1,482 research outputs found
Physical Origin, Evolution and Observational Signature of Diffused Antiworld
The existence of macroscopic regions with antibaryon excess in the baryon
asymmetric Universe with general baryon excess is the possible consequence of
practically all models of baryosynthesis. Diffusion of matter and antimatter to
the border of antimatter domains defines the minimal scale of the antimatter
domains surviving to the present time. A model of diffused antiworld is
considered, in which the density within the surviving antimatter domains is too
low to form gravitationally bound objects. The possibility to test this model
by measurements of cosmic gamma ray fluxes is discussed. The expected gamma ray
flux is found to be acceptable for modern cosmic gamma ray detectors and for
those planned for the near future.Comment: 9 page
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Onset and Saturation of Ion Heating by Odd-parity Rotating-magnetic-fields in a Field-reversed Configuration
Heating of figure-8 ions by odd-parity rotating magnetic fields (RMFο) applied to an elongated field-reversed configuration (FRC) is investigated. The largest energy gain occurs at resonances (s ≡ ω(sub)R⁄ω) of the RMFο frequency, ω(sub)R, with the figure-8 orbital frequency, ω, and is proportional to s^2 for s – even resonances and to s for s – odd resonances. The threshold for the transition from regular to stochastic orbits explains both the onset and saturation of heating. The FRC magnetic geometry lowers the threshold for heating below that in the tokamak by an order of magnitude
Osmium isotope evidence for two pulses of increased continental weathering linked to Early Jurassic volcanism and climate change
Large igneous provinces (LIPs) are proposed to have caused a number of episodes of abrupt environmental change by increasing atmospheric CO2 levels, which were subsequently alleviated by drawdown of CO2 via enhanced continental weathering and burial of organic matter. Here the sedimentary records of two such episodes of environmental change, the Toarcian oceanic anoxic event (T-OAE) and preceding Pliensbachian–Toarcian (Pl-To) event (both possibly linked to the Karoo-Ferrar LIP), are investigated using a new suite of geochemical proxies that have not been previously compared. Stratigraphic variations in osmium isotope (187Os/188Os) records are compared with those of mercury (Hg) and carbon isotopes (d13C) in samples from the Mochras core, Llanbedr Farm, Cardigan Bay Basin, Wales. These sedimentary rocks are confirmed as recording an open-marine setting by analysis of molybdenum/uranium enrichment trends, indicating that the Os isotope record in these samples reflects the isotopic composition of the global ocean. The Os isotope data include the first results across the Pl-To boundary, when seawater 187Os/188Os increased from ~0.40 to ~0.53, in addition to new data that show elevated 187Os/188Os (from ~0.42 to ~0.68) during the T-OAE. Both increases in 187Os/188Os correlate with negative carbon isotope excursions and increased mercury concentrations, supporting an interplay between terrestrial volcanism, weathering, and climate that was instrumental in driving these distinct episodes of global environmental change. These observations also indicate that the environmental impact of the Karoo-Ferrar LIP was not limited solely to the T-OAE
Multifragmentation of non-spherical nuclei
The shape influence of decaying thermalized source on various characteristics
of multifragmentation as well as its interplay with effects of angular momentum
and collective expansion are first studied and the most pertinent variables are
proposed. The analysis is based on the extension of the statistical
microcanonical multifragmentation model.Comment: 5 pages, 4 figure
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Quantifying seawater exchange rates in the Eocene Arctic Basin using osmium isotopes
The closure of seaways that connected the Arctic Ocean to the global ocean during the early Paleogene led to severe hydrographic restriction. We present new osmium isotope data from organic-rich sediments deposited in the central Arctic Ocean during the Early–Middle Eocene. The new data show that the long term isotopic composition of osmium in Arctic seawater began to diverge from that of the global ocean at ∼54 Ma, after the Eocene Thermal Maximum 2 hyperthermal event. This divergence was probably caused by the gradual closure of seaways connecting the Arctic Ocean to the global ocean. The Os data are used to calculate water exchange rates between the Arctic and surrounding oceans and to calculate Arctic Ocean salinity during the Early Eocene. The results show that the development of severe, long term Arctic Basin restriction after ∼54 Ma occurred as open ocean seawater input decreased below ∼0.01 Sv, resulting in a mean basin salinity between 8–16 PSU, depending on model assumptions
Contextual Agent Deliberation in Defeasible Logic
This article extends Defeasible Logic to deal with the contextual deliberation process of cognitive agents. First, we introduce meta-rules to reason with rules. Meta-rules are rules that have as a consequent rules for motivational components, such as obligations, intentions and desires. In other words, they include nested rules. Second, we introduce explicit preferences among rules. They deal with complex structures where nested rules can be involved
Trapping of Single Atoms with Single Photons in Cavity QED
Two recent experiments have reported the trapping of individual atoms inside
optical resonators by the mechanical forces associated with single photons
[Hood et al., Science 287, 1447 (2000) and Pinkse et al., Nature 404, 365
(2000)]. Here we analyze the trapping dynamics in these settings, focusing on
two points of interest. Firstly, we investigate the extent to which
light-induced forces in these experiments are distinct from their free-space
counterparts. Secondly, we explore the quantitative features of the resulting
atomic motion and how these dynamics are mapped onto variations of the
intracavity field. Not surprisingly, qualitatively distinct atomic dynamics
arise as the coupling and dissipative rates are varied. For the experiment of
Hood et al., we show that atomic motion is largely conservative and is
predominantly in radial orbits transverse to the cavity axis. A comparison with
the free-space theory demonstrates that the fluctuations of the dipole force
are suppressed by an order of magnitude. This effect is based upon the
Jaynes-Cummings eigenstates of the atom-cavity system and represents
qualitatively new physics for optical forces at the single-photon level. By
contrast, even in a regime of strong coupling in the experiment of Pinkse et
al., there are only small quantitative distinctions between the free-space
theory and the quantum theory, so it is not clear that description of this
experiment as a novel single-quantum trapping effect is necessary. The atomic
motion is strongly diffusive, leading to an average localization time
comparable to the time for an atom to transit freely through the cavity and to
a reduction in the ability to infer aspects of the atomic motion from the
intracavity photon number.Comment: 19 pages, 22 figure files, REVTEX, corrected spelling, LaTeX now
produces postscript which includes figures, minor changes to figures. Final
version to be published in Physical Review A, expanded summary of results in
introduction, minor changes to figures and tex
Schizotypy as an organizing framework for social and affective sciences
Schizotypy, defined in terms of commonly occurring personality
traits related to the schizophrenia spectrum, has been
an important construct for understanding the neurodevelopment
and stress-diathesis of schizophrenia. However, as
schizotypy nears its sixth decade of application, it is important
to acknowledge its impressively rich literature accumulating
outside of schizophrenia research. In this article, we
make the case that schizotypy has considerable potential
as a conceptual framework for understanding individual
differences in affective and social functions beyond those
directly involved in schizophrenia spectrum pathology. This
case is predicated on (a) a burgeoning literature noting
anomalies in a wide range of social functioning, affiliative,
positive and negative emotional, expressive, and social cognitive
systems, (b) practical and methodological features
associated with schizotypy research that help facilitate
empirical investigation, and (c) close ties to theoretical
constructs of central importance to affective and social science
(eg, stress diathesis, neural compensation). We highlight
recent schizotypy research, ie providing insight into
the nature of affective and social systems more generally.
This includes current efforts to clarify the neurodevelopmental,
neurobiological, and psychological underpinnings
of affiliative drives, hedonic capacity, social cognition, and
stress responsivity systems. Additionally, we discuss neural
compensatory and resilience factors that may mitigate the
expression of stress-diathesis and functional outcome, and
highlight schizotypy's potential role for understanding cultural
determinants of social and affective functions
Isospin Fluctuations from a Thermally Equilibrated Hadron Gas
Partition functions, multiplicity distributions, and isospin fluctuations are
calculated for canonical ensembles in which additive quantum numbers as well as
total isospin are strictly conserved. When properly accounting for
Bose-Einstein symmetrization, the multiplicity distributions of neutral pions
in a pion gas are significantly broader as compared to the non-degenerate case.
Inclusion of resonances compensates for this broadening effect. Recursion
relations are derived which allow calculation of exact results with modest
computer time.Comment: 10 pages, 5 figure
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