Pulse propagation in discrete excitatory networks of integrate-and-fire neurons

We study the propagation of solitary waves in a discrete excitatory network of integrate-and-fire neurons. We show the existence and the stability of a fast wave and a family of slow waves. Fast waves are similar to those already described in continuum networks. Stable slow waves have not been previously reported in purely excitatory networks and their propagation is particular to the discrete nature of the network. The robustness of our results is studied in the presence of noise

Complex high-pressure polymorphism of barium tungstate

We have studied BaWO 4 under compression at room temperature by means of x-ray diffraction and Raman spectroscopy. When compressed with neon as a pressure-transmitting medium (quasihydrostatic conditions), we found that BaWO 4 transforms from its low-pressure tetragonal structure into a much denser monoclinic structure. This result confirms our previous theoretical prediction based on ab initio calculations that the scheelite to BaWO 4-II transition occurs at room temperature if kinetic barriers are suppressed by pressure. However, our experiment without any pressure- transmitting medium has resulted in a phase transition to a completely different structure, suggesting nonhydrostaticity may be responsible for previously reported rich polymorphism in BaWO 4. The crystal structure of the low- and high-pressure phases from the quasihydrostatic experiments has been Rietveld refined. Additionally, for the tetragonal phase the effects of pressure on the unit-cell volume and lattice parameters are discussed. Finally, the pressure evolution of the Raman modes of different phases is reported and compared with previous studies. © 2012 American Physical Society.This research was supported by Spanish MEC (Grant No. MAT2010-21270-C04-01/04), MALTA Consolider Ingenio 2010 (Grant No. CSD2007-00045), and Vicerrectorado de Investigacion y Desarrollo of the Universitat Politecnica de Valencia (Grants No. UPV2011-0914 PAID-05-11 and No. UPV2011-0966 PAID-06-11). XRD data were collected at HPCAT, Advanced Photon Source (APS), Argonne National Laboratory. HPCAT is supported by CIW, CDAC, UNLV, and LLNL through funding from DOE-NNSA, DOE-BES, and NSF. APS is supported by DOE-BES under Contract No. DEAC02-06CH11357.Gomis Hilario, O.; Sans, JA.; Lacomba-Perales, R.; Errandonea, D.; Meng, Y.; Chervin, JC.; Polian, A. (2012). Complex high-pressure polymorphism of barium tungstate. Physical Review B. 86:54121-1-54121-10. https://doi.org/10.1103/PhysRevB.86.054121S54121-154121-1086Gürmen, E., Daniels, E., & King, J. S. (1971). Crystal Structure Refinement of SrMoO4, SrWO4, CaMoO4, and BaWO4 by Neutron Diffraction. The Journal of Chemical Physics, 55(3), 1093-1097. doi:10.1063/1.1676191Errandonea, D., & Manjón, F. J. (2008). Pressure effects on the structural and electronic properties of ABX4 scintillating crystals. Progress in Materials Science, 53(4), 711-773. doi:10.1016/j.pmatsci.2008.02.001Tan, D., Xiao, W., Zhou, W., Chen, M., Zhou, W., Li, X., … Liu, J. (2012). High pressure X-ray diffraction study on BaWO4-II. High Pressure Research, 1-8. doi:10.1080/08957959.2012.658789Lacomba-Perales, R., Errandonea, D., Segura, A., Ruiz-Fuertes, J., Rodríguez-Hernández, P., Radescu, S., … Muñoz, A. (2011). A combined high-pressure experimental and theoretical study of the electronic band-structure of scheelite-type AWO4 (A = Ca, Sr, Ba, Pb) compounds. 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High-pressure x-ray and neutron powder diffraction study of PbWO4and BaWO4scheelites. Journal of Physics: Condensed Matter, 18(11), 3017-3029. doi:10.1088/0953-8984/18/11/008Errandonea, D., Pellicer-Porres, J., Manjón, F. J., Segura, A., Ferrer-Roca, C., Kumar, R. S., … Aquilanti, G. (2006). Determination of the high-pressure crystal structure ofBaWO4andPbWO4. Physical Review B, 73(22). doi:10.1103/physrevb.73.224103Panchal, V., Garg, N., Chauhan, A. K., Sangeeta, & Sharma, S. M. (2004). High pressure phase transitions in BaWO4. Solid State Communications, 130(3-4), 203-208. doi:10.1016/j.ssc.2004.01.043Jayaraman, A., Batlogg, B., & VanUitert, L. G. (1983). High-pressure Raman study of alkaline-earth tungstates and a new pressure-induced phase transition in BaWO4. Physical Review B, 28(8), 4774-4777. doi:10.1103/physrevb.28.4774Kawada, I., Kato, K., & Fujita, T. (1974). BaWO4-II (a high-pressure form). Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry, 30(8), 2069-2071. doi:10.1107/s0567740874006431Fujita, T., Yamaoka, S., & Fukunaga, O. (1974). Pressure induced phase transformation in BaWO4. Materials Research Bulletin, 9(2), 141-146. doi:10.1016/0025-5408(74)90193-7Manjon, F. J., Errandonea, D., Garro, N., Pellicer-Porres, J., López-Solano, J., Rodríguez-Hernández, P., … Muñoz, A. (2006). Lattice dynamics study of scheelite tungstates under high pressure II.PbWO4. Physical Review B, 74(14). doi:10.1103/physrevb.74.144112Errandonea, D., Martínez-García, D., Lacomba-Perales, R., Ruiz-Fuertes, J., & Segura, A. (2006). Effects of high pressure on the optical absorption spectrum of scintillating PbWO4 crystals. Applied Physics Letters, 89(9), 091913. doi:10.1063/1.2345228Mao, H. K., Xu, J., & Bell, P. M. (1986). Calibration of the ruby pressure gauge to 800 kbar under quasi-hydrostatic conditions. Journal of Geophysical Research, 91(B5), 4673. doi:10.1029/jb091ib05p04673Klotz, S., Chervin, J.-C., Munsch, P., & Le Marchand, G. (2009). Hydrostatic limits of 11 pressure transmitting media. Journal of Physics D: Applied Physics, 42(7), 075413. doi:10.1088/0022-3727/42/7/075413Hammersley, A. P., Svensson, S. O., Hanfland, M., Fitch, A. N., & Hausermann, D. (1996). Two-dimensional detector software: From real detector to idealised image or two-theta scan. High Pressure Research, 14(4-6), 235-248. doi:10.1080/08957959608201408Holland, T. J. B., & Redfern, S. A. T. (1997). Unit cell refinement from powder diffraction data: the use of regression diagnostics. Mineralogical Magazine, 61(404), 65-77. doi:10.1180/minmag.1997.061.404.07Toby, B. H. (2001). EXPGUI, a graphical user interface forGSAS. Journal of Applied Crystallography, 34(2), 210-213. doi:10.1107/s0021889801002242Kraus, W., & Nolze, G. (1996). POWDER CELL – a program for the representation and manipulation of crystal structures and calculation of the resulting X-ray powder patterns. Journal of Applied Crystallography, 29(3), 301-303. doi:10.1107/s0021889895014920Birch, F. (1978). Finite strain isotherm and velocities for single-crystal and polycrystalline NaCl at high pressures and 300°K. Journal of Geophysical Research, 83(B3), 1257. doi:10.1029/jb083ib03p01257Liu, H., Ding, Y., Somayazulu, M., Qian, J., Shu, J., Häusermann, D., & Mao, H. (2005). Rietveld refinement study of the pressure dependence of the internal structural parameteruin the wurtzite phase of ZnO. Physical Review B, 71(21). doi:10.1103/physrevb.71.212103Liu, H., Hu, J., Shu, J., Häusermann, D., & Mao, H. (2004). Lack of the critical pressure for weakening of size-induced stiffness in 3C–SiC nanocrystals under hydrostatic compression. Applied Physics Letters, 85(11), 1973-1975. doi:10.1063/1.1789240Ruiz-Fuertes, J., Errandonea, D., Lacomba-Perales, R., Segura, A., González, J., Rodríguez, F., … Tu, C. Y. (2010). High-pressure structural phase transitions inCuWO4. Physical Review B, 81(22). doi:10.1103/physrevb.81.224115Santamaría-Pérez, D., Gracia, L., Garbarino, G., Beltrán, A., Chuliá-Jordán, R., Gomis, O., … Segura, A. (2011). High-pressure study of the behavior of mineral barite by x-ray diffraction. Physical Review B, 84(5). doi:10.1103/physrevb.84.054102Finger, L. W., Kroeker, M., & Toby, B. H. (2007). DRAWxtl, an open-source computer program to produce crystal structure drawings. Journal of Applied Crystallography, 40(1), 188-192. doi:10.1107/s0021889806051557Achary, S. N., Patwe, S. J., Mathews, M. D., & Tyagi, A. K. (2006). High temperature crystal chemistry and thermal expansion of synthetic powellite (CaMoO4): A high temperature X-ray diffraction (HT-XRD) study. Journal of Physics and Chemistry of Solids, 67(4), 774-781. doi:10.1016/j.jpcs.2005.11.009Machon, D., Dmitriev, V. P., Bouvier, P., Timonin, P. N., Shirokov, V. B., & Weber, H.-P. (2003). Pseudoamorphization ofCs2HgBr4. Physical Review B, 68(14). doi:10.1103/physrevb.68.144104Ruiz-Fuertes, J., Friedrich, A., Pellicer-Porres, J., Errandonea, D., Segura, A., Morgenroth, W., … Polian, A. (2011). Structure Solution of the High-Pressure Phase of CuWO4and Evolution of the Jahn–Teller Distortion. Chemistry of Materials, 23(18), 4220-4226. doi:10.1021/cm201592hErrandonea, D., Meng, Y., Somayazulu, M., & Häusermann, D. (2005). Pressure-induced transition in titanium metal: a systematic study of the effects of uniaxial stress. Physica B: Condensed Matter, 355(1-4), 116-125. doi:10.1016/j.physb.2004.10.030Errandonea, D., Kumar, R. S., Ruiz-Fuertes, J., Segura, A., & Haussühl, E. (2011). High-pressure study of substrate material ScAlMgO4. Physical Review B, 83(14). doi:10.1103/physrevb.83.144104Wang, J.-T., Chen, C., & Kawazoe, Y. (2011). Low-Temperature Phase Transformation from Graphite tosp3Orthorhombic Carbon. Physical Review Letters, 106(7). doi:10.1103/physrevlett.106.075501Errandonea, D., & Manjón, F. J. (2009). On the ferroelastic nature of the scheelite-to-fergusonite phase transition in orthotungstates and orthomolybdates. Materials Research Bulletin, 44(4), 807-811. doi:10.1016/j.materresbull.2008.09.024Maczka, M., Souza Filho, A. G., Paraguassu, W., Freire, P. T. C., Mendes Filho, J., & Hanuza, J. (2012). Pressure-induced structural phase transitions and amorphization in selected molybdates and tungstates. Progress in Materials Science, 57(7), 1335-1381. doi:10.1016/j.pmatsci.2012.01.001Flórez, M., Contreras-García, J., Recio, J. M., & Marqués, M. (2009). Quantum-mechanical calculations of zircon to scheelite transition pathways inZrSiO4. 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Determination of the aldosterone/plasma renin activity ratio for the screening of primary hyperaldosteronism in essential hypertension: a multicentric study

El hiperaldosteronismo primario (HAP) es una afección caracterizada por la producción inapropiadamente elevada y una relativa autonomía del sistema renina-angiotensina. Estimaciones previas, basadas sólo en la evaluación de hipertensos con hipokalemia, consideraban al HAP como una causa poco frecuente de hipertensión (1%). Sin embargo, estudios actuales fundamentados en el cálculo de la relación aldosterona/ actividad de renina plasmática (RAA) arrojan una incidencia mayor (5-10%), siendo la hipertensión arterial (HTA) normokalémica la presentación más frecuente. Dada la amplitud de los valores de corte de la RAA, el Departamento de Suprarrenal de SAEM diseñó un estudio multicéntrico prospectivo en una población de Argentina con el objetivo de establecer nuestro propio valor y determinar así la prevalencia de HAP. Fueron estudiados 353 individuos de ambos sexos, 104 controles normotensos, sin antecedentes familiares de HTA y 249 pacientes hipertensos. Se indicó dieta normosódica y la suspensión de antihipertensivos que interfieran con el eje mineralocorticoideo. Las determinaciones de la actividad de renina plasmática (ARP), DIA-SorinRIA, y de aldosterona, RIA-DPC, fueron realizadas en un único laboratorio. Se realizó ionograma y se evaluaron parámetros clínicos y bioquímicos de síndrome metabólico. La RAA calculada según el percentilo 95 en los controles, fue establecida en la cifra de 36 como valor de corte para sospechar HAP en los hipertensos, requiriéndose una concentración de aldosterona >15 ng/ml. Con una RAA≥36, se realizaron pruebas confirmatorias de sobrecarga salina o de fludrocortisona. La RAA fue ≥36 en 31/249 pacientes, confirmándose HAP en 8 (7 adenomas y 1 hiperplasia), con una prevalencia del 3.2%. Los restantes no completaron estudios confirmatorios. La presencia de síndrome metabólico fue similar en los hipertensos con y sin HAP. En conclusión, este primer estudio multicéntrico argentino determinó nuestro valor de corte de la RAA en 36. Su aplicación permitió establecer una prevalencia de HAP del 3,2% que, aunque podría estar subestimada, resulta significativamente mayor que la previa histórica y concuerda con la incidencia referida en la bibliografía.Primary hyperaldosteronism (PHA) or Conn's disease was classically suspected in the presence of hypertension (H) and hypokalemia. It was previously considered as a rare cause of H, being reported in only 1% of hypertensive patients. It can be caused by an adrenal adenoma (the former usual presentation) or by adrenal hyperplasia. But since the use of the aldosterone/plasma renin activity ratio (AAR) as the screening method in the last years, it is currently considered as almost the most frequent cause of secondary H., accounting for 5-10% of essential H. Plasma rennin activity (PRA) determination is a laborious procedure with low reproducibility and it directly affects the AAR; thus each laboratory must assess its own cut-off value. Therefore, in the Adrenal Department of the Argentine Society of Endocrinology and Metabolism (SAEM), we performed this multicentric prospective study of a population of Argentina with the aim of assessing our own AAR cut-off level in normotensive controls in order to apply it for PHA screening in essential hypertensive patients. We studied 353 adult subjects: 104 controls, aged 45,18 ± 13,78 years-old ( X±SD), with no history of arterial hypertension in their first-degree relatives and with two separate day-registry of blood pressure≤ 139/85 mmHg and 249 hypertensive patients, aged 51± 13,6 years-old ( X ± SD), with arterial blood pressure≥ 140/90 mmHg in the sitting position. Subjects with cardiac, renal, hepatic and neurological diseases were excluded as well as those with Cushing´s syndrome, hyperthyroidism, untreated hypothyroidism, diabetes mellitus and patients under glucocorticoids, oral contraceptive pills or estrogen therapy. A normal sodium diet was indicated and potassium was supplemented when needed. Blood was withdrawn between 8 and 10:00 a.m. with the subjects in the upright position. Aldosterone (A) was determined by DPC radioimmunoassay (RIA) and PRA, by DIA-Sorin RIA. The A normal levels are 4-30 ng/dl for ambulatory individuals on a normal sodium diet and the PRA normal values are < 3,3 ng/ml/h. In order to avoid false positive results in the hypertensive group, AAR was calculated when A was above 15 ng/dl. We measured the waist circumference and we determined the body mass index. Blood sodium, potassium, calcium, urea, creatinine, cholesterol, HDL-C, LDL-C, triglyceride and liver function tests were performed. Statistical Analysis and Results Since the AAR variable showed a non-normal distribution, the cut-off value was considered as the 95th percentile in the control group, which was calculated as 36. This is also in accordance to the function of the empirical distribution of Collings and Hamilton. In our 249 hypertensive patients, 31 had an AAR ≥ 36. PHA was confirmed in 8: seven has an adrenal adenoma and one had hyperplasia. The prevalence of PHA in our population was 3,2 %, with a 95th confidence interval ranging from 1,4 to 6,2 %. In the remaining 23 patients, confirmatory tests could not be completed. There was no correlation between the severity of the hypertension and the AAR value, with no statistical significant differences between those with or without PHA. Likewise, we found no correlation between PRA and advancing age. In hypertensive patients, metabolic syndrome was more prevalent than in controls, but it was present to the same extent in those with or without PHA. Conclusions To our knowledge, this is the first multicentric study performed in Argentina to determine the aldosterone/ plasma renin activity ratio in our normotensive control population. Our AAR value of 36 agrees with the levels reported in the international literature: thus an AAR ≥ 36 along with an aldosterone ≥ 15 ng/ml in hypertensive patients lead us to suspect PHA and to perform confirmatory tests. Applying these criteria, we found a prevalence of 3,2% of PHA in essential HTA. It is possible that this value may be underestimated due to the fact that confirmatory tests could not be completed in all the hypertensive subjects with an AAR≥ 36. In spite of this, our prevalence is significantly greater than the historical one and it lies in the range reported in the literature.Fil: Pardes, E.. Gobierno de la Ciudad de Buenos Aires. Hospital General de Agudos "Ramos Mejía"; ArgentinaFil: Belli, S.. Hospital Dr. C. Durand; ArgentinaFil: Cornaló, D.. Hospital Rivadavia; ArgentinaFil: Contreras, Liliana Noemi. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Houssay. Instituto de Investigaciones Medicas; ArgentinaFil: Costa, L.. Hospital Dr. A. Posadas; ArgentinaFil: Chervin. R.. Universidad de Buenos Aires. Facultad de Medicina. Hospital de Clínicas General San Martín; ArgentinaFil: Damilano, S.. Laboratorio de Bioanalítica; ArgentinaFil: Fenili, C.. Laboratorio de Bioanalítica; ArgentinaFil: Gómez, R. M.. Universidad de Buenos Aires. Facultad de Medicina. Hospital de Clínicas General San Martín; ArgentinaFil: Leal Reyna, M.. Complejo Médico Policial "Churruca"; ArgentinaFil: Lupi, S.. Gobierno de la Ciudad de Buenos Aires. Hospital General de Agudos "Ramos Mejía"; ArgentinaFil: Martínez, M.. Hospital Francés; ArgentinaFil: Nofal, M.. Clínica Bazterrica; ArgentinaFil: Ruibal, G.. Gobierno de la Ciudad de Buenos Aires. Hospital General de Agudos "Dr. Teodoro Álvarez"; Argentin

Impairments in Attention in Occasionally Snoring Children: An Event-Related Potential Study

Objective—To determine whether minimal snoring is benign in children. Procedure—22 rarely snoring children (mean age=6.9 years, 11 females) and age- and sexmatched controls participated in an auditory oddball task wearing 128-electrode nets. Parents completed Conner’s Parent Rating Scales-Revised Long (CPRS-R:L). Results—Snorers scored significantly higher on 4 CPRS-R:L subscales. Stepwise regression indicated that two ERP variables from a region of the ERP that peaked at 844 ms post-stimulus onset predicted CPRS-R:L ADHD Index scores. Conclusions—Occasional snorers according to parental report do exhibit ADHD-like behaviors. Basic sensory processing is longer than in controls, suggesting that delayed frontal activation requires more effort in snorers

Two chemically similar stellar overdensities on opposite sides of the plane of the Galaxy

Our Galaxy is thought to have undergone an active evolutionary history dominated by star formation, the accretion of cold gas, and, in particular, mergers up to 10 gigayear ago. The stellar halo reveals rich fossil evidence of these interactions in the form of stellar streams, substructures, and chemically distinct stellar components. The impact of dwarf galaxy mergers on the content and morphology of the Galactic disk is still being explored. Recent studies have identified kinematically distinct stellar substructures and moving groups, which may have extragalactic origin. However, there is mounting evidence that stellar overdensities at the outer disk/halo interface could have been caused by the interaction of a dwarf galaxy with the disk. Here we report detailed spectroscopic analysis of 14 stars drawn from two stellar overdensities, each lying about 5 kiloparsecs above and below the Galactic plane - locations suggestive of association with the stellar halo. However, we find that the chemical compositions of these stars are almost identical, both within and between these groups, and closely match the abundance patterns of the Milky Way disk stars. This study hence provides compelling evidence that these stars originate from the disk and the overdensities they are part of were created by tidal interactions of the disk with passing or merging dwarf galaxies.Comment: accepted for publication in Natur

Synthesis of fluorosugar reagents for the construction of well-defined fluoroglycoproteins.

2-Deoxy-2-fluoroglycosyl iodides are privileged glycosyl donors for the stereoselective preparation of 1-Nu-β-fluorosugars, which are useful reagents for chemical site-selective protein glycosylation. Ready access to such β-fluorosugars enables the mild and efficient construction of well-defined fluoroglycoproteins.We thank the European Commission (Marie Curie CIG, O.B. and G.J.L.B.), MICINN, Spain (Juan de la Cierva Fellowship, O.B.), MINECO, Spain (CTQ2011-22872BQU) and Generalitat de Catalunya (M.S.) for generous financial support. We also thank Mr. Adrià Cardona-Benages (URV) for technical assis-tance. G.J.L.B. thanks the Royal Society (University Research Fellowship), Fundação para a Ciência a Tecnologia, Portugal (FCT Investigator), and the EPSRC for funding.This is the final version of the article. It first appeared from ACS via http://pubs.acs.org/doi/abs/10.1021/acs.orglett.5b01259

Heterogeneity assessment of functional T cell avidity.

The potency of cellular immune responses strongly depends on T cell avidity to antigen. Yet, functional avidity measurements are rarely performed in patients, mainly due to the technical challenges of characterizing heterogeneous T cells. The mean functional T cell avidity can be determined by the IFN-γ Elispot assay, with titrated amounts of peptide. Using this assay, we developed a method revealing the heterogeneity of functional avidity, represented by the steepness/hillslope of the peptide titration curve, documented by proof of principle experiments and mathematical modeling. Our data show that not only natural polyclonal CD8 T cell populations from cancer patients, but also monoclonal T cells differ strongly in their heterogeneity of functional avidity. Interestingly, clones and polyclonal cells displayed comparable ranges of heterogeneity. We conclude that besides the mean functional avidity, it is feasible and useful to determine its heterogeneity (hillslope) for characterizing T cell responses in basic research and patient investigation