611 research outputs found
OpenSwarm: an event-driven embedded operating system for miniature robots
This paper presents OpenSwarm, a lightweight easy-to-use open-source operating system. To our knowledge, it is the first operating system designed for and deployed on miniature robots. OpenSwarm operates directly on a robot’s microcontroller. It has a memory footprint of 1 kB RAM and 12 kB ROM. OpenSwarm enables a robot to execute multiple processes simultaneously. It provides a hybrid kernel that natively supports preemptive and cooperative scheduling, making it suitable for both computationally intensive and swiftly responsive robotics tasks. OpenSwarm provides hardware abstractions to rapidly develop and test platformindependent code. We show how OpenSwarm can be used to solve a canonical problem in swarm robotics—clustering a collection of dispersed objects. We report experiments, conducted with five e-puck mobile robots, that show that an OpenSwarm implementation performs as good as a hardware-near implementation. The primary goal of OpenSwarm is to make robots with severely constrained hardware more accessible, which may help such systems to be deployed in real-world applications
QFT, String Temperature and the String Phase of De Sitter Space-time
The density of mass levels \rho(m) and the critical temperature for strings
in de Sitter space-time are found. QFT and string theory in de Sitter space are
compared. A `Dual'-transform is introduced which relates classical to quantum
string lengths, and more generally, QFT and string domains. Interestingly, the
string temperature in De Sitter space turns out to be the Dual transform of the
QFT-Hawking-Gibbons temperature. The back reaction problem for strings in de
Sitter space is addressed selfconsistently in the framework of the `string
analogue' model (or thermodynamical approach), which is well suited to combine
QFT and string study.We find de Sitter space-time is a self-consistent solution
of the semiclassical Einstein equations in this framework. Two branches for the
scalar curvature R(\pm) show up: a classical, low curvature solution (-), and a
quantum high curvature solution (+), enterely sustained by the strings. There
is a maximal value for the curvature R_{\max} due to the string back reaction.
Interestingly, our Dual relation manifests itself in the back reaction
solutions: the (-) branch is a classical phase for the geometry with intrinsic
temperature given by the QFT-Hawking-Gibbons temperature.The (+) is a stringy
phase for the geometry with temperature given by the intrinsic string de Sitter
temperature. 2 + 1 dimensions are considered, but conclusions hold generically
in D dimensions.Comment: LaTex, 24 pages, no figure
The effect of concurrent infections with Pasteurella multocida and Ascaridia galli on free range chickens
Pasteurella multocida and Ascaridia galli are observed with high prevalences in free range chickens in Denmark, but the impact is unknown. A study was carried out to examine the interaction between A. galli and P. multocida in chickens and the impact on production. Five groups, each with 20 18-week-old Lohmann Brown chickens were infected. Group I was orally infected with 1000 +/- 50 embryonated A. galli eggs. Group 2 received 10(4) cfu p. multocida intratracheally. Group 3 was infected with A. galli and subsequently with P. multocida. Group 4 was infected with P. multocida followed by A. galli. Group 5 was the control. The study ran for I I weeks where clinical manifestations, weight gain and egg production were recorded. Excretion of P. multocida was determined on individual basis and blood smears were made for differential counts. At the end of the study pathological lesions and the number of adult worms, larvae and eggs in the faeces were recorded. The birds were more severely affected when infected with both pathogens compared to single infections with A. galli or P. multocida, respectively. A lower weight gain and egg production was observed with dual infections. A. galli infection followed by a secondary P. multocida infection resulted in more birds with pathological lesions and continued P. multocida excretion. In conclusion a negative interaction between A. galli and R multocida was observed and it is postulated that free range chickens are at higher risk of being subjected to outbreaks of fowl cholera when they are infected with A. galli
Prediction of individual probabilities of livebirth and multiple birth events following in vitro fertilization (IVF): a new outcomes counselling tool for IVF providers and patients using HFEA metrics
In vitro fertilization (IVF) has become a standard treatment for subfertility after it was demonstrated to be of value to humans in 1978. However, the introduction of IVF into mainstream clinical practice has been accompanied by concerns regarding the number of multiple gestations that it can produce, as multiple births present significant medical consequences to mothers and offspring. When considering IVF as a treatment modality, a balance must be set between the chance of having a live birth and the risk of having a multiple birth. As IVF is often a costly decision for patients—financially, medically, and emotionally—there is benefit from estimating a patient’s specific chance that IVF could result in a birth as fertility treatment options are contemplated. Historically, a patient’s “chance of success” with IVF has been approximated from institution-based statistics, rather than on the basis of any particular clinical parameter (except age). Furthermore, the likelihood of IVF resulting in a twin or triplet outcome must be acknowledged for each patient, given the known increased complications of multiple gestation and consequent increased risk of poor birth outcomes. In this research, we describe a multivariate risk assessment model that incorporates metrics adapted from a national 7.5-year sampling of the Human Fertilisation & Embryology Authority (HFEA) dataset (1991–1998) to predict reproductive outcome (including estimation of multiple birth) after IVF. To our knowledge, http://www.formyodds.com is the first Software-as-a-Service (SaaS) application to predict IVF outcome. The approach also includes a confirmation functionality, where clinicians can agree or disagree with the computer-generated outcome predictions. It is anticipated that the emergence of predictive tools will augment the reproductive endocrinology consultation, improve the medical informed consent process by tailoring the outcome assessment to each patient, and reduce the potential for adverse outcomes with IVF
Steady-State Dynamics of the Forest Fire Model on Complex Networks
Many sociological networks, as well as biological and technological ones, can
be represented in terms of complex networks with a heterogeneous connectivity
pattern. Dynamical processes taking place on top of them can be very much
influenced by this topological fact. In this paper we consider a paradigmatic
model of non-equilibrium dynamics, namely the forest fire model, whose
relevance lies in its capacity to represent several epidemic processes in a
general parametrization. We study the behavior of this model in complex
networks by developing the corresponding heterogeneous mean-field theory and
solving it in its steady state. We provide exact and approximate expressions
for homogeneous networks and several instances of heterogeneous networks. A
comparison of our analytical results with extensive numerical simulations
allows to draw the region of the parameter space in which heterogeneous
mean-field theory provides an accurate description of the dynamics, and
enlights the limits of validity of the mean-field theory in situations where
dynamical correlations become important.Comment: 13 pages, 9 figure
Casimir Effect, Achucarro-Ortiz Black Hole and the Cosmological Constant
We treat the two-dimensional Achucarro-Ortiz black hole (also known as (1+1)
dilatonic black hole) as a Casimir-type system. The stress tensor of a massless
scalar field satisfying Dirichlet boundary conditions on two one-dimensional
"walls" ("Dirichlet walls") is explicitly calculated in three different vacua.
Without employing known regularization techniques, the expression in each
vacuum for the stress tensor is reached by using the Wald's axioms. Finally,
within this asymptotically non-flat gravitational background, it is shown that
the equilibrium of the configurations, obtained by setting Casimir force to
zero, is controlled by the cosmological constant.Comment: 20 pages, LaTeX, minor corrections, comments and clarifications
added, version to appear in Phys. Rev.
Rescuing Valuable Arctic Vegetation Data for Biodiversity Models, Ecosystem Models and a Panarctic Vegetation Classification
Modeling magnetospheric fields in the Jupiter system
The various processes which generate magnetic fields within the Jupiter
system are exemplary for a large class of similar processes occurring at other
planets in the solar system, but also around extrasolar planets. Jupiter's
large internal dynamo magnetic field generates a gigantic magnetosphere, which
is strongly rotational driven and possesses large plasma sources located deeply
within the magnetosphere. The combination of the latter two effects is the
primary reason for Jupiter's main auroral ovals. Jupiter's moon Ganymede is the
only known moon with an intrinsic dynamo magnetic field, which generates a
mini-magnetosphere located within Jupiter's larger magnetosphere including two
auroral ovals. Ganymede's magnetosphere is qualitatively different compared to
the one from Jupiter. It possesses no bow shock but develops Alfv\'en wings
similar to most of the extrasolar planets which orbit their host stars within
0.1 AU. New numerical models of Jupiter's and Ganymede's magnetospheres
presented here provide quantitative insight into the processes that maintain
these magnetospheres. Jupiter's magnetospheric field is approximately
time-periodic at the locations of Jupiter's moons and induces secondary
magnetic fields in electrically conductive layers such as subsurface oceans. In
the case of Ganymede, these secondary magnetic fields influence the oscillation
of the location of its auroral ovals. Based on dedicated Hubble Space Telescope
observations, an analysis of the amplitudes of the auroral oscillations
provides evidence that Ganymede harbors a subsurface ocean. Callisto in
contrast does not possess a mini-magnetosphere, but still shows a perturbed
magnetic field environment. Callisto's ionosphere and atmospheric UV emission
is different compared to the other Galilean satellites as it is primarily been
generated by solar photons compared to magnetospheric electrons.Comment: Chapter for Book: Planetary Magnetis
The effect of concurrent infections with Pasteurella multocida and Ascaridia galli on free range chickens
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