A performance study of four index structures for set-valued attributes of low cardinality

The efficient retrieval of data items on set-valued attributes is an important research topic that has attracted little attention so far. We studied and modified four index structures (sequential signature files, signature trees, extendible signature hashing, and inverted files) for a fast retrieval of sets with low cardinality. We compared the index structures by implementing them and subjecting them to extensive experiments, investigating the influence of query set size, database size, domain size, and data distribution (synthetic and real). The results of the experiments clearly indicate that inverted files exhibit the best overall behavior of all tested index structures.Received: 0 May 2000, Accepted: 18 October 2000, Published online: 17 September 2003Edited by E. Bertino     

A coaxial antenna with miniaturized choke for minimally invasive interstitial heating

We present a new coaxial antenna for microwave interstitial coagulative therapy, working at 2450 MHz and endowed with a miniaturized sleeve choke in order to reduce back heating effects and make the system response less dependent on the antenna insertion depth into the tissue; the way the choke is implemented makes the overall transversal size minimum and allows small adjustments of the choke section length even during operation. We describe the main technical features of the antenna and show experimental results clearly proving the choke effectiveness. Numerical simulations well agree with experimental data, confirming the suitability of the proposed device for minimally invasive medical applications.     

Oil mobility in a saturated water-wetted bed of glass beads

The mobilization of an oil bank in a packed bed of glass beads saturated with an aqueous phase has been studied both theoretically and experimentally. The size of the glass beads was varied in the range between 0.5 and 5mm. Two oils (hexadecane and hexane) with viscosities different for an order of magnitude and densities smaller than that of water have been used. A few more runs have been carried out using perchloroethylene (PCE), with density greater than that of water. The interfacial tension in the aqueous phase was varied in a quite large range (0.38-39.1 dyn/cm) by adding surfactants to the water. The glass assembly made it possible to follow the evolution of the dyed oily phase by the use of a digital camera. A very simple stochastic model for describing the porous structure of the packed bed made it possible to set a criterion for determining the probability of mobilization of ganglia which are produced by the fragmentation of the oil bank. The same model permits also to estimate the probability function of the velocity of a ganglion of an assigned size.     

Radiation initiated grafting on fluoro polymers I. Grafting of N-vinylpyrrolidone on poly(vinyl fluoride) by accelerated electrons

The radiation initiated grafting of N-vinylpyrrolidone on poly(vinyl fluoride) films by means of accelerated electrons using the preirradiation technique in vacuo has been investigated. The time conversion curves showed a steady increase of the initial grafting rate with temperature whereas the saturation grafting yield passes a maximum around 333 K. The Arrhenius plot reveals two straight lines with different slope intersecting around 328 K. Two different overall activation energies are found: 248 kJ mol^?1 for grafting below this temperature and 65 kJ mol^?1 for grafting above this temperature. This behaviour presumably is correlated to a glass transition of the trunk polymer arising from amorphous material under restraint by crystallites. The grafting yield is independent on the dose rate but strongly dependent on the dose. The penetration of the grafting front into the trunk polymer film was quantitatively followed by “Differential Interference Contrast”-microscopy: For any grafting yield the penetration depth of the grafting front increases with decreasing dose. The higher the dose, the higher the grafting yield to achieve grafting through. For a given dose increasing temperature shortens the time to obtain grafting through. On the basis of these experimental results a model was derived to explain the graft kinetics.     

Extraction of cephalosporin C from fermentation broths via lipophilic intermediates and the production of 7-aminocephalosporanic acid (7-ACA)

The extraction of cephalosporin C from fermentation broths chemically via aryl and alkylsulphonyl chlorides was studied, with the aim of developing a method which is comparable with regard to yield, but independent as to the patent from the chromato-graphic method. A study was also carried out on the reaction conditions for the transformation of N-arylsulphonylcephalosporin C into 7-ACA.     

THE EFFECTS OF GAMMA-IRRADIATION OF PILSNER BEER

A commercial Belgian Pilsner beer was irradiated with 0, 40, 80 and 120 krad of Cesium¹³⁷ gamma-rays. Analysis of the resultant beers showed that the analytical data for polyphenolics to a great extent had remained unaffected, that the treatment had no impact upon the liability to haze formation, the pH, the foam stability and the levels of dimethyl sulphide, ethyl acetate, isoamyl acetate, and diacetyl. There was an increase in the concentration of acetaldehyde, and a small decrease in the concentration of iso-alpha-acids and n-propanol, the changes being roughly proportional to the dosage applied. The sum of the fast and the moderately fast reducing agents increases with increasing irradiation dosages and in the same way the concentration of slow reducing agents diminishes. The treatment at the same time leads to a drastic loss of colour. The flavour of irradiated beer is totally unacceptable, even at the lowest dosages, the odour reminding one of hydrogen sulphide .     

An investigation on the effect of undercutting on the propagation parameters in single and coupled quasi-TEM lines in a multilayered dielectric

The effect of undercutting on the electrical parameters of general single and coupled quasi-TEM lines in a multilayered dielectric is studied by an efficient quasistatic numerical method. Results are presented for characteristic impedance, propagation constant, and attenuation constant in single lines; two symmetrical coupled lines; and a four-line system. In all cases studied a significant increase of losses has been observed.     

Whiskered tori with prefixed frequencies and Lyapunov spectrum

A classical mechanics problemthe existence of whiskered tori for an almost integrable Hamiltonian systemis analyzed with techniques reminiscent of the quantum field theoryfollowing the strategy developed in recent worksThe system consists of a collection of rotators interacting with a pendulum via a small potential depending only on the angle variablesThe proof of the existence of the stable and unstable manifolds ('whiskers') of the rotators invariant tori corresponding to dio- phantine rotation numbers is simplified by setting the Lyapunov spectrum to prefixed values via the introductionin the Hamiltonian functionof'counterterms7 depending on the strength of the interaction; this is a feature usual in quantum field theoryand emphasizes the analogy between the field theory and the KAM framework pointed out already in the mentioned works