Electron Spin Resonance Above Tc In Layered Manganites

We have performed electron spin resonance (ESR) and dc magnetization measurements on single crystals of La2(1-x)Sr1+2xMn2O7 up to 800 K with special emphasis on the x = 0.4 composition. The ESR linewidth shows behavior similar to that observed in the three-dimensional perovskites and above ∼500 K can be described by a universal expression ΔHpp(T)=[C/Tχ(T)]ΔHpp (∞). The linewidth and the resonance field become anisotropic below ∼500 K. The anisotropy in the resonance field is proportional to the magnetization M, and we concluded that it is intrinsic to the system. We show that demagnetization effects can explain only part of the anisotropy. The remainder arises from short-range uniaxial terms in the Hamiltonian that are associated with the crystal field and Dzialozhinsky-Moriya interactions. The anisotropy in the linewidth is attributed to the easy-plane ferromagnetic ordering, which also arises from the short-range anisotropy.631717441311744136Ruddlesden, S.N., Popper, P., (1958) Acta Crystallogr., 11, p. 54Moritomo, Y., Asamitsu, A., Kuwahara, H., Tokura, Y., (1996) Nature (London), 380, p. 141Causa, M.T., Tovar, M., Caneiro, A., Prado, F., Ibanez, G., Ramos, C.A., Butera, A., Oseroff, S.B., (1998) Phys. Rev. B, 58, p. 3233Causa, M.T., Alejandro, G., Tovar, M., Pagliuso, P.G., Rettori, C., Oseroff, S.B., Subramanian, M.A., (1999) J. Appl. Phys., 85, p. 5408Huber, D.L., Alejandro, G., Caneiro, A., Causa, M.T., Prado, F., Tovar, M., Oseroff, S.B., (1999) Phys. Rev. B, 60, p. 12155Oseroff, S.B., Moreno, N.O., Pagliuso, P.G., Rettori, C., Huber, D.L., Gardner, J.S., Sarrao, J.L., Alascio, B.R., (2000) J. Appl. Phys., 87, p. 5810Seehra, M.S., Ibrahim, M.M., Babu, V.S., Srinivasan, G., (1996) J. Phys.: Condens. Matter, 8, p. 11283Dominguez, M., Lofland, S.E., Bhagat, S.M., Raychaudhuri, A.K., Ju, H.L., Venkates, T., Greene, R.L., (1996) Solid State Commun., 97, p. 193Lofland, S.E., Kim, P., Dahiroc, P., Bhagat, S.M., Tyagi, S.D., Karabashev, S.G., Shultyatev, D.A., Mukovskii, Y., (1997) Phys. Lett. A, 233, p. 476Kimura, T., Tomioka, Y., Kuwahara, H., Asamitsu, A., Tamura, M., Tokura, Y., (1996) Science, 274, p. 1698Perring, T.G., Aeppli, G., Moritomo, Y., Tokura, Y., (1997) Phys. Rev. Lett., 78, p. 3197Zhou, J.-S., Goodenough, J.B., Mitchell, J.F., (1998) Phys. Rev. B, 58, p. 579Zhou, J.-S., Goodenough, J.B., (1998) Phys. Rev. Lett., 80, p. 2665Kelley, T.M., Argyriou, D.N., Robinson, R.A., Nakotte, H., Mitchell, J.F., Osbron, R., Jorgensen, J.D., (1998) Physica B, 241-243, p. 439Heffner, R.H., MacLaughlin, D.E., Nieuwenhuys, G.J., Kimura, T., Luke, G.M., Tokura, Y., Uemura, Y.J., (1998) Phys. Rev. Lett., 81, p. 1706Potter, C.D., Swiatek, M., Bader, S.D., Argyriou, D.N., Mitchell, J.F., Miller, D.J., Hinks, D.G., Jorgensen, J.D., (1998) Phys. Rev. B, 57, p. 72Chauvet, O., Goglio, G., Molinie, P., Corraze, B., Brohan, L., (1998) Phys. Rev. Lett., 81, p. 1102Hirota, K., Moritomo, Y., Fujioka, H., Kubota, M., Yoshizawa, H., Endoh, Y., (1998) J. Phys. Soc. Jpn., 67, p. 3380Li, J.Q., Matsui, Y., Kimura, T., Tokura, Y., (1998) Phys. Rev. B, 57, pp. R3205Kimura, T., Kumai, R., Tokura, Y., Li, J.Q., Matsui, Y., (1998) Phys. Rev. B, 58, p. 11081Hayashi, T., Miura, N., Tokunaga, M., Kimura, T., Tokura, Y., (1998) J. Phys.: Condens. Matter, 10, p. 11525Suryanarayanan, R., Dhalenne, G., Revcolevschi, A., Prellier, W., Renard, J.P., Dupas, C., Caliebe, W., Chatterji, T., (2000) Solid State Commun., 113, p. 267Kubota, M., Fujioka, H., Ohoyama, K., Hirota, K., Moritomo, Y., Yoshizawa, H., Endoh, Y., (1999) J. Phys. Chem. Solids, 60, p. 116Bhagat, S.M., Lofland, S.E., Mitchell, J.F., (1999) Phys. Lett. A, 259, p. 326Kittel, C., (1997) Introduction to Solid State Physics, , Wiley, New YorkOkochi, M., (1970) J. Phys. Soc. Jpn., 28, p. 897Victoria, C., Barker, R.C., Yelon, A., (1967) Phys. Rev. Lett., 19, p. 792Nagata, K., (1976) J. Phys. Soc. Jpn., 40, p. 1209Nagata, K., Yamamoto, I., Takano, H., Yokozawa, Y., (1977) J. Phys. Soc. Jpn., 43, p. 857. , and references thereinHuber, D.L., Seehra, M.S., (1976) Phys. Status Solidi B, 74, p. 145Stanger, J.-L., Andre, J.-J., Turek, P., Hosokoshi, Y., Tamura, M., Kinoshita, M., Rey, P., Veciana, J., (1997) Phys. Rev. B, 55, p. 8398Van Vleck, J.H., (1950) Phys. Rev., 78, p. 266Kittel, C., (1948) Phys. Rev., 73, p. 15

Boundary value problems for the stationary axisymmetric Einstein equations: a disk rotating around a black hole

We solve a class of boundary value problems for the stationary axisymmetric Einstein equations corresponding to a disk of dust rotating uniformly around a central black hole. The solutions are given explicitly in terms of theta functions on a family of hyperelliptic Riemann surfaces of genus 4. In the absence of a disk, they reduce to the Kerr black hole. In the absence of a black hole, they reduce to the Neugebauer-Meinel disk.Comment: 46 page

Magnetic Structure Of Cerhin5 As A Function Of Pressure And Temperature

We report magnetic neutron-diffraction and electrical resistivity studies on single crystals of the heavy-fermion antiferromagnet CeRhIn5 at pressures up to 2.3 GPa. These experiments show that the staggered moment of Ce and the incommensurate magnetic structure change weakly with applied pressure up to 1.63 GPa, where resistivity, specific heat and nuclear quadrupole resonance measurements confirm the presence of bulk superconductivity. This work places important constraints on an interpretation of the relationship between antiferromagnetism and unconventional superconductivity in CeRhIn 5.692244031244036Heffner, R.H., Norman, M.R., (1996) Comments Condens. Matter Phys., 17, p. 361Stewart, G.R., (2001) Rev. Mod. 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Cosmological Variation of the Fine Structure Constant from an Ultra-Light Scalar Field: The Effects of Mass

Cosmological variation of the fine structure constant $\alpha$ due to the evolution of a spatially homogeneous ultra-light scalar field ($m \sim H_0$) during the matter and $\Lambda$ dominated eras is analyzed. Agreement of $\Delta \alpha/\alpha$ with the value suggested by recent observations of quasar absorption lines is obtained by adjusting a single parameter, the coupling of the scalar field to matter. Asymptotically $\alpha(t)$ in this model goes to a constant value $\bar{\alpha} \approx \alpha_0$ in the early radiation and the late $\Lambda$ dominated eras. The coupling of the scalar field to (nonrelativistic) matter drives $\alpha$ slightly away from $\bar{\alpha}$ in the epochs when the density of matter is important. Simultaneous agreement with the more restrictive bounds on the variation $|\Delta \alpha/\alpha|$ from the Oklo natural fission reactor and from meteorite samples can be achieved if the mass of the scalar field is on the order of 0.5--0.6 $H_\Lambda$, where $H_\Lambda = \Omega_\Lambda^{1/2} H_0$. Depending on the scalar field mass, $\alpha$ may be slightly smaller or larger than $\alpha_0$ at the times of big bang nucleosynthesis, the emission of the cosmic microwave background, the formation of early solar system meteorites, and the Oklo reactor. The effects on the evolution of $\alpha$ due to nonzero mass for the scalar field are emphasized. An order of magnitude improvement in the laboratory technique could lead to a detection of $(\dot{\alpha}/\alpha)_0$.Comment: 22 pages, 15 figures Version 2: The Oklo event is now considered as localized in time. The initial conditions for the scalar field have been refined. The numbers in the Table have been recomputed. Added Ref

Quasifree kaon-photoproduction from nuclei in a relativistic approach

We compute the recoil polarization of the lambda-hyperon and the photon asymmetry for the quasifree photoproduction of kaons in a relativistic impulse-approximation approach. Our motivation for studying polarization observables is threefold. First, polarization observables are more effective discriminators of subtle dynamics than the unpolarized cross section. Second, earlier nonrelativistic calculations suggest an almost complete insensitivity of polarization observables to distortions effects. Finally, this insensitivity entails an enormous simplification in the theoretical treatment. Indeed, by introducing the notion of a ``bound-nucleon propagator'' we exploit Feynman's trace techniques to develop closed-form, analytic expressions for all photoproduction observables. Moreover, our results indicate that polarization observables are also insensitive to relativistic effects and to the nuclear target. Yet, they are sensitive to the model parameters, making them ideal tools for the study of modifications to the elementary amplitude --- such as in the production, propagation, and decay of nucleon resonances --- in the nuclear medium.Comment: 15 pages and 6 figures - submitted to PR

Isospin-Violating Meson-Nucleon Vertices as an Alternate Mechanism of Charge-Symmetry Breaking

We compute isospin-violating meson-nucleon coupling constants and their consequent charge-symmetry-breaking nucleon-nucleon potentials. The couplings result from evaluating matrix elements of quark currents between nucleon states in a nonrelativistic constituent quark model; the isospin violations arise from the difference in the up and down constituent quark masses. We find, in particular, that isospin violation in the omega-meson--nucleon vertex dominates the class IV CSB potential obtained from these considerations. We evaluate the resulting spin-singlet--triplet mixing angles, the quantities germane to the difference of neutron and proton analyzing powers measured in elastic $\vec{n}-\vec{p}$ scattering, and find them commensurate to those computed originally using the on-shell value of the $\rho$-$\omega$ mixing amplitude. The use of the on-shell $\rho$-$\omega$ mixing amplitude at $q^2=0$ has been called into question; rather, the amplitude is zero in a wide class of models. Our model possesses no contribution from $\rho$-$\omega$ mixing at $q^2=0$, and we find that omega-meson exchange suffices to explain the measured $n-p$ analyzing power difference~at~183 MeV.Comment: 20 pages, revtex, 3 uuencoded PostScript figure

Magnetic structure of CeRhIn_5 as a function of pressure and temperature

We report magnetic neutron-diffraction and electrical resistivity studies on single crystals of the heavy-fermion antiferromagnet CeRhIn$_{5}$ at pressures up to 2.3 GPa. These experiments show that the staggered moment of Ce and the incommensurate magnetic structure change weakly with applied pressure up to 1.63 GPa, where resistivity, specific heat and NQR measurements confirm the presence of bulk superconductivity. This work places new constraints on an interpretation of the relationship between antiferromagnetism and unconventional superconductivity in CeRhIn$_{5}$.Comment: 6 pages, 6 figures, submitted to Phys. Rev.

The power of suggestion: examining the impact of presence or absence of shared first language in the antenatal clinic

© 2019 Foundation for the Sociology of Health & Illness Healthcare encounters involving participants from diverse linguistic backgrounds are becoming more common due to the globalisation of health care and increasing migration levels. Research suggests that this diversity has a significant impact on health outcomes; however less is known about how it is managed in the actual consultation process. This article presents an analysis of antenatal screening consultations video recorded in Hong Kong, using conversation analysis. We consider how the use of a second or subsequent language impacts on these consultations, and on discussions and decisions about further action. The presence or absence of shared first language did not appear to affect the extent to which particular courses of action were promoted or recommended. Recommendations were a common occurrence across consultations with and without shared first language. However, we argue that the routine use of recommendations can be consequential, as second language speakers may have more limited resources to interrogate or contest these. This finding has implications for the ability for professionals to maximise patient involvement in decision-making

Singularly Perturbed Monotone Systems and an Application to Double Phosphorylation Cycles

The theory of monotone dynamical systems has been found very useful in the modeling of some gene, protein, and signaling networks. In monotone systems, every net feedback loop is positive. On the other hand, negative feedback loops are important features of many systems, since they are required for adaptation and precision. This paper shows that, provided that these negative loops act at a comparatively fast time scale, the main dynamical property of (strongly) monotone systems, convergence to steady states, is still valid. An application is worked out to a double-phosphorylation ``futile cycle'' motif which plays a central role in eukaryotic cell signaling.Comment: 21 pages, 3 figures, corrected typos, references remove

Models of quintessence coupled to the electromagnetic field and the cosmological evolution of alpha

We study the change of the effective fine structure constant in the cosmological models of a scalar field with a non-vanishing coupling to the electromagnetic field. Combining cosmological data and terrestrial observations we place empirical constraints on the size of the possible coupling and explore a large class of models that exhibit tracking behavior. The change of the fine structure constant implied by the quasar absorption spectra together with the requirement of tracking behavior impose a lower bound of the size of this coupling. Furthermore, the transition to the quintessence regime implies a narrow window for this coupling around $10^{-5}$ in units of the inverse Planck mass. We also propose a non-minimal coupling between electromagnetism and quintessence which has the effect of leading only to changes of alpha determined from atomic physics phenomena, but leaving no observable consequences through nuclear physics effects. In doing so we are able to reconcile the claimed cosmological evidence for a changing fine structure constant with the tight constraints emerging from the Oklo natural nuclear reactor.Comment: 13 pages, 10 figures, RevTex, new references adde