416 research outputs found
An Agent-Based Model of Collective Emotions in Online Communities
We develop a agent-based framework to model the emergence of collective
emotions, which is applied to online communities. Agents individual emotions
are described by their valence and arousal. Using the concept of Brownian
agents, these variables change according to a stochastic dynamics, which also
considers the feedback from online communication. Agents generate emotional
information, which is stored and distributed in a field modeling the online
medium. This field affects the emotional states of agents in a non-linear
manner. We derive conditions for the emergence of collective emotions,
observable in a bimodal valence distribution. Dependent on a saturated or a
superlinear feedback between the information field and the agent's arousal, we
further identify scenarios where collective emotions only appear once or in a
repeated manner. The analytical results are illustrated by agent-based computer
simulations. Our framework provides testable hypotheses about the emergence of
collective emotions, which can be verified by data from online communities.Comment: European Physical Journal B (in press), version 2 with extended
introduction, clarification
Geographic hierarchical population genetic structuring in British European whitefish (Coregonus lavaretus) and its implications for conservation
The European whitefish Coregonus lavaretus complex represents one of the most diverse radiations within salmonids, with extreme morphological and genetic differentiation across its range. Such variation has led to the assignment of many populations to separate species. In Great Britain, the seven native populations of C. lavaretus (two in Scotland, four in England, one in Wales) were previously classified into three species, and recent taxonomic revision resurrected the previous nomenclature. Here we used a dataset of 15 microsatellites to: (1) investigate the genetic diversity of British populations, (2) assess the level of population structure and the relationships between British populations. Genetic diversity was highest in Welsh (HO = 0.50, AR = 5.29), intermediate in English (HO = 0.41–0.50, AR = 2.83–3.88), and lowest in Scottish populations (HO = 0.28–0.35, AR = 2.56–3.04). Population structure analyses indicated high genetic differentiation (global FST = 0.388) between all populations but for the two Scottish populations (FST = 0.063) and two English populations (FST = 0.038). Principal component analysis and molecular ANOVA revealed separation between Scottish, English, and Welsh populations, with the Scottish populations being the most diverged. We argue that the data presented here are not sufficient to support a separation of the British European whitefish populations into three separate species, but support the delineation of different ESUs for these populations
A 750 mW, continuous-wave, solid-state laser source at 313 nm for cooling and manipulating trapped 9Be+ ions
We present a solid-state laser system that generates 750 mW of
continuous-wave single-frequency output at 313 nm. Sum-frequency generation
with fiber lasers at 1550 nm and 1051 nm produces up to 2 W at 626 nm. This
visible light is then converted to UV by cavity-enhanced second-harmonic
generation. The laser output can be tuned over a 495 GHz range, which includes
the 9Be+ laser cooling and repumping transitions. This is the first report of a
narrow-linewidth laser system with sufficient power to perform fault-tolerant
quantum-gate operations with trapped 9Be+ ions by use of stimulated Raman
transitions.Comment: 9 pages, 4 figure
The design, construction and performance of the MICE target
The pion-production target that serves the MICE Muon Beam consists of a titanium cylinder that is dipped into the halo of the ISIS proton beam. The design and construction of the MICE target system are described along with the quality-assurance procedures, electromagnetic drive and control systems, the readout electronics, and the data-acquisition system. The performance of the target is presented together with the particle rates delivered to the MICE Muon Beam. Finally, the beam loss in ISIS generated by the operation of the target is evaluated as a function of the particle rate, and the operating parameters of the target are derived
Standard Model baryogenesis through four-fermion operators in braneworlds
We study a new baryogenesis scenario in a class of braneworld models with low
fundamental scale, which typically have difficulty with baryogenesis. The
scenario is characterized by its minimal nature: the field content is that of
the Standard Model and all interactions consistent with the gauge symmetry are
admitted. Baryon number is violated via a dimension-6 proton decay operator,
suppressed today by the mechanism of quark-lepton separation in extra
dimensions; we assume that this operator was unsuppressed in the early Universe
due to a time-dependent quark-lepton separation. The source of CP violation is
the CKM matrix, in combination with the dimension-6 operators. We find that
almost independently of cosmology, sufficient baryogenesis is nearly impossible
in such a scenario if the fundamental scale is above 100 TeV, as required by an
unsuppressed neutron-antineutron oscillation operator. The only exception
producing sufficient baryon asymmetry is a scenario involving
out-of-equilibrium c quarks interacting with equilibrium b quarks.Comment: 39 pages, 5 figures v2: typos, presentational changes, references and
acknowledgments adde
Infrared absorption study of charge ordered
Infrared absorption study has been carried out on a series of half doped
manganites, , with
varying magnetic ground state. The charge ordering transition observed in
samples with {\normalsize is accompanied by a mode at
in addition to the stretching mode at and bending
mode at . Phonon hardening is found to occur below the CE - type
antiferromagnetic ordering temperature. The value of the insulating gap
decreases on doping with Sr from to }Comment: 14 pages, 5 figures, To appear in Physica
To wet or not to wet: that is the question
Wetting transitions have been predicted and observed to occur for various
combinations of fluids and surfaces. This paper describes the origin of such
transitions, for liquid films on solid surfaces, in terms of the gas-surface
interaction potentials V(r), which depend on the specific adsorption system.
The transitions of light inert gases and H2 molecules on alkali metal surfaces
have been explored extensively and are relatively well understood in terms of
the least attractive adsorption interactions in nature. Much less thoroughly
investigated are wetting transitions of Hg, water, heavy inert gases and other
molecular films. The basic idea is that nonwetting occurs, for energetic
reasons, if the adsorption potential's well-depth D is smaller than, or
comparable to, the well-depth of the adsorbate-adsorbate mutual interaction. At
the wetting temperature, Tw, the transition to wetting occurs, for entropic
reasons, when the liquid's surface tension is sufficiently small that the free
energy cost in forming a thick film is sufficiently compensated by the fluid-
surface interaction energy. Guidelines useful for exploring wetting transitions
of other systems are analyzed, in terms of generic criteria involving the
"simple model", which yields results in terms of gas-surface interaction
parameters and thermodynamic properties of the bulk adsorbate.Comment: Article accepted for publication in J. Low Temp. Phy
The Kuiper Belt and Other Debris Disks
We discuss the current knowledge of the Solar system, focusing on bodies in
the outer regions, on the information they provide concerning Solar system
formation, and on the possible relationships that may exist between our system
and the debris disks of other stars. Beyond the domains of the Terrestrial and
giant planets, the comets in the Kuiper belt and the Oort cloud preserve some
of our most pristine materials. The Kuiper belt, in particular, is a
collisional dust source and a scientific bridge to the dusty "debris disks"
observed around many nearby main-sequence stars. Study of the Solar system
provides a level of detail that we cannot discern in the distant disks while
observations of the disks may help to set the Solar system in proper context.Comment: 50 pages, 25 Figures. To appear in conference proceedings book
"Astrophysics in the Next Decade
Search for lepton-flavor violation at HERA
A search for lepton-flavor-violating interactions and has been performed with the ZEUS detector using the entire HERA I
data sample, corresponding to an integrated luminosity of 130 pb^{-1}. The data
were taken at center-of-mass energies, , of 300 and 318 GeV. No
evidence of lepton-flavor violation was found, and constraints were derived on
leptoquarks (LQs) that could mediate such interactions. For LQ masses below
, limits were set on , where
is the coupling of the LQ to an electron and a
first-generation quark , and is the branching ratio of
the LQ to the final-state lepton ( or ) and a quark . For
LQ masses much larger than , limits were set on the four-fermion
interaction term for LQs that couple to an electron and a quark
and to a lepton and a quark , where and are
quark generation indices. Some of the limits are also applicable to
lepton-flavor-violating processes mediated by squarks in -Parity-violating
supersymmetric models. In some cases, especially when a higher-generation quark
is involved and for the process , the ZEUS limits are the most
stringent to date.Comment: 37 pages, 10 figures, Accepted by EPJC. References and 1 figure (Fig.
6) adde
Multijet production in neutral current deep inelastic scattering at HERA and determination of alpha_s
Multijet production rates in neutral current deep inelastic scattering have
been measured in the range of exchanged boson virtualities 10 < Q2 < 5000 GeV2.
The data were taken at the ep collider HERA with centre-of-mass energy sqrt(s)
= 318 GeV using the ZEUS detector and correspond to an integrated luminosity of
82.2 pb-1. Jets were identified in the Breit frame using the k_T cluster
algorithm in the longitudinally invariant inclusive mode. Measurements of
differential dijet and trijet cross sections are presented as functions of jet
transverse energy E_{T,B}{jet}, pseudorapidity eta_{LAB}{jet} and Q2 with
E_{T,B}{jet} > 5 GeV and -1 < eta_{LAB}{jet} < 2.5. Next-to-leading-order QCD
calculations describe the data well. The value of the strong coupling constant
alpha_s(M_Z), determined from the ratio of the trijet to dijet cross sections,
is alpha_s(M_Z) = 0.1179 pm 0.0013(stat.) {+0.0028}_{-0.0046}(exp.)
{+0.0064}_{-0.0046}(th.)Comment: 22 pages, 5 figure
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