Phase Truncation Research Articles

Asymmetric cryptosystem based on phase-truncated Fourier transforms

We propose an asymmetric cryptosystem based on a phase-truncated Fourier transform. With phase truncation in Fourier transform, one is able to produce an asymmetric ciphertext as real-valued and stationary white noise by using two random phase keys as public keys, while a legal user can retrieve the plaintext using another two different private phase keys in the decryption process. Owing to the nonlinear operation of phase truncation, high robustness against existing attacks could be achieved. A set of simulation results shows the validity of proposed asymmetric cryptosystem.

Identification of the Cooling Condition in 2-D and 3-D Continuous Casting Processes

In this article, the reconstruction of the function describing the boundary conditions along the primary and secondary cooling zones in the 2-D and 3-D continuous casting processes of pure metal is presented. The process is modeled by the inverse Stefan problem, where additional information consists of temperature measurements at selected points of the domain. In numerical calculations, Tikhonov's regularization, a genetic algorithm, and an alternating phase truncation method are used. The featured examples of calculations show very good approximation of the exact solution. The influence of the number and accuracy of measurements are also investigated.

A new method of spur reduction in phase truncation for DDS

DDS (Direct digital synthesizer) is widely used for frequency synthesis. The factors that contribute to spurious signals are analyzed. Adding a random signal to DDS system was used for spurious reduction formerly. Those methods assuredly reduce the spurs while the noise floor of signals is worsened. A new spurious reduction technique based on two DDS is proposed. The first DDS generates the conventional sine signal. The other DDS produces the error signal which compensates for the phase truncation error in traditional DDS system. A spurious reduction circuit has been developed. The experimental result indicates that the spurious signal due to phase truncation can be reduced 8dBc at least.

BANDWIDTH CONSIDERATIONS FOR A MICROSTRIP REFLECTARRAY

The paper describes a theoretical investigation into a limited bandwidth operation of a microstrip reflectarray. Two main factors limiting the bandwidth are considered. One is related to the requirement of phase compensation to convert a spherical wavefront launched by a feed into a planar wavefront. The other one is linked to the limited phasing range of microstrip antenna elements. The two factors contribute to the reflectarray phasing errors that in turn reduce its gain as a function of frequency. Simple formulas for an upper bound of gain bandwidth are derived, assuming the phase compensation by the elements is independent of frequency changes and verified against the results produced by other researchers. It is shown that the phase errors incurred in the path equalization to obtain conversion from spherical to planar wavefronts have a more profound effect on the reduction of operational bandwidth of the reflectarray than the phase truncation implemented on the required phase from each element.

Solving the inverse Stefan design problem using genetic algorithms

The article presents an algorithm of a solution of the two-phase inverse Stefan design problem. Based on the given information about the partial position of a moving interface, a functional was built defining the error of an approximate solution. To find the functional's minimum, a genetic algorithm was used, whereas for solution of the Stefan problem, the alternating phase truncation method was applied. Stability of the procedure was guaranteed using the Tikhonov regularization method. The results obtained corroborate the usefulness of the presented approach.

Using genetic algorithms for the determination of an heat transfer coefficient in three-phase inverse Stefan problem

In the paper, an example is presented of the application of a genetic algorithm to a design inverse Stefan problem. The problem consists in the reconstruction of the function which describes the heat transfer coefficient, where the positions of phase change moving interfaces are well-known. In numerical calculations, the Tikhonov regularization, a genetic algorithm and a generalized alternating phase truncation method were used. The featured examples of calculations show a very good approximation of the exact solution.

Digital Frequency Synthesizer Based on Two Coprime Moduli DDS

A new concept for direct digital synthesizer (DDS) design is presented in this brief. The originality of the method consists on the use of a traditional modulus 2L DDS and a novel modulus (2 L-1) DDS whose outputs are digitally mixed by means of a complex multiplier. This way, the number of different frequencies achievable equals 2L(2L-1) using two independent L-bits wide accumulators. No phase truncation is required resulting in extremely low spurs, while the size of the memories for the trigonometric look-up tables is only 2L positions. The design has been implemented in a field-programmable gate array to demonstrate its performance and logic requirements

The Design of Virtual Low-Voltage Power Line Noise Generator

Proposed to apply the virtual instrument way to structure the noise generator, according to the complex features of the noises on the low-voltage power line. It talks about the design of the core circuit. used the CPLD-based DDS to stimulate the PLL frequency synthesiser to form the clock generator. Analyzed the method to suppress the phase-noise and the spurious signals of the frequency-synthesis system, proposed to use the balanced scrambling system to suppress the spurious noises from the phase truncation, solved the difficulties in the broad-band signal coupling.

A Direct Digital Frequency Synthesizer With Fourth-Order Phase Domain<tex>$DeltaSigma$</tex>Noise Shaper and 12-bit Current-Steering DAC

This paper presents a direct digital frequency synthesizer (DDFS) with a 16-bit accumulator, a fourth-order phase domain single-stage /spl Delta//spl Sigma/ interpolator, and a 300-MS/s 12-bit current-steering DAC based on the Q/sup 2/ Random Walk switching scheme. The /spl Delta//spl Sigma/ interpolator is used to reduce the phase truncation error and the ROM size. The implemented fourth-order single-stage /spl Delta//spl Sigma/ noise shaper reduces the effective phase bits by four and reduces the ROM size by 16 times. The DDFS prototype is fabricated in a 0.35-/spl mu/m CMOS technology with active area of 1.11mm/sup 2/ including a 12-bit DAC. The measured DDFS spurious-free dynamic range (SFDR) is greater than 78 dB using a reduced ROM with 8-bit phase, 12-bit amplitude resolution and a size of 0.09 mm/sup 2/. The total power consumption of the DDFS is 200mW with a 3.3-V power supply.

Traffic Signal Phase Truncation in Event of Traffic Flow Restriction

This paper proposes an improvement to traffic signal controller logic. The concept consists of truncating a phase on which there is demand but with zero or minimal flow owing to a restriction of traffic. Flow restrictions occur for a variety of reasons including queue spillback, stalled vehicles, and railroad blockages. The logic presented in this paper recognizes such a flow restriction and, consequently, terminates the phase in favor of a conflicting call for service. The theory of the concept is addressed, and methods of implementation are explored. Although this research focuses on phase truncation, terminating a phase may not always be the most strategic decision; other priorities can override tactical detection of minimal flow. Therefore, this research considers the feasibility and potential benefit of including phase truncation logic as one component of a more intelligent and strategic controller algorithm. A limited experimental analysis was conducted to qualify the benefit of the phase truncation...

Traffic Signal Phase Truncation in Event of Traffic Flow Restriction

This paper proposes an improvement to traffic signal controller logic. The concept consists of truncating a phase on which there is demand but with zero or minimal flow owing to a restriction of traffic. Flow restrictions occur for a variety of reasons including queue spillback, stalled vehicles, and railroad blockages. The logic presented in this paper recognizes such a flow restriction and, consequently, terminates the phase in favor of a conflicting call for service. The theory of the concept is addressed, and methods of implementation are explored. Although this research focuses on phase truncation, terminating a phase may not always be the most strategic decision; other priorities can override tactical detection of minimal flow. Therefore, this research considers the feasibility and potential benefit of including phase truncation logic as one component of a more intelligent and strategic controller algorithm. A limited experimental analysis was conducted to qualify the benefit of the phase truncation concept. This analysis was conducted with VISSIM simulation software in conjunction with a hardware-in-the-loop configuration. On the basis of the results of this analysis, which was limited in scope, it was concluded that the phase truncation concept could result in reduced vehicle delay under at least one traffic scenario.

On the Accuracy of Semi-Lagrangian Numerical Simulation of Internal Gravity Wave Motion in the Atmosphere

We have investigated the accuracy ofthe semi-implicit semi-Lagrangian (SISL) method in simulating internal gravity wave (IGW) motion. We have focused on the relative accuracy of the hydrostatic, and nonhydrostatic IGW solutions. The analysis is based on a linearized model and a Global Circulation Model-Dynamic Core (GCM-DC) with a stretched grid.The nonhydrostatic version of the GCM-DC model produces the familiar IGW train disturbance anchored to an isolated hypothetical mountain. The wave has a distinct tilt away from the vertical direction, which is consistent with classical theory. For the hydrostatic version of the model, the axis of the resulting IGW train rests nearly perpendicular to the mountain top, thus again consistent with classical theory. Increasing the time step from 10 s; Courant number (Cn) = 0.5; to 60 s (Cn = 3.0), results in stable solutions for both the hydrostatic and nonhydrostatic versions of the model. The nonhydrostatic solution is in close agreement with the control run however, the hydrostatic solution exhibits large phase truncation errors.The solutions for the one-dimensional linearized SISL model confirm the GCM-DC results that the nonhydrostatic IGW train is less damped and shifted by the SISL scheme than the corresponding hydrostatic IGW motion. The linear solutions indicate very high accuracy of the physical mode of the solution, but it rapidly deteriorates when Cn exceeds unity. As Δt → 0 the amplitude of the computational mode tends to zero and its frequency to infinity. However, as Δt → ∞, the frequency of the computational SISL mode asymptotically approaches the value of the frequency of the corresponding SISL physical mode. Furthermore, the amplitude of the SISL computational mode is directly proportional to the size of the time step. Therefore, at large time steps, the amplification of the computational mode could offset some of the numerical damping of the physical mode by the SISL scheme.

A Numerically Controlled Oscillator with a Fine Phase Tuner and a Rounding Processor

We propose a fine phase tuner and a rounding processor for a numerically controlled oscillator (NCO), yielding a reduced phase error in generating a digital sine waveform. By using the fine phase tuner presented in this paper, when the ratio of the desired sine wave frequency to the clock frequency is expressed as a fraction, an accurate adjustment in representing the fractional value can be achieved with simple hardware. In addition, the proposed rounding processor reduces the effects of phase truncation on the output spectrum. Logic simulation results of the NCO using these techniques show that the noise spectrum and mean square error (MSE) for eight output bits of a 3.125 MHz sine waveform are reduced by 8.68 dB and 5.5 dB, respectively, compared to those of the truncation method, and 2.38 dB and 0.83 dB, respectively, compared to those of Paul's scheme.

A 14-b direct digital frequency synthesizer with sigma-delta noise shaping

This paper describes a 14-b direct digital frequency synthesizer (DDFS) utilizing a sigma-delta noise shaping technique to reduce spurs arising from phase truncation. A new phase accumulator architecture adopting a second-order sigma-delta modulator is proposed. The sigma-delta noise shaping eliminates periodicity inherent in the phase truncation error. With the proposed phase accumulator, the significant spurs are reduced, and the spectral characteristics of the DDFS are then determined by finite precision of sine-amplitude output. A prototype DDFS IC in 0.25-/spl mu/m CMOS was fabricated on 0.12-mm/sup 2/ die area. The measured spurious-free dynamic range (SFDR) is greater than 110 dB for 16-b phase value and 14-b sine-amplitude output. The fabricated IC consumes 100 mW with a 2.5-V supply, and correctly operates up to 250 MHz.

Exact analysis of spurious signals in direct digital frequency synthesisers due to phase truncation

The spurious signals in direct digital frequency synthesisers caused by phase truncation are analysed. A simple and intuitive algorithm for the exact characterisation of those spurs is presented.

DDFS phase mapping technique

Phase accumulating direct digital frequency synthesis (DDFS) uses table lookup with truncated phase addressing to map from the phase to amplitude domain. A phase mapping technique is presented, precisely equivalent to table lookup without phase truncation, but requiring significantly reduced lookup table memory. Error performance is determined entirely by sample quantisation.

Spurious signals in direct digital frequency synthesizers due to the phase truncation

Direct digital frequency synthesizers (DDS or DDFS) are widely used in modern communications and measurement devices. Their advantages are small size and power consumption together with excellent frequency stability, high frequency resolution, and short switching times. The difficulties are rather low output frequencies (500 MHz at the present state of the art) and a large set of the spurious signals very often above the -80 dB level. One source of spurious signals in DDS is the use of smaller number, W, of the most significant bits (MSB) applied for the output sine wave reconstruction from all R bits stored in the accumulator. The result is a phase modulation of the output signal. The problem was first solved in a rather complicated way with the result that the level of the largest spurious signal is about -6 W dB below the carrier with an increase of 3.9 dB in some instances. A simpler solution of the problem of spurious signal level due to the phase truncation in DDS was found earlier. However, no attention was paid to the validity of the corrections suggested. In this paper we will be concerned with this problem and investigate the validity and correctness of these generally cited results and provide a simple way for finding positions, levels, and numbers of these spurious signals generated by truncation to W bits of the phase information stored in the DDS accumulator memory of R bits (W<R).

Numerical simulation of continuous casting solidification by boundary element method

The problem of casting solidification modelling on the basis of the BEM is a rather difficult one. Yet, essential advantages of the BEM suggest that the use of this method for numerical simulation of Stefan's problem should be the subject of numerous scientific investigations in the range of effective algorithms construction. The most satisfactory algorithm is presented in Refs 1 and 2. The boundary element method is associated with the so-called temperature recovery method and both for metal solidification at constant temperature as well as in the case of solidification in an interval of temperatures. This paper presents a different algorithm. The boundary element method and the alternating phase truncation method APTM 4 are used in order to identify the solidication front and temperature field in the volume of rectangular copper continuous casting. Using the idea of 'wandering cross section '5 the author has obtained a three dimensional solution, as a superposition of a certain number of two dimensional solutions.

Prevention of gonadotropin-releasing hormone antagonist induced luteal regression by concurrent exogenous pulsatile gonadotropin administration in monkeys

We studied the effects of a gonadotropin-releasing hormone (GnRH) antagonist given in midluteal phase. Monkeys received the antagonist (n = 6), [N-Ac-D-p-Cl-Phe1,2,D-Trp3,D-Arg6,D-Ala10]-GnRH: hydrochloride or vehicle (n = 5). Absent luteinizing hormone (LH) pulsatility, diminished progesterone (P) secretion (P less than 0.01), luteal phase truncation and premature menstruation were observed in all receiving the antagonist. To investigate the site of action, four females received pulsatile exogenous human menopausal gonadotropins (hMG) concurrently, whereby P secretion was sustained and premature menstruation was averted. Equivalent treatment using "pure" FSH, failed to sustain P levels and timely menstruation occurred, confirming the continuing dependence of the corpus luteum on LH. The antagonist acts by central suppression and in turn, diminishes P biosynthesis. LH is luteotropic, since pulsatile LH (hMG), not "pure" FSH, prevented luteolysis.

Mathematical model for corundum single crystal growth by Verneuil method

A mathematical model which is an attempt to describe the complex process of monocrystallization by the Verneuil method is presented. The problem has been solved through the method of finite differences and at the same time making use of a certain modification of the mathematical description of Stefan's problem called the the alternating phase truncation method [9]. The elaborated algorithm and the examples of solutions given at the end of the present study point at the usefulness of the presented method of numerical simulation for modern designing and controlling the processes of crystal production.