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  • 1
    ISSN: 1432-8798
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Rotaviruses were isolated from Australian farm animals (calf, pig and foal) with diarrhoea. Reciprocal cross neutralisation studies showed antigenic similarities with overseas animal strains and with human strains including a newly defined fifth human serotype.
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  • 2
    ISSN: 1432-8798
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The neutralization epitopes of human rotavirus VP4 were studied by using a panel of neutralizing monoclonal antibodies previously shown to be strain-specific (RV-3:3), serotype-specific (RV-5:2, ST-3:3) or cross-reactive (F45:4). Antigenic variants of human rotaviruses RV-3, ST-3, RV-5 and F45 resistant to neutralization by the appropriate of VP4 specific monoclonal antibodies (RV-3:3, ST-3:3, RV-5:2 and F45:4 respectively) were selected. By nucleotide sequence analysis and single strand conformational polymorphism analysis of these variants, three sites of neutralization on VP5* and one site on VP8* were identified. At or near to the putative fusion region on VP5*, a strain-specific site (aa383), a serotype P1A-P2 cross-reactive site (aa392) and a serotype P2-specific site (aa397) were found. On VP8*, a serotype P1B-specific site at aa148 was detected. These results confirmed the importance of the putative fusion region in neutralization and have identified a new neutralization site in the hypervariable region of VP8* which is specific for serotype P1B human rotaviruses.
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  • 3
    ISSN: 1432-5411
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract the general problem of pairing correlations within a many-fermion system of identical particles is discussed at some length. We show in this first work in a series how the ground-state version of the [exp(S) or] coupled-cluster formalism (CCF) of quantum many-body theory may be rather generally applied to this problem, and how it thereby provides a very powerful and unifying approach to it. At the so-called SUB2 level of truncation, which is the lowest natural level of approximation for homogeneous systems, the CCF may be cast as a nonlinear integral equation for a four-point correlation function,S 2, which provides a measure of the two-particle/two-hole component in the true “ground-state” wavefunction. This approximation couples the particle-particle, hole-hole and particle-hole correlations simultaneously, and treats them all on an equal footing. In the present work we concentrate particular attention on particle-particle and hole-hole correlations by focussing on the formulation of generalised ladder approximations within the CCF. These are therefore likely to be physically applicable in the low-density regime. In particular, we show that the well-known Galitskii approximation may be formulated within the CCF as that drastic sub-approximation to the full SUB2 equation which keeps only the so-called complete ladder (CLAD) terms, which we describe. A second paper applies the CCF to the particular case of a general (non-local) separable potential, and obtains exact analytic solutions within the CLAD approximation for the corresponding wavefunctions of the simultaneous particle-particle and hole-hole substructures within the many-fermion system.
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  • 4
    ISSN: 1432-5411
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this series of papers, the so-called ground-state version of the [exp(S) or] coupled-cluster formalism (CCF) of quantum many-body theory is applied to the general problem of pairing correlations within a many-body system of identical fermions. In this second work in the series we restrict ourselves to exact calculations and concentrate on analytic solutions to the generalised ladder approximations formulated in the first paper. We focus attention on the particular model case of a general (non-local) separable potential, and work within the so-called complete ladder (CLAD) approximation which was shown in the earlier paper to be the CCF formulation of the well-known Galitskii approximation. We show how the CLAD approximation reduces in this case to a highly non-trivial pair of coupled nonlinear integral equations for the four-point correlation function,S 2, which provides a measure of the two-particle/two-hole component in the true “ground-state” wave-function. In the further derivation of exact analytic solutions for bothS 2 and the corresponding “ground-state” energy, we also see how various types of composite pairs within the many-body medium manifest themselves as “virtual (de-)excitations”. We thus show how our CCF provides an efficient and unified framework in which to describe all aspects of pairing, such as: (i) a possible free bound pair and its gradual approach to “dissolution” as the density is increased; (ii) the possible appearance of a second bound pair of predominantly hole-like quasi-particles above some lower critical density (which depends on the total momentum of the pair); (iii) the unstable but bound resonant pairs that can exist for densities above a comparable upper critical density at which the two previous types of real bound pairs have “dissolved”; and (iv) Cooper pairs. Even though each of these composite pairs leads to a new “condensed-pair phase” of lower energy, we further show that our so-called ground-state CCF leads only to the fluid-like state of uncondensed particles. In a third paper in this series we use the solutions obtained here as input to the analogous excited-state version of the CCF, and show how these various composite pairs materialise as “negative energy (de-)excitations”.
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  • 5
    ISSN: 1432-8798
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary During longitudinal epidemiological studies of rotavirus infections in children in Melbourne, Australia human G3P2 rotavirus strains causing asymptomatic or symptomatic infections have been identified. Eleven strains (AS strains) associated with asymptomatic infection of newborn babies from 1974–1984, and five strains (S strains) associated with symptomatic infection of newborn babies (4) or a 22 week old infant (1) during 1980–1986 were studied. The entire nucleotide sequences of genes coding for VP4, VP7, NSP4 and VP6 were derived for representative AS and S strains. The nucleotide sequences of neutralization epitope regions present on the outer capsid proteins VP4 and VP7 (regions C and F) showed extensive conservation of nucleotide and deduced amino acid sequence in all strains. Minor variations were observed over the 12 year period in VP7 epitope regions A and B in some strains. Specific conserved amino acids differences between the asymptomatic and symptomatic strains were observed in the genes encoding VP4 at aa133 and 303 (asparagine or threonine) and 380 (serine or isoleucine), VP7 at aa27 (threonine or isoleucine), aa29 (isoleucine or threonine), aa42 (valine or alanine) and aa238 (asparagine or aspartic acid/serine) and NSP4 at aa135 (isoleucine or valine). No amino acid changes were identified in gene 6. The observed amino acid differences occurred in proteins that have been implicated in virulence, and correlate with differences in clinical symptoms of infants infected with these strains. These results permit speculation about the genetic basis for virulence of human strains.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 80 (1991), S. 95-148 
    ISSN: 1432-2234
    Keywords: Coupled cluster theory ; Normal coupled cluster method (NCCM) ; Extended coupled cluster method (ECCM) ; Quantum many-body techniques ; Electron gas ; Atomic nuclei ; Nuclear matter ; Quantum field theory ; Quantum hydrodynamics ; Positron annihilation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary What has since become known as the normal coupled cluster method (NCCM) was invented about thirty years ago to calculate ground-state energies of closed-shell atomic nuclei. Coupled cluster (CC) techniques have since been developed to calculate excited states, energies of open-shell systems, density matrices and hence other properties, sum rules, and the sub-sum-rules that follow from imbedding linear response theory within the NCCM. Further extensions deal both with systems at nonzero temperature and with general dynamical behaviour. More recently, a new version of CC theory, the so-called extended coupled cluster method (ECCM) has been introduced. It has the potential to describe such global phenomena as phase transitions, spontaneous symmetry breaking, states of topological excitation, and nonequilibrium behaviour. CC techniques are now widely recognized as providing one of the most universally applicable, most powerful, and most accurate of all microscopicab initio methods in quantum many-body theory. The number of successful applications within physics is now impressively large. In most such cases the numerical results are either the best or among the best available. A typical case is the electron gas, where the CC results for the correlation energy agree over the entire metallic density range to within less than 1 millihartree (or 〈1%) with the essentially exact Green's function Monte Carlo results. The role of CC theory within modern quantum many-body theory is first surveyed, by a comparison with other techniques. Its full range of applications in physics is then reviewed. These include problems in nuclear physics, both for finite nuclei and infinite nuclear matter; the electron gas; various integrable and nonintegrable models; various relativistic quantum field theories; and quantum spin chain and lattice models. Particular applications of the ECCM include the quantum hydrodynamics of a zero-temperature, strongly-interacting condensed Bose fluid; a charged impurity in a polarizable medium (e.g., positron annihilation in metals); and various anharmonic oscillator and spin systems.
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  • 7
    ISSN: 1432-2234
    Keywords: Coupled cluster method ; Quantum spin lattice models ; XXZ-model Hamiltonian ; Low-dimensional anisotropic quantum antiferromagnets ; Phase transitions ; Calculation of staggered magnetization and correlation functions ; Ground states and excited states
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary We extend the domain of applicability of the coupled-cluster method (CCM) to include quantum-mechanical spin-1/2 systems on discrete lattices. We study the specific case of anisotropic antiferromagnetic interactions described by the nearest-neighbour XXZ-model Hamiltonian. The isotropic version of this model on a two-dimensional (2-d) square lattice is of great current interest as a possible description of the interactions between the electrons in the singly-occupied $$d_{x^2 - y^2 } $$ orbitals on the copper atoms in the ceramic copper oxide materials displaying high-temperature superconductivity. Although very few exact results are known for the 2-d XXZ-model, its 1-d counterpart has been exactly solved by Bethe-ansatz techniques, and we therefore use it here as a benchmark for our new CCM techniques. Even starting with the classical Néel state as the model reference state, we find that the CCM is capable at relatively low levels of truncation of giving accurate values for the ground-state energies. In this regard, we discuss several new CCM truncation hierarchies which have not previously been applied to either atoms and molecules or continuous extended systems. Furthermore, the method gives a good qualitative description of most of the known or anticipated behaviour of the correlation functions, order parameters, and elementary excitations over an entire (zero-temperature) phase, right up to the transition point, as the anisotropy is varied.
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  • 8
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this second paper of a series the coupled cluster method (CCM) or exp(S) formalism is applied to two-component Fermi superfluids using a Bardeen-Cooper-Schrieffer (BCS) ground state as a zeroth-order approximation. We concentrate on developing the formalism necessary for carrying out eventual numerical calculations on realistic superconducting systems. We do this by generalising the one-component formalism in an appropriate manner and by using the results in the first paper of this series, where we studied two-component Fermi fluids. We stress the previous successes of the CCM, both from the point of view of analytic and numerical results, and we further indicate its potential for studying superconductivity. We restrict ourselves here to a so-called ring plus single particle energy (RING+SPE) approximation for general potentials and show how it can be formulated as a set of four coupled, bilinear integral equations for the cluster-integrated amplitudes. These latter amplitudes are themselves derived from the four-point functions of the system which provide a measure of the two-particle/two-hole component in the true ground-state wavefunction with respect to the BCS model state. We indicate how to obtain possible analytic solutions.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 71 (1988), S. 527-529 
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The states $$\hat \theta $$ |A 1 A 2〉 are considered, where the operators $$\hat \theta $$ are associated with a unitary representation of the groupSp(4,ℝ), and the two-mode Glauber coherent states |A 1 A 2〉 are joint eigenstates of the destruction operatorsa 1 anda 2 for the two independent oscillator modes. We show that they are ordinary coherent states with respect to new operatorsb 1 andb 2, which are themselves general linear (Bogolibov) transformations of the original operatorsa 1,a 2 and their hermitian conjugatesa δ 1 ,a δ 2 . We further show how they may be regarded as the most general two-mode squeezed states. Most previous work on two-mode squeezed states appears to be based on more restrictive definitions than our own, and thereby reduces to special cases which are unified within our treatment.
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  • 10
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The low-energy atom-atom scattering properties are studied for various combinations of He isotopes interacting via a family of semiphenomenological potentials. Some of the potentials bind the (4He)2 molecule and some do not, and it is observed that molecular beam scattering measurements at energies currently accessible cannot resolve the difference between the two types of potentials. Our results are discussed within the framework of possible measurements to resolve this discrepancy. We present a method for solving the Schrödinger equation which is uniformly applicable for both bound and scattering state solutions and which is particularly suited to the types of potentials describing interactions for the rare gas atoms.
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