ESTIMATION OF pH OF SUGAR CANE JUICES A . T HIGH TEMPERATURE
A Philips digital pH-meter (PW9422) equipped with a Philips high temperature pH-electrode (CH 85D-SD) and platinum 100 thermometer was used in the autocalibrate mode to standardise itself using 2 NBS-buffers (phthalate and borax solutions). The instrument automatically identifies each buffer and uses the current temperature to select the exact buffer value from its look-up table. Temperature compensation for electrode slope changes due to temperature changes was also automatic.
A COMPARATIVE STUDY OF SUCROSE DEGRADATION IN DIFFERENT EVAPORATORS
Theoretical calculations based on measured conditions of pH, brix, temperature and residence time suggested that sucrosedegradation in the Pongola evaporatorwasalmost0,5% and that almost all of the lossoccurredin the first two effects of the evaporator. When data from all South African factories were considered there appeared to be a correlation between the relative size of the first two evaporator effects and the undetermined loss. Sucrose degradation in 5 different evaporators was then monitored by measuring changes in glucose:sucrose ratios. Changes in juice pH, and concentration of acetic acid in condensateswerealso monitored. Thesemeasurementshave indicated that appreciable degradation occurs in two of the evaporators (Pongola and Felixton). At both of these factories a large portion of the evaporation is done in the first two effects whereas at Mount Edgecombe where much less evaporation occurs in the first two effects no such degradation could be detected. The measured inversion for all five evaporators correlates well with the area of heatingsurface in the first two effects per unit of sucrose throughput. The observations illustrate that energy savings made by extensive vapour bleeding may sometimes be worth less than the consequential destruction of sucrose.
Speci fi cation Test for Panel Data Models with Interactive Fixed E ff ects ∗
In this paper, we propose a consistent nonparametric test for linearity in a large dimensional panel data model with interactive fixed effects. Both lagged dependent variables and conditional heteroskedasticity of unknown form are allowed in the model. We estimate the model under the null hypothesis of linearity to obtain the restricted residuals which are then used to construct the test statistic. We show that after being appropriately centered and standardized, the test statistic is asymptotically normally distributed under both the null hypothesis and a sequence of Pitman local alternatives by using the concept of conditional strong mixing that was recently introduced by Prakasa Rao (2009). To improve the finite sample performance, we propose a bootstrap procedure to obtain the bootstrap -value. A small set of Monte Carlo simulations illustrates that our test performs well in finite samples. An application to an economic growth panel dataset indicates significant nonlinear relationships between economic growth, initial income level and capital accumulation.