Wistar Lewis (W~), Long Eva~s (LE) and.other rat strain~ develoP4complete resistance to CNS dlsease when lnoculated lntracerebrally wlth 5xlO PFU/ml of murine hepatitis JHM virus (JHHV) after the lOth day of age (1). Immunosuppression of WL rats following onset of the age-related resistance demonstrated that cyclosporin A (CsA) was partially able to abrogate resistance. Studies on nude (rnu/rnu) rats, their heterozygous (rnu/+) litter mates and genet i ca lly related LE rats showed that rnu/ + and LE ani rna 1 s becalile completely resistant to JHHV before the age of weaning, whereas some rnu/rnu rats, challenged as late as 70 days of age, developed disease symptoms, albeit after a long latent period. These observations indicated that the cellular irllmune system plays an important role in suppressing the viral disease process in the CNS. When the infection of nude rats was initiated on or after the 15th day of life, the histological lesions were generally small and present in both grey and white matter but were seldom seen in the spinal cord. By contrast in rnu/+, LE and WL rats with late-onset disease symptoms, only the demyelinating-type white matter lesions were present. ~lononuclear infiltrates, evident throughout the CNS, of nude rats were sometimes massive near the meningies and within ventricular spaces. JHMV KNA was detectable by dot-blotting analysis in the CNS of both paralysed and asymptomatic rnu/rnu and rnu/+ rats. In-situ hybridization with cDNA probes for JHNV RNA showed that neurons in the nTPPocampus and cerebellum, as well as cells in the white matter, were frequently infected. The present data indicate that in the rat T cells have an illiportant function in maintaining resistance to the JHlvIVrelated CNS disease. However, even without a functional T cell compartment after 15 days of age nude rats did not develop an acute encephalitis, suggesting that an age-dependent, non-immunological mechanism is also involved in restricting the spread of infection. 383 M. M. C. Lai et al. (eds.

We formulate a method to study two-body correlations in a system of N identical bosons interacting via central two-body potentials. We use the adiabatic hyperspherical approach and assume a Faddeev-like decomposition of the wave function. For a fixed hyperradius we derive variationally an optimal integro-differential equation for hyperangular eigenvalue and wave function. This equation reduces substantially by assuming the interaction range much smaller than the size of the N -body system. At most one-dimensional integrals then remain. We view a Bose-Einstein condensate pictorially as a structure in the landscape of the potential given as a function of the one-dimensional hyperradial coordinate. The quantum states of the condensate can be located in one of the two potential minima. We derive and discuss properties of the solutions and illustrate with numerical results. The correlations lower the interaction energy substantially. The new multi-body Efimov states are solutions independent of details of the two-body potential. We compare with mean-field results and available experimental data.

We study two-body correlations in systems of identical bosons. We use a Faddeev type of decomposition of the wave function where all pairs of particles are treated equally. We focus on a new multi-particle Efimov effect at large scattering length, where infinitely many loosely bound many-body states appear. A confining external trap only allows a finite number of such spatially extended negative energy states inside the trap. The stability of a Bose condensate is determined by the decay into these model independent intermediate states which in turn decay into dimers.PACS numbers: 31.15. Ja, 05.30.Jp, 21.65.+f Introduction. The novel theoretical formulation in [1] was constructed to describe correlations in boson systems and applied for a realistic short-range repulsive interaction to Bose-Einstein condensates. The method goes beyond the mean-field approximation [2,3] and is as well applicable to attractive finite range potentials with very large scattering lengths where the Efimov effect occurs [4,5]. Experimental properties are available for various condensates from the first observations of both effectively repulsive [6] and attractive [7] interatomic interactions to the recent observations [8,9] of condensates in a magnetic field used to tune the effective interaction via a Feshbach resonance to almost any scattering length.The condensate [2] being an excited state of the full many-body system is clearly unstable. The three-body recombination into bound dimers is a dominating decay channel [10,11,12]. In the condensate this occurs independently for neighbouring pairs and much more frequently in a coherent process best described as a collective or macroscopic collapse [13,14]. Two-body correlations therefore must be crucial for this collapse, which becomes more likely and eventually inevitable as the scattering length is increased. Unfortunately a theoretical description is hindered by the difficulties, especially pronounced for large scattering lengths, of finding the decisive correlated structure [2,15,16].A promising form of a correlated wave function suggested for nucleons [17] was recently extended to more general systems [18]. Another related formulation uses generalized hyperspherical coordinates and an adiabatic expansion with the hyperradius as the adiabatic coordinate [19]. It was applied for many identical bosons, still only with a zero-range interaction and the lowest (constant and thus non-correlated) hyperspherical angular wave function. These crude approximations are removed in a novel method still using hyperspherical coordinates and adiabatic expansion, but now the wave function is determined from a variationally established equation [1]. The purpose of this letter is to investigate the structure of boson systems as a function of (large) scattering length for attractive finite range potentials with emphasis on an emerging novel many-body Efimov effect.

We formulate a method to study two-body correlations in a condensate of N identical bosons. We use the adiabatic hyperspheric approach and assume a Faddeev like decomposition of the wave function. We derive for a fixed hyperradius an integro-differential equation for the angular eigenvalue and wave function. We discuss properties of the solutions and illustrate with numerical results. The interaction energy is for N ≈ 20 five times smaller than that of the Gross-Pitaevskii equation. PACS number(s): 03.75.Fi, 05.30.Jp Introduction. Few-body correlations often express the distinguishing characteristic features of an N -body system [1]. Two-body correlations are not only the simplest but in most cases also the most important. Higher order correlations have a tendency to either strongly confine spatially or correlate into clusters of particles effectively reducing the correlations to lower order. Exceptions are the three-body correlations decisive for the stability of Borromean systems known for dripline nuclei [2].Non-correlated mean-field computations of nuclei with the free two-body nucleon-nucleon interaction produce disastrously wrong results. Two-body correlations compensating for the short range hard core repulsion are absolutely necessary [3]. For atoms the effective interaction is also strongly repulsive at shorter distances. Furthermore for an atomic Bose condensate a short-range twobody attraction produces diatomic recombination and thereby the atoms decay out of the condensate [4]. For both nuclei and molecules correlations are decisive. For nuclei various methods have been designed to deal with this problem, i.e. Jastrow theory, Bruckner theory, effective interactions in model spaces [5].For Bose condensates the Gross-Pitaevskii (noncorrelated) mean-field equation has been the starting point since the first observation of the condensate in 1995 [6]. The wave function does not include any correlations and the assumed repulsive δ-interaction has the immediate consequence that the short range behavior cannot be described even qualitatively correct. Repulsive zero range potentials are not physically meaningful [7] although sometimes useful in selected Hilbert spaces. Attractive δ-interactions in three dimensions lead to divergencies demanding renormalization [8,9] or a change of boundary conditions [10]. When two-body bound states appear even dimer condensates may be possible [11].To include correlations we must necessarily go beyond the mean-field Hartree-Fock-Boguliubov approximation. Then finite range potentials with realistic features can as well be used as the starting point in the theoretical formulation. The other crucial ingredient is the degrees of freedom or, equivalently, the Hilbert space. An interesting formulation was recently introduced in terms of generalized hyperspherical coordinates and an adiabatic expansion with the hyperradius as the adiabatic

III.

Level IV.

We investigate systems of identical bosons with the focus on two-body correlations and attractive finiterange potentials. We use a hyperspherical adiabatic method and apply a Faddeev type of decomposition of the wave function. We discuss the structure of a condensate as a function of particle number and scattering length. We establish universal scaling relations for the critical effective radial potentials for distances where the average distance between particle pairs is larger than the interaction range. The correlations in the wave function restore the large-distance mean-field behavior with the correct two-body interaction. We discuss various processes limiting the stability of condensates. With correlations we confirm that macroscopic tunneling dominates when the trap length is about half of the particle number times the scattering length.

Intracerebral inoculation of JHM virus (JHMV), the neuropathic strain of mouse hepatitis virus, into Wistar Furth, Wistar Lewis, and Fischer 344 rats at various ages indicated that Wistar Furth rats are more susceptible to the virus than are the other strains. Fischer 344 and Wistar Lewis rats were more resistant to inoculation at 2 and 5 days of age and completely resistant by 10 days of age. In contrast, Wistar Furth rats which were very susceptible at both 2 and 5 days of age remained susceptible until 21 days of age. Intracerebral challenge of an Fl cross between Wistar Furth and Wistar Lewis rats at 10 days of age indicated that resistance to JHMV infection is dominant. Cyclophosphamide treatment 28 days after intracerebral inoculation exacerbated an inapparent infection, leading to paralysis in eight of nine and death in six of nine Wistar Furth test rats. In such immunosuppressed animals, grey-and white-matter lesions were noted throughout the central nervous system, in contrast to the purely demyelinating lesions noted previously. Since rats, unlike mice, were not susceptible to disease after intracerebral injection with the serorelated viscerotropic strain MHV-3, we wished to extend our understanding of the neurological disease process elicited by the two viruses in rodents. For this reason, various mouse strains, including some with recognized immunodeficiencies, were challenged by different routes of inoculation. Intraperitoneal infection of nude and beige mice with JHMV indicated that lack of natural killer cell functions does not markedly enhance the susceptibility to virus, whereas T-cell activity appears to be essential for resisting infection. JHMV and MHV-3 replication in peritoneal macrophages from highly resistant A/J mice was reduced in comparison with that noted in macrophages from susceptible C57BL6/J mice. An initial intraperitoneal inoculation of JHMV was able to protect C57BL6/J mice against fatal intracerebral challenge within 3 days, whereas A/J mice remained susceptible beyond day 3. The protective effect did not appear to result from increased levels of circulating interferon, preceded elevation in serum JHMV-neutralizing antibody titers, and persisted for at least several weeks after intraperitoneal inoculation. Based on the combined studies described here and on previous work by us and others, it appears that the factors influencing the outcome of coronavirus disease in rodents are age at inoculation, route of challenge, genetic constitution of the virus and host, and competence of the immune system, particularly cellular immunity involving T-cells. Our previous experiments (27) demonstrated example, in SJL mice, the only known strain that intracerebral (i.c.) inoculation of suckling showing resistance to i.c. inoculation with rats with JHM virus (JHMV), the neurotropic JHMV (10, 28, 29), lack of susceptibility is age strain of mouse hepatitis virus (MHV), offers an dependent (31) and apparently connected with attractive model for investigating virus-induced the ability to replicate...