Experimental and numerical investigation of a porous receiver equipped with Raschig Rings for CSP applications

In the context of central solar tower systems, tubular receivers are among the most appealing absorber solutions: the absorbed solar radiation is transferred from the tube external surface to the heat transfer fluid (HTF) flowing within the absorber. In the case of air as HTF, very high temperatures of the coolant can be obtained in principle, thus increasing the efficiency of the downstream thermodynamic cycle. To explore the possible applicability of a porous medium made of Raschig Rings (RRs), already successfully adopted in the heat removal from the resonant cavity of a technological device, the gyrotron, where the heat flux can go up to 20–25 MW/m2 and removed by subcooled water, a mock-up of a planar receiver equipped with RRs has been tested in a solar furnace, using air as coolant. The test results are presented here and analyzed1. Furthermore, a numerical model of the mock-up, where the RRs are modeled in detail by the Discrete Element Method, is presented and its capability to reproduce the measured data demonstrated. The model shows, for the tested configuration, an enhancement of the heat transfer of a factor of ~5 with respect to a plain channel with the same envelope, and a Performance Evaluation Criteria of 2–2.5 when the device is compared to the same receiver configuration, but without RRs

STAT3-mediated astrocyte reactivity associated with brain metastasis contributes to neurovascular dysfunction

© 2020 American Association for Cancer Research. Astrocytes are thought to play a pivotal role in coupling neural activity and cerebral blood flow. However, it has been shown that astrocytes undergo morphologic changes in response to brain metastasis, switching to a reactive phenotype, which has the potential to significantly compromise cerebrovascular function and contribute to the neurological sequelae associated with brain metastasis. Given that STAT3 is a key regulator of astrocyte reactivity, we aimed here to determine the impact of STAT3- mediated astrocyte reactivity on neurovascular function in brain metastasis. Rat models of brain metastasis and ciliary neurotrophic factor were used to induce astrocyte reactivity. Multimodal imaging, electrophysiology, and IHC were performed to determine the relationship between reactive astrocytes and changes in the cerebrovascular response to electrical and physiological stimuli. Subsequently, the STAT3 pathway in astrocytes was inhibited with WP1066 to determine the role of STAT3- mediated astrocyte reactivity, specifically, in brain metastasis. Astrocyte reactivity associated with brain metastases impaired cerebrovascular responses to stimuli at both the cellular and functional level and disrupted astrocyte-endothelial interactions in both animal models and human brain metastasis samples. Inhibition of STAT3-mediated astrocyte reactivity in rats with brain metastases restored cerebrovascular function, as shown by in vivo imaging, and limited cerebrovascular changes associated with tumor growth. Together these findings suggest that inhibiting STAT3-mediated astrocyte reactivity may confer significant improvements in neurological outcome for patients with brain metastases and could potentially be tested in other brain tumors

Reactive astrocyte nomenclature, definitions, and future directions

Reactive astrocytes are astrocytes undergoing morphological, molecular, and functional remodeling in response to injury, disease, or infection of the CNS. Although this remodeling was first described over a century ago, uncertainties and controversies remain regarding the contribution of reactive astrocytes to CNS diseases, repair, and aging. It is also unclear whether fixed categories of reactive astrocytes exist and, if so, how to identify them. We point out the shortcomings of binary divisions of reactive astrocytes into good-vs-bad, neurotoxic-vs-neuroprotective or A1-vs-A2. We advocate, instead, that research on reactive astrocytes include assessment of multiple molecular and functional parameters-preferably in vivo-plus multivariate statistics and determination of impact on pathological hallmarks in relevant models. These guidelines may spur the discovery of astrocyte-based biomarkers as well as astrocyte-targeting therapies that abrogate detrimental actions of reactive astrocytes, potentiate their neuro- and glioprotective actions, and restore or augment their homeostatic, modulatory, and defensive functions

Bayesian Comparison of Neurovascular Coupling Models Using EEG-fMRI

Functional magnetic resonance imaging (fMRI), with blood oxygenation level-dependent (BOLD) contrast, is a widely used technique for studying the human brain. However, it is an indirect measure of underlying neuronal activity and the processes that link this activity to BOLD signals are still a topic of much debate. In order to relate findings from fMRI research to other measures of neuronal activity it is vital to understand the underlying neurovascular coupling mechanism. Currently, there is no consensus on the relative roles of synaptic and spiking activity in the generation of the BOLD response. Here we designed a modelling framework to investigate different neurovascular coupling mechanisms. We use Electroencephalographic (EEG) and fMRI data from a visual stimulation task together with biophysically informed mathematical models describing how neuronal activity generates the BOLD signals. These models allow us to non-invasively infer the degree of local synaptic and spiking activity in the healthy human brain. In addition, we use Bayesian model comparison to decide between neurovascular coupling mechanisms. We show that the BOLD signal is dependent upon both the synaptic and spiking activity but that the relative contributions of these two inputs are dependent upon the underlying neuronal firing rate. When the underlying neuronal firing is low then the BOLD response is best explained by synaptic activity. However, when the neuronal firing rate is high then both synaptic and spiking activity are required to explain the BOLD signal

Ciliary Neurotrophic Factor Protects Striatal Neurons against Excitotoxicity by Enhancing Glial Glutamate Uptake

Ciliary neurotrophic factor (CNTF) is a potent neuroprotective cytokine in different animal models of glutamate-induced excitotoxicity, although its action mechanisms are still poorly characterized. We tested the hypothesis that an increased function of glial glutamate transporters (GTs) could underlie CNTF-mediated neuroprotection. We show that neuronal loss induced by in vivo striatal injection of the excitotoxin quinolinic acid (QA) was significantly reduced (by ∼75%) in CNTF-treated animals. In striatal slices, acute QA application dramatically inhibited corticostriatal field potentials (FPs), whose recovery was significantly higher in CNTF rats compared to controls (∼40% vs. ∼7%), confirming an enhanced resistance to excitotoxicity. The GT inhibitor dl-threo-β-benzyloxyaspartate greatly reduced FP recovery in CNTF rats, supporting the role of GT in CNTF-mediated neuroprotection. Whole-cell patch-clamp recordings from striatal medium spiny neurons showed no alteration of basic properties of striatal glutamatergic transmission in CNTF animals, but the increased effect of a low-affinity competitive glutamate receptor antagonist (γ-d-glutamylglycine) also suggested an enhanced GT function. These data strongly support our hypothesis that CNTF is neuroprotective via an increased function of glial GTs, and further confirms the therapeutic potential of CNTF for the clinical treatment of progressive neurodegenerative diseases involving glutamate overflow

Role of the multidisciplinary team in the care of the tracheostomy patient

Barbara Bonvento,1 Sarah Wallace,1,2 James Lynch,1 Barry Coe,1 Brendan A McGrath1 1Acute Intensive Care Unit, University Hospital South Manchester, Manchester, 2Royal College of Speech and Language Therapists, London, UK Abstract: Tracheostomies are used to provide artificial airways for increasingly complex patients for a variety of indications. Patients and their families are dependent on knowledgeable multidisciplinary staff, including medical, nursing, respiratory physiotherapy and speech and language therapy staff, dieticians and psychologists, from a wide range of specialty backgrounds. There is increasing evidence that coordinated tracheostomy multidisciplinary teams can influence the safety and quality of care for patients and their families. This article reviews the roles of these team members and highlights the potential for improvements in care. Keywords: tracheotomy, physiotherapist, Speech & Language, Nursin