scholarly journals Flow-sensory contact electrification of graphene

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Xiaoyu Zhang ◽  
Eric Chia ◽  
Xiao Fan ◽  
Jinglei Ping
Keyword(s):  
Performance Metrics ◽  
Low Flow ◽  
Monolayer Graphene ◽  
Dual Phase ◽  
Ultra Low Power ◽  
Blood Flows ◽  
Sensory Contact ◽  
Flow Sensing ◽  
Contact Electrification ◽  
Aqueous Flow

AbstractAll-electronic interrogation of biofluid flow velocity by electrical nanosensors incorporated in ultra-low-power or self-sustained systems offers the promise of enabling multifarious emerging research and applications. However, existing nano-based electrical flow sensing technologies remain lacking in precision and stability and are typically only applicable to simple aqueous solutions or liquid/gas dual-phase mixtures, making them unsuitable for monitoring low-flow (~micrometer/second) yet important characteristics of continuous biofluids (such as hemorheological behaviors in microcirculation). Here, we show that monolayer-graphene single microelectrodes harvesting charge from continuous aqueous flow provide an effective flow sensing strategy that delivers key performance metrics orders of magnitude higher than other electrical approaches. In particular, over six-months stability and sub-micrometer/second resolution in real-time quantification of whole-blood flows with multiscale amplitude-temporal characteristics are obtained in a microfluidic chip.

Multilayer Graphene-Based Carbon Interconnect

2012 ◽  
Vol 1407 ◽  
Author(s):  
Tianhua Yu ◽  
Edwin Kim ◽  
Nikhil Jain ◽  
Bin Yu
Keyword(s):  
Performance Metrics ◽  
Monolayer Graphene ◽  
Multilayer Graphene ◽  
Large Area ◽  
Electrical Stress ◽  
Oxygen Plasma Etching ◽  
Doping Technique ◽  
System Breakdown ◽  
Grown Graphene ◽  
On Chip

ABSTRACT3D stacked (or uncorrelated) multilayer graphene (s-MLG) is investigated as a potential material platform for carbon-based on-chip interconnects. S-MLG samples are prepared by repeatedly transferring and stacking the large-area CVD-grown graphene monolayers, followed by wire patterning and oxygen plasma etching of graphene. We observed superior wire conduction of s-MLG over that of monolayer graphene or ABAB-stacked multilayer graphene. Further reduction of s-MLG resistivity is anticipated with increasing number of stacked layers. Electrical stress-induced doping technique is used to engineer the Dirac point, as well as to reduce graphene-to-metal contact resistance, improving the overall performance metrics of the s-MLG system. Breakdown experiments show that the current-carrying capacity of s-MLG is significantly enhanced as compared with that of monolayer graphene.

scholarly journals The influence of conceptual model structure on model performance: a comparative study for 237 French catchments

2013 ◽  
Vol 17 (10) ◽  
pp. 4227-4239 ◽  
Author(s):  
W. R. van Esse ◽  
C. Perrin ◽  
M. J. Booij ◽  
D. C. M. Augustijn ◽  
F. Fenicia ◽  
...  
Keyword(s):  
Conceptual Model ◽  
Performance Metrics ◽  
Low Flow ◽  
Multiple Time ◽  
Large Set ◽  
Model Structure ◽  
Flow Measurements ◽  
Flexible Approach ◽  
Fixed Model ◽  
Model Structures

Abstract. Models with a fixed structure are widely used in hydrological studies and operational applications. For various reasons, these models do not always perform well. As an alternative, flexible modelling approaches allow the identification and refinement of the model structure as part of the modelling process. In this study, twelve different conceptual model structures from the SUPERFLEX framework are compared with the fixed model structure GR4H, using a large set of 237 French catchments and discharge-based performance metrics. The results show that, in general, the flexible approach performs better than the fixed approach. However, the flexible approach has a higher chance of inconsistent results when calibrated on two different periods. When analysing the subset of 116 catchments where the two approaches produce consistent performance over multiple time periods, their average performance relative to each other is almost equivalent. From the point of view of developing a well-performing fixed model structure, the findings favour models with parallel reservoirs and a power function to describe the reservoir outflow. In general, conceptual hydrological models perform better on larger and/or wetter catchments than on smaller and/or drier catchments. The model structures performed poorly when there were large climatic differences between the calibration and validation periods, in catchments with flashy flows, and in catchments with unexplained variations in low flow measurements.

The Effect of Altered Cerebral Blood Flow on the Cerebral Kinetics of Thiopental and Propofol in Sheep

2000 ◽  
Vol 93 (4) ◽  
pp. 1085-1094 ◽  
Author(s):  
Richard N. Upton ◽  
Guy L. Ludbrook ◽  
Cliff Grant ◽  
David J. Doolette
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Random Order ◽  
High Flow ◽  
Low Flow ◽  
Flow State ◽  
Concentration Difference ◽  
Blood Flows ◽  
Kinetics Of ◽  
The Brain

Background Thiopental and propofol are highly lipid-soluble, and their entry into the brain often is assumed to be limited by cerebral blood flow rather than by a diffusion barrier. However, there is little direct experimental evidence for this assumption. Methods The cerebral kinetics of thiopental and propofol were examined over a range of cerebral blood flows using five and six chronically instrumented sheep, respectively. Using anesthesia (2.0% halothane), three steady state levels of cerebral blood flow (low, medium, and high) were achieved in random order by altering arterial carbon dioxide tension. For each flow state, 250 mg thiopental or 100 mg propofol was infused intravenously over 2 min. To quantify cerebral kinetics, arterial and sagittal sinus blood was sampled rapidly for 20 min from the start of the infusion, and 1.5 h was allowed between consecutive infusions. Various models of cerebral kinetics were examined for their ability to account for the data. Results The mean baseline cerebral blood flows for the "high" flow state were over threefold greater than those for the low. For the high-flow state the normalized arteriovenous concentration difference across the brain was smaller than for the low-flow state, for both drugs. The data were better described by a model with partial membrane limitation than those with only flow limitation or dispersion. Conclusions The cerebral kinetics of thiopental and propofol after bolus injection were dependent on cerebral blood flow, despite partial diffusion limitation. Higher flows produce higher peak cerebral concentrations.

scholarly journals Streamflow characteristics from modeled runoff time series – importance of calibration criteria selection

2017 ◽  
Vol 21 (11) ◽  
pp. 5443-5457 ◽  
Author(s):  
Sandra Pool ◽  
Marc J. P. Vis ◽  
Rodney R. Knight ◽  
Jan Seibert
Keyword(s):  
Time Series ◽  
Model Calibration ◽  
Performance Metrics ◽  
Low Flow ◽  
Flow Conditions ◽  
Ungauged Catchments ◽  
Calibration Process ◽  
Model Efficiency ◽  
Runoff Model ◽  
Calibration Approach

Abstract. Ecologically relevant streamflow characteristics (SFCs) of ungauged catchments are often estimated from simulated runoff of hydrologic models that were originally calibrated on gauged catchments. However, SFC estimates of the gauged donor catchments and subsequently the ungauged catchments can be substantially uncertain when models are calibrated using traditional approaches based on optimization of statistical performance metrics (e.g., Nash–Sutcliffe model efficiency). An improved calibration strategy for gauged catchments is therefore crucial to help reduce the uncertainties of estimated SFCs for ungauged catchments. The aim of this study was to improve SFC estimates from modeled runoff time series in gauged catchments by explicitly including one or several SFCs in the calibration process. Different types of objective functions were defined consisting of the Nash–Sutcliffe model efficiency, single SFCs, or combinations thereof. We calibrated a bucket-type runoff model (HBV – Hydrologiska Byråns Vattenavdelning – model) for 25 catchments in the Tennessee River basin and evaluated the proposed calibration approach on 13 ecologically relevant SFCs representing major flow regime components and different flow conditions. While the model generally tended to underestimate the tested SFCs related to mean and high-flow conditions, SFCs related to low flow were generally overestimated. The highest estimation accuracies were achieved by a SFC-specific model calibration. Estimates of SFCs not included in the calibration process were of similar quality when comparing a multi-SFC calibration approach to a traditional model efficiency calibration. For practical applications, this implies that SFCs should preferably be estimated from targeted runoff model calibration, and modeled estimates need to be carefully interpreted.

Update on extracorporeal carbon dioxide removal: a comprehensive review on principles, indications, efficiency, and complications

Perfusion ◽  
2020 ◽  
Vol 35 (6) ◽  
pp. 492-508
Author(s):  
Thomas Staudinger
Keyword(s):  
Carbon Dioxide ◽  
Carbon Dioxide Removal ◽  
Low Flow ◽  
Chronic Obstructive ◽  
Extracorporeal Carbon Dioxide Removal ◽  
Obstructive Pulmonary Disease ◽  
Blood Flows ◽  
Non Invasive ◽  
Non Invasive Ventilation ◽  
Exchange Membrane

Technology: Extracorporeal carbon dioxide removal means the removal of carbon dioxide from the blood across a gas exchange membrane without substantially improving oxygenation. Carbon dioxide removal is possible with substantially less extracorporeal blood flow than needed for oxygenation. Techniques for extracorporeal carbon dioxide removal include (1) pumpless arterio-venous circuits, (2) low-flow venovenous circuits based on the technology of continuous renal replacement therapy, and (3) venovenous circuits based on extracorporeal membrane oxygenation technology. Indications: Extracorporeal carbon dioxide removal has been shown to enable more protective ventilation in acute respiratory distress syndrome patients, even beyond the so-called “protective” level. Although experimental data suggest a benefit on ventilator induced lung injury, no hard clinical evidence with respect to improved outcome exists. In addition, extracorporeal carbon dioxide removal is a tool to avoid intubation and mechanical ventilation in patients with acute exacerbated chronic obstructive pulmonary disease failing non-invasive ventilation. This concept has been shown to be effective in 56-90% of patients. Extracorporeal carbon dioxide removal has also been used in ventilated patients with hypercapnic respiratory failure to correct acidosis, unload respiratory muscle burden, and facilitate weaning. In patients suffering from terminal fibrosis awaiting lung transplantation, extracorporeal carbon dioxide removal is able to correct acidosis and enable spontaneous breathing during bridging. Keeping these patients awake, ambulatory, and breathing spontaneously is associated with favorable outcome. Complications: Complications of extracorporeal carbon dioxide removal are mostly associated with vascular access and deranged hemostasis leading to bleeding. Although the spectrum of complications may differ, no technology offers advantages with respect to rate and severity of complications. So called “high-extraction systems” working with higher blood flows and larger membranes may be more effective with respect to clinical goals.

scholarly journals Objective functions used as performance metrics for hydrological models: state-of-the-art and critical analysis

RBRH ◽  
2020 ◽  
Vol 25 ◽  
Author(s):  
Paloma Mara de Lima Ferreira ◽  
Adriano Rolim da Paz ◽  
Juan Martín Bravo
Keyword(s):  
Time Series ◽  
Model Calibration ◽  
Hydrological Model ◽  
Performance Metrics ◽  
Low Flow ◽  
Hydrological Models ◽  
Objective Functions ◽  
Flow Rates ◽  
Daily Streamflow ◽  
Synthetic Time Series

ABSTRACT Hydrological models (HMs) can be applied for different purposes, and a key step is model calibration using objective functions (OF) to quantify the agreement between observed and calculated discharges. Fully understanding the OF is important to properly take advantage of model calibration and interpret the results. This study evaluates 36 OF proposed in the literature, considering two watersheds of different hydrological regimes. Daily simulated streamflow time-series, using a distributed hydrological model (MGB-IPH), and ten daily streamflow synthetic time-series, generated from the observed and calculated streamflows, were used in the analysis of each watershed. These synthetic data were used to evaluate how does each metric evaluate hypothetical cases that present isolated very well known error behaviors. Despite of all NSE-derived (Nash-Sutcliffe efficiency) metrics that use the square of the residuals in their formulation have shown higher sensitivity to errors in high flows, the ones that use daily and monthly averages of flow rates in absolute terms were more stringent than the others to assess HMs performance. Low flow errors were better evaluated by metrics that use the flow logarithm. The constant presence of zero flow rates deteriorate them significantly, with the exception of the metrics TRMSE (Transformed root mean square error) did not demonstrate this problem. An observed limitation of the formulations of some metrics was that the errors of overestimation or underestimation are compensated. Our results reassert that each metric should be interpreted specifically thinking about the aspects it has been proposed for, and simultaneously taking into account a set of metrics would lead to a broader evaluation of HM ability (e.g. multiobjective model evaluation). We recommend that the use of synthetic time series as those proposed in this work could be useful as an auxiliary step towards better understanding the evaluation of a calibrated hydrological model for each study case, taking into account model capabilities and observed hydrologic regime characteristics.

scholarly journals Streamflow characteristics from modelled runoff time series – importance of calibration criteria selection

2016 ◽  
Author(s):  
Sandra Pool ◽  
Marc J. P. Vis ◽  
Rodney R. Knight ◽  
Jan Seibert
Keyword(s):  
Model Calibration ◽  
Performance Metrics ◽  
Model Performance ◽  
Specific Model ◽  
Low Flow ◽  
Flow Conditions ◽  
Ungauged Catchments ◽  
Practical Applications ◽  
Runoff Model ◽  
Calibration Approach

Abstract. Ecologically relevant streamflow characteristics (SFCs) of ungauged catchments are often estimated from simulated runoff of hydrologic models. Estimated SFCs can be substantially uncertain when models are calibrated using traditional approaches based on minimization or maximization of statistical performance metrics (e.g. Nash–Sutcliffe efficiency). To evaluate model performance, we tested how well SFCs are simulated when the model objective function was calibrated using one or more SFCs. We calibrated a bucket-type runoff model for 25 catchments in the Tennessee River basin and evaluated the proposed calibration approach on 13 selected SFCs representing major flow regime components and different flow conditions. While the model tends to underestimate SFCs related to mean and high-flow conditions, SFCs related to low flow are overestimated. The highest estimation accuracies were achieved by a SFC-specific model calibration. Estimates of SFCs not included in the calibration process were of similar quality when comparing a multi-SFC calibration approach to a traditional Nash–Sutcliffe efficiency calibration. For practical applications, this implies that SFCs should preferably be estimated from targeted runoff model calibration and modelled estimates need to be carefully interpreted.

Reversal of intracerebral steal by STA-MCA anastomosis

1982 ◽  
Vol 57 (5) ◽  
pp. 629-632 ◽  
Author(s):  
John P. Laurent ◽  
Pablo M. Lawner ◽  
Michael O'Connor
Keyword(s):  
Perfusion Pressure ◽  
Superficial Temporal Artery ◽  
Temporal Artery ◽  
Arterial System ◽  
Low Flow ◽  
Neurological Deficits ◽  
Mean Flow ◽  
Content Type ◽  
Blood Flows ◽  
Fine Print

✓ A major factor determining the severity of neurological deficits caused by cerebral ischemia is the ability of the vasculature to provide collateral circulation to the ischemic areas. By establishing a major conduit by means of extracranial-intracranial anastomosis, the increased perfusion pressure through the collateral arterioles may reduce morbidity in these patients. Twenty-seven patients were selected for superficial temporal artery to middle cerebral artery (STA-MCA) anastomosis based on clinical and angiographic evidence of lesions of the internal carotid arterial system. Cerebral blood flows (CBF's) were determined by the xenon-133 inhalation method using 16 symmetrically placed scintillator probes; two-compartment analysis was used to compute a mean flow for the compartment. An average mean flow was computed for each hemisphere, and for four regions with the lowest mean CBF in each hemisphere. The CBF was measured preoperatively and within 8 weeks postoperatively. The average mean flow was 29 ml/100 gm/min in the symptomatic hemisphere, and 30 ml/100 gm/min in the asymptomatic hemisphere. In 11 patients, the mean flow for the symptomatic hemisphere increased by 24% postoperatively, and for the asymptomatic hemisphere by 23%. Regions with lowest CBF showed an increase of 32% in the symptomatic hemisphere, and of 35% in the asymptomatic hemisphere. The low-flow regions differed from the total hemisphere (symptomatic: p < 0.02; asymptomatic: p < 0.05). Areas of lowest blood flow preoperatively had the greatest increase in flow postoperatively. Postoperative elevation of CBF in the contralateral hemisphere is consistent with an “intracerebral steal” before surgery. The postoperative elevation of flow in the asymptomatic hemisphere is related to improved perfusion pressure in the symptomatic hemisphere.

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