A New Hash Competition

Since the discovery of collision attacks against several well-known cryptographic hash functions in 2004, a rush of new cryptanalytic results cast doubt on the current hash function standards. The relatively new NIST SHA-2 standards aren't yet immediately threatened, but their long-term viability is now in question. The US National Institute of Standards and Technology (NIST) has therefore begun an international competition to select a new SHA-3 standard. This article outlines the competition, its rules, the requirements for the hash function candidates, and the process that NIST will use to select the final winning SHA-3 standard.     

Iterative Channel Estimation Based on B-splines for Fast Flat Fading Channels

We propose novel low-complexity iterative channel estimators based on B-splines. Local splines are adopted for computational simplicity. Minimum mean square error (MMSE) local splines with integral sampling are derived. The MSE of the proposed estimators depends on signal-to-noise ratio, fading rate, sampling interval, spline order and the number of weighting coefficients; these dependencies are investigated. The linear and cubic local splines with as few as seven weighting coefficients are capable of achieving MSE and BER performance comparable to those of the Wiener filter and the spheroidal basis expansion. However, a significantly lower complexity is achieved using B-splines     

Copolymers of starch and polyacrylonitrile: The dilution effect

In the ceric ammonium nitrate-initiated graft polymerization of acrylonitrile (AN) with starch, grafting frequencies and molecular weights of grafted polyacrylonitrile changed from 600 anhydroglucose units (AGU)/graft and 120000 to 280 AGU/graft and 36000 when concentrations of starch and AN were varied from 0.27 and 1.20 to 0.023 and 0.235 moles/l. of water, respectively. The influence of variety of starch, size of the starch granules, and reaction time was studied, and possible reasons for the influence of reactant concentration on the composition of the copolymer are considered.     

Absorbents from Saponified Starch-g-poly (acrylonitrile-co-2-acrylamido-2-methyl-propanesulfonic acid). Some Practical Considerations

Ceric-initiated graft polymerizations of monomer systems containing 90–99 mole % acrylonitrile and 1–10 mole % 2-acrylamido-2-methyl-propanesulfonic acid onto gelatinized starch, followed by alkaline saponification of the polyacrylonitrile (PAN) moiety, were carried out under more practical conditions. Highest absorbencies of both water and 0.9% NaCl were obtained when starch was gelatinized either by stirring in water at 95°C or by jet cooking and when the temperature of the exothermic graft polymerization was not allowed to exceed 30°C. Saponifications should be run at the lowest practical polymer concentration and for a period of time somewhat longer than that required for loss of the red color characteristic of alkali-treated PAN. Moreover, the alkaline saponificate should not be neutralized prior to methanol precipitation. Increased conversions of monomers to polymer were obtained by adding a second equal portion of ceric ammonium nitrate initiator.     

Graft polymerization of vinyl acetate onto starch. Saponification to starch–g–poly(vinyl alcohol)

Graft polymerizations of vinyl acetate onto granular corn starch were initiated by cobalt-60 irradiation of starch-monomer-water mixtures, and ungrafted poly(vinylacetate) was separated from the graft copolymer by benzene extraction. Conversions of monomer to polymer were quantitative at a radiation dose of 1.0 Mrad. However, over half of the polymer was present as ungrafted poly-(vinyl acetate) (grafting efficiency less than 50%), and the graft copolymer contained only 34% grafted synthetic polymer (34% add-on). Lower irradiation doses produced lower conversions of monomer to polymer and gave graft copolymers with lower % add-on. Addition of minor amounts of acrylamide, methyl acrylate, and methacrylic acid as comonomers produced only small increases in % add-on and grafting efficiency. However, grafting efficiency was increased to 70% when a monomer mixture containing about 10% methyl methacrylate was used. Grafting efficiency could be increased to over 90% if the graft polymerization of vinyl acetate-methyl methacrylate was carried out near 0°C, although conversion of monomers to polymer was low and grafted polymer contained 40-50% poly(methyl methacrylate). Selected graft copolymers were treated with methanolic sodium hydroxide to convert starch–g–poly(vinyl acetate) to starch–g–poly(vinyl alcohol). The molecular weight of the poly(vinyl alcohol) moiety was about 30,000. The solubility of starch–g–poly(vinyl alcohol) in hot water was less than 50%; however, solubility could be increased by substituting either acid-modified or hypochlorite-oxidized starch for unmodified starch in the graft polymerization reaction. Vinyl acetate was also graft polymerized onto acid-modified starch which had been dispersed and partially solubilized by heating in water. A total irradiation dose of either 1.0 or 0.5 Mrad gave starch–g–poly(vinyl acetate) with about 35% add-on, and a grafting efficiency of about 40% was obtained. A film cast from a starch–g–poly(vinyl alcohol) copolymer in which homopolymer was not removed exhibited a higher ultimate tensile strength than a comparable physical mixture of starch and poly(vinyl alcohol).     

Promotion of iron-induced rat liver microsomal lipid peroxidation by copper

Although copper has been demonstrated to promote lipid peroxidation in a number of systems, the mechanisms involved have not been fully defined. In this study, the role of copper in modifying lipid peroxidation has been explored in rat hepatic microsomes. In an in vitro system containing reduced glutathione (GSH, 200 μM) and Tris buffer, pH 7,4, cupric sulfate (1–50 μM) potentiated lipid peroxidation induced by ferrous sulfate (10 μM) but was unable to elicit peroxidation in the absence of iron. Higher levels of cupric sulfate (100 μM or greater) were inhibitory. The nature as well as the extent of the peroxidative response of microsomes to cupric sulfate were dependent on glutathione levels in addition to those of iron. Cupric sulfate (100 μM) strongly potentiated ferrous ion-induced lipid peroxidation in the presence of 400–800 μM GSH, while it inhibited peroxidation at lower levels of GSH (0–200 μM) and did not affect ferrous ion-induced peroxidation with glutathione levels of 3–10 mM. The potentiating effect of copper on ferrous ion-induced lipid peroxidation was further explored by investigating: (1) potential GSH-mediated reduction of cupric ions; (2) potential copper/GSH-mediated reduction of ferric ions (formed by oxidation during incubation); and (3) possible promotion of propagation reactions by copper/GSH. Our results indicate that cupric ions are reduced by GSH and thus are converted from an inhibitor to an enhancer of iron-induced lipid peroxidation. Cuprous ions appear to potentiate lipid peroxidation by reduction of ferric ions, rather than by promoting propagation reactions. Iron (in a specific Fe⁺²/Fe⁺³ ratio) is then an effective promoter of initiation reactions.     

Number of neighbours for staged decoding of block coded modulation

A method is presented for determining the effective number of neighbours for staged decoding of block coded modulation, for both coded 8-PSK and 16-QAM. The results are compared with ML decoding for 8-PSK, and it is shown that if the second row code has Hamming distance greater than 2, the number of neighbours is greater in staged decoding by a large factor, and causes a degradation in coding gain approaching 1 dB.<>     

Irreducible BER of COFDM on an IIR channel

The author considers the performance of coded orthogonal frequency division multiplexing (COFDM) on an infinite impulse response channel, and gives equations for intersymbol and interchannel interference (ISI and ICI). The trade-off between code rate and guard period length is considered, and it is shown that for optimum results both coding and a guard period are required. However, the advantage of coding at low redundancy is small     

Adaptive architecture for signal separation and interferencesuppression in DS-CDMA systems

In multi-user DS-CDMA cellular communications systems, the conventional (MF) detector performs poorly, making no use of the structure of the interferers. Various detectors offering improved performance have been suggested. The authors describe a new architecture, the `hybrid', which combines two known techniques, and offers better performance than is achieved separately with either technique