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Frequency locking of single-mode 3.5-THz quantum cascade lasers using a gas cell

Ren, Y. (author), Hovenier, J.N. (author), Cui, M. (author), Hayton, D.J. (author), Gao, J.R. (author), Klapwijk, T.M. (author), Shi, S.C. (author), Kao, T.Y. (author), Hu, Q. (author), Reno, J.L. (author)

We report frequency locking of two 3.5-THz third-order distributed feedback (DFB) quantum cascade lasers (QCLs) by using methanol molecular absorption lines, a proportional-integral-derivative controller, and a NbN bolometer. We show that the free-running linewidths of the QCLs are dependent on the electrical and temperature tuning coefficients....

journal article 2012

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Terahertz heterodyne spectrometer using a quantum cascade laser

Ren, Y. (author), Hovenier, J.N. (author), Higgins, R. (author), Gao, J.R. (author), Klapwijk, T.M. (author), Shi, S.C. (author), Bell, A. (author), Klein, B. (author), Williams, B.S. (author), Kumar, S. (author), Hu, Q. (author), Reno, J.L. (author)

A terahertz (THz) heterodyne spectrometer is demonstrated based on a quantum cascade laser (QCL) as a local oscillator (LO) and an NbN hot electron bolometer as a mixer, and it is used to measure high-resolution molecular spectral lines of methanol (CH3OH) between 2.913–2.918 THz. The spectral lines are taken from a gas cell containing methanol...

journal article 2010

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High-resolution heterodyne spectroscopy using a tunable quantum cascade laser around 3.5 THz

Ren, Y. (author), Hovenier, J.N. (author), Higgins, R. (author), Gao, J.R. (author), Klapwijk, T.M. (author), Shi, S.C. (author), Klein, B. (author), Kao, T.Y. (author), Hu, Q. (author), Reno, J.L. (author)

A frequency tunable terahertz heterodyne spectrometer, based on a third-order distributed feedback quantum cascade laser as a local oscillator, has been demonstrated by measuring molecular spectral lines of methanol (CH3OH) gas at 3.5 THz. By varying the bias voltage of the laser, we achieved a tuning range of ? 1?GHz of the lasing frequency,...

journal article 2011

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An integrated approach for efficient biomethane production from solid bio-wastes in a compact system

Wang, H. (author), Tao, Y. (author), Temudo, M. (author), Schooneveld, M. (author), Bijl, H. (author), Ren, N. (author), Wolf, M. (author), Heine, C. (author), Foerster, A. (author), Pelenc, V. (author), Kloek, J. (author), Van Lier, J.B. (author), De Kreuk, M.K. (author)

Background Solid bio-wastes (or organic residues) are worldwide produced in high amount and increasingly considered bioenergy containers rather than waste products. A complete bioprocess from recalcitrant solid wastes to methane (SW2M) via anaerobic digestion (AD) is believed to be a sustainable way to utilize solid bio-wastes. However, the...

journal article 2015

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Bandwidth Analysis of Functional Interconnects Used as Test Access Mechanism

Van den Berg, A. (author), Ren, P. (author), Marinissen, E.J. (author), Gaydadjiev, G. (author), Goossens, K. (author)

Test data travels through a System on Chip (SOC) from the chip pins to the Core-Under-Test (CUT) and vice versa via a Test Access Mechanism (TAM). Conventionally, a TAM is implemented using dedicated communication infrastructure. However, also existing functional interconnect, such as a bus or Network on Chip (NOC), can be reused as TAM; this...

journal article 2010

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First-principles study of the effect of functional groups on polyaniline backbone

Chen, X.P. (author), Jiang, J.K. (author), Liang, Q.H. (author), Yang, N. (author), Ye, H.Y. (author), Cai, M. (author), Shen, L. (author), Yang, D.G. (author), Ren, T.L. (author)

We present a first-principles density functional theory study focused on how the chemical and electronic properties of polyaniline are adjusted by introducing suitable substituents on a polymer backbone. Analyses of the obtained energy barriers, reaction energies and minimum energy paths indicate that the chemical reactivity of the polyaniline...

journal article 2015

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Stabilized hot electron bolometer heterodyne receiver at 2.5?THz

Hayton, D.J. (author), Gao, J.R. (author), Kooi, J.W. (author), Ren, Y. (author), Zhang, W. (author), De Lange, G. (author)

We report on a method to stabilize a hot electron bolometer (HEB) mixer at 2.5 THz. The technique utilizes feedback control of the local oscillator (LO) laser power by means of a swing-arm actuator placed in the optical beam path. We demonstrate that this technique yields a factor of 50 improvement in the spectroscopic Allan variance time which...

journal article 2012

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Kilometer-range, high resolution depth imaging via 1560 nm wavelength single-photon detection

McCarthy, A. (author), Krichel, N.J. (author), Gemmell, N.R. (author), Ren, X. (author), Tanner, M.G. (author), Dorenbos, S.N. (author), Zwiller, V. (author), Hadfield, R.H. (author), Buller, G.S. (author)

This paper highlights a significant advance in time-of-flight depth imaging: by using a scanning transceiver which incorporated a free-running, low noise superconducting nanowire single-photon detector, we were able to obtain centimeter resolution depth images of low-signature objects in daylight at stand-off distances of the order of one...

journal article 2013

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Frequency and amplitude stabilized terahertz quantum cascade laser as local oscillator

Ren, Y. (author), Hayton, D.J. (author), Hovenier, J.N. (author), Cui, M. (author), Gao, J.R. (author), Klapwijk, T.M. (author), Shi, S.C. (author), Kao, T.Y. (author), Hu, Q. (author), Reno, J.L. (author)

We demonstrate an experimental scheme to simultaneously stabilize the frequency and amplitude of a 3.5 THz third-order distributed feedback quantum cascade laser as a local oscillator. The frequency stabilization has been realized using a methanol absorption line, a power detector, and a proportional-integral-derivative (PID) loop. The amplitude...

journal article 2012

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Magmatism on rift flanks: Insights from ambient noise phase velocity in Afar region

Korostelev, F. (author), Weemstra, C. (author), Leroy, S. (author), Boschi, L. (author), Keir, D. (author), Ren, Y. (author), Molinari, I. (author), Ahmed, A. (author), Stuart, G.W. (author), Rolandone, F. (author), Khanbari, K. (author), Hammond, J.O.S. (author), Kendall, M.K. (author), Doubre, C. (author), Al Ganad, I. (author), Goitom, B. (author), Ayele, A. (author)

During the breakup of continents in magmatic settings, the extension of the rift valley is commonly assumed to initially occur by border faulting and progressively migrate in space and time toward the spreading axis. Magmatic processes near the rift flanks are commonly ignored. We present phase velocity maps of the crust and uppermost mantle of...

journal article 2015

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Hot electron bolometer heterodyne receiver with a 4.7-THz quantum cascade laser as a local oscillator

Kloosterman, J.L. (author), Hayton, D.J. (author), Ren, Y. (author), Kao, T.Y. (author), Hovenier, J.N. (author), Gao, J.R. (author), Klapwijk, T.M. (author), Hu, Q. (author), Walker, C.K. (author), Reno, J.L. (author)

We report on a heterodyne receiver designed to observe the astrophysically important neutral atomic oxygen [OI] line at 4.7448?THz. The local oscillator is a third-order distributed feedback quantum cascade laser operating in continuous wave mode at 4.741?THz. A quasi-optical, superconducting NbN hot electron bolometer is used as the mixer. We...

journal article 2013

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Spin accumulation and decay in magnetic Schottky barriers

Bauer, G.E.W. (author), Tserkovnyak, Y. (author), Brataas, A. (author), Ren, J. (author), Xia, K. (author), Zwierzycki, M. (author), Kelly, P.J. (author)

journal article 2005

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Measurement of spin-dependent conductivities in a two-dimensional electron gas

Ebrahimnejad, H. (author), Ren, Y. (author), Frolov, S.M. (author), Adagideli, I. (author), Folk, J.A. (author), Wegscheider, W. (author)

Spin accumulation is generated by injecting an unpolarized charge current into a channel of GaAs two-dimensional electron gas subject to an in-plane magnetic field, then measured in a nonlocal geometry. Unlike previous measurements that have used spin-polarized nanostructures, here the spin accumulation arises simply from the difference in bulk...

journal article 2010

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Beam and phase distributions of a terahertz quantum cascade wire laser

Cui, M. (author), Hovenier, J.N. (author), Ren, Y. (author), Vercruyssen, N. (author), Gao, J.R. (author), Kao, T.Y. (author), Hu, Q. (author), Reno, J.L. (author)

We report on both measurements and simulations of the beam profile and wavefront of a single-mode, 3.5?THz quantum cascade wire laser, incorporating a lateral corrugated metal-metal waveguide, 3rd-order distributed feedback grating. The intrinsic wavefront was measured by using a Hartmann wavefront sensor (HWS) without any optical components...

journal article 2013

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Monte Carlo renormalization: The triangular Ising model as a test case

Guo, W. (author), Blöte, H.W.J. (author), Ren, Z. (author)

journal article 2005

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Terahertz wavefronts measured using the Hartmann sensor principle

Cui, M. (author), Hovenier, J.N. (author), Ren, Y. (author), Polo, A. (author), Gao, J.R. (author)

We demonstrate for the first time that the Hartmann wavefront sensor (HWS) principle can be applied for characterizing the wavefronts of terahertz (THz) electromagnetic radiation. The THz Hartmann wavefront sensor consists of a metallic plate with an array of holes and a twodimensional scanable pyro-electric detector. The THz radiation with...

journal article 2012

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A Comparative Study on the Degradation of Alkali-Activated Slag/Fly Ash and Cement-Based Mortars in Phosphoric Acid

Ren, Jie (author), Zhang, Lihai (author), Zhu, Yingcan (author), Li, Z. (author), San Nicolas, Rackel (author)

This study compares the degradation behavior of the alkali-activated slag/fly ash (AASF) and ordinary Portland cement (OPC) mortars exposed to phosphoric acid with different pH values. The experimental results show that AASF mortars exhibit better resistance than OPC mortars against surface damage, although both systems get white deposits on the...

journal article 2022

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Boundary-layer stability of supercritical fluids in the vicinity of the Widom line

Ren, J. (author), Marxen, Olaf (author), Pecnik, Rene (author)

We investigate the hydrodynamic stability of compressible boundary layers over adiabatic walls with fluids at supercritical pressure in the proximity of the Widom line (also known as the pseudo-critical line). Depending on the free-stream temperature and the Eckert number that determines the viscous heating, the boundary-layer temperature...

journal article 2019

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A CAST-Based Analysis of the Metro Accident That Was Triggered by the Zhengzhou Heavy Rainstorm Disaster

Zhao, Jiale (author), Yang, Fuqiang (author), Guo, Yong (author), Ren, X. (author)

Emergency management research is used to deal with the increasing number of extreme weather threats in urban areas. This paper uses causal analysis based on systems theory (CAST) to review the subway water ingress accident and the government's emergency management actions in Zhengzhou, Henan Province, during the heavy rainstorm disaster on 20...

journal article 2022

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A Weekly Diary Study on Playful Study Design, Study Engagement, and Goal Attainment: The Role of Proactive Personality

Wang, Huatian (author), Ren, Yue (author), Liu, W. (author)

Students’ learning processes are heavily impeded by the COVID-19 pandemic. Students are experiencing more online learning environment and less face-to-face idea exchange, which may make them feel exhausted and demotivated. Using self-determination and proactivity theories, we propose and examine whether playful study design (PSD)—a proactive...

journal article 2022