Covariant description of parametrized nonrelativistic Hamiltonian systems

The various phase spaces involved in the dynamics of parametrized nonrelativistic Hamiltonian systems are displayed by using Crnkovic and Witten's covariant canonical formalism. It is also pointed out that in Dirac's canonical formalism there exists a freedom in the choice of the symplectic structure on the extended phase space and in the choice of the equations that define the constraint surface with the only restriction that these two choices combine in such a way that any pair (of these two choices) generates the same gauge transformation. The consequence of this freedom on the algebra of observables is also discussed.Comment: 15 pages, latex file. corrected typos, minor changes done to match published versio

Pilot Study Examining Pregnancy-specific Equations to Estimate Percent Body Fat in an Overweight/obese Pregnant Hispanic Population

Background and Purpose: Over half of women entering pregnancy are overweight or obese, increasing metabolic risk. This pilot study investigated whether established equations for estimating maternal percent body fat using anthropometry are accurate for Hispanic, overweight or obese pregnant women. Methods: The Siri technique of calculating percent body fat from direct measurements of body density and total body water was the gold-standard. Other pregnancy-specific equations were also examined. The study population included 15 normoglycemic, pregnant Hispanic women in their third trimester (33.2±1.9 gestational week) with a pre-pregnancy body mass index ≥25 to <40kg/m2 , and with no history of chronic disease, or illicit drug, cigarette or alcohol use. Five skinfold sites, pre-pregnancy weight, current weight, and wrist circumference were measured. Body density was measured using air displacement plethysmography. Total body water was measured using 2H2O. Results: Paired t-tests showed that the Paxton equation (intended for use at gestational week 37) overestimated percent body fat compared to the Siri method, p<0.001, whereas the Presley equation (intended for use at gestational week 30) produced statistically similar results to the gold-standard, p=0.842. Discussion: Using skinfold thickness measurements and the Presley equation to assess percent body fat may be useful and accessible for this population

The diacylglycerol lipases: structure, regulation and roles in and beyond endocannabinoid signalling

The diacylglycerol lipases (DAGLs) hydrolyse diacylglycerol to generate 2-arachidonoylglycerol (2-AG), the most abundant ligand for the CB(1) and CB(2) cannabinoid receptors in the body. DAGL-dependent endocannabinoid signalling regulates axonal growth and guidance during development, and is required for the generation and migration of new neurons in the adult brain. At developed synapses, 2-AG released from postsynaptic terminals acts back on presynaptic CB(1) receptors to inhibit the secretion of both excitatory and inhibitory neurotransmitters, with this DAGL-dependent synaptic plasticity operating throughout the nervous system. Importantly, the DAGLs have functions that do not involve cannabinoid receptors. For example, 2-AG is the precursor of arachidonic acid in a pathway that maintains the level of this essential lipid in the brain and other organs. This pathway also drives the cyclooxygenase-dependent generation of inflammatory prostaglandins in the brain, which has recently been implicated in the degeneration of dopaminergic neurons in Parkinson's disease. Remarkably, we still know very little about the mechanisms that regulate DAGL activity—however, key insights can be gleaned by homology modelling against other α/β hydrolases and from a detailed examination of published proteomic studies and other databases. These identify a regulatory loop with a highly conserved signature motif, as well as phosphorylation and palmitoylation as post-translational mechanisms likely to regulate function