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Search Results: 1 - 10 of 201045 matches for " P. Atkinson "
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Same formula, different figures: Change and persistence in class inequalities
Sociologia, Problemas e Práticas , 2010,
Abstract: many contemporary social theorists have argued that the social changes of the last few decades have shattered the hold of class over life histories, identities and politics and put in its place reflexive choice and individualism. this paper presents a summary of a recently completed research project in the uk designed to put these claims to the test. starting out from a “phenomeno-bourdieusian” model of class and deploying life history interviews it reveals not the decline of class in advanced capitalism, but its reinvention. new practices and pathways have emerged, but they represent only the shifting substance of class - the underlying structure of relational difference that defines class and produces different outcomes remains as patent as ever.
Chiral Symmetry Breaking with the Curtis-Pennington Vertex
D. Atkinson,V. P. Gusynin,P. Maris
Physics , 1992, DOI: 10.1016/0370-2693(93)90061-L
Abstract: We study chiral symmetry breaking in quenched QED$_4$, using a vertex Ansatz recently proposed by Curtis and Pennington. Bifurcation analysis is employed to establish the existence of a critical coupling and to estimate its value. The main results are in qualitative agreement with the ladder approximation, the numerical changes being minor.
Longitudinal dispersion in natural channels: 3. An aggregated dead zone model applied to the River Severn, U.K.
P. M. Davis,T. C. Atkinson
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2000,
Abstract: An Aggregated Dead Zone (ADZ) model is presented for longitudinal dispersion of tracer in river channels, in which the channel cross-section is divided into two parallel regions: the bulk flow and dead zone storage. Tracer particles in the bulk flow are assumed to obey plug-flow advection at the discharge velocity U without any mixing effects. The dispersive properties of the model are completely embodied in the residence time for tracer storage in the dead zone. The model provides an excellent description and prediction of empirical concentration-time distributions, for times t < x/U. Its physical realism is demonstrated by using it to describe the evolution of a tracer cloud in the River Severn, U.K., and by comparing it with a more complex model which incorporates the additional effects of shear flow dispersion within the bulk flow. The ADZ model is a potentially useful tool for practical prediction of dispersion in natural channels. Keywords: Channels; dispersion; dead zones; tracers; River Severn
Longitudinal dispersion in natural channels: l. Experimental results from the River Severn, U.K.
T. C. Atkinson,P. M. Davis
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2000,
Abstract: : A tracer experiment using Rhodamine WT dye was carried out to measure longitudinal dispersion in a 14-km reach of the River Severn in Wales, U.K. The river’s discharge was measured at six points and the depth, width and cross-sectional area were measured at 86 points along the test reach. The channel geometry was close to being statistically uniform. Discharge and velocity were both nearly constant. Dye concentrations were recorded at stations between 210 and 13775 m downstream of injection. Dye was injected over a short interval as a near-uniform line source across the channel. These conditions make the data useful for testing mathematical theories of dispersion. They are presented in full. Keywords: Channels; dispersion; tracers; River Severn
Surgical excision of periocular basal cell carcinomas
Taherian K,Shekarchian M,Atkinson P
Indian Journal of Ophthalmology , 2007,
Abstract: The purpose of this study was to determine the histological clearance and clinical recurrence rates following excision of primary periocular biopsy-proven basal cell carcinomas (BCCs) in a teaching hospital in United Kingdom and compare it with other published reports. Records of consecutive patients with a biopsy proven diagnosis of primary periocular BCCs treated surgically at our hospital between 1995 and March 2003 were reviewed. Twenty seven cases (25 patients) were identified. Intra-operative frozen sections (IFS) were performed in 17 (63%) of the cases with clear margins on IFS in 16/17 (94%) of these cases. Histology revealed complete excision in 25/27 (92.5%) of cases. The results of excision of periocular BCCs in our setting particularly with IFS are comparable with other published reports. A reaudit is recommended in 5 years to allow a larger patient population with greater follow up, which would enable us to give more definitive judgment on this treatment modality.
The c axis optical conductivity of layered systems in the superconducting state
W. A. Atkinson,J. P. Carbotte
Physics , 1997, DOI: 10.1103/PhysRevB.55.12748
Abstract: In this paper, we discuss the c axis optical conductivity Re [sigma_c(omega)] in the high T_c superconductors, in the superconducting state. The basic premise of this work is that electrons travelling along the c axis between adjacent CuO_2 layers must pass through several intervening layers. In earlier work we found that, for weak inter-layer coupling, it is preferable for electrons to travel along the c axis by making a series of interband transitions rather than to stay within a single (and very narrow) band. Moreover, we found that many of the properties of the normal state optical conductivity, including the pseudogap could be explained by interband transitions. In this work we examine the effect of superconductivity on the interband conductivity. We find that, while the onset of superconductivity is clearly evident in the spectrum, there is no clear signature of the symmetry of the superconducting order parameter.
Effect of Proximity Coupling of Chains and Planes on the Penetration Depth Anisotropy in Y_1Ba_2Cu_3O_7
W. A. Atkinson,J. P. Carbotte
Physics , 1995, DOI: 10.1103/PhysRevB.52.10601
Abstract: We calculate the penetration depth $\lambda$ in the $a$, $b$ and $c$ directions for a simple model of YBa$_2$Cu$_3$O$_7$. In this model there are two layers---representing a CuO$_2$ plane and a CuO chain---per unit cell. There is a BCS--like pairing (both $s$ wave and $d$ wave are considered) interaction localised in the CuO$_2$ planes. The CuO chains become superconducting at temperatures lower than $T_c$ because of their proximity to the planes, and there is an induced gap in the chains. Since the temperature dependence of the penetration depth in the $b$ direction (along the chains) is sensitive to the size of the induced gap, the difference between the shapes of the penetration depth curves in the $a$ and $b$ directions reveals a great deal about the nature of the condensate in the chains. We find that in our proximity model there are always regions of the chain Fermi surface on which the induced gap is much smaller than $T_c$, so that the temperature dependence of $\lambda_b$ is always different than that of $\lambda_a$. Experimental observations of the of the $ab$ anisotropy show nearly identical temperature dependences. The main result of our paper, then, is that a simple proximity model in which the pairing interaction is localized to the planes, and the planes are coherently coupled to the chains cannot account for the superfluid on the chains.
Critical Josephson Current in a Model Pb/YBa_2Cu_3O_7 Junction
W. A. Atkinson,J. P. Carbotte
Physics , 1995, DOI: 10.1103/PhysRevB.52.6894
Abstract: In this article we consider a simple model for a c--axis Pb/YBa_2Cu_3O_{7-\delta} Josephson junction. The observation of a nonzero current in such a junction by Sun et al. [A. G. Sun, D. A. Gajewski, M. B. Maple, R. C. Dynes, Phys. Rev. Lett. 72, 2267 (1994)] has been taken as evidence against d--wave superconductivity in YBa_2Cu_3O_{7-\delta}. We suggest, however, that the pairing interaction in the CuO_2 planes may well be d--wave but that the CuO chains destroy the tetragonal symmetry of the system. We examine two ways in which this happens. In a simple model of an incoherent junction, the chains distort the superconducting condensate away from d_{x^2-y^2} symmetry. In a specular junction the chains destroy the tetragonal symmetry of the tunneling matrix element. In either case, the loss of tetragonal symmetry results in a finite Josephson current. Our calculated values of the critical current for specular junctions are in good agreement with the results of Sun and co-workers.
Interband effects in the c-axis optical conductivity in YBaCuO
W. A. Atkinson,J. P. Carbotte
Physics , 1996, DOI: 10.1103/PhysRevB.55.3230
Abstract: The normal state optical conductivity is calculated for a layered metal with two layers per unit cell coupled through a transverse hopping matrix element $t_\perp$. The optical response involves an interband term in addition to the more familiar intraband term which leads to the usual Drude form. The interband term is only weakly temperature dependent, even for an inelastic scattering rate which is linear in T. It gives a $c$-axis response which extends in frequency over the entire band width although there can be structure on this energy scale which reflects details of the electronic structure. In particular, at low energy, the $c$-axis response can develop a gap or pseudogap as the temperature is lowered. At high temperature, a Drude response will be seen only if the intraband transitions, which are of order $t_\perp^4$, become important compared with the interband transitions which are of order $t_\perp^2$.
Density of states of a layered S/N d-wave superconductor
W. A. Atkinson,J. P. Carbotte
Physics , 1994, DOI: 10.1103/PhysRevB.51.1161
Abstract: We calculate the density of states of a layered superconductor in which there are two layers per unit cell. One of the layers contains a d-wave pairing interaction while the other is a normal metal. The goal of this article is to understand how the d-wave behaviour of the system is modified by the coupling between the layer-types. This coupling takes the form of coherent, single particle tunneling along the c-axis. We find that there are two physically different limits of behaviour, which depend on the relative locations of the Fermi surfaces of the two layer-types. We also discuss the interference between the interlayer coupling and pairing interaction and we find that this interference leads to features in the density of states.
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