In situ study of volcanic ash resuspension using a portable wind tunnel.

2020 ◽  
Author(s):  
Jacopo Taddeucci ◽  
Elisabetta del Bello ◽  
Jonathan P Merrison ◽  
Keld R Rasmussen ◽  
Jens J Iversen ◽  
...  
Keyword(s):  
Wind Speed ◽  
Wind Tunnel ◽  
High Speed ◽  
Volcanic Ash ◽  
Field Experiments ◽  
Critical Parameters ◽  
Test Bed ◽  
High Definition ◽  
Sustained Activity

<p>The resuspension of volcanic ash deposits by wind is a well-known source of hazard following explosive eruptions. Besides the mail control exerted by the local wind field, ash resuspension is also influenced by: 1) atmospheric humidity; 2) features of the deposit (grain size distribution, sedimentary structures, etc.), and 3) features of the substrate (i.e. moisture, roughness). Ash resuspension is modeled using numerical simulations, which however require physical characterization and identification of the critical parameters controlling ash resuspension. Wind tunnel studies on volcanic particles are very limited and restricted to laboratory parameterizations, with in-situ effects not been parameterized. We tested field experiments of volcanic ash resuspension developing a portable wind tunnel and deploying on proximal (3 km) ash deposits from the semi-sustained activity of Sakurajima volcano (Japan) and from distal (250 km ca.) ash deposits from the 2011 Cordon Caulle eruption (Chile). The wind tunnel is calibrated with both LDA and pitot tubes measurements. The device allows generating a controlled wind profile within a 110x12x12 cm test section, which is placed directly on an untouched test bed of naturally deposited ash. Two types of experiments were performed: 1) ramp up speed experiments, where the wind speed is increased until reaching the threshold friction speed on four different substrates; 2) constant speed experiments, where three wind speed values where kept for 20 minutes using the same substrate. The threshold friction speed is measured with a hot wire anemometer, and the movement of resuspended ash is detected by means of multiple high speed and high definition digital camcorders. In-situ measured threshold friction speeds are compared to 1) in situ observed episodes of resuspension driven by local winds and 2) laboratory determination of threshold friction speed in controlled environmental conditions, and using the same ash deposited homogeneously.</p><p> </p>

scholarly journals Coronal hole evolution from multi-viewpoint data as input for a STEREO solar wind speed persistence model

2018 ◽  
Vol 8 ◽  
pp. A18 ◽  
Author(s):  
Manuela Temmer ◽  
Jürgen Hinterreiter ◽  
Martin A. Reiss
Keyword(s):  
Solar Wind ◽  
Wind Speed ◽  
High Speed ◽  
Solar Wind Speed ◽  
Coronal Holes ◽  
In Situ Measurements ◽  
False Alarms ◽  
Wind Speed Profile ◽  
Persistence Model

We present a concept study of a solar wind forecasting method for Earth, based on persistence modeling from STEREO in situ measurements combined with multi-viewpoint EUV observational data. By comparing the fractional areas of coronal holes (CHs) extracted from EUV data of STEREO and SoHO/SDO, we perform an uncertainty assessment derived from changes in the CHs and apply those changes to the predicted solar wind speed profile at 1 AU. We evaluate the method for the time period 2008–2012, and compare the results to a persistence model based on ACE in situ measurements and to the STEREO persistence model without implementing the information on CH evolution. Compared to an ACE based persistence model, the performance of the STEREO persistence model which takes into account the evolution of CHs, is able to increase the number of correctly predicted high-speed streams by about 12%, and to decrease the number of missed streams by about 23%, and the number of false alarms by about 19%. However, the added information on CH evolution is not able to deliver more accurate speed values for the forecast than using the STEREO persistence model without CH information which performs better than an ACE based persistence model. Investigating the CH evolution between STEREO and Earth view for varying separation angles over ∼25–140° East of Earth, we derive some relation between expanding CHs and increasing solar wind speed, but a less clear relation for decaying CHs and decreasing solar wind speed. This fact most likely prevents the method from making more precise forecasts. The obtained results support a future L5 mission and show the importance and valuable contribution using multi-viewpoint data.

scholarly journals DSRC versus 4G-LTE for Connected Vehicle Applications: A Study on Field Experiments of Vehicular Communication Performance

2017 ◽  
Vol 2017 ◽  
pp. 1-10 ◽  
Author(s):  
Zhigang Xu ◽  
Xiaochi Li ◽  
Xiangmo Zhao ◽  
Michael H. Zhang ◽  
Zhongren Wang
Keyword(s):  
Collision Avoidance ◽  
High Speed ◽  
Field Experiments ◽  
Traffic Information ◽  
Connected Vehicle ◽  
Vehicular Communication ◽  
Test Bed ◽  
Traffic Sign ◽  
Communication Performance ◽  
4G Lte

Dedicated short-range communication (DSRC) and 4G-LTE are two widely used candidate schemes for Connected Vehicle (CV) applications. It is thus of great necessity to compare these two most viable communication standards and clarify which one can meet the requirements of most V2X scenarios with respect to road safety, traffic efficiency, and infotainment. To the best of our knowledge, almost all the existing studies on comparing the feasibility of DRSC or LTE in V2X applications use software-based simulations, which may not represent realistic constraints. In this paper, a Connected Vehicle test-bed is established, which integrates the DSRC roadside units, 4G-LTE cellular communication stations, and vehicular on-board terminals. Three Connected Vehicle application scenarios are set as Collision Avoidance, Traffic Text Message Broadcast, and Multimedia File Download, respectively. A software tool is developed to record GPS positions/velocities of the test vehicles and record certain wireless communication performance indicators. The experiments have been carried out under different conditions. According to our results, 4G-LTE is more preferred for the nonsafety applications, such as traffic information transmission, file download, or Internet accessing, which does not necessarily require the high-speed real-time communication, while for the safety applications, such as Collision Avoidance or electronic traffic sign, DSRC outperforms the 4G-LTE.

Impact of shelter on crop microclimates: a synthesis of results from wind tunnel and field experiments

2002 ◽  
Vol 42 (6) ◽  
pp. 679 ◽  
Author(s):  
H. A. Cleugh ◽  
D. E. Hughes
Keyword(s):  
Wind Speed ◽  
Wind Tunnel ◽  
Field Experiments ◽  
Surface Wind ◽  
Mixing Layer ◽  
Flow Region ◽  
Near Surface ◽  
Wind Speeds ◽  
Temperature And Humidity ◽  
Wake Zone

The purpose of this paper is to synthesise data from the literature, and acquired during an extensive set of wind tunnel and field experiments, to quantify the effect of porous windbreaks on airflow, microclimates and evaporation fluxes. The paper considers flow oriented both normal (i.e. at right angles) and oblique to the windbreak, in addition to the confounding effects of topography. The wind tunnel results confirm the validity of the turbulent mixing layer as a model for characterising the airflow around a windbreak and for predicting the locations of the quiet and wake zones. This mixing layer is initiated at the top of the windbreak and grows with distance downwind until it intersects the vegetation or surface, marking the downwind extent of the quiet zone where the maximum shelter occurs. The 3 factors that determine the growth of this mixing layer are the windbreak porosity, windbreak height and the nature of the terrain upwind. For wind that is flowing normal to a porous windbreak in the field, the latter 2 have the primary influence on the size of the sheltered zone, while windbreak porosity is the main factor determining the amount of shelter. Analyses of the effect of porosity revealed that the amount of wind shelter increases as windbreak porosity is reduced, but the downwind extent of the sheltered zone does not vary with windbreak porosity. Thus, the suggestion from older studies that low-porosity (i.e. dense) windbreaks lead to a reduced sheltered area is not supported by the wind tunnel measurements. In the absence of shading effects, temperature and/or humidity are increased in the quiet zone, mirroring the pattern and magnitude of wind shelter. Thus, the increase in temperature and humidity is greatest where the minimum wind speed occurs, and the magnitude of the increase is smaller for more porous windbreaks. The humidity and air (but not surface) temperatures are decreased very slightly in the wake zone, although these small changes were not significant in a field situation. Microclimate changes, therefore, occur over a much smaller distance downwind than wind shelter, and are negligible for the very porous windbreak. For example, at 20 windbreak heights downwind, the wind speed may still be 80% of its upwind value, while the air and surface temperature and humidity have returned to their upwind values after 12–15 windbreak heights. Furthermore, these changes in temperature and humidity vary with the type of land cover, surface moisture status and the temperature and humidity of the 'regional' air. Over the course of a growing season, these changes can be masked by soil and climate variability. The turbulent scalar fluxes, i.e. evaporation and heat fluxes, also differ from the pattern of near-surface wind speeds. While significantly reduced in the quiet zone, they show a very large peak at the start of the wake zone — the location where the mixing layer intersects the surface. Thus, caution is required when extrapolating from the spatial pattern of shelter to microclimates and turbulent fluxes. Wind flowing at angles other than normal to the windbreak has 2 effects on the pattern of wind shelter. First, for the medium and low porosity windbreaks used in the wind tunnel, the amount of wind shelter is increased slightly in the bleed flow region near the windbreak, i.e. there is an apparent reduction in windbreak porosity as the wind direction becomes more oblique to the windbreak. Second, the profile of near surface wind speeds is similar to that for flow oriented normal to the windbreak, providing that the changes in distance from the windbreak are accounted for using simple geometry. The field data agree with these results, but show an even greater influence of the windbreak structure on the pattern of wind shelter in the bleed flow region, extending from the windbreak to at least 3 windbreak heights downwind, precluding any generalisations about the flow in this region.

Transport of Lycopodium spores and other small particles to rough surfaces

1967 ◽  
Vol 296 (1444) ◽  
pp. 45-70 ◽  
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Wind Tunnel ◽  
Field Experiments ◽  
Rough Surfaces ◽  
Pollen Grains ◽  
Eddy Diffusion ◽  
Terminal Velocity ◽  
Effective Height ◽  
Roughness Elements

Measurements have been made in the field and in a wind tunnel of the transport of Lycopodium spores to grass an d other surfaces, and wind tunnel experiments also have been done with aerosols of various smaller particle sizes. The spores and other particles were made radioactive to enable the deposition of small numbers on rough surfaces to be detected. In principle the experiments in the wind tunnel were similar to those previously done with gases (Chamberlain 1966), but the mechanisms by which particles and gases are transported across the boundary layer are different. The velocity of deposition v g of the particle to the surface is equal to the terminal velocity v s if the wind speed is very small, but at higher speeds deposition by impaction on roughness elements becomes progressively more important. If the roughness elements are of a form which gives good impaction efficiency, and have a sticky surface, v g is determined by the rate of eddy diffusion in the turbulent boundary layer above the surface, and may equal or even exceed the analogous velocity of deposition of momentum. The effect of surface texture and stickiness was investigated by comparing the catch of particles on segments of real leaves with the catch on similarity shaped segments of PVG treated with adhesive. Stickiness is important in determining v g for particles of about 10 μ m diameter upwards, but not for smaller particles. In the field experiments, the use of radioactive tagging enabled the presence of a few Lycopodium spores in several grams of grass or soil to be detected, and the deposition could be measured at ranges up to 100 m from the source. At low wind speeds, v g was only a little greater than v s but at higher speeds the contribution of impaction became evident. A particularly high value was obtained when the grass was wet after recent rain. The field results with Lycopodium give a ratio of velocity of deposition to wind speed of 0·01, and this value is used to calculate the percentage of large spores or pollen grains which will travel various distances in normal meteorological conditions. It is found that the median range is about 1 km if the particles are liberated at a height of 50 cm, but 10 km if the height is 10 m. The relative importance of direct deposition to the ground and washout by rain of the air spora is considered, and is shown to depend on the effective height of the cloud of particles. For an effective height of 500 m, derived from vertical profiles of concentration observed from aircraft, it is calculated that about 25% of the total deposition of pollen grains may be in rain.

An atomic-resolution microscope study of Al contracts on GaAs

1986 ◽  
Vol 44 ◽  
pp. 726-727
Author(s):  
Z. Liliental-Weber ◽  
C. Nelson ◽  
R. Ludeke ◽  
R. Gronsky ◽  
J. Washburn
Keyword(s):  
High Speed ◽  
Schottky Contacts ◽  
Detailed Knowledge ◽  
The Past ◽  
Semiconductor Interfaces ◽  
Deposited Metal ◽  
Microwave Applications ◽  
Free Interfaces ◽  
Potential Use

The properties of metal/semiconductor interfaces have received considerable attention over the past few years, and the Al/GaAs system is of special interest because of its potential use in high-speed logic integrated optics, and microwave applications. For such materials a detailed knowledge of the geometric and electronic structure of the interface is fundamental to an understanding of the electrical properties of the contact. It is well known that the properties of Schottky contacts are established within a few atomic layers of the deposited metal. Therefore surface contamination can play a significant role. A method for fabricating contamination-free interfaces is absolutely necessary for reproducible properties, and molecularbeam epitaxy (MBE) offers such advantages for in-situ metal deposition under UHV conditions

Fundamental Considerations for CDM Failure in 90nm Products

2006 ◽  
Author(s):  
Nobuyuki Wakai ◽  
Yuji Kobira ◽  
Hidemitsu Egawa ◽  
Masayoshi Tsutsumi
Keyword(s):  
Breakdown Voltage ◽  
High Speed ◽  
Gate Oxide ◽  
Critical Parameters ◽  
Protection Device ◽  
Oxide Breakdown ◽  
Technology Products ◽  
Charged Device ◽  
Device Size ◽  
Fundamental Consideration

Abstract Fundamental consideration for CDM (Charged Device Model) breakdown was investigated with 90nm technology products and others. According to the result of failure analysis, it was found that gate oxide breakdown was critical failure mode for CDM test. High speed triggered protection device such as ggNMOS and SCR (Thyristor) is effective method to improve its CDM breakdown voltage and an improvement for evaluated products were confirmed. Technological progress which is consisted of down-scaling of protection device size and huge number of IC pins of high function package makes technology vulnerable and causes significant CDM stress. Therefore, it is expected that CDM protection designing tends to become quite difficult. In order to solve these problems in the product, fundamental evaluations were performed. Those are a measurement of discharge parameter and stress time dependence of CDM breakdown voltage. Peak intensity and rise time of discharge current as critical parameters are well correlated their package capacitance. Increasing stress time causes breakdown voltage decreasing. This mechanism is similar to that of TDDB for gate oxide breakdown. Results from experiences and considerations for future CDM reliable designing are explained in this report.

Extremely Gusty Winds from a Viewpoint of Aerodynamic Force

2020 ◽  
Author(s):  
Junji Maeda ◽  
Takashi Takeuchi ◽  
Eriko Tomokiyo ◽  
Yukio Tamura
Keyword(s):  
Wind Speed ◽  
Wind Tunnel ◽  
Rise Time ◽  
Aerodynamic Force ◽  
Step Function ◽  
Object Size ◽  
Aerodynamic Forces ◽  
Wind Force ◽  
Wind Observation

To quantitatively investigate a gusty wind from the viewpoint of aerodynamic forces, a wind tunnel that can control the rise time of a step-function-like gust was devised and utilized. When the non-dimensional rise time, which is calculated using the rise time of the gusty wind, the wind speed, and the size of an object, is less than a certain value, the wind force is greater than under the corresponding steady wind. Therefore, this wind force is called the “overshoot wind force” for objects the size of orbital vehicles in an actual wind observation. The finding of the overshoot wind force requires a condition of the wind speed recording specification and depends on the object size and the gusty wind speed.

scholarly journals Rapid evolution and host immunity drive the rise and fall of carbapenem resistance during an acute Pseudomonas aeruginosa infection

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Rachel Wheatley ◽  
Julio Diaz Caballero ◽  
Natalia Kapel ◽  
Fien H. R. de Winter ◽  
Pramod Jangir ◽  
...  
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Efflux Pump ◽  
Rapid Evolution ◽  
Carbapenem Resistance ◽  
Host Immunity ◽  
High Definition ◽  
Loss Of Resistance ◽  
Pseudomonas Aeruginosa Infection ◽  
Second Wave

AbstractIt is well established that antibiotic treatment selects for resistance, but the dynamics of this process during infections are poorly understood. Here we map the responses of Pseudomonas aeruginosa to treatment in high definition during a lung infection of a single ICU patient. Host immunity and antibiotic therapy with meropenem suppressed P. aeruginosa, but a second wave of infection emerged due to the growth of oprD and wbpM meropenem resistant mutants that evolved in situ. Selection then led to a loss of resistance by decreasing the prevalence of low fitness oprD mutants, increasing the frequency of high fitness mutants lacking the MexAB-OprM efflux pump, and decreasing the copy number of a multidrug resistance plasmid. Ultimately, host immunity suppressed wbpM mutants with high meropenem resistance and fitness. Our study highlights how natural selection and host immunity interact to drive both the rapid rise, and fall, of resistance during infection.

scholarly journals Spatially Resolved Experimental Modal Analysis on High-Speed Composite Rotors Using a Non-Contact, Non-Rotating Sensor

Sensors ◽  
2021 ◽  
Vol 21 (14) ◽  
pp. 4705
Author(s):  
Julian Lich ◽  
Tino Wollmann ◽  
Angelos Filippatos ◽  
Maik Gude ◽  
Juergen Czarske ◽  
...  
Keyword(s):  
High Speed ◽  
Natural Frequencies ◽  
Mode Shapes ◽  
Fiber Reinforced ◽  
Structural Dynamic ◽  
Spatially Resolved ◽  
Glass Fiber Reinforced ◽  
Vibration Responses ◽  
And Performance

Due to their lightweight properties, fiber-reinforced composites are well suited for large and fast rotating structures, such as fan blades in turbomachines. To investigate rotor safety and performance, in situ measurements of the structural dynamic behaviour must be performed during rotating conditions. An approach to measuring spatially resolved vibration responses of a rotating structure with a non-contact, non-rotating sensor is investigated here. The resulting spectra can be assigned to specific locations on the structure and have similar properties to the spectra measured with co-rotating sensors, such as strain gauges. The sampling frequency is increased by performing consecutive measurements with a constant excitation function and varying time delays. The method allows for a paradigm shift to unambiguous identification of natural frequencies and mode shapes with arbitrary rotor shapes and excitation functions without the need for co-rotating sensors. Deflection measurements on a glass fiber-reinforced polymer disk were performed with a diffraction grating-based sensor system at 40 measurement points with an uncertainty below 15 μrad and a commercial triangulation sensor at 200 measurement points at surface speeds up to 300 m/s. A rotation-induced increase of two natural frequencies was measured, and their mode shapes were derived at the corresponding rotational speeds. A strain gauge was used for validation.

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