The Declining Role of Private Defined Benefit Pension Plans: Who is Affected, and How

This chapter analyzes the impact of future freezes among corporate defined benefit (DB) pension plans. We simulate the impact on expected future pension wealth by assuming all existing private DB plans immediately freeze accruals for new employees. While this indicates the potential reduction in retirement wealth attributable to such plans, it does not recognize that sponsors freezing accruals may increase employer contributions to existing defined contribution (DC) plans or establish new DC plans. Using an empirical distribution of enhanced contributions to DC plans from sponsors freezing their DB plans, we simulate the nominal annuity that could be purchased at retirement age from these enhanced contributions. We then back out the net pension loss experienced by employees in the future

CELLULAR FORCES AND MECHANICAL COUPLING USING MICROENGINEERED DEVICES

The biological response of cells to mechanical forces is integral to both normal cell function and the progression of many diseases. Physical cues experienced by cells arise from internally generated contractile forces, as well as from external sources of force and strain in the local environment. We have used arrays of flexible micron-scale poly(dimethylsiloxane) (PDMS) cantilevers (posts) to probe the behavior of cell-generated contractile forces under varying chemical and mechanical conditions. The cells’ contractile forces displace the tops of the underlying posts, which are individually tracked through microscopy and image analysis, yielding a dynamic, micron-scale map of the cells’ mechanical activity. I have applied these techniques to study cell generated forces in two experimental systems. First, force generation by cardiac fibroblasts (CFs) in order to elucidate mechanical coupling between these cells and the myocytes responsible for the heart’s pumping action, which may contribute to certain types of cardiac arrhythmias. These experiments were part of a collaborative effort which demonstrated that modulation of both CF contractile forces, and the cellular structures on which these forces can act when coupled to cardiac myocytes, had direct influence on the electrical conduction mechanisms that are critical for the proper functioning of cardiac muscle tissue. The second experimental system studied the impact of force application through an applied global stretch on the traction force dynamics of arterial smooth muscle cells. These cells, resident within the inner walls of arteries, are constantly exposed to global stretching forces as a result of changes in blood pressure and flow. I developed an enhanced version of the micropost array that enabled the application of controlled global stretch to cells while the evolution of traction forces could be measured in real time. These measurements revealed a heterogeneous response to imposed strain, as a portion of the tested cells responded by increasing their force generation against the micropost substrate, while others underwent plastic deformation and exhibited relatively small changes in force generation. Upon reversal of stretch direction, all cells exhibited decreasing force generation that is characteristic of a viscoelastic response. Following stretch completion and left at rest, all cells demonstrated active recovery and re-establishment of contractile forces. I have also demonstrated the combined use of a laminar flow technique, micropipette “spritzing”, with both micropost arrays and microfabricated tissue gauges for application of local chemical stimulation to single cells or single tissues while observing contractile dynamics in real time

Letter to the Editor Concerning Simultaneous, Single-Particle Measurements of Size and Loading Give Insights into the Structure of Drug-Delivery Nanoparticles

The vexing error of excess variance in the sizing of single particles degrades accuracy in applications ranging from quality control of nanoparticle products to hazard assessment of nanoplastic byproducts. The particular importance of lipid nanoparticles for vaccine and medicine delivery motivates this comment on a publication$^{\textrm{1}}$ in ACS Nano. In ref 1, the benchmark measurements of a nanoparticle standard manifest large errors of the size distribution that contradict the claim of validation. Such errors can bias the correlation of fluorescence intensity as an optical proxy for the molecular loading of lipid nanoparticles and give misleading insights from power-law models of intensity$-$size data. Looking forward, measurement error models have the potential to address this widespread issue.Comment: Peer reviewed and pending acceptance by ACS Nan

Subnanometer traceability of localization microscopy

In localization microscopy, subnanometer precision is possible but supporting accuracy is challenging, and no study has demonstrated reliable traceability to the International System of Units (SI). To do so, we measure the positions of nanoscale apertures in a reference array by traceable atomic-force microscopy, creating a master standard. We perform correlative measurements of this standard by optical microscopy, correcting position errors from optical aberrations by a Zernike calibration. We establish an uncertainty field due to localization errors and scale uncertainty, with regions of position traceability to within a 68 % coverage interval of +/- 1.0 nm. These results enable localization metrology with high throughput, which we apply to measure working standards, validating the subnanometer accuracy of lithographic pitch