On structural properties of the value function for an unbounded jump Markov process with an application to a processor sharing retrial queue

The derivation of structural properties for unbounded jump Markov processes cannot be done using standard mathematical tools, since the analysis is hindered due to the fact that the system is not uniformizable. We present a promising technique, a smoothed rate truncation method, to overcome the limitations of standard techniques and allow for the derivation of structural properties. We introduce this technique by application to a processor sharing queue with impatient customers that can retry if they renege. We are interested in structural properties of the value function of the system as a function of the arrival rate.     

Solving a bi-criterion cutting stock problem with open-ended demand: a case study

We consider a real-life cutting stock problem with two types of orders. All orders have to be cut from a given number of raws (also known as stock unit, master reel or jumbo). For each order the width of the final (also known as reels or units) and the number of finals is given. An order is called an exact order when the given number of finals must be produced exactly. An order is called an open order when at least the given number of finals must be produced. There is a given maximum on the number of finals that can be produced from a single raw which is determined by the number of knives on the machine. A pattern specifies the number of finals of a given width that will be produced from one raw. A solution consists of specifying a pattern for each raw such that in total the number of finals of exact orders is produced exactly and at least the number of finals of open orders is produced. There are two criteria defined for a solution. One criterion is the cutting loss: the total width of the raws minus the total width of the produced finals. The second criterion is the number of different patterns used in the solution. We describe a branch-and-bound algorithm that produces all Pareto-optimal solutions.     

Genetics education for non-genetic health care professionals in the Netherlands (2002)

OBJECTIVE: The aim of the present study was to investigate whether medical care providers in the Netherlands are adequately educated in genetics by collecting information about the current state of genetics education of non-genetics health care professionals. METHOD: The curricula of the 8 universities providing medical education and of all varieties of specialised medical training were examined for the year 2002. RESULTS: In most universities, the number of hours spent on genetics education is small, and genetics is relatively invisible, being integrated within several courses, comprising only a small proportion of the total course (a mean of 8%). Only 3 of the programmes for medical specialist training and the training of medical doctors for mentally handicapped people indicated a formal genetics education programme. Continued education courses on genetics are offered irregularly. Training in midwifery involves at least 3 weeks of genetics education. Courses on genetics are offered frequently to practicing midwives. CONCLUSION: There appear to be no general, nationally defined final goals for education in genetics for non-genetics health care professionals in the Netherlands. Furthermore, the lack of visibility of genetics in medical education in the Netherlands was striking.     

Liquid chromatographic assay for the protease inhibitor atazanavir in plasma

Atazanavir is the most recently introduced protease inhibitor for the suppression of the anti-human immunodeficiency virus. A sensitive and selective reversed-phase liquid chromatographic assay for this drug in human plasma has been developed and validated. Atazanavir was isolated from a 500 microL plasma sample using liquid-liquid extraction with dichloromethane. After evaporation and reconstitution of the extract the sample was analysed using liquid chromatography and ultraviolet detection at 280 nm. In the evaluated concentration range (44-4395 ng/mL atazanavir), intra-day precisions were < or =7% and inter-day precisions were < or =14%. Accuracies between 96 and 106% were found. The lower limit of quantification was 44 ng/mL with an intra-day precision of 7%, an inter-day precision of 14% and an accuracy of 87%. There was no interference from 32 tested potentially co-administrated drugs and metabolites. The usefulness of the assay was demonstrated for samples obtained from an HIV-infected patient treated with atazanavir.     

Laser Doppler perfusion imaging with a complimentary metal oxide semiconductor image sensor

We utilized a complimentary metal oxide semiconductor video camera for fast flow imaging with the laser Doppler technique. A single sensor is used for both observation of the area of interest and measurements of the interference signal caused by dynamic light scattering from moving particles inside scattering objects. In particular, we demonstrate the possibility of imaging the distribution of the moving red blood cell concentration. This is a first step toward laser Doppler imaging without scanning parts, leading to a much faster imaging procedure than with existing mechanical laser Doppler perfusion imagers.     

Finite element modeling and intravascular ultrasound elastography of vulnerable plaques: parameter variation

BACKGROUND AND GOAL: More than 60% of all myocardial infarction is caused by rupture of a vulnerable plaque. A vulnerable plaque can be described as a large, soft lipid pool covered by a thin fibrous cap. Plaque material composition, geometry, and inflammation caused by infiltration of macrophages are considered as major determinants for plaque rupture. For diagnostic purposes, these determinants may be obtained from elastograms (i.e. radial strain images), which are derived from intravascular ultrasound (IVUS) measurements. IVUS elastograms, however, cannot be interpreted directly as tissue component images, because radial strain depends upon plaque geometry, plaque material properties, and used catheter position. To understand and quantify the influence of these parameters upon measured IVUS elastograms, they were varied in a finite element model (FEM) that simulates IVUS elastograms of vulnerable plaques. MATERIALS AND METHODS: IVUS elastography measurements were performed on a vessel mimicking phantom, with a soft plaque embedded in a hard wall, and an atherosclerotic human coronary artery containing a vulnerable plaque. Next, FEMs were created to simulate IVUS elastograms of the same objects. In these FEMs the following parameters were varied: Young's modulus (E), Poisson's ratio (nu) in range 0.49-0.4999, catheter position (translation of 0.8 mm), and cap thickness (t) in range 50-350 microm. Hereby the resulting peak radial strain (PRS) was determined and visualized. RESULTS: Measured static E for phantom was 4.2 kPa for plaque and 16.8 kPa for wall.Variation of E-wall in range 8.4-33.2 kPa and/or E-plaque in range 2.1-8.4 kPa using the phantom FEM, gave a PRS variation of 1.6%, i.e. from 1.7% up to almost 3.3%; for variation in nu this was only 0.07%, i.e. from 2.37% up to 2.44%. Variation of E-lipid in range 6.25-400 kPa and E-cap in range 700-2300 kPa using the artery FEM, gave a PRS variation of 3.1%, i.e. from 0.6% up to 3.7%. The PRS was higher for lower E-lipid and E-cap; it was located at a shoulder of the lipid pool. Variation of nu gave only a variation of 0.17%. Variation of t and E-cap resulted in a PRS variation of 1.4%, i.e. from 0.3% up to 1.7%; thinner and weaker caps gave higher PRS. Catheter position variation changed radial strain value. CONCLUSIONS: Measured IVUS elastograms of vulnerable plaques depend highly upon the Young's modulus of lipid and cap, but not upon the Poisson's ratio. Different catheter positions result in different IVUS elastograms, but the diagnostically important high strain regions at the lipid shoulders are often still detectable. PRS increases when cap weakens or cap thickness decreases.