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https://www.readbyqxmd.com/read/29142220/imaging-spectroscopy-of-solar-radio-burst-fine-structures
#1
E P Kontar, S Yu, A A Kuznetsov, A G Emslie, B Alcock, N L S Jeffrey, V N Melnik, N H Bian, P Subramanian
Solar radio observations provide a unique diagnostic of the outer solar atmosphere. However, the inhomogeneous turbulent corona strongly affects the propagation of the emitted radio waves, so decoupling the intrinsic properties of the emitting source from the effects of radio wave propagation has long been a major challenge in solar physics. Here we report quantitative spatial and frequency characterization of solar radio burst fine structures observed with the Low Frequency Array, an instrument with high-time resolution that also permits imaging at scales much shorter than those corresponding to radio wave propagation in the corona...
November 15, 2017: Nature Communications
https://www.readbyqxmd.com/read/29099215/are-gravitational-waves-spinning-down-psr-j1023-0038
#2
B Haskell, A Patruno
The pulsar J1023+0038 rotates with a frequency ν≈592  Hz and has been observed to transition between a radio state, during which it is visible as a millisecond radio pulsar, and a low-mass x-ray binary (LMXB) state, during which accretion powered x-ray pulsations are visible. Timing during the two phases reveals that during the LMXB phase the neutron star is spinning down at a rate of ν[over ˙]≈-3×10^{-15}  Hz/s, which is approximately 27% faster than the rate measured during the radio phase, ν[over ˙]≈-2...
October 20, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/29041222/coherent-detection-of-thz-laser-signals-in-optical-fiber-systems
#3
Thomas G Folland, Owen P Marshall, Harvey E Beere, David A Ritchie, Subhasish Chakraborty
Terahertz (THz) coherent detectors are crucial for the stabilization and measurement of the properties of quantum cascade lasers (QCLs). This paper describes the exploitation of intra-cavity sum frequency generation to up-convert the emission of a THz QCL to the near infrared for detection with fiber optic coupled components alone. Specifically, a low cost infrared photodiode is used to detect a radio frequency (RF) signal with a signal-to-noise ratio of approximately 20dB, generated by beating the up-converted THz wave and a near infrared local oscillator...
October 16, 2017: Optics Express
https://www.readbyqxmd.com/read/29041219/stability-of-period-one-p1-oscillations-generated-by-semiconductor-lasers-subject-to-optical-injection-or-optical-feedback
#4
Lyu-Chih Lin, Ssu-Hsin Liu, Fan-Yi Lin
We study the stability of period-one (P1) oscillations experimentally generated by semiconductor lasers subject to optical injection (OI) and by those subject to optical feedback (OF). With unique advantages of broad frequency tuning range and large sideband rejection ratio, P1 oscillations can be useful in applications such as photonic microwave generation, radio-over-fiber communication, and laser Doppler velocimeter. The stability of the P1 oscillations is critical for these applications, which can be affected by spontaneous emission and fluctuations in both temperature and injection current...
October 16, 2017: Optics Express
https://www.readbyqxmd.com/read/29019909/effect-of-ge-nanocrystals-on-1-54-%C3%AE-m-photoluminescence-enhancement-in-er%C3%A2-o%C3%A2-zno-and-ge-co-sputtered-films
#5
Ranran Fan, Fei Lu, Kaikai Li
Photoluminescence (PL) of Er and Ge co-doped ZnO films synthesized by radio frequency magnetron co-sputtering was investigated. X-ray diffraction (XRD) patterns showed that the annealing process at 400-800 °C led to the formation of nanocrystal (nc) Ge. Samples containing nc-Ge showed a strong visible PL with a peak at 582-593 nm, which was consistent with the calculated energy of the exciton of the ~5 nm-sized nc-Ge, according to the quantum confinement effect. The formation of nc-Ge could greatly enhance the 1...
October 11, 2017: Nanomaterials
https://www.readbyqxmd.com/read/28964191/high-voltage-performance-of-a-dc-photoemission-electron-gun-with-centrifugal-barrel-polished-electrodes
#6
C Hernandez-Garcia, D Bullard, F Hannon, Y Wang, M Poelker
The design and fabrication of electrodes for direct current (dc) high voltage photoemission electron guns can significantly influence their performance, most notably in terms of maximum achievable bias voltage. Proper electrostatic design of the triple-point junction shield electrode minimizes the risk of electrical breakdown (arcing) along the insulator-cable plug interface, while the electrode shape is designed to maintain <10 MV/m at the desired operating voltage aiming at little or no field emission once conditioned...
September 2017: Review of Scientific Instruments
https://www.readbyqxmd.com/read/28792041/high-performance-metal-insulator-graphene-diodes-for-radio-frequency-power-detection-application
#7
Mehrdad Shaygan, Zhenxing Wang, Mohamed Saeed Elsayed, Martin Otto, Giuseppe Iannaccone, Ahmed Hamed Ghareeb, Gianluca Fiori, Renato Negra, Daniel Neumaier
Vertical metal-insulator-graphene (MIG) diodes for radio frequency (RF) power detection are realized using a scalable approach based on graphene grown by chemical vapor deposition and TiO2 as barrier material. The temperature dependent current flow through the diode can be described by thermionic emission theory taking into account a bias induced barrier lowering at the graphene TiO2 interface. The diodes show excellent figures of merit for static operation, including high on-current density of up to 28 A cm(-2), high asymmetry of up to 520, strong maximum nonlinearity of up to 15, and large maximum responsivity of up to 26 V(-1), outperforming state-of-the-art metal-insulator-metal and MIG diodes...
August 24, 2017: Nanoscale
https://www.readbyqxmd.com/read/28772460/investigations-on-the-role-of-n%C3%A2-n%C3%A2-ch%C3%A2-ratio-on-the-growth-of-hydrophobic-nanostructured-hydrogenated-carbon-nitride-thin-films-by-plasma-enhanced-chemical-vapor-deposition-at-low-temperature
#8
Noor Hamizah Khanis, Richard Ritikos, Shafarina Azlinda Ahmad Kamal, Saadah Abdul Rahman
Nanostructured hydrogenated carbon nitride (CNx:H) thin films were synthesized on a crystal silicon substrate at low deposition temperature by radio-frequency plasma-enhanced chemical vapor deposition (PECVD). Methane and nitrogen were the precursor gases used in this deposition process. The effects of N₂ to the total gas flow rate ratio on the formation of CNx:H nanostructures were investigated. Field-emission scanning electron microscopy (FESEM), Auger electron spectroscopy (AES), Raman scattering, and Fourier transform of infrared spectroscopies (FTIR) were used to characterize the films...
January 24, 2017: Materials
https://www.readbyqxmd.com/read/28704929/radio-frequency-based-nh%C3%A2-selective-catalytic-reduction-catalyst-control-studies-on-temperature-dependency-and-humidity-influences
#9
Markus Dietrich, Gunter Hagen, Willibald Reitmeier, Katharina Burger, Markus Hien, Philippe Grass, David Kubinski, Jaco Visser, Ralf Moos
The upcoming more stringent automotive emission legislations and current developments have promoted new technologies for more precise and reliable catalyst control. For this purpose, radio-frequency-based (RF) catalyst state determination offers the only approach for directly measuring the NH₃ loading on selective catalytic reduction (SCR) catalysts and the state of other catalysts and filter systems. Recently, the ability of this technique to directly control the urea dosing on a current NH₃ storing zeolite catalyst has been demonstrated on an engine dynamometer for the first time and this paper continues that work...
July 12, 2017: Sensors
https://www.readbyqxmd.com/read/28687798/achieving-low-emissivity-materials-with-high-transmission-for-broadband-radio-frequency-signals
#10
Liu Liu, Huiting Chang, Tao Xu, Yanan Song, Chi Zhang, Zhi Hong Hang, Xinhua Hu
The use of low-emissivity (low-e) materials in modern buildings is an extremely efficient way to save energy. However, such materials are coated by metallic films, which can strongly block radio-frequency signals and prevent indoor-outdoor wireless communication. Here, we demonstrate that, when specially-designed metallic metasurfaces are covered on them, the low-e materials can remain low emissivity for thermal radiation and allow very high transmission for a broad band of radio-frequency signals. It is found that the application of air-connected metasurfaces with subwavelength periods is critical to the observed high transmission...
July 7, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28661675/hot-carrier-mediated-photon-upconversion-in-metal-decorated-quantum-wells
#11
Gururaj V Naik, Alex J Welch, Justin A Briggs, Michelle L Solomon, Jennifer A Dionne
Manipulating the frequency of electromagnetic waves forms the core of many modern technologies, ranging from imaging and spectroscopy to radio and optical communication. The process of converting photons from higher to lower energy is easily accomplished and technologically widespread. However, upconversion, which is the process of converting lower-energy photons into higher-energy photons, is still a growing field of study with nascent applications and burgeoning interest. Here, we experimentally demonstrate a new photon upconversion technique mediated by hot carriers in plasmonic nanostructures...
July 3, 2017: Nano Letters
https://www.readbyqxmd.com/read/28617604/directional-emission-from-dielectric-leaky-wave-nanoantennas
#12
Manuel Peter, Andre Hildebrandt, Christian Schlickriede, Kimia Gharib, Thomas Zentgraf, Jens Förstner, Stefan Linden
An important source of innovation in nanophotonics is the idea to scale down known radio wave technologies to the optical regime. One thoroughly investigated example of this approach are metallic nanoantennas which employ plasmonic resonances to couple localized emitters to selected far-field modes. While metals can be treated as perfect conductors in the microwave regime, their response becomes Drude-like at optical frequencies. Thus, plasmonic nanoantennas are inherently lossy. Moreover, their resonant nature requires precise control of the antenna geometry...
June 21, 2017: Nano Letters
https://www.readbyqxmd.com/read/28572587/electrically-driven-deep-ultraviolet-mgzno-lasers-at-room-temperature
#13
Mohammad Suja, Sunayna Binte Bashar, Bishwajit Debnath, Longxing Su, Wenhao Shi, Roger Lake, Jianlin Liu
Semiconductor lasers in the deep ultraviolet (UV) range have numerous potential applications ranging from water purification and medical diagnosis to high-density data storage and flexible displays. Nevertheless, very little success was achieved in the realization of electrically driven deep UV semiconductor lasers to date. In this paper, we report the fabrication and characterization of deep UV MgZnO semiconductor lasers. These lasers are operated with continuous current mode at room temperature and the shortest wavelength reaches 284 nm...
June 1, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28555640/attosecond-interferometry-with-self-amplified-spontaneous-emission-of-a-free-electron-laser
#14
Sergey Usenko, Andreas Przystawik, Markus Alexander Jakob, Leslie Lamberto Lazzarino, Günter Brenner, Sven Toleikis, Christian Haunhorst, Detlef Kip, Tim Laarmann
Light-phase-sensitive techniques, such as coherent multidimensional spectroscopy, are well-established in a broad spectral range, already spanning from radio-frequencies in nuclear magnetic resonance spectroscopy to visible and ultraviolet wavelengths in nonlinear optics with table-top lasers. In these cases, the ability to tailor the phases of electromagnetic waves with high precision is essential. Here we achieve phase control of extreme-ultraviolet pulses from a free-electron laser (FEL) on the attosecond timescale in a Michelson-type all-reflective interferometric autocorrelator...
May 30, 2017: Nature Communications
https://www.readbyqxmd.com/read/28530605/screening-of-passiflora-l-mineral-content-using-principal-component-analysis-and-kohonen-self-organizing-maps
#15
Cleber Galvão Novaes, Ivana Lago da Silva Romão, Berlane Gomes Santos, Jéssica Palhares Ribeiro, Marcos Almeida Bezerra, Erik Galvão Paranhos da Silva
A method using digestion with diluted nitric acid and inductively coupled plasma optical emission spectrometry was applied to determine metal ions in the peel, pulp, and seed of Passiflora edulis f. flavicarpa and Passiflora cincinnata cultivated in the Bahia state, Brazil. Plasma parameters (radio frequency power and argon flow rates) were optimized. The quantification limits (µg g(-1)) were: Ca (43.0); Co (1.3); Cu (10.0); Fe (10.0); K (20.0); Mg (26.6); Mn (0.33); Na (56.6) and Zn (10.0). The accuracy of the method was evaluated by the analysis of certified reference materials (NIST 1567a Wheat Flour and NIST 1577b Bovine Liver)...
October 15, 2017: Food Chemistry
https://www.readbyqxmd.com/read/28513144/rapid-elemental-analysis-of-aerosols-using-atmospheric-glow-discharge-optical-emission-spectroscopy
#16
Lina Zheng, Pramod Kulkarni
A new, low-cost approach based on the application of atmospheric radio frequency glow discharge (rf-GD) optical emission spectroscopy (OES) has been developed for near real-time measurement of multielemental concentration in airborne particulate phase. This method involves deposition of aerosol particles on the tip of a cathode in a coaxial microelectrode system, followed by ablation, atomization, and excitation of the particulate matter using the rf-GD. The resulting atomic emissions are recorded using a spectrometer for elemental identification and quantification...
June 20, 2017: Analytical Chemistry
https://www.readbyqxmd.com/read/28451625/optical-resonance-imaging-an-optical-analog-to-mri-with-sub-diffraction-limited-capabilities
#17
Marco A Allodi, Peter D Dahlberg, Richard J Mazuski, Hunter C Davis, John P Otto, Gregory S Engel
We propose here optical resonance imaging (ORI), a direct optical analog to magnetic resonance imaging (MRI). The proposed pulse sequence for ORI maps space to time and recovers an image from a heterodyne-detected third-order nonlinear photon echo measurement. As opposed to traditional photon echo measurements, the third pulse in the ORI pulse sequence has significant pulse-front tilt that acts as a temporal gradient. This gradient couples space to time by stimulating the emission of a photon echo signal from different lateral spatial locations of a sample at different times, providing a widefield ultrafast microscopy...
December 21, 2016: ACS Photonics
https://www.readbyqxmd.com/read/28335216/investigation-of-the-structural-electrical-and-optical-properties-of-the-nano-scale-gzo-thin-films-on-glass-and-flexible-polyimide-substrates
#18
Fang-Hsing Wang, Kun-Neng Chen, Chao-Ming Hsu, Min-Chu Liu, Cheng-Fu Yang
In this study, Ga₂O₃-doped ZnO (GZO) thin films were deposited on glass and flexible polyimide (PI) substrates at room temperature (300 K), 373 K, and 473 K by the radio frequency (RF) magnetron sputtering method. After finding the deposition rate, all the GZO thin films with a nano-scale thickness of about 150 ± 10 nm were controlled by the deposition time. X-ray diffraction patterns indicated that the GZO thin films were not amorphous and all exhibited the (002) peak, and field emission scanning electron microscopy showed that only nano-scale particles were observed...
May 10, 2016: Nanomaterials
https://www.readbyqxmd.com/read/28272492/homogeneous-spectral-spanning-of-terahertz-semiconductor-lasers-with-radio-frequency-modulation
#19
W J Wan, H Li, T Zhou, J C Cao
Homogeneous broadband and electrically pumped semiconductor radiation sources emitting in the terahertz regime are highly desirable for various applications, including spectroscopy, chemical sensing, and gas identification. In the frequency range between 1 and 5 THz, unipolar quantum cascade lasers employing electron inter-subband transitions in multiple-quantum-well structures are the most powerful semiconductor light sources. However, these devices are normally characterized by either a narrow emission spectrum due to the narrow gain bandwidth of the inter-subband optical transitions or an inhomogeneous broad terahertz spectrum from lasers with heterogeneous stacks of active regions...
March 8, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28257069/a-technical-approach-to-the-evaluation-of-radiofrequency-radiation-emissions-from-mobile-telephony-base-stations
#20
Raimondas Buckus, Birute Strukčinskienė, Juozas Raistenskis, Rimantas Stukas, Aurelija Šidlauskienė, Rimantė Čerkauskienė, Dorina Nicolina Isopescu, Jan Stabryla, Igor Cretescu
During the last two decades, the number of macrocell mobile telephony base station antennas emitting radiofrequency (RF) electromagnetic radiation (EMR) in residential areas has increased significantly, and therefore much more attention is being paid to RF EMR and its effects on human health. Scientific field measurements of public exposure to RF EMR (specifically to radio frequency radiation) from macrocell mobile telephony base station antennas and RF electromagnetic field (EMF) intensity parameters in the environment are discussed in this article...
March 1, 2017: International Journal of Environmental Research and Public Health
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