536 research outputs found
Experimental Evidence for Two-Dimensional Magnetic Order in Proton Bombarded Graphite
We have prepared magnetic graphite samples bombarded by protons at low
temperatures and low fluences to attenuate the large thermal annealing produced
during irradiation. An overall optimization of sample handling allowed us to
find Curie temperatures K at the used fluences. The
magnetization versus temperature shows unequivocally a linear dependence, which
can be interpreted as due to excitations of spin waves in a two dimensional
Heisenberg model with a weak uniaxial anisotropy.Comment: 4 pages, 3 figure
On the background in the reaction and mixed event simulation
In this paper we evaluate sources of background for the , with the detected through its decay channel, to
compare with the experiment carried out at ELSA. We find background from
followed by decay of a into two ,
recombining one and one , and from the reaction with subsequent decay of the into two photons. This
background accounts for the data at invariant masses beyond 700
MeV, but strength is missing at lower invariant masses which was attributed to
photon misidentification events, which we simulate to get a good reproduction
of the experimental background. Once this is done, we perform an event mixing
simulation to reproduce the calculated background and we find that the method
provides a good description of the background at low invariant
masses but fakes the background at high invariant masses, making background
events at low invariant masses, which are due to misidentification
events, responsible for the background at high invariant masses which is due to
the and reactions.Comment: 10 pages, 5 figure
Magnetic moments of the low-lying , resonances within the framework of the chiral quark model
The magnetic moments of the low-lying spin-parity ,
resonances, like, for example, ,
, as well as their transition magnetic moments, are
calculated using the chiral quark model. The results found are compared with
those obtained from the nonrelativistic quark model and those of unitary chiral
theories, where some of these states are generated through the dynamics of two
hadron coupled channels and their unitarization
The , interaction in finite volume and the resonance
In this work the interaction of the coupled channels and
in an SU(4) extrapolation of the chiral unitary theory, where the
resonance appears as dynamically generated from that
interaction, is extended to produce results in finite volume. Energy levels in
the finite box are evaluated and, assuming that they would correspond to
lattice results, the inverse problem of determining the phase shifts in the
infinite volume from the lattice results is solved. We observe that it is
possible to obtain accurate phase shifts and the position of the
resonance, but it requires the explicit consideration of the
two coupled channels. We also observe that some of the energy levels in the box
are attached to the closed channel, such that their use to induce the phase shifts via L\"uscher's formula leads to incorrect results.Comment: 10 pages, 13 figures, accepted for publication in Eur. Phys. J.
Meeting Report: Hackathon-Workshop on Darwin Core and MIxS Standards Alignment
The Global Biodiversity Information Facility and the Genomic Standards Consortium convened a joint workshop at the University of Oxford, 27–29 February 2012, with a small group of experts from Europe, USA, China and Japan, to continue the alignment of the Darwin Core with the MIxS and related genomics standards. Several reference mappings were produced as well as test expressions of MIxS in RDF. The use and management of controlled vocabulary terms was considered in relation to both GBIF and the GSC, and tools for working with terms were reviewed. Extensions for publishing genomic biodiversity data to the GBIF network via a Darwin Core Archive were prototyped and work begun on preparing translations of the Darwin Core to Japanese and Chinese. Five genomic repositories were identified for engagement to begin the process of testing the publishing of genomic data to the GBIF network commencing with the SILVA rRNA database
Effects of pseudoscalar-baryon channels in the dynamically generated vector-baryon resonances
We study the interaction of vector mesons with the octet of stable baryons in
the framework of the local hidden gauge formalism using a coupled channels
unitary approach, including also the pseudoscalar-baryon channels which couple
to the same quantum numbers. We examine the scattering amplitudes and their
poles, which can be associated to known baryon resonances,
and determine the role of the pseudoscalar-baryon channels, changing the width
and eventually the mass of the resonances generated with only the basis of
vector-baryon states
Penta-quark states with hidden charm and beauty
More and more hadron states are found to be difficult to be accommodated by
the quenched quark models which describe baryons as 3-quark states and mesons
as antiquark-quark states. Dragging out an antiquark-quark pair from the gluon
field in hadrons should be an important excitation mechanism for hadron
spectroscopy. Our recent progress on the penta-quark states with hidden charm
and beauty is reviewed.Comment: Plenary talk at the 5th Asia-Pacific Conference on Few-Body Problems
in Physics 2011 (APFB2011), 22-26 Aug., 2011, Seoul, Kore
Expressive and Instrumental Offending: Reconciling the Paradox of Specialisation and Versatility
Although previous research into specialisation has been dominated by the debate over the existence of specialisation versus versatility, it is suggested that research needs to move beyond the restrictions of this dispute. The current study explores the criminal careers of 200 offenders based on their criminal records, obtained from a police database in the North West of England, aiming to understand the patterns and nature of specialisation by determining the presence of differentiation within their general offending behaviours and examining whether the framework of Expressive and Instrumental offending styles can account for any specialised tendencies that emerge. Fifty-eight offences were subjected to Smallest Space Analysis. Results revealed that a model of criminal differentiation could be identified and that any specialisation is represented in terms of Expressive and Instrumental offending styles
Quantum Histories and Quantum Gravity
This paper reviews the histories approach to quantum mechanics. This
discussion is then applied to theories of quantum gravity. It is argued that
some of the quantum histories must approximate (in a suitable sense) to
classical histories, if the correct classical regime is to be recovered. This
observation has significance for the formulation of new theories (such as
quantum gravity theories) as it puts a constraint on the kinematics, if the
quantum/classical correspondence principle is to be preserved. Consequences for
quantum gravity, particularly for Lorentz symmetry and the idea of "emergent
geometry", are discussed.Comment: 35 pages (29 pages main body), two figure
Towards a global platform for linking soil biodiversity data
Soil biodiversity is immense, with an estimated 10–100 million organisms belonging to over 5000 taxa in a handful of soil. In spite of the importance of soil biodiversity for ecosystem functions and services, information on soil species, from taxonomy to biogeographical patterns, is incomplete and there is no infrastructure to connect pre-existing or future data. Here, we propose a global platform to allow for greater access to soil biodiversity information by linking databases and repositories through a single open portal. The proposed platform would for the first time, link data on soil organisms from different global sites and biomes, and will be inclusive of all data types, from molecular sequences to morphology measurements and other supporting information. Access to soil biodiversity species records and information will be instrumental to progressing scientific research and education. Further, as demonstrated by previous biodiversity synthesis efforts, data availability is key for adapting to, and creating mitigation plans in response to global changes. With the rapid influx of soil biodiversity data, now is the time to take the first steps forward in establishing a global soil biodiversity information platform
- …