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Biomedical subjects

U Andersen

Publications and source records attributed to U Andersen.

7 recordsLinked to original sources
PubMed2002

Surpassing the standard quantum limit for optical imaging using nonclassical multimode light.

Using continuous wave superposition of spatial modes, we demonstrate experimentally displacement measurement of a light beam below the standard quantum limit. Multimode squeezed light is obtained by mixing a vacuum squeezed beam and a coherent beam that are spatially orthogonal. Although the resultant beam is not squeezed, it is shown to have strong internal spatial correlations. We show that the position of such a light beam can be measured using a split detector with an increased precision compared to a classical beam. This method can be used to improve the sensitivity of small displacement measurements.

Journal Article↗
PubMed1999

Vacuum assisted venous drainage (VAVD).

Poor venous drainage is a common problem in cardiac surgery, causing trouble for the surgeon and adverse effects to the patient. Smaller incisions for minimally invasive cardiac surgery require smaller venous catheters. In this study the function, safety and possible benefits of a system for vacuum assisted venous drainage has been tested experimentally and applied clinically. A vacuum regulator ('The Hamlet box') and safety procedures were developed. The system was characterized in vitro in regard to the relationship between vacuum, catheter size, and blood temperature and flow. The clinical study included 54 adult patients, coronary artery bypass graft surgery and valve operations. Venous cannulation was bi-caval with two 24 Fr catheters. All the perfusions were essentially event free, and the system was easy to manage and regulate. Venous drainage was totally adequate, irrespective of the position of the heart, and less fluid was added during the perfusions (a median of 250 ml/patient compared to a median of 1000 ml/patient in the control group). There has been no evidence of increased haemolysis or other adverse effects. All patients were hospital survivors and had uneventful postoperative courses. Vacuum assisted venous drainage is now used routinely, and further studies are under way to develop the system and clarify the physiological effects.

Cardiac Surgical Procedures↗
PubMed1994

Survival analysis and neural nets.

We consider feed-forward neural nets and their relation to regression models for survival data. We show how the back-propagation algorithm may be used to obtain maximum likelihood estimates in certain standard regression models for survival data, as well as in various generalizations of these. Examples concerning malignant melanoma and post-partum amenorrhoea during lactation are used as illustration. We conclude that although problems with the substantial number of parameters and their interpretation remain, the feed-forward neural network models are flexible extensions to the standard regression models and thereby candidates for use in prediction and exploratory analyses in larger data sets.

Algorithms↗