Modelling of the electromagnetic field in the interplanetary space and in the Earth's magnetosphere

A magnetohydrodynamic model of the solar wind flow is constructed using a kinematic approach. It is shown that a phenomenological conductivity of the solar wind plasma plays a key role in the forming of the interplanetary magnetic field (IMF) component normal to the ecliptic plane. This component is mostly important for the magnetospheric dynamics which is controlled by the solar wind electric field. A simple analytical solution for the problem of the solar wind flow past the magnetosphere is presented. In this approach the magnetopause and the Earth's bow shock are approximated by the paraboloids of revolution. Superposition of the effects of the bulk solar wind plasma motion and the magnetic field diffusion results in an incomplete screening of the IMF by the magnetopause. It is shown that the normal to the magnetopause component of the solar wind magnetic field and the tangential component of the electric field penetrated into the magnetosphere are determined by the quarter square of the magnetic Reynolds number. In final, a dynamic model of the magnetospheric magnetic field is constructed. This model can describe the magnetosphere in the course of the severe magnetic storm. The conditions under which the magnetospheric magnetic flux structure is unstable and can drive the magnetospheric substorm are discussed. The model calculations are compared with the observational data for September 24–26, 1998 magnetic storm (Dst _min=−205 nT) and substorm occurred at 02:30 UT on January 10, 1997. This revised version was published online in August 2006 with corrections to the Cover Date.     

Superiority of canards in homing missiles

We suggest a first-order model to distinguish between nose control (canards) and tail control. We present optimal guidance strategies and demonstrate the superiority of nose control. This simple model enables us to develop simple and robust guidance strategies based on three approaches: unconstrained optimal control, constrained optimal control, and constrained differential games. It turns out that nose control requires low gain and is capable of forcing small miss distance in the presence of a maneuvering target.     

A method for estimating parameters of K-distributed clutter

A method for estimating the parameters of K-distributed clutter when the available sample size of the data is limited is proposed. In this method, the arithmetic mean and geometric mean of the given data are used to estimate the model parameters. Expressions characterizing the performance of the proposed estimator are presented, along with some simulation results. For spiky clutter, simulations show that parameter estimates obtained from the arithmetic and geometric mean are approximately equal to the numerically evaluated maximum-likelihood (ML) estimates. The method is also used to estimate the parameter of the Weibull density     

Energy coupling between the solar wind and the magnetosphere

This paper describes in detail how we are led to the first approximation expression for the solar wind-magnetosphere energy coupling function , which correlates well with the total energy consumption rate U _T of the magnetosphere. It is shown that is the primary factor which controls the time development of magnetospheric substorms and storms. The finding of this particular expression indicates how the solar wind couples its energy to the magnetosphere; the solar wind and the magnetosphere constitute a dynamo. In fact, the power P generated by the dynamo can be identified as by using a dimensional analysis. Furthermore, the finding of indicates that the magnetosphere is closer to a directly driven system than to an unloading system which stores the generated energy before converting it to substorm and storm energies. Therefore, the finding of and its implications have considerably advanced and improved our understanding of magnetospheric processes. The finding of has also led us to a few specific future problems in understanding relationships between solar activity and magnetospheric disturbances, such as a study of distortion of the solar current disk and the accompanying changes of . It is also pointed out that one of the first tasks in the energy coupling study is an improvement of the total energy consumption rate U _T of the magnetosphere. Specific steps to be taken in this study are suggested.     

Interference Immunity Effects in CPSK Systems with Hard-Limiting Transponders

Transmission characteristics are described for M-ary coherent phase-shift keyed (CPSK) systems with N-stage hard-limiting transponders where noise and multiple continuous wave (CW) interference sources are additively combined in each link. A general expression for the probability density function of the composite phase at the final link is derived; the overall error probability is then obtained from this general expression. Comparisons with N-cascaded linear amplifier systems clearly show the noise and interference immunity that result from the use of bandpass hard limiters (BPHLs). The BPHL system's error probability improvement versus interference sources is shown to be much larger than the improvement versus noise.     

Stability of Gyro in a Vehicle Spinning with Uncertain Angular Velocity

The analysis of a single-axis rate gyroscope mounted in a vehicle which is spinning with uncertain angular velocity about the spin axis of the gyro is presented. The nonlinearity in the equation of motion of the gimbal is retained. Using circle criterion, it is shown that the gimbal motion is globally asymptotically stable if Nyquist plot of the linear transfer function of the gyro lies in the interior of a certain disk. A simple analytical relation for the selection of gyro parameters for stability is derived.     

Concatenated Sequences for Spread Spectrum Systems

Concatenated sequences are suggested and developed for use in spread spectrum (SS) systems. Special receiver realization is discussed and it is shown that the concatenated sequences offer great advantage in reducing the size of the matched filter correlators (MFC) in the SS receiver. Experimental systems have been built using concatenated sequences and their performance is reported here. It has been shown that a processing gain of 60 is obtainable with a 15 × 4 concatenated sequence which requires three tapped delay lines (TDL), two of length 15 and one of 4. Thus a total of only 34 delay units (with a nonlinear interface network, only 19 delay units) are required. Teleprinter signals can be transmitted over telephone channels using a bandwidth (BW) expansion of 60 with an input signal-to-noise ratio (SNR) of only -5.1 dB, resulting in a character- error-rate of 1 in 103. Techniques have been developed to reduce the sidelobe levels in the aperiodic autocorrelation functions (ACF) of the pseudonoise (PN) codes. For 15 length and 7 length PN sequences, sidelobes are reduced by 9 dB and 9.4 dB, respectively, using transversal filters. Application of the SS systems to the problem of multiaccessing and antijamming are discussed.     

Mismatched Filtering of Sonar Signals

A replica correlator (matched filter) is an optimum processor for a receiver employing a pulse of continuous wave (CW) signal in a white Gaussian noise background. In an active sonar, however, when the target of interest has low Doppler shift and is embedded in a high reverberation background, this is not so. High sidelobes of the correlator frequency response pass a significant portion of the signal contained in the mainlobe of the reverberation spectrum. In order to reduce the sidelobes of the correlator output spectrum and at the same time keep the increase in its 3 dB bandwidth to a small amount, we propose lengthening of the replica of the transmitted signal and weighting it by a Kaiser window. It is demonstrated that by extending the weighted replica by 50 percent compared with the transmitted signal, it is possible to reduce the sidelobe levels to at least 40 dB below the mainlobe peak, with the concomitant increase of the 3 dB band-width by less than 5 percent. The degradation in signal-to-noise ratio (SNR) performance for such a ?mismatched? filter receiver with respect to the matched filter is less than 1.5 dB.     

Tapped-inductor filter assisted soft-switching PWM DC-DC power converter

A novel high-frequency transformer linked full-bridge type soft-switching phase-shift pulsewidth modulated (PWM) controlled dc-dc power converter is presented, which can be used as a power conditioner for small-scale photovoltaic and fuel cell power generation systems as well as isolated boost dc-dc power converter for automotive ac power supply. In these applications with low-voltage large-current sources, the full-bridge circuit is the most attractive topology due to the possibility of using low-voltage high-performance metal-oxide-semiconductor field-effect transistor (MOSFET) and achieving high efficiency of the dc-dc power converter. A tapped-inductor filter including the freewheeling diode is newly implemented in the output stage of the full-bridge phase-shift PWM dc-dc converter to achieve soft-switching operation for the wide load variation range. Moreover, in the proposed converter circuit, the circulating current is effectively minimized without using additional resonant circuit and auxiliary power switching devices. The practical effectiveness of the proposed soft-switching dc-dc power converter was verified in laboratory level experiment with 1 kW 100 kHz breadboard setup using power MOSFETs. Actual efficiency of 94-97% was obtained for the wide duty cycle and load variation ranges.