3,005 research outputs found
K-Band Spectroscopy of (Pre-)Cataclysmic Variables: Are Some Donor Stars Really Carbon Poor?
We present a new sample of -band spectral observations for CVs:
non-magnetic and magnetic as well as present day and pre CVs. The purpose of
this diverse sample is to address the recent claim that the secondary stars in
dwarf novae are carbon deficient, having become so through a far more evolved
evolution than the current paradigm predicts. Our new observations, along with
previous literature results, span a wide range of orbital period and CV type.
In general, dwarf novae in which the secondary star is seen show weak to no CO
absorption while polar and pre-CV donor stars appear to have normal CO
absorption for their spectral type. However, this is not universal. The
presence of normal looking CO absorption in the dwarf nova SS Aur and the
hibernating CV QS Vir and a complete lack of CO absorption in the long period
polar V1309 Ori cloud the issue. A summary of the literature pointing to
non-solar abundances including enhanced NV/CIV ratios is presented. It appears
that some CVs have non-solar abundance material accreting onto the white dwarf
suggesting an evolved secondary star while for others CO emission in the
accretion disk may play a role. However, the exact mechanism or combination of
factors causing the CO absorption anomaly in CVs is not yet clear.Comment: Accepted in A
Reflection confocal nanoscopy using a super-oscillatory lens
A Superoscillatory lens (SOL) is known to produce a sub-diffraction hotspot
which is useful for high-resolution imaging. However, high-energy rings called
sidelobes coexist with the central hotspot. Additionally, SOLs have not yet
been directly used to image reflective objects due to low efficiency and poor
imaging properties. We propose a novel reflection confocal nanoscope which
mitigates these issues by relaying the SOL intensity pattern onto the object
and use conventional optics for detection. We experimentally demonstrate
super-resolution by imaging double bars with 330 nm separation using a 632.8 nm
excitation and a 0.95 NA objective. We also discuss the enhanced contrast
properties of the SOL nanoscope against a laser confocal microscope, and the
degradation of performance while imaging large objects.Comment: 17 pages, 15 figures, supplementary include
Book Reviews
ANATOMY OF THE LAW. By Lon L. Fuller, RIOTS, REVOLTS AND INSURRECTIONS. By Raymond M. Momboisse.
CASES AND MATERIALS RELATING TO JUVENILE COURTS. By Orman W. Ketcham and Monrad G. Paulsen.
TEACHERS, SCHOOL BOARDS, AND COLLECTIVE BARGAINING: A CHANGING OF THE GUARD. By Robert E. Doherty and Walter E. Oberer.
DOLLARS, DELAY AND THE AUTOMOBILE VICTIM. Sponsored by the Walter E. Meyer Research Institute of Law
Collective behaviour without collective order in wild swarms of midges
Collective behaviour is a widespread phenomenon in biology, cutting through a
huge span of scales, from cell colonies up to bird flocks and fish schools. The
most prominent trait of collective behaviour is the emergence of global order:
individuals synchronize their states, giving the stunning impression that the
group behaves as one. In many biological systems, though, it is unclear whether
global order is present. A paradigmatic case is that of insect swarms, whose
erratic movements seem to suggest that group formation is a mere epiphenomenon
of the independent interaction of each individual with an external landmark. In
these cases, whether or not the group behaves truly collectively is debated.
Here, we experimentally study swarms of midges in the field and measure how
much the change of direction of one midge affects that of other individuals. We
discover that, despite the lack of collective order, swarms display very strong
correlations, totally incompatible with models of noninteracting particles. We
find that correlation increases sharply with the swarm's density, indicating
that the interaction between midges is based on a metric perception mechanism.
By means of numerical simulations we demonstrate that such growing correlation
is typical of a system close to an ordering transition. Our findings suggest
that correlation, rather than order, is the true hallmark of collective
behaviour in biological systems.Comment: The original version has been split into two parts. This first part
focuses on order vs. correlation. The second part, about finite-size scaling,
will be included in a separate paper. 15 pages, 6 figures, 1 table, 5 video
Finite-size scaling as a way to probe near-criticality in natural swarms
Collective behaviour in biological systems is often accompanied by strong
correlations. The question has therefore arisen of whether correlation is
amplified by the vicinity to some critical point in the parameters space.
Biological systems, though, are typically quite far from the thermodynamic
limit, so that the value of the control parameter at which correlation and
susceptibility peak depend on size. Hence, a system would need to readjust its
control parameter according to its size in order to be maximally correlated.
This readjustment, though, has never been observed experimentally. By gathering
three-dimensional data on swarms of midges in the field we find that swarms
tune their control parameter and size so as to maintain a scaling behaviour of
the correlation function. As a consequence, correlation length and
susceptibility scale with the system's size and swarms exhibit a near-maximal
degree of correlation at all sizes.Comment: Selected for Viewpoint in Physics; PRL Editor's Suggestio
Differential effects on membrane permeability and viability of human keratinocyte cells undergoing very low intensity megasonic fields
Among different therapeutic applications of Ultrasound (US), transient membrane sonoporation (SP) - a temporary, non-lethal porosity, mechanically induced in cell membranes through US exposure - represents a compelling opportunity towards an efficient and safe drug delivery. Nevertheless, progresses in this field have been limited by an insufficient understanding of the potential cytotoxic effects of US related to the failure of the cellular repair and to the possible activation of inflammatory pathway. In this framework we studied the in vitro effects of very low-intensity US on a human keratinocyte cell line, which represents an ideal model system of skin protective barrier cells which are the first to be involved during medical US treatments. Bioeffects linked to US application at 1 MHz varying the exposure parameters were investigated by fluorescence microscopy and fluorescence activated cell sorting. Our results indicate that keratinocytes undergoing low US doses can uptake drug model molecules with size and efficiency which depend on exposure parameters. According to sub-cavitation SP models, we have identified the range of doses triggering transient membrane SP, actually with negligible biological damage. By increasing US doses we observed a reduced cells viability and an inflammatory gene overexpression enlightening novel healthy relevant strategies
An Army of Me: Sockpuppets in Online Discussion Communities
In online discussion communities, users can interact and share information
and opinions on a wide variety of topics. However, some users may create
multiple identities, or sockpuppets, and engage in undesired behavior by
deceiving others or manipulating discussions. In this work, we study
sockpuppetry across nine discussion communities, and show that sockpuppets
differ from ordinary users in terms of their posting behavior, linguistic
traits, as well as social network structure. Sockpuppets tend to start fewer
discussions, write shorter posts, use more personal pronouns such as "I", and
have more clustered ego-networks. Further, pairs of sockpuppets controlled by
the same individual are more likely to interact on the same discussion at the
same time than pairs of ordinary users. Our analysis suggests a taxonomy of
deceptive behavior in discussion communities. Pairs of sockpuppets can vary in
their deceptiveness, i.e., whether they pretend to be different users, or their
supportiveness, i.e., if they support arguments of other sockpuppets controlled
by the same user. We apply these findings to a series of prediction tasks,
notably, to identify whether a pair of accounts belongs to the same underlying
user or not. Altogether, this work presents a data-driven view of deception in
online discussion communities and paves the way towards the automatic detection
of sockpuppets.Comment: 26th International World Wide Web conference 2017 (WWW 2017
The Chromospheric Activity and Ages of M Dwarf Stars in Wide Binary Systems
We investigate the relationship between age and chromospheric activity for
139 M dwarf stars in wide binary systems with white dwarf companions. The age
of each system is determined from the cooling age of its white dwarf component.
The current limit for activity-age relations found for M dwarfs in open
clusters is 4 Gyr. Our unique approach to finding ages for M stars allows for
the exploration of this relationship at ages older than 4 Gyr. The general
trend of stars remaining active for a longer time at later spectral type is
confirmed. However, our larger sample and greater age range reveals additional
complexity in assigning age based on activity alone. We find that M dwarfs in
wide binaries older than 4 Gyr depart from the log-linear relation for clusters
and are found to have activity at magnitudes, colors and masses which are
brighter, bluer and more massive than predicted by the cluster relation. In
addition to our activity-age results, we present the measured radial velocities
and complete space motions for 161 white dwarf stars in wide binaries.Comment: 22 pages including 9 figures and 5 tables. Accepted for publication
in The Astronomical Journa
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