Lynne Wong's PhD thesis

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Table 6.4. The GAB model maximum net isosteric heat of sorption, q st , and entropy of sorption, S d , and the corresponding EMC/% db for the nine cane components aged 52 and 36 weeks. Sample Maximum q st/kJ mol -1 Maximum S d/kJ mol -1 52 weeks EMC/% db 36 weeks EMC/% db 52 weeks EMC/% db 36 weeks EMC/% db Stalk fibre 27.27 3 40.88 0 -69.77 3 -93.87 1 Stalk pith 130.77 0.01 14.08 5 -363.07 1 -33.51 5 Rind fibre 31.30 3 64.28 0.1 -83.93 3 -173.40 2 Rind fines 15.89 4 20.92 2 -38.49 4 -46.95 3 Top fibre 40.81 3 25.17 4 -109.80 4 -66.96 4 Dry leaf fibre 43.24 3 64.82 2 -117.87 3 -182.59 2 Dry leaf fines 23.59 5 41.95 0.01 -63.55 5 -98.93 2 Green leaf fibre 9.75 5 53.92 2 -22.97 6 -146.76 2 Green leaf fines 24.70 3 49.67 2 .62.47 4 -136.16 3 6.6 ENTHALPY-ENTROPY COMPENSATION A promising theory that has been widely considered to investigate the physical and chemical phenomena involved in water sorption (Aguerre et al., 1986, Madamba et al., 1996) is the enthalpy-entropy compensation theory, or isokinetic relationship, as originally applied by Bell (1937). This theory states that compensation arises from changes in the nature of the interaction between the solute and the solvent causing the reaction, and that the relationship between enthalpy and entropy for a specific reaction is linear. When this theory is applied to a sorption process, the enthalpy corresponds to the net isosteric heat of sorption. For a linear enthalpy and entropy relation, the isokinetic temperature (T β ) can be determined from the slope of the line and, if the theory is valid, should be constant at any point (Heyrovsky, 1970). It represents the temperature at which all the reactions in the series proceed at the same rate (Heyrovsky, 1970), and the free energy at T β , ΔG, provides a criterion to evaluate whether the water sorption is a spontaneous (-ΔG) or a nonspontaneous process (+ΔG). To test the validity of the compensation theory, the isokinetic temperature is compared with the harmonic mean temperature (T hm ), and T β ≠ T hm . T hm is defined as: T hm = ni ∑ = n i i 1 1/ T where n i is the total number of isotherms and, T is the Kelvin temperature (K). 257
Moreover, if T β > T hm the process is enthalpy-driven, and if T β < T hm , the process is considered to be entropy-controlled (Telis et al., 2000). If the net isosteric heat of sorption q st is plotted as ordinate against the entropy of sorption S d as abscissa, the slope of the plot gives the isokinetic temperature T β and the intercept gives the free energy ΔG at the isokinetic temperature. The harmonic mean temperature for this study can be calculated to be 320.23 K, since the isotherm was investigated at four different temperatures of 30, 45, 55 and 60 °C. 4 T hm = − 1 − 1 − 1 − 1 (303.15) + (318.15) + (328.15) + (333.15) = 320.23 K The plots of the net heat of sorption q st (kJ mol -1 ) against the entropy of sorption S d (kJ mol - 1 K -1 ) for the nine cane components of R 570 aged 52 and 36 weeks are shown in Fig 6.10, the coefficient of determination R 2 , the slope and the intercept for the enthalpy-entropy relationship are shown in Table 6.5. The slope corresponds to the isokinetic temperature T β, and the intercept, ΔG. It can be seen from Table 6.5 that T β for all cane components aged 52 and 36 weeks is greater than the harmonic mean temperature T hm of 320.23 K except in the case of stalk pith aged 36 weeks, hence, all processes except stalk pith aged 36 weeks are enthalpycontrolled. Hence the driving force for the adsorption of moisture on these fibres is the strength of binding of water molecules to the surface of the fibre. The positive sign of ΔG (except for the case of rind fines aged 36 weeks) indicates that the water sorption process in the cane components is non-spontaneous, and that the enthalpy-entropy compensation theory was satisfied. Beristain et al. (1996) applied the enthalpy-entropy compensation theory to water adsorption in starchy materials. Two isokinetic temperatures were observed, suggesting that during the initial stages (at low water activity) the isotherm process was entropycontrolled, whereas in the later stage, the process was controlled by changes in the enthalpy of water. They also reported a spontaneous sorption isotherm for starch materials. 258
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THE BRIX-FREE WATER CAPACITY AND SO
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dissolved and hydrated waters, and
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ACKNOWLEDGEMENTS I am particularly
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Page 1.5 THE DELETERIOUS EFFECTS OF
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Page 2.2 THE PHENOMENON OF BRIX-FRE
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Page 3.4.3.3 Cane tops 83 3.4.4 Cha
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4.3.3 Temperature at which Brix-fre
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4.6.1 Materials 143 4.6.1.1 Samples
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CHAPTER 6. PROPERTIES OF THE SORBED
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APPENDIX 3. CALCULATIONS LEADING TO
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LIST OF FIGURES Page Figure 1.1. Fi
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Figure 3.1. Glucose and fructose an
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Figure 5.11. Residual plots for the
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total adsorbed water (m) and the pr
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Table 2.18. Moisture content in sug
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Page Table 4.4. Results of the dete
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Page Table 4.24. Analysis of varian
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Page Table 5.13. Table 5.14. Equili
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Table 6.3. Heat of sorption of the
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GLOSSARY OF TERMS Absorption is the
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Filterability of a raw sugar is mea
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Sorption is the generic term used w
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LIST OF MAIN SYMBOLS Symbol Descrip
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s c s Slope of Caurie I isotherm pl
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number of 255, and cane land covere
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Nouvelle Mon In Trésor ustrie and
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Figure 1.3. Cane sampling by core s
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In Mauritius, most of the sugar fac
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are: cane tops, dry and green leave
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1.4 TRENDS IN CANE QUALITY RECEIVED
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campaign was launched to encourage
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The level of extraneous matter in c
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In Australia (Cargill, 1976), cane
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The effect of soil on factory perfo
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leaves increased the level of impur
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• From 1976 to 1980, when the pro
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Clerget purity of molasses 40 Clerg
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CHAPTER 2. IMPACT OF EXTRANEOUS MAT
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Since the extrapolated purity of mo
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Figure 2.1. Jeffco cutter grinder.
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2.1.4 Results The analytical result
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Table 2.3. Analytical results of re
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Table 2.5. Composition of dry trash
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Table 2.7. Predicted factory perfor
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Boiling house recovery 91.0 89.8 89
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0 5 10 15 20 % EM in cane y = 0.572
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% EM in cane 0 5 10 15 20 0 -2 -4 -
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1 y = 0.020 (% D) R 2 = 1.00 = 0.03
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% EM in cane 0 5 10 15 20 0 -2 y =
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esulting in 0.015 unit sucrose loss
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2.2.1 Experimental procedure Cane m
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filter paper, rejecting the first f
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Table 2.9. Effect of increased addi
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Table 2.11. Effect of increased add
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Table 2.13. Effect of increased add
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various components such as stalk fi
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in the presence of dry leaves, if c
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Table 2.17. Moisture content in sug
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CHAPTER 3. SEPARATION OF THE SUGAR
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Table 3.1. It can be seen that the
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Table 3.2. Fibrous physical composi
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R 579 R 570 M 1557/70 M 1400/86 74
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loosen the fibre. The woody core is
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agitate the mixture in the pot, and
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Figure 3.7. Custom-built fibre-pith
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The extraction of fibres starting f
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pre-treatment in a Jeffco cutter-gr
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Figure 3.19. Stalk cake washed free
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not have many dry leaves attached t
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Table 3.5. Masses of cane samples a
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Table 3.7. Masses of cane samples a
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Table 3.9. Masses of cane component
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3 57.6 126.3 23.7 97.2 31.1 53.8 11
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Table 3.12. Material loss (%) from
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3.5.3 Fibre/pith ratios in cane com
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Table 3.15. Effect of extraneous ma
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Snow (1974) investigated the season
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from Figure 2.9 that the change in
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Table 3.18. Fibre % cane results by
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110
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(a). Dry leaf (b). Green leaf (c).
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dry fibre, or a factor, is used in
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Steuerwald (1912) applied sucrose s
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solution/fibre ratio was lowered fr
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leave some residual moisture on the
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instead of 150 g of 10° Brix sucro
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Table 4.2. Determination of Brix-fr
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Table 4.3. Comparison of Brix-free
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Table 4.4. Results of the determina
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In order to test for homogeneity of
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Table 4.7. Results of the repeat de
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The experiment was repeated with th
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e any residual moisture in the samp
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By means of the same technique, Won
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was still hot. Since the filter was
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value determined could be corrected
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Qin and White’s finding was confi
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A sample size of 3.5 g with 75 g co
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Figure 4.4. Fibre samples drying in
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- One large fibre sample (rind) of
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Table 4.18. Brix-free water values/
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Table 4.20. Brix-free water values/
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4.7.3 Statistical analysis It is es
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Table 4.23. Analysis of variance (B
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pointing out that at 52 weeks old,
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The crop of R 570 sampled in 2001 w
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4.7.4. Estimated Brix-free water co
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The main difference in the two sets
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Table 4.27. Predicted Brix-free wat
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4.8 SUMMARY AND CONCLUSIONS An anal
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component parts, and verify the Bri
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3) Thermodynamic, water in equilibr
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Langmuir (1916, 1917, 1918) propose
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to determine the moisture sorption
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Table 5.1. Some commonly used isoth
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Lomauro et al. (1985) found that wi
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and on agricultural products such a
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Bruijn (1963) studied the mass incr
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After measuring the EMC of dry corn
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approached, that is, either by adso
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Table 5.4. Water activity (a w ) of
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5.6.3 Procedure to determine equili
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5.6.4 Results and discussion An exa
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Table 5.8. Equilibrium moisture con
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Table 5.10. Equilibrium moisture co
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Table 5.12. Equilibrium moisture co
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30 o C 45 o C 55 o C 60 o C Water w
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m/m of 96% activity, a w (g/100g dr
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vaporisation generally decreases fr
Page 259 and 260: 30 o C isotherm 45 o C isotherm 55
Page 261 and 262: 4 0 Stalk fibre 5 0 Stalk pith 5 0
Page 263 and 264: 5.6.4.4 Fitting of sorption models
Page 265 and 266: Table 5.19. Parameters of the sorpt
Page 275 and 276: Modified GAB Kuhn Iglesias - Chirif
Page 277 and 278: Table 5.28. Classification of resid
Page 279 and 280: Stalk fibre Stalk pith Rind fibre 4
Page 281 and 282: 5.6.4.5 Calculated EMC values of re
Page 283 and 284: Table 5.30. Calculated equilibrium
Page 285 and 286: m/m of 96% Table 5.32. Calculated e
Page 287 and 288: Table 5.33. Parameters of the Hailw
Page 289 and 290: CHAPTER 6. PROPERTIES OF THE SORBED
Page 291 and 292: where m is the equilibrium moisture
Page 297 and 298: 6.2 THE NUMBER OF ADSORBED MONOLAYE
Page 299 and 300: 6.3 TOTAL SOLID SURFACE AREA AVAILA
Page 301 and 302: Thus, for each cane component of ea
Page 303 and 304: abscissa. For each moisture level (
Page 307 and 308: A similar procedure was followed to
Page 309: 10 0 Stalk fibre Stalk pith Rind fi
Page 313 and 314: Table 6.5. Characteristic parameter
Page 315 and 316: Binding energy/kJ (kg mol) -1 2 0 0
Page 317 and 318: 6.8 CALCULATION OF BOUND WATER AND
Page 319 and 320: The values of K 1 , K 2 and W were
Page 321 and 322: Table 6.7. Separation of the total
Page 323 and 324: Table 6.7. (Contd.) Sample 30 o C 4
Page 325 and 326: 3 0 S talk fibre 4 0 Stalk pith 3 0
Page 327 and 328: 3 0 Reconstituted cane at 30 o C 3
Page 329 and 330: when water is added to dry wood, wh
Page 331 and 332: It is evident that in some cases ma
Page 333 and 334: The number of adsorbed monolayers,
Page 335 and 336: Data in Tables 2.9 and 2.11 show th
Page 337 and 338: particular fibre is systematically
Page 339 and 340: Anon. (1985b). Laboratory manual fo
Page 341 and 342: Blanchi R.H. and A.G. Keller (1952)
Page 343 and 344: Day D.L. and G.L. Nelson (1965). De
Page 345 and 346: Heyrovsky J. (1970). Determination
Page 347 and 348: Kuhn I.J. (1964). A new theoretical
Page 349 and 350: Madamba P.S., R.H. Driscoll and K.A
Page 351 and 352: Prinsen Geerligs, H.C. (1897). Stud
Page 353 and 354: Sing K.S.W., D.H. Everett, R.A.W. H
Page 355 and 356: Van der Pol C., C.M. Young and K. D
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Lynne Wong's PhD thesis

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