Analysis of a Modified Feedback Control Technique for Suppressing Electrical Alternans in Cardiac Tissue

Alternans is an abnormal cardiac rhythm in which action potential duration alternates from beat-to-beat. In order for an implanted pacemaker to successfully seize control of the heart rhythm, its electrical stimuli have to be carefully timed relative to the firing of the heart’s specialized pacemaker cells. In this manuscript, we use mathematical techniques to analyze a novel feedback control algorithm for suppressing alternans. We model the cardiac rhythm and the effect of the controller using a system of two nonlinear difference equations. Our analysis reveals that it is often advantageous not to allow the pacemaker to intervene in every beat when attempting to control alternans

Distribution of Trace Metals in Fine-grained Bed Sediments and Benthic Insects in the Clark Fork River, Montana

The downstream distribution of Cu, Cd, and Pb in fine-grained sediments and benthic insect larvae of the Clark Fork River, Montana is characterized. This river has been heavily con laminated as a result of past mining and smelling operations near its headwaters. Concentrations of all metals in bed sediments displayed a simple exponential downstream decrease through the upper 181 km of the river. The trend suggested metal contamination originated from source(s) in the headwaters, with physical dilution occurring downstream. Additional data suggested floodplain sediments also were contaminated by the original source(s). Secondary inputs from cutbanks in the floodplains may have extended the downstream influence of the contamination. The exponential model predicted that sediment contamination should extend at least 550 km downstream, a result that was verified with data from a separate, independent study. Metal contamination, as observed in all taxa of insect larvae collected from the upper Clark Fork. Concentrations in the insect larvae were highest in the upper 100 km of the river, but downstream trends were more complex than those of the sediments. Some differences in trends occurred among taxa and metals. Areas in the river of enhanced or reduced metal contamination also were apparent. Metal contamination, however, was still evident at 381 km, the most downstream station sampled. Metal concentrations in sediments and insects decreased at the confluences of uncontaminated tributaries, but the influence of tributaries on metal contamination in the Clark Fork River was localized, extending for only 1-2 kin below the confluences

Preliminary results of the Mariner IV radio occultation measurements of the upper atmosphere of Mars

Mariner IV radio occultation measurements of Mars upper atmospher

Preliminary results of the Mariner IV OCCULATION measurement of the atmosphere of Mars

Mariner IV radio occultation measurement of Mars atmospher

Feature weighting techniques for CBR in software effort estimation studies: A review and empirical evaluation

Context : Software effort estimation is one of the most important activities in the software development process. Unfortunately, estimates are often substantially wrong. Numerous estimation methods have been proposed including Case-based Reasoning (CBR). In order to improve CBR estimation accuracy, many researchers have proposed feature weighting techniques (FWT). Objective: Our purpose is to systematically review the empirical evidence to determine whether FWT leads to improved predictions. In addition we evaluate these techniques from the perspectives of (i) approach (ii) strengths and weaknesses (iii) performance and (iv) experimental evaluation approach including the data sets used. Method: We conducted a systematic literature review of published, refereed primary studies on FWT (2000-2014). Results: We identified 19 relevant primary studies. These reported a range of different techniques. 17 out of 19 make benchmark comparisons with standard CBR and 16 out of 17 studies report improved accuracy. Using a one-sample sign test this positive impact is significant (p = 0:0003). Conclusion: The actionable conclusion from this study is that our review of all relevant empirical evidence supports the use of FWTs and we recommend that researchers and practitioners give serious consideration to their adoption

Effects of the sodium–glucose co-transporter 2 inhibitor dapagliflozin in patients with type 2 diabetes and Stages 3b–4 chronic kidney disease

BACKGROUND: The sodium–glucose co-transporter 2 inhibitor dapagliflozin decreases haemoglobin A1c (HbA1c), body weight, blood pressure (BP) and urinary albumin:creatinine ratio (UACR) in patients with type 2 diabetes. The efficacy and safety of this drug have not been properly defined in patients with type 2 diabetes and Stages 3b–4 chronic kidney disease (CKD). METHODS: In a pooled analysis of 11 phase 3 randomized controlled clinical trials, we determined least square mean changes in HbA1c, body weight, BP, estimated glomerular filtration rate (eGFR) and UACR over 102 weeks in patients with type 2 diabetes and an eGFR between 12 to less than 45 mL/min/1.73 m2 receiving placebo (n = 69) or dapagliflozin 5 or 10 mg (n = 151). Effects on UACR were determined in a subgroup of patients with baseline UACR ≥30 mg/g (n = 136). RESULTS: Placebo-corrected changes in HbA1c with dapagliflozin 5 and 10 mg were 0.03% [95% confidence interval (CI) −0.3–0.3] and 0.03% (95% CI −0.2–0.3) during the overall 102-week period. Dapagliflozin 5 and 10 mg compared with placebo reduced UACR by − 47.1% (95% CI −64.8 to − 20.6) and −38.4% (95% CI −57.6 to − 10.3), respectively. Additionally, dapagliflozin 5 and 10 mg compared with placebo reduced BP and body weight. eGFR increased with placebo during the first 4 weeks but did not change with dapagliflozin. There were no between-group differences in eGFR at the end of follow-up. Adverse events associated with renal function occurred more frequently in the dapagliflozin 10-mg group. These events were mainly asymptomatic increases in serum creatinine. CONCLUSIONS: Dapagliflozin did not decrease HbA1c in patients with type 2 diabetes and Stages 3b–4 CKD, but decreased UACR, BP and body weight to a clinically meaningful extent. These results support a large outcome trial in this population to confirm long-term safety and efficacy in reducing adverse clinical endpoints

Recent Decisions

Comments on recent decisions by Joseph V. Stodola, Kenneth J. Konop, John H. Tuberty, William M. Cain, John D. Voss, Alvin G. Kolski, and W. D. Rollison

Rate-dependent propagation of cardiac action potentials in a one-dimensional fiber

Action potential duration (APD) restitution, which relates APD to the preceding diastolic interval (DI), is a useful tool for predicting the onset of abnormal cardiac rhythms. However, it is known that different pacing protocols lead to different APD restitution curves (RCs). This phenomenon, known as APD rate-dependence, is a consequence of memory in the tissue. In addition to APD restitution, conduction velocity restitution also plays an important role in the spatiotemporal dynamics of cardiac tissue. We present new results concerning rate-dependent restitution in the velocity of propagating action potentials in a one-dimensional fiber. Our numerical simulations show that, independent of the amount of memory in the tissue, waveback velocity exhibits pronounced rate-dependence and the wavefront velocity does not. Moreover, the discrepancy between waveback velocity RCs is most significant for small DI. We provide an analytical explanation of these results, using a system of coupled maps to relate the wavefront and waveback velocities. Our calculations show that waveback velocity rate-dependence is due to APD restitution, not memory.Comment: 17 pages, 7 figure