Browsing by Author "Joubert, J."

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    Assessment of pre-harvest physiological infiltration methods for predicting commercial bitter pit in 'Braeburn' and 'Golden Delicious'
    (2010) Lotze, Elm.; Theron, K. I.; Joubert, J.
    Although management practices are followed to reduce the incidence of bitter pit in commercial orchards, this defect still surfaces and causes serious problems with fruit quality that lead to losses in especially export produce. Current methods e.g. fruit mineral analysis, magnesium (Mg) infiltration and ethylene forcing that were developed to predict bitter pit incidence, vary in reliability. However, there is still a need to predict bitter pit incidence, before it becomes visible. The effectiveness of ethylene forcing and Mg infiltration-were assessed under local conditions for 'Braeburn' and 'Golden Delicious' apples. The correlation coefficients for the two methods were compared, as well as the correlations between the bitter pit-like incidence induced by the individual methods and actual bitter pit after storage. During the first season, the coefficient determination for Mg infiltration and actual bitter pit (R2 = 0.45) was higher compared to the coefficient for ethylene forcing and actual bitter pit (R2= 0.13). The R2 for the linear relationship between bitter pit incidence with Mg-infiltration and ethylene forcing was 0.43. The actual bitter pit incidence per season influenced the accuracy of the methods.
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    Boson analyses in the Ge isotopes
    (1994) Joubert, J.; Hahne, F.J.W.; Navrtil, P.; Geyer, H.B.; Joubert, J.; Hahne, F.J.W.; Navrtil, P.; Geyer, H.B.
    The strong variation in energy of the first excited 0+ state in the even-even Ge isotopes is investigated with pairing type interactions in various model spaces. Although it had been possible in previous work to describe this variation in a BCSrandom-phase-approximation (RPA) calculation in the neutron configuration only, the corresponding exact diagonalization disagrees with the BCS-RPA results and experiment. It is furthermore shown that the behavior of the first excited 0+ state cannot be obtained by a reasonable variation of parameters in the exact neutron pair calculations. This suggests that the model space be enlarged to include proton, neutron, and proton-neutron pairing. The construction of the corresponding basis is then simplified by performing a boson mapping and employing the ideal collective boson basis. This, however, may lead to the occurrence of spurious states, even at fairly low energies, and three separate methods by means of which they can be identified are discussed. Although the enlarged model space gives a desired lowering of excitation energy of the first excited 0+ states in an exact diagonalization, the strong experimental variation could not be achieved with this simple interaction. Nevertheless, the analysis yields further and new insight into applications of boson mappings, specifically about how and when spurious states may be identified in calculations which are performed in a truncated space not invariant under a given collective algebra. © 1994 The American Physical Society.
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    Evaluating pre-harvest foliar calcium applications to increase fruit calcium and reduce bitter pit in 'Golden Delicious' apples
    (2008) Lotze, Elmi; Joubert, J.; Theron, K. I.
    In all major apple producing countries, applications of foliar calcium (Ca) products to increase fruit Ca content and reduce the incidence of bitter pit in apples are used. Calcium nitrate (Ca(NO3)2), Calcimax and Ca acetate were applied, commencing at three different developmental stages (early, mid and late) of fruit growth. Late Ca(NO3)2 (80 days after full bloom (dafb)) applications increased the Ca content of fruit at harvest more than early (six dafb) and mid (40 dafb) applications. There was a trend towards an increase in bitter pit from early to late applications of Ca(NO3)2 and Calcimax, confirming previous results obtained when applying only Ca(NO3)2. In spite of the very low incidences of bitter pit during these seasons (less than 7%), significant differences between treatments were found between Ca(NO3)2 Mid and other treatments in 2004/2005, as well as Ca(NO3)2 and Calcimax Early and other treatments in 2005/2006. Ca acetate applications did not show any trends in fruit Ca content or bitter pit incidence when applied during the three stages. Thus, products may differ in efficiency of Ca absorption and effectiveness in decreasing bitter pit in fruit when applied during different developmental stages. © 2008 Elsevier B.V. All rights reserved.
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    First report of aster yellows phytoplasma in grapevines in South Africa
    (2010) Engelbrecht, M.; Joubert, J.; Burger, J.T.; Engelbrecht, M.; Joubert, J.; Burger, J.T.
    [No abstract available]
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    Haemophilus influenzae lobar pneumonia with underlying multiple myeloma : a case report
    (Health & Medical Publishing Group, 1980) Maritz, F. J.; Joubert, J.
    Haemophilus influenzae is an uncommon but important cause of lobar pneumonia, specifically in patients whose host defence mechanisms are impaired by unrecognized underlying diseases. A case of H. influenzae lobar pneumonia in a patient with underlying multiple myeloma is presented. The clinical features, treatment and procedures which aid in making the diagnosis are briefly discussed.