1,209 research outputs found
Acciones, políticas y estrategias para el balance de género en el ámbito STEM: Resultados de una dinámica World Café
[EN]W-STEM project is working to reduce the existing gender gap in Science, specifically in STEM
fields in Latin America. During an International Leadership Summit, held in Cartagena de Indias
(Colombia) on November 26th, 2019 within the project scope, forty-four people, including
researchers and policymakers at the higher education institutions, participated in a World Café
conversation to discuss about the potential actions, policies and strategies might be develop in
the universities to reduce the above mentioned gender gap in STEM studies. Four tables were
conducted, and this paper summarizes the most outstanding conclusions of the conversations
Efficient single-step rapeseed oleosome extraction using twin-screw press
Oil in seeds is encapsulated in oleosomes, which are small lipid droplets surrounded by a phospholipid-protein monolayer. The currently proposed method to extract intact oleosomes includes mixing seeds with alkaline media in a ratio 1:7, batch blending and filtering. In this work, we propose the use of a twin-screw press to perform the oleosome extraction at pH 7. The results show that similarly to blender extraction, twin-screw press recovers ⁓60% of the oleosomes; however the twin-screw press is able to achieve this yield even when just pure water is used. While in the blender extraction, the yield depends on ionic strength and pH of the extraction media, when using twin-screw press, the oleosome extraction yield predominantly depends on the mechanical forces. These shear forces are able to break the cell walls and release the cellular material while maintaining the integrity of oleosomes. The oleosomes extracted with twin-screw press have similar characteristics than those obtained by the blending process. Overall, twin-screw press seems a promising alternative to scale-up the oleosome aqueous extraction, especially as neutral pH can be used and the water usage is significantly reduced. Additionally, preliminary results showed that the yield can increase up to 90 wt%.</p
n-Heptane hydroconversion over nickel-loaded aluminum- and/or boron-containing BEA zeolites prepared by recrystallization of magadiite varieties
Phase-pure [Al]BEA and [Al,B]BEA zeolites, prepared by solid-state recrystallization of synthetic aluminum-containing magadiites and conventionally synthesized [B]BEA, were tested, after ion exchange with nickel, as bifunctional catalysts for hydroconversion of n-heptane. The reducibility of nickel ions incorporated into BEA zeolites by ion exchange was investigated by temperature-programmed reduction (TPR). The acidity of the samples was characterized with strong (pyridine (Py), ammonia (NH3)) and weak (nitrogen) bases. The adsorbed bases were studied by transmission FT-IR (Py), diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy (N2), and temperature-programmed ammonia evolution (TPAE, NH3). Over Ni/H-[B]BEA the reactants were completely converted via fast hydrogenolysis, whereas this reaction pathway plays only a negligible role in the hydroconversion over Ni/H-[Al]BEA and Ni/H-[Al,B]BEA zeolites. Boron-containing BEA zeolites were less active catalysts than the boron-free catalyst in the principal unimolecular hydroconversion reactions. However, incorporation of boron into the framework of BEA zeolite results in a considerable selectivity shift towards isomerization. Results suggest that the acid strength of bridged hydroxyls, probed with weak (N2) and strong basis (pyridine), was found to be similar in the boron-free and boron-containing BEA samples. The decrease in the isomerization rate and the increase of the apparent activation energy upon incorporation of boron may be attributed to the decrease in the heat of n-heptane adsorption
Illusions of general relativity in Brans-Dicke gravity
Contrary to common belief, the standard tenet of Brans-Dicke theory reducing
to general relativity when omega tends to infinity is false if the trace of the
matter energy-momentum tensor vanishes. The issue is clarified in a new
approach using conformal transformations. The otherwise unaccountable limiting
behavior of Brans-Dicke gravity is easily understood in terms of the conformal
invariance of the theory when the sources of gravity have radiation-like
properties. The rigorous computation of the asymptotic behavior of the
Brans-Dicke scalar field is straightforward in this new approach.Comment: 16 pages, LaTeX, to appear in Physical Review
Estimation of the hydraulic parameters of unsaturated samples by electrical resistivity tomography
In situ and laboratory experiments have shown that electrical resistivity tomography (ERT) is an effective tool to image transient phenomena in soils. However, its application in quantifying soil hydraulic parameters has been limited. In this study, experiments of water inflow in unsaturated soil samples were conducted in an oedometer equipped to perform three-dimensional electrical measurements. Reconstructions of the electrical conductivity at different times confirmed the usefulness of ERT for monitoring the evolution of water content. The tomographic reconstructions were subsequently used in conjunction with a finite-element simulation to infer the water retention curve and the unsaturated hydraulic conductivity. The parameters estimated with ERT agree satisfactorily with those determined using established techniques, hence the proposed approach shows good potential for relatively fast characterisations. Similar experiments could be carried out on site to study the hydraulic behaviour of the entire soil deposi
The SOCS3-independent expression of IDO2 supports the homeostatic generation of T regulatory cells by human dendritic cells.
Dendritic cells (DCs) are professional APCs that have a role in the initiation of adaptive immune responses and tolerance. Among the tolerogenic mechanisms, the expression of the enzyme IDO1 represents an effective tool to generate T regulatory cells. In humans, different DC subsets express IDO1, but less is known about the IDO1-related enzyme IDO2. In this study, we found a different pattern of expression and regulation between IDO1 and IDO2 in human circulating DCs. At the protein level, IDO1 is expressed only in circulating myeloid DCs (mDCs) and is modulated by PGE2, whereas IDO2 is expressed in both mDCs and plasmacytoid DCs and is not modulated by PGE2. In healthy subjects, IDO1 expression requires the presence of PGE2 and needs continuous transcription and translation, whereas IDO2 expression is constitutive, independent from suppressor of cytokine signaling 3 activity. Conversely, in patients suffering from inflammatory arthritis, circulating DCs express both IDO1 and IDO2. At the functional level, both mDCs and plasmacytoid DCs generate T regulatory cells through an IDO1/IDO2-dependent mechanism. We conclude that, in humans, whereas IDO1 provides an additional mechanism of tolerance induced by proinflammatory mediators, IDO2 is stably expressed in steady-state conditions and may contribute to the homeostatic tolerogenic capacity of DCs
Towards a population of HMXB/NS microquasars as counterparts of low-latitude unidentified EGRET sources
The discovery of the microquasar LS 5039 well within the 95% conficence
contour of the Unidentified EGRET Source (UES) 3EG J1824-1514 was a major step
towards the possible association between microquasars (MQs) and UESs. The
recent discovery of precessing relativistic radio jets in LS I +61 303, a
source associated for long time with 2CG 135+01 and with the UES 3EG
J0241+6103, has given further support to this idea. Finally, the very recently
proposed association between the microquasar candidate AX J1639.0-4642 and the
UES 3EG J1639-4702 points towards a population of High Mass X-ray Binary
(HMXB)/Neutron Star (NS) microquasars as counterparts of low-latitude
unidentified EGRET sources.Comment: 12 pages, 7 figures. Proceedings of the Conference "The
Multiwavelength Approach to Unidentified Gamma-ray Sources", to appear in the
journal Astrophysics and Space Scienc
Solamen Vaillanti Mollusk powder as an efficient biosorbent for removing cobalt ions from aqueous solution: Kinetic and equilibrium studies
In this research, Solamen Vaillanti mollusk (SVM) skin biosorbent was synthesized and used as a low-cost and environmentally friendly adsorbent to eliminate cobalt (Co2+) heavy metal ion from aqueous solution. The surface morphology and specific surface area of SVM were analyzed by SEM and BET analyses. Also, the impact of various effective factors like pH, temperature, contact time, biosorbent dose, and cobalt ion concentration was studied on the uptake process. According to our study, the highest biosorption efficiency of Co2+ (97.31%) was attained at pH 5, a mixing speed of 200 rpm, Co2+ ion concentration of 5 mg l-1, and biosorbent dosage of 2 g l-1 after 50 min. Also, the maximum biosorption capacity of SVM biosorbent was 16.23 mg l-1, which was achieved at pH 5 and temperature of 25 °C. Moreover, kinetic and equilibrium studies demonstrated that the quasi-second-order kinetic model and the Langmuir isotherm model are better compatible with the experimental data. Furthermore, the reusability of the bioadsorbent showed that it can be reused in 4 cycles in the bioadsorption process.Campus Lima Centr
Theoretical overview on high-energy emission in microquasars
Microquasar (MQ) jets are sites of particle acceleration and synchrotron
emission. Such synchrotron radiation has been detected coming from jet regions
of different spatial scales, which for the instruments at work nowadays appear
as compact radio cores, slightly resolved radio jets, or (very) extended
structures. Because of the presence of relativistic particles and dense photon,
magnetic and matter fields, these outflows are also the best candidates to
generate the very high-energy (VHE) gamma-rays detected coming from two of
these objects, LS 5039 and LS I +61 303, and may be contributing significantly
to the X-rays emitted from the MQ core. In addition, beside electromagnetic
radiation, jets at different scales are producing some amount of leptonic and
hadronic cosmic rays (CR), and evidences of neutrino production in these
objects may be eventually found. In this work, we review on the different
physical processes that may be at work in or related to MQ jets. The jet
regions capable to produce significant amounts of emission at different
wavelengths have been reduced to the jet base, the jet at scales of the order
of the size of the system orbital semi-major axis, the jet middle scales (the
resolved radio jets), and the jet termination point. The surroundings of the
jet could be sites of multiwavelegnth emission as well, deserving also an
insight. We focus on those scenarios, either hadronic or leptonic, in which it
seems more plausible to generate both photons from radio to VHE and high-energy
neutrinos. We briefly comment as well on the relevance of MQ as possible
contributors to the galactic CR in the GeV-PeV range.Comment: Astrophysics & Space Science, in press (invited talk in the
conference: The multimessenger approach to the high-energy gamma-ray
sources", Barcelona/Catalonia, in July 4-7); 10 pages, 6 figures, 2 tables
(one reference corrected
Conformally flat spacetimes and Weyl frames
We discuss the concepts of Weyl and Riemann frames in the context of metric
theories of gravity and state the fact that they are completely equivalent as
far as geodesic motion is concerned. We apply this result to conformally flat
spacetimes and show that a new picture arises when a Riemannian spacetime is
taken by means of geometrical gauge transformations into a Minkowskian flat
spacetime. We find out that in the Weyl frame gravity is described by a scalar
field. We give some examples of how conformally flat spacetime configurations
look when viewed from the standpoint of a Weyl frame. We show that in the
non-relativistic and weak field regime the Weyl scalar field may be identified
with the Newtonian gravitational potential. We suggest an equation for the
scalar field by varying the Einstein-Hilbert action restricted to the class of
conformally-flat spacetimes. We revisit Einstein and Fokker's interpretation of
Nordstr\"om scalar gravity theory and draw an analogy between this approach and
the Weyl gauge formalism. We briefly take a look at two-dimensional gravity as
viewed in the Weyl frame and address the question of quantizing a conformally
flat spacetime by going to the Weyl frame.Comment: LATEX - 18 page
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