Ammonia-induced toxicity in developing brain cells and strategies for neuroprotection

RESUME L'hyperammonémie est particulièrement toxique pour le cerveau des jeunes patients et entraîne une atrophie corticale, un élargissement des ventricules et des défauts de myélinisation, responsables de retards mentaux et développementaux. Les traitements actuels se limitent à diminuer le plus rapidement possible le taux d'ammoniaque dans l'organisme. L'utilisation de traitements neuroprotecteurs pendant les crises d'hyperammonémie permettrait de contrecarrer les effets neurologiques de l'ammoniaque et de prévenir l'apparition des troubles neurologiques. Au cours de cette thèse, nous avons testé trois stratégies de neuroprotection sur des cultures de cellules en agrégats issues du cortex d'embryons de rats et traitées à l'ammoniaque. - Nous avons tout d'abord testé si l'inhibition de protéines intracellulaires impliquées dans le déclenchement de la mort cellulaire pouvait protéger les cellules de la toxicité de l'ammoniaque. Nous avons montré que L'exposition à l'ammoniaque altérait la viabilité des neurones et des oligodendrocytes, et activait les caspases, la calpaïne et la kinase-5 dépendante des cyclines (cdk5) associée à son activateur p25. Alors que l'inhibition pharmacologique des caspases et de la calpaïne n'a pas permis de protéger les cellules cérébrales, un inhibiteur de la cdk5, appelé roscovitine, a réduit significativement la mort neuronale. L'inhibition de la cdk5 semble donc être une stratégie thérapeutique prometteuse pour prévenir 1es effets toxiques de 1'ammoniaque sur les neurones. - Nous avons ensuite étudié les mécanismes neuroprotecteurs déclenchés par le cerveau en réponse à la toxicité de l'ammoniaque. Nous avons montré que l'ammoniaque induisait la synthèse du facteur neurotrophique ciliaire (CNTF) par les astrocytes, via l'activation de la protéine kinase (MIAPK) p38. D'autre part, l'ajout de CNTF a permis de protéger les oligodendrocytes mais pas les neurones des cultures exposées à l'ammoniaque, via les voies de signalisations JAK/STAT, SAPK/JNK et c-jun. - Dans une dernière partie, nous avons voulu contrecarrer, par l'ajout de créatine, le déficit énergétique cérébral induit par l'ammoniaque. La créatine a permis de protéger des cellules de type astrocytaire mais pas les cellules cérébrales en agrégats. Cette thèse amis en évidence que les stratégies de neuroprotection chez les patients hyperammonémiques nécessiteront de cibler plusieurs voies de signalisation afin de protéger tous les types cellulaires du cerveau. Summary : In pediatric patients, hyperammonemia is mainly caused by urea cycle disorders or other inborn errors of metabolism, and leads to neurological injury with cortical atrophy, ventricular enlargement and demyelination. Children rescued from neonatal hyperammonemia show significant risk of mental retardation and developmental disabilities. The mainstay of therapy is limited to ammonia lowering through dietary restriction and alternative pathway treatments. However, the possibility of using treatments in a neuroprotective goal may be useful to improve the neurological outcome of patients. Thus, the main objective of this work was to investigate intracellular and extracellular signaling pathways altered by ammonia tonicity, so as to identify new potential therapeutic targets. Experiments were conducted in reaggregated developing brain cell cultures exposed to ammonia, as a model for the developing CNS of hyperammonemic young patients. Theses strategies of neuroprotection were tested: - The first strategy consisted in inhibiting intracellular proteins triggering cell death. Our data indicated that ammonia exposure altered the viability of neurons and oligodendrocytes. Apoptosis and proteins involved in the trigger of apoptosis, such as caspases, calpain and cyclin-dependent kinase-5 (cdk5) with its activator p25, were activated by ammonia exposure. While caspases and calpain inhibitors exhibited no protective effects, roscovitine, a cdk5 inhibitor, reduced ammonia-induced neuronal death. This work revealed that inhibition of cdk5 seems a promising strategy to prevent the toxic effects of ammonia on neurons. - The second strategy consisted in mimicking, the endogenous protective mechanisms triggered by ammonia in the brain. Ammonia exposure caused an increase of the ciliary neurotrophic factor (CNTF) expression, through the activation of the p38 mitogen-activated protein kinase (MAPK) in astrocytes. Treatment of cultures exposed to ammonia with exogenous CNTF demonstrated strong protective effects on oligodendrocytes but not on neurons. These protective effects seemed to involve JAK/STAT, SAPK/JNK and c-jun proteins. - The third strategy consisted in preventing the ammonia-induced cerebral energy deficit with creatine. Creatine treatment protected the survival of astrocyte-like cells through MAPKs pathways. In contrast, it had no protective effects in reaggregated developing brain cell cultures exposed to ammonia. The present study suggests that neuroprotective strategies should optimally be directed at multiple targets to prevent ammonia-induced alterations of the different brain cell types.

What energy level is required to avoid nutrient depletion after surgery in oropharyngeal cancer?

The rate of energy expenditure was repeatedly measured by indirect calorimetry both in the basal state (BMR) and in the resting fed state (RMR) in 8 middle-aged male patients operated for oropharyngeal cancer. In the postsurgical phase, two sequential energy levels were administered by nasogastric tube: (1) a 'maintenance' level (days 3-5) at 1.4 X measured presurgery BMR; (2) a 'supramaintenance' level (days 6-9) at 1.7 X measured BMR on day 6. Before surgery the patients had a BMR averaging (23.7 +/- 1.0 kcal/kg.day). After surgery BMR increased to 27.6 +/- 2.7 kcal/kg.day (day 6), then it decreased to 24.4 +/- 1.4 kcal/kg.day (day 10). The difference between RMR and BMR yielded a nutrient-induced thermogenesis averaging 5 +/- 1 and 8.5 +/- 2% (p less than 0.05) on levels 1 and 2, respectively. It is concluded that an energy level corresponding to 1.4 X presurgery BMR is sufficient to maintain energy and substrate equilibrium in nondepleted patients, whereas 1.7 X BMR induces positive protein and fat balances concomitant to a decrease efficiency of energy utilization.

Exchange-correlation effects on quantum wires with spin-orbit interactions under the influence of in-plane magnetic fields.

Within the noncollinear local spin-density approximation, we have studied the ground state structure of a parabolically confined quantum wire submitted to an in-plane magnetic field, including both Rashba and Dresselhaus spin-orbit interactions. We have explored a wide range of linear electronic densities in the weak (strong) coupling regimes that appear when the ratio of spin-orbit to confining energy is small (large). These results are used to obtain the conductance of the wire. In the strong coupling limit, the interplay between the applied magnetic field¿irrespective of the in-plane direction, the exchange-correlation energy, and the spin-orbit energy-produces anomalous plateaus in the conductance vs linear density plots that are otherwise absent, or washes out plateaus that appear when the exchange-correlation energy is not taken into account.

Anomalous specific-heat jump in a two-component ultracold Fermi gas

The thermodynamic functions of a Fermi gas with spin population imbalance are studied in the temperature-asymmetry plane in the BCS limit. The low-temperature domain is characterized by an anomalous enhancement of the entropy and the specific heat above their values in the unpaired state, decrease of the gap and eventual unpairing phase transition as the temperature is lowered. The unpairing phase transition induces a second jump in the specific heat, which can be measured in calorimetric experiments. While the superfluid is unstable against a supercurrent carrying state, it may sustain a metastable state if cooled adiabatically down from the stable high-temperature domain. In the latter domain the temperature dependence of the gap and related functions is analogous to the predictions of the BCS theory.

Oxygen consumption in collagenase-liberated rat adipocytes in relation to cell size and age.

Oxygen consumption of collagenase-liberated rat adipocytes was measured by two different techniques: a microspectrophotometric method using hemoglobin as indicator of respiration and a technique using the oxygen electrode. These two completely different techniques gave similar values for oxygen consumption. With the spectrophotometric method, the oxygen consumption of single fat cells was determined. A close positive correlation (r = greater than 0.90) between oxygen consumption and fat cell size was observed in each tissue examined. With the oxygen electrode technique, oxygen consumption of adipocyte suspensions from young (40 days, 180 g) and old (90 days, 480 g) rats was examined. Fat cells of the suspensions were separated into classes of different size by a flotation technique. A significant positive correlation between fat cell size and oxygen consumption was observed in both young (r = 0.88) and old (r = 0.95) rats. However, the slope was much steeper in young rats. At a cell weight of 0.1 microgram the oxygen consumption was 0.364 and 0.086 microL O2/10(6) cells/min-1 in young and old rats, respectively. In the literature, a number of separate metabolic pathways have been found to be related positively to fat cell size and negatively to age. We conclude that these scattered metabolic observations are in agreement with integrated data on energy expenditure as evaluated from oxygen consumption. Estimations of the energy expenditure of adipose tissue indicates that this tissue is responsible for about 1% and 0.5% of the total energy expenditure in young and old rats, respectively.

The influence of the symmetry energy on the giant monopole resonance of neutron-rich nuclei analyzed in Thomas-Fermi theory

We analyze the influence of the density dependence of the symmetry energy on the average excitation energy of the isoscalar giant monopole resonance (GMR) in stable and exotic neutron-rich nuclei by applying the relativistic extended Thomas-Fermi method in scaling and constrained calculations. For the effective nuclear interaction, we employ the relativistic mean field model supplemented by an isoscalar-isovector meson coupling that allows one to modify the density dependence of the symmetry energy without compromising the success of the model for binding energies and charge radii. The semiclassical estimates of the average energy of the GMR are known to be in good agreement with the results obtained in full RPA calculations. The present analysis is performed along the Pb and Zr isotopic chains. In the scaling calculations, the excitation energy is larger when the symmetry energy is softer. The same happens in the constrained calculations for nuclei with small and moderate neutron excess. However, for nuclei of large isospin the constrained excitation energy becomes smaller in models having a soft symmetry energy. This effect is mainly due to the presence of loosely-bound outer neutrons in these isotopes. A sharp increase of the estimated width of the resonance is found in largely neutron-rich isotopes, even for heavy nuclei, which is enhanced when the symmetry energy of the model is soft. The results indicate that at large neutron numbers the structure of the low-energy region of the GMR strength distribution changes considerably with the density dependence of the nuclear symmetry energy, which may be worthy of further characterization in RPA calculations of the response function.

Negative impact of hypocaloric feeding and energy balance on clinical outcome in ICU patients

Résumé Introduction : Les patients nécessitant une prise en charge prolongée en milieu de soins intensifs et présentant une évolution compliquée, développent une réponse métabolique intense caractérisée généralement par un hypermétabolisme et un catabolisme protéique. La sévérité de leur atteinte pathologique expose ces patients à la malnutrition, due principalement à un apport nutritionnel insuffisant, et entraînant une balance énergétique déficitaire. Dans un nombre important d'unités de soins intensifs la nutrition des patients n'apparaît pas comme un objectif prioritaire de la prise en charge. En menant une étude prospective d'observation afin d'analyser la relation entre la balance énergétique et le pronostic clinique des patients avec séjours prolongés en soins intensifs, nous souhaitions changer cette attitude et démonter l'effet délétère de la malnutrition chez ce type de patient. Méthodes : Sur une période de 2 ans, tous les patients, dont le séjour en soins intensifs fut de 5 jours ou plus, ont été enrôlés. Les besoins en énergie pour chaque patient ont été déterminés soit par calorimétrie indirecte, soit au moyen d'une formule prenant en compte le poids du patient (30 kcal/kg/jour). Les patients ayant bénéficié d'une calorimétrie indirecte ont par ailleurs vérifié la justesse de la formule appliquée. L'âge, le sexe le poids préopératoire, la taille, et le « Body mass index » index de masse corporelle reconnu en milieu clinique ont été relevés. L'énergie délivrée l'était soit sous forme nutritionnelle (administration de nutrition entérale, parentérale ou mixte) soit sous forme non-nutritionnelle (perfusions : soluté glucosé, apport lipidique non nutritionnel). Les données de nutrition (cible théorique, cible prescrite, énergie nutritionnelle, énergie non-nutritionnelle, énergie totale, balance énergétique nutritionnelle, balance énergétique totale), et d'évolution clinique (nombre des jours de ventilation mécanique, nombre d'infections, utilisation des antibiotiques, durée du séjour, complications neurologiques, respiratoires gastro-intestinales, cardiovasculaires, rénales et hépatiques, scores de gravité pour patients en soins intensifs, valeurs hématologiques, sériques, microbiologiques) ont été analysées pour chacun des 669 jours de soins intensifs vécus par un total de 48 patients. Résultats : 48 patients de 57±16 ans dont le séjour a varié entre 5 et 49 jours (motif d'admission : polytraumatisés 10; chirurgie cardiaque 13; insuffisance respiratoire 7; pathologie gastro-intestinale 3; sepsis 3; transplantation 4; autre 8) ont été retenus. Si nous n'avons pu démontrer une relation entre la balance énergétique et plus particulièrement, le déficit énergétique, et la mortalité, il existe une relation hautement significative entre le déficit énergétique et la morbidité, à savoir les complications et les infections, qui prolongent naturellement la durée du séjour. De plus, bien que l'étude ne comporte aucune intervention et que nous ne puissions avancer qu'il existe une relation de cause à effet, l'analyse par régression multiple montre que le facteur pronostic le plus fiable est justement la balance énergétique, au détriment des scores habituellement utilisés en soins intensifs. L'évolution est indépendante tant de l'âge et du sexe, que du status nutritionnel préopératoire. L'étude ne prévoyait pas de récolter des données économiques : nous ne pouvons pas, dès lors, affirmer que l'augmentation des coûts engendrée par un séjour prolongé en unité de soins intensifs est induite par un déficit énergétique, même si le bon sens nous laisse penser qu'un séjour plus court engendre un coût moindre. Cette étude attire aussi l'attention sur l'origine du déficit énergétique : il se creuse au cours de la première semaine en soins intensifs, et pourrait donc être prévenu par une intervention nutritionnelle précoce, alors que les recommandations actuelles préconisent un apport énergétique, sous forme de nutrition artificielle, qu'à partir de 48 heures de séjour aux soins intensifs. Conclusions : L'étude montre que pour les patients de soins intensifs les plus graves, la balance énergétique devrait être considérée comme un objectif important de la prise en charge, nécessitant l'application d'un protocole de nutrition précoce. Enfin comme l'évolution à l'admission des patients est souvent imprévisible, et que le déficit s'installe dès la première semaine, il est légitime de s'interroger sur la nécessité d'appliquer ce protocole à tous les patients de soins intensifs et ceci dès leur admission. Summary Background and aims: Critically ill patients with complicated evolution are frequently hypermetabolic, catabolic, and at risk of underfeeding. The study aimed at assessing the relationship between energy balance and outcome in critically ill patients. Methods: Prospective observational study conducted in consecutive patients staying 5 days in the surgical ICU of a University hospital. Demographic data, time to feeding, route, energy delivery, and outcome were recorded. Energy balance was calculated as energy delivery minus target. Data in means+ SD, linear regressions between energy balance and outcome variables. Results: Forty eight patients aged 57±16 years were investigated; complete data are available in 669 days. Mechanical ventilation lasted 11±8 days, ICU stay 15+9 was days, and 30-days mortality was 38%. Time to feeding was 3.1 ±2.2 days. Enteral nutrition was the most frequent route with 433 days. Mean daily energy delivery was 1090±930 kcal. Combining enteral and parenteral nutrition achieved highest energy delivery. Cumulated energy balance was between -12,600+ 10,520 kcal, and correlated with complications (P<0.001), already after 1 week. Conclusion: Negative energy balances were correlated with increasing number of complications, particularly infections. Energy debt appears as a promising tool for nutritional follow-up, which should be further tested. Delaying initiation of nutritional support exposes the patients to energy deficits that cannot be compensated later on.

Mutations in the DNA-binding domain of NR2E3 affect in vivo dimerization and interaction with CRX.

BACKGROUND: NR2E3 (PNR) is an orphan nuclear receptor essential for proper photoreceptor determination and differentiation. In humans, mutations in NR2E3 have been associated with the recessively inherited enhanced short wavelength sensitive (S-) cone syndrome (ESCS) and, more recently, with autosomal dominant retinitis pigmentosa (adRP). NR2E3 acts as a suppressor of the cone generation program in late mitotic retinal progenitor cells. In adult rod photoreceptors, NR2E3 represses cone-specific gene expression and acts in concert with the transcription factors CRX and NRL to activate rod-specific genes. NR2E3 and CRX have been shown to physically interact in vitro through their respective DNA-binding domains (DBD). The DBD also contributes to homo- and heterodimerization of nuclear receptors. METHODOLOGY/PRINCIPAL FINDINGS: We analyzed NR2E3 homodimerization and NR2E3/CRX complex formation in an in vivo situation by Bioluminescence Resonance Energy Transfer (BRET(2)). NR2E3 wild-type protein formed homodimers in transiently transfected HEK293T cells. NR2E3 homodimerization was impaired in presence of disease-causing mutations in the DBD, except for the p.R76Q and p.R104W mutant proteins. Strikingly, the adRP-linked p.G56R mutant protein interacted with CRX with a similar efficiency to that of NR2E3 wild-type and p.R311Q proteins. In contrast, all other NR2E3 DBD-mutant proteins did not interact with CRX. The p.G56R mutant protein was also more effective in abolishing the potentiation of rhodospin gene transactivation by the NR2E3 wild-type protein. In addition, the p.G56R mutant enhanced the transrepression of the M- and S-opsin promoter, while all other NR2E3 DBD-mutants did not. CONCLUSIONS/SIGNIFICANCE: These results suggest different disease mechanisms in adRP- and ESCS-patients carrying NR2E3 mutations. Titration of CRX by the p.G56R mutant protein acting as a repressor in trans may account for the severe clinical phenotype in adRP patients.

Role of structural saturation and geometry in the luminescence of silicon-based nanostructured materials

The structural saturation and stability, the energy gap, and the density of states of a series of small, silicon-based clusters have been studied by means of the PM3 and some ab initio (HF/6-31G* and 6-311++G**, CIS/6-31G* and MP2/6-31G*) calculations. It is shown that in order to maintain a stable nanometric and tetrahedral silicon crystallite and remove the gap states, the saturation atom or species such as H, F, Cl, OH, O, or N is necessary, and that both the cluster size and the surface species affect the energetic distribution of the density of states. This research suggests that the visible luminescence in the silicon-based nanostructured material essentially arises from the nanometric and crystalline silicon domains but is affected and protected by the surface species, and we have thus linked most of the proposed mechanisms of luminescence for the porous silicon, e.g., the quantum confinement effect due to the cluster size and the effect of Si-based surface complexes.

GLUT2 in pancreatic and extra-pancreatic gluco-detection (review).

Detection of variations in blood glucose concentrations by pancreatic beta-cells and a subsequent appropriate secretion of insulin are key events in the control of glucose homeostasis. Because a decreased capability to sense glycemic changes is a hallmark of type 2 diabetes, the glucose signalling pathway leading to insulin secretion in pancreatic beta-cells has been extensively studied. This signalling mechanism depends on glucose metabolism and requires the presence of specific molecules such as GLUT2, glucokinase and the K(ATP) channel subunits Kir6.2 and SUR1. Other cells are also able to sense variations in glycemia or in local glucose concentrations and to modulate different physiological functions participating in the general control of glucose and energy homeostasis. These include cells forming the hepatoportal vein glucose sensor, which controls glucose storage in the liver, counterregulation, food intake and glucose utilization by peripheral tissues and neurons in the hypothalamus and brainstem whose firing rates are modulated by local variations in glucose concentrations or, when not protected by a blood-brain barrier, directly by changes in blood glucose levels. These glucose-sensing neurons are involved in the control of insulin and glucagon secretion, food intake and energy expenditure. Here, recent physiological studies performed with GLUT2-/- mice will be described, which indicate that this transporter is essential for glucose sensing by pancreatic beta-cells, by the hepatoportal sensor and by sensors, probably located centrally, which control activity of the autonomic nervous system and stimulate glucagon secretion. These studies may pave the way to a fine dissection of the molecular and cellular components of extra-pancreatic glucose sensors involved in the control of glucose and energy homeostasis.

Effects of mental stress on insulin-mediated glucose metabolism and energy expenditure in lean and obese women.

The effects of the sympathetic activation elicited by a mental stress on insulin sensitivity and energy expenditure (VO(2)) were studied in 11 lean and 8 obese women during a hyperinsulinemic-euglycemic clamp. Six lean women were restudied under nonselective beta-adrenergic blockade with propranolol to determine the role of beta-adrenoceptors in the metabolic response to mental stress. In lean women, mental stress increased VO(2) by 20%, whole body glucose utilization ([6,6-(2)H(2)]glucose) by 34%, and cardiac index (thoracic bioimpedance) by 25%, whereas systemic vascular resistance decreased by 24%. In obese women, mental stress increased energy expenditure as in lean subjects, but it neither stimulated glucose uptake nor decreased systemic vascular resistance. In the six lean women who were restudied under propranolol, the rise in VO(2), glucose uptake, and cardiac output and the decrease in systemic vascular resistance during mental stress were all abolished. It is concluded that 1) in lean subjects, mental stress stimulates glucose uptake and energy expenditure and produces vasodilation; activation of beta-adrenoceptors is involved in these responses; and 2) in obese patients, the effects of mental stress on glucose uptake and systemic vascular resistance, but not on energy expenditure, are blunted.

Binding free energy differences in a TCR-peptide-MHC complex induced by a peptide mutation: a simulation analysis.

Recognition by the T-cell receptor (TCR) of immunogenic peptides presented by class I major histocompatibility complexes (MHCs) is the determining event in the specific cellular immune response against virus-infected cells or tumor cells. It is of great interest, therefore, to elucidate the molecular principles upon which the selectivity of a TCR is based. These principles can in turn be used to design therapeutic approaches, such as peptide-based immunotherapies of cancer. In this study, free energy simulation methods are used to analyze the binding free energy difference of a particular TCR (A6) for a wild-type peptide (Tax) and a mutant peptide (Tax P6A), both presented in HLA A2. The computed free energy difference is 2.9 kcal/mol, in good agreement with the experimental value. This makes possible the use of the simulation results for obtaining an understanding of the origin of the free energy difference which was not available from the experimental results. A free energy component analysis makes possible the decomposition of the free energy difference between the binding of the wild-type and mutant peptide into its components. Of particular interest is the fact that better solvation of the mutant peptide when bound to the MHC molecule is an important contribution to the greater affinity of the TCR for the latter. The results make possible identification of the residues of the TCR which are important for the selectivity. This provides an understanding of the molecular principles that govern the recognition. The possibility of using free energy simulations in designing peptide derivatives for cancer immunotherapy is briefly discussed.

Major mite allergen Der f 1 concentration is reduced in buildings with improved energy performance.

BACKGROUND: Environmental conditions play a crucial role in mite growth, and optimal environmental control is key in the prevention of airway inflammation in chronic allergic rhinoconjunctivitis or asthma. OBJECTIVE: To evaluate the relationship between building energy performance and indoor mite allergen concentration in a cross-sectional study. METHODS: Major allergen concentration (Der f 1, Der p 1, mite group 2, Fel d 1 and Bla g 2) was determined by quantitative dot blot analysis from mattress and carpet dust samples in five buildings designed for low energy use (LEB) and in six control buildings (CB). Inhabitants had received 4 weeks prior to mite measurement a personal validated questionnaire related to the perceived state of health and comfort of living. RESULTS: Cumulative mite allergen concentration (with Der f 1 as the major contributor) was significantly lower in LEB as compared with CB both in mattresses and in carpets. In contrast, the two categories of buildings did not differ in Bla g 2 and Fel d 1 concentration, in the amount of dust and airborne mould collected. Whereas temperature was higher in LEB, relative humidity was significantly lower than in CB. Perceived overall comfort was better in LEB. CONCLUSIONS: Major mite allergen Der f 1 preferentially accumulates in buildings not specifically designed for low energy use, reaching levels at risk for sensitization. We hypothesize that controlled mechanical ventilation present in all audited LEB may favour lower air humidity and hence lower mite growth and allergen concentration, while preserving optimal perceived comfort.

Impingement jet cooling of end windings in a high-speed electric machine

The rotational speed of high-speed electric machines is over 15 000 rpm. These machines are compact in size when compared to the power rate. As a consequence, the heat fluxes are at a high level and the adequacy of cooling becomes an important design criterion. In the high-speed machines, the air gap between the stator and rotor is a narrow flow channel. The cooling air is produced with a fan and the flow is then directed to the air gap. The flow in the gap does not provide sufficient cooling for the stator end windings, and therefore additional cooling is required. This study investigates the heat transfer and flow fields around the coil end windings when cooling jets are used. As a result, an innovative and new assembly is introduced for the cooling jets, with the benefits of a reduced amount of hot spots, a lower pressure drop, and hence a lower power need for the cooling fan. The gained information can also be applied to improve the cooling of electric machines through geometry modifications. The objective of the research is to determine the locations of the hot spots and to find out induced pressure losses with different jet alternatives. Several possibilities to arrange the extra cooling are considered. In the suggested approach cooling is provided by using a row of air jets. The air jets have three main tasks: to cool the coils effectively by direct impingement jets, to increase and cool down the flow that enters the coil end space through the air gap, and to ensure the correct distribution of the flow by forming an air curtain with additional jets. One important aim of this study is the arrangement of cooling jets in such manner that hot spots can be avoided to wide extent. This enables higher power density in high-speed motors. This cooling system can also be applied to the ordinary electric machines when efficient cooling is needed. The numerical calculations have been performed using a commercial Computational Fluid Dynamics software. Two geometries have been generated: cylindrical for the studied machine and Cartesian for the experimental model. The main parameters include the positions, arrangements and number of jets, the jet diameters, and the jet velocities. The investigated cases have been tested with two widely used turbulence models and using a computational grid of over 500 000 cells. The experimental tests have been made by using a simplified model for the end winding space with cooling jets. In the experiments, an emphasis has been given to flow visualisation. The computational analysis shows good agreement with the experimental results. Modelling of the cooling jet arrangement enables also a better understanding of the complex system of heat transfer at end winding space.

Water, energy and early postnatal growth in preterm infants.

Non-invasive methods, including stable isotope techniques, indirect calorimetry, nutritional balance and skinfold thickness, have given a new insight into early postnatal growth in neonates. Neonates and premature infants in particular, create an unusual opportunity to study the fluid and metabolic adaptation to extrauterine life because their physical environment can be controlled, fluid and energy balance can be measured and the link between metabolism and the energetics of their postnatal growth can be assessed accurately. Thus the postnatal time course of total body water, heat production, energy cost of growth and composition of weight gain have been quantified in a series of "healthy" low-birth-weight premature infants. These results show that total body water is remarkably stable between postnatal days 3-21. Energy expenditure and heat production rates increase postnatally from mean values of 40 kcal/kg/day during the first week to 60 kcal/kg/day in the third week. An apparent energy balance deficit of 180 kcal/kg can be ascribed to premature delivery. The cost of protein metabolism is the highest energy demanding process related to growth. The fact that nitrogen balance becomes positive within 72 h after birth places the newborn in a transitional situation of dissociated balance between energy and protein metabolism during early postnatal growth: skinfold thickness, dry body mass and fat decrease, while there is a gain in protein and increase in supine length. This particular situation ends during the second postnatal week and soon thereafter the rate of weight gain matches statural growth. The goals of the following review are to summarize data on total body water and energy metabolism in premature infants and to discuss how they correlate with physiological aspects of early postnatal growth.