4,784 research outputs found
Is the New Resonance Spin 0 or 2? Taking a Step Forward in the Higgs Boson Discovery
The observation of a new boson of mass \sim 125\gev at the CERN LHC may
finally have revealed the existence of a Higgs boson. Now we have the
opportunity to scrutinize its properties, determining its quantum numbers and
couplings to the standard model particles, in order to confirm or not its
discovery. We show that by the end of the 8 TeV run, combining the entire data
sets of ATLAS and CMS, it will be possible to discriminate between the
following discovery alternatives: a scalar or a tensor
particle with minimal couplings to photons, at a statistical
confidence level at least, using only diphotons events. Our results are based
on the calculation of a center-edge asymmetry measure of the reconstructed {\it
sPlot} scattering polar angle of the diphotons. The results based on
asymmetries are shown to be rather robust against systematic uncertainties with
comparable discrimination power to a log likelihood ratio statistic.Comment: 11 pages, 6 figures, 1 table. References added, minor typos correcte
Scale-free memory model for multiagent reinforcement learning. Mean field approximation and rock-paper-scissors dynamics
A continuous time model for multiagent systems governed by reinforcement
learning with scale-free memory is developed. The agents are assumed to act
independently of one another in optimizing their choice of possible actions via
trial-and-error search. To gain awareness about the action value the agents
accumulate in their memory the rewards obtained from taking a specific action
at each moment of time. The contribution of the rewards in the past to the
agent current perception of action value is described by an integral operator
with a power-law kernel. Finally a fractional differential equation governing
the system dynamics is obtained. The agents are considered to interact with one
another implicitly via the reward of one agent depending on the choice of the
other agents. The pairwise interaction model is adopted to describe this
effect. As a specific example of systems with non-transitive interactions, a
two agent and three agent systems of the rock-paper-scissors type are analyzed
in detail, including the stability analysis and numerical simulation.
Scale-free memory is demonstrated to cause complex dynamics of the systems at
hand. In particular, it is shown that there can be simultaneously two modes of
the system instability undergoing subcritical and supercritical bifurcation,
with the latter one exhibiting anomalous oscillations with the amplitude and
period growing with time. Besides, the instability onset via this supercritical
mode may be regarded as "altruism self-organization". For the three agent
system the instability dynamics is found to be rather irregular and can be
composed of alternate fragments of oscillations different in their properties.Comment: 17 pages, 7 figur
Top Quark Physics at the Tevatron
We review the field of top-quark physics with an emphasis on experimental
techniques. The role of the top quark in the Standard Model of particle physics
is summarized and the basic phenomenology of top-quark production and decay is
introduced. We discuss how contributions from physics beyond the Standard Model
could affect top-quark properties or event samples. The many measurements made
at the Fermilab Tevatron, which test the Standard Model predictions or probe
for direct evidence of new physics using the top-quark event samples, are
reviewed here.Comment: 50 pages, 17 figures, 2 tables; version accepted by Review of Modern
Physic
Phase transition in a spatial Lotka-Volterra model
Spatial evolution is investigated in a simulated system of nine competing and
mutating bacterium strains, which mimics the biochemical war among bacteria
capable of producing two different bacteriocins (toxins) at most. Random
sequential dynamics on a square lattice is governed by very symmetrical
transition rules for neighborhood invasion of sensitive strains by killers,
killers by resistants, and resistants by by sensitives. The community of the
nine possible toxicity/resistance types undergoes a critical phase transition
as the uniform transmutation rates between the types decreases below a critical
value above which all the nine types of strain coexist with equal
frequencies. Passing the critical mutation rate from above, the system
collapses into one of the three topologically identical states, each consisting
of three strain types. Of the three final states each accrues with equal
probability and all three maintain themselves in a self-organizing polydomain
structure via cyclic invasions. Our Monte Carlo simulations support that this
symmetry breaking transition belongs to the universality class of the
three-state Potts model.Comment: 4 page
Defensive alliances in spatial models of cyclical population interactions
As a generalization of the 3-strategy Rock-Scissors-Paper game dynamics in
space, cyclical interaction models of six mutating species are studied on a
square lattice, in which each species is supposed to have two dominant, two
subordinated and a neutral interacting partner. Depending on their interaction
topologies, these systems can be classified into four (isomorphic) groups
exhibiting significantly different behaviors as a function of mutation rate. On
three out of four cases three (or four) species form defensive alliances which
maintain themselves in a self-organizing polydomain structure via cyclic
invasions. Varying the mutation rate this mechanism results in an ordering
phenomenon analogous to that of magnetic Ising model.Comment: 4 pages, 3 figure
Evolutionary instability of Zero Determinant strategies demonstrates that winning isn't everything
Zero Determinant (ZD) strategies are a new class of probabilistic and
conditional strategies that are able to unilaterally set the expected payoff of
an opponent in iterated plays of the Prisoner's Dilemma irrespective of the
opponent's strategy, or else to set the ratio between a ZD player's and their
opponent's expected payoff. Here we show that while ZD strategies are weakly
dominant, they are not evolutionarily stable and will instead evolve into less
coercive strategies. We show that ZD strategies with an informational advantage
over other players that allows them to recognize other ZD strategies can be
evolutionarily stable (and able to exploit other players). However, such an
advantage is bound to be short-lived as opposing strategies evolve to
counteract the recognition.Comment: 14 pages, 4 figures. Change in title (again!) to comply with Nature
Communications requirements. To appear in Nature Communication
Final clinical practicum, transition experience and turnover intentions among newly graduated nurses: A cross sectional study
BackgroundThe shortage of nurses is a global issue, and turnover rates are especially high for newly graduated nurses. The transition from student to nurse is often described as challenging, and the final clinical practicum before graduation is suggested to be important in preparing graduating students for the transition. However, little is known about the actual relationships between the final clinical practicum, transition and turnover intentions.ObjectivesTo examine whether the final clinical practicum experience is associated with the transition experience and turnover intentions of newly graduated nurses, and whether the transition experience mediates the potential relationship between the practicum and turnover intentions.DesignCross-sectional survey study.SettingsThe study was carried out in Finland (October–December 2018).ParticipantsRegistered nurses graduated within the past two years (n = 712).MethodsA new survey instrument with five subscales was developed for measuring the final clinical practicum experience. Transition experience was measured on four scales that demonstrated the emotional, physical, socio-developmental and intellectual domains of the transition: Psychological distress, sleep quality, role conflict/ambiguity, perception of transition and educational preparation. Turnover intentions from job and profession were asked about with two questions. Structural equation modelling was used to explore the associations between the variables. The models were adjusted for multiple potential confounders.ResultsFinal clinical practicum experience was associated with all domains of the transition experience and turnover intentions. The association between the practicum and turnover intentions was partly mediated by the emotional (psychological distress) and socio-developmental (role conflict and ambiguity) domains of the transition.ConclusionsOur findings provide new evidence about the associations between the specific final clinical practicum dimensions and turnover intentions and the specific mechanisms linking this association. These results highlight the importance of final clinical practicums and suggest targets for improving nurses' transition processes during their first years in practice.</div
The associations between the final clinical practicum elements and the transition experience of early career nurses: A cross-sectional study
The final clinical practicum before graduation prepares nursing students for the transition from a student to a nurse, but the essential elements of the final clinical practicum that enhance successful transition are not known. We examined the associations of five elements of the final clinical practicum with four indicators of the transition experience in new nurses. We also tested whether psychosocial work characteristics modified these associations. The study sample comprised 712 Finnish nurses who had graduated within the previous two years before the data collection (response rate: 18%). The data were collected using a questionnaire survey in 2018. The elements of the final clinical practicum included (1) the systematicness of the practicum, (2) teacher involvement, (3) the quality of supervision, (4) preparing for the demands of a nurse's work and (5) being part of a professional team. Our results, based on linear regression analysis, showed that all the elements except the quality of supervision were associated with indicators of the transition experience (beta range: from 0.08 to 0.35). Job demands modified several of these associations. The findings of this study highlight the potential for well-implemented final clinical practicums to promote a smoother transition for new nurses.</p
Sociobiological Control of Plasmid copy number
Background:
All known mechanisms and genes responsible for the regulation of plasmid replication lie with the plasmid rather than the chromosome. It is possible therefore that there can be copy-up mutants. Copy-up mutants will have within host selective advantage. This would eventually result into instability of bacteria-plasmid association. In spite of this possibility low copy number plasmids appear to exist stably in host populations. We examined this paradox using a computer simulation model.

Model:
Our multilevel selection model assumes a wild type with tightly regulated replication to ensure low copy number. A mutant with slightly relaxed replication regulation can act as a “cheater” or “selfish” plasmid and can enjoy a greater within-host-fitness. However the host of a cheater plasmid has to pay a greater cost. As a result, in host level competition, host cell with low copy number plasmid has a greater fitness. Furthermore, another mutant that has lost the genes required for conjugation was introduced in the model. The non-conjugal mutant was assumed to undergo conjugal transfer in the presence of another conjugal plasmid in the host cell.

Results:
The simulatons showed that if the cost of carrying a plasmid was low, the copy-up mutant could drive the wild type to extinction or very low frequencies. Consequently, another mutant with a higher copy number could invade the first invader. This process could result into an increasing copy number. However above a certain copy number within-host selection was overcompensated by host level selection leading to a rock-paper-scissor (RPS) like situation. The RPS situation allowed the coexistence of high and low copy number plasmids. The non-conjugal “hypercheaters” could further arrest the copy numbers to a substantially lower level.

Conclusions:
These sociobiological interactions might explain the stability of copy numbers better than molecular mechanisms of replication regulation alone
Determination of the Jet Energy Scale at the Collider Detector at Fermilab
A precise determination of the energy scale of jets at the Collider Detector
at Fermilab at the Tevatron collider is described. Jets are used in
many analyses to estimate the energies of partons resulting from the underlying
physics process. Several correction factors are developed to estimate the
original parton energy from the observed jet energy in the calorimeter. The jet
energy response is compared between data and Monte Carlo simulation for various
physics processes, and systematic uncertainties on the jet energy scale are
determined. For jets with transverse momenta above 50 GeV the jet energy scale
is determined with a 3% systematic uncertainty
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