A5050111981- Advanced Frequency and Time Standards
- Atomic and Subatomic Physics Research
- GNSS positioning and interference
- Scientific Measurement and Uncertainty Evaluation
- Control Systems and Identification
- Structural Health Monitoring Techniques
- Fault Detection and Control Systems
- Neural Networks and Applications
- Cold Atom Physics and Bose-Einstein Condensates
- Machine Fault Diagnosis Techniques
- stochastic dynamics and bifurcation
- Scientific Research and Discoveries
- Nonlinear Dynamics and Pattern Formation
- Image and Signal Denoising Methods
- Blind Source Separation Techniques
- Probabilistic and Robust Engineering Design
- Radioactive Decay and Measurement Techniques
- Geophysics and Sensor Technology
- Sensor Technology and Measurement Systems
- Time Series Analysis and Forecasting
- Chaos control and synchronization
- Spectroscopy and Laser Applications
- Quantum Mechanics and Applications
- Experimental and Theoretical Physics Studies
- Advanced Fiber Laser Technologies
Polytechnic University of Turin
2014-2024
Chung-Ang University
2007
City University of New York
2002-2006
Hunter College
2002-2004
Istituto Nazionale di Fisica Nucleare, Galileo Galilei Institute for Theoretical Physics
2003
Ferrari (Italy)
2003
U.S. Air Force Institute of Technology
2002
Wright-Patterson Air Force Base
2002
City College
2002
City College of New York
2002
The two-state model provides an effective description of the atomic clock noise. We present construction model, which is useful to understand statistics Furthermore, we derive discrete-time version can be used for numerical simulations. illustrate our results through examples.
In this article, we discuss the important role of time-frequency (TF) signal representations in enhancing global navigation satellite system (GNSS) receiver performance. Both linear transforms and quadratic TF distributions (QTFDs) are considered. We review recent advances antijam techniques that exploit distinction signatures between desired undesired signals, enabling effective jammer excision with minimum distortion to signals. The characterization jammers by their instantaneous...
A mathematical model for the clock phase and frequency deviation based on theory of stochastic differential equations (SDEs) is discussed. In particular, we consider a that includes what are called `white random walk noises' in time metrology, which give rise context to Wiener an integrated process phase. Due particular simple expression functions involved exact solution exists, determine it by considering wider theoretical context, suitable generalizations more complex instances. Moreover,...
We present and discuss the dynamic Allan variance, a measure of time-varying stability an atomic clock. First, variance is mathematically defined, then its behavior extensively tested on simulated experimental data. The results prove validity effectiveness proposed new tool.
This article reviews applications of the Kalman filter to atomic timing. The objectives are twofold - present diverse and concepts in a consistent fashion, both regard notation mathematical concepts. develop key ideas tutorial form by introducing basic then applications.we apply clock estimation, monitoring, time-scale definition. Furthermore, GPS composite algorithm along with numerical simulations is described. Finally, advantages criticalities application timing, highlighting issues that...
Due to their stability atomic clocks represent the core of navigation systems such as GPS and future European Galileo system. To identify possible anomalies, it is fundamental detect when clock varies with time. The dynamic Allan variance (DAVAR) makes this monitoring process possible. We extend DAVAR case a time series missing data, we analyze presence periodic behaviors, two common phenomena in space clocks.
Frequency jumps are common anomalies in atomic clocks aboard navigation system satellites. These anomalous behaviors must be detected quickly and accurately to minimize the impact on user positioning. We develop a detector for frequency based Kalman filter. Numerical simulations show that is fast, with high probability of detection low false alarms. It also has computational cost because it takes advantage recursive nature Therefore, can used applications which little power available, such as
An atomic time scale is a method for marking events and the passage of by using frequency standards. Thanks to superior performance clocks based on optical transitions, scales generated with have potential be more accurate stable than those microwave clocks. In this work, we demonstrate an experimental INRiM Yb lattice clock hydrogen maser as flywheel oscillator, showing sub-nanosecond accuracy over months-long periods nanosecond 1-year period. The obtained results show that competitive...
In this paper, the problem of identifying variations in nature atomic clock noise is addressed. Two methods are proposed. One method based on a generalized likelihood ratio test (GLRT), and other dynamic Allan variance (DAVAR), which representation instantaneous stability that able to point out possible nonstationary behaviors. Both efficiently track experimental data and, thus, appear as suitable tools for detection anomalies
When an anomaly occurs in atomic clock, its stability and frequency spectrum change with time. The variation time of the can be evaluated dynamic Allan variance. described spectrogram, a time–frequency distribution. We develop method that uses variance spectrogram to detect identify typical anomalies clock. apply simulated data.
The stability of an atomic clock can change with time due to several factors, such as temperature, humidity, radiations, aging, and sudden breakdowns. dynamic Allan variance, or DAVAR, is a representation the time-varying clock, it be used monitor behavior. Unfortunately, computational DAVAR grows very quickly length analyzed series. In this article, we present fast algorithm for computation also extend case missing data. Numerical simulations show that dramatically reduces time. useful when...
The Kalman filter is a very useful tool of estimation theory, successfully adopted in wide variety problems. As recursive and optimal technique, the seems to be correct also for building precise timescales, various attempts have been made past giving rise, example, TA(NIST) timescale. Despite promising expectations, completely satisfactory implementation has never found, due intrinsic non-observability clock time readings, which makes problem underdetermined. However, case applied difference...
We introduce the dynamic Allan variance, a quantity that characterizes variation in time of stability an atomic clock. connect variance to Wigner spectrum, time-frequency representation can reveal time-varying frequencies generally present clock error noise under nonstationary conditions. also propose practical implementation for quasi-stationary noises, and we show numerical results prove validity our approach, both on simulated real data.
Periodicities in a DNA sequence contain information about its function and structure. Frequency analysis can be used to reveal such periodicities. A definition of spectrum for sequences is proposed, based on an entropy minimization criterion. It shown that the properties proposed are those expected from symbolic sequence. Applications simulated experimental presented compared against classical techniques prove effectiveness method.
The dynamic Allan variance (DAVAR) is a surface which describes the stability of high-precision clock with respect to time. When DAVAR evaluated from experimental data, its shows random fluctuations caused by estimation process. It fundamental assign statistical significance these fluctuations, so that they can be differentiated variations anomalies. First, we develop confidence surfaces estimator. Then, introduce detection reveal We validate obtained results through numerical simulations.
Due to its small size, low weight, and power consumption, the Rb atomic frequency standard (RAFS) is routinely first choice for timekeeping in space. Consequently, though device has very good stability (rivaling passive hydrogen masers), there interest uncovering fundamental processes limiting long-term performance, with goal of improving future space systems missions. The ac Stark shift (i.e., light shift) one more likely RAFS' ability, yet manifestation RAFS remains poorly understood. In...
Abstract The recently concluded collaborative European project “Robust optical clocks for international timescales” (ROCIT) tackled some of the key challenges on roadmap towards a redefinition SI second. This paper gives an overview progress made improving robustness and automation verifying their uncertainty budgets through coordinated comparison campaigns. It also presents work incorporation into time scales, covering both use to steer local physical scales evaluations hydrogen masers...
Several clock and time scale steering methods have been developed according to different viewpoints by various laboratories. By resorting control theory ideas, we propose a common theoretical framework encompassing these methods. A comparison of the most methodologies, namely, classical approach, GPS bang-bang method, linear quadratic Gaussian technique, is carried out. We believe that use can potentially lead better understanding algorithms.
Abstract When observed from the ground, frequency of atomic clocks flying on satellites a Global Navigation Satellite System is referred to as apparent frequency, because it through on-board signal generation chain, propagation path, relativistic effects, measurement system, and clock estimation algorithm. As consequence, affected by periodic variations different origins such as, for example, component J2 effect, due oblateness earth, errors induced orbital errors. We present detailed...
We present a new method to study linear systems that exhibit time-varying characteristics and are governed by ordinary differential equations. The transforms the equation into governing for ambiguity function time-frequency domain. advantage of is in domain an immense simplification occurs, both mathematically physically. applies deterministic stochastic approach applied classical RC filter driven white noise. obtain characterization output spectra.