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Aging and brown adipose tissue activity decline in human: does the brain extinguish the fire?
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Endocannabinoids, sperm functions and energy metabolism
No full textCannabinoids, the main active components of marijuana, have been shown to exert different adverse effects on male reproduction both in vertebrates and invertebrates. The main effects of endocannabinoids, a particular group of endogenously produced cannabinoids, in sperm are the inhibition of motility, capacitation and acrosome reaction, all fundamental processes necessary for oocyte penetration, whose alteration leads to the inhibition of sperm fertilizing ability. These inhibitory effects are mediated by the direct action of endocannabinoids on sperm through the activation of the cannabinoid receptor subtype 1 that has been shown to be expressed in mature sperm. In many different cell types it has been demonstrated that endocannabinoids negatively influence mitochondrial activity. In the present paper it will be briefly reviewed the role of endocannabinoids, on sperm motility, capacitation and acrosome reaction with particular attention on the possible interference of endocannabinoids with sperm mitochondrial activity
THEORETICAL AND EXPERIMENTAL STUDY OF ENHANCED HEAT EXCHANGERS FOR AIR CONDITIONING APPLICATIONS
Full text linkNowadays the use of different techniques for the performance enhancement of heat exchangers is widespread and plays an important role in the design of energy systems.
This work focuses on the study of heat exchangers that use extended surfaces to increase the heat transfer coefficient and the heat transfer area of water-to-air, refrigerant-to-air and water-to-refrigerant units.
This work has been possible thanks to the financial support of Eurapo S.r.l.
The present thesis is divided in five Chapters. The first Chapter presents the experimental activity performed in the laboratory of Eurapo S.r.l. in order to determine the thermal performance of a water/air finned tube heat exchanger with three rows and 12 tubes per row. This HX has been tested varying the inlet conditions of water and air, simulating the working conditions in winter (only sensible heat transfer) and summer (sensible and latent heat transfer on the air side when dehumidification is present). Moreover, the same unit has been tested with three different inclination angles with respect to the direction of air flow, in order to investigate the effect of the tilt angle on the thermal performance in devices such as fan coils. Similar tests have been performed also in an enthalpy tunnel, which allowed the measurement of air volumetric flow rate during the heat transfer. This is particularly interesting in order to understand the influence of the condensate moisture and of the tilt angle on the pressure drop, which affects the air mass flow rate and the total heat flow rate exchanged.
The second Chapter reports the experimental activity performed with the aim to investigate the performance of a multiple aluminium minichannels heat exchanger working as evaporator and condenser. A special prototype has been designed, built and instrumented in order to measure pressure drop and quasi local heat transfer coefficient during single and two phase flow with different working fluids having low Global Warming Potential (GWP) as R32 and R1234ze(E). This prototype can be considered as a module of a bar-and-plate heat exchanger, which is an innovative solution for air conditioning applications. The results of these measurements have been compared with the prediction of several literature correlations.
In the third Chapter, a model has been developed in Matlab® to evaluate the thermal performance of finned tubes heat exchangers working with water inside and air outside the tubes. The model divides the heat exchanger in several elements that represent a small length of tube with the corresponding fins attached, and it is able to simulate different circuitries working with and without dehumidification. The heat transfer coefficients on the water and on the air side can be calculated respectively with two and eight different correlations. Using the experimental data obtained during the activity described in Chapter one, it was possible to assess the best predictive correlations for the heat transfer coefficient in the tested finned coil.
A model for a finned coil evaporator was also developed in the fourth Chapter. The model is able to simulate the behaviour of finned tubes heat exchangers working with a refrigerant fluid that evaporates inside the tubes. This allows to evaluate the performance of a dehumidification device working as the evaporator of an inverse cycle machine.
The last Chapter reports the numerical models developed in Matlab® to simulate the performance of bar-and-plate heat exchangers working as evaporators and condensers in refrigerant/water devices. The experimental analysis reported in the second Chapter allowed to choose the best predictive correlations, while the results of experimental tests on direct expansion systems provided by a different laboratory are used to validate the models
Confounding factors in the evaluation of alpha fetoprotein plasma levels in patients with testis cancer
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