Error probabilities of an FFH/BFSK self-normalizing receiver in aRician fading channel with multitone jamming

We derive the analytical bit-error rate (BER) expressions for a fast frequency-hopped binary frequency-shift keying self-normalizing receiver over a fading channel with the worst-case band multitone jamming (MTJ) and additive white Gaussian noise (AWGN). The desired signal and MTJ are assumed to undergo independent Rician fading and our analyses, validated with simulation results, show that the system performance is not sensitive to different types of MTJ fading conditions. The self-normalizing receiver is found to be superior to the linear-combining receiver when the signal amplitude does not experience severe fading, while the converse is true under Rayleigh fading signal conditions. Under a Rician fading channel and AWGN conditions, the worst-case MTJ and the worst-case partial-band noise jamming are shown to have similar effects on the BER performance of the self-normalizing receiver with diversity     

Multitone jamming rejection of FFH/BFSK spread-spectrum system overfading channels

Analytical expressions for bit-error probability are derived for a fast frequency-hopping binary frequency-shift keying (FFH/BFSK) spread-spectrum communication system over a fading channel with worst-case band multitone jamming (MTJ) and additive white Gaussian noise (AWGN). An FFH system employing either a linear-combining receiver or a clipper receiver is investigated. The desired signal and MTJ are assumed to undergo independent fading, and our analysis, validated with simulation results, shows that the performance of the system is slightly improved as the severity of the MTJ fading is increased. The clipper receiver is found to be superior to the linear-combining receiver when the jamming power is strong. The worst-case MTJ is shown to be more harmful than the corresponding worst-case partial-band noise jamming over a fading channel with AWGN     

Transient cavitation effects in fluid piping systems

An accurate prediction of pressure transients and associated loadings in nuclear power plant piping systems requires a treatment of cavitation. A technique for calculating this effect in a general fluid-hammer analysis by the method of characteristics is developed. Cavitation is treated by a modified column separation model and is assumed to be a local phenomenon occurring whenever the pressure drops below the vapor pressure of the fluid. While the model is a simplification of the actual phenomena it reproduces the essential features of transient cavitation. Computational results obtained for a variety of piping arrangements demonstrate the versatility of the approach, and clearly illustrate the fact that neglecting cavitation leads to erroneous pressure-time loadings in the piping systems. Comparisons of calculated results with available experimental data, for a simple piping arrangement, show good agreement and provide validation for the computational cavitation model.     

Effect of plastic deformation of piping on fluid-transient propagation

A simple computational model is developed for incorporating the effect of elastic-plastic deformation of piping on pressure transient propagation in a fluid system. A computer program (PLWV) is described which incorporates this structural interaction model into a one-dimensional method-of-characteristics procedure for fluid hammer analysis. Computed results are shown to be in good agreement with available experimental data. The most significant effect of plastic deformation is to limit the peak pressure of a pulse leaving a pipe to approximately the yield pressure of the pipe, if the pipe is sufficiently long.     

The complete spectrum of image line

A derivation is presented of the complete orthonormalized spectrum, under LSA/LSM (longitudinal-section electric/magnetic) assumptions, for image line waveguiding structures by using a so-called method of partial wave phase shifts. The analysis is developed for the even LSM (TM^y) polarization, having H_y=0 and E_y as the main electric field component: the LSE analysis proceeds along dual lines. An arbitrary radiation field is described as a superposition of the LSM and LSE continua     

The stochastic model of evolution of scientific disciplines

In the paper science is regarded as a self-adapting system consisting of two subsystems. The stochastic model of one of the subsystems is proposed. The model reflects changes of the structure of a scientific discipline. As an example a model for the physics of elementary particles is presented.     

Multitone jamming rejection of FFH/BFSK linear-combining receiverover Rayleigh-fading channels

A computationally efficient BER expression for an FFH/BFSK linear-combining receiver against multitone jamming and AWGN over Rayleigh-fading channels is derived based on a Taylor series expansion. The analytical expression, validated by simulation results, allows us to efficiently analyse the system performance with higher diversity levels, which is otherwise mathematically intractable     

Computation of turbulent flows past arbitrary two-dimensional surface-mounted obstructions

The modelled equations of turbulent flow over two-dimensional bluff surface obstructions are solved numerically, using body-fitted coordinates and the k-? two-equation model of turbulence. Emphasis is placed on demonstrating a method capable of treating arbitrary geometrical configurations.Computations have been made for a number of geometrical configurations, including, amongst others, a rectangular block as well as triangular and semi-circular obstructions. Upstream conditions were purposely selected to simulate a neutrally stable atmospheric boundary layer.The low-Reynolds number version of the turbulence model was used in order to accommodate near-wall viscous effects, and some effort was devoted to the choice of empirical constants based on comparison with empirical information. Making due allowance for a number of discrepancy-causing factors, reattachment lengths obtained are deemed to be under-predicted. This is attributed to theoretical weaknesses of the two-equation model as well as numerical inaccuracies associated with the difference scheme.     

The effect of nisin on the physiology of Bifidobacterium thermophilum

The effects of nisin on lactate accumulation, growth, and Fe(III) binding by Bifidobacterium thermophilum (ATCC 25866) and Bifidobacterium breve (ATCC 15700) were investigated. Nisin inhibited lactate production by B. thermophilum at concentrations of less than 1 microg/ml, but this effect could be largely eliminated by pretreatment of the organism with 100 to 400 microM Al(III) or La(III). Nisin also inhibited the growth of B. thermophilum at concentrations of 2 to 3 microg/ml, with lower concentrations showing lag periods and/or slower rates of growth. However, Al(III) could not negate these effects, most likely because of Al(III) chelation by the trypticase-proteose-yeast extract medium. Nisin was able to increase instantaneous Fe(III) binding by both B. thermophilum and B. breve, though prolonged-time experiments (up to 120 min) with B. thermophilum indicated no difference in total Fe(III) bound. Nisin was thus able to increase the free radical reaction rate with bifidobacteria and the resultant rate of Fe(III) binding. It was concluded that nisin will normally inhibit the metabolic activity of B. thermophilum along with that of certain bacterial pathogens; however, this effect may in some instances, be abated by a pretreatment with Al(III). Moreover, by accelerating free radical action and the binding of iron by bifidobacteria, nisin may be able to potentiate their normal probiotic action.