1,183 research outputs found
The dynamical environment of asteroid 21 Lutetia according to different internal models
One of the most accurate models currently used to represent the gravity field
of irregular bodies is the polyhedral approach. In this model, the mass of the
body is assumed to be homogeneous, which may not be true for a real object. The
main goal of the present paper is to study the dynamical effects induced by
three different internal structures (uniform, three- and four-layers) of
asteroid (21) Lutetia, an object that recent results from space probe suggest
being at least partially differentiated. The Mascon gravity approach used in
the present work, consists of dividing each tetrahedron into eight parts to
calculate the gravitational field around the asteroid. The zero-velocity curves
show that the greatest displacement of the equilibrium points occurs in the
position of the E4 point for the four-layers structure and the smallest one
occurs in the position of the E3 point for the three-layers structure.
Moreover, stability against impact shows that the planar limit gets slightly
closer to the body with the four-layered structure.
We then investigated the stability of orbital motion in the equatorial plane
of (21) Lutetia and propose numerical stability criteria to map the region of
stable motions. Layered structures could stabilize orbits that were unstable in
the homogeneous model.Comment: 10 pages, 7 figures, and 4 Tables. Accepted for publication in MNRA
Do Cash Transfers Improve Birth Outcomes? Evidence from Matched Vital Statistics, Program and Social Security Data
There is limited empirical evidence on whether cash transfers to poor pregnant women improve children's birth outcomes and potentially help weaken the cycle of intergenerational poverty. Using a unique array of program and social security administrative micro-data matched to longitudinal vital statistics in Uruguay, we estimate that participation in a generous social assistance program led to a sizable reduction in the incidence of low birthweight. The effect is due to faster intrauterine growth rather than longer gestational length. Our findings are consistent with improved maternal nutrition during pregnancy being a key driver of improved birthweight. (JEL I14, I32, I38, J13, J16, O15) </jats:p
4,4′-Di-tert-butyl-2,2′-dipyridinium dichloride
In the title compound, C18H26N2
2+·2Cl−, the complete dication is generated by crystallographic inversion symmetry; both N atoms are protonated and engaged in strong and highly directional N—H⋯Cl hydrogen bonds. Additional weak C—H⋯Cl contacts promote the formation of a tape along ca. [110]. The crystal structure can be described by the parallel packing of these tapes. The crystal studied was a non-merohedral twin with twin law [−1 0 0, 0 −1 0, −0.887 0.179 1] and the final BASF parameter refining to 0.026 (2)
Fermentative enzymes activity in soybean roots and nodules under hypoxia and post-hypoxia conditions.
AER Auditory Filtering and CPG for Robot Control
Address-Event-Representation (AER) is a
communication protocol for transferring asynchronous events
between VLSI chips, originally developed for bio-inspired
processing systems (for example, image processing). The event
information in an AER system is transferred using a highspeed
digital parallel bus. This paper presents an experiment
using AER for sensing, processing and finally actuating a
Robot. The AER output of a silicon cochlea is processed by an
AER filter implemented on a FPGA to produce rhythmic
walking in a humanoid robot (Redbot). We have implemented
both the AER rhythm detector and the Central Pattern
Generator (CPG) on a Spartan II FPGA which is part of a
USB-AER platform developed by some of the authors.Commission of the European Communities IST-2001-34124 (CAVIAR)Comisión Interministerial de Ciencia y TecnologÃa TIC-2003-08164-C03-0
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