Showing papers by "Aarhus University published in 1992"

Design at work: cooperative design of computer systems

Abstract: Contents: J. Greenbaum, M. Kyng, Preface: Memories of the Past. J. Greenbaum, M. Kyng, Introduction: Situated Design. Part I:Reflecting on Work Practice. L. Bannon, From Human Factors to Human Actors: The Role of Psychology and Human-Computer Interaction Studies in System Design. E. Wynn, Taking Practice Seriously. L.A. Suchman, R.H. Trigg, Understanding Practice: Video as a Medium for Reflection and Design. P.B. Andersen, B. Holmqvist, Language, Perspectives, and Design. K. Bodker, J.S. Pedersen, Workplace Cultures: Looking at Artifacts, Symbols, and Practices. Part II:Designing for Work Practice. S. Bodker, J. Greenbaum, M. Kyng, Setting the Stage for Design as Action. F. Kensing, K.H. Madsen, Generating Visions: Future Workshops and Metaphorical Design. P. Ehn, M. Kyng, Cardboard Computers: Mocking-it-up or Hands-on the Future. S. Bodker, K. Gronboek, Design in Action: From Prototyping by Demonstration to Cooperative Prototyping. A. Henderson, M. Kyng, There's No Place Like Home: Continuing Design in Use. P. Ehn, D. Sjogren, From System Descriptions to Scripts for Action. J. Greenbaum, M. Kyng, Epilogue: Design by Doing.

Wave-function approach to dissipative processes in quantum optics.

Abstract: A novel treatment of dissipation of energy from a ``small'' quantum system to a reservoir is presented. We replace the usual master equation for the small-system density matrix by a wave-function evolution including a stochastic element. This wave-function approach provides new insight and it allows calculations on problems which would otherwise be exceedingly complicated. The approach is applied here to a two- or three-level atom coupled to a laser field and to the vacuum modes of the quantized electromagnetic field.

Wallet Databases with Observers

Abstract: Previously there have been essentially only two models for computers that people can use to handle ordinary consumer transactions: (1) the tamper-proof module, such as a smart card, that the person cannot modify or probe: and (2) the personal workstation whose inner working is totally under control of the individual. The first part of this article argues that a particular combination of these two kinds of mechanism can overcome the limitations of each alone, providing both security and correctness for organizations as well as privacy and even anonymity for individuals.Then it is shown how this combined device, called a wallet, ran carry a database containing personal information. The construction presented ensures that no single part of the device (i.e. neither the tamper-proof part nor the workstation) can learn the contents of the database -- this information can only be recovered by the two parts together.

Glomerular number and size in relation to age, kidney weight, and body surface in normal man.

Abstract: The number and size of glomeruli in normal, mature human kidneys were estimated by a direct and unbiased stereological method, the fractionator. The number was 617,000 on average, and the mean size 6.0 M microns3. Both glomerular number and size showed significant negative correlation to age and significant positive correlation to kidney weight. Apparently, humans loose glomeruli with age. Body surface area correlated positively to kidney weight and total glomerular volume but not to number of glomeruli. Body surface area correlates significantly with metabolic rate (Robertson and Reid, Lancet, 1: 940-943, 1952). Thus, intraspecies adaptation of kidney filtration capacity to the metabolic demand is performed by changing the size of glomeruli, i.e., the number of glomeruli in individuals of a given species is independent of the metabolic rate.

Denitrification in sediment determined from nitrogen isotope pairing

Abstract: A new method for accurate and easy measurement of denitrification in sediments is presented. The water overlying intact sediment cores was enriched with 15NO3− which mixed with the 14NO3− of the natural sources of NO3−. The formation by denitrification of single-labeled (14N15N) and double-labeled (15N15N) dinitrogen pairs was measured by mass spectrometry after a few hours incubation. Total denitrification including the formation of unlabeled (14N14N) dinitrogen could be calculated assuming random isotope pairing by denitrification of the uniformly mixed NO3− species. In contrast to previous approaches, by this method it is possible to measure denitrification of both NO3− diffusing from the overlying water and NO3− from nitrification within the sediment.

The Na,K-ATPase.

Abstract: The energy dependent exchange of cytoplasmic Na+ for extracellular K+ in mammalian cells is due to a membrane bound enzyme system, the Na,K-ATPase. The exchange sustains a gradient for Na+ into and for K+ out of the cell, and this is used as an energy source for creation of the membrane potential, for its de- and repolarisation, for regulation of cytoplasmic ionic composition and for transepithelial transport. The Na,K-ATPase consists of two membrane spanning polypeptides, an α-subunit of 112-kD and a β-subunit, which is a glycoprotein of 35-kD. The catalytic properties are associated with the α-subunit, which has the binding domain for ATP and the cations. In the review, attention will be given to the biochemical characterization of the reaction mechanism underlying the coupling between hydrolysis of the substate ATP and transport of Na+ and K+.

Lotus japonicus, an autogamous, diploid legume species for classical and molecular genetics

Abstract: Summary In the Leguminosae plant family, few of the individual plant species have been used for plant molecular biology research. Among the species investigated no obvious representative ‘model’ legume has emerged. Here a member of the tribe Loteae, Lotus japonicus (Regel) Larsen is proposed as a candidate. L. japonicus is a diploid, autogamous species, with a good seed set, and a generation time of approximately 3 months. The haploid genome consists of six chromosomes and the genome size was estimated to be relatively small (0.5 pg per haploid complement). L. japonicus is susceptible to Agrobacterium tumefaciens and transgenic plants can be regenerated after hygromycin or kanamycin selection. Tissue culture conditions and procedures for transformation and regeneration are described. Stable transformation is demonstrated by segregation of the hygromycin selectable marker after selfing of transgenic plants or test crosses. The possibility of mapping polymorphic DNA markers inbred lines of L. japonicus is also discussed.

Semantics With Applications: A Formal Introduction

Abstract: Part 1 Introduction: semantic description methods the example language While semantics of expressions properties of the semantics. Part 2 Operational semantics: natural semantics structural operational semantics an equivalence result extensions of While blocks and procedures. Part 3 Provably correct implementation: the abstract machine specification of the translation correctness an alternative proof technique. Part 4 Denotational semantics: direct style semantics - specification fixed point theory direct style semantics - existence an equivalence result extensions of While. Part 5 Static program analysis: properties and property states the analysis safety of the analysis bounded iteration. Part 6 Axiomatic program verification: direct proofs of program correctness partial correctness assertions soundness and completeness extensions of the axiomatic systems assertions for execution time. Part 7 Further reading. Appendices: Review of notation introduction to Miranda implementations - abstract syntax evaluation of expressions operational semantics in Miranda - natural semantics structural operational semantics extensions of While provably correct implementation denotational semantics in Miranda - direct style semantics extensions of While static program analysis.

Coloured Petri Nets

Abstract: This paper describes a Petri net model, called Coloured Petri nets (CP-nets), where information is attached to each token. The information can be inspected and modified when a transition fires. For most applications, this generalization of ordinary Petri nets allows the user to make more manageable descriptions, due to the fact that equal subnets can be folded into each other, yielding a much smaller net. The paper investigates how to analyse Coloured Petri nets. It turns out that place-invariants and reachability trees, two of the most important methods for ordinary Petri nets, can be generalized to apply for Coloured Petri nets.

Distribution of the alpha 2-macroglobulin receptor/low density lipoprotein receptor-related protein in human tissues.

Abstract: The hepatic alpha 2-macroglobulin receptor (alpha 2MR)/low density lipoprotein receptor-related protein (LRP) binds and endocytoses alpha 2-macroglobulin-proteinase complexes in plasma. In addition, it binds lipoproteins, a novel 40 kDa protein, and complexes between plasminogen activators and plasminogen activator inhibitor type-1. This study shows, for the first time, the tissue distribution of alpha 2MR/LRP as determined by immunohistochemistry with specific monoclonal antibodies. The analysis revealed alpha 2MR/LRP-expression in a restricted spectrum of cell types, including neurons and astrocytes in the central nervous system, epithelial cells of the gastrointestinal tract, smooth muscle cells, fibroblasts, Leydig cells in testis, granulosa cells in ovary, and dendritic interstitial cells of kidney. Monocyte-derived cells displayed marked alpha 2MR/LRP expression in the phagocytes of liver, lung and lymphoid tissues, but no or low expression in antigen-presenting cells including Langerhans' cells of the skin. The high abundance of alpha 2MR/LRP in certain cell types of most organs suggests two main routes for alpha 2MR/LRP-mediated ligand clearance: (1) systemic removal in liver of circulating ligands, and (2) non-hepatic interstitial removal in different organs, including the brain.

Internal pressurization and convective gas flow in some emergent freshwater macrophytes

Abstract: Internal pressurization and convective through-flow are demonstrated to be common attributes of wetland plants with cylindrical culms or linear leaves. Eight of 14 species tested produced static internal gas pressure differentials of 200-1,300 Pa relative to ambient and internal convective airflows of 0.2 to > 10 cm3 min-’ culm-I, depending on species. Four species produced internal static pressure differentials of < 100 Pa. Two species did not pressurize. The driving forces are gradients in temperature and water vapor between the internal gas spaces of the plants and the ambient atmosphere (thermal transpiration and humidity-induced pressurization). A clear diel variation in pressurization and convective flow was observed; rates were highest in the afternoon and lowest at night, responding to ambient changes in light, temperature, and humidity. The resistance to airflow at the stem-rhizome junction was very high for some species, resulting in a low ability to convert internal pressurization into convective airflow through the rhizomes. Species with a high potential for internal pressurization and a low internal resistance to convective flow seem to have a competitive advantage over species that rely exclusively on diffisive gas transport, which allows them to grow in deeper waters.

Apolipoprotein E polymorphism in a Danish population compared to findings in 45 other study populations around the world.

Abstract: Apolipoprotein E (apoE) phenotypes were determined in a random sample of 466 Danish men born in 1948. The frequencies of the common alleles of the apoE gene were (with 95% confidence intervals) epsilon 2 = 0.085 (0.068-0.105), epsilon 3 = 0.741 (0.712-0.769), and epsilon 4 = 0.174 (0.150-0.200). These frequencies were compared to findings in 45 other study populations around the world (n greater than 100). The Danish population was found to cluster with populations from Iceland, Norway, Iceland, Scotland, the Netherlands, Germany, France (Paris), and Caucasian populations in Canada and the USA. The compiled data further show that dissimilarities in apoE allele frequencies among Caucasian populations are comparable to dissimilarities between some Caucasian and Asian populations. Notably, the frequency of epsilon 4 appears to be higher in northern regions of Europe (the Nordic countries, Scotland, Germany, and the Netherlands) than in southern regions (Switzerland, Tyrol, France [Nancy], Italy, and Spain).

Bacterial Sulfate Reduction Above 100°C in Deep-Sea Hydrothermal Vent Sediments

Abstract: The currently known upper temperature limit for growth of organisms, shared by a number of archaebacteria, is 110°C. However, among the sulfate-reducing bacteria, growth temperatures of greater than 100°C have not been found. A search for high-temperature activity of sulfate-reducing bacteria was done in hot deep-sea sediments at the hydrothermal vents of the Guaymas Basin tectonic spreading center in the Gulf of California. Radiotracer studies revealed that sulfate reduction can occur at temperatures up to 110°C, with an optimum rate at 103° to 106°C. This observation expands the upper temperature limit of this process in deep-ocean sediments by 20°C and indicates the existence of an unknown group of hyperthermophilic bacteria with a potential importance for the biogeochemistry of sulfur above 100°C.

The isector: a simple and direct method for generating isotropic, uniform random sections from small specimens

Abstract: SUMMARY The very simple and strong principle of vertical sections devised by Baddeley et al. has been a major advance in stereology when any kind of anisotropy is present in the specimen under study. On the other hand, some important stereological estimators still require isotropic, uniform random sections. This paper deals with a simple technique for embedding specimens in rubber moulds with spherical cavities. After the embedding, any handling of the resulting sphere independent of the specimen will induce isotropy of the final histological sections.

Microsensor Measurements of Sulfate Reduction and Sulfide Oxidation in Compact Microbial Communities of Aerobic Biofilms

Abstract: The microzonation of O2 respiration, H2S oxidation, and SO42- reduction in aerobic trickling-filter biofilms was studied by measuring concentration profiles at high spatial resolution (25 to 100 μm) with microsensors for O2, S2-, and pH. Specific reaction rates were calculated from measured concentration profiles by using a simple one-dimensional diffusion reaction model. The importance of electron acceptor and electron donor availability for the microzonation of respiratory processes and their reaction rates was investigated. Oxygen respiration was found in the upper 0.2 to 0.4 mm of the biofilm, whereas sulfate reduction occurred in deeper, anoxic parts of the biofilm. Sulfate reduction accounted for up to 50% of the total mineralization of organic carbon in the biofilms. All H2S produced from sulfate reduction was reoxidized by O2 in a narrow reaction zone, and no H2S escaped to the overlying water. Turnover times of H2S and O2 in the reaction zone were only a few seconds owing to rapid bacterial H2S oxidation. Anaerobic H2S oxidation with NO3- could be induced by addition of nitrate to the medium. Total sulfate reduction rates increased when the availability of SO42- or organic substrate increased as a result of deepening of the sulfate reduction zone or an increase in the sulfate reduction intensity, respectively.

A quantitative study of the human cerebellum with unbiased stereological techniques.

Abstract: Estimates of total number of different neuron and glial cell types in the dentate nuclei and the four major regions of the human cerebellum were obtained by new stereological methods. With the optical disector and Cavalieri methods, the total number of neurons and glial cells in the human cerebellum of five elderly men was estimated to be 105,000 × 106 (coefficient of variation, CV = 0.13). Of this total, the granule cells comprised 101,000 × 106 (CV = 0.13) and the Purkinje cells comprised 30.5 × 106 (CV = 0.13) of the neurons. The mean of the total number of neurons in the dentate nucleus was 5.01 × 106 (CV = 0.28). The average surface area of the human cerebellum was estimated to be 1160 cm2 (CV = 0.29). The rationale for the different sampling schemes used to quantify the various cell types is described. © 1992 Wiley-Liss, Inc.

A new automated method for phenotyping arylesterase (EC 3.1.1.2) based upon inhibition of enzymatic hydrolysis of 4-nitrophenyl acetate by phenyl acetate.

Abstract: A new method for phenotyping human serum arylesterase (EC 3.1.1.2) is described and evaluated. The aromatic esters, phenyl acetate and 4-nitrophenyl acetate, were compared as substrates for spectrophotometric measurement of arylesterase activity. A method for arylesterase phenotyping, based upon inhibition of the enzymatic hydrolysis of 4-nitrophenyl acetate by phenyl acetate, was developed. The method was applied to serum samples from 158 blood donors and showed a distinct separation of the three phenotypes defined by a reference method based on the ratio of paraoxonase activity to arylesterase activity using paraoxon and phenyl acetate as substrates. The method was adapted to a Cobas-Fara centrifugal analyser.

Provable Security Against Differential Cryptanalysis

Abstract: The purpose of this paper is to show that there exist DES-like iterated ciphers, which are provably resistant against differential attacks The main result on the security of a DES-like cipher with independent round keys is Theorem 1, which gives an upper bound to the probability of r-round differentials, as defined in [3] and this upper bound depends only on the round function of the iterated cipher Moreover, it is shown that there exist functions such that the probabilities of differentials are less than or equal to 22 − n where n is the length of the plaintext block We also show a prototype of an iterated block cipher, which is compatible with DES and has proven security against differential attacks

Action semantics

Abstract: A distinguishing characteristic of action semantics is its facet system, which defines the variety of information flows in a language definition. The facet system can be analyzed to validate the well-formedness of a language definition, to infer the typings of its inputs and outputs, and to calculate the operational semantics of programs. We present a single framework for doing all of the above. The framework exploits the internal subsorting structure of the facets so that sort checking, static analysis, and operational semantics are related, sound instances of the same underlying analysis. The framework also suggests that action semantics's extensibility can be understood as a kind of "weakening rule" in a "logic" of actions. In this paper, the framework is used to perform type inference on specific programs, to justify meaning-preserving code transformations, and to "stage" an action semantics definition of a programming language into a static semantics stage and a dynamic semantics stage.

Protein synthesis, posttranslational modifications, and aging.

Abstract: Posttranslational modifications of proteins are involved in determining their activities, stability, and specificity of interaction. More than 140 major and minor modifications of proteins have been reported. Of these, only a few have been studied in relation to the aging of cells, tissues, and organisms. These include phosphorylation, methylation, ADP-ribosylation, oxidation, glycation, and deamidation. Several of these modifications occur on proteins involved in crucial cellular processes, such as DNA synthesis, protein synthesis, protein degradation, signal transduction, cytoskeletal organization, and the components of extracellular matrix. Some of the modifications are the markers of abnormal and altered proteins for rapid degradation. Others make them less susceptible to degradation by normal proteolytic enzymes, and hence these accumulate during aging.

Development and application of a new method to extract bacterial DNA from soil based on separation of bacteria from soil with cation-exchange resin.

Abstract: A new method for the extraction of bacterial DNA from soil has been developed. Soil samples of 50 g were dispersed, and bacteria were released by use of a cation-exchange resin; subsequently, bacteria were separated from soil particles by low-speed centrifugation and lysed with lysozyme and ionic detergent, and the DNA was then purified by CsCl-ethidium bromide equilibrium density centrifugation. The extracted DNA was of high molecular weight and sufficiently pure for restriction enzyme digestion, DNA-DNA hybridization, and amplification by the polymerase chain reaction. The advantages of the new method are that the separation of bacteria from soil is considerably faster than by repeated blending, more samples can be handled, and furthermore no aerosols are formed during separation. Also, we investigated whether the CsCl-ethidium bromide equilibrium density centrifugation could be replaced by purification using Gene-Clean. However, this method produced DNAs which were insufficiently pure for several types of analysis. The new method was used to study survival of a 2,4-dichlorophenoxyacetic acid (2,4-D)-degrading Pseudomonas cepacia DBO1 (pRO101) in unamended soil and in soil amended with 2,4-D. We found that the degrading strain, irrespective of inoculation level, was able to grow to the same high numbers in soil amended with 2,4-D, while the strain in nonamended soil were maintained at the inoculation level. Detection based on DNA extraction and subsequent dot blot DNA-DNA hybridization was in accordance with detection by plating on selective medium. Images

Do Doctoral StudentsA Financial Support Patterns Affect Their Times-to-Degree and Completion Probabilities

Abstract: Projections of forthcoming shortages of Ph.D.s abound. Part of the reason is that American college graduates are much less likely to receive doctorates today than thcy were 20 years ago. Two important factors in this decline may be the increase in the length of time necessary for doctorate students to complete their programs that occurred over the period and the low completion rates of entrants into doctoral programs. Among the policies urged to prevent future Ph.D. shortages are increasing support for graduate students. Surprisingly little empirical evidence is available on how different types of support (fellowships. research assistantships, teaching assistantships) are likely to influence times-to-degree and completion rates. Our paper uses data on all graduate students who entered Ph.D. programs in four fields during a 25-year period at a single major doctorate producing university to estimate how graduate student financial support patterns influence these outcomes. We find that completion rates and mean durations of times-to-completion are sensitive to the types of financial support the students received. Other things held constant, students who receive fellowships or research assistantships have higher completion rates and shorter times-to-degree than students who receive teaching assistantships or tuition waivers, or who are totally self-supporting. A major finding Is that the Impact of financial support patterns on the fraction of students who complete programs is much larger than its impact on mean durations of times-to-degree.