M.Ing. / A steady-state model was developed to predict the performance of the highpressure side' of vapour-compression air-conditioning systems. The model consists of two segments; the compressor model and condenser model. The compressor model consists of a single empirical equation, for reciprocating compressors, operating with R-22, and having a cooling capacity from 2.6 to 3.5 kW. An important advantage of the approach is that the compressor performance indexes are based on operating conditions. The condenser model displays an exact method to determine physical dimensions of heat exchangers, and a simple, accurate manner to calculate the heat transfer variables. The correctness of the condensing temperature is obtained by an iterative procedure, using terms from both the compressor and condenser studies. The feasibility of the proposed model is demonstrated via a comparison with experimental data and a simulation study. Results indicate a good correlation between the mathematical model and its counterparts.

The air conditioning system in a car is, in addition to the heating system, installed to increase the comfort in the passenger compartment. Comfort is not the only reason for automotive air conditioning systems, as road safety also improves with the comfort of the driver, as a pleasant environment reduces driver fatigue. The rising environmental problems and, hence, resulting stringent legislation are forcing the automobile industry to develop cars with ever decreasing fuel consumptions. The question of better fuel consumption and energy utilisation does not stop with the engine and aerodynamics, but is required of the air-conditioning system as well. Thus, incessantly innovative technologies are developed to decrease the energy required by the air-conditioning systems. The interaction of the refrigerant cycle components and the rapidly changing operating conditions of the car (speed, revolutions per minute, etc.) places extensive demands on the control system. In addition, the air-conditioning system is also designed for high ambient temperatures (cool down), but is mostly used in fairly moderate conditions. This operation allows for energy saving control strategies such as externally controlled compressors, blower motor control, etc. The experimental comparison of different air-conditioning systems, components or control strategies is very time consuming and extensive, and the use of an air-conditioned wind tunnel is inevitable when experiments need to be done with reproducible ambient conditions.This, combined with the high costs of installation and operation of a wind tunnel is a major problem. Furthermore, the effect of component or control strategy enhancements should be available as soon as possible in the early stages of design. The above considerations have prompted the rapid development of new powerful simulation tools, but in most cases the simulation tools are focused on one specific component or problem only. A more holistic approach would be to combine the calculations of two or more programs. This implies the adaptation of the model to more programs which leads to a lack of transparency. Obviously, the entire development work cannot be done entirely by simulation, especially in the later phases of the development where it would still be necessary to build prototypes to evaluate the done work experimentally. However, in the early stages of development, it would be advantagous to work without expensive prototypes.

M.Ing. / Wet compression versus dry compression in refrigeration cycles working with pure refrigerants or non-azeotropic mixtures is investigated in this paper. In total 34 pure refrigerants as well as 31 non-azeotropic binary mixtures are considered. This resulted in approximately 300 different mixtures being analysed. The pure refrigerants and refrigerant mixtures were analysed for one cooling application, namely that of spatial air conditioning at an evaporating temperature of 7°C, and a condensing temperature of 50°C. The investigation was conducted with cycle analyses calculating performances at different wet and dry compressor inlet values. Use was made of thermodynamic refrigerant properties calculated from a computer database. It was concluded that for both pure and non-azeotropic refrigerants analysed, all those with re-entrant saturation vapour lines produce better cooling COP's when the refrigerant is superheated before entering the compressor. Only a few of the refrigerants with bell-shaped T-s curves consistently produce higher cooling COP's when wet compression is used. However, their cooling capacities decreased while the compressor displacement rates increased. It was concluded that in general dry compression is more favourable than wet compression. From the exceptions that do exist, some manage to produce relatively high COP c 's while retaining competitive cooling capacities. A by-product of this study is that, from the vast amount of refrigerant mixtures analysed, valuable knowledge was gathered regarding refrigerants not commonly used in the applications considered.

Thesis advisor: Michael A. McDannald / Identifying the neural circuits underlying adaptive fear is fundamental to understanding and developing more effective treatments for anxiety disorders. Adaptive behavior requires fear to scale to the level of threat and dysfunction in this capacity is a hallmark of fear-related anxiety disorders. Identifying the neural circuits underlying adaptive fear is fundamental to understanding anxiety disorders and propelling more effective treatments for patients. Fear is adaptive when the level of the response rapidly scales to degree of threat. Using a discrimination procedure consisting of danger, uncertainty, and safety cues, our laboratory has found rapid fear scaling (within 2 s of cue presentation). However, the neural underpinnings of this behavior are unknown. The overarching goal of this dissertation is to examine a role for the nucleus accumbens core (NAcc) in scaling fear to degree of threat. In three experiments I used neurotoxic lesions, optogenetic inhibition, and in vivo electrophysiology combined with an intricate fear learning procedure to elucidate a role for the NAcc in both general and rapid scaling of fear. Permanent NAcc dysfunction, via neurotoxic lesion, generally disrupted the ability to scale fear to degree of threat and specifically impaired one component of scaling: rapid discrimination of uncertain threat and safety. Reversible NAcc dysfunction, via optogenetic inhibition, specifically impaired rapid discrimination of uncertain threat and safety. Further, I demonstrated that NAcc activity is threat responsive and exhibits heterogeneity in the timing and specific nature of threat firing. The results reveal that the NAcc is essential to scale fear to degree of threat and responds to threat cues across both rapid and general timescales. Taken together, the results reveal a novel role for the NAcc in scaling fear and identify it as a plausible source of dysfunction in stress and anxiety disorders. Identifying the brain regions underlying adaptive fear is fundamental to understanding and developing more effective treatments for anxiety disorders. / Thesis (PhD) — Boston College, 2021. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Psychology.

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The fact" that behavior can be conditioned through the use of verbal reinforcement is well documented (c.f. Kanf er, 1968 ; Flanders , 1968 ) • Specific critical responses of a subject, reinforced by praise or utterance of the word "good, " tend to increase in frequency, in this type of conditioning.