8,202 research outputs found
Observation of mixed anisotropy in the critical susceptibility of an ultrathin magnetic film
Measurements of the magnetic susceptibility of Fe/W(110) films with thickness
in the range of 1.6 to 2.4 ML Fe, show that in addition to the large response
along the easy axis associated with the Curie transition, there is a much
smaller, paramagnetic hard axis response that is not consistent with the 2D
anisotropic Heisenberg model used to describe homogeneous in-plane ferromagnets
with uniaxial anisotropy. The shape, amplitude, and peak temperature of the
hard axis susceptibility, as well as its dependence upon layer completion close
to 2.0 ML, indicate that inhomogeneities in the films create a system of mixed
anisotropy. A likely candidate for inhomogeneities that are magnetically
relevant in the critical region are the closed lines of step edges associated
with the incomplete layers. According to the Harris criterion, the existence of
magnetically relevant inhomogeneities may alter the critical properties of the
films from those of a 2D Ising model. Experiments in the recent literature are
discussed in this context.Comment: 9 two-column pages, 6 figures. This replacement has a new title and
abstract, and one additional figur
Specifying the Caltech asynchronous microprocessor
The action systems framework for modelling parallel programs is used to formally specify a microprocessor. First the microprocessor is specified as a sequential program. The sequential specification is then decomposed and refined into a concurrent program using correctness-preserving program transformations. Previously this microprocessor has been specified at Caltech, where an asynchronous circuit for the microprocessor was derived from the specification. We propose a specification strategy that is based on the idea of spatial decomposition of the program variable space
Systematics of heavy-ion fusion hindrance at extreme sub-barrier energies
The recent discovery of hindrance in heavy-ion induced fusion reactions at
extreme sub-barrier energies represents a challenge for theoretical models.
Previously, it has been shown that in medium-heavy systems, the onset of fusion
hindrance depends strongly on the "stiffness" of the nuclei in the entrance
channel. In this work, we explore its dependence on the total mass and the
-value of the fusing systems and find that the fusion hindrance depends in a
systematic way on the entrance channel properties over a wide range of systems.Comment: Submitted to Phys. Rev. Lett., 5 pages, 3 figure
The composition of Event-B models
The transition from classical B [2] to the Event-B language and method [3] has seen the removal of some forms of model structuring and composition, with the intention of reinventing them in future. This work contributes to thatreinvention. Inspired by a proposed method for state-based decomposition and refinement [5] of an Event-B model, we propose a familiar parallel event composition (over disjoint state variable lists), and the less familiar event fusion (over intersecting state variable lists). A brief motivation is provided for these and other forms of composition of models, in terms of feature-based modelling. We show that model consistency is preserved under such compositions. More significantly we show that model composition preserves refinement
Simultaneous observation of high order multiple quantum coherences at ultralow magnetic fields
We present a method for the simultaneous observation of heteronuclear
multi-quantum coherences (up to the 3rd order), which give an additional degree
of freedom for ultralow magnetic field (ULF) MR experiments, where the chemical
shift is negligible. The nonequilibrium spin state is generated by Signal
Amplification By Reversible Exchange (SABRE) and detected at ULF with
SQUID-based NMR. We compare the results obtained by the heteronuclei Correlated
SpectroscopY (COSY) with a Flip Angle FOurier Series (FAFOS) method. COSY
allows a quantitative analysis of homo- and heteronuclei quantum coherences
Towards Symbolic Model-Based Mutation Testing: Combining Reachability and Refinement Checking
Model-based mutation testing uses altered test models to derive test cases
that are able to reveal whether a modelled fault has been implemented. This
requires conformance checking between the original and the mutated model. This
paper presents an approach for symbolic conformance checking of action systems,
which are well-suited to specify reactive systems. We also consider
nondeterminism in our models. Hence, we do not check for equivalence, but for
refinement. We encode the transition relation as well as the conformance
relation as a constraint satisfaction problem and use a constraint solver in
our reachability and refinement checking algorithms. Explicit conformance
checking techniques often face state space explosion. First experimental
evaluations show that our approach has potential to outperform explicit
conformance checkers.Comment: In Proceedings MBT 2012, arXiv:1202.582
Fission Hindrance in hot 216Th: Evaporation Residue Measurements
The fusion evaporation-residue cross section for 32S+184W has been measured
at beam energies of E_beam = 165, 174, 185, 196, 205, 215, 225, 236, 246,and
257 MeV using the ATLAS Fragment Mass Analyzer. The data are compared with
Statistical Model calculations and it is found that a nuclear dissipation
strength, which increases with excitation energy, is required to reproduce the
excitation function. A comparison with previously published data show that the
dissipation strength depends strongly on the shell structure of the nuclear
system.Comment: 15 pages 9 figure
Identified particles in Au+Au collisions at sqrt{s_NN} = 200 GeV
The yields of identified particles have been measured at RHIC for Au+Au
collisions at sqrt{s_NN} = 200 GeV using the PHOBOS spectrometer. The ratios of
antiparticle to particle yields near mid-rapidity are presented. The first
measurements of the invariant yields of charged pions, kaons and protons at
very low transverse momenta are also shown.Comment: 4 pages, 4 figures, Contribution to Quark Matter 2002, Nantes,
France, July 200
Bone quality changes as measured by Raman and FTIR spectroscopy in primiparous cows with humeral fracture from New Zealand.
The occurrence of spontaneous humeral fractures in primiparous dairy cows from New Zealand prompted the study of bone material from affected cows to further characterize this condition and to outline a likely pathogenesis. Previous studies indicate that these cows developed osteoporosis due to periods of suboptimal bone formation followed by increased bone resorption during the period of lactation complicated by copper deficiency. We hypothesized that there are significant differences in the chemical composition/bone quality in bones from cows with spontaneous humeral fracture compared to cows without humeral fractures. In this study, Raman and Fourier transform infrared spectroscopy band ratios were, for the first time, measured, calculated, and compared in bone samples from 67 primiparous dairy cows that suffered a spontaneous fracture of the humerus and 14 age-matched post-calving cows without humeral fractures. Affected bone showed a significantly reduced mineral/matrix ratio, increased bone remodeling, newer bone tissue with lower mineralization and, lower carbonate substitution, and reduced crystallinity. As such, is likely that these have detrimentally impacted bone quality and strength in affected cows.Published onlin
Fusion-Fission of 16O+197Au at Sub-Barrier Energies
The recent discovery of heavy-ion fusion hindrance at far sub-barrier
energies has focused much attention on both experimental and theoretical
studies of this phenomenon. Most of the experimental evidence comes from
medium-heavy systems such as Ni+Ni to Zr+Zr, for which the compound system
decays primarily by charged-particle evaporation. In order to study heavier
systems, it is, however, necessary to measure also the fraction of the decay
that goes into fission fragments. In the present work we have, therefore,
measured the fission cross section of 16O+197Au down to unprecedented far
sub-barrier energies using a large position sensitive PPAC placed at backward
angles. The preliminary cross sections will be discussed and compared to
earlier studies at near-barrier energies. No conclusive evidence for
sub-barrier hindrance was found, probably because the measurements were not
extended to sufficiently low energies.Comment: Fusion06 - Intl. Conf. on Reaction Mechanisms and Nuclear Structure
at the Coulomb Barrier, San Servolo, Venezia, Italy, March 19-223, 2006 5
pages, 4 figure
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