1,721,045 research outputs found
Nuclear peroxisome proliferator activated receptor-gamma (PPARγ) as a therapeutic target to treat neurodegeneration and dependence elicited by drugs of abuse
Full text linkPeroxisome proliferator activated receptors (PPARs) are ligand-activated transcription factors that are located in the cytoplasm. After activation by specific ligands, PPARs enter the nucleus and heterodimerize with the retinoid x receptor. This heterodimer binds to PPAR response element in DNA to regulate the transcription of genes that are involved in different physiological processes, including insulin sensitization inflammatory response, and neuroprotection (Kapadia et al., 2008). The PPAR receptor family is composed of three isoforms—PPARalpha, PPARgamma and PPARdelta—that are expressed in both peripheral tissues and the brain. Endogeneous ligands of PPAR include polyunsatured fatty acids (e.g., oleic acid and arachidonic acid), prostaglandins, and low-density lipoproteins. PPAR can also be targeted by specific synthetic agonists that belong to the class of thiazolidinediones (TZDs), including pioglitazone and rosiglitazone. Because of their ability to bind PPARgamma, TZDs are approved for the treatment of type 2 diabetes and insulin resistance, improving insulin sensitivity in muscle, liver, and adipose tissue
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Recognition of Structures Leading to Transition in a Low Pressure Turbine Cascade Under Unsteady Inflow Conditions
No full textThe boundary layer developing over the suction side of a low pressure turbine cascade operating under unsteady inflow conditions has been experimentally investigated. Time-resolved Particle Image Velocimetry (PIV) measurements have been performed in two orthogonal planes, the blade to blade and a wall parallel plane embedded within the boundary layer, for two different wake reduced frequencies. Proper Orthogonal Decomposition (POD) has been used to analyze the data and to provide an interpretation of the most significant flow structures for each phase of the wake passing cycle. To this purpose, a POD based procedure that sorts the data synchronizing the measurements of the two planes has been developed. Phase averaged data are then obtained for both cases. Moreover, once properly sorted, POD has been applied to sub-ensembles of data at the same relative phase within the wake passing cycle. Detailed information on the most energetic turbulent structures at a particular phase are obtained with this procedure (called phased POD), overcoming the limit of classical phase average that just provides a statistical representation of the turbulence field. Furthermore, the synchronization of the measurements in the two planes allows the computation of the characteristic dimension of boundary layer structures that are responsible for transition. These structures are often identified as vortical filaments parallel to the wall, typically referred to as boundary layer streaks. The largest and most energetic structures are observed when the wake centerline passes over the rear part of the suction side, and they appear practically the same for both reduced frequencies. The passing wake forces transition leading to the breakdown of the boundary layer streaks. Otherwise, the largest differences between the low and high reduced frequency are observed in the calmed region. The post-processing of these two planes further allowed us to compute the spacing of the streaks and make it non-dimensional by the boundary layer displacement thickness observed for each phase. The non-dimensional value of the streaks spacing is about constant, irrespective of the reduced frequency
EFFECTS OF RIBBED SURFACES ON PROFILE LOSSES OF LOW-PRESSURE-TURBINE BLADES
No full textIn this work, streamwise oriented riblets were installed on a flat plate exposed to an adverse pressure gradient simulating the diffusing part of a low-pressure turbine (LPT) blade and, successively, on the suction side of an LPT cascade operating under unsteady inflow condition. Different riblets heights, spacings and positions have been tested, and complementary measuring techniques have been used to quantify their effects on the boundary layer evolution, and on losses. Experiments carried out on the flat plate allowed the detailed description of the riblet effects on the coherent structures developing within the boundary layer affecting transition, thus providing a rationale for the identification of the optimal riblet geometry once scaled in wall units. For riblet heights equal to about 20 wall-units, a maximum loss reduction of 8% was observed with respect to the smooth case. Otherwise, for larger riblet dimensions, earlier transition occurs due to enhanced boundary layer instability and losses significantly increase. Interestingly, the streamwise extension of the ribbed surfaces with respect to the transition region was found to play a minor role compared with the riblet dimension. The riblet configurations providing the highest reductions of viscous losses on the flat plate were then tested in the LPT blade cascade for different Reynolds numbers. In this case tests have been carried out with impinging upstream wakes. An overall reduction of the profile losses comparable to that observed in the flat plate case has been confirmed also in the unsteady operation of the turbine cascade. Low sensitivity of the profile losses to the riblet streamwise extension was also observed in the cascade application. This confirms that positive effects in terms of loss reduction can be obtained even when the exact transition position is not known a priori
SEALING FLOW RATE EFFECTS ON UNSTEADY LOSS PRODUCTION IN A LOW PRESSURE TURBINE STAGE
No full textEfforts to increase efficiency in aircraft and power generation turbines have raised turbine inlet temperatures (TIT), necessitating advanced cooling technologies to maintain material integrity. Preventing the ingestion of hot gases into components not suited for high temperatures, like stator/rotor cavity disks, is crucial. Current gas turbine performance strategies focus on minimizing leakage and optimizing sealing systems. Notably, losses from main flow and cavity interactions are prominent in stator/rotor systems. Using Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations, this study explores the unsteady interaction in a low-pressure turbine’s stator/rotor cavity. Numerical simulations of the University of Genova’s cavity rig are validated against experimental results. The investigation examines stator/rotor interaction effects, including wake ingestion from upstream rotor bars and the blocking impact of downstream rotor bars on cavity sealing. Varied cooling air injection rates in multiple calculations reveal insights into stage efficiency and cavity leakage. Emphasis is on unsteady loss mechanisms downstream of the vane row and in the region where the cavity flow is reintroduced in the main channel, providing a better understanding of losses influenced by cooling flow rates. The analysis of the loss amount along the axial direction demonstrates that losses generated in the vane row are increased prior to entering into the downstream rotor bars, due to cavity main flow interaction. This provide useful information about the production of losses due to sealing flow rate
Ostreopsis cf. ovata abundances on different benthic substrata: how to compare them?
Full text linkIn the framework of benthic harmful algal bloom monitoring, the most common sampling strategy is based on the collection of macroalgae, and the abundance of epiphytic microalgae are mainly expressed as cells g−1 macroalgal fresh weight (fw). However, this methodology has some inherent problems, due to (i) the thallus-specific weights that markedly differ among algal species, (ii) the thallus architecture, and (iii) the production of allelopathic compounds that affects the epiphyte abundances among macroalgae, irrespective of the available colonizable surface. This study proposes a method to compare the abundances of Ostreopsis cf. ovata cells on different substrata, using a conversion factor that converts the abundances expressed as cells g−1 fw (or dry weight) to cells cm−2. Expressing abundances in terms of cells cm−2, the abundances can be compared (i) among different macroalgal species and (ii) between macroalgae and other substrata (such as rocks, pebbles, or shellfish shells). We also propose to normalize abundances when different macroalgae are sampled throughout the bloom period, considering the different epiphyte loads of different macroalgal species regardless of the available surface area
Trend of Ostreopsis cf. ovata (Dinophyceae) along the Conero Riviera (northern Adriatic Sea) over two decades
Full text linkHarmful blooms of the toxic dinoflagellate Ostreopsis cf. ovata have been a recurrent phenomenon along the Mediterranean coasts in the last decades. Since first recorded, there has been a widespread belief that the extension of this dinoflagellate, well-known in tropical areas, to higher latitudes was due to global warming and the general rise of seawater temperature. Blooms of O. cf. ovata along the Conero Riviera (northern Adriatic Sea) occur between the end of the summer and the beginning of the autumn since 2006. The Ostreopsis cf. ovata abundances collected from its first record to today were analysed to better define the interannual trend of this phenomenon and its possible linking to certain climate change predictors. A significant increasing trend in the magnitude of Ostreopsis phenomenon was observed up to year 2012, then a stabilization at relatively low values was observed. This trend does not follow the incessant increase in water temperature observed during the last three decades in the Adriatic Sea, but rather recalls patterns seen in invasive species, although the provenience of O. cf. ovata in the Mediterranean Sea is still unresolved. Even if the Ostreopsis bloom in this area seems to slightly lessen in the last decade, Ostreopsis abundances still reach values of up to 103 cells cm-2 which could be harmful to human health
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