6,716 research outputs found
Exploring the role of Facebook in re-shaping backpacker’s social interactions
The recent Facebook launch of Timeline, Social Graph Search, and the increased use of the mobile Facebook apps has resulted in some important implications for the use of Facebook by backpackers. The purpose of this paper is to (re) explore how Facebook has impacted social relationships between backpackers and their personal, professional, and ‘fellow traveller’ networks, particularly in-light of these recent changes to Facebook and the increased reduction of anonymity while travelling. An exploratory survey was administered to 216 backpackers through social media. Descriptive analysis was conducted to explore the perceived social risks and benefits of Facebook in the context of the backpacking experience
Marginal states of the resistive tearing mode with flow in cylindrical geometry
The linear stability of tearing modes in a cylindrical plasma subject to a sub-Alfvénic equilibrium shear flow along the equilibrium magnetic field is considered. The equations in the resistive boundary layer at the rational surface are solved numerically using a Fourier transform combined with a finite-element approach. The behaviour of the growth rate as a function of the flow and the various parameters (including a perpendicular fluid viscosity) is obtained. Marginal stability curves showing the dependence of the familiar matching parameter Δ' with flow and shear are also given
Nonlocal compensation of pure phase objects with entangled photons
We suggest and demonstrate a scheme for coherent nonlocal compensation of
pure phase objects based on two-photon polarization and momentum entangled
states. The insertion of a single phase object on one of the beams reduces the
purity of the state and the amount of shared entanglement, whereas the original
entanglement can be retrieved by adding a suitable phase object on the other
beam. In our setup polarization and momentum entangled states are generated by
spontaneous parametric downconversion and then purified using a programmable
spatial light modulator, which may be also used to impose arbitrary space
dependent phase functions to the beams. As a possible application, we suggest
and demonstrate a quantum key distribution protocol based on nonlocal phase
compensation.Comment: 7 pages, 5 figure
Phase transitions related to the pigeonhole principle
Since Paris introduced them in the late seventies (Paris1978), densities turned out to be useful for studying independence results. Motivated by their simplicity and surprising strength we investigate the combinatorial complexity of two such densities which are strongly related to the pigeonhole principle. The aim is to miniaturise Ramsey's Theorem for -tuples. The first principle uses an unlimited amount of colours, whereas the second has a fixed number of two colours. We show that these principles give rise to Ackermannian growth. After parameterising these statements with respect to a function f:N->N, we investigate for which functions f Ackermannian growth is still preserved
Exploring the influence of Facebook on backpacker's social experience in hostels
The primary purpose of this study was to explore the relationship between Facebook usage and the corresponding impact on travel relationships within the hostel and backpacker community. An online survey was administered to backpackers which were both hostel and Facebook users by way of travel-centric online communities. The impact of Facebook on backpacker behaviors, decision making, and relationships was examined. Analysis indicates that Facebook is shaping the evolution of social, behavioral, and communicative norms within the backpacker hostel environment and that there is still a gap in the research that examines the impact of social networking websites on the hostel experience
Observing the very low-surface brightness dwarfs in a deep field in the VIRGO cluster: constraints on Dark Matter scenarios
We report the discovery of 11 very faint (r< 23), low surface brightness
({\mu}_r< 27 mag/arcsec^2) dwarf galaxies in one deep field in the Virgo
cluster, obtained by the prime focus cameras (LBC) at the Large Binocular
Telescope (LBT). These extend our previous sample to reach a total number of 27
galaxies in a field of just of 0.17 deg^2 located at a median distance of 390
kpc from the cluster center. Their association with the Virgo cluster is
supported by their separate position in the central surface brightness - total
magnitude plane with respect to the background galaxies of similar total
magnitude. For a significant fraction (26\%) of the sample the association to
the cluster is confirmed by spectroscopic follow-up. We show that the mere
abundance of satellite galaxies corresponding to our observed number in the
target field provides extremely tight constraints on Dark Matter models with
suppressed power spectrum compared to the Cold Dark Matter case, independently
of the galaxy luminosity distribution. In particular, requiring the observed
number of satellite galaxies not to exceed the predicted abundance of Dark
Matter sub-halos yields a limit m_X >3 keV at 1-{\sigma} and m_X > 2.3 keV at
2-{\sigma} confidence level for the mass of thermal Warm Dark Matter particles.
Such a limit is competitive with other limits set by the abundance of
ultra-faint satellite galaxies in the Milky Way, is completely independent of
baryon physics involved in galaxy formation, and has the potentiality for
appreciable improvements with next observations. We extend our analysis to Dark
Matter models based on sterile neutrinos, showing that our observations set
tight constraints on the combination of sterile neutrino mass m_{\nu} and
mixing parameter sin^2(2{\theta}). We discuss the robustness of our results
with respect to systematics.Comment: Accepted for publication in Astronomy & Astrophysic
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