scholarly journals Geomagnetic pulsations in the Pc5/Pi3 frequency range and fluctuations of foF2 frequency

2019 ◽  
Author(s):  
Nadezda Yagova ◽  
Alexander Kozlovsky ◽  
Evgeny Fedorov ◽  
Olga Kozyreva
Keyword(s):  
Spatial Distribution ◽  
Critical Frequency ◽  
Dynamic Pressure ◽  
Pressure Fluctuations ◽  
Automatic Detection ◽  
Geomagnetic Pulsations ◽  
Frequency Range ◽  
Spectral Content ◽  
Using Data ◽  
Fof2 Critical Frequency

Abstract. Using data of the ionosonde in Sodankyla, (SOD, 67° N, 27° E, Finland), parameters of variations of foF2 critical frequency in the Pc5/Pi3 (1–5 mHz) frequency range are studied. For that, a technique of automatic detection of critical frequency from an ionogram is developed. The variations of foF2 are compared with the Pc5/Pi3 geomagnetic pulsations on the ground and in the magnetosphere. The variations of foF2 are in the majority of cases decoupled from the Pc5/Pi3 on the ground. Meanwhile, the analysis of geomagnetic and foF2 variations at SOD show intervals with noticeable coherence for both horizontal components. These coherent pulsations are predominantly registered in the afternoon MLT sector. Statistically, their spectral content, polarization and spatial distribution differs from those of background variations. Coherent pulsation tend to occur under moderate geomagnetic and auroral activity, SW speed, and dynamic pressure fluctuations. The fraction of coherent geomagnetic and foF2 pulsations is higher for the geomagnetic pulsations registered in the magnetosphere, than on the ground.

scholarly journals Even moderate geomagnetic pulsations can cause fluctuations of foF2 frequency of the auroral ionosphere

2020 ◽  
Author(s):  
Nadezda Yagova ◽  
Alexander Kozlovsky ◽  
Evgeny Fedorov ◽  
Olga Kozyreva
Keyword(s):  
Space Weather ◽  
Critical Frequency ◽  
Dynamic Pressure ◽  
Solar Wind Speed ◽  
Pressure Fluctuations ◽  
Weather Conditions ◽  
Geomagnetic Pulsations ◽  
Station Pair ◽  
Using Data ◽  
Magnetic Meridian

Abstract. Using data of the ionosonde in Sodankyla, (SOD, 67° N, 27° E, Finland), variations of the critical frequency of o-mode radiowave reflected from ionospheric F2 layer (foF2) in 1–5 mHz frequency range and their possible association with long period (Pc5/Pi3) geomagnetic pulsations are studied. For that, a technique of automatic detection of the foF2 critical frequency from an ionogram is developed and applied to daytime Pc5/Pi3 geomagnetic pulsations and foF2 fluctuations during several months of years 2014–2015 near the maximum of 24-th Solar cycle. The variations of foF2 are compared with the Pc5/Pi3 geomagnetic pulsations at SOD station, and the influence of pulsations' spatial scale is analyzed with the data of a station pair located at the same magnetic meridian but separated in latitude. The variations of foF2 are in the majority of cases decoupled from the geomagnetic pulsations on the ground. Meanwhile, the analysis of geomagnetic and foF2 variations show intervals with noticeable coherence for both horizontal components. These coherent pulsations are predominantly registered in the afternoon sector of the magnetic local time (MLT). Statistically, their spectral content, polarization and spatial distribution differ from averaged parameters of post-noon Pc5 pulsations. The pulsations, coherent to foF2 fluctuations, demonstrate features typical for Alfven field-line resonance. The analysis of space weather conditions favorable for the occurrence of coherent geomagnetic/foF2 pulsations show that these pulsations are registered mostly under moderately disturbed conditions. Comparison of space weather parameters for all the intervals analyzed and the intervals of high geomagnetic/foF2 coherence show that the latter correspond mostly to intermediate values of indexes of geomagnetic (Dst) and auroral (AE) activity, solar wind speed and dynamic pressure fluctuations.

Experimental Measurement of Dynamic Bulk Modulus Using Holography

1985 ◽  
Vol 58 (2) ◽  
pp. 258-268 ◽  
Author(s):  
B. P. Holownia
Keyword(s):  
Bulk Modulus ◽  
Room Temperature ◽  
Dynamic Pressure ◽  
Pressure Fluctuations ◽  
Limiting Factor ◽  
Frequency Range ◽  
Holographic Method ◽  
Indirect Methods ◽  
Servo Valve ◽  
Hydraulic Servo

Abstract The results show that the dynamic bulk modulus for NBR at room temperature is about 50% higher than the static bulk modulus in the frequency range of 1–200 Hz. The limiting factor was the servo-valve used which does not give enough dynamic pressure fluctuations above 200 Hz to obtain accurate results of the dynamic bulk modulus. The holographic method discussed here offers a number of advantages over other methods used in measuring dynamic bulk modulus. (i) The samples are of realistic size and any soft spots in the sample which would distort the results can be immediately identified. (ii) Dynamic bulk modulus can be measured accurately in the frequency range of 1 Hz–1000 Hz or higher, provided the hydraulic servo-valve used can respond in the frequency range. Work is already in hand which extends this frequency range to 1200 Hz. (iii) The change of volume of the sample is a direct measurement unlike other indirect methods, therefore, there is more confidence in the results.

The Growth and Shifting Spatial Distribution of Tent Encampments in Oakland, California

2021 ◽  
Vol 693 (1) ◽  
pp. 284-300
Author(s):  
Ryan Finnigan
Keyword(s):  
Spatial Distribution ◽  
West Coast ◽  
Spatial Dynamics ◽  
Transitional Housing ◽  
Using Data ◽  
The City

Tent encampments have become an especially common form of homelessness in West Coast cities like Oakland, California, where the number of people living in tent encampments increased by 130 percent between 2017 and 2019. Living in tent encampments provides residents both benefits and risks, depending on the encampments’ location, size, and stability. Using data from Google Street Views, I document the growth and spatial dynamics of tent encampments in west and central Oakland over the last decade. The number and size of tent encampments rapidly increased between 2014 and 2019, varying widely in their stability. City interventions like the city’s outdoor transitional housing sites displaced several large tent encampments. Combined with overall tent encampment growth, these displacements dispersed the encampments throughout nearby neighborhoods and other parts of the city.

scholarly journals Picking up the hydrothermal whisper at Ischia Island in the Covid-19 lockdown quiet

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Mariarosaria Falanga ◽  
Paola Cusano ◽  
Enza De Lauro ◽  
Simona Petrosino
Keyword(s):  
Pressure Fluctuations ◽  
Hydrothermal Fluids ◽  
Shallow Aquifer ◽  
Two Phase ◽  
Spectral Content ◽  
Ischia Island ◽  
Continuous Noise ◽  
Organ Pipes ◽  
Source Signals ◽  
Phase Fluid

AbstractIn this paper, we analyse the seismic noise at Ischia Island (Italy) with the objective of detecting the hydrothermal source signals taking advantage of the Covid-19 quiescence due to lockdown (strong reduction of anthropogenic noise). We compare the characteristics of the background noise in pre-, during and post-lockdown in terms of spectral content, energy release (RMS) and statistical moments. The continuous noise is decomposed into two independent signals in the 1−2 Hz and 2−4 Hz frequency bands, becoming sharpened around 1 Hz and 3 Hz respectively in lockdown. We propose a conceptual model according to which a dendritic system of fluid-permeated fractures plays as neighbour closed organ pipes, for which the fundamental mode provides the persistent whisper and the first higher mode is activated in concomitance with energy increases. By assuming reasonable values for the sound speed in low vapor–liquid mass fraction for a two-phase fluid and considering temperatures and pressures of the shallow aquifer fed by sea, meteoric and deep hydrothermal fluids, we estimate pipe lengths in the range 200–300 m. In this scheme, Ischia organ-like system can play both continuous whisper and transients, depending on the energy variations sourced by pressure fluctuations in the hydrothermal fluids.

scholarly journals An Efficient Clustering Approach for Automatic Detection of Calcification in Low Dose Chest CT

2019 ◽  
pp. 163-168
Author(s):  
P. Tamijiselvy ◽  
N. Kavitha ◽  
K. M. Keerthana ◽  
D. Menakha
Keyword(s):  
Data Mining ◽  
Low Dose ◽  
Early Stage ◽  
Clustering Algorithms ◽  
Automatic Detection ◽  
Chest Ct ◽  
Data Mining Algorithm ◽  
Fuzzy C Means ◽  
Data Mining Algorithms ◽  
Using Data

The degree of aortic calcification has been appeared to be a risk pointer for vascular occasions including cardiovascular events. The created strategy is fully automated data mining algorithm to segment and measure calcification using Low-dose Chest CT in smokers of age 50 to 70 .The identification of subjects with increased cardiovascular risk can be detected by using data mining algorithms. This paper presents a method for automatic detection of coronary artery calcifications in low-dose chest CT scans using effective clustering algorithms with three phases as Pre-Processing, Segmentation and clustering. Fuzzy C Means algorithm provides accuracy of 80.23% demonstrate that Fuzzy C means detects the Cardio Vascular Disease at early stage.

scholarly journals STUDY OF PROCESSES OF PRESSURE AND IMPULSE FREQUENCY INFLUENCE ON PENETRATION OF LIQUIDS IN THE SAND SAMPLES

2016 ◽  
pp. 120-125
Author(s):  
M. Ya. Habibullin ◽  
R. R. Shangareyev
Keyword(s):  
Experimental Data ◽  
Oil Recovery ◽  
Pressure Fluctuations ◽  
Experimental Studies ◽  
Regression Equations ◽  
Linear Variation ◽  
Frequency Range ◽  
Impulse Frequency ◽  
Overburden Pressure

The article deals with the issues related to the hydrocarbon reservoirs oil recovery enhancement. It describes the bench laboratory experimental studies. The results obtained during determination of fluid leakage through the rock samples and the amount of absorption of pressure fluctuations at various regime parameters are presented. Using the experimental data the regression analysis was performed on the basis of which the qualitative correlations between factorial and resultant features were identified. Using the regression equations the graphic relations were constructed. It was found that with increasing the oscillation frequency of the fluid the amount of fluid passing through the sample of porous medium increased, with the highest value of q reached at the frequency range of 600 ... 1000 Hz. With increase in the oscillations penetration depth the absorption of the amplitude of the pressure fluctuations corresponds to the linear decrease, and with the overburden pressure increase the linear variation of absorption is distorted.

scholarly journals Large-scale integrated subglacial drainage around the former Keewatin Ice Divide, Canada reveals interaction between distributed and channelised systems

2020 ◽  
Author(s):  
Emma L. M. Lewington ◽  
Stephen J. Livingstone ◽  
Chris D. Clark ◽  
Andrew J. Sole ◽  
Robert D. Storrar
Keyword(s):  
Spatial Distribution ◽  
Dynamic Response ◽  
Large Scale ◽  
Water Pressure ◽  
Pressure Fluctuations ◽  
Drainage System ◽  
Different Types ◽  
Form Part ◽  
Subglacial Meltwater ◽  
Subglacial Drainage

Abstract. We identify and map traces of subglacial meltwater drainage around the former Keewatin Ice Divide, Canada from ArcticDEM data. Meltwater tracks, tunnel valleys and esker splays exhibit several key similarities, including width, spacing, their association with eskers and transitions to and from different types, which together suggest they form part of an integrated drainage signature. We collectively term these features 'meltwater corridors' and propose a new model for their formation, based on observations from contemporary ice masses, of pressure fluctuations surrounding a central conduit. We suggest that eskers record the imprint of a central conduit and meltwater corridors the interaction with the surrounding distributed drainage system. The widespread aerial coverage of meltwater corridors (5–36 % of the bed) provides constraints on the extent of basal uncoupling induced by basal water pressure fluctuations and variations in spatial distribution and evolution of the subglacial drainage system, which will modulate the ice dynamic response.

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