21 research outputs found
Interplay of quantum magnetic and potential scattering around Zn or Ni impurity ions in superconducting cuprates
To describe the scattering of superconducting quasiparticles from
non-magnetic (Zn) or magnetic (Ni) impurities in optimally doped high T
cuprates, we propose an effective Anderson model Hamiltonian of a localized
electron hybridizing with -wave BCS type superconducting
quasiparticles with an attractive scalar potential at the impurity site. Due to
the strong local antiferromagnetic couplings between the original Cu ions and
their nearest neighbors, the localized electron in the Ni-doped materials is
assumed to be on the impurity sites, while in the Zn-doped materials the
localized electron is distributed over the four nearest neighbor sites of the
impurities with a dominant symmetric form of the wave function.
With Ni impurities, two resonant states are formed above the Fermi level in the
local density of states at the impurity site, while for Zn impurities a sharp
resonant peak below the Fermi level dominates in the local density of states at
the Zn site, accompanied by a small and broad resonant state above the Fermi
level mainly induced by the potential scattering. In both cases, there are no
Kondo screening effects. The local density of states and their spatial
distribution at the dominant resonant energy around the substituted impurities
are calculated for both cases, and they are in good agreement with the
experimental results of scanning tunneling microscopy in
BiSrCaCuO with Zn or Ni impurities, respectively.Comment: 24 pages, Revtex, 8 figures, submitted to Physical Review B for
publication. Sub-ject Class: Superconductivity; Strongly Correlated Electron
Critical properties of the Fermi-Bose Kondo and pseudogap Kondo models: Renormalized perturbation theory
Magnetic impurities coupled to both fermionic and bosonic baths or to a
fermionic bath with pseudogap density of states, described by the Fermi-Bose
Kondo and pseudogap Kondo models, display non-trivial intermediate coupling
fixed points associated with critical local-moment fluctuations and local
non-Fermi liquid behavior. Based on renormalization group together with a
renormalized perturbation expansion around the free-impurity limit, we
calculate various impurity properties in the vicinity of those
intermediate-coupling fixed points. In particular, we compute the conduction
electron T matrix, the impurity susceptibility, and the residual impurity
entropy, and relate our findings to certain scenarios of local quantum
criticality in strongly correlated lattice models.Comment: 16 pages, 5 figs; (v2) large-N results for entropy of Bose-Kondo
model added; (v3) final version as publishe
FORUM: âThat donât look like me.â Stereotypic images of science: Where do they come from and what can we do with them?
The influence of germinating seeds and developing roots on re-establishment of micro-organisms in fumigated soil
Physiological races and vegetative compatibility groups within Fusarium oxysporum f.sp. gladioli
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Complex spatiotemporal haemodynamic response following sensory stimulation in the awake rat
Detailed understanding of the haemodynamic changes that underlie non-invasive neuroimaging techniques such as blood oxygen level dependent functional magnetic resonance imaging is essential if we are to continue to extend the use of these methods for understanding brain function and dysfunction. The use of animal and in particular rodent research models has been central to these endeavours as they allow in-vivo experimental techniques that provide measurements of the haemodynamic response function at high temporal and spatial resolution. A limitation of most of this research is the use of anaesthetic agents which may disrupt or mask important features of neurovascular coupling or the haemodynamic response function. In this study we therefore measured spatiotemporal cortical haemodynamic responses to somatosensory stimulation in awake rats using optical imaging spectroscopy. Trained, restrained animals received non-noxious stimulation of the whisker pad via chronically implanted stimulating microwires whilst optical recordings were made from the contralateral somatosensory cortex through a thin cranial window. The responses we measure from un-anaesthetised animals are substantially different from those reported in previous studies which have used anaesthetised animals. These differences include biphasic response regions (initial increases in blood volume and oxygenation followed by subsequent decreases) as well as oscillations in the response time series of awake animals. These haemodynamic response features do not reflect concomitant changes in the underlying neuronal activity and therefore reflect neurovascular or cerebrovascular processes. These hitherto unreported hyperemic response dynamics may have important implications for the use of anaesthetised animal models for research into the haemodynamic response function
Operation for Cataract: Closure of the Wound. Frequency of Complications with Different Methods of Extraction
A genealogy of calculations at an early Queensland sugar mill
This study of a unique historic situation is sociologically framed and politically contextualized. It examines the technical and persuasive rhetorical dimensions of calculations employed at a nineteenth-century Queensland sugar plantation and mill in relation to the employment of indentured labour. Historical archival data is interpreted through the lens of the rhetoric of rationality. Queensland legislation permitted the employment of indentured Pacific islanders to assist in the development of its sugar industry. Accounting practices employed at the Colonial Sugar Refinery (CSR) Companyâs Goondi Plantation and Mill focused on recording and controlling labour costs to maximize profits and maintain a healthy dividend to shareholders. The use of this single perspective, while it provides a restricted interpretation of events, nevertheless enables some unique insights about the practice of accounting in this historic context