1,489 research outputs found
Adaptive walks in a gene network model of morphogenesis: insights into the Cambrian explosion
The emergence of complex patterns of organization close to the Cambrian
boundary is known to have happened over a (geologically) short period of time.
It involved the rapid diversification of body plans and stands as one of the
major transitions in evolution. How it took place is a controversial issue.
Here we explore this problem by considering a simple model of pattern formation
in multicellular organisms. By modeling gene network-based morphogenesis and
its evolution through adaptive walks, we explore the question of how
combinatorial explosions might have been actually involved in the Cambrian
event. Here we show that a small amount of genetic complexity including both
gene regulation and cell-cell signaling allows one to generate an extraordinary
repertoire of stable spatial patterns of gene expression compatible with
observed anteroposterior patterns in early development of metazoans. The
consequences for the understanding of the tempo and mode of the Cambrian event
are outlined.Comment: to appear in International Journal of Developmental Biology, special
issue on Evo-Devo (2003
Integrability of Five Dimensional Minimal Supergravity and Charged Rotating Black Holes
We explore the integrability of five-dimensional minimal supergravity in the
presence of three commuting Killing vectors. We argue that to see the
integrability structure of the theory one necessarily has to perform an Ehlers
reduction to two dimensions. A direct dimensional reduction to two dimensions
does not allow us to see the integrability of the theory in an easy way. This
situation is in contrast with vacuum five-dimensional gravity. We derive the
Belinski-Zakharov (BZ) Lax pair for minimal supergravity based on a symmetric
7x7 coset representative matrix for the coset G2/(SL(2,R) x SL(2,R)). We
elucidate the relationship between our BZ Lax pair and the group theoretic Lax
pair previously known in the literature. The BZ Lax pair allows us to
generalize the well-known BZ dressing method to five-dimensional minimal
supergravity. We show that the action of the three-dimensional hidden symmetry
transformations on the BZ dressing method is simply the group action on the BZ
vectors. As an illustration of our formalism, we obtain the doubly spinning
five-dimensional Myers-Perry black hole by applying solitonic transformations
on the Schwarzschild black hole. We also derive the Cvetic-Youm black hole by
applying solitonic transformations on the Reissner-Nordstrom black hole.Comment: 44 pages, 4 figure
A Fuzzy Data Fusion Solution to Enhance the QoS and the Energy Consumption in Wireless Sensor Networks
Usability analysis of a novel biometric authentication approach for android-based mobile devices
Mobile devices are widely replacing the standard personal computers thanks to their small size and user-friendly use. As a consequence, the amount of information, often confidential, exchanged through these devices is raising. This makes them potential targets of malicious network hackers. The use of simple passwords or PIN are not sufficient to provide a suitable security level for those applications requiring high protection levels on data and services. In this paper a biometric authentication system, as a running Android application, has been developed and implemented on a real mobile device. A system test on real users has been also carried out in order to evaluate the human-machine interaction quality, the recognition accuracy of the proposed technique, and the scheduling latency of the operating system and its degree of acceptance. Several measures, such as system usability, users satisfaction, and tolerable speed for identification, have been carried out in order to evaluate the performance of the proposed approach
An investigation of a three-dimensional natural convection problem using an adapted multigrid method
Available from British Library Document Supply Centre- DSC:DX86001 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo
Tuning branching in ceria nanocrystals
Branched nanocrystals (NCs) enable high atomic surface exposure within a crystalline network that provides avenues for charge transport. This combination of properties makes branched NCs particularly suitable for a range of applications where both interaction with the media and charge transport are involved. Herein we report on the colloidal synthesis of branched ceria NCs by means of a ligand-mediated overgrowth mechanism. In particular, the differential coverage of oleic acid as an X-type ligand at ceria facets with different atomic density, atomic coordination deficiency, and oxygen vacancy density resulted in a preferential growth in the [111] direction and thus in the formation of ceria octapods. Alcohols, through an esterification alcoholysis reaction, promoted faster growth rates that translated into nanostructures with higher geometrical complexity, increasing the branch aspect ratio and triggering the formation of side branches. On the other hand, the presence of water resulted in a significant reduction of the growth rate, decreasing the reaction yield and eliminating side branching, which we associate to a blocking of the surface reaction sites or a displacement of the alcoholysis reaction. Overall, adjusting the amounts of each chemical, well-defined branched ceria NCs with tuned number, thickness, and length of branches and with overall size ranging from 5 to 45 nm could be produced. We further demonstrate that such branched ceria NCs are able to provide higher surface areas and related oxygen storage capacities (OSC) than quasi-spherical NCs
The electronic Space Weather upper atmosphere (eSWua) project at INGV: advancements and state of the art
The eSWua project is based on measurements performed by all the instruments installed by the upper atmosphere physics group of the Istituto Nazionale di Geofisica e Vulcanologia, Italy and on all the related studies. The aim is the realization of a hardware-software system to standardize historical and real-time observations for different instruments. <br><br> An interactive Web site, supported by a well organized database, can be a powerful tool for the scientific and technological community in the field of telecommunications and space weather. The most common and useful database type for our purposes is the relational one, in which data are organized in tables for petabytes data archiving and the complete flexibility in data retrieving. <br><br> The project started in June 2005 and will last till August 2007. In the first phase the major effort has been focused on the design of hardware and database architecture. The first two databases related to the DPS4 digisonde and GISTM measurements are complete concerning populating, tests and output procedures. Details on the structure and Web tools concerning these two databases are presented, as well as the general description of the project and technical features
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