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Displaying 1226 - 1250 of 2503

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

Spectral dependence of carrier lifetimes in silicon for photovoltaic applications

December 21, 2016
Author(s)
John F. Roller, Yu-Tai Li, Mario Dagenais, Behrang H. Hamadani
Charge carrier lifetimes in photovoltaic-grade silicon wafers were measured by a spectral-dependent, quasi-steady-state photoconductance technique. Narrow bandwidth LEDs were used to excite excess charge carriers within the material, and the effective

Entropy Theory of Polymer Glass-Formation in Variable Spatial Dimension

December 20, 2016
Author(s)
Jack F. Douglas, Wensheng Xu, Karl Freed
The importance of packing frustration is broadly appreciated to be an important aspect of glass formation. Recently, great interest has focused on probing the dependence on spatial dimension d as a theoretical tool for exploring essential aspects of glass

A Versatile Technique to Enable Sub-Milli-Kelvin Instrument Stability for Precise Radial Velocity Measurements: Tests with the Habitable-Zone Planet Finder

December 16, 2016
Author(s)
Ryan C. Terrien, Guomundur K. Stefansson, Fred Hearty, Paul Robertson, Suvrath Mahadevan, Tyler Anderson, Chad Bender, Matthew Nelson, Andrew Monson, Basil Blank, Samuel Halverson, Chuck Henderson, Lawrence Ramsey, Arpita Roy, Christian Schwab
Insufficient instrument thermo-mechanical stability is one of the fundamental roadblocks for achieving 10 cm s −1 Doppler radial velocity (RV) precision, the precision needed to detect Earth-twins orbiting Solar-type stars. Exquisite temperature and

Bound Layers Cloak Nanoparticles in Strongly Interacting Polymer Nanocomposites

December 16, 2016
Author(s)
Jack F. Douglas, Francis W. Starr, Sanat K. Kumar
Polymer-nanoparticle (NP) interfacial interactions are expected to strongly influence the properties of nanocomposites, but surprisingly, experiments often report small or no changes in the glass transition temperature, Tg. To understand this paradoxical

60 Year Anniversary of Applied Radiation and Isotopes

December 14, 2016
Author(s)
Bert M. Coursey
Those readers who have a library with the first bound copies of ARI may find it enjoyable to compare Volume 1, No.1 from 1956 with an issue from Volume 118 in 2016. The range of applications has shifted away from agricultural and industrial uses of

An ultra-low noise, high-voltage piezo driver

December 8, 2016
Author(s)
Neal C. Pisenti, Alessandro Restelli, Ben J. Reschovsky, Daniel Barker, Gretchen K. Campbell
We present an ultra-low noise, high-voltage driver suited for use with piezoelectric actuators and other low- current applications. The architecture uses a flyback switching regulator to generate up to 250V in our current design, with an output of 1 kV or

Doppler Sensitivity and Its Effect on Transatlantic TWSTFT Links

December 6, 2016
Author(s)
Shengkang Zhang, Tom Parker, Victor S. Zhang
Two Way Satellite Time and Frequency Transfer (TWSTFT or TW) is a commonly used technique to compare time and frequency precisely among the time and frequency laboratories. The precision of TWSTFT on time comparison is about 0.5 ns or even better, which

Enriching and purifying silicon epilayers for quantum information

December 6, 2016
Author(s)
Joshua M. Pomeroy, Kevin J. Dwyer, Ke Tang, Hyun S. Kim, Aruna N. Ramanayaka, David S. Simons
High quality, enriched silicon contains an exceptionally low density of defects and unpaired electron and nuclear spins that allow candidate qubits (single donors or quantum dots) to exhibit very long dephasing times compared to silicon with a natural

Communication-Comparison of Nanoscale Focused Ion Beam and Electrochemical Lithiation in beta-Sn Microspheres

December 5, 2016
Author(s)
Saya Takeuchi, William R. McGehee, Jennifer L. Schaefer, Truman M. Wilson, Kevin A. Twedt, Christopher L. Soles, Vladimir P. Oleshko, Eddie H. Chang, Jabez J. McClelland
The development of Li focused ion beams (Li-FIB) enables controlled Li ion insertion into materials with nanoscale resolution. We take the first step toward establishing the relevance of the Li-FIB for studies of ion dynamics in electrochemically active

Coordinated Universal Time and the Leap Second

December 1, 2016
Author(s)
Judah Levine
I will discuss the considerations that were important in the design of the current version of Coordinated Universal Time. The design includes the addition of additional “leap” seconds to keep Coordinated Universal time within 0.9 s of the UT1 time scale

The sixth spectrum of platinum (Pt VI)

November 25, 2016
Author(s)
Vladimir I. Azarov, R R. Gayasov
The spectrum of platinum was observed in the (300 to 2100) A wavelength region. The (5d5 + 5d46s) - 5d46p transition array of five times ionized platinum, Pt VI, has been investigated and 1390 spectral lines have been classified in the region of (399 to
Displaying 1226 - 1250 of 2503
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