On the design of multiple key hashing files for concurrent orthogonal range retrieval between two disks

This paper concerns the following problem: given a set of multi-attribute records, a fixed number of buckets and a two-disk system, arrange the records into the buckets and then store the buckets between the disks in such a way that, over all possible orthogonal range queries (ORQs), the disk access concurrency is maximized. We shall adopt the multiple key hashing (MKH) method for arranging records into buckets and use the disk modulo (DM) allocation method for storing buckets onto disks. Since the DM allocation method has been shown to be superior to any other allocation methods for allocating an MKH file onto a two-disk system for answering ORQs, the real issue is knowing how to determine an optimal way for organizing the records into buckets based upon the MKH concept.

A performance formula that can be used to evaluate the average response time, over all possible ORQs, of an MKH file in a two-disk system using the DM allocation method is first presented. Based upon this formula, it is shown that our design problem is related to a notoriously difficult problem, namely the Prime Number Problem. Then a performance lower bound and an efficient algorithm for designing optimal MKH files in certain cases are presented. It is pointed out that in some cases the optimal MKH file for ORQs in a two-disk system using the DM allocation method is identical to the optimal MKH file for ORQs in a single-disk system and the optimal average response time in a two-disk system is slightly greater than one half of that in a single-disk system.     

Flame temperature, fuel structure, and fuel concentration effects on soot formation in inverse diffusion flames

Insights into soot formation processes are gained from chemical sampling and thermocouple probing of co-flowing inverse diffusion flames (IDFs), with the oxidizer in the center. The transition from near-to slightly sooting flames and the effects of flame temperature, fuel concentration, and fuel structure (using methane, ethene, propene and 1-butene) are investigated. The aromatic content of IDFS scales with the fuel's sooting tendency, and suggests that the formation of the aromatic ring is a controlling step in soot formation. In addition to the relatively well-established reactions involving C4 and C2 species, benzene may form directly from two C3 species for fuels that readily produce C3 species during pyrolysis and/or oxidative pyrolysis. The total concentration of growth species increases almost linearly with fuel concentration, but depends more weakly on flame temperature than would be expected if pure pyrolysis governed the intermediate hydrocarbon behavior.     

Response of simulated propellant and explosives to projectile impact—II. Fragmentation

This paper is the second of a series concerned with the penetration and perforation phenomena in two types of propellant and explosive simulant, named Propergol, due to the impact at normal incidence of both blunt and conically-tipped steel strikers. The collision results in fragmentation, plug formation and generation of a cloud of debris that includes particles of measurable dimensions traveling with significant velocities. Both the fragment size and area as well as the ejecta mass are determined experimentally as a function of Propergol specimen thickness and impact velocity or energy. The cumulative number of fragments as a function of size for the Propergol is uniformly found to be a bi-linear semi-logarithmic relationship with the bifurcation occurring at the mean crystal radius. Individual crystals and the crater generated are examined by means of a scanning electron microscope.

A phenomenological model of the fragmentation process is constructed, based on an assumed spherical shape of the fragments and the bi-linear fragment distribution, using energy methods. This is combined with a perforation analysis that considers the process to be sequentially composed of initial indentation, fragmentation, and sliding and deflection of the Propergol disks. An evaluation of this model providing fragment volumes as a function of impact velocity is compared with experimental results and found to be in good agreement.     

Simulation of programmable logic controller

The development and test of a PLC control program takes time, increases equipment down-time, and might damage hardware due to program errors. All of these problems can be eliminated if there is a computer simulation system for testing control programs off line. This paper presented a new method, called Direct Sequential Method, for simulating PLCs. This method resolves a ladder logic sequentially by applying a series of logic deductions. This simulation system has been implemented in C and tested successfully.     

Heat transfers in treatment furnaces

For heat treating cylindrical metal billets, their lay-out in a furnace usually resembles that of an in-line heat-exchanger tube bank, with the air flows orthogonal to the billets. For maximum effectiveness of transferring thermal energy from the forced convecting air to the billets, the optimal horizontal pitch-to-diameter ratio for the billets should be 1·33 ± 0·05. For this same purpose it is advantageous to employ a vertical spacing (between the billets) as large as can be permitted for a given load of billets.     

Improvement options for a former water-driven-mill building now used as a theatre

After investigating the financial feasibility (and so abandoning the idea) of providing self-generated electricity using hydro-power, it was recommended that the top priority should be the direct connection of an electricity supply, from the mains grid to the building; this would cost £8800. Thereby, the theatre would receive a relatively unrestricted supply of electricity at cheaper unit tariffs. This improvement should be followed by the most urgent repairs being carried out to the building fabric, at an estimated cost of £6990. These repairs are necessary to ensure the continued integrity of the building's structure, thereby inhibiting the on-going deterioration.

The energy and financial appraisal also suggested a priority listing of overall improvements to the building in order to achieve a significant, economically justifiable reduction in energy demand; the recommended options are estimated to cost in total £39819. However, the capital cost of such an upgrading would only be recouped, and the theatre achieve a sustainable future, if the building were to be used more intensively and for a wider range of activities than at present in order to increase its revenue significantly.

All prices as stated are those at August 1991.     

Indexed in current contents

Indexed in current contents     

Application of the blind source separation method to feature extraction of machine sound signals

As the result of vibration emission in air, a machine sound signal carries important information about the working condition of machinery. But in practice, the sound signal is typically received with a very low signal-to-noise ratio. To obtain features of the original sound signal, uncorrelated sound signals must be removed and the wavelet coefficients related to fault condition must be retrieved. In this paper, the blind source separation technique is used to recover the wavelet coefficients of a monitored source from complex observed signals. Since in the proposed blind source separation (BSS) algorithms it is generally assumed that the number of sources is known, the Gerschgorin disk estimator method is introduced to determine the number of sound sources before applying the BSS method. This method can estimate the number of sound sources under non-Gaussian and non-white noise conditions. Then, the partial singular value analysis method is used to select these significant observations for BSS analysis. This method ensures that signals are separated with the smallest distortion. Afterwards, the time-frequency separation algorithm, converted to a suitable BSS algorithm for the separation of a non-stationary signal, is introduced. The transfer channel between observations and sources and the wavelet coefficients of the source signals can be blindly identified via this algorithm. The reconstructed wavelet coefficients can be used for diagnosis. Finally, the separation results obtained from the observed signals recorded in a semi-anechoic chamber demonstrate the effectiveness of the presented methods .