198 research outputs found
Topology of the conceptual network of language
We define two words in a language to be connected if they express similar
concepts. The network of connections among the many thousands of words that
make up a language is important not only for the study of the structure and
evolution of languages, but also for cognitive science. We study this issue
quantitatively, by mapping out the conceptual network of the English language,
with the connections being defined by the entries in a Thesaurus dictionary. We
find that this network presents a small-world structure, with an amazingly
small average shortest path, and appears to exhibit an asymptotic scale-free
feature with algebraic connectivity distribution.Comment: 4 pages, 2 figures, Revte
Signatures of small-world and scale-free properties in large computer programs
A large computer program is typically divided into many hundreds or even
thousands of smaller units, whose logical connections define a network in a
natural way. This network reflects the internal structure of the program, and
defines the ``information flow'' within the program. We show that, (1) due to
its growth in time this network displays a scale-free feature in that the
probability of the number of links at a node obeys a power-law distribution,
and (2) as a result of performance optimization of the program the network has
a small-world structure. We believe that these features are generic for large
computer programs. Our work extends the previous studies on growing networks,
which have mostly been for physical networks, to the domain of computer
software.Comment: 4 pages, 1 figure, to appear in Phys. Rev.
Palynological evidence for environmental and climatic change in the lower Guadiana valley, Portugal, during the last 13 000 years
Pollen analysis of a 48 m AMS radiocarbon-dated sediment sequence from the Guadiana estuary provides the first record of Lateglacial and Holocene vegetation history in the Algarve province of Portugal. This paper focuses on the record of terrestrial pollen taxa, which document a series of forest expansions and declines during the period 13 000 cal. BP to 1600 cal. BP and provide insights into climate evolution in southwestern Iberia. The main vegetation phases identified in the Guadiana valley are (1) Lateglacial interstadial (Allerød) forest with Quercus and Pinus under a temperate, moist, continental climate;
(2) a Younger Dryas forest decline (Quercus) and expansion of pinewoods, xeric scrub and open ground habitats (with Juniperus, Artemisia, Ephedra distachya type, Centaurea scabiosa type) under arid and cold conditions; (3) an early Holocene forest/scrub/open-ground vegetation mosaic developing under a warm, dry and continental climate; (4) a maximum of Quercus forest and thermomediterranean evergreen taxa (Olea, Phillyrea, Pistacia) reflecting a warm, moist oceanic climate between c. 9000 cal. BP and c. 5000 cal. BP; and (5) the expansion of shrublands with Cistaceae and Ericaceae under a drier climatic regime and increasing anthropogenic activity since c. 5000 cal. BP. Holocene episodes of maximum climatic aridity are identified in the record of xerophytic taxa (Juniperus, Artemisia, Ephedra distachya type) centred around 10 200 cal. BP, 7800 cal. BP, 4800 cal. BP, 3100 cal. BP and 1700 cal. BP. Regional comparisons suggest a correlation of arid phases across southern Iberia and northwest Africa, which can be related to abrupt North Atlantic coolings (Bond events).Research Council studentship for WJF (NERC/S/A/2001/06109), with the support of Trinity College and the Department of Geography, University of Cambridg
Projectile breakup dynamics for Li + Co: kinematical analysis of - coincidences
A study of the kinematics of the - coincidences in the Li +
Co system at a bombarding energy of MeV is presented.
With exclusive measurements performed over different angular intervals it is
possible to identify the respective contributions of the sequential projectile
breakup and direct projectile breakup components. A careful analysis using a
semiclassical approach of these processes provides information on both their
lifetime and their distance of occurrence with respect to the target. Breakup
to the low-lying (near-threshold) continuum is delayed, and happens at large
internuclear distances. This suggests that the influence of the projectile
breakup on the complete fusion process can be related essentially to direct
breakup to the Li high-lying continuum spectrum. %Comment: Revised version including new Fig.3 and Fig.4 with new CDCC
calculations. Accepted for publication at Eur. Phys. Jour. A. 11 pages, 6
figure
- …