Characteristics of negative values of polar cap index as an indicator of reversed convection

The polar cap (PC) index sometimes shows negative values in the summer hemisphere. The Hall current induced by reversed convection causes the negative values of PC index. This means that the negative PC is an indicator of reversed convection in the polar cap of the summer hemisphere. Using the northern PC index (PCN) for 1995 to 1999, we have statistically examined the occurrence characteristics of negative values of PCN. The results of our data analysis show that a negative value of PCN frequently occurs when the solar zenith angle is less than 75° and when the IMF BY and BZ are positive. These results are consistent with those obtained by the previous studies. Further, we found that the occurrence of negative PCN increases with solar wind electric field projected onto the GSM YZ plane (ET), if the clock angle is less than 60° When the clock angle is from 60 to 80°, the occurrence of negative PCN increases with ET in the cases when ET is less than 4 mV/m, and decreases with increasing ET in the cases of ET greater than 4 mV/m. Further, the occurrence of negative PCN increases with increasing magnitude of IMF projected onto the GSM YZ plane (BT) and decreases with increasing solar wind velocity. These results suggest that the occurrence of reversed convection in the polar cap is not a simple function of IMF clock angle. Their occurrences are also controlled by the magnitude of BT and solar wind velocity

Long Josephson junctions with spatially inhomogeneous driving

The phase dynamics of a long Josephson junction with spatially inhomogeneously distributed bias current is considered for the case of a dense soliton chain (regime of the Flux Flow oscillator). To derive the analytical solution of the corresponding sine-Gordon equation the Poincare method has been used. In the range of the validity of the theory good coincidence between analytically derived and numerically computed current-voltage characteristics have been demonstrated for the simplest example of unitstep function distribution of bias current (unbiased tail). It is shown, that for the considered example of bias current distribution, there is an optimal length of unbiased tail that maximizes the amplitude of the main harmonic and minimizes the dynamical resistance (thus leading to reduction of a linewidth).Comment: 7 pages, 5 figure

A Wideband On-Chip Radiator Driven by a Traveling-Wave Photodetector

An integrated broadband Vivaldi antenna driven by an on-chip traveling-wave photodetector is reported. The silicon photonic chip radiates between 21 and 67 GHz with−65 dBm coupled power at 44 GHz

Fotonički izvori milimetarskih i terahercnih valova i njihova primjena

This paper describes recent advances in the generation of millimeter and terahertz waves based on photonic techniques, which provides low-phase noise, wide frequency tunability, and high output power. Basic component technologies such as an optical frequency comb generator, photonic light-wave circuits for signal processing, and antenna-integrated photodiode modules, and their applications to high-performance measurement and communications are presented.U radu su opisani rezultati najnovijih istraživanja izvora milimetarskih i teraherc valova, zasnovanih na fotoničkim rješenjima, koji generiraju signale velike izlazne snage s niskim faznim šumom u širokom frekvencijskom području. Prikazana je tehnologija izrade osnovnih komponenata kao što su optički frekvencijski češljasti generator, fotonički valni krugovi za procesiranje signala, integrirani antenski moduli koji sadrže fotodiodu, kao i njihova primjena u mjernim sustavima visoke preciznosti i komunikacijskim sustavima

Response of convection electric fields in the magnetosphere to IMF orientation change

[1] The transient response of convection electric fields in the inner magnetosphere to southward turning of the interplanetary magnetic field (IMF) is investigated using in‐situ electric field observations by the CRRES and Akebono spacecraft. Electric fields earthward of the inner edge of the electron plasma sheet show quick responses simultaneously with change in ionospheric electric fields, which indicates the arrival of the first signal related to southward turning. A coordinated observation of the electric field by the CRRES and Akebono spacecraft separated by 5 RE reveals a simultaneous increase in the dawn‐dusk electric field in a wide region of the inner magnetosphere. A quick response associated with the southward turning of the IMF is also identified in in‐situ magnetic fields. It indicates that the southward turning of the IMF initiates simultaneous (less than 1 min) enhancements of ionospheric electric fields, convection electric fields in the inner magnetosphere, and the ring or tail current and region 2 FACs. In contrast, a quick response of convection electric fields is not identified in the electron plasma sheet. A statistical study using 161 events of IMF orientation change in 1991 confirms a prompt response within 5 min for 80% of events earthward of the electron plasma sheet, while a large time lag of more than 30 min is identified in electric fields in the electron plasma sheet. The remarkable difference in the response of electric fields indicates that electric fields in the electron plasma sheet are weakened by high conductance in the magnetically conjugated auroral ionosphere.https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2009JA014277https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2009JA014277Published versio

Constructing Model of Bicycle Behavior on Non-signalized lntersection Using Nonlinear Autoregressive Exogenous Model

This study focuses on bicycle travel flow to prevent traffic accidents at non-signalized intersections. A bicycle's behavior can be characterized by various parameters, such as travel speed position, trajectory, acceleralion, and deceleration. The prevention of vehicle collisions with bicycles traveling at 10-15 km/h was regulated in the Advanced Emergency Braking System (AEBS) for passenger cars in regulation No. 152 of the World Forum for Harmonization of Vehicle Regulations in the United Nations. Therefore, it is essential to analyze the characteristics of bicycles in a reall trafflc environment to prevent traffic accidents involving cyclists. Meijer et. al. (2017) investigated bicycle behavior and charactericics using measurement devices installed on biccycles [1 ]. Ma et al. (2016) conducted a model of acceleration behavior on eleven cyclists using GPS data [2]. And it was pointed out that there was a need for modeling research for more cyclists.Hirose et al. (2021) examined bicycles' both travel speed and trajectory as bicycle travel flows based on data obtained from fixed-point observations at a non-signalized intersection in Tokyo, Japan [3]. This used fixed-point observalions to obtain raw data of bicycle travel flows in real traffic environment and reported various traffel speed, trajectory, and acceleration/deceleration patterns for bicycles entering intersections. The purpose of this study was to construct a model of bicycle travel flows based on fixed-point observations. It could simulate actual bicycle behaviors based on data that was obtained from measuring bicycle travel flows for 2828 cases from fixed-point observations. Furthermore, the data was divided into five patterns of bicycles entering intersections, and the accuracy of the model was evaluated for each pattern

Form and width of spectral line of Josephson Flux-Flow oscillator

The behavior of a Josephson flux-flow oscillator in the presence of both bias current and magnetic field fluctuations has been studied. To derive the equation for slow phase dynamics in the limit of small noise intensity the Poincare method has been used. Both the form of spectral line and the linewidth of the flux-flow oscillator have been derived exactly on the basis of technique presented in the book of Malakhov, known limiting cases are considered, limits of their applicability are discussed and appearance of excess noise is explained. Good coincidence of theoretical description with experimental results has been demonstrated.Comment: 10 pages, 5 figure

Exceeding octave tunable Terahertz waves with zepto-second level timing noise

Spectral purity of any millimeter wave (mmW) source is of the utmost interest in low-noise applications. Optical synthesis via photomixing is an attractive source for such mmWs, which usually involves expensive spectrally pure lasers with narrow linewidths approaching monochromaticity due to their inherent fabrication costs or specifications. Here, we report an alternative option for enhancing the spectral purity of inexpensive semiconductor diode lasers via a self-injection locking technique through corresponding Stokes waves from a fiber Brillouin cavity exhibiting greatly improved phase noise levels and large wavelength tunability of ~1.8 nm. We implement a system with two self-injected diode lasers on a common Brillouin cavity aimed at difference frequency generation in the mmW and THz region. We generate tunable sub-mmW (0.3 and 0.5 THz) waves by beating the self-injected two wavelength Stokes light on a uni-travelling carrier photodiode and characterize the noise performance. The sub-mmW features miniscule timing noise levels in the zepto-second (zs.Hz^-0.5) scale outperforming the state of the art dissipative Kerr soliton based micro-resonator setups while offering broader frequency tunability. These results suggest a viable inexpensive alternative for mmW sources aimed at low-noise applications featuring lab-scale footprints and rack-mounted portability while paving the way for chip-scale photonic integration.Comment: 31 page