Enhancing the Quality of Data on Income and Wealth

Over the last decade or so, a substantial effort has gone into the design of a series of methodological investigations aimed at enhancing the quality of survey data on income and wealth. These investigations have largely been conducted at the Survey Research Center at the University of Michigan, and have mainly involved two longitudinal surveys: the Health and Retirement Study (HRS), with a first wave beginning in 1992 and continued thereafter every other year through 2004; and the Assets and Health Dynamics Among the Oldest Old (AHEAD) Study, begun in 1993 and continued in 1995 and 1998, then in every other year through 2004. This provides and overview of the main studies and summarizes what has been learned about correcting longitudinal inconsistencies that arise.

Can fitness tests be used to predict the vascular health of physically active older adults?

Objective There is an increased risk of cardiovascular diseases among older adults. This research aimed to determine which fitness tests could predict the vascular health of older adults using the gold standard pulse wave velocity (PWV) (applanation tonometry). Methods This cross-sectional study analysed 81 physically active adults (n=57 females) aged 64-91 (M=78±6.42) residing in independent living communities. A four-component fitness test included the 4-stage balance test (balance and falling assessment), six-minute walk test (SMWT) (aerobic exercise capacity), 30-second sit-to-stand test (postural hypotension and falling assessment), and the grip strength test (upper body strength) along with a PWV measurement. A regression use the four fitness tests as predictors of PWV for all participants. Pearson correlations then analysed these variables by subgroups of sex and age. Results When including all 81 participants, the four component fitness test significantly accounted for 20% of the variance in PWV (R2=.20; F(4,76)=4.70, p=.002) among older adults. Of the four components, higher sit-to-stand scores correlated with having healthy arteries (β=-.27, p=.027), but higher grip strength scores correlated with having unhealthy arteries (β=.23, p=.036). Neither the SMWT nor the balance test significantly contributed to the regression model. Pearson correlations indicated for men that better balance correlated significantly with healthy arteries (r=-.47, p=.011). For women, higher sit-to-stand scores (r=-.43, p ≤.001) and better balance (r=-.23, p=.045) correlated significantly with healthy arteries. Among 70-79 year olds, higher sit-to-stand scores (r=-.41, p =.002) and better balance (r=-.32, p=.014) correlated significantly with healthy arteries. Among 80-89 year olds, higher SMWT (r=-.40, p =.024) correlated significantly with healthy arteries. Conclusions The four-component fitness test did significantly predict arterial stiffness in older adults, but grip strength scores were unexpectedly negatively related to healthy arteries whereas sit-to-stand was positively related. In most groups, better balance and higher sit-to-stand scores were correlated to healthy arteries which was somewhat surprising. Finally, older participants were the only subgroup which showed a correlation between healthier arteries and higher SMWT scores. Given the SMWT is an aerobic exercise capacity assessment, it is surprising it did not correlate stronger to PWV

Investigating the relationships between lifestyle physical activity and diet on vascular health among older adults

Purpose This research aimed to investigate how behaviours of lifestyle physical activity (PA) and diet predict and correlate with vascular health in older adults using the gold standard measure of pulse wave velocity (PWV). Methods This cross-sectional study analysed 83 adults aged 64-91 years (M=78±6.44) residing in independent living communities. Dietary questions were taken from the Harvard disease risk tool. The Yale physical activity survey allowed the calculation of metabolic equivalents of task (METmins). PWV was collected using a non-invasive device (applanation tonometry). A hierarchical regression was calculated whereby covariates of taking blood pressure medication (BPM) and age (both known to affect PWV) were controlled in model 1 and diet and METmins were added into model 2. Pearson correlations were then calculated to determine individual correlations with PWV by subgroups of sex and age. Results The model 1 regression (R²=.29; F(2,79)=16.00, p<.001) indicated that covariates of BPM and age accounted for 29% (p≤.000) of the variance in PWV, but when diet and METmins were added in model 2 (R²=.31; F(4,77)=8.56, p<.001) they only contributed 2% more (non-significant change, p=.35) to the prediction of PWV. Healthier arteries in males correlated significantly with higher METmins (r=-.54, p=.004) and younger participants (r=.40, p=.027). Healthier arteries in females correlated significantly with younger participants (r=.49, p=.000), no BPM (r=.36, p=.002), and higher METmins (r=-.25, p=.029). Among 64-78 year olds, healthier arteries were correlated with no BPM (r=.35, p=.011), and healthier diets (r=-.26, p=.046), but not with METmins. Alternatively, 79-91 year-olds showed healthier arteries correlated with higher METmins (r=-.36, p=.012), but not with diet. Conclusions After controlling for age and BPM (model 1) in the regression, diet and METmins (model 2) were unable to significantly contribute to the prediction of arterial stiffness in older adults. Both males and females showed correlations between healthier arteries and higher METmins, but not between arterial health and diet, suggesting LPA is more correlated to arterial health than diet. Those aged 64-78 had healthy arteries in correlation with a healthy diet, whereas 79-91 year olds had healthy arteries in correlation with higher METmins

Characterization of early cortical population response to thalamocortical input in vitro

The in vitro thalamocortical slice preparation of mouse barrel cortex allows for stimulation of the cortex through its natural afferent thalamocortical pathway. This preparation was used here to investigate the first stage of cortical processing in the large postsynaptic dendritic networks as revealed by voltage sensitive dye imaging (VSDI). We identified the precise location and dimensions of two clearly distinguishable dendritic networks, one in the granular layer (GL) IV and one in the infragranular layer (IGL) V and VI and showed that they have different physiological properties. DiI fluorescent staining further revealed that thalamocortical axons project on to these two networks in the typical barrel like form, not only in the granular but also in the IGL. Finally we investigated the short-term dynamics of both the VSDI signal and the local field potential (LFP) in response to a train of eight-pulses at various frequencies in both these layers. We found evidence of differences in the plasticity between the first two response peaks compared to the remaining six peaks as well as differences in short-term plasticity between the VSDI response and the LFP. Our findings suggest, that at least early cortical processing takes place in two separate dendritic networks that may stand at the beginning of further parallel computation. The detailed characterization of the parameters of these networks may provide tools for further research into the complex dynamics of large dendritic networks and their role in cortical computation

Design and fabrication of highly efficient non-linear optical devices for implementing high-speed optical processing

We present the design and fabrication of micro-cavity semiconductor devices for enhanced Two-Photon-Absorption response, and demonstrate the use of these devices for implementing sensitive autocorrelation measurements on pico-second optical pulses

High-sensitivity two-photon absorption microcavity autocorrelator

A GaAs-AlAs microcavity device has been used as a photodetector in an autocorrelator for measuring the temporal pulsewidth of 1.5-/spl mu/m optical pulses. Enhancement of the two-photon absorption photocurrent due to the microcavity structure results in an autocorrelation (average power times peak power) sensitivity of 9.3/spl times/10/sup -4/ (mW)/sup 2/, which represents two orders of magnitude improvement when compared with conventional autocorrelators

Two-photon absorption in microcavities for optical autocorrelation and sampling

We have designed novel semiconductor microcavity structures for the enhancement of the two-photon absorption (TPA) photocurrent. We report a TPA autocorrelation technique for short optical pulses that uses the microcavity structure instead of a second harmonic generation crystal. Knowledge of these characteristics is important for implementation in applications such as optical switching and sampling in optical time division multiplexed (OTDM) communications systems

A novel approach towards two-photon absorption based detectors

Summary: We have demonstrated that the inherent inefficiency of the TPA process in semiconductors can be overcome by incorporating the semiconductor in a microcavity structure. Proof of concept devices with a 0.27μm Ga0.7Al0.3As active region and two Bragg reflectors with the cavity resonance of 890 nm were fabricated. We measured the TPA photocurrent of these devices and have demonstrated a factor of 12000 enhancement over a nonmicrocavity device at 890 nm. Our active length of 0.27 nm is as efficient as 5.4 mm without a microcavity, overcoming the very long detector lengths limiting the use of TPA in practical autocorrelators, optical switches and sampling devices for real telecommunication systems. The effect of the cavity is to enhance the intra-cavity optical intensity, which leads to an increase in the nonlinear response of the active region. We studied, theoretically and experimentally, the impact of the cavity on the temporal response and the sensitivity of the device, which are critical considerations for commercial applications. This cavity design has a 3 pico-second response time and the autocorrelation trace is comparable with the BBO crystal response for an input 1.6 ps pulse. Devices designed for 1550 nm have also been realised and our measurements indicate these two-photon absorption based detectors are potential candidates for optical autocorrelation of short optical pulses, and for optical switching and sampling in optical time division multiplexed (OTDM) communications systems