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Search Publications by: Xifeng Lu (Assoc)

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Displaying 1 - 25 of 31

On Digital Signal Processing of Time Series for Spectrum Estimation

September 11, 2024
Author(s)
Dazhen Gu, Jake Rezac, Xifeng Lu, Dan Kuester
We present a study of power spectral density (PSD) estimation from data sampled in the time domain. This work was motivated by our recent development of digital radiometry, where radiation spectra were obtained by processing the digitally sampled signal

Radio Spectrum Occupancy Measurements Amid COVID-19 Telework and Telehealth

October 14, 2022
Author(s)
Dan Kuester, Xifeng Lu, Dazhen Gu, Azizollah Kord, Jake Rezac, Katie Carson, Marla L. Dowell, Elizabeth Eyeson, Ari Feldman, Keith Forsyth, Vu Le, John Marts, Mike McNulty, Kyle Neubarth, Andre Rosete, Matthew Ryan, Maija Teraslina
During the COVID-19 pandemic, NIST began a targeted campaign of measurements of averaged power and occupancy rate in the radio spectrum. The purpose was to sample real environments to offer timely insights into data infrastructure where it might be

Digital Radiometer for Traceable Spectrum Sensing

September 14, 2020
Author(s)
Xifeng Lu, Dazhen Gu, Daniel G. Kuester
This paper describes a metrology instrument designed for detecting noise and interference in digital communications. A quadrature detector downconverts in-phase (I) and quadrature (Q) channels, which are each digitized at high speed. This architecture

Sub-nanosecond Tuning of Microwave Resonators Fabricated on Ruddlesden-Popper Dielectric Thin Films

July 9, 2018
Author(s)
Aaron M. Hagerstrom, Xifeng Lu, Natalie Dawley, H. Nair, Jordi Mateu, Robert D. Horansky, Charles A. Little, James C. Booth, Christian J. Long
Voltage-tunable dielectric materials are widely used for microwave-frequency signal processing. Among tunable dielectric thin films, (SrTiO3)nSrO Ruddlesden-Popper (RP) superlattices have exceptionally low loss at high frequencies. This paper reports the

Efficient Rectangular Waveguide to Stripline Transition in D Band

August 7, 2017
Author(s)
Dazhen Gu, Xifeng Lu, Ronald A. Ginley
We present a waveguide-to-stripline transition for a full {\it D}-band operation from 110 GHz to 170 GHz. An E-plane probe in parallel with waveguide main axis is configured to effectively couple the signal in the primary $\text{TE}_{10}$ mode from the

Strain and Magnetic-Field Characterization of a Bronze-Route Nb 3 Sn ITER Wire: Benchmarking of Strain Measurement Facilities at NIST and University of Twente

June 1, 2012
Author(s)
Najib Cheggour, Arend Nijhuis, H J. Krooshoop, Xifeng Lu, Jolene D. Splett, Theodore C. Stauffer, Loren F. Goodrich, Matthew C. Jewell, Arnaud Devred, Y Nabara
A benchmarking experiment was conducted to compare strain measurement facilities at the National Institute of Standards and Technology (NIST) and the University of Twente. The critical current of a bronze-route Nb 3Sn wire, which was fabricated for the

Correlation Between the Pressure Dependence of the Critical Temperature and the Reversible Strain Effect on the Critical Current and Pinning Force in Bi 2 Sr 2 CaCu 2 O 8+x Wires

December 16, 2011
Author(s)
Xifeng Lu, Loren F. Goodrich, Daniel C. van der Laan, Jolene D. Splett, Najib Cheggour, T G. Holesinger, F J. Baca
Bi 2Sr 2CaCu 2O 8+x round wires are among the most promising high-temperature superconductor candidates for making high-field magnets that operate at fields above 20 Tesla. Owing to the brittle nature of high-temperature superconductors, their electro

Reversible effect of strain on transport critical current in Bi 2 Sr 2 CaCu 2 O 8+x superconducting wires: A modified descriptive strain model

December 5, 2011
Author(s)
Najib Cheggour, Xifeng Lu, T G. Holesinger, Theodore C. Stauffer, J Jiang, Loren F. Goodrich
A reversible strain effect on transport critical current I c was found in Bi 2Sr 2CaCu 2O 8+x (Bi-2212) high-temperature superconducting round wires. I c showed unambiguous reversibility at 4 K and 16 T up to an irreversible strain limit of about 0.3 % in

Method for determining the irreversible strain limit of Nb 3 Sn wires

June 6, 2011
Author(s)
Loren F. Goodrich, Najib Cheggour, Xifeng Lu, Jolene D. Splett, Theodore C. Stauffer, Bernard J. Filla
We have defined a rigorous and reliable method for determining the irreversible strain limit of Nb 3Sn wires. The critical current (I c) is measured as a function of applied longitudinal strain (ε), I c(ε), at one magnetic field and a temperature of 4.0 K

Strain and Magnetization Properties of High Subelement Count Tube-type Nb3Sn Strands

June 6, 2011
Author(s)
Najib Cheggour, X Peng, E Gregory, M Tomsic, M D. Sumption, A. K. Ghosh, Xifeng Lu, Theodore C. Stauffer, Loren F. Goodrich, Jolene D. Splett
Abstract—A tubular technique for economical production of Nb3Sn material with large numbers of subelements is being explored by Supergenics I LLC and Hyper Tech Research Inc. The number of subelements was increased to 919 (744 subelements plus 175 Cu