Optimizing Filter-Probe Diffusion Weighting in the Rat Spinal Cord for Human Translation

Diffusion tensor imaging (DTI) is a promising biomarker of spinal cord injury (SCI). In the acute aftermath, DTI in SCI animal models consistently demonstrates high sensitivity and prognostic performance, yet translation of DTI to acute human SCI has been limited. In addition to technical challenges, interpretation of the resulting metrics is ambiguous, with contributions in the acute setting from both axonal injury and edema. Novel diffusion MRI acquisition strategies such as double diffusion encoding (DDE) have recently enabled detection of features not available with DTI or similar methods. In this work, we perform a systematic optimization of DDE using simulations and an in vivo rat model of SCI and subsequently implement the protocol to the healthy human spinal cord. First, two complementary DDE approaches were evaluated using an orientationally invariant or a filter-probe diffusion encoding approach. While the two methods were similar in their ability to detect acute SCI, the filter-probe DDE approach had greater predictive power for functional outcomes. Next, the filter-probe DDE was compared to an analogous single diffusion encoding (SDE) approach, with the results indicating that in the spinal cord, SDE provides similar contrast with improved signal to noise. In the SCI rat model, the filter-probe SDE scheme was coupled with a reduced field of view (rFOV) excitation, and the results demonstrate high quality maps of the spinal cord without contamination from edema and cerebrospinal fluid, thereby providing high sensitivity to injury severity. The optimized protocol was demonstrated in the healthy human spinal cord using the commercially-available diffusion MRI sequence with modifications only to the diffusion encoding directions. Maps of axial diffusivity devoid of CSF partial volume effects were obtained in a clinically feasible imaging time with a straightforward analysis and variability comparable to axial diffusivity derived from DTI. Overall, the results and optimizations describe a protocol that mitigates several difficulties with DTI of the spinal cord. Detection of acute axonal damage in the injured or diseased spinal cord will benefit the optimized filter-probe diffusion MRI protocol outlined here

Do the Rich Save More?

The issue of whether higher lifetime income households save a larger fraction of their income is an important factor in the evaluation of tax and macroeconomic policy. Despite an outpouring of research on this topic in the 1950s and 1960s, the question remains unresolved and has since received little attention. This paper revisits the issue, using new empirical methods and the Panel Study on Income Dynamics, the Survey of Consumer Finances, and the Consumer Expenditure Survey. We first consider the various ways in which life cycle models can be altered to generate differences in saving rates by income groups: differences in Social Security benefits, different time preference rates, non-homothetic preferences, bequest motives, uncertainty, and consumption floors. Using a variety of instruments for lifetime income, we find a strong positive relationship between personal saving rates and lifetime income. The data do not support theories relying on time preference rates, non-homothetic preferences, or variations in Social Security benefits. Instead, the evidence is consistent with models in which precautionary saving and bequest motives drive variations in saving rates across income groups. Finally, we illustrate how models that assume a constant rate of saving across income groups can yield erroneous predictions.

Precautionary Saving and Social Insurance

Microdata studies of household saving often find a significant group in the population with virtually no wealth, raising concerns about heterogeneity in motives for saving. In particular, this heterogeneity has been interpreted as evidence against the life-cycle model of saving. This paper argues that a life-cycle model can replicate observed patterns in household wealth accumulation after accounting explicitly for precautionary saving and asset-based means- tested social insurance. We demonstrate theoretically that social insurance programs with means tests based on assets discourage saving by households with low expected lifetime income. In addition, we evaluate the model using a dynamic programming model with four state variables. Assuming common preference parameters across lifetime- income groups, we are able to replicate the empirical pattern that low-income households are more likely than high-income households to hold virtually no wealth. Low wealth accumulation can be explained as a utility-maximizing response to asset-based means-tested welfare programs.

Sisyphus effects in a microwave-excited flux-qubit resonator system

Sisyphus amplification, familiar from quantum optics, has recently been reported as a mechanism to explain the enhanced quality factor of a classical resonant (tank) circuit coupled to a superconducting flux qubit. Here we present data from a coupled system, comprising a quantum mechanical rf SQUID (flux qubit) reactively monitored by an ultrahigh quality factor noise driven rf resonator and excited by microwaves. The system exhibits enhancement of the tank-circuit resonance, bringing it significantly closer (within 1%) to the lasing limit, than previously reported results. 2010 The American Physical Society

Determination of Oxidized Lipids in Commonly Consumed Foods and Their Binding Affinity for PPARγ

Background: Foods rich in polyunsaturated fatty acids (PUFA) are susceptible to oxidation through heating or storage. Oxidized lipids are known to act as ligands for a transcription factor (PPAR-gamma) that affects adipocyte differentiation and insulin sensitivity. Objective: The purpose of this study was to determine the amounts of oxidation products of a variety of PUFA containing foods over time, and to determine whether extracted fats from these foods act as ligands for PPAR-gamma. Method: To study the effect of room-temperature storage on oxidation, 5 foods (walnuts, sunflower seeds, ground flax, fish oil capsules, and infant formula) were purchased and stored at room temperature for 1, 2, and 3 months. To determine oxidation levels in fried foods, French fries and chicken nuggets were used. Fat was extracted from each food and the levels of oxidation products were analyzed by spectrophotometry and kits designed to measure oxidation products. Using a fluorescence polarization-based ligand screening assay kit, fat extracted from foods was analyzed for its binding affinity for PPAR-gamma. Results: Among foods stored at room temperature, the levels of oxidation products did not change significantly with time. Most foods exhibited the highest levels of oxidation at the purchase date. Infant formula and ground flax demonstrated higher levels of oxidation products than did other foods. In preliminary ligand binding assays, extracted fat from French fries showed the greatest binding affinity for PPAR-gamma; a select few other oils showed slight affinity. Discussion: Surprisingly, storage time did not affect oxidation levels. The greatest amount of oxidation may occur during pre-purchase storage conditions. The processing of formula and ground flax may be the cause of the relatively higher oxidation levels in those foods. The binding affinity for PPAR-gamma demonstrated by French fries needs further investigation. Conclusion: Certain oxidized lipids from foods may act as ligands for PPAR-gamma. Further research is required not only to determine which component of these PUFA-containing foods activates PPAR-gamma but also to determine whether that component acts as an agonist or antagonist for PPAR-gamma

TB102: A Markov Analysis of Structural Change and Output Prediction in the New England Egg Industry

The purpose of this study is to examine changes in the size distribution of egg farms as a Markov process in the three-state region consisting of Connecticut, Massachusetts, and New Hampshire. In 1978 these three states together received cash receipts of 83 million dollars from egg sales. In addition to examining the size distribution of farms, the occurrence of a marked structural change in the egg industry during the period 1967 to 1978 is statistically tested. Also, the future size distribution of egg farms, total number of layers, and egg output are projected.https://digitalcommons.library.umaine.edu/aes_techbulletin/1086/thumbnail.jp

Cancelling Capitalism?

Grow the Pie’s defense of capitalism is a tremendous contribution, albeit one which Edmans himself downplays. While the author largely bills his work as one aiming to correct the factual record about profitmaximization— while providing pointers for managers and policymakers—Edmans reaffirms the validity and viability of corporate capitalism as an ideology that, in practice, advances human welfare. Injecting this viewpoint into the academic debate is critically important at a time when voices of stakeholderists seem the loudest. Sociological research long ago confirmed that societal expectations (as often shaped by academic discourse) have real impact on our social systems and institutions. Popularly, the phenomenon is recognizable as the “Oedipus effect.” Renowned economist George Soros translated that concept into economics, giving us good reason to think that what people are told about capitalism from the so-called experts will, in turn, dictate the shape of our markets and economy for many years to come. These are not petty stakes. Souring on capitalism prematurely, or based on factual inaccuracy, risks discarding decades of economic institution building. Between the lines, one could read Grow the Pieto admonish its readers not to forget that capitalism has raised standards of living globally and fuels the innovation that enables human progress. The main goal of this Review is to highlight what I see as Edmans’s most important contribution in writing Grow the Pie—to explain why profits are prosocial—and then to expand the connection between his analysis to law and macroeconomic policy. The Review thus urges that Grow the Pieprovides a compelling foundation for considering why our existing legal frameworks should support the status quo, as enabling free-market capitalism, and proposals for radical reform should be abandoned. Ultimately, and ideally, this Review will draw attention to the ways in which Edmans’s data synthesis provides a compelling defensive of a free-market corporate law landscape, influencing the trajectory of U.S. corporate law and financial regulatory reform in the next few years

Spatial structures in a simple model of population dynamics for parasite-host interactions

Spatial patterning can be crucially important for understanding the behavior of interacting populations. Here we investigate a simple model of parasite and host populations in which parasites are random walkers that must come into contact with a host in order to reproduce. We focus on the spatial arrangement of parasites around a single host, and we derive using analytics and numerical simulations the necessary conditions placed on the parasite fecundity and lifetime for the populations long-term survival. We also show that the parasite population can be pushed to extinction by a large drift velocity, but, counterintuitively, a small drift velocity generally increases the parasite population.Comment: 6 pages, 6 figure