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 Coordinate time in the vicinity of the Earth

1986 ◽  
Vol 114 ◽  
pp. 299-313 ◽  
Author(s):  
D. W. Allan ◽  
N. Ashby
Keyword(s):  
General Relativity ◽  
Atomic Clock ◽  
Space Vehicles ◽  
Atomic Clocks ◽  
Coordinate Time ◽  
The Earth ◽  
Frequency Comparison ◽  
New Applications ◽  
Frequency Metrology

Atomic clock accuracies continue to improve rapidly, requiring the inclusion of general relativity for unambiguous time and frequency clock comparisons. Atomic clocks are now placed on space vehicles and there are many new applications of time and frequency metrology. This paper addresses theoretical and practical limitations in the accuracy of atomic clock comparisons arising from relativity, and demonstrates that accuracies of time and frequency comparison can approach a few picoseconds and a few parts in 1016, respectively.

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.

Physical Ultrasonics of Composites

2011 ◽  
Author(s):  
Dale Chimenti ◽  
Stanislav Rokhlin ◽  
Peter Nagy
Keyword(s):  
Composite Laminates ◽  
Stiffness Matrix ◽  
Composite Plates ◽  
Anisotropic Media ◽  
Anisotropic Materials ◽  
Ultrasonic Waves ◽  
Laminated Plates ◽  
Structure Characteristic ◽  
Major Advance

Physical Ultrasonics of Composites is a rigorous introduction to the characterization of composite materials by means of ultrasonic waves. Composites are treated here not simply as uniform media, but as inhomogeneous layered anisotropic media with internal structure characteristic of composite laminates. The objective here is to concentrate on exposing the singular behavior of ultrasonic waves as they interact with layered, anisotropic materials, materials which incorporate those structural elements typical of composite laminates. This book provides a synergistic description of both modeling and experimental methods in addressing wave propagation phenomena and composite property measurements. After a brief review of basic composite mechanics, a thorough treatment of ultrasonics in anisotropic media is presented, along with composite characterization methods. The interaction of ultrasonic waves at interfaces of anisotropic materials is discussed, as are guided waves in composite plates and rods. Waves in layered media are developed from the standpoint of the "Stiffness Matrix", a major advance over the conventional, potentially unstable Transfer Matrix approach. Laminated plates are treated both with the stiffness matrix and using Floquet analysis. The important influence on the received electronic signals in ultrasonic materials characterization from transducer geometry and placement are carefully exposed in a dedicated chapter. Ultrasonic wave interactions are especially susceptible to such influences because ultrasonic transducers are seldom more than a dozen or so wavelengths in diameter. The book ends with a chapter devoted to the emerging field of air-coupled ultrasonics. This new technology has come of age with the development of purpose-built transducers and electronics and is finding ever wider applications, particularly in the characterization of composite laminates.

scholarly journals Characterization of the main frequency shifts for the brazilian 133Cs atomic beam frequency standard

2005 ◽  
Vol 35 (4a) ◽  
Author(s):  
A. Bebeachibuli ◽  
M. S. Santos ◽  
D. V. Magalhães ◽  
S. T. Müller ◽  
V.S. Bagnato
Keyword(s):  
Atomic Beam ◽  
Frequency Standard ◽  
Frequency Shifts ◽  
Main Frequency

A large-scale cold atom source in an integrating sphere

2014 ◽  
Vol 28 (14) ◽  
pp. 1450116 ◽  
Author(s):  
Ben-Chang Zheng ◽  
Hua-Dong Cheng ◽  
Yan-Ling Meng ◽  
Peng Liu ◽  
Xiu-Mei Wang ◽  
...  
Keyword(s):  
Large Scale ◽  
Cold Atoms ◽  
Signal To Noise Ratio ◽  
Atomic Clock ◽  
Cold Atom ◽  
Integrating Sphere ◽  
Cooling Power ◽  
Atom Number ◽  
Atom Source ◽  
Good Signal

An integrating sphere with a diameter of 10 cm is developed for cooling atoms. The maximum number of 2 × 1010 cold atoms is obtained from a background vapor with 220 mW cooling laser power. The cold atom number can be increased by further increasing the cooling power. Such cold atom source would have potential use for Raman–Ramsey atomic clock with good signal-to-noise ratio (SNR).

scholarly journals Optical atomic phase reference and timing

2017 ◽  
Vol 375 (2099) ◽  
pp. 20160241 ◽  
Author(s):  
L. Hollberg ◽  
E. H. Cornell ◽  
A. Abdelrahmann
Keyword(s):  
Special Relativity ◽  
Real World ◽  
High Performance ◽  
Cold Atoms ◽  
Cold Atom ◽  
New Physics ◽  
Atomic Clocks ◽  
Commercial World ◽  
Commercial Applications ◽  
Quantum Technology

Atomic clocks based on laser-cooled atoms have made tremendous advances in both accuracy and stability. However, advanced clocks have not found their way into widespread use because there has been little need for such high performance in real-world/commercial applications. The drive in the commercial world favours smaller, lower-power, more robust compact atomic clocks that function well in real-world non-laboratory environments. Although the high-performance atomic frequency references are useful to test Einstein's special relativity more precisely, there are not compelling scientific arguments to expect a breakdown in special relativity. On the other hand, the dynamics of gravity, evidenced by the recent spectacular results in experimental detection of gravity waves by the LIGO Scientific Collaboration, shows dramatically that there is new physics to be seen and understood in space–time science. Those systems require strain measurements at less than or equal to 10 −20 . As we discuss here, cold atom optical frequency references are still many orders of magnitude away from the frequency stability that should be achievable with narrow-linewidth quantum transitions and large numbers of very cold atoms, and they may be able to achieve levels of phase stability, Δ Φ / Φ total  ≤ 10 −20 , that could make an important impact in gravity wave science. This article is part of the themed issue ‘Quantum technology for the 21st century’.

The molecular and genetic manipulation of nitrogen fixation

1981 ◽  
Vol 292 (1062) ◽  
pp. 589-599 ◽  
Keyword(s):  
Biological Process ◽  
Genetic Manipulation ◽  
Plant Genome ◽  
Population Pressure ◽  
Major Advance ◽  
Regulated Expression ◽  
Substantial Progress ◽  
World Agriculture ◽  
Physiological Background

The fundamental importance of dinitrogen fixation for world agriculture, in relation to projected energy supplies, population pressure and food requirements over the next decades, obliges scientists to reconsider ways of exploiting this biological process. Genetic manipulation offers several options in principle. Existing symbiotic systems such as the legumes and seemingly inefficient systems such as the grass associations could be improved; new symbioses could be developed by nif gene transfer to rhizosphere commensals or by somatic hybridization of appropriate plants. A major advance would be to render plants independent of microbes by manipulation of expressable nif into the plant genome. This goal is discussed. It requires the complete genetic and physical characterization of nif in particular its regulation, and an understanding of the physiological background within which nif can be expressed, as well as the ability to fuse nif to alien genetic systems. Substantial progress in these directions has been made by using the n if genes of Klebsiella pneumoniae this progress is reviewed. Strategies for the further manipulation of nif towards regulated expression in the plant genome are considered.

Comb characterization of Erbium All-fiber Hybrid Mode-locked ultra-short pulse Ring laser for Frequency Metrology

2015 ◽  
Author(s):  
Lazarev Vladimir ◽  
Krylov Alexander ◽  
Dvoretskiy Dmitriy ◽  
Sazonkin Stanislav ◽  
Pnev Alexey ◽  
...  
Keyword(s):  
Ring Laser ◽  
Short Pulse ◽  
Hybrid Mode ◽  
Ultra Short Pulse ◽  
Frequency Metrology
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