaked
structure around the Fermi level that strongly changes as a function of both
the interatomic distance and local atomic environment, a result that
anticipates a non trivial magnetic behavior. In fact, our DFT calculations
reveal, in each one of our clusters systems, the existence of different
magnetic solutions (ferromagnetic, ferrimagnetic, and antiferromagnetic) with
very small energy differences among them, a result that could lead to the
existence of complex finite-temperature magnetic properties. Finally, we
compare our results with recent experimental measurements.Comment: 7 pages and 4 figure
A Digital Predistortion Technique Based on a NARX Network to Linearize GaN Class F Power Amplifiers (poster)
This work presents a novel Digital Predistortion (DPD) scheme based on a NARX network, suitable for linearizing power amplifiers (PAs). The NARX network is a Recurrent Neural Network (RNN) with embedded memory that allows efficient modeling of nonlinear systems. Its neural architecture is very effective to model long term dependencies, such as the typical memory effects of PAs. To demonstrate the feasibility of the NARX network as a DPD system, a GaN class F PA with two LTE signals with 5 MHz of bandwidth is used. Experimental results show a distortion correction better than 10 dB
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