The Choice of Institutions: The Role of Risk and Risk-Aversion

Institutions can affect individual behavior both via their efficiency impact and via their risk reducing mechanisms. However there has been little study of the relative importance of these two channels in how individuals choose between simultaneously extant institutions. This paper presents a simple model of institutional choice in a labor market when there is a risk/reward trade-off, and tests the predictions of the theory. Using a novel empirical approach that adapts an ARCH-in-mean to cross-sectional survey data from China, we find that risk and risk aversion are strongly related to the choice of a labor market institution. Further, risk and risk aversion are quantitatively more important than the sectoral wage differential in explaining employment institution choices. Specifically, we find that wage risk has two orders of magnitude greater impact on labor market institutional choice than the wage difference, with a one standard deviation increase in earnings risk reducing the number of workers choosing jobs in the private (risky) sector by 22%.Institutions, Risk, Labor Market, Risk Aversion

Phospholipid metabolism in the developing liver : I. The biosynthesis of choline glycerophosphatides by liver slices from fetal, newborn and adult rats

1. 1. The biosynthesis of choline glycerophosphatides was evaluated in fetal, neonatal and adult female rat liver. The two main pathways were assessed by studying the rates of incorporation of [Me-14C]choline and [Me-14C]methionine by liver slices.2. 2. Over 96% of the lipid radioactivity from [Me-14C] choline was located in choline glycerophosphatides. In adult liver slices 93% of the total lipid radioactivity from [Me-14C]methionine was located in choline glycerophosphatides. An appreciable amount of radioactivity from [Me-14C]methionine was incorporated into fatty acids by fetal liver slices.3. 3. Liver slices from fetal rats incorporated the same amount of [Me-14C]choline into lecithin as did adult liver slices except for a drop 2 days before birth. Liver slices from 3-day-old neonatal rats incorporated about twice as much [Me-14C]choline as the adult liver slices.4. 4. Liver slices from fetal and young rats incorporated about 8-10 times more [Me-14C]choline into phosphoryl choline than did liver slices from adults. Adult levels were reached at 10 days after birth.5. 5. The incorporation of radioactivity from [Me-14C]methionine into lecithin by fetal liver slices was much lower than that by adult liver slices and increased to twice adult levels by 10-12 days after birth. Adult levels were reached by 25 days after birth.6. 6. Studies with [1,2-14C2, Me-14H]choline indicated that the choline was incorporated intact and that little, if any, of the methyl groups of choline were used for the methylation of phosphatidyl ethanolamine.7. 7. The mechanism of choline incorporation into lecithin is discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32929/1/0000311.pd

Clinical Outcomes and Cadaveric Biomechanical Analysis of Endoscopic Percutaneous Achilles Tendon Rupture Repair With Absorbable Suture

Background: Percutaneous repair of acute Achilles tendon rupture (ATR) continues to gain in popularity. The primary aim of the study was to review the outcomes of a patient cohort undergoing a novel technique of endoscopic percutaneous Achilles tendon repair with absorbable suture. A secondary purpose of this study was to evaluate the basic biomechanical properties of the technique. Methods: A cohort of 30 patients who underwent percutaneous ATR repair was retrospectively analyzed with Achilles Tendon Rupture Scores (ATRS), complications, and additional outcome measures. For a biomechanical analysis portion of the study, 12 cadaveric specimens were paired and randomized to either novel percutaneous repair or open Kessler repair with absorbable suture. These specimens were subjected to 2 phases of cyclical testing (100 cycles 10-43 N followed by 200 cycles 10-86 N) and ultimate strength testing. Results: In the clinical portion of the study we report excellent patient reported outcomes (mean ATRS 94.1), high level of return to sport, and high patient satisfaction. One partial re-rupture was reported but with no major wound or neurologic complications. In the biomechanical portion of the study we found no significant difference in tendon gapping between percutaneous and open repairs in phase 1 of testing. In phase 2, increased gapping occurred between percutaneous (17.8 mm [range 10.7-24.1, SD 6.4]) and open repairs (10.8 mm [range 7.6-14.9, SD 2.7, P = .037]). The ultimate load at failure was not statistically different between the 2 repairs. Conclusions: A percutaneous ATR repair technique using endoscopic assistance and absorbable suture demonstrated low complications and good outcomes in a cohort of patients, with high satisfaction, and excellent functional outcomes including high rates of return to sport. Cadaveric biomechanical testing demonstrated excellent survival during testing and minimal increase in gapping compared with open repair technique, representing sufficient strength to withstand forces seen in early rehabilitation. A percutaneous Achilles tendon repair technique with absorbable suture may minimize risks associated with operative repair while still maintaining the benefit of operative repair. Level of Evidence: Level IV, retrospective case series

Properties of diacylglycerol kinase in adult and fetal rat lung

Diacylglycerol kinase activity is found in both adult and fetal lung. Approximately 27 and 52% of the total activity is found in microsomes and cytosol, respectively. The activity is maximal at pH 7.4. The apparent Km for ATP is 0.11 mM and 0.21 mM for cytosol and microsomes, respectively. The apparent Km for dioleoylglycerol is 0.05 mM for cytosol and 0.14 mM for microsomes. Maximal activity in cytosol and microsomes is obtained with 2.0 mM deoxycholate. Other detergents cannot substitute for deoxycholate. Phosphatidylglycerol stimulates activity in the absence and in the presence of deoxycholate. Phosphatidylserine also stimulates activity, whereas phosphatidylethanolamine was inactive and phosphatidylcholine inhibited the reaction. Linoleic acid produced inhibition. The general properties of the enzyme were similar for fetal and adult lung. Diacylglycerol kinase from microsomes and cytosol fraction from both fetal and adult lung was most active with dioleoylglycerol and diacylglycerol from egg phosphatidylcholine. Significantly lower activity was obtained with dipalmitoylglycerol. Phosphatidylglycerol did not alter the relative substrate preferences. The activity in microsomes increased with development from 19 days gestation to a maximal activity at 21 days gestation. Maximal activity was about 2-fold higher than the adult. The activity dropped rapidly reaching adult values prior to birth (22 days gestation). The activity in cytosol fractions increased gradually from 19 days gestation, reaching adult values by 22 days gestation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23770/1/0000006.pd

The content of diacylglycerol, triacylglycerol and monoacylglycerol and a comparison of the structural and metabolic heterogeneity of diacylglycerols and phosphatidylcholine during rat lung development

The content of diacylglycerol in fetal rat lung is approx. 36% of the adult and rapidly increases to adult levels by 1 day after birth. Triacylglycerol content is also low (23%) and increases to adult levels between 1 and 2 days following birth. Monoacylglycerol content is relatively low at all stages of development. The analysis of the molecular species of diacylglycerols showed that the disaturated species accounted for 30-40% of the diacylglycerols and the monoene species 20-28%. Phosphatidylcholine contained 40-45% disaturated and approx. 30% monoene species. The overall pattern of molecular species of phosphatidylcholine was similar to the pattern for diacylglycerol. The in vivo incorporation of [2-3H]glycerol into molecular species of diacylglycerol and phosphatidylcholine in -1-day-fetal (i.e., 1 day before birth) lung showed that the disaturated species of diacylglycerol had the highest incorporation and appeared to have a higher rate of turnover. In contrast, [2-3H]glycerol was incorporated by fetal liver most actively in the monoenoic and dienoic species of diacylglycerol. The relative incorporation of radioactivity into disaturated, monoene and diene species of phosphatidylcholine in fetal lung was very similar to that for the corresponding diacylglycerol species. The rate of the reaction from the disaturated species of diacylglycerol to the disaturated species of phosphatidylcholine, calculated from the in vivo data, was one of the higher rates and indicated considerable potential for the synthesis of disaturated phosphatidylcholine via this route. The overall results suggests that de novo synthesis of disaturated phosphatidylcholine from the disaturated species of diacylglycerol can be a major route for the synthesis of dipalmitoylphosphatidylcholine in fetal lung.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24392/1/0000662.pd

Base-exchange reactions of the phospholipids in cardiac membranes

Canine cardiac microsomes were shown to incorporate the nitrogenous bases, serine, ethanolamine, and choline, into their respective phospholipids by the energy-independent, Ca2+-stimulated base-exchange reactions. The optimal Ca2+ concentration was 2.5 mM. Metal ions other than Ca2+ either inhibited or had no effect on the activities. La3+ and Mn2+ were both potent inhibitors. The pH optimum for the reactions at 2.5 mM Ca2+ was approx. 7.8 and depended upon Ca2+ concentration. Apparent Km values at 2.5 mM Ca2+ were 0.06 mM for -serine, 0.13 mM for ethanolamine and 0.49 mM for choline. The kinetic and metal ion inhibition studies suggest that the choline-exchange reaction is a separate process from the serine and ethanolamine reactions. The ATPstimulated Ca2+ binding system of the cardiac membranes was not related to the base-exchange reactions; however, the energy-independent Ca2+ binding to the membranes appears to be related to the exchange reactions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23240/1/0000173.pd

Ethanolamine phosphokinase: Activity and properties during liver development

The conditions for maximal activity of ethanolamine phosphokinase from rat liver were determined. All of the activity was located in the supernatant fraction after centrifugation at 100 000 x g for 60 min. The enzyme activity had a pH optimum at 8.5 and an apparent Km for ethanolamine of 1[middle dot]10-4 M at an ATP and Mg2+ concentration of 3.0 mM. The enzyme uses the Mg-ATP complex as substrate and is inhibited by free ATP. Choline inhibits ethanolamine phosphokinase. Maximal inhibition is obtained at choline concentrations of 0.4 mM. Treatment of the supernatant with Sephadex G-25 or by dialysis causes an increase in the maximal amount of inhibition obtained with choline. The inhibition by choline is non-competitive with ethanolamine and competitive with ATP. Ethanolamine phosphokinase is inhibited by N,N-dimethylethanolamine and N-methylethanolamine but not by betaine, phosphoryl choline, CDP-choline or phosphorylethanolamine.The activity of ethanolamine phosphokinase is low in -5-day fetal liver. The activity increases from -5 days to -2 days and drops at 1 day after birth. An endogenous inhibitor of ethanolamine phosphokinase is present in all preparations but at different levels. The drop in activity in 1-day-old animals is due to the presence of higher amounts of inhibition by the endogenous inhibitor within the preparation. Evidence indicates that the endogenous inhibitor is choline.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/34067/1/0000345.pd

Biomechanical risk factors of non-contact ACL injuries: A stochastic biomechanical modeling study

Background Significant efforts have been made to identify modifiable risk factors of non-contact anterior cruciate ligament (ACL) injuries in male and female athletes. However, current literature on the risk factors for ACL injury are purely descriptive. An understanding of biomechanical relationship between risk and risk factors of the non-contact ACL injury is necessary to develop effective prevention programs.PurposeTo compare lower extremity kinematics and kinetics between trials with and without non-contact ACL injuries and to determine if any difference exists between male and female trials with non-contact ACL injuries regarding the lower extremity motion patterns.Methods In this computer simulation study, a stochastic biomechanical model was used to estimate the ACL loading at the time of peak posterior ground reaction force (GRF) during landing of the stop-jump task. Monte Carlo simulations were performed to simulate the ACL injuries with repeated random samples of independent variables. The distributions of independent variables were determined from in vivo laboratory data of 40 male and 40 female recreational athletes.ResultsIn the simulated injured trials, both male and female athletes had significantly smaller knee flexion angles, greater normalized peak posterior and vertical GRF, greater knee valgus moment, greater patella tendon force, greater quadriceps force, greater knee extension moment, and greater proximal tibia anterior shear force in comparison to the simulated uninjured trials. No significant difference was found between genders in any of the selected biomechanical variables in the trials with simulated non-contact ACL injuries.Conclusion Small knee flexion angle, large posterior GRF, and large knee valgus moment are risk factors of non-contact ACL injury determined by a stochastic biomechanical model with a cause-and-effect relationship

Reliability of Intra-Retinal Layer Thickness Estimates

Purpose Measurement of intra-retinal layer thickness using optical coherence tomography (OCT) has become increasingly prominent in multiple sclerosis (MS) research. Nevertheless, the approaches used for determining the mean layer thicknesses vary greatly. Insufficient data exist on the reliability of different thickness estimates, which is crucial for their application in clinical studies. This study addresses this lack by evaluating the repeatability of different thickness estimates. Methods Studies that used intra-retinal layer segmentation of macular OCT scans in patients with MS were retrieved from PubMed. To investigate the repeatability of previously applied layer estimation approaches, we generated datasets of repeating measurements of 15 healthy subjects and 13 multiple sclerosis patients using two OCT devices (Cirrus HD-OCT and Spectralis SD-OCT). We calculated each thickness estimate in each repeated session and analyzed repeatability using intra-class correlation coefficients and coefficients of repeatability. Results We identified 27 articles, eleven of them used the Spectralis SD-OCT, nine Cirrus HD-OCT, two studies used both devices and two studies applied RTVue-100. Topcon OCT-1000, Stratus OCT and a research device were used in one study each. In the studies that used the Spectralis, ten different thickness estimates were identified, while thickness estimates of the Cirrus OCT were based on two different scan settings. In the simulation dataset, thickness estimates averaging larger areas showed an excellent repeatability for all retinal layers except the outer plexiform layer (OPL). Conclusions Given the good reliability, the thickness estimate of the 6mm-diameter area around the fovea should be favored when OCT is used in clinical research. Assessment of the OPL was weak in general and needs further investigation before OPL thickness can be used as a reliable parameter