2,407 research outputs found
High-resolution spectroscopy of triplet states of Rb2 by femtosecond pump-probe photoionization of doped helium nanodroplets
The dynamics of vibrational wave packets in triplet states of rubidium dimers
(Rb2) formed on helium nanodroplets are studied using femtosecond pump-probe
photoionization spectroscopy. Due to fast desorption of the excited Rb2
molecules off the droplets and due to their low internal temperature, wave
packet oscillations can be followed up to very long pump-probe delay times
>1.5ns. In the first excited triplet state (1)^3\Sigma_g^+, full and fractional
revivals are observed with high contrast. Fourier analysis provides
high-resolution vibrational spectra which are in excellent agreement with ab
initio calculations
A new perspective on the irregular satellites of Saturn - II Dynamical and physical origin
The origin of the irregular satellites of the giant planets has been long
debated since their discovery. Their dynamical features argue against an
in-situ formation suggesting they are captured bodies, yet there is no global
consensus on the physical process at the basis of their capture. In this paper
we explore the collisional capture scenario, where the actual satellites
originated from impacts occurred within Saturn's influence sphere. By modeling
the inverse capture problem, we estimated the families of orbits of the
possible parent bodies and the specific impulse needed for their capture. The
orbits of these putative parent bodies are compared to those of the minor
bodies of the outer Solar System to outline their possible region of formation.
Finally, we tested the collisional capture hypothesis on Phoebe by taking
advantage of the data supplied by Cassini on its major crater, Jason. Our
results presented a realistic range of solutions matching the observational and
dynamical data.Comment: 26 Pages, 21 Figure
Cooling dynamics of a dilute gas of inelastic rods: a many particle simulation
We present results of simulations for a dilute gas of inelastically colliding
particles. Collisions are modelled as a stochastic process, which on average
decreases the translational energy (cooling), but allows for fluctuations in
the transfer of energy to internal vibrations. We show that these fluctuations
are strong enough to suppress inelastic collapse. This allows us to study large
systems for long times in the truely inelastic regime. During the cooling stage
we observe complex cluster dynamics, as large clusters of particles form,
collide and merge or dissolve. Typical clusters are found to survive long
enough to establish local equilibrium within a cluster, but not among different
clusters. We extend the model to include net dissipation of energy by damping
of the internal vibrations. Inelatic collapse is avoided also in this case but
in contrast to the conservative system the translational energy decays
according to the mean field scaling law, E(t)\propto t^{-2}, for asymptotically
long times.Comment: 10 pages, 12 figures, Latex; extended discussion, accepted for
publication in Phys. Rev.
Collision of One-Dimensional Nonlinear Chains
We investigate one-dimensional collisions of unharmonic chains and a rigid
wall. We find that the coefficient of restitution (COR) is strongly dependent
on the velocity of colliding chains and has a minimum value at a certain
velocity. The relationship between COR and collision velocity is derived for
low-velocity collisions using perturbation methods. We found that the velocity
dependence is characterized by the exponent of the lowest unharmonic term of
interparticle potential energy
Field water dynamics in integrated systems in the Brazilian.
Agroforestry systems were established as a viable option for Brazilian farmers in recent decades. Shading is expected to affect the system?s microclimate and thus it is likely to alter water fluxes to the atmosphere via evapotranspiration. In this study we measured the evapotranspiration (ET) with micro-lysimeters in four different treatments as a proxy for different land use systems at EMBRAPA Beef Cattle, the Brazilian Agricultural Research Corporation, located in Campo Grande-MS, Brasil. The four treatments are: Integrated systems with rows of Eucalypt (Eucalyptus urograndis) trees (ICLF), integrated systems without Eucalypt trees (ICL), continuous pasture (CP) and native Cerrado (Savannah) vegetation. In the ICLF and ICL plots Bracchiaria brizantha was planted and in the CP plots Brachiaria decumbens. To measure the evapotranspiration lysimeters (diameter of 10 cm and a depth of 20 cm) were inserted into the ground and weighed daily during a period of 8 weeks. Within the ICLF systems, measurements were conducted in three different distances to the tree rows. In the treatments without trees the lysimeters were distributed randomly. Results were linked to data from the microclimate, i.e. wind speed, air humidity, and global radiation
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