1,071 research outputs found
Dynamics of an exclusion process with creation and annihilation
We examine the dynamical properties of an exclusion process with creation and
annihilation of particles in the framework of a phenomenological domain-wall
theory, by scaling arguments and by numerical simulation. We find that the
length- and time scale are finite in the maximum current phase for finite
creation- and annihilation rates as opposed to the algebraically decaying
correlations of the totally asymmetric simple exclusion process (TASEP).
Critical exponents of the transition to the TASEP are determined. The case
where bulk creation- and annihilation rates vanish faster than the inverse of
the system size N is also analyzed. We point out that shock localization is
possible even for rates proportional to 1/N^a, 1<a<2.Comment: 16 pages, 8 figures, typos corrected, references added, section 4
revise
Forage Data Hub – A Platform for Sharing Valuable Datasets for Resilience
In accord with the necessity to enhance ecosystem services and productivity in food systems, is the increase of data availability at multiple scales and over time. To help meet this need, we discuss the development of a National Forage Data Hub which will act as a platform to curate, share, and analyze data pertaining to forage systems. This centralized hub will leverage existing datasets by bridging multiple sources including forage crop—soil, water, and nutrient availability—yield (animal and crop) potential (and gaps)— climate—management systems at high spatial and temporal resolution enabling system interaction assessments through next-generation analytics. This novel approach to existing datasets will integrate Big Data at the soilwater- plant-animal-climate nexus to advance data storage technology systems for multiple trophic-level research projects
Manipulation of drugs to achieve the required dose is intrinsic to paediatric practice but is not supported by guidelines or evidence
Background: A lack of age-appropriate formulations can make it difficult to administer medicines to children. A manipulation of the dosage form may be required to achieve the required dose. This study aimed to describe medicines that are manipulated to achieve the required dose in paediatric practice.Method: A structured, undisguised observational study and postal survey. The observational study investigated drug manipulations occurring in clinical practice across three sites. The questionnaire, administered to a sample of paediatric nurses throughout the UK, surveyed manipulations conducted and nurses' experiences and views.Results: The observational study identified 310 manipulations, of which 62% involved tablets, 21% were intravenous drugs and 10% were sachets. Of the 54 observed manipulations 40 involved tablets with 65% of the tablets being cut and 30% dispersed to obtain a smaller dose. 188 manipulations were reported by questionnaire respondents, of these 46% involved tablets, 12% were intravenous drugs, and 12% were nebuliser solutions. Manipulations were predominantly, but not exclusively, identified in specialist clinical areas with more highly dependent patients. Questionnaire respondents were concerned about the accuracy of the dose achieved following manipulations and the lack of practice guidance.Conclusion: Manipulations to achieve the required dose occur throughout paediatric in-patient settings. The impact of manipulations on the efficacy of the drugs, the accuracy of the dose and any adverse effects on patients is not known. There is a need to develop evidence-based guidance for manipulations of medicines in children
The Essential Interactions in Oxides and Spectral Weight Transfer in Doped Manganites
We calculate the value of the Fr\"ohlich electron-phonon interaction in
manganites, cuprates, and some other charge-transfer insulators and show that
this interaction is much stronger than any relevant magnetic interaction. A
polaron shift due to the Fr\"ohlich interaction, which is about 1 eV, suggests
that carriers in those systems are small (bi)polarons at all temperatures and
doping levels, in agreement with the oxygen isotope effect and other data. An
opposite conclusion, recently suggested in the literature, is shown to be
incorrect. The frequency and temperature dependence of the optical conductivity
of ferromagnetic manganites is explained within the framework of the bipolaron
theory.Comment: 6 pages, REVTeX 3.1 with 3 eps-figures. Journal versio
First-principles predictions of potential hydrogen storage materials: Nanosized Ti(core)/Mg(shell) hydrides
Spontaneous symmetry breaking in a two-lane model for bidirectional overtaking traffic
First we consider a unidirectional flux \omega_bar of vehicles each of which
is characterized by its `natural' velocity v drawn from a distribution P(v).
The traffic flow is modeled as a collection of straight `world lines' in the
time-space plane, with overtaking events represented by a fixed queuing time
tau imposed on the overtaking vehicle. This geometrical model exhibits platoon
formation and allows, among many other things, for the calculation of the
effective average velocity w=\phi(v) of a vehicle of natural velocity v.
Secondly, we extend the model to two opposite lanes, A and B. We argue that the
queuing time \tau in one lane is determined by the traffic density in the
opposite lane. On the basis of reasonable additional assumptions we establish a
set of equations that couple the two lanes and can be solved numerically. It
appears that above a critical value \omega_bar_c of the control parameter
\omega_bar the symmetry between the lanes is spontaneously broken: there is a
slow lane where long platoons form behind the slowest vehicles, and a fast lane
where overtaking is easy due to the wide spacing between the platoons in the
opposite direction. A variant of the model is studied in which the spatial
vehicle density \rho_bar rather than the flux \omega_bar is the control
parameter. Unequal fluxes \omega_bar_A and \omega_bar_B in the two lanes are
also considered. The symmetry breaking phenomenon exhibited by this model, even
though no doubt hard to observe in pure form in real-life traffic, nevertheless
indicates a tendency of such traffic.Comment: 50 pages, 16 figures; extra references adde
Anisotropic Colossal Magnetoresistance Effects in Fe_{1-x}Cu_xCr_2S_4
A detailed study of the electronic transport and magnetic properties of
FeCuCrS () on single crystals is presented. The
resistivity is investigated for K in magnetic fields up to
14 Tesla and under hydrostatic pressure up to 16 kbar. In addition
magnetization and ferromagnetic resonance (FMR) measurements were performed.
FMR and magnetization data reveal a pronounced magnetic anisotropy, which
develops below the Curie temperature, , and increases strongly
towards lower temperatures. Increasing the Cu concentration reduces this
effect. At temperatures below 35 K the magnetoresistance, , exhibits a strong dependence on the direction of the
magnetic field, probably due to an enhanced anisotropy. Applying the field
along the hard axis leads to a change of sign and a strong increase of the
absolute value of the magnetoresistance. On the other hand the
magnetoresistance remains positive down to lower temperatures, exhibiting a
smeared out maximum with the magnetic field applied along the easy axis. The
results are discussed in the ionic picture using a triple-exchange model for
electron hopping as well as a half-metal utilizing a band picture.Comment: some typos correcte
Transient processing and analysis using AMPEL: alert management, photometry, and evaluation of light curves
Context. Both multi-messenger astronomy and new high-throughput wide-field surveys require flexible tools for the selection and analysis of astrophysical transients. Aims. Here we introduce the alert management, photometry, and evaluation of light curves (AMPEL) system, an analysis framework designed for high-throughput surveys and suited for streamed data. AMPEL combines the functionality of an alert broker with a generic framework capable of hosting user-contributed code; it encourages provenance and keeps track of the varying information states that a transient displays. The latter concept includes information gathered over time and data policies such as access or calibration levels. Methods. We describe a novel ongoing real-time multi-messenger analysis using AMPEL to combine IceCube neutrino data with the alert streams of the Zwicky Transient Facility (ZTF). We also reprocess the first four months of ZTF public alerts, and compare the yields of more than 200 different transient selection functions to quantify efficiencies for selecting Type Ia supernovae that were reported to the Transient Name Server (TNS). Results. We highlight three channels suitable for (1) the collection of a complete sample of extragalactic transients, (2) immediate follow-up of nearby transients, and (3) follow-up campaigns targeting young, extragalactic transients. We confirm ZTF completeness in that all TNS supernovae positioned on active CCD regions were detected. Conclusions. AMPEL can assist in filtering transients in real time, running alert reaction simulations, the reprocessing of full datasets as well as in the final scientific analysis of transient data. This is made possible by a novel way of capturing transient information through sequences of evolving states, and interfaces that allow new code to be natively applied to a full stream of alerts. This text also introduces a method by which users can design their own channels for inclusion in the AMPEL live instance that parses the ZTF stream and the real-time submission of high-quality extragalactic supernova candidates to the TNS
The Localization Transition of the Two-Dimensional Lorentz Model
We investigate the dynamics of a single tracer particle performing Brownian
motion in a two-dimensional course of randomly distributed hard obstacles. At a
certain critical obstacle density, the motion of the tracer becomes anomalous
over many decades in time, which is rationalized in terms of an underlying
percolation transition of the void space. In the vicinity of this critical
density the dynamics follows the anomalous one up to a crossover time scale
where the motion becomes either diffusive or localized. We analyze the scaling
behavior of the time-dependent diffusion coefficient D(t) including corrections
to scaling. Away from the critical density, D(t) exhibits universal
hydrodynamic long-time tails both in the diffusive as well as in the localized
phase.Comment: 13 pages, 7 figures
Carrier Density Collapse and Colossal Magnetoresistance in Doped Manganites
A novel ferromagnetic transition, accompanied by carrier density collapse, is
found in doped charge-transfer insulators with strong electron-phonon coupling.
The transition is driven by an exchange interaction of polaronic carriers
with localized spins; the strength of the interaction determines whether the
transition is first or second order. A giant drop in the number of current
carriers during the transition, which is a consequence of bound pairs formation
in the paramagnetic phase close to the transition, is extremely sensitive to an
external magnetic field. This carrier density collapse describes the
resistivity peak and the colossal magnetoresistance of doped manganites.Comment: 5 pages, REVTeX 3.0, 3 EPS-figures embedded via epsf. Added - inset
in Fig. 2; Ref.[32]; footnotes [29], [30], [33
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