Minimal surfaces and particles in 3-manifolds

We use minimal (or CMC) surfaces to describe 3-dimensional hyperbolic, anti-de Sitter, de Sitter or Minkowski manifolds. We consider whether these manifolds admit ``nice'' foliations and explicit metrics, and whether the space of these metrics has a simple description in terms of Teichm\"uller theory. In the hyperbolic settings both questions have positive answers for a certain subset of the quasi-Fuchsian manifolds: those containing a closed surface with principal curvatures at most 1. We show that this subset is parameterized by an open domain of the cotangent bundle of Teichm\"uller space. These results are extended to ``quasi-Fuchsian'' manifolds with conical singularities along infinite lines, known in the physics literature as ``massive, spin-less particles''. Things work better for globally hyperbolic anti-de Sitter manifolds: the parameterization by the cotangent of Teichm\"uller space works for all manifolds. There is another description of this moduli space as the product two copies of Teichm\"uller space due to Mess. Using the maximal surface description, we propose a new parameterization by two copies of Teichm\"uller space, alternative to that of Mess, and extend all the results to manifolds with conical singularities along time-like lines. Similar results are obtained for de Sitter or Minkowski manifolds. Finally, for all four settings, we show that the symplectic form on the moduli space of 3-manifolds that comes from parameterization by the cotangent bundle of Teichm\"uller space is the same as the 3-dimensional gravity one.Comment: 53 pages, no figure. v2: typos corrected and refs adde

A new synaptic player leading to autism risk: Met receptor tyrosine kinase

The validity for assigning disorder risk to an autism spectrum disorder (ASD) candidate gene comes from convergent genetic, clinical, and developmental neurobiology data. Here, we review these lines of evidence from multiple human genetic studies, and non-human primate and mouse experiments that support the conclusion that the MET receptor tyrosine kinase (RTK) functions to influence synapse development in circuits relevant to certain core behavioral domains of ASD. There is association of both common functional alleles and rare copy number variants that impact levels of MET expression in the human cortex. The timing of Met expression is linked to axon terminal outgrowth and synaptogenesis in the developing rodent and primate forebrain, and both in vitro and in vivo studies implicate this RTK in dendritic branching, spine maturation, and excitatory connectivity in the neocortex. This impact can occur in a cell-nonautonomous fashion, emphasizing the unique role that Met plays in specific circuits relevant to ASD

Early phase of plasticity-related gene regulation and SRF dependent transcription in the hippocampus

Hippocampal organotypic cultures are a highly reliable in vitro model for studying neuroplasticity: in this paper, we analyze the early phase of the transcriptional response induced by a 20 \ub5M gabazine treatment (GabT), a GABA-Ar antagonist, by using Affymetrix oligonucleotide microarray, RT-PCR based time-course and chromatin-immuno-precipitation. The transcriptome profiling revealed that the pool of genes up-regulated by GabT, besides being strongly related to the regulation of growth and synaptic transmission, is also endowed with neuro-protective and pro-survival properties. By using RT-PCR, we quantified a time-course of the transient expression for 33 of the highest up-regulated genes, with an average sampling rate of 10 minutes and covering the time interval [10 3690] minutes. The cluster analysis of the time-course disclosed the existence of three different dynamical patterns, one of which proved, in a statistical analysis based on results from previous works, to be significantly related with SRF-dependent regulation (p-value<0.05). The chromatin immunoprecipitation (chip) assay confirmed the rich presence of working CArG boxes in the genes belonging to the latter dynamical pattern and therefore validated the statistical analysis. Furthermore, an in silico analysis of the promoters revealed the presence of additional conserved CArG boxes upstream of the genes Nr4a1 and Rgs2. The chip assay confirmed a significant SRF signal in the Nr4a1 CArG box but not in the Rgs2 CArG box

Small molecule activators of the Trk receptors for neuroprotection

The neurotophin signaling network is critical to the development and survival of many neuronal populations. Especially sensitive to imbalances in the neurotrophin system, cholinergic neurons in the basal forebrain are progressively lost in Alzheimer's disease. Therapeutic use of neurotrophins to prevent this loss is hampered, however, by a number of pharmacological challenges. These include a lack of transport across the blood-brain barrier, rapid degradation in the circulation, and difficulty in production. In this review we discuss the evidence supporting the neurotrophin system's role in preventing neurodegeneration and survey some of the pharmacological strategies being pursued to develop effective therapeutics targeting neurotrophin function

Structural and photocatalytic properties of perovskite-type (La,Ca)Ti(O,N)(3) prepared from A-site deficient precursors

Two series of oxide precursors for perovskite-type (La,Ca)Ti(O,N)(3) were prepared by adding Ca2+ to A-site deficient LaTiO3.5 heterogeneously (Ca2+-backfilling) or by substituting Ca2+ for La3+ in stoichiometric LaTiO3.5 homogeneously (Ca2+-substitution). Activity of the resultant (La,Ca)Ti(O,N)(3) for photocatalytic O-2 evolution was tested in the presence of an electron acceptor (Ag+) and a superior activity of Ca2+-backfilled LaTiO2N compared to Ca2+-substituted LaTiO2N and unsubstituted LaTiO2N was demonstrated. X-ray diffraction patterns of the precursor oxides revealed a higher degree of crystallinity in La1-xTiO3.5-3x/2 compared to La1-xCaxTiO3.5-x/2. The higher crystallinity in La1-xTiO3.5-3x/2 resulted in lower Ti3+ defect formation during the ammonolysis reaction. This was evidenced by the lower background absorption of the diffuse reflectance spectra in Ca2+-backfilled compared to Ca2+-substituted LaTiO2N. Structural refinement of the diffraction patterns revealed growing crystal sizes with the Ca2+ content, which was more pronounced for Ca2+-backfilled than for Ca2+-substituted LaTiO2N. Thus, the enhanced photocatalytic activity of Ca2+-backfilled LaTiO2N was related to the quality of the precursor oxides, which influenced the defect concentrations and crystallite sizes of the resulting oxynitrides

The influence of defects formed by Ca excess and thermal post-treatments on the persistent luminescence of CaTiO_3:Pr

Red emitting CaTiO3:Pr phosphors with a nominal composition of Ca0.998+xPr0.002TiO3+δ (0.02≤x≤0.04) were prepared by solid state reactions with different thermal post treatments and characterized by X-ray diffraction, transmission electron microscopy and photoluminescence. The Ca excess exhibited complete solubility up to 4% in the samples treated at 1400 °C but segregation in the form of Ruddlesden-Popper phases (Ca3Ti2O7 - Ca4Ti3O10) was observed in samples prepared at 1500 °C. The increase in temperature for stoichiometric samples showed a monotonic increase of decay time due to the reduction of non-radiative recombination defects. It was found that the Ca excess favored the formation of oxygen vacancies which are known to act as trap. In the samples treated at 1400 °C, 3% of Ca excess showed to be the best concentration to increase the decay time of persistent luminescence. For the samples treated at 1500 °C, the segregation of Ruddlesden-Popper phases left a constant amount of Ca soluble in all the CaTiO3 samples. This constant concentration of Ca caused the same density of defects and, consequently, the same decay time in all samples

Evaluation of proton density fat fraction (PDFF) obtained from a vendor-neutral MRI sequence and MRQuantif software

International audienceObjectiveTo validate the proton density fat fraction (PDFF) obtained by the MRQuantif software from 2D chemical shift encoded MR (CSE-MR) data in comparison with the histological steatosis data.MethodsThis study, pooling data from 3 prospective studies spread over time between January 2007 and July 2020, analyzed 445 patients who underwent 2D CSE-MR and liver biopsy. MR derived liver iron concentration (MR-LIC) and PDFF was calculated using the MRQuantif software. The histological standard steatosis score (SS) served as reference. In order to get a value more comparable to PDFF, histomorphometry fat fraction (HFF) were centrally determined for 281 patients. Spearman correlation and the Bland and Altman method were used for comparison.ResultsStrong correlations were found between PDFF and SS (r(s) = 0.84, p &lt; 0.001) or HFF (r(s) = 0.87, p &lt; 0.001). Spearman's coefficients increased to 0.88 (n = 324) and 0.94 (n = 202) when selecting only the patients without liver iron overload. The Bland and Altman analysis between PDFF and HFF found a mean bias of 5.4% and PLUSMN; 5.7 [95% CI 4.7, 6.1]. The mean bias was 4.7% and PLUSMN; 3.7 [95% CI 4.2, 5.3] and 7.1% and PLUSMN; 8.8 [95% CI 5.2, 9.0] for the patients without and with liver iron overload, respectively.ConclusionThe PDFF obtained by MRQuantif from a 2D CSE-MR sequence is highly correlated with the steatosis score and very close to the fat fraction estimated by histomorphometry. Liver iron overload reduced the performance of steatosis quantification and joint quantification is recommended. This device-independent method can be particularly useful for multicenter studies

Perovskite-Type LaTiO2N Oxynitrides for Solar Water Splitting: Influence of the Synthesis Conditions

Oxynitrides with the nominal composition LaTiO2N were prepared from a La2Ti2O7 precursor by thermal ammonolysis of the oxide under an NH3 flow for different durations t (4 30 h). X-ray diffraction (XRD) indicated that phase-pure LaTiO2N samples were obtained when t 13 h. The material was further characterised by scanning electron microscopy (SEM), surface area measurements based on the BET method, thermogravimetric analysis (TGA) and UV-visible diffuse reflectance spectroscopy (DRS). The powders displayed an increased crystallite size and a decreased surface area with increasing t. The ratio of N/(N+O) increased with t from 0.22 0.27. Correlated to this nitrogen increase, a small variation of the bandgap energy was observed from 2.19 to 2.12 eV with t. All LaTiO2N samples oxidised H2O into O2 in the presence of an electron acceptor (Ag+). The O2 evolution was increased from 12 μmol/h (t = 13 h) to 22 24 μmol/h (16 h t 30 h). It was found that the nitrogen content and the amount of defects played a key role in the photocatalytic O2 evolution.ISSN:1876-610

LaTiO2N/In2O3 photoanodes with improved performance for solar water splitting

LaTiO2N photoanodes for solar water splitting were prepared by electrophoretic deposition and demonstrated the best photo-currents ever reported for this material. Further important enhancement of the performance was obtained by the use of a sputtered In2O3 overlayer