Read by QxMD icon Read

radio frequency emission

Andrew Mezentsev, Nikolai Lehtinen, Nikolai Østgaard, F J Pérez-Invernón, Steven A Cummer
We compared the modeled energy spectral density of very low frequency (VLF) radio emissions from terrestrial gamma ray flashes (TGFs) with the energy spectral density of VLF radio sferics recorded by Duke VLF receiver simultaneously with those TGFs. In total, six events with world wide lightning location network (WWLLN) defined locations were analyzed to exhibit a good fit between the modeled and observed energy spectral densities. In VLF range the energy spectral density of the TGF source current moment is found to be dominated by the contribution of secondary low-energy electrons and independent of the relativistic electrons which play their role in low-frequency (LF) range...
January 16, 2018: Journal of Geophysical Research. Atmospheres: JGR
Nissim Kanekar, Tapasi Ghosh, Jayaram N Chengalur
We have used the Arecibo Telescope to carry out one of the deepest-ever integrations in radio astronomy, targeting the redshifted conjugate satellite OH 18 cm lines at z≈0.247 towards PKS 1413+135. The satellite OH 1720 and 1612 MHz lines are, respectively, in emission and absorption, with exactly the same line shapes due to population inversion in the OH ground state levels. Since the 1720 and 1612 MHz line rest frequencies have different dependences on the fine structure constant α and the proton-electron mass ratio μ, a comparison between their measured redshifts allows one to probe changes in α and μ with cosmological time...
February 9, 2018: Physical Review Letters
Montaña Rufo, Alicia Antolín, Jesús M Paniagua, Antonio Jiménez
A comparative study was made of three methods of interpolation - inverse distance weighting (IDW), spline and ordinary kriging - after optimization of their characteristic parameters. These interpolation methods were used to represent the electric field levels for three emission frequencies (774kHz, 900kHz, and 1107kHz) and for the electrical stimulation quotient, QE, characteristic of complex electromagnetic environments. Measurements were made with a spectrum analyser in a village in the vicinity of medium-wave radio broadcasting antennas...
January 18, 2018: Environmental Research
Alejandro Luque
We present a full electromagnetic model of streamer propagation where the Maxwell equations are solved self-consistently together with electron transport and reactions including photoionization. We apply this model to the collision of counter-propagating streamers in gaps tens of centimeters wide and with large potential differences of hundreds of kilovolts. Our results show that streamer collisions emit electromagnetic pulses that, at atmospheric pressure, dominate the radio frequency spectrum of an extended corona in the range from about 100 MHz to a few gigahertz...
October 16, 2017: Journal of Geophysical Research. Atmospheres: JGR
Kyu Been Kwon, Teyoun Kang, Hyung Seon Song, Young-Kuk Kim, Bernhard Ersfeld, Dino A Jaroszynski, Min Sup Hur
Emission of radiation from electrons undergoing plasma oscillations (POs) at the plasma frequency has attracted interest because of the existence of intriguing and non-trivial coupling mechanism between the electrostatic PO and the emitted electromagnetic wave. While broadband emission from plasma waves in inhomogeneous plasma is well known, the underlying physics of narrowband emission at the plasma frequency observed in experiments and in solar radio-bursts is obscure. Here we show that a spatially-localized plasma dipole oscillation (PDO) can be generated when electrons are trapped in a moving train of potential wells produced by the ponderomotive force of two slightly detuned laser pulses that collide in plasma and give rise to a burst of quasi-monochromatic radiation...
January 9, 2018: Scientific Reports
Kai-Huang Chen, Tsung-Ming Tsai, Chien-Min Cheng, Shou-Jen Huang, Kuan-Chang Chang, Shu-Ping Liang, Tai-Fa Young
In this study, the hopping conduction distance and bipolar switching properties of the Gd:SiOx thin film by (radio frequency, rf) rf sputtering technology for applications in RRAM devices were calculated and investigated. To discuss and verify the electrical switching mechanism in various different constant compliance currents, the typical current versus applied voltage (I-V) characteristics of gadolinium oxide RRAM devices was transferred and fitted. Finally, the transmission electrons' switching behavior between the TiN bottom electrode and Pt top electrode in the initial metallic filament forming process of the gadolinium oxide thin film RRAM devices for low resistance state (LRS)/high resistance state (HRS) was described and explained in a simulated physical diagram model...
December 28, 2017: Materials
Qijun Zhang, Lin Wu, Xiaozhen Fang, Mingyue Liu, Jing Zhang, Min Shao, Sihua Lu, Hongjun Mao
In order to obtain VOCs emission characteristics and emission factors from vehicle, a tunnel experiment was conducted in the Fu Gui Mountain Tunnel in Nanjing, China. The tunnel is located in the middle of city, with total length of 480m and speed limit of 50km/h. The studied vehicle fleet was composed of 87% light duty vehicles and 13% heavy duty vehicles (liquefied natural gas bus, LNGB). The emerging radio frequency identification (RFID) technology was used to divide fine vehicles type including China I, China II, China III, China IV, China V and LNGB...
December 21, 2017: Science of the Total Environment
Marissa L Weichman, Bess Vlaisavljevich, Jessalyn A DeVine, Nicholas S Shuman, Shaun G Ard, Toru Shiozaki, Daniel M Neumark, Albert A Viggiano
The chemi-ionization reaction of atomic samarium, Sm + O → SmO+ + e-, has been investigated by the Air Force Research Laboratory as a means to modify local electron density in the ionosphere for reduction of scintillation of high-frequency radio waves. Neutral SmO is a likely unwanted byproduct. The spectroscopy of SmO is of great interest to aid in interpretation of optical emission spectra recorded following atmospheric releases of Sm as part of the Metal Oxide Space Cloud (MOSC) observations. Here, we report a joint experimental and theoretical study of SmO using slow photoelectron velocity-map imaging spectroscopy of cryogenically cooled SmO- anions (cryo-SEVI) and high-level spin-orbit complete active space calculations with corrections from second order perturbation theory (CASPT2)...
December 21, 2017: Journal of Chemical Physics
Weiwei Pan, Lei Zhang, Jiaqi Zhou, Xuezong Yang, Yan Feng
The mode locking of a Raman fiber laser with an amplified spontaneous emission (ASE) pump source is investigated for performance improvement. Raman dissipative solitons with a compressed pulse duration of 1.05 ps at a repetition rate of 2.47 MHz are generated by utilizing nonlinear polarization rotation and all-fiber Lyot filter. A signal-to-noise ratio as high as 85 dB is measured in a radio-frequency spectrum, which suggests excellent temporal stability. Multiple-pulse operation with unique random static distribution is observed for the first time, to the best of our knowledge, at higher pump power in mode-locked Raman fiber lasers...
December 15, 2017: Optics Letters
Thorsten Feichtner, Silke Christiansen, Bert Hecht
The emission rate of a point dipole can be strongly increased in the presence of a well-designed optical antenna. Yet, optical antenna design is largely based on radio-frequency rules, ignoring, e.g., Ohmic losses and non-negligible field penetration in metals at optical frequencies. Here, we combine reciprocity and Poynting's theorem to derive a set of optical-frequency antenna design rules for benchmarking and optimizing the performance of optical antennas driven by single quantum emitters. Based on these findings a novel plasmonic cavity antenna design is presented exhibiting a considerably improved performance compared to a reference two-wire antenna...
November 24, 2017: Physical Review Letters
C M Raiteri, M Villata, J A Acosta-Pulido, I Agudo, A A Arkharov, R Bachev, G V Baida, E Benítez, G A Borman, W Boschin, V Bozhilov, M S Butuzova, P Calcidese, M I Carnerero, D Carosati, C Casadio, N Castro-Segura, W-P Chen, G Damljanovic, F D'Ammando, A Di Paola, J Echevarría, N V Efimova, Sh A Ehgamberdiev, C Espinosa, A Fuentes, A Giunta, J L Gómez, T S Grishina, M A Gurwell, D Hiriart, H Jermak, B Jordan, S G Jorstad, M Joshi, E N Kopatskaya, K Kuratov, O M Kurtanidze, S O Kurtanidze, A Lähteenmäki, V M Larionov, E G Larionova, L V Larionova, C Lázaro, C S Lin, M P Malmrose, A P Marscher, K Matsumoto, B McBreen, R Michel, B Mihov, M Minev, D O Mirzaqulov, A A Mokrushina, S N Molina, J W Moody, D A Morozova, S V Nazarov, M G Nikolashvili, J M Ohlert, D N Okhmat, E Ovcharov, F Pinna, T A Polakis, C Protasio, T Pursimo, F J Redondo-Lorenzo, N Rizzi, G Rodriguez-Coira, K Sadakane, A C Sadun, M R Samal, S S Savchenko, E Semkov, B A Skiff, L Slavcheva-Mihova, P S Smith, I A Steele, A Strigachev, J Tammi, C Thum, M Tornikoski, Yu V Troitskaya, I S Troitsky, A A Vasilyev, O Vince
Blazars are active galactic nuclei, which are powerful sources of radiation whose central engine is located in the core of the host galaxy. Blazar emission is dominated by non-thermal radiation from a jet that moves relativistically towards us, and therefore undergoes Doppler beaming. This beaming causes flux enhancement and contraction of the variability timescales, so that most blazars appear as luminous sources characterized by noticeable and fast changes in brightness at all frequencies. The mechanism that produces this unpredictable variability is under debate, but proposed mechanisms include injection, acceleration and cooling of particles, with possible intervention of shock waves or turbulence...
December 21, 2017: Nature
Siddharth Malu, Abhirup Datta, Sergio Colafrancesco, Paolo Marchegiani, Ravi Subrahmanyan, D Narasimha, Mark H Wieringa
Electrons at relativistic speeds, diffusing in magnetic fields, cause copious emission at radio frequencies in both clusters of galaxies and radio galaxies through non-thermal radiation emission called synchrotron. However, the total power radiated through this mechanism is ill constrained, as the lower limit of the electron energy distribution, or low-energy cutoffs, for radio emission in galaxy clusters and radio galaxies, have not yet been determined. This lower limit, parametrized by the lower limit of the electron momentum - pmin - is critical for estimating the total energetics of non-thermal electrons produced by cluster mergers or injected by radio galaxy jets, which impacts the formation of large-scale structure in the universe, as well as the evolution of local structures inside galaxy clusters...
December 5, 2017: Scientific Reports
Markus Dietrich, Gunter Hagen, Willibald Reitmeier, Katharina Burger, Markus Hien, Philippe Grass, David Kubinski, Jaco Visser, Ralf Moos
Current developments in exhaust gas aftertreatment led to a huge mistrust in diesel driven passenger cars due to their NOx emissions being too high. The selective catalytic reduction (SCR) with ammonia (NH₃) as reducing agent is the only approach today with the capability to meet upcoming emission limits. Therefore, the radio-frequency-based (RF) catalyst state determination to monitor the NH₃ loading on SCR catalysts has a huge potential in emission reduction. Recent work on this topic proved the basic capability of this technique under realistic conditions on an engine test bench...
November 28, 2017: Sensors
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
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
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
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
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
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
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
Fetch more papers »
Fetching more papers... Fetching...
Read by QxMD. Sign in or create an account to discover new knowledge that matter to you.
Remove bar
Read by QxMD icon Read

Search Tips

Use Boolean operators: AND/OR

diabetic AND foot
diabetes OR diabetic

Exclude a word using the 'minus' sign

Virchow -triad

Use Parentheses

water AND (cup OR glass)

Add an asterisk (*) at end of a word to include word stems

Neuro* will search for Neurology, Neuroscientist, Neurological, and so on

Use quotes to search for an exact phrase

"primary prevention of cancer"
(heart or cardiac or cardio*) AND arrest -"American Heart Association"