CHARACTERIZATION OF NONSTATIONARY ATOMIC CLOCKS

2007 ◽  
Vol 07 (04) ◽  
pp. L461-L471 ◽  
Author(s):  
LORENZO GALLEANI ◽  
PATRIZIA TAVELLA
Keyword(s):  
Navigation System ◽  
Atomic Clock ◽  
Allan Variance ◽  
Atomic Clocks ◽  
Time Varying ◽  
The Core ◽  
The Stability ◽  
Very High

Atomic clocks are the core of a navigation system. Since an error in time results in an error in the user localization, it is fundamental that the stability is very high and constant with time. In this paper we discuss the dynamic Allan variance, or DAVAR, a representation of the time-varying stability of an atomic clock. We show by simulation its effectiveness in tracking common nonstationary behaviors of a clock.

scholarly journals Identifying Nonstationary Clock Noises in Navigation Systems

2008 ◽  
Vol 2008 ◽  
pp. 1-5 ◽  
Author(s):  
Lorenzo Galleani ◽  
Patrizia Tavella
Keyword(s):  
Experimental Data ◽  
Numerical Simulations ◽  
Navigation System ◽  
Atomic Clock ◽  
Allan Variance ◽  
Atomic Clocks ◽  
Navigation Systems ◽  
Time Varying ◽  
The Stability ◽  
Physical Phenomena

The stability of the atomic clocks on board the satellites of a navigation system should remain constant with time. In reality there are numerous physical phenomena that make the behavior of the clocks a function of time, and for this reason we have recently introduced the dynamic Allan variance (DAVAR), a measure of the time-varying stability of an atomic clock. In this paper we discuss the dynamic Allan variance for phase and frequency jumps, two common nonstationarities of atomic clocks. The analysis of both numerical simulations and experimental data proves that the dynamic Allan variance is an effective way of characterizing nonstationary behaviors of atomic clocks.

scholarly journals The Brazilian time and frequency atomic standards program

2008 ◽  
Vol 80 (2) ◽  
pp. 217-252 ◽  
Author(s):  
Mushtaq Ahmed ◽  
Daniel V. Magalhães ◽  
Aida Bebeachibuli ◽  
Stella T. Müller ◽  
Renato F. Alves ◽  
...  
Keyword(s):  
Atomic Beam ◽  
Atomic Clock ◽  
Cold Atom ◽  
Telecommunication Networks ◽  
Atomic Clocks ◽  
Major Advance ◽  
Optical Cooling ◽  
Global Positioning ◽  
Frequency Metrology

Cesium atomic beam clocks have been the workhorse for many demanding applications in science and technology for the past four decades. Tests of the fundamental laws of physics and the search for minute changes in fundamental constants, the synchronization of telecommunication networks, and realization of the satellite-based global positioning system would not be possible without atomic clocks. The adoption of optical cooling and trapping techniques, has produced a major advance in atomic clock precision. Cold-atom fountain and compact cold-atom clocks have also been developed. Measurement precision of a few parts in 10(15) has been demonstrated for a cold-atom fountain clock. We present here an overview of the time and frequency metrology program based on cesium atoms under development at USP São Carlos. This activity consists of construction and characterization of atomic-beam, and several variations of cold-atom clocks. We discuss the basic working principles, construction, evaluation, and important applications of atomic clocks in the Brazilian program.

scholarly journals Preparation and Characterization of Double-Layered Microcapsules Containing Nano-SiO2

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Xue Sun ◽  
Jingcheng Su ◽  
Rui Zhang ◽  
Fangyu Fan
Keyword(s):  
Moisture Content ◽  
Droplet Size ◽  
Gum Arabic ◽  
Core Material ◽  
Wall Material ◽  
Scanning Calorimetry ◽  
Nano Sio2 ◽  
The Core ◽  
The Stability

The double-layered microencapsulation technology has been used in many fields. In this study, the double-layered microencapsulated anthocyanin of Passiflora edulis shells (APESs) was prepared via complex coacervation using gelatin and gum Arabic as the first wall materials (single-layered microcapsules (SMs)) and using gum Arabic containing nano-SiO2 as the second wall material (double-layered microcapsules (DMs)/nano-SiO2) to enhance the stability of the core material. Properties of microcapsules were analyzed on the basis of EE, morphology, scanning electron microscopy (SEM), droplet size, moisture content, and differential scanning calorimetry (DSC). The results showed that the EE values of SMs, DMs, and DMs/nano-SiO2 were 96.12%, 97.24%, and 97.85%, respectively. DMs/nano-SiO2 had the lowest moisture content (2.17%). The average droplet size of DMs/nano-SiO2 (34.93 μm) was higher than those of SMs and DMs. DSC indicated that the melting temperature of DMs/nano-SiO2 was 73.61°C and 45.33°C higher than those of SMs and DMs, respectively. SEM demonstrated that DMs/nano-SiO2 had the smoothest surface compared with the other two kinds of microcapsules. The storage stability of APESs and their microcapsules indicated that the stability of the microcapsules was improved by adding DMs/nano-SiO2 into the wall material of microcapsules. These results indicated double-layered microcapsules containing silica nanoparticles contribute to the stability of the core material.

scholarly journals Prospects and challenges for squeezing-enhanced optical atomic clocks

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Marius Schulte ◽  
Christian Lisdat ◽  
Piet O. Schmidt ◽  
Uwe Sterr ◽  
Klemens Hammerer
Keyword(s):  
Dead Time ◽  
Atomic Clock ◽  
Frequency Noise ◽  
Squeezed States ◽  
Atomic Clocks ◽  
Atom Number ◽  
Order Of Magnitude ◽  
Clock Stability ◽  
Servo Loop ◽  
The Stability

AbstractOptical atomic clocks are a driving force for precision measurements due to the high accuracy and stability demonstrated in recent years. While further improvements to the stability have been envisioned by using entangled atoms, squeezing the quantum mechanical projection noise, evaluating the overall gain must incorporate essential features of an atomic clock. Here, we investigate the benefits of spin squeezed states for clocks operated with typical Brownian frequency noise-limited laser sources. Based on an analytic model of the closed servo-loop of an optical atomic clock, we report here quantitative predictions on the optimal clock stability for a given dead time and laser noise. Our analytic predictions are in good agreement with numerical simulations of the closed servo-loop. We find that for usual cyclic Ramsey interrogation of single atomic ensembles with dead time, even with the current most stable lasers spin squeezing can only improve the clock stability for ensembles below a critical atom number of about one thousand in an optical Sr lattice clock. Even with a future improvement of the laser performance by one order of magnitude the critical atom number still remains below 100,000. In contrast, clocks based on smaller, non-scalable ensembles, such as ion clocks, can already benefit from squeezed states with current clock lasers.

scholarly journals Controlled size and high stability SiO2@ZnO QD’s with high green emission obtained by a simple colloidal route

2019 ◽  
Author(s):  
Rene Perez Cuapio ◽  
Jose Alberto A G Alvarado Garcia ◽  
Mauricio Pacio Castillo ◽  
Antonio Arce Plaza ◽  
Carlos Bueno Avendaño ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Green Emission ◽  
Morphological Characterization ◽  
The Core ◽  
Ft Ir ◽  
Uv Lamp ◽  
Size And Morphology ◽  
The Stability ◽  
Average Size

In this work the synthesis of visible ZnO quantum dots (QDs) functionalized/stabilized with oleic acid and core-shelled with SiO2 is presented. A colloidal route was followed to synthesize ZnO QDs with 5 nm average size. Several characterizations were done to identify and assure the core, the stabilization, grain size and QDs emission characteristics. Techniques like FT-IR, XRD, TEM, SEM, UV-Vis, PL and an UV lamp were used to test composition, structural, morphological and emission of the as obtained quantum dots. After the structural and morphological characterization of the particles, they were functionalized with (3-aminopropyl) trimethoxysilane (APTMS).  It was observed that the size and morphology are unchanged but the stability depends directly on the APTMS oversaturation which is due to the formation of a thick SiO2 layer. From the PL characterization results it was noticed that the strong green emission is related to the APTMS content and directly related to the shell formation, this emission decreases as the core-shell thickness increases.

scholarly journals Stability of Time Varying Systems

1995 ◽  
Author(s):  
Fritz Colonius ◽  
Wolfgang Kliemann
Keyword(s):  
Linear Time ◽  
Hyperbolic Systems ◽  
Type Theorem ◽  
Time Varying ◽  
Time Varying Systems ◽  
Stable Manifold Theorem ◽  
The Stability ◽  
Stability Type ◽  
Stability Radii

Abstract The stability behavior of time varying systems can be studied using the concept of Lyapunov exponents and their corresponding Lyapunov subspaces. For linear time varying systems the entire Lyapunov spectrum can be approximated by the Floquet exponents of periodic systems. This leads to a variety of stability results, including the characterization of stability radii. Furthermore, a structural stability type theorem shows that stability features of time varying hyperbolic systems persist under small perturbations. For nonlinear time varying systems a stable manifold theorem allows us to interpret the linear results for the nonlinear system locally around an equilibrium point.

scholarly journals Arbitration and Stability in Cooperative Games with Overlapping Coalitions

2014 ◽  
Vol 50 ◽  
pp. 847-884 ◽  
Author(s):  
Y. Zick ◽  
E. Markakis ◽  
E. Elkind
Keyword(s):  
Cooperative Games ◽  
Allocation Of Resources ◽  
Unified Framework ◽  
The Core ◽  
Depth Study ◽  
The Stability ◽  
The One ◽  
To Receive ◽  
Stability Concepts

Overlapping Coalition Formation (OCF) games, introduced by Chalkiadakis, Elkind, Markakis, Polukarov and Jennings in 2010, are cooperative games where players can simultaneously participate in several coalitions. Capturing the notion of stability in OCF games is a difficult task:deviating players may continue to contribute resources to joint projects with non-deviators, and the crucial question is what payoffs the deviators expect to receive from such projects. Chalkiadakis et al. introduce three stability concepts for OCF games---the conservative core, the refined core, and the optimistic core---that are based on different answers to this question. In this paper, we propose a unified framework for the study of stability in the OCF setting, which encompasses the stability concepts considered by Chalkiadakis et al. as well as a wide variety of alternative stability concepts. Our approach is based on the notion of arbitration functions, which determine the payoff obtained by the deviators, given their deviation and the current allocation of resources. We provide a characterization of stable outcomes under arbitration. We then conduct an in-depth study of four types of arbitration functions, which correspond to four notions of the core; these include the three notions of the core considered by Chalkiadakis et al. Our results complement those of Chalkiadakis et al. and answer questions left open by their work. In particular, we show that OCF games with the conservative arbitration function are essentially equivalent to non-OCF games, by relating the conservative core of an OCF game to the core of a non-overlapping cooperative game, and use this result to obtain a strictly weaker sufficient condition for conservative core non-emptiness than the one given by Chalkiadakis et al.

TEM characterization of Au/Polysilicon interactions

1990 ◽  
Vol 48 (4) ◽  
pp. 650-651
Author(s):  
N. David Theodore ◽  
Leslie H. Allen ◽  
C. Barry Carter ◽  
James W. Mayer
Keyword(s):  
Solid Phase ◽  
Single Crystal Silicon ◽  
Chemical Vapor ◽  
Electrical Contacts ◽  
Silicon Substrates ◽  
Crystal Silicon ◽  
Transmission Electron ◽  
Polysilicon Films ◽  
The Stability

Metal/polysilicon investigations contribute to an understanding of issues relevant to the stability of electrical contacts in semiconductor devices. These investigations also contribute to an understanding of Si lateral solid-phase epitactic growth. Metals such as Au, Al and Ag form eutectics with Si. reactions in these metal/polysilicon systems lead to the formation of large-grain silicon. Of these systems, the Al/polysilicon system has been most extensively studied. In this study, the behavior upon thermal annealing of Au/polysilicon bilayers is investigated using cross-section transmission electron microscopy (XTEM). The unique feature of this system is that silicon grain-growth occurs at particularly low temperatures ∽300°C).Gold/polysilicon bilayers were fabricated on thermally oxidized single-crystal silicon substrates. Lowpressure chemical vapor deposition (LPCVD) at 620°C was used to obtain 100 to 400 nm polysilicon films. The surface of the polysilicon was cleaned with a buffered hydrofluoric acid solution. Gold was then thermally evaporated onto the samples.

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