624 research outputs found
Size effects in the magnetic behaviour of TbAl_2 milled alloys
The study of the magnetic properties depending upon mechanical milling of the
ferromagnetic polycrystalline TbAl_2 material is reported. The Rietveld
analysis of the X-ray diffraction data reveals a decrease of the grain size
down to 14 nm and -0.15 % of variation of the lattice parameter, after 300
hours of milling time. Irreversibility in the zero field cooled - field cooled
(ZFC-FC) DC-susceptibility and clear peaks in the AC susceptibility between 5
and 300 K show that the long-range ferromagnetic structure is inhibited in
favour of a disordered spin arrangement below 45 K. This glassy behaviour is
also deduced from the variation of the irreversibility transition with the
field (H^{2/3}) and frequency. The magnetization process of the bulk TbAl_2 is
governed by domain wall thermal activation processes. By contrast, in the
milled samples, cluster-glass properties arise as a result of cooperative
interactions due to the substitutional disorder. The interactions are also
influenced by the nanograin structure of the milled alloys, showing a variation
of coercivity with the grain size, below the crossover between the multi- and
single-domain behaviours.Comment: 23 pages, 11 figures, to appear in J. Phys.: Condens. Ma
Projective Ring Line of a Specific Qudit
A very particular connection between the commutation relations of the
elements of the generalized Pauli group of a -dimensional qudit, being a
product of distinct primes, and the structure of the projective line over the
(modular) ring \bZ_{d} is established, where the integer exponents of the
generating shift () and clock () operators are associated with submodules
of \bZ^{2}_{d}. Under this correspondence, the set of operators commuting
with a given one -- a perp-set -- represents a \bZ_{d}-submodule of
\bZ^{2}_{d}. A crucial novel feature here is that the operators are also
represented by {\it non}-admissible pairs of \bZ^{2}_{d}. This additional
degree of freedom makes it possible to view any perp-set as a {\it
set-theoretic} union of the corresponding points of the associated projective
line
Projective Ring Line Encompassing Two-Qubits
The projective line over the (non-commutative) ring of two-by-two matrices
with coefficients in GF(2) is found to fully accommodate the algebra of 15
operators - generalized Pauli matrices - characterizing two-qubit systems. The
relevant sub-configuration consists of 15 points each of which is either
simultaneously distant or simultaneously neighbor to (any) two given distant
points of the line. The operators can be identified with the points in such a
one-to-one manner that their commutation relations are exactly reproduced by
the underlying geometry of the points, with the ring geometrical notions of
neighbor/distant answering, respectively, to the operational ones of
commuting/non-commuting. This remarkable configuration can be viewed in two
principally different ways accounting, respectively, for the basic 9+6 and 10+5
factorizations of the algebra of the observables. First, as a disjoint union of
the projective line over GF(2) x GF(2) (the "Mermin" part) and two lines over
GF(4) passing through the two selected points, the latter omitted. Second, as
the generalized quadrangle of order two, with its ovoids and/or spreads
standing for (maximum) sets of five mutually non-commuting operators and/or
groups of five maximally commuting subsets of three operators each. These
findings open up rather unexpected vistas for an algebraic geometrical
modelling of finite-dimensional quantum systems and give their numerous
applications a wholly new perspective.Comment: 8 pages, three tables; Version 2 - a few typos and one discrepancy
corrected; Version 3: substantial extension of the paper - two-qubits are
generalized quadrangles of order two; Version 4: self-dual picture completed;
Version 5: intriguing triality found -- three kinds of geometric hyperplanes
within GQ and three distinguished subsets of Pauli operator
De la faille alpine à la fosse de Puysegur (Nouvelle-Zélande) : résultats de la campagne de cartographie multifaisceaux GEODYNZ-SUD, Leg 2
Le Leg 2 de la campagne GEODYNZ-SUD, menée au SW de la Nouvelle-Zélande, a permis de reconnaître les structures qui accompagnent du Nord au Sud le passage de la faille alpine à la subduction oblique sous la marge du Fiodland, puis à celle naissante, intra-océanique sous la ride de Macquarie. Au Nord et au-dessus de la plaque australienne subductée vers l'Est, un faisceau longitudinal de décrochements converge vers le système transpressif de la faille alpine en découpant la marge continentale. Au Sud, la déformation décrochante est strictement localisée au sommet de la ride de Macquarie. (Résumé d'auteur
Trade openness, income levels, and economic growth: the case of developing countries, 1970–2009.
This paper attempts to investigate the extent to which trade openness has had an impact on the levels of income and rates of growth in a sample of 115 developing countries for the period 1970–2009. Additionally, to assess whether there is an income level threshold for a country to benefit from international trade, the sample is broken down into three mutually exclusive groups of countries: low-income, lower middle-income, and upper middleincome countries. The main novelty of the paper lies on the use, on the one hand, of a new and better trade openness measure and, on the other hand, of non-stationary heterogeneous panel cointegration techniques to cope with the problem of cross-sectional dependence. The results show a positive bidirectional relationship between trade openness and income level in the long run, thus suggesting that trade openness is both a cause and a consequence of the level of income. The results for the short run, that is, the link between openness growth and economic growth, go in the same direction
A Further Examination of the Export-Led Growth Hypothesis
This paper challenges the common view that exports generally contribute more to GDP growth than a pure change in export volume, as the export-led growth hypothesis predicts. Applying panel cointegration techniques to a production function with non-export GDP as the dependent variable, we find for a sample of 45 developing countries that: (i) exports have a positive short-run effect on non-export GDP and vice versa (short-run bidirectional causality), (ii) the long-run effect of exports on non-export output, however, is negative on average, but (iii) there are large differences in the longrun effect of exports on non-export GDP across countries. Cross-sectional regressions indicate that these cross-country differences in the long-run effect of exports on nonexport GDP are significantly negatively related to cross-country differences in primary export dependence and business and labor market regulation. In contrast, there is no significant association between the growth effect of exports and the capacity of a country to absorb new knowledge
Critical properties of random anisotropy magnets
The problem of critical behaviour of three dimensional random anisotropy
magnets, which constitute a wide class of disordered magnets is considered.
Previous results obtained in experiments, by Monte Carlo simulations and within
different theoretical approaches give evidence for a second order phase
transition for anisotropic distributions of the local anisotropy axes, while
for the case of isotropic distribution such transition is absent. This outcome
is described by renormalization group in its field theoretical variant on the
basis of the random anisotropy model. Considerable attention is paid to the
investigation of the effective critical behaviour which explains the
observation of different behaviour in the same universality class.Comment: 41 pages, 10 figure
Health professionals' and managers' definitions of developmentally appropriate healthcare for young people:Conceptual dimensions and embedded controversies
Objectives: We aimed to (i) explore how health professionals and managers who work with young people seek to define developmentally appropriate healthcare (DAH), (ii) identify the range of conceptual dimensions present in their definitions and (iii) explore the controversies embedded in their characterisations of DAH.
Methods: A qualitative multisite ethnographic study was conducted across three hospitals in England. We undertook face-to-face semi-structured interviews with health professionals and managers; and non-participant observation in clinics, wards and meetings. Anonymised field notes and interview transcripts were analysed using thematic analysis. The theme conceptualisations of DAH' was then further analysed, and the resulting themes categorised to form conceptual dimensions.
Results: We recruited 192 participants and conducted 65 interviews (41 with health professionals and 24 with managers) and approximately 1600 hours of non-participant observations (involving 103 health professionals and 72 managers). Despite the wide range of definitions provided by participants, five conceptual dimensions of DAH were identified: (i) biopsychosocial development and holistic care, (ii) acknowledgement of young people as a distinct group, (iii) adjustment of care as the young person develops, (iv) empowerment of the young person by embedding health education and health promotion and (v) interdisciplinary and interorganisational work. Also, some controversies were identified within most dimensions.
Conclusions: This study illustrates the lack of a generalised definition of DAH for young people among UK health professionals and managers, and presents a set of five core dimensions that can inform future research to help define and evaluate DAH for young people
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