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Physics

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Displaying 1201 - 1225 of 2493

A Clock Ensemble Using Only Active Hydrogen Masers

January 31, 2017
Author(s)
Thomas E. Parker, Stefania Romisch
The current real-time timescale at NIST, AT1, as well as the post-processed scale TP162, both contain hydrogen masers and commercial cesium frequency standards. The cesium standards are much nosier in the short term than the hydrogen masers and

A Study on Using the SDR Receiver for the Europe-Europe and Transatlantic TWSTFT Links

January 31, 2017
Author(s)
Victor S. Zhang, Thomas E. Parker, Joseph Achkar, Dirk Piester, Yi-Jiun Huang, Shinn-Yan Lin, Zhiheng Jiang
The BIPM and the CCTF Working Group on TWSTFT have stimulated a pilot study on using software defined radio (SDR) receivers for TWSTFT in the framework of the realization of International Atomic Time (TAI). The SDR receivers based on a software developed

Accurate TWSTFT time transfer with indirect links

January 31, 2017
Author(s)
Victor S. Zhang, Zhiheng Jiang, Thomas E. Parker, Jian Yao, Yi-Jiun Huang, Shinn-Yan Lin
The conventional wisdom suggests a direct Two-Way Satellite Time and Frequency Transfer (TWSTFT or TW) time link should result in a smaller uncertainty than that of an indirect TW link over the same baseline [12]. This is why all Coordinated Universal Time

Local Distribution and Calibration of Timing Signals at NIST

January 31, 2017
Author(s)
Joshua J. Savory, Liz C. Forero, Kristopher Maurer, Stefania Romisch
The National Institute of Standards and Technology (NIST) timescale produces a real-time realization of UTC(NIST) in the form of a pulse-per-second (PPS) time signal and a 5 MHz frequency reference. The timing signals are distributed to the international

Long-term instability in UTC time links

January 31, 2017
Author(s)
Victor S. Zhang, Demetrios Matsakis, Zhiheng Jiang
Calibration and link stability are the key issues for the UTC time transfer. This study is made in the framework of a joint task group of the CCTF Working Group on TWSTFT and Working Group on GNSS Time Transfer to investigate the long-term instability of

The development of a new Kalman-filter time scale at NIST

January 31, 2017
Author(s)
Jian Yao, Thomas E. Parker, Judah Levine
We report on a preliminary design of a new Kalman-filter Hydrogen-maser time scale at NIST. The time scale is composed of a few Hydrogen masers and a Cs clock. The Cs clock is used as a reference clock, just for easy operations with the existing data. All

The effects of the January 2016 UTC offset anomaly on GPS clocks monitored at NIST

January 31, 2017
Author(s)
Jian Yao, Michael A. Lombardi, Andrew N. Novick, Bijunath Patla, Jeffrey A. Sherman, Victor S. Zhang
Errors in the Coordinated Universal Time (UTC) offset parameters broadcast by Global Positioning System (GPS) satellites caused many thousands of GPS clocks to be in error by approximately -13 µs on January 25-26, 2016. The erroneous UTC offset information

Trapped-ion optical atomic clocks at the quantum limits

January 31, 2017
Author(s)
David R. Leibrandt, Samuel M. Brewer, Jwo-Sy Chen, Aaron M. Hankin, David B. Hume, David J. Wineland, Chin-Wen Chou
Frequency and its inverse, time, are the most accurately measured quantities. Historically, improvements in the accuracy of clocks have enabled advances in navigation, communication, and science. Since 1967, the definition of the SI second has been based

A New Generation of Magnetoencephalography: Room Temperature Measurements using Optically-Pumped Magnetometers

January 25, 2017
Author(s)
Elena Boto, Sofie S. Meyer, Vishal Shah, Orang Alem, Svenja A. Knappe, Peter Kruger, Mark Fromhold, Peter G. Morris, Richard W. Bowtell, Gareth R. Barnes, Matthew J. Brookes, Mark Lim
Significant advances in the field of quantum sensing mean that magnetic field detectors, operating at room temperature, are now able to achieve sensitivity similar to that of cryogenically cooled devices (SQUIDs). This means that room temperature

A microfabricated optically-pumped magnetic gradiometer

January 18, 2017
Author(s)
Abigail R. Perry, Sean P. Krzyzewski, John E. Kitching, S. Geller, Sheng D., Svenja A. Knappe
We report on the development of a microfabricated atomic magnetic gradiometer based on optical spectroscopy of alkali atoms in the vapor phase. The gradiometer, with a length of 60 mm and a cross section diameter of 12 mm, is made of two chip-scale atomic

Coherent UV-to-Visible Light Arrays

January 9, 2017
Author(s)
Dong Yoon Oh, Scott Diddams, Ki Youl Yang, Kerry J. Vahala, Connor Fredrick, Gabriel Ycas
Short duration, intense pulses of light can experience dramatic spectral broadening when propagating through lengths of optical fiber. This continuum generation process is caused by a combination of nonlinear optical effects including the formation of so

Preflight Radiometric Calibration of Orbiting Carbon Observatory 2

January 9, 2017
Author(s)
Stephen Maxwell, B. Carol Johnson, Robert Rosenberg, Lars Chapsky, Richard A. Lee, Randy Pollock
This paper describes the prelaunch radiometric calibration of the imaging spectrometers used on the second Orbiting Carbon Observatory (OCO-2). The gain and dark response were characterized for each focal plane array detector element. An integrating sphere

Ultra-stable optical clock with two cold-atom ensembles

January 1, 2017
Author(s)
Marco Schioppo, Roger Brown, Will McGrew, Nathan M. Hinkley, Robert J. Fasano, Kyle Beloy, Gianmaria Milani, Daniele Nicolodi, Jeffrey Sherman, Nate B. Phillips, Christopher W. Oates, Andrew Ludlow
Atomic clocks based on optical transitions are the most stable, and therefore precise, timekeepers available. These clocks operate by alternating intervals of atomic interrogation with ‘dead' time required for quantum state preparation and readout. This

Stoner vs. Heisenberg: Ultrafast exchange reduction and magnon generation during laser-induced demagnetization

December 28, 2016
Author(s)
Thomas J. Silva, Hans T. Nembach, Justin M. Shaw, Emrah Turgut, Dmitriy Zusin, Dominik Legut, Karel Carva, Ronny Knut, Cong Chen, Zhensheng Tao, Stefan Mathias, Martin Aeschlimann, Peter Oppeneer, Henry Kapteyn, Margaret Murnane, Patrik Grychtol
Understanding how the electronic band structure of a ferromagnetic material is modified during laser-induced demagnetization on femtosecond timescales has been a long-standing question in condensed matter physics. Here, we use ultrafast high harmonics to

Adaptive Terahertz Dual Frequency Comb Spectrometer

December 26, 2016
Author(s)
Flavio Caldas da Cruz, Francisco S. Vieira, David F. Plusquellic, Scott A. Diddams
Terahertz dual frequency comb spectroscopy (THz-DFCS) yields high spectral resolution without compromising bandwidth. Nonetheless, the resolution of THz-DFCS is usually limited by the laser repetition rate, which is typically between 80 MHz and 1 GHz. In

Generalized entropy theory of glass-formation in fully flexible polymer melts

December 21, 2016
Author(s)
Jack F. Douglas, Wensheng Xu, Karl Freed
The generalized entropy theory (GET) offers many insights into how molecular parameters influence polymer glass-formation. Given the fact that chain rigidity often plays a critical role in understanding the glass- formation of polymer materials, the GET
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