The impact of nonlinearity on degenerate parametric amplifiers

This work investigates the effects of system nonlinearities on degenerate parametric amplifiers. A simple, Duffing-type nonlinearity is appended to a representative equation of motion for a mechanical or electromechanical parametric amplifier, and classical perturbation methods are used to characterize the resulting effects on the amplifier\u27s frequency response and performance. Ultimately, the work demonstrates that parametric amplification can be realized in nonlinear, dynamic-range limited systems, such as resonant micro-or nanosystems, but at the expense of performance degradation. Additionally, it is shown that nonlinear amplifiers can be operated above their linear instability threshold but that doing so results in bistable amplified responses

Non-linear modal analysis of structural systems using multi-mode invariant manifolds

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76304/1/AIAA-1994-1672-138.pd

Reliability and validity of pendulum test measures of spasticity obtained with the Polhemus tracking system from patients with chronic stroke

<p>Abstract</p> <p>Background</p> <p>Spasticity is a common impairment accompanying stroke. Spasticity of the quadriceps femoris muscle can be quantified using the pendulum test. The measurement properties of pendular kinematics captured using a magnetic tracking system has not been studied among patients who have experienced a stroke. Therefore, this study describes the test-retest reliability and known groups and convergent validity of the pendulum test measures obtained with the Polhemus tracking system.</p> <p>Methods</p> <p>Eight patients with chronic stroke underwent pendulum tests with their affected and unaffected lower limbs, with and without the addition of a 2.2 kg cuff weight at the ankle, using the Polhemus magnetic tracking system. Also measured bilaterally were knee resting angles, Ashworth scores (grades 0–4) of quadriceps femoris muscles, patellar tendon (knee jerk) reflexes (grades 0–4), and isometric knee extension force.</p> <p>Results</p> <p>Three measures obtained from pendular traces of the affected side were reliable (intraclass correlation coefficient ≥ .844). Known groups validity was confirmed by demonstration of a significant difference in the measurements between sides. Convergent validity was supported by correlations ≥ .57 between pendulum test measures and other measures reflective of spasticity.</p> <p>Conclusion</p> <p>Pendulum test measures obtained with the Polhemus tracking system from the affected side of patients with stroke have good test-retest reliability and both known groups and convergent validity.</p

Foreword

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43329/1/11071_2004_Article_BF00162230.pd

Analysis of Genetic Variants Associated with Levels of Immune Modulating Proteins for Impact on Alzheimer’s Disease Risk Reveal a Potential Role for SIGLEC14

Genome-wide association studies (GWAS) have identified immune-related genes as risk factors for Alzheimer’s disease (AD), including TREM2 and CD33, frequently passing a stringent false-discovery rate. These genes either encode or signal through immunomodulatory tyrosine-phosphorylated inhibitory motifs (ITIMs) or activation motifs (ITAMs) and govern processes critical to AD pathology, such as inflammation and amyloid phagocytosis. To investigate whether additional ITIM and ITAM-containing family members may contribute to AD risk and be overlooked due to the stringent multiple testing in GWAS, we combined protein quantitative trait loci (pQTL) data from a recent plasma proteomics study with AD associations in a recent GWAS. We found that pQTLs for genes encoding ITIM/ITAM family members were more frequently associated with AD than those for non-ITIM/ITAM genes. Further testing of one family member, SIGLEC14 which encodes an ITAM, uncovered substantial copy number variations, identified an SNP as a proxy for gene deletion, and found that gene expression correlates significantly with gene deletion. We also found that SIGLEC14 deletion increases the expression of SIGLEC5, an ITIM. We conclude that many genes in this ITIM/ITAM family likely impact AD risk, and that complex genetics including copy number variation, opposing function of encoded proteins, and coupled gene expression may mask these AD risk associations at the genome-wide level

Balanced Literacy in an Urban School District

This is the authors' accepted manuscript, post peer-review. The publisher's official version is available electronically from: http://dx.doi.org/10.3200/JOER.98.5.272-280.Balanced literacy is a philosophical orientation that assumes that reading and writing achievement are developed through instruction and support in multiple environments using various approaches that differ by level of teacher support and child control. This study describes one urban school district’s real-world attempt to create a balance between reading and writing, between teacher-directed and student-centered activities, and between skillsbased and meaning based approaches to literacy instruction. A triangulation strategy using multiple methods of data collection, including classroom observations, inventories of the physical environment of classrooms and school buildings, teacher surveys, and student interviews, was used to measure balanced literacy components. Results suggest that teacherdirected instruction, a fundamental aspect of balanced literacy, was implemented less often than either independent reading or writing activities. Teachers appeared to be allocating instructional time as directed by district administrators, and they were implementing components of a balanced literacy program. Additionally, most school buildings had a physical environment supportive of balanced literacy. However, the amount of time devoted to instruction and modeling effective reading and writing strategies seemed too limited for a group of students with poorly developed reading and writing skills

The construction of non-linear normal modes for systems with internal resonance

ABSTRACT A numerical method for constructing nonlinear normal modes for systems with internal resonances is presented based on the inw~riant manifold approach. In order to parameterize the nonlinear notxnal modes, multiple pairs of system state variables involved in the internal resonance are kept as &apos;seeds&apos; for the construction of the multi-mode invariant manifold. All the remaining degrees of freedom are constrained to these &apos;seed&apos; variables, resulting in a system of nonlinear partial differential equations governing the constraint relationships, which must be solved numerically. The solution procedure uses a combination of finite difference schemes and Galerkin-based expansion approaches. It is illustrated using two examples, both of which focus on the construction of two-mode models. The first example is based on the analysis of a simple three-degree-of-freedom example system, and is used to demonstrate the approach. An invariant manifold that captures two nonlinear normal modes is constructed, resulting in a reduced-order model that accurately captures the system dynamics. The methodology is then applied to a more large system, namely an 18-degree-of-freedom rotating beam model that features a three-to-one internal resonance between the first two flapping modes. The accuracy of the nonlinear two-mode reduced-order model is verified by time-domain simulations

Non-linear normal modes, invariance, and modal dynamics approximations of non-linear systems

Non-linear systems are here tackled in a manner directly inherited from linear ones, that is, by using proper normal modes of motion. These are defined in terms of invariant manifolds in the system's phase space, on which the uncoupled system dynamics can be studied. Two different methodologies which were previously developed to derive the non-linear normal modes of continuous systems — one based on a purely continuous approach, and one based on a discretized approach to which the theory developed for discrete systems can be applied-are simultaneously applied to the same study case-an Euler-Bernoulli beam constrained by a non-linear spring-and compared as regards accuracy and reliability. Numerical simulations of pure non-linear modal motions are performed using these approaches, and compared to simulations of equations obtained by a classical projection onto the linear modes. The invariance properties of the non-linear normal modes are demonstrated, and it is also found that, for a pure non-linear modal motion, the invariant manifold approach achieves the same accuracy as that obtained using several linear normal modes, but with significantly reduced computational cost. This is mainly due to the possibility of obtaining high-order accuracy in the dynamics by solving only one non-linear ordinary differential equation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43333/1/11071_2004_Article_BF00045620.pd

A clinical and cost-effectiveness analysis of the HeartMate 3 left ventricular assist device for transplant-ineligible patients: a United Kingdom perspective

Background: The clinical and cost-effectiveness of left ventricular assist device (LVAD) therapy for patients with advanced heart failure (HF) who are ineligible for heart transplantation is debated in the UK. This study develops an indirect comparison between the fully magnetically levitated HeartMate 3 (HM 3) LVAD and medical therapy (MT) to evaluate expected clinical and cost-effectiveness in the UK National Health Service (NHS) context. Methods: We performed an economic analysis comparing the HM3 pump against the HeartMate II LVAD (MOMENTUM 3), and then another analysis comparing MT with the first- and second-generation HeartMate XVE pump LVAD and HeartMate II LVAD for the same patient population (REMATCH and ROADMAP, respectively). By bridging those 2 analyses, an indirect comparison between HM3 and MT in the form of a network meta-analysis was developed. A literature search was performed to select the most appropriate pair of studies for this purpose. Outcomes were adjusted to produce Kaplan-Meier curves for the cost-effectiveness evaluation by using a decision-analytic model. Data were extrapolated linearly over a 5-year time horizon. Uncertainty and additional scenarios were addressed by one-way and probabilistic sensitivity analysis. Local costs and health utility were used from England, thereby representing the UK context. Results: The incremental cost-effectiveness ratio (ICER) for LVAD vs MT in transplant ineligible patients with advanced HF was estimated to be £47,361 per quality-adjusted life year gained, with a 97.1% probability of being cost-effective at £50,000. In a subgroup of patients who are inotropic therapy dependent (INTERMACS 1-3 severity profile), the ICER was £45,616, while for a population with less-ill ambulatory HF (INTERMACS profile 4-7) the ICER changed to £64,051. Conclusions: This study provides evidence that HM3 LVAD therapy in advanced HF patients ineligible for heart transplantation may be cost-effective compared to MT in the NHS UK-England context. The ICER is lowest for patients dependent on inotropic support, but exceeds the willingness to pay threshold of £50,000 in ambulatory noninotropic therapy dependent advanced HF patients