Degeneracy and networked buffering: principles for supporting emergent evolvability in agile manufacturing systems

This article introduces new principles for improving upon the design and implementation of agile manufacturing and assembly systems. It focuses particularly on challenges that arise when dealing with novel conditions and the associated requirements of system evolvability, e.g. seamless reconfigurability to cope with changing production orders, robustness to failures and disturbances, and modifiable user-centric interfaces. Because novelty in manufacturing or the marketplace is only predictable to a limited degree, the flexible mechanisms that will permit a system to adequately respond to novelty cannot be entirely pre-specified. As a solution to this challenge, we propose how evolvability can become a pervasive property of the assembly system that, while constrained by the system??s historical development and domain-specific requirements, can emerge and re-emerge without foresight or planning. We first describe an important mechanism by which biological systems can cope with uncertainty through properties described as degeneracy and networked buffering. We discuss what degeneracy means, how it supports a system facing unexpected challenges, and we review evidence from simulations using evolutionary algorithms that support some of our conjectures in models with similarities to several assembly system contexts. Finally, we discuss potential design strategies for encouraging emergent changeability in assembly systems. We also discuss practical challenges to the realization of these concepts within a systems engineering context, especially issues related to system transparency, design costs, and efficiency. We discuss how some of these difficulties can be overcome while also elaborating on those factors that are likely to limit the applicability of these principles.     

Computer simulation of ESD from voluminous objects compared totransient fields of humans

Computer simulation of electrostatic discharge (ESD) for simplified objects is described and compared to measured transient fields of human/metal ESD. The simulation algorithm uses the method of moments in time domain, coupled with nonlinear arc resistance model. Transient currents and fields are analyzed from the electromagnetic compatibility (EMC) point of view. Validation of the numerical simulation is done by comparison to experimental data. The simulated structure models the human/metal ESD in its peak current and field values and their derivatives reasonably well     

Lack of effects on heart rate and blood pressure inketamine-anesthetized rats briefly exposed to ultra-widebandelectromagnetic pulses

Fourteen Sprague-Dawley rats were exposed to pulses produced by a Bournlea ultra-wideband (UWB) pulse generator (rise time, 318-337 ps; maximum E field, 19-21 kV/m). Exposures at a repetition frequency of 1 kHz for 0.5 s or to repetitive pulse trains (2-s exposure periods alternating with 2 s of no exposure, for a total of 2 min) resulted in no significant changes in heart rate or mean arterial blood pressure. These results suggest that acute whole-body exposure to UWB pulses does not have a detrimental effect on the cardiovascular system     

Long-term, low-level exposure of mice prone to mammary tumors to 435 MHz radiofrequency radiation

Six hundred and thirty four interviews of injecting drug users were performed between 1992 and 1994 as part of a study of injecting drug use and HIV prevalence in Edinburgh, Scotland. Amphetamine was injected by more subjects (44%) than any other drug. Preference for injection as the route of administration of amphetamine increased over the period despite no change in the popularity of the drug generally. Simultaneously, heroin use and injection declined. Analyses indicated that amphetamine injectors comprised two distinct sub-groups. The majority were polydrug injectors who injected frequently, had a longer injecting history and were more likely to share injection equipment. About one-fifth were stimulant-only injectors who injected infrequently, were relatively recent initiates to injecting and whose numbers increased over the 3 years. Drug treatment and prevention services may need to explore alternative methods to respond effectively to these emerging trends.     

An approach for fabricating high-performance inductors onlow-resistivity substrates

Porous Si layers up to 250 μm in thickness are used to isolate spiral inductors from low resistivity substrates. Wafer curvature and secondary ion mass spectroscopy (SIMS) analysis are done to address the manufacturability issue of porous Si. Spiral inductors with a single level Al on 2 in, p-type substrates of 0.008 Ω-cm resistivity are demonstrated with Q<6 at 3 GHz for an L of ~8 nH. Large inductors with L~100 nH have been shown with the first resonance frequency at 1 GHz. The expected performance potential as well as factors that could be limiting the Q are discussed     

Cutaneous diphtheria in returning vacationers--mirror of inappropriate vaccination practice?

The causative agent for diphtheria is Corynebacterium diphtheriae, which is transmitted from person to person from the throat of carriers or from patients with active cutaneous diphtheria. The disease occurs in preexisting ulcers, but it may also appear on apparently normal skin. Although primary cutaneous diphtheria starts as a vesicle or pustule, most patients feature a reddish ulcer with undermined borders. The lesion is tender but hypesthesia develops after 2 weeks. The clinical diagnosis is based on the history of travelling in endemic regions and bacteriological studies. The current increase of diphtheria in the Western world is partly caused by rising tourism and a decline of booster vaccination in adults. After trauma with ulcerations of the skin we suggest to perform a booster vaccination not only for tetanus but also for diphtheria. In addition, persons travelling to endemic regions should receive a booster vaccination for tetanus and diphtheria, which is available as a combined preparation.     

IL-6-deficient mice resist myelin oligodendrocyte glycoprotein-induced autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is induced by immunization with myelin components including myelin oligodendrocyte glycoprotein (MOG). Myelin-specific Th1 cells enter the central nervous system (CNS) via binding of very late antigen 4 (VLA-4) to the endothelial vascular cell adhesion molecule 1 (VCAM-1). In the present study, mice with a homologous disruption of the gene encoding IL-6 are found to be resistant to MOG-induced EAE as evidenced by absence of clinical symptoms, minimal infiltration of CD3+ T cells and monocytes into the CNS and lack of demyelination. The failure to induce EAE in IL-6-/- mice is not due to the absence of priming, since lymphocytes of immunized IL-6-/- mice proliferate in response to MOG and produce pro-inflammatory cytokines including IL-2 and IFN-gamma. However, in MOG-immunized IL-6-/- mice, serum anti-MOG antibody titers were found to be drastically reduced. This observation is unlikely to be responsible for resistance to EAE, because B cell-deficient (microMT) mice proved to be fully susceptible to the disease. A striking difference between MOG-immunized wild-type (wt) and IL-6-/- mice was the expression of endothelial VCAM-1 and ICAM-1, which were dramatically up-regulated in the CNS in wt but not in IL-6-/- mice. Taking into account recent studies on the role of VCAM-1 in the entry of Th1 cells into the CNS, the absence of VCAM-1 on endothelial cells in IL-6-/- mice may explain their resistance to EAE.     

Early high dose antioxidant vitamins do not prevent bronchopulmonary dysplasia in premature baboons exposed to prolonged hyperoxia: a pilot study

The effect of two different types of functional ankle-foot orthosis on the gait of patients with spastic hemiplegia was studied. A gap was cut into the conventional stiff orthosis to allow a limited dorsiflexion of 10-15 degrees, while plantarflexion was blocked (spring type). This gap was bridged by an aluminum bar to stiffen the orthosis for the experiment. Fourteen patients of different ages (6.5-20.1 years) walked barefoot and with the orthosis, once springy and once stiff. Kinetics and kinematics were analyzed. Gait was significantly improved into normal pattern by using any type of ankle-foot orthosis. While walking barefoot with a toe-heel-toe gait, the physiological heel-toe gait was restored with any type of orthosis. The spring type of orthosis was significantly superior to the stiff orthosis. This was most clearly expressed in the general parameters of gait-like cadence, velocity, and step length. Kinetic data gave a significant improvement by using any ankle-foot orthosis. Whereas break force was similar with both types, push-off was further improved with the spring type. Kinematics revealed little statistical difference between the two types, although gait was more dynamic and physiological with the spring type of orthosis. Any functional ankle-foot orthosis ameliorates the gait pattern in patients with spastic hemiplegia, but a spring type of orthosis renders the gait more dynamic and best corrects the pathology of gait.     

Troponin T in patients with low grade or atypical angina. Identification of a high risk group for short- and long-term cardiovascular events

AIMS: Cardiac troponin T is an established marker of cardiovascular risk in patients with severe angina pectoris. Data are scarce on patients admitted to a coronary care unit with low grade or atypical angina pectoris to rule out myocardial infarction. METHODS AND RESULTS: We investigated 106 patients (57.4 SD 11.6 years) with low grade (Braunwald class I) or atypical symptoms out of 702 patients admitted to the coronary care unit with suspected acute myocardial infarction. Serum concentrations of troponin T were measured at admission and 4 h later. In hospital cardiovascular events including acute myocardial infarction, life threatening cardiac arrhythmias, congestive heart failure, and death were recorded. Patients were additionally observed after 3 and 6 months post-discharge regarding acute myocardial infarction, unstable angina, rehospitalization for cardiac causes and death. The patients were divided into a troponin T positive (> or =0.2 microg x 1(-1) at admission or 4 h later; n=11) and a troponin T negative group. The mean value of troponin T 4 h after admission in the positive group was 0.58 microg x 1(-1). Of the troponin T positive patients, 0.82 (0.95 CI: 0.48-0.98) had a cardiovascular event during their stay in hospital vs 0.41 (0.95 CI: 0.31-0.52) of troponin T negative patients (P<0.05). In the troponin T positive group 0.64 (0.95 CI: 0.31-0.89) developed myocardial infarction in hospital vs 0.07 (0.95 CI: 0.03-0.15) in the troponin T negative group (P<0.001). Troponin T predicts outcome after 3 and 6 months significantly (P<0.05). CONCLUSION: Troponin T identifies patients with low grade or atypical angina at risk of severe short- and long-term cardiovascular events. Therefore, troponin T adds substantial information in patients with ruled out acute myocardial infarction. Troponin T positive patients have to be observed carefully regardless of their symptom intensity and may have to receive early cardiac catheterization; troponin T negative patients could be released safely from the coronary care unit early.