Showing papers by "Aalborg University published in 1989"

HUGIN: a shell for building Bayesian belief universes for expert systems

Abstract: Causal probabilistic networks have proved to be a useful knowledge representation tool for modelling domains where causal relations in a broad sense are a natural way of relating domain objects and where uncertainty is inherited in these relations. This paper outlines an implementation the HUGIN shell - for handling a domain model expressed by a causal probabilistic network. The only topological restriction imposed on the network is that, it must not contain any directed loops. The approach is illustrated step by step by solving a genetic breeding problem. A graph representation of the domain model is interactively created by using instances of the basic network components-- nodes and arcs--as building blocks. This structure, together with the quantitative relations between nodes and their immediate causes expressed as conditional probabilities, are automatically transformed into a tree structure, a junction tree. Here a computationally efficient and conceptually simple algebra of Bayesian belief universes supports incorporation of new evidence, propagation of information, and calculation of revised beliefs in the states of the nodes in the network. Finally, as an exam ple of a real world application, MUNIN an expert system for electromyography is discussed.

Risk theory in a Markovian environment

Abstract: We consider risk processes t t⩾0 with the property that the rate β of the Poisson arrival process and the distribution of B of the claim sizes are not fixed in time but depend on the state of an underlying Markov jump process {Zt } t⩾0 such that β=β i and B=Bi when Zt=i . A variety of methods, including approximations, simulation and numerical methods, for assessing the values of the ruin probabilities are studied and in particular we look at the Cramer-Lundberg approximation and diffusion approximations with correction terms. The mathematical framework is Markov-modulated random walks in discrete and continuous time, and in particular Wiener-Hopf factorisation problems and conjugate distributions (Esscher transforms) are involved.

Bisimulation Through Probabilistic Testing.

Abstract: We propose a language for testing concurrent processes and examine its strength in terms of the processes that are distinguished by a test. By using probabilistic transition systems as the underlying semantic model, we show how a testing algorithm can distinguish, with a probability arbitrarily close to one, between processes that are not bisimulation equivalent. We also show a similar result (in a slightly stronger form) for a new process relation called 2 3 - bisimulation —which lies strictly between that of simulation and bisimulation. Finally, the ultimately strength of the testing language is shown to identify a new process relation called probabilistic bisimulation—which is strictly stronger than bisimulation.

On fully automatic feature measurement for banded chromosome classification.

Abstract: Procedures for fully automatic location of chromosome axis and centromere in metaphase chromosomes are described for a practical interactive chromosome analysis system that omits the usual stages of interactive axis and centromere correction. Accuracy of centromere finding and consequential determination of a chromosome's polarity, i.e., which end is which, is measured experimentally. The saving in interaction by not correcting centromeres is compared to the increase in errors at the classification stage and the consequent increase in interaction needed to correct these errors. Some previously unreported features for banded chromosome classification are described, and in particular a set of global shape features is introduced. The discrimination capability of the feature measurements is evaluated by use of simple statistics and by reference to the performance of classifiers trained with various feature subsets. Class discrimination capability of the global shape feature set is shown to be comparable to that of centromere position, a widely used local shape feature. The variability of feature measurements that might occur in data from different laboratories on account of differing tissue, preparation methods, and digitiser hardware is assessed using three data bases of G-banded human metaphase cells. It is shown that the differences can be considerable and that appropriate feature selection and classifier training substantially improve classification performance.

Changes in muscle fiber conduction velocity, mean power frequency, and mean EMG voltage during prolonged submaximal contractions

Abstract: Average muscle fiber conduction velocity, mean power frequency, and mean EMG voltage have been measured in human vastus lateralis during prolonged isometric knee extensions at 10, 20, 30, and 40% of the maximum knee extension force. During contractions at 10 and 20% of maximum force, conduction velocity and mean power frequency rose as the contraction progressed, whereas the conduction velocity and mean power frequency fell at 30 and 40% of the maximum force. The mean EMG voltage rose during the contractions, with steeper increases for higher forces. It is argued that two principal factors influence the EMG during prolonged submaximal contractions: firstly, the fatigue of current active motor units, and, secondly, recruitment of fresh motor units. These factors act in opposition to muscle fiber conduction velocity. Recruitment gives an increase in average conduction velocity, whereas fatigue provokes a slowing in conduction velocity.

Measurement of muscle fiber conduction velocity in humans: techniques and applications.

Abstract: Different methods of measuring human muscle fiber conduction velocity (MFCV) are outlined. A major division can be made between invasive (needle) and noninvasive [surface electromyographic (EMG)] recording techniques. The benefits and limitations associated with the different approaches are discussed. The conduction velocity of individual muscle fibers are measurable with needle recordings on routine EMG apparatus. Velocities measured with electrical stimulation of single fibers or bundle of fibers are in general lower than recordings made during voluntary contraction. With surface EMG, an average estimate of the MFCV from many fibers and motor units can be determined with computerized data analyses--both frequency and time domain approaches. The cross-correlation method is widely used to calculate the time lag between two EMGs recorded along the muscle. Using the surface EMG-based methods, MFCV can be calculated at all contraction levels. Thus, the change in sarcolemmal function during local muscle fatigue can be assessed. Physiological factors influencing the MFCV and the utility of the MFCV estimation in clinical practice are discussed. Compared to nerve conduction velocity studies, the clinical interest in MFCV has been limited.

Bisimulation through probabilistic testing (preliminary report)

Abstract: We propose a language for testing concurrent processes and examine its strength in terms of the processes that are distinguished by a test. By using probabilistic transition systems as the underlying semantic model, we show how a testing algorithm with a probability arbitrary close to 1 can distinguish processes that are not bisimulation equivalent. We also show a similar result (in a slightly stronger form) for a new process relation called 2/3-bisimulation — lying strictly between that of simulation and bisimulation. Finally, the ultimately strength of the testing language is shown to identify an even stronger process relation, called probabilistic bisimulation.

Quality assurance guidelines for ESHO protocols

Abstract: (1989). Quality assurance guidelines for ESHO protocols. International Journal of Hyperthermia: Vol. 5, No. 4, pp. 421-428.

A munin network for the median nerve-a case study on loops

Abstract: Causal probabilistic networks have proved to be a useful knowledge representation tool for domains having a natural description in terms of causal relations involving uncertainty between domain concepts. This article describes a network modeling diseases affecting the median nerve. The qualitative structure of the model and the quantitative pathophysiological

Multicriterion structural optimization via bound formulation and mathematical programming

Abstract: Multicriterion structural optimization problems pertaining to minimization of the maximum (or maximization of the minimum) of a set of weighted criteria are considered. In order to alleviate the inherent difficulty of non-differentiability of min-max problems, we adopt a so-called “bound formulation” and show that this approach even provides us with a very simple means of performing a switch from a prescribed-resource to a cost-minimization formulation of a given type of problem. The bound approach was found very useful in admitting the treatment of min-max problems by usual variational analysis; we demonstrate in this paper that the technique is also extremely well-suited to mathematical programming. Illustrative examples are presented at the end of the paper.

Vascular response of human skin after analgesia with emla cream

Abstract: We investigated vascular responses after cutaneous application of EMLA cream (a eutectic mixture of lignocaine and prilocaine) by skin reflectance spectroscopy and laser Doppler blood flowmetry. In healthy subjects, EMLA cream produced a biphasic vascular response with an initial vasoconstriction, maximal after 1.5 h of application. After prolonged application (> 3 h, vasodilatation occurred, presumably because of a smooth muscle relaxant effect of the analgesics. Vasoconstriction was also observed initially with two non-EMLA creams applied under occlusion, whereas the occlusive plastic film alone did not alter the vascular state. Thus late vasodilatation was unique to EMLA cream.

Passive tension of the ankle before and after stretching

Abstract: The passive tension resulting from dorsiflexion of the ankle was measured in relation to stretching in six handball players and six soccer players. Corresponding values of ankle angle and passive tension were measured by a strain gauge and a potentiometer connected to a pedal system. The passive tension versus ankle angle was measured before and 90 minutes after a single contract-relax stretching program of the plantar flexors. Stretching lowered the passive tension by up to 18%. Contract-relax stretching performed twice a day for 3 weeks lowered the passive tension in the plantar flexors by up to 36%. Before the last measurements, no stretching was performed for 20 hours or more. Stretching thus had both a short-term effect, matching the length of a training session, and a long-term effect, shown in a reduction of passive tension after 3 weeks. The relative decrease in passive tension after stretching exercises was constant from a neutral position of the ankle to maximal dorsiflexion. There was no correlation between 1) flexibility and the short-term effect of stretching, 2) flexibility and the long-term effect of stretching, or 3) the short-term and long-term effects of stretching. This indicates that passive tension was decreased in all subjects irrespective of their flexibility, and that subjects who had short-term effects after stretching did not necessarily demonstrate a long-term effect.

Major Vascular Injury during Gynecologic Laparoscopy: Report of a case and review of published cases

Abstract: Serious complications following gynecologic laparoscopy are rare. We report a case of a 24-year-old woman who had a common iliac artery and vein injured by the trocar, resulting in deep shock. The arterial lesion was repaired with an allograft and the vein sutured. The patient recovered with light sequelae. The literature was reviewed and we found 15 cases described in varying detail. In most cases the injury was caused by the pneumoperitoneum-needle and in only 2 by the trocar. Characteristically the terminal aorta and its major branches were injured. All the patients had a large retroperitoneal hematoma and only minimal free blood in the peritoneum. Signs of bleeding were nearly always acute. Most lesions could be treated by simple suture. Recovery is the rule, but 2 of the 15 died. Examiner's experience and correct technique are important to prevent this potentially lethal complication which is also probably underreported.

Decomposition of maximum likelihood in mixed graphical interaction models

Abstract: SUMMARY We show how decompositions of marked graphs induce corresponding decompositions of maximum likelihood estimates in mixed graphical interaction models. We use this result to obtain explicit formulae for the estimates in decomposable models and to obtain factorizations of likelihood ratio statistics.

Changing smoking, drinking, and eating behaviour among pregnant women in Denmark. Evaluation of a health campaign in a local region.

Abstract: Health behaviour during pregnancy was examined before and after a comprehensive health campaign targeted at pregnant women in Odense, Denmark Furthermore, lifestyle habits were compared before and during the campaign with similar habits in Aalborg, Denmark All 13,815 pregnant women (equal numbers from each city) were enrolled in the study, and 11,980 gave information on eating, drinking, and smoking habits during pregnancy Data collection in both cities took place from April 1984 to April 1987 The campaign, which was entitled "Healthy Habits for Two", ran from April 1985 to April 1987 in the city of Odense only No significant change in health behaviour in the Odense area was noted after the start of the campaign

Germ cell function and hormonal status in patients with testicular cancer.

Abstract: Sperm counts, serum gonadotropins, and androgen levels were investigated in 39 seminoma patients and 58 patients with a nonseminomatous germ cell tumor of the testis after unilateral orchiectomy. In 58% of the patients, the total sperm count was below the lower reference value (80 million). A multiregression analysis demonstrated a correlation between a decreased total sperm count and the following three explanatory variables: (1) an elevated serum alpha-fetoprotein (AFP), (2) a history of chryptorchidism, or (3) a seminomatous tumor. In 42% of the patients, the sperm concentration and the sperm motility met criteria considered sufficient for cryopreservation. Serum follicle-stimulating hormone (FSH) was elevated in 33% of the patients. Androgens (serum testosterone [T] or urine 17-oxy-steroids [17-OS]) were subnormal in 5% of the patients, whereas serum luteinizing hormone (LH) was elevated in 14% of the patients without human chorionic gonadotropin beta-subunit (beta-HCG) in serum.

Mechanical and electromyographic responses to stretch of the human anterior tibial muscle at different levels of contraction.

Abstract: The EMG response and the mechanical response to 2 degree stretch of the human anterior tibial muscle was studied during contractions ranging from 0% to 80% of maximal voluntary contraction (MVC). The EMG response showed three distinct peaks M1, M2, and M3 with peak latencies of 59 ms, 86 ms, and 120 ms respectively. At low background torques M1 dominated while M2 and M3 were small or absent. M2 and M3 dominated above 40% of MVC and M2 in particular showed "automatic gain compensation", i.e. it constituted a - more or less - constant proportion of the background EMG for all contraction levels. The ratio between M1 amplitude and background EMG steadily decreased with contraction level. Even though the summed contributions of M1, M2, and M3 to some degree showed automatic gain compensation, this was not the case for the mechanical response to stretch. Between 0% and 30% of MVC the reflex mediated mechanical response increased approximately in proportion to the contraction level, but the reflex mediated mechanical response peaked at 40% of MVC and declined to zero at 80% of MVC. This discrepancy between EMG and mechanical response was explained by a simple model. The regression line between rectified and filtered tibialis anterior EMG and torque was used to predict the mechanical response from the EMG response. At increasing contraction levels the twitch elicited by supramaximal electrical stimulation decreases, and we reduced the predicted mechanical response by the same factor as the twitch.(ABSTRACT TRUNCATED AT 250 WORDS)

On Accuracy Problems for Semi-Analytical Sensitivity Analyses

Abstract: The semi-analytical method of sensitivity analysis combines ease of implementation with computational efficiency. A major drawback to this method, however, is that severe accuracy problems have recently been reported. A complete error analysis for a beam problem with changing length is carried out in this paper. It is shown that the sensitivity error is proportional to the relative length difference, but in agreement with Eq. 3.8. The approximate pseudo loads thus violate moment equilibrium for rigid body motion while the correct pseudo loads do not. It might be a good idea to modify the approximate pseudo loads in order to obtain general load equilibrium with rigid body motions. Such a method would be readily applicable for any element type, whether analytical expressions for the element stiffnesses are available or not. This topic is postponed for a future study.

Back to thinking mode: diaries for the management of information systems development projects

Abstract: From a practical point of view, systems development methods are important sources of inspiration for the planning and establishment projects, but only to a limited extent do they support the reflections and actions of the participants. We propose the use of diaries as a supplement to conventional methods of reflection on what actually happens and what could happen during the course of a project, i.e., we propose diaries as a medium for the management of information systems development projects. This idea is based on an exploratory study carried out in co-operation with a bank and a research department, and the idea is supported by theoretical arguments from different fields. In conclusion, some practical advice on how to use diaries is given together with some questions for further investigation.

Modulation of type I immediate and type IV delayed immunoreactivity using direct suggestion and guided imagery during hypnosis.

Abstract: Cutaneous reactivity against histamine skin prick test (Type I) and purified tuberculin protein derivative (Mantoux reaction, Type IV) was studied in eight volunteers under hypnosis. Types I and IV immunoreactivity were modulated by direct suggestion (Type I) and guided imagery (Type IV). The volunteers were highly susceptible subjects, selected by means of the Harvard Group Scale of Hypnotic Susceptibility, Form A. When the volunteers underwent hypnotic suggestion to decrease the cutaneous reaction to histamine prick test, a significant (P less than 0.02) reduction of the flare reaction (area of erythema) was observed compared with control histamine skin prick tests. The wheal reaction did not respond to hypnotic suggestion. Neither wheal nor flare reaction could be increased in size by hypnotic suggestion compared with control histamine skin prick tests. A hypnotic suggestion of increasing the Type IV reaction on one arm and decreasing the reaction on the other revealed a significant difference in both erythema size (P less than 0.02) and palpable induration (P less than 0.01). In two cases the reactions were monitored by laser doppler blood flowmetry and skin thickness measurement by ultrasound. The difference between the suggested increased and decreased reaction was 19% for the laser doppler bloodflow (in favor of the augmented side), and 44% for the dermal infiltrate thickness. This study objectively supports the numerous uncontrolled case reports of modulation of immunoreactivity in allergic diseases involving both Type I and Type IV skin reactions following hypnotic suggestions.

Paroxetine: pharmacokinetic and antidepressant effect in the elderly

Abstract: To evaluate the pharmacokinetic properties, efficacy, and tolerability of paroxetine in elderly depressed patients, a clinical study was set up - initially at Aalborg Psychiatric Hospital in Denmar ...

Testicular Function in Patients With Testicular Cancer Treated With Orchiectomy Alone or Orchiectomy Plus Cisplatin-Based Chemotherapy

Abstract: Gonadal function was evaluated in 25 patients with metastatic testicular cancer who were treated with orchiectomy plus chemotherapy with cisplatin, vinblastine, and bleomycin (PVB) and in 21 patients with clinical stage I disease who were treated only with orchiectomy and then kept under surveillance. Four years after PVB treatment, none of the patients were azoospermic; after 5 years, the total sperm counts in 46% of the patients had reached their pretreatment levels. In the group under surveillance, sperm counts below the reference level persisted or developed in 55% of the patients. Sperm production was similar in the two groups of patients 1.5 years after treatment and beyond. We conclude that spermatogenesis is not restored in all patients treated with PVB because of both preexisting germ cell defects and treatment toxicity.

Double-blind study of naproxen vs placebo in the treatment of acute migraine attacks

Abstract: Naproxen was compared with placebo in a double-blind, crossover trial in classic and common migraine. The trial was terminated at a fixed date; 37 patients had entered, 5 of whom were excluded. Naproxen was given as 750 mg at the first symptom of the attack, a total of 1250 mg per 24 h was allowed. Patients were followed for six attacks or three months in each phase, whichever came first. The severity of the headache was significantly less with naproxen in the first 2 h of the attack (p = 0.047), whereas there was no difference when the whole attack was considered. Significantly more patients preferred naproxen (p = 0.042). Side effects occurred in five patients, causing withdrawal of one patient while on naproxen.

Quantitation of the stretch reflex. Technical procedures and clinical applications.

Abstract: The stretch reflex should ideally be quantitated for better clinical use by standardizing the muscle stretch and measuring the resulting muscle contraction. Quantitation of muscle contraction can be done by force measurements or electromyographic recordings. The electromyographic response to stretch consists of one component (short latency response) for short stretches (less than 15 ms) and of 2 or 3 components (short and long latency responses) for longer stretches (greater than 40-50 ms). The magnitude of the phasic stretch reflex is reflected by the short latency response, whereas the magnitude of the tonic stretch reflex is reflected by both the short and the long latency responses. In clinical studies of upper motor neuron syndromes, the knee jerk and the muscle tone correlated with the magnitude of the short latency response. In patients with paralysis agitans an increased long latency response, which correlated to the rigidity, was found.

Incidence and prevalence of motor neuron disease in two Danish counties.

Abstract: A total of 186 cases of motor neuron disease (MND) was identified in two Danish counties during the period 1974–1986. The average annual incidence rate was 1.4/100,000 population, and the male:female