3,940 research outputs found
Spin-1 Heisenberg antiferromagnetic chain with exchange and single-ion anisotropies
Using density matrix renormalization group calculations, ground state
properties of the spin-1 Heisenberg chain with exchange and single-ion
anisotropies in an external field are studied. Our findings confirm and refine
recent results by Sengupta and Batista, Physical Review Letters 99, 217205
(2007) (2007), on the same model applying Monte Carlo techniques. In
particular, we present evidence for two types of biconical (or supersolid) and
for two types of spin-flop (or superfluid) structures. Basic features of the
quantum phase diagram may be interpreted qualitatively in the framework of
classical spin models.Comment: Ref. 1 corrected (also in the abstract
Valuing Strategic Alliances in the Pharmaceutical/Biotechnology Industry
In an era of rapid and changing technological advances, a firm's survival and growth depends on its' ability to introduce products to the market. Since a firm's growth and survival depends on its' ability to develop products and services over time (Penrose, 1959), the question posed by this study is what determines a firm's ability to introduce products to market? In this study, a firm's ability to introduce product to markets are influenced by its' "absorptive capacity" to identify and internalize the resource benefits of its' alliance partners. Such an integrated view is absent in firm level and strategic alliance studies of product development. A conceptual model of firm product introductions is developed and empirically tested. Results generally support the hypotheses of this study.Research and Development/Tech Change/Emerging Technologies,
Levy-stable distributions revisited: tail index > 2 does not exclude the Levy-stable regime
Power-law tail behavior and the summation scheme of Levy-stable distributions
is the basis for their frequent use as models when fat tails above a Gaussian
distribution are observed. However, recent studies suggest that financial asset
returns exhibit tail exponents well above the Levy-stable regime (). In this paper we illustrate that widely used tail index estimates (log-log
linear regression and Hill) can give exponents well above the asymptotic limit
for close to 2, resulting in overestimation of the tail exponent in
finite samples. The reported value of the tail exponent around 3 may
very well indicate a Levy-stable distribution with .Comment: To be published in Int. J. Modern Physics C (2001) vol. 12 no.
Warren McCulloch and the British cyberneticians
Warren McCulloch was a significant influence on a number of British cyberneticians, as some British pioneers in this area were on him. He interacted regularly with most of the main figures on the British cybernetics scene, forming close friendships and collaborations with several, as well as mentoring others. Many of these interactions stemmed from a 1949 visit to London during which he gave the opening talk at the inaugural meeting of the Ratio Club, a gathering of brilliant, mainly young, British scientists working in areas related to cybernetics. This paper traces some of these relationships and interaction
Classical and quantum anisotropic Heisenberg antiferromagnets
We study classical and quantum Heisenberg antiferromagnets with exchange
anisotropy of XXZ-type and crystal field single-ion terms of quadratic and
cubic form in a field. The magnets display a variety of phases, including the
spin-flop (or, in the quantum case, spin-liquid) and biconical (corresponding,
in the quantum lattice gas description, to supersolid) phases. Applying
ground-state considerations, Monte Carlo and density matrix renormalization
group methods, the impact of quantum effects and lattice dimension is analysed.
Interesting critical and multicritical behaviour may occur at quantum and
thermal phase transitions.Comment: 13 pages, 14 figures, conferenc
In Search of Professional Dispositions that Yield Cultural Relevance in Primary Grade Pedagogy: A Cautionary Tale of One Kindergarten Teacher
Primary grade teachers are challenged to establish firm learning foundations for all children, yet for many teachers cultural diversity makes this a complex pedagogical challenge. It is widely assumed that the success with which teachers meet this challenge is reflected in their dispositions toward diversity, and ultimately toward culturally relevant pedagogy as a professional orientation. This article describes a multi-year study of cultural relevance in early mathematics teaching. Using the case of one kindergarten teacher who exhibited positive dispositions toward cultural relevance, the authors examine factors that seemed to work against its adoption in her pedagogy
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