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Search Results: 1 - 10 of 489160 matches for " Peter A. Mattei "
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X-ray observations through the outburst cycle of the dwarf nova YZ Cnc
Frank Verbunt,Peter J. Wheatley,Janet A. Mattei
Physics , 1999,
Abstract: We have observed YZ Cnc at two day intervals from 6 to 24 April 1998, covering two full outburst cycles. The 0.1-2.4 keV flux is lower during optical outburst than in quiescence, and lowest at the end of the outburst. The decline of the X-ray flux in the quiescent interval appears to be in contrast to prediction of simple models for accretion-disk instabilities. Variability on \~hour time scales is present, but appears not related to the orbital phase. YZ Cnc was less luminous in X-rays during our 1998 observations than in earlier ROSAT observations.
The X-ray and extreme-ultraviolet flux evolution of SS Cygni throughout outburst
Peter J. Wheatley,Christopher W. Mauche,Janet A. Mattei
Physics , 2003, DOI: 10.1046/j.1365-8711.2003.06936.x
Abstract: We present the most complete multiwavelength coverage of any dwarf nova outburst: simultaneous optical, Extreme Ultraviolet Explorer, and Rossi X-ray Timing Explorer observations of SS Cygni throughout a narrow asymmetric outburst. Our data show that the high-energy outburst begins in the X-ray waveband 0.9--1.4d after the beginning of the optical rise and 0.6d before the extreme-ultraviolet rise. The X-ray flux drops suddenly, immediately before the extreme-ultraviolet flux rise, supporting the view that both components arise in the boundary layer between the accretion disc and white dwarf surface. The early rise of the X-ray flux shows the propagation time of the outburst heating wave may have been previously overestimated. The transitions between X-ray and extreme-ultraviolet dominated emission are accompanied by intense variability in the X-ray flux, with timescales of minutes. As detailed by Mauche & Robinson, dwarf nova oscillations are detected throughout the extreme-ultraviolet outburst, but we find they are absent from the X-ray lightcurve. X-ray and extreme-ultraviolet luminosities imply accretion rates of 3e15g/s in quiescence, 1e16g/s when the boundary layer becomes optically thick, and \~1e18g/s at the peak of the outburst. The quiescent accretion rate is two and a half orders of magnitude higher than predicted by the standard disc instability model, and we suggest this may be because the inner accretion disc in SS Cyg is in a permanent outburst state.
Modifications of Default-Mode Network Connectivity in Patients with Cerebral Glioma
Roberto Esposito, Peter A. Mattei, Chiara Briganti, Gian Luca Romani, Armando Tartaro, Massimo Caulo
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0040231
Abstract: Purpose The aim of the study was to evaluate connectivity modifications in the Default Mode Network (DMN) in patients with cerebral glioma, and to correlate these modifications to tumor characteristics. Methods Twenty-four patients with a left-hemisphere cerebral tumor (14 grade II and 10 grade IV gliomas) and 14 healthy age-matched right-hand volunteers were enrolled in the study. Subjects underwent fMRI while performing language tasks for presurgical mapping. Data was analyzed with independent component analysis in order to identify the DMN. DMN group maps were produced by random-effect analysis (p<0.001, FDR-corrected). An analysis of variance across the three groups (p<0.05) and post-hoc t-test contrasts between pairs of groups were calculated (p<0.05, FDR-corrected). Results All three groups showed typical DMN areas. However, reduced DMN connectivity was detected in tumor patients with respect to controls. A significantly increased and reduced integration of DMN areas was observed in the hippocampal and prefrontal regions, respectively. Modifications were closely related to tumor grading. Moreover, the DMN lateralized to the hemisphere contralateral to tumor in the low-grade, but not in the high-grade tumor patients. Conclusion Modifications of DMN connectivity were induced by gliomas and differed for high and low grade tumors.
Unveiling complexity: non-linear and fractal analysis in neuroscience and cognitive psychology
Tobias A. Mattei
Frontiers in Computational Neuroscience , 2014, DOI: 10.3389/fncom.2014.00017
Abstract:
Is it all about Contact? Neurodegeneration as a “Protein Freeze Tag Game” Inside the Central Nervous System
Tobias A. Mattei
Frontiers in Neurology , 2013, DOI: 10.3389/fneur.2013.00075
Abstract:
Combination Training in Aging Individuals Modifies Functional Connectivity and Cognition, and Is Potentially Affected by Dopamine-Related Genes
Valentina Pieramico, Roberto Esposito, Francesca Sensi, Franco Cilli, Dante Mantini, Peter A. Mattei, Valerio Frazzini, Domenico Ciavardelli, Valentina Gatta, Antonio Ferretti, Gian Luca Romani, Stefano L. Sensi
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0043901
Abstract: Background Aging is a major co-risk factor in many neurodegenerative diseases. Cognitive enrichment positively affects the structural plasticity of the aging brain. In this study, we evaluated effects of a set of structured multimodal activities (Combination Training; CT) on cognitive performances, functional connectivity, and cortical thickness of a group of healthy elderly individuals. CT lasted six months. Methodology Neuropsychological and occupational performances were evaluated before and at the end of the training period. fMRI was used to assess effects of training on resting state network (RSN) functional connectivity using Independent Component Analysis (ICA). Effects on cortical thickness were also studied. Finally, we evaluated whether specific dopamine-related genes can affect the response to training. Principal Findings Results of the study indicate that CT improves cognitive/occupational performances and reorganizes functional connectivity. Intriguingly, individuals responding to CT showed specific dopamine-related genotypes. Indeed, analysis of dopamine-related genes revealed that carriers of DRD3 ser9gly and COMT Val158Met polymorphisms had the greatest benefits from exposure to CT. Conclusions and Significance Overall, our findings support the idea that exposure to a set of structured multimodal activities can be an effective strategy to counteract aging-related cognitive decline and also indicate that significant capability of functional and structural changes are maintained in the elderly.
Transcriptome analysis of antigenic variation in Plasmodium falciparum - var silencing is not dependent on antisense RNA
Stuart A Ralph, Emmanuel Bischoff, Denise Mattei, Odile Sismeiro, Marie-Agnès Dillies, Ghislaine Guigon, Jean-Yves Coppee, Peter H David, Artur Scherf
Genome Biology , 2005, DOI: 10.1186/gb-2005-6-11-r93
Abstract: In addition to oligonucleotides for all predicted protein-coding genes, oligonucleotide probes specific to each known var gene of the FCR3 background were designed and added to the microarray, as well as tiled sense and antisense probes for a subset of var genes. In parasites selected for adhesion to CSA, one full-length var gene (var2csa) was strongly upregulated, as were sense RNA molecules emanating from the 3' end of a limited subset of other var genes. No global relationship between sense and antisense production of var genes was observed, but notably, some var genes had coincident high levels of both antisense and sense transcript.Mutually exclusive expression of PfEMP1 proteins results from transcriptional silencing of non-expressed var genes. The distribution of steady-state sense and antisense RNA at var loci are not consistent with a silencing mechanism based on antisense silencing of inactive var genes. Silencing of var loci is also associated with altered regulation of genes distal to var loci.Plasmodium falciparum is a parasite belonging to the phylum apicomplexa, a group characterized by intracellular parasitism. A striking feature of apicomplexans' intracellular lifestyle is their ability to modify host cells though export of macromolecules. P. falciparum parasitizes erythrocytes, which it proceeds to alter via the secretion of a large number of proteins. Much of this protein content is represented by the Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) molecules, ligands that span the erythrocyte membrane and mediate cytoadhesion to human receptors exposed to circulating parasites. PfEMP1 proteins are encoded by var genes, and field isolates possess approximately 60-70 distinct var genes. Each var gene consists of a large variable 5' exon (around 4-9 kb in length), and a smaller, more conserved 3' exon (around 1 kb in length) that encodes the intracellular portion of the PfEMP1 protein. Individual parasites do not express all PfEMP1 isof
The Interaction between Endopolygalacturonase from Fusarium moniliforme and PGIP from Phaseolus vulgaris Studied by Surface Plasmon Resonance and Mass Spectrometry
Benedetta Mattei,Felice Cervone,Peter Roepstorff
Comparative and Functional Genomics , 2001, DOI: 10.1002/cfg.113
Abstract: A combination of surface plasmon resonance (SPR) and matrix-assisted laser-desorptionionization- time-of-flight mass spectrometry (MALDI-TOF-MS) was used to study the interaction between endopolygalacturonase (PG) from Fusarium moniliforme and a polygalacturonase-inhibiting protein (PGIP) from Phaseolus vulgaris. PG hydrolyses the homogalacturonan of the plant cell wall and is considered an important pathogenicity factor of many fungi. PGIP is a specific inhibitor of fungal PGs and is thought to be involved in plant defence against phytopathogenic fungi. SPR was used either to study the effect of the PG glycosylation on the formation of the complex with PGIP, and as a sensitive affinity capture of an interacting peptide from a mixture of PG fragments obtained by limited proteolysis. Mass spectrometry allowed to characterise the interacting peptide eluted from the sensor surface.
Brevenal Inhibits Pacific Ciguatoxin-1B-Induced Neurosecretion from Bovine Chromaffin Cells
César Mattei, Peter J. Wen, Truong D. Nguyen-Huu, Martha Alvarez, Evelyne Benoit, Andrea J. Bourdelais, Richard J. Lewis, Daniel G. Baden, Jordi Molgó, Frédéric A. Meunier
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0003448
Abstract: Ciguatoxins and brevetoxins are neurotoxic cyclic polyether compounds produced by dinoflagellates, which are responsible for ciguatera and neurotoxic shellfish poisoning (NSP) respectively. Recently, brevenal, a natural compound was found to specifically inhibit brevetoxin action and to have a beneficial effect in NSP. Considering that brevetoxin and ciguatoxin specifically activate voltage-sensitive Na+ channels through the same binding site, brevenal has therefore a good potential for the treatment of ciguatera. Pacific ciguatoxin-1B (P-CTX-1B) activates voltage-sensitive Na+ channels and promotes an increase in neurotransmitter release believed to underpin the symptoms associated with ciguatera. However, the mechanism through which slow Na+ influx promotes neurosecretion is not fully understood. In the present study, we used chromaffin cells as a model to reconstitute the sequence of events culminating in ciguatoxin-evoked neurosecretion. We show that P-CTX-1B induces a tetrodotoxin-sensitive rise in intracellular Na+, closely followed by an increase in cytosolic Ca2+ responsible for promoting SNARE-dependent catecholamine secretion. Our results reveal that brevenal and β-naphtoyl-brevetoxin prevent P-CTX-1B secretagogue activity without affecting nicotine or barium-induced catecholamine secretion. Brevenal is therefore a potent inhibitor of ciguatoxin-induced neurotoxic effect and a potential treatment for ciguatera.
The evolution of the Mira variable R Hydrae
Albert A. Zijlstra,T. R. Bedding,J. A. Mattei
Physics , 2002, DOI: 10.1046/j.1365-8711.2002.05467.x
Abstract: The Mira variable R Hydrae is well known for its declining period, which Wood & Zarro (1981) attributed to a possible recent thermal pulse. Here we investigate the long-term period evolution, covering 340 years, going back to its discovery in AD 1662. Wavelets are used to determine both the period and semi-amplitude. We show that the period decreased linearly between 1770 and 1950; since 1950 the period has stabilized at 385 days. The semi-amplitude closely follows the period evolution. Detailed analysis of the oldest data shows that before 1770 the period was about 495 days. We find no evidence for an increasing period during this time as found by Wood & Zarro. IRAS data shows that the mass loss dropped dramatically around AD 1750. The decline agrees with the mass-loss formalism from Vassiliadis & Wood, but is much larger than predicted by the Bloecker mass-loss law. An outer detached IRAS shell suggests that R Hya has experienced such mass-loss interruptions before. The period evolution can be explained by a thermal pulse occuring around AD 1600, or by an non-linear instability leading to an internal relaxation of the stellar structure. The elapsed time between the mass-loss decline giving rise to the outer detached shell, and the recent event, of approximately 5000 yr suggests that only one of these events could be due to a thermal pulse. Further monitoring of R Hya is recommended, as both models make strong predictions for the future period evolution. R Hya-type events, on time scales of 10^2-10^3 yr, could provide part of the explanation for the rings seen around some AGB and post-AGB stars.
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