7,448 research outputs found
Onset of phase correlations in YBa2Cu3O{7-x} as determined from reversible magnetization measurements
Isofield magnetization curves are obtained and analyzed for three single
crystals of YBa2Cu3O{7-x}, ranging from optimally doped to very underdoped, as
well as the BCS superconductor Nb, in the presence of magnetic fields applied
both parallel and perpendicular to the planes. Near Tc, the magnetization
exhibits a temperature dependence \sqrt{M} [Ta(H)-T]^m. In accordance with
recent theories, we associated Ta(H) with the onset of coherent phase
fluctuations of the superconducting order parameter. For Nb and optimally doped
YBaCuO, Ta(H) is essentially identical to the mean-field transition line Tc(H).
The fitting exponent m=0.5 takes its mean-field value for Nb, and varies just
slightly from 0.5 for optimally doped YBaCuO. However, underdoped YBCO samples
exhibit anomalous behavior, with Ta(H)>Tc for H applied parallel to the c axis,
suggesting that the magnetization is probing a region of temperatures above Tc
where phase correlations persist. In this region, the fitting exponent falls in
the range 0.5 < m < 0.8 for H\parallel c, compared with m~0. for $H\parallel ab
planes. The results are interpreted in terms of an anisotropic pairing symmetry
of the order parameter: d-wave along the ab planes and s-wave along the c axis.Comment: 5 pages, 4 figure
A comparative study of high-field diamagnetic fluctuations in deoxygenated YBa2Cu3O(7-x) and polycrystalline (Bi-Pb)2Sr2Ca3O(10)
We studied three single crystals of YBa2Cu3O{7-x} with Tc= 62.5, 52, and 41
K, and a textured specimen of (Bi-Pb)2Sr2Ca2Cu3O10 with Tc=108 K, for H//c
axis. The reversible data were interpreted in terms of 2D lowest-Landau-level
fluctuation theory. The data were fit well by the 2D LLL expression for
magnetization obtained by Tesanovic etal., producing reasonable values of kappa
but larger values of dHc2/dT. Universality was studied by obtaining a
simultaneous scaling of Y123 data and Bi2223. An expression for the 2D x-axis
LLL scaling factor used to obtain the simultaneous scaling was extracted from
theory, and compared with the experimental values. The comparison between the
values of the x-axis produced a deviation of 40% which suggests that the
hypothesis of universality of the 2D-LLL fluctuations is not supported by the
studied samples. We finaly observe that Y123 magnetization data for
temperatures above obbey a universal scaling obtained for the diamagnetic
fluctuation magnetization from a theory considering non-local field effects.
The same scaling was not obbeyed by the corresponding magnetization calculated
from the two-dimensional lowest-Landau-level theory.Comment: 7 pages 5 figures, accept in Journ. Low Temp. Phy
A Robust Solution Procedure for Hyperelastic Solids with Large Boundary Deformation
Compressible Mooney-Rivlin theory has been used to model hyperelastic solids,
such as rubber and porous polymers, and more recently for the modeling of soft
tissues for biomedical tissues, undergoing large elastic deformations. We
propose a solution procedure for Lagrangian finite element discretization of a
static nonlinear compressible Mooney-Rivlin hyperelastic solid. We consider the
case in which the boundary condition is a large prescribed deformation, so that
mesh tangling becomes an obstacle for straightforward algorithms. Our solution
procedure involves a largely geometric procedure to untangle the mesh: solution
of a sequence of linear systems to obtain initial guesses for interior nodal
positions for which no element is inverted. After the mesh is untangled, we
take Newton iterations to converge to a mechanical equilibrium. The Newton
iterations are safeguarded by a line search similar to one used in
optimization. Our computational results indicate that the algorithm is up to 70
times faster than a straightforward Newton continuation procedure and is also
more robust (i.e., able to tolerate much larger deformations). For a few
extremely large deformations, the deformed mesh could only be computed through
the use of an expensive Newton continuation method while using a tight
convergence tolerance and taking very small steps.Comment: Revision of earlier version of paper. Submitted for publication in
Engineering with Computers on 9 September 2010. Accepted for publication on
20 May 2011. Published online 11 June 2011. The final publication is
available at http://www.springerlink.co
An exploratory study on social entrepreneurship in Egypt
Purpose
The purpose of this paper is to add to the existing wealth of knowledge on the benefits and challenges of social entrepreneurship in Egypt, a challenging emerging economy.
Design/methodology/approach
The research combines secondary and primary research with the latter including interviews across the public, private and social entrepreneurship sectors, together with surveys to gather Egyptian and international perspectives.
Findings
The study addresses several political, cultural and economic themes that significantly influence the emergence and growth of social entrepreneurship organisations in Egypt.
Research limitations/implications
Egypt is undergoing significant change at present; hence, this research provides a snapshot of what may be considered a very dynamic environment.
Practical implications
Recommendations are made that have practical implications for each of the public, private, development and non-profit sectors in Egypt. It is suggested that the public sector ought to unite its efforts under one umbrella organisation, the private sector could benefit from growing social awareness across the region, while development groups should continue to focus on education generally. Non-profit entities can seek to collaborate with others, and all organisations can make better use of developing global communications technology.
Social implications
A base of social entrepreneurship is already established in Egypt, but this research suggests that further encouragement of these initiatives could help develop the economy and foster a more socially aware culture and political landscape.
Originality/value
Social entrepreneurship in Egypt continues to evolve, and this research identifies a number of economic, cultural and political perspectives that, if addressed, could help accelerate progress
Non-centro-symmetric superconductors Li2Pd3B and Li2(Pd0.8Pt0.2)3B: amplitude and phase fluctuations analysis of the experimental magnetization data
We report on magnetization data obtained as a function of temperature and
magnetic field in Li2 (Pd0.8Pt0.2)3B and Li2Pd3B non-centro-symmetric
superconductors. Reversible magnetization curves were plotted as M1/2 vs. T.
This allows study of the asymptotic behavior of the averaged order parameter
amplitude (gap) near the superconducting transition. Results of the analysis
show, as expected, a mean field superconducting transition for Li2Pd3B. On
contrary, a large deviation from the mean field behavior is revealed for
Li2(Pd0.8Pt0.2)3B. This is interpreted as due to the strength of the non s-wave
spin-triplet pairing in this Pt-containing compound which produces nodes in the
order parameter and consequently, phase fluctuations. The diamagnetic signal
above Tc(H) in Li2Pd3B is well explained by superconducting Gaussian
fluctuations, which agrees with the observed mean field transition. For
Li2(Pd0.8Pt0.2)3B the diamagnetic signal above Tc(H) is much higher than the
expected Gaussian values and appears to be well explained by three dimensional
critical fluctuations of the lowest-Landau-level type, which somehow agrees
with the scenario of a phase mediated transition.Comment: 7 pages (1 column) 3 figure
English Language Learners and Special Education: One District\u27s Journey Through the Collaborative Problem Solving Process
English Language Learners are a growing population in schools in the United States. There are many challenges that face this group of students in addition to learning English as a new language. A major issue for teachers, schools, and districts is determining whether an English Language Learner is experiencing academic difficulties based on issues primarily related to language acquisition or whether a learning disability is contributing to the academic challenges. As a result, English Language Learners are often misidentified for Special Education services and may be placed in classrooms that are not adequately prepared or appropriate to meet their needs.
The purpose of this study is to describe the perceptions of educators in an urban, midwestern school district who participated in a collaborative problem solving process for identifying and addressing the academic needs of English Language Learners who may require a future referral for Special Education services.
Deciphering the differences between language acquisition and learning disabilities is difficult for educators. I used a narrative method of inquiry for this qualitative study in order to describe the perceptions and experiences of the educators involved in the English Language Learner/Special Education Collaborative Problem Solving Process pilot. Collecting the stories of the participants provided an opportunity to make sense of their experiences. By better understanding the perceptions and experiences of educators, a more efficient and systematic process could be developed for schools to follow when making decisions about which English Language Learners to recommend for a referral for a Special Education evaluation.
Advisor: Mary Beth Lehmanowsk
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