Comments and Discussion [The Measurement and Determination of Loanable-Funds Saving]

macroeconomics, saving, capital formation, interest

Using Yellowdig in Marketing Courses: An Analysis of Individual Contributions and Social Interactions in Online Classroom Communities and Their Impact on Student Learning and Engagement

Students in four marketing classes participated in a pilot program where they used Yellowdig in the classroom. Yellowdig is a private network for collaboration targeted towards educational institutions to increase student engagement. Yellowdig seeks to engage students using a broad array of resources including videos, news articles, blogs and more. It offers a Facebook-like experience (a platform the majority of students are very familiar with) for ease of use. In the classes, Yellowdig was used for two purposes: as a way to create a community inside and outside of the classroom and as a means by which students create and share course-relevant content throughout the semester. To achieve those goals, students posted items of interest relating to course content to Yellowdig and commented on and up-voted others’ posts. Yellowdig data was used to capture insights about students’ individual contributions and social interactions. The manuscript summarizes academic literature on social learning and social media, followed by a description of Yellowdig and how it was used in the marketing classes to benefit student learning and engagement. The results of quantitative analyses, including data visualization and social network analysis, are used to help educators understand both individual contributions to and social interactions in the network. In addition, multiple linear regression results suggest that engagement through Yellowdig activities does benefit student learning. Strategies for instructors to enhance student engagement and learning using these types of analyses are provided

Quantitative analysis and modeling of microembolic phenomena

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (p. 131-136).This thesis explores parameters that govern microvascular occlusion secondary to embolic phenomenon. Bulk and individual properties of microembolic particles were characterized using light microscopy, SEM and optically-based particle analysis. Particulate probability distributions were created from imaging data using Matlab. Size distribution, volume, morphology and chemical properties were quantified using in-vivo and model flow systems to correlate particulate characteristics and occlusive efficacy. This study focused on novel expandable/deformable Polyacrylic acid microspheres (PAA-MS) for use as catheter-deliverable therapeutic emboli. These emboli expand in aqueous media such as blood and remain unexpanded in custom delivery media. The techniques developed to investigate therapeutic microemboli were applied to the analysis of clot dissolution byproducts. PAA-MS expand volumetrically in seconds when placed in aqueous environments. PAA-MS were modified to resist fragmentation based upon failure analysis. Degradation testing demonstrated PAA-MS chemical stability. Charge characteristics inherent to the PAA-MS acid matrix were leveraged to develop low-viscosity media that prevent expansion. Cationic dyes were found that bind the charged matrix within PAA-MS to enhance visualization.(cont.) Unexpanded PAA-MS were delivered through standard catheters and microcatheters at concentrations that induce durable occlusions. Non-expandable microspheres could not be delivered through microcatheters. PAA-MS required less embolic mass to occlude in-vitro flow systems at significantly higher pressures than nonexpandable microspheres. Preliminary biocompatibility tests demonstrated safety and PAA-MS were able to occlude both porcine renal and coronary vasculature in-vivo. An ultrasonic clot dissolution device generated microemboli from synthetic acellular fibrin-only clots and whole blood clots. The average particle size for whole blood clots was less than 100 microns and acellular clots produced larger average emboli than whole blood clots, indicating that cellular components may limit thromboembolic size. The expandable/deformable properties of PAA-MS allow them to traverse microcatheters when unexpanded. Once in blood, PAA-MS expand 140-fold to create a space-filling, pressure resistant occlusion.(cont.) These results have implications for intravascular embolization procedures where smaller catheters minimize vasospasm and allow more precise targeting while stronger occlusions resist occlusive breakdown and associated distal embolization. These embolic improvements could reduce procedural complications while increasing efficacy. Future work will solidify correlations between microembolic properties, microvascular occlusion and tissue infarction.by Michael J. Feldstein.S.M

Prediction of suicidal ideation and attempt in 9 and 10 year-old children using transdiagnostic risk features

The objective of the current study was to build predictive models for suicidal ideation in a sample of children aged 9–10 using features previously implicated in risk among older adolescent and adult populations. This case-control analysis utilized baseline data from the Adolescent Brain and Cognitive Development (ABCD) Study, collected from 21 research sites across the United States (N = 11,369). Several regression and ensemble learning models were compared on their ability to classify individuals with suicidal ideation and/or attempt from healthy controls, as assessed by the Kiddie Schedule for Affective Disorders and Schizophrenia–Present and Lifetime Version. When comparing control participants (mean age: 9.92±0.62 years; 4944 girls [49%]) to participants with suicidal ideation (mean age: 9.89±0.63 years; 451 girls [40%]), both logistic regression with feature selection and elastic net without feature selection predicted suicidal ideation with an AUC of 0.70 (CI 95%: 0.70–0.71). The random forest with feature selection trained to predict suicidal ideation predicted a holdout set of children with a history of suicidal ideation and attempt (mean age: 9.96±0.62 years; 79 girls [41%]) from controls with an AUC of 0.77 (CI 95%: 0.76–0.77). Important features from these models included feelings of loneliness and worthlessness, impulsivity, prodromal psychosis symptoms, and behavioral problems. This investigation provided an unprecedented opportunity to identify suicide risk in youth. The use of machine learning to examine a large number of predictors spanning a variety of domains provides novel insight into transdiagnostic factors important for risk classification

Quantifying the improvement of surrogate indices of hepatic insulin resistance using complex measurement techniques

We evaluated the ability of simple and complex surrogate-indices to identify individuals from an overweight/obese cohort with hepatic insulin-resistance (HEP-IR). Five indices, one previously defined and four newly generated through step-wise linear regression, were created against a single-cohort sample of 77 extensively characterised participants with the metabolic syndrome (age 55.6±1.0 years, BMI 31.5±0.4 kg/m2; 30 males). HEP-IR was defined by measuring endogenous-glucose-production (EGP) with [6–62H2] glucose during fasting and euglycemic-hyperinsulinemic clamps and expressed as EGP*fasting plasma insulin. Complex measures were incorporated into the model, including various non-standard biomarkers and the measurement of body-fat distribution and liver-fat, to further improve the predictive capability of the index. Validation was performed against a data set of the same subjects after an isoenergetic dietary intervention (4 arms, diets varying in protein and fiber content versus control). All five indices produced comparable prediction of HEP-IR, explaining 39–56% of the variance, depending on regression variable combination. The validation of the regression equations showed little variation between the different proposed indices (r2 = 27–32%) on a matched dataset. New complex indices encompassing advanced measurement techniques offered an improved correlation (r = 0.75, P<0.001). However, when validated against the alternative dataset all indices performed comparably with the standard homeostasis model assessment for insulin resistance (HOMA-IR) (r = 0.54, P<0.001). Thus, simple estimates of HEP-IR performed comparable to more complex indices and could be an efficient and cost effective approach in large epidemiological investigations

Recombinant tissue-type plasminogen activator versus a novel dosing regimen of urokinase in acute pulmonary embolism: a randomized controlled multicenter trial

AbstractThrombolysis of acute pulmonary embolism can be accomplished more rapidly and safely with 100 mg of recombinant human tissue-type plasminogen activator (rt-PA) (Activase) than with a conventional dose of urokinase (Abbokinase) given as a 4,400-U/kg bolus dose, followed by 4,400 U/kg per h for 24 h. To determine the effects of a more concentrated urokinase dose administered over a shorter time course, this trial enrolled 90 patients with baseline perfusion lung scans and angiographically documented pulmonary embolism. They were randomized to receive either 100 mg/2 h of rt-PA or a novel dosing regimen of urokinase: 3 million U/2 h with the initial 1 million U given as a bolus injection over 10 min. Both drugs were delivered through a peripheral vein.To assess efficacy after initiation of therapy, repeat pulmonary angiograms at 2 h were performed in 87 patients and then graded in a blinded manner by a panel of six investigators. Of the 42 patients allocated to rt-PA therapy, 79% showed angiographic improvement at 2 h, compared with 67% of the 45 patients randomized to urokinase therapy (95% confidence interval for the difference in these proportions [rt-PA minus urokinase] is −6.6% to 30.4%; p = 0.11). The mean change in perfusion lung scans between baseline and 24 h was similar for both treatments. Three patients (two treated with rt-PA and one with urokinase) had an intracranial hemorrhage, which was fatal in one.The results indicate that a 2-h regimen of rt-PA and a new dosing regimen of urokinase exhibit similar efficacy and safety for treatment of acute pulmonary embolism

The effect of smoothed solar wind inputs on global modeling results

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95500/1/jgra20071.pd

Asymmetric WIMP dark matter

In existing dark matter models with global symmetries the relic abundance of dark matter is either equal to that of anti-dark matter (thermal WIMP), or vastly larger, with essentially no remaining anti-dark matter (asymmetric dark matter). By exploring the consequences of a primordial asymmetry on the coupled dark matter and anti-dark matter Boltzmann equations we find large regions of parameter space that interpolate between these two extremes. Interestingly, this new asymmetric WIMP framework can accommodate a wide range of dark matter masses and annihilation cross sections. The present-day dark matter population is typically asymmetric, but only weakly so, such that indirect signals of dark matter annihilation are not completely suppressed. We apply our results to existing models, noting that upcoming direct detection experiments will constrain a large region of the relevant parameter space.Comment: 32 pages, 6 figures, updated references, updated XENON100 bounds, typo in figure caption correcte

The CMB and the measure of the multiverse

In the context of eternal inflation, cosmological predictions depend on the choice of measure to regulate the diverging spacetime volume. The spectrum of inflationary perturbations is no exception, as we demonstrate by comparing the predictions of the fat geodesic and causal patch measures. To highlight the effect of the measure---as opposed to any effects related to a possible landscape of vacua---we take the cosmological model, including the model of inflation, to be fixed. We also condition on the average CMB temperature accompanying the measurement. Both measures predict a 1-point expectation value for the gauge-invariant Newtonian potential, which takes the form of a (scale-dependent) monopole, in addition to a related contribution to the 3-point correlation function, with the detailed form of these quantities differing between the measures. However, for both measures both effects are well within cosmic variance. Our results make clear the theoretical relevance of the measure, and at the same time validate the standard inflationary predictions in the context of eternal inflation.Comment: 28 pages; v2: reference added, some clarification

WIMP-nucleus scattering in chiral effective theory

We discuss long-distance QCD corrections to the WIMP-nucleon(s) interactions in the framework of chiral effective theory. For scalar-mediated WIMP-quark interactions, we calculate all the next-to-leading-order corrections to the WIMP-nucleus elastic cross-section, including two-nucleon amplitudes and recoil-energy dependent shifts to the single-nucleon scalar form factors. As a consequence, the scalar-mediated WIMP-nucleus cross-section cannot be parameterized in terms of just two quantities, namely the neutron and proton scalar form factors at zero momentum transfer, but additional parameters appear, depending on the short-distance WIMP-quark interaction. Moreover, multiplicative factorization of the cross-section into particle, nuclear and astro-particle parts is violated. In practice, while the new effects are of the natural size expected by chiral power counting, they become very important in those regions of parameter space where the leading order WIMP-nucleus amplitude is suppressed, including the so-called "isospin-violating dark matter" regime. In these regions of parameter space we find order-of-magnitude corrections to the total scattering rates and qualitative changes to the shape of recoil spectra.Comment: 23 pages, 6 figures, 1 tabl