We study layered queueing systems comprised two interlacing finite M/M/• type queues, where users of each layer are the servers of the other layer. Examples can be found in file sharing programs, SETI@home project, etc. Let Li denote the number of users in layer i, i=1, 2. We consider the following operating modes: (i) All users present in layer i join forces together to form a single server for the users in layer j (j≠i), with overall service rate μjLi (that changes dynamically as a function of the state of layer i). (ii) Each of the users present in layer i individually acts as a server for the users in layer j, with service rate μj.

These operating modes lead to three different models which we analyze by formulating them as finite level-dependent quasi birth-and-death processes. We derive a procedure based on Matrix Analytic methods to derive the steady state probabilities of the two dimensional system state. Numerical examples, including mean queue sizes, mean waiting times, covariances, and loss probabilities, are presented. The models are compared and their differences are discussed.

We consider a system consisting of a single server serving a fixed number of stations. At each station, there is an infinite queue of customers that have to undergo a preparation phase before being served. This model is connected to layered queueing networks, to an extension of polling systems and surprisingly to random graphs. We are interested in the waiting time of the server. For the case where the server polls the stations cyclically, we give a sufficient condition for the existence of a limiting waiting-time distribution and we study the tail behavior of the stationary waiting time. Furthermore, assuming that preparation times are exponentially distributed, we describe in depth the resulting Markov chain. We also investigate a model variation where the server does not necessarily poll the stations in a cyclic order, but always serves the customer with the earliest completed preparation phase. We show that the mean waiting time under this dynamic allocation never exceeds that of the cyclic case, but that the waiting-time distributions corresponding to both cases are not necessarily stochastically ordered. Finally, we provide extensive numerical results investigating and comparing the effect of the system's parameters to the performance of the server for both models.

The so called “Israeli Queue” is a single server polling system with batch service of an unlimited size, where the next queue to be visited is the one in which the first customer in line has been waiting for the longest time. The case with finite number of queues (groups) was introduced by Boxma, Van der Wal and Yechiali [3]. In this paper we extend the model to the case with a (possibly) infinite number of queues. We analyze the M/M/1, M/M/c, and M/M/1/N—type queues, as well as a priority model with (at most) M high-priority classes and a single lower priority class. In all models we present an extensive probabilistic analysis and calculate key performance measures.

On 24 August 2008, an outbreak alert regarding cases of acute gastroenteritis in Podgorica triggered investigations to guide control measures. From 23 August to 7 September, 1699 cases were reported in Podgorica (population 136 000) and we estimated the total size of the outbreak to be 10 000–15 000 corresponding to an attack rate of ~10%. We conducted an age- and neighbourhood-matched case-control study, microbiologically analysed faecal and municipal water samples and assessed the water distribution system. All cases (83/83) and 90% (89/90) of controls drank unboiled chlorinated municipal water [matched odds ratio (mOR) 11·2, 95% confidence interval (CI), 1·6–∞]. Consumption of bottled water was inversely associated with illness (mOR 0·3, 95% CI 0·1–0·8). Analyses of faecal samples identified six norovirus genotypes (21/38 samples) and occasionally other viruses. Multiple defects in the water distribution system were noted. These results suggest that the outbreak was caused by faecally contaminated municipal water. It is unusual to have such a large outbreak in a European city especially when the municipal water supply is chlorinated. Therefore, it is important to establish effective multiple-barrier water-treatment systems whenever possible, but even with an established chlorinated supply, sustained vigilance is central to public health.

The question of Drosophila laterality has been investigated in two species and in several strains by attempting to modify degrees of laterality (wing folding and directional choices in mazes) via selection and by ascertaining individual courtship behaviour preferences (circling, foreleg tapping, and wing extending). The results of courtship studies in D. paulistorum strains and in D. melanogaster indicate that, although individual members of a strain may be entirely right or left dominant, the majority of individuals are ambidextrous. As a group, there was no preference for right or left behaviours, and laterality was not a factor in success of courtship. The absence of lateral preference in courtship is consistent with the failure to demonstrate any genetic component for D. melanogaster left and right wing folding and maze behaviours.

Summary

Background and objective: Anaesthesia information management systems, though still not used widely, will inevitably replace handwritten records and may eventually serve as a core for the development of computerized decision support. We investigated staff expectations and the accuracy of data entry in a recently implemented commercially available anaesthesia information management system. Methods: A structured questionnaire was administered to the staff before and 1 week and 3 months after implementation in order to assess their opinion. The quality of manual data entry, and of automatic data record was evaluated by looking for missing data and the prevalence of artefacts. Results: Despite initial fears the users quickly accepted the system. Both automatic and manual data entry were found to be accurate and reliable while the prevalence of artefacts was relatively low. Conclusions: A commercially available anaesthesia information management system can be easily implemented and used instead of paper charts.

Summary

Background and objectives: The On-Line Electronic Help (OLEH) is a point-of-care information system for anaesthesia providers prepared by the European Society of Anaesthesiologists. In this preliminary study the effect of the OLEH availability on the incidence of knowledge-based errors during the management of case scenarios and participants' subjective evaluation of the OLEH were evaluated. Methods: After a short training session, 48 anaesthesiologists (24 junior residents, 12 senior residents and 12 board-certified) were presented randomly with six computer screen-based case scenarios with, and six without, the option of using the OLEH. Two reviewers evaluated the answers independently according to preconfigured guidelines. Results: The availability of the OLEH was associated with higher scores in 11 of the 12 scenarios, and with a decrease in the incidence of critical errors in 10 scenarios. Time to task completion was increased in one scenario only when the OLEH was used. The degree of professional experience was associated with better scores in five of the scenarios and with a reduced occurrence of critical errors in three scenarios. Forty-two out of 48 participants stated that finding information in the OLEH software was easy and that the system was helpful in managing the scenarios. Conclusions: This preliminary study demonstrates the potential value of the OLEH in decreasing the number of knowledge-based errors made by anaesthesiologists. According to the encouraging results, the OLEH system is currently under evaluation using full-scale simulation scenarios in an operating room environment.

Major depression in the elderly is often a relapsing, chronic illness with high risk for chronic invalidism, poor treatment compliance, and suicide. In most cases, maintenance treatment to prevent recurrence and to enhance the quality of life is thought to be indicated. We review recent data from our onging studies that support both the efficacy and the safety of pharmacotherapeutic and psychotherapeutic maintenance treatments. However, the challenges of conducting maintenance therapy research (particularly with a placebo control) with the elderly are many, involving such areas as recruitment, retention, compliance, choice of outcome measures, and informed consent. We discuss each of these challenges and our responses to them. Finally, we suggest that maintenance therapy trials should be extended in several directions: (a) long-term treatment of bipolar and delusional subtypes in the elderly, as well as depression associated with progressive neurodegenerative disorders such as Alzheimer's dementia; (b) assessment of the benefits and risks of long-term therapy with other than tricyclic and monoamine oxidase inhibitor antidepressant agents, such as selective serotonin reuptake inhibitors; and (c) development of models of long-term course, including the interaction of treatments with medical and psychosocial variables that can have a profound impact on illness onset and offset. These issues are illustrated with a discussion of a new protocol designed to test the acute and maintenance efficacy of antidepressant therapy for depressed patients with Alzheimer's disease.

Summary

Background and objective: In this preliminary study we wanted to explore the attitudes of anaesthesiologists to a point-of-care information system in the operating room. The study was conducted as a preliminary step in the process of developing such a system by the European Society of Anaesthesiologists (ESA).

Methods: A questionnaire was distributed to all 2240 attendees of the ESA's annual meeting in Gothenburg, Sweden, which took place in April 2001.

Results: Of the 329 responders (response rate of 14.6%), 79% were qualified specialists with more than 10 yr of experience (68%), mostly from Western Europe. Most responders admitted to regularly experiencing lack of medical knowledge relating to real-time patient care at least once a month (74%) or at least once a week (46%), and 39% admitted to having made errors during anaesthesia due to lack of medical information that can be other-wise found in a handbook. The choice of a less optimal but more familiar approach to patient management due to lack of knowledge was reported by 37%. Eighty-eight percent of responders believe that having a point-of-care information system for the anaesthesiologists in the operating room is either important or very important.

Conclusions: This preliminary survey demonstrates that lack of knowledge of anaesthesiologists may be a significant source of medical errors in the operating room, and suggests that a point-of-care information system for the anaesthesiologist may be of value.

Background and objective: The arterial thermodilution technique offers the ability to measure cardiac output using only central venous and arterial catheters. However, the technique has been reported to overestimate cardiac output because of a higher loss of cold indicator due to the increased distance between the sites of injection and measurement. In this study, the two techniques were compared with respect to conditions of low cardiac output in which a longer passage time may further increase loss of indicator.

Methods: Seventeen anaesthetized dogs were studied during hypovolaemic shock and fluid resuscitation. Cardiac output measurements were carried out simultaneously by arterial and pulmonary artery thermodilution techniques.

Results: One-hundred-and-two measurements were performed. The mean cardiac output was 2.28 ± 1.4 L min−1 by the pulmonary arterial technique and 2.29 ± 1.56 L min−1 by the arterial thermodilution technique. The correlation coefficient between the two measurements was 0.95, the precision −0.04 ± 0.41 L min−1 and the limits of agreement from −0.86 to 0.78 L min−1. The agreement was also consistent at low cardiac outputs.

Conclusions: The arterial thermodilution technique may serve as a less invasive cardiac output monitor in conditions of severe bleeding and shock.

Unilateral malignant hyperinflation of the lungs during positive pressure mechanical ventilation was described during aggressive respiratory therapy of unilateral lung disease or in situations of significant difference in compliance between the two lungs. We report a case of malignant hyperinflation of the nondependent lung during chest surgery. The differential diagnosis and treatment with differential lung ventilation are described.

This study explored admission factors which predicted the successful return to the community of patients entering a Geriatric Assessment and Rehabilitation Program (GARP). A stepwise logistic regression technique was used to determine predictive factors from a consecutive sample of 100 medical or surgical geriatric patients admitted for a four to six week rehabilitation program. The significant independent predictors of discharge which could be determined at the time of admission were ability to safely medicate, admission from the community, GDS score and the number of supports. The ability to safely medicate may be an important but under-utilized predictor.

The eigenstates of electrons and holes confined in cylindrical quantum wires with infinite potential barrier are found. The degree of linear polarization of luminescence is calculated.

The Electrohydrodynamic (EHD) method of spraying fine liquid droplets from a liquid state, in a vacuum environment, was developed and used to produce amorphous, microcrystalline, single crystal, bicrystalline and tricrystalline powders. Studies of these powders have contributed towards increasing the knowledge of extended solubility, nucleation, metastable phases, undercooling effects, etc. Coatings and films have been produced by collecting the liquid droplets before solidification. An automated instrument based upon the EHD method, the Micro-Particle Processor, is computer operated and allows a material scientist not completely acquainted with the EHD process to perform sophisticated experiments on materials of his choosing. Electron transparent powders close to 3μm and large powders up to l00μm have been collected and observed. Cooling rates above 107K/s have been achieved. Applications using powders include: new alloy compositions, use as AEM standards, in-situ remelt experiments in the electron microscope, etc.