Robust risk aggregation with neural networks

We consider settings in which the distribution of a multivariate random variable is partly ambiguous. We assume the ambiguity lies on the level of the dependence structure, and that the marginal distributions are known. Furthermore, a current best guess for the distribution, called reference measure, is available. We work with the set of distributions that are both close to the given reference measure in a transportation distance (e.g., the Wasserstein distance), and additionally have the correct marginal structure. The goal is to find upper and lower bounds for integrals of interest with respect to distributions in this set. The described problem appears naturally in the context of risk aggregation. When aggregating different risks, the marginal distributions of these risks are known and the task is to quantify their joint effect on a given system. This is typically done by applying a meaningful risk measure to the sum of the individual risks. For this purpose, the stochastic interdependencies between the risks need to be specified. In practice, the models of this dependence structure are however subject to relatively high model ambiguity. The contribution of this paper is twofold: First, we derive a dual representation of the considered problem and prove that strong duality holds. Second, we propose a generally applicable and computationally feasible method, which relies on neural networks, in order to numerically solve the derived dual problem. The latter method is tested on a number of toy examples, before it is finally applied to perform robust risk aggregation in a real-world instance.

Modelling and simulation of the TLR4 pathway with coloured petri nets

This paper demonstrates the first steps of an automation process to develop models of signal transduction pathways using discrete modelling languages. The whole approach consists of modelling, validation, animation, linking databases to simulation tools and also the qualitative analysis of the data. In this paper, we detail the modelling and simulation of the TLR4 pathway with a coloured petri net simulation tool and the validation of this model against the semantic and mechanistic map from a biological database. These graphical maps contain all necessary reactions as a figure. We start with an UML class diagram to understand the static structure of molecules involved in the TLR4 pathway. Afterwards we model and simulate each "pathway step reaction" - one after another - to get the behaviour of the final system. The result is a model of the pathway which can be used in simulations, derived solely from basic chemical reactions in the database. Also, it is a lesson on critical points where human decision-making is needed, because not all the required information is stored directly in the database.

Clinical and genetic analysis of Staphylococcus aureus nasal colonisation and exit-site infection in patients undergoing peritoneal dialysis

Few data exist regarding the clonal identity of Staphylococcus aureus (SA) that colonises the nostrils and causes exit-site infections in peritoneal dialysis patients. Nasal and exit-site swabs were taken monthly from 41 patients undergoing peritoneal dialysis, and a genetic analysis of SA isolates was performed by pulsed-field-gel electrophoresis. When SA was identified at the exit-site, the clonal identity of nasal and exit-site isolates was demonstrated. In 50% of the SA carriers, nasal isolates were genetically constant over time; in the other 50% a change of colonising SA strains was observed. The risk of exit-site infection was identical in both groups.

[Value of ultrasound after endoprosthesis implantation of the knee joint]

PURPOSE

Ultrasound is often applied in the course of treatment after knee arthroplasty, although sonographic normal findings have not been described so far. Characterising these and comparing them to clinical disorders was the purpose of this study. Intra- and extra-articular hematoma and the imaging of the traumatised extension apparatus of the knee joint were of special interest.

METHODS

During 4 weeks all consecutive patients after knee arthroplasty were examined clinically and sonographically. Furthermore, the blood parameters were controlled for signs of inflammation or coagulation disorders. These findings were then re-checked before the end of hospital rehabilitation treatment.

RESULTS

In all of the patients, ultrasound revealed intra-articular fluid at the beginning and at the end of hospital treatment. The fluid area, differing in extension, was markedly reduced or showed less echogenicity concomitant with an organisation. The patellar tendon in all of the patients showed a loss of echogenicity at the site of operative incision, mostly at the patellar insertion, and a thickening extending throughout the middle part of the tendon even at control. Dynamic ultrasound examination displayed one case of a major defect which had to be revised. Blood parameters of inflammation were decreased, coagulation parameters were normal.

CONCLUSION

After knee arthoplasty, extended intra-articular knee hematomas are not rare, only being resorbed or organised to a small degree during a rehabilitation period of three weeks, therefore not yielding relevant information for the course of treatment.

CLINICAL RELEVANCE

The patellar ligaments show alterations comparable to acute tendopathy, thus not recommending use of maximal forces or too high stretching of the tendon tissue. Soft tissue defects with the need for interruption of the rehabilitation programme may be detected sonographically. Further studies will be necessary to explore the course of restructuring. Disorders of patellar sliding movement and signs of prosthetic loosening cannot be sufficiently judged at the present time.

[Electroretinography study of unanesthetized young children]

BACKGROUND

The electroretinogram (ERG) ist an important examination method for the evaluation of retinal dysfunction in children. However it is often difficult and sometimes almost impossible to examine especially younger children with usual methods. Because of its risks, general anesthesia is rarely used.

METHODS

ERG examinations were performed without general anesthesia or sedation with DTL (Dawson-Trick-Litzkow) electrodes. These are conjunctival electrodes made of thin microfibers. Several additional modifications of the standard examination technique were utilized, which enabled us to examine children of almost any age. 10 volunteers and 34 children between 6 month and 9 years of age were examined.

RESULTS

62 eyes of 34 children were evaluated. The diagnostic problem could be solved in three quarters of the patients with the ERG.

CONCLUSION

With the DTL electrode and some methodical changes in the standard ERG technique it is possible to perform ERG's in little children without anesthesia or sedation. This method can be applied in children over 2 years of age. Below this age an sedation of any kind is necessary.