The application of the concurrent seek technique in order to improve the performance of disk storage devices

This paper considers the performance evaluation of a mass storage device, composed of a number of independent movable head magnetic disk units, which are all connected to the same I/O-channel. The question we want to answer is the following: what performance improvement can we expect if we apply the concurrent seek technique to this device, i.e., if we allow the (slow) seekoperations on different disk units to overlap? To that end Markov chain models are developed both for the situation without concurrent seeks and the situation with concurrent seeks. These models are analyzed under the assumption that a stochastic equilibrium is achieved. From the probability generating function of the system occupancy important performance measures, such as throughput and mean system occupancy are obtained, partially as explicit functions of the system parameters, partially in a numerical way. A quantitative and qualitative comparison between the different approaches is made.     

Comparison of single and double channel I/O-configurations

This paper is concerned with the performance evaluation of I/O-configurations composed of channels and I/0 devices (magnetic disk, drum ...). The question to be answered is: what performance improvement can be expected when the number of channels is increased or when the I/0-devices are multiple-ported instead of single-ported? To that end Markov chain models are developed for three different I/0-configurations. These models are analyzed under the assumption that a stochastic equilibrium is reached, and the probability generating function of the system occupancy is derived. From this function important performance measures, such as throughput and mean system occupancy are obtained as explicit functions of the system parameters. A quantitative comparison between the three alternatives is made.     

Methyl α- -fructofuranoside: Synthesis and conversion into carboxylates

Methyl α- -fructofuranoside was synthesized by methylation of -fructose and subsequent isolation of the α-furanoside from the anomeric mixture. This fructofuranoside was used as a starting material for the syntheses of several carboxylates, applying glycolic oxidation, selective oxidation of the primary alcohol function at the C-6 position and carboxymethylation.     

Effect of global FCFS and relative load distribution in two-class queues with dedicated servers

In this paper, we investigate multi-class multi-server queueing systems with global FCFS policy, i.e., where customers requiring different types of service—provided by distinct servers—are accommodated in one common FCFS queue. In such scenarios, customers of one class (i.e., requiring a given type of service) may be hindered by customers of other classes. The purpose of this paper is twofold: to gain (qualitative and quantitative) insight into the impact of (i) the global FCFS policy and (ii) the relative distribution of the load amongst the customer classes, on the system performance. We therefore develop and analyze an appropriate discrete-time queueing model with general independent arrivals, two (independent) customer classes and two class-specific servers. We study the stability of the system and derive the system-content distribution at random slot boundaries; we also obtain mean values of the system content and the customer delay, both globally and for each class individually. We then extensively compare these results with those obtained for an analogous system without global FCFS policy (i.e., with individual queues for the two servers). We demonstrate that global FCFS, as well as the relative distribution of the load over the two customer classes, may have a major impact on the system performance.     

A mathematical model for discrete-time buffer systems with correlated output process

This article considers an infinite buffer system with one or more input channels and multiple output channels. Transmission of messages from the buffer is synchronous and the arrival process of messages to the buffer is general. Each of the output channels is subjected to a random interruption process, i.e., the number of available output channels varies in time and is stochastic. The analysis of this system is carried out under the assumption that the output process can be described as a first order Markov process, i.e., the probability distribution of the number of available output channels during some clock time interval depends only on the number of available output channels during the previous clock time interval.A set of equations describing the behavior of this buffer system is derived. For a number of interesting special cases this set is solved and explicit expressions are obtained for the probability generating function of the number of messages in the buffer. Several prior studies are found as special cases of the present one. An illustrative example is treated and the results are compared to the ones obtained for an uncorrelated output process with the same equilibrium distribution. Some considerable deviations from these results are found.     

The photodimerisation of trans-cinnamic acid and its derivatives: a study by vibrational microspectroscopy

Infrared and Raman spectroscopies have been used to monitor the [2 + 2] photodimerisation reactions of alpha-trans-cinnamic acid and of a number of its derivatives. The principal changes observed in the spectra upon dimerisation are decay of a band around 1637 cm(-1), which is assigned to v(C=C) of the ethene bond of the monomer, and growth of bands just above 3000 cm(-1), which result from v(C-H) of saturated carbon atoms of the dimer. The use of microscope attachments has allowed us to follow the reactions of single crystals and we conclude that the reactions are topotactic in nature. We have carried out preliminary kinetic experiments in which spectra of one single crystal are recorded after sequential periods of photolysis. We find that the rates of dimerisation of differently substituted cinnamic acids are similar, with physical effects, such as the thickness of an individual crystal, outweighing any observed electronic effects (inductive or mesomeric).     

Complexation of Ln(III) and Ca(II) Cations with 3,4-Dicarboxyinulin and Model Compounds: Methyl 3,4-Dicarboxy-alpha-D-fructofuranoside and 3,4-Dicarboxynystose, As Studied by Multinuclear Magnetic Resonance Spectroscopy and Potentiometry

Complexes of Ln(III) and Ca(II) cations with 3,4-dicarboxyinulin (DCI) and model compounds, methyl 3,4-dicarboxy-alpha-D-fructofuranoside (DCF) and 3,4-dicarboxynystose (DCN) were studied using multinuclear magnetic resonance spectroscopy and potentiometric methods. Complexes of the model compounds with Ln(III) ions provided a feasible way in which to study complexation phenomena of the dicarboxyinulin/Ca(II) system using NMR techniques. Information on complex geometry was derived from the effect of Ln(III) ions on chemical shifts and longitudinal relaxation rates. Metal-ligand stoichiometries of 1:2 and 1:1, in which the ligand coordination was tridentate as well as tetradentate, were found. Potentiometric measurements carried out with Ca(II) yielded information on the stoichiometry as well as the cooperativity of metal ion binding by the ligands.     

Aqueous sol–gel processing of precursor oxides for ZrW<Subscript>2</Subscript>O<Subscript>8</Subscript> synthesis

This paper describes the synthesis of ZrW₂O₈ by the use of an aqueous citrate-gel method in order to prepare a fine, pure and homogeneous oxide mixture suitable for ceramic processing. The thermal expansion coefficient thus obtained for α-ZrW₂O₈ is −10.6 × 10⁻⁶ °C⁻¹ (50–125 °C) whereas for the β-ZrW₂O₈ a value of −3.2 × 10⁻⁶ °C⁻¹ (200–300 °C) is obtained. The advantages of the use of a sol–gel method is expressed in the very homogeneous end-products. The paper describes crystallographic data, morphological structure and the thermal expansion properties of the ZrW₂O₈ material. Moreover, photoluminescence and photochromic properties specific to the precursor gel are described and analyzed. These effects support our views that the precursors show homogeneity up to nanometer level.