scholarly journals The Effect of Modal Interference on VLF Long-Range Lightning Location Networks Using the Waveform Correlation Technique

2011 ◽  
Vol 28 (8) ◽  
pp. 993-1006 ◽  
Author(s):  
A. J. Bennett ◽  
C. Gaffard ◽  
J. Nash ◽  
G. Callaghan ◽  
N. C. Atkinson
Keyword(s):  
Long Range ◽  
Selection Criteria ◽  
Network Performance ◽  
Arrival Time ◽  
Low Frequency ◽  
Correlation Technique ◽  
The Earth ◽  
Modal Interference ◽  
Ionospheric Height ◽  
Waveform Selection

Abstract The arrival time difference (ATD) long-range lightning location network (ATDnet) is the long-range very low frequency (VLF) lightning location network owned and operated by the Met Office, locating lightning using a waveform correlation technique. Pronounced differences in the waveform shape with distance to lightning have been observed and attributed to interference between different propagation modes within the earth–ionosphere waveguide. During the day, waveform correlations were significantly degraded at a distance of 450 km from the sensor, with the main degradations occurring during the night centered at propagation distances of 650 and 2150 km. The observation and simple modeling of modal interference spacing allowed the effective ionospheric height during summer over Europe to be estimated for day and night as 69 and 88.5 km, respectively, for 13.7 kHz. Wider distribution of sensor sites, lowering of the receiver frequency, and adaptation of the reference waveform selection criteria have been suggested to mitigate the effect of this interference on network performance.

scholarly journals A novel method of quantifying hemodynamic delays to improve hemodynamic response, and CVR estimates in CO2 challenge fMRI

2021 ◽  
pp. 0271678X2097858
Author(s):  
Jinxia (Fiona) Yao ◽  
Ho-Ching (Shawn) Yang ◽  
James H Wang ◽  
Zhenhu Liang ◽  
Thomas M Talavage ◽  
...  
Keyword(s):  
Arrival Time ◽  
Stress Test ◽  
Low Frequency ◽  
Hemodynamic Response ◽  
Blood Oxygen Level Dependent ◽  
Cerebrovascular Reactivity ◽  
Bold Signal ◽  
Hemodynamic Response Function ◽  
Carbon Dioxide Co2 ◽  
Co2 Challenge

Elevated carbon dioxide (CO2) in breathing air is widely used as a vasoactive stimulus to assess cerebrovascular functions under hypercapnia (i.e., “stress test” for the brain). Blood-oxygen-level-dependent (BOLD) is a contrast mechanism used in functional magnetic resonance imaging (fMRI). BOLD is used to study CO2-induced cerebrovascular reactivity (CVR), which is defined as the voxel-wise percentage BOLD signal change per mmHg change in the arterial partial pressure of CO2 (PaCO2). Besides the CVR, two additional important parameters reflecting the cerebrovascular functions are the arrival time of arterial CO2 at each voxel, and the waveform of the local BOLD signal. In this study, we developed a novel analytical method to accurately calculate the arrival time of elevated CO2 at each voxel using the systemic low frequency oscillations (sLFO: 0.01-0.1 Hz) extracted from the CO2 challenge data. In addition, 26 candidate hemodynamic response functions (HRF) were used to quantitatively describe the temporal brain reactions to a CO2 stimulus. We demonstrated that our approach improved the traditional method by allowing us to accurately map three perfusion-related parameters: the relative arrival time of blood, the hemodynamic response function, and CVR during a CO2 challenge.

Quantifying the Predictive Skill in Long-Range Forecasting. Part II: Model Error in Coarse-Grained Markov Models with Application to Ocean-Circulation Regimes

2012 ◽  
Vol 25 (6) ◽  
pp. 1814-1826 ◽  
Author(s):  
Dimitrios Giannakis ◽  
Andrew J. Majda
Keyword(s):  
Long Range ◽  
Ocean Circulation ◽  
Climate Models ◽  
Markov Models ◽  
Low Frequency ◽  
Model Error ◽  
Ocean Model ◽  
Coarse Grained ◽  
Predictive Skill ◽  
Relaxation To Equilibrium

Abstract An information-theoretic framework is developed to assess the predictive skill and model error in imperfect climate models for long-range forecasting. Here, of key importance is a climate equilibrium consistency test for detecting false predictive skill, as well as an analogous criterion describing model error during relaxation to equilibrium. Climate equilibrium consistency enforces the requirement that long-range forecasting models should reproduce the climatology of prediction observables with high fidelity. If a model meets both climate consistency and the analogous criterion describing model error during relaxation to equilibrium, then relative entropy can be used as an unbiased superensemble measure of the model’s skill in long-range coarse-grained forecasts. As an application, the authors investigate the error in modeling regime transitions in a 1.5-layer ocean model as a Markov process and identify models that are strongly persistent but their predictive skill is false. The general techniques developed here are also useful for estimating predictive skill with model error for Markov models of low-frequency atmospheric regimes.

Foreshock ULF fluctuations near the Moon: THEMIS observations

2021 ◽  
Author(s):  
Anna Salohub ◽  
Jana Šafránková ◽  
Zdeněk Němeček
Keyword(s):  
Solar Wind ◽  
Rest Frame ◽  
Low Frequency ◽  
Solar Wind Plasma ◽  
Turbulent Plasma ◽  
Bow Shock ◽  
Ulf Waves ◽  
The Moon ◽  
Shock Surface ◽  
The Earth

<p>The foreshock is a region filled with a turbulent plasma located upstream the Earth’s bow shock where interplanetary magnetic field (IMF) lines are connected to the bow shock surface. In this region, ultra-low frequency (ULF) waves are generated due to the interaction of the solar wind plasma with particles reflected from the bow shock back into the solar wind. It is assumed that excited waves grow and they are convected through the solar wind/foreshock, thus the inner spacecraft (close to the bow shock) would observe larger wave amplitudes than the outer (far from the bow shock) spacecraft. The paper presents a statistical analysis of excited ULF fluctuations observed simultaneously by two closely separated THEMIS spacecraft orbiting the Moon under a nearly radial IMF. We found that ULF fluctuations (in the plasma rest frame) can be characterized as a mixture of transverse and compressional modes with different properties at both locations. We discuss the growth and/or damping of ULF waves during their propagation.</p>

Technical photography of surface motion

1962 ◽  
Vol 52 (5) ◽  
pp. 1007-1016
Author(s):  
B. Carder ◽  
J. Hefferman ◽  
D. Barnes
Keyword(s):  
New Mexico ◽  
Long Range ◽  
Short Range ◽  
Surface Displacement ◽  
Earth Surface ◽  
Peak Displacement ◽  
Surface Motion ◽  
Target Weight ◽  
The Earth ◽  
Analysis Of Results

abstract Photographic measurements of the earth-surface displacement were made on the gnome event, an underground nuclear detonation near Carlsbad, New Mexico, November 1961. One long range and three short range photo stations were used to provide complementary coverage. Motionless inertia weights were measured against graduated targets rigidly anchored to the surface. The experiment is described in detail including target/weight arrangement, camera specifications, and photo station locations in relation to Surface Zero. Analysis of results from 6 films from close-in stations and one film from the long range station are reported. The peak displacement measured was slightly greater than six feet at a location 106 feet from surface zero.

Low-frequency vibrational spectroscopy: a new tool for revealing crystalline magnetic structures in iron phosphate crystals

2021 ◽  
Vol 23 (39) ◽  
pp. 22241-22245
Author(s):  
Zihui Song ◽  
Xudong Liu ◽  
Anish Ochani ◽  
Suling Shen ◽  
Qiqi Li ◽  
...  
Keyword(s):  
Lithium Ion Batteries ◽  
Long Range ◽  
Vibrational Spectroscopy ◽  
Strong Dependence ◽  
Low Frequency ◽  
Lithium Ion ◽  
Iron Phosphate ◽  
Promising Material ◽  
Vibrational Dynamics ◽  
Magnetic Structures

In this report, the strong-dependence of low-frequency (terahertz) vibrational dynamics on weak and long-range forces in crystals is leveraged to determine the bulk magnetic configuration of iron phosphate – a promising material for cathodes in lithium ion batteries.

WORKING DEPTHS FOR LOW FREQUENCY ELECTRICAL PROSPECTING

Geophysics ◽  
1945 ◽  
Vol 10 (1) ◽  
pp. 63-75 ◽  
Author(s):  
William Bradley Lewis
Keyword(s):  
Low Frequency ◽  
Electrical Measurements ◽  
The Earth ◽  
Electrical Prospecting

Electrical measurements were made on the surface of the earth with low frequency commutated current using nineteen separate frequencies and six electrode separations. Analysis of the data indicates that there is an effect of appreciable magnitude attributable to an interface 6000 feet below the surface.

scholarly journals Precision Pulsar Timing with NASA's Deep Space Network

2015 ◽  
Vol 11 (A29B) ◽  
pp. 367-369
Author(s):  
Lawrence Teitelbaum ◽  
Walid Majid ◽  
Manuel M. Franco ◽  
Daniel J. Hoppe ◽  
Shinji Horiuchi ◽  
...  
Keyword(s):  
Low Frequency ◽  
Radio Waves ◽  
Deep Space ◽  
Radio Pulsars ◽  
Deep Space Network ◽  
Space Network ◽  
The Earth ◽  
Pulsar Timing ◽  
Initial Results ◽  
Stable Rotation

AbstractMillisecond pulsars (MSPs) are a class of radio pulsars with extremely stable rotation. Their excellent timing stability can be used to study a wide variety of astrophysical phenomena. In particular, a large sample of these pulsars can be used to detect low-frequency gravitational waves. We have developed a precision pulsar timing backend for the NASA Deep Space Network (DSN), which will allow the use of short gaps in tracking schedules to time pulses from an ensemble of MSPs. The DSN operates clusters of large dish antennas (up to 70-m in diameter), located roughly equidistant around the Earth, for communication and tracking of deep-space spacecraft. The backend system will be capable of removing entirely the dispersive effects of propagation of radio waves through the interstellar medium in real-time. We will describe our development work, initial results, and prospects for future observations over the next few years.

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