scholarly journals Three different glacier surges at a spot: What satellites observe and what not

2021 ◽  
Author(s):  
Frank Paul ◽  
Livia Piermattei ◽  
Désirée Treichler ◽  
Lin Gilbert ◽  
Luc Girod ◽  
...  
Keyword(s):  
Short Pulse ◽  
Linear Increase ◽  
Low Flow ◽  
Wide Range ◽  
Satellite Sensors ◽  
Glacier Surges ◽  
Radar Satellite ◽  
Velocity Changes ◽  
Steep Terrain ◽  
Flow Velocities

Abstract. In the Karakoram, dozens of glacier surges occurred in the past two decades, making the region one of its global hot spots. Detailed analyses of dense time series from optical and radar satellite images revealed a wide range of surge behaviour in this region: from slow advances longer than a decade at low flow velocities to short, pulse-like advances over one or two years with high velocities. In this study, we present an analysis of three currently surging glaciers in the central Karakoram: North and South Chongtar Glaciers and an unnamed glacier referred to as NN9. All three glaciers flow towards the same region but differ strongly in surge behaviour. A full suite of satellite sensors and digital elevation models (DEMs) from different sources are used to (a) obtain comprehensive information about the evolution of the surges from 2000 to 2021 and (b) to compare and evaluate capabilities and limitations of the different satellite sensors for monitoring relatively small glaciers in steep terrain. A strongly contrasting evolution of advance rates and flow velocities is found, though the elevation change pattern is more similar. For example, South Chongtar Glacier had short-lived advance rates above 10 km y−1, velocities up to 30 m d−1 and surface elevations increased by 200 m. In contrast, the neighbouring and three times smaller North Chongtar Glacier had a slow and near linear increase of advance rates (up to 500 m y−1), flow velocities below 1 m d−1 and elevation increases up to 100 m. The even smaller glacier NN9 changed from a slow advance to a full surge within a year, reaching advance rates higher than 1 km y−1. It seems that, despite a similar climatic setting, different surge mechanisms are at play and a transition from one mechanism to another can occur during a single surge. The sensor inter-comparison revealed a high agreement across sensors for deriving flow velocities, but limitations are found on small and narrow glaciers in steep terrain, in particular for Sentinel-1. All investigated DEMs have the required accuracy to clearly show the volume changes during the surges and elevations from ICESat-2 ATL06 data fit neatly. We conclude that the available satellite data allow for a comprehensive observation of glacier surges from space when combining different sensors to determine the temporal evolution of length, elevation and velocity changes.

Surface Radiation Effects on Flame Spread Over Thermally Thick Fuels in an Opposing Flow

1994 ◽  
Vol 116 (3) ◽  
pp. 646-651 ◽  
Author(s):  
J. West ◽  
S. Bhattacharjee ◽  
R. A. Altenkirch
Keyword(s):  
Flow Velocity ◽  
Gas Phase ◽  
Flame Spread ◽  
Radiation Effects ◽  
Solid Phase ◽  
Surface Radiation ◽  
Low Flow ◽  
Fuel Surface ◽  
Wide Range ◽  
Flow Velocities

A computational model of flame spread over a thermally thick solid fuel in an opposing-flow environment is presented. Unlike thermally thin fuels, for which the effect of fuel surface radiation is negligible for high levels of opposing flow, fuel surface radiation is important for thermally thick fuels for all flow levels. This result is shown to derive from the fact that the ratio of the rate of heat transfer by re-radiation from the surface to that by conduction from the gas to the solid is proportional to the length over which heat can be conducted forward of the flame to sustain spreading. For thin fuels, this length decreases with increasing flow velocity such that while radiation is important at low flow velocities it is not at the higher velocities. For thick fuels at low flow velocities, the conduction length is determined by gas-phase processes and decreases with increasing flow velocity. But at higher flow velocities, the conduction length is determined by solid-phase processes and is rather independent of the gas-phase flow. The result is that over a wide range of flow velocities, the conduction length of importance does not change substantially as it switches from one phase to another so that the ratio of radiation to conduction is of unit order throughout that wide range of flow.

scholarly journals Optical Micro-Wire Flow-Velocity Sensor

Sensors ◽  
2021 ◽  
Vol 21 (12) ◽  
pp. 4025
Author(s):  
Matej Njegovec ◽  
Simon Pevec ◽  
Denis Donlagic
Keyword(s):  
Response Time ◽  
Flow Velocity ◽  
Time Constant ◽  
Gas Flow ◽  
Low Flow ◽  
Velocity Sensor ◽  
Short Response Time ◽  
Wide Range ◽  
Cost Efficient ◽  
Flow Velocities

This paper presents a short response time, all-silica, gas-flow-velocity sensor. The active section of the sensor consists of a 16 µm diameter, highly optically absorbing micro-wire, which is heated remotely by a 980 nm light source. The heated microwire forms a Fabry–Perot interferometer whose temperature is observed at standard telecom wavelengths (1550 nm). The short response time of the sensor allows for different interrogation approaches. Direct measurement of the sensor’s thermal time constant allowed for flow-velocity measurements independent of the absolute heating power delivered to the sensor. This measurement approach also resulted in a simple and cost-efficient interrogation system, which utilized only a few telecom components. The sensor’s short response time, furthermore, allowed for dynamic flow sensing (including turbulence detection). The sensor’s bandwidth was measured experimentally and proved to be in the range of around 22 Hz at low flow velocities. Using time constant measurement, we achieved a flow-velocity resolution up to 0.006 m/s at lower flow velocities, while the resolution in the constant power configuration was better than 0.003 m/s at low flow velocities. The sensing system is constructed around standard telecommunication optoelectronic components, and thus suitable for a wide range of applications.

scholarly journals Status of Phenological Research Using Sentinel-2 Data: A Review

2020 ◽  
Vol 12 (17) ◽  
pp. 2760
Author(s):  
Gourav Misra ◽  
Fiona Cawkwell ◽  
Astrid Wingler
Keyword(s):  
Vegetation Index ◽  
Temporal Frequency ◽  
Short Wave ◽  
Current State ◽  
Red Edge ◽  
Natural Grasslands ◽  
Wide Range ◽  
Normalised Difference Vegetation Index ◽  
Satellite Sensors ◽  
Sentinel 2

Remote sensing of plant phenology as an indicator of climate change and for mapping land cover has received significant scientific interest in the past two decades. The advancing of spring events, the lengthening of the growing season, the shifting of tree lines, the decreasing sensitivity to warming and the uniformity of spring across elevations are a few of the important indicators of trends in phenology. The Sentinel-2 satellite sensors launched in June 2015 (A) and March 2017 (B), with their high temporal frequency and spatial resolution for improved land mapping missions, have contributed significantly to knowledge on vegetation over the last three years. However, despite the additional red-edge and short wave infra-red (SWIR) bands available on the Sentinel-2 multispectral instruments, with improved vegetation species detection capabilities, there has been very little research on their efficacy to track vegetation cover and its phenology. For example, out of approximately every four papers that analyse normalised difference vegetation index (NDVI) or enhanced vegetation index (EVI) derived from Sentinel-2 imagery, only one mentions either SWIR or the red-edge bands. Despite the short duration that the Sentinel-2 platforms have been operational, they have proved their potential in a wide range of phenological studies of crops, forests, natural grasslands, and other vegetated areas, and in particular through fusion of the data with those from other sensors, e.g., Sentinel-1, Landsat and MODIS. This review paper discusses the current state of vegetation phenology studies based on the first five years of Sentinel-2, their advantages, limitations, and the scope for future developments.

scholarly journals Machine learning for multi-dimensional optimisation and predictive visualisation of laser machining

2021 ◽  
Author(s):  
Michael D. T. McDonnell ◽  
Daniel Arnaldo ◽  
Etienne Pelletier ◽  
James A. Grant-Jacob ◽  
Matthew Praeger ◽  
...  
Keyword(s):  
Short Pulse ◽  
Surface Texturing ◽  
Laser Surface Texturing ◽  
Laser Machining ◽  
Laser Materials ◽  
Parameter Optimisation ◽  
Short Pulse Laser ◽  
Alternative Approach ◽  
Highly Nonlinear ◽  
Wide Range

AbstractInteractions between light and matter during short-pulse laser materials processing are highly nonlinear, and hence acutely sensitive to laser parameters such as the pulse energy, repetition rate, and number of pulses used. Due to this complexity, simulation approaches based on calculation of the underlying physical principles can often only provide a qualitative understanding of the inter-relationships between these parameters. An alternative approach such as parameter optimisation, often requires a systematic and hence time-consuming experimental exploration over the available parameter space. Here, we apply neural networks for parameter optimisation and for predictive visualisation of expected outcomes in laser surface texturing with blind vias for tribology control applications. Critically, this method greatly reduces the amount of experimental laser machining data that is needed and associated development time, without negatively impacting accuracy or performance. The techniques presented here could be applied in a wide range of fields and have the potential to significantly reduce the time, and the costs associated with laser process optimisation.

Neutrophil-dependent augmentation of PAF-induced vasoconstriction and albumin flux in coronary arterioles

1998 ◽  
Vol 275 (4) ◽  
pp. H1138-H1147 ◽  
Author(s):  
Qiaobing Huang ◽  
Mac Wu ◽  
Cynthia Meininger ◽  
Katherine Kelly ◽  
Yuan Yuan
Keyword(s):  
Platelet Activating Factor ◽  
Microvascular Dysfunction ◽  
Low Flow ◽  
Intercellular Adhesion Molecule ◽  
Neutrophil Adhesion ◽  
Intercellular Adhesion Molecule 1 ◽  
Apparent Permeability ◽  
Inflammatory Reactions ◽  
Coronary Arterioles ◽  
Flow Velocities

Platelet-activating factor (PAF) has been implicated in the pathogenesis of ischemic heart disease, reperfusion injury, and inflammatory reactions. Although neutrophils have been shown to primarily mediate PAF-induced microvascular dysfunction, the vasoactive effect of PAF and its neutrophil-dependent mechanism have not been directly and systematically studied in coronary resistance vessels. Therefore, the aim of this study was to examine the effects of PAF on coronary arteriolar function and neutrophil dynamics using an isolated and perfused microvessel preparation. Topical application of PAF to the vessels induced a dose-dependent decrease in the diameter but an increase in the apparent permeability coefficient of albumin. Disruption of the endothelium abolished the vasomotor response to PAF, and perfusion of neutrophils significantly augmented PAF-induced changes in vasomotor tone and permeability. Furthermore, the interaction between neutrophils and the endothelium was studied in the intact perfused coronary arterioles. Under control conditions, there were no adherent neutrophils observed in the vessels at varied intraluminal flow velocities. However, administration of PAF caused neutrophil adhesion to the endothelium of coronary arterioles at low flow velocities. Western blot analysis indicated that PAF upregulated the expression of intercellular adhesion molecule-1 in cultured coronary microvascular endothelial cells. Taken together, the results suggest that 1) PAF induces vasoconstriction and hyperpermeability in coronary arterioles via an endothelium-dependent and neutrophil-mediated mechanism, and 2) PAF is able to stimulate neutrophil adhesion in coronary arterioles under a condition of low flow rate.

The Dynamics of a Cantilevered Pipe Aspirating Fluid Studied by Experimental, Numerical and Analytical Methods

2010 ◽  
Author(s):  
Dana Giacobbi ◽  
Stephanie Rinaldi ◽  
Christian Semler ◽  
Michael P. Pai¨doussis
Keyword(s):  
Analytical Model ◽  
Low Flow ◽  
Computational Fluid Dynamics Cfd ◽  
Computational Structural Mechanics ◽  
Cantilevered Pipe ◽  
The Galerkin Method ◽  
Csm Model ◽  
Ocean Mining ◽  
Flow Experiments ◽  
Flow Velocities

This paper investigates the dynamics of a slender, flexible, aspirating cantilevered pipe, ingesting fluid at its free end and conveying it towards its clamped end. The problem is interesting not only from a fundamental perspective, but also because applications exist, notably in ocean mining [1]. First, the need for the present work is demonstrated through a review of previous research into the topic — spanning many years and yielding often contradictory results — most recently concluding that the system loses stability by flutter at relatively low flow velocities [2]. In the current paper, that conclusion is refined and expanded upon by exploring the problem in three ways: experimentally, numerically and analytically. First, air-flow experiments, in which the flow velocity of the fluid was varied and the frequency and amplitude of oscillation of the pipe were measured, were conducted using different elastomer pipes and intake shapes. Second, a fully-coupled Computational Fluid Dynamics (CFD) and Computational Structural Mechanics (CSM) model was developed in ANSYS in order to simulate experiments and corroborate experimental results. Finally, using an analytical approach, the existing linear equation of motion describing the system was significantly improved upon, and then solved via the Galerkin method in order to determine its stability characteristics. Heavily influenced by a CFD analysis, the proposed analytical model is different from previous ones, most notably because of the inclusion of a two-part fluid depressurization at the intake. In general, both the actual and numerical experiments suggest a first-mode loss of stability by flutter at relatively low flow velocities, which agrees with the results from the new analytical model.

scholarly journals Exploring the physical controls of regional patterns of flow duration curves – Part 4: A synthesis of empirical analysis, process modeling and catchment classification

2012 ◽  
Vol 16 (11) ◽  
pp. 4483-4498 ◽  
Author(s):  
M. Yaeger ◽  
E. Coopersmith ◽  
S. Ye ◽  
L. Cheng ◽  
A. Viglione ◽  
...  
Keyword(s):  
Low Flow ◽  
Middle Portion ◽  
Qualitative Synthesis ◽  
Statistical Parameters ◽  
Regional Patterns ◽  
Flow Duration ◽  
Analysis Process ◽  
Wide Range ◽  
Physical Controls ◽  
Flow Duration Curves

Abstract. The paper reports on a four-pronged study of the physical controls on regional patterns of the flow duration curve (FDC). This involved a comparative analysis of long-term continuous data from nearly 200 catchments around the US, encompassing a wide range of climates, geology, and ecology. The analysis was done from three different perspectives – statistical analysis, process-based modeling, and data-based classification – followed by a synthesis, which is the focus of this paper. Streamflow data were separated into fast and slow flow responses, and associated signatures, and both total flow and its components were analyzed to generate patterns. Regional patterns emerged in all aspects of the study. The mixed gamma distribution described well the shape of the FDC; regression analysis indicated that certain climate and catchment properties were first-order controls on the shape of the FDC. In order to understand the spatial patterns revealed by the statistical study, and guided by the hypothesis that the middle portion of the FDC is a function of the regime curve (RC, mean within-year variation of flow), we set out to classify these catchments, both empirically and through process-based modeling, in terms of their regime behavior. The classification analysis showed that climate seasonality and aridity, either directly (empirical classes) or through phenology (vegetation processes), were the dominant controls on the RC. Quantitative synthesis of these results determined that these classes were indeed related to the FDC through its slope and related statistical parameters. Qualitative synthesis revealed much diversity in the shapes of the FDCs even within each climate-based homogeneous class, especially in the low-flow tails, suggesting that catchment properties may have become the dominant controls. Thus, while the middle portion of the FDC contains the average response of the catchment, and is mainly controlled by climate, the tails of the FDC, notably the low-flow tails, are mainly controlled by catchment properties such as geology and soils. The regime behavior explains only part of the FDC; to gain a deeper understanding of the physical controls on the FDC, these extremes must be analyzed as well. Thus, to completely separate the climate controls from the catchment controls, the roles of catchment properties such as soils, geology, topography etc. must be explored in detail.

Cerebral microdialysis monitoring: determination of normal and ischemic cerebral metabolisms in patients with aneurysmal subarachnoid hemorrhage

2000 ◽  
Vol 93 (5) ◽  
pp. 808-814 ◽  
Author(s):  
Mette K. Schulz ◽  
Lars Peter Wang ◽  
Mogens Tange ◽  
Per Bjerre
Keyword(s):  
Subarachnoid Hemorrhage ◽  
Cerebral Ischemia ◽  
Delayed Cerebral Ischemia ◽  
Neuronal Injury ◽  
Low Flow ◽  
Cerebral Microdialysis ◽  
Intracerebral Microdialysis ◽  
Content Type ◽  
Wide Range ◽  
Fine Print

Object. The success of treatment for delayed cerebral ischemia is time dependent, and neuronal monitoring methods that can detect early subclinical levels of cerebral ischemia may improve overall treatment results. Cerebral microdialysis may represent such a method. The authors' goal was to characterize patterns of markers of energy metabolism (glucose, pyruvate, and lactate) and neuronal injury (glutamate and glycerol) in patients with subarachnoid hemorrhage (SAH), in whom ischemia was or was not suspected.Methods. By using low-flow intracerebral microdialysis monitoring, central nervous system extracellular fluid concentrations of glucose, pyruvate, lactate, glutamate, and glycerol were determined in 46 patients suffering from poor-grade SAH. The results in two subgroups were analyzed: those patients with no clinical or radiological signs of cerebral ischemia (14 patients) and those who succumbed to brain death (five patients).Significantly lower levels of energy substrates and significantly higher levels of lactate and neuronal injury markers were observed in patients with severe and complete ischemia when compared with patients without symptoms of ischemia (glucose 0 compared with 2.12 ± 0.15 mmol/L; pyruvate 0 compared with 151 ± 11.5 µmol; lactate 6.57 ± 1.07 compared with 3.06 ± 0.32 mmol/L; glycerol 639 ± 91 compared with 81.6 ± 12.4 µmol; and glutamate 339 ± 53.4 compared with 14 ± 3.33 µmol). Immediately after catheter placement, glutamate concentrations declined over the first 4 to 6 hours to reach stable values. The remaining parameters exhibited stable values after 1 to 2 hours.Conclusions. The results confirm that intracerebral microdialysis monitoring of patients with SAH can be used to detect patterns of cerebral ischemia. The wide range from normal to severe ischemic values calls for additional studies to characterize further incomplete and possible subclinical levels of ischemia.

scholarly journals Adaptive capacity of 2- to 5-month-old infants to the flow, shape, and flexibility of different teats during bottle feeding: a cross-sectional study

2019 ◽  
Vol 19 (1) ◽  
Author(s):  
M. L. J. Lagarde ◽  
N. van Alfen ◽  
S. A. F. de Groot ◽  
A. C. H. Geurts ◽  
L. van den Engel-Hoek
Keyword(s):  
Cross Sectional Study ◽  
Bottle Feeding ◽  
Low Flow ◽  
Complex Activity ◽  
Cross Sectional ◽  
Feeding Difficulties ◽  
Nutritive Sucking ◽  
Healthy Infants ◽  
Wide Range ◽  
Complex Development

Abstract Background Nutritive sucking is a complex activity, the biomechanical components of which may vary in relation to respiratory phase, swallow-rate per minute, suck-swallow ratio, and swallow non-inspiratory flow (SNIF). Quantitative measurement of these components during nutritive sucking in healthy infants could help us to understand the complex development of sucking, swallowing, and breathing. This is important because the coordination between these components is often disturbed in infants with feeding difficulties. The aims of this study were to describe the biomechanical components of sucking and swallowing in healthy 2- to 5-month-old infants during bottle feeding, to assess whether infants adapt to the characteristics of two different teats, and to determine which independent variables influence the occurrence of SNIF. Methods Submental muscle activity, nasal airflow, and cervical auscultation were evaluated during bottle-feeding with two different teats. Results Sixteen term-born infants (6 boys) aged 2–5 months were included. All infants showed variable inhalation and exhalation after swallowing. The swallow rate per minute was significantly higher when infants fed with a higher flow teat (Philips Avent Natural 2.0™). Infants had suck:swallow ratios ranging from 1:1 to 4:1. A suck:swallow ratio of 1:1 occurred significantly more often when infants fed with a higher flow teat, whereas a suck:swallow ratio of 2:1 occurred significantly more often when infants fed with a low-flow teat (Philips Avent Classic+™). A suck:swallow ratio of 1:1 was negatively correlated with SNIF, whereas a suck:swallow ratio of 2:1 was positively correlated with SNIF. Conclusion Healthy infants aged 2–5 months can adapt to the flow, shape, and flexibility of different teats, showing a wide range of biomechanical and motor adaptations.

Flow-Induced Instability of Heat-Exchanger Tubes due to Axial Flow in a Diffuser-Shaped, Loose Intermediate Support

1989 ◽  
Vol 111 (4) ◽  
pp. 428-434 ◽  
Author(s):  
A. Yasuo ◽  
M. P. Paidoussis
Keyword(s):  
Heat Exchanger ◽  
Fluid Dynamic ◽  
Axial Flow ◽  
Low Flow ◽  
Baffle Plate ◽  
Intermediate Point ◽  
Flow Passage ◽  
Fluid Forces ◽  
Dynamic Damping ◽  
Flow Velocities

In some heat exchangers and steam generators, the flow is predominantly axial, and the external fluid flows between baffled compartments through enlarged holes in the baffles around the heat exchanger tubes. Thus, the tube is subjected to relatively high flow velocities over small portions of its length, in the baffle locations. In this paper, the dynamics of such an idealized system is investigated, involving a cylindrical beam with pinned ends in axial flow, going through a baffle plate of finite thickness at some intermediate point, with small radial clearance. The fluid forces along the tube are formulated in a manner reminiscent of the transfer-matrix technique, since the character of these forces changes drastically along the tube. The fluid forces are determined approximately by means of potential flow theory, and viscous effects are taken into account only in a global sense. It was found that if the flow passage through the baffle plate is diffuser-shaped, negative fluid-dynamic damping is generated therein, destabilizing the system and leading to flutter at relatively low flow velocities. The instability depends critically on the shape of the hole through the baffle and on the clearance; thus a convergent-type flow passage does not lead to instability. The negative fluid-dynamic damping is linearly proportional to the flow velocity through the baffle.

Sign in / Sign up

Export Citation Format

Share Document