1,310 research outputs found
Presymmetry beyond the Standard Model
We go beyond the Standard Model guided by presymmetry, the discrete
electroweak quark-lepton symmetry hidden by topological effects which explain
quark fractional charges as in condense matter physics. Partners of the
particles of the Standard Model and the discrete symmetry associated with this
partnership appear as manifestations of a residual presymmetry and its
extension from matter to forces. This duplication of the spectrum of the
Standard Model keeps spin and comes nondegenerated about the TeV scale.Comment: 6 pages, 11 figures. To be published in the proceedings of DPF-2009,
Detroit, MI, July 2009, eConf C09072
Intracellular Ca2+ release through ryanodine receptors contributes to AMPA receptor-mediated mitochondrial dysfunction and ER stress in oligodendrocytes
Overactivation of ionotropic glutamate receptors in oligodendrocytes induces cytosolic Ca2+ overload and excitotoxic death, a process that contributes to demyelination and multiple sclerosis. Excitotoxic insults cause well-characterized mitochondrial alterations and endoplasmic reticulum (ER) dysfunction, which is not fully understood. In this study, we analyzed the contribution of ER-Ca2+ release through ryanodine receptors (RyRs) and inositol triphosphate receptors (IP3Rs) to excitotoxicity in oligodendrocytes in vitro. First, we observed that oligodendrocytes express all previously characterized RyRs and IP3Rs. Blockade of Ca2+-induced Ca2+ release by TMB-8 following α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate (AMPA) receptor-mediated insults attenuated both oligodendrocyte death and cytosolic Ca2+ overload. In turn, RyR inhibition by ryanodine reduced as well the Ca2+ overload whereas IP3R inhibition was ineffective. Furthermore, AMPA-triggered mitochondrial membrane depolarization, oxidative stress and activation of caspase-3, which in all instances was diminished by RyR inhibition. In addition, we observed that AMPA induced an ER stress response as revealed by α subunit of the eukaryotic initiation factor 2α phosphorylation, overexpression of GRP chaperones and RyR-dependent cleavage of caspase-12. Finally, attenuating ER stress with salubrinal protected oligodendrocytes from AMPA excitotoxicity. Together, these results show that Ca2+ release through RyRs contributes to cytosolic Ca2+ overload, mitochondrial dysfunction, ER stress and cell death following AMPA receptor-mediated excitotoxicity in oligodendrocytes
AGN counts at 15um. XMM observations of the ELAIS-S1-5 sample
Context: The counts of galaxies and AGN in the mid infra-red (MIR) bands are
important instruments for studying their cosmological evolution. However, the
classic spectral line ratios techniques can become misleading when trying to
properly separate AGN from starbursts or even from apparently normal galaxies.
Aims: We use X-ray band observations to discriminate AGN activity in
previously classified MIR-selected starburst galaxies and to derive updated
AGN1 and (Compton thin) AGN2 counts at 15 um.
Methods: XMM observations of the ELAIS-S1 15um sample down to flux limits
~2x10^-15 erg cm^-2 s^-1 (2-10 keV band) were used. We classified as AGN all
those MIR sources with a unabsorbed 2-10 keV X-ray luminosity higher that
~10^42 erg/s.
Results: We find that at least about 13(+/-6) per cent of the previously
classified starburst galaxies harbor an AGN. According to these figures, we
provide an updated estimate of the counts of AGN1 and (Compton thin) AGN2 at 15
um. It turns out that at least 24% of the extragalactic sources brighter than
0.6 my at 15 um are AGN (~13% contribution to the extragalactic background
produced at fluxes brighter than 0.6 mJy).Comment: Accepted for publication on A&
Optimal dispatch model for PV-electrolysis plants in self-consumption regime to produce green hydrogen: a Spanish case study
The production of green hydrogen from renewable energy by means of water electrolysis is a promising approach to support energy sector decarbonization. This paper presents a techno-economic model of plants with PV sources connected to electrolysis in self-consumption regime that considers the dynamics of electrolysis systems. The model calculates the optimal hourly dispatch of the electrolysis system including the operational states (production, standby, and idle), the load factor in production, and the energy imports and exports to the electricity grid. Results indicate that the model is a useful decision support tool to operate electrolysis plants connected to PV plants in self-consumption regimes with the target of reducing hydrogen production costs
A Deep Double Ritz Method (D2RM) for solving Partial Differential Equations using Neural Networks
Residual minimization is a widely used technique for solving Partial Differential Equations in variational form. It minimizes the dual norm of the residual, which naturally yields a saddle-point (min–max) problem over the so-called trial and test spaces. In the context of neural networks, we can address this min–max approach by employing one network to seek the trial minimum, while another network seeks the test maximizers. However, the resulting method is numerically unstable as we approach the trial solution. To overcome this, we reformulate the residual minimization as an equivalent minimization of a Ritz functional fed by optimal test functions computed from another Ritz functional minimization. We call the resulting scheme the Deep Double Ritz Method (DRM), which combines two neural networks for approximating trial functions and optimal test functions along a nested double Ritz minimization strategy. Numerical results on different diffusion and convection problems support the robustness of our method, up to the approximation properties of the networks and the training capacity of the optimizers
The XMM-Newton survey of the ELAIS-S1 field II: optical identifications and multiwavelength catalogue of X-ray sources
We present optical identifications and a multi-band catalogue of a sample of
478 X-ray sources in the XMM and Chandra surveys of the central 0.6 deg^2 of
the ELAIS-S1 field. The optical/infrared counterpart of each X-ray source was
identified using R and IRAC 3.6 um bands. This method was complemented by the
precise positions obtained through Chandra observations. Approximately 94% of
the counterparts are detected in the R band, while the remaining are blank
fields in the optical down to R~24.5, but have a near-infrared counterpart
detected by IRAC within 6 arcsec from the XMM centroid. The multi-band
catalogue contains photometry in ten photometric bands (B to the MIPS 24 um).
We determined redshift and classification for 237 sources (~50% of the sample)
brighter than R=24. We classified 47% of the sources with spectroscopic
redshift as broad-line active galactic nuclei (BL AGNs) with z=0.1-3.5, while
sources without broad-lines are about 46% of the spectroscopic sample and are
found up to z=2.6. We identified 11 type 2 QSOs among the sources with X/O>8,
with z=0.9-2.6, high 2-10 keV luminosity (log(L2-10keV)>=43.8 erg/s) and hard
X-ray colors suggesting large absorbing columns at the rest frame (logN_H up to
23.6 cm^-2). BL AGNs show on average blue optical-to-near-infrared colors,
softer X-ray colors and X-ray-to-optical colors typical of optically selected
AGNs. Conversely, narrow-line sources show redder optical colors, harder X-ray
flux ratio and span a wider range of X-ray-to-optical colors. On average the
SEDs of high-luminosity BL AGNs resemble the power-law typical of unobscured
AGNs. The SEDs of NOT BL AGNs are dominated by the galaxy emission in the
optical/near-infrared, and show a rise in the mid-infrared which suggests the
presence of an obscured active nucleus.Comment: 15 pages, A&A accepted, affiliations correcte
An exponential integration generalized multiscale finite element method for parabolic problems
We consider linear and semilinear parabolic problems posed in high-contrast multiscale media in two dimensions.
The presence of high-contrast multiscale media adversely affects the accuracy, stability, and overall efficiency of
numerical approximations such as finite elements in space combined with some time integrator. In many cases,
implementing time discretizations such as finite differences or exponential integrators may be impractical because
each time iteration needs the computation of matrix operators involving very large and ill-conditioned sparse matrices.
Here, we propose an efficient Generalized Multiscale Finite Element Method (GMsFEM) that is robust against the
high-contrast diffusion coefficient. We combine GMsFEM with exponential integration in time to obtain a good
approximation of the final time solution. Our approach is efficient and practical because it computes matrix functions
of small matrices given by the GMsFEM method. We present representative numerical experiments that show the
advantages of combining exponential integration and GMsFEM approximations. The constructions and methods
developed here can be easily adapted to three-dimensional domains
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