Bi-level Systems Research Articles

Non-invasive positive pressure ventilation in the home setting.

Noninvasive ventilation is becoming a more commonly used long-term treatment for various conditions in which the patient experiences chronic hypercapnic respiratory failure (type 2 respiratory failure). This article aims to discuss why patients require long-term noninvasive positive pressure ventilation (NPPV), and to describe some of the care considerations required for this patient group, in addition to challenges that nurses in the home care environment face when supporting these patients at home. The article provides a brief pathophysiological overview, while also discussing the use of NPPV as symptom support for patients with severe disease in the later stages of their lives. The term 'noninvasive positive pressure ventilation' is used to cover a number of different noninvasive systems, although the study primarily focuses on bi-level ventilation systems.

Data envelopment analysis for bi-level systems with multiple followers

This study aims to evaluate the performance of a bi-level system including two kinds of players: a leader positioned at the upper level and multiple followers located at the lower level. The overall system tries to use inputs to produce outputs in a cost-efficient way. However, each player in the bi-level system controls different decision variables and has varying objectives. Based on this, a novel bi-level data envelopment analysis model with multiple followers is developed, in order to evaluate the performance of overall bi-level system as well as each player in detail. Then the extended Kuhn–Tucker conditions are used to solve the proposed model. An illustrative example is presented to validate the proposed approach by evaluating supply chains with a single plant and two distribution centers. A comparative analysis is conducted to demonstrate that the developed model has stronger discriminating power and can provide more managerial insights. Several conclusions can be reached from this study: the lower level subsystem is cost-efficient if and only if every follower is cost-efficient, and the lower level cost efficiency lies between the smallest cost efficiency and the largest cost efficiency among all followers; being cost-efficient at both the upper level and the lower level results in an achievement of overall cost efficiency in a bi-level structure, and the overall cost efficiency falls in between the upper level and the lower level cost efficiencies.

Stimulated emission of an atomic system under coherent excitation

The possibility of collective spontaneous emission was first indicated by Dicke [1]. Later, these effects were detected in cesium atomic beams [2], as well as in ensembles of rubidium atoms [3,4]. The ideas of Dicke were subsequently developed in numerous publications (see for instance [5, 6]), which included mostly bi-level systems with different ways of population inversion, possibly leading to superradiance high intensity pulses, followed by a certain delay in relation to the inverse state formation time. It should be emphasized that generally speaking, population inversion is not a necessary condition for the creation of superradiance. This phenomenon can occur if a dipole moment is induced on the upper state [7, 9]. This is known as induced superradiance. The present work is not directly related to superradiance as such. Below, within the framework of the ideas used for superradiance, we will investigate the collective polarization emission of a complex atomic system which has been placed in a strong magnetic field, the lower state of which, is populated by axially symmetric interactions.

A non-cooperative neuro-fuzzy system for integrating ATIS and ATMS decisions

This paper addresses the problem of integrating successful existing implementations of Advanced Traveler Information Systems (ATIS) and Advanced Traffic Management Systems (ATMS). The methodologies and challenges to integrate ATIS and ATMS are addressed in details. This paper discusses in details the development of a rule-based neuro-fuzzy logic to integrate existing ATIS and ATMS when they operate in a non-cooperative manner. The individual existing logics are initially upgraded to the so-called ATIS and ATMS stand-alone systems, which may be regarded as bi-level optimization systems. The upper level (of the bi-level optimization system) represents an augmented process for guessing the counter system's decisions, and the lower level represents the existing logic (of ATIS or ATMS). The stand-alone systems are then replicated by simulation-based optimization algorithms, which are used to generate the training data necessary to calibrate the neuro-fuzzy logic. The role of the neural nets and the methodology of fuzzy-logic calibration are discussed in details. The effectiveness and robustness (of the neuro-fuzzy integrated ATIS/ATMS system) are assessed using simulation-based experiments with two different hypothetical networks.

Airway support management: a teaching module.

N ONINVASIVE airway support management is a relatively new treatment modality for pediatric patients requiring ventilatory assistance. Continuous positive airway pressure (C-PAP) and bilevel systems (Bi-PAP, Bi-PAP S/W) are examples of mechanisms presently being used to provide this support (Respironics, Inc., 1988). Children with poor respiratory effort such as sleep apnea, neuromuscular disorders, and spinal cord injury can benefit from noninvasive airway support management. Both methods of airway support can be used in acute as well as chronic situations, thereby avoiding complications associated with intubation and surgery. There are 10 children currently being followed at Children’s Hospital of Duke University Medical Center who are using C-PAP or bilevel systems. These children have been diagnosed with a variety of disorders from traumatic spinal cord injury to muscular dystrophy. Most are on a bilevel system because it is better tolerated and offers increased comfort. Therefore, it has a higher home compliance rate than C-PAP (Respironics, Inc., 1988). Because the C-PAP and bilevel systems are used infrequently in pediatric settings, it was necessary to develop a program to educate the nursing staff in the airway systems and preparing families for discharge and home use. The teaching module for staff includes a brief description, criteria checklists for family training, and guidelines for discharge preparations.

The cost advantage of hysteretic controls for bi-level production systems

Frequently, production systems can be designed to be flexible in that the output rate of the system can be changed depending upon the demand requirements that the system faces. In such systems, the problem is considered to be the determination of the optimal point at which the system switches between its output levels. Simple control has one switching point between adjacent output levels. In this paper, it is shown that hysteretic control, the determination of two switching points, always provides for a lower operating cost than simple control. Based upon the characteristics of the performance measures, a procedure is developed that easily finds the optimal switching points. The procedure, when applied to a small midwest job shop, resulted in a cost savings of 9-97%.

Gender and family therapy: Adding a bi-level belief systems component to assessment

This article proposes that most couples requesting therapy describe gender socialized patterns as part of their relationship issues. Adding a component to assessment derived from principles of strategic and systemic family therapies and post-modernist feminist psychology which examines the couple's gendered belief system context is described. The belief system context is identified as the family's epistemology about gendering at the family belief system and sociocultural belief system level contexts. Three dimensions of the gendered belief system and a method for assessing the functionality of the belief system are discussed.

Internal Forces and Moments in Transpedicular Spine Instrumentation The Effect of Pedicle Screw Angle and Transfixation— The 4R-4Bar Linkage Concept

The three-dimensional components of force and moment within the plates and screws of a bilevel transpedicular spine implant construct subjected to different physiological loads were determined by experimental and finite element methods. The effect of pedicle screw angle and transfixation were studied. Untransfixed 0 degrees pedicle-to-pedicle (P-P) angle constructs with limited screw-bone torsional resistance are unstable 4R-4bar linkages. They will not resist lateral load or (when not in a rectangular position) axial load until the spinal column load shares. Untransfixed constructs with (0 degrees less than P-P angle less than 60 degrees) are structures. However, as P-P angle approaches 0 degrees, the structure becomes more flexible (unstable) and some internal force and moment components exponentially increase (starting at approximately a 30 degrees P-P angle). Transfixation eliminated the linkage instability and associated exponential increase in internal loads. These observations apply to all bilevel systems that allow no relative joint motion between pedicle screw and longitudinal member. If relative motion does exist, other types of linkage instability can occur.