994 research outputs found
The Effects of Boxy/Peanut Bulges on Galaxy Models
We examine the effects that the modelling of a Boxy/Peanut (B/P) bulge will
have on the estimates of the stellar gravitational potential, forces, orbital
structure and bar strength of barred galaxies. We present a method for
obtaining the potential of disc galaxies from surface density images, assuming
a vertical density distribution (height function), which is let to vary with
position, thus enabling it to represent the geometry of a B/P. We construct a
B/P height function after the results from a high-resolution, N-body+SPH
simulation of an isolated galaxy and compare the resulting dynamical model to
those obtained with the commonly used, position-independent "flat" height
functions. We show that methods that do not allow for a B/P can induce errors
in the forces in the bar region of up to 40% and demonstrate that this has a
significant impact on the orbital structure of the model, which in turn
determines its kinematics and morphology. Furthermore, we show that the bar
strength is reduced in the presence of a B/P. We conclude that neglecting the
vertical extent of a B/P can introduce considerable errors in the dynamical
modelling. We also examine the errors introduced in the model due to
uncertainties in the parameters of the B/P and show that even for generous but
realistic values of the uncertainties, the error will be noticeably less than
that of not modelling a B/P bulge at all.Comment: Accepted for publication in MNRA
Time, Discipline and Subjectivity: Performing Arts Worker Mobilisations in Italy during the Pandemic
Based on the results of a qualitative study, this article aims to contribute to the debate on collective mobilisations, using the example of the labour struggles of Italian artists during the Covid-19 pandemic. The conditions typical to performing arts workers, such as precariousness, self-employment, individualisation, self-exploitation, social fragmentation, and geographical dispersion, have long been associated with low probabilities of collective mobilisation. In Italy, however, in the context of the numerous labour-related conflicts that emerged during the pandemic, mobilisations by performing arts workers were some of the most intense, widespread, and sustained. Addressing this counterintuitive finding and drawing on mobilisation theory, this article aims to identify the sources of conflict and antagonism of this mobilisation, and to investigate the factors and circumstances underlying it. We argue that the collective action of artists was motivated by a number of factors: a simultaneous mass experience of economic vulnerability and social insecurity; the breakdown of disciplinary mechanisms in artistic work; and the greater availability of âfree timeâ. The findings shed new light on the mobilisation of precarious workers in work contexts characterised by disciplinary regimes based on subjective participation, self-exploitation and consensus
On the torque on birefringent plates induced by quantum fluctuations
We present detailed numerical calculations of the mechanical torque induced
by quantum fluctuations on two parallel birefringent plates with in plane
optical anisotropy, separated by either vacuum or a liquid (ethanol). The
torque is found to vary as , where represents the angle
between the two optical axes, and its magnitude rapidly increases with
decreasing plate separation . For a 40 m diameter disk, made out of
either quartz or calcite, kept parallel to a Barium Titanate plate at nm, the maximum torque (at ) is of the order of
Nm. We propose an experiment to observe this torque
when the Barium Titanate plate is immersed in ethanol and the other
birefringent disk is placed on top of it. In this case the retarded van der
Waals (or Casimir-Lifshitz) force between the two birefringent slabs is
repulsive. The disk would float parallel to the plate at a distance where its
net weight is counterbalanced by the retarded van der Waals repulsion, free to
rotate in response to very small driving torques.Comment: 7 figures, submitted to Phys. Rev.
Computation and visualization of Casimir forces in arbitrary geometries: non-monotonic lateral forces and failure of proximity-force approximations
We present a method of computing Casimir forces for arbitrary geometries,
with any desired accuracy, that can directly exploit the efficiency of standard
numerical-electromagnetism techniques. Using the simplest possible
finite-difference implementation of this approach, we obtain both agreement
with past results for cylinder-plate geometries, and also present results for
new geometries. In particular, we examine a piston-like problem involving two
dielectric and metallic squares sliding between two metallic walls, in two and
three dimensions, respectively, and demonstrate non-additive and non-monotonic
changes in the force due to these lateral walls.Comment: Accepted for publication in Physical Review Letters. (Expected
publication: Vol. 99 (8) 2007
Direct experimental evidence of free fermion antibunching
Fermion antibunching was observed on a beam of free noninteracting neutrons.
A monochromatic beam of thermal neutrons was first split by a graphite single
crystal, then fed to two detectors, displaying a reduced coincidence rate. The
result is a fermionic complement to the Hanbury Brown and Twiss effect for
photons.Comment: 4 pages, 2 figure
Precision measurement of the Casimir-Lifshitz force in a fluid
The Casimir force, which results from the confinement of the quantum
mechanical zero-point fluctuations of the electromagnetic fields, has received
significant attention in recent years for its effect on micro- and nano-scale
mechanical systems. With few exceptions, experimental observations have been
limited to conductive bodies interacting separated by vacuum or air. However,
interesting phenomena including repulsive forces are expected to exist in
certain circumstances between metals and dielectrics when the intervening
medium is not vacuum. In order to better understand the effect of the Casimir
force in such situations and to test the robustness of the generalized
Casimir-Lifshitz theory, we have performed the first precision measurements of
the Casimir force between two metals immersed in a fluid. For this situation,
the measured force is attractive and is approximately 80% smaller than the
force predicted by Casimir for ideal metals in vacuum. We present experimental
results and find them to be consistent with Lifshitz's theory.Comment: 6 pages, 3 figures. (version before final publication
Comment on "On the temperature dependence of the Casimir effect"
Recently, Brevik et al. [Phys. Rev. E 71, 056101 (2005)] adduced arguments
against the traditional approach to the thermal Casimir force between real
metals and in favor of one of the alternative approaches. The latter assumes
zero contribution from the transverse electric mode at zero frequency in
qualitative disagreement with unity as given by the thermal quantum field
theory for ideal metals. Those authors claim that their approach is consistent
with experiments as well as with thermodynamics. We demonstrate that these
conclusions are incorrect. We show specifically that their results are
contradicted by four recent experiments and also violate the third law of
thermodynamics (the Nernst heat theorem).Comment: 11 pages, 3 figures, changed in accordance with the final published
versio
Frequency-dependent Drude damping in Casimir force calculations
The Casimir force is calculated between Au thin films that are described by a
Drude model with a frequency dependent damping function. The model parameters
are obtained from available experimental data for Au thin films. Two cases are
considered; annealed and nonannealed films that have a different damping
function. Compared with the calculations using a Drude model with a constant
damping parameter, we observe changes in the Casimir force of a few percent.
This behavior is only observed in films of no more than 300 thick.Comment: Proceedings of the meeting "60 years of Casimir effect", Brasilia,
200
Early labour midwifery care in Italy: local and cross-cultural challenges
INTRODUCTION. The definition of early labour and its management are debatable issues at a local, national and international level. In Italy, this issue is also of concern.
APPROACH. This is a descriptive discussion paper designed to portray the cross-cultural issues and the comparisons between Italian and international early labour care.
KEY ISSUES. Many of the issues regarding early labour care in Italy resonate with what emerged from the international literature. These include the dilemmas of diagnosis and management of early labour, appropriate timing for womenâs admission to hospitals in the latent phase and the type of maternity service available to women in early labour. The lack of a mapping of the geographically variable services offered to women in the Italian peninsula makes the task of offering national data to international research on early labour care challenging as little is known about the availability, efficiency and effectiveness of triage systems for women in the latent phase of labour.
THE WAY FORWARD. The organisation of maternity services within the Italian national health system requires a review to consider how best to meet womenâs needs during early labour. Research in this field needs to be carried out in Italian birthing settings in order to be able to understand what would work best for women within the specific socio-cultural context and what is required to enhance midwifery knowledge and skill
- âŠ