Staged Contact Optimization: Combining Contact-Implicit and Multi-Phase Hybrid Trajectory Optimization

Trajectory optimization problems for legged robots are commonly formulated with fixed contact schedules. These multi-phase Hybrid Trajectory Optimization (HTO) methods result in locally optimal trajectories, but the result depends heavily upon the predefined contact mode sequence. Contact-Implicit Optimization (CIO) offers a potential solution to this issue by allowing the contact mode to be determined throughout the trajectory by the optimization solver. However, CIO suffers from long solve times and convergence issues. This work combines the benefits of these two methods into one algorithm: Staged Contact Optimization (SCO). SCO tightens constraints on contact in stages, eventually fixing them to allow robust and fast convergence to a feasible solution. Results on a planar biped and spatial quadruped demonstrate speed and optimality improvements over CIO and HTO. These properties make SCO well suited for offline trajectory generation or as an effective tool for exploring the dynamic capabilities of a robot

Nucleation Rate of Hadron Bubbles in Baryon-Free Quark-Gluon Plasma

We evaluate the factor $\kappa$ appearing in Langer's expression for the nucleation rate extended to the case of hadron bubbles forming in zero baryon number cooled quark-gluon plasma. We consider both the absence and presence of viscosity and show that viscous effects introduce only small changes in the value of $\kappa$Comment: 9 pages, revtex, no figures Full postscript version available at via the WWW at http://nucth.physics.wisc.edu/preprints/ or by via from ftp://nucth.physics.wisc.edu/pub/preprints/mad-nt-95-06.p

Amplitude and phase representation of quantum invariants for the time dependent harmonic oscillator

The correspondence between classical and quantum invariants is established. The Ermakov Lewis quantum invariant of the time dependent harmonic oscillator is translated from the coordinate and momentum operators into amplitude and phase operators. In doing so, Turski's phase operator as well as Susskind-Glogower operators are generalized to the time dependent harmonic oscillator case. A quantum derivation of the Manley-Rowe relations is shown as an example

Reduction of myocardial infarction by postischemic administration of the calpain inhibitor A-705253 in comparison to the Na(+)/H(+) exchange inhibitor Cariporide (R) in isolated perfused rabbit hearts

The calpain inhibitor A-705253 and the Na(+)/H(+) exchange inhibitor Cariporide (R) were studied in isolated perfused rabbit hearts subjected to 60 min occlusion of the ramus interventricularis of the left coronary artery (below the origin of the first diagonal branch), followed by 120 min of reperfusion. The inhibitors were added to the perfusion fluid solely or in combination at the beginning of reperfusion. Hemodynamic monitoring and biochemical analysis of perfusion fluid from the coronary outflow were performed. Myocardial infarct size and area at risk (transiently not perfused myocardium) were determined from left ventricular slices after a special staining procedure with Evans blue and 2,3,5-triphenyltetrazolium chloride. The infarcted area (dead myocardium) was 72.7 +/- 4.0% of the area at risk in untreated controls, but was significantly smaller in the presence of the inhibitors. The largest effect was observed with 10(-6) M A-705253, which reduced the infarcted area to 49.2 +/- 4.1% of the area at risk, corresponding to a reduction of 33.6%. Cariporide (R) at 10(-6) M reduced the infarct size to the same extent. The combination of both inhibitors, however, did not further improve cardioprotection. No significant difference was observed between the experimental groups in coronary perfusion, left ventricular pressure, heart rate, or in the release of lactate dehydrogenase and creatine kinase from heart muscle

Tryptophan pathway abnormalities in a murine model of hereditary glaucoma

Background: It has been shown that a possible pathogenetic mechanism of neurodegenera-tion in the mouse model of glaucoma (DBA/2J) may be an alteration of kynurenic acid (KYNA) in the retina. This study aimed to verify the hypothesis that alterations of tryptophan (TRP) metabolism in DBA/2J mice is not limited to the retina. Methods: Samples of the retinal tissue and serum were collected from DBA/2J mice (6 and 10 months old) and control C57Bl/6 mice of the same age. The concentration of TRP, KYNA, kynurenine (KYN), and 3-hydroxykynurenine (3OH-K) was measured by HPLC. The activity of indoleamine 2,3-dioxygenase (IDO) was also determined as a KYN/TRP ratio. Results: TRP, KYNA, L-KYN, and 3OH-K concentration were significantly lower in the retinas of DBA/2J mice than in C57Bl/6 mice. 3OH-K concentration was higher in older mice in both strains. Serum TRP, L-KYN, and KYNA concentrations were lower in DBA/2J than in age-matched controls. However, serum IDO activity did not differ significantly between compared groups and strains. Conclusions: Alterations of the TRP pathway seem not to be limited to the retina in the murine model of hereditary glaucoma

Tryptophan and Kynurenine Pathway Metabolites in Animal Models of Retinal and Optic Nerve Damage: Different Dynamics of Changes

Kynurenines, products of tryptophan (TRP) metabolism, display neurotoxic (e.g., 3-hydroxykynurenine; 3-HK), or neuroprotective (e.g., kynurenic acid; KYNA) properties. Imbalance between the enzymes constituting the kynurenine pathway (KP) plays a role in several disease, including neurodegeneration. In this study, we track changes in concentrations of tryptophan and its selected metabolites after damage to retinal ganglion cells and link this data with expression of KP enzymes. Brown-Norway rats were subjected to intravitreal N-methyl-D-aspartate (NMDA) injection or partial optic nerve crush (PONC). Retinas were collected 2 and 7 days after the completion of PONC or NMDA injection. Concentrations of TRP, kynurenine (KYN), and KYNA were determined by high performance liquid chromatography (HPLC). Data on gene expression in the rat retina were extracted from GEO, public microarray experiments database. Two days after NMDA injection concentration of TRP decreased, while KYN and KYNA increased. At day 7 compared to day 2 decrease of KYN, KYNA and further reduction of TRP concentration were observed, but on day 7 KYN concentration was still elevated when compared to controls. At day 2 and 7 after NMDA injection no statistically significant alterations of 3-HK were observed. TRP and 3-HK concentration was higher in PONC group than in controls. However, both KYN and KYNA were lower. At day seven concentration of TRP, 3-HK, and KYN was higher, whereas concentration of KYNA declined. In vivo experiments showed that retinal damage or optic nerve lesion affect TRP metabolism via KP. However, the pattern of changes in metabolite concentrations was different depending on the model. In particular, in PONC KYNA and KYN levels were decreased and 3-HK elevated. These observations correspond with data on expression of genes encoding KP enzymes assessed after optic nerve crush or transection. After intraorbital optic nerve crush downregulation of KyatI and KyatIII between 24 h and 3 days after procedure was observed. Kmo expression was transiently upregulated (12 h after the procedures). After intraorbital optic nerve transsection (IONT) Kmo expression was upregulated after 48 h and 7 days, KyatI and KyatIII were downregulated after 12, 48 h, 7 days and upregulated after 15 days. Collected data point to the conclusion that development of therapeutic strategies targeting the KP could be beneficial in diseases involving retinal neurodegeneration