1,675 research outputs found
Damping-Antidamping Effect on Comets Motion
We make an observation about Galilean transformation on a 1-D mass variable
systems which leads us to the right way to deal with mass variable systems.
Then using this observation, we study two-bodies gravitational problem where
the mass of one of the bodies varies and suffers a damping-antidamping effect
due to star wind during its motion. For this system, a constant of motion, a
Lagrangian and a Hamiltonian are given for the radial motion, and the period of
the body is studied using the constant of motion of the system. Our theoretical
results are applied to Halley's comet.Comment: 19 pages, 5 figures. arXiv admin note: substantial text overlap with
arXiv:0910.468
Early star formation traced by the highest redshift quasars
The iron abundance relative to alpha-elements in the circumnuclear region of
quasars is regarded as a clock of the star formation history and, more
specifically, of the enrichment by SNIa. We investigate the iron abundance in a
sample of 22 quasars in the redshift range 3.0<z<6.4 by measuring their rest
frame UV FeII bump, which is shifted into the near-IR, and by comparing it with
the MgII 2798 flux. The observations were performed with a device that can
obtain near-IR spectra in the range 0.8-2.4 um in one shot, thereby enabling an
optimal removal of the continuum underlying the FeII bump. We detect iron in
all quasars including the highest redshift (z=6.4) quasar currently known. The
uniform observational technique and the wide redshift range allows a reliable
study of the trend of the FeII/MgII ratio with redshift. We find the FeII/MgII
ratio is nearly constant at all redshifts, although there is marginal evidence
for a higher FeII/MgII ratio in the quasars at z~6. If the FeII/MgII ratio
reflects the Fe/alpha abundance, this result suggests that the z~6 quasars have
already undergone a major episode of iron enrichment. We discuss the possible
implications of this finding for the star formation history at z>6. We also
detect a population of weak iron emitters at z~4.5, which are possibly hosted
in systems that evolved more slowly. Alternatively, the trend of the FeII/MgII
ratio at high redshift may reflect significantly different physical conditions
of the circumnuclear gas in such high redshift quasars.Comment: Replaced to match the accepted version (ApJL in press), 5 page
Privacy Preserving Internet Browsers: Forensic Analysis of Browzar
With the advance of technology, Criminal Justice agencies are being
confronted with an increased need to investigate crimes perpetuated partially
or entirely over the Internet. These types of crime are known as cybercrimes.
In order to conceal illegal online activity, criminals often use private
browsing features or browsers designed to provide total browsing privacy. The
use of private browsing is a common challenge faced in for example child
exploitation investigations, which usually originate on the Internet. Although
private browsing features are not designed specifically for criminal activity,
they have become a valuable tool for criminals looking to conceal their online
activity. As such, Technological Crime units often focus their forensic
analysis on thoroughly examining the web history on a computer. Private
browsing features and browsers often require a more in-depth, post mortem
analysis. This often requires the use of multiple tools, as well as different
forensic approaches to uncover incriminating evidence. This evidence may be
required in a court of law, where analysts are often challenged both on their
findings and on the tools and approaches used to recover evidence. However,
there are very few research on evaluating of private browsing in terms of
privacy preserving as well as forensic acquisition and analysis of privacy
preserving internet browsers. Therefore in this chapter, we firstly review the
private mode of popular internet browsers. Next, we describe the forensic
acquisition and analysis of Browzar, a privacy preserving internet browser and
compare it with other popular internet browser
Splash control of drop impacts with geometric targets
Drop impacts on solid and liquid surfaces exhibit complex dynamics due to the
competition of inertial, viscous, and capillary forces. After impact, a liquid
lamella develops and expands radially, and under certain conditions, the outer
rim breaks up into an irregular arrangement of filaments and secondary
droplets. We show experimentally that the lamella expansion and subsequent
break up of the outer rim can be controlled by length scales that are of
comparable dimension to the impacting drop diameter. Under identical impact
parameters, ie. fluid properties and impact velocity, we observe unique
splashing dynamics by varying the target cross-sectional geometry. These
behaviors include: (i) geometrically-shaped lamellae and (ii) a transition in
splashing stability, from regular to irregular splashing. We propose that
regular splashes are controlled by the azimuthal perturbations imposed by the
target cross-sectional geometry and that irregular splashes are governed by the
fastest-growing unstable Plateau-Rayleigh mode
Yttria and Ceria Doped Zirconia Thin Films Grown by Pulsed Laser Deposition
The Yttria stabilized Zirconia (YSZ) is a standard electrolyte for solid oxide fuel cells (SOFCs), which are potential candidates for next generation portable and mobile power sources. YSZ electrolyte thin films having a cubic single phase allow reducing the SOFC operating temperature without diminishing the electrochemical power density. Films of 8 mol % Yttria stabilized Zirconia (8YSZ) and films with addition of 4 weight % Ceria (8YSZ + 4CeO2) were grown by pulsed laser deposition (PLD) technique using 8YSZ and 8YSZ + 4CeO2 targets and a Nd-YAG laser (355 nm). Films have been deposited on Soda-Calcia-Silica glass and Si(100) substrates at room temperature. The morphology and structural characteristics of the samples have been studied by means of X-ray diffraction and scanning electron microscopy. Films of a cubic-YSZ single phase with thickness in the range of 1-3 µm were grown on different substrates.Fil: Saporiti, F.. Universidad de Buenos Aires. Facultad de IngenierĂa. Departamento de IngenierĂa Mecánica. Grupo de Materiales Avanzados; Argentina;Fil: Juarez, R. E.. Universidad de Buenos Aires. Facultad de IngenierĂa. Departamento de IngenierĂa Mecánica. Grupo de Materiales Avanzados; Argentina;Fil: Audebert, Fernando Enrique. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Houssay. Instituto de TecnologĂas y Ciencias de la IngenierĂa; Argentina; Universidad de Buenos Aires. Facultad de IngenierĂa. Departamento de IngenierĂa Mecánica. Grupo de Materiales Avanzados; Argentina;Fil: Boudard, M.. Centre National de la Recherche Scientifique. Laboratoire des MatĂ©riaux et du GĂ©nie Physique; Francia
Motility of small nematodes in disordered wet granular media
The motility of the worm nematode \textit{Caenorhabditis elegans} is
investigated in shallow, wet granular media as a function of particle size
dispersity and area density (). Surprisingly, we find that the nematode's
propulsion speed is enhanced by the presence of particles in a fluid and is
nearly independent of area density. The undulation speed, often used to
differentiate locomotion gaits, is significantly affected by the bulk material
properties of wet mono- and polydisperse granular media for .
This difference is characterized by a change in the nematode's waveform from
swimming to crawling in dense polydisperse media \textit{only}. This change
highlights the organism's adaptability to subtle differences in local structure
and response between monodisperse and polydisperse media
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