scholarly journals GNSS-to-GNSS time offsets: study on the broadcast of a common reference time

GPS Solutions ◽  
2021 ◽  
Vol 25 (2) ◽  
Author(s):  
Ilaria Sesia ◽  
Giovanna Signorile ◽  
Tung Thanh Thai ◽  
Pascale Defraigne ◽  
Patrizia Tavella
Keyword(s):  
Time Scales ◽  
Time Scale ◽  
Reference Time ◽  
Single Time ◽  
Common Reference ◽  
Prediction Quality ◽  
Common Time ◽  
Time Offset ◽  
The Impact ◽  
Low Uncertainty

AbstractWe present two different approaches to broadcasting information to retrieve the GNSS-to-GNSS time offsets needed by users of multi-GNSS signals. Both approaches rely on the broadcast of a single time offset of each GNSS time versus one common time scale instead of broadcasting the time offsets between each of the constellation pairs. The first common time scale is the average of the GNSS time scales, and the second time scale is the prediction of UTC already broadcast by the different systems. We show that the average GNSS time scale allows the estimation of the GNSS-to-GNSS time offset at the user level with the very low uncertainty of a few nanoseconds when the receivers at both the provider and user levels are fully calibrated. The use of broadcast UTC prediction as a common time scale has a slightly larger uncertainty, which depends on the broadcast UTC prediction quality, which could be improved in the future. This study focuses on the evaluation of two different common time scales, not considering the impact of receiver calibration, at the user and provider levels, which can nevertheless have an important impact on GNSS-to-GNSS time offset estimation.

Time-scale dependent mechanism of atmospheric CO2 concentration drivers of watershed water-energy balance

2021 ◽  
Author(s):  
Jing Zhao
Keyword(s):  
Energy Balance ◽  
River Basin ◽  
Time Scales ◽  
Time Scale ◽  
Hydrological Processes ◽  
Multiple Time Scales ◽  
Multiple Time ◽  
The Wei River Basin ◽  
Balance Dynamics ◽  
The Impact

<p>The elevated atmospheric carbon dioxide concentration (CO<sub>2</sub>), as a key variable linking human activities and climate change, seriously affects the watershed hydrological processes. However, whether and how atmospheric CO<sub>2</sub> influences the watershed water-energy balance dynamics at multiple time scales have not been revealed. Based on long-term hydrometeorological data, the variation of non-stationary parameter n series in the Choudhury's equation in the mainstream of the Wei River Basin (WRB), the Jing River Basin (JRB) and Beiluo River Basin (BLRB), three typical Loess Plateau regions in China, was examined. Subsequently, the Empirical Mode Decomposition method was applied to explore the impact of CO<sub>2</sub> on watershed water-energy balance dynamics at multiple time scales. Results indicate that (1) in the context of warming and drying condition, annual n series in the WRB displays a significantly increasing trend, while that in the JRB and BLRB presents non-significantly decreasing trends; (2) the non-stationary n series was divided into 3-, 7-, 18-, exceeding 18-year time scale oscillations and a trend residual. In the WRB and BLRB, the overall variation of n was dominated by the residual, whereas in the JRB it was dominated by the 7-year time scale oscillation; (3) the relationship between CO<sub>2 </sub>concentration and n series was significant in the WRB except for 3-year time scale. In the JRB, CO<sub>2 </sub>concentration and n series were significantly correlated on the 7- and exceeding 7-year time scales, while in the BLRB, such a significant relationship existed only on the 18- and exceeding 18-year time scales. (4) CO<sub>2</sub>-driven temperature rise and vegetation greening elevated the aridity index and evaporation ratio, thus impacting watershed water-energy balance dynamics. This study provided a deeper explanation for the possible impact of CO<sub>2</sub> concentration on the watershed hydrological processes.</p>

A Study of Impacts of Coupled Model Initial Shocks and State–Parameter Optimization on Climate Predictions Using a Simple Pycnocline Prediction Model

2011 ◽  
Vol 24 (23) ◽  
pp. 6210-6226 ◽  
Author(s):  
S. Zhang
Keyword(s):  
Time Scales ◽  
Parameter Optimization ◽  
Time Scale ◽  
Model Simulation ◽  
Coupled Model ◽  
State Parameter ◽  
Model Parameters ◽  
Forecast Errors ◽  
Long Time ◽  
The Impact

Abstract A skillful decadal prediction that foretells varying regional climate conditions over seasonal–interannual to multidecadal time scales is of societal significance. However, predictions initialized from the climate-observing system tend to drift away from observed states toward the imperfect model climate because of the model biases arising from imperfect model equations, numeric schemes, and physical parameterizations, as well as the errors in the values of model parameters. Here, a simple coupled model that simulates the fundamental features of the real climate system and a “twin” experiment framework are designed to study the impact of initialization and parameter optimization on decadal predictions. One model simulation is treated as “truth” and sampled to produce “observations” that are assimilated into other simulations to produce observation-estimated states and parameters. The degree to which the model forecasts based on different estimates recover the truth is an assessment of the impact of coupled initial shocks and parameter optimization on climate predictions of interests. The results show that the coupled model initialization through coupled data assimilation in which all coupled model components are coherently adjusted by observations minimizes the initial coupling shocks that reduce the forecast errors on seasonal–interannual time scales. Model parameter optimization with observations effectively mitigates the model bias, thus constraining the model drift in long time-scale predictions. The coupled model state–parameter optimization greatly enhances the model predictability. While valid “atmospheric” forecasts are extended 5 times, the decadal predictability of the “deep ocean” is almost doubled. The coherence of optimized model parameters and states is critical to improve the long time-scale predictions.

Optical Coating Properties for Enhanced Blown-Sand Abrasion Resistance

2006 ◽  
Vol 977 ◽  
Author(s):  
Christopher Drew ◽  
Suzanne Bosselman ◽  
David Ziegler
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Time Scales ◽  
Time Scale ◽  
Silica Glass ◽  
Particle Diameter ◽  
Momentum Balance ◽  
Sand Abrasion ◽  
The Impact ◽  
Scanning Electron

AbstractLenses and other transparent optical materials suffer rapid damage when subjected to blowing abrasive particulates. The time-scale of these impact event falls between typical scratch tests (less than 1m/s) and ballistic tests (100s of m/s) and has not been studied in depth to date. Polymeric lens materials like polycarbonate are usually treated with a scratch-resistant coating, which is commonly silica-based. The coating provides some protection, yet is not sufficient at resisting abrasion from blown sand in most commercial products. We demonstrate that silicone elastomeric coatings are superior to polycarbonate and silica glass at resisting damage by blown sand particles. Sand abrasion tests were conducted using a custom-built test apparatus that exposes the sample to 400 micron diameter quartz silica moving at 16.5 m/s (approx. 38 mph). Scanning electron microscopy revealed the presence of small cracks and pits in polycarbonate, coated polycarbonate, and silica glass after sand exposure. No such damage was observed in the silicone-coated samples after an identical exposure.We speculate that the elastic tensile strain at the surface is an important predictor of the material response at the time-scale of the impact. A simple mathematical model was developed using a momentum balance pre- and post-impact, and was used to approximate the maximum deformation and impact time-scale. A semispherical interaction volume was used in the model with a radius of 1.5x the particle diameter, determined through profilometry experiments. The material’s resistance to deformation was measured experimentally through a static mechanical test using a spherical indenter to represent the particle. Tensile tests were performed on both materials to identify the maximum elastic strain.Additionally, dynamic mechanical tests were performed to confirm that the mechanical behavior at long time-scales was valid at shorter time-scales of the impacts. DMA curves were shifted using the WLF equation. Profilometry and scanning electron microscopy (SEM) imaging were used to confirm the presence or absence of blown-sand induced damage.

scholarly journals Multi-scale event synchronization analysis for unravelling climate processes: A wavelet-based approach

2017 ◽  
Author(s):  
Ankit Agarwal ◽  
Norbert Marwan ◽  
Maheswaran Rathinasamy ◽  
Bruno Merz ◽  
Jürgen Kurths
Keyword(s):  
Time Series ◽  
Time Scales ◽  
Time Scale ◽  
Temporal Dynamics ◽  
Multiple Scales ◽  
Nonlinear Interactions ◽  
Reference Time ◽  
Multi Scale ◽  
Spatio Temporal ◽  
Different Time Scales

Abstract. The temporal dynamics of climate processes are spread across different time scales and, as such, the study of these processes only at one selected time scale might not reveal the complete mechanisms and interactions within and between the (sub-) processes. For capturing the nonlinear interactions between climatic events, the method of event synchronization has found increasing attention recently. The main drawback with the present estimation of event synchronization is its restriction to analyse the time series at one reference time scale only. The study of event synchronization at multiple scales would be of great interest to comprehend the dynamics of the investigated climate processes. In this paper, wavelet based multi-scale event synchronization (MSES) method is proposed by combining the wavelet transform and event synchronization. Wavelets are used extensively to comprehend multi-scale processes and the dynamics of processes across various time scales. The proposed method allows the study of spatio-temporal patterns across different time scales. The method is tested on synthetic and real-world time series in order to check its replicability and applicability. The results indicate that MSES is able to capture relationships that exist between processes at different time scales.

scholarly journals An uncertainty principle for star formation – III. The characteristic emission time-scales of star formation rate tracers

2020 ◽  
Vol 498 (1) ◽  
pp. 235-257
Author(s):  
Daniel T Haydon ◽  
J M Diederik Kruijssen ◽  
Mélanie Chevance ◽  
Alexander P S Hygate ◽  
Mark R Krumholz ◽  
...  
Keyword(s):  
Star Formation ◽  
Statistical Method ◽  
Time Scales ◽  
Time Scale ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Initial Mass Function ◽  
Uv Filters ◽  
Reference Time ◽  
Filter Width

ABSTRACT We recently presented a new statistical method to constrain the physics of star formation and feedback on the cloud scale by reconstructing the underlying evolutionary timeline. However, by itself this new method only recovers the relative durations of different evolutionary phases. To enable observational applications, it therefore requires knowledge of an absolute ‘reference time-scale’ to convert relative time-scales into absolute values. The logical choice for this reference time-scale is the duration over which the star formation rate (SFR) tracer is visible because it can be characterized using stellar population synthesis (SPS) models. In this paper, we calibrate this reference time-scale using synthetic emission maps of several SFR tracers, generated by combining the output from a hydrodynamical disc galaxy simulation with the SPS model slug2. We apply our statistical method to obtain self-consistent measurements of each tracer’s reference time-scale. These include H α and 12 ultraviolet (UV) filters (from GALEX, Swift, and HST), which cover a wavelength range 150–350 nm. At solar metallicity, the measured reference time-scales of H α are ${4.32^{+0.09}_{-0.23}}$ Myr with continuum subtraction, and 6–16 Myr without, where the time-scale increases with filter width. For the UV filters we find 17–33 Myr, nearly monotonically increasing with wavelength. The characteristic time-scale decreases towards higher metallicities, as well as to lower star formation rate surface densities, owing to stellar initial mass function sampling effects. We provide fitting functions for the reference time-scale as a function of metallicity, filter width, or wavelength, to enable observational applications of our statistical method across a wide variety of galaxies.

Anomalous Diffusion in Short-Pulse Laser Interactions With Random Media

1996 ◽  
Vol 118 (3) ◽  
pp. 781-786 ◽  
Author(s):  
M. C. Hipwell ◽  
C.-L. Tien
Keyword(s):  
Time Scales ◽  
Anomalous Diffusion ◽  
Time Scale ◽  
Random Media ◽  
Energy Transport ◽  
Short Pulse ◽  
Homogeneous Medium ◽  
Short Time Scale ◽  
Short Time ◽  
The Impact

This work applies fractal percolation theory to examine the impact of anomalous diffusion in short time-scale applications of random media. It is shown that there exist three regimes of heat transport corresponding to transport over the basic percolation unit (particle), the fractal cluster, and the homogeneous medium. Scaling is performed to determine the characteristic time scales of anomalous diffusion. The dependence of these time scales on both material properties and structure is examined to assess the impact of the anomalous diffusion regime on short time-scale energy transport. Additional criteria that determine the importance of anomalous diffusion relative to other transport phenomena and properties, such as radiation and thermal boundary resistance, are established.

Time scales of the Greenland Freshwater Anomaly in the Subpolar North Atlantic

2021 ◽  
pp. 1-58
Author(s):  
D.S. Dukhovskoy ◽  
I. Yashayaev ◽  
E.P. Chassignet ◽  
P.G. Myers ◽  
G. Platov ◽  
...  
Keyword(s):  
Steady State ◽  
Response Time ◽  
Time Scales ◽  
Residence Time ◽  
North Atlantic ◽  
Time Scale ◽  
Freshwater Discharge ◽  
Lagrangian Analysis ◽  
Decadal Time Scale ◽  
The Impact

AbstractThe impact of increasing Greenland freshwater discharge on the subpolar North Atlantic (SPNA) remains unknown as there are uncertainties associated with the time scales of the Greenland freshwater anomaly (GFWA) in the SPNA. Results from numerical simulations tracking GFWA and an analytical approach are employed to estimate the response time suggesting a decadal time scale (13 years) required for the SPNA to adjust for increasing GFWA. Analytical solutions obtained for a long-lasting increase of freshwater discharge show a non-steady state response of the SPNA with increasing content of the GFWA. In contrast, solutions for a short-lived pulse of freshwater demonstrate different responses of the SPNA with a rapid increase of freshwater in the domain followed by an exponential decay after the pulse has passed. Derived theoretical relation between time scales show that residence time scales are time-dependent for a non-steady state case and asymptote the response time scale with time. Residence time of the GFWA deduced from Lagrangian experiments is close to and smaller than the response time, in agreement with the theory. The Lagrangian analysis shows dependence of the residence time on the entrance route of the GFWA and on the depth. The fraction of the GFWA exported through Davis Strait has limited impact on the interior basins, whereas the fraction entering the SPNA from the southwest Greenland shelf spreads into the interior regions. In both cases, the residence time of the GFWA increases with depth demonstrating long persistence of the freshwater anomaly in the subsurface layers.

scholarly journals Diffusion of COVID-19 impact across selected stock markets: a wavelet coherency analysis

2020 ◽  
Vol 17 (4) ◽  
pp. 202-214 ◽  
Author(s):  
Taufeeque Ahmad Siddiqui ◽  
Haseen Ahmed ◽  
Mohammad Naushad
Keyword(s):  
Financial Markets ◽  
Time Scales ◽  
Time Scale ◽  
Stock Markets ◽  
Stock Exchange ◽  
Stock Index ◽  
The World ◽  
The Uk ◽  
The Impact ◽  
Wavelet Coherency

COVID-19 has impacted the world economy in an unprecedented manner; the financial markets indicate the same. This spontaneous event landed most of the stock markets into extreme volatility. Large capital outflow and extreme rapid fall were seen among almost all the world financial markets. Though similar trend prevailed everywhere during this pandemic, the impact could not be accumulated in absolute terms. Using the data of five stock markets, the current study endeavored to draw an impact of COVID-19 on major stock exchanges. The study uses wavelet coherency analysis on one-year daily data from June 2019 to May 2020 of five stock markets: Bombay Stock Exchange (BSE), London Stock Exchange (LSE), NASDAQ, Tokyo Stock Exchange (Nikkei), and Shanghai Stock Exchange. It is observed that there are time-variation and scale-variation in co-movements between the studied markets. During the crisis, the co-movement concentrates on a short time scale, even for two days. These results have significant implications for international investors, which will help them in portfolio diversification with time elements. All the stock markets under study have indicated co-movement at different time scales and frequencies with varying cross-power levels. However, the concentration of co-movement is found the most between the UK and the US stock markets. It is the least between Japan and the UK. In BSE, co-movement at shorter time scales started late. NASDAQ is leading only in one case, i.e., Shanghai Stock Exchange. BSE is not leading any stock index. LSE is in the leading position in all four cases. It has also been observed that co-movement started to concentrate at a shorter time scale as soon as the impact of the crisis increased.

scholarly journals Current and future realizations of coordinate time scales

2009 ◽  
Vol 5 (S261) ◽  
pp. 95-101
Author(s):  
E. Felicitas Arias
Keyword(s):  
Time Scales ◽  
Time Scale ◽  
Proper Time ◽  
Frequency Stability ◽  
Reference Time ◽  
Weights And Measures ◽  
Coordinate Time ◽  
Future Improvement ◽  
Stability And Accuracy ◽  
Atomic Time

AbstractTwo atomic time scales maintained at the International Bureau of Weights and Measures (BIPM) are realizations of terrestrial time: International Atomic Time (TAI) and TT(BIPM). They are calculated from atomic clocks realizing proper time in national laboratories. The algorithm for the calculation of TAI has been designed to optimize the frequency stability and accuracy of the time scale. Plans for the future improvement of the reference time scales are presented.

scholarly journals An Enhanced Intrinsic Time-Scale Decomposition Method Based on Adaptive Lévy Noise and Its Application in Bearing Fault Diagnosis

Symmetry ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 617
Author(s):  
Jianpeng Ma ◽  
Shi Zhuo ◽  
Chengwei Li ◽  
Liwei Zhan ◽  
Guangzhu Zhang
Keyword(s):  
Fault Diagnosis ◽  
Time Scale ◽  
Lévy Noise ◽  
Model Parameters ◽  
Rolling Bearings ◽  
Intrinsic Time ◽  
Time Scale Decomposition ◽  
Weak Fault ◽  
Levy Noise ◽  
The Impact

When early failures in rolling bearings occur, we need to be able to extract weak fault characteristic frequencies under the influence of strong noise and then perform fault diagnosis. Therefore, a new method is proposed: complete ensemble intrinsic time-scale decomposition with adaptive Lévy noise (CEITDALN). This method solves the problem of the traditional complete ensemble intrinsic time-scale decomposition with adaptive noise (CEITDAN) method not being able to filter nonwhite noise in measured vibration signal noise. Therefore, in the method proposed in this paper, a noise model in the form of parameter-adjusted noise is used to replace traditional white noise. We used an optimization algorithm to adaptively adjust the model parameters, reducing the impact of nonwhite noise on the feature frequency extraction. The experimental results for the simulation and vibration signals of rolling bearings showed that the CEITDALN method could extract weak fault features more effectively than traditional methods.

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