Showing papers by "Technical University of Denmark published in 1993"
TL;DR: A unifying characterization of various regularization methods is given and it is shown that the measurement of “size” is dependent on the particular regularization method chosen, and a new method is proposed for choosing the regularization parameter based on the L-curve.
Abstract: Regularization algorithms are often used to produce reasonable solutions to ill-posed problems. The L-curve is a plot—for all valid regularization parameters—of the size of the regularized solution versus the size of the corresponding residual. Two main results are established. First a unifying characterization of various regularization methods is given and it is shown that the measurement of “size” is dependent on the particular regularization method chosen. For example, the 2-norm is appropriate for Tikhonov regularization, but a 1-norm in the coordinate system of the singular value decomposition (SVD) is relevant to truncated SVD regularization. Second, a new method is proposed for choosing the regularization parameter based on the L-curve, and it is shown how this method can be implemented efficiently. The method is compared to generalized cross validation and this new method is shown to be more robust in the presence of correlated errors.
2,841 citations
Book•
01 Jan 1993TL;DR: This paper presents a guide to the literature the self-applicable scheme specializer, a partial evaluator for a subset of scheme for a first-order functional languages.
Abstract: Functions, types and expressions programming languages and their operational semantics compilation partial evaluation of a flow chart languages partial evaluation of a first-order functional languages the view from Olympus partial evaluation of the Lambda calculus partial evaluation of prolog aspects of Similix - a partial evaluator for a subset of scheme partial evaluation of C applications of partial evaluation termination of partial evaluation program analysis more general program transformation guide to the literature the self-applicable scheme specializer.
1,549 citations
TL;DR: A stable digestion of cattle manure could be maintained with ammonia concentrations up to 6 g N/l after 6 months of operation, however, the methane yield was reduced and the concentration of volatile fatty acids increased from 1 to 3 g/l as acetate, compared to controls with an ammonia concentration of 2.5 gN/l.
Abstract: Ammonia concentrations of 4 g N/l or more inhibited thermophilic digestion of cattle manure. A stable digestion of cattle manure could be maintained with ammonia concentrations up to 6 g N/l after 6 months of operation. However, the methane yield was reduced and the concentration of volatile fatty acids increased from 1 to 3 g/l as acetate, compared to controls with an ammonia concentration of 2.5 g N/l. The temporary strong inhibition following an one-step increase in ammonia concentration was reduced by applying a gradual increase. The specific methanogenic activity of ammonia-inhibited reactors (6 g N/l) with acetate or hydrogen as substrate was reduced by 73 and 52%, respectively. Tests of ammonia toxicity on the acetate- and hydrogen-utilizing populations showed a higher sensitivity of the aceticlastic compared to the hydrogenotrophic methanogens; the specific growth rate for the aceticlastic methanogens was halved at ammonia concentrations of 3.5 g N/l, compared to 7 g N/l for the hydrogenotrophic methanogens.
765 citations
TL;DR: In this article, a potential function of the components of the crack face displacements is used to generate the tractions along the interface where the fracture processes causing separation occur, and the two main parameters characterizing this potential are the work of separation per unit area and a peak normal stress.
Abstract: Calculations are reported for the mixed mode toughness of an interface joining an elastic-plastic solid to a solid which does not yield plastically. A potential function of the components of the crack face displacements is used to generate the tractions along the interface where the fracture processes causing separation occur. The two main parameters characterizing this potential are the work of separation per unit area and a peak normal stress. This description of the interface separation process is embedded within the continuum description as a boundary condition on the interface linking the adjoining solids. Small-scale yielding in plane strain is considered with the remote field specified by the magnitude and phase of the mixed mode stress intensity factors. Crack growth resistance curves are computed for a range of the most important nondimensional material parameters and for various combinations of remote mixed mode loading. Particular emphasis is placed on the ratio of the steady-state interface toughness to the “intrinsic” work of separation as it depends on plastic yielding and on the combination of modes 1 and 2. Plasticity enhances the interface toughness for all modes of loading, but substantially more so in the presence of a significant mode 2 component of loading than in near-mode 1 conditions.
675 citations
TL;DR: The phase behavior of the triblock copolymers dissolved in water has been studied using SANS as discussed by the authors, and the structural properties have been studied as a function of polymer concentration and temperature.
Abstract: The phase behavior of the triblock copolymers dissolved in water has been studied using SANS. The structural properties have been studied as a function of polymer concentration and temperature. At low temperature (T ≤ 15°C) and low polymer concentrations the unimers are fully dissolved Gaussian chains with radius R g =17 A. Close to ambient temperature, the hydrophobic nature of PPO causes aggregation of the polymers into spherical micelles with core sizes of the order of 40-50 A, somewhat temperature dependent. The concentration of micelles increased roughly linearly with temperature, until either a saturation is reached,where all the polymers are part of a micelle, or the volume density of micelles is so high that they lock into a crystalline structure of hard spheres
669 citations
TL;DR: A mathematical model for anaerobic degradation of complex organic material, such as manure, has been developed and results compare favorably with experimental data.
Abstract: A mathematical model for anaerobic degradation of complex organic material, such as manure, has been developed. The model includes an enzymatic hydrolytic step and four bacterial steps and involves 12 chemical compounds. The model focuses on ammonia inhibition and includes a detailed description of pH and temperature characteristics in order to accurately simulate free ammonia concentration. Free ammonia and acetate constitute the primary modulating factors in the model. The model has been applied for the simulation of digestion of cattle manure in continuously stirred tank reactors (CSTRs), and results compare favorably with experimental data.
409 citations
TL;DR: A review of the present understanding of the chemisorption of oxygen on metal surfaces such as Cu, Ni, and Ag is given in this paper, with special emphasis on how recent scanning tunneling microscopy results for the dynamics of oxygen-induced reconstructions in many cases give new insight also into the static surface structures.
391 citations
TL;DR: In this article, a simple description of wave breaking in shallow water is incorporated in the Boussinesq equations by using the concept of surface rollers, where the roller is considered as a volume of water being carried by the wave with the wave celerity.
353 citations
TL;DR: It is shown that morpholinepropanesulfonic acid (MOPS) is a suitable buffer for L. lactis and may be applied in high concentrations.
Abstract: A minimal growth medium containing glucose, acetate, vitamins, and eight amino acids allowed for growth of Lactococcus lactis subsp. lactis, with a specific growth rate in batch culture of μ = 0.3 h-1. With 19 amino acids added, the growth rate increased to μ = 0.7 h-1 and the exponential growth phase proceeded until high cell concentrations were reached. We show that morpholinepropanesulfonic acid (MOPS) is a suitable buffer for L. lactis and may be applied in high concentrations.
325 citations
TL;DR: In this paper, the amount of organic matter taken up by the phosphorus accumulating bacteria during the anaerobic phase affects the total denitrification rate, as well as the rate at which the organisms take up phosphate under anoxic conditions.
318 citations
TL;DR: In this paper, a micromechanics-based theoretical model is proposed which captures the essential features of the stress-crack width relationships at small crack widths (less than 0.3 mm).
Abstract: The stress-crack width relationship has been determined experimentally for concretes reinforced with two types of fibres, steel and polypropylene, of various fibre volume fractions. A micromechanics-based theoretical model is proposed which captures the essential features of the stress-crack width relationships at small crack widths (less than 0.3 mm). Micromechanisms accounted for include the bridging actions due to aggregates and fibres, Cook-Gordon interface debonding and fibre pre-stress. The fibre bridging action involves interface slip-dependent friction as well as snubbing friction for fibres bridging at inclined angles. Theoretical predictions based on independent parametric inputs compare favourably with experimental measurements of the stress-crack width relationship. Findings in this research provide confidence in the use of the proposed model for materials engineering targeted at prescribed structural performance.
TL;DR: Two intermediate phases have been observed upon heating an asymmetric poly(ethylenepropylene)-poly(ethylethylene) diblock copolymer between lamellar and hexagonal cylinder phases near the order-disorder transition.
Abstract: Two intermediate phases have been observed upon heating an asymmetric poly(ethylenepropylene)-poly(ethylethylene) diblock copolymer between lamellar and hexagonal cylinder phases near the order-disorder transition. Phase transitions betwen ordered morphologies are indicated by the temperature dependence of the dynamic shear moduli, and SANS experiments are used to identify these structures as hexagonally modulated lamellae and layered hexagonal packed channels. The observed wavevectors associated with the interlayer scattering for these structures are incommensurate, leading to an a periodic structure in which the long range translational order of the layers is destroyed
TL;DR: In this paper, the degradation of the full song of the Turdus merula was quantified by measuring excess attenuation, reduction of the signal-to-noise ratio, and blur ratio, the latter measure representing the degree of blurring of amplitude and frequency patterns over time.
Abstract: The habitat‐induced degradation of the full song of the blackbird (Turdus merula) was quantified by measuring excess attenuation, reduction of the signal‐to‐noise ratio, and blur ratio, the latter measure representing the degree of blurring of amplitude and frequency patterns over time. All three measures were calculated from changes of the amplitude functions (i.e., envelopes) of the degraded songs using a new technique which allowed a compensation for the contribution of the background noise to the amplitude values. Representative songs were broadcast in a deciduous forest without leaves and rerecorded. Speakers and microphones were placed at typical blackbird emitter and receiver positions. Analyses showed that the three degradation measures were mutually correlated, and that they varied with log distance. Their variation suggests that the broadcast song could be detected across more than four, and discriminated across more than two territories. The song’s high‐pitched twitter sounds were degraded more rapidly than its low‐pitched motif sounds. Motif sounds with a constant frequency projected best. The effect of microphone height was pronounced, especially on motif sounds, whereas the effect of speaker height was negligible. Degradation was inversely proportional to microphone height. Changing the reception site from a low to a high position reduced the degradation by the same amount as by approaching the sound source across one‐half or one‐whole territory. This suggests that the main reason for a male to sing from a high perch is to improve the singer’s ability to hear responses to its songs, rather than to maximize the transmission distance. The difference in degradation between low and high microphone heights may explain why females, which tend to perch on low brush, disregard certain degradable components of the song.
TL;DR: The temperature dependence of the cluster magnetization is found to be well described by an effective power law, with a size-dependent, but structure-independent, exponent larger than the bulk value.
Abstract: The spin-wave spectrum of Heisenberg spin clusters of various structures (bcc, fcc, and disordered) ranging in size between 9 and 749 spins is calculated by a self-consistent diagonalization of the equation of motion of ${\mathit{S}}^{+}$ in real space. The spin-wave spectrum of the clusters is strongly modified relative to the bulk, and the consequent neutron-scattering cross section exhibits discretely spaced wave-vector-broadened eigenstates. The implications of the finite size on thermodynamic properties, like the temperature dependence of the magnetization and the critical temperature, are also elucidated. We find the temperature dependence of the cluster magnetization to be well described by an effective power law, ${\mathit{M}}_{\mathrm{mean}}$\ensuremath{\propto}1-${\mathit{BT}}^{\mathrm{\ensuremath{\alpha}}}$, with a size-dependent, but structure-independent, exponent larger than the bulk value. The critical temperature of the clusters is calculated from the spin-wave spectrum by a method based on the correlation theory and the spherical approximation generalized to the case of finite systems. A size-dependent reduction of the critical temperature by up to 50% for the smallest clusters is found. The trends found for the model clusters are extrapolated to the size regime of nanoscale particles.
TL;DR: In this article, a kinetic approach is presented that allows a quantitative description of the reactivity of ferric oxides for both synthetic polydisperse ferrihydrite and assemblages of ferrous oxides found in natural sediments.
TL;DR: The ODEON room acoustics program is intended to be a base for research in objective and subjective room acoustic research, and a useful tool for consultants, in which an initial ray tracing is carried out to determine potential reflection sequences.
TL;DR: In this article, the authors investigated the conscious experience of thermal transients, both experimentally and by means of a model of dynamic thermoreception, by taking the subcutaneous depth of cold thermoreceptors to be less than that of warm units.
Abstract: This paper investigates the conscious experience of thermal transients, both experimentally and by means of a model of dynamic thermoreception. The experiments involved a sample of twelve human subjects, each undergoing twelve different ambient temperature step-changes. The research design included both temperature up-steps and down-steps, clothed and naked subjects, and transients both away from, and towards, neutrality. Each experiment lasted three hours, with the step- change occurring after 1.5 h when the subjects crossed between the twin climate chambers. Immediate sensations resulting from the temperature up-steps closely resembled later steady-state responses to the warmer environment, while initial impressions of temperature down-steps were typically twice the magnitude of their up-step counterparts. These experimental findings were accurately simulated by a simple thermoreceptor model coupled to a numerical model of heat transfer through clothing and cutaneous tissue. This heightened subjective sensitivity to temperature down-steps was achieved with the model by taking the subcutaneous depth of cold thermoreceptors to be less than that of the warm units, as noted by Hensel in his review of this specialized field (1981).
TL;DR: In this paper, a preliminary method for evaluating environmental consequences containing the major environmental effects is presented, which quantifies the term "environmental friendly" so it can be used as a “yardstick” in evaluating different technical solutions.
Abstract: Summary The Life cycle concept will become the backbone in a new industrial culture named sustainable production. Sustainability means that products are designed for their whole life cycle i.e. production, distribution, usage and disposal with minimized (acceptable) influence on the environment, occupational health and use of resources. A key element in this new engineering life cycle approach is a method/tool to assess and evaluate environmental, occupational health and resource consequences in all life cycle phases at the product development stage. In this paper a preliminary method for evaluating environmental consequences containing the major environmental effects is presented. The method outlined quantifies the term “environmental friendly” so it can be used as a “yardstick” in evaluating different technical solutions. The complex problems in the final design decisions are discussed and future perspectives outlined.
01 Jan 1993
TL;DR: The work discussed here presents a formulation to address the simultaneous optimization of the topology, shape and size of the structure to find the optimum layout of a linearly elastic structure.
Abstract: An overview of the method of homogenization to find the optimum layout of a linearly elastic structure is presented. The work discussed here presents a formulation to address the simultaneous optimization of the topology, shape and size of the structure. The discussion includes optimization of plane, plate and three dimensional shell structures.
01 Jan 1993
TL;DR: The proof theory of Duration Calculus is extended such that results proven using mathematical analysis can be used freely in the logic and provides a flexible interface to conventional control theory.
Abstract: Duration Calculus is a real-time interval logic which can be used to specify and reason about timing and logical constraints on discrete states in a dynamic system It has been used to specify and verify designs for a number of real-time systems This paper extends the Duration Calculus with notations to capture properties of piecewise continuous states This is useful for reasoning about hybrid systems with a mixture of continuous and discrete states The proof theory of Duration Calculus is extended such that results proven using mathematical analysis can be used freely in the logic This provides a flexible interface to conventional control theory
Book•
01 Nov 1993TL;DR: The Models of Parallel Processes Specification and the Behaviour of the Circuits Verification of Parallel System Behaviour Through Formal Models and the Relationship between the State and Event Models are reviewed.
Abstract: The Models of Parallel Processes Specification and the Behaviour of the Circuits Verification of Parallel System Behaviour Through Formal Models The Relationship between the State and Event Models Behaviour Identification and Circuit Analysis Transformation of the Behaviour Specifications Language Meccano Methods for Direct Translation of Specification into Circuits Formal Methods for Self-Timed Circuit Synthesis Reducing Specification to the Form Implementable Through Circuits Abridged Review of the State of the Art in Self-Timing Use of the CAD System 'FORCAGE' in the Design of Self-Timed Circuits.
TL;DR: Experimental data on hydrate formation kinetics, including induction times for methane, ethane and a mixture of the two gases, are presented in this article, where the data were measured using a stirred batch reactor recording the pressure as a function of time at constant temperature.
TL;DR: In this paper, an indirect identification technique to predict the mechanical properties of composite plate specimens is presented, which makes use of experimental eigenfrequencies, the corresponding numerical eigenvalue evaluation, sensitivity analysis and optimization.
TL;DR: A set of simple design and performance analysis techniques that have been successfully used to design a number of non-trivial delay-insensitive circuits, including a vector multiplier using a serial-parallel multiply and accumulate algorithm are described.
TL;DR: An efficient technique for calculating surface properties of random alloys based on the coherent-potential approximation within a tight-binding linear-muffin-tin-orbitals basis is presented and it is found that the noble metals segregate strongly towards the surface of their alloys.
Abstract: We present an efficient technique for calculating surface properties of random alloys based on the coherent-potential approximation within a tight-binding linear-muffin-tin-orbitals basis The technique has been applied in the calculation of bulk thermodynamic properties as well as (001) surface energies and work functions for three fcc-based alloys (Cu-Ni, Ag-Pd, and Au-Pt) over the complete concentration range The calculated mixing enthalpies for the Ag-Pd and Au-Pt systems agree with experimental values, and the calculated concentration dependence of the lattice parameters agrees with experiment for all three systems We find that the calculated surface energies and work functions in the unsegregated case exhibit a small positive deviation from a linear concentration dependence Finally, we performed a segregation analysis based on the calculated surface energies by means of a simple thermodynamic model and found in complete agreement with experiment that the noble metals segregate strongly towards the surface of their alloys
TL;DR: No significant differences in the stimulation of the degradation rates were observed when the disintegrated granules were supplied with methanogens that utilized hydrogen only or hydrogen and formate, indicating that interspecies formate transfer was not important for stimulation of propionate and butyrate degradation.
Abstract: Degradation of propionate and butyrate in whole and disintegrated granules from a thermophilic (55 degrees C) upflow anaerobic sludge blanket reactor fed with acetate, propionate, and butyrate as substrates was examined. The propionate and butyrate degradation rates in whole granules were 1.16 and 4.0 mumol/min/g of volatile solids, respectively, and the rates decreased 35 and 25%, respectively, after disintegration of the granules. The effect of adding different hydrogen-oxidizing bacteria (both sulfate reducers and methanogens), some of which used formate in addition to hydrogen, to disintegrated granules was tested. Addition of either Methanobacterium thermoautotrophicum delta H, a hydrogen-utilizing methanogen that does not use formate, or Methanobacterium sp. strain CB12, a hydrogen- and formate-utilizing methanogen, to disintegrated granules increased the degradation rate of both propionate and butyrate. Furthermore, addition of a thermophilic sulfate-reducing bacterium (a Desulfotomaculum sp. isolated in our laboratory) to disintegrated granules improved the degradation of both substrates even more than the addition of methanogens. By monitoring the hydrogen partial pressure in the cultures, a correlation between the hydrogen partial pressure and the degradation rate of propionate and butyrate was observed, showing a decrease in the degradation rate with increased hydrogen partial pressure. No significant differences in the stimulation of the degradation rates were observed when the disintegrated granules were supplied with methanogens that utilized hydrogen only or hydrogen and formate. This indicated that interspecies formate transfer was not important for stimulation of propionate and butyrate degradation.
TL;DR: Both increased dry deposition and canopy exchange in the tree tops contribute to the higher solute fluxes found close to the tree trunk, which may be due to variabilities in the processes taking part in altering the distribution and composition of the precipitated water as it moves through the canopy.
TL;DR: The apparent LDA underestimation of the barrier height is shown to be intimately linked with the LDA underbinding of core electrons and it is suggested to be a general phenomenon not limited to the particular nonlocal exchange-correlation approximation used or the particular system studied.
Abstract: The barrier for dissociative adsorption of ${\mathrm{H}}_{2}$ on Al(110) has been calculated within the generalized gradient approximation. A pronounced increase of the barrier height is found compared with what is calculated in the local density approximation (LDA). The apparent LDA underestimation of the barrier height is shown to be intimately linked with the LDA underbinding of core electrons and we suggest it to be a general phenomenon not limited to the particular nonlocal exchange-correlation approximation used or the particular system studied.
TL;DR: Different approaches towards designing disabled strains without seriously reducing their beneficial effects are presented, mainly two types of strain design: actively contained bacteria based on the introduction of controlled suicide systems, and passively contained strains based on genetic interference with their survival under environmental-stress conditions.
Abstract: The potential risks of unintentional releases of gene tically modifie d orga nisms, and the lack of predictable behavior of these in the environment, are the subject of consid erabl e concern. This concern is accentuated in conne ctio n