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  • 1
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Oculocutaneous albinism (OCA2) is the most common autosomal recessive disorder in the South African Negroid population, occurring with a prevalence of 1/3900 individuals. The OCA2 locus, P, has been mapped to chromosome 15q11–q13 and a 2.7-kb interstitial deletion has been found to be the common mutation in Africa. This study reports the detection of the deletion allele in OCA2-affected individuals from the southern African, Zambian and Central African Republic (CAR) Negroid populations (0.77, 131/170 OCA2 chromosomes; 0.79, 11/14; 0.33, 4/12, respectively). Normally pigmented individuals from different African countries were also tested. The deletion mutation was found at a frequency of 0.013 (10/780) in the normally pigmented southern African Negroid population and at a lower frequency in individuals from central Africa (0.002; 2/834), including individuals from Zambia, Cameroon, Zaire and the CAR. The study confirms the African origin of this deletion allele. Haplotype analysis suggests that the deletion mutation probably occurred only once and that it arose before the divergence of these African populations, which is estimated to be about 2000– 3000 years ago. The unusually high frequency of OCA2 mutations, in particular the 2.7-kb deletion, suggests some selective agent or genetic drift.
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  • 2
    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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  • 3
    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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  • 4
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Zusammenfassung Die Gewinnung eines neuen, tierexperimentell und klinisch hochwirksamen Diureticums der Formel III (6-Chlor-7-sulfamyl-3,4-dihydro-1,2,4-benzothiadiazin-1,1-dioxyd) wird beschrieben.
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  • 5
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Zusammenfassung In der Reihe der Dihydro-benzothiadiazine wurde mit Hydrotrichlorthiazid (III) ein neues, ausserordentlich stark wirksames Diuretikum gefunden. Herstellung und pharmakologische Evaluation werden kurz beschrieben. Im Vergleich zu Hydrochlorthiazid (I) ist III beim Hundper os bis zu 20mal stärker diuretisch wirksam.
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  • 6
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Zusammenfassung Ausgewähltecis- undtrans-Isomere, Derivate des 1,2,3,4-Tetrahydro-1,2-diphenylnaphthalins, wurden beschrieben. Der basische Äther VII blokkierte die Nidation in der Ratte bei einer täglichen Dosis von 20γ/kg per os.
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  • 7
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Zusammenfassung Synthese und Wirkung gengen Coccidia des 6,7-bis(Cyclopropylmethoxy)-4-hydroxy-chinolin-3-carbonsäureäthylesters werden beschrieben.
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  • 8
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The locus for Tyrosinase-Positive Oculocutaneous Albinism (ty-pos OCA) has not yet been localised. The search for the ty-pos OCA locus has included a search for linkage to candidate pigment loci and a candidate chromosomal region, as well as a random search using highly polymorphic markers in 42 families, including 271 individuals of whom 79 are affected. The lod scores for the tyrosinase (TYR) locus (11q14–q21), homologous to the albino locus, c, in the mouse and the CAS2/TRP1 locus (9p22-pter), homologous to the brown locus, b, in the mouse were -5.89 and -7.22, respectively, at a recombination fraction of θ=0.01, thus excluding them from being the ty-pos OCA locus. In the candidate chromosomal region, 11p, four loci (probes) were tested, SAA (pSAA82), CALC (pHC36), HBB (Gamma-globin haplotype) and an AC repeat polymorphism at the Wilm's Tumour locus (WT1). A portion of 11p was excluded with the following lod scores: pSAA82 lod=-2.05 at θ=0.10; pHC36 lod=-3.87 at θ=0.05; gamma-globin haplotype lod=-2.80 at θ=0.10; and WT1 lod=-2.34 at θ=0.10. Thirty-three polymorphic markers randomly distributed on 13 different chromosomes were all excluded from close linkage to ty-pos OCA.
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  • 9
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A two-component (core-halo) emission model has been applied reconciling hard and soft X-ray burst emissions with the microwave burst radiation. The core region is represented by a nonthermal energy distribution (Maxwellian+power law tail) and assumed to be surrounded by a thermal halo. Parameters characterizing the energy distribution and emission measures have been derived numerically from soft and hard X-ray measurements. Using an artificial magnetic field model the microwave flux spectrum has been calculated on the basis of gyro-synchrotron emission and absorption by solving the equation of radiation transfer along the ray trajectories. Open parameters were used to adapt the spectrum to the radio measurements. Thus probable informations about the most appropriate magnetic field parameters as well as about the time- and frequency- dependent source diameters (yielding growth velocities of the core region during the impulsive phase) are deduced for the burst of 1972 May 18 as an example. A fit of the observed spectrum at the burst maximum is consistent with a magnetic field of 150O G at the core centre decreasing up to about 40 G at the top of the halo at a height of 50 000 km above the centre, a core density of 1010 cm−3 decreasing to 109 cm−3 at the outer halo boundary, and a core diameter of 15 000 km (∼]20″). Due to the simple geometry and emission process adopted,- the model refers primarily to special impulsive bursts. For the representation of broad band microwave bursts, e.g. type IV μ, events, a more complex source geometry and/or other variants of the emission mechanism must be invoked.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Cellulose 1 (1994), S. 26-56 
    ISSN: 1572-882X
    Keywords: low-temperature degradation ; kinetics ; mechanisms ; electrical insulation ; transformers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A critical review is given of the degradation of cellulose in the low-temperature region (below about 300°C) of power transformer operation. The large number of kinetic studies, under a variety of environmental conditions from Kraft paper in insulating oil, to cotton and paper in oxygen, are considered in terms of a first-order polymer chain scission model. In many cases, the data are replotted to suit the model. A common activation energy of 111±6 kjmol−1 is calculated and it is shown that the pre-exponential factor, rather than the activation energy, is sensitive to the oxidizing nature of the environment and the susceptibility to degradation of the material. The chemical mechanisms of degradation are reviewed, and conclusions and recommendations are made regarding chemical condition monitoring and life prediction of electrical insulation.
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