I - Matter, antimatter and geometry II - The twin universe model : a solution to the problem of negative energy particles III - The twin universe model plus electric charges and matter-antimatter symmetry

We introduce a new dynamical group whose coadjoint action on its momentum space takes account of matter-antimatter symmetry on pure geometrical grounds. According to this description the energy and the spin are unchanged under matter-antimatter symmetry. We recall that the antichron components of the Poincar\'{e} group, ruling relativistic motions of a mass-point particle, generate negative energy particles. The model with two twin universes, inspired by Sakharov's one, solves the stability issue. Positive and negative energy particles motions hold in two distinct folds. The model is extended to charged particles. As a result, the matter-antimatter duality holds in both universes.Comment: 19 Fevrier 200

Agglomeration and the Adjustment of the Spatial Economy

We consider the literatures on urban systems and New Economic Geography to examine questions concerning agglomeration and how areas respond to shocks to the economic environment. We first propose a diagrammatic framework to compare the two approaches. We then use this framework to study a number of extensions and to consider several policy relevant issues.Urban systems, New Economic Geography, Urban and regional policy, diagrammatic exposition

Agglomeration and the Adjustment of the Spatial Economy

We consider the literature on urban systems and New Economic Geography to examine questions concerning agglomeration and how areas respond to shocks to the economic environment. We first propose a diagrammatic framework to compare the two approaches. We then use this framework to study a number of extensions and to consider several policy relevant issues

Mono Lake or Laschamp geomagnetic event recorded from lava flows in Amsterdam Island (southeastern Indian Ocean)

We report a survey carried out on basalt flows from Amsterdam Island in order to check the presence of intermediate directions interpreted to belong to a geomagnetic field excursion within the Brunhes epoch, completing this paleomagnetic record with paleointensity determinations and radiometric dating. The directional results corroborate the findings by Watkins and Nougier (1973) : normal polarity is found for two units and an intermediate direction, with associated VGPs close to the equator, for the other two units. A notable result is that these volcanic rocks are well suited for absolute paleointensity determinations. Fifty percent of the samples yields reliable intensity values with high quality factors. An original element of this study is that we made use of the PTRM-tail test of Shcherbakova et al. (2000) to help in the interpretation of the paleointensity measurements. Doing thus, only the high temperature intervals, beyond 400 degres C, were retained to obtain the most reliable estimate of the strength of the ancient magnetic field. The normal units yield Virtual Dipole Moments (VDM) of 6.2 and 7.7 10e22 Am2 and the excursional units yield values of 3.7 and 3.4 10e22 Am2. These results are quite consistent with the other Thellier determinations from Brunhes excursion records, all characterized by a decrease of the VDM as VGP latitude decreases. 40Ar/39Ar isotopic age determinations provide an estimate of 26+-15 Kyr and 18+-9 Kyr for the transitional lava flows, which could correspond to the Mono Lake excursion. However, the large error bars associated with these ages do not exclude the hypothesis that this event is the Laschamp

1H-localized broadband 13C NMR spectroscopy of the rat brain in vivo at 9.4 T

Localized (13)C NMR spectra were obtained from the rat brain in vivo over a broad spectral range (15-100 ppm) with minimal chemical-shift displacement error (<10%) using semi-adiabatic distortionless enhancement by polarization transfer (DEPT) combined with (1)H localization. A new gradient dephasing scheme was employed to eliminate unwanted coherences generated by DEPT when using surface coils with highly inhomogeneous B(1) fields. Excellent sensitivity was evident from the simultaneous detection of natural abundance signals for N-acetylaspartate, myo-inositol, and glutamate in the rat brain in vivo at 9.4 T. After infusion of (13)C-labeled glucose, up to 18 (13)C resonances were simultaneously measured in the rat brain, including glutamate C2, C3, C4, glutamine C2, C3, C4, aspartate C2, C3, glucose C1, C6, N-acetyl-aspartate C2, C3, C6, as well as GABA C2, lactate C3, and alanine C3. (13)C-(13)C multiplets corresponding to multiply labeled compounds were clearly observed, suggesting that extensive isotopomer analysis is possible in vivo. This unprecedented amount of information will be useful for metabolic modeling studies aimed at understanding brain energy metabolism and neurotransmission in the rodent brain

Measurement of reduced glutathione (GSH) in human brain using LCModel analysis of difference-edited spectra

The concentration of reduced glutathione (GSH), an antioxidant, may be altered in various brain diseases. MEGA-PRESS was used to edit for the (1)H NMR signal from GSH in the occipital lobe of 12 normal humans. In all studies, GSH was clearly detected with a spectral pattern consistent with spectra acquired from a phantom containing GSH. Retention of singlet resonances in the subspectra, a key advantage of this difference-editing technique, provided an unambiguous reference for the offset and phase of the edited signal. Linear combination model (LCModel) analysis provided an unbiased means for quantifying signal contribution from edited metabolites. GSH concentration was estimated from the in vivo spectra as 1.3 +/- 0.2 micro mol/g (mean +/- SD, n = 12)

Bonded Cumomer Analysis of Human Melanoma Metabolism Monitored by 13C NMR Spectroscopy of Perfused Tumor Cells.

A network model for the determination of tumor metabolic fluxes from (13)C NMR kinetic isotopomer data has been developed and validated with perfused human DB-1 melanoma cells carrying the BRAF V600E mutation, which promotes oxidative metabolism. The model generated in the bonded cumomer formalism describes key pathways of tumor intermediary metabolism and yields dynamic curves for positional isotopic enrichment and spin-spin multiplets. Cells attached to microcarrier beads were perfused with 26 mm [1,6-(13)C2]glucose under normoxic conditions at 37 °C and monitored by (13)C NMR spectroscopy. Excellent agreement between model-predicted and experimentally measured values of the rates of oxygen and glucose consumption, lactate production, and glutamate pool size validated the model. ATP production by glycolytic and oxidative metabolism were compared under hyperglycemic normoxic conditions; 51% of the energy came from oxidative phosphorylation and 49% came from glycolysis. Even though the rate of glutamine uptake was ∼50% of the tricarboxylic acid cycle flux, the rate of ATP production from glutamine was essentially zero (no glutaminolysis). De novo fatty acid production was ∼6% of the tricarboxylic acid cycle flux. The oxidative pentose phosphate pathway flux was 3.6% of glycolysis, and three non-oxidative pentose phosphate pathway exchange fluxes were calculated. Mass spectrometry was then used to compare fluxes through various pathways under hyperglycemic (26 mm) and euglycemic (5 mm) conditions. Under euglycemic conditions glutamine uptake doubled, but ATP production from glutamine did not significantly change. A new parameter measuring the Warburg effect (the ratio of lactate production flux to pyruvate influx through the mitochondrial pyruvate carrier) was calculated to be 21, close to upper limit of oxidative metabolism

Editing through multiple bonds: Threonine detection

In in vivo H-1 spectroscopy, the signal at 1.32 ppm is usually assigned to lactate. This resonance position is shared with threonine at physiological pH. The similarity of spectral patterns of lactate and threonine renders the separate measurement of either threonine or lactate without and even with editing technically challenging. In this study, the threonine signal was detected using a single-shot multiple-bond editing technique and quantified in vivo in both rat and human brains. A threonine concentration was estimated at 0.8 +/- 0.3 mM (mean +/- SD, n = 6) in the rat brain and at similar to 0.33 mM in the human brain

Toward dynamic isotopomer analysis in the rat brain in vivo: automatic quantitation of 13C NMR spectra using LCModel

The LCModel method was adapted to analyze localized in vivo (13)C NMR spectra obtained from the rat brain in vivo at 9.4 T. Prior knowledge of chemical-shifts, J-coupling constants and J-evolution was included in the analysis. Up to 50 different isotopomer signals corresponding to 10 metabolites were quantified simultaneously in 400 microl volumes in the rat brain in vivo during infusion of [1,6-(13)C(2)]glucose. The analysis remained accurate even at low signal-to-noise ratio of the order of 3:1. The relative distribution of isotopomers in glutamate, glutamine and aspartate determined in vivo in 22 min was in excellent agreement with that measured in brain extracts. Quantitation of time series of (13)C spectra yielded time courses of total (13)C label incorporation into up to 16 carbon positions, as well as time courses of individual isotopomer signals, with a temporal resolution as low as 5 min (dynamic isotopomer analysis). The possibility of measuring in vivo a wealth of information that was hitherto accessible only in extracts is likely to expand the scope of metabolic studies in the intact brain

Direct, noninvasive measurement of brain glycogen metabolism in humans

The concentration and metabolism of the primary carbohydrate store in the brain, glycogen, is unknown in the conscious human brain. This study reports the first direct detection and measurement of glycogen metabolism in the human brain, which was achieved using localized 13C NMR spectroscopy. To enhance the NMR signal, the isotopic enrichment of the glucosyl moieties was increased by administration of 80 g of 99% enriched [1-13C]glucose in four subjects. 3 h after the start of the label administration, the 13C NMR signal of brain glycogen C1 was detected (0.36+/-0.07 micromol/g, mean+/-S.D., n=4). Based on the rate of 13C label incorporation into glycogen and the isotopic enrichment of plasma glucose, the flux through glycogen synthase was estimated at 0.17+/-0.05 micromol/(gh). This study establishes that brain glycogen can be measured in humans and indicates that its metabolism is very slow in the conscious human. The noninvasive detection of human brain glycogen opens the prospect of understanding the role and function of this important energy reserve under various physiological and pathophysiological conditions