Showing papers by "Helsinki University of Technology published in 1982"
TL;DR: In this paper, it was shown that in pure iron monovacancies are mobile at stage III around 220 K causing vacancy clustering into small three-dimensional agglomerates.
Abstract: Positron-lifetime measurements are reported on electron-irradiated high-purity $\ensuremath{\alpha}$-iron and on iron doped with controlled amounts of carbon impurities. We show that in pure iron monovacancies are mobile at stage III around 220 K causing vacancy clustering into small three-dimensional agglomerates. These clusters anneal out between 500 and 600 K. In carbon-doped iron a competing mechanism is the formation of a highly asymmetric carbon-vacancy pair at 200 K. These pairs dissociate around 490 K, resulting in another release of free vacancies in the lattice. Controversial aspects on vacancy properties in earlier investigations are discussed.
444 citations
TL;DR: In this article, an analysis of two partial processes is presented, in which a set of numerical representations assumes the correct order, and in the second one the final map of the representations converges to its asymptotic form.
Abstract: This paper contains mathematical results relating to a recently discovered self-organizing process. In particular, an analysis of two partial processes is presented. In the first one, a set of numerical representations assumes the correct order, and in the second one the final map of the representations converges to its asymptotic form.
431 citations
TL;DR: It is concluded that the auditory vertex response contains both modality specific and non-specific components, both of which are dependent on the ISI used.
356 citations
TL;DR: In this paper, the authors analyzed the problem of obtaining unique estimates of the parameters μ m and K s of the Michaelis-Menten equation for a microbial batch growth process.
Abstract: The reason for difficulties in obtaining unique estimates of the parameters μ m and K s of the Michaelis-Menten equation are analysed for a microbial batch growth process. With the aid of simulation studies in which the influences of different types of noise on the parameter estimates are compared, it is shown that, although theoretically identifiable in the deterministic case with ideal measurements, the parameters cannot in general be correctly determined from noisy measurements. The difficulties are further illuminated by estimation examples using real data. It certain situations, in which the value of the ratio K s / s o is high or in which only few and noisy measurements are available, the linear approximation of the Michaelis-Menten equation gives a better fit. The practical difficulties in obtaining correct values of the model parameters do not limit the applicability of the Michaelis-Menten model, which in most cases explains the bacterial growth behavior excellently. Rather, they underline the fact that care must be taken when utilizing parameter estimates for biological interpretations.
290 citations
TL;DR: A cubic magnetically shielded room has been constructed in this paper, which consists of three concentric cubic shields, and the side length of the smallest shell is 2A5 m. It utilizes ferromagnetic and eddy current shielding, active noise compensation, and shaking to achieve a shielding factor of about 400 000 between 1 Hz and 100 Hz.
Abstract: A cubic magnetically shielded room has been constructed. The room consists of three concentric cubic shields, and the side length of the smallest shell is 2A5 m. It utilizes ferromagnetic and eddy current shielding, active noise compensation, and shaking to achieve a shielding factor of about 400 000 between 1 Hz and 100 Hz. At lower frequencies, the shielding drops gradually and is about 16 000 for a 0.1-Hz disturbance. The residual magnetic induction in the room is less than 5 nT, and the magnetic noise above 0.5 Hz is lower than that of the superconducting quantum interference device (SQUID) magnetometer used in the measurements. When the room was completed, its performance in shielding was better than that of any other room made before.
196 citations
TL;DR: In Helsinki, a Small but General Set of Manipulative Operations for Boundary Models of Solid Objects has been used to Construct a Comprehensive Solid Modeling System.
Abstract: In Helsinki, a Small but General Set of Manipulative Operations for Boundary Models of Solid Objects Has Been Used to Construct a Comprehensive Solid Modeling System.
167 citations
TL;DR: It was shown that the Michaelis-Menten model is not practically identifiable and a recursive state-estimation algorithm for control and supervision purposes was developed and its application in combination with both the aggregated and the age distribution model was demonstrated.
158 citations
TL;DR: In this article, a Ni-Mo/SiO 2 -Al 2 O 3 hydrocracking catalyst was used for the treatment of phenol, o -cresol, anisole, and guaiacol.
92 citations
TL;DR: In this paper, the authors show that the scaled stability region of a method, satisfying some reasonable conditions, cannot be properly contained in the scaled stabilizer region of another method, for general nonlinear ordinary differential systems, for systems obtained from parabolic problems, and for hyperbolic problems.
Abstract: Stability regions of explicit "linear" time discretization methods for solving initial value problems are treated. If an integration method needsm function evaluations per time step, then we scale the stability region by dividing bym. We show that the scaled stability region of a method, satisfying some reasonable conditions, cannot be properly contained in the scaled stability region of another method. Bounds for the size of the stability regions for three different purposes are then given: for "general" nonlinear ordinary differential systems, for systems obtained from parabolic problems and for systems obtained from hyperbolic problems. We also show how these bounds can be approached by high order methods.
83 citations
TL;DR: In this article, living Lactobacillus delbrueckii cells were entrapped in calcium alginate gel beads and employed both in recycle batch and continuous column reactors to produce l-lactic acid from glucose.
Abstract: Living Lactobacillus delbrueckii cells were entrapped in calcium alginate gel beads and employed both in recycle batch and continuous column reactors to produce l-lactic acid from glucose. The substrate contained l% (w/v) yeast extract as nutrient and 4.8% (w/v) solid calcium carbonate as buffer. The maxiumum lactic acid yield obtained was 97%, of which more than 90% was l-lactic acid. The biocatalyst activity half-life in continuous operation was about 100 d, and only about 10% of the activity was lost during intermittent storage of the bioreactor at +7°C for about 5 months.
80 citations
TL;DR: In this article, three new tetraoxygenated xanthones (garcinones A, B and C), each disubstituted with C5-units, have been isolated from the chloroform extract of the fruit hulls of Garcinia mangostana.
01 Jan 1982
TL;DR: The extendible cell (EXCELL) method provides a data structure for efficient geometric access that stores geometric data into computer storage blocks corresponding to disjoint variable sized rectangular cells accessible by an address calculation type directory.
Abstract: The extendible cell (EXCELL) method provides a data structure for efficient geometric access. It stores geometric data into computer storage blocksm corresponding to disjoint variable sized rectangular cells accessible by an address calculation type directory. We describe the method for point files and files of more complicated figures analyzing performance. We report algorithms for the nearest neighbour and point-in-polygon-network problems and describe applications to geographical data bases, hidden line elimination and geometric modeling.
TL;DR: The extendible cell method is an application of order preserving extendible hashing to multidimensional point files that derives some of its performance characteristics and shows its expected case optimality for closest point problems.
Abstract: The extendible cell method is an application of order preserving extendible hashing to multidimensional point files We derive some of its performance characteristics and show its expected case optimality for closest point problems
01 Jan 1982
TL;DR: It is claimed that the brains might also more generally produce ordered maps that are directly or indirectly related to sensory or somatic information.
Abstract: There exist many kinds of maps or images in the brain; the most familiar ones may be the retinotopic, somatotopic, and tonotopic projections in the primary sensory areas, as well as the somatotopic order of cells in the motor cortex. There is also some experimental evidence (cf., e.g. Lynch et al., 1978) for that topographic maps of the exterior environment are formed in the hippocampus. In this work it is claimed that the brains might also more generally produce ordered maps that are directly or indirectly related to sensory or somatic information. It does not seem impossible that formation of feature maps at various levels of abstraction is the main mode of information processing in the brain.
TL;DR: In this article, a model compound, guaiacol, is used for the study of the behavior of the carbon-oxygen bonds under thermolytic conditions, and the thermodynamic properties of the compound are studied in tetralin, naphthalene and without solvent under hydrogen or nitrogen pressure at 578-618 K.
TL;DR: In this article, the abrasive wear of ion-plated titanium nitride coatings on hardened tool steel and on hardened and plasma-nitrided tool was studied, and wear tests were made with a dry sand-rubber wheel set-up and the initial surface roughness of the specimen was one of the test parameters.
TL;DR: The treatment of general linear discretization methods for initial value problems is extended to cover also implicit schemes, and by placing the accuracy of the schemes into a more central position in the discussion general ‘method-free’ statements are again obtained.
Abstract: This paper continues earlier work by the same authors concerning the shape and size of the stability regions of general linear discretization methods for initial value problems. Here the treatment is extended to cover also implicit schemes, and by placing the accuracy of the schemes into a more central position in the discussion general `method-free' statements are again obtained. More specialized results are additionally given for linear multistep methods and for the Taylor series method.
TL;DR: In this paper, the positron lifetime and Doppler-broadening measurements were used to study positron trapping at vacancy-type defects in magnesium, and positron-vacancy binding energy of the order of 0.3...0.4 eV was obtained.
Abstract: Trapping of positrons at vacancy-type defects in magnesium was studied by positron lifetime and Doppler-broadening measurements. Vacancy defects were produced by quenching, electron irradiation and deformation at low temperatures as well as by thermal agitation at elevated temperatures. In the first three cases we observed trapping at multiple vacancies, which anneal out between 77...400 K. Thermal equilibrium measurements show S-shape behaviour originating from positron trapping at magnesium monovacancies. However, changes in the positron parameters were very small, which is due to the weakness of the positron-vacancy interaction. A detrapping analysis yielded a positron-vacancy binding energy of the order of 0.3...0.4 eV.
TL;DR: Results and techniques from the theory of Volterra integral equations are used to investigate the existence, uniqueness, positivity, and boundedness of solutions, the existence of equilibrium solutions, and the stability of equilibria of a nonlinear age-dependent model for bacterial growth in a continuous fermentation process.
Abstract: Using results and techniques from the theory of Volterra integral equations, we investigate the existence, uniqueness, positivity, and boundedness of solutions, the existence of equilibrium solutions, and the stability of equilibria of a nonlinear age-dependent model for bacterial growth in a continuous fermentation process. The demographic parameters of the model, such as the growth, death, and fission rates of the cells, depend (in a nonlinear way) on the substrate concentration in the reactor tank.
TL;DR: In this paper, a simple dynamic model of the activated sludge process including the volatile suspended solids (VSS) concentration in the aeration basin, the VSS or suspended liquid concentration in recycle flow and the SS concentration in effluent was obtained by simplifying a comprehensive model using empirically verified assumptions, which can be used for on-line estimation of the influent BOD load and the effluent BOD, in combination with a recursive algorithm for oxygen uptake rate (OUR) and k L a estimation requiring only dissolved oxygen and air flow rate measurements.
TL;DR: Aspergillus niger ATCC 9142 mycelium was entrapped in calcium alginate beads and employed in an air-lift completely stirred reactor for continuous production of citric acid.
Abstract: Aspergillus niger ATCC 9142 mycelium was entrapped in calcium alginate beads and employed in an air-lift completely stirred reactor for continuous production of citric acid. Maximum yield obtained from 10% (w/v) sucrose was 12 g dm-3 with about 40% fermentation efficiency. Maximum rate of production 70 mg g-1 h-1 was about five times that obtained in classical batch fermentation.
TL;DR: In this article, the kinetics of the alkaline isomerization of D -glucose and D -fructose in 01 M ethanol-water solutions of sodium hydroxide were studied.
TL;DR: Recent work on immobilized biocatalysts at Helsinki University of Technology, Finland, is described, with starch processing, Β-galactosidase, glucose isomerase, invertase, and the immobilization of live cells as special examples.
Abstract: Recent work on immobilized biocatalysts at Helsinki University of Technology, Finland, is described, with starch processing, Β-galactosidase, glucose isomerase, invertase, and the immobilization of live cells as special examples.
TL;DR: A phase transition was observed in the nuclear spin system of metallic copper in external fields less than 0.02 mT and at entropies in the range of $(0.4\ensuremath{-}0.6)R\mathrm{ln}4$; the transition temperature was estimated to be of the order of 100 nK as mentioned in this paper.
Abstract: A phase transition was observed in the nuclear spin system of metallic copper in external fields less than 0.22 \ifmmode\pm\else\textpm\fi{} 0.02 mT and at entropies in the range of $(0.4\ensuremath{-}0.6)R\mathrm{ln}4$; the transition temperature was estimated to be of the order of 100 nK. Indications of a second anomaly at 0.08 \ifmmode\pm\else\textpm\fi{} 0.01 mT were also seen. The transition is antiferromagnetic and of first order. It is accompanied with large overcooling of the paramagnetic phase, which explains the discrepancies in the previous results.
TL;DR: Amorphous Fe80B20 and Fe40Ni40P14B6 alloys were studied before and after low temperature electron irradiations by positron lifetime and magnetic after effect methods as mentioned in this paper.
Abstract: Amorphous Fe80B20 and Fe40Ni40P14B6 alloys are studied before and after low temperature electron irradiations by positron lifetime and magnetic after-effect methods. The results show that in amorphous state all positrons are trapped by quenched-in voids of less than one atomic volume. Electron irradiation produces vacancy-like defects which recover continuously up to room temperature making only a few reorientation jumps before annealing.
TL;DR: In this article, a new method of nitriding in low pressure plasmas was developed, which can be used to combine the benefits of low pressure ion plating with plasma Nitriding to produce wear-resistant coatings for various applications.
TL;DR: A satellite peak has been observed in the NMR spectrum of rotating /sup 3/He-A; the peak intensity depends linearly on..cap omega.. at the high angular velocities,..Cap omega.. = 0.6-1.5 rad/s, needed to resolve it.
Abstract: A satellite peak has been observed in the NMR spectrum of rotating /sup 3/He-A; the peak intensity depends linearly on ..cap omega.. at the high angular velocities, ..cap omega.. = 0.6--1.5 rad/s, needed to resolve it. The frequency shift of the satellite is independent of ..cap omega... These results strongly suggest the existence of vortices in rotating /sup 3/He-A with the vortex density proportional to ..cap omega... Another satellite peak also has been observed which probably is due to solitons.
02 Jun 1982
TL;DR: The method utilizes a geometric file structure based on extendible cells together with a so-called topological representation of areas to have O(1) expected access cost for the "point-in-polygonnetwork-query" in typical situations.
Abstract: We present a file organization scheme providing fast access to spatially referenced objects in a data base. The method utilizes a geometric file structure based on extendible cells together with a so-called topological representation of areas. It is shown to have O(1) expected access cost for the "point-in-polygonnetwork-query" in typical situations. The method can be used as a spatial directory to a data base. Performance indicators are reported.