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Physics

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Displaying 2226 - 2250 of 2574

Shear Thinning Near the Critical Point of Xenon

April 17, 2008
Author(s)
Robert F. Berg, Michael R. Moldover, M Yao, G A. Zimmerli
We measured shear thinning, a viscosity decrease ordinarily associated with complex liquids, near the critical point of xenon. The data span the range of reduced shear rates: 0.001 < γτ < 700, where γτ is the shear rate scaled by the relaxation time τ of

Optical Lattice Induced Light Shifts in a Yb Atomic Clock

March 14, 2008
Author(s)
Zeb Barber, Jason Stalnaker, Nathan D. Lemke, Christopher W. Oates, Tara M. Fortier, Scott A. Diddams, Leo W. Hollberg, C Hoyt
We present an experimental study of the lattice induced light shifts on the $^1S_0\rightarrow\,^3P_0$ clock transition of ytterbium. The ``magic'' frequency for the $^{174}$Yb isotope was determined to be $u_{magic} = 394\,799\,475(35)$MHz. The

Lack of charge offset drift is a robust property of Si single electron transistors

February 12, 2008
Author(s)
Emmanouel S. Hourdakis, J A. Wahl, Neil M. Zimmerman
Single electron transistors (SETs) face several challenges before they can be considered technologically useful devices. One of them is the random, low frequency, charge offset drift that inhibits their use in parallel. Recently, tunable barrier Si SETs

MACS-a new high intensity cold neutron spectrometer at NIST

January 30, 2008
Author(s)
J A Rodriguez, Daniel Adler, P C Brand, Collin L. Broholm, Jeremy Cook, Christoph Brocker, R Hammond, Z Huang, P Hundertmark, J W Lynn, N C Maliszewskyj, J Moyer, J Orndorff, Donald J. Pierce, T D Pike, G Scharfstein, S A Smee, Rodrigo Vilaseca
We describe a novel cold neutron spectrometer under development at NIST optimized for wave vector resolved spectroscopy with incident energies between 2.1 meV and 20 meV and energy resolution from 0.05 meV (Ei = 2.1 meV) to 3.0 meV (Ei = 20 meV). By using

Large-scale MCHF Calculation of the Li I 4d-4f Energy Separation

November 1, 2007
Author(s)
Yuri Ralchenko, Charlotte Fischer
The calculational methods in atomic structure are currently capable of providing the level of accuracy close to that of the most precise experiments. The multiconfiguration Hartree-Fock method is applied to calculation of the 4d--4f energy difference in Li

Passive Cooling of a Micromechanical Oscillator with a Resonant Electric Circuit

September 28, 2007
Author(s)
Kenton R. Brown, Joseph W. Britton, Ryan Epstein, John Chiaverini, Dietrich G. Leibfried, David J. Wineland
Currently there is considerable interest in the cooling of macroscopic mechanical oscillators, as strong cooling may allow one to reach the quantum regime of such oscillators. Recent advances in microfabrication and cooling techniques have brought this

Lattice-based optical clock using an even isotope of Yb

September 12, 2007
Author(s)
Zeb Barber, C Hoyt, Jason Stalnaker, Nathan D. Lemke, Christopher W. Oates, Tara M. Fortier, Scott A. Diddams, Leo W. Hollberg
We describe progress toward an optical lattice clock based on an even isotope of Yb. The 1S_0 - P_0 clock resonance in 174Yb is accessed using a magnetically induced spectroscopic technique. Using ~1 mT static magnetic fields and ~10 uW of probe light

Frequency-Tunable Josephson Junction Resonator for Quantum Computing

June 23, 2007
Author(s)
Kevin Osborn, Joshua Strong, Adam J. Sirois, Raymond W. Simmonds
We have fabricated and measured a high-Q Josephson junction resonator with a tunable resonance frequency. A dc magnetic flux allows the resonance frequency to be changed by over 10%. Weak coupling to the environment allows a quality factor of 7000 in the

Optical Fiber Vibration and Acceleration Model

May 29, 2007
Author(s)
Neil Ashby, David A. Howe, Jennifer A. Taylor, Archita Hati, Craig W. Nelson
We derive expressions for the group velocities of transverse electric and transverse magnetic electromagnetic waves in a stretched single-mode fiber. Stretching can occur either as a result of temperature changes of the spool on which the fiber is wound

Testing Local Position Invariance with Four H Masers AND Four Cs Fountains

May 28, 2007
Author(s)
Neil Ashby, Thomas P. Heavner, Steven R. Jefferts, A Radnaev, Y Dudin
We report the most sensitive tests to date of the assumption of local position invariance (LPI) underlying general relativity, based on a seven year comparison of cesium and hydrogen atomic clocks (frequency standards). The latest results place an upper

Multiwall carbon nanotube absorber on a thin-film pyroelectric detector

April 1, 2007
Author(s)
John H. Lehman, Katie Hurst, Anne Dillon, A. M. Radojevic, R M. Osgood
Multiwall carbon nanotubes (MWNTs) were applied in a bulk layer to a pyroelectric film to increase the detector sensitivity nearly fourfold without a substantial penalty to the low-frequency response (4 to 100 Hz). In addition, the spectral sensitivity

Characterization of an Optical Time Domain Reflectometer Calibrator

March 1, 2007
Author(s)
Donald R. Larson, Nicholas G. Paulter Jr., Kenneth C. Blaney
We report the results of an investigation into the signal characteristics and behavior of an instrument used to calibrate Optical Time Domain Reflectometers. This instrument implements the Telecommunications Industry Association standard TIA/EIA-455-226

Solvation Structure of Ions in Water

February 14, 2007
Author(s)
Raymond D. Mountain
Molecular dynamics simulations of ions in water are reported for solutionsof varying solute concentration at ambient conditions for6 cations and 4 anions in 10 solutes. The solutes were selected to show trends inproperties as the size and charge density of

Quantum Computing with Very Noisy Devices

February 13, 2007
Author(s)
Emanuel H. Knill
This lecture was presented at the Workshop on Trapped Ion Quantum Computing hosted by NIST, February 21 - 24, 2006. It discussed the basic principles of fault-tolerant architectures for quantum computing, why we should be concerned with the resources used

Frequency Uncertainty for Optically Referenced Femtosecond Laser Frequency Combs

February 1, 2007
Author(s)
Long-Sheng Ma, Zhiyi Bi, A Bartels, Kyoungsik Kim, Lennart Robertsson, Massimo Zucco, Robert Windeler, G Wilpers, Christopher W. Oates, Leo W. Hollberg, Scott Diddams
We present measurements and analysis of the currently known residual frequency uncertainty of femtosecond laser frequency combs (FLFCs) based on Kerr-lens mode-locked Ti:sapphire lasers. Broadband frequency combs generated directly from the laser

Molecular Dynamics Calculations of the Viscosity of Xenon Gas

February 1, 2007
Author(s)
Raymond D. Mountain
The density variation of the viscosity of xenon gas is determined using molecular dynamics simulation with a semi-empirical pair potential fit to low density gas properties. The gas states ranged in density from 48.4 kg m-3 to 999 kg m-3 and varied in

Long-Term Stability of Chip-Scale Atomic Clock Physics Packages

January 20, 2007
Author(s)
Svenja A. Knappe, Vladislav Gerginov, V Shah, Alan Brannon, Hugh Robinson, Leo W. Hollberg, John E. Kitching
We present measurements regarding the long-term stability of chip-scale atomic clock (CSAC) physics packages. The tight requirements for the temperature stability of vapor cell and laser in these packages currently limit their frequency stability after 100

Long-term Stability of NIST Chip-Scale Atomic Clock Physics Packages

December 5, 2006
Author(s)
Svenja A. Knappe, V Shah, Vladislav Gerginov, Alan Brannon, Leo W. Hollberg, John E. Kitching
We present measurements regarding the long-term frequency instability of NIST CSAC physics packages. Changes of the clock frequency are caused mainly through time-dependent light shifts by the frequency-modulated VCSEL and properties of the vapor cell. We
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