Quasi-Static Pull-in: an Instability in Electrostatic Actuators.

We identify a new instability in electrostatic actuators dubbed quasi-static pull-in. We report experimental evidence of the instability and study its characteristics in two types of micro actuators operating in ambient air. We found that the underlying mechanism is a fast-slow dynamic interaction between slowly-varying electrostatic excitation and fast resonator response that instigate large non-resonant oscillatory orbits and eventually disappears in a global Shilnikov bifurcation. Based on these findings, we formulate and present a new taxonomy of pull-in instabilities in electrostatic actuators.

Out-of-Plane Continuous Electrostatic Micro-Power Generators.

This paper presents an out-of-plane electrostatic micro-power generator (MPG). Electret-based continuous MPGs with different gaps and masses are fabricated to demonstrate the merits of this topology. Experimental results of the MPG demonstrate output power of 1 mW for a base acceleration amplitude and frequency of 0.08 g and 86 Hz. The MPGs also demonstrate a wideband harvesting bandwidth reaching up to 9 Hz. A free-flight and an impact mode model of electrostatic MPGs are also derived and validated by comparison to experimental results.

Falls in elderly hemodialysis patients.

The elderly, (age ≥ 65 years) hemodialysis (HD) patient population is growing rapidly across the world. The risk of accidental falls is very high in this patient population due to multiple factors which include aging, underlying renal disease and adverse events associated with HD treatments. Falls, the most common cause of fatal injury among elderly, not only increase morbidity and mortality, but also increase costs to the health system. Prediction of falls and interventions to prevent or minimize fall risk and associated complications will be a major step in helping these patients as well as decreasing financial and social burdens. Thus, it is vital to learn how to approach this important problem. In this review, we will summarize the epidemiology, risk factors, pathophysiology and complications of falls in elderly HD patients. We will also focus on available methods to assess and predict the patients at higher risk of falling and will provide recommendations for interventions to reduce the occurrence of falls in this population.

An unusual case of anti-glomerular basement membrane disease presenting with nephrotic syndrome.

Anti-glomerular basement membrane (anti-GBM) disease is a vasculitic disease characterized by acute kidney injury, oliguria, hematuria and proteinuria. Proteinuria is rarely in the nephrotic range. A case of anti-GBM disease with proteinuria of 22.5 g/day is discussed. Immunofluorescence showed strong linear IgG deposits while electron microscopy showed widespread visceral epithelial cell foot cell process effacement. No electron dense immune complex-type deposits were identified. Pathology findings were not suggestive of simultaneous presentation of anti-GBM disease and other diseases associated with nephrotic range proteinuria. Anti-GBM disease should be considered in a comprehensive differential diagnosis of severe proteinuria.

Antibiotic resistance and prevalence of beta-lactamase in Haemophilus influenzae isolates-a surveillance study of patients with respiratory infection in Saudi Arabia.

Haemophilus influenzae was isolated from patients with respiratory tract infections in five centers in Saudi Arabia. All of the 129 isolates tested by MIC agar dilution were fully susceptible to ceftazidime and ciprofloxacin but 13.2% were resistant to ampicillin, 7% to tetracycline, 5.4% to chloramphenicol, 3.9% to roxithromycin, and 1.6% to amoxicillin/clavulanic acid. Seventeen (13.2%) of all isolates produced TEM-1 type beta-lactamase, the majority (82%) characterized as biotype I or II with 4 (23.5%) encapsulated and belonging to serotype b. There was a clear distinction between the prevalence of beta-lactamase production in hospital patients (26.3% of 19 isolates) compared with community based patients (10.9% of 110 isolates). In addition, we report an increase in the prevalence of beta-lactamase negative, ampicillin intermediate strains (BLNAI) compared to previous studies in this defined geographical region. Changes in the frequency and nature of antimicrobial resistance in common respiratory pathogens confirms the need to maintain surveillance.

Angiotensin II and nitric oxide: a question of balance.

The vasoconstrictor peptide angiotensin II (Ang II) and the endogenous vasodilator nitric oxide (NO) have many antagonistic effects, as well as influencing each other's production and functioning. In the short-term, Ang II stimulates NO release, thus modulating the vasoconstrictor actions of the peptide. In the long-term, Ang II influences the expression of all three NO synthase (NOS) isoforms, while NO downregulates the Ang II Type I (AT1) receptor, contributing to the protective role of NO in the vasculature. Within the cardiovascular system, Ang II and NO also have antagonistic effects on vascular remodeling and apoptosis. In the kidney, the distribution of the NOS isoforms coincides with the sites of the components of the renin-angiotensin system. NO influences renin secretion from the kidney, and NO-Ang II interactions are important in the control of glomerular and tubular function. In the adrenal gland, NO has been shown to affect Ang II-induced aldosterone synthesis, while in the brain NO appears to influence Ang II-induced drinking behavior, although conflicting data have been reported. In this review, we focus on the diverse ways in which Ang II and NO interact, and on the importance of maintaining a balance between these two important mediators.

Three-dimensional dynamic behaviour of the human knee joint under impact loading.

The objective of this study is to determine the three-dimensional dynamic response of the human knee joint. A three-dimensional anatomical dynamic model was thus developed and consists of two body segments in contact (the femur and tibia) executing a general three-dimensional dynamic motion within the constraints of the different ligamentous structures. Each of the articular surfaces at the tibio-femoral joint was represented mathematically by a separate mathematical function. The joint ligaments were modelled as nonlinear elastic springs. The six-degrees-of-freedom joint motions were characterized by using six kinematic parameters, and ligamentous forces were expressed in terms of these six parameters. Knee response was studied by considering sudden external forcing pulse loads applied to the tibia. Model equations consist of nonlinear second-order ordinary differential equations coupled with nonlinear algebraic constraint conditions. Constraint equations were written to maintain at least one-point contact throughout motion; one- and two-point contact versions of the model were developed. This Differential-Algebraic Equations (DAE) system was solved by employing a DAE solver: the Differential/Algebraic System Solver (DASSL) developed at Lawrence Livermore National Laboratory. A solution representing the response of this three-dimensional dynamic system was thus obtained for the first time. Earlier attempts to determine the system's response were unsuccessful owing to the inherent numerical instabilities in the system and the limitations of the solution techniques. Under the conditions tested, evidence of "femoral roll back" on both medial and lateral tibial plateaus was not observed from the model predictions. In the range of 20 degrees to 66 degrees of knee flexion, the lateral tibial contact point moved posteriorly while the medial tibial contact point moved anteriorly. In the range of 66 degrees to 90 degrees of knee flexion, contact was maintained only on the medial side and the tibial contact point (on the medial side) continued to move anteriorly. It was further found that increasing pulse amplitude and/or duration caused a decrease in the magnitude of the tibio-femoral contact force at a given flexion angle. These results suggest that increasing load level caused a decrease in joint stiffness. The results of this study also show that the anterior fibres of the posterior cruciate and the medial collateral ligaments are the primary restraints for a posterior forcing pulse in the range of 20 degrees to 90 degrees of knee flexion; this explains why most isolated posterior cruciate ligament injuries and combined injuries to the posterior cruciate and the medial collateral result from a posterior impact on a flexed knee.

Characteristics of long-term peritoneal dialysis survivors: 18 years experience in one center.

OBJECTIVES: Long-term experience of patients on peritoneal dialysis (PD) in general, and in diabetic patients specifically, is limited. Few patients have been followed on PD for over 8 years. Our aim was to evaluate and characterize long-term survivors (LTS) on PD for more than 100 months. A retrospective analysis of 20 patients who survived on PD for more than 100 months was performed. Data on long-term survivors was compared to data of 103 patients who died or switched to hemodialysis (HD) in less than 100 months. DESIGN: The study included all patients starting PD prior to 1 January 1986. Demographic, biochemical, dialysis prescription, and morbidity data were obtained on these patients. Characteristics of long-term survivors on PD (more than 100 months), was compared with those who died or switched to HD in less than 100 months, using Student t-test. SETTING: An experienced single center, university-based dialysis program. PATIENTS: 165 patients started PD at the University of Wisconsin prior to 1 January 1986. Forty three had type I diabetes mellitus and 24 had type II diabetes mellitus as the cause of their renal failure. RESULTS: Twenty patients survived on PD more than 100 months (LTS). Long-term survival of type I diabetic patients was seen in 7 of 43 patients at risk. Seventeen type I diabetics received renal transplants and ten died. 103 patients either died or switched to HD in less than 100 months. Long-term survivors were significantly younger, weighed less, had fewer episodes of peritonitis, fewer hospital days, and were prescribed more dialysis per kg body weight, than those who died or switched to HD prior to 100 months. CONCLUSIONS: Long-term survival on CAPD for longer than 100 months is possible with survival periods up to 18 years in both males and females and in nondiabetics as well as patients with type I diabetes mellitus. No patient with type II diabetes mellitus survived longer than 100 months on CAPD. In comparison to short-term survivors, long-term survivors were characterized by being younger, weighing less, having fewer episodes of peritonitis, fewer hospital days, and were prescribed more dialysis/kg body weight.

End-stage renal disease (ESRD) in patients with eating disorders.

We report on the development of end-stage renal disease in four young women with long duration of eating disorders. No other reason for end-stage renal disease could be identified in these patients. Long standing hypokalemia was noted in all. Renal ultrasonography in three patients showed small kidneys with increased cortical echogenicity and multiple small bilateral cysts. A renal biopsy in one showed chronic tubulo-interstitial disease and non-specific glomerulosclerosis consistent with hypokalemic nephropathy. The development of end-stage renal disease is yet another medical complication to be considered in patients with long-standing eating disorder. Chronic hypokalemia may play a role in the pathogenesis of renal disease in this setting.