Showing papers by "Aarhus University published in 1991"

Unbiased stereological estimation of the total number of neurons in the subdivisions of the rat hippocampus using the optical fractionator

Abstract: A stereological method for obtaining estimates of the total number of neurons in five major subdivisions of the rat hippocampus is described. The new method, the optical fractionator, combines two recent developments in stereology: a three-dimensional probe for counting neuronal nuclei, the optical disector, and a systematic uniform sampling scheme, the fractionator. The optical disector results in unbiased estimates of neuron number, i.e., estimates that are free of assumptions about neuron size and shape, are unaffected by lost caps and over-projection, and approach the true number of neurons in an unlimited manner as the number of samples is increased. The fractionator involves sampling a known fraction of a structural component. In the case of neuron number, a zero dimensional quantity, it provides estimates that are unaffected by shrinkage before, during, and after processing of the tissue. Because the fractionator involves systematic sampling, it also results in highly efficient estimates. Typically only 100–200 neurons must be counted in an animal to obtain a precision that is compatible with experimental studies. The methodology is compared with those used in earlier works involving estimates of neuron number in the rat hippocampus and a number of new stereological methods that have particular relevance to the quantitative study of the structure of the nervous system are briefly described in an appendix.

Non-Interactive and Information-Theoretic Secure Verifiable Secret Sharing

Abstract: It is shown how to distribute a secret to n persons such that each person can verify that he has received correct information about the secret without talking with other persons. Any k of these persons can later find the secret (1 ? k ? n), whereas fewer than k persons get no (Shannon) information about the secret. The information rate of the scheme is 1/2 and the distribution as well as the verification requires approximately 2k modular multiplications pr. bit of the secret. It is also shown how a number of persons can choose a secret "in the well" and distribute it veritably among themselves.

A threshold cryptosystem without a trusted party

Abstract: In a threshold cryptosystem n members share the secret key of an organization such that k members (1 ≤ k ≤ n) must cooperate in order to decipher a given ciphertext. In this note it is shown how to implement such a scheme without having a trusted party, which selects the secret key and distributes it to the members. In stead, the members choose the secret key and distributes it verifiably among themselves. Subsequently, this key can be used for authentication as well as secret communication.

Coloured Petri Nets: a high level language for system design and analysis

Abstract: This paper describes how Coloured Petri Nets (CP-nets) have been developed — from being a promising theoretical model to being a full-fledged language for the design, specification, simulation, validation and implementation of large software systems (and other systems in which human beings and/or computers communicate by means of some more or less formal rules).

Towards Practical Public Key Systems Secure Against Chosen Ciphertext Attacks

Abstract: We present two efficient constructions aimed at making public key systems secure against chosen ciphertext attacks. The first one applies to any deterministic public key system and modifies it into a system that is provably as hard to break under a passive attack as the original one, but has the potential of making a chosen ciphertext attack useless to an enemy. The second construction applies to the El Gamal/Diffie-Hellman public key system. Again, the modified system is provably as hard to break under a passive attack as the original one, and under an additional cryptographic assumption, a chosen ciphertext attack is provably useless to an enemy. We also point out a connection between such public-key systems and efficient identification schemes.

Interactive systems: bridging the gaps between developers and users

Abstract: Three development contexts are examined to provide a framework for understanding interactive software development projects. These contexts are the competitively bid, commercial product, and in-house/custom contexts development. Factors influencing interactive systems development are examined. Specific strategies to cope with the gaps between developers and prospective users are explored at the general level of the three development paradigms. >

Pathways and microbiology of thiosulfate transformations and sulfate reduction in a marine sediment (kattegat, denmark)

Abstract: Reductive and oxidative pathways of the sulfur cycle were studied in a marine sediment by parallel radiotracer experiments with SO(4), H(2)S, and S(2)O(3) injected into undisturbed sediment cores. The distributions of viable populations of sulfate- and thiosulfate-reducing bacteria and of thiosulfate-disproportionating bacteria were concurrently determined. Sulfate reduction occurred both in the reducing sediment layers and in oxidized and even oxic surface layers. The population density of sulfate-reducing bacteria was >10 cm in the oxic layer, high enough that it could possibly account for the measured rates of sulfate reduction. The bacterial numbers counted in the reducing sediment layers were 100-fold lower. The dominant sulfate reducers growing on acetate or H(2) were gas-vacuolated motile rods which were previously undescribed. The products of sulfide oxidation, which took place in both oxidized and reduced sediment layers, were 65 to 85% S(2)O(3) and 35 to 15% SO(4). Thiosulfate was concurrently oxidized to sulfate, reduced to sulfide, and disproportionated to sulfate and sulfide. There was a gradual shift from predominance of oxidation toward predominance of reduction with depth in the sediment. Disproportionation was the most important pathway overall. Thiosulfate disproportionation occurred only as cometabolism in the marine acetate-utilizing sulfate-reducing bacteria, which could not conserve energy for growth from this process alone. Oxidative and reductive cycling of sulfur thus occurred in all sediment layers with an intermediate "thiosulfate shunt" as an important mechanism regulating the electron flow.

Object-oriented type inference

Abstract: We present a new approach to inferring types in untyped object-oriented programs with inheritance, assignments, and late binding. It guarantees that all messages are understood, annotates the program with type information, allows polymorphic methods, and can be used as the basis of an optimizing compiler. Types are finite sets of classes and subtyping is set inclusion. Using a trace graph, our algorithm constructs a set of conditional type constraints and computes the least solution by least fixed-point derivation.

Hierarchies in Coloured Petri Nets

Abstract: The paper shows how to extend Coloured Petri Nets with a hierarchy concept. The paper proposes five different hierarchy constructs, which allow the analyst to structure large CP-nets as a set of interrelated subnets (called pages). The paper discusses the properties of the proposed hierarchy constructs, and it illustrates them by means of two examples. The hierarchy constructs can be used for theoretical considerations, but their main use is to describe and analyse large real-world systems. All of the hierarchy constructs are supported by the editing and analysis facilities in the CPN Palette tool package (see [1–5]).

Volatile Organic Compounds, Indoor Air Quality and Health

Abstract: This publication summarizes field investigations and controlled experiments on the relation between low levels of indoor air pollution with volatile organic compounds (VOC) and human health and comfort. The Henle-Kock criteria from epidemiology are revised for the dose-response relation between VOC's and health as comfort effects and existing evidence for each criterion are discussed. A biological model for human responses is suggested, based on three mechanisms: sensory perception of the environment, weak inflammatory reactions, and environmental stress reactions. Further, the TVOC-indicator concept for exposure is discussed. The conclusion is that no experimental or field data contradict the proposed causality. On the contrary, evidence supports the suggested causality. The biological model, however, is not yet based on acceptable measures of the variables for exposures, co-variables or health effects. A tentative guideline for VOC's in non-industrial indoor environments is suggested. The no-effect level seems to be about 0.2 mg/m3. A multi-factorial exposure range may exist between 0.2 and 3 mg/m3. Above 3 mg/m3 discomfort is expected.

Distributed provers with applications to undeniable signatures

Abstract: This paper introduces distributed prover protocols. Such a protocol is a proof system in which a polynomially bounded prover is replaced by many provers each having partial information about the witness owned by the original prover. As an application of this concept, it is shown how the signer of undeniable signatures can distribute part of his secret key to n agents such that any k of these can verify a signature. This facility is useful in most applications of undeniable signatures, and as the proposed protocols are practical, the results in this paper makes undeniable signatures more useful. The first part of the paper describes a method for verifiable secret sharing, which allows non-interactive verification of the shares and is as secure as the Shamir secret sharing scheme in the proposed applications.

Sulfide oxidation in the anoxic Black Sea chemocline

Abstract: The depth distributions of O2 and H2S and of the activity of chemical or bacterial sulfide oxidation were studied in the chemocline of the central Black Sea. Relative to measurements from earlier studies, the sulfide zone had moved upwards by 20–50 m and was now (May 1988) situated at a depth of 81–99 m. Oxygen in the water column immediately overlying the sulfide zone was depleted to undetectable levels resulting in a 20–30-m deep intermediate layer of O2 - and H2S-free water. Radiotracer studies with 35S-labelled H2S showed that high rates of sulfide oxidation, up to a few micromoles per liter per day, occurred in anoxic water at the top of the sulfide zone concurrent with the highest rates of dark CO2 assimilation. The main soluble oxidized products of sulfide were thiosulfate (68–82%) and sulfate. Indirect evidence was presented for the formation of elemental sulfur which accumulated to a maximum of 200 nmol l−1 at the top of the sulfide zone. Sulfide oxidation was stimulated by particles suspended at the chemocline, probably by bacteria. Green phototrophic sulfur bacteria were abundant in the chemocline, suggesting that photosynthetic H2S oxidation took place. Flux calculations showed that the measured H2S oxidation rates were 4-fold higher than could be explained by the downward flux of organic carbon and too high to balance the availability of electron acceptors such as oxidized iron or manganese. A nitrate maximum at the lower boundary of the O2 zone did not extend down to the sulfide zone.

Designing for cooperation: cooperating in design

Abstract: This article will discuss how to design computer applications that enhance the quality of work and products, and will relate the discussion to current themes in the field of Computer-Supported Cooperative Work (CSCW). Cooperation is a key element of computer use and work practice, yet here a specific “CSCW approach is not taken.” Instead the focus is cooperation as an important aspect of work that should be integrated into most computer support efforts in order to develop successful computer support, however, other aspects such as power, conflict and control must also be considered.

Cooperative prototyping: users and designers in mutual activity

Abstract: In most development projects, descriptions and prototypes are developed by system designers on their own utilizing users as suppliers of information on the use domain. In contrast, we are proposing a cooperative prototyping approach where users are involved actively and creatively in design and evaluation of early prototypes. This paper illustrates the approach by describing the design of computer support for casework in a technical department of a Danish municipality. Prototyping is viewed as an ongoing learning process, and we analyse situations where openings for learning occur in the prototyping activity. The situations seem to fall into four categories: (1) Situations where the future work situation with a new computer application is simulated to some extent to investigate the future work activity; (2) situations where the prototype is manipulated and used as a basis for idea exploration; (3) situations focusing on the designers' learning about the users' work practice; (4) situations where the prototyping tool or the design session as such becomes the focus. Lessons learned from the analysis of these situations are discussed. In particular we discuss a tension between the need for careful preparation of prototyping sessions and the need to establish conditions for user and designer creativity. Our conclusion is that users and designers should prepare to learn from breakdowns and focus shifts in cooperative prototyping sessions rather than trying to avoid them.

Evolution of the MIP family of integral membrane transport proteins.

Abstract: Six integral membrane proteins of bacterial, animal, and plant origin, which are believed to function in solute transport, share sequence identity and are grouped together as members of the MIP family. These include the Escherichia coli glycerol facilitator, the major intrinsic protein from bovine lens fibre junction membranes, a plant tonoplast membrane protein, a soybean protein from the peribacteroid membrane, and a Drosophila neurogenic protein. These proteins, each of which appears to consist of six transmembrane helical segments per subunit, apparently arose by internal duplication of a three-transmembrane segment. Phylogenetic 'trees' interrelating these proteins and segments are presented.

Causes and prevention.

Abstract: .n important aim in epidemiology is not -only to lentify causes of diseases but also to quantify their nportance to society. However, to identify and uantify causes one needs an idea of the concept of cause” as it relates to research and in daily practice. )ur understanding of causes influences our undertanding of terms like aetiological fractions and meaures of susceptibility. Furthermore, the concept is I f importance in designing studies in epidemiology md for success in the implementation of preventive ictions. It often seems difficult to persuade people o change unhealthy behaviours if our concept of iisease aetiology is in conflict with a common sense :oncept of cause. The concept of cause has long been debated by philosophers. Many claim that it is a waste of time to try to reach a common definition for such a complicated term which we all “understand” anyway. When we step on the brake, the car stops. When we turn on the tap, the water starts running. We see causes as events that precede a given effect in time and the cause-effect relationship is asymmetric. If A then B does not entail, if B then A. If traffic accident then a broken leg does not translate into, if a broken leg then the cause was a traffic accident. Our common sense understanding 01 causes is probably being instilled during our upbringing. When we explored our surrbundings in early childhood we discovered that the light could be turned on by manipulating the light switch in a certain way. Later we realized that the mechanism is a bit more complicated. Pressing the switch is only a cause of turning on the light, which in turn is dependent on a given set of conditions. The electrical power must be on, and the light bulb, and the electrical cord must be in order. We accept that, these conditions (additional component causes) fulfilled, pressing of the switch turns on the light. We have identified a cause and the effect and it always works; if not, we expect to find the reason when examining the other component causes in the causal field.

Projective Reed-Muller codes

Abstract: A class of codes in the Reed-Muller family, the projective Reed-Muller codes (PRM codes), is studied. The author defines the PRM codes of all orders and discusses their relation to polynomial codes. The exact parameters of PRM codes are given. The duals are characterized, and, in parallel to the classical works on generalized Reed-Muller codes, the cyclic properties are studied. Tables over parameters of the codes are given. >

The anabolic effects of human parathyroid hormone (hPTH) on rat vertebral body mass are also reflected in the quality of bone, assessed by biomechanical testing: a comparison study between hPTH-(1-34) and hPTH-(1-84).

Abstract: PTH has a proven anabolic effect on bone mass, as has been shown in several animal models and treatment regimens. The aim of this study was to ascertain whether the positive effect on bone mass is also reflected in the quality of bone formed. The study was performed in a rat model using human PTH (hPTH). One hundred and twenty male Wistar rats, divided into 10 groups, were given either hPTH-(1-34) or hPTH-(1-84) in daily sc doses. Dose levels ranged from 0.11-3.00 nmol/100 g BW.day for a period of 30 days. At death all six lumbar vertebrae were obtained from each rat. A combination of methods was applied to these vertebral bodies in order to ascertain the effect of hPTH on vertebral bone volume, density, trabecular structure, and biomechanical competence. The results revealed a dose-dependent increase in total volume, dry weight, ash weight, and trabecular bone volume. Also, a dose-dependent increase in load values could be demonstrated. The increase in bone strength remained significant after normalization for both cross-sectional area and bone mass. This indicates that the increase in bone size and bone mass was not achieved at the expense of the quality of the bone present. When the two treatments were administered at the same molar dose level, no difference between hPTH-(1-34) and hPTH-(1-84) was revealed. On the basis of this study, it is concluded that PTH could prove to be a promising treatment in the management of osteopenic states.

A review of recent progress in our understanding of aeolian sediment transport

Abstract: We review recent progress in our understanding of aeolian sediment transport, with emphasis on work published since 1985. The current conceptual model of sediment transport is discussed at length, with attention given to problems of definition that have arisen. We discuss in depth the collision (grain impact) and aerodynamic entrainment (initial motion) processes. The effect of the evolving population of moving grains on the wind (the wind feedback mechanism) is treated in the context of recent modelling of the self-regulating saltation process. The link between saltation and suspension is discussed briefly. We conclude by outlining future research directions that must involve a greater symbiosis of experimentalists and theoreticians, working both at the grain and the bedform scales.