Objective: Assessment of a possible relationship between perception of satiety and diet-induced thermogenesis, with different macronutrient compositions, in a controlled situation over 24 h. Design: Two diets with different macronutrient compositions were offered to all subjects in randomized order. Setting: The study was executed in the respiration chambers at the department of Human Biology, Maastricht University. Subjects: Subjects were eight females, ages 23 ± 33 y, BMI 23 AE3 kgam 2 , recruited from University staff and students.Interventions: Subjects were fed in energy balance, with proteinacarbohydrateafat: 29a61a10 and 9a30a61 percentage of energy, with ®xed meal sizes and meal intervals, and a ®xed activity protocol, during 36 h experiments in a respiration chamber. The appetite pro®le was assessed by questionnaires during the day and during meals. Diet induced thermogenesis was determined as part of the energy expenditure. Results: Energy balance was almost complete, with non-signi®cant deviations. Diet-Induced-Thermogenesis (DIT) was 14.6 AE2.9%, on the high proteinacarbohydrate diet, and 10.5 AE3.8% on the high fat diet (P`0.01). With the high proteinahigh carbohydrate diet, satiety was higher during meals (P`0.001; P`0.05), as well as over 24 h (P`0.001), than with the high fat diet. Within one diet, 24 h DIT and satiety were correlated (r 0.6; P`0.05). The difference in DIT between the diets correlated with the differences in satiety (r 0.8; P`0.01). Conclusion: In lean women, satiety and DIT were synchronously higher with a high proteinahigh carbohydrate diet than with a high fat diet. Differences (due to the different macronutrient compositions) in DIT correlated with differences in satiety over 24 h.

We measured energy expenditure with the doubly labeled water technique during heavy sustained exercise in the Tour de France, a bicycle race lasting more than 3 wk. Four subjects were observed for consecutive intervals of 7, 8, and 7 days. Each interval started with an oral isotope dose to reach an excess isotope level of 200 ppm 18O and 130 ppm 2H. The biological half-lives of the isotopes were between 2.25 and 3.80 days. Energy expenditure was compared with simultaneous measurements of energy intake, and body mass and body composition did not change significantly. The doubly labeled water technique gave higher values for energy expenditure than the food record technique. The discrepancy showed a systematic increment from the first to the third interval, being 12.9 +/- 7.9, 21.4 +/- 9.8, and 35.3 +/- 4.4% of the energy expenditure calculated from dietary intake, respectively. Possible explanations for the discrepancy are discussed. The subjects reached an average daily metabolic rate of 3.4-3.9 or 4.3-5.3 times basal metabolic rate based on the food record technique and the doubly labeled water technique, respectively. Thus, when measured with the same technique, the energetic ceiling for performance in humans is comparable with that of animals like birds.

In adults, body mass (BM) and its components fat-free mass (FFM) and fat mass (FM) are normally regulated at a constant level. Changes in FM and FFM are dependent on energy intake (EI) and energy expenditure (EE). The body defends itself against an imbalance between EI and EE by adjusting, within limits, the one to the other. When, at a given EI or EE, energy balance cannot be reached, FM and FFM will change, eventually resulting in an energy balance at a new value. A model is described which simulates changes in FM and FFM using EI and physical activity (PA) as input variables. EI can be set at a chosen value or calculated from dietary intake with a database on the net energy of foods. PA can be set at a chosen multiple of basal metabolic rate (BMR) or calculated from the activity budget with a database on the energy cost of activities in multiples of BMR. BMR is calculated from FFM and FM and, ifnecessary, FFM is calculated from BM, height, sex and age, using empirical equations. The model uses existing knowledge on the adaptation of energy expenditure (EE) to an imbalance between EI and EE, and to resulting changes in FM and FFM. Mobilization and storage of energy as FM and FFM are functions of the relative size of the deficit (EI/EE) and of the body composition. The model was validated with three recent studies measuring EE at a fixed EI during an interval with energy restriction, overfeeding and exercise training respectively. Discrepancies between observed and simulated changes in energy stores were within the measurement precision of EI, EE and body composition. Thus the consequences of a change in dietary intake or a change in physical activity on body weight and body composition can be simulated.Energy intake : Physical activity : Simulation model Body mass (BM) in adult man is regulated at a constant level, an everyday experience backed by surprisingly little data in the literature. One of the few studies providing information on the constancy of BM is the Framingham Study, a long-term sampling of 5209 adults, 30-59 years of age, living in the town of Framingham at the start of the study from 1948 to 1949. They underwent, every 2 years, a standard medcal examination, including the measurement of BM, for at least 20 years if not prevented by illness or death. Most subjects lost or gained no more than 5-10 kg over some part of the 20-year period as calculated by James (1985). This demonstrates a nearly perfect system for preserving energy balance as the total energy turnover of an average adult subject over 20 years is 73000 MJ. A discrepancy of 1 % between energy intake (EI) and energy expenditure (EE) would add up to 730 MJ over 20 years, equivalent to about 24 kg BM as fat tissue with an energy density of 30 MJ/kg. Thus, in the long term EI matches EE within 1 YO.There are situations where subjects are brought into a positive or negative energy balance by an intervention and where one wants to know the resulting consequences for BM. Examples are overeating or undereating and a restriction of physical...

A review of the kinetics and mechanism for the selective hydrogenation of ethyne and ethene on palladium catalysts is presented. The progress made in the last fifteen years is mainly discussed. It has become clear that the classical view, where the selectivity of the reaction was believed to be due to the thermodynamic factor is an oversimplification. Currently, it is generally assumed that at least two different sites are active during the selective hydrogenation, one of these might possibly involve the support. Ethene hydrogenation also occurs in the presence of high ethyne concentrations, which cannot be explained by the classical theory. Besides the two main hydrogenation reactions and the oligomerisation, there exists a direct route from ethyne to ethane, which, however, is only of minor importance. Possibly due to the rather complex nature of the system, there have been relatively few kinetic studies presenting practical rate expressions. Properties of PI/Al, 0, catalysts For the selective hydrogenation of ethynejethene, low surface area alumina supports are mostly used, while the palladium content typically amounts to only 0.01-O. 1% by weight. Industrially, for the selective hydrogenation

Accumulation of the reactant supplied to a cooled semibatch reactor (SBR) will occur if the mass transfer rate across the interface is insufficient to keep pace with the supply rate. Then, due to a low starting temperature or supercooling, the reaction temperature does not rise fast enough to the desired value. This accumulation may eventually lead to a temperature runaway. We investigated the possibility of such an event for reactions of the type "chemically enhanced mass transfer" or "fast" and found that only low distribution coefficients, i.e. or lower, can lead to accumulation. At higher distribution coefficients, the mass transfer rate across the interface of a well-mixed dispersion is generally sufficient to prevent accumulation. A thermal runaway in the fast regime exerts a moderate effect, because the effective activation energy is halved. Calculations for the "instantaneous" reaction regime, regarded as a special case of fast reactions, show that there is no runaway possible.* Dr. ir. M. Steensma,

Weight loss is a well-known phenomenon at high altitude. It is not clear whether the negative energy balance is due to anorexia only or an increased energy expenditure as well. The objective of this study was to gain insight into this matter by measuring simultaneously energy intake, energy expenditure, and body composition during an expedition to Mt. Everest. Subjects were two women and three men between 31 and 42 yr of age. Two subjects were observed during preparation at high altitude, including a 4-day stay in the Alps (4,260 m), and subsequently during four daytime stays in a hypobaric chamber (5,600-7,000 m). Observations at high altitude on Mt. Everest covered a 7- to 10-day interval just before the summit was reached in three subjects and included the summit (8,872 m) in a fourth. Energy intake (EI) was measured with a dietary record, average daily metabolic rate (ADMR) with doubly labeled water, and resting metabolic rate (RMR) with respiratory gas analysis. Body composition was measured before and after the interval from body mass, skinfold thickness, and total body water. Subjects were in negative energy balance (-5.7 +/- 1.9 MJ/day) in both situations, during the preparation in the Alps and on Mt. Everest. The loss of fat mass over the observation intervals was 1.4 +/- 0.7 kg, on average two-thirds of the weight loss (2.2 +/- 1.5 kg), and was significantly correlated with the energy deficit (r = 0.84, P < 0.05). EI on Mt. Everest was 9-13% lower than during the preparation in the Alps.(ABSTRACT TRUNCATED AT 250 WORDS)

Data on design and operation of trickle beds at elevated pressures are scarce. In this study the influence of the gas density on the liquid holdup, the pressure drop, and the transition between trickle and pulse flow has been investigated in a tricklebed reactor operating up to 7.5 MPa and with nitrogen or helium as the gas phase. Gas-liquid Part 1: Gas-Liquid Interfacial Areas IntroductionGas-liquid mass transfer processes in trickle-flow columns can be performed either in the cocurrent or countercurrent operation. From a hydrodynamic point of view, the cocurrent operation is preferable because it has no limitations in the gas and the liquid throughput. In cocurrent operation, only one equilibrium stage can be reached. The cocurrent gas-liquid trickle-flow operation is suitable when the transferred component is removed by a chemical reaction as is the case in threephase catalytic trickle-bed reactors. In this application, the transfer rate of the gaseous reaction component to the liquid bulk can play an important role on the overall conversion rate, especially when the intrinsic rate of reaction is relatively fast.Several published studies have dealt with gas-liquid mass transfer in the cocurrent downflow operation with packings typically used in absorption and desorption processes, such as AIChE JournalDecember 1991 saddles and rings, as well as for relatively small packings, dp< 4 mm with cylindrical or spherical geometry as generally used in catalytic trickle-bed reactors (see, for example, Gianetto and Silveston, 1986). From these studies, it can be concluded that the gas-liquid mass transfer rate, especially the gas-liquid interfacial area, depends strongly on the hydrodynamic flow pattern. In the trickle-flow regime, resistances for mass transfer are larger than the resistances in the spray-, pulse-and bubbleflow regime. Further, investigations on gas-liquid mass transfer at pressures above atmospheric conditions are hardly available. In industrial practice, the catalytic trickle beds always operate at elevated pressures to increase the concentration of the gaseous component in the liquid phase. In previous studies (Wammes et al., 1990a,b), we have shown that pressure has a strong influence on the hydrodynamics in a trickle-flow col- Vol. 37, No. 12 1849umn. The operating region for trickle flow becomes larger at higher pressures. In contrast to atmospheric trickle-flow conditions, the liquid holdup depends strongly on the gas velocity at elevated pressures. In this study, we investigate whether or not pressure also has an influence on the specific gas-liquid interfacial areas in the cocurrent trickle-flow operation. Greenfield (1978, 1979) and Levec et al. 1986Levec et al. , 1988 found experimentally that the liquid holdup and the pressure drop can exhibit hysteresis. Because the gas-liquid interfacial area is likely to be related to the holdup and pressure drop, we also pay attention to possible hysteresis phenomena for the interfacial areas.The gas-liquid interfacial area can be determined by usi...

Accumulation of the reactant supplied to a cooled semibatch reactor (SBR) will occur if the mass transfer rate across the interface is insufficient to keep pace with the supply rate. Then, due to a low starting temperature or supercooling, the reaction temperature does not rise fast enough to the desired value. This accumulation may eventually lead to a temperature runaway. We investigated the possibility of such an event for reactions of the type "chemically enhanced mass transfer" or "fast" and found that only low distribution coefficients, i.e. or lower, can lead to accumulation. At higher distribution coefficients, the mass transfer rate across the interface of a well-mixed dispersion is generally sufficient to prevent accumulation. A thermal runaway in the fast regime exerts a moderate effect, because the effective activation energy is halved. Calculations for the "instantaneous" reaction regime, regarded as a special case of fast reactions, show that there is no runaway possible.