Final report for the field-reversed configuration power plant critical-issue scoping study
Santarius, John F.; Mogahed, Elsayed A.; Emmert, Gilbert A.; Khater, Hesham Y.; Nguyen, Canh N.; Ryzhkov, Sergei V.; Stubna, Michael D.; Steinhauer, Loren C.; Miley, George H.
2001-03-01
This report describes research in which a team from the Universities of Wisconsin, Washington, and Illinois performed a scoping study of critical issues for field-reversed configuration (FRC) power plants. The key tasks for this research were (1) systems analysis of deuterium-tritium (D-T) FRC fusion power plants, and (2) conceptual design of the blanket and shield module for an FRC fusion core.
NASA Astrophysics Data System (ADS)
Kolk, B.; Bleloch, A. L.
1988-02-01
By applying magnetic fields up to 2 kG, the equation of state and the critical dynamics of a spin system near its critical point can be studied with the Mössbauer effect. As an example, the equation of state near the Curie temperature of iron is investigated yielding the critical exponent δ=4.84±0.15.
Heat transport study of field-tuned quantum criticality in CeIrIn5
NASA Astrophysics Data System (ADS)
Shakeripour, H.; Tanatar, M. A.; Petrovic, C.; Taillefer, Louis
2016-02-01
The in-plane electrical resistivity, ρ , and thermal conductivity, κ , of the heavy-fermion superconductor CeIrIn5 were measured down to 40 mK in magnetic fields up to 11 T applied along the c axis. For all fields above Hc 2=4 T of filamentary superconductivity, we find that the ratio of heat and charge conductivities in the T →0 limit obeys the Wiedemann-Franz law, κ /T =L0/ρ , where L0=2.45 ×10-8 WΩ K-2 is the Sommerfeld value of the Lorenz number. The temperature-dependent parts of both the electrical and thermal resistivity, w ≡T /L0κ , follow the functional dependence expected for the Fermi liquid theory of metals with ρ -ρ0=A T2 , w -w0=B T2 , with ρ0=w0 and B ≈2 A . The coefficient B does not show a significant field dependence even upon approaching Hc 2=0.4 T of the bulk superconducting state. The weak response to the magnetic field is in stark contrast with the behavior found in the closely related CeCoIn5, in which the field-tuned quantum critical point coincides with Hc 2. The value of the electron-electron mass enhancement, as judged by the A and B coefficients, is about one order of magnitude reduced in CeIrIn5 as compared to CeCoIn5 (in spite of the fact that the zero field γ0 in CeIrIn5 is twice as large as γ0 in CeCoIn5), which suggests that the material is significantly farther away from the magnetic quantum critical point at bulk Hc 2 and at all of the studied fields. A suppressed Kadowaki-Woods ratio in CeIrIn5 compared to CeCoIn5 suggests a notably more localized nature of f electrons in the compound.
Field-Reversed Configuration Power Plant Critical-Issue Scoping Study
Santarius, J. F.; Mogahed, E. A.; Emmert, G. A.; Khater, H. Y.; Nguyen, C. N.; Ryzhkov, S. V.; Stubna, M. D.
2000-03-31
A team from the Universities of Wisconsin, Washington, and Illinois performed an engineering scoping study of critical issues for field-reversed configuration (FRC) power plants. The key tasks for this research were (1) systems analysis for deuterium-tritium (D-T) FRC fusion power plants, and (2) conceptual design of the blanket and shield module for an FRC fusion core. For the engineering conceptual design of the fusion core, the project team focused on intermediate-term technology. For example, one decision was to use steele structure. The FRC systems analysis led to a fusion power plant with attractive features including modest size, cylindrical symmetry, good thermal efficiency (52%), relatively easy maintenance, and a high ratio of electric power to fusion core mass, indicating that it would have favorable economics.
Design and analysis of field studies with bees: A critical review of the draft EFSA guidance.
Bakker, Frank
2016-07-01
The specific protection goal, primary assessment endpoints, acceptable effect thresholds, and experimental design proposed in the European Food Safety Authority (EFSA) update of the bee guidance document are subjected to critical review. It is concluded that the negligible effect criteria were established without sufficient regulatory definition and without convincing scientific argumentation. For the assessment endpoints, effects on hive strength lack temporal definition and the reduction to numbers of bees is inappropriate to evaluate effects. Restricting mortality assessments to homing failure is not theoretically justified and specific criteria were incorrectly derived. The combination of acute effect estimates with models for chronic stressors is biased risk assessment and a temporal basis for the acceptability of effects is missing. Effects on overwintering success cannot be experimentally assessed using the proposed criteria. The experimental methodology proposed is inappropriate and the logistical consequences, in particular those related to replication and land use are such that field studies are no longer a feasible option for the risk assessment. It may be necessary to explore new lines of thought for the set-up of field studies and to clearly separate experimentation from monitoring. Integr Environ Assess Manag 2016;12:422-428. © 2015 SETAC. PMID:26436642
Critical temperature enhancement of topological superconductors: A dynamical mean-field study
NASA Astrophysics Data System (ADS)
Nagai, Yuki; Hoshino, Shintaro; Ota, Yukihiro
2016-06-01
We show that a critical temperature Tc for spin-singlet two-dimensional superconductivity is enhanced by a cooperation between the Zeeman magnetic field and the Rashba spin-orbit coupling, where a superconductivity becomes topologically nontrivial below Tc. The dynamical mean-field theory with the segment-based hybridization-expansion continuous-time quantum Monte Carlo impurity solver is used for accurately evaluating a critical temperature, without any fermion sign problem. A strong-coupling approach shows that spin-flip-driven local pair hopping leads to part of this enhancement, especially effects of the magnetic field. We propose physical settings suitable for verifying the present calculations, a one-atom-layer system on Si(111) and ionic-liquid-based electric double-layer transistors.
Outdoor urban nanomaterials: The emergence of a new, integrated, and critical field of study.
Baalousha, Mohammed; Yang, Yi; Vance, Marina E; Colman, Benjamin P; McNeal, Samantha; Xu, Jie; Blaszczak, Joanna; Steele, Meredith; Bernhardt, Emily; Hochella, Michael F
2016-07-01
Engineered nanomaterials (ENMs) are currently widely incorporated in the outdoor urban environmental fabric and numerous new applications and products containing ENMs are expected in the future. As has been shown repeatedly, products containing ENMs have the potential, at some point in their lifetime, to release ENMs into their surrounding environment. However, the expanding body in environmental nanomaterial research has not yet shifted toward ENMs in the context of the complex outdoor urban environment. This is especially surprising because the world's human populations are on a steady march toward more and more urbanization and technological development, accompanied with increased applications for ENMs in the outdoor urban environment. Our objective for this paper is therefore to review, assess, and provide new information in this emerging field. We provide an overview of nanomaterials (NMs, encompassing both ENMs and incidental nanomaterials, INMs) that are likely to be released in the urban environment from outdoor sources by discussing 1) the applications of ENMs that may lead to release of ENMs in urban areas, 2) the recently published data on the release of ENMs from novel nano-enabled applications in the outdoor urban environment, 3) the available literature on the occurrence of INMs in the atmosphere and within/on dust particles, and 4) the potential pathways and fate of NMs in the outdoor urban environment. This review is then followed by three case studies demonstrating the importance of NMs in the outdoor urban environment. The first and second case studies illustrate the occurrence of NMs in urban dust and stormwater ponds, respectively, whereas the third case study discusses the lessons learned from the release of NMs (e.g. Pt, ph and Rh) from automotive vehicle catalytic convertors. This article ends with a discussion of the research priorities needed to advance this emerging field of "outdoor urban nanomaterials" and to assess the potential risks
ERIC Educational Resources Information Center
Boxley, Simon
2015-01-01
Education Studies as an academic discipline within HE in the UK is a contested area. One thing most Education Studies programmes might agree on is that they are "critical". But what is a genuinely critical Education Studies degree? And, how could such a programme survive within the hostile neoliberal environment of the contemporary UK?…
Peter Jaffe; Herschel Rabitz
2003-02-14
The objective of this project was to gain an insight into the modeling support needed for the understanding, design, and operation of trace metal/radionuclide bioremediation. To achieve this objective, a workshop was convened to discuss the elements such a model should contain. A ''protomodel'' was developed, based on the recommendations of the workshop, and was used to perform sensitivity analysis as well as some preliminary simulations in support for bioremediation test experiments at UMTRA sites. To simulate the numerous biogeochemical processes that will occur during the bioremediation of uranium contaminated aquifers, a time-dependent one-dimensional reactive transport model has been developed. The model consists of a set of coupled, steady state mass balance equations, accounting for advection, diffusion, dispersion, and a kinetic formulation of the transformations affecting an organic substrate, electron acceptors, corresponding reduced species, and uranium. This set of equations is solved numerically, using a finite element scheme. The redox conditions of the domain are characterized by estimating the pE, based on the concentrations of the dominant terminal electron acceptor and its corresponding reduced specie. This pE and the concentrations of relevant species are passed to a modified version of MINTEQA2, which calculates the speciation and solubilities of the species of interest. Kinetics of abiotic reactions are described as being proportional to the difference between the actual and equilibrium concentration. A global uncertainty assessment, determined by Random Sampling High Dimensional Model Representation (RS-HDMR), was performed to attain a phenomenological understanding of the origins of output variability and to suggest input parameter refinements as well as to provide guidance for field experiments to improve the quality of the model predictions. Results indicated that for the usually high nitrate contents found ate many DOE sites, overall
Superconductivity in Strong Magnetic Field (Greater Than Upper Critical Field)
Tessema, G.X.; Gamble, B.K.; Skove, M.J.; Lacerda, A.H.; Mielke, C.H.
1998-08-22
The National High Magnetic Field Laboratory, funded by the National Science Foundation and other US federal Agencies, has in recent years built a wide range of magnetic fields, DC 25 to 35 Tesla, short pulse 50 - 60 Tesla, and quasi-continuous 60 Tesla. Future plans are to push the frontiers to 45 Tesla DC and 70 to 100 Tesla pulse. This user facility, is open for national and international users, and creates an excellent tool for materials research (metals, semiconductors, superconductors, biological systems ..., etc). Here we present results of a systematic study of the upper critical field of a novel superconducting material which is considered a promising candidate for the search for superconductivity beyond H{sub c2} as proposed by several new theories. These theories predict that superconductors with low carrier density can reenter the superconducting phase beyond the conventional upper critical field H{sub c2}. This negates the conventional thinking that superconductivity and magnetic fields are antagonistic.
Critical Magnetic Field Determination of Superconducting Materials
Canabal, A.; Tajima, T.; Dolgashev, V.A.; Tantawi, S.G.; Yamamoto, T.; /Tsukuba, Natl. Res. Lab. Metrol.
2011-11-04
Superconducting RF technology is becoming more and more important. With some recent cavity test results showing close to or even higher than the critical magnetic field of 170-180 mT that had been considered a limit, it is very important to develop a way to correctly measure the critical magnetic field (H{sup RF}{sub c}) of superconductors in the RF regime. Using a 11.4 GHz, 50-MW, <1 {mu}s, pulsed power source and a TE013-like mode copper cavity, we have been measuring critical magnetic fields of superconductors for accelerator cavity applications. This device can eliminate both thermal and field emission effects due to a short pulse and no electric field at the sample surface. A model of the system is presented in this paper along with a discussion of preliminary experimental data.
NASA Astrophysics Data System (ADS)
Wang, Yinshun; Dai, Shaotao; Zhao, Xiang; Xiao, Liye; Lin, Liangzhen; Hui, Dong
2006-12-01
The effect of the local critical current on the self-field loss in single tapes and multi-parallel tapes is investigated computationally. Generally, the self-AC loss of a superconductor can be described using the Norris equation based on Bean's critical state model with elliptical, circular or strip cross-sections. However, because of its intrinsic characteristics, the critical current of high-temperature superconducting (HTS) tape is inhomogeneous. It is reasonable to expect the local critical currents to have a Gaussian statistical distribution, according to the central limit theorem; a detailed analysis of self-AC loss is made to develop an interesting calculation procedure for both single tapes and multi-parallel tapes. The results show that the inhomogeneity of local critical currents has an important effect on the self-field loss. One of the goals in this paper is to provide an accurate method for estimating quality, or what level of critical current inhomogeneity in HTS tape is permissible in practical application. As manufacturing processes are refined through powder in tube and coating technologies, and the sources of extrinsic macroscopic defects are decreased, electromagnetic and mechanical performances of Bi2223 and YBCO tapes are greatly improved. Nevertheless, intrinsic microscopic defects such as weak links, microcracks and small second-phase formations still exist in the tapes, which will lead to statistically local critical current variations. Therefore, it is very important to study the effect that variation in local critical currents may have on the self-field losses of practical long single and multi-parallel HTS tapes.
Critical Density Interaction Studies
Young, P; Baldis, H A; Cheung, P; Rozmus, W; Kruer, W; Wilks, S; Crowley, S; Mori, W; Hansen, C
2001-02-14
Experiments have been performed to study the propagation of intense laser pulses to high plasma densities. The issue of self-focusing and filamentation of the laser pulse as well as developing predictive capability of absorption processes and x-ray conversion efficiencies is important for numerous programs at the Laboratory, particularly Laser Program (Fast Ignitor and direct-drive ICF) and D&NT (radiography, high energy backlighters and laser cutting). Processes such as resonance absorption, profile modification, linear mode conversion, filamentation and stimulated Brillouin scattering can occur near the critical density and can have important effects on the coupling of laser light to solid targets. A combination of experiments have been used to study the propagation of laser light to high plasma densities and the interaction physics of intense laser pulses with solid targets. Nonparaxial fluid codes to study nonstationary behavior of filamentation and stimulated Brillouin scattering at high densities have also been developed as part of this project.
Bridging Fields at a Critical Time
ERIC Educational Resources Information Center
Baggaley, Jon
2014-01-01
The launch of the "Journal of Learning for Development" occurs at a critical time for the education and development field. The "massive open online course" concept currently being implemented by Western educators is considered as a potential cost-saver in developing nations also. MOOCs based on reliable pedagogical principles…
Upper critical field of cellular magnesium diboride
NASA Astrophysics Data System (ADS)
Grinenko, V. A.
2007-08-01
A cellular superconducting material consisting of thin (1 20 μm) MgB2-x layers and magnesium granules of about 100 μm has been produced. The critical temperature T c of this superconductor decreases with the thickness of the MgB2-x layers. In unalloyed magnesium diboride, the curvature of the temperature dependence of the upper critical field H c2(T) changes gradually from downward to pronounced upward as the temperature T c decreases from 38 to 36 K.
Fox, P.B.
2005-07-11
This report provides minimum critical values for various 30-cm water-reflected uranium and plutonium oxide and nitrate aqueous mixtures as calculated by the SCALE CSAS1X sequence using the 238-group ENDF/B-V neutron cross-section library. The minimum values were determined through parametric searches in one-dimensional geometry. The calculations have been performed to obtain the minimum values: critical volume and mass for spheres, critical radius for cylinders, critical thickness for slabs, and minimum critical concentration (infinite geometry) for the following homogeneous mixtures: (1) UO{sub 2}-H{sub 2}O for 3, 4, 5, 20, and 100 wt % {sup 235}U; (2) UNH for 3, 4, 5, 20, and 100 wt % {sup 235}U; (3) PuO{sub 2}-H{sub 2}O for 100/0/0, 95/5/0, 90/5/5, 80/10/10, and 71/17/11/1 wt % of {sup 239}Pu/{sup 240}Pu/{sup 241}Pu(/{sup 242}Pu); and (4) PuNH for 100/0/0, 95/5/0, 90/5/5, 80/10/10, and 71/17/11/1 wt % of {sup 239}Pu/{sup 240}Pu/{sup 241}Pu(/{sup 242}Pu). All bounding surfaces were fully reflected by 30 cm of H{sub 2}O.
Upper critical field of copper molybdenum sulfide
NASA Technical Reports Server (NTRS)
Alterovitz, S. A.; Woollam, J. A.
1978-01-01
The upper critical field of sintered and sputtered copper molybdenum sulfide Cu(x)Mo6S8 was measured and found to exceed the Werthamer, Helfand, and Hohenberg (1966) value for a type II superconductor characterized by dirty limit, weak isotropic electron phonon coupling, and no paramagnetic limiting. It is suggested that the enhancement results from anisotropy or clean limit or both. Other ternary molybdenum sulfides appear to show similar anomalies.
A Critically Reflective Social Studies?
ERIC Educational Resources Information Center
Clarke, Marge
1990-01-01
Examines social studies in the twenty-first century from a critical theory perspective. Traces critical reflection's origins from Marxist educational theories to Jurgen Habermas's critical theory. Highlights Fred Newmann's curricular model, "Education for Citizen Action," for developing competent action in public affairs. Advocates infusing…
Further Evidence for Weak Field Critical Adsorption
NASA Astrophysics Data System (ADS)
Franck, Carl; Peach, Sarah; Polak, Robert D.
1997-03-01
Following our unexpected discovery of weak short-range surface field effects on the critical mixing transition of a binary liquid,(N.S. Desai, S. Peach, and C. Franck, Phys. Rev. E52), 4129 (1995) we have directly addressed our concern that these results might have been affected by surface heterogeneity. We have used octadecyltrichlorosilane (OTS) to cover borosilicate glass surfaces with partial monolayers. Reference substrates with identical treatment had OTS patches no larger than the bulk correlation length within 40 mK of the critical transition. The present reflectivity experiment employs uncovered reference surfaces for comparison in a single sample cell. We confirm our earlier discovery of a persistent (down to 3 mK above the critical point) deviation of the degree of critical adsorption from the maximum value expected. We have also improved our earlier analysis in order to examine the scaling behavior. Supported by the NSF under DMR-9320910, and through central facilities of the Materials Science Center at Cornell Univ.
Conformal field theory of critical Casimir forces
NASA Astrophysics Data System (ADS)
Emig, Thorsten; Bimonte, Giuseppe; Kardar, Mehran
2015-03-01
Thermal fluctuations of a critical system induce long-ranged Casimir forces between objects that couple to the underlying field. For two dimensional conformal field theories (CFT) we derive exact results for the Casimir interaction for a deformed strip and for two compact objects of arbitrary shape in terms of the free energy of a standard region (circular ring or flat strip) whose dimension is determined by the mutual capacitance of two conductors with the objects' shape; and a purely geometric energy that is proportional to conformal charge of the CFT, but otherwise super-universal in that it depends only on the shapes and is independent of boundary conditions and other details. The effect of inhomogenous boundary conditions is also discussed.
Education Studies: Issues & Critical Perspectives
ERIC Educational Resources Information Center
Kassem, Derek; Mufti, Emmanuel; Robinson, John
2006-01-01
This major text for Education Studies students provides a critical account of key issues in education today. The text features: (1) A critical analysis of key issues in Education Studies to encourage students' thinking about education in the broadest terms; (2) Themed sections with introductions to link the issues discussed in each chapter; (3)…
Critical frontier of the triangular Ising antiferromagnet in a field
NASA Astrophysics Data System (ADS)
Qian, Xiaofeng; Wegewijs, Maarten; Blöte, Henk W.
2004-03-01
We study the critical line of the triangular Ising antiferromagnet in an external magnetic field by means of a finite-size analysis of results obtained by transfer-matrix and Monte Carlo techniques. We compare the shape of the critical line with predictions of two different theoretical scenarios. Both scenarios, while plausible, involve assumptions. The first scenario is based on the generalization of the model to a vertex model, and the assumption that the exact analytic form of the critical manifold of this vertex model is determined by the zeroes of an O(2) gauge-invariant polynomial in the vertex weights. However, it is not possible to fit the coefficients of such polynomials of orders up to 10, such as to reproduce the numerical data for the critical points. The second theoretical prediction is based on the assumption that a renormalization mapping exists of the Ising model on the Coulomb gas, and analysis of the resulting renormalization equations. It leads to a shape of the critical line that is inconsistent with the first prediction, but consistent with the numerical data.
Technique development for uiper critical field studies of SmFeAs(O,F) in the 300T single turn system
Mcdonald, Ross D; Balakirev, F. F.; Altarawneh, M. M.; Betts, J; Mielke, C. H.; Moll, Philip Jw; Zhigadlo, N D; Karpinski, J; Batlogg, B.
2011-01-14
In high temperature superconductors, such as the most recent class of iron pnictides, extremely high upper critical fields H{sub c2} are common. The determination of H{sub c2}(T) is crucial to understand the detailed nature of the superconductor, in particular H{sub c2}(T = 0K) is of great interest. It is not only related to fundamental properties of the system, it is furthermore of great importance for materials science, as it is the ultimate limit of applicability of this superconductor in high field applications. However, this important quantity can only be estimated by extrapolation, as H{sub c2}(T = 0K) well exceeds hundreds of Tesla in optimally doped SillFeAs(O,F). We are developing methods to measure Ha(T) in direct transport in the extreme magnetic fields generated by the LANL single turn magnet.
Critical Theory and Information Studies: A Marcusean Infusion
ERIC Educational Resources Information Center
Pyati, Ajit K.
2006-01-01
In the field of library and information science, also known as information studies, critical theory is often not included in debates about the discipline's theoretical foundations. This paper argues that the critical theory of Herbert Marcuse, in particular, has a significant contribution to make to the field of information studies. Marcuse's…
Thermodynamic critical fields in high T c superconductivity
NASA Astrophysics Data System (ADS)
Clougherty, Dennis P.; Johnson, Keith H.
1988-06-01
Using the free electron approximation, a real space mechanism of how magnetic fields of sufficient strength destroy the superconducting state is outlined. Using the resultant equation together with the molecular orbital model of superconductivity 1,2, the thermodynamic critical magnetic field is calculated and compared to experiment for type I elemental superconductors and type II superconductors, including high-Tc superconductors. The expression for critical field compares favorably with an expression derived by Schrieffer.
Boyarinov, V. F.; Garin, V. P.; Glushkov, E. S.; Zimin, A. A.; Kompaniets, G. V.; Nevinitsa, V. A.; Polyakov, D. N.; Ponomarev, A. S.; Ponomarev-Stepnoi, N. N.; Smirnov, O. N.; Fomichenko, P. A.; Chunyaev, E. I.; Marova, E. V.; Sukharev, Yu. P.
2010-12-15
The paper presents the results obtained from the computational/experimental studies of the spatial distribution of the {sup 235}U fission reaction rate in a critical assembly with an annular core and poison profiling elements inserted into the inner graphite reflector. The computational analysis was carried out with the codes intended for design computation of an HTHR-type reactor.
NASA Astrophysics Data System (ADS)
Agarwal, S. K.; Kumaraswamy, B. V.
2005-05-01
Measurements of the a.c.susceptibility (χ=χ‧+iχ″) have been made on the Mg substituted high TC superconducting system, CuBa2(MgxCa1-x)3Cu4O12-y (Cu-1234) with x=0, 0.10 & 0.20, at different values of the a.c.field amplitude. Estimates of the intergranular critical current density(JC) made from the field dependent χ″-T curves show an improvement in the Mg-substituted Cu-1234 system. Results have been analysed in the light of the crystal structure and the superconducting anisotropy factor (γ=ξab/ξc) of the Cu-1234 system. Lower superconducting anisotropy emanating from Mg substitution has been found to be significant, resulting in better superconducting properties.
Upper critical field under hydrostatic pressure in UCoGe
NASA Astrophysics Data System (ADS)
Bastien, Gaël; Knebel, Georg; Aoki, Dai; Flouquet, Jacques
2015-03-01
We report on the pressure dependence of the upper superconductivity critical field Hc2 of the ferromagnetic superconductor UCoGe for field along the c axis, which is the easy magnetization axis. The surprising result is the upward curvature and strong enhancement of the upper critical field on cooling. This enhancement is even more pronounced above the critical pressure pc in the paramagnetic phase than in the ferromagnetic phase below pc. This effect cannot be explained by models based on the suppression of pair building magnetic fluctuations under magnetic field. That points out either decrease of the pair breaking mechanism under field or fluctuations favorable for the Cooper pairing linked to the wing structure of ferromagnetism near the critical pressure, where ferromagnetism is suppressed.
Upper critical field of the noncentrosymmetric superconductor BiPd
NASA Astrophysics Data System (ADS)
Peets, Darren C.; Maldonado, Ana; Enayat, Mostafa; Sun, Zhixiang; Wahl, Peter; Schnyder, Andreas P.
2016-05-01
The superconducting parameters and upper critical field of the noncentrosymmetric superconductor BiPd have proven contentious. This material is of particular interest because it is a rare example of a 4 f -electron-free noncentrosymmetric superconductor of which crystals may be grown and cleaved, enabling surface-sensitive spectroscopies. Here, using bulk probes augmented by tunneling data on defects, we establish that the lower of the previously reported upper critical fields corresponds to the bulk transition. The material behaves as a nearly weak-coupled BCS s -wave superconductor, and we report its superconducting parameters as drawn from the bulk upper critical field. Possible reasons behind the order-of-magnitude discrepancy in the reported upper critical fields are discussed.
Participative Critical Enquiry in Graduate Field-Based Learning
ERIC Educational Resources Information Center
Reilly, Kathy; Clavin, Alma; Morrissey, John
2016-01-01
This paper outlines a critical pedagogic approach to field-based learning (FBL) at graduate level. Drawing on student experience stemming from a FBL module and as part of an MA programme in Environment, Society and Development, the paper addresses the complexities associated with student-led, participative critical enquiry during fieldwork in…
Magnetic field dependence of critical currents in superconducting polycrystals
Kugel, K.I.; Lisovskaya, T.Y. ); Mints, R.G. )
1992-02-10
The authors study the dependence of critical current j{sub c} on magnetic field H in superconducting polycrystals which are considered as system of superconducting crystallites (isotropic or anisotropic) with Josephson contacts between them. Isotropy or anisotropy of contacts depends on the orientation of their crystallographic axes relatively to edges of contact planes. In this paper it is shown that for a system of randomly oriented isotropic contacts, the dependence j{sub c}(H) in a relatively wide field range has the asymptotic form j{sub c} {approximately} (InH)/H{sup 2}. This differs drastically from j{sub c}(H) for single contacts. Anisotropy effects due to large differences in London penetration depth {lambda} values corresponding to external magnetic field directed along different axes are analyzed in detail. It is shown that for uniaxal crystals with {lambda}{sub 1} = {lambda}{sub 2} {lt} {lambda}{sub 3}, this anisotropy leads to the relation j{sub c} {approximately} {radical}{lambda}{sub 3}/{lambda}{sub 1} for chaotic orientation of crystallites. The form of j{sub c}(H) curves for two different orientations of the magnetic field relatively to the transport current through the sample is found.
Critical validation studies of neurofeedback.
Gruzelier, John; Egner, Tobias
2005-01-01
The field of neurofeedback training has proceeded largely without validation. In this article the authors review studies directed at validating sensory motor rhythm, beta and alpha-theta protocols for improving attention, memory, and music performance in healthy participants. Importantly, benefits were demonstrable with cognitive and neurophysiologic measures that were predicted on the basis of regression models of learning to enhance sensory motor rhythm and beta activity. The first evidence of operant control over the alpha-theta ratio is provided, together with remarkable improvements in artistic aspects of music performance equivalent to two class grades in conservatory students. These are initial steps in providing a much needed scientific basis to neurofeedback. PMID:15564053
Reply to criticisms of the B (3) field
NASA Astrophysics Data System (ADS)
Evans, M. W.
1995-12-01
The confusion and self-contradiction among recent critics of the B (3) (Evans-Vigier) field are analysed. Barron [17] and Buckingham [18] assert that the field is zero by symmetry. Grimes [21] asserts that the field is non-zero but fortuitous. Lakhtakia in one paper [19] asserts that B (3) is non-zero but not fundamental, and in a second paper that it is unknowlable and therefore may as well be zero. A rebuttal is given of each the individual papers, and it is shown that the Evans-Vigier field is the fundamental magnetizing field of electromagnetic radiation.
Static Magnetic Field Therapy: A Critical Review of Treatment Parameters
Wahbeh, Helané; Harling, Noelle; Connelly, Erin; Schiffke, Heather C.; Forsten, Cora; Gregory, William L.; Markov, Marko S.; Souder, James J.; Elmer, Patricia; King, Valerie
2009-01-01
Static magnetic field (SMF) therapy, applied via a permanent magnet attached to the skin, is used by people worldwide for self-care. Despite a lack of established SMF dosage and treatment regimens, multiple studies are conducted to evaluate SMF therapy effectiveness. Our objectives in conducting this review are to:(i) summarize SMF research conducted in humans; (ii) critically evaluate reporting quality of SMF dosages and treatment parameters and (iii) propose a set of criteria for reporting SMF treatment parameters in future clinical trials. We searched 27 electronic databases and reference lists. Only English language human studies were included. Excluded were studies of electromagnetic fields, transcranial magnetic stimulation, magnets placed on acupuncture points, animal studies, abstracts, posters and editorials. Data were extracted on clinical indication, study design and 10 essential SMF parameters. Three reviewers assessed quality of reporting and calculated a quality assessment score for each of the 10 treatment parameters. Fifty-six studies were reviewed, 42 conducted in patient populations and 14 in healthy volunteers. The SMF treatment parameters most often and most completely described were site of application, magnet support device and frequency and duration of application. Least often and least completely described were characteristics of the SMF: magnet dimensions, measured field strength and estimated distance of the magnet from the target tissue. Thirty-four (61%) of studies failed to provide enough detail about SMF dosage to permit protocol replication by other investigators. Our findings highlight the need to optimize SMF dosing parameters for individual clinical conditions before proceeding to a full-scale clinical trial. PMID:18955243
Quantum size effect on the paramagnetic critical field in free-standing superconducting nanofilms.
Wójcik, P; Zegrodnik, M
2014-11-12
The quantum size effect on the in-plane paramagnetic critical field in Pb(1 1 1) free-standing nanofilms is investigated with the use of the spin-generalized Bogoliubov-de Gennes equations. It is shown that the critical field oscillates as a function of the nanofilm thickness with the period ∼ 2 ML (even-odd oscillations), modulated by the beating effect. The calculated values of the critical field for different nanofilm thicknesses are analyzed in the context of the Clogston-Chandrasekhar limit. It is found that the critical field for superconducting nanofilms differs from this limit. This phenomena is explained in terms of quantization of the electron energy caused by the confinement of electron motion in a direction perpendicular to the film. The thermal effect and thickness-dependence of electron-phonon coupling on the value of the critical magnetic field are also studied. PMID:25318561
Anisotropic Upper Critical Field of Iron-Based Superconductors
NASA Astrophysics Data System (ADS)
Huang, Ruiqi; She, Weilong
2016-09-01
The upper critical field and its anisotropy are the easiest properties to examine in the research of iron-based superconductors. Based on warped cylindrical Fermi surface models, we investigate the temperature and angle dependence of the upper critical field in detail by employing the quasi-classical formalism of the Werthamer-Helfand-Hohenberg (WHH) theory. Our numerical results reveal the anisotropy of the upper critical field, which may be caused by an anisotropic gap function (e.g., d-wave pairing) or an anisotropic Fermi surface, respectively. Further, according to our analysis, this anisotropy can be modulated by the deformation of the Fermi surface and will be strongly suppressed by the Pauli paramagnetic effect.
Effects of an externally imposed electric field on subcooled boiling critical heat flux
Masson, V.; Carrica, P.M.
1995-07-01
The effects of an externally imposed electric field on critical heat flux in subcooled pool boiling have been experimentally studied. The test section was a 0.3 mm diameter platinum wire electrically heated. A coaxial cage with high voltage provided the outer electrode forming a cylindrical symmetric electric field around the heater. It was observed that the effect of the electric field on critical heat flux decreases as subcooling increases.
Magnesium boride superconductors: Processing, characterization and enhancement of critical fields
NASA Astrophysics Data System (ADS)
Bhatia, Mohit
In this work, the basic formation of in-situ MgB2, and how variations in the formation process influence the electrical and magnetic properties of this material was studied. Bulk MgB2 samples were prepared by stoichiometric, elemental powder mixing and compaction followed by heat-treatment. Strand samples were prepared by a modified powder-in-tube technique with subsequent heat-treatment. The influence of various heat-treatment schedules on the formation reaction was studied. Two different optimum heat-treatment windows were indentified, namely, low-temperature heat-treatment (below the melting point of Mg i.e. between 620--650°C) and high-temperature heat-treatment (>650°C) for the preparation of MgB2 with good transport properties. XRD was used to confirm phase formation and microstructural variations were studied with the help of SEM. Following a study of the reaction temperature regimes, the focus turned to critical field enhancement via doping with various compounds targeting either the Mg or the B sites. The effects of these dopants on the superconducting properties, in particular the critical fields, were studied. Large increases in irreversibility field, muoH irr, and upper critical field, Bc2, of bulk and strand superconducting MgB2 were achieved by separately adding SiC, amorphous C, and selected metal diborides (NaB2, ZrB 2, TiB2) in bulk samples and three different sizes of SiC (˜200 nm, 30 nm and 15 nm) in strand samples. Lattice spacing shifts and resistivity measurements (on some samples) were consistent with dopant introduction to the lattice. It was also found that both muoH irr and Bc2 depend on the sensing current level which may be an indication of current path percolations. These increases in the Bc2 were also complimented by an increase in the transport Jcs, especially for the SiC doped samples. It was important to differentiate between the effects on the transport properties arising from possible particulate enhanced flux pinning from that
NASA Astrophysics Data System (ADS)
Matsui, H.; Ootsuka, T.; Ogiso, H.; Yamasaki, H.; Sohma, M.; Yamaguchi, I.; Kumagai, T.; Manabe, T.
2016-06-01
In high-temperature superconductor (HTSC) films, the magnetic-field-angle (θ) dependence of critical current density (J c) is often observed to have a characteristic local maximum at intermediate θ between H||ab and H||c. This local maximum appears as a ‘shoulder’ when J c(θ) has a predominant peak at H||c, and when such a peak is absent, it appears as a ‘dimple edge’ in a very broad dome-like J c(θ) that is centered and dimpled at H||c. Despite such common observation, there is still no consensus on the physical origin of this anomalous J c(θ). In this work, to determine this physical origin. we measured the temperature and microstructure dependence of J c(B, θ) in YBa2Cu3O7 films irradiated with 3 MeV Au, 500 keV Si, and 200 keV B ions (where B is magnetic induction). The film microstructure was controlled by varying the mass of irradiation ions (M i) known to alter the size and spacing of collision cascades. Results revealed two observations: (i) the dimple structure diminishes with decreasing temperature, and (ii) the maximum pinning force density in a θ profile, which is recorded at the dimple edge, systematically becomes more B-dependent with decreasing M i. Both experimental findings suggest that the sharp-shaped anomaly in J c(θ) in HTSC films originates from flux-line-lattice shear and electron mass anisotropy.
Critical Casimir forces in the presence of random surface fields
NASA Astrophysics Data System (ADS)
Maciołek, A.; Vasilyev, O.; Dotsenko, V.; Dietrich, S.
2015-03-01
We study critical Casimir forces (CCFs) fC for films of thickness L which in the three-dimensional bulk belong to the Ising universality class and which are exposed to random surface fields (RSFs) on both surfaces. We consider the case in which, in the absence of RSFs, the surfaces of the film belong to the surface universality class of the so-called ordinary transition. We carry out a finite-size scaling analysis and show that for weak disorder, CCFs still exhibit scaling, acquiring a random field scaling variable w that is zero for pure systems. We confirm these analytic predictions by Monte Carlo (MC) simulations. Moreover, our MC data show that fC varies as fC(w →0 ) -fC(w =0 ) ˜w2 . Asymptotically, for large L , w scales as w ˜L-0.26→0 , indicating that this type of disorder is an irrelevant perturbation of the ordinary surface universality class. However, for thin films such that w ≃1 , we find that the presence of RSFs with vanishing mean value increases significantly the strength of CCFs, as compared to systems without them, and it shifts the extremum of the scaling function of fC toward lower temperatures. But fC remains attractive.
High upper critical field in disordered niobium nitride superconductor
Baskaran, R. Thanikai Arasu, A. V.; Amaladass, E. P.; Janawadkar, M. P.
2014-10-28
Superconducting Niobium Nitride thin films have been deposited on glass, aluminum nitride buffered glass, and oxidized silicon substrates by reactive DC magnetron sputtering at ambient substrate temperatures. The crystal structure of these thin films has been determined to be cubic fcc B1 structure by Glancing Incidence X-Ray Diffraction analysis. The superconducting transition temperatures of the thin films were measured to be greater than 11.6 K with a maximum of 13.4 K. The negative temperature coefficient of resistance observed in these thin films indicates the presence of disorder. Magneto-resistance measurements have been carried out on these thin films patterned into standard four probe geometry upto a maximum magnetic field of 12 T for two films and upto 15 T for the other two films. The dependence of transition temperature on the applied field is analyzed to estimate the upper critical field. The upper critical field for most of the films was estimated to exceed 35 T, while one of the most disordered films had an estimated upper critical field greater than 70 T.
Criticality safety basics, a study guide
V. L. Putman
1999-09-01
This document is a self-study and classroom guide, for criticality safety of activities with fissile materials outside nuclear reactors. This guide provides a basic overview of criticality safety and criticality accident prevention methods divided into three parts: theory, application, and history. Except for topic emphasis, theory and history information is general, while application information is specific to the Idaho National Engineering and Environmental Laboratory (INEEL). Information presented here should be useful to personnel who must know criticality safety basics to perform their assignments safely or to design critically safe equipment or operations. However, the guide's primary target audience is fissile material handler candidates.
Electromagnetic Near Field Measurements of Two Critical Assemblies
NASA Astrophysics Data System (ADS)
Goettee, Jeffrey; Goorley, Tim; Mayo, Douglas; Myers, William; Goda, Joetta; Sage, Frank
2015-04-01
Preliminary measurements of the fast metal nuclear reactors at the National Criticality Experiments Research Center (NCERC) and at White Sands Missile Range (WSMR) within the past year characterize the very near field environment of these critical assemblies. Both reactors are fast, highly enriched uranium metal reactors and can be operated in a burst mode above prompt supercritical. Initial measurements of the electric and the magnetic fields within the reactor cell are consistent between the two facilities, and begin to describe the dependance on distance and polarization as might be assumed from initial Monte Carlo modelling of these facilities. The amplitude and time variation of the electric and magnetic fields are consistent with burst time scales. The polarization is consistent with the geometry of the source and with Compton scattering from fission gammas as the dominant ionization mechanism. An overview of the two fast neutron sources and the excursion dynamics, the experimental details, and summary of the modelling calculations will be provided as background.
Teaching Critical Reflexivity in Short-Term International Field Courses: Practices and Problems
ERIC Educational Resources Information Center
Glass, Michael R.
2015-01-01
This study critiques the use of critical reflexivity in short-term international field courses. Critical reflexivity's benefits include preparing students for professional research, deepening their learning, and giving the chance to see how student perspectives on fieldwork sites are influenced by their own identity and positionality. I use an…
Scalar field critical collapse in 2 +1 dimensions
NASA Astrophysics Data System (ADS)
JałmuŻna, Joanna; Gundlach, Carsten; Chmaj, Tadeusz
2015-12-01
We carry out numerical experiments in the critical collapse of a spherically symmetric massless scalar field in 2 +1 spacetime dimensions in the presence of a negative cosmological constant and compare them against a new theoretical model. We approximate the true critical solution as the n =4 Garfinkle solution, matched at the light cone to a Vaidya-like solution, and corrected to leading order for the effect of Λ <0 . This approximation is only C3 at the light cone and has three growing modes. We conjecture that pointwise it is a good approximation to a yet unknown true critical solution that is analytic with only one growing mode (itself approximated by the top mode of our amended Garfinkle solution). With this conjecture, we predict a Ricci-scaling exponent of γ =8 /7 and a mass-scaling exponent of δ =16 /23 , compatible with our numerical experiments.
Experimental investigation of the critical magnetic fields of transition metal superconductors
NASA Technical Reports Server (NTRS)
Mcevoy, J. P.
1973-01-01
The isothermal magnetic transitions of a type 2 superconductor have been studied by AC susceptibility techniques as a function of the amplitude and frequency of the exciting field. The field variation of the complex susceptibility was used to determine the critical fields. The research was planned to clarify the determination (both experimentally and theoretically) of the maximum field at which the superconductive phase spontaneously nucleates in the bulk and on the surface of the metal.
Near field optical probe for critical dimension measurements
Stallard, Brian R.; Kaushik, Sumanth
1999-01-01
A resonant planar optical waveguide probe for measuring critical dimensions on an object in the range of 100 nm and below. The optical waveguide includes a central resonant cavity flanked by Bragg reflector layers with input and output means at either end. Light is supplied by a narrow bandwidth laser source. Light resonating in the cavity creates an evanescent electrical field. The object with the structures to be measured is translated past the resonant cavity. The refractive index contrasts presented by the structures perturb the field and cause variations in the intensity of the light in the cavity. The topography of the structures is determined from these variations.
Near field optical probe for critical dimension measurements
Stallard, B.R.; Kaushik, S.
1999-05-18
A resonant planar optical waveguide probe for measuring critical dimensions on an object in the range of 100 nm and below is disclosed. The optical waveguide includes a central resonant cavity flanked by Bragg reflector layers with input and output means at either end. Light is supplied by a narrow bandwidth laser source. Light resonating in the cavity creates an evanescent electrical field. The object with the structures to be measured is translated past the resonant cavity. The refractive index contrasts presented by the structures perturb the field and cause variations in the intensity of the light in the cavity. The topography of the structures is determined from these variations. 8 figs.
Critical Studies in Art and Design Education.
ERIC Educational Resources Information Center
Thistlewood, David, Ed.
This book brings together British and U.S. contributions to the debate of a critical studies approach to art and design education. The approach links practice and appreciation. But critical differences exist in definitions of the term design, with the U.S. recognition of design as the use of principles and elements of art in works and a British…
Direct measurement of the upper critical field in cuprate superconductors
NASA Astrophysics Data System (ADS)
Grissonnanche, G.; Cyr-Choinière, O.; Laliberté, F.; René de Cotret, S.; Juneau-Fecteau, A.; Dufour-Beauséjour, S.; Delage, M.-È.; Leboeuf, D.; Chang, J.; Ramshaw, B. J.; Bonn, D. A.; Hardy, W. N.; Liang, R.; Adachi, S.; Hussey, N. E.; Vignolle, B.; Proust, C.; Sutherland, M.; Krämer, S.; Park, J.-H.; Graf, D.; Doiron-Leyraud, N.; Taillefer, Louis
2014-02-01
In the quest to increase the critical temperature Tc of cuprate superconductors, it is essential to identify the factors that limit the strength of superconductivity. The upper critical field Hc2 is a fundamental measure of that strength, yet there is no agreement on its magnitude and doping dependence in cuprate superconductors. Here we show that the thermal conductivity can be used to directly detect Hc2 in the cuprates YBa2Cu3Oy, YBa2Cu4O8 and Tl2Ba2CuO6+δ, allowing us to map out Hc2 across the doping phase diagram. It exhibits two peaks, each located at a critical point where the Fermi surface of YBa2Cu3Oy is known to undergo a transformation. Below the higher critical point, the condensation energy, obtained directly from Hc2, suffers a sudden 20-fold collapse. This reveals that phase competition—associated with Fermi-surface reconstruction and charge-density-wave order—is a key limiting factor in the superconductivity of cuprates.
Direct measurement of the upper critical field in cuprate superconductors
Grissonnanche, G.; Cyr-Choinière, O.; Laliberté, F.; René de Cotret, S.; Juneau-Fecteau, A.; Dufour-Beauséjour, S.; Delage, M. -È.; LeBoeuf, D.; Chang, J.; Ramshaw, B. J.; Bonn, D. A.; Hardy, W. N.; Liang, R.; Adachi, S.; Hussey, N. E.; Vignolle, B.; Proust, C.; Sutherland, M.; Krämer, S.; Park, J. -H.; Graf, D.; Doiron-Leyraud, N.; Taillefer, Louis
2014-01-01
In the quest to increase the critical temperature Tc of cuprate superconductors, it is essential to identify the factors that limit the strength of superconductivity. The upper critical field Hc2 is a fundamental measure of that strength, yet there is no agreement on its magnitude and doping dependence in cuprate superconductors. Here we show that the thermal conductivity can be used to directly detect Hc2 in the cuprates YBa2Cu3Oy, YBa2Cu4O8 and Tl2Ba2CuO6+δ, allowing us to map out Hc2 across the doping phase diagram. It exhibits two peaks, each located at a critical point where the Fermi surface of YBa2Cu3Oy is known to undergo a transformation. Below the higher critical point, the condensation energy, obtained directly from Hc2, suffers a sudden 20-fold collapse. This reveals that phase competition—associated with Fermi-surface reconstruction and charge-density-wave order—is a key limiting factor in the superconductivity of cuprates. PMID:24518054
Predicting the critical density of topological defects in O(N) scalar field theories
Antunes, Nuno D.; Bettencourt, Luis M. A.; Yates, Andrew
2001-09-15
O(N) symmetric {lambda}{phi}{sup 4} field theories describe many critical phenomena in the laboratory and in the early Universe. Given N and D{<=}3, the spatial dimension, these models exhibit topological defect classical solutions that in some cases fully determine their critical behavior. For N=2 and D=3, it has been observed that the defect density is seemingly a universal quantity at T{sub c}. We prove this conjecture and show how to predict its value based on the universal critical exponents of the field theory. Analogously, for general N and D we predict the universal critical densities of domain walls and monopoles, for which no detailed thermodynamic study exists, to our knowledge. Remarkably this procedure can be inverted, producing an algorithm for generating typical defect networks at criticality, in contrast with the usual procedure [Vachaspati and Vilenkin, Phys. Rev. D 30, 2036 (1984)], which applies only in the unphysical limit of infinite temperature.
Magnetic-field control of quantum critical points of valence transition.
Watanabe, Shinji; Tsuruta, Atsushi; Miyake, Kazumasa; Flouquet, Jacques
2008-06-13
We study the mechanism of how critical end points of first-order valence transitions are controlled by a magnetic field. We show that the critical temperature is suppressed to be a quantum critical point (QCP) by a magnetic field, and unexpectedly, the QCP exhibits nonmonotonic field dependence in the ground-state phase diagram, giving rise to the emergence of metamagnetism even in the intermediate valence-crossover regime. The driving force of the field-induced QCP is clarified to be cooperative phenomena of the Zeeman and Kondo effects, which create a distinct energy scale from the Kondo temperature. This mechanism explains the peculiar magnetic response in CeIrIn(5) and the metamagnetic transition in YbXCu(4) for X=In as well as the sharp contrast between X=Ag and Cd. PMID:18643524
High critical field NbC superconductor on carbon spheres.
Bhattacharjee, Kaustav; Pati, Satya Prakash; Maity, Arjun
2016-06-01
Niobium carbide (NbC) nanoparticles embedded on the surface of carbon spheres (CS) were synthesized at 1350 °C by the carbothermal reduction of niobium oxide precursor in flowing argon (Nbc@CS). The morphology, crystal structure, and magnetic properties of the hybrid nanocomposite were investigated by means of electron microscopy, X-ray diffraction and a superconducting quantum interference device. It was found that the NbC@CS nanocomposites exhibit type-II superconductivity with a critical temperature (Tc) of 8-12 K, typical for stoichiometric NbC. The superconducting hysteresis loop reveals several interesting traits, including strong vortex pinning, the presence of asymmetry and a high penetration field. Moreover, the sample shows much improved irreversible (Hirr), lower (Hc1) and upper (Hc2) critical fields. The coherence length (ξ), penetration depth (λ), and Ginzburg-Landau (κ) parameters for the sample were estimated to be 9.78 nm, 33 nm and 3.39, respectively. PMID:27212586
NASA Astrophysics Data System (ADS)
Boryta, M. D.; Walker, B.; Long, T.
2011-12-01
Although field experiences for introductory geoscience students have tremendous potential with respect to recruiting and retaining majors and enriching their understanding of geologic concepts, implementing field trips that promote critical thinking for introductory students is challenging. After observing that many of our students struggled at applying concepts they learned in the classroom to unfamiliar field areas, we developed teaching strategies and instructional materials for the classroom and the field to promote critical thinking and self-directed learning on field trips. We assessed the effectiveness of these modifications using video, interviews, student field trip reports and field notebooks. Student co-inquirers played a vital role during the project in field instruction and data analysis. We will discuss think-alouds, the importance of repetition in the classroom, allowing adequate processing time, field trip preparation exercises for the classroom, and other significant pedagogical changes that we made. Video of students in the field at the beginning, middle, and end of the project will be shown to illustrate the progressive changes in students' approaches to outcrop analysis over the course of the project.
Critical current density and trapped field in HTS with asymmetric magnetization loops
NASA Astrophysics Data System (ADS)
Gokhfeld, D.
2016-03-01
Applications of the extended critical state model are considered. The trapped magnetic field, the penetration field and the field dependence of the critical current density are analysed. The critical current density and the trapped field in superconducting grains depend on the grain size. Asymmetry of the hysteresis curves relative to the M = 0 axis is related to the scale of the current circulation.
[Critical reading of analytical observational studies].
García Villar, C; Marín León, I
2015-11-01
Analytical observational studies provide very important information about real-life clinical practice and the natural history of diseases and can suggest causality. Furthermore, they are very common in scientific journals. The aim of this article is to review the main concepts necessary for the critical reading of articles about radiological studies with observational designs. It reviews the characteristics that case-control and cohort studies must have to ensure high quality. It explains a method of critical reading that involves checking the attributes that should be evaluated in each type of article using a structured list of specific questions. It underlines the main characteristics that confer credibility and confidence on the article evaluated. Readers are provided with tools for the critical analysis of the observational studies published in scientific journals. PMID:26123855
Neural networks, field theory, directed percolation, and critical branching
NASA Astrophysics Data System (ADS)
Buice, Michael A.
We describe the dynamics of neural activity using field-theoretic methods for non-equilibrium statistical processes. Using a Markov assumption, we introduce the "spike model". The spike model permits a characterization of both neural fluctuations and response, presenting a tractable way to extend the mean field (Wilson-Cowan) equations used in much of theoretical and computational neuroscience. We also demonstrate the formalism's application to the Cowan models, one of which is equivalent to the forest fire model with immune trees. We argue that neural activity under mild conditions exhibits a dynamical phase transition which is in the universality class of directed percolation (DP). Owing to the spatial extent of neural interactions, there is a region in which the critical behavior is that of a branching process before crossing over into the DP region, consistent with measurements in cortical slice preparations. From the perspective of theoretical neuroscience, a principal contribution of this work is the connection of the problem of non-linear, non-Gaussian systems with the problem of dealing with infrared singularities in field theory. This work suggests a general characterization of epilepsy as a manifestation of a directed percolation phase transition.
Phase diagram and critical behavior of the antiferromagnetic Ising model in an external field
NASA Astrophysics Data System (ADS)
Jeferson Lourenço, Bruno; Dickman, Ronald
2016-03-01
We study the critical properties of the antiferromagnetic spin-1/2 Ising model in an external field on the square lattice. Using tomographic entropic sampling, a flat-histogram simulation method, we estimate the number of configurations, Ω , and related microcanonical averages in the energy-magnetization space, for system sizes L = 10-30. The critical line and exponents are calculated using finite-size scaling analysis in the temperature-external field plane. With these estimates in hand, we perform detailed studies of critical behavior using Metropolis sampling of larger systems (L≤slant 320 ). These results are compared to several approximate theoretical methods. Our estimates of critical exponents and Binder’s reduced fourth cumulant along the critical line are in very good agreement with their respective literature values for the two-dimensional Ising universality class. We verify as well that the specific heat scales ˜ \\ln L along the critical line, as expected for an Ising-like critical point.
Magnetic behavior of dirty multiband superconductors near the upper critical field
NASA Astrophysics Data System (ADS)
Silaev, Mikhail
2016-06-01
Magnetic properties of dirty multiband superconductors near the upper critical field are studied. The parameter κ2 characterizing magnetization slope is shown to have a significant temperature variation which is quite sensitive to the pairing interactions and relative strengths of intraband impurity scattering. In contrast to single-band superconductors the increase of κ2 at low temperatures can be arbitrarily large determined by the ratio of maximal and minimal diffusion coefficients in different bands. Temperature dependencies of κ2(T ) in two-band MgB2 and iron-based superconductors are shown to be much more sensitive to the multiband effects than the upper critical field Hc 2(T ) .
Field-induced quantum criticality in low-dimensional Heisenberg spin systems
NASA Astrophysics Data System (ADS)
Azzouz, Mohamed
2006-11-01
We study the quantum critical behavior in the antiferromagnetic Heisenberg chain and two-leg Heisenberg ladder resulting from the application of an external magnetic field. In each of these systems a finite-temperature crossover line between two different ferromagnetic phases ends with a quantum critical point at zero temperature. Using the bond-mean-field theory, we calculate the field dependence of the magnetization and the mean-field spin bond parameters in both systems. For the Heisenberg chain, we recover the existing exact results and show in addition that the saturation of the zero-temperature magnetization at the field hc=2J is accompanied by a quantum phase transition, where the bond parameter vanishes. Here J is the exchange coupling constant along the chain. For the two-leg ladder, we also recover the known results, like the two magnetization plateaus, and show that at the upper critical field, which corresponds to the appearance of the saturation magnetization plateau, the chain and rung spin bond parameters vanish. The identification of the order parameters that govern the field-induced quantum criticality in the systems we study here constitutes an original contribution. Because no long-range order, which breaks symmetry, characterizes the bond order, the latter could be a proposal for the so-called hidden order. We calculate analytically the bond parameters in both systems as functions of the field in the low- and high-field limits at zero temperature. At nonzero temperatures, the calculation of the magnetization and bond parameters is carried out by solving the mean-field equations numerically.
Knapp, R.M.; McInerney, M.J.; Menzie, D.E.; Coates, J.D.; Chisholm, J.L.
1993-05-01
A multi-well microbially enhanced oil recovery field pilot has been performed in the Southeast Vassar Vertz Sand Unit in Payne County, Oklahoma. The primary emphasis of the experiment was preferential plugging of high permeability zones for the purpose of improving waterflood sweep efficiency. Studies were performed to determine reservoir chemistry, ecology, and indigenous bacteria populations. Growth experiments were used to select a nutrient system compatible with the reservoir that encouraged growth of a group of indigenous nitrate-using bacteria and inhibit growth of sulfate-reducing bacteria. A specific field pilot area behind an active line drive waterflood was selected. Surface facilities were designed and installed. Injection protocols of bulk nutrient materials were prepared to facilitate uniform distribution of nutrients within the pilot area. By the end of December, 1991, 82.5 tons (75.0 tonnes) of nutrients had been injected in the field. A tracer test identified significant heterogeneity in the SEVVSU and made it necessary to monitor additional production wells in the field. The tracer tests and changes in production behavior indicate the additional production wells monitored during the field trial were also affected. Eighty two and one half barrels (13.1 m[sup 3]) of tertiary oil have been recovered. Microbial activity has increased CO[sub 2] content as indicated by increased alkalinity. A temporary rise in sulfide concentration was experienced. These indicate an active microbial community was generated in the field by the nutrient injection. Pilot area interwell pressure interference test results showed that significant permeability reduction occurred. The interwell permeabilities in the pilot area between the injector and the three pilot production wells were made more uniform which indicates a successful preferential plugging enhanced oil recovery project.
Critical Issues in Supporting Self-Study
ERIC Educational Resources Information Center
Lunenberg, Mieke; Zwart, Rosanne; Korthagen, Fred
2010-01-01
In this article, we focus on an analysis of critical issues in supporting teacher educators conducting a self-study. As data, we have used the digital logbooks written by the participating teacher educators, the outcomes of the interviews we held at the end of the support process, and of a follow-up questionnaire answered by the participating…
Critical Quantitative Study of Immigrant Students
ERIC Educational Resources Information Center
Conway, Katherine M.
2014-01-01
The author discusses the importance of critical quantitative research for studies of immigrant students, a large and growing group, whose higher education experience is crucial to the future of the United States. The author outlines some of the distinctions to be made among immigrant students and recommends areas of future inquiry.
Effect of diagonal disorder on the upper critical field of the local electron pair system
NASA Astrophysics Data System (ADS)
Li, Yan-Min; Zhang, Li-Yuan
1989-06-01
The effect of diagonal disorder on the upper critical magnetic field (Hc2) of the local electron pair system is studied in the framework of the mean-field approximation. It is found that the disorder strongly perturbs the temperature dependences of Hc2. The theoretical calculations are also compared with experimental Hc2 data on the heavy fermion superconductors CeCu2Si2 and UPt3. Similar temperature dependences are found.
Electric field effects on a near-critical fluid in microgravity
NASA Technical Reports Server (NTRS)
Zimmerli, G.; Wilkinson, R. A.; Ferrell, R. A.; Hao, H.; Moldover, M. R.
1994-01-01
The effects of an electric field on a sample of SF6 fluid in the vicinity of the liquid-vapor critical point is studied. The isothermal increase of the density of a near-critical sample as a function of the applied electric field was measured. In agreement with theory, this electrostriction effect diverges near the critical point as the isothermal compressibility diverges. Also as expected, turning on the electric field in the presence of density gradients can induce flow within the fluid, in a way analogous to turning on gravity. These effects were observed in a microgravity environment by using the Critical Point Facility which flew onboard the Space Shuttle Columbia in July 1994 as part of the Second International Microgravity Laboratory Mission. Both visual and interferometric images of two separate sample cells were obtained by means of video downlink. The interferometric images provided quantitative information about the density distribution throughout the sample. The electric field was generated by applying 500 Volts to a fine wire passing through the critical fluid.
Electric field effects on a near-critical fluid in microgravity
NASA Astrophysics Data System (ADS)
Zimmerli, G.; Wilkinson, R. A.; Ferrell, R. A.; Hao, H.; Moldover, M. R.
1994-04-01
The effects of an electric field on a sample of SF6 fluid in the vicinity of the liquid-vapor critical point is studied. The isothermal increase of the density of a near-critical sample as a function of the applied electric field was measured. In agreement with theory, this electrostriction effect diverges near the critical point as the isothermal compressibility diverges. Also as expected, turning on the electric field in the presence of density gradients can induce flow within the fluid, in a way analogous to turning on gravity. These effects were observed in a microgravity environment by using the Critical Point Facility which flew onboard the Space Shuttle Columbia in July 1994 as part of the Second International Microgravity Laboratory Mission. Both visual and interferometric images of two separate sample cells were obtained by means of video downlink. The interferometric images provided quantitative information about the density distribution throughout the sample. The electric field was generated by applying 500 Volts to a fine wire passing through the critical fluid.
Improved critical current in confined superconductors in parallel field configuration
NASA Astrophysics Data System (ADS)
Glatz, Andreas; Aronson, Igor; Wang, Yonglei; Xiao, Zhili
2015-03-01
We present results on the re-entrance of the superconducting state in systems placed into a magnetic field parallel to the applied current. In experiments it was observed that the magneto-resistance first increases with magnetic field, but at higher field drops again such that superconductivity is recovered. This effect is strongly temperature dependent and can lead to a suppression of resistance below the measurable threshold over a range of a few kG. We study the vortex dynamics and magneto-resistance in this situation in the framework of a large-scale time-dependent Ginzburg Landau simulation. A small external current as well as the magnetic field are applied in the x-direction, the latter is then ramped up. Our simulations reproduce this effect and reveal the mechanism for the observed behavior: the intermediate resistive state is due to a vortex instability leading to an unwinding of twisted vortex configurations. This leads to a periodic dynamic resistive state. When the field increases these instabilities get stabilized due to a higher vortex density and the resistance drops upon increasing the magnetic field. Work was supported by the Scientific Discovery through Advanced Computing (SciDAC) program funded by U.S. Department of Energy, Office of Science, Advanced Scientific Computing Research and Basic Energy Sciences, and by the Office of Science, Materials Sc.
Knapp, R.M.; McInerney, M.J.; Menzie, D.E.; Chisholm, J.L.
1990-11-01
This report covers progress made during the first year of the Microbial Field Pilot Study project. Information on reservoir ecology and characterization, facility and treatment design, core experiments, bacterial mobility, and mathematical modeling are addressed. To facilitate an understanding of the ecology of the target reservoir analyses of the fluids which support bacteriological growth and the microbiology of the reservoir were performed. A preliminary design of facilities for the operation of the field pilot test was prepared. In addition, procedures for facilities installation and for injection treatments are described. The Southeast Vassar Vertz Sand Unit (SEVVSU), the site of the proposed field pilot study, is described physically, historically, and geologically. The fields current status is presented and the ongoing reservoir simulation is discussed. Core flood experiments conducted during the last year were used to help define possible mechanisms involved in microbial enhanced oil recovery. Two possible mechanisms, relative permeability effects and changes in the capillary number, are discussed and related to four Berea core experiments' results. The experiments were conducted at reservoir temperature using SEVVSU oil, brine, and bacteria. The movement and activity of bacteria in porous media were investigated by monitoring the growth of bacteria in sandpack cores under no flow conditions. The rate of bacteria advancement through the cores was determined. A mathematical model of the MEOR process has been developed. The model is a three phase, seven species, one dimensional model. Finite difference methods are used for solution. Advection terms in balance equations are represented with a third- order upwind differencing scheme to reduce numerical dispersion and oscillations. The model is applied to a batch fermentation example. 52 refs., 26 figs., 21 tabs.
Review of Yucca Mountain Disposal Criticality Studies
Scaglione, John M; Wagner, John C
2011-01-01
The U.S. Department of Energy (DOE), Office of Civilian Radioactive Waste Management, submitted a license application for construction authorization of a deep geologic repository at Yucca Mountain, Nevada, in June of 2008. The license application is currently under review by the U.S. Nuclear Regulatory Commission. However,on March 3, 2010 the DOE filed a motion requesting withdrawal of the license application. With the withdrawal request and the development of the Blue Ribbon Commission to seek alternative strategies for disposing of spent fuel, the status of the proposed repository at Yucca Mountain is uncertain. What is certain is that spent nuclear fuel (SNF) will continue to be generated and some long-lived components of the SNF will eventually need a disposition path(s). Strategies for the back end of the fuel cycle will continue to be developed and need to include the insights from the experience gained during the development of the Yucca Mountain license application. Detailed studies were performed and considerable progress was made in many key areas in terms of increased understanding of relevant phenomena and issues regarding geologic disposal of SNF. This paper reviews selected technical studies performed in support of the disposal criticality analysis licensing basis and the use of burnup credit. Topics include assembly misload analysis, isotopic and criticality validation, commercial reactor critical analyses, loading curves, alternative waste package and criticality control studies, radial burnup data and effects, and implementation of a conservative application model in the criticality probabilistic evaluation as well as other information that is applicable to operations regarding spent fuel outside the reactor. This paper summarizes the work and significant accomplishments in these areas and provides a resource for future, related activities.
Critical currents of YBCO tapes and Bi-2212 wires at different temperatures and magnetic fields
Lombardo, V.; Barzi, e.; Turrioni, D.; Zlobin, A.V.; /Fermilab
2010-08-01
Design studies for the cooling channel of a Muon Collider call for straight and helical solenoids generating field well in excess of the critical fields of state of the art Low Temperature Superconductors (LTS) such as Nb{sub 3}Sn or NbTi. Therefore, High Temperature Superconductors (HTS) will need to be used for the manufacturing of all or certain sections of such magnets to be able to generate and withstand the field levels at the cryogenic temperatures required by the new machine. In this work, two major High Temperature Superconductors - Bi2212 round wires and YBCO coated conductor tapes - are investigated to understand how critical current density of such conductors scales as a function of external field and operating temperature. This is vital information to make conductor choices depending on the application and to proceed with the design of such magnets.
Knapp, R.M.; McInerney, M.J.; Menzie, D.E.; Chisholm, J.L.
1992-03-01
The objective of this project is to perform a microbial enhanced oil recovery field pilot in the Southeast Vassar Vertz Sand Unit (SEVVSU) in Payne County, Oklahoma. Indigenous, anaerobic, nitrate reducing bacteria will be stimulated to selectively plug flow paths which have been referentially swept by a prior waterflood. This will force future flood water to invade bypassed regions of the reservoir and increase sweep efficiency. This report covers progress made during the second year, January 1, 1990 to December 31, 1990, of the Microbial Field Pilot Study project. Information on reservoir ecology, surface facilities design, operation of the unit, core experiments, modeling of microbial processes, and reservoir characterization and simulation are presented in the report. To better understand the ecology of the target reservoir, additional analyses of the fluids which support bacteriological growth and the microbiology of the reservoir were performed. The results of the produced and injected water analysis show increasing sulfide concentrations with respect to time. In March of 1990 Mesa Limited Partnership sold their interest in the SEVVSU to Sullivan and Company. In April, Sullivan and Company assumed operation of the field. The facilities for the field operation of the pilot were refined and implementation was begun. Core flood experiments conducted during the last year were used to help define possible mechanisms involved in microbial enhanced oil recovery. The experiments were performed at SEVVSU temperature using fluids and inoculum from the unit. The model described in last year's report was further validated using results from a core flood experiment. The model was able to simulate the results of one of the core flood experiments with good quality.
Knapp, R.M.; McInerney, M.J.; Menzie, D.E.; Chisholm, J.L.
1992-03-01
The objective of this project is to perform a microbial enhanced oil recovery field pilot in the Southeast Vassar Vertz Sand Unit (SEVVSU) in Payne County, Oklahoma. Indigenous, anaerobic, nitrate reducing bacteria will be stimulated to selectively plug flow paths which have been referentially swept by a prior waterflood. This will force future flood water to invade bypassed regions of the reservoir and increase sweep efficiency. This report covers progress made during the second year, January 1, 1990 to December 31, 1990, of the Microbial Field Pilot Study project. Information on reservoir ecology, surface facilities design, operation of the unit, core experiments, modeling of microbial processes, and reservoir characterization and simulation are presented in the report. To better understand the ecology of the target reservoir, additional analyses of the fluids which support bacteriological growth and the microbiology of the reservoir were performed. The results of the produced and injected water analysis show increasing sulfide concentrations with respect to time. In March of 1990 Mesa Limited Partnership sold their interest in the SEVVSU to Sullivan and Company. In April, Sullivan and Company assumed operation of the field. The facilities for the field operation of the pilot were refined and implementation was begun. Core flood experiments conducted during the last year were used to help define possible mechanisms involved in microbial enhanced oil recovery. The experiments were performed at SEVVSU temperature using fluids and inoculum from the unit. The model described in last year`s report was further validated using results from a core flood experiment. The model was able to simulate the results of one of the core flood experiments with good quality.
Critical wetting of a class of nonequilibrium interfaces: a mean-field picture.
de Los Santos, Francisco; Romera, Elvira; Al Hammal, Omar; Muñoz, Miguel Angel
2007-03-01
A self-consistent mean-field method is used to study critical wetting transitions under nonequilibrium conditions by analyzing Kardar-Parisi-Zhang (KPZ) interfaces in the presence of a bounding substrate. In the case of positive KPZ nonlinearity a single (Gaussian) regime is found. On the contrary, interfaces corresponding to negative nonlinearities lead to three different regimes of critical behavior for the surface order parameter: (i) a trivial Gaussian regime, (ii) a weak-fluctuation regime with a trivially located critical point and nontrivial exponents, and (iii) a highly nontrivial strong-fluctuation regime, for which we provide a full solution by finding the zeros of parabolic-cylinder functions. These analytical results are also verified by solving numerically the self-consistent equation in each case. Analogies with and differences from equilibrium critical wetting as well as nonequilibrium complete wetting are also discussed. PMID:17500666
Critical point of a para-ferrimagnetic phase transition of the ANNNI model in a field
NASA Astrophysics Data System (ADS)
Sznajd, J.
2012-10-01
The finite field para-ferrimagnetic phase transition in the axial next-nearest-neighbor Ising (ANNNI) model is studied by using the linear perturbation real space renormalization group transformation. The method is examined in systems of ferromagnetic and antiferromagnetic Ising chains coupled by ferromagnetic interactions in the longitudinal field. As one would expect, the external field in the first case destroys the continuous phase transition and in the second shifts the critical point toward a lower temperature according to the square law. For the ferromagnetic chains coupled by the competing interchain nearest-neighbor J1 < 0 and next-nearest-neighbor J2 < 0 interactions, the external field changes the character of the phase transition from continuous to discontinuous. However, it has been found that for the ratio J2/J1 around 0.5 there is a critical value of the field for which an isolated critical point exists. The temperature dependences of the specific heat for several values of J2/J1 and the external field are presented.
NASA Technical Reports Server (NTRS)
Brenning, N.; Faelthammar, C.-G.; Marklund, G.; Haerendel, G.; Kelley, M. C.; Pfaff, R.
1991-01-01
The quasi-dc electric fields measured in the CRIT I ionospheric release experiment are studied. In the experiment, two identical barium shaped charges were fired toward a main payload, and three-dimensional measurements of the electric field inside the streams were made. The relevance of proposed mechanisms for electron heating in the critical ionization velocity (CIV) mechanism is addressed. It is concluded that both the 'homogeneous' and the 'ionizing front' models probably are valid, but in different parts of the streams. It is also possible that electrons are directly accelerated by a magnetic field-aligned component of the electric field. The coupling between the ambient ionosphere and the ionized barium stream is more complicated that is usually assumed in CIV theories, with strong magnetic-field-aligned electric fields and probably current limitation as important processes.
Electron profile stiffness and critical gradient studies
DeBoo, J. C.; Petty, C. C.; Burrell, K. H.; Smith, S. P.; White, A. E.; Doyle, E. J.; Hillesheim, J. C.; Rhodes, T. L.; Schmitz, L.; Wang, G.; Zeng, L.; Holland, C.; McKee, G. R.
2012-08-15
Electron profile stiffness was studied in DIII-D L-mode discharges by systematically varying the heat flux in a narrow region with electron cyclotron heating and measuring the local change produced in {nabla}T{sub e}. Electron stiffness was found to slowly increase with toroidal rotation velocity. A critical inverse temperature gradient scale length 1/L{sub C} {approx} 3 m{sup -1} was identified at {rho}=0.6 and found to be independent of rotation. Both the heat pulse diffusivity and the power balance diffusivity, the latter determined by integrating the measured dependence of the heat pulse diffusivity on -{nabla}T{sub e}, were fit reasonably well by a model containing a critical inverse temperature gradient scale length and varying linearly with 1/L{sub T} above the threshold.
Critical Currents of MgB2 Wire and Tape in Magnetic Field under Bending Deformations
NASA Astrophysics Data System (ADS)
Abin, D. A.; Mineev, N. A.; Osipov, M. A.; Pokrovsky, S. V.; Rudnev, I. A.
Nowadays MgB2 wires are attractive for designing real devices like motors and magnets. The latest production technologies allow to increase critical current value of wires. However, there is a problem of wire performance degradation under bending strain. Thus, there is a problem of manufacturing solenoids with small diameters, especially from ex situ MgB2 wires produced by powder-in-tube (PIT) technology. In this work, influence of bending on critical current Ic multifilament PIT ex situ MgB2 tape and wire has been studied. Critical current dependencies on external magnetic field Ic(H) were measured at liquid helium temperature in the range of fields from 2.5 T up to 8 T. Measurements were carried out in parallel (H||), and perpendicular (H⊥) orientation of external magnetic field to the sample surface. Voltage current characteristics (V-I) on tape samples were measured with bending on diameters D=30; 40; 60; 70; 80; 90;100 mm. It was shown that critical current density (Jc) decreases by 24% and by 28% for tape and wire respectively with decreasing bending diameter from 100 mm to 60 mm. It was found that the tape still had superconductive properties even with bending diameter D=30 mm, but its Jc decreased by 44% in comparison with Jc(D=100 mm). One more feature that was found is the appearance of resistive component in the voltage current characteristics for all bend diameters in magnetic fields H>3.5 T.
A Critical Analysis of Transverse Dispersivity Field Data
NASA Astrophysics Data System (ADS)
Attinger, Sabine; Zech, Alraune; Bellin, Alberto; Cvetkovic, Vladimir; Dagan, Gedeon; Dietrich, Peter; Fiori, Aldo; Teutsch, Georg
2016-04-01
Spreading of solute plumes in groundwater is often quantified by macrodispersivity. Thereby, the transverse αT and vertical αV characterize the broadening of the plume in the vertical plane, perpendicular to the flow direction. Determining αT and αV from field experiments is difficult and costly. Still, it is an important parameter for making predictions of contaminant transport e.g. for stationary contamination plumes, bio-degradation and natural attenuation. Measured values of αT and αV at field scale are only available for a few sites. Gelhar and coworkers classified in 1992 the values into three reliability groups: highly, moderately and lowly reliable. Only recently, we could show for the longitudinal macrodispersivity αL, that the values of low reliability need to be excluded for further analysis, based on a re-evaluation of the experiments. Furthermore, new studies emerged in the meantime, which requires evaluation of reliability and incorporation, when appropriate. This work focuses on collecting reliable field data of transverse and vertical macrodispersivities. The ensemble of reliable αT and αV values is then used to answer the following questions: (i) Is there an upper limit of αT and αV or the tendency of increasing values with increasing travel distance of tracer plumes? (ii) Can the field data be predicted by theoretical models? (iii) What can we learn from the field based ratios αV/αT and αT/αL? The investigation may provide valuable information for modeling and predicting contaminant transport in groundwater.
Non-mean-field critical exponent in a mean-field model: dynamics versus statistical mechanics.
Ogawa, Shun; Patelli, Aurelio; Yamaguchi, Yoshiyuki Y
2014-03-01
Mean-field theory tells us that the classical critical exponent of susceptibility is twice that of magnetization. However, linear response theory based on the Vlasov equation, which is naturally introduced by the mean-field nature, makes the former exponent half of the latter for families of quasistationary states having second order phase transitions in the Hamiltonian mean-field model and its variances, in the low-energy phase. We clarify that this strange exponent is due to the existence of Casimir invariants which trap the system in a quasistationary state for a time scale diverging with the system size. The theoretical prediction is numerically confirmed by N-body simulations for the equilibrium states and a family of quasistationary states. PMID:24730814
Magnetic field oscillations of the critical current in long ballistic graphene Josephson junctions
NASA Astrophysics Data System (ADS)
Rakyta, Péter; Kormányos, Andor; Cserti, József
2016-06-01
We study the Josephson current in long ballistic superconductor-monolayer graphene-superconductor junctions. As a first step, we have developed an efficient computational approach to calculate the Josephson current in tight-binding systems. This approach can be particularly useful in the long-junction limit, which has hitherto attracted less theoretical interest but has recently become experimentally relevant. We use this computational approach to study the dependence of the critical current on the junction geometry, doping level, and an applied perpendicular magnetic field B . In zero magnetic field we find a good qualitative agreement with the recent experiment of M. Ben Shalom et al. [Nat. Phys. 12, 318 (2016), 10.1038/nphys3592] for the length dependence of the critical current. For highly doped samples our numerical calculations show a broad agreement with the results of the quasiclassical formalism. In this case the critical current exhibits Fraunhofer-like oscillations as a function of B . However, for lower doping levels, where the cyclotron orbit becomes comparable to the characteristic geometrical length scales of the system, deviations from the results of the quasiclassical formalism appear. We argue that due to the exceptional tunability and long mean free path of graphene systems a new regime can be explored where geometrical and dynamical effects are equally important to understand the magnetic field dependence of the critical current.
ERIC Educational Resources Information Center
Zeller-Berkman, Sarah
2010-01-01
A critical theory lens is used to explore the role of evaluation in youth development, a field aimed at recognizing youth as assets. A theory of change in the field is questioned for its emphasis on individual youth outcomes as programmatic outcome measures. A review of 209 evaluations of 131 programs in the Harvard Family Research Project's…
Critical Inquiry in the Social Studies Classroom: Portraits of Critical Teacher Research
ERIC Educational Resources Information Center
Manfra, Meghan McGlinn
2009-01-01
This study demonstrates the potential for teacher research to lead to critical inquiry and change in social studies classrooms. It presents four portraits of experienced social studies teachers engaged in critical teacher research. These teachers posed critical questions about the means and purposes of schooling, while engaging their students in…
Critical field enhancement of asymptotic optical bound states in the continuum
Yoon, Jae Woong; Song, Seok Ho; Magnusson, Robert
2015-01-01
We study spectral singularities and critical field enhancement factors associated with embedded photonic bound states in subwavelength periodic Si films. Ultrahigh-Q resonances supporting field enhancement factor exceeding 108 are obtained in the spectral vicinity of exact embedded eigenvalues in spite of deep surface modulation and vertical asymmetry of the given structure. Treating relations between the partial resonance Q and field enhancement factors with an analytical coupled-mode model, we derive a general strategy to maximize the field enhancement associated with these photonic bound states in the presence of material dissipation. The analytical expression for the field enhancement quantitatively agrees with rigorous numerical calculations. Therefore, our results provide a general knowledge for designing practical resonance elements based on optical bound states in the continuum in various applications. PMID:26673548
Critical field enhancement of asymptotic optical bound states in the continuum.
Yoon, Jae Woong; Song, Seok Ho; Magnusson, Robert
2015-01-01
We study spectral singularities and critical field enhancement factors associated with embedded photonic bound states in subwavelength periodic Si films. Ultrahigh-Q resonances supporting field enhancement factor exceeding 10(8) are obtained in the spectral vicinity of exact embedded eigenvalues in spite of deep surface modulation and vertical asymmetry of the given structure. Treating relations between the partial resonance Q and field enhancement factors with an analytical coupled-mode model, we derive a general strategy to maximize the field enhancement associated with these photonic bound states in the presence of material dissipation. The analytical expression for the field enhancement quantitatively agrees with rigorous numerical calculations. Therefore, our results provide a general knowledge for designing practical resonance elements based on optical bound states in the continuum in various applications. PMID:26673548
Critical field enhancement of asymptotic optical bound states in the continuum
NASA Astrophysics Data System (ADS)
Yoon, Jae Woong; Song, Seok Ho; Magnusson, Robert
2015-12-01
We study spectral singularities and critical field enhancement factors associated with embedded photonic bound states in subwavelength periodic Si films. Ultrahigh-Q resonances supporting field enhancement factor exceeding 108 are obtained in the spectral vicinity of exact embedded eigenvalues in spite of deep surface modulation and vertical asymmetry of the given structure. Treating relations between the partial resonance Q and field enhancement factors with an analytical coupled-mode model, we derive a general strategy to maximize the field enhancement associated with these photonic bound states in the presence of material dissipation. The analytical expression for the field enhancement quantitatively agrees with rigorous numerical calculations. Therefore, our results provide a general knowledge for designing practical resonance elements based on optical bound states in the continuum in various applications.
Electromagnetic Field Penetration Studies
NASA Technical Reports Server (NTRS)
Deshpande, M.D.
2000-01-01
A numerical method is presented to determine electromagnetic shielding effectiveness of rectangular enclosure with apertures on its wall used for input and output connections, control panels, visual-access windows, ventilation panels, etc. Expressing EM fields in terms of cavity Green's function inside the enclosure and the free space Green's function outside the enclosure, integral equations with aperture tangential electric fields as unknown variables are obtained by enforcing the continuity of tangential electric and magnetic fields across the apertures. Using the Method of Moments, the integral equations are solved for unknown aperture fields. From these aperture fields, the EM field inside a rectangular enclosure due to external electromagnetic sources are determined. Numerical results on electric field shielding of a rectangular cavity with a thin rectangular slot obtained using the present method are compared with the results obtained using simple transmission line technique for code validation. The present technique is applied to determine field penetration inside a Boeing-757 by approximating its passenger cabin as a rectangular cavity filled with a homogeneous medium and its passenger windows by rectangular apertures. Preliminary results for, two windows, one on each side of fuselage were considered. Numerical results for Boeing-757 at frequencies 26 MHz, 171-175 MHz, and 428-432 MHz are presented.
[Contributions from the critical leisure field to the health promotion].
Bacheladenski, Miguel Sidenei; Matiello Júnior, Edgard
2010-08-01
The studies about leisure for health promotion still tend to choose the active body occupation in the free-time (leisure activities), revealing the influence of the functionalist way of thinking, which trying to reduce the links between society and health-disease process, undoubtedly do not keep with the purpose of population health promotion. Focusing on this idea, and keeping in mind the premise that in the Brazilian physical training there are different opinions since the earliest 80s which try to achieve the purpose to avoid the ideas of the functionalist way of thinking. However, those opinions are almost unknown both in the Brazilian public health system and the collective health system, once the bibliography revision about leisure activities development was made in the country, looking for ideas taken in common knowledge for health promotion presuppositions, this report has the aim to show critical and alternatives concepts of leisure in the way it is linked to healthy as a real social change, using a political-pedagogical proposal called lazerania. In general, this is an emancipatory concept of leisure, which comes from the sport phenomenon as a problem and provides the feeling, thinking and behavior of the population, trying to build a society based on solidarity and consumer participation. PMID:20802889
Notions of Criticality: Singaporean Teachers' Perspectives of Critical Thinking in Social Studies
ERIC Educational Resources Information Center
Baildon, Mark C.; Sim, Jasmine B.-Y.
2009-01-01
In this article we explore the ways critical thinking is conceived by a group of Singaporean social studies teachers, what they see as its purposes as well as perceived constraints to critical thinking and teaching critical thinking in Singapore's schools. Using a case study research design and constant comparative method we analysed data from…
Second-order magnetic critical points at finite magnetic fields: Revisiting Arrott plots
NASA Astrophysics Data System (ADS)
Bustingorry, S.; Pomiro, F.; Aurelio, G.; Curiale, J.
2016-06-01
The so-called Arrott plot, which consists in plotting H /M against M2, with H the applied magnetic field and M the magnetization, is used to extract valuable information in second-order magnetic phase transitions. Besides, it is widely accepted that a negative slope in the Arrott plot is indicative of a first-order magnetic transition. This is known as the Banerjee criterion. In consequence, the zero-field transition temperature T* is reported as the characteristic first-order transition temperature. By carefully analyzing the mean-field Landau model used for studying first-order magnetic transitions, we show in this work that T* corresponds in fact to a triple point where three first-order lines meet. More importantly, this analysis reveals the existence of two symmetrical second-order critical points at finite magnetic field (Tc,±Hc) . We then show that a modified Arrott plot can be used to obtain information about these second-order critical points. To support this idea we analyze experimental data on La2 /3Ca1 /3MnO3 and discuss an estimate for the location of the triple point and the second-order critical points.
Criticality in neural ensembles: a mean field approach to expand network size from measured data
NASA Astrophysics Data System (ADS)
Wasnik, Vaibhav; Caracheo, Barak; Seamans, Jeremy; Emberly, Eldon
2014-03-01
At the point of a second order phase transition also termed as a critical point, systems display long range order and their macroscopic behaviours are independent of the microscopic details making up the system. This makes the idea of criticality interesting for studying biological systems which even though are different microscopically still have similar macroscopic behaviours. Recent high-throughput methods in neuroscience are making it possible to explore whether criticality exists in neural networks. Despite being high-throughput, many data sets are still only a minute sample of the neural system and methods towards expanding these data sets have to be considered in order to study the existence of criticality. Using measurements of firing neurons from the pre-frontal cortex (PFC) of rats, we map the data to a system of Ising spins and calculate the specific heat as a function of the measured network size, looking for the existence of critical points. In order to go to the thermodynamic limit, we propose a mean field approach for expanding such data. Our preliminary results show that such an approach can capture the statistical properties of much larger neuronal populations even when only a smaller subset is measured.
The distribution of 3D superconductivity near the second critical field
NASA Astrophysics Data System (ADS)
Kachmar, Ayman; Nasrallah, Marwa
2016-09-01
We study the minimizers of the Ginzburg–Landau energy functional with a uniform magnetic field in a three dimensional bounded domain. The functional depends on two positive parameters, the Ginzburg–Landau parameter and the intensity of the applied magnetic field, and acts on complex-valued functions and vector fields. We establish a formula for the distribution of the L 2-norm of the minimizing complex-valued function (order parameter). The formula is valid in the regime where the Ginzburg–Landau parameter is large and the applied magnetic field is close to and strictly below the second critical field—the threshold value corresponding to the transition from the superconducting to the normal phase in the bulk of the sample. Earlier results are valid in 2D domains and for the L 4-norm in 3D domains.
Fielding: A Collection of Critical Essays. Twentieth Century Views Series.
ERIC Educational Resources Information Center
Paulson, Ronald, Ed.
One of a series of works aimed at presenting contemporary critical opinion on major authors, this collection includes essays by Ronald Paulson, A. R. Humphreys, Winfield H. Rogers, Ian Watt, Maynard Mack, Mark Spilka, Aurelien Digeon, Andre Gide, Arnold Kettle, John Middleton Murry, William Empson, George Sherburn, and John S. Coolidge--all…
ERIC Educational Resources Information Center
Kanpol, Barry, Ed.; McLaren, Peter, Ed.
This collection explores the way in which critical theory and practice can unite in a common vision of democratic hope. Separate viewpoints are drawn together to constitute a democratic platform for an enlightened critical education agenda. Case studies from narrative and critical ethnography explore the multicultural and power struggles of…
Criticality studies of actinides within fissures
NASA Astrophysics Data System (ADS)
Wilcox, Trevor
The storage of nuclear waste in underground storage facilities presents numerous engineering challenges and risks. Experimental verification of engineered underground storage is impractical or prohibitively expensive, leaving scientists with few options. A 1995 report by Bowman and Venneri of the Los Alamos National Laboratory generated considerable controversy by hypothesizing that wastes composed of fissionable plutonium leached from underground storage containers could pose a nuclear criticality hazard. They proposed cases where plutonium collected in underground fractures could lead to sustained nuclear fission. In overmoderated cases, they argued that the resulting release of energy from fission could result in steam explosions, or even an underground nuclear explosion (autocriticality). Their hypothesis had severe implications for the feasibility of long-term nuclear waste storage in geologic repositories. The Bowman and Venneri hypothesis led to the need for a study of conditions that could lead to a critical event in a geologic repository due to releases of uranium or plutonium. Information about the likely consequences of a critical event is also important in repository design. To accomplish this study a numerical simulation code, GEOCRIT, was written to model radionuclide transport from the repository into a fracture below the repository. Once sufficient material has accumulated in the fracture and rock matrix, the neutronics portion of the code is started to simulate heat generation and fluid flow. The thermohydraulics portion of the code calculates heat generation from fission, stream functions, velocity, and pressure of the fluid in the fracture and rock matrix. The transport portion of the code incorporates numerous parameters that can be varied to simulate different radionuclide buildup in the fracture and rock matrix. Variation of the solubility, diffusion, deposition coefficients in the program yield different accumulations of radionuclides in the
Curator and Critic: Role of the Assessor in Aesthetic Fields
ERIC Educational Resources Information Center
Jacobs, Rachael
2012-01-01
Assessment in aesthetic fields presents a myriad of challenges in the higher education environment. This paper uses a metaphorical representation to explore the role of assessors within aesthetic assessment settings in higher education. It begins with a discussion of aesthetic fields and an exploration of the role of assessment in this area.…
The Field of Educational Development: Histories and Critical Questions
ERIC Educational Resources Information Center
Manathunga, Catherine
2011-01-01
The field of educational development has a 40-year history of providing continuing education or professional development for academic staff, particularly focusing on improving teaching and learning. However, little has yet been written on the historical origins and development of this field, apart from content analyses of some key journals and…
Superconducting critical fields of alkali and alkaline-earth intercalates of MoS2
NASA Technical Reports Server (NTRS)
Woollam, J. A.; Somoano, R. B.
1976-01-01
Results are reported for measurements of the critical-field anisotropy and temperature dependence of group-VIB semiconductor MoS2 intercalated with the alkali and alkaline-earth metals Na, K, Rb, Cs, and Sr. The temperature dependences are compared with present theories on the relation between critical field and transition temperature in the clean and dirty limits over the reduced-temperature range from 1 to 0.1. The critical-field anisotropy data are compared with predictions based on coupled-layers and thin-film ('independent-layers') models. It is found that the critical-field boundaries are steep in all cases, that the fields are greater than theoretical predictions at low temperatures, and that an unusual positive curvature in the temperature dependence appears which may be related to the high anisotropy of the layer structure. The results show that materials with the largest ionic intercalate atom diameters and hexagonal structures (K, Rb, and Cs compounds) have the highest critical temperatures, critical fields, and critical-boundary slopes; the critical fields of these materials are observed to exceed the paramagnetic limiting fields.
Critical Multicultural Education Competencies Scale: A Scale Development Study
ERIC Educational Resources Information Center
Acar-Ciftci, Yasemin
2016-01-01
The purpose of this study is to develop a scale in order to identify the critical mutlicultural education competencies of teachers. For this reason, first of all, drawing on the knowledge in the literature, a new conceptual framework was created with deductive method based on critical theory, critical race theory and critical multicultural…
A kinematic study of critical and non-critical articulators in emotional speech production.
Kim, Jangwon; Toutios, Asterios; Lee, Sungbok; Narayanan, Shrikanth S
2015-03-01
This study explores one aspect of the articulatory mechanism that underlies emotional speech production, namely, the behavior of linguistically critical and non-critical articulators in the encoding of emotional information. The hypothesis is that the possible larger kinematic variability in the behavior of non-critical articulators enables revealing underlying emotional expression goal more explicitly than that of the critical articulators; the critical articulators are strictly controlled in service of achieving linguistic goals and exhibit smaller kinematic variability. This hypothesis is examined by kinematic analysis of the movements of critical and non-critical speech articulators gathered using eletromagnetic articulography during spoken expressions of five categorical emotions. Analysis results at the level of consonant-vowel-consonant segments reveal that critical articulators for the consonants show more (less) peripheral articulations during production of the consonant-vowel-consonant syllables for high (low) arousal emotions, while non-critical articulators show less sensitive emotional variation of articulatory position to the linguistic gestures. Analysis results at the individual phonetic targets show that overall, between- and within-emotion variability in articulatory positions is larger for non-critical cases than for critical cases. Finally, the results of simulation experiments suggest that the postural variation of non-critical articulators depending on emotion is significantly associated with the controls of critical articulators. PMID:25786953
Particle and flow field holography: A critical survey
NASA Technical Reports Server (NTRS)
Trolinger, James D.
1987-01-01
A brief background is provided for the fields of particle and flow visualization holography. A summary of methods currently in use is given, followed by a discussion of more recent and unique applications. The problem of data reduction is discussed. A state of the art summary is then provided with a prognosis of the future of the field. Particle and flow visualization holography are characterized as powerful tools currently in wide use and with significant untapped potential.
Critical-field theory of the Kondo lattice model in two dimensions
Kim, Ki-Seok
2005-05-15
In the context of the U(1) slave-boson theory we derive a critical-field theory near the quantum-critical point of the Kondo lattice model in two spatial dimensions. First, we argue that strong gauge fluctuations in the U(1) slave-boson theory give rise to confinement between spinons and holons, thus causing 'neutralized' spinons in association with the slave-boson U(1) gauge field. Second, we show that critical fluctuations of Kondo singlets near the quantum-critical point result in a new U(1) gauge field. This emergent gauge field has nothing to do with the slave-boson U(1) gauge field. Third, we find that the slave-boson U(1) gauge field can be exactly integrated out in the low-energy limit. As a result we find a critical-field theory in terms of renormalized conduction electrons and neutralized spinons interacting via the new emergent U(1) gauge field. Based on this critical-field theory we obtain the temperature dependence of the specific heat and the imaginary part of the self-energy of the renormalized electrons. These quantities display non-Fermi-liquid behavior near the quantum-critical point.
Upper critical field enhancements of TMB HPCVD magnesium diboride
NASA Astrophysics Data System (ADS)
Hunte, F.; Jaroszynski, J.; Gurevich, A.; Larbalestier, D. C.; Zhu, Y.; Voyles, P. M.; Wilke, R. H.; Xi, X. X.
2008-03-01
The Hc2 of four well textured carbon-doped MgB2 films grown by HPCVD from tri-methyl boron (TMB) at flow rates from 2.5 to 10 sccm was measured in fields up to 45T. Hc2 derived from low- current, four-point magnetoresistance clearly increases with increasing TMB flow rate. TMB appears to be a more uniform dopant than the (C6H7)2Mg used earlier. These earlier films exhibited Hc2^(0) up to 70 T but also were imperfectly connected (ρ(50 K)˜200-800 μφcm) due to excess amorphous C-rich phases observed between the MgB2 grains. In strong contrast, ρ(50 K) was only 10-20 μφcm for the TMB films. When first measured, the linearly extrapolated Hc2^(0) reached ˜40 T for the film with the highest TMB flow rate, but after about 3 months of aging, this value rose to ˜50 T. The angular dependence of Hc2 for this sample was measured up to 45 T yielding Hc2^(4.2 K) = 45.8 T and showing the good Ginzburg-Landau scaling with an Hc2 anisotropy of 2.88 at 4.2 K. These results are discussed in terms of the theory of dirty two-gap superconductors as a part of an in-depth study of the effect of ternary doping of magnesium diboride.
NASA Astrophysics Data System (ADS)
Watanabe, Shinji; Tsuruta, Atsushi; Miyake, Kazumasa; Flouquet, Jacques
2009-03-01
Valence instability and its critical fluctuations have attracted much attention recently in the heavy-electron systems. Valence fluctuations are essentially charge fluctuations, and it is highly non-trivial how the quantum critical point (QCP) as well as the critical end point is controlled by the magnetic field. To clarify this fundamental issue, we have studied the mechanism of how the critical points of the first-order valence transitions are controlled by the magnetic field [1]. We show that the critical temperature is suppressed to be the QCP by the magnetic field and unexpectedly the QCP exhibits nonmonotonic field dependence in the ground-state phase diagram, giving rise to emergence of metamagnetism even in the intermediate valence-crossover regime. The driving force of the field-induced QCP is clarified to be a cooperative phenomenon of Zeeman effect and Kondo effect, which creates a distinct energy scale from the Kondo temperature. This mechanism explains a peculiar magnetic response in CeIrIn5 and metamagnetic transition in YbXCu4 for X=In as well as a sharp contrast between X=Ag and Cd. We present the novel phenomena under the magnetic field to discuss significance of the proximity of the critical points of the first-order valence transition. [1] S. Watanabe et al. PRL100, (2008) 236401.
Automated Critical Peak Pricing Field Tests: Program Descriptionand Results
Piette, Mary Ann; Watson, David; Motegi, Naoya; Kiliccote, Sila; Xu, Peng
2006-04-06
California utilities have been exploring the use of critical peak prices (CPP) to help reduce needle peaks in customer end-use loads. CPP is a form of price-responsive demand response (DR). Recent experience has shown that customers have limited knowledge of how to operate their facilities in order to reduce their electricity costs under CPP (Quantum 2004). While the lack of knowledge about how to develop and implement DR control strategies is a barrier to participation in DR programs like CPP, another barrier is the lack of automation of DR systems. During 2003 and 2004, the PIER Demand Response Research Center (DRRC) conducted a series of tests of fully automated electric demand response (Auto-DR) at 18 facilities. Overall, the average of the site-specific average coincident demand reductions was 8% from a variety of building types and facilities. Many electricity customers have suggested that automation will help them institutionalize their electric demand savings and improve their overall response and DR repeatability. This report focuses on and discusses the specific results of the Automated Critical Peak Pricing (Auto-CPP, a specific type of Auto-DR) tests that took place during 2005, which build on the automated demand response (Auto-DR) research conducted through PIER and the DRRC in 2003 and 2004. The long-term goal of this project is to understand the technical opportunities of automating demand response and to remove technical and market impediments to large-scale implementation of automated demand response (Auto-DR) in buildings and industry. A second goal of this research is to understand and identify best practices for DR strategies and opportunities. The specific objectives of the Automated Critical Peak Pricing test were as follows: (1) Demonstrate how an automated notification system for critical peak pricing can be used in large commercial facilities for demand response (DR). (2) Evaluate effectiveness of such a system. (3) Determine how customers
Leading Critically: A Grounded Theory of Applied Critical Thinking in Leadership Studies
ERIC Educational Resources Information Center
Jekins, Daniel M.; Cutchens, Amanda B.
2011-01-01
This study describes the development of a grounded theory of applied critical thinking in leadership studies and examines how student-centered experiential learning in leadership education bridged critical thinking with action. Over three semester undergraduate students in an upper level leadership studies course at a large four-year public…
JBI's Systematic Reviews: Study selection and critical appraisal.
Porritt, Kylie; Gomersall, Judith; Lockwood, Craig
2014-06-01
This article is the fourth in a series on the systematic review from the Joanna Briggs Institute, an international collaborative supporting evidence-based practice in nursing, medicine, and allied health fields. The purpose of the series is to describe how to conduct a systematic review-one step at a time. This article focuses on the study selection and critical appraisal steps in the process. These steps ensure that the review produces valid results capable of providing a useful basis for informing policy, clinical practice, and future research. PMID:24869584
Critical Differences in Aided Sound Field Thresholds in Children.
ERIC Educational Resources Information Center
Stuart, Andrew; And Others
1990-01-01
Variability of aided sound field thresholds (ASFTs) was examined in 30 hearing-impaired children comprising 2 age groups (5-9 and 10-14 years). Findings showed that 2 ASFTs would have to differ by more than 10 decibels across signal test frequencies to attain statistical significance. (Author/DB)
Critical behavior of non-order-parameter fields.
Mócsy, Agnes; Sannino, Francesco; Tuominen, Kimmo
2003-08-29
We show that all of the relevant features of a phase transition can be determined using a non-order-parameter field which is a physical state of the theory. This fact allows us to describe the deconfining transition of the pure Yang-Mills theory via the physical excitations rather than using the Polyakov loop. PMID:14525174
When Sex and Power Collide: An Argument for Critical Sexuality Studies.
Fahs, Breanne; McClelland, Sara I
2016-01-01
Attentive to the collision of sex and power, we add momentum to the ongoing development of the subfield of critical sexuality studies. We argue that this body of work is defined by its critical orientation toward the study of sexuality, along with a clear allegiance to critical modalities of thought, particularly feminist thought. Critical sexuality studies takes its cues from several other critical moments in related fields, including critical psychology, critical race theory, critical public health, and critical youth studies. Across these varied critical stances is a shared investment in examining how power and privilege operate, understanding the role of historical and epistemological violence in research, and generating new models and paradigms to guide empirical and theoretical research. With this guiding framework, we propose three central characteristics of critical sexuality studies: (a) conceptual analysis, with particular attention to how we define key terms and conceptually organize our research (e.g., attraction, sexually active, consent, agency, embodiment, sexual subjectivity); (b) attention to the material qualities of abject bodies, particularly bodies that are ignored, overlooked, or pushed out of bounds (e.g., viscous bodies, fat bodies, bodies in pain); and (c) heteronormativity and heterosexual privilege, particularly how assumptions about heterosexuality and heteronormativity circulate in sexuality research. Through these three critical practices, we argue that critical sexuality studies showcases how sex and power collide and recognizes (and tries to subvert) the various power imbalances that are deployed and replicated in sex research. PMID:27105445
NASA Astrophysics Data System (ADS)
Contoyiannis, Y.; Potirakis, S. M.; Eftaxias, K.; Hayakawa, M.; Schekotov, A.
2016-06-01
The ultra-low-frequency (ULF) magnetic variations recorded prior to the 11 March 2011 Tohoku earthquake (EQ) are analyzed using the method of critical fluctuations (MCF). The first application of this specific method to ULF magnetic variations is performed on the unprocessed H- (horizontal) and Z- (vertical) components, as well as on the unprocessed total intensity, F, of the recorded magnetic field. The motivation for the present study was given by recent research results reporting criticality features in the ULF magnetic fields prior to the 2011 Tohoku EQ. These results call for a further analysis in order to verify the existence of criticality embedded in the specific ULF recordings using an independent method, as well as to investigate the type of the embedded criticality. The application of MCF indeed verifies the existence of criticality in the ULF magnetic fields a few days to one week before the occurrence of the main shock. Specifically, clear signatures of intermittent criticality are found in the recordings of 4 March 2011, while indications of critical behavior are also found in 3 and 6 March recordings, although not of the "stability" of those of 4 March. Moreover, it is found that only the ULF data of the nearest, to the epicenter of the EQ, geomagnetic observatory presented criticality. This finding further corroborates the view that the presented signal is indeed a precursor to the specific EQ.
Moosavi, S Amin; Montakhab, Afshin
2015-11-01
Critical dynamics of cortical neurons have been intensively studied over the past decade. Neuronal avalanches provide the main experimental as well as theoretical tools to consider criticality in such systems. Experimental studies show that critical neuronal avalanches show mean-field behavior. There are structural as well as recently proposed [Phys. Rev. E 89, 052139 (2014)] dynamical mechanisms that can lead to mean-field behavior. In this work we consider a simple model of neuronal dynamics based on threshold self-organized critical models with synaptic noise. We investigate the role of high-average connectivity, random long-range connections, as well as synaptic noise in achieving mean-field behavior. We employ finite-size scaling in order to extract critical exponents with good accuracy. We conclude that relevant structural mechanisms responsible for mean-field behavior cannot be justified in realistic models of the cortex. However, strong dynamical noise, which can have realistic justifications, always leads to mean-field behavior regardless of the underlying structure. Our work provides a different (dynamical) origin than the conventionally accepted (structural) mechanisms for mean-field behavior in neuronal avalanches. PMID:26651741
NASA Astrophysics Data System (ADS)
Moosavi, S. Amin; Montakhab, Afshin
2015-11-01
Critical dynamics of cortical neurons have been intensively studied over the past decade. Neuronal avalanches provide the main experimental as well as theoretical tools to consider criticality in such systems. Experimental studies show that critical neuronal avalanches show mean-field behavior. There are structural as well as recently proposed [Phys. Rev. E 89, 052139 (2014), 10.1103/PhysRevE.89.052139] dynamical mechanisms that can lead to mean-field behavior. In this work we consider a simple model of neuronal dynamics based on threshold self-organized critical models with synaptic noise. We investigate the role of high-average connectivity, random long-range connections, as well as synaptic noise in achieving mean-field behavior. We employ finite-size scaling in order to extract critical exponents with good accuracy. We conclude that relevant structural mechanisms responsible for mean-field behavior cannot be justified in realistic models of the cortex. However, strong dynamical noise, which can have realistic justifications, always leads to mean-field behavior regardless of the underlying structure. Our work provides a different (dynamical) origin than the conventionally accepted (structural) mechanisms for mean-field behavior in neuronal avalanches.
NASA Astrophysics Data System (ADS)
Kormos, Márton; Wu, Jianda; Si, Qimiao
2014-03-01
When the transverse-field Ising chain at its quantum critical point is subjected to a small longitudinal field, the perturbed conformal field theory led to a field theory with an exotic E8 symmetry. Recent neutron scattering experiments have provided evidence for the lightest two particles in this E8 model in the quasi-1D Ising ferromagnet CoNb2O6. While the zero temperature dynamic of the model is well known, its finite-temperature counterpart has not yet been systematically studied. We study the low-frequency dynamical spin structure factor at finite temperatures using the form-factor method. We show that the dominant contribution to the spin dynamics comes from the channel between two lightest particles, and demonstrate how the spin dynamics differ from a diffusion form. Using these results, we determine the temperature dependence of the NMR relaxation rate. We suggest that, for CoNb2O6, measurements of the NMR relaxation rate provide a means to further test the applicability of the E8 model.
NASA Astrophysics Data System (ADS)
Krieg, Todd D.; Salinas, Felipe S.; Narayana, Shalini; Fox, Peter T.; Mogul, David J.
2015-08-01
Objective. Transcranial magnetic stimulation (TMS) represents a powerful technique to noninvasively modulate cortical neurophysiology in the brain. However, the relationship between the magnetic fields created by TMS coils and neuronal activation in the cortex is still not well-understood, making predictable cortical activation by TMS difficult to achieve. Our goal in this study was to investigate the relationship between induced electric fields and cortical activation measured by blood flow response. Particularly, we sought to discover the E-field characteristics that lead to cortical activation. Approach. Subject-specific finite element models (FEMs) of the head and brain were constructed for each of six subjects using magnetic resonance image scans. Positron emission tomography (PET) measured each subject’s cortical response to image-guided robotically-positioned TMS to the primary motor cortex. FEM models that employed the given coil position, orientation, and stimulus intensity in experimental applications of TMS were used to calculate the electric field (E-field) vectors within a region of interest for each subject. TMS-induced E-fields were analyzed to better understand what vector components led to regional cerebral blood flow (CBF) responses recorded by PET. Main results. This study found that decomposing the E-field into orthogonal vector components based on the cortical surface geometry (and hence, cortical neuron directions) led to significant differences between the regions of cortex that were active and nonactive. Specifically, active regions had significantly higher E-field components in the normal inward direction (i.e., parallel to pyramidal neurons in the dendrite-to-axon orientation) and in the tangential direction (i.e., parallel to interneurons) at high gradient. In contrast, nonactive regions had higher E-field vectors in the outward normal direction suggesting inhibitory responses. Significance. These results provide critical new
Critical behavior of vortices in epitaxial Tl-2201 films at zero external field
NASA Astrophysics Data System (ADS)
Chen, H. Q.; Johansson, L.-G.; Ivanov, Z. G.
2004-12-01
The resistive transition and current-voltage characteristics of a Tl-2201 superconducting microbridge are measured close to the critical temperature in zero external magnetic field. The dissipation mechanism is studied by analyzing dV/dI and power dissipation P(= IV) as functions of transport current. The Jc-T curves exhibit three distinct types of behavior depending on temperature. In the low temperature regime, the critical current density is proportional to (1 - T/Tc). At intermediate temperatures, thermally activated flux creep dominates and Jc is proportional to 1 - n(T/Tc) - m(T/Tc)2. In the high temperature regime, Jc is equal to the G-L depairing current. The depinning current, Jc1, is determined, taking into account thermally activated flux motion and flux motion induced by the transport current. Jc1 depends linearly on temperature and vanishes at 82 K, Jc1 = Jc1(0) (1 - T/Tc1).
ERIC Educational Resources Information Center
Au, Wayne
2011-01-01
"Critical Curriculum Studies" offers a novel framework for thinking about how curriculum relates to students' understanding of the world around them. Wayne Au brings together curriculum theory, critical educational studies, and feminist standpoint theory with practical examples of teaching for social justice to argue for a transformative…
[Research in two-dimensional critical phenomena and conformal field theory]. Final report
Not Available
1990-12-31
A very theoretical description is given of research in two- dimensional critical phenomena and conformal field theory. Major progress is reported in the field of fluctuating two-dimensional surfaces. A discretized representation of fluctuating geometry is used where surfaces are represented by triangulations; continuum surfaces are recovered by taking the size of the triangles to zero. One of the central goals of the theory of critical phenomena is to find all possible universality classes of n-dimensional critical phenomena; this goal has been translated into the problem of clasifying all possible scale-invariant euclidean quantum field theories. (RWR)
NASA Astrophysics Data System (ADS)
Podbielski, Jan; Heitmann, Detlef; Grundler, Dirk
2007-11-01
We have studied the spin dynamics of microscopic permalloy rings at GHz frequencies. Increasing the irradiation power, we observe first nonlinear spin dynamics and second microwave-assisted switching (MAS). We explore the MAS phase diagram as a function of microwave power and frequency f and, in particular, extract the critical microwave field hc(f). Its frequency dependence reflects characteristic eigenfrequencies from both the linear and nonlinear spin-wave spectrum. By comparing hc(f) with the different susceptibilities, we gain insight into the microscopic processes which might be the basis of a predictive theory of MAS.
Critical field measurements in superconductors using ac inductive techniques
NASA Astrophysics Data System (ADS)
Campbell, S. A.; Ketterson, J. B.; Crabtree, G. W.
1983-09-01
The ac in-phase and out-of-phase response of type II superconductors is discussed in terms of dc magnetization curves. Hysteresis in the dc magnetization is shown to lead to a dependence of the ac response on the rate at which an external field is swept. This effect allows both Hc1 and Hc2 to be measured by ac techniques. A relatively simple mutual inductance bridge for making such measurements is described in the text, and factors affecting bridge sensitivity are discussed in the Appendix. Data for the magnetic superconductor ErRh4B4 obtained using this bridge are reported.
Deviation from mean-field behavior in a low molecular weight critical polymer blend
NASA Astrophysics Data System (ADS)
Hair, D. W.; Hobbie, E. K.; Nakatani, A. I.; Han, C. C.
1992-06-01
A deviation from mean-field behavior is observed in the static susceptibility and correlation length measured with small angle neutron scattering as a function of temperature near the phase boundary of a relatively low molecular weight critical polymer mixture. The possibility of a fluctuation influenced crossover from mean-field to nonmean-field behavior is considered.
Nonmonotonic pressure evolution of the upper critical field in superconducting FeSe
NASA Astrophysics Data System (ADS)
Kaluarachchi, Udhara S.; Taufour, Valentin; Böhmer, Anna E.; Tanatar, Makariy A.; Bud'ko, Sergey L.; Kogan, Vladimir G.; Prozorov, Ruslan; Canfield, Paul C.
2016-02-01
The pressure dependence of the upper critical field, Hc 2 ,c, of single crystalline FeSe was studied using measurements of the interplane resistivity, ρc, in magnetic fields parallel to tetragonal c axis. Hc 2 ,c(T ) curves obtained under hydrostatic pressures up to 1.56 GPa, the range over which the superconducting transition temperature, Tc, of FeSe exhibits a nonmonotonic dependence with local maximum at p1≈0.8 GPa and local minimum at p2≈1.2 GPa. The slope of the upper critical field at Tc,(dHc2,c/dT)Tc , also exhibits a nonmonotonic pressure dependence with distinct changes at p1 and p2. For p
Nonmonotonic pressure evolution of the upper critical field in superconducting FeSe
Kaluarachchi, Udhara S.; Taufour, Valentin; Böhmer, Anna E.; Tanatar, Makariy A.; Bud'ko, Sergey L.; Kogan, Vladimir G.; Prozorov, Ruslan; Canfield, Paul C.
2016-02-01
The pressure dependence of the upper critical field, Hc2,c, of single crystalline FeSe was studied using measurements of the interplane resistivity, ρc, in magnetic fields parallel to tetragonal c axis. Hc2,c(T) curves obtained under hydrostatic pressures up to 1.56 GPa, the range over which the superconducting transition temperature, Tc, of FeSe exhibits a nonmonotonic dependence with local maximum at p1 ≈ 0.8 GPa and local minimum at p2 ≈ 1.2 GPa. The slope of the upper critical field at Tc,(dHc2,c/dT)Tc, also exhibits a nonmonotonic pressure dependence with distinct changes at p1 and p2. For p < p1 the slope canmore » be described within a multiband orbital model. For both p1 < p < p2 and p > p2 the slope is in good semiquantitative agreement with a single band, orbital Helfand-Werthamer theory with Fermi velocities determined from Shubnikov–de Haas measurements. Lastly, this finding indicates that Fermi surface changes are responsible for the local minimum of Tc(p) at p2 ≈ 1.2 GPa.« less
NASA Astrophysics Data System (ADS)
Moosavi, S. Amin; Montakhab, Afshin
2014-05-01
Motivated by recent experiments in neuroscience which indicate that neuronal avalanches exhibit scale invariant behavior similar to self-organized critical systems, we study the role of noisy (nonconservative) local dynamics on the critical behavior of a sandpile model which can be taken to mimic the dynamics of neuronal avalanches. We find that despite the fact that noise breaks the strict local conservation required to attain criticality, our system exhibits true criticality for a wide range of noise in various dimensions, given that conservation is respected on the average. Although the system remains critical, exhibiting finite-size scaling, the value of critical exponents change depending on the intensity of local noise. Interestingly, for a sufficiently strong noise level, the critical exponents approach and saturate at their mean-field values, consistent with empirical measurements of neuronal avalanches. This is confirmed for both two and three dimensional models. However, the addition of noise does not affect the exponents at the upper critical dimension (D =4). In addition to an extensive finite-size scaling analysis of our systems, we also employ a useful time-series analysis method to establish true criticality of noisy systems. Finally, we discuss the implications of our work in neuroscience as well as some implications for the general phenomena of criticality in nonequilibrium systems.
Teaching for Critical Literacy in Social Studies
ERIC Educational Resources Information Center
Wolk, Steven.
2003-01-01
Critical literacy is about how people see and interact with the world; it is about having, as a regular part of one's life, the skills and desire to evaluate society and the world. It is especially focused on issues of power: Who has it and who is denied it; how it is used and how it is abused. More specifically, it often revolves around issues of…
Critical Thinking and Online Supplemental Instruction: A Case Study
ERIC Educational Resources Information Center
Shaw, Cassandra S.; Holmes, Karen E.
2014-01-01
A wealth of research is available regarding supplemental instruction; however, a dearth exists regarding online supplemental instruction and critical thinking. This case study explored what was assumed to be known of critical thinking and investigated the extent to which critical thought was promoted within a university's online supplemental…
NASA Astrophysics Data System (ADS)
van der Laan, D. C.; Ekin, J. W.; Douglas, J. F.; Clickner, C. C.; Stauffer, T. C.; Goodrich, L. F.
2010-07-01
A large, magnetic-field-dependent, reversible reduction in critical current density with axial strain in Y Ba2Cu3O7-δ coated conductors at 75.9 K has been measured. This effect may have important implications for the performance of Y Ba2Cu3O7-δ coated conductors in applications where the conductor experiences large stresses in the presence of a magnetic field. Previous studies have been performed only under tensile strain and could provide only a limited understanding of the in-field strain effect. We now have constructed a device for measuring the critical current density as a function of axial compressive and tensile strain and applied magnetic field as well as magnetic field angle, in order to determine the magnitude of this effect and to create a better understanding of its origin. The reversible reduction in critical current density with strain becomes larger with increasing magnetic field at all field angles. At 76 K the critical current density is reduced by about 30% at - 0.5% strain when a magnetic field of 5 T is applied parallel to the c-axis of the conductor or 8 T is applied in the ab-plane, compared to a reduction of only 13% in self-field. Differences in the strain response of the critical current density at various magnetic field angles indicate that the pinning mechanisms in Y Ba2Cu3O7-δ coated conductors are uniquely affected by strain. Contribution of NIST, not subject to US copyright.
ERIC Educational Resources Information Center
Børhaug, Kjetil
2014-01-01
Current Norwegian curricular guidelines oblige schools to educate citizens with a critical perspective on society. From a discourse theoretical perspective, this obligation implies that various school subjects, and in particular social studies, offer discourses on social issues that allow for different points of view and critical evaluation.…
Statistics of Critical Points of Gaussian Fields on Large-Dimensional Spaces
Bray, Alan J.; Dean, David S.
2007-04-13
We calculate the average number of critical points of a Gaussian field on a high-dimensional space as a function of their energy and their index. Our results give a complete picture of the organization of critical points and are of relevance to glassy and disordered systems and landscape scenarios coming from the anthropic approach to string theory.
Critical review of studies on atmospheric dispersion in coastal regions
Shearer, D.L.; Kaleel, R.J.
1982-09-01
This study effort was required as a preliminary step prior to initiation of field measurements of atmospheric dispersion in coastal regions. The Nuclear Regulatory Commission (NRC) is in the process of planning an extensive field measurement program to generate data which will serve as improved data bases for licensing decisions, confirmation of regulations, standards, and guides, and for site characterizations. The study being reported here is an effort directed to obtaining as much information as is possible from existing studies that is relevant toward NRC's objectives. For this study, reports covering research and meteorological measurements conducted for industrial purposes, utility needs, military objectives, and academic studies were obtained and critically reviewed in light of NRC's current data needs. This report provides an interpretation of the extent of existing usable information, an indication of the potential for tailoring existing research toward current NRC information needs, and recommendations for several follow-on studies which could provide valuable additional information through reanalysis of the data. Recommendations are also offered regarding new measurement programs. Emphasis is placed on the identification and acquisition of data from atmospheric tracer studies conducted in coastal regions. A total of 225 references were identified which deal with the coastal atmosphere, including meteorological and tracer measurement programs, theoretical descriptions of the relevant processes, and dispersion models.
Electric field induced critical points and polarization rotations in relaxor ferroelectrics
NASA Astrophysics Data System (ADS)
Kutnjak, Zdravko; Blinc, Robert; Ishibashi, Y.
2007-09-01
The giant electromechanical response in ferroelectric relaxors such as Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) is of great importance for a number of ultrasonic and medical applications as well as in telecommunications. On the basis of the dielectric, heat capacity, and piezoelectric investigations on PMN-PT crystals of various PT compositions and bias fields, we have recently shown the existence of a line of critical points for the paraelectric to ferroelectric transformations in the composition-temperature-electric field (x-T-E) phase diagram. Here, we show the piezobehavior in more detail and present a theoretical evaluation of the Widom line and the critical line. This line effectively terminates a surface of first order transitions. Above this line, supercritical evolution has been observed. On approaching the critical point, both the enthalpy cost to induce the intermediate monoclinic states and thus the barrier for polarization rotations decrease significantly. The maximum of the piezoelectric response is not at E=0 , but at the critical field values. It is shown that the critical fluctuations in the proximity of the critical points are directly responsible for the observed enhancement of the electromechanical response in the PMN-PT system. In view of the large electric field dependence of the dielectric constant near the critical point, these systems may also be important as electric field tunable elements.
Magnetic relaxation and lower critical field in MgB2 wires
NASA Astrophysics Data System (ADS)
Y, Feng; G, Yan; Y, Zhao; Pradhan, A. K.; F, Liu C.; X, Zhang P.; L, Zhou
2003-09-01
Magnetic relaxation behaviour, critical current density Jc and lower critical field Hc1 have been investigated in MgB2/Ta/Cu wires. It is found that Jc and Hc1 decrease linearly with temperature in the whole temperature region below Tc. The relaxation rate is very small and has a weak temperature dependence compared to high-Tc superconductors. Also, the pinning potential is much larger and the temperature and field dependences of the pinning potential are briefly discussed.
Clusters and Fluctuations at Mean-Field Critical Points and Spinodals
Klein, W.; CNLS, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 ; Gould, Harvey; Tobochnik, J.; Alexander, F. J.; Anghel, M.; Johnson, Gregory
2000-08-07
We show that the structure of the fluctuations close to spinodals and mean-field critical points is qualitatively different from the structure close to non-mean-field critical points. This difference has important implications for many areas including the formation of glasses in supercooled liquids. In particular, the divergence of the measured static structure function in near-mean-field systems close to the glass transition is suppressed relative to the mean-field prediction in systems for which a spatial symmetry is broken. (c) 2000 The American Physical Society.
High-field magnets using high-critical-temperature superconducting thin films
Mitlitsky, F.; Hoard, R.W.
1994-05-10
High-field magnets fabricated from high-critical-temperature superconducting ceramic (HTSC) thin films which can generate fields greater than 4 Tesla are disclosed. The high-field magnets are made of stackable disk-shaped substrates coated with HTSC thin films, and involves maximizing the critical current density, superconducting film thickness, number of superconducting layers per substrate, substrate diameter, and number of substrates while minimizing substrate thickness. The HTSC thin films are deposited on one or both sides of the substrates in a spiral configuration with variable line widths to increase the field. 4 figures.
High-field magnets using high-critical-temperature superconducting thin films
Mitlitsky, Fred; Hoard, Ronald W.
1994-01-01
High-field magnets fabricated from high-critical-temperature superconducting ceramic (HTSC) thin films which can generate fields greater than 4 Tesla. The high-field magnets are made of stackable disk-shaped substrates coated with HTSC thin films, and involves maximizing the critical current density, superconducting film thickness, number of superconducting layers per substrate, substrate diameter, and number of substrates while minimizing substrate thickness. The HTSC thin films are deposited on one or both sides of the substrates in a spiral configuration with variable line widths to increase the field.
Quantum oscillations and upper critical magnetic field of the iron-based superconductor FeSe
NASA Astrophysics Data System (ADS)
Audouard, Alain; Duc, Fabienne; Drigo, Loïc; Toulemonde, Pierre; Karlsson, Sandra; Strobel, Pierre; Sulpice, André
2015-01-01
Shubnikov-de Haas (SdH) oscillations and upper critical magnetic field (Hc2) of the iron-based superconductor FeSe (Tc = 8.6 \\text{K}) have been studied by tunnel diode oscillator-based measurements in magnetic fields of up to 55 T and temperatures down to 1.6 K. Several Fourier components enter the SdH oscillations spectrum with frequencies definitely smaller than predicted by band structure calculations indicating band renormalization and reconstruction of the Fermi surface at low temperature, in line with previous ARPES data. The Werthamer-Helfand-Hohenberg model accounts for the temperature dependence of (Hc2) for magnetic field applied both parallel (\\textbf{H} \\| ab) and perpendicular (\\textbf{H} \\| c) to the iron conducting plane, suggesting that one band mainly controls the superconducting properties in magnetic fields despite the multiband nature of the Fermi surface. Whereas Pauli pair breaking is negligible for \\textbf{H} \\| c , a Pauli paramagnetic contribution is evidenced for \\textbf{H} \\| ab with Maki parameter α = 2.1 , corresponding to Pauli field HP = 36.5 \\text{T} .
Flux flow resistivity and upper critical field in ideal type II amorphous superconductors
NASA Astrophysics Data System (ADS)
Poon, S. J.; Wong, K. M.
1984-01-01
Flux flow resistivity ρ f and upper critical field H c2 of ideal type II amorphous bulk supercbnductors Zr3Ni and Zr3Rh on both as-quenched and thermally relaxed states have been studied. It is found that thermal annealing does not change the temperature dependence of H c2 in homogeneous superconductors. The temperature and field dependence of ρ f in all samples studied exhibits a universal scaling relation of the form ρ f /ρ n =f(h, t), where ρ n is the normal state resistivity, and h and t are the reduced field and reduced temperature, respectively. The results are compared with predictions of the time-dependent microscopic theories for bulk superconductors in the dirty limit. In the low-field region ( H≪H c2 ) the viscosity coefficient contains both the ordinary (Bardeen-Stephen, Tinkham) and anomalous (Gor'kov-Kopnin) terms. For H⋍H c2 the results agree qualitatively with the theory of Imai with pair-breaking in the anomalous term. Implications of the present results are discussed.
Pressure-dependent upper critical field of FeSe superconductor
NASA Astrophysics Data System (ADS)
Kaluarachchi, Udhara; Taufour, Valentin; Böhmer, Anna; Tanatar, Makariy; Bud'Ko, Sergey; Kogan, Vladimir; Prozorov, Ruslan; Canfield, Paul
In FeSe, the superconducting transition temperature Tc (~ 9 K at ambient pressure) has a complicated pressure dependence with a local maximum near p1 ~ 0.8 GPa and a local minimum at p2 ~ 1.2GPa. In this work, we study the upper critical field, Hc 2 , c (T) , of FeSe using c-axis resistivity measurements under hydrostatic pressure up to 1.56 GPa with the magnetic field H ∥c. Application of both current and magnetic field along the same axis reduces the flux flow motion and give sharper transition in applied fields. We observe a non-monotonic evolution of the slope of Hc 2 , c (T) |Tc with pressure, with changes around p1 and p2. We employ two-band orbital Hc 2 , c calculation to show that the data can be explained using the Fermi velocities extracted from the recent quantum oscillations study [ 1 ] over the whole pressure range. [ 1 ] Terashima et al. arXiv:1510.01840v1 [cond-mat.supr-con] (2015) This work is supported by the US DOE, Basic Energy Sciences under Contract No. DE-AC02-07CH11358.
Magnetic Field Dependence of the Critical Current in S-N Bilayer Thin Films
NASA Technical Reports Server (NTRS)
Sadleir, John E.; Lee, Sang-Jun; Smith, Stephen James; Bandler, Simon; Chervenak, James; Kilbourne, Caroline A.; Finkbeiner, Fred M.; Porter, Frederick S.; Kelley, Richard L.; Adams, Joseph S.; Eckart, Megan E.; Busch, Sarah; Porst, Jan-Patrick
2013-01-01
Here we investigate the effects a non-uniform applied magnetic field has on superconducting transition-edge sensors (TESs) critical current. This has implications on TES optimization. It has been shown that TESs resistive transition can be altered by magnetic fields. We have observed critical current rectification effects and explained these effects in terms of a magnetic self-field arising from asymmetric current injection into the sensor. Our TES physical model shows that this magnetic self-field can result in significantly degraded or improved TES performance. In order for this magnetically tuned TES strategy to reach its full potential we are investigating the effect a non-uniform applied magnetic field has on the critical current.
Critical Race Theory and Social Studies: Centering the Native American Experience
ERIC Educational Resources Information Center
Chandler, Prentice T.
2010-01-01
This article looks at the ways in which the topic of race is treated in social studies classrooms and the conceptual application of the field of critical race theory (CRT) to the teaching of American history. The author discusses the field of the social studies in terms of its stated goals and how these goals are not met because of a lack of…
Critical Thinking in Adult Education: An Elusive Quest for a Definition of the Field.
ERIC Educational Resources Information Center
Vaske, Joann M.
A study attempted to derive the meaning of critical thinking in adult education through exploration of graduate faculty members' perceptions and perceived practices of critical thinking in adult education. Grounded theory methodology was used to explain the meaning of critical thinking to adult educators. The primary data sources were unstructured…
Eremeev, Grigory; Palczewski, Ari
2013-09-01
At SRF 2011 we presented the study of quenches in high gradient SRF cavities with dual mode excitation technique. The data differed from measurements done in 80's that indicated thermal breakdown nature of quenches in SRF cavities. In this contribution we present analysis of the data that indicates that our recent data for high gradient quenches is consistent with the magnetic breakdown on the defects with thermally suppressed critical field. From the parametric fits derived within the model we estimate the critical breakdown fields.
Quantum criticality and confinement effects in an Ising chain in transverse field
NASA Astrophysics Data System (ADS)
Coldea, Radu
2011-03-01
The Ising chain in transverse field is one of the key paradigms for the theory of continuous zero-temperature quantum phase transitions. We have recently realized this system experimentally by applying strong magnetic fields to the quasi- 1D, low-exchange Ising ferromagnet CoNb2O6 to drive it to its quantum critical point where the spontaneous long-range magnetic order is suppressed by magnetic field. Using high-resolution single-crystal neutron scattering we have probed how the spin dynamics evolves with the applied field and have observed a dramatic change in the character of spin excitations at the quantum critical point, from pairs of domain-wall (kink) quasiparticles in the magnetically-ordered phase, to sharp spin- flip quasiparticles in the paramagnetic phase. The weak, but finite couplings between the chains significantly enrich the physics by stabilizing a complex structure of two-kink bound states due to mean-field confinement effects. In zero field the rich spectrum of bound states can be quantitatitively understood following McCoy and Wu's analytic theory of weak confinement. Just below the critical field the energies of the two lowest bound states approach the ``golden ratio'' as predicted by Zamolodchikov's E8 scaling limit solution of the off-critical Ising model in a weak longitudinal field.
Relativistic electron distribution function of a plasma in a near-critical electric field
Sandquist, P.; Sharapov, S. E.; Helander, P.; Lisak, M.
2006-07-15
A corrected relativistic collision operator is used to derive a Fokker-Planck equation for the distribution function of relativistic suprathermal electrons in a weakly relativistic plasma, which is then solved by a procedure similar to that employed in Connor and Hastie [Nucl. Fusion 15, 415 (1975)]. Analytical expressions are derived for the electron distribution function in plasmas with the electric field close to critical, which is typical of plasmas with grassy sawteeth on the Joint European Torus. A numerical solution is used for determining the normalization constant, which matches the relativistic region onto the weakly relativistic region. It is found that the scaling of the runaway rate with the electric field obtained by Connor and Hastie is a good approximation in spite of their use of an incomplete form of the collision operator not conserving number of particles. The present analysis determines the proportionality constant and introduces corrections to the earlier scaling of the runaway rate with respect to the electric field. The results obtained for the electron distribution function constitute a basis for studies of experimentally observed phenomena in near-threshold electric field plasmas with a significant suprathermal electron population.
NASA Astrophysics Data System (ADS)
Ben Shalom, M.; Zhu, M. J.; Fal’Ko, V. I.; Mishchenko, A.; Kretinin, A. V.; Novoselov, K. S.; Woods, C. R.; Watanabe, K.; Taniguchi, T.; Geim, A. K.; Prance, J. R.
2016-04-01
Graphene-based Josephson junctions provide a novel platform for studying the proximity effect due to graphene’s unique electronic spectrum and the possibility to tune junction properties by gate voltage. Here we describe graphene junctions with a mean free path of several micrometres, low contact resistance and large supercurrents. Such devices exhibit pronounced Fabry-Pérot oscillations not only in the normal-state resistance but also in the critical current. The proximity effect is mostly suppressed in magnetic fields below 10 mT, showing the conventional Fraunhofer pattern. Unexpectedly, some proximity survives even in fields higher than 1 T. Superconducting states randomly appear and disappear as a function of field and carrier concentration, and each of them exhibits a supercurrent carrying capacity close to the universal quantum limit. We attribute the high-field Josephson effect to mesoscopic Andreev states that persist near graphene edges. Our work reveals new proximity regimes that can be controlled by quantum confinement and cyclotron motion.
NASA Technical Reports Server (NTRS)
Bonavito, N. L.; Nagai, O.; Tanaka, T.
1975-01-01
Previous spin wave theories of the antiferromagnet hematite were extended. The behavior of thermodynamic quantities around the Morin transition temperature was studied, and the latent heat of the Morin transition was calculated. The temperature dependence of the antiferromagnetic resonance frequency and the parallel and perpendicular critical spin-flop magnetic fields were calculated. It was found that the theory agrees well with experiment.
The effect of self field on the critical current determination of multifilamentary superconductors
Garber, M.; Ghosh, A.K.; Sampson, W.B.
1988-01-01
In determining the short sample critical current of conductors of large cross section or high current density the self field produced by the transport current must be taken account in order to obtain a ''true value'' for the critical current. A simple model calculation for determining this effect is described. Measurements on wires, cables, and monoliths show the validity and self consistency of the procedures. 9 refs., 13 figs., 1 tab.
Low-field critical current density in porous MgB2 powders
NASA Astrophysics Data System (ADS)
Agassi, Y. D.
2013-09-01
Porous MgB2 powders are comprised of an ensemble of irregularly shaped constituents. In this work we introduce a model for the critical current density in such powders in the presence of a low external field H (H < 4 T) and in the high-porosity limit, where effects of vortex-lattice elasticity can be neglected and vortex pinning takes place within the powder-constituents. The ensuing critical current-density expression is a product of three decoupled factors: The first sets the scale for the critical current-density magnitude, while the second and third factors contain the field and powder-constituent size-parameters dependencies, respectively. The field dependent factor is of the form H-n and 0.5⩽n⩽1.0, where the limiting exponents n = 0.5 and n = 1.0 correspond to vortex configurations within a powder-constituent of a linear array and a two-dimensional lattice, respectively. For the calculations, we assume for the powder constituent shape a cylinder of arbitrary height and radius, where an external field and a single pinned vortex are aligned in parallel to the cylinder’s axis. The exact fields of this configuration are derived. The size-parameters dependence implies enhanced critical current density for a cigar-like shape powder-constituent aligned with the field, and of radius smaller than about three times the penetration depth. These conclusions are consistent with pertaining data.
Critical current density and current distribution in field cooled superconducting disks
NASA Astrophysics Data System (ADS)
Bernstein, Pierre; Noudem, Jacques; Dupont, Louis
2016-07-01
Applications of bulk superconductors concern superconducting motors and generators, the levitation of vehicles, the generation of high magnetic fields with small size cryo-magnets, the shielding of magnetic fields and other applications. For all of them, it is essential to determine the critical current density, and to understand the effect of the shape and size of the bulks on the properties of interest. In this contribution, we show how the combination of levitation force and trapped field measurements allow one to determine the characteristics and the potential performances of superconducting disks using analytical modeling. As examples of applications we detail the effects of the magnetizing field and of the bulk sheet critical current density on the levitation force. An important result of the reported measurements is that in field-cooled samples, the shielding currents possibly do not flow along the whole thickness of the disks.
Field-induced magnetization jumps and quantum criticality in the 2D J-Q model
NASA Astrophysics Data System (ADS)
Iaizzi, Adam; Sandvik, Anders
The J-Q model is a `designer hamiltonian' formed by adding a four spin `Q' term to the standard antiferromagnetic S = 1 / 2 Heisenberg model. The Q term drives a quantum phase transition to a valence-bond solid (VBS) state: a non-magnetic state with a pattern of local singlets which breaks lattice symmetries. The elementary excitations of the VBS are triplons, i.e. gapped S=1 quasiparticles. There is considerable interest in the quantum phase transition between the Néel and VBS states as an example of deconfined quantum criticality. Near the phase boundary, triplons deconfine into pairs of bosonic spin-1/2 excitations known as spinons. Using exact diagonalization and the stochastic series expansion quantum monte carlo method, we study the 2D J-Q model in the presence of an external magnetic field. We use the field to force a nonzero density of magnetic excitations at T=0 and look for signatures of Bose-Einstein condensation of spinons. At higher magnetic fields, there is a jump in the induced magnetization caused by the onset of an effective attractive interaction between magnons on a ferromagnetic background. We characterize the first order quantum phase transition and determine the minimum value of the coupling ratio q ≡ Q / J required to produce this jump. Funded by NSF DMR-1410126.
Critical behavior in a massless scalar field collapse with self-interaction potential
NASA Astrophysics Data System (ADS)
Zhang, Xuefeng; Lü, H.
2015-02-01
We examine a one-parameter family of analytical solutions representing spherically symmetric collapse of a nonlinear massless scalar field with self-interaction in an asymptotically flat spacetime. The time evolution exhibits a type of critical behavior. Depending on the scalar charge parameter q as compared to a critical value q*, the incoming scalar wave collapses either to a globally naked central singularity if q field) or to a scalar-hairy black hole if q >q* (strong field), both having finite asymptotic masses. Near the critical evolution, the black hole mass follows a product-logarithmic scaling law: -M2ln M ˜q -q* with 0
Sogo, T.; Roepke, G.; Lazauskas, R.
2009-05-15
{alpha}-particle (quartet) condensation in homogeneous spin-isospin symmetric nuclear matter is investigated. The usual Thouless criterion for the critical temperature is extended to the quartet case. The in-medium four-body problem is strongly simplified by the use of a momentum-projected mean-field ansatz for the quartet. The self-consistent single-particle wave functions are shown and discussed for various values of the density at the critical temperature. Excellent agreement of the critical temperature with a numerical solution of the Faddeev-Yakubovsky equation is obtained.
Secularism, Criticism, and Religious Studies Pedagogy
ERIC Educational Resources Information Center
Britt, Brian
2006-01-01
Secularization, the idea that religion would gradually diminish over time, was once widely assumed to be true by scholars of religion, but the unexpected resurgence of religious traditions has called it into question. Related debates on the distinction between religion and the secular have destabilized religious studies further. What does the…
Critical Appraisal of Mixed Methods Studies
ERIC Educational Resources Information Center
Heyvaert, Mieke; Hannes, Karin; Maes, Bea; Onghena, Patrick
2013-01-01
In several subdomains of the social, behavioral, health, and human sciences, research questions are increasingly answered through mixed methods studies, combining qualitative and quantitative evidence and research elements. Accordingly, the importance of including those primary mixed methods research articles in systematic reviews grows. It is…
Promoting Critical Thinking through an Interdisciplinary Study Abroad Program
ERIC Educational Resources Information Center
Cai, WeiWei; Sankaran, Gopal
2015-01-01
This paper discusses the promotion of critical thinking through an interdisciplinary curriculum design using multidisciplinary faculty as well as details the implementation of an experiential short-term study abroad program in China. To achieve this educational goal of critical thinking, along with meeting the requirements specific to each course,…
Self-Magnetic Field Effects on Electron Emission as the Critical Current is Approached
Ottinger, P. F.; Cooperstein, G.; Schumer, J. W.; Swanekamp, S. B.
2001-09-28
The self-magnetic field associated with the current in a planar diode is shown to reduce electron emission below the Child-Langmuir current density. As the magnetic field increases, the diode current is limited to the critical current. Here, a ID analysis is carried out to calculate the suppressed current density in the presence of a transverse magnetic field. The problem is shown to be similar to that of the limiting current (i.e., Hull current) calculated in a crossed field gap, in which a constant transverse magnetic field is applied across the gap to insulate the electron flow. In the case considered here, the magnetic field is produced by the diode current itself and this self-magnetic field decreases with distance along the gap. It is shown that the emitted current density is only modestly reduced from the Child-Langmuir current density. The 1-D analysis remains valid until critical current is approached, at which point orbit crossing occurs and a 2-D kinetic analysis is required. The minimum diode length required to reach critical current is also derived.
(Studies in quantum field theory)
Not Available
1990-01-01
During the period 4/1/89--3/31/90 the theoretical physics group supported by Department of Energy Contract No. AC02-78ER04915.A015 and consisting of Professors Bender and Shrauner, Associate Professor Papanicolaou, Assistant Professor Ogilvie, and Senior Research Associate Visser has made progress in many areas of theoretical and mathematical physics. Professors Bender and Shrauner, Associate Professor Papanicolaou, Assistant Professor Ogilvie, and Research Associate Visser are currently conducting research in many areas of high energy theoretical and mathematical physics. These areas include: strong-coupling approximation; classical solutions of non-Abelian gauge theories; mean-field approximation in quantum field theory; path integral and coherent state representations in quantum field theory; lattice gauge calculations; the nature of perturbation theory in large order; quark condensation in QCD; chiral symmetry breaking; the 1/N expansion in quantum field theory; effective potential and action in quantum field theories, including OCD; studies of the early universe and inflation, and quantum gravity.
Study of critical ricochet angle for conical nose shape projectiles
NASA Astrophysics Data System (ADS)
Murali, Vijayalakshmi; Law, Manish G.; Naik, Smita D.
2012-09-01
The purpose of this research is to formulate a generic analytical model to assess the phenomena of water ricochet for a conical nose shaped projectile. A theoretical model is analyzed to study the critical angle of conical nose shaped projectile entering in water and is extended for different mediums as normal sand and mercury. Numerical Simulation has been carried out to find the effect of tip angle of the conical nose shaped projectile on the critical angle. Critical angle is defined as that angle of impact of the projectile above which ricochet will occur. This angle is obtained by balancing the momentums acting on the projectile at the time of impact on the basis of Newtonian theory. Major factors affecting critical angle are impact velocity, impact angle, density of the projectile and the target. An attempt has been made to study the effect of longitudinal spin of the projectile on the critical angle.
ERIC Educational Resources Information Center
Subedi, Binaya
2008-01-01
There is limited research in the field of social studies that documents how immigrant teachers are working to make social studies classrooms a space for critical dialogue, especially within settings where immigrant and nonimmigrant students interact. By using data from a yearlong qualitative study in which interviews and observations were…
Benchmark field study of deep neutron penetration
NASA Astrophysics Data System (ADS)
Morgan, J. F.; Sale, K.; Gold, R.; Roberts, J. H.; Preston, C. C.
1991-06-01
A unique benchmark neutron field has been established at the Lawrence Livermore National Laboratory (LLNL) to study deep penetration neutron transport. At LLNL, a tandem accelerator is used to generate a monoenergetic neutron source that permits investigation of deep neutron penetration under conditions that are virtually ideal to model, namely the transport of mono-energetic neutrons through a single material in a simple geometry. General features of the Lawrence Tandem (LATAN) benchmark field are described with emphasis on neutron source characteristics and room return background. The single material chosen for the first benchmark, LATAN-1, is a steel representative of Light Water Reactor (LWR) Pressure Vessels (PV). Also included is a brief description of the Little Boy replica, a critical reactor assembly designed to mimic the radiation doses from the atomic bomb dropped on Hiroshima, and its us in neutron spectrometry.
Benchmark field study of deep neutron penetration
Morgan, J.F.; Sale, K. ); Gold, R.; Roberts, J.H.; Preston, C.C. )
1991-06-10
A unique benchmark neutron field has been established at the Lawrence Livermore National Laboratory (LLNL) to study deep penetration neutron transport. At LLNL, a tandem accelerator is used to generate a monoenergetic neutron source that permits investigation of deep neutron penetration under conditions that are virtually ideal to model, namely the transport of mono-energetic neutrons through a single material in a simple geometry. General features of the Lawrence Tandem (LATAN) benchmark field are described with emphasis on neutron source characteristics and room return background. The single material chosen for the first benchmark, LATAN-1, is a steel representative of Light Water Reactor (LWR) Pressure Vessels (PV). Also included is a brief description of the Little Boy replica, a critical reactor assembly designed to mimic the radiation doses from the atomic bomb dropped on Hiroshima, and its us in neutron spectrometry. 18 refs.
Lower critical field measurements in NbN bulk and thin films.
NASA Technical Reports Server (NTRS)
Mathur, M. P.; Deis, D. W.; Gavaler, J. R.
1972-01-01
Low-field magnetization measurements were made at 4.2 K on thin-film and bulk NbN samples by using a vibrating-sample Foner magnetometer with a 50-kG superconducting solenoid. Values of the lower and upper critical fields are calculated, using magnetization curves as the basis. The significance of the Pauli spin paramagnetism and spin-orbit scattering in these materials is discussed.
Stochastic geometry of critical curves, Schramm Loewner evolutions and conformal field theory
NASA Astrophysics Data System (ADS)
Gruzberg, Ilya A.
2006-10-01
Conformally invariant curves that appear at critical points in two-dimensional statistical mechanics systems and their fractal geometry have received a lot of attention in recent years. On the one hand, Schramm (2000 Israel J. Math. 118 221 (Preprint math.PR/9904022)) has invented a new rigorous as well as practical calculational approach to critical curves, based on a beautiful unification of conformal maps and stochastic processes, and by now known as Schramm-Loewner evolution (SLE). On the other hand, Duplantier (2000 Phys. Rev. Lett. 84 1363; Fractal Geometry and Applications: A Jubilee of Benot Mandelbrot: Part 2 (Proc. Symp. Pure Math. vol 72) (Providence, RI: American Mathematical Society) p 365 (Preprint math-ph/0303034)) has applied boundary quantum gravity methods to calculate exact multifractal exponents associated with critical curves. In the first part of this paper, I provide a pedagogical introduction to SLE. I present mathematical facts from the theory of conformal maps and stochastic processes related to SLE. Then I review basic properties of SLE and provide practical derivation of various interesting quantities related to critical curves, including fractal dimensions and crossing probabilities. The second part of the paper is devoted to a way of describing critical curves using boundary conformal field theory (CFT) in the so-called Coulomb gas formalism. This description provides an alternative (to quantum gravity) way of obtaining the multifractal spectrum of critical curves using only traditional methods of CFT based on free bosonic fields.
Universal self-field critical current for thin-film superconductors
Talantsev, E. F.; Tallon, J. L.
2015-01-01
For any practical superconductor the magnitude of the critical current density, Jc, is crucially important. It sets the upper limit for current in the conductor. Usually Jc falls rapidly with increasing external magnetic field, but even in zero external field the current flowing in the conductor generates a self-field that limits Jc. Here we show for thin films of thickness less than the London penetration depth, λ, this limiting Jc adopts a universal value for all superconductors—metals, oxides, cuprates, pnictides, borocarbides and heavy Fermions. For type-I superconductors, it is Hc/λ where Hc is the thermodynamic critical field. But surprisingly for type-II superconductors, we find the self-field Jc is Hc1/λ where Hc1 is the lower critical field. Jc is thus fundamentally determined and this provides a simple means to extract absolute values of λ(T) and, from its temperature dependence, the symmetry and magnitude of the superconducting gap. PMID:26240014
Critical Teaching in Higher Education: An Interview with the Front Range Critical Studies Group.
ERIC Educational Resources Information Center
McLaren, Peter
1996-01-01
The Front Range Critical Studies Group, comprised of four California State University teacher educators, aims to provide a scholarly, informal forum for interdisciplinary discussion of theoretical, political, and cultural issues. The group facilitates collegial scholar/student relationships, promotes enlightened discussion through lecture series…
Pressure dependence of upper critical fields in FeSe single crystals
NASA Astrophysics Data System (ADS)
Kang, Ji-Hoon; Jung, Soon-Gil; Lee, Sangyun; Park, Eunsung; Lin, Jiunn-Yuan; Chareev, Dmitriy A.; Vasiliev, Alexander N.; Park, Tuson
2016-03-01
We investigate the pressure dependence of the upper critical fields (μ 0 H c2) for FeSe single crystals with pressure up to 2.57 GPa. The superconducting (SC) properties show a disparate behavior across a critical pressure where the pressure-induced antiferromagnetic phase coexists with superconductivity. The magnetoresistance for H//ab and H//c is very different: for H//c, magnetic field induces and enhances a hump in the resistivity close to the T c for pressures higher than 1.2 GPa, while it is absent for H//ab. Since the measured μ 0 H c2 for FeSe samples is smaller than the orbital limited upper critical field ({{{H}}{{orb}}}{{c}2}) estimated by the Werthamer, Helfand and Hohenberg model, the Maki parameter (α) related to Pauli spin-paramagnetic effects is additionally considered to describe the temperature dependence of μ 0 H c2(T). Interestingly, the α value is hardly affected by pressure for H//ab, while it strongly increases with pressure for H//c. The pressure evolution of the μ 0 H c2(0) for the FeSe single crystals is found to be almost similar to that of T c(P), suggesting that the pressure-induced magnetic order adversely affects the upper critical fields as well as the SC transition temperature.
Magnetic Field Dependence of the Critical Current of Planar Geometry Josephson Junctions
NASA Astrophysics Data System (ADS)
Ma, Meng; Cho, Ethan; Huynh, Chuong; Cybart, Shane; Dynes, Robert
2015-03-01
We report a study on the magnetic field dependence of the critical current of planar geometry Josephson junctions. We have fabricated Josephson junctions by using a focused helium ion beam to irradiate a narrow barrier in the plane of a 25 nm thick Y-Ba-Cu-O film. The London penetration depth λL is large (~1 μm) because of the ultra-thin thickness of the film. As a result, calculations of the Josephson penetration depth λJ are not realistic nor physical. Therefore in this work, we measure λJ experimentally. We tested devices with bridge widths ranging from 4 to 50 μm, and present measurements of the Fraunhofer quantum diffraction pattern (IC (B)). We observe a crossover from short to long junction behavior, which gives an experimentally measured λJ that ranges between 3 μm to 5 μm. The shape of the IC (B) pattern is strongly affected by the width of the bridge because of self-field effects. As the bridge width increases, Josephson vortices enter the junction and skew the patterns. This work shows that the electronic properties of the planar junctions are very different than those classical ``sandwich'' junctions due to the differences in geometry.
Electromagnetic waves destabilized by runaway electrons in near-critical electric fields
Komar, A.; Pokol, G. I.; Fueloep, T.
2013-01-15
Runaway electron distributions are strongly anisotropic in velocity space. This anisotropy is a source of free energy that may destabilize electromagnetic waves through a resonant interaction between the waves and the energetic electrons. In this work, we investigate the high-frequency electromagnetic waves that are destabilized by runaway electron beams when the electric field is close to the critical field for runaway acceleration. Using a runaway electron distribution appropriate for the near-critical case, we calculate the linear instability growth rate of these waves and conclude that the obliquely propagating whistler waves are most unstable. We show that the frequencies, wave numbers, and propagation angles of the most unstable waves depend strongly on the magnetic field. Taking into account collisional and convective damping of the waves, we determine the number density of runaways that is required to destabilize the waves and show its parametric dependences.
Criticality features in ULF magnetic fields prior to the 2011 Tohoku earthquake.
Hayakawa, Masashi; Schekotov, Alexander; Potirakis, Stelios; Eftaxias, Kostas
2015-01-01
The criticality of ULF (Ultra-low-frequency) magnetic variations is investigated for the 2011 March 11 Tohoku earthquake (EQ) by natural time analysis. For this attempt, some ULF parameters were considered: (1) Fh (horizontal magnetic field), (2) Fz (vertical magnetic field), and (3) Dh (inverse of horizontal magnetic field). The first two parameters refer to the ULF radiation, while the last parameter refers to another ULF effect of ionospheric signature. Nighttime (L.T. = 3 am ± 2 hours) data at Kakioka (KAK) were used, and the power of each quantity at a particular frequency band of 0.03-0.05 Hz was averaged for nighttime hours. The analysis results indicate that Fh fulfilled all criticality conditions on March 3-5, 2011, and that the additional parameter, Dh reached also a criticality on March 6 or 7. In conclusion, criticality has reached in the pre-EQ fracture region a few days to one week before the main shock of the Tohoku EQ. PMID:25743063
Criticality features in ULF magnetic fields prior to the 2011 Tohoku earthquake
NASA Astrophysics Data System (ADS)
Hayakawa, Masashi; Schekotov, Alexander; Potirakis, Stelios; Eftaxias, Kostas
2015-01-01
The criticality of ULF (Ultra-low-frequency) magnetic variations is investigated for the 2011 March 11 Tohoku earthquake (EQ) by natural time analysis. For this attempt, some ULF parameters were considered: (1) Fh (horizontal magnetic field), (2) Fz (vertical magnetic field), and (3) Dh (inverse of horizontal magnetic field). The first two parameters refer to the ULF radiation, while the last parameter refers to another ULF effect of ionospheric signature. Nighttime (L.T. = 3 am ± 2 hours) data at Kakioka (KAK) were used, and the power of each quantity at a particular frequency band of 0.03-0.05 Hz was averaged for nighttime hours. The analysis results indicate that Fh fulfilled all criticality conditions on March 3-5, 2011, and that the additional parameter, Dh reached also a criticality on March 6 or 7. In conclusion, criticality has reached in the pre-EQ fracture region a few days to one week before the main shock of the Tohoku EQ.
Criticality features in ULF magnetic fields prior to the 2011 Tohoku earthquake
HAYAKAWA, Masashi; SCHEKOTOV, Alexander; POTIRAKIS, Stelios; EFTAXIAS, Kostas
2015-01-01
The criticality of ULF (Ultra-low-frequency) magnetic variations is investigated for the 2011 March 11 Tohoku earthquake (EQ) by natural time analysis. For this attempt, some ULF parameters were considered: (1) Fh (horizontal magnetic field), (2) Fz (vertical magnetic field), and (3) Dh (inverse of horizontal magnetic field). The first two parameters refer to the ULF radiation, while the last parameter refers to another ULF effect of ionospheric signature. Nighttime (L.T. = 3 am ± 2 hours) data at Kakioka (KAK) were used, and the power of each quantity at a particular frequency band of 0.03–0.05 Hz was averaged for nighttime hours. The analysis results indicate that Fh fulfilled all criticality conditions on March 3–5, 2011, and that the additional parameter, Dh reached also a criticality on March 6 or 7. In conclusion, criticality has reached in the pre-EQ fracture region a few days to one week before the main shock of the Tohoku EQ. PMID:25743063
NASA Astrophysics Data System (ADS)
Xue, Cun; He, An; Yong, Huadong; Zhou, Youhe
2013-12-01
We present an exact analytical approach for arbitrary field-dependent critical state of high-Tc superconducting strip with transport current. The sheet current and flux-density profiles are derived by solving the integral equations, which agree with experiments quite well. For small transport current, the approximate explicit expressions of sheet current, flux-density and penetration depth for the Kim model are derived based on the mean value theorem for integration. We also extend the results to the field-dependent critical state of superconducting strip in the simultaneous presence of applied field and transport current. The sheet current distributions calculated by the Kim model agree with experiments better than that by the Bean model. Moreover, the lines in the Ia-Ba plane for the Kim model are not monotonic, which is quite different from that the Bean model. The results reveal that the maximum transport current in thin superconducting strip will decrease with increasing applied field which vanishes for the Bean model. The results of this paper are useful to calculate ac susceptibility and ac loss.
Xue, Cun; He, An; Yong, Huadong; Zhou, Youhe
2013-12-15
We present an exact analytical approach for arbitrary field-dependent critical state of high-T{sub c} superconducting strip with transport current. The sheet current and flux-density profiles are derived by solving the integral equations, which agree with experiments quite well. For small transport current, the approximate explicit expressions of sheet current, flux-density and penetration depth for the Kim model are derived based on the mean value theorem for integration. We also extend the results to the field-dependent critical state of superconducting strip in the simultaneous presence of applied field and transport current. The sheet current distributions calculated by the Kim model agree with experiments better than that by the Bean model. Moreover, the lines in the I{sub a}-B{sub a} plane for the Kim model are not monotonic, which is quite different from that the Bean model. The results reveal that the maximum transport current in thin superconducting strip will decrease with increasing applied field which vanishes for the Bean model. The results of this paper are useful to calculate ac susceptibility and ac loss.
Poverty in Latin America: A Critical Analysis of Three Studies.
ERIC Educational Resources Information Center
Boltvinik, Julio
1996-01-01
Critically evaluates the methodologies used in three recent studies on poverty in Latin America. Maintains that some studies measure the relative nature of nutritional poverty while others record the absolute nature of nutritional poverty (physical survival). Includes a comparative analysis of the studies' results. (MJP)
[Introduction to critical reading of articles: study design and biases].
García Villar, C
2015-01-01
The critical evaluation of an article enables professionals to make good use of the new information and therefore has direct repercussions for the benefit of our patients. Before undertaking a detailed critical reading of the chosen article, we need to consider whether the study used the most appropriate design for the question it aimed to answer (i.e., whether the level of evidence is adequate). To do this, we need to know how to classify studies in function of their design (descriptive or analytical; prospective or retrospective; cross-sectional or longitudinal) as well as their correlation with the levels of evidence. In critical reading it is also important to know the main systematic errors or biases that can affect a study. Biases can appear in any phase of a study; they can affect the sample, the development of the study, or the measurement of the results. PMID:25458123
Chaboyer, W; Najman, J; Dunn, S
2001-04-01
This study sought to identify the relationship between three predictor variables, perceived collaboration with medical staff, autonomy and independent actions and an outcome, the value hospital nurses placed on their work. In total 189 critical care and 366 non-critical care nurses completed a mailed survey. Critical care nurses perceived themselves to have a more collaborative relationship with the medical staff, described performing actions independent of medical orders more frequently and perceived their jobs to have more value than non-critical care nurses. However the latter group perceived themselves to have more autonomy in their work. Within both groups collaboration and autonomy were significantly, but weak to moderately correlated with job valuation. Simply expanding the work hospital nurses do is unlikely to result in nurses valuing their jobs more, however promoting an environment of respect and sharing between the medical and nursing staff and supporting nurses when they act in an autonomous fashion may positively influence nurses' perceptions of their work. PMID:11223056
Study of HTS Insert Coils for High Field Solenoids
Lombardo, Vito; /Fermilab
2009-09-01
Fermilab is currently working on the development of high field magnet systems for ionization cooling of muon beams. The use of high temperature superconducting materials (HTS) is being considered for these solenoids using Helium refrigeration. Several studies have been performed on insert coils made of BSCCO-2223 tapes and second generation (2G) YBCO coated conductors, which are tested at various temperatures and at external fields of up to 14 T. Critical current (I{sub c}) measurements of YBCO short samples are presented as a function of bending stress, magnetic field and field orientation with respect to the sample surface. An analytical fit of critical current data as a function of field and field orientation is also presented. Results from several single-layer and double-layer pancake coils are also discussed.
Low field critical current density of titanium sheathed magnesium diboride wires
NASA Astrophysics Data System (ADS)
Rostila, L.; Grasso, G.; Demenčík, E.; Tumino, A.; Brisigotti, S.; Kováč, P.
2010-06-01
Magnesium diboride (MgB2) is replacing some of the conventional superconductors due to its low cost and availability in kilometer lengths. MgB2 has also been considered for AC applications. In order to model the AC losses and the critical currents of the applications, intrinsic Jc(B)-dependence is an important factor also at low fields. In this work Jc(B)-dependence of an MgB2 sample is extracted from the standard in field voltage-current measurements. The proposed method is applied to a non magnetic titanium sheathed sample at 16 and 20 K and a simple formula for Jc(B) aligns with the measurements. In the fitting process, the critical current distribution inside the wire is numerically simulated in order to take the self field of the sample into account. Moreover, the same formula aligns with measurements of a different sample. These critical current measurements, performed at 4.2 K, were based on magnetization. In the self field computations, the superconducting cross section must be determined accurately. Therefore, we tailored an image processing tool for MgB2 wires to obtain the geometry from a photograph.
Hysteresis, critical fields and superferromagnetism of the film with perpendicular anisotropy
NASA Astrophysics Data System (ADS)
Kalita, V. M.; Kulyk, M. M.; Ryabchenko, S. M.
2016-08-01
This paper is focused on the analysis of hysteresis and critical phenomena of magnetization reversal of superferromagnetic (SFM) state in nanogranular (NG) Co/Al2O3 film with perpendicular anisotropy. It was demonstrated that the transition from the multidomain SFM state to the homogeneous SFM state, during the magnetization process, occurs critically. The value of the field of critical transition to the homogeneous state depends on the demagnetization field, granular anisotropy and interparticle exchange anisotropy. It turned out that the temperature dependence of the coercive force of the film, despite its SFM state, accords with the Neel-Brown formula for anisotropic single-domain ferromagnetic particles, but has an anomalous angular dependence. It was concluded that domain wall motion affects these features of the coercive field. The domain wall movement may occur due to the overturn of magnetic moments of particles in the boundaries between the superdomains. At the same time, the main factors influencing the coercivity are the anisotropy of the particles, which blocks their magnetic moment reorientation, and demagnetizing factor of the film. Together they lead to the anomalous angular dependence of the coercive field.
Upper critical magnetic fields in quasi-one-dimensional layered superconductors
NASA Astrophysics Data System (ADS)
Sepper, Otar
This thesis presents a theoretical analysis of upper critical magnetic fields in quasi-one-dimensional (Q1D), layered superconductors with highly anisotropic electron spectra. It is shown quantitatively how the temperature dependence and spacial orientation of the upper critical magnetic fields, Hc2(T), can reveal important microscopic properties of such superconductors, including the nature of their pairing symmetry. The results obtained show that highly anisotropic, layered compounds can possess exotic superconducting properties such as: non-analytical angular dependence in the upper critical fields at low temperature, the rare spin-triplet Cooper pairing, and a novel quantum limit reentrant superconducting phase occurring in Q1D compounds under ultra-high magnetic fields. For this purpose, two unconventional superconductors are examined: the highly anisotropic Q1D organic superconductor (DMET)2I3, and the layered transition metal oxide superconductor Li0.9Mo6O 17. In the first case, an angular dependence of H c2 that varies as theta3/2 is predicted in (DMET) 2I3 for small angles and low temperatures, in contrast to the well-established (Ginzburg-Landau) quadratic angular dependence near the transition temperature. For Li0.9Mo6O17, spin-triplet pairing is shown to be the most likely scenario, supported by theoretical analysis of the recent experimental data on H c2(T when the field is aligned parallel to the most conducting axis. Furthermore, in Li0.9Mo6O17, a novel quantum limit (QL) superconducting phase is theoretically predicted as a consequence of dimensional crossover in ultra-high magnetic field. If confirmed experimentally, the QL phase would be the first example of existence of superconductivity in magnetic fields greater than 100 Tesla, and in addition would unequivocally confirm spin-triplet Cooper pairing in Li0.9Mo 6O17.
Magnetocaloric effect and magnetic cooling near a field-induced quantum-critical point
Wolf, Bernd; Tsui, Yeekin; Jaiswal-Nagar, Deepshikha; Tutsch, Ulrich; Honecker, Andreas; Remović-Langer, Katarina; Hofmann, Georg; Prokofiev, Andrey; Assmus, Wolf; Donath, Guido; Lang, Michael
2011-01-01
The presence of a quantum-critical point (QCP) can significantly affect the thermodynamic properties of a material at finite temperatures T. This is reflected, e.g., in the entropy landscape S(T,r) in the vicinity of a QCP, yielding particularly strong variations for varying the tuning parameter r such as pressure or magnetic field B. Here we report on the determination of the critical enhancement of ∂S/∂B near a B-induced QCP via absolute measurements of the magnetocaloric effect (MCE), (∂T/∂B)S and demonstrate that the accumulation of entropy around the QCP can be used for efficient low-temperature magnetic cooling. Our proof of principle is based on measurements and theoretical calculations of the MCE and the cooling performance for a Cu2+-containing coordination polymer, which is a very good realization of a spin-½ antiferromagnetic Heisenberg chain—one of the simplest quantum-critical systems.
NASA Astrophysics Data System (ADS)
Hughes, K. J.; Magette, W. L.; Kurz, I.
2005-03-01
Phosphorus (P) in agricultural runoff is a major pollutant in many of Ireland's surface waters. Identification of areas that are at a high risk for P loss to surface waters is a critical component of river basin management. Two P ranking schemes (PRS's) were developed for Ireland, based on multi-criteria analysis approaches proposed in both the US and Europe, to predict the relative likelihood of P loss at both the field and catchment scales. The Field PRS was evaluated by comparing predicted rankings of potential P loss and transport against measured edge-of-field Dissolved Reactive P (DRP) loss for three fields with varying soil P levels. Qualitatively, results indicated that the Field PRS rankings corresponded to the magnitudes of measured P loss for the field sites, as well as to a reasoned evaluation of the relative likelihood that the fields would lose P that would subsequently make its way to surface water. The Catchment PRS was evaluated on a total of 31 catchments and sub-catchments by comparing predicted rankings of potential P loss and transport against measured in-stream median Molybdate Reactive P (MRP). Rankings of the relative likelihood of P loss and transport predicted by the Catchment PRS were positively correlated with median in-stream MRP ( r=0.51, P<0.05). Although the data available for these evaluations were limited, especially at field scale, and further research may identify the opportunity for modifications, both field and catchment scale P ranking schemes demonstrated a potential for identifying critical P source areas within catchments dominated by grass-based agricultural production systems, such as those in Ireland.
NASA Astrophysics Data System (ADS)
Putzke, C.; Carrington, A.; Walmsley, P.; Malone, L.; Fletcher, J. D.; See, P.; Vignolles, D.; Proust, C.; Badoux, S.; Kasahara, S.; Mazukami, Y.; Shibauchi, T.; Matsuda, Y.
2014-03-01
BaFe2(As1-xPx)2 presents one of the cleanest and clearest systems in which to study the influence of quantum critical fluctuations on high temperature superconductivity. In this material a sharp maximum in the magnetic penetration depth has been found at the quantum critical point (QCP x = 0 . 3) where Tc is maximal1. Specific heat and de Haas-van Alphen effect measurements2 show that this peak is driven by a corresponding increase in the quasiparticle effective mass. Based on these previous results a simple one-band theory would suggest that at the QCP we should expect a large increase in Hc 2 and a corresponding dip in Hc 1 . Actual measurements of these critical fields, which we present here, shows quite different behavior which we suggest is caused by an anomalous enhancement in the vortex core energy close to the QCP. 1 K.Hashimoto et.al., Science 336, 1554 (2012) 2 P.Walmsley, C.Putzke et.al., Phys. Rev. Lett. 110, 257002 (2013) This work was supported by the Engineering and Physical Sciences Research Council, EuroMagNET II, and KAKENHI from JSPS.
Ambrosio, G.; Andreev, N.; Bartlett, S.E.; Barzi, E.; Denarie, C.-H.; Dietderich, D.; Ghosh, A.K.; Verweij, A.P.; Zlobin, A.V.; /Fermilab
2004-11-01
Rutherford-type cables made of high critical current Nb{sub 3}Sn strands are being used in several laboratories for developing new generation superconducting magnets for present and future accelerators and upgrades. Testing of cable short samples is an important part of these R&D programs and the instability problem found in some short model magnets at Fermilab made these tests even more significant. Fermilab in collaboration with BNL, CERN and LBNL has developed sample holders and sample preparation infrastructure and procedures for testing Nb{sub 3}Sn cable short samples at BNL and CERN test facilities. This paper describes the sample holders, sample preparation and instrumentation, and test results. Several samples made of MJR or PIT strands 1 mm in diameter have been tested. Some samples were unstable (i.e. quenched at low transport currents) at low fields and reached the critical surface at higher fields.
McCann, J; Kavet, R; Rafferty, C N
1997-01-01
In order to assess the potential of electromagnetic fields (EMF) to influence the process of carcinogenesis, it will be necessary to supplement epidemiological studies with controlled laboratory studies in animals. There are now a number of suitable assays available that focus on different histopathological forms of cancer and on different stages of carcinogenesis--induction, promotion, progression. In this review we discuss eight major systems in the context of this generalized carcinogenesis paradigm. Our aim is to bring together what is currently known about the biology of carcinogenesis in these systems in order to provide a context for evaluating EMF results as they become available. We also critically discuss EMF test results that have so far been obtained in the animal models reviewed. Most of the 19 completed studies identified were negative. However, suggestive positive results were reported in three promotion assays (in rat mammary gland, in rat liver, and in mouse skin), and in one multigeneration study in mice. Results in the rat liver assay and in the multigeneration study have only been reported in abstract form and cannot be adequately evaluated. Positive results reported in both the rat mammary gland and the mouse skin systems are of weak statistical significance and have not been independently replicated. However, it may be of interest that effects in both systems appear primarily to involve the progression stage of carcinogenesis. We suggest that more definitive conclusions as to the carcinogenic potential of EMF may require expanded test protocols that reinforce traditional carcinogenesis end points with biochemical or other parameters reflective of biological processes known to be associated with carcinogenesis in the different systems. PMID:9114279
The Composing Process: A Critical Review of Some Recent Studies.
ERIC Educational Resources Information Center
Crismore, Avon
Six of the 10 existing research studies that attempt to characterize the composing process by examining certain components and behaviors are critically reviewed in this paper. For each study, the aims and data gathering and sampling procedures are described, and the findings, interpretations, design, and rationale of the research are critically…
White Lies: A Critical Race Study of Power and Privilege
ERIC Educational Resources Information Center
Brainard, Patricia Jones
2009-01-01
This was a phenomenological study of racial privilege as experienced by White people who have struggled to become more racially aware and socially active in dismantling racism and White privilege. The primary conceptual framework for this study was Critical Race Theory with Transformative Learning theory and Racial Identity Development as…
Micron SR Studies of High Critical Temperature Superconductor Lead
NASA Astrophysics Data System (ADS)
Wu, Wei-Dong
1995-01-01
Flux depinning phenomena in the rm Bi_2Sr_2CaCu_2O_8 (Bi2212) and rm Pb_{0.7}Bi_ {1.3}Sr_2CaCu_2O_8 (Pb-Bi2212) systems have been studied using the technique of transverse field (TF) muSR. Comparison of field-cooled (FC) and zero-field-cooled (ZFC) results defines an irreversibility (depinning) temperature T _{rm irr}: the ZFC and FC relaxation rates are essentially identical above T _{rm irr}, while the ZFC relaxation rate is larger than the FC relaxation rate below T_{rm irr}, reflecting the increased inhomogeneity of the local fields in the ZFC measurements due to flux pinning. The irreversibility line T_{irr}(H) of Bi2212 obtained by muSR measurements is compared with those from dc and ac-susceptibility, and mechanical oscillator measurements. I show that the results from muSR and these other techniques can be explained consistently within a framework of the flux creep model. The irreversibility temperature in Pb -Bi2212, determined by muSR measurements, is significantly higher than that in the pure Bi2212 system. This result, together with the larger critical current and the higher activation energy U_0 in the Pb-Bi2212 crystals as found by the dc-susceptibility measurements, suggests an enhancement of flux pinning by the Pb doping. In order to fit the muSR asymmetry measured in Y_{1-x} U_{x}Pd _3, I have performed Monte Carlo simulations for spin glasses with impurity concentration x between 0 and 1; I found that the stretched exponential decay of muon polarisation found empirically in many spin glasses above the spin freezing temperature T_{g } is consistent with a lognormal distribution of the fluctuation rate nu. Our muSR measurements of Y_ {1-x}U_{x}Pd _3 and UPd_4 demonstrate the disappearance of magnetic order with decreasing U concentration x with a threshold U concentration x _{rm th} ~ 0.2. I show that the behavior is consistent with Sherrington's induced spin glass model based on the competition between exchange interaction coupling {cal T } and the
Oliveira, L. L.; Dantas, J. T. S.; Souza, R. M.; Carriço, A. S.; Dantas, Ana L.
2014-05-07
We report a theoretical study of dipolar effects on the switching current density of soft ferromagnetic elliptical nanoelements. Relevant changes on the critical current value are found according to the orientation of the magnetization and the spin polarization with the major axis. We show that the critical current density may be reduced by as much as 92% for thin nanoelements magnetized along the minor axis direction, using in-plane spin polarization parallel to the magnetization.
NASA Astrophysics Data System (ADS)
Costa, Pedro; Ferreira, Márcio; Hansen, Hubert; Menezes, Débora P.; Providência, Constança
2014-03-01
The location of the critical end point (CEP) in the QCD phase diagram is determined under different scenarios. The effect of strangeness, isospin/charge asymmetry and an external magnetic field is investigated. The discussion is performed within the 2+1 flavor Nambu-Jona-Lasinio model with Polyakov loop. It is shown that isospin asymmetry shifts the CEP to larger baryonic chemical potentials and smaller temperatures. At large asymmetries the CEP disappears. However, a strong enough magnetic field drives the system into a first order phase transition.
Critical Current Test of Liquid Hydrogen Cooled HTC Superconductors under External Magnetic Field
NASA Astrophysics Data System (ADS)
Shirai, Yasuyuki; Shiotsu, Masahiro; Tatsumoto, Hideki; Kobayashi, Hiroaki; Naruo, Yoshihiro; Nonaka, Satoshi; Inatani, Yoshifumi
High-Tc (HTC) superconductors including MgB2 will show excellent properties under temperature of Liquid Hydrogen (LH2:20K), which has large latent heat and low viscosity coefficient. In order to design and fabricate the LH2 cooled superconducting energy devices, we must clear the cooling property of LH2 for superconductors, the cooling system and safety design of LH2 cooled superconducting devices and electro-magnetic property evaluation of superconductors (BSCCO, REBCO and MgB2) and their magnets cooled by LH2. As the first step of the study, an experimental setup which can be used for investigating heat transfer characteristics of LH2 in a pool and also in forced flow (circulation loop with a pump), and also for evaluation of electro-magnetic properties of LH2 cooled superconductors under external magnetic field (up to 7 T). In this paper, we will show a short sketch of the experimental set-up, practical experiences in safety operation of liquid hydrogen cooling system and example test results of critical current evaluation of HTC superconductors cooled by LH2.
Using Critical Incident Reflections: A Self-Study as a Mathematics Teacher Educator
ERIC Educational Resources Information Center
Goodell, Joanne E.
2006-01-01
In this paper, I report the results of a 4-year study into how my students learn to become mathematics teachers during the combined 15-week methods and field placement course I teach. At the start of most weekly methods class meetings, groups of three or four students reported their critical incidents to each other, and then chose one incident to…
Field-structured composite studies.
Martin, James Ellis; Williamson, Rodney L.
2004-04-01
Field-structured composites (FSCs) were produced by hosting micron-sized gold-coated nickel particles in a pre-polymer and allowing the mixture to cure in a magnetic field environment. The feasibility of controlling a composite's electrical conductivity using feedback control applied to the field coils was investigated. It was discovered that conductivity in FSCs is primarily determined by stresses in the polymer host matrix due to cure shrinkage. Thus, in cases where the structuring field was uniform and unidirectional so as to produce chainlike structures in the composite, no electrical conductivity was measured until well after the structuring field was turned off at the gel point. In situations where complex, rotating fields were used to generate complex, three-dimensional structures in a composite, very small, but measurable, conductivity was observed prior to the gel point. Responsive, sensitive prototype chemical sensors were developed based on this technology with initial tests showing very promising results.
Superconductivity with extremely large upper critical fields in Nb2Pd0.81S5
Zhang, Q.; Li, G.; Rhodes, D.; Kiswandhi, A.; Besara, T.; Zeng, B.; Sun, J.; Siegrist, T.; Johannes, M. D.; Balicas, L.
2013-01-01
Here, we report the discovery of superconductivity in a new transition metal-chalcogenide compound, i.e. Nb2Pd0.81S5, with a transition temperature Tc ≅ 6.6 K. Despite its relatively low Tc, it displays remarkably high and anisotropic superconducting upper critical fields, e.g. μ0Hc2 (T → 0 K) > 37 T for fields applied along the crystallographic b-axis. For a field applied perpendicularly to the b-axis, μ0Hc2 shows a linear dependence in temperature which coupled to a temperature-dependent anisotropy of the upper critical fields, suggests that Nb2Pd0.81S5 is a multi-band superconductor. This is consistent with band structure calculations which reveal nearly cylindrical and quasi-one-dimensional Fermi surface sheets having hole and electron character, respectively. The static spin susceptibility as calculated through the random phase approximation, reveals strong peaks suggesting proximity to a magnetic state and therefore the possibility of unconventional superconductivity. PMID:23486091
Spin-dependent masses and field-induced quantum critical points
NASA Astrophysics Data System (ADS)
McCollam, A.; Daou, R.; Julian, S. R.; Bergemann, C.; Flouquet, J.; Aoki, D.
2005-04-01
We discuss spin-dependent mass enhancements associated with field-induced quantum critical points in heavy-fermion systems. We have recently observed this phenomenon on a branch of the Fermi surface of CeRu2Si2 above its metamagnetic transition, complementing earlier work. In CeCoIn5, at high fields above a field-induced quantum critical point, we see a strong spin-dependence of the effective mass on the thermodynamically dominant sheets of the Fermi surface. These observations reinforce the suggestion that ‘missing mass’ in some cerium-based heavy-fermion systems will be found on heavy spin-polarised branches of the Fermi surface. In all cases where this phenomenon is observed the linear coefficient of specific heat is field dependent; however, CeCoIn5 seems to be the first such heavy-fermion system in which the f-electrons are definitely contributing to the Fermi volume, which puts it beyond the existing theory intended for metamagnetic systems.
Critical point in the QCD phase diagram for extremely strong background magnetic fields
NASA Astrophysics Data System (ADS)
Endrödi, Gergely
2015-07-01
Lattice simulations have demonstrated that a background (electro)magnetic field reduces the chiral/deconfinement transition temperature of quantum chromodynamics for eB < 1 GeV2. On the level of observables, this reduction manifests itself in an enhancement of the Polyakov loop and in a suppression of the light quark condensates (inverse magnetic catalysis) in the transition region. In this paper, we report on lattice simulations of 1 + 1 + 1-flavor QCD at an unprecedentedly high value of the magnetic field eB = 3 .25 GeV2. Based on the behavior of various observables, it is shown that even at this extremely strong field, inverse magnetic catalysis prevails and the transition, albeit becoming sharper, remains an analytic crossover. In addition, we develop an algorithm to directly simulate the asymptotically strong magnetic field limit of QCD. We find strong evidence for a first-order deconfinement phase transition in this limiting theory, implying the presence of a critical point in the QCD phase diagram. Based on the available lattice data, we estimate the location of the critical point.
NASA Astrophysics Data System (ADS)
Mo, Jie-Xiong; Li, Gu-Qiang; Xu, Xiao-Bao
2016-04-01
The effects of a power-law Maxwell field on the critical phenomena of higher dimensional dilaton black holes are probed in detail. We successfully derive the analytic solutions of the critical point and carry out some checks to ensure that these critical quantities are positive. It is shown that the constraint on the parameter α describing the strength of the coupling of the electromagnetic field and the scalar field turns out to be 0 <α2<1 , which is tighter than that in the nonextended phase space. It is also shown that these critical quantities and the ratio Pcvc/Tc are affected by the power-law Maxwell field. Moreover, critical exponents are found to coincide with those of other anti-de Sitter black holes, showing the powerful influence of mean field theory.
Kiloampere, Variable-Temperature, Critical-Current Measurements of High-Field Superconductors
Goodrich, LF; Cheggour, N; Stauffer, TC; Filla, BJ; Lu, XF
2013-01-01
5 K to those measured on the same specimen in flowing helium gas (“gas” or Ic gas) at the same temperature. These comparisons indicate the temperature control is effective over the superconducting wire length between the voltage taps, and this condition is valid for all types of sample investigated, including Nb-Ti, Nb3Sn, and MgB2 wires. The liquid/gas comparisons are used to study the variable-temperature measurement protocol that was necessary to obtain the “correct” critical current, which was assumed to be the Ic liq. We also calibrated the magnetoresistance effect of resistive thermometers for temperatures from 4 K to 35 K and magnetic fields from 0 T to 16 T. This calibration reduces systematic errors in the variable-temperature data, but it does not affect the liquid/gas comparison since the same thermometers are used in both cases. PMID:26401435
Critical Studies: A Trojan Horse for an Alternative Cultural Agenda?
ERIC Educational Resources Information Center
Swift, John
1993-01-01
Asserts that the introduction of the term "critical studies" to British art education reflects art educators' views that the practice of art alone is insufficient to gain a full experience and coincides with a political will to return to traditional forms of content and knowledge. (CFR)
Post-Fordism, Political Economy, and Critical Organizational Communication Studies.
ERIC Educational Resources Information Center
Nadesan, Majia Holmer
2001-01-01
Introduces readers to the literature on post-Fordism by first describing the social and economic phenomena that it seeks to explain and then by introducing the divergent research approaches that contest the scope and effects of post-Fordist phenomena. Suggests that critical organizational communication studies has much to gain, analytically and…
Constructing Critical Autoethnographic Self-Studies with White Educators
ERIC Educational Resources Information Center
Pennington, Julie L.; Brock, Cynthia H.
2012-01-01
Autoethnography was used as a tool for white in-service elementary teachers to examine their racial identity from a Critical White Studies (CWS) perspective. Two white in-service teachers participated in two yearlong university courses focused on teaching linguistically and culturally diverse students. Each teacher collected their own data at…
Interpretive and Critical Phenomenological Crime Studies: A Model Design
ERIC Educational Resources Information Center
Miner-Romanoff, Karen
2012-01-01
The critical and interpretive phenomenological approach is underutilized in the study of crime. This commentary describes this approach, guided by the question, "Why are interpretive phenomenological methods appropriate for qualitative research in criminology?" Therefore, the purpose of this paper is to describe a model of the interpretive…
Going Critical: The Problem of Problematizing Knowledge in Education Studies
ERIC Educational Resources Information Center
Moore, Rob
2007-01-01
This paper raises the issue of what it is to be "critical" in education studies and in social theory more generally. It argues that this idea has for a long time been associated with forms of social constructionism and sociological reductionism. These understand the idea that knowledge is social in terms of reducing it to the experiences and…
Critical Practice in Teacher Education: A Study of Professional Learning
ERIC Educational Resources Information Center
Heilbronn, Ruth, Ed.; Yandell, John, Ed.
2010-01-01
This timely book uncovers all of the processes that should be considered when high-quality teacher education is designed, delivered and studied around the world. Written by experienced teacher educators, this book shows what critical practice is and how it can be used to facilitate a deeper understanding of practice that draws upon personal…
Disability and Diversity on CSU Websites: A Critical Discourse Study
ERIC Educational Resources Information Center
Gabel, Susan L.; Reid, Denise; Pearson, Holly; Ruiz, Litzy; Hume-Dawson, Rodney
2016-01-01
With more than 325,000 students, the California State University (CSU) system is 1 of the largest in the United States, making it a useful unit of analysis for studying disability and diversity. Using a critical discourse theoretical framework and borrowing strategies from Astroff (2001) and Pauwells (2012), we found disability information on CSU…
Promoting Critical Multicultural Citizenship: A Case Study of Preparing Social Studies Teachers
ERIC Educational Resources Information Center
Castro, Antonio Jamie
2009-01-01
Given the growing cultural and economic diversity of today's students, this qualitative case study investigates how 4 social studies preservice teachers taught for critical multicultural citizenship during their student teaching semester. The tenets of critical citizenship emerge out of the intersection of critical pedagogy and multicultural…
Critical Current Properties in Longitudinal Magnetic Field of YBCO Superconductor with APC
NASA Astrophysics Data System (ADS)
Kido, R.; Kiuchi, M.; Otabe, E. S.; Matsushita, T.; Jha, A. K.; Matsumoto, K.
The critical current density (Jc) properties of the Artificial Pinning Center (APC) introduced YBa2Cu3O7 (YBCO) films in the longitudinal magnetic field were measured. Y2O3 or Y2BaCuO5 (Y211) was introduced as APCs to YBCO, and YBCO films with APC were fabricated on SrTiO3 single crystal substrate. The sizes of Y2O3 and Y211 were 5-10 nm and 10-20 nm, respectively. As a result, Jc enhancement in the longitudinal magnetic field was observed in Y2O3 introduced YBCO films. However, it was not observed in Y211 introduced YBCO films. Therefore, it was considered that Jc properties in the longitudinal magnetic field were affected by introducing of small size APC, and it was necessary that APC does not disturb the current pathway in the superconductor.
Josephson critical current of long SNS junctions in the presence of a magnetic field
NASA Astrophysics Data System (ADS)
Meier, Hendrik; Fal'Ko, Vladimir I.; Glazman, Leonid I.
We evaluate the Josephson critical current of a long and wide two-dimensional superconductor-normal metal-superconductor (SNS) junction, taking into account the effect of electron reflection off the side edges of the junction. Considering clean junctions, we find that the effect of edges alters the usual Fraunhofer-like dependence of the Josephson critical current Ic on the magnetic flux Φ. At relatively weak fields, B <~Φ0 /W2 , the edge effect lifts zeros of the Ic (Φ) dependence and gradually shifts the maxima of that function by Φ0 / 2 . (Here W is the width of the junction and Φ0 the magnetic flux quantum.) At higher fields, B >~Φ0 /W2 , the edge effect leads to an accelerated decay of the critical current Ic (Φ) with increasing Φ. Our results are robust with respect to the roughness of realistic boundaries. Finally, we discuss the role of mesoscopic fluctuations of Ic (Φ) originating from the scattering off the edges, and compare our findings to recent experiments.
NASA Astrophysics Data System (ADS)
Mukherjee, Sudip; Rajak, Atanu; Chakrabarti, Bikas K.
2015-10-01
We study the critical behavior of the Sherrington-Kirkpatrick model in transverse field (at finite temperature) using Monte Carlo simulation and exact diagonalization (at zero temperature). We determine the phase diagram of the model by estimating the Binder cumulant. We also determine the correlation length exponent from the collapse of the scaled data. Our numerical studies here indicate that critical Binder cumulant (indicating the universality class of the transition behavior) and the correlation length exponent cross over from their "classical" to "quantum" values at a finite temperature (unlike the cases of pure systems, where such crossovers occur at zero temperature). We propose a qualitative argument supporting such an observation, employing a simple tunneling picture.
Finite-temperature scaling at the quantum critical point of the Ising chain in a transverse field
NASA Astrophysics Data System (ADS)
Haelg, Manuel; Huvonen, Dan; Guidi, Tatiana; Quintero-Castro, Diana Lucia; Boehm, Martin; Regnault, Louis-Pierre; Zheludev, Andrey
2015-03-01
Inelastic neutron scattering is used to study the finite-temperature scaling behavior of spin correlations at the quantum critical point in an experimental realization of the one-dimensional Ising model in a transverse field. The target compound is the well-characterized, anisotropic and bond-alternating Heisenberg spin-1 chain material NTENP. The validity and the limitations of the dynamic structure factor scaling are tested, discussed and compared to theoretical predictions. For this purpose neutron data have been collected on the three-axes spectrometers IN14 at ILL and FLEXX at HZB as well as on the time of flight multi-chopper spectrometer LET at ISIS. In addition to the general statement about quantum criticality and universality, present study also reveals new insight into the properties of the spin chain compound NTENP in particular.
The local field dependent effect of the critical distance of energy transfer between nanoparticles
NASA Astrophysics Data System (ADS)
Viet Ha, Chu; Thi Nga, Do; Ai Viet, Nguyen; Hong Nhung, Tran
2015-10-01
The fluorescence resonance energy transfer between various types of fluorophore pairs was investigated. Dye molecules, quantum dots, fluorescent nanoparticles (dye molecules encapsulated in polymer matrices) were used as donor D. Dye molecules and gold nanoparticles were used as acceptor A. We found that the experimental Förster critical transfer distance R0 is 1-10 nm when both D and A are dye molecules, and becomes larger than 10 nm when the donor is fluorescent nanoparticles. When the acceptors A are gold nanoparticles, the case is considered as localized plasmon coupled nanosurface energy transfer (NSET), the experimental critical distance d0 increases up to few ten nanometers when D are dye molecules or quantum dots. For the first time, un-expected giant resonance energy transfer (G-RET) phenomenon is observed in our experiments with very large critical transfer distance d0, which increases from few ten nanometers to micrometers when the donors are fluorescent and the acceptors are gold nanoparticles. A model "nanowave emitter station and antenna" is given to explain the local field dependence of the critical distance of energy transfer between those nanoparticles. Moreover, a simple theoretical model with size-number contribution (for fluorescent nanoparticles) and surface plasmon coupled enhancement effect (for gold nanoparticles) is proposed to explain these obtained experimental results.
NASA Astrophysics Data System (ADS)
Zhang, Min; Kim, Jae-Ho; Pamidi, Sastry; Chudy, Michal; Yuan, Weijia; Coombs, T. A.
2012-04-01
This paper presents the modeling of second generation (2 G) high-temperature superconducting (HTS) pancake coils using finite element method. The axial symmetric model can be used to calculate current and magnetic field distribution inside the coil. The anisotropic characteristics of 2 G tapes are included in the model by direct interpolation. The model is validated by comparing to experimental results. We use the model to study critical currents of 2 G coils and find that 100 μV/m is too high a criterion to determine long-term operating current of the coils, because the innermost turns of a coil will, due to the effect of local magnetic field, reach their critical current much earlier than outer turns. Our modeling shows that an average voltage criterion of 20 μV/m over the coil corresponds to the point at which the innermost turns' electric field exceeds 100 μV/m. So 20 μV/m is suggested to be the critical current criterion of the HTS coil. The influence of background field on the coil critical current is also studied in the paper.
Anisotropy in upper critical field of FeTe{sub 0.55}Se{sub 0.45}
Shruti,; Sharma, G.; Patnaik, S.
2015-06-24
The anisotropic properties of FeTe{sub 0.55}Se{sub 0.45} single crystals are studied using transport measurements. FeTe{sub 0.55}Se{sub 0.45} shows onset superconducting transition at 14.2 K. The data measured on single crystals give a high upper critical field H{sub c2}(0) equal to 93.95 T and 67.32 T for magnetic field applied perpendicular and parallel to c axis of the sample respectively. Corresponding electronic anisotropy is estimated to be γ∼1.4 and Ginzburg-Landau coherence lengths are ξ{sub ab}=22.12 Å and ξ{sub c}=15.8 Å. Temperature and field dependent specific heat data are also reported.
Studies in quantum field theory
NASA Astrophysics Data System (ADS)
Polmar, S. K.
The theoretical physics group at Washington University has been devoted to the solution of problems in theoretical and mathematical physics. All of the personnel on this task have a similar approach to their research in that they apply sophisticated analytical and numerical techniques to problems primarily in quantum field theory. Specifically, this group has worked on quantum chromodynamics, classical Yang-Mills fields, chiral symmetry breaking condensates, lattice field theory, strong-coupling approximations, perturbation theory in large order, nonlinear waves, 1/N expansions, quantum solitons, phase transitions, nuclear potentials, and early universe calculations.
Field measurement of critical shear stress for erosion and deposition of fine muddy sediments
NASA Astrophysics Data System (ADS)
Salehi, M.; Strom, K. B.; Field Study
2010-12-01
The movement of muddy sediment from one region to another is linked to the fate and transport of pollutants that can be attached to this sediment. Important in understanding this movement is the need to know the critical conditions for erosion and deposition of the fine muddy sediment. For non-cohesion sediment, such as sands and gravels, reasonable estimates for the critical conditions can often be made theoretically without in situ measurements of the critical fluid condition or sediment transport rate. However, the shear stress needed for the incipient motion of the mud (cohesive sediments) is inherently difficult to calculate theoretically or in research flumes due to the influence of (1) flow history; (2) local sediment composition; (3) biological activity within the bed; (4) water content of the bed; and (5) salinity of the water column. The complexity of the combination of these factors makes the field measurement necessary. A field experiment was conducted under tidal flow in the region surrounding the Houston Ship Channel (near Houston, TX) to determine these conditions. Observations were made using single point, simultaneous, in situ measurement of turbulent flow and suspended sediment concentration within bottom boundary layer. Measurements were primarily made with a 6 MHz Nortek Vector velocimeter (ADV). The ADV was programmed to record 3-minute turbulent velocity with 32 Hz frequency every 10 minute. The suspended sediment concentration (SSC) was measured using the calibration of acoustic backscatter recorded by ADV against sample derived SSC. Different methods such as turbulent kinetic energy (TKE), TKEw and direct covariance method (COV) are compared together. TKE showed much more reasonable estimation on bed shear stress. Combination of time varying SSC, distance from the bed to the sampling volume recorded by ADV and calculation of shear stress made the determination of critical conditions for erosion and deposition possible.
Self-field effects upon the critical current density of flat superconducting strips
NASA Astrophysics Data System (ADS)
Babaei Brojeny, Ali A.; Clem, John R.
2005-06-01
We develop a general theory to account self-consistently for self-field effects upon the average transport critical current density Jc of a flat type-II superconducting strip in the mixed state when the bulk pinning is characterized by a field-dependent depinning critical current density Jp(B), where B is the local magnetic flux density. We first consider the possibility of both bulk and edge-pinning contributions but conclude that bulk pinning dominates over geometrical edge-barrier effects in state-of-the-art YBCO films and prototype second-generation coated conductors. We apply our theory using the Kim model, JpK(B) = JpK(0)/(1+|B|/B0), as an example. We calculate Jc(Ba) as a function of a perpendicular applied magnetic induction Ba and show how Jc(Ba) is related to JpK(B). We find that Jc(Ba) is very nearly equal to JpK(Ba) when Ba>=Ba*, where Ba* is the value of Ba that makes the net flux density zero at the strip's edge. However, Jc(Ba) is suppressed relative to JpK(Ba) at low fields when Ba< Ba*, with the largest suppression occurring when Ba*/B0 is of order unity or larger.
Mean-field cluster model for the critical behaviour of ferromagnets
NASA Astrophysics Data System (ADS)
Chamberlin, Ralph V.
2000-11-01
Two separate theories are often used to characterize the paramagnetic properties of ferromagnetic materials. At temperatures T well above the Curie temperature, TC (where the transition from paramagnetic to ferromagnetic behaviour occurs), classical mean-field theory yields the Curie-Weiss law for the magnetic susceptibility: χ(
Critical fields of Fe{sub 4}N/NbN ferromagnetic/superconducting multilayers
Mattson, J.E.; Potter, C.D.; Conover, M.J.; Sowers, C.H.; Bader, S.D.
1997-01-01
Structural, magnetic, and superconducting properties of ferromagnetic/superconducting multilayers of Fe{sub 4}N/NbN are explored for a variety of thickness combinations. The superconducting properties show that 11 {Angstrom} ferromagnetic layers are sufficient to decouple the superconducting layers and to yield anisotropic behavior. The upper critical field data are well described by theory for ferromagnetic/superconducting multilayers. This analysis yields an interfacial parameter which characterizes the electron scattering at the ferromagnetic/superconducting boundary. {copyright} {ital 1997} {ital The American Physical Society}
Growth and decay of runaway electrons above the critical electric field under quiescent conditions
Paz-Soldan, C.; Eidietis, N. W.; Wesley, J. C.; Granetz, R.; Hollmann, E. M.; Moyer, R. A.; Zhang, J.; Crocker, N. A.; Austin, M. E.; Wingen, A.; Zhu, Y.
2014-02-15
Extremely low density operation free of error field penetration supports the excitation of trace-level quiescent runaway electron (RE) populations during the flat-top of DIII-D Ohmic discharges. Operation in the quiescent regime allows accurate measurement of all key parameters important to RE excitation, including the internal broadband magnetic fluctuation level. RE onset is characterized and found to be consistent with primary (Dreicer) generation rates. Impurity-free collisional suppression of the RE population is investigated by stepping the late-time main-ion density, until RE decay is observed. The transition from growth to decay is found to occur 3–5 times above the theoretical critical electric field for avalanche growth and is thus indicative of anomalous RE loss. This suggests that suppression of tokamak RE avalanches can be achieved at lower density than previously expected, though extrapolation requires predictive understanding of the RE loss mechanism and magnitude.
Not Available
1990-01-01
A very theoretical description is given of research in two- dimensional critical phenomena and conformal field theory. Major progress is reported in the field of fluctuating two-dimensional surfaces. A discretized representation of fluctuating geometry is used where surfaces are represented by triangulations; continuum surfaces are recovered by taking the size of the triangles to zero. One of the central goals of the theory of critical phenomena is to find all possible universality classes of n-dimensional critical phenomena; this goal has been translated into the problem of clasifying all possible scale-invariant euclidean quantum field theories. (RWR)
NASA Astrophysics Data System (ADS)
Friedman, Nir; Jennings, Andrew T.; Tsekenis, Georgios; Kim, Ju-Young; Tao, Molei; Uhl, Jonathan T.; Greer, Julia R.; Dahmen, Karin A.
2012-08-01
We show that slowly sheared metallic nanocrystals deform via discrete strain bursts (slips), whose size distributions follow power laws with stress-dependent cutoffs. We show for the first time that plasticity reflects tuned criticality, by collapsing the stress-dependent slip-size distributions onto a predicted scaling function. Both power-law exponents and scaling function agree with mean-field theory predictions. Our study of 7 materials and 2 crystal structures, at various deformation rates, stresses, and crystal sizes down to 75 nm, attests to the universal characteristics of plasticity.
Microstructure, critical current density and trapped field experiments in IG-processed Y-123
NASA Astrophysics Data System (ADS)
Muralidhar, M.; Ide, N.; Koblischka, M. R.; Diko, P.; Inoue, K.; Murakami, M.
2016-05-01
In this paper, we adapted the top-seeded infiltration growth ‘IG’ technique and produced several YBa2Cu3O y ‘Y-123’ samples with an addition of Y2BaCuO5 ‘Y-211’ secondary phase particles with varying sizes by the sintering process and the ball milling technique. For the first set of samples, Y-211 disks were sintered at temperatures ranging between 900 °C and 1100 °C and were used for the production of Y-123 material by the IG process. Magnetization measurements showed a sharp superconducting transition with an onset T c at around 92 K, irrespective of the sintering temperature. However, the trapped field and critical current density (J c) values were dependent on the sintering temperature and it was found that the best temperature is around 925 °C. Further, the trapped field distribution measurements at 77 K indicated that all samples are of single grain nature. The highest trapped field was recorded around 0.31 T at 77 K for the Y-123 sample with 20 mm in diameter and 5 mm thickness produced by Y-211 pre-from around 925 °C. On the other hand, a second set of samples Y-211 were controlled by ball milling technique combined with an optimized slow cooling process. As a result, the critical current density (J c) at 77 K and zero field was determined to be 225 kA cm-2. The improved performance of the Y-123 material can be understood in terms of homogeneous distribution of fine secondary phase particles which is demonstrated by AFM micrographs.
Numerical study of multicomponent droplet vaporization at near critical conditions
NASA Technical Reports Server (NTRS)
Hsieh, Kwang-Chung; Shuen, Jian-Shun; Yang, Vigor
1988-01-01
A comprehensive numerical analysis of multicomponent droplet vaporization at near critical conditions has been carried out. The model is based on the full time-dependent conservation equations and accommodates various important high-pressure phenomena. As an example, the case involving a two-component (n-pentane and n-octane) fuel droplet in nitrogen gas is studied. The influences of transient effects, surface regression, ambient gas solubility, and phase-equilibrium relations on vaporization mechanisms are examined in detail.
Use of intuition by critical care nurses: a phenomenological study
Hassani, Parkhide; Abdi, Alireza; Jalali, Rostam; Salari, Nader
2016-01-01
Background Intuition is defined as an irrational unconscious type of knowing. This concept was incorporated into nursing discipline for 3 decades, but nowadays its application is uncertain and ignored by educational institutions. Therefore, this study aimed to explore critical care nurses’ understanding of the use of intuition in clinical practice. Materials and methods In a descriptive phenomenological study, 12 nurses employed in critical care units of the hospitals affiliated with Kermanshah University of Medical Sciences, were recruited to a study using purposive, semistructured interviews, which were then written down verbatim. The data were managed by MaxQDA 10 software and analyzed as qualitative, with Colaizzi’s seven-stage approach. Results Of the 12 nurses who participated in the study, seven (58.3%) were female and married, 88.3% (ten) had a Bachelor of Nursing (BSc) degree, and the means ± SD of age, job experience, and critical care experience were 36.66±7.01, 13.75±6.82, and 7.66±3.36 years, respectively. We extracted three main themes, namely “patient conditions”, “nurse readiness”, and “outcome”, and seven subthemes – including “clinical signs”, “patient behaviors”, “prognosis”, “being sensitive”, “desire to act”, “prediction”, and “satisfaction” – integral to understanding the use of intuition in clinical practice by critical care nurses. Conclusion The findings showed that some nurses were attracted by the patients’ conditions and were more intuitive about them, and following their intuition prepared the nurses to under-take more appropriate measures. The positive results that the majority of the nurses experienced convinced them to follow their intuitions more often. PMID:26929677
Critical and noncritical long-range entanglement in Klein-Gordon fields
Marcovitch, S.; Reznik, B.; Retzker, A.; Plenio, M. B.
2009-07-15
We investigate the entanglement between two spatially separated intervals in the vacuum state of a free one-dimensional Klein-Gordon field by means of explicit computations in the continuum limit of the linear harmonic chain. We demonstrate that the entanglement, which we quantify by the logarithmic negativity, is finite with no further need for renormalization. We find that in the critical regime, the quantum correlations are scale invariant as they depend only on the ratio of distance to length. They decay much faster than the classical correlations as in the critical limit long-range entanglement decays exponentially for separations larger than the size of the blocks, while classical correlations follow a power-law decay. With decreasing distance of the blocks, the entanglement diverges as a power law in the distance. The noncritical regime manifests richer behavior, as the entanglement depends both on the size of the blocks and on their separation. In correspondence with the von Neumann entropy also long-range entanglement distinguishes critical from noncritical systems.
Positive-overlap transition and critical exponents in mean field spin glasses
NASA Astrophysics Data System (ADS)
Agostini, Alessandra; Barra, Adriano; DeSanctis, Luca
2006-11-01
In this paper we obtain two results for the Sherrington-Kirkpatrick (SK) model, and we show that they both emerge from a single approach. First, we prove that the average of the overlap takes positive values when it is non-zero. More specifically, the average of the overlap, which is naively expected to take values in the whole interval [-1,+1], becomes positive if we 'first' apply an external field, so as to destroy the gauge invariance of the model, and 'then' remove it in the thermodynamic limit. This phenomenon emerges at the critical point. This first result is weaker than the one obtained by Talagrand (not limited to the average of the overlap), but we show here that, at least on average, the overlap is proven to be non-negative with no use of the Ghirlanda-Guerra identities. The latter are instead needed to obtain the second result, which is to control the behaviour of the overlap at the critical point: we find the critical exponents of all the overlap correlation functions.
Critical behavior of a tumor growth model: directed percolation with a mean-field flavor.
Lipowski, Adam; Ferreira, António Luis; Wendykier, Jacek
2012-10-01
We examine the critical behavior of a lattice model of tumor growth where supplied nutrients are correlated with the distribution of tumor cells. Our results support the previous report [Ferreira et al., Phys. Rev. E 85, 010901(R) (2012)], which suggested that the critical behavior of the model differs from the expected directed percolation (DP) universality class. Surprisingly, only some of the critical exponents (β, α, ν([perpendicular]), and z) take non-DP values while some others (β', ν(||), and spreading-dynamics exponents Θ, δ, z') remain very close to their DP counterparts. The obtained exponents satisfy the scaling relations β=αν(||), β'=δν(||), and the generalized hyperscaling relation Θ+α+δ=d/z, where the dynamical exponent z is, however, used instead of the spreading exponent z'. Both in d=1 and d=2 versions of our model, the exponent β most likely takes the mean-field value β=1, and we speculate that it might be due to the roulette-wheel selection, which is used to choose the site to supply a nutrient. PMID:23214560
Quantum entanglement and criticality of the antiferromagnetic Heisenberg model in an external field
NASA Astrophysics Data System (ADS)
Liu, Guang-Hua; Li, Ruo-Yan; Tian, Guang-Shan
2012-06-01
By Lanczos exact diagonalization and the infinite time-evolving block decimation (iTEBD) technique, the two-site entanglement as well as the bipartite entanglement, the ground state energy, the nearest-neighbor correlations, and the magnetization in the antiferromagnetic Heisenberg (AFH) model under an external field are investigated. With increasing external field, the small size system shows some distinct upward magnetization stairsteps, accompanied synchronously with some downward two-site entanglement stairsteps. In the thermodynamic limit, the two-site entanglement, as well as the bipartite entanglement, the ground state energy, the nearest-neighbor correlations, and the magnetization are calculated, and the critical magnetic field hc = 2.0 is determined exactly. Our numerical results show that the quantum entanglement is sensitive to the subtle changing of the ground state, and can be used to describe the magnetization and quantum phase transition. Based on the discontinuous behavior of the first-order derivative of the entanglement entropy and fidelity per site, we think that the quantum phase transition in this model should belong to the second-order category. Furthermore, in the magnon existence region (h < 2.0), a logarithmically divergent behavior of block entanglement which can be described by a free bosonic field theory is observed, and the central charge c is determined to be 1.
Chang, Kuan Y.; Lin, Tung-pei; Shih, Ling-Yi; Wang, Chien-Kuo
2015-01-01
Antimicrobial peptides (AMPs) are potent drug candidates against microbes such as bacteria, fungi, parasites, and viruses. The size of AMPs ranges from less than ten to hundreds of amino acids. Often only a few amino acids or the critical regions of antimicrobial proteins matter the functionality. Accurately predicting the AMP critical regions could benefit the experimental designs. However, no extensive analyses have been done specifically on the AMP critical regions and computational modeling on them is either non-existent or settled to other problems. With a focus on the AMP critical regions, we thus develop a computational model AMPcore by introducing a state-of-the-art machine learning method, conditional random fields. We generate a comprehensive dataset of 798 AMPs cores and a low similarity dataset of 510 representative AMP cores. AMPcore could reach a maximal accuracy of 90% and 0.79 Matthew’s correlation coefficient on the comprehensive dataset and a maximal accuracy of 83% and 0.66 MCC on the low similarity dataset. Our analyses of AMP cores follow what we know about AMPs: High in glycine and lysine, but low in aspartic acid, glutamic acid, and methionine; the abundance of α-helical structures; the dominance of positive net charges; the peculiarity of amphipathicity. Two amphipathic sequence motifs within the AMP cores, an amphipathic α-helix and an amphipathic π-helix, are revealed. In addition, a short sequence motif at the N-terminal boundary of AMP cores is reported for the first time: arginine at the P(-1) coupling with glycine at the P1 of AMP cores occurs the most, which might link to microbial cell adhesion. PMID:25803302
Incubating knowledge: A critical exploration with teachers studying live chickens
NASA Astrophysics Data System (ADS)
Rauchwerk, Susan I.
This thesis documents a professional development workshop conducted with eight teachers who worked at Drumlin Farm, an outdoor education center, organic farm and wildlife sanctuary (Appendix C). The participants studied live chickens for eight consecutive workshop sessions. Seven years later the same group met for two follow-up sessions to discuss the effects of the workshop on their teaching practice. The workshop and follow-up sessions were conducted using a teaching-research method developed by Eleanor Duckworth called critical exploration (Duckworth, in press). In this thesis, findings from the eight-week workshop and the two followup sessions are documented in a narrative format showing how and what individuals and the group as a whole, came to understand from studying live chickens, as well as the process and application of the critical exploration method. Over the course of the workshop and the follow-up sessions, group explorations focused on the biological concept of broodiness (the desire to sit, tend, and hatch eggs) in domestic laying hens. In the process of developing and investigating their questions about broodiness, the participants developed and used a scientific process. Their experiences as learners in critical exploration with chickens as the subject matter, resulted in participants both thinking about, and modifying, their ideas about teaching and learning.
Precise determination of critical exponents and equation of state by field theory methods
NASA Astrophysics Data System (ADS)
Zinn-Justin, J. Z.
2001-04-01
Renormalization group, and in particular its quantum field theory implementation has provided us with essential tools for the description of the phase transitions and critical phenomena beyond mean field theory. We therefore review the methods, based on renormalized φ34 quantum field theory and renormalization group, which have led to a precise determination of critical exponents of the N-vector model (Le Guillou and Zinn-Justin, Phys. Rev. Lett. 39 (1977) 95; Phys. Rev. B 21 (1980) 3976; Guida and Zinn-Justin, J. Phys. A 31 (1998) 8103; cond-mat/9803240) and of the equation of state of the 3D Ising model (Guida and Zinn-Justin, Nucl. Phys. B 489 [FS] (1997) 626, hep-th/9610223). These results are among the most precise available probing field theory in a non-perturbative regime. Precise calculations first require enough terms of the perturbative expansion. However perturbation series are known to be divergent. The divergence has been characterized by relating it to instanton contributions. The information about large-order behaviour of perturbation series has then allowed to develop efficient “summation” techniques, based on Borel transformation and conformal mapping (Le Guillou and Zinn-Justin (Eds.), Large Order Behaviour of Perturbation Theory, Current Physics, vol. 7, North-Holland, Amsterdam, 1990). We first discuss exponents and describe our recent results (Guida and Zinn-Justin, 1998). Compared to exponents, the determination of the scaling equation of state of the 3D Ising model involves a few additional (non-trivial) technical steps, like the use of the parametric representation, and the order dependent mapping method. From the knowledge of the equation of state a number of ratio of critical amplitudes can also be derived. Finally we emphasize that few physical quantities which are predicted by renormalization group to be universal have been determined precisely, and much work remains to be done. Considering the steady increase in the available
Automated Critical PeakPricing Field Tests: 2006 Pilot ProgramDescription and Results
Piette, Mary Ann; Watson, David; Motegi, Naoya; Kiliccote, Sila
2007-06-19
During 2006 Lawrence Berkeley National Laboratory (LBNL) and the Demand Response Research Center (DRRC) performed a technology evaluation for the Pacific Gas and Electric Company (PG&E) Emerging Technologies Programs. This report summarizes the design, deployment, and results from the 2006 Automated Critical Peak Pricing Program (Auto-CPP). The program was designed to evaluate the feasibility of deploying automation systems that allow customers to participate in critical peak pricing (CPP) with a fully-automated response. The 2006 program was in operation during the entire six-month CPP period from May through October. The methodology for this field study included site recruitment, control strategy development, automation system deployment, and evaluation of sites' participation in actual CPP events through the summer of 2006. LBNL recruited sites in PG&E's territory in northern California through contacts from PG&E account managers, conferences, and industry meetings. Each site contact signed a memorandum of understanding with LBNL that outlined the activities needed to participate in the Auto-CPP program. Each facility worked with LBNL to select and implement control strategies for demand response and developed automation system designs based on existing Internet connectivity and building control systems. Once the automation systems were installed, LBNL conducted communications tests to ensure that the Demand Response Automation Server (DRAS) correctly provided and logged the continuous communications of the CPP signals with the energy management and control system (EMCS) for each site. LBNL also observed and evaluated Demand Response (DR) shed strategies to ensure proper commissioning of controls. The communication system allowed sites to receive day-ahead as well as day-of signals for pre-cooling, a DR strategy used at a few sites. Measurement of demand response was conducted using two different baseline models for estimating peak load savings. One was the CPP
A Multinational Study of Thromboprophylaxis Practice in Critically Ill Children*
Faustino, Edward Vincent S.; Hanson, Sheila; Spinella, Philip C.; Tucci, Marisa; O'Brien, Sarah H.; Nunez, Antonio Rodriguez; Yung, Michael; Truemper, Edward; Qin, Li; Li, Simon; Marohn, Kimberly; Randolph, Adrienne G.
2015-01-01
Objectives Although critically ill children are at increased risk for developing deep venous thrombosis, there are few pediatric studies establishing the prevalence of thrombosis or the efficacy of thromboprophylaxis. We tested the hypothesis that thromboprophylaxis is infrequently used in critically ill children even for those in whom it is indicated. Design Prospective multinational cross-sectional study over four study dates in 2012. Setting Fifty-nine PICUs in Australia, Canada, New Zealand, Portugal, Singapore, Spain, and the United States. Patients All patients less than 18 years old in the PICU during the study dates and times were included in the study, unless the patients were 1) boarding in the unit waiting for a bed outside the PICU or 2) receiving therapeutic anticoagulation. Interventions None. Measurements and Main Results Of 2,484 children in the study, 2,159 (86.9%) had greater than or equal to 1 risk factor for thrombosis. Only 308 children (12.4%) were receiving pharmacologic thromboprophylaxis (e.g., aspirin, low-molecular-weight heparin, or unfractionated heparin). Of 430 children indicated to receive pharmacologic thromboprophylaxis based on consensus recommendations, only 149 (34.7%) were receiving it. Mechanical thromboprophylaxis was used in 156 of 655 children (23.8%) 8 years old or older, the youngest age for that device. Using nonlinear mixed effects model, presence of cyanotic congenital heart disease (odds ratio, 7.35; p < 0.001) and spinal cord injury (odds ratio, 8.85; p = 0.008) strongly predicted the use of pharmacologic and mechanical thromboprophylaxis, respectively. Conclusions Thromboprophylaxis is infrequently used in critically ill children. This is true even for children at high risk of thrombosis where consensus guidelines recommend pharmacologic thromboprophylaxis. PMID:24351371
ERIC Educational Resources Information Center
Renn, Peter C.
2012-01-01
This study was conducted to investigate the effects of critical reflection and field experiences on pre-service teachers' beliefs about diversity. A convenience sample of 64 students enrolled in two sections of an education course at a Midwestern university participated in the study. Participants in the intervention group completed field…
NASA Astrophysics Data System (ADS)
Arias, F. J.
2010-04-01
The effect of a magnetic field on critical heat flux-CHF in liquids metal is discussed within framework of Helmholtz instabilities. Utilizing a classical simplified model and considering the effect of magnetic field, an analytical expression for the critical heat flux-CHF was derived. Combining this equation with the expression for the heat transfer coefficients deduced in previous work yields an analytical equation for the temperature difference at the minimum. The above equations to predict an enhancement for critical heat flux which is reasonable due to stabilizer effect of magnetic field, however, disagree with the available experimental measurements made on mercury where a indication of the premature onset of critical heat flux with a horizontal magnetic field was observed. Therefore, the reason for this is not clear and the behavior of the CHF in the same manner that the bubble frequency is still unresolved.
Soil Production and Transport Perspectives on Critical Zone Studies
NASA Astrophysics Data System (ADS)
Heimsath, A. M.; Foster, M.; Whipple, K. X.
2015-12-01
Quantifying soil production and transport rates and processes is a key aspect of most critical zone studies. Methodologies range from relatively straightforward, low cost studies like sediment traps and basin volume estimates to sophisticated and expensive studies using chemical and physical tracers and isotope geochemistry. Inherent in all methodologies are assumptions and simplifications that enable any measurement to be translated to a rate and interpreted in terms of process mechanics. For example, quantifying soil production using in situ cosmogenic nuclides measured in the parent material beneath an upland mobile regolith mantle depends on assuming a locally steady state soil thickness (i.e. neither thinning or thickening with time). Similarly, utilizing hillslope-scale sediment traps or landscape-scale basin analyses depends on assumptions of steady state processes and constraining the timescales represented by the captured sediment. As our analyses of landscapes have expanded into the details of how spatial and temporal gradients of all driving variables (lithology, climate, tectonics, distribution of biota, etc.) influence landscape evolution, our adherence to the assumptions and simplifications necessitated by our methods becomes questionable. Here we provide content analyses of recent and ongoing studies quantifying soil production and transport processes across a range of climatic, geologic and tectonic regimes. We code the studies for their inclusion and use of assumptions and simplifications necessary to ensure that the methodologies apply to their intended use. These analyses provide an important perspective on the use of quantitative methods and offer both a complimentary and cautionary views on critical zone studies in general.
ERIC Educational Resources Information Center
Valenzuela, Jorge; Nieto, Ana M.; Saiz, Carlos
2011-01-01
Introduction: The present work reports the characteristics of an instrument measuring the degree of motivation that people possess to think critically. The "Critical Thinking Motivation Scales" ("CTMS") is based on a theoretical option that affords precedence to the perspective of motivation for over the perspective of dispositions. Motivation is…
ERIC Educational Resources Information Center
Simon, Roger I.; And Others
Through discussions of teaching practice and actual lesson suggestions, this book clarifies how the viewpoint of critical pedagogy can be used to develop a clear and principled practice of work education. The introduction provides a brief discussion of how critical pedagogy is understood and how it relates to work education. Chapter 1 situates the…
Gapud, Albert Agcaoili; Feenstra, Roeland; Christen, David K; Thompson, James R; Holesinger, T. G.
2005-01-01
Several applications of high-temperature super-conducting wire require high currents at intermediate magnetic fields B and over a range of orientations; however, such conditions are at present achievable only at low temperatures (-30 K). The goal of this study is to determine the feasibility of higher operating temperatures for these applications by investigating temperature dependent, low- and high-field pinning properties of YBCO coated conductor samples. The YBCO films were grown on RABiTS templates by a PVD ex situ BaF{sub 2} process. Variations in pinning properties were induced by introducing excess yttrium (Y) in the precursor and controllably increasing the growth rate. The main result is a more uniform dependence of J{sub c} over all orientations of B, along with high irreversibility field B{sub irr} and high critical current densities J{sub c}. Results also show that for films with various pinning properties and processed under different conditions the self-field J{sub c} at 77 K is an effective indicator of performance in the temperatures and fields of interest.
NASA Astrophysics Data System (ADS)
Kalai Selvan, Ganesan; Singh Thakur, Gohil; Manikandan, Krishnan; Uwatoko, Yoshia; Haque, Zeba; Gupta, Laxmi Chand; Ganguli, Ashok Kumar; Arumugam, Sonachalam
2015-12-01
Critical current density (Jc), thermal activation energy (U0), and upper critical field (Hc2) of La1-xSmxO0.5F0.5BiS2 (x = 0.2, 0.8) superconductors are investigated from magnetic field dependent ρ(T) studies. The estimated upper critical field (Hc2) has low values of 1.04 T for x = 0.2 and 1.41 T for x = 0.8. These values are lower than Sm free LaO0.5F0.5BiS2 superconductor (1.9 T). The critical current density (Jc) is estimated to be 1.35 × 105 and 5.07 × 105 A/cm2 (2 K) for x = 0.2 and 0.8 respectively, using the Bean's model. The thermal activation energy (U0/kB) is 61 K for x = 0.2 and 140 K for x = 0.8 as calculated from Arrhenius plots at low magnetic field (1 T) and indicates a strong flux pinning potential which might be co-existing with applied magnetic field.
Critical care physician cognitive task analysis: an exploratory study
Fackler, James C; Watts, Charles; Grome, Anna; Miller, Thomas; Crandall, Beth; Pronovost, Peter
2009-01-01
Introduction For better or worse, the imposition of work-hour limitations on house-staff has imperiled continuity and/or improved decision-making. Regardless, the workflow of every physician team in every academic medical centre has been irrevocably altered. We explored the use of cognitive task analysis (CTA) techniques, most commonly used in other high-stress and time-sensitive environments, to analyse key cognitive activities in critical care medicine. The study objective was to assess the usefulness of CTA as an analytical tool in order that physician cognitive tasks may be understood and redistributed within the work-hour limited medical decision-making teams. Methods After approval from each Institutional Review Board, two intensive care units (ICUs) within major university teaching hospitals served as data collection sites for CTA observations and interviews of critical care providers. Results Five broad categories of cognitive activities were identified: pattern recognition; uncertainty management; strategic vs. tactical thinking; team coordination and maintenance of common ground; and creation and transfer of meaning through stories. Conclusions CTA within the framework of Naturalistic Decision Making is a useful tool to understand the critical care process of decision-making and communication. The separation of strategic and tactical thinking has implications for workflow redesign. Given the global push for work-hour limitations, such workflow redesign is occurring. Further work with CTA techniques will provide important insights toward rational, rather than random, workflow changes. PMID:19265517
Field-line Torsion (FLT) / (SOC) Self-Organized Criticality Correspondence and Duality
NASA Astrophysics Data System (ADS)
Bekhor, S. H.
2008-12-01
Magnetic potential energy is stored when an incident disturbance such as the propagating solar wind interacts with the undisturbed magnetosphere resulting in the twisting and bending of the Earth's magnetic field. The energy that is stored in turn becomes a reservoir for dissipative wave interactions and instabilities that ultimately result in auroral phenomena that are observed on Earth. The topological structure of the Earth's magnetic field can provide clues about the timing and intensity of these events even during relatively quiescent periods. In particular, the presence of magnetic field-line torsion (FLT), a putative signature of magnetic storms and sub-storms, results in an increase in the fundamental standing Alfvén wave (SAW) field-line resonance (FLR) frequencies corresponding to a particular Alfvén speed profile. These frequencies can be dynamically calculated in an arbitrary boundary-constrained non-orthogonal geomagnetic flux coordinate (GFC) system in conjunction with chronological magnetic field data, provided by magnetospheric models such as BATSRUS and Tsyganenko (T05). A comparison of these frequencies to those computed in a purely meridional geometry yields a parameter that is useful in forecasting the triggering and evolution of ionospheric phenomena, such as the formation of localized auroral density cavities, which interact with lower and upper hybrid waves or Z modes resulting in mode conversion processes that lead to the formation of discrete auroral arcs via an escaping electromagnetic mode. There is strong evidence that this evolution describes a dynamical self-organized critical (SOC) phase transition due to an abrupt change in the pressure distribution in the near-Earth plasma sheet and the intrusion of convective flows into the inner magnetosphere.
Critical Pertussis Illness in Children, A Multicenter Prospective Cohort Study
Berger, John T.; Carcillo, Joseph A.; Shanley, Thomas P.; Wessel, David L.; Clark, Amy; Holubkov, Richard; Meert, Kathleen L.; Newth, Christopher J.L.; Berg, Robert A.; Heidemann, Sabrina; Harrison, Rick; Pollack, Murray; Dalton, Heidi; Harvill, Eric; Karanikas, Alexia; Liu, Teresa; Burr, Jeri S.; Doctor, Allan; Dean, J. Michael; Jenkins, Tammara L.; Nicholson, Carol E.
2013-01-01
Objective Pertussis persists in the United States despite high immunization rates. The present report characterizes the presentation and acute course of critical pertussis by quantifying demographic data, laboratory findings, clinical complications, and critical care therapies required among children requiring admission to the pediatric intensive care unit (PICU). Design Prospective cohort study. Setting Eight PICUs comprising the Eunice Kennedy Shriver National Institute for Child Health and Human Development Collaborative Pediatric Critical Care Research Network and 17 additional PICUs across the United States. Patients Eligible patients had laboratory confirmation of pertussis infection, were < 18 years of age, and died in the PICU or were admitted to the PICU for at least 24 hours between June 2008 and August 2011. Interventions None. Measurements and Main Results 127 patients were identified. Median age was 49 days, and 105 (83%) patients were < 3 months of age. Fifty-five (43%) required mechanical ventilation. Twelve (9.4%) died during initial hospitalization. Pulmonary hypertension was found in 16 patients (12.5%), and was present in 75% of patients who died, compared with 6% of survivors (p< 0.001). Median white blood cell count (WBC) was significantly higher in those requiring mechanical ventilation (p<0.001), those with pulmonary hypertension (p<0.001) and non-survivors (p<0.001). Age, sex and immunization status did not differ between survivors and non-survivors. Fourteen patients received leukoreduction therapy (exchange transfusion (12), leukopheresis (1) or both (1)). Survival benefit was not apparent. Conclusions Pulmonary hypertension may be associated with mortality in pertussis critical illness. Elevated WBC is associated with the need for mechanical ventilation, pulmonary hypertension, and mortality risk. Research is indicated to elucidate how pulmonary hypertension, immune responsiveness, and elevated WBC contribute to morbidity and mortality
NASA Technical Reports Server (NTRS)
Subramanyam, Guru; VanKeuls, Fred W.; Miranda, Felix A.; Canedy, Chadwick L.; Aggarwal, Sanjeev; Venkatesan, Thirumalai; Ramesh, Ramamoorthy
2000-01-01
The correlation of electric field and critical design parameters such as the insertion loss, frequency ability return loss, and bandwidth of conductor/ferroelectric/dielectric microstrip tunable K-band microwave filters is discussed in this work. This work is based primarily on barium strontium titanate (BSTO) ferroelectric thin film based tunable microstrip filters for room temperature applications. Two new parameters which we believe will simplify the evaluation of ferroelectric thin films for tunable microwave filters, are defined. The first of these, called the sensitivity parameter, is defined as the incremental change in center frequency with incremental change in maximum applied electric field (EPEAK) in the filter. The other, the loss parameter, is defined as the incremental or decremental change in insertion loss of the filter with incremental change in maximum applied electric field. At room temperature, the Au/BSTO/LAO microstrip filters exhibited a sensitivity parameter value between 15 and 5 MHz/cm/kV. The loss parameter varied for different bias configurations used for electrically tuning the filter. The loss parameter varied from 0.05 to 0.01 dB/cm/kV at room temperature.
Field and temperature scaling of the critical current density in commercial REBCO coated conductors
NASA Astrophysics Data System (ADS)
Senatore, Carmine; Barth, Christian; Bonura, Marco; Kulich, Miloslav; Mondonico, Giorgio
2016-01-01
Scaling relations describing the electromagnetic behaviour of coated conductors (CCs) greatly simplify the design of REBCO-based devices. The performance of REBCO CCs is strongly influenced by fabrication route, conductor architecture and materials, and these parameters vary from one manufacturer another. In the present work we have examined the critical surface for the current density, J c(T, B, θ), of coated conductors from six different manufacturers: American Superconductor Co. (US), Bruker HTS GmbH (Germany), Fujikura Ltd (Japan), SuNAM Co. Ltd (Korea), SuperOx ZAO (Russia) and SuperPower Inc. (US). Electrical transport and magnetic measurements were performed at temperatures between 4.2 K and 77 K and in magnetic fields of up to 19 T. Experiments were conducted at three different orientations of the field with respect to the crystallographic c-axis of the REBCO layer, θ = 0°, 45° and 90°, in order to probe the angular anisotropy of J c. In spite of the large variability of the CCs’ performance, we show here that field and temperature dependences of J c at a given angle can be reproduced over wide ranges using a scaling relation based only on three parameters. Furthermore, we present and validate a new approach combining magnetic and transport measurements for the determination of the scaling parameters with minimal experimental effort.
Mentoring Field Directors: A National Exploratory Study
ERIC Educational Resources Information Center
Ellison, Martha L.; Raskin, Miriam S.
2014-01-01
In social work field education, mentoring is underused and lacks research data. There is a paucity of research that examines the effect mentoring has on social work field directors who administer field programs at the undergraduate and/or graduate level. This exploratory study fills this void by examining the mentoring opportunities and…
Recent biophysical studies in high magnetic fields
NASA Astrophysics Data System (ADS)
Maret, Georg
1990-06-01
A brief overview of biophysical effects of steady magnetic fields is given. The need of high field strength is illustrated by several recent diamagnetic orientation experiments. They include rod-like viruses, purple membranes and chromosomes. Results of various studies on bees, quails, rats and pigeons exposed to fields above 7 T are also resumed.
[Economic evaluation studies in diagnostic imaging: justification and critical reading].
Rueda Martínez de Santos, J R
2015-11-01
First, this article describes the concepts and tools most widely used for economic evaluation in healthcare. Second, it discusses some elements that must be taken into account in the social decision about how much we are willing to spend to prolong a person's life by one year. Third, it describes the criteria recommended for the critical analysis of publications that evaluate the economic aspects of health interventions. Finally, several studies about ultrasound screening for aneurysms of the abdominal aorta are used as illustrative examples to show how these elements and criteria can be applied. PMID:26563613
Critical Behavior of K1-xLixTaO3 with the Tri-Critical Concentration of Li under an Electric Field
NASA Astrophysics Data System (ADS)
Yokota, Hiroko; Uesu, Yoshiaki
2008-02-01
Temperature dependences of the optical second harmonic generation in Li-doped KTaO3 (KLT) with different Li concentrations x are measured to determine the coefficients in the Landau-Devonshire free energy function. The result specifies the tri-critical Li concentration xc. Temperature dependences of the dielectric constant of KLT with Li concentrations nearly located at xc are also measured under dc bias fields and the result suggests that these compounds lie in close vicinity of the line of critical end points. The tertiary phase diagram (T, x, E) of KLT is disclosed from the experiments.
On some p-Laplacian equation with electromagnetic fields and critical nonlinearity in ℝN
NASA Astrophysics Data System (ADS)
Liang, Sihua; Zhang, Jihui
2015-04-01
In this paper, we consider the existence and multiplicity of solutions for p-Laplacian equation with electromagnetic fields and critical nonlinearity in ℝN: - ɛ p Δ p , A u + V ( x ) |u| p - 2 u = |u| p* - 2 u + h ( x , |u| p ) |u| p - 2 u for x ∈ ℝN, where Δ p , A u ( x ) ≔ div ( |u ∇ u + i A ( x ) u | p - 2 ( ∇ u + i A ( x ) u ) . By using Lions' second concentration compactness principle and concentration compactness principle at infinity to prove that the (PS)c condition holds locally and by variational method, we show that this equation has at least one solution provided that ɛ < E , for any m ∈ ℕ, it has m pairs of solutions if ɛ < E m , where E and E m are sufficiently small positive numbers.