Foreground memory management in data path synthesis

The management of foreground memory is a main issue in data path synthesis. the storage of values in registers and register files not only determines the number of each of them but also has a major impact on the interconnect structure. Both the amount of multiplexing and interconnect are crucial factors to both the delay and area of a circuit. In this paper it is shown that when values are grouped into register files before being assigned to actual registers, significant savings (20 per cent) can be obtained in the number of local interconnections and the amount of global interconnect at the expense of only slightly more register area. These results can be enhanced by splitting the read and write phases of registers and even more by introducing serial (re)write operations for the same value. the value grouping is based on edge-colouring algorithms that provide a sharp upper bound on the number of register groups needed. After value grouping, the registers are allocated for each register file separately. Algorithms for register allocation published up till now have only considered loop-free data flow graphs. When these algorithms are applied to data flow graphs with loops, unnecessary register transfer operations can be introduced. In this paper a new algorithm is presented that performs a minimal register allocation eliminating all superfluous register transfer operations. Experiments on a benchmark set have shown that in all cases all register transfers could be eliminated at no increase in register cost. This paper provides a deeper insight to the computational complexity of some problems in the area of data path synthesis. It shows that the various subtasks can be solved exactly using polynomial time algorithms.     

The Influence of Model Parameters on BEG/MEG Single Dipole Source Estimation

This paper deals with source localization and strength estimation based on EEG and MEG data. It describes an estimation method (inverse procedure) which uses a four-spheres model of the head and a single current dipole. The dependency of the inverse solution on model parameters is investigated. It is found that sphere radii and conductivities influence especially the strength of the EEG equivalent dipole and not its location or direction. The influence on the equivalent dipole of the gradiometer is investigated. In general the MEG produces better location estimates than the EEG whereas the reverse is found for the component estimates. An inverse solution simultaneously based on EEG and MEG data appears slightly better than the average of separate EEG and MEG solutions. Variances of parameter estimators which can be calculated on the basis of a linear approximation of the model, were tested by Monte Carlo simulations.     

Comparison of diverse optical CDMA codes using a normalized throughput metric

A new method of comparing optical CDMA codes of different families, sizes and weights is described. We outline why the traditional performance metric of bit-error rate versus number of simultaneous users is lacking and propose a new performance measure - the peak throughput normalized with respect to the size of the code. This new metric is used to show that optical-orthogonal codes (OOCs) with a weight of 4 perform best at low offered loads while OOCs with weight 5 should be used at higher offered loads. By applying the technique across different families of codes, we demonstrate that multi-wavelength OOCs (MWOOCs) perform better than both OOCs (by a factor of approximately 1.25) and asymmetric prime-hop codes (by a factor of approximately 3.5), over a wide range of offered loads.     

Cathodic reduction of acids in dimethylformamide on platinum

A linear correlation was shown to exist between the acidity and the cyclic voltammetric half-potential of the reduction of acids in DMF for carboxylic and N-acids in the pK_a range of 6-16. Chlorophenols are reduced at slightly lower potentials giving a separate parallel line. Applying the obtained equation and employing the same method to literature data in DMSO, the pK_a values for conjugate aids of DMF and DMSO can be calculated, showing DMSO·H⁺ to be more acidic (pK_a = 2.9) than DMF·H⁺ (pK_a = 5.7). The analysis of cyclovoltammetric data demonstrated that a CE mechanism operates in the reduction of strong acids, including the conjugate acid of DMF. Weaker acids are reduced by direct discharge or a mixed mechanism.     

Defect structure and chemical diffusion in nickel sulfide β-Ni3S2

The chemical composition, defect structure, and diffusion in nickel sulfide -Ni₃S₂ have been investigated in H₂S-H₂ mixtures containing between 1 and 65% H₂S between 560 and 700°C. Gravimetric, density, and X-ray studies were carried out. In the thermodynamically stable compound the ratio of Ni/S varied between 1.3 and 1.75. The X-ray examination showed a step change in the lattice parameter at the Ni/S ratio 1.4. A linear dependence of the density values (between 5.5 and 6.2 g/cm³) on the composition was observed. On the basis of the chemical composition and density measurements the number of nickel and sulfur atoms in 1 cm³ were determined. It has been shown that the Ni₃S₂ phase is defected in both anion and cation sublattices and that its chemical formula may be described as follows: Ni_3±yS_2x, where y 2x. It has been found that in the mixture containing 10% H₂S the process of defect formation is determined by their diffusion in the sulfide. The temperature dependence of the diffusion coefficient is described by the equation D = 13.15 exp(-30,000/RT) cm²/sec. No dependence of D on the sulfur partial pressure was observed, but this may be due to the relatively large uncertainties in the measurement of the diffusion coefficients.     

Kinetics of copper sulfidation at temperatures 570–1123 K

The kinetics of copper sulfidation have been studied as a function of temperature (570–1120 K) by the use of the modified Wagner's pellet method. It has been found that sulfidation follows a parabolic rate law with different activation energies in the low- and high-temperature ranges: $$k_{p}^{'} = 10.2 exp - (70 \pm 4)[kJ/mole]/RT (570 - 780 K)$$ and $$k_{p}^{'} = 1.69 \times 10^{ - 3} exp - (13 \pm 1.0)[kJ/mole]/RT (780 - 1120 K)$$ Using thermodynamic data as well as interfacial chemical potentials and ionic conductivity, the parabolic rate constants of sulfidation of copper have been calculated with good agreement with experimental results. Parabolic rate constants of sulfidation have been used to calculate average self-diffusion coefficients of copper in Cu₂S, the temperature dependence of which is as follows: $$\bar D_{Cu} = 8.76 \times 10^{ - 4} exp - (22.4 \pm 1)[kJ/mole]/RT$$      

Blended systems with calcium aluminate and calcium sulphate expansive additives

The high alumina cements were ground together with special sulphate–lime sinter to produce an expansive additive to Portland cement. This expansive additive in the environment of hydrating cement transforms into the hydrated calcium sulfoaluminate phase known as ettringite at “right time” to give the expansion before the early hardening process is completed. The studies were focused at first on the synthesis of the sulphate–lime sinter and subsequently on the mixture proportions between the basic Portland cement, calcium aluminate cement and sulphate–lime component giving the compensation of shrinkage or expansion effect during the hydration process. The measurements of volume changes of cementitious materials thus produced, followed by the compressive strength tests, rate of hydration determination, phase composition studies and microstructure of hydration products observations have been carried out to find the optimum proportions of blended cementitious material, as the controlled expansion and hardening are concerned.     

Electro/magnetic shielding effectiveness of soft magnetic Fe80Nb6B14 amorphous alloy

Application of the Fe₈₀Nb₆B₁₄ amorphous alloy to electromagnetic shielding was examined in detail using different experimental techniques. For shields made of the optimized (annealing at 700 K/1 h) amorphous ribbons the shielding effectiveness b was measured versus frequency f and shield thickness h. It was shown that for h = 200 μm in the frequency range 2 MHz < f < 15 MHz (the near-zone, electric field) b decreases from 55 dB to 20 dB. In the frequency range 0.2 kHz < f < 10 kHz (the near-zone, magnetic field) b > 20 dB. The best shielding effectiveness, i.e. b > 100 dB was obtained for electromagnetic field in the frequency range 200 MHz < f < 1000 MHz (the far-zone).     

System performance comparison of optical CDMA and WDMA in a broadcast local area network

The performance of optical code-division multiple-access (CDMA) systems with wavelength-hopping/time-spreading codes is compared to that of a wavelength-division multiple-access (WDMA) system. The multiple-access techniques are applied in a time-slotted broadcast local area network. The utilization, defined as the throughput per unit of time-domain bandwidth expansion, and packet delay are used as metrics of performance. When more than seven wavelengths are available, optical CDMA systems using asymmetric prime-hop codes and all-optical signal processing are shown to have higher peak utilization and lower corresponding delay than a WDMA system with the same number of wavelengths. When the encoders/decoders operate at the chip rate, the utilization of optical CDMA exceeds that of WDMA at high offered loads; however, the peak utilization of the WDMA system is still superior.