328 research outputs found
Does higher sampling rate (multiband + SENSE) improve group statistics - An example from social neuroscience block design at 3T
Multiband (MB) or Simultaneous multi-slice (SMS) acquisition schemes allow the acquisition of MRI signals from more than one spatial coordinate at a time. Commercial availability has brought this technique within the reach of many neuroscientists and psychologists. Most early evaluation of the performance of MB acquisition employed resting state fMRI or the most basic tasks. In this study, we tested whether the advantages of using MB acquisition schemes generalize to group analyses using a cognitive task more representative of typical cognitive neuroscience applications. Twenty-three subjects were scanned on a Philips 3 âT scanner using five sequences, up to eight-fold acceleration with MB-factors 1 to 4, SENSE factors up to 2 and corresponding TRs of 2.45s down to 0.63s, while they viewed (i) movie blocks showing complex actions with hand object interactions and (ii) control movie blocks without hand object interaction. Data were processed using a widely used analysis pipeline implemented in SPM12 including the unified segmentation and canonical HRF modelling. Using random effects group-level, voxel-wise analysis we found that all sequences were able to detect the basic action observation network known to be recruited by our task. The highest t-values were found for sequences with MB4 acceleration. For the MB1 sequence, a 50% bigger voxel volume was needed to reach comparable t-statistics. The group-level t-values for resting state networks (RSNs) were also highest for MB4 sequences. Here the MB1 sequence with larger voxel size did not perform comparable to the MB4 sequence. Altogether, we can thus recommend the use of MB4 (and SENSE 1.5 or 2) on a Philips scanner when aiming to perform group-level analyses using cognitive block design fMRI tasks and voxel sizes in the range of cortical thickness (e.g. 2.7 âmm isotropic). While results will not be dramatically changed by the use of multiband, our results suggest that MB will bring a moderate but significant benefit
Permeability and Selectivity of PPO/Graphene Composites as Mixed Matrix Membranes for CO2 Capture and Gas Separation
We fabricated novel composite (mixed matrix) membranes based on a permeable glassy
polymer, Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), and variable loadings of few-layer graphene,
to test their potential in gas separation and CO2 capture applications. The permeability, selectivity
and diffusivity of different gases as a function of graphene loading, from 0.3 to 15 wt %, was measured
at 35 and 65 \u25e6C. Samples with small loadings of graphene show a higher permeability and
He/CO2 selectivity than pure PPO, due to a favorable effect of the nanofillers on the polymer
morphology. Higher amounts of graphene lower the permeability of the polymer, due to the
prevailing effect of increased tortuosity of the gas molecules in the membrane. Graphene also
allows dramatically reducing the increase of permeability with temperature, acting as a \u201cstabilizer\u201d
for the polymer matrix. Such effect reduces the temperature-induced loss of size-selectivity for He/N2
and CO2/N2, and enhances the temperature-induced increase of selectivity for He/CO2. The study
confirms that, as observed in the case of other graphene-based mixed matrix glassy membranes,
the optimal concentration of graphene in the polymer is below 1 wt %. Below such threshold,
the morphology of the nanoscopic filler added in solution affects positively the glassy chains packing,
enhancing permeability and selectivity, and improving the selectivity of the membrane at increasing
temperatures. These results suggest that small additions of graphene to polymers can enhance their
permselectivity and stabilize their propertie
Estudiar en pandemia, experiencias en la virtualidad: Encuesta a los y las estudiantes de la Universidad Nacional del Comahue
Desde la SecretarĂa de Planeamiento y Desarrollo Institucional de la Universidad Nacional del Comahue implementamos un relevamiento institucional para conocer el impacto de la pandemia en la comunidad universitaria, que incluyĂł encuestas al personal Nodocente y Docente1 y culminĂł con la encuesta a estudiantes que aquĂ presentamos
Alkylation of methyl linoleate with propene in ionic liquids in the presence of metal salts
Vegetable oils and fatty acid esters are suitable precursor molecules for the production of a variety of bio-based products and materials, such as paints and coatings, plastics, soaps, lubricants, cosmetics, pharmaceuticals, printing inks, surfactants, and biofuels. Here, we report the possibility of using Lewis acidic ionic liquids (ILs) to obtain polyunsaturated ester dimerization-oligomerization and/or, in the presence of another terminal alkene (propene), co-polymerization. In particular, we have tested the Lewis acidic mixtures arising from the addition of a proper amount of GaCl3 (X > 0.5) to two chloride-based (1-butyl-3-methylimidazolium chloride, [bmim]Cl, and 1-butylisoquinolium chloride, [BuIsoq]Cl) or by dissolution of a smaller amount of Al(Tf2N)3 (X = 0.1) in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [bmim][Tf2N]. On the basis of product distribution studies, [bmim][Tf2N]/Al(Tf2N)3 appears the most suitable medium in which methyl linoleate alkylation with propene can compete with methyl linoleate or propene oligomerization
The COMIX polarimeter: a compact device for XUV polarization analysis
We report on the characterization of a novel extreme-ultraviolet polarimeter based on conical mirrors to simultaneously detect all the components of the electric field vector for extreme-ultraviolet radiation in the 45â90â
eV energy range. The device has been characterized using a variable polarization source at the Elettra synchrotron, showing good performance in the ability to determine the radiation polarization. Furthermore, as a possible application of the device, Faraday spectroscopy and time-resolved experiments have been performed at the Fe M2,3-edge on an FeGd ferrimagnetic thin film using the FERMI free-electron laser source. The instrument is shown to be able to detect the small angular variation induced by an optical external stimulus on the polarization state of the light after interaction with magnetic thin film, making the device an appealing tool for magnetization dynamics research
Diurnal patterns in lightning activity over South America
Ponencia presentada en 2nd TEAâIS Summer School, June 23rd â June 27nd 2014, Collioure, France.Satellite and ground network observations of lightning flash distribution data are used to examine the diurnal cycle of lightning activity over the tropical and subtropical regions of South America. The results show in the subtropical South America, particularly the area limited by [-25°; -40°] of latitude and [-70°; -50°] of longitude, the time of maximum lightning activity was shifted to nocturnal hours, extending from close to midnight to early morning hours. This behavior can be associated to the peak in MCSs in the morning hours in the region. A close connection between peak time of lightning activity and peak time of precipitation events have been observed by comparing the current results with other published studies. On the other hand, storms over northern Argentina are known as leading Transient Luminous Events (TLE) generators on Earth (Thomas et al., 2007).Fil: Nicora, M. Gabriela. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Instituto de Investigaciones CientĂficas y TĂ©cnicas para la Defensa. Departamento de Investigaciones en LĂĄseres y sus aplicaciones; Argentina.Fil: Nicora, M. Gabriela. Ministerio de Defensa. Instituto de Investigaciones CientĂficas y TĂ©cnicas para la Defensa. Departamento de Investigaciones en LĂĄseres y sus aplicaciones; Argentina.Fil: Castellano, Nesvit. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Instituto de FĂsica Enrique Gaviola; Argentina.Fil: Castellano, Nesvit. Universidad Nacional de CĂłrdoba. Instituto de FĂsica Enrique Gaviola; Argentina.Fil: Ăvila, Eldo E. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Instituto de FĂsica Enrique Gaviola; Argentina.Fil: Ăvila, Eldo E. Universidad Nacional de CĂłrdoba. Instituto de FĂsica Enrique Gaviola; Argentina.Fil: BĂŒrgesser, Rodrigo E. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Instituto de FĂsica Enrique Gaviola; Argentina.Fil: BĂŒrgesser, Rodrigo E. Universidad Nacional de CĂłrdoba. Instituto de FĂsica Enrique Gaviola; Argentina.MeteorologĂa y Ciencias AtmosfĂ©rica
A non-involutory selfduality
We report the effect of the aluminum oxide substrate on the emission of monolithic AlGaAs-on-insulator nonlinear nanoantennas. By coupling nonlinear optical measurements with electron diffraction and microscopy observations, we find that the oxidation-induced stress causes negligible crystal deformation in the AlGaAs nanostructures and only plays a minor role in the polarization state of the harmonic field. This result highlights the reliability of the wet oxidation of thick AlGaAs optical substrates and further confirms the bulk chi(2) origin of second harmonic generation at 1.55 um in these nanoantennas, paving the way for the development of AlGaAs-on-insulator monolithic metasurfaces
Loss of Npn1 from motor neurons causes postnatal deficits independent from Sema3A signaling
AbstractThe correct wiring of neuronal circuits is of crucial importance for the function of the vertebrate nervous system. Guidance cues like the neuropilin receptors (Npn) and their ligands, the semaphorins (Sema) provide a tight spatiotemporal control of sensory and motor axon growth and guidance. Among this family of guidance partners the Sema3A-Npn1 interaction has been shown to be of great importance, since defective signaling leads to wiring deficits and defasciculation. For the embryonic stage these defects have been well described, however, also after birth the organism can adapt to new challenges by compensational mechanisms. Therefore, we used the mouse lines Olig2-Cre;Npn1cond and Npn1Semaâ to investigate how postnatal organisms cope with the loss of Npn1 selectively from motor neurons or a systemic dysfunctional Sema3A-Npn1 signaling in the entire organism, respectively. While in Olig2-Cre+;Npn1condâ/â mice clear anatomical deficits in paw posturing, bone structure, as well as muscle and nerve composition became evident, Npn1Semaâ mutants appeared anatomically normal. Furthermore, Olig2-Cre+;Npn1cond mutants revealed a dysfunctional extensor muscle innervation after single-train stimulation of the N.radial. Interestingly, these mice did not show obvious deficits in voluntary locomotion, however, skilled motor function was affected. In contrast, Npn1Semaâ mutants were less affected in all behavioral tests and able to improve their performance over time. Our data suggest that loss of Sema3A-Npn1 signaling is not the only cause for the observed deficits in Olig2-Cre+;Npn1condâ/â mice and that additional, yet unknown binding partners for Npn1 may be involved that allow Npn1Semaâ mutants to compensate for their developmental deficits
Silicon Photomultiplier Research and Development Studies for the Large Size Telescope of the Cherenkov Telescope Array
The Cherenkov Telescope Array (CTA) is the the next generation facility of
imaging atmospheric Cherenkov telescopes; two sites will cover both
hemispheres. CTA will reach unprecedented sensitivity, energy and angular
resolution in very-high-energy gamma-ray astronomy. Each CTA array will include
four Large Size Telescopes (LSTs), designed to cover the low-energy range of
the CTA sensitivity (20 GeV to 200 GeV). In the baseline LST design, the
focal-plane camera will be instrumented with 265 photodetector clusters; each
will include seven photomultiplier tubes (PMTs), with an entrance window of 1.5
inches in diameter. The PMT design is based on mature and reliable technology.
Recently, silicon photomultipliers (SiPMs) are emerging as a competitor.
Currently, SiPMs have advantages (e.g. lower operating voltage and tolerance to
high illumination levels) and disadvantages (e.g. higher capacitance and cross
talk rates), but this technology is still young and rapidly evolving. SiPM
technology has a strong potential to become superior to the PMT one in terms of
photon detection efficiency and price per square mm of detector area. While the
advantage of SiPMs has been proven for high-density, small size cameras, it is
yet to be demonstrated for large area cameras such as the one of the LST. We
are working to develop a SiPM-based module for the LST camera, in view of a
possible camera upgrade. We will describe the solutions we are exploring in
order to balance a competitive performance with a minimal impact on the overall
LST camera design.Comment: 8 pages, 5 figures. In Proceedings of the 34th International Cosmic
Ray Conference (ICRC2015), The Hague, The Netherlands. All CTA contributions
at arXiv:1508.0589
Palliative short-course radiotherapy (RAPASH study) in patients with rectal cancer
Background: Palliative radiation therapy (RT) is used to treat symptomatic rectal cancer although clinical benefits and toxicities are poorly documented. There is no consensus about the optimal RT regimen and clinical practice undergoes significant changes. Our aim was to evaluate the efficacy and toxicity of short-course (SC) RT in this setting of patients.
Materials and methods: Charts from patients with locally advanced disease not candidates for standard treatment or with symptomatic metastatic rectal cancer treated with SCRT (25 Gy/5 fractions in 5 consecutive days) were retrospectively reviewed. Clinical outcome measures were symptomatic response rate and toxicity.
Results: From January 2007 to December 2017, 59 patients (median age 80 years) received SCRT; 53 were evaluable. The median follow-up was 8 months (range, 1â70). Clinical response to RT for bleeding, pain and tenesmus was 100%, 95% and 89%, respectively. The compliance with the treatment was 100% and no patient experienced acute severe (â„ grade 3) toxicities. Median time to symptoms recurrence was 11 months (range 3-69). Globally, the median overall survival was 12 months.
Conclusions: SCRT is a safe and effective regimen in symptomatic rectal cancer and may be considered the regimen of choice for standard treatment in unfit patients
- âŠ