A Multiscale Model of the Enhanced Heat Transfer in a CNT-Nanofluid System

Over the last decade, much research has been done to understand the role of nanoparticles in heat transfer fluids. While experimental results have shown "anomalous" thermal enhancements and non-linear behavior with respect to CNT loading percentage, little has been done to replicate this behavior from an analytical or computational standpoint. This study is aimed towards using molecular dynamics to augment our understanding of the physics at play in CNT-nanofluid systems. This research begins with a heat transfer study of individual CNTs in a vacuum environment. Temperature gradients are imposed or induced via various methods. Tersoff and AIREBO potentials are used for the carbon-carbon interactions in the CNTs. Various chirality CNTs are explored, along with several different lengths and temperatures. The simulations have shown clear dependencies upon CNT length, CNT chirality, and temperature. Subsequent studies simulate individual CNTs solvated in a simple fluidic box domain. A heat flux is applied to the domain, and various tools are employed to study the resulting heat transfer. The results from these simulations are contrasted against the earlier control simulations of the CNT-only domain. The degree by which the solvation dampens the effect of physical parameters is discussed. Effective thermal conductivity values are computed, however the piecewise nature of the temperature gradient makes Fourier's law insufficient in interpretting the heat transfer. Nevertheless, the computed effective thermal conductivities are applied to classical models and better agreement with experimental results is evident. Phonon spectra of solvated and unsolvated CNTs are compared. However, a unique method utilizing the Irving-Kirkwood relations reveals the spatially-localized heat flux mapping that fully illuminates the heat transfer pathways in the solid-fluid composite material. This method confirms why conventional models fail at predicting effective thermal conductivity. Specifically, it reveals the volume of influence that the CNT has on its surrounding fluid

Clinical associations and prognostic value of MRI-visible perivascular spaces in patients with ischemic stroke or TIA: a pooled analysis

BACKGROUND AND OBJECTIVES: Visible perivascular spaces are an MRI marker of cerebral small vessel disease and might predict future stroke. However, results from existing studies vary. We aimed to clarify this through a large collaborative multicenter analysis. METHODS: We pooled individual patient data from a consortium of prospective cohort studies. Participants had recent ischemic stroke or transient ischemic attack (TIA), underwent baseline MRI, and were followed up for ischemic stroke and symptomatic intracranial hemorrhage (ICH). Perivascular spaces in the basal ganglia (BGPVS) and perivascular spaces in the centrum semiovale (CSOPVS) were rated locally using a validated visual scale. We investigated clinical and radiologic associations cross-sectionally using multinomial logistic regression and prospective associations with ischemic stroke and ICH using Cox regression. RESULTS: We included 7,778 participants (mean age 70.6 years; 42.7% female) from 16 studies, followed up for a median of 1.44 years. Eighty ICH and 424 ischemic strokes occurred. BGPVS were associated with increasing age, hypertension, previous ischemic stroke, previous ICH, lacunes, cerebral microbleeds, and white matter hyperintensities. CSOPVS showed consistently weaker associations. Prospectively, after adjusting for potential confounders including cerebral microbleeds, increasing BGPVS burden was independently associated with future ischemic stroke (versus 0-10 BGPVS, 11-20 BGPVS: HR 1.19, 95% CI 0.93-1.53; 21+ BGPVS: HR 1.50, 95% CI 1.10-2.06; = 0.040). Higher BGPVS burden was associated with increased ICH risk in univariable analysis, but not in adjusted analyses. CSOPVS were not significantly associated with either outcome. DISCUSSION: In patients with ischemic stroke or TIA, increasing BGPVS burden is associated with more severe cerebral small vessel disease and higher ischemic stroke risk. Neither BGPVS nor CSOPVS were independently associated with future ICH

Impact of Cerebral Microbleeds in Stroke Patients with Atrial Fibrillation

OBJECTIVES: Cerebral microbleeds are associated with the risks of ischemic stroke and intracranial hemorrhage, causing clinical dilemmas for antithrombotic treatment decisions. We aimed to evaluate the risks of intracranial hemorrhage and ischemic stroke associated with microbleeds in patients with atrial fibrillation treated with Vitamin K antagonists, direct oral anticoagulants, antiplatelets, and combination therapy (i.e. concurrent oral anticoagulant and antiplatelet) METHODS: We included patients with documented atrial fibrillation from the pooled individual patient data analysis by the Microbleeds International Collaborative Network. Risks of subsequent intracranial hemorrhage and ischemic stroke were compared between patients with and without microbleeds, stratified by antithrombotic use. RESULTS: A total of 7,839 patients were included. The presence of microbleeds was associated with an increased relative risk of intracranial hemorrhage (aHR 2.74, 95% confidence interval 1.76 - 4.26) and ischemic stroke (aHR 1.29, 95% confidence interval 1.04 - 1.59). For the entire cohort, the absolute incidence of ischemic stroke was higher than intracranial hemorrhage regardless of microbleeds burden. However, for the subgroup of patients taking combination of anticoagulant and antiplatelet therapy, the absolute risk of intracranial hemorrhage exceeded that of ischemic stroke in those with 2-4 microbleeds (25 vs 12 per 1,000 patient-years) and ≥11 microbleeds (94 vs 48 per 1,000 patient-years). INTERPRETATION: Patients with atrial fibrillation and high burden of microbleeds receiving combination therapy have a tendency of higher rate of intracranial hemorrhage than ischemic stroke, with potential for net harm. Further studies are needed to help optimize stroke preventive strategies in this high-risk group. This article is protected by copyright. All rights reserved

Genome-wide Analyses Identify KIF5A as a Novel ALS Gene

To identify novel genes associated with ALS, we undertook two lines of investigation. We carried out a genome-wide association study comparing 20,806 ALS cases and 59,804 controls. Independently, we performed a rare variant burden analysis comparing 1,138 index familial ALS cases and 19,494 controls. Through both approaches, we identified kinesin family member 5A (KIF5A) as a novel gene associated with ALS. Interestingly, mutations predominantly in the N-terminal motor domain of KIF5A are causative for two neurodegenerative diseases: hereditary spastic paraplegia (SPG10) and Charcot-Marie-Tooth type 2 (CMT2). In contrast, ALS-associated mutations are primarily located at the C-terminal cargo-binding tail domain and patients harboring loss-of-function mutations displayed an extended survival relative to typical ALS cases. Taken together, these results broaden the phenotype spectrum resulting from mutations in KIF5A and strengthen the role of cytoskeletal defects in the pathogenesis of ALS.Peer reviewe

Antarctic ice shelf potentially stabilized by export of meltwater in surface river

Meltwater stored in ponds1 and crevasses can weaken and fracture ice shelves, triggering their rapid disintegration2. This ice-shelf collapse results in an increased flux of ice from adjacent glaciers3 and ice streams, thereby raising sea level globally4. However, surface rivers forming on ice shelves could potentially export stored meltwater and prevent its destructive effects. Here we present evidence for persistent active drainage networks—interconnected streams, ponds and rivers—on the Nansen Ice Shelf in Antarctica that export a large fraction of the ice shelf’s meltwater into the ocean. We find that active drainage has exported water off the ice surface through waterfalls and dolines for more than a century. The surface river terminates in a 130-metre-wide waterfall that can export the entire annual surface melt over the course of seven days. During warmer melt seasons, these drainage networks adapt to changing environmental conditions by remaining active for longer and exporting more water. Similar networks are present on the ice shelf in front of Petermann Glacier, Greenland, but other systems, such as on the Larsen C and Amery Ice Shelves, retain surface water at present. The underlying reasons for export versus retention remain unclear. Nonetheless our results suggest that, in a future warming climate, surface rivers could export melt off the large ice shelves surrounding Antarctica—contrary to present Antarctic ice-sheet models1, which assume that meltwater is stored on the ice surface where it triggers ice-shelf disintegration

Stroke Risk and Antithrombotic Treatment During Follow-up of Patients With Ischemic Stroke and Cortical Superficial Siderosis.

BACKGROUND AND OBJECTIVES In patients with ischemic stroke (IS) or TIA and cortical superficial siderosis (cSS), there are few data regarding the risk of future cerebrovascular events and also about the benefits and safety of antithrombotic drugs for secondary prevention. We investigated the associations of cSS and stroke risk in patients with recent IS or TIA. METHODS We retrospectively analyzed the Microbleeds International Collaborative Network (MICON) database. We selected patients with IS or TIA from cohorts who had MRI-assessed cSS, available data on antithrombotic treatments, recurrent cerebrovascular events [Intracranial hemorrhage -ICrH-, IS, or any stroke (ICrH or IS)], and mortality. We calculated incidence rates (IR) and performed univariable and multivariable Cox regression analyses. RESULTS Of 12.669 patients (mean age 70.4±12.3 years, 57.3% men), cSS was detected in 273 (2.2%) patients. During a mean follow-up of 24±17 months, IS was more frequent than ICrH in both cSS (IR 57.1 versus 14.6 per 1000 patient-years) and non-cSS groups (33.7 versus 6.3 per 1000 patient years). Compared to the non-CSS group, cSS was associated with any stroke on multivariable analysis [IR 83 versus 42 per 1000 patient-years, adjusted HR for cSS 1.62 (95%CI: 1.14-2.28; p=0.006)]. This association was not significant in subgroups of patients treated with antiplatelet drugs (n=6.554) or with anticoagulants (n=4.044). Patients with cSS who were treated with both antiplatelet drugs and anticoagulants (n=1.569) had a higher incidence of ICrH (IR 107.5 vs 4.9 per 1000 patient-years, adjusted HR 13.26; 95%CI: 2.90-60.63; p=0.001) and of any stroke (IR 198.8 vs 34.7 per 1000 patient-years, adjusted HR 5.03; 95%CI: 2.03-12.44; p<0.001) compared to the non-CSS group. DISCUSSION Patients with IS or TIA with cSS are at increased risk of stroke (ICrH or IS) during follow-up; the risk of IS exceeds that of ICrH for patients receiving antiplatelet or anticoagulant treatment alone, but the risk of ICrH exceeds that of IS in patients receiving both treatments. The findings suggest that either antiplatelet or anticoagulant treatment alone should not be avoided in patients with cSS, but combined antithrombotic therapy might be hazardous. Our findings need to be confirmed by randomized clinical trials